TAP CHi H 6 A HQC T. 52(3) 299-304 THANG 6 NAM 2014
CAU TRUC VA HOAT TINH QUANG XUC TAC C O A BOT NANO W-TiOj BU'gC DI^U CH^ B A N G PHU'ONG PHAP'U'OT
Nguyin Vao Hirag*', Dang Th| Thanh Le^
'Khoa Hda hgc, Tnrdng Dgi hgc Dong Thdp
^Trung tdm Nghiin cuu phdt trien vd Chuyin giao cdng nghi, Dgi hoc Cdng nghiep Hd Ngi D6n Tda soan 5-6-2013
Abstract
Tungsten-doped nanosized Ti02 powders were synthesized by a simple wet method, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-Vis diffuse reflectance spectra (UV-Vis DRS).
The photocatalytic activity of undoped Ti02 and W-doped TiOz photocatalysts was evaluated by the photocatalytic oxidation of methylene blue in aqueous solution under visible light irradiation to study the influence of the tungsten doping degree on the photocatalytic degradation performance of Ti02. The results showed that the photocatalytic activity of the W-doped Ti02 photocatalyst is much higher than that of undoped Ti02, and the optimum W/Ti molar ratio is 0.5%. Moreover, the study also showed that, the doping W atoms suppress the growth of the TiOi crystal and phase transformation.
Keywords: Titanium dioxide. Tungsten, photocatalyst, W-doped Ti02, methylene blue, wet method.
I.Gl6lTHI$U
Chit quang xiie tae TiO; da dupe nghien cu'u rpng rSi de phan hiiy eae ehIt 6 nhilm hiru co trong dung djeh nude [I]. Tuy nhien, TiOi d dang tinh khiet cd n^ng lupng viing cam rpng (khoang 3,05 den 3,26 eV) [1] nen chi hoat dpng quang xuc tac (QXT) trong viing anh sang tu" ngogi gan. Dieu nay hgn che kha n^ng tan dung nguon anh sang ddi dao ti> mat trdi vk anh sang nhin thay tir eae ngudn buc xg khdc. Do do, nhieu nguyen td khae nhau da dupc pha tap vao mang tinh the Ti02 nhlm nang cao hon nira hogt tinh QXT eiia nd trong vimg anh sang nhin thay. Vi?e pha tgp eae ion kim logi, dae biet la cac ion kim lo^i chuyen tiep cd th8 giiip thu hep nang lupng viing elm, tSng dung lupng hip phu cac hpp chat hihi ea vk do do tang cudng boat tfnh QXT trong viing dnh sdng nhin thay cCia Ti02 [1,2].
Do ban kfnh cua ion W(Vi) la 41 pm be hon so vdi ban kfnh ion Ti(rV) 53 pm nen ion W*"^ cd the thay the ion Ti(IV) trong mgng tinh thS Ti02. Ddng thdi, nang lupng viing cam ciia WO3 la 2,8 eV nen khi cd sy tham gJa cua W(VI) vao mang tinh the TiO: se tgo nen nhihig khuySt tgt cd Ipi, giiip thu h?p nfing lupng viing elm, giam qua trinh tai hpp eleetron-lo trong v^ ed th8 nang cao hoat tinh QXT trong v6ng dnh sang nhin thiy ciia TiO: [2]. Da cd m$t vdi cdn? trinh nghien cuu dieu che vgt lieu W-TIOi bSng cde phuang phap khae nhau va danh
gia hoat tinh QXT eua san pham dieu che dupc. S. S.
Lee diSu ch6 vgt li$u W-Ti02 tir su thiiy phan dung dich TiCU va WCI4. Ket qua cho thay, vgt li?u W-Ti02 cd kha nang phan hiiy khi acetandehit trong vimg anh sang tu ngoai cao hon so vdi vat lieu Ti02 tinh khiet [3]. X. Z. Li dieu che thanh cdng bpt nano WOj/TiOi bang phuong phap sol-gel vdi ngudn chat dau la titan(IV) n-butoxit va amoni wonframat. X. Z.
Li nhan thay, bpt W0x/TiO2 cd kha nang phan hiiy xanh metylen cao hon so vdi mau Ti02 khong pha tgp. X. Z. Li cho rang, W(V1) da giiip thu hep viing cam, giam sir tai hpp giira electron va Id trong trong mang tinh the Ti02 [4].
