Role of Nanodiamond Grains in the Exfoliation of WS₂ Nanosheets and Their Enhanced Hydrogen-Sensing Properties

Abstract

Herein, for the first time, a combination of detonation nanodiamond (DND)–tungsten disulfide (WS2) was devised and studied for its selective H2-sensing properties at room temperature. DND–WS2 samples were prepared by a sonication-assisted (van der Waals interaction) liquid-phase exfoliation process in low-boiling solvents with DND as a surfactant. The samples were further hydrothermally treated in an autoclave under high pressure and temperature. The as-prepared samples were separated as two parts named DND–WS2 BH (before hydrothermal) and DND–WS2 AH (after hydrothermal). The exfoliated bilayer to few-layer DND-doped WS2 nanosheets were confirmed by ultraviolet–visible spectra, atomic force microscopy, and transmission electron microscopy studies. It was observed that the DND powder not only acted as a surfactant but also doped and expanded on WS2 nanosheets. The difference between samples BH and AH treatment was further investigated using Raman spectroscopy. The WS2 and DND–WS2 samples on SiO2/Si were fabricated using a sputtered Pd/Ag interdigitated electrode and utilized for H2 gas-sensing measurements. Surprisingly, the DND–WS2 exhibits an ultrahigh sensor response of 72.8% to H2 at 500 ppm when compared to only 9.9% for WS2 alone. Also, the DND–WS2 shows a fast response/recovery time, high selectivity, and stability toward H2 gas. It can be attributed to the correlation of the intergrain phase of DND nanoparticles and WS2 nanosheets, which contributes to the easy transportation of charge carriers when exposed to the air and H2 gas atmosphere. Moreover, it is believed that DND-induced WS2 exfoliation might inspire future synthesis of transition metal dichalcogenides induced by DND in green solvents.

Chemical Sensors Based on Graphene and 2D Graphene Analogs

“…The WS 2 -based heterojunction can be an effective strategy in improving the sensing performance at room temperature. In case of chemoresistive gas sensors, WS 2 -based nanostructures such as 2D nanoflakes, [130,131] and nanosheets [132][133][134][135][136][137] are widely utilized due to the facile control of nanostructure morphology and numerous edge sites. The exposure of edge sites of 2D nanostructures is proven beneficial in chemoresistive gas sensing, which was reported in several research works.…”

Hydrogen Sensing Mechanism of WS2 Gas Sensors Analyzed with DFT and NAP-XPS

“…For these reasons, TMDCs have been investigated as active materials for several years [ 15 ], with MoS 2 and WS 2 as the two most studied TMDCs. While MoS 2 has been reported mainly as useful for detecting NO 2 and NH 3 [ 19 ], WS 2 has been found useful for detecting NH 3 [ 20 ], NO 2 [ 21 , 22 , 23 ], H 2 S [ 21 , 24 , 25 ], or H 2 [ 26 , 27 ]. Therefore, WS 2 is a good candidate material for detecting hydrogen at moderate operating temperatures or even at room temperature.…”

“…Sensing mechanisms can involve many changes, such as charge transfer and doping, intercalation, and shifts in permittivity and lattice vibrations [ 17 ]. However, recent theoretical studies show that the gas sensing mechanisms of TMDCs and related layered materials have charge transfer processes as the main route for detecting gases [ 27 , 28 , 29 , 30 ], in which the sensing materials act as charge acceptors or donors [ 4 , 28 , 29 , 30 ]. For example, Changjie Zhou et al reported that hydrogen adsorption brings a relatively small amount of charge transfer from the WS 2 monolayer to the adsorbed hydrogen molecule [ 31 ].…”