Efficient Removal of Cobalt(II) and Strontium(II) Metals from Water using Ethylene Diamine Tetra‐acetic Acid Functionalized Graphene Oxide

Graphene oxide (GO) with high specific surface area was prepared and functionalized with ethylene diamine tetra‐acetic acid (EDTA). The as‐prepared GO and the functionalized one (GO‐EDTA) were characterized using high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), and Raman spectroscopy. The as‐prepared and EDTA funcationalized GO were applied as adsorbent to remove strontium(II) and cobalt(II) from water. The results indicated that the prepared materials are efficient adsorbents for strontium(II) and cobalt(II) removal. The adsorption of Co^II and Sr^II under effects of contact time, temperature, and pH was investigated It is concluded that the maximum adsorption capacities of GO for Co^II and Sr^II were about 168 and 140 mg · g^–1, whereas of GO‐EDTA the values were about 197 and 158 mg · g^–1, respectively. It is indicated that pH 6 and temperature 40 °C are the best condition for Co^II and Sr^II removal from water. The application of Langmuir and Freundlich isotherms indicated that Langmuir isotherm is best fit for Co^II and Sr^II equilibrium adsorption. Adsorption kinetics were studied by applying pseudo first‐order, pseudo second‐order, and intraparticle diffusion models on the experimental data. The results proved that pseudo second‐order model is the best represented adsorption kinetics. Appling the intraparticle diffusion regressions on the experimental data indicated that intraparticle diffusion involved in adsorption process, which was not the only rate‐controlling step.     

Preparation and characterization of L-glutamic acid-functionalized graphene oxide for adsorption of Pb(II)

An efficient adsorbent (L-Glu/GO) was successfully synthesized by the reaction between L-glutamic acid (L-Glu) and graphene oxide (GO). The structure and morphology of this adsorbent were characterized by FTIR, SEM, XRD, and TGA. The SEM result indicated that the adsorbent was a nanomaterial with a size of about 50–400 nm. The adsorption experiments of various heavy ions on L-Glu/GO demonstrated that the adsorption performance of Pb(II) was better than others. Various variables affecting the adsorption of L-Glu/GO for Pb(II) were systematically explored. The experimental results indicated that the maximum adsorption capacity and equilibrium time of Pb(II) on L-Glu/GO were 513.4 mg g^?1 and 40 minute, respectively. The sorption kinetics and isotherm fitted well with the pseudo-second-order model and Langmuir model, respectively. The sorption mainly was a chemical process. Thermodynamic studies revealed that the adsorption was a spontaneous and exothermic process. The adsorbent could be regenerated with HCl solution. Hence, it was suggested that the L-Glu/GO could be applied in the removal of Pb(II) from wastewaters.     

Synthesis and application of modified poly (styrene‐alt‐maleic anhydride) networks as a nano chelating resin for uptake of heavy metal ions

A chelating resin based on modified poly (styrene‐alt‐maleic anhydride) with 3‐aminobenzoic acid was synthesized. This modified resin was further reacted by 1,2‐diaminoethane or 1,3‐diaminopropane in the presence of ultrasonic irradiation to prepare tridimensional chelating resin for the removal of heavy metal ions from aqueous solutions. The adsorption behavior of Fe(II), Cu(II), Zn(II) and Pb(II) ions was investigated by synthesized chelating resins in various pH. Among the synthesized resins, CSMA‐AB1 and CSMA‐AB2 demonstrated a high affinity for the selected metal ions compared to SMA‐AB, and the order of removal percentage changes as follow: Fe(II) > Cu(II) > Zn(II) > Pb(II). The adsorption of all metal ions in acidic medium was moderate, and it was favored at the pH value of 6 and 7. Also, the prepared resins were examined for removal of metal ions from industrial wastewater and were shown to have a very efficient adsorption in the case of Cu(II), Fe(II) and Pb(II); however, the adsorption of Zn(II) was lower than others. The resin was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction analysis and thermogravimetric analysis/derivative thermogravimetry. Copyright © 2012 John Wiley & Sons, Ltd.     

