Synthesis and Characterization of PEG-Modified Polystyrene Particles and Isothermal Equilibrium Adsorption of Bovine Serum Albumin on these Particles

A series of monodisperse submicron polystyrene (PS) particles with different surface monomethoxy poly(ethylene glycol) (mPEG) densities were prepared and characterized. The effects of the chemically grafted mPEG chains (MW = 2,000) on the adsorption of bovine serum albumin (BSA) molecules onto these negatively charged particles at pHs 5 and 3 were investigated. The native particles at both pH values showed the largest values of q _max (maximum amount of BSA adsorbed on the particle surface). The surface mPEG chains were very effective in retarding the BSA adsorption and q _max decreased significantly with increasing surface mPEG density. The values of q _max were greater for both the native and mPEG-modified particles at pH 5 compared to those counterparts at pH 3, due to the different adsorption mechanisms. Hydrophobic interaction predominated in the adsorption of BSA molecules on the particles at pH 5, whereas electrostatic interaction had a crucial influence on the BSA adsorption at pH 3. At pH 5, the adsorption behaviors were qualitatively explained by the calculated values of the free energy barrier against the BSA adsorption. A schematic model was also proposed to qualitatively describe the conformations of BSA molecules adsorbed on the particle surfaces.     

Adsorption of bismuth(III) by bayberry tannin immobilized on collagen fiber

The adsorption behavior of collagen fiber‐immobilized bayberry tannin towards Bi(III) at acidic pH values was investigated. The adsorption capacity of the adsorbent towards Bi(III) was 0.348 mmol g^?1 at 303 K, and increased with the rise in temperature. The adsorption isotherms of Bi(III) were in the shape of so‐called type II isotherms and could be described by an empirical equation, ln q_e = k + (1/n)C_e, which implies that chemical adsorption is predominant at lower concentrations of Bi(III) and that physical adsorption is involved at higher concentrations. The adsorption kinetics of Bi(III) on the immobilized bayberry tannin could be well described by the pseudo‐second‐order rate model, and the adsorption capacities calculated by the model were almost the same as those determined by actual measurements. The adsorbent could be regenerated by using 0.02 mol dm^?3 ethylenediaminetetraacetic acid (EDTA) solution after adsorption of Bi(III). The adsorption selectivity of the immobilized bayberry tannin towards Bi(III) in a Cu(II)–Bi(III) binary solution in acidic medium was remarkable. Therefore, it is strongly suggested that the immobilized bayberry tannin could be applied to the removal of Bi(III) from crude Cu(II) samples under proper conditions. Copyright © 2006 Society of Chemical Industry     

Electrochemical characterization of the protective film formed by the unsymmetrical Schiff's base on the mild steel surface in acid media

The corrosion inhibition efficiency of a newly synthesized Schiff's base for the corrosion of mild steel was studied in 1.0 M HCl and 0.5 M H₂SO₄ solutions. The results of weight loss measurements, electrochemical impedance and potentiodynamic polarization measurements consistently demonstrated that the Schiff's base synthesized is a good corrosion inhibitor with an inhibitory efficiency of approximately 92% at an optimum inhibitor concentration of 600 mg/L. The inhibition in both of the corrosive media was observed to be a mixed type. The potential of zero charge (PZC) at the metal–solution interface was determined for both the inhibited and uninhibited solutions to provide the mechanism of inhibition. The inhibitor formed a film on the metal surface through chloride or sulfate bridges depending upon the medium. The temperature dependence of the corrosion rate was also studied in the temperature range from 27 to 50 °C. The value of the activation energy (E_a) calculated showed that the inhibition film formation on the metal surface occurred through chemisorption. The thermodynamic parameters such as the adsorption equilibrium constant (K_ads) and the free energy of adsorption (ΔG_ads) were calculated and discussed. Several adsorption isotherms were tested and the experimental data fit well with the Langmuir adsorption isotherm.     

