Synthesis of TiO2-Graphene nanoplatelets (TiO2/GNPs) composite from ilmenite and natural graphite for photocatalysis in enviromental treatment

Chemistry & Environment 
T.N. Tuan, N.T.H. Phuong, T.V. Chinh, “Synthesis of TiO2  environmental treatment.” 106 
SYNTHESIS OF TiO2 - GRAPHENE NANOPLATELETs (TiO2/GNPs) 
COMPOSITE FROM ILMENITE AND NATURAL GRAPHITE FOR 
PHOTOCATALYSIS IN ENVIROMENTAL TREATMENT 
Truong Ngoc Tuan*, Nguyen Thi Hoai Phuong, Tran Van Chinh 
Abstract: In the present study, titanium dioxide/graphene nanoplatelets 
(TiO2/GNPs) composites have been synthesized from precursors of ilmenite and 
natural graphite flakes with difference in pH of medium. As-prepared composite 
materials were characterized by XRD, SEM, TEM, EDX and BET techniques, UV-
VIS diffuse reflectance. 
Keywords: Graphene nanoplatelets (GNPs); TiO2/GNPs composites; Ilmenite; Photocatalysis; Graphite flakes. 
1. INTRODUCTION 
Environmental pollution has attracted much attention these decades. Millions of 
tons of wastewater are generated every day and discharged to the rivers and 
oceans. Under most circumstances, it contains both inorganic and organic 
pollutants [1]. Since wastewater contains both inorganic and organic pollutants, it 
is ideal if they can be removed through a single process. Photocatalysis is famous 
AOP which is one of the most economical and facile approaches to treat both 
inorganic and organic contaminants in the water [2]. Titanium dioxide, one of the 
most widely used photo-catalysts, has the ability to reduce heavy metal ions has 
higher valance to which has lower valance under UV radiation. Beside TiO2 also 
can help degrade many kinds of organics under UV light [3]. Moreover, TiO2 is 
desirable because of its high efficiency, low cost, nontoxicity, and high stability. 
Graphene is composed of sp2-hybridized carbon atoms. Graphene has gained 
significant attention due to its incredibly high specific surface area (theoretical 
value: 2620 m2/g), high thermal conductivity, and outstanding electrical 
conductivity [4]. Moreover, graphene also is supporting material for enhancement 
of the photoactive properties of photocatalysis due to its large surface area, high 
conductivity, ionic mobility, and superior mechanical flexibility. Degradation 
reaction would happen after pollutants are adsorbed on graphene if TiO2 is 
attached on graphene [5]. In addition to serving as a platform to help collect 
pollutants, graphene can improve electron transfer rate and thus expedite the 
degradation process. 
To achieve this goal, herein we designed a nanocomposite, graphene 
nanoplatelets attached with TiO2 (TiO2/GNPs) via a simple one-pot hydrothermal 
method. Ilmenite ore (FeTiO3) in Viet Nam has abundant reserves (about 35 
million tons) which is a popullar precusor in order to synthesis TiO2. Titanium slag 
85% is a by-product of manufacture of TiO2 92%. Thus, indirect synthetic 
TiO2/GNPs will improve commercial efficiency. 
2. EXPERIMENTAL 
2.1. Materials and equipments 
Materials: Titanium slag 85% (by-product of titanium 92% manufacture from 
Binh Dinh Ilmenite,) C2H5OH 96% (PA- Duc Giang), acetone, H2SO4, KHSO4, 
K2S2O8, natural graphite flake (China, <180 micrometer). 
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Journal of Military Science and Technology, Special Issue, No.57A, 11 - 2018 107
Equipments: Autoclave reactor; ultrasonic device (China, 20 kHz); heating oven 
(30-300°C) (China); hot plate magnetic stirrer (China). 
2.2. Preparation 
2.2.1. Preparation TiOSO4 solution 
Titanium slag 85% was washed with distilled water, dried in heating oven and 
milled in mill ball machine until particles size was about bellow 0,149 mm (pass 
through 100 mesh sieve). Mixture of 10 g milled titanium slag (85%) and 70 g 
KHSO4 was calcined at 600
oC in two hours. After the calcination, the slag was 
leached in distilled water, filter insoluble precipitate and remove remained 
solution. An then insoluble solids were leached in H2SO4 10%. The leaching 
product solution was obtained. 
2.2.2. Preparation GNPs 
GNPs was synthesized by facile one pot method as described in [10]. Natural 
graphite flakes were washed with distilled water several times and dispersed 2g 
graphite flakes in concentrated sulphuric acid (98%). The mixture was stirred on 
magnetic stirrer and then 10g K2S2O8 was added. The reaction mixture was stirred 
continuously in three hours. After that the residue was filtrated, washed with 
distilled water several times, finally washed with acetone one time and dried at 
90oC in two hours in heating oven. 
