Cr Sorption Capacity Research Articles

PAN/PVP/CD-MOF Composite Beads for the Removal of Methylene Blue and Congo Red in Water

Cyclodextrin metal-organic frameworks (CD-MOFs) are synthesized from green precursors, making them an ideal material for green adsorbents. However, CD-MOFs are unstable in water, thus limiting their applications. Here, we report encapsulating CD-MOFs in polyacrylonitrile (PAN) and polyvinylpyrrolidone (PVP) polymeric support to produce PAN/PVP/CD-MOF composite beads. Batch adsorption studies showed that high dye adsorption capacities could be obtained at intermediate PVP, high PAN, and low CD-MOF loadings. Maximum MB and CR sorption capacities under optimum bead formulation: PAN = 6.96 wt.%, PVP = 2.20 wt.%, and CD-MOF = 2.88 wt.%. The optimized composite beads have a sorption capacity of 37.40 mg/g for MB and 18.42 mg/g for CR. We showed that PAN/PVP/CD-MOF composite beads could be an excellent adsorbent for textile dye removal in water.

Adsorption of Chromium (VI) from Aqueous Solution Using Nano TiO2 Doped Strong Base Anion Exchange Resin

Background: The evolution of environmentally-safe methods for treating hazardous chemicals in wastewater, particularly urban and industrial wastewater, has increased interest over recent years. The chromium-containing wastewater is produced by industries from steel, metallurgical, electroplating, chemical, refractory, leather tanning, dye manufacturing, mining, cementing, textiles, etc. Consequently, advanced techniques are essential for treating chromium-polluted water. Objective: The prime objective of this effort was to assess the adsorption performance of nanoTiO2 (nanoparticles of average crystallite size 19.15 nm) doped strong base anion exchange resin (TDTulsion) for Cr(VI)to that of the host Tulsion A-62 (MP). Methods: The tests were carried out in batches in the temperature-controlled water bath shaking unit, with 30 ml of the aqueous solution containing Cr(VI) and a certain amount of resin being stirred for 6 hours at 303 K. Using a standard diphenylcarbazide (DPC) procedure at 540 nm, the solution was spectrophotometrically analyzed for Cr(VI). Results: The majority of the Cr(VI) ions are adsorbed by the anion exchange resins Tulsion A- 62(MP), and TD-Tulsion is in the pH range of 4.0 to 5.0. The maximal sorption capacity of Cr (VI) was established to be 181.5 and 204.8 mg/g for Tulsion A-62(MP) and TD-Tulsion, respectively. Conclusion: The TD-Tulsion has a substantially better adsorption capacity than Tulsion A-62(MP) under similar conditions. The outcomes show that modifying anion-exchange resin with nano titanium dioxide improves adsorption performance in Cr(VI) removal from drinking water and contaminated water.

Design and Preparation of Magnetically-Oriented Poly(styr-co-MMA)-3MPS Capped Fe(ZnO) Hybrid Microspheres for Ion Exchange Removal of Toxic Pollutants from Wastewater

In this work, polymeric microspheres derived from polystyrene-co-methyl methacrylate embedded with magnetic ZnO nanoparticles (poly(styrene-co-MMA)-3MPS-Fe (ZnO)) were synthesized using the suspension polymerization method. The surfaces of polymeric Fe(ZnO) microspheres were improved by functionalization with amino and sulphonate groups. The physicochemical analysis indicated a large number of positively charged (anion exchange) groups (91 mmol/g) on the amine-modified polymeric microsphere (MFZPI) and a large number of negatively charged (cation exchange) groups (90 mmol/g) on the sulphonate-modified polymeric microsphere (SMFZPI)—revealing ambivalent character of obtained sorbent. The characterization of the synthesized compounds using various analytical techniques such as TGA, FTIR, XRD, SEM/EDX, UV-VIS and VSM indicated that synthesized microspheres were thermally stable, semi-crystalline in structure with hollow irregular morphology, optically active in UV region and slightly magnetic in nature. Due to the introduction of groups having ion exchange properties, these modified poly(styrene-co-MMA)-3MPS-Fe(ZnO) microspheres were used for the ion exchange sorptive removal of Cr(III) and fluorescein from aqueous matrix. The equilibrium sorption capacity of Cr(III) was 16.79 mg/g whereas of fluorescein was 12.03 mg/g under optimized conditions. Therefore, SMFZPI was found to be a promising sorbent for both cationic heavy metals and anionic dyes due to the presence of both acidic and basic groups. The mathematical modelling revealed that the sorption phenomenon followed pseudo-second-order kinetics with Freundlich equilibrium isotherm, indicating multilayer chemisorption of the pollutants on the synthesized ion exchange sorbents. This work establishes the utilization of polymeric magnetic ZnO-based ion exchange sorbents to effectively remove harmful toxins from wastewater.