Trong cong trinh nay, chiing tdi thdng bao mpt sd ket qua ve anh hudng ciia su pha tap ion W(VI) den cau triic va tinh chat ciia Ti02 dupc dieu che bing phuong phap udt don gian. Dong thdi, danh gia hogt tinh QXT ciia san pham thong qua kha ndng phan huy quang xanh metylen trong dung djch nudc dudi buc xa anh sang den Compact.
2. PHU'ONG PHAP NGHIEN CUXJ 2.1. Thurc nghiem
Cac hda chat su dyng trong thyc nghi?m dupc nhan tir hang Merck ma khdng can che hda bo sung, bao gdm: TiOS04, (NH4)6H2W,2O40, NaOH va C.HiOH.
TCHH, T. 53(1), 2014 - Dieu chi bgt W-Ti02 va TiOi
Hda tan 4 gam TiOS04 vao 100 ml nude, thu dupc dung djeh TiOS04. Nhd eham 80 ml dung djeh NaOH 0,5 M vao dung dich TiOS04, khuly trpn.d nhi^.4p phdng Jchoang 1,5 gid. Hdykn phu sau khi thiiy phan dupe rira vai \hv bSng nudccit va sau^d la etanol eho den khi khdng edn phat hi?n ion SO4"
trong nudc rua (thu vdi dung dich BaCb 0 ^ M)- Cho tilp 100 ml dung dich hdn hop etanol- nudc (ty 1? thg tich etanol/nudc la 1/1) ciing vdi lupng amoni wonframat thich hpp vao titan hydroxit udt thu dupe. Hdn hpp dupe khuay dhx d nhiet dp phdng khoang 15 gid, sau dd say khd, nghien min rdi nung trong 2 gid d nhiet dp thich hpp thu dupc bpt nano W-Ti02. Mau Ti02 khdng pha tap dupc dieu che tuong tu nhimg khdng cd su bd sung amoni wonframat.
- Ddnh gid hogt tfnh QXT cua sdn pham Hogt tfnh QXT eiia cae mlu dupc danh gid bang each trpn 0,15 gam bdt san phIm vao 200 ml dung djch xanh metylen cd nong dp 10 mg/l. Khuly trpn hdn hop 30 phut trong bdng tdi de dat can bang hap phy-giai hip. Sau do ehi6u xg hdn hop bang den Compact Golstar 40 W (cd 3 viing bude sdng dac trung la 435, 545 va 610 nm) trong 45 phut. Hi?u suat phan umg quang xiic tae dupc xae dinh bang each so sdnh dp hap thy quang (Abs) ciia dung djch trudc va sau phan ung d cue dai hap thy X. = 664 nm.
2.2. Cac phirong phap xac dinh
Gian do nhieu xg tia X (XRD) ciia eae mlu bpt T1O2 dupc ghi tren nhieu xa ke tia X D8 Advance Brucker (Dire) vdi tia CuK^, cd >. = 0,154056 nm, ghi d 25 °C, gdc quet 26 tir 20 d8n 70°, tde dp quet 0,037s. Kich thudc hgt trung binh va thanh phin pha dupc xae dinh dua vao cac pie dac tnmg cua pha anata (101) va pha rutin (HO) tren gian dd XRD theo [5].
Cac anh TEM ciia san phIm dupc chup tren kinh hiSn vi di?n tii truyen qua JEMIOIO (JEOL-Nhgt Bdn) vdi h? sd phdng dgi khoang x50 dgn x600.000, dp phan giai 3 A, di?n ap gia tdc U khoang 40 den 100 kV.
Phd UV-Vis-DRS eiia cac miu bdt Ti02 dupc ghi bdi may JASCO-V550 (Nhat Ban) tren n6n BaS04. Ham Kubelk-Munk dupc sir dyng de xac djnh nang lupng viing cam cCia eae mau Ti02 bdng each ve do thi tuang quan giua [F(R.)E]"^ va nang lupng anh sang. Ngudng hip thy quang (Xg) dupc xac djnh dya vao phuang trinh \ = I240/Eg, trong dd Eg la ndng lupng viing cam [5].
