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CHEMICAL ENGINEERING TRANSACTIONS
VOL. 43, 2015
A publication of
The Italian Association
of Chemical Engineering
Online at www.aidic.it/cet
Chief Editors: Sauro Pierucci, Jiří J. Klemeš
Copyright © 2015, AIDIC Servizi S.r.l.,
ISBN 978-88-95608-34-1; ISSN 2283-9216
A Novel Approach for the Production of Nitrogen Doped TiO2
Nanoparticles
Yana Ruzmanova, Marco Stoller*, Marco Bravi, Angelo Chianese
Sapienza University of Rome, via Eudossiana 18, 00184, Rome
marco.stoller@uniroma1.it
In this study a visible light active nitrogen doped nanostructure titanium dioxide was synthesized by a simple
mixing of Degussa P25 and Urea powder and further thermal treatment under the adequate conditions.
Photocatalytic activity of produced nanoparticles was verified by providing of photocatalytic degradation of
phenol aqueous solution. Mainly this work was focused on the investigation of the following effects: urea
concentration, temperature treatment, catalyst loading and initial phenol concentration. Kinetics study was
also carried out. The approach appears to be successful and may be applied for example during the
photocatalytic treatment of wastewater streams without or with a limited aid of UV lamps.
1. Introduction
In recent years humanity has faced a number of critical environmental problems among which the shortage of
drinking water in many parts of the world. According to the United Nations report (The United Nations World
Water Development Report 4: Managing Water under Uncertainty and Risk, Vol. 1, 2012) “Around 700
million people in 43 countries suffer today from water scarcity and by 2025, 1.8 billion people will be living in
countries or regions with absolute water scarcity, and two-thirds of the world's population could be living under
water stressed conditions”. In search of an optimal solution of water pollution problem scientists have drawn
attention to the heterogeneous photocatalysis because of its great potential to remove aqueous and air
pollutants through complete mineralization. Among the known semiconductor photocatalysts titanium dioxide
is the most widely used due to its high photocatalytic activity, chemical stability and low cost. Technologies for
the synthesis of photocatalysts for industrial production already exist, by bottom-up approaches of core-shell-
shell nanoparticles (Ruzmanova et al., 2013a), doped titania nanoparticles (Ruzmanova et al., 2013b) or
undoped titania (Vaiano et al., 2014). As well, top-down approaches exists such as the commercial Degussa
P25. In many wastewater treatment processes, such as those already adopted in the agricultural (Ochando et
al., 2014), textile (Stoller et al., 2011) and tannery industries, photocatalysis may be used successfully to aid
the purification by means of biotechnology (Cicci et al., 2013), NF (Stoller et al., 2014) or RO (Ochando and
Stoller, 2014) membrane processes. Nevertheless there are a number of technological problems concerned
with the industrial-scale using of TiO2. For example, TiO2 (anatase) has a relatively wide band gap 3.2 eV,
therefore it can be excited only by UV light which is quite expensive and requires the use of special protective
measures. This leads to high operating costs, which affects sensibly the total treatment costs.
In this study a visible light active nitrogen doped nanostructure titanium dioxide was synthesized and
photocatalytic activity of produced nanoparticles was verified by providing of photocatalytic test in liquid phase.
Phenol aqueous solution was adopted as a pollutant model. Commercial photocatalyst Degussa P25 was
used as a base of doped nanoparticles. Urea was used as a precursor of nitrogen. The doping process
suggested by Nawawi (Nawawi and Nawi, 2014) was adopted in this work.
DOI: 10.3303/CET1543121
Please cite this article as: Ruzmanova Y., Stoller M., Bravi M., Chianese A., 2015, A novel approach for the production of nitrogen doped tio2
nanoparticles, Chemical Engineering Transactions, 43, 721-726 DOI: 10.3303/CET1543121
721
2. Experimental procedure
2.1 Materials
The chemicals used in this work are reported in Table 1.
