Publish in this journal
Journal Information
Share
Share
Download PDF
More article options
Visits
182
Original Article
DOI: 10.1016/j.jmrt.2017.05.019
Visible light photocatalytic degradation of malachite green using modified titania
Visits
182
Atul B. Lavanda, Minakshi N. Bhatub, Yuvraj S. Malghea,
Corresponding author
ymalghe@yahoo.com

Corresponding author.
a Department of Chemistry, The Institute of Science, 15, Madame Cama Road, Mumbai 400032, Maharashtra, India
b Chemistry Department, Annasaheb Vartak College, Vasai road (west), Mumbai, Maharashtra, India
This item has received
182
Visits
Received 12 June 2016, Accepted 16 May 2017
Article information
Abstract
Full Text
Bibliography
Download PDF
Statistics
Tables (1)
Table 1. Some characteristic properties of photocatalyst.
Abstract

Nanoparticles of titanium dioxide co-doped with carbon and iron (III) were prepared using the microemulsion method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Photoluminescence spectroscopy (PL), and UV-visible diffuse reflectance spectroscopy were used to characterize pure and doped TiO2 nanoparticles. Doped C atoms exist as the O–Ti–C structure or interstitial C in TiO2 lattice, while the doped Fe3+ atoms substitute some of Ti4+ to form the Ti–O–Fe structure. In comparison with the pure and C-doped TiO2, all C, Fe co-doped TiO2 samples exhibit a narrower band gap and stronger visible light absorption. The assistance of the C and Fe3+ ion enhances the photocatalytic activity in the visible light region and also inhibits the electron–hole recombination. The photocatalyst co-doped with C and 2.01wt% Fe shows the excellent photocatalytic activity and degradation efficiency was improved by 78% under visible light irradiation as compared with the pure TiO2.

Keywords:
Photocatalysis
Microemulsion technique
Titanium dioxide
X-ray methods
Photoluminescence
Full Text
1Introduction

Titanium dioxide TiO2 (titania) is an important technological material having wide range of applications such as degradation of pollutants [1], water splitting [2], component material in dye sensitized solar cells [3], gas sensors [4], etc. TiO2 is commonly used as photocatalyst, due to its nontoxic nature, chemical stability, low cost, specific optical and electronic properties [5]. Anatase form of TiO2 shows relatively better reactivity and chemical stability for water and air purifications than rutile and brookite phases [6]. However, there are several limitations, as titania has a large band gap (Eg=3.2eV) hence only small fraction (about 5%) of solar light can be utilized for its photoexcitation [7]. To enhance the effective exploitation and conversion of solar energy, i.e., for the improvement of catalytic performance in visible light and also to influence generation of charge carriers if irradiated with light, TiO2 has been to be modified by doping it with transition-metal cations [8,9] non-metal anions [10,11] and coating dye on TiO2 surface [12,13]. Simultaneous doping of two kinds of atoms into TiO2 has shown higher photocatalytic activity as compared to single element doping. TiO2 doped with transition metal cations was reported as a good tool to improve photocatalytic properties under visible light irradiation. Among them, Fe doping has been intensively studied [14,15]. Fe replaces some of Ti4+ ions and reduces the band gap of TiO2 by introducing new energy level within the band gap of TiO2. Also, Fe dopants could act as hole and electron traps to inhibit recombination of the photogenerated charge carriers, leading to improved photocatalytic activity [16]. Photocatalytic activity is highly dependent on Fe concentration as the doping sites could also act as the electron–hole recombination centers at higher concentration. One of the advantages of Fe doping is that the trace amount of Fe that might be leached out from host lattice is non-toxic. Also, doping of TiO2 with non-metals such as N, C, S, P, showed potential to induce visible-light activity. Among these C doped TiO2 showed excellent photocatalytic activity for degradation of various organic pollutants under visible light irradiation [17].

Particle size is one of the most significant factor, which affects the photocatalytic activity of titania. Many researchers reported that photocatalytic activity increases with decrease in particle size of titania (in to nanometer scale region), due to high surface area and short interface migration distances for photo-induced holes and electrons [18,19]. There are numerous techniques used to synthesize nano-crystalline titania such as sol–gel method [20,21], hydrothermal method [22], chemical vapor deposition [23], chemical precipitation [24]. These methods need vigorous stirring, high temperature processing and long aging time which results in formation of big particles with wide size distribution. On the other hand, microemulsion method is very efficient for synthesis of nanosized TiO2[25]. Major advantages of this method are low reaction temperature, short processing time and prevents agglomeration of nanoparticles synthesized [26,27].

In this study iron is used as a transition metal modification on carbon doped titania using reverse microemulsion route. The enhanced photocatalytic activity of C, Fe modified TiO2 was attributed to small particle size, increase in visible light absorption capacity and effective separation of electron–hole pair.

