Chitosan-multilayered graphene oxide hybrid beads for Zn 2 + and metoprolol adsorption

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A Wide Adsorption Range Hybrid Material Based on Chitosan, Activated Carbon and Montmorillonite for Water Treatment

Numerous adsorbent materials are developed and are able to face specific types of pollution, but none of them can manage the whole pollution. The purpose of this work is to develop a novel hybrid adsorbent, based on chitosan (CS) biopolymer, clay minerals and activated carbon (AC), having complementary adsorption properties and achieving a wide-spectrum water decontamination in a single treatment. Hybrid CS beads, containing dispersed clay and AC, were prepared from dispersions of solid adsorbents in a CS solution and its further coagulation in a basic medium. The porosity and the homogeneity of the hybrid beads were characterized by N2 adsorption at 77 K and Cryo-Scanning Electron Microscopy respectively. The interaction between CS and clay was characterized using X-ray diffraction. Water content and the amount of each adsorbent in the hydrogel beads were determined by thermogravimetric analysis. Such a composite material was still porous and presented a wide adsorption spectrum. As shown by their adsorption kinetics, hydrophobic anionic clofibric acid (CBA) and cationic metoprolol (MTP) were well adsorbed on AC containing beads (21 and 26 mg/g), respectively. Clays containing beads showed interesting adsorption properties towards cationic Zn2+ and MTP. The obtained composite beads were able to adsorb all the pollutant types: Zinc cations, and hydrophobic-charged organic molecules, such as pharmaceutical derivatives (clofibric acid and MTP)

Chitosan-multilayered graphene oxide hybrid beads for \protect \text{Zn}^{2+} and metoprolol adsorption

Chitosan (CS) hydrogel beads and hybrid beads made of a blending of CS hydrogels and Multilayer Graphene Oxide (MGO) were synthesized. The hybrid beads were prepared by gelation in NaOH solution of a 1 wt% CS acid solution with addition of MGO at either 1.5 wt% or 3 wt% loading rates. Prepared beads were characterized by infrared spectroscopy, thermogravimetric analysis (TGA), scanning electron cryo-microscopy and Brunauer–Emmett–Teller (BET) specific surface area measurements. $\text{Zn}^{2+}$ and Metoprolol (MTP) adsorption kinetics and isotherms were studied on the pristine and hybrid CS hydrogel beads. The adsorption kinetics of $\text{Zn}^{2+}$ and MTP in hybrid beads is limited by the diffusion to the MGO sites depending on their accessibility. While pure CS is not efficient for the MTP adsorption, the Langmuir-type isotherms of the 3 wt% MGO hydrogel beads (dose: 5 mg/100 mL) show 163 mg$\cdot$g$^{-1}$ maximum adsorption uptake. The MTP adsorption kinetics and isotherm suggest a MTP trapping on the MGO anionic sites (carboxylate groups) by electrostatic interactions. The $\text{Zn}^{2+}$ adsorption capacities are the highest for the 3 wt% MGO hydrogel beads (236 mg$\cdot$g$^{-1}$), and only of 40 mg$\cdot$g$^{-1}$ for the pure CS beads. The presence of $\text{Zn}^{2+}$ adsorption sites in the hybrid bead, such as MGO carboxylate groups giving electrostatic interactions, and CS amine groups leading to complexation, provides synergic adsorption effects. The competitive adsorption of $\text{Zn}^{2+}$ with respect to MTP in equimolar mixture was observed on hybrid beads (dose: 200 mg/100 mL) at 2 mmol$\cdot$L$^{-1}$ initial total concentration. At pollutant initial total concentration lower than 1.5 mmol$\cdot$L$^{-1}$, no competition occurs. The regeneration at pH 4 of the hybrid beads toward MTP or $\text{Zn}^{2+}$ adsorption was found to be 35–40% of the initial adsorption uptake for five adsorption/regeneration cycles