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In present study, nitrate anion containing CdCr layered double hydroxides (LDH) was synthesized, and characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) and energy-dispersive X-ray-scanning electron microscopy techniques (EDX-SEM). The characteristic diffraction peaks in the XRD pattern of CdCr-NO3 LDH at 2? values of 15.10 and 26.02° correspond to (003) and (006) planes (hkl), respectively of crystal system of the LDH, revealing layered structure of material with basal (d) spacing of d003: 0.59 nm and d006: 0.34 nm, containing intercalated water and nitrate anions. Stretching vibrations in FT-IR spectrum of the LDH at 3,378.01 and 1,355.51 cm–1 confirmed the intercalation of water and nitrate ions, respectively, in between hydrotalcite-like layers. EDX study confirmed that CdCr-NO3 LDH contained 20.07%, 72.75% and 7.18% of O, Cd(II) and Cr(III), respec-tively. SEM image revealed that nanostructured material is porous and layered in nature. TGA-DSC confirmed the thermal stability of material at below 509.44°C. CdCr-NO3 LDH was investigated as an efficient adsorbent for capturing of Cr(VI) ions form industrial effluents. The adsorption was opti-mized by factorial design approach. Maximum response of CdCr-NO3 LDH for capturing/adsorption of Cr(VI) ions was achieved at optimum concentration of Cr(VI) ions: 10 mg L–1, pH: 4.0, adsorbent amount: 40 mg and shaking time: 30 min at 25°C. Method worked well on real wastewater samples. © 2022 Desalination Publications. All rights reserved.

Nanostructured ZnNiBi-NO3-Layered Double Hydroxides (LDHs) was synthesised, followed by the simple co-precipitation method using Zn(NO3)2.6 H2O, Ni(NO3)2.6 H2O and Bi(NO3)3 as the precursors. Synthesised LDHs was characterised by various techniques such as infrared (IR) spectroscopy, x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray (EDX) and thermal gravimetric analysis (TGA). ZnNiBi-NO3 LDHs were applied as efficient adsorbents for speciation analysis and preconcentration/separation of Cr(VI)/Cr(III) ions in aqueous samples prior to their trace determinations by microsample injection system-coupled flame atomic absorption spectrometry (MIS-FAAS). ZnNiBi-NO3 LDHs worked well for speciation and preconcentration/separation of Cr(VI)/Cr(III) ions at an optimum of pH 3.0 and adsorbent dosage of 400 mg. LOD and LOQ of Cr(VI) ions were calculated to be 0.03 and 0.10 μg L−1, respectively with a preconcentration factor of 400. The total saturation capacity of ZnNiBi-NO3 LDHs for Cr(VI) ions was investigated and found to be 46.0 mg g−1. The mthod was reproduced with RSD ≤1.4% of five replicates. The accuracy of method was evaluated by analysing 10–100 μg L−1 Cr(VI) ions standard solutions, and Cr(VI) ions were recovered ≥96.9% with RSD ≤2.4%. The developed method worked well on wastewater samples.

Magnetic mesoporous carbon (MMC) and magnetic activated carbon (MAC) are good functionalized carbon materials to use when applying environmental techniques. In this work, a series of efficient magnetic composite adsorbents containing Fe3O4 and carbon were prepared successfully and used for the adsorption of Cr(VI) ions in petrochemical wastewater. The morphology and structure of these magnetic adsorbents were characterized with FTIR, TG, XRD, VSM, BET, and SEM technologies. The effect of different factors, such as pH, adsorption time, initial Cr(VI) ions’ concentration, Fe3O4 loading, and adsorption time, on the adsorption behavior were discussed. The results showed that the 8%Fe3O4@MMC adsorbent exhibited a high removal rate, reutilization, and large adsorption capacity. The corresponding adsorption capacity and removal rate could reach 132.80 mg·g−1 and 99.60% when the pH value, adsorption time, and initial Cr(VI) ions’ concentration were 2, 180 min, and 80 mg·L−1 at 298 K. Four kinds of adsorption isotherm models were used for fitting the experimental data by the 8%Fe3O4@MMC adsorbent at different temperatures in detail, and a kinetic model and thermodynamic analysis also were performed carefully. The reutilization performance was investigated, and the Fe3O4@MMC adsorbent exhibited greater advantage in the adsorption of Cr(VI) ions. These good performances can be attributed to a unique uniform pore structure, different crystalline phases of Fe3O4 particles, and adsorption potential rule. Hence, the 8%Fe3O4@MMC adsorbent can be used in industrial petrochemical wastewater treatment.

