Directional manipulation of electron transfer in copper/nitrogen doped carbon by Schottky barrier for efficient anodic hydrazine oxidation and cathodic oxygen reduction

Development of bifunctional hydrazine oxidation and oxygen reduction electrocatalysts with high activity and stability is of great significance for the implementation of direct hydrazine fuel cells. Combining zero-dimensional metal nanoparticles with three-dimensional nitrogen-doped carbon nanosheets is an attractive strategy for balancing performance and cost. However, the precise construction of these composites remains a significant challenge, and thorough study of their interaction mechanisms is lacking. Herein, the CuNPs/CuSA-NPCF catalyst was constructed by anchoring copper nanoparticles on a three-dimensional nitrogen-doped porous carbon nanosheet framework through coordination of polyvinyl pyrrolidone and copper ions. The Schottky barrier of metal-semiconductor matched the Fermi level of the rectifying contact, thus enabling directional electron transfer. The resulting electron-deficient Cu nanoparticles surface exhibited Lewis acidity, which was beneficial to adsorption of hydrazine molecule. While the electron-enriched Cu-N4/carbon surface improved the adsorption of oxygen molecule, and accelerated electron supply from Cu-N4 active sites to various oxygen intermediates. The CuNPs/CuSA-NPCF Mott-Schottky catalyst exhibited excellent catalytic activity for hydrazine oxidation reaction and oxygen reduction reaction in an alkaline media. The directional manipulation of electron transfer in heterogeneous materials was an attractive universal synthesis method, providing new approach for the preparation of efficient and stable hydrazine fuel cell catalysts.

Development and characterization of active starch-based films incorporating graphene/polydopamine/Cu2+ nanocomposite fillers

With increasing environmental awareness and food safety concern worldwide, biodegradable active food packaging gained wide attention in recent years. Starch has been regarded as one of the most potential biomaterials to produce biodegradable films. However, relatively poor functional performance of starch-based films severely limits their application as food packaging materials. Carbon-based fillers can be used to enhance the functional attributes of starch-based films, but they are often difficult to incorporate because of their poor matrix dispersibility. In this study, we developed a simple green method to improve the dispersity of graphene in starch-based films by modifying the graphene surfaces using mussel-inspired polydopamine and copper ions. Spectroscopy and morphology analyses showed the surface of graphene was successfully modified. The addition of the nanocomposites positively influenced the microstructure of the starch-based films, as well as impacting their mechanical, barrier, and thermal properties. Additionally, the composite films exhibited antibacterial activity against food borne pathogens, suggesting promising potential of the films acting as active food packaging. Overall, the method developed in this study has the potential for optimizing and endowing extra properties of starch-based films so as to increase their application in biodegradable food packaging.

Novel luteolin sensor of tannic acid-stabilized copper nanoclusters with blue-emitting fluorescence

In this work, the fluorescent copper nanoclusters (Cu NCs) were firstly adopted to detect luteolin with excellent performance. The blue-emitting Cu NCs was successfully prepared through a facile one-pot approach by protection of tannic acid (TA) and chemical reduction of ascorbic acid (AA). The water-soluble nanoclusters possessed uniform size and displayed good stability. The TA-Cu NCs showed maximum luminescence at 434 nm when excited at 366 nm. Based on the static quenching and inner filter effect (IFE) mechanism, the TA-Cu NCs was efficiently and selectively quenched by luteolin. The detection limit was 0.12 μM and linear relationship existed in the range of 0.2-100 μM. Moreover, the TA-Cu NCs probe was successfully employed to detect luteolin in bovine serum samples with satisfactory recoveries. This novel platform was expected to expand the possible detection method based on fluorescence properties.

A new method for cartap detection with high sensitivity and selectivity based on the inner filter effect between GSH-Cu NCs and Au NPs

Herein, a novel and sensitive fluorescence method for cartap determination is established on the basis of the inner filter effect (IFE) of gold nanoparticles (Au NPs) on the fluorescence of glutathione protected Cu NCs (GSH-Cu NCs). In the presence of Au NPs, the fluorescence of GSH-Cu NCs was strongly quenched by the IFE because the absorption spectra of Au NPs overlap well with the emission spectra of GSH-Cu NCs. Upon addition of cartap, cartap could induce the aggregation of Au NPs whose absorption spectrum does not overlap with the emission spectrum of GSH-Cu NCs. Then, with the increase in cartap concentration, the IFE-decreased fluorescence was gradually recovered, realizing the fluorescence sensing of cartap. Under optimal conditions, the proposed method has a good linear relationship with cartap concentration in the range of 7-100 nM, and the detection limit is 3.34 nM. In addition, satisfactory results were obtained for cartap analysis using tap water and cabbage as real samples, which demonstrated that the method as-developed would have great practical application prospects.