Removal of Mn(II) from Acidic Wastewaters Using Graphene Oxide–ZnO Nanocomposites

Pollution due to acidic and metal-enriched waters affects the quality of surface and groundwater resources, limiting their uses for various purposes. Particularly, manganese pollution has attracted attention due to its impact on human health and its negative effects on ecosystems. Applications of nanomaterials such as graphene oxide (GO) have emerged as potential candidates for removing complex contaminants. In this study, we present the preliminary results of the removal of Mn(II) ions from acidic waters by using GO functionalized with zinc oxide nanoparticles (ZnO). Batch adsorption experiments were performed under two different acidity conditions (pH1 = 5.0 and pH2 = 4.0), in order to evaluate the impact of acid pH on the adsorption capacity. We observed that the adsorption of Mn(II) was independent of the pH_PZC value of the nanoadsorbents. The qmax with GO/ZnO nanocomposites was 5.6 mg/g (34.1% removal) at pH = 5.0, while with more acidic conditions (pH = 4.0) it reached 12.6 mg/g (61.2% removal). In turn, the results show that GO/ZnO nanocomposites were more efficient to remove Mn(II) compared with non-functionalized GO under the pH2 condition (pH2 = 4.0). Both Langmuir and Freundlich models fit well with the adsorption process, suggesting that both mechanisms are involved in the removal of Mn(II) with GO and GO/ZnO nanocomposites. Furthermore, adsorption isotherms were efficiently modeled with the pseudo-second-order kinetic model. These results indicate that the removal of Mn(II) by GO/ZnO is strongly influenced by the pH of the solution, and the decoration with ZnO significantly increases the adsorption capacity of Mn(II) ions. These findings can provide valuable information for optimizing the design and configuration of wastewater treatment technologies based on GO nanomaterials for the removal of Mn(II) from natural and industrial waters.     

Kinetic and Thermodynamic Investigations of Zn(II) Adsorption on Microcrystalline Anthracene Modified with 8‐Hydroxyquinoline and Its Application to the Preconcentration and Determination of Trace Zinc

A new method that utilizes microcrystalline anthracene modified with 8‐hydroxyquinoline as an adsorbent has been developed for the preconcentration of trace Zinc(II). The possible reaction mechanism is discussed in detail. The influences of different parameters, such as acidity, other metal ions, the amounts of 8‐hydroxyquinoline and anthracene, etc. on the enrichment yield of Zn(II) have been studied to optimize the experimental conditions. The experimental data were fitted well with the pseudo‐second‐order kinetic model and Langmuir model at all studied temperatures and the maximum adsorption capacity was 32.58 mg·g^?1 (300 K). The thermodynamic parameters (ΔG^θ, ΔH^θ and ΔS^θ) showed the feasibility, exothermic and spontaneous nature of the adsorption at 280～320 K. Experiments indicate that Zn(II) can be completely separated from Cu(II), Co(II), Cd(II), Mn(II), Ni(II) in the eluent. The recovery of this method is in the range of 96.0%～105.0% with preconcentration factor of 100 and the limit of detection after preconcentration is 0.068 μg·L^?1. The proposed method has been successfully applied to the determination of trace Zn(II) in effluents and synthetic water sample having a composition similar to certified water sample SLRS‐4 (NRC, Canada). Analytical results obtained by this recommended method were very satisfactory.     

Graphene Oxides Prepared by Hummers’, Hofmann’s,and Staudenmaier’s Methods: Dramatic Influences on Heavy‐Metal‐Ion Adsorption

