Novel hybrid biosorbents of agar: Swelling behaviour, heavy metal ions and dye removal efficacies

Laboratory horror stories: Poison in the agars

The fission yeast Schizosaccharomyces pombe is a single-celled eukaryote that can be cultured as a haploid or as a diploid. Scientists employ mating, meiosis, and the plating of ascospores and cells to generate strains with novel genotypes and to discover biological processes. Our two laboratories encountered independently sudden-onset, major impediments to such research. Spore suspensions and vegetative cells no longer plated effectively on minimal media. By systematically analyzing multiple different media components from multiple different suppliers, we identified the source of the problem. Specific lots of agar, from different suppliers, were toxic. Interestingly, the inhibitory effect was attenuated on rich media. Consequently, quality control checks that use only rich media can provide false assurances on the quality of the agar. Lastly, we describe likely sources of the toxicity and we provide specific guidance for quality control measures that should be applied by all vendors as preconditions for their sale of agar.

Novel soy protein isolate/sodium alginate-based functional aerogel for efficient uptake of organic dye from effluents

In response to the increasing global concern regarding water pollution, there is a growing demand for the development of novel adsorbents capable of effectively eliminating hazardous organic pollutants from effluents. In this study, we present a functional soy protein isolate (SPI)/sodium alginate (ALG)/polyethyleneimine (PEI) aerogel prepared via a facile chemical crosslinking process as a novel adsorbent with excellent capabilities for removing toxic methyl blue (MB) dye from effluents. Thanks to the synergistic dense oxygen and nitrogen-containing functional groups in the networks, the ALG/SPI/PEI (ASP) aerogel displayed high adsorption capacity for MB (106.3 mg/g) complying the adsorption kinetics and isotherm with the pseudo-second-order and Langmuir models, respectively. Remarkably, the MB adsorption capability of the ASP aerogel surpasses that of its pristine counterpart and outperforms recently reported adsorbents. Moreover, the aerogel maintained >80% of initial adsorption capability in the fourth regenerative cycle, indicating excellent reusability. The superior MB adsorbability coupled with high-efficiency regenerability in this study reveal the significant potential of ASP aerogel in efficiently eliminating organic dye from wastewater.

Agar/gelatin hydro-film containing EGF and Aloe vera for effective wound healing

In the current study, we produced a hydro-film dressing for the treatment of chronic wounds. The hydro-film structure was composed of gelatin cross-linked with citric acid, agar and Aloe vera extract (AV); additionally epidermal growth factor (EGF) was loaded to promote wound healing. Due to the excellent hydrogel-forming ability of gelatin, the obtained hydro-film was able to swell 884 ± 36% of its dry weight, which could help controlling wound moisture. To improve gelatin mechanical properties, polymer chains were cross-linked with citric acid and agar, reaching an ultimate tensile strength that was in the highest range of human skin. In addition, it showed a slow degradation profile that resulted in a remaining weight of 28 ± 8% at day 28. Regarding, biological activity, the addition of AV and citric acid provided the ability to reduce human macrophage activation, which could help reverse the permanent inflammatory state of chronic wounds. Moreover, loaded EGF, together with the structural AV of the hydro-film, promoted human keratinocyte and fibroblast migration, respectively. Furthermore, the hydro-films presented excellent fibroblast adhesiveness, so they could be useful as provisional matrices for cell migration. Accordingly, these hydro-films showed suitable physicochemical characteristics and biological activity for chronic wound healing applications.

Biodegradable Preformed Particle Gel (PPG) Made of Natural Chitosan Material for Water Shut-Off Application

Oil and gas extraction frequently produces substantial volumes of produced water, leading to several mechanical and environmental issues. Several methods have been applied over decades, including chemical processes such as in-situ crosslinked polymer gel and preformed particle gel, which are the most effective nowadays. This study developed a green and biodegradable PPG made of PAM and chitosan as a blocking agent for water shutoff, which will contribute to combating the toxicity of several commercially used PPGs. The applicability of chitosan to act as a crosslinker has been confirmed by FTIR spectroscopy and observed by scanning electron microscopy. Extensive swelling capacity measurements and rheological experiments were performed to examine the optimal formulation of PAM/Cs based on several PAM and chitosan concentrations and the effects of typical reservoir conditions, such as salinity, temperature, and pH. The optimum concentrations of PAM with 0.5 wt% chitosan were between 5-9 wt%, while the optimum chitosan amount with 6.5 wt% PAM was in the 0.25-0.5 wt% range, as these concentrations can produce PPGs with high swellability and sufficient strength. The swelling capacity of PAM/Cs is lower in high saline water (HSW) with a TDS of 67.2976 g/L compared with fresh water, which is related to the osmotic pressure gradient between the swelling medium and the PPG. The swelling capacity in freshwater was up to 80.37 g/g, while it is 18.73 g/g in HSW. The storage moduli were higher in HSW than freshwater, with ranges of 1695-5000 Pa and 2053-5989 Pa, respectively. The storage modulus of PAM/Cs samples was higher in a neutral medium (pH = 6), where the fluctuation behavior in different pH conditions is related to electrostatic repulsions and hydrogen bond formation. The increase in swelling capacity caused by the progressive increment in temperature is associated with the amide group's hydrolysis to carboxylate groups. The sizes of the swollen particles are controllable since they are designed to be 0.63-1.62 mm in DIW and 0.86-1.00 mm in HSW. PAM/Cs showed promising swelling and rheological characteristics while demonstrating long-term thermal and hydrolytic stability in high-temperature and high-salinity conditions.

