Colorimetric assays have drawn increasing research interest with respect to the quantitative detection of hydrogen peroxide (H 2 O 2 ) based on artificial enzymes because of their advantages with respect to natural enzymes, including design flexibility, low cost, and high stability. Regardless, the majority of the artificial enzymes exhibit low affinity to H 2 O 2 with large Michaelis−Menten constants (K m ). This indicates that the catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to blue-colored oxTMB requires a high H 2 O 2 concentration, hindering the sensitivity of the colorimetric assay. To address this problem, novel reduced Co 3 O 4 nanoparticles (R-Co 3 O 4 ) have been synthesized in this study via a step-by-step procedure using ZIF-67 as the precursor. R-Co 3 O 4 exhibits a considerably enhanced peroxidase-like activity when compared with that exhibited by pristine Co 3 O 4 (P-Co 3 O 4 ). The catalytic process in the case of R-Co 3 O 4 occurs in accordance with the typical Michaelis−Menten equation, and the affinity of R-Co 3 O 4 to H 2 O 2 is apparently higher than that of P-Co 3 O 4 . Furthermore, the density functional theory calculations revealed that the introduction of oxygen vacancies to R-Co 3 O 4 enhances its H 2 O 2 adsorption ability and facilitates the decomposition of H 2 O 2 to produce •OH radicals, resulting in improved peroxidase-like activity. A simple and convenient colorimetric assay has been established based on the excellent peroxidase-like activity of R-Co 3 O 4 for detecting H 2 O 2 in concentrations of 1−30 μM with a detection limit of 4.3 × 10 −7 mol/L (S/N = 3). Furthermore, the R-Co 3 O 4 -based colorimetric method was successfully applied to glucose detection in human serum samples, demonstrating its potential for application in complex biological systems.

A highly selective construction of 4-substituted 2-aminothiazoles and 4-substituted 5-thiocyano-2-aminothiazoles, respectively, catalyzed by palladium(II) acetate and promoted by iron(III) bromide from vinyl azides and potassium thiocyanate has been developed. Use of readily available starting materials, high selectivity, as well as mild reaction conditions make this practical method particularly attractive.

Plasma cutting arc characteristics are investigated for different turbulence models, i.e. the Reynolds stress model (RSM), the k–ϵ model and its variants, the renormalization group (RNG) k–ϵ model, the RNG k–ϵ model taking into account the low Reynolds number effect and the realizable k–ϵ model. The results of the RSM and the RNG k–ϵ model taking into account the low Reynolds number effect are in reasonable agreement with experiment. They both predict very close voltage, shock wave location and temperature variation along the axis to experiment. On the other hand, the other three models overestimate the turbulence effects and predict much lower velocity and temperature, especially the standard k–ϵ model, which predicts that the temperature is about 10 000 K lower than the experiment in certain plasma jet regions.

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