Modified Magnetite Nanoparticles for Hexavalent Chromium Removal from Water

Novel Nanocomposites and Biopolymer-Based Nanocomposites for Hexavalent Chromium Removal from Aqueous Media

Designing new engineered materials derived from waste is essential for effective environmental remediation and reducing anthropogenic pollution in our economy. This study introduces an innovative method for remediating metal-contaminated water, using two distinct waste types: one biowaste (eggshell) and one industrial waste (fly ash). We synthesized three novel, cost-effective nanoadsorbent types, including two new tertiary composites and two biopolymer-based composites (specifically k-carrageenan and chitosan), which targeted chromium removal from aqueous solutions. SEM analysis reveals that in the first composite, EMZ, zeolite, and magnetite nanoparticles are successfully integrated into the porous structure of the eggshell. In the second composite (FMZ), fly ash and magnetite particles are similarly loaded within the zeolite pores. Each biopolymer-based composite is derived by incorporating the corresponding tertiary composite (FMZ or EMZ) into the biopolymer framework. Structural modifications of the eggshell, zeolite, chitosan, and k-carrageenan resulted in notable increases in specific surface area, as confirmed by BET analysis. These enhancements significantly improve chromium adsorption efficiency for each adsorbent type developed. The adsorption performances achieved are as follows: EMZ (89.76%), FMZ (84.83%), EMZCa (96.64%), FMZCa (94.87%), EMZC (99.64%), and FMZC (97.67%). The findings indicate that chromium adsorption across all adsorbent types occurs via a multimolecular layer mechanism, which is characterized as spontaneous and endothermic. Desorption studies further demonstrate the high reusability of these nanomaterials. Overall, this research underscores the potential of utilizing waste materials for new performant engineered low-cost composites and biocomposites for environmental bioremediation applications.

Speciation of Hexavalent Chromium in Aqueous Solutions Using a Magnetic Silica-Coated Amino-Modified Glycidyl Methacrylate Polymer Nanocomposite

A new magnetic amino-functionalized polymeric sorbent based on glycidyl methacrylate was synthesized and used in the separation of chromium Cr(VI) oxyanions sorption from aqueous solutions in a static batch system. The kinetic and isothermal parameters of the sorption process were determined. The experimental data were best fitted by a pseudo-second-order model with R² = 0.994 and χ² = 0.004. The sorption process of Cr(VI) removal by amino-functionalized sorbent was controlled by both intraparticle diffusion and liquid film diffusion. The equilibrium results showed that the sorption process is best described by the Freundlich model, followed closely by the Sips isotherm model, with a maximum sorption capacity of 64 mg/g. Quantum chemical modeling revealed that the sorption sites on the sorbent surface are fragments with diethylenetriamine and aminopropyl silane groups that coated the magnetic nanoparticles. The calculations showed that Cr(VI) oxyanions (Cr₂O₇^2-, CrO₄^2- and HCrO₄^-) bind to both sorption sites, with diethylenetriamine centers slightly favored. The X-ray photoelectron spectroscopy (XPS) spectra demonstrate that the chromium bound to the sorbent in the form of Cr(III), indicating that the Cr(VI) can be converted on the surface of the sorbent to a less harmful form Cr(III) due to the sorbent's chemical composition.

Effect of hexavalent chromium on the environment and removal techniques: A review

Despite the importance of chromium (Cr) in most anthropogenic activities, the subsequent environmental adulteration is now a source of major concern. Cr occurs in numerous oxidation states, with the furthermost stable and frequently occur states being Cr(0), Cr(III) and Cr(VI). Cr(0) and Cr(III) are vital trace elements while Cr(VI) is dispensable and noxious to living organisms. Predominantly in plants, Cr at low concentrations of about 0.05-1 mg/L assist to boost growth as well as increase productivity. However, accumulation of Cr could represent a potential threat to living organisms. Cr absorption, displacement and accretion depend on its speciation, which also determines its toxicity which is often diverse. Indications of its toxicity include; reduction of seed germination, retardation of growth, reduction of yield, inhibition of enzymatic activities, weakening of photosynthesis, nutrient, oxidative disparities and genetic mutation in plants as well as several injurious diseases in animals and humans. In this study, we have presented a comprehensive review as well as an informative account of the influence of Cr on the environment drawn from researches carried out over the years following an analytical approach. Uniquely, this work presents a review of the effects and remediation of Cr from soil and wastewater drawn from several evidence and meta-data-based articles and other publications. Accordingly, the write-up is intended to appeal to the consciousness of the general public that the significance of Cr notwithstanding, its environmental toxicity should not be taken for granted.

