Effect of Organic Additives during Hydrothermal Syntheses of Rutile

Subscriber access provided by Macquarie University

Article

Effect of Organic Additives during Hydrothermal Syntheses of Rutile TiO2 Nanorods for Photocatalytic Applications Yukari Yamazaki, Mamoru Fujitsuka, and Suzuko Yamazaki ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.9b01334 • Publication Date (Web): 28 Aug 2019 Downloaded from pubs.acs.org on August 29, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Nano Materials

Effect of Organic Additives during Hydrothermal Syntheses of Rutile TiO2 Nanorods for Photocatalytic Applications Yukari Yamazaki1, Mamoru Fujitsuka2, Suzuko Yamazaki1* 1 Department

of Chemistry, College of Science, Graduate School of Sciences and Technology for

Innovation, Yamaguchi University, Yamaguchi 753-8512, Japan 2 The

Institute of Scientific and Industrial Research (SANKEN), Osaka University, Osaka 567-

0047, Japan KEYWORDS: TiO2 nanorods, rutile phase, photocatalytic oxygen evolution, structuredirecting agents, hydrothermal method

ACS Paragon Plus 1 Environment

ACS Applied Nano Materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT: TiO2 nanorods have been widely investigated for various applications as catalyst support, photoanode, bioanalytical platform and photocatalyst because of their unique properties due to the high length-to-width ratio. In this study, we examined the effect of eight organic additives for the hydrothermal synthesis and clarified that α-hydroxy acids are good structure directing agents to synthesize rutile TiO2 nanorod. Depending on the structure of the α-hydroxy acid used for the synthesis, i.e., glycolic acid (GA), lactic acid (LA), and 2-hydroisobutyric acid (2-HIBA), the length and the width of the nanorod are varied. Under the hydrothermal treatment of 200oC for 12 h, small particles consisting of anatase and brookite or anatase particles coexist surrounding the rutile nanorod synthesized with LA or 2-HIBA, respectively, whereas GA yields only rutile nanorod. With increasing the hydrothermal time, nanoparticles surrounding the nanorod are disappeared and 100% rutile nanorod is synthesized with LA for 96 h (TiO2_LA_96h) or 2HIBA for 48 h (TiO2_2-HIBA_48h). For these 100% rutile nanorods synthesized with GA, LA and 2-HIBA, the shape of quadrangular prism with non-flat ends is observed. The selected area electron diffraction patterns indicate that the crystal growth occurs in the [001] direction and the side or the end surface of the nanorods is attributable to {110} or {111} facet, respectively. The photocatalytic activity for the oxygen evolution through water oxidation is the following order: TiO2_GA_12h > TiO2_LA_96h > TiO2_2-HIBA_48h. Time-resolved diffuse reflectance spectra suggest that the highest photocatalytic activity obtained with TiO2_GA_12h is attributable to the rapid decay of the photogenerated electrons to the deep trapping sites. Our results indicate that GA is the most appropriate as the structure directing agent to synthesize rutile TiO2 nanorod because of the shortest hydrothermal time and the highest photocatalytic activity.

INTRODUCTION


Page 2 of 34

Page 3 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Many semiconductor materials have been investigated for converting solar energy efficiently into electricity or chemical energy. Among them, titanium dioxide (TiO2) is the most studied material as a photocatalyst, a photoanode for water splitting and an anode for dye-sensitized solar cell.1-3 Recently, one-dimensional TiO2, especially vertically aligned rutile TiO2 nanorods on fluorinedoped tin oxide (FTO) glass have been used in various photoelectrochemical application.4-10 Such an array grown on FTO has been proven to reduce the number of the recombination centers on TiO2/FTO interface because FTO acts as a seed layer for an epitaxial growth.4,5 Furthermore, light harvest is enhanced on the TiO2 nanorod array due to multiple reflections. Various modification of the TiO2 nanorod array with CdS or SnO2 quantum dots11,12, Ag nanoparticles13, and oxygen evolution electrocatalyst shell14 have been reported to improve the photoelectrochemical performance. Three-dimensional photoanodes with heterojunction have been fabricated by growing CdS nanoflower15 and Sn3O416 or MoS217 nanosheet on the TiO2 nanorod array. UVphotodetector18, resistive switching memory devices19 and capacitors20 based on the TiO2 nanorod array have been developed. The TiO2 nanorod array has been utilized for application as a platform for photoelectrochemical bioanalysis21 and capture of tumor cells22-24. Synthesis of TiO2 nanorod without use of FTO is generally complicated and consists of multi-steps. To fabricate TiO2 nanorods as a catalyst support, Abbas et al. performed a hydrothermal treatment of 10 M NaOH aqueous solution suspended with commercial anatase TiO2 microparticles and then calcined the obtained product at 550oC.25 Fathy et al. synthesized anatase TiO2 nanorods by a solvothermal method of titanium isopropoxide (TTIP) in ethylene glycol followed by thermal treatment at 400 - 600oC.26 Kakihana and his coworkers synthesized a water soluble glycolato peroxotitanium complex and then treated hydrothermally to prepare rutile and TiO2(B) nanorods.27-31 They controlled selective synthesis of TiO2 polymorphs by the



solvothermal treatment of the water soluble titanium complex.27 Mamakhel et al. reported on a facile synthesis of rutile TiO2 nanorods by hydrothermal method using TTIP and an aqueous solution of glycolic acid at pH ≈ 1.6.32 However, in these studies, the photocatalytic activity of the synthesized TiO2 nanorod was not examined. For the photocatalytic application, Yang et al. prepared rutile, anatase, and brookite TiO2 nanorods by the hydrothermal method using peroxide titanium acid solution of different pH values and indicated that the rutile TiO2 nanorod showed the optimal activity for the oxidation of methylene blue whereas the brookite TiO2 nanorod exhibited the highest activity for the reduction of Cr(VI).10 Nguyen-Phan et al. synthesized TiO2 nanorods immobilized with RuO2 for visible light-driven hydrogen evolution. They prepared the TiO2 nanorods by the hydrothermal treatment of a mixture of titanium n-butoxide and hydrochloric acid followed by the calcination at 200oC for 2 h.33 Previously, we synthesized rutile TiO2 nanorods by using TTIP as a starting material and studied the effect of the morphological change from rod-shape to sub-sphere by the subsequent thermal treatment.34 We selected glycolic acid as the structure directing agent and TTIP as Ti source precursor because TTIP is often used for the synthesis of TiO2. Facile hydrothermal synthesis of the rutile TiO2 nanorod has been reported by using TiCl4 and TiCl3 as the Ti source.3537

However, we did not select them because their hydrolysis reactions are highly exothermic and

produce HCl fume and the resulting Cl- ion affects the crystallization process of the rutile phase.3739

We compared the photocatalytic activity of the nanorod and the sub-sphere for O2 evolution

from water oxidation because this reaction was hardly affected by the specific surface area of photocatalysts.40 We clarified that the TiO2 nanorods possess the longest lifetime of photogenerated electrons by time-resolved microwave conductivity measurements although the photocatalytic activity of the nanorod was lower than that sintered at 800oC.34


Page 4 of 34

Page 5 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


In this study, we report the effect of organic additives on the synthesis of TiO2 nanorod from TTIP by the hydrothermal method. Facile synthesis of the nanorod having different lengths and widths only by changing organic additives will be useful for the application as catalyst supports or bioanalytical platforms. Furthermore, we describe the water oxidation on the rutile TiO2 nanorod to estimate the effect of organic additives on the photocatalytic activity.

