Removal of Chromium(VI) from Aqueous Solutions Using Fe₃O₄ Magnetic Polymer Microspheres Functionalized with Amino Groups

Polypyrrole Coating via Lemieux-von Rudloff Oxidation on Magnetite Nanoparticles for Highly Efficient Removal of Chromium(VI) from Wastewater

An alternative way for the coating of polypyrrole (PPy) polymer on hydrophobic magnetite (Fe3O4) nanoparticles is reported here to capture toxic chromium ions, Cr (VI), present in water. Iron oxide magnetic nanoparticles (Fe3O4) were synthesized by the conventional coprecipitation technique using FeCl3·6H2O and FeSO4·7H2O iron precursors and subsequently modified with oleic acid (OA). Then OA-Fe3O4 hydrophobic nanoparticles were oxidized using the Lemieux-von Rudloff reaction to transfer OA into hydrophilic azelaic acid (AA) (HOOC(CH2)7COOH-modified magnetic nanoparticles (AA-Fe3O4). Finally, a PPy polymer coating was formed by a seeded polymerization of pyrrole, using AA-Fe3O4 as seeds. The average size of PPy/Fe3O4 nanocomposites is 12.33 nm and is almost spherical in shape. The surface composition is confirmed by FTIR and thermogravimetry analyses. An X-ray diffraction study confirmed the formation of highly crystalline Fe3O4 nanoparticles, and the crystallinity was retained after the surface modification. The adsorption study suggested that the Cr(VI) ion adsorption is highly pH-dependent and the maximum amount of adsorption is obtained at pH 2.0. The adsorption results revealed that the Langmuir model provided the best fit for the isotherm, with a maximum adsorption capacity reaching approximately 173.22 mg g-1 at 323 K. Spontaneous and endothermic adsorption processes were confirmed by evaluating the thermodynamic parameters obtained in this investigation. The kinetics study showed that the interaction between Cr(VI) ions and magnetic nanocomposites was directed by a pseudo-second-order rate process indicating chemisorption. The prepared PPy/Fe3O4 nanocomposites would be promising adsorbents to purify water by eliminating Cr(VI) metal ions from wastewater.

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.

Removal of Chromium Species by Adsorption: Fundamental Principles, Newly Developed Adsorbents and Future Perspectives

Emerging chromium (Cr) species have attracted increasing concern. A majority of Cr species, especially hexavalent chromium (Cr(VI)), could lead to lethal effects on human beings, animals, and aquatic lives even at low concentrations. One of the conventional water-treatment methodologies, adsorption, could remove these toxic Cr species efficiently. Additionally, adsorption possesses many advantages, such as being cost-saving, easy to implement, highly efficient and facile to design. Previous research has shown that the application of different adsorbents, such as carbon nanotubes (carbon nanotubes (CNTs) and graphene oxide (GO) and its derivatives), activated carbons (ACs), biochars (BCs), metal-based composites, polymers and others, is being used for Cr species removal from contaminated water and wastewater. The research progress and application of adsorption for Cr removal in recent years are reviewed, the mechanisms of adsorption are also discussed and the development trend of Cr treatment by adsorption is proposed.

Highly Efficient Visible Light Photodegradation of Cr(VI) Using Electrospun MWCNTs-Fe3O4@PES Nanofibers

The development of highly efficient photocatalysis has been prepared by two different methods for the photodegradation of Cr(VI) from an aqueous solution under visible light. The electrospun polyethersulfone (PES)/iron oxide (Fe3O4) and multi-wall carbon nanotubes (MWCNTs) composite nanofibers have been prepared using the electrospinning technique. The prepared materials were characterized by SEM and XRD analysis. The result reveals the successful fabrication of the composite nanofiber with uniformly and smooth nanofibers. The effect of numerous parameters were explored to investigate the effects of pH value, contact time, concentration of Cr(VI), and reusability. The MWCNTs-Fe3O4@PES composite nanofibers exhibited excellent photodegradation of Cr(VI) at pH 2 in 80 min. The photocatalysis materials are highly stable without significant reduction of the photocatalytic efficiency of Cr(VI) after five cycles. Therefore, due to its easy separation and reuse without loss of photocatalytic efficiency, the photocatalysis membrane has tremendous potential for the removal of heavy metals from aqueous solutions.

