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In this research, a solvothermal approach is introduced to synthesize a metal-organic frameworks (MOFs) nanocomposite (GO/UiO-66-NDC) for the removal of Cr(VI) from water. A comprehensive analysis was performed to understand the physical, chemical, and structural properties of the MOF nanocomposite. The adsorption behavior of Cr(VI) was investigated by changing various parameters, such as pH, dosage, and concentration, to determine isotherms, thermodynamics, and kinetics. The results showed that the nanocomposite had a high tolerance to pH and thermal stability, with a high adsorption capacity of 157.23 mg g−1 for Cr(VI) at pH 3 due to the presence of zirconium oxide clusters. The density functional theory simulations showed that the nanocomposite had ten times more dynamic delocalized surface states, which enhanced the adsorption capacity and agreed with the experimental results. Furthermore, the nanocomposite exhibited better regeneration performance compared to previously reported materials, making it a promising super-adsorbent for removing Cr(VI) from water. [ABSTRACT FROM AUTHOR]

Metal-based adsorbents are limited for hexavalent chromium [Cr(VI)] adsorption from aqueous solutions because of their low adsorption capacities and slow adsorption kinetics. In the present study, decorated zinc oxide (ZnO) nanoparticles (NPs) on graphene oxide (GO) nanoparticles were synthesized via the solvothermal process. The deposition of ZnO NPs on graphene oxide for the nanohybrid (ZnO-GO) improves Cr(VI) mobility in the nanocomposite or nanohybrid, thereby improving the Cr(VI) adsorption kinetics and removal capacity. Surface deposition of ZnO on graphene oxide was characterized through Fourie Transform Infra-red (FTIR), UV–Visible, X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), and Brunauer–Emmett–Teller (BET) techniques. These characterizations suggest the formation of ZnO-GO nanocomposite with a specific area of 32.95 m2/g and pore volume of 0.058 cm2/g. Batch adsorption analysis was carried to evaluate the influence of operational parameters, equilibrium isotherm, adsorption kinetics and thermodynamics. The removal efficiency of Cr(VI) increases with increasing time and adsorbent dosage. FTIR, FESEM and BET analysis before and after the adsorption studies suggest the obvious changes in the surface functionalization and morphology of the ZnO-GO nanocomposites. The removal efficiency increases from high-acidic to neutral pH and continues to decrease under alkaline conditions as well. Mathematical modeling validates that the adsorption follows Langmuir isotherm and fits well with the pseudo 2nd order kinetics (Type 5) model, indicating a homogeneous adsorption process. The thermodynamics study reveals that Cr(VI) adsorption on ZnO-GO is spontaneous, endothermic, and entropy-driven. A negative value of Gibb's Free Energy represents the thermodynamic spontaneity and feasibility of the sorption process. To the best of our knowledge, this is the first study of Cr(VI) removal from aqueous solution using this hybrid nanocomposite at near-neutral pH. The synthesized nanocomposites prove to be excellent candidates for Cr(VI) removal from water bodies and natural wastewater systems. [ABSTRACT FROM AUTHOR]

A novel green nanocomposite has been prepared by immobilizing CaO nanoparticles (CaO NPs) on the surface of graphene oxide. Biogenic CaO-NPs were synthesized from Lala clamshells. Morphological and structural characterizations of the nanocomposite were studied extensively. The adsorption capacity (q max) of the nanocomposite for removing Cr(VI) was 38.04 mg g−1. In addition to this, the adsorption data were adequately simulated with Langmuir, Freundlich, Temkin, and pseudo-second-order models, suggesting that the adsorption process was the combination of external mass transfer and chemisorption. Electrostatic interaction was the dominant mechanism for Cr(VI) removal. In addition, the synthesized nanocomposites also serve as an excellent sensor for Cr(VI) sensing, with a limit of detection (LOD) of 0.02 μM utilizing electrochemical methods. Therefore, this green nanocomposite can simultaneously serve as an adsorbent and sensor for Cr(VI)removal from aqueous solutions. [Display omitted] • Clam Sea shell waste was used for production of nanocomposites using CaO and GO. • Nanocomposite showed maximum adsorption capacity of 38.04 mg/g. • Chemisorption mechanisms accounted for Cr (VI) removal using CaO-GO. • The developed sensor exhibited catalytic behavior towards the Cr(VI) sensing in terms of selectivity and sensitivity. • Real-world sample analysis was carried out using tap water samples. [ABSTRACT FROM AUTHOR]

Herein, for the adsorption and detection of As (III), multifunctional nanohybrid have been synthesized using a solvothermal approach. Structural and functional characterizations confirmed the impregnation of the ZnO over graphene oxide. Nanohybrid exhibits a remarkable q max (maximum adsorption capacity) of 8.17 mg/g, at an adsorbent dose of 3 g/L and pH of 8.23. Higher adsorption with nanohybrid was attributed to a large BET surface area of 32.950 m2/g. The chemical nature and adsorption behaviour of As(III) on ZnO-GO were studied by fitting the data with various adsorption isotherms (Langmuir & Freundlich) and kinetics models (six models). It is observed from the findings that removal of As(III) with ZnO-GO nanocomposite appears to be technically feasible with high removal efficiency. The feasibility of the nanocomposite to function as a sensor for the detection of As(III) was also evaluated. The fabricated sensor could detect As(III) with a lower limit of detection of 0.24 μM and linear range up to 80 μM. Overall, this study is significant in nanohybrid as a multifunctional composite for the adsorption and detection of As (III) from wastewater. [Display omitted] • ZnO-GO nanohybrid was synthesized by a solvothermal approach using ZnO nanoparticles and graphene oxide. • ZnO-GO nanocomposite exhibited exemplary removal efficiencies for As(III) from an aqueous matrix. • Optimum conditions for adsorption of As(III) by ZnO-GO nanohybrid were determined. • Nanohybrid acts as a sensing material for electrochemical detection of As(III) in environmental matrices. [ABSTRACT FROM AUTHOR]