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.     

Preparation of graphene oxide aerogel and its adsorption for Cu2+ ions

Graphene oxide (GO) aerogels were prepared by a unidirectional freeze-drying method (UFDM), their structure was observed and their adsorption performance for Cu²⁺ in aqueous solution was evaluated. The results show that GO aerogels have unidirectional porous structure and good adsorption ability for Cu²⁺. The adsorption system is depended on the Cu²⁺ concentration and follows a pseudo second-order kinetic model. The adsorption equilibrium is reached soon. The adsorption isotherms are simulated well by the Langmuir model. The adsorption of Cu²⁺ on GO aerogels is strongly dependent on pH, indicating an ion exchange mechanism. The obtained results demonstrated that the GO aerogels can be used as an effective adsorbent for Cu²⁺ removal from water.     

Development of an activated carbon-geopolymer composite for treatment of Pb(II) polluted water and soil

An activated carbon-geopolymer composite (ACGC) was prepared by using fly ash as raw materials via a simple geopolymerization process for treating the Pb(II) contaminant in wastewater and soil. The phase composition, microtopography, pore structure, and surface groups of the composites were studied by X-ray diffractometer, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, N₂ adsorption-desorption isotherm, and Fourier transform infrared spectroscope. It was discovered that there was a synergistic effect between geopolymer matrix and activated carbon (AC), that is, addition of AC particles could increase the pores in geopolymer while strong alkalis condition provided by geopolymer enhanced the contents of oxygenic groups of AC. When the composite was used as the adsorbent, the sample containing 20 wt% AC (40ACGC) showed the maximum adsorption capacity (319.72 mg/g), and its adsorption isotherm fitted the Langmuir model well, suggesting the monolayer adsorption of Pb²⁺ on the 40ACGC. The kinetics of Pb²⁺ adsorption on the 40ACGC belonged to the pseudo-second-order model, indicating that Pb²⁺ adsorption on the composite followed chemical adsorption. In addition, the 40ACGC sample showed excellent stabilization performance for Pb²⁺ in soil. This work offered a new thinking to the application of geopolymers into remediation of heavy metal-polluted soil.     

Pectin graft copolymer-montmorillonite composite: Synthesis,swelling and divalent metal ion adsorption

A novel graft copolymer gel made up of pectin (Pec), 2-(methacryloyloxyethyl)trimethylammonium chloride (METAC), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) and its composite with montmorillonite (MMT) were prepared using methylenebisacrylamide (MBA) as cross-linker via microwave irradiation and characterized using Fourier transform infrared (FTIR), Thermogravimetric Analysis (TGA) and Scanning electron microscopy (SEM) techniques. Swelling studies were carried out under different pH conditions. The graft copolymer gel and its composite showed maximum swelling in neural medium (pH 7.1) and the swelling process followed second order kinetics. The mechanism of water transport is found to be a Less Fickian diffusion process. The adsorption capacities of the graft copolymer gel and the composite towards divalent metal ions (Cu²⁺, Pb²⁺ and Hg²⁺) were evaluated. The adsorption capacity of the representative samples, Pec-g-poly(METAC-co-AMPS)-A5 and Pec-g-poly(METAC-co-AMPS)/MMT-C2 respectively for Cu²⁺ are 30.71 and 39.18 mg/g; for Pb²⁺ are 58.06 and 79.78 mg/g and for Hg²⁺ are 12.16 and 19.58 mg/g. The re-usability of the materials was also evaluated. The % recovery for the above two systems towards metals ion are 87.91 and 63.46 for Cu²⁺, 32.13 and 58.30 for Pb²⁺ and 78.53 and 51.92 for Hg^2+. respectively. The adsorption isotherm studies indicated the adsorption of Pb²⁺, Cu²⁺ and Hg²⁺ in both samples is explained best by the Freundlich model except of Hg²⁺ by Pec-g-poly(METAC-co-AMPS)-A5, which is best explained by the Langmuir model.     

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⁺.     

