Gas Sensors Based on Copper‐Containing Metal‐Organic Frameworks, Coordination Polymers, and Complexes

Uncovering tetrazoles as building blocks for constructing discrete and polymeric assemblies

Metal-organic self-assembly with flexible moieties is a budding field of research due to the possibility of the formation of unique architectures. Tetrazole, characterised by four nitrogen atoms in a five-member ring, exhibits immense potential as a component. Tetrazole offers four coordination sites for binding to the metal centre with nine distinct binding modes, leading to various assemblies. This review highlights different polymeric and discrete tetrazole-based assemblies and their functions. The meticulous manipulation of stoichiometry, ligands, and metal ions required for constructing discrete assemblies has also been discussed. The different applications of these architectures in separation, catalysis and detection have also been accentuated. The latter section of the review consolidates tetrazole-based cage composites, highlighting their applications in cell imaging and photocatalytic applications.

Determining Factors to Understand the External Quantum Efficiency Values: Study Carried Out with Copper(I)-I and 1,2-Bis(4-pyridyl)ethane Coordination Polymers as Downshifters in Photovoltaic Modules

Downshifters refer to compounds with the capacity to absorb UV photons and transform them into visible light. The integration of such downshifters has the potential to improve the efficiency of commercial photovoltaic modules. Initially, costly lanthanide derivatives and organic fluorescent dyes were introduced, resulting in a heightened module efficiency. In a novel research direction guided by the same physicochemical principles, the utilization of copper(I) coordination compounds is proposed. This choice is motivated by its simpler and more economical synthesis, primarily due to copper being a more abundant and less toxic element. Our proposal involves employing 1,2-bis(4-pyridyl) ethane (bpe), an economically viable commercial ligand, in conjunction with CuI to synthesize coordination polymers: [CuI(bpe)]n(1), [Cu3I3(bpe)3]n(2), and [CuI(bpe)0.5]n(3). These polymers exhibit the ability to absorb UV photons and emit light within the green and orange spectra. To conduct external quantum efficiency studies, the compounds are dispersed on glass and then encapsulated with ethylene vinyl acetate through heating to 150 °C. Interestingly, during these procedural steps, the solvents and temperatures employed induce a phase transformation, which has been thoroughly examined through both experimental analysis and theoretical calculations. The outcomes of these studies reveal an enhancement in external quantum efficiency with [Cu3I3(bpe)3]n(2), at a cost significantly lower (between 340 and 350 times) than that associated with lanthanide DS complexes.

2D Cu(I)-I Coordination Polymer with Smart Optoelectronic Properties and Photocatalytic Activity as a Versatile Multifunctional Material

This work presents two isostructural Cu(I)-I 2-fluoropyrazine (Fpyz) luminescent and semiconducting 2D coordination polymers (CPs). Hydrothermal synthesis allows the growth of P-1 space group single crystals, whereas solvent-free synthesis produces polycrystals. Via recrystallization in acetonitrile, P2₁ space group single crystals are obtained. Both show a reversible luminescent response to temperature and pressure. Structure determination by single-crystal X-ray diffraction at 200 and 100 K allows us to understand their response as a function of temperature. Applying hydrostatic/uniaxial pressure or grinding also generates significant variations in their emission. The high structural flexibility of the Cu(I)-I chain is significantly linked to the corresponding alterations in structure. Remarkably, pressure can increase the conductivity by up to 3 orders of magnitude. Variations in resistivity are consistent with changes in the band gap energy. The experimental results are in agreement with the DFT calculations. These properties may allow the use of these CPs as optical pressure or temperature sensors. In addition, their behavior as a heterogeneous photocatalyst of persistent organic dyes has also been investigated.

Advances in the synthesis and applications of 2D MXene-metal nanomaterials

MXenes, two-dimensional (2D) materials that consist of transition metal carbides, nitrides and/or carbonitrides, have recently attracted much attention in energy-related and biomedicine fields. These materials have substantial advantages over traditional carbon graphenes: they possess high conductivity, high strength, excellent chemical and mechanical stability, and superior hydrophilic properties. Furthermore, diverse functional groups such as -OH, -O, and -F located on the surface of MXenes aid the immobilization of numerous noble metal nanoparticles (NP). Therefore, 2D MXene composite materials have become an important and convenient option of being applied as support materials in many fields. In this review, the advances in the synthesis (including morphology studies, characterization, physicochemical properties) and applications of the currently known 2D MXene-metal (Pd, Ag, Au, and Cu) nanomaterials are summarized based on critical analysis of the literature in this field. Importantly, the current state of the art, challenges, and the potential for future research on broad applications of MXene-metal nanomaterials have been discussed.

