Research paper Surface interactions of pyrene and phenanthrene on Cu-montmorillonite Hadas Joseph-Ezra, Ahmed Nasser ⁎, Uri Mingelgrin Institute of Soils, Water and Environmental Sciences, ARO, Volcani Center, PO Box 6, Bet Dagan 50250, Israel abstract article info Article history: Received 11 December 2013 Received in revised form 20 April 2014 Accepted 29 April 2014 Available online xxxx Keywords: Abiotic degradation Cu-montmorillonite PAH Phenanthrene Pyrene The feasibility of promoting degradation of pyrene and phenanthrene (PHE) at the surface of soil minerals is demonstrated. Samples of magnetite, birnessite, Na-montmorillonite and Cu-montmorillonite (Cu-Mt) were loaded with pyrene and PHE. While no significant degradation of the PAHs was observed on Na- montmorillonite, birnessite or magnetite, considerable degradation took place on Cu-Mt loaded with pyrene (60 ± 2% in 24 h). The initial load of pyrene affected the extent of degradation, with the highest degradation rate observed at a load of 1000 μg/g clay mineral. Pyrene degradation on Cu-Mt was inhibited by grinding the loaded mineral as well as by wetting it. Loading PHE on Cu-Mt resulted in little degradation of the PAH, but when the clay mineral was loaded with pyrene and PHE together, the degradation of pyrene was enhanced as compared to its degradation in the absence of PHE. The degradation of PHE may be inhibited by its higher ioni- zation potential which reduces its tendency to participate in electron transfer reactions. The observed difference between the two PAHs in their affinity to various sites on the mineral's surface may also contribute to the dispar- ity in their tendency to degrade at the surface. In experiments performed on soil samples mixed with Cu-Mt and loaded with the PAHs, patterns of degradation similar to those on the mineral itself were observed, but with lower degradation rates than those on neat Cu-Mt. LC–MS analysis revealed that pyrene underwent on Cu-Mt ox- idation as well as dimerization. Elemental analysis conducted by SEM–EDS, revealed that both PHE and pyrene displayed a higher affinity to the edges of the clay mineral particles than to their planar surfaces. PHE displayed a higher affinity than pyrene to Cu-Mt, both at the planar surfaces and at the edges of the particles of the clay min- eral. The surface sites which displayed the highest affinity to the PAHs were not catalytically active and hence, loading Cu-Mt with a PHE and pyrene mixture resulted in saturation of the more strongly adsorbing sites with PHE and the diversion of more pyrene molecules to the catalytically active sites. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are widespread organic pollutants, created by the incomplete combustion of organic matter. PAHs pose a significant danger to human health due to their recalci- trance in the environment and their carcinogenic potential (Jenning, 2012). The PAHs pyrene and phenanthrene (PHE) were frequently de- tected as contaminants in soils (e.g., Harayama, 1997). Removal of PAHs from soils is often necessary because of their resistance to break- down by natural processes and their resultant slow attenuation (ATSDR, 1995). There are many methods for enhancing the degradation of organic pollutants in the soil, and most are based on biological proce- dures (e.g., Khan et al., 2004). However, biological breakdown methods often display shortcomings such as a slow removal of the organic sub- strate or relatively high concentrations of residues remaining in the soil at the end of the process (Mulder et al., 2001). PAHs, due to their hy- drophobic nature and resultant low solubility, tend to sorb to the organ- ic fraction of soils. This sorption increases their resistance to microbial degradation (Alexander, 2000; Mulder et al., 2001). It is expedient, therefore, to develop complementary, abiotic remediation methods and those are being pursued by various groups (e.g., Manariotis et al., 2011; Usman et al., 2012; Yap et al., 2012). Montmorillonite, manganese oxides and iron oxides are common soil minerals and are known to induce abiotic transformations of organ- ic pollutants, including hydrolysis, oxidation–reduction or rearrange- ment (e.g., Di Leo, 2000; Jia et al., 2012; Mingelgrin and Saltzman, 1979; Mortland and Halloran, 1976; Nasser et al., 1997, 2000, 2009; Nasser et al., 2012; Pizzigallo et al., 1995). Hinedi et al. (1993) studied the degradation of benzene on Cu-montmorillonite (Cu-Mt) and report- ed that when benzene molecules came in contact with Cu ions, free radicals formed, causing rapid oxidation and polymerization of the ben- zene. The possibility that a similar process occurs when PAH molecules interact with Cu-Mt is investigated in the present study. The overall objective of this work is to demonstrate that it is possible to degrade PAHs by bringing them in contact with common minerals and to establish the potential of abiotic processes to remediate soils con- taminated by PAHs. The impact of applying a mechanical force to Cu-Mt loaded with pyrene, PHE or a mixture of both, on the surface-enhanced degradation of the PAHs was explored. Applied Clay Science xxx (2014) xxx–xxx ⁎ Corresponding author. Tel.: +972 39683306; fax: +972 39683301. E-mail address: nasser@volcani.agri.gov.il (A. Nasser). CLAY-03011; No of Pages 9 http://dx.doi.org/10.1016/j.clay.2014.04.037 0169-1317/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Please cite this article as: Joseph-Ezra, H., et al., Surface interactions of pyrene and phenanthrene on Cu-montmorillonite, Appl. Clay Sci. (2014), http://dx.doi.org/10.1016/j.clay.2014.04.037