Preferential, synergistic sorption and reduction of Cr(VI) from chromium–rhodamine B mixed wastewater by magnetic porous biochar derived from wasted Myriophyllum aquaticum biomass

Eradication of heavy metals and dyes simultaneously from wastewater is urgently needed to safeguard public and environmental health. In this study, magnetic porous biochar derived from wasted Myriophyllum aquaticum (MPMaB) was synthesized by KOH-activation and co–precipitation method to treat chromate and rhodamine B (RhB)-bearing wastewater. The KOH activation significantly improved the pore structure of biochar with a high specific surface area of 937.1 m2 g−1. The sorption performance of MPMaB for Cr(VI) and RhB in single and co-solutes conditions was evaluated. In single system, a pH-dependent sorption pattern for Cr(VI) by MPMaB was revealed and the estimated sorption capability reached 175.4 mg g−1, whereas the Langmuir-based sorption capacity of RhB was 175.4 mg g−1 pH-independently. MPMaB partially transformed Cr(VI) to less toxic Cr(III) (approximately 59.3%). Synergistic sorption of Cr(VI) with the coexistence of RhB was observed, where synergistic effect ranged from 119% to 527% depending on pH. For example, the sorption capacity of Cr(VI) on MPMaB, at pH 2, augmented from 175.4 mg g−1 (single system) to 208.3 mg g−1 (binary system). Preferential sorption of Cr(VI) was found and was further confirmed by the post-sorption of Cr(VI) (or RhB) by MPMaB pre-sorbed with RhB (or chromate). Chromate sorption mechanisms mainly include electrostatic interactions and complexation, while the sorption of RhB is ascribed to π–π interactions, pore filling and hydrogen bonding. Additionally, MPMaB showed excellent reusability and maintained high removal efficiency after 5 cycles. In short, MPMaB can efficiently treat chromium and dyes–containing wastewater as sustainable and environmentally friendly adsorbent.

Removal and concurrent reduction of Cr(VI) by thermoacidophilic Cyanidiales: a novel extreme biomaterial enlightened for acidic and neutral conditions.

Thermoacidophilic Cyanidiales maintain a competitive edge in inhabiting extreme environments enriched with metals. Here, species of Cyanidioschyzon merolae (Cm), Cyanidium caldarium (Cc), and Galdieria partita (Gp) were exploited to remove hexavalent chromium [Cr(VI)]. Cm and Gp could remove 168.1 and 93.7mgg-1 of Cr(VI) at pH 2.0 and 7.0, respectively, wherein 89% and 62% of sorbed Cr on Cm and Gp occurred as trivalent chromium [Cr(III)]. Apart from surface-sorbed Cr(VI), the in vitro Cr(III) bound with polysaccharide and in vivo chromium(III) hydroxide [Cr(OH)3] attested to the reduction capability of Cyanidiales. The distribution of Cr species varied as a function of sorbed Cr amount, yet a relatively consistent proportion of Cr(OH)3, irrespective of Cr sorption capacity, was found only on Cm and Cc at pH 2.0. In conjunction with TXM (transmission X-ray microscopy) images that showed less impaired cell integrity and possible intracellular Cr distribution on Cm and Cc at pH 2.0, the in vivo Cr(OH)3 might be the key to promoting the Cr sorption capacity (≥ 152 mg g-1). Cyanidiales are promising candidates for the green and sustainable remediation of Cr(VI) due to their great removal capacity, the spontaneous reduction under oxic conditions, and in vivo accumulation.

