Boosted Visible-Light Photocatalytic Reduction of Cr (VI) via Plasmonic Ag-TiO2 Nanocomposite

Ag-TiO₂ nanocomposites containing 1, 3, and 5 wt.% Ag was synthesized via a precipitation-assisted sol-gel process followed by chemical reduction and evaluated for visible-light-driven reduction of Cr(VI). Structural, morphological, surface chemical, and optical properties were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy (UV-DRS), and photoluminescence (PL) spectroscopy. The formation of anatase TiO₂ decorated with well-dispersed metallic Ag nanoparticles was confirmed. Among all samples, 3 wt.% Ag-TiO₂ (AT-3) exhibited the highest photocatalytic activity, achieving 99.3% Cr(VI) reduction within 120 min under visible-light irradiation at pH 4. The enhanced performance is attributed to localized surface plasmon resonance (SPR)-induced visible-light absorption, efficient interfacial charge separation, and reduced electron-hole recombination. UV-DRS analysis showed a decrease in the apparent band-gap energy from 3.44 eV (TiO₂) to 3.12 eV (AT-3), which is mainly attributed to SPR and interfacial charge transfer rather than to lattice modification. PL results confirmed suppressed recombination of charge carriers. The hierarchical macro-mesoporous fibrous structure further enhanced mass transport and surface accessibility. These findings demonstrate the potential of plasmonic Ag-TiO₂ photocatalysts for efficient solar-driven remediation of Cr(VI) in wastewater treatment.