Elaboration and characterization of poly (acrylic acid-co-crotonic acid) copolymers: Application to extraction of metal cations Pb(II), Cd(II) and Hg(II) by complexation in aqueous media

Acylation modification of konjac glucomannan and its adsorption of Fe (Ⅲ) ion

A biodegradable adsorbent, modified konjac glucomannan (MKGM), was prepared by konjac glucomannan (KGM) acylated with phthalic anhydride catalyzed using concentrated sulfuric acid. The modified conditions such as reaction temperature, mass ratio of phthalic anhydride to KGM, catalyst dosage and reaction time were investigated, respectively. MKGM exhibited preferable adsorption performance for the removal of Fe (Ⅲ) ion. The adsorption behavior was discussed using the Langmuir and Freundlich isotherm models. The results showed that the Freundlich linear model was suitable for describing the adsorption process of Fe (Ⅲ). The maximum adsorption capacity of MKGM for Fe (Ⅲ) ion was 31.87 mg g^-1 at 298 K. The kinetics studies suggested that adsorption process followed the pseudo-second-order model and the adsorption process was mainly controlled by both surface reactivity and intra-particle diffusion. Together with the evaluation of the thermodynamic parameters such as Gibbs free energy, enthalpy and entropy changes, the results indicated that the adsorption process of Fe (Ⅲ) was endothermic, feasible, and spontaneous in nature. Hence, as a bioadsorbent, the MKGM has a promising potential for the removal of Fe (Ⅲ) ion from aqueous solutions.

Effect of Grafted Hydroquinone on the Acid-Base Properties of Poly(acrylic acid) in the Presence of Copper (II)

Potentiometric titration of poly(acrylic acid) and hydroquinone-functionalized poly(acrylic acid) was conducted in the presence of copper (II). The effects of hydroquinone functionalizing and copper (II) complexing on the potentiometric titration of poly(acrylic acid) were studied in an ionic environment and in its absence. Henderson-Hasselbalch equation was applied to assess its validity for this titration. Coordination number and the stability constants of the copper- (II-)complexed polymers were determined, and results showed the formation of mostly monodentate and bidentate copper- (II-)polymer complexes.

Non-solvent-based pretreatment of poly(3-hydroxybutyrate) for improved bio-based crotonic acid production

Production of high purity crotonic acid from bio-based resources is an alternative to petroleum-based synthesis and omits the need for a purification process.

Bio-based products from solar energy and carbon dioxide

Producing bio-based products directly from CO₂ and solar energy is a desirable alternative to the conventional biorefining that relies on biomass feedstocks. The production paradigm is based on an artificial photosynthetic system that converts sunlight to electricity and H₂ via water electrolysis. An autotrophic H₂-oxidizing bacterium fixes CO₂ in dark conditions. The assimilated CO₂ is stored in bacterial cells as polyhydroxybutyrate (PHB), from which a range of products can be derived. Compared with natural photosynthesis of a fast-growing cyanobacterium, the artificial photosynthetic system has much higher energy efficiency and productivity of bio-based products. The new technology looks promising because of possible cost reduction in feedstock, equipment, and operation.

Metal ions: driving the orderly assembly of polyelectrolytes at a hydrophobic surface

The accumulation of polyelectrolytes at the interface between water and nonpolar fluids is an important process in both environmental and biological systems. For instance, polyelectrolytes such as humic acids are highly charged molecules that play a role in the remediation of water contaminated by oil, and the adsorption of other polyelectrolytes such as proteins and DNA to cellular surfaces is essential in biological processes. The properties of these naturally occurring polyelectrolytes are highly tunable and depend strongly on the binding of metal ions commonly found in environmental and biological systems. While the metal complexation behaviors of many polyelectrolytes and biomolecules are well characterized in bulk solution, this work shows in molecular detail that the behavior of a common polyelectrolyte in the presence of metal ions can be quite different when it adsorbs to a hydrophobic-aqueous liquid interface. In these studies, vibrational sum frequency spectroscopy and interfacial tension measurements conducted on poly(acrylic acid) (PAA) at a model oil-water interface show how small amounts of monovalent and divalent cations significantly alter the interfacial conformation of PAA at the interface and act to enhance its interfacial adsorption. The results provide important new insights that have direct relevance for understanding the effect of metal ions on the adsorption of charged macromolecules to a hydrophobic-aqueous boundary layer, specifically in biological and environmental systems.

