N-Doped Mesoporous TiO2 Nanoparticles Synthesized
N-doped mesoporous TiO2 nanoparticles synthesized by using biological renewable nanocrystalline cellulose as template for the degradation of pollutants under visible and sun light
Xiaoyun Chen a,b, Dong-Hau Kuo a,⇑, Dongfang Lu c
3.2. FTIR analysis
Fig. 2 indicates the TiO2-NT sample’s FTIR spectra having under 500 ̊C with differing quantities of N-doping. The figure shows different absorption bands situated at 3450, 1630, 1061, and 480–680 cm_1. The peaks achieved at the 3450 and 1630 cm_1 are potentially due to the hydroxyl stretching as well as bending vibration. Such could result from the water absorbed from the surface or surface hydroxyl groups. The Ti-O stretching vibration was reflected by the 480–680 cm_1 peaks. The subsequent N-doping enhances Ti-O broadening at its peak, indicating its stretching vibration, which is possibly as a result of its interaction with the nitrogen that has been doped as well as the hydroxyl group’s hydrogen. An observation was made that the typical adsorption of Ti-O-N peak was at 1061 cm_1 [51,52]. Another observation was that the absorption peak intensity went up when the amount of N-doping was increased.
Synthesis and characterization of substitutional and interstitial nitrogen-doped titanium dioxides with visible light photocatalytic activity
Feng Peng_, Lingfeng Cai, Hao Yu, Hongjuan Wang, Jian Yang
School of Chemical and Energy Engineering, South China University of Technology, Guangzhou 510640, PR China Received 19 July 2007; received in revised form 4 November 2007; accepted 12 November 2007Available online 19 November 2007
Fig. 4 shows the FTIR spectra in which there are two peaks, one at 3422 and the other at 1630 cm_1. The adsorbed water is the reason for the first peak, while the second one is assigned to the TiO2 surface hydroxyl. In the spectra’s low frequency section, the development of the fluctuant bands is observed at around 500 cm_1. The factor behind this phenomenon is the TiO2 anatase phase. The organic compounds’ C–H (υCH2, CH3 and δCH2,CH3) remaining on N-TiO2-M are the reasons for the peaks at 2925, 2858, and 1359 cm_1. Following the heat treatment at the temperature of 300 1C, the peaks are no longer present in N-TiO2-M-300. In N-TiO2-M, in comparison to P25–TiO2, new peaks appear at 1110 cm_1. These new peaks are potentially due to hyponitrite ((N2O2)2_) formation [30, 40], as the XPS analysis shows. The observation did not reveal any peak relating to N–H of NH3 or surface absorption of urea in the N-TiO2-M’s FTIR spectrum. Such observation that for N-TiO2-M made using microwave technique, the interstitial N’s typical structure is hyponitrite.
Synthesis and Catalytic Activity of TiO2 Nanoparticles for Photochemical Oxidation of Concentrated Chlorophenols under Direct Solar Radiation
Muneer M. Ba-Abbad1,*, Abdul Amir H. Kadhum1, Abu Bakar Mohamad 1, Mohd S. Takriff 1, Kamaruzzaman Sopian2
3.1.4. FT-IR of TiO2 nanoparticles
Figure 6. FT-IR spectra of (a) TiO2 as prepared (b) 400oC (c) 500oC (d) 600oC
As indicated in figure Fig. 6, preparation of the FT-IR spectra of TiO2 nanoparticles was done at various calcination temperatures. The analysis indicated appearance of different adsorption bands belonging to different organic factions like OH and alkane. A broad band was reveled in the preparation of the sample of TiO2 between 3800 and 3000 cm-1. The potential reason was because of hydroxyl (O-H), which was stretched to represent water as moisture. The stretching of titanium carboxilate led to the peak at 1635 cm-1, emanating from two precursors, TTIP, and ethanol . The Ti-O stretching bands represented the peaks between 800 and 450 cm-1. Following TiO2 sample’s calcination at diverse temperatures, there was disappearance of almost peaks of hydroxyl and carboxilate. Attributed to the formation of TiO2 nanoparticles, the strong absorptions between 800 and 450 cm-1 endured.
Synthesis and characterization of N-dopedTiO2 nanoparticles and their application in photocatalytic oxidation of dibenzothiophene under visible light
KavehKalantari a, MansourKalbasi a,n, MortezaSohrabi a,b, SayedJavidRoyaee
Fig. 3. FT-IRspectraofN–TiO2 and TiO2–P25.