Cac gia trj dp hap thy quang eiia dung dich xanh metylen dupc xae dinh bang each ghi pho hip thy UV-VIS tren may UV2450 - Shimadzu, Nhat Ban.
Nguyin Vdh Hungvdcgh§^
3. KET QUA VA THAO L U A N 3.1. Anh hirdng cua n h i | t do nung
J.6.
- N h i ^ ap nung cd anh fiirdng manh ddn eatf tme
|)ha.va hoat- tinh QXT eiia sanlphim TiOi diSu ehS.
Dd khao sat anh hudng, mlu W-TiOi (t^ le mol W/Ti 0,50 %) dupc.nung d cae nhietdp khac nhau:
500; 600, 700, 750 va 800 "C. Cac mlu nay duoc ki hi?u tuang ling tir TW500 d6n TW800. D^ so sanh, bpt khd Ti02 khdng. pha tap eung duac nung d cac nhiet dp tren va cac mlu duac ki hieu tuang ung tur T560 ddn T800. Gian dd XRD ciia mlu Ti02 va W-Ti02 d ede nhiet dd nung khac nhau dupc dua ra tuong ung d hinh I va hinh 2. Gia trj kfch thude hgt trung binh, thanh phan pha va hi^u suat phan hiiy quang dupe trinh bay trong bang 1.
Tir hinh I, 2 va bang I nhan thiy, ea hai mau Ti02 va W-Ti02 dupc nung d 500 "C va 600 "C d6u ket tinh chua tdt. Khi tang din nhift dp nung, dp k8t tinh va kich thudc hat trung binh tang din. Cae mau W-Ti02 deu cd kich thudc hat trung binh be hon so vdi mau Ti02 d cung nhiet dp nung tuang ung. Nhu vay, ion W(VI) da uc eh8 sy phat triln cac hat tinh the Ti02. Mau Ti02 trong khoang nhiet dp nung tir 500 den 750 "C la dan pha anata vdi dinh pie dge trung ung gdc 26 xIp xi 25,3°. Nhipt dd bit diu ehuyen pha tir anata sang rutin tren mlu Ti02 khoang 800 *'C vdi dinh pie dac trung cho pha rutin xIp xi 27,5°. Trong khi dd, mlu W-Ti02 d khoang nhiet dd nung tir 500 d8n 800 "C la do'n pha anata.
Didu nay ehung to ring, su cd mat ciia ion W(VI) trong mgng tinh thd Ti02 da ire che qua trinh chuyin pha tir anata sang rutin. L. J. Alemany cho ring, sy khuech tan eiia cac nhdm hydroxyl la qua trinh chii yeu cho sy ehuyen pha. Do tuang tac giua eae ion W(VI) vdi cae nhdm hydroxyl bS mgt lam han ch6 su khuyech tdn ciia cac nhdm hydroxyl nen giam toe dp nung ket va ire ch6 qua trinh chuyin pha [6]. Tac dung kim ham qua trinh chuydn pha cua ion W(VI) cung duac tim thay trong edng trinh nghien curu [7].
