Enhanced fluoride sorption using La(III) incorporated carboxylated chitosan beads

The carboxylated chitosan beads (CCB), which have a defluoridation capacity (DC) of 1385 mg F(-)/kg, have been further chemically modified by incorporating La(3+) ion (La-CCB) and its DC was found to be 4711 mg F(-)/kg whereas the raw chitosan beads (CB) possess only 52 mg F(-)/kg. The fluoride removal by La-CCB is governed by both adsorption and complexation mechanism. The functional groups present in beads were identified by FTIR analysis. The surface condition and existence of fluoride on the beads was confirmed by SEM with EDAX analysis. The experimental data have been analyzed using Freundlich and Langmuir isotherm models. Thermodynamic parameters such as DeltaG(o), DeltaH(o) and DeltaS(o) were calculated to predict the nature of sorption. The kinetic studies were investigated with reaction-based and diffusion-based models. A field trial was carried out with fluoride water collected from a nearby fluoride-endemic village.     

Selective sorption of fluoride using Fe(III) loaded carboxylated chitosan beads

Chitosan beads (CB) as such have very low defluoridation capacity (DC) of 52 mgF⁻/kg have been suitably modified by carboxylation followed by chelation with Fe³⁺ ion (Fe-CCB), in order to effectively utilize both hydroxyl and amine groups for defluoridation. The modified beads showed enhanced DC to a very significant level of 4230 mgF⁻/kg. The fluoride removal process is governed by both adsorption and complexation mechanism. The sorbent was characterized using Fourier transform infrared spectrometer (FTIR) and scanning electron microscope (SEM) analysis. The experimental data have been analysed using isotherm and kinetic models. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated to predict the nature of sorption. A field trial was carried out with fluoride water collected from a nearby fluoride-endemic village.     

Study of Protein Adsorption/Adhesion Behaviors on Solid Beads Surface with Different Surface Properties

Three kinds of chitosan (CS) derivatives have been prepared via polyethyleneimine (PEI) or polyethylene glycol (PEG) together with PEI modified chitosan. FTIR, x-ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA)/differential thermal analysis (DTA) proved the successful linkage, and XPS and zeta potential analysis show that these derivatives beads possess different surface nature. The PEI modified chitosan derivative is made in acid solution (A-PEI-CS) and the one added with additional PEG (PEG–CS-PEI) has showed higher swelling degree than their counterpart derivative prepared at basic condition (B-PEI-CS). Although the nitrogen content of A-PEI-CS is higher than that of B-PEI-CS, due to the better surface hydrophilicity, the B-PEI-CS beads are more capable of adsorbing bovine serum albumin (BSA) protein. Electrostatic attraction facilitates protein adsorption in a narrow acidic pH range while hydrophilicity hinders protein adhering to the beads’ surface at any pH.     

Fluoride removal using lanthanum incorporated chitosan beads

Highly selective material based on naturally occurring biomaterial namely chitosan has been designed for the defluoridation of water. Lanthanum incorporated chitosan beads (LCB) were prepared using precipitation method. The synthesis was optimized by varying different synthesis parameters namely lanthanum loading, complexation and precipitation time, strength of ammonia solution used for precipitation, drying time, etc. Lanthanum incorporated chitosan beads were characterized using SEM, FTIR, XRD and EDX. Surface area of LCB was observed to be 2.76 m² g⁻¹. The equilibrium adsorption data fitted well to Langmuir adsorption isotherm and showing maximum fluoride adsorption capacity of 4.7 mg g⁻¹ with negligible lanthanum release. Kinetic study reveals that adsorption of fluoride is fast and follows pseudo-first-order kinetics. The effect of pH was also studied and the best efficiency was observed at pH 5. Presence of sulphate, nitrate and chloride marginally affected the removal efficiency, however drastic reduction in fluoride uptake was observed in the presence of carbonate and bicarbonate. Negative value of change in free energy (ΔG°) and positive value of change in entropy (ΔS°) suggest the adsorption of fluoride by LCB is feasible and spontaneous process. Positive value of change in enthalpy (ΔH°) suggests the process of fluoride adsorption is endothermic in nature. Regeneration study reveals that 1 M ammonium chloride solution appears to be the promising regeneration media showing 81.22% regeneration. The adsorption capacity of LCB was similar in fluoride-contaminated ground water collected from Dhar district of Madhya Pradesh, India, as compared to simulated water.     

