Photocatalytic Co-Reduction of N2 and CO2 with CeO2 Catalyst for Urea Synthesis.

The effective conversion of carbon dioxide (CO2 ) and nitrogen (N2 ) into urea by photocatalytic reaction under mild conditions is considered to be a more environmentally friendly and promising alternative strategies. However, the weak adsorption and activation ability of inert gas on photocatalysts has become the main challenge that hinder the advancement of this technique. Herein, we have successfully established mesoporous CeO2-x nanorods with adjustable oxygen vacancy concentration by heat treatment in Ar/H2 (90 % : 10 %) atmosphere, enhancing the targeted adsorption and activation of N2 and CO2 by introducing oxygen vacancies. Particularly, CeO2 -500 (CeO2 nanorods heated treatment at 500 °C) revealed high photocatalytic activity toward the C-N coupling reaction for urea synthesis with a remarkable urea yield rate of 15.5 µg/h. Besides, both aberration corrected transmission electron microscopy (AC-TEM) and Fourier transform infrared (FT-IR) spectroscopy were used to research the atomic surface structure of CeO2 -500 at high resolution and to monitor the key intermediate precursors generated. The reaction mechanism of photocatalytic C-N coupling was studied in detail by combining Density Functional Theory (DFT) with specific experiments. We hope this work provides important inspiration and guiding significance towards highly efficient photocatalytic synthesis of urea.

An electrochemical sensor based on AuPd@FexOy nanozymes for a sensitive and in situ quantitative detection of hydrogen peroxide in real samples.

The hydrogen peroxide (H2O2) levels in living organisms and environment have strong effects on many biological processes inducing cell apoptosis/cell necrosis and wound disinfection. Therefore, it is important to have an accurate and in situ detection of H2O2. Herein, an AuPd@FexOy nanozyme-based electrochemical (EC) sensor (termed as AuPd@FexOy NPs/GCE) with good stability and anti-interference ability has been prepared for the detection of H2O2 by differential pulse voltammetry (DPV) and chronoamperometry dual-measurement modes. The AuPd@FexOy NPs/GCE exhibits good linear relationships in the ranges from 13.0 to 6.0 × 103 µM (DPV measurement) and 50 to 1.0 × 103 µM (chronoamperometry measurement), low detection limits (LODs) of 1.6 µM (DPV measurement) and 3.0 µM (chronoamperometry measurement) and high sensitivities of 83.8 nA µM-1 cm-2 (DPV measurement) and 120.7 nA µM-1 cm-2 (chronoamperometry measurement). The practicability of the as-prepared AuPd@FexOy NPs/GCE has been demonstrated by an in situ real-time detection of H2O2 released from adherent living MCF-7 cells triggered by varying amounts of N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) from 0.5 to 3.0 µM and the quantitative determination of H2O2 in commercial disinfectants.

Inhibition mechanism of melanin formation based on antioxidant scavenging of reactive oxygen species.

The production of reactive oxygen species (ROS) leads to the generation of oxidative stress, which will result in the excessive production and accumulation of melanin in the body and even the occurrence of some skin diseases. The intervention of antioxidants can slow down the rate of melanin formation to some extent. In order to explore the relationship between ROS, melanin and antioxidants, this work investigated the effects of antioxidants on melanin formation by the scavenging of ROS in vitro, where zebrafish were used as the model organism in in vivo experiments. The results showed that the inhibition order of natural antioxidants on melanin formation was GSH > AA > GA and PG > BHT > BHA for synthetic antioxidants. Between natural antioxidants and synthetic antioxidants, the former mainly have a strong scavenging ability on ˙OH and 1O2, while the latter have a strong scavenging ability on O2˙-. At the same time, the results in vivo showed that GSH and PG within a certain concentration not only did not affect the hatchability, survival rate and teratogenic rate of zebrafish embryos, but also can significantly inhibit melanin formation in zebrafish embryos. The results of this study have an important guiding significance for the dosage of antioxidants used in the cosmetics and food industries.

FRET Modulated Signaling: A Versatile Strategy to Construct Photoelectrochemical Microsensors for In Vivo Analysis.

Microelectrode-based electrochemical (EC) and photoelectrochemical (PEC) sensors are promising candidates for in vivo analysis of biologically important chemicals. However, limited selectivity in complicated biological systems and poor adaptability to electrochemically non-active species restrained their applications. Herein, we propose the concept of modulating the PEC output by a fluorescence resonance energy transfer (FRET) process. The emission of energy donor was dependent on the concentration of target SO2 , which in turn served as the modulator of the photocurrent signal of the photoactive material. The employment of optical modulation circumvented the problem of selectivity, and the as-fabricated PEC microelectrode showed good stability and reproducibility in vivo. It can monitor fluctuations of SO2 levels in brains of rat models of cerebral ischemia-reperfusion and febrile seizure. More significantly, such a FRET modulated signaling strategy can be extended to diverse analytes.