Copper nanoclusters: designed synthesis, structural diversity, and multiplatform applications

Atomically precise metal nanoclusters (MNCs) have gained tremendous research interest in recent years due to their extraordinary properties. The molecular-like properties that originate from the quantized electronic states provide novel opportunities for the construction of unique nanomaterials possessing rich molecular-like absorption, luminescence, and magnetic properties. The field of monolayer-protected metal nanoclusters, especially copper, with well-defined molecular structures and compositions, is relatively new, about two to three decades old. Nevertheless, the massive progress in the field illustrates the importance of such nanoobjects as promising materials for various applications. In this respect, nanocluster-based catalysts have become very popular, showing high efficiencies and activities for the catalytic conversion of chemical compounds. Biomedical applications of clusters are an active research field aimed at finding better fluorescent contrast agents, therapeutic pharmaceuticals for the treatment and prevention of diseases, the early diagnosis of cancers and other potent diseases, especially at early stages. A huge library of structures and the compositions of copper nanoclusters (CuNCs) with atomic precisions have already been discovered during last few decades; however, there are many concerns to be addressed and questions to be answered. Hopefully, in future, with the combined efforts of material scientists, inorganic chemists, and computational scientists, a thorough understanding of the unique molecular-like properties of metal nanoclusters will be achieved. This, on the other hand, will allow the interdisciplinary researchers to design novel catalysts, biosensors, or therapeutic agents using highly structured, atomically precise, and stable CuNCs. Thus, we hope this review will guide the reader through the field of CuNCs, while discussing the main achievements and improvements, along with challenges and drawbacks that one needs to face and overcome.

Novel synthesis of orange-red emitting copper nanoclusters stabilized by methionine as a fluorescent probe for norfloxacin sensing

In the present work, we report a novel chemical approach for the synthesis of orange-red emitting copper nanoclusters (Cu NCs) using L-methionine as stabilizing agent at room temperature for the first time. The synthetic route is facile, economical and viable. The methionine stabilized copper nanoclusters (Cu NCs/Met) were thoroughly characterized by TEM, FT-IR, XPS, UV-Vis, steady state and transient fluorescence spectroscopy. The results show the synthesized Cu NCs/Met with a fluorescence quantum yield of 4.37% possessed high stability and excellent optical features such as large Stokes shift and long fluorescence lifetime (8.3 μs). Significantly, the fluorescence intensity of Cu NCs/Met could be efficiently quenched by norfloxacin (NOR) pharmaceutical. A fast and cost-effective NOR sensor was proposed employing Cu NCs/Met as the fluorescent nanoprobe, and the quenching mechanisms were attributed to inner filter effect and agglomeration-induced quenching. The developed sensor exhibited a high sensitivity and selectivity towards NOR in a wide linear range from 0.05 to 250 μM with a detection limit as low as 17 nM. Moreover, the practicability of the developed NOR sensor for real sample assay was validated with satisfactory recoveries, indicating this sensing platform with great potential for label-free pharmaceutical detection in complex systems.

Mussel-Inspired Magnetic Nanoflowers as an Effective Nanozyme and Antimicrobial Agent for Biosensing and Catalytic Reduction of Organic Dyes

Mussel-inspired chemistry has been embodied as a method for acquiring multifunctional nanostructures. In this research, a novel mussel-inspired magnetic nanoflower was prepared through a mussel-inspired approach. Herein, magnetic PDA-Cu nanoflowers (NFs) were assembled via incorporating magnetic Fe3O4@SiO2-NH2 core/shell nanoparticles (NPs) into mussel-inspired polydopamine (PDA) and copper phosphate as the organic and inorganic portions, respectively. Accordingly, the flower-like morphology of MNPs PDA-Cu NFs was characterized by scanning electron microscopy (SEM) images. X-ray diffraction (XRD) analysis confirmed the crystalline structure of magnetic nanoparticles (MNPs) and copper phosphate. Vibrating sample magnetometer (VSM) data revealed the superparamagnetic behavior of MNPs (40.5 emu/g) and MNPs PDA-Cu NFs (35.4 emu/g). Catalytic reduction of MNPs PDA-Cu NFs was evaluated through degradation of methylene blue (MB). The reduction of MB pursued the Langmuir-Hinshelwood mechanism and first-order kinetics, in which the apparent reduction rate K app of MB was higher than 1.44 min-1 and the dye degradation ability was 100%. MNPs PDA-Cu NFs also showed outstanding recyclability and reduction efficiency, for at least six cycles. Furthermore, the prepared MNPs PDA-Cu NFs demonstrated a peroxidase-like catalytic activity for catalyzing 3,3',5,5'-tetramethylbenzidine (TMB) to a blue oxidized TMB (oxTMB) solution in the presence of H2O2. Antimicrobial assays for MNPs PDA-Cu and PDA-Cu NFs were conducted on both Gram-negative and Gram-positive bacteria. Moreover, we demonstrated how the existence of magnetic nanoparticles in PDA-Cu NFs influences the inhibition of an increasing zone. Based on the results, mussel-inspired magnetic nanoflowers appear to have great potential applications, including those relevant to biological, catalysis, and environmental research.