Tap chi Hoa hgc,
T. 48(6), Tr. 732 - 736, 2010
NGHIEN Cl/U MO HINH VA TOI l/U QUA TRINH HOA TONG HOP BOT NANO TiOs BANG PHLfONG PHAP
THUY PHAN TRONG PHA HOI
Den Tda sogn 8-6-2010
CAO X U A N T H A N G , PHAM V A N T H I E M , NGUYEN V A N X A , MAI NGOC H A ,
NGUYEN THI V A N ANH
Khoa Cdng nghe Hod hgc, Trudng Dgi hgc Bdch khoa Hd Ndi
ABSTRACT
Synthesis of metal oxide nano-sized and micro-sized particles by chemical vapor-phase route is a technologically and commercially competitive process. Linking reactor operation parameters to the particle properties represents the most critical task in designing such process. Nanometer sized titania particles were prepared by hydrolysis in gas phase of titanium tetrachloride (TiCl4) in a furnace type aerosol reactor, which is valid at high conversion, was found to be improper at high concentration and low conversion. The Ti02 nano-particles are crystallized in anatase and rutile phase depending on the experimental conditions. The size varies from 10 nm to 100 nm.
The main advantage of the process is operating at lower temperature (150°C - 400°C) and using water vapour instead of pure oxygen as in the existing chloride process. The explanation of the relationship between Ti02 particle characteristics and the process conditions, a mechanism of niicleation and particle growth will be done. The different methods as XRD, SEi\4, TEM, micro- Raman, size particles distribution were used to characterize the Ti02 nano-powder in order to find the optimal conditions for the TiO2 fabrication process in aerosol reactor.
Keywords: nano Ti02, aerosol reactor, vapor hydrolysis.
I - G K 3 I THIEU trong cdng nghiep dac biet Qng dyng trong viec
xQ ly mdi trudng [1]. Vat lieu bgt nano TiOj da Titan dioxit da dugc su dyng rdng rai lam dugc nghien cQu va tdng hgp d Viet Nam bgt mau, kem chd'ng ndng, md bdi da, kem danh khoang han mudi nam trd lai day vd chu ylu rang... k l tQ ddu the ky 20 khi bgt titan dioxit tiln hdnh theo phuang phap sol-gel vdi quy mo trd thanh vat lieu thuang mai. Nam 1972, nhd va tfnh thyc tiln khdng cao [2]. Mgt sd loai Fujishima va Honda da phat hien ra hien tugng vat lieu cd tfnh Qng dung cao trong boat tfnh xuc quang xuc tae tach nudc tren mgt dien eye Ti02 t^c, dien tQ hay ky thuat sinh hgc dugc sdn xuat dudi tia cue tfm (UV). Ke tQ dd, nhirng nd luc to bdng thiet bi aerosol d quy md cdng nghiep.
!dn da dugc danh cho cac nghien cQu vl vat lieu Thilt bi aerosol cho nang suai cao vd lien tuc, TiOz, trong dd da ddn din nhilu Qng dyng hQa gidm eac tac dgng mdi trudtig vd dl dang dilu hen trong cac linh vuc khac nhau nhu: quang chinh chat Mgng san pham. C5 quy md ldn nhu dien tQ va quang xuc tac dl c h i tao linh kien cdng nghiep, quy trinh aerosol Qng dung tdt cho quang vd linh kien vi dien tu va cam biln. Vat sdn xudt C den trong cdng nghiep cao su vat lieu bgt nano Ti02 da dugc Qng dyng rdng rai
lieu quang hgc va hgi silica dung trong viln thdng, Ti02 dung trong chat mdu. 6 quy md nhd han, quy trinh aerosol cd thi dilu chinh kfch cd cdc hat tao thanh. Vdi quy md nay cd thi san xudt AI2O3, SnOj va cac kim loai thugc nhdm ddu nhu Pt hay Au ma Qng dyng Iam ldp phu mdng cd micro, cam bie'n khf, cac thanh phdn mach dien [8].
