Chromate Anions Research Articles

Metal-organic-framework and walnut shell biochar composites for lead and hexavalent chromium removal from aqueous environments

Extensive research in recent years has explored the realm of porous carbon composites for various applications, including electrochemistry, structural materials, environmental remediation, and more. In particular, the fabrication of porous carbon composites using a metal-organic framework (MOF) and biochar (BC) for aqueous remediation is a fairly new avenue of research. In this study, a MOF-BC composite was synthesized with unmodified and chemically modified BCs using solvothermal synthesis. The composites were used as adsorbents to remediate heavy metals, such as lead (II) and chromium (VI), from aqueous environments. It was verified that the MOF was homogeneously deposited onto the BC's surface using various material characterization techniques. Lead and chromium adsorption studies revealed a high adsorption capacity with greater than 99% removal for lead and ∼65% for chromium, respectively. Impressively, for lead, the highest observed experimental adsorption capacity of the MOF-chemically modified BC composite was 535 mg/g, compared to 240 mg/g for pristine BC. Meanwhile, the adsorption capacity of the same MOF-BC composite for chromium ions was low at 18 mg/g, compared to 80 mg/g for the chemically modified BC. The MOF-BC had a rapid adsorption rate, achieving equilibrium at only 150 min of reaction time for lead ions. MOF-BCs have higher adsorption for cationic lead through physisorption and ion-exchange mechanisms, whereas, for anionic chromium, removal is dominated only by physisorption mechanisms. The outcomes and methodological developments attained in this study offer a novel and compelling approach for synthesizing MOF-BC composites for aqueous remediation applications.

Simultaneous Removal of Eriochrome Black T and Chromate Anions from Aqueous Solution Using Functionalized Hybrid Magnetic Polymers

Simultaneous Removal of Eriochrome Black T and Chromate Anions from Aqueous Solution Using Functionalized Hybrid Magnetic Polymers

An europium complex assembled by a flexible derivative of imidazole-4,5-dicarboxylic acid as a fluorescence turn-off chemosensor to detect Cr(VI) anions

A new europium(III) CP [Eu(HBBIDA)(H2O)]n (1) (H4BBIDA = 1,1′-(butane-1,4-diyl)bis(1H-imidazole-4,5-dicarboxylic acid) was successfully constructed by hydrothermal synthesis method and detailed characterization was performed. Crystal structure analysis reveals that CP 1 presents a 2D layered structure composed of cage-like SBUs with a TiS2 topological network. CP 1 can maintain framework integrity in an air environment below 260 °C, as well as in a certain pH range of acid-base aqueous solutions and common organic reagents, showing better thermal and chemical stability. Fluorescence measurements show that CP 1 exhibited excellent sensing activities toward CrO42− and Cr2O72− anions through fluorescence quenching, and their average quenching Ksv values of 3.99 × 103 M−1 (CrO42−) and 4.36 × 103 M−1 (Cr2O72−) and the LOD of 3.30 × 10−6 M (CrO42−) and 3.02 × 10−6 M, which makes it very suitable for the detection of hexavalent chromium anions contaminants in aqueous solutions. Furthermore, possible sensing mechanisms have been studied and discussed in detail, and the results show that static photocompetitive absorption should be the primary cause for the fluorescence quenching of the sensor.

Fast and efficient chromium(VI) extraction by colloidal Mg/Al layered double hydroxide nanoparticles

Due to the constraints associated with diffusion and mixing time, traditional kinetic and thermodynamic approaches were inadequate for probing the true mechanism of interaction between chromate and Layered Double Hydroxide (LDH). To circumvent these limitations, colloidal suspensions of Mg/Al-NO3 LDH, characterized by a positively charged surface (approximately +50 mV) in ultrapure water and a mean average diameter of 140 nm, allowing the formation of stable suspensions for days, were swiftly mixed with Cr(VI) suspensions at both pH = 4 and 9 using a stopped flow technique. This rapid mixing, accomplished in <5 milliseconds, enabled the examination of the initial stages of interaction between the toxic anion and the host compound. Two distinct steps in the adsorption process were identified: a very fast step (completed in <5 ms), representing up to 80% of the measured variation, and a slower step lasting up to 100 s. The fast step assumed to be driven by electrostatic interaction (ζ ∼ +50 mV) with the surface, and sites close to the surface are easily accessible to the chromate anions. The slower step corresponded to a diffusion process close or inside the particles. Chromate extraction efficiency was investigated through ultrafiltration tests, varying the LDH and chromate amounts, indicating that 2 nitrate ions are exchanged for 1 chromate, regardless of the pH considered, and a total exchange can be fulfilled with 0.1 g L−1 of LDH within the explored concentration range.