Graphene oxide (GO), an up‐and‐coming material rich in oxygenated groups, shows much promise in pollution management. GO is synthesised using several synthetic routes, and the adsorption behaviour of GO is investigated to establish its ability to remove the heavy‐metal pollutants of lead and cadmium ions. The GO is synthesised by Hummers’ (HU), Hofmann’s (HO) and Staudenmaier’s (ST) methodologies. Characterisation of GO is performed before and after adsorption experiments to investigate the structure–function relationship by using Fourier‐transform infrared spectroscopy and X‐ray photoelectron spectroscopy. Scanning electron microscopy coupled with elemental detection spectroscopy is used to investigate morphological changes and heavy‐metal content in the adsorbed GO. The filtrate, collected after adsorption, is analysed by inductively coupled plasma mass spectrometry, through which the efficiency and adsorption capacity of each GO for heavy‐metal‐ion removal is obtained. Spectroscopic analysis and characterisation reveal that the three types of GO have different compositions of oxygenated carbon functionalities. The trend in the affinity towards both Pb^II and Cd^II is HU GO>HO GO>ST GO. A direct correlation between the number of carboxyl groups present and the amount of heavy‐metal ions adsorbed is established. The highest efficiency and highest adsorption capacity of heavy‐metal ions is achieved with HU, in which the relative abundance of carboxyl groups is highest. The embedded systematic study reveals that carboxyl groups are the principal functionality responsible for heavy‐metal‐ion removal in GO. The choice of synthesis methodology for GO has a profound influence on heavy‐metal‐ion adsorption. A further enrichment of the carboxyl groups in GO will serve to enhance the role of GO as an adsorbent for environmental clean‐up.     

氧化石墨烯对水中内分泌干扰物双酚A的吸附性能

以氧化石墨烯(GO)为吸附剂, 内分泌干扰物双酚A (BPA)为目标污染物, 考察了GO对水中BPA的吸附性能. 结果表明: GO对BPA的最大吸附量(q_m)约为87.80 mg·g^-1 (25℃), 30 min左右即可达到吸附平衡, 远快于活性碳; 吸附动力学和等温线数据分别符合准二级动力学模型和Langmuir 吸附模型; 在溶液接近中性和低温的条件下有利于吸附的进行, 在溶液中存在电解质的条件下不利于吸附的进行. GO具有优异的循环吸附性能, 经过多次循环使用后依然可以保持良好的吸附能力. GO对BPA的吸附机理主要是由于GO本身的片状结构以及表面的含氧极性基团, 会与BPA之间产生π-π色散作用和氢键作用. 虽然GO对BPA的吸附能力不如石墨烯, 但是相比于石墨烯, GO表面含有大量极性基团, 具有良好的亲水性, 且GO合成方法相对简单, 可批量生产用于工业污水处理. 因此, 在水处理领域, GO有能力成为新型高效的吸附剂.     

Electrochemical Evaluation of Pollutants in the Environment: Interaction Between the Metal Ions Zn(II) and Cu(II) with the Fungicide Thiram in Billings Dam

Pesticides are organic molecules used in the control of various pests in different crops. These molecules show functional groups that can interact with metal ions, forming new species with different properties. These new compounds have been attracting attention because they can become a new environmental problem. In this work the interaction of copper and zinc metal ions with Thiram pesticide was studied using electrochemical techniques. Studies in ultrapure water showed the formation of Zn?Thiram complex with reduction potential at ?1.330 V; Cu?Thiram complex showed a cathodic peak at 0.020 V. Thiram causes a different effect on the two metal ions studied. It was observed that the ligand stabilizes more the Cu(II) than Zn(II). Both systems proved to be quasi‐reversible, controlled by the adsorption of the species on the electrode surface. The formation constants of the complexes were calculated to be 2.1×10⁵ for Zn?Thiram and 1.5×10¹⁹ for Cu?Thiram. In the samples from Billings dam, the Zn‐complex showed reduction potential at ?1.403 V; Cu‐complex exhibited a reduction peak at 0.012 V. Although there are interferers in river waters, the interaction of these metals with the pesticide showed high affinity, being possible to detect them in natural samples. The Cu(II) complex showed to be more stable in natural matrices when compared to the Zn(II) complex. The sensitivity for thiram electroanalytical determination decreases in the presence of Zn(II) and Cu(II).     

