Jyoti P. Ghosh 1 Gopal Achari 1 Cooper H. Langford 2 1 Department of Civil Engineering, University of Calgary, Calgary, Alberta, Canada 2 Department of Chemistry, University of Calgary, Calgary, Alberta, Canada Research Article Reductive Dechlorination of PCBs Using Photocatalyzed UV Light Feasibility of photocatalytic dechlorination of PCB-138 and Aroclor-1254 using platinum loaded TiO 2 (P25) in an alkaline 2-propanol medium has been investigated. Experiments were conducted in batch mode using a Rayonet photo-reactor under aerated and deaerated conditions with black lamps emitting around 350 nm as light source. Two forms of platinum deposition were investigated: Photochemically loaded P25 as well as addition of potassium hexachloroplatinate into the reaction medium. Partial dechlorination of PCBs was observed after 7 h of irradiation with pure TiO 2 as catalyst when the reaction vessel was kept open to air. Complete dechlorination was observed after 5 h of irradiation in a deaerated environment. Enhanced photocatalytic efficiency was observed when platinum deposited P25 was used as catalyst, with the best result being obtained when aqueous potassium hexachloroplatinate was added into the reaction medium. Lower potassium hexachloroplatinate concentration (0.1 mM) yielded better performance. Keywords: Deaerated environment; Hexachloroplatinate; Photocatalyst; Photochemistry; TiO 2 Received: April 4, 2011; revised: July 20, 2011; accepted: August 10, 2011 DOI: 10.1002/clen.201100186 1 Introduction Photochemical dechlorination of PCBs in alkaline 2-propanol (IPA) using 254-nm UV light leads to complete dechlorination within a short period of time. The chemistry of dechlorination is a chain reaction, that has a quantum yield >1 [1, 2]. As this is an efficient photolytic reaction with no chemicals being further required, it is an attractive option for scaling the technology to field use [3]. In our attempt to make the technology more affordable by lowering the cost of energy per order of dechlorination we investigate here the possibility of using longer wavelength light sources. The dechlori- nation mechanism of PCBs as elucidated by [1] is a chain reaction initiated in alkaline 2-propanol following an excitation and cleavage of PCB (Ar-Cl) into Ar and Cl radicals. The highly reducing ketyl radical anion, generated by the abstraction of hydrogen from the 2- propanol followed by loss of proton, transfers an electron to a PCB molecule that results in a cleavage leading to the ejection of the chloride ion from the PCB molecule, forming a radical (Ar . ). The Ar radical can abstract an H atom from alkaline 2-propanol to regen- erate the ketyl radical anion and the chain reaction proceeds. This suggests that any chemistry that can lead to abstraction of a hydro- gen atom from 2-propanol in an alkaline medium could start the chain reaction and dechlorinate PCBs. TiO 2 , a known photocatalyst [4] has been used to dechlorinate PCBs using conventional 365-nm Hg vapor lamps [5, 6]. The pathway of dechlorination passed through oxidation with hydroxylated inter- mediates. These investigations focused on PCBs in aqueous media and none of them reported 100% dechlorination. Reductive dechlori- nation of PCBs (i.e., by electron transfer) from excited TiO 2 has not yet been attempted. Reductive dechlorination of PCBs using TiO 2 based photocatalysis has the potential to lower the energy required to dechlorinate PCBs. The quantum efficiency of TiO 2 is limited by elec- tron hole recombinations [7]. Deposition of a noble metal such as Pt, Ag, Au on to TiO 2 surface is known to increase the photocatalytic efficiency significantly by ensuring that the electron hole combination is delayed [8–11]. The objective of this study is to investigate the feasibility of reductively dechlorinating PCB using TiO 2 and platinum deposited TiO 2 under 350 nm UV light irradiation. The effectiveness of platinum deposition on TiO 2 was studied in two ways: (i) Platinum deposited on TiO 2 under irradiation at 350 nm and (ii) by adding hexachloroplatinate directly in an alkaline IPA–PCB–TiO 2 slurry. 2 Materials and methods 2.1 Materials The following chemicals and materials were procured and used as received: IPA (ACS grade) from VWR International, P25 TiO 2 from Degussa Corporation, reagent grade (98%) potassium hexachloro- platinate from Sigma–Aldrich, PCB-138, and Aroclor-1254 from Chromatographic Specialties Inc. and Fisher Scientific, ultra high purity nitrogen from Praxair Inc., 97% pure sodium hydroxide from BDH Inc. and Filtropur S/S 0.2-mm syringe filter from Sarstedt Aktiengesellschaft & Co. Ultrapure water was used as a solvent for NaOH and potassium hexachloroplatinate. 2.2 Photoreactor A Rayonet photoreactor equipped with 14’’,8-W black lamps (output centered at 350 nm) was used for the experiments. The reaction Correspondence: Dr. G. Achari, Department of Civil Engineering, University of Calgary, Calgary, Alberta, T2N1N4 Canada E-mail: gachari@ucalgary.ca Clean – Soil, Air, Water 2012, 40 (5), 455–460 455 ß 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com