This work explores the synthesis and characterization of two novel nanocomposites that can be used in various applications, such as aqueous solution adsorption of pollutants. The first nanocomposite consists of tin (Sn)-doped titanium dioxide (TiO2) on activated carbon, while the other one consists of polypyrole (PPy), chitosan (CS), and Sn-doped TiO2. A contrast was made of their effective adsorbent materials for the removal of Cibacron Brilliant Yellow dye from aqueous solutions. Different analytical techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray analysis (EDX), and Fourier transform - infrared (FT-IR) were used to analysis the nanocomposite samples. SEM images show that the average particle diameter of PPy-CS/Sn-doped TiO2 NC is 75 ± 3 nm, while Sn-doped TiO2/AC particles have an average diameter of 40 ± 2 nm. The greater PPy-CS/Sn-doped TiO2 nanocoposite particle diameter indicates that the polymers cover the Sn-doped TiO2 nanoparticles, which leads to higher in the diameter of the particles. The adsorption efficiency of Sn-doped TiO2/AC was higher than that of PPy-CS/Sn-doped TiO2 sample due to its smaller particle size which resulted in a higher surface area which provides more adsorption sites. However, both samples showed remarkable adsorption capacity, where the adsorption capacity of Sn-doped TiO2/AC and PPy-CS/Sn-doped TiO2 were 104 and 103 mg/g, respectively.

Effluent from the textile industry is a major source of water pollution. Textile effluents contain a high amount of color, turbidity, BOD, and COD, which are highly toxic and affect aquatic organisms as well as human beings. Physical and chemical treatments of these effluents are difficult and costly. Adsorption is an effective method to treat textile industry effluent. In the present study, chitosan is selected as an adsorbent, derived from the exoskeleton of marine crustaceans like shrimp and crab by chemical processing. The color was removed using chitosan from shrimp and crab shells separately. On the sixth day of treatment, shrimp shell chitosan removed 100% of color from textile industry effluent and proved to be a better adsorbent.

Uranium, a radionuclide, is a predominant element utilized for speciality requirements in industrial applications, as fuels and catalyst. The radioactive properties and chemical toxicity of uranium causes a major threat to the ecosystem. The hazards associated with Uranium pollution includes the cancer in bones, liver, and lungs. The toxicological properties of Uranium are discussed in detail. Although there are many methods to eliminate those hazards, this research work is aimed to describe the application of bioremediation methods. Bioremediation methods involve elimination of the hazards of uranium, by transforming into low oxidation form using natural microbes and plants. This study deeply elucidates the methods as bioleaching, biosorption, bioreduction and phytoremediation. Bioleaching process involves bio-oxidation of tetravalent uranium when it gets in contact with acidophilic metal bacterial complex to obtain leach liquor. In biosorption, chitin/chitosan derived sorbents act as chelators and binds with uranium by electrostatic attraction. Bio reduction employs a bacterial transformation into enzymes which immobilize and reduce uranium. Phytoremediation includes phytoextraction and phytotranslocation of uranium through xylems from soil to roots and shoots of plants. The highest uranium removal and uptake reported using the different methods are listed as follows: bioleaching (100% uranium recovery), biosorption (167 g kg⁻¹ uranium uptake), bioreduction (98.9% uranium recovery), and phytoremediation (49,639 mg kg⁻¹ uranium uptake). Among all the techniques mentioned above, bioleaching has been proved to be the most efficient for uranium remediation.

It has been shown that chemical modification of chitosan with sulfur (S) functional groups could significantly enhance its chelating capability with heavy metals included Cd(II). However, a molecular level understanding has been lacking. Here, we carried out X-ray absorption fine structure (XAFS) and Fourier transformed infrared (FTIR) spectra studies to bridge this knowledge gap. The results indicate that both Cd–O/N and Cd–S bonds exist in the complex of Cd(II) with dithiocarbamate chitosan (DTC-CTS). S functional groups (dithiocarbamate) in DTC-CTS play the major role in complexation with Cd(II) and S content affects the adsorption mechanism. At low S content, Cd(II) is mainly adsorbed on DTC-CTS as an outer-sphere complex with two monodentate amino groups and two water molecules in tetrahedral configuration. At high S content, Cd adsorption dominantly occurs by formation of an inner-sphere complex with two bidentate mononuclear S ligands in tetrahedral configuration. This investigation provides information on the effectiveness and mechanisms of Cd(II) removal that is critical for evaluating modified chitosan applications for stabilization of Cd(II) in surface water, groundwater, soils and sediments.

