Efficient solar-driven degradation of a tire wear pollutant using floating K-doped g-C3N4 photocatalyst in secondary municipal wastewater

Graphitic carbon nitride (g-C 3 N 4 ) is a promising photocatalyst for solar-driven degradation of contaminants of emerging concern (CECs). However, its powdered form complicates recovery for large-scale applications in water treatment. In this study, we developed potassium-doped g-C 3 N 4 (KCN) supported on expanded perlite (EP), a non-toxic volcanic glass, to address these recovery challenges. KCN was synthesized in situ by adding varying amounts of KOH to urea and EP, followed by calcination. The EP/KCN composites were characterized and tested for the degradation of 1,3-diphenyl guanidine (DPG), a tire wear pollutant. SEM images showed that KCN coverage increased with higher urea loading on EP, with EP/KCN20 (20:1 urea to EP, 1 wt% KOH) having nearly complete surface coverage. FT-IR spectra confirmed stronger C-N and C=N stretching vibrations with increased KCN content, confirming the successful incorporation of KCN into the composite. XRD patterns displayed distinct KCN peaks at higher loadings, while PL analysis suggested slightly reduced charge recombination in the EP/KCN20 composite, indicating enhanced photocatalytic efficiency. Furthermore, EP/KCN20 achieved 96.1 % degradation of DPG under simulated solar exposure in 5 h, with over 80 % efficiency maintained across four consecutive cycles. The composite also demonstrated robust performance under more complex conditions, including natural solar light and in DPG-spiked secondary municipal wastewater, with a cost of 5.57 USD/m 3 . These findings highlight the potential of the EP/KCN composite as a scalable, cost-effective solution for the removal of CECs from wastewater, driven by renewable solar energy.