GreenApproach to Decorate Multi-walled Carbon Nanotubes by Metal/Metal Oxide Nanoparticles

Electrocatalysis of Endosulfan Based on Fe3O4: An Experimental and Computational Approach

The present work reports the electrocatalytic oxidation of the organochlorine pesticide endosulfan (EDS) using iron oxide (Fe₃O₄) nanoparticles synthesized from Callistemon viminalis leaf extracts. As a sensor for EDS, Fe₃O₄ was combined with functionalized multiwalled carbon nanotubes (f-MWCNTs) on a glassy carbon electrode (GCE). Cyclic voltammetry, electrochemical impedance spectroscopy, and the differential pulse voltammetry experiment were conducted to investigate the electrochemistry of EDS on the GCE/f-MWCNT/Fe₃O₄ sensor. Based on optimized experimental conditions, the reports of analytical parameters show a limit of detection of 3.3 μM and an effective sensitivity of 0.06464 μA/μM over a range of concentrations from 0.1 to 20 μM. With the proposed method, we were able to demonstrate recoveries between 94 and 110% for EDS determinations in vegetables. Further, a series of computational modeling studies were carried out to better understand the EDS surface adsorption phenomenon on the GCE/f-MWCNT/Fe₃O₄ sensor. The highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap (-5.18 eV) computed by density functional theory (DFT) supports the layer-by-layer electrode modification strategy's charge transfer and stability. Finally, transition state modeling was able to predict and confirm the mechanism of endosulfan oxidation.

Efficiency and stability evaluation of Cu2O/MWCNTs filters for virus removal from water

Both multi-walled carbon nanotubes (MWCNTs) and metal or metal oxides have demonstrated virus removal efficacy in drinking water applications. In this study, MWCNTs were coated with copper(I) oxide (Cu₂O) using three distinct synthesis procedures (copper ion attachment, copper hydroxide precipitation, and [Cu(NH₃)₄]²⁺ complex attachment) and virus removal efficacy (using MS2 bacteriophages) was evaluated. All synthesis procedures resulted in the presence of adsorbed, nanosized Cu₂O particles on the MWCNTs, shown using X-ray diffraction. Further, transmission electron microscopy confirmed uniform copper(I) oxide distribution along the MWCNTs for all three materials. Virus removal efficacy was assessed for all three synthesised composites both before and after material conditioning (filtering for at least 24 h/280 mL/h), and accounting for additional MS2 inactivation in the permeate due to continued copper inactivation from dissolved/desorbed copper in permeate (time-control). Material conditioning influenced virus removal, with the first litres of water containing higher concentrations of copper than the sixth litres of water, suggesting excess or non-bonded copper species dissolve from filters. Higher copper dissolution was observed for water at pH 5 than at pH 7, which decreased with time. Copper dissolution most likely caused an associated decrease in copper adsorbed to MWCNTs in the filters, which may explain the observed lower MS2 removal efficacy after conditioning. Additionally, the time-control study (immediately after filtration as compared to 2 h after filtration) highlighted continued MS2 inactivation in the permeate over time. The obtained results indicate that the synthesis procedure influences virus removal efficacy for MWCNTs coated with copper oxides and that virus removal is likely due to not only virus electrostatic adsorption to the coated MWCNTs, but also through antiviral properties of copper which continues to act in the permeate. In conclusion, it is highly important to revise the methods of testing filter materials for virus removal, as well as procedure for virus concentration evaluation.

Preparation of Carbon Nanotubes with Supported Metal Oxide Nanoparticles: Effect of Metal Precursor on Thermal Decomposition Behavior of the Materials

To develop new catalysts based on carbon nanomaterials with supported metal oxide nanoparticles for oxidative transformations of sulfur compounds, a series of metal oxide nanoparticle-decorated carbon nanotubes (MOx/CNTs) were prepared by incipient wetness impregnation at a variation of the active metal type (M = Ce, Mo, Cu). The thermal decomposition of bulk and CNT supported metal precursors used in the preparation of MOx/CNTs was analyzed under inert atmosphere employing several thermoanalytical techniques (thermogravimetry, differential thermogravimetry and differential scanning calorimetry) coupled with mass spectrometry. The thermolysis parameters of the bulk and supported metal precursors were compared and the effect of CNT support on the decomposition pattern of compounds was elucidated. It was established that the decomposition of metal precursors supported on CNTs was started and completed at temperatures of 15‒25 and 25‒70 °C lower, respectively, compared with the bulk active metal precursor. The enhancement of CNT support stability against thermal degradation is observed in the following row of metal cations: Ce < Cu < Мо < pristine and metal anions of precursor: nitrate < chloride < sulfate. The optimal mode of thermal treatment of catalyst and appropriate active metal precursors were selected for advanced synthesis of nanosized MOx/CNT catalyst.