Chromate Anions Research Articles

Metal-Organic Frameworks with Tb4 Clusters as Nodes: Luminescent Detection of Chromium(VI) and Chemical Fixation of CO2.

Two multifunctional metal-organic frameworks based on cubane-like tetrahedron Tb4 clusters as nodes have been synthesized and characterized. Compound 1 exhibits a 2D lanthanide-organic framework with Tb4 clusters as nodes, and compound 2 possesses a 3D framework with Tb4 clusters and Mn2+ as nodes. Interestingly, luminescent investigations on them reveal that the two compounds can act as recyclable luminescent probes for chromium(VI) anion species and the corresponding detection limit can reach 10-7 mol/L. Furthermore, 1 and 2 own efficient catalytic activity for the chemical fixation of CO2 with epoxides under mild conditions. Importantly, they both can be recycled at least three times without compromising the activity.

Hydrolytically Stable Luminescent Cationic Metal Organic Framework for Highly Sensitive and Selective Sensing of Chromate Anions in Natural Water Systems.

Effective detection of chromate anions in aqueous solution is highly desirable because of their high solubility, environmental mobility, carcinogenicity, and bioaccumulation effect. A new strategy for precise detection of chromate anions in the presence of a large excess of other anions, such as Cl-, NO3-, and HCO3-, in drinking water and natural water systems remains a challenge. Herein, a hydrolytically stable cationic luminescent europium(III)-based metal organic framework (MOF), 1, was successfully synthesized and investigated as a luminescent sensor that exhibits instant and selective luminescence quenching properties toward chromate ions in aqueous solutions. Moreover, 1 can be introduced into high-ionic-strength water system (e.g., seawater) for chromate detection as a consequence of the excellent sensing selectivity. The real environmental application of 1 as a chromate probe is studied in deionized water, lake water, and seawater. The detection limits in these aqueous media are calculated to be 0.56, 2.88, and 1.75 ppb, respectively. All of these values are far below the maximum contamination standard of Cr(VI) in drinking water of 100 ppb, defined by the U.S. Environmental Protection Agency. This excellent chromate sensing capability originates from the fast enrichment of chromate ions in solids of 1 from solutions, followed by efficient energy transfer from the MOF skeleton to the chromate anion, as demonstrated by solution absorption spectroscopy, X-ray diffraction, and chromate uptake kinetics and isotherm investigations. To the best of our knowledge, 1 possesses the lowest chromate detection limit among all reported MOFs up to date and is the only MOF material reported for chromate sensing application under environmentally relevant conditions with high ionic strengths.

Adsorption of Chromium (VI) on Calcium Phosphate: Mechanisms and Stability Constants of Surface Complexes

The adsorption of chromate on octacalcium phosphate (OCP) was investigated as a function of contact time, surface coverage, and solution pH [...]

Mechanochemical and Conventional Synthesis of Zn(II)/Cd(II) Luminescent Coordination Polymers: Dual Sensing Probe for Selective Detection of Chromate Anions and TNP in Aqueous Phase.

Isostructural Zn(II)/Cd(II) mixed ligand coordination polymers (CPs) {[M(IPA)(L)]}n (CP1 and CP2) built from isophthalic acid (H2IPA) and 3-pyridylcarboxaldehyde nicotinoylhydrazone (L) were prepared using versatile synthetic routes: viz., diffusion of precursor solutions, conventional reflux methods, and green mechanochemical (grinding) reactions. Both robust CPs synthesized by different routes were characterized by various analytical methods, and their thermal and chemical stability as well as the phase purity was established. Crystallographic studies revealed that CP1 and CP2 are isostructural frameworks and feature a double-lined two-dimensional network composed of Zn2+/Cd2+ nodes connected through IPA and pillared by the Schiff base ligand L with a double-walled edge. The photoluminescent (PL) properties of CP1 and CP2 have been exploited as dual detection fluorosensors for hexavalent chromate anions (CrO42-/Cr2O72-) and 2,4,6-trinitrophenol (TNP) because it was observed that the emission intensity of aqueous suspensions of CPs selectively quenches by chromate anions or TNP among large pools of different anions or nitro compounds, respectively. Competitive experiments in the presence of interfering anions/other nitro compounds also revealed no major effect in the quenching efficiency, suggesting the selective detection of hexavalent chromate anions as well as TNP by the LCPs. The limits of detection by CP1 for CrO42-/Cr2O72- and TNP are 4 ppm/4 ppm and 28 ppb, respectively, whereas the limits of detection by CP2 for the same analytes are 1 ppm/1 ppm and 14 ppb, respectively. A probable mechanism for the quenching phenomena is also discussed.

