Static Adsorption Research Articles

Amino-rich nanofiber membrane with favorable hemocompatibility for highly efficient removal of bilirubin from plasma

Bilirubin is a serious toxin in the blood of liver failure patients, and the development of bilirubin adsorbent with high removal efficiency, excellent hemocompatibility is crucial to improve the efficacy of hemoperfusion therapy. Herein, PAN/PEI nanofiber membrane (NFM) with amino-rich and smooth surface structure was prepared through a more facile co-blended electrospun method. During simulated adsorption experiments in vitro, PAN/PEI NFMs exhibited a high adsorption capacity of 142.79 mg g−1 for free bilirubin at clinical bilirubin concentration (100 mg L-1) in patients with liver failure. In addition, the bilirubin removal efficiency in static adsorption exceeded 96% when the PAN/PEI NFMs addition was greater than 120 mg. In particular, PAN/PEI NFMs displayed excellent hemocompatibility, presented a low hemolysis rate (0.4%), favorable anti-adhesion properties for hemocyte and plasma protein, and had no significant effect on coagulation. The development of this facile method promotes the feasibility of nanofibrous membranes for the treatment of hyperbilirubinemia with significant implications for improving therapeutic efficacy.

Study on the adsorption behavior of chlorogenic acid from Eucommia ulmoides Oliver leaf extract by a self-synthesized resin

Chlorogenic acid (CGA) has various biological activities and is widely existed in plants. In this work, the GMA-10 resin modified by glycidyl methacrylate was prepared to investigate the adsorption behaviors toward CGA. N2 adsorption-desorption isotherms, SEM, FT-IR spectroscopy were used to characterize structural changes of GMA-10 before and after adsorption. The adsorption performance of GMA-10 and other resins (Amberlite 732, ST-DVB, AB-8, and X-5) were compared under different initial pH value, adsorbent dosage, chlorogenic acid concentration, and desorbent concentration by static adsorption experiments. Dynamic adsorption and desorption experiments showed a 5.12-folds increase in chlorogenic acid content from 7.37% to 37.78% with a recovery of 84.91% after treatment with GMA-10 resin. Reusability experiments showed the decrease of adsorption capacity was under 1.78% in 5 cycles. In addition, adsorption isotherms revealed that the adsorption conformed to Langmuir model. Adsorption kinetics studies showed that the pseudo-second-order model accurately described the adsorption process, and both intra-particle diffusion and liquid film diffusion together limited the mass transfer rate. In summary, these results show the potential of GMA-10 to separate and purify CGA from Eucommia ulmoides Oliver leaf.

Effective adsorption of crystal violet onto magnetic nanoparticles decorated bacteria: Kinetic and site energy distribution analysis

The discharge of crystal violet wastewater will cause extremely serious harm to the natural environment and human health, due to its certain toxicity and carcinogenicity. The adsorption characteristics and mechanism of crystal violet on magnetic nanoparticles decorated bacteria (Fe3O4 @bacteria) were investigated especially the adsorption kinetic, equilibrium, mass transfer mechanism, and site energy distribution analysis. With the initial concentration of crystal violet 40 mg/L, pH= 4, the addition of 0.003 g Fe3O4 @bacteria, after adsorption for 2 h under 25 °C, the static maximum adsorption capacity of crystal violet was up to 114.8 mg/g, which was 2.07 times that of Fe3O4 under the same conditions. Fe3O4 @bacteria could be recycled more than 6 times, also exhibited a 76.2% reduction in COD for actual dyeing wastewater. The adsorption data fitted well with the Temkin isotherm model, Elovich kinetic, and pseudo-second-order kinetic models. As for the mass transfer mechanism of the adsorption process, the IPD model was more suitable to describe the mass transfer process of the crystal violet adsorption by Fe3O4 @bacteria, while the intraparticle diffusion is not the only mechanism controlling the adsorption process. The adsorption process is spontaneous and exothermic according to the thermodynamics study. Based on the analysis of site energy distribution, the biosorbent had a heterogeneous surface and most of the crystal violet sorption occurred on the sites with energy over 13.0 kJ/mol, which supported that crystal violet sorption was physical-chemical sorption. Therefore, the magnetic nanoparticles decorated bacteria can serve as promising adsorbents to eliminate the organic dye pollutants caused by textile industry.

