Iranian Journal of

Background and Objective: The activities of various industries produce a wide range of pollutants and toxic compounds. One of these compounds is the catechol, a cyclic organic compound with high toxicity and resistant to degradation. Therefore, the purpose of this study was to investigate efficiency of powder activated carbon magnetized with Fe₃O₄ nanoparticles in the removal of catechol from aqueous solutions by response surface methodology.
Materials and Methods: The co-precipitation method was used to synthesize magnetic powder activated carbon and its properties were analyzed by SEM and XRD analysis. Then, the effect of the parameters such as pH, contact time, absorbent dose, initial concentration of catechol and temperature on the efficiency of adsorption process were investigated using a response surface methodology (Box–Behnken). The residual concentration of catechol was measured by HPLC at 275 nm.
Results: The results showed that the maximum efficiency of the adsorption process was obtained at concentration of 20 mg/L, pH=3, contact time 90 minutes, at 25 °C and absorbent dose of 1.5 g/L. The study of isotherm and kinetics showed that the experimental data of the catechol adsorption process correlated with the Langmuir and pseudo-second order models, respectively. Thermodynamic study of the reaction also expresses the Exothermic and Spontaneous process.
Conclusion: The results showed that the adsorption process using powder activated carbon magnetized with Fe₃O₄ nanoparticles at acidic pH had better efficiency. As a result, the studied process as an effective, rapid and inexpensive method for removal of catechol from aqueous solutions is proposed. Due to its short reaction time, it is economically affordable process.
 

Background and Objective: Due to the existence of industries such as stainless steel, the presence of nickel (II) ions in water and wastewater has been reported at high concentrations. Removal of nickel (II) ions from wastewater and the environment are of primary importance. In this study, iron (III) oxide nanoparticles were studied as an adsorbent for removal of Ni (II) ions from water in the batch equilibrium system.
Materials and Methods: FT-IR, SEM and XRD techniques were used to characterize the structure of the sample. To determine the optimum adsorption, the effect of important parameters such as pH, contact time, adsorbent weight and initial concentration were investigated. Also, thermodynamic study (Gibbs standard energy variations, enthalpy and entropy), isothermal studies (absorption capacity) and kinetic studies (absorbent effect with time) were investigated.
Results: The results showed that the magnetic adsorbent had the highest removal efficiency of nickel (II) at pH 7, contact time 60 min, adsorbent dosage of 200 mg, and maximum removable concentration of 400 mg/L.
Conclusion: With thermodynamic studies, it was determined that the reaction was endothermic and the spontaneous process was controlled using the entropy factor (ΔG°=-2.7 KJ/mol, ΔS°=+165.17 J/mol.K). In order to better understand the mechanism of adsorption, kinetics studies were carried out using the pseudo-first-order and pseudo-second-order models. Then, Langmuir and Freundlich adsorption isotherms were investigated to determine the adsorption capacity, and it was found that the adsorption data were well fitted to Freundlich model and the maximum adsorption capacity was 43.5 mg/g, which indicated high adsorption capacity and its multi-layers.Then, Langmuir and Freundlich adsorption isotherms were investigated and it was found that the adsorption data were well fitted to Freundlich model and maximum adsorption capacity (q_max=43.5 mg/g) was obtained which indicates good adsorption capacity of adsorbent and its multi-layers.
 

