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Facile preparation of extremely photoactive boron-doped TiO2 nanotubes arrays
... Literatür çalışmalarında sıklıkla tercih edilen elektrokimyasal yöntem yardımıyla, üretilmiş TiO 2 nanotüp levha anot ve platin levha katot olarak kullanılarak bor katkılaması yapılmıştır. Elektrotlar arasındaki mesafe 3 cm olarak ayarlanmış ve 0,5 M borik asit çözeltisi elektrolit olarak kullanılmıştır (Szkoda, Siuzdak, Lisowska-Oleksiak, Karczewski, & Ryl, 2015). Elektrokimyasal katkılama süresi literatüre uygun olarak 1,8 V'luk gerilim altında 30 dakika olarak gerçekleştirilmiştir (Szkoda et al., 2015). ...
... Elektrotlar arasındaki mesafe 3 cm olarak ayarlanmış ve 0,5 M borik asit çözeltisi elektrolit olarak kullanılmıştır (Szkoda, Siuzdak, Lisowska-Oleksiak, Karczewski, & Ryl, 2015). Elektrokimyasal katkılama süresi literatüre uygun olarak 1,8 V'luk gerilim altında 30 dakika olarak gerçekleştirilmiştir (Szkoda et al., 2015). Son olarak, numuneler (saf ve katkılı TiO 2 nanotüpler) deiyonize su ile durulanarak oda koşullarında kurumaya bırakılmıştır. ...
TiO2 nanotüp fotokatalizörleri titanyum levhaların anodizasyonu ile sentezlenmiştir. Sentezlenmiş olan TiO2 nanotüp fotokatalizörlerinin bor katkılaması, borik asit içeren elektrolit içerisinde elektrokimyasal muamele ile gerçekleştirilmiştir. Elde edilen saf ve katkılı fotokatalizörlerin karakterizasyonu SEM-EDS, XRD ve kronoamperometri ölçümleri ile yapılmıştır. Üretilen fotokatalizörlerin fotokatalitik aktiviteleri Orange G boyası kullanılarak gerçekleştirilmiş ve B katkılı TiO2 nanotüp fotokatalizörünün, katkısız TiO2 fotokatalizörüne göre % 24,75 oranında daha fazla giderim gösterdiği belirlenmiştir.
... 117 Boron doping can easily be achieved by an electrochemical route. Szkoda et al. 106 electrochemically doped TiO 2 nanotubes with boron in a two-electrode electrochemical cell containing 0.5 M aqueous solution of boric acid (H 3 BO 3 ) as the boron precursor. The TiO 2 nanotube arrays grown on the titanium foil and a platinum mesh foil were used as the anode and cathode, respectively. ...
... It has also been found that the probability of a B 3+ dopant ion substituting a lattice oxygen is extremely low. 106,121 Moreover, this substitution makes the system less stable. Often the boron ions at the substitutional positions move to the interstitial positions, thereby creating oxygen vacancies. ...
TiO2 and other titanium oxide-based nanomaterials have drawn immense attention from researchers in different scientific domains due to their fascinating multifunctional properties, relative abundance, environmental friendliness, and bio-compatibility. However, the physical and chemical properties of titanium oxide-based nanomaterials are found to be explicitly dependent on the presence of various crystal defects. Oxygen vacancies are the most common among them and have always been the subject of both theoretical and experimental research as they play a crucial role in tuning the inherent properties of titanium oxides. This review highlights different strategies for effectively introducing oxygen vacancies in titanium oxide-based nanomaterials, as well as a discussion on the positions of oxygen vacancies inside the TiO2 band gap based on theoretical calculations. Additionally, a detailed review of different experimental techniques that are extensively used for identifying oxygen vacancies in TiO2 nanostructures is also presented.
... In recent years, many different TiO 2 nanostructures (nanoparticles, nanofibers, nanowires, nanotubes, etc.) have been constructed successfully by different methods [1][2][3][4][5][6][7]. Especially, as an important member of one-dimensional TiO 2 nanomaterials, the self-organized highly ordered TiO 2 nanotube arrays (NTAs) formed on Ti substrate by electrochemical anodization have excellent photocatalytic activity due to its unique architecture, large specific surface area, oriented charge transfer channel, and contracted transport path [8][9][10][11][12][13]. ...
... In dark condition, the anodic current comes from the electrochemical oxidation, including oxygen evolution and the direct oxidation of (NH 4 ) 2 C 2 O 2 . High anodic current in dark and rapid increase with potential indicate the easy direct electrochemical oxidation of (NH 4 Figure 7 shows CVs of TiO 2 NTAs in buffer solution containing 10 mM BQ under different conditions including in dark or under illumination, and without or with BQ addition. Curves (a) and (b) compare CVs of TiO 2 NTAs without and with BQ in buffer solution in dark. ...
