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.

High removal efficiency and excellent recyclability are the fundamental qualities that an outstanding adsorbent used for organic dye removal should possess. In this study, two recyclable gels (sodium alginate/Ca/fiber: SCFA hydrogels; cellulose nanofiber/chitosan: CNFCS aerogels) were successfully fabricated using the facile method. Additionally, the as-prepared adsorbents were investigated using a series of characterizations. The adsorption behavior and anti-interference performance of the synthesized gels were compared by choosing methylene blue (MB) as the model pollutant. The kinetic behavior of the gels towards MB was consistent with the pseudo first-order model, and the SCFA hydrogels reached adsorption equilibrium faster than the CNFCS aerogels. The maximum adsorption capacity of MB on the SCFA hydrogels and CNFCS aerogels was 1335.0 and 164.5 mg g⁻¹ (pH = 7.0, dosage: 0.5 g/L; initial concentration from 15 to 180 mg L⁻¹), respectively. More specifically, we found that the co-existing anions had different effects on MB adsorption over the gels used for MB removal. Furthermore, for the SCFA hydrogels, co-existing natural organic matter (NOM) at low concentrations enhanced MB adsorption, and then stabilized as the concentration of NOM increased. However, this increasing trend was not observed for MB adsorption on CNFCS aerogels; these gels exhibited a slight decrease at first, and then showed no change. Nevertheless, both the gels exhibited superior regeneration and recycling abilities.

Controlled-release fertilizers (CRFs) are an effective approach in providing essential nutrients for plant growth while minimizing the loss of nutrients in water and air, reducing contamination risks. However, commercial CRFs often release nutrients either too quickly or slowly due to the properties of their coating materials (polymer or sulfur). In this work, a novel CRF technology was developed using chitosan (CS) and graphene oxide (GO) nanocomposites as coating materials. CS and GO solutions were applied at varying ratios in preparing different nanocomposites. CS and GO formed homogeneous nanocomposite films through their interactions with each other. Fertilizer beads were successfully encapsulated by the CS-GO films using the simple dipping method. Resulting CRFs showed controlled-release behaviors, with nutrient release lasting for about a week. Although additional investigations are required for further evaluation and optimization, this method presents a promising concept for an alternative fertilizer-coating technology.

In this study, the synthesis of iron oxide stabilized by chitosan was carried out for the application and optimization in the removal process of aqueous Cr(VI) by central composite design (CCD). The calculation of these effects allowed to know, quantitatively, the variables and the interaction between them that could affect the Cr(VI) removal process. It was also verified that the most favorable conditions for chromium removal were the following: pH 5.0, Cr(VI) concentration of 130 mg L⁻¹, adsorbent mass of 5 mg, and Fe(II) content of 45% (w/w) in the CT-Fe beads. The adsorption kinetics performed under these conditions showed that the chitosan/iron hybrid composite is an adsorbent material with high chromium removal capacity (46.12 mg g⁻¹). It was found that all variables were statistically significant. However, it was observed that the variable that most affected Cr(VI) removal was the pH of the solution, followed by the concentration of chromium ions in solution and the interaction between them. Therefore, the studied experimental conditions are efficient in chromium adsorption, besides the operational simplicity coming from statistical design. Theoretical calculations showed that the most stable chitosan was that with Fe(II) in the structure, that is, in the reaction mechanism, there is no competition of Fe(II) with Cr(III, VI) in the available sites of chitosan. Thus, the theoretical calculations show that the proposed Cr(VI) removal is effective.

This study has compared the harvesting efficiency of four flocculation methods, namely, induced by pH, FeCl₃, AlCl₃ and chitosan. No changes were observed on M. aeruginosa cells. Flocculation assays performed at pH 3 and 4 have shown the best harvesting efficiency among the pH-induced tests, reaching values above 90% after 8 h. The adjustment of zeta potential (ZP) to values comprised between − 6.7 and − 20.7 mV enhanced significantly the settling rates using flocculant agents, being FeCl₃ the best example where increments up to 88% of harvesting efficiency were obtained. Although all the four methods tested have presented harvesting efficiencies above 91% within the first 8 h after the optimization process, the highest performance was obtained using 3.75 mg L⁻¹ of FeCl₃, which allowed reaching 92% in 4 h.

In this work, hexavalent chromium adsorption onto LDPE and agave fiber composites coated with chitosan or cellulose was studied in batch experiments. Chemical modifications consisting in cross-linked chitosan, cross-linked chitosan xanthate, and cellulose xanthate were applied to the polysaccharide-coated sorbents in order to increase their stability and adsorption capacity. The sorbents were characterized in terms of morphology by scanning electron microscopy and their chemical composition was evaluated by infrared and nuclear magnetic resonance spectroscopies. The results showed that the adsorption kinetics followed the pseudo-second-order model in all cases (i.e., chemisorption as the rate-limiting step of the adsorption reaction). Moreover, the isotherms evidenced a monolayer adsorption on homogeneous sites described by the Langmuir model. The maximum adsorption capacity of 284.7 mg Cr(VI)/g was obtained for the cross-linked chitosan xanthate sorbent at pH 4 which represents an increase of 43% against the chitosan-coated sorbent (199.1 mg Cr(VI)/g). Besides, functionalized cellulose sorbent also increased its capacity from 84.5 to 106.0 mg Cr(VI)/g cellulose due to the xanthate group. Up to six adsorption-desorption cycles were completed for the case of functionalized chitosan sorbent, confirming that the stability was increased with the cross-linking and the material could be reused several times without losing its adsorption capacity. In the case of cellulose xanthate, only three adsorption cycles were completed. However, improvements were observed in the desorption capacity considering that it decreased below 20% after two cycles in the cellulose-coated sorbent.

