Research On The Removal Of Chromium Ion Contamination Based On Adsorption-photocatalytic Reduction-desorption Technology

Heavy metal water pollution has been always an important branch in water pollution control.Among the numerous heavy metal ions pollution,the most serious one is Cr?VI?.Cr?VI?pollution has the characteristics of long-lasting toxic effect and non-biodegradation,which is able to accumulate within creatures through food chain,attracting the attention of enormous environmentalists.The current heavy metal wastewater treatment technologies,including electrolytic process,precipitation,membrane separation process,ion exchange process,active carbon adsorption and evaporation concentration method.However,these processes ordinary transfer the pollutants from one phase to another,consume a large amount of chemical reagents but don't make the pollutants harmless,therefore,secondary pollution or waste is usually caused.In recent years,photocatalytic technology has been applied to the treatment of Cr?VI?wastewater because of its mild reaction conditions,easy operation,and ability to directly utilize the advantages of sunlight,especially outstanding in the low concentration of Cr?VI?wastewater.However,the research has been carried out slowly.Compared with traditional adsorbent,photocatalyst has smaller specific area,so that the photon-generated carrier recombines easily,causing low rate of reduction of Cr?VI?in wastewater,In addition,the products of reduced Cr?III?adhere to the photocatalyst,which easily causes the inactivation of photocatalyst.There is a process of the photoreduction of Cr?VI?.Firstly,Cr?VI?ions are absorbed to the surface of photocatalyst,helping quickly removing the pollution of water or air,then pollutants are thoroughly reduced,therefore,there is coordination between absorption and photocatalyst.According to the rule of Cr?VI?reduction on the catalyst,we aims to eliminate Cr?VI?in wastewater with the coordinated technology of absorption-photocatalysis-desorption,recombination of electron-hole is reduced due to the selection of high-stability,cheap and nontoxic TiO₂ as photocatalyst which is surface modified and is strengthened by exterior pressure,and the selective adsorption performance of Cr?VI?is increased,thus improving catalytic efficiency.According to the above goals,the paper's main content and main innovation points are divided into the following three aspects:?1?Mesoporous single crystal TiO₂ photocatalyst is modified by loading carbon dots.Increase the number of surface oxygen groups such as hydroxyl and carboxyl.Researches show that it is beneficial to the selective adsorption of Cr?VI?and the improvement of the photocatalytic performance with modified carbon dots.Through the characterization of catalyst with the mesurements of XRD,TEM,BET,FT-IR and XPS,the surface of synthesized CD/MT has many oxygen groups,so in acid environment,the electric property of surface of catalyst is corrected,and the modification of carbon dot is also beneficial to transfer of electron,reduces the recombination of electron hole pair,and improves the quantum efficiency of photocatalyst and its photocatalytic activity.?2?At the same time,we found that the change of carbon dots morphology has an effect on Cr?VI?photocatalytic reduction.The self-assembly process of carbon dots on the surface of the catalyst to form a carbon film modified mesoporous single crystal TiO₂ photocatalyst,the property of the surface is also changed.Mesoporous single crystal TiO₂ composite modified by carbon film is developed in suitable temperature and vacuum conditions.Researches show that carbon film structure is beneficial to improve the photocatalytic reduction capacity of Cr?VI?in TiO₂.Various characterization methods are used to characterize it's morphology and structure and the formation mechanism of the carbon film is also researched and discussed.and the results show that TiO₂ with carbon film can speed up transfer of electrons,more effectively separate electrons and holes in the same condition,and improve the quantum efficiency of photocatalyst and its photocatalytic activity.?3?Based on the change of surface charge to control the adsorption and desorption of Cr?VI?on the surface of the catalyst,we designed the electrochemical treatment of Cr?VI?.The TiO₂ catalyst on foam nickel to serve as electrode adsorption materials.Then the catalyst is able to treat Cr?VI?anion by electrochemical photocatalytic technology.Experiments show that the use of power-on and power-off method and and the anode and cathode interchange technologies,the adsorption and reduction of Cr?VI?is realized,and the desorption and separation process of the reduction product is realized at the same time.so in such a way not only reduction is done,so does the separation of reactants and products.