One-step mechanochemical modification of biochar for enhanced Cd(II) removal

Abstract

Cadmium-contaminated wastewater from rapidly expanding industrial activities has become a pressing environmental challenge. Here, we developed a one-step mechanochemical modification strategy to enhance Cd(Ⅱ) removal by reconstructing endogenous Si–O and –OH networks in rice straw-derived biochar. By coupling alkaline treatment activation with mechanical ball milling, inherent silicates in the straw were effectively activated to form SiVO–Si and Si–O–C anchoring sites, while mechanical shear fractured polysaccharide chains and promoted the enrichment of surface –OH groups. The optimized adsorbent (Al-bmST1) exhibited a bifunctional adsorption interface with improved coordination affinity toward Cd(Ⅱ), achieving a removal efficiency of 88.01% and the adsorption capacity reached 27.1 mg/g. This performance was significantly superior to that of both the two-step modified biochar (Al-bmST2) and the biochar prepared solely via mechanical milling (bmST). In situ Fourier-transform infrared (FTIR) analysis and density functional theory (DFT) calculations confirmed that Cd(Ⅱ) formed stable ≡Si–O–Cd⁺ complexes, while surface –OH groups further strengthened adsorption stability. Life cycle assessment (LCA) further showed that the one-step mechanical chemical treatment reduced carbon emissions by 56.72% relative to the conventional straw pyrolysis process, without generating significant harmful gas emissions. These findings provide a low-carbon and efficient route for converting agricultural waste into functional adsorbents for heavy metal wastewater treatment.

Graphical abstract

Keywords

Straw biochar / Mechanochemistry / Cadmium removal / One-step modification / Silicon activation

Highlight

	● One-step mechanochemistry builds Si–O/–OH networks, replacing pyrolysis.
	● Al-bmST1 achieves 88.01% Cd(II) removal with high stability and reusability.
	● In-situ FT-IR and DFT reveal Si–O and –OH as key sites for Cd(II) complexation.
	● The process cuts CO2 emissions by 56.72%, enabling green soil remediation.

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