Preparation of magnetic zeolite/chitosan composite using silane as modifier for adsorption of Cr(VI) from aqueous solutions

This study aimed to prepare an efficient, cost-effective, and separable magnetic zeolite/chitosan composite (MZFA/CS) adsorbent from solid waste to deal with the water pollution of Cr(VI). The MZFA/CS was characterized by X-ray fluorescence (XRF), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) techniques. Then, the effect of pH, temperature, initial concentration of Cr(VI) ions, and contact time was considered in the study. For a sorbent dose of 0.1 g in 50 mL of a Cr(VI) solution, at a contact time of 30 min, temperature of 30°C, and a pH of 3, an adsorption capacity (q_e) of 16.96 mg g⁻¹ was achieved. Adsorption kinetics and isotherm data obtained for all adsorption systems were well-fitted by pseudo-second-order and Langmuir models, respectively. The thermodynamic study suggested that the adsorption process is spontaneous and endothermic in nature. In summary, the adsorbent with better separability (Ms = 16.83 emu g⁻¹) and adsorbability was successfully fabricated.     

A simple sulfuric acid pretreatment method to improve the adsorption of Cr(VI) by chitosan

An optimum pH of 5.0 for the adsorption of Cr⁶⁺ by chitosan was determined by using a stirred‐batch reactor method at constant pH. When a column containing chitosan was used to bind Cr⁶⁺ in a situation where pH could not be held constant because of pH changes caused by the chitosan itself, significant binding occurred only at solution pH 1 and 2. When chitosan was pretreated with sulfuric acid in a range of 7–70 mol % sulfuric acid : moles glucosamine residue, maximum binding occurred at pH 6.0. Under these conditions, a column containing 0.500 g acid‐treated chitosan (35% mole ratio) reduced the concentration of Cr⁶⁺ in 713 bed volumes of 25 ppm Cr⁶⁺ solution to ≤5 ppm in the effluent. A similar column of pretreated chitosan reduced Cr⁶⁺ concentration in 1042 bed volumes of industrial chromium plating rinse water initially containing 18 ppm Cr⁶⁺ to ≤5 ppm. Capacity experiment results indicated 60 mg chromium bound per gram of treated chitosan at pH 6.0. Commercial resin IRA‐67 was also investigated as a Cr⁶⁺ binding agent. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2808–2814, 2004     

Removal of Cr(VI) from wastewater by adsorption on iron nanoparticles

Due to rapid industrialisation, the presence of heavy metals in water and wastewater is a matter of environmental concern. Though some of the metals are essential for our system but if present beyond their threshold limit value (TLV), they are harmful and their treatment prior to disposal becomes inevitable. The present communication has been addressed to the removal of Cr(VI) from aqueous solutions by nanoparticles of iron. Nanoparticles of iron were prepared by sol–gel method. The characterisation of the nanoparticles was carried out by XRD and TEM analysis. Batch experiments were adopted for the adsorption of Cr(VI) from its solutions. The effect of different important parameters such as contact time and initial concentration, pH, adsorbent dose, and temperature on removal of chromium was studied. The removal of chromium increased from 88. 5% to 99.05% by decreasing its initial concentration from 15 to 5 mg L^?1 at optimum conditions. Removal of Cr(VI) was found to be highly pH dependent and a maximum removal (100%) was obtained at pH 2.0. The process of removal was governed by first and pseudo‐second‐order kinetic equations and their rate constants were determined. The process of removal was also governed by intraparticle diffusion. Values of the thermodynamic parameters viz. ΔG°, ΔH°, and ΔS° at different temperatures were determined. The data generated in this study can be used to design treatment plants for chromium rich industrial effluents. Adsorption results indicate that nanoiron particles can be effective for the removal of chromium from aqueous solutions.     

