Fabrication of graphene oxide decorated with poly(dimethyl amino ethyl methacrylate) brush for efficient Cr(Ⅵ) adsorption from aqueous solution

Confronting the severe health threats and environmental impacts of Cr(Ⅵ) in aquatic environments demands innovative and effective remediation approaches. In this study, Graphene oxide(GO)-decorated poly(dimethyl amino ethyl methacrylate)(PDMAEMA) brush nanocomposites(GOP1, GOP2, GOP3, and GOP4) were fabricated using atom transfer radical polymerization(ATRP) by the “graft from” method.The resulting nanocomposites were utilized for removing Cr(Ⅵ) with good adsorption performance due to the electrostatic interaction of protonated nitrogen groups in the brush chains with negatively charged particles in the solution. The kinetic model of pseudo-second-order best represented the contaminants' adsorption characteristics. The Weber-Morris model further indicated that surface adsorption and intraparticle diffusion mechanisms primarily controlled the adsorption procedure. Additionally, the Langmuir and Temkin isotherm models were found to most accurately represent the adsorption characteristics of the pollutants on the nanocomposites, and GOP4 can achieve the maximum adsorption capacity of 164.4 mg·g^(-1). The adsorbents' capacity maintains above 85% after five cycles of adsorption-desorption. The nanocomposites in this study demonstrate promising potential for eliminating Cr(Ⅵ) from aqueous solutions.

Effective Elimination of Hazardous Chromium (VI) Using Periodic Elements and Contemporary Adsorption Methods by Using Magnesium Ferrite Nanoparticle: A Review

A well-known hazardous metal and top contaminant in wastewater is hexavalent chromium. The two forms of most commonly found chromium are chromate ( CrO 4 2− ) and dichromate ( Cr 2 O 7 2− ). Leather tanning, cooling tower blow-down, plating, electroplating, rinse water sources, anodizing baths etc. are the main sources of Cr (VI) contamination. The Cr (VI) is not only non-biodegradable in the environment but also carcinogenic to living population. It is still difficult to treat Cr contaminated waste water effectively, safely, eco-friendly, and economically. As a result, many techniques have been used to treat Cr (VI)-polluted wastewater, including adsorption, chemical precipitation, coagulation, ion-exchange, and filtration. Among these practices, the most practical method is adsorption for the removal of Cr (VI) from aqueous solutions, which has gained widespread acceptance due to the ease of use and affordability of the equipment and adsorbent. It has been revealed that Fe-based adsorbents’ oxides and hydroxides have high adsorptive potential to lower Cr (VI) content below the advised threshold. Fe-based adsorbents were also discovered to be relatively cheap and toxic-free in Cr (VI) treatment. Fe-based adsorbents are commonly utilized in industry. It has been discovered that nanoparticles of Fe-, Ti-, and Cu-based adsorbents have a better capacity to remove Cr (VI). Cr (VI) was effectively removed from contaminated water using mixed element-based adsorbents (Fe-Mn, Fe-Ti, Fe-Cu, Fe-Zr, Fe-Cu-Y, Fe-Mg, etc.). Initial findings suggest that Cr (VI) removal from wastewater may be accomplished by using magnesium ferrite nanomaterials as an efficient adsorbent.

Adsorption of Chromium （Ⅵ） from Aqueous Solution Using Zeolite/Chitosan Hybrid Composite

This study investigated the adsorption ability of ZCHC （zeolite/chitosan hybrid composite） as adsorbent for chromium （Cr（Ⅵ））, ZCHC was prepared with sol-gel method by mixing zeolite and chitosan. Adsorption experiment from aqueous solutions containing known amount of Cr（Ⅵ） using zeolite, chitosan and ZCHC was explored to evaluate the efficiency of ZCHC as adsorbent for Cr in a batch system. The amount of Cr（Ⅵ） adsorbed at different pH values, initial concentrations, adsorbent dosages, and contact times were determined by ICP-AES （inductively coupled plasma-atomic emission spectrometry） in order to determine the optimum conditions for Cr（Ⅵ） adsorption. Furthermore, the adsorption mechanism of Cr（Ⅵ） by zeolite, chitosan and ZCHC was investigated by applying Langmuir and Freundlich isotherm equations to the data obtained. In addition, the rates of adsorption were found to conform to pseudo-second order kinetics.

