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 (-HCNH), 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.

在这项研究中，通过热解方法以 1:1 和 1:3 的比例加载不同数量的尿素，设计了具有不同结构特征的 N 功能化生物炭。尿素的加入显着增加了生物炭的氮含量，促进了胺（-NH-、-NH ₂）、亚胺（-HC NH）、苯并咪唑（-C ₇ H ₅ N ₂）、咪唑（-C ₃ H ₃ N ₂ ) 和嘧啶 (-C ₄ H ₃ N ₂) 基团由于取代反应和美拉德反应。pH 值对 Cr(VI) 去除的影响表明，溶液 pH 值的降低有利于质子化官能团和 HCrO ₄ ^-之间形成静电引力^-. 并且，通过实验和密度泛函理论研究来探讨 N 功能化生物炭与 Cr(VI) 相互作用的吸附行为和吸附机制。质子化能计算表明，新形成的含氮基团中的 N 原子是更好的质子受体。吸附动力学和等温线实验表明，N 功能化生物炭对 Cr(VI) 具有更高的去除率和去除能力。N-功能化生物炭对 Cr(VI) 的去除率是未处理生物炭的 10.5-15.5 倍。同时，NB3的N-官能化生物炭对-C ₇ H ₅ N ₂、-NH ₂、-OH、-C ₃ H ₃ N ₂的吸附位点数量最多和邻苯二甲酸（-C ₈ H ₅ O ₄）通过H键对Cr（VI）表现出最高的吸附能力，最高吸附能为-5.01 kcal/mol。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 功能化生物炭的功能，从而为其在各种环境应用中的使用提供指导。