The surface electrochemical reactions of TiO2 nanotube arrays (NTAs) corresponding to different active species of TiO2 NTAs (·OH, h⁺, and ·O2⁻) play key roles during the photoelectrochemical process. Effect of the active species and surface electrochemical reactions are studied by adding capture agents of isopropyl alcohol (IPA) for ·OH, ammonium oxalate ((NH4)2C2O2) for h⁺, and benzoquinone (BQ) for ·O2⁻ radicals. The changes of photocurrent with addition of capture agents confirm the existence of ·OH, h⁺, and ·O2⁻ during photoelectrochemical process. IPA and (NH4)2C2O2 additions are found to enhance the photocurrent by accelerating the consumption velocity of h⁺ indirectly and directly and restricting the chargers recombination. BQ can decrease the photocurrent stepwise to 0 due to the indirect consumption of e⁻ on surface of TiO2 NTAs. The consumption of h⁺ by forming ·OH is 38% that of the whole consumption of h⁺. The ratio of chargers recombination is higher than 80.8% that of the whole photogenerated chargers.
... Raman spectra of electrodes after calcination are shown in Fig. 2. A number of bands characteristic for the pure anatase crystalline form were identified in samples of pristine TiO 2 (Fig. 2a) and the composite material (Fig. 2b). The bands located at 144, 198, 395, 516 and 637 cm À1 are attributed to E g(1) , E g (2) , B 1g , A 1g , and E g (3) active anatase modes, respectively [45,46]. All bands characteristic for monoclinic BiVO 4 are observed in Fig. 2c. ...
... A wide absorption band in the visible range with a maximum at about 620 nm is observed due to: i) the presence of the sub-bandgap states or ii) stems from the unusual nanostructure of the titania nanotubes that can trap light inside the tube [43]. However, IPCE measurements show that the photocurrent is not generated when titania nanotubes have been illuminated with visible light [45], thus the second proposed explanation is more acceptable. The spectrum of Ti/TiO 2 /Au was added for comparison (Fig. 3). ...
Titania nanotubes (TNT) modified with thin films of bismuth vanadate (BiVO4) and gold nanoparticles (GNP) were photoelectrochemically characterized as photoanodes for water photooxidation. Presence of bismuth vanadate enhanced efficiency of photocurrent generation in comparison with pristine TNTs under visible light illumination. Besides an extended range of absorbed light, the presence of both BiVO4 and GNP reduced the charge transfer resistance as confirmed by using electrochemical impedance spectroscopy. A possible mechanism of photoexcited charge-carrier transfer based on the locations of valence and conduction bands of TiO2 and BiVO4 has been proposed. The photocurrent of the most active photoanode (Ti/TiO2/Au/BiVO4/Au) reached a stable value of about 123 μA cm⁻² and was nearly 3.5 times higher than registered for pure TiO2 and c.a. 8 times higher than recorded for BiVO4.
... 68 However, incident photon-to-electron conversion efficiency (IPCE) measurements show that no significant photocurrent is generated when the pristine TNTs are illuminated with purely visible light. 69 Therefore, the absorption above 500 nm in all the samples could arise not only from the distinctive highly periodically porous structure of TNTs, as previously reported 70,71 but also from the LSPR of NCs active in the visible range. The photoluminescence (PL) spectra of Au x Cu 1-x (x = 1, 0.75, 0.5, 0.25 and 0) NC-decorated TNTs samples, measured at an excitation of 310 nm, are presented in Figure 6b. ...
The photoelectrochemical (PEC) water splitting reaction on bimetallic Au x Cu 1-x (x = 1, 0.75, 0.5, 0.25 and 0) nanocluster-decorated TiO 2 nanotubes (TNTs) photoanode was investigated using a solar simulator. A strong...
... When these pairs drift in opposite directions, a photocurrent is formed [1]. Titanium dioxide (TiO2) thin films are widely used in solar cells [2], gas sensors [3], photocatalysis [4], etc., due to their electrical and optical properties. It is an n-type semiconductor suitable for various applications such as TiO2 has three different crystal structures as rutile, anatase and brookite, with an indirect band gap of 3.0-3.2 ...
In this study, titanium dioxide (TiO2) nanotubes were produced by anodization method using glycerol-based electrolyte. Structural characterization was investigated with SEM images and XRD pattern. The rectifying properties of n-type semiconductor TiO2 nanotubes were investigated. Current-voltage (I-V) measurements of the Pt/TiO2 nanotubes/Ti device were made at room temperature, in the dark and under different illumination conditions. The basic diode parameters were calculated by using thermionic emission (TE), Cheung and Norde functions from the I-V measurements of the devices in dark conditions. The ideality factors and barrier height of the Pt/TiO2 nanotubes/Ti device were calculated 1.25 and 0.91 eV, respectively by the TE method. According to the results obtained, the Pt/TiO2 nanotubes contact has a rectifying feature. In addition, the photovoltaic properties of the devices were examined by making I-V measurements at illumination intensities between 30 and 100 mW/cm2. As a result, it has been evaluated that the device can also be used as a photodiode.
