Spectroscopic and antibacterial activities of cobalt and nickel nanoparticles: a comparative analysis

This study aimed to compare the spectroscopy, morphological, electrocatalytic properties, and antibacterial activities of cobalt nanoparticles (CoNPs) with nickel nanoparticles (NiNPs). Cobalt nanoparticles and NiNPs were prepared via a chemical reduction approach and characterized utilizing transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD) techniques. The result from XRD and TEM analysis revealed that the synthesized nanoparticles exhibit face-centered cubic with smooth spherical shape, having average particles size of 12 nm (NiNPs) and 18 nm (CoNPs). The electrochemical properties of the nanoparticles were examined via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. The CV results showed that GCE-Ni (35.6 μA) has a higher current response compared to GCE-Co (10.5 μA). The EIS analysis revealed that GCE-Ni (1.39 KΩ) has faster electron transport capability compared to GCE-Co (2.99 KΩ) as indicated in their Rct values. The power density of the synthesized nanoparticles was obtained from their "knee" frequency (f°) values, with GCE-Ni (3.16 Hz) having higher f° values compared to GCE-Co (2.00 Hz). The antibacterial activity of the nanoparticles was evaluated against multidrug-resistant Escherichia coli O157, Escherichia coli O177, Salmonella enterica, Staphylococcus aureus, and Vibrio cholerae. The result from the antibacterial study revealed that at low concentrations both CoNPs and NiNPs have significant antibacterial activities against E. coli O157, E. coli O177, S. enterica, S. aureus, and V. cholerae. NiNPs showed better antibacterial activities at low concentrations of 61.5, 61.5, 125, 61.5, and 125 µg/mL compared to CoNPs with minimum inhibitory concentrations of 125, 125, 250, 61.5, and 125 µg/mL against E. coli O157, E. coli O177, S. enterica, S. aureus, and V. cholerae, respectively. These promising antibacterial activities emphasize the potential of CoNPs and NiNPs as effective antibacterial agents, which could aid in the development of novel antibacterial medicines.

Xanthan gum-based copper nano-magnetite doped carbon aerogel: A promising candidate for environmentally friendly catalytic dye degradation

In this work, a novel copper nano-magnetite doped carbon aerogel (CXMCA) was created utilizing a simple graft co-polymerization approach with xanthan gum (XG) as a template to tackle the agglomeration problem caused by magnetic nanoparticle magnetism. The results indicated that the XG based CXMCA exhibited outstanding magnetic properties (Ms = 36.52 emu/g) as well as strong catalytic activity for the degradation of cationic and anionic dyes. Among all organic dyes, methylene blue and crystal violet (MB, CV) as cationic dyes, as well as congo red and methyl orange (CR, and MO) as anionic dyes, CXMCA demonstrated an exceptional dye degradation rate (8.06 × 10-3 s-1-1.12 × 10-2 s-1) and was highly competent for cationic dyes with degradation (90 %-98 %) as compared to its unsupported magnetic nanoparticles. The formation of CXMCA catalyst is clearly confirmed by the FTIR, XRD, XPS, VSM, SEM & TEM analyses. We report a very effective xanthan gum-based copper nano-magnetite doped carbon aerogel dye scavenger with application in percentage dye degradation and kinetic investigations, as well as a remarkable reusability assay up to 7 repetition cycles. The findings suggested that using biological macromolecules like xanthan gum as a foundation to generate magnetic aerogels might be a good choice for evaluating environmental aspects.

Core-shell structured Co@CN nanocomposites as highly efficient dual function catalysts for reduction of toxic contaminants and hydrogen evolution reaction

In this study, we have reported nitrogen-doped graphite C coated Co nanocomposite (Co@CN) catalysts synthesized by one-step arc discharge method. The surface compositions, morphologies and the catalytic properties of the Co@CN nanocomposites were studied minutely. The results reveal that the prepared Co@CN nanocomposites have typical core-shell structure and show highly efficient catalytic performance in a reduction of 4-nitrophenol (4-NP), rhodamine and methylene blue. Their rate constant (K_app) is 0.074 s^-1 in a reduction of 4-NP, which is much higher than that of reported transition metal-based catalysts. Moreover, the overpotential of Co@CN is only 96 mV at a current density of 10 mA cm^-2 in alkaline solution, showing high electrocatalytic activities in the hydrogen evolution reaction. The excellent synergistic effect between nitrogen-doped graphite C shell and magnetic Co core enables the Co@CN nanocomposites catalysts to hold abundant active sites and to transmit rapidly electron ability, resulting in Co@CN nanocomposite catalysts having a highly efficient catalytic nature.