Saccharomyces cerevisiae (SC) is a widely available biobased source for function material. In this work, a kind of new efficient magnetic composite adsorbent containing Fe3O4 and SC was prepared successfully and used for the removal of Cr(VI) ions in petrochemical wastewater. The morphology and structure of this magnetic adsorbent were characterized with FT-IR, TG, XRD, VSM, SEM and XPS. The effect of the different factors such as pH, adsorption time, initial Cr(VI) ions concentration and adsorption temperature on the adsorption behavior were investigated. The results showed that 10%-Fe3O4@SC exhibited high removal rate, reutilization and large removal capacity. The corresponding removal capacity and removal rate could reach 128.03 mg/g and 96.02% when the pH value was 2, adsorption time was 180 min, and initial Cr(VI) ions concentration were 80 mg/L at 298 K. The kinetics followed the pseudo-first-order, which indicated that the adsorption behavior of 10%-Fe3O4@SC for Cr(VI) ions belonged to the physical adsorption and chemical adsorption co-existence. The thermodynamic study showed that the adsorption process was spontaneous and exothermic. It still showed better adsorption performance and reutilization after the fifth adsorption-desorption experiment. The possible mechanism of Cr(VI) ions adsorption onto the 10%-Fe3O4@SC magnetic adsorbent has been discussed. Hence, this new adsorbent will be a candidate for industry-level applications in petrochemical wastewater containing Cr(VI) ions.

A modified homogeneous precipitation method has been used to synthesize ZnS nanoparticles. Starch and polyvinyl alcohol (PVA) were utilized as capping molecules, and later, the ZnS–PVA-capped nanoparticles were then incorporated with chitosan to form ZnS–chitosan nanocomposites for the removal of Cr(vi) ion from wastewater. The optical measurements of the synthesized ZnS nanoparticles showed the band gap which was blue-shifted when compared with the bulk ZnS material. The crystalline structures were determined by X-ray diffraction, and the crystalline sizes were estimated from the Scherer formula. XRD spectra confirmed the formation of hexagonal phase for the uncapped ZnS nanoparticles with an average crystalline size of 3.71 nm whereas the starch- and PVA-capped ZnS nanoparticles showed the formation of cubic phase structures with crystalline sizes of 3.26 and 2.88 nm. The TEM image showed spherical particles with regular morphologies and significantly narrow size distributions. The calculated average particle diameters were in good agreement with the estimated XRD result. The removal of Cr(vi) ion from wastewater was studied through the adsorption process. The effect of pH, dosage, and contact time was investigated. More than 95% of the metal ion recovery was achieved through using ZnS–chitosan nanocomposites.

This work describes the synthesis of a novel magnetic graphene oxide composite for removal of Cr(VI) ions. The synthesized nanosorbent were characterized with various techniques such as FT-IR, X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis and vibrating sample magnetometry (VSM). This material is illustrated to represent a viable sorbent for the removal of Cr(VI) ions. A Box-Behnken design was applied to optimize the parameters affecting the removal of Cr(VI). Three variables including sorption time, amount of the magnetic sorbent and sample pH were optimized in the removal process. Besides, the recovery of the sorbent was studied. Equilibrium isotherms were studied, and three models were applied to analyze the equilibrium adsorption data. The results revealed that the adsorption process obeyed the Langmuir model. Kinetic studies indicated the adsorption process followed a pseudo-second-order model. Maximum sorption capacity of the sorbent for Cr(VI) ions was 250 mg g-1.

