Impact factors and thermodynamic characteristics of aquatic humic acid loaded onto kaolin

The adsorption of humic acid (HA) on kaolin particles was studied at various conditions of initial solution pH, ionic strength and solid-to-liquid ratio. The resulting affinity of interactions between humic acid and kaolin was attributed to the surface coordination of HA in ambient suspensions of mineral particles and the strong electrostatic force at low pH. Addition of inorganic salt can also influence the adsorption behavior by affecting the HA molecular structure, the clay particle zeta potential and so on. Equilibrium data were well fitted by the Freundlich model and implied the occurrence of multilayer adsorption in the process. In addition, the enthalpy dependent of system temperature was 79.17 kJ/mol, which proved that the mechanism of HA adsorption onto kaolin was comprehensive, including electrostatic attraction, ligand complexation and hydrogen bonding.     

Preparation and physical properties of chitosan-coated calcium sulphate whiskers

To improve the performance of calcium sulphate whiskers (CSWs) in the papermaking industry, a series of chitosan-coated (CS) calcium sulphate whiskers (CS-CSWs) was prepared, with the aim of effectively reducing their solubility in aqueous solutions. The CS-CSWs were prepared by immersing CSWs in a chitosan acid solution and then cross-linking with alkaline gel via hydrogen-bonding interaction. The CS-CSWs were characterised in terms of water solubility, zeta potential, contact angle, scanning electron microscopy, thermo gravimetric analysis and X-ray photoelectron spectroscopy (XPS). The results indicated that chitosan had a good effect on the surface modification of CSWs. Under optimal conditions, the water solubility of CS-CSWs decreased by 50 %, and the contact angle increased by 63 %. The XPS measurement indicated that the relative thickness of the chitosan coating was 9.8 nm.     

Coagulation of bitumen with kaolinite in aqueous solutions containing Ca2+, Mg2+ and Fe3+: effect of citric acid

Heterocoagulation experiments of kaolinite with solvent-diluted-bitumen were carried out to investigate the effect of hydrolyzable metal cations and citric acid on the liberation of bitumen from kaolinite. The adsorption of Ca(2+) and Mg(2+) on kaolinite, and zeta potentials of kaolinite and bitumen droplets in solutions containing 10(-3)mol/L of Ca(2+), Mg(2+) and Fe(3+) with or without citric acid were also measured. It was found that the heterocoagulation of bitumen with kaolinite was enhanced in the presence of the metal cations from pH 7 to pH 10.5, accompanied by a decrease in the magnitude of the zeta potentials and an increase in the adsorption of the metal cations on kaolinite and possibly on bitumen droplets. The addition of 5 x 10(-4)mol/L citric acid reduced the degree of coagulation from 90% to less than 40% in the presence of 10(-3)mol/L Ca(2+) and Mg(2+) cations at pH approximately 10, and at pH approximately 8 for Fe(3+). It was found that hydrolyzable metal cations enhanced bitumen-kaolinite interactions through electrical double layer compression and specific adsorption of the metal hydrolysis species on the surface of kaolinite. The effect of metal cations was removed by citric acid through formation of metal-citrate complexes and/or the adsorption of citrate anions, which restored the zeta potentials of both kaolinite and bitumen. Therefore, electrostatic attraction or repulsion was responsible for the coagulation or dispersion of kaolinite particles from bitumen droplets in the tested system.     

腐植酸对砷的吸附作用研究

腐植酸中含有大量的极性基团,对金属离子有较强的吸附性能。运用氢化物-原子荧光光谱法,以泥炭腐植酸为原料,研究了腐植酸对砷(V)离子的吸附作用和腐植酸吸附剂中砷的回收,并得出了最佳的吸附和脱附条件。实验考察了酸度、时间分别对吸附和脱附的影响。结果表明,泥炭腐植酸对砷吸附的最佳模型为Freundlich吸附方程,当溶液成中性时腐植酸对砷的吸附量较大且趋于平稳。砷的浓度为1μg/mL,溶液的pH值为7,吸附时间控制在55min时,吸附效果最佳,最大吸附率为85.49%。脱附的最佳条件为:pH值14,脱附时间20min。     

