GEL TONG HOP CO3O4 KICH THLf6C NANOMET BANG PHUONG PHAP DOT

Tap chi Hoa hgc,

T. 48

(6), Tr. 683 - 686, 2010

TONG HOP CO3O4 KICH THLf6C NANOMET BANG PHUONG PHAP DOT

C H A Y

GEL

Den Tda sogn 24-7-2009

LUU MINH DAI', NGUYEN THI TO LOAN'

'Vien Khoa hgc Vdt lieu - Vien Khoa hgc vd Cdng nghe Viet Nam 'Trudng Dgi hgc Suphgm Thdi Nguyen

ABSTRACT

C03O4 powder has been synthesised at low temperature (600°C) by the combustion of gel prepared from polyvinyl alcohol (PVA) and cobalt nitrates. Factors affecting on synthesis process of nanometer oxides C0}04 including temperature andpH of gel formation, molar ratio of

cobalt concentration and polyvinyl alcohol concentration, temperature of calcining on structure and parcticles sizes were investigated. The crystalline process and the morphology of oxides particles were considered by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM).

Surface areas of oxides were determined by the BET (Brunaure-Emmet-Teller) method. Further thermal treatment at 400 - JOO^C for 2 hours yields the single phase C03O4 with a specific surface area 39.68 m'/g.

I - MC) D A U

Phuang phdp dot chay gel d nhiet dd thap tao ra nhiing san phdm oxit kfch thudc nanomet dugc Qng dung cho cac linh vuc xuc tdc, huynh quang, bao ve mdi trudng [1 - 6], sQ dung cac hda chdt va thiet bi thdng dyng. Phuang phap nay da dugc dung d l tdng hgp mdt so oxit kim loai [7, 8]. Trong bai bao nay chung tdi sQ dung phuang phdp ddt chay gel d nhiet do thdp d l nghien cQu tim dilu kien tdi uu tdng hgp oxit C03O4 kfch thudc nanomet.

II - THUC NGHIEM

- Cac hod chat sQ dyng trong nghien cQu diu la loai tinh khiet phan tfch: Co(N03)2.6H20, poll vinyl ancol, NH3, HNO3

- C03O4 dugc dilu c h i bang phugng phap ddt chay gel d nhiet do thap: dung dich mudi Co(N03)2 dugc khuay trgn vdi dung dich polivinyl ancol (PVA) theo ti le moi tuang Qng.

Hdn hgp dugc gia nhiet va khudy lien tuc tren may khudy tQ cho din khi Mnh thanh gel trong sudt, sdy khd gel vd nung mdu d nhiet dd khac nhau trong hai gid.

- Gian dd nhilu xa Roughen dugc do tren may SIEMENS D5000 cua DQc vdi A^^^ = 1,5406 A d nhiet dd phdng, gdc quet 2 ^ = 0 - 70^ budc nhay 0,03°, dien dp 30KV, cudng do d'ng phdt 0,03 A. Kfch thudc hat trung binh (nm) cua cac oxit dugc tfnh theo phuong triiih

— 0 89 X ~ Scherrer: r = -^—'—, trong dd: r la kfch thudc

y9cos6'

hat trung binh (nm), A, la budc sdng K^cua.

anot Cu (0,154056 nm), fi la do rdng cua pic Qng vdi nQa chieu cao cua pic cue dai (FWHM) tfnh theo radian, 0 la gdc nhilu xa Bragg Qng vdi pic eye dai (do).

- Anh vi cdu tnic va hinh thai hgc cua oxit dugc chyp bang Idnh hiln vi dien tQ quit (SEM) 683

JEOL- 5300 (Nhat Ban).

- Dien tfch b l mat rieng cua vat lieu dugc do tren may COULTER-SA 3100 cua My bang phuong phap hap phy N2 ldng d 77 K.

