Bioinspired Cocatalysts Decorated WO 3 Nanotube Toward Unparalleled Hydrogen Sulfide Chemiresistor

Transcription

1 Supporting Information Bioinspired Cocatalysts Decorated WO 3 Nanotube Toward Unparalleled Hydrogen Sulfide Chemiresistor Dong-Ha Kim, Ji-Soo Jang, Won-Tae Koo, Seon-Jin Choi, Hee-Jin Cho, Min-Hyeok Kim, Sang-Joon Kim and Il-Doo Kim, * Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States *Corresponding author idkim@kaist.ac.kr S-1

2 Table of Contents S1. Schematic illustration of gas sensor test system. S2. Photograph and optical micrographic images of the sensor.. S3. Schematic illustration of cellulose nanocrystals (CNC) and its structural formula and SEM images of CNC. S4. Schematic illustration of apoferritin encapsulated Pt NPs (Apo-Pt NPs), a particle size distribution histogram of Apo-Pt NPs, and TEM image of Apo-Pt NPs. S5. PXRD analysis of before and after calcination of cellulose nanocrystal (CNC) and SEM image of after calcination of CNC. S6. Thermal gravimetric and differential colorimetric analysis. S7. SEM images of Na 2 W 4 O 13 loaded WO 3 NFs after calcination at low temperature. S8. Isothermal adsorption/desorption plot and pore size distribution analyses. S9. Elemental dispersive spectroscopy (EDS) line profile images of Pt-Na 2 W 4 O 13 loaded WO 3 NTs and Na 2 W 4 O 13 loaded WO 3 NTs. S10. PXRD analysis of dense WO 3 NFs, Na 2 W 4 O 13 loaded WO 3 NTs, and Pt-Na 2 W 4 O 13 loaded WO 3 NTs. S11. Dynamic hydrogen sulfide sensing characteristics depending on the various Pt catalyst loading content. S12. Limit of detection of Pt-Na 2 W 4 O 13 loaded WO3 NTs toward H 2 S detection. S13. Dynamic hydrogen sulfide sensing characteristics of Pt-WO 3 NFs. S14. UPS spectrum of pristine WO 3 NFs and Na 2 W 4 O 13 loaded WO 3 NTs. S15. XPS spectra of O - and O 2- in pristine WO 3 NFs and Na 2 W 4 O 13 loaded WO 3 NTs. S16. Stability of 0.05 wt% Pt-Na 2 W 4 O 13 loaded WO 3 NTs toward 1 ppm H 2 S molecules during 25 cycles of response and recovery at 450 C. S17. XPS analysis of Pt-Na 2 W 4 O 13 loaded WO 3 NTs in the vicinity of W 4f, O 1s, and Pt 4f. S18. Ex-situ XPS analysis of WO 3 NFs in the vicinity of S 2p before and after H 2 S exposure. S19. SEM images of as-spun and after calcination of Na 2 W 4 O 13 NFs as well as XRD result. S20. Hydrogen sulfide sensing characteristics of Na 2 W 4 O 13 NFs and selectivity toward 7 other interfering molecules. Table S1. Recent publications on SMOs based chemi-resistive gas sensors for detection of hydrogen sulfide molecules under highly humid ambient (75 95 % RH). S-2

3 Figure S1. (a) Schematic illustration of gas sensor test system and (b) photo image of a sensor chamber. S-3

4 Figure S2. (a) Photograph image and (b) optical micrographic image of the sensor; the Pt- Na 2 W 4 O 13 loaded WO 3 NTs as sensing layers are drop-coated on the alumina substrate. S-4

5 Figure S3. (a) TEM image of as-synthesized apoferritin templated Pt NPs (Apo-Pt NPs), (b) particle size distribution of Apo-Pt NPs. S-5

6 Figure S4. (a) TEM image of as-synthesized apoferritin templated Pt NPs (Apo-Pt NPs), (b) particle size distribution of Apo-Pt NPs. S-6

7 Figure S5. (a) PXRD analysis of before calcination of cellulose nanocrystal(cnc) and after calcination of CNC at 600 C for 1 h, (b) SEM image after calcination of CNC at 600 C for 1 h. S-7

8 Figure S6. (a) Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis of as-spun W precursor/pvp composite NFs in a temperature range of C, (b) TGA and DSC analysis of as-spun CNC/W precursor/pvp composite NFs in a temperature range of C. In order to investigate the thermal decomposition behavior of CNC template toward formation of tubular WO 3 nanostructure, thermal gravimetric (TG) and differential scanning calorimetry (DSC) analyses were conducted for two samples, i.e., pristine as-spun W precursor/pvp composite NFs (hereafter, pristine composite NFs) (Figure S6a) and as-spun CNC embedded W precursor/pvp composite NFs (hereafter, CNC@composite NFs) (Figure S6b). The slight weight loss at low temperature (< 150 C) was attributed to evaporation of residual solvent (DI water). Then, about 10% of noticeable weight loss with a small exothermic peak was observed at 270 C for CNC@composite NFs, which was attributed to the decomposition of partially amorphous sulfate regions of CNC surface. 1 In the temperature range of C, PVP side chains gradually decomposed, in consistency with previous literatures. 2 The following exothermic peak is related to crystallization of WO 3, exhibiting larger exothermic peak at higher temperature (429 C) for CNC@composite NFs compared to that (410 C) of pristine W precursor/pvp composite NFs. The crystallization peak of Na 2 W 4 O 13 was not distinctly observed because the weight percentage of Na 2 W 4 O 13 was negligible com- S-8

