Functionalized graphene oxide/carboxymethyl chitosan composite aerogels with strong compressive strength for water purification

A new type of polydopamine functionalized graphene oxide/carboxymethyl chitosan (DGO/CMC) composite aerogels was synthesized via sol–gel once-forming self-assembly and lyophilization. Polydopamine (PDA) on the surface of GO nanosheets replaced those traditional crosslinking agents to connect CMC chains via hydrogen bonding for the establishment of 3D porous aerogels. With the increasing proportion of CMC, the microstructure of aerogels changed from small pores to large plate-bridge-like pores. In addition, their maximum compressive strengths were 6.767, 11.94, and 16.98 MPa under 90% compressions, respectively, which increased in accordance with CMC content. Furthermore, the adsorption system of the aerogels was simulated well by the pseudo second-order kinetic model and the Langmuir isotherm model, with maximum mass adsorption capacities of 170.3, 186.8, and 312.8 mg/g for Cu²⁺, Ni²⁺, and Pb²⁺ ions, respectively. These composite materials have potential applications for water purification because of their simple and efficient synthesis and excellent recyclability and reusability.     

Preparation of graphene oxide/carboxymethyl chitosan/polyvinyl alcohol composite nanofiber membranes by electrospinning for heavy metal adsorption

In this paper, a graphene-oxide/carboxymethyl-chitosan/polyvinyl-alcohol (GO/CMC/PVA) composite nanofiber membrane was prepared by electrospinning and cross-linking with glutaraldehyde (GA) to improve the water resistance. The composite nanofiber membrane can be used in the field of heavy metal adsorption. The membrane was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The effects of GO concentration, adsorption time, and initial concentration of heavy-metal ion (Ni²⁺, Cu²⁺, Ag⁺, and Pb²⁺) solution on the adsorption performance of the fiber membranes were investigated. The results showed that the addition of GO can reduce the diameter of nanofibers. GO, CMC, and PVA exhibited good compatibility, and the intermolecular hydrogen bonding improved. The addition of GO also improved the crystalline properties of the composite fiber membrane. In the optimal cross-linking condition, GA was saturated by steam cross-linking for 6 h. The introduction of GO improved the adsorption capacity of the membrane for heavy metals in water. The utmost adsorption capacities for Ni²⁺, Cu²⁺, Ag⁺, and Pb²⁺ were 262.1, 237.9, 319.3, and 413.6 mg/g when using the cross-linked composite fiber membranes, respectively. The results of adsorption kinetics and thermodynamics showed that the adsorption process accorded with the pseudo-second-order kinetic model and Langmuir–Freundlich isotherm model.     

Competitive adsorption of Pb, Cu and Cd ions from aqueous solutions by multiwalled carbon nanotubes

The individual and competitive adsorption capacities of Pb²⁺, Cu²⁺ and Cd²⁺ by nitric acid treated multiwalled carbon nanotubes (CNTs) were studied. The maximum sorption capacities calculated by applying the Langmuir equation to single ion adsorption isotherms were 97.08 mg/g for Pb²⁺, 24.49 mg/g for Cu²⁺ and 10.86 mg/g for Cd²⁺ at an equilibrium concentration of 10 mg/l. The competitive adsorption studies showed that the affinity order of three metal ions adsorbed by CNTs is Pb²⁺>Cu²⁺>Cd²⁺. The Langmuir adsorption model can represent experimental data of Pb²⁺ and Cu²⁺ well, but does not provide a good fit for Cd²⁺ adsorption data. The effects of solution pH, ionic strength and CNT dosage on the competitive adsorption of Pb²⁺, Cu²⁺ and Cd²⁺ ions were investigated. The comparison of CNTs with other adsorbents suggests that CNTs have great potential applications in environmental protection regardless of their higher cost at present.     

