C₂H₅OH Sensor Using Porous Cr₂O₃ Nano-Hexaprisms

pISSN 1225-5475/eISSN 2093-7563

Ÿ¯∫

Cr

O

C

H

OH

§ˆ¨^• ÃæÁ+

C₂H₅OH Sensor Using Porous Cr₂O₃Nano-Hexaprisms

Hyun-Mook Jeong and Jong-Heun Lee⁺

Abstract

Dense Cr-precursor nano-hexaprisms were prepared by heating the Cr-nitrate aqueous solution containing Hexamethylenetetramine and polyvinylpyrrolidone, which were converted into porous Cr₂O₃nano-hexaprisms containing nanoparticles by heat treatment of Cr- precursors at 600…for 2 h in air atmosphere. At the sensor temperature of 300_…, porous Cr₂O₃nano-hexaprism showed the high response (R_g/R_a, R_g: resistance in gas, R_a: resistance in air) to 100 ppm C₂H₅OH (R_g/R_a=69.8) with negligible cross-responses to 100 ppm CO and 5 ppm C₆H₆. The sensitive and selective detection of C₂H₅OH in porous Cr₂O₃nano-hexaprism were discussed in relation to the morphology of nanostructures.

Keywords : Cr₂O₃, C₂H₅OH, Gas sensors, Selectivity

1. ≠ –

Í≠∞ ›μº¸ °∫æ≠¬ ¿∞˙« •È˙ «À °∫° ›

¿œ© fl˝œ¬ ˙◊ Ø≠¶ Îÿ Œ≠∫°∫Õ ∂∫ «¬ ¯fl∫

°∫¶ À‚—Ÿ[1]. ^{°∫ ¿∞˙Œ}SnO₂[2], ZnO[3], In₂O₃[4], TiO₂[5] ^Ó«n-¸ Í≠∞ ›μº° ÷Œ ¨∏«˙Ÿ. ^÷Ÿp-^¸

Í≠∞ ›μºŒNiO[6], CuO[7], Co₃O₄[8]^Õp-^{¸ ›μºŒ} CNT[9] Óà °∫ ¿ ∞˙Œ ¨∏«Ì ÷ˆ∏, ^{°∫« μÕ ±}

√∫« Æ∏° ÷Ó ¨∏«  ‚‹Ë° ÷Ÿ.

›μº¸ °∫æ≠« ¿∞˙∫ Ù∫ °∫ μ, ^{¸• ¿‰”μ}

Õ ∏π”μ¶ °Æfl œÁ ö ßÿ Ò•È˚à ÙÌ °∫ ßı°

¸• Ÿ¯∫ ™Î ∏∂° ØÆœŸ[10].

Cr₂O₃^¬p-¸ Í≠∞ ›μº¸ °∫æ≠ ∞˙Œ •È° Í“°

Ω∏Œ θ» Û¬Œ ̯… ÊÏ(O^-) ^§¯(hole)^{à ‡˚» ¸μ∫}

«shell ^{˛Ã ¸∫«¬•}, ^{د∫ °∫Õ}O^-° ›¿“ ÊÏ ¸⁄°

Ê‚«Ì, ^{§¯˙ Á·’}(recombination)œ«Œ æ≠« ˙◊ª Ù

Ñ »Ÿ[11]. ^ˆÁ Cr₂O₃^{¬ ¸‚ÊÁÊ˝}[12], ^߸˝[13], MWCNT ¤√¥ª ÃΗ ’∫˝[14] Ó° «ÿ ‹œ °∫ ¿∞

˙Œ ’∫» Ÿ ÷∏Á, ^’∫»Cr₂O₃™Î ∏∂º« ÊÏ œ›˚

∏Œ د∫ °∫° Η μ° Ùˆ  ∫ Õ∏Œ ∏Ì«Ì ÷Ÿ.

