Studies On Preparation Of Imprinted Mesoporous Adsorbents And Their Selective Adsorption Properties Of Heavy Metal Ions

With the rapid development of social economy, heavy metal pollution has increasingly become a prominent environmental problem, and wastewater discharge constitutes a major portion of heavy metal pollution. Adsorption is an effective way to separate heavy metals and other toxic refractory substance from wastewater. Therefore, to get new and efficient adsorption materials becomes the research focus for wastewater heavy metal treatment.With the support of Jiangsu Natural Science Foundation（BK2012135）, based on the combination of mesoporous material functionalization and imprinting technology, a series of research steps were gradually carried out on synthesis materials se lection, proportion optimization, synthesis methods of imprinted mesoporous adsorbents, wastewater heavy metals purification mechanism and other relevant key issues. The major conclusions of this study are as follows:（1） Using EISA technology, amine func tionalized mesoporous silica material was synthesized in alkaline system. Through a variety of characterization methods like SAXRD, FTIR, N2 adsorption-desorption, spectroscopy, and through adsorption tests, PEG-2000 was screened and finally identified as a template, and TMAOH as an auxiliary template. Synthesized PEG-S samples have fine mesoporous structure（average pore size: 17.9nm, specific surface area: 113.1m2/g, pore volume: 0.507cm3/g） and have best performance in heavy metals adsorption.（2） The dosing method of imprinted ions and hydrothermal crystallization temperature were determined. Based on uniform design experiment and response surface analysis, the optimized proportion of APTES（monoamine）/N-AEAPTES（diamine）/TESPD（triamine）: Pb²⁺/Cu²⁺/Zn²⁺: TMAOH: PEG-2000: TEOS: of Anhydrous ethanol were 0.270: 0.065: 0.25: 0.073: 1:50. Ultrasound and microwave measures were also introduced to improve preparation conditions.（3） Adsorption experiment results showed that the introduction of imprinting technology significantly improved adsorption properties of amine-functionalized mesoporous materials. The final equilibrium adsorption capacity of imprinted samples on corresponding metal ions was 28.9%⁶2.5% higher than non- imprinted samples. Nonlinear fitting based on the data from the heavy metal ion isothermal adsorption experiments followed Redlich-Peterson isotherm models very well. Compared with non- imprinted materials, imprinted materials possessed better adsorption kinetics properties, and presented more powerful spontaneous adsorption.（4） The adsorption mechanism of ions imprinted mesoporous adsorbents can be explained as follows: in weak acid or near-neutral environment, the amine N atom had high coordination ability, and could form stable chelates with metal ions. Moreover, imprinting technology treatment promoted the formation of cavities on the mesoporous material pore surface and inner wal.（5） Adsorptive selectivity study based on two component solution showed that imprinted samples had much better performance than non-imprinted samples in corresponding ion adsorption. The selectivity coefficient Kd, k’IIP /NIP also testified imprinted samples’ better adsorption capacity on target ions.（6） The adsorption breakthrough curve on the data obtained fr om the self- made dynamic adsorption device showed that breakthrough time was 260 min, 180 min and 220 min separately, and at the saturation point adsorption capacity of Pb-IIP-A, Cu-IIP-A, Zn-IIP-A samples on the corresponding ions were 179.05mg/g, 49.53mg/g and 57.34mg/g respectively, consistent with the change trend of static adsorption capacity.（7） Dynamic adsorption experiments were carried out on comprehensive wastewater discharged from an electroplating industrial park. Since the wastewater was with high Cu²⁺, Zn²⁺ content, distribution coefficient for Cu-IIP-A, Zn-IIP-A samples adsorption on corresponding ions was relatively better. Consider Cu-IIP-A regeneration performance, the final adsorption rate after five recycles remained over 80%.To sum up this paper, with the combination of mesoporous material functionalization and imprinting technology, imprinted amine functionalized mesoporous adsorbents were synthesized in an alkaline system in one step. In terms of green chemistry, a simple efficient and low toxic method was put forward to synthesize ions imprinted amine functionalized mesoporous silica adsorbents. The synthesized samples proved to have fine selective adsorption and regeneration property. The above research results provided a good option for wastewater heavy metal treatment and removal of pollutants.