EXPERIMENTAL SECTION Synthesis.

Rutile TiO2 nanorods were synthesized by the hydrothermal method in the presence

of organic compounds such as acetic acid (CH3COOH, AA), glycolic acid (HOCH2CO2H, GA), lactic acid (HO(CH3)CHCO2H, LA), 2-hydroisobutyric acid (HO(CH3)2CCO2H, 2-HIBA), 3hydroxy propionic acid (HOC2H5CO2H, 3-HPA), glycerin acid (HOCH2CH(OH)CO2H, GRA), oxalic acid (H2C2O4, OA), and ethylene glycol (HOC2H4OH, EG). These chemical structures are shown in Scheme 1. Briefly, approximately 5.0 mL of TTIP (Ti(OC3H7)4) and 5.0 mL of isopropanol were poured into 50 mL of aqueous solution containing 1.6 mol dm-3 organic compounds (0.8 mol dm-3 was used only for OA because of its low solubility). When GA, LA, or OA was used, the mixed solution turned transparent, and when GRA was used, the mixed solution changed to an orange transparent solution under stirring. However, in the case of other compounds, the solution did not become transparent even after being stirred for 1.5 h under slightly heating. The resulting solution was sealed in a Teflon-lined stainless-steel autoclave (100 mL) and followed by heating at 200oC for 12 – 96 h. After the solution was cooled to room temperature, TiO2 powders were separated in a centrifuge. The powders were washed with ethanol three times and then washed thoroughly with Milli-Q water. TiO2 powder synthesized with GA, LA, or 2-HIBA was collected by filtration and dried at room temperature. TiO2 powder synthesized by using the other



Page 6 of 34

compounds could not be collected by filtration due to the small particle size. Hence, in these cases, the suspension of the TiO2 powder which was washed with water by repeating the centrifugation was dried at 40oC to remove water. The synthesized samples are denoted as TiO2_X_Y where X is the organic additive and Y is the hydrothermal time.

Scheme 1. Organic Compounds used for Synthesis of TiO2.

H3C

O

O

O OH

HO

HO

HO OH

OH

H3C

CH3 AA

GA

LA

O HO

OH

HO OH

3-HPA

Characterization.

GRA

OH CH3 2-HIBA

O

O

OH

O

HO

OH

HO

OH

O

OA

EG

Field-emission scanning electron microscopy (FESEM) and transmission

electron microscopy (TEM) images of the TiO2 were recorded with JSM-7600F and JEM-2100 instrument (JEOL, Japan), respectively. X-ray diffraction (XRD) analysis was measured on MiniFlex600 (Rigaku, Japan) with Cu Kα radiation. The crystallite sizes of the TiO2 were estimated using the Scherrer formula. The crystalline phase compositions of TiO2 were estimated by Rietveld analysis with PDXL software (Rigaku, Japan). The degree of crystallinity of the synthesized TiO2 was evaluated by the Rietveld analysis using nickel oxide as an internal standard and the fraction of amorphous components. The details were described in Supporting Information.


Page 7 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Nitrogen adsorption-desorption isotherm measurements were performed by using a TriStar II 3020 analyzer (Micromeritics, USA) to estimate the specific surface areas by using the BrunauerEmmett-Teller (BET) method. The lifetime of the photogenerated electrons was evaluated by measuring time-resolved diffuse reflectance (TDR) spectra using a regeneratively amplified titanium sapphire laser (Spectra-Physics, Spitfire Pro F, 1 kHz) pumped by a Nd:YLF laser (Spectra-Physics, Empower 15). The seed pulse was generated by a titanium sapphire laser (Spectra-Physics, Mai Tai VFSJW, fwhm 80 fs). The output of the optical parametric amplifier (Spectra-Physics, OPA-800CF) was used as the excitation pulse (365 nm, 4 μJ pulse-1). The white light continuum pulse, which was generated by focusing the residual of the fundamental light on a sapphire crystal, was used as the probe light. Details of the TDR measurement were reported previously.41,42 The synthesized sample was dispersed in ethanol by ultrasonication and then spread on a glass cover slip. The probe and reference lights were both directed at the glass cover slip coated with the sample and the reflected lights were detected by a linear InGaAs array detector with a polychromator (Solar, MS3504). The %absorption (%Abs) is defined as (R0 – R)/R0 x 100 where R0 and R indicate the intensities of the diffuse reflected monitor light with and without excitation, respectively. Evaluation of Photocatalytic Activity.

The synthesized TiO2 sample (0.3 g) was suspended

in a Pyrex reactor containing 0.05 mol dm-3 AgNO3 solution (150 mL). After air dissolved in the reactant solution was removed by bubbling argon gas for 1 h, the suspension was irradiated with UV from a 250 W super-high-pressure Hg lamp (Ushio Inc., Japan) through a U330 bandpass filter (HOYA CANDEO OPTRONICS, Japan). Vigorous stirring with magnetic stirrer was performed throughout the experiments. The reaction temperature was maintained at 30oC by using a thermostatic water bath. The amount of O2 evolution under UV irradiation was measured with a



Page 8 of 34

gas chromatograph equipped with a thermal conductivity detector (Shimadzu, Japan, GC-8A with MS-5A column).

RESULTS AND DUSCUSSION Effect of organic additives on the morphology of TiO2.

Scheme 2 indicates schematic

representation of TiO2 synthesized by the hydrothermal treatment for 12 h with and without organic additives and their TEM images are shown in Figure 1. As reported previously,34 TiO2 nanorod is formed by using GA as the organic additive (Figure 1b). In the case of LA or 2-HIBA, TiO2 nanorod is surrounded by many or a few small nanoparticles, respectively (Figure 1c and 1d). Shapes of nanorods in these samples are different, i.e. the average length is the following order: TiO2 _LA (385 nm) > TiO2 _GA (297 nm) > TiO2 _2-HIBA (193 nm) as shown in Table S1. On the other hand, the other samples show only nanoparticles. Their particle sizes measured on the TEM images indicate that TiO2 _OA is much larger whereas TiO2 _AA, 3-HPA, GRA, or EG is smaller than that without the organic additives (Table S1). Figure S1 shows the XRD patterns of all samples and Table 1 lists their crystal phase composition obtained by the Rietveld analysis together with the BET specific surface area. TiO2 synthesized without organic additives consists of anatase and brookite. Both phases have a characteristic 2 value at around 25.3o but the brookite phase also has a characteristic peak at around 30.8o.30,43,44 Three samples in which nanorod structure was observed by TEM, i.e. TiO2_GA, LA, and 2-HIBA mainly consist of the rutile phase, 100, 48.4 and 94.8%, respectively and other nanoparticulate samples except for TiO2_OA consist of 100% anatase. TiO2_OA is a mixture of 19.0 % rutile and 81.0% anatase. Crystallite size in Table 1 was evaluated from the XRD peaks attributable to rutile (110) at 2 = 27.4o, anatase (101) at 25.3o or brookite (121) at 30.8o. The crystallite size of rutile is in the range of 21 – 39 nm, which


Page 9 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


is larger than anatase and brookite. The latter two phases are small in the range of 4 – 12 nm except for TiO2_OA. It is worthy to note that the crystallite size of rutile on TiO2_LA or 2-HIBA (21, 39 nm) is much larger than the size of nanoparticles as shown in Table S1, suggesting that the nanorod consists of rutile and the surrounding particles are anatase or brookite.

