Investigation of the Performance of Heterogeneous MOF-Silver Nanocube Nanocomposites as CO2 Reduction Photocatalysts by In Situ Raman Spectroscopy

Advancements in silver-based nanocatalysts for organic transformations and other applications: a comprehensive review (2019-2024)

Over time, nanocomposites have revolutionized materials science, offering numerous applications in fields such as catalysis, environmental purification and treatment, biomedicine and various industries. Among these, silver-based nanocomposites are particularly notable for their remarkable stability, reusability, biocompatibility, and multifunctional medicinal properties. Hence, we present a comprehensive summary of recent developments (2019-2024) in silver-based nanomaterials, focusing on their applications across multiple domains, including catalytic organic transformations, biomedical uses, environmental remediation, and industrial sectors such as food packaging, agriculture and textiles. By highlighting recent advancements and emerging trends, we aim to provide a thorough understanding of the role of silver-based nanocomposites in contemporary science and technology, emphasizing their potential to drive innovation across diverse disciplines.

State-of-the-Art, Insights, and Perspectives for MOFs-Nanocomposites and MOF-Derived (Nano)Materials

Composite structures created from metal‒organic framework (MOF) matrices are reviewed in this work. Depending on the nature of the second component apart from the MOF platform, several synergistic properties may arise; at the same time, the initial features of the single constituent materials are usually maintained, and individual shortcomings are mitigated. Currently, timely energy and environmental challenges necessitate the quest for more advanced materials and technologies. Significant developments in MOF-nanocomposites have enabled their application across a wide range of modern and traditional fields. This review demonstrates in an exhaustive and critical way a broad range of MOF-based nanocomposites, namely, MOF/perovskite nanoparticles (NPs), MOF/metal (non-iron) oxide NPs, MOF/Fe3O4 NPs, MOF/metal chalcogenide NPs, MOF/metal NPs, and MOF/carbon-based materials, as well as nanocomposites of MOFs with other semiconductor NPs. Key points related to the synthesis, characterization, and applications of these materials are provided. Depending on their configuration, the composites under discussion can be applied in domains such as photoelectrochemical sensing, antibiotic/dye degradation, optoelectronics, photovoltaics, catalysis, solar cells, supercapacitors, batteries, water remediation, and drug loading. Sometimes, MOFs can undergo certain processes (e.g. pyrolysis) and act as precursors for composite materials with appealing characteristics. Therefore, a special section in the manuscript is devoted to MOF-derived NP composites. Toward the end of the text, we conclude while also describing the challenges and possibilities for further investigations in the umbrella of material categories analyzed herein. Despite the progress achieved, key questions remain to be answered regarding the relationships among the morphology, properties, and polyvalent activity of these materials. The present work aims to shed light on most of their aspects and innovative prospects, facilitating a deeper comprehension of the underlying phenomena, functionality, and mechanistic insights governing their behavior.

Plasmonic Nanocrystal-MOF Nanocomposites as Highly Active Photocatalysts and Highly Sensitive Sensors for CO2 Reduction over a Wide Range of Solar Wavelengths

Plasmonic nanocrystals have the potential to be widely used in green energy-related applications, due to their excellent optical properties and high reactivity over a wide range of solar wavelengths. Another benefit of using plasmonic nanocrystals for optical applications is that these nanocrystals strongly enhance Raman scattering and are therefore widely used in sensors. Recently, nanocomposites of porous materials deposited on plasmonic nanocrystals are demonstrated to enhance chemical reactivity by concentrating reactants on the surface of plasmonic nanocrystals. Here, three different plasmonic nanocrystals producing plasmonic responses within 400-900 nm are used as templates, and MOF-801 (Zr-based MOF) is produced on these nanocrystals as photocatalysts for the CO2 reduction reaction. Using nanocomposites as CO2 reduction reaction photocatalysts, the CO2 conversion rate can reach >50% within 30 min. The CO2 reduction reactivity of nanocomposites can be improved by the composition and morphology of plasmonic nanocrystals (increased by 40-50%), due to stronger synergistic effects and higher surface area to volume ratio. This report demonstrates that by controlling the plasmonic responses of nanocrystals, it is possible to realize photocatalysts that can be used for CO2 reduction reactions over a wide range of solar wavelengths.

Photocatalytic Oxidative Coupling of Methane to Ethane Using CO2 as a Soft Oxidant over the Au/TiO2-Vo Nanosheets

Photocatalytic oxidative coupling of methane (OCM) offers an appealing route for converting greenhouse gas into valuable C2 hydrocarbons. However, O2, as the most commonly used oxidant, tends to result in inevitable overoxidation and waste of methane feedstock. Herein, we first report a photocatalytic OCM using CO2 as a soft oxidant for C2H6 production under mild conditions, where an efficient photocatalyst with unique interface sites is designed and constructed to facilitate CO2 adsorption and activation, while concurrently boosting CH4 dissociation. As a prototype, the Au quantum dots anchored on oxygen-deficient TiO2 nanosheets are fabricated, where the Au-Vo-Ti interface sites for CO2 adsorption and activation are collectively disclosed by in situ Kelvin probe force microscopy, quasi in situ X-ray photoelectron spectroscopy and theoretical calculations. Compared with single metal site, the Au-Vo-Ti interface sites exhibit the lower CO2 adsorption energy and decrease the energy barrier of the *CO2 hydrogenation step from 1.05 to 0.77 eV via Au-C and Ti-O dual-site bonding. The adsorbed CO2 on the photocatalyst reduces the energy barrier of *CH4 dissociation to *CH3 from 2.13 to 1.59 eV, contributing to CH4 oxidation. Additionally, in situ Fourier-transform infrared spectroscopy unveils the Au site facilitates ethane production by engaging in *CH3-Au interaction and accelerating CH3-CH3 coupling. Thus, the photocatalyst demonstrates a high C2H6 evolution rate of 2.60 mmol g-1 h-1 for OCM using CO2 as the soft oxidant, surpassing most of previously reported photocatalysts regardless of OCM and nonoxidative coupling of methane. This work highlights the importance of soft oxidants for improving oxidation reaction efficiency and provides atomic scale insight into the design of photocatalysts for CH4 conversion.

