Fast Adsorption Equilibrium Research Articles

Scalable fabrication of sulfated silk fibroin nanofibrous membranes for efficient lipase adsorption and recovery

Fabricating adsorptive materials for fast and high efficient adsorption of enzymes is critical to match the great demands for separation and recovery of enzymes used as biocatalysts. However, it has proven extremely challenging. Here, we report a cost-effective strategy to construct the sulfated group surface-functionalized silk fibroin nanofibrous membranes (SS-SFNM) under mild conditions for positively charged Candida rugosa lipase adsorption. The naturally abundant silk is thus reconstructed into nanofibrous membranes with tunable surface functions. Thereby, the resultant SS-SFNM exhibited excellent adsorption performance towards lipase, including a superior adsorption capacity of 148 mg g−1, fast adsorption equilibrium within 3 h and good reversibility. The fabrication of such fascinating silk-based materials may provide new chance into the design and development of multi-functional membranes for various separated applications.

Fe3O4@Polypyrrole Microspheres with High Magnetization and Superparamagnetism for Efficient and Fast Removal of Pb(II) Ions

Core-shell structured Fe3O4@PPy microspheres are synthesized successfully through a facile polyol reduction method in combination with a modified Stober method. We show that the as-prepared Fe3O4@PPy microspheres with high saturation magnetization, superparamagnetism, and good dispersibility have a high efficient adsorption capacity for high efficient removal of Pb(II) ions of up to 391.71 mg g–1 and a fast adsorption equilibrium time of 20 min. Furthermore, the lead-adsorbed Fe3O4@PPy microspheres can be rapidly separated from solution because of the excellent superparamagnetic properties. The composite Fe3O4@PPy microspheres are characterized using X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The adsorption data from our experiments show that the adsorption process fits well with the pseudosecond- order kinetic model and the adsorption isotherm follows the Langmuir isotherm model. The thermodynamic studies show that the adsorption of Pb(II) on Fe3O4@PPy microspheres is an endothermic and spontaneous process. Comprehensive comparison among adsorbents for the removal of Pb(II) ions that literature reported, reusability, high adsorption efficiency, fast adsorption equilibrium, and rapid magnetic separation make these Fe3O4@PPy microspheres very promising application for removal of Pb(II) ions from contaminated water.

Facile and green preparation of novel adsorption materials by combining sol-gel with ion imprinting technology for selective removal of Cu(II) ions from aqueous solution

A novel green adsorption polymer was prepared by ion imprinted technology in conjunction with sol-gel process under mild conditions for the selective removal of Cu(II) ions from aqueous solution. Effects of preparation conditions on adsorption performance of prepared polymers were studied. The ion-imprinted polymer was prepared using Cu(II) ion as template, N-[3-(2-aminoethylamino) propyl] trimethoxysilane (AAPTMS) as functional monomer and tetraethyl orthosilicate (TEOS) as cross-linker. Water was used as solvent in the whole preparation process. The imprinted and non-imprinted polymers were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscope (AFM), Brunauer, Emmett and Teller (BET) and zeta potential. Three-dimensional network structure was formed and functional monomer was successfully cross-linked into the network structure of polymers. Effects of adsorption conditions on adsorption performance of prepared polymers were studied too. The pH value is of great influence on adsorption behavior. Adsorption by ion-imprinted polymer was fast (adsorption equilibrium was reached within 60min). The adsorption capacity of Cu(II) ion-imprinted polymer was always larger than that of non-imprinted polymer. Pseudo-second-order kinetics model and Freundlich isotherm model fitted well with adsorption data. The maximum adsorption capacity of Cu(II) ion-imprinted polymer was 39.82 mg·g−1. However, the preparation conditions used in this work are much milder than those reported in literatures. The Cu(II) ion-imprinted polymer showed high selectivity and relative selectivity coefficients for Pb(II), Ni(II), Cd(II) and Co(II). In addition, the prepared ion-imprinted polymer could be reused several times without significant loss of adsorption capacity.

Preparation and Evaluation of Core⁻Shell Magnetic Molecularly Imprinted Polymers for Solid-Phase Extraction and Determination of Sterigmatocystin in Food.

