pH affects the reaction rate due to a variety of reasons. At a low pH, complexation of  also occurs, leading to lower availability of  to form reactive oxidative species (OH). Lower pH also results in the scavenging of OH by excess , hence reducing its reaction rate. Whereas at high pH, the reaction slows down due to precipitation of Fe(OH), lowering the concentration of the  species in solution. Solubility of iron species is directly governed by the solution's pH.  is about 100 times less soluble than  in natural water at near-neutral pH, the ferric ion concentration is the limiting factor for the reaction rate. Under high pH conditions, the stability of the HO is also affected, resulting in its self-decomposition. Higher pH also decreased the redox potential of OH thereby reducing its effectiveness. pH plays a crucial role in the formation of free radicals and hence the reaction performance. Thus ongoing research has been done to optimize pH and amongst other parameters for greater reaction rates.