Mye dfeh nghien cQu cua chung tdi la thiet kl, che tao, idp dat va van hanh he thd'ng thilt bi tdng hgp bgt nano Ti02 su dyng each thuy phan trong pha hoi TiCl4 va tdi tm hda qua trinh tdng hgp theo phuong phap quy hoach thyc nghiem de tim ra che do lam viec thfeh hgp vdi he thd'ng thilt bi tugng Qng.
II - THUC NGHIEM
Ngi dung nghien cdu: Phuong phap aerosol la mgt trong nhQng phuang phdp dugc lya chgn dl tdng hgp vat lieu nano bdi tfnh thuan lgi vd chi phf thdp. Qua trinh aerosol dl tdng hgp vat lieu dugc chia ra thanh phuang phap chuyin hoa M thi hai sang hat rdn vd chuyen hod tQ long hoac rdn thanh hat rdn [5]. Cac kit qua nghien cQu da cdng bd tren t h i gidi vl qua trinh tdng hgfp nano Ti02 trong pha hoi cd hai xu hudng chfnh khi dung chdt mang la khf O2 va khf N2 [6]. Qua trinh tdng hgp cd su dyng khf O2 lam chdt mang yeu cdu he thd'ng thilt bi rdt phQc tap va tdn kem, qua trinh tdng hgfp dung khf mang la N2 sQ dung cd he thdng bi dan gian han nhilu; hai TiCU tac dung tryc tilp vdi hai nudc nen qud trinh tdng hgp ndy cd tfnh kha thi cao khi xay dyng md hinh, thiet bi thf nghiem vdi dilu kien d Viet Nam. Ca chi tdng hgp cua vat lieu nano titan dioxit d nhiet do thdp tQ hod chat ban ddu la TiCl4 dya vao phdn Qng sau:
TiCl4 + 4H2O -^ Ti(OH)4 + 4HC1 Phan Qng tiep tuc xdy ra Ididng cd su tham gia cua chdt kfch boat:
Ti(OH)4 -^ Ti02.H20 -^ TiO,
(amorphous) -HjO (anatase/rutile) Hai TiCl4 va hai H2O tilp xue vdi nhau thdng qua Id phan Qng hinh dug chilu dai L va dudng kinh D. Tai trang thai dn dinh, phan Qng
hoa hgc xuat hien giua TiCU va HjO hinh thanh HCl va Ti(0H)4 [7]. Cac hat nhan Ti(0H)4 ldn ien bdi sy hinh thanh nhung cdu hydroxyl.
Nhifng hat nay dugc ngung tu thanh dioxit titan d trang thdi pha vd dinh hinh va trong va trong cac dilu kien nhiet do nung khac nhau se cho pha anatase vdi nhiet do nhd han 700°C hoac pha rutile vdi nhiet do ldn 950°C [3].
Md hinh thuc nghiem:
KhiNi
TiCl,
Khi nen
Tbietbi Aerosol
H.0 D.dicli NaOH
lUhan khong
Hinh 1: Md hinh thyc nghiem
He thd'ng thilt bi tdng hgp bgt nano Ti02 dugc chung tdi sQ dyng trong qua trinh thyc nghiem thi hien tren hinh 1 bao gdm: Cac binh thuy tinh chQa nudc cat; TiCl4 cd ndp kin vd cd dudng xyc Jchf; van dilu chinh luu lugng khf;
bep dien cap nhiet; d'ng nhya ddn hoi TiCl4, hgi nudc va khf mang N2; ddng hd do Itm Mgng hgi nudc vd hoi TiCl4, ddng hd do do hut chan khdng, thilt bi phan Qng aerosol (vat lieu bdng thach anh, dilu khien nhiet do tQ 0 - 700°C, chilu dai L = 1000 mm, chilu ddi chuyin nhiet 1
= 800 mm, dudng kfnh d = 40 mm).
