摘要
本文采用纳米材料做为吸附剂,研究了在不同浓度、不同pH值、不同温度条件下的溶液中对铊的吸附性能及其机理。研究结果表明:
1.微量铊的测定方法-镉试剂2B分光光度法,确定了在镉试剂2B分光光度法测定微量铊体系中各试剂的最佳用量为:5.0 mL pH 12的氨水缓冲溶液;1.0 mL 1%曲拉通-100;1.5 mL镉试剂2B溶液。整个体系10 min之后显色完全,12 h内显色稳定;最大吸收波长为500 nm;表观摩尔吸光系数为7.29×104 L·mol-1·cm-1。
2.纳米TiO2和纳米Al2O3对Tl(III)离子的吸附性能良好,通过控制溶液的pH值,可定量的吸附和解吸Tl(III)离子。最佳吸附条件为pH 4.5,超声1 min,静置15 min,吸附率接近100%。可以用1mol/L HCl从纳米Al2O3,以及用水在微波照射下从纳米TiO2上把铊洗脱下来,Tl(III)的回收率接近100%,即能被定量解脱。常温下纳米TiO2和纳米Al2O3的饱和吸附量分别为4.09 mg g-1,5.78 mg g-1;富集倍数分别为12.5,25。
3.该吸附过程符合准二级反应动力学模型,因此,对Tl(III)的吸附是一个化学吸附过程。纳米TiO2和纳米Al2O3的常温反应的速率常数分别为4.55 g mg- 1min- 1,11.89 g mg- 1min- 1;反应活化能分别为13.20 kJ mol-1,19.02 kJ·mol-1。
4.纳米TiO2和纳米Al2O3对铊的等温吸附线呈现可逆的Langmuir吸附形式。本文还考察了吸附反应的焓变ΔH0和熵ΔS0均为正值,说明该过程是吸热化学吸附反应;ΔG0为负值,说明该吸附过程是一个自发的反应过程。纳米TiO2和纳米Al2O3对铊离子吸附的常温平均吸附能分别为12.06 kJ·mol-1,8.39 kJ·mol-1,说明此反应属于化学反应。
5.本实验方法中纳米TiO2和纳米Al2O3的检出限分别为0.09μg mL-1和0.84μg mL-1,精密度分别为6.18%和2.37%。除Cd(II),Cu(II),Pb(II),Mn(II)离子对该吸附方法有一定的干扰外,其余离子的允许量均较大,基本不干扰对Tl(III)离子的吸附。用该富集方法对水样和实际样品进行分析,测定值与参考值一致,结果令人满意。
In this paper, we used nano-material as sorbents. The adsorptive capability and mechanism of Tl on nano-material in the different temperature, pH value, and concentration were studied in thesis. The research contents and experimental results as follows:
1. Among the experiment mainly research the material conditions of Cadion 2B spectrophotometry to determine thallium, and the best conditions of Cadion 2B spectrophotometry to determine thallium are as follow: The dosage of different reagents are: 5.0 mL pH 12 NH3?H2O buffer solution, 1.0 mL 1% Triton X-100 solution and 1.5 mL Cadion 2B. The best pH of solution was 4.5, after 10 min the color development reaction completeded, steadied in 12 h, the wavelength of largest absorption was 500 nm, and the apparent molar absorptivity was 7.29×104 L·mol-1·cm-1.
2. Both adsorption and desorption of nano-TiO2 and nano-Al2O3 to Tl(Ш) ions depended on the initial pH of the solution. The Tl(Ш) ions can be adsorbed and desorbed quantificationally at proper pH values. The optimum pH value to adsorb Tl(Ш) ions from solution was considered to be 4.5, after ultrasonically dispersed for 1 min and static adsorption for 15 min, and the adsorption percentage was closed to 100%. 1mol/L HCl was used for the desorption of Tl(Ш) on nano-Al2O3, and water for the desorption of Tl(Ш) on nano-TiO2 by microwave irradiation. The maximum adsorption capacity of thallium ions on nano-TiO2 and nano-Al2O3 were 4.09 mg g- 1, 5.78 mg g-1 at room temperature, respectively. The enrichment factor values of nano-TiO2 and nano-Al2O3 were 12.5 and 25, respectively.
3. The adsorption of Tl(III) ions on nano-TiO2 and nano-Al2O3 properly correlate with the second-order rate equation, thus, the type of the adsorption are chemical adsorption. The rate constant of second-order adsorption of nano-TiO2 and nano-Al2O3 were 4.55 g mg- 1min- 1, 11.89 g mg- 1min- 1, respectively. The activation energy of nano-TiO2 and nano-Al2O3 were 13.20 kJ mol-1, 19.02 kJ·mol-1, respectively.
4. The Langmuir model could describe the adsorption of nano-TiO2 and nano-Al2O3 to Tl(Ш) ions successfully over the whole range of concentration studied. The value of standard enthalpy and standard entropy (ΔH0,ΔS0 >0) may be interpreted as the endothermic adsorption process. The negative value ofΔG0 showed the adsorptions of thallium by nano-TiO2 and nano-Al2O3 were spontaneous process. The adsorption energy of nano-TiO2 and nano-Al2O3 were 12.06 kJ·mol-1, 8.39 kJ·mol-1, respectively, which indicate that the process belongs to chemical adsorption.
5. The detection limits of determining Tl(Ш)ions with nano-TiO2 and nano-Al2O3 as sorbents were 0.09μg mL-1and 0.84μg mL-1, respectively, and the relative standard deviations were 6.18% and 2.37%, respectively. Except for Cd(II), Cu(II), Pb(II), Mn(II), other coexisting ions almost didn’t have effects and the allowable volume for these species were large. Water and practical samples have been analyzed by this enrichmental way. The results are accord to the reference.
引文
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