Preparation of ZnCr₂O₄-ZnO composite photocatalyst based on the hydrotalcite precursor and its performance in hydrogen production

ZnCr₂O₄-ZnO composite photocatalyst with heterogeneous structure was synthesized by grinding hydrothermal method and characterized by TG-DTA, XRD, SEM, HRTEM, DRS, and N₂ absorption; its photocatalytic activity in H₂ production was evaluated by using oxalic acid as the sacrificial agent under simulated sunlight irradiation and compared with those of the ZnCr₂O₄-ZnO samples prepared by coprecipitation, urea reflux and urea hydrothermal methods. The results indicate that Zn-Cr precursors prepared by four methods show a certain hydrotalcite structure; the catalyst samples prepared at 500℃ are spherical nanoparticles, but different in agglomeration status, specific surface area and pore structure parameters. The ZnCr₂O₄-ZnO nanoparticles prepared by a grinding hydrothermal method exhibits the optimized photocurrent response and photocatalytic activity; the yield of hydrogen production is 0.956 mmol/(h·g_cat), which is 2.3, 1.5 and 3.0 times higher than that of the catalyst samples prepared by coprecipitation, urea reflux and urea hydrothermal methods, respectively. On the basis of these results, a possible mechanism for the hydrogen production over ZnCr₂O₄-ZnO composite photocatalyst with heterogeneous structure was then proposed.