Surfactant-assisted UV-photolysis of nitroarenes Claude A. Diehl a , Chad T. Jafvert a, * , Karen A. Marley b , Richard A. Larson b a School of Civil Engineering, Purdue University, West Lafayette, IN 47907-1284, USA b The Department of Natural Resources and Environmental Sciences, The University of Illinois, Urbana-Champaign, IL 61801-4723, USA Received 9 August 2000; received in revised form 3 January 2001; accepted 30 January 2001 Abstract Photochemical transformations (k ¼ 254 nm) of 2,4-dinitrotoluene (2,4-DNT) in aqueous solutions containing the cationic surfactant cetyltrimethylammonium (CTA) and the anionic nucleophile borohydride (BH  4 ) were investigated. The overall decay rate was enhanced at CTA concentrations above the critical micelle concentration (cmc) when stoichiometric excess BH  4 was present in solution. A kinetic model that separates the overall reaction rate into micellar and aqueous pseudo-phase components indicates transformation in micelles is 17 times faster that in the homoge- neous water phase under those conditions investigated. Intermediate products were identified by comparing the HPLC retention times and ultraviolet-visible absorption spectra of product peaks to those of analytical standards. 2-Methyl-5- nitroaniline, 4-nitrotoluene, 2-nitrotoluene, 4-methyl-3-nitroaniline, 2,4-diaminotoluene, o-toluidine, 1,3-dinitrobenzene, 3-nitroaniline, p-cresol, and 2,4-diaminophenol were identified as photo-transformation intermediates or prod- ucts. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Nitrotoluenes; Borohydride; Cetyltrimethylammonium bromide; Micelle 1. Introduction Large quantities of nitroaromatic compounds are produced each year by the munitions industry for use as explosives and byother industries for use as intermediates in the manufacture of dyes, pesticides, and polyurethane foams. Production of 2,4-dinitrotoluene, for example, was reported at 3:27  10 8 kg in 1982 (Boopathy and Kulpa, 1993). As a result of large production volumes, occurrence in the environment, toxicity, and environ- mental decay pathways through which even more toxic compounds may form (azo, azoxy, and nitroso com- pounds), this class of compounds is of great environ- mental concern. Industrial production of nitroaromatic compounds results in wastestreams that must be treated prior to discharge to the environment. In the manufacture of TNT for example, the crude TNT goes through a puri- fication step in which sodium sulfite (sellite) is added to sulfonate the other isomers of trinitrotoluene. The aqueous wash that remove the sulfonated compounds includes up to 5% of the 2,4,6-TNT product and is re- ferred to as redwater. Redwater consists of many com- pounds, some of which are sulfonated nitrotoluenes and dinitrotoluenes (2,4- and 2,6-isomers) (Kaye, 1978; Larson et al., 1996), and before the 1960s was dis- charged directly to the environment without treatment (Kaye, 1978). It has a blood red color and generally is incinerated as a hazardous waste at a 1993 cost of ap- proximately $600/ton (Grasso, 1993). Many alternate treatment methods have been suggested to treat red- water and other wastestreams that contain nitroaro- matic compounds including biological, zero-valent iron, and photochemical processes. The purpose of this study was to further exam- ine photochemical treatment methods using 2,4-DNT as a model contaminant. Impediments to photochemical Chemosphere 46 (2002) 553–560 www.elsevier.com/locate/chemosphere * Corresponding author. Tel.: +1-765-494-2196; fax: +1-765- 496-1107. E-mail address: jafvert@ecn.purdue.edu (C.T. Jafvert). 0045-6535/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0045-6535(01)00042-X