Adsorption Performance For Cr Research Articles

Influence of the iron-oxide mass fractions of magnetic powdered activated carbon on its hexavalent chromium adsorption performance in water

Magnetic powdered activated carbon (Mag-PAC) is an effective adsorbent to remove hexavalent chromium (Cr(VI)) from water and can be recovered for reuse. However, the tradeoff between the adsorption performance of Cr(VI) and magnetic properties of Mag-PAC remains unclear. Herein, we prepared a series of Mag-PAC adsorbents containing various iron-oxide mass fractions with FeSO4·7H2O as the precursor, using a facile wet-chemical precipitation route and conducted batch experiments to evaluate the Cr(VI) adsorption performance. Results revealed that Mag-PAC was functionalized by magnetic iron oxide comprising crystalline goethite and magnetite structures. Furthermore, its adsorption performance was highly dependent on pH and was most effective at an initial solution pH of 2. Both the sorption rate constant and Cr(VI) adsorption capacity were greatly influenced by magnetization, and they gradually decreased as the iron-oxide mass fraction increased. Among the prepared adsorbents, Mag-PAC-75 (∼32% wt iron) exhibited not only an excellent Cr(VI) adsorption performance (Langmuir adsorption capacity: 75.76 mg/g) but also effective magnetic properties (saturation magnetization: 9.66 emu/g). Coexisting anions had a negligible competitive effect on Cr(VI) removal by Mag-PAC-75 at an initial pH of 2, whereas the presence of tannic acid markedly improved the Cr(VI) elimination. The presence of trivalent chromium on the surface of Mag-PAC-75 confirmed via X-ray photoelectron spectroscopy indicated that some synergistic redox reactions may occur during the sorption process. After five regeneration cycles using NaOH, Mag-PAC-75 continued to exhibit a high Cr(VI) removal efficiency and magnetic stability. These findings indicate that optimizing the adsorption performance and magnetic properties is a key factor for realizing the practical application of Mag-PAC for Cr(VI) removal. Overall, Mag-PAC may have been a promising application prospect for Cr(VI) removal from water due to its high adsorption capacity and magnetic properties, coupled with its good reusability and magnetic stability after regeneration cycles.

Removal of trivalent chromium ions in model contaminated groundwater using hexagonal boron nitride as an adsorbent

The feasibility of using hexagonal boron nitride (h-BN) to treat heavy metal Cr(III) from model contaminated groundwater was evaluated in this study by adsorption experiments and characterizations. To the best of our knowledge, this study is the first attempt to conduct the adsorption of Cr(III) by h-BN under various experimental conditions such as exposure time, ratio of adsorbates and adsorbents, solution pH, background ions with different ionic strength, and the presence of humic acids (HA) in model contaminated groundwater. The optimized h-BN showed excellent maximum adsorption capacity (i.e., 177 mg ∙ g−1) when the concentrations of Cr(III) and h-BN were 10 and 10 mg ∙ L−1, respectively. Subsequently, we confirmed there was a negligible change in the adsorption performance of Cr(III) by h-BN in the presence of co-ions (i.e., K and Mg) in concentrations in a range from 50 to 1000 mg ∙ L−1. Furthermore, the adsorption performance of Cr(III) gradually improved with HA concentrations from 2.5 to 25 mg ∙ L−1. Interestingly, the maximum adsorption performance of Cr(III) by both HA and h-BN increased until 500 mg ∙ g−1 in the presence of 25 mg ∙ L−1 HA. The adsorption mechanism was clarified by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Additionally, we successfully confirmed that h-BN could be reused until five cycles. On the basis of the adsorption performance results and characterizations, h-BN can be utilized as an efficient and practical adsorbent to treat Cr(III) in groundwater treatment.

The co-pyrolysis of waste urea-formaldehyde resin with pine sawdust: co-pyrolysis behavior, pyrocarbon and its adsorption performance for Cr (VI).