N–TiO2 and TiO2–P25 are evident in Fig. 3, which is the FT-IR spectra. In the figure, there is evidence of wide and strong peaks, ranging between 400 and 800cm-1 which are potentially as a result of the bonds, Ti–O and Ti–O–Ti within the doped as well as undoped TiO2 . Evidence from the figure shows one of the strong peaks at 3425 cm-1 representing the O–H water’s stretching vibration. It also shows Ti–OH, indicating the existence of hydroxyl groups within the framework of TiO2 of N–TiO2 as well as TiO2–P25. Additionally, the peaks at 1620– 1640 cm-1 reflects the O–H molecular water absorption bending modes on TiO2. [36, 39] The hydroxyl group has a critical role to play within the photocatalytic corrosion through generation of hydroxyl radicals . The peak belonging to hydroxyl group in N–TiO2 sample has stronger intensity, when compared to TiO2, which is undoped and generated in the doping with nitrogen. Thus, for DBT oxidation, there would be greater activity in the catalyst that has been synthesized compared to TiO2–P25. The peaks at about 1160, 1274, 1430, 1340, and 1490 cm-1 in N–TiO2, are corresponding to the nitrogen ions that are doped, in the TiO2 lattice, as substitutional as well as interstitial forms. The conclusion drawn is that nitrogen effectively embeds into the N–TiO2’s TiO2 structure. Such causes bonds to be created through substitution of some structural oxygen as well as Ti–O–N bonds through interstitial addition [39, 47–50].
Enhanced visible-light-driven photocatalytic activity of mesoporous TiO2_xNx derived from the ethylenediamine-based complex
Zheng Jiang,*ab Liang Kong,a Feraih Sh. Alenazey,c Yangdong Qian,a Liam France,aTiancun Xiaoa and Peter P. Edwards*a
A X’Pert, PANALS diffractometer was used in performing two patterns, low-angle (0.5–10ᶱ) as well as wide-angle X-ray powder diffraction (XRD). The experiment was done utilizing Cu Ka1 radiation (40 kV, 40 mA). In this case, the Scherrer equation was used in calculating the meso-TON materials’ crystallite size. A JEOL 3000F electron microscope took high-resolution transmission electron microscopy (HRTEM) pictures. Before the deposition on carbon–copper grids, there was dispersal of the samples into ethanol for HRTEM characterizations. The samples were degassed at 300 ᶱC for 3 h, after which the researchers obtained, on a Micromeritics ASAP 202, Nitrogen adsorption isotherms at 77 K. Calculation of the surface area of Brunauer–Emmett–Teller (BET) was done from the BET plot’s linear section. Together with Halsey equation, the Barrett–Joyner–Halenda (BJH) model was utilized in calculating the Pore-size distributions. A Perkin-Elmer Lambda 35 UV-vis spectrophotometer was applied in recording the N-doped TiO2 sample’s UV-vis spectra ranging between 260 and 800 nm. The reference used was BaSO4. X-ray photoelectron spectroscopy (XPS) was used in describing the surface characteristics of the TON samples. This was done on the Perkin-Elmer PHI 1600 ESCA system using the source as monochromatic Mg Ka together with a neutralizer for charge. In fitting the XPS peaks, Shirley backgrounds were used. A Magnettech Miniscope MS200 EMX spectrometer recorded the electron spin resonance (ESR) spectra. This was done when working a 100 kHz magnetic field modulation (room temperature), power attenuation 15 dB, and a 98.66 GHz constant microwave frequency.
Results and Discussion
The SG-meso-TON and SE-meso-TON samples’ wide-angle XRD patterns are showed in Fig. 1A as calculated at 450 ̊C. effective indexing of the meso-TON samples’ Bragg diffraction data to the crystal phase (JCPDS: 84-1285) (anatase) 22,23 The SE-meso-TON sample’s diffraction peak intensities, compared to the ones of SG-meso-TON, are weaker. The results suggest the former has crystallite dimension, which is smaller. The SE-meso-TON’s crystallite size, as shown in Table 1, is about 10 nm. The size is about two thirds of the size of the SG-meso-TON at 15.6 nm. Such reveals that the SEISA is a successful path in preparing mesoporous nanocrystalline TON.
