Study On The Preparation Of Thin-layer Carbon Nitride Composite Photocatalytic Material And Its Performance In Degrading Pollutants

Recently,energy crisis and environmental pollution have been threatening the life and health of humans.Photocatalysis,a simple,efficient,environmentally friendly and advanced oxidation technology,can drive a series of chemical reactions with sun light,converting proton into hydrogen,realizing carbon dioxide reduction and directly degrading environmental pollutants.However,traditional photocatalysts,such as titanium dioxide?TiO₂?,can only response to ultraviolet light due to the wide band gap,and the quantum efficiency is quite low.Therefore,developing photocatalysts with the nature of high-efficiency,stable and low-cost is necessary.The metal-free graphite carbon nitride?g-C₃N₄?,a layered semiconductor material,has been developed as an efficient catalyst that can remove pollutants under visible light irradiation due to its narrow band gap?².7 eV?,low price,non-toxic and high stability.However,bulk g-C₃N₄ presents small surface area and high recombination rate of electron-hole pairs.Herein,the paper focuses on improving the activity of g-C₃N₄ by combining morphology control and semiconductor composite method.That is,coupling the exfoliated 2D g-C₃N₄ with layered BN,SnS₂ and Co₃O₄respectively to construct 2D/2D composites to enhance its photocatalytic performance.In addition,the structure,morphology and its influence to pollutant degradation activity of the as-prepared composites are analyzed.The main results of this paper are as follows:?1?The few-layer BN has been selected to modify 2D g-C₃N₄ to construct a novel metal-free photocatalyst,and the 2D BN/g-C₃N₄ composites have been successfully prepared through a facile hydrothermal method.The structure,morphology,photoelectrical property and Rhodamine B?RhB?degradation activity of the composites are investigated by a series of characterizations.2D BN/g-C₃N₄composites have a large specific surface area,which can provide abundant adsorption site for the contaminants.In addition,the 2D/2D structure can increase the contact area and shorten the charge transport distance,thereby promoting the charge transfer.The experimental results of photocurrent and electrochemical impedance spectroscopy can prove the higher separation efficiency of electron-hole pairs and the lower charge transfer resistance in the 2D BN/g-C₃N₄ composites.Furthermore,the introduction of BN terminated with-OH can provide catalytic sites for oxygen activation to form active species during the reaction process.Therefore,compared with 2D g-C₃N₄,the degradation activities of 2D BN/g-C₃N₄ composites under visible light are improved significantly,and the RhB degradation efficiency achieves 98.2%within 120 min.?2?The 2D SnS₂/g-C₃N₄ composites have been successfully fabricated by a simple solvothermal method.The hexagonal SnS₂ is utilized to modify 2D g-C₃N₄,which is prepared by thermal oxidative exfoliation method.The structure,morphology,photoelectrical property and RhB degradation activity of the composites are investigated by a series of characterization methods.It can be found that SnS₂ is tightly attached to the 2D g-C₃N₄ nanosheet to form a Z type heterojunction.Photocurrent,electrochemical impedance spectroscopy and photoluminescence results reveal that when compared with pure 2D g-C₃N₄,the separation efficiency of photo-generated charges in 2D SnS₂/g-C₃N₄ composites is higher and the charge transfer resistance is lower.The Z-scheme channel between SnS₂ and 2D g-C₃N₄ can promote the separation of photo-excited electron-hole pairs,and remain relatively higher oxidation and reduction potentials.Therefore,2D SnS₂/g-C₃N₄ composites possess significantly enhanced photocatalytic properties,achieving the high RhB removal efficiency of 94.8%within 60 min.?3?2D Co₃O₄/g-C₃N₄ composites have been prepared by a novel catalytic synthesis method.The introduction of Co₃O₄ nanosheets can not only promote the formation of ultrathin 2D g-C₃N₄ nanosheets,but also form Z-scheme interface with2D g-C₃N₄.The structure,morphology,photoelectrical property and RhB degradation activity of the composites are investigated by a series of characterizations.The tight contact interface of 2D/2D in the composite is beneficial to shorten the transmission distance of the photo-generated carrier and promote its separation.Through ESR analysis,it can be seen that the Z-scheme channel is formed between Co₃O₄ and 2D g-C₃N₄,which can facilitate the holes on CB of Co₃O₄ to recombine with electrons on VB of 2D g-C₃N₄,thereby promoting the effective space charge separation on Co₃O₄and g-C₃N₄ themselves,and maintaining stronger redox potentials.Therefore,the degradation performance of 2D Co₃O₄/g-C₃N₄ composites is greatly improved,and RhB degradation efficiency reaches 98.3%within 60 min.This work can provide insights for the design of other 2D/2D composite catalysts for highly efficient degradation towards pollutant in environment.