Detection of Trace Water Based on Electro-oxidation of Molybdenum Disulfide Nanomaterials to Form Molybdenum Oxysulfide

A "turn-on" fluorescent sensor based on three-component covalent organic framework for trace water detection

Trace amount of H2O is difficult to eliminate in laboratory environments and chemical industries as impurities. In some chemical reactions, trace amount of H2O can alter final reaction products, yield, and selectivity. So, the detection of trace H2O is very important. Herein, a series of TFPT[X]-BMTH- covalent organic frameworks (COFs) (X = 0, 33, 50, 67, 100 %) with intramolecular charge transfer effect (ICT) and aggregate-induced emission (AIE) characteristics were synthesized by amino-aldehyde condensation reaction between 2,5-bis(2-methoxyethoxy)terephthalohydrazide (BMTH)/ 1,3,5-tris(p-formylphenyl)benzene (TFPB) and 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde (TFPT). By changing TFPT' content in TFPT[X]-BMTH-COFs, the ICT and AIE of TFPT[X]-BMTH-COFs can be controlled, and accordingly the response to trace H2O can be adjusted. A H2O sensor based on TFPT[67]-BMTH-COF with a wide linear range from 0 wt% to 0.5 wt% was developed and the detection limit was 0.00007 wt%. In addition, a portable fluorescent test paper based on TFPT[67]-BMTH-COF for visual detection of trace H2O in honey samples and salt was constructed. This work has important guiding significance for the development of fluorescent probes for the visual detection of trace water.

Physical adsorption and oxidation of ultra-thin MoS2crystals: insights into surface engineering for 2D electronics and beyond

The oxidation mechanism of atomically thin molybdenum disulfide (MoS2) plays a critical role in its nanoelectronics, optoelectronics, and catalytic applications, where devices often operate in an elevated thermal environment. In this study, we systematically investigate the oxidation of mono- and few-layer MoS2flakes in the air at temperatures ranging from 23 °C to 525 °C and relative humidities of 10%-60% by using atomic force microscopy (AFM), Raman spectroscopy and x-ray photoelectron spectroscopy. Our study reveals the formation of a uniform nanometer-thick physical adsorption layer on the surface of MoS2, which is attributed to the adsorption of ambient moisture. This physical adsorption layer acts as a thermal shield of the underlying MoS2lattice to enhance its thermal stability and can be effectively removed by an AFM tip scanning in contact mode or annealing at 400 °C. Our study shows that high-temperature thermal annealing and AFM tip-based cleaning result in chemical adsorption on sulfur vacancies in MoS2, leading to p-type doping. Our study highlights the importance of humidity control in ensuring reliable and optimal performance for MoS2-based electronic and electrochemical devices and provides crucial insights into the surface engineering of MoS2, which are relevant to the study of other two-dimensional transition metal dichalcogenide materials and their applications.