Effective removal of heavy metal ions Cd2+, Zn2+, Pb2+, Cu2+ from aqueous solution by polymer-modified magnetic nanoparticles

We prepared novel Fe(3)O(4) magnetic nanoparticles (MNPs) modified with 3-aminopropyltriethoxysilane (APS) and copolymers of acrylic acid (AA) and crotonic acid (CA). The MNPs were characterized by transmission electron microscopy, X-ray diffraction, infra-red spectra and thermogravimetric analysis. We explored the ability of the MNPs for removing heavy metal ions (Cd(2+), Zn(2+), Pb(2+) and Cu(2+)) from aqueous solution. We investigated the adsorption capacity of Fe(3)O(4)@APS@AA-co-CA at different pH in solution and metal ion uptake capacity as a function of contact time and metal ion concentration. Moreover, adsorption isotherms, kinetics and thermodynamics were studied to understand the mechanism of the synthesized MNPs adsorbing metal ions. In addition, we evaluated the effect of background electrolytes on the adsorption. Furthermore, we explored desorption and reuse of MNPs. Fe(3)O(4)@APS@AA-co-CA MNPs are excellent for removal of heavy metal ions such as Cd(2+), Zn(2+), Pb(2+) and Cu(2+) from aqueous solution. Furthermore, the MNPs could efficiently remove the metal ions with high maximum adsorption capacity at pH 5.5 and could be used as a reusable adsorbent with convenient conditions.

Study of Konjac Glucomannan Esterification with Dicarboxylic Anhydride and Effect of Degree of Esterification on Water Absorbency

Dicarboxylic anhydride esterified Konjac glucomannan (DCKGM) was prepared to reduce the unusual water absorbency of native Konjac Glucomannan (KGM). The dependence of degree of substitution (DS) on the reaction conditions and influence of the DS on water absorbency were studied. The esterification was conducted using refluxing KGM in hot acetic acid which contains phthalic anhydride and pyridine catalyst. The chemical structure and characteristic of DCKGM were analyzed by GPC-MALLS and FI-IR. The results showed that the water absorbency for DCKGM is inversely proportional to DS increase. DCKGM may be a promising biomaterial in application of drug carrier, heavy metal ion adsorption and functional packing materials.

Adsorption characteristics of Ni(II) onto MA-DTPA/PVDF chelating membrane

The melamine-diethylenetriaminepentaacetic acid/polyvinylidene fluoride (MA-DTPA/PVDF) chelating membrane bearing polyaminecarboxylate groups was prepared for the removal of Ni(II) from wastewater effluents. The membrane was characterized by SEM, (13)C NMR and FTIR techniques. Quantitative adsorption experiments were performed in view of pH, contact time, temperature, the presence of Ca(II) and lactic acid as the controlling parameters. Adsorption kinetics and equilibrium were examined regarding the single Ni(II) system, binary Ni(II) and Ca(II) system and nickel-lactic acid complexes system. The desorption efficiency was also evaluated, and the adsorption mechanism was suggested based on experimental data. The results show that the sorption kinetics fit well to Lagergren second-order equation and the isotherms can be well described by Langmuir model. At 298 K, the second-order rate constant is calculated to be 4.171, 11.39, 6.203 cm(2)/(mg min) and the equilibrium uptake is 0.0264, 0.0211 and 0.0216 mg/cm(2) in the aforementioned three systems. The distribution coefficient of Ni(II) slowly decreases from 4.27 to 2.72, and the separation factor (f(Ni(II)/Ca(II))) increases from 3.10 to 8.46 when the initial Ca(II) concentration varies from 20 to 200mg/L. This reveals the chelating membrane shows more affinity for Ni(II) than Ca(II) ions. In the studied range of lactic acid concentration, Ni(II) uptake decreases with the maximum ratio of 10%. Chemical bonding (chelation) dominates in the adsorption process, and the negative ΔG° and ΔH° indicate the spontaneous and exothermic nature of adsorption.

Removal of copper and lead from aqueous solution by carboxylic acid functionalized deacetylated konjac glucomannan

Carboxylic acid functionalized deacetylated konjac glucomannan was synthesized by free radical graft copolymerization of methyl acrylate (MA) and methyl methacrylate (MMA) onto the backbone of deacetylated konjac glucomannan with subsequent chemical activation of the ester groups in the side chains of the resulting graft copolymer by sodium hydroxide. Effects of sodium hydroxide concentration and hydrolyzed time on the conversion of ester groups into carboxylic acid groups were studied. A comprehensive adsorption study of Cu(2+) and Pb(2+) ions from aqueous solution was also conducted regarding the effects of initial pH, adsorbent dosage, time, and initial concentration. The new konjac glucomannan adsorbent offered high removal efficiency, fast adsorption rate and high uptake capacity for Cu(2+) and Pb(2+) ions. The maximum removal efficiency at pH 5.0 was found to 98% for Cu(2+) and 99% for Pb(2+) ions. The kinetic data were fitted well to pseudo-second-order model. The maximum uptake capacity of Cu(2+) and Pb(2+) ions onto carboxylic acid functionalized deacetylated konjac glucomannan was found to 64.5 mg g(-1) and 191.3 mg g(-1), respectively. The isotherm adsorption data was well described by the Langmuir isotherm model.