Scheme 2. Schematic Representation of the Synthesis of TiO2.

Hydrothermal at 200oC for 12 h

Ti(OC3H7)4 CH3CH(OH)CH3 H2O + 2-HIBA + GA

+ AA 3-HPA GRA EG

+ LA

+ OA

anatase brookite rutile



(a)

Page 10 of 34

(b)

50 nm

(c)

200 nm

(d)

200 nm

200 nm

(e)

(f)

50 nm

(g)

50 nm

(h)

20 nm

20 nm

(i)

20 nm

Figure 1. TEM images of TiO2 synthesized by the hydrothermal method at 200oC for 12h (a) without additives, with (b) GA, (c) LA, (d) 2-HIBA, (e) OA, (f) AA, (g) 3-HPA, (h) GRA, and (i) EG.


Page 11 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. Mass Fraction and Crystallite Size of Each Crystalline Phase, Average Crystallite Size and BET Surface Area of TiO2 Synthesized with Various Organic Additives.

Rutile

Anatase

Brookite

Average crystallite size (nm)

Without additives

-

74.1 [9]

25.9 [8]

9

133.0

GA

100 [24]

-

-

24

38.9

LA

48.4 [21]

17.2 [9]

34.4 [9]

15

94.6

2-HIBA

94.8 [39]

5.2 [9]

-

37

22.1

OA

19.0 [26]

81.0 [23]

-

24

34.9

AA

-

100 [12]

-

12

107.5

3-HPA

-

100 [6]

-

6

192.4

GRA

-

100 [4]

-

4

232.2

EG

-

100 [8]

-

8

159.5

Mass fraction (%) [Crystallite size (nm)]

BET surface area (m2 g-1)

Figure 2 shows bar chart of the degree of the crystallinity of the samples, in which the composition of the crystal phases is classified by color. The samples containing the rutile phase, i.e. TiO2_OA, GA, LA, and 2-HIBA possess crystallinity higher than 93%. TiO2_GRA shows the lowest crystallinity (43.2%), indicating remarkable inhibition of GRA to the crystal growth. This fact is consistent with the smallest crystallite size of TiO2_GRA (4 nm in Table 1). However, there is no correlation between the crystallite size and the degree of the crystallinity. On the other hand, the BET surface area increases as the crystallite size decreases in all the samples. Nitrogen adsorption and desorption isotherm revealed that TiO2 synthesized without additives, TiO2_AA, 3-HPA, GRA, and EG which had the BET surface area higher than 100 m2 g-1 exhibited hysteresis loop, indicating the presence of mesopore (Figure S2).



100 Degree of crystallinity (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 34

80 60 40 20 0

Without additives

EG

OA

rutile

AA

3-HPA

brookite

GRA

GA

LA

2-HIBA

anatase

Figure 2. Degree of crystallinity and crystalline phase of the synthesized TiO2. Figure 3 shows TEM images of TiO2_LA and 2-HIBA which were synthesized by the hydrothermal treatment for more than 24 h, indicating that the nanoparticles around the nanorods decrease and completely disappear on TiO2_LA_96 h and TiO2_2-HIBA_24 h. The XRD patterns also indicated that small peaks attributable to anatase and brookite disappeared and pure rutile nanorods were formed (Figure S3). Figure 4 summarizes effect of the hydrothermal time on degree of the crystallinity, the phase composition and the crystallite size which is evaluated as average for the mixed phase TiO2 by using the mass fraction and the crystallite size for each phase (Table S2). As the hydrothermal time for TiO2_LA increases, the phase transition to rutile as well as the crystal growth are enhanced and then the crystallite size increases to 40 nm which is almost equivalent to that for TiO2_2-HIBA_12h or 24h. Table 2 lists average length, average width and aspect ratio of the rutile nanorod. The former average values are evaluated by measuring 50 nanorods selected randomly and might be overestimated in the case where nanoparticles coexist. As the hydrothermal


Page 13 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


time increases, both length and width of TiO2_LA tends to increase. Similar behavior was observed for TiO2_2-HIBA although the aspect ratio hardly changed. (b)

(a)

200 nm

200 nm

(d)

(c)

200 nm

200 nm

(e)

(f)

200 nm

200 nm

Figure 3. TEM images of TiO2 synthesized with LA after the hydrothermal treatment for (a) 24 h, (b) 48 h, (c) 72 h, and (d) 96 h, and (e) TiO2 synthesized with 2-HIBA after the hydrothermal treatment for 24 h and (f) 48 h.


Page 14 of 34

100

50

80

40

60

30

40

20

20

10

0

0 GA 12 h rutile

LA 12 h

LA 24 h

brookite

LA 48 h

LA 72 h

anatase

Average crystallite size (nm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Degree of crystalinity (%)


LA 2-HIBA 2-HIBA 96 h 12 h 24 h

Average crystallite size

Figure 4. Effect of the hydrothermal time on degree of the crystallinity, the phase composition and the crystallite size. Table 2. Length, Width and Aspect Ratio of TiO2 Nanorods. Length (nm)

Width (nm)

Aspect ratioa

GA 12 h

297 ± 103

33 ± 10

9

LA 12 h

385 ± 153

28 ± 11

14

LA 24 h

422 ± 175

31 ± 21

14

LA 48 h

469 ± 173

38 ± 23

12

LA 72 h

396 ± 150

33 ± 22

12

LA 96 h

454 ± 156

54 ± 38

8

2-HIBA 12 h

193 ± 110

39 ± 26

5

2-HIBA 24 h

262 ± 118

41 ± 18

6

2-HIBA 48 h

249 ± 122

46 ± 26

5

aAspect

ratio was defined as the average length divided by the average width.

Effect of organic compounds to crystal growth of TiO2.