Superior comprehensive performance of modified activated carbon as a hexavalent chromium adsorbent

The presence of hexavalent chromium species (CrVI) in wastewater from manufacturing industries such as electroplating and leather production can pose serious health hazards. To address these concerns, this study developed a novel adsorbent based on activated carbon as the primary material to attract CrVI. Activated carbon has been modified with several other components to improve its comprehensive performance, including adsorption capacity, chemical stability, collectability, and reusability. Specifically, decoration with magnetite nanoparticles made it possible to collect the adsorbent magnetically and reuse it several times. On the one hand, the addition of chitosan not only increased the chemical stability of activated carbon, especially under acidic conditions, but also enhanced the Cr adsorption capacity at pH higher than 4, where adsorption of only activated carbon was significantly decreased, probably because the protonated amino groups attracted chromate anions. In addition, the co-existence of tannic acid did not increase the adsorption capacity significantly but appeared to promote the reductive adsorption of CrVI, where the reduction of CrVI means lowering the toxicity of Cr species. It was demonstrated that activated carbon modified with magnetite, chitosan, and tannic acid exhibited superior comprehensive performance that could be repeatedly used over a wide pH range as compared to the parent activated carbon.

Synthesis, structural characterization, and anion binding studies of bisamide functionalized molecular clefts

The utilization of amide functional groups as anion-binding sites in the structure of synthetic anion receptors has received significant attention. In this study, three new compounds, namely, N,N′-bis(2-(pyridin-2-yl)ethyl)pyridine-2,6-dicarboxamide (L1), N,N′-bis(2-(pyridin-3-yl)ethyl)pyridine-2,6-dicarboxamide (L2), and N,N′-bis(2-(pyridin-4-yl)ethyl)pyridine-2,6-dicarboxamide (L3), have been successfully synthesized. These compounds were fully characterized using a combination of spectroscopic techniques such as Fourier transform infrared spectroscopy, gas chromatography–mass spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, elemental analysis, and ultraviolet–visible (UV–Vis) spectroscopy. Further investigation on the potential of these compounds to bind with anions, such as chloride, nitrate, chromate, and phosphate, has been conducted using UV–Vis titration and a fluorescence titration method, and the results revealed that compound L2 has high potential to bind with chloride, chromate, and phosphate anions compared with other investigated hosts and analytes. This has opened a good opportunity for further application bisamide compound as anion sensing materials in the future.

ATR activation by Cr-DNA damage is a major survival response establishing late S and G2 checkpoints after Cr(VI) exposure

Inhalation exposure to hexavalent chromium is known to cause lung cancer and other pulmonary toxicity. Cellular metabolism of chromium(VI) entering cells as chromate anion produces different amounts of reactive Cr(V) intermediates and finally yields Cr(III). Direct reduction of Cr(VI) by ascorbate (Asc), the dominant metabolic reaction in vivo but not in standard cell cultures, skips production of Cr(V) but still permits extensive formation of Cr-DNA damage. To understand the importance of different forms of biological injury in Cr(VI) toxicity, we examined activation of several protein- and DNA damage-sensitive stress responses in human lung cells under Asc-restored conditions. We found that Asc-restored cells suppressed upregulation of oxidant-sensitive stress systems by Cr(VI) but showed a strong activation of the apical DNA damage-responsive kinase ATR. ATR signaling was triggered in late S phase and persisted upon entry of cells into G2 phase. Inhibition of ATR prevented the establishment of late-S and G2 cell cycle checkpoints and did not lead to a compensatory activation of a related kinase ATM. Inactivation of ATR also strongly impaired viability of Cr(VI)-treated lung cells including stem-like cells and revealed a significant formation of toxic Cr-DNA damage at low Cr(VI) doses. Our findings identified a major Cr(VI) resistance mechanism involving sensing of Cr-DNA damage by ATR in late S phase and a subsequent establishment of protective cell cycle checkpoints.