Developing low-cost and high-performance biosorbent for water purification continues drawing more and more attention. In this study, cellulose-chitosan composite hydrogels were fabricated via a co-dissolution and regeneration process using a molten salt hydrate (a 60 wt% aqueous solution of LiBr) as a solvent. The addition of chitosan not only introduced functionality for metal adsorption but also increased the specific surface area and improved the mechanical strength of the composite hydrogel, compared to pure cellulose hydrogel. Batch adsorption experiments indicated that the composite hydrogel with 37% cellulose and 63% chitosan exhibited an adsorption capacity of 94.3 mg/g (1.49 mmol/g) toward Cu²⁺ at 23 °C, pH 5, and initial metal concentration of 1500 mg/L, which was 10 times greater than the adsorption capacity of pure cellulose hydrogel. Competitive adsorption from a mixed metals solution revealed that the cellulose-chitosan composite hydrogel exhibited selective adsorption of the metals in the order of Cu²⁺ > Zn²⁺ > Co²⁺. This study successfully demonstrated an innovative method to fabricate biosorbents from abundant and renewable natural polymers (cellulose and chitosan) for removing metal ions from water.

This review is intended to evaluate the use of ferrate (Fe(VI)), being a green coagulant, sustainable and reactive oxidant, to remove micro pollutants especially pharmaceutical pollutants in contaminated water. After a brief description of advanced oxidation processes, fundamental dimensions regarding the nature, reactivity, and chemistry of this oxidant are summarized. The degradation of contaminants by Fe(VI) involves several mechanisms and reactive agents which are critically evaluated. The efficiency and chemistry of Fe(VI) oxidation differs according to the reaction conditions and activation agent, such as soluble Fe(VI) processes, which involve Fe(VI), UV light, and electro-Fe(VI) oxidation. Fe(VI) application methods (including single dose, multiple doses, chitosan coating etc), and Fe(VI) with activating agents (including sulfite, thiosulfate, and UV) are also described to degrade the micro pollutants. Besides, application of Fe(VI) to remove pharmaceuticals in wastewater are intensely studied. Electrochemical prepared Fe(VI) has more wide application than wet oxidation method. Meanwhile, we elaborated Fe(VI) performance, limitations, and proposed innovative aspects to improve its stability, such as the generation of Fe(III), synergetic effects, nanopores entrapment, and nanopores capsules. This study provides conclusive direction for synergetic oxidative technique to degrade the micro pollutants.

In the present study, the competitive adsorption of Cu²⁺, Pb²⁺, and Cd²⁺ by a novel natural adsorbent (i.e., argillaceous limestone) modified with chitosan (C-AL) was investigated. The results demonstrated that both intraparticle diffusion and chemisorption marked significant contributions to the Cu²⁺ adsorption process by both raw argillaceous limestone (R-AL) and C-AL in mono-metal adsorption systems. Antagonism was found to be the predominant competitive effect for Cu²⁺, Pb²⁺ and Cd²⁺ adsorptions by C-AL in the multi-metal adsorption system. The three-dimensional simulation and FTIR analysis revealed that the presence of Cu²⁺ suppressed Pb²⁺ and Cd²⁺ adsorptions, while the effect of Cd²⁺ on Cu²⁺ and Pb²⁺ adsorptions was insignificant. The spectroscopic analyses evidenced that amide groups in C-AL played a crucial role in metal adsorption. The preferential adsorptions of Pb²⁺ > Cu²⁺ > Cd²⁺ were likely due to the different affinities of the metals to the lone pair of electrons on the N atom from the amide groups and/or the O atoms from the –OH and -COO⁻ groups on C-AL. The interactions between C-AL and metal ions and between various metal species influenced their competitive adsorption behaviors. C-AL exhibited a superior metal adsorption capacity in comparison with that the capacities of other natural adsorbents reported during the last decade, suggesting its potential practical applications.

