Liquid Phase Synthesis And Visible-light Photocatalytic Property Studies Of BiOCl/Bi₂S₃ Complex

Photocatalytic technology is an important means of environmental treatment.Photocatalytic degradation of organic pollutants is the redox reaction between the active groups produced in the reaction system and the molecules of organic pollutants under the combined action of light and catalyst,then the organic pollutants were degraded into inorganic small molecules.Therefore,the development of stable and efficient photocatalytic materials is an important topic in the field of photocatalysis.In bismuth-based semiconductor materials,BiOCl has attracted extensive attention because of its unique layered structure and excellent optical and electrical properties.However,the wide band gap structure（E_g=3.2–3.6 eV）limits its absorption of visible light,and then it shows weak visible light catalytic performance.In this paper,the narrow-band gap Bi₂S₃（E_g=1.3–1.7 eV）and the BiOCl are combined to form a three-dimensional unitary composite catalytic material by mild liquid phase ion exchange method,which effectively improved the visible light response range of the BiOCl.At the same time,the matching band structure of the two bismuth-based materials can promote the rapid separation of photogenerated carriers（e^--h⁺）,so as to obtain excellent visible light catalytic degradation of organic pollutant molecules.The mechanism of visible light catalysis was investigated by adjusting the reaction parameters（reaction time,reaction temperature,type of surfactant,etc.）to control the size,composition and morphology of BiOCl-Bi₂S₃ composite photocatalytic materials.The paper mainly consists of three parts:In the first part,flower-like BiOCl/Bi₂S₃ composites were successfully synthesized in acidic environment with bismuth chloride（BiCl₃）as bismuth source,thioacetamide as sulfur source and sodium tartrate as complexing agent.In the preparation process,BiOCl precursor was formed at 50℃,the reaction temperature was increased to 80℃,and the chlorine atom on the surface of BiOCl was gradually replaced by S^2-released by thioacetamide to form BiOCl/Bi₂S₃ composite.The effects of the amount of complexing agent,type of complexing agent,surfactant,solvent and bismuth source on the composition and morphology of the composite were investigated.The structure,morphology and optical properties of the materials were characterized by X-ray diffraction,scanning electron microscopy and solid-state ultraviolet.Using Rhodamine B（RhB）as a model pollutant molecule,the visible light catalytic activity of flower-like BiOCl/Bi₂S₃ composite photocatalyst was studied,and the photodegradation mechanism of the composite photocatalyst was studied by capture experiment.In the second part,under the inducement of PVP K30 molecule,a series of BiOCl/Bi₂S₃ microsphere were successfully prepared by low temperature liquid phase precipitation and ion exchange method.By changing the amount of PVP K30,the composition of composite micron spheres can be controlled by ensuring that the size of the assembly structure was similar（about 2μm）.The effects of reactant concentration and reaction temperature on the morphology and scale of assembly structure were investigated.A series of BiOCl/Bi₂S₃ microsphere samples were used for degradation of ciprofloxacin under visible light.The experimental results show that the degradation efficiency of the composite catalyst samples increased first and then decreased with the increase of the amount of PVP,That is to say,there is the best amount of PVP,which is closely related to the specific surface area of the samples.The effective active substances in the degradation of ciprofloxacin by BiOCl/Bi₂S₃ microsphere were further studied by capture experiments,and the possible mechanism of visible light catalytic degradation of colorless organic pollutants was deduced.In the third part,bismuth sulfide micro-assembly structure was prepared by using ethylene glycol-water as mixed solvent,Bi（NO₃）₃·5H₂O as bismuth source and thiourea（CH₄N₂S）as sulfur source,and then CuCl₂ solution was introduced.Ion substitution reaction took place on the surface of Bi₂S₃ assembly structure,and the Bi₂S₃/BiOCl composite assembly material with a scale of about 2μm was successfully obtained.The results of photocatalytic degradation showed that this kind of composite structure had excellent properties of visible light catalytic degradation of colored dye Rhodamine B and colorless pollutants sulfamethoxazole and levofloxacin.The active species and photocatalytic mechanism in the degradation process were analyzed from the capture experiment results.