Nano-Cu Derived from a Copper Nitride Precatalyst for Reductive Coupling of Nitroaromatics to Azo Compounds.

The study of structural reconstruction is vital for the understanding of the real active sites in heterogeneous catalysis and guiding the improved catalyst design. Herein, we applied a copper nitride precatalyst in the nitroarene reductive coupling reaction and made a systematic investigation on the dynamic structural evolution behaviors and catalytic performance. This Cu3N precatalyst undergoes a rapid phase transition to nanostructured Cu with rich defective sites, which act as the actual catalytic sites for the coupling process. The nitride-derived defective Cu is very active and selective for azo formation, with 99.6% conversion of nitrobenzene and 97.1% selectivity to azobenzene obtained under mild reaction conditions. Density functional theory calculations suggest that the defective Cu sites play a role for the preferential adsorption of nitrosobenzene intermediates and significantly lowered the activation energy of the key coupling step. This work not only proposes a highly efficient noble-metal-free catalyst for nitroarenes coupling to valuable azo products but also may inspire more scientific interest in the study of the dynamic evolution of metal nitrides in different catalytic reactions.

Generalizable Descriptors of Highly Sensitive Detection of As(III) over Transition-Metal Single Atoms: A Combined Density Function Theory and Gradient Boosting Regression Approach.

Traditional nanomodified electrodes have made great achievements in electrochemical stripping voltammetry of sensing materials for As(III) detection. Moreover, the intermediate states are complicated to probe because of the ultrashort lifetime and complex reaction conditions of the electron transfer process in electroanalysis, which seriously hinder the identification of the actual active site. Herein, the intrinsic interaction of highly sensitive analytical behavior of nanomaterials is elucidated from the perspective of electronic structure through density functional theory (DFT) and gradient boosting regression (GBR). It is revealed that the atomic radius, d-band center (εd), and the largest coordinative TM-N bond length play a crucial role in regulating the arsenic reduction reaction (ARR) performance by the established ARR process for 27 sets of transition-metal single atoms supported on N-doped graphene. Furthermore, the database composed of filtered intrinsic electronic structural properties and the calculated descriptors of the central metal atom in TM-N4-Gra were also successfully extended to oxygen evolution reaction (OER) systems, which effectively verified the reliability of the whole approach. Generally, a multistep workflow is developed through GBR models combined with DFT for valid screening of sensing materials, which will effectively upgrade the traditional trial-and-error mode for electrochemical interface designing.

Sensing Material-Dependent Interference of Multiple Heavy Metal Ions: Experimental and Simulated Thermodynamics Study on Cu(II), Cd(II), and As(III) Electroanalysis.

Interference among multiple heavy metal ions (HMIs) is a significant problem that must be solved in electroanalysis, which extremely restricts the practical popularization of electrochemical sensors. However, due to the limited exploration of the intrinsic mechanism, it is still difficult to confirm the influencing factors. In this work, a series of experimental and theoretical electroanalysis models have been established to investigate the electroanalysis results of Cu(II), Cd(II), As(III), and their mixtures, which were based on the simple structure and stable coordination of nickel single-atom catalysts. X-ray absorption spectroscopy and density functional theory calculations were used to reveal the underlying detection mechanism of the 50-fold boosting effect of Cu(II) on As(III) while Cd(II) inhibits As(III). Combining the application of the thermodynamic model and Fourier transform infrared reflection, the specific interaction of the nanomaterials and HMIs on the interface is considered to be the fundamental source of the interference. This work opens up a new way of thinking about utilizing the unique modes of interplay between nanomaterials and HMIs to achieve anti-interference intelligent electrodes in stripping analysis.

Enhanced electrochemical sensing performance for trace Hg(II) by high activity of Co3+ on Co3O4-NP/N-RGO surface.

Constructing a highly sensitive and selective electrochemical interface is of great significance for the effective detection of Hg2+ in water and biological samples. Herein, Co3O4 nanopolyhedron (NP) anchored on nitrogen-doped reduced graphene oxide (N-RGO) is utilized as the electrode material for the detection of Hg2+ in the range of 0.1 µM-1.0 µM, with high sensitivity (1899.70 µA µM-1 cm-2) and low detection limits (0.03 µM) in natural water. Moreover, the Co3O4-NP/N-RGO modified electrode possesses reasonable anti-interference ability for Hg2+ in the presence of inorganic ions and glucose, which is the basis of its good response to trace Hg2+ in serum. Besides, combined with X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations, the electron transfer tendency is revealed. Additionally, combined with the electron state density of Co-p, it is speculated that Co3+ is an optimum active site for catalytic reaction. The above results elucidate an electrochemically sensitive interface is constructed to realize the efficient detection of Hg2+, which provides some theoretical guidance for the development of electrochemical sensors.

Close band center and rapid adsorption kinetics facilitate selective electrochemical sensing of heavy metal ions.

Combining density functional theory calculation with experiments and kinetics simulation, a multiscale framework describing the influence of reactant-substrate interaction on electrochemical performance was proposed. It was found that the close band center and the rapid adsorption kinetics facilitated the highly selective response of Ni(111) toward Cu(ii), providing a useful tactic to investigate the mechanism of electro-selectivity. This work not only verified that the interaction strength in the ex situ conditions, and kinetics rate could be applied to evaluate the electrochemical selectivity, but also contributed to the options and forecasting of selective electrode materials for heavy metal ions.

Electrons in Oxygen Vacancies and Oxygen Atoms Activated by Ce3+/Ce4+ Promote High-Sensitive Electrochemical Detection of Pb(II) over Ce-Doped α-MoO3 Catalysts.

Modulating the active sites of oxygen vacancies (OVs) to enhance the catalytic properties of nanomaterials has attracted much research interest in various fields, but its intrinsic catalytic mechanism is always neglected. Herein, we establish an efficient strategy to promote the electrochemical detection of Pb(II) by regulating the concentration of OVs in α-MoO3 nanorods via doping Ce3+/Ce4+ ions. α-MoO3 with the Ce-doped content of 9% (C9M) exhibited the highest detection sensitivity of 106.64 µM µA-1 for Pb(II), which is higher than that achieved by other metal oxides and most precious metal nanomaterials. It is found that C9M possessed the highest concentration of OVs, which trapped some electrons for strong affinity interaction with Pb(II) and provided numerous atomic level interfaces of high surface free energy for catalysis reactions. X-ray absorption fine structure spectra and density functional theory calculation indicate that Pb(II) was bonded with the surface-activated oxygen atoms (Os) around Ce ions and obtained some electrons from Os. Besides, the longer Pb-O bonds on C9M were easier to break, causing a low desorption energy barrier to effectively accelerate Pb(II) desorbing to the electrode surface. This study helps to understand the changes in electronic structure and catalytic performance with heteroatom doping and OVs in chemically inert oxides and provide a reference for designing high-active electrocatalytic interfaces to realize ultrasensitive analysis of environmental contaminants.