Supporting Information

Transcription

1 Electronic Supplementary Material (ESI) for Nanoscale. This journal is The Royal Society of Chemistry 2014 Supporting Information Experimental All the chemicals were of analytical grade and used without further purification. Synthesis of H 2 WO 4 and WO 3 nanoplates The experiment was modified slightly according to our previous work. 1 In a typical experiment of H 2 WO 4, 1.5 g Na 2 WO 4 2H 2 O was firstly dissolved into 70.5 ml of distilled water. Next, 4.5 ml HBF 4 solution (w, 40%) was added dropwise to the above solution under vigorous magnetic stirring at 60 ºC for 10 h. The obtained powder sample was centrifuged, washed with distilled water and dried. To obtain WO 3 nanoplates, the resulting H 2 WO 4 was further heated at 320 ºC for 4 h. Synthesis of Ni(OH) 2 and NiO nanoplates The experiment was carried out in a similar way according to our previous work g Ni(NO 3 ) 2 6H 2 O was firstly dissolved into 12 ml distilled water, and then 3 ml n-butylamine was added dropwise to the above solution under vigorous magnetic stirring. The mixture was hydrothermally reacted at 180 C for 12 h. The obtained powder sample was centrifuged, washed with distilled water and dried. To obtain NiO nanoplates, the resulting Ni(OH) 2 was further heated at 320 ºC for 4 h. Preparation of plate-like heterogeneous NiO/WO 3 nanocomposites In a typical process, 1 mmol Ni(OH) 2 and 1 mmol H 2 WO 4 were sonicated into 50ml alcohol for 1 h, and dried at 60 C in air. After that, the mixed power was heated at 320 ºC for 4 h. Characterization The morphology and structural characteristics were observed using X-ray diffraction (XRD, Rigaku D/max 2500 diffractometer), scanning electron microscopy (SEM, Hitachi S4800) and transmission electron microscope (TEM; JEOL 2010 with an accelerating voltage of 200 kv).

2 Gas sensing measurements The fabrication and testing principles of the gas sensor are similar to that described in our previous reports. 3 Here, the gas concentration was confirmed through calculating the added volume of tested gas in container. Firstly, the gas-sensing samples were mixed with terpineol to form a paste and then coated onto the outside surface of an alumina tube with a diameter of 1 mm and a length of 5 mm. A platinum coil through the tube was employed as a heater to control the operating temperature. To improve their stability and reproducibility, the gas sensors were aged at 300 ºC for 10 h in air. Here, the sensing properties of the sensors were measured by a NS-4003 series gassensing measurement system (China Zhong-Ke Micro-nano IOT, Internet of Things, Ltd.). The relative humidity (RH) is about 45%. The response and recovery times were defined as the time required for a change of the resistance to reach 90 % of the equilibrium value after injecting and that for removing the detected gas, respectively. When air and ppm-level target gas were flowed through the sensor element, the corresponding steady-state resistances of the sensor in air (R air ) and in the air gas mixture (R gas ) were recorded, respectively. The NiO or NiO/WO 3 sensor gas response (S) for oxidizing gases (NO or NO 2 ) is defined as the ratio of R air /R gas, while the response (S) for reducing gases (H 2 S, CH 4, SO 2 or CO) is defined as the ratio of R gas /R air. The NiO or NiO/WO 3 sensor gas response (S) for reducing gases (H 2 S, CH 4, SO 2 or CO) is defined as the ratio of R gas /R air, while the response (S) for oxidizing gases (NO or NO 2 ) is defined as the ratio of R air /R gas. References 1 J. M. Ma, J. Zhang, S. R. Wang, T. H. Wang, J. B. Lian, X. C. Duan and W. J. Zheng, J. Phys. Chem. C, 2011, 115, J. M. Ma, J. Q. Yang, L. F. Jiao, Y. H. Mao, T. H. Wang, X. C. Duan, J. B. Lian and W. J. Zheng, CrystEngComm, 2012, 14, J. W. Deng, J. M. Ma, L. Mei, Y. J. Tang, Y. J. Chen, T. Lv, Z. Xu and T. H. Wang, J. Mater. Chem. A, 2013, 1,

3 Fig. S1 SEM image of NiO nanoplates.

4 Fig. S2 SEM image of WO 3 nanoplates.

5 Fig. S3 SEM image of NiO/WO 3 nanocomposites.

6 o C Resistance (M o C 60 o C 120 o C 240 o C 300 o C Time (s) Fig. S4 The real-time response curves of the WO 3 sensor to 30 ppm NO 2 at different temperatures.

7 o C Resistance(M ) o C 120 o C 180 o C 240 o C 300 o C Time (s) Fig. S5 The real-time response curves of the NiO sensor to 30 ppm NO 2 at different temperatures.