Fabrication of Robust and Porous Lead Chloride-Based Metal-Organic Frameworks toward a Selective and Sensitive Smart NH3 Sensor

Fabrication of an Optical Sensor Based on Eosin-Y-Doped Electrospun Fibers for Ammonia Detection via Wavelength Shifts

This research presents a simple and effective technique to fabricate an optical sensor for ammonia detection, leveraging emission wavelength shifts as the sensing mechanism. The sensor comprises a cellulose acetate matrix doped with Eosin-Y, which serves as the electrospinning material. Photoluminescent micro/nanofibers were successfully fabricated using electrospinning and were stimulated by a 380 nm central wavelength LED. The Eosin-Y-doped electrospun fiber membranes exhibited a red emission peak at 580 nm, allowing ammonia to be detected in the linear concentration range of 0-500 ppm. The experimental results demonstrated a high sensitivity of 8.11, with a wavelength shift sensitivity of 0.029 nm/ppm in response to ammonia concentration changes. This optical sensing method effectively mitigates the influence of fluctuations in excitation light intensity, offering improved reliability. The Eosin-Y-containing electrospun fibers show great potential as a practical sensing material for detecting ammonia gas concentrations with high precision, supporting diverse applications in medical diagnostics, environmental monitoring, and industrial processes.

Novel Gas Sensing Approach: ReS2/Ti3C2Tx Heterostructures for NH3 Detection in Humid Environments

Continuous monitoring of ammonia (NH3) in humid environments poses a notable challenge for gas sensing applications because of its effect on sensor sensitivity. The present work investigates the detection of NH3 in a natural humid environment utilizing ReS2/Ti3C2Tx heterostructures as a sensing platform. ReS2 nanosheets were vertically grown on the surface of Ti3C2Tx sheets through a hydrothermal synthetic approach, resulting in the formation of ReS2/Ti3C2Tx heterostructures. The structural, morphological, and optical properties of ReS2/Ti3C2Tx were investigated using various state-of-the-art techniques, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, zeta potential, Brunauer-Emmett-Teller technique, and Raman spectroscopy. The heterostructures exhibited 1.3- and 8-fold increases in specific surface area compared with ReS2 and Ti3C2Tx, respectively, potentially enhancing the active gas adsorption sites. The electrical investigations of the ReS2/Ti3C2Tx-based sensor demonstrated enhanced selectivity and superior sensing response ranging from 7.8 to 12.4% toward 10 ppm of NH3 within a relative humidity range of 15-85% at room temperature. These findings highlight the synergistic effect of ReS2 and Ti3C2Tx, offering valuable insights for NH3 sensing in environments with high humidity, and are explained in the gas sensing mechanism.

A novel optical dual sensor based on a coaxial electrospinning method for simultaneous sensing of oxygen and ammonia

The coaxial electrospinning method is widely used in a wide range of applications, including medical devices and sensing technology. This study proposes a novel optical dual sensor for simultaneous detection of oxygen (O2) and ammonia (NH3) based on coaxial electrospinning method to produce core-shell fiber membrane doped fluorescent dyes. The O2 (core) and NH3 (shell) sensitive dye membranes were successfully fabricated using coaxial electrospinning method by dissolving a polymer matrix, cellulose acetate (CA), with platinum (II) meso-tetrakis (pentafluorophenyl) porphyrin (PtTFPP) and Eosin-Y, respectively. The optical dual sensor was illuminated by an UV LED to monitor the intensity change and wavelength shift in the presence of selected analyte gases. The experimental data show that the sensitivities of optical dual sensor were found to be 6.4 and 3.2 for O2 and NH3, respectively. The response and recovery times of O2 and NH3 sensing probes were measured to be 12 s/29 s and 65 s/66 s, respectively. Also, when exposed to NH3 gas gradually from 0 to 500 ppm, the wavelength shift data of Eosin-Y was started at 569.5 nm, 573.9 nm, 578.4 nm, 579.4 nm, 580.8 nm, and 582.2 nm, respectively. In applications, the proposed optical dual sensor based on coaxial electrospinning method can detect O2 and NH3 gases simultaneously.

