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A facile synthesis of mesoporous titania cubes and their photocatalytic application
Accepted Manuscript A facile synthesis of mesoporous titania cubes and their photocatalytic application Ipsita Hazra Chowdhury, Pallab Bose, Milan Kanti Naskar PII:
S0925-8388(16)30168-2
DOI:
10.1016/j.jallcom.2016.01.167
Reference:
JALCOM 36518
To appear in:
Journal of Alloys and Compounds
Received Date: 26 September 2015 Revised Date:
28 December 2015
Accepted Date: 21 January 2016
Please cite this article as: I.H. Chowdhury, P. Bose, M.K. Naskar, A facile synthesis of mesoporous titania cubes and their photocatalytic application, Journal of Alloys and Compounds (2016), doi: 10.1016/ j.jallcom.2016.01.167. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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A facile synthesis of mesoporous titania cubes and their photocatalytic application
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Ipsita Hazra Chowdhury, Pallab Bose, Milan Kanti Naskar* Sol-Gel Division , CSIR-Central Glass and Ceramic Research Institute, Kolkata 700032, India
Abstract
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Cube shaped mesoporous anatase TiO2 was synthesized by hydrothermal technique at 180oC/24h in the presence of glucose followed by calcination at 600oC/2h. The particles
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were characterized by XRD, DTA/TG, Raman spectroscopy, N2 adsorption-desorption study, FESEM and TEM. The BET surface area, pore volume and pore diameter of the calcined product were found to be 67.3 m2g-1, 0.24 cm3g-1 and 9 nm, respectively. The FESEM images exhibited cube shaped particles of size 300-600 nm. TEM images revealed
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the aggregation of 10-20 nm size particles in the cubes. The photocatalytic degradation of methylene blue (MB) and and 4-chlorophenol (4-CP), the environmental pollutants was studied with the synthesized calcined product. It showed 93.9% and 92.9%
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photodegradataion of MB and 4-CP, respectively after 2h of irradiation. Keywords: Titania; Chemical synthesis; Microstructure; TEM; Optical spectroscopy
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*Corresponding author: Ph: +91 33 2473 3496 (Ext. 3516), E-mail: [email protected] 1. Introduction
Titania (TiO2) due to its unique electrical, chemical and physical properties is a wellknown material for its wide range of applications in the fields of electronics, photonics, sensors and catalysis [1]. It has been extensively studied for its efficiency towards photocatalytic degradation of organic and inorganic pollutants in waste water. The
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functionality of TiO2 depends upon its crystallinity, mesoporosity and morphology [2]. To improve its photocatalytic efficiency, different shaped TiO2 such as nanorods, nanoparticles, nanotubes, nanosphers, nanowires etc. was designed [3-7]. Different
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methods have been reported for the synthesis of titania, such as sol-gel, co-precipitation, microemulsion, hydrothermal, sovothermal, microwave etc [8-13].
In the present study, we have synthesized cube shaped TiO2 by hydrothermal
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process in the presence of titania precursor, glucose, water and ethanol followed by calcination at 600oC/2h. Photocatalytic activity of calcined TiO2 for the degradation of
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methylene blue (MB) and phenol derivative i.e., 4-chlorophenol (4-CP) was studied. To understand the effects of glucose on mesoporous cube shaped anatase TiO2 obtained after calcinations at 600oC toward morphological change along with other properties like crystallization behaviors, Raman spectra, N2 adsorption-desorption studies, and also the
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photocatalytic activities for the degradation of environmental pollutants, MB and 4-CP, the results were compared with those of TiO2 obtained in the absence of glucose keeping the experimental parameters same. Synthesis of cube shaped TiO2 using glucose in the
Experimental procedure
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2.
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absence of any templates is the first time we report to the best of our knowledge.
2.1 Preparation of cube shaped TiO2 All the chemicals used were analytically pure. In a typical synthesis, 20.1 mmol
glucose was dissolved in 60 mL deionized (DI) water followed by slow addition of 10 mmol titanium (IV) oxysulfate (TIOS) under vigorous stirring. After complete dissolution, 10 mL ethanol was added into the above solution. The resultant solution was
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transferred into a 100 mL Teflon lined autoclave and heated in an oven at 1800C for 24 h. A black product was obtained. It was washed with distilled water and alcohol and dried at 600C for 6 h. The above experiment was performed in the absence of glucose keeping all
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the experimental parameters same. The as-prepared samples (prepared in the presence and absence of glucose) were calcined at 600oC for 2 h with a heating rate of 2oC min-1. 2.2 Characterization
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X-ray diffraction (XRD) studies of the samples were performed by Philips X’Pert Pro PW 3050/60 powder diffractometer using Ni-filtered Cu-Kα radiation (λ = 0.15418
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nm) operated at 40 kV and 30 mA. The thermal behavior of the as-prepared (uncalcined) sample was studied by differential thermal analysis (DTA) and thermogravimetry (TG) (Netzsch STA 449C, Germany) from 30o to 1000oC in air atmosphere at the heating rate of 10oC min-1. The Raman spectrum was recorded using a RENISHAW spectrometer
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with 514 nm radiation from an argon laser at room temperature. Nitrogen adsorption and desorption measurements were performed at liquid nitrogen temperature (77 K) on a Quantachrome (ASIQ MP) instrument. The sample was outgassed in vacuum at 200 oC
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for 4 h prior to measurement. The total surface area was determined by BET method. The total pore volume was estimated from the amount of nitrogen adsorbed at the relative
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pressure (p/po) of ca 0.99. The morphology of the particles was examined by FESEM (Model: Zeiss, SupraTM 35VP, Oberkochen, Germany) operating with an accelerating voltage of 10 kV, and transmission electron microscopy (TEM), using a Tecnai G2 30ST (FEI) instrument operating at 300 kV. UV-Visible spectra were recorded using UV-VISNIR spectrophotometer (UV-3101PC, Shimadzu) in the wavelength range of 200 nm to 800 nm.
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2.3 Photocatalytic Study Photocatalytic test was performed for the degradation of methylene blue (MB) and and 4-chlorophenol (4-CP). In a typical photocatalytic test, for MB degradation, 2 mg
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of the TiO2 sample was mixed with 12 mL of 10−5 M MB dye solution, and for 4-CP degradation, 5 mg of the TiO2 sample was mixed with 10 mL of 1.5x10−4 M 4-CP solution. Both the dispersions were stirred for 60 min in dark to achieve adsorption
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equilibrium. Then the aliquots were taken out, filtered by Millipore filter paper (pore dia 0.22 µm). The filtrates were analyzed using a UV-visible spectrophotometer. Rest of the
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dye solution was placed in a rectangular box (36 cm x 30 cm x 44 cm) fitted with eight tubes with a power source of 6 W each placed at the inside top of the box. The solution was irradiated from a distance of 11 cm with UV (λ= 365 nm) light at room temperature in the photoreactor. After a certain interval of irradiation, aliquots were collected, filtered
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and monitored by UV-visible spectrophotometer. The decrease in absorption intensity at λmax=664 nm and λmax=225 nm indicates the photocatalytic degradation of the MB and
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4-CP, respectively.
Result and Discussion:
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3.1 XRD analysis
XRD patterns of (i) as-prepared (uncalcined) and calcined (600oC) samples
obtained in the (ii) presence and (iii) absence of glucose are shown in Fig. 1(a). The appearance of diffraction peaks at around 25.09o, 37.65o, 48.02o, 53.89o, 55.07o, 62.38o, 68.7o, 70.07o and 75o corresponding to the crystal planes of [101], [004], [200], [105], [211], [204], [116], [220], and [215], respectively is due to the presence of anatase TiO2
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(JCPDS No. 21-1272) in all the samples. It was noticed that after calcinations, crystallization of TiO2 obtained in the presence of glucose increased significantly compared to that prepared in the absence of glucose. It signifies that carbon particle
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during thermal decomposition of glucose could enhance the crystallization of TiO2. The crystallite sizes (D) of the particles obtained from Scherrer formula were found to be
the presence and absence of glucose, respectively. 3.2 Raman study
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14.1, 33.3 and 25 nm for the as-prepared (uncalcined), and calcined samples prepared in
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The Raman spectra of (i) as-prepared (uncalcined) and calcined (600oC) samples obtained in the (ii) presence and (iii) absence of glucose is shown in Fig. 1b. For all the samples, the appearance of sharp and intense peak at 144-150 cm-1 and a very weak peak at around 196 cm-1 assigning to Eg mode of vibration is the characteristic of anatase TiO2.