Preparation and adsorption mechanism of polyvinyl alcohol/graphene oxide-sodium alginate nanocomposite hydrogel with high Pb(II) adsorption capacity

A series of polyvinyl alcohol (PVA)/graphene oxide (GO)-sodium alginate (SA) nanocomposite hydrogel beads were prepared through in situ crosslinking for Pb²⁺ removal. It was found that PVA and SA molecules were intercalated into GO layers through hydrogen bonding interactions, leading to the destruction of orderly structure of GO, while GO uniformly distributed in PVA matrix. With increasing PVA solution concentration, the hydrogel beads became more regular, a large number of polygonal pores with thin walls and open pores formed, the average pore size decreased, and the dense network structure formed. Meanwhile, the permeability of the composite hydrogel decreased, leading to the decline of Pb²⁺ adsorption capacity of the composite hydrogel. With increasing GO content, the ballability of the hydrogel beads was weakened, the pore size increased, and relatively loose network structure formed, resulting in an increase in permeability and Pb²⁺ adsorption capacity of the hydrogel, reaching up to 279.43 mg g⁻¹. Moreover, the composite hydrogel presented relatively good reusability for Pb²⁺ removal. The adsorption mechanism was explored and showed that the adsorption system of the composite hydrogel belonged to the second-order kinetic model and fitted Langmuir adsorption isotherm model for Pb²⁺ removal, which might be mono-layer chemical adsorption. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47318.     

Simultaneous adsorptive removal of methylene blue and copper ions from aqueous solution by ferrocene‐modified cation exchange resin

Resin was modified with ferrocene (Fc) to enhance removal of Methylene Blue (MB) and Cu²⁺ from simulated wastewater. The FTIR, N₂‐BET, and X‐ray fluorescence analysis confirmed that Fc was successfully grafted onto the surface of resin. The adsorption capacity of Fc modified cation exchange resin (FMCER) was calculated to be 392.16 mg/g Cu²⁺ and 10.01 mg/g MB. Both processes were spontaneous and exothermic, best described by Langmuir equation. Pseudo‐first‐order kinetic model satisfied the adsorption of MB, while the intraparticle‐diffusion model fitted the kinetics of Cu²⁺ adsorption best. The result revealed a multilayer adsorption of Cu²⁺ on FMCER, and the kinetics maybe controlled by intraparticle diffusion, film diffusion, and competition force. The adsorption of MB and Cu²⁺ on FMCER were physicosorptive, with activation energies of 2.09 and 1.27 kJ/mol. pH 2–7 and 4–5 are optimum for the removal of MB and Cu²⁺, and pH 4 is optimal for the simultaneous removal of MB and Cu²⁺. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41029.     

In situ crosslinking of poly(vinyl alcohol)/graphene oxide Nano-composite hydrogel: intercalation structure and adsorption mechanism for advanced Pb(II) removal

Based on the industrialized graphene oxide (GO) product, poly(vinyl alcohol) (PVA)/GO nano-composite hydrogels were prepared through in situ crosslinking by incorporation of N-[(trimethoxysilyl)propyl] ethylenediamine-triacetic acid sodium (CSA) as a compatibilizer. Introduction of CSA led to more efficient grafting of PVA molecules onto GO surface with increasing average layer thickness through covalent and hydrogen bonding interaction, while GO was exfoliated and uniformly distributed in PVA matrix. Addition of appropriate content of GO can improve the storage modulus and the effective crosslinking density (υ_e) of the composite hydrogel, and the network structure with GO as crosslinking point formed, resulting in the remarkable increase of the hydraulic impact resistance, mechanical strength and toughness of the hydrogel. Pb²⁺ adsorption capacity of the hydrogel increased with GO content, while the adsorption belonged to the second-order kinetic model and fitted Langmuir adsorption isotherm model, indicating the homogeneous nature of monolayer chemical adsorption of Pb²⁺. A relatively good reusability of the composite hydrogel beads for Pb²⁺ removal can be achieved.     