A potential remediation of chromium (VI) containing aqueous media onto surface-treated clinoptilolite vs. brief evaluation of other natural materials

A broad range of various natural and commercial adsorption materials and waste products was examined in order to verify the removal of commonly occurring cationic, anionic and some organic pollutants and briefly to compare each other. The inland natural zeolites of clinoptilolite type and its surface-treated modifications were used too. Actually, untreated clinoptilolite can compete with other natural materials or even waste products, occurring in the markets of many countries at very low prices. Industrial adsorbents are usually characterized with a high surface area, mechanical stability and uniformly accessible and interlinked pores. Abundantly occurring clinoptilolite tuffs, the Slovak one used in this research, possess the necessary interparticle mesoporosity. Moreover it is a natural cost-effective resource. The most extensive uptake of the studied chromate oxyanions at laboratory measure was observed by montmorillonite (142.86 mg/g), probably based on the large interplanar dimensions of this microcrystallite. The octadecyl ammonium hydrophobized i.e. ODA-clinoptilolite approached the second highest adsorption capacity to chromate (64.93 mg/g), while the MnOx-zeolite (clinoptilolite) proved the lowest adsorption ability (12.99 mg/g). Almost for all the systems studied, the Langmuir isotherm fitted better for mathematical description of the above adsorption process. From the breakthrough curves recorded, the Pb – and ODA – clinoptilolite packed column quantitatively removed chromate anion from the solution, apparently more efficiently using the lower flow rate.

Asymmetric Alternative Current Electrochemical Method Coupled with Amidoxime-Functionalized Carbon Felt Electrode for Fast and Efficient Removal of Hexavalent Chromium from Wastewater

A large amount of Cr (VI)-polluted wastewater produced in electroplating, dyeing and tanning industries seriously threatens water ecological security and human health. Due to the lack of high-performance electrodes and the coulomb repulsion between hexavalent chromium anion and cathode, the traditional DC-mediated electrochemical remediation technology possesses low Cr (VI) removal efficiency. Herein, by modifying commercial carbon felt (O-CF) with amidoxime groups, amidoxime-functionalized carbon felt electrodes (Ami-CF) with high adsorption affinity for Cr (VI) were prepared. Based on Ami-CF, an electrochemical flow-through system powered by asymmetric AC was constructed. The mechanism and influencing factors of efficient removal of Cr (VI) contaminated wastewater by an asymmetric AC electrochemical method coupling Ami-CF were studied. Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) characterization results showed that Ami-CF was successfully and uniformly loaded with amidoxime functional groups, and the adsorption capacity of Cr (VI) was more than 100 times higher than that of O-CF. In particular, the Coulomb repulsion effect and the side reaction of electrolytic water splitting were inhibited by the high-frequency anode and cathode switching (asymmetric AC), the mass transfer rate of Cr (VI) from electrode solution was increased, the reduction efficiency of Cr (VI) to Cr (III) was significantly promoted and a highly efficient removal of Cr (VI) was achieved. Under optimal operating conditions (positive bias 1 V, negative bias 2.5 V, duty ratio 20%, frequency 400 Hz, solution pH = 2), the asymmetric AC electrochemistry based on Ami-CF can achieve fast (30 s) and efficient removal (>99.11%) for 0.5-100 mg·L-1 Cr (VI) with a high flux of 300 L h-1 m-2. At the same time, the durability test verified the sustainability of the AC electrochemical method. For Cr (VI)-polluted wastewater with an initial concentration of 50 mg·L-1, the effluent concentration could still reach drinking water grade (<0.05 mg·L-1) after 10 cycling experiments. This study provides an innovative approach for the rapid, green and efficient removal of Cr (VI) containing wastewater at low and medium concentrations.

Efficient adsorption of cesium cations and chromate anions by one-step process using surfactant-modified zeolite

Natural zeolite is organically modified with the surfactant cetyltrimethylammonium bromide (CTAB) and employed as a dual-function material for simultaneous adsorption of Cs+ cations and HCrO4− anions from aqueous solutions. Unmodified and modified zeolites are characterized by Fourier transform infrared (FTIR), dynamic light scattering (DLS), nitrogen adsorption–desorption isotherms, and X-ray diffraction (XRD). The results showed that CTAB-zeolite had the efficiency to simultaneously adsorb the concerned species in the pH range 2.5–4.2. The kinetic data showed that 90 and 300 min for Cs(I) and Cr(VI), respectively, were sufficient to attain equilibrium and the data are well-fitted by the double-exponential kinetic model. Of the studied adsorption isotherm models, Redlich-Peterson was the best one for describing the equilibrium adsorption isotherms. Values of ∆H°, ∆S°, and ∆G° for the present adsorption processes are estimated. CTAB-zeolite exhibited adsorption capacities of 0.713 and 1.216 mmol/g for Cs(I) and Cr(VI), respectively, which are comparable with the data reported in the literature. The adsorption mechanism of the concerned (radio)toxicants is proposed.

