Preparation Of Mineral Composites And Their Application In Degradation Of Organic Pollutants

In recent decades,organic pollution of water and soil environments has become a serious problem worldwide.Natural purification and conventional treatment processes are not effective in removing most of the organic pollutants.Therefore,the development of advanced organic pollutant degradation technologies has become one of the important issues in environmental field.Advanced oxidation processes（AOPs）are an organic pollutant treatment technology developed in the 1980s.The principle of AOPs is to attack organic pollutant molecules using strong oxidizing radicals generated in the catalytic reaction system,which eventually oxidizes organic pollutants to CO₂,H₂O and other non-toxic inorganic molecules.It is a green and efficient technology for organic pollutant treatment.AOPs are mainly divided into ozone oxidation,electrocatalytic oxidation,photocatalytic oxidation,Fenton and Fenton-like reaction,and persulfate oxidation,etc..Nowadays,photocatalytic oxidation,Fenton and Fenton-like reaction,and persulfate oxidation have become popular in the field of soil and water remediation due to their mild reaction conditions,high oxidation capacity,simple operation equipment and low energy consumption.The development of suitable catalysts is the key to the catalytic degradation of organic pollutants by AOPs.Currently,most of the catalysts applied in AOPs are synthetic materials,which have the disadvantages of expensive raw materials,numerous synthesis steps and poor environmental compatibility,limiting their development in the field of AOPs.Natural clay and metallic mineral semiconductor materials have attracted much attention because of their abundant reserves,low price,non-toxicity and good chemical stability.The development of new mineral catalysts with high catalytic degradation activity is important for the removal of organic pollutants from soil and water.In this thesis,we tried to prepare three composites:SnS₂@ZnIn₂S₄@kaolinite,hematite@Bi₂WO₆,pyrolusite@Fe₂O₃ by in-situ growth method using natural mineral materials as carriers to degrade organic pollutants in water and soil environment through photocatalytic reaction,photo-Fenton-like reaction,and Fenton-like Fenton reaction,respectively.The main research results are summarized as follows.A Z-scheme SnS₂@ZnIn₂S₄@kaolinite heterojunction photocatalyst was successfully synthesized by hydrothermal method.Compared with a single catalyst,the SnS₂@ZnIn₂S₄@kaolinite heterojunction exhibits excellent adsorption-photocatalytic degradation ability in removing tetracycline hydrochloride（TC）.Under visible light irradiation,the pseudo-first-order reaction rate of SnS₂@ZnIn₂S₄@kaolinite heterojunction reached 0.0231 min^-1,which was 20.81 times and 2.37 times that of SnS₂and ZnIn₂S₄,respectively.The results showed that·O₂^–and ¹O₂ were the main active species involved in the degradation process.According to the results of high performance liquid chromatography-mass spectrometry（HPLC-MS）,the intermediates produced by the degradation reaction were analyzed,and the possible photodegradation pathway of TC was proposed.The excellent degradation performance of SnS₂@ZnIn₂S₄@kaolinite heterojunction catalyst was mainly attributed to the enhancement of catalyst adsorption capacity,the improvement of light capture ability and the synergistic effect of each component.Natural hematite（α-Fe₂O₃）,as a potential Fenton-like reagent,can remove organic pollutants through AOPs.However,natural hematite is difficult to improve its catalytic degradation activity due to its rapid recombination of charge carriers.Heterojunction of hematite and Bi₂WO₆（hematite@Bi₂WO₆,BW@NH）were constructed for the degradation of organic pollutants through the combination of peroxymonosulfate（PMS）activation and photocatalysis.The BW@NH heterojunction exhibits high activity and stability in activating PMS to generate free radicals(SO₄^·-and·OH)for removing several representative antibiotics under visible light（Vis）,including tetracycline hydrochloride（TC,91%）,ofloxacin（OFX,94%）,amoxicillin trihydrate（AMX,100%）,sulfamethoxazole（SMZ,72%）and metronidazole（MNZ,89%）.The pseudo-first-order reaction rate coefficients of BW/NH/PMS/Vis system in photo-Fenton-like reaction system were 7.77 and 1.95 times that of BW/NH/Vis and BW/NH/PMS systems,respectively.In addition,the BW/NH/PMS/Vis system achieved TOC removal efficiencies of 67.44%（TC）,75.53%（OFX）,78.96%（AMX）,62.34%（SMZ）and59.62%（MNZ）within 200 minutes.In addition,the main reactive oxygen species in BW/NH/PMS/Vis system were investigated,and the possible degradation pathway of OFX and the catalytic enhancement mechanism of photo-Fenton-like system were proposed.For in-situ chemical oxidation（ISCO）technology in soil remediation,one of the key challenges is the limited diffusion range of chemical oxidants in soil without external agitation.Therefore,we developed a self-propelled micromotor based on natural pyrolusite,which can enhance the mass transfer of soil remediation agents by generating abundant micro/nanobubbles.Micromotors composed of natural pyrolusite and Fe₂O₃ were used as activators of peroxymonosulfate（PMS）and H₂O₂ for dynamic remediation of polycyclic aromatic hydrocarbons（PAHs）contaminated soil.The prepared micromotor exhibits a high speed（185μm/s）at 1wt%H₂O₂ fuel concentration.The dual role of pyrolusite@Fe₂O₃ micromotor in catalytic degradation and mass transfer makes the degradation efficiency of pyrene in soil reach 100%,and the TOC removal rate reaches 93.36%.Based on the results of reactive oxygen species（ROS）and gas chromatography,the degradation pathway of pyrene was proposed.This study shows that micromotors based on natural pyrolusite have great potential in in-situ remediation of organic contaminated sites.