# THE ROLE OF HIGHER EDUCATION IN A CHANGING WORLD: WHY EMPLOYABILITY MATTERS

### *Carlo Terzaroli (University of Florence)*\*

Abstract: The transformations of work are increasingly introducing new scenarios at a global level. In fact, the disruptive importance of innovation in all workplace contexts anticipates the challenge of skills and capabilities for the work of the future. In this sense, education has a crucial role in supporting the development of students and future workers. This paper analyses in depth the link between education, work and the pedagogical instrument of work pedagogy that is derived directly from John Dewey's thought. This theoretical standpoint represents the base for the development of employability in higher education and its future challenges of innovation, development, and social inclusion.

Keywords: work pedagogy, employability, innovation, higher education.

### *1. The transformation of the world of work*

In the coming decades, global competition will be about attracting innovative human capital and innovative companies. The importance of geography and the forces of agglomeration in determining the location of human capital will keep growing. The number and strength of a country's brain hubs will determine whether it will prosper or decline. Physical factories will keep losing importance, but cities with a large percentage of interconnected, highly educated workers will become the new factories where ideas and knowledge are forged (Moretti 2012: 2900).

This is one of the main conclusions of the economist Enrico Moretti's famous book *The Geography of Jobs*1 (Moretti 2012) that illustrates the changes in the United States job market. *«*The New Human Capital Century» (Moretti 2012: 2900), as he calls it, represents the result of a global

\* Carlo Terzaroli, PhD Student, Department of Education and Psychology, University of Florence, Italy. Email<EMAIL_ADDRESS>His research interests focus on employability, career services, and the entrepreneurial education of adults.

1 In his volume *The Geography of Jobs*, Enrico Moretti, Professor of Economics at the University of California-Berkeley, analyses why some places are more prosperous than others. He explores the factors that create a concentration of innovative industries in specific hubs. Through a study of the increase in economic differences among 300 areas in the USA over the last 30 years, he points out the main reasons for the birth of those clusters (such as labour market effectiveness, availability of intermediate services and human capital spillovers). From this, he states that the innovative economic sectors (i.e. high-tech or pharmaceutical) generate a multiplier effect that can create in the longterm, for each new job in these sectors, five new opportunities in non-innovative sectors (i.e. services and non-traded activities).

shift from a traditional manufacturing economy towards a knowledgeintensive one. This trend has potent effects on job markets and people's professional pathways. As Moretti analyses in his volume, the transformation of work is shaping not just the size and location of industries but the structure of cities as well. In the past, good jobs and high salaries were directly linked to large-scale manufacturing. Industries were the places where economic value was created. Today, the globalization of markets and the relevance of innovation in the creation of products and services has led to a revolution (Ito, Howe 2017): the quality of employment and wages are increasingly related to the realization of innovative ideas, knowledge, and technologies (Moretti 2012).

These trends are producing a *«*Great Divergence*»* (Moretti 2012: 76) between cities with a high percentage of innovative firms (and skilled workers) and ones that are unable to attract knowledge-intensive ones. However, this phenomenon impacts not just the development of inventive companies, but also the environment: «the presence of many collegeeducated residents changes the local economy in profound ways, affecting both the kinds of jobs available and the productivity of every worker who lives there, including the less skilled. This results in high wages not just for skilled workers but for most workers*»* (Moretti 2012: 80).

In this framework, cities become the fulcrum of opportunities for the development of social interactions that can generate innovative ideas. The agglomeration of smart jobs in the same environment can enhance innovation as well as life quality at all levels: moreover, it can attract further innovators and high-skilled workers (Moretti 2012: 232).

The Great Divergence of territories, which could be highlighted both in the USA and Europe, is reflected in employment too. As Paolo Federighi stated, *«*the changing structure of employment, together with the growing number of jobs that are more knowledge- and skill-intensive, increases demand for professional growth among the employed*»* (Federighi 2013: 13). The study by Ilaria Maselli effectively explains the Job Polarization trend within European job market: indeed, Figure 1 shows that *«*there is a trend towards polarization on the labour demand side with respect to occupations in most European countries, whereas on the supply side, the trend is towards a linear upskilling of the population. Depending on the speed of these changes and on the skill content of current demand and supply, there is a risk that in some countries a skill mismatch problem will arise*»* (Maselli 2012: 26).

Furthermore, the complexity of this new scenario has been increased by the development of Industry 4.0 (Smit, Kreutzer, Moeller, Carlberg 2016) and will further expand with Industry 5.0 (Rai, Rai 2015). These latest trends impose a crucial role for adult education, conceived as a discipline that *«*goes beyond the boundaries of the school system and professional training*»* (Federighi 1999: 5).

Figure 1 – Demand and Supply of Work with Respect to Skills/Tasks in the EU27, 2010- 2020. [Maselli 2012: 26]

Facing the evolution of work requires the capability to critically analyse the context and its evolution, interpreting future tendencies and unrevealed challenges. In this framework, staying in the job market does not mean creating a skills supply that can match the skills demand (or, at least, no longer). The speed at which production settings change drives organizations and individuals to continuously renew their aims, projects, and competences. From this perspective, it could prove inadequate, if not ineffective, to create formative pathways that simply answer the present skills demand. In fact, the new creation of value is characterised by ongoing transformation, mobility of space and contents and a capacity to innovate products, internal relationships, and organizational structures (Ito, Howe 2017).

The brilliant research by Enrico Moretti, which directly reveals the relationship between the presence of innovative firms and the development of cities and employment, suggests a crucial point for adult education. Indeed, given that innovation has immense importance for high-, medium- and low-skilled workers, the centrality of skills growth, both in firms and at an educational level, become a vital challenge for the whole of society. Contributing to increasing the educational rates, skills, and capabilities of people is not just a matter of one part of the workers. On the contrary, the challenge of up-skilling is a task of the production and educational systems, especially in this knowledge-intensive context which is, today more than ever, centred on human added value (Samans, Davis 2017).

Care of these processes is one of the aims of adult education, not just in the workplace, but also within schools and higher education facilities (Boffo 2015, 2017) where it seems more complex. University is not simply the place where people acquire competences for entering the job market. It is a space for human education that allows students to grow up globally as subjects, citizens, and workers (Boffo 2012, 2015). However, what matters most is the new relevance of higher education in the advance of innovation. Given the capability of creating better work opportunities and higher wages (Moretti 2012) increasingly related to the value of humans' creativity, the future of our communities is increasingly linked to skills development and entrepreneurial attitudes. Which is why, over the last decades, educational institutions have been charged with the new mission of creating new relationships with multiple stakeholders such as public bodies, companies, associations, and non-profit organizations. The Third Mission of Universities (ANVUR 2015) is intended to enhance and disseminate knowledge and technologies to local, national, and international socio-economic contexts to improve the quality of the economy, work, and human life. These efforts could generate great benefits to all the actors involved: graduates could be equipped with skills to enter the job market and contribute with innovative work; industries could integrate new knowledge into their production processes; communities could take advantage of the presence of innovative firms that can also create opportunities for the low- and medium-skilled.

### *2. The relationship between education and work: why employability matters*

In this framework, the debate on the development of students' work capabilities arises as a key issue for the growth of our countries. The specific contribution of adult education could inform the processes through which young adults acquire capabilities for their personal and professional life. In this sense, it seems interesting to highlight the specific added value of a pedagogical and educational perspective on this relationship alongside the traditional approach elaborated by economic and sociological studies (Gazier 1998).

The connection between education and work originally referred to John Dewey's studies. The American philosopher laid great stress on the relevance of this relationship. In his volume *The School and Society* (1899) he suggested going beyond the conception of school through the mere standpoint of teachers and children. As he clearly showed, school has been transformed by the new patterns of economy and society in broader terms: *«*the modification going on in the method and curriculum of education is as much a product of the changed social situation, and as much an effort to meet the needs of the new society that is forming, as are changes in modes of industry and commerce*»* (Dewey 1932: 4). In this sense, the innovation in education can be considered *«*as part and parcel of the whole social evolution, and, in its more general features at least, as inevitable*»* (Dewey 1932: 5).