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In the higher frequency region, the other peaks at around 400, 516 and 639 cm-1 corresponding to B1g, A1g and Eg modes also confirm the presence of anatase TiO2 [14] in the samples. Interestingly, the most intense peak at 150 cm-1 of as-prepared
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(uncalcined) sample shifted to 145 cm-1 and 144 cm-1 after calcination of the samples prepared in the absence and presence of glucose, respectively. The blue shift of Raman
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spectra was due to increase in crystallite sizes of calcined samples [15] prepared in the presence and absence of glucose. However, a little peak shifting was noticed for the calcined sample obtained in the presence of glucose compared to that prepared in the absence of glucose instead of their difference in crystallite size. 3.3 Textural properties
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Fig. 1c shows the N2 adsorption-desorption isotherms of (i) as-prepared (uncalcined) and calcined (600oC) samples obtained in the (ii) presence and (iii) absence of glucose. All the curves indicated type IV isotherm according to IUPAC classification,
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which signifies mesoporous characteristic of the sample. The appearance of H-2 type hysteresis loop of the isotherms demonstrates ink-bottle-like mesopores and/or pore constrictions, where pore mouth is smaller than the pore body [16]. The corresponding
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BJH pore size distributions (PSDs) derived from desorption data of the isotherms are shown in the inset of Fig. 1c showing a monomodal PSDs. The textural properties (the
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BET surface area, pore volume and pore size) of the particles are shown in Table 1. It revealed that BET surface area and pore volume of the samples decreased in the order of as-prepared (uncalcined) > calcined (with glucose) > calcined (without glucose). However, pore size increased from 4.7 nm to 9 after calcination of the samples. From the
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above results it is clear that glucose played a significant role in enhancing the BET surface area and pore volume of TiO2. 3.4 Thermal analysis
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Figure 1d shows the DTA and TG curves of the as-prepared (uncalcined) TiO2 particles. In the DTA curve, the appearance of broad endothermic peak at around 165oC
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was attributed to the removal of adsorbed water, which accompanied a mass loss of about 7% up to 300oC in the TG curve. Two broad exothermic peaks at around 350o and 500oC were due to decomposition of inorganic moieties from the precursor (TIOS) and the carbonaceous materials derived from glucose [17], respectively. The TG curve shows a significant weight loss of about 70% in the temperature range of 300-550oC. Practically no weight loss was found above 5500C.
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3.5 FESEM study Figure 2a shows the FESEM image of the calcined product obtained in the presence of glucose. It indicated the formation of TiO2 cubes of size about 300-600 nm.
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During the reaction process, nucleation and growth of the particles take place via Ostwald ripening in which larger aggregated particles are formed with the cost of smaller seed particles. Figure 2b shows the growth evolution process of TiO2 cubes. It is shown
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schematically that the sharp edged cube shaped particles were formed via surface reconstruction and surface edging process. To understand the effect of glucose on the
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morphological change of cube shaped particles, the same experiment was performed in the absence of glucose followed by calcinations at 600oC. FESEM image (Fig. S1, ESI) of the particles obtained in the absence of glucose resembles large agglomerated particles without having any particular shapes. It is clear that glucose played an important role for
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the formation of cube shaped particles. Under hydrothermal condition, glucose was converted to its dehydrated species, which were linked together in a chain-like fashion through the oxygen atom [18]. The dehydrated glucose was adsorbed on some specific
3.6 TEM study
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facets of TiO2 particles inducing cube shaped particles.
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Figure 3 shows the TEM images of 600oC-treated sample obtained in the presence
of glucose. It indicated that the nanoparticles of size 10-20 nm were aggregated to form TiO2 cubes. The interparticle porosity can also be observed from high magnification TEM images (Fig. 3a). The high resolution TEM (HRTEM) (Fig. 3b) shows the lattice spacing of 0.35 nm corresponding to the (101) plane, and selected area electron diffraction (SAED) reveals the polycrystalline nature of the titania nanoparticles (Fig.
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3c). The bright spots of the concentric rings matched well with the anatase TiO2 planes obtained from XRD. 3.7 Diffuse Reflectance Spectroscopy (DRS) study
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Different materials absorb radiation at different wavelengths. The yield of photo generated electron-hole pair depends on the intensity of incident photons with energy exceeding or equaling the band gap energy. The optical properties of the samples: (a) as-
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prepared (uncalcined) and calcined (600oC) obtained in the (b) presence and (c) absence of glucose, derived from UV-Vis diffuse reflectance spectroscopy as a function of
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wavelength are shown in Fig. S2 (ESI). Figure 4 exhibits the corresponding KubelkaMunk reflection plots extracted from the UV-Visible spectra in reflection mode. The band gap was determined by extrapolating and intersecting the linear portion of (K*hν)1/2 [eV1/2] to the energy axis hν [19]. The band gap energy values were calculated as 3.61,
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3.46 and 3.79 eV for as-prepared (uncalcined), and calcined (600oC) samples obtained in the presence and absence of glucose, respectively. 3.8 Photocatalytic activity
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Before irradiation with UV light, adsorption ability of the samples: as-prepared (uncalcined), calcined (prepared with glucose), calcined (prepared without glucose), and
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Degussa P25 (standard) onto the MB and 4-CP ( both kept in the dark for 60 min for homogenization) were studied. Table 2 shows that the adsorption ability follows as: asprepared (uncalcined) > calcined (prepared with glucose) > calcined (prepared without glucose) > Degussa P25 (standard), which corroborated to their BET surface area values. The BET surface area of Degussa P25 is reported as 56 m2g-1 [20], which is found to be less than the synthesized TiO2 i.e, as-prepared (uncalcined), calcined (prepared with
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glucose) and calcined (prepared without glucose) samples (Table 1). The photocatalytic activity of as-prepared (uncalcined), calcined (prepared with glucose), calcined (prepared without glucose), and Degussa P25 (standard) samples were studied for the degradation
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of MB and 4-CP solution under UV light irradiation (365 nm). Figures 5 and 6 show the UV-visible absorption spectra of (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25 (standard)
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samples each for the degradation of MB and 4-CP as a function of irradiation time, respectively. It shows a gradual depletion of the characteristic absorbance peaks at 664
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nm and 225 nm with time for MB and 4-CP, respectively. The amount of MB and 4-CP photodegradataion with time by the samples: (i) as-prepared (uncalcined), (ii) calcined (prepared with glucose), (iii) calcined (prepared without glucose), and (iv) Degussa P25 (standard) each is shown in Fig. 7a and 7b, respectively. For both the pollutants (MB and
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4-CP), the degradation follows as: Degussa P25> calcined (prepared with glucose) > calcined (prepared without glucose) > as-prepared (uncalcined). The relatively high photocatalytic efficiency of P25 could be due the presence of both anatase and rutile
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phase of TiO2 (4:1) rendering suppressed recombination of photo-generated electron and holes [21-24]. However, the better photocatalytic acivity of calcined cube shaped TiO2
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prepared in the presence of glucose compared to that of as-prepared (uncalcined) and calcined TiO2 (prepared in the absence of glucose) could be due to the lower band gap energy (mentioned in section 3.7) of the former rendering more surface active sites for photocatalysis. Figures 8 and 9 show the logarithm plots of the absorbance (-lnA/Ao) with reaction time for MB and 4-CP, respectively by the samples: (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without
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glucose), and (d) Degussa P25 (standard) each. It reveals pseudo first order reaction for all the samples. The apparent rate constants, percentage degradation of the pollutants are shown in Table 2. In the insets of the corresponding Figs. 8 and 9, the reusability of the
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samples (the experiments were repeated using the same catalysts for another four cycles each to identify the potential reusability of the material) are shown. It shows that photocatalytic activity of the calcined samples remained almost the same up to 2-3 cycles
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as the original sample indicating recyclability of the catalyst.