Robust and simple composite films for the removal of methyl orange (MO) and Cr(VI) have been prepared by combining chitosan, saponin, and bentonite at a specific ratio. There are several composite films (chitosan-saponin-bentonite (CSB)) prepared; among them, the composite films CSB₂:₃ and CSB₁:₁ have the highest removal efficiency toward MO and Cr(VI) where the maximum removal is 70.4% (pH 4.80) and 92.3% (pH 5.30), respectively. It was found that different types of adsorbate have different thermodynamic properties of the adsorption process; the adsorption of MO onto CSB₂:₃, chitosan, and acid-activated bentonite (AAB) proceeded endothermically, while the adsorption of Cr(VI) onto CSB₁:₁, chitosan, and AAB proceeded exothermically. The parameters of the adsorption were modeled by using isotherm and kinetic equations. The models of Langmuir, Freundlich, Redlich-Peterson, Sips, and Toth were used for fitting the adsorption isotherm data at a temperature of 30, 45, and 60 °C; all of the isotherm models could represent the data well. The result indicates that CSB₂:₃ has the highest adsorption capacity toward MO with qₘ of 360.90 mg g⁻¹ at 60 °C; meanwhile, CSB₁:₁ has the highest adsorption capacity toward Cr(VI) with qₘ 641.99 mg g⁻¹ at 30 °C. The pseudo-second-order model could represent the adsorption kinetics data better than the pseudo-first-order equation. The adsorption mechanism was proposed, and the thermodynamic properties of the adsorption were also studied.

Chitosan/Co-Fe-layered double hydroxides (CS/LDHs) were prepared by coprecipitation method, which is a kind of composite material with excellent properties. The structure of CS/LDHs was characterized by SEM, FTIR, and XRD, which proved that chitosan (CS) was successfully induced into hydrotalcite and CS/LDHs still possess the structural characteristics of hydrotalcite. The adsorption of 2,4-dichlorophenol (2,4-DCP) was studied with CS/LDHs and LDHs as adsorbent separately. The activity of immobilized laccase (L-CS/LDHs) with CS/LDHs as carrier is significantly better than that of the one (L-LDHs) using LDHs as carrier. Under the optimum conditions (pH = 6, 55 °C, 48 h), L-CS/LDHs exhibited better removal performance for 2,4-DCP (81.53%, 100 mg/L) than LDHs (63.55%); the removal of 2,4-DCP by L-CS/LDHs is excellent, exceeding 97% as its initial concentration below 60 mg/L. It includes the catalytic action of laccase and dechlorination of Fe³⁺ and Co²⁺, and the adsorption can be ignored under the optimal conditions. After 5 cycles, it maintained 67% (L-CS/LDHs) and 54% (L-LDHs) of the original removal.

There is a growing trend to implement biosecurity measures in small commercial broiler flocks and trying to replace ineffective antimicrobial with alternative materials to interevent a strategy for the control of Campylobacter bacteria in these farms. This study was designed to determine the prevalence rate of Campylobacter spp. in broiler flocks and their environment. Thereafter, assess the efficiency of chitosan, zinc oxide nanoparticles (ZnO NPs), and chitosan/ZnO NPs composite against Campylobacter strains to adopt a novel control strategy based on the ability to use those nanocomposites. A total of 220 samples were collected from broiler flocks, their environment, and farm attendants that direct contact with birds. All samples were subjected to microbiological investigation for isolation, then molecular identification of bacteria using PCR. ZnO NPs and chitosan/ZnO NPs composite were synthesized then characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared spectrum (FT-IR), and X-ray diffraction (X-RD). The efficiency of testing compounds was examined against 30 strains of Campylobacter coli (C. coli) to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The highest percentages of C. coli were isolated from the manure storage area, and broiler litter followed by flies, and feeders (66.7, 53.3, 40.0, and 33.3%, respectively). Both chitosan/ZnO NPs and ZnO NPs at a concentration of 0.5 μg/mL and 1.5 μg/mL, respectively showed complete efficiency (100%) against C. coli compared with chitosan compound. In conclusion, manure storage area and broiler litter represented the main reservoir of Campylobacter bacterial contaminant followed by flies in broiler poultry farms. Chitosan/ZnO NPs composite can be used in any biosecurity program of poultry farms as an alternative to ineffective antimicrobial agents.

In this study, magnetic bio-adsorbent based on chitosan with high molecular weight was prepared. To stabilize under acidic condition, the synthesized magnetic chitosan was cross-linked with κ-carrageenan (mChitoCar). The magnetic bio-adsorbent was characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results indicated that mChitoCar had desirable magnetic-sorption properties, and magnetic/bio-adsorbent was successfully synthesized and cross-linked. The present nanocomposite was applied to remove and immobilize Cd²⁺ from water and soil systems. Adsorption and desorption of cadmium by the chitosan bio-adsorbent were investigated using batch experiments. Isotherm data were described by using Freundlich, Langmuir, Dubinin-Radushkevich, and Temkin models, and better fitting was introduced by Freundlich model in both water and soil systems. The maximum adsorption capacity (b) of cadmium onto mChitoCar appeared to increase from the water system to the soil system, from 750.2 to 992.7 μmol/g, respectively. The adsorption mechanism with the help of potential theory indicates the adsorption of cadmium onto the mChitoCar surface is following chemical adsorption type. To evaluate the efficiency of the modified chitosan as a good bio-adsorbent in water and soil system, the difference between adsorption and desorption amounts, Δq, was calculated. By comparing the amounts of Δq, the bio-adsorbent is not economically feasible at high initial concentrations in the water system. But, the bio-adsorbent used can be relatively economic as a soil modifier.