Preparation Of Mesoporous Ce-Ti Oxide Millispheres For Efficient Catalytic Ozonation:Performance And Mechanism

Large amount of wastewater from various industries such as textile printing and chemical industry usually contains a variety of toxic organics,and has to be subjected to critical treatment to meet the discharge standards.In recent years,the discharge standards of the key industries and sensitive regions have been increasingly stringent,thus posing new challenges for the advanced treatment of wastewater.Ozonation has gradually become one of the routine processes for advanced treatment of wastewater due to its advantages of simple operation,clean and sludge-free merits.Direct ozonation is selective during reaction with organics and thus results in low mineralization of the pollutants.In order to achieve efficient degradation and mineralization of organic pollutants,it is necessary to develop high-efficiency catalytic ozonation technology to increase the conversion of O3 into hydroxyl radicals,which have higher reactivity and stronger oxidizing ability.However,most ozonation catalysts have a long way to go to meet the demand for high-efficiency water treatment applications,especially on account of the easy mass loss,difficult separation,and poor hydrodynamic performance of the catalyst in powder forms.To be used in a bubble column,which is the most widely applied reactor type for water ozonation,efficient catalyst should be qualified in terms of particle size,shape,pore structure,stability,mechanical strength,etc.Meanwhile,the corresponding green and economical preparation methods are in great demand due to mass production considerations.Therefore,it is of great significance to develop catalysts combining high activity and excellent hydrodynamic properties towards efficient technology for ozonation of wastewater.In this study,a template method employing the low cost inorganic metal salts as the raw materials was developed to preprare Ce-Ti oxide mesoporous millisphere through a precursor sol premixing-alginate hydrogel bead template route,which successfully overcame the low permeation of inorganic metal salt into the alginate hydrogel via introducing the metal oxide precursor colloid into the sol phase in advance.The cost of the developed preparation method was reduced by several orders of magnitude in comparison with the prevailing metal alkoxide method,thus achieving economical preparation of Ce-Ti oxide mesoporous millisphere catalysts.The prepared catalysts were comprehensively characterized by N2 adsorption/desorption,XRD,XPS,SEM-EDS,TEM-SAED,Raman spectroscopy,and NH3-TPD.The effects of Ce/Ti ratio and calcination temperature on the structure and activity of the catalyst were investigated,and the performance and mechanism of the corresponding catalytic ozonation were explored.The results showed that the activities of amorphous catalysts were higher than the crystalline ones,and the catalytic activity was positively correlated with the density of surface acidic sites.Mesoporous CexTi1-xO2 oxide millispheres with different Ce/Ti ratios and Ceo.5Tio.5O2oxide millispheres calcined at different temperatures were prepared,with a narrow pore size distribution(3-4nm),compressive mechanical strength of2.46-10.91 N,specific surface area of 29.4-282m2 g-1,and pore volume of 0.100-0.382cm3g-1.The crystalline structure of the catalysts could be tuned via Ce/Ti ratio and calcining temperature.The amorphous structure favored the formation of more acidic sites and Ce-O-Ti bonds,playing a key role in adsorption and catalytic ozonation of oxalic acid as a probe of OH.EPR spectra and radical scavenging experiments proved that OH was the predominant reactive oxidative species in the catalytic ozonation of oxalic acid by Ce0.5Ti0.5O2.The optimized Ce0.5Ti0.5O2 mesoporous millisphere catalyst with high specific surface area(199m2g-1)and suitable mesoporous structure(average pore diameter of 3.59nm)was rich in Ce-O-Ti active sites and exhibited high catalytic ozonation activity.Almost complete(99%)mineralization of 100mg·L-1oxalic acid could be achieved during the catalytic ozonation in 90min by Ce0.5Ti0.5O2.Moreover,negligible loss of catalytic activity was observed in five consecutive experiments.In addition,as compared to the catalyst free circumstance,Ce0.5Ti0.5O2 could increase the TOC removal by18.7-54.0%during ozonation of four organic pollutants such as diclofenac,thus exhibiting promising potential in full-scale water treatment.This study provides methods to develop environmentally friendly inorganic mesoporous millisphere catalysts with low cost and the corresponding efficient catalytic ozonation water treatment technologies.