Chemical mechanisms of DNA damage by carcinogenic chromium(VI).

Hexavalent chromium is a firmly established human carcinogen with documented exposures in many professional groups. Environmental exposure to Cr(VI) is also a significant public health concern. Cr(VI) exists in aqueous solutions as chromate anion that is unreactive with DNA and requires reductive activation inside the cells to produce genotoxic and mutagenic effects. Reduction of Cr(VI) in cells is nonenzymatic and in vivo principally driven by ascorbate with a secondary contribution from nonprotein thiols glutathione and cysteine. In addition to its much faster rate of reduction, ascorbate-driven metabolism avoids the formation of Cr(V) which is the first intermediate in Cr(VI) reduction by thiols. The end-product of Cr(VI) reduction is Cr(III) which forms several types of Cr-DNA adducts that are collectively responsible for all mutagenic and genotoxic effects in Cr(VI) reactions with ascorbate and thiols. Some Cr(V) forms can react with H2O2 to produce DNA-oxidizing peroxo species although this genotoxic pathway is suppressed in cells with physiological levels of ascorbate. Chemical reactions of Cr(VI) with ascorbate or thiols lack directly DNA-oxidizing metabolites. The formation of oxidative DNA breaks in early studies of these reactions was caused by iron contamination. Production of Cr(III)-DNA adducts in cells showed linear dose-dependence irrespective of the predominant reduction pathway and their processing by mismatch repair generated more toxic secondary genetic lesions in euchromatin. Overall, Cr(III)-DNA adduction is the dominant pathway for the formation of genotoxic and mutagenic DNA damage by carcinogenic Cr(VI).

Role of Smart-Release Pigments in Preventing Corrosion Driven Cathodic Disbondment of Organically Coated Hot Dip Galvanised Steel

The role of smart-release corrosion inhibitive pigments in preventing cathodic delamination of organically coated hot-dip galvanized steel (HDG) is investigated. The pigments consisted of hydrotalcite (HT) exchanged with a range of inorganic and organic anionic species and were dispersed in a model PVB coating. A scanning Kelvin probe (SKP) technique was used to determine cathodic delamination rates, and the inhibition efficiencies obtained for inorganic ions increased in the order < < < < < < The inhibition efficiencies for organic-based pigments increased in the order triazole <phenylphosphonate <trans-cinnamate <benzoate <salicylate <benzotriazole. The inhibition efficiency afforded by the best performing organic inhibitor, benzotriazole (BTA), rivalled that of HT containing stored chromate anions. Findings are consistent with HT-BTA acting to sequester anions from the underfilm electrolyte, releasing BTA− which subsequently strongly adsorbs on the underfilm metal surface but can also form an insoluble Zn-BTA precipitate at the coating-defect boundary.

Chemically grafting Cu(ii)-Schiff base complex on magnetic graphene oxide–cobalt ferrite (GO/CoFe2O4) nanocomposite for the selective and ultrafast removal of toxic anionic dyes and dichromate–chromate anions from water

A copper(ii) Schiff base complex was grafted onto a magnetic graphene oxide–cobalt ferrite (GO/CoFe2O4) composite using 3-aminopropyltriethoxysilane as a linker and used as a rapid and selective adsorbent to remove anionic organic dyes from water.

Synthesis of Two Neutral Silver Alkynyl Nanoclusters by a Single Divalent Tetrahedral Anion Template and a Study of Their Optical Features.

The synthesis of nanoclusters from simple structural units is usually a challenging process because of the complexity and unpredictability of the self-assembly process of these types of compounds. Herein, two new neutral 19-nuclearity silver nanoclusters based on alkynyl ligands with the formulas [(CrO4)@Ag19(C≡CtBu)8(Ph2PO2)6(tfa)3(CH3OH)2] (1) and [(SO4)@Ag19(C≡CtBu)8(Ph2PO2)6(tfa)3(CH3OH)2] (2), in which tfa = trifluoroacetate, were synthesized, and their structures were investigated by single-crystal and powder X-ray diffraction, electrospray ionization mass spectrometry, elemental analyses, and Fourier transform infrared spectroscopy. The surface ligands of Ph2PO2H and trifluoroacetate were assembled through hydrogen bonding, metal-aromatic interactions, and coordination bonding around 19 silver atoms as the metal skeletons of the nanoclusters. Sulfate and chromate anions, as a template within the metal skeleton of clusters through bonding with silver atoms, stabilized the structure. In addition, the UV-vis absorption spectroscopy, luminescence properties, and thermal stability of the nanoclusters were investigated.