Urea-formaldehyde (UF) resin is difficult to degrade and classified as hazardous organic waste. To address this concern, the co-pyrolysis behavior of UF resin with pine sawdust (PS) was studied, and the adsorption properties of pyrocarbon were evaluated with Cr (VI). Thermogravimetric analysis revealed that adding a small amount of PS can improve the pyrolysis behavior of UF resin. Based on the Flynn Wall Ozawa (FWO) method, the kinetics and activation energy values were estimated. It was observed that when the amount of UF resin exceeded twice that of PS, the activation energy of the reaction decreased, and they acted synergistically. The characterization of pyrocarbon samples showed that the specific surface area increased with the increase of temperature, while the content of functional groups showed the opposite trend. Intermittent adsorption experiments showed that 5UF + PS400 achieved 95% removal of 50mg/L Cr (VI) at 0.6g/L dosage and at pH 2. The adsorption process was consistent with the Langmuir isotherm and pseudo-second-order kinetics, and the maximum adsorption was 143.66mg/g at 30 ℃. Furthermore, the adsorption process consisted of electrostatic adsorption, chelation, and redox reaction. Overall, this study provides a useful reference for the co-pyrolysis of UF resin and the adsorption capacity of pyrocarbon.

Preparation of Sulfhydryl Functionalized MCM-48 and Its Adsorption Performance for Cr(VI) in Water

In this study, we modify the Mobil Composition of Matter No. 48 (MCM-48) silica material (MCM-48-SH) using Mercapto. The preparation conditions of MCM-48-SH are then explored, its structural characteristics are analyzed using characterization, and it is used to adsorb Cr(VI) from wastewater. A series of experiments are then designed to adsorb Cr(VI) in experimental water, and the influence of solution environment changes (such as time, temperature, pH, and coexisting ions) on the adsorption effect was explored. The experimental data showed that the MCM-48-SH material not only retained the basic structure of MCM-48 but also successfully grafted the functional group -SH. The adsorption of Cr(VI) on MCM-48-SH followed the Langmuir isotherm model and the kinetic adsorption was fitted with a pseudo-second-order kinetic model. Under these conditions, the adsorption capacity of MCM-48-SH (17.9 mg/g) on Cr(VI) was much larger than that of unmodified MCM-48 (4.0 mg/g) and amino-modified MCM-48-NH2 (0.5 mg/g). The adsorption effect was the most obvious when the pH = 2 but the adsorption effect was not good under alkaline conditions. Other competitive ions in the solution had an influence on the adsorption effect, among which anions had a great influence. Within 3 d, when the concentration of Cr(VI) was 80 mg/L, the maximum adsorption capacity reached 17.9 mg/g and the maximum removal rate reached 93.45%. In the comparative adsorption experiment, the adsorption effect of MCM-48-SH (17.9 mg/g) on Cr(VI) was notably better than that of the other two common adsorbents: coconut shell activated carbon (9.2 mg/g) and bentonite (1.2 mg/g). In summary, MCM-48-SH can be used to effectively eliminate Cr(VI) in waste water.

Dispersing Bentonite by Electron Beam Irradiation and Its Adsorption Performance of Cr(VI) in the Aqueous Solution

Dispersing Bentonite by Electron Beam Irradiation and Its Adsorption Performance of Cr(VI) in the Aqueous Solution

Efficient adsorption H3AsO4 and Cr(VI) from strongly acidic solutions by La-Zr bimetallic MOFs: Crystallinity role and mechanism

