Dual-Defective Two-Dimensional/Two-Dimensional Z-Scheme Heterojunctions for CO₂ Reduction

Thetarget of photocatalytic CO2 reduction is to achievehigh selectivity, efficiency, and stability for a single chemical/fuelproduction. The construction of conventional Z-scheme heterojunctionsis beneficial to improve the interfacial charge separation and redoxcapacities. However, the random dimensions of junction component(s)undermine the charge-to-surface transport for catalytic reactions,and the limited chemical structures of catalysts restrict surfaceactivity/selectivity tailoring. In this work, we successfully overcomethese issues by stacking/constructing an ultrathin dual-defectivetwo-dimensional (2D)/2D Z-scheme heterojunction with growing functionalanionic vacancies onto both reductive and oxidative components ofthe Z-scheme. The O-vacancy-rich BiOCl/N-vacancy-rich g-C3N4-based 2D Z-scheme exhibits excellent photoactivityin CO2 reduction. The rate of CO2 photoreductionto CO is around 45.33 mu mol g(-1) h(-1), which is 11.7- and 12.2-fold those of untreated bulk g-C3N4 and pristine BiOCl, respectively. Among them, N-vacancy-richg-C3N4 exhibits active and selective photoreductionability, accompanied with oxidation reactions from O-vacancy-richBiOCl. Such ultrathin defective Z-schemes not only retain their originalfeatures, i.e., enhanced charge separation and redox capacities, butalso extend to lower energy photon absorption and ameliorate charge-to-surfacetransport in two redox components. Besides, density functional theorycalculations unveiled the thermodynamically favored CO2-to-CO reduction path and energy barrier's stepwise reductionat the COOH-to-CO rate-limiting step from defective g-C3N4 to the single redox component defective junction andfurther to the defective junction with both redox components. Thiswork provides an effective adaptable dual-defect engineering on 2D/2Dheterojunctions to enhance CO2 photoreduction.