Effect Of Preparation Methods On Surface Properties Of Iron-titanium Compound Oxides And Their Phosphate Adsorption Properties

Phosphorus is an essential nutrient element for biological growth,but it may lead to eutrophication when it exceeds a certain value in water.In recent years,the degree of eutrophication of water body in China had been deepened.Water blooms and red tide occurred more frequently,which seriously affects the water ecosystem,coastal tourism and fishery production.Therefore,phosphate removal from water is getting more and more attentions.Recently,metal compound oxides have attracted extensive attention due to their excellent adsorption properties.However,due to the complexity of the composition and structure,there are a few studies on the reasons for the excellent adsorption properties.Preparation methods will affect the morphology,specific surface area,pore structure and particle size of metal composite oxides,and furtherly affect the adsorption properties.The study of the relationship between preparation methods,surface properties and adsorption properties of the metal composite oxides has an important guiding role in the development of new,economical and efficient adsorbents.In this study,a series of iron and titanium composite oxides were prepared by mechanical physical mixing,coprecipitation and hydrothermal method.The surface characteristics of iron-titanium compound oxide such as morphology,surface area,surface hydroxyl concentration were systematically characterized via XRD,SEM,EDS-Mapping,BET,Zeta,FTIR,amorphous degree and surface hydroxyl content techniques.The adsorption ability of phosphate was studied by batch adsorption experiments.The results were obtained as following:1.The phosphate adsorption capacity of ^CFe-Ti prepared by coprecipitation method is higher than that of pure iron oxide FeOOH and pure titanium oxide TiO₂,which indicates that the ^CFe-Ti exhibits an synergistic effect of iron oxide and titanium oxide.When the molar ratio of iron and titanium is 4.25:1,the phosphorus adsorption capacity is improved significantly.Moreover,the molar ratio of iron and titanium is 4.25:1 is chosen and used in ^MFe-Ti and ^HFe-Ti preparation,which by mechanical mixing method and hydrothermal method,respectively.The pH of preparation process has little effect on phosphate adsorption properties of iron-titanium compound oxide and pH 7±0.1 is chosed.During the preparation of ^HFe-Ti by hydrothermal method,glycerol content and temperature have a certain influence on phosphate adsorption properties.Two kinds of iron-titanium compound oxide ^HFe-Ti-100 and ^HFe-Ti-120 were prepared by using 20%glycerol content,at100℃and 120℃,respectively.2.SEM and EDS-Mapping images show that the particles of ^CFe-Ti are looser and its distribution uniformity of elements are higher than ^MFe-Ti.The particles of ^HFe-Ti-100 and ^HFe-Ti-120 are sharper than ^CFe-Ti.BET results show that the pore size and pore volume and specific surface area of ^CFe-Ti were higher than that of ^MFe-Ti,^HFe-Ti-100 and ^HFe-Ti-120.Zeta potential of these oxides decreases in the order of ^CFe-Ti>^MFe-Ti>^HFe-Ti-100>^HFe-Ti-120.The amorphous degree of these oxides decreases in the order of ^CFe-Ti>^MFe-Ti>^HFe-Ti-100>^HFe-Ti-120.The surface hydroxyl content of these oxides decreases in the order of ^CFe-Ti>^MFe-Ti>^HFe-Ti-100>^HFe-Ti-120.3.The maximum phosphorus adsorption capacity of ^MFe-Ti is 22.7 mg·g^-1,which is colse to the theoretical value calculated according to the molar ratio of iron and titanium.The maximum phosphorus adsorption capacity of ^CFe-Ti is 40.6 mg·g^-1,which is higher than the single component oxides and exhibits an significant synergistic effect.The maximum phosphorus adsorption capacity of ^HFe-Ti-100 and ^HFe-Ti-120 is 20.3 mg·g^-1 and 16.4 mg·g^-1,respectively.The adsorption capacity of ^HFe-Ti gradually decreases with the increase of preparation temperature.Chemical adsorption occurs at the surface of FeOOH,TiO₂,^MFe-Ti,^CFe-Ti,^HFe-Ti-100 and ^HFe-Ti-120 through the formation of inner-sphere complexes by replacing hydroxyl groups.4.The preparation method is an important factor affecting the morphology,surface properties and phosphate adsorption properties of the iron-titanium compound oxide.Mild preparation conditions lead to loose particles,well-developed pore structure,low crystallinity,rich surface hydroxyl groups,and high phosphorus adsorption capacity.The elements of materials prepared by the coprecipitation method are evenly distributed compared with the mechanical mixing method,which is conductive to fully exerting the interaction force between them and producing a synergistic effect,increasing the phosphate adsorption amount.Therefore,the surface characters and adsorption properties of iron-titanium compound oxide are closely related to their preparation methods.Compared with mechanical mixing method and hydrothermal method,coprecipitation method is a more simple and economical way to fabricate high effective iron-titanium compound oxide for phosphate removal from water.