Enhanced Electrocatalytic Activity and Ultrasensitive Enzyme-Free Glucose Sensing Based on Heterogeneous Co(OH)₂ Nanosheets/CuO Microcoral Arrays via Interface Engineering

The rational construction of semiconductor nano-heterostructures is a feasible strategy to modulate electronic structure and increase active area of the electrocatalysts for biosensing. Herein, we develop an in situ approach, electrochemical (EC−) rebuilding of the smooth Cu surface, to construct hierarchical Co­(OH)2 nanosheets/CuO microcoral arrays (Co­(OH)2 NSs/CuO MCAs). Through engineering the heterostructures by optimizing EC-rebuilding time, the electrocatalytic activity is significantly enhanced with a higher current density of glucose oxidation. The incorporation of Co­(OH)2 NSs into CuO MCAs also leads to a large active surface area and benefits surface/interface reactions and mass transport for shorter response for glucose oxidation, higher current density, and better selectivity for glucose sensing. Both photoelectron spectra and density functional theory (DFT) calculations prove that interface charge transfers from CuO to Co­(OH)2, resulting in electron redistribution and a significant increase in the adsorption energy of glucose. Compared with recently reported enzyme-free glucose sensors, the fabricated Co­(OH)2 NSs/CuO MCAs electrode exhibits excellent performance for enzyme-free glucose-sensing in alkaline electrolytes with a short response time (3 s), wide linear range of 500 nM to 2.311 mM, ultrasensitivity of 2269 mA mM–1 cm–2, low limit of detection (LOD, 378 nM), and favorable reproducibility and stability. Noticeably, the outstanding response time, favorable ultrasensitivity, and great LOD are achieved in the glucose sensing. Therefore, the proposed sensor can be used for accurate quantification of glucose concentration in human serum with good repeatability, which will provide a new platform based low-cost semiconductor nano-heterostructures for rapid diagnostic tests and health monitoring

Active Site Engineering in CoP@NC/Graphene Heterostructures Enabling Enhanced Hydrogen Evolution

As the core of an electrocatalyst, the active site is critical to determine its catalytic performance in the hydrogen evolution reaction (HER). In this work, porous N-doped carbon-encapsulated CoP nanoparticles on both sides of graphene (CoP@NC/GR) are derived from a bimetallic metal–organic framework (MOF)@graphene oxide composite. Through active site engineering by tailoring the environment around CoP and engineering the structure, the HER activity of CoP@NC/GR heterostructures is significantly enhanced. Both X-ray photoelectron spectroscopy (XPS) results and density functional theory (DFT) calculations manifest that the electronic structure of CoP can be modulated by the carbon matrix of NC/GR, resulting in electron redistribution and a reduction in the adsorption energy of hydrogen (ΔGH*) from −0.53 to 0.04 eV. By engineering the sandwich-like structure, active sites in CoP@NC/GR are further increased by optimizing the Zn/Co ratio in the bimetallic MOF. Benefiting from this active site engineering, the CoP@NC/GR electrocatalyst exhibits small overpotentials of 105 mV in 0.5 M H2SO4 (or 125 mV in 1 M KOH) to 10 mA cm–2, accelerated HER kinetics with a low Tafel slope of 47.5 mV dec–1, and remarkable structural and HER stability

Two new monoterpenoid indole alkaloids from <i>Tabernaemontana divaricata</i>

Two new monoterpenoid indole alkaloids, tabervarines A (1) and B (2), along with seven known monoterpenoid indole alkaloids, were isolated from the methanol extract of the twigs and leaves of Tabernaemontana divaricata. The structures including the absolute configurations of the new alkaloids were elucidated based on MS, NMR, and ECD calculation. The in vitro cytotoxic activities of the isolated alkaloids against several human cancer cell lines were also evaluated.</p