Design And Synthesis Of Novel M-O-Ti-based Catalyts For Advanced Oxidative Degradation Of Organic Pollutants

Advanced oxidation technology based on catalytic decomposition of hydrogen peroxide(H2O2)or potassium peroxymonosulfate(PMS)to produce·OH or SO4·-free radicals by transition metal-based materials has attracted more and more attention in the field of organic wastewater treatment due to its advantages of simple operation,high efficiency,broad spectrum,quick effect,recycling and low secondary pollution.The treatment efficiency of·OH or SO4·-based advanced oxidation technology depends on the catalyst to a great extent,so the development of transition metal-based catalytic materials with excellent physical and chemical properties,high catalytic activity and long operation life is a hot research topic in this field.Among various reported advanced oxidation catalytic materials,manganese-based materials(such as MnSiO3,MixFe3-xO4,etc.)and cobalt-based materials(such as Co3O4,Co2O3,etc.)have shown excellent application prospects in catalyzing hydrogen peroxide and PMS,respectively,due to their advantages of easy preparation and high activity.Therefore,it is of great significance to design and synthesize manganese-based and cobalt-based materials with large specific surface area and easy mass transfer by simple and controllable methods,as well as to improve the activity and stability of metal sites(manganese and cobalt sites)on the surface of materials,but there are also considerable challenges.In this paper,simple and controllable one-pot hydrothermal method was developed,and a series of new manganese-based and cobalt-based materials with different morphology(short rod,nanodiscs,nanoflower structures,polycrystalline chain)and compositions of M-O-Ti(M=Mn and Co)have been designed and synthesized,which showed good application results in the degradation of organic dyes,antibiotics and other pollutants in water.The main contents and conclusions are summarized as follows:1.Our laboratory recently found that the Mn-O-Ti material obtained by incorporating Mn(II)into anatase lattice is an efficient Fenton catalyst with high catalytic activity and cyclic stability,but there are some shortcomings such as complicated preparation process,low crystallinity and low Mn(II)content.In view of this,a simple and controllable one-pot hydrothermal method was explored in this paper.Manganese-doped nano-titanium dioxide with spindle-shaped short rod structure with good dispersion,uniform particle size and high crystallinity were successfully obtained.some parameters such as the amount of H2O,NaCl and reaction time were carefully optimized.The effects of these parameters on the morphology of the products were clarified,and the formation mechanism of the materials was proposed.Furthermore,the spindle structure material was applied to catalyze the degradation of MB by hydrogen peroxide.It was proved that Mn-TiO2(4.6wt%)had obvious catalytic activity.2.On the basis of the hydrothermal process in the previous chapter,three-dimensional and hierarchically spherical Mn(Ⅱ)-doped TiO2(RFMTO)catalytic materials with large specific surface area were synthesized by a simple one-step template-free solvothermal method for the first time by changing the key hydrothermal process parameters.The characterization results show that the RFMTO is a flower-like nanosphere(～1.5 m)composed of a large number of 4-8 nm diameter nanofibers radiating outward from the spherical center.Thanks to such a unique structure,the RFMTO not only has a large specific surface area of 413.3 m2 g-1,but also contains a large number of highly open pore structures(20-60 nm).In addition,the XPS and ICP-OES test results show that the Mn2+ content in RFMTO material is as high as 17 wt%.Furthermore,RFMTO was used as heterogeneous Fenton catalyst to evaluate the performance.The results showed that the material not only has the ability of highly effective catalytic degradation of high concentration organic dyes and different types of organic dyes,but also the unique structure of Mn-O-Ti endows the material excellent cyclic stability.3.In order to further improve the crystallinity and activity of Mn-O-Ti structural materials,we have successfully prepared MnTiO3 nanodiscs with high crystallinity and rich Mn-O-Ti structural units by controlling the synthetic reaction conditions(Mn/Ti ratio,H2O content and reaction time).It is the first time to clarify the potential application of this material in the oxidation degradation process mediated by hydrogen peroxide.The SEM and XRD show that the prepared nano-materials possess monodisperse disk structure with uniform size(diameter to 333 nm,thickness to 16.2 nm),and excellent MnTiO3 crystal form.The HRTEM and SAED showed that the MnTiO3 nanodiscs own a high exposure(001)crystal surface.In addition,we propose the possible formation mechanism of MnTiO3 nanodiscs.Thanks to the unique two-dimensional open surface structure,abundant active metal sites and excellent crystallinity of the nanodiscs,MnTiO3 exhibits high catalytic decomposition ability for a series of organic pollutants,and its activity remains basically unchanged after six reuses.4.A novel hierarchical Co(Ⅱ)-doped TiO2(hCTO)nanostructure with abundant and easily accessible active sites was fabricated through a simple one-pot hydrothermal route and innovatively studied as the potential alternative to conventional cobalt-based catalysts for peroxymonosulfate(PMS)activation.Detailed characterization indicated that hCTO was well organized by two-dimensional porous crystalline nanosheets,exhibiting a corolla-like morphology with large surface area(131.2 m2 g-1)and highly open structure.More interestingly,it was also found that Co(Ⅱ)ions were preferentially doped into the surface lattice of titanium dioxide,which resulted in more abundant active sites on the surface of hCTO.Due to the combination of multiple unique characteristics,hCTO displayed an excellent catalytic efficiency in PMS solution,and its catalytic activity is much higher than that of commercial Co3O4.The catalytic mechanism of PMS/hCTO system and the possible degradation pathway of ofloxacin(OFX)were proposed by identifying the active species and intermediate products in the degradation process.Moreover,hCTO was demonstrated to be highly efficient in activating PMS for degradation of other recalcitrant organic pollutants.Besides,the hCTO exhibited excellent catalytic reusability,without obvious activity loss after reuse several times.5.Based on the above results,we successfully prepared another doped octahedral crystalline chain Co(Ⅱ)-Fe2TiO4(CFTO)material by adjusting one-pot hydrothermal process.The SEM show that the CFTO is a chain-like structure material formed by a large number of smooth octahedral single crystals superimposed on a specific crystal surface.The XRD and EDS Mapping indicate CFTO has possesses excellent phase structure and uniform element distribution;the XPS and ICP-OES show that the valence state of doped ions is+2,and the doping amount is 3.2wt%.The results of performance evaluation not only show that the activation capacity of the CFTO for PMS is much higher than that of Co3O4,but also prove that the material has the advantages of wide application range of pH,strong anti-interference ability,good universality and high cycle stability.The free radical quenching experiments and ESR tests confirm that PMS/CFTO can induce a large amount of SO4·-and·OH at neutral pH.In addition,we proposed the degradation pathway of RhB with the help of LC-MS.