Study On The Fabrication Of Sodium Titanate-based Adsorbents For Purifying Pb(?)-contaminated Wastewater

With rapid developing industry,a large number of heavy metal wastes have being discharged into water bodies without proper treatment,which caused severe pollution.The environmental problems and health risks caused by these pollutants have been paid more and more attention.Since the heavy metals are non-degradable and highly toxic in the environment,they do great harm to organisms and human beings after the gradual accumulation through the biological chain.Therefore,it is urgent to control the heavy metal pollution in water bodies.Due to the advantages of low cost,easy operability and high efficiency,adsorption becomes a widely used technology for the treatment of heavy metal polluted water.Enhancing the adsorption capacity,adsorption rate and adsorption selectivity of adsorbents towards heavy mental ions is the key problem for the efficient treatment of heavy metal polluted water by adsorption method.In this paper,we aimed to dispose lead contaminated water.Titanate possessed inherent drawbacks,such as poor mechanical intensity,difficult to separation,easy agglomeration and strong pressure drop inside packed column,so their application has been limited.To solve these problems,we synthesized four novel titanate materials in this paper,which possessed the special structure and excellent performance for efficiently and selectively adsorbing lead ion from wastewater.The physical and chemical structures of the as-sythesized titanate materials were characterized by transmission electron microscopy(TEM),scanning electron microscopy(SEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),Fourier infrared spectroscopy(FTIR)and BET surface analysis.The adsorption mechanism was proposed by analysing the transformations of titanate structure before and after Pb(II)adsorption.By batch adsorption experiment and packed column dynamic adsorption experiment,the adsorption characteristics of the as-sythesized titanate materials were studied,which provided experimental basis for its practical application.The main contributions of this paper are summerized as following:1.Hierarchical titanate microtube(HTMT)has been fabricated by simple alkaline hydrothermal,using titanium glycolate microrods as precursor.In the hydrothermal process,the NaOH concentration was only 1 mol/L,which was greatly reduced comparing to the traditional preparation of sodium titanate nanomaterials(5-10 mol/L).The obtained HTMT presented large specific surface area as 80.4 m²g^-1 and hollow structure with large interior voids and countless external nanosheets.HTMT exhibited superior adsorption performance to eliminate Pb(II)from wastewater due to their attractive structure.HTMT showed maximum adsorption capacity as 540.5 mg/g at 298 K,fast adsorption rate and good reusability to remove Pb(II).Moreover,HTMT could selectively remove Pb(II)in the environment containing high concentration of interference cations(Na(I),K(I),Ca(II),Mg(II),Al(III))and heavy metals(Cu(II),Cd(II),Zn(II)and Ni(II))with high efficiency.The adsorption mechanism was mainly ions exchange and inner-sphere complexation.The high adsorption capacity,fast adsorption rate,strong selectivity and good reusability make HTMT attractive for practical removal of Pb(II)from contaminated water.2.Three dimensional porous sodium titanate monoliths(TNM)were prepared by simple alkaline hydrothermal method and subsequent freeze-drying with titania glycolate microrods as precursor.The prepared TNM possessed two kinds of coexisting microstructure:thin nanosheets and nanofibers.The thin sheets were stacked with each other and the needle-like fibers were cross-linked with each other,which formed a porous three-dimensional structure and maintained the mechanical strength of the material.Eliminating Pb(II)from wastewater by adsorption in the same condition,after 48 h,the removal efficiency of TNM(99%)was much higher than that of the bulk n TNM material obtained with nano-Ti O₂ as the precursor(57%),which demonstrated the superiority of the three-dimensional porous network structure of TNM.TNM had a high adsorption capacity for Pb(II)in a wide range of p H values.Langmiur model fit best for the adsorption of Pb(II)by TNM,and the maximum adsorption capacity is 534.7 mg/g.TNM adsorbents could remove Pb(II)with high efficiency,which was slightly influenced by high concentration of interfering cations(Na(I),K(I),Ca(II),Mg(II),Al(III)).In the mixed system containing Pb(II),Cd(II),Cu(II),Zn(II)and Ni(II),the adsorbent could efficiently and selectively remove Pb(II).When the dosage of TNM was more than 1 g/L,the concentration of Pb(II)in the wastewater will be less than 15?g/L,meeting the standard of drinking water.TNM is a kind of adsorption material with practical application value because of its large size and easy separation and recovery.3.Magnetic graphene oxide-titanate composites(MGO@TNs)were synthesized via growing titanate nanosheets on the graphene oxide sheets with magnetite nanoparticles anchored on.The as-prepared MGO@TNs showed a hierarchical structure and large specific surface area(193.4 m²g^-1),which were suitable for rapid and effective adsorption of Pb(II)from wastewater.Moreover,the loaded magnetite nanoparticles guaranteed the effective magnetic separation of MGO@TNs,avoiding secondary pollution.The adsorption mechanism was illuminated to be ion exchange and surface complexation.Batch adsorption experiments showed the maximum adsorption capacity of MGO@TNs reached322.7 mg/g for Pb(II)removal.The removal efficiency retained 89.6%after six adsorption-desorption-regeneration cycles.In addition,the efficiency reached up to99.8%when applying MGO@TNs for removal of Pb(II)from simulated realistic battery wastewater,ensuring the safe discharge of treated water.The good adsorption performance,recyclability and easy magnetic separation ability made sure that the MGO@TNs has great potential for purification of Pb(II)contaminated wastewater.4.Here,graphene oxide(GO)nanosheets were utilized as template for sodium titanate nanosheets to grown on.The GO-titanate(GOTNs)composites with large size were fabricated by stacking of those nanosheets during lyophilization.The GOTNs were packed into column and applied in dynamic adsorption of Pb(II)contaminated wastewater.GOTNs composites exhibited the advantages of fast adsorption and high adsorption capacity large content of titanate nanosheets.The maximum adsorption capacities for Pb(II),Cd(II)and Cu(II)were 530.5,201 and130.5 mg/g(2.56,1.79 and 2.03 mmol/g)at 298 K and p H 5,respectively.The removal efficiency could be almost reserved after six cycles.Pb(II),Cd(II),Cu(II),Zn(II)and Ni(II)could be effectively removed with 3 g/L dosage of GOTNs composites.GOTNs presented higher selective adsorption towards Pb(II)than other ions in both bath and column process.In column experiments(2 g GOTNs inside one column),the effective treatment volume of reached to 2760 BV(15.45 L)of the single Pb(II)polluted battery manufactory wastewater and 2280 BV(12.76 L)of the multiple heavy metal(Pb(II),Cd(II),Cu(II)and Zn(II))polluted estuary effluent,before Pb(II)concentration exceeds the discharge limit of 1 mg/L.Our study demonstrates the great potential of GOTNs composites to be applied in practical treatment of heavy metals.