Although rutile is the most stable

thermodynamically, the relative stability of TiO2 polymorphs depends on the particle size: anatase is the most stable at size below ca. 11 nm while brookite in the range of ca. 11-35 nm.45 Indeed,


Page 15 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


our results indicate that TiO2 particles consisting of 74.1% anatase (9 nm) and 25.9% brookite (8 nm) are formed without organic additives. In the case of OA, anatase particles grow to 23 nm with the formation of rutile. This finding is attributable to the strong complexing property of C2O42because it is known as a rigid bidentate ligand that can chelate or bind two metal centers. On the other hand, nanorod is formed in the presence of α-hydroxy acids such as GA, LA and 2-HIBA, suggesting that coordination of Ti4+ with OH and COOH promotes the formation of nanorods. Because the anatase powder was formed in the case of β-hydroxy acid such as 3-HPA, tight coordination of α-hydroxy acids by forming five-membered ring is beneficial for the formation of nanorod. In the case of GRA which CH3 in LA is hydroxylated, TiO2 nanoparticles instead of nanorods are produced, suggesting that the presence of OH at β-carbon acts as another branching point of the crystal growth. Some research groups have investigated the effect of organic additives on the selective synthesis of anatase, brookite and rutile by using water-soluble titanium complexes as starting materials. Dambournet et al. reported that thermolysis of a titanium oxysulfate in an aqueous solution promoted the phase transition from anatase to rutile in the presence of oxalate at the molar ratio of [C2O42-]/[Ti4+] of 2.0.46 Kobayashi et al. synthesized single crystals of an ammonium trilactate titanium complex ((NH4)2[Ti(C3H4O3)3]) by using Ti metal powder, H2O2, NH3 and L-lactic acid and investigated the crystal growth from [Ti(C3H4O3)3]2- under hydrothermal conditions.47 They reported that rod-like rutile TiO2 with 295 nm in length and 67 nm in width were obtained without organic additives and the addition of LA or 2-HIBA increased both the length and the width of the nanorod, i.e., 883 nm and 138 nm in length and width, respectively, for LA and 902 nm and 132 nm for 2-HIBA under the hydrothermal treatment of 200oC for 48 h. It is worthy to note that these sizes are much larger than the nanorods we synthesized in this study. Furthermore, no significant differences were observed for the size of the



Page 16 of 34

nanorod synthesized with the addition of LA and 2-HIBA in their synthetic system whereas the TiO2_2-HIBA is much shorter than TiO2_LA in this study. These facts indicate that water-soluble complex such as [Ti(C3H4O3)3]2- can promote the formation of nanorod more easily than TTIP. Generally, in aqueous solution, hydrolysis and condensation of TTIP occurs stepwise to form TiO-Ti network.

Hydrolysis: Ti(OC3H7)4 + n H2O → Ti(OC3H7)4-n(OH)n + n C3H7OH

(n = 1 – 4)

Condensation: Ti-OH + Ti-OR → Ti-O-Ti + R-OH Complexation: Ti(OC3H7)4-n(OH)n + HOCR2COOH → Ti(OCR2COO)(OH)2, Ti(OCR2COO)2 GA: R = H, LA: R = CH3 and H, 2-HIBA: R = CH3

In our study, the hydrolysis and the subsequent condensation compete with the formation of Ti complex with α-hydroxy acids. On TiO2_LA_12h, the rutile nanorod is surrounded by many small nanoparticles of anatase and brookite, suggesting that the hydrolysis and the condensation occur similarly to some extent as those without additives. On the other hand, GA can coordinate to Ti most easily among these three α-hydroxy acids because of less steric hindrance, leading to the formation of pure rutile nanorod. By increasing the hydrothermal time, the nanoparticles on the TiO2_LA nanorod disappears via Ostwald ripening mechanism where small particles are dissolved and redeposited on the growing rod.32, 48 The size of TiO2_LA nanorod is much longer whereas that of TiO2_2-HIBA is shorter and thicker compared with TiO2_GA. This finding might suggest that the crystal growth along short axis, i. e. the direction of the width, consumes brookite rather than anatase by Ostwald ripening. The complexation of α-hydroxy acids with the Ti precursor plays an important role for the


Page 17 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


formation of rutile nanorod. Effect of the organic additives on the formation of anatase, brookite and rutile can be explained in terms of the interaction with TiO6 octahedron which is used as a building unit for TiO2. Ti(OH)4 which is formed by hydrolyzing TTIP corresponds to Ti(OH)4(H2O)2 with octahedral symmetry. The growth of the TiO2 can be accomplished by the connection of the TiO6 octahedra via oxolation (dehydration) between OH ligands. In rutile, two opposing edges of each TiO6 are shared to form linear chains along [001] direction and the TiO6 chains are then linked together via corner sharing. Anatase has no corner sharing but has four edges shared per octahedron. Brookite has three edges and some corners shared, which is midway between the structures of anatase and rutile in terms of the shared edges. 43, 49, 50 In the presence of α-hydroxy acids, the coordination suppresses the formation of the edge-shared bonding because one edge-shared bonding needs two oxolation reactions between two TiO6 units to occur simultaneously. As a result, the formation of anatase with four edges shared is significantly suppressed. The rod shape consisting of four {110} facets on the side and growing along [001] directions is the most stable structure of rutile because the surface energy of the {110} facets is the lowest whereas the {001} is the highest.51 Hong et al. reported that Cl- ions are selectively adsorbed on the {110} facets of rutile so that they inhibit the growth along the [110] directions, leading to the formation of the rod-shape.51 Therefore, in our case, the anisotropic growth of rutile might be caused by the selective adsorption of α-hydroxy acids on {110}. Photocatalytic activity.

The photocatalytic O2 evolution by water oxidation was performed on

the samples under UV irradiation for 5 h, which were synthesized under hydrothermal treatment for 12 h (Figure S4). Photocatalytic activity is the following order: TiO2_GA > 2-HIBA > without additives > OA > LA. The higher activity of TiO2_GA or 2-HIBA is attributable to the rutile phase because the rutile TiO2 with large particle size is the most favorable in the photocatalytic water



oxidation.40, 52-54 On other samples such as TiO2_AA, EG, 3-HPA, and GRA, no O2 evolution was observed. These four samples are nanoparticles consisting of only anatase. TiO2 synthesized without additives and TiO2_OA which exhibit low activity are two-phase nanoparticles consisting of anatase/brookite or anatase/rutile, respectively. Mixed phase TiO2 have been proven to exhibit higher photocatalytic activities than single phase TiO2 by enhancing electron-hole charge separation and thus inhibiting their recombination.43, 55 Hereafter, TiO2_GA, 2-HIBA and LA were investigated in detail to clarify the effect of nanorod structure on the O2 evolution. Figure 5 shows that the photocatalytic activity of TiO2_LA increases with an increase in the hydrothermal time and that of TiO2_LA_72h is almost the same as TiO2_LA_96h. Similarly, the photocatalytic activity of TiO2_2-HIBA_48h is higher than that of TiO2_2-HIBA_12h. Comparison of 100% rutile nanorod indicates that the photocatalytic activity is the following order: TiO2_GA_12h > TiO2_LA_96h > TiO2_2-HIBA_48h. As we reported previously34, the O2 evolution rate on TiO2_GA was the highest when being treated hydrothermally for 12 h and gradually decreased as the hydrothermal time increased. These findings suggest that the photocatalytic activity of the rutile nanorod varies with the structure directing agents used for the synthesis.