In the present study, nanostructured ?-Cd(OH)2 adsorbent was synthesized, characterized by Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy analysis, and applied for Cr(VI) ions capturing (adsorption) from environmental aqueous samples. The central composite design of 18 adsorption experiments was employed for multivariate sorption optimization. Maximum adsorption (%) of Cr(VI) ions was calculated and found to be 98.5% with relative standard deviation (RSD) ? 3.5 at optimum concentration 15 mg L–1, pH 4.0, adsorbent dosage 50 mg, shaking time 20 min and shaking speed 120 rpm at 25°C. Langmuir, Freundlich and Dubinin–Radushkevich isotherms fitted well to adsorption data with correlation coefficient (R2) of 0.993, 0.982 and 0.994, respectively. Mono-layered (Qm ) and multi-layered (Kf ) capacities of ?-Cd(OH)2 adsorbent for Cr(VI) ions retention were calculated and found to be 202.02 ± 2.0 and 4.95 ± 2.5 mg g–1, respectively. Sorption energy was calculated and found to be 8.45 ± 2.0 kJ mol–1, indicated chemisorption or ion exchange mechanism for Cr(VI) ions adsorption onto ?-Cd(OH)2 adsorbent. © 2021 Desalination Publications. All rights reserved.

Metal-free and Cu(II)-lipophilic porphyrins [H2Pp and Cu(II)Pp] loaded on titanium dioxide in the anatase phase (TiO2) were prepared and used as a heterogeneous catalyst for the photoreduction of Cr(VI) to Cr(III) in aqueous suspensions under UV–Vis light irradiation. TiO2 impregnated with copper(II) porphyrin [TiO2@Cu(II)Pp] was the most effective in photocatalyst reduction of toxic chromate Cr(VI) to non-toxic chromium Cr(III). We further evaluated an experimental design with the scope of fast optimization of the process conditions related to the use of TiO2 or TiO2-porphyrin based photocatalysts. A full factorial design as a chemometric tool was successfully employed for screening the affecting factors involved in photoconversion catalysis, with the modification of TiO2 both with porphyrin H2Pp and Cu(II)Pp. The studied experimental factors were the catalyst amount, the concentration of Cr(VI) ions, and the pH of the medium. The performed multivariate approach was successfully used for fast fitting and better evaluation of significant factors affecting the experimental responses, with the advantage of reducing the number of available experiments. Thus, the stability of the optimized TiO2 embedded Cu(II)Pp was investigated, confirming the high reproducibility and suitability for environmental purposes.

International audience; In the current study, an in-situ oxidative polymerization method was used to synthesize polyaniline-coated tungsten trioxide biphasic composite (PANI@WO3). The as-developed composite material properties were elucidated using different characterization tools such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), N2 sorption-desorption isotherm, and X-ray photoelectron spectroscopy (XPS). The PANI@WO3 was further applied to remove hexavalent chromium (Cr(VI)) from aqueous solutions. The results demonstrated that the optimal removal efficacy was achieved at pH 2. Meanwhile, the pseudo-second-order kinetic and isotherm of the Langmuir model were fitted for Cr(VI) adsorption. Cr(VI) amount of 549.37 mg·g−1 was the maximum capacity of adsorption attained for PANI@WO3, which is significantly higher than that of existing adsorbents. From a thermodynamic point of view, the Cr(VI) adsorption process occurred spontaneously and endothermically. Importantly, PANI@WO3 still exhibited an excellent adsorption capability after five regeneration cycles, indicating the potential reusability of the PANI@WO3 composite. XPS analysis of PANI@WO3 surface after adsorption of Cr(VI) confirmed its adsorption and concomitant reduction into Cr(III) ions. The transfer of mass phenomenon, electrostatic attraction, and reduction reaction were the primary processes for Cr(VI) ions elimination. These findings revealed that the synthesized PANI@WO3 exhibited a high potential for wastewater treatment containing Cr(VI).