The mechanism of photoexcitation and decomposition of pollutants (MB and 4-
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CP) using TiO2 photocatalyst upon irradiation with light is shown schematically in Fig. 10 [25]. The photocatalyst upon irradiation with light of suitable wavelength renders migration of electrons from the valance band to the conduction band, generating electron deficient holes in the valence band. Thus, formation of electron-hole pairs occurs. The
(.OH). The O2⋅
−
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holes and electrons generate superoxide radical anions (O2⋅ −) and hydroxyl radicals react with H2O to furnish ⋅OH and HOO⋅ having powerful oxidizing
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ability. On reacting with these powerful oxidizing agents, the pollutants gets oxidized.
4. Conclusions
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In summary, cube shaped anatase TiO2 was obtained by a facile hydrothermal process
at 180 °C/24 h in the presence of glucose followed by calcination at 600oC/2h. The dehydrated species of glucose was adsorbed on some specific facets of TiO2 particles inducing cube shaped particles. To understand the effect of glucose on cube shaped TiO2 toward
their
physicochemical
properties
and
photodegradation
efficiency
of
environmental pollutants (MB and 4-CP), the results were compared with those of TiO2
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obtained in the absence of glucose. The photocatalytic acivity of calcined cube shaped TiO2 prepared in the presence of glucose was better than that of as-prepared (uncalcined) and calcined TiO2 (prepared in the absence of glucose), which was due to the lower band
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gap energy of the former rendering more surface active sites for photocatalysis. The cube shaped calcined TiO2 obtained in the presence of glucose having higher BET surface area than that obtained without glucose, rendered 93.9% and 92.9% photodegradation of MB
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and 4-CP, respectively within 2 h. The process is useful to design shape controlled synthesis of TiO2 and other oxide particles which could have potential applications in the
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field of environment and energy sectors. Acknowledgement:
The authors would like to thank the Director of this institute for his kind permission to publish this paper. They acknowledge the help rendered by Nano-structured Materials
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Division and Material Characterization Division for material characterization. The authors I. H. C. and P. B. are thankful to UGC and DST, Government of India for their fellowships, respectively. The work was funded by DST-SERB Project (Grant No.
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SR/S3/ME/0035/2012), Government of India (No. GAP 0616).
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Figure caption: Fig. 1: (a) XRD patterns, (b) Raman spectra and (c) N2 adsorption-desorption isotherms (Inset: BJH pore size distributions) of TiO2 particles: (i) as-prepared (uncalcined) and
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calcined (600oC) samples obtained in the (ii) presence and (iii) absence of glucose; (d) DTA/TG of as-prepared (uncalcined) samples obtained in the presence of glucose.
Fig. 2: FESEM images of cube shaped TiO2 (a) low and high magnifications, and (b)
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shape evolution during the growth process (schematically shown by arrow).
images and (c) SAED pattern.
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Fig. 3: TEM images of cube shaped TiO2 (a) low and high magnifications, (b) HRTEM
Fig. 4: Kubelka-Munk reflection plots extracted from the UV-Visible spectra in reflection mode of (a) as-prepared (uncalcined) and calcined (600oC) samples obtained in the (b) presence and (c) absence of glucose.
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Fig. 5: UV-visible absorption spectra of (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25 (standard) samples for the degradation of MB as a function of irradiation time.
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Fig. 6: UV-visible absorption spectra of (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25
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(standard) samples for the degradation of 4-CP as a function of irradiation time. Fig. 7: Degradation of (a) MB and (b) 4-CP with reaction time by the (i) as-prepared (uncalcined), (ii) calcined (prepared with glucose), (iii) calcined (prepared without glucose), and (iv) Degussa P25 (standard) samples each. Fig. 8: The logarithm plots of the absorbance (-lnA/Ao) with reaction time for MB by the samples: (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined
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(prepared without glucose), and (d) Degussa P25 (standard); the insets show the reusability of the corresponding samples. Fig. 9: The logarithm plots of the absorbance (-lnA/Ao) with reaction time for 4-CP by
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the samples: (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25 (standard); the insets show the reusability of the corresponding samples.
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using cube shaped TiO2 photocatalyst.
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Fig. 10: Mechanism of photoexcitation and decomposition of pollutants (MB and 4-CP)
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B1g
Eg
(iii) (i)
200
80
400 600 -1 Raman Shift (cm )
0.04
0.00 0
10
20 30 Pore diameter(nm)
40
50
80 40
80 60
0
0.2
0.4 0.6 0.8 Relative pressure (P/P0)
1.0
200
400 600 0 Temperature( C)
40 20 800
1000
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0 0.0
Exo
0.02
100
Endo
120
0.06
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3 -1
-1
dV/dD(cm g nm )
3 -1
160
d
800
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asprepared TiO2 (with glucose) calcined cube TiO2 calcined TiO2 (without glucose)
Eg
(ii)
200 0.08
A1g
Residual Weight(%)
60
(iii) (ii) (i)
Intensity (a.u)
(215)
(204)
(116) (220)
(200)
40 2θ/degree
0.10
Volume adsorbed (cm g STP)
(105) (211)
(004)
20
c
Eg
b
Intensity (a.u)
a
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(101)
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Fig. 1: (a) XRD patterns, (b) Raman spectra and (c) N2 adsorption-desorption isotherms (Inset: BJH pore size distribution) of TiO2 particles: (i) as-prepared (uncalcined) and
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calcined (600oC) samples obtained in the (ii) presence and (iii) absence of glucose; (d)
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DTA/TG of as-prepared (uncalcined) samples obtained in the presence of glucose.
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200 nm
b
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200 nm
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a
200 nm
Surface reconstruction
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Ostwald ripening
Surface edging
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Fig. 2: FESEM images of cube shaped TiO2 (a) low and high magnifications, and (b)
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shape evolution during the growth process (schematically shown by arrow).
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b
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a
c
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d=0.35 nm (101)
(105) (200) (103) (101)
Fig. 3: TEM images of cube shaped TiO2 (a) low and high magnifications, (b)
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HRTEM images and (c) SAED pattern.
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1400
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3.61 ev
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K*hν (ev1/2)
K*hν (ev1/2)
1200
4.0
1
4.5
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5
6
hν (ev)
Fig. 4: Kubelka-Munk reflection plots extracted from the UV-Visible spectra in reflection
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mode of (a) as-prepared (uncalcined) and calcined (600oC) samples obtained in the (b)
1.0
0.6 0.4
0.8
Absorbance
Absorbance
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600
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Absorbance
a
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presence and (c) absence of glucose.
700
Wavelength (nm)
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0.0 500
600
700
800
Wavelength
Fig. 5: UV-visible absorption spectra of (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25 (standard) samples for the degradation of MB as a function of irradiation time. 21
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2.0
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b 0 min after 1hr adsorption 15 min 30 min 45 min 60 min 75 min 90 min 105 min 120 min
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c Absorbance
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1.0
1.5 Absorbance
Absorbance
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a
1.0
0.5
0.0 200
0 min after 1 hr adsorption 15 min 30 min 45 min 60 min 75 min 90 min 105 min 120 min
300 Wavelength (nm)
400
Fig. 6: UV-visible absorption spectra of (a) as-prepared (uncalcined), (b) calcined
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(prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25
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(standard) samples for the degradation of 4-CP as a function of irradiation time.
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a1.0
b 1.0 0.8
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(iii)
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60 80 Time (min)
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Fig. 7: Degradation of (a) MB and (b) 4-CP with reaction time by the (i) as-prepared (uncalcined), (ii) calcined (prepared with glucose), (iii) calcined (prepared without
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glucose), and (iv) Degussa P25 (standard) samples each.
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0.004
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0.000 1
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0
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Time (min)
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0
Fig. 8: The logarithm plots of the absorbance (-lnA/Ao) with reaction time for MB by the samples: (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined
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(prepared without glucose), and (d) Degussa P25 (standard); the insets show the
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reusability of the corresponding samples.
