Highly efficient and selective removal of anionic dyes from aqueous solutions using polyacrylamide/peach gum polysaccharide/attapulgite composite hydrogels with positively charged hybrid network

To avoid the weakness (lower adsorption rate and selectivity) of peach gum polysaccharide (PGP) and improve the adsorption performance of polyacrylamide (PAAm) hydrogel (lower adsorption capacity), in the present work, the PGP was chemically tailored to afford ammoniated PGP (APGP) and quaternized PGP (QPGP), and attapulgite (ATP) was bi-functionalized with cation groups and carbon‑carbon double bond. Then, PAAm/APGP and PAAm/QPGP/ATP hydrogels were synthesized via redox polymerization. The synthesis procedure and properties of hydrogels were traced by FTIR, SEM, XPS, TGA, TEM, and BET methods, and the dye adsorption performance of the hydrogels was evaluated using the new coccine (NC) and tartrazine (TTZ) aqueous solutions as the model anionic dyes. Effects of initial dye concentration, pH, and ionic strength on the adsorption were investigated. Compared with PAAm/APGP hydrogel, PAAm/APGP/ATP hydrogel exhibits higher adsorption rate, superior adsorption capacity, stability, and selectivity towards anionic dye. The adsorption process of PAAm/QPGP/ATP hydrogel reached equilibrium in about 20 min and followed the pseudo-second-order kinetic model and Langmuir isotherm. The adsorption capacities towards NC and TTZ of PAAm/QPGP/ATP hydrogel were calculated as 873.235 and 731.432 mg/g. This hydrogel adsorbent originating from PAAm, PGP, and ATP shows great promise for application in practical water treatment.

Quaternization of cassava starch and determination of antimicrobial activity against bacteria and coronavirus

This study describes the novel development of quaternized cassava starch (Q-CS) with antimicrobial and antiviral properties, particularly effective against the MHV-3 coronavirus. The preparation of Q-CS involved the reaction of cassava starch (CS) with glycidyltrimethylammonium chloride (GTMAC) in an alkaline solution. Q-CS physicochemical properties were determined by FTIR, NMR, elemental analysis, zeta potential, TGA, and moisture sorption. FTIR and NMR spectra confirmed the introduction of cationic groups in the CS structure. The elemental analysis revealed a degree of substitution (DS) of 0.552 of the cationic reagent on the hydroxyl groups of CS. Furthermore, Q-CS exhibited a positive zeta potential value (+28.6 ± 0.60 mV) attributed to the high positive charge density shown by the quaternary ammonium groups. Q-CS demonstrated lower thermal stability and higher moisture sorption compared to CS. The antimicrobial activity of Q-CS was confirmed against Escherichia coli (MIC = 0.156 mg mL-1) and Staphylococcus aureus (MIC = 0.312 mg mL-1), along with a remarkable ability to inactivate 99% of MHV-3 coronavirus after only 1 min of direct contact. Additionally, Q-CS showed high cell viability (close to 100%) and minimal cytotoxicity effects, guaranteeing its safe use. Therefore, these findings indicate the potential use of Q-CS as a raw material for antiseptic biomaterials.

Synthesis of graphite/rGO-modified fungal hyphae for chromium (VI) bioremediation process

Bioremediation is a promising technology that can eliminate the drawbacks of conventional treatment methods in removing harmful toxic metals including chromium(VI). Therefore, in this study, fungal hyphae modified with graphite and reduced graphene oxide were synthesized and assessed for their potential to bioremediate heavy metals for the first time in the literature. The effects of the carbon-based materials on microbial structure were characterized using scanning electron microscopy analysis. Thermogravimetric, RAMAN, X-ray diffraction, and enzymatic analyzes were performed to determine the role of functional groups. In addition, batch adsorption experiments utilizing response surface methodology were conducted to optimize operating parameters such as time (1-11 h), chromium (10-50 mg/L), and graphite/reduced graphene oxide (0.1-1 g/L). The maximum adsorption capacity with the graphene fungal hyphae was determined to be 568 mg.g-1, which is 9.7 times that of the crude fungal hyphae. The Cr(VI) removal for fungal hyphae-graphite and fungal hyphae-reduced graphene oxide biocomposites was 98.25% and 98.49%, respectively. The isothermal and kinetic results perfectly matched the 2nd order pseudo-model and Langmuir model in terms of the nature of the adsorption process. The laboratory scale test results indicate that fungal hyphae modified with graphite and reduced graphene oxide have a high adsorption capacity, suitable for the removal of chromium (VI) from wastewater.