This is why nowadays it is extremely crucial to understand the new trends in the economy and job market: through these analyses educators could better plan pathways to offer students the opportunity to acquire capabilities for their future lives. This is crucial since, as Dewey had already illustrated in 1899, the first transformation that impacts the structure of education is the economic and industrial one:

the change that comes first to mind, the one that overshadows and even controls all others, is the industrial one – the application of science resulting in the great inventions that have utilized the forces of nature on a vast and inexpensive scale the growth of a world-wide market as the object of production, of vast manufacturing centres to supply this market, of cheap and rapid means of communication and distribution between all its parts (Dewey 1932: 5).

It is almost indispensable to point out that these factors have become vastly more disruptive in the current situation, considering the innovations in technologies and industries. Following Dewey's standpoint, these trends have progressively generated a radical metamorphosis of society. We could spend a long time discussing how the past structure was able to better create social and community links or a more settled relationship between people and the world, *«*but it is useless to bemoan the departure of the good old days […]. It is radical conditions which have changed, and only an equally radical change in education suffices*»* (Dewey 1932: 9). We must take note of those in progress to give people the right tools to avoid suffering from their effect.

Work completely permeates human life, in its deepest meaning and its organization of time (Boffo 2012). In line with this, Dewey suggested including manual activities within the school curriculum, to integrate life into the educational process: in fact, *«*we must conceive of work in wood and metal, of weaving, sewing, and cooking, as methods of living and learning, not as distinct studies*»* (Dewey 1932: 11). These kinds of activity must be considered *«*as instrumentalities through which the school itself shall be made a genuine form of active community life, instead of a place set apart in which to learn lessons*»* (Dewey 1932: 11).

What are the implications for pedagogy? How could we plan formative pathways, at all levels, that can *«*consider the relationship of the school to the life and development of the children in the school*»* (Dewey 1932: 31)? This is a tough task for the whole discipline, especially for adult education, which is fundamentally based on subjects' growth in their working and living contexts. This challenge reflects the research into the most effective ways through which to generate learning linked to human life needs (in any individual, personal, or social scope considered).

As Dewey lucidly stated in *Experience and Education* (1938),

it is part of the educator's responsibility to see equally to two things: first, that the problem grows out of the conditions of the experience being had in the present, and that it is within the range of the capacity of students; and, secondly, that it is such that it arouses in the learner an active quest for information and for production of new ideas. The new facts and new ideas thus obtained become the ground for further experiences in which new problems are presented. The process is a continuous spiral (Dewey 1976: 79).

The relevance that the American philosopher assigned to the generation of innovative ideas is extremely relevant in our contemporary context. The new patterns of global economies and job markets (Moretti 2012) outline the vital role of creativity in work. The ability to imagine innovative projects, to face new situations, and to renovate the plans of individual careers or organizational business plans are progressively strategic characteristics (Ito, Howe 2017). Education has the task of supporting the development of those skills, both in school and in other learning contexts. How can we do this? How can we integrate the free and disruptive dimensions of play and creativity with the structure of adults' learning pathways?

Traditionally, the ancient philosophers divided the meaning for these actions through different words: public affairs and work (*negotium*) were separated from free time (*otium)*, where play could happen. It seems that they were referring to different fields of life, quite clearly separate. On the contrary, what Dewey outlined reveals a unique perspective on the relationship between these two aspects: «in their intrinsic meaning, play and industry are by no means so antithetical to one another as is often assumed, any sharp contrast being due to undesirable social conditions. Both involve ends consciously entertained and the selection and adaptations of materials and processes designed to effect the desired ends*»* (Dewey 1930: 237).

In this sense, the integration of these dimensions in education could generate new patterns for the development of skills and capabilities. The active occupations represent interesting forms of generating learning, including work-related learning. In fact, if work permeates people's lives and their meaning, and this work is increasingly characterised by creativity, mobility, and other forms of innovation (both for business and career), it is meaningless to maintain this separation. Dewey's contribution to pedagogical reflection clashed with the antithesis *«*between education in preparation for useful labour and education for a life of leisure*»* (Dewey 1930: 293). Furthermore, it added that *«*the bare terms useful labour and leisure confirm the statement already made that the segregation and conflict of values are not self-enclosed, but reflect a division within social life*»* (Dewey 1930: 293). In the present situation, in which work feeds on creativity and resourcefulness, this division wanes immediately. How can higher education support this process within its specific pathways? This is one of the key points for present and future research.

What we should be focusing on is the deeper meaning of work, conceived as profession and career, and its relationship with the formation of the self. Dewey provided a precious reflection on this in *Democracy and Education* (1916):

A vocation means nothing, but such a direction of life activities as renders them perceptibly significant to a person, because of the consequences they accomplish, and also useful to his associates. The opposite of a career is neither leisure nor culture, but aimlessness, capriciousness, the absence of cumulative achievement in experience, on the personal side, and idle display, parasitic dependence upon the others, on the social side. Occupation is a concrete term for continuity. It includes the development of artistic capacity of any kind, of special scientific ability, of effective citizenship, as well as professional and business occupations, to say nothing of mechanical labour or engagement in gainful pursuits (Dewey 1930: 358-359).

The concept of 'employability', which is going to be analysed in the next chapter, slots neatly into the pedagogical framework traced by John Dewey throughout the nineteenth century. What is the relation between school and work? How can we help students develop skills and capabilities to better create their own personal and professional pathway? What are the global changes that people need to tackle in their career? How could higher education support both economies and citizens, while increasing the quality of life? These questions, and many others, represent the foundations of the educational reflection on the concept of employability based on Dewey's pedagogical instrument.

### *3. Higher Education facing the challenge of work: the concept of employability*

The category of employability arose along with the evolution of job market trends at a global level. It has been considered a new construct for the development of students' and graduates' work capabilities, especially in countries with high levels of unemployment. In this sense, it represents a reaction to the mismatch between education and employment to increase the support to transitions towards the job market (Boffo, Fedeli, Lo Presti, Melacarne, Vianello 2017). Economists and sociologists were the first who already discussed employability as a way to reduce mismatches in the twentieth century (Gazier 1998). However, these forms ignored the development of the subject and the deep perspective of the construction of skills and capabilities within the course of life. In 1998, Hillage and Pollard recovered the individual perspective, focusing on subjects' capability to stay in the job market thanks to their knowledge, skills, and aptitude: «In simple terms, employability is about being capable of getting and keeping fulfilling work. More comprehensively employability is the capability to move self-sufficiently within the job market to realise potential through sustainable employment*»* (Hillage, Pollard 1998: 3).

Anyhow, the pedagogical elaboration of the concept mainly refers to important scholars who operated within the *Enhancing Student Employability Co-ordination Team* (ESECT) research group at the Higher Education Academy in York (UK)2 . Lee Harvey, Mantz Yorke and Peter Knight guided the team that intensively analysed many aspects of employability. In fact, the ESECT traced an interesting didactic and pedagogical approach aimed at transforming higher education to tackle innovation and the changes in the current social and economic situation.

The problem is not merely the power distribution within the university-economy relationship, or an instrumental view of higher education. On the contrary, the added value of the pedagogical standpoint on employability concerns the university as a place where young adults can develop critical and reflective thought: this may help them deal with the challenges of their lifespan as global citizens, workers, and active participants in the learning process as well (Harvey 1999). Lee Harvey clarified this point thus:

Employability raises fundamental questions about the purpose and structure of higher education. Employability is not about training or providing add-on skills to gain employment. On the contrary, employability is about how higher education develops critical, reflective, empowered learners. Despite appearances to the contrary, the real challenge is not how to accommodate employability but how to shift the traditional balance of power from the education provider to those participating in the learning experience (Harvey 1999: 13).

This is why Harvey emphasized how the conception of employability, as a simple indicator, is reductive in measuring academic performance. Yorke & Knight found themselves within the same framework (Yorke, Knight 2006). They described a competence-centred approach (European Commission/EACEA/Eurydice 2014) that has been widely adopted as a reference point for the creation of specific programmes.

2 The Higher Education Academy started working on employability in 2006 through a series of papers. These works, coordinated by Prof. Mantz Yorke, were carried out by Professor Peter Knight (Open University), Professor Lee Harvey (Sheffield Hallam University), Professor Stephen McNair (Surrey University), Dr Brenda Little (CHERI), Professor Kate Purcell (University of the West of England), Mike Hill (Graduate Prospects) and Val Butcher from the Higher Education Academy.

From their perspective, employability meant: *«[*…] a set of achievements – skills, understandings and personal attributes – that make graduates more likely to gain employment and be successful in their chosen occupations, which benefits themselves, the workforce, the community and the economy» (Yorke 2006: 8).

