Photocatalytic enhancement of immobilized Ag-TiO₂/ENR/PVC by reversed photodeposition method for photodegradation of methylene blue dye

This study proposed a reversed photodeposition technique to increase the reaction of modified semiconductor with the organic pollutant. This technique requires the introduction of Ag onto the surface of immobilized TiO₂, in contrast to the standard method of applying photodeposition on TiO₂ to produce Ag doped TiO₂ prior to immobilization. The immobilization approach employed a dip-coating technique using a coating solution consisting of Degussa P-25 TiO₂, epoxidized natural rubber (ENR-50) and polyvinyl chloride (PVC) as the organic binder. This study focused on the coating of Ag on TiO₂/ENR/PVC materials forming ATEP plates. The coating was carried out at different concentrations (100-500 ppm) using reversed (R) and standard (S) approaches at various photodeposition times (1-6 h). The photocatalytic efficacy of the immobilized ATEP(R) and ATEP(S) was investigated in the degradation of 12 mg L⁻¹ methylene blue (MB) dye. XRD and FESEM study revealed that the photoetching of ENR/PVC in the reversed approach exposed more TiO₂ crystals. The composition of Ag in the reversed approach was higher at wt% = 28.3 than wt% = 0.1 in the standard approach, as confirmed by EDX analysis. Additionally, Ag exhibits a strong surface plasmonic resonance (SPR) effect, giving a decrease in PL intensity in the reversed sample suggesting the deposition of Ag lowered the e⁻/h⁺ recombination. UV-Vis DRS analysis demonstrated that the reversed sample has reduced the band gap energy at Eg = 2.30 eV compared to the standard sample with Eg = 2.62 eV and shifted the adsorption edge into the visible region. 3D profiler revealed that the surface porosity of ATEP-300 (R 5h) was higher with surface roughness, Ra = 6556.93 nm than Ra = 5138.02 nm for ATEP-400 (S 1h). PEC analysis confirmed that the ATEP-300 (R 5h) sample showed better separation of charge transfer in light conditions thus increasing its conductivity.