Preparation and application of the thermo-/pH-/ ion-sensitive semi-IPN hydrogel based on chitosan

Chitosan based hydrogels with multiple stimulus responses have broad application prospects in many fields. Considering the advantages of semi interpenetrating network (IPN) technology and the special temperature and ion responsiveness of polymers containing zwitterionic groups, a semi-IPN hydrogel was prepared through in situ free radical polymerization of N,N-dimethyl acrylamide and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide with polyethylene glycol dimethacrylate as a crosslinker and carboxymethyl chitosan as filler. The gel mass fraction and swelling ratio were measured, and the preparation conditions were optimized. The result indicated that the hydrogel possessed a unique thermo-/pH-/ ion-sensitive behavior. The swelling ratio increased with the increase of temperature and ion concentration, and showed a decreasing trend with the increase in pH. In addition, the hydrogel was stable when the stimuli changed. Adsorption behavior of the hydrogel to Eosin Y (EY) was systematically investigated. The adsorption process can be described well by the pseudo-second-order kinetic model and Langmuir isotherm model, indicating that it was a chemical adsorption. The experiments indicated that the hydrogel exhibited good antifouling and reusability features. Therefore, the semi-IPN hydrogel with antifouling properties and thermo-/pH-/ion-sensitivity can be easily manufactured is expected to find applications in water treatment fields.

Efficient antibacterial and dye adsorption by novel fish scale silver biochar composite gel

A silver-loaded carbon-chitosan-polyvinyl alcohol gel (C/CTS/PVA) was designed for suppressing microbial growth and dye adsorption. The antibacterial test results showed that C/CTS/PVA gel had a good antibacterial ability against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The inhibition rate in water was 100 %, and the antibacterial rate remained above 95 % within 35 days after preparation. The tight spatial structure provided by the adhesive effect of PVA and CTS effectively prevented water loss and enhanced the stability of the gel. The adsorption curves of the gel were fitted by establishing the pseudo-first order and pseudo-second order kinetic models. The adsorption curves were more consistent with the pseudo-second-order kinetic model. The best adsorption effect for Malachite green was 128.12 mg/g. C/CTS/PVA gel had a remarkable adsorption effect on Malachite green, Congo red, Methyl orange, and Methylene blue. In general, C/CTS/PVA gels have great potential for the treatment of sewage in the future.

Polysaccharide-based biopolymer hydrogels for heavy metal detection and adsorption

BACKGROUND

With rapid development in agriculture and industry, water polluted with heavy metallic ions has come to be a serious problem. Adsorption-based methods are simple, efficient, and broadly used to eliminate heavy metals. Conventional adsorption materials have the problems of secondary environmental contamination. Hydrogels are considered effective adsorbents, and those prepared from biopolymers are biocompatible, biodegradable, non-toxic, safe to handle, and increasingly used to adsorb heavy metal ions.

AIM OF REVIEW

The natural origin and easy degradability of biopolymer hydrogels make them potential for development in environmental remediation. Its water absorption capacity enables it to efficiently adsorb various pollutants in the aqueous environment, and its internal pore channels increase the specific surface area for adsorption, which can provide abundant active binding sites for heavy metal ions through chemical modification.

KEY SCIENTIFIC CONCEPT OF REVIEW

As the most representative of biopolymer hydrogels, polysaccharide-based hydrogels are diverse, physically and chemically stable, and can undergo complex chemical modifications to enhance their performance, thus exhibiting superior ability to remove contaminants. This review summarizes the preparation methods of hydrogels, followed by a discussion of the main categories and applications of polysaccharide-based biopolymer hydrogels.

Facile fabrication of semi-IPN hydrogel adsorbent based on quaternary cellulose via amino-anhydride click reaction in water

Clean and safe water resources play a key role in environmental safety and human health. Recently, hydrogels have attracted extensive attention due to their non-toxicity, controllable performance, and high adsorption. Herein, a semi- interpenetrating network hydrogel (semi-IPN-Gel) adsorbent based on quaternary cellulose (QC) was prepared by the amino-anhydride click reaction between maleic anhydride copolymer and polyacrylamine hydrochloride (PAH), and its adsorption properties for Eosin Y were studied. First, a binary copolymer (PAM) of acrylamide and maleic anhydride was synthesized by free radical polymerization. Then, the PAM, QC and PAH were dissolved in water, and the pH of the solution was adjusted to alkaline. Semi-IPN-Gel was successfully prepared by fast anhydride-amino click reaction. The preparation conditions of hydrogels were optimized by single-factor experiments. Finally, taking Eosin Y as a model pollutant, the adsorption performance of Eosin Y was studied. The factors influencing the adsorption capacity of the absorbents such as initial concentration of the Eosin Y, temperature, the amount of absorbent, ionic strength and pH of the Eosin Y solutions were investigated. And adsorption data were analyzed via the kinetic model and the isothermal model, indicating that the adsorption process of the hydrogel is a single layer chemisorption process.