Facile synthesis of layered superparamagnetic Fe3O4-MoS2 nanosheets on chitosan for efficient removal of chromium and ciprofloxacin from aqueous solutions

The discharge of toxic metal ions and pharmaceutical pollutants has become a global issue. This work evaluated the efficiency of the hydrothermally synthesized superparamagnetic Fe3O4-MoS2 nanosheets and its fabrication with chitosan (Fe3O4-MoS2@CS) to remove Cr(VI) and ciprofloxacin (CIP) from simulated wastewater. These nanohybrid materials are characterized by SEM-Mapping, Raman, TEM, XRD, XPS, zeta potential, FTIR, and BET analyses. The affinity and selectivity of Fe3O4-MoS2@CS nanomaterial towards a mixture of Cr(VI), As(II), Pb(II), and Cd(II) metal ions from synthetic solution is studied through ICP-MS at trace levels. The distribution coefficient (Kd) for Cr(VI) (1.2 × 104 mL/g) is higher than the other metal ions, which reveals high selectivity of Fe3O4-MoS2@CS. The Fe3O4-MoS2@CS has also displayed enhanced removal efficiency for ciprofloxacin (emerging contaminant) from synthetic solutions. The Fe3O4-MoS2 and Fe3O4-MoS2@CS nanomaterials possess high saturation magnetization values of 68.00 emu/g and 59 emu/g, respectively. The adsorption process of Cr(VI) highly depends upon the solution pH, and the adsorption isotherm is followed by the Langmuir isotherm model. The kinetics of sorption is followed well by the pseudo-second-order model. The adsorption mechanism is assumed due to functional group complexation, and electrostatic interactions. Fe3O4-MoS2@CS has displayed maximum sorption capacity for Cr(VI) (175.4 mg g−1) and CIP (190.7 mg g−1) respectively. Fe3O4-MoS2@CS has been used in practical applications to remove Cr(VI) (97 %) and CIP (62 %) from real simulated wastewater. The enhanced adsorption efficiency and excellent magnetic recyclability of Fe3O4-MoS2@CS nanohybrid material make it a promising sustainable adsorbent for clean production and wastewater treatment.

Preparation of MnOx-Modified Biochar and Its Removal Mechanism for Cr(VI) in Aqueous Solution

Biochar (BC) is considered to be a great potential adsorbent to remove various contaminants, but the sorption capacity for chromium (Cr) is predominantly limited for the net negative charge. In this study, BC from rice husk was impregnated with Mn(NO3)2 solution to synthesize MnOx-modified BC (MnOBCs) for enhancing Cr(VI) removal in an aqueous solution. MnOBCs were characterized, and MnOx (manganese ore) was found to be the dominant crystal in MnOBCs. Batch sorption and kinetic experiments combined with spectral analysis were carried out to elucidate the sorption capacity and mechanisms of Cr(VI) sorption onto BC and MnOBCs. Results showed that the sorption kinetic process fitted to the Elovich model, and the modification enhanced the sorption capacity of Cr(VI) on BC. Compared to ion strength, pH is the main control factor for Cr(VI) fixed on BC and MnOBCs, and the sorption amount decreased with the pH value increasing. Moreover, X-ray photoelectron spectroscopy results showed that the proportion of Mn(II) decreased from 33.59% to 8.33%, and that of Mn(VI) increased from 30.58% to 52.72% after Cr(VI) sorption on MnOBCs. Meanwhile, the reduction reaction of Cr(VI) occurred during the sorption process on the BC and MnOBCs surface, and the reduction reaction was more obvious on the MnOBCs surface. MnOx loaded in BC can enhance the electrostatic attraction and redox capacity, which can improve the removal of Cr(VI) in an aqueous solution. This study provides information on the sorption and redox of Cr(VI) on BC, and allows us to better understand the mechanism of Cr(VI) removal in solutions by MnOBCs.