... The excitation of electrons from this interstage energy level to the conductance band (CB) induces the redshift of UV−vis spectra. 50 Typically, the interstage energy level of the bands introduced by the Nm dopants increased with decreasing electronegativity. 51 In this case, the electronegativities of the C, Si, and P elements were 2.5, 1.8, and 2.1, respectively, so the distance of the interstage energy level with respect to the VB was ranked in the order of Si > P > C. Too short or too long distance between the interstage energy level and the VB may lessen the capability of electron excitation from the VB to the interstage level and/or from the interstage level to the CB. ...
A series of nonmetal-doped titanium dioxide (Nmx/TiO2, where x is the weight fraction of nonmetal elements) photocatalysts was prepared via ultrasonic-assisted impregnation for simultaneous hydrogen (H2) production and chemical oxygen demand (COD) removal from industrial wastewater. Three types of Nm elements, carbon (C), silicon (Si), and phosphorus (P), were explored. The P1/TiO2 exhibited a higher photocatalytic activity for H2 production and COD removal than the C1/TiO2 and Si1/TiO2 photocatalysts. Approximately 6.43 mmol/g photocatalyst of H2 was produced, and around 26% COD removal was achieved at a P1/TiO2 loading of 4.0 g/L, a light intensity of 5.93 mW/cm², and a radiation time of 4 h. This is because the P1/TiO2 photocatalyst exhibited lower point of zero charge values and a more appropriate band position compared with other Nmx/TiO2 photocatalysts to produce H⁺, which can consequently form H2, and reactive oxygen species (HO· and O2·–), which serve as oxidizing agents to degrade the organic pollutants. Increasing the content of the P element doped into the TiO2-based material up to 7.0% by weight enhanced the H2 production and COD removal up to 8.34 mmol/g photocatalyst and 50.6%, respectively. This is attributed to the combined effect of the point of zero charge value and the SBET of the prepared photocatalysts. The photocatalytic activity of the P7/TiO2 photocatalyst was still higher than the TiO2-based material after the fourth use.
... In this backdrop, here, we have designed the inorganic/organic nano-heterostructures (NHs), consisting of boron-doped TiO 2 (B-TiO 2 ) nanorods and donor-acceptor-donor (D-A-D) type N,N'-bis( 2-ethylhexyl)-2,6-dithiophene-1,4,5,8 naphthalene diimide (NDIEHTh) small molecule (the NHs are referred as B-TiO 2 / NDIEHTh henceforth). Different research works reveal that boron doping in TiO 2 can enhance carrier mobility and electrical conductivity [30,31]. Moreover, boron doping can also accelerate the electron injection from the excited dye molecules to TiO 2 photoanodes, resulting in a better power conversion efficiency [32]. ...
This research article reports the visible-light-driven photoelectrochemical water oxidation performances of the plasmonic Au-Pd nanoparticle-decorated inorganic/organic nano-heterostructures (NHs)—B-TiO2/NDIEHTh@Au-Pd. The inorganic constituent of the NHs consists of boron-doped TiO2 nanorods (NRs) grown on fluorine-doped tin oxide (FTO) coated glass substrate. The organic part (NDIEHTh) consists of an acceptor naphthalene diimide (NDI)-based donor–acceptor-donor (D-A-D) type small molecule, in which thiophene serves as the donor. Because of the benefits of the localized surface plasmon resonance (LSPR) effect, the Au-Pd binary alloy nanoparticles substantially ameliorate the visible-light-driven photoelectrochemical performances of the B-TiO2/NDIEHTh@Au-Pd NHs photoanode compared to the B-TiO2/NDIEHTh NHs photoanode. The photocurrent densities exhibited by the B-TiO2/NDIEHTh NHs, and B-TiO2/NDIEHTh@Au-Pd NHs photoanodes at 1 V vs Ag/AgCl are 0.68 mA/cm2 and 1.59 mA/cm2, respectively, manifesting 209% and 623% increments in the photocurrent density compared to that shown by B-TiO2 NRs photoanode. Besides, the B-TiO2/NDIEHTh@Au-Pd NHs photoanode offers a significantly cathodically shifted water oxidation potential, reduced charge transfer resistance, better surface injection efficiency, and most importantly, superior photostability compared to the B-TiO2/NDIEHTh NHs photoanode. The enhancement in the different photoelectrochemical performances could be attributed to the various advantages of LSPR, such as enhanced light absorbance, light concentration, hot electron injection, and plasmon-induced resonance energy transfer.
... There are several ways, as with ordinary structures, to increase the photoelectroactivity of nanotubes. Here, we have doping with non-metals [33,34], metal doping [35], and the use of systems with a co-catalyst as reported for Fe 3 O 4 and CoO x decorated titania nanotubes towards water splitting [36,37]. ...