胶原纤维负载锆对氟离子和磷酸根的吸附去除

将Zr(Ⅳ)负载在胶原纤维基质上制备吸附材料,研究了该吸附材料对水溶液中氟离子和磷酸根离子的吸附特性。结果表明,胶原纤维负载Zr(Ⅳ)(ZrCF)对氟离子和磷酸根离子均有较强的吸附能力,在pH=4～9,胶原纤维负载Zr(Ⅳ)对氟离子保持较高的吸附容量;ZrCF吸附磷酸根的适宜pH=3.0～6.0。胶原纤维负载Zr(Ⅳ)对氟离子和磷酸根离子的吸附等温线均符合Langmuir方程;吸附动力学研究表明,胶原纤维负载Zr(Ⅳ)对氟离子和磷酸根离子的吸附动力学可以用准二级速率方程来描述。水中常见的Cl-、NO3-、CO23-和SO24-对ZrCF吸附氟离子和磷酸根离子的影响不大,模拟地下水体系的动态实验结果表明,ZrCF对磷酸根的亲和力更强。     

Study on flotation performances and adsorption mechanism of 2-carboxyethylphenylphosphinic acid to cassiterite

A novel collector, 2-carboxyethylphenylphosphinic acid (CEPPA), was first used in the flotation of cassiterite. The flotation performances and the adsorption mechanism of CEPPA on cassiterite were investigated by flotation tests, adsorption experiments, zeta potential measurements, Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. The results indicated that CEPPA had strong collecting power for cassiterite and fluorite over a wide pH range but little on quartz. In the separation of the cassiterite–quartz mixture, a concentrate containing 90.9% SnO₂ was obtained with a recovery of 95.7% at pH 7.0. The cassiterite in the cassiterite–fluorite mixture could be effectively separated using 300 mg/L sodium silicate in conjunction with 60 mg/L CEPPA, and a concentrate with a grade of 90.3% SnO₂ and a recovery of 92.6% was achieved at neutral pH. Zeta potential analysis demonstrated that the adsorption process involved both physical and specific forces. The results of FTIR and XPS further suggested that the four O atoms of CEPPA reacted with the Sn atoms on cassiterite surface, forming a complex which was similar to the Sn–CEPPA precipitate, and hydrogen bonding adsorption could have taken place between the terminal hydroxyl groups and CEPPA anions.     

Changes in porosity of treated lint cotton fibers. I. Purification and swelling treatments

Changes in the internal morphology of lint cotton fibers during purification and swelling treatments were investigated by measurement of nitrogen adsorption at liquid nitrogen temperature. Surface areas and pore size distributions were calculated from the adsorption isotherms and compared with findings from measurements of changes in crystallinity and in fibrillar aggregation as shown by electron micrographs. The adsorption measurements were made on fibers which were either preswollen in water or taken from the rinse water after treatment and solvent exchanged through methanol and n-pentane to helium. The large changes found in surface area, pore size distribution, and fibrillar aggregation were accompanied by changes in crystal structure in fibers treated with 5.0M sodium hydroxide. Large changes following treatment with phosphoric acid occurred in pore structure and fibrillar aggregation without concomitant change in crystallinity.     

Electrochemical and surface properties of aluminium in citric acid solutions

The electrochemical and surface properties of aluminium in 0.05 M citric acid solutions of pH 2–8 were studied by means of open circuit potential (OCP), potentiodynamic polarization and potentiostatic current–time transient measurements. The OCP reached a steady-state value very slowly, probably due to the slow rate of detachment of surface complexes into the solution. Aluminium exhibits passive behaviour in citric acid solutions of pH 4–8. Tafel slopes b _c were characteristic for hydrogen evolution on aluminium covered by an oxide film. The corrosion kinetic parameters E _corr, i _corr and b _a suggest that surface processes are involved in the dissolution kinetics, especially in the pH range 3–6. Current–time transient measurements confirm that, in citric acid solutions of pH 3–6, the dissolution is controlled by surface processes, that is, by the rate of detachment of surface complexes, while in solutions of pH 2, 7 and 8 dissolution is under mass-transport control. The addition of fluoride ions to citric acid changes the controlling steps of the dissolution process. Citrate and fluoride ions compete for adsorption sites at the oxide surface, and adsorption of these ions is a competitive and reversible adsorption.     