Due to the non-degradable of heavy metal, adsorption has been extensively applied to abatement it. Most studies were focused on uptake metal ions via electrostatic attraction and ion exchange, and load molecule H3AsO4 from strongly acidic wastewater was still challenging. To solve the problem, bimetallic La–Zr MOFs was facilely fabricated in this work, and the fcu topology structure of La-Zr MOFs was remained well under the investigate crystallization time and crystallization temperature. However, the crystallinity of the obtained La-Zr MOFs was influenced by the synthesized factors. The obtained La–Zr MOFs was employed as adsorbent to removal Cr(VI) and As(V), and the performance was evaluated by the batch experiment. The result indicated that the adsorption performance of Cr(VI) and As(V) was positively correlated with the crystallinity, and the optimal sample was 1LaUN12. From the XPS characterization, it was found that H3AsO4 was successfully uptake over 1LaUN12 surface, and the maximum monolayer adsorption capacity was 83.40 mgH3AsO4/g via ligand exchange and coordination reactions with La−OH and Zr−OH. In addition, the sample 1LaUN12 also exhibited the excellent Cr(VI) load performance, and the maximum monolayer adsorption capacity of Cr(VI) was 222.5 mg/g. Above 40% Cr(VI) was reduced to Cr(III) by amino groups, and immobilized over the surface of 1LaUN12. Eventually, 1LaUN12 displayed a good structural stability in the acidic medium, which was in favor of removing Cr(VI) and As(V) efficiently from strongly acidic solutions.

Adsorption of Cr(Ⅵ) and dyes by plant leaves: Effect of extraction by ethanol, relationship with element contents and adsorption mechanism

Plant leaves are eco-friendly, low-cost and renewable biosorbents. This study utilized the recyclable ethanol solvent to pre-treat plant leaves against coloring the treated effluent and explore its adsorption performance for Cr(Ⅵ) and dyes. Six types of plant leaves and six corresponding extracted leaves were characterized by elemental analyzer, FT-IR and BET and leaf powders adsorbed Cr(Ⅵ) were characterized by SEM, FTIR and XPS. After the extraction treatment, the adsorption amounts of Cr(Ⅵ) declined, conversely, those of Congo red and Rhodamine B onto most leaves increased. For leaf powders, the adsorption of the three pollutants was mainly related with hydroxyl, nitrogen contents and the O/C value. Therefore, it could be concluded that the adsorption performance of plant leaves could be predicted through the element contents, in favor of the wide application of leaves in wastewater treatment. In addition, adsorption behaviors of leaf powders were obtained via kinetic, isotherm and thermodynamic studies. It was found that the difference in the adsorption rate of leaf powders on Cr(VI), Congo red and Rhodamine B was mainly related to whether the adsorption process needed the protonation of leaf powders. The maximum adsorption capacities of Cr(Ⅵ), Congo red and Rhodamine B on the E-FS-LP were 80.00, 232.56 and 74.63 mg/g (308 K). The possible adsorption mechanism of the three pollutants onto leaf powders was proposed.

The Improvement of Natural Thai Bentonite Modified with Cationic Surfactants on Hexavalent Chromium Adsorption from an Aqueous Solution

This work was performed to evaluate the adsorption properties of modified Thai bentonites (MTBs) on hexavalent chromium (Cr(VI)) by using a popularly capable surfactant (hexadecyltrimethylammonium bromide (HDTMA)) compared to an alternative surfactant (cetylpyridinium chloride (CPC)). The adsorption properties of the surfactant load, adsorbent weight, contact time, initial Cr(VI) concentration, and temperature of the MTBs were evaluated. The results revealed that a higher surfactant load significantly affected the Cr(VI) adsorption, and the equilibrium adsorption was achieved at 60 min. The adsorption capacity improved when the adsorbent weight, contact time, initial concentration, and temperature increased as the highest adsorption capacities of 1CPC and 1HDTMA were 45.55 and 46.03 mg g-1, respectively. The isotherm and kinetic adsorptions were described by the Freundlich model and pseudo-second-order model, respectively, while thermodynamics indicated endothermic adsorption. After adsorption, X-ray absorption near-edge structure and extended X-ray absorption fine structure data showed that Cr ions did not change the valency state between Cr(VI) and Cr(III). Additionally, the adsorption mechanism can be depicted as the ion exchange between the Cr(VI) ion and the surfactant molecule. Structural evaluations by XRD, FTIR, FESEM, EDS, and TEM found that both MTBs (1CPC and 1HDTMA) with the best adsorption performance for Cr(VI) had obvious changes at both the interlayer structure and the external surface. The interlayer spacing was expanded from 14.85 Å to 20.48 Å (1CPC) and 18.79 Å (1HDTMA), and the new functional groups (CH2 scissoring, C–H symmetric stretching, C–H asymmetric stretching, and N–CH3 scissoring) and elemental compositions (Br and Cl) were observed in both MTBs. They demonstrated that the complete intercalation of surfactant molecules on bentonite structures supported Cr(VI) adsorption. Overall, the data indicate that MTBs were perfectly adsorbed on Cr(VI), and CPC was demonstrated to be a cheap alternative agent due to its adsorption capacity compared to the popularly capable HDTMA.

