Rare Earth Modified TiO 2Photocatalytic Degradation Of Benzyl Hydroxamic Acid

In the flotation process,the discharge of mineral processing wastewater contained a large number of flotation reagents,and many flotation reagents has toxicity,or slowly enriched in the water,which would be harm to the environment.Benzohydroxamic acid as a high-effect chelating collector of oxidized ore,which is widely used in the flotation of lead rare earth ore.Besides,benzohydroxamic acid is difficult to be decomposed,which would bring physiological toxicity when accumulated.It is harmful to the environment.Therefore,it has very important and realistic meaning to seek an efficient and rapid method for the removal of benzohydroxamic acid in the flotation wastewater.Photocatalytic oxidation technology has been widely used in the water pollution control due to the simplicity of operation,mild reactive conditions,low energy-consumption and without secondary pollution.However,photocatalytic oxidation was less used in the treatment of flotation reagents in the wastewater.Thus,this thesis aimed to prepare rare earth doped TiO₂ nano photocatalyst,benzohydroxamic acid was used to as the objective pollutant to investigate the photocatalytic activity,and discussed the mechanism of degradation of benzohydroxamic acid.The research contents and results are summarized as follows:?1?Rare earth elements La,Ce,Gd,Yb doped TiO₂ were synthesized by sol-gel method.The physicochemical properties of prepared materials were characterized by X-ray diffraction,X-ray photoelectron spectroscopy,UV-vis diffuse reflectance spectroscopy,specific surface area and porosity,scanning electron microscopy and transmission electron microscopy.The results of XRD,BET,SEM and TEM showed that the doping of the rare earth La,Ce,Gd,Yb could inhibit the crystal growth of TiO₂,retain a smaller grain size,increase its specific surface area,which has good crystallinity and particle dispersion.The samples have mesoporous structure.The result of XPS showed that after rare earth Re doped,the orbital peak of Ti2p and O1s has a weak offset,lattice oxygen and hydroxyl oxygen existed on the surface of samples after the doping of Yb.The result of UV-vis DRS showed that after the doping of La,Ce and Gd,light response of TiO₂ increased,red shift in the band-gap transition and enhanced the ability of light absorption.Blue shift and red shift existed in the band-gap transitin after the doping of Yb.?2?Benzohydroxamic acid as the degradation object,the effects of rare earth doping amount and calcination temperature were investigated.The optimal catalysts were 0.75%La/TiO₂?500??,0.20%Ce/TiO₂?500??,0.70%Gd/TiO₂?500??,0.50%Yb/TiO₂?450??.Original p H value of 30mg·L^-1 benzohydroxamic acid solution under the irradiation of 300 W mercury lamp,and Re/TiO₂amount of 0.3 g·L^-1,the degradation rates of four kinds of catalysts were 94.9%,94.1%,95.1%and95.3%,respectively.The degradation rate of Yb/TiO₂ was more than 90%after 60 min.89.2%of the total organic carbon was eliminated after 120 min irradiation.The results showed that La/TiO₂,Ce/TiO₂,Yb/TiO₂ and Gd/TiO₂ still kept high photocatalytic activity on the photodegradation of benzohydroxamic acid for a long time,so they have good stabilities.?3?The effects of inorganic anions and inorganic cations on the photocatalytic degradation of benzohydrooxamic acid by Yb/TiO₂ were studied.Cl^-has little effect on the photocatalytic degradation of benzohydroxamic acid,NO₃^-?HCO₃^-and SO₄^2-have different inhibition effects.As HCO₃^-and·OH can react quickly and generate carbonate free radical which has a lower oxidation than·OH;the effects of Na⁺,K⁺,Ca²⁺and Mg²⁺on the degradation of benzohydrxamic acid were relatively small due to they were all in the highest oxidation state.In the photocatalytic reaction,Capture experiment showed that·OH is the active species in the photocatalytic degradation of benzohydroxamic acid.After two hours'photocatalytic degradation of benzohydroxamic acid by Yb/TiO₂,which produced some NO₂^-and NO₃^-,thus maybe formed nitrate compounds.It is speculated that the degradation pathway of the TiO₂ photocatalytic degradation of the rare earth modified:it was degraded into intermediate products,such as alkanes or esters,and the intermediate products continued to degrade and produced small molecular substances such as NO₃^-,CO₂ and H₂O.