Regulation of pyrolysis temperature on the structural evolution of maize stover biochar and its mechanism of Cd2+ adsorption

Cadmium (Cd) pollution has emerged as a grave global environmental concern, rendering it imperative to develop cost - effective, environmentally friendly, and highly efficient adsorbents for the remediation of Cd 2+ . Biochar derived from agricultural waste is recognized as a promising material for heavy metal removal. However, the regulatory effect and internal mechanism of pyrolysis temperature on Cd 2+ adsorption remain ambiguous. In this study, maize stover was chosen as the raw material to prepare biochar under three typical pyrolysis temperatures (300 °C, 500 °C, and 700 °C). A comprehensive exploration was conducted on the disparities in pore microstructure, surface chemical characteristics, mineral composition, and Cd 2+ adsorption capacity of biochar at different temperatures. The findings indicated that an increase in pyrolysis temperature significantly enhanced the specific surface area, total pore volume, and average pore size of biochar. Among them, RSB700 exhibited the optimal pore structure. High - temperature pyrolysis led to a reduction in surface oxygen content, an increase in carbon content, and the retention of abundant mineral elements (Mg, Si, Ca, K), which could promote Cd 2+ immobilization through ion exchange and complexation. XRD analysis confirmed that high - temperature treatment induced the formation of Fe 2 O 3 and turbostratic graphitic carbon crystals. FTIR results corroborated that high temperature caused the decomposition of oxygen - containing functional groups (−OH, −COOH) and strengthened the aromatic structure of biochar. The adsorption process conformed to the pseudo - second - order kinetic model and Langmuir isotherm model, suggesting that monolayer chemical adsorption played a dominant role in Cd 2+ fixation. RSB500 demonstrated the fastest adsorption rate, while RSB700 achieved a maximum adsorption capacity of 40.68 mg g −1 at 25 °C. In summary, pyrolysis temperature serves as a crucial regulatory factor that can reshape the pore structure, surface functional groups, and crystalline phase composition of biochar, thereby significantly mediating its Cd 2+ adsorption behavior and underlying mechanism.