Preparation of amidoximated bacterial cellulose and its adsorption mechanism for Cu2+ and Pb2+

Amidoximated bacterial cellulose (Am‐BC) was prepared through successive polymer analogous reactions of bacterial cellulose with acrylonitrile in an alkaline medium followed by reaction with aqueous hydroxylamine. It was used as an adsorbent to remove Cu²⁺ and Pb²⁺ from aqueous solutions. The adsorption behaviors of Cu²⁺ and Pb²⁺ onto Am‐BC were observed to be pH‐dependent. The maximum adsorption capacity of 84 and 67 mg g^–1 was observed, respectively, for Cu²⁺ and Pb²⁺ at pH 5. Scanning electronic microscopy (SEM) indicated that the microporous network structure of Am‐BC was maintained even after the modifacation. The adsorption mechanisms for Cu²⁺ and Pb²⁺ onto Am‐BC were investigated by fourier transform infrared spectroscopy (FTIR), ζ potential measurement and X‐ray photoelectron spectroscopy (XPS). The results revealed that the mechanism for the adsorption of Cu²⁺ onto Am‐BC could be mainly described as between metal ions and nitrogen atom in the amidoxime groups or oxygen atom in the hydroxyl groups. However, in the adsorption process for Pb²⁺, precipitation played the important role along with electrostatic interactions, although chelation action also existed in the process accounted for the adsorption process. The regeneration of Am‐BC was studied by treatment with a strong complexing agent, ethylenediaminetetracetic acid (EDTA). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Simultaneous adsorption of phenol and Cu2+ from aqueous solution by activated carbon/chitosan composite

A multifunction adsorbent was synthesized by incorporating AC into CTS, and the ratio of AC to CTS was 1/1. The resultant was called activated carbon (AC)/chitosan (CTS) composite. The simultaneous adsorption of phenol and Cu²⁺ from aqueous solution onto AC/CTS composite was investigated by a batch procedure. The adsorption processes for both Cu²⁺ and phenol obeyed the pseudo second-order kinetic model. Phenol was prone to be adsorbed more quickly as compared with Cu²⁺ when they coexisted in solution. The adsorption behavior of both phenol and Cu²⁺ followed the Langmuir isotherm. The maximum adsorption capacities of phenol and Cu²⁺ were 34.19 mg/g and 74.35 mg/g at 293 K, respectively. No obvious competitive adsorption existed between phenol and Cu²⁺.     

Hydrothermal-Freeze-Casting of Poly(amidoamine)-Modified Graphene Aerogels towards CO2 Adsorption

This article presents novel poly(amidoamine) (PAMAM) dendrimer-modified with partially-reduced graphene oxide (rGO) aerogels, obtained using the combined solvothermal synthesis-freeze-casting approach. The properties of modified aerogels are investigated with varying synthesis conditions, such as dendrimer generation (G), GO:PAMAM wt. ratio, solvothermal temperature, and freeze-casting rate. Scanning electron microscopy, Fourier Transform Infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy are employed to characterize the aerogels. The results indicate a strong correlation of the synthesis conditions with N content, N/C ratio, and nitrogen contributions in the modified aerogels. Our results show that the best CO₂ adsorption performance was exhibited by the aerogels modified with higher generation (G7) dendrimer at low GO:PAMAM ratio as 2:0.1 mg mL⁻¹ and obtained at higher solvothermal temperature and freeze-casting in liquid nitrogen. The enclosed results are indicative of a viable approach to modify graphene aerogels towards improving the CO₂ capture.     

Novel design of microsphere adsorbent for efficient heavy metals adsorption

The fabrication of high-efficiency and low-cost adsorbent for the wastewater treatment is a challenging task. In this study, a hollow sphere adsorbent was synthesized from solid waste coal gangue through a facile spray drying method and subsequent calcination. The structure of the synthesized coal gangue microsphere (CM) have been characterized by multimethods including X-ray diffraction, scanning electron microscope, Fourier transform infrared, and others. The factors influencing the adsorption for Cu²⁺ and Pb²⁺ by CM were also investigated systemically; pH between 6 and 8 was found to be optimal for Cu²⁺ and Pb²⁺ adsorption. The isotherm and kinetic analysis reveal that the adsorption process could be well represented by Langmuir and pseudo–second-order model with a higher R² and low χ² value. According to Langmuir model, the maximum adsorption capacity was calculated to be 6.570 and 18.904 mg/g for Cu²⁺ and Pb²⁺ at 25°C, respectively. The adsorption mechanism was proposed to contain not only the surface reaction process, but also the diffusion process. Consequently, the economic and environmental benefits make CM a promising adsorbent in wastewater treatment.     

