Impact of Morphology and Nitrogen and Carbon Codoping on

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Impact of morphology and nitrogen and carbon co-doping on photocatalytic activity of TiO2 as environmental catalysts Saman Jafari, Mohammad Reza Mohammadi, and Hamid Reza Madaah Hosseini Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b03053 • Publication Date (Web): 07 Nov 2016 Downloaded from http://pubs.acs.org on November 7, 2016

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Industrial & Engineering Chemistry Research

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Impact of morphology and nitrogen and carbon co-doping on photocatalytic activity of TiO2 as environmental catalysts S. Jafari, M.R. Mohammadi *, H.R. Madaah Hosseini Department of Materials Science and Engineering, Sharif University of Technology, Azadi Street, Tehran, Iran * Corresponding author: E-mail: [email protected], Tel: +98 21 6616 5211

Abstract We present three different morphologies of TiO2 structures, namely nanoparticles, nanowires and dandelion-like particles, by wet chemistry routes as environmental catalysts for degradation of Methylene Blue. The band-gap energy of these morphologies is tuned by codoping with carbon and nitrogen atoms and controlling the synthesis processing parameters. The physical and chemical properties of the synthesized samples are characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), field emission electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The nanoparticles (15-40 nm) and nanowires (diameter of ~100 nm) have mainly anatase structure, whereas the dandelion-like particles (diameter of 15-20 µm) show rutile phase. The reduction percentage in band-gap energy of TiO2 is dependent upon its morphology, with the order of: nanoparticles ˃ nanowires ˃ dandelionlike particles, with the lowest value of 3.05 eV. The impact of TiO2 morphology, crystal structure, band-gap energy and carbon and nitrogen co-doping is studied on degradation of Methylene Blue under ultraviolet A (UVA) irradiation.

Keywords: Environmental catalysts; Carbon and nitrogen co-doped TiO2; Nanoparticle; Nanowire; Dandelion-like particle.

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1. Introduction TiO2 is an important semiconductor with mainly three allotropies, being anatase, rutile and brookite. It has widespread applications based on photocatalytic activities such as toxic gas removal1, organic compound degradation2, dye-sensitized solar cells3 and photodynamic therapy4. TiO2 shows higher photocatalytic activity than the other oxide semiconductors due to suitable band gap energy, cost effective and compatible with human body and environment.5 The main stream of the efforts on photocatalytic activity is focused on (1) improving specific surface area to increase the photocatalytic reaction sites6, (2) tuning the band gap energy by different means so that lower energy photons can excite the electrons from valance band to conduction band7 and (3) reduction of electron-hole recombination to enhance the efficiency of electron-hole creation.8 Therefore, different approaches have been made to enhance photocatalytic activity of TiO2 such as preparing a range of morphologies9,10; doping and co-doping with different elements11,12,13, compositing with various materials14, heat treatment in various atmospheres15, sensitizing with dye molecules16 and capping.17 Carbon and nitrogen co-doped TiO2 has been studied previously12. The doping of TiO2 with nonmetal elements has shown promising results and leads to higher photocatalytic activity. Such enhancement in photocatalytic property of TiO2 is higher for the atoms have radii similar to that of oxygen such as carbon and nitrogen.18,19 However, codoping of TiO2 with different elements shows an even higher efficiency as a photocatalyst due to a synergistic effect between different doping agents, as reported previously.20,21,22,23,24 So far controlling the processing parameters of synthesis method as well as the impact of doping on various morphologies has not been reported. TiO2 nanoparticles are generally prepared

by

different

methods

including

hydrothermal/solvothermal25,26,

sol-gel27

sputtering28, ultrasonic spray pyrolysis29, laser-assisted pyrolysis30, co-precipitation method31 and anodization.32 Sol-gel and hydrothermal routes offer important advantages over other



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techniques due to excellent compositional control, high homogeneity, low crystallisation temperature and controlling the morphology of the product. In the present work, we prepared three different morphologies of TiO2 structures (i.e., nanoparticles, nanowires and dandelion-like particles) in the forms of pure and carbon and nitrogen co-doped by a combination of sol-gel and hydrothermal methods. The effect of precursor contents and processing temperature on band-gap energy of synthesized morphologies were studied. One of the lowest band-gap energy of 3.05 eV was achieved by controlling the processing parameters. Furthermore, the impact of morphology and co-doping on the photocatalytic activity of the compounds was studied.

