Treatment of textile effluents by chloride-intercalated Zn-, Mg- and Ni-Al layered double hydroxides

This work involved the preparation, characterization and dyes removal ability of Zn-Al, Mg-Al and Ni-Al layered double hydroxide (LDH) minerals intercalated by chloride ions. The materials were synthetized by the co-precipitation method. X-ray diffraction, Fourier transform infrared, thermogravimetric-differential thermal analysis and transmission electron microscopy characterization exhibited a typical hydrotalcite structure for all the samples. Adsorption experiments for methyl orange were performed in terms of solution pH, contact time and initial dye concentration. Experimental results indicate that the capacity of dye uptake augmented rapidly within the first 60 min and then stayed practically the same regardless of the concentration. Maximum adsorption occurred with acidic pH medium. Kinetic data were studied using pseudo-first-order and pseudo-second-order kinetic models. Suitable correlation was acquired with the pseudo-second-order kinetic model. Equilibrium data were fitted to Langmuir and Freundlich isotherm models. The maximum Langmuir monolayer adsorption capacities were 2,758, 1,622 and 800 mg/g, respectively, for Zn-Al-Cl, Mg-Al-Cl and Ni-Al-Cl. The materials were later examined for the elimination of color and chemical oxygen demand (COD) from a real textile effluent wastewater. The results indicated that the suitable conditions for color and COD removal were acquired at pH of 5. The maximum COD removal efficiency from the effluent was noted as 92.84% for Zn-Al-Cl LDH

Performance of Zn‐, Mg‐ and Ni‐Al layered double hydroxides in treating an industrial textile wastewater

In this study, Zn‐Al, Mg‐Al and Ni‐Al layered double hydroxides were successfully synthesized via co‐precipitation method. Samples were characterized by XRD, FTIR, TGA‐DTA, TEM and pHPZC analysis. XRD patterns showed a basal spacing increase in the order of Zn‐AlNO3 (8.85Å)> Mg‐AlNO3 (7.95Å)> Ni‐AlNO3 (7.82Å). TEM images indicated that the Zn‐AlNO3 presents circular to shaped particles with an average particle size of approximately 30 to 40 nm. Small plates assigned to sheets with hexagonal form were observed in the case of Mg‐AlNO3. Ni‐AlNO3 display nanostructured sphere in diameter between 5 and 10 nm. The materials were used for the removal of methyl orange (MO), as a model dye and for the treatment of a real effluent generated by a textile factory. Maximum adsorption was occurred in acidic pH solution. Kinetic data were tested using pseudo‐first‐order, pseudo‐second‐order kinetic and intra‐particle diffusion models. The best fit was obtained with the pseudo‐second‐order kinetic model. Equilibrium data were correlated to Langmuir, Freundlich, Sips and Redlich–Peterson isotherm models. The best conditions for color and COD removal from the textile effluent sample were obtained at lower values of pH. Reduction of COD to limits authorized by Moroccan standards was obtained with 0.5g/L of LDH dosage

Synthesis, characterization and efficient photocatalytic properties of spinel materials for dye degradation

In this research, Co0.5Zn0.5Al2O4 spinel oxides photocatalysts were elaborated from layered double hydroxides Co-Zn-Al/CO3 precursor by calcination at 300, 400, 500, 600, 800, and 1000 °C. XRD, FTIR, TGA/DTA, and SEM/EDX analysis were used for characterized of prepared photocatalysts. The photocatalytic efficiency of the prepared materials was tested by photodegradation of methyl orange (MO) azo dye as a model of textile contaminants under UV illumination. The effect of various operational factors such as irradiation time, initial pH, catalyst dose, methyl orange concentration and reuse were investigated. The enhancement of the photodegradation was strongly dependent on the calcination temperature. A synergic effect between the adsorption and photodegradation was observed. After 50 min of irradiation, the catalyst calcined at 400 °C showed the highest efficiency (98.2%). After regeneration (up to five cycles), the photocatalyst showed high stability