Influence of 2,5-bis(4-dimethylaminophenyl)-1,3,4-thiadiazole on corrosion inhibition of mild steel in acidic media

An example of a new class of corrosion inhibitors, namely, 2,5-bis(4-dimethylaminophenyl)-1,3,4-thiadiazole (DAPT) was synthesized and its inhibiting action on the corrosion of mild steel in 1 M HCl and 0.5 M H₂SO₄ at 30 °C was investigated by various corrosion monitoring techniques. A preliminary screening of the inhibition efficiency was carried out using weight loss measurements. At constant acid concentration, inhibitor efficiency increases with concentration of DAPT and is found to be more efficient in 0.5 M H₂SO₄ than in 1 M HCl. Potentiostatic polarization studies showed that DAPT is a mixed-type inhibitor. The effect of temperature on the corrosion behaviour of mild steel in 1 M HCl with addition of DAPT was studied in the temperature range from 25 to 60 °C. Its was shown that adsorption is consistent with the Langmuir isotherm for 30 °C. The negative free energy of adsorption in the presence of DAPT suggests chemisorption of thiadiazole molecules on the steel surface.     

pH-responsive variation of biomineralization via collagen self-assembly and the simultaneous formation of apatite minerals

Collagen self-assembly and simultaneous mineralization by incubating a mixture containing collagen, calcium, and phosphate ions under physiological conditions, is an effective method to prepare bone-like biomimetic materials. The formation of fibrils and minerals is related to pH of system. In the present work, we evaluated the effect of pH (7.9–10.4) on biomineralization process and synthesized composites. Turbidity kinetics and X-ray diffraction (XRD) measurements revealed that increasing pH delayed the crystallization process from nucleation phase to plateau phase because of promoting chelation of Ca²⁺ with collagen. Typical peaks of phosphate in Fourier transform infrared spectroscopy coupling with characteristic peaks of hydroxyapatite (HAp) in XRD spectra illustrated the formation of HAp after biomineralization. Scanning electron microscopy measurements indicated that the increase of pH promoted the deposition of spherical minerals in fibrils. Especially, the minerals tended to form cluster-like structure at pH 10.4. The hyp content, Ca and P contents, and gel strength measurements suggested that higher pH promoted the formation of HAp with a Ca/P closed to 1.67 and the prolongation of crystallization gave the time for collagen self-assembly leading to the increase of gel strength at higher pH (9.4–10.4). These results might provide some new ideas for designing biomimetic materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48876.     

Adsorption behavior of aqueous europium on kaolinite under various disposal conditions

This work investigated the adsorption behavior of europium on kaolinite under various disposal conditions. Batch-wise adsorption and precipitation experiments and equilibrium model calculations were performed over a pH range of 4–10 and CO₂ concentration range of 0%, 0.03%, and 10%. Experimental precipitation behaviors are in agreement with the results of equilibrium model calculations using the geochemical code MINTEQA2. Aqueous species of Eu³⁺ exists mainly at pH 5 or below and solid phases of Eu(OH)₃(s), Eu(OH)CO₃(s), and Eu₂(CO₃)₃·3H₂O(s) are formed at higher pH ranges. Adsorption behavior of Eu on kaolinite in the low pH range can be explained by interlayer ion-exchange reaction. The significant increase in adsorbed amount at pH 5–6 is due to the surface complexation at the edge site of kaolinite. In the high pH range, precipitation of Eu contributes mainly to the adsorption quantity. The rapid decrease in adsorbed amount above pH 7 under 10% CO₂ condition occurs by the formation of anionic europium species of Eu(CO₃) ₂ ^- .The adsorption of Eu on kaolinite could be well interpreted by the Freundlich adsorption isotherm. The data except for the highest equilibrium concentration ranges were also explained by Langmuir isotherm and the maximum adsorbed quantity of Eu on kaolinite,b, is 1.2 mg/g.     

Adsorption behavior of β-lactoglobulin onto polyethersulfone membrane surface

The adsorption of whey protein onto polyethersulfone (PES) membrane was investigated by static adsorption experiments to understand fouling mechanism and optimize the process condition to minimize the membrane fouling. Adsorption isotherm was applied to calculate the isotherm parameters such as adsorption capacity (K_F) and surface heterogeneity (1/n). The K_F values increased about 3.7 times at pH 3.0, 1.5 times at pH 5.2, and 2.3 times at pH 9.0 compared to that at pH 7.0. The hydrophobic interaction by dissociation of dimer structure of β-lactoglobulin to monomer structure at acidic and alkaline conditions showed the greatly increasing of the amount of protein adsorption by the protein and membrane interaction which might form the strong and rigid protein layer on the polymeric membrane surface. The addition of salt reduced the protein adsorption on PES membrane because of the interactions between charged protein molecules and salt ions.     