Synthesis of novel reduced graphene oxide decorated β-cyclodextrin epichlorohydrin composite and its application for Cr(VI) removal: Batch and fixed-bed studies

• The novel RGO-βCD-ECH composite was synthesized as a new adsorbent by wet chemical method. • The Cr(VI) adsorption was pH-dependent, equilibrium time was 75 min and the optimum temperature is 30 °C. • The data were fitted by Langmuir Isotherm and maximum capacity was 1321.01 mg/g. • The rate of adsorption was in good agreement with the pseudo-second-order kinetic model. • From FBAC study it was confirmed that at low flow rate and at higher bed height the performance was maximum. A novel ternary composite was synthesized comprising reduced graphene oxide (RGO), beta-cyclodextrin (βCD), and epichlorohydrin (RGO-βCD-ECH). The electrical and structural properties of the composite were analyzed by using Zeta potential, RAMAN, XRD, FTIR, BET, and SEM. It was encouraging to find out that the composite shows exceptional adsorption performance for Cr(VI) removal from water both in batch as well as Fixed bed adsorption column (FBAC) study. The optimized adsorption parameters were: adsorbent dosage 0.2 g/L, initial Cr(VI) concentration 300 mg/L, contact time 75 min, temperature 30 °C, and solution pH 1.0. Among the isotherm models, the Langmuir model proved to be a better fit, and maximum capacity ( q m ) can reach up to 1321.01 mg/g, whereas kinetic data follows the pseudo-second-order kinetic model. From the Boyd plot, it was confirmed that the rate-limiting step was controlled by intra-particle diffusion. The thermodynamic analysis confirmed that the adsorption process was an endothermic, entropy-driven, and spontaneous process. From the FBAC study, it was observed that with an increase in bed height, the parameters like bed capacity ( q bed ), breakthrough time ( t b ), and exhaustion time ( t e ) of the composite increase, and as the Cr(VI) flow rate increases the value decreases. To fit experimental data of the FBAC study, Thomas, Yoon-Nelson, and BDST model was used. Besides, it can easily and efficiently regenerate with a small effect on removal percentage. In binary solution, the results showed that coexisting ions like S O 4 2 - , N O 3 - , C l - , C u 2 + , C o 2 + , and, N i 2 + had no such substantial effect on Cr(VI) adsorption. These characteristics implied the applicability of these novel composites in the application of Cr(VI) contaminated groundwater or industrial wastewater in both batch and continuous mode.

Fe(III) modified Egeria najas driven-biochar for highly improved reduction and adsorption performance of Cr(VI)

A novel Egeria najas driven-biochar was activated by loading ferric chloride onto surface (FeCl3@EN-BC). The synthesized composite was evaluated for its physicochemical properties and Cr(VI) adsorption behavior and mechanism. The result of SEM showed that the modified biochar is less porous than raw Egeria najas biochar, but loaded with γ-Fe2O3 and Fe3O4 crystals. In addition, the results of FTIR, XRD and XPS also confirmed that Fe was successfully loaded on the Egeria najas biochar. Cr(VI) was efficiently removed by FeCl3@EN-BC within the pH range from 2.5–8.5. The thermodynamics parameters suggested that the adsorption processes of Cr(VI) were all spontaneous and endothermic. The overall removal mechanism was regarded as adsorption, surface complex formation, reduction and ion exchange reaction. Therefore, this modified biochar derived from Egeria najas has a potential of practical application in the removal of Cr(VI) from wastewater.

