Paddy fields are a major emission source of greenhouse gases (GHGs) [for instance, methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂)] among agricultural fields. Biochar has been deemed a potential candidate for the reduction of GHGs in paddy fields. However, there is no consistent conclusion that biochar can simultaneously reduce emissions of CH₄, N₂O, and CO₂. Herein, we proposed the FeN₃-doped biochar (FG) as an excellent material for GHGs restriction in paddy fields via the first-principles calculation. The computation results indicated that the FG exhibited satisfactory adsorption ability for CH₄, CO₂, and N₂O, which improved the adsorption energies to −1.37 , −1.54, and −2.91 eV, respectively. Moreover, the density of state (DOS) analyses revealed that the factor responsible for FeN₃-doped biochar to exhibit excellent adsorption ability was the occurrence of drastic energy up- or down-shift of the electron for Fe d, C p, O p, or N p orbital upon adsorption of CH₄, CO₂, or N₂O. Our study suggested an advanced modified biochar material for reducing the GHGs emissions in paddy fields, in addition to exploring the adsorption properties and mechanisms of FeN₃-doped biochar for GHGs mitigation, which provided a strategy to explore biochar modification and efficient emission reduction materials. Graphical Abstract

Cadmium (Cd) contamination in agricultural soils has caused extensive concern to researchers. Biochar with iron-compound modifications could give rise to the synergistic effect for Cd restriction. However, the related capture mechanism based on physicochemical properties is unclear. In this study, first principles calculations are proposed to explore the adsorption ability and potential mechanism of the ferric hydroxide modified graphene (Fe@G) for capturing CdCl₂. The simulation results show that the adsorption energy to CdCl₂ could enhance to −1.60 eV when Fe(OH)₃ is introduced on graphene. Subsequently, analyses of electronic properties demonstrated a significant electron transfer between Cd s-orbital and O p-orbital, thereby leading to strong adsorption energy. This theoretical study not only identifies a powerful adsorption material for Cd reduction in agricultural soils and reveals the capture mechanism of Fe@G for Cd but also provides a foundation and strategy for Cd reduction in agricultural soils.

Cadmium (Cd) contamination in paddy soils severely threatens rice safety and human health. Currently, the high costs and technical barriers of existing Cd remediation methods limit their development, so it’s urgent to find an economical and feasible method. Herein, the synergistic effects of rhodochrosite slag and biochar on Cd immobilization in slightly acidic Cd-contaminated paddy soils have been investigated. A field experiment with four treatments—control (CK), rhodochrosite slag (R), biochar (B), and combined rhodochrosite slag + biochar (RB)—was conducted in Hunan Province, China. Results demonstrated that RB treatment significantly increased soil pH, transferred the mobile Cd to the residual fraction, and reduced Cd availability in the soil. Cd concentrations in rice roots, stems, leaves, and brown rice decreased by 26.37%, 47.20%, 31.03%, and 51.85%, respectively, under RB treatment, achieving the lowest TF and BCF values. Furthermore, RB treatment increased rice yield by 18.73%. The synergistic interaction between biochar’s adsorption capacity and rhodochrosite slag-derived competitive ions effectively transformed Cd into stable fractions, reducing bioavailability. This study proposes a novel remediation strategy that not only enhances the Cd immobilization ability of biochar but also achieves simultaneous waste valorization and soil remediation.