Kinetic peculiarities of <Emphasis Type="Italic">Quillaja Saponaria Molina</Emphasis> saponin sorption by chitosan

A relationship between adsorption layer structure at different stages of sorbent filling, hydrophilicity, and spatial orientation of saponin in chitosan phase is revealed by joint analysis of the kinetic curves of saponin sorption, IR spectra of chitosan and saponin samples, and computer-simulation data. The sorbent–sorbate complex is formed due to electrostatic interactions between protonated amino groups in chitosan and carboanions of glucuronic acid in saponin, as well as hydrogen bonding between NH₂ and OH groups in chitosan molecules and OH groups in the carbohydrate moiety of saponin molecules.     

Evaluating the surface charge of C18 stationary phases

The surface charge of four C18 stationary phases was investigated by measuring the flow induced streaming potential, a well known electrokinetic property of charged surfaces. Three of the stationary phases (Symmetry, Gemini, and Xterra-MS) had significantly positive streaming potentials at both pH 3 and 4.5. The fourth (Zorbax-SB) appeared to be essentially neutral at pH 3 and became negative at pH 4.5. Apparent zeta potentials ranged from approximately +16 to -4 mV. The retention behavior was also investigated using chloride as model anion and glycinamide (in its protonated form) as model cation. When the retention factor (k) of glycinamide was subtracted from k of chloride anion, the resulting delta k values showed very similar trends as apparent zeta potential values, suggesting that the simple chromatographic method could be used to estimate zeta potential values, or that the zeta potential values could be useful for ranking columns according to ion exchange or exclusion behavior. The anion exchange capacity of the Symmetry and Gemini columns was also estimated, using a published chromatographic procedure, and the results suggest about 2 microEq. capacity per gram of packing.     

Study on CM-chitosan/activated carbon hybrid gel films formed with EB irradiation

A series of novel hybrid gel films were prepared from carboxymethylated chitosan (CM-chitosan) and activated carbon (AC) by irradiation of compression-molded CM-chitosan/AC mixture in physical gel state with electron beam (EB) at room temperature. The formation, properties and structure of CM-chitosan/AC hybrid gel films were discussed in terms of gel fraction, swelling, mechanical property, SEM image and XPS spectra. Compared with pure crosslinked CM-chitosan gel, the gel fraction and mechanical property of the hybrid sample were obviously improved after adding AC into CM-chitosan film. The morphology analyses indicated that the hybrid gel films exhibited a rough and folded surface and a relatively interior uniform structure was sustained between CM-chitosan and AC. XPS revealed that the content of protonated amino groups of CM-chitosan macromolecule was promoted by AC. In addition, the adsorptive property of the gel films against humic acid was investigated by batch adsorption method. It was found that the adsorption efficiency of CM-chitosan is significantly improved by adding AC. These preliminary evaluations suggest that the CM-chitosan/AC gel films have great potential for applications in industrial field and biomedical field.     

Effect of humic acid on the sorption of technetium on hematite colloids using <Superscript>95m</Superscript>Tc and <Superscript>96</Superscript>Tc as tracers

Sorption of technetium on hematite colloids, at varying pH (3–10), has been studied in absence and presence of humic acid using ^95mTc-⁹⁶Tc radiotracers. Technetium was found to be weakly sorbed on hematite at lower pH (<5) values, while no sorption was observed at higher pH values. Humic acid was found to have no effect on the sorption of technetium on hematite under aerobic conditions, while at lower pH values small reduction was observed which was attributed to the reduced zeta potential of the hematite colloids owing to the strong sorption of humic acid.     

