Understanding of the interaction of graphene with natural polysaccharides (e.g., alginate) is crucial to elucidate its environmental fate. We investigated the impact of alginate on the agglomeration and stability of ¹⁴C-labeled few-layer graphene (FLG) in varying concentrations of monovalent (NaCl) and divalent (CaCl₂) electrolytes. Enhanced agglomeration occurred at high CaCl₂ concentrations (≥5 mM) due to the alginate gel networks formation in the presence of Ca²⁺. FLG enmeshed within extended alginate gel networks was observed under transmission electron microscope and atomic force microscope. However, background Na⁺ competition for binding sites with Ca²⁺ at the alginate surfaces shielded the gelation of alginate. FLG was readily dispersed by alginate under environmentally relevant ionic strength conditions (i.e., <200 mM Na⁺ and <5 mM Ca²⁺). In comparison with the bare FLG, the slow sedimentation of the alginate-stabilized FLG (158 μg/L) caused continuous exposure of this nanomaterial to freshwater snails, which ingested 1.9 times more FLG through filter-feeding within 72 h. Moreover, surface modification of FLG by alginate significantly increased the whole-body and intestinal levels of FLG, but reduced the internalization of FLG to the intestinal epithelial cells. These findings indicate that alginate will act as a stabilizing agent controlling the transport of FLG in aqueous systems. This study also provides the first evidence that interaction of graphene with natural polysaccharides affected the uptake of FLG in the snails, which may alter the fate of FLG in aquatic environments.

Silica nanoparticles (SiO2 NPs) can cause health hazard after their release into the environment. Adsorption of natural organic matter and biomolecules on SiO2 NPs alters their surface properties and cytotoxicity. In this study, SiO2 NPs were treated by bovine serum albumin (BSA) and humic acid (HA) to study their effects on the integrity and fluidity of model cell membranes. Giant and small unilamellar vesicles (GUVs and SUVs) were prepared as model cell membranes in order to avoid the interference of cellular activities. The microscopic observation revealed that the BSA/HA treated (BSA-/HA-) SiO2 NPs took more time to disrupt membrane than untreated-SiO2 NPs, because BSA/HA adsorption covered the surface SiOH/SiO- groups and weakened the interaction between NPs and phospholipids. The deposition of SiO2 NPs on membrane was monitored by a quartz crystal microbalance with dissipation (QCM-D). Untreated- and HA-SiO2 NPs quickly disrupted the SUV layer on QCM-D sensor; BSA-SiO2 NPs attached on the membranes but only caused slow vesicle disruption. Untreated-, BSA- and HA-SiO2 NPs all caused the gelation of the positively-charged membrane, which was evaluated by the generalized polarity values. HA-SiO2 NPs caused most serious gelation, and BSA-SiO2 NPs caused the least. Our results demonstrate that the protein adsorption on SiO2 NPs decreases the NP-induced membrane damage.

In this study, an electrokinetic technique for remediation of Pb²⁺, Zn²⁺ and Cu²⁺ contaminated soil was explored using sodium alginate (SA) and chitosan (CTS) as promising biodegradable complexing agents. The highest Cu²⁺ (95.69%) and Zn²⁺ (95.05%) removal rates were obtained at a 2 wt% SA dosage, which demonstrated that SA significantly improved the Cu²⁺ and Zn²⁺ removal efficiency during electrokinetic process. The abundant functional groups of SA allowed metal ions desorption from soil via ion-exchange, complexation, and electrolysis. Pb²⁺ ions were difficult to remove from soil by SA due to the higher gelation affinity with Pb²⁺ than Cu²⁺ and Zn²⁺, despite the Pb²⁺ exchangeable fraction partially transforming to the reducible and oxidizable fractions. CTS could complex metal ions and migrate into the catholyte under the electric field to form crosslinked CTS gelations. Consequently, this study proved the suitability of biodegradable complexing agents for treating soil contaminated with heavy metals using electrokinetic remediation.

