| Up to now,antibiotics have played a huge role in medicine,health care,fisheries,animal husbandry and more.The use of antibiotics helps living organisms get rid of diseases.However,the improper discharge of antibiotics will cause serious pollution to the water environment and pose a serious threat to human health and the ecosystem.For example,excessive tetracycline concentration in water environment has been found to have certain carcinogenic and mutagenic effects.Therefore,the removal or degradation of tetracycline from water has become an important means to control antibiotic pollution.Among them,photocatalytic technology has shown excellent performance in removing organic pollutants in water,and has the characteristics of sustainability,economy,environmental protection and safety.Bismuth tungstate(Bi2WO6)is a kind of photocatalyst with narrow band gap and strong visible light response.It has the advantages of durability,convenient synthesis and low cost.However,the limited charge transfer efficiency of photon-producing carriers and the fast recombination rate limit the practical application of Bi2WO6 as a visible light response catalyst.It is usually used to compound with other substances to improve the catalytic performance.Meanwhile,in previous studies,the mechanism of the thermal effect of Bi2WO6 as a photocatalyst is still lacking,and further studies are needed.As a kind of non-metallic semiconductor catalyst,graphitized carbon nitride(g-C3N4)nanosheets have attracted much attention due to their special structure,green color,high specific surface area and excellent thermal stability.However,the simple carrier recombination of g-C3N4 limits its photocatalytic performance.Based on the above analysis,the g-C3N4 composite Bi2WO6 nanostructures were prepared by a simple solvothermal method.On the one hand,the separation efficiency of photogenerated electrons and holes was enhanced by the builtin polarized electric field.On the other hand,the catalytic degradation ability of g-C3N4 to tetracycline was enhanced by the thermal effect of Bi2WO6.At the same time,this paper also systematically studied the influence of different factors on the catalytic performance in the process of photocatalysis,and proposed the possible reaction mechanism.The specific research contents are as follows:(1)Series g-C3N4/Bi2WO6 nanocomposites are fabricated by a facile solvothermal technique.A series of photocatalysts with different mass ratios of g-C3N4/Bi2WO6 were synthesized by solvothermal method(mass ratios of g-C3N4 were 1%,2%,5%,10%and 20%,respectively).The photocatalytic experiment confirmed that g-C3N4/Bi2WO6 with mass ratio of 1%g-C3N4 had the best photocatalytic tetracycline degradation performance.The tetracycline degradation efficiency reached 75%within 180 minutes,which was 1.38 times that of pure Bi2WO6.The structure,morphology and physicochemical properties of the catalyst were analyzed by XRD and TEM,and it was found that the catalyst has good morphological characteristics and excellent physicochemical properties.In addition,the effects of g-C3N4/Bi2WO6 catalyst with a mass ratio of 1%g-C3N4 on the photocatalytic degradation of tetracycline under different initial pH values,light irradiation wavelength and the presence of Canion and canion were investigated.It was found that the catalyst has excellent physicochemical properties and stability,and under the condition of pH=10,The degradation rate of tetracycline reached 99%within 60 min,showing excellent application potential.(2)The degradation mechanism of TC by the g-C3N4/Bi2WO6 nanocomposites is demonstrated in a microperspective.The 1%g-C3N4/Bi2WO6(0.01CN/BWO)photocatalyst was used as the study object,and the·O2-and h+were identified as the reactive radicals that play a major role in the degradation process through trapping agent experiments.(3)A self-heating system to enhance the photocatalytic degradation rate based on the self-heating effect of Bi2WO6 and the different catalytic performance of g-C3N4 at different temperatures is successfully constructed.The SEM,XPS,and electrochemical experiments are utilized to prove the enhancement of photocatalysis by the polar electric field induced by the formation of the composites.More importantly,through the implementation of the electrochemistry and photocatalytic experiments at different temperatures,it is proved that the Bi2WO6 could be divided into three different parts.One is the part that direct contact with the g-C3N4,the second part that may contribute to the photocatalytsis directly,and the third part may happen the recombination process of the photoelectrons and holes to generate heat after being excited by light.The heat generated by the third part may enhance the local temperature around the nanocomposite,especially the g-C3N4,whose photocatalytic performance could then be greatly enhanced by increasing the separation rate of the photoelectrons and holes,and decreasing the resistance value,and thus the photocatalytic performance of the composites is greatly increased.These results indicate that 1%g-C3N4/Bi2WO6 has great application potential in removing tetracycline antibiotics from wastewater,and also the strategy to accelerate the photocatalytic rate by utilizing the self-heating effect has great reference value in the design and preparation of novel photocatalysts. |
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