功能化单壁碳纳米管去除Hg^(0)性能及机理研究

Study on the performance and mechanism of gaseous elemental mercury removal by functionalized single-walled carbon nanotubes

对单壁碳纳米管(SWCNTs)改性,制备了羟基化碳纳米管(SWCNTs-OH)、羧基化碳纳米管(SWCNTs-COOH)和氨基化碳纳米管(SWCNTs-NH2),并测试了其对气态单质汞(Hg^(0))的吸附性能.采用SEM、BET、FTIR、XPS等技术对碳纳米管的物理结构和化学特性进行了表征,探讨了不同碳纳米管脱汞性能差异原因和脱汞机理.结果表明,SWCNTs-NH2的脱汞性能最为优异,在初始汞浓度为250μg·m^(-3),反应温度为100℃条件下,脱汞效率可达99.97%,相较于SWCNTs脱汞性能提高14.30%.SWCNTs-NH2比表面积较高,表面活性含氧基团丰富且表面氨基对汞有较强的亲和力,有利于Hg^(0)的吸附.XPS和汞程序升温脱附(Hg-TPD)分析表明,吸附在碳纳米管上的汞物种主要为物理吸附Hg^(0)和HgO,而SWCNTs-NH2上还存在弱结合态汞N−Hg−O,可能是由SWCNTs-NH2表面的活性含氧基团−COOH、C=O氧化Hg^(0)产生的中间产物−C−O−Hg与表面−NH2进一步相互作用产生.

The hydroxylated carbon nanotubes(SWCNTs-OH),carboxylated carbon nanotubes(SWCNTs-COOH)and aminocarbon nanotubes(SWCNTs-NH2)were prepared from the modification of single-wall carbon nanotubes(SWCNTs)and their gaseous elemental mercury(Hg^(0))adsorption performance was evaluated.The reasons for Hg^(0)removal performance differences and the related Hg^(0)removal mechanism were investigated.The results indicate that SWCNTs-NH2 shows the most excellent Hg^(0)removal performance among the four types of carbon nanotubes.With the mercury concentration of 250μg·m^(-3)and reaction temperature of 100℃,the Hg^(0)removal efficiency of SWCNTs-NH2 can reach 99.97%,which is 14.30%higher than that of SWCNTs.The high specific surface area,the abundance of surface reactive oxygen groups and existence of amino groups with strong affinity to mercury greatly promote the Hg^(0)adsorption by SWCNTs-NH2.XPS and mercury-temperature programmed desorption(Hg-TPD)analyses show that the mercury species adsorbed on carbon nanotubes are mainly physically adsorbed Hg^(0)and HgO,while weakly bound mercury N−Hg−O is also generated on SWCNTs-NH2,possibly owing to the interaction of−C−O−Hg with surface−NH2.−C−O−Hg is an intermediate product generated by the oxidation of Hg^(0)by the reactive oxygen-containing groups such as−COOH and C=O on the surface of SWCNTs-NH2.