Additionally, the broad single distraction peaks are only around 2̊ C. such are evident in these meso-TON samples’ small-angle XRD patterns (Fig. 1B), suggesting that disordered mesopores are possessed by the materials.12 previously, the same patterns of low-angle XRD (SAXRD) were evident after systhesizing meso-TiO2 through organic amine surfactant templates24–26. There was observed disappearance of the peaks through the SAXRD because above 300 ̊C, the structure collapses. It was revealed that the SE-meso-TON’s SAXRD patterns are strong and hence, resist sintering compared to the SG-meso-TON. The SE-meso-TON has a high thermal stability promising its huge potential for applicability in photocatalysis as well as solar cells that have been dye sensitized. 5, 12, 27.
In Fig. 3A, there is evidence of the SG-meso-TON and SE-meso-TON samples’ nitrogen adsorption–desorption isotherms, calcined at 450 ̊C. Their mesoporous features were further justified by the samples’ type-IV isotherm curves.28, 29 Within the comparative pressure (P/P0) ranging between 0.4 to 0.8, their hysteresis loops of type 2 reveal the ink-bottle-shaped pores within the materials. The meso-TON’s pore size distribution profiles as computed applying Barrett–Joyner–Halenda (BJH) model are indicated in Fig. 3B. The results reveal that the materials making the meso-TON have the same pore size distributions, while there are larger mean pore sizes (4.5 nm) in SE-meso-TON. Below the 2 nm range, the BJH profiles below reveal that SE-meso-TON, compared to SG-meso-TON has more micropores. There was an attempt to carry out ultrasonic synthesis using pure porous TiO2 with extremely huge SSA (above 600 m2 g-1) applying DDA template. However, after calcination it at 350 ̊C due to the originally porous TiO2, the SSA value of TiO2 radically decreased to 38 m2 g-1. The idea is that during thermal treatments, the micropores merged.24 After calcination at 450 ̊C, the SEmeso- TON’s SSA value 101m2 g-1 was almost two times that of SG-meso-TON at55 m2 g-1. That kind of a huge SSA indicated that the method of synthesis, the use of EDA and DDA, possibly retained the emergent porosity at the time of thermal crystallization.
In Fig. 4, the researchers compared between the P25 TiO2 UV-vis diffuse reflectance spectra and the calcinations at 450 ̊C of the meso-TON materials. It is revealed that compared to SE-meso-TON, the SG-meso-TON has the potential of absorbing more visible light. However, it absorbs less UV. For SG-meso-TON, the adsorption edges are 650nm, while those of SE-meso-TON photocatalysts are 550 nm. The reason for the difference is the red-shifts resulting from the typical impurity.3, 9 The features involved in the absorption of light for meso-TON samples reveal the incorporation of nitrogen into theTiO2 matrix, potentially changing their energy bands.2, 3, 27 The SE-meso-TON’s bandgaps as calculated was found to be is 2.98 eV, while SG-meso- TON’s is 2.9 eV. The calculation was done with the use of the Kubelka–Munk function applied to the diffusion reflectance spectra. These two are smaller compared to that of Degussa P25, which is 3.2 eV. The meso-TON’s decreased bandgap energy is the basis for the development of the midgap status emanating from the doping with nitrogen.
RhB was decomposed through irradiation using visible light in performing the evaluation of the meso-TON samples’ photocatalytic activities as well as commercial P25 TiO2 (Degussa TiO2 aerosol). The photocatalytic reaction was done using the optical systems made up of an overhead xenon lamp, 300 W, (Beijing TrustTech- PLS-SXE 300) with UV as well as IR cut-off filters (IR filter and UVCUT 400 as well as Beijing TrustTech). To ensure irradiation only with visible light, the purpose of the attachment of these to the lamp was to get rid of the light of wavelength shorter that 390 nm and those higher than 800 nm. For every test, the measurement of the intensity of light was taken and maintained at 50 mW cm-2. In all the experiments, RhB (20 mg L-1) of 0.1 g photocatalyst was added a 100 mL aqueous solution in preparing the reaction suspension. The suspension was well stirred before the irradiation, for one hour in the darkness to realize dye’ adsorption–desorption equilibrium on the surfaces of the catalyst. The experimenters collected about 3 mL of the mixture at particular intervals, during photo-reaction. For the purpose of removing the photocatalyst particles, 10 000 rpm, 4 min was then centrifuged. A Perkin-Elmer Lambda 750S UV-visible spectrometer was used in analyzing the collected supernatant solution. The degradation extent of RhB was determined using the RhB’s typical absorption peak at 554 nm.
