Adsorption of Cu(II) ion from aqueous solutions on hydrogel prepared from Konjac glucomannan

Effect and characterization of konjac glucomannan on xanthan gum/κ-carrageenan/agar system

A mixed polysaccharide system is an important strategy to improve the performance of a single polysaccharide. Herein, quaternary polysaccharide gels were prepared by konjac glucomannan (KGM), xanthan gum (XG), κ-carrageenan (κ-CA), and agar (AR). The effects of KGM were evaluated by combining water holding capacity (WHC), rheological analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and texture profile analysis (TPA). More KGM gradually increased the springiness of the compounded gels. WHC increased and then decreased with the addition of KGM, performing best at KGM4 (KGM: κ-CA:XG:AR = 2:2:1:2). Rheological analysis showed that the compounded gels exhibited a pseudoplastic characteristic of shear thinning, KGM endowed the gel with a stronger shear thinning behavior and improved the solid-like nature of the gels at high temperatures. The thermal stability of the composite gel was improved by the participation of KGM. FTIR analysis showed that the interactions were mainly related to intermolecular hydrogen bonds and acetyl groups. The microscopic morphology of KGM4 was significantly continuous, smooth, and compact, exhibiting the best practical performance and taking the maximum advantage.

Removal of Cu (II) by calcinated electroplating sludge

Electroplating sludge consists of various heavy metal oxides, which may be utilized as adsorbent to remove Cu (II) present in aqueous environment. This study evaluated the adsorption performance of calcinated electroplating sludge. The adsorption isotherm based on Langmuir equation proved that calcinated electroplating sludge had a higher adsorption performance than raw electroplating sludge, with maximum adsorption capacity 92 mg/g and 76.34 mg/g, respectively. Findings of the conducted kinetic study revealed that both surface adsorption and intra-particular diffusion were involved during the adsorption process. Moreover, the comparison between the experimental and calculated data of equilibrium adsorption capacity demonstrated that the pseudo second-order kinetic equation fitted well with 38.31 mg/g of calcinated sludge and 33.66 mg/g of raw sludge, approximate to real-world data. Furthermore, adsorption mechanism research demonstrated that while OH group plays a vital role in raw sample, Ca²⁺, in addition to OH group, was involved in ion exchange in calcinated sample.

RETRACTED: Preparation of molecularly imprinted metal-organic frameworks by in situ self-assembly template strategy for selective adsorption of antibiotics

This article has been retracted: please see Elsevier Policy on Article Withdrawal ( https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Authors. The corresponding author informed the journal that there were severe problems with the testing instrument that rendered the subsequent conclusions invalid. The authors apologise for any inconvenience caused.

Modified xanthan gum for methyl orange uptake: Kinetic, isotherm, and thermodynamic behaviors

A novel hydrogel, named XGTTE, was prepared by modification of acrylamide and trimethylolpropane triglycidyl ether (TTE) on xanthan gum (XG). XGTTE was utilized as an adsorbent to remove methyl orange (MO) from an aqueous solution. Functional groups present in the external surface of XGTTE, such as carboxyl, hydroxyl, and amino groups, were identified, and these functional groups are responsible for the occurrence of the mechanism for MO adsorption. The structure of XGTTE after MO adsorption became more disordered. The adsorption dynamics and isotherms of MO onto XGTTE conformed well to the pseudo-second-order kinetics and the Freundlich equation, indicated that the adsorption included physical and chemical adsorption, with electrostatic interaction and hydrogen-bonding interaction. The calculated values of the thermodynamic parameters, such as changes in enthalpy (ΔH) and entropy (ΔS) were 27.30 kJ/mol and 125.63 J/mol/K, respectively. The changes in free energy (ΔG) were - 9.53 kJ/mol (293.15 K), -10.16 kJ/mol (298.15 K), -10.78 kJ/mol (303.15 K), -11.41 kJ/mol (308.15 K), and - 12.04 kJ/mol (313.15 K), respectively, indicating the adsorption process is endothermic, spontaneous, and entropic. The maximum adsorption capacities of XGTTE2, XGTTE3, XGTTE4, XGTTE5, and XGTTE6 for MO were 18.62 ± 0.99, 21.92 ± 0.84, 28.60 ± 0.84, 29.56 ± 0.99, and 12.38 ± 0.84 mg/g, respectively.

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.