2Experimental2.1Materials

Titanium isopropoxide Ti(iOPr)4 (Sigma Aldrich, Mumbai, India) is used as a source of titanium. Cyclohexane, n-butanol (AR grade, SD Fine, Mumbai, India) and distilled water were used as solvents. N,N,N-cetyl trimethyl ammonium bromide (CTAB) (AR Grade, SD Fine, Mumbai, India) was used as surfactant. Ferric nitrate (Fe(NO3)3·9H2O) (SD Fine, Mumbai, India) was used as Iron source. Malachite green (MG) was procured from Hi Media Laboratories, Mumbai and used without any further purification.

2.2Catalyst preparation

TiO2 as well as C and Fe doped TiO2 nanoparticles were prepared using microemulsion method. In a typical method, cylclohexane (120mL), n-butanol (30mL) and CTAB (12g) were mixed and solution was stirred for 15min. To this micro emulsion double distilled water (6mL) and titanium isopropoxide (18mL, 1mol/L) solution were added dropwise with constant stirring. This mixture was transferred to autoclave (with teflon-inner-liner) and autoclave was kept in an oven at 423K for 2h. Later, it was cooled to the room temperature. The precipitate formed was separated using centrifugation, washed several times with ethanol and distilled water and dried at 313K. The product obtained was used as a precursor. This precursor was calcined in furnace at 773K for 2h to get nanosized TiO2. Similarly, C doped TiO2 was prepared. To get C doped TiO2, precursor was calcined at 573K for 2h. To prepare C, Fe co-doped TiO2 stoichiometric amount of Ferric nitrate was added in a microemulsion and precursor was calcined at 573K for 2h. Average particle size of pure and doped TiO2 prepared in present work varies between 5 and 16nm.

2.3Catalyst characterization

Precursors (pure and doped) were heat treated at 573, 673 and 773K for 2h and the XRD patterns of the product obtained at different temperatures were recorded using X-ray diffractometer (Rigaku, Model-Miniflex II) using monochromatized CuKα radiation (λ=0.15405nm) with scanning rate of 2° 2θmin−1. Morphology of samples were examined using Scanning electron microscope (JEOL-JSM6360A) and transmission electron microscope (Philips, CM200). Elemental composition study was carried out using energy dispersive X-ray (EDX) spectroscope equipped with scanning electron microscope and X-ray photoelectron spectrum (XPS) with PHI VersaProbe-II photoelectron spectroscope (Physical Electronics, USA) with Al Kα radiation. Photoluminescence spectra of samples were recorded at room temperature using Fluorescence spectrophotometer (Perkin Elmer-LS-55) with excitation wavelength 325nm. UV-visible diffuse reflectance spectra of the samples were recorded using UV-Vis spectrophotometer (Shimadzu, UV-1800) equipped with integrating sphere and BaSO4 was used as a reference. The scanning range was from 200 to 800nm. The band gap energy value was calculated using Kubelka–Munk plot.

2.4Measurement of photocatalytic activity

Photocatalytic activities of pure and doped TiO2 photocatalysts were investigated for degradation of MG solution. Reaction suspension was prepared by adding 0.05g photocatalyst in 50mL (10ppm) MG solution. pH of this solution was found to be 6.71. This aqueous suspension was stirred in the dark for 30min to attain adsorption-desorption equilibrium. Amount of malachite green dye adsorbed on different photocatalysts in the dark varies between 0 and 10% (Fig. 9). Later the solution was irradiated with visible light. The visible light irradiation was carried out in a photo reactor using a compact fluorescent lamp (65W, λ>420nm, Philips, Mumbai). The distance between the fluorescent lamp and the reaction vessel was fixed at 10cm. Intensity of the light reaching to the test solution is 42Wm−2. Temperature of test solution was maintained constant throughout the experiment by circulating water around the solution. The reactant solution was irradiated under visible light for different time intervals. The catalyst was separated by centrifugation and the concentration of MG in the supernatant solution was estimated using UV-visible spectrum recorded in the wavelength range 200–800nm.

3Results and discussion3.1Structural analysis

XRD patterns of precursor heated at various temperatures were recorded and are presented in Fig. S1. The peaks at 2θ values 25.26, 38.16, 48.17, 54.03, 64.69, 68.16, 71.10 and 76.4° are fitted and their hkl planes were identified as (101), (004), (200), (105), (211), (204), (110), (220) and (215), respectively, which are consistent with JCPD card number 84-1285 (anatase TiO2). The diffraction pattern reveals that, as synthesized TiO2 nanoparticles consists of pure anatase phase having tetragonal structure. As the calcinations temperature increases from 573K to 773K intensity of diffraction peaks increases which indicates the increase in crystal size. XRD patterns of C, Fe co-doped precursor calcined at 573K are presented in Fig. 1, which consists of purely anatase phase. No additional peaks are observed for C and Fe doping, which might be due to lower Fe concentration in TiO2 samples. Here Ti4+ ions are substituted by Fe3+ ions, as Ti4+ and Fe3+ have comparable radii, 0.745Å and 0.69Å, respectively [28–30]. As the Fe concentration increases diffraction peaks are shifted toward lower angles which indicate successful doping of Fe into TiO2 lattice. The shifting of diffraction peak positions generally depends on synthesis procedures and precursor used. The average crystallite sizes of pure and doped TiO2 were calculated using Debye–Scherrer equation and results indicate that doping of Fe3+ decreases the crystal size of TiO2 (Table 1).