Magnetic molecularly imprinted polymers (MMIPs), combination of outstanding magnetism with specific selective binding capability for target molecules, have proven to be attractive in separation science and bio-applications. Herein, we proposed the core–shell magnetic molecularly imprinted polymers for food analysis, employing the Fe3O4 particles prepared by co-precipitation protocol as the magnetic core and MMIP film onto the silica layer as the recognition and adsorption of target analytes. The obtained MMIPs materials have been fully characterized by scanning electron microscope (SEM), Fourier transform infrared spectrometer (FT-IR), vibrating sample magnetometer (VSM), and re-binding experiments. Under the optimal conditions, the fabricated Fe3O4@MIPs demonstrated fast adsorption equilibrium, a highly improved imprinting capacity, and excellent specificity to target sterigmatocystin (ST), which have been successfully applied as highly efficient solid-phase extraction materials followed by high-performance liquid chromatography (HPLC) analysis. The MMIP-based solid phase extraction (SPE) method gave linear response in the range of 0.05–5.0 mg·L−1 with a detection limit of 9.1 µg·L−1. Finally, the proposed method was used for the selective isolation and enrichment of ST in food samples with recoveries in the range 80.6–88.7% and the relative standard deviation (RSD) <5.6%.

Fast and efficient removal of copper using sandwich-like graphene oxide composite imprinted materials

A sandwich-like ion-imprinted polymer (IIP) was prepared using functional graphene oxide (GO) as the support, acrylamide as the functional monomer, and ethylene glycol dimethacrylate as the crosslinking agent in the presence of copper ions with various solvents (porogen). The effect of solvent type on polymerization process and properties of polymers was investigated. Methanol/acetonitrile was considered as the best porogen, and almost no redundant secondary polymer particles were produced. This can be explained by the good thermodynamic compatibility and slow phase separation property of monomers and crosslinking agents in polymerization process. Fourier-transform infrared spectroscopy, Energy dispersive X-ray spectroscopy, thermogravimetric analysis, and scanning electron microscopy were used to confirm the prepared IIP. The effects of pH, initial concentration of the Cu(II) aqueous solution, and contact time on adsorption behavior were investigated. Adsorption by prepared IIP was fast (adsorption equilibrium was reached within 15min) and followed pseudo-second-order kinetic and Freundlich isotherm models. The IIP showed a good imprinted factor and the maximum adsorption capacity was up to 132.77mgg−1, which is higher than that of IIP prepared by bulk polymerization, owing to the large surface area of GO and surface imprinted technology. The selectivity factors for Cu/Zn, Cu/Ni, Cu/Co, and Cu/Cd were 36.33, 8.44, 77.3, and 8.5, respectively. The polymer showed a widely application prospect for recovery of Cu ions from aqueous solutions.

Spontaneous and efficient adsorption of lysozyme from aqueous solutions by naturally polyanion gel beads

In this study, polyanionic alginate gel beads crosslinked by Ca2+ and glutaraldehyde have demonstrated a strong electrostatic interaction with specific proteins. Due to the naturally abundant carboxyl groups, the prepared alginate gel beads exhibited a relatively superior integrated adsorption performance toward lysozyme, including a superior adsorption capacity of 213mgg−1, fast adsorption equilibrium within 12h, good selectivity, and good reversibility. Compared with other protein adsorbents, the as-prepared adsorptive beads have the advantages of excellent adsorption performance, easy to prepare, convenient, efficient, reliable and environment-friendly to apply, which can serve as a more sustainable material in protein separation and purification.

Poly(styrene-co-N-methacryloyl-l-phenylalanine methyl ester)-functionalized magnetic nanoparticles as sorbents for the analysis of sodium benzoate in beverages.