Doping and modification of TiO2 nanotubes were carried out using the hydrothermal method. The introduction of small amounts of cobalt (0.1 at %) into the structure of anatase caused an increase in the absorption of light in the visible spectrum, changes in the position of the flat band potential, a decrease in the threshold potential of water oxidation in the dark, and a significant increase in the anode photocurrent. The material was characterized by the SEM, EDX, and XRD methods, Raman spectroscopy, XPS, and UV-Vis reflectance measurements. Electrochemical measurement was used along with a number of electrochemical methods: chronoamperometry, electrochemical impedance spectroscopy, cyclic voltammetry, and linear sweep voltammetry in dark conditions and under solar light illumination. Improved photoelectrocatalytic activity of cobalt-doped TiO2 nanotubes is achieved mainly due to its regular nanostructure and real surface area increase, as well as improved visible light absorption for an appropriate dopant concentration.
... Figure 4 shows the structural information of BVBT from Raman spectroscopy implying the BVBT was successfully prepared. Four main characteristic Raman peaks at 158.1, 416.0, 512.0, and 628.0 cm −1 were observed and assigned to E 1g , B 1g , A 1g, and E g3 , respectively, which belong to a mixed brookite, anatase, and rutile phases (Szkoda et al. 2015;Taziwa et al. 2017;Wang et al. 2019). Raman bands at 248 and 350 cm −1 could assign for the black TiO 2 nanocrystals as reported earlier [20]. ...
Finding a facile and practical method to produce black TiO2 remains a challenge. Bismuth-vanadium co-doped black TiO2 (BVBT) was synthesized as a visible light driven photocatalyst by a simple one-pot hydrothermal method. The synthesized BVBT was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-Vis DRS). The light absorption of the synthesized Bi-V co-coped black TiO2 nanoparticles was significantly improved in the visible and infrared regions. The XRD patterns indicated that the black TiO2 contained mixed phases of brookite, anatase, and rutile of TiO2. This was further confirmed by Raman spectroscopy. The photocatalytic activity of the sample was evaluated by reduction of hexavalent chromium (Cr(VI)) under visible light irradiation. Among investigated hole (h⁺) scavengers, ethylenediaminetetraacetic acid (EDTA) led to the highest reduction of Cr(VI) with a molar ratio of 1:5 (EDTA:Cr(VI)). The results indicated that the Bi-V co-coped black TiO2 nanocomposite can reduce 94% of 1 mg/L of Cr(VI) within 20 min irradiation time (pH 3 and catalyst dose of 1 g/L). Introducing a simple method to synthesize black TiO2 which has absorption in the visible and infrared region can open up new applications.
... Compared with TiO 2 and TiO 2 -BiVO 4 , two additional peaks at 1592 and 1380 cm − 1 in the amplified Raman spectra ( Fig. 2 (b)) were related to the G-and D-bands (She et al., 2016), attributed to the presence of sp 3 defects and the E 2g mode within the hexagonal graphitic structure, indicating that graphite was formed in the as-prepared TiO 2 -C and TiO 2 -C-BiVO 4 films after the in situ carbonization of glucose through the ring opening and polymerization steps ( Fig. 2 (c)). Furthermore, the peaks at 149, 402, 518, and 645 cm − 1 were attributed to TiO 2 (Mariusz et al., 2015), while the peak at 826 cm − 1 was attributed to the stretching mode of the V-O band in BiVO 4 (Trzciński et al., 2016) in the as-prepared catalysts. ...
... Among of these methods, doping is extensively used to extend TiO 2 to the visible light spectrum by narrowing the band gap, separating photoelectrons, and reducing the recombination rate of valance hole. 17,18 A variety of materials including transition metals and nonmetal elements (e.g., C, 20−23 N, 24 S, 25 B, 26 I, 27 etc.) have been doped into TiO 2 to achieve solar light activation. 28,29 However, doping with metal elements may cause poor thermal stability 30 and an increment of recombination centers due to aggregation and larger particle size. ...
In this work, C-doped TiO2 nanorods were synthesized through doping carbon black into hydrothermally synthesized solid-state TiO2 nanowires (NWs) via calcination. The effects of carbon content on the morphology, phase structure, crystal structure, and photocatalytic property under both UV and solar light by the degradation of methylene blue (MB) were explored. Besides, the photoelectrochemical property of C-TiO2 was systematically studied to illustrate the solar light degradation mechanism. After doping with C, TiO2 NWs were reduced into nanorods and the surface became rough with dispersed particles. Results showed that C has successfully entered the TiO2 lattice, resulting in the lattice distortion, reduction of band gap, and the formation of C–Ti–O, which expands TiO2 to solar light activation. Comparing with P25 and anatase TiO2 NWs, doping with carbon black showed much higher UV light and solar light photocatalytic activity. The photocatalytic activity was characterized via the degradation of MB, showing that Kap was 0.0328 min–1 under solar light, while 0.1634 min–1 under UV irradiation. The main free radicals involved in methylene blue degradation are H⁺ and OH•–. Doping with carbon black led to the reduction of photocurrent in a long-term operation, while C-doping reduced the electron–hole recombination and enhanced the carrier migration.
