Physico-chemical characterization of walnut shell biochar from uncontrolled pyrolysis in a garden oven and surface modification by ex-situ chemical magnetization

Abstract The shells of walnuts (WS) are major refuse in the global fruits and nuts trade. This, otherwise discarded, lignin-rich material can be carbonized to biochar—a value-added product with environmental applications such as carbon sequestration, soil amelioration, pollutant adsorption. These dictated by structural chemical characteristics biochar carbon. Conventional controlled pyrolysis (CPy) biomass is cost-intensive technically too complex for widespread adoption, especially emerging economies. Here, walnut shell (BWS0) derived through uncontrolled (UCPy) a oven further hybridized magnetic ex-situ co-precipitation. physico-chemical its water-extractable fractions comprehensively investigated understand their structure applicability. sp 2 amorphous sequestered BWS0 0.84 kg CO2 /kg BET (N ) surface area 292 m /g comparable from CPy terms structure. polyaromatic hydrocarbons present only trace amounts naphthalene, biphenyl, phenanthrene. magnetization decreases porosity while greatly facilitating separation aqueous media. suitable adsorption cations (between pH 2.8 9.45) hydrophobic pollutants 19 mg L ?1 fouling intrinsic dissolved organic In combination fast-release N, P fertilizers, (C/N 24.8) application hydrophilic soils at higher loading rates. results suggest an avenue where WS also prepared via UCPy direct applications. Future investigations into incubation tests recommended. Graphical abstract