Synthesis and characterization of CMC/MMT nanocomposite for Cu<Superscript>2+</Superscript> sequestration in wastewater treatment

Organic–inorganic hybrid nanocomposites are promising materials for remediation of pollutants from wastewater, as they exhibit the unique characteristics of both inorganic and organic materials. In this study, carboxymethyl cellulose/montmorillonite Nanocomposite (CMC/MMT-NC) was prepared and applied for Cu²⁺ sequestration. CMC/MMT-NC was characterized by FTIR and SEM before and after the sequestration process, indicating fundamental changes in surface morphology after treatment experiments. The parameters affecting the process such as pH, contact time, CMC/MMT-NC mass, Cu²⁺ concentration and temperature were experimentally adjusted. Statistical regression variables (R², RMSE, RSS, F-Value and P-Value) were calculated to predict the best-applied isotherm, kinetic and thermodynamic modeling. Freundlich isotherm model successfully described the equilibrium data, which implies a multilayer adsorption process. Kinetic results were well fitted to pseudo-second-order kinetic model. Intraparticle diffusion (IPD) model showed the control of the boundary layer moreover, IPD model cannot be accepted as the only rate-determining step. The apparent activation energy (Ea) was 35.65 kJ/mol, which revealed a physisorption process. The thermodynamic study in means of ΔG⁰, ΔH⁰, and ΔS⁰ demonstrated the feasibility, spontaneity and exothermicity of Cu²⁺ sequestration. Application study confirmed the efficiency of CMC/MMT nanocomposite to remediate Cu²⁺ from synthetic and natural polluted seawater.     

Synthesis and characterization of monolithic carbon/silicon carbide composite aerogels

Resorcinol–formaldehyde/silica composite (RF/SiO₂) aerogels were synthesized using sol–gel process followed by supercritical CO₂ drying. Monolithic carbon/silicon carbide composite (C/SiC) aerogels were formed from RF/SiO₂ aerogels after carbothermal reduction. X-ray diffraction and transmission electron microscopy demonstrate that β-SiC was obtained after carbothermal reduction. Scanning electron microscopy and nitrogen adsorption/desorption reveal that the as-prepared C/SiC aerogels are typical mesoporous materials. The pore structural properties were measured by nitrogen adsorption/desorption analysis. The resulting C/SiC aerogels possess a BET surface area of 564 m²/g, a porosity of 95.1 % and a pore volume of 2.59 cm³/g. The mass fraction of SiC in C/SiC aerogels is 31 %.     

Magnetic mesoporous iron oxide/silica composite aerogels with high adsorption ability for organic pollutant removal

In this paper, a kind of magnetic mesoporous iron oxide/silica composite aerogels with high adsorption ability is prepared by ambient pressure drying method. The results indicate that the obtained magnetic aerogels with Fe/Si (molar ratio) >0.91 % have higher specific surface area with 310.8–411.0 m² g^?1 and pore volume with 0.85–1.12 cm³ g^?1. The adsorption test indicates that the obtained magnetic aerogels showed prominent adsorption capability with the adsorption rate for Rhodamine B in aqueous solution could attain to 95.8 % within 80 min. Moreover, all the composite aerogels exhibited good magnetic properties and could be easily separated from the water after adsorption.     

Ion imprinted beads embedded cryogels for in vitro removal of iron from β-thalassemic human plasma

Molecular recognition based Fe³⁺ imprinted poly(GMA-MAC) (MIP) beads embedded PHEMA composite cryogel was prepared for selective removal of Fe³⁺ ions from β-thalassemia patient plasma. The precomplexation was achieved by the coordination of Fe³⁺ ions with N-methacryloyl-(L )-cysteine methyl ester (MAC-Fe³⁺). MIP beads were prepared by dispersion polymerization in the presence of MAC-Fe³⁺ complex and glycidyl methacrylate (GMA) monomer. Then the MIP beads were embedded into poly(hydroxyethyl methacrylate) (PHEMA) cryogel. The specific surface area and the swelling degree of the PHEMA-MIP composite cryogel were found to be 76.8 m²/g and 7.7 g H₂O/g cryogel, respectively. The maximum adsorption amount of Fe³⁺ ions was 2.23 mg/g. The relative selectivity of PHEMA-MIP composite cryogel towards the Fe³⁺ ions was 135.0, 61.4, and 57.0 times greater than that of the PHEMA-NIP cryogel as compared with the Ni²⁺, Zn²⁺, and Fe²⁺ ions, respectively. PHEMA-MIP composite cryogel was recovered and reused many times without any significant decrease in its adsorption capacity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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.     