... A low-level incorporation of non-metals in TiO 2 is found to be a promising approach to red-shifts the absorption spectra and improve the photocatalytic performance [20]. Among different non-metals like nitrogen, carbon, iodine and boron atoms, some work has already been done on boron doping in titania [21]. In addition, doping of non-metals into the lattice of wide bandgap semiconductor such as TiO 2 could raise the valence band (VB) energy which results in enhancing the performance of photoelectrode in water splitting reaction [22,23]. ...
The present study highlights the significant impact of trace level doping of boron in titanium dioxide (TiO2) nanotubes by investigating the structural, optical and electronic properties of samples, TNT and B-TNT. TEM analysis of boron-doped sample confirms the formation of crystalline nanotube structures and the trace level quantification of boron was confirmed by XPS analysis, where B shows feature of Ti–O–B bonding. Raman analysis revealed that the rutile phase becomes prominent after boron doping and Raman bands shift towards higher wavenumber was observed with increase in the tube diameter. The boron incorporation in TiO2 nanotubes reduces the band gaps from 3.3 eV to 3.1 eV and the mid-gap states were created within the band gap of the B-TNT sample. The change in valance band position from 2.5 eV to 2.9 eV after boron doping significantly changed the Fermi level position in TiO2 nanotubes. The work function of pristine and boron doped TiO2 samples are observed as 4.23 eV and 4.27 eV, respectively, as measured by Kelvin probe force microscopy. Here, we have investigated the band alignment of TNT and B-TNT by using state-of-the-art material characterization surface sensitive techniques. It can also be concluded that the electron affinity of the B-TNT sample is enhanced ∼4.07 eV than that of TNT ∼ 3.43 eV. The type –II band alignment is observed to be in between TNT and B-TNT with a valence band offset (VBO) ∼ 0.4 eV and conduction band offset (CBO) ∼ 0.6 eV.
... In Raman analysis (Fig. 2), the vibrational bands at 133.1, 204.3, 363.5, and 816.5 cm ?1 were observed, in which 816.5 cm ?1 was assigned to the asymmetric and symmetric V-O stretching modes, other vibrational peaks were related to the external vibration modes and asymmetric-symmetric bending vibrations of VO 4 3? [29] in as-prepared pure BiVO 4 . Meanwhile, peaks at 150.3 cm ?1 (E g ), 402.5 cm ?1 (B 1g ), 517.6 cm ?1 (B 1g ), and 643.5 cm ?1 (E g ) originated from as-prepared anatase TiO 2 [30]. In Raman analysis of TiO 2 -BiVO 4 film, all the peaks could still be observed implying the composite film was successfully prepared, whereas the peaks at 133.1 cm ?1 and 204.3 cm ?1 related to VO 4 3? weakened demonstrating the strong interaction between TiO 2 and BiVO 4 . ...
Type II heterojunction TiO2-BiVO4 composite films were designed via modified sol-gel-hydrothermal method for solar photoelectrocatalysis (SPEC) to restrain the recombination of electrons and holes as well as expand light absorption range. Fiddlehead-shaped morphology resulted in a larger specific surface area (157.63 m²·g⁻¹) and an intensification of light-harvesting efficiency. In comparison with photocatalytic (PC) system (79.3%), the degradation efficiency of RhB increased significantly to 93.9% in SPEC system. The enhancement mechanism and degradation path of SPEC systems was further discussed based on energy band adjustment, main active group determination, and quantum chemical calculation. Furthermore, the acute ecotoxicity of RhB and its degradation products were tested by Vibrio fischeri. The ecotoxicity was almost completely eliminated in SPEC system but it increased in PC system. The nanocomposite film also represented an excellent recyclability and stability, which may greatly reduce the economic cost and limit the probability of secondary pollution. Therefore, TiO2-BiVO4 nanocomposite films exhibited great potential in SPEC, providing a sustainable and harmless technique to treat organic wastewater.
... Recent experimental and theoretical studies dealt with the investigation and understanding of the TiO 2 nanotubes. Szkoda et al. (2015) investigated boron-doped TiO 2 nanotube arrays (B-TiO 2 NTAs) and examined the response by means of PEC and PC under UV-vis irradiation. They found that the density of B-TiO 2 NTAs is remarkably higher (7.5 times) than that of individual TiO 2 nanotube arrays. ...