Page 18 of 34

Page 19 of 34

120.00 GA 12 h LA 96 h

Amount of O2 evolved (μmol)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100.00

LA 72 h 2-HIBA 48 h

80.00

LA 48 h 2-HIBA 12 h

60.00

LA 24 h LA 12 h

40.00 20.00 0.00 0

60

120

180

240

300

Irradiation time (min)

Figure 5. Oxygen evolution on TiO2 synthesized with GA, LA, and 2-HIBA by changing the hydrothermal time.



　　 (a)

(d)

50 nm

(b)

(e)

50 nm

(c)

(f)

50 nm

Figure 6. HRTEM images with the selected area electron diffraction pattern (a – c) and FESEM images (d – f). TiO2_GA_12h (a, d), TiO2_LA_96h (b, e), TiO2_2-HIBA_48h (c, f).

Figure 6 shows the HRTEM and the FESEM images of TiO2_GA_12h, TiO2_LA_96h and TiO2_2HIBA_48h. The shape of quadrangular prism with non-flat ends is observed in the FESEM images


Page 20 of 34

Page 21 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


for these samples. The selected area electron diffraction patterns (inset in Figure 6a-c) indicate that the crystal growth occurs in the [001] direction and the side or the end surface is attributable to {110} or {111} facet, respectively. This structural property is similar to the equilibrium shape of rutile TiO2.10, 47 There is no significant difference in the rod shape of these samples except for the different lengths and widths. Yang et al. reported that the {111} facet provides the oxidation site and the {110} facet acts as the reduction site, which is favorable to separation of the photogenerated holes and electrons.54 To get information about the photogenerated carriers, we measured TDR spectra of TiO2_GA_12h, TiO2_LA_96h and TiO2_2-HIBA_48h (Figure 7a-c). The TDR spectra of TiO2_GA_12h and TiO2_2-HIBA_48h exhibit a transient absorption peak at 850 – 900 nm although %Abs of TiO2_GA_12h increases at the wavelength longer than 1100 nm. The TDR spectra having a peak at 850 – 900 nm were also obtained with commercially available TiO2 P-25 which was used as a reference to justify our experimental set-up (Figure S5). On the other hand, %Abs of TiO2_LA_96h tends to increase with increasing the wavelength. Such differences might be attributable to the overlap of the absorption of the trapped electron (600 – 1000 nm) and that of free electrons which increases monotonically from visible to near-infrared regions.42,56-58 Yamakata et al. reported that in the case of anatase TiO2, the trapped electrons are in equilibrium with free electrons because the electron traps are shallow, and then the lifetime of the electron becomes longer than 1 ms, leading to the higher activity for the reduction. On the other hand, the electron traps in rutile TiO2 are much deeper and most of the photogenerated electrons are trapped quickly at these sites within a few picoseconds whereas the recombination of electrons and holes occurs more slowly via the deep trapping.59,60 The decay profiles at 1000 nm in Figure 7d are analyzed by two-exponential curve fitting and the determined lifetimes are listed in Table 3. It is reasonable to consider that the 1 and 2 values are assigned to the lifetime of the



photogenerated electrons being relaxed to the deep trapping sites and that of the trapped electrons for the recombination with the photogenerated holes, respectively. Table 3 shows that both 1 and 2 are the following order: TiO2_GA_12h < TiO2_2-HIBA_48h < TiO2_LA_96h, which is not correlated with the photocatalytic activity for O2 evolution, i.e. TiO2_GA_12h > TiO2_LA_96h > TiO2_2-HIBA_48h. However, the relative amplitudes which are estimated from the fitting parameters (A1 and A2) indicate that the 1 path (54%) is more predominant than the 2 path (46%) for TiO2_GA_12h whereas the 2 path of 89% or 79% is obtained for TiO2_2-HIBA_48h or TiO2_LA_96h, respectively. Therefore, the highest photocatalytic activity obtained with TiO2_GA_12h is attributable to the rapid decay of the photogenerated electrons to the deep trapping sites. This is beneficial to increase the lifetime of the photogenerated holes which are needed for O2 evolution by water oxidation. Higher photocatalytic activity of TiO2_LA_96h than TiO2_2-HIBA_48h can be ascribed to the larger A1 and the longer 2 values for TiO2_LA_96h. Our results indicate that the dynamics of the photogenerated charge carriers are varied in the rutile TiO2 nanorods which are synthesized by using different α-hydroxy acids as the structure directing agents. It is reported that the origin of the electron trap is a defect such as an oxygen vacancy or Ti interstitial.59, 60 The formation of the defect might be affected by the hydrothermal time needed for the formation of the rutile nanorod. Further studies are being conducted to clarify the factor affecting the dynamics of the photogenerated charge carriers in the TiO2 nanorod.


Page 22 of 34

Page 23 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a)

(b)

(c)

(d)

Figure 7. TDR spectra of (a) TiO2_GA_12h, (b) TiO2_LA_96h, and (c) TiO2_2-HIBA_48h and (d) their decay profile at 1000 nm.

Table 3. Lifetimes of the Photogenerated Electrons. τ1 (ps)

τ2 (ps)

GA_12h

16 (54%)

135 (46%)

LA_96h

36 (21%)

187 (79%)

2-HIBA_48h 24 (11%) 162 (89%) Values in parentheses were relative amplitudes which were estimated from A1 and A2 in the following equation: %Abs(t) = A1 exp(-t/τ1) and A2 exp(-t/τ2) + Const.

CONCLUSIONS One-dimensional nanostructures such as TiO2 nanorod have been widely investigated for various



applications because of their unique properties due to their high length-to-width ratio. We have clarified that α-hydroxy acids are good structure directing agents to synthesize rutile TiO2 nanorod and demonstrated the effective control on the length and the width of the nanorod by changing the structure of α-hydroxy acids. Our synthetic method has no use of rather aggressive chemicals such as Ti metal, H2O2, peroxide titanic acid, TiCl4 and TiCl3 which are often used for the hydrothermal synthesis of TiO2 nanorod. The facile synthesis of the rutile TiO2 nanorod with various lengths and widths will be useful for the application as catalyst support or bioanalytical platform. For the photocatalytic application, we compared the activity of the rutile nanorods for the O2 evolution from water. We have demonstrated that GA is the best structure directing agent because of the shortest hydrothermal time needed for the synthesis and the highest photocatalytic activity. The TDR spectra suggest that the highest photocatalytic activity of TiO2_GA_12h is attributable to the rapid decay of the photogenerated electrons to the deep trapping sites. In the future, we will obtain a design guideline to synthesize more active TiO2 nanorod photocatalysts by clarifying the reason why the rapid decay of the electrons is accelerated by using GA.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ….. Method for determining the degree of crystallinity; morphology and size of TiO2 synthesized with and without organic additives; XRD patterns; N2 adsorption and desorption isotherm; mass fraction and crystallite size of the crystalline phases of TiO2 synthesized with LA and 2HIBA;oxygen evolution on TiO2 synthesized at 200oC for 12h; TDR spectra of P-25.