Studies of adsorption behavior of crosslinked chitosan for Cr(VI), Se(VI)

In this work, it was found that crosslinked chitosan (CCTS) had strong adsorption ability for some anions under certain conditions. Cr(VI) and Se(VI) existed in anion forms in aqueous solution, and their adsorption rates by CCTS were 97% for Cr(VI) at pH 3.0 and 95% for Se(VI) at pH 4.0. In addition, the adsorption balance time and isotherm of CCTS for Cr(VI) and Se (VI) were discussed and adsorption mechanism was explained. This research will be useful for designing CCTS‐based adsorption for metallic toxin removal and preconcentrating Cr(VI) and Se(VI) in their trace analysis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3216–3219, 2000     

Removal of chromium (VI) from aqueous solutions using poly(4‐vinyl pyridine) beads

Sorption of hexavalent chromium ions from aqueous solution by poly 4‐vinyl pyridine [Poly(4‐VP)] was studied. The batch method was applied for adsorption processes. The effects of initial ion concentration, time, pH and temperature on adsorption were investigated. A treatment time of 60 min was found to be sufficient to reach equilibrium. pH 3.0 was found as the optimum pH value for the process. The maximum adsorption performance was achieved at 86.7 mg g^?1 using 500 mg L^?1 Cr (VI) solutions. The process of adsorption of Cr (VI) was explained by Langmuir isotherm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2865–2870, 2006     

生物质吸附材料对Cr(VI)的吸附还原研究进展

重金属污染是当今工业发展所面临的一个重要环境问题,传统处理含铬废水的方法具有工艺简单、操作方便等优点,但存在二次污染、处理成本高等问题。寻找成本低、去除效率高的重金属废水处理方法是当下研究的一个重要方向。本工作介绍了生物质吸附法对含铬废水的处理研究,简述了生物质材料在金属吸附回收领域的优势,分析了当前生物质吸附材料的研究内容和发展现状,归纳了目前常用的物理、化学改性方法,并详细介绍了改性生物质材料对Cr(VI)的吸附效果,然后根据吸附剂表面活性基团与吸附质之间相互作用的类型,分析总结了生物质吸附材料对Cr(VI)的四种吸附机理以及在吸附过程中氨基、羟基、硫醇等活性基团作为电子供体对Cr(VI)的还原机理。最后,从研究与应用的角度,对生物质吸附材料吸附还原Cr(VI)的未来研究方向做出展望。     

Heterocyclic modification of chitosan for the adsorption of Cu (II) and Cr (VI) ions

A heterocyclic modification of chitosan has been attempted for development of an effective adsorbent material for removal of metal ions. The modified polymer was characterized using infrared (IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) techniques. The adsorption capacity exhibited for Cu (II) and Cr (VI) were 83.75 and 85.0 mgg^?1, respectively, which is a significant improvement over chitosan. The adsorption on the modified polymer was a second-order kinetic process and followed Langmuir isotherm model. The thermodynamic analysis indicated exothermic and spontaneous nature of adsorption. About 80% of the adsorbed metal ions were desorbed in appropriate stripping solutions indicating reusability.     

Removal of Cr(V1) from aqueous solutions by adsorption on fly ash-wollastonite

The ability of a homogeneous mixture of fly ash and wollastonite (1:1) to remove Cr(V1) from aqueous solutions by adsorption has been investigated. The extent of removal is dependent on concentration, pH and temperature of the solution. The applicability of the Langmuir isotherm for the present system has been tested and the surface mass transfer coefficient at 30°C and pH 2.0 determined. Maximum removal was observed at pH 2.0 and 30°C. The adsorption is first governed by diffusion followed by surface compound formation. The thermodynamic parameters, desorption results and infrared studies indicated that the surface compounds, formed by interaction of adsorbate ions and different constituents of mixed adsorbent, were stable in nature.     