Atrazine, one of the most widespread herbicides in the world, is considered as an environmental estrogen and has potential carcinogenicity. In this study, atrazine was degraded on boron-fluorine co-doped TiO2 nanotube arrays (B, F-TiO2 NTAs), which had similar morphology with the pristine TiO2 NTAs. The structure and morphology of TiO2 nanotube samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-visible diffuse reflectance spectroscopy (DRS). It showed that the decoration of fluorine and boron made both the absorption in the visible region enhanced and the band edge absorption shifted. The efficiency of atrazine degradation by B, F-TiO2 NTAs through photoelectrocatalysis was investigated by current, solution pH, and electrolyte concentration, respectively. The atrazine removal rate reached 76% through photoelectrocatalytic reaction by B, F-TiO2 NTAs, which was 46% higher than that under the photocatalysis process. Moreover, the maximum degradation rate was achieved at pH of 6 in 0.01 M of Na2SO4 electrolyte solution under a current of 0.02 A and visible light for 2 h in the presence of B, F-TiO2 NTAs. These results showed that B, F-TiO2 NTAs exhibit remarkable photoelectrocatalytic activity in degradation of atrazine.
... 16 Different chemical and physical methods have been used to modify the structure of TiO 2 in attempts to improve its photocatalytic efficiency. 17-21 Multiple methods for TiO 2 modification have been suggested, including doping with transition metal ions like Cu, Co, Ni, Cr, Mn, Mo, Nb, V, Fe, Ru, and Au 22,23 and non-metal ions like N, S, C, B, P, I, and F. 24,25 In particular, nitrogen doping is a promising approach to modify the structure of TiO 2 . Nitrogen-doped titanium dioxide (N-TiO 2 ) shows catalytic activity in some reactions under visible-light irradiation. ...
We investigated the influence of nitrogen doping on the electrocatalytic effect of TiO2 nanofibers by electrochemical methods. The electrocatalytic activities of nitrogen-doped TiO2 nanofibers (N-TiO2) produced using urea as the source of nitrogen and undoped TiO2 nanofibers were compared. The results showed that the N-TiO2 nanofibers possessed high activity in electrocatalytic oxidation of hydroquinone in buffer solution. The N-TiO2 nanofibers exhibited excellent catalytic activity because nitrogen doping changed the morphology of the nanofibers. Thus, nitrogen doping is a promising approach to enhance the electrocatalytic activity of TiO2 nanofibers in hydroquinone oxidation.
... According to our previously developed procedure [24], a twostage electrochemical oxidation of pure titanium foil (Strem Chemicals, 99.7%) immersed in an electrolyte containing fluoride ions was performed. Titanium substrates were first cleaned in ethanol, acetone and isopropanol for 10 min. ...
Herein, the heterojunction composed of an inorganic substrate: ordered hydrogenated titania nanotubes (H-TiO2NTs) and a deposited organic film: poly(3,4-ethylenedioxythiophene) (PEDOT) is reported. The conducting polymer is modified with different transition metal haxacyanoferrates (Mehcf), wherein as metal: copper, iron, cobalt and nickel are introduced. The presence of various metal centres provides characteristic redox activity and allows to investigate the impact of the particular Prussian Blue analogues onto the photoactivity of the p-n heterojunction. The formed composites were inspected by means of scanning electron microscopy, spectroscopic techniques, i.e. UV–Vis, Raman and Secondary Ion Mass spectrometry and using electrochemical methods. It is shown that electrochemical and photoelectrochemical performance of the so-fabricated materials is significantly affected by the nature of the redox species introduced into the PEDOT matrix.
... The electrochemical strategy for boron doping of TNTA is aiming at more simple production method and at more effective photoelectrocatalytic behavior [22][23][24][25]. Several papers are devoted to B,N-co-doped TiO2 particles [26][27][28][29]. ...
Highly ordered TiO2 nanotube arrays (TNTA) have attracted much attention due to the excellent photocatalytic, optical and electrical properties. However, their absorption range is limited to ultraviolet (UV) spectrum only due to the wide band gap (3.2 eV). One of the strategies to overcome this problem is doping with boron and nitrogen. They are produced via titanium sheet anodization and subsequent electrochemical treatment of titania in an electrolyte containing boric acid. The as-prepared B-TNTA are annealed in N2 atmosphere at 500 °C for 2 hours to obtain B,N-TNTA. The samples are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). The B,N-TNTA consist of uniform and well aligned nanotubes with an average inner diameter of 80–100 nm and a length not exceeding 1 μm. The photocurrent response measurements of undoped TNTA, N-doped and B,N-co-doped samples are performed under UV and visible light (Vis) illumination and a comparison is made. The obtained results show that the B,N-doping leads to remarkable photocurrent enhancement and better photocatalytic activity for methyl orange (MO) degradation due to the synergistic effects of B,N-co-doping and lower electron-hole recombination rates.
... The electrochemical strategy for boron doping of TNTA is aiming at more simple production method and at more effective photoelectrocatalytic behavior [22][23][24][25]. Several papers are devoted to B,N-co-doped TiO2 particles [26][27][28][29]. ...
A simplified approach is applied to produce B,N-co-doped TNTA. It consists in combining the electrochemical boron doping method with subsequent annealing in N2 atmosphere. This method is environment-sparing compared with ammonia atmosphere. It is handier and less expensive than many others methods to implant nitrogen in TNTA.