Page 24 of 34

Page 25 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


AUTHOR INFORMATION Corresponding Author *Suzuko Yamazaki, Tel & Fax: +81-83-933-5763; e-mail: [email protected] ORCID Suzuko Yamazaki: 0000-0002-9440-1213 Mamoru Fujitsuka: 0000-0002-2336-4355 Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was partially supported by JSPS KAKENHI Grant No. 18K05298 and performed under the Cooperative Research Program of "Network Joint Research Center for Materials and Devices”. We thank Yamaguchi University Science Research Center and Innovation Center for the SEM, TEM, TG-DTA, and XRD measurements. We also thank Dr. Naoto Nishiyama for his help to measure the TDR spectra.

REFERENCES (1) Chu, L.; Zhang, J.; Liu, W.; Yang, J.; Hu, R.; Li, X.; Huang, W. A Facile and Green Approach to Synthesize Mesoporous Anatase TiO2 Nanomaterials for Efficient Dye-sensitized and Hole-



Conductor-Free Perovskite Solar Cells. ACS Sustainable Chem. Eng. 2018, 6, 5588-5597. (2) Chu, L.; Qin, Z.; Zhang, Q.; Chen, W.; Yang, J.; Yang, J.; Li, X. Mesoporous Anatase TiO2 Microspheres with Interconnected Nanoparticles Delivering Enhanced Dye-loading and Charge Transport for Efficient Dye-sensitized Solar Cells. Appl. Surf. Sci. 2016, 360, 634-640. (3) Chu, L.; Qin Z.; Liu, W.; Ma, X. Inhibition of Charge Recombination for Enhanced DyeSensitized Solar Cells and Self-Powdered UV Sensors by Surface Modification. Appl. Surf. Sci. 2016, 389, 802-809. (4) Liu, B.; Aydil, E. S. Growth of Oriented Single-Crystalline Rutile TiO2 Nanorods on Transparent Conducting Substrates for Dye-Sensitized Solar Cells. J. Am. Chem. Soc. 2009, 131, 3985-3990. (5) Ros, C.; Fabrega, C.; Monllor-Satoca, D.; Hernandez-Alonso, M. D.; Penelas-Perez, G.; Morante, J. R.; Andreu, T. Hydrogenation and Structuration of TiO2 Nanorod Photoanodes: Doping Level and the Effect of Illumination in Trap-States Filling. J. Phys. Chem. C 2018, 122, 3295-3304. (6) Dhar, S.; Chakraborty, P.; Majumder, T.; Mondal, S. P. Acid-Treated PEDOT:TSS Polymer and TiO2 Nanorod Schottky Junction Ultraviolet Photodetectors with Ultrahigh External Quantum Efficiency, Detectivity, and Responsivity, ACS Appl. Mater. Interfaces 2018, 10, 41618-41626. (7) Wu, S.; Chen, C.; Wang, J.; Xiao, J.; Peng, T. Controllable Preparation of Rutile TiO2 Nanorod Array for Enhanced Photovoltaic Performance of Perovskite Solar Cells. ACS Appl. Energy Mater. 2018, 1, 1649-1657. (8) Huang, C.; Bian, J.; Zhang, R. Role of Cl Ion Desorption in Photocurrent Enhancement of the Annealed Rutile Single-Crystalline TiO2 Nanorod Arrays. J. Phys. Chem. C 2017, 121, 1889218899.


Page 26 of 34

Page 27 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(9) Sutiono, H.; Tripathi, A. M.; Chen, H.; Chen, C.; Su, W.; Chen, L.; Dai, H.; Hwang, B. Facile Synthesis of [101]-Oriented Rutile TiO2 Nanorod Array on FTO Substrate with a Tunable AnataseRutile Heterojunction for Efficient Solar Water Splitting. ACS Sustainable Chem. Eng. 2016, 4, 5963-5971. (10) Yang, Z.; Wang, B.; Cui, H.; An, H.; Pan, Y.; Zhai, J. Synthesis of Crystal-Controlled TiO2 Nanorods by a Hydrothermal Method: Rutile and Brookite as Highly Active Photocatalysts. J. Phys. Chem. C 2015, 119, 16905-16912. (11) Chen, Y.; Chen, Y.; Chen, J.; Cao, F.; Li, L.; Luo, Z.; Leu, I.; Pu, Y. New Insights into the Electron-Collection Efficiency Improvement of CdS-Sensitized TiO2 Nanorod Photoelectrodes by Interfacial Seed-Layer Mediation. ACS Appl. Mater. Interfaces 2019, 11, 8126-8137. (12) Sun, B.; Chen, Y.; Tao, L.; Zhao, H.; Zhou, G.; Xia, Y.; Wang, H.; Zhao, Y. Nanorod Array of SnO2 Quantum Dot Interspersed Multiphase TiO2 Heterojunctions with Highly Photocatalytic Water Splitting and Self-Rechargeable Battery-Like Applications. ACS Appl. Mater. Interfaces 2019, 11, 2071-2081. (13) Zhao, H.; Huang, F.; Liu, Z.; Wu, Q.; Cao, H.; Jing, Q.; Peng, S.; Cao, G. Efficiency Enhancement of Quantum Dot Sensitized TiO2/ZnO Nanorod Arrays Solar Cells by Plasmonic Ag Nanoparticles. ACS Appl. Mater. Interfaces 2016, 8, 26675-26682. (14) Schpper, D.; Zhao, Z.; Leitner, A. P.; Xie, L.; Qin, F.; Alam, M. K.; Chen, S.; Wang, D.; Ren, Z.; Bao, J.; Whitmire K. H. A TiO2/FeMnP Core/Shell Nanorod Array Photoanode for Efficient Photoelectrochemical Oxygen Evolution. ACS Nano 2017, 11, 4051-4059. (15) David, S.; Mahadik, M. A.; Chung, H. S.; Ryu, J. H.; Jang, J. S. Facile Hydrothermally Synthesized a Novel CdS Nanoflower/Rutile-TiO2 Nanorod Heterojunction Photoanode Used for Photoelectrocatalytic Hydrogen Generation. ACS Sustainable Chem. Eng. 2017, 5, 7537-7548.



