Nanotubes Decorated by Pt Nanoparticles and - American Chemical

Subscriber access provided by UNIV OF NEWCASTLE

Article 2

Highly Visible-Light Photoactive Heterojunction Based on TiO Nanotubes Decorated by Pt Nanoparticles and BiS Quantum Dots 2

3

Pawe# Mazierski, Joanna Nadolna, Grzegorz Nowaczyk, Wojciech Lisowski, Micha# Jerzy Winiarski, Tomasz Klimczuk, Marek Kobyla#ski, Stefan Jurga, and Adriana Zaleska-Medynska J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b03895 • Publication Date (Web): 20 Jul 2017 Downloaded from http://pubs.acs.org on July 21, 2017

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 free 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 accessible to all readers and 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.

The Journal of Physical Chemistry C 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 31

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

The Journal of Physical Chemistry

Highly Visible-light Photoactive Heterojunction Based on TiO2 Nanotubes Decorated by Pt Nanoparticles and Bi2S3 Quantum Dots Paweł Mazierskia*, Joanna Nadolnaa, Grzegorz Nowaczykb, Wojciech Lisowskic, Michał Jerzy Winiarskid, Tomasz Klimczukd, Marek Piotr Kobylańskia, Stefan Jurgab, Adriana ZaleskaMedynskaa*. a

Department of Environmental Technology, University of Gdansk, Poland

b

NanoBioMedical Center, Adam Mickiewicz University, Poland

c

Institute of Physical Chemistry, Polish Academy of Sciences, Poland

d

Department of Solid State Physics, Gdansk University of Technology, Poland

ABSTRACT A heterojunction with excelent visible light response and stability based on titanium dioxide nanotubes (TiO2 NTs), bismuth sulfide quantum dots (Bi2S3 QDs) and platinum nanoparticles (Pt NPs) was proposed. Both, Pt NPs (3.0 ± 0.2 nm) and Bi2S3 QDs (3.50 ± 0.20 nm) were well distributed on the (i) top parts, (ii) inner and (iii) outer walls of the TiO2 NTs. Visible light induced photoreaction was initialized by excitation of narrow band gap Bi2S3 QDs, followed by electron injection to the conduction band of TiO2, while Pt NPs acted as electron traps, enhacing O2-• generation. Phenol in the aqueous phase and toluene in the gas phase were efficiently

ACS Paragon Plus Environment

1


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 2 of 31

degraded over Bi2S3-Pt-NTs even for wavelength longer than 455 and 465 nm, respectively, while no model compounds degradation was observed over pristine TiO2 NTs in the same irradiation conditions. Photocatalytic tests of phenol degradation in the presence of scavengers revealed that superoxide radicals were responsible for the visible light degradation of organic compounds in the aqueous phase. 1.

Introduction

In recent years, heterogeneous photocatalysis based on TiO2 has been paid particular attention and widely applied in e.g. degradation of organic pollutants in water inactivation of microorganisms 5, hydrogen production

6–8

1–3

and gas phase 4,

and photoconversion of CO2 9. The

development of photocatalysts with remarkable activity to degrade pollutants in aqueous and gas phase requires visible-light-responded stable photomaterials. In contrast to TiO2 in the form of powder, ordered TiO2 nanotubes (NTs) obtained by electrochemical method have attracted increased attention due to oriented charge transfer, highly ordered array structure, large surface area and especially low recombination rate of photogenerated charge carriers

10

. Considering

their unique properties, NTs can be used as effective photocatalytic materials. However, the low visible light utilization, since TiO2 absorbs mainly high energy photons in the UV region of the solar spectrum, and the recombination rate of photogenerated electron-hole pairs limits their applications in some fields. Until today, to enhance the photocatalytic response of the TiO2 NTs in the visible range and improve the electron-hole separation, various ways were applied such as transition metal cation doping 11,12, nonmetal doping 2,13,14, dye sensitization 15, surface modification with noble metals, rare earth metals and with low band gap semiconductors

16–21

. Especially, the formation of

heterojunctions formed by coupling different semiconductors such as CdS, Ag2O, Cu2O, CdSe


2

Page 3 of 31

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


and Bi2O3 is thought to be one of the most effective strategies to improve light absorption, photoinduced charge separation efficiency and the photocatalytic properties. More attention has been focused recently on the application of metal sulphides for photocatalyst modification, because of their narrow band gaps and resulting visible light absorption 22. Among the narrow band gap metal chalcogenides, Bi2S3 (band gap equal to 1.3 – 1.7 eV, depending on the NPs size 23) is a nontoxic and chemically stable material 24,25. Moreover, the conduction band (CB) of Bi2S3 is positioned to a more negative side than that of TiO2. Therefore, Bi2S3 could be excited by visible light irradiation, and the photogenerated electrons can be injected into the CB of TiO2, because the CB level of TiO2 is lower than that of Bi2S3. Thus, the electron transfer behaviour effectively reduces the probability of Bi2S3 photocorrosion and improves the separation between the photogenerated electrons and holes of TiO2 photocatalysts 26,27. Kim et al. 22

studied the photocatalytic activity of Bi2S3 (5, 10, 15 wt.%) modified TiO2. The study

exhibited that the Bi2S3 modification can enhance the production of hydrogen. Based on cyclic voltammetry results, the high photoactivity was due to the decreased recombination between the excited electrons and holes. Lu et al. 28 prepared TiO2/Bi2S3 heterojunctions with a nuclear-shell structure by the precipitation method. The photocatalytic experiments performed under UV irradiation using methyl orange, as pollutant, revealed that an appropriate amount of Bi2S3 improved the photocatalytic activity of TiO2 due to its huge surface area and narrow band gap. Yang et al. 26 synthesized TiO2 nanotube arrays modified by single crystalline, three dimensional (3D) white fungus-like mesoporous Bi2S3 crystals by pulsed electrodeposition technique. The resulting Bi2S3/TiO2 nanotube arrays showed much higher adsorption capacity and photocatalytic activity under UV-Vis light irradiation than the unmodified TiO2 due to the mesoporous property of narrow bandgap Bi2S3 balls. Solis et al.

27

reported the use of chemically deposited Bi2S3 for


3


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 4 of 31

sensitization of TiO2 nanotube arrays. Impedance electrochemical measurements demonstrated superior electron lifetimes in Bi2S3/TiO2 nanotube arrays, due to a large recombination resistance as well as a large chemical capacitance. Notably, the size of metal sulphide photocatalysts can have impact on its physicochemical properties. It is proved that semiconductor nanocrystals with the radius smaller or equal to excitation Bohr radius (so-called quantum dots (QDs)), exhibit exotic optical and electrical behaviours not found in their bulk counterparts. Having excitons confined in all three spatial dimensions, quantum dots have properties that are between those of bulk semiconductors and those of discrete molecules

29

. On the other hand, recently, literature data demonstrated that the

three- component systems could have higher photocatalytic activity than the single-and twocomponent systems

30,31

. In view of this, Pt nanoparticles (NPs) seem to be excellent co-

catalysts, because they occupy the largest work function (5.65 eV) among the noble metals and they are one of the most promising co-catalysts for trapping electrons. Considering the points in the above discussion, the modification of NTs by Pt NPs and Bi2S3 QDs should be beneficial, and this type of heterojunction theoretically could be an effective photocatalyst with remarkable activity. Thus, we present here for the first time a new heterojunction composed of Bi2S3 quantum dots and Pt nanoparticles vertically arranged on highly ordered TiO2 nanotube arrays. The morphology, structure and photocatalytic properties in two model reactions including the excitation by different irradiation range and source in the presence of pristine TiO2 NTs, TiO2 NTs loaded by Pt NPs, Bi2O3 QDs and Pt NPs/Bi2O3 QDs were systematically investigated and discussed. An excitation mechanism under visible light was presented as well. The as-prepared Bi2S3-Pt-TiO2 NTs junction exhibited enhanced light


4

Page 5 of 31

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


absorption capacity and facilitated the photogenerated charges separation/transfer and therefore a significantly improved photocatalytic activity. 2.