Preparation of highly visible-light active N-doped TiO2 photocatalyst†
Guidong Yang,ab Zheng Jiang,b Huahong Shi,b Tiancun Xiao*b and Zifeng Yan*a
Received 10th February 2010, Accepted 5th May 2010 First published as an Advance Article on the web 24th May 2010 DOI: 10.1039/c0jm00376j
2.4 Tests- Photocatalytic Activity
The two common dyes for industrial purposes are Methlyene blue (MB) as well as Methyl orange (MO). As such, they have been used in many experiments for the purpose of establishing photocatalytic degradation, as model pollutant over titania catalysts, N-doped 28–31 It is important to note that MB is a dye that is photosensitive, which means that under irritation with light, it would gradually degrade devoid of having a photocatalyst. On the other hand, MO is a dye that is highly stable. To affirm the performance of the catalyst, a test was carried out to establish the two dyes’ degradation as the catalysts that would be used in the experiment. A self-designed 200 ml reactor was used in testing the two models, with the temperature maintained at constant using a circulating water cooling system. The researchers used Trusttech, PLS-SXE300, a xenon lamp as the point from which the visible light was obtained. A glass filter was used to remove the ultraviolet light below 420 nm. A space of 15cm was maintained between the level of the fluid and the strip lamp. The beginning concentration of the solution of the dye was 10 mg L-1. 100 mg. This was the prepared as TiO2 catalyst, N-doped, which was added into the reaction system together with model dye’s 100 ml of aqueous solution. The solution was stirred magnetically for two hours before the illumination. This was done in the darkness to make sure that the mixture attained the adsorption equilibrium. The experiment involved removal of three mls of the suspension at a regular time, during the photoreaction process. This would ensure the separation of the photocatalyst from the solution by centrifugation. UV visible spectroscopy was used in testing the remaining clear liquid’s concentration. During the photoreaction, no oxygen was allowed to bubble into the suspension.
Fig. 7 UV-vis indicate the diffuse reflectance spectra of MB solution before and after visible light irradiation (λ > 420 nm) for various times of exposure amid TON-2.
The model organic pollutant used in the experiment was MB. The model was used in evaluating the N-doped TiO2 nanomaterials’ photocatalytic activity. In Fig. 7, there is indication of the MB solution’s UV-vis diffuse reflectance spectra prior to and after irradiating using the visible light (λ > 420 nm) together with TON-2, for numerous exposure times. With increasing irradiation time, the model solution at 664 nm had the typical absorption bands decreasing in intensity at a significant rate. After illumination for 100 min, the absorbance of the peak approached 0, while the ultimate position moved to ~ 600 nm. In fact, this was the indication of the complete discoloration of the solution with a 1.0g L-1 TON-2 solution.
Synthesis and Catalytic Activity of TiO2 Nanoparticles for Photochemical Oxidation of Concentrated Chlorophenols under Direct Solar Radiation
Figure 1. TGA curve of TiO2 precursor
3.1.1. Thermal Analysis
The TiO2 precursor’s TGA curve is shown in Fig. 1, following drying at 80◦C for four hours. Based on the heat profile, three stages of TiO2 sample’s TGA curve are evident. There was an increase in temperature to 180 from 25°C during the first stage, meant for removal of the remnant ethanol and water. approximately14 % loss of weight took place. In the temperature ranging between 180 and 380 °C, complete organic compounds’ decomposition took place, leading to approximately 9.0 % loss in weight . The anatase phase emerged from the conversion of the amorphous precursor with the increasing in the temperature to 500 from 425◦C. from the anatase phase, the TiO2 moved to the rutile phase which occurred at the temperatures between 550 to 600◦C . The XRD results shown in Fig.2 confirmed the observations. The TGA curve did not indicate any loss of weight for the temperatures after 400 °C, which indicated that TiO2 precursor’s decomposition had become complete at this point and marked the beginning of calcination temperature. The results also agree with the FT-IR analysis as evident in section 3.2.4.
