Integral approach of adsorption and photo-degradation of Bisphenol A using pyrolyzed rice straw biochar coated with metal oxide: batch, mechanism and optimization

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The bodies of water across the world are being polluted by trace organic pollutants like Endocrine Disrupting Chemicals (EDC’s). A well-known example of EDC’s is Bisphenol A (BPA). Therefore, it is a pressing requirement of the current times to find a viable technique for effectively removing these type of pollutants from water. With that intention, a composite material was fabricated using an activated biochar made from rice straw (ARSB) and Titanium Dioxide (TiO2). The synthesized composite, ARSB-TiO2 was used for removing BPA by a combination of adsorption and photocatalytic degradation. From the Tauc plot analysis, it was observed that the band gap of the TiO2 decreased due to its combination with ARSB as the band gap of ARSB-TiO2 was 2.4 eV where as that of TiO2 was 3.36 eV and that of ARSB was 3.31 eV. This was attributed to the formation of a new energy state, formed due to the combination of TiO2 with ARSB during the hydrothermal reaction, resulting in the generation of a Ti-O-C bond. As a consequence, ARSB-TiO2 was able to be activated by visible radiation (2-2.75 eV). A set of batch studies were conducted to evaluate the experimental conditions under which the optimal removal of BPA could be attained. From there the highest removal of BPA was found to be 95.73 % which was obtained at BPA concentration of 10 mg/L, ARSB-TiO2 dosage of 2 g/L, pH 2 and temperature 303 K. Further optimization of the process operation was done with the optimization tools Response Surface Methodology (RSM) and Artificial Neural Network (ANN). From the RSM study, the highest removal of BPA was found to be 99.91 % which was attained under the experimental conditions of pH 1.95, ARSB-TiO2 dosage of 2 g/L and contact time of 60 min. In case of ANN, the Levenberg-Marquardt back propagation algorithm was found to be the most suitable function for the optimization process. A radical quenching study was performed and from there it was observed that superoxide anion radical (center dot O2-) exhibited the highest effectivity for degrading BPA, followed by holes (H+) and hydroxyl radical (center dot OH). Lastly, a detailed comparative study was performed to compare the findings of the present study with that of the previously reported literatures.