N-containing hollow carbon spheres derived from polycyclophosphazene possess versatile adsorption and photocatalytic functions for air and wastewater purification

This study aims to develop materials that can serve as efficient adsorbents and photocatalysts with multiple functions for various pollutant removal applications. Poly[cyclotriphosphazene-co-1,3,5-triol nitrobenzene] (PCTNB) microspheres were synthesized using a one-pot, sonication-assisted precipitation polymerization method and then calcined in N 2 gas to generate N and P doped hollow carbon microspheres (PCTNB-500) with a size of 1–2 μm, large surface area , and high porosity. The PCTNB-500 microspheres were tested as an adsorbent for removing methylene blue (cationic dye), methyl orange (anionic dye), and arsenic (toxic metal) from aqueous solutions. PCTNB-500 showed a higher adsorption capacity for methylene blue under different conditions than a commercial activated carbon product. Also, it displayed a high adsorption capacity for volatile organic compounds, such as formaldehyde and methanol, in the gas phase. Structural characterizations showed that PCTNB-500 contained Pyridinic-N, Pyrrolic-N, Graphitic-N, and P-O-C bonds, making it capable of adsorbing various guest molecules with high capacity. The PCTNB was also immobilized on alumina beads for easy recovery, cost-effectiveness, and photocatalytic degradation of two representative pharmaceutical compounds (triclosan and diclofenac sodium). The Alumina@PCTNB-500 beads showed high photocatalytic efficiencies for degrading diclofenac and triclosan , with reaction rate constants of k = 0.0178 (min −1 ) and 0.0476 (min −1 ), respectively. It was found that the presence of • OH radicals was the main contributor to the photocatalytic degradation process, as confirmed by EPR analysis and other characterizations. The synthesized material possesses both adsorbent and photocatalytic functions that can be utilized for various applications, including wastewater treatment and air pollution reduction, serving as a comprehensive solution.