Multifunctional Platform Based on a Copper(I) Complex and NaYF4:Tm3+,Yb3+ Upconverting Nanoparticles Immobilized into a Polystyrene Matrix: Downshifting and Upconversion Oxygen Sensing

This work presents an innovative approach to obtain a multifunctional hybrid material operating via combined anti-Stokes (upconversion) and Stokes (downshifting) emissions for oxygen gas sensing and related functionalities. The material is based on a Cu(I) complex exhibiting thermally activated delayed fluorescence emission (TADF) and infrared-to-visible upconverting Tm³⁺/Yb³⁺-doped NaYF₄ nanoparticles supported in a polystyrene (PS) matrix. Excitation of the hybrid material at 980 nm leads to efficient transfer of Tm³⁺ emission in the ultraviolet/blue region to the Cu(I) complex and consequently intense green emission (560 nm) of the latter. Additionally, the green emission of the complex can also be directly generated with excitation at 360 nm. Independently of the excitation wavelength, the emission intensity is efficiently suppressed by the presence of molecular oxygen and the quenching rate is properly characterized by the Stern-Volmer plots. The results indicate that the biocompatible hybrid material can be applied as an efficient O₂ sensor operating via near-infrared or ultraviolet excitation, unlike most optical oxygen sensors currently available which only work in downshifting mode.

Advanced microstructure, morphology and CO gas sensor properties of Cu/Ni bilayers at nanoscale

In this study, we investigated the morphology of synthesized Cu/Ni nanoparticles in trace of carbon sources by the co-deposition process of RF sputtering and RF-PECVD methods and localized surface plasmon resonance of CO gas sensing of Cu/Ni nanoparticles. The surface morphology was studied by analyzing 3D micrographs of atomic force microscopy using image processing techniques and fractal/multifractal analyses. The MountainsMap® Premium software with the two-way ANOVA (Variance analysis) and least-significant differences tests were used for statistical analysis. The surface nano-patterns have a local and global particular distribution. Experimental and simulated Rutherford backscattering spectra confirm the quality of nanoparticles. Then, prepared samples were exposed to CO gas flue to study their gas sensor application using the localized surface plasmon resonance method. Increasing the Ni layer over Cu one shows an interesting result in both morphology and gas sensing sides. Advanced stereometric analyses for the surface topography of thin films in conjunction with Rutherford backscattering spectrometry and Spectroscopic analysis make a unique study in the field.

Multi-stimulus semiconductor Cu(i)–I-pyrimidine coordination polymer with thermo- and mechanochromic sensing

The 1D-[Cu(aClpym)I]n coordination polymer behaves as an intelligent material with response to different stimuli since its emission is altered with temperature and with varying modes of pressure, making it a potential multi-response material.

Layered Double Oxides for Sensing Reducing Volatile Organic Compounds: The Effect of Local Charge Region Modulation

Multi-metal oxides with uniform distribution of various metal elements have potential for an enhanced gas-sensing response due to the strong heterogeneous and synergistic effects involved. In this study, three layered double oxides, labeled as CuCr-, ZnCr-, and ZnTi-LDOs, respectively, were prepared with corresponding LDHs (layered double hydroxides) as precursors and self-sacrificial templates. The elemental mapping confirms the uniform distribution of hetero-metal elements in whole LDOs. The CuCr-LDOs exhibits a much larger sensing response towards reducing VOCs at room temperature, which is 3.5 or 13.3 times that of ZnCr- or ZnTi-LDOs, respectively. The response differences are analyzed in terms of the local charge region modulation associated with heterojunction formation, and it is further demonstrated based on first-principles calculations and valence electron theory. The present work suggests a possible strategy for developing highly sensitive oxide-based gas sensors for VOCs detection.