Preparation And Characterization Of Visible-light Response TiO₂ And TiO₂/Activited Carbon Composite Materials

In the present work, nano-size TiO₂ photocatalyst,the N-doped visible-light responsenanosize TiO₂ photocatalyst (TON),the S-doped visible-light response nanosize TiO₂photocatalyst (TiS_xO_2-y),TiO₂/AC composite photocatalyst, Activated carbon supportedvisible-light response N-doped TiO₂ photocatalyst (TON/AC) and adsorption-photocatalysis hi-functional activated carbon materials were prepared by acid catalyzed hydrolysis method usingTiCl₄ as precursor. DRS,XRD,SEM,FTIR,XPS and N₂ (77K) adsorption isotherm wereused for materials characterization. The details were as follows:The N-doped visible-light response nanosize TiO₂ photocatalyst was prepared by acidcatalyzed hydrolysis method followed by calcination in NH₃/N₂ atmosphere. The resultsshowed that the N-doped TiO₂ showed obvious photocatalytic activity under visible lightirradiation. The TON catalyst calcined at 500℃for 5 h exhibited the highest activity in bothUV and visible light region. N-doping showed little effect on the crystalline structure, surfacearea and crystal size of TiO₂. The Ti-O-N bond formed on the surface of N-doped TiO₂, whichcan not only extend the adsorption edge to visible light region (490～550nm), but alsobenefitial the photocatalytic acitivity of TiO₂ under UV irradiation. The newly formed Ti-O-Nbonds and the less agglomeration of single crystal mainly lead to the high activity of N-dopedTiO₂ in both UV and visible light region.A yellowish Ti_1-xS_yO₂ photocatalyst exhibited high activity in wide light spectrum range wasprepared by acid catalyzed hydrolysis method. The results showed that cationic S⁶⁺ wasincorporated into TiO₂ lattice and substitutes part of Ti⁴⁺. Ti_1-xS_yO₂ with optimum S-dopingexhibited the highest activity in both Vis and UV region. The new band-gap formed by doped-Scan induce a second adsorption edge (450～550nm) which can be excited by Vis irradiationand induce Vis activity. Under UV irradiation, the new formed band-energy can accept holesgenerated by bulk TiO₂ and formed a composite semiconductor structure, then improve hole-electron pairs separation. In addition, doped-S also beneficial for TiO₂ dispersion, increase S_BETand retard phase transformation.TiO₂/xAC composite photocatalysts were prepared by acid catalyzed hydrolysis methodfollowed by calcinations in N₂ atmosphere. The results showed that TiO₂/xAC catalysts withoptimal AC content 5%(wt) exhibited more higher activity than P-25(TiO₂) and TiO₂, as wellas good decantability, less activity lost after several runs and less sensitive to pH change. Result of DRS revealed no electronic change when activated carbon (AC) added. Better TiO₂distribution and less agglomeration can be achieved when optimal AC content adopted. Resultof FTIR suggest a conjugation effect was present between the AC bulk and Ti-O bond.Suitable pollutant concentration environment and less agglomeration provided by AC was themian cause for the high activity of TiO₂/5AC. The performance of the prepared TiO₂/5ACcatalyst revealed great practical potential in wastewater deeply treatment field. Another, effectof activated carbon modification on the structure chracteristics and photocatalytic activity ofTiO₂ photocatalyst were system investigated. The results showed that TiO₂/AC exhibitedhigher activity than TiO₂ within a wide range calcination temperature. AC was beneficial toTiO₂ size control and phase transformation retardment.Effect of activated carbon properties on the photocatalytic activity of TiO₂/AC compositephotocataylyst was investigated. The results showed that microstructure and surface oxygenacid groups of AC were disadvantage to the dispersion of nano-size TiO₂. Larger number ofmesopores and less surface oxygen containing acid groups were beneficial to the higheractivity. Surface oxygen acid groups of AC exhibited more significant effect on metal ionreduction than organics oxidation for the TiO₂/AC composite photocataylyst. Result of DRS,XRD revealed that surface properties of AC has less effect on the electronic structure,crystalline size and crystal phase of TiO₂.Activated carbon (AC) supported nitrogen doped TiO₂ photocatalysts (TON/AC) with widerange light response were prepared by calcination of the TiO₂/AC precurse which wereprepared by acid catalyzed hydrolysis method in NH₃/N₂ atmosphere. The results showed thatTON/AC with suitable nitrogen doping exhibited the high activity in UV light, visible light andsolar light. Nitrogen doped can form a new bond gap, and the adsorption edge to visible lightregion 450～550 nm, that can induce TiO₂ visible light activity. And better TON distribution,less agglomeration and increase surface area can be achieved when AC supported, which canenhance photocatalyst activity. In addition, AC supported could also beneficial for TiO₂decantability and less activity lost after several runs.Based on the synergy mechanism obtained, adsorption-photocatalysis bi-functional carbonmaterials (xTiO₂/AC) could be prepared by deposition of TiO₂ precursor on the surface ofporous AC followed by calcinations under N₂ or CO₂ atmosphere. Although the absorptioncapability of xTiO₂/AC reduced under dark, but it increased greatly when light irradiated. The8TiO₂/AC in calcined under CO₂ at 600℃for 2 h exhibited the highest pollutant removal capability when light irradiated.