Hgi nghi Khoa hoc ky' niem 35 ndm Vien KH&CNVN-Hd Noi -10/2010
NGHIEN c u t ; TOI UtJ HOA QUI TRINH DIEU CHE XUC TAC QUANG HOA Ti02 TlT TINH QUANG ILMENITE BANG PHUTONG PHAP SULFATE V 6 l DIEU KIEN THUY PHAN TRONG MICROWAVE
SIMPLEX OPTIMIZATION OF THE PREPARATION OF PHOTOCATALYST TiOj FROM VIET NAM ILMENITE ORE BY SULFATE PROCESS WITH MICROWAVE-ASSISTED HYDROLYSIS
Nguyen Hiep Hoa'^, Cu Thanh Long^', Hoang Hai Phong'', Nguyen Van Dzung'' ''institute of Applied Materials Science
01 Mac Dinh Chi Street, District 1, HCM City, Vietnam Email: [email protected]
^ ' H C M C University of Natural Sciences
227 Nguyen Van Cu Street, District 5, HCM City, Vietnam Abstract:
In this work, the whole nano-sized Ti02 preparation process from ilmenite ore by the sulfate process with microwave-assisted hydrolysis was divided into three fllaving stages for experimental optimizing by simplex matrix method. The first stage; acidulating ilmenite ore with sulfuric acid to form a titanium sulfate solution. The second stage; hydrolysis of titanium sulfate solution in microvs'ave condUion to form hydrous titanium dioxide. The third stage; heat treatment of hydrous titanium dioxide to gain nano-sized Ti02 products using for photocatalytic applications. In each stage of the optimization, a simplex matrix is
established with appropriate response and experimental factors for optimization process. The responses of stages are the rate of dissolving titanium in the
hydrolysis solution, the average anatase crystalline size of hydrous titanium dioxide, the rate of photocatalytic degradation ofremazol orange 16, respectively.
The result of the optimization process proposed the best preparation parameters of the microwave-assisted sulfate process for gaining TiO2 products
having the purity above 99.5%Ti02, the average anatase crystalline size about 20nm, the specific area of 37m'/g, which are favourable to photocatalytic applications.
Tom tat:
Trong cdng trinh ndy, todn bd qui trinh diiu chi xuc tdc Ti02 tir tinh qugng ilmenit, theo phucmg phdp sunfat vdi diiu kiin thiiy phdn hd trg bdng ky thudt vi sdng microwve, dugc chia thdnh 3 giai dogn liin tiip di tdi uu hda bdng phuang phdp ma Iran simplex. Giai dogn I; qud trinh hda tdch qugng ilmenit bdng axit
sunfuric di chuyin than tit qugng vdo dung dich dudi dgng cdc mudi sunfat ciia nd. Giai dogn 2; qud trinh thiiy phdn dung dich sunfat titan trong diiu kiin microwave di tgo thdnh kit tua axit metatitanic. Giai dogn 3; qud trinh xu li nhiit axU metatitanic di tgo thdnh bdt Ti02. Trong mdi giai dogn, mdt ma Iran simplex dugc thiit lap vdi cdc thdng sd kiim sodt qud trinh cdng nghi tuang img vdi mot ddp itng thich hgp cho viic tdi uu hda qui trinh diiu chi. Ddp ung ciia cdc giai doan tuang itng gdm; hiiu sudt hda tdch titan vdo dung dich thuy phdn, kich thuac hgt trung binh ciia hydroxU titan vd hiiu sudt quang phdn hiiy ddi vdi remazol orange 16.
Tiiu ban Khoa hgc vdt lieu ISBN: 978-604-913-0 I
Kit qud nghiin ciru tdi uu cho cdc ihdng sd kiim sodt qui irinh diiu chi Ti02 tir tinh qugng ilmenit vdi dd sgch lan han 99.5%, kich thuac tinh ihi anatase khadng 20nm vd diin lich bi mgt riing 3 7m'/g, thich hgp cho cdc irng dung ldm vdt lieu xiic tdc quang hda.
I. INTRODUCTION
Nano-sized Ti02 has attracted much attention owing to their peculiar physical and chemical properties. Recently, based on the sulfate process, our group was successfully prepared nano-sized Ti02 with applying microwave condition in hydrolysis [1]. In general, the sulfate process is a complex chemical process and consist of many continuing stages, the technological parameters in each preparation stage have affected the properties of the final product. The results of preliminary experiments with the microwave-assisted method also showed that the technological parameters well affected the produced nano-sized Ti02 properties [1, 2]. So with the aim to prepare TiOi for using as photoeatalyst, this work considers simultaneous affects of preparation stages on the applying character of Ti02 product by the simplex matrix optimization.
The success of an optimization method depends on the ability of the method to locate the optimum correctly and effectively. Optimization is often effected by varying conditions one- at-a-time, while keeping the others fixed, until an optimum is reached for each variable.
However, this is far from adequate and requires a large number of experiments to be performed. This can be very time-consuming and, probably more important for complex chemical systems; interactions between the variables might mean that the optimum obtained will depend on the initial conditions chosen.