Novel green strategy for CuO–ZnO–C nanocomposites fabrication using marigold (Tagetes spp.) flower petals extract with and without CTAB treatment for adsorption of Cr(VI) and Congo red dye

The CuO–ZnO-Carbon (CZC) nanocomposites (NCs) were synthesized via a green method at 300 and 400 °C calcinated temperatures, using waste marigold (Tagetes spp.) flower petal extract as a reducing agent and carbon source. A novel green strategy for the synthesis of highly effective CZC NCs was developed which showed better adsorption of toxic Cr(VI) and Congo red (CR) dye compared to unsupported carbon NCs. In this strategy, fine powder of petals as carbon source were passed with the flower liquid extract during the filtration process, which supported the metal oxides nanorods(NRs)/nanoparticles(NPs) on the surface. Furthermore, the surface of the synthesized NCs was modified by Cetyl Trimethyl Ammonium Bromide (CTAB) cationic surfactant to increase surface functionality, surface area, and positive charge density of NCs. Additionally, the adsorption performance of Cr(VI) and CR dye improved from acidic pH to neutral pH after surfactant modification of NCs compared to unmodified NCs. The characterization techniques such as Powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) surface area analysis, Point of zero charge (pHpzc), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were performed to examine physio-chemical properties of NCs and CTAB modified NCs. The FTIR and BET analysis confirmed that CTAB modified NCs showed excellent functionality and more than 49% and ~67% greater surface area than CZC-300 and CZC-400, respectively, which prepared at 300 and 400 °C temperature. XRD analysis confirmed that NCs were highly crystalline and no phase change after surfactant modification. The FE-SEM and TEM analysis confirmed the pentagonal NRs and spherical NPs of ZnO and CuO, respectively, were formed on the carbon surface. After CTAB modification, no change in the surface morphology of NCs was observed. Thus, comparative study of NCs and CTAB modified NCs was done for Cr(VI) and CR dye adsorption by varying batch conditions, such as initial pH, contact time, temperature, and initial concentration of Cr(VI)/CR dye. The equilibrium time and concentration data were fitted with non-linear forms of kinetic and isotherm models, respectively. CTAB modified CZC-300 NCs showed excellent adsorption capacity for both pollutants up to pH 6 compared to CZC-300 and CZC-400 NCs. Additionally, the maximum adsorption capacity of CTAB modified NCs for Cr(VI) and CR dye were 201.56 and 331.36 mg/g, respectively, at pH 2 and 30 °C and increased with increasing temperature. The effect of co-existing anions on adsorption capacity of both NCs for Cr(VI) and CR dye adsorption was investigated. The regeneration and reusability experiments of both NCs were also performed.

Enhanced removal of Cr(III)-EDTA chelates from high-salinity water by ternary complex formation on DETA functionalized magnetic carbon-based adsorbents