Ket qua d bang 1 cdn cho thiy, ban diu khi tang dan nhi^t dp nung, ea hai vat iipu TiOi va W-TiOi deu ed hieu suat phan hiiy quang tang va dgt gia trj eye dai ung vdi mlu dupc nung d 750 °C (d6i vdi mlu Ti02) va 700 °C (doi vdi mlu W-TiOz). Dilu nay dupc cho la khi tang din nhi?t dp nung vgt li?u on dinh han ve mat clu triic. Nhung nlu tilp tye tang nhi?t dp nung Idn han 750 "C (doi vdi mlu Ti02) va 700 °C (ddi vdi mlu W-TiOj), hi|u suit phan hiiy quang giam. Nguyen nhan do kich thudc hgt trung binh tang. Cae tae gia [7] cung phdt hi§n thay quy luat giam hieu suit phan hiiy quang khi tang nhipt dp nung qua ngumig thich hpp. Nhin chung, vgt lieu W-TiOi deu cd hi?u suit phan hiiy quang cao
T O D i T . 52(3), 2014
hon so vdi TiO; khmig pha t ^ d cac nht^ dp nung tuang «mg. Nhu vg^, nhi$t dp mmg tfifch hop cho
Cau true va hogt tinh qmmg xuc tdc. „ qua t r i n h n u n g h d n h p p bpt k h d g o m Ti(OH)4 v i amoni w o n f r a m a t )a k h o a n g 7 0 0 "C t r o n g 2 g i d . Bang 1: Kieh t h u d e hgt t r u n g b i n h ( D ) , tfidnh p h i n p h a va bipu s u i t phSn hiiy q u a n g ( H ) eiia c a c m l u T1O2
v i W - T i O : d c a c nhiet d p n u n g k h a c nhau: 500, 6 0 0 , 7 0 0 , 7 5 0 v i 800 "C Mau
T1O2 T500 T600 T700 T750 T80O
D . n m 8,4 13,1 - 24,7 28,1 , 35,2
T h a n h phan pha , , Anata, %
100 100 100 100 . 70
Ri|tin,%
0 0 0 0 30
• H , % 25,43 29,80, 37,82 4 1 3 4 ' 32.73
Mau W - T i O i T W 5 0 0 TW60O TW700 TW750 TW800
D, nm 6,8 11,9 20,0 25,2 27,9
Thanh phan pha Anata, %
100 100 100 100, 100
Rutin, % 0 0 0 0 0
H,%
68,70 8 U 5 98,47 , 93,56
• 84,79
Hmh 1: Gidn d6. X R D c d a cdc m l u T i 0 2 d cdc nhi?t dp n u n g k h a c nhau: 5 0 0 , 6 0 0 ; 7 0 0 , 750 va
800 °C (thur t y tijf d u d i len) 3.2. A n h h u d n g c u a t y 1$ % m o l W / T i
D I khao sdt a n h h u d n g ciia ion W ( V I ) den c l u triic va hogt tinh Q X T tren bpt n a n o W-TiOz, l u p n g muoi amoni wonframat eho v a o h u y i n phu T i ( 0 H ) 4 Ihay doi sao cho dgt ty 1? m o l W / T i la: 0; 0,25; 0,50;
0,75; 1,00 va 1,50 % . C a c m l u d u p c ki hi?u tucmg ijmg tiJr TWO d i n T W 1 , 5 . H d n h p p bpt khd mudi vonfram va T i ( 0 H ) 4 d u p c n u n g d 700 °C trong 2 gid. Gidn d o X R D c u a cac m a u t h e o ty 1? % mol W/Ti khac nhau d u p c d u a r a d hinh 3 . Gia tri kich thudc hgt trung binh, t h d n g sd m a n g va dgng p h a cua cac m a u ndy d u p e trinh b a y t r o n g bdng 2.
Tur hinh 3 cho t h i y , t r o n g k h o a n g ty 1? % mol W/Ti tir 0 den 1,50 % san p h I m ton tgi d dgng d a n pha anata vdi dinh pic d§e t r u n g limg v d i c a e gdc 20 x I p xi 25,3°. N g o a i pic d^e t r u n g cho pha anata khdng t h i y x u l t hipn p h a WO3 h o a c pha Ig nao khdc trong m l u . Dieu nay c d t h e d o ion W ( V I ) d a tham gia vao c l u t n i c m g n g tinh t h i T i 0 2 [8, 9 ] . Cde tac gid [8, 9] cho r i n g , d o e d s y t u a n g d o n g v l ban kinh giOa ion WfVI) va ion T i ( I V ) nen Ion W(VI) d l d i n g thay t h i ion T i ( i y ) t r o n g m g n g tinh the T i O ; d l hinh t h i n h d u n g djeh r l n W J i . - x O i . S y t h a y t h i nay
Hinh 2: G i i n db X R D e u a cde m l u W - T i O : d c a c nhi?t d $ nung: 5 0 0 , 6 0 0 , 7 0 0 , 750 vd
800 "C ( t h u t y tir d u d i len)
Hinh 3: Gian d o X R D ciia cdc m a u T i 0 2 d cac t y 1? % mol W / T i : 0; 0,25; 0,50; 0,75; 1,00 vd 1,50 %
d i n den sai khde t h d n g so m g n g ludi giita cdc m l u W - T i 0 2 so v d i m l u T1O2 k h d n g p h a tgp. Tir b a n g 2 nhan t h i y , trong k h o a n g ty 1? % m o l W/Ti tir 0,25 d i n 0 , 7 5 % c a e m l u W - T i 0 2 cd h l n g s o mgng a Idn hon s o vdi m l u T i O i k h d n g pha tgp. N g u y e n n h a n cd the trong khoang t y 1? % mol nay n o n g dp W ( V I ) trong e l u true m g n g tinh the T i O : edn t h i p nen lyc
301
TCHH, T. 52(1), 2014
diy giiia cac ion W(VI) trong mang tinh thi chiem uu the v i din dSn su sai khac hing so mang a nhu vira neu [2]. NSu tiep tyc tang ty le % mol W/Ti lot;
hon 0,75 %, din den ion W(VI) tham gia dang ke vao clu triic mang tinh th6 T1O2 va luc nay yeu to bin kinh co tinih quy6t dinh. Do ban kinh ion cua W(VI) 41 pm, be hem so vdi bin kinh ion Ti(IV) 51 pm nen cic mlu W-TiOz cd hlng s6 mang a be hon so vdi miu TiO; khong pha tap [2]. Nhu v4y,_tft sir sai khie hSng s5 mang tinh the giiia cic mau W- TiOi so vdi TiOi khong ^ha tap cd the cho rang ion W(VI) da tham gia vao clu triic mang tinh the TiOi.
