Enriched oxygen vacancies of Cu2O/SnS2/SnO2 heterostructure for enhanced photocatalytic reduction of CO2 by water and nitrogen fixation.

When two semiconductors are electronically coupled, their photocatalytic performance can be greatly enhanced. Herein, we formed a heterostructure between Cu2O and SnS2/SnO2 nanocomposite using a solvothermal reactor, which reduced CO2 by H2O at ambient conditions to produce CO, H2, and CH4. With inclusion of Cu2O, apparent quantum yield, a measure of photoactivity, has increased from 7.16% to 8.62%. Also, the selectivity of CH4 over CO was approximately 1.8-times higher than that of SnS2/SnO2. Interestingly, the as-synthesized catalysts were able to fix N2 to NH3 under light illumination at ambient conditions. Dissecting the mechanism into basic steps, it is shown that oxygen vacancies within the catalysts act as trapping sites for photo-induced charge carriers which strongly influenced the reactivity and selectivity of product. Additionally, oxygen vacancies act as active sites to chemisorb nitrogen molecules, which follow associative steps to generate NH3. In absence of sacrificial agent, the NH4+ generation rate was66.35μmol.g-1h-1 for Cu2O/SnS2/SnO2, which is 1.9-fold higher than SnS2/SnO2. Formation of a p-n heterojunction between Cu2O and SnS2/SnO2 nanocomposite offered favorable photoreductive potentials and high stability, mainly owing to their intimate interfacial contact. The results clearly illustrate a promising strategy to use oxygen vacancies rich heterostructure for wide application in photocatalysis.