A novel amino-functionalized magnetic adsorbent (Fe3O4@C@DETA) was developed for adsorption of Cr(III) and Cr(III)-EDTA from wastewater. Fe3O4@C@DETA were successfully prepared by modification of Fe3O4@C with diethylenediamine (DETA), which exhibits a core-shell structure and sufficient saturation magnetization. Fe3O4@C@DETA exhibits much better adsorption performance for Cr(III) and its chelates than the Fe3O4@C because of newly introduced amino active sites. The enhanced adsorption capacity of Fe3O4@C@DETA for Cr(III) is 44.74 mg g−1 (at 25 °C and pH 3.0), which is due to the surface coordination with the newly introduced amino functional sites. The Cr(III)-EDTA anions as a whole was adsorbed through the electrostatic interaction with protonated amino species of the Fe3O4@C@DETA and have maximum adsorption capacity of 47.27 mg g−1 (at 25 °C and pH 3.0). The adsorption data of free and EDTA coordinated Cr(III) were followed the Langmuir equation, while the adsorption dynamics was well explained by pseudo second order model indicating the chemical nature of adsorption process. The higher concentration of Ca2+ ions in the wastewater compete for adsorption sites and inhibit the Cr(III) removal, while on other hand Ca2+ ions promotes the adsorption of Cr(III)-EDTA, because of electrostatic interaction with adsorbent active sits. Furthermore, the adsorbent can be easily separated by external magnetic field and regenerated in acidic solution. The adsorbent is stable, recyclable and have more than 75% regeneration efficiency and can be repeatedly used in the adsorption process.

Enhanced Cr(VI) removal from water using a green synthesized nanocrystalline chlorapatite: Physicochemical interpretations and fixed-bed column mathematical model study

Apatite-based minerals have attracted much attention in the remediation of heavy metal-contaminated environment. However, exploring apatite with efficient adsorption performance for inorganic oxyanions such as Cr(VI) remains a challenge. Herein, a novel nanocrystalline chlorapatite (ClAP) was promptly prepared by a green method using eggshell wastes as calcium source with the purpose to enhance Cr(VI) adsorption capability. The generated ClAP was characterized by XRD, SEM-EPMA, TEM, FTIR, and BET analyses. Batch and column experiments were subsequently carried out to explore the influencing factors, adsorption capacity and removal mechanism. Results showed that ClAP exhibited excellent stability and adsorption performance for Cr(VI) (63.47 mg g−1), which was much greater than that of hydroxyapatite and most reported materials. The adsorption process was fitted well by the pseudo-second-order model and the Langmuir model. In fixed bed column experiments, a novel time-fractional derivative model exhibited much better suitability in interpreting the observed breakthrough curves of Cr(VI) than traditional models. Furthermore, the reusability of ClAP in column was evaluated. Results showed that the adsorption capacity maintained well after consecutively reused for five cycles. Studies of the effect of pH, as well as FTIR and XPS investigations indicated that Cr(VI) adsorption was mainly ascribed to electrostatic interactions and surface complexation, while the reduction of Cr(VI) to the low-toxicity Cr(III) also existed in the adsorption process. The ClAP adsorbent was also successfully used for Cr(VI) remediation from real wastewater. Hence, nanocrystalline ClAP can be a promising material for enhancing the elimination of oxyanion contaminants such as Cr(VI) from water.

Removal of Cr(VI) using polyaniline based Sn(IV), Ce(IV) and Bi(III) iodomolybdate hybrid ion exchangers: Mechanistic and comparative study

The adsorption performance of Cr(VI) on newly synthesized hybrid ion exchangers, polyaniline-Sn(IV) iodomolybdate, polyaniline-Ce(IV) iodomolybdate and polyaniline-Bi(III) iodomolybdate has been studied. The physico-chemical characteristics of the synthesized hybrid ion exchangers viz., structure, surface area, surface morphology, composition and thermal stability were studied by FT-IR, UV–vis, XRD, SEM-EDS, TGA, DSC and XPS studies. Percentage removal of Cr(VI) from aqueous solution is found to increase with initial adsorbent dose, contact time, surface area and decrease with Cr(VI) concentration, temperature and pH. The removal of Cr(VI) is highly pH dependent, maximum at pH 1 and negligible at alkaline pH. A suitable mechanism has been proposed for Cr(VI) removal, involving adsorption of Cr(VI) on hybrid exchangers in a rate controlling step followed by reduction of Cr(VI) to Cr(III). Very low % of Cr(VI) desorption shown by spent hybrid materials with NaOH and NH4OH was explained by the reduction of major portion of adsorbed Cr(VI) to Cr(III) species. The observed order of % removal of Cr(VI) among different iodomolybdate hybrid ion exchangers has been explained by their surface area and surface morphology. Validation of pseudo-first-order, pseudo-second-order and Elovich kinetic models demonstrates that adsorption follows chemisorption process. Among Freundlich, Langmuir and Temkin adsorption isotherm models tested, the adsorption data are not fitted with Freundlich isotherm model. The calculated thermodynamic parameters reveal that the nature of Cr(VI) adsorption is spontaneous and exothermic. No appreciable decrease in Cr(VI) removal efficiency is observed in the presence of other ions like Cu2+, Zn2+, NO3− and SO42-, and with regenerated materials using 2 M HCl even after three cycles. Studies with industrial effluents proved that the synthesized materials can be used for industrial wastewater treatment.