Bang 2 con cho thiy, khi tang din ty le % mol W/Ti, kich thudc hat trung binh giim din. Dieu nay chirng td ion W(V1) da ire che su phat trijn cic hat tinh the TiOi. Tie dung Ore ch6 sir phit triSn cic hjt tinh the Ti02 cua ion W(VI) cung dupc cong bd d cac cong trinh nghien ciiru [8, 9].
Anh TEM ciia mlu T1O2 khong pha t?p va miu W-TiOz (d ty le % mol W/Ti 0,50 %, nung d 700 °C)
Nguyin Van Hung vd cpng sir dupc dua ra tuong ihig » hmh 4 va 5. Tii cac inh TEM cho thay, mlu W-TiOz co kich thudc h | t be vi phan bo tuong doi dong dSu hem so vdi mau TiOj khdng dupc pha tap.
Bdng 2: Kich thudc hat trung binh (D), thong so mang va d»ng pha ciia cic miu TiOi d cac 1^ 16 %
mol W/Ti khie nhau Klhieu
mau TWO TW0,2S TW0,50 TW0,75 TWl.OO TWI,50
Tyle%
molW/ri 0 0,25 0,50 0,75 1,00 1,50
D, nm 23,5 22,1 21,2 20,7 19,8 16,1
Thong s6ni?ng a = b ,
A 3,781 3,781 3,782 3,788 3,775 3,774
c, A 9,504 9,493 9,498 9,509 9,493 9,502
D?ng pha Anata
"Anata Anata Anata Anata Anata
Hinh 4: Anh TEM ciia mlu TiO; khdng pha tgp (nung d 700 °C trong 2 gid) Pho UV-Vis pha rdn ciia cac mlu bdt Ti02 d cdc ty 1? % mol W/Ti: 0 (TWO); 0,50 (TW0,5) va 1,50
% (TW1,50) dupe dua ra d hinh 6. Tii hinh 6 eho thay, hai mlu W-Ti02 deu cd bd hap thu quang chuydn dieh v€ vung anh sang nhin thay hon so vdi mlu TiOj. Khi tdng ty 1? % mol WA"! dSn 1,50 % dp hip thy quang cd xu hudng gidm. Gia tri nang lupng viing elm eiia ba mlu: TWO; TW0,50 va TW1,50 qua s\r tinh toan tii hinh 6 cd gia tri tuang ung la:
3,30, 3,03 va 3,10 eV. Nhu vgy, su tham gia eiia ion W(V1) vao trong mang tinh thS Ti02 cd the giiip chuyen djch dp hap thu quang v6 viing anh sang
Hmh 5: Anh TEM cua mlu W-TiO; (d ty I? % mol W/Ti 0,50 % va nung d 700 "C trong 2 gid) nhin thay va thu hep nang lupng vung elm cua TiOi-
Gid tri hipu suat phdn hiiy quang cac mau TiOj theo ty le % mol W/Ti khde nhau dupc trinh b ^ trong bang 3. Ket ciua cho thiy, khi tang dan ty-1? % mol W/Ti, hipu suat phan huy quang tang din va dgt gia tri cue dai d mlu cd ty le % mol W/Ti 0,50 %.
