High index surfaces of Au-nanocrystals supported on one-dimensional MoO3-nanorod as a bi-functional electrocatalyst for ethanol oxidation and oxygen reduction

High-Energy Facet Engineering for Electrocatalytic Applications

The design of high-energy facets in electrocatalysts has attracted significant attention due to their potential to enhance electrocatalytic activity. In this review, the significance of high-energy facets in various electrochemical reactions are highlighted, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), and carbon dioxide reduction reaction (CRR). Their importance in various electrochemical reactions and present strategies for constructing high-energy facets are discussed, including alloying, heterostructure formation, selective etching, capping agents, and coupling with substrates. These strategies enable control over crystallographic orientation and surface morphology, fine-tuning electrocatalytic properties. This study also addresses future directions and challenges, emphasizing the need to better understand fundamental mechanisms. Overall, high-energy facets offer exciting opportunities for advancing electrocatalysis.

A dual-electrode label-free immunosensor based on in situ prepared Au-MoO3-Chi/porous graphene nanoparticles for point-of-care detection of cholangiocarcinoma

A novel label-free electrochemical immunosensor was prepared for the detection of carbohydrate antigen 19-9 (CA19-9) and carcinoembryonic antigen (CEA) as biomarkers of cholangiocarcinoma (CCA). A nanocomposite of gold nanoparticles, molybdenum trioxide, and chitosan (Au-MoO3-Chi) was layer-by-layer assembled on the porous graphene (PG) modified a dual screen-printed electrode using a self-assembling technique, which increased surface area and conductivity and enhanced the adsorption of immobilized antibodies. The stepwise self-assembling procedure of the modified electrode was further characterized morphologically and functionally. The electroanalytical detection of biomarkers was based on the interaction between the antibody and antigen of each marker via linear sweep voltammetry using ferrocyanide/ferricyanide as an electrochemical redox indicator. Under optimized conditions, the fabricated immunosensor showed linear relationships between current change (ΔI) and antigen concentrations in two ranges: 0.0025-0.1 U mL-1 and 0.1-1.0 U mL-1 for CA19-9, and 0.001-0.01 ng mL-1 and 0.01-1.0 ng mL-1 for CEA. The limits of detection (LOD) were 1.0 mU mL-1 for CA19-9 and 0.5 pg mL-1 for CEA. Limits of quantitation (LOQ) were 3.3 mU mL-1 for CA19-9 and 1.6 pg mL-1 for CEA. The selectivity of the developed immunosensor was tested on mixtures of antigens and was then successfully applied to determine CA19-9 and CEA in human serum samples, producing satisfactory results consistent with the clinical method.

Gold nanocrystals: optical properties, fine-tuning of the shape, and biomedical applications

Noble metal nanomaterials with special physical and chemical properties have attracted considerable attention in the past decades. In particular, Au nanocrystals (NCs), which possess high chemical inertness and unique surface plasmon resonance (SPR), have attracted extensive research interest. In this study, we review the properties and preparation of Au NCs with different morphologies as well as their important applications in biological detection. The preparation of Au NCs with different shapes by many methods such as seed-mediated growth method, seedless synthesis, polyol process, ultrasonic method, and hydrothermal treatment has already been introduced. In the seed-mediated growth method, the influence factors in determining the final shape of Au NCs are discussed. Au NCs, which show significant size-dependent color differences are proposed for preparing biological probes to detect biomacromolecules such as DNA and protein, while probe conjugate molecules serves as unique coupling agents with a target. Particularly, Au nanorods (NRs) have some unique advantages in the application of biological probes and photothermal cancer therapy compared to Au nanoparticles (NPs).

Laser-assisted synthesis of Au aerogel with high-index facets for ethanol oxidation

Gold (Au) can be used as an ideal metal electrocatalyst for ethanol and glucose oxidation reactions due to its high performance-to-cost ratio. In this paper, the Au aerogel with high-index facets was synthesized by using the laser ablation in liquid technology, which can improve the electrocatalytic activity of Au. The as-prepared Au aerogel showed excellent mass activity and specific activity toward ethanol oxidation reaction, which are 4.6 times and 2.1 times higher than Au/C, respectively. The 3D porous nature and rich defect of the Au aerogel provide more active sites. In addition, the high-index facets with under-coordinated atoms enhance the adsorption of ethanol and glucose molecules, thus improving the intrinsic catalytic activity of Au aerogel. The effect of high-index facets has also been investigated by density functional theory calculations. Furthermore, the Au aerogels also show good electrocatalytic activity and stability toward glucose oxidation reaction. These results are conducive to promote the practical application of Au in electrocatalysis.

An Electrocatalytic Activity of AuCeO2/Carbon Catalyst in Fuel Cell Reactions: Oxidation of Borohydride and Reduction of Oxygen

This paper describes the investigation of electrocatalytic activity of the AuCeO2/C catalyst, prepared using the microwave irradiation method, towards the oxidation of sodium borohydride and oxygen reduction reactions in an alkaline medium. It was found that the obtained AuCeO2/C catalyst with Au loading and electrochemically active surface area of Au nanoparticles (AuNPs) equal to 71 µg cm−2 and 0.05 cm2, respectively, showed an enhanced electrocatalytic activity towards investigated reactions, compared with the Au/C catalyst with an Au loading and electrochemically active surface area of AuNPs equal to 78 µg cm−2 and 0.19 cm2, respectively. The AuCeO2/C catalyst demonstrated ca. 4.5 times higher current density values for the oxidation of sodium borohydride compared with those of the bare Au/C catalyst. Moreover, the onset potential of the oxygen reduction reaction (0.96 V) on the AuCeO2/C catalyst was similar to the commercial Pt/C (0.98 V).