Hydrothermal conversion of black liquor to phenolics and hydrochar: Characterization, application and comparison with lignin

The hydrothermal conversion (HTC) of black liquor solid (BLS) was investigated for producing phenolics and hydrochar. For comparison, the precipitated lignin (PL) was also investigated. The HTC experiments were conducted under different temperatures, holding times and reaction solvents to examine the optimum conditions for producing bio-oil. The maximum bio-oil yield of BLS of 53.3% was achieved at 50 wt% ethyl acetate/water cosolvent under 300 °C for 30 min. For PL, it was 86.7% at 50 wt% ethanol/water cosolvent under 300 °C for 30 min. GC–MS analysis showed that phenolics were the main products in bio-oil. The phenolics obtained from PL HTC were mainly S-type, followed by G-type; while H-type phenols were the main products in bio-oil from BLS. The hydrochar was characterized by FT-IR, BET and SEM. Moreover, the adsorption performance for Cr(VI) was investigated, which indicated that hydrochar from BLS was a promising candidate for heavy metals adsorption.

Hierarchical multi-shell hollow micro\u2013meso\u2013macroporous silica for Cr(VI) adsorption

The development of easier, cheaper, and more effective synthetic strategies for hierarchical multimodal porous materials and multi-shell hollow spheres remains a challenging topic to utilize them as adsorbents in environmental applications. Here, the hierarchical architecture of multi-shell hollow micro–meso–macroporous silica with pollen-like morphology (MS-HMS-PL) has been successfully synthesized via a facile soft-templating approach and characterized for the first time. MS-HMS-PL sub-microspheres showed a trimodal hierarchical pore architecture with a high surface area of 414.5 m2 g−1, surpassing most of the previously reported multishelled hollow nanomaterials. Due to its facile preparation route and good physicochemical properties, MS-HMS-PL could be a potential candidate material in water purification, catalysis, and drug delivery. To investigate the applicability of MS-HMS-PL as an adsorbent, its adsorption performance for Cr(VI) in water was evaluated. Important adsorption factors affecting the adsorption capacity of adsorbent were systematically studied and Kinetics, isotherms, and thermodynamics parameters were computed via the non-linear fitting technique. The maximum capacity of adsorption computed from the Langmuir isotherm equation for Cr(VI) on MS-HMS-PL was 257.67 mg g−1 at 293 K and optimum conditions (pH 4.0, adsorbent dosage 5.0 mg, and contact time 90 min).

Acidification Chicken Feather as Sorbent for Selectively Achicken feather as sorbent for selectively adsorbing of Cr(VI) ions in aqueous solution