Magnesium ferrite-reinforced polypyrrole hybrids as an effective adsorbent for the removal of toxic ions from aqueous solutions: Preparation, characterization, and adsorption experiments

Contaminated waters with high contents of toxic anions are detrimental to the human health and wildlife. Thus, the quality of drinking water should be carefully monitored. Adsorption technique has been determined to be a reasonable strategy out of several methods used to remove toxic anions from water. Novel MgFe₂O₄-reinforced polypyrrole (Ppy@x%MgFe₂O₄) (x = 1%, 2%, and 5% of MgFe₂O₄) hybrids were synthesized from a pyrrole monomer and MgFe₂O₄ using a simple chemical oxidation method. The fabricated hybrids were studied for their capability to remove PO₄^3-, NO₃^-, and Cr(VI) from aqueous solutions. The results showed that PO₄^3-, NO₃^-, and Cr(VI) removal was highly pH-dependent. The adsorption isotherms of hybrids were fitted well by the Langmuir model, with the maximum adsorption efficiency of 116.90, 76.14, and 138.60 mg/g for PO₄^3-, NO₃^-, and Cr(VI), respectively. In addition, the above-mentioned toxic anions could be efficiently desorbed from spent Ppy@x%MgFe₂O₄ using a 0.1 M NaOH solution, and the hybrids exhibited good regenerability. The prepared materials are promising candidates for PO₄^3-, NO₃^-, and Cr(VI) removal and exhibit high adsorption efficiency, rapid adsorption-desorption behavior, and appropriate recovery from the aqueous medium under external magnetic field.

Immobilization and mitigation of chromium toxicity in aqueous solutions and tannery waste-contaminated soil using biochar and polymer-modified biochar

This study was conducted to investigate the potential of Jujube (Ziziphus jujube L) wood waste-derived biochar (BC) and its derivative polymer-modified biochar (PBC) in removing hexavalent chromium (Cr^VI) from aqueous solutions and in achieving Cr stabilization in tannery waste-contaminated soil. BC was produced at three different pyrolysis temperature (300 °C, 500 °C, 700 °C) and was polymerized with acrylamide and N, N1 methylenebisacrylamide. The results showed that Cr^VI adsorption is a function of the pH and Cr^VI initial concentration of the solution. The PBC showed highest sorption efficiency for Cr^VI removal, which amounted to 76.4%-99.6% of the Cr^VI overall initial concentrations (5-40 mg L^-1) at an initial pH of 2. In greenhouse, wheat (Triticum aestivum L) was cultivated as a test crop in pots with tannery waste-contaminated soil along with BCs and PBCs amendments. The BC and PBC amended soil showed 47.7% and 65% less Cr uptake by the plant roots in comparison with unamended soil, respectively. In addition, zero concentration of Cr in the plant shoots was noted with the PBC-amended soil, while the Cr concentration in the shoots was decreased by 89% with the BC-amended soil. Thus, it was concluded that BC and PBC have great potential in removing Cr^VI from aqueous phases and in decreasing the Cr mobility and bioavailability in soil.

Chromium stress induced oxidative burst in Vigna mungo (L.) Hepper: physio-molecular and antioxidative enzymes regulation in cellular homeostasis

Vigna mungo (L.) Hepper commonly known as blackgram is an important legume crop with good quality dietary proteins and vitamins. Low production of blackgram in the chromium rich soil of Odisha is a serious concern against its demand. Chromium (VI) was tested on V. mungo var. B3-8-8 at 100, 150, 200, 250 and 300 µM concentration on growth, anti-oxidative enzymes and chromium content at 15, 30 and 45 d of treatments. Seed germination and growth decreased with increase dose and duration. Cr uptake induced oxidative burst with significant increase of osmolytes was observed in cell at lower doses but failed to adjust homeostasis at higher dose. Increase of GPX and SOD and decrease of CAT was observed as dose dependent. Increased protein content was detected in < 200 µM Cr concentration whereas, significant decrease of protein was noted thereafter. Down regulation of proteins (29.2 kDa and 32.6 kDa) was observed at > 250 µM of Cr. Total Cr uptake was greater in root than in shoot which might be due to poor translocation of heavy metal or detoxification. Thus, blackgram was able to maintain homeostasis at lower concentrations of Cr by activating the cascade of enzymes following cellular detoxification mechanism.

SUPPLEMENTARY INFORMATION

The online version of this article contains supplementary material available at (10.1007/s12298-021-00941-3).