Nanostructured MoO3 for Efficient Energy and Environmental Catalysis

This paper mainly focuses on the application of nanostructured MoO₃ materials in both energy and environmental catalysis fields. MoO₃ has wide tunability in bandgap, a unique semiconducting structure, and multiple valence states. Due to the natural advantage, it can be used as a high-activity metal oxide catalyst, can serve as an excellent support material, and provide opportunities to replace noble metal catalysts, thus having broad application prospects in catalysis. Herein, we comprehensively summarize the crystal structure and properties of nanostructured MoO₃ and highlight the recent significant research advancements in energy and environmental catalysis. Several current challenges and perspective research directions based on nanostructured MoO₃ are also discussed.

Top-down synthesis of polyoxometalate-like sub-nanometer molybdenum-oxo clusters as high-performance electrocatalysts

The top-down fabrication of catalytically active molecular metal oxide anions, or polyoxometalates, is virtually unexplored, although these materials offer unique possibilities, for catalysis, energy conversion and storage. Here, we report a novel top-down route, which enables the scalable synthesis and deposition of sub-nanometer molybdenum-oxo clusters on electrically conductive mesoporous carbon. The new approach uses a unique redox-cycling process to convert crystalline MoIVO2 particles into sub-nanometer molecular molybdenum-oxo clusters with a nuclearity of ∼1-20. The resulting molybdenum-oxo cluster/carbon composite shows outstanding, stable electrocatalytic performance for the oxygen reduction reaction with catalyst characteristics comparable to those of commercial Pt/C. This new material design could give access to a new class of highly reactive polyoxometalate-like metal oxo clusters as high-performance, earth abundant (electro-)catalysts.

Electroporation of outer membrane vesicles derived from Pseudomonas aeruginosa with gold nanoparticles

Abstract

Since their discovery, extracellular vesicles have gained considerable scientific interest as a novel drug delivery system. In particular, outer membrane vesicles (OMVs) play a critical role in bacteria–bacteria communication and bacteria–host interactions by trafficking cell signalling biochemicals (i.e. DNA, RNA, proteins). Although previous studies have focused on the use of OMVs as vaccines, little work has been done on loading them with functional nanomaterials for drug delivery. We have developed a novel drug delivery system by loading OMVs with gold nanoparticles (AuNPs). AuNPs are versatile nanoparticles that have been extensively used in disease therapeutics. The particles were loaded into the vesicles via electroporation, which uses an electric pulse to create a short-lived electric field. The resulting capacitance on the membrane generates pores in the lipid bilayer of the OMVs allowing AuNPs (or any nanoparticle under 10 nm) inside the vesicles. Closure of the pores of the lipid membrane of the OMVs entraps the nanoparticles as cargo. Transmission electron microscopy was used to confirm the loading of AuNPs inside the OMVs and dynamic light scattering (DLS) and cryogenic scanning electron microscopy (cryo-SEM) verified the size and integrity of the OMVs. This is the first report to load nanoparticles into OMVs, demonstrating a potential method for drug delivery.

Graphic abstract

Nanostructured hexagonal ReO3 with oxygen vacancies for efficient electrocatalytic hydrogen generation

We report oxygen vacancies (OVs) rich hexagonal ReO₃ nanostructured electrocatalysts for efficient hydrogen generation. Through a simple argon plasma exposure, OVs are introduced into the ReO₃ nanoparticles (NP) and nanosheets to enhance electrocatalytic activities with decreasing overpotentails from 157 mV and 178 mV to 138 mV and 145 mV at the current density of 10 mA cm^-2, respectively. As-processed OVs rich ReO₃ NP exhibit a good stability during electrochemical measurements for 20 h in acidic electrolyte. The huge active surface area, abundant OVs and excellent conductivity contribute to the performance according to the experimental data. Further theoretical calculations show that the abundant OVs adsorb H with lower Gibbs free energy facilitating hydrogen evolution.

Low- and High-Index Faceted Pd Nanocrystals Embedded in Various Oxygen-Deficient WO x Nanostructures for Electrocatalytic Oxidation of Alcohol (EOA) and Carbon Monoxide (CO)

This work suggests a modest hydrothermal method applied for the synthesis of oxygen-deficient WO _x ( x = 2.75, 2.83, and 2.94) nanomaterials with various morphologies, such as bundled nanorods (NR), nanobelts (NB), and nanosheets (NS), by changing the inorganic additives, such as HCl, NaHSO₄, and HNO₃. In addition, WO _x-supported high- and low-index faceted Pd nanoparticles (Pd-WO_2.75 NB, Pd-WO_2.83 NR, and Pd-WO_2.94 NS) have been successfully synthesized by a facile sonochemical method to enhance the high electrocatalytic activity of electrocatalysts for alcohol electrooxidation, including ethanol, ethylene glycol, and glycerol. Among the three different electrocatalysts, the versatile high-index {520} faceted Pd nanoparticles on WO_2.75 NB (Pd-WO_2.75 NB) show better electrocatalytic performance compared to low-index {100} faceted Pd-WO_2.83 NR and Pd-WO_2.94 NS nanocomposites. This work has identified that the high-density low-coordinated surface atom of Pd strongly interacts with alcohol, which facilitates C-C bond cleavage and may prevent the CO poisoning of nanoparticles. Furthermore, the high concentration of oxygen-deficient nano composites provided additional benefit for the generation of OH species and boosted the electrocatalytic performance of alcohols as well.

Quantitative detection of procalcitonin using an electrochemical immunosensor based on MoO3/Au@rGO nanocomposites

In this work, a sandwich-type electrochemical immunosensor for the detection of procalcitonin (PCT) is constructed layer-by-layer with a novel label based on MoO₃/Au@rGO nanocomposites.