Fig. 1.
(0.14MB).

XRD patterns of (a) Pure TiO2 and TiO2 doped with (b) 1.16, (c) 2.01, (d) 3.08, (e) 4.87, (f) 6.68% Fe precursor calcined at 573K.

Table 1.

Some characteristic properties of photocatalyst.

No.  Sample  Particle size (nm)a  C content (wt%)b  Fe content (wt%)b  Band gap (Eg) (eV)c 
Pure TiO2  16.2  –  –  3.14 
C doped TiO2  13.4  7.59  –  2.86 
C, Fe codoped TiO2  12.3  3.10  1.16  2. 84 
C, Fe codoped TiO2  10.1  2.76  2.01  2.81 
C, Fe codoped TiO2  12.1  2.93  3.08  2.77 
C, Fe codoped TiO2  13.1  3.10  4.87  2.29 
C, Fe codoped TiO2  13.8  2.81  6.68  2.15 
a

Particle sizes are calculated from XRD results using Debye–Scherrer equation.

b

C and Fe content obtained from EDX measurement.

c

λ values are obtained from onset of light absorption edges and Eg values were calculated using Kubelka–Munk plot.

3.2Elemental composition analysis

EDX spectra of (a) undoped TiO2 precursor calcined at 773K, (b) 573K and Fe doped precursor with (c) 1.16 (d) 2.01 (e) 3.08 (f) 4.87 and (g) 6.68% Fe calcined at 573K were shown in Fig.S2. Elemental composition of C and Fe in TiO2 are presented in Table 1.

3.3Morphology and size analysis

The surface morphology and size of pure and doped TiO2 samples were investigated using SEM and TEM techniques. Fig. 2 represents SEM images of pure and doped TiO2 samples. It shows that TiO2 particles are having a spherical shape and are uniformly distributed. The particle size of as synthesized samples was measured using TEM technique (Fig. 3). These images show that TiO2 particles are spherical in shape. Surface morphologies are not affected by C and Fe doping, indicating that C and Fe are successfully incorporated into the TiO2 lattice crystal. Selected area electron diffraction (SAED) pattern confirms the crystalline nature of TiO2 nanostructures. The d-spacing of the rings corresponding to the hkl planes (101), (103), (200) and (105) are identified. The hkl planes of pure anatase TiO2 phase indicating tetragonal structure and is in good agreement with the XRD data. It can be seen from the TEM images that the particle sizes of TiO2 particles are in the range 6–15nm, which is in good agreement with the crystallite size obtained from XRD results.

Fig. 2.
(0.41MB).

SEM images of undoped TiO2 precursor calcined at (a) 773K, (b) 573K and TiO2 precursor doped with (c) 1.16, (d) 2.01, (e) 3.08, (f) 4.87, (g) 6.68% Fe calcined at 573K.

Fig. 3.
(0.61MB).

TEM images of (a) pure TiO2, (c) C doped TiO2, (e) C,Fe (2.01wt%) co-doped TiO2 and SAED patterns of (b) pure TiO2, (d) C doped TiO2, (f) C,Fe (2.01wt%) co-doped TiO2.

These images indicate that particle size goes on decreasing with introduction of C and C, Fe co-doping into TiO2 lattice. The decrease in crystallite size may be caused by a number of defects in the anatase crystals produced by the substitution of part of the Ti4+ site by Fe3+ ions. It also indicates that in case of pure TiO2 particle size varies between 8 and 15nm (Fig. 3a). Whereas C doped TiO2 prepared at 573K (Fig. 3c) having particle sizes between 8 and 11nm. C, Fe co-doped TiO2 with 2.01wt% of Fe have a particle size varies between 6 and 9nm.

3.4Chemical composition analysis

Fig. 4 shows the XPS survey spectra for Pure, C doped and C, Fe (2.01wt%) co-doped TiO2 nanoparticles. The Ti 2p3/2 and Ti 2p1/2 spin-orbital splitting photoelectrons for TiO2 are located at binding energies of 457 and 463eV, respectively, which is consistent with the values of Ti4+ in the TiO2 lattices [31]. The comparison between the Ti 2p3/2 spectra of undoped TiO2 and those of C and C, Fe doped TiO2 indicates that the doped TiO2 samples exhibit small binding energy shifts. It infers that the doped C and Fe ions may diffuse into TiO2 lattices to form the O–Ti–C and Fe–O–Ti bond. The O 1s main peak at 528eV is assigned to the metallic oxides, which is consistent with the binding energy of O2 in the TiO2 lattices [32].

Fig. 4.
(0.29MB).

(a) XPS survey spectra for pure TiO2, C doped TiO2 and C, Fe (2.01wt%) co-doped TiO2 photocatalysts and (b) high resolution XPS spectra of Ti 2p, O 1s, C 1s and Fe 2p.