Figure 2. XRD pattern of the TiO2 powder at various calcining temperatures.
3.1.2. X-ray diffraction (XRD)
X-ray diffraction analysis was utilized in the evaluation of the TiO2 materials’ composition phase and the crystallite size. The calcined TiO2 powder’s XRD patterns, as showed in Fig. 2, emerged at diverse temperatures, 400, 500,600 and 700oC respectively. At 400 and 500oC, the samples’ peaks were identified by carrying out an assessment of the relationship with JCPDS-84-1286 in accordance with 2θ. This affirmed the anatase constitution at 2θ=25.4ᶱ. It is important to note that at the rutile phase (2θ=27.36 ᶱ), the samples’ diffractograms do not reflect any peak. The estimation of the TiO2’s average crystallite size was done based on the Scherrer’s equation  as shown in the equation below, Eq. (5):
K represents the Scherer constant,
λ the X-ray wavelength,
β the peak width of half maximum, and
θ is the Bragg diffraction angle.
The calculation of the content of two phases, anatase and rutile, for all TiO2 samples was done as follows Eq. (6):
Where XA represented the anatase’ weight fraction in the solution, IA and IR, the anatase’ intensity of (101) and rutile (110) diffraction .
From TiO2 sample’s XRD spectrum calcined at 400oC, the observation as only made for the anatase phase, with wide peaks. Such observation indicated incomplete crystallization due to the reality that it contained an amorphous constituent. For nanoparticles, the results of TiO2 sample are a general characteristic [22, 23]. With an increase in the calcined temperature to 500oC, the TiO2’s crystallinity enhanced devoid of any changes during the anatase phase. For the rutile peaks, however, become considerable once the temperature went up to 600oC and quantity of rutile was computed at approximately 25.49 %. The calcination temperature effect during the anatase phase as it moves to rutile phase agrees with the findings from the thermal analysis (TGA). There was an increase up to 78.68% of the rutile phase quantity leading to sharper peaks when compared to those at the anatase phase. There is also a drastic increase in the particle size, during the change from the anatase to rutile phase  as evident in Table 1.
Synthesis and Characterization of Nitrogen-Doped TiO2 Nanophotocatalyst with
High Visible Light Activity
Ye Cong,† Jinlong Zhang,*,† Feng Chen,† and Masakazu Anpo‡
Figure 8 shows the diffuse reflectance spectra of pure TiO2, Degussa P-25, and nitrogen-doped TiO2. The results occurred under diverse concentrations. The Degussa P-25, undoped TiO2, TiO2-N-1, TiO2-N-2, and TiO2-N-4 samples reveal gaps in band length with the onset of absorption at 400, 412, 425, 447, and 451 nm. The results corresponded to band gaps of 3.04, 2.95, 2.86, 2.72, and 2.70 eV, in that order. As a result, the doped samples’ optical absorption edges shifted to a lower region of energy in comparison to those of the undoped samples. In addition, in wavelengths ranging between 400 and 600 nm, the absorption following nitrogen doping are radical and stronger. Still, there is strengthening of absorption with any increase in doping concentration. As a result of the band gap becoming narrower, it is anticipated that the red shift would emanate from nitrogen doping.
Photocatalytic degradation of Orange G on nitrogen-doped TiO2 catalysts under visible light and sunlight irradiation
Jianhui Suna,∗, Liping Qiao a,b, Shengpeng Suna, Guoliang Wang a
2.2. Catalyst Characterization
Xray powder diffraction was used in the analysis of the catalysts’ crystal structures. A Bruker-D8-AXS diffractometer system (Bruker Co., Germany) was used in the XRD analysis, which was fitted with a CuKα radiation (λ = 0.15406 nm). Another tool used in the process was the graphite monochromatic operating at 45 kV and 40 mA. The scan rate at which the patterns were obtained was 0.020◦/0.4 s. As such, the Scherrer equation estimated the average crystal size applying the complete width at half maximum (FWHM) data. The information was obtained following correction of the instrumental broadening. UV–vis spectroscopy was the tool used in studying the catalysts’ light absorption characteristics. A Jasco V-550 spectrophotometer was utilized in recording the UV–vis spectra, embedded in a sphere and utilizing BaSO4 as reference. The XPS investigated the catalysts’ elements composition and the related chemical states. An Axis Ultra-Kratos spectrometer acquired the XPS spectra, applying Al Kα radiation as the source of X-ray. The calibration of the binding energies was done to the C1s peak at 284.8 eV of the adventitious carbon’s surface.