Porous dye affinity beads for nickel adsorption from aqueous solutions: A kinetic study

We investigated a new adsorbent system, Reactive Red 120 attached poly(2‐hydroxyethyl methacrylate ethylene dimethacrylate) [poly(HEMA–EDMA)] beads, for the removal of Ni²⁺ ions from aqueous solutions. Poly(HEMA–EDMA) beads were prepared by the modified suspension copolymerization of 2‐hydroxyethyl methacrylate and ethylene dimethacrylate. Reactive Red 120 molecules were covalently attached to the beads. The beads (150–250 μm), having a swelling ratio of 55% and carrying 25.5 μmol of Reactive Red 120/g of polymer, were used in the removal of Ni²⁺ ions. The adsorption rate and capacity of the Reactive Red 120 attached poly(HEMA–EDMA) beads for Ni²⁺ ions was investigated in aqueous media containing different amounts of Ni²⁺ ions (5–35 mg/L) and having different pH values (2.0–7.0). Very high adsorption rates were observed at the beginning, and adsorption equilibria were then gradually achieved in about 60 min. The maximum adsorption of Ni²⁺ ions onto the Reactive Red 120 attached poly(HEMA–EDMA) beads was 2.83 mg/g at pH 6.0. The nonspecific adsorption of Ni²⁺ ions onto poly(HEMA–EDMA) beads was negligible (0.1 mg/g). The desorption of Ni²⁺ ions was studied with 0.1M HNO₃. High desorption ratios (>90%) were achieved. The intraparticle diffusion rate constants at various temperatures were calculated as k_20°C = 0.565 mg/g min^0.5, k_30°C = 0.560 mg/g min^0.5, and k_40°C = 0.385 mg/g min^0.5. Adsorption–desorption cycles showed the feasibility of repeated use of this novel adsorbent system. The equilibrium data fitted very well both Langmuir and Freundlich adsorption models. The pseudo‐first‐order kinetic model was used to describe the kinetic data. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:5056–5065, 2006     

Surface Charge of Variable Porosity Al2O3(s) and SiO2(s) Adsorbents

The surface charge properties of two SiO₂ and three Al₂O₃ mineral adsorbents with varying degrees of framework porosity were investigated using discontinuous titration and ion adsorption methodologies. Points of zero net charge (p.z.n.c) for porous and non-porous SiO₂ were <2.82 and for Al₂O₃ minerals ranged from 6.47–6.87. Silica surfaces possessed very slight negative charge in the acid pH range (pH < 7) and significant dissociation of silanol groups occurred at pH > 7. Variation of surface charge density with aqueous proton concentration was nearly identical within a mineral type (i.e., SiO₂ or Al₂O₃) irrespective of the degree of framework porosity, indicating that the densities of dissociable surface sites are equivalent, when normalized to surface area. The results suggest that the use of titration methods alone may be insufficient for thorough surface charge characterization, particularly at low and high pH. Proton titrations should be coupled with concurrent ion adsorption measurements to confirm surface charge development. Discontinuous proton titration and ion adsorption data, which were in agreement in the slightly acidic through slightly basic pH range, both indicated that p.z.n.c. was equal to the point of zero net proton charge (p.z.n.p.c.) for the variable charge minerals investigated.     

The Structural Interactions of Molecular and Fibrillar Collagen Type I with Fibronectin and Its Role in the Regulation of Mesenchymal Stem Cell Morphology and Functional Activity

The observed differences in the structure of native tissue and tissue formed in vitro cause the loss of functional activity of cells cultured in vitro. The lack of fundamental knowledge about the protein mechanism interactions limits the ability to effectively create in vitro native tissue. Collagen is able to spontaneously assemble into fibrils in vitro, but in vivo, other proteins, for example fibronectin, have a noticeable effect on this process. The molecular or fibrillar structure of collagen plays an equally important role. Therefore, we studied the interaction of the molecular and fibrillar structure of collagen with fibronectin. Atomic force and transmission electron microscopy showed that the presence of fibronectin does not affect the native structure and diameter of collagen fibrils. Confocal microscopy demonstrated that the collagen structure affects the cell morphology. Cells are better spread on molecular collagen compared with cells cultured on fibrillar collagen. Fibronectin promotes the formation of a large number of focal contacts, while in combination with collagen of both forms, its effect is leveled. Thus, understanding the mechanisms of the relationship between the protein structure and composition will effectively manage the creation in vitro of a new tissue with native properties.     