Poly (vinyl alcohol)/graphene oxide nanocomposite films and hydrogels prepared by gamma ray

ABSTRACT

Poly (vinyl alcohol)/graphene oxide (PVA/GO) gamma irradiated nanocomposite films and hydrogels were prepared. In composite films, GO was initially irradiated by gamma ray in order to improve interactions between GO and PVA. The film containing 1?wt-% GO was very strong where tensile modulus and tensile yield strength were 45 and 115% higher than those of pure PVA. In the second set of experiments PVA/GO hydrogels were made by irradiating PVA/GO suspensions by gamma ray at various doses. It was an interesting finding that GO increased the gel portion of hydrogels through contribution of H-bonds between PVA and GO. The hydrogels prepared at 20?kGy had remarkable water swelling ratio that reached as high as 20 at water temperature of 80°C. The hydrogel metal ion adsorption capability was tested on Cu²⁺ ions. It was shown that the GO contributed significantly to the adsorption capacity of PVA hydrogels.     

Synthesis of polystyrene‐supported glucosamine resin and its adsorption properties for metal ions

A novel chelating resin polystyrene‐supported glucosamine was prepared by the reaction of chloromethylated polystyrene with glucosamine hydrochlorate, using anhydrous potassium carbonate as catalyst and dimethylformamide as solvent. Infrared spectra and elementary analysis were used to confirm its structure. The adsorption of the resin for Cu²⁺, Ni²⁺, Hg²⁺, Co²⁺, Cd²⁺, and Pb²⁺ was investigated, as well as various factors affecting the adsorption such as time, temperature, ion concentration, and pH. The results showed that the resin had good adsorption capacities for Cu²⁺, Ni²⁺, and Hg²⁺. The adsorption was controlled by liquid film diffusion and adsorption isothermal data could be well interpreted by the Freundlich equation. Values of adsorption activation energy and adsorption Gibbs free energy were calculated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 890–896, 2005     

KLPAAM复合高吸水树脂吸附

采用自制高岭土/木质素磺酸钠接枝丙烯酸-丙烯酰胺复合高吸水树脂(KLPAAM),测定了其在CuCl²、ZnCl²溶液中的吸附性能;通过FTIR、TG、SEM及吸附动力学方程模拟,对其吸附机理进行了探讨。KLPAAM对Cu²⁺的吸附量随Cu²⁺相似文献   

Adsorption for metal ions of chitosan coated cotton fiber

A kind of adsorbent for metal ions, cotton fiber coated by high loading of chitosan (SCCH) was prepared. Its structure was characterized by elemental analysis, scanning electronic microscopy (SEM), Fourier transform infrared spectrum (FTIR), and wide‐angle X‐ray diffraction (WAXD). The adsorption properties of SCCH for Cu²⁺, Ni²⁺, Pb²⁺, Cd²⁺, such as saturated adsorption capacities, static kinetics, and isotherm were investigated. The adsorption for Ni²⁺, Pb²⁺, and Cd²⁺ was controlled by liquid film diffusion, but by particle diffusion for Cu²⁺. The adsorption process for Cu²⁺, Ni²⁺, Cd²⁺ could be described with Langmuir or Freundlich equation, but only with Freundlich equation for Pb²⁺. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Adsorption kinetics and equilibrium of copper from ethanol fuel on silica-gel functionalized with amino-terminated dendrimer-like polyamidoamine polymers