Self-template impregnated silver nanoparticles in coordination polymer gel: photocatalytic CO2 reduction, CO2 fixation, and antibacterial activity

CO2 fixation and light-assisted conversion of CO2 in the presence of water into fuels and feedstocks are clean and sustainable techniques to alleviate the energy crisis and global climate change. In this regard, herein, a waterborne multifunctional metal-organic coordination polymer gel (Ag@GMP) was prepared from silver nitrate and guanosine 5'-monophosphate. Electron microscopy exhibits that Ag@GMP has a flower-like structure, which is composed of vertically grown sheets, and corresponding high magnification images display the presence of silver nanoparticles on the vertically grown sheets. Ag@GMP demonstrates remarkable photocatalytic performance, achieving a CO2 conversion rate of 18.6 μmol g-1 with approximately 85% selectivity towards CO at ambient temperature without using sacrificial agents. In situ diffuse reflectance infrared Fourier transform spectroscopy was employed to elucidate the proposed mechanism for photocatalytic CO2 reduction. Additionally, Ag@GMP exhibits significant catalytic activity in the fixation of CO2 with epoxides, leading to the formation of valuable chemicals under atmospheric pressure. Ag@GMP demonstrated efficient antibacterial activity against both Gram-negative and Gram-positive bacteria. The highest zone of inhibition was observed against S. aureus MTCC 3160 (15.83 ± 1.1 mm), and for E. coli, P. aeruginosa PAO1, and B. subtilis, it was found to be 12.66 ± 0.9, 14.33 ± 0.8 and 12.8 ± 0.8 mm, respectively.

Manipulation of interfacial charge dynamics for metal-organic frameworks toward advanced photocatalytic applications

Compared to other known materials, metal-organic frameworks (MOFs) have the highest surface area and the lowest densities; as a result, MOFs are advantageous in numerous technological applications, especially in the area of photocatalysis. Photocatalysis shows tantalizing potential to fulfill global energy demands, reduce greenhouse effects, and resolve environmental contamination problems. To exploit highly active photocatalysts, it is important to determine the fate of photoexcited charge carriers and identify the most decisive charge transfer pathway. Methods to modulate charge dynamics and manipulate carrier behaviors may pave a new avenue for the intelligent design of MOF-based photocatalysts for widespread applications. By summarizing the recent developments in the modulation of interfacial charge dynamics for MOF-based photocatalysts, this minireview can deliver inspiring insights to help researchers harness the merits of MOFs and create versatile photocatalytic systems.

Metal dimer nanojunction-magnetic material composites for magnetic field sensing

Noble metal nanocrystals are used as high sensitivity optoelectronic sensors, such as surface-enhanced Raman scattering, SERS. The sensing performance of metal nanocrystals can be further improved by forming dimer nanojunctions with strong "plasmonic coupling". Since the strength of "plasmonic coupling" is highly sensitive to the sub-nanoscale spacing between plasmonic nanocrystals in nanojunctions, nanojunctions can be used to detect external stimuli that can change the spacing of nanocrystals in the nanojunction and thus change the sensitivity of the Raman scattering spectrum. Here, we utilize this principle to detect the direction and strength of an external magnetic field (MF) using dimer nanojunctions surrounded by magnetic materials as a sensing platform. The results reveal that the changes in nanocrystal spacing in the nanojunction are caused by the rearrangement of the magnetic material under an external MF, which strongly depends on the interaction between the magnetic material and the ligands on the nanocrystal surface and the steric repulsion generated by the ligand configuration on the nanocrystal surface. Compared with the Raman spectrum without an external MF, the enhancement factors of the Raman scattering spectrum under an external MF can reach up to ∼900%, which makes dimer nanojunctions with magnetic materials suitable for "magnetic field" sensing applications.

Microwave-Assisted Synthesis of MoS2/BiVO4 Heterojunction for Photocatalytic Degradation of Tetracycline Hydrochloride

Compared with traditional hydrothermal synthesis, microwave-assisted synthesis has the advantages of being faster and more energy efficient. In this work, the MoS₂/BiVO₄ heterojunction photocatalyst was synthesized by the microwave-assisted hydrothermal method within 30 min. The morphology, structure and chemical composition were characterized by X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and high-resolution transmission electron microscopy (HRTEM). The results of characterizations demonstrated that the synthesized MoS₂/BiVO₄ heterojunction was a spherical structure with dimensions in the nanorange. In addition, the photocatalytic activity of the samples was investigated by degrading tetracycline hydrochloride (TC) under visible light irradiation. Results indicated that the MoS₂/BiVO₄ heterojunction significantly improved the photocatalytic performance compared with BiVO₄ and MoS₂, in which the degradation rate of TC (5 mg L^-1) by compound where the mass ratio of MoS₂/BiVO₄ was 5 wt% (MB5) was 93.7% in 90 min, which was 2.36 times of BiVO₄. The active species capture experiments indicated that •OH, •O₂^- and h⁺ active species play a major role in the degradation of TC. The degradation mechanism and pathway of the photocatalysts were proposed through the analysis of the band structure and element valence state. Therefore, microwave technology provided a quick and efficient way to prepare MoS₂/BiVO₄ heterojunction photocatalytic efficiently.