Determination of sulfadimethoxine in milk with aptamer‐functionalized Fe3O4/graphene oxide as magnetic solid‐phase extraction adsorbent prior to HPLC

An aptamer (Apt) functionalized magnetic material was prepared by covalently link Apt to Fe₃O₄/graphene oxide (Fe₃O₄/GO) composite by 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide hydrochloride and N‐hydroxysuccinimide, and then characterized by FTIR spectroscopy, X‐ray diffraction, and vibration sample magnetometry. The obtained composite of Fe₃O₄/GO/Apt was employed as magnetic solid‐phase extraction adsorbent for the selective preconcentration of sulfadimethoxine prior to analysis by high‐performance liquid chromatography. Under the optimal conditions (sample pH of 4.0, sorbent dosage of 20 mg, extraction time of 3 h, and methanol‐5% acetic acid solution as eluent), a good linear relationship was obtained between the peak area and concentration of sulfadimethoxine in the range of 5.0 to 1500.0 µg/L with correlation coefficient of 0.9997. The limit of detection (S/N = 3) was 3.3 µg/L. The developed method was successfully applied to the analysis of sulfadimethoxine in milk with recoveries in the range of 75.9‐92.3% and relative standard deviations less than 8.1%. The adsorption mechanism of Fe₃O₄/GO/Apt toward sulfadimethoxine was studied through the adsorption kinetics and adsorption isotherms, and the results show that the adsorption process fits well with the pseudo‐second‐order kinetic model and the adsorbate on Fe₃O₄/GO/Apt is multilayer and heterogeneous.     

Graphene Oxide Nanosheets at the Water–Organic Solvent Interface: Utilization in One‐Pot Adsorption and Reactive Extraction of Dye Molecules

Graphene oxide (GO) is amphiphilic in nature, due to its structure, which consists of hydrophilic oxygen‐containing functional groups and a hydrophobic basal plane of polyaromatic benzene rings. Due to this amphiphilicity, GO can create stable bubbles at water–organic solvent interfaces. In this study, the formation of bubbles at aqueous–organic interfaces in the presence of GO is investigated with different organic solvents. Bubble formation and transfer of GO from water to the organic phase is more prominent in aromatic solvents compared to aliphatic solvents, due to π–π interactions. Maximum transfer of GO from the aqueous to the organic phase is achieved at pH 2, and decreases with rising pH of the aqueous phase. Based on this property, and the ability of GO to adsorb cationic and anionic dye molecules, its application as a carrier for reactive extraction of cationic and anionic dye molecules is explored in toluene, kerosene, and carbon tetrachloride at pH 2 and 25 °C. The kinetics of the adsorption of the dyes onto GO nanosheets that takes place in the aqueous phase is also evaluated with different models, and a pseudo‐second‐order (linear) model is found to be the best fit. The adsorption isotherm data are also analyzed with different isotherm models. The electrostatic interaction and π–π interaction between the dye molecules and GO nanosheets leads to dye extraction of up to 98.2 % using this technique. The dye extraction is maximum in toluene and at low dye concentration.     

A new efficient adsorbent in the preconcentration studies of the Cr(III) and Fe(III) ions

In this study, the imine‐graphene hybrid material (HM) was used as an adsorbent for removal of Fe(III) and Cr(III) metal ions from the drinking waters. The adsorbent material (HM) was prepared at three steps. At the first step, the graphite was oxidized by Hummer's method for preparation of graphene oxide (GO), in the second step, the silanization derivative (GO‐APTES) was obtained from the reaction of the 3‐(trimethoxysilyl) propylamine and GO. In the final step, the hybrid material (HM) was synthesized from the reaction of the 3,5‐diiodosalicylaldehyde and GO‐APTES. The chemical structures of three materials GO, GO‐APTES and HB were characterized by using the FT‐IR, XRD, EDX, SEM, TEM and UV‐vis methods. Thermal properties of the materials GO, GO‐APTES and HB were investigated by TGA/DTA methods in the 25–1000°C temperature range. Adsorption and desorption studies of the hybrid material toward Fe(III) and Cr(III) metal ions were investigated using the Batch method. The effect of pH, contact time, temperature, concentration on the adsorption properties of the hybrid material were investigated by ICP‐OES. The Fe(III) and Cr(III) ions have the maximum adsorption at the pH 7. The adsorption capacity decreases with the increase in pH values because above pH 9 the adsorption decreases due to the precipitation of metal hydroxide.     

