New TiO2hybrid composites were prepared from
kaolin
clay, predried and carbonized biomass, and titanium tetraisopropoxide
and explored for tetracycline (TET) and bisphenol A (BPA) removal
from water. Overall, the removal rate is 84% for TET and 51% for BPA.
The maximum adsorption capacities (qm)
are 30 and 23 mg/g for TET and BPA, respectively. These capacities
are far greater than those obtained for unmodified TiO2. Increasing the ionic strength of the solution does not change the
adsorption capacity of the adsorbent. pH changes only slightly change
BPA adsorption, while a pH > 7 significantly reduces the adsorption
of TET on the material. The Brouers–Sotolongo fractal model
best describes the kinetic data for both TET and BPA adsorption, predicting
that the adsorption process occurs via a complex mechanism involving
various forces of attraction. Temkin and Freundlich isotherms, which
best fit the equilibrium adsorption data for TET and BPA, respectively,
suggest that adsorption sites are heterogeneous in nature. Overall,
the composite materials are much more effective for TET removal from
aqueous solution than for BPA. This phenomenon is assigned to a difference
in the TET/adsorbent interactions vs the BPA/adsorbent interactions:
the decisive factor appears to be favorable electrostatic interactions
for TET yielding a more effective TET removal.