A shoulder to the main O 1s peak observed at high binding energy, which can be attributed to the hydroxyl groups or chemisorbed water molecules adsorbed on TiO2 surface [33]. It is noted that the O 1s spectra of C and C, Fe co-doped TiO2 have a small binding energy shift compared with undoped TiO2. The results can be ascribed to an increase in the ionic state of the oxygen bond causing the binding energies of all electronic states of oxygen to shift and successful incorporation of C and Fe atoms [34,35]. The oxygen content increases from 31.6%, and 36.8 (C, Fe co-doped TiO2 and C doped TiO2 prepared at 573K) to 46.3% in pure TiO2 prepared at 773K as a result of the decomposition of the carbonaceous groups at high temperature. Fe 2p spectrum was used to evaluate the electronic nature of Iron in C, Fe doped TiO2. Fe2p core level spectrum indicates that binding energy centers of Fe 2p3/2 and Fe 2p1/2 peaks are located at 710 and 724eV, respectively. Binding energy at 718eV suggests that Fe is incorporated into the TiO2 lattice in Fe3+ ionic state [36] and have Fe–O–Ti environment within the TiO2 lattice. The C 1s peaks located at 284 and 287eV, which may be due to the remaining organic precursor not yet completely removed at 573K. The doping of C species in TiO2 might exist as O–Ti–C and Ti–O–C [37,38]. From the XPS elemental analysis of samples, it was confirmed that carbon-containing species exist in the samples. This may be due to during the reaction between titanium isopropoxide, cyclohexane, n-butanol and CTAB the carbon-containing species get trapped in the growing TiO2. At appropriate post calcinations temperature around 573K, C may get incorporated into TiO2 lattice. At higher calcination temperature (773K) C may get decomposed and replaced by oxygen atoms.

3.5Band gap energy

The color of C doped TiO2 sample prepared at 573K is gray; however, the sample prepared at 773K is almost white. C, Fe co-doped TiO2 sample is grayish brown in color and as the concentration of Fe increases it changes to dark brown. Their optical properties were studied using UV–Visible diffuse reflectance spectra and the results are presented in Fig. 5 and Fig. S3.

Fig. 5.
(0.16MB).

Diffuse reflectance spectra and plot of (F(R)hv)2 vs photon energy (eV) using Kubelka–Munk method for un doped TiO2 precursor calcined at (a) 773K, (b) 573K and TiO2 doped with (c) 1.16, (d) 2.01, (e) 3.08, (f) 4.87, (g) 6.68% Fe precursor and calcined at 573K.

The band gap energies of pure and doped TiO2 samples were calculated from the diffuse-reflectance spectra by performing a Kubelka–Munk analysis using the equation: F(R)=(1R)2/2R. Where, R is the diffuse reflectance. The band gap energies can be calculated by plotting the (F(R)hv)2 as a function of the energy in electron volts. The pure anatase TiO2 is having the band gap energy 3.14eV. The band gap for C modified TiO2 sample is 2.86eV, which is lower than that of pure anatase TiO2. It is due to the fact that C 2p level from the interstitial carbon could hybridize with O 2p level to form an upshift valence band and then narrows the band gap [39]. The absorption edge shifts to lower energies/higher wavelength with increasing Fe concentration. The band gap was 2.84eV for 1.16 Fe/C–TiO2, 2.81eV for 2.01Fe/C–TiO2, 2.77eV for 3.08 Fe/C–TiO2, 2.29eV for 4.87 Fe/C–TiO2, and 2.15eV for 6.68 Fe/C–TiO2. This result is consistent with the changes in the color of the samples. Besides the effect of C, the origin of this visible light absorption was also due to the formation of a dopant energy level within the band gap of TiO2 with iron doping [9]. Shift in visible region (Red shift) upon increasing the doping concentration corresponds to a sp-d exchange interaction between the band electrons and the localized d electrons of the substituted dopant ions.

3.6Photoluminiscence study

The photoluminescence emission (PL) is a useful technique to reveal the efficiency of electron–hole pair trapping, immigration and transfer in semiconductor particles. The PL emission spectra of all samples are presented in Fig. 6. Pure TiO2 exhibits emission bands at 403 and 460nm. Emission centered at 403nm is attributed to excitonic recombination corresponding to the near band edge emission of TiO2. The emission in the blue-green region at 460nm is attributed to the electron transition between a shallow donor and a deep acceptor. It is observed that the peak positions were similar, but PL intensities varies among these samples. It is known that photoluminescence effect, is a result of direct radiative recombination of electron–holes and lower recombination of generated carriers causes the decrease of PL intensity [40]. Lower the excitonic PL intensity, stronger the capacity of dopants to capture photo-induced electrons, higher the separation rate of photoinduced electrons and holes, and higher the photocatalytic activity [41]. The PL intensity of pure TiO2 is highest among all samples, indicates the increase of recombination of electron and hole. C and Fe co-doped TiO2 shows decrease in PL intensity which confirms that the recombination of electron–hole pairs is effectively suppressed because Fe(III) cations could act as shallow traps in the lattice of TiO2. Here, Fe(III) cations are acting as photogenerated hole trappers. The trapped holes by Fe(III) cations migrate to the surface adsorbed hydroxyl ion to produce hydroxyl radicals. 2.01 Fe-CT sample shows lowest PL intensity, impling that the charge carriers are separated more effectively, which reasonably led to a higher photocatalytic activity.