Effects of tannic acid on the transport behavior of trivalent chromium in soils and its mechanism

Trivalent chromium [Cr(III)] and tannins serve as necessary substances in leather processing and coexist in tannery site, which lead to the chromium contamination in site soil when disposed improperly. However, coexisting tannins are very likely to complex with Cr(III) and affect its properties, ultimately changing the mobility of chromium in soil. In this study, tannic acid (TA) was selected to investigate the complexation with Cr(III) and the influence on the solubility and sorption of Cr(III) in soils. Then, the transport behavior and mechanism of Cr(III)-TA complexes in soil was clarified. Dialysis results showed that the increase of TA concentration and solution pH promoted the formation of complexed Cr(III). The results of UV–Vis absorption spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations indicated that the adjacent ionized phenolic hydroxyls in TA functioned as the binding sites with Cr(III) to form the Cr–O bonds and the degree of complexation increased with pH. The Cr(III)-TA complexes had higher solubility than free Cr(III) at pH ≥ 6.0. Batch sorption experiments demonstrated that the sorption capacity of Cr(III)-TA to soils with different pH was always lower than that of free Cr(III). These reasons led to the stronger mobility of Cr(III)-TA in soil columns than Cr(III). Our research reveals that the enhanced mobility of Cr(III) in soils coexisting with TA.

Robust Al3+ MOF with Selective As(V) Sorption and Efficient Luminescence Sensing Properties toward Cr(VI).

Herein, we report the synthesis and characterization of a new robust Al3+ metal-organic framework MOF, [Al(OH)(PATP)]·solvent (Al-MOF-1, with PATP2- = 2-((pyridin-2-ylmethyl)amino)terephthalate). Al-MOF-1 exhibits excellent stability from highly acidic (pH = 2) to basic (pH = 12) aqueous solutions or in the presence of oxoanionic species [As(V) and Cr(VI)]. On the contrary, the related MIL-53(Al) MOF (Al(OH) (BDC), with BDC2- = terephthalate) shows a partial structure collapse under these conditions, signifying the superior chemical robustness of Al-MOF-1. Al-MOF-1 was proved to be an effective sorbent toward As(V) with efficient sorption capacity (71.9 ± 3.8 mg As/g), rapid sorption kinetics (equilibrium time ≤1 min), and high selectivity in the presence of various competing anions. Furthermore, Al-MOF-1 revealed high sorption capacities for Cr(VI) species in both neutral (124.5 ± 8.6 mg Cr/g) and acidic (63 ± 2 mg Cr/g) aqueous media, combining fast kinetics and relatively good selectivity. The limited porosity (BET = 38 m2/g) and small pores (2-3 Å) of the material indicate that the sorption process occurs exclusively on the external surface of Al-MOF-1 particles. The driving force for the capture of oxoanions by Al-MOF-1 is the strong electrostatic interactions between the oxoanionic species and the positively charged surface of MOF particles. Aiming at a practical wastewater treatment, we have also immobilized Al-MOF-1 on a cotton substrate, coated with polydopamine. The fabric sorbent exhibited highly effective removal of the toxic oxoanionic species from aqueous media under either batch or dynamic (continuous flow) conditions. In addition, Al-MOF-1 was found to be a promising luminescence sensor for detecting trace amounts of Cr(VI) in real water samples, with Cr(VI) being successfully detected at concentrations well below the acceptable limits (<50 ppb). Moreover, Al-MOF-1 was demonstrated to be a sufficient water sensor in organic solvents (LOD ≤0.25% v/v). All the above indicate that Al-MOF-1 represents a multifunctional material with a multitude of potential applications, such as environmental remediation, industrial wastewater treatment, chemical analysis, and water determination in biofuels.

Valorization of Cladophora glomerata Biomass and Obtained Bioproducts into Biostimulants of Plant Growth and as Sorbents (Biosorbents) of Metal Ions.

