Constructing S-scheme 2D/0D g-C3N4/TiO2 NPs/MPs heterojunction with 2D-Ti3AlC2 MAX cocatalyst for photocatalytic CO2 reduction to CO/CH4 in fixed-bed and monolith photoreactors

Abstract

• 2D MAX Ti 3 AlC 2 anchored g-C 3 N 4 /TiO 2 synthesized for photocatalytic CO 2 to fuels. • 2D MAX mediated TiO 2 /g-C 3 N 4 heterojunction found efficient for CO 2 to CH 4 reduction. • Photoactivity of g-C 3 N 4 /MAX/TiO 2 found 97.70 folds higher than TiO 2 under visible light. • MAX promoted CO 2 methanation in TiO 2 /g-C 3 N 4 composite with higher selectivity. • Performance of fixed-bed and monolith photoreactor further confirms higher productivity. Exfoliated 2D MAX Ti 3 AlC 2 conductive cocatalyst anchored with g-C 3 N 4 /TiO 2 to construct 2D/0D/2D heterojunction has been explored for enhanced CO 2 photoreduction in a fixed-bed and monolith photoreactor. The TiO 2 particle sizes (NPs and MPs) were systematically investigated to determine effective metal-support interaction with faster charge carrier separation among the composite materials. When TiO 2 NPs were anchored with 2D Ti 3 AlC 2 MAX structure, 10.44 folds higher CH 4 production was observed compared to anchoring TiO 2 MPs. Maximum CH 4 yield rate of 2103.5 µmol g −1 h −1 achieved at selectivity 96.59% using ternary g-C 3 N 4 /TiO 2 /Ti 3 AlC 2 2D/0D/2D composite which is 2.73 and 7.45 folds higher than using binary g-C 3 N 4 /Ti 3 AlC 2 MAX and TiO 2 NPs/Ti 3 AlC 2 samples, respectively. A step-scheme (S-scheme) photocatalytic mechanism operates in this composite, suppressed the recombination of useful electron and holes and provides higher reduction potential for efficient CO 2 conversion to CO and CH 4 . More importantly, when light intensity was increased by 5 folds, CH 4 production rate was increased by 3.59 folds under visible light. The performance of composite catalyst was further investigated in a fixed-bed and monolith photoreactor and found monolithic support increased CO production by 2.64 folds, whereas, 53.99 times lower CH 4 production was noticed. The lower photocatalytic activity in a monolith photoreactor was due to lower visible light penetration into the microchannels. Thus, 2D MAX Ti 3 AlC 2 composite catalyst can be constructed for selective photocatalytic CO 2 methanation under visible light in a fixed-bed photoreactor.