Unveiling the synergistic effect of an nZVI–SiO2–TiO2 nanocomposite for the remediation of dye contaminated wastewater†

Water contamination and scarcity pose critical global challenges. Existing water remediation technologies such as membrane technologies lack hydrophilic surface properties, prompting the need for novel, highly efficient supportive materials. Photocatalysis emerges as a promising solution for degrading organic pollutants in wastewater. However, existing photocatalysts such as titanium dioxide (TiO₂) suffer from rapid recombination of photogenerated charge carriers and lower catalytic activity, hindering performance. Herein, a novel, high sorption capacity nZVI–SiO₂–TiO₂ nanocomposite material was synthesized via a combined chemical reduction approach. The influence of synthesis pH and the synergistic effects of nZVI, SiO₂, and TiO₂ on the physicochemical properties and overall performance of the nZVI–SiO₂–TiO₂ nanocomposite were investigated. Three sets of nZVI–SiO₂–TiO₂ nanocomposites were synthesized by varying synthesis pH from 2 to 4. MB dye degradation experiments and thermal analysis revealed that the nZVI–SiO₂–TiO₂ nanocomposite synthesized under pH 2 synthesis conditions exhibited the fastest dye degradation rate, highest removal efficiency (100%), and thermal stability. Characterization techniques, including FTIR, EDS (energy dispersive X-ray spectroscopy), SEM, BET (Brunauer–Emmett–Teller), XRD, TGA (thermogravimetric analysis), and DSC (differential scanning calorimetry), revealed that lower nZVI–SiO₂–TiO₂ synthesis pH enhanced the material's specific surface area, crystallinity, and the interfacial interactions of nZVI, SiO₂, and TiO₂ components in the nanocomposite. The reusability test showed >90% efficiency after 5 successive cycles. The sorption mechanism and methylene blue (MB) dye speciation test corroborated the synergistic adsorption and reduction potential of nZVI–SiO₂–TiO₂ functional materials with 100% mineralized methylene blue (MB⁺ species) at MB dye solution pH above 6.0. After economic considerations, it is believed that the exceptional adsorption and recycling abilities of the novel nZVI–SiO₂–TiO₂ material, coupled with its thermal stability, could counterbalance its upfront expenses, potentially making it a feasible choice for wastewater treatment applications.