Enhancing the room temperature formaldehyde gas sensing properties of tungsten trioxide nanorods by compositing with graphitic carbon nitride

초록

WO3 nanorods having diameters less than 100 nm were composited with g-C3N4 using a two-step chemical synthesis that involved hydrothermal reaction and thermal poly-condensation process. The structures and morphologies were studied via X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. The nanocomposites contained nanocrystals of monoclinic WO3 and hexagonal g-C3N4 forming heterojunctions. Thermogravimetric analysis showed retention of at least 20 % mass corresponding to WO3 content even after thermal treatment at a temperature of 600-800 degrees C for several hours. The BrunauerEmmett-Teller (BET) surface area of WO3/g-C3N4 powders were measured by nitrogen adsorption desorption method. The surface area of 25 % WO3/75 % g-C3N4 nanocomposite was measured to be 25.152 m2 g-1 which was about four times larger than that of pure WO3. The chemical states of various elements in WO3/g-C3N4 were identified by X-ray photoelectron spectroscopy. The binding energy of W4f5 electron in WO3/g-C3N4 was observed to be at least 0.2 eV less than that in pure WO3 that indicated a strong binding between WO3 and gC3N4.The optical properties were studied via photoluminescence spectroscopy. Intensity of the blue-green luminescence from g-C3N4 decreased significantly due to compositing with WO3 that evidenced the charge separation at WO3/g-C3N4 hetero-interface. The formaldehyde gas sensing properties of the WO3/g-C3N4 nanocomposites were investigated at room temperature (30 degrees C). The 75 % WO3/25 % g-C3N4 and 50 % WO3/ 50 % g-C3N4 nanocomposite based gas sensors exhibited 85 % and 67 % responses respectively towards 28 ppm formaldehyde gas at room temperature (30 degrees C). The baseline resistance drift for 50 % WO3/50 % g-C3N4 nanocomposite based gas sensor was as small as 6.0 % after sensing 28 ppm formaldehyde gas for 50 s. The limit of detection corresponding to formaldehyde gas was 4.0 ppm, and the corresponding sensitivity was 0.36 ppm- 1. The WO3/g-C3N4 nanocomposite based gas sensor was highly selective to formaldehyde gas.

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