Construction of an S-Scheme heterojunction with oxygen-vacancy-rich trimetallic CoAlLa-LDH anchored on titania-sandwiched Ti3C2 multilayers for boosting photocatalytic CO2 reduction under visible light

A well-designed two-dimensional 2D/2D architecture was constructed by coupling oxygen-vacancy-rich trimetallic CoAlLa layered double hydroxide (CoAlLa-LDH) with titania-sandwiched Ti3C2 MXene multilayers to achieve enhanced photocatalytic CO2 reduction. First, through a controlled etching process, in situ anatase/rutile-phase titania was grown over Ti3C2 multilayers with a controlled morphology. In the next stage, through controlled growth, a highly active oxygen-vacancy-rich ternary CoAlLa-LDH was formed in the presence of La3+ to create coordinatively unsaturated metal centers for enhancement of reductive sites. An intimate contact between the trimetallic CoAlLa layered double hydroxide (CoAlLa-LDH) and Ti3C2Tx with a unique 2D/2D hierarchical architecture was achieved. This step (S)-scheme heterojunction provided pathways to effectively stimulate the photoinduced electron-hole separation. Compared to bimetallic Co2Al1-LDH, higher photoactivity was achieved with trimetallic Co2Al0.95LA0.05-LDH due to the presence of electron-rich La3+. The photocatalytic reduction of CO2 with H2O resulted in the formation of CO and CH4 with yield rates of 46.32 and 31.02 μmol g-1 h-1, respectively, over the Co2Al0.95LA0.05-LDH/TiO2/Ti3C2 MXene nanocomposite, much higher than pristine samples. This significantly enhanced performance was due to the better sorption process with superior charge carrier separation due to oxygen defective sites, good interfacial contact, and the presence of dual-phase titania as a bridge for separating charges. The composite performance was further explored through photocatalytic dry reforming of methane (DRM) and bireforming of methane (BRM), whereas higher CO and H2 production was obtained for BRM due to the effective attachment of reactants over electron-rich defective sites. Additionally, the quantum efficiency and stability study confirmed the high durability of the Ti3C2T/CoAlLa-LDH composite catalyst in several cycles owing to the stable structures of Ti3C2TA/R with basic characteristics of CoAlLa-LDH