Mussel-inspired immobilization of Au on bare and graphene-wrapped Ni nanoparticles toward highly efficient and easily recyclable catalysts

Bimetallic nanocatalysts have been gaining huge research attention in the heterogeneous catalysis community recently owing to their tunable properties and multifunctional characteristics. In this work, we fabricated a bimetallic core-shell nanocomposite catalyst by employing a mussel-inspired strategy for immobilizing gold nanoparticles (AuNP) on the surface of nickel nanoparticles (NiNP). NiNPs obtained from the reduction of Ni(ii) were first coated with polydopamine to provide the anchoring sites towards the robust immobilization of AuNPs. The as-synthesized nanocomposite (Ni-PD-Au) exhibited outstanding catalytic activity while reducing methylene blue (MB) and 4-nitrophenol (4-NP) yielding rate constants 13.11 min-1 and 4.21 min-1, respectively, outperforming the catalytic efficiency of its monometallic counterparts and other similar reported catalysts by large margins. The superior catalytic efficiency of the Ni-PD-Au was attributed to the well-known synergistic effect, which was experimentally investigated and compared with prior reports. Similar bio-inspired immobilization of AuNPs was also applied on graphene-wrapped NiNPs (Ni-G) instead of bare NiNPs to synthesize another composite catalyst (Ni-G-PD-Au), which yet again exhibited synergistic catalytic activity. A comparative study between the two nanocomposites suggested that Ni-PD-Au excelled in catalytic activity but Ni-G-PD-Au provided noteworthy stability showing ∼100% efficiency over 17 repeated cycles. However, along with excellent synergistic performance, both nanocomposites demonstrated high magnetization and thermal stability up to 350 °C ascertaining their easy separation and sustainability for high-temperature applications, respectively.

A new V-doped Bi2(O,S)3 oxysulfide catalyst for highly efficient catalytic reduction of 2-nitroaniline and organic dyes

A new type of convenient, and environmentally friendly, Vanadium (V)-doped Bi₂(O,S)₃ oxysulfide catalyst with different V contents was successfully synthesized via a simple and facile method. The obtained V-doped Bi₂(O,S)₃ solid solution catalysts were fully characterized by conventional methods. The catalytic performance of the samples was tested by using the reduction of 2-nitroaniline (2-NA) in aqueous solution. The reduction/decolorization of methylene blue (MB) and rhodamine B (RhB) was also chosen to evaluate the universality of catalysts. It was observed that the introduction of V can improve the catalytic performance, and 20%V-Bi₂(O,S)₃ was found to be the optimal V doping concentration for the reduction of 2-NA, MB, and RhB dyes. For comparative purposes, a related V-free Bi₂(O, S)₃ oxysulfide material was synthesized and tested as the catalyst. The superior activity of V-doped Bi₂(O,S)₃ over pure Bi₂(O,S)₃ was ascribed mainly to an increase in active sites of the material and also due to the presence of synergistic effects. The presence of V⁵⁺ as found from XPS analysis may interact with Bi atoms and enhancing the catalytic activity of the sample. In the catalytic reduction of 2-NA, MB and RhB, the obtained V-doped Bi₂(O,S)₃ oxysulfide catalyst exhibited excellent catalytic activity as compared with other reported catalysts. Furthermore this highly efficient, low-cost and easily reusable V-doped Bi₂(O,S)₃ catalyst is anticipated to be of great potential in catalysis in the future.

Synthesis of a hierarchical structured NiO/NiS composite catalyst for reduction of 4-nitrophenol and organic dyes

The synthesis approach of the catalyst is simple and facile. The NiO/NiS catalyst is effective and universal towards reduction. NiS facilitates electron transfer for reduction reactions.