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Purpose The purpose of this study was to the synthesis of Fe3O4@SiO2 nanocomposites and using it as an adsorbent for removal of diazinon from aqueous solutions. Structural characteristics of the synthesized magnetic nanocomposite were described by Fourier transform infrared spectroscopy and scanning electron microscopy. Design/methodology/approach The effects of different parameters including pH (2-10), contact time (1-180 min), adsorbent dosage (100-2000 mg L−1) and initial diazinon concentration (0.5–20 mg L−1) on the removal processes were studied. Finally, isotherm and kinetic and of adsorption process of diazinon onto Fe3O4@SiO2 nanocomposites were investigated. Findings The maximum removal efficiency of diazinon (96%) was found at 180 min with 1000 mg L−1 adsorbent dosage using 0.5 mg L−1 diazinon concentration at pH = 7. The experimental results revealed that data were best fit with the pseudo-second-order kinetic model (R2 = 0.971) and the adsorption capacity was 10.90 mg g−1. The adsorption isotherm was accordant to Langmuir isotherm. Originality/value In the present study, the magnetic nanocomposites were synthesized and used as an absorbent for the removal of diazinon. The developed method had advantages such as the good ability of Fe3O4@SiO2 nanocomposites to remove diazinon from aqueous solution and the magnetic separation of this absorbent that make it recoverable nanocomposite. The other advantages of these nanocomposites are rapidity, simplicity and relatively low cost.

a b s t r a c tToday, environmental pollution by various pollutants such as dyes is one of the most important issues of the world. Colored wastewaters are entering to the environment by many industries (for instance, textile and paper industries). Various technologies have been used to remove these pollutants. In this study, we have demonstrated the effectiveness of bentonite nanoparticles as a low cost adsorbent for removal of Reactive Yellow 15 (RY15) and Reactive Yellow 42 (RY42). The effects of variables such as pH, contact time, dye concentrations, adsorbent dosage and solution temperature, on the removal process have been studied. Residual of RY15 and RY42 dyes concentration was measured using a spectrophotometer set in 420 and 430 nm wavelengths, respectively. Also, the bentonite nanoparticles were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and Brunauer-Emmett-Teller. Finally, the data were examined by isotherms of Langmuir, Freundlich, pseudo-first-order and pseudo-second-order kinetics and thermodynamic parameters. The maximum amount of adsorption for both dyes was at the pH = 3. With increasing the contact time and concentration of dye, adsorption capacity increased as well. Also, increasing the adsorbent dosage resulted decreasing the adsorption capacity. In optimum conditions, the maximum absorption capacity was 156.9 mg/g for RY15 and 170.7 mg/g for RY42. It was shown that removal of dyes of RY15 and RY42 follow, respectively, Freundlich isotherm and Langmuir isotherm and pseudo-second-order kinetics. The results of examining temperature and thermodynamics of the process showed that ΔS° and ΔH° are negative for both dyes. However, ΔG° was positive or negative for different temperatures. Since bentonite nanoparticles of this research were effective, cheap and available, so it can be used as an effective adsorbent for removal of RY15 and RY42.

The purpose of this study was to examine the nitrate adsorption by cobalt ferrite (CFO) nanoparticles. The adsorbent was synthesized by co-precipitation method and its structure was characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and Vibrating-Sample Magnetometer (VSM). In batch adsorption studies, the effects of various parameters like pH (3–11), adsorbent dose (0.2–0.8 g/L), contact time (5–120 min), initial nitrate concentration (50–200 mg/L), and temperature (283–313 K) on the adsorption process were examined. The results of this study indicated that the maximum adsorption capacity was 107.8 mg/g (optimum condition pH = 3, adsorbent dosage: 0.2 g/L, nitrate concentration: 200 mg/L, contact time: 20 min and temperature 313 K). The adsorption isotherm had a proper match with Langmuir (R2 = 0.99) and Freundlich (R2 = 0.99) models. The adsorption of nitrate by CFO has followed pseudo second-order kinetics. The results of the thermodynamics of the nitrate adsorption process by CFO showed that all the values of ΔG, ΔH and ΔS were positive. Therefore, this process was endothermic and non-spontaneous.