Table 1: Chemicals used in the N-TiO2 preparation procedure and photocatalitic degradation of phenol
Chemical Formula Purity
Degussa P25 TiO2 Anatase – 70%
Rutile – 30 %
Urea NH2CONH2
Hydrochloric acid HCl 38%
Phenol C6H6 87%
2.2 Photocatalyst synthesis
3 g of commercial TiO2 Degussa P25 was mixed with 0.5, 1, 1.5, 2 g of urea powder by mechanical mixing. In
order to achieve homogeneity stirring lasts for 20 min. After this period of time, every sample was divided in
four equal parts, which were calcinated under at atmospheric pressure for 2 h at 300, 350, 400 and 450 °C,
respectively. After the thermal treatment the samples were cooled down to ambient temperature and treated
by ultrasound in a 0.1 N HCl solution to eliminate possible impurities. Finally, the samples were washed with
distilled water and centrifuged. The so obtained yellow coloured precipitate was dried at 85 °C.
2.3 Phenol degradation mechanism
The main reaction site for the elimination of phenol is the bulk liquid, where the attack of hydroxyl radicals on
the ring carbons results in various oxidation intermediates. Among them the most numerous are
hydroquinone, catechol, and p-benzoquinone. The secondary products like chloro-hydroquinone, 4-
chlorocatechol and resorcinol are eventually converted to acetylene, maleic acid, carbon monoxide and
carbon dioxide (Ahmet, 2010). Figure 1 shows the degradation mechanism of phenol.
Figure 1: Mechanism for the degradation of phenol (Sivalingam, 2004)
3. Results and discussion
3.1 Effect of urea concentration
In order to study the effect of dopant precursor concentration N-TiO2 nanoparticles with different amount of
urea were prepared. The result is shown in Figure 2. It was found that 1 g of urea was the optimal
concentration to use. Both increasing and decreasing the dopant precursor amount a reduction of the
photocatalytic activity of the catalyst was observed.
3.2 Effect of temperature treatment
In order to determine an optimal temperature for N-TiO2 nanoparticles, thermal treatment samples with various
amount of urea were calcined at 300, 350, 400, 450 °C. Figure 3 shows the result of photocatalytic
degradation of 12 ppm phenol aqueous solution assisted by N-TiO2 calcined at different temperatures.
Photocatalyst calcined at 350 °C shows much higher activity if compared to the other samples. The worst
result were achieved by the N-TiO2 calcined at 300 °C. This may be justified by the low calcination
temperature (300°C) that appears to not be sufficient for a correct anatase crystalline structure formation.
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Figure 2: Effect of urea concentration`(catalyst – N-TiO2 [calcination at 350 °C], phenol initial concentration –
12 ppm, phenol volume – 200 mL, pH of solution – 6.8, irradiation – 140 W visible light lamp, irradiation time –
90 min)
Figure 3: Effect of N-TiO2 thermal treatment in the photocatalytic degradation of phenol (catalyst – N-TiO2 (1g
of urea), phenol initial concentration – 12 ppm, phenol volume – 200 mL, pH of solution – 6.8, irradiation – 140
W visible light lamp, irradiation time – 90 min)
3.3 Effect of initial catalyst loading
Chapter 2 Efficiency of the photocatalytic degradation process strongly depends on the loading of the catalyst.
This parameter can be considered as one of the key factors influencing the reaction kinetics. In this work, an
optimal catalyst loading of 1 g/L was determined experimentally. For this purpose, the photocatalytic tests with
0.5, 1 and 1.5 g/L of N-TiO2 were reported. Figure 4 visibly shows that 0.5 g/L are not a sufficient loading for
the maximum efficiency of 12 ppm phenol degradation. Increasing of the catalyst loading to 1 g/L significantly
increases the reaction rate. But a further enhancement of N-TiO2 leads to the decreasing of phenol
degradation efficiency. This can be justified by the contrasting effects of catalyst addition: promotion,
enhanced catalytical activity, and demotion, limited light penetration (Zulfacar, 2011). Nanoparticles create the
effect of shielding hiding each other from the light flux and thus decreasing the effective light irradiation that
reaches TiO2 active sites.