Fig. 6.
(0.22MB).

Photoluminescence spectra for undoped TiO2, C doped TiO2 and C, Fe co-doped TiO2 photocatalyst.

3.7Visible-light photocatalytic activity study

Visible light photocatalytic degradation of malachite green (MG) was studied in presence of nanosized pure and doped TiO2 photocatalysts. UV visible spectra of aqueous solution of MG irradiated with visible light at different time intervals in presence of C, Fe (2.01wt%) co-doped TiO2 (obtained at 573K) photocatalyst were recorded at different time intervals and are presented in Fig. 7. These spectra show characteristic peak maxima located at 616nm. As irradiation time increases the height of peak at 616nm decreases. This is due to photocatalytic degradation of malachite green. Appearance of a peak around 370nm in the UV-Visible spectra after 75 and 90min may be due to the formation of less hazardous byproducts.

Fig. 7.
(0.17MB).

UV-visible spectra of MG solution irradiated with visible light at different time intervals in presence of C, Fe co-doped TiO2 photocatalyst.

3.7.1Effect of calcination temperature of catalyst

UV-visible spectra of MG solution (20ppm) irradiated with visible light for different time intervals in presence of TiO2 photocatalyst obtained by calcining precursor at various temperatures were recorded. Effect of calcination temperature on the degradation of MG in the presence of visible light (90min of irradiation time) is presented in Fig. 8. It reveals that photocatalytic activity depends on calcination temperature of catalyst. In absence of catalyst there is slight decrease in MG concentration it indicates that MG is quite stable in visible light. Photocatalyst prepared at 573K exhibits better photocatalytic activity and as calcination temperature increases the photocatalytic activity decreases. This is due to the fact that with increasing the calcination temperature particle size of catalyst increases and photocatalytic activity decreases. Also, TiO2 prepared at 573K contains 7.59% C and as the calcination temperature increases the amount of C on TiO2 decreases. It is known that C doped TiO2 exhibit better photocatalytic activity than bare TiO2. Precursor calcined at 573K exhibit better visible light activity as compared to the precursors calcined at high temperatures. Therefore, the C, Fe co-doped precursors were calcined at 573K and used for further study.

Fig. 8.
(0.07MB).

Photocatalytic degradation of MG solution by visible light illumination using TiO2 calcined at various temperatures (irradiation time is 90 in).

3.7.2Effect of co-doping

Compared to bare TiO2, C doped TiO2 exhibit better visible light catalytic activity for degradation of MG. To enhance the visible light activity further, TiO2 was co-doped with Fe and the photocatalytic activity of C, Fe co-doped TiO2 was studied and results are presented in Fig. 9. It shows that compared to bare and C doped TiO2, C, Fe co-doped TiO2 has better degradation efficiency. As the amount of Fe increases degradation of MG increases up to 2.01% Fe doping. Further increase in the amount of Fe results in decrease in MG degradation. The photocatalytic activity of Fe and C modified TiO2 is higher due to Fe doping, because it effectively captures photo induced electrons and inhibits the electron–hole recombination and improves photocatalytic activity. Synergistic effects of C and Fe co-doping increases the utilization of visible light by narrowing the band gap and also enhances the separation of photo generated holes and electrons which leads to increase in photo degradation rate of malachite green [42]. Higher doping of Fe, i.e., above 2.01wt% may be responsible for recombination of electron and holes and hence photocatalytic activity decreases.

Fig. 9.
(0.12MB).

Effect of C and Fe co-doping on MG photodegradation, (a) C (7.59%) doped TiO2 and C, Fe co-doped TiO2 with (b) 1.16, (C) 2.01, (d) 3.08, (e) 4.87, and (f) 6.68% Fe.

3.7.3Recycling of catalyst

Stability of photocatalyst during photodegradation process is an important factor for practical application. Stability tests were performed by repeating the reaction three times using recovered photocatalyst. The data obtained is presented in Fig. 10. This figure shows that up to the third cycle there is no noticeable decrease in photocatalytic efficiency. It indicates that C, Fe co-doped TiO2 prepared in the present work is stable and reusable photocatalyst.

Fig. 10.
(0.09MB).

Cyclic runs showing photocatalytic degradation of MG.

