Preparation, characterization, and kinetic and thermodynamic studies of
mixed-phase TiO
2
nanoparticles prepared by detonation method
Yandong Qu
a,⇑, Conghuang Sun
a, Guilei Sun
b, Xiangqing Kong
a, Wenjiao Zhang
aa
School of Civil and Architectural Engineering, Liaoning University of Technology, Jinzhou 121001, China
b
Department of Safety Engineering, China Institute of Industrial Relations, Beijing 100037, China
a r t i c l e i n f o
Article history:
Received 10 December 2015 Accepted 22 February 2016 Available online 2 March 2016 Keywords: Transformation TiO2nanoparticles Growth kinetics Detonation method Thermal treatment
a b s t r a c t
Although detonation method has been reported to prepare TiO2nanoparticles, phase transformation and crystal growth of detonation-prepared TiO2nanoparticles have not been explored extensively. In this study, mixed-phase TiO2nanoparticles, consisting of anatase (34.8 wt%,9.4 nm) and rutile (65.2 wt%, 18.2 nm), were prepared by the detonation method. The phase transformation in the TiO2sample at dif-ferent annealing temperatures was modeled to understand the transformation behaviors. Thermal treat-ment experitreat-ments of the detonation-prepared TiO2 nanoparticles indicated that the initial process involved an anatase-to-rutile transformation. The TiO2grains coarsened drastically after thermal treat-ment at 600°C for 1 h. In contrast to a normal transformation, the anatase-to-rutile transformation was followed by conversion of rutile to anatase in large crystals. Moreover, smaller TiO2particles could gain more kinetic energy and combine rapidly with the increase in temperature, forming larger particles. Anatase was transformed completely to rutile after thermal treatment at 720°C for 3.5 h. The transfor-mation temperature from anatase to rutile of the detonation-prepared TiO2nanoparticles was approxi-mately 80°C lower than that of TiO2prepared by conventional methods. Therefore, thermal treatment may be employed to control the particle size and phase content of detonation-prepared TiO2 nanoparticles.
Ó 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction
The bulk material of TiO2 commonly consists of three main phases: anatase (tetragonal, space group I41/amd), brookite (orthorhombic, space Pcab), and rutile (tetragonal, space group P42/mmm). Among these phases, TiO2exists mostly as rutile and anatase phases. In recent years, TiO2nanostructures have received remarkable attention because of their specific physical and chem-ical properties, such as excellent catalytic activity, gas sensing properties, dielectric and electronic properties, for various applica-tions, such as dye-sensitized solar cells[1]and nanoscale additives on solid propellants[2]and polymer matrix composites[3]. Never-theless, some properties of TiO2 nanostructures are strongly dependent on TiO2 crystalline structure [4], phase composition [5], particle size [6], processing conditions [7], and preparation methods[8,9]. Therefore, understanding of the factors that affect phase stability, growth, and phase transformation kinetics in nanocrystalline materials is critical for the preparation of nanos-tructures with the desired properties and quantification of material
behavior [10,11]. Previous studies have investigated the grain growth kinetics and thermal stability of TiO2nanostructures pre-pared using conventional preparation methods. For instance, Ohtani and his coworkers[12]calcined amorphous TiO2samples non-isothermally from 300°C to 800 °C in air. They inferred that each amorphous particle was transformed into an anatase particle without crystal growth. Lee and Byeon[13]investigated the effect of ultrasonic processing on the phase transformation of flame-synthesized anatase TiO2nanoparticles heated to the rutile phase. They found that variations in surface characteristics caused by the different preparation methods can change the growth rate of the second phase, or even the transformation sequence[14]. Exarhos and Aloi[15] studied the transformation kinetics in amorphous TiO2films deposited on silica substrates. Moreover, Ko et al.[16] studied the crystallite growth kinetics of TiO2 modified with 9 mol% ZnO. Charbonneau et al. [17] investigated rutile TiO2 nanoparticles by forced hydrolysis of aqueous Ti(IV) chloride solu-tions in terms of precipitation kinetics, nucleation, and growth mechanism. Clearly, understanding of the factors that dictate the sequence of phase transformations may provide insights into how phase composition, microstructures, and properties of TiO2 nanostructures could be manipulated. However, further studies
http://dx.doi.org/10.1016/j.rinp.2016.02.006
2211-3797/Ó 2016 The Authors. Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
⇑Corresponding author.
