Synthesis of a chromium terephthalate metal organic framework and use as nanoporous adsorbent for removal of diazinon organophosphorus insecticide from aqueous media

MIL-101(Cr), as a chromium terephthalate metal organic framework (MOF), is synthesized hydrothermally and used for removal of diazinon from aqueous media. Different methods such as FT-IR, FE-SEM, TGA, XRD and BET analysis were applied for characterization of prepared MIL-101(Cr). The results revealed that MIL-101(Cr) has octahedral structure, 96% crystallinity, thermal stability up to 550 degrees C and about 2600 m(2)/g BET surface area with microporous structure. Adsorption experiments were designed by Design expert software and the effect of parameters such as pH (2-10), temperature (25-61 ), contact time (5-85 minutes) and adsorbent dosage (0.1-0.9 g/L) was investigated. Adsorption process was optimized by response surface methodology (RSM) and the optimum conditions of adsorption process was achieved in pH 6.5, temperature 25 degrees C, contact time 64 minutes and adsorbent dosage 0.74g/L which is lead to 96% removal of diazinon. In order to investigate the reusability and life time of MIL-101(Cr), the adsorbent is used in five successive cycles for adsorption of diazinon in fresh samples and good results are obtained. Langmuir and Freundlich isotherm models were deliberated by adsorption equilibrium data and Langmuir model show better conformity (R-2 = 0.985) with the experimental results. Kinetic study was carried out using pseudo first order, pseudo second order and intraparticle diffusion kinetic models. Experimental data were better fitted to the pseudo second order with a correlation coefficient of 0.997 which signified that the experimental outcome of the adsorption of diazinon was a chemical adsorption.