This definition outlines a crucial connection between learning and employability and can determine innovative methodologies. This point considers not just the students' perspective, but calls into question the construction of curricula, didactic methods, interdisciplinary contents, but also career services. In fact, it is a learning process, curricular and extra-curricular, that connects, within educational action, concrete experiences, and key aspects for personal and professional growth. In conclusion, the category of employability is extremely disruptive in the pedagogical field since it highlights the formative process of subjects in relation with the social value of traditional university missions such as research and didactics in conjunction with the Third Mission.

### *4. Final remarks*

The job market is changing extremely rapidly. If we acknowledge the trend of the last ten years (especially since the 2008 economic crisis), we can only imagine the extent of the changes we are going to meet in the next decades (Moretti 2012). Today's challenge for the university is not simply the ability to answer the mismatch by strengthening the skills supply. In fact, the timeframe of education does not coincide with the current work demand, which is constantly changing: the risk is to continually (and ineffectively) chase after the economy and the market. Besides, this is not the role of the university, even today when it is being asked to bring more and more added value in terms of innovation (Ito, Howe 2017). As Ulrich Teichler stated, *«*Higher education has to take care primarily to avoid the danger of *«*ivory tower knowledge delivery*»*. It does not express warnings against the opposite possible disaster of higher education, i.e. to subordinate itself simply to the presumed demands of the employment system*»* (Teichler 2004: 7-8).

The Academy should look to the future, trying to understand the current trends also in terms of skill (Davies, Fidler, Gorbis 2011), and above all training people able to always deal with different challenges at personal, social, and political levels.

The change, for the future of countries, starts from higher education's ability to prepare people who can contribute to innovation, development, and social inclusion (Boffo, Gioli, Terzaroli 2017). If work really does represent the tool by which people build sense and their place in the world (Boffo 2012), then people should progressively develop the ability to create new and better opportunities, for as many people as possible, to increase the quality of their life. This is primarily the task of Universities, for today and for the future as well.

## *References*


**7. Biofilm formation and cellulose expression amongst other pseudomonads**

Having discovered that *P. fluorescens* SBW25 could express cellulose in the WS biofilm (and subsequently in the VM biofilm), we were interested to see if related environmental pseudomonads could produce similar cellulose-matrix–based A-L interface biofilms. We therefore undertook a survey of environmental pseudomonads, including water, soil, plantassociated and plant pathogenic isolates (we did not include human or other animal pathogens in this survey) [15]. The ability of each to produce an A-L interface biofilm was assessed in static King's B liquid media microcosms. Importantly, this assay did not differentiate between isolates that constitutively produced biofilms, with those that might utilise quorum sensing-like signalling to initiate biofilm-formation, or those that had mutated into a biofilm-forming genotype. Of the 185 environmental pseudomonads tested, 76% were found to produce observable biofilms within 15 days incubation. The phenotypes of these were variable, with biofilm strengths ranging 1500*x*, but could be categorised into the physically-cohesive (PC), floccular mass (FM), waxy aggregate (WA) and viscous mass (VM)-class biofilms described in Table 2 (see also Figure 2) [15, 46].

Calcofluor-fluorescent microscopy identified cellulose as the matrix component of 20% of the biofilm-forming isolates, indicating that at least seven *Pseudomonas* species were capable of expressing cellulose under the conditions tested. These included *P. corrugata* (tomato pathogens), *P. fluorescens* (plant-associated isolates), *P. marginalis* (alfalfa and parsnip pathogens), *P. putida* (rhizosphere and soil isolates), *P. savastanoi* (olive pathogens), *P. stutzeri* (represented by a single clinical isolate), and *P. syringae* (celery, cucumber, tobacco, and tomato isolates or pathogens) (isolates from another eleven *Pseudomonas* spp. were tested, including *P. aeruginosa* PA01 and PA14, and were not found to produce cellulose). For two of the celluloseexpressing isolates, *P. putida* KT2440 and *P. syringae* DC3000, the whole genome sequences were available and SBW25 *wss*-like cellulose synthase operons had been annotated [74-75], though no experimental reports of either expressing cellulose had been made.

14 Cellulose – Medical, Pharmaceutical and Electronic Applications

attachment factor that is also required for the WS phenotype.

**pseudomonads**

**7. Biofilm formation and cellulose expression amongst other**

(VM)-class biofilms described in Table 2 (see also Figure 2) [15, 46].

**Figure 7. Activation of the WS phenotype.** The Wrinkly Spreader (WS) phenotype is controlled by the membrane-associated Wsp complex and associated DGC response regulator WspR. **(A)** In wild-type *Pseudomonas fluorescens* SBW25, when an appropriate environmental signal is received the Wsp complex phosphorylates WspR which then results in the production of c-*di*-GMP. However, in the absence of signal, the Wsp complex is silent and c-*di*-GMP levels remain low. **(B)** In the Wrinkly Spreader a mutation in a Wsp subunit (WspF) alters the sensitivity of the Wsp complex such that it activates WspR in the absence of the environmental signal. The resulting increase in c-*di*-GMP activates the membraneassociated cellulose synthase complex to produce cellulose, and also activates the unidentified

Having discovered that *P. fluorescens* SBW25 could express cellulose in the WS biofilm (and subsequently in the VM biofilm), we were interested to see if related environmental pseudomonads could produce similar cellulose-matrix–based A-L interface biofilms. We therefore undertook a survey of environmental pseudomonads, including water, soil, plantassociated and plant pathogenic isolates (we did not include human or other animal pathogens in this survey) [15]. The ability of each to produce an A-L interface biofilm was assessed in static King's B liquid media microcosms. Importantly, this assay did not differentiate between isolates that constitutively produced biofilms, with those that might utilise quorum sensing-like signalling to initiate biofilm-formation, or those that had mutated into a biofilm-forming genotype. Of the 185 environmental pseudomonads tested, 76% were found to produce observable biofilms within 15 days incubation. The phenotypes of these were variable, with biofilm strengths ranging 1500*x*, but could be categorised into the physically-cohesive (PC), floccular mass (FM), waxy aggregate (WA) and viscous mass Many environmental pseudomonads can also be induced to form A-L interface biofilms and to express cellulose using WspR19. When expressed *in trans* in wild-type SBW25 it produces the WS phenotype [60, 70], though in other pseudomonads the impact was found to be more variable. In a test of 16 pseudomonads known to form biofilms and express cellulose, WspR19 was found to significantly increase biofilm attachment, strength, and cellulose expression in *P. fluorescens* 54/96, *P. syringae* DC3000, *P. syringae* T1615 and *P. syringae* 6034 [15] (WspR19 induction of cellulose production by SBW25 and DC3000 is shown in Figure 5). WspR19 also induced a WS-like phenotype in *P. putida* KT2440, despite the fact that biofilm-formation or cellulose expression in this pseudomonad had not been observed in the initial survey (cellulose expression was subsequently reported for both wild-type and WspR19-carrying strains under different experimental conditions by [76]). Similarly, nine of ten non-biofilm– forming and non-cellulose expressing *P. syringae* isolates were found to produce biofilms when induced with WspR19, and two of these also expressed detectable levels of cellulose [15]. These findings suggest that biofilm-formation and cellulose expression in pseudomonads closely related to *P. fluorescens* SBW25 are probably controlled by the same c-*di*-GMP– mediated regulatory system or are sensitive to non-specific increases in c-*di*-GMP levels.

\* Estimated from a sub-sample of 25 isolates. Data compiled from [15] and unpublished research from **a,** R. Ahmed, AK & AJS; **b,** B. Varun, AK & AJS; **c,** D.S. Kumar, AK & AJS; **d,** M. Robertson & AJS; and **e,** AK & AJS.

**Table 4.** Prevalence of A-L interface biofilm formation and cellulose expression amongst environmental pseudomonads

We have conducted additional surveys of pseudomonads isolated from other habitats, including pond water, pitcher plant (*Sarracenia* spp.) deadfall trap-water, spoilt cold-stored meat and mushrooms (Table 4). These confirm the wide-spread ability of environmental pseudomonads to form A-L interface biofilms and to express cellulose under the experimental conditions used previously [15]. It is also evident that pseudomonads are capable of producing a wide range of EPS in addition to cellulose, including alginate, levan, marginalan, PEL, PSL, and a number of other polymers, which may be utilised as biofilm matrix components [77-80].

