TAPCHIHOAHQC T. 52(1) 130-132 THANG 2 NAM 2014
T 6 N G HCyP PEROVSKIT LaFeOs CAU TRUC NANO B A N G PHU'aNG PHAP DOT C H A Y GEL
Lini Minh Dai', Dao Ngpc Nhiem'*, Vu The Ninh', Pham Nggc Chiic', Dtfoiig Thj Lim^
' Viin Khoa hpc vdt liiu, Vien Hdn ldm Khoa hpc vd Cong nghe Viit Nam
^ Viin Dja ly, Viin Hdn ldm Khoa hpc vd Cdng nghi Viet Nam Din Tda soan 10-9-2012; chinh lgi sau phan bien 10-10-2012; chip nhin ding 9-12-2013 Abstract
The nanostructured powder of LaFeOs has been synthesised at low temperature (550 "C) via the combustion of gel prepared by polyvinyl alcohol (PVA) and corresponding metal nitrates Samples were characterized by diffracUon (XRD), scanning electton microscopy (SEM). Further themial tteatment at 550 °C for 2 hours yields the single phase LaPeOs with average size < 50 nm.
Keywords: LaFeOj, hydrothermal method, polyvinyl alcohol (PVA), combustion method.
1. MO DAU
Phin idn cic chat xuc tic sii dung trong cdng nghiep hoa hpc diu dya tren cic oxit phurc hgp.
Trong eic oxit kim loai phiic hgp, oxit kieu perovskite (ABO3) cd nhirng tinh chit ndi bat nhu hoat tinh oxi - hoa khir cao, khi ning chdng nhiem dpc tdt dugc sur dung trong ITnh vyc xu ly khi thai thieu ddt ric thii mdi trudng [1,2].
Perovskit ABOj cd hogt tinh xuc tie cho nhilu phan ling oxi - hoa khir, khu NO^, SOx, oxi hoi CO [3, 4]. Hoat tinh xiic tic ciia perovskite cd ciu triic nano gin diy nhin dugc nhilu sy quan tam tren thi gidi. Trong bai bao nay se nghien ciiru tdng hgp LaFeOs ciu tnic nano bing phuang phap ddt chiy gel.
2. THUC NGHIEM
Tdng hgp LaFeOj dugc tien hinh theo cic budc nhu nghidn ciru chl tao LaCrOj, NiFe204 bing phuang phap ddt chiy gel [5, 6]. Dung dich muoi nih-at (La^"^, Fe'"") dang hda chit tinh khilt dugc khuay trdn lien tyc vdi dung dich nudc Poly Vinyl Alcohol (PVA) tren may khuiy tijr gia nhiet. Gel tgo thinh dugc lim gia trong tii siy va nung d nhipt do thdch hgp de tao pha perovskite.
Giin do nhieu xg Roughen (X-Ray) dugc thyc hi$n tren miy Siemens D-5b00 (CHLB Diic) vdi biic xg CuKa budc sdng X = 1,5406.
Anh vi cau true va hinh thai hgc cda bdt oxit dugc chyp bing kinh hiin vi di^n tii quet (SEM) JEOL- 5300 (Nhgt Ban).
3. KET QUA VA THAO LUAN 3.1. Anh hirdng cua nhiet do nung
Polyme PVA dugc sii dyng lam chat nen giiip cho sy phin bd cac ion kim loai m^t cich ddng diu, ting nhiet lugng toa ra qua trinh phan huy (ddt) gel.
Mau tdng d nhiet do thip vdi cau tnic nano.
Cac mau tgo gel dugc dilu chl d nhiet dp 80 °C, mdi trudng tgo Gel pH = 4, ty Ie tdng moi ion kim loai/PVA = 1:1. Tir ket qua khio sit qiia trinh phan huy nhiet ciia gel. Chung tdi lya chgn nhiet d^ nung d 250 "C, 350 "C, 450 "C, 500 "C v i 550 °C trong 2 gid. Ket qua phan tich xac djnh ciu true cua cac miu tren may Siemens D-5000 dugc dua ra a hinh 1.