Metal‐imprinted microsphere prepared by surface template polymerization and its application to chromatography

A metal ion‐imprinted microsphere was prepared by surface molecular template polymerization. Trimethylolpropane trimethacrylate (TRIM), zinc ions, 1,12‐dodecanediol‐O, O′‐diphenyl phosphonic acid (DDDPA) were used as a crosslinking agent, an imprint molecule, and a functional host molecule. The Zn(II)‐imprinted microspheres, which are spherically well‐defined particles, were prepared by using water‐in‐oil‐in‐water (W/O/W) multiple emulsions. The combination of TRIM and DDDPA serves to align the recognition sites resulting in better template sites produced on the polymer surface. We firstly conducted diagnostic zinc‐ and copper‐ion adsorption tests with the Zn(II)‐imprinted and unimprinted microspheres in order to make an assessment on the effectiveness of the molecular imprinting technique. Further, the metal‐imprinted microspheres were applied to the column operation. The separation and recovery of metals were carried out by an adsorption column packed with the Zn(II)‐imprinted microspheres. This performance was compared to that of commercial chelating resins that possess similar phosphoric functional groups. The Zn(II)‐imprinted polymer shows an extremely high selectivity to the imprinted zinc ions compared to that of the commercial chelating resin. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 689–696, 2000     

活性炭纤维电吸附重金属及磺胺甲恶唑性能研究

使用盐酸对吸附剂活性炭纤维（activated carbon fiber,ACF）进行改性,通过SEM、BET和FTIR对改性前后的ACF形貌及结构进行系统表征发现,改性后ACF较改性前表面杂质减少且沟壑更加明显,比表面积提高22%,微孔体积增加5%,含氧官能团（C-O和C=O）明显增多. 以水中重金属离子（Zn(II)及Cr(VI)）和抗生素磺胺甲恶唑（Sulfamethoxazole,SMX）为目标污染物,研究改性后ACF对目标污染物的吸附（静吸附和电吸附）性能,考察了浓度、pH、外加电压对吸附的影响. 结果表明,ACF用量为5 g,电压为1.2 V,Zn(II)、Cr(VI)及SMX浓度均为10 mg·L^-1,Zn(II)溶液pH为5时,ACF吸附水中Zn(II)的最大吸附量为9.25 mg·g^-1,是静吸附条件的2.15倍;Cr(VI)溶液pH为4时,ACF吸附Cr(VI)的最大吸附量为8.86 mg·g^-1,是静吸附条件的1.96倍;SMX溶液pH为6时,ACF吸附SMX的最大吸附量为8.32 mg·g^-1,是静吸附条件的1.84倍. ACF吸附Zn(II)、Cr(VI)及SMX的动力学曲线均符合准二级动力学模型,吸附过程为化学吸附. Freundlich等温模型能更好地描述ACF对Zn(II)、Cr(VI)及SMX的吸附特性,其吸附形式为多分子层吸附. ACF通过电极反接方式进行循环再生,脱附速率快且脱附效果明显,经4次循环再生后,ACF对Zn(II)、Cr(VI)及SMX的去除率均在90%以上.     

Lignite fired fly ash modified by chemical treatment for adsorption of zinc from aqueous solution

The purpose of the study described in this paper was to compare removal of Zn(II) from aqueous solutions by use of two adsorbents—alkali-modified fly ash (FAN) and alkali and dye-modified fly ash (FAN-MO). The effects of four conditions (solution pH, contact time, initial metal ion concentration, and dose of adsorbent) on removal of Zn(II) at 27 ± 5 °C were studied in batch mode. Adsorption of Zn(II) was greater at pH 4.0 for FAN (76.49 %) and at pH 5.0 for FAN-MO (24.72 %). Maximum adsorption of Zn(II) by FAN and FAN-MO was achieved after 50 min. The linear forms of the Langmuir, Freundlich, Tempkin, D–R, Harkin–Jura, and Frenkel–Halsey isotherms were used for experiments with different concentrations of the metals. Adsorption of Zn(II) ions satisfied the Langmuir isotherm model only. The adsorption capacity of both adsorbents was also investigated by column studies. Adsorption of Zn(II) ions on FAN in column studies (45.33 %) was lower than in batch mode studies. For FAN-MO, adsorption was 37.88 % in column studies, again lower than in batch mode studies. Fly ash modified by alkali had a higher adsorption capacity for Zn(II) ions than fly ash modified by alkali followed by addition of dye.     

