Preparation Of CoWO₄-based Composite Material And Its Catalytic Ultrasonic Degradation Of Tetracycline Wastewater

As a kind of tungstate,cobalt tungstate（CoWO₄）has been applied in many fields due to its narrow band gap,good thermal stability,good electrochemical properties and absorption of visible light.In recent years,its photocatalytic performance has gradually attracted widespread attention.The literature shows that CoWO₄ has a good removal effect on organic pollutants such as dyes.Since the sonocatalytic mechanism is similar to that of photocatalysis,and sonocatalysis can produce sonoluminescence（SL）,the sonocatalytic activity of CoWO₄ has also been studied.However,due to the structural defects of cobalt tungstate,its sonocatalytic effect is limited.Therefore,in this paper,CoWO₄ is combined with other materials to improve its sonocatalytic degradation activity.The main research contents and results are as follows.Firstly,silver phosphate/cobalt tungstate（Ag₃PO₄/CoWO₄）composites with different composite ratios were prepared by simple hydrothermal method and chemical precipitation method.The prepared materials were systematically characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,Automatic specific surface and porosity analyzer（BET）,UV-Vis diffuse reflectance spectroscopy（DRS）.The results showed that Ag₃PO₄/CoWO₄ composites were successfully prepared.The average particle size was 20～50 nm,and the band gap was 2.60 e V.The specific surface area and visible light absorption range of CoWO₄/Ag₃PO₄ composites increased.In addition,the ultrasonic catalytic degradation of tetracycline（TC）by Ag₃PO₄/CoWO₄ composites under ultrasonic irradiation was studied,and the effects of different factors on the degradation performance during the degradation process were investigated.The results showed that under the optimal degradation conditions,the degradation rate of TC by Ag₃PO₄/CoWO₄ composites for 90 min could reach 75.3%.Since potassium persulfate（K₂S₂O₈）can be activated to form sulfate（SO₄^-·）under ultrasound,it is a strong oxidant and can be used as an environmentally friendly technology in sonocatalysis.The effect of K₂S₂O₈ on the degradation efficiency of Ag₃PO₄/CoWO₄ was investigated.The results showed that the degradation rate could reach 97.89%in 10 min after adding 10 mg K₂S₂O₈.Free radical capture experiments showed that holes（h⁺）were the main active substances for TC degradation,and free radicals（·OH）and superoxide anion radicals（·O₂^-）were auxiliary active substances.The mechanism study shows that the degradation mechanism of Ag₃PO₄/CoWO₄ is to form an S-type heterojunction,which improves the separation efficiency of electron-hole pairs（e^--h⁺）and enhances the degradation activity.Reuse experiments show that Ag₃PO₄/CoWO₄ composites have good stability and repeatability.Finally,the sonocatalytic activity of ZIF-8/CoWO₄ composites was evaluated by TC degradation experiments,and the optimal ultrasonic parameters were found by influencing factor experiments.The results showed that the degradation rate of 35 mg/L TC solution was 89.41%when the amount of ZIF-8/CoWO₄ was 1:1,the ultrasonic power was 500 W and the ultrasonic time was 2 h.After adding K₂S₂O₈ and hydrogen peroxide（H₂O₂）,the degradation rate reached 94.3%and 96.4%.The scavenger experiment showed that h⁺was the main active substance.The degradation mechanism shows that the reason for the improved sonocatalytic activity of ZIF-8/CoWO₄composites is the formation of Z-type heterojunction,which accelerates the separation of e^--h⁺pairs.The ZIF-8/CoWO₄ sonocatalyst still has good degradation effect after 4cycles of degradation,and the structure is complete,indicating that it has good stability and reusability.In summary,CoWO₄ can be combined with Ag₃PO₄ with narrow band gap and ZIF-8 with large specific surface area to improve the sonocatalytic activity.This paper provides a feasible idea for the modification of CoWO₄ and provides a direction for solving the problem of tetracycline wastewater treatment.