Journal of Photochemistry and Photobiology A: Chemistry 242 (2012) 1–12 Contents lists available at SciVerse ScienceDirect Journal of Photochemistry and Photobiology A: Chemistry journa l h o me pa g e: www .elsevier.com/locate/jphotochem Inﬂuence of substituent type and position on photooxidation of phenolic compounds: Response surface methodology approach Hrvoje Kusic ∗ , Natalija Koprivanac, Sanja Papic, Ana Loncaric Bozic ∗∗ Faculty of Chemical Engineering and Technology, University of Zagreb, Marulicev trg 19, Zagreb 10000, Croatia a r t i c l e i n f o Article history: Received 11 April 2012 Received in revised form 14 May 2012 Accepted 22 May 2012 Available online 1 June 2012 Keywords: Wastewater Phenols Photooxidation Response surface modeling Structural relationship a b s t r a c t The combined inﬂuence of process (pH and [H 2 O 2 ]) and structural (substituent type and position) param- eters inﬂuencing the degradation of phenolic pollutants in water by UV/H 2 O 2 processes is studied using modiﬁed miscellaneous 3 4 full factorial design and response surface methodology (RSM). The model wastewaters consisted of eight phenolic pollutants containing hydroxyl (–OH), chloro (–Cl), nitro (–NO 2 ), and methyl (–CH 3 ) substituents in ortho and para position. It was determined that all studied phenols obey ﬁrst-order degradation kinetic, which is inﬂuenced signiﬁcantly by all studied process and structural parameters. The quadratic polynomial model is used to describe these effects. Different optimal operat- ing conditions and values of observed ﬁrst-order degradation rate constants (k obs ) were determined for each of the phenolic pollutants indicating the signiﬁcant inﬂuence of type and position of substituent to parent pollutant degradation and structurally determined degradation pathway. k obs were correlated with the second-order degradation rates with hydroxyl radicals (k HO • ) as well as with several physical and structure related properties of studied phenolics using Spearman rank coefﬁcient. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Among single-benzene ring organic pollutants generated by man-made activities, a sizable fraction pertains to phenolic com- pounds. Phenols are widely used in various industries such as chemical, agriculture, pharmaceutical, food, dyestuff, petrochem- ical etc., and they represent a direct and serious threat to all living organisms in aquatic systems and soil [1,2]. According to U.S. EPA [3] and European Commission [4] phenols, chloro- and nitro-substituted phenols are characterized as the priority pollu- tants. They are hardly biodegradable and difﬁcult to remove from the environment, and moreover highly toxic, mutagenic and car- cinogenic [3–8]. Considering the need for environmental protection, the promis- ing option for removal of such toxic and non-biodegradable organic compounds from industrial wastewaters, which could overcome the shortcomings of common treatment technologies, are advanced oxidation technologies (AOTs) [8,9]. Nowadays, AOTs have received increased interest due to their potential to completely oxidize the majority of organics present in the water [9,10]. Among various types and combinations of AOTs, photochemical processes based on usage of strong oxidants, e.g. H 2 O 2 , are shown to be suitable for ∗ Corresponding author. Tel.: +385 1 4597 160; fax: +385 1 4597 143. ∗∗ Corresponding author. Tel.: +385 1 4597 123; fax: +385 1 4597 143. E-mail addresses: hkusic@fkit.hr (H. Kusic), abozic@fkit.hr (A. Loncaric Bozic). the degradation of various phenols and other aromatic pollutants [5,6,11–14]. All AOTs, including UV/H 2 O 2 process, are multifactor systems. The efﬁciency of UV/H 2 O 2 strongly depends on process parame- ters such as operating pH, concentration of H 2 O 2 , radiant power, effective length path, ﬂow regime, characteristics of wastewater (structure of targeted pollutants, presence of HO • scavengers and suspended solids) [15]. The optimization of such system is com- plex and often rather costly. In order to reduce laboratory studies and save time and money, the application of modeling tools in combination with experimental approach, such as: artiﬁcial neural networking, mechanistic modeling, structure–activity relationship modeling, or response surface modeling, is favorable. The latter is appropriate method for soft modeling of complex systems such as UV/H 2 O 2 process. It involves the interactions between considered process factors, does not require involvement of complex degra- dation schemes, and does not consider large number of pollutants [11,16]. In this study UV/H 2 O 2 process was applied for the degrada- tion of substituted phenols containing hydroxyl (–OH), chloro (–Cl), nitro (–NO 2 ), and methyl (–CH 3 ) groups in ortho and para posi- tion. In order to investigate the combined inﬂuence of process parameters and wastewater characteristics on the degradation efﬁciency a modiﬁed miscellaneous 3 4 full factorial design and response surface methodology were employed. The intention was to correlate the degradation rates and determined opti- mal pH and [H 2 O 2 ] with the structural characteristics of studied phenols. 1010-6030/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jphotochem.2012.05.026