Experimental design using the variable size sequential simplex matrix can be a powerful tool optimization, because all conditions can be varied in a small number of experiments, in contrast with the approach of varying each factor in a separate experiment. The simplex matrix directs the simultaneous adjustment of all experimental conditions away from those giving a poor response. This method is based on a direct sequential search procedure and progresses with the displacement of a geometric figure, called a simplex, defined by a number of vertexes equal to one more than the number of variables in the optimization process. It is performed according to a set of logical rules, consisting of reflection, expansion, and contraction of the geometric figure in multidimensional space [3].
II. EXPERIMENTS 1. Nano-sized TiOi preparation:
The preparation of nano-sized Ti02 by the microwave-assisted sulfate process was described in detail elsewhere [3], including the sequential stages illustrated in figure I.
Firstly, grinded ilmenite ore (BIMAL Co., 52% Ti02) was digested with sulfuric acid 89%
(China, technical grade). This stage is controlled by main factors such as the molar ratio of H2SO4 to Ti02. annealing temperature, annealing time. After the reaction stopped, the reaction product was converted to a porous cake. This cake was dissolved in water to form a black liquor. The liquor is then clarified by sedimentation to remove insoluble residues such as silica, zircon and residual unreacted ore. The ferrium in the solution was removed by reducing Fe^^ to Fe""" as FeS04.7H20, chilled it at about - 4°C and filtrated.
Next, the liquor was hydrolyzed in microwave condition to produce a precipitate of hydrous titanium dioxide with controlling of main parameters as Ti(lV) concentration and hydrolysis time.
Hoi nghi Khoa hoc ky- niim 35 ndm Vien KH&CNVN- Hd Ngi -10'2010
Finally, the hydrous titanium dioxide was calcinated to produce nano-sized Ti02 with controlling of main parameters as calcination temperature and time.
2. Optimization by simplex matrix:
The optimization process was carried out through sequential stages illustrated in figure I.
The result of the previous stage was used for the next stage.
Contro I Parameters
Preparajion
Process Opthntzatlon
Process
H 2 S 0 4 . - T : I O .
Temperature, time
Ti(IV) Concentration, time
Temperature, tune
Cjrinded i l m e i i i t e H2SO4
-f A n e a l i t i g
-¥
D i s s o l v i n g in w a t e r
+
F i l t e r
•f R.eraovijig F e
•••
S u l f a t e Titanixmi s o l u t i o n H y d r o l y s i s i n • n i i c r o \ v a v e o v e n
•
H y d r o x i d e t i t a u u u n
•f W a s h i n g , d n / i n g ( 1 1 0 ° C )
C a l c i n a t i o n +
• * •
TsTaiio-sized TiOz
J
\
T b e first s t a g e
_J
1
> s e c o n d T h e s t a g e
J y
T b e tllird s t a g e
Fig. I; Preparation and optimization process.
2.1. The first stage:
The response (Y=Ymax) was chosen as the rate of dissolving titanium in hydrolysis solution - H (%), and the variables as the molar ratio of H2S04/Ti02 - U„; annealing temperature - Ui2 ( C); annealing hme - Ujs (min.). The optimization experiments were carried out follow the experimental matrix design in table I.
Table 1; Experimental matrix design for the first optimization stage.
Vertex number (i)
1 2 3 4
Experimental matrix (Uij) Un
2.1 2.9 2.3 2.3
Ui2
170 177 198 177
Ui3
120 134 134 177 2.2. The second stage:
The response (Y=Yniin) was chosen as the average anatase crystalline size of dried titanium h>'droxide products - d (nm) and the variables as the Ti02 concentration - V„ (g/L);
Tiiu ban Khoa hoc vdt liiu ISBN: 978-604-91
hydrolysis time - Vi2 (min.). The optimization experiments were carried out follow the experirhental matrix design in table II.
Table II; Experimental matrix design for the second optimization stage.
Vertex number (i)
1 2 3
Experimental matrix (Vy)
V i ,
120.0 216.6 145.9
Vi2
180 221 335 2.3. The third stage:
The response (Y=Ymax) was chosen as rate of photodegradation of remazol orange^ 16 (ROI6) - E (%)) after 3h UV irradiation, the variables as calcination temperature - N,i ( C);
calcination hme - Ni2 (min.). The ophmization experiments were carried out follow the experimental matrix design in table III.
Table III; Experimental matrix design for the third optimization stage.
Vertex number (i)
1 2 3
Experimental matrix (Njj)
N i ,
675 844 720
Ni2
120 136 178 3. Analysis:
The concentration of Ti02 in solution was analyzed by titration method with indicator as FeNH4(S04)2.12H20 (the color changes from colorless to red blood).
The average anatase crystalline size was determinated through XRD pattern (SIEMENS D5000) with Warren Averbach method [4].
