Enhancing triethylamine sensing of ZIF-derived ZnO microspheres arising from cobalt doping and defect engineering

Reasonable doping is beneficial to the generation of defects, which is a feasibility strategy to improve the ZnO sensing performance. Herein, we presented an in situ self-sacrificing template strategy for fabricating Co doped h-ZnO core-shell structures (h-ZnO/ZnCo_x) with different defect contents, pyrolyzing hierarchical porous ZnO (h-ZnO) sub-microspheres coated by zeolite imidazolate frameworks (h-ZnO/ZIF-ZnCo_x). The investigations of X-ray photoelectron (XPS), photoluminescence (PL) and Raman spectra indicate that donor defects include zinc interstitial (Zn_i) and oxygen vacancy (V_O) in h-ZnO/ZnCo_x can be tuned by Co dopant (x = 0-30%). Resultantly, the h-ZnO/ZnCo_x exhibits a significantly enhanced response and selectivity towards triethylamine (TEA), beyond the undoped h-ZnO, and 15% Co-doped h-ZnO (h-ZnO/ZnCo_15%) conducts the maximum responses of 1020 to 50 ppm TEA at 573 K, in the top set for the similar type of sensors. Further, the sensing mechanism of h-ZnO/ZnCo_x is elaborated, possibly resulting from abundant active oxygen species conversed from more oxygen adsorbed which corresponds to cobalt doping generating rich donor-related defects and additional electrons in h-ZnO/ZnCo_15%.

The photocatalytic reduction of U(VI) into U(IV) by ZIF-8/g-C3N4 composites at visible light

The development of new photocatalyst towards the highly efficient photo-reduction of U(VI) was highly desirable. In this study, ZIF-8/g-C₃N₄ photocatalyst was fabricated to photo-reduce U(VI) from aqueous solutions under different water chemistry. It is demonstrated that ZIF-8/g-C₃N₄ exhibited the fast-photocatalytic rate (completely photoreduction within 30 min), high photocatalytic activity (K_d > 10⁵ mL/g) and superior chemical stability (No significant decrease after fifth cycles). The photoreduction rate of U(VI) significantly decreased with increasing pH, H₂O₂ radicals and photo-generated electrons play an important role in U(VI) photoreduction by quenching experiments and ESR analysis. According to XPS and XANES analysis, adsorbed U(VI) was partly photo-reduced into U(IV) by ZIF-8/g-C₃N₄ photocatalyst. The highly efficient removal of U(VI) on ZIF-8/g-C₃N₄ photocatalyst was attributed to the synergistic effect of ZIF-8 and g-C₃N₄ photocatalyst. The present study may provide a new strategy to apply new photocatalyst for in-situ photoreduction of U(VI) in actual environmental remediation.

Simple and Continuous Fabrication of Self-Propelled Micromotors with Photocatalytic Metal-Organic Frameworks for Enhanced Synergistic Environmental Remediation

This work reports on a simple and general strategy for continuous fabrication of self-propelled micromotors with photocatalytic metal-organic frameworks (MOFs) for enhanced synergistic degradation of organic contaminants. With emulsion microdroplets from microfluidics as templates, uniform porous micromotors decorated with Fe₃O₄@Ag nanoparticles (Fe₃O₄@AgNPs) at the bottom and zeolitic imidazolate framework-8@ZnO nanoparticles (ZIF-8@ZnONPs) on the surface can be synthesized. The spatial location of ZIF-8@ZnONPs and Fe₃O₄@AgNPs in micromotors is accurately controlled in one step via their directional migration in the confined microspace of emulsion droplets driven by interfacial energy and magnetic field. The nanoengines Fe₃O₄@AgNPs enable asymmetric decomposition of H₂O₂ for bubble-propelled motion and easy magnetic recycling of the micromotor. The porous structures of micromotors provide a large surface area, benefiting decoration of Fe₃O₄@AgNPs and their contact with H₂O₂ for promoting bubble generation and reduced micromotor weight for promoting bubble-propelled motion. The nanophotocatalysts ZIF-8@ZnONPs allow enrichment of organic contaminant molecules via adsorption for efficient photocatalytic degradation. With synergistic coupling of the photocatalysis of ZIF-8@ZnONPs and advanced oxidation of the H₂O₂/UV system, the micromotors with bubble-propelled motion for improved mixing can achieve enhanced degradation of organic contaminants via dual synergistic degradation mechanisms. As highlighted by degradation of rhodamine B, the micromotors exhibit the highest degradation performance as compared to control groups with a single degradation mechanism and with dual degradation mechanisms but without self-propelled motion. This simple fabrication strategy is general and can be flexibly extended to other MOF materials, which may open up new avenues for developing advanced MOF-integrated micromotors for myriad applications.