Magnetite doped metal–organic framework nanocomposites: an efficient adsorbent for removal of bisphenol-A pollutant

The removal of bisphenol-A (BPA) from the aqueous environment is a vital issue for public health due to its toxic effect.

A review: a comparison of different adsorbents for removal of Cr (VI), Cd (II) and Ni (II)

A review of the studies dealing with the removal of chromium, cadmium, and nickel ions with different adsorbents published in the literature between 2014 and 2018 is given in tabular form, along with the adsorption conditions, adsorption isotherm, and kinetic models applied by the authors to model the experimental data and adsorption capacities. The review focuses on the efficiency of ion removal.

The magnetic covalent organic framework as a platform for high-performance extraction of Cr(VI) and bisphenol a from aqueous solution

The magnetic covalent organic framework with β-ketoenamine linkage (Fe₃O₄@COF(TpPa-1)) was fabricated by the hydrothermal method. The obtained Fe₃O₄@TpPa-1 integrated four advantages, namely easy preparation, high stability, excellent adsorption performance (485.2 m²/g) and good recoverability (19.5 emu/g), which enabled it an ideal sorbent for wastewater treatment. Fe₃O₄@TpPa-1 exhibited excellent adsorption capacities for Cr (VI) (245.45 mg/g) and bisphenol A (1220.97 mg/g). The adsorption kinetics and isotherms were in alignment to the pseudo-second-order and Langmuir model, respectively. After five times cycles, the adsorption capacity of Fe₃O₄@TpPa-1 still retained at a high level. According to Materials Studio simulation and XPS analysis, the adsorption mechanism was attributed to the presence of the homogeneously distributed imine and carbonyl functional groups in the framework of TpPa-1, allowing them to serve as platforms for anchoring heavy metals and organic pollutants. Besides, the hydrophobic skeleton structures of TpPa-1 endowed them good adsorption performance towards organic pollutants via hydrogen -bonding (NH^…O^…HO) and π-π interaction. Therefore, the recyclable Fe₃O₄@TpPa-1 showed a broad application prospects in environmental remediation.

Chromium Hyper-Tolerant Bacillus sp. MH778713 Assists Phytoremediation of Heavy Metals by Mesquite Trees (Prosopis laevigata)

Heavy metal accumulation in mesquite trees (Prosopis laevigata) growing in aluminum, titanium, chromium and zirconium-polluted soils of a semi-arid region in Mexico was investigated using wavelength dispersive X-ray fluorescence analysis. The results showed that P. laevigata trees can hyper accumulate up to 4100 mg/kg of Al, 14000 mg/kg of Fe, 1600 mg/kg of Ti, 2500 mg/kg of Zn, but not chromium, regarding high chromium concentrations found in soils (435 mg/kg). Since plant-associated microorganism can modulate phytoremediation efficiency, the biodiversity of P. laevigata associated bacteria was studied. Eighty-eight isolates from P. laevigata nodules were obtained; all isolates tolerated high concentrations of Al, Fe, Zn and Cr in vitro. The top-six chromium tolerant strains were identified by 16S rRNA sequence analysis as belonging to genus Bacillus. Bacillus sp. MH778713, close to Bacillus cereus group, showed to be the most resistant strain, tolerating up to 15000 mg/L Cr (VI) and 10000 mg/L of Al. Regarding the bioaccumulation traits, Bacillus sp. MH778713 accumulated up to 100 mg Cr(VI)/g of cells when it was exposed to 1474 mg/L of Cr VI. To assess Bacillus sp. MH778713 ability to assist Prosopis laevigata phytoremediation; twenty plants were inoculated or non-inoculated with Bacillus sp. MH778713 and grown in nitrogen-free Jensen's medium added with 0, 10 and 25 mg/L of Cr(VI). Only plants inoculated with Bacillus sp. grew in the presence of chromium showing the ability of this strain to assist chromium phytoremediation. P. laevigata and Bacillus spp. may be considered as good candidates for soil restoration of arid and semiarid sites contaminated with heavy metals.

