Study On Crystal Transformation And Active Plane Regulation Of ZnIn₂S₄ By Inorganic Anions

In recent decades,with the development of economy and the improvement of people’s living standard,the problem of environmental pollution has been exposed increasingly.Among them,due to the heavy dependence of medical and aquaculture industry on antibiotics,many kinds of antibiotics,large emissions into the natural water body,a serious threat to the safety of human drinking water and ecological environment safety,therefore,it is urgent to find a green,safe and effective technology to deal with antibiotics in water bodies.Semiconductor photocatalysis technology stands out among advanced oxidation methods because of its high degradation efficiency,no secondary pollution,energy saving and high efficiency.Traditional photocatalysts represented by Ti O₂ have a large band gap and only respond to UV light,which limits their application range.Therefore,the development of a new photocatalyst that can efficiently use visible light has become a research hotspot of semiconductor photocatalysts.Zn In₂S₄,as a direct band gap semiconductor photocatalyst for terpolymer metal sulfides,can efficiently utilize visible light,and has the characteristics of narrow band gap width,easy preparation,low cost and low toxicity.It is widely used in the treatment of environmental pollutants,such as the degradation of persistent organic pollutants,gas deodorization and low toxicity conversion of heavy metal ions.However,the development of Zn In₂S₄ is limited by the problems of photocorrosion,low efficiency of photogenerated carrier separation and poor stability.Based on the above problems,this paper mainly modified Zn In₂S₄ by means of crystal structure regulation,that is,to improve the photocatalytic activity of single-phase Zn In₂S₄ by regulating the growth of active crystal faces under different crystal types,and discussed the crystal transformation process of Zn In₂S₄.The effects of three kinds of internal and external inorganic anions on crystal transformation and active crystal surface growth of Zn In₂S₄ were studied.The ZIS-Zn Cl₂ series,ZIS-Zn（NO₃）₂series and ZIS-Zn SO₄ series photocatalysts were prepared respectively.Taking tetracycline hydrochloride and Cr（VI）as target pollutants,the photocatalytic oxidation and photocatalytic reduction properties of the catalysts were investigated respectively,and the relationship between the structure and properties of the materials was analyzed through various modern instrument characterization techniques,and the electron transfer mechanism and pollutant removal mechanism inside the materials were proposed.The main research contents are as follows:（1）ZIS-Zn Cl₂ series photocatalytic materials were prepared by in-situ hydrothermal method with Zn Cl₂ and In（NO₃）₃ as metal precursors modified by exogenous inorganic anions.The crystal structure,physicochemical properties and photocatalytic activity of Zn In₂S₄ were changed by the introduction of exogenous inorganic anions.In this system,the introduction of Cl^-and SO₄^2-made the cubic Zn In₂S₄ into hexagonal phase,and with the growth of different crystal plane,the relative content ratio of（102）crystal plane of ZIS-Zn Cl₂-p H_H2SO4 reached 41.12%.Moreover,the photocatalytic activity of the catalyst was investigated by photocatalytic oxidation degradation of HTC and photocatalytic reduction of Cr（VI）.The results showed that ZIS-Zn Cl₂-p H_H2SO4 had superior photocatalytic performance.At the dosage of 0.5 g/L,the removal rates of HTC and Cr（VI）reached 95.18%and 99.95%,respectively.The（102）and（311）crystal faces were identified as hexagonal and cubic phase active crystal plane by photocatalytic evaluation experiments.The results of free radical capture experiment and EPR detection showed that·O₂^-and h⁺were the main active species in visible light catalytic degradation of HTC by ZIS-Zn Cl₂-p H_H2SO4.The intermediates and possible degradation paths of HTC were analyzed by 3D-EEM and high resolution mass spectrometry,and the internal electron transfer mechanism and photocatalysis mechanism of the material were deduced.（2）using Zn（NO₃）₂ and In（NO₃）₃ as metal precursors,the influence of foreign inorganic anions on the crystal structure of Zn In₂S₄ was investigated under the same p H condition.The characterization results showed that when the types of exogenous inorganic anions were NO₃^-and SO₄^2-,the synthesized Zn In₂S₄ was cubic phase,and the crystal plane ratio of（311）of ZIS-Zn（NO₃）₂-p H_H2SO4 was higher than that of ZIS-Zn（NO₃）₂-p H_HNO3,which was 27.47%.Under Cl^-modification,Zn In₂S₄ changed from cubic to hexagonal phase,accompanied by high exposure growth of the（102）crystal plane.In addition,the reduction of Zn In₂S₄ was enhanced under the action of inorganic anions.Combined with the photocatalytic activity evaluation experiment of this series of materials,it can be seen that ZIS-Zn（NO₃）₂-p H_HCl had excellent photocatalytic performance,and the removal rates of HTC and Cr（VI）reached 91.78%and 99.48%,respectively.·O₂^-and h⁺were the main active species at the photocatalytic degradation of HTC by ZIS-Zn（NO₃）₂-p H_HCl.The intermediates and possible degradation paths of HTC were analyzed by 3D-EEM and high resolution mass spectrometry.The internal electron transfer mechanism and photocatalysis mechanism of the material were deduced.（3）ZIS-Zn SO₄ series materials were prepared by In-situ hydrothermal synthesis using Zn SO₄ and In（NO₃）₃ as metal precursors and adding exogenous inorganic anions under the same p H condition.The structural characterization of the material showed that the synthesized Zn In₂S₄ was still hexagonal phase under the modification of Cl^-,while the proportion of crystal planes changed,the（006）and（104）crystal planes were dominant.Under the modification of SO₄^2-and NO₃^-,the crystal structure of Zn In₂S₄would change from hexagonal to cubic phase,and the ratio of（311）crystal plane of ZIS-Zn SO₄-p H_H2SO4 was 33.87%,while that of ZIS-Zn SO₄-p H_HNO3 was 49.98%.The photocatalytic activity of ZIS-Zn SO₄-p H_H2SO4 had the better photocatalytic activity,with the removal rates of HTC and Cr（VI）reaching 89.50%and 98.21%,respectively.·O₂^-and h⁺were the main active species in photocatalytic degradation of HTC by ZIS-Zn SO₄-p H_H2SO4.The intermediates and possible degradation paths of HTC were analyzed by 3D-EEM and high resolution mass spectrometry.The internal electron transfer mechanism and photocatalysis mechanism of the material were deduced.