Cellulose Expression in *Pseudomonas fluorescens* SBW25 and Other Environmental Pseudomonads 17

cellulose expression under some environmental conditions, or that such gene duplications

Finally, the clustering of WssB homologue sequences (Figure 8) generally follows the 16S phylogenetic relationships between bacteria. However, we are surprised to find that *P. fluorescens* SBW25 and *P. syringae* DC300 cluster with many of the *Burkholderia* and *Xanthomonas*, whilst *P. putida* and *P. stutzeri* strains cluster with the enteric bacteria. We have yet to compare the clustering patterns of the WssC, WssD and WssE homologues, where conserved patterns may reflect different functional roles for cellulose and host lifestyles, whilst aberrant placements of single proteins might reflect the random mutation of a

**Figure 8. Cladogram of WssB homologues.** The structure of the WssB cladogram is similar to that constructed using 16s rRNA sequences, with the enteric bacteria and pseudomonads forming two distinct clusters. Within the pseudomonads, the *P. fluorescens-syringae* complex has diverged earlier than the *P. putida-stutzeri* group. The cladogram was constructed using Geneious 5.5.5 (Biomatters Ltd, NZ) default parameters after multiple sequence alignment of 58 WssB proteins by ClustalW 2.0 [82].

phenotype no longer of functional value or under positive selection.

may persist for some time before deletion.


2.1. Use of ZnO/graphene photocatalysts

Photocatalysts are based on semiconductor materials, which are activated by radiation with higher energy than the bandgap of the used semiconductor, in order to create hole-electron pairs, once the electron passes from valence to conduction band. The promoted electron, toward conduction band, and the hole remained in valence band react in the photocatalyst interface with adsorbed substances in order to create reactive entities (free radicals and/or radical anions), which interact with contaminants to degrade them. All these processes imply the sorption on the photocatalyst's interface, its activation by radiation, creation of reactive species, and the recombination of electron to hole. The last could occur very fast that the creation of reactive

species does not take place at great extent, giving ineffective photodegradation process.

groups also consider the modifications with electron-rich species like graphene.

bismuth oxychloride have gained attention for photocatalytic process.

phenol is presented and discussed.

58 Photocatalysts - Applications and Attributes

2. Zinc oxide

parameters implied in the photocatalysis.

In this context, the research regarding photocatalysis, in recent years, is focused to decrease the bandgap of photocatalyst in order to use solar light rather than UV light, which implies additional cost during the treatment process. In addition, minimization of the recombination process, in order to improve the photocatalytic performance, is quite important too. Some approaches to face these issues consider the doping with metals; meanwhile other research

TiO2 has been the photocatalyst by excellence and has been widely studied in its pristine form and/or doped with metals like gold and other elements. Nevertheless, other metal oxides, such as ZnO, have shown better photocatalytic performance, especially when visible light is used. ZnO has also been doped with metals like gold or silver. More recently, other metal oxides like

In this chapter, discussion about the modification of ZnO with graphene is presented and discussed in terms of the implied mechanism (hybridization), in addition to the obtained results when such hybrid photocatalyst was used for the photodegradation of triclosan under visible light. Additionally, the modification method of ZnO with silver nanoparticles and its effect on photocatalytic performance for bisphenol A, Rhodamine B (RhB), and Triclosan is presented.

Finally, the use of an attractive photocatalyst, bismuth oxychloride (BiOCl), and its respective modification with silver and graphene oxide for RhB photodegradation along with the result and mechanism for the photocatalyst based on TiO2-BiOCl used for photodegradation of

The three different photocatalysts show how effective photocatalyst can be obtained and modified. The presented and discussed results contribute to understand some of the key

Zinc oxide (ZnO) is a II-VI group semiconductor with wurtzite structure with lattice parameters a = 0.3296 nm and c = 0.52065 nm. Zn2+ atoms are tetrahedrally coordinated with O2 atoms stacked alternately along the c axis so that d-electrons of zinc are hybridized with 2p-electrons of oxygen [2]. ZnO has the potential to become an important material for photocatalysis because it

is nontoxic (it is often included in pharmaceuticals), photostable, and low cost.

Nowadays, solar energy, radiant light, and heat from the sun are the most abundant available sources of clean energy. Thus, research studies and development of materials that can efficiently harvest solar irradiation and used for green environmental pollution management are essential. Photocatalysis, which could use renewable solar energy to activate the chemical reactions via oxidation and reduction, such as that occurs in advance oxidation processes (AOPs), is a sustainable technology to provide solution for environmental issue. This photocatalysis system has attracted great interest from science community as the most promising way to solve the environmental problems, especially getting rid of residual pollutants from wastewater stream.

In the field of photocatalysis, ZnO has emerged as the leading candidate for green environmental management systems because of its unique characteristics, such as wide bandgap (3.37 eV) in the near-UV spectral region, a large electron exciton binding energy of 60 eV at room temperature, strong oxidation ability, and good photocatalytic property [4]. It is a wellknown fact that ZnO occurs as white hexagonal crystal or white powder known as white zinc. ZnO crystallizes in the wurtzite structure and is available as large bulk single crystals [5]. As an important semiconductor material, ZnO has been applied in catalysis, rubber and paint industries, ceramic bodies, varistors, fertilizers, and cosmetics [6].

Recently, the development of ZnO with precisely controllable features has gained significant scientific interest. The electrical, optical, and magnetic properties of ZnO can be altered or improved by the use of ZnO in nanoscale and efforts have been developed to improve the properties of ZnO photocatalyst [7]. Moreover, ZnO is an environmental friendly material as it is compatible with living organisms [8]. Since ZnO has almost the same bandgap energy as TiO2 (3.2 eV), its photocatalytic capability is anticipated to be similar to that of TiO2. However, ZnO is relatively cheaper compared to TiO2, whereby the usage of titanium dioxide is uneconomic for large-scale water treatment operations [9]. The greatest advantage of ZnO is the ability to absorb a wide range of solar spectrum and more light quanta than some semiconducting metal oxides including the capacity to absorb visible light energy, which is due to its wide band energy. This results in fast recombination of photogenerated charges and thus caused low photocatalytic efficiency.

The recombination of photogenerated hole (hVB+ ) and electron (eCB) is one of the major disadvantages in semiconductor photocatalysis. This recombination step lowers the quantum yield and causes energy wasting. Therefore, the e/h+ recombination process should be inhibited to ensure efficient photocatalysis. Metal doping could counter the recombination problem with efficient charge separation between electrons and holes in ZnO photocatalyst. In addition, the dopants may trap electrons, reducing the chances of e/h+ recombination that deactivate the photocatalytic system [10]. Furthermore, the generation of hydroxyl radicals and active oxygen species will greatly increase resulting from the enhancement in charge separation efficiency [11]. Semiconductors as graphene have been proven as a couple semiconductor that can improve the visible-light photocatalytic efficiency of ZnO due to its remarkable chemical, physical, and mechanical properties, such as large surface area (2600 m2 /g), excellent electrical and thermal conductivity, high mechanical strength, flexibility, and efficient wide range of light adsorption. Due to the properties of graphene-based materials, several ranges of environmental applications have been developed such as absorption, transformation, and detection [12]. So far, numerous methods have been used to design and synthesize ZnO/ graphene hybrid photocatalysts with various morphologies. However, most of these methods rely on chemical and/or high-energy consumption resulting in a costly, environmentally hazardous, and especially inefficient photocatalyst for complete degradation of organic pollutants as triclosan, which has been classified as potential endocrine disrupting compound (EDC). Triclosan was ranked as the most abundant compound among all investigated pharmaceuticals and personal care products with its mean concentration of 12.6 3.8 mg/Kg in 110 biosolids samples collected from 94 US wastewater treatment plants across 32 states and the District of Columbia using EPA Method 1694 [13]. In addition, the highest initial concentrations of triclosan detected in municipal biosolids were 2715 and 1265 μg/Kg [14].