Mechanistic insights into the migration behavior of cadmium (Cd) in the soil and groundwater systems at a construction site: Experimental and numerical analysis

The environmental fates of cadmium (Cd) in the soil and groundwater systems largely depend on its adsorption isotherms and kinetic with the soil matrix. Combined with HYDRUS–1D software, batch and column studies were conducted in this study to investigate the adsorption and movement process of Cd in soil and groundwater systems. The results from static adsorption experiment indicated that the second order model and Langmuir model could provide the better description for adsorption behavior of Cd. The results from SEM –EDS and XPS analysis revealed that the main adsorption mechanism of Cd were ion exchange, complexation and precipitation. The results from Tessier's sequential extraction suggested that more Cd would be diffused to the deeper soils, since the higher percentage of Cd were found in the exchangeable fractions. The results from soil column experiments and numerical analyses demonstrated that standard convection–dispersion equation (CDE) could better describe Cd breakthrough curve (BTCs) of column adsorption than the other three solute transport models within HYDRUS–1D software. Noteworthy, the horizontal and vertical migration distance of Cd (II) reached about 8 m after 50,000 days and 10 m after 15,000 days, respectively, indicating the easily mobile Cd (II) might be eventually released from contaminated soils to groundwater. Based on the above results, this study not only provided a new insight into the migration mechanism of Cd in the soil and groundwater environment, but was also beneficial to formulating remediation strategies of contaminated sites.

Adsorption Characteristics of a Cationic Gemini Surfactant on Carbonate Outcrops: Adsorption Reduction Using Methylene Blue

Surfactant adsorption has been a great challenge for surfactant-based chemically enhanced oil recovery (cEOR) techniques as it directly reflects the overall efficiency of a cEOR project. The static adsorption of an in-house-synthesized cationic Gemini surfactant (GS12) has been investigated on carbonate outcrops as a function of concentration, time, salinity, and temperature. Three different types of carbonate outcrop samples taken from the Al-Lidam area with an increasing percentage of silica and clay impurities were investigated. It was found that the higher the presence of silicate and clay minerals in the carbonate outcrops, the higher will be the surfactant adsorption. The adsorption of GS12 was found to decrease at elevated temperatures and in a highly saline environment, especially at very high concentrations of divalent salts (CaCl2 and MgCl2). In addition, a novel adsorption inhibitor─methylene blue─has been proposed in this study, which reduced the surfactant adsorption dramatically on carbonate outcrops. The GS12 adsorption on carbonate samples 1, 2, and 3 was reduced to 0.14 mg/g-rock, 0.48 mg/g-rock, and 2.31 mg/g-rock, respectively, by the addition of 500 ppm methylene blue in a 1500 ppm surfactant solution. Moreover, curve fitting was also performed to analyze the adsorption isotherm and kinetic data. Redlich–Peterson and pseudo-second-order models were found to be the best to describe the adsorption isotherm and kinetics, respectively.

Adsorption of glyphosate and metabolite aminomethylphosphonic acid (AMPA) from water by polymer-based spherical activated carbon (PBSAC)

Glyphosate (GLY) is the most commonly used herbicide worldwide, and aminomethylphosphonic acid (AMPA) is its main metabolite. Their occurrence in ground and surface waters causes diseases in humans, while complex physico-chemical properties hinder detection and effective removal. Polymer-based spherical activated carbon (PBSAC) can adsorb many micropollutants efficiently and, hence, overcome the shortfalls of conventional treatment methods. The static adsorption of a mixture of GLY and AMPA by PBSAC was investigated with varying PBSAC properties and relevant solution chemistry. The results show that PBSAC can remove 95% GLY and 57% AMPA from an initial concentration of 1 µg/L at pH 8.2. PBSAC properties (size, activation level, and surface charge) have a strong influence on herbicide removal, where surface area plays a key role. Low to neutral pH favors non-charge interactions and results in good adsorption, while higher temperatures equally enhance GLY/AMPA adsorption by PBSAC. The work demonstrated the effective removal of GLY to meet the European guideline concentration (0.1 µg/L), while AMPA could not be removed to the required level.