Ill - KET QUA VA T H A O LUAN Ket qua phd nhiiu xa tia X (phd X-Ray)
Cac mdu che tao dugc thuc hien d cdc nhiet do Jdiac nhau va cho cac kit qua sau:
STT 1 2 3
• 4 5 •
6
Nhiet dd
150''C, 200^0, 250"C, 300°C, 350°C,^OO^C
^mrJ^jiai 5 12 17 20 25 30
Dang thu hmh Vd dinh hinh Vd dinh hinh
Anatase Anatase Anatase
• Anatase Dung phuong phdp nhilu xa tia X de xac
dinh tinh chat va kfch thudc (Mong ddi) cua cdc mdu bgt da tdng hgp. Trong bao cdo nay sQ dyng hai loai bgt Ti02 thugng pham cd kfch thudc khac nhau de so sanh (hinh 2 va 3), kfch thudc nano cua mdu: dd la bgt Ti02 cua Nhat Ban, dgn pha anatase, kfch thudc 7 nm va bgt TiO, cua DQc, kfch thudc 25 nm bao gdm hai pha anatase va rutile. Hinh 4 trinh bay gian dd nhilu xa tia X cua cac mdu bgt Ti02 dugc che tao d nMet do 250°C vdi ty le moi nH2o/nTici4 (Id mdu tieu bilu trong so lugng cdc mdu da tdng hgp). Mdu bgt dugc c h i tao don pha tinh thi anatase. Gian dd nhilu xa nay dugc so sanh vdi hai gian dd nhilu xa tia cua bgt Ti02 25 nm va bgt TiO, 7 nm. Pic nhilu xa diu md rdng han so vdi pic Mang Qng trong gian dd cua mdu Ti02
kfch thudc 25 nm. Tuy nhien, cac vach nay diu cd bdn do rdng nhd ban mgt chut so vdi cac vach cua mdu TiOj kich thudc 7 nm. Dung cdng thQc Sherrer [3]:
r-(0,89x;L)/pcos6'
r: Kich thudc tmh the (nm), X = 0,154056 nm: budc sdng tia X cua Cu.
P: radian ban dd rdng cua vach phd, 6: gdc nhilu xa.
Kfch thudc bgt TiOj dugc e h l tao d nMet do 250°C vdi ty le moi nH2o/nTia4 Id 25 cd kfch thudc khoang 8 nm.
Hinh 2: Gian dd nhilu xa tia X cua mdu bgt TiOj 7 nm
Hinh 3: Gian dd nMlu xa tia X mdu bgt TiOz 25 nm
\ J . / ^ ^ . . . J U - « , ^ t I \ . A ^ A ^ . ^ V ^ A M / V^^^A^.^r/i y^-..../yvJ..^jV^, fJW^^.w/^r..^^ J.IH..'
Hinh 4: Gidn dd nhilu xa tia X mdu bdt Ti02 dugc nung d nhiet do 250''C 734
Ket qua phan tich m i u bdng phuong phap hien vi dien tu quet (SEM)
Kit qua anh SEM tren hinh 5 mdu bgt che tao d 250°C cd kfch thudc nano met va cac hat vd cdc hat ttrang ddi diu nhau nhung ddi chd cdn cd sy kit ty nhung hat nhd thdnh cdc dam ldn.
*->•
' ^ ^ ^
"^
?
• ' • , ' ' ' , " . • ' •
^ g d ^ ^
^ - : » _ '
IMS-NKLx200kSE(M.LA0)
0,
M
»*
****
W J
^r.«^*i
tk.-' •'•"•
%,A
W
•• % i |
.m'
200nmHinh 5: Anh SEM mdu bdt Ti02 nung d nhiet dd 250''C
Ki^t qua phan Micro-Raman
Circmg do dao dong
tich mSu bang phd
T1O2 ( Dire Z.^^mii) Ti02 (Nliat " m i l ) T1O2 ( 2?0''C ) T1O2 (, ^OO^C )
thdy mdu c h i tao la vat lieu Ti02 dan pha anatase cd cac dinh dac trung tai cdc budc sdng 149 cm"', 397 cm"'. Kit qua nay hoan todn phu hgp vdi kit qua phd nhilu xa tia X.
Ket qua phan tich tap hgp kich thudc hat
'JP 5?