... Highly ordered titania nanotubes were prepared via a two-step electrochemical anodization of a Ti plate (Strem, 99.7%) in a fluoride-containing solution. The procedure that leads to the formation of TiO 2 nanotubes was described in our previous report [19]. Anodization was performed in a two-electrode configuration with a platinum grid as a cathode and the Ti plate acting as an anode. ...
Flexible dye-sensitized solar cells (DSSCs) are getting more attention compared to standard glass covered DSSCs due to their unique commercial applications (e.g. tents or sail surfaces) and the possibility of rolling up into a small, portable device. In this work, titania nanotubes (TiO2 NT) modified with titania nanoparticles (TiO2 NP) were photoelectrochemically characterized as an anode for flexible dye-sensitized solar cells. The morphology of the prepared electrode materials was inspected using scanning electron microscopy. Electrochemical activity of titania in contact with anaqueous electrolyte containing iodine species was investigated using cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA). The anode with deposited TiO2 NP exhibits enhanced efficiency of photocurrent generation in comparison to pure titania NT. The new type of comb-shaped Ti electrode with poly(3,4-ethylenedioxythiophene):poly(2-styrenesulphonate) (pEDOT:PSS) layer deposited onto the PET foil substrate was proposed as a counter electrode and compared with a conventional Pt catalytic layer as well as with a typical Pt/FTO counter electrode. Overall photoconversion efficiency of pEDOT-based counter-electrode DSSC reached 0.61% and was almost 40% higher than for counter electrode with Pt.
... The most often tested metal oxide as photocatalyst is TiO 2 , however relatively wide energy band gap ca. 3.2 eV makes titania photoactive only under UV illumination [1]. Thus, great effort has been taken to research on new materials that exhibit the highest photoactivity under visible light illumination in order to use natural solar light for excitation. ...
In this work, we present a simple method of the formation of MoO3 microstructures via an electrochemical anodization of Mo plate carried out under varied conditions. The morphology, composition and structure of samples were investigated by SEM, EDX, XRD and Raman spectroscopy. The band gap energy was estimated using the Kubelka–Munk function and was found to be 2.87 eV. Finally, the photocatalytic activities of MoO3 samples were evaluated using the decolorisation of methylene blue (MB) as a model organic contamination. Additionally, photostability of the materials were verified and the formation of hydroxyl ions was investigated by photoluminescence (PL) spectra of terephthalic acid as a probe molecule. Various conditions of MB decolorization allow the main mechanism of dye decomposition to be identified. It was shown that the presence of F⁻ during anodization positively affects photocatalytic properties of tested samples. After 2 h of constant illumination, the degradation reached 34% of the initial value of MB when α-MoO3 (prepared without F⁻) was used as photocatalyst, whereas the degradation efficiency equals 57% in the case of α-MoO3 (with F⁻). Furthermore, photoluminescence intensity of the 2-hydroxyterephthalic acid formed in the presence of α-MoO3(F⁻) was higher comparing to the intensity of spectra recorded in the presence of α-MoO3.
... The Raman spectroscopy measurements of electrode materials were carried out to confirm the crystalline phase of TiO 2 and successful deposition of polymer films onto the titania layer. A number of bands characteristic for the pure anatase crystalline form of TiO 2 were identified for pristine as well as for hydrogenated titania and composite material (see Fig. 2a) The maxima located at 144, 198, 395, 516 and 637 cm −1 are attributed to E g(1) , E g(2) , B 1g , A 1g , and E g(3) active anatase modes, re- spectively [18,19]. Fig. 2b illustrates the XRD patterns of pristine and hydrogenated titania nanotubes. ...
In this work we present the outstanding energy storage of prepared inorganic-organic heterojunction where hy-drogenated ordered titania nanotubes (H-TiO 2 NT) were modified by the hybrid made of poly(3,4-ethylenedioxythiophene) (pEDOT) and iron hexacyanoferrate centres (Fehcf, Prussian Blue). The material TiO 2 NT/pEDOT:Fechf was obtained electrochemically by means of: anodization, hydrogenation and finally, electropolymerization of EDOT in the presence of Fe(CN) 6 3−/4− ions. Inorganic-organic hybrids were characterized using Raman spectroscopy and secondary ion mass spectrometry (SIMS). The morphology of obtained materials was inspected using scanning electron microscopy (SEM). Electrodes were tested using cyclic voltammetry and galvanostatic charge/discharge cycles in an aqueous electrolyte. The characterization of capac-itance was studied by means of multiple (up to 10,000) charge/discharge cycles with the current density of 0.45 mA cm −2. Electrode materials consisting of H-TiO 2 , pEDOT and Prussian Blue exhibited the highest capaci-tance of 26 mF cm −2 even after 10,000 cycles. Thus, the capacitance of TiO 2 NT/pEDOT:Fehcf was c.a. 15 and 8 times higher than the capacitance registered for pure and hydrogenated TiO 2 , respectively.
