Adsorption Propertiest Of Nanometer-size Titanium Dioxide On Heavy Metals

Rapid development of chemistry,material,metallurgy and pharmaceuticals,brings serious heavy metal pollution,with it poses a serious threat to ecological environment.Anatase titanium dioxide nanometer powder(NTO)contains much defects and dislocations,and a large number of unsaturated state atom are exposed on it’s surface,which can combine with a variety of metal ions.Thus NTO has a good application prospect in the harmful metal waste water treatment.In this thesis,the adsorption properties of NTO on heavy metals,such as Cr(Ⅵ),Cd(Ⅱ),Mn(Ⅶ),Pb(Ⅱ)were systematically studied.First of all,the influence of pH on the adsorption quantity was studied.The results show that the pH value had the same effect on Cr(Ⅵ)and Mn(Ⅶ)anion adsorption in lower pH range,the adsorption rate rises sharply with the pH rising,and then became flat,while the adsorption quantity decreases sharply with the pH rising during higher pH range.The optimal adsorption pH range were 3～5 and 6～9 for Cr(VI)and Mn(Ⅶ)respectively.The effect of pH value on the absorption of cation such as Cd2+ is different from that of anion Cr(VI)and Mn(VII).For example,with the increasing of pH value,the adsorption of Cd2+ by NTO rise constantly untill pH value reaches 4～5,then the rise of adsorption quantity became flat with pH increasing.Under the optimal adsorption pH value and fixed initial concentration of metal ions,the adsorption capacity(Qt)over time(t)was studied.It is indicated that the adsorption kinetics of NTO on Cr(Ⅵ),Mn(Ⅶ),Cd(Ⅱ),Pb(Ⅱ)consistent with secondary adsorption dynamics equation.Under the optimal adsorption pH value the relationship between the equilibrium adsorption capacity(Qe)and the equilibrium concentration of metal ions(Ce)was studied.It is shown that adsorption isotherm of the NTO on the above-mentioned ion accord with Langmuir equation,and the saturated adsorption capacity(Qnmax)were 31.75,21.02,6.14 and 23.28 mg·g-1,respectively.To explore the adsorption mechanism of NTO,the changes of the microstructure of the adsorbent before and after adsorption were studied by powder X ray diffraction(XRD)and infrared spectroscopy(IR).Before and after the adsorption of the ions,the absorbent both exibits anatase,and the diffraction peak position remains unchanged,which reveals that the cell parameters of the adsorbent are changed before and after adsorption.So the metal ion adsorption should occur on the surface of NTO.When it reaches saturated adsorption,the(101)diffraction peak intensity is obviously stronger,presumably because the defects and dislocations on(101)surface are repaired by combination with additional metal ions,and in turn,the surface energy of NTO is reduced.Before absorption,the absorption peak in 650 cm-1 in IR specfrum is attributed to Ti-O stretching vibration.After adsorption,the absorption peak of 3350,1640 cm-1 which correspond to stretching vibration and bending vibration of hydroxyl from the adsorption water,respectively.It shows that Cr(Ⅵ),Mn(Ⅶ),Cd(Ⅱ),Pb(Ⅱ)is adsorbed as the form of hydrated ions.At the same time,the adsorption absorption peak of Ti-O bonds are decreased,indicating that Ti-O-Cr,Ti-O-Cd,Ti-O-Mn and Ti-O-Pb bonds are formed in the adsorption process.NTO has good application prospect in the field of heavy metal waste water treatment.This study provides abundant basis data for the NTO adsorption of heavy metal,which breaks the way for the practical application of NTO.