Schiff Base-functionalized Metal-organic Frameworks for Selective Sensing of Chromate and Dichromate in Water.

In this research, Zn- or Cd-based metal-organic frameworks (coded ZnMOF-1 and CdMOF-1) containing benzene-1,4-dicarboxylic acid (H2bdc) and pyridyl-based Schiff base (4-pyridylcarboxaldehydeisonicotinoylhydrazone (L)) dual ligands were successfully assembled via a conventional solvothermal method. The photoluminescence quenching response of ZnMOF-1 and CdMOF-1 and their sensing sensitivity and selectivity towards various inorganic anions were evaluated in aqueous media. Crystallographic and thermogravimetric studies confirm the formation of both MOFs with good crystallinity and thermal stability. Photoluminescence studies also verify the selectivity of ZnMOF-1 and CdMOF-1 for efficient sensing of inorganic oxyanions (like chromate/dichromate: CrO42- and Cr2O72-). Further, it was noted that only chromate/dichromate (CrO42-/Cr2O72-) anions showed a significant turn-off quenching effect while other anions (like F-, Br-, I-, Cl-, ClO4-, SCN-, SO42-, NO3-, and NO2-) have a low/negligible effect on the photoluminescence intensity of both MOFs. The limit of detection (LOD) of chromate/dichromate by ZnMOF-1 and CdMOF-1 was 9.79/10.94µM and 2.68/1.48µM, respectively. A probable mechanism for turn-off quenching response towards chromate and dichromate anions could be attributed to the spectral overlap of both excitation and emission spectra of ZnMOF-1/CdMOF-1 with the absorption spectra ofchromate/dichromate anions. As a result, the energy transfer from ZnMOF-1 or CdMOF-1 to the target chromate and dichromate anions decreased fluorescence intensity (i.e., fluorescence quenching effect).

Adsorption of Hexavalent Chromium Using Activated Carbon Produced from Sargassum ssp.: Comparison between Lab Experiments and Molecular Dynamics Simulations.

Adsorption is one of the most successful physicochemical approaches for removing heavy metal contaminants from polluted water. The use of residual biomass for the production of adsorbents has attracted a lot of attention due to its cheap price and environmentally friendly approach. The transformation of Sargassum—an invasive brown macroalga—into activated carbon (AC) via phosphoric acid thermochemical activation was explored in an effort to increase the value of Sargassum seaweed biomass. Several techniques (nitrogen adsorption, pHPZC, Boehm titration, FTIR and XPS) were used to characterize the physicochemical properties of the activated carbons. The SAC600 3/1 was predominantly microporous and mesoporous (39.6% and 60.4%, respectively) and revealed a high specific surface area (1695 m2·g−1). To serve as a comparison element, a commercial reference activated carbon with a large specific surface area (1900 m2·g−1) was also investigated. The influence of several parameters on the adsorption capacity of AC was studied: solution pH, solution temperature, contact time and Cr(VI) concentration. The best adsorption capacities were found at very acid (pH 2) solution pH and at lower temperatures. The adsorption kinetics of SAC600 3/1 fitted well a pseudo-second-order type 1 model and the adsorption isotherm was better described by a Jovanovic-Freundlich isotherm model. Molecular dynamics (MD) simulations confirmed the experimental results and determined that hydroxyl and carboxylate groups are the most influential functional groups in the adsorption process of chromium anions. MD simulations also showed that the addition of MgCl2 to the activated carbon surface before adsorption experiments, slightly increases the adsorption of HCrO4− and CrO42− anions. Finally, this theoretical study was experimentally validated obtaining an increase of 5.6% in chromium uptake.

Modified and pristine biochars for remediation of chromium contamination in soil and aquatic systems.

Chromium (Cr) contamination in soil and water poses high toxicity risks to organisms and threatens food and water security worldwide. Biochar has emerged as a promising material for cleaning up Cr contamination owing to biochar's strong capacity to immobilize Cr. This paper synthesizes information on biochar modification for the efficient remediation of Cr contamination in soil and water, and critically reviews mechanisms of Cr adsorption on pristine and modified biochars. Biochar modification methods include physical activation via ball milling or ultraviolet irradiation, chemical activation via magnetization, alkali/acid treatment, nano-fabrication or loading of reductive agents, and biological activation via integrating biochars with microorganisms and their metabolites. Modified biochars often have multi-fold enhancement in Cr adsorption/reduction capacity than pristine biochars. Iron (Fe)-supported magnetic biochars have the most promising Cr removal abilities with high reusability of the biochars. Pre-pyrolysis modification with Fe could load Fe3O4 micro-/nanoparticles on biochars, and increase the surface area and electrostatic attraction between chromate anions and biochar surfaces, and reduce Cr(VI) to Cr(III). Post-pyrolysis modification could enrich oxygen-containing functional groups such as CO and -OH on biochar surfaces and promote Cr reduction and adsorption. Future research directions for Cr mitigation using advanced biochar products are discussed in this review.