This work is focused on the removal of Cr(VI) ions from aqueous solution using polymer-enhanced ultrafiltration (PEUF) techniques with water-soluble poly(N,N-dimethylaminoethyl methacrylate), PDMAEMA, used as sorbent. The polymer was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization at different reaction times, characterized by size exclusion chromatography (SEC) and proton nuclear magnetic resonance (1H NMR). The sorption of Cr(VI) was studied by PEUF as a function of pH, the polymer:Cr(VI) molar ratio, and the presence of interfering ions. The PEUF-enrichment mode was used to saturate the polymer and further determine the release of Cr(VI) and regeneration of the polymer using sorption-desorption process. The RAFT polymerization showed a yield in the range 46% to 79% (determined by 1H NMR) for polymers with molecular weight (Mn) between 28 and 195 kg mol−1. The polydispersity estimated by SEC was between 1.1 and 1.8. The capacity of PDMAEMA as sorbent of Cr(VI), by the PEUF technique showed an efficient removal of Cr(VI) (100%, 25 mg L−1 in the feed) at pH 4 using polymer:Cr molar ratio of 40:1. The presence of interfering ions does not significantly decrease the retention capacity of PDMAEMA. Finally the results indicated that PDMAEMA can release Cr(VI) and be regenerated.

Chitosan as adsorbent has been used widely, however it was not effective yet for metal ions adsorption in industrial scale. In acidic condition, chitosan’s active site tends to decrease. This drawback can was solved by coating of chitosan active site on alumina. This paper discloses to overcome that limitation. The charateristic of the active side was analysed by FTIR spectrometry toward vibration N-H group at 1679.15 cm-1, C=O group of oxalate at 1703.30 cm-1, and Al-O group of alumina at 924.07 cm-1. The adsorption capacity of the developed adsorbent was tester to adsorb Cr(VI) ions under various of pH value such as 1, 2, 3, 4, 5, 6, and 7. The contact time affect toward the adsorption was also reported in 20, 30, 40 50, 60, 70, and 80 minute. In addition, the concentration effects (100, 200, 300, 400, 500, and 600 ppm) was also studied. Chromium (VI) was measured using spectronic-20. Adsorption capacity was obtained at 66.90 mg/g under optimum conditions pH 2, and contact time 60 minute, respectively.

Low-cost chitosan beads were prepared by dropping chitosan solution into an alkaline bath and then were used for Cr(VI) and Zn(II) ions adsorption from aqueous solution. Prepared chitosan beads were characterized by Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) measurements, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The effect of solution-pH, contact time, initial ion concentration, and temperature on both metal ions adsorption was investigated. The kinetics of adsorption suggested a pseudo-second-order model fits better than pseudo-first-order model for both metals. The equilibrium adsorption isotherm of both metals matches well with the Langmuir isotherm model. The maximum adsorption capacity of chitosan beads was 79.56 mg Cr(VI)/g and 109.18 mg Zn(II)/g at initial ion concentration 1,000 mg/L, and temperature 10 °C. Thermodynamic parameters showed that the adsorption of Cr(VI) and Zn(II) ions onto chitosan beads was feasible, spontaneous, and exothermic under the studied conditions. While the chitosan beads enabled a good adsorption application, further lab work and field studies are necessary before using in a practical adsorption process.

Crown ethers 12-crown-4 (12C4), benzo-15-crown-5 (B15C5), 18-crown-6 (18C6), nitrobenzo-18-crown-6 (NB18C6) dibenzo-18-crown-6 (DB18C6) and dicyclohexyl-18-crown-6 (DC18C6), dissolved in dichloromethane, are able to form oxonium-ion complexes in contact with aqueous sulfuric and hydrochloric acid solutions. This ability allows the transfer of Cr(VI) oxanions from the acid media, through an organic liquid membrane, into a distilled water receiving phase. Among the studied crown ethers, DC18C6 shows the highest transport efficiency.The effect of parameters influencing the process such as the crown ether concentration in the membrane, types of the organic diluent, acid concentration in the feed phase and time is investigated and discussed. Four replicate experiments show that an average of 95.6 (±1.3)% of the initial chromium in the source phase (10-3 M Cr(VI), 6 M H2SO4, 10 ml) is extracted into the distilled water(10 ml) through the membrane (DC18C6 0.05 M in CH2Cl2, 20 ml) after 8 h. The corresponding result, under similar conditions, in the presence of hydrochloric acid solution (4 M) was found to be 95.0 (±1.2)%. The selectivity of the process was assessed by performing the competitive transport experiments on a solution containing Cr(VI), Ni(II), Co(II), Pb(II), Mn(II), Zn(II) and Fe(III) ions. The method was used for the recovery of chromium from two real samples provided by chromium-electroplating industries.