Iron Carbide@Carbon Nanocomposites: A Tool Box of Functional Materials

Iron carbide (Fe₃C) is a ceramic magnetic material with high potential for applications in different fields, including catalysis, medicine imaging, coatings, and sensors. Despite its interesting properties, it is still somehow largely unexplored, probably due to challenging synthetic conditions. In this contribution, we present a sol-gel-based method that allows preparing different Fe₃C@C nanocomposites with tailored properties for specific applications, in particular, we have focused on and discussed potential uses for adsorption of noxious gas and waste removal. Nanocomposites were prepared using readily available and "green" sources, such as urea, simple and complex sugars, and chitosan. The nanocomposite prepared from chitosan was found to be more efficient for CO₂ uptake, while the sample synthetized from cellulose had optimal capability for dye absorption and waste oil removal from water.

Removal of chromium (VI) from aqueous solution using vesicular basalt: A potential low cost wastewater treatment system

In this study, vesicular basalt volcanic rock was taken and its application for adsorption of chromium (VI) from aqueous solution was investigated. Different physical and chemical properties of the powdered rock was studied using Fourier transform infrared spectroscopy (FT-IR), Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). A series of batch experiments were carried out to study the effect of various experimental parameters (pH, ionic strength and contact time) on chromium (VI) adsorption. It was found that the removal efficiency of chromium (VI) decreased with increasing pH and ionic strength. The adsorption process was optimal at pH 2. The maximum adsorption capacity was 79.20 mg kg⁻¹ at an initial concentration of 5.0 mg L⁻¹ and adsorbent dosage of 50 g L⁻¹. In individual adsorption tests, Pseudo-second-order kinetic and Freundlich isotherm models could better describe chromium (VI) adsorption on the vesicular basalt. This study indicated that vesicular basalt, which is inexpensive, has the potential to remove chromium (VI) from polluted water.

Functionalization of Magnetic Chitosan Particles for the Sorption of U(VI), Cu(II) and Zn(II)-Hydrazide Derivative of Glycine-Grafted Chitosan

A new magnetic functionalized derivative of chitosan is synthesized and characterized for the sorption of metal ions (environmental applications and metal valorization). The chemical modification of the glycine derivative of chitosan consists of: activation of the magnetic support with epichlorohydrin, followed by reaction with either glycine to produce the reference material (i.e., Gly sorbent) or glycine ester hydrochloride, followed by hydrazinolysis to synthesize the hydrazide functionalized sorbent (i.e., HGly sorbent). The materials are characterized by titration, elemental analysis, FTIR analysis (Fourrier-transform infrared spectrometry), TGA analysis (thermogravimetric analysis) and with SEM-EDX (scanning electron microscopy coupled to energy dispersive X-ray analysis). The sorption performances for U(VI), Cu(II), and Zn(II) are tested in batch systems. The sorption performances are compared for Gly and HGly taking into account the effect of pH, the uptake kinetics (fitted by the pseudo-second order rate equation), and the sorption isotherms (described by the Langmuir and the Sips equations). The sorption capacities of the modified sorbent reach up to 1.14 mmol U g^-1, 1.69 mmol Cu g^-1, and 0.85 mmol Zn g^-1. In multi-metal solutions of equimolar concentration, the chemical modification changes the preferences for given metal ions. Metal ions are desorbed using 0.2 M HCl solutions and the sorbents are re-used for five cycles of sorption/desorption without significant loss in performances.

Higher adsorption capacity of Spirulina platensis alga for Cr(VI) ions removal: parameter optimisation, equilibrium, kinetic and thermodynamic predictions

This study discusses about the biosorption of Cr(VI) ion from aqueous solution using ultrasonic assisted Spirulina platensis (UASP). The prepared UASP biosorbent was characterised by Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmet-Teller, scanning electron spectroscopy and energy dispersive X-ray and thermogravimetric analyses. The optimum condition for the maximum removal of Cr(VI) ions for an initial concentration of 50 mg/l by UASP was measured as: adsorbent dose of 1 g/l, pH of 3.0, contact time of 30 min and temperature of 303 K. Adsorption isotherm, kinetics and thermodynamic parameters were calculated. Freundlich model provided the best results for the removal of Cr(VI) ions by UASP. The adsorption kinetics of Cr(VI) ions onto UASP showed that the pseudo-first-order model was well in line with the experimental data. In the thermodynamic study, the parameters like Gibb's free energy, enthalpy and entropy changes were evaluated. This result explains that the adsorption of Cr(VI) ions onto the UASP was exothermic and spontaneous in nature. Desorption of the biosorbent was done using different desorbing agents in which NaOH gave the best result. The prepared material showed higher affinity for the removal of Cr(VI) ions and this may be an alternative material to the existing commercial adsorbents.