E-mail address:[email protected](Y. Qu).
Contents lists available atScienceDirect
Results in Physics
are still necessary to understand the influence of particle size on the phase transformation of TiO2nanostructures synthesized by other preparation methods.
As one of the complementary approaches, the detonation method is an efficient, promising technique to manufacture nanos-tructures. The particle sizes of detonation-prepared nanostructures can be controlled to some extent by adjusting the detonation parameters[18]. Mixtures composed of precursor and explosives can lead to complex physical and chemical reactions in the detona-tion process[19,20]. High pressure, high temperature, rapid mate-rial motion, and short duration of the explosive shock event force matter through a complex process [18], such as crystallization, conglomeration, and phase-translation, to the extent that synthesis can occur in the microsecond duration of the high pressure pulse, and chemical processing can be conducted at extremely high pres-sure. Previous studies have investigated the morphologies, phase content, and microstructures of the detonation-prepared nanopar-ticles, such as diamond[21,22], graphite[23], Al2O3[24,25], TiO2 [26,27], ZnO[28], SrAl2O4[18,29], Al5O6N[30], and LiMn2O4[31]. Quenching of pressure and temperature from transient states allows the formation of metastable states[29]. Several particular properties of detonation-prepared nanostructures have been found based on previous research results. For instance, when detonation-prepared TiO2particles were oxidized to eliminate the impurities through the combined action of CrO3and concentrated nitric acid, anatase appears to be the stable phase of TiO2at small crystallite sizes and rutile could be transformed to anatase [27]. The microstructures of detonation-synthesized nanostructures also changed during the detonation process[32]. Moreover, magnetiza-tion of nickelferrite nanostructures synthesized by shock wave treatment was significantly improved[33]. The agglomerate struc-tures of detonation-prepared TiO2 nanoparticles could be improved to some extent after thermal treatment[34,35]. Given that particle sizes and morphologies can be manipulated by nucle-ation and growth conditions of nanostructures, controlling the transformation and crystal growth is necessary for preparing nanostructures with the desired properties by the detonation method. However, phase transformation and crystal growth of detonation-prepared TiO2nanostructures have not been explored extensively.
In this study, mixed-phase TiO2nanoparticles consisting of ana-tase and rutile were prepared by detonation method. A study on the kinetics and thermodynamics of the TiO2 nanoparticles was conducted by isothermal and isochronal annealing treatments. Crystal growth and phase transformation of the mixtures of ana-tase and rutile were characterized. The size-dependent transfor-mation observed in the TiO2 samples was explained within the framework of classical nucleation theory and standard model of crystal growth. Thermodynamic and kinetic analyses of the results can provide new insights into the interplay between size and phase stability of detonation-prepared TiO2nanoparticles.
Experimental
TiOSO42H2O, NaOH, and NH4NO3were employed as the main raw materials. All starting materials were of analytical purity. First, TiOSO42H2O was dissolved in distilled, deionized water. Second, the solution was added into the NaOH solution with certain con-centration and stirred vigorously for 1 h at room temperature to form the TiO(OH)2suspended liquid. After the simple treatment, the obtained TiO(OH)2was mixed with (CH2NNO2)3and NH4NO3 to form the mixed explosives with certain density. The mixed explosives were detonated by a No. 8 detonator in a 3 m diameter sealed explosive chamber. All experiments were carried out under normal pressure (1 atm). The experimental procedure was similar
to that reported in Refs.[26,27]. The detonation soot was collected after the explosion and annealed in air at 600–720°C. The mor-phologies and particle sizes of the detonation soot and that annealed at different temperatures were observed with a Tecnai G220 S-Twin TEM. All samples were examined by XRD to deter-mine the phase contents and particle sizes of anatase and rutile. Coarsening of the grains of both anatase and rutile phases could also be inferred from the XRD patterns. Diffraction patterns were collected using a XRD-6000 Diffractometer with Cu Ka radiation (40 kV, 30 A) in step scanning mode. The scanning 2h range was 20–60°, the 2h step size was 4°, and the collecting time at each step was 60 s. All measurements were performed at room temperature. In the 2h range, percent composition calculations of the TiO2 samples were carried out using the following equations[7]:
XR¼ IR I0¼ 1 1:0 þ 0:8IA=IR ð1Þ XA¼ 1 XR ð2Þ
where XRis the weight percentage of the rutile phase and IAand IR are the intensity of the anatase (1 0 1) and rutile (1 1 0) diffraction peaks, respectively.
