what can be other reasons such as surface charge, absorption etc. Please provide detailed explanation and reading material.
Photocatalytic processes are considered redox processes initiated by charge carriers (electrons and holes) separated after excitation of the photocatalyst. As it is known - the valence band and conduction band of photocatalyst lies around certain potential values. When the redox potential of the reaction is higher than conduction band edge potential - then the reaction is impossible due to the fact that electron wants to decrease its energy. The same happens when reaction redox potential lies under the potential of the edge of valence band. Pollutants can be also degraded by radicals which arise in described processes or in the case in which the organic molecule (most often dye - it is called a sensitizer) is excited and then the electron can be transferred from the LUMO orbital of this molecule to the conduction band of the semiconductor and then radicals can arise in reaction with the electron from conduction band. Of course the LUMO orbital of sensitizer must have greater energy than conduction band of the photocatalyst. This process in known in literature as photosensitization. In some cases the pollutant can be a sensitizer itself.
These phenomena, as well as possibility of adsorption of pollutants on photocatalyst surface or possibility of absorption of the light from certain range, or the rate of charge carrier recombination etc. can affect photocatalytic activity of the material.
Some photocatalysts are unable to degrade certain pollutants in the process of photocatalysis because it is necessary to choose the effective catalyst for a particular application.
Determine the necessary characteristics and properties of the catalyst before its use in the degradation reaction.
For this, a bibliographic study is needed to find the conditions favorable to this degradation.
Initially you can think of changing light source which will supply the photons of appropriate wavelength or try adding some activators like hydrogen peroxide or persulphate. However, a quick literature survey is recommended to find out the nature of pollutant and the catalyst you are using.
Amruta Deshmukh Ponkshe
Catalyst dose, pH, temperature, light source, concentration of the solution, nature of the water matrix, band gap energy of the photocatalyst, presence of electron scavengers etc etc...There are so many reasons....You need to specify the catalyst and pollutant first.
Strongly agree with Anna Jakimińska. Moreover, selection of photocatalyst is a main thing in order to know about certain bandgap values and their effective use for specific pollutant degradation
you can see this paper Article Role of Fe(III) in aqueous solution or deposited on ZnO surf...
Convinced with this answer:
Photocatalytic processes are considered redox processes initiated by charge carriers (electrons and holes) separated after excitation of the photocatalyst. As it is known - the valence band and conduction band of photocatalyst lies around certain potential values. When the redox potential of the reaction is higher than conduction band edge potential - then the reaction is impossible due to the fact that electron wants to decrease its energy. The same happens when reaction redox potential lies under the potential of the edge of valence band. Pollutants can be also degraded by radicals which arise in described processes or in the case in which the organic molecule (most often dye - it is called a sensitizer) is excited and then the electron can be transferred from the LUMO orbital of this molecule to the conduction band of the semiconductor and then radicals can arise in reaction with the electron from conduction band. Of course the LUMO orbital of sensitizer must have greater energy than conduction band of the photocatalyst. This process in known in literature as photosensitization. In some cases the pollutant can be a sensitizer itself.
These phenomena, as well as possibility of adsorption of pollutants on photocatalyst surface or possibility of absorption of the light from certain range, or the rate of charge carrier recombination etc. can affect photocatalytic activity of the material.