(16) Zhu, L.; Lu, H.; Hao, D.; Wang, L.; Wu, Zihua, Wang, L.; Li, P.; Ye, J. Three-Dimensional Lupinus-like TiO2 Nanorod@Sn3O4 Nanosheet Hierarchical Heterostructured Arrays as Photoanode for Enhanced Photoelectrochemical Performance. ACS Appl. Mater. Interfaces 2017, 9, 38537-38544. (17) Pi, Y.; Li, Z.; Xu, D.; Liu, J.; Li, Y.; Zhang, F.; Zhang, G.; Peng, W.; Fan, X. 1T-Phase MoS2 Nanosheets on TiO2 Nanorod Arrays: 3D Photoanode with Extraordinary Catalytic Performance. ACS Sustainable Chem. Eng. 2017, 5, 5175-5182. (18) Gao, Y.; Xu, J.; Shi, S.; Dong, H.; Wei, C.; Zhang, X.; Yin, S.; Li, L. TiO2 Nanorod Arrays Based Self-Powered UV Photodetector: Heterojunction with NiO Nanoflakes and Enhanced UV Photoresponse. ACS Appl. Mater. Interfaces 2018, 10, 11268-11279. (19) Xiao, M.; Musselman, K. P.; Duley, W. W.; Zhou, Y. N. Reliable and Low-Power Multilevel Resistive Switching in TiO2 Nanorod Arrays Structured with a TiOx Seed Layer. ACS Appl. Mater. Interfaces 2017, 9, 4808-4817. (20) Yao, L.; Pan, Z.; Liu, S.; Zhai, J.; Chen, H. H. D. Significantly Enhanced Energy Density in Nanocomposite Capacitors Combining the TiO2 Nanorod Array with Poly(vinylidene fluoride). ACS Appl. Mater. Interfaces 2016, 8, 26343-26351. (21) Yu, L.; Zhu, Y.; Liu, Y.; Qu, P.; Xu, M.; Shen, Q.; Zhao, W. Ferroelectric Perovskite Oxide@TiO2 Nanorod Heterostructures: Preparation, Characterization, and Application as a Platform for Photoelectrochemical Bioanalysis. Anal. Chem. 2018, 90, 10803-10811. (22) Li, R.; Chen, F. F.; Liu, H. Q.; Wang, Z. X.; Zhang, Z. T.; Wang, Y.; Cui, H.; Liu, W.; Zhao, X. Z.; Sun, Z. J.; Guo, S. S. Efficient Capture and High Activity Release of Circulating Tumor Cells by Using TiO2 Nanorod Arrays Coated with Soluble MnO2 Nanoparticles. ACS Appl. Mater. Interfaces 2018, 10, 16327-16334.


Page 28 of 34

Page 29 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Sun, N.; Li, X.; Wang, Z.; Zhang, R.; Wang, J.; Wang, K.; Pei, R. A Multiscale TiO2 Nanorod Array for Ultrasensitive Capture of Circulating Tumor Cells. ACS Appl. Mater. Interfaces 2016, 8, 12638-12643. (24) Liu, H.; Ruan, M.; Xiao, J.; Zhang, Z.; Chen, C.; Zhang, W.; Cao, Y.; He, R.; Liu, Y.; Chen, Y. TiO2 Nanorod Arrays with Mesoscopic Micro-Nano Interfaces for in Situ Regulation of Cell Morphology and Nucleus Deformation. ACS Appl. Mater. Interfaces 2018, 10, 66-74. (25) Abbas, T.; Tahir, M.; Amin, N. A. S. Enhanced Metal-Support Interaction in Ni/Co3O4/TiO2 Nanorods toward Stable and Dynamic Hydrogen Production from Phenol Steam Reforming. Ind. Eng. Chem. Res. 2019, 58, 517-530. (26) Fathy, M. Hamad, H.; Kashyout, A. E. H. Influence of Calcination Temperatures on the Formation of Anatase TiO2 Nano Rods with a Polyol-Mediated Solvothermal Method. RSC Adv. 2016, 6, 7310-7316. (27) Kobayashi, M.; Kato, H.; Kakihana, M. Synthesis of Titanium Dioxide Nanocrystals with Controlled Crystal- and Micro-structures from Titanium Complexes. Nanomater. Nanotechnol. 2013, 3, 1-10. (28) Osada, M.; Kobayashi, M.; Kakihana, M. Enhanced Dielectric Response Induced by Controlled Morphology in Rutile TiO2 Nanocrystals. J. Ceramic Soc. Jpn. 2013, 121, 593-597. (29) Yamamoto, K.; Tomita, K.; Fujita, K.; Kobayashi, M. Petrykin, V.; Kamihana, M. Synthesis of TiO2(B) Using Glycolato Titanium Complex and Post-synthetic Hydrothermal Crystal Growth of TiO2(B). J. Crys. Growth, 2009, 311, 619-622. (30) Kobayashi, M.; Tomita, K.; Petrykin, V.; Yoshimura, M.; Kakihana, M. Direct Synthesis of Brookite-Type Titanium Oxide by Hydrothermal Method Using Water-Soluble Titanium Complexes. J. Mater. Sci. 2008, 43, 2158-2162.



(31) Kobayashi, M.; Petrykin, V.; Kakihana, M.; Tomita, K. Morphology Control of Rutile Nanoparticles in a Hydrothermal Synthesis From Water-Soluble Titanium Complex Aqueous Solution. J. Ceramic Soc. Jpn. 2007, 115, 835-839. (32) Mamakhel, A.; Tyrsted, C.; Bojesen, E. D.; Hald, P.; Iversen, B. B. Direct Formation of Crystalline Phase Pure Rutile TiO2 Nanostructures by a Facile Hydrothermal Method. Cryst. Growth Des. 2013, 13, 4730-4734. (33) Nguyen-Phan, T.; Luo, S.; Vovchok, D.; Llorca, J.; Graciani, J.; Sanz, J.; Sallis, S.; Xu, W.; Bai, J.; Piper, L. F. J.; Polyansky, D. E.; Fujita, E.; Senanayake, S. D.; Stacchiola, D. J.; Rodriguez, J. A. Visible Light-Driven H2 Production over Highly Dispersed Ruthenia on Rutile TiO2 Nanorods. ACS Catal. 2016, 6, 407-417. (34) Yamazaki, Y.; Azami, K.; Katoh, R.; Yamazaki, S. Developing Active TiO2 Nanorods by Examining the Influence of Morphological Changes from Nanorods to Nanoparticles on Photocatalytic Activity. ACS Appl. Nano Mater. 2018, 1, 5927-5935. (35) Leong, S.; Li, D.; Hapgood, K.; Zhang, X.; Wang, H. Ni(OH)2 Decorated Rutile TiO2 for Efficient Removal of Tetracycline from Wastewater. Appl. Catal. B: Environ. 2016, 198, 224-233. (36) Tahr, M. N.; Theato, P.; Oberle, P.; Melnyk Gennadii, Faiss, S.; Kolb, U.; Janshoff, A.; Stepputat, M.; Tremel, W. Facile Synthesis and Characterization of Functionalized, Monocrystalline Rutile TiO2 Nanorods. Langmuir 2006, 22, 5209-5212. (37) Huang, X.; Pan, C. Large-Scale Synthesis of Single-Crystalline Rutile TiO2 Nanorods via A One-Step Solution Route. J. Cryst. Growth, 2007, 306, 117-122. (38) Addamo, M.; Augugliaro, V.; Paola, A. D.; Garcia-Lopez, E.; Loddo, V.; Marci, G.; Molinari, R.; Palmisano, L.; Schiavello, M. Preparation, Characterization, and Photoactivity of Polycrystalline Nanostructured TiO2 Catalysts. J. Phys. Chem. B 2004, 108, 3303-3310.