2. Experimental 2.1. Preparation of TiO2 nanoparticles TiO2 nanoparticles (NP) were prepared via sol-gel route based on the optimised methodology reported before.33 Titanium tetraisopropoxide (TTIP) (97%, Aldrich) was used as precursor; analytical grade hydrochloric acid (HCl) (37%, Merck) was used as a catalyst for the peptisation and deionised water was used as a dispersing media. Water-acid mixture was stabilised at a constant temperature together with continuous stirring. TTIP was added, forming a white thick precipitate, which gradually peptised after 2 h. The sol was dried at 60°C and annealed at 300°C to obtain TiO2 nanoparticles.

2.2. Preparation of C, N-doped TiO2 nanoparticles C and N co-doped TiO2 nanoparticles were synthesized by a modified hydrothermal method similar to the procedure reported previously.34 1-Butanol (99.5%, Merck) and ammonium hydroxide (32%, Merck) were used as carbon and nitrogen dopants, respectively. A mixture of 3 g TiO2 nanoparticles and carbon and nitrogen precursors with different ratios was


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transferred into a Teflon-lined stainless steel autoclave. The autoclave was heated at various temperatures for 4 h. The collected precipitates were then washed with dilute ethanol for three times and dried at 40°C. Table 1 shows details of the processing parameters of synthesized co-doped TiO2 nanoparticles.

Table 1. Synthesis parameters of C and N co-doped TiO2 nanoparticles by hydrothermal method. Sample NP10-10-100 NP12-10-100 NP14-10-100 NP10-12-100 NP10-14-100 NP10-10-140 NP10-10-180

Ammonium hydroxide (mL) 1-Butanol (mL) Synthesis temperature (°C) 10 12 14 10 10 10 10

10 10 10 12 14 10 10

100 100 100 100 100 140 180

2.3. Preparation of TiO2 nanowires TiO2 nanowires (W) were grown by a hydrothermal procedure according to an analogous procedure reported in the literature.35 The synthesized TiO2 nanoparticles and 10M NaOH solution (99%; Merck) were firstly mixed for 5 min under vigorous stirring and transferred into a Teflon-lined stainless steel autoclave. The autoclave was heated at 180°C for 48 h. The obtained powders were washed with deionized water four times, dried at 40°C and finally heat treated at 700°C for 1 h at air atmosphere.

2.4. Preparation of TiO2 dandelion-like particles TiO2 dandelion-like particles (D) were synthesized by a modified hydrothermal process based on our previous work.36 A mixture of TiCl4 (99%, Merck), HCl (37%, Merck) and deionized water was prepared. NaCl (99%, Merck) was added to the solution to control the pH with molar ratio of TiCl4:HCl:H2O:NaCl = 0.025:0.65:0.44: 0.053. The final solution was 4 ACS Paragon Plus Environment


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transferred into a Teflon-lined stainless steel autoclave. The autoclave was heated at 80°C for 3 h and at 180°C for 4 h. The collected precipitates were washed with ethanol two times, with deionized water three times and finally dried at 40°C.

2.5. Preparation of C and N co-doped TiO2 nanowires and dandelion-like particles The pure nanowires and dandelion-like particles were added to a mixture of 14 mL ammonium hydroxide and 10 mL 1-Butanol and then transferred into a Teflon-lined stainless steel autoclave. The autoclave was heated at 100°C for 4 h. The products were washed with ethanol and deionized water several times and then dried at 40°C.

2.6. Characterization and measurements The crystal structure and phase composition of samples were studied by XRD using A Stadi P, Cu-Kα radiation. The mass fraction of anatase (WA), rutile (WR) and brookite (WB) phases in the crystal lattice of the samples can be calculated based on the relationship among the integrated intensities of anatase (1 0 1), rutile (1 1 0) and brookite (1 2 1) peaks by the following equations:37 =

(Eq. 1)

=

=

(Eq. 2)

(Eq. 3)

where AA, AR and AB are the integrated peak intensities of the anatase (1 0 1), rutile (1 1 0) and brookite (1 2 1) peaks, respectively. and are two coefficients optimized by Gribb and Banfield38 and Zhang and Banfdield37 with values of = 0.886 and = 2.721. The average crystallite size of samples was calculated by Scherrer equation:39


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d=

kλ B cos θ

(Eq. 4)

where d is the crystallite size, k is a constant of 0.9, λ is the X-ray wavelength of Cu which is 1.5406 A°, θ is the Bragg angle in degree, and B is the full width at half maximum (FWHM) of the peak. The morphology of TiO2 samples was investigated by FE-SEM, MIRA III TESCAN. DRS measurements of the samples were recorded using an Avaspec-2048-TEC spectrometer. XPS, BESTEC and FTIR, ABB-Bomem were performed for doped samples.