In this study, the alginate/hydroxyapatite/graphene oxide (AHGO) nanocomposite hydrogel beads (nhb) were designed, synthesized by an ionotropic gelation technique, and studied as an efficient, environment-friendly adsorbent for cationic dyes. The adsorptive capacities of AHGO nanocomposite toward methylene blue (MB) as a model dye solution were investigated through batch adsorption experiments in which the effects of initial dye concentration, adsorbent dosage, pH, temperature, ionic strength, and contact time on MB removal efficiency were examined. To explore the adsorption mechanisms, adsorption kinetics, isotherm analyses, XRD, FTIR, SEM–EDS, and point of zero charge (pHPZC) were performed. The results showed that AHGO-nhb had a maximum adsorption capacity of 311.81 mg/g for MB. This suggests that AHGO could be a good adsorbent for getting dyes out of water. Adsorption kinetics measurements proved to be closely correlated with both first and pseudo-second order (PSO) kinetics at the start, with the PSO taking control after 75 min, whereas the Sips model best described the MB adsorption isotherm process on AHGO. Based on the thermodynamic values ΔG°, ΔS°, and ΔH°, the process was spontaneous and exothermic in nature for cationic dyes. The mechanism underlying MB removal by AHGO is primarily a surface phenomenon involving electrostatic interaction, n-π interaction, and π-π interaction without intercalation. The process was shown to be a sequence of film diffusion followed by intra-particle diffusion, as demonstrated by the Weber-Moris and Boyed models. The adsorbent still maintains its adsorption ability for up to five cycles and could be a good alternative for treating wastewater.

Electrokinetic remediation of groundwater pollutants uses electrical fields to draw contaminants towards electrodes, where they are removed through diverse mechanisms. Conventional electrodes are installed in discrete positions in the soil. Here, we develop unconventional electrodes for the electrokinetic remediation of Cr(VI). Our electrodes are fluids comprised of sodium alginate and graphene particles in aqueous solution and can therefore be injected in the location of interest to facilitate their installation. The subsequent injection of CaCl₂ solutions induces gelation (as demonstrated by shear rheology), forming a conductive material (as demonstrated by voltammetry experiments). This material sorbed Cr(VI), as demonstrated in sorption experiments conducted under no-flow conditions and even without any applied electric potential. Therefore, it could be placed downstream of the pollutant to act as a barrier, controlling Cr(VI) migration and providing protection for human or ecological receptors. In a saturated model sandy aquifer, Cr(VI) was drawn towards our unconventional electrode barrier using a 12 V differential voltage, thereby decreasing its concentrations by approximately 70% in 30 min (starting from 0.35 mM Cr(VI), as demonstrated using a spectrophotometer). The net reduction of Cr(VI) concentrations in water was achieved without its extraction from the electrode proximity, because our graphene-alginate electrodes sorbed Cr(VI). Our findings provide a proof of concept of a novel remediation approach, which combines electrokinetic remediation with injectable barriers.

High-siliceous/calcareous mineral granules may cause cytotoxicity by attaching to cell membranes. In this research, giant (GUVs) and small unilamellar vesicles (SUVs) were used as model membranes for studying the interaction between high-siliceous/calcareous mineral granules (micro calcite, micro quartz, nano calcium carbonate, and nano silica) and artificial membranes. Confocal laser scanning microscopy (CLSM) and fluorescence labeling experiments suggest that nano calcium carbonate (nano CaCO₃) and nano silica (nano SiO₂) induce gelation by disrupting the oppositely charged membranes, indicating the important role of electrostatic forces. Thereby, the mineral granule size affects the electrostatic interactions and thus leading to the damage of the membranes. FTIR spectra and molecular dynamics reveal that mineral granules mainly interact with -PO₂⁻, -OH, and -C-N(CH₃)₃⁺ groups in phospholipids. The electrostatic force between nano minerals and phospholipids is greater in the case SiO₂ when compared to CaCO₃. Moreover, nano SiO₂ forms the strongest hydrogen bond with the -PO₂⁻ group as confirmed by FTIR. Thus, nano SiO₂ causes the greatest damage to membranes. This research provides a deeper understanding of the mechanism regarding the interaction between inhalable mineral granules and cell membranes.