Adsorption mechanism of synthetic reactive dye wastewater by chitosan

Chitosan was able to remove the color from synthetic reactive dye wastewater (SRDW) under acidic and caustic conditions. The effect of the initial pH on SRDW indicated that electrostatic interaction occurred between the effective functional groups (amino groups) and the dye under acidic conditions. Moreover, SRDW adsorption under caustic conditions was also affected by the covalent bonding of dye and hydroxyl groups of chitosan. In addition, elution tests confirmed that chemical adsorption occurred under acidic conditions, while both physical and chemical adsorption appeared under caustic conditions. The spectra of attenuated total reflectance Fourier transform infrared spectrometry confirmed the functional groups of chitosan that affected the SRDW adsorption. However, the maximum adsorption capacities of chitosan increased when the temperature increased. The maximum adsorption capacity of chitosan obtained from the Langmuir model was 68, 110, and 156 mg g(-1) under a system pH of 11.0 at 20, 40, and 60 degrees C, respectively. The negative values of enthalpy change (DeltaH), free energy change (DeltaG), and entropy change (DeltaS) indicated an exothermic, spontaneous process and decreasing disorder of the system, respectively. Therefore, the mechanism of SRDW adsorption by chitosan was probably by chemical adsorption for a wide range of pH's and at high temperatures.     

Effect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes

A streaming potential analyzer has been used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes. Zeta potentials of these membranes were analyzed for aqueous solutions of various chemical compositions over a pH range of 2 to 9. In the presence of an indifferent electrolyte (NaCl), the isoelectric points of these membranes range from 3.0 to 5.2. The curves of zeta potential versus solution pH for all membranes display a shape characteristic of amphoteric surfaces with acidic and basic functional groups. Results with salts containing divalent ions (CaCl₂, Na₂SO₄, and MgSO₄) indicate that divalent cations more readily adsorb to the membrane surface than divalent anions, especially in the higher pH range. Three sources of humic acid, Suwannee River humic acid, peat humic acid, and Aldrich humic acid, were used to investigate the effect of dissolved natural organic matter on membrane surface charge. Other solution chemistries involved in this investigation include an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (dodecyltrimethylammonium bromide). Results show that humic substances and surfactants readily adsorb to the membrane surface and markedly influence the membrane surface charge.     

金属有机框架MIL-101(Fe)对水中微囊藻毒素-LR的吸附

通过溶剂热法制备了性质稳定的金属有机框架材料MIL-101(Fe),并用于吸附去除水中的微囊藻毒素-LR。采用电子显微镜、傅立叶变换红外光谱(FT-IR)、Zeta电位和N_2吸附-脱附等方法对制备的纳米材料进行了表征。MIL-101(Fe)具有多孔结构和较高的比表面积(375.2 m~2/g),尺寸约为500 nm。考察了pH值、离子强度、温度、吸附时间、浓度等参数对吸附剂吸附能力的影响。结果表明,静电作用和配位作用是主要的作用机理。MIL-101(Fe)对微囊藻毒素-LR的吸附速度很快(20 min内达到吸附平衡),吸附过程符合准二级动力学模型;MIL-101(Fe)对微囊藻毒素-LR表现出良好的吸附性能,其最大吸附量为256.4 mg/g。溶液中存在的腐植酸对MIL-101(Fe)的吸附性能产生一定的影响。受腐殖酸、盐类的影响,相同条件下MIL-101(Fe)对江水中微囊藻毒素-LR的吸附性能有所下降,但仍可达到68.1 mg/g。因此,该方法简便、高效,适用于快速除去污染水体中的微囊藻毒素-LR。     

Adsorption of polyethyleneimine and polymethacrylic acid onto synthesized hematite

An influence of different functional groups of polymer, its molecular weight, polydispersity ratio (M(w)/M(n)) and presence of impurities on its adsorption in different pH values (3, 6 and 9) onto synthesized hematite (Fe(2)O(3)) was measured. A structure of adsorbed macromolecules of PMA and PEI was obtained according to S-F theory. Two polymers were used: polymethacrylic acid (PMA) of 6500 and 75,100 molecular weight as well as polyethyleneimine (PEI) 25,000 commercial and fractionated. Electrokinetic properties of the interface oxide-polymer solution (surface charge density and zeta potential) were also measured as well as adsorption layer thicknesses (with use of viscosimetric measurements). Obtained data show, that all above-mentioned factors do influence not only the adsorption process itself but also a surface charge, zeta potential and structure of adsorbed polymer layers on polymer/hematite interface.     