˚Û≠, ^{∑∫ °∫ μ°}p-¸ ›μº¸ °∫æ≠« ¿¯Æ°

‚Œ— ÕŒˆ, «¬ ™Î∏∂º« ¿˝° «— «À°∫Õ« ›¿

“° «— ÕŒˆ° Îÿ≠ ºË˚Œ ¨∏°  ‰œÁ, ^{Ù∫ ±√}

∫ ◊ μ« °∫æ≠¶p-^¸«Cr₂O₃Í≠∞ ›μºŒ ∏ˆœ¬

Õà fl‰œŸ.

ª ¨∏°≠¬HMTA(Hexamethylenetetramine)^{« –ÿ° «}

— ߸˝∏Œ ∞¢‚’Á«Cr-^{¸∏º¶ ¶∂œÌ}, ^̬°≠

≠≥Æœ© Ÿ¯˙«Cr₂O₃™Î ∞¢‚’ ∏∂º¶ ’∫fl∏Á,

ö ÃÎœ©C₂H₅OH °∫° Îÿ Ù∫ μÕ ¸• ∏π”μ¶

∏ì °∫æ≠¶ ∏ˆflŸ.

2. «Ë Ê˝

2.1 Cr₂O₃^{« ’∫}

¶∂ ¯§ ƒμ¬Fig.1^{° ™∏ª˙Ÿ}. 0.4001 g^«Cr(NO₃)₃ (98.0-103.0% Kanto Chemical Co., Inc., Japan)^Õ2.000 g^« Hexamethylenetetramine (ACS reagent, Sigma-Aldrich Co.,

1̡Ζ≥ ≈“Á¯–˙(Department of Materials Science and Engineering, Korea University)

Anam Dong, Seongbuk Gu, Seoul 136-713, Korea

+Corresponding author: [email protected]

(Received : Sep. 4. 2012, Revised : Nov. 21, 2012, Accepted : Nov. 21, 2012)

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons.org/licenses/by- nc/3.0)which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

2.2 ^{√Ì –Æ}

’∫» –ª« Áª –Æœ‚ ßÿField-emission ^÷Á¸⁄

ˆÃÊ(FE-SEM, S-4300, Hitachi Co. Ltd., Japan)^{à ÁΫ˙}

∏ÁX-^{± ∏˝–Æ‚}(Rigaku D/MAX-2500V/PC, Cu K line = 1.5418 A)¶ ÃÎœ© –ª« Û˙ ·§∏∂¶ –Æœ¥Ÿ. 2.3 æ≠ “⁄ ¶¤ ◊ ¯§

’∫»Cr₂O₃™Î Öªª ı˘ˆÕ •’œ©slurry^¸¬Œ

∏Á ƒ, Au ¸ÿà –Õ◊» ÀÁÙ ‚« ß° μ˜œ© °∫

¿ “⁄¶ ¶¤œ¥Ÿ. Û‚ ¿ “⁄« ‚« ⁄° ¯» ªŒ

˜Õ(Pt)^{¶ ÃÎÿ}500^ΔC^°≠2 √£ ø» ≠≥ƶ œ© °∫ 

¿ “⁄¶ »§≠ √◊∏Á, °∫° ›¿√∞‚° ’≠ ¢¢« æ≠

ø¤¬μ°≠1 √£ ø» ≠≥Æ œ© »§≠ √≤ ƒ °∫¿ ¯

§ª œ¥Ÿ. ^{°∫« Ø”∫}500 cm³/min^{∏Œ ̧œ¥Ì}, 100 ppm ^Ûμ«C₂H₅OH, CO^Õ5 ppm ^Ûμ«C₆H₆^Ó3 ^{æ˘« Ø}

¯∫ °∫° Îœ©250, 300, 350…°≠ ¢¢ °∫ ¿∫ª ¯§

œ¥Ÿ.

