A B S T R A C TThe decolorization and removal of chemical oxygen demand (COD) of a textile dye, Navy blue CE-RN (NB), were investigated from aqueous solutions by combined process of coagulation-flocculation(C-F) and adsorption. Common coagulants (alum, lime, poly aluminum chloride (PACl), and ferric chloride) and clay [montmorillonite (Mt) and nanomontmorillonite (NMt)] were used in C-F and adsorption steps, respectively. The maximum COD and dye removal was observed by coagulant of PACl in the C-F process. The optimum conditions for dye removal by PACl were occurred by coagulant dose of 0.1 g/L at pH 6. In the adsorption process, the optimum contact times of 120 and 20 min were obtained for Mt and NMt, respectively. The findings indicated that the optimum conditions for the dye sorption were observed at pH 2 and the adsorbent dose 1.8 g/L. The sorption data also showed that the adsorption of NB onto the sorbents was better followed the pseudo-second order kinetic models. The dye and COD concentrations during the combined treatment process were decreased from 300 to 2-4.5 mg/L and from 732 to 2-35 mg/L, respectively. This indicates that the combined process of C-F followed by adsorption can be used as a proper alternative for the treatment of NB dye-containing wastewaters.

An amino-functionalized MIL-68(Al) metal–organic framework (amino-MIL-68(Al) MOF) was synthesized by solvothermal method and then characterized by FESEM, XRD, FTIR, EDX-mapping, and BET-BJH techniques. In order to predict arsenate (As(V)) removal, a robust quadratic model (R2 > 0.99, F-value = 2389.17 and p value < 0.0001) was developed by the central composite design (CCD) method and then the genetic algorithm (GA) was utilized to optimize the system response and four independent variables. The results showed that As(V) adsorption on MOF was affected by solution pH, adsorbent dose, As(V) concentration and reaction time, respectively. Predicted and experimental As(V) removal efficiencies under optimal conditions were 99.45 and 99.87%, respectively. The fitting of experimental data showed that As(V) adsorption on MOF is well described by the nonlinear form of the Langmuir isotherm and pseudo-second-order kinetic. At optimum pH 3, the maximum As(V) adsorption capacity was 74.29 mg/g. Thermodynamic studies in the temperature range of 25 to 50 °C showed that As(V) adsorption is a spontaneous endothermic process. The reusability of MOF in ten adsorption/regeneration cycles was studied and the results showed high reusability of this adsorbent. The highest interventional effect in inhibiting As(V) adsorption was related to phosphate anion. The results of this study showed that amino-MIL-68(Al) can be used as an effective MOF with a high surface area (> 1000 m2/g) and high reusability for As(V)-contaminated water.

Wastewaters discharged from different industries and hospitals may contain pharmaceuticals, especially dexamethasone (DEX). Thus, we applied the UV/H2O2 photocatalytic method in the presence of the MgO nanoparticles to remove dexamethasone from synthetic wastewater. Moreover, the effects of parameters such as pH (3–11), hydrogen peroxide concentration (1–8 mM), initial DEX concentration (5–30 mg/L), and catalyst dosage (0.01–0.2 g/L) during the reaction times (0–30 min) were investigated. Furthermore, the efficiency of UV/H2O2 in the presence and absence of catalysts was investigated. The photocatalyst is characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and Fourier-transform infrared spectroscopy (FTIR) techniques. It was found that the removal rate was enhanced by decreasing pH and the initial dexamethasone concentration. The removal rate was enhanced somewhat with concentrations of hydrogen peroxide and MgO. In the case of UV/H2O2/MgO, 87% removal efficiency was achieved, under the optimal conditions: pH 3, contact time of 30 min, dexamethasone concentration of 20 mg/L, H2O2 of 0.5 mM, and UV radiation of 55 watts. The kinetic data indicated that the reaction followed the second-order kinetic model. The results showed that the UV/H2O2 photochemical process can efficiently remove dexamethasone from aqueous in the presence of a MgO catalyst, and the mineralization efficiency was reached at about 98%.

An amino-functionalized MIL-68(Al) metal-organic framework (amino-MIL-68(Al) MOF) was synthesized by solvothermal method and then characterized by FESEM, XRD, FTIR, EDX-mapping, and BET-BJH techniques. In order to predict arsenate (As(V)) removal, a robust quadratic model (R2 > 0.99, F-value = 2389.17 and p-value < 0.0001) was developed by the central composite design (CCD) method and then the genetic algorithm (GA) was utilized to optimize the system response and four independent variables. The results showed that As(V) adsorption on MOF was affected by solution pH, adsorbent dose, As(V) concentration and reaction time, respectively. Predicted and experimental As(V) removal efficiencies under optimal conditions were 99.45 and 99.87 %, respectively. The fitting of experimental data showed that As(V) adsorption on MOF is well described by the nonlinear form of the Langmuir isotherm and pseudo-second-order kinetic. At optimum pH 3, the maximum As(V) adsorption capacity was 74.29 mg/g. Thermodynamic studies in the temperature range of 25 to 50 °C showed that As(V) adsorption is a spontaneous endothermic process. The reusability of MOF in ten adsorption/regeneration cycles was studied and the results showed high reusability of this adsorbent. The highest interventional effect in inhibiting As(V) adsorption was related to phosphate anion. The results of this study showed that amino-MIL-68(Al) can be used as an effective MOF with a high surface area (> 1000 m2/g) and high reusability for As(V)-contaminated water.

Wastewaters discharged from different industries and hospitals may contain pharmaceuticals, especially dexamethasone (DEX). Thus, we applied the UV/H2O2 photocatalytic method in the presence of the MgO nanoparticles to remove dexamethasone from synthetic wastewater. Moreover, the effects of parameters such as pH = 3–11, hydrogen peroxide concentration = 1–8 mM, initial DEX concentration (5–30 mg/L), catalyst dosage = 0.01–0.2 g/l were investigated at the contact times of 0–30 min. Furthermore, the efficiency of UV/H2O2 in the presence and absence of catalyst was investigated. Additionally, this catalyst was characterized by means of XRD and FT-IR analyses and SEM imaging. It was found that the removal rate was enhanced with decreasing pH and initial dexamethasone concentration. The removal rate was enhanced somewhat with concentrations of hydrogen peroxide and MgO. In the case of UV/H2O2/MgO, 87% removal efficiency achieved, under the optimal conditions: pH 3, contact time of 30 min, dexamethasone content of 20 mg/L, H2O2 of 0.5 mM, and UV radiation of 55 watts. The kinetic data indicated that the reaction followed the second-order kinetic model. The results showed that the UV/H2O2 photochemical process can efficiently remove dexamethasone from aqueous in the presence of MgO catalyst, and the mineralization efficiency was reached at about 98%.