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Removal of Cr(VI) from Wastewater Using Graphene Oxide Chitosan Microspheres Modified with α-FeO(OH).

ABSTRACT: Graphene oxide and chitosan microspheres modified with α-FeO(OH) (α-FeO(OH)/GOCS) are prepared and utilized to investigate the performance and mechanism for Cr(VI) removal from aqueous solutions and the possibility of Fe secondary pollution. Batch experiments were carried out to identify the effects of pH, mass, and volume ratio (m/v), coexisting ions, time (t), temperature (T), and Cr(VI) initial concentration (C₀) on Cr(VI) removal, and to evaluate adsorption kinetics, equilibrium isotherm, and thermodynamics, as well as the possibility of Fe secondary pollution. The results showed that Cr(VI) adsorption increased with C₀, t, and T but decreased with increasing pH and m/v. Coexisting ions inhibited Cr(VI) adsorption, and this inhibition increased with increasing concentration. The influence degrees of anions and cations on the Cr(VI) adsorption in descending order were SO₄^2- > PO₄^2- > NO₃^- > Cl^- and Ca²⁺ > Mg²⁺ > Mn²⁺, respectively. The equilibrium adsorption capacity of Cr(VI) was the highest at 24.16 mg/g, and the removal rate was 97.69% under pH = 3, m/v = 1.0 g/L, T = 298.15 K, and C₀ = 25 mg/L. Cr(VI) adsorption was well fitted to a pseudo-second-order kinetic model and was spontaneous and endothermic. The best fit of Cr(VI) adsorption with the Langmuir and Sips models indicated that it was a monolayer and heterogeneous adsorption. The fitted maximum adsorption capacity was 63.19 mg/g using the Sips model under 308.15 K. Cr(VI) removal mainly included electrostatic attraction between Cr(VI) oxyanions with surface Fe-OH₂⁺, and the adsorbed Cr(VI) was partially reduced to Cr(III) and then precipitated on the surface. In addition, there was no Fe secondary pollution during Cr(VI) adsorption.

SUBMITTER: Liu Y

PROVIDER: S-EPMC9319010 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Heavy metal ions in water refer to significant risks to the biological system due to their high toxicity. Therefore, the decontamination of water polluted by heavy metal ions attracts significant interest of researchers. Adsorption by nanomaterials has been a widely used technique for removing heavy metal ions from water. Chitosan was extracted from shrimp shellfish and mixed with laboratory-prepared AgNPs/GO in the ratio of 3 : 1. A series of tests evaluates the best condition of pH, amount of adsorbent, retention time, stirring speed, temp, and initial concentration. The research was conducted under various conditions. Langmuir, Freundlich, Tempkin, and Dubinin-Radushkevich isotherms were also tested. Also, the column adsorption experiment was carried out on industrial wastewater at different flow rates and column bed heights. The optimal values of the contact time, pH, and adsorbent dose of Cr(vi) were found to be 80 min, 4, and 0.1 g 100 mL-1, respectively, at room temperature (30 °C), agitation at 150 rpm, and initial concentration of 50 ppm. On the other hand, the optimal value of contact time, pH, and adsorbent dose of Fe(iii) were found to be 30 min, 6, and 0.02 g 100 mL-1, respectively, at room temp (30 °C) with a stirring speed of 250 rpm and an initial concentration of 40 ppm. For Cr(vi) and Fe(iii), equilibrium studies show that the data fit the Freundlich isotherm well (correlation coefficient, R 2 = 0.98) (III). A link between the pseudo-second order active model and data fitting the pseudo-first order active models were made. Within the intraparticle diffusion model, there are four stages that the mechanism must go through before it is at equilibrium. The adsorbent was tested in an industrial adsorbent column. This test proves that the nanocomposite's adsorption capacity can be restored by washing it with 0.1 M HCl, as shown by the periodicity test. After four cycles, the amount of Cr(vi) adsorbed on AgNPs/GO/chitosan was just 20%, which is insufficient for further adsorption experiments. Cr(vi) removal rates (%R) decreased slightly.

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Removal of Cr(VI) from Wastewater Using Graphene Oxide Chitosan Microspheres Modified with α-FeO(OH).

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