Photocatalysts For Photogenerated Carrier Separation Regulated By Piezoelectric Field

With the rapid development of biomedicine technology,the abuse of antibiotic drugs has become increasingly serious.Tetracycline antibiotic（TC）residues have been detected in more and more water sources.The long-term release of low-dose antibiotics into the environment will increase the drug resistance of bacteria,which has become a very urgent problem.Semiconductor photocatalysis technology is a degradation technology which utilize solar energy to remove pollutants,possesses the features of low energy consumption and green cleaning,and is considered as one of the most promising methods to solve antibiotic pollution in water.However,the rapid recombination of photogenerated electrons and holes in the process of photocatalysis seriously limits the photocatalytic reaction.Hence,how to reduce the recombination rate of photogenerated electrons and holes has become a key factor in the development of photocatalysis technology.In order to realize the effective separation of photogenerated electrons and holes,three kinds of piezoelectric photocatalyst materials with excellent piezoelectric properties were synthetized in this work.The photocatalytic efficiency was improved by introducing a piezoelectric built-in electric field into the photocatalyst,which significantly enhanced the effective charge concentration in the photocatalyst reaction and the separation efficiency of photogenerated carriers.Therefore,the photocatalytic degradation efficiency of TC wastewater was also significantly improved.The specific contents of this study are as follows:（1）Visible light-driven copper oxide/sodium niobate（Cu O/Na Nb O₃）piezoelectric photocatalysts with different mass ratios were synthetized via hydrothermal and subsequent precipitation method to eliminate wastewater containing TC residues.XRD,XPS,FT-IR,PFM,SEM,TEM and UV-vis DRS were conducted to characterize the elemental composition,piezoelectric coefficient,surface morphology and light response ability of the photocatalysts.Besides,the degradation performance of the Cu O/Na Nb O₃ piezoelectric photocatalysts for TC was evaluated with the assistances of ultrasonic vibration and visible light irradiation.The degradation experiments of TC indicated that the degradation efficiency of 1.5 wt%Cu O/Na Nb O₃（CNNO-0.15）for TC was 73.0%under visible light irradiation and ultrasound conditions within 120 min,which was 1.2 times that of CNNO-0.15 without ultrasound under the same conditions.Piezoelectric microscope test results show that CNNO-0.15 possesses excellent piezoelectric properties.It can produce an internal electric field under the action of ultrasonic stress,which could provide opposite driving force for photoinduced electrons and holes to improve the photocatalytic efficiency.This work realizes the coupling of built-in electric field and photocatalytic reaction through Cu O/Na Nb O₃ piezoelectric photocatalyst,providing a new idea for piezoelectric photocatalytic materials in the field of antibiotic degradation.（2）A series of silver-loaded bismuth vanadate（Ag/Bi VO₄）piezoelectric photocatalysts with visible light response were synthesized by hydrothermal method and photoreduction method to remove the wastewater containing tetracycline hydrochloride（TC）under the irradiation of visible light.Among them,Ag/Bi VO₄（Ag/BVO-1.0）containing 1.0 wt%Ag possessed the best piezoelectric photocatalytic activity.The narrow band gap piezoelectric photocatalyst Bi VO₄ exhibited prominent visible light absorption performance.Furthermore,the introduction of Ag not only enhances the visible light response of the photocatalyst,but also forms heterojunction at the catalyst interface,which provides power for the separation of photogenerated carriers.After introducing ultrasonic wave to assist photocatalytic reaction,the purification ability of the Ag/Bi VO₄ photocatalyst for TC is enhanced.The built-in electric field of BVO under ultrasonic vibration may cause the improvement of photocatalytic efficiency,which drives the photoinduced electrons and holes to the different surface of catalyst in the opposite direction and participate in the degradation reaction of TC.It is worth noting that the photocatalyst still maintains outstanding degradation ability after four times of cyclic piezoelectric photocatalytic degradation of TC.In general,this work provides new insights for the design of piezoelectric photocatalysts with visible light response and the degradation of antibiotic wastewater.（3）The monoclinic bismuth vanadate（m-BVO）with piezoelectric effect was synthesized by precipitation method,and the wastewater containing TC was treated by activating peroxymonosulfate（PMS）.Moreover,tetragonal bismuth vanadate（t-BVO）without piezoelectric effect was also synthesized to compare and study the effect of piezoelectric built-in electric field on PMS activation.Furthermore,the piezoelectric photocatalyst was analyzed by piezoelectric microscope to obtain the piezoelectric coefficient of the prepared sample and serve as evidence for the successful introduction of piezoelectric effect.Photocurrent density response tests were carried out under visible light irradiation and ultrasound conditions to research the effect of piezoelectric built-in electric field on photogenerated carrier concentration.The changes of the degradation efficiency of the piezoelectric photocatalyst on TC wastewater after different initial p H values and multiple cyclic degradation experiments were studied to systematically evaluate its practicability and stability.In addition,the possible degradation pathway of TC and the toxicity of related intermediate products were also analyzed.This study proposes a PMS activation method with potential application,which is of great significance for the purification of antibiotic wastewater.