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3.0
b
0.0006 0.0005
-1
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3 No. of cycles
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Rate constant = 0.0011 min
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Fig. 9: The logarithm plots of the absorbance (-lnA/Ao) with reaction time for 4-CP by the samples: (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25 (standard); the insets show the
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reusability of the corresponding samples.
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.OOH
.OH
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H+
e
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CB
hν
VB
.OH
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Fig. 10: Mechanism of photoexcitation and decomposition of pollutants (MB and 4-CP)
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using cube shaped TiO2 photocatalyst.
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Table 1: Textural properties of the samples.
Vp-Total (cm3 g-1)b
DBJH (nm)c
Calcined TiO2 cube (with glucose)
67.3
0.24
9
As-prepared TiO2 (with glucose)
143.9
0.27
4.7
Calcined TiO2 (without glucose)
56.87
0.23
9
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SBET (m2g-1 )a
BET surface area; bTotal pore volume; cpore diameter by BJH desorption
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a
Sample
Table 2: The apparent rate constants, percentage adsorption and degradation of the
Calcined TiO 2 cube (with glucose)
% of MB degradation
Rate constant for MB degradation (K) (min-1)
% of 4-CP adsorption
% of 4-CP degradation
Rate constant for 4-CP degradation (K) (min-1)
2.5
93.9
0.0196
1.4
92.9
0.0221
21.2
32.2
0.0031
4.5
6.4
0.0005
1.4
40.3
0.0042
0.7
14.7
0.0011
0.5
95.2
0.0252
0.2
94.4
0.0234
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As-prepared TiO2 (with glucose)
% of MB adsorption
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Sample
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pollutants by the samples.
Calcined TiO 2 (without glucose) P25
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Electronic Supporting Information
500nm
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Fig. S1: FESEM image of calcined TiO2 prepared in absence of glucose.
b
EP
82 81 80 79
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Reflectance %
83
78
95
c
100 90
Reflectance %
84
Reflectance %
85
a
80 70
500 600 700 Wavelength (nm)
80 75 70 65
76
400
85
60
77
300
90
800
50 300
400
500 600 700 wavelength (nm)
800
200
300
400 500 600 Wavelength (nm)
Fig. S2: UV-Vis diffuse reflectance spectroscopy as a function of wavelength of the samples: (a) as-prepared (uncalcined) and calcined (600oC) obtained in the (b) presence and (c) absence of glucose.
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700
800
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Graphical representation
0.05
80 60 40
0.02 0.01 0.00 0
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-1
100
10
20 30 Pore diameter(nm)
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200 nm
0.03
-1 3
120
0.04 dV/dD(cm g nm )
140
3
-1
TiO2 cubes
Volume adsorbed (cm g STP)
160
40
50
20 0
0.2
0.4
0.6
0.8
Relative pressure (P/P0)
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0.0
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1.0
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Research Highlights
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Mesoporous TiO2 cube was synthesized hydrothermally at 180oC/24h followed by calcination (600oC/2h). The BET surface area of the calcined TiO2 cube was found to be 67.3 m2 g-1.
Calcined TiO2 cube showed 93.9% and 92.9% photodegradataion of MB and 4-CP,
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respectively.
S0925-8388(16)30168-2
DOI:
10.1016/j.jallcom.2016.01.167
Reference:
JALCOM 36518
To appear in:
Journal of Alloys and Compounds
Received Date: 26 September 2015 Revised Date:
28 December 2015
Accepted Date: 21 January 2016
Please cite this article as: I.H. Chowdhury, P. Bose, M.K. Naskar, A facile synthesis of mesoporous titania cubes and their photocatalytic application, Journal of Alloys and Compounds (2016), doi: 10.1016/ j.jallcom.2016.01.167. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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A facile synthesis of mesoporous titania cubes and their photocatalytic application
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Ipsita Hazra Chowdhury, Pallab Bose, Milan Kanti Naskar* Sol-Gel Division , CSIR-Central Glass and Ceramic Research Institute, Kolkata 700032, India
Abstract
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Cube shaped mesoporous anatase TiO2 was synthesized by hydrothermal technique at 180oC/24h in the presence of glucose followed by calcination at 600oC/2h. The particles
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were characterized by XRD, DTA/TG, Raman spectroscopy, N2 adsorption-desorption study, FESEM and TEM. The BET surface area, pore volume and pore diameter of the calcined product were found to be 67.3 m2g-1, 0.24 cm3g-1 and 9 nm, respectively. The FESEM images exhibited cube shaped particles of size 300-600 nm. TEM images revealed
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the aggregation of 10-20 nm size particles in the cubes. The photocatalytic degradation of methylene blue (MB) and and 4-chlorophenol (4-CP), the environmental pollutants was studied with the synthesized calcined product. It showed 93.9% and 92.9%
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photodegradataion of MB and 4-CP, respectively after 2h of irradiation. Keywords: Titania; Chemical synthesis; Microstructure; TEM; Optical spectroscopy
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*Corresponding author: Ph: +91 33 2473 3496 (Ext. 3516), E-mail: [email protected] 1. Introduction
Titania (TiO2) due to its unique electrical, chemical and physical properties is a wellknown material for its wide range of applications in the fields of electronics, photonics, sensors and catalysis [1]. It has been extensively studied for its efficiency towards photocatalytic degradation of organic and inorganic pollutants in waste water. The
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functionality of TiO2 depends upon its crystallinity, mesoporosity and morphology [2]. To improve its photocatalytic efficiency, different shaped TiO2 such as nanorods, nanoparticles, nanotubes, nanosphers, nanowires etc. was designed [3-7]. Different
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methods have been reported for the synthesis of titania, such as sol-gel, co-precipitation, microemulsion, hydrothermal, sovothermal, microwave etc [8-13].
In the present study, we have synthesized cube shaped TiO2 by hydrothermal
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process in the presence of titania precursor, glucose, water and ethanol followed by calcination at 600oC/2h. Photocatalytic activity of calcined TiO2 for the degradation of
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methylene blue (MB) and phenol derivative i.e., 4-chlorophenol (4-CP) was studied. To understand the effects of glucose on mesoporous cube shaped anatase TiO2 obtained after calcinations at 600oC toward morphological change along with other properties like crystallization behaviors, Raman spectra, N2 adsorption-desorption studies, and also the
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photocatalytic activities for the degradation of environmental pollutants, MB and 4-CP, the results were compared with those of TiO2 obtained in the absence of glucose keeping the experimental parameters same. Synthesis of cube shaped TiO2 using glucose in the
Experimental procedure
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2.
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absence of any templates is the first time we report to the best of our knowledge.
2.1 Preparation of cube shaped TiO2 All the chemicals used were analytically pure. In a typical synthesis, 20.1 mmol
glucose was dissolved in 60 mL deionized (DI) water followed by slow addition of 10 mmol titanium (IV) oxysulfate (TIOS) under vigorous stirring. After complete dissolution, 10 mL ethanol was added into the above solution. The resultant solution was
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transferred into a 100 mL Teflon lined autoclave and heated in an oven at 1800C for 24 h. A black product was obtained. It was washed with distilled water and alcohol and dried at 600C for 6 h. The above experiment was performed in the absence of glucose keeping all
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the experimental parameters same. The as-prepared samples (prepared in the presence and absence of glucose) were calcined at 600oC for 2 h with a heating rate of 2oC min-1. 2.2 Characterization
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X-ray diffraction (XRD) studies of the samples were performed by Philips X’Pert Pro PW 3050/60 powder diffractometer using Ni-filtered Cu-Kα radiation (λ = 0.15418
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nm) operated at 40 kV and 30 mA. The thermal behavior of the as-prepared (uncalcined) sample was studied by differential thermal analysis (DTA) and thermogravimetry (TG) (Netzsch STA 449C, Germany) from 30o to 1000oC in air atmosphere at the heating rate of 10oC min-1. The Raman spectrum was recorded using a RENISHAW spectrometer
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with 514 nm radiation from an argon laser at room temperature. Nitrogen adsorption and desorption measurements were performed at liquid nitrogen temperature (77 K) on a Quantachrome (ASIQ MP) instrument. The sample was outgassed in vacuum at 200 oC
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for 4 h prior to measurement. The total surface area was determined by BET method. The total pore volume was estimated from the amount of nitrogen adsorbed at the relative
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pressure (p/po) of ca 0.99. The morphology of the particles was examined by FESEM (Model: Zeiss, SupraTM 35VP, Oberkochen, Germany) operating with an accelerating voltage of 10 kV, and transmission electron microscopy (TEM), using a Tecnai G2 30ST (FEI) instrument operating at 300 kV. UV-Visible spectra were recorded using UV-VISNIR spectrophotometer (UV-3101PC, Shimadzu) in the wavelength range of 200 nm to 800 nm.