3. ·˙ ◊ Ì˚

3.1 ’∫» –ª« Á˙ Û

˝∫ ˙§ª ÆŒ“ ˆ ¯˙∏™ZnO^{« ’∫°≠} HMTA^° Capping agent ™“ª —Ÿ¬ ¨∏ ·˙[16]° ∏Ì» Ÿ ÷Ó Ã Õ ØÁ— ¤Îª —ŸÌ «‹»Ÿ. ^{«— ŸÆ«}HMTA^{° –ÿ«Ó}

˝∫» ΔŒ˙ ˜ß À•˜Â° ◊Û¯§ª Η ¸∏º« ’∫˙

§°≠ Ωì˙ Áìª ¸∫œ© §¸‚˚ ∂≥ª œÌ, ^ȺÂ

·’ª ¸∫‘° ˚Û ∞¢‚’ Áª ¸∫œ¬ Õ∏Œ «‹»Ÿ.

à ¸∏º¬600^{…°≠ œ“ ƒ}Fig. 2(c),(d)^{Õ ∞à Ÿ¯∫ª}

°ˆ¬ ™Î ∞¢‚’ ∏∂ºŒ Ø≠«˙Ÿ. ì œ“ ˙§°≠ • È˙ ªŒ°≠ ∞¢‚’¸ ∏∂º¶ ¸∫œÌ ÷¬ Ø‚∞˙à – ÿ «È≠ ‚¯∏∂¶ ¸∫œ¬ ˙§∏Œ Ãÿ»Ÿ.

Fig. 1. Flow sheets to prepare porous Cr2O3nano-hexaprisms.

Fig. 2. SEM images of (a,b) as-prepared Cr₂O₃precursors and (c,d) porous Cr2O3nano- hexaprisms after heat treatment at 600

…^{for 2 h.}

Fig. 3. X-ray diffraction pattern of porous Cr₂O₃nano-hexaprisms after heat treatment at 600…^{for 2 h.}

(a) (b)

(c) (d)

¸∫» ™Î ∞¢‚’ ∏∂º¬ Ÿ¯∫ª ÏÓ °∫« ÆÍ˙ ß ı° ÎÃœ«Œ ∞∫ Œ«« ∏¸ –⁄° Òÿ °∫Õ ›¿“ ˆ

÷¬ •È˚à –Ó °∫ ˆ° ÷Ó ØÆ“ Õ∏Œ «‹»Ÿ.

œ“ ƒ –ª«XRD ^{–œ –Æ ·˙}Rhombohedral ^{∏∂¶ Æ}

¬Cr₂O₃^{Œ ÆŒ«˙Ÿ}(Fig. 3).

3.2 °∫ ¿ Ø∫ Ú°

°∫ ¿∫ œ“» –ªÈª Îÿ Ú°«˙∏Á, ^{æ≠ “⁄«}

»§≠¶ ßœ©250, 300, 350^{… ¢¢« ¬μ°≠}1 ^{√£ ø» ≠}

≥Æ ƒ °∫ ¿ Ú° «˙Ÿ. «À °∫Œ¬ د∫ °∫Œ100 ppm C₂H₅OH, 100 ppm CO ^◊5 ppm C₆H₆^{ª ÁÎœ¥Ÿ}.

250… æ≠ ø¤¬μ°≠C₂H₅OH, CO, C₆H₆ ^{º °∫° Η}

μ¬Fig. 5^{°≠Õ ∞Ã}26.5, 3.3 ^◊3.1^{Œ ™∏μŸ}. ^©‚°≠

μ¬Rg/Ra^{Œ §«fl¬•}, Rg¬ °∫ ÷‘ƒ« ˙◊ ™

(resistance in gas)^ÃÌ, Ra^{¬ ¯‚fl« ˙◊™}(resistance in air)