2.7. Photocatalytic activity The photocatalytic activity of the samples for photo-degradation of Methylene Blue (MB, Chem-Lab) aqueous solution was carried out in a home-built reactor. Two Hitachi UVA lamps with power of 8 Watt and maximum peak at 369 nm were used as photon sources. The distance between lamps and sample was fixed 13 cm and the test was carried out in a container with 9 cm inside radius and the depth of the solution was 1.6 cm. For the measurements, 0.05 g of TiO2 powder was dispersed in 100 mL of MB solution with concentration of 10-5 M and stirred for 1 h. The absorbance spectrum was measured by a UV– vis spectrophotometer (6705 JENWAY).

3. Results and discussion 3.1. Crystal structure The band-gap energy and photocatalytic activity of TiO2 nanoparticles depend on their crystal structure. The effect of doping on crystal structure of nanoparticles was investigated by XRD analysis, as shown in Fig. 1. The phase of both pure and C and N co-doped TiO2 nanoparticles was a mixture of anatase and brookite phases. Table 2 shows the anatase and brookite percentages as well as the average crystallite size of the samples. As expected,



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NP10-10-180 showed the highest crystallite size and anatase content among all synthesized samples due to higher process temperature. Furthermore, a slight shift of the anatase structure for 2θ=25.3° (1 0 1) was observed for the co-doped TiO2 nanoparticles, as shown in Fig. 2. This can be related to smaller ionic radius of C4+ and N3+ (i.e., 30 picometer) than O2- (126 picometer) and Ti (74.5 picometer).

Fig. 1. XRD patterns of synthesized pure and C and N co-doped TiO2 nanoparticles (A: anatase and B: brookite).

Table 2. The average crystallite size and phase composition of pure and C and N co-doped TiO2 nanoparticle. Sample Crystallite size (Ȧ) Anatase (%) Brookite (%) TiO2 57 77 33 NP14-10-100 56 77 33 NP10-14-100 55 76 34 NP10-10-180 66 79 31

Fig. 2. Comparison of the strongest peak of the anatase at 2θ=25.3° for synthesized pure and C and N codoped TiO2 nanoparticles.

XRD patterns of pure and C and N co-doped TiO2 nanowires and dandelion-like particles are shown in Figs. 3 and 4, respectively. It is clear that TiO2 nanowires contain a mixture of anatase and rutile structures with dominant anatase (i.e., 96%), whereas TiO2 dandelion-like particles have a mixture of anatase and rutile structures with dominant rutile (i.e., 97%). Moreover, co-doped nanowires show smaller crystallite size than pure nanowires and no significant change in crystallite size of pure and co-doped dandelion-like particles was observed.

Fig. 3. XRD patterns of pure and C and N co-doped TiO2 nanowires (A: anatase and R: rutile).


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Fig. 4. XRD patterns of pure and C and N co-doped TiO2 dandelion-like particles.

3.2. DRS analysis The band-gap energies (Eg) of synthesized samples were calculated using DRS analysis using Kubelka-Munk function and Tauc plot (Fig. 5). Table 3 lists the Eg of pure and C and N co-doped TiO2 with various morphologies. Eg of pure TiO2 nanoparticles (i.e., 3.17 eV) was decreased with increasing dopant concentration and process temperature, reaching the lowest value of 3.05 eV for NP10-10-180 and NP14-10-100. It is evident that nitrogen had more impact on Eg of nanoparticles than carbon (compare NP10-14-100 and NP14-10-100 samples), as reported previously.40 The higher process temperature the easier diffusion of the dopants and, therefore, the lower the band-gap energy of nanoparticles.

Fig. 5. Tauc plot of TiO2 nanoparticles derived from DRS analysis.