Using the full width at half maximum data of each phase after correcting the instrumental broadening, the average particle sizes of anatase and rutile were calculated by Scherrer equation[7]:
D¼ Kk
b cos h ð3Þ
where D is the crystallite size of TiO2particles, k is the Scherrer con-stant (k = 0.89),k is the Cu Ka radiation wavelength (0.15406 nm), B is the full width in radiation at half-maximum of the peak, andh is the Bragg angle of the XRD peak.
The average particle sizes of anatase and rutile were also esti-mated[36]by assuming that all particles have the same spherical shape and size. The particle size, D, is given by Eq.(4):
D¼ 6=ðSBET
q
Þ ð4Þwhere SBETis the BET specific surface area and
q
is the density of the particles, whereq
= 4.1 g cm3.Results and discussion X-ray diffraction analysis
Fig. 1shows the XRD patterns of the detonation-prepared TiO2 nanoparticles without thermal treatment and the high-resolution (1 0 1), (1 1 0) peak scans for the sample. Comparison of the results inFig. 1confirms that the mixed-phase TiO2nanoparticles, consist-ing of anatase and rutile, were prepared within the X-ray detection limit. The TiO2sample consists of nanocrystalline anatase (34.8 wt %) and rutile (65.2 wt%) according to Eqs.(1) and (2). The average particle diameter of anatase and rutile was 9.4 nm and 18.2 nm, respectively, based on Eq.(3). TEM observations confirmed that the average sizes of the mixed-phase TiO2nanoparticles were in good agreement with the XRD results.
Isothermal and isochronal experiments were also carried out using the mixed-phase TiO2 nanoparticles to understand the impact of particle size and detonation process on phase stability and phase transformation during the growth of nanocrystalline aggregates. Fig. 2 shows the XRD patterns of the TiO2 samples annealed at 600 and 720°C. The growth of particles and the struc-tural phase transformation were reflected in the differences in the electron diffraction patterns of the TiO2 samples. An increase in intensity and a significant narrowing of XRD peaks are observed inFig. 2.
Fig. 2(a) shows that the anatase and rutile phases coexisted at 600°C. A transformation from anatase to rutile occurred, and the grain of the TiO2nanoparticles coarsened drastically at 600°C for 1 h. With the increase in annealing temperature, the anatase was totally transformed to rutile at 720°C for 3.5 h. The average crys-tallite sizes of anatase and rutile were calculated according to Eq.
(3). For example, the crystallite sizes of anatase and rutile at 600°C for 1 h were 30±10 nm and 20 ± 5 nm, respectively. The crystallite sizes of anatase and rutile phases at 720°C for 5 h were
25 ± 5 nm and 30 ± 10 nm, respectively. Anatase was totally trans-formed to rutile at 720°C after 3.5 h.
Transmission electron microscopy (TEM) analysis
Morphologies of the mixed-phase TiO2nanoparticles without thermal treatment and those annealed at higher temperatures (600, and 720°C) in air for 5 h are presented inFig. 3. A comparison of the images inFig. 3showed that the particle size became larger and non-uniform. Some small TiO2particles melted and grew into larger crystals. These crystallite sizes are close to the value calcu-lated based on Scherrer’s equation. Comparison betweenFig. 3(a) andFig. 3(b) shows that the grain growth rate of the detonation-prepared TiO2 nanoparticles is mainly determined by annealing temperature and duration.
