L.-C. Chuang, C.-H. Luo / Materials Research Bulletin 48 (2013) 238–244
239
2. Experimental
The surface areas of three prepared TiO2-based catalysts were
determined by the Brunauer–Emmett–Teller (BET) method using
an ASAP 2010 instrument and N2 as the adsorbent. X-ray powder
2.1. Preparation of Titania powders
diffraction (XRPD) patterns were obtained using the Scintag X1
˚
Titanium tetrachloride (99.0% TiCl4, Showa, Japan) was served
as the main starting material for fabricating TiO2 nano-powders
through a proposed method shown below. First, an aqueous TiOCl2
solution with 1.5 M of Ti4+ ions was prepared by slowly adding
pieces of pure water ice to TiCl4 to limit vigorous hydrolysis
reaction. Yellow unstable intermediate products of TiO(OH)2
formed as the ice pieces slowly melted, and then dissolved as
more ice was added. A yellow aqueous TiOCl2 solution was
produced. Distilled water was added to the solution to produce a
transparent TiOCl2 solution with 0.5 M of Ti4+ ions. Three TiO2
powders (TH O, TNH OH, and TFeSO4 ) were prepared by further
adding distilled water, 3.7% NH4OH (Shimakyu’s Chemicals, Japan),
and 0.02 M FeSO4 (Shimakyu’s Chemicals, Japan), respectively. The
solutions were thoroughly dispersed by stirring for 30 min and
allowed to stand for 4 h at 50 8C for homogeneous precipitation.
The TiO2 powders were washed several times with a 0.1 M solution
of NaCl (Union, Taiwan) at 4 8C, collected using a centrifuge at
7000 rpm/min, and then dried at 80 8C for 20 h. Nearly pure rutile
instrument with Cu Ka radiation (l = 1.54056 A) as the incident X-
ray (MAC science, MXP 18, Japan). The surface morphology of
prepared TiO2-based catalysts was studied using a scanning
electron microscopy (Hitachi 4700, SEM) equipped with a X-ray
energy dispersive spectrometer (EDS).
2.2. Catalysts coated on supporting materials
A
5% (w/w) TiO2 suspension solution was prepared by
ultrasonic vibration for 20 min. TiO2 powders were coated on
Pyrex glass beads (diameter of 3 mm, specific gravity of 2.45–2.60,
mean hardness of 515 kg/mm2, weight ratio of SiO2 3 70.0%) and
PP (polypropylene) fibers (diameter of 0.4 mm, specific gravity of
0.9, specific surface area of 0.126 cm2/g, and a total surface area of
756.673 m2/g), respectively. The glass beads substrates were
etched with a 5 M solution of NaOH for 5 h at 100 8C before
coating. The PP fibers were treated by the dip-coating method. A
dip-coating apparatus equipped with a velocity-controlled adjust-
able motor was used to submerge and extract the substrate at a
preset constant rate. The coated Pyrex glass beads and PP fibers
were dried at room temperature for 36 h.
2
4
TiO2 was prepared by Kim et al. [21] at temperature < 65 8C.
2À
NH4OH and SO4
were added to improve homogeneous
precipitation of rutile TiO2 at temperature of 70–100 8C according
to Kim and Park [26] and Xie et al. [27]. Considering green
synthesis and integration of above-mentioned processes, we
controlled the temperature of homogeneous precipitation at
50 8C in this study. A comparison between the proposed method
and various preparation processes of nano-TiO2 is shown in Table
1. Their operating costs for instruments, personnel, raw materials,
and energy consumption were relatively and semi-quantitatively
ranked. The modified method has several environmentally friendly
advantages of low cost and low energy consumption: (1)
crystallization temperature for rutile phase is around room
temperature, exceptionally in extreme conditions (T < À10 8C
and T > 80–100 8C); (2) it is solvent-free during the preparing
process; and (3) the equipment and processing required are simple
and safe.
2.3. Photocatalytic equipment
Fig. 1 shows a schematic diagram of the photoreactor system
used in this study. Photocatalytic experiments were performed in a
hollow cylindrical photoreactor with dimensions 20 cm  10 cm
(high  diameter) equipped with a UV lamp (18 W, 365 nm and
1.25 mW/cm2). The photoreactor’s inner wall of Pyrex was coated
with Teflon1 and lined with a cylindrical Teflon1 paper which two
supporting materials coated with TiO2 nanopowders were sticked
on. The UV lamp was vertically inserted into the center of the
photoreactor. The real reaction volume of the photoreactor is about
1.178 L. The outlet of the photoreactor was equipped with a switch
valve for vacuuming and sampling. An equilibration period of
Table 1
Comparison of various preparation methods for nano TiO2-based catalysts.
Preparation method
Chloride process [1,2]
Major raw
materials
Heating conditions
Key characteristics
Operating
costa
TiCl4
HCl
>1000 8C
Supplementary protection devices for HCl and Cl2 gas are
required; rutile
I: $$$
P: $$
R: $
E: $$$$
I: $
Sol–gel [3–5]
Metal-alkoxide
alkoxide
Room temp. or 70 8C for 24 h
180–200 8C for 3 h to 3 days
Alkoxide can be hydrolyzed intensely in air; reaction processes
are complicate; calcining treatment and organic solvent (EtOH)
are needed; amorphous
P: $$
R: $$$
E: $$
I: $$$$
P: $$
R: $$$
E: $$$
I: $$$$
P: $
Hydrothermal [6–8]
Detonation [9,10]
Vapor-thermal [11]
Ti(OC4H9)4
A continuous process is impossible; high pressure and a special
apparatus are needed; pH, reactant conc. and temp. have a great
influence on the reaction process; amorphous
TiOSO4
NaOH
Starting materials are mixed at
110–140 8C, and then heated at
700 8C for 1 h
A special detonation device is needed; amorphous
NH4NO3
R: $$
E: $$$
I: $$$
P: $$
R: $$$
E: $$
I: $
Ti(OC4H9)4
120–200 8C for 1–48 h
An autoclave apparatus is needed; anatase
Tetrabutyl titanate
The modified method
in this study
TiCl4
50 8C for 4 h
Reacting in an aqueous solution; no organic solvent and special
devices are required; rutile
P: $
R: $
E: $
a
Instrument cost (I), personnel cost (P), raw material cost (R), and energy consumption (E) are included; $: ranking costs.