Welan Gum-Modified Cellulose Bead as an Effective Adsorbent of Heavy Metal Ions (Pb2+, Cu2+, and Cd2+) in Aqueous Solution

A novel welan gum-modified cellulose adsorbent was prepared through emulsification, regeneration, and modification. SEM and FTIR were used to characterize the modified cellulose adsorbent. The adsorption isotherms of metal ions on the adsorbent were well fitted by Langmuir model, with the maximum adsorption capacities of 83.6, 77.0, and 67.4 mg/g for Cd²⁺, Pb²⁺, and Cu²⁺, respectively. The adsorption kinetics was well described using the pseudo-first-order model. Moreover, the adsorption capacities for the three metal ions increased with the increase of temperature, and the optimal pH was 5. Furthermore, the thermodynamic analysis indicated that the adsorption processes were spontaneous and endothermic.     

Comparative studies on the physical properties of TEOS,TMOS and Na<Subscript>2</Subscript>SiO<Subscript>3</Subscript> based silica aerogels by ambient pressure drying method

In order to compare the various precursors of silica aerogels, three different precursors namely TMOS, TEOS and Na₂SiO₃ were studied in this paper. The property differences of the aerogels caused by the three precursors were discussed in terms of reaction process, gelation time, pore size distributions, thermal conductivity, SEM, hydrophobicity and thermal stability. It has been found that the gelation time of the silica gel is strongly dependent on the type of precursor used. During the surface modification process, organic groups were attached to the wet gel skeletons transforming the hydrophilic to the hydrophobic which were characterized by Fourier Transform Infrared spectroscopy (FTIR). It has been found that the contact angle of the Na₂SiO₃ and TMOS precursor based aerogels with water have the higher contact angle of 149° and whereas Na₂SiO₃ precursor based aerogel has the lower contact angle of 130°. The thermal conductivities of the Na₂SiO₃ and TMOS based aerogels have been found to be lower (0.025 and 0.030 W m^?1 K^?1, respectively) compared to the TEOS based (0.050 W m^?1 K^?1) aerogels. The pore sizes obtained from the N₂ adsorption measurements varied from 40 to 180, 70 to 190, and 90 to 200 nm for the TEOS, TMOS and Na₂SiO₃ precursor based aerogels, respectively. The scanning electron microscopy studies of the aerogels indicated that the Na₂SiO₃ and TMOS based aerogels show narrow and uniform pores while the particles of SiO₂ network are very small. On the other hand, TEOS aerogel show non-uniform pores such that the numbers of smaller size pores are less compared to the pores of larger size while the SiO₂ particles of the network are larger as compared to both Na₂SiO₃ and TMOS aerogels. Hence, the surface are of the aerogels prepared using TEOS precursor has been found to be the lowest (~620 m² g^?1) compared to the Na₂SiO₃ (~868 m² g^?1) and TMOS (~764 m² g^?1) aerogels.     

Adsorption Behaviour of Ethylene Vinyl Acetate and Polycaprolactone-Bentonite Composites for Pb2+ Uptake

The results presented in this work show that the hydrophobic thermoplastics, namely ethylene vinyl acetate (EVA) and polycaprolactone (PCL), could be good matrices for the synthesis of polymer/bentonite composites via the melt-blending method for the removal of heavy metals from water. The hydrophobic nature of the polymers was countered by using dry Na₂SO₄ to form large free-volume pores. These pores, formed after the removal of the Na₂SO₄ by washing, improved the contact ratio between bentonite particles and Pb²⁺ ions. The composites were able to achieve up to 78% Pb²⁺ removal at an initial concentration of 200 mg/L in 10 h with a clay loading of 3% (w/w). The results confirmed that the PCL/bentonite composite was more effective and efficient in the adsorption of Pb²⁺ than the EVA/bentonite composite. The experimental data for both composites followed Langmuir and Freundlich models. The uptake of Pb²⁺ was found to be a result of a chemical interaction between the heavy metal, silanol (Si–OH) and aluminol (Al–OH) groups. The adsorption of Pb²⁺ onto the composites was found to follow pseudo-first-order kinetics and the results supported a monomolecular reaction mechanism.     

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.     