graphene sheets as dopant in ZnO nanocatalyst. It is important to mention that wurtzite has been the structure used in this study with a bandgap of 3.21 eV obtained by UV-vis spectrophotometer, while a value of 3.15 eV for ZnO/graphene composite was obtained. This reduction in the bandgap value is associated to a structure based on good interaction between ZnO nanocatalyst and graphene sheets, which creates intermediate energy levels between both materials, a property that allows to transfer the electrons promoted from the valence band to the conductive band of the ZnO semiconductor to graphene sheets that capture and retain the transferred electrons, improving the photocatalytic performance of ZnO as it is illustrated in Figure 2. This important first approximation has been the result of the evaluation of the effect of the loaded graphene amount in zinc oxide nano-photocatalyst. Graphene concentrations of 0.25 and 0.5 wt% were evaluated for this purpose and the obtained results showed enhancement of the ZnO photocatalytic activity under visible light radiation even using minimum contents of graphene sheets. Thus, 34 and 36% of the initial concentration of triclosan (8 ppm) was degraded using ZnO/graphene composites loaded with 0.25 and 0.5 wt% of graphene, respectively, and the bandgap values were 3.19 and 3.18 eV, for such ZnO/graphene composites. In contrast with 25% of initial triclosan degraded using pristine ZnO (bandgap: 3.21 eV). These results can be compared with those reported in previous investigations related with the photodegradation of triclosan using dopants such as rare-earth elements as Ce (47%) [17], metals such as Au (10% after 5 h) [18], Ag [19], and Cu [20]; as well as oxide compounds as

Figure 1. Schematic illustration of the interaction between ZnO photocatalyst doped with graphene sheets and its

Modified Metallic Oxides for Efficient Photocatalysis http://dx.doi.org/10.5772/intechopen.80834 61

interaction with triclosan.

MgO, WO3, TiO2, ZnO, or graphene oxide [21] using dopant contents up to 10%.

The adsorption properties of the as-prepare ZnO/graphene hybrid photocatalysts doped with different amounts of graphene sheets were one of the most important characteristics to improve the degradation efficiency of the ZnO. The specific area of ZnO and ZnO/graphene

Hydrothermal and chemical reductions have been the main methods studied to obtain ZnO/ graphene hybrid photocatalysts. However, photodeposition method [15] has been reported as an efficient method to generate hybrid photocatalyst to degrade pollutants. This study proposes the synthesis of ZnO/graphene semiconductors by developing a facile, cheap, environmentally and high reproducibility approach to obtain an efficient material to degrade organic pollutants, as triclosan (TCS), under visible light. For instance, it has been demonstrated that inductive irradiation method is possible to synthesize ZnO composites due to its polarity [16]. In particular, graphene has the ability to accept electrons efficiently due to the absence of oxygen chemical groups on its surface preventing the recombination and providing a favorable π-π conjugation between TCS and aromatic region of graphene (Figure 1). The trapped electrons on graphene react with the dissolved oxygen and water to form reactive superoxide and hydroxyl radicals, which further oxidizes triclosan.

The modified photodeposition method has resulted in a successful process to prepare ZnO/ graphene hybrid photocatalysts with enhanced photocatalytic activity under visible light radiation. The obtained results show degradation of 1% of triclosan (8 ppm) in absence of catalyst (photolysis) while this degradation percentage increases up to 42% using 0.5 wt% of

wide band energy. This results in fast recombination of photogenerated charges and thus

disadvantages in semiconductor photocatalysis. This recombination step lowers the quantum yield and causes energy wasting. Therefore, the e/h+ recombination process should be inhibited to ensure efficient photocatalysis. Metal doping could counter the recombination problem with efficient charge separation between electrons and holes in ZnO photocatalyst. In addition, the dopants may trap electrons, reducing the chances of e/h+ recombination that deactivate the photocatalytic system [10]. Furthermore, the generation of hydroxyl radicals and active oxygen species will greatly increase resulting from the enhancement in charge separation efficiency [11]. Semiconductors as graphene have been proven as a couple semiconductor that can improve the visible-light photocatalytic efficiency of ZnO due to its remarkable

electrical and thermal conductivity, high mechanical strength, flexibility, and efficient wide range of light adsorption. Due to the properties of graphene-based materials, several ranges of environmental applications have been developed such as absorption, transformation, and detection [12]. So far, numerous methods have been used to design and synthesize ZnO/ graphene hybrid photocatalysts with various morphologies. However, most of these methods rely on chemical and/or high-energy consumption resulting in a costly, environmentally hazardous, and especially inefficient photocatalyst for complete degradation of organic pollutants as triclosan, which has been classified as potential endocrine disrupting compound (EDC). Triclosan was ranked as the most abundant compound among all investigated pharmaceuticals and personal care products with its mean concentration of 12.6 3.8 mg/Kg in 110 biosolids samples collected from 94 US wastewater treatment plants across 32 states and the District of Columbia using EPA Method 1694 [13]. In addition, the highest initial concentra-

chemical, physical, and mechanical properties, such as large surface area (2600 m2

tions of triclosan detected in municipal biosolids were 2715 and 1265 μg/Kg [14].

and hydroxyl radicals, which further oxidizes triclosan.

Hydrothermal and chemical reductions have been the main methods studied to obtain ZnO/ graphene hybrid photocatalysts. However, photodeposition method [15] has been reported as an efficient method to generate hybrid photocatalyst to degrade pollutants. This study proposes the synthesis of ZnO/graphene semiconductors by developing a facile, cheap, environmentally and high reproducibility approach to obtain an efficient material to degrade organic pollutants, as triclosan (TCS), under visible light. For instance, it has been demonstrated that inductive irradiation method is possible to synthesize ZnO composites due to its polarity [16]. In particular, graphene has the ability to accept electrons efficiently due to the absence of oxygen chemical groups on its surface preventing the recombination and providing a favorable π-π conjugation between TCS and aromatic region of graphene (Figure 1). The trapped electrons on graphene react with the dissolved oxygen and water to form reactive superoxide

The modified photodeposition method has resulted in a successful process to prepare ZnO/ graphene hybrid photocatalysts with enhanced photocatalytic activity under visible light radiation. The obtained results show degradation of 1% of triclosan (8 ppm) in absence of catalyst (photolysis) while this degradation percentage increases up to 42% using 0.5 wt% of

) and electron (eCB) is one of the major

/g), excellent

caused low photocatalytic efficiency.

60 Photocatalysts - Applications and Attributes

The recombination of photogenerated hole (hVB+

Figure 1. Schematic illustration of the interaction between ZnO photocatalyst doped with graphene sheets and its interaction with triclosan.

graphene sheets as dopant in ZnO nanocatalyst. It is important to mention that wurtzite has been the structure used in this study with a bandgap of 3.21 eV obtained by UV-vis spectrophotometer, while a value of 3.15 eV for ZnO/graphene composite was obtained. This reduction in the bandgap value is associated to a structure based on good interaction between ZnO nanocatalyst and graphene sheets, which creates intermediate energy levels between both materials, a property that allows to transfer the electrons promoted from the valence band to the conductive band of the ZnO semiconductor to graphene sheets that capture and retain the transferred electrons, improving the photocatalytic performance of ZnO as it is illustrated in Figure 2. This important first approximation has been the result of the evaluation of the effect of the loaded graphene amount in zinc oxide nano-photocatalyst. Graphene concentrations of 0.25 and 0.5 wt% were evaluated for this purpose and the obtained results showed enhancement of the ZnO photocatalytic activity under visible light radiation even using minimum contents of graphene sheets. Thus, 34 and 36% of the initial concentration of triclosan (8 ppm) was degraded using ZnO/graphene composites loaded with 0.25 and 0.5 wt% of graphene, respectively, and the bandgap values were 3.19 and 3.18 eV, for such ZnO/graphene composites. In contrast with 25% of initial triclosan degraded using pristine ZnO (bandgap: 3.21 eV). These results can be compared with those reported in previous investigations related with the photodegradation of triclosan using dopants such as rare-earth elements as Ce (47%) [17], metals such as Au (10% after 5 h) [18], Ag [19], and Cu [20]; as well as oxide compounds as MgO, WO3, TiO2, ZnO, or graphene oxide [21] using dopant contents up to 10%.