Production of novel hazelnut shell-based semi-IPN biocomposite absorbents and their use in removing heavy metal ions from water

In this study, a hazelnut shell (HS) filled semi-interpenetrating polymer networks (semi-IPN) biocomposite adsorbent with novel and different compositions was developed that will enable the removal of lead ions, which are commonly found in water, by adsorption reactions. The structural and morphological properties of the produced adsorbents were characterized by FT-IR, XRD, TGA, DSC, BET, FE-SEM, EDX, and zeta potential measurements, and the production mechanism of these adsorbents was discussed. The effects of parameters such as different adsorbent dosages, different heavy metal concentrations, type of adsorbent, contact time, pH, and temperature on the swelling abilities and adsorption properties of adsorbents were investigated in detail. It has been determined that the adsorbent, which exhibits optimum adsorption and swelling properties, is a biocomposite containing 5% by weight HS filler, and it has been observed that it can remove up to 85% of lead ions under different parameters and conditions. In addition, the adsorption behaviors of the produced biocomposites are discussed using isothermal, kinetic, and thermodynamic models. Moreover, studies have been carried out on the reusability of the adsorbent, and it has been observed that the adsorbent produced within the scope of the study is still usable even after four cycles.

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.

Pretreatment Techniques and Green Extraction Technologies for Agar from Gracilaria lemaneiformis

Optimizing the alkali treatment process alone without tracking the changes of algae and agar quality with each pretreatment process will not achieve the optimal agar yield and final quality. In this study, we monitored the changes of the morphology and weight of algae with each treatment process, and comprehensively analyzed the effects of each pretreatment process on the quality of agar by combining the changes of the physicochemical properties of agar. In conventional alkali-extraction technology, alkali treatment (7%, w/v) alone significantly reduced the weight of algae (52%), but hindered the dissolution of algae, resulting in a lower yield (4%). Acidification could solve the problem of algal hardening after alkali treatment to improve the yield (12%). In enzymatic extraction technology, agar with high purity cannot be obtained by enzyme treatment alone, but low gel strength (405 g/cm²) and high sulfate content (3.4%) can be obtained by subsequent acidification and bleaching. In enzyme-assisted extraction technology, enzyme damage to the surface fiber of algae promoted the penetration of low-concentration alkali (3%, w/v), which ensured a high desulfurization efficiency and a low gel degradation rate, thus improving yield (24.7%) and gel strength (706 g/cm²), which has the potential to replace the traditional alkali-extraction technology.

Synthesis, Characterization and Sorption Capacity Examination for a Novel Hydrogel Composite Based on Gellan Gum and Graphene Oxide (GG/GO)

A novel hydrogel composite based on gellan gum and graphene oxide (GG/GO) was synthesized, characterized and tested for sorption capacity in this work. The microstructural, thermogravimetric and spectroscopic analysis confirmed the formation of the GG/GO composite. Comparative batch sorption experiments revealed a sorption capacity of the GG/GO composite for Zn (II) ions of approximately 2.3 higher than that of pure GG. The GG/GO composite exhibits a maximum sorption capacity of 272.57 mg/g at a pH of Zn (II) initial solution of 6. Generally, the sorption capacity of the sorbents is approximately 1.5 higher in slightly acidic conditions (pH 6) comparative with that for strong acidic conditions (pH 3). The sorption isotherms revealed that the sorption followed a monolayer/homogenous behavior. The sorption kinetic data were well fitted by the pseudo-second-order kinetic model, and were consistent with those derived from sorption isotherms. The intraparticle diffusion was considered to be the rate-determining step. Two main sorption mechanisms for Zn (II) were identified namely, ion exchange at low pH values, and both ion exchange and chemisorption in weekly acidic conditions.

The Effect of Cross-Linking with Citric Acid on the Properties of Agar/Fish Gelatin Films

The aim of this work was to assess the effect of fish gelatin-citric acid nucleophilic substitution and agar-citric acid esterification reactions on the properties of agar/fish gelatin films. Since temperature is an important cross-linking parameter, films were treated at 90 °C and 105 °C and film properties were compared to those of non-cured films. It was observed that temperature favored the aforementioned reactions, which induced physical and morphological changes. In this regard, darker films with a rougher surface were obtained for the films with a higher cross-linking degree. While mechanical properties were slightly modified, the barrier properties were enhanced due to the reactions that occurred. Therefore, these agar/fish gelatin films cross-linked through two different reactions can be considered to be promising materials as active films for different purposes, such as active packaging or pharmaceutical applications.