Chemistry of aqueous silica nanoparticle surfaces and the mechanism of selective peptide adsorption

Control over selective recognition of biomolecules on inorganic nanoparticles is a major challenge for the synthesis of new catalysts, functional carriers for therapeutics, and assembly of renewable biobased materials. We found low sequence similarity among sequences of peptides strongly attracted to amorphous silica nanoparticles of various size (15-450 nm) using combinatorial phage display methods. Characterization of the surface by acid base titrations and zeta potential measurements revealed that the acidity of the silica particles increased with larger particle size, corresponding to between 5% and 20% ionization of silanol groups at pH 7. The wide range of surface ionization results in the attraction of increasingly basic peptides to increasingly acidic nanoparticles, along with major changes in the aqueous interfacial layer as seen in molecular dynamics simulation. We identified the mechanism of peptide adsorption using binding assays, zeta potential measurements, IR spectra, and molecular simulations of the purified peptides (without phage) in contact with uniformly sized silica particles. Positively charged peptides are strongly attracted to anionic silica surfaces by ion pairing of protonated N-termini, Lys side chains, and Arg side chains with negatively charged siloxide groups. Further, attraction of the peptides to the surface involves hydrogen bonds between polar groups in the peptide with silanol and siloxide groups on the silica surface, as well as ion-dipole, dipole-dipole, and van-der-Waals interactions. Electrostatic attraction between peptides and particle surfaces is supported by neutralization of zeta potentials, an inverse correlation between the required peptide concentration for measurable adsorption and the peptide pI, and proximity of cationic groups to the surface in the computation. The importance of hydrogen bonds and polar interactions is supported by adsorption of noncationic peptides containing Ser, His, and Asp residues, including the formation of multilayers. We also demonstrate tuning of interfacial interactions using mutant peptides with an excellent correlation between adsorption measurements, zeta potentials, computed adsorption energies, and the proposed binding mechanism. Follow-on questions about the relation between peptide adsorption on silica nanoparticles and mineralization of silica from peptide-stabilized precursors are raised.     

Effects of pH and phosphate on the adsorptive fractionation of purified Aldrich humic acid on kaolinite and hematite

The molecular weight (MW) fractionation of purified Aldrich humic acid (PAHA) resulting from adsorption on kaolinite and hematite was investigated for different solution pH and phosphate conditions. Adsorption was highly pH-dependent, with higher uptake at lower pH values. For all pH conditions, the weight-average MW (MWw) of residual PAHA remaining in solution after adsorption deviated from the original MWw, indicating that preferential adsorption of certain MW components occurred. The extent of preferential adsorption depended on the percent carbon adsorption at a given pH condition. For similar percent carbon adsorption ranges, a greater extent of preferential adsorption of the higher MW PAHA components was observed with higher pH values as demonstrated by the lowest residual MWw value occurring at pH 9. Detailed analyses of selected residual PAHA samples clearly showed that adsorption selectivity for particular MW components was strongly influenced by solution pH. The extent of preferential adsorption of lower MW PAHA components decreased in the presence of a small amount of phosphate. This effect was more evident for hematite than kaolinite, and became greater with lower solution pH irrespective of the mineral type. The different fractionation patterns observed for PAHA were reasonably well explained by the physicochemical trends occurring in its MWw fractions and the underlying sorption processes.     

Fabrication of titanate nanotubes/iron oxide magnetic composite for the high efficient capture of radionuclides: a case investigation of 109Cd(II)