2.2.3. Preparation TiO2/GNPs 
* Sample M1 
50 ml ethanol and 0.05 g GNP was added to 50 ml TiOSO4 solution. The 
mixture was then ultrasonicated for 30 minutes at 46oC and stirred for 30 minutes. 
On the flowing step, 40 ml of a 2 M NaOH solution was slowly added to the 
reaction mixture under stirring. The stirring was continued for 30 minutes. The 
resulting mixture was transferred to an autoclave. Set temperature for heating oven 
at 150oC for 2 hours. The precipitate was washed with distilled water and absolute 
ethanol then dried at 60oC for 2 hours. 
* Sample M2 
Sample M2 was prepared via same process performed on Sample M1 except the 
presence of 2M NaOH solution. 
2.3. Material characterization 
The chemical composition of the material was characterized by Energy-
dispersive X-ray (EDX) spectrometry on Hitachi S-4800. The morphology of the 
material was characterized by scanning electron microscope (SEM; Hitachi S-
4600) and transmission electron microscope (TEM; EMLab NIHE). The specific 
surface areas were measured by nitrogen sorption experiments based on BET 
equation on equipment TriStar II 3020 Version 3.02. The phase transitions and 
crystal structure of as-prepared materials were studied by the X-ray diffraction 
(XRD) method with the X'Pert Pro instrument using Cu Kα-radiation. The tests 
were conducted by the stepwise method (of 0.5 step degree), X-ray source 
voltage of 40 kV and electron beam current of 100 mA with scanning angle 2θ 
from 5 to 90o. Raman scattering measurements were performed at room 
Chemistry & Environment 
T.N. Tuan, N.T.H. Phuong, T.V. Chinh, “Synthesis of TiO2  environmental treatment.” 108 
temperature on micro-Raman system using Renishaw Invia spectrometer. The 
Raman spectra were excited with the 633 nm of the He-Ne laser operating at low 
incident power in order to avoid sample heating. Ultraviolet-visible (UV-vis) 
spectra of the specimens (Model V-670, Jasco) were obtained using the diffuse 
reflectance (DR) technique in the range of 200 to 2500 nm using a BaSO4 plate 
as the reflectance standard. 
3. RESULTS AND DISCUSSION 
The morphology of the TiO2/GNPs material was characterized by scanning 
electron microscope (SEM) and transmission electron microscope (TEM) with 
images showed in Figure 1. It can be clearly seen that the obtained GNPs have the 
multilayers structure with thin overlapping sheets which had a diameter of tens of 
microns. TEM images also show the uniform nano-sized TiO2 particles were 
distributed over the surface of GNPs sheets 
Figure 1. SEM and TEM images of TiO2/GNPs M1 sample (a, b) and of M2 
sample (c, d). 
The chemical composition of the material was characterized by Energy-
dispersive X-ray (EDX) spectrometry. The results obtained in Table 1 below show 
that this material is a combination of narrow multilayer graphene that is 
represented by the element C in the chemical composition along with the presence 
of oxygen and titanium elements. The absence of other elments in as-prepared is 
the result of the removing impurity completely. 
a 
b 
c 
d 
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Journal of Military Science and Technology, Special Issue, No.57A, 11 - 2018 109
Table 1. Chemical composition of the TiO2/GNPs composite material. 
X-ray diffraction (XRD) measurements were applied to investigate the 
crystallographic structure of the as prepared materials. The XRD patterns of GNPs 
and TiO2/GNPs (M1 and M2) are shown in Fig. 2. M2's patterns all exhibit peaks 
at 25.35°, 38.15°, 47.95° and 54.35°, corresponding to the (101), (004), (200) and 
(105) planes of the anatase phase. XRD Patterns of GNPs and once of M2 had a 
peak which ovelap peak at 26,65o of graphite corresponding to (002) plane but 
intensity of the peak different between the materials. Absence of peaks in M1's 
patterns that indicated amorphous structure of TiO2/GNPs. And Peak (002) plane 
of graphitic structure was also disappeared because content of Ti in M1 was higher 
content of C. Calculated size of TiO2 particles in M2 sample according to the 
Debye Scherrer equation was about 16,4 nm. 
Figure 2. The XRD patterns of the Graphite, GNPs and TiO2/GNPs (M1 and M2). 