Assembly of Polyacrylamide-Sodium Alginate-Based Organic-Inorganic Hydrogel with Mechanical and Adsorption Properties

Hydrogels have been widely used in water purification. However, there is not much discussion and comparison about the effects of different nanofillers on the reinforcement and adsorption performances of hydrogels, which can be subjected to rapid water flow and possess strong adsorption ability. In this work, polyacrylamide (PAAM)-sodium alginate (SA) interpenetrating polymer network-structured hydrogels were prepared by in situ polymerization. PAAM formed the first flexible network and SA constructed the second rigid network. Three kinds of inorganic nanoparticles including carbon nanotubes (CNTs), nanoclays (NCs), and nanosilicas (NSs) were incorporated into a PAAM-SA matrix via hydrogen bond. The obtained hydrogels exhibited a macroporous structure with low density (≈1.4 g/cm³) and high water content (≈83%). Compared with neat PAAM-SA, the hydrogels with inorganic nanoparticles possessed excellent mechanical strengths and elasticities, and the compression strength of PAAM-SA-NS reached up to 1.3 MPa at ε = 60% by adding only 0.036 g NS in a 30 g polymer matrix. However, CNT was the best filler to improve the adsorption capacity owing to its multi-walled hollow nanostructure, and the adsorption capacity of PAAM-SA-CNT was 1.28 times higher than that of PAAM-SA. The prepared hydrogels can be potential candidates for use as absorbents to treat wastewater.

Modified xanthan gum for crystal violet uptake: kinetic, isotherm, and thermodynamic behaviors

Modified xanthan gum (XG-AM-TTE) was employed as an adsorbent to study the adsorption behavior, thermodynamics and kinetics of crystal violet (CV) from an aqueous solution. Fourier transform infrared spectroscopy analysis indicates that the functional groups present in the adsorbent, such as carboxyl, ester and hydroxyl groups, are included on the external surface of the material, and these groups are potential active sites for interaction with CV. According to X-ray diffraction results, the structure of XG-AM-TTE after CV adsorption became more disordered, and the microstructure change is an indication of effective adsorption of CV to the surface, with CV becoming remarkably dispersed in the adsorbent according to the scanning electron microscopy observations. The adsorption kinetics and adsorption equilibrium were best described by the pseudo-second-order model and Freundlich isotherms, respectively. The thermodynamic parameters, as the Gibbs-free energy (ΔG), enthalpy (ΔH) and entropy (ΔS), indicated that the adsorption is a spontaneous, endothermic and entropy increase process. The maximum adsorption capacity of XG-AM-TTE was 183 ± 12 mg/g, suggesting that XG-AM-TTE is an efficient adsorbent.

Effects of deacetylation of konjac glucomannan on the physico-chemical properties of surimi gels from silver carp (Hypophthalmichthys molitrix)

This work studied the effects of KGM with different degrees of deacetylation (DDs) on the physicochemical properties of silver carp (Hypophthalmichthys molitrix) surimi gels. Compared with KGM, deacetylated KGM (DKGM) weakened the water-holding capacity, but increased the gel strength of surimi gels. The storage modulus (G′) and loss modulus (G′′) of surimi showed an upward trend, and the aggregation rate of surimi with DKGM changed. The number of ionic bonds of mixed surimi gels increased on the whole, but those of hydrogen bonds declined; a hydrophobic interaction was the main driving force, and improved with the DDs of DKGM. FT-IR results indicated that the deacetylation of KGM had a slight influence on the secondary structure of the proteins. SDS-PAGE results showed that DKGM enhanced the intensity of the main heavy chains of myosin and actin. Examination of the network structure of the surimi gels revealed that DKGM might combine around the filaments of myofibrillar proteins like a rosary through hydrophobic interactions and hydrogen bonding. As a consequence, the myfibrillar protein aggregation was changed and the microstructures of the surimi became more compact and fibrous. The results indicated that the deacetylation of KGM led to an increase in hydrophobicity, which influenced the hydrophobic interaction of the myofibrillar proteins. As a result, the aggregation of the myofibrillar proteins was promoted and the physico-chemical properties of the surimi gel were improved.

This work studied the effects of KGM with different degrees of deacetylation (DDs) on the physicochemical properties of silver carp (Hypophthalmichthys molitrix) surimi gels.

A Review on Konjac Glucomannan Gels: Microstructure and Application

Konjac glucomannan (KGM) has attracted extensive attention because of its biodegradable, non-toxic, harmless, and biocompatible features. Its gelation performance is one of its most significant characteristics and enables wide applications of KGM gels in food, chemical, pharmaceutical, materials, and other fields. Herein, different preparation methods of KGM gels and their microstructures were reviewed. In addition, KGM applications have been theoretically modeled for future uses.