| At present,one of the main problems restricting the development of human society is environmental pollution.Photocatalysis technology is a technology with broad application prospects in environmental protection.Graphite-like carbon nitride（g-C3N4）is a non-metallic semiconductor material with a unique 2D lamellar structure,good acid and alkali resistance,thermal stability and chemical stability.The structure and performance is easy to control,and it can respond to visible light.This material exhibits advantages of being green,environmentally friendly,non-toxic,and easy to prepare and attracts attention in the field of photocatalysis.However,according to practical application experience,it is found that the single g-C3N4 material has low quantum yield and fast photogenerated electron-hole recombination,which affects its photocatalytic degradation effect on pollutants.Therefore,using g-C3N4 as a matrix for multi-element composites to improve the utilization efficiency of sunlight and the separation rate of photo-generated electron-hole pairs,thereby enhancing the photocatalytic efficiency of composite materials,has very important theoretical and application value.In this paper,six kinds of photocatalysts were prepared.Scanning electron microscope（SEM）,transmission electron microscope（TEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,ultraviolet-visible spectrophotometry（UV-vis）and fluorescence spectroscopy（PL）were used to analyze the phase structure,morphology structure and optical properties of the materials.And studied their catalytic activity and stability under visible light conditions,and further discussed the mechanism of improving the photocatalytic activity of composite materials.The main research contents and conclusions are as follows:（1）Using ammonium sulfate assisted high-temperature polycondensation of urea to prepare semiconductor material g-C3N4,the output is improved,up to 2.67 times that of a single urea preparation,when the mass ratio of urea to ammonium sulfate is 10:1.5,the photocatalytic performance of the prepared g-C3N4 is the best,and the degradation rate of tetracycline hydrochloride（TC）solution is increased from 44.97%to 61.99%.（2）Using g-C3N4 as the matrix,binding bismuth vanadate（BiVO4）with matching energy band,and introducing reduced graphene oxide（RGO）with excellent carrier mobility,the composite photocatalytic material g-C3N4/BiVO4,RGO/g-C3N4,RGO/BiVO4 and RGO/g-C3N4/BiVO4 was prepared.the photocatalytic activity RGO/g-C3N4/BiVO4-8wt%is highest,visible light irradiation for 120 min,and the degradation rate of the initial concentration of 20 mg/L tetracycline hydrochloride solution was 77.87%.After 4 cycles of testing,the degradation rate of each composite material did not exceed 5%,showing good stability.According to the UV-vis and PL test results,the enhanced photocatalytic performance of RGO/g-C3N4/BiVO4 is attributed to the efficient electron migration rate of RGO and the Z-type heterojunction structure of the composite material,which can improve its absorption of visible light and the separation speed of photogenerated electron-hole pairs.（3）Carry out the free radical trapping experiment of the ternary composite heterojunction material RGO/g-C3N4/BiVO4.The degradation rate after adding 1,4p-benzoquinone（BQ）is only 4.92%.After adding ammonium oxalate（AO）and isopropyl alcohol,the effect on the degradation effect is small,which is 72.13%and68.03%respectively,indicating that superoxide anion free radical（·O2-）is the main active substance in the process of catalytic degradation.（4）Carrying out a photocatalytic effect research experiment on formaldehyde purification.g-C3N4,BiVO4,g-C3N4/BiVO4,RGO/g-C3N4,RGO/BiVO4 and RGO/g-C3N4/BiVO4 were used to treat formaldehyde in visible light（the initial concentration is 0.400mg/m3）for 180 min,and the degradation rates were 39.00%,25.18%,42.40%,44.12%,40.69%,and 56.05%,respectively,which proved that the degradation performance of formaldehyde was also enhanced by constructing a composite heterojunction. |
