| In this paper,we used nano-Al2O3 as sorbent.The adsorption properties and mechanisms of rhodium on nano-Al2O33 at different time,temperature,pH value and concentration were systematically studied in thesis.The research contents and experimental results are as follows:1.The optimum conditions of determining trace Rh(III)by 5-Br-PADAP Color reaction spectropHotometry was obtained:4.0 mL Hac-NaAc buffer solution,1.0 mL 0.03%5-Br-PADAP,with boiling water bath 50 min,then 2 mL ethanol added to clean the wall.The color development reaction completeded immediately and kept stable until 9 h.The wavelength of the largest absorption was 597nm,and the apparent molar absorptivity was 1.0×105 L·mol-1·cm-1.2.The effect of different sorbents on the behavior for rhodium in aqueous solution was studied,and nano-Al2O3 was the best sorbent.Both adsorption and desorption rate of nano-Al2O3 to rhodium ion depended on the initial pH of the solution.The sorption has been optimized with respect to the pH of the solution.A adsorption percentage of Rh(III)was found over 95%.The optimal conditions of static adsorption method are as follows:the sorption was carried out after shaking dispersed for 5 min with the sorbent dose of 300 mg at room temperature.A 15 mL of sample solution was adopted and the enrichment factor was 5 with 5.0 mL of 0.3 mol·L-1 H2SO4 elution.3.The adsorption of Rh(III)ions onto nano-Al2O3 properly correlated with the pseudo-second-order rate equation.The rate constant of second-order adsorption of Rh(III)was 0.478 g·mg-1·min-1,2.714g·mg·min-1,10.525 g·mg·min-1 respectively at 273 K,298 K,323 K,the activation energy was 3.321 kJ·mol-1.The dynamic data indicated that the particle diffusion was not the solely the rate controlling process for Rh(Ⅲ);namely,the overall rate process appears to be influenced by both the boundary layer resistance and the intraparticle diffusion.4.The Langmuir model and D-R could describe the adsorption of nano-Al2O3 to Rh(Ⅲ)ions successfully over the whole range of concentration studied.The equilibrium constants RL for Rh(Ⅲ)lies between 0 and 1,indicating the sorption could be easily ongoing.At 273 K,298 K,323 K,the saturated sorption capacity for Rh(Ⅲ)are 2.81 mg·g-1、5.52 mg·g-1、6.94 mg·g-1 respectively.The values of Gibbs free energy and standard enthalpy(△Gθ<0,△Hθ>0)for Rh(Ⅲ)may be interpreted as the spontaneous endothermic adsorption process.The adsorption energy of nano-Al2O3 was 0.79,1.08 and 2.07 kJ·mol-1(between 0-8 kJ·mol-1),which indicated that the process belongs to physical adsorption.5.The detection limits(3σ)of determining rhodium(Ⅲ)ions with nano-Al2O3 as sorbent was 0.042 μg·mL-1(n=11),and the relative standard deviations was 3.76%(n=11).Nano-Al2O3 displayed an excellent selectivity for rhodium adsorption from the common metals including Pb2+,Co2+,Cd2+,Ni2+,Cu2+,Zn2+,Fe3+ together.The proposed method was applied to the determination of trace amount of rhodium(Ⅲ)added to the certified reference material(GBW07201),and the results are in good agreement with the certified values. |
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