3.7.4Origin of visible light absorption and photoexcitation mechanism over C, Fe co-doped TiO2

Carbon and iron co-doping have synergistic effects on improving the photocatalytic activity of TiO2 under visible light irradiation. We proposed a possible mechanism for the synergistic effects of C and Fe, which is illustrated in Fig. 11. Pure TiO2 due to its large band gap can be activated in UV light only. For C-doped TiO2, C can create new energy level just above the valence band of TiO2 and reduces the band gap. Hence, C-doped TiO2 can be activated in visible light. On the one hand, C, Fe co-doped TiO2 shows further decrease in band gap due to simultaneous doping of two atoms. Here, interstitial carbon dopant could create intra-band-gap states close to the valence band edges and Fe3+ present in the substitutional positions into the TiO2 lattice would introduce a dopant energy level below the conduction band of TiO2. Due to this reason C and Fe modified TiO2 shows highest absorption in visible light region. Consequently, more photons from visible region are utilized to generate photogenerated electrons and holes. C and Fe doping in TiO2 systems may improve the separation efficiency of photogenerated electrons and holes. Under visible light irradiation, Fe ions act as shallow electron-trapping centers. Subsequently, Fe2+ could be oxidized to Fe3+ by transferring electrons to absorbed O2 on the surface of TiO2 and a neighboring surface Ti4+, which then lead to interfacial electron transfer [15].

Fig. 11.
(0.16MB).

Possible mechanism for the photocatalytic degradation of organic pollutants by undoped TiO2, C doped TiO2 and C, Fe co-doped TiO2.

In the intervening time, the C species could trap the part of photogenerated holes [17]. Thus, the recombination rate of photogenerated electrons and holes is concealed. As a consequence, the photocatalytic degradation efficiency of C and Fe modified TiO2 is improved. The synergistic effects of C and Fe not only enhance the utilization efficiency of solar energy due to narrowing the band gap because of C and Fe co-doping, but also sufficiently endorse the separation of photogenerated electrons and holes and then lead to high photodegradation of MG under the visible light irradiation.

4Conclusions

In the present work, the synthesis and characterization of TiO2 and C, Fe modified TiO2 prepared by a microemulsion method was described. The photocatalysts calcined at 573K are spherical particles with a crystallite size about 7–20nm and the crystal phase is purely anatase. Diffuse reflectance spectra indicate that C and Fe co-doping improves visible light absorption capacity of TiO2 samples. The results of the XPS study suggest that Fe ions are predominantly in Fe3+ states and have Fe–O–Ti environment within the TiO2 lattices. The C and Fe(III) doped TiO2 samples shows better photocatalytic activity as compared to bare and C doped TiO2 and the optimum doping amount of Fe is 2.01wt%. The high rate of photodegradation of MG with visible light irradiation is due to synergistic effect of C and Fe, which efficiently promotes separation of photo generated electrons and holes. Also, synthesized photocatalyst is highly stable and reusable photocatalyst.

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgements

Authors are thankful to Sophisticated Analytical Instrument Laboratory (SAIF) IIT, Mumbai, India for availing TEM facilities. One of the authors (Atul B. Lavand) is grateful to UGC-New Delhi, India for providing BSR fellowship.

Appendix A
Supplementary data

The following are the supplementary data to this article:

References
[[1]]
V. Yargeau,C. Metcalfe
Photocatalytic degradation of contaminants with titanium dioxide: a 40-year retrospective on the paper by John Carey and colleagues published in BECT
Bull Environ Cont Toxicol, 98 (2017), pp. 147-148
[[2]]
K. Xu,A. Chatzitakis,T. Norby
Solid-state photoelectrochemical cell with TiO2 nanotubes for water splitting”
Photochem Photobiol Sci, 16 (2017), pp. 10-16 http://dx.doi.org/10.1039/c6pp00217j
[[3]]
Y. Ding,T. Zhang,C. Liu,Y. Yang,J. Pan,J. Yao
Shape-controlled synthesis of single-crystalline anatase TiO2 micro/nanoarchitectures for efficient dye-sensitized solar cells
Sustain Energy Fuels, (2017), http://dx.doi.org/10.1039/C6SE00041J
[[4]]
K. Zakrzewska,M. Radecka
TiO2-based nanomaterials for gas sensing—influence of anatase and rutile contributions
Nanoscale Res Lett, 12 (2017), pp. 1-8 http://dx.doi.org/10.1186/s11671-016-1773-2
[[5]]
A. Fujishima,X.T. Zhang,D.A. Tryk
TiO2 photocatalysis and related surface phenomena
Surf Sci Rep, 63 (2008), pp. 515-582
[[6]]
J. Yu,Q. Xiang,M. Zhou
Preparation, characterization and visiblelight-driven photocatalytic activity of Fe-doped titania nanorods and firstprinciples study for electronic structures
Appl Catal B: Environ, 90 (2009), pp. 595-602
[[7]]
M.R. Hoffmann,S.T. Martin,W. Choi,D.W. Bahnemann
Environmental applications of semiconductor photocatalysis
Chem Rev, 95 (1995), pp. 69-96
[[8]]
X.H. Wang,J.G. Li,H. Kamiyama,Y. Moriyoshi,T. Ishigaki
Wavelength-sensitive photocatalytic degradation of methyl orange in aqueous suspension over iron(III)-doped TiO2 nanopowders under UV and visible light irradiation
J Phys Chem B, 110 (2006), pp. 6804-6809 http://dx.doi.org/10.1021/jp060082z
[[9]]
W. Choi,A. Termin,M.R. Hoffmann
The role of metal ion dopants in quantumsized TiO2: correlation between photoreactivity and charge carrier recombination dynamics
J Phys Chem, 98 (1994), pp. 13669-13679
[[10]]
C.C. Chen,M. Long,H. Zeng,W. Cai,B. Zhou,J. Zhang
Preparation, characterization and visible-light activity of carbon modified TiO2 with two kinds of carbonaceous species
J Mol Catal A: Chem, 314 (2009), pp. 35-41
[[11]]
H. Li,Y. Hao,H. Lu,L. Liang,Y. Wang,J. Qiu
A systematic study on visible-light N-doped TiO2 photocatalyst obtained from ethylenediamine by sol–gel method
Appl Surf Sci, 344 (2015), pp. 112-118
[[12]]
D. Liu,P.V. Kamat,K.G. Thomas,K.J. Thomas,S. Das,M.V. George
Picosecond dynamics of an IR sensitive squaraine dye. Role of singlet and triplet excited states in the photosensitization of TiO2 nanoclusters
J Chem Phys, 106 (1997), pp. 6404-6411
[[13]]
A. Kay,R. Humphry-Baker,M. Graetzel
Artificial photosynthesis. 2. Investigations on the mechanism of photosensitization of nanocrystalline TiO2 solar cells by chlorophyll derivatives
J Phys Chem, 98 (1994), pp. 952-995
[[14]]
H. Yamashita,M. Harada,J. Misaka,M. Takeuchi,B. Neppolian,M. Anpo
Photocatalytic degradation of organic compounds diluted in water using visible light responsive metal ion-implanted TiO2 catalysts: Fe ion-implanted TiO2
Catal Today, 84 (2003), pp. 191-196
[[15]]
J.F. Zhu,F. Chen,J.L. Zhang,H.J. Chen,M. Anpo
Fe3+–TiO2 photocatalysts prepared by combining sol–gel method with hydrothermal treatment and their characterization
J Photochem Photobiol A: Chem, 180 (2006), pp. 196-204
[[16]]
C. Adan,A. Bahamonde,M. Fernandez-Garcia,A. Martinez-Arias
Structure and activity of nanosized iron-doped anatase TiO2 catalysts for phenol photocatalytic degradation
Appl Catal B: Environ, 72 (2007), pp. 11-17
[[17]]
Y. Park,W. Kim,H. Park,T. Tachikawa,T. Majima,W. Choi
Carbon-doped TiO2 photocatalyst synthesized without using an external carbon precursor and the visible light activity
Appl Catal B: Environ, 91 (2009), pp. 355-361
[[18]]
N.P. Xu,Z.F. Shi,Y.Q. Fan,J.H. Dong,J. Shi,M.Z.C. Hu
Effects of particle size of TiO2 on photocatalytic degradation of methylene blue in aqueous suspensions
Ind Eng Chem Res, 38 (1999), pp. 373-379
[[19]]
J. Klongdee,W. Petchkroh,K. Phuempoonsathaporn,P. Praserthdam,A.S. vangnai,V. Pavarajarn
Activity of nanosized titania synthesized from thermal decomposition of titanium (IV) n-butoxide for the photocatalytic degradation of diuron Many factors affect the photocatalytic activity of titania
Sci Technol Adv Mater, 6 (2005), pp. 290-295
[[20]]
S. Pavasupree,Y. Suzuki,S. Art,S. Yoshikawa
Preparation and characterization of mesoporous MO2 (M = Ti, Ce, Zr and Hf) nanopowders by a modified sol–gel method
Ceram Int, 31 (2005), pp. 959-963
[[21]]
N. Venkatachalam,M. Palanichamy,V. Murugesan