In this study, poly(styrene-co-N-methacryloyl-l-phenylalanine methyl ester)-functionalized magnetic nanoparticles were constructed and used as magnetic solid-phase extraction sorbents for analysis of food preservatives in beverages. To prepare the poly(amino acid)-based sorbents, N-methacryloyl-l-phenylalanine methyl ester, and styrene served as the functional monomers and modified onto the magnetic nanoparticles via free radical polymerization. Interestingly, compared with propylparaben and potassium sorbate, the proposed poly(amino acid)-based sorbents showed a good selectivity to sodium benzoate. The adsorption capacity of the sorbents to sodium benzoate was 6.08 ± 0.31 mg/g. Moreover, the fast adsorption equilibrium could be reached within 5 min. Further, the resultant poly(amino acid)-based sorbents were applied in the analysis of sodium benzoate in real beverage samples. The results proved that the proposed magnetic solid-phase extraction sorbents have a great potential for the analysis of preservatives in food samples.

Tartaric acid modified graphene oxide as a novel adsorbent for high-efficiently removal of Cu(II) and Pb(II) from aqueous solutions

A novel adsorbent, tartaric acid modified graphene oxide (GO-TA), was successfully prepared by a simple esterification reaction and applied to remove Cu(II) and Pb(II) metal ions from aqueous solutions. The obtained composites were characterized by Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy and transmission electron microscopy (TEM). Batch experiments were carried out to investigate the effect of pH value, contact time, concentration of metal ions and temperature on Cu(II) and Pb(II) adsorption. The maximum adsorption capacities for Cu(II) and Pb(II) are 374.53mgg−1 and 125.63mgg−1, respectively, which were higher than those of pristine graphene oxide (GO). The obtained experimental data showed a good correlation with the Langmuir adsorption model. The adsorption kinetics of Cu(II) and Pb(II) onto GO-TA composite was found to be well fit for the pseudo-second-order model. Moreover, thermodynamic parameters including ΔGθ< 0, ΔHθ> 0 and ΔSθ> 0, indicating that the adsorption of Cu(II) and Pb(II) onto GO-TA composite was spontaneous and endothermic in nature. All these results indicated that GO-TA composite with such high adsorption efficiency and fast adsorption equilibrium could be used to clean up heavy metal pollution in the future.

Microfiltration/ultrafiltration polyamide-6 membranes for copper removal from aqueous solutions

Microfiltration/ultrafiltration (MF/UF) Adsorptive polyamide-6 (PA-6) membranes were prepared using wet phase inversion process. The prepared PA-6 membranes are characterized by scanning electron microscopy (SEM), porosity and swelling degree. In this study, the membranes performance has examined by adsorptive removal of copper ions from aqueous solutions in a batch adsorption mode. The PA-6/H2O membranes display sponge like and highly porous structures, with porosities of 41-73%. Under the conditions examined, the adsorption experiments have showed that the PA-6/H2O membranes had a good adsorption capacity (up to 120-280 mg/g at the initial copper ion concentration (C0) = 680 mg/L, pH7), fast adsorption rates and short adsorption equilibrium times (less than 1.5-2 hrs) for copper ions. The fast adsorption in this study may be attributed to the high porosities and large pore sizes of the PA-6/H2O membranes, which have facilitated the transport of copper ions to the adsorption. The results obtained from the study illustrated that the copper ions which have adsorbed on the polyamide membranes can be effectively desorbed in an Ethylene dinitrilotetra acetic acid Di sodium salt (Na2 EDTA) solution from initial concentration (up to 92% desorption efficiency) and the PA-6 membranes can be reused almost without loss of the adsorption capacity for copper ions. The results obtained from the study suggested that the PA-6/H2O membranes can be effectively applied for the adsorptive removal of copper ions from aqueous solutions.

Adsorption of antimony(III) from aqueous solution by mercapto-functionalized silica-supported organic–inorganic hybrid sorbent: Mechanism insights