Synthesis of La-incorporated chitosan beads for fluoride removal from water

In this study, lanthanum incorporated chitosan beads (LCB) were synthesized using precipitation method and tested for fluoride removal from drinking water. The effect of various parameters like complexation and precipitation time, lanthanum loading and ammonia strength on fluoride removal have been studied. It is observed that the parameters for the synthesis of LCB have significant influence on development of LCB and in turn on fluoride removal capacity. The optimal condition for synthesis of LCB includes lanthanum loading: 10 wt%, complexation time: 60 min, precipitation time: 60 min, drying temperature: 75 °C for 72 h. The maximum fluoride adsorption capacity of LCB was found to be 4.7 mg/g and negligible release of lanthanum ion was observed. XRD analysis shows the presence of lanthanum hydroxide and amorphous nature of LCB. SEM of LCB shows the presence of oval lanthanum hydroxide particles spread over the chitosan matrix. Fluoride adsorption capacity has been calculated by applying Langmuir and Freundlich isotherms. The comparative study suggests that LCB shows four times greater fluoride adsorption capacity than the commercially used activated alumina.     

Adsorption of tannic acid, humic acid, and dyes from water using the composite of chitosan and activated clay

Chitosan is a well-known excellent adsorbent for a number of organics and metal ions, but its mechanical properties and specific gravity should be enhanced for practical operation. In this study, activated clay was added in chitosan slurry to prepare composite beads. The adsorption isotherms and kinetics of two organic acids (tannic acid, humic acid) and two dyes (methylene blue, reactive dye RR222) using composite beads, activated clay, and chitosan beads were compared. With composite beads as an adsorbent, all the isotherms were better fitted by the Freundlich equation. The adsorption capacities with composite beads were generally comparable to those with chitosan beads but much larger than those with activated clay. The pseudo-first-order and pseudo-second-order equations were then screened to describe the adsorption processes. It was shown that the adsorption of larger molecules such as tannic acid (MW, 1700 g mol(-1)), humic acid, and RR222 from water onto composite beads was better described by the pseudo-first-order kinetic model. The rate parameters of the intraparticle diffusion model for adsorption onto such adsorbents were also evaluated and compared to identify the adsorption mechanisms.     

Adsorption of chromium from aqueous solution using chitosan beads

A basic investigation on the removal of Cr(III) and Cr(VI) ions from aqueous solution by chitosan beads was conducted in a batch adsorption system. The chitosan beads were prepared by casting an acidic chitosan solution into an alkaline solution. The influence of different experimental parameters; pH, agitation period and different concentration of Cr(III) and Cr(VI) ions was evaluated. A pH 5.0 was found to be an optimum pH for Cr(III) adsorption, and meanwhile pH 3.0 was the optimum pH for the adsorption of Cr(VI) onto chitosan beads. The Langmuir and Freundlich adsorption isotherm models were applied to describe the isotherms and isotherm constants for the adsorption of Cr(III) and Cr(VI) onto chitosan beads. Results indicated that Cr(III) and Cr(VI) uptake could be described by the Langmuir adsorption model. The maximum adsorption capacities of Cr(III) and Cr(VI) ions onto chitosan beads were 30.03 and 76.92 mg g⁻¹, respectively. Results showed that chitosan beads are favourable adsorbents. The Cr(III) and Cr(VI) ions can be removed from the chitosan beads by treatment with an aqueous EDTA solution.     

The effects of pH and ionic strength on fulvic acid uptake by chitosan hydrogel beads

The objective of this work is to investigate the effects of pH and ionic strength on the adsorption capacity for fulvic acid (FA) by chitosan hydrogel beads. The results indicated that the sorption amount increased with decreasing pH and increasing ionic strength concentration. The sorption isotherms were well described by using non-linear Langmuir, Freundlich and Redliche–Peterson equation. The adsorption kinetics of FA onto chitosan hydrogel beads could be described by pseudo-second-order rate model. The extent of FA removal in the presence of other ions decreases in the order Ca²⁺ > Mg²⁺ > Na⁺ ≈ K⁺ and Cl⁻ > NO₃⁻ > CO₃²⁻. FTIR along with XPS analyses revealed the amine groups on the beads were involved in the sorption of FA and the organic complex between the protonated amino groups and FA was formed after FA uptake. Sorption mechanisms including electrostatic interaction and surface complexation were found to be involved in the complex sorption of FA on the chitosan hydrogel beads.     