Ligand-induced flocculation of neurotoxic fibrillar Abeta(1-42) by noncovalent crosslinking

Aggregation of the amyloid-beta (Abeta) peptides has a pivotal role in Alzheimer's disease (AD). Small molecules and short peptides/peptidomimetics can exert their full protective effects against Abeta within a short time-frame, but the exact mechanism of action is unclear. Time-dependent NMR spectroscopic binding and replacement experiments were carried out for peptide LPFFD and thioflavine T (ThT) on neurotoxic fibrillar Abeta(1-42), which revealed transient binding behavior for both compounds, and complex time-dependent features in the replacement experiments. The results of particle size measurements through the use of diffuse light-scattering and transmission electron microscopy support the conclusions that the studied ligands induced interfibrillar association on a short timescale, which explains the NMR spectroscopic binding and replacement results. zeta-Potential measurements revealed a slightly increased electrostatic stability of the Abeta fibrils upon ligand binding; this suggests that the interfibrillar assembly is driven by specific noncovalent cross-linking interactions. A specific surface and mobility decrease due to the ligand-induced flocculation of the Abeta fibrils can explain the neuroprotective effects.     

The Binding of Anionic Dyes by Cross-Linked Cationic Starches

Adsorption of anionic dyes on the cross-linked with epichlorohydrin starches containing quaternary ammonium groups (CCS) was investigated and compared with that of modified starches containing only quaternary ammonium groups (CS). The adsorption of anionic dyes on CS and CCS closely follows the Langmuir model of adsorption. The computed Langmuir saturation capacity Q _o increases with increasing degree of substitution (DS) of CS or CCS and has the value from 0.81 mol/kg to 3.22 mol/kg for CCS and from 0.88 mol/kg to 1.87 mol/kg for CS. The effectiveness of the cationic groups in dye binding was about 1 mol/equiv for CSS with DS from 0.47 to 0.62 and all the cationic groups had attached one anionic groups of the dye. Increasing DS of CS decreases the effectiveness of dye binding due to the increase in solubility of CS, and the soluble part of CS binds the dye as a typical soluble polyelectrolyte. CCS are more suitable than CS for the anionic dye adsorption from a textile dyeing solution. DS of CCS should be about 0.5–0.6. They adsorb the anionic dyes in few minutes and acts in the wide range of pH of the solutions. The Langmuir saturation capacity Q _o and the effectiveness of the cationic groups in dye binding increase with an increase of the adsorption temperature. The positive values of the enthalpy and entropy suggest that the adsorption is endothermic and during the adsorption of the anionic dye on CCS the randomness of the system increases.     

Influence of annealing treatments on the essential work of fracture of biaxially drawn poly(ethylene terephthalate)

The biaxial sequential stretching process of poly(ethylene terephthalate) produces films with a fibrillar microstructure in which fibrils are parallel to the transverse extrusion direction. The mechanical properties of such films are strongly anisotropic due to both the orientation of crystallites and the properties of the intrafibrillar and interfibrillar amorphous phases. The idea is to modulate the properties of the amorphous phase without altering the fibrillar structure by annealing treatments. The morphology (crystallinity and orientation of the crystalline phase) of the annealed films is characterized and their mechanical properties (tensile tests and essential work of fracture) are tested in the longitudinal direction (parallel to the micro fibrils) and in the transverse direction (perpendicular to the micro fibrils). The crystalline phase orientation is the key parameter governing modulus anisotropy. Concerning crack propagation, annealing treatments lead to opposite evolution of the specific essential work of fracture parameter (w_e) in the longitudinal and transverse directions. Thus, it is possible to erase fracture propagation anisotropy through an adequate annealing treatment. Copyright © 2012 Society of Chemical Industry     