Experimental section

2.1

Materials

Titanium foil (0.127 mm thickness, 99.7% purity), toluene, H2Cl6Pt·xH2O, Bi(NO3)3·5H2O as well as terephthalic acid (98%) were purchased from Sigma-Aldrich. Isopropanol, acetone, methanol and phenol were purchased from P.P.H. STANLAB, while ethylene glycol (EG) from CHEMPUR and ammonium fluoride from ACROS ORGANICS. 2.2

Preparation of TiO2 NTs

The titanium foils were cleaned by sonication in acetone, isopropanol, methanol and deionized water for 10 min in each solvent. Then, the Ti foils were dried in an air stream. The anodization experiments were carried out in a two-electrode electrochemical set-up. A piece of Ti foil (3 x 2 cm) was used as working electrode, and a platinum mesh was used as counter electrode. Additionally, an Ag/AgCl reference electrode was used to control the process and obtain information about the actual working electrode potential. Anodization was performed in an electrolyte composed of ethylene glycol, deionized water (2 vol%) and ammonium fluoride (0.09 M) for 1 h at 40 V using a programmable DC power supply (MCP M10-QS1005). To measure the actual current and potential of the Ti electrode versus Ag/AgCl, a reference electrode digital multimeter (BRYMEN BM857a) was applied. The as-prepared NTs were rinsed with deionized water followed by sonication in deionized water (5 min), drying in air at 80°C (24 h) and calcination at 450°C (in air, heating rate of 2°C/min) for 1 h. 2.3

Decoration of TiO2 NTs with Pt NPs and Bi2S3 QDs


5


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 6 of 31

TiO2 NTs decorated by Pt NPs and Bi2S3 QDs were obtained by Pt photodeposition and followed by Bi2S3 deposition using SILAR technique as described in our patent application

32

. Pt NPs

were deposited on the surface of TiO2 NTs using the photodeposition method. The as-prepared NTs were immersed in a HCl solution at pH 5 for 10 min. Then, without rinsing, the NTs were immersed in 30 mL of metal precursor solution (H2Cl6Pt·xH2O). After 2 h, 0.69 mL of isopropanol was added to a photoreactor, followed by 1 h of nitrogen bubbled through the solution to remove the air and illuminated by 250 W Xe lamp (UV flux 30 mW/cm2) used as an irradiation source for 2 h. The obtained samples were rinsed with deionized water and dried at 80°C. Bi2S3 QDs were assembled onto TiO2 NTs by a successive ionic layer adsorption and reaction (SILAR) technique. Firstly, the as-prepared TiO2 NTs or Pt-TiO2 NTs were immersed in a solution containing 0.05 M Bi(NO3)3·5H2O for 5 min, and then the samples were rinsed with pure acetone and dried. Secondly, the samples were immersed into a 0.01 M Na2S·9H2O solution for another 5 min, rinsed with deionized water and dried. This procedure was repeated four times and finally, the samples were dried at 80°C. 2.4

Surface properties characterization

The morphology of the obtained Pt NPs and Bi2S3 QDs modified- NTs was determined by using scanning electron microscopy (SEM, FEI Quanta 250 FEG). NT lengths were measured using a tilted (30°) sample holder. The results given in the text are corrected for the effect of tilt. The morphology, distribution and location of Bi2S3 quantum dots and Pt nanoparticles in the modified- NT samples were studied using High-Resolution Transmission Electron Microscopy (HRTEM Jeol ARM 200F). The UV-Vis reflectance spectra of modified-NT arrays were recorded on Shimadzu UV-Vis Spectrophotometer (UV 2600) equipped with an integrating


6

Page 7 of 31

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


sphere. X-ray photoelectron spectroscopic (XPS) measurements were performed using the PHI 5000 VersaProbe (ULVAC-PHI) spectrometer with monochromatic Al Kα radiation (hν = 1486.6 eV) from an X-ray source operating at 100 µm spot size, 25 W and 15 kV. The highresolution (HR) XPS spectra were collected with a hemispherical analyzer at the pass energy of 23.5 eV, the energy step size of 0.1 eV and the photoelectron take off angle 45° with respect to the surface plane. The binding energy (BE) scale of all detected spectra was referenced by setting the BE of the aliphatic carbon peak (C-C) signal to 285.0 eV. The sample’s composition was checked by X-ray diffraction method using X’Pert Pro MPD Philips diffractometer, with Cu Kα radiation λ = 1.5418 Ǻ. The measurements were performed on the 2θ range of 20 to 80 degrees. The photoluminescence (PL) measurements were carried out at room temperature using LS-50B Luminescence Spectrophotometer equipped with Xenon discharge lamp as an excitation source and a R928 photomultiplier as detector. The excitation radiation (300 nm) was directed on the sample’s surface at an angle of 90°. 2.5 Photocatalytic tests Photocatalytic properties of pristine and modified- TiO2 NTs were studied using three model reactions: phenol decomposition, purification of air from toluene and •OH radicals generation efficiency (using terephthalic acid) under different range of visible light irradiation. Phenol degradation and •OH radicals generation tests were carried out in a photoreactor made of quartz with the working volume of about 10 mL. The NT samples with the surface area of 4 cm2 were immersed in phenol (C0 = 0.21 mM) or terephthalic acid solution (C0=0.5 mM) for 30 min in the dark to achieve adsorption-desorption equilibrium. Reference phenol and terephthalic acid samples (0.5 mL) were taken just before starting the irradiation and the subsequent samples (0.5 mL) were collected at regular time periods (20 min) during the irradiation. The aqueous


7


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 8 of 31

solution containing the model compound was continuously stirred (500 rpm) and irradiated using a 1000 W Xenon lamp (Oriel 66021). To perform Vis light induced photoreaction, the light beam was passed through GG420 and GG455 filter to cut-off wavelengths shorter than 420 and 455 nm, respectively. The irradiation intensity was measured by an optical power meter (HAMAMATSU, C9536-01) and it reached 4 and 3 mW/cm2 for λ > 420 and 455 nm, respectively. The phenol concentration was estimated by the colorimetric method after derivatization with p-nitroaniline using a UV–Vis spectrophotometer (λmax = 480 nm). Fluorescence spectra were recorded at room temperature by using a LS-50B Luminescence Spectrophotometer equipped with a Xenon discharge lamp as an excitation source (excitation wavelength 315 nm) and a R928 photomultiplier detector. The toluene photodegradation experiments were carried out in a stainless-steel reactor of a volume of ca. 35 cm3. The reactor included a quartz window, two valves and a septum. The light source consisting of an array of 25 LEDs (λmax = 415 and 465 nm) was located above the sample. The irradiation intensity was measured by an optical power meter (HAMAMATSU, C9536-01) and it reached 14.1 and 14.5 mW/cm2 for LEDs with λmax = 415 and 465 nm, respectively. The anodized foil was placed at the bottom side of the reactor and it was closed with the quartz window. A gas mixture (200 ppm) was passed through the reactor during 1 min, then the valves were closed and the reactor was kept in the dark for 30 min in order to achieve the equilibrium. Before starting the irradiation, a reference toluene sample was taken. The toluene concentration was determined by using a gas chromatograph (TRACE 1300, Thermo Scientific), equipped with an ionization flame detector (FID) and an Elite-5 capillary column. The samples (200 µL) were dosed with a gas-tight syringe each 10 min. The analysis of CO2 concentration was performed using gas chromatograph (Trace 1300, Thermo Scientific) equipped with Thermal conductivity