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2.3 Photocatalytic Study Photocatalytic test was performed for the degradation of methylene blue (MB) and and 4-chlorophenol (4-CP). In a typical photocatalytic test, for MB degradation, 2 mg
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of the TiO2 sample was mixed with 12 mL of 10−5 M MB dye solution, and for 4-CP degradation, 5 mg of the TiO2 sample was mixed with 10 mL of 1.5x10−4 M 4-CP solution. Both the dispersions were stirred for 60 min in dark to achieve adsorption
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equilibrium. Then the aliquots were taken out, filtered by Millipore filter paper (pore dia 0.22 µm). The filtrates were analyzed using a UV-visible spectrophotometer. Rest of the
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dye solution was placed in a rectangular box (36 cm x 30 cm x 44 cm) fitted with eight tubes with a power source of 6 W each placed at the inside top of the box. The solution was irradiated from a distance of 11 cm with UV (λ= 365 nm) light at room temperature in the photoreactor. After a certain interval of irradiation, aliquots were collected, filtered
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and monitored by UV-visible spectrophotometer. The decrease in absorption intensity at λmax=664 nm and λmax=225 nm indicates the photocatalytic degradation of the MB and
3.
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4-CP, respectively.
Result and Discussion:
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3.1 XRD analysis
XRD patterns of (i) as-prepared (uncalcined) and calcined (600oC) samples
obtained in the (ii) presence and (iii) absence of glucose are shown in Fig. 1(a). The appearance of diffraction peaks at around 25.09o, 37.65o, 48.02o, 53.89o, 55.07o, 62.38o, 68.7o, 70.07o and 75o corresponding to the crystal planes of [101], [004], [200], [105], [211], [204], [116], [220], and [215], respectively is due to the presence of anatase TiO2
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(JCPDS No. 21-1272) in all the samples. It was noticed that after calcinations, crystallization of TiO2 obtained in the presence of glucose increased significantly compared to that prepared in the absence of glucose. It signifies that carbon particle
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during thermal decomposition of glucose could enhance the crystallization of TiO2. The crystallite sizes (D) of the particles obtained from Scherrer formula were found to be
the presence and absence of glucose, respectively. 3.2 Raman study
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14.1, 33.3 and 25 nm for the as-prepared (uncalcined), and calcined samples prepared in
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The Raman spectra of (i) as-prepared (uncalcined) and calcined (600oC) samples obtained in the (ii) presence and (iii) absence of glucose is shown in Fig. 1b. For all the samples, the appearance of sharp and intense peak at 144-150 cm-1 and a very weak peak at around 196 cm-1 assigning to Eg mode of vibration is the characteristic of anatase TiO2.
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In the higher frequency region, the other peaks at around 400, 516 and 639 cm-1 corresponding to B1g, A1g and Eg modes also confirm the presence of anatase TiO2 [14] in the samples. Interestingly, the most intense peak at 150 cm-1 of as-prepared
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(uncalcined) sample shifted to 145 cm-1 and 144 cm-1 after calcination of the samples prepared in the absence and presence of glucose, respectively. The blue shift of Raman
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spectra was due to increase in crystallite sizes of calcined samples [15] prepared in the presence and absence of glucose. However, a little peak shifting was noticed for the calcined sample obtained in the presence of glucose compared to that prepared in the absence of glucose instead of their difference in crystallite size. 3.3 Textural properties
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Fig. 1c shows the N2 adsorption-desorption isotherms of (i) as-prepared (uncalcined) and calcined (600oC) samples obtained in the (ii) presence and (iii) absence of glucose. All the curves indicated type IV isotherm according to IUPAC classification,
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which signifies mesoporous characteristic of the sample. The appearance of H-2 type hysteresis loop of the isotherms demonstrates ink-bottle-like mesopores and/or pore constrictions, where pore mouth is smaller than the pore body [16]. The corresponding
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BJH pore size distributions (PSDs) derived from desorption data of the isotherms are shown in the inset of Fig. 1c showing a monomodal PSDs. The textural properties (the
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BET surface area, pore volume and pore size) of the particles are shown in Table 1. It revealed that BET surface area and pore volume of the samples decreased in the order of as-prepared (uncalcined) > calcined (with glucose) > calcined (without glucose). However, pore size increased from 4.7 nm to 9 after calcination of the samples. From the
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above results it is clear that glucose played a significant role in enhancing the BET surface area and pore volume of TiO2. 3.4 Thermal analysis
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Figure 1d shows the DTA and TG curves of the as-prepared (uncalcined) TiO2 particles. In the DTA curve, the appearance of broad endothermic peak at around 165oC
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was attributed to the removal of adsorbed water, which accompanied a mass loss of about 7% up to 300oC in the TG curve. Two broad exothermic peaks at around 350o and 500oC were due to decomposition of inorganic moieties from the precursor (TIOS) and the carbonaceous materials derived from glucose [17], respectively. The TG curve shows a significant weight loss of about 70% in the temperature range of 300-550oC. Practically no weight loss was found above 5500C.
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3.5 FESEM study Figure 2a shows the FESEM image of the calcined product obtained in the presence of glucose. It indicated the formation of TiO2 cubes of size about 300-600 nm.
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During the reaction process, nucleation and growth of the particles take place via Ostwald ripening in which larger aggregated particles are formed with the cost of smaller seed particles. Figure 2b shows the growth evolution process of TiO2 cubes. It is shown
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schematically that the sharp edged cube shaped particles were formed via surface reconstruction and surface edging process. To understand the effect of glucose on the
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morphological change of cube shaped particles, the same experiment was performed in the absence of glucose followed by calcinations at 600oC. FESEM image (Fig. S1, ESI) of the particles obtained in the absence of glucose resembles large agglomerated particles without having any particular shapes. It is clear that glucose played an important role for
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the formation of cube shaped particles. Under hydrothermal condition, glucose was converted to its dehydrated species, which were linked together in a chain-like fashion through the oxygen atom [18]. The dehydrated glucose was adsorbed on some specific
3.6 TEM study
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facets of TiO2 particles inducing cube shaped particles.
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Figure 3 shows the TEM images of 600oC-treated sample obtained in the presence
of glucose. It indicated that the nanoparticles of size 10-20 nm were aggregated to form TiO2 cubes. The interparticle porosity can also be observed from high magnification TEM images (Fig. 3a). The high resolution TEM (HRTEM) (Fig. 3b) shows the lattice spacing of 0.35 nm corresponding to the (101) plane, and selected area electron diffraction (SAED) reveals the polycrystalline nature of the titania nanoparticles (Fig.