The aim of this study was to propose a complete approach for macroalgae biomass valorization into products useful for sustainable agriculture and environmental protection. In the first stage, the effects of macroalgal extracts and ZnO NPs (zinc oxide nanoparticles) on the germination and growth of radish were examined. Macroalgal extract was produced from freshwater macroalga, i.e., Cladophora glomerata by ultrasound assisted extraction (UAE). The extract was used to biosynthesize zinc oxide nanoparticles. In germination tests, extracts and solutions of ZnO NPs were applied on paper substrate before sowing. In the second stage, sorption properties of macroalga, post-extraction residue, and ZnO NPs to absorb Cr(III) ions were examined. In the germination tests, the highest values of hypocotyl length (the edible part of radish), i.e., 3.3 and 2.6 cm were obtained for 60 and 80% extract (among the tested concentrations 20, 40, 60, 80, and 100%) and 10 and 50 mg/L NPs, respectively. The highest sorption capacity of Cr(III) ions (344.8 mg/g) was obtained by both macroalga and post-extraction residue at a pH of 5 and initial Cr(III) ions concentration of 200 mg/L. This study proves that macroalgae and products based on them can be applied in both sustainable agriculture and wastewater treatment.

Enhanced removal of hexavalent chromium from aqueous solution by functional polymer-wrapped gamma-alumina composite adsorbent

Here we reported a novel xanthated chitosan-entrapped gamma-alumina (XCSA) composite sorbent that presents effective removal toward toxic hexavalent chromium ions [Cr(VI)] from water. The samples were characterized by FTIR, SEM-EDS, XRD, TGA, and XPS. Batch sorption experiments were performed to investigate the influences of component ratio, initial solution pH, and competing ions on the Cr(VI) removal. An adsorption-coupled reduction mechanism controlled the Cr(VI) removal processes, in which xanthation groups played a key part. The sorption process revealed that ∼ 65% Cr(VI) (50 mg/L) was adsorbed within 5 min, and kinetic data fitted well with the pseudo-second-order model. The sorption isotherm data fitted well with Freundlich model, and the experimental maximum sorption capacity for Cr(VI) by XCSA-1.0 (with the alumina-to-polymer mass ratio of 1:1) was ∼ 110.5 mg/g. In addition, XCSA-1.0 expressed the good anti-interference ability of the competing ions. Moreover, the exhausted adsorbent, which could be regenerated by 1.0 M KCl solution, exhibited good reusability after five cycles. Overall, this study shows XCSA as a promising sorbent for anionic heavy metal removal from water. • Xanthated chitosan wrapping γ -alumina sorbents were prepared for Cr(VI) removal. • Fast kinetics of adsorption (within 120 min) over this composite adsorbent. • A better adsorption capacity ( ∼ 110.5 mg/g) than many other similar sorbents. • An adsorption-coupled reduction mechanism controlled Cr(VI) removal processes.

Biochar-supported polyaniline hybrid for aqueous chromium and nitrate adsorption

Biochar adsorbents can remove environmental pollutants and the remediation of Cr(VI) and nitrate are considered. Cr(VI) is a proven carcinogen causing serious health issues in humans and nitrate induced eutrophication causes negative effect on aquatic systems around the world. Douglas fir biochar (DFBC), synthesized by fast pyrolysis during syn gas production, was treated with aniline. Then, a polyaniline biochar (PANIBC) composite containing 47 wt% PANI was prepared by precipitating PANI on DFBC surfaces by oxidative chemical polymerization of aniline in 2M HCl. PANIBC exhibited a point of zero charge (PZC) of 3.0 and 8.2 m2/g BET (N2) surface area. This modified biochar was characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM) morphology and surface elements, and oxidation states by X-ray photoelectron spectroscopy (XPS). PANIBC exhibited positive surface charge below pH 3, making it an outstanding adsorbent, for Cr(VI) removal. Cr(VI) and nitrate removal mechanisms are presented based on XPS analysis. DFBC and PANIBC Cr(VI) and nitrate adsorption data were fitted to Langmuir and Freundlich isotherm models with maximum Langmuir adsorption capacities of 150 mg/g and 72 mg/g, respectively. Cr(VI) and nitrate removal at pH 2 and 6 were evaluated by reducing the amount of PANI (9 wt%) dispersed on to DFBC. Adsorption capacities verses temperature studies revealed that both Cr(VI) and nitrate adsorption are endothermic and thermodynamically favored. Regeneration studies were conducted on both DFBC and PANIBC using 0.1M NaOH and PANIBC exhibited excellent sorption capacities for Cr(VI) and nitrate in lake water samples and in the presence of competitive ions.

