Abstract. In this article, we present a process to synthesize new material using urea
modified nitrogen TiO2 nano using the hydrometallurgical method. A solution that was a
mixture of TiCl4, (NH2)2CO, NH4NO3 and PVA was hydrolyzed at a „suitable‟
temperature and stirring speed and then calcined at 600 oC in 3 hours. The obtained
product has the diameter in range 20 - 30 nm nanometers, and the organic removal
efficiency of this material is high. Using about 30 minutes of sunlight, the COD value at
the inflow was about 300 - 500 mg/L while at the outflow it was 0 mg/L, and the bacteria
in the outflow was 20 CFU/100mL. Covering TiO2 nano on laterite saved in material,
also save amount of money needed to separate the material from water.
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JOURNAL OF SCIENCE OF HNUE DOI: 10.18173/2354-1059.2015-00082
Chemical and Biological Sci. 2015, Vol. 60, No. 9, pp. 83-90
This paper is available online at
Received October 16, 2015. Accepted December 30, 2015.
Contact Tran Thi Hong Van, e-mail address: hongvan0505@yahoo.com
83
CREATING NITROGEN MODIFIED TiO2 NANO MATERIAL BY UREA
COVERED ON LATERITE IN ORDER TO TREAT ORGANIC COMPOUNDS
AND BACTERIA IN BIOLOGICAL TREATMENT SYSTEM OUTFLOW
Nguyen Hoang Nam1, Nguyen Hoang Hiep2, Tran Thi Hong Van3
and Nguyen Thi Thanh Huong4
1
Faculty of Environment, Hanoi University of Mining and Geology
2
Department of Environment, Tampere University Finland
3
Faculty of Chemistry, Hanoi National University of Education
4
Faculty of Chemistry, Military Medical University
Abstract. In this article, we present a process to synthesize new material using urea
modified nitrogen TiO2 nano using the hydrometallurgical method. A solution that was a
mixture of TiCl4, (NH2)2CO, NH4NO3 and PVA was hydrolyzed at a „suitable‟
temperature and stirring speed and then calcined at 600 oC in 3 hours. The obtained
product has the diameter in range 20 - 30 nm nanometers, and the organic removal
efficiency of this material is high. Using about 30 minutes of sunlight, the COD value at
the inflow was about 300 - 500 mg/L while at the outflow it was 0 mg/L, and the bacteria
in the outflow was 20 CFU/100mL. Covering TiO2 nano on laterite saved in material,
also save amount of money needed to separate the material from water.
Keywords: TiO2 nano, urea, treat, COD, organic compound.
1. Introduction
Organic pollutants in water is a major problem in Vietnam and elsewhere around the
globe. A variety of organic treatment methods have been provided and chemical, biological
and physical methods have been used in waste treatment. Choice of method depends on
factors such as flow rate, degree of contamination, weather conditions, economical feasibility,
availability of treatment materials and the object to be treated.
Nguyen Hoang Nam, Nguyen Hoang Hiep, Tran Thi Hong Van d Nguyen Thi Thanh Huong
84
Nowadays, nanotechnologies are commonly applied to treat water containing organic
compounds because they are economically beneficial and environmentally friendly. However,
an adequate amount of light is required for photochemical reactions to occur efficiently,
effectively and economically. Starting from above demand, it appear: TiO2 is a s miconductor
material, has wide forbidden zone. Pure TiO2 is effective only in the ultraviolet zone of < 380
nm. Ultraviolet radiation portion from the sun to earth's surface only account for nearly 4% so
using this radiation for environmental treatment and TiO2 c talyst purposes is reduced.
Therefore, to use sun radiation in visible light zone in photo-catalyst reaction require reducing
forbidden zone energy of TiO2. Previously, a good deal of research has been done on
modifying TiO2 such as using Cr, Zretc., especially modify by nitrogen to new structure
which achieve higher photo-catalysi ability [1]. In the presence of sunlight, TiO2 nano
becomes a stronger oxidizer, 1.5 times stronger than O3 and twice that of Cl2, two of the most
common substances used in environmental treatment. TiO2 nano can decompose sustainable
organic compounds and highly toxic such as such as dioxin and benzene, as well as some
viruses and disease microorganisms, more efficiently than others methods [2].