Facile Fabrication of ZnMgAl/LDH/Algae Composites as a Potential Adsorbent for Cr(VI) Ions from Water: Fabrication and Equilibrium Studies

In order to improve the adsorption capacity of natural layered double hydroxyl (LDH) materials, the natural organic sources such as algae containing hydroxyl groups, amino groups, peptide connections, and alginate structures were used to improve LDH for the preparation of ZnMgAl LDH-algae composites (LDH-Ax). The structure of prepared composites was established and characterized via various techniques such as scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The LDH-A2 sample displayed the highest efficiency for Cr(VI) removal, which reached to 99% at the optimum conditions. The prepared composite LDH-A2 showed high stability and reusability (91.7%) after five cycles. The kinetic studies revealed that the Cr uptake by LDH-A1 is described as pseudo-first order, while the case of LDH-A2 is described as pseudo-second order. This study reported that the easily synthesized LDH-Ax has an interesting environmental approval process to eliminate Cr ions from aqueous media quickly and effectively.

Insight into the Adsorption and Photocatalytic Behaviors of an Organo-bentonite/Co3O4 Green Nanocomposite for Malachite Green Synthetic Dye and Cr(VI) Metal Ions: Application and Mechanisms

A green composite of organically modified bentonite supported by Co3O4 nanoparticles (OB/Co) was successfully fabricated and investigated as a potential eco-friendly, low-cost adsorbent and photocatalyst for promising removal of both malachite green dye (MG.D) and Cr(VI) ions. The composite showed high adsorption properties and achieved experimental q max values of 223 and 139 mg/g for MG.D and Cr(VI) after equilibration times of 360 min and 480 min for the inspected contaminants, respectively. The kinetic and equilibrium inspection reflected the best description of their adsorption behaviors by the pseudo-first-order kinetic model and the Langmuir isotherm model, respectively. This revealed favorable and homogeneous uptake of both MG.D and Cr(VI) in a monolayer form with theoretical Langmuir q max values of 343.6 and 194.5 mg/g, respectively. The theoretical adsorption energies of MG.D (0.6 kJ/mol) and Cr(VI) (0.5 kJ/mol) from the Dubinin-Radushkevich (D-R) model revealed physisorption properties that might be resulted from some types of Coulombic attractive forces, achieving theoretical q max values of 226.5 and 144.6 mg/g, respectively. The suggested adsorption mechanism was confirmed by the main mathematical parameters of thermodynamic studies that revealed physical, spontaneous, and exothermic uptake processes. Also, the composite showed high photocatalytic performance under visible light, which resulted in a 100% removal percentage of 100 mg/L of MG.D and Cr(VI) after about 180 and 240 min, respectively, from the adsorption equilibrium time.

Core-Shell Bimagnetic Nanoadsorbents for Hexavalent Chromium Removal from Aqueous Solutions

Novel nanoadsorbents based on core-shell bimagnetic nanoparticles (CoFe₂O₄@ɣ-Fe₂O₃) with two different mean sizes were elaborated, characterized and applied as potential sorbents for Cr(VI) removal from aqueous solutions through magnetically assisted chemical separation. The nanoadsorbents were characterized by XRD, TEM, FTIR, XPS, potentiometric-conductometric titrations, BET and vibrating sample magnetometry. The influence of contact time, shaking rate, pH, pollutant concentration, temperature and competing ions on Cr(VI) adsorption were evaluated. The results were analyzed in the framework of Langmuir and Freundlich models to evaluate the maximum adsorption capacity and the extent of affinity. The nanoadsorbents showed a good selectivity for Cr(VI) adsorption and were more effective at pH = 2.5, with a shaking rate of 400 RPM. The adsorption process was spontaneous, endothermic and presented an increased randomness. The contact time required to reach the equilibrium was relatively short and the kinetic date followed the pseudo-second-order model. The maximum adsorption capacity was nearly 40% higher for the nanoadsorbent of smaller mean size due to its higher surface area. Regeneration studies revealed that the nanoadsorbents can be recovered for reuse. These results indicate that prepared nanoadsorbents can be used as a powerful tool for Cr(VI) removal from contaminated water.