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Herein, a magnetic MXenes based composite (Fe

A highly efficient fiber-based adsorbent (DAVFs-CS) was developed via decoration of chitosan (CS) on the dialdehyde viscose fibers (DAVFs) substrate, and employed to selective separation of precious metals from simulated contaminated water. The surface functionalization of the solid material was probed using the Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA) and nuclear magnetic resonance (NMR) technique. The batch characteristic results showed that the maximum uptake capacities of DAVFs-CS were higher up to 322 mg/g and 207 mg/g for Au(III) and Pd(II) at optimal pH 2.0 and 3.0, which exhibited competitiveness with the majority of the reported adsorbents. Meanwhile, the adsorption data were in accordance with Langmuir and PSO equations, which indicated that the monolayer chemisorption dominated the adsorption process. The competitive adsorption study showed that the removal efficiency of Au(III) was not susceptible to the co-existing impurities. Adsorption mechanism study revealed that the negative Au(III) or Pd(II) species were firstly adsorbed on DAVFs-CS via the protonated amino groups, subsequently the partially reduction of them to zero-valent gold and palladium with the help of reductive functional groups. Thus, DAVFs-CS could be as a promising adsorbent to recovery of precious metals owning to its unique adsorption mechanism and excellent adsorption performance.

A novel bio-adsorbent (DAVF-PT) was prepared by the introduction of persimmon tannin (PT) on the surface of viscose fiber (VF) through condensation reaction. The adsorbent was applied to the adsorption of Au(III) and Pd(II) from aqueous solution. Batch adsorption experiment found that the adsorption performance of DAVF-PT for Au(III) and Pd(II) was closely related to pH of solution, initial metal ion concentration as well as co-existing metal ions. The adsorption isotherms data of Au(III) and Pd(II) on DAVF-PT could be best explained by the Langmuir equation, and the fitted maximum adsorption amounts for Au(III) and Pd(II) were 535 mg/g and 214 mg/g, much higher than those similar adsorbents reported in the literatures. The thermodynamic study revealed that adsorption reaction was an endothermic, spontaneous and entropy increase process. Furthermore, the kinetics data of Au(III) and Pd(II) adsorption on DAVF-PT obeyed the Pseudo-second-order equation, indicating that the chemical adsorption was the mainly rate-limiting step. The EDS, XPS and XPD analysis confirmed that the gold and palladium ions were reduced to metallic state following adsorption, while the phenolic group was simultaneously converted into quinone group, indicating the potential use of this novel fiber-based adsorbent in the recovery of precious metal ions from wastewater.

A low-cost and environmentally green biosorbent (PTCS) was prepared by grafting chitosan onto persimmon tannin extract and its potentiality for efficient adsorption of palladium ion (Pd(II)) from aqueous solution was evaluated. Various adsorption parameters such as pH, the initial Pd(II) concentration and temperature were investigated. The maximum adsorption capacity reached 330 mg/g at 323 K and pH 5.0 when the initial Pd(II) concentration was 100 mg/L. The equilibrium adsorption data were satisfactorily fitted with Freundlich isotherm model and biosorption kinetics was found to be in good agreement with pseudo-second-order kinetics model. Thermodynamic calculations indicated that the adsorption process was endothermic and spontaneous in nature because of the negative value of free energy change (Δ G ) and positive value of enthalpy change (Δ H ). The positive value of entropy change (Δ S ) revealed the increased randomness at the solid–liquid interface. FT-IR and XRD analysis verified that Pd(II) adsorption on PTCS was electrostatic interaction and redox reaction. Moreover, selective adsorption study revealed that the adsorbent exhibited good adsorption ability to Pd(II) in the mixture metal ions solutions. All these results indicated that the PTCS biosorbent could be used as a low-cost alternative for the adsorption of Pd(II) in waste-water treatment.