Thus, to recover catalyst materials economically, the catalyst must remain on a carrier
which has a large surface area such as active carbon, crystal, silica gel, polymer materials,
zeolite, cotton and cellulose.
* Reaction mechanism
Heterogeneous photo-catalysis process can occurs in gas phase or liquid phase. Similar to
other heterogeneous catalyst processes, the heterogeneous photo-catalysis process is divided
in 6 steps:
- Diffuse react substances from liquid or gas phase to catalyst surface.
- Absorb react substances on catalyst surface.
- Adsorb light photons, moleculesshift from basic stage to electron stimulation stage.
- Photochemical reaction.
- Desorb products.
- Defuse products into gas or liquid phase.
* Conditions for a substance to have photo-catalysis ability
- Having photo-activity.
- Having suitable forbidden zone energy to adsorb ultraviolet or visible ight.
hυ + (SC) → e- + h+
A(ads) + e
-
→ A- (ads)D(ads) + h+ → D+ (ads)
Ion A- (ads) and D+ (ads) after formed will react together through a series of
mediatereactions and then form the final products.
Figure 1. Photochemical reaction mechanism [5]
Creating nitrogen modified TiO2 nano material by urea covered on laterite in order to treat...
85
Therefore, the photons adsorption process is the beginning step for the whole reaction
series. In the photo-catalysis process, quantum efficiency can be reduced by the
recombination of electrons and holes.
e
-
+ h
+
→ (SC) + E
In which (SC) is neutralizing semiconductor center and E is the energy released in the
form of electromagnet radiation ( hυ’ ≤ hυ ) or heat.
In the presence of light, TiO2 nano become hydrophobic or hydrophilic depending on
manufacture technology. This ability is applied to create self-cleaning without chemical
compound surface and mechanical impact or freezing device without electricity. The powerful
photo-catalysis ability of TiO2 nano remains being researched and applied in fuel battery and
treating CO2 causing greenhouse effect.
TiO2 nano operates in the catalysis mechanism so it doesn't reduce, meaning its use
involves a once time investment and long term use.
2. Content
2.1. Materials and methods
* Chemicals
PVA, (NH2)2CO, NH4NO3, TiCl4, NH2OH.HCl, C2H5OH, methylene blue: produced by
Merck Germany.
Triple times distilled water: Produced in our laboratory.
Dispense TiCl4 3M (produced by mixing TiCl4 in cold water then diluting it to a 0.5 M
solution by adding cold water).
* Analytical methods
Instruments used to perform the experiments were:
- COD was determined with Optizen 2120 UV/Shimadzu.
- Nano particle size was determined using a Scanning Electron Microscope (SEM) Jeol
5410 LV produced in Japan and TEM LIBRA120 produced in Germany.
- Drying cabinet (produced in Germany), ove (Carbolite model AAF-11/7 produced in
England).
- Ultra-distilled water
* Produce TiO2 nano
TiO2 nano production
- Mix chemicals in exact volume ratio then stir, heatìg it to 70 oC in 24 hours.
- Then raise the temperature to 90 oC in 12 hours.
- Dry at 120 oC in 12 hours.
- Calcine at 250 oC in 8 hours.
- Calcine at 600 oC in 3 hours.
* Cover TiO2 material on laterite carrier
The process of covering material on laterite occurs in the steps below:
First, calcine crushed laterite and sieve to a particle diameter of 1mm at 1000 oC over 3
hours with a heat acceleration velocity of 10 oC/min.
After that, wash it with 1 time distilled water till clear, then continue to wash with triple
distilled water. Dry at 120 oC in 8 hours.
Produce solgel solution add to la erite and continue to stir using a stirrer with wings, keep
at 90 oC for 24 hours.
Dry products, combust solgel at 250 oC, continue to calcine at 600 oC over 3 hours with a
heat acceleration rateof 10 oC/min.
Nguyen Hoang Nam, Nguyen Hoang Hiep, Tran Thi Hong Van d Nguyen Thi Thanh Huong
86
* Testing material activity
Photo-activity
To ensure that these materials have photochemical ability require testing their photo-
activity property using methylene blue.
The steps:
- Add 100 mL standard methylene blu to 0.1 g material.
- Test ability to remove material in the sunlight, ultraviolet and dark.
- Sampling times are: 30', 60‟, 90‟, 120‟, 150´, 180'.