ß. 250^…°≠C₂H₅OH ^{°∫° Η}90% ^{∏π√£∫}208 ^Œ

¿Æ‘ ™∏μŸ. 250…« ¿¬μ°≠ æ≠« ˙◊à “»§—

≈øª ∏©90% ›¿√£∫ ¯§œ¬ Õà “°…œ¥Ÿ. ^{ì ª}

¨∏« Ÿ¯∫Cr₂O₃™Î∏∂¶ °∫æ≠Œ ÃΓ ÊÏ, ^æ≠«

»§∫ ¸°°≠300… ÃÛ« ø¤¬μ°  ‰‘ª «Ã—Ÿ. 300… æ≠ ø¤¬μ°≠C₂H₅OH, CO, C₆H₆^{º °∫ ° Η}

μ¬ ¢¢69.8, 4.9, 3.7Œ Ÿ• ¯§¬μ° Òÿ Ù‘ ™∏μŸ

(Fig. 5). C₂H₅OH ^{°∫° Η}90% ^›¿√£˙90% ^{∏π√£∫}

¢¢87, 58 ^{Œ ™∏μŸ}(Fig. 6). ^›È350… æ≠ ø¤¬μ°≠

C₂H₅OH, CO, C₆H₆º °∫° Η μ¬63.1, 1.9, 2.1 ^Œ300

…°≠ ¯§» μ∏Ÿ¬ ∑‘ ™∏μˆ∏(Fig. 5), C₂H₅OH ^°∫

° Η90% ^›¿√£˙90% ^{∏π√£∫}78, 8 ^{Œ °Â ¸• Õ}

∏Œ ™∏μŸ(Fig. 6). Cr₂O₃^{™Î∏∂°}350… °≠ Ò≥˚ ¸•

¿‰ ◊ ∏π ”μ¶ ™∏ª¬ Õ∫ ‚¯∫« ™Î∏∂¶ Îÿ «À

°∫« ÆÍà ÎÃœÌ, °∫ ›¿ ◊ ̯ Ó« •È›¿Ã ̬

°≠ À¯«‚ ßÆ∏Œ «‹»Ÿ.

¶¤»Cr₂O₃°∫æ≠¬ Á ø¤¬μ°≠CO, C₆H₆ ^°∫°

Îÿ≠5Ãœ« Ò≥˚ ∑∫ μ¶ ∏¥Ì, C₂H₅OH ^{°∫° Îÿ}

≠¬ Á æ≠ ø¤¬μ°≠20 ÃÛ« Ò≥˚ Ù∫ μ¶ ™∏

ª˙Ÿ. ì ’∫» ¿∞˙ÃC₂H₅OH °∫« ±√˚ ˆ°

˚Î… ˆ ÷Ωª ∏ŒŸ. ›¿”μÕ ∏π”μ¶ Ì¡“ ß, ^Ò≥

˚ Ù∫ μ¶ ∏ì350…°≠ ∏øœ¬ Õà °Â Ÿ˜˜— Õ

∏Œ «‹»Ÿ.

Fig.4. Gas sensing transient to 100 ppm C2H5OH at 350….

Fig. 5. Gas responses to 100 ppm C2H5OH, 100 ppm CO, and 5 ppm benzene at 250-350….

Fig. 6. The 90% response and recovery times upon exposure to 100 ppm C2H5OH and air at 250-350…^.

4. ·–

ª ¨∏°≠¬HMTAª ∑°∞Œ ÃΗ Î◊›¿˝° «œ©

∞¢‚’ Á« ©Œ≈ ¸∏º¶ ’∫œ¥∏Á, ^ö600^{… °≠}

≠≥Æœ© °∫ ßıÕ ÆÍà Î× Ÿ¯∫« ©Œ≈ Í≠∞ ™ Î ∏∂º¶ ¶∂œ¥Ÿ. ^{°∫¿ ·˙}250-350^{… æ≠ ø¤¬μ}

°≠C₂H₅OH °∫° Îÿ ±√˚Œ ¿ª ™∏ª˙∏Á ؘ350

… °≠ ›¿”μÕ ∏π”μ° ŸÓ≠ °∫¿ Ø∫ª ∏¥Ÿ.

Á« ¤

ª ¨∏¬ ≥∞˙–‚˙Œ ◊ —π¨∏Á‹ ÷¸ ¤Œ˙ ⁄Á Á ŒÏ (Global Ph.D. Fellowship)Á˜« ¨∏Ò ˆ¯∏Œ ˆ‡«

˙¿œŸ.

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§ ˆ ¨(Hyun-Mook Jeong)

U2012^‚2˘ ̡Ζ≥ ≈“Á¯–Œ(^¯

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U1999 ~ 2000^‚ National Institute for Research in Inorganic Materials, Japan, STA fellow

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