Effectiveness of beetroot seeds and H3PO4 activated beetroot seeds for the removal of dyes from aqueous solutions

Raw beetroot seeds (BS) and H3PO4 activated beetroot seeds (H3PO4-BS) were evaluate for their effectiveness in removing methylene blue (MB) and malachite green (MG) from aqueous solution. BS were carbonized at 500°C for 2 h, and then impregnated with phosphoric acid (phosphoric acid to BS ratio of 1.5 g/g). The impregnated BS were activated in a tubular vertical furnace at 450°C for 2 h. Batch sorption experiments were carried out under various parameters, such as solution pH, adsorbent dosage, contact time, initial dyes concentration and temperature. The experimental results show that the dye sorption was influenced by solution pH and it was greater in the basic range. The sorption yield increases with an increase in the adsorbent dosage. The equilibrium uptake was increased with an increase in the initial dye concentration in solution. Adsorption kinetic data conformed more to the pseudo-second-order kinetic model. The experimental isotherm data were evaluated by Langmuir, Freundlich, Toth and Dubinin–Radushkevich isotherm models. The Langmuir maximum monolayer adsorption capacities were 61.11 and 74.37 mg/g for MB, 51.31 and 213.01 mg/g for MG, respectively in the case of BS and H3PO4-BS. The thermodynamic parameters are also evaluated and discussed

Defluoridation of groundwater by calcined Mg/Al layered double hydroxide

The present study evaluated calcined Mg/Al layered double hydroxide (CLDH) availability for the removal of fluoride from local groundwaters. The Mg/Al layered double hydroxide (LDH) was synthesized by co-precipitation method and characterized by XRD, FT-IR and TGA-TDA analyses. Batch defluoridation experiments were performed under various conditions such as calcination, solution pH, contact time, temperature, material dosage and reuse. Experimental results indicate that fluoride removal strongly increased after calcination of the LDH up to 600 °C. The maximum fluoride removal was obtained at solution pH of 6.85. Kinetics of fluoride removal followed the pseudo-second order kinetic model. The rise in solution temperature strongly enhances the removal efficiency. The adsorption mechanism involved surface adsorption, ion exchange interaction and original LDH structure reconstruction by rehydration of mixed metal oxides and concomitant intercalation of fluoride ions into the interlayer region. The optimum dosages required to meet the national standard for drinking water quality were found to be 0.29 and 0.8 g/L, respectively, for Bejaad and Settat goundwaters. A decrease in the fluoride uptake with increasing the number of regeneration cycles was observed

Adsorption of textile dyes on raw and decanted Moroccan clays: Kinetics, equilibrium and thermodynamics

AbstractInexpensive and easily available Moroccan natural clays were investigated for the removal availability of textile dyes from aqueous solution. For this purpose, the adsorption of methylene blue (MB) as reference molecule, malachite green (MG) representative of cationic dyes and methyl orange (MO) representative of anionic dyes, was studied in batch mode under various parameters. The clays were characterized by means of XRD, cationic exchange capacity and BET surface area analysis. The experimental results show that, the adsorption was pH dependent with a high adsorption capacity of MB and MG in basic range and high adsorption of MO in acidic range. The pseudo-second-order kinetic model provided the best fit to the experimental data for the adsorption of MB and MG by the clays. However, the adsorption of MO was more suitable to be controlled by an intra-particle diffusion mechanism. The equilibrium adsorption data were analyzed by Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. The adsorption process was found to be exothermic in nature in the case of MB and MO. However, the adsorption of MG was endothermic

Factorial experimental design for the optimization of catalytic degradation of malachite green dye in aqueous solution by Fenton process

