N self-doping hierarchical porous biochar from Chinese medicine residues for efficient removal of malachite green: Critical contribution of N doping to π-π electron donor-donor interactions

• Published in: Industrial crops and products Vol. 221; p. 119367
• Main Authors: Feng, Xiaoyun, Ma, Xuedong, Niu, Chengyu, Zhang, Ruiying, Yang, Xiurong, Ma, Haixia, Li, Weiqi, Li, Shuang
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2024
• Subjects: Chinese medicinal residues; DFT; Malachite green; N self-doped biochar; π-π electron donor-acceptor interactions; N self-doped biochar; Chinese medicinal residues; DFT; π-π electron donor-acceptor interactions; Malachite green
• ISSN: 0926-6690
• DOI: 10.1016/j.indcrop.2024.119367

N self-doping hierarchical porous biochars are prepared from three kinds of Chinese medicine residues (Lophatherum Gracile (LG), Licorice Radix (LR) and Radix Isatidis (RI)) using KHCO3 as a foaming agent. Among them, LGC shows the best adsorption performance with a maximum adsorption capacity of 3791.5 mg g−1 at 298 K for malachite green (MG). Significant differences of the biochar adsorption behavior are found and the main reason are attributed to differences in sp2 conjugated carbon (ID/IG = 1.46–1.50) and heteroatomic nitrogen (pyridinic-N, pyrrolic-N and graphitic-N) doping. The quasi-secondary kinetic and Langmuir isothermal models are more suitable for describing the adsorption process of biochar towards MG. Further characterization and density functional theory (DFT) calculations showed that the good adsorption of MG by biochar increased with increasing specific surface area (SSA) and pyrrolic-N content. Pore filling effect and π-π electron donor-acceptor (EDA) interactions have been demonstrated to be the predominant driving force of adsorption. Among them, pyridinic-N and graphitic-N further enhance the adsorption performance through the π-π stacking and π-π EDA interactions between MG and biochar, respectively. Pyrrolic-N and other surface functional groups (-COOH, -OH) promote the hydrogen bonding effect. In addition, the good recycling efficiency (close to 70 % after four cycles), excellent multifunctionality and low fabrication cost (13.01 US$ kg−1) of the LGC reveal the potential for practical applications. In addition, all biochar has a wide range of pH suitability (pH = 2.0–10.0). This study provides new ideas for the rapid removal of MG using biochar. In addition, the effects of N self-doping and microscopic N species on the adsorption of biochar provide theoretical guidance for enhancing the adsorption of other macromolecular dyes. [Display omitted] •N self-doped porous biochars were prepared using Chinese medicine residues.•LGC exhibited an extremely high adsorption capacity (3791.52 mg g−1) for MG.•DFT and quantum chemical calculations were used to simulate the MG adsorption.•π-π EDA interactions enhance the adsorption performance of biochar.•LGC offers excellent versatility and renewability, low cost and high application potential.