Enhanced photocatalytic degradation of dyes using a novel waste toner-based TiO2/Fe2O3@nanographite nanohybrid: A sustainable approach

This study synthesized a ferric oxide–nanographite (NG) nanocomposite (Fe₂O₃@NG) from waste toner powder through carbonization. Subsequently, a TiO₂/Fe₂O₃@NG nanohybrid was fabricated using the sol–gel technique to improve the photocatalytic degradation of dyes. TiO₂/Fe₂O₃@NG nanocomposites were prepared at TiO₂:Fe₂O₃@NG ratios of 2:1 (Ti:T-21), 1:1 (Ti:T-11), and 1:2 (Ti:T-12). The porosity, morphology, surface chemistry, and chemical interactions between TiO₂, Fe₂O₃, and graphite in the prepared TiO₂/Fe₂O₃@NG nanocomposites were characterized using the Brunauer–Emmett–Teller (BET) method and microscopic and spectroscopic analyses. The TiO₂/Fe₂O₃@NG nanohybrid exhibited a reduced bandgap (2.4–2.9 eV) and enhanced charge carrier separation through charge transfer at the junction of the hetero-structured TiO₂/Fe₂O₃@NG nanohybrid. Preliminary experiments revealed that Ti:T-21 was the most effective photocatalyst for degrading acid blue-25 (AB-25) compared to Ti:T-11, Ti:T-12, sole TiO₂, and Fe₂O₃@NG. This study also investigated the impacts of catalyst dose and initial dye concentration on the AB-25 photocatalytic degradation. Notably, 97% of 5-mg/L AB-25 was removed using 1.25-g/L Ti:T-21 at an unmodified pH of 6.4 within 120 min. Furthermore, Ti:T-21 exhibited remarkable recyclability in its immobilized form, achieving degradation ratios of 74.7%–71.8% over five consecutive runs, compared to removal efficiencies of 85.0%–62.3% in the suspended mode. Trapping experiments identified hydroxyl radicals, holes, and superoxide as the principal reactive radicals. The TiO₂/Fe₂O₃@NG/light system was effective in disintegrating and mineralizing other synthetic dyes such as Congo red, methylene blue, and methyl red, indicating its potential for industrial-scale degradation of authentic dye wastewater. The utilization of waste toner for water treatment is highlighted as a strategy to promote environmental sustainability, foster a circular economy, and contribute to pollution remediation.