- Measure optical absorption of methylene blue at a wavelength of 664 nm
2.2. Resuls and discussion
2.2.1. Produce TiO2 nano
The preparation nano TiO2 was conducted according to the composition and volume ratio
of the material is shown in Table 1.
Table 1. Composition and volume rate of substances for the preparation of nano-TiO2
PVA (4%) TiCl4 (0.5M) (NH2)2CO
(1M)
NH4NO3(1M)
180 60 450 60
Faculty of Chemistry, HUS, VNU, D8 ADVANCE-Bruker - Sample TiO2
01-078-2486 (C) - Anatase, syn - TiO2 - Y: 95.69 % - d x by: 1. - WL: 1.5406 - Tetragonal - a 3.78450 - b 3.78450 - c 9.51430 - alpha 90.000 - beta 90.000 - gamma 90.000 - Body-centered - I41/amd (141) -
1)
File: Dung mau TiO2.raw - Type: 2Th/Th locked - Start: 20.000 ° - End: 70.010 ° - Step: 0.030 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 17 s - 2-Theta: 20.000 ° - Theta: 10.000 ° - Chi: 0.00 ° -
Left Angle: 24.200 ° - Right Angle: 26.660 ° - Left Int.: 27.4 Cps - Right Int.: 25.6 Cps - Obs. Max: 25.314 ° - d (Obs. Max): 3.516 - Max Int.: 394 Cps - Net Height: 368 Cps - FWHM: 0.423 ° - Chord Mid.: 2
Lin
(C
ps
)
0
100
200
300
400
500
2-Theta - Scale
20 30 40 50 60 70
d=
3.
51
5
d=
2.
43
0
d=
2.
37
6
d=
2.
33
2
d=
1.
89
1
d=
1.
69
9
d=
1.
66
8
d=
1.
48
1
d=
1.
36
5
Figure 2. Schematic X-ray of nano TiO2
Schematic X-ray diffraction (XRD) showed that the peaks are sharp demonstrate the
material's purity TiO2 modulation is high. The characteristic peak structure in the form of
Anatase TiO2 at positions 2θ = 25.3º, 37.8º, 48º, 53.90º, 55º, 62.52º appear. Thus, in the form
of Anatase TiO2 structure was confirmed.
After modulation, pictures were taken of produced materials SEM and TEM.
Results from SEM and TEM images have illustrated that the size of he TiO2 particles is
to nano size which is approximately 20 - 30 nm. Mechanisms that proceeded material
modulation are: at from 70 to 90 oC, urea is hydrolyzed gradually to form NH3 and CO2, NH3
continues to be hydrolyzed to form NH4
+ and OH-, providing OH- for Ti4+ precipitation
process to form Ti(OH)4. The gradual hydrolysisofurea have created suitable condition for
hydroxide precipitation to have tiny particles and avoid to be localized precipitation.
Creating nitrogen modified TiO2 nano material by urea covered on laterite in order to treat...
87
Figure 3. SEM image of TiO2 prepared by solgel method
Figure 4. TEM image of TiO2 prepared by solgel method
Polyvinyl alcohol (PVA) is u ed to reduce localized titanium hydroxide particles. In a
solution containing Ti4+ and PVA it occurs reaction that creates complex of Ti4+ ions with
OH- in polymer network. Ti4+ ions break the space circuit in theorganic polymer. When
particles reach the limit stage, very small titaniumoxide particles are formed beside network [3].
Ammonia and nitrate ions were taken to system which play the role of avoiding
flocculation, simultaneously modifying material [4].
According to results of Luu Minh Dai, calcination temperature of 600 oC and a retention
time of 3 hours would be most efficient. With longer calcination times, the materials‟ particle
structure will alter unexpectedly [4].
2.2.2. Photochemical ability of TiO2 nano
The test of photo-catalysis activity of material is very important because it decides
whether the material have the ability to provide electrons and holes in the presence of light.