8

Page 9 of 31

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


detector (TCD) and Elite-5 capillary column. The samples (200 µL) were dosed by using a gastight syringe. For better understating of phenol and toluene degradation pathway, the concentration of main degradation intermediates in the aqueous phase has been measured. Kinetics of phenol degradation by-products have been followed by high performance liquid chromatography (HPLC, Shimadzu). The HPLC system was equipped with a Kinetex C18 column (150 mm x 3 mm; particle size of 2.6 µm; pore diameter 100 Å). The flow rate was maintained at 0.4 ml/min with a mobile phase composed of acetonitrile and water (v/v: 7.5/92.5), with a sample injection volume of 30 µL, and the SPD-M20A diode array detector was operated at 205 nm. 3. Results and discussion To investigate the effect of amount of platinum NPs and Bi2S3 QDs on the visible light induced photoactivity of Pt-Bi2S3-TiO2 NTs, a series of photocatalysts have been prepared. Preparation conditions as well as the impact of the amount of Pt NPs and Bi2S3 QDs on the photoactivity of TiO2 NTs in the gas phase (toluene degradation) under UV LEDs (λmax= 375 nm) and Vis LEDs (λmax= 465 nm) irradiation are presented in Table 1. The obtained results indicated that the PtNTs sample containing 3.46 at% of Pt NPs (based on XPS analysis) revealed the highest photoactivity (80% and 30% under UV and Vis, respectively) among the series with different amount of Pt NPs. Both reducing and increasing the amount of Pt (1.36 and 5.56 at.%) resulted in lower photoactivity, as shown in Table 1. A similar trend has been observed for TiO2 NTs decorated by Bi2S3 QDs obtained by SILAR method at different number of cycles (see Table 1). When the SILAR cycles were increased from 2 to 4, the highest photocatalytic activity under both UV and Vis irradiation was achieved, providing a degradation level 90 and 40%,


9


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 10 of 31

respectively. This phenomenon can be attributed to the increase of the junction interface, which would facilitate the separation of photogenerated electrons and holes at the surface of TiO2 NTs. In turn, increase the number of SILAR cycles to 6 caused lower photoactivity (85 and 33% under UV and Vis, respectively). Similar relationships for both series (Pt modified- TiO2 and metal sulphides - modified TiO2) were observed by others

16,33–39

. Thus, under both UV and Vis

irradiation, the efficiency enhancement might be associated with the existence of optimal contents of Pt NPs and Bi2S3 QDs, which can play significant roles in the electron–hole separation process and are responsible for lowering the number of recombination centers. An excess Pt NPs and Bi2S3 QDs content can cause recombination centers of photogenerated electrons, decreasing photocatalytic activity. Based on these results, TiO2 NTs decorated by Pt NPs and Bi2S3 QDs have been prepared using preliminary selected amount of modifiers and condition of synthesis. Finally, this sample, as well as, reference samples (pristine TiO2 NTs and decorated by one modifier) have been subsequently characterized taking into account morphology, structural and optical properties; elemental composition, thereby interactions between TiO2 NTs surface, Pt NPs and Bi2S3 QDs. These thorough characteristics let us to conclude about mechanism and the role of Pt NPs and Bi2S3 QDs in photocatalytic activity improvement under UV and visible irradiation. Table 1. The effect of the amount of Pt NPs and Bi2S3 QDs on the photoactivity of TiO2 nanotubes samples in the gas phase (toluene degradation) under UV LEDs (λmax=375 nm) and Vis LEDs (λmax= 465 nm)

Sample label NTs*

Brief description of the preparation

Amount of modifier (at.%) based on XPS

described in experimental section

0

Photocatalytic toluene degradation (%) 375 nm, after 20 min of irradiation

465 nm, after 60 min of irradiation

65

3


10

Page 11 of 31

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


1.03·10-4 M H2Cl6Pt·xH2O, other parameters have not been changed Pt-NTs* 2.07·10-4 M H2Cl6Pt·xH2O, other parameters have not been changed 2Pt-NTs 2.59·10-4 M H2Cl6Pt·xH2O, other parameters have not been changed 2Bi2S3-NTs two SILAR cycles, other parameters have not been changed Bi2S3-NTs* four SILAR cycles, other parameters have not been changed 6Bi2S3-NTs six SILAR cycles, other parameters have not been changed Bi2S3-Pt-NTs* Optimal conditions, 2.07·10-4 M H2Cl6Pt·xH2O, four SILAR cycles * samples described in detail in presented work 1Pt-NTs

1.36 3.46 5.56 1.99 2.94 3.89 1.65 Pt 2.19 Bi2S3

77

25

80

30

72

22

85

33

90

40

81

36

100

47

3.1 Morphology of the obtained photocatalysts To determine the geometric parameters of the obtained photocatalysts, SEM images have been performed. The surface and cross-sectional morphologies of the obtained pristine and modifiedTiO2 NTs are presented in Figure 1.

Figure 1. Surface and cross-sectional morphologies of pristine and modified-TiO2 NTs As evident from SEM images, all of the samples were vertically ordered and uniform over all of the examined area. The top parts of the pristine and modified- TiO2 NTs were open, without initial layer, and oxide ripples on the outer walls of both pristine and modified-TiO2 NTs were not formed. The as-prepared samples were characterized by the same dimensions, namely the


11


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 31

outer diameter, wall thickness and tube length were equal to 85 ± 3, 15 ± 0.5 nm and 2.5 ± 0.06 µm, respectively. The developed surface area and porosity were calculated based on geometric parameters of NTs

40,41

, and all of the samples’ values were equal to 617 ± 5 cm2 and

0.70 ± 0.1, respectively. Thus, the applied synthesis method did not influence the dimensions of the NTs (diameter, wall thickness and tube length) and thus, only the presence of modifiers could affect the photocatalytic performance. Pt NPs and Bi2S3 QDs were not detectable from the SEM images because the size of the species was smaller than the resolution of the scanning electron microscope. Thus, to observe the distribution and location of these species in the modified-NTs, TEM and EDX elemental mappings were performed, and the results are shown in Figure 2.

Figure 2. Distribution and location of Pt NPs and Bi2S3 QDs in the modified- TiO2 NTs TEM images indicated that Pt NPs and Bi2S3 QDs were (i) deposited on the NTs and (ii) located inside the NTs. Based on these observations, the platinum NPs were in small size at approximately 3.0 ± 0.2 nm, whereas the Bi2S3 QDs were spherical with size of 3.50 ± 0.20 nm. In addition, both Pt NPs and Bi2S3 QDs were well distributed on the (i) top parts, (ii) inner and


12

Page 13 of 31

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


(iii) outer walls of the modified- NTs. On the other hand, the aggregation of Pt NPs or Bi2S3 QDs was not observed (see Figure 2, EDX elemental mappings and TEM images). Concluding, the TEM images revealed the effective deposition of Pt (in form of NPs) and Bi2S3 (in form of QDs) on the surface of TiO2 NTs, and confirmed the vertical homogeneous distribution of the Pt NPs and Bi2S3 QDs onto the TiO2 NTs, which, combined with the results of EDS mapping, allows to conclude that the Bi2S3 QDs and Pt NPs onto the TiO2 NTs have a homogeneous distribution among the TiO2 NTs in all dimensions. 3.2

