Study On Preparation, Photocatalytic And Gas-sensing Properties Of Graphitic Carbon Nitride And Its Composites

Graphitic carbon nitride?GCN?,an artificial polymeric photocatalyst with excellent chemical stability,good biocompatibility and easily-modified bandgap energy,has attracted considerable attention from material and medical fields.Similar to graphite,GCN is constructed by conjugated aromatic planes with plenty of amino-groups,so the gas adsorption capacity is good.In addition,due to the semiconductor characteristics,GCN has good potential application in the field of gas-sensing.In this paper,carbon nitride micro-/nanorods?CNMNR?was synthesized in a muffle furnace via high-temperature sintering with melamine and acetic acid as starting material.Relative structures and properties of CNMNR were characterized.The photocatalytic properties of this material were evaluated by degrading aqueous rhodamine B?RhB?under simulated visible light,the improvement of photoactivity was then discussed.Besides,GCN-based composites were prepared and the photocatalytic and gas-sensing properties of the composites were tested,the mechanisms of improved performances were studied as well.?1?CNMNR was synthesized in a muffle furnace via high-temperature sintering the precursor,which was prefabricated through acidization and hydrothermal process with melamine and acetic acid as starting material.Then the structures,morphology and photoelectric properties of CNMNR were characterized,and the photoactivity was also tested.Compared with that of bulk carbon nitride?BCN?,the morphology of CNMNR was greatly changed,and the surface area was increased,but the bandgap energy was slightly decreased,the photoactivity was correspondingly improved.After illuminated under simulate visible light for 20min,the degradation rate of RhB for best CNMNR was 98%,and the pseudo-first order kinetic rate constant was 0.212min^-1.But for BCN,the degradation rate and pseudo-first order kinetic rate constant were 54%and 0.068min^-1 only.The enhanced photoactivity was mainly caused by larger surface area,wider range of visible-light-response and lower recombination rate of photoinduced electron-hole pairs.?2?Graphitic carbon nitride/partially reduced graphene oxide?GCN/rGO?was prepared by high-temperature sintering with graphene oxide and the precursor up-mentioned as starting material.Then the structures,morphology and optical properties of GCN/rGO were characterized,and the photoactivity was also tested.Compared with that of GCN,the crystalline structure of GCN/rGO was not changed,but the bandgap energy and recombination rate of electron-hole pair were decreased significantly,the photoactivity was then enhanced.After illuminated under simulate visible light for20min,the degradation rate of RhB for best GCN/rGO was 99%,and the pseudo-first order kinetic rate constant was 0.283min^-1.But for GCN,the degradation rate and pseudo-first order kinetic rate constant were 94%and 0.140 min^-1,respectively.The heterojunction generated in GCN/rGO was the main reason for the decline of the bandgap energy,decreased recombination rate of electron-hole pairs and modified photoactivity.?3?Graphitic carbon nitride/stannic oxide?GCN/SnO₂?was fabricated by high-temperature sintering with Tin???chloride pentahydrate?SnCl₄·5H₂O?and the up-mentioned precursor as starting material.Then the crystalline structures,morphology and optical properties of GCN/SnO₂ were characterized,and the gas-sensing property was also tested.Compared with that of GCN,the conductivity of GCN/SnO₂ was improved greatly,and the surface area was enlarged,resulting in better gas-sensing property;Compared with that of pure SnO₂,the grain size and dispersity of SnO₂ in the composite were modified.In the gas-sensing test with ethanol gas as garget gas?300^oC and 20ppm?,the sensitivity of best GCN/SnO₂ was 13.38,but only 1.02 for GCN?barely response?.GCN/SnO₂ had better selectivity of volatile organic compounds than that of inorganic gas.The improved gas-sensing properties were due to good gas-sensing material SnO₂,enlarged surface area and high-sensitive heterojunction.