Modification Of Graphite Phase Carbon Nitride And Its Photocatalytic Reduction Of Hexavalent Chromium In Water

The phenomenon of excessive chromium exists in many groundwater systems in China.Hexavalent chromium can cause various diseases,such as kidney,liver damage and cancer.Converting hexavalent chromium to trivalent chromium is an important way to reduce chromium toxicity.Traditional methods for controlling hexavalent chromium include physical methods,chemical methods,and biological methods.However,these traditional methods have low removal rate,high cost and easy secondary pollution.Therefore,it is urgent to study a new and efficient method for reducing hexavalent chromium.Photocatalytic technology is used to reduce the concentration of hexavalent chromium due to its high efficiency,economy and environmental protection.There are three main processes for the reduction of hexavalent chromium by photocatalytic technology.First,the semiconductor material absorbs light energy to excite photoelectrons to generate electron-hole pairs,and then photoelectrons transition from valence band to conduction band.Finally,photoelectrons on the conduction band reduce hexavalent chromium to Trivalent chromium.Most photocatalysts are toxic and have low utilization of visible light,while graphite-type carbon nitride(g-C3N4),a novel semiconductor non-metal,has low chemical and thermal stability,low cost and no toxicity.It has a small optical band gap value(2.7 eV)and a visible light response,and is widely used in the field of photocatalysis.When we study the mechanism of hexavalent chromium reduction efficiency of g-C3N4,we found that single g-C3N4 has a small specific surface area and high photoelectron and hole recombination rate,so it does not achieve the desired effect,and graphene oxide has good electrical conductivity.And a certain adsorption performance,combined with g-C3N4,reduces the recombination efficiency of photoelectrons and holes,improves the binding rate of materials and hexavalent chromium,and thus greatly accelerates the reaction rate.This paper combines the above studies:(1)In this paper,the development of g-C3N4 in the field of photocatalysis,the improvement methods of photocatalysis performance and its application in the field of photoelectricity are reviewed and the development and application of GO were also reviewedand Cr(?)pollution and removal are introduced.In this paper,the mechanism of g-C3N4 is discussed.(2)Based on the theoretical method of material chemistry,applied to the environmental field,using g-C3N4 photocatalytic Cr(?)to reduce to Cr(?)to reduce the toxicity of heavy metals.Using a high temperature thermal polymerization method,melamine was selected as a precursor to prepare a pale yellow bulk g-C3N4.The morphology,structure and chemical composition of the materials were characterized by SEM,TGA,BET,FI-IR,EDS,ESR,TEM and PL.The effects of carbon monoxide concentration,light intensity,pH value and catalytic time on the efficiency of g-C3N4 reduction of hexavalent chromium were investigated,and the effects of hole scavengers and interfering ions on the photocatalytic reduction process were investigated.The research on the reaction conditions showed that the reduction rate was optimal under acidic pH conditions,and the reduction efficiency increased with the increase of light intensity.The reduction rates of NaNO3,KCl,Na2SO4 and CaCl2 were higher in different ions,and the reduction rates of Na3PO4 and NaCl were lower.A study using hole and superoxide radical scavengers showed that both conduction band electrons and O2·-are responsible for the decrease in Cr(VI).(3)Graphene oxide modified g-C3N4(GO/g-C3N4)has high photocatalytic ability under visible light,and photoirradiation is prepared by sonochemical method.The results of TEM image experiments show that GO is a two-dimensional sheet with chiffon corrugations,while g-C3N4 has such a corrugation and a layered structure.In the GO/g-C3N4 hybrid system,GO covers the surface of g-C3N4.Ultraviolet absorption diffuse reflectance spectroscopy analysis showed that the graphene oxide/g-C3N4 hybrid product had strong light absorption characteristics in the visible light region.Photoluminescence spectroscopy confirmed the separation efficiency of the method.The photogenerated charge of GO/g-C3N4 is stronger than the original g-C3N4,indicating that the role of graphene oxide is as the separation center and electron acceptor of the GO/g-C3N4 composite product.The effective photoreduction charge separation efficiency significantly improves the visible light photocatalytic performance.The reduction of Cr(?)by GO/g-C3N4 composite has higher efficiency.The ratio of g-C3N4 to GO is 3:1,which has the best effect.The lower pH value is beneficial to the composite material to reduce Cr(?),through 8 cycles of experiments,it can be seen that the composite has stability and reusability,is a green and environmentally friendly new material,and has great significance in the environmental field.This result indicates that the non-metallic GO/g-C3N4 hybrid photocatalyst is a promising waste control material,and graphene oxide is a good waste control material combined with other semiconductors to form a composite material.