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Figure 4: Effect of N-TiO2 loading in the photocatalytic degradation of phenol (catalyst – N-TiO2 (1g of urea,
calcination 350 °C), phenol initial concentration – 10 ppm, phenol volume – 200 mL, pH of solution – 6.8,
irradiation – 140 W visible light lamp, irradiation time – 90 min)
3.4 Effect of initial phenol concentration
Photocatalytic degradation of 12, 50, and 100 ppm phenol aqueous solutions were assisted by 1g/L of N-TiO2
nanoparticles. The result is reported in Figure 5. The increasing of pollutant concentration in this case
decreases the efficiency of photocatalytic process. Excessively high concentration of organic compounds
leads to the saturation of the surface of titanium dioxide and decreases the absorption of photons by the photo
catalyst particles, which naturally reduces its activity or deactivates it (Chong, 2010).
Figure 5: Effect of initial pollutant concentration in the photocatalytic degradation of phenol (catalyst – N-TiO2
(1g of urea, calcination 350 °C), catalyst loading – 1 g/L, phenol volume – 200 mL, pH of solution – 6.8,
irradiation – 140 W visible light lamp, irradiation time – 90 min)
Phenol photocatalytic degradation can be considered as a pseudo-first order chemical reaction. All the kinetic
parameters are summarized in Table 2.
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Table 2: Kinetic parameters of phenol photocatalytic degradation assisted by N-TiO2 nanoparticles (in bold the
parameters that have been changed in the search for the optimal value)
TiO2,
g
Urea,
g
Thermal
treatment, °C
Phenol
concentration, ppm
Catalyst loading,
g/L k, min
-1 R2
3 2 350 12 1 0.0024 0.986
3 1.5 350 12 1 0.0034 0.987
3 0.5 350 12 1 0.0059 0.967
3 1 350 12 1 0.0066 0.976
3 1 300 12 1 0.0037 0.995
3 1 400 12 1 0.0049 0.991
3 1 450 12 1 0.0044 0.994
3 1 350 100 1 0.0016 0.985
3 1 350 50 1 0.0033 0.966
3 1 350 12 1 0.0066 0.976
3 1 350 12 0.5 0.002 0.988
3 1 350 12 1 0.0066 0.976
3 1 350 12 1.5 0.0053 0.991
Figure 6 shows a comparison between photolysis of phenol and photocatalysis assisted by N-TiO2
nanoparticles.
Figure 6: Comparison between photolysis of phenol and photocatalysis assisted by N-TiO2 nanoparticles
(catalyst – N-TiO2 (0.3 g of urea for 1 g of TiO2, calcination 350 °C), catalyst loading – 1 g/L, phenol volume –
200 ml, pH of solution – 6.8, irradiation – 140 W visible light lamp, irradiation time – 90 min)
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4. Conclusions
Chapter 4 In this study nitrogen doped titanium dioxide nanoparticles were synthesized by mechanical mixing
of Degussa P25 and urea powder followed by thermal treatment. The effect of urea concentration,
temperature of calcination, phenol initial concentration and catalyst loading were studied. The results showed
that increasing of initial pollutant concentration affect negatively on the photocatalysis efficiency. Excess
amount of catalyst decreases the light penetration which leads to the worse catalytic activity of nanoparticles.
Thermal treatment plays a key role in the formation of TiO2 crystalline structure that why it’s important to
determine an optimal calcination temperature. In this study the sufficient temperature was determined as 350
°C. Finally, the concentration of dopant precursor can strongly effect on the reaction rate. Degradation of
phenol was considered as a pseudo-first order reaction. The maximum efficiency 41 % of photocatalytic
degradation of 12 ppm phenol aqueous solution in 90 min was achieve under the optimal conditions: urea
concentration 0.3g for 1g of TiO2 calcinated at 350 °C for 2h, catalyst loading 1g/L.
Chapter 5 The use of doped titania nanocatalyst may be of importance to reduce the operating costs of
wastewater treatment processes.
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