Adsorption of Sb(III) ions onto mercapto-functionalized silica-supported organic–inorganic hybrid sorbent from aqueous solutions was studied by a batch technique. The mercapto-functionalized hybrid sorbent was prepared via sol–gel method and characterized by Fourier transform infrared spectra and scanning electron microscopy coupled to an energy dispersive spectrometer. The effects of parameters (such as pH, contact time, initial concentration and temperature) on the adsorption of Sb(III) onto mercapto-functionalized hybrid sorbent were investigated. Mercapto-functionalized hybrid sorbent had a tendency toward higher adsorption affinity for Sb(III) compared with the Sb(V), a fast adsorption equilibrium time within 20min, and a wide pH range (3–8) for Sb(III) adsorption. The Langmuir, Freundlich and Dubbin–Radushkevich isotherm models were applied to describe the equilibrium data of Sb(III) adsorption. The analysis of adsorption isotherms indicated that Langmuir model described well the equilibrium data of Sb(III) adsorption. The capacity of mercapto-functionalized hybrid sorbent for Sb(III) was found to be 108.8mgg−1. The analysis of the kinetic data by the pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion kinetic models revealed that pseudo-second-order model gave the best fit for Sb(III) adsorption. Thermodynamic parameters demonstrated that adsorption of Sb(III) ions onto mercapto-functionalized hybrid sorbent was an endothermic, spontaneous and thermodynamically feasible process. As the results indicated, mercapto-functionalized hybrid sorbent has a suitable potential for the removal of Sb(III) ions in practical process.

In situ cross-linked and highly carboxylated poly(vinyl alcohol) nanofibrous membranes for efficient adsorption of proteins.

Creating adsorptive materials for the fast, efficient, and high-throughput adsorption and purification of proteins is critical to meet the great demands for highly purified proteins, yet it has proven to be a highly challenging task. Here, we report that cross-linked and highly carboxylated poly(vinyl alcohol) (PVA) nanofibrous membranes were fabricated by a combination of electrospinning and the in situ graft polymerization of PVA and maleic anhydride (MAH) under mild conditions. Taking advantage of the large surface area available for protein binding, the highly tortuous porous structure, and the robust mechanical properties, the resultant PVA/MAH nanofibrous membranes exhibited a good integrated adsorption performance towards lysozyme, including a superior adsorption capacity of 177 mg g-1, fast adsorption equilibrium within 4 h, good selectivity, and good reversibility. Moreover, the saturation dynamic adsorption amount towards lysozyme reached 159 mg g-1 under 750 Pa driven solely by gravity, which conformed to the specified requirements for high adsorption capacity under relatively low pressure drops. Furthermore, the adsorption performance towards a protein mixture was analyzed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and the resultant PVA/MAH nanofibrous membranes retained excellent stability under depyrogenation conditions. The successful fabrication of such fascinating nanofibrous materials by using this simple and intriguing approach may provide new insights into the design and development of adsorptive materials for the purification of proteins with superior adsorption performance.

Introduction and demonstration of a novel Pb(II)-imprinted polymeric membrane with high selectivity and reusability for treatment of lead contaminated water

Lead contaminant in water has become an issue of great concern due to its high toxicity and easy accumulation in human body. In this study, a novel Pb(II)-imprinted polyvinyl alcohol (PVA)/polyacrylic acid (PAA) membrane (Pb-IM) was prepared based on semi-interpenetrating polymer network for selective lead removal. The chemical stability and lead adsorption performance of the Pb-IM were evaluated. The results revealed that the Pb-IM exhibited high adsorption capacity of 1.003mmol/g for lead, fast adsorption equilibrium within 1.5h, and the adsorption process obeyed Langmuir isotherm model and intraparticle pore diffusion model. The Pb-IM retained high adsorption of lead in the presence of competitive factor, i.e. cadmium. In comparison with non-imprinted PVA/PAA membrane, the Pb-IM possessed a much higher selectivity toward lead versus cadmium, with selectivity coefficient of 70.7. Furthermore, the Pb-IM displayed a high reusability for lead uptake and could maintain 96.32% of the adsorption capacity of virgin Pb-IM after six adsorption/desorption cycles. The FTIR and XPS analyses indicated that carboxyl groups in PAA and hydroxyl groups in PVA were mainly associated with the lead adsorption. Finally, the stability study showed that Pb-IM was quite stable and suitable for water treatment. It can be concluded that the Pb-IM can be provided as a powerful material for the selective removal of lead from aqueous solution.

