Characteristics Of Water Purification During Catalytic Ozonation Induced On Natural Mineral Interfaces And Design And Synthesis Of Novel Catalysts

Ozonation has been considered as a safe and effective water treatment technology which has been applied in various water treatment fields in different countries.However,traditional ozonation should be improved since the amount and concentrations of organic pollutants entered water body increased rapidly.Heterogeneous catalytic ozonation has gradually drawn more and more attention from researchers as a kind of potential highly effective and safe water treatment technology.Researchers have devoted a lot of time and effort to search and develop novel catalysts which are suitable for catalytic ozonation processes and obtained fruitful outcomes.In order to obtain potential catalysts for catalytic ozonation,we started searching from natural minerals and acquired some catalysts that reveal high ozone decomposition abilities.After that,detailed characterization and catalytic ozonation efficiencies were investigated in order to clarify the relationship between catalysts surface properties and catalytic oxidation efficiencies.Then artificial catalysts for catalytic ozonation were designed according to the above results and characterizations and catalytic ozonation ability tests of the synthesized catalysts would prove the accuracy of design principles.In this study,we chose ?-quartz,?-cristobalite light-weight granular mixedquartz sand(L-GQS)and quartz glass as selected simplest natural silicate minerals,and then chose L-GQS as target catalyst after basic characterization and ozone decomposition tests.Characterization revealed that L-GQS was composed by ?-quartz,?-cristobalite and anorthoclase with average diameter of 4 mm and thickness of 1 mm.L-GQS was further characterized by surface element distribution and valence state analysis,specific surface area and pore size analysis,zero charge point potential analysis,internal atomic structure and surface group exposure analysis.The results presented that the surface of L-GQS contained abundant surface hydroxyl groups and Lewis acid active sites.Atrazine(ATZ)was selected as model pollutant and treated in semi continuous flow catalytic ozonation reaction system with L-GQS.Compared with ozonation alone,the ATZ degradation rate and TOC removal rate was higher in presence of the L-GQS catalyst under the condition of 293 K and p H=7.0.Increasing p H,reaction temperature,reaction rotation speed,L-GQS dosage and decreasing L-GQS particle size enhanced ATZ degradation and TOC removal rate.L-GQS revealed high and stable catalytic ozonation ability either in the presence of NOM or in real water system.Hydroxyl radicals(OH·)were proved to be the main reactive oxygen species(ROS)by chemical inhibition and EPR analysis.The reaction mechanism of ozone decomposition and OH· generation was attribute to Br?nsted and Lewis acid active sites provided by Si-O and Al-O bonds on the surface of L-GQS.According to the mechanism of catalytic ability revealed by simplest natural silicate minerals,we kept searching other catalysts from composite oxide natural silicate minerals in order to find minerals which contained more surface-exposed metal active sites.Bench catalytic ozonation reaction system was chosen to test the ATZ degradation ability in the presence of tourmaline and the same characterization as what was performed for L-GQS was applied for tourmaline.Results showed that the rhombohedral structure tourmaline was composed of framework contained B,Fe,Al,Si and O complexing Ca,Na,and Fe cations.Compared with L-GQS,the tourmaline surface exposed more Br?nsted and Lewis acid active sites due to the function of surface Al-O,Si-O and Fe-O bonds which resulted in higher catalytic ozonation ability especially under low temperature conditions.Toxicity test proved that toxicity of solution after catalytic ozonation was reduced due to the dechlorination and futher decomposition of ATZ.With the guide of above research results and catalyst design principles,ilmenite-type MTi O 3(M=Mn or Fe)catalysts were successfully synthesized.Mn Ti O 3 was chosen for detailed research of p-chlorophenol degradation during catalytic ozonation processes.Characterization results revealed that the catalytic ozonation ability of Mn Ti O 3 mainly contributed by the surface medium and strong surface Lewis acid active sites provided by surface exposed Mn and Ti metallic ions.By analyzing the changing of crystal structure,crystal form,exposure ratio of high energy crystal surface and specific surface area of Mn Ti O 3 under different synthesis conditions,the key influencing factors which should be considered during the design of catalysts were summarized.The single-crystal hexagonal Mn Ti O 3 nanosheets synthesized under optimum conditions presented high catalytic activity and stability,1O 2,O2?-and OH? were the mian ROS during the reaction processes.Above all,all the selected minerals and deliberately designed ilmenite-type MTi O 3(M=Mn and Fe)catalysts revealed high activity during the catalytic ozonation of resistant or high concentration pollutants.The principles proposed for selecting and design catalytic ozonation catalysts in this study may guide the future selection and design of more novel catalysts.