Ill - KET QUA vA

T H A O

LUAN

1. Khao sat anh hudng cua ty le moi Co'VPVA de'n su tao thanh pha va kich thudc hat

Dilu c h i cdc gel vdi ti le moi Co^'^fPNA ldn Mgt la 1/1; 1/2; 1/3; 2/1 va 3/1, d 80°C va pH = 4. Sdy khd vd nung gel d 500''C trong 2 gid. Ghi gian do nhilu xa Ranghen cua cac mdu hot. Kit qua dugc chi ra d bang 1.

Nhu vay, kfch thudc hat cd xu hudng giam theo chilu tang lugng PVA, cd thi do su tang mQc do phan bd dong deu cua cdc ion kim loai trong dung dich PVA lam cho qua trinh chay diln ra thuan lgi. Vdi ti le moi Co'^fPNA la 1/3 thu dugc dgn pha cua C03O4 cd kfch thudc hat nhd nhdt. Do vay chung tdi chgn ti le moi nay cho cac thf nghiem tie'p theo.

2. Khao sat anh hudng cua nhiet do tao gel de'n su tao thanh pha va kich thudc hat

Dieu c h i cac gel vdi ti le moi Co'^'/PVA = 1/3, d nhiet dd 40, 60, 80 vd lOO^C, vd pH = 4.

Say khd va nung gel d 500°C trong 2 gid. Ghi gian dd nhilu xa Ranghen cua cdc mdu hot. Kei qua dugc chi ra d bang 2.

Bdng 1: Cdc pha tao thanh va kfch thudc cua oxit d ti le moi Co'"" /PVA khde nhau

Ty le moi Co'-'/PVA Pha tao thdnh Kfch thudc hat,

nm

3/1

C03O4

45,18

2/1

C03O4

42,68

1/1

C03O4

CoO 35,63

1/2

C03O4

CoO 31,54

1/3

C03O4

28,31

Bdng 2: Cac pha tao thanh va kfch thudc cua C03O4 khi tao gel d nhiet do khac nhau Nhiet do tao gel, "C

Pha tao thanh Kfch thudc hat, nm

40

C03O4

27,15

60

C03O4

27,85

80

C03O4

29,31

100

C03O4

31,36 Kit qua bang 2 cho thdy, nhiet do tao gel

anh hudng khdng dang ke den sy tao thanh pha cua C03O4 va chi anh hudng din kfch thudc hat cua oxit tao thdnh. O nhiet do 40, 60°C cac hat oxit thu dugc cd kfch thudc nhd va khac nhau khdng nhilu. Tuy nhien thdi gian tdng hgp mdu d nhiet do tao gel 40°C keo ddi, vi vay nhiet do tao gel la 60°C dugc lya chgn cho cac thf nghiem tiep theo.

3. Khao sat anh hudng cua pH tao gel de'n su tao thanh pha va kich thudc hat

Dieu che cac gel vdi cung ti le moi Co'-'/PVA = 1/3, d OO^C va pH tao gel la 2, 3, 4 va 5. Sdy khd va nung gel d 500''C trong 2 gid.

Ghi gian do nhilu xa Ranghen cua cac mdu bdt.

Ket qua dugc chi ra d bang 3.

Qua kit qua d bang 3 cho thdy, khi tao gel d pH = 4 thu dugc don pha C03O4 vdi kfch thudc nhd nhai. Do dd chung tdi chgn pH = 4 de tiln hanh cdc thf nghiem tilp theo.

4. Khao sat anh hudng cua nhiet do nung den su tao thanh pha va kich thudc hat

Nhiet do nung mdu la ylu to rat quan trgng ddi vdi sy hinh thdnh pha va kfch thudc cua cdc hat oxit tao thanh. D l tim dugc dieu kien nung thfeh hgfp cho su tao thdnh C03O4 chung tdi tiln hanh ghi gian do phan tfch nhiet cua gel giQa PVA va Co(N03)2 (hinh 1).

