Synthesis,Characterization And Photocatalytic Performance Of Mesoporous Silicate SBA15 With Titanium And Tungsten

In recent years,semiconductor photocatalysis as an advanced catalysis or oxidation technology was attracted extensive attention of national and international experts.Titanium dioxide?TiO₂?,as a popular photocatalysts,has been widely used due to its non-toxicity,chemical stability and low cost.However,TiO₂ with high electron-hole recombination rate,can only be excited by ultraviolet light,which greatly restricted its application.Many researchers have been devoted to improve the photocatalytic performance of TiO₂ via several approaches:morphology controlled,doping with other ions or nonmetal,depositing by noble metal,coupling with other semiconductors to form a hetero-junction.Coupling with other semiconductor with suitable band gap has been widely used to improve the photocatalytic performance via extending the light harvest and improving the charge separation efficiency.Furthermore,the surface acidity of the TiO₂ catalyst can also be increased,which facilitates the adsorption of OH^-or H₂O moleculesand target molecules and thereby improves the photocatalytic activity of TiO₂.In addition,loading or incorporation of composites onto a stable matrix can achieve both goals of particle sizes control and increasing adsorption of reactant molecules around active sites as a consequence of large specific surface areas of selected matrixes,likely mesoporous silicate SBA15 with ordered hexagonal morphologies,large specific surface areas,tunable pore sizes,good hydrothermal stability,and unique electron delocalization capacity by frameworkThis paper consists three parts as follows:?1?In this investigation,we reported A facile and one-step hydrothermal procedure was adopted to fabricate a series of W-Ti-SBA15 composites?WTS?.These as-prepared composites were systematically characterized by a collection of analytic and spectroscopic techniques.It was found that dual phases of titanium and tungsten species coexisted in mesoporous structures of p6mm hexagonal symmetry.The existence of Ti O₂ nanoparticles were detected,because of the plentiful Ti.The W species?with a spot of WO₃?wre confirmed as well.These composites were visible-light responsive and exhibited enhanced photocatalytic capability toward degradation of Rhodamine B?Rh B?and 2,4-dichlorophenol?2,4-DCP?upon visible-light irradiation.Active species trapping measurements revealed that hydroxyl radical?·OH?played a leading roles in photocatalysis,and a possible reaction mechanism was proposed.?2?Based on the agglomeration of titanium dioxide,we reported the preparation,characterization,and photocatalytic evaluation of WTS series with low content of titanium species.As a result,the well-ordered mesoporous degree was improved with the decrease of titanium component,and the adsorption capability was significantly enhanced.Photocatalytic performance suggested that the catalytic properties of small percentage of series WTS was obviously better than those of the WTS composites.A same catalytic mechanism as WTS series was proposed.A series of Ag loaded WTS composite materials were prepared by a simple photo reduction method with the highest photocatalytic efficiency of 5%WTS0.1 materials as raw materials,and the photocatalytic properties were further promoted.After a series of characterization,it was found that the addition of Ag had no influence on the mesoporous structure,and the specific surface area of the material was not significantly changed.Photocatalytic perforemance displayed that Ag loaded WTS series materials obviously has better photocatalytic activity mainly due to the surface plasmon resonance?SPR?of Ag,which enhanced the electron transfer ability during the degradation process to further improve the separation efficiency of electron hole.Active species trapping measurements revealed that hydroxyl radical?·OH?and superoxide radical?·O₂^-?are the major active species,and a possible photocatalytic mechanism was proposed.?3?In this investigation,tungsten-containing mesoporous SBA15 materials were fabricated by means of a direct co-condensation sol-gel route and characterized by a collection of analytical techniques.1)The as-synthesized samples in different concentration of HCl were all of mesoporous structures.Tungsten species were substituted to corresponding silicon atoms or coated evenly on surface of channels in forms of crystalline WO₃,which caused the change of pore diameter of the samples.Comparing with the SBA15,tungsten species-contained samples showed better adsorption ability towards dyes rhodamine B?RhB?and ethylene blue?MB?.Specifically,the adsorption ability towards anionic dye MB was more obvious,mainly attributing to the appropriate molecular size.2)The as-synthesized samples with diffierent content were all of mesoporous structures and the tungsten form was changed from incorporated tungsten species to isolated tungsten species or low oligomeric tungsten oxide species,and finally to crystalline WO₃ with the increase of tungsten precursor content.These samples showed a excellent photocatalytic ability for RhB decomposition.The enhancement of photocatalytic performanc may be attributed to the enlarged surface areas,relatively negative charged surface,and suitable tungsten forms.Active species trapping experiments revealed that holes played a important role during photocatalytic degradation reactions,and a possible photocatalytic mechanism was proposed.