Photocatalytic treatment of 4-chlorophenol in aqueous ZnO suspensions: Intermediates, influence of dosage and inorganic anions

Abstract

The photocatalytically driven removal of eco-persistent 4-chlorophenol from water using ZnO is reported here. Kinetic dependence of transformation rate on operating variables such as initial 4-chlorophenol concentration and photocatalyst doses was investigated. A complete degradation of 4-chlorophenol at 50 mg L(-1) levels was realised in 3h. Analytical profiles on 4-chlorophenol transformation were consistent with the best-line fit of the pseudo zero-order kinetics. The addition of small amounts of inorganic anions as SO(4)(2-), HPO(4)(-), S(2)O(8)(2-) and Cl(-) revealed two anion types: active site blockers and rate enhancers. Fortunately, Cl(-) and SO(4)(2-) commonly encountered in contaminated waters enhanced the rate of 4-chlorophenol degradation. The reaction intermediates and route to 4-chlorophenol mineralisation were elucidated by combined RP-HPLC and GC-MS methods. In addition to previously reported pathway products of 4-chlorophenol photo-oxidation catechol was detected. A radical mechanism involving o-hydroxylation is proposed to account for the formation of catechol.

Antibacterial properties of F-doped ZnO visible light photocatalyst

“…As a result, in recent years continuous efforts have been made to develop innovative technologies in order to remediate polluted environment. Among them, photocatalysis serves as an attractive tool due to its efficiency and relatively low cost [4]. Currently the most widely used and studied photocatalyst is titanium dioxide (TiO 2 ).…”

Photocatalytic Degradation of 2,4-dichlorophenol in Irradiated Aqueous ZnO Suspension

“…Air was bubbled from the lower part of the apparatus by a specular draft tube hung vertically from the top of the reactor. Other features of the reactor have been described previously (Gaya et al, 2009). The apparatus was maintained at controlled temperature of 299 K by circulating water in and out of the outer jacket.…”

“…Similarly, in photodefluoridation of pentafluorobenzoic acid, the reaction rate was reduced by both HPO 4 2-and SO 4 2-and accordingly, the former demonstrated the highest inhibition (Ravichandran et al, 2007). The mechanism of rate inhibition by HPO 4 2-has not been clear but the blockage of the active sites of the semiconductor particles has recently been suggested (Gaya et al, 2009). The reduction in removal rate in presence of Cl -and SO 4 2-has been attributed to the scavenging of hydroxyl radical by these anions as shown in Eq.…”

“…A wide range of chloroaromatics have been eliminated by this process utilising mainly TiO 2 and ZnO as semiconductor photocatalyst (Djebbar and Sehili, 1998;Konstantinou et al, 2001;Bahnemann et al, 2007;Gaya et al, 2009;Meng et al, 2002). We are prompted to report our investigation of the photocatalytic degradation of DCP over ZnO photocatalyst for the following reasons.…”

Enhanced Removal of Trichloroethylene in Water Using Nano-ZnO/Polybutadiene Rubber Composites

“…In the last three decades, heterogeneous photocatalytic oxidation processes with TiO 2 -based materials and binary oxides have been investigated for the remediation of water resources contaminated by recalcitrant hydrocarbons [1][2][3][4][5][6][7][8][9][10][11]. These studies have reported that highly reactive transitory species (e.g., superoxide radical (O 2 · − ), hydroxyl radicals (·OH), and hydrogen peroxide (H 2 O 2 )) involved in the heterogeneous photocatalytic reactions effectively degrade various ambiguous…”