Structural properties

Figure 3 shows the XRD patterns of pristine and modified-TiO2 NTs. The peak diffraction observed at the 2ϴ value of 25.33° can be assigned to (101) crystallographic plane of anatase TiO2 with tetragonal (I41/amd) crystal structure. Other peaks at 2ϴ values of 37.82°, 48.05° and 53.86° can be described to (004), (200) and (105) crystallographic planes, which are also characteristic for anatase phase (JCPDS card). The peaks at 35.12°, 40.17°, and 52.96° originated from the Ti foil substrate. For all samples, only pure anatase TiO2 phase was found and other phases corresponding to Pt NPs and Bi2S3 QDs were not observed. The absence of peaks corresponding to Pt NPs and Bi2S3 QDs in the XRD patters may be due to the low content or/and small size of these species and also in the case of the Bi2S3 QDs, the amorphous character or the short-range crystalline. The above results are in good agreement with the results presented by other researchers

16,42

. The TiO2 lattice parameters were estimated by the LeBail method using

the FullProf package

43

, and the average crystallite size was calculated using the Scherrer

equation. The anatase lattice parameters did not change after Pt NPs and Bi2S3 QDs deposition (results are not shown), and the unit cell volume was approximately 136.57, 136.57, 136.61 and 136.65 Å3 for pristine TiO2 NTs, Pt-NTs, Bi2S3-NTs and Bi2S3-Pt-NTs, respectively. The average


13


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 14 of 31

crystallite size varied from 38 to 40 nm. Considering the above-mentioned results, both cell volume and crystallite size, we can conclude that the presented method is reproducible.

Figure 3. X-ray diffraction patterns of pristine and modified- TiO2 NTs (A- stands for anatase phase) 3.3

Chemical composition of Pt-Bi2S3-TiO2 NTs

The chemical composition of Bi2S3-Pt-NTs samples was analysed using XPS. The exemplary HR XPS spectra of elements recorded on the Bi2S3-Pt-NTs sample are presented in Figure 4 and the elemental atomic composition detected in the surface of the prepared samples is summarized in Table 2. The successful deposition of Pt NPs and Bi2S3 QDs on TiO2 NTs is evidenced by HR spectra of Pt 4f and Bi 4f, respectively (Figure 4). Although the Pt 4f spectrum is partially overlapped by Ti 3s satellite peak, the asymmetric Pt 4f7/2 signal at 71.4 eV can be assigned to Pt at zero valent state

44,45

and to PtTix species

formed as a result of the Pt atoms interaction with TiO2 matrix environment 44. The curve fitting procedure is necessary to separate the Bi 4f features from the overlapped S 2p spectra. The prominent Bi 4f7/2 signal at BE close to 159.5 eV, evidences successful deposition of Bi2S3


14

Page 15 of 31

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


species

44

and the peak asymmetry at lower BE indicates coexistence of oxidized form of

bismuth species. The deconvoluted S 2p spectra confirm also the presence of sulfide (S 2p3/2 peak located at BE 162 eV)

46

and sulfate (BE close to 168.9 eV)

44

states of Bi. The Ti 2p

spectrum overlays with the Bi 4d3/2 signals but, after decomposition, can be resolved into two components represented by the Ti 2p3/2 peaks at 459.2 eV and 457.2 eV, which are assigned to Ti4+ and Ti3+, respectively (Figure 4 and Table 2). The contribution of the Ti3+ state was found to be relatively most pronounced for Bi2S3-Pt-NTs sample (Table 2).

Figure 4. HR XPS spectra of elements recorded on the Bi2S3-Pt-NTs Table 2. Surface properties of pristine and modified-TiO2 NTs evaluated by XPS analysis

Chemical composition of as-prepared samples based on XPS analysis Sample label

NTs Pt - NTs Bi2S3 - NTs Bi2S3 - Pt - NTs

Ti (at.%)

Ti 4+ 459 eV (%)

Ti 3+ 458 eV (%)

O (at.%)

C (at.%)

Pt0 (at.%)

22.93 19.42 18.96 16.82

96.8 95.3 97.2 93.4

3.2 4.7 2.8 6.6

57.82 55.39 63.02 58.32

19.25 21.73 10.23 14.05

0 3.46 0 1.65

Bi3+ (Bi2S3) (at.%) 0 0 2.94 2.19

S (at.%) 0 0 4.85 6.97


15


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 16 of 31

3.4 Optical and photoluminescence properties The UV-Vis diffuse reflectance spectra (UV-Vis DRS) of pristine and modified-TiO2 NTs were measured to characterize the optical absorption properties and the results are shown in Figure 5a.

Figure 5. Absorbance (a) and photoluminescence (b) spectra of pristine and modified-TiO2 NTs The pristine TiO2 NTs exhibited an absorption band in the UV range due to the charge from the O 2p valence band to the Ti 3d conduction band 47 and a broad band in the range of 400-700 nm that can be attributed to organic contaminants or is caused by trapped electrons at the Ti3+ centre 48

. The modified-TiO2 NTs had higher absorbance intensity in both UV and visible light regions

compared to the pristine TiO2 NTs. Furthermore, the absorption band of modified-TiO2 NTs showed a red shift compared to the pristine one. This red shift might be related to the electronic interaction between Pt and TiO2 as well as QDs, Pt and TiO2 16,49. Additionally, the Bi2S3-Pt-NTs exhibited the strongest absorption in the visible light region among all samples. Above mentioned results, confirmed that the Bi2S3-Pt-NTs could be an effective visible light photocatalyst.


16

Page 17 of 31

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


Photoluminescence (PL) spectroscopy was applied to characterize the electron–hole recombination behaviour of pristine and modified-TiO2 NTs and the results are shown in Figure 5b. These results indicated that the modified-TiO2 NTs were extremely more efficient than pristine TiO2 NTs in the charge carrier separation process. The PL intensity decreased in the order of Bi2S3-Pt-NTs < Bi2S3-NTs < Pt-NTs < NTs. Especially, the Bi2S3-Pt-NTs possessed the highest ability to inhibit electron–hole recombination (approximately 10 times lower PL intensity than that of pristine NTs, see Figure 5b), which suggests a synergistic effect between Pt NPs and Bi2S3 QDs synthesized on TiO2 NTs. The reduction in the charge carrier recombination exhibited that the NPs and QDs may facilitate electron-hole separation and promote the interfacial electron transfer process 47,50. PL spectroscopy is also a useful tool to determinate the presence of surface defects, trap states and sub-band states 51. Therefore, the peaks at approximately 440 and 480 nm can be ascribed to the interstitial defects (Ti3+), which came from non-stoichiometric TiO2, surface defects and oxygen vacancies (see Figure 5b)

52

. Concluding, the proposed material

(heterojunction consisting of two semiconductors and a noble metal) with suitable electronic structures causes that the photogenerated electrons and holes can be separated effectively, driven by the built-in field at the interface, thus promoting the charge separation and utilization efficiency and improving the photocatalytic performance. 3.5 Photocatalytic properties The photocatalytic properties of pristine and modified-TiO2 NTs were studied using photocatalytic reactions of toluene and phenol degradation in gas and aqueous phase, respectively, under different range of visible light irradiation. The reactions in gas phase were performed using low powered and low-cost light-emitting diodes (LEDs, λmax=415 nm and 465 nm) as irradiation sources, while the degradation of phenol was studied using 1000 W Xe


17


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 18 of 31

lamp (λ > 420 and > 455 nm). As evident from Figure 6, all modified-NTs exhibited significantly higher photoactivity under Vis irradiation than the pristine TiO2 NTs, which suggests a synergistic effect between the Pt NPs and Bi2S3 QDs.