The adsorption kinetics and equilibrium of silica-gel functionalized with amino-terminated dendrimer-like polyamidoamine (PAMAM) polymers SiO₂-G1.0, SiO₂-G2.0 and SiO₂-G3.0 for Cu²⁺ in ethanol fuel were investigated by using batch method. The results indicated that the all the adsorptions of the three adsorbents followed well the pseudo second-order model. The adsorption isotherms were fitted by Langmuir model, Freundlich model and Dubinin–Radushkevich (D–R) model. The results showed that Langmuir model was more suitable to describe the equilibrium data than the Freundlich model. From the D–R isotherm model, the mean free energy E calculated of the three adsorbents showed that the adsorptions were taken place by physical processes. Thermodynamic parameters, ΔG⁰, ΔH⁰ and ΔS⁰ indicated the Cu²⁺ adsorption to be endothermic and spontaneous with decreased randomness at the solid-solution interface, resulting in their higher adsorption capacities at higher temperature. The effect of generation number of PAMAM polymers loaded on silica-gel, contact time, initial concentration and temperatures on the adsorption capabilities were studied in detail. Moreover, the adsorption mechanism of copper from ethanol fuel was also presumed.     

Cu<Superscript>2+</Superscript> adsorption onto ion-imprinted composite hydrogels: thermodynamics and mechanism studies

In the current study, in situ free radical polymerization was employed to prepare Cu²⁺-imprinted composite hydrogel (Cu²⁺-ICH). The cross-sectional morphology of the Cu²⁺-ICH evaluated by scanning electron microscopy indicated that the copper-loaded Cu²⁺-ICH became rougher and the pore size of the gel became smaller compared to the unloaded Cu²⁺-ICH. The ability of the Cu²⁺-ICH to adsorb Cu²⁺ from aqueous solutions was assessed using batch adsorption technique. The adsorption capacity increased with the initial concentration of Cu²⁺, but decreased as the temperature rose from 298 to 318 K. Thermodynamic parameters such as Gibbs free energy (ΔG ⁰), enthalpy (ΔH ⁰), and entropy (ΔS ⁰) for the Cu²⁺ adsorption were evaluated. It was suggested that the adsorption process was a spontaneous, exothermic process that had positive entropy. Selectivity study indicated that ion imprinting technique resulted in excellent affinity of the Cu²⁺-ICH toward Cu²⁺. Finally, the adsorption mechanism was studied by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results indicated that copper adsorption was mainly through interactions with the amine and carbonyl groups.     

Synthesis of novel copper ion-selective material based on hierarchically imprinted cross-linked poly(acrylamide-co-ethylene glycol dimethacrylate)

A novel hierarchically imprinted cross-linked poly(acrylamide-co-ethylene glycol dimethacrylate) using a double-imprinting approach for the Cu²⁺ selective separation from aqueous medium was prepared. In the imprinting process, both Cu²⁺ ions and surfactant micelles (cetyltrimethylammonium bromide – CTAB) were employed as templates. The hierarchically imprinted organic polymer named (IIP-CTAB), single-imprinted (IIP-no CTAB) and non-imprinted (NIP-CTAB and NIP-no CTAB) polymers were characterized by SEM, FTIR, TG, elemental analysis and textural data from BET (Brunauer–Emmett–Teller) and BJH (Barrett–Joyner–Halenda). Compared to these materials, IIP-CTAB showed higher selectivity, specific surface area and adsorption capacity toward Cu²⁺ ions. Good selectivity for Cu²⁺ was obtained for the Cu²⁺/Cd²⁺, Cu²⁺/Zn²⁺ and Cu²⁺/Co²⁺ systems when IIP-CTAB was compared to the single-imprinted (IIP-no CTAB) and non double-imprinted polymer (NIP-CTAB), thereby confirming the improvement in the polymer selectivity due to double-imprinting effect. For adsorption kinetic data, the best fit was provided with the pseudo-second-order model for the four materials, thereby indicating the chemical nature of the Cu²⁺ adsorption process. Cu²⁺ adsorption under equilibrium was found to follow dual-site Langmuir–Freundlich model isotherm, thus suggesting the existence of adsorption sites with low and high binding energy on the adsorbent surface. From column experiments 600 adsorption–desorption cycles using 1.8 mol L⁻¹ HNO₃ as eluent confirmed the great recoverability of adsorbent. The synthesis approach here investigated has been found to be very attractive for the designing of organic ion imprinted polymer and can be expanded to the other polymers to improve performance of ion imprinted polymers in the field of solid phase extraction.     