The rate of photodegradation of ROI6 was determined by the reaction of 0.4g Ti02 with 200mL ROI6 solution (30mg/L concentration) in stirring and 3 hours UVA irradiahon condition. The concentration of ROI6 in reaction solution was determinated by UV-VIS spectmm (JASCO V550).
III. RESULTS AND DISCUSSION 1. The first optimization stage:
The results of the first optimization stage is presented in table IV.
The reflection operahons (3->5, l->6, ...) based on replacement of the vertex which has minimum response of the initial vertex into new vertex that has higher response until reaching optimal area. After five reflection operations, the response increase into vertex 7 and reduce into vertex 8, 9. The optimization process was stopped at vertex 7; it is optimal vertex with experiment parameters as H2S04/Ti02 3.4; annealing temperature 153 C; annealing time 141 minutes. This result was used for the next optimization stage.
Hoi nghi Khoa hoc ky niim 35 ndm Viin KH&CNVN- Hd Ngi -10/2010
Table IV; Summary table of the resuU in the first optimization stage.
Vertex number (i)
1 2 3 4 5 6 7 8 9
Vertex
I I I I R R R R R
Reflex operation
- - - - 3 ^ 5
1 - > 6 4 - > 7 5 - > 8 2 ^ 9
Experimental matrix (Ujj) Ui,
2.1 2.9 2.3 2.3 2.6 3.1 3.4 3.7 3.9
Ui2 170 177 198 177 151 167 153 180 156
Ui3 120 134 134 177 153 190 141 156 190
Yi H(%)
49.1 65.7 44.1 57.3 63.5 70.1 72.0 68.9 67.3
/." initial vertex: R: reflection vertex
2. The second optimization stage:
The result of the second optimization stage is presented in table V.
Doing the same in the first optimization stage, that mean the vertex with minimum response was reflected in succession into new vertex until reaching to optimal area. After three reflex operations, the optimization process was stopped at vertex 5, that is the optimal vertex with Ti02 concentration in hydrolysis solution 23.4g/L and hydrolysis time 139 minutes. This result was used for the next optimization stage.
Table V; Summary table of the result in the second optimization stage.
Vertex number (i)
1 2 3 4 5 6
Vertex
I I I R R R
Reflex operation
- - - 2 ^ 4 3 ^ 5 4 ^ 6
Experimental matrix (Uij)
Vi, 120.0 216.6 145.9 49.3 23.4 94.1
Vi2 180 221 335 293 139 26,0
Yi d(nm)
3.7 6.3 5.4 4.4 3.0 nd
I: initial vertex: R: reflection vertex: nd: not detected.
3. The third stage optimization:
The result of the third optimization stage is presented in table VI.
Similar with above optimization stage, the vertex with minimum response was reflected in
succession into new vertex until reaching to optimal area. After three reflex operations, the
optimization process was returned to vertex 1, that is the optimal vertex with calcination
temperature 675 C and calcination time 120 minutes.
Tiiu ban Khoa hoc vdt lieu ISBN: 978-604-91
Table VI; Summary table of the result in the third optimization stage Vertex
number (i) 1 2
4 5 6
Vertex
I 1 I R R R
Reflex operation
- - - 2 ^ 4 3 ^ 5 4-^6
Experimental matrix (Uij)
Vi,
675 844 720 551 506 630
Vi2
120 136 178 162 105 62
Yi
E(%) 75.3 10.4 37.2 49.3 56.8 65.2
/." initial vertex: R: reflection vertex
IV. CONCLUSIONS
This paper described the optimization preparation of nano-sized Ti02 from ilmenite ore by the microwave-assisted sulfate process. The results showed that the best conditions for preparation of Ti02 for catalytic applications include:
In the stage of acidulating ilmenite ore with sulfuric acid to form a solution titanium sulfate: ratio of H2S04/Ti02
minutes.
3.4, annealing temperature 153 C and annealing time 141 In the second of hydrolysis of titanium sulfate solution in microwave condition to form of hydrous titanium dioxide: concentration of Ti02 23.4g/L, hydrolysis time 139 minutes. In the stage of heat treatment of hydrous titanium dioxide to gain nano-sized Ti02 products: calcination temperature 675''C and calcination time 120 minutes.
With the mentioned preparation parameters, the microwave-assisted sulfate process gained Ti02 products having the purity above 99.5%)Ti02, the average anatase crystalline size about 20nm, the specific area of 37m /g, which are favourable to photocatalytic applications.
Acknowledgments
Tbe authors would like to express their thanks to the Vietnam Academy of Science and Technology for financial support of this project: "Research on the preparadon of photocatalytic materials Ti02 from Vietnam ilmenite" (2007 - 2009).
4.
REFERENCES
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F.H. Walters. S.L. Morgan, L.R. Paker. S.N. Deming, Sequential Simplex Optimization. CRC Press, USA, 1991.
N.V. Dzung. H.H. Phong, RT.T Loan. D.V. Luong. A novel preparation of nanoctystaUUe Ti02 and Us photocatalytic activity. Proceedings of The Second Intemational Workshop on Nanophysics and Nanotechnology (2004). pp.213-216.
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