Ultrafiltration membrane for effective removal of chromium ions from potable water

The objective of the present work was to investigate the efficacy of indigenously developed polyacrylonitrile (PAN) based ultrafiltration (UF) membrane for chromium ions removal from potable water. The hydrolyzed PAN membranes effectively rejected chromium anions in the feed ranging from 250 ppb to 400 ppm and a rejection of ≥90% was achieved for pH ≥ 7 at low chromate concentration (≤25 ppm) in feed. The rejection mechanism of chromium ions was strongly dependent on Donnan exclusion principle, while size exclusion principle for UF did not play a major role on ions rejection. Feed pH played a vital role in changing porosity of membrane, which influenced the retention behavior of chromate ions. Cross-flow velocity, pressure did not play significant role for ions rejection at low feed concentration. However, at higher feed concentration (≥400 ppm), concentration polarization became important and it reduced the chromate rejection to 32% at low cross flow and high pressure. Donnan steric-partitioning pore and dielectric exclusion model (DSPM-DE) was applied to evaluate the chromate ions transport through PAN UF membrane as a function of flux by using optimized model parameters and the simulated data matched well with experimental results.

A specific fluorescence probe for chromium (VI) anions and its application

A facile fluorescent receptor for Cr(VI) anions was designed and prepared by 9-ethyl-9H-carbazole-3,6-dicarbaldehyde and 2-aminobenzenethiol. The interactions of the receptor with various anions were investigated through UV–vis absorption and fluorescence emission spectra, respectively. Experimental results revealed that the receptor could recognize Cr(VI) anions with high selectivity and sensitivity in H2O/DMSO mixed medium. A fluorescence “on-off” signal of the receptor to Cr(VI) anions was observed and verified by 1H NMR and density functional theory (DFT). The detection limit of the receptor for Cr(VI) may be up to 10−7mol/L. Additionally, the receptor as a fluorescent probe can be used to detect the content of Cr(VI) anions in milks, and displayed good accuracy and sensitivity. The work provides a new strategy for detecting Cr(VI) and developing the application in practical samples and systems.

Novel hexamethylene diamine-functionalized macroporous copolymer for chromium removal from aqueous solutions

Macroporous copolymers of poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) [PGME] with different crosslinker (EGDMA) concentrations and porosity parameters and additionally functionalized with hexamethylene diamine [PGME-HD] were tested as a potential Cr(VI) oxyanions sorbents from aqueous solutions. Kinetics of Cr(VI) sorption was investigated in the temperature range of 298–343 K and the results were fitted to chemical-reaction and particle-diffusion models. The Cr(VI) sorption obeys the pseudo-second-order model with definite influence of pore diffusion. The temperature rise promotes chromium removal, with the maximum experimental uptake capacity of 4.21 mmol g−1 at 343 K for the sample with the highest amino group concentration. Equilibrium data were analysed with Langmuir, Freundlich and Tempkin adsorption isotherm models. Thermodynamic parameters, i.e. Gibbs free energy (ΔG0), enthalpy (ΔH0) and entropy change (ΔS0) and activation energy of sorption (Ea) were calculated. The Cr(VI) adsorption onto PGME-HD was found to be spontaneous and endothermic, with increased randomness in the system. Desorption experiments show that the chromium anions sorption was reversible and the PGME-HD sample GMA 60 HD was easily regenerated with 0.1M NaOH up to 90 % recovery in the fourth sorption/desorption cycle. In the fifth cycle, the substantial sorption loss of 37 % was observed.

The influence of metal centres on the exchange interaction in heterometallic complexes with oxalate-bridged cations.