Investigation on the Sulfadiazine Schiff Base Adsorption Ability of Y(III) Ions from Nitrate Solutions, Kinetics, and Thermodynamic Studies

ABSTRACT Sulfadiazine Schiff base (SDSB) was prepared using an inexpensive technique by modification of sulfadiazine drug (SD) to be used as an adsorbent material for recovery of Y(III) ions from aqueous solutions. Chemical and physical characterizations of SDSB were performed using different techniques. The maximum static adsorption capacity of the modified SD was 0.9 mmolg−1 for Y(III) ions and at pH 5.0. The kinetics results revealed that the sorption of Y(III) ions upon the synthesized SDSB followed the pseudo-second-order with R2 of >0.999. Temkin, Dubinin – Radushkevich, Freundlich, and Langmuir models accurately described the adsorption isotherm data. The activation energy (Ea) for adsorption was 17.52 kJmol−1, indicating the process is to be chemisorption. Thermodynamic characteristics with ΔHo of 11.33 kJmol−1 and a ΔSo 110.2 Jmol−1K−1. Using FT-IR and EDAX analysis proved the yttrium adsorption upon the SDSB. The desorption process for Y(III) ions was successfully achieved using 1 M HNO3 and it reduced from 95% to 70% after five consecutive cycles. A pre-concentration process for yttrium ions presented in a waste solution was achieved using SDSB adsorbent with a pre-concentration factor of about 10. As a result, it is regarded as a promising adsorbent for Y(III) ions in a variety of industrial applications.

Mechanisms of adsorbing hydrogen gas on metal decorated graphene

Hydrogen is a key player in global strategies to reduce greenhouse gas emissions. In order to make hydrogen a widely used fuel, we require more efficient methods of storing it than the current standard of pressurized cylinders. An alternative method is to adsorb ${\mathrm{H}}_{2}$ in a material and avoid the use of high pressures. Among many potential materials, layered materials such as graphene present a practical advantage as they are lightweight. However, graphene and other 2D materials typically bind ${\mathrm{H}}_{2}$ too weakly to store it at the typical operating conditions of a hydrogen fuel cell, meaning that high pressure would still be required. Modifying the material, for example by decorating graphene with adatoms, can strengthen the adsorption energy of ${\mathrm{H}}_{2}$ molecules, but the underlying mechanisms are still not well understood. In this work, we systematically screen alkali and alkaline-earth metal decorated graphene sheets for the static thermodynamic adsorption of hydrogen gas from first principles and focus on the mechanisms of binding. We show that there are three mechanisms of adsorption on metal decorated graphene and each leads to distinctly different hydrogen adsorption structures. The three mechanisms can be described as weak van der Waals physisorption, metal adatom facilitated polarization, and Kubas adsorption. Among these mechanisms, we find that Kubas adsorption is easily perturbed by an external electric field, providing a way to tune ${\mathrm{H}}_{2}$ adsorption. This work is foundational and builds our understanding of ${\mathrm{H}}_{2}$ adsorption under idealized conditions.

Two-dimensional borocarbonitrides nanosheets engineered sulfonated polyether sulfone microspheres as highly efficient and photothermally recyclable adsorbents for hemoperfusion

Adsorbents, which can be used to directly eliminate uremic toxins from blood, are decisive for hemoperfusion that maintains human renal function. However, developing adsorbents with large adsorption capacity, excellent chemical stability, high hemocompatibility and good cyclicity for toxins is still challenging. Herein, we proposed a type of two-dimensional (2D) carbon materials-borocarbonitrides (BCN) nanosheets as a novel uremic toxin adsorbent for blood perfusion. Theoretical analysis firstly confirmed the stronger binding capacity of BCN layer towards small molecular toxins than that of graphene. To make it applicable for practical perfusion, BCN nanosheets engineered sulfonated polyether sulfone (SPES) microspheres (B-PES) are thus constructed. Through static adsorption, the B-PES-4 achieves effective toxin adsorption capacities of 26, 40 and 197 mg g−1 on creatinine, uric acid and bilirubin respectively, which are 550%, 508% and 1756% outperforming pure SPES microspheres. In addition, simulated perfusion experiments demonstrate a good toxin removal efficiency for the microspheres, for example, over 80% of bilirubin is removed at a high perfusion rate of 20 mL min−1. Moreover, the B-PES microspheres neither induce hemolysis and immunoreaction in the blood nor affect cell viability. As a proof of concept, the photothermal property of BCN nanosheets is innovatively exploited for fast-drying and efficient recycling of the used B-PES microspheres. These features, together with the reusability, blood and cell compatibility, make the platform highly promising for clinical blood purification and artificial kidney application.