^..J-..^.
Hinh 1: Giin do nhilu xg tia X ciia miu nung d nhipt dp khac nhau
Tren gian do cho thay cac mlu nung d 250 "C va 350 °C chua xuit hien pha tinh thi (vd djnh hinh), khi nung mau d 450 "C bit diu xuit hipn cic pic dgc trung ciia perovskit LaFeOs nhung chua ro
TCHH.T. 52(1),2014
rang, khi nung mau d 500 "C va 550 °C thu dugc cac pic die trung dan pha tinh thi ciia perovskite LaFeOj. Do dd, nhipt do nung d 550 "C trong 2 gid dugc chgn cho cac thi nghiem tilp theo.
3.2. Anh hirdng cua pH tao gel
De khio sit pH tgo gel cic miu dugc dilu che tuong ty nhu d phin tren nhung pH tgo gel duge thay ddi (pH = 2, 3, 4, 5), nung mau d 550 "C. Ciu tnic pha ciia cic mau dugc xie d inh tren may Siemens D - 5000 (hinh 2).
Ddo Ngpc Nhiim vd cdng sy miu dugc phin tich xie dinh ciu tnic tren may Siemens D-5000. Ket qui dugc ghi lgi d hinh 3.
25 30 35 40 45 50 55 60 65 70
Hinh 2 Giin dd nhieu xg tia X ciia mlu tdng hgp d pH tgo gel khac nhau
Hinh 2 cho thiy, miu dilu chl d pH = 5 vi pH
= 2 xuit hi?n cic pic dgc trung pha perovskit nhung cdn lan mpt phin nhd cic pha LazCOa vi Fe203.
d pH = 5 qui trinh tao gel khdng tdt dan tdi hipn tugng thuy phan mdt phin La(0H)3, khi dot chay gel d550 "C sinhraLa203.
La(0H)3 - La203 + H2O (1) Mit khic, trong qui trinh ddt chiy gel mgt iugng khi CO2 dugc sinh ra ngay lap tire tham gia phan ling vdi La203 sinh ra La2C05.
LajOj + CO2 = LajCOs (2) CJ pH = 2 miu bit diu xiy ra qui trinh kit tiia mpt phan keo miu nau dd (son sit) ciia Fe(0H)3, khi dot chay d 550 "C sinh ra Fe203.
Fe(0H)3 = Fe203 + H2O (3) Cic miu dieu chl d pH = 3 va 4 thu dugc cac pic d§c trung cho dom pha tinh thi perovskit LaFeOs. Do dd, pH = 4 dugc chgn cho cic nghien ciiu tilp theo.
3.3. Anh hvdng ciia nhiet dg tao gel
Miu dugc dieu chl tucmg ty nhu d phan chi thay doi nhipt dp tgo gel (40, 60, 80, 100 °C). Cic
25 30 35 40 45 50 55 60 65 70
Hinh 3: Giin dd nhieu xg tia X cCia miu tdng hgp d nhiet dg tgo gel khac nhau Tren hinh 3 cho thay mau dieu che d nhiet dp tgo gel la 40 "C va 60 °C cd xuit hien ddng thdi cic pic dgc trung chii yeu cho pha tinh the perovskit va mpt sd pic die trung cho pha La203 va LajCOs (khi nhiet dp tao gel < 60 °C, thdi gian phan iirng tao gel xiy ra chim han dan tdi hien tugng thiiy phan mpt phan La(0H)3, khi ddt chiy gel d nhiet dp cao tuang ty nhu d phin tren sinh ra pha La203 va La2COs).
Miu dieu che d nhiet dp tao gel d 80 "C vi 100 "C cd cac pic dac trung don pha duy nhit ciia perovskit LaFeOs- Nhipt dp tao gel 80 °C dugc chpn cho dieu kien tdng hgp miu.