The surface area of GNPs and TiO2/GNPs materials which was measured by 
nitrogen sorption experiments in the pressure range of 0.080 to 0.292 at and at 
77.3oK based on BET equation was showed in table 2. With these value, we can 
see that the surface area and the ability to expose to adsorption object of 
TiO2/GNPs materials increased compared to GNPs and pure TiO2. Thus, the 
presence of nanoscale TiO2 particles on GNPs surface made the increase of 
Elements 
GNPs M1 M2 
Wt% At% Wt% At% Wt% At% 
C 82.57 87.05 26.74 41.16 28.94 44.22 
O 15.28 12.1 39.16 45.25 36.84 42.27 
S 2.15 0.85 2.22 1.28 2.11 1.21 
Ti 31.87 12.30 32.11 12.30 
Total 100 100 100 100 100 100 
Chemistry & Environment 
T.N. Tuan, N.T.H. Phuong, T.V. Chinh, “Synthesis of TiO2  environmental treatment.” 110 
capability of as-prepared TiO2/GNPs materials. However, surface area of M1 was 
higher than M2 which could cause the difference on crystallographic structure 
between M1 and M2. 
Table 2. BET surface area, pore size and pore volume. 
 BET Surface Area (m2/g) 
Pore volume 
(cm3/g) 
Pore size (nm) 
GNPs 119.9 0.051 2.165 
M1 198.6 0.086 2.19 
M2 160.1 0.112 2.40 
Fig. 3 shows the [F(R)hν]1/2 plot for indirect transition corresponding to 
anatase structure. The Kubelka-Munk function F(R) is equivalent to absorbance in 
these UV-Vis DRS spectra and hν is the photon energy, hν = (1239/λ) eV, where λ 
is the wavelength in nm. The value of hν extrapolated to F(R)hν = 0, which gives 
an absorption energy, corresponds to a band gap Ebg [12]. It could see that Ebg of 
M1 (2,85 eV) reduced more than that of M2 (2,95 eV) and energy band gap of two 
TiO2/GNPs materials was both lower than TiO2. Thus TiO2/GNPs materials could 
have photo activity in VIS and shift their optical absorption edge from UV into 
visible light range. 
Figure 3. UV-VIS Diffuse Reflectance of the TiO2/GNPs materials. 
4. CONCLUSIONS 
The TiO2/GNPs composite was successfully synthesized by hydrothermal 
method from titanium slag and natural graphite. TiO2 particle with nanoscale size 
(16 nm with M2) was disturbed uniformity on GNPs surface. The morphology of 
TiO2 particle, energy band gap, BET surface area of titanium dioxide on the 
graphene nanoplatelets composite depend on pH value of prepared medium. BET 
surface area of as-prepared materials were determined to be 198.6 m²/g (M1) and 
160.1 m²/g (M2) while their Ebg were 2,85 ev (M1) and 2,95 eV (M2). the results 
of this study, this TiO2/GNPs composite is promising in the field of environmental 
treatment in practice as photo catalyst in VIS. 
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Journal of Military Science and Technology, Special Issue, No.57A, 11 - 2018 111
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TÓM TẮT 
TỔNG HỢP VẬT LIÊU TỔ HỢP TIO2 - GRAPHENE NANOPLATELETS 
(TIO2/GNPs) TỪ ILMENITE VÀ GRAPHIT TỰ NHIÊN LÀM XÚC TÁC 
QUANG TRONG XỬ LÝ MÔI TRƯỜNG 
Trong nghiên cứu này, vật liệu tổ hợp oxit titan/graphene nanoplatelets 
(TiO2/GNPs) được tổng hợp từ các tiền chất ilmenite và graphit tự nhiên dạng phiến 
với sự khác nhau về giá trị độ pH của môi trường tổng hợp. Các vật liệu tổ hợp đã 
tổng hợp được xác định các đặc trưng thông qua các phương pháp như XRD, SEM, 
TEM, kỹ thuật BET và phổ UV-VIS phản xạ khuếch tán. Vật liệu tổ hợp TiO2/GNP 
gồm các hạt có kích thước nano (khoảng 16 nm), có diện tích bề mặt 196,8 m2/g 
(M1) và 160,1 m2/g (M2), có hoạt tính quang trong vùng ánh sáng khả kiến. 
Từ khóa: Graphene nanoplatelets (GNPs); Vật liệu tổ hợp TiO2/GNPs; Xúc tác quang; Graphite flakes. 
Received 19th April 2018 
Revised 22th June 2018 
Accepted 18th October 2018 
Author affiliations: Academy of Military Science and Technology; 
 *Corresponding author: ngoctuan109@gmail.com.