3 - Different strategies of surface modification to improve the photocatalysis properties: pollutant adsorption, visible activation, and catalyst recovery

Abstract

The objective of this chapter is to describe our work in developing various strategies of surface modification in order to (1) enhance the adsorption capacity of the organic pollutants, (2) accelerate the kinetics of degradation, (3) shift the light activation toward visible and solar light, and (4) facilitate the catalyst recovery to be able to reuse easily the catalyst. The different options are compared for the degradation of methyl orange under the same experimental conditions. In order to enhance the adsorption capacity of the organic pollutants (1), two original approaches have been developed. The first one leads to the modification of the hydrophilic/hydrophobic properties of the catalyst via the grafting of organosilane onto TiO2. The aim of the second approach is to increase the surface area of the photocatalyst thanks to the immobilization of TiO2 onto bentonite clay. To accelerate the kinetics of degradation of the pollutant (2), the mixing of TiO2 and ZnO to produce ZnO/TiO2 systems has been evaluated. To improve the photochemical properties of the catalyst (3), the grafting of photosensitizers (PSs) such as monocarboxylic tetraphenyl porphyrin, chlorin e6, tetrakis(4-carboxyphenyl)porphyrin, and protoporphyrin IX has been conducted. These PSs serve as visible light antenna to modify the ultraviolet-limited photoresponse properties of the hybridized TiO2 nanoparticles toward visible light activation. In order to facilitate the catalyst recovery (4), the use of thermoresponsive photocatalyst has been developed. Thermoresponsive copolymers based on 2-(2-methoxyethoxy) ethyl methacrylate and oligo (ethylene glycol) methacrylate have been grown from the surface of the ZnO photocatalyst. The recovery of the particles is based on the aggregation of the particles at high temperature and their redispersion at low temperature.