Synthesis Of Efficient Ternary Composite Photocatalysts And Their Mechanism Study Of Removing Antibiotic Pollutants From Water

With the continuous development of society,environmental pollution has become more and more serious.The increased attention has been paid to the environmental risks of organic pollutants in water,especially for the new-type antibiotic pollutions.Effective control of antibiotic pollutants in water has become a research hotspot.Because of the low efficiency,secondary pollution,complex reaction device and high cost of traditional pollutant treatment technology,it is urgent to develop a new efficient pollutant treatment technology.The photocatalytic technology using sunlight is a new technology with high efficiency,energy saving and environmental protection.However,the practical application of photocatalytic technology is limited by the low separation efficiency of carriers,low utilization of sunlight and unstable photocatalysts.To solve these problems,four new and efficient ternary composite photocatalysts were prepared by means of morphology control,semiconductor composite and material sensitization.In order to evaluate the photocatalytic properties of different systems of photocatalytic materials,four most common antibiotics,sulfamethazine(SAZ),ciproflfloxacin hydrochloride(CFH),cloxacillin(CXS)and tetracycline hydrochloride(TCH),were selected as the research objects to study their degradation mechanism.The composition,morphology,carrier separation and optical-electrical characteristic of photocatalytic materials were analyzed by diversiform characterization methods.Meanwhile,based on density functional theory(DFT),the mechanism of photocatalytic reaction is further investigated through theoretical calculation,which could provide experimental and theoretical basis for the construction of efficient composite photocatalytic materials.The details are summarized briefly as follows:(1)In the second chapter,the novel ternary composite photocatalysts of Ag₃PO₄/Bi₂S₃-Bi₂O₃ were synthesized by the facile means.The crystal texture,chemical states,morphology and optical characteristics of prepared photocatalysts were investigated by XRD,FTIR,XPS,SEM,TEM,N₂ adsorption-desorption analysis,UV-vis DRS,and PL etc.techniques,respectively.Meanwhile,the band structures and the density of states of samples had been calculated based on density functional theory.For assessing the photocatalytic performance of these samples,the visible light photodegradation of SAZ antibiotic was performed.The effects of initial antibiotic concentration,reaction p H,supporting electrolyte and surfactant on photocatalytic performance were all investigated.The results indicated that the ternary composite exhibited higher photocatalytic performance than other comparison samples.Furthermore,four cycle experiments confirmed the ternary composite also exhibited satisfactory photostability.The scavenger tests and ESR data demonstrated that the active species h⁺,·O₂^-,and·OH worked together in the photocatalytic process,and the h⁺and·O₂^-play a more important role than·OH.All in all,the increased photocatalytic performance of ABB composite could owe to the photosensitization of Bi₂S₃ and the double Z-scheme photocatalytic system.(2)Considering the risk of metal pollution in the water environment of all-metal Ag₃PO₄/Bi₂S₃-Bi₂O₃ ternary photocatalysts,and the relatively higher cost of metal-based photocatalytic materials.In the third chapter,the ternary composite photocatalysts of g-C₃N₄/Bi₂O₃-nitrogen doped hollow mesoporous carbon spheres(NHMCs)were synthesized by a facile thermal process.The morphology,structure,elements,and photoelectrochemical properties of the as-prepared samples were characterized by SEM,TEM,N₂ sorption-desorption,XRD,XPS,UV-vis DRS,and so on.Meanwhile,the band structures and the density of states of samples had been calculated based on density functional theory.The photocatalytic efficiency was evaluated toward degradation of CFH antibiotic under visible-light irradiation,and the results showed that the ternary composite exhibited superior photocatalytic efficiency than other comparison samples,which could be attributed to the synergistic action of g-C₃N₄/Bi₂O₃ Z-scheme photocatalytic system and the NHMCs.The characterization techniques revealed that NHMCs play three vital roles in improving photocatalytic efficiency.First,NHMCs could serve as a photosensitizer to enhance visible-light absorption.Second,NHMCs are an excellent conductive material to transfer the photoexcited electrons quickly to hinder the electron-hole pairs recombination.Third,NHMCs could provide more active sites in the photocatalytic process.The scavenger experiments and electron-spinresonance results revealed that the active substances h⁺,·O₂^-,and·OH performed together in the photodegradation system.Additionally,the ternary composite showed favorable photostability after six rounds of recycling,suggesting the great prospects of the practical application of the ternary composite.(3)Compared with bulk photocatalytic materials,low-dimensional(0D,1D,2D)photocatalytic materials could show more efficient photocatalytic performance.In the fourth chapter,the high surface area and efficient visible light induced ternary composite photocatalysts,namely 2D/0D g-C₃N₄/Cd S-NHMCs have been prepared.Firstly,the physicochemical,photoelectric and electronic structures(including band structure,density of state and charge density difference)properties of the obtained samples were studied.Then,the photocatalytic experiments indicated that the ternary composite performed a markedly improved visible light photocatalytic performance and photostability for CXS antibiotic degradation compared with pure g-C₃N₄,Cd S and g-C₃N₄/Cd S heterojunction.The enhanced photocatalytic performance of g-C₃N₄/Cd S-NHMCs composites could ascribe to the synergy between g-C₃N₄/Cd S heterojunction and NHCs,which obviously improved the specific surface area,the absorption of visible light,the transfer rate of electrons and the separation efficiency of photogenerated electron-hole pairs of the photocatalysts.Finally,the mechanism analysis showed that active substances h⁺,·O₂^-,and·OH worked together in the photocatalytic process,which attack the?-lactam,thiazolidine ring and amide group should be the fatal act for CLX mineralization.(4)In addition to g-C₃N₄ nanosheets,black phosphorus nanosheets(BP)are also a promising low dimensional metal-free photocatalytic material.In the fifth chapter,early transition-metal carbide and nitride(MXene)decorated BP(2D/0D-2D Ti₃C₂T_x/TiO₂-BP)ternary composites were constructed by a hydrothermal method,in which TiO₂ was produced in the hydrothermal process.The optimized ternary composites exhibited a higher visible-light photodegradation efficiency of TCH antibiotic degradation(92.70%)pollutants than that of pristine BP(9.35%).Diverse characterization techniques and density functional theory calculations have revealed that such enhanced photocatalytic performance was because of the synergistic effect of BP and Ti₃C₂T_x/TiO₂,which could markedly improve the stability of BP,increase visible light absorption,prolong the photoexcited electron lifetime,accelerate the photoinduced electron transfer and hinder the electron-hole pairs recombination.Meanwhile,the mechanism analysis indicated that·O₂^-radicals played a leading role in the photocatalytic process.