Enhanced and selective adsorption of mercury ions on chitosan beads grafted with polyacrylamide via surface-initiated atom transfer radical polymerization

Enhanced and selective removal of mercury ions was achieved with chitosan beads grafted with polyacrylamide (chitosan-g-polyacrylamide) via surface-initiated atom transfer radical polymerization (ATRP). The chitosan-g-polyacrylamide beads were found to have significantly greater adsorption capacities and faster adsorption kinetics for mercury ions than the chitosan beads. At pH 4 and with initial mercury concentrations of 10-200 mg/L, the chitosan-g-polyacrylamide beads can achieve a maximum adsorption capacity of up to 322.6 mg/g (in comparison with 181.8 mg/g for the chitosan beads) and displayed a short adsorption equilibrium time of less than 60 min (compared to more than 15 h for the chitosan beads). Coadsorption experiments with both mercury and lead ions showed that the chitosan-g-polyacrylamide beads had excellent selectivity in the adsorption of mercury ions over lead ions at pH < 6, in contrast to the chitosan beads, which did not show clear selectivity for either of the two metal species. Mechanism study suggested that the enhanced mercury adsorption was due to the many amide groups grafted onto the surfaces of the beads, and the selectivity in mercury adsorption can be attributed to the ability of mercury ions to form covalent bonds with the amide. It was found that adsorbed mercury ions on the chitosan-g-polyacrylamide beads can be effectively desorbed in a perchloric acid solution, and the regenerated beads can be reused almost without any loss of adsorption capacity.     

氟离子对无胺法合成高硅丝光沸石的结构导向作用

 在含氟无胺体系中合成了高硅丝光沸石，研究了合成条件对丝光沸石产物的影响．结果表明，投料n（SiO2）／n（Al2O3）＝20～200时，控制晶化条件可得到高硅丝光沸石纯相．由含氟无胺体系中丝光沸石的热力学稳定相区可见，氟离子的引入对方沸石的生成的相区无影响，ZSM－5和镁碱沸石生成的相区消失，丝光沸石生成的相区扩大，石英生成的相区缩小，且基本上变为两相共存区．合成产物丝光沸石的硅铝比随着氟硅比的升高同步增大，证明氟离子在无胺合成高硅丝光沸石时具有结构导向作用．     

Calorimetric studies of the association of chitin and chitosan with sodium dodecyl sulfate

The interaction of hydrophobic chitin and chitosan with sodium dodecyl sulfate (SDS) has been studied by titration calorimetry at 298.15K. The nature of interaction of the surfactant and biopolymers was followed by enthalpy interaction profiles. The mixing enthalpy curves were determined by mixing SDS solutions above their critical micelle concentration with chitin and chitosan suspensions in different concentrations. The Gibbs free energy of aggregation values were -23.21, -22.71 and -21.53 kJ mol(-1) for chitin in 0.02, 0.05 and 0.1% concentration, respectively, and 28.30, 24.38 and 24.20 kJ mol(-1) for chitosan in 0.02, 0.05 and 0.1% concentration, respectively. The critical aggregation concentration (cac) obtained by calorimetric data gave 6.32, 7.07 and 9.14 mmol kg(-1) in 0.02, 0.05 and 0.1% concentration, respectively, for chitin and 2.09, 4.91 and 5.11 mmol kg(-1) for chitosan in 0.02, 0.05 and 0.1% concentration, respectively.     

ZSM-5分子筛填充壳聚糖膜的制备与性能研究

采用液相共混的方法制备了ZSM-5分子筛填充壳聚糖膜.扫描电镜表征表明分子筛在膜中分散均匀,膜表面没有明显缺陷.考察了填充膜在碳酸二甲酯/甲醇混合液中的溶胀和吸附行为,探讨了填充膜中分子筛含量及操作温度对渗透汽化膜分离性能的影响.结果表明膜优先吸附甲醇,其分离性能主要由溶解过程控制;随着膜中分子筛含量的增加,膜的溶胀度增大,渗透通量大幅度提高;渗透通量与操作温度符合Arrhenius关系式.与壳聚糖均质膜相比,ZSM-5分子筛填充壳聚糖膜对甲醇和碳酸二甲酯混合物具有更好的分离效果.     

Immobilization of cellulose extracted from Robinia Pseudoacacia seed fibers onto chitosan: Chemical characterization and study of methylene blue removal

The design of economical adsorbents to remove pollutants from contaminated water is attracting more attention. In this study, cellulose was successfully extracted from Robinia Pseudoacacia seed fibers and immobilized onto chitosan beads. The prepared spherical beads were then used for the biosorption of methylene blue dye from aqueous media. Samples were investigated using several analytical methods, namely FT-IR, XRD, EDX, SEM, and TGA analyses. The adsorption experiments showed that combining cellulose with chitosan improved the removal of methylene blue. The maximum uptake amount of methylene blue using cellulose–chitosan composite beads was 55 mg/g. However, it was about 35 mg/g at 20 °C for chitosan beads. The kinetic data complied strongly with the pseudo-second order equation, suggesting that the biosorption phenomenon has predominantly a chemical nature. Overall, the current study has shown a promising technique to design new adsorbents from abundant natural polymers for eliminating cationic dyes from water.     

