Study On The Removal Performance Of Phosphate By Modified UiO-66 And Zirconium Hydroxide

Eutrophication still exists in most water bodies,and the key to curbing eutrophication is to control the emission of phosphate.Adsorption is considered as the most promising method for phosphorus removal and is widely studied,and the most important of adsorption is the selection of adsorbents.This paper selects the phosphate in the wastewater as the research object.Firstly,the metal–organic frameworks UiO-66 doping with different amounts of lanthanum and obtained the optimum conditions for the combination of zirconium and lanthanum.Combining the excellent phosphate removal performance of zirconium and lanthanum to achieve the standard discharge of phosphate in wastewater.Secondly,the zirconium hydroxide was modified by different ammonium and formation of positively charged quaternary ammonium groups on the surface of magnesium hydroxide.Enhanced phosphate removal performance by increasing the utilization of zirconium hydroxyl groups,and achieve efficient removal of phosphate from wastewater.The main research contents are summarized as follows:?1?In this paper,UiO-66 and lanthanum terephthalate tetrahydrate?La-BDC?were synthesized by solvothermal method.In the process of UIO-66 synthesis,lanthanum was added by La:Zr molar ratio of 0.1:1?0.1La-UiO-66?,0.2:1?0.2La-UiO-66?,0.25:1?0.25La-UiO-66?,0.5:1?0.5La-UiO-66?,0.75:1?0.5:1?to achieve the lanthanum doping UiO-66.The results of PXRD show that the standards of UiO-66 and the synthesis of UiO-66 is completely consistent,and there is the characteristic crystal?1,1,1?of UiO-66 in La-UiO-66.From SEM and EDS,UiO-66 and 0.2La-UiO-66 have the same shape,and there is a very obvious distribution of lanthanum in 0.2La-UiO-66.All these show that the lanthanum is doped on UiO-66 and this is its first synthesis.?2?In this work,UiO-66,La-BDC,La-UiO-66 were synthesized and applied to adsorb phosphate.The isothermal adsorption showed that the adsorption capacity of La-UiO-66 was much higher than that of UiO-66 and La-BDC,and the maximum adsorption capacity was 348.43mg g^-1 from 0.2La-UiO-66.And all the adsorption processes were well-fitted with the Langmuir model,which belongs to monolayer adsorption.The adsorption kinetics suggests that 0.2La-UiO-66 had a better mass transfer rate?K₂?and initial adsorption rate?h_o?than UiO-66,and the adsorption equilibrium could be achieved within 120min.The adsorption process fitted well with the pseudo-second-order kinetics model,which belongs to chemical adsorption.UiO-66 and 0.2La-UiO-66 showed a strong pH-dependence for the adsorption of phosphate,and the ligand exchange was much greater than that of the electricity in this process.The selectivity factor???of 0.2La-UiO-66 is far greater than that of UiO-66,which shows its strong selectivity to the phosphate,and the adsorption process belongs to the inner-sphere complex adsorption.After ten sorption/desorption cycles,0.2La-UiO-66still maintain almost 92%of removal efficiency for the phosphate of 20mg L^-1,which shows the great potential in phosphate removal as a sustainable adsorbent.The analysis of FT-IR and XPS showed that zirconium hydroxyl and lanthanum hydroxyl played an important role in the adsorption of phosphate through inner-sphere complex and ligand exchange.?3?In this paper,the zirconium hydroxide was modified by dimethylamine,N-ethylmethylamine,N-methylaniline,diethylamine,thus its surface was connected to the quaternary ammonium group of positive.From isothermal adsorption,the maximum capacity is 155.04 mg g^-1 from the zirconium hydroxide modified by dimethylamine,which is much higher than 118.91mg g^-1 of zirconium hydroxide.The adsorption processes were well-fitted with the Langmuir model,which belongs to monolayer adsorption.Dubnin-Radushkevich isothermal adsorption model showed that the adsorption of phosphate was realized by ligand exchange.The adsorption kinetics of phosphate suggests that the adsorption process fitted well with the pseudo-second-order kinetics model,and the mass transfer rate K₂ also increase 4 times using ammonium.Zirconium hydroxide and dimethylamine modified zirconium hydroxide showed a strong pH-dependence on the adsorption of phosphate.The ammonium modified zirconium hydroxide shows a better selectivity for the phosphate,and the adsorption process belongs to the inner-sphere complex adsorption.The analysis of Zeta,FT-IR and XPS showed that the adsorption mechanism is ligand exchange of zirconium hydroxyl and electrostatic interaction of quaternary ammonium group,and the utilization ratios of hydroxyl groups on adsorbents were improved from 22.9%to 33.9%by dimethylamine modification.In addition,the adsorption capacity of dimethylamine modified zirconium hydroxide for phosphate is 76.22 mg g^-1,which shows excellent practical application potential.