Chicken feathers (CFs) were acidized by nitric acid, and the structure and morphology of acid treated feathers (NF) were characterized by FT-IR, XRD and SEM. The adsorption performance of Cr(VI) ions by NF was explored by batch and fixed bed experiments. Some of the amino groups of keratin were cationic after being treated with nitric acid, indicating that NF is a potential adsorbent for eliminating Cr(VI) ions from water. For Cu(II), Mn(II) and Co(II) ions, NF did not show any adsorption, while Cr(VI) could be adsorbed by NF. And NF still shows higher selectivity to Cr (VI) ions even in the presence of Cl−, SO42-, or NO3− ions. Langmuir and Freundlich isotherm models were used to fit the equilibrium sorption isotherms of Cr(VI) ions. In addition, breakthrough and desorption curves were obtained by using fixed bed columns packed with NF at different desorption flow rates and NaOH concentrations. The results showed that 0.05 mol·L-1 of an aqueous NaOH solution is an appropriate desorption agent, with 5 times the theoretical desorption amount and a flow rate lower than 12.3 mL⋅min-1. An aqueous solution of HNO3 with a mass fraction of 0.34 % is a feasible regeneration regent. The fixed bed adsorption capacity of NF was 39.04 mg⋅g-1 (0.751 mmol⋅g-1). CFs can serve as a low-cost alternative for adsorbing acid and selectively enriching toxic Cr(VI) ions from water.

Insight into the adsorption mechanisms of aqueous hexavalent chromium by EDTA intercalated layered double hydroxides: XRD, FTIR, XPS, and zeta potential studies

To understand the possible mechanisms of Cr(vi) adsorption on the surface of modified LDHs, we synthesized EDTA intercalated MgAl-LDH and its magnetic product, and evaluated their adsorption performance for Cr(vi) by batch experiments.

Removal of Chromium from Liquid Waste by Gamma Aluminum Oxide (γ-Al2O3) Nanoparticles Synthesized using Citrate Sol–gel Method

Abstract Gamma Aluminum oxide (γ-Al2O3) nanoparticles of particle size less than 8 nm were synthesized from aluminum nitrate nonahydrate and citric acid fuel via a citrate sol-gel method. The prepared alumina products were characterized by means of X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscope (FE-SEM) and High Resolution Transmission Electron Microscope (HR-TEM). Different phases of alumina like amorphous, γ- Al2O3 and α/γAl2O3 nanoparticles were obtained on changing the calcination temperature for the alumina samples. The adsorption properties of the active phase γ-Al2O3 for the removal of Cr(VI) from liquid waste were examined by batch adsorption study. The effect of different parameters such as initial pH value in solution, contact time and temperature on the adsorption performance of Cr (VI) onto γ-Al2O3 was studied . The adsorption process reached the equilibrium at 75 min and was found to be maximum at pH =3. The removal efficiency percent of Cr(VI) using γ-Al2O3 was increased with increasing temperature .The equilibrium adsorption was described with Langmuir model and the adsorption kinetics fits well pseudo- second-order model.

Adsorption performance of Cr(VI)-imprinted poly(4-VP-co-MMA) supported on activated Indonesia (Ende-Flores) natural zeolite structure for Cr(VI) removal from aqueous solution

The adsorption performance of Cr(VI) on the Cr(VI)-imprinted poly(4-VP-co-MMA) (IIP) supported on Activated Indonesia (Ende-Flores) natural zeolite (ANZ) structure for Cr(VI) removal from aqueous solution have been studied. Cr(VI)-imprinted-poly(4-VP-co-MMA)-ANZ (IIP-ANZ) was synthesized using Cr(VI) as a template, 4-vinylphiridine (4-VP) as a complex agent, methyl methacrylate (MMA) as a monomer agent, ethylene glycol dimethylacrylate (EGDMA) as cross-linker and benzoyl peroxide (BPO) as an initiator. XRD, FTIR, SEM-EDX and BET was performed to characterize the synthesized materials. The maximum adsorption capacity was 4.365 mg/g adsorbent at pH 2, 30 min contact time, under 303 K respectively. Five kinetic and four isotherm models were used to find out the reaction rate of Cr(VI) adsorption processes on this adsorbent. Under the competitive condition, the adsorption capacity of this adsorbent for Cr(VI) is greater than Cr(III), Mn(II) or Ni(II) ions but it less selective if present of Pb(II) ion. Moreover, the reusability of the IIP-ANZ was tested for five times and no significant loss in adsorption capacity observed.