BET analysis
A NOVA 4000 high-capacity surface area and pore size analyzer (Quantachrome Instruments, USA) was used to study the specific surface area of mixed-phase TiO2 nanoparticles. The results showed the specific surface area of the TiO2sample without treat-ment of 26.12 m2g1. The particle diameters of the detonation-prepared TiO2nanoparticles were approximately 56 nm based on the BET results. The crystallite size is larger than the value calcu-lated from Scherrer’s equation.Fig. 4shows the nitrogen adsorp-tion–desorption isotherms of the TiO2 samples. The isotherm of the detonation-prepared TiO2sample is a combination of types I and IV (BDDT classification) with two very distinct regions. The isotherm exhibits high adsorption at low relative pressures (below
Fig. 1. XRD patterns of the detonation-prepared TiO2 nanoparticles without
thermal treatment.
Fig. 2. Comparison of XRD patterns of the TiO2nanoparticles annealed at: (a) 600°C; (b) 720 °C.
0.4), indicating that the powders contain mesopores. However, the curve exhibits a hysteresis loop at high relative pressures (P/P0) between 0.4 and 1.0, indicating the presence of mesopores (type IV). The TiO2sample shows the formation of mesoporous struc-tures, which is attributed to the aggregation of TiO2 crystallites. The average pore diameter is approximately 15.74 nm.
Thermodynamic and Kinetic analysis
The average particle sizes of the prepared TiO2nanoparticles as a function of annealing temperature are plotted inFig. 5for com-parison of the growth rates of anatase and rutile. The initial particle sizes of anatase and rutile inFig. 5are approximately 9.4 nm and 18.2 nm, respectively. Upon heating, the particles of anatase and rutile first coarsened at 600°C for 1 h (Fig. 5(a)). The slopes of the particle size versus time curves are very close for rutile and anatase, supporting the similarity in the coarsening behaviors of the two phases. The particle sizes of rutile and anatase then sub-stantially decreased. Finally, the particle size of anatase increased rapidly with a further increase in annealing time. Conversely, the particle size of rutile substantially decreased. The slow growth rate of rutile is also shown inFig. 5(a). Most particles have diameters close to the average particle sizes. The particle size of anatase increased rapidly at 600°C for an annealing time above 3.5 h, indi-cating that anatase coarsens faster than rutile, and two or more anatase particles may form one anatase particle. The average size data indicate that the grain growth of both anatase and rutile more
or less occurred during kinetic experiments. Meanwhile, the parti-cles of anatase and rutile first coarsened at 720°C for 2 h (Fig. 5(b)). The slopes of the particle size versus time curves are also very close for rutile and anatase, supporting the similarity in the coarsening behaviors of the two phases. The particle size of rutile then sub-stantially increased for an annealing time less than 3.5 h. Finally, the particle size of rutile decreased with a further increase in annealing time. Conversely, the particle size of anatase substan-tially decreased, and then disappeared at 720°C for 3.5 h.
