Defect Engineering in 0D/2D S-Scheme Heterojunction Photocatalysts for Water Activation: Synergistic Roles of Nickel Doping and Oxygen Vacancy

Photocatalytic hydrodechlorination(HDC) is a promising methodfor eliminating chlorinated organic compounds (COCs) from water, butit requires catalysts with excellent water activation ability. Defectengineering is a feasible way to enhance the catalytic performanceof photocatalysts by improving light adsorption, charge carrier dynamics,and surface reactions. Herein, a well-designed 0D/2D S-scheme heterojunctionwith favorable band structures and defective interfaces was constructedvia defect tailoring on TiO2 quantum dots (QDs) and theinterface structure. The optimized catalyst Ni-TiO2-x /g-C3N4 with 1% Ni doping afterthermal treatment at 300 & DEG;C under nitrogen resulted in superiorvisible-light-driven activity in trichloroethylene (TCE) photocatalyticHDC, approximately an 18.2-fold increase as compared with g-C3N4. Ni doping and thermal-induced oxygen vacancieswere verified to synergistically endow the catalyst with improvedvisible-light absorption efficiency, ameliorated charge separationand migration, and enhanced redox potential. Experimental and theoreticalresults showed that the synergy of multifold defects in promotingvisible-light harvesting was mainly due to the characteristic multiplemidgap states, in terms of different intermediate energy levels andnarrowed bandgap. Furthermore, the contradicting effects of midgapstates on photogenerated charge carrier dynamics were mediated bythe defective S-scheme heterojunction, where the detrimental chargerecombination relating to excessive defects was considerably inhibitedvia superior spatial charge separation and promoted surface redoxreactions. The design of defect-engineered heterojunctions and therole of controlled defects in adjusting band structures provide valuableinsights for creating highly efficient artificial photosystems inthe visible region.