In this work, chitosan/alginate composites were developed by the gelation method with the addition of different amounts of activated carbon produced from tannery waste (ACTW). The performance of these composites was verified through the adsorption of the textile dye Remazol Brilliant Blue R (RBBR). A synergistic effect was observed by the addition of ACTW; with a specific surface area up to 45.584 m²/g, the maximum adsorption capacity was 300.96 mg/g. The synergy was due to the reduction in steric hindrance, with the adsorption capacity 1.2 times higher than expected. The material was regenerated with sodium hydroxide for 10 cycles. The composite containing 30% ACTW (AC30) was applied in the treatment of real textile effluent, with 30% reductions in the biochemical oxygen demand (BOD), 39% in the chemical oxygen demand (COD), 78% in turbidity, and 67% in color.

Sodium alginate (SA) is a linear biopolymer, which is the nontoxic, biodegradable, and rich in carboxyl and hydroxyl groups. In the paper, the SA-based hydrogel bead was prepared by the cationic hectorite clay and anionic sodium alginate with a simple ionic gelation method under freeze-drying, and the adsorption properties were evaluated by the removal of copper ions from aqueous solutions. The composites were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherm (BET), thermal analysis (TG), and Fourier transform infrared spectroscopy (FT-IR). The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic data and the Langmuir, Freundlich, Dubinin–Radushkevich (D-R), and Temkin models were applied to describe the adsorption isotherms. The results showed that the adsorption process was found to follow the Freundlich isotherm model and the maximum sorption capacity was observed to be 160.28 mg/g under the initial concentration from 10 to 700 mg/L at 45 °C. Adsorption kinetics data fitted well with pseudo-second-order rate model. The porous structure of the composite was responsible for the adsorption of Cu²⁺ ions. But the adsorption ability could be improved by pH. Finally, the adsorption mechanism was suggested. Graphical abstract

In order to remedy the environmental pollution caused by oil spills, new materials with gelation capacity of organic solvents and fuels have been synthetized during the recent years. Among them, some of the most promising materials contain amide groups, which are often incorporated into the chemical structure of organogelators due to their effectiveness in gelling organic solvents through hydrogen bonds. A bisamide derivative of hydroxybenzoic acid (Bis-HUB1) was designed and synthesized in two steps and is able to congeal organic solvents. Gelation tests, critical gelation concentrations, and gel-sol transition temperatures were discussed in terms of its supramolecular interactions. Intermolecular hydrogen bonds and π-π stacking were studied through variable-temperature FTIR and UV-visible spectroscopy, while the structural characterization was performed via freeze-fracture TEM. Interestingly, Bis-HUB1 showed the ability to gel gasoline and diesel from monophasic and biphasic systems, which implies its potential use as a remediation agent in fuel spills. The results encourage further research.

A family of alkoxybenzoate derivatives was synthesized and were found to selectivity congeal protic/aprotic polar solvents, gasoline, and oils over water; therefore, these organogelators could be used in water remediation as removal agents of fuels and oils. Due to their thermoreversibility, they can be easily separated from the mixtures and be reused; being good candidates for fuel recovery. The π-π stacking interactions were evaluated to establish a relationship between their chemical structure and the gelation process through UV–vis spectroscopy; the three-dimensional network was studied with polarized optical microscopy (POM) and scanning electron microscopy (SEM). It was found that the aromatic ring acts as a stacking unit due to the π-π interactions; the ester group provides a source of dipole–dipole interactions; and the alkyl chains in the ether group showed a significant influence in gelation with the increase of carbon atoms, which increases the effect of nonpolar dispersion interactions.