Fig. 6shows the phase contents of anatase and rutile treated at different annealing temperatures (600 and 720°C). The results in
Fig. 6(a) indicate that the initial process involves anatase-to-rutile transformation in the starting mixed-phase TiO2 nanoparti-cles. This process was followed by conversion of rutile to anatase at 600°C. However, the relative mass content of the rutile phase is still higher than that of rutile annealed at 600°C for 1 h, indicat-ing that only a small quantity of rutile particles in large crystals may transform to the anatase phase. However, the phase contents of rutile and anatase did not change with the increase in annealing time. The phase transformation from rutile to anatase was rela-tively slow at 600°C for an annealing time of less than 3.5 h [Fig. 6(a)]. The particle size should be determined by both particle coarsening and phase transformation. Fig. 5(a) shows that the average particle size of rutile is almost constant at longer annealing times, whereas the average particle size of anatase increased. The changes in the content of anatase and rutile were minor. Therefore, data showed that coarsening rather than recrystallization occurred. Comparison ofFigs. 5(a) and6(a) shows that the overall effects of the factors that govern the coarsening rate of anatase include particle packing and surface energies.Fig. 6(b) shows that the initial process involves the transformation of anatase in the starting mixed-phase TiO2 nanoparticles to rutile at 720°C. The increase in weight content of the rutile phase with annealing indi-cates the transformation of anatase phase to rutile phase. The lar-ger slope for the data collected indicates that both coarsening and recrystallization occurred at 720°C for 1 h. The smaller TiO2 parti-cles could gain more kinetic energy, combine rapidly, and form lar-ger particles at 720°C. Furthermore, anatase totally transformed to rutile at 720°C for 3.5 h.
Kinetics mechanism analysis
Fig. 7shows the schematic model of the phase transformation in the TiO2sample at different annealing temperatures to under-stand the transformation behaviors of the detonation-synthesized TiO2nanoparticles during thermal treatment. The isothermal and isochronal experiments indicated that anatase transformed to
Fig. 4. Nitrogen gas adsorption–desorption isotherm of the mixed-phase TiO2
nanoparticles.
rutile at higher temperatures (720°C). The transformation between anatase and rutile may be reversible at lower tempera-tures (600°C). This transformation can be considered as a conse-quence of the dependence of thermodynamic stability on particles, indicating that polymorph growth rates differ, thereby causing changes in relative stability during thermal treatment pro-cess. Therefore, two or more anatase particles can also merge to form a larger anatase particle by diffusion of atoms annealed at 600°C for 5 h, as shown inFig. 5(a). Meanwhile, the rutile particles also grew into larger particles. The small amounts of reversible transformation from rutile to anatase in this region may be associ-ated with anatase coarsening at the expense of rutile. With a fur-ther increase in annealing temperature (720°C), the particle size of the rutile phase gradually grew. With the increase in annealing time [Fig. 6(b)], the relative weight content of rutile increased gradually at 720°C. With a further increase in annealing time, the particle size of anatase grew rapidly. These changes may be associated with the high surface energy and surface melting of TiO2particles (anatase phase). The unstable anatase particles min-imize the surface energy by increasing their size and the agglomer-ation of particles. Conversely, the slow growth rate of the rutile particle is also shown inFig. 5. The TiO2particles of anatase and rutile gained more kinetic energy and collision between the parti-cle increases. Anatase is totally transformed to rutile at 720°C for 3.5 h. As for the reasons for the different growth kinetics of anatase and rutile during the isothermal and isochronal processes (at 600°C and 720 °C), it is possible that the content and particle size of rutile phase have a certain effect on the growth of TiO2particles (anatase phase). Due to the growth of anatase crystal, small TiO2
nanoparticles (anatase phase) are up to the critical size, and are transformed into rutile structures. This leads to the growth of the anatase TiO2nanoparticles, while the other anatase nanoparticles grow more easily. Also, it has relationship with the particle size and agglomerate structures of the TiO2nanoparticles. As for the detail reasons, it still needs to be further investigated, and the rel-ative research is still under progress.
Experimental work and the accompanying theoretical explana-tions showed that macrocrystalline rutile is thermodynamically stable relative to macrocrystalline anatase at ambient pressures and temperatures [37–39]. Anatase-to-rutile transformation in TiO2nanoparticles is a metastable to stable irreversible transfor-mation[40]. Based on the calorimetric data for the transformation enthalpies of anatase-to-rutile and brookite-to-rutile, Zhang and Banfield concluded that the thermodynamic phase stability for the three polymorphs is rutile > brookite > anatase, and that ana-tase could either transform directly to rutile, or to brookite, and then to rutile[41]. When the particle size decreases below approx-imately 14 nm, anatase is more stable than rutile, and rutile trans-forms to anatase at small sizes[41]. Both electron diffraction and XRD patterns showed that the detonation-prepared mixed-phase TiO2nanoparticles have more metastable anatase structures rather than the stable rutile structures. Although the anatase-to-rutile transformation in the mixed-phase TiO2system is the main pro-cess, the isothermal and isochronal experiments also indicated that the transformation between anatase and rutile in large crystals may be reversible at lower temperatures (600°C). These changes may be associated with the more influence of thermal treatment on the rutile particles with larger crystallite size at lower
Fig. 6. Phase contents of the TiO2nanoparticles at different annealing temperatures: (a) 600°C; (b) 720 °C.