Studies in the development of nateglinide loaded calcium alginate and chitosan coated calcium alginate beads

Nateglinide loaded alginate-chitosan beads were prepared by ionic gelation method for controlling the drug release by using various combinations of chitosan and Ca2+ as cation and alginate as anion. IR spectrometry, scanning electron microscopy, differential scanning calorimetry and X-ray powder diffractometry were used to investigate the physicochemical characteristics of the drug in the bead formulations. The calcium content in beads was determined by atomic absorption spectroscopy. The swelling ability of the beads in different media (pH 1.2, 4.5, 6.8) has been found to be dependent on the presence of polyelectrolyte complex of the beads and the pH of the media. The ability to release the Nateglinide was examined as a function of chitosan and calcium chloride content in the gelation medium. It is evident that the rate of drug release and its kinetics could be controlled by changing the chitosan and the calcium chloride concentrations. Calcium alginate beads released more than 95% of drug with in 8 h; whereas coated beads sustained the drug release and released only 75-80% of drug. The drug release mechanism analyzed indicates that the release follows either "anomalous transport" or "case-II transport".     

Microscopic examination of chitosan-polyphosphate beads with entrapped spores of the biocontrol agent, Streptomyces melanosporofaciens EF-76.

Spores of the biocontrol agent, Streptomyces melanosporofaciens EF-76, were entrapped by complex coacervation in beads composed of a macromolecular complex (MC) of chitosan and polyphosphate. A proportion of spores entrapped in beads survived the entrapment procedure as shown by treating spores from chitosan beads with a dye allowing the differentiation of live and dead cells. The spore-loaded chitosan beads could be digested by a chitosanase, suggesting that, once introduced in soil, the beads would be degraded to release the biocontrol agent. Spore-loaded beads were examined by optical and scanning electron microscopy because the release of the biological agent depends on the spore distribution in the chitosan beads. The microscopic examination revealed that the beads had a porous surface and contained a network of inner microfibrils. Spores were entrapped in both the chitosan microfibrils and the bead lacuna.     

Kinetic study of chitosan‐tripolyphosphate complex reaction and acid‐resistive properties of the chitosan‐tripolyphosphate gel beads prepared by in‐liquid curing method

Chitosan gel beads were prepared using an in‐liquid curing method by the ionotropic crosslinking with sodium tripolyphosphate. Crosslinking characteristics of the chitosan‐TPP beads were improved by the modification of in‐liquid curing mechanism of the beads in TPP solution. Chitosan gel beads cured in pH value lower than 6 were really ionic‐crosslinking controlled, whereas chitosan gel beads cured in pH values higher than 7 were coacervation‐phase inversion controlled accompanied with slightly ionic‐crosslinking dependence. According to the result, significantly increasing the ionic‐crosslinking density of chitosan beads could be achieved by transferring the pH value of the curing agent, TPP, from basic to acidic. The swelling behavior of various chitosan beads in acid appeared to depend on the ionic‐crosslinking density of the chitosan‐TPP beads that were deeply affected by the curing mechanism of the beads. The mechanism of chitosan‐TPP beads swollen in weak acid was chain‐relaxation controlled, while the mechanism of chitosan‐TPP beads swollen in strong acid seem to be not only chain‐relaxation but also chain‐scission controlled. Chitosan‐TPP beads prepared in acidic TPP solution decreased the chain‐scission ability due to the increase of ionic crosslinking density of the beads. By the transition of curing mechanism, the swelling degree of chitosan‐TPP beads was depressed, and the disintegration of chitosan‐TPP beads would not occur in strong acid. The mechanism of ionic‐crosslinking reaction of chitosan beads could be investigated by an unreacted core model, and the curing mechanism of the chitosan beads is mainly diffusion controlled when higher than 5% of chitosan was employed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1551–1564, 1999     

Effect of MWCNTs Doping on the Morphology,Structure and Properties of Chitosan Beads

