The Study Of Modified G-C₃N₄ Based Materials With High Visible-light Photocatalytic Activity

In recent years,energy demand and environmental crisis have become a growing threat.Photocatalytic technology has the potential of solving these problems because it can use solar energy directly and realize the conversion between solar energy and chemical energy.The development of visible-light photocatalysts with high performance plays a crucial role in promoting the evolution of photocatalytic technology.Graphitic carbon nitride（g-C₃N₄）quickly became a hotspot in the field of photocatalysis since it was first reported as a metal-free conjugated semiconductor photocatalyst.And this is due to its earth abundant raw materials,facile synthesis methods,narrow band gap energy（2.7 eV）and stable physicochemical property.This paper mainly focus on the two key issues of high recombination rate and the lack of visible-light absorption.Herein,we modified g-C₃N₄ by morphology control and combining it with carbon material,then characterized the structures and properties of the samples.First,a simple template-free method was used to control the morphology of g-C₃N₄,of which acetic acid-treated melamine was used as a precursor to synthesize porous g-C₃N₄ nanomaterials（MACN）directly by one-step pyrolysis process.The nanoscale porous morphology is conductive to increase the specific surface area of the photocatalysts which can provide more reactive sites,thereby enhancing the visible-light absorption capabitily and accelerating the photocatalytic reaction rate;Acetic treatment can introduce a proper amount of defects which can reduce the direct recombination of photogenerated electrons and holes,and further enhance the photocatalytic activities of MACN in degrading Rhodamine B（RhB）under visible-light irradiation.Second,in order to further enhance the visible-light absorption ability of the photocatalysts,a molecular self-assembly method was adopted to control the morphology.An aqueous solution of acetic acid was used as a reaction system,and melamine-cyanuric acid supramolecular polymer was used as a precursor to synthesize the hexagonal pillared porous g-C₃N₄ materials（HACN）via hydrothermal and pyrolysis process.Compared with the bulk g-C₃N₄,HACN exhibit stronger photocatalytic degradation abilities because the larger specific surface area can provide more active sites,making the charges can be quickly consumed on the surface of HACN.And these can help to reduce the recombination rate of photogenerated electrons and holes,and then enhance the photocatalytic degradation efficiency of HACN under visible-light irradiation.In addition,the porous structure can multiply-scatter incident light and improve the utilization efficiency of visible light.Finally,on the basis of the previous work,g-C₃N₄/mullti-walled carbon nanotubes（MWCNTs）nanocomposite photocatalysts were constructed by combining g-C₃N₄ with MWCNTs via an in-situ synthesis method.The introduction of appropriate amount of MWCNTs can work as both electron transport channels and reactive sites,which can effectively enhance the electronic storage capability and inhibit the recombination of photogenerated carriers of the nanocomposite photocatalysts,and further improve their visible-light photocatalytic performance.The above research work may provide reference for the modification of g-C₃N₄materials,exploring the relationship between the structures of the modified photocatalysts and their photocatalytic performances,and designing visible-light responsive photocatalysts with high performance and high stability.