temperatures than that on the anatase phase, thereby increasing the weight percentage of anatase increases. Meanwhile, the aver-age size of the detonation-prepared TiO2sample, including anatase and rutile, grew larger because of the absorption energy. This growth may also be associated with the different surface energies of anatase and rutile at small crystallite sizes.
In conclusion, detonation is an unbalanced process in which a short duration of high temperature and high pressure is generated, thereby preventing the TiO2nanoparticles to have enough time to grow into large and fine crystallites[28,29]. A large number of spherical TiO2 nanoparticles were generated. Considerable micro stresses and larger crystal lattice parameters[32,42]can result in special kinetics of grain growth and different transformation behaviors of detonation-prepared TiO2nanoparticles during ther-mal treatment. Therther-mal treatment can be employed to control the particle size and phase contents of detonation-prepared TiO2 nanoparticles.
Conclusion
The mixed-phase TiO2 nanoparticles, consisting of anatase (34.8 wt %, 9.4 nm) and rutile (65.2 wt%, 18.2 nm) were pre-pared by detonation method. The microstructures, crystal sizes, phase contents, thermal stability, and kinetics of grain growth of the mixed-phase TiO2nanoparticles were studied to control the phases and particle sizes of the TiO2nanoparticles. The initial pro-cess involves the anatase-to-rutile transformation. Subsequently, the grains of the TiO2 nanoparticles coarsened drastically at 600°C for 1 h, followed by the conversion of rutile to anatase at 600°C. However, the relative mass content of the rutile phase is still less than that of rutile annealed at 600°C for 1 h. This finding indicates that a small quantity of rutile particles in large crystals may transform into anatase phase. Smaller TiO2particles can gain more kinetic energy and combine rapidly with the increase in tem-perature and then form larger particles at 720°C. Furthermore, anatase totally transformed into rutile by thermal treatment at 720°C for 3.5 h. The transformation temperature from anatase to rutile was approximately 80°C lower than that prepared by con-ventional methods. The phase transformation in the TiO2sample at different annealing temperatures was modeled to understand the transformation behaviors of the detonation-synthesized TiO2 nanoparticles during thermal treatment. Therefore, thermal treat-ment can be employed to control the particle size and phase con-tent of mixed-phase TiO2 nanoparticles prepared by detonation method.
Acknowledgments
The authors acknowledge financial support from the National Natural Science Foundation of China (Grant Nos 11302094, and 11302093), the Program for Liaoning Excellent Talents in Univer-sity (grant no. LJQ2014063, and LJQ 2015047), Beijing Higher Edu-cation Young Elite Teacher Project.
References
[1]Chou CS, Chen CY, Lin SH, Lu WH, Wu P. Preparation of TiO2
/bamboo-charcoal-powder composite particles and their applications in dye-sensitized solar cells. Adv Powder Technol 2015;26(3):711–7.
[2]Reid D, Draper R, Richardson D, Demko A, Allen T, Petersen E, Seal S. In situ synthesis of polyurethane–TiO2 nanocomposite and performance in solid
propellants. J Mater Chem A 2014;2(7):2313–22.
[3]Lee SH, Choi Y. Effect of nano-sized oxide particles on thermal and electrical properties of epoxy silica composites. Phys Met Metallogr 2014;115 (13):1295–9.
[4]Lou S, Teng F, Xu J, Liu Z, Zhu Y. Electrochemical properties of novel titania nanostructures. Nanotechnology. 2015;26(22):225603.