Sol–gel preparation and characterization of alkaline earth metal doped nano TiO2: efficient photocatalytic degradation of 4-chlorophenol
J Mol Catal A: Chem, 273 (2007), pp. 177-185
[[22]]
J. Yu,M. Zhou,B. Cheng,X. Zhao
Preparation, characterization and photocatalytic activity of in situ N S-codoped TiO2 powders
J Mol Catal A: Chem, 246 (2006), pp. 176-184
[[23]]
D. Byun,Y. Jin,B. Kim,J. Lee,D. Park
Photocatalytic TiO2 deposition by chemical vapor deposition
J Hazard Mater, 73 (2000), pp. 199-206
[[24]]
P. Borse,L. Kankate,F. Dassenoy,W. Vogel,J. Urban,S. Kulkarni
Synthesis and investigation of rutile phase nanoparticles of TiO2
J Mater Sci, 13 (2002), pp. 553-559
[[25]]
Y. Lai,Y. Chen,H. Zhuang,C. Lin
A facile method for synthesis of Ag/TiO2 nanostructures
Mater Lett, 62 (2008), pp. 3688-3690
[[26]]
W. Liu,R. Guo
The photostabilization of hemoglobin in triton X-100 aqueous solution and triton X-100/n-C5H11OH/H2O microemulsion
J Photochem Photobiol, 86 (2010), pp. 835-843
[[27]]
C. Lu,W. Wu,R. Kale
Microemulsion-mediated hydrothermal synthesis of photocatalytic TiO2 powders
J Hazard Mater, 154 (2008), pp. 649-654 http://dx.doi.org/10.1016/j.jhazmat.2007.10.074
[[28]]
A.B. Lavand,Y.S. Malghe
Visible-light photocatalytic degradation of ethidium bromide using carbon- and iron-modified TiO2 photocatalyst
J Thermal Anal Calorim, 123 (2015), pp. 1163-1172
[[29]]
C. Wang,C. Bottcher,D. Bahnemann,J.A. Dohrmann
Comparative study of nanometer sized Fe(III)-doped TiO2 photocatalyst: synthesis, characterization and activity
J Mater Chem, 13 (2003), pp. 22-29
[[30]]
J. Zhu,W. Zheng,B. He,J. Zhang,M. Anpo
Characterization of Fe–TiO2 photocatalyst synthesized by hydrothermal method and their photocatalytic reactivity for photodegradation of XRG dye diluted in water
J Mol Catal A: Chem, 216 (2004), pp. 35-43
[[31]]
B. Erdem,R.A. Hunsicker,G.W. Simmons,E.D. Sudol,V.L. Dimonie,M.S. El-Aasser
XPS and FTIR surface characterization of TiO2 particles used in polymer encapsulation
Langmuir, 17 (2001), pp. 2664-2669
[[32]]
N. Serpone,D. Lawless,R. Khairutdinov
Subnanosecond relaxation dynamics in TiO2 colloidal sols: relevance to heterogeneous photocatalysis
J Phys Chem, 99 (1995), pp. 16655-16661
[[33]]
J.C. Yu,W. Ho,J. Yu,S.K. Hark,K. Iu
Effects of trifluoroacetic acid modification on the surface microstructures and photocatalytic activity of mesoporous TiO2 thin films
Langmuir, 19 (2003), pp. 3889-3896
[[34]]
S.A. Naseer
X-ray photoelectron spectroscopy study on the composition and structure of BaTiO3 thin films deposited on silicon
Appl Surf Sci, 157 (2000), pp. 14-22
[[35]]
W.C. Hung,Y.C. Chen,H. Chu,T.K. Tseng
Synthesis and characterization of TiO2 and Fe/TiO2 nanoparticles and their performance for photocatalytic degradation of 1,2-dichloroethane
Appl Surf Sci, 255 (2008), pp. 2205-2213
[[36]]
M. Hirano,T. Joji,M. Inagaki,H. Iwata
Direct formation of iron (III)-doped titanium oxide (Anatase) by thermal hydrolysis and its structural property
J Am Ceram Soc, 87 (2004), pp. 35-41
[[37]]
E. Papirer,R. Lacroix,J.B. Donnet,G. Nanse,P. Fioux
XPS study of the halogenations of carbon black. Part 2
Chlor Carbon, 33 (1995), pp. 63-72
[[38]]
S. Sakthivel,H. Kisch
Daylight photocatalysis by carbon-modified titanium dioxide
Angew Chem Int Ed, 42 (2003), pp. 4908-4911
[[39]]
H. Liu,A. Imanishi,Y. Nakato
Mechanisms for photooxidation reactions of water and organic compounds on carbon-doped titanium dioxide, as studied by photocurrent measurements
J Phys Chem C, 111 (2007), pp. 8603-8610
[[40]]
K. Nagaveni,M.S. Hegde,G. Madras
Structure and photocatalytic activity of Ti1−xMxO2 (M = W, V, Ce, Zr, Fe, and Cu) synthesized by solution combustion method
J Phys Chem B, 108 (2004), pp. 20204-20212
[[41]]
H. Tang,K. Prasad,R. Sanjines,P.E. Schmidd,F. Levy
Electrical and optical properties of TiO2 anatase thin films
J Appl Phys, 75 (1994), pp. 2042-2047
[[42]]
Y. Wu,J. Zhang,L. Xiao,F. Chen
Properties of carbon and iron modified TiO2 photocatalyst synthesized at low temperature and photodegradation of acid orange 7 under visible light
Appl Surf Sci, 256 (2010), pp. 4260-4268
Copyright © 2018. Brazilian Metallurgical, Materials and Mining Association
Journal of Materials Research and Technology

Subscribe to our Newsletter

Article options
Tools
Supplemental materials
Cookies policy
To improve our services and products, we use cookies (own or third parties authorized) to show advertising related to client preferences through the analyses of navigation customer behavior. Continuing navigation will be considered as acceptance of this use. You can change the settings or obtain more information by clicking here.