Synthesis and study of catalytic activity of carbon-capped CNT/nickel nanospheres

Abstract

Efficiently designed metal nanoparticles (MNPs) for nanotechnology for catalytic application, energy storage and energy conversion, fuel cells, antimicrobial materials, and sensinghave attracted the interest of scientists due to their excellentnanoscale characteristics. In this work, we reported a facile strategy for synthesizing magnetically retrievable carbon-capped carbon nanotubeNi nanospheres (C-capped CNT/Ni) and their application for the catalytic reduction of 4-nitrophenol (4-NP) and enzyme mimicking nanozyme activity.The C-capped CNT/Ni nanospheres were synthesized by combining the reduction of Ni2+ salt and the hydrothermal process. The phase purity and structural composition, morphology, and structure were characterized byemploying X-ray Diffraction (XRD), Energy Dispersive X-ray (EDX), and Field Emission Scanning Electron Microscope (FESEM) techniques. The XRD and EDS confirm the purity and successful formation of C-capped CNT/Ni nanosphere. The XRD revealed that the crystal structure of Ni nanospheres is face-centered cubic(fcc).The FESEM image indicates the finely immobilized Ni nanospheres utilizing uniform capping of the carbon layer via interconnected firmly dispersed CNT. The FESEM study showed that the Ni nanoparticles possess a spherical shape, with an average size between ~24 to 30 nm, maintaining an interconnection via CNT with C-layer. The C-capped CNT/Ni nanosphere exhibits enhanced catalytic activity for reducing 4-NP to 4-aminophenol (4-AP). The kinetic rate constant of the C-capped CNT/Ni (kapp=0.6167 min-1) is about six-fold larger than that of bare Ni nanospheres (kapp=0.1056 min-1). The significant difference in catalytic activity is attributed to the better synergistic effect between the spherical Ni core and capped C layer via interconnected CNT compared to bare Ni nanospheres. Furthermore, the C-capped CNT/Ni nanosphere displays outstanding reusability for reducing 4-NP. In addition to nano-catalytic activity, the C-capped CNT/Ni nanosphere exhibits intrinsic peroxidase-mimetic activity towards 3,3′,5,5′-tetramethylbenzidine (TMB), and H2O2. The peroxidase-mimicking activity of the C-capped CNT/Ni nanosphere was investigated through catalytic oxidation of TMB in the presence of H2O2. The results showed that nanoparticles follow typical Michaelis Menten kinetics and exhibit excellent affinity towards TMB and H2O2 with estimated Km and VMax values of 2.818mM and 50×10-8Ms-1for TMB, and 3.672 mM and 65×10-8 Ms-1for H2O2, respectively. Thus, the C-capped CNT/Ni nanosphere showed comparable or superior activity for reducing 4-NP and peroxidase mimetic activity compared to other nanomaterials.