The reaction of bis(phenanthroline)metal(ii) cations (M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+) with bis(oxalato)chromium(iii) anions in a water/ethanol solution gives rise to a series of compounds with oxalate-bridged cations, [{M(phen)2}2(μ-C2O4)][Cr(phen)(C2O4)2]2·4H2O [Mn2Cr2 (1), Co2Cr2 (2), Ni2Cr2 (3), Cu2Cr2 (4) and Zn2Cr2 (5)]. Their structural analysis reveals that all the prepared compounds crystallize in the triclinic system, space group P1[combining macron], having similar unit cell parameters, molecular structures and crystal packing features. All metal centres in 1-5 are octahedrally coordinated: M2+ in homodinuclear cations are coordinated with two phen molecules and one bridging oxalate ligand; Cr3+ in anions is coordinated with one phen ligand and two bidentate oxalate groups. The copper atom in Cu2Cr2 (4) exhibits a Jahn-Teller-distorted octahedral coordination. Owing to the considerable number of pyridyl groups present in 1-5 (from phen ligands) the crystal packing of cations and anions is driven by stacking interactions appearing in offset-face-to-face (OFF) and edge-to-face (EF) orientations. The hydrogen bonds between the anions and water molecules of crystallization form 1D ladder-like motifs. In addition to the single crystal X-ray diffraction studies, the characterization of the new complexes was accomplished by means of IR and UV/Vis spectroscopy and magnetization measurements on a SQUID magnetometer. The temperature dependence of magnetic susceptibility reveals different magnetic super exchange interactions taking place in homodinuclear oxalate-bridged cations depending on the transition metal centre (Mn2+, Co2+, Ni2+ and Cu2+). Oxalate ligands mediate the ferromagnetic coupling of Cu2+ metal cations in Cu2Cr2 (4), whereas in Mn2Cr2 (1), Co2Cr2 (2) and Ni2Cr2 (3), antiferromagnetic interactions are observed between Mn2+, Co2+ and Ni2+ cations, respectively. Also, relatively large zero-field splitting parameters for Cr3+ ions (from mononuclear anions), D ≈ 1 cm-1, were observed.

In Situ Molecular Imaging of the Biofilm and Its Matrix.

Molecular mapping of live biofilms at submicrometer resolution presents a grand challenge. Here, we present the first chemical mapping results of biofilm extracellular polymeric substance (EPS) in biofilms using correlative imaging between super resolution fluorescence microscopy and liquid time-of-flight secondary ion mass spectrometry (TOF-SIMS). Shewanella oneidensis is used as a model organism. Heavy metal chromate (Cr2O72-) anions consisting of chromium Cr(VI) was used as a model environmental stressor to treat the biofilms. Of particular interest, biologically relevant water clusters have been first observed in the biofilms. Characteristic fragments of biofilm matrix components such as proteins, polysaccharides, and lipids can be spatially imaged. Furthermore, characteristic fatty acids (e.g., palmitic acid), quinolone signal, and riboflavin fragments were found to respond after the biofilm is treated with Cr(VI), leading to biofilm dispersal. Significant changes in water clusters and quorum sensing signals indicative of intercellular communication in the aqueous environment were observed, suggesting that they might result in fatty acid synthesis and inhibition of riboflavin production. The Cr(VI) reduction seems to follow the Mtr pathway leading to Cr(III) formation. Our approach potentially opens a new avenue for mechanistic insight of microbial community processes and communications using in situ imaging mass spectrometry and super resolution optical microscopy.

Impact of Fe(III) as an effective electron-shuttle mediator for enhanced Cr(VI) reduction in microbial fuel cells: Reduction of diffusional resistances and cathode overpotentials

The role of Fe(III) was investigated as an electron-shuttle mediator to enhance the reduction rate of the toxic heavy metal hexavalent chromium (Cr(VI)) in wastewaters, using microbial fuel cells (MFCs). The direct reduction of chromate (CrO4−) and dichromate (Cr2O72−) anions in MFCs was hampered by the electrical repulsion between the negatively charged cathode and Cr(VI) functional groups. In contrast, in the presence of Fe(III), the conversion of Cr(VI) and the cathodic coulombic efficiency in the MFCs were 65.6% and 81.7%, respectively, 1.6 times and 1.4 folds as those recorded in the absence of Fe(III). Multiple analytical approaches, including linear sweep voltammetry, Tafel plot, cyclic voltammetry, electrochemical impedance spectroscopy and kinetic calculations demonstrated that the complete reduction of Cr(VI) occurred through an indirect mechanism mediated by Fe(III). The direct reduction of Cr(VI) with cathode electrons in the presence of Fe(III) was insignificant. Fe(III) played a critical role in decreasing both the diffusional resistance of Cr(VI) species and the overpotential for Cr(VI) reduction. This study demonstrated that the reduction of Cr(VI) in MFCs was effective in the presence of Fe(III), providing an alternative and environmentally benign approach for efficient remediation of Cr(VI) contaminated sites with simultaneous production of renewable energy.