9 pared to that of WO 3. After decomposition of PVP main chains in NFs (536 C), an additional exothermic peak related to decomposition of CNC main crystalline chains was observed (555 C), resulting in larger weight loss than that of the pristine composite NFs at a temperature above 500 C, which corresponds to previous analysis of CNC. 1 Thus, CNC@composite NFs exhibited lower residual weight (31.2 wt%) than that of pristine composite NFs (42.5 wt%). To confirm the importance of calcination temperature toward effective generation of tubular WO 3, we calcined CNC@composite NFs at 500 C for 1 h. Since, according to TG/DSC analysis, CNC templates entirely decompose above the temperature of about 550, dense NFs were observed in SEM images (Figure S7a b). Therefore, to form tubular oxide structures, calcination temperature should be higher than 550 C to completely remove residual CNC. S-9

10 Figure S7. SEM images of (a b) Na 2 W 4 O 13 loaded WO 3 NFs calcined at 500 C for 1 h. S-10

11 Figure S8. (a) Isothermal adsorption/desorption plot of Pt-Na 2 W 4 O 13 loaded WO 3 NTs, and (b) pore size distribution of Pt-Na 2 W 4 O 13 loaded WO 3 NTs. S-11

12 Figure S9. (a) STEM image of Pt-Na 2 W 4 O 13 loaded WO 3 NTs, (b) elemental dispersive spectroscopy (EDS) line-scan profile of W, O, and Pt, (c) STEM image of Na 2 W 4 O 13 loaded WO 3 NTs, and (d) EDS line-scan profile of W and O. S-12

13 Figure S10. PXRD analysis of dense WO 3 NFs, Na 2 W 4 O 13 loaded WO 3 NTs, and Pt- Na 2 W 4 O 13 loaded WO 3 NTs. S-13

14 Figure S11. Dynamic hydrogen sulfide (5 1 ppm) response characteristics at 450 C at different loading amounts of Pt catalysts. S-14

15 Figure S12. Exponential approximation of the limit of detection of Pt-Na 2 W 4 O 13 loaded WO 3 NTs. S-15

16 Figure S13. Dynamic hydrogen sulfide (5 1 ppm) response characteristics of 0.05 wt% Pt loaded WO 3 NFs at 350 and 450 C. S-16

17 Figure S14. (a) UPS spectrum of pristine WO 3 NFs and Na 2 W 4 O 13 loaded WO 3 NTs, (b) high-binding-energy region, and (c) low-binding-energy region. S-17

18 Figure S15. XPS spectra of O - and O 2- in (a) pristine WO 3 NFs and (b) Na 2 W 4 O 13 loaded WO 3 NTs with (c) a spectra table. S-18

19 Figure S16. Stability of 0.05 wt% Pt-Na 2 W 4 O 13 loaded WO 3 NTs toward 1 ppm H 2 S molecules during 25 cycles of response and recovery at 450 C. S-19

20 Figure S17. XPS analysis of Pt-Na 2 W 4 O 13 loaded WO 3 NTs in the vicinity of (a) W 4f, (b) O 1s, and (c) Pt 4f. S-20

21 Figure S18. Ex-situ XPS analysis of pristine WO 3 NFs in the vicinity of S 2p peak (a) before exposure to hydrogen sulfide and (b) after exposure to hydrogen sulfide. S-21

22 Figure S19. SEM images of (a) as-spun W precursor/na precursor/pvp composite NFs, (b) pristine Na 2 W 4 O 13 NFs after calcination in air at 600 C for 1 h, (c) high resolution SEM image of Na 2 W 4 O 13 NFs and XRD analysis in the inset. Synthesis of Na 2 W 4 O 13 nanofibers. Firstly, 0.2 g of AMH, g of NaCl, and 0.25 g of PVP were dissolved in 2 g of DI water. The molar ratio between W precursor and Na precursor were controlled to be 2:1 for successful synthesis of Na 2 W 4 O 13 crystal phase after calcination. The solution was vigorously stirred at 500 rpm for 6 h at room temperature. Electrospinning and subsequent calcination step were carried out at the same conditions as other samples. Figure S19a b exhibits SEM images of as-spun and calcined Na 2 W 4 O 13 NFs. Figure S19c exhibits high resolution SEM image of Na 2 W 4 O 13 NFs. Triclinic Na 2 W 4 O 13 crystal structure (JCPDS# ) was verified by PXRD analysis as shown in the inset of Figure S19c. S-22

23 Figure S20. (a) Hydrogen sulfide sensing performance of pristine Na 2 W 4 O 13 NFs from 5 to 1 ppm at 450 C and (b) selective detection characteristics toward 8 different biomarker gas molecules at 5 ppm with sensing layers of pristine Na 2 W 4 O 13 NFs. Although Na 2 W 4 O 13 has never been reported as a gas sensing material because of its poor sensing properties, Na 2 W 4 O 13 NFs represented a superior selectivity toward H 2 S sensing (Figure S20a b), strongly supporting the suggested chemical reactions between H 2 S and Na. S-23

24 Table S1. Recent publications on SMOs-based chemiresistive gas sensors for detection of hydrogen sulfide molecule in highly humid ambient (75 95 % RH). S-24

25 References (1) Kumar, A.; Negi, Y. S.; Choudhary, V.; Bhardwaj, N. K., Characterization of cellulose nanocrystals produced by acid-hydrolysis from sugarcane bagasse as agro-waste. J. Mater. Phys. Chem. 2014, 2, (1), 1-8. (2) Choi, S. J.; Choi, C.; Kim, S.-J.; Cho, H.-J.; Hakim, M.; Jeon, S.; Kim, I. D., Highly efficient electronic sensitization of non-oxidized graphene flakes on controlled poreloaded WO 3 nanofibers for selective detection of H 2 S molecules. Sci. Rep. 2015, 5. S-25