Page 30 of 34

Page 31 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(39) Addamo, M.; Augugliaro, V.; Paola, A. D.; Garcia-Lopez, E.; Loddo, V.; Marci, G.; Palmisano, L. Preparation and Photoactivity of Nanostructured TiO2 Particles Obtained by Hydrolysis of TiCl4. Colloids and Surf. A: Physicochem. Eng. Aspects 2005, 265, 23-31. (40) Nishimoto, Y.; Hasegawa, Y.; Adachi, K.; Yamazaki, S. Factors Affecting Oxygen Evolution Through Water Oxidation on Polycrystalline Titanium Dioxide. RSC Adv. 2016, 6, 46994-47000. (41) Bian, Z.; Tachikawa, T.; Zhang, P.; Fujitsuka, M.; Majima, A Nanocomposite Superstructure of Metal Oxides with Effective Charge Transfer Interfaces. Nature Commun. 2014, 5, 4038-4046. (42) Bian, Z.; Tachikawa, T.; Zhang, P.; Fujitsuka, M.; Majima, T. Au/TiO2 Superstructure-Based Plasmonic Photocatalysts Exhibiting Efficient Charge Separation and Unprecedented Activity. J. Am. Chem. Soc. 2014, 136, 458-465. (43) Tay, Q.; Liu, X.; Tang, Y.; Jiang, Z.; Sum, T. C.; Chen, Z. Enhanced Photocatalytic Hydrogen Production with Synergistic Two-Phase Anatase/Brookite TiO2 Nanostructures. J. Phys. Chem. C 2013, 117, 14973-14982. (44) Simonarson, G.; Sommer, S.; Lotsari, A.; Elgh, B.; Iversen, B. B.; Palmqvist, E. C. Evolution of the Polymorph Selectivity of Titania Formation under Acidic and Low-Temperature Conditions. ACS Omega 2019, 4, 5750-5757. (45) Zhang, H.; Banfield, J. F. Understanding Polymorphic Phase Transformation Behavior during Growth of Nanocrystalline Aggregates: Insights from TiO2. J. Phys. Chem. B 2000, 104, 34813487. (46) Dambournet, D.; Belharouak, I.; Amine, K. Tailored Preparation Methods of TiO2 Anatase, Rutile, Brookite: Mechanism of Formation and Electrochemical Properties. Chem. Mater. 2010, 22, 1173-1179. (47)　Kobayashi, M.; Lee, S.; Kato, H.; Kakihana, M. Effect of Hydroxy and Carboxy Groups on



Anisotropic Growth of Rutile-type Titania under Hydrothermal Conditions. J. Asian Ceramic Soc. 2017, 5, 320-325. (48) Hu, K.; E, L.; Zhao, D.; Hu, C.; Cui, J.; Lai, L.; Xiong, Q.; Liu, Z. Hydrothermal Synthesis of a Rutile/Anatase TiO2 Mixed Crystal From Potassium Titanyl Oxalate: Crystal Structure and Formation Mechanism. CrystEngComm. 2018, 20, 3363-3369. (49) Testino, A.; Bellobono, I. R.; Buscaglia, V.; Canevali, C.; D’Arienzo, M.; Polizzi, S.; Scotti, R.; Morazzoni, F. Optmizing the Photocatalytic Properties of Hydrothermal TiO2 by the Control of Phase Composition and Particle Morphology. A Systematic Approach. J. Am Chem. Soc. 2007, 129, 3564-3575. (50) Li, J-G.; Ishigaki, T.; Sun, X. Anatase, Brookite, and Rutile Nanocrystals via Redox Reactions under Mild Hydrothermal Conditions: Phase-Selective Synthesis and Physicochemical Properties. J. Phys. Chem. C 2007, 111, 4969-4976. (51) Hong, S.-P.; Park, J.; Bhat, S. S. M.; Lee, T. H.; Lee, S. A.; Hong, K.; Choi, M.; Shokouhimehr, M.; Jang, H. W. Comprehensive Study on the Morphology Control of TiO2 Nanorods on Foreign Substrates by the Hydrothermal Method. Cryst. Growth Des. 2018, 18, 6504-6512. (52) Kominami, H.; Murakami, S.; Kato, J.; Kera, Y.; Ohtani, B. Correlation Between Some Physical Properties of Titanium Dioxide Particles and Their Photocatalytic Activity for Some Probe Reactions in Aqueous Systems. J. Phys. Chem. B 2002, 106, 10501-10507. (53) Maeda, K. Effects of the Physicochemical Properties of Rutile Titania Powder on Photocatalytic Water Oxidation. ACS Catal. 2014, 4, 1632-1636. (54) Yang, Z.; Wang, B.; Zhang, J.; Cui, H.; Pan, Y.; An, H.; Zhai, J. Factors Influencing the Photocatalytic Activity of Rutile TiO2 Nanorods with Different Aspect Ratios for Dye Degradation and Cr(VI) Photoreduction. Phys. Chem. Chem. Phys. 2015, 17, 18670-18676.


Page 32 of 34

Page 33 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(55) Liao, Y.; Que, W.; Jia, Q.; He, Y.; Zhang, J.; Zhong, P. Controllable Synthesis of Brookite/Anatase/Rutile TiO2 Nanocomposites and Single-crystalline Rutile Nanorods Array. J. Mater. Chem. 2012, 22, 7937-7944. (56) Yoshihara, T.; Katoh, R.; Furube, A.; Tamaki, Y.; Murai, M.; Hara, K.; Murata, S.; Arawaka, H.; Tachiya, M. Identification of Reactive Species in Photoexcited Nanocrystalline TiO2 Films by Wide-Wavelength-Range (400 – 2500 nm) Transient Absorption Spectroscopy. J. Phys. Chem. B 2004, 108, 3817-3823. (57) Tamaki, Y.; Hara, K.; Katoh, R.; Tachiya, M.; Furube, A. Femtosecond Visible-to-IR Spectroscopy of TiO2 Nanocrystalline Films: Elucidation of the Electron Mobility before Deep Trapping. J. Phys. Chem. C 2009, 113, 11741-11746. (58) Katoh, R.; Murai, M.; Furube, A. Transient Absorption Spectra of Nanocrystalline TiO2 Films at High Excitation Density. Chem. Phys. Lett. 2010, 500, 309-312. (59) Yamakata, A.; Vequizo, J. J. M.; Matsunaga, H. Distinctive Behavior of Photogenerated Electrons and Holes in Anatase and Rutile TiO2 Powders. J. Phys. Chem. C 2015, 119, 2453824545. (60) Yamakata, A.; Vequizo, J. J. M. Curious Behaviors of Photogenerated Electrons and Holes at the Defects on Anatase, Rutile and Brookite TiO2 Powders: A Review. J. Photochem. Photobiol. C: Photochem. Rev. 2018, https://doi.org/10.1016/j.jphotochemrev.2018.12.001.



TOC

120

Ti(OC3H7)4 CH3CH(OH)CH3 H2O

GA 12 h

Hydrothermal at 200oC for 12 h

+ 2-HIBA + LA + AA 3-HPA GRA EG

+ OA

LA 96 h

100

+ GA

Amount of O2 evolved (μmol)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

LA 72 h 2-HIBA 48 h

80

LA 48 h 2-HIBA 12 h

60

LA 24 h LA 12 h

40

20 anatase brookite rutile

0 0

60

120 180 240 Irradiation time (min)

300


Page 34 of 34

Effect of Organic Additives during Hydrothermal Syntheses of Rutile

Recommend Documents