Removal of three anionic orange-type dyes and Cr(VI) oxyanion from aqueous solutions onto strongly basic anion-exchange resin. The effect of single-component and competitive adsorption

Adsorption of three anionic Orange-type dyes (i.e., Methyl Orange, Orange II, Orange G) and divalent chromate oxyanion onto Amberlite® IRN-78 from single- and bi-solute aqueous solutions have been investigated in view of testing the removal technologies for dye-contaminated wastewater. The research methodology was based on a combination of equilibrium adsorption, isothermal titration calorimetry, and 13C CP MAS NMR studies. The adsorption followed the pathway of anion exchange between the pristine OH− ions and the oncoming anionic species. The supernatant solution thus became more alkaline, which, in some cases, gave rise to new dye species with an additionally ionized R-N-NH-R moiety, e.g., OII2− or even OG3−. In the single-solute systems, the retention capacity of the resin towards various anionic solutes, on a per-mole basis, decreased in the following order: CrO42−>OG>OII≈MO. The retention of dyes was irreversible even in strongly alkaline media contrary to CrO42−, which was completely desorbed from the resin by a 1molL−1 NaOH solution. The competition between dye and chromate anions from their equimolar solutions mainly caused a marked decrease in the uptake of CrO42−, thereby pointing to preferential dye retention by Amberlite® IRN-78.

Cr(salophen) Complex Catalyzed Cyclic Carbonate Synthesis at Ambient Temperature And Pressure

The combination of a chromium(III) salophen bromide complex and tetrabutylammonium bromide is shown to catalyze the reaction between terminal epoxides and carbon dioxide at ambient temperature and 1 bar carbon dioxide pressure and between internal epoxides and carbon dioxide at 80 °C and 10 bar carbon dioxide pressure to form cyclic carbonates. The optimal conditions involve the use of 1.5–2.5 mol % of both the chromium(III) salophen bromide complex and tetrabutylammonium bromide and result in the formation of cyclic carbonates in 57–92% isolated yields after a reaction time of 24 h. Under these conditions, no polycarbonate formation is observed except when cyclohexene oxide is used as substrate. The reactions were found to proceed with retention of epoxide stereochemistry. A study of the reaction kinetics revealed that the chromium(III) complex and tetrabutylammonium bromide react together to form a six-coordinate anionic chromium complex which is the actual catalyst, and a catalytic cycle is proposed wh...

Regeneration of HDTMA-modified minerals after sorption with chromate anions

Surfactant-modified minerals have been widely used for the sorption of anionic and non-polar organic contaminants. This paper investigates the regeneration of various hexadecyltrimethylammonium bromide (HDTMA)-modified natural minerals saturated with chromate anions using different solutions for the extraction of chromates that has been sorbed at optimum conditions. The examined minerals include HDTMA-modified zeolite (clinoptilolite), exfoliated vermiculite, bentonite and attapulgite (palygorskite). Deionized water and sodium chloride, potassium chloride and sodium cyanide solutions at different concentrations (0.1–3 M) were employed as chromate desorption solutions. The HDTMA/Cr(VI)-mineral type, the desorbing solution type and its concentration and the mineral–solution contact time are key parameters that affect the process. From our results it was deduced that regeneration and reuse of HDTMA-modified minerals saturated with chromate is feasible. Bentonite exhibited greater stability than the other minerals studied in adsorption/desorption processes, maintaining 73% of its initial adsorption capacity after 14 successive regeneration cycles. The regeneration performance of the examined minerals follows the order: Bentonite > Attapulgite > Zeolite > Vermiculite. Kinetic study revealed that desorption was faster than adsorption, while the pseudo-second-order equation simulated better the experimental data.

