In this current work, the magnetic composite microsphere containing glutamine modified chitosan and silica coated Fe3O4 nanoparticles (CS-Gln-MCM) has been successfully prepared and extensively characterized, which is a kind of biodegradable materials. CS-Gln-MCM shows enhanced removal efficiency for both acid green 25 (AG25), an amphoteric dye, and mercury ions (Hg²⁺) from water in the respective while measured pH range compared with chitosan magnetic composite microsphere (CS-MCM) without modification. It is due to the fact that the grafted amino acid provides a variety of additional adsorption active sites and diverse adsorption mechanisms are involved. In AG25 and Hg²⁺ aqueous mixture, the modified adsorbents bear preferential adsorption for AG25 over Hg²⁺ in strong acidic solutions ascribed to multiple interactions between AG25 and CS-Gln-MCM, such as hydrogen bonding and electrostatic interactions. While, in weak acidic conditions, an efficient simultaneous removal is observed for different adsorption effects involved in aforementioned two pollutants. Besides, CS-Gln-MCM illuminates not only short equilibrium time for adsorption of each pollutant less than 20.0 min but also rapid magnetic separation from water and efficient regeneration after saturated adsorption. Therefore, CS-Gln-MCM bears great application potentials in water treatment.

Physicochemical properties of nanoparticles influence their environmental fate and toxicity, and studies investigating this are vital for a holistic approach towards a comprehensive and adequate environmental risk assessment. In this study, we investigated the effects of size, surface coating (charge) of silver nanoparticles (AgNPs) – a most commonly-used nanoparticle-type, on the bioaccumulation in, and toxicity (survival, growth, cocoon production) to the earthworm Lumbricus rubellus. AgNPs were synthesized in three sizes: 20, 35 and 50 nm. Surface-coating with bovine serum albumin (AgNP_BSA), chitosan (AgNP_Chit), or polyvinylpyrrolidone (AgNP_PVP) produced negative, positive and neutral particles respectively. In a 28-day sub-chronic reproduction toxicity test, earthworms were exposed to these AgNPs in soil (0–250 mg Ag/kg soil DW). Earthworms were also exposed to AgNO3 at concentrations below known EC50. Total Ag tissue concentration indicated uptake by earthworms was generally highest for the AgNP_BSA especially at the lower exposure concentration ranges, and seems to reach a plateau level between 50 and 100 mg Ag/kg soil DW. Reproduction was impaired at high concentrations of all AgNPs tested, with AgNP_BSA particles being the most toxic. The EC50 for the 20 nm AgNP_BSA was 66.8 mg Ag/kg soil, with exposure to <60 mg Ag/kg soil already showing a decrease in the cocoon production. Thus, based on reproductive toxicity, the particles ranked: AgNP_BSA (negative) > AgNP_PVP (neutral) > Chitosan (positive). Size had an influence on uptake and toxicity of the AgNP_PVP, but not for AgNP_BSA nor AgNP_Chit. This study provides essential information on the role of physicochemical properties of AgNPs in influencing uptake by a terrestrial organism L. rubellus under environmentally relevant conditions. It also provides evidence of the influence of surface coating (charge) and the limited effect of size in the range of 20–50 nm, in driving uptake and toxicity of the AgNPs tested.

In the current study, biocompatible and biodegradable blends based on poly(vinyl alcohol) nanoparticles – PVAn mixed with either chitosan (Ch) or starch (St) – were prepared and investigated as nanoabsorbents for oil elimination from wastewater. The use of water/dimethyl sulfoxide (DMSO) as a mixed solvent is the key factor for preparing aggregated PVAn, which is further mixed with Ch or St. Nanoblends were applied as oil absorbents, and the results showed that PVAn/St possess high adsorption capacity than PVAn/Ch and PVAn. The maximum sorption capacities (qg/g) of the PVAn/Ch sorbents for hydraulic oil, kerosene, and toluene were 33.6, 73.96, and 93.1g/g, respectively. The absorbed oil could be rapidly recovered by simple mechanical squeezing and reused without any other modification. The blends showed excellent reusability and could be reused for at least 10 times with minimal losses. The current study demonstrates the application of these blends as an ideal alternative sorbent for oil spillage cleanup.

