Controllable Synthesis Of ZrO₂ And LaCoO₃ Nanopowders And Their Visible-light Photocatalytic Properties

With the acceleration of urbanization process,antibiotics become one of the important factors of water pollution.It is of great significance to study the advanced treatment technology of antibiotics.ZrO₂ as a transition metal oxide is extensively applied in industrial catalysis domain due to its suitable redox potential,surface acid-base characteristics,chemical stability,low cost and nontoxic nature,etc.However,a wide band-gap in the intrinsic ZrO₂ makes it responsive only in the UV light,which limits its application in photocatalytic degradation of organic pollutants.In addition,LaCoO₃ as a transition metal oxide with perovskite structure,has also applied in the catalysis domain owing to its high oxidation activity,low cost and nontoxic nature.The catalytic performance of LaCoO₃ is significantly influenced by synthetic procedures.Therefore,the objectives of this paper is to study the influence of synthestic process parameters on structure and photocatalytic performances of ZrO₂ and LaCoO₃ nanomaterials.Meanwhile,their photocatalytic oxidation mechanism will be studied.The main contents are as follows:Tetragonal ZrO₂?t-ZrO₂?nanopowders were successfully prepared through sol-gel process by using zirconium n-propoxide and zirconium oxychloride,respectively.The t-ZrP2 powders synthesized by using zirconium n-propoxide show small grain due to the existence of carbonaceous residuals and exhibit low specific surface area of-20 m2/g resulting from the agglomeration of small grain.Those synthesized by zirconium oxychloride exhibit high specific surface area of?76 m2/g,along with a great deal of oxygen vacancies,which shows excellently photocatalytic performance for degrading rhodamine B and tetracycline hydrochloride?TCH?.Especially,the degradation rate of TCH reaches up to?84%within 150 min and stabilizes at?80%within 150 min after the fourth cycle.Combined with the free radical trapping experiment and UV-vis spectroscopy of ZrO₂ catalyst before and after adsorption of TCH,we deduce that there exsit two possible photocatalytic mechanism:?I?the photogenerated electrons excited from ZrO₂ irradiated under visible-light are trapped by oxygen vacancies,which react with the dissolved O₂ to create ·O₂-radicals.Meanwhile,holes are captured to induce oxidation.?II?the electrons injection from the excited state of the surface-complexed TCH molecules into the conduction band of ZrO₂ and successive capture by electrons acceptors such as O₂.Monoclinic ZrO₂?m-ZrO₂?nanopowders with high specific surface area??271 m2/g?were successfully prepared through solvothermal process by using zirconium n-propoxide.m-ZrO₂ nanopowders solvothermally derived at 220 ? have C-containing attachments and rich oxygen vacancy defects,which show strong visible-light absorption and photocurrent response.Accordingly,the degradation rate of TCH reaches?67%.When annealed at 350 ?,the C-containing attachments were eliminated,leading to the significant decrease of specific surface area??177 m2/g?.Although the elimination of the C-containing attachments results in the weakening of visible-light absorption and photocurrent respongse,the degradation rate of TCH reaches up to?80%.With further increasing the annealing temperature,the degradation rate of TCH is reduced.Based on the free radical trapping experiment and UV-vis spectroscopy of ZrO₂ catalyst before and after adsorption of TCH,we deduce that the catalytic oxidation of TCH in the presence of annealing ZrO₂ catalyst is mainly ascribed for the above???mechanism.The photodegraded products were further analyzed by HPLC-MS technology and the possible degradation process was proposed.LaCoO₃ nanopowders was successfully prepared through hydrothermal process.The influence of different mineralizer,pH value,annealing temperature,atmosphere and pressure on structure and photocatalytic performances of LaCoO₃ nanopowders was investigated.It was found that the requirements of pH and annealing temperature were alkaline and 550?when ammonia was used as mineralizer.LaCoO₃ nanopowders have the best photodegradation performance of TCH when the pH value is 11 and the annealing temperature is 550?.The degradation rate is 58.52%.When KOH is used as mineralizer,the effect of pressure and oxygen partial pressure on LaCoO₃ nanopowders The degradation rate of LaCoO₃ nanopowders was up to 62.93%under the conditions of 450psi pressure and air oxygen partial pressure.Combined with photocurrent response and the absorption of TCH in dark reaction and photocatalytic reaction,we deduce that the photocatalytic degradation of TCH in the presence of LaCoO₃ catalyst is mainly ascribed for the Co2+/Co3+ Fenton-like reaction and the above?I?mechanism.