3.4. Anh hudng cua ty If kim lo^i/PVA Miu dugc dieu che tucmg ty nhu d phan tren ty Ip kim loai/PVA dugc thay ddi (2:1, 1:1, 1:2, 1:3).
Miu dugc phin tich xac dmh cau triic trSn miy Siemens D-5000. Kit qui dugc chi ra d hinh 4.
25 30 35 40 45 50 55 60 65 70 Hinh 4: Gian dd nhilu xg tia X ciia mau tong hgp d
ty Ip kim logi/PVA khic nhau
TCHH, T. 52(0,2014
Tren gian do cho thay mau dieu che theo ty le 1:3 ngoai cac pic dgc trung cho pha perovskit cdn mgt sd pic nhd die trung cho pha LajOs, ddi vdi cac mau dilu chl d ty lp I;2; 1:1 vi 2:1 cd cic pic dgc trung cho dan tinh thi perovskit LaFeOs. Ty Ie kim logi/PVA =1:1 dugc chgn lim dilu kien tdng hgp mau cho cac thi nghiem tiep theo.
3.5. Xac dinh hinh thai hgc cua mau toi un Miu dugc dilu chl d pH = 4, nhiet do tgo gel 80
"C, ty le kim logi/ PVA = 1/1, nung d 550 "C trong 2 gid v i dugc xac dinh hinh thai hgc tren Idnh hien vi dien tu quet (SEM) JEOL-S.4800 (Nhgt Bin). Kit qui chi r a d hinh 5.
Hinh 5: Anh SEM ciia miu tdng hgp d dilu kien toi uu
Qua hinh 5 thiy ring miu LaFeOs cd ciu tnic nano ddng nhat (< 50 nm), cic khung Id xdp dugc tgo thanhbdi eic hat nano, ed rit nhilu khoang hde vdi cic Id xop ddng nhit dilu niy rit phii hgp cho vipc sir dyng Iam xiic tic de xu ly mdi trudng.
4. KET LUAN
Da khio sit mpt sd dilu kien hinh thinh pha
Tdng hpp perovskit LaFeOj cdu trUc...
perovskit LaFeOs, dilu kipn tdi uu dl tdng hgp perovskit LaFeOs cd ciu true nano dong nhit (< 50 run ) d nhiet do thap bang phuong phip dot chay gel PVA la pH = 4, nhiet dd tao gel 80 °C, ty \i moi PVA/ldm Ioai I/l nung d 550 "C trong 2 gid.
TAI LIEU THAM KHAO
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Ladavos. Samarium Based High Surface Area Perovskite Type Oxides SmFe,.jiAlxOj (X = 0.00, 0.50. 0.95). Part U. Catalytic Combustion of CH^, Reaction Kinettcs and Catalysis Letters, 72(1), 49-55 (2001).
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Handbook on the physis and Chemistry of Rare Earths, 3, North-Holland (1978).
5. Luu Minh Dai, Dao Ngpc Nhifim, Vu Thi Ninh, Pham Ngpc Chiic. Tdng hpp spinen NiFe^O^ bdng phuang phdp ddt chdy gel a nhiet dp thdp. Tap chl Hoa hpc, 46(6), 675-680 (2008).
6. S. T. Aruna and A. S. Mukasyan. Combustion synthesis and nanomaterials. Current Opinion in Solid State & Materials Science (2008).
7 Phan V9n Tudng. Vdt liiu vo ca, Trudng DHKHTN - DHQG - Hi NOi (2005).
8. Soo Lee, Luu Minh Dai, Dao Ngoc Nhiem, Nguyen Xuan Dung. Synthesis ofLaCrO, at low temperature by the PVA gel combustion Method, the 37'''KSIEC Meeting, p. 122 (2008).
Lien hi: Dao Ngpc Nhi|in Vien Khoa hgc vit lieu
Vipn Han lam Khoa hpc va Cong nghe Viet Nam Sd 18, Dudng Hoang Qudc Viet, Qugn Ciu Giiy, Ha Npi Email: [email protected]
Dien thogi: 0915417696.
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