- Results and discussion
3.1. Photocatalyst characterization
3.1.1. Structure analysis
For the catalysts, N-doped as well as the non-doped XRD patterns are indicated in Fig. 3. The diffraction peaks were the only ones recognized as anatase structures devoid of possible contagion from any other phase like brookite or rutile structure. Estimation of the average particle sizes was performed using the Scherrer equation, and 14.0 nm was the value obtained for doped and 15.3 nm non-doped TiO2. It is worth noting that even the doped materials show the characteristic structures of TiO2 crystal devoid of detectable peaks associated with the doping. Such might be as a result of the low concentration of the species that are doped, as well as the restricted dopants. Such could have either shifted to the TiO2 crystal structure’s substitutional sites or interstitial positions .
3.1.3. UV–vis diffuse reflectance spectroscopy
Fig. 6 shows the optical absorption spectra of different elements, the doped, non-doped, as well as the P25 TiO2. For the N-doped TiO2 powders, an emergent absorption band was revealed by absorption measurements. The band is evident visibly ranging between 400 and 550 nm. For the non-doped and P25 TiO2, the only visible element was the basic absorption edge of TiO2, situated at approximately 387 nm in the UV region. A comparison of the spectra between the N-doped and non-doped TiO2, it was revealed in the latter case that the C atoms might not have an effect on the TiO2’s optical absorption aspects. Therefore, the emergent absorption band is attributed to the nitrogen atom used in the doping process. Besides, the doped powders’ color was bright yellow and that of the other two forms of TiO2 was white. Generally, a solid’s color is decided by the placement of absorption edges. Thus, a move of the absorption edge toward greater wavelengths can cause absorption spectra range, which is visible. The shift for the N-doped samples, which were colored could be explained by the doping process. In essence, the shift supported the analysis that nitrogen doping yielded the new absorption band that existed in the visible areas in the doped powders.
Fig. 6. UV–vis absorption spectra of (a) the N-doped TiO2, (b) Degussa P25 TiO2, and (c) the non-doped TiO2.
3.2.1. Visible-light-induced degradation of OG
Fig. 7. The Photodegradation of OG under the visible light
The photodegradation of OG is showed in Fig. 7(a), on differing catalysts under irradiation by visible light. At 96.29% of OG, the doped TiO2 revealed a considerably high level of degradation efficiency in 150 min. This is when compared to the non-doped TiO2 at less than 13.0% and P25 at 42.55% conversion, also in 150 min. In comparison with P25, which is regarded as standard and excellent photocatalyst, the improvement in OG degradation in the doped TiO2 is considerable. There are several explanations for the results.
First, for the non-doped TiO2, the relatively low degradation efficiency revealed that C atoms were not the basis for the visible activity. Such a conclusion is in line with the non-doped catalysts’ zero optical absorption properties. Fig. 6 shows the visible range. Additionally, the emergent absorption band mentioned in Section 3.1.3 could possibly explain the major improvement in the N-doped TiO2’s OG degradation. The N-doped TiO2’s bandgap energy was low because of the nitrogen doping, which also caused the red shift of band catalysts’ absorption. Therefore, visible light could be absorbed by doped catalysts and activation take place to create electrons–holes (h+–e−) pairs that would directly contribute to the photocatalytic reaction.
Second, the doped TiO2’s smaller particle sizes, which could affect the TiO2 surface by increasing active sites, are another reason for the observation. Additionally, some degradation efficiency evident in the non-doped TiO2 and P25 revealed another potential explanation known as photosensitized oxidation mechanism. The mechanism proposes that the adsorbed dye, under visible light, is animated to suitable states, singlet (1Dye*) or triplet (3Dye*), afterward there is injection onto the electron’s conduction band from the animated dye molecule. Such occurs in the TiO2 particles. Conversely, the there is conversion of the dye to the cation dye radical (Dye•+) which go through dilapidation to produce the outcome below (Eqs. (2)–(5)) [5,26–28]:
Novel cake-like N-doped anatase/rutile mixed phase TiO2 derived from metal-organic frameworks for visible light photocatalysis
Jinliang Lia,1, Xingtao Xua,1, Xinjuan Liub,⁎, Wei Qinc, Likun Pana,⁎
Fig. 3. XRD patterns of TiO2, N-TiO2-1, N-TiO2-2 and N-TiO2-3.
