Visible/solar light active photocatalysts for organic effluent treatment: Fundamentals, mechanisms and parametric review

Intensive research work is being undertaken globally to effectively use the process of photocatalysis for the degradation of organic pollutants from industrial effluents. For the same, TiO2 has been extensively explored, which however, has a limitation of being able to utilise the UV spectrum only, due to its high band gap property. Since a substantial percentage of the solar spectrum is visible light, it is imperative that for an effective and versatile utilisation of the incident solar energy, visible light active photocatalysts, having a relatively smaller band gap are developed. Smaller band gap, however, often results in rapid recombination and conversion of photonic energy into non-usable heat. This article is a review of the science behind the performance of visible/solar light active photocatalysts. The first part includes the fundamentals of photocatalysis, including thermodynamics, reaction kinetics and recombination. The second part reviews the visible/solar light active photocatalytic materials as well as the significant research efforts made so far in the exploration of possible mechanisms of photoexcitation and remedies for minimization of recombination. Finally, an operational overview is provided which is helpful in assessing the influence of key parameters on the photocatalytic activity. This review presents a single point reference for a comparative study and ready assimilation of the basics and new directions in photocatalysis, thus making it more conducive to further research and active commercialisation.