Synthesis Of G-C₃N₄ Based Composites And Their Photocatalytic Degradation Of NO Gas Under Visible Light Irradiation

Nowadays,air pollution has become an increasingly serious environmental problem in many countries,which seriously hinders the healthy development of human society.NO as an air pollutant can cause the formation of photochemical smog and acid rain,which will cause environmental damage and endanger human health.Therefore,it is necessary to carry out research on the elimination of NO gases.Photocatalytic technology is considered to be an effective method for the degradation of NO gas because of its green environmental protection,good stability,high photocatalytic activity and low energy consumption.In recent years,graphite carbon nitride?g-C₃N₄?with a two-dimensional layered structure exhibits a certain photocatalytic performance under visible light due to its suitable band gap?2.7 eV?.It is considered to be a very promising photocatalytic material due to the unique electronic structure,high stability,non-toxic and cheap and easy preparation,etc.However,the photocatalytic activity of g-C₃N₄ is low due to some intrinsic shortcomings such as the low visible light utilization rate,the small surface area and the fast electron-hole recombination,which greatly limits its practical application.In order to solve the issue of low photocatalytic activity,the photocatalytic performance can be improved by forming g-C₃N₄ with other band gap-matched semiconductor materials to form heterojunction.In this paper,we prepared MoS₂/g-C₃N₄ nanocomposites by an simple ultrasonic technique.The crystal structure and morphology of MoS₂/g-C₃N₄ nanocomposites were characterized by X-ray diffraction?XRD?,transmission electron microscopy?TEM?,scanning electron microscopy?SEM?and Fourier transform infrared spectroscopy?FT-IR?.Ultraviolet-visible absorption spectrum?UV-vis abs?and photoluminescence spectra?PL?were used to characterize the optical properties of the composites.Finally,to evaluate the photocatalytic performance of the composites,the ability to remove NO gas was measured under visible light?>420 nm?irradiation.The main conclusions and innovations of this study are summarized as follows:?1?The experimental results show that the nano-layered MoS₂ is well attached to g-C₃N₄ and forms heterojunction.The absorption intensity of MoS₂/g-C₃N₄ composites in the visible wavelengths is obviously enhanced with the increase of MoS₂ content,and the fluorescence intensity of the composite is obviously weakened,which indicates that the prepared composites accelerate the separation of the photogenerated carrier.In addition,the pore volume of the material has also been significantly increased.?2?In this thesis,nitric oxide?NO?was used as the target degradation product.The results show that the photocatalytic performance of g-C₃N₄ was improved obviously after adding a small amount of MoS₂.MoS₂ and g-C₃N₄ could form band-matched heterojunction to accelerate the conduction of electrons,which could promoting the separation of photogenerated carriers and improve photocatalytic efficiency.MoS₂/g-C₃N₄ with the mass ratio of 1.5wt% had the highest activity under visible light irradiation,reaching 51.67%,which was 65.5% higher than that of pure g-C₃N₄.?3?In order to further improve its performance,we also added the graphene oxide?GO?in the composite process,and successfully prepared MoS₂/rGO/g-C₃N₄ ternary nanocomposite material.Their crystal phase,structure,optical properties and photocatalytic performance were also been studied.It is found that rGO can effectively increase the charge transfer between the interfaces and inhibit the recombination of carriers.At the same time,it can also increase the active adsorption sites and the photocatalytic reaction centers.Since rGO has the characteristics of semi-metal,it can form Schottky barrier between MoS₂ and g-C₃N₄,which can reduce the potential difference and bend the band between the two materials,hence promoting the electrons transfer between the interface.When the MoS₂/rGO/g-C₃N₄ was with a mass ratio of rGO of 5wt%,the degradation rate of NO was 61.87%,which was increased by 19.7%,compared with that of MoS₂/g-C₃N₄.This study provides a new idea for improving the catalytic activity of g-C₃N₄,and provides a new technical method for the effective degradation of harmful gases of NO,which has a great significance to promote the application of g-C₃N₄.