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3c). The bright spots of the concentric rings matched well with the anatase TiO2 planes obtained from XRD. 3.7 Diffuse Reflectance Spectroscopy (DRS) study
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Different materials absorb radiation at different wavelengths. The yield of photo generated electron-hole pair depends on the intensity of incident photons with energy exceeding or equaling the band gap energy. The optical properties of the samples: (a) as-
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prepared (uncalcined) and calcined (600oC) obtained in the (b) presence and (c) absence of glucose, derived from UV-Vis diffuse reflectance spectroscopy as a function of
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wavelength are shown in Fig. S2 (ESI). Figure 4 exhibits the corresponding KubelkaMunk reflection plots extracted from the UV-Visible spectra in reflection mode. The band gap was determined by extrapolating and intersecting the linear portion of (K*hν)1/2 [eV1/2] to the energy axis hν [19]. The band gap energy values were calculated as 3.61,
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3.46 and 3.79 eV for as-prepared (uncalcined), and calcined (600oC) samples obtained in the presence and absence of glucose, respectively. 3.8 Photocatalytic activity
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Before irradiation with UV light, adsorption ability of the samples: as-prepared (uncalcined), calcined (prepared with glucose), calcined (prepared without glucose), and
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Degussa P25 (standard) onto the MB and 4-CP ( both kept in the dark for 60 min for homogenization) were studied. Table 2 shows that the adsorption ability follows as: asprepared (uncalcined) > calcined (prepared with glucose) > calcined (prepared without glucose) > Degussa P25 (standard), which corroborated to their BET surface area values. The BET surface area of Degussa P25 is reported as 56 m2g-1 [20], which is found to be less than the synthesized TiO2 i.e, as-prepared (uncalcined), calcined (prepared with
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glucose) and calcined (prepared without glucose) samples (Table 1). The photocatalytic activity of as-prepared (uncalcined), calcined (prepared with glucose), calcined (prepared without glucose), and Degussa P25 (standard) samples were studied for the degradation
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of MB and 4-CP solution under UV light irradiation (365 nm). Figures 5 and 6 show the UV-visible absorption spectra of (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25 (standard)
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samples each for the degradation of MB and 4-CP as a function of irradiation time, respectively. It shows a gradual depletion of the characteristic absorbance peaks at 664
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nm and 225 nm with time for MB and 4-CP, respectively. The amount of MB and 4-CP photodegradataion with time by the samples: (i) as-prepared (uncalcined), (ii) calcined (prepared with glucose), (iii) calcined (prepared without glucose), and (iv) Degussa P25 (standard) each is shown in Fig. 7a and 7b, respectively. For both the pollutants (MB and
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4-CP), the degradation follows as: Degussa P25> calcined (prepared with glucose) > calcined (prepared without glucose) > as-prepared (uncalcined). The relatively high photocatalytic efficiency of P25 could be due the presence of both anatase and rutile
EP
phase of TiO2 (4:1) rendering suppressed recombination of photo-generated electron and holes [21-24]. However, the better photocatalytic acivity of calcined cube shaped TiO2
AC C
prepared in the presence of glucose compared to that of as-prepared (uncalcined) and calcined TiO2 (prepared in the absence of glucose) could be due to the lower band gap energy (mentioned in section 3.7) of the former rendering more surface active sites for photocatalysis. Figures 8 and 9 show the logarithm plots of the absorbance (-lnA/Ao) with reaction time for MB and 4-CP, respectively by the samples: (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without
9
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glucose), and (d) Degussa P25 (standard) each. It reveals pseudo first order reaction for all the samples. The apparent rate constants, percentage degradation of the pollutants are shown in Table 2. In the insets of the corresponding Figs. 8 and 9, the reusability of the
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samples (the experiments were repeated using the same catalysts for another four cycles each to identify the potential reusability of the material) are shown. It shows that photocatalytic activity of the calcined samples remained almost the same up to 2-3 cycles
SC
as the original sample indicating recyclability of the catalyst.
The mechanism of photoexcitation and decomposition of pollutants (MB and 4-
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CP) using TiO2 photocatalyst upon irradiation with light is shown schematically in Fig. 10 [25]. The photocatalyst upon irradiation with light of suitable wavelength renders migration of electrons from the valance band to the conduction band, generating electron deficient holes in the valence band. Thus, formation of electron-hole pairs occurs. The
(.OH). The O2⋅
−
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holes and electrons generate superoxide radical anions (O2⋅ −) and hydroxyl radicals react with H2O to furnish ⋅OH and HOO⋅ having powerful oxidizing
EP
ability. On reacting with these powerful oxidizing agents, the pollutants gets oxidized.
4. Conclusions
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In summary, cube shaped anatase TiO2 was obtained by a facile hydrothermal process
at 180 °C/24 h in the presence of glucose followed by calcination at 600oC/2h. The dehydrated species of glucose was adsorbed on some specific facets of TiO2 particles inducing cube shaped particles. To understand the effect of glucose on cube shaped TiO2 toward
their
physicochemical
properties
and
photodegradation
efficiency
of
environmental pollutants (MB and 4-CP), the results were compared with those of TiO2
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obtained in the absence of glucose. The photocatalytic acivity of calcined cube shaped TiO2 prepared in the presence of glucose was better than that of as-prepared (uncalcined) and calcined TiO2 (prepared in the absence of glucose), which was due to the lower band
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gap energy of the former rendering more surface active sites for photocatalysis. The cube shaped calcined TiO2 obtained in the presence of glucose having higher BET surface area than that obtained without glucose, rendered 93.9% and 92.9% photodegradation of MB
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and 4-CP, respectively within 2 h. The process is useful to design shape controlled synthesis of TiO2 and other oxide particles which could have potential applications in the
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field of environment and energy sectors. Acknowledgement:
The authors would like to thank the Director of this institute for his kind permission to publish this paper. They acknowledge the help rendered by Nano-structured Materials
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Division and Material Characterization Division for material characterization. The authors I. H. C. and P. B. are thankful to UGC and DST, Government of India for their fellowships, respectively. The work was funded by DST-SERB Project (Grant No.
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EP
SR/S3/ME/0035/2012), Government of India (No. GAP 0616).
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[2] D. Chen, L. Cao, F. Huang, P. Imperia, Y-B. Cheng and R.A. Caruso, Synthesis of monodisperse mesoporous titania beads with controllable diameter, high surface areas,
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[3] K.T Kim , G. Ali , K.Y Chung , C.S Yoon , H. Yashiro , Y.K Sun, J. Lu, K. Amine ,
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[5] J. Akilavasan, K. Wijeratne, H. Moutinho, M. Al-Jassim, A. R. M. Alamoud, R. M. G. Rajapaksed and J. Bandara, Hydrothermally synthesized titania nanotubes as a promising electron transport medium in dye sensitized solar cells exhibiting a record
EP
efficiency of 7.6% for 1-D based devices, J. Mater. Chem. A, 1(2013) 5377-5385. [6] T.H Kim, K.H Lee, Y.K Kwon, Monodisperse hollow titania nanospheres prepared
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[8] N. Wang, H. Li, H. He, L. Han. Low-temperature wet-chemical preparation of titania nanocrystalline by utilizing γ-Al2O3 as fluorion scavenger, J. Alloys Compd. 501 (2010) L38-L41.
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[9] X. Quan, T. Huaiqin, Z. Qinghua, S. Xuemei, Preparation of lanthanum-doped TiO2 photocatalysts by co-precipitation, J. Mater. Sci. 42 (2007) 6287-6296.
[10] M.H. Zori, Synthesis of TiO2 nanoparticles by microemulsion/heat treated method
SC
and photodegradation of methylene blue, J. Inorg. Organomet Polym. 21 (2011) 81-90.
[11] K.M. Reddy, D. Guin, S.V. Manorama, A.R. Reddy, Selective synthesis of
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nanosized TiO2 by hydrothermal route: Characterization, structure property relation, and photochemical application, J. Mater. Res. 19 (2004) 2567-2575.
[12] R.A. Roca and E.R. Leite, Size and shape tailoring of titania nanoparticles synthesized by solvothermal route in different solvents, J. Am. Ceram. Soc., 96 (2013)
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[13] M.B. Suwarnkar, R.S. Dhabbe, A.N. Kadam, K.M. Garadkar, Enhanced photocatalytic activity of Ag doped nanoparticles synthesized by a microwave assisted
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[14] W. Ma, Z. Lu, M. Zhang, Investigation of structural transformations in nanophase
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titanium dioxide by Raman Spectroscopy, Appl. Phys. A. 66 (1988) 621-627. [15] A. Li Bassi, D. Cattaneo, V. Russo, C.E. Bottani, E. Barborini, T. Mazza, P. Piseri, P. Milani, F.O. Ernst, K. Wegner, S.E. Pratsinis, Raman spectroscopy characterization of titania nanoparticles produced by flame pyrolysis: the influence of size and stoichiometry, J. Appl. Phys 98 (2005) 074305.