In this paper, the capture of radiocadmium (Cd(II)) by adsorption onto the titanate nanotube/iron oxide (TNT/IOM) magnetic composite as a function of contact time, pH, ionic strength, foreign cation and anion ions, humic acid (HA) and fulvic acid (FA) was studied using batch technique. The results indicated that the adsorption of Cd(II) onto the TNT/IOM magnetic composite was dependent on ionic strength at pH <9.0, but was independent of ionic strength at pH >9.0. Outer-sphere surface complexation were the main mechanism of Cd(II) adsorption onto the TNT/IOM magnetic composite at low pH values, whereas the adsorption was mainly dominated via inner-sphere surface complexation at high pH values. The adsorption of Cd(II) onto the TNT/IOM magnetic composite was dependent on foreign cation and anion ions at low pH values, but was independent of foreign cation and anion ions at high pH values. A positive effect of HA/FA on Cd(II) adsorption onto the TNT/IOM magnetic composite was found at low pH values, while a negative effect was observed at high pH values. From the results of Cd(II) removal by the TNT/IOM magnetic composite, the optimum reaction conditions can be obtained for the maximum removal of Cd(II) from water. It is clear that the best pH values of the system to remove Cd(II) from solution by using the TNT/IOM magnetic composite are 7.0–8.0. Considering the low cost and effective disposal of Cd(II)-contaminated wastewaters, the best condition for Cd(II) capture by the TNT/IOM magnetic composite is at room temperature and solid content of 0.5 g L^?1. These results are quite important for estimating and optimizing the removal of Cd(II) and related metal ions by the TNT-based magnetic composite.     

Electrosteric Stabilization of Al(2)O(3), ZrO(2), and 3Y-ZrO(2) Suspensions: Effect of Dissociation and Type of Polyelectrolyte

The mechanisms of eight anionic polyelectrolytes stabilizing colloidal sized alpha-Al(2)O(3), pure ZrO(2), and Y(2)O(3)-doped ZrO(2) particles in aqueous solution are discussed. The polyelectrolytes studied were the Na(+) and NH(4)(+) salts of polyacrylic acid and polymethacrylic acid having different molecular weights. The particle-dispersant interactions were studied by measuring adsorption isotherms, particle size, thickness of adsorbed layer, and zeta potentials by elektrokinetic sonic analysis at different powder volume fractions (straight phi=0.01-0.3), pH, and electrolyte (KCl) content. The dissociation of the polyelectrolytes was studied by potentiometric titrations. The dissociation constant of the polymethacrylates was found to be 0.6 pH unit higher than that for the polyacrylates. High-affinity adsorption isotherms were observed over the pH range when the polyelectrolytes were fully ionized. The results show good correlation between adsorption isotherms and zeta potential data in systems of dispersed, dilute alumina particles. When particles and polymers were of equal charge (the same sign of charge) the polymer shell was thicker. At higher volume fractions (straight phi=0.3), and when alumina particles/added ammonium polyelectrolyte were of equal charge, a maximum in the absolute value of zeta potential resulted. Due to adsorption all the anionic polyelectrolytes studied provided electrosteric stabilization of the alpha-Al(2)O(3), and Y(2)O(3)-doped ZrO(2) suspensions by enhancing the zeta potential to 40 mV or over and by shifting the isoelectric point to lower pH, the low-molecular-weight polyelectrolytes decreasing the isoelectric point more than the polyelectrolytes having higher molecular weight. The polyelectrolytes studied failed to stabilize pure monoclinic ZrO(2) particles. Due to the shortness of the chain of polyelectrolytes studied, no bridging was observed between oppositely charged polyelectrolyte/alumina particles. Copyright 2000 Academic Press.     

Model Studies on the Interaction of Amino Acids with Biominerals: The Effect of L-Serine at the Hydroxyapatite-Water Interface

The effect of L-serine in supersaturated solutions of calcium phosphate was investigated under plethostatic conditions. The rates of crystal growth measured in the presence of L-serine at relatively high concentrations and in the range between 2x10(-3) and 1x10(-2) mol dm(-3) were appreciably reduced. The inhibitory effect of L-serine was found to be due to blocking of a portion of the active growth sites by adsorption. Kinetics measurements in the presence of L-serine as well as adsorption isotherm analysis suggested Langmuir-type adsorption of L-serine on the surface of hydroxyapatite (HAP) with a relatively low affinity for the substrate. Adsorption experiments showed that at pH 7.4 considerable adsorption of L-serine onto HAP takes place, whereas at pH 10.0 the adsorption was negligible, suggesting that electrostatic interactions are dominant. Attraction between the positively charged protonated amino group of the L-serine molecule and the negatively charged HAP surface contributed largely to the adsorption. This was corroborated by the fact that, in the presence of L-serine in the solution, a significant shift of zeta-potential of the HAP particles to less negative values was found at pH values close to 7.4. At pH values higher than 10.0 essentially no shift of zeta-potential takes place. On the basis of the experimental results, a model was proposed according to which L-serine absorbs on the surface of HAP through electrostatic attractions exerted between one negative site of the HAP surface, i.e., phosphate or hydroxyl ion, and the positively charged protonated amino group of one L-serine molecule, forming a surface ion pair. Copyright 2001 Academic Press.     