The adsorption properties of the as-prepare ZnO/graphene hybrid photocatalysts doped with different amounts of graphene sheets were one of the most important characteristics to improve the degradation efficiency of the ZnO. The specific area of ZnO and ZnO/graphene hybrid photocatalysts was determined via N2 adsorption isotherms using the Brunauer Emmett Teller (BET) method. The results revealed that the graphene monolayers (44.2 g/m2 ) showed the highest surface area for the analyzed pristine material, while ZnO had a specific area of 10.8 g/m2 . Among the three investigated composites, the photocatalyst loaded with 0.5 wt% of graphene had the highest surface area (18.3 g/m2 ), followed by ZnO/graphene 0.25 wt% (14 g/m2 ) and ZnO/graphene 0.1 wt% (13.3 g/m2 ) catalysts. Thus, the addition of graphene sheets increases the surface area of the hybrid catalysts up to 69% of the initial area of zinc oxide and improve their adsorption capacities, resulting in the first property of the asprepare hybrid composites to increase the degradation of triclosan, as it has been reported previously [22].

confirms the interaction between ZnO and GO given by sp3 defects. The results given hereinabove are consistent with the results in FTIR characterization, revealing the reestablishment of the conjugated graphene oxide network. In contrast, the ratio ID/IG for the composite prepared with graphene sheets was calculated and corresponds to the value of 1.04 (higher than ID/IG of pristine graphene, 0.36) indicating the presence of more defects in the graphene oxide lattice, which implies a decrease in the size of the in-plane sp2 domains and formation of the defects and disorders in the graphene sheets, revealing the reestablishment of the conjugated graphene network (sp2 carbon) [23] in the ZnO/GO photocatalysts due to the hybridization of graphene via photoirradiation method but resulting in a weak interaction due to the absence of chemical groups on the surface of graphene sheets as are presented on GO surface. The interaction between graphene oxide sheets was improved by the interaction of ZnO-polarized structure and the chemical surface of graphene oxide, which contains carbonyl, carboxyl,

The degradation curves of triclosan for ZnO/GO hybrid photocatalyst are presented in Figure 3. It is noticed that the composites obtained by the photodeposition method are the materials with the best performance to degrade triclosan under visible light radiation compared with photolysis

In addition to the photodegradation curves presented in Figure 3, the rate constants are presented

The results show the highest apparent degradation rate constant for the hybrid catalyst syn-

Figure 3. Triclosan photodegradation curves with ZnO/graphene and ZnO/GO hybrid photocatalysts under visible light.

semiconductor, corroborating the importance of interaction between ZnO and GO.

), almost four times higher than the pristine ZnO

Modified Metallic Oxides for Efficient Photocatalysis http://dx.doi.org/10.5772/intechopen.80834 63

experiment and with the degradation using the bare ZnO photocatalyst.

epoxy, and hydroxyl groups.

thesized with graphene oxide (0.003 min1

in Table 1.

Conditions: 23C, pH = 7.

In order to study the effect of the method of synthesis in the ZnO/graphene hybrids, composites were prepared by impregnation method with graphene contents of 0.5 wt% using continuous stirring in the absence of UV radiation. The resultant photocatalysts were tested to degrade triclosan under visible light radiation, and it was obtained that 15% of the initial concentration of triclosan was degraded, 53% less than the composites synthesized by photodeposition method as it can be observed in Figure 2.

The hybridization of ZnO with graphene has been studied and confirmed by Raman spectroscopy integrating the intensity ratio of the D to G bands characteristic for carbon materials. The G peak arises from the stretching of C-C bond of graphite materials and is highly sensitive to strain effects in sp2 system, while D peak is caused by the disordered structure of graphene material. Regarding the sp3 and sp2 hybridizations ID/IG value, in the case of pristine graphene oxide was 0.93, indicating that the intensity of the G band is higher than D band, which results in a lower amount of sp3 defects and less structural disorder. Compared with graphene oxide (0.93), the reduction of ID/IG ratio for ZnO/GO 0.5 wt% hybrid photocatalyst (ID/IG = 0.91) is observed, implying a reduction of sp3 defects compared with pure graphene oxide. This fact

Figure 2. Degradation curves of triclosan under visible light radiation conditions: 23C, pH = 7.

confirms the interaction between ZnO and GO given by sp3 defects. The results given hereinabove are consistent with the results in FTIR characterization, revealing the reestablishment of the conjugated graphene oxide network. In contrast, the ratio ID/IG for the composite prepared with graphene sheets was calculated and corresponds to the value of 1.04 (higher than ID/IG of pristine graphene, 0.36) indicating the presence of more defects in the graphene oxide lattice, which implies a decrease in the size of the in-plane sp2 domains and formation of the defects and disorders in the graphene sheets, revealing the reestablishment of the conjugated graphene network (sp2 carbon) [23] in the ZnO/GO photocatalysts due to the hybridization of graphene via photoirradiation method but resulting in a weak interaction due to the absence of chemical groups on the surface of graphene sheets as are presented on GO surface. The interaction between graphene oxide sheets was improved by the interaction of ZnO-polarized structure and the chemical surface of graphene oxide, which contains carbonyl, carboxyl, epoxy, and hydroxyl groups.

hybrid photocatalysts was determined via N2 adsorption isotherms using the Brunauer Emmett Teller (BET) method. The results revealed that the graphene monolayers (44.2 g/m2

showed the highest surface area for the analyzed pristine material, while ZnO had a specific

graphene sheets increases the surface area of the hybrid catalysts up to 69% of the initial area of zinc oxide and improve their adsorption capacities, resulting in the first property of the asprepare hybrid composites to increase the degradation of triclosan, as it has been reported

In order to study the effect of the method of synthesis in the ZnO/graphene hybrids, composites were prepared by impregnation method with graphene contents of 0.5 wt% using continuous stirring in the absence of UV radiation. The resultant photocatalysts were tested to degrade triclosan under visible light radiation, and it was obtained that 15% of the initial concentration of triclosan was degraded, 53% less than the composites synthesized by

The hybridization of ZnO with graphene has been studied and confirmed by Raman spectroscopy integrating the intensity ratio of the D to G bands characteristic for carbon materials. The G peak arises from the stretching of C-C bond of graphite materials and is highly sensitive to strain effects in sp2 system, while D peak is caused by the disordered structure of graphene material. Regarding the sp3 and sp2 hybridizations ID/IG value, in the case of pristine graphene oxide was 0.93, indicating that the intensity of the G band is higher than D band, which results in a lower amount of sp3 defects and less structural disorder. Compared with graphene oxide (0.93), the reduction of ID/IG ratio for ZnO/GO 0.5 wt% hybrid photocatalyst (ID/IG = 0.91) is observed, implying a reduction of sp3 defects compared with pure graphene oxide. This fact

0.5 wt% of graphene had the highest surface area (18.3 g/m2

photodeposition method as it can be observed in Figure 2.

Figure 2. Degradation curves of triclosan under visible light radiation conditions: 23C, pH = 7.

) and ZnO/graphene 0.1 wt% (13.3 g/m2

. Among the three investigated composites, the photocatalyst loaded with

area of 10.8 g/m2

62 Photocatalysts - Applications and Attributes

0.25 wt% (14 g/m2

previously [22].

)

), followed by ZnO/graphene

) catalysts. Thus, the addition of

The degradation curves of triclosan for ZnO/GO hybrid photocatalyst are presented in Figure 3. It is noticed that the composites obtained by the photodeposition method are the materials with the best performance to degrade triclosan under visible light radiation compared with photolysis experiment and with the degradation using the bare ZnO photocatalyst.

In addition to the photodegradation curves presented in Figure 3, the rate constants are presented in Table 1.

The results show the highest apparent degradation rate constant for the hybrid catalyst synthesized with graphene oxide (0.003 min1 ), almost four times higher than the pristine ZnO semiconductor, corroborating the importance of interaction between ZnO and GO.

Figure 3. Triclosan photodegradation curves with ZnO/graphene and ZnO/GO hybrid photocatalysts under visible light. Conditions: 23C, pH = 7.

stronger than those for O2

trons [24] as shown in Figure 5.

development of ZnO/graphene hybrid photocatalysts.

