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

• PAM degradation kinetics and intermediates was investigated by a novel TiO2 TF.
• Energy efficient alternative treatment strategies were successfully determined.
• Reaction rates and intermediates were investigated for both UVvis and UV wavelengths.
• UVvis activity of Ag-Ti nanocomposite was improved by an outer Si core shell.
• A new h+ blocking activity was identified.

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 λ > 400 nm with a kobs 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 α-cyano-4-hydroxicinnamic acid (αPHC) formation as a result of photo-addition reactions under UV C irradiation. Experimental results also indicated that αPHC 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.