Preparation, characterization, and selective adsorption for lead(II) of imprinted silica-supported organic–inorganic hybrid sorbent functionalized with chelating S,N-donor atoms

The current paper presents a novel Pb(II) ion-imprinted silica-supported organic–inorganic hybrid sorbent functionalized with chelating S,N-donor atoms by coupling a surface imprinting technique with a sol–gel process for the selective adsorption of Pb(II) ions from aqueous solution. Fourier transmission infrared spectroscopy, scanning electron microscopy, and N2 adsorption–desorption isotherms were used to characterize the Pb(II)-imprinted hybrid sorbent. The results revealed that the Pb(II)-imprinted hybrid sorbent had high adsorption capacity (54.9 mg g−1), fast adsorption equilibrium rate within 30 min, wide pH range (3.5–6.5) for constant adsorption capacity, high selectivity, and good regeneration performance.

Synthesis and characterization of core–shell magnetic molecularly imprinted polymers for solid-phase extraction and determination of Rhodamine B in food

Core–shell magnetic molecularly imprinted polymers (MIPs) nanoparticles (NPs), in which a Rhodamine B-imprinted layer was coated on Fe3O4 NPs. were synthesized. First, Fe3O4 NPs were prepared by a coprecipitation method. Then, amino-modified Fe3O4 NPs (Fe3O4@SiO2-NH2) was prepared. Finally, the MIPs were coated on the Fe3O4@SiO2-NH2 surface by the copolymerization with functional monomer, acrylamide, using a cross-linking agent, ethylene glycol dimethacrylate; an initiator, azobisisobutyronitrile and a template molecule, Rhodamine B. The Fe3O4@MIPs were characterized using a scanning electron microscope, Fourier transform infrared spectrometer, vibrating sample magnetometer, and re-binding experiments. The Fe3O4@MIPs showed a fast adsorption equilibrium, a highly improved imprinting capacity, and significant selectivity; they could be used as a solid-phase extraction material and detect illegal addition Rhodamine B in food. A method was developed for the selective isolation and enrichment of Rhodamine B in food samples with recoveries in the range 78.47–101.6% and the relative standard deviation was <2%.

Optimization and application of solid phase extraction of Cu(II) from aqueous solutions using new environmentally friendly modification of silica gel

A new solid phase extractor named silica gel immobilized indapamide (4-chloro-N-(2-methyl-2,3-dihydroindol-1-yl)-3-sulfamoylbenzamide) (SG-INDP) was synthesized by microwave free-solvent technique as a new environmentally friendly modification method. This new phase was investigated for removal of copper ions from aqueous media. It was characterized by the FT-IR, scan electron microscope and X-ray diffraction analyses. The effects of sample pH, time of equilibrium, sorbent weight, copper ions concentrations and interfering ions were studied and optimized using batch technique at room temperature. The maximum percentage of extraction of Cu(II) (99.90±0.1%) using SG-INDP was achieved. The fast adsorption equilibrium could be reached within 20min and the kinetic data were fitted well by a pseudo-second-order equation (r2=0.999). Results of sorption isotherms of the sorbent were better fitted with the Langmuir (r2=0.994) and Freundlich (r2=0.985) models. The new synthesized solid phase extractor was applied for removal of Cu(II) from natural water samples.

Selective Removal of Lead(II) from Aqueous Solution by an Ion-Imprinted Silica Sorbent Functionalized with Chelating N-Donor Atoms

A Pb(II)-imprinted silica sorbent functionalized with chelating N-donor atoms for the selective removal of Pb(II) ion from aqueous solution had been synthesized by hydrothermal assisted surface imprinting technique. This sorbent was characterized by Fourier transmission infrared spectra, scanning electron microscopy and N2 adsorption. The results revealed that the Pb(II)-imprinted silica sorbent had high adsorption capacity (61.9 mg/g for Pb(II)), fast adsorption equilibrium rate within 30 min, wide pH range (3.5 to 6.5) for constant adsorption capacity, high selectivity and good regeneration performance. Compared with Langmuir, Freundlich and Dubinin–Radushkevich isotherm models, the best interpretation for the experimental data was given by the Langmuir isotherm. Its adsorption kinetics was better represented by pseudo-second-order rate equation in comparison to pseudo-first-order, Elovich and intraparticle diffusion models. The thermodynamic results showed that the adsorption of Pb(II) onto the imprint...