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[16] S. Ghosh, M.K. Naskar, Understanding the Role of Triblock Copolymers for the Synthesis of Mesoporous Alumina, and Its Adsorption Efficiency for Congo Red J. Am. Ceram. Soc. 97 (2014) 100-106.
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[17] M. K. Naskar, Soft Solution Processing for the Synthesis of Alumina Nanoparticles in the Presence of Glucose, J. Am. Ceram. Soc. 93 (2010) 1260-1263.
[18] M-M. Titirici, M. Antonietti and A. Thomas, A generalized synthesis of metal oxide
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semiconductor films, and application to photochemical water splitting, Sol. Energy Mater. Sol. Cells, 91 (2007) 1326-1337.
[20] K. J. A. Raj and B. Viswanathan, Effect of surface area, pore volume and particle size of P25 titania on the phase transformation of anatase to rutile, Ind. J. Chem. 48A
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(2009) 1378-1382.
[21] A. Hu, R. Liang, X. Zhang, S. Kurdi, D. Luong, H. Huang, P. Peng, E. Marzbanrad, K.D. Oakes, Y. Zhou, M.R. Servos, Enhanced photocatalytic degradation of dyes by TiO2
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nanobelts with hierarchical structures, J. Phoechem. Photbiol: A Chem. 256 (2013) 7-15. [22] Z. Wang, W. Cai, X. Hong, X. Zhao, F. Xu, C. Cai, Photocatalytic degradation of
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phenol in aqueous nitrogen-doped TiO2 suspensions with various light sources, Appl. Catal B: Environmental 57 (2005) 223-231. [23] Z. Zheng, H. Liu, J. Ye, J. Zhao, E.R. Waclawik, H. Zhu. Structure and contribution to photocatalytic activity of the interfaces in nanofibres with mixed anatase and TiO2 (B) phases, J. Mol. Cata. A: Chemical 316 (2010) 75-82.
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[24] I. H. Chowdhury, S. Ghosh, M. K. Naskar, Aqueous-based synthesis of mesoporous TiO2 and Ag-TiO2 nanopowders for efficient photodegradation of methylene blue, Ceram. Intl. DOI: org/10.1016/j.ceramint. 2015.10.049.
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[25] N Sobana, M. Muruganadham, M. Swaminathan. Nano-Ag particles doped TiO2 for efficient photodegradation of direct azo dyes, J. Mol. Catal A: Chemical. 258 (2006) 124-
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132.
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Figure caption: Fig. 1: (a) XRD patterns, (b) Raman spectra and (c) N2 adsorption-desorption isotherms (Inset: BJH pore size distributions) of TiO2 particles: (i) as-prepared (uncalcined) and
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calcined (600oC) samples obtained in the (ii) presence and (iii) absence of glucose; (d) DTA/TG of as-prepared (uncalcined) samples obtained in the presence of glucose.
Fig. 2: FESEM images of cube shaped TiO2 (a) low and high magnifications, and (b)
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shape evolution during the growth process (schematically shown by arrow).
images and (c) SAED pattern.
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Fig. 3: TEM images of cube shaped TiO2 (a) low and high magnifications, (b) HRTEM
Fig. 4: Kubelka-Munk reflection plots extracted from the UV-Visible spectra in reflection mode of (a) as-prepared (uncalcined) and calcined (600oC) samples obtained in the (b) presence and (c) absence of glucose.
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Fig. 5: UV-visible absorption spectra of (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25 (standard) samples for the degradation of MB as a function of irradiation time.
EP
Fig. 6: UV-visible absorption spectra of (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25
AC C
(standard) samples for the degradation of 4-CP as a function of irradiation time. Fig. 7: Degradation of (a) MB and (b) 4-CP with reaction time by the (i) as-prepared (uncalcined), (ii) calcined (prepared with glucose), (iii) calcined (prepared without glucose), and (iv) Degussa P25 (standard) samples each. Fig. 8: The logarithm plots of the absorbance (-lnA/Ao) with reaction time for MB by the samples: (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined
16
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(prepared without glucose), and (d) Degussa P25 (standard); the insets show the reusability of the corresponding samples. Fig. 9: The logarithm plots of the absorbance (-lnA/Ao) with reaction time for 4-CP by
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the samples: (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25 (standard); the insets show the reusability of the corresponding samples.
AC C
EP
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using cube shaped TiO2 photocatalyst.
SC
Fig. 10: Mechanism of photoexcitation and decomposition of pollutants (MB and 4-CP)
17
B1g
Eg
(iii) (i)
200
80
400 600 -1 Raman Shift (cm )
0.04
0.00 0
10
20 30 Pore diameter(nm)
40
50
80 40
80 60
0
0.2
0.4 0.6 0.8 Relative pressure (P/P0)
1.0
200
400 600 0 Temperature( C)
40 20 800
1000
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0 0.0
Exo
0.02
100
Endo
120
0.06
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3 -1
-1
dV/dD(cm g nm )
3 -1
160
d
800
SC
asprepared TiO2 (with glucose) calcined cube TiO2 calcined TiO2 (without glucose)
Eg
(ii)
200 0.08
A1g
Residual Weight(%)
60
(iii) (ii) (i)
Intensity (a.u)
(215)
(204)
(116) (220)
(200)
40 2θ/degree
0.10
Volume adsorbed (cm g STP)
(105) (211)
(004)
20
c
Eg
b
Intensity (a.u)
a
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(101)
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Fig. 1: (a) XRD patterns, (b) Raman spectra and (c) N2 adsorption-desorption isotherms (Inset: BJH pore size distribution) of TiO2 particles: (i) as-prepared (uncalcined) and
EP
calcined (600oC) samples obtained in the (ii) presence and (iii) absence of glucose; (d)
AC C
DTA/TG of as-prepared (uncalcined) samples obtained in the presence of glucose.
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200 nm
b
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200 nm
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a
200 nm
Surface reconstruction
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Ostwald ripening
Surface edging
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Fig. 2: FESEM images of cube shaped TiO2 (a) low and high magnifications, and (b)
AC C
EP
shape evolution during the growth process (schematically shown by arrow).
19
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b
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SC
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a
c
EP
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d=0.35 nm (101)
(105) (200) (103) (101)
Fig. 3: TEM images of cube shaped TiO2 (a) low and high magnifications, (b)
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HRTEM images and (c) SAED pattern.
20
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1400
a
b
1200
1200
c
1100
800
1000
900 800 700
3.61 ev
600 1
2
3
800
600
4
5
6
7
3.46 ev
1.5
2.0
2.5
3.0
3.79 ev
3.5
hν (ev)
hν (ev)
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1000
K*hν (ev1/2)
1000
K*hν (ev1/2)
K*hν (ev1/2)
1200
4.0
1
4.5
2
3
4
5
6
hν (ev)
Fig. 4: Kubelka-Munk reflection plots extracted from the UV-Visible spectra in reflection
SC
mode of (a) as-prepared (uncalcined) and calcined (600oC) samples obtained in the (b)
1.0
0.6 0.4
0.8
Absorbance
Absorbance
0.8
0.6 0.4
600
500
600 700 Wavelength (nm)
800
1.0
d 0.8 0.6 0.4
0 min after 1hr adsoption 15 min 30 min 45 min 60 min 75 min 90 min 105 min 120 min
0.2
0.2
0.0 500
0.4
0.0
800
0 min after 1hr adsorption 15 min 30 min 45 min 60 min 75 min 90 min 105 min 120 min
AC C
Absorbance
0.8
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c
600 700 Wavelength (nm)
EP
1.0
0.6
0 min after 1 hr adsorption 15 min 30 min 45 min 60 min 75 min 90 min 105 min 120 min
0.2
0.2 0.0 500
1.0
b
0 min after 1hr adsorption 15 min 30 min 45 min 60 min 75 min 90 min 105 min 120 min
Absorbance
a
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presence and (c) absence of glucose.