684

Bdng 3: Cac pha tao thdnh va kfch thudc cua oxit khi tao gel d pH khde nhau pH tao gel

Pha tao thanh Kfch thudc hat, nm

2

C03O4

CoO 38,44

3

C03O4

CoO 34,53

4

C03O4

27,48

5

C03O4

28,85

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Hinh 1: Gian do TGA cua gel PVA va Co(N03)2 Hinh 1 cho thay sy gidm khdi lucmg cua gel

chu yeu xay ra d nhiet do thdp han 200°C. (3 vung nhiet do thdp hon 150°C xay ra sy mdt nudc kit tinh, phan huy ion NO3" va phan huy mgt phdn PVA. Trong khoang nhiet do tQ 150 - 350''C sy giam khdi lugng kem theo sy tda nhiet diln ra manh do sy phan buy PVA. d nhiet do ldn ban 350°C khdng cd sy bien ddi nao ve khdi Mgng, nhu vay cd thi gdn cho su hinh thanh C03O4 tinh khilt.

Dya tren kit qua phan tfch nhiet, tong hgfp C03O4 cdn dugc tie'n hanh nung gel d nhiet do ldn ban 350°C. Do dd chung tdi tien hdnh Idiao sat nhiet dd nung tQ 400°C de'n 700°C. Dieu chi cac mdu cua Co''": PVA vdi ti le moi tuang Qng la 1:3, nhiet do tao gel la 60''C, sau do nung gel

d cac nhiet do 400°C, 500°C, 600°C, 700°C trong 2 gid. Tie'n hanh ghi gian dd nhilu xa Ranghen ciia cac mdu tren. Kit qua dugc chi ra d bang 4.

TQ bang 4 cho thdy, d nhiet do cang cao thi kfch thudc hat cang ldn do sy kit ty vd dl thu dugc dgn pha cua C03O4 vdi kfch thudc nhd nhdt d nhiet do nung tdi uu la 500°C. Nhiet do nay da dugc lya chgn dl tien hanh cac thf nghiem tie'p theo.

5. Xac djnh hinh dang, kich thudc, dien tich be mat rieng ciia san pham

Qua khao sat cho thay, dilu kien tdi uu dl tong hgp C03O4 la ti le moi Co'-'/PVA = 1:3, nhiet dg tao gel eOT, nhiet do nung 500°C. Tien hanh tdng hgfp mdu trong dilu kien tren va ghi 685

gian dd nhilu xa Ronghen, chup anh Min vi (BET). Kit qua dugc chi ra d hinh 2 va 3.

dien tu quit (SEM) va do dien tfch b l mat rieng

Bdng 4: Cac pha tao thanh va kfch thudc cua san pham khi nung d nhiet do khac nhau

Nhiet do nung, °C Pha tao thanh Kfch thudc hat, nm

400

C03O4

CoO 26,31

500

C03O4

27,48

600

C03O4

29,89

700

C03O4

32,94

Hinh 2: Gian do nMeu xa Ranghen cua C03O4

TQ hinh 2 va 3 cho thay, dang thu hinh cua san pham thu dugc la C03O4 cd dang Mnh trdn, kich thudc < 30 nm. Dien tfch b l mat rieng cua 00304 do dugc la 39,68 mVg.

r v - KET LUAN

- Da xdc dinh dugc dilu kien tdi mi di tong hgp C03O4 kfch thudc nanomet bang phuong phdp ddt chdy gel: Ti le moi Co'-'/PVA = 1:3, nhiet dd tao gel 60°C, pH tao gel 1 - 4, nMet do nung la 500°C.

- C03O4 thu dugc cd dang hinh trdn, kfch thudc hat < 30 nm. Dien tfch be mat rieng cua C03O4 la 39,68 mVg.

- Vdi dien tfch b l mat rieng ldn, C03O4 kfch thudc nanomet hQa hen la mgt vat Ueu xuc tac xu If khf thai rat tdt trong xQ If mdi trudng khf.

T A I LIEU THAM K H A O

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Nanocrystalline mixed metal oxides novel

Hinh 3: Anh Men vi dien quet (SEM) cua C03O4

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Mater. Chem., 13, 2261 - 2265 (2003) 5. Nano Materials. Edited by D. Chakavorty

Mdian National Science Academy 47, Bahadur Shah Zafar Marg, New DelM, 47 - 68 (2001).

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