Octahedral Molybdenum Iodide Clusters Supported on Graphene for Resistive and Optical Gas Sensing

Octahedral molybdenum iodide clusters with pyrazole or pyrazolate ligands

Due to the combination of useful physicochemical properties (luminescence, X-ray contrast, etc.), octahedral molybdenum halide cluster complexes [Mo6X8L6]n have been the subject of active investigation during the last decades. The most common methods for synthesizing new compounds with organic ligands involve the use of silver salts of organic acids or the substitution of terminal methylate ligands. However, these methods often necessitate the use of special conditions, such as an inert atmosphere, absolute solvents, and silver salts, which can be costly. In contrast, aqua-hydroxo complexes formed by hydrolysis of many complexes are considered final unreactive products, despite the tendency for them to form. This work proposes a simple and affordable method for the preparation of hexaaqua and hexahydroxo iodide clusters of molybdenum from [Mo6I14]2- in a single step. Furthermore, the possibility of using such compounds as starting complexes for the synthesis of clusters with organic ligands such as pyrazole is discussed. The paper presents synthetic approaches, detailed characterization both in solid and in solution, and a study of the reactivity and luminescence properties of the obtained compounds.

N-doped titania nanoparticles containing Mo6 bromide and iodide clusters: Activity in photodegradation of rhodamine B and tetracycline

Contamination of water sources is a major environmental problem with far-reaching consequences for humanity. Organic substances are among the most widespread and persistent pollutants. Advanced oxidation processes, especially photocatalysis, have been considered as one of the most promising technologies for organic pollution control. In this study, hybrid photocatalysts based on N-doped TiO2, which exhibits activity in the visible region of the spectrum, and different content of octahedral Mo6 bromide and iodide cluster complexes were synthesized to achieve the highest efficiency of the formed S-scheme photocatalytic system under white light irradiation. According to the data obtained, the resulting materials are nanoparticles with a diameter of ∼10 nm exhibiting absorption up to ∼550 nm. Photocatalytic studies were performed using model organic molecules - the more colored rhodamine B (RhB) and the less colored antibiotic tetracycline (TET). The most active samples showed high efficiencies against both pollutants with keff ∼0.3-0.4 and 0.4-0.5 min-1, respectively, while the activity of iodide complexes was ∼1.3 times higher than that of bromide complexes. The stability of the catalysts is preserved for up to 5 cycles of TET photodegradation.

Graphene Oxide Sheets Decorated with Octahedral Molybdenum Cluster Complexes for Enhanced Photoinactivation of Staphylococcus aureus

The emergence of multidrug-resistant microbial pathogens poses a significant threat, severely limiting the options for effective antibiotic therapy. This challenge can be overcome through the photoinactivation of pathogenic bacteria using materials generating reactive oxygen species upon exposure to visible light. These species target vital components of living cells, significantly reducing the likelihood of resistance development by the targeted pathogens. In our research, we have developed a nanocomposite material consisting of an aqueous colloidal suspension of graphene oxide sheets adorned with nanoaggregates of octahedral molybdenum cluster complexes. The negative charge of the graphene oxide and the positive charge of the nanoaggregates promoted their electrostatic interaction in aqueous medium and close cohesion between the colloids. Upon illumination with blue light, the colloidal system exerted a potent antibacterial effect against planktonic cultures of Staphylococcus aureus largely surpassing the individual contributions of the components. The underlying mechanism behind this phenomenon lies in the photoinduced electron transfer from the nanoaggregates of the cluster complexes to the graphene oxide sheets, which triggers the generation of reactive oxygen species. Thus, leveraging the unique properties of graphene oxide and light-harvesting octahedral molybdenum cluster complexes can open more effective and resilient antibacterial strategies.

A chemiresistive-potentiometric multivariate sensor for discriminative gas detection

Highly efficient gas sensors able to detect and identify hazardous gases are crucial for numerous applications. Array of conventional single-output sensors is currently limited by problems including drift, large size, and high cost. Here, we report a sensor with multiple chemiresistive and potentiometric outputs for discriminative gas detection. Such sensor is applicable to a wide range of semiconducting electrodes and solid electrolytes, which allows to tailor and optimize the sensing pattern by tuning the material combination and conditions. The sensor performance is boosted by equipping a mixed-conducting perovskite electrode with reverse potentiometric polarity. A conceptual sensor with dual sensitive electrodes achieves superior three-dimensional (sub)ppm sensing and discrimination of humidity and seven hazardous gases (2-Ethylhexanol, ethanol, acetone, toluene, ammonia, carbon monoxide, and nitrogen dioxide), and enables accurate and early warning of fire hazards. Our findings offer possibilities to design simple, compact, inexpensive, and highly efficient multivariate gas sensors.

Enhanced NH3 Sensing Performance of Mo Cluster-MoS2 Nanocomposite Thin Films via the Sulfurization of Mo6 Cluster Iodides Precursor

The high-performance defect-rich MoS₂ dominated by sulfur vacancies as well as Mo-rich environments have been extensively studied in many fields, such as nitrogen reduction reactions, hydrogen evolution reactions, as well as sensing devices for NH₃, which are attributed to the under-coordinated Mo atoms playing a significant role as catalytic sites in the defect area. In this study, the Mo cluster-MoS₂ composite was creatively synthesized through a one-step sulfurization process via H₂/H₂S gas flow. The Mo₆ cluster iodides (MIs) coated on the fluorine-doped tin oxide (FTO) glass substrate via the electrophoretic deposition method (i.e., MI@FTO) were used as a precursor to form a thin-film nanocomposite. Investigations into the structure, reaction mechanism, and NH₃ gas sensing performance were carried out in detail. The results indicated that during the gas flowing, the decomposed Mo₆ cluster iodides played the role of template and precursor, forming complicated Mo cluster compounds and eventually producing MoS₂. These Mo cluster-MoS₂ thin-film nanocomposites were fabricated and applied as gas sensors for the first time. It turns out that after the sulfurization process, the response of MI@FTO for NH₃ gas increased three times while showing conversion from p-type to n-type semiconductor, which enhances their possibilities for future device applications.