Synthesis and characterization of novel nanofiber based calixarene and its binding efficiency towards chromium and uranium ions

The objective of this study is to obtain nanofibrous precursor based calixarene with high ion adsorption capacity by electrospinning of blended solution of polyacrylonitrile (PAN) and upper rim functionalized calix[4]arene bearing N-methylglucamine (Calix-NMG). The obtained electrospun fibers were characterized using fourier transform infrared (FT-IR-ATR), scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectrometry (EDX) and thermogravimetric analyses (TGA and DSC). Analysis indicated that preparation of nanofibers based Calix-NMG was successfully achieved. The ion binding studies exhibited that the nanofiber based Calix-NMG could be efficiently used for the binding of chromate anions and uranium cations. Nanofiber based calix[4]arene with N-methylglucamine chelating groups may be a good candidate as a filter material for treatment of a large quantity of wastewater owing to their very large surface area as well as both the inclusion and donor–acceptor complexation capability of all surfaces associated with the calixarene skeleton.

Application of superporous magnetic cationic cryogels for persistent chromate (toxic chromate and dichromate) uptake from aqueous environments

ABSTRACTPoly((3‐Acrylamidopropyl)trimethylammonium chloride) (p(APTMACl)) cryogels were prepared with cryopolymerization technique and employed for the removal of toxic chromate and dichromate anions from aqueous media. The maximum adsorption capacities of 94 mg/g and 135 mg/g for chromate and dichromate anions, respectively, were determined with the application of the Langmuir isotherm. These values are very close to the experimental values of about 77 and 128 mg/g from 100 mL, 100 ppm chromate, and dichromate solutions using 0.03 g cryogel. The removal efficiency of chromate and dichromate anions were increased with the increase in the amount of cryogel and the removal percentage of chromate and dichromate toxic anions were estimated as 99.21 and 93.61%, respectively, for 0.15 g of p(APTMACl) cryogels used in 100 mL, 100 ppm chromate, and dichromate solutions. Furthermore, magnetic p(APTMACl) cryogels were also prepared and used in the removal of chromate and dichromate, and the maximum adsorption capacities were 30 mg/g and 40 mg/g, respectively. Additionally, the adsorption of these anions were investigated from different media such as drinking water, tap water, seawater, and creek water; and the maximum adsorption amounts in drinking water were 65.5 ± 15, and 125.5 ± 11 mg/g for chromate and dichromate anions, respectively. The reusability of p(APTMACl) cryogels for the removal of chromate and dichromate anions was also investigated, and it was found that the adsorption capacity for chromate anions decreased to 71.23 ± 4.3 from 97.37 ± 4.5 mg/g, whereas the adsorption capacity of dichromate anions only decreased to 123.69 ± 3.5 mg/g from 129.9 ± 7 mg/g at the end of five adsorption‐desorption cycles. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43438.

Adsorption and determination of Cr(VI) in environmental samples using triazine-modified Fe3O4 nanoparticles: kinetics and equilibrium modeling

A facile and highly sensitive adsorbent for the determination of Cr(VI) ions has been developed for the first time. The sorbent was based on triazine-functionalized Fe3O4 nanoparticles and was prepared by direct silylation of magnetic nanoparticles with 3-aminopropyltriethoxysilane-2,4-bis(3,5-dimethylpyrazol)-triazine and was characterized by infrared spectroscopy, transmission electron microscopy, X-ray powder diffraction, and electron-dispersive X-ray analyses. The sorbent was applied to adsorption, preconcentration, and determination of chromate anions by the solid-phase extraction method. The effects of various factors including the pH of the solution, concentration of the adsorbate, adsorption time, and temperature on removal of Cr(VI) ions were optimized. The Cr(VI) removal efficiency of 85.8 % was achieved at the optimum initial pH of 3. The maximum adsorption capacity was 170.68 mg g−1 at an initial concentration of 75.0 mg L−1 and adsorbent dosage of 0.1 g L−1. The equilibrium data were analyzed using the Langmuir and Freundlich isotherm models by nonlinear regression analysis. The results obtained from adsorption isotherm indicated that these data can be better fitted to the Langmuir equation than the Freundlich equation. The kinetic analysis revealed that the adsorption process was successfully fitted with the pseudo-second-order kinetic model. The thermodynamic investigation demonstrated that the adsorption process is endothermic, spontaneous, and feasible in nature. Furthermore, the new sorbent was successfully applied for the determination of Cr(VI) anions in a few environmental samples using a continuous method.