Kaempferol molecularly imprinted polymers: preparation, characterization and application to the separation of kaempferol from ginkgo leaves

AbstractIn this work, kaempferol molecularly imprinted polymers (MIPs) were screened in detail and were applied to the separation of kaempferol from real complex systems. Kaempferol‐MIPs with high affinity and selectivity for kaempferol could be prepared successfully by using kaempferol as the template molecule, 4‐vinylpyridine as the functional monomer, ethylene glycol dimethacrylate or divinylbenzene as the crosslinker, acetone or acetonitrile as the solvent. Scanning electron microscopy observation and Brunauer–Emmett–Teller measurement showed that the prepared MIPs had a heterogeneous pore structure and large specific surface area. Static and dynamic adsorption experiments and solid‐phase extraction application were performed to evaluate the performance of the prepared MIPs. Only the MIPs with both higher distribution coefficient and higher imprinting factor in the dynamic experiments had better ability to retain kaempferol. Using the screened MIPs as solid‐phase extraction sorbents, kaempferol and quercetin were extracted directly from the crude ginkgo leaves hydrolysate with high recovery and purity. Control experiments also showed that the screened MIPs were superior to commercially available adsorbents in terms of the separation of kaempferol from crude extracts. © 2023 Society of Industrial Chemistry.

Enhanced Adsorption of Two Reactive Dyes onto Al-Based Waterworks Sludge Modified by Calcination

Al-based waterworks sludge (ABWS) modified by calcination was reused as an adsorbent for the removal two reactive dyes, namely, reactive yellow 176 (RY-176) and reactive red 195 (RR-195) from aqueous solution. 800ºC was proved to be the optimal calcination temperature in the range of 200-900ºC. A series of static adsorption experiments were carried out using ABWS calcinated at 800ºC (ABWS-800) as adsorbent. The results indicated that the adsorption of both the two dyes by ABWS-800 was almost independent of initial solution pH, and the adsorption capacity of ABWS-800 for RR-195 was about 1.4 times higher than that for RY-176. The pseudo-second-order kinetic model was best among the three models to describe the adsorption of the two reactive dyes, and Freundlich isotherm model was better matched than the Langmuir isotherm model to describe the adsorption process. Na2SO4 inhibited the adsorption of the two dyes onto ABWS-800. This work provided the theoretical basis and technical support for the optimization of reaction conditions for the decontamination of dyes wastewater by “waste” ABWS.

Static adsorption of a novel cationic gemini surfactant: A mineralogical study

Surfactants are deemed as an advantageous chemical in enhanced oil recovery (EOR) because of their potential of lowering the interfacial tension and modifying the wettability. However, the surfactant loss by adsorption on the rock surface is one of the major shortcomings of surfactant-based flooding techniques. The static adsorption of an in-house synthesized cationic gemini surfactant (GS12) is investigated as a function of mineral type, salinity, and concentration. Both clay and non-clay minerals have been examined. Surfactant adsorption was increased continuously by the increase of concentration till 1000 ppm and then an adsorption plateau was observed in all minerals except montmorillonite and kaolinite. It was found that clay minerals may cause more detrimental effects as compared to silicate minerals and carbonate minerals showed the least adsorption. The maximum amount of surfactant adsorbed on the mineral surface was in the order of montmorillonite > kaolinite > illite > K-feldspar > quartz > dolomite > calcite. Lower adsorption of GS12 was detected because of the presence of multivalent ions (Ca2+ and Mg2+). Methylene blue (MB) has been revealed as a novel adsorption inhibitor for cationic GS12 on various minerals. MB adsorbs on the negative binding sites of both clay and non-clay minerals. Therefore, an electrostatic repulsion takes place between the cationic dye (MB) and cationic GS12, leading to the reduction of GS12 adsorption on the mineral surface. Only the addition of 100 ppm of MB in the surfactant solution at the highest concentration (1500 ppm) reduced GS12 adsorption on quartz surface to 0.67 mg/g-rock. This study will help in designing the chemical EOR process using GS12 on carbonate formation containing silica and clay minerals as impurities.

