Enhanced bifunctional photocatalytic performances for H2 evolution and HCHO elimination with an S-scheme CoWO4/CdIn2S4 heterojunction

Designing and establishing dual-functional S-scheme heterojunction photocatalysts with efficient separation of photoproduced carriers and intense oxidation/reduction capabilities holds immense practical value for their photocatalytic application in energy conversion and environmental purification. Herein, a novel series of x% CoWO₄/CdIn₂S₄ (x% reflects the weight ratio of CWO to CIS; x = 10, 20, 30, 40 and 50) composites have been systematically designed and synthesized via electrospinning technique and hydrothermal methods. Their photocatalytic properties were assessed through HCHO removal and H₂ generation under visible light. As anticipated, the optimized 30 % CWO/CIS heterojunction presented an outstanding H₂ generation performance of 865.14 μmol g⁻¹ h⁻¹ with AQE = 3.6 % at λ = 420 nm, and achieved a 69 % removal percentage for HCHO within 1 h. Meanwhile, the pathway of HCHO degradation was presented based on in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) technique. The great catalytic performance was primarily ascribed to the enhancement in the visible–light absorption, number of active sites, and the construction of S-scheme heterojunction. Furthermore, the S-scheme charge transfer mechanism for the CWO/CIS catalyst system has been confirmed by in situ X–ray photoelectron spectroscopy (in situ XPS), electron spin resonance data, radical capturing experiments, and density functional theory (DFT) calculations. This research contributes valuable understanding for the systematic design and development of bifunctional S-scheme heterojunctions for gaseous pollutants removal and H₂ production.