Chemical Behavior of Chromium in Soils: Ⅲ. Mechanism of Cr(Ⅵ) Adsorption by Soils

An analysis of Cr (Ⅵ)-sorbed surface of the soils by using a scanning electron microscope and an electron probe microscope has proved that aluminium is the chief element affecting Cr (Ⅵ) adsoption. As the ionic strength of the solution increased, the amounts of Cr (Ⅵ) adsorbed by goethite and soils decreased. Cr (Ⅵ) adsorption was greatly depressed in the presence of SO42-, WO42-, MoO42-, HPO42- and H2PO4- which competed for anion adsorption sites. The depressing extent of these anions was found to follow the sequence: HPO42-, H2PO4-> MoO42-> WO42-> SO42-> > Cl-, NO3-. The amounts of Cr (Ⅵ) desorption varied with different extractants. 0.5 M NH4F and 0.1 M KH2PO4 could be regarded as the best extractants for Cr (Ⅵ) sorbed in the soils. The mechanism of Cr (Ⅵ) adsorption by goethite and soils seemed to be similar to that of phosphate. Basically, Cr (Ⅵ) was adsorbed through specific adsorption and could not be desorbed by Cl- and NO3-. Cr (Ⅵ) adsorption on goethite released OH-. There was a significant correlation between the amounts of Cr (Ⅵ) adsorbed and pH variation in goethite suspension.

Adsorption of copper(Ⅱ) and chromium(Ⅵ) on diaspore

The adsorption of Cu(Ⅱ)and Cr(Ⅵ)on diaspore was studied with the help of X-ray diffraction analysis,BET measurement,zeta potential measurement and atomic adsorption spectrometry.The adsorption equilibrium almost reaches within 60 min.The adsorption isotherms of Cu(Ⅱ)and Cr(Ⅵ)could be well described by the Langmuir equation.The adsorption capacities of Cu(Ⅱ)and Cr(Ⅵ)are 1.944 and 1.292 mg/g,respectively.The adsorption percentage of Cr(Ⅱ)increases with the increment of solution pH,but the adsorption percentage of Cr(Ⅵ)decreases.This could be explained by zeta potential theoretical and electrostatic attraction between metal ions and diaspore surface.

Adsorption of Cr(Ⅵ) in Water with Phosphoric Acid Modified and Ordinary Walnut Shells

A comparison between the effects of ordinary walnut shell and phosphoric acid modified walnut shell on adsorption of Cr（Ⅵ） was carried out. The experimental results showed that owing to larger surface void of modified walnut shell its adsorption of Cr（Ⅵ） was better. When the temperature was 35 ℃, adsorbent particle size was 1.0-1.6 mm, shaker shock rate was 200 r/min, and dosage of walnut shell was 0.80 g, the Cr（Ⅵ） removal rate reached 99.4%. The fitting of adsorption isotherm and kinetics model showed that, Langmuir isotherm model could reflect the adsorption process of modified walnut shell; and both the adsorption processes of ordinary and modified walnut shells accorded with the pseudo-second-order kinetic equations.

Cr^(Ⅵ) adsorption on four typical soil colloids: equilibrium and kinetics

It is observed that the adsorption of chromium are greater on kaolinite minerals, red soil (R) and laterite (L) colloids than that on montmorillonite, indicotic black (IB) and yellow brown (YB) soil colloids. The adsorption process of Cr Ⅵ on these media can be further described by Langmuir or Freundlich equation quite well. The adsorption reaction of Cr Ⅵ is fast, and the adsorption equilibrium can be reached within the first two hours in moderate temperature. The adsorption quantity of Cr Ⅵ to kaolinite mineral increased with the increasing pH in the range of 2.0 to 7.0, then decreased at higher pH. But it showed some consistence among the four soil colloids. The lower the pH, the stronger the adsorption. The possible mechanisms are further discussed here. Meanwhile the influence of temperature on Cr Ⅵ adsorption on different soil colloid and clay minerals are also investigated.