Neu tilp tyc tang ty 1^ ndy Idn hon 0,50 %, hi$u suat phan hiiy quang giam. Theo H. Tian [10], ion W(VI) trong mgng tinh the Ti02 de dang bj khi> xu6ng W(V), cac electron bj kieh thich quang trong viing din cua TiOz cd the dupc nhdn bdi W(VI) theo phuang trinh (1).
Bdng 3: Hi?u suat phan huy quang cCia cae mau Ti02 d nhiing ty le % mol W/Ti khdc nhau Ki hieu mau
T y l ? % mol W/Ti Hi?u suit phan hiiy, %
TWO 0 38,17
TW0,2S 0,25 74,72
TW0,50 0,50 98,52
TW0,75 0,75 87,89
TW1,00 1,00 72,49
TWl,50i]
1,50 ' 61,27
n^nn, I. j^>j, zui't Cdu trUc-vd hogt tmh quang xuc tdc...
1 2
J
- ( 1 ) TW-0- ( 2 ) 7W-0.5
200 250 800 3S0 400 BiAjc Sting,
(a)
450 500 5S0 eoo 050
Ning liffhig vAng ctfin, eV (b)
Hmh 6: Pho UV-Vis cua cac mlu Ti02 d ty le % mol W/Ti: 0; 0,50 va 1,50 (a) v i phd UV-Vis ciia cac mau Ti02 sau khi chuyen tucmg iJmg tir budc sdng anh sang sang nang lupng vimg cam
theo ham Kubelka-Munk (b)
*W(V) (1)
W(VD+«^^u
Trong trudng hop nay, pha tap ion W(V1) giup biy cac dipn tii quang sinh nhdm giam s\r tdi ket hpp gi&a cac di?n tu va Id trong nen tang eudng hogt tinh QXT. Tuy nhien, n^u pha tap ion W(V!) d n6ng dp qud eao, nd se boat dpng nhu cac tam tai hpp electron vi Id trdng vd lim giam hieu suit i^hdn hiiy QXT theo phuang trinh (2) va (3):
W(VI)+e(-„o,)^->W(V) W(V) + V7--o.u^W(V0
(2) (3)
Nhin chung, cde mau W-Ti02 deu cd hi^u suat phan hiiy xanh metylen eao ban so vdi mau Ti02 khdng phap tgp. Mlu W-Ti02 d ty le % mol W/Ti 0,5% cd hi?u suit phan buy quang cao nhat va cao hem khoang 2,58 lin so vdi mlu Ti02 khong pha tap sau chi 45 ph^t chi^u sang.
4. KET LUAN
Da dieu ch^ thdnh cdng vgt li?u nano W-Ti02 bdng phuang phap udt dan gidn tii chat dau la titanyl sunfat vd amoni wonframat. Vat li?u W-Ti02 dl^u che dupc d dgng dan pha anata, kich thudc hgt tnmg binh khoing 16 den 22 nm. Mlu W-Ti02 d ty le % mol W/Ti 0,50 % v i dupc nung d 700 "C trong 2 gid cd hogt tinh chuang xiic tie cao nhat. Dung dich xanh metylen gdn nhu bj phan hiiy hodn toan chi sau 45 phiit ehieu sing bdi den Compact. Mlu W-TiOj d tJ I? % mol W/Ti 0,50% cd hi?u suat phfin hiiy quang eao hem khoang 2,58 lan so vdi mlu TiOi khdng pha tgp. K^t qud niy cho thiy tiem ning img dyng cila vgt lifu W-TiOj trong xd li cac chit 6 nhilm hihi ca. Ngoii ra, nghien cuu cdn cho
thdy, ion W(VI) the hien vai trd thu h?p ndng lupng viing elm, urc chi su phdt trien cac hat tinh thi va qud trinh chuyen pha tir anata sang rutin eua Ti02.
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Lien he: Nguyen Van Himg
Khoa Hda hpc, Trudng Dai hoc Ddng Thap
So 783, Pham Hiru Lau, Phudng 6, Thanh phd Cao Lanh, Tinh Ddng Thap Email: [email protected].
