RESUMEN

In this study, the synthesis and experimental theoretical evaluation of a new chitosan/alginate/hydrozyapatite nanocomposite doped with Mn2 and Fe2O3 for Cr removal was reported. The physicochemical properties of the obtained materials were analyzed using the following methods: SEM-EDX, XRD, FTIR, XPS, pH drift measurements, and thermal analysis. The adsorption properties were estimated based on equilibrium and adsorption kinetics measurements. The Langmuir, Freundlich and Temkin isotherms were applied to analyze the equilibrium data. The thermodynamic analysis of adsorption isotherms was performed. A number of equations and kinetic models were used to describe the adsorption rate data, including pseudo-first (PFOE) and pseudo-second (PSOE) order kinetic equations. The obtained test results show that the synthesized biomaterial, compared to pure chitosan, is characterized by greater resistance to high temperatures. Moreover, this biomaterial had excellent adsorption properties. For the adsorption of Cr (VI), the equilibrium state was reached after 120 min, and the sorption capacity was 455.9 mg/g. In addition, DFT calculations and NCI analyses were performed to get more light on the adsorption mechanism of Cr (VI) on the prepared biocomposite.

Asunto(s)

Quitosano , Nanocompuestos , Contaminantes Químicos del Agua , Purificación del Agua , Óxidos , Aguas Residuales , Quitosano/química , Cromo/química , Adsorción , Alginatos/química , Compuestos Férricos/química , Contaminantes Químicos del Agua/química , Purificación del Agua/métodos , Cinética , Materiales Biocompatibles , Nanocompuestos/química , Concentración de Iones de Hidrógeno

RESUMEN

Nitrates level in water is a worldwide problem that represents a risk to the environment and people's health; efforts are currently devoted to the development and implementation of new biomaterials for their removal. In this study, chitosan (Ch) from shrimp waste and the related epichlorohydrin-modified crossover chitosan (Ch-EPI) were used to remove nitrates from aqueous solutions. The mechanism of selective nitrate removal was elucidated and validated by theoretical calculations. The physicochemical performance of Ch and Ch-EPI was investigated through the main parameters pH, adsorption capacity, contact time, initial nitrate concentration, coexisting anions, and temperature. The experimental data were fitted to widely used adsorption kinetic models and adsorption isotherms. The maximum percentage of nitrate adsorption was reached at an equilibrium pH of 4.0 at an adsorbent dose of 2.0 g/L after a contact time of 50 min. Competing anion experiments show that chloride and sulfate ions have minimal and maximal effects on nitrate adsorption by Ch-EPI. Experimental adsorption data are best fitted to pseudo-second-order kinetic and isothermal Langmuir models. The maximum adsorption capacities of Ch and Ch-EPI for nitrate removal were 12.0 mg/g and 38 mg/g, respectively.

Asunto(s)

Quitosano , Contaminantes Químicos del Agua , Humanos , Nitratos , Epiclorhidrina , Aniones , Agua , Adsorción , Cinética , Modelos Teóricos , Concentración de Iones de Hidrógeno

RESUMEN

A novel polymer bio-composite based on nano-hydroxyapatite (n-Hap) and chitosan (CS) (CS/n-Hap) was synthesized to effectively address toxic cadmium ions removal from water. The composition and structure of CS/n-Hap bio-composite were analyzed through different characterization techniques. XRD patterns affirmed that the crystalline structure of n-Hap remained unaltered during CS/n-Hap synthesis, while FT-IR spectrum sustained all the characteristic peaks of both CS and n-Hap, affirming the successful synthesis of CS/n-Hap. Adsorption studies, including pH, adsorbent dosage, contact time, initial Cd(II) concentration, and temperature, were carried out to explain and understand the adsorption mechanism. Comparatively, CS/n-Hap bio-composite exhibited better Cd(II) adsorption capacity than pristine CS, with an experimental maximum uptake of 126.65 mg/g under optimized conditions. In addition, the kinetic data were well fitted to the pseudo-second-order model, indicating the formation of chemical bonds between Cd(II) and CS/n-Hap during adsorption. Furthermore, the thermodynamic study suggested that Cd(II) adsorption onto CS/n-Hap was endothermic and spontaneous. The regeneration study showed only about a 3% loss in Cd(II) uptake by CS/n-Hap after five consecutive cycles. Thus, a simple and facile approach was here developed to synthesize an eco-friendly and cost-effective material that can be successfully employed for the removal of toxic heavy metal ions from water.

RESUMEN

Herein, a chitosan (CH) and fluroapatite (TNP) based CH-TNP composite was synthesized by utilizing seafood waste and phosphate rock and was tested for divalent copper (Cu(II)) adsorptive removal from water. The XRD and FT-IR data affirmed the formation of a CH-TNP composite, while BET analysis showed that the surface area of the CH-TNP composite (35.5 m2/g) was twice that of CH (16.7 m2/g). Mechanistically, electrostatic, van der Waals, and co-ordinate interactions were primarily responsible for the binding of Cu(II) with the CH-TNP composite. The maximum Cu(II) uptake of both CH and CH-TNP composite was recorded in the pH range 3-4. Monolayer Cu(II) coverage over both CH and CH-TNP surfaces was confirmed by the fitting of adsorption data to a Langmuir isotherm model. The chemical nature of the adsorption process was confirmed by the fitting of a pseudo-second-order kinetic model to adsorption data. About 82% of Cu(II) from saturated CH-TNP was recovered by 0.5 M NaOH. A significant drop in Cu(II) uptake was observed after four consecutive regeneration cycles. The co-existing ions (in binary and ternary systems) significantly reduced the Cu(II) removal efficacy of CH-TNP.