Photocatalytic and Photoelectrocatalytic systems for water remediation and energy applications

Abstract

This PhD work consists of two main parts. The first part focuses on photocatalytic systems for water remediation from bacteria and phenolic compounds, and the second part deals with photoelectrocatalytic systems for biomass conversion to fuel.

Due to the diminishing access to safe drinking water, there is an emerging need for a sustainable technology that decontaminates water from all major contaminants such as dyes, phenolics, and pathogenic bacteria. In this thesis, two different photocatalytic systems are developed for treating these pollutants. The first system studied is Niobia based photocatalytic system. To enhance the photocatalytic activity, metals such as Sr, Y, Zr and Ag were incorporated into the crystal structure of Nb2O5. This led to increase in the surface area as well as increase in the lifetime of the charge carriers. As a result, there was enhancement in the photocatalytic activity towards the degradation of the pollutants. The second system studied is AgBiO3 perovskite based photocatalytic system. The catalyst was synthesized via hydrothermal route and were characterized for their optical and electrochemical properties. Further, a facile method was developed to strongly couple AgBiO3 onto a membrane consisting of Polyvinylidene fluoride (PVDF) and Poly (butylene succinate-co-adipate) (PBSA). Due to the strong coupling, the integrity of the catalyst was retained and no significant leaching of Ag or Bi ions from the composite membranes was observed. The bactericidal response of this composite membrane was assessed using E.coli as the model bacterium. In addition, the efficacy of this strategy was extended to decontaminate secondary wastewater. The photocatalytic activity of the composite membrane was durable and highly effective in degrading nitrophenol as well. Besides improving the flux, this facile strategy also enhanced the protein fouling resistance against Bovine serum albumin (BSA) and rendered robust bactericidal action.

Photoelectrochemical cells have been used as one of the most common artificial photosynthetic approaches to mimic natural photosynthetic water splitting reactions. However, despite the tremendous advances made to improve the affordability and efficiency of photoelectrochemical water splitting, it is still not an economically feasible method to produce solar fuels; currently only the H2 evolving reduction half-reaction generates valuable fuels. Herein, we show that besides water oxidation, photoelectrocatalytic reaction can be utilized for combining biomass valorisation to fuels and H2 production, thus offering possibilities for artificial photosynthetic applications which generate valuable products in both reduction and oxidation half reactions.