The TiO2, N-TiO2-1, N-TiO2-2 and NTiO2- 3 XRD patterns are shown in Fig. 3. The figure is evident of various diffraction peaks at 25.3°, 37.8°, 48.0°, 53.9°, and 62.7°. These peaks are indexed to (101), (004), (200), (105) and (204) the koechlinite phase’s crystal planes (JCPDS 21-1272) [36, 37]. Increasing the annealing temperature (N-TiO2-2 and N-TiO2-3), results in emergent diffraction peaks at 27.4°, 36.1°, 41.2°, 54.3° and 56.6° and 69.0°, which corresponds to (110), (101), (111), (211), (220) and (301) rutile TiO2’s crystal planes (JCPDS 21-1276). Such results have an implication that a anatase/rutile blend phase structure is displayed by NTiO2- 2 and N-TiO2-3 [38, 39]. It is evident that for rutile phase of NTiO2- 2, the diffraction peaks are weaker compared to those of the TiO2. The reason is due to the reality that the N doping could successfully deter the transformation of a phase of TiO2 to rutile, from anatase. The same case is evident in F-doped TiO2 .
Fig. 6. Plots of transformed Kubelka-Munk function versus photon energy based on theUV–vis diffuse absorption spectra of TiO2, N-TiO2-1, N-TiO2-2 and N-TiO2-3.
The transformed Kubelka-Munk function’s plot against those of photon energy is shown in Fig. 6, for the purpose of calculating the band gap energies of TiO2, N-TiO2-1, N-TiO2-2 and NTiO2- 3. Beer-Lambert equation (αhν)2=A(hν−Eg) can be used in estimating the band gap energy,
where α represent the absorption coefficient,
hν, photon energy, and
A, is a constant.
It can be assumed as the intercept of Beer-Lambert equation’s linear part at (αhν)2=0 . These elements’, TiO2, N-TiO2-1, NTiO2-2, and N-TiO2-3, band gap energies are 3.07, 3.00, 2.86 and 2.77 eV, in that order. Such indicates possible narrowing of TiO2’s band gap by the N doping [44, 47]. Such reality is attributed to the lattice disorder effect as well as dopant-induced mid-gap electronic states’ synergistic effect .
3.6. Surface area and pore size analyses
N2 adsorption–desorption isotherms are shown in Fig. 6 (a), while TiO2-N and TiO2-NT samples’ pore size distribution curves at 500 ̊C are shown in (b). The first figure indicates that the samples, TiO2-N and TiO2-NT demonstrate hysteresis loops and type IV adsorption–desorption isotherms. The adsorption aptitude, at a comparatively low pressure, increase with a rise in relative pressure because of the N2 molecules being adsorbed at the mesoporous surface as multilayer or monolayer. Upon reaching 0.8, the relative pressure of N2 instigated the capacity for adsorption to radically increase because of the emergent of TiO2 mesopores through capillary condensation of the nitrogen molecule. Within the catalyst, the presence of mesoporous structure was proven by hysteresis loop curve. At more than 0.95, the relative pressure of the nitrogen molecule initiated the capacity to absorb to remain constant. In fact, this stage indicated the saturation level of adsorption. Fig. 6(b) reveals the pore size distribution curve. For mesoporous TiO2-NT, a 2–9 nm pore diameter as well as a 0.29 cm3/g pore volume were attained, while for TiO2-N, they were 1–30 nm and 0.20 cm3/g correspondingly. The BET measurements’ calculated data are provided in summary in Table 3. The TiO2-NT’s particular surface area is revealed as 131 m2/g, at 84% higher compared to that of TiO2-N, which was 71.5 m2/g. The findings reveal that the NCC template used in the preparation of mesoporous TiO2 has an advantage. The reason for this is the higher total pore volume and narrower pore size distribution, as well as a particular surface area. This could be explained by the decomposition of NCC template at higher temperatures as well as the porous network structure’s formation, for a TiO2.