Two solvent-stable MOFs as a recyclable luminescent probe for detecting dichromate or chromate anions

Two unique 2D Zn-MOFs with the formulas {[Zn(btz)]n} (1) and {[Zn2(ttz)H2O]n} (2) were synthesized using in situ generated ligands under hydro(solvo)thermal conditions. Both 1 and 2 exhibit high thermo-stability, solvent-stability and pH-stability. Thermogravimetric analyses (TGA) reveal that 1 and 2 remain intact until about 365 °C and 332 °C, respectively. The samples of 1 and 2 were immersed in twelve common solvents for 24 hours, and the obtained PXRD patterns remain well consistent with the simulated ones. They were immersed in a series of solutions with pH values ranging from 1.0 to 14.0 for five hours, and the PXRD patterns of these samples remain unchanged spanning the pH range of 1–13. The luminescence investigations reveal that the compounds 1 and 2 can efficiently and selectively detect Cr2O72− or CrO42− among twenty-one anions. Importantly, they can be regenerated by a fast and simple method in detecting Cr2O72− or CrO42−.

Biosorbent immobilized nanotube reinforced hydrogel carriers for heavy metal removal processes

AbstractA series of natural composite hydrogels containing a “3-in-1” type triple adsorbent system are designed. For this purpose, Spirulina (Sp) biosorbent is immobilized on/in halloysite nanotubes in different loadings and then physically crosslinked chitosan composite hydrogels are prepared. The water absorbency and Cr (VI) adsorption capacity in neutral pH medium and wet mechanical strength as well as their morphologies are all reported as a function of Sp immobilized nanotube loadings. The use of Sp biosorbent results in composite hydrogels with high water absorbency, wet strength and thermal stability. Spirulina enlarges the metal adsorption windows efficiently and the Freundlich isotherm model can fit the fundamental metal adsorption data well. It is believed that with optimized special composite hydrogel morphologies, all positively charged receptors of the Sp and the nanotubes behave as collector domains for chromate anions.

Chromate surface-imprinted silica gel sorbent for speciation of Cr in surface waters

This study is focused on the synthesis of chromate anion imprinted sorbent supported on silica gel for nonchromatographic Cr speciation in surface waters. The preparation procedure is based on grafting of 3-methyl-1-trimethoxysilylpropylimidazolium, preliminarily coordinated to CrO$_{4}^{2-}$ as a template ion, onto the surface of silica gel. Sorption and desorption characteristics of surface-imprinted sorbent toward Cr(III) and Cr(VI) were examined by batch solid-phase extraction. An excellent separation of Cr(VI), selectively retained on the sorbent, from Cr(III) remained in the solution, was achieved at pH 2-3 for 20 min. A freshly prepared mixture of ascorbic acid and nitric acid was selected as the most efficient eluent for quantitative desorption of the retained Cr(VI). An analytical procedure for Cr speciation in surface waters was developed and validated through analysis of certified reference materials. Detection limits achieved and relative standard deviations for typical concentration levels of Cr(VI) in surface waters matched the requirements of analytical procedures used in monitoring programs.

Hexavalent chromium removal performance of anionic functionalized monolithic polymers: column adsorption, regeneration and modelling.

Anionic functionalized monolithic macro-porous polymers were used for the removal of hexavalent chromium(VI) anions from aqueous solution in column experiments. At a flux of 1.0 cm min and 30 mg Cr(VI) L(-1) feed concentration, breakthrough capacity and apparent capacity were 0.066 g Cr(VI) g(-1) anionic monolith and 0.144 g Cr(VI) g(-1) anionic monolith, respectively. The degree of column utilization was found to lie in the range 41-46%. Two kinetic models, theoretical and Thomas models, were applied to experimental data to predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design. The simulation of the whole breakthrough curve was effective with the models. At a flux of 1.0 cm min and 30 mg Cr(VI) L(-1) feed concentration, the dispersion coefficient and adsorption equilibrium constant (K) were 3.14 × 10(-7) m s(-1) and 3,840, respectively. Also, Thomas model parameters k1 (rate constant of adsorption) and qm (equilibrium solid-phase concentration of sorbed solute) were 1.08 × 10(-3) L mg(-1) min(-1) and 0.124 g g(-1), respectively. After reaching equilibrium adsorption capacity, the monoliths were regenerated using 1 N HCl and were subsequently re-tested. It was found that the regeneration efficiency reduced from 98% after second usage to 97% after the third usage.