Figure 6. Photocatalytic properties of pristine and modified-TiO2 NTs in gas phase degradation of toluene (a, b) and aqueous phase degradation of phenol (c, d) under the influence of different irradiation ranges The results of the photocatalytic reactions of toluene degradation are presented in Figure 6a-b. Under both irradiation wavelengths, Pt NPs and Bi2S3 QDs synthesized together on TiO2 NTs gave the highest photocatalytic activity in toluene degradation reaction, the degradation efficiency reached approximately 76% (λmax = 415 nm, see Figure 6a) and 46% (λmax = 465 nm, Figure 6b), Bi2S3 QDs modified-NTs exhibited lower photoactivity (approximately 40% and


18

Page 19 of 31

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


60%, respectively) compared to Bi2S3-Pt-NTs and simultaneously higher degradation in comparison with Pt-NTs. In both conditions, the most photoactive sample exhibited the highest photocatalytic reaction rate constant and the highest initial reaction rate. Initial reaction rate calculated for the first 10 min of irradiation equalled 0.0031 and 0.0063 µmol·min-1 under λmax =465 nm and λmax =415 nm, respectively. The photocatalytic properties of pristine and modified-TiO2 NTs were also investigated in aqueous phase under visible light irradiation (λ > 420 and> 455 nm), as shown in Figure 6c-d. Phenol was selected as a model aqueous phase pollutant. A general trend of the photocatalytic activity in aqueous phase was maintained. Under both irradiation ranges, the photocatalytic efficiency of phenol degradation increased in the order of NTs < Pt-NTs < Bi2S3-NTs < Bi2S3-Pt-NTs. Especially, the Bi2S3-Pt-NTs possessed the highest ability to phenol degradation. Thus, under shorter irradiation wavelength (λ > 420 nm, see Figure 6c), the photocatalytic efficiency of phenol degradation in the presence of modifiedTiO2 NTs was higher than under longer irradiation wavelength (λ> 455 nm, see Figure 6d). In the case of the shorter irradiation wavelength (λ > 420 nm), the efficiency of phenol degradation over Pt-Bi2S3- TiO2 NTs reached approximately 31% after 60 min of irradiation, while under longer irradiation wavelength (λ> 455 nm), lower effectivity of phenol removal (but still high) was observed, namely degradation efficiency reached 26% after 60 min of irradiation. In comparison with longer irradiation wavelength λmax = 465 nm (toluene degradation) and λ > 455 nm (phenol degradation), under shorter irradiation wavelength λmax =415 nm and λ > 420 nm, the efficiency enhancement might be associated with the utilization of a greater amount of incident photons. The differences in photoabsorption properties could be considered as the reason for higher photocatalytic activity since Pt NPs and Bi2S3 QDs synthesized together on TiO2 NTs exhibited the strongest absorption among all samples (especially in the region near


19


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 20 of 31

415-420 nm) and more photons could be absorbed, as shown by diffuse reflectance spectra (DRS) in Figure 5a.

Figure 7. Visible light induced activity of TiO2 nanotube arrays decorated by Pt nanoparticles and Bi2S3 QDs: (a) •OH radical generation efficiency under visible light, (b) photocatalytic decomposition of phenol in the presence of the Bi2S3-Pt-NTs sample under the influence of visible light and in the presence of scavengers, (c) proposed photocatalytic mechanism over the Bi2S3-Pt-NTs under visible light and (d) photostability in phenol degradation reaction in subsequent cycles under visible light 4.

Mechanism discussion

To look deeper into the visible light excitation mechanism in the presence of Pt NPs and Bi2S3 QDs modified-TiO2 NTs, several different experiments in aqueous phase and experiment in gas


20

Page 21 of 31

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


phase were conducted. Firstly, to determine the role of active species during the decomposition of phenol under Vis irradiation (λ > 420 nm), •OH radical generation tests were performed. Figure 7a shows that pristine and modified-TiO2 NTs exhibited nearly the same FL intensity which suggests that TiO2 NTs modification does not lead to increase the production of •OH radicals under visible light irradiation. Thus, other forms of reactive oxygen species such as O2•−, HO2• and H2O2 could be more responsible for the photocatalytic degradation of phenol under Vis light than •OH radicals. To confirm the formation of the above-mentioned radicals and their impact on the phenol degradation, experiments were conducted in the presence of Bi2S3-Pt-NTs sample and different scavengers, namely tert-butanol, benzoquinone, silver nitrate and ammonium oxalate were used as scavengers of hydroxyl radicals, O2•− radicals, e- and h+, respectively (see Figure 7b). The photocatalytic efficiency of phenol degradation in the presence of benzoquinone and silver nitrate reached 5 and 4%, respectively, whereas adding tert- butanol and ammonium oxalate caused a negligible decrease in the photocatalytic efficiency (approximately 3 and 2%, respectively). These results confirm the crucial role of O2•− in the photocatalytic degradation of phenol under Vis irradiation. The photocatalytic mechanism under Vis light over heterojunctions composed of Pt NPs, Bi2S3 QDs and TiO2 NTs should be considered very carefully, because such photocatalysts are composed of three phases (TiO2, Bi2S3 and Pt0), and can be explained by the energetic diagram shown in Figure 7c. TiO2 NTs have a wide band gap (anatase, 3.2 eV 53) which can only absorb UV light, and Bi2S3 QDs have a narrower band gap (1.3 – 1.7 eV 27), which can absorb both UV and visible light. Thus, Bi2S3 QDs can absorb photons to generate electrons and holes, as shown in Figure 7c. The electrons from the conduction band of Bi2S3 QDs are injected to the conduction band of TiO2 NTs, while holes from the valance band of Bi2S3 QDs remain unmoved, thus the


21


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 22 of 31

photogenerated electrons and holes can be efficiently separated. Electrons from the conduction band of TiO2 NTs migrate to the Pt NPs where are involved in the formation of superoxide anion radicals (O2•−) and then H2O2 and HO2•. The interface of Pt NPs and TiO2 NTs can form a Schottky barrier with a barrier height that is the energy difference between the work function of the Pt and the electron affinity of the TiO2

54

. Under these conditions, the photogenerated

electrons will continuously transfer across the Pt-TiO2 interface to Pt, and thus the recombination is effectively inhibited. At the same time, the photogenerated holes in the valance band of Bi2S3 QDs are unable to generate •OH radicals because the band edge potential is 0.64 eV than the necessary for generating •OH radicals with electrode potential of 2.53 eV

55 56

, lower

. Under

visible light irradiation, photogenerated charge carriers can be effectively separated in heterojunctions, which leads to higher energy utilization efficiency and improve the photocatalytic performance. Thus, the photocatalytic degradation mechanism of both phenol and toluene under Vis irradiation, presented in reactions, was proposed as follows: Bi2S3-Pt-NTs + hv (visible light) → e− +h+

(1)

e− + O2→ O2•−

(2)

O2•− + H+→ HO2•

(3)

e− + O2•− +2H+→ H2O2

(4)

h+; H2O2; O2•−; HO2• + phenol, toluene → by-products +CO2 + H2O

(5)

The active oxygen species can cause mineralization and oxidize organic molecules into CO2 and H2O. To confirm mineralization ability of obtained photocatalysts, evolution of CO2 during photocatalytic degradation of toluene in the presence of the Bi2S3-Pt-NTs sample was monitored using gas chromatography (GC-TCD). It was observed that the amount of CO2 increased with


22

Page 23 of 31

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


decreasing toluene concentration indicating the successful mineralization process (results not shown). To investigate the photostability of Bi2S3-Pt-NT photocatalysts under visible light (λ > 420 nm), phenol degradation experiments were chosen and evaluated in four subsequent cycles. All experimental parameters were kept constant in each reaction cycle. The obtained results presented in Figure 7d revealed only a slight decrease of the photocatalytic degradation (less than 3%) in four subsequent cycles. Thus, the obtained results suggest that the photocatalytic properties of Bi2S3-Pt-NTs were not changed during the irradiation and consequently, the photocatalysts could be recycled. Other experiment applied to explore the photocatalytic properties of the as-prepared photocatalysts, namely Bi2S3-Pt-NTs, was focused to detect intermediates during phenol degradation under Vis irradiation (λ > 420 nm). The obtained results presented in Figure 8 revealed that catechol (RT = 3.2 min), hydroquinone (RT = 3.7 min) and benzoquinone (RT = 5.4 min) were primary intermediates generated during phenol degradation under Vis irradiation (λ > 420 nm).