Magnetic vinylphenyl boronic acid microparticles, poly(ethylene glycol dimethacrylate(EG)-vinylphenyl boronic acid(VPBA)) [m-poly(EG-VPBA)], produced by suspension polymerization and characterized, was found to be an efficient solid polymer for Cr(VI) adsorption. The m-poly(EG-VPBA) microparticles were prepared by copolymerizing of ethylene glycol dimethylacrylate (EG) with 4-vinyl phenyl boronic acid (VPBA). The m-poly(EG-VPBA) microparticles were characterized by N-2 adsorption/desorption isotherms, electron spin resonance (ESR), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), elemental analysis, scanning electron microscope (SEM) and swelling studies. The m-poly(EG-VPBA) microparticles were used at adsorbent/Cr(VI) ion ratios. The influence of pH, Cr(VI) initial concentration, temperature of the removal process was investigated. The maximum removal of Cr(VI) was observed at pH 2. Langmuir isotherm and Dubinin-Radushkvich isotherm were found to better fit the experiment data rather than Fruendlich isotherm. The kinetics of the adsorption process of Cr(VI) on the m-poly(EG-VPBA) microparticles were investigated using the pseudo first-order, pseudo-second-order, Ritch-second-order and intraparticle diffusion models, results showed that the pseudo-second order equation model provided the best correlation with the experimental results. The thermodynamic parameters (free energy change, Delta G(0) enthalpy change, Delta H-0; and entropy change, Delta S-0) for the adsorption have been evaluated.

This work is presenting data for the efficiency of carbon black for adsorption of hexavalent chromium ions from aqueous solutions. The Cr(VI) ion removal was studied by the batch adsorption technique. The paper is focused on the effect of different temperatures (293, 313 and 333 K) on the adsorption of Cr(VI) ions from aqueous solutions. Equilibrium modeling of the adsorption process was carried out and the equilibrium parameters were determined. Thermodynamic parameters were calculated using the adsorption equilibrium constant. The results suggest that the process is a typical example of exothermic adsorption.

The batch removal of Cr(VI) ions from aqueous solution under different experimental conditions using steel-making slag as low-cost adsorbent was investigated in this paper. The obtained results showed that steel-making slag was effective adsorbents for the removal of Cr(VI) ions from aqueous solutions. The adsorption of Cr(VI) by steel-making slag follows Langmuir isotherm equation. Among the tested kinetics models in this study (pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion model), the pseudo-second-order equation successfully predicted the adsorption. Thermodynamic parameters for the adsorption process were determined and discussed.

The magnetic-poly(divinylbenzene-1-vinylimidazole) [m-poly(DVB-VIM)] microbeads (average diameter 53-212 mu m) were synthesized and characterized; their use as adsorbent in removal of Cr(VI) ions from aqueous solutions was investigated. The m-poly(DVB-VIM) microbeads were prepared by copolymerizing of divinylbenzene (DVB) with 1-vinylimidazole (VIM). The m-poly(DVB-VIM) microbeads were characterized by N-2 adsorption/desorption isotherms, ESR, elemental analysis, scanning electron microscope (SEM) and swelling studies. At fixed solid/solution ratio the various factors affecting adsorption of Cr(VI) ions from aqueous solutions such as pH, initial concentration, contact time and temperature were analyzed. Langmuir, Freundlich and Dubinin-Radushkvich isotherms were used as the model adsorption equilibrium data. Langmuir isotherm model was the most adequate. The pseudo-first-order, pseudo-second-order, Ritch-second-order and intraparticle diffusion models were used to describe the adsorption kinetics. The apparent activation energy was found to be 5.024 kJ mol(-1), which is characteristic of a chemically controlled reaction. The experimental data fitted to pseudo-second-order kinetic. The study of temperature effect was quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy and entropy changes. The thermodynamic parameters obtained indicated the endothermic nature of adsorption of Cr(VI) ions. Morever, after the use in adsorption, the m-poly(DVB-VIM) microbeads with paramagnetic property were separeted via the applied magnetic force. The magnetic beads could be desorbed up to about 97% by treating with 1.0 M NaOH. These features make the m-poly(DVB-VIM) microbeads a potential candidate for support of Cr(VI) ions removal under magnetic field.