A Study of Chromium Adsorption on Natural Goethite Biomineralized with Iron Bacteria

Goethite, especially biogenic goethite, has high specific surface area and great capacity for the adsorption of many contaminants including metal ions and organic chelates. Chromium is a redox actively toxic metal ion that exists as either Cr^Ⅲ or Cr^Ⅵ in nature, and as such it is essential to understand its behavior of adsorption on natural goethite mineralized by iron bacteria, as Gallionella and Leptothrix in water body. The adsorption of Cr^3＋ and Cr^Ⅵ on naturally biomineralized goethite is studied in this paper. The results show that both Langmuir and Freundlich adsorption isothermal models are able to accurately describe the adsorption of these two ions. Investigation of SEM/EDS, TEM/EDS indicates that the two ions do not adsorb homogeneously on goethite owing to the different microstructures of goethite, and that the microspherical goethite has a greater adsorption capacity for chromium ions than the helical one. XPS data show that redox reaction of chromium on the surface of biomineralized goethite takes place in the adsorption of both Cr^3＋ and Cr^Ⅵ. The CrvI adsorbed on biogoethite is much easier to transform into CrIII than the oxidization of Cr^Ⅲ on the bio-goethite.

Efficient adsorption to hexavalent chromium by iron oxalate modified D301:Characterization,performance and mechanisms

Chromium is a common harmful pollutant with high toxicity and low bearing capacity of soil and water.Excellent salinity resistance,a wide pH range,and high regeneration capacity were essential for qualified adsorbents used in removing hexavalent chromium(Cr(VI))from polluted water.Herein,iron oxalate modified weak basic resin(IO@D301)for the removal of Cr(VI)was prepared by the impregnation method.The IO@D301 was characterized by scanning electron microscope(SEM),Fourier transform infrared spectroscopy(FTIR),X-Ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).Owing to abundant amine,carboxyl groups and iron ions existing on the surface,IO@D301 possesses high adsorption and salinity resistance capacity for Cr(VI).The maximum adsorption capacity of IO301 towards Cr(VI)reached 201.30 mg·g^(-1) at 293 K and a pH of 5.The adsorption equilibrium was well fitted by the Freundlich model,and the adsorption process was described by the pseudofirst-order kinetics model as spontaneous and exothermic.The mechanism may be identified as electrostatic attraction,coordination,and reduction,which was confirmed by FT-IR and X-ray photoelectron spectroscopy.

Modelling and Fixed Bed Column Adsorption of Cr(Ⅵ) onto Orthophosphoric Acid-activated Lignin

The advantage of using an available and abundant residual biomass, such as lignin, as a raw material for activated carbons is that it provides additional economical interest to the technical studies. In the current investigation, a more complete understanding of adsorption of Cr（VI） from aqueous systems onto HaPO4-acid activated lignin has been achieved via microcolumns, which were operated under various process conditions. The practice of using microcolumn is appropriate for defining the adsorption parameters and for screening a large number of poten- tial adsorbents. The effects of solution pH （2-8）, initial metal ion concentration （0.483-1.981 mmol.L-1）, flow rate （1.0-3.1 cm3-min-1）, ionic strength （0.01-0.30 mmol-L-1） and adsorbent mass （0.11 0.465 g） on Cr（VI） adsorption were studied by assessing the microcolmnn breakthrough curve. The microcolumn data were fitted by the Thomas model, the modified Dose model and the BDST model. As expected, the adsorption capacity increased with initial Cr（VI） concentration. High linear flow rates, pH values and ionic strength led to early breakthrough of Cr（VI）. The model constants obtained in this study can be used for the design of pilot scale adsorption process.

