Ternary lanthanum cobaltite perovskite and titania based nanocomposites for photocatalytic renewable hydrogen production

Abstract

Photocatalytic hydrogen (H2) production via water splitting is one of the favourable technologies to overcome concerns of exploitation of fossil fuels and issues of global warming. Thus, it is recognized as clean solar to energy conversion for replacing non-renewable fossil fuels. However, available semiconductors and photoreactors are less efficient for splitting water into renewable H2 under solar energy. The objective of this study is to design and develop structured photocatalysts and photoreactors for stimulating photocatalytic H2 production. Specifically, cocatalyst including titanium aluminium carbide (Ti3AlC2) and titanium carbide (Ti3C2) MXene multilayers heterojunctions with TiO2 and graphitic carbon nitride nanosheets (PCN) were fabricated to promote conductive properties. Further modification of TiO2 and PCN was carried out to form ternary nanocomposites involving lanthanum cobaltite (LaCoO3) perovskite and nickel phosphide (Ni2P) to maximize photoactivity under visible light irradiations. Initially, the hydrofluoric acid etching process was employed to get Ti3C2 multilayers, whereas, LaCoO3 nanotextures were obtained through hydrothermal method. Good morphology, improved light absorption, and superior charge separation were observed in the Ti3AlC2/TiO2/Ni2P, and LaCoO3/g-C3N4/TiO2@Ti3C2 nanocomposites. The performance of nanocomposites was determined in a liquid phase slurry photoreactor under visible irradiation. The TiO2 grown Ti3C2 modified LaCoO3/g-C3N4 composite generated 125 μmol of H2, significantly higher than pure components, attributing to the visible light activity, efficient mobility and charge separation, good interfacial contact and conductivity of Ti3C2. Comparatively, Ti3AlC2 modified TiO2/Ni2P generated 1300 μmol of H2 based on the inhibited charge recombination, improved visible light response and good redox potential of TiO2. The comparative performance of slurry, fixed bed, and monolith photoreactors over Ti3AlC2/TiO2/Ni2P was conducted. The monolith photoreactor generated 2050 μmol of H2 under ultraviolet light which was 136 times higher than H2 generated from monolith photoreactor under visible light. This is attributed to the improved light penetration of ultraviolet light into monolith channels for maximum interaction with catalysts. The highest H2 generating Ti3AlC2/TiO2/Ni2P nanocomposite was involved in testing of operating parameters using response surface methodology for optimization with the amount of H2 as the response. Optimization revealed 10.5 methanol concentration, 0.11 g catalyst loading and 3.59 h reaction time as optimum conditions for maximum H2 generation. Finally, a modified Langmuir-Hinshelwood (L-H) mechanism-based kinetic model was developed for TiO2 and PCN based nanocomposites and calculation of adsorption and rate constants were also carried out for investigating the adsorption behaviours. In conclusion, this study will contribute to the development of an efficient photo-technology for H2 production towards sustainable solar fuels.