23


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 24 of 31

Figure 8. Evolution of primary intermediates of phenol degradation under Vis irradiation (λ > 420 nm) in the presence of the Bi2S3-Pt-NTs sample (inserts present the chemical structures of intermediates formed during phenol irradiation) Indeed, the concentration of benzoquinone and catechol increased during the irradiation, and reached approximately 7.5 and 6.5 µmol·dm-3, respectively, while hydroquinone content reached an optimum (after 40 min of irradiation) and then started decreasing. Alaoui et al

57

observed

similar behaviour of intermediates during phenol degradation in the presence of Pd-TiO2 photocatalysts. The same tendency has been observed in other studies 58,59. Conclusions In summary, we have developed an effective strategy to realize highly unique Bi2S3 quantum dots and Pt nanoparticles deposited inside and outside of the vertically oriented TiO2 nanotubes. The heterojunction composed of three phases (TiO2, Bi2S3 and Pt0) substantially increased the photogenerated electron hole separation/transfer, and notably improved the photocatalytic properties in both toluene and phenol degradation, indicating the synergistic effect between the ordered structure of TiO2 NTs and the well distributed Pt NPs and Bi2O3 QDs. The photocatalytic activity of Bi2S3-Pt-TiO2 NTs heterojunction depends on the irradiation range, the highest photodegradation of both toluene (76%) and phenol (31%) under visible light was observed for the range with the strongest light photoabsorption (especially in the region near 415-420 nm) as a consequence of higher light utilization. In addition to the excellent photocatalytic degradation performance, the Bi2S3-Pt-TiO2 NTs exhibited good photostability during the degradation of phenol, it remained after four photodegradation cycles under visible light. The phenol irradiation over the as-prepared heterojunction led to the formation of three


24

Page 25 of 31

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


primary intermediates: catechol, hydroquinone and benzoquinone. The superoxide radicals are responsible for the visible light degradation of both phenol and toluene. The heterojunction composed of TiO2 NTs, Bi2S3 QDs and Pt NPs represents a strategy on extending the light absorption of photocatalysts from the aspect of solar energy harvesting and on improving the charge separation process. AUTHOR INFORMATION Corresponding Authors: * Paweł Mazierski email: [email protected] * Adriana Zaleska-Medynska email: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This research was supported by the National Centre for Research and Development and National Fund

for

Environmental

Protection

and

Water

Management,

Gekon

Program

(GEKON1/03/214483/16/2014) and supported by the Foundation for Polish Science (FNP).

REFERENCES (1)

Kowalski, D.; Kim, D.; Schmuki, P. TiO2 Nanotubes, Nanochannels and Mesosponge: Self-Organized Formation and Applications. Nano Today 2013, 8, 235–264.

(2)

Antony, R. P.; Mathews, T.; Johnson, J. A.; Krishna, D. N.; Dash, S.; Tyagi, A. K. Kinetics of Dye Destruction Using Electrochemically Synthesized Sunlight Active NDoped and C and N Co-Doped TiO2 Nanotubular Photocatalysts. Energy Environ. Focus 2013, 2, 139–148.

(3)

Mazierski, P.; Nischk, M.; Gołkowska, M.; Lisowski, W.; Gazda, M.; Winiarski, M. J. M. J.; Klimczuk, T.; Zaleska-Medynska, A. Photocatalytic Activity of Nitrogen Doped TiO2


25


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 26 of 31

Nanotubes Prepared by Anodic Oxidation: The Effect of Applied Voltage, Anodization Time and Amount of Nitrogen Dopant. Appl. Catal. B Environ. 2016, 196, 77–88. (4)

Nischk, M.; Mazierski, P.; Gazda, M.; Zaleska, A. Ordered TiO2 Nanotubes: The Effect of Preparation Parameters on the Photocatalytic Activity in Air Purification Process. Appl. Catal. B Environ. 2014, 144, 674–685.

(5)

Podporska-Carroll, J.; Panaitescu, E.; Quilty, B.; Wang, L.; Menon, L.; Pillai, S. C. Antimicrobial Properties of Highly Efficient Photocatalytic TiO2 Nanotubes. Appl. Catal. B Environ. 2015, 176–177, 70–75.

(6)

Nguyen, N. T.; Yoo, J.; Altomare, M.; Schmuki, P. Pt Nanoparticles over TiO2 Nanotubes for Enhanced Photocatalytic H2 Evolution. Chem. Commun. 2014, 50, 9653–9656.

(7)

Antony, R. P.; Mathews, T.; Ramesh, C.; Murugesan, N.; Dasgupta, A.; Dhara, S.; Dash, S.; Tyagi, A. K. Efficient Photocatalytic Hydrogen Generation by Pt Modified TiO2 Nanotubes Fabricated by Rapid Breakdown Anodization. Int. J. Hydrogen Energy 2012, 37, 8268–8276.

(8)

Preethi, L. K.; Antony, R. P.; Mathews, T.; Loo, S. C. J.; Wong, L. H.; Dash, S.; Tyagi, A. K. Nitrogen Doped Anatase-Rutile Heterostructured Nanotubes for Enhanced Photocatalytic Hydrogen Production: Promising Structure for Sustainable Fuel Production. Int. J. Hydrogen Energy 2016, 41, 5865–5877.

(9)

Li, Q.; Zong, L.; Li, C.; Yang, J. Reprint of “Photocatalytic Reduction of CO2 on MgO/TiO2 Nanotube Films.” Appl. Surf. Sci. 2014, 319, 16–20.

(10)

Roy, P.; Berger, S.; Schmuki, P. TiO2 Nanotubes: Synthesis and Applications. Angew. Chemie Int. Ed. 2011, 50, 2904–2939.

(11)

Momeni, M. M.; Ghayeb, Y. Fabrication, Characterization and Photoelectrochemical Behavior of Fe–TiO2 Nanotubes Composite Photoanodes for Solar Water Splitting. J. Electroanal. Chem. 2015, 751, 43–48.

(12)

Yuan, R.; Zhou, B.; Hua, D.; Shi, C. Enhanced Photocatalytic Degradation of Humic Acids Using Al and Fe Co-Doped TiO2 Nanotubes under UV/ozonation for Drinking Water Purification. J. Hazard. Mater. 2013, 262, 527–538.

(13)

Bessegato, G. G.; Cardoso, J. C.; Zanoni, M. V. B. Enhanced Photoelectrocatalytic Degradation of an Acid Dye with Boron-Doped TiO2 Nanotube Anodes. Catal. Today 2015, 240, 100–106.

