Determination of optimum extinction wavelength for paracetamol removal through energy efficient thin film reactor

Abstract

Paracetamol (PAM) mineralization through nano-composite thin film (TF) based photocatalytic system was investigated under variable operational conditions. The experiments were conducted using a non stirred flow through coated tubular quartz reactor (TQR). Elimination of energy demand arising from stirring and aeration through the developed TF reactor configuration was also among the main research interests. Ag-doped Si-TiO2 TFs were grown on Si-decorated inner surface of the TQR using sol-gel dip coating technique. The fabricated TF was characterized by SEM-EDS, TEM, AFM, XPS and UVvis spectroscopy methods. TF-based PAM mineralization kinetics were observed for both UVvis and UV wavelengths using pure, Si-Ti and Ag-doped Si-TiO2 TF(s). The direct and indirect optical ban gap energies (BGE) for the Ag doped Si-TiO2 TF were estimated to be 2.56 eV and 2.86 eV respectively. While no visible light activity was observed for pure TiO2 TF, Ag-doped Si-TiO2 TF exhibited significant PAM degradation activity for lambda > 400 nm with a k(obs) value of 2.1 +/- 0.1 10(-3) min(-1). In addition to known phenolic and carboxylated intermediates, UVvis spectroscopy, HPLC-MS and UPLC-MS/MS measurements indicated alpha-cyano-4-hydroxicinnamic acid (alpha PHC) formation as a result of photo-addition reactions under UV C irradiation. Experimental results also indicated that alpha PHC blocks h(+)/e(-) formation completely. Paracetamol could be degraded economically under UV B irradiation through the fabricated TF reactor without stirring, aeration or adding external electron acceptors. (C) 2016 Elsevier B.V. All rights reserved.