Sorption and desorption behaviour of chromium in soils of Punjab

The present study was carried out to understand soil chromium (Cr) sorption/desorption phenomena, and hence Cr bioavailability in surface soils collected from Jalandhar, Ludhiana and Mandi Gobindgarh in Punjab. Chromium sorption isotherms were derived by sorption of Cr from solutions containing a range of concentrations equivalent to 50, 100, 300 600 and 900 μg Cr g−1 soil in the presence of a background electrolyte, 0.01 M Ca(NO3)2. Chromium desorption isotherms were derived from the Cr desorbed (μg g1 soil) after each of five desorption periods, carried out by sequentially equilibrating same soil samples used for Cr sorption study in Cr-free 0.01 M Ca(NO3)2. It was observed that with the increase in rate of Cr application, amount of Cr sorbed by the soils also increased; however, the per cent Cr sorbed decreased. The Cr sorption data of the three selected soil samples were best described by Freundlich (R2 = 0.986 to 0.994) followed by Langmuir (R2 = 0.959 to 0.995), and Dubinin-Radushkevich (D-R) adsorption isotherms (R2 = 0.926 to 0.973). The constants measuring adsorption capacity, derived from all the three adsorption isotherms, indicated that the soil from Mandi Gobindgarh has higher Cr sorption capacity than the other two soils. Desorption of Cr as well as per cent Cr desorbed from the selected soils increased with the increase in added Cr concentration. The Cr desorption data of the soils were very well described by Langmuir desorption isotherm (R2 = 0.96 to 0.99). Desorption maxima derived was also observed to be higher in case of Mandi Gobingarh soil which implies that this soil has maximum desorption capacity. The differences in amounts of Cr sorbed and desorbed by experimental soils may be due to variation in soil parameters such as organic carbon and cation exchange capacity.

Synthesis of a new ion-imprinted polymer for selective Cr(VI) adsorption from aqueous solutions effectively and rapidly

Removing hexavalent chromium (Cr(VI)) from aqueous solution is strategically important. A novel and selective adsorbent was synthesized using a high electron beam irradiation pre-grafting and post-surface ion imprinting method using Cr(VI) and polypropylene (PP) fibers as the template and substrates, respectively. The results obtained using Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TG) indicated that the prepared sorbent was successfully synthesized. At the same time, the adsorption performances were studied through batch experiments. The results exhibited rapid adsorption kinetics, a wide working pH range, and excellent selectivity and regeneration. The equilibrium adsorption was achieved within 30 min, the maximum sorption capacity of Cr(VI)-IIPs was 156.5 mg g−1 and partition coefficients (PC) was 0.591 mg g−1 uM−1 at 400 mg L−1 initial concentration and 298 K. The relative selectivity coefficients of the ion-imprinted polymer (IIP) for Cr2O72−/HPO42− and Cr2O72−/NO3− were 36.7 and 39.9, respectively. In addition, the prepared sorbent has a negligible loss in adsorption capacity after five cycles. IIP has good application prospects in the selective removal of Cr(VI) ions.