The dissolution of Ag (citrate, gelatin, polyvinylpyrrolidone and chitosan coated), ZnO, CuO and carbon coated Cu nanoparticles (with two nominal sizes each) has been studied in artificial aqueous media, similar in chemistry to environmental waters, for up to 19 days. The dissolved fraction was determined using DGT (Diffusion Gradients in Thin films), dialysis membrane (DM) and ultrafiltration (UF). Relatively small fractions of Ag nanoparticles dissolved, whereas ZnO dissolved nearly completely within few hours. Cu and CuO dissolved as a function of pH. Using DGT, less dissolved Ag was measured compared to UF and DM, likely due to differences in diffusion of organic complexes. Similar dissolved metal concentrations of ZnO, Cu and CuO nanoparticles were determined using DGT and UF, but lower using DM. The results indicate that there is a need to apply complementary techniques to precisely determine dissolution of nanoparticles in aqueous media.

In this study, we treated harmful Microcystis aeruginosa cyanobacteria using chitosan-modified nanobubbles. The chitosan-modified nanobubbles (255 ± 19 nm) presented a positive zeta potential (15.36 ± 1.17 mV) and generated significantly (p < 0.05) more hydroxyl radicals than the negatively charged nanobubbles (−20.68 ± 1.11 mV). Therefore, the interaction between the positively charged chitosan-modified nanobubbles and negatively charged M. aeruginosa (−34.81 ± 1.79 mV) was favored. The chitosan-modified nanobubble treatment (2.20 × 10⁸ particles mL⁻¹) inactivated 73.16% ± 2.23% of M. aeruginosa (2.00 × 10⁶ cells mL⁻¹) for 24 h without causing significant cell lysis (≤0.25%) and completely inhibited the acute toxicity of M. aeruginosa toward Daphnia magna. The inactivation was correlated (r² = 0.97) with the formation of reactive oxygen species (ROS) in M. aeruginosa. These findings indicated that the hydroxyl radicals generated by the chitosan-modified nanobubbles disrupted cell membrane integrity and enhanced oxidative stress (ROS formation), thereby inactivating M. aeruginosa. Moreover, the penetration of the chitosan-modified nanobubbles and cell alterations in M. aeruginosa were visually confirmed. Our results suggested that the chitosan-modified nanobubble treatment is an eco-friendly method for controlling harmful algae. However, further studies are required for expanding its practical applications.

At present, the simultaneous removal of organic dyes and heavy metals in complex wastewater has raised considerable concern, owing to their striking differences in physicochemical properties. Adsorption, as one of the few removal methods, has attracted extensive attention and gained popularity. Herein, a versatile EDTA and chitosan bi-functionalized magnetic bamboo biochar adsorbent (ECMBB) was synthesized for coinstantaneous adsorption of methyl orange (MO) and heavy metals (Cd(II) and Zn(II)). In this case, the as-synthesized ECMBB composites inherited favorable anionic MO removal performance from bamboo biochar (BB) obtained at 700 °C through electrostatic attraction, hydrogen bonding and π-π interaction, also enhanced the binding of cationic metals by introducing amino groups of chitosan and carboxyl groups of EDTA. In the unitary system, the removal of MO, Cd(II) and Zn(II) by three as-prepared adsorbents can be well illuminated by pseudo-second-order kinetic model and Langmuir isotherm theory. The saturated capture amounts of ECMBB at 25 °C are 305.4 mg g⁻¹ for MO, 63.2 mg g⁻¹ for Cd(II) and 50.8 mg g⁻¹ for Zn(II), which, under the same conditions, are 1.3, 2.6 and 2.5 times those of chitosan-modified magnetic bamboo biochar (CMBB) and 1.9, 6.1 and 5.4 times those of magnetic bamboo biochar (MBB), respectively. Remarkably, in MO-metal binary system, coexisting MO visibly enhanced the adsorption of Cd(II) and Zn(II), while coexisting heavy metals had no significant impact on MO adsorption. Furthermore, ECMBB exhibited no significant loss in adsorption efficiency even after eight adsorption-desorption experiments. This study lays the foundation for fabricating desired integrative biochar adsorbents in the simultaneous purification of organic and metallic pollutants from complex wastewater.