Chitosan grafted with crown ether with high selectivity and adsorption on lithium-ion

Currently, Lithium is the lightest metal known in nature, which is widely applied in most walks of life. However, the present storage of lithium resources in the world is far from meeting the consumption market surge demand for lithium resources. Liquid lithium resources such as Salt Lake brine and seawater brine will become the primary source and inevitable choice for lithium extraction in the future due to a large amount of lithium, and its recovery requires a simple and effective process. This study synthesized TEG4MEC, a pseudo-crown ether monomer with a ring unit, to achieve effective Lithium-ion (Li+) recognition through specific interaction with Li+. Then, the TEG4MEC monomer was grafted onto the surface of cross-linked chitosan microspheres (CCS) by surface initiation polymerization. A series of static and dynamic adsorption studies showed that the pH value of the solution had a significant effect on Li+ adsorption. For CCS-TEG4MEC microspheres, the best adsorption effect was observed at pH = 7.0. The maximum adsorption capacity of Li+ on CCS-TEG4MEC microspheres obtained by Langmuir isotherm fitting is 156.16 mg g−1. In addition, CCS-TEG4MEC microspheres also showed effective regeneration performance and highly stable adsorption capacity, which could be reused.

Naphthenic Acids Removal from Model Transformer Oil by Diethylamine Modified Resins.

Resins have enormous potential in the removal of naphthenic acids (NAs) from transformer oil due to their rich porosity and high mechanical and diversified functionality, whereas their poor adsorption capacity limits application. In this work, the polystyrene-diethylamine resin (PS-DEA-x) was prepared by grafting diethylamine (DEA) onto chloromethylated polystyrene (PS-Cl) resin to efficiently adsorb cyclopentane carboxylic acid from transformer oil for the first time. The characterization analysis results indicated that amine contents were significantly enhanced with the increase in DEA. Particularly, resin with a molar ratio of 1:5 depending on chloromethyl to DEA (PS-DEA-5) exhibited the highest amine contents and efficient adsorption of cyclopentane carboxylic acid (static adsorption capacity up to 110.0 mg/g), which was about 5 times higher than that of the pristine PS-Cl. The thermodynamic and kinetic studies showed that the adsorption behaviors could be well fitted to the Langmuir isotherm equation and pseudo-second-order rate equation. Moreover, it was found that 1 g of the PS-DEA-5 can decontaminate about 760 mL transformer oil to meet reuse standards by a continuous stream, indicating its potential application in industry.

Ce-MOF composite electrospinning as antibacterial adsorbent for the removal of 2,4-dichlorophenoxyacetic acid

2,4-dichlorophenoxyacetic acid (2,4-D) is one of the most widely used herbicides with strong environmental toxicity, and it is necessary to be removed from water. However, some traditional adsorbents may be contaminated by bacteria during the removal process, which will affect the adsorption performance. Therefore, a novel adsorbent (Ce-MOF@ABP) with antibacterial properties was developed for the removal of 2,4-D. The adsorbent is prepared by in-situ growth of Ce-based MOF with UiO-66 structure on the surface of electrospun nanofibers by solvothermal method. The results of static adsorption experiments show that the composite fibrous membrane has a good removal effect on 2,4-D. The adsorption process is more consistent with the pseudo-second-order model and Langmuir model. The theoretical maximum adsorption capacity is 200.80 mg/g. The dynamic filtration experiment also shows a removal rate of 90.3% within 6 min (the membrane thickness is 0.12 mm). And most importantly, the haloperoxidase activity of Ce-MOF could endows fibrous membrane with excellent antibacterial properties, and the bacteriostatic rate of Escherichia coli is 92.91%. This study provides an innovative idea for the development of adsorbents/membranes with organic contaminant removal and antibacterial capabilities.