Evaluation of the Adsorption of Hexavalent Chromium on Kaolinite and Illite

The adsorption of hexavalent chromium on Kaolinite and Illite was studied in order to evaluate their potential for the reduction of hexavalent chromium mobility and their possible application for the treatment of polluted sediment. The influence of various parameters affecting the adsorption of hexavalent chromium, such as the pH of aqueous solution, the ionic strength and the initial metal ion concentration were investigated. The optimal pH range corresponding to the hexavalent chromium adsorption maximum on the Kaolinite and Illite is 2 - 4 and 2 - 2.6, respectively. The results showed that hexavalent chromium sorption on Kaolinite and Illite was strongly influenced by the pH, the ionic strength and the initial metal ion concentration. Langmuir and Freundlich adsorption isotherms are employed to understand the nature of adsorption at room temperature. The characteristic parameters for each isotherm have been determined. This showed that the Freundlich isotherm model well described the equilibrium data. The data suggest that the charge of the clay mineral surface is one of the main factors controlling hexavalent chromium desorption at alkaline pHs.

Adsorption of XSD-296 resin for Cr(Ⅵ)

The adsorption properties of XSD-296 for Cr(Ⅵ) were studied by using chemical analysis and infrared spectrometry. Experimental results show that XSD-296 resin has a good adsorption ability for Cr(Ⅵ) at pH=2.6 in the HAc-NaAc medium. The statically saturated adsorption capacity is 235 mg/g resin. The apparent activation energy of adsorption reaction, Ea, is 16.73 kJ/mol, and the thermodynamic parameters are △H=11.62 kJ/mol, △G298 K=-4.13 kJ/mol. The adsorption behavior of resin for Cr(Ⅵ) is in accordance with Freundlich adsorption isotherm. Cr( Ⅵ ) adsorbed on resin can be eluted by 5%NaCl-5%NaOH or 5%NH4Cl-5%NH3·H2O quantitatively. Infrared spectra and adsorption mechanism show that the functional group of resin coordinates with Cr(Ⅵ) to form co-ordination compound. The coordination molar ratio of the functional group of resin to Cr(Ⅵ) is 1:1.

Hexavalent Chromium Adsorption from Aqueous Solution by Agricultural Waste Materials

Abilities of agricultural waste materials (walnut shell-WS, rice husk-RH, and peanut hull-PH) were tested as adsorbents for the adsorption of Cr(Ⅵ) from aqueous solution. Batch adsorption experiments were carried out to study the adsorption kinetics mechanism of Cr(Ⅵ) effect of adsorbent dosage, pH, contact time, and temperature. The best results are obtained at 15g/L adsorbent concentration, 60min contact time, 298K temperature, and 50mg/L adsorbate initial concentration at pH 2. The adsorption isotherms, using initial concentrations of Cr(Ⅵ) between 10 and 500mg/L for the Cr(Ⅵ) removal, show the maximum metal uptake capacities of adsorbent were 10.48, 6.71, and 8.54mg/g for WS, RH, and PH, respectively. And the adsorption data fitted well to the Langmuir adsorption isotherm for WS, RH, and PH with correlation coefficients of 0.9862, 0.9723, and 0.9714, respectively. Moreover, the FTIR analysis of WS, RH, and PH before and after adsorption of Cr(Ⅵ) suggested that Cr ions were combined to some functional groups of compounds contained in these materials.

Removal of Chromium from Chromium（VI） Solutions by Adsorption and Reduction Using Immobilized Persimmon Gel

The removal of chromium（Vl） from an aqueous solution using persimmon gel was examined. The amount of chromium（VI） removed was strongly affected by the pH of the solution, with all ehromium（VI） being removed at pH 2 or lower. However, in a solution containing, 15 mg dry weight of immobilized persimmon gel, the amount of removed chromium（VI） decreased as the pH increased. A part of chromium（VI） was reduced another oxidation stage, mainly chromium（III）, by immobilized persimmon gel. The amount of reduced chromium（III） in the solution was increased with decreasing the pH of the solution. As a result, the amount of total chromium removed was maximal at pH 2. The amount of chromium removed were affected by the chromium concentration and the amount of gel. The maximal amount of chromium removed by the column system was also discussed.