MoS2/ZnO-Heterostructures-Based Label-Free, Visible-Light-Excited Photoelectrochemical Sensor for Sensitive and Selective Determination of Synthetic Antioxidant Propyl Gallate.

Propyl gallate (PG) as one of the important synthetic antioxidants is widely used in the prevention of oxidative deterioration of oils during processing and storage. Determination of PG has received extensive concern because of its possible toxic effects on human health. Herein, we report a photoelectrochemical (PEC) sensor based on ZnO nanorods and MoS2 flakes with a vertically constructed p-n heterojunction. In this system, the n-type ZnO and p-type MoS2 heterostructures exhibited much better optoelectronic behaviors than their individual materials. Under an open circuit potential (zero potential) and visible light excitation (470 nm), the PEC sensor exhibited extraordinary response for PG determination, as well as excellent anti-inference properties and good reproducibility. The PEC sensor showed a wide linear range from 1.25 × 10-7 to 1.47 × 10-3 mol L-1 with a detection limit as low as 1.2 × 10-8 mol L-1. MoS2/ZnO heterostructure with proper band level between MoS2 and ZnO could make the photogenerated electrons and holes separated more easily, which eventually results in great improvement of sensitivity. On the other hand, formation of a five membered chelating ring structure of Zn(II) with adjacent oxygen atoms of PG played significant roles for selective detection of PG. Moreover, the PEC sensor was successfully used for PG analysis in different samples of edible oils. It demonstrated the ability and reliability of the MoS2/ZnO-based PEC sensor for PG detection in real samples, which is beneficial for food quality monitoring and reducing the risk of overuse of PG in foods.

A label-free PEC aptasensor platform based on g-C3N4/BiVO4 heterojunction for tetracycline detection in food analysis.

A simple low-cost label-free photoelectrochemical (PEC) biosensing platform based on red blood cell shaped BiVO4 modified g-C3N4 was designed for tetracycline detection under room temperature. The prepared g-C3N4/BiVO4 heterojunction not only demonstrated a high surface area, excellent physicochemical stability and favorable PEC activity, but also can be employed as nanostructure support for aptamers to construct a visible-light-driven PEC aptasensor due to rich π-π accumulation sites. More importantly, the proposed PEC aptasensor showed a favorable linear toward tetracycline in the range from 5 × 10-9 to 2 × 10-7 M with a detection limit of 1.6 nM, which well covered the Food Standards Testing requirements. Practical food sample analysis further revealed the accuracy and feasibility of the g-C3N4/BiVO4 heterostructure based PEC platform. It is expected that such a label-free and cost-effective PEC strategy should act as a promising candidate for tetracycline determination in food quality control and supervision.

Oxidized titanium carbide MXene-enabled photoelectrochemical sensor for quantifying synergistic interaction of ascorbic acid based antioxidants system.

Antioxidants can protect organization from damage by scavenging of free radicals. When two kinds of antioxidants are consumed together, the total antioxidant capacity might be enhanced via synergistic interactions. Herein, we develop a simple, direct, and effective strategy to quantify the synergistic interaction between ascorbic acid (AA) and other different antioxidants by photoelectrochemical (PEC) technology. MXene Ti3C2-TiO2 composites fabricated via hydrogen peroxide oxidation were applied as sensing material for the antioxidants interaction study. Under excitation of 470 nm wavelength, the photogenerated electrons transfer from the conduction band of TiO2 nanoparticles to the Ti3C2 layers, and the holes in TiO2 can oxidize antioxidants, leading to an enhanced photocurrent as the detection signal. This PEC sensor exhibits a good linear range to AA concentrations from 12.48 to 521.33 µM as well as obvious antioxidants capability synergism. In particular, the photocurrents of AA + gallic acid (GA) and AA + chlorogenic acid (CHA) mixtures at 476.19 µM increase 1.95 and 2.35 times respectively comparing with the sum of photocurrents of AA and GA or CHA. It is found that the synergistic effect is mainly depending on the fact that AA with the low redox potential (0.246 V vs NHE) can reduce other antioxidants radical to promote regeneration, improving the overall antioxidant performance. Moreover, it is proved that the greater redox potential of antioxidants, the more obvious the synergistic effect. In addition, the sensor was used to real sample assay, which provides available information towards food nutrition analysis, health products design and quality inspection.