Adsorption Properties of a Polyamine Special Ion Exchange Resin for Removing Molybdenum from Ammonium Tungstate Solutions

A polyamine special ion exchange resin was used to adsorb Mo from ammonium tungstate solutions. The effects of adsorption time, S2− concentration, adsorption temperature, CO32− concentration, mass ratio of WO3 to Mo, and Mo concentration on the Mo and WO3 adsorption capacities were investigated. Energy dispersive spectrometer plane scans were used to study the distributions of Mo, W, S, and Na on the loaded polyamine special ion exchange resin and the desorbed polyamine special ion exchange resin. The results showed that the polyamine special ion exchange resin performed well during adsorption and desorption. Under the optimum conditions for the static adsorption experiments, the adsorption capacities for Mo and WO3 were 99.29 mg/mL and 31.97 mg/mL, respectively, and the desorption rates for Mo and WO3 were 99.35% and 99.43%, respectively. Adsorption and desorption of molybdenum and tungsten on the polyamine special ion exchange resin were investigated by dynamic adsorption experiments with an ammonium tungstate solution containing 125.0 g/L WO3, 12.50 g/L Mo, 15.65 g/L S2−, and 0 g/L CO32−. The adsorption capacities for Mo and WO3 were 53.48 mg/mL and 9.79 mg/mL, and the adsorption rates for Mo and WO3 were 99.05% and 1.81%, respectively. The loaded polyamine special resin was desorbed with a 45 g/L sodium hydroxide solution, and the dynamic desorption rates for Mo and WO3 were 99.02% and 99.29%, respectively.

An efficient and green separation method of total alkaloids by resorcinol-formaldehyde aerogel during extraction of Coptis chinensis

Alkaloids are the most medicinally valuable ingredients in plant crop Coptis chinensis (C. chinensis). However, the separation of these small-molecule compounds is challenging because C. chinensis also contains a lot of impurities such as proteins and saccharides. Adsorption separation stands out in the field of biological separation by virtue of its efficiency and greenness. Here, this paper aimed to selectively separate the total alkaloids during extraction of C. chinensis by resorcinol-formaldehyde (RF) aerogel based on electrostatic interaction and size-sieving effect. First, RF aerogels with different surface area (40.6–674.9 m2/g) and pore size (2–25 nm approximately) were synthesized by adjusting the ratio of catalyst (C). The results of static adsorption showed that the optimum alkaloids selective separation was achieved at R/C of 10/1: alkaloids adsorption capacity (Qe), protein retention ratio (Pr), saccharides retention ratio (Sr) and the coefficient of selectivity were 487.93 mg/g, 87.40 %, 95.90 % and 2.23, respectively. Methanol containing 1 % hydrochloric acid was considered as the most suitable eluent with the desorption efficiency of 95.88 %. In addition, the adsorption process conformed to pseudo-second-order kinetics, intra-particle diffusion and Langmuir isotherm models, and was a spontaneous endothermic process. It was found from the dynamic adsorption experiment that the dynamic adsorption capacity was 497.81 mg/g, and the purity of total alkaloids increased from 39.19 % to 90.22 %. Compared with resin adsorption and salt precipitation method, RF aerogel separation could more efficiently separate the alkaloids from C. chinensis (the total alkaloids yield of 57.40 mg/g C. chinensis). In addition, the alkaloids separated by RF aerogel had better antioxidant and antibacterial activities than that separated by salt precipitation method. In summary, RF aerogel separation was potential as an efficient and green method for the separation of total alkaloids from C. chinensis.

Recovery of chlorogenic acid from the DES-based extract of Eucommia ulmoides leaves by molecularly imprinted solid-phase extraction

To develop new ideas about the recovery of target components from the deep eutectic solvent (DES)-based extract, molecularly imprinted polymers (MIPs) were adopted as fillers for the solid-phase extraction to recover the chlorogenic acid (CGA) from the DES-based extract of Eucommia ulmoides leaves (EULs). Specifically, the CGA was taken as a template molecule to combine with three functional monomers (methacrylic acid (MAA), acrylamide (AM), and 2-vinylpyridine (2-VP)), respectively, through bulk polymerization to form MIPs. Then, the interaction between the CGA and these monomers by computational simulation was studied. Results show that MAA-MIPs are highly selective, with high adsorption capacity (120.70 mg/g) and rate (reaching the adsorption equilibrium at 40 min). Their static and dynamic adsorption behaviors conform to the Langmuir model and quasi-second-order kinetic model, respectively. In addition, the adsorption properties of these polymers confirm the conclusion that the pre-assembly system of CGA-MAA has the most hydrogen bonds and the largest binding energy. The recovery of CGA from the DES-based extract of EULs by MAA-MIPs are optimized to obtain the optimal solid-phase extraction conditions, in which the CGA shows a recovery rate of 75.15% and a purity of 65.20%. Notably, the addition of water in the loading solution could break the interaction between the components and DES to effectively improve the recovery. MAA-MIPs, as fillers for the molecularly imprinted solid-phase extraction, can achieve the specific adsorption and recycling of the template molecule CGA, which provides new ideas for the separation and purification of target products from the DES-based extract.