Bimetallic metal-organic frameworks and their derivatives

Bimetallic metal-organic frameworks (MOFs) have two different metal ions in the inorganic nodes. According to the metal distribution, the architecture of bimetallic MOFs can be classified into two main categories namely solid solution and core-shell structures. Various strategies have been developed to prepare bimetallic MOFs with controlled compositions and structures. Bimetallic MOFs show a synergistic effect and enhanced properties compared to their monometallic counterparts and have found many applications in the fields of gas adsorption, catalysis, energy storage and conversion, and luminescence sensing. Moreover, bimetallic MOFs can serve as excellent precursors/templates for the synthesis of functional nanomaterials with controlled sizes, compositions, and structures. Bimetallic MOF derivatives show exposed active sites, good stability and conductivity, enabling them to extend their applications to the catalysis of more challenging reactions and electrochemical energy storage and conversion. This review provides an overview of the significant advances in the development of bimetallic MOFs and their derivatives with special emphases on their preparation and applications.

Synthesis of Ag and AgCl co-doped ZIF-8 hybrid photocatalysts with enhanced photocatalytic activity through a synergistic effect

Recently, Ag/AgCl composites with different structures have been widely studied and used as photocatalysts to degrade dye pollutants, due to their high separation efficiency of electron-hole pairs under visible light irradiation. Herein, we adopted a nucleation, precipitation, growth and photoreduction method to prepare Ag and AgCl co-doped ZIF-8 hybrid photocatalysts and explored the influence of Ag content on their physical and chemical properties. All as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) measurements, energy dispersive spectroscopy (EDS), UV-vis diffuse reflectance and X-ray photoelectron spectroscopy (XPS). XRD indicated that ZIF-8 and AgCl were formed and some of the AgCl was reduced into Ag0 after 30 min of UV light irradiation. SEM and TEM images verified that Ag/AgCl nanoparticles were inlaid in the body of ZIF-8 and Ag ions could hinder the growth of the ZIF-8 crystal. BET data indicated that Ag/AgCl nanoparticles did not alter the pore size of ZIF-8. The UV-vis diffuse reflectance spectra showed that Ag/AgCl@ZIF-8 has excellent ability to absorb visible light, indicating the high efficiency of the electron-hole pair separation of Ag/AgCl@ZIF-8. Finally, the photocatalytic activities of all of the as-synthesized samples were evaluated by degradation of RhB under visible light irradiation. Ag and AgCl co-doped ZIF-8 hybrid photocatalysts exhibited high photocatalytic activity due to the synergistic effect of ZIF-8, AgCl and Ag. After 60 min of visible light irradiation, Ag/AgCl(15)@ZIF-8 exhibited the best photocatalytic activity and could degrade 99.12% RhB, which was higher than Ag/AgCl (94.24%) and ZIF-8 (5.17%). Additionally, a photocatalytic mechanism for dye pollutant degradation over the Ag and AgCl co-doped ZIF-8 hybrid photocatalysts was proposed.

Recent Progress on Engineering Highly Efficient Porous Semiconductor Photocatalysts Derived from Metal-Organic Frameworks

Porous structures offer highly accessible surfaces and rich pores, which facilitate the exposure of numerous active sites for photocatalytic reactions, leading to excellent performances. Recently, metal-organic frameworks (MOFs) have been considered ideal precursors for well-designed semiconductors with porous structures and/or heterostructures, which have shown enhanced photocatalytic activities. In this review, we summarize the recent development of porous structures, such as metal oxides and metal sulfides, and their heterostructures, derived from MOF-based materials as catalysts for various light-driven energy-/environment-related reactions, including water splitting, CO₂ reduction, organic redox reaction, and pollution degradation. A summary and outlook section is also included.

Influence of Zn and Co co-doping on oxygen evolution reaction electrocatalysis at MOF-derived N-doped carbon electrodes

Schematic illustration of the synthesis of the Zn_1−xCo_x/NC catalyst.

Doping Ag/AgCl in zeolitic imidazolate framework-8 (ZIF-8) to enhance the performance of photodegradation of methylene blue

In this work, zeolitic imidazolate framework-8 (ZIF-8) was successfully synthesized by a facile reaction via water and alcohol solvents at room temperature. Additionally, Ag/AgCl@ZIF-8 was successfully fabricated by doping Ag/AgCl onto ZIF-8, which were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), along with UV-visible diffuse reflectance spectra (UV-vis DRS). The Ag/AgCl@ZIF-8 nanoparticles exhibited high photocatalytic activity, durability, and efficiency for the degradation of methylene blue dye (MB). The results illustrate that the band gap of Ag/AgCl@ZIF-8 is lower than that of ZIF-8, which explains the enhancement of MB degradation under UV light irradiation. The conditions affecting the photocatalytic degradation, including the dosage of photocatalyst, the initial concentration of MB, pH value, and hardness of water were systematically evaluated. In addition, the photocatalytic mechanism was explored by three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy, the effect of ZnO to photocatalytic activity was excluded, and a possible pathway of MB degradation was proposed by analysis of intermediates via liquid chromatography in combination with hybrid quadrupole time-of-flight mass spectrometry (LC-QTOF-MS). The high photocatalytic ability of Ag/AgCl@ZIF-8 shows great application potential for the oxidation of organic pollutants in water.

Synthesis of ZnO/ZIF-8 hybrid photocatalysts derived from ZIF-8 with enhanced photocatalytic activity

Controllable conjunction of semiconductors with metal organic frameworks (MOFs) has been an efficient tool to enhance the chemical and physical properties of semiconductors by forming semiconductor–MOF hybrid structures.