Mwcnt

MWCNTs were purchased from NanoIntegris Inc. (Skokie, IL, USA). According to the manufacturer, these MWCNTs had the purity of > 95 wt% and the length of 10–30 μm. The specific surface area was 233 m²/g with 10–20 nm and 3–5 nm on the outer and inner diameter, respectively. The preparation procedure of MWCNTs filters was similar as our previous study [13 (link)]. Briefly, the as-received MWCNTs were suspended in 50% dimethylsulfoxide (DMSO) at the concentration of 3 mg/mL. The MWCNTs suspensions were sonicated for 15 min and then deposited onto the Isopore^TM RTTP membranes filters with a diameter of 25 mm and a pore size of 1.2 μm (Merck Millipore Ltd., Carrigtwohill, Ireland) with various loadings by varying the depositing volumes. The membranes loaded with MWCNTs were sit at room temperature for 2 h, and were washed by filtering with 2 mL ethanol first and then 5 mL deionized water (DI-H₂O).
TTO and LEO were purchased from Sigma-Aldrich (St. Louis, MO, USA). For the preparation of TTO-MWCNTs filters and LEO-MWCNTs filters, various volumes of TTO or LEO was added onto the surface of MWCNTs filters to coat MWCNTs. Mixture of 1:1 (v/v) TTO and LEO also used to coat MWCNTs filters, and denoted as Mix-MWCNTs filters. The filters were then washed with 5 mL DI-H₂O to remove the un-adsorbed EO and were used immediately.

Unless otherwise stated, all materials were used as received. MWCNTs (diameter 50–80 nm and aspect ratio >100) were purchased from Sigma Aldrich (St. Louis, MO, USA). The SYLGARD 184 PDMS was purchased from Dow Corning (Midland, MI, USA). SYLGARD 184 is a two-part PDMS, consisting of the base elastomer (part A) and curing agent (part B). Tetrahydrofuran (THF) was used as the solvent for MWCNT dispersion and was purchased from Sigma Aldrich.

We fabricated a CNT thin film using MWCNTs (Sigma-Aldrich, St. Louis, MO, USA), the average length and diameter of which were in the ranges of 6–13 nm and 2.5–20 μm, respectively. MWCNTs and methanol were mixed in the ratio of 0.2 g per 100 mL, added with 0.5 wt % PEI (Sigma-Aldrich), and the mixture was stirred for 12 h. Thereafter, the mixture was homogenized for 1h using ultrasonic equipment. After fully dispersed, a vacuum filtration process was conducted with 8 μm filter paper (Whatman, Marlborough, MA, USA). After drying the CNT thin film by heating at 70 °C for 1 h, it was placed on a polyimide substrate to make a silver electrode with a gap of approximately 2 cm at both ends of the sample. Subsequently, the silver electrode was heated at 90 °C for 15 min and dried to fabricate a gas sensor. Figure 1 shows the image of the filtration production system, the fabricated sensor, and the flexibility of the sensor.