L-cystein modified bentonite-cellulose nanocomposite (cellu/cys-bent) for adsorption of Cu2+, Pb2+, and Cd2+ ions from aqueous solution

In this study, L-cystein modified bentonite-cellulose (cellu/cys-bent) nanocomposite was synthesized and characterized by XRD, FTIR, SEM with EDS, TGA, and TEM techniques. In order to optimize the process the effect of various operational parameters such as pH, adsorbent dosage, contact time, and temperature were also investigated. The adsorption experiments were carried out in initial concentrations range of 20-100 mg L^?1and the adsorbent affinity for metal ions was found to be in order of Cu²⁺ > Pb²⁺ > Cd²⁺. The optimum pH for adsorption of Cu²⁺ and Cd²⁺ was observed at 5 while for Pb²⁺ it was pH 6. Based on the Langmuir model, the maximum adsorption capacity of Cu²⁺, Pb²⁺, and Cd²⁺ at 50^?C was found to be 32.36, 18.52, and 16.12 mg g^?1, respectively. The Langmuir isotherm and pseudo-second order model were found to be better fitted than the other isotherms and kinetic models. The results of thermodynamic parameters confirmed the process to be endothermic and spontaneous in nature.     

Adsorption of Cu2+ and Ni2+ from Aqueous Solution by Arabinoxylan Hydrogel: Equilibrium,Kinetic, Competitive Adsorption

In this work, arabinoxylan-graft-acrylic acid (AX-g-AA) hydrogel was prepared and used as an adsorbent to remove and recover Cu²⁺ and Ni²⁺ from aqueous solutions. The influences of pH, ligand content on the adsorption capacity of the hydrogel, adsorption equilibrium, and kinetic were studied in detail. The competitive adsorption and recovery of heavy metal ions, regeneration and reusability of the hydrogel were present. Furthermore, the relationship between the physiochemical properties of the adsorbent and its adsorption performance was also studied. The results showed that a more expanded network favored the diffusion and adsorption of metal ions. Cu²⁺ and Ni²⁺ uptake by this hydrogel was pH and concentration dependent with the maximum loading of 330.1 mg/g for Cu²⁺ and 248.7 mg/g for Ni²⁺. The pseudo-second-order kinetics suggested that the ion exchange process was chemisorption-controlled. The Langmuir equation could well describe the isotherm data. Cu²⁺ and Ni²⁺ adsorbed on the hydrogel could be effectively recovered in a diluted HNO₃ solution (0.01 M) in 30 min. AX-g-AA hydrogel also exhibited highly efficient reusability, and thus could be used repeatedly.     

测试——聚乙烯亚胺改性磁性膨润土对Pb2+和Cu2+的吸附性能(测试稿件)

在磁性膨润土(MBent)表面接枝聚乙烯亚胺(PEI)制备了聚乙烯亚胺改性磁性膨润土(PEI/KH560/MBent),采用FTIR、VSM、XRD、TGA、EA、SEM和EDS对其进行了表征,考察了其对水溶液中Pb_²⁺和Cu_²⁺的吸附性能。结果表明,聚乙烯亚胺已成功接枝于磁性膨润土表面,并有效提高其对Pb_²⁺和Cu_²⁺吸附量；溶液初始pH对吸附量影响较大,随着pH的增大,吸附量增加。在pH=5,溶液初始质量浓度为300 mg/L,PEI/KH560/MBent对Pb_²⁺和Cu_²⁺吸附量分别为96.21和61.08 mg/g；吸附过程符合准二级动力学模型,吸附行为符合Langmuir吸附等温模型。热力学研究表明,吸附为自发吸热过程。经过5次循环利用后,其吸附容量仍保持初始的60%以上,表明PEI/KH560/MBent具有一定的重复利用性。