[5]Burns A, Hayes G, Li W, Hirvonen J, Derek Demareed J, Ismat ShahS. Neodymium ion dopant effects on the phase transformation in sol–gel derived titania nanostructures. Mater Sci Eng B 2004;111(2–3):150–5. [6]Li W, Ni C, Lin H, Huang CP, Shah SI. Size dependence of thermal stability of
TiO2nanoparticles. J Appl Phys 2004;96:6663.
[7]Qu YD, Li XJ, Li RY, Yan HH, Ouyang X, Wang XH. Preparation and characterization of the TiO2ultrafine particles by detonation method. Mater
Res Bull 2008;43(1):97–103.
[8]Korotin MA, Zainullina VM. Investigation of the influence of nonstoichiometry and doping with carbon and nitrogen on the electronic spectrum of rutile by the coherent potential method. Phys Solid State 2013;55(5):952–9. [9]Nasrin F, Serge A, Charpentier PA. Fe doped TiO2-graphene nanostructures:
synthesis, DFT modeling and photocatalysis. Nanotechnology 2014;25 (30):305601.
[10] Zhang HZ, Banfield JF. Kinetics of crystallization and crystal growth of nanocrystalline anatase in nanometer-sized amorphous titania. Chem Mater 2002;14(10):4145–54.
[11]Khan Z, Al-Thabaiti SA, El-Mossalamy EH, Obaid AY. Studies on the kinetics of growth of silver nanoparticles in different surfactant solutions. Colloid Surf B 2009;73(2):284–8.
[12]Ohtani B, Ogawa Y, Nishimoto SI. Photocatalytic activity of amorphousanatase mixture of titanium(iv) oxide particles suspended in aqueous solutions. J Phys Chem B 1997;101(19):3746–52.
[13]Lee GW, Byeon JH. Effects of ultrasonic processing on phase transition of flame-synthesized anatase TiO2 nanoparticles. Mater Char 2009;60
(12):1476–81.
[14]Yanagisawa K, Yamamoto Y, Feng Q, Yamasaki N. Formation mechanism of fine anatase crystals from amorphous titania under hydrothermal conditions. J Mater Res 1998;13(4):825–9.
[15]Exarhos GJ, Aloi M. Crystallite growth kinetics in isothermally annealed sol– gel films. Thin Solid Films 1990;193(194):42–50.
[16]Ko HH, Hsi CS, Wang MC, Zhao XJ. Crystallite growth kinetics of TiO2surface
modification with 9 mol% ZnO prepared by a coprecipitation process. J Alloy Comp 2014;588:428–39.
[17]Charbonneau C, Gauvin R, Demopoulos GP. Nucleation and growth of self-assembled nanofibre-structured rutile (TiO2) particles via controlled forced
hydrolysis of titanium tetrachloride solution. J Cryst Growth 2009;312 (1):86–94.
[18]Li XJ, Qu YD, Xie XH, Wang ZL, Li RY. Preparation of SrAl2O4: Eu2+, Dy3+
nanometer phosphors by detonation method. Mater Lett 2006;60(29– 30):3673–7.
[19]Qu YD, Li XJ, Zhao Z, Sun GL. Titania nanocrystalline prepared by detonation method and calculation of detonation parameters. Propell Explos Pyrotech 2011;36(1):75–9.
[20] Graham RA, Morosin B, Venturini EL, Carr MJ. Materials modification and synthesis under high pressure shock compression. Annu Rev Mater Sci 1986;16(16):315–41.
[21]Shenderova OA, Vlasov II, Turner S, Tendeloo GV, Orlinskii SB, Shiryaev AA, Khomich AA, Sulyanov SN, Jelezko F, Wrachtrup J. Nitrogen control in nanodiamond produced by detonation shock-wave-assisted synthesis. J Phys Chem C 2011;115(29):14014–24.
