Experimental and DFT investigation on N-functionalized biochars for enhanced removal of Cr(VI).
Experimental and DFT investigation on N-functionalized biochars for enhanced removal of Cr(VI).
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DOI：
10.1016/j.envpol.2021.118244
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发表时间：
2021-09
影响因子：
8.9
通讯作者：
Nan Zhao;Chuanfang Zhao;Kunyuan Liu;Weihua Zhang;Daniel C W Tsang;Zai-Lei Yang;Xixiang Yang;B. Yan;J. Morel;R. Qiu
中科院分区：
文献类型：
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作者：
Nan Zhao;Chuanfang Zhao;Kunyuan Liu;Weihua Zhang;Daniel C W Tsang;Zai-Lei Yang;Xixiang Yang;B. Yan;J. Morel;R. Qiu
本研究通过热解方法在杨树叶片中分别以1：1和1：3的比例负载不同量的尿素，设计出具有不同结构特征的N功能化生物炭。尿素的加入显著增加了生物炭的N含量，并通过取代反应和美拉德反应，促进了胺(-NH-，-NH)、亚胺(-HC双键NH)、苯并咪唑(-C7H5N2)、咪唑(-C3H3N2)和嘧啶(-C4H3N2)基团的形成。PH对去除六价铬的影响表明，溶液pH的降低有利于质子化官能团与HCrO4-−之间形成静电引力。并通过实验和密度泛函理论研究探讨了N-官能化生物炭与铬(VI)相互作用的吸附行为和吸附机理。质子化能计算表明，新形成的含N基团中的N原子是较好的质子受体。吸附动力学和吸附等温线实验表明，N功能化生物炭对六价铬有较大的去除速率和去除能力。N功能化生物炭对六价铬的去除效率是未处理生物炭的10.5~15.5倍。同时，N-官能化生物炭对-C7H5N_2、-NH_2、-OH、-C_3H_3N_2和邻苯二甲酸(-C_8H_5O_4)具有最大的氢键吸附能力，最大吸附能为−5.01kcal/m o l。这些关于质子化和吸附能力的机理发现有助于更好地理解N-官能化生物炭的功能，从而为其在各种环境应用中的应用提供指导。
In this study, N-functionalized biochars with varied structural characteristics were designed by loading poplar leaf with different amounts of urea at 1:1 and 1:3 ratios through pyrolysis method. The addition of urea significantly increased the N content of biochar and facilitated the formation of amine (-NH-, -NH2), imine (-HCdouble bondNH), benzimidazole (-C7H5N2), imidazole (-C3H3N2), and pyrimidine (-C4H3N2) groups due to substitution reaction and Maillard reaction. The effect of pH on Cr(VI) removal suggested that decrease in solution pH favored the formation of electrostatic attraction between the protonated functional groups and HCrO4−. And, experimental and density functional theory study were used to probe adsorption behaviors and adsorption mechanism which N-functionalized biochars interacted with Cr(VI). The protonation energy calculations indicated that N atoms in newly formed N-containing groups were better proton acceptors. Adsorption kinetics and isotherm experiments exhibited that N-functionalized biochars had greater removal rate and removal capacity for Cr(VI). The removal rate of Cr(VI) on N-functionalized biochar was 10.5–15.5 times that of untreated biochar. Meanwhile, N-functionalized biochar of NB3 with the largest number of adsorption sites for -C7H5N2, -NH2, -OH, -C3H3N2, and phthalic acid (-C8H5O4) exhibited the supreme adsorption capacity for Cr(VI) through H bonds and the highest adsorption energy was −5.01 kcal/mol. These mechanistic findings on the protonation and adsorption capacity are useful for better understanding the functions of N-functionalized biochars, thereby providing a guide for their use in various environmental applications.