Multifunctional core-shell Fe0@SiO2@nCaO2 nanocomposite for sequential oxidative degradation and immobilization of coexisting organic and inorganic contaminants

A spatially regulated Fe⁰@SiO₂@nCaO₂ nanocomposite was rationally designed. • A multifunctional material integrates oxidation, precipitation, and flocculation. • Fe loading regulates ROS generation and pollutant-specific removal pathways. • Sequential activation of oxidation, precipitation, and flocculation pathways was revealed. The simultaneous removal of coexisting organic and inorganic contaminants remains a major challenge for wastewater treatment because conventional technologies fail to integrate oxidative degradation with inorganic immobilization in a single reaction system. Herein, a spatially regulated Fe 0 @SiO 2 @nCaO 2 multifunctional nanocomposite was developed to achieve synergistic purification of representative organic pollutants (sulfamethoxazole and atrazine) and inorganic contaminants (As(III) and phosphate). Batch experiments showed that the optimized Fe 0 @SiO 2 @nCaO 2 composite (Fe loading of 170.2 mg g −1 , 1 g L −1 ) removed 97.9% of sulfamethoxazole and 99.9% of atrazine, As(III), and phosphate within 24 h at an initial concentration of 20 mg L −1 for each contaminant. Radical–quenching experiments combined with electron paramagnetic resonance analysis revealed the involvement of 1 O 2 and •O 2 - , with a possible contribution from •OH. Notably, 1 O 2 showed the strongest apparent influence on sulfamethoxazole oxidation under the present alkaline conditions. Arsenic removal involved an initial As(III) oxidation step, followed by adsorption onto Fe-based sites and final immobilization through Fe/Ca–Si flocculation, rather than direct precipitation. Phosphate was primarily immobilized through rapid calcium-induced precipitation followed by incorporation into Fe/Ca–Si flocs. In the ternary sulfamethoxazole–As(III)–phosphate system, phosphate precipitation, organic oxidation, and arsenic immobilization exhibited distinct temporal separation. Matrix-effect experiments further showed that humic acid mainly inhibited As immobilization. Nevertheless, in a real-water matrix, 24-h removal efficiencies remained 92.1%, 99.5%, and 97.0% for SMX, phosphate, and As, respectively. These results demonstrated that Fe 0 @SiO 2 @nCaO 2 integrated complementary oxidation, precipitation, and immobilization pathways while maintaining effective performance under complex water-matrix conditions.