Removal of Cr(Ⅲ) and Cr(Ⅵ) from aqueous solution by adsorption on sugarcane pulp residue

Sugarcane pulp residue （SPR）, a waste from sugar-refinery, which possesses a large surface area, can be used for removing chromium （Cr（Ⅲ） and Cr（Ⅵ）） from wastewater. In this work, the kinetics, isotherms of Cr（Ⅲ） and Cr（V[） adsorption and their removal by SPR were investigated. The results show that the removal percentages of Cr（Ⅵ） and Cr（Ⅲ） increase with increasing SPR dosage and temperature and decrease with increasing SPR particle size and the initial concentration of chromium ions. However, the influence of pH value on the Cr（Ⅵ） removal differs from that of the Cr（Ⅲ） removal. The Cr（Ⅵ） removal percentage decreases with increasing pH values, while the Cr（Ⅲ） removal percentage increases with increasing pH value. The adsorption kinetics of Cr（Ⅵ） and Cr（Ⅲ） well fits with pseudo-second-order model. Langmuir adsorption isotherm can well describe the adsorption phenomena of chromium ions with the maximum adsorption capacity of 0.567 mg/g for Cr（Ⅵ） and 3.446 mg/g for Cr（Ⅲ）. Moreover, SPR reveals higher adsorption capacity for Cr（Ⅲ） than that for Cr（Ⅵ）, which implies that SPR has more potential application for Cr（Ⅲ）-containing wastewater treatment than that for Cr（Ⅵ）-containing wastewater treatment.

Study on Chromium Ion Adsorption from Wastewater by Sugarcane Residues

With the application of chromium increasing, wastewater shows an increase of chromium pollution. In particular, Cr(Ⅵ) has become a major concern because of its high toxicity. Cr(Ⅵ) is recognized to be much more toxic than Cr(Ⅲ). Sugarcane residue is a byproduct of the sugar industry, and it is an important renewable biomass resource. In this paper, sugarcane residues were used to remove chromium ions from wastewater in order to develop cheap and efficient heavy metal adsorption materials. The effects of pH, sugarcane residue dosage, sugarcane residue particle size and chromium ion initial concentration on chromium ion removal and the kinetics of chromium ion removal at normal temperature were investigated. The results showed that the removal rate of Cr(Ⅵ) and Cr(Ⅲ) increased with an increase of sugarcane residue concentration, and decreased with an increase of particle size and the initial concentration of chromium. The removal effect of Cr(Ⅲ) increased with increasing pH, and the removal effect of Cr(Ⅵ) decreased with increasing pH. The removal kinetics of chromium fitted well with a pseudo-second-order-model. Sugarcane residues had a higher adsorption capacity for Cr(Ⅲ) than for Cr(Ⅵ). This paper provides a basis for the treatment of chromium containing wastewater or other heavy metal wastewater in the future.

Adsorption and desorption properties of D318 resin for Cr(Ⅵ)

The adsorption capability of D318 resin for Cr（Ⅵ） was investigated by chemistry analysis. Experimental results show that D318 resin has the best adsorption ability for Cr（Ⅵ） at pH=3.16 in HAc-NaAc medium. The statically saturated adsorption capacity of the resin is 265.4 mg/g. The thermodynamic adsorption parameters, enthalpy change AH and free energy change AG298 of the adsorption reaction are 4.81 and -5.16 kJ/mol, respectively. The apparent activation energy Ea is 22.4 kJ/mol. The adsorption behavior obeys the Freundlich isotherm. The molar coordination ratio of the functional group of resin to Cr（Ⅵ） is 3：2. Cr（Ⅵ） adsorbed on D318 resin can be eluted by 5%NaOH-5%NaCl quantitatively.