This work focuses on the optimization of the catalytic degradation of malachite green dye (MG) by Fenton process “Fe2+/H2O2”. A 24 full factorial experimental design was used to evaluate the effects of four factors considered in the optimization of the oxidative process: concentration of MG (X1), concentration of Fe2+ (X2), concentration of H2O2 (X3) and temperature (X4). Individual and interaction effects of the factors that influenced the percentage of dye degradation were tested. The effect of interactions between the four parameters shows that there is a dependency between concentration of MG and concentration of Fe2+; concentration of Fe2+ and concentration of H2O2, expressed by the great values of the coefficient of interaction. The analysis of variance proved that, the concentration of MG, the concentration of Fe2+ and the concentration of H2O2 have an influence on the catalytic degradation while it is not the case for the temperature. In the optimization, the great dependence between observed and predicted degradation efficiency, the correlation coefficient for the model (R2=0.986) and the important value of F-ratio proved the validity of the model. The optimum degradation efficiency of malachite green was 93.83%, when the operational parameters were malachite green concentration of 10 mg/L, Fe2+ concentration of 10 mM, H2O2 concentration of 25.6 mM and temperature of 40 °C

Novel Ag-ZnO-La2O2CO3 photocatalysts derived from the Layered Double Hydroxide structure with excellent photocatalytic performance for the degradation of pharmaceutical compounds

In this work, we have prepared the Ag-ZnO-La2O2CO3 nanomaterials as promising photocatalysts for the photocatalytic degradation of pharmaceutical pollutants. Firstly, a series of ZnAl1-xLax(CO3) (0 ≤ x ≤ 0.5) layered double hydroxides (LDHs) were synthesized by the co-precipitation method at the component molar ratio of Zn/(Al + La = 3, where La/Al = 0, 0.25 and 0.5). Photocatalysts were prepared by the calcination of the LDH precursors at different temperatures of 300, 400, 500, 600, 800 and 1000 °C. The effects of the La/Al molar ratio and the calcination temperature on the photocatalytic activity of the catalysts were evaluated by the degradation of caffeine as a model pharmaceutical pollutant in aqueous solutions under the UV irradiation. Thereafter, in order to increase the photocatalytic activity, the catalysts obtained at the optimal La/Al molar ratio and calcination temperature were doped with the Ag noble metal at various concentrations (i.e. 1, 3 and 5 wt%) using the ceramic preparation process to obtain the desired Ag-ZnO-La2O2CO3 catalysts. The synthesized photocatalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX) and UV-visible diffuse reflectance spectroscopy (UV-Vis DRS). Detailed photocatalytic experiments based on the effects of the irradiation time, the dopant amount, the catalyst dose, the initial solution pH and reuseability were performed and discussed in this study. The Ag doped material showed significantly a higher photocatalytic activity compared to the undoped, pure ZnO and P-25 catalysts. The experimental results show that the highest photocatalytic activity was obtained from the Ag (5%) doped Zn-0.75Al-0.25La-CO3 photocatalysts calcined at 500 °C with a degradation efficiency of 99,4% after 40 min of irradiation only. This study could provide a new route for the fabrication of high performance photocatalysts and facilitate their application in the environmental remediation issues. Keywords: Layered double hydroxides, Photocatalyst, Doping, Photocatalytic degradation, Caffein

Effect of natural phosphate to remove silver interference in the detection of mercury(II) in aquatic algae and seawater samples

AbstractA silver particles impregnated onto natural phosphate (Ag/NP) was synthesized using reaction in solid state. The obtained powder was characterized by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The (Ag/NP) was used as modifier of carbon paste electrode (CPE) to determine mercury by square wave voltammetry. The calibration graph obtained is linear from 1.0×10−8mol·L−1 to 1.0×10−5mol·L−1 at preconcentration time of 5min, percentage loading of 7%, with correlation coefficient of 0.993. The limits of detection (DL,3σ) and quantification (QL,10σ) were 5.8×10−9mol·L−1 and 19.56×10−9mol·L−1 respectively. The repeatability of the method expressed as relative standard deviation (R.S.D.) is 2.1% (n=8). The proposed method was successfully applied to determine mercury(II) in aquatic algae and seawater samples