Background and Objective: In the present research, the synthesis and characterization of ZnS nanoparticles in zinc blend crystallite phase via hydrothermal method were reported. Advanced oxidation processes using nanophotocatalysts are one of the most efficient methods for removing the dyes with complex organic compounds from textile and industrial wastewaters. The photocatalytic performance of nanoparticles is drastically affected by their structural and optical properties. One of the most important features affecting the photocatalytic degradation of nanoparticles is their optical bandgap width, which is an important factor in the radiant photons in the visible and UV region and the production of active radicals to destroy the complex carbon pollutants. The optical bandgap width, like other properties of nanoparticles is affected by three important geometric parameters, including particle size, dimension and shape. It is also a function of synthetic chemistry, i.e. the precursors and the fabrication methods. The aim of the present study was to investigate the nanostructure of zinc-sulfide synthesized nanoparticles, optical properties and photocatalytic effect on the degradation of Methylene Orange dye.
Materials and Methods: The experiment of degradation of dye consisted of 70 mg of synthesized nanoparticles in 100 mL of dye solution containing 3.75 ppm of Methylene Orange dye at pH = 5.5. The experimental steps were repeated three times. Nanostructure characterization of three-dimension ZnS nanoparticles was specified by X-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, transmission electron microscopy, Furrier transform infrared, ultraviolet-visible spectroscopy and N₂ adsorption-desorption.
Results: The lattice characteristics such as density, specific surface area, size, strain, stress and deformation energy density are specified using Williamson-Hall (W-H) and Halder-Wagner (H-W) analysis. The photocatalytic degradation rate (k) of Methylene Orange was calculated to be 0.052 1/min, whilst after 60 minutes about 95% of the dye was photodegraded. The N₂ adsorption-desorption calculations determined the mean pore diameter, specific surface area (S_BET) and total porosity volume as 20.69 nm, 19.12 m²/g and 0.065 m³/g, respectively. The bandgap of fabrication ZnS has been evaluated from the Tauc's equation to be 3.47 eV. Compared with ZnS nanoparticles made by the hydrothermal method in the wurtzite crystallite phase (sample 2), the synthesized sample (sample 1) shows less lattice strain and stress, less crystallite size and also revealed the higher photocatalytic activity.
Conclusion: The pure zinc-sulfide nanoparticles without metal or ceramic dopants in the cubic zinc-blend crystallite phase are synthesized using the hydrothermal method. The precursors used in the synthesis of zinc-sulfide nanoparticles include zinc chloride and thioacetamide in the presence of oleic acid as a collecting agent. High photocatalytic activity of ZnS nanoparticles was confirmed by the degradation or dechlorination of Methylene Orange solution under UV light irradiation. Compared to similar studies, the results show that reducing the optical bandgap from 3.84 eV to 3.47 eV increases the degradation rate from 0.031 to 0.052. In this study, it was shown that synthesized zinc-sulfide nanoparticles by hydrothermal method, was able to decrease optical gap bandwidth and subsequently increased photocatalytic activity.

Background and Objective: With increasing water pollution, serious water shortages and increased pressure to save water, recycling and reuse of water has attracted more attention in various industries. Removal of silica from cooling water is essential for recycling and reuse of water. The aim of this study was to remove silica from water using magnesium oxide nanoparticles (MgO) synthesized by chemical deposition method.
Materials and Methods: Synthetic nanoparticles were successfully determined using field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FTIR) and X-ray diffraction (XRD). To determine the optimal adsorption conditions the batch system, the effect of important parameters such as pH (2-8), contact time (0-150 min), initial concentration of silica solution (50-1000 mg/L), adsorbent amount (0.01-0.14 g) and temperature (25-60 ˚C) were studied.
Results: Under optimal conditions, an almost removal of 200 mg/L silica solution was achieved in 60 min reaction time. Equilibrium data were analyzed using the Langmuir and Freundlich isotherms. The adsorption process can be well described by the Langmuir model, and the maximum adsorption capacity was calculated as 75.76 mg/g. Synthetic data were analyzed using pseudo-first-order and pseudo-second-order equations. The pseudo-second-order model showed good agreement with the obtained data (R² = 0.9949).
Conclusion: Due to the high potential of magnesium oxide nanoparticles in silica removal, it can be a good candidate for the removal of silica and industrial wastewater treatment.
 

Background and Objective: This study aimed to provide an effective electro-catalytic system for the simultaneous reduction of nitrate and disinfection of contaminated water by the electro-catalytic performance of Ni-Fe/Fe₃O₄ cathode.
Materials and Methods: At first, the Ni-Fe electrode was synthesized by the electro-deposition process. Then its physical properties were analyzed by scanning electron microscopy (FESEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, and photoelectron X-ray spectroscopy (XPS). Simultaneous disinfection and reduction of nitrate were performed under the following conditions: 15 mg Fe₃O₄ nanoparticles, pH 6.5, NaCl 10 mM, 50 mg/L nitrate, 10⁵ CFU/mL and current density 4 mA/cm².
Results: According to the results obtained in the absence of nitrate, 100 % of Escherichia coli bacteria were disinfected after 12 minutes. In the presence of nitrate, the time of complete disinfection increased to 120 minutes. In the absence of bacteria, 83% of nitrate was removed in 240 minutes, and in the presence of bacteria, the nitrate reduction efficiency increased slightly to 88%. In the nitrate reduction process, nitrite (0.22 mg/L) and ammonium (3.6 mg/L) were produced. In the presence of bacteria, the amounts of nitrite and ammonium produced increased to 0.42 mg/L and 7.3 mg/L.
Conclusion: The results show the outstanding ability of Ni-Fe/Fe₃O₄ electrode in electro-catalytic reduction of nitrate and disinfection of contaminated water separately and simultaneously with high efficiency and high selectivity to nitrogen.