A series of chitosan (CS)/multi-walled carbon nanotubes (MWCNTs) composite hydrogel beads with different MWCNTs contents are prepared via a solution blending method. The effects of MWCNTs on the morphology, structure and properties of chitosan beads have been investigated. Digital pictures show that the composite beads obtained are of good morphological characteristics, and the SEM micrographs indicate that the addition of MWCNTs into CS beads made the surface of the CS/MWCNTs hydrogel beads contain much larger wrinkles. Fourier transform infrared spectra (FTIR) show that the main chain of CS bead is not changed, but there are some electrostatic interactions between CS and MWCNTs, which lead to very significant changes in the crystallization behavior of CS and MWCNTs. The thermal stability of CS/MWCNTs composites at high temperatures is increased with the existence of MWCNTs, indicating a possible electrostatic interaction between MWCNTs and CS lattices to limit the motivation of CS. The adsorption capacity of CS beads doped with a lower percentage of MWCNTs (0.02 wt%) for acid fuchsin is 112.76 mg/g, higher than that of pure CS beads (35.62 mg/g).     

氨基酸修饰壳聚糖对胆固醇的吸附作用

通过将不同脱乙酰度的壳聚糖粉末与戊二醛交联,再经苯丙氨酸和色氨酸修饰,得到了两种珠状壳聚糖吸附剂,并进而研究了有关吸附剂对胆因醇的吸附性能。实验表明,交联壳聚糖珠对ＣＨＯ的吸附能力比壳聚糖粉末降低,而经不同氨基酸修饰后的壳聚糖珠对ＣＨＯ吸附能力提高,用Ｐｈｅ修饰比用Ｔｒｙ修饰的珠吸附性能更好些。     

Uncertainty of measurement for the determination of fluoride in water and wastewater by direct selective electrode potentiometry

A procedure to estimate the uncertainty of measurement applied to the fluoride determination of waters and wastewaters matrices by selective electrode potentiometry was implemented based on Eurachem Guide. The major sources of uncertainty were identified as the calibration standard solutions, fluoride concentration obtained by potential interpolation of the regression line and the precision. However the relative uncertainties depend on the anion concentration levels. The methodology proposed was presented to two fluoride concentration levels that are in the range of surface water samples (C _sample=1.12 mgF l⁻¹) and of wastewater matrices (C _sample=101.4 mgF l⁻¹). The expanded uncertainties calculated were 0.40 and 9.1 mg l⁻¹ for low and high concentration levels, respectively, using the reproducibility uncertainty as precision evaluation. The relative expanded uncertainty was around ±10% for the highest concentration, which can be considered acceptable for the ion selective electrode potenciometric methods and ±36% for the lowest concentrations. In this case the sample fluoride content is very close to the limit of quantification which has a relative uncertainty of about ±30%. If the repeatability was used in spite of duplicate analysis the same conclusions were obtained (C _sample=1.12 ± 0.39 mgF l⁻¹ and C _sample=101.4 ± 7.0 mgF l⁻¹). Although the calculated expanded uncertainties and consequently the combined uncertainty, do not vary significantly in the cases where it was used the repeatability or reproducibility for evaluating the precision, each relative variances uncertainty contributions do. When the repeatability is used to determine the combined uncertainty, the CSS and uncertainties contributions are the most dominant ones. However, if reproducibility is used, relative uncertainty variance contributions are distributed among CSS, C _F, and precision. In both cases, the contribution increases and r _CSS contribution decreases with the increasing of the concentration level. The precision variance contribution is only significant in the case where the reproducibility is used, and increases with the increasing of the concentration level. The uncertainty in the result calculated using the proposed methodology (C _sample ± U _sample = 2.17 ± 0.42 mgF l⁻¹) is in satisfactory agreement with the estimated expanded uncertainty obtained using the relative reproducibility standard deviation obtained in interlaboratory studies ().     

Comparative Adsorption of Lead(II) on Flake and Bead‐Types of Chitosan

The adsorption of Pb(II) ions from aqueous solutions by chitosan flakes and beads was studied. The chitosan beads were prepared by casting an acidic chitosan solution into alkaline solution. Experiments were carried out as a function of pH, agitation period and initial concentration of Pb²⁺ ions. The uptake of Pb²⁺ ions from aqueous solution was determined from changes in concentration as measured by atomic absorption spectroscopy. The maximum uptake of Pb²⁺ ions on chitosan beads was greater than that on chitosan flakes. Adsorption isothermal data could be interpreted by the Langmuir equation. The experimental data of the adsorption equilibrium from Pb²⁺ ion solutions correlated well with the Langmuir isotherm equation. SEM analyses were also conducted for visual examination of the chitosan flakes and beads. Physical properties including surface area and average pore diameter were characterized by N₂ adsorption experiment.