Adsorption and Detection of Iodine Species by a Thorium-Based Metal-Organic Framework

Actinide-bearing metal-organic frameworks (MOFs) encompass intriguing structures and properties, but the radioactivity of actinide cripples their applications. Herein, we have constructed a new thorium-based MOF (Th-BDAT) as a bifunctional platform for the adsorption and detection of radioiodine, a more radioactive fission product that can readily spread through the atmosphere in its molecular form or via solution as anionic species. The iodine capture within the framework of Th-BDAT from both the vapor phase and the cyclohexane solution has been verified, showing that Th-BDAT features maximum I₂ adsorption capacities (Q_max) of 959 and 1046 mg/g, respectively. Notably, the Q_max of Th-BDAT toward I₂ from cyclohexane solution ranks among the highest value for Th-MOFs reported to date. Furthermore, incorporating highly extended and π-electron-rich BDAT^4- ligands renders Th-BDAT as a luminescent chemosensor whose emission can be selectively quenched by iodate with a detection limit of 1.367 μM. Our findings thus foreshadow promising directions that might unlock the full potential of actinide-based MOFs from the point of view of practical application.

Organolead Halide-Based Coordination Polymers: Intrinsic Stability and Photophysical Applications

ConspectusOrganolead halide-based photovoltaics are one of the state-of-the-art solar cell systems with efficiencies increasing to 25% over the past decade, ascribed to their high light-absorption coefficient, broad wavelength coverage, tunable band structure, and excellent carrier mobility. Indeed, these optical characteristics are highly demanding in photocatalysis and photoluminescence (PL), which also involve the solar energy utilization and charge transport. However, the vast majority of organolead halides are ionically bonded structures and susceptible to degradation upon high-polarity protic molecules (e.g., water (vapor) and alcohol), which are often inevitable in many photochemical applications. Encapsulation is a commonly used stabilization approach by coating protective layers, avoiding the direct contact between organolead halides and polar molecules. However, this may partially hinder the light penetration to the inner hybrid halide materials, and introduce new interface problems that are important in photocatalysis and luminescent sensing. Therefore, developing intrinsically stable organometal halide hybrids is a major target for their applications in optoelectronic applications.In this Account, recent research progress on the synthesis of organolead halide-based coordination polymers for a variety of photoactive applications is described. Herein, we propose a general strategy to advance the intrinsic stability of organometal halide crystalline materials by using coordinating anionic organic linkers, which occupy the excellent photophysical features analogous to those of perovskites. Unlike the organoammonium cations as for ionically bonded structures, the anionic structure-directing agents (e.g., organocarboxylates) render well-defined metal-carboxylate coordination motifs in extended architectures spanning from low-dimensional (0D, 1D) to high-dimensional cationic inorganic Pb-X-Pb (X = F^-/Cl^-/Br^-/I^-) sublattices. This family of organolead halide coordination polymers can endure chemically reactive environments over a wide range of pH and aqueous boiling condition, which have been systematically investigated by experimental studies and theoretical calculations. Many chloride/bromide-based coordination polymers show air-stable, broadband self-trapped emission with large Stokes shift and high color rendition, exhibiting the absolute quantum yields of 35-72%. Among them, the porous frameworks with low-dimensional (0D, 1D) inorganic blocks are recognized as a rare class of porous metal-organic frameworks (MOFs) constructed by lead halides as secondary building units (SBUs). They not only occupy substantially higher light-harvesting and carrier-transport properties than conventional metal oxide-based MOFs, but also allow for isoreticular modification to regulate the PL characteristics by guest molecules. More importantly, combining the high stability with excellent carrier characteristics, a layered organolead iodide coordination polymer shows the overall photocatalytic water splitting without the use of any sacrificial agent under simulated sunlight illumination. Given the wide choice of structurally diverse organocarboxylate linkers, we hope this Account provides deep insights on the importance of coordination chemistry in the discovery of a wide family of intrinsically stable organolead halides to expand their photophysical applications.