Adsorption of metal ions onto Moroccan stevensite: kinetic and isotherm studies

The aim of this paper is to study the adsorption of the heavy metals (Cd(II), Cu(II), Mn(II), Pb(II), and Zn(II)) from aqueous solutions by a natural Moroccan stevensite called locally rhassoul. We carried out, first, a mineralogical and physicochemical characterization of stevensite. The surface area is 134 m2/g and the cation exchange capacity (CEC) is 76.5 meq/100 g. The chemical formula of stevensite is Si3.78Al0.22Mg2.92Fe0.09Na0.08K0.08O10(OH)2.4H2O. Adsorption tests of Cd(II), Cu(II), Mn(II), Pb(II), and Zn(II) in batch reactors were carried out at ambient temperature and at constant pH. Two simplified models including pseudo-first-order and pseudo-second- order were used to test the adsorption kinetics. The equilibrium time and adsorption rate of adsorption were determined. The increasing order of the adsorption rates follows the sequence Mn(II) > Pb(II) > Zn(II) > Cu(II) > Cd(II). The Dubinin-Radushkevich (D-R), Langmuir, and Redlich-Peterson (R-P) models were adopted to describe the adsorption isotherms. The maximal adsorption capacities at pH 4.0 determined from the D-R and Langmuir models vary in the following order: Cu(II) > Mn(II) > Cd(II) > Zn(II) > Pb(II). The equilibrium data fitted well with the three-parameter Redlich-Peterson model. The values of mean energy of adsorption show mainly an ion-exchange mechanism. Also, the influence of solution pH on the adsorption onto stevensite was studied in the pH range 1.5-7.0.     

Removal performance and mechanism of Fe3O4/graphene oxide as an efficient and recyclable adsorbent toward aqueous Hg(II)

Decontamination of aqueous heavy metal is a challenging task of environmental remediation. Herein, we demonstrated an adsorptive method for efficient removal of aqueous Hg(II) using a magnetic nanocomposite Fe₃O₄/graphene oxide (Fe₃O₄/GO). Adsorption of Hg(II) onto Fe₃O₄/GO equilibrated in 4 min, with the adsorption percent and quantity of 91.17% and 547.01 mg g^?1, respectively. Fe₃O₄/GO can be easily recovered from solution via magnetic separation for reuse, and retaining 73.5% of its original capacity after five consecutive cycles. The Temkin model and PSO model were most suitable for describing adsorption in equilibrium and non-equilibrium state, respectively. Both GO and Fe₃O₄ adsorbed Hg(II) via donating electrons in oxygen atoms toward Hg(II). Moreover, GO made a major contribution, while Fe₃O₄ made a minor one to adsorption. The facile preparation, high adsorption efficiency, easy recovery, and reusability may enable Fe₃O₄/GO to be a promising adsorbent for aqueous Hg(II).

     

Characterization of radioactive cobalt on graphene oxide by macroscopic and spectroscopic techniques

Graphene oxide (GO) was synthesized using the modified Hummers method and characterized by XRD and FTIR. The sorption of ⁶⁰Co(II) on GO as a function of contact time, pH, polyacrylic acid, ionic strength, temperature and solution concentration was studied by batch technique. The sorption kinetics indicated that the sorption of ⁶⁰Co(II) on GO could be simulated by the pseudo-second-order model very well. The maximum sorption capacities of GO for ⁶⁰Co(II) calculated from Langmuir model at pH 6.40 and T = 300 K was ~62.0 mg/g. The thermodynamic parameters from the temperature-dependent sorption isotherms indicated that the ⁶⁰Co(II) sorption on GO was an endothermic and spontaneous process. The interaction mechanism between GO and Co(II) were outer-sphere surface complexation or ion exchange at pH <7, whereas the inner-sphere surface complexation was observed at pH 7–9 in terms of the analysis of XPS spectra.     

