Design, Synthesis And Photocatalytic Performance Of Polypyrrole/graphite Carbon Nitride Composite Materials

The rapid-growing world population requires the increasing energy consumptionwhich is exacerbating the current energy crisis and environmental problems,so thedevelopment of clean,affordable and renewable energy sources is imperativelyrequired.Hydrogen?H₂?has the highest energy density in allfuels except for nuclear power,so it is of great significance to convert the inexhaustible solar energy directly into hydrogen energy by means of photocatalytic technology.Graphitic carbon nitride?g-C₃N₄?,as anincreasingly promising polymer semiconductor photocatalystdriven by visible light has gained considerable interests,owingto its suitable band gap?2.7 e V?,high unoccupiedmolecular orbital?LUMO?energy level,high thermalstability and unique 2D?-conjugated structure.However,itsphotocatalytic activity is not ideal owing to its fast recombinationof photogenerated electron-hole pairs.Therefore,it is crucial for g-C₃N₄ to improve the photocatalytic activity by promoting thecharge separation.This paper has carried out polypyrrole/g-C₃N₄heterojunction photocatalysts.The strategies of PPy nanoparticles,cheap multi-hydroxyl Mg-O bridges between heterojunctions and PPy two-dimensional nanosheets were adopted to enhance the interface connection of the heterojunction,promote the separation of photogenerated charges and improve the photocatalytic activity of g-C₃N₄.This work explores the transfer and separation mechanism of photogenerated charges.Firstly,polypyrrole/g-C₃N₄composite was designed and synthesizedby the wet chemical method.Nano-sized PPy?NPPy?particles werefurther synthesized by the soft templates,and NPPy/g-C₃N₄nanocomposite were synthesized by constructing the heterojunction with NPPy and g-C₃N₄.Based on the resultsof produced·OH amount evaluation,photoluminescence spectra,photoelectrochemical I-t curves,steady-state surface photovoltage spectra and photocatalytic H₂ evolution,it is confirmed that NPPy nanoparticles can increase its effective contact area and interface contact with g-C₃N₄,which promotes the separation of photogenerated charges.The photocatalytic H₂evolution of NPPy/g-C₃N₄ nanocomposite is approximately 3 times that of g-C₃N₄.Secondly,in order to enhance the interface connection of g-C₃N₄/NPPy nanocomposite,Mg-O bridged g-C₃N₄/NPPy nanocomposite was fabricated by introducing Mg-O bridges with multi-hydroxyl groups between heterojunctions.Based on the results of fourier transforminfrared spectra,X-ray photoelectron spectra,surface photovoltage responses,transient surface photovoltage spectra,transient photoluminescence spectra and EIS Nyquist plots,it can be inferred that Mg-O bridgesare constructed between NPPy and g-C₃N₄ by interactingwith N-H groups of NPPy and O-H groups of g-C₃N₄,and the closely-contacted nano-heterojunctionphotocatalysts are fabricated,which accelerates the electron transfer and improves the lifetime of photogenerated charges.Therefore,g-C₃N₄/NPPy nanocomposite shows the enhanced visible-light photocatalytic H₂ evolution,?9-time that of g-C₃N₄.Interestingly,accordingto single-wavelength photocurrent action spectra and·OH amount evaluation,it is confirmedthat the promoted charge separation mainly depends on the excitedhigh-level electron transfer of g-C₃N₄,along withvisible photosensitizationfrom NPPy,resulting in the enhanced visible-light photocatalytic H₂evolution.Finally,in order to further enhance the interfacial connection and promote the charge separation,two-dimensional PPy/g-C₃N₄ nanosheet heterojunction was constructed.g-C₃N₄ultrathin nanosheets?CN-s?and PPy nanosheets?PPy-ns?were prepared by acid stripping and template method,respectively.PPy-ns/CN-s composite was successfully prepared by the wet chemical method.Based on the results of atomic force microscopy,produced·OH amount evaluation and surface photovoltage spectra,it is confirmed that the photogenerated charge separation of the two-dimensional nanosheet heterojunction of CN-s with 3.3 nmthickness and PPy-ns with 2.9nmthicknessis significantly improved,thereby enhancing visible-light photocatalytic H₂evolution,?5-time that of CN-s.This paper provides aneffective strategy and feasible approachfor designing and preparing visible light-driven g-C₃N₄-based polymer heterojunction photocatalysts for energy production.