(14)

Sun, L.; Cai, J.; Wu, Q.; Huang, P.; Su, Y.; Lin, C. N-Doped TiO2 Nanotube Array Photoelectrode for Visible-Light-Induced Photoelectrochemical and Photoelectrocatalytic Activities. Electrochim. Acta 2013, 108, 525–531.

(15)

Zheng, Q.; Kang, H.; Yun, J.; Lee, J.; Park, J. H.; Baik, S. Hierarchical Construction of Self-Standing Anodized Titania Nanotube Arrays and Nanoparticles for Efficient and Cost-Effective Front-Illuminated Dye-Sensitized Solar Cells. ACS Nano 2011, 5, 5088– 5093.


26

Page 27 of 31

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


(16)

Lv, J.; Gao, H.; Wang, H.; Lu, X.; Xu, G.; Wang, D.; Chen, Z.; Zhang, X.; Zheng, Z.; Wu, Y. Controlled Deposition and Enhanced Visible Light Photocatalytic Performance of PtModified TiO2 Nanotube Arrays. Appl. Surf. Sci. 2015, 351, 225–231.

(17)

Long, L.; Li, J.; Wu, L.; Li, X. Enhanced Photocatalytic Performance of Platinized CdS/TiO2 by Optimizing Calcination Temperature of TiO2 Nanotubes. Mater. Sci. Semicond. Process. 2014, 26, 107–111.

(18)

Wu, Z.; Su, Y.; Yu, J.; Xiao, W.; Sun, L.; Lin, C. Enhanced Photoelectrocatalytic Hydrogen Production Activity of SrTiO3–TiO2 Hetero-Nanoparticle Modified TiO2 Nanotube Arrays. Int. J. Hydrogen Energy 2015, 40, 9704–9712.

(19)

Mazierski, P.; Lisowski, W.; Grzyb, T.; Winiarski, M. J.; Klimczuk, T.; Mikołajczyk, A.; Flisikowski, J.; Hirsch, A.; Kołakowska, A.; Puzyn, T.; et al. Enhanced Photocatalytic Properties of Lanthanide-TiO2 Nanotubes: An Experimental and Theoretical Study. Appl. Catal. B Environ. 2017, 205, 376–385.

(20)

Mazierski, P.; Malankowska, A.; Kobylański, M.; Diak, M.; Kozak, M.; Winiarski, M. J.; Klimczuk, T.; Lisowski, W.; Nowaczyk, G.; Zaleska-Medynska, A. Photocatalytically Active TiO2/Ag2O Nanotube Arrays Interlaced with Silver Nanoparticles Obtained from the One-Step Anodic Oxidation of Ti–Ag Alloys. ACS Catal. 2017, 7, 2753–2764.

(21)

Nevárez-Martínez, M. C.; Kobylański, M. P.; Mazierski, P.; Wółkiewicz, J.; Trykowski, G.; Malankowska, A.; Kozak, M.; Espinoza-Montero, P. J.; Zaleska-Medynska, A. SelfOrganized TiO2–MnO2 Nanotube Arrays for Efficient Photocatalytic Degradation of Toluene. Molecules 2017, 22, 565.

(22)

Kim, J.; Kang, M. High Photocatalytic Hydrogen Production over the Band Gap-Tuned Urchin-like Bi2S3-Loaded TiO2 Composites System. Int. J. Hydrogen Energy 2012, 37, 8249–8256.

(23)

Bernechea, M.; Cao, Y.; Konstantatos, G. Size and Bandgap Tunability in Bi2S3 Colloidal Nanocrystals and Its Effect in Solution Processed Solar Cells. J. Mater. Chem. A 2015, 3, 20642–20648.

(24)

Salunkhe, D. B.; Dubal, D. P.; Sali, J. V.; Sankapal, B. R. Linker Free Synthesis of TiO2/Bi2S3 Heterostructure towards Solar Cell Application: Facile Chemical Routes. Mater. Sci. Semicond. Process. 2015, 30, 335–342.

(25)

Zeng, Q.; Bai, J.; Li, J.; Li, Y.; Li, X.; Zhou, B. Combined Nanostructured Bi2S3/TNA Photoanode and Pt/SiPVC Photocathode for Efficient Self-Biasing Photoelectrochemical Hydrogen and Electricity Generation. Nano Energy 2014, 9, 152–160.

(26)

Yang, L.; Sun, W.; Luo, S.; Luo, Y. White Fungus-like Mesoporous Bi2S3 ball/TiO2 Heterojunction with High Photocatalytic Efficiency in Purifying 2,4Dichlorophenoxyacetic acid/Cr(VI) Contaminated Water. Appl. Catal. B Environ. 2014, 156–157, 25–34.

(27)

Solís, M.; Rincón, M. E.; Calva, J. C.; Alvarado, G. G. Bismuth Sulfide Sensitized TiO2


27


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 28 of 31

Arrays for Photovoltaic Applications. Electrochim. Acta 2013, 112, 159–163. (28)

Lu, J.; Han, Q.; Wang, Z. Synthesis of TiO2/Bi2S3 Heterojunction with a Nuclear-Shell Structure and Its High Photocatalytic Activity. Mater. Res. Bull. 2012, 47, 1621–1624.

(29)

Pisanic II, T. R.; Zhang, Y.; Wang, T. H. Quantum Dots in Diagnostics and Detection: Principles and Paradigms. Analyst 2014, 139, 2968–2981.

(30)

Zhu, Y.; Chen, Z.; Gao, T.; Huang, Q.; Niu, F.; Qin, L.; Tang, P.; Huang, Y.; Sha, Z.; Wang, Y. Construction of Hybrid Z-Scheme Pt/CdS–TNTAs with Enhanced Visible-Light Photocatalytic Performance. Appl. Catal. B Environ. 2015, 163, 16–22.

(31)

Tada, H.; Mitsui, T.; Kiyonaga, T.; Akita, T.; Tanaka, K. All-Solid-State Z-Scheme in CdS-Au-TiO2 Three-Component Nanojunction System. Nat Mater 2006, 5, 782–786.

(32)

Dytrych, W.; Zaleska-Medynska, A.; Nischk, M.; Mazierski, P. Modyfikowane Powłoki Porowate I Urządzenie Modułowe Do Oczyszczania Powietrza Zawierające Modyfikowane Powłoki Porowate. Polish patent application no P.417116 2016.

(33)

Diak, M.; Grabowska, E.; Zaleska, A. Synthesis, Characterization and Photocatalytic Activity of Noble Metal-Modified TiO2 Nanosheets with Exposed {001} Facets. Appl. Surf. Sci. 2015, 347, 275–285.

(34)

Qamar, M.; Ganguli, A. K. Self-Assembling Behaviour of Pt Nanoparticles onto Surface of TiO2 and Their Resulting Photocatalytic Activity. Bull. Mater. Sci. 2013, 36, 945–951.

(35)

Vaiano, V.; Iervolino, G.; Sannino, D.; Murcia, J. J.; Hidalgo, M. C.; Ciambelli, P.; Navío, J. A. Photocatalytic Removal of Patent Blue V Dye on Au-TiO2 and Pt-TiO2 Catalysts. Appl. Catal. B Environ. 2016, 188, 134–146.

(36)

Zhu, Y.; Wang, Y.; Chen, Z.; Qin, L.; Yang, L.; Zhu, L.; Tang, P.; Gao, T.; Huang, Y.; Sha, Z.; et al. Visible Light Induced Photocatalysis on CdS Quantum Dots Decorated TiO2 Nanotube Arrays. Appl. Catal. A Gen. 2015, 498, 159–166.