A bacterial consortium composed by four metagenomic clones and Bacillus subtilis strain CBMAI 707, all derived from petroleum reservoirs, was entrapped in chitosan beads and evaluated regarding hydrocarbon degradation capability. Experiments were carried out in mesocosm scale (3000L) with seawater artificially polluted with crude oil. At different time intervals, mesocosms were sampled and subjected to GC-FID and microbiological analyses, as total and heterotrophic culturable bacterial abundance (DAPI and CFU count), biological oxygen demand (BOD) and taxonomic diversity (massive sequencing of 16S rRNA genes). The results obtained showed that degradation of n-alkane hydrocarbons was similar between both treatments. However, aromatic compound degradation was more efficient in bioaugmentation treatment, with biodegradation percentages reaching up to 99% in 30days. Community dynamics was different between treatments and the consortium used in the bioaugmentation treatment contributed to a significant increase in aromatic hydrocarbon degradation.

This study aims to produce and apply a biosurfactant from Gordonia westfalica GY40 for enhancing fuel oil solubilization and degradation in seawater. The immobilization of G. westfalica GY40 cells on chitosan flakes increased biosurfactant yield, and we achieved a biosurfactant concentration as high as 1.85 g L⁻¹ when using 2 % soybean oil as the carbon source. The critical micelle dilution (CMD) value of cell-free broth was 25 % and the lowest surface tension was 35 mN m⁻¹. The cell-free broth was able to solubilize and disperse fuel oil, at efficiencies corresponding to biosurfactant concentrations and CMD values. The surface activity of cell-free broth was stable under wide ranges of salinity, temperature, and pH. For the oil degradation test, cell-free broth at 0.5× CMD was added along with polyurethane foam-immobilized Gordonia sp. JC11, an efficient oil-degrading bacterial inoculum, to fuel oil spiked seawater. The system removed 81 % of 1 g L⁻¹ fuel oil in nutrient seawater medium within 6 days. When tested with three seawater samples collected along the Thai coastal area, the addition of both biosurfactant and immobilized Gordonia sp. JC11 was able to remove 60–70 % of 1 g L⁻¹ fuel oil, while the natural attenuation (control) removed only 26–35 % of fuel oil. The application of cell-free broth reduced the extraction and purification steps. In addition, the simple production of G. westfalica GY40 biosurfactant and Gordonia sp. JC11 inoculum suggested that they are suitable for cleaning-up oil spills in seawater.

A granular hydrogel of chitosan-g-poly(vinylimidazole-co-2-acrylamido-2-methyl propane sulfonic acid) was successfully synthesized by one-step free radical polymerization based on the grafting backbone of chitosan and the monomers of vinylimidazole and 2-acrylamido-2-methyl propane sulfonic acid. The resulting hydrogel could be used as the adsorbent for the efficient and selective removal of Hg²⁺ ions from the aqueous solution. The adsorption results could be well described by the pseudo-second-order kinetic mode and the Langmuir isotherm model with a maximum adsorption capacity of 363.55 mg/g for Hg²⁺. Furthermore, the as-prepared granular hydrogel exhibited an excellent cycling stability for the adsorption of Hg²⁺ after multiple repeated adsorption-desorption process. It suggested that the obtained granular hydrogel has potential application for Hg²⁺ removal and recovery from wastewater. Graphical Abstract A kind of granular hydrogel with excellent selectivity adsorption of Hg2+ ions was successfully synthesized by grafting polymerization of VIM and AMPS onto the CTS backbone via a facile free radical polymerization.