Table 2. Results of testing the photo-activity of TiO2 using methylene blue
Sample/Time (min) 30 60 90 120
Efficiency (%) 34.7% 62.6% 86.6% 97.0%
Nguyen Hoang Nam, Nguyen Hoang Hiep, Tran Thi Hong Van d Nguyen Thi Thanh Huong
88
Results have shown that photochemical ability of the material is highly effected and
reached an efficiency of 97% after 120 minutes. This means that when TiO2 is n a material, it
can become a photo-catalyst. The processes occurs as presented below [2, 5]:
TiO2 + hv → TiO2 (h
+ + e-)
TiO2(h
+) + H2O →
∙OH + H+ + TiO2
TiO2(h
+) + OH- →∙OH + TiO2
TiO2 (h
+) + R → R∙ + TiO2
TiO2(e
-) + O2 → O
2-∙ + TiO2
TiO2(e
-) + H2O2 → OH
- + ∙OH + TiO2
O2-∙ + H+ → HO2∙
HO2
∙ → O2 + H2O2
H2O2 + O2 → O2 + OH
- + ∙OH
These activated products have strong oxidizing properties, oxidizing organic compounds
to CO2 and H2O. The results above confirm that TiO2 nano modulated have very good
photochemical ability.
2.2.3. Efficiency of COD removal by laterite and laterite covered by TiO2
Research on COD removal efficiency has been done using as a sample the outflow of a
system's filtration columns on two materials: treated laterite and laterite covered by TiO2
under various conditions. Next, testing is done to determine whether it was organic
compounds and microorganisms that were absorbed or removed.
Figure 5 indicates the results of COD removal on laterite and laterite covered by TiO2 in
dark, sunlight and ultraviolet light conditions.
The results illustrate that the amount of COD at the inflow is 180 mg, and after 1 hour of
treatment, COD removal by TiO2 material in the presence of sunlight is most efficient.
Outflow is at only 20 mg. Meanwhile, in the presence of ultraviolet light, the amount of
outflow COD is at 120 mg, and in dark conditions reached 60 mg. As the retention time
increased to 2 hours, it was found that in sunlight as well as ultraviolet light, the amount of
COD was insignificant. Results also indicate that even in dark condition, TiO2 material can
absorb organic compound very well after 2.5 hours.
Figure 5. COD removal in various conditions
Creating nitrogen modified TiO2 nano material by urea covered on laterite in order to treat...
89
Compared to just laterite, in similar conditions and amount of time, their removal
efficiency is lower (Figure 5). However, laterite absorption ability was significant and it can
remove COD complete y after 3 hours under all research conditions.
As we can see, nitrogen modified TiO2 material covered on laterite shows absorption
ability and it can remove organic compounds through photochemical reaction. Therefore, this
material is highly efficiency in organic removal in a short retention time.
2.2.4. Bacteria removal efficiency by laterite and laterite covered by TiO2
Research has been done on bacteria removal efficiency using samples from the outflow
of a filter column in a treatment system on laterite covered by TiO2 in various conditions.
Figure 6 illustrates the results of bacteria removal by laterite covered by TiO2 nano in
conditions of darkness, natural light and ultraviolet light.
Research has indicated that the amount of coliform bacteria in the inflow s 350 mg and,
after 1 hour of treatment, the removal efficiency of sunlight and ultraviolet light are relatively
high with an outflow of 70 microorganisms/100 mL. Meanwhile, the amount of bacteria is
150 individuals/100 mL. As the retention time extends to 2 hours, it was found that in the
presence of sunlight or ultraviolet light, the amount of bacteria in the outflow was about 40
individuals/100 mL. Results also indicate that TiO2 material has the ability to absorb bacteria
very well after 2 hours.
Figure 6. Bacteria removal process in various conditions
As can be seen, nitrogen modified TiO2 material covered on laterite, besides having
absorption ability, can remove bacteria through photochemical reactions. Therefore, this
material provides highly efficient bacteria removal even with a short retention time and can be
useful for domestic water regulation.
3. Conclusion
Nitrogen modified TiO2 material covered on laterite is a new photo-catalyst material that
can be used in visible light effecively and can efficiently treat organic compounds as well as
bacteria. Saving material and without centrifugalization to separate materials after treatment,
money is saved in the treatment processes.
Acknowledgment. This work was funded by the German Federal Ministry of Education and
Research (BMBF), grant number 02WB0957 and 02WB0958. The authors would like to
thank P. Kuschk, J. Richter, K. Puschendorf, C. Pietsch, I. Mäusezahl, J. Mattusch, J. Steffen,
and U. Kappelmeyer for their technical assistance and support.
Nguyen Hoang Nam, Nguyen Hoang Hiep, Tran Thi Hong Van d Nguyen Thi Thanh Huong
90
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