Insights into the adsorption performance and mechanism of Cr(Ⅵ)onto porous nanocomposite prepared from gossans and modified coal interface:Steric,energetic,and thermodynamic parameters interpretations

Herein,iron oxide/hydroxides deposits(gossans)were utilized,for the first time,in the fabrication of magnetite nanoparticles(MNPs)to load modified coal(MC).The as-synthesized MNPs@MC composite was characterized via different techniques and utilized for the Cr(Ⅵ)remediation.Experimental studies supported by theoretical treatment were applied to offer a new overview of the Cr(Ⅵ)adsorption geometry and mechanism at 25-45℃.Experimental results suggested that the Cr(Ⅵ)uptake was mainly governed by adsorption-reduction coupled mechanism.The Langmuir model fitted well the Cr(Ⅵ)adsorption data with maximum adsorption capacities extended from 115.24 to 129.63 mg·g^(-1).Theoretical calculations indicated that Cr(Ⅵ)ions were adsorbed on the MNPs@MC following the theory of the advanced monolayer statistical model.The number of ions removed per site ranged from 1.88 to1.23 suggesting the involvement of vertical geometry and multi-ionic mechanism at all temperatures.The increment of the active sites density and the adsorption capacity at saturation with improving temperature reflected an endothermic process.Energetically,the Cr(Ⅵ)adsorption was controlled by physical forces as the adsorption energies were less than 40 kJ·mol^(-1).The calculated free enthalpy,entropy.and internal energy explained the spontaneous nature and the viability of Cr(Ⅵ)adsorption on the MNPs@MC adsorbent.These results offer a new approach in utilizing the iron-rich deposits as gossans in the preparation of magnetic and low-cost adsorbents for wastewater remediation.

A study on the adsorption of chromium on laterite from Guizhou Province,China

The adsorption behaviors of Cr(VI) on laterite from Guizhou Province were studied in this paper, and the adsorption mechanism was discussed as well. Results showed that different mineral compositions in the laterite would cause differences in the capacity of laterite to absorb Cr(VI). Gibbsite, iron oxide minerals and non-crystalloids are the main contributors to enhancing the capacity of laterite to absorb Cr(VI). The pH of the solution is an important factor affecting the adsorption of Cr(VI) on laterite. Acidic environment (pH=2-5) is favorable to the adsorption of Cr(VI). The amount of adsorbed Cr(VI) decreases with increasing pH of the solution. With increasing initial concentrations of Cr(VI), the amount of adsorbed Cr(VI) increases first, and then decreases. The optimal adsorption concentration of Cr(VI) on laterite is 250 μg/mL. The adsorption of Cr(VI) on laterite is a rapid process, about 80% Cr(VI) will be adsorbed within 2 hours. And the adsorption of Cr(VI) on kaolinite is a slow process.

Adsorptive potential of Acacia nilotica based adsorbent for chromium(Ⅵ) from an aqueous phase

The objective of this research was to enhance adsorption capacity of Acacia nilotica （keekar） sawdust for the abatement of chromium bearing wastewater and to investigate the effect of process parameters on adsorption capacity. The sawdust was activated by acid wash and functionalized subsequently with formaldehyde. Functionalization of activated sawdust raised its chromium removal efficiency of almost 10% as compared to its adsorption removal efficiency of HCl treated sawdust in a batch adsorption study. Adsorption kinetic data provided better fitting with pseudo second order model. Maximum adsorption capacity calculated through the best fitting Langmuir model was 6.34 mg·g^-1 and 8.2 mg·g^-1 for HCl treated and formaldehyde functionalized sawdust adsorbents, respectively. The adsorption of Cr（VI） was endothermic when studied by varying temperature from 20℃ to 50℃ for both activated and functionalized adsorbents.