改性丝胶生物吸附剂对Ag^+的选择性吸附

Selective sorption of Ag^+ on chemically modified silk sericin

以蚕丝丝胶(SS)为基材,通过接枝2,5-二硫二脲制备了改性丝胶生物吸附剂(SO),探讨了影响生物吸附的因素,并对比研究了不同体系中生物吸附剂对Ag^+的吸附行为.结果表明,在p H 1.0—6.0范围,吸附率随着p H升高而增大.相同条件下,SO吸附容量和吸附率明显优于SS,在单组分Ag^+溶液中,p H5.0时,SO和SS对Ag^+的吸附率分别为96.2%和57.8%,吸附容量分别为20.8 mg·g^(-1)和12.5 mg·g^(-1).在三组分(Ag^+-Cu^(2+)-Zn^(2+))及五组分(Ag^+-Cu^(2+)-Zn^(2+)-Ni^(2+)-Pb^(2+))溶液中,SO对Ag^+显示出良好的吸附选择性.p H5.0时,SO对其它金属离子很少吸附,而对Ag^+的吸附率分别高达95.8%和93.7%;SS尽管对其它贱金属离子吸附率也较低,但其对Ag^+的吸附率仅为25.4%和23.7%.吸附动力学表明,吸附剂对Ag^+的吸附符合准二级动力学模型,吸附过程为化学吸附,吸附过程活化能Ea(SO)=43.23 k J·mol^(-1),Ea(SS)=59.32 k J·mol^(-1).吸附热力学表明吸附过程为放热的自发过程.25℃吸附平衡时,Ag^+在固液两相的分配系数为K_D~Θ(SO)=5111.K_D~Θ(SS)=273.SO对Ag^+吸附机理主要为配位作用,粒子内扩散为吸附过程的速控步骤.

A silk sericin-based novel bio-adsorbent,named ＂SO＂,was synthesized by immobilizing bisthiourea（ BTU） ligand on silk sericin（ SS）. The factors which influence biosorption were discussed and biosorption behaviors towards Ag^＋along with other coexisting metal ions were also comparably studied by batch tests. The results indicated that higher pH favoured biosorption in both single and multiple metal ion solutions in pH1.0—6.0.Biosorption efficiency of SO was much higher than that of SS under the same conditions. In single component Ag^＋solution at pH5.0,the adsorption efficieny of SO and SS was 96. 2% and 57. 8%,and adsorption capacity was 20. 8 mg·g^-1and12.5 mg·g^-1,respectively. SO exhibited better selectivity than that of SS for Ag^＋over other metal ions in both Ag^＋-Cu^2＋-Zn^2＋and Ag^＋-Cu^2＋-Zn^2＋-Ni^2＋-Pb^2＋solutions. Both SO and SS adsorbed little coexisting metal ions at pH5.0 in both systems.The adsorption efficiency of SO for Ag^＋was 95.8% in the former and 93. 7% in the latter solution,while for SS,the corresponding values were merely25.4% and 23. 7% respectively. Biosorption kinetics revealed that adsorption of Ag^＋obeyed the pseudo-second-order equation, which indicated that adsorption involved chemisorption. The activation energy,Eafor SO and SS were 43. 23 kJ·mol^-1and 59. 32 kJ·mol^-1respectively.Biosorption thermodynamics showed that biosorption process was exothermic and spontaneous. The partition coefficients（ KD^Θ） between biosorbent and aqueous phase at 25 ℃ in equilibrium for SO and SS were 5111 and 273 respectively. Possible mechanism of biosorption mainly contributes to coordination through the thiocarbonyl group,and intraparticle diffusion step is probably the rate limiting step in biosorption.