Graphene oxide‐SiO2 hybrid nanostructure as coating material for capillary electrochromatography

Graphene oxide (GO) has been considered as a promising stationary phase for chromatographic separation. However, the very strong adsorption of the analytes on the GO surface lead to the severe peak tailing, which in turn resulting in decreased separation performance. In this work, GO and silica nanoparticles hybrid nanostructures (GO/SiO₂ NPs@column) were coated onto the capillary inner wall by passing the mixture of GO and silica sol through the capillary column. The successful of coating of GO/SiO₂ NPs onto the capillary wall was confirmed by SEM and electroosmotic flow mobilities test. By partially covering the GO surface with silica nanoparticles, the peak tailing was decreased greatly while the unique high shape selectivity arises from the surface of remained GO was kept. Consequently, compared with the column modified with GO (GO@column), the column modified with GO and silica nanoparticles through layer‐by‐layer method (GO‐SiO₂ NPs@column), or the column modified with silica nanoparticles (SiO₂ NPs@column), GO/SiO₂ NPs@column possessed highest resolutions. The GO/SiO₂ NPs@column was applied to separate egg white and both acidic and basic proteins as well as three glycoisoforms of ovalbumin were separated in a single run within 36 min. The intra‐day, inter‐day, and column‐to‐column reproducibilities were evaluated by calculating the RSDs of the retention of naphthalene and biphenyl in open‐tubular capillary electrochromatography. The RSD values were found to be less than 7.1%.     

Removal of cadmium(II) and zinc(II) metal ions from binary aqueous solution by rice husk ash

The present study reports the competitive adsorptive removal of cadmium (Cd(II)) and zinc (Zn(II)) ions from binary systems using rice husk ash (RHA), a waste obtained from the rice husk-fired furnaces, as an adsorbent. The initial pH (pH₀) affects significantly the capacity of RHA for adsorbing the metallic ions in the aqueous solution. The pH₀ ≈ 6.0 is found to be the optimum for the removal of Cd(II) and Zn(II) ions by RHA. The single ion equilibrium adsorption from the binary solution is better represented by the non-competitive Redlich–Peterson (R–P) and the Freundlich models than by Langmuir model in the initial metal concentration range of 10–100 mg/l. The adsorption of Zn(II) ion is more than that of Cd(II) ion, and this trend is in agreement with the single-component adsorption data. The equilibrium metal removal decreases with increasing concentrations of the other metal ion and the combined effect of Cd(II) and Zn(II) ions on RHA is generally found to be antagonistic. Non-modified Langmuir, modified Langmuir, extended-Langmuir, extended-Freundlich, Sheindorf–Rebuhn–Sheintuch (SRS), non-modified R–P and modified R–P adsorption models were tested to find the most appropriate competitive adsorption isotherm for the binary adsorption of Cd(II) and Zn(II) ions onto RHA by minimizing the Marquardt's percent standard deviation (MPSD) error function. The extended-Freundlich model satisfactorily represents the adsorption equilibrium data of Cd(II) and Zn(II) ions onto RHA.     

Enhanced adsorption performance of the graphene oxide with metallic ion impurities by elution

The graphene oxides (GOs) with various content of metallic ions impurities were prepared, and the adsorption performance of the GO before and after elution was evaluated. The prepared GOs were characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, inductively coupled plasma and atomic force microscopy. The results indicated that the metallic ion impurities hardly affected the interlayer distance, microstructure and thickness of the prepared GOs. The adsorption isotherm and adsorption kinetic results showed that the metallic ions adsorbed on the GO surface had a negative influence on both the adsorption capacity and rate. After eluted by HNO₃ or HCl, most of the metallic ions adsorbed on the GO‐91 surface were ion‐exchanged by the protons of the acid eluents, and the purified GO showed enhanced equilibrium capacities and improved adsorption rate. The elution efficiency of HCl was better than that of HNO₃, and the adsorption capacity and rate of the GO eluted by HCl approximately reached to those of the GO prepared from the graphite with high purity. It indicated that HCl could efficiently remove the metallic ions adsorbed on the GO surface. Copyright © 2017 John Wiley & Sons, Ltd.