Study On Degradation Of Tetracycline Hydrochloride In Water By Advanced Oxidation Of Halloysite-based Composites

In recent years,the expansion of human production activities and the abuse of antibiotics had led to the inevitable entry of antibiotics into aquatic environments.Residual of antibiotics in various aquatic environments had huge negative effects on human health and ecosystems.Among various antibiotics,tetracycline hydrochloride（TCH）is widely used in the treatment of biological diseases,as well as animal husbandry and fisheries.TCH containing wastewater is difficult to degrade and also toxic to microorganisms.Moreover,when bacteria are affected by TCH,their genetic information may be modified to produce highly antibiotic-resistant biobacteria,and antibiotics in water bodies are not effectively removed by traditional wastewater treatment processes.Advanced oxidation technology（AOPs）is a new method to efficiently degrade refractory organic pollutants in water.The reactive oxygen species（ROS）produced in the process can effectively degrade macromolecular organic matter,and even eventually mineralize it into CO₂and H₂O.This method has the advantages of strong oxidation capacity,high treatment efficiency,wide application range and small secondary pollution.In this study,nano-zero valent iron（n ZVI）/halloysite nanotubes（HNTs）composites and zinc oxide（Zn O）/halloysite nanotubes（HNTs）composites were prepared,which used the degradation of tetracycline hydrochloride in water by activated persulfate and photocatalytic advanced oxidation technology,respectively.The adsorption and catalytic degradation of TCH were investigated,the degradation mechanism of TCH was explored,and the acute toxicity and mutagenicity of TCH and degradation intermediates were predicted.The main study results are presented as follows:（1）Composite materials of n ZVI/HNTs and Zn O/HNTs were prepared by liquid-phase reduction and high-temperature calcination,respectively.The analysis results of transmission electron microscope（TEM）,X-ray photoelectron spectroscopy（XPS）and X-ray diffraction（XRD）proved that n ZVI/Zn O was successfully loaded on the surface of HNTs,and the dispersion effect was excellent.The BET test results showed that the pore size of HNTs was mainly distributed in the mesopore range（2nm～50nm）,and the specific surface area was54.91 m²/g.The specific surface areas of n ZVI/HNTs and Zn O/HNTs were 56.33 m²/g and29.97 m²/g,respectively.Compared with HNTs,the pore volume in the mesopore region increased and decreased,respectively.The halloysite nanotube structure was not destroyed in the composite,and the composites had good stability.（2）As the initial concentration of TCH increases,the adsorption capacity of halloysite nanotubes increases accordingly.The maximum adsorption capacity of HNTs at 0.08 g was11.16 mg/g.The temperature increase facilitates the adsorption of TCH.The optimal adsorption efficiency of HNTs for TCH is 18.11%at p H=3.Increasing the mass ratio of n ZVI in n ZVI/HNTs composites favors the adsorption of TCH.The TCH removal efficiency increases with increasing n ZVI/HNTs dose,temperature,and PS concentration.TCH removal efficiency decreases with increasing TCH concentration and initial p H concentration.With the increase of Zn O/HNTs and the initial concentration of TCH decreased,the TCH removal efficiency is increasing.Salinity（Na Cl concentration）has a"high promotion,low inhibition"effect on the photocatalytic degradation of TCH.In order to verify the applicability of the composite for other organic pollutants,methylene blue（MB）degradation experiment was carried out.The experimental results show that within 90minutes,the removal efficiency of MB with an initial concentration of 7.5 mg/L could reach99.94%.The degradation efficiency of TCH by n ZVI/HNTs and Zn O/HNTs was 84.21%and 79.73%,respectively,and after three reuses,the catalytic degradation efficiency of TCH was 65.80%and 65.57%,respectively.This indicates that composite materials have excellent reusability..（3）According to the fitting analysis of the data on the adsorption thermodynamics and adsorption dynamics,the TCH adsorption of HNTs fits the Langmuir adsorption model,while n ZVI/HNTs and Zn O/HNTs were more consistent with the Freundlich model,Therefore,it is believed that the adsorption of composite materials has a transition from monolayer adsorption to multilayer adsorption.Using the Van’t Hoff equation to calculate the values ofΔG⁰are all negative,indicating that the adsorption process is spontaneous.HNTs and n ZVI/HNTs fit the pseudo-second-order adsorption kinetic model,while Zn O/HNTs were more consistent with the pseudo-first-order adsorption kinetic model,internal diffusion did not play a leading role.Therefore,it is considered that there is a chemical adsorption about HNTs and n ZVI/HNTs for TCH,while Zn O/HNTs is mainly physical adsorption.（4）The quenching experiment and EPR test showed that SO₄^·-and h⁺were the main active species in the catalytic degradation of TCH involving n ZVI/HNTs and Zn O/HNTs,respectively.But h⁺,¹O₂,·O₂^-and·OH all function in the catalytic degradation of Zn O/HNTs.According to the analysis of LC-MS results,possible degradation routes were speculated,and the toxicity of degradation intermediates was predicted by quantitative structure and activity relationship（QSAR）of toxicity estimator software（TEST）.The results showed that the toxicity of intermediates of TCH degradation process was fading.The results show that the two catalytic advanced oxidation techniques of the halloysite composites can effectively degrade tetracycline hydrochloride in water.The degradation process is green,environmentally friendly and less harmful.This study provides a theoretical basis for preparation of halloysite-based composites and the treatment of tetracycline hydrochloride wastewater.