Table 3. Eg of pure and C and N co-doped TiO2 compounds with various morphologies. Sample Morphology Eg (eV) TiO2 3.17 NP10-10-100 3.15 NP12-10-100 3.10 NP14-10-100 3.05 nanoparticle NP10-12-100 3.09 NP10-14-100 3.08 NP10-10-140 3.09 NP10-10-180 3.05 W 3.13 nanowire DW 3.05 D dandelion-like 3.07 particle DD 3.05

Eg of pure nanowires was decreased as a result of carbon and nitrogen doping from 3.13 eV to 3.05 eV, while it was almost constant for pure and co-doped dandelion-like particles. Therefore, the reduction percentage in band-gap energy of TiO2 compound is dependent upon its morphology, with 8 ACS Paragon Plus Environment


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the order of: nanoparticles ˃ nanowires ˃ dandelion-like particles. This can be explained by the fact that the higher surface area of the morphology, the greater reduction of Eg as a result of faster diffusion of the dopants. Indeed, nanoparticles have higher surface area than nanowires and dandelion-like particles. It has been reported that Eg of the rutile structure can be altered either by heavily doping of carbon, substituted oxygen atoms, or by nitrogen dopant, substituted titanium atoms.41 Since the concentration of canbon is low and nitrogen is substituted oxygen, no considerable change is observed for Eg of C and N co-doped rutile dandelion-like particles.

3.3. XPS and FTIR analyses Figure 6-a shows XPS spectrum of NP14-10-100. In addition, Fig. 6-b to Fig. 6-e show the high resolution XPS spectra of the C1s, Ti2p, O1s and N1s respectively. It is found that the C1s spectrum (Fig. 6-b) can be fitted to three peaks. The peak of typical graphitic carbon at 284.6 eV is attributed to C-C bond. The set of two peaks with higher binding energies located at 285.3 and 288.7 eV can be assigned to C=O, and C-O-Ti bonding energies, respectively.34 Curve fitting of Ti2p identified two peaks at 458.85 eV and 464.27 eV that originated from Ti 2p3/2 and 2p1/2 electrons, respectively (Fig. 6-c). The O1s peaks can be fitted to a main peak at 530.2 eV and two minor peaks at 532 and 533.4 eV (Fig. 6-d). The minor peaks can be related to oxygen vacancies and surface contamination, respectively.42 The nitrogen spectrum (Fig. 6-e) shows a small peak around 400.1 eV. FTIR analysis was also carried out for further confirmation of nitrogen doping for NP14-10-100, as shown in Fig. 7. The nitrogen incorporation is found with the peak at 1390 cm-1 for co-doped sample which is corresponded to 400 eV XPS peak. Such peak is not observed for pure TiO2 nanoparticles. The set of two bands located at 2896 and 2970 cm-1 are attributed to CH3 and CH2 stretching vibrations.43 The water incorporation of H-O-H band is found with the peak localized at 1631 cm−1.44 Furthermore, the broad band centered at 3410 cm–1 is due to the stretching vibration of the hydroxyl (O–H) bond.


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Fig. 6. (a) XPS spectrum of C and N co-doped TiO2 nanoparticles (i.e., NP14-10-100) and high resolution XPS spectra of (b) C1s peak, (c) Ti2p peak, (d) O1s peak, and (e) N1s peak.

Fig. 7. FTIR spectra of pure and C and N co-doped (i.e., NP14-10-100) TiO2 nanoparticles.

3.4. Microstructure The microstructure of synthesized pure and C and N co-doped TiO2 compounds is shown in Fig. 8. The pure and co-doped TiO2 nanoparticles (Figs. 8-a and 8-b) had narrow particle size distribution in the range 15-35 nm and 15-40 nm, respectively. Moreover, pure and co-doped nanowires (Figs. 8-c and 8-d) showed length of several µm and diameter around 100 nm. The overall 3-dimensional structure of pure and co-doped dandelion-like TiO2 morphology (Figs. 8-e and 8-f) appeared to be elegant particles with diameter of 15-20 µm. Furthermore, the dandelion-like particles composed of close packed nanorods (inset of Fig. 8-e).

Fig. 8. FE-SEM images of various morphologies of TiO2: (a) pure nanoparticles, (b) C and N co-doped (NP14-10-100) nanoparticles, (c) pure nanowires, (d) C and N co-doped nanowires, (e) pure dandelion-like particles (the inset shows that the dandelion-like particles are composed of close packed nanorods) and (f) C and N co-doped dandelion-like particles.