Adsorption behavior of reactive dyes from aqueous solutions on chitosan

The capability of the use of chitosan for removing vinyl sulfone and chlorotriazine reactive dyes from aqueous solutions was examined, including equilibrium and dynamic studies. Experiments were performed as a function of dye concentration, and the amount and particle size of chitosan. It was shown that the adsorption capacities of chitosan were comparatively high for the three investigated dyes. The equilibrium data could be best fitted by the Redlich–Peterson equation over the entire concentration range (50–500 g m⁻³). A comparison of the adsorption capacity among such adsorbents as chitin and powdered activated carbon was made. Two rate parameters were finally obtained to describe the adsorption process on a quantitative basis. These parameters could be well correlated to the amount and particle size of dry chitosan. ©1997 SCI     

Mechanisms of Cr(VI) removal from water by various types of activated carbons

The removal mechanisms of Cr(VI) from water using different types of activated carbons, produced from coconut shell, wood and dust coal, were investigated in this project. Different types of activated carbons have different surface characteristics. The coconut shell and dust coal activated carbons have protonated hydroxyl groups on the surface (H‐type carbons), while the surface of the wood‐based activated carbon has ionised hydroxyl groups (L‐type carbons). The adsorption kinetics of chromium onto the activated carbons at pH values ranging from 2 to 6 were investigated. It was found that the optimum pH to remove total chromium was 2 for wood‐based activated carbon, while for coconut shell and dust coal activated carbons, the optimum pH was around 3–4. The difference in the optimum pH for different activated carbons to remove Cr(VI) from water can be explained by the different surface characteristics and capacity of the activated carbons to reduce Cr(VI) to Cr(III). © 1999 Society of Chemical Industry     

Studies of adsorption properties of crosslinked chitosan for vanadium(V), tungsten(VI)

In this article, the adsorption properties of crosslinked chitosan (CCTS) for V(V) and W(VI) were studied. Experimental results showed the adsorption rates of CCTS for V(V) and W(VI) were closely related to the acidity of solution. The adsorption rates were 97% for V(V) at pH 4.0 and 96% for W(VI) at pH 4.5. The adsorption balance times, adsorption capacities, and adsorption mechanism were explored. This research is of significance for removal of V(V) and W(VI) in industrial wastewater and their preconcentration in trace analysis. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1584–1588, 2004     

Chromium electrodeposition from Cr(VI) low concentration solutions

This work presents a study of a hard chromium plating process using low concentration H₂CrO₄ baths. In particular, the effect of different values of CrO₃/H₂SO₄ ratio on coating properties such as adhesion, hardness, surface roughness, apparent density and microstructure were considered. To increase the solution conductivity, avoiding long deposition times and low throwing power typical of dilute solutions, the behaviour of various inorganic compounds was investigated. Specifically, the compounds suitable for obtaining brighter coatings with lower surface roughness values than those obtained using Fink’s solutions were Na₂SO₄ and Al₂(SO₄)₃ × 18H₂O. A bath composition was identified, with a limited use of Cr(VI) in a solution able to produce coatings with a better surface roughness than those of conventional industrial baths.     

磁性聚合物微球在Cr(VI)吸附分离中的应用(英文)

The magnetic poly-(methacrylate-divinyl benzene) microspheres with micron size were synthesized by modified suspension polymerization method.Adsorption of Cr(VI) from aqueous solution by magnetic poly-(MA-DVB) microspheres with surface amination was investigated.The adsorption processes were carried out under diversified conditions of pH value,adsorption time and temperature to evaluate the performance of the mag-netic microspheres.The optimum pH value for Cr(VI) adsorption was found as 3.The adsorption capacity increased with adsorption time and attained an optimum at 60 min.The adsorption processes for magnetic microspheres was endothermic reaction,and the adsorption capacity increased with increasing temperature.     

