Optimizing the photocatalytic properties of macroporous geopolymer foam: Influence of SILAR-technique synthesis conditions

Abstract

Macroporous cross-linked materials such as 3D honeycomb foams are used as substrates for heterogeneous photocatalysis. They offer a number of interesting properties. They are highly open-porosity substrates, guaranteeing optimum mass and radiation transfer, making them ideal for photo-conversion applications such as photo-oxidation or photo-reduction, which take place in photo-reactors for pollutant degradation or solar fuel production. Many cross-linked supports such as polymeric and metallic foams studied in the literature have revealed photocatalytic capacities similar to those obtained for the catalyst nanoparticle suspensions used as a reference. To reduce the production costs of this type of material, geopolymers, widely used in civil engineering, offer a wide range of properties suitable for shaping cellular foams. In addition to their low cost and mechanical properties, it is also possible to impart porous properties and modulate their characteristics according to the synthesis operating conditions so as to elaborate macroporous cellular foams. In this study, we propose to investigate the photocatalytic properties of honeycomb geopolymer foams coated with a catalyst: ZnO. To achieve ZnO deposition, the SILAR technique was applied by modifying the key synthesis operating conditions, i.e. precursor concentration and the number of quenching cycles applied. The results obtained make it possible to define the optimum operating conditions (pH, temperature) and, above all, the number of cycles and precursor concentration required to obtain the best photocatalytic efficiency. These innovative and promising materials, little studied in the literature, are prime candidates for solar photo-conversion applications.