Adsorption mechanisms of alginate oligosaccharides with specific degree of polymerizations on a novel ion-exchange resin: Experiments and simulations

Alginate oligosaccharides (AOS) with a specific degree of polymerization (DP) have unique physiological activity, but industrialization and high-value applications of AOS are restricted due to the paucity of study on its precise separation mechanism. In the process design of adsorption separation chromatography, the adsorption behaviors of the adsorbent are crucial. Herein, the adsorption properties of AOS with DPs 1–4 (AOS1-4) on novel SM-7 resin were clarified by combining adsorption experiments and theoretical calculations. The effect of various parameters on the adsorption process of AOS1-4 was investigated using a series of static adsorption tests. Molecular dynamics modeling was implemented to determine the interaction energy and diffusion between AOS1-4 and SM-7 resin. The results of the adsorption equilibrium demonstrated that the adsorption of AOS1-4 complied with the Langmuir model and exhibited ion dependency and pH stability. The saturation adsorption capacities of AOS1-4 on SM-7 resin were 1.144 mmol/g, 0.810 mmol/g, 0.730 mmol/g, and 0.582 mmol/g, respectively. The external diffusion was the primary rate-limiting phase in the adsorption kinetics of AOS1-4, which followed the pseudo-second-order kinetic model. As the increasing of DPs of AOS, the hydroxyl, carboxyl, and molecular volume rose, which decreased the adsorption capacity and rate. Simulation results showed that interaction energies between SM-7 resin and AOS enhanced while the diffusion coefficient declined with rising DPs of AOS. Hydrogen bond interaction and electrostatic attraction promoted the adsorption of AOS on the novel resin. The fundamental theoretical data in this study can provide guidance for the large-scale preparation of AOS with specific DPs.

Selective Adsorption of Quercetin by the Sol-Gel Surface Molecularly Imprinted Polymer.

Quercetin, as one of the most biologically active natural flavonoids, is widely found in various vegetables, fruits and Chinese herbs. In this work, molecularly imprinted polymer (MIP) was synthesized through surface molecular imprinting technology with sol-gel polymerization mechanism on SiO2 at room temperature using quercetin as the template, SiO2 as the supporter, 3-aminopropyltriethoxysilane (APTES) as the functional monomer, and tetraethoxysilane (TEOS) as the cross-linker. The prepared MIP was characterized via scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption measurements to validate its surface morphology, structure and functionality. SEM images revealed that the morphology of MIP was rough and spherical with the particle size of 260 nm larger than that of the support SiO2. In the FTIR spectra of MIP, the band around 1499 cm-1 and 2932 cm-1 were assigned to N-H and C-H groups, respectively. The results indicated that the imprinted polymer layers were grafted on the surface of SiO2 and the MIP had been successfully prepared. Since the specific surface area and pore volume of MIP were markedly higher than those of NIP and SiO2 and were 52.10 m2 g-1 and 0.150 cm3 g-1, respectively, it was evident that the imprinting process created corresponding imprinted cavities and porosity. The MIP for adsorbing quercetin was evaluated by static adsorption experiment. The results indicated that the adsorption equilibrium could be reached within 90 min and the maximum adsorption capacity was as high as 35.70 mg/g. The mechanism for adsorption kinetics and isotherm of MIP for quercetin was proved to conform the pseudo-second-order kinetics model (R2 = 0.9930) and the Freundlich isotherm model (R2 = 0.9999), respectively, revealing that chemical adsorption and heterogeneous surface with multilayer adsorption dominated. In contrast to non-imprinted polymer (NIP), the MIP demonstrated high selectivity and specific recognition towards quercetin whose selectivity coefficients for quercetin relative to biochanin A were 1.61. Furthermore, the adsorption capacity of MIP can be maintaining above 90% after five regeneration cycles, indicating brilliant reusability and potential application for selective adsorption of quercetin.