Comparison Study on Immobilization of Ag-Doped TiO2 using Normal and Reverse Methods for Photodegradation of Methylene Blue Dye

Immobilized Ag/TiO2 was prepared using reverse (R) and normal (N) methods, employing epoxidized natural rubber (ENR-50) and polyvinyl chloride (PVC) as polymer binders to form a Ag-TiO2/ENR/PVC (ATEP(R)) plate in order to address the solvent interference issue.The immobilization of TiO2 was performed prior to the photodeposition of Ag (50, 100 and 400 ppm), by irradiation with a 250-Watt metal halide lamp for 90 minutes.TiO2 was coated onto glass plates using a dip-coating technique.Methylene blue (MB) was employed as a model pollutant to evaluate the photocatalytic activity of the prepared immobilized Ag/TiO2.Several instruments were used for characterization, including Ultraviolet-Visible Diffuse Reflectance Spectroscopy (UV-Vis DRS), Fourier Transform Infrared spectroscopy (FTIR) and photoelectrochemical (PEC) analysis.The UV-Vis DRS results indicated that the band gap for 100 ppm of Ag-TiO2/ENR/PVC (100-ATEP(R)) was 2.42 eV, with its absorption edge shifted towards the visible region.FTIR analysis showed a peak at 1382 cm -1 , confirming the successful doping of Ag onto TiO2, while a less intense peak for OH at 3400 cm -1 indicated the low hydrophilicity of the photocatalyst.PEC analysis revealed that 100-ATEP(R) exhibited higher current density in linear sweep voltammetry (LSV) curves, lower charge transfer resistance in Nyquist plots and higher photocurrent response in chronoamperometry (CA) plots, compared to TiO2/ENR/PVC (reverse) TEP(R).All immobilized ATEP(R) samples showed excellent photocatalytic degradation of methylene blue (MB) dye and achieved 52 % decolorization within 1 hour of light irradiation, indicating higher photocatalytic activity compared to the normal method.The photocatalytic degradation of all samples followed the pseudo-first-order reaction model of Langmuir Hinshelwood, with R 2 values above 0.90.The results indicate that this new immobilization method may be used for all photocatalysts as it can prevent disruption of the immobilized photocatalyst by the solvent, which is a disadvantage of the normal immobilization method.