Influence of chemically modified short hemp fiber structure on biosorption process of Zn2+ ions from waste water

Short hemp fibers, acquired as a waste from textile industry, were used as an efficient biosorbent for removal of zinc ions from polluted water. In order to obtain the material with better sorption properties, short hemp fibers were subjected to oxidative and alkali treatment. The following factors that may influence the sorption properties of short hemp fibers were examined: fiber structure and morphology were characterized by iodine sorption, water retention and scanning electron microscopy, while specific surface area was determined by BET method. Additionally, the amount of carboxyl groups was determined by calcium-acetate method, and the point of zero charge of the short hemp fibers samples was determined by the solid addition method. Biosorption of zinc ions was evaluated through the total uptake capacity, equilibrium and kinetic data. Obtained data were analyzed by nonlinear Langmuir and Freundlich isotherms, as well as pseudo-first and pseudo-second order kinetic models, and the best fitting model was chosen using Akaike information criterion. Chemical modification, used in this work, leads to structural and morphological changes of short hemp fibers, and improvement of their sorption properties. It was found that sorption properties of short hemp fibers are predominantly influenced by surface acidity and the amount of functional groups, while fiber structure and specific surface area have a secondary role in the biosorption of zinc ions. Akakike information criterion values showed that biosorption of zinc ions on all tested hemp fiber samples obey the pseudo-second order adsorption kinetics, while experimental isotherm data fit better with Langmuir model. Biosorption of zinc ions on the hemp fibers is a predominantly chemical process, which mainly follows the mechanism of ion exchange on acidic functional groups, and occurs through the fast surface adsorption, intraparticle diffusion and final equilibrium stage.

SiO2/graphene composite for highly selective adsorption of Pb(II) ion

SiO2/graphene composite was prepared through a simple two-step reaction, including the preparation of SiO2/graphene oxide and the reduction of graphene oxide (GO). The composite was characterized by UV–Vis spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscope, and X-ray photoelectron spectroscopy, and what is more, the adsorption behavior of as-synthesized SiO2/graphene composite was investigated. It was interestingly found that the composite shows high efficiency and high selectivity toward Pb(II) ion. The maximum adsorption capacity of SiO2/graphene composite for Pb(II) ion was found to be 113.6mgg−1, which was much higher than that of bare SiO2 nanoparticles. The results indicated that SiO2/graphene composite with high adsorption efficiency and fast adsorption equilibrium can be used as a practical adsorbent for Pb(II) ion.

Adsorptive removal of copper ions with highly porous chitosan/cellulose acetate blend hollow fiber membranes

In this study, highly porous adsorptive hollow fiber membranes were directly prepared from chitosan (CS) and cellulose acetate (CA) blend solutions and were examined for copper ion removal from aqueous solutions in a batch adsorption mode. Four types of hollow fiber membranes were spun from two CS/CA blends (with a CS/CA/forming acid ratio of 3/12/85 or 2/18/80) in two types of coagulants (water or 3 wt.% NaOH solution). All the CS/CA blend hollow fiber membranes displayed sponge-like and macrovoids-free structures, with specific surface areas in the range of 12.2–15.2 m 2/g, porosities of 70.4–79.7%, and pore sizes of 0.05–0.2 μm, depending on the CS/CA ratios and the type of coagulants used. Adsorption experiments showed that the CS/CA blend hollow fiber membranes had good adsorption capacity (up to 35.3–48.2 mg/g), fast adsorption rates and short adsorption equilibrium times (less than 20–70 min) for copper ions, and can work effectively at low copper ion concentrations (<6.5 mg/L) to reduce the residual level to as low as 0.1–0.6 mg/L in the solution. X-ray photoelectron spectroscopic (XPS) study confirmed that the adsorption of copper ions on the CS/CA blend hollow fiber membranes was mainly attributed to the formation of surface complexes with the nitrogen atoms of CS in the hollow fiber membranes, hence higher CS contents in the blend hollow fiber membranes rendering the membranes more adsorptive to copper ions. It was found that the copper ions adsorbed on the hollow fiber membranes can be effectively desorbed in an EDTA solution (up to 99% desorption efficiency) and the hollow fiber membranes can be reused almost without loss of the adsorption capacity for copper ions.