Gas Sensing and Electrochemical Properties of CNT/WS2 Core–shell Nanostructures

Tungsten disulfide (WS2) layers with different thicknesses were deposited on carbon nanotubes (CNTs) by atomic layer deposition (ALD) to obtain CNT/WS2 core–shell heteronanostructures. WS2 conformally grows like small platelet-flakes on the CNTs initially at low ALD cycles, while, with increasing the number of ALD cycles, WS2 platelets further grow to form a continuous film. The electrical and electrochemical properties of the synthesized CNT/WS2 hierarchical heterostructures were evaluated for sensing and electrocatalysis applications. First, a CNT/WS2 conductometric sensor was developed for gas-sensing monitoring of nitrogen dioxide (NO2). CNT/WS2 heteronanostructures were also tested as effective electrochemical probes for detecting riboflavin (vitamin B6) and as electrocatalysts for CO2 reduction. The results of gas sensing and electrochemical tests were discussed and correlated to the morphology and surface coverage of WS2 shell on CNT core. CNT/WS2 with 200–300 ALD cycles demonstrated the best performances because of the optimal catalytic WS2 properties and the formation of CNT/WS2 junctions, allowing the sensitive and selective detection of NO2 gas and riboflavin with a limit of detection (LOD) of 70 ppb and 0.4 μM, respectively, and formate production in the electrocatalytic reduction of CO2.