Ni^(2+)掺杂钛纳米管的制备及其对亚甲基蓝的吸附

On the preparation of Ni-doped titanate nanotubes and the adsorption behaviors of methylene blue onto the nanotubes

采用水热法,以硝酸镍为镍源,利用商业二氧化钛(P25)制备Ni2+掺杂钛纳米管。对样品进行扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)和比表面积仪(BET)的表征。结果表明:采用水热法生成了均匀的钛纳米管,管壁多层且两端开口;Ni2+掺杂基本没有改变钛纳米管的形态和晶型结构;掺杂5%Ni2+的钛纳米管的比表面积为233.89 m2/g,大于未掺杂的纳米管(187.52m2/g),远大于原料P25(45.6 m2/g)。以亚甲基蓝溶液为降解对象,研究Ni2+的掺杂量、pH值、振荡时间和温度对Ni2+掺杂钛纳米管吸附性能的影响。Ni2+的掺杂量、pH值、振荡时间和温度对Ni2+掺杂钛纳米管的吸附性能具有显著影响。用非线性回归分析对吸附等温线进行拟合,Langmuir吸附模型比Freundlich吸附模型拟合效果好。

This paper intends to introduce the synthesis of Ni2＋- doped titanate nanotubes in a simple hydr-thermal process of the commercial titanium dioxide （Degussa P25 ） by taking nickel nitrate as the nickel source. The morphology and structure of the samples we have chosen are characterized by scanning the electronic microscope techniques （SEM）, the transmission of the electronic microscopy （TEM）, X-ray diffraction （XRD） and the Brunauer-Emmett-Teller method （BET）. The SEM and TEM methodology has shown that the regularly uniform nanotubes can be fabricated via the hydrothermal processing, and the regularly uniform nanotubes prove to have homogeneous multi-walled tubular structure with the open ends. The internal and external diameters, and the length of titanate nanotubes prove to have approximately 5 rim, 10 nm, and 100-200 nm, respectively. Thus, the XRD results show that the titanium dioxide precursors have completely been transformed to titanate nanotubes and no anatase or rutile phase would emerge in the obtained nanotubes. Therefore, in terms of morphology and structure, there seems no sig- nificant difference between the Ni2＋ -doped titanate nanotubes and with-no doping samples. Moreover, the BET results indicate that the titanate nanotubes tend to exhibit a Type IV adsorption isotherm, which is typically characterized by mesoporous materials. The specific surface of the tri-doped sample TNTS - 5 tends to have an area of 233.89 m2/g, much larger than that of the pure titanate nanotube （187.52 m2/g） , and than the P25＇s （45.6 m2/g）. In addition, we have also investigated the adsorption of methylene blue to the titanate nanotubes, and the influential factors of the adsorption process, such as Ni/ ＋ concentration, the pH value, the contact time and the temperature to be used. The experimental results concerned indicate that the adsorption power of the prepared samples tend to increase with the increase of Ni2＋ concentration in the said nanotubes. Under the same experimental conditions, when Ni2＋ concentration achieved 5 mol%, the sample would reach its maximum adsorption power. With the increase of pH value, the adsorption power of the samples tend to increase as well. With the pH value of 10, the adsorptive power of the tridoped sample TNTS - 5 tends to reach its maximum value. Besides, we have also found that the increase of temperature may result in higher dye loadings per unit weight of the sorbent, whose equilibrium concentration and adsorption power can be determined at equilibrium of the tridoped sample TNTS - 5 by using two different adsorption models, namely： Langmuir and Freundlicb isotherms. All in all, it would be possible to achieve the best agreement by the Langmuir isotherm with the correlation coefficient of 0.982, in correspondence with the maximum adsorption power of 388.07 mg/g.