A facile synthetic approach for SiO₂@Co₃O₄ core–shell nanorattles with enhanced peroxidase-like activity

Abstract

SiO2@Co3O4 coreshell nanorattles with different Co3O4 shell thickness have been successfully synthesized by the calcination of SiO2@-Co(OH)2 at 500 o C. The synthetic approach is facile, economical, and requires no surface modification. The synthesized materials were thoroughly characterized using powder Xray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), BrunauerEmmettTeller (BET) analysis, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and diffuse reflectance spectroscopy (DRS). SEM analysis indicates hierarchical coreshell morphology for SiO2@Co3O4 and the TEM results indicate the coreshell nanorattle morphology. Diffuse reflectance spectroscopy studies indicate that the SiO2@Co3O4 coreshell nanorattles show two absorption bands in the range 420450 nm and 700750 nm related to ligand to metal charge transfer transitions (O 2 → Co 2+ and O 2 → Co 3+ ). The SiO2@Co3O4 coreshell nanorattles act as an artificial peroxidase enzyme mimic with enhanced intrinsic peroxidaselike activity compared to pure Co3O4 nanoparticles and horseradish peroxidase (HRP), a natural enzyme. The SiO2@Co3O4 coreshell nanorattles show higher kcat and kcat/Km values compared to pure Co3O4 and HRP indicating their applicability as artificial enzyme mimic in biomedicine and biosensing.

Effect of the Silica Cover on the Properties of Co 3 O 4 Nanoparticles

“…Figure 8 shows the FT-IR absorption spectrum of the uncoated cobalt oxide nanoparticles together with the IR absorption spectrum of coated and functionalized nanoparticles. Cobalt oxide nanoparticles show two characteristic bands located at 560 and 667 cm −1 attributed to Co(II)-O stretching when Co 2+ ions are in tetrahedral coordination [59]. In this case, both samples show these bands, which corroborates the presence of cobalt oxide in the coated sample.…”

Synthesis of Silica@Ni‐Co Mixed Metal Oxide Core–Shell Nanorattles and Their Potential Use as Effective Adsorbents for Waste Water Treatment

“…The third step shows a minor weight loss (ca. 2.5 %) between 300 and 860 °C owing to the decomposition of NiCo 2 O 4 48. The SiO 2 @Ni‐Co LDH samples (PM1, PM2, and PM3) show weight loss from both silica and Ni‐Co LDH, and the overall weight loss values up to 1000 °C are 24.7, 21.7, and 28.1 % for samples PM1, PM2, and PM3, respectively.…”

“…α‐Ni(OH) 2 loses its hydroxy groups between 250 and 320 °C, whereas α‐Co(OH) 2 loses hydroxy groups between 220 and 300 °C 46,48. The SiO 2 @Ni‐Co LDH samples exhibit different thermal decomposition behavior, which is an indication that the dehydroxylation and decomposition steps depend on the Ni/Co molar ratio used during the preparation of the LDHs.…”

“…For the formation of SiO 2 @Ni‐Co mixed metal oxide core–shell nanorattles, the following mechanism (Scheme ) based on adsorption–nucleation–coalescence–anisotropic growth–self‐assembly is proposed 48. Urea as a precipitating agent slowly releases OH – ions through controlled hydrolysis 39.…”

“…The single ultrathin nanoplatelets of Ni‐Co LDH possess high surface energy and, to minimize the overall surface energy, the formed ultrathin nanoplatelets of Ni‐Co LDH undergo coalescence and self‐assembly to produce thicker nanoplatelets of Ni‐Co LDH. During this process, the pH of the solution decreases, and dominant Ostwald ripening growth leads to flowerlike hierarchical Ni‐Co LDH particles on the surface of the SiO 2 48. In the final step, the calcination of SiO 2 @Ni‐Co LDHs in air at 500 °C leads to the formation of SiO 2 @Ni‐Co mixed metal oxide core–shell nanorattles through a self‐template route, and the morphology of SiO 2 @Ni‐Co LDHs is retained.…”