The study was carried out with the objective of developing suitable and sustainable low cost adsorbent materials for diazinon, an organophosphate pollutant used as a pesticide. Montmorillonite modified with iron was used. Two different types of iron-montmorillonite, each having different contents of iron and synthesized with different pH and levels of Fe hydrolysis were used. One was denoted “Fe-modified” and the other denoted as “FeOH-modified”. The color of the samples changed from greyish green to light-reddish brown after the modification. X-ray diffraction and physical observations were used for characterization of the samples. The d-spacing of the samples was greater than 15 ?, indicating the formation of iron hydroxides in the interlayer space of montmorillonite. The amount of adsorption was calculated from the difference between the initial and the final concentration of diazinon. The adsorption data were analyzed using the Langmuir adsorption isotherms. The amounts of diazinon adsorbed were 58.8 and 54.1 mmolkg-1 for Fe-modified and FeOH-modified respectively. The steep rise in their adsorption isotherms indicated the possibility of adsorption for low level of diazinon in polluted water.
 G. Z. Memon, M. I. Bhanger, M. Akhtar, F. N. Talpur and J. R. Memon, “Adsorption of Methyl Parathion Pesticides from Water Using Water Melon Peels as a Low Cost Adsorbent,” Chemical Engineering Journal, Vol. 138, No. 1-3, 2008, pp. 616-612.
 P. C. H. Li, E. J. Swason and F. A. P. C. Gobas, “Diazinon and Its Degradation Products in Agricultural Water Courses in British Columbia, Canada,” Bulletin of Environmental Contamination and Toxicology, Vol. 69, No. 1, 2002, pp. 59-65.
 H. Shemer and K. G. Linden, “Degradation and By-Product Formation of Diazinon in Water during UV and UV/ H2O2 Treatment” Journal of Hazardous Materials, Vol. 136, No. 3, 2006, pp. 553-559.
 “Diazinon: Phase out of All Residential Uses of the Insecticide,” 2011.
 E. Iglesias-Jimenez, M. J. Sanchez-Martin and M. Sanchez-Camazano, “Pesticide Sorption in a Soil-Water System in the Presence of Surfactants,” Chemosphere, Vol. 32, No. 9, 1996, pp. 1771-1782.
 L. Nemeth-Konda, G. Füleky, G. Morovjan and P. Csokan, “Sorption Behaviour of Acetochlor, Atrazine, Carbendazim, Diazinon, Imidacloprid and Isoproturon on Hungarian Agricultural Soil,” Chemosphere, Vol. 48, No. 5, 2002, pp. 545-552.
 J. Lemic, D. Kovacevic, M. Tomasevic-Canovic, D. Kovacevic, T. Stanic and R. Pfend, “Removal of Atrazine, Lindane and Diazinone from Water by Organo-Zeolites,” Water Research, Vol. 40, No. 5, 2006, pp. 1079-1085.
 B. Sawhney and S. Singh, “Sorption of Atrazine by Aland Casaturated Smectite,” Clays and Clay Minerals, Vol. 45, No. 3, 1997, pp. 333-338.
 M. Sa′nchez-Camazano and M. Sa′nchez-Marti′n, “Hydrolysis of Azinphosmethyl Induced by the Surface of Smectites,” Clays and Clay Minerals, Vol. 39, No. 6, 1991, pp. 609-613.
 D. A. Laird, E. Barriuso, R. H. Dowdy and W. C. Koskinen, “Adsorption of Atrazine on Smectites,” Soil Science Society of America Journal, Vol. 56, No. 1, 1992, pp. 62-67. http://dx.doi.org/10.2136/sssaj1992.03615995005600010010x
 G. Rytwo, S. Nir and L. Margulies, “A Model for Adsorption of Divalent Organic Cations to Montmorillonites: Adsorption Studies and Model Calculations,” Journal of Colloid and Interface Science, Vol. 181, No. 2, 1996, pp. 551-560. http://dx.doi.org/10.1006/jcis.1996.0412
 A. Pusini, I. Braschi and C. Gessa, “Adsorption and Degradation of Triasulfuron on Homoionic Montmorillonites,” Clays and Clay Minerals, Vol. 48, No. 1, 2000, pp. 19-25. http://dx.doi.org/10.1346/CCMN.2000.0480103
 L. Margulies and H. Rozen, “Adsorption of Methyl Green on Montmorillonite,” Journal of Molecular Structure, Vol. 141, 1986, pp. 219-226.
 P. X. Wu ,W. M. Wu , S. Z. Li, N. Xing, N. W. Zhu, P. Li, J. H. Wu, C. Yang and Z. Dang, “Removal of Cd2+ from Aqueous Solution by Adsorption Using Fe-Montmorillonite,” Journal of Hazardous Materials, Vol. 169, No. 1-3, 2009, pp. 824-830.
 E. G. Rightor, M. S. Tzou and T. J. Pinnavaia, “Iron Oxide Pillared Clay with Large Gallery Height: Synthesis and Properties as a Fischer-Tropsch Catalyst,” Journal of Catalysts, Vol. 130, No. 1, 1991, pp. 29-40.
 P. Yuan, F. Annabi-bergaya, Q. Tao, et al., “A Combined Study by XRD, FTIR, TG and HRTEM on the Structure of Delaminated Fe-Intercalated/Pillared Clay,” Journal of Colloid Interface Science, Vol. 324, No. 1-2, 2008, pp. 142-149. http://dx.doi.org/10.1016/j.jcis.2008.04.076
 J. L. Marco-Brown, C. Martín Barbosa-Lema and R. M. Torres Sánchez, “Adsorption of Picloram Herbicide on Iron Oxide Pillared Montmorillonite,” Applied Clay Science, Vol. 58, 2012, pp. 25-33.
 N. Kozaia, K. Inadab, Y. Adachib, S. Kawamurab, Y. Kashimotob, T. Kozakib, S. Satob, T. Ohnukia, T. Sakaic, T. Satoc, M. Oikawac, F. Esakad and H. Mitamura, “Characterization of Homoionic Fe2+-Type Montmorillonite: Potential Chemical Species of Iron Contaminant,” Journal of Solid State Chemistry, Vol. 180, No. 8, 2007, pp. 2279-2289.
 J.-P. Jolivet, C. Chanéac and E, Tronc, “Iron Oxide Chemistry. From Molecular Clusters to Extended Solid Networks,” Chemical Communications, No. 5, 2004, pp. 481-483. http://dx.doi.org/10.1039/b304532n
 T. Grygar, D. Hradil, P. Bezdicka, B. Dousova, L. Capek and O. Schneeweiss, “Fe(III)-Modified Montmorillonite and Bentonite: Synthesis, Chemical and UV-Vis Spectral Characterisation, Arsenic Sorption and Catalysis of Oxidative Dehydrogenation of propane,” Clays and Clay Minerals, Vol. 55, No. 2, 2007, pp. 165-176.