Efficiency And Mechanism Of Removal Of Heavy Metal Ions In Aqueous Solution By Black TiO_x And Porous Na⁺-SiO₂ Microspheres

With the increasingly serious pollution of heavy metals in water,people's daily water security is threatened.Unfortunately,the conventional water treatment technology can not effectively remove heavy metal ions from water,it is therefore necessary to find a new effective way to completely remove these pollutants.In this paper,two new adsorbents for heavy metal ions removal have been prepared,and their adsorption performance and mechanism for removal of typical heavy metal ions in water have been studied.In this paper,two adsorbents for heavy metal ions removal,black TiOx and porous Na+—SiO2 microspheres,were successfully prepared by Mg reduction process and multi-step synthesis process respectively.The black TiOx with different color(different x value)can be obtained by controlling the reduction degree of TiO2 by controlling the dosage of Mg powder.The pore structure and Na+ content of porous Na+-SiO2 microspheres can be controlled by controlling the time of etching SiO2 microsphere by NaOH.The physical and chemical properties of the product were characterized and analyzed by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HR-TEM),N2 adsorption-desorption,X-ray photoelectron spectroscopy(XPS),and etc.The kinetics,thermodynamics,adsorption isotherm and possible adsorption mechanism of adsorption of Pb2+ by black TiOx were investigated.The prosess of the Pb2+ adsorption by black TiOx was well fitted to the pseudo-second-order kinetic adsorption model.The adsorption isotherms of Pb2+ by black TiOx are in accordance with the Langmuir adsorption equation.The saturated adsorption capacity of Pb2+ by black TiOx is 36.9 mg/g,53.4 mg/g and 59.2 mg/g at 15 ?,25 ? and 35 ?,respectively.X-ray photoelectron spectroscopy(XPS)showed that Pb2+ adsorption on black TiOx is mainly due to Ti-OH groups on the surface of TiOx to adsorb Pb2+.The kinetics,thermodynamics,adsorption isotherm and possible adsorption mechanism of adsorption of Cr3+ by porous Na+-SiO2 microspheres were also investigated.The adsorption of Cr3+ by porous Na+-SiO2 microspheres is consistent with the pseudo-second-order kinetic adsorption model.The saturated adsorption capacity of Cr3+ by porous Na+-SiO2 microspheres at 25 ? is 16.7 mg/g.The analysis of surface elemental energy spectrum clearly revealed that the removal of Cr3+ by porous Na+-SiO2 microspheres is partly becaused of the ion-exchange between Cr3+and Na+,and partly because of the weak coordination of Cr3+ with Si-OH groups on the surface of porous Na+-SiO2 microspheres.Finally,the removal efficiency of Pb2+ and Cr3+ by these two adsorbents were studied using tap water,West Lake water and Qiantang River water as the background.It was found that these two adsorbents had the samilar effect on the adsorption of these two heavy metal ions,witch indicated that the two adsorbents synthesized in this study have potential applications.