Polypyrrole coated molybdenum disulfide composites as adsorbent for enhanced removal of Cr(VI) in aqueous solutions by adsorption combined with reduction

In this study, polypyrrole coated molybdenum disulfide organic–inorganic composites (PPy/MoS2) were fabricated by a simple in-situ oxidative polymerization, and used as a novel adsorbent for removal Cr(VI). The sorption of Cr(VI) was consumingly pH-reliant behavior, which the optimal elimination efficiency was attained at pH 2. Meanwhile, the adsorption of Cr(VI) on PPy and PPy/MoS2 followed the pseudo-second-order kinetic model and Langmuir isotherm model. Compared with PPy, PPy/MoS2 exhibited better elimination ability for Cr(VI) because of its well-dispersion and massive surface active sites. The maximum sorption capacity of Cr(VI) by PPy/MoS2 reached 257.73 mg/g at 298 K, which was obviously higher than that of Cr(VI) by PPy (151.29 mg/g). The thermodynamic parameters demonstrated that the sorption process was endothermic and spontaneous. The coexisting ions like K+, Na+, Ca2+, Mg2+, NO3–, Cl- and SO42- had no significant influence for Cr(VI) elimination, whereas H2PO4- was main competitors. Mechanism investigation indicated that the ion exchange, electrostatic interactions, chemical reduction (Cr(VI) to Cr(III)) and surface chelation played a crucial role in the elimination of Cr(VI). In addition, the PPy/MoS2 composites could be employed for three continuous cycles without significantly reducing the sorption capacity of Cr(VI). This work demonstrated that PPy/MoS2 composites were a promising sorbent for efficient treatment Cr(VI) in polluted water.

Removal of aqueous Cr(VI) by Zn- and Al-modified hydrochar

Pristine hydrochar is a carbonaceous material that can sorb hexavalent chromium (Cr(VI)), a kind of toxic pollutants and difficult to removal, from aqueous solution but its capacity is limited. With the goal of improving this ability, two modified hydrochars were produced by co-hydrothermal carbonization (200 °C, 7h) of bamboo sawdust with zinc chloride (ZnCl2) or aluminum chloride (AlCl3). Compared to the pristine hydrochar, the ZnCl2-and AlCl3-modified hydrochars were more fully carbonized (higher C content and lower H/C) and had higher surface area (increased by 26 and 4.3 times, respectively) and larger pore volume (increased by 43 and 5.5 times, respectively). Due to these improved properties, the Cr(VI) maximum adsorption capacity (modeled via Langmuir isotherms) of ZnCl2-and AlCl3-modified hydrochar increased by 3.4 and 2.8 times, respectively. In addition, Cr(VI) adsorption kinetic of modified hydrochar was well fitted by the pseudo-second-order model. Cr sorption capacity increased at low pH and ion strengths, suggesting the potential roles of electrostatic interaction and ion exchange mechanisms. These results indicate that hydrochars modified by ZnCl2 and AlCl3 treatment are promising in environmental applications that require Cr(VI) removal.

A 3D porous fluorescent hydrogel based on amino-modified carbon dots with excellent sorption and sensing abilities for environmentally hazardous Cr(VI)

To effectively detect and remove environmentally hazardous Cr(VI), a novel 3D porous fluorescent hydrogel was synthesised using amino-modified carbon dots and cellulose nanofibers. The synthesised fluorescent hydrogel was characterized to determine its morphology, crystalline structure, chemical composition and optical property using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, UV–vis absorption spectroscopy and photoluminescence spectroscopy. The sorption properties of the synthesised fluorescent hydrogel were further analyzed. The maximum sorption capacity for Cr(VI) reached 534.4 mg/g, the adsorption isotherm was well fitted using Langmuir model, and the adsorption kinetics were well fitted using a pseudo-second-order model. The sensing ability of the synthesized hydrogel for Cr(VI) was also determined. Furthermore, the mechanism of Cr(VI) sorption and sensing was determined. Accordingly, this novel 3D porous fluorescent hydrogel was identified to be a promising sorbent with advantages of excellent sorption and sensing abilities for environmentally hazardous Cr(VI).

