Chemical anchoring of CaO2 on phosphate-modified rice husk biochar for stabilized oxygen release

Abstract To address the high environmental sensitivity of oxygen release from calcium peroxide (CaO 2 ) in practical applications, this study proposes and validates a synergistic regulatory strategy combining chemical anchoring and physical confinement. Three modified rice husk biochars were prepared via nitric acid oxidation, KOH activation, and phosphate loading, followed by CaO 2 loading. The biochar prepared via KOH activation (B Si- ) possessed an ultra-high specific surface area (2629.49 m 2 g −1 ). Consequently, the CaO 2 @B Si- composite exhibited high loading capacity (15.74%) and rapid oxygen release. In contrast, nitric acid oxidation resulted in a biochar carrier (B N ) with a damaged pore structure and a strongly acidic surface, which led to the lowest CaO 2 loading (1.31%). The phosphate-modified biochar (B P ) enabled CaO 2 @B P to achieve both high loading capacity (10.49%) and sustained slow oxygen release, which was attributed to the formation of stable Ca−P bonds. The CaO 2 @B P exhibited superior environmental robustness, being largely independent of pH, ionic strength, and initial dissolved oxygen concentration. Partial least squares regression modeling quantitatively revealed that both phosphorus content and mesopore volume were core factors determining the loading capacity, whereas both H/C ratio and surface functional groups regulated the oxygen release kinetics. The phosphate modification may be an optimal strategy for preparing environmentally adaptive oxygen-releasing materials with both high loading and good stability. Graphical Abstract