Study on the efficiency of ethylene vinyl acetate–fly ash composites for the uptake of phenols from synthetic waste water

In this study, ethylene vinyl acetate–fly ash (EVA‐FA) composites were prepared by the melt mixing technique using a rheomixer for the purpose of removing 2,4,6‐trichlorophenol (TCP) and p‐nitrophenol (PNP) from water. The fly ash was characterized by X‐ray fluorescence spectroscopy, scanning electron microscopy (SEM) and X‐ray diffraction (XRD); the composites were characterized using SEM and XRD. Brunauer, Emmett, and Teller (BET) measurements revealed a surface area (S_BET) of 0.07110 m²/g for the fly ash. The adsorption of TCP and PNP were monitored by UV–Vis spectrophotometer. The maximum adsorption of PNP was obtained at pH 5 after a contact period of 12 h, whereas that of the TCP was obtained at pH 4 after a period of 10 h has elapsed. The equilibrium adsorption data were evaluated using Langmuir and Freundlich adsorption isotherm models. The Langmuir adsorption model gave the better correlation coefficients for the equilibrium adsorption data. The kinetics data followed the pseudo‐second‐order model for both TCP and PNP. The theoretical maximum adsorption capacity (q_max) of the adsorbent used in the study was found to be 3.424 mg/g and 2.544 mg/g for TCP and PNP, respectively. The desorption of the phenols from the composites was performed using 0.2M NaOH. About 82.6% and 76.3% of TCP and PNP were recovered, respectively. The study showed that the pH of the solution and contact time play a significant role in the adsorption process. Furthermore, we have demonstrated that EVA‐FA composites have the potential to adsorb phenols from acidic water solutions. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electrostatic and electrosteric stabilization of aqueous slips of 3Y–ZrO2 powder

Yttria-doped zirconia powder (3Y-ZrO₂) was characterized and dispersed in distilled water. The state of dispersion was evaluated in terms of zeta potential, apparent viscosity and the mean particle size of solid phase in the slip. Zeta potential, apparent viscosity and the mean particle size as a function of pH indicated the pH range of electrostatic stabilization. These results showed that electrostatic stabilization of the slip can be accomplished in low acidic and high basic range of pH. Dissolution of yttria from the powder surface in acidic pH was found to be high and fast, risky to the stability of the slip as well as the microstructure of the sintered body. Electrosteric stabilisation by addition of an anionic polyelectrolyte (PMAA-NH₃) shifted the isoelectric point (IEP) to lower pH. The state of dispersion was further investigated by particle size measurements of the solid phase in the slip. The optimum amount of dispersant is discussed in terms of zeta potential and viscosity. The adsorption of polyelectrolyte is considered at pH 4, native pH of suspension and at pH 10, below and above the IEP of powder and correlated with the dissociation rate of polymer and the net surface charge of particles at given pH. Higher adsorption of dissociated polymer to the positively charged surfaces justifies the higher optimum amount of polyelectrolyte at pH 4.     

Effect of iodide ions on corrosion inhibition of mild steel by 3,5-bis(4-methylthiophenyl)-4H-1,2,4-triazole in sulfuric acid solution

The synergistic effect of iodide ions on the corrosion inhibition of mild steel in 0.5 M sulfuric acid (H₂SO₄) in the presence of 3,5-bis(4-methylthiophenyl)-4H-1,2,4-triazole (4-MTHT) was investigated using weight loss measurements and different electrochemical techniques such as potentiostatic polarization curves and electrochemical impedance spectroscopy (EIS). The inhibition efficiency (E, %) increased with 4-MTHT concentration, but the desorption potential (E _d) remained unchanged with increasing 4-MTHT concentration. The addition of potassium iodide (KI) enhanced E considerably and increased the value of E _d. A synergistic effect was observed between KI and 4-MTHT with an optimum mass ratio of [4-MTHT]/[KI] = 4 × 10^–2. The synergism parameters (S ) calculated from surface coverage were found to be more than unity. This result clearly showed the synergistic influence of iodide ions on the corrosion inhibition of mild steel in 0.5 M H₂SO₄ by 4-MTHT. The adsorption of this inhibitor alone and in combination with iodide ions followed Langmuir's adsorption isotherm.