Controllable synthesis of cellulose/methylene bisacrylamide aerogels for enhanced adsorption performance

Cellulose-based aerogels have been regarded as potential adsorbent materials because of their unique structural features and chemical stability. Herein, we prepared the composite aerogels containing cellulose and N,N′-methylene bisacrylamide (MBA) using N-methylmorpholine-N-oxide (NMMO) as a green solvent via a freeze-drying process. Owing to the strong chemical interaction between CC bonds of MBA and the functional groups of cellulose, as-obtained cellulose/MBA aerogels present favorable MBA-induced thermal/mechanical stable three-dimensional network structure, in which the abundant macroporous structure, low density and high porosity lead to a significantly enhanced adsorption capacity (260.31 mg∙g⁻¹) toward congo red dye in aqueous solution compared with the pure cellulose aerogels. Moreover, the effect of the cellulose concentration and cross-linking degree on the morphology and adsorption properties for cellulose/MBA aerogels was systematically investigated. This present work provides a low-cost and environmental-friendly synthesis method for designing the functionalization of cellulose-based aerogel, which may be achieved the advanced performance in wastewater treatment.     

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 heavy metals and methylene blue from aqueous solution with citric acid modified peach stone

Peach stones (PS) modified by citric acid (MPS) were used to remove heavy metals and methylene blue (MB) from wastewater. The effects of experimental factors such as pH, adsorbent dosage and contact time, etc. were conducted. Moreover, the adsorption kinetics and isotherm studies also were investigated. According to the Langmuir isotherm model, the maximum adsorption capacities of Pb²⁺, Cd²⁺, Cu²⁺ and MB were 118.76, 37.48, 32.22 and 178.25 mg/g, respectively. Finally, column experiments were also carried out to investigate the adsorption of Pb²⁺ and MB. All results indicated that PS has a good potential for the treatment of wastewater.     

Effects of drying conditions on physicochemical properties of epoxide sol−gel derived α-Fe2O3 and NiO: A comparison between xerogels and aerogels

A simple and easily operated supercritical CO₂ dryer was designed and manufactured with the aim of producing high-surface-area mesoporous α-Fe₂O₃ (hematite) and NiO aerogels. The gels were synthesized by a sol?gel method with the aid of propylene oxide (PO), as the gelation agent, and then dried and calcined at different conditions. The effects of drying and calcination conditions on the physicochemical properties of the final aerogels were investigated using X-ray diffraction (XRD), N₂ adsorption-desorption, Fourier-transformed infrared spectroscopy (FT-IR), and field emission scanning electron microscopy (FE-SEM) analyses. It was demonstrated that α-Fe₂O₃ and NiO aerogels with high surface areas and mesoporosities could be successfully synthesized using the home-made supercritical CO₂ dryer. Supercritical drying of the gels resulted in α-Fe₂O₃ (186 m²/g) and NiO (178 m²/g) aerogels with 186% and 34% higher surface areas, respectively, than xerogels obtained via simple drying at 80°C using a laboratory oven. In addition, the results showed that supercritical CO₂ drying could enhance preservation of the porous network of the oxide nanostructures at high calcination temperatures via suppression of sintering phenomenon. Calcination of α-Fe₂O₃ and NiO aerogels at 600°C yielded 225% and 53% higher surface areas than the corresponding xerogel, confirming the significance of drying step in the sol?gel method. Asphaltene adsorption from a model oil with asphaltene concentration of 3000 ppm indicated that the aerogels possessed higher adsorption capacities for the bulky asphaltene molecules than xerogels calcined at the same temperature of 600°C, which was due to their enhanced textural properties.     

Waste cotton Fabric/MXene composite aerogel with heat generation and insulation for efficient electromagnetic interference shielding

Electromagnetic interference (EMI) shielding materials have become more and more indispensable due to serious electromagnetic-radiation pollution. Herein, waste cotton cellulose aerogels were prepared by dissolving waste cotton fabrics (WCF) in NaOH/urea aqueous solution, and MXene nanosheets were subsequently deposited on the cellulose aerogels by a facile dip coating method to obtain WCF/MXene composite aerogels. The WCF/MXene composite aerogels with highly porous network structure show remarkable electrical conductivity (8.2 Ω/sq of surface resistance), high EMI shielding effectiveness (EMI SE) in the range of 2–18 GHz (39.3–48.1 dB). The WCF/MXene aerogel possesses high SSE and SSE/t of 677.94–829.74 dB cm³ g^?1 and 3512.62–4299.17 dB cm² g^?1, respectively (2–18 GHz). In addition, the heating temperature of WCF/MXene composite aerogels reaches 199 °C when 3 V positive voltage is applied on them. The WCF/MXene composite aerogels possess excellent electromagnetic shielding effectiveness, heat generation property and insulation, which can be potentially used as multifunctional materials for EMI shielding, electrical-heating and high temperature protection.