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An investigation on the reduction of Cr (VI) pollutant from tannery effluents using TiO2, SB/TiO2, and c-SB/TiO2 nano photocatalysts was presented in this study. For the preparation of Biochar-based TiO2 photocatalyst (SB/TiO2), tannery sludge was utilized as a precursor. Hydrothermal pre-treatment was adopted to prepare chemically activated SB/TiO2 and SB/TiO2 nanocomposites. The morphology, crystal structure, optical properties, and elemental composition of the prepared catalysts were analyzed by XRD, FT-IR, SEM–EDX, BET analysis, ZPC, PL, TGA, and Raman spectroscopy. The band gap analysis of Photocatalyst was measured using a DRS instrument, and band gap energy of 3.39 eV was obtained for c-SB/TiO2 photocatalyst. The developed c-SB/TiO2 catalyst exhibits a larger specific surface area of 646.85 m2/g than TiO2 and SB/TiO2 (74.58 m2/g and 573.74 m2/g), respectively. The enhanced photocatalytic activity for the pollutant removal was achieved by the photocatalyst due to their wide band gap and effective charge separation. The kinetic rate constant was achieved in the pseudo-first-order model, which fits well for the reduction of Cr (VI). Furthermore, at the optimal conditions of 10 mg/L contaminant concentration, pH 2, and 0.5 g/L catalyst dosage, 98.56% reduction was observed after 180 min of reaction. The OH acts as a major removal pathway for Cr (VI) contaminants with more than 50% reduction in COD. This study proves that c-SB/TiO2 photocatalysts can remove toxic contaminants under UV light irradiation with good recycling performance up to 5 times. [ABSTRACT FROM AUTHOR]

The preparation of biochar from Tannery (chrome) sludge has gained recent attention among many scientists globally. Hydrothermal pre-treatment method was adopted to load TiO2 nanoparticles on the surface of sludge biochar to develop a safe, low-cost, and novel nanocomposite. Chemical activation of sludge with KOH solution for 48 h was done before pyrolyzing the sludge to produce biochar. This novel c-SB/TiO2 nanocomposite exhibits a higher surface area of 636.23 m2/g when compared with the sludge biochar/TiO2 nanocomposite without chemical activation. The present research work mainly focuses on the synthesis and investigation of structural properties of c-SB/TiO2 nanocomposite prepared by hydrothermal pre-treatment. The morphological and structural properties of sludge biochar/TiO2 nanocomposite were identified by Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD). The porosity of the nanocomposite was investigated using a BET surface area analyser. The Thermal decomposition and surface functional group was identified using TGA, FT-IR, PL and Raman spectrophotometer, respectively. c-SB/TiO2 nanocomposite was used to degrade Cr (VI) by varying its initial concentration, catalyst dosage and initial pH. Results indicate that c-SB/TiO2 nanocomposite shows an enhanced photocatalytic activity under UV light irradiation. Further, it was found that under optimal conditions of 10 mg/L of pollutant concentration, pH of 2 and catalyst dosage of 0.3 g/L, degradation efficiency of 98.65% Cr (VI) has been achieved for a reaction time of 180 min. Additionally, COD measurement shows a 69.4% reduction for a reaction time of 180 min, which is found to be more recalcitrant under photocatalytic activity. [ABSTRACT FROM AUTHOR]