3.5. Photocatalytic activity measurements We ran photocatalytic activity measurements of the samples by UVA lamp and UV-Vis spectroscopy, as illustrated in Fig. 9. One more sample without any photocatalyst was used as the reference to measure the photolysis of MB under UVA irradiation. The results show that photolysis sample degrades 6.5% of MB after 2 h UVA radiation. The degradation of MB, under UVA light for 2 h, using pure nanoparticles is 29.0%, while it is 90.5% for co-doped nanoparticles. The most likely reason is that Eg of co-doped TiO2 nanoparticles was decreased so that photons with lower energy can excite electrons from valance band and create more efficient electron-holes under UVA 10 ACS Paragon Plus Environment


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radiation. Although degradation of MB using dandelion-like particles is higher than those using pure nanoparticles, co-doping of such morphology with carbon and nitrogen has no significant influence on their photocatalytic property (i.e., 42.0% degradation for both D and DD). The photocatalytic activity of NP10-14-100 nanoparticles is much higher than that of dandelion-like particles, although both morphologies have the same Eg. Such phenomenon can be related to their crystal structure, being rutile for dandelion-like particles and anatase for the nanoparticles. Rutile phase has a direct band-gap, while anatase structure shows an indirect one. Therefore, for the rutile phase the electronhole recombination process is higher, resulting in lower photocatalytic activity.45 The dandelion-like particles have lower surface area than the nanoparticles due to their micron size particles. In case of nanowires, the highest photocatalytic property among all morphologies is observed, being 95.0% degradation for both pure and co-doped nanowires. This can be explained due to their highly pure anatase structure, whereas TiO2 nanoparticles contain 33% brookite with higher Eg than the anataseTiO2. Since Eg of pure and co-doped nanowires is almost the same, they show a similar photocatalytic property. It has been reported that doping of nitrogen makes a connection between TiO2 valence band and carbon-doped TiO2 bands, resulting in higher photocatlytic activity.46 The co-doping also reduces the band gap energy of TiO2, as observed in this study. Fig. 10 shows the light scattering properties of different powders in the range 300-800 nm wavelengths. Considering the pattern at 369 nm (the lamp’s wavelength) it can be seen that pure nanoparticles have the least reflectance percentage which is due to smaller particle size. However, after doping they show high scattering property almost the same as the Dandelion like particles due to agglomeration. The nanowires have the highest scattering. Although the scattering properties of co-doped TiO2 nanowires and dandelion-like particles are increased 10% compared to their pure samples, the photocatalytic activity of co-doped nanowires and dandelion-like particles are remarkably improved.


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Fig. 9. Photocatalytic activity of pure and C and N co-doped TiO2 with various morphologies on degrading of MB under UVA light.

Fig. 10. Diffuse reflectance spectra of of pure and C and N co-doped TiO2 with various morphologies.

4. Conclusions Three different morphologies of pure TiO2 (i.e., nanoparticles, nanowires and dandelion-like particles) were synthesized by sol-gel and a modified hydrothermal processes. These morphologies were also prepared in the form of C and N co-doped TiO2 and their photocatalytic property was investigated. The Eg of nanoparticles was tuned in the range 3.05-3.17 eV by controlling the synthesis processing parameters. It was found that nitrogen had more impact on Eg of nanoparticles than carbon. The Eg of pure nanowires was decreased as a result of carbon and nitrogen doping, while it was almost constant for pure and co-doped dandelion-like particles. The photocatalytic activity of three C and N co-doped TiO2 morphologies was higher than that of pure TiO2 nanoparticles. Such phenomenon can be related to tuning Eg to produce more efficient electron-holes under UVA radiation. The low degradation of MB using dandelion-like particles (i.e., 42.0%) was related to their rutile crystal structure, having a direct band-gap and, therefore, high electron-hole recombination process. The results showed that 95.0% and 90.5% degradation of methylene blue under UVA radiation was obtained for co-doped TiO2 nanowires and nanoparticles, respectively.

