Graphical abstract

No abstract

Recently, arsenic-contaminated water has become a big concern. Therefore, the present study aimed to absorb arsenic from the aqueous solution using modified saxaul tree ash. Arsenic adsorption process was performed in vitro by investigating the effect of various parameters such as pH, contact time, arsenic concentrations, temperature and adsorbent dosage on the adsorption efficiency. Isotherms, kinetics and thermodynamic studies were also conducted to better understand the process of adsorption. Maximum level of arsenic adsorption was obtained at a pH of 7, adsorbent dosage of 1.5 g/L, contact time of 60 min, initial arsenic concentration of 250 µg/l and temperature of 323 K. The amount of adsorbed arsenic was increased with increasing initial concentration of arsenic and temperature. Freundlich adsorption isotherm clearly described the arsenic adsorption by modified saxaul ash. Based on the results obtained, it could be concluded that the modified saxaul ash can efficiently remove arsenic from its aqueous solutions.

In the current work, neodymium oxide (Nd2O3) nanoparticles were synthesized and characterized by means of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The major aim/investigation of this research was to fit/model and optimize the removal of Acid Blue 92 (AB92) dye from synthetic effluents (aqueous solutions) using the adsorption process based on neodymium oxide (Nd2O3) nanoparticles. To optimize the adsorption conditions, central composite design (CCD) based on response surface methodology (RSM) was applied. The effects of pH (3–9), adsorbent dosage (0.1–1 g/L), initial concentration of AB92 (100–300 mg/L), and contact time (10–100 min) on the adsorption process were investigated. Apart from equilibrium and kinetic experiments, thermodynamic evaluation of the adsorption process was also undertaken. The adsorption process was found to have the best fitting to Langmuir isotherm model and pseudo-second-order kinetic equation. Also, the process was found to be spontaneous and favorable with increased temperature. The optimal conditions found were: pH = 3.15, AB92 concentration equal to 138.5 mg/L, dosage of nanoadsorbent equal to 0.83 g/L, and 50 min as contact time, which resulted in 90.70% AB92 removal. High values for the coefficient of determination, R2 (0.9596) and adjusted R2 (0.9220) indicated that the removal of AB92 dye using adsorption can be explained and modeled by RSM. The Fisher’s F-value (25.4683) denotes that the developed model was significant for AB92 adsorption at a 95% confidence level.

Thermally activated persulfate (TAP) was applied for the degradation of Acid Blue 92 (AB92) dye in its aqueous solution. The effects of pH (3-11), temperature (298-333 K), contact time (15-75 min), sodium persulfate (SPS) concentration (0.05-0.5 mM) and initial AB92 concentration (50-400 mg/L) on the degradation of AB92 using TAP were examined. The initial and residual AB92 concentrations were determined spectrophotometrically at the wavelength of 260 nm and the dye mineralization was examined via the total organic carbon analysis. In addition, the chemical oxygen demand was also measured. The activation energy (E a) of AB92 degradation was calculated as 17.38 kJ mol −1 based on the Arrhenius equation. Maximum degradation efficiency of 86.47% was reached after 75 min of treatment at a pH of 5, AB92 concentration of 200 mg/L, SPS concentration of 0.5 mM and temperature of 333 K. The degradation efficiency declined with the addition of different sodium chloride concentrations and organic radical scavengers. AB92 degradation was reduced from 86.5 to 74%, 65, and 59.1% using ethylenediaminetetraacetic acid, tert-butanol, and ethanol, respectively. A kinetic model was also developed to estimate the pseudo-first-order constants as a function of the main operational parameters (initial dye concentration and TAP concentration). Decolorization rate constants (k) of 0.0009, 0.001, 0.0012, 0.0014, and 0.0018 min −1 were obtained at 303, 308, 313, 328, and 333 K, respectively, using the Langmuir-Hinshelwood kinetic model. The results obtained indicate that the TAP degradation process has great potential for the reduction of azo dyes in aqueous environments.