Preparation And Photocatalytic Properties Of G-C₃N₄-based Photocatalysts

In recent years,heterogeneous photocatalysis using semiconductor and solar energy has gained a lot of attention owing to its potential applications in many fields such as the generation of renewable and sustainable hydrogen fuel,degradation of organic pollutants,and CO₂ photoreduction.Due to its photostability,non-toxicity,ease of synthesis,and effective light harvesting accompanied by suitable bandgap energy of～2.7 e V,graphitic carbon nitride（g-C₃N₄）has been considered as a promising metal-free photocatalyst for solving the energy crisis and environmental problems.Nevertheless,due to the low-charge carrier mobility,and low specific surface area,its photocatalytic efficiency is limited.To solve the problems above,the g-C₃N₄-based composites with large specific surface area,enhanced light absorption capacity and efficient separation and transmission of photoinduced charges were prepared by the acid-treated silicate minerals/g-C₃N₄ composites and g-C₃N₄/Zeolitic imidazolate framework-67（g-C₃N₄/ZIF-67）composites in the paper.The specific research contents are as follows:（1）The acid-treated silicate minerals/g-C₃N₄ photocatalysts were prepared by simple one-pot methods using acid-treated silicate minerals and melamine as precursors.The acid-treated sepiolite,talc and kaolin minerals were used as the carriers of g-C₃N₄,respectively,and combined with g-C₃N₄ in three distinctively different ways to form three kinds of composites.The larger specific surface area and better the distribution of g-C₃N₄ in the composites were obtained through the in-situ growth of g-C₃N₄ on acid-treated silicate minerals,which enhanced the light absorption,increased the active sites,facilitated the charge transfer and significantly improved the photocatalytic activity.With the optimized the acid-treated sepiolite,talc and kaolin minerals content,the highest hydrogen production rates of the acid-treated sepiolite minerals/g-C₃N₄,the acid treated talc minerals/g-C₃N₄ and the acid treated kaolin minerals/g-C₃N₄ composites were 241.5μmol·g^-1·h^-1,267.2μmol·g^-1·h^-1 and 385.4μmol·g^-1·h^-1,respectively,which were 2.51,2.77 and 4.00times higher than that of bare g-C₃N₄(96.4μmol·g^-1·h^-1).The CO evolution rates of three composites were 2.11μmol·g^-1·h^-1,2.25μmol·g^-1·h^-1 and 3.03μmol·g^-1·h^-1,respectively,which were 2.32,2.47 and 3.33 times higher than that of bare g-C₃N₄(0.91μmol·g^-1·h^-1).（2）g-C₃N₄ was prepared by calcination treatment of melamine as precursors,and g-C₃N₄/ZIF-67 composites were prepared by simple impregnation method.With the introduction of ZIF-67,the specific surface area of the composites became larger,the light absorption capacity was stronger and the photoinduced charge transfer ability was enhanced,which significantly improved the photocatalytic activity.After the introduction of ZIF-67,the maximum hydrogen production rates of g-C₃N₄/ZIF-67composites were 214.4μmol·g^-1·h^-1,which were 2.22 folds greater than that of bare g-C₃N₄(96.4μmol·g^-1·h^-1).The CO evolution rates of g-C₃N₄/ZIF-67 composites were 1.87μmol·g^-1·h^-1,which were 2.05 folds greater than that of bare g-C₃N₄(0.91μmol·g^-1·h^-1).（3）The photocatalytic degradation of rhodamine B was tested by acid-treated sepiolite minerals/g-C₃N₄,acid treated talc minerals/g-C₃N₄,acid treated kaolin minerals/g-C₃N₄ and g-C₃N₄/ZIF-67 composites.The results showed that four composites exhibited photocatalytic activity for the degradation of rhodamine B,and the degradation rates of rhodamine B reached up to 98.7%,98.9%,99.1%and 98.4%,respectively,which were 2.49,2.73,3.08 and 2.22 times than that of bare g-C₃N₄.