(37)

Wang, Q.; Jin, R.; Yin, C.; Wang, M.; Wang, J.; Gao, S. Photoelectrocatalytic Removal of Dye and Cr(VI) Pollutants with Ag2S and Bi2S3 Co-Sensitized TiO2 Nanotube Arrays under Solar Irradiation. Sep. Purif. Technol. 2017, 172, 303–309.

(38)

Yang, X.; Wang, Y.; Wang, Z.; Lv, X.; Jia, H.; Kong, J.; Yu, M. Preparation of CdS/TiO2 Nanotube Arrays and the Enhanced Photocatalytic Property. Ceram. Int. 2016, 42, 7192– 7202.

(39)

Kowalska, E.; Remita, H.; Colbeau-Justin, C.; Hupka, J.; Belloni, J. Modification of Titanium Dioxide with Platinum Ions and Clusters: Application in Photocatalysis. J. Phys. Chem. C 2008, 112, 1124–1131.

(40)

Ngaboyamahina, E.; Cachet, H.; Pailleret, A.; Sutter, E. M. M. Photo-Assisted Electrodeposition of an Electrochemically Active Polypyrrole Layer on Anatase Type Titanium Dioxide Nanotube Arrays. Electrochim. Acta 2014, 129, 211–221.


28

Page 29 of 31

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


(41)

Kontos, A. G.; Katsanaki, A.; Maggos, T.; Likodimos, V.; Ghicov, A.; Kim, D.; Kunze, J.; Vasilakos, C.; Schmuki, P.; Falaras, P. Photocatalytic Degradation of Gas Pollutants on Self-Assembled Titania Nanotubes. Chem. Phys. Lett. 2010, 490, 58–62.

(42)

Zumeta-Dubé, I.; Ruiz-Ruiz, V.-F.; Díaz, D.; Rodil-Posadas, S.; Zeinert, A. TiO2 Sensitization with Bi2S3 Quantum Dots: The Inconvenience of Sodium Ions in the Deposition Procedure. J. Phys. Chem. C 2014, 118, 11495–11504.

(43)

Rodríguez-Carvajal, J. Recent Advances in Magnetic Structure Determination by Neutron Powder Diffraction. Phys. B Condens. Matter 1993, 192, 55–69.

(44)

Naumkin, A. V; Kraut-Vass, A.; Gaarenstroom, S. W.; Powell, C. J. NIST X-Ray Photoelectron Spectroscopy Database 20, Version 4.1. http://srdata.nist.gov/xps/. 2012.

(45)

Zoontjes, M. G. C.; Han, K.; Huijben, M.; van der Wiel, W. G.; Mul, G. The Effect of Rh[small Delta]+ Dopant in SrTiO3 on the Active Oxidation State of Co-Catalytic Pt Nanoparticles in Overall Water Splitting. Catal. Sci. Technol. 2016, 6, 7793–7799.

(46)

Thomson, J. W.; Cademartiri, L.; MacDonald, M.; Petrov, S.; Calestani, G.; Zhang, P.; Ozin, G. A. Ultrathin Bi2S3 Nanowires: Surface and Core Structure at the ClusterNanocrystal Transition. J. Am. Chem. Soc. 2010, 132 (26), 9058–9068.

(47)

Ge, M.; Cao, C.; Li, S.; Zhang, S.; Deng, S.; Huang, J.; Li, Q.; Zhang, K.; Al-Deyab, S. S.; Lai, Y. Enhanced Photocatalytic Performances of N-TiO2 Nanotubes by Uniform Creation of P–n Heterojunctions with P-Bi2O3 Quantum Dots. Nanoscale 2015, 7, 11552– 11560.

(48)

Mazierski, P.; Nadolna, J.; Lisowski, W.; Winiarski, M. J.; Gazda, M.; Nischk, M.; Klimczuk, T.; Zaleska-Medynska, A. Effect of Irradiation Intensity and Initial Pollutant Concentration on Gas Phase Photocatalytic Activity of TiO2 Nanotube Arrays. Catal. Today 2017, 284, 19–26.

(49)

Sang, L.; Tan, H.; Zhang, X.; Wu, Y.; Ma, C.; Burda, C. Effect of Quantum Dot Deposition on the Interfacial Flatband Potential, Depletion Layer in TiO2 Nanotube Electrodes, and Resulting H2 Generation Rates. J. Phys. Chem. C 2012, 116, 18633– 18640.

(50)

Klein, M.; Nadolna, J.; Gołąbiewska, A.; Mazierski, P.; Klimczuk, T.; Remita, H.; Zaleska-Medynska, A.; Gołabiewska, A.; Mazierski, P.; Klimczuk, T. The Effect of Metal Cluster Deposition Route on Structure and Photocatalytic Activity of Mono- and Bimetallic Nanoparticles Supported on TiO2 by Radiolytic Method. Appl. Surf. Sci. 2016, 378, 37–48.

(51)

Cummings, F. R.; Le Roux, L. J.; Mathe, M. K.; Knoesen, D. Structure Induced Optical Properties of Anodized TiO2 Nanotubes. Mater. Chem. Phys. 2010, 124, 234–242.

(52)

Nishanthi, S. T. T.; Subramanian, E.; Sundarakannan, B.; Padiyan, D. P. P. An Insight into the Influence of Morphology on the Photoelectrochemical Activity of TiO2 Nanotube Arrays. Sol. Energy Mater. Sol. Cells 2015, 132, 204–209.


29


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 30 of 31

(53)

Ohtani, B. Photocatalysis A to Z—What We Know and What We Do Not Know in a Scientific Sense. J. Photochem. Photobiol. C Photochem. Rev. 2010, 11, 157–178.

(54)

Chen, H.; Chen, S.; Quan, X.; Yu, H.; Zhao, H.; Zhang, Y. Fabrication of TiO2−Pt Coaxial Nanotube Array Schottky Structures for Enhanced Photocatalytic Degradation of Phenol in Aqueous Solution. J. Phys. Chem. C 2008, 112, 9285–9290.

(55)

Bessekhouad, Y.; Robert, D.; Weber, J. V. Bi2S3/TiO2 and CdS/TiO2 Heterojunctions as an Available Configuration for Photocatalytic Degradation of Organic Pollutant. J. Photochem. Photobiol. A Chem. 2004, 163, 569–580.

(56)

Fujishima, A.; Rao, T. N.; Tryk, D. A. Titanium Dioxide Photocatalysis. J. Photochem. Photobiol. C Photochem. Rev. 2000, 1, 1–21.

(57)

Tahiri Alaoui, O.; Herissan, A.; Le Quoc, C.; Zekri, M. el M.; Sorgues, S.; Remita, H.; Colbeau-Justin, C. Elaboration, Charge-Carrier Lifetimes and Activity of Pd-TiO2 Photocatalysts Obtained by Gamma Radiolysis. J. Photochem. Photobiol. A Chem. 2012, 242, 34–43.

(58)

Ye, H.; Lu, S. Photocatalytic Selective Oxidation of Phenol in Suspensions of Titanium Dioxide with Exposed {001} Facets. Appl. Surf. Sci. 2013, 277, 94–99.

(59)

Nischk, M.; Mazierski, P.; Wei, Z.; Siuzdak, K.; Kouame, N. A. N. A.; Kowalska, E.; Remita, H.; Zaleska-Medynska, A. Enhanced Photocatalytic, Electrochemical and Photoelectrochemical Properties of TiO2 Nanotubes Arrays Modified with Cu, AgCu and Bi Nanoparticles Obtained via Radiolytic Reduction. Appl. Surf. Sci. 2016, 387, 89–102.


30

Page 31 of 31

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


TOC Graphic


31

Nanotubes Decorated by Pt Nanoparticles and - American Chemical

Recommend Documents