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Fig. 1. XRD patterns of synthesized pure and C and N co-doped TiO2 nanoparticles (A: anatase and B: brookite). Fig. 2. Comparison of the strongest peak of the anatase phase at 2θ=25.3° (1 0 1) for synthesized pure and C and N co-doped TiO2 nanoparticles. Fig. 3. XRD patterns of pure and C and N co-doped TiO2 nanowires (A: anatase and R: rutile). Fig. 4. XRD patterns of pure and C and N co-doped TiO2 dandelion-like particles. Fig. 5. Tauc plot of TiO2 nanoparticles derived from DRS analysis. Fig. 6. (a) XPS survey spectrum of C and N co-doped TiO2 nanoparticles (i.e., NP14-10-100 sample) and high resolution XPS spectra of (b) C1s peak, (c) Ti2p peak, (d) O1s peak, and (e) N1s peak. Fig. 7. FTIR spectra of pure and C and N co-doped (i.e., NP14-10-100) TiO2 nanoparticles. Fig. 8. FE-SEM images of various morphologies of TiO2: (a) pure nanoparticles, (b) C and N codoped (NP14-10-100) nanoparticles, (c) pure nanowires, (d) C and N co-doped nanowires, (e) pure dandelion-like particles (the inset shows that the dandelion-like particles are composed of close packed nanorods) and (f) C and N co-doped dandelion-like particles. Fig. 9. Photocatalytic activity of pure and C and N co-doped TiO2 structures with various morphologies on degrading of MB under UVA light. Fig. 10. Diffuse reflectance spectra of of pure and C and N co-doped TiO2 with various morphologies.



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Fig. 1. XRD patterns of synthesized pure and C and N co-doped TiO2 nanoparticles (A: anatase and B: brookite). 690x432mm (96 x 96 DPI)



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Fig. 2. Comparison of the strongest peak of the anatase phase at 2θ=25.3° (1 0 1) for synthesized pure and C and N co-doped TiO2 nanoparticles. 654x412mm (96 x 96 DPI)


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Fig. 3. XRD patterns of pure and C and N co-doped TiO2 nanowires (A: anatase and R: rutile). 682x432mm (96 x 96 DPI)



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Fig. 4. XRD patterns of pure and C and N co-doped TiO2 dandelion-like particles. 660x431mm (96 x 96 DPI)


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Fig. 5. Tauc plot of TiO2 nanoparticles derived from DRS analysis. 680x432mm (96 x 96 DPI)



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Fig. 6. (a) XPS survey spectrum of C and N co-doped TiO2 nanoparticles (i.e., NP14-10-100 sample) 907x432mm (96 x 96 DPI)


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Fig. 6. high resolution XPS spectra of (b) C1s peak 910x432mm (96 x 96 DPI)



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Fig. 6. high resolution XPS spectra of (c) Ti2p peak 910x432mm (96 x 96 DPI)


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Fig. 6. high resolution XPS spectra of (d) O1s peak 861x418mm (96 x 96 DPI)



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Fig. 6. high resolution XPS spectra of (e) N1s peak. 910x457mm (96 x 96 DPI)


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Fig. 7. FTIR spectra of pure and C and N co-doped (i.e., NP14-10-100) TiO2 nanoparticles. 677x432mm (96 x 96 DPI)



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Fig. 8. FE-SEM images of various morphologies of TiO2: (a) pure nanoparticles 389x431mm (96 x 96 DPI)


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Fig. 8. FE-SEM images of various morphologies of TiO2: (b) C and N co-doped (NP14-10-100) nanoparticles 387x432mm (96 x 96 DPI)



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Fig. 8. FE-SEM images of various morphologies of TiO2: (c) pure nanowires 373x432mm (96 x 96 DPI)


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Fig. 8. FE-SEM images of various morphologies of TiO2: (d) C and N co-doped nanowires 373x432mm (96 x 96 DPI)



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Fig. 8. FE-SEM images of various morphologies of TiO2: (e) pure dandelion-like particles (the inset shows that the dandelion-like particles are composed of close packed nanorods) 523x584mm (96 x 96 DPI)


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Fig. 8. FE-SEM images of various morphologies of TiO2: (f) C and N co-doped dandelion-like particles. 373x432mm (96 x 96 DPI)



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Fig. 9. Photocatalytic activity of pure and C and N co-doped TiO2 structures with various morphologies on degrading of MB under UVA light. 684x432mm (96 x 96 DPI)


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Fig. 10. Diffuse reflectance spectra of of pure and C and N co-doped TiO2 with various morphologies. 634x356mm (96 x 96 DPI)



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Table 1. Synthesis parameters of C and N co-doped TiO2 nanoparticles by hydrothermal method. 1028x356mm (96 x 96 DPI)


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Table 2. The average crystallite size and phase composition of pure and C and N co-doped TiO2 nanoparticle. 1205x356mm (96 x 96 DPI)



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Table 3. Band-gap energies of pure and C and N co-doped TiO2 compounds with various morphologies. 778x450mm (96 x 96 DPI)


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Impact of Morphology and Nitrogen and Carbon Codoping on

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