Chitosan-coated polystyrene microplate for covalent immobilization of enzyme

Microplates made of polystyrene have been widely used for immunoassays. Protein molecules that have been immobilized on a hydrophobic polystyrene microplate by passive adsorption lose their activity and suffer considerable denaturation. A new chitosan-coated microplate suitable for the covalent immobilization of enzymes has been developed. The primary amino groups of chitosan were exploited for this covalent coupling of proteins. The optical transmittance of the chitosan-coated microplate, at wavelengths of 400–800 nm, was estimated to be suitable for its application in chromogenic reaction-based bioassays. The immobilization efficiency of the chitosan-coated microplate was demonstrated to be far superior to that of a conventional microplate when tested using acetylcholinesterase (AChE) and β-glucosidase as model biomolecules, and the chitosan-coated microplate may thus have potential applications in biosensing and bioreactor systems.     

Comparison of n-tetradecane/electrolyte emulsions properties stabilized by DPPC and DPPC vesicles in the electrolyte solution

The properties of n-tetradecane/electrolyte emulsions with DPPC or DPPC vesicles in the electrolyte solution were investigated. The DPPC molecules form different aggregates, which possess different surface affinity, size and structure, and therefore we assumed some differences in the adsorption at the oil droplet/water interface. The n-tetradecane emulsions in 1:1, 1:2 and 1:3 electrolytes were prepared by mechanical stirring in the presence of DPPC at natural pH. Electrokinetic properties of the systems were investigated taking into account the effective diameter and multimodal size distribution of the droplets as well as the zeta potentials using the dynamic light scattering technique. The zeta potential of the droplets was negative in all systems with NaCl. In the emulsions with CaCl(2) at a higher concentration of electrolyte and emulsions with LaCl(3) with all investigated concentrations, positive values were observed. Similar measurements were performed for DPPC vesicles in the electrolyte solution. The pH and ionic strength changes induce those in the electrical charge of DPPC layer or vesicle surface. This is due to the fact that the DPPC molecule contains -PO(-) and -N(CH(3))(3) groups, which are in equilibrium with H(+) and OH(-), as well as other ions present in the solution, i.e. Na(+), Ca(2+), La(3+) or Cl(-). In the n-tetradecane/electrolyte emulsion stabilized by DPPC or DPPC vesicles the zeta potential may be also related to acid-base interactions. The effect of the ions from the solution on the DPPC layer adsorbed on n-tetradecane droplets or DPPC vesicles is discussed.     

Chitosan modified poly(L-lactide) microspheres as cell microcarriers for cartilage tissue engineering

The surfaces of poly(l-lactide) (PLLA) microspheres were modified by chitosan via a method of hydrolysis and grafting-coating to improve their compatibility to chondrocytes. The PLLA microspheres with a diameter of 74-150mum were fabricated by an oil/water emulsion solvent evaporation method, followed by hydrolysis in alkaline solution to produce a larger number of carboxyl groups. Using water-soluble carbodiimide as a coupling reagent, chitosan was covalently grafted onto the microspheres. Due to the physical entanglement and insolubility at neutral pH, unbonded chitosan molecules were stably remained to yield a large amount of coated chitosan. Biological performance of the control PLLA and the chitosan-coated PLLA microspheres were assessed by in vitro culture of rabbit auricular chondrocytes. After 24h and 7d culture, the chitosan-coated PLLA microspheres, especially the ones with larger chitosan amount, exhibited stronger ability to promote cell attachment and proliferation, and maintain the secretion function of the chondrocytes. Therefore, the chitosan-coated PLLA microspheres can be potentially used as the injectable cell microcarriers for chondrogenesis in cartilage tissue engineering.