[22]Mitev DP, Townsend AT, Paull B, Nesterenko PN. Microwave-assisted purification of detonation nanodiamond. Diam Relat Mater 2014;48:37–46. [23]Sun GL, Li XJ, Qu YD, Wang XH, Yan HH, Zhang YJ. Preparation and
characterization of graphite nanosheets from detonation technique. Mater Lett 2008;62(4–5):703–6.
[24]Bukaemskii AA, Avramenko SS, Tarasova LS. Ultrafine a-Al2O3 explosive
method of synthesis and properties. Combust Explos Shock Waves 2002;38 (4):478–83.
[25]Li RY, Li XJ, Yan HH, Peng J. Experimental investigations of the controlled explosive synthesis of ultrafine Al2O3. Combust Explos Shock Waves 2013;49
(1):105–8.
[26]Yan HH, Huang XC, Xi SX. Using ethanol for preparation of nanosized TiO2by
gaseous detonation. Combust Explos Shock Waves 2014;50(2):192–5. [27]Qu YD, Li XJ, Wang XH, Liu DH. Detonation synthesis of nanosized titanium
dioxide powders. Nanotechnology 2007;18(20):205602.
[28]Xie XH, Li XJ, Yan HH. Detonation synthesis of zinc oxide nanometer powders. Mater Lett 2006;60(25):3149–52.
[29]Qu YD, Li XJ, Zhao Z, Ouyang X. Synthesis of SrAl2O4: Eu2+, Dy3+nanometer
phosphors by detonation and combustion method. Chin J High Pressure Phys 2008;22(2):175–80.
[30] Lei FB, Wang ZS, Zhao BG. Preparation and mechanism of nanometer Al5O6N
via shock wave plasma technique. Mater Res Bull 2009;44(1):198–201. [31]Xie XH, Li XJ, Zhao Z, Wu H, Qu YD, Huang W. Growth and morphology of
nanometer LiMn2O4powder. Powder Technol 2006;169(3):143–6.
[32]Li XJ, Qu YD, Sun GL, Jiang DA, Ouyang X. Study on the lattice distortion of the as-prepared nanosized TiO2particles via detonation method. J Phys Chem
Solids 2007;68(12):2405–10.
[33]Liu JJ, He HL, Jin XG, Hao Z, Hu Z. Synthesis of nanosized nickel ferrites by shock waves and their magnetic properties. Mater Res Bull 2001;36 (13):2357–63.
[34]Qu YD, Li XJ, Liu Y. Study on the agglomerate structures of TiO2nanoparticles.
Chin J High Pressure Phys 2010;24(6):438–42.
[35]Qu YD, Kong XQ, Li XJ, Yan HH. Effect of thermal treatment on the structural phase transformation of the detonation-prepared TiO2 mixed crystal
[36]Joseph Antony RK, Viswanathan B. Effect of surface area, pore volume and particle size of P25 titania on the phase transformation of anatase to rutile. Indian J Chem A 2009;48(10):1378–82.
[37]Zhang HZ, Banfield JF. Thermodynamic analysis of phase stability of nanocrystalline titania. J Mater Chem 1998;8(9):2073–6.
[38]Barnard AS, Curtiss LA. Prediction of TiO2 nanoparticle phase and shape
transitions controlled by surface chemistry. Nano Lett 2005;5(7):1261–6. [39]Zhang HZ, Finnergan M, Banfield JF. Preparing single-phase nanocrystalline
anatase from amorphous titania with particle sizes tailored by temperature. Nano Lett 2001;1(2):81–5.
[40]Kumar KNP, Keizer K, Burggraaf AJ. Textural stability of titania–alumina composite membranes. J Mater Chem 1993;3(3):917–22.
[41]Gribb AA, Banfield JF. Particle size effects on transformation kinetics, phase stability in nanocrystalline TiO2. Am Mineral 1997;82(7–8):717–28.
[42]Qu YD, Li XJ, Zhang YJ, Sun GL, Wang XH. Preparation of nanosized TiO2
particles utilizing Ti2(SO4)3by detonation method. J Funct Mater 2006;37