Preparation of novel N-doped biochar and its high adsorption capacity for atrazine based on π–π electron donor-acceptor interaction

Novel nitrogen (N)-doped cellulose biochar (NC1000-10) with large adsorption capacity (103.59 mg g-1) for atrazine (ATZ) was synthesized through the one-pot method. It has the best adsorption efficiency than N-doped biochars prepared from hemicellulose and lignin. The adsorption behaviors of ATZ by N-doped biochars with different N doping ratios (NC1000-5, NC1000-10, NC1000-20 and NC1000-30) were significantly different, which was attributed to the difference of sp2 conjugate C (ID/IG = 0.99-1.18) and doped heteroatom N (pyridinic N, pyrrolic N and graphitic N). Adsorption performance of ATZ on NC1000-10 conformed to the pseudo-second-order kinetic and Langmuir adsorption isotherm model. Thermodynamic calculations showed that adsorption performance was favorable. Besides, wide pH adaptability (pH = 2-10), good resistance to ionic strength and excellent recycling efficiency make it have extensive practical application potential. Further material characterizations and the density functional theory (DFT) calculations indicated that good adsorption performance of NC1000-10 for ATZ mainly depended on chemisorption, and π-π electron donor-acceptor (EDA) interaction contributed the most due to high graphitization degree. Specifically, pyridinic N and graphitic N further promoted adsorption performance by hydrophobic effect and π-π EDA interaction between ATZ and NC1000-10, respectively. Pyrrolic N and other surface functional groups (-COOH, -OH) facilitated the hydrogen bond effect.