Improved activity and stability of ZnIn2S4 for H-2 production under visible light through cerium UiO-66

Indium zinc sulfide (ZnIn2S4) has been reported to be highly photoactive for H2 production with Na2S and Na2SO3 as sacrificial reagents, but it still suffers from serious corrosion. In this work, we report an efficient composite of hexagonal ZnIn2S4 microspheres (ZIS) and cerium UiO-66 metal-organic framework (MOF) octahedra, both of which harvest light at wavelengths up to 550 nm. Under a 420 nm LED lamp and in a Na2S/Na2SO3 aqueous solution, the amount of H2 evolved at 2 h (nH2h) was negligible for the MOF. After 18, 27, 37, and 47% MOF loading, however, ZIS had an increased nH2h by factors of approximately 4.8, 5.6, 4.2, and 3.2, respectively. This trend for the nH2h coincided with that for the efficiency of charge separation, inferred by emission spectroscopy. A five-repeat test for H2 production showed that ZIS partially decomposed into metallic indium, while MOF/ZIS was much more stable than ZIS. Moreover, for proton reduction or for water photo-oxidation on an electrode, MOF/ZIS was also more active than ZIS, followed by the MOF. According to the measured band parameters, a possible mechanism is proposed, including the electron transfer from ZIS to Ce-U66, and the hole transfer from Ce-U66 to ZIS, which improves the efficiency of charge separation. It is worth noting that 30% Ce-MOF/ZIS is approximately 1.4 times more active than 30% Zr-MOF/ZIS.