The Mechanism Of Adsorption Andphotocatalytic Oxidation For As???by TiO₂

Two kinds of Titanium dioxide were used to remedy arsenic pollution in the water,we carried out systermatic experiments to investigate their performance for removing arsenic by adsorption without UV,the mechanism of As???photooxidation by was built in above two TiO₂/UV system.We chosed 3D-TiO₂ as pure TiO₂ system and Ti-Mn hybrid oxide as complex TiO₂ system,Both of them can be used as bi-function material:adsorbent and catalyst.1.The adsorption performance for 3D-TiO₂ adsorbing arsenateAs?V?and arseniteAs???was explored without UV light.Series of relevant experiments were carried out:pH value effect on both As?V?and As???adsorption processes;adsorption kinetic for both As?V?and As???;adsorption isotherm;adsorbent solid effect on adsorption processes;deep treatment ability for arsenic removal from water.In addition,discuss the arsenic forms after adsorption by Raman.The experiment of pH effect on adsorption give information about reaction between adsorbent and adsorbate,3D-TiO₂ absorb As???through inner-sphere complex mode,however,it remove As?V?from water by electrostatic force,so that the capacity for latter is not good as former's.3D-TiO₂ has potential to remove 100%As???from water.The fitting datas for adsorption kinetic proved that adsorption process of 3D-TiO₂+As???/As?V?system is achieved by three steps,including mesopores rapid diffusion,micropores filling,surface adsorbing reaction.2.The photooxidation performance of 3D-TiO₂ was explored by oxidizing As???into As?V?under UV light so that confirm the main oxidant in above process.Firstly,3D-TiO₂'s optical properties such as excitation wavelength,optical stability,effect of stiring method on absorption of light intensity were investigated to make sure it has stable optical characters,in addition,the effect of As???'s existing on catalyst's optical properties was tested.Furthermore,it should be maintained that whether other oxidation processes have influence on As???photooxidation by 3D-TiO₂.Secondly,three kinds of scavengers including electron scavenger Cu²⁺,holescavenger sodium formate?SF?,hydroxyl radicalscavenger tertiary butanol?TB?were put into adsorption system prior to inputting UV light to test its interference to adsorption capacity of3D-TiO₂ for As???.The main oxidant was decided by combining scavengers in different ways such as single Cu²⁺,single sodium formate,single tertiary butanol,Cu²⁺+SF,Cu²⁺+TBet al.Basing on above datas and analysises,the main oxidant for3D-TiO₂+As???+UV is attributed to superoxide radical or O-products produced by oxygen reacting with reactive substance in 3D-TiO₂/UV system,and photogenerated holes is assisting oxidizing agent.The hydroxyl radical is suspected to take part in As???photooxidation process in 3D-TiO₂/UV system because of photogenerated electrons reduced As?IV?to As???probably.The unique microstructure of 3D-TiO₂bring about above mechanism,photogenerated holes and hydroxyl radicals can not enter micropores of catalyst where As???is adsorbed so that they have no access to react with As???.3.We prepared hybrid oxide by hydrothermal method combined with a Teflon-sealed autoclave reactor,named Ti-Mn hybrid oxide?Ti-Mn-HO?,applying it to arsenite adsorption without UV light and photocatalytic oxidization under UV irradiation.X-ray diffraction?XRD?,scanning electron microscopy with Energy Dispersive Spectrometer?SEM/EDS?,Transmission Electron Microscopy?TEM?and N₂adsorption–desorption methods were used to characterize its morphology.Kinetics experiments achieved by different materials:Ti-Mn-HO,pure anatase-TiO₂,pure Mn oxide in under UV or Ti-Mn-HO without UV exposure can reflect whether Mn₃O₄could better prompt the adsorption-photooxidation process of As???.We investigated the reason for this phenomenon using Fourier-transform infrared spectroscopy?FTIR?,Raman and X-ray photoelectron spectroscopy?XPS?characterization.Finally,we supposed the synergistic interaction between anatase-TiO₂ and Mn₃O₄ and attributed promotion mechanism of Mn oxide for As???photooxidation to the transformation of photoproduct holes and electrons between the TiO₂ and Mn₃O₄ phases,which prohibit the re-combination reaction between photogenerated electrons and photogenerated holes which are produced by anatase-TiO₂.4.Basing on above three parts,we can close the mechanism of As???photooxidation by TiO₂/UV system vary with catalyst kinds and experimental setting-up,hoping to provide reference to controversy about the main oxidant in TiO₂+As???+UV+O₂system.