| Tetracycline has a wide range of applications in treating bacterial infections and promoting animal growth,but its misuse can lead to an increasingly serious situation of contaminated water bodies,which greatly threatens human health and safety.The efficient and green semiconductor photocatalytic degradation technology can effectively solve the problem of tetracycline water contamination.With its high stability,strong oxidation capacity and abundant oxygen vacancies,cerium dioxide（CeO2）is one of the most promising photocatalytic semiconductor materials for the treatment of environmental pollutants.The photocatalytic degradation performance of CeO2 can be improved by structural modulation or defect engineering strategies,such as the construction of CeO2-based heterojunctions and oxygen vacancy anion defects,which can significantly enhance the separation efficiency of its photogenerated carriers and visible light absorption capacity The present work is based on the main exposed crystalline surface.In this study,we investigated the relationship between the formation of heterojunctions and the concentration of oxygen vacancies on the performance and intrinsic mechanism of photocatalytic degradation of tetracycline by using CeO2 with{110}and{100}as the main exposed crystalline planes,and constructing heterojunctions in combination with g-C3N4 and regulating the concentration of oxygen vacancies at different calcination temperatures.The details and conclusions are as follows.（1）The photocatalytic activity is closely related to the type of crystallographic exposure,and CeO2 nanoparticles with different crystallographic facets will interact differently with the g-C3N4 carrier at the interface,thus having different energy band structures and electron-hole separation capabilities.In this work,rod-shaped CeO2 with exposed crystalline planes of{110}and cubic CeO2 with{100}crystalline planes were synthesized by hydrothermal method,and then heterojunction structures were constructed with g-C3N4 by methanol sonication,respectively.The next structural tests showed that the CeO2/g-C3N4 heterojunction structures with different crystalline facets had different interaction forces,and this interaction facilitated the light-induced charge separation and migration during the photocatalytic process and promoted the photocatalytic degradation performance.When the mass ratio of g-C3N4 in CeO2/g-C3N4 was 25%,the best tetracycline degradation rates of 92.61%and 89.67%were achieved for both{110}CeO2/g-C3N4 and{100}CeO2/g-C3N4,respectively.The mechanism analysis showed that the type-II heterojunction structure formed by{110}CeO2 and g-C3N4 increased the carrier separation and mobility,thus exhibiting the highest photocatalytic performance.While the{100}CeO2/g-C3N4 composite is more in line with the Z-type heterojunction structure,this structure exhibits great in carrier separation efficiency,resulting in an increase in the photocatalytic degradation rate of pure{100}CeO2 by a factor of about 7.（2）Oxygen vacancy generation is highly correlated with the crystalline surface,and there is some controversy over the regulation of oxygen vacancy concentration by high-temperature calcination and uncalcined treatments in a reducing atmosphere.In this work,two morphological samples of rod-shaped CeO2 with{110}crystal faces and cubic CeO2 with{100}crystal faces were synthesised by hydrothermal method,and then calcined at 300°C,500°C and 700°C in Ar/H2 atmosphere to compare with uncalcined CeO2 samples.Structural characterisation tests showed that the uncalcined{110}CeO2 had the highest oxygen vacancy concentration,however,the oxygen vacancy concentration of{110}CeO2 decreased as the calcination temperature increased.Furthermore,for{100}crystalline CeO2,high temperature calcination reduction and uncalcined treatment had little effect on the increase in oxygen vacancy concentration.Secondly,the photocatalytic performance of different crystalline CeO2was evaluated by photocatalytic degradation of tetracycline,where the degradation rates of R-60（uncalcined{110}CeO2 sample）and R-300（300°C calcined{110}CeO2 sample）were94.64%and 91.07%,respectively.Finally,the analysis concluded that the uncalcined{110}CeO2 had the highest oxygen vacancy concentration and photocatalytic degradation of tetracycline,and the decrease in oxygen vacancy concentration after calcination may be related to the damage to the structure caused by high temperature calcination. |