2.2. ZnO modification by inorganic molecules: silver

•, which suggests the predominance of oxidative reactions whose

Modified Metallic Oxides for Efficient Photocatalysis http://dx.doi.org/10.5772/intechopen.80834 65

holes are responsible for the degradation of triclosan. Furthermore, ZnO photocatalyst presents visible light photocatalytic activity but generates stronger visible light after graphene hybridization, showing that graphene oxide is responsible for the visible light performance, which is induced by the injection of an excited electron from the lowest unoccupied molecular orbit (LUMO) of graphene to the conduction band (CB) of ZnO. The introduction of the graphene semiconductors can possibly cause the rapid separation of electron-hole pairs during irradiation [11] prolonging the electron-hole pair lifetime and accelerating the transfer rate of elec-

In conclusion, the adsorption properties, good interaction between ZnO- and graphene-based materials, chemical structure of graphene, method of synthesis, and concentration of the dopant used to hybridize ZnO catalyst are the most important properties that affect the

Silver nanoparticles are linked to the ZnO surface through the alkanethiol surfactant (Figure 6a). The stabilizer ligands COOH-(CH2)n-S-Ag keep nanoparticles as small as 7 nm in the solution and 15–26 nm in the Ag/ZnO photocatalyst, corroborated by XRD; although TEM analysis shows Ag nanoparticles of spherical shape and defined boundaries smallest as 3 nm over ZnO surface (Figure 6b-d). We studied the effect of the pH and time on the functionalization of ZnO nanoagglomerates by two methods denominated as photodeposition (PD) and impregnation (IMP) [15]. We propose to replace the ambiguous terms "doping" with functionalization when spoke of superficial ZnO modification. For instance, the sample 1%Ag/ZnO-PD11,1 synthesized by the PD method using 1 wt.% Ag at pH 11 and 1 h under UV light, a functionalization yield of 100% was corroborated by elemental analysis by inductively coupled plasma spectrometry ICP-OES and SEM-EDX. The UV irradiation produces free radicals (●OH, ●O) that degrade the ligand and release the silver nanoparticles onto the ZnO surface (Figure 6c). Byproducts of surfactant decomposition accumulate in ZnO are observed by IR. This functionalization of the

Figure 5. Schematic illustration of the photocatalytic process in the ZnO/GO hybrid semiconductor.

Table 1. Apparent rate constants for triclosan photodegradation under visible light.

Figure 4. EPR spectra of ZnO/GO hybrid photocatalyst irradiated under visible light in (a) water and (b) ethanol solvents. DMPO was used as a radical trapper.

The mechanism of the best as-prepare ZnO/GO hybrid composite was proposed. Thus, the ESR spin-trap technique (with DMPO) was used to monitor the reactive oxygen species generated during the irradiation of the hybrid photocatalyst and the results are shown in Figure 4. Both signals of DMPO-• OH and DMPO-O2 • are clearly observed when pristine ZnO and ZnO/GO were exposed to visible radiation. Therefore, a dual mechanism involving both hydroxyl radicals and superoxide radicals is expected in the photocatalytic process. However, the signals for hybrid photocatalysts are stronger than the signals in pristine ZnO, thus accounting for the higher and stable photocatalytic performance of hybrid composites than bare ZnO toward the degradation of triclosan. The hydroxyl radicals trapped by DMPO (DMPO-• OH) and superoxide radicals (DMPO-O2 •) for ZnO and hybrid photocatalysts were characterized by detecting four characteristic signals in water, and six signals in ethanol for DMPO-• OH and DMPO-O2 •, respectively. In both cases, it is noticed that the signals for hybrid material are more pronounced than those for the ZnO pristine sample, thus accounting for the better photocatalytic performance.

Thus, the enhanced photocatalytic activity of ZnO/GO photocatalyst is due to the introduction of carbon material, which promotes an increase in charge separation to effective utilization of electrons to produce more • OH and O2 • radicals. In this case, the signals of • OH radicals are stronger than those for O2 •, which suggests the predominance of oxidative reactions whose holes are responsible for the degradation of triclosan. Furthermore, ZnO photocatalyst presents visible light photocatalytic activity but generates stronger visible light after graphene hybridization, showing that graphene oxide is responsible for the visible light performance, which is induced by the injection of an excited electron from the lowest unoccupied molecular orbit (LUMO) of graphene to the conduction band (CB) of ZnO. The introduction of the graphene semiconductors can possibly cause the rapid separation of electron-hole pairs during irradiation [11] prolonging the electron-hole pair lifetime and accelerating the transfer rate of electrons [24] as shown in Figure 5.

In conclusion, the adsorption properties, good interaction between ZnO- and graphene-based materials, chemical structure of graphene, method of synthesis, and concentration of the dopant used to hybridize ZnO catalyst are the most important properties that affect the development of ZnO/graphene hybrid photocatalysts.

### 2.2. ZnO modification by inorganic molecules: silver

The mechanism of the best as-prepare ZnO/GO hybrid composite was proposed. Thus, the ESR spin-trap technique (with DMPO) was used to monitor the reactive oxygen species generated during the irradiation of the hybrid photocatalyst and the results are shown in

Figure 4. EPR spectra of ZnO/GO hybrid photocatalyst irradiated under visible light in (a) water and (b) ethanol solvents.

• are clearly observed when pristine

•) for ZnO and hybrid photocatalysts were

OH radicals are

•, respectively. In both cases, it is noticed that the signals for

• radicals. In this case, the signals of •

OH and DMPO-O2

ZnO and ZnO/GO were exposed to visible radiation. Therefore, a dual mechanism involving both hydroxyl radicals and superoxide radicals is expected in the photocatalytic process. However, the signals for hybrid photocatalysts are stronger than the signals in pristine ZnO, thus accounting for the higher and stable photocatalytic performance of hybrid composites than bare ZnO toward the degradation of triclosan. The hydroxyl radicals trapped by DMPO

characterized by detecting four characteristic signals in water, and six signals in ethanol for

hybrid material are more pronounced than those for the ZnO pristine sample, thus accounting

Thus, the enhanced photocatalytic activity of ZnO/GO photocatalyst is due to the introduction of carbon material, which promotes an increase in charge separation to effective utilization of

Figure 4. Both signals of DMPO-•

DMPO was used as a radical trapper.

64 Photocatalysts - Applications and Attributes

OH and DMPO-O2

electrons to produce more •

for the better photocatalytic performance.

OH) and superoxide radicals (DMPO-O2

Table 1. Apparent rate constants for triclosan photodegradation under visible light.

OH and O2

(DMPO-•

DMPO-•

Silver nanoparticles are linked to the ZnO surface through the alkanethiol surfactant (Figure 6a). The stabilizer ligands COOH-(CH2)n-S-Ag keep nanoparticles as small as 7 nm in the solution and 15–26 nm in the Ag/ZnO photocatalyst, corroborated by XRD; although TEM analysis shows Ag nanoparticles of spherical shape and defined boundaries smallest as 3 nm over ZnO surface (Figure 6b-d). We studied the effect of the pH and time on the functionalization of ZnO nanoagglomerates by two methods denominated as photodeposition (PD) and impregnation (IMP) [15]. We propose to replace the ambiguous terms "doping" with functionalization when spoke of superficial ZnO modification. For instance, the sample 1%Ag/ZnO-PD11,1 synthesized by the PD method using 1 wt.% Ag at pH 11 and 1 h under UV light, a functionalization yield of 100% was corroborated by elemental analysis by inductively coupled plasma spectrometry ICP-OES and SEM-EDX. The UV irradiation produces free radicals (●OH, ●O) that degrade the ligand and release the silver nanoparticles onto the ZnO surface (Figure 6c). Byproducts of surfactant decomposition accumulate in ZnO are observed by IR. This functionalization of the

Figure 5. Schematic illustration of the photocatalytic process in the ZnO/GO hybrid semiconductor.

stirring results in heterogeneously distributed silver nanoparticles of average size of 15 nm determined by Scherrer equation. The surfactant decomposes almost completely during the heating (at 300C) that releases AgNPs onto ZnO surface. As before, residuals S-H and C-H functionalizing the ZnO surface was observed by IR (Figure 6a). Similarly, the as-synthesized 1%Ag/ZnO-IMP samples absorb in visible region of the spectrum and silver nanoparticles

It is challenging to control the metallic particle size because the nanoparticles have the trend to form agglomerates. The deposition of silver nanoparticles over metallic oxides from preformed nanoparticles using, for example, chemical vapor deposition [27] has been used, but IMP and PD methods demonstrate to be a successful bulk functionalization of ZnO at room temperature and atmospheric pressure. The increase of photocatalytic efficiency by silvermodified ZnO is demonstrated on the degradation of endocrine disruptors (i.e., bisphenol-A), an emergent contaminant (i.e., triclosan), and a dye (i.e., RhB) under visible light, which represents an important achievement in the use of solar-driven Ag/ZnO photocatalysts.

