介孔蔗渣碳的氮官能化改性及其对Hg^(2+)吸附的影响

Effect of Modification with Nitrogen Functional Groups on Structure and Adsorption Performence of Biomass Active Carbon

以甘蔗渣为原料、磷酸作为改性剂制备了生物质碳BAC,用硝酸氧化和乙二胺对其修饰后制备出多胺介孔蔗渣基生物质碳BAC-EDA。采用低温液氮吸附/脱附,根据BET、BJH、t-plot、FTIR分析改性前后蔗渣碳BAC、BAC-EDA的孔结构和表面化学官能团,研究了改性对重金属汞吸附的影响。结果表明,生物质碳BAC和BAC-EDA由介孔和少量微孔组成,在改性后的多胺介孔蔗渣基生物质碳表面新增了羧基、内酯基等含氧酸性官能团以及氨基含氮官能团,而且改性前后生物质碳的微介孔所占比例恒定。这些结果表明,官能团的引入是在微介孔上同时进行的。吸附试验结果表明,改性后的蔗渣碳BAC-EDA的最大吸附量为137 mg·g^(-1),远高于未改性的蔗渣碳AC的吸附量73 mg·g^(-1),说明硝酸氧化和乙二胺改性提高了生物质碳的吸附性能。使用Langmuir模型能更好地描述汞在BAC-EDA上的吸附,进一步说明改性后碳材料活性位点的均一性。同时,温度升高有利于吸附,说明这个过程是一个自发吸热过程。

Nitrogen-doped bagasse biochar BAC-EDA was prepared via a two-step process, namely,the bagasse biochar was prepared with bagasse as raw material and phosphoric acid as modifying agent and then on which nitrogen-containing functional groups were further coupled with ethylenediamine as dressing agent. The pore structure of BAC and BAC-EDA was characterized by means of BET, BJH and tplot methods based on the experimental data of liquid nitrogen adsorption/desorption. Meanwhile acidic groups were characterized by FTIR method. Results show that pores of biochar BAC and BAC-EDA are mainly of mesopores with a small amount of micropores. There existed oxygen-containing acidic functional groups on the surface the nitrogen-doped bagasse biochar BAC-EDA, such as carboxyl groups, lactone groups and amino nitrogen-containing functional groups etc. The proportions of the micro-mesopores of the biomass carbon are constant before and after modification, which indicating that the introduction of the functional groups is realized simultaneously on the surface of both the micro-and meso-pores.Adsorption experiments show that the maximum adsorption amount of the modified BAC-EDA is 137 mg·g-1,much higher than that of the plain BAC 73 mg·g-1,indicating that the nitric acidoxidation and ethylenediamine modification effectively improve the adsorption capacity of biomass biochar.The Langmuir model can better describe the adsorption of Hg(Ⅱ)by BAC-EDA,further illustrating the homogeneity of the active sites of the modified carbon.Besides,the temperature is conducive to adsorption,showing that the process is a spontaneous endothermic process.