700
Wavelength (nm)
800
0.0 500
600
700
800
Wavelength
Fig. 5: UV-visible absorption spectra of (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25 (standard) samples for the degradation of MB as a function of irradiation time. 21
7
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2.0
2.0
b 0 min after 1hr adsorption 15 min 30 min 45 min 60 min 75 min 90 min 105 min 120 min
0.5
0.0 200
300
0.5
400
Wavelength
0.0 200
300 Wavelength (nm)
400
2.0
2.0
d 0 min after 1hr adsorption 15 min 30 min 45 min 60 min 75 min 90 min 105 min 120 min
1.0
0.5
300 Wavelength (nm)
400
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0.0 200
1.5
Absorbance
1.5
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c Absorbance
1.0
0 min after 1hr adsorption 15 min 30 min 45 min 60 min 75 min 90 min 105 min 120 min
SC
1.0
1.5 Absorbance
Absorbance
1.5
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a
1.0
0.5
0.0 200
0 min after 1 hr adsorption 15 min 30 min 45 min 60 min 75 min 90 min 105 min 120 min
300 Wavelength (nm)
400
Fig. 6: UV-visible absorption spectra of (a) as-prepared (uncalcined), (b) calcined
EP
(prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25
AC C
(standard) samples for the degradation of 4-CP as a function of irradiation time.
22
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a1.0
b 1.0 0.8
0.6
(iii)
(iii)
0.6 0.4
0.4
0.2
0.2
(ii) (iv)
0.0 20
40
60 80 Time (min)
100
0.0 0
120
20
SC
0
RI PT
(i) C/C0
C/C0
0.8
(i)
40
60 80 Time (min)
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Fig. 7: Degradation of (a) MB and (b) 4-CP with reaction time by the (i) as-prepared (uncalcined), (ii) calcined (prepared with glucose), (iii) calcined (prepared without
AC C
EP
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glucose), and (iv) Degussa P25 (standard) samples each.
23
(ii) (iv) 100
120
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0.004
b
0.002
2.0
0.001
0.010
0.005
0.000 1
2
3
4
5
-ln (A/A0)
-ln(A/A0)
0.015
No. of cycles
0.2
0.1
0.000
1.5
1
2
3
1.0 0.5
-1
Rate constant= 0.0031 min
0
20
40
60
80
100
120
0
20
40
Time (min)
4
0.00
5
-ln(A/A0)
3
120
0.01
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0.000 2
100
SC
2.5 1
80
0.02
0.002 0.001
-ln (A/A0)
3.0
-1
-1
k (min )
0.003
0.3
60
0.03
3.5
k (min )
d
0.004
0.4
-1
Time (min)
0.005
0.5
c
5
Rate constant = 0.0196 min
0.0
0.0
4
No. of cycles
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0.3
0.020
2.5 -1
-1
k (min )
0.003
k (min )
0.4
a
No. of cycles
0.2
-1
Rate constant= 0.0042 min
0.1
1
2.0
2
3
4
5
No. of cycles
1.5
-1
Rate constant= 0.0252 min
1.0 0.5 0.0
0.0 20
40
60 80 Time (min)
100
120
0
20
40
60
80
100
120
Time (min)
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0
Fig. 8: The logarithm plots of the absorbance (-lnA/Ao) with reaction time for MB by the samples: (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined
EP
(prepared without glucose), and (d) Degussa P25 (standard); the insets show the
AC C
reusability of the corresponding samples.
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3.0
b
0.0006 0.0005
-1
k (min )
-1
0.0003 0.0002
0.0000
0.04
1
2
3
4
5
No. of cycles
0.03 -1
0.00 1
2
1.5 1.0
0.0
0.00 20
40
60 80 Time (min)
100
120
0.20
0
d
20
3.5
-1
40
60 80 Time (min)
100
120
0.025
3.0
0.0012
5
SC
0
4
Rate constant= 0.0221 min
0.5
0.01
3 No. of cycles
Rate constant= 0.0005 min
0.02
c
0.01
2.0
0.0001
-ln(A/A0)
-ln(A/A0)
0.05
0.02
2.5
0.0004 k (min )
0.06
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0.07
0.020 0.015
0.0008
-1
-1
k (min )
0.15
k (min )
a
2.5 0.0004
0.010
0.10
2
3
4
-ln (A/A0)
1
5
No. of cycles
0.05
2.0
0.000
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-ln (A/A0)
0.005
0.0000
1
2
3
4
5
No. of cycles
1.5 1.0
-1
Rate constant = 0.0011 min
0.00
-1
0.5
Rate constant = 0.0284 min
0.0
0
20
40
60
80
Time (min)
100
120
0
20
40
60 80 Time (min)
100
120
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Fig. 9: The logarithm plots of the absorbance (-lnA/Ao) with reaction time for 4-CP by the samples: (a) as-prepared (uncalcined), (b) calcined (prepared with glucose), (c) calcined (prepared without glucose), and (d) Degussa P25 (standard); the insets show the
AC C
EP
reusability of the corresponding samples.
25
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.OOH
.OH
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H+
e
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SC
CB
hν
VB
.OH
EP
Fig. 10: Mechanism of photoexcitation and decomposition of pollutants (MB and 4-CP)
AC C
using cube shaped TiO2 photocatalyst.
26
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Table 1: Textural properties of the samples.
Vp-Total (cm3 g-1)b
DBJH (nm)c
Calcined TiO2 cube (with glucose)
67.3
0.24
9
As-prepared TiO2 (with glucose)
143.9
0.27
4.7
Calcined TiO2 (without glucose)
56.87
0.23
9
SC
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SBET (m2g-1 )a
BET surface area; bTotal pore volume; cpore diameter by BJH desorption
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a
Sample
Table 2: The apparent rate constants, percentage adsorption and degradation of the
Calcined TiO 2 cube (with glucose)
% of MB degradation
Rate constant for MB degradation (K) (min-1)
% of 4-CP adsorption
% of 4-CP degradation
Rate constant for 4-CP degradation (K) (min-1)
2.5
93.9
0.0196
1.4
92.9
0.0221
21.2
32.2
0.0031
4.5
6.4
0.0005
1.4
40.3
0.0042
0.7
14.7
0.0011
0.5
95.2
0.0252
0.2
94.4
0.0234
AC C
As-prepared TiO2 (with glucose)
% of MB adsorption
EP
Sample
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pollutants by the samples.
Calcined TiO 2 (without glucose) P25
27
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Electronic Supporting Information
500nm
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Fig. S1: FESEM image of calcined TiO2 prepared in absence of glucose.
b
EP
82 81 80 79
AC C
Reflectance %
83
78
95
c
100 90
Reflectance %
84
Reflectance %
85
a
80 70
500 600 700 Wavelength (nm)
80 75 70 65
76
400
85
60
77
300
90
800
50 300
400
500 600 700 wavelength (nm)
800
200
300
400 500 600 Wavelength (nm)
Fig. S2: UV-Vis diffuse reflectance spectroscopy as a function of wavelength of the samples: (a) as-prepared (uncalcined) and calcined (600oC) obtained in the (b) presence and (c) absence of glucose.
28
700
800
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Graphical representation
0.05
80 60 40
0.02 0.01 0.00 0
RI PT
-1
100
10
20 30 Pore diameter(nm)
SC
200 nm
0.03
-1 3
120
0.04 dV/dD(cm g nm )
140
3
-1
TiO2 cubes
Volume adsorbed (cm g STP)
160
40
50
20 0
0.2
0.4
0.6
0.8
Relative pressure (P/P0)
AC C
EP
TE D
M AN U
0.0
29
1.0
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Research Highlights
RI PT
Mesoporous TiO2 cube was synthesized hydrothermally at 180oC/24h followed by calcination (600oC/2h). The BET surface area of the calcined TiO2 cube was found to be 67.3 m2 g-1.
Calcined TiO2 cube showed 93.9% and 92.9% photodegradataion of MB and 4-CP,
AC C
EP
TE D
M AN U
SC
respectively.