Rust triggers rapid reduction of Cr6+ by red phosphorus: The importance of electronic transfer medium of Fe3.

Red phosphorus (P) is one of the metalloid materials, with five external electrons, it should be an excellent electron donor. However, the activity of red P to reduce Cr6+ is limited. Due to electrostatic repulsion, it is difficult for the electrons on the red P to transfer to the chromate anion (Cr6+). Interestingly, we found that Fe3+ derived from rust, waste iron or Fe3+ reagents can be used as the electron transport medium to solve the electron transport obstacles between red P and Cr6+. As a result, the reduction of Cr6+ by red P/rust system takes only 20min, which is far lower than the 140min of red P. The reduction rate of Cr6+ in the red P/rust system is about 12.3 times that of red P. The reaction mechanism is that red P is not easy to access chromate anions but can easily adsorb Fe3+. The adsorbed Fe3+ will be reduced to Fe2+ by red P, and the regenerated Fe2+ will diffuse into the solution to rapidly reduce Cr6+. Therefore, this work provides an alternative waste iron reuse pathway and also sheds light on the important role of electron medium in reduction reaction.

Hexavalent chromium adsorption by tetrahexylphosphonium modified beidellite clay

The fixation of the hexavalent chromium (CrVI), a toxic component in the wastewater, from the aqueous solutions into the interlayer space of beidellite (Bd) clay was studied, combining theoretical and experimental methods. The structure of intercalated CrVI anionic species to beidellite modified by tetrahexylphosphonium cation (Cr-THP-Bd) was examined using the density functional theory (DFT) calculations on representative structural models. The computed basal spacing (d001) of the Cr-THP-Bd model (15.5 Å) showed a good agreement with the experimental value (15.3 Å) obtained by the XRD method. Calculated intercalation energy of −214.2 kJ/mol demonstrated strong stabilization of chromate anion in the THP-Bd structure. C–H⋅⋅⋅O and O–H⋅⋅⋅O hydrogen bond interactions present in the Cr-THP-Bd model significantly affected the structural stability of the whole studied system. The calculated vibrational spectra from the ab initio molecular dynamics (AIMD) helped identify the Cr–O stretching and O–Cr–O bending vibrational modes of (CrO4)2− anion in the complex FTIR spectra. The amount of (CrO4)2− anion determined by the experiment clearly confirmed that Bd modified by the THP surfactant significantly increased the adsorption of the chromate anion in comparison to pure Na-Bd clay.

Hybrid amino-terminated lignin microspheres loaded with magnetite and manganese oxide nanoparticles: An effective hazardous oxyanions adsorbent

Highly effective lignin-based microspheres were prepared by inverse copolymerization of lignin (kraft) from suspension, with poly(ethylene imine) and amino-functionalized magnetite nanoparticles (A-LMS_Fe3O4) or manganese(IV)oxide nanoparticles (A-LMS_MnO2). The XRD, FTIR, SEM, BET, TEM techniques, including the porosity determination, were performed to analyze morphological and structural properties of synthesized microspheres. The effect of pH, the adsorbent dosage, temperature and contact duration on a batch-mode adsorption efficiency of arsenate and chromate (oxy)anions removal was tested. Spontaneous adsorption was found to be feasible, reaching the adsorption capacities of Cr(VI) (62.9 mg g−1), As(V) (47.8 mg g−1) by A-LMS_Fe3O4, and of Cr(VI) (73.9 mg g−1), As(V) (62.5 mg g−1) using A-LMS_MnO2 adsorbent. Fast removal rates were confirmed via kinetic study, using pseudo-second order, the Weber-Morris and the single resistance mass-transfer model, with a limiting step of the diffusion transport through pores. The correlation of fixed-bed-column results with Bohart–Adams, Thomas, Yoon–Nelson and Dose Response models displayed that breakthrough behavior was influenced by flow rate and the inlet concentration. Significant potential of produced bio-adsorbent is further confirmed by the pore surface diffusion modeling, desorption study and adsorption from multi-component system using artificial water.