J.
i
_irtt
p.o10.00
Diameter (|jffl)
Hinh 7: Phan bd kfch thudc hat cua mdu bgt d 250°C
Tai nhiet do 250°C sy phan bd kfch thudc hat cd su ddng diu ban, ti le cac hat cd kfch thudc trung binh tQ 0,1 - 1 (pm). Dilu ndy cd thi giai thfeh la do sy tfch ty cua cac hat nhd tao thdnh cdc hat cd kfch thudc lan han.
Quy hoach thuc nghiem tim diem tdi uu cua he thdng thiet bi
Sau khi kiem tra vl chdt lugng sdn phdm, ta tim cdc dilu kien tdi uu cho qua trinh tdng hgp bgt nano Ti02 dugc tdng hgp d 250°C bdng phuong phdp quy hoach thyc nghiem. Da tien hdnh lap k l hoach true giao bae hai hai mQc tdi tm vdi gia tri canh tay ddn sao a = 1. Ham mye tieu la khdi Mgng Ti02 thu dugc sau mdi thf nghiem (tfnh bang gam). Phuong trinh hdi qui cd dang [9]:
200 400 600
So song ( c n r ' )
A t /t k
y^b„+^bjXj+ ^ bj^x^x^+Y^bjjx]
Hinh 6: Phd Micro Raman mdu bgt d 250°C
Ma tran thyc nghiem cua ke hoach true giao Kit qua phan tfch phd Micro-Raman cua mdu bae hai la:
Ti02 d 250°C dugc so sanh vdi cdc mdu chudn Ti02 7 nm, 25 nm. Qua phd micro-Raman cho
STT 1 2 3 4 5 6 7 8 9
Biln thuc 1,2
z,
1,8 1,2 1,8 1,2 1,8 1,5 1,5 1,5
Z2 0,2 0,2 0,8 0,8 0,5 0,5 0,2 0,8 0,5
Biln ma hda
Xo -1-1 + 1 + 1 + 1 +1 -1-1 + 1 +1 + 1
X,
-1 +1
-1 +1
-i +1
0 0
x.
-1 -1 -1-1 -Hi 0 0 -1 -1-1
0 1 0
X, X2
-t-1 -1 -1 -t-1
0 0 0 0 0
y 3,45 3,82 2,96 2,62 2,55 4,15 4,18 3,56 4,23 Ta cd phuang tnnh hdi quy nhu sau:
A
y = 4,449-0,732x] -0,689x1 (*) De xdc dinh gid tri tdi tm cua hieu suat phan Qng ta la'y dao ham hai ve cua phuang trinh (*) theo biln x,, x, vd ldn Mgt cho bdng 0, ta dugc:
x,s = 0 va X2s = 0 (tQc Id Zj = 1,5 Ift/phut va Z2 = 0,5 Ift/phut). Thay cdc gid tri dd vdo phuang trinh (*) tim dugc y = 3,63. Chuyen phugng trinh (*) vl dang biln thyc ta cd:
7 = -13,158 + 2,196Z, + 0,6892^ - 0,732Z,' - 0,6892^' (**) IV - KET LUAN
- Da nghien cQu, xay dyng hoan chinh he thd'ng thilt bi sdn xudt bgt nano TiOj bdng phugng phap thuy phan trong pha hai (phuang phap aerosol) va dua ra duge phuang trinh hdi quy thye nghiem.
- Da che tao dugc bgt nano Ti02 vdi kfch thudc tQ nhd ban 100 nm bdng phuang phap thuy phan TiC^ trong pha hai.
- Da xac dinh dugc ty le nong do thfeh hgp cua nH2o/nTici4 Id 25 va dugc tdng hgp d 250°C va dua ra cac thd'ng so' tdi uu cho qua trinh tdng hgp.
Ldi cam on. Cdng trinh ndy duac thuc hien vai su hd trg ve kinh phi ho trg ciia Trung tdm Gido
due vd Phdt trien Sdc ky - Trudng Dgi hgc Bdch khoa Hd Ndi.
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