Chitosan-montmorillonite composite was extensively used for the removal of heavy metals from wastewater. In wastewater, copper (Cu²⁺) usually coexist with the organic ligands, which had unknown effect on Cu²⁺ adsorption by the composite materials. In order to understand further on that, the adsorption of copper by the composite materials must be studied. In the present study, montmorillonite was coated with chitosan, and X-ray diffraction (XRD) patterns of the composite proved the intercalation of chitosan in the montmorillonite. Fourier transform infrared (FTIR) spectra of the composite identified the presence of amino group on the composite, and that of the composite saturated with metals identified the interaction between the amino groups and metals. Langmuir adsorption isotherm indicated that the composite had more capacity to adsorb Cu²⁺ from wastewater than montmorillonite. The adsorption capacity of Cu²⁺ by montmorillonite and chitosan-montmorillonite composite was studied, respectively, as a function of pH and in the presence of acetate. Compared to the montmorillonite at low ligand concentration (0.08 mmol/L) or low pH (<4.0), the coexisting acetate increased more Cu²⁺ adsorption by the composite. The acetate ligand presented less depression on the adsorption by the composite than that by montmorillonite at high ligand concentration (4 mmol/L) or high pH (>4.5). Therefore, the composite is more suitable for removing Cu²⁺ than montmorillonite in acid aqueous medium.

A novel concept with the result of enzyme stabilization against microbial degradation in real bioremediation processes was developed through the encapsulation of laccase in chitosan nanoparticles. Besides of abundant information on laccase-chitosan conjugates, we report the laccase encapsulation into nanoparticles based in chitosan. The chitosan-tripolyphosphate technique was applied for the production of morphologically homogeneous enzymatic nanoparticles, with high enzyme encapsulation efficiency, small asymmetric sizes (from 40 to 90 nm), and rough surfaces. Contrary to macroscopic immobilized enzymes, temperature and pH activity profiles of nano-sized laccase were similar to those of free enzyme. The substrate affinity constant (K M) of nano-encapsulated laccase was similar to these from free enzyme, while its activity rate constant (k cₐₜ) represented 60 % of these obtained with free enzyme. Importantly, stability of nano-encapsulated laccase against microbial degradation in soil, compost, and wastewater was significantly increased. After 24 h exposure to wastewater from a treatment plant, the laccase activity of the nanoparticles was 82.8 % of initial activity, compared with only 7.8 % retained activity for free enzyme. After 36 h incubation in compost extract, the laccase nanoparticles showed 72.4 % of the initial activity, while the free enzyme was almost completely inactivated. Finally, after 84 h incubation in soil extract, the nanoparticles and free preparations showed 57.9 and 17.3 % of the initial activity, respectively. Thus, the nanoencapsulation of enzymes able to transform pollutants is an alternative to improve the operational lifetime of enzymes in real environmental applications.

Pristine chitosan beads were modified with sulfur (S)-containing functional groups to produce thiolated chitosan beads (ETB), thereby increasing S donor ligands and crosslinks. The effect of temperature, heating time, carbon disulfide (CS₂)/chitosan ratio, and pH on total S content of ETB was examined using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The total S content of ETB increased with increasing CS₂/chitosan ratio and decreased with decreasing pH and increasing temperature (>60 °C) and heating time (at 60 °C). Spectroscopic analyses revealed the presence of thiol (–SH)/thione, disulfide (–S–S–), and sulfonate groups in ETB. The thiolation mechanism involves decomposition of dithiocarbamate groups, thereby forming thiourea crosslinks and trithiocarbonate, resulting in –SH oxidation to produce –S–S– crosslinks. The partially formed ETB crosslinks contribute to its acid stability and are thermodynamically feasible in adsorbing Cd and Cu. The S-containing functional groups added to chitinous wastes act as sorbents for metal remediation from acidic environments.

For the synthesis of a highly active TiO₂-chitosan nanocomposite, pH plays a crucial role towards controlling its morphology, size, crystallinity, thermal stability, and surface adsorption properties. The presence of chitosan (CS) biopolymer facilitates greater sustainability to the photoexcited electrons and holes on the catalysts’ surface. The variation of synthesis pH from 2 to 5 resulted in different physico-chemical and photocatalytic properties, whereby a pH of 3 resulted in TiO₂-chitosan nanocomposite with the highest photocatalytic degradation (above 99 %) of methylene orange (MO) dye. This was attributed to the efficient surface absorption properties, high crystallinity, and the presence of reactive surfaces of –NH₂ and –OH groups, which enhances the adsorption-photodegradation effect. The larger surface oxygen vacancies coupled with reduced electron-hole recombination further enhanced the photocatalytic activity. It is undeniable that the pH during synthesis is critical towards the development of the properties of the TiO₂-chitosan nanocomposite for the enhancement of photocatalytic activity.