Figure 6e-g shows the progress of the contaminant photodegradation under visible light

show that 25% of bisphenol-A (10 mg/L) was destroyed after 3 h using Ag/ZnO-PD, and it represents an improvement of 100% compared with ZnO. A total of 35% of initial triclosan (20 mg/L) was destroyed within 3 h using Ag/ZnO-IMP11, represents an improvement of 45% compared with ZnO. Finally, 90% of dye discoloration is obtained with Ag/ZnO-PD11, being

Similarly, the photocatalysts were tested under UV light (302 nm). The use of BET surface area normalization of the apparent rate constant (kapp/BET ssa) in photocatalysis was proposed to clearly demonstrate that ZnO nanoagglomerates is 400% faster than Pi-25, a TiO2 well-known and extensively used photocatalyst from Degussa. The bandgap energy of ZnO and titanium dioxide (TiO2) is basically the same (3.2 eV). However, the valence and conduction bands exhibit differences in electric potential values; whose reported values are in the range of 0.45 to 2.75 eV vs. NHE and 0.1 to 3.1 eV vs. NHE, for ZnO and TiO2, respectively [28, 29]. Thus, the photogenerated holes in ZnO have strong enough oxidizing power to decompose most organic compounds. Furthermore, 1%Ag/ZnO-PD11,1 photocatalytic activity is 370% faster than ZnO attributed to the photoexcited electron trapping in the metallic primary (e/h+ pair)

effect of pH, photocatalyst dosage, and bisphenol-A concentration on the kinetic rate constant

The utilization of powder photocatalyst may end unpractical for industrial scales because of the technical challenges like efficient dispersion and finally difficult separation of photocatalyst after the reaction that may entail important energetic costs and sometimes even producing a secondary pollution. Besides, photocorrosion is an important drawback in photocatalysis, and the anchoring of silver has been proved to control its progress. The

, 8 W 3UV-38 UVP Inc. lamp, lab-made reactor) at 20C. The results

OH) for the oxidation of bisphenol-A. The

Modified Metallic Oxides for Efficient Photocatalysis http://dx.doi.org/10.5772/intechopen.80834 67

induce a surface-localized plasmon resonance.

(365 nm, 0.97 mW/cm2

only 20% better than ZnO.

and secondary active species (free radicals, i.e., •

2.3. ZnO immobilization by organic molecules: poly (acrylic acid)

were also studied extensively and reported [3].

Figure 6. FTIR (a) and TEM image (b) of the as-synthesized photocatalyst functionalized ZnO by silver nanoparticles. Schematic illustration of the functionalization by PD method. (c). Histogram of silver particle size (d). Photocatalytic degradation of bisphenol A (e), triclosan (f), and RhB (g).

photocatalyst surface with S-H, C-O, and hydroxyl groups (OH) creates defect sites advantageous in photocatalysis. Silver-experienced redox processes during PD functionalization, for instance, oxidation (Ag+ /Ag0 , +0.799 eV vs. SHE) by photogenerated holes (+2.75 eV, vs. SHE) and free radicals. They reduce again into the zero-valence form (Ag0 ) by photoexcited electrons. This method favors insertion of ionic silver Ag+ into ZnO crystalline structure perceived as an expansion of lattice parameters measured by XRD. The new attached silver possibly anchors on the surface defect sites of ZnO [25, 26]. The role of the metallic modifier in Ag/ZnO is to promote the pair electron-hole (e/h+ ) separation and to increase the photocatalyst sensitivity toward visible light, in our case, evidenced as an absorption in the visible region by UV-Vis spectroscopy.

The IMP functionalization mechanism is different in the sense that silver nanoparticles and ZnO interaction is a function of the reaction time for an optimum of 2 h. For instance, the sample 1%Ag/ZnO-IMP11,2 synthesized using 1 wt.% Ag at pH 11 and 2 h under vigorous stirring results in heterogeneously distributed silver nanoparticles of average size of 15 nm determined by Scherrer equation. The surfactant decomposes almost completely during the heating (at 300C) that releases AgNPs onto ZnO surface. As before, residuals S-H and C-H functionalizing the ZnO surface was observed by IR (Figure 6a). Similarly, the as-synthesized 1%Ag/ZnO-IMP samples absorb in visible region of the spectrum and silver nanoparticles induce a surface-localized plasmon resonance.

It is challenging to control the metallic particle size because the nanoparticles have the trend to form agglomerates. The deposition of silver nanoparticles over metallic oxides from preformed nanoparticles using, for example, chemical vapor deposition [27] has been used, but IMP and PD methods demonstrate to be a successful bulk functionalization of ZnO at room temperature and atmospheric pressure. The increase of photocatalytic efficiency by silvermodified ZnO is demonstrated on the degradation of endocrine disruptors (i.e., bisphenol-A), an emergent contaminant (i.e., triclosan), and a dye (i.e., RhB) under visible light, which represents an important achievement in the use of solar-driven Ag/ZnO photocatalysts.

Figure 6e-g shows the progress of the contaminant photodegradation under visible light (365 nm, 0.97 mW/cm2 , 8 W 3UV-38 UVP Inc. lamp, lab-made reactor) at 20C. The results show that 25% of bisphenol-A (10 mg/L) was destroyed after 3 h using Ag/ZnO-PD, and it represents an improvement of 100% compared with ZnO. A total of 35% of initial triclosan (20 mg/L) was destroyed within 3 h using Ag/ZnO-IMP11, represents an improvement of 45% compared with ZnO. Finally, 90% of dye discoloration is obtained with Ag/ZnO-PD11, being only 20% better than ZnO.

Similarly, the photocatalysts were tested under UV light (302 nm). The use of BET surface area normalization of the apparent rate constant (kapp/BET ssa) in photocatalysis was proposed to clearly demonstrate that ZnO nanoagglomerates is 400% faster than Pi-25, a TiO2 well-known and extensively used photocatalyst from Degussa. The bandgap energy of ZnO and titanium dioxide (TiO2) is basically the same (3.2 eV). However, the valence and conduction bands exhibit differences in electric potential values; whose reported values are in the range of 0.45 to 2.75 eV vs. NHE and 0.1 to 3.1 eV vs. NHE, for ZnO and TiO2, respectively [28, 29]. Thus, the photogenerated holes in ZnO have strong enough oxidizing power to decompose most organic compounds. Furthermore, 1%Ag/ZnO-PD11,1 photocatalytic activity is 370% faster than ZnO attributed to the photoexcited electron trapping in the metallic primary (e/h+ pair) and secondary active species (free radicals, i.e., • OH) for the oxidation of bisphenol-A. The effect of pH, photocatalyst dosage, and bisphenol-A concentration on the kinetic rate constant were also studied extensively and reported [3].


**15. Conclusion**

Nuclear medicine techniques supply physiological information that is complementary to that provided by radiological techniques and can play a fundamental role not only for the examination and treatment of articular disorders but also in overall patient evaluation.

Though scintigraphical examination is ideal in the early stages of diseases, it also plays a complementary role to radiographical investigations in more advanced disease stages. An assessment as complete as possible which includes different complementary studies must be performed to achieve the best diagnostic and prognostic accuracy. In this context, conventional scintigraphy is still a major test in a limited number of rheumatological diseases such as Paget, reflex sympathetic dystrophy and osteonecrosis, and can be a useful complementary study in other diseases. New molecular imaging tools for the evaluation of musculoskeletal diseases are now available and these particular tools will advance the understanding and management of several chronic musculoskeletal diseases. In the next decade, PET/CT and SPECT/CT will be the major workhorses for molecular imaging, with the advantage that PET-based technologies have high sensitivity and the ability to use biologic molecules that can be radiolabelled.

Despite the important role of the anatomic imaging techniques in the evaluation of primary bone tumors and metastases, radionuclide imaging techniques have all been used in the assessment of these disorders. PET and hybrid PET/CT imaging are becoming the most important modalities in this field.

Β-radiation emission from some radionuclides has been exploited by nuclear medicine and has been used to treat benign joint pathologies, as well as treating several forms of neoplasia. It is of interest in the field of rheumatology, since it is as a safe procedure and, after intra-articular administration of suitable radiopharmaceuticals, is able to control proliferation of the inflamed synovial membrane in the treatment of chronic arthropathies, particularly in the initial stages of the disease.