Optimization using central composite design (CCD) of response surface methodology (RSM) for biosorption of hexavalent chromium from aqueous media

In this study, unmodified biosorbent was obtained from Arachis hypogea husk and applied to remove hexavalent chromium [Cr(VI)] from aqueous media through batch technique. The independent variables (contact time, pH of the solution and initial Cr(VI) concentration) influencing the adsorption process were optimized by central composite design (CCD) found in response surface methodology of the Design-Expert software 12.0.0 at a fixed temperature of 30 ± 0.5 °C. Furthermore, equilibrium sorption isotherms and kinetics studies were also investigated. The ANOVA component of the CCD indicated that all the process independent variables investigated had significant impacts on the sorption capacity of Cr(VI) by Arachis hypogea husk. The obtained experimental data showed that at the optimized 120 min contact time, 8.0 pH of the aqueous solution and 50 mg/L initial Cr(VI) concentration resulted in an optimum adsorption capacity of 2.355 mg/g. Equilibrium sorption isotherm and kinetic studies showed that Redlich–Peterson adsorption isotherm and pseudo-second-order kinetic models fitted well to the equilibrium data. The unmodified adsorbent from Arachis hypogea husk was found to be efficient for Cr(VI) decontamination from the aqueous media.

Contribution of Cross-Linker and Silica Morphology on Cr(VI) Sorption Performances of Organic Anion Exchangers Embedded into Silica Pores.

Removal of Cr(VI) from the environment represents a stringent issue because of its tremendous effects on living organisms. In this context, design of sorbents with high sorption capacity for Cr(VI) is getting a strong need. For this purpose, poly(vinylbenzyl chloride), impregnated into porous silica (PSi), was cross-linked with either N,N,N’,N’-tetramethyl-1,2-ethylenediamine (TEMED) or N,N,N’,N’-tetramethyl-1,3-propanediamine, followed by the reaction of the free -CH2Cl groups with N,N-diethyl-2-hydroxyethylamine to generate strong base anion exchangers (ANEX) inside the pores. The PSi/ANEX composite sorbents were deeply characterized by FTIR spectroscopy, SEM-energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), and water uptake. The sorption performances of composites against Cr(VI) were investigated as a function of pH, contact time, initial concentration of Cr(VI), and temperature. It was found that the cross-linker structure and the silica morphology are the key factors controlling the sorption capacity. The adsorption process was spontaneous and endothermic and well described by pseudo-second-order kinetic and Sips isotherm models. The maximum sorption capacity of 311.2 mg Cr(VI)/g sorbent was found for the composite prepared with mesoporous silica using TEMED as cross-linker. The PSi/ANEX composite sorbents represent an excellent alternative for the removal of Cr(VI) oxyanions, being endowed with fast kinetics, equilibrium in about 60 min, and a high level of reusability in successive sorption/desorption cycles.

Decontamination and optimization study of hexavalent chromium on modified chicken feather using response surface methodology

Present research highlighted the efficacy of alkali-treated (1% NaOH) chicken feather toward removal of Cr(VI) from aqueous solution through batch study. Box–Behnken design (BBD) by response surface methodology was used to optimize the adsorption process. Kinetics and sorption isotherms have been determined considering the effect of initial metal concentration, adsorbent dose, contract time, and temperature. Batch sorbent data were fitted to various sorption models, and results indicate that Cr(VI) sorption process using alkali-treated chicken feathers followed the pseudo-second-order rate model, while sorption isotherms were described properly by both Langmuir (R2: 0.997) and Freundlich isotherms (R2: 0.979). Based on BBD design, the quadratic models were developed co-relating the adsorption variables to removal efficiency. Analysis of variance (ANOVA) was incorporated to judge the adequacy of model (F:3484.72). Model predicted optimized conditions are initial concentration 5.64 mg/L, adsorption dose 0.15 g, contract time 29.60 min, pH 1.06 gave 88.9% removal efficiency. Sorption isotherms show that the experimental maximum sorption capacity of Cr(VI) was found to be 90.91 mg/g at 40 °C and pH 2. Therefore, present results demonstrate that alkali-treated chicken features should be regarded as a low-cost alternative for the removal of Cr(VI) from aqueous solution.