Facile and Large-Area Preparation of Porous Ag3PO4 Photoanodes for Enhanced Photoelectrochemical Water Oxidation

Metal-Organic Framework (MOF) Derivatives as Promising Chemiresistive Gas Sensing Materials: A Review

The emission of harmful gases has seriously exceeded relative standards with the rapid development of modern industry, which has shown various negative impacts on human health and the natural environment. Recently, metal-organic frameworks (MOFs)-based materials have been widely used as chemiresistive gas sensing materials for the sensitive detection and monitoring of harmful gases such as NO_x, H₂S, and many volatile organic compounds (VOCs). In particular, the derivatives of MOFs, which are usually semiconducting metal oxides and oxide-carbon composites, hold great potential to prompt the surface reactions with analytes and thus output amplified resistance changing signals of the chemiresistors, due to their high specific surface areas, versatile structural tunability, diversified surface architectures, as well as their superior selectivity. In this review, we introduce the recent progress in applying sophisticated MOFs-derived materials for chemiresistive gas sensors, with specific emphasis placed on the synthesis and structural regulation of the MOF derivatives, and the promoted surface reaction mechanisms between MOF derivatives and gas analytes. Furthermore, the practical application of MOF derivatives for chemiresistive sensing of NO₂, H₂S, and typical VOCs (e.g., acetone and ethanol) has been discussed in detail.

Metal-Organic-Framework-Derived Ball-Flower-like Porous Co3O4/Fe2O3 Heterostructure with Enhanced Visible-Light-Driven Photocatalytic Activity

A porous ball-flower-like Co3O4/Fe2O3 heterostructural photocatalyst was synthesized via a facile metal-organic-framework-templated method, and showed an excellent degradation performance in the model molecule rhodamine B under visible light irradiation. This enhanced photocatalytic activity can be attributed to abundant photo-generated holes and hydroxyl radicals, and the combined effects involving a porous structure, strong visible-light absorption, and improved interfacial charge separation. It is notable that the ecotoxicity of the treated reaction solution was also evaluated, confirming that an as-synthesized Co3O4/Fe2O3 catalyst could afford the sunlight-driven long-term recyclable degradation of dye-contaminated wastewater into non-toxic and colorless wastewater.

Facile controlled synthesis of Ag3PO4 with various morphologies for enhanced photocatalytic oxygen evolution from water splitting

A facile and green hydrothermal method has been developed for the synthesis of Ag3PO4 with a variety of morphologies, including cubic, rhombic dodecahedral, spherical and roughly spherical, by using Ag4P2O7 as a sacrificial precursor. The as-prepared catalysts were characterized by carrying out X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The morphology of Ag3PO4 was controlled by simply adjusting the hydrothermal reaction temperature and time, without adding any templates and organic additives. Kinetics studies and characterization results revealed that the transformation from P2O7 4- to a PO4 3- radical was a rate-determining step, and influenced the morphology of Ag3PO4. Different oxygen evolution rates were observed for samples subjected to different hydrothermal reaction times, and the highest initial rate of O2 evolution achieved was 582.55 μmol h-1 g-1. Furthermore, for the samples prepared using a hydrothermal reaction time of 96 h, as the hydrothermal reaction temperature was increased, the oxygen evolution rate of the resulting sample decreased first and then increased, and the highest initial rate of O2 evolution was 856.06 μmol h-1 g-1, about twice the 418.34 μmol h-1 g-1 value for the sample prepared using the coprecipitation method. A possible mechanism has been proposed to explain how the hydrothermal reaction temperature and time influenced the Ag3PO4 morphology. Our method provides a guiding hydrothermal strategy for the synthesis of insoluble electrolytes with various morphologies from relatively soluble electrolytes without the need to use templates and organic additives.

Insights Into Highly Improved Solar-Driven Photocatalytic Oxygen Evolution Over Integrated Ag3PO4/MoS2 Heterostructures

Oxygen evolution has been considered as the rate-determining step in photocatalytic water splitting due to its sluggish four-electron half-reaction rate, the development of oxygen-evolving photocatalysts with well-defined morphologies and superior interfacial contact is highly important for achieving high-performance solar water splitting. Herein, we report the fabrication of Ag₃PO₄/MoS₂ nanocomposites and, for the first time, their use in photocatalytic water splitting into oxygen under LED light illumination. Ag₃PO₄ nanoparticles were found to be anchored evenly on the surface of MoS₂ nanosheets, confirming an efficient hybridization of two semiconductor materials. A maximum oxygen-generating rate of 201.6 μmol · L⁻¹ · g⁻¹ · h⁻¹ was determined when 200 mg MoS₂ nanosheets were incorporated into Ag₃PO₄ nanoparticles, which is around 5 times higher than that of bulk Ag₃PO₄. Obvious enhancements in light-harvesting property, as well as electron-hole separation and charge transportation are revealed by the combination of different characterizations. ESR analysis verified that more active oxygen-containing radicals generate over illuminated Ag₃PO₄/MoS₂ composite photocatalysts rather than irradiated Ag₃PO₄. The improvement in oxygen evolution performance of Ag₃PO₄/MoS₂ composite photocatalysts is ascribed to wide spectra response in the visible-light region, more efficient charge separation, and enhanced oxidation capacity in the valence band (VB). This study provides new insights into the design and development of novel composite photocatalytic materials for solar-to-fuel conversion.