Preparation of titanium dioxide nanoparticles supported on hexagonal mesoporous silicate (HMS) modified by oak gall tannin and its photocatalytic performance in degradation of azo dye

• TiO2 based on HMS loaded by oak gal tannin, OGT, was synthesized.
• TEM images show uniform distribution of TiO2 on the surface of OGT-HMS.
• Tannin prevents the aggregation of TiO2 on the surface of OGT-HMS unlike HMS.
• TiO2 based on HMS loaded by 0.6 wt.% tannin showed the highest photocatalytic activity.
• Photocatalytic reactions are endothermic and followed the first-order kinetic model.

In this study, a new type of photocatalyst, TiO2 based on hexagonal mesoporous silicate (HMS) loaded by different concentrations of natural polyphenol oak gall tannin,OGT, (TiO2–OGTx-HMS, x = 0.3, 0.6, 1 wt.%) was synthesized and used in batch photocatalytic experiments. The synthesized catalysts were characterized using XRD, SEM, EDX and TEM analysis. The analysis showed that tannin was immobilized on the surface of HMS and TiO2 nanoparticles were distributed well and uniform on the surface of OGT-HMS without aggregation, while TiO2 nanoprticles aggregated on the surface of tannin free HMS. The performance of TiO2–OGTx-HMS phtocatalysts for degredation of anionic dye (i.e., Direct yellow 86) in aqueous solution were also compared with the performance of TiO2 (P-25) and TiO2–HMS. TiO2–OGT0.6%-HMS Photocatalyst exhibited higher performance than that of other photocatalysts with the adsorption and degradation efficiencies of 36.7% and 92.2%, respectively. The relative high value of activation energy, 24.8 kJ/mol, confirms the effect of temperature to accelerate the photocatalytic reaction. It was also shown that photocatalytic reaction follows first order kinetic and up to 120 mg/l of dye solution, Langmuir–Hinshelwood (L–H) kinetic model is acceptable.

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