Functionalized chitosan with butylammonium ionic liquids for removal of Cr(VI) from aqueous solution

Environmental pollution by heavy metals is currently a problem of great concern for human health. In this context, this study aims to contribute with the synthesis and characterization of chitosan functionalized with three different ionic liquids (n-butylammonium acetate, sec-butylammonium acetate, and tert-butylammonium acetate) followed by its application in hexavalent chromium effluent treatment. The adsorbents synthesized (ChN, ChS, and ChT) were characterized by SEM, EDS, FTIR, BET, RDD, PSD, and XRD techniques. Afterward, the influences of temperature, contact time, and pH on the Cr(VI) adsorption process were evaluated. The solution with pH 3 displayed the highest adsorption capacities (107.31, 104.60, and 107.97 mg.g^-1 for ChN, ChS, and ChT, respectively). The kinetic data were better adjusted to the Weber-Morris kinetic model with an ideal time of 2 h. Furthermore, the influence of temperature was evaluated using the Freundlich and Langmuir isotherms, with maximum capacities of 142.05 (ChN), 131.58 (ChS), and 146.63 mg.g^-1 (ChT). The adsorbent displayed enhanced adsorption properties in comparison with raw chitosan by an intensification of the electrostatic interaction between amino groups and hexavalent chromium. Finally, the reusability was investigated, and significant results were observed (84.33 ± 4.87%) in the adsorption process after 4 cycles.     

Removal of Cr(VI) from aqueous solution by London plane leaves

The effect of initial metal concentration, contact time and solution temperature on the removal of Cr(VI) from solution by waste London plane leaves, generated by the pruning of street trees, was investigated in batch mode conditions. The removal of Cr(VI) was highly concentration‐dependent and mainly governed by physico‐chemical adsorption under the weak acidic conditions studied. The equilibrium data fit well in the Langmuir isotherm model. The Langmuir constants were calculated at different temperatures and both the adsorption capacity and adsorption intensity increased with rising temperature. The endothermic nature of the Cr(VI) adsorption was confirmed by the thermodynamic parameters. The study has shown that the waste leaves can be used as an effective adsorbent for removal of Cr(VI) from wastewater. Copyright © 2003 Society of Chemical Industry     

DNA adsorption on poly(N,N‐dimethylacrylamide)‐grafted chitosan hydrogels

In this study, poly(N,N‐dimethylacrylamide) grafted chitosan (PDMAAm‐g‐CT) hydrogels were prepared for deoxyribonucleic acid (DNA) adsorption. Instead of directly grafting the N,N‐dimethylacrylamide (DMAAm) monomer onto the chitosan (CT) chains, poly(N,N‐dimethylacrylamide) with carboxylic acid end group (PDMAAm‐COOH) was firstly synthesized by free‐radical polymerization using mercaptoacetic acid (MAAc) as the chain‐transfer agent and then grafted onto the CT having amino groups. The synthesis of PDMAAm‐COOH and its grafting onto the CT chains were confirmed by attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy. From gel permeation chromatography measurements, the number‐average molecular weight (M _n) and polydispersity index of PDMAAm‐COOH were found as 2400 g/mol and 2.3, respectively. The PDMAAm‐g‐CT hydrogels were utilized as the adsorbents in DNA adsorption experiments conducted at +4°C in a trisEDTA solution of pH 7.4. The hydrogels produced with higher PDMAAm‐COOH content exhibited higher DNA adsorption capacity. The DNA adsorption capacity up to 4620 μg DNA/g dry gel could be achieved with the PDMAAm‐g‐CT hydrogels prepared in 80.0 wt % PDMAAm‐COOH feed concentration. This value is approximately seven times higher than that of CT alone. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

水杨醛接枝壳聚糖的制备及其吸附性能

以壳聚糖和水杨醛为原料,采用超声波辐射技术制备了水杨醛接枝壳聚糖,并用红外光谱对产物的结构进行了表征,同时研究了接枝壳聚糖的吸附性能.结果表明:采用超声波辐射,大大提高了壳聚糖的接枝反应速度.所制得的水杨醛接枝壳聚糖对Cu2 、Cr6 的吸附容量和吸附速度要大于壳聚糖,在25℃下,其对Cu2 、Cr6 的吸附容量分别达到117.84 mg·g-1和58.14 mg·g-1,并且对Cu2 、Cr6 的吸附在1 h内即可达到饱和.