Effects of Precursor Concentration on Dimensional Size, Defect State, and Gas Sensing Performance of MoS₂ Sheets Synthesized by Hydrothermal Method

Abstract

The objective of this study is to investigate effects of precursor concentration on dimensional size, defect state, and gas sensing performance of MoS 2 sheets synthesized by hydrothermal method with various precursor concentrations (0.14-1.4 M) in fixed HCl solution (7 M). The MoS 2 sheets show a defect-rich and strained structure. When precursor concentration is increased, dimensional size of the sheet is increased while the specific surface area of the sheet is decreased. The MoS 2 sensor made with 0.14 M precursor solution exhibits superior sensing performance with high sensitivity (372%) and rapid recovery time (<16 min) at room temperature in a 500 ppm NO 2 gas atmosphere due to enhanced active site resulting from the highest specific surface area. In addition, all MoS 2 samples show a complete recovery after response to NO 2 gas probably related to the defective and strained surface resulting from the use of HCl surfactant.

Controlled synthesis of ultrathin MoS2nanoflowers for highly enhanced NO2sensing at room temperature

“…17,37 However, some other works indicated that in spite of slow rates of gas adsorption and desorption, the pristine MoS 2 -based sensors showed the complete recovery at RT to target gases. 20,[38][39][40] This characteristic can be attributed to several factors, such as high specic surface area, defective/strained surface and weak van der Waals binding between the target gas and the MoS 2 surface. 20,38,39 In addition, Ikram et al indicated that the high specic surface area not only increases the response of the sensor but also plays an important role in fast response and recovery times.…”

“…20,[38][39][40] This characteristic can be attributed to several factors, such as high specic surface area, defective/strained surface and weak van der Waals binding between the target gas and the MoS 2 surface. 20,38,39 In addition, Ikram et al indicated that the high specic surface area not only increases the response of the sensor but also plays an important role in fast response and recovery times. 41 Thus, understanding the detailed mechanism for the complete recovery of the sensor is still under debate because of the combined effects of physi-, chemi-sorption, role of defects sites and transduction mechanism 37 .…”

Enhanced Gas Sensing Performance of Surface‐Activated MoS2 Nanosheets Made by Hydrothermal Method with Excess Sulfur Precursor

“…In our previous reports, we evaluated the effect of the precursor concentration on the microstructure of hydrothermally grown MoS 2 nanosheets in excess thiourea conditions. Low concentration conditions resulted in high sensitivity and a good recovery behavior, which were attributed to the synergistic effects ofsize reduction (providing abundant edge sites) and defective basal planes with high concentration of S vacancies . In particular, we observed short‐range ordering (nano‐domains) on the MoS 2 surface, which seemed to generate additional edge sites.…”

“…The basal plane of MoS 2 nanosheets has an inert surface, while the edge of these nanosheets consists of dangling bonds that are that is chemically active toward gas molecules . Thus, a high sensitivity can be achieved by exposing more edge sites and/or activating the basal plane via the formation of vacancies and heterojunctions …”

“…In this work, we extended our previous study and focused on evaluating the effect of the nano‐domains on the sensing performance. We synthesized MoS 2 nanosheets of similar size and variable nano‐domain densities using a hydrothermal method with different precursor ratios.…”