2D Palladium Sulphate for Visible‐Light‐Driven Optoelectronic Reversible Gas Sensing at Room Temperature

Abstract

2D metal sulphides (MSs) have attracted enormous amounts of attention in developing high‐performance gas sensors. 2D noble metal sulphides and their derivatives, however, have been less studied due to their predominant nonlayered crystal structures for inefficient exfoliation, despite their surface and peculiar optoelectronic properties. Herein, we successfully synthesize 2D palladium sulphate (PdSO4) from palladium sulphide (PdS) bulk crystals by liquid‐phase exfoliation, in which the presence of oxygen species in the exfoliation solvent plays a key role in the sulphate transformation. Ultrathin 2D PdSO4 planar nanosheets, with thicknesses of ≈3 nm and submicrometer lateral dimensions, exhibit a broad absorption across the visible spectrum, a narrow bandgap of ≈1.35 eV, and a nanosecond scaled long exciton lifetime, which are all suitable for the visible‐light‐driven optoelectronic gas sensing applications. The 2D PdSO4‐based sensor demonstrates a reversible, selective, and sensitive response toward ppb‐leveled NO2 gas at blue light irradiation, featuring a response factor of ≈3.28% for 160 ppb NO2, a low limit of detection of 1.84 ppb, and a > 3 times response factor enhancement over other gases. Herein, the possibility of realizing 2D ultrathin noble metal sulphide compounds from their nonlayered crystal structures and strong potentials in developing high‐performance chemical sensors is explored.

Reversible Room Temperature H2 Gas Sensing Based on Self-Assembled Cobalt Oxysulfide

“…The crystal transformation was confirmed by the XRD pattern. From Figure 1 c, the feature peaks of hexagonal cobalt sulfide at 31.3°, 35.3°, 47.2° and 55.0° can be ascribed as the crystal plane of (100), (101), (102), and (110), which is in good agreement with the reported literatures [ 41 , 42 ]. Such a crystal structure was transformed to an orthorhombic system (space group Pnma , a = 8.62400 Å, b = 6.71500 Å, and c = 4.74400 Å) after the annealing treatment, showing the distinct peaks at 31.3°, 36.8°, 44.8°, 59.3°, and 65.2°, matching well with the simulated lattice plane of (211), (002), (410), (141), and (422) of cobalt oxysulfide [ 43 ].…”

“…The sensor was also tested towards 1% H 2 at 40% relative humidity (RH). As shown in Figure S5 , the response factor of cobalt sulfide sensor slightly drops ~4% in a humidified environment compared to that of the dry condition possibly due to the adsorption of water vapor [ 42 ].…”

“…Metal oxysulfides are intermediates during the transition from metal sulfides to oxides, which have recently received attention for their strong potentials in gas sensing [ 41 ]. Within the metal-sulfide framework, part of the sulfide atoms is replaced by oxygen atoms through power-intensive approaches (e.g., calcination and probe-sonication) [ 41 , 42 ], resulting in the modification of the electronic band structure and more importantly the improvement of long term stability [ 41 , 42 ]. Furthermore, physisorption remains the dominant gas adsorption interaction with the oxysulfides.…”

Ultrathin 2D silver sulphate nanosheets for visible-light-driven NO2 sensing at room temperature

“…[11][12][13] Up to now, a variety of non-layered materials have been synthesized successfully in the 2D ultrathin form, including noble metals (such as Au, Ag, and Pd), metal oxides (such as TiO 2 , In 2 O 3 , and WO 3 ), and metal sulphides (such as PdS, CuS, CdS, and In 2 S 3 ) utilizing diverse exfoliation techniques ranging from novel methods to facile and environmentally friendly exfoliation techniques. [14][15][16][17][18][19][20][21][22] In particular, silver sulphide (Ag 2 S) has stimulated enormous interest due to its potential applications in photoconductors, photovoltaics, and gas-sensing applications owing to its intrinsic electrical and electronics properties. 19,[23][24][25] Using wet chemical exfoliation, recent work has successfully exfoliated 2D Ag 2 S nanosheets from their bulk counterpart, exhibiting small lateral dimensions and a thickness of B40 nm, a narrow bandgap of 1.51 eV, and excellent optical properties.…”

Facile Synthesis of Template‐Free SnS2 with Different Morphologies and Excellent Gas‐Sensing Performance for NO2 Gas‐Sensor Applications

“…In metal chalcogenides, the formal stoichiometry of 2D materials is MX, MX 2 , and MX 3 (M: metal, X: chalcogen). Materials such as MoS 2 , [ 13 ] MoSe, [ 14 ] PdS, [ 15 ] and SnS [ 16 ] demonstrated high sensitivity and selectivity to NO 2 at low temperatures, but there was a problem with the recovery rate. The optical method exhibits a fast response and recovery rate, but has cost limitations and is difficult to apply in MEMS gas sensors.…”