3.7. TEM analysis
The TEM images of TiO2-N, (a) as well as TiO2-NT, (b) are shown in Fig. 7. Both images show the elements as prepared at 500 ̊C. In Fig. 7(b), the sample of TiO2-NT not only demonstrate a particle dispersion, which is superior, but also had particle size, smaller, at 10–30 nm. On the other hand, TiO2-N had a significant level of agglomeration as well as a particles size, larger, at 30–100 nm as shown in Fig. 7 (a). The narrow particle size distribution was attributed to avoidance of the particle aggregation in the preparation of N-doped TiO2. However, TiO2’s smaller particle size has the advantage of improving the photocatalytic reaction’s quantum efficiency. Rapid movement of light-excited carriers to the surface of the particle is eased by the smaller granularity, hence lowering the rate of carrier recombination [55,56].
A Historical Overview and Future Prospect
Kazuhito Hashimoto1,2, Hiroshi Irie2 and Akira Fujishima3
6.2 Visible-light-sensitive TiO2
Resulting from oxygen vacancies, the Ti 3d impurity (donor) level is revealed to be nonvisible light sensitive. Evidently, TiO2 (TiO2-x) powders, which are hydrogen-reduced are gray in color, thus not showing visible sensitivity to light. Compared to the Ti 3d donor level, the existence of the N 2p level exists is deeper. Hence, it is considered that compared to Ti 3d level, the N 2p level has greater power of oxidation. Thus, the N 2p narrow band is potentially the source of the nitrogen-doped TiO2’s visible light sensitivity. Therefore, there is a reason why the use of UV light to irradiate the nitrogen-doped TiO2 with led to a greater photocatalytic activity compared to using visible light. The use of UV light cause excitement of electrons in the narrow band made up of N 2p as well as the valence band made up of O 2p and, use of visible light only causes excitement at the narrow band of N 2p. As well, the isolated narrow band’s hole mobility ought to be low. Consequently, when using the UV light, the hydrophilic properties were higher compared to when using visible light. Regardless of the increase in the nitrogen concentration, the density of states (DOS) calculations do not suggest that narrowing the band gap by blending N 2p with O 2p takes place.
Preparation of nitrogen-doped titanium dioxide with visible-light photocatalytic activity using a facile hydrothermal method
Feng Peng_, Lingfeng Cai, Lei Huang, Hao Yu, Hongjuan Wang
- Results and discussion
3.1. Photocatalyst characterization
The TEM images as well as the TiO2 and N-TiO2 particles’ size-histograms are shown in Fig. 1. The TiO2 nanoparticles’ raw material, in Fig. (1a), display an uneven spherical form. The range in the size is between 15 and 35 nm as shown in Fig. (1c). There was a decrease in the particle size of TiO2 following hydrothermal treatment as seen in Fig. (1b). In fact, around 2075nm, N-TiO2 sample was shown to have more consistent particle size as revealed in Fig. (1d). In essence, under the hydrothermal conditions it is palpable that the particle’s microstructure undergo a change.
Efficient visible-light induced photocatalysis on nanoporous nitrogen-doped titanium dioxide catalysts
Hyun Uk Lee a,⇑, Soon Chang Lee b, Saehae Choi c, Byoungchul Son d, Sang Moon Lee a, Hae Jin Kim Jouhahn Lee a,⇑
For the purpose of investigating the N-TiO2 and _N-TiO2 aggregates’ properties, Fig. 2 shows the HR-TEM images. Interconnected TiO2 nanoparticles made up the structure comprised of the nanoporous frameworks (Figs. 2a and c). The fact that the walls of the pores consisted of aggregated nanocrystalline anatase was also revealed by the HR-TEM images (Fig. 2b and d). They were shown as having a standard crystallite dimension of _5.7 nm in line with the value of the XRD. Sets of evident fringes of resolved lattice were contained in the crystallites, hence providing evidence of the elevated crystallinity of samples of the N-TiO2 and _N-TiO2 particles. The N-TiO2 and _N-TiO2 materials’ electron diffraction patterns were evident in selected areas of electron diffraction (SAED) (inside, Fig. 2b and d). With the anatase phase, the patterns were evident as (101), (004), (200), (105), and (204) polycrystals’ diffractions. It is indicated by the HR-TEM images as well as the XRD patterns that with the phase of anatase, the two samples are made up of nanoporous structures. The spacing, as observed between the planes of lattice of the two samples was 0.35 nm, in line with (101) of the anatase crystal’s plane.