WS(2)/g-C(3)N(4) composite as an efficient heterojunction photocatalyst for biocatalyzed artificial photosynthesis

A heterogeneous WS(2)/g-C(3)N(4) composite photocatalyst was prepared by a facile ultrasound-assisted hydrothermal method. The WS(2)/g-C(3)N(4) composite was used for photocatalytic regeneration of NAD(+) to NADH, which were coupled with dehydrogenases for sustainable bioconversion of CO(2) to methanol under visible light irradiation. Compared with pristine g-C(3)N(4) and the physical mixture of WS(2) and g-C(3)N(4), the fabricated WS(2)/g-C(3)N(4) composite catalyst with 5 wt% of WS(2) showed the highest activity for methanol synthesis. The methanol productivity reached 372.1 μmol h(−1) g(cat)(−1), which is approximately 7.5 times higher than that obtained using pure g-C(3)N(4). For further application demonstration, the activity of the WS(2)/g-C(3)N(4) composite catalyst toward photodegradation of Rhodamine B (RhB) was evaluated. RhB removal ratio approaching 100% was achieved in 1 hour by using the WS(2)/g-C(3)N(4) composite catalyst with 5 wt% of WS(2), at an apparent degradation rate approximately 2.6 times higher than that of pure g-C(3)N(4). Based on detailed investigations on physiochemical properties of the photocatalysts, the significantly enhanced reaction efficiency of the WS(2)/g-C(3)N(4) composite was considered to be mainly benefiting from the formation of a heterojunction interface between WS(2) and g-C(3)N(4). Upon visible-light irradiation, the photo-induced electrons can transfer from the conduction band of g-C(3)N(4) to WS(2), thus recombination of electrons and holes was decreased and the photo-harvesting efficiency was enhanced.