... The Raman spectroscopy measurements of electrode materials were carried out to confirm the crystalline phase of TiO 2 and the presence of pEDOT:Fehcf in the formed junction. As it is presented in Fig. 3, the spectrum of the as-annealed inorganic layer exhibits signals typical for anatase phase [36,37]. The bands are located at 144, 198, 395, 516 and 637 cm −1 that could be respectively assigned to E g(1), E g (2) , B 1g , A 1g , B 1g and E g(3) phonons characteristic for active anatase modes. ...
... Obviously, the poor overlapping with the visible-light spectrum for TiO 2 has greatly limited its application in the PEC fields. As a result, a lot of efforts have been made to induce red shift of the response of TiO 2 to sunlight, such as ion doping [35][36][37][38][39][40][41] and coupling with narrow-bandgap semiconductors [22,[25][26][27][28]42]. Although ion doping could extend light absorption, this method introduced midgap energy levels between the conduction band and valence band of TiO 2 . ...
In this work, the capping layer atop anodic TiO2 nanotube arrays (NTAs), which hinders filling of other guest materials and transport of charge carriers, is discerned to be TiO2 nanotapes. Then, it is completely removed by a novel sonication-polishing (SP) treatment, after which Sb2S3 is subsequently introduced to fill the nanotubes by chemical bath deposition. The morphological, structural, and optical properties of the SP-treated TiO2 NTAs and TiO2 NTAs/Sb2S3 heterogeneous structures are characterized systematically. The results indicate that SP treatment opens the tops of nanotubes with diameters of ∼120 nm, which endure a phase conversion from amorphous to anatase after calcination at 450 °C; besides, stibnite Sb2S3 with a band gap of ∼1.75 eV inside the TiO2 networks is formed upon heat treatment at 330 °C in Ar, which enhances the absorption in visible light range. The photoelectrochemical (PEC) and photovoltaic properties for the SP-treated TiO2 NTAs are investigated. Results shows that the photoresponse of TiO2 NTAs is improved by the SP treatment, and the photocurrent for the TiO2 NTAs/Sb2S3 electrode is substantially enhanced as compared to the bare TiO2 one. A high efficiency of 6.28 % is achieved in a TiO2 NTAs/Sb2S3 PEC cell. In addition, charge recombination in the photoanode of dye-sensitized solar cells (DSSCs) is observed to be greatly retarded by using the SP-treated TiO2 NTAs as compared to TiO2 nanoparticles (NPs). Thus, the SP anodic TiO2 NTAs are promising in applications in various PEC areas such as photocatalysis and sensitized solar cells.
... Taking into account only oxygen linked to boron and titanium, the atomic ratio of Ti/ O/B found at the material surface equals: 1:2.39:0.73. However, XPS investigation performed after subsequent [42]. Therefore, because of significant amount of surface boron species, the increase in hydroxyl groups amount observed on FTIR spectra comparing to pristine titania provides the neutrality of B-TiO 2 surface [43]. ...
In this work, we were focused on the development of the electrochemical approach resulting in a stable boron doping of titania nanotubes. The doping procedure concerns anodic polarization of as-anodized titania in a H3BO3 solution acting as n boron precursor. The series of attempts were taken in order to elaborate the most beneficial doping conditions. The parameters of electrochemical doping allowing to obtain boron-doped titania characterized by the highest photoconversion efficiency are as follows: reaction voltage 1.8 V, process duration 0.5 h, and the concentration of boric acid 0.5 M. Spectroscopy techniques such as UV-vis, X-ray diffraction, photoluminescence emission, and X-ray photoelectron spectroscopy were used to characterize the absorbance capability and the crystalline phase, to confirm the presence of boron atoms and to study the nature of chemical compounds, respectively. The well-ordered structure of titania and resistance of its morphology toward electrochemical treatment in H3BO3 were confirmed by scanning electron microscopy images. However, cyclic voltammetry and electrochemical impedance spectroscopy studies showed the significant difference in conductivity and capacitance between doped and pristine titania. Moreover, the photocurrent densities of the B-doped sample were about seven times higher in comparison with those generated by the pure titania nanotube electrode.
... Among them, doping with non-metal atoms is regarded as simple and effective, providing materials that are stable and that exhibit their activity under visible light illumination. For the intentional doping of titania, nitrogen [8], sulfur [9], phosphorus [10], boron [11,12], and iodine [13] atoms were proposed as favorable non-metallic candidates. Taking into account a number of scientific reports, nitrogen and boron are the most popular dopant atoms, and their presence in titania structures results in a highly active material, whereas the investigation of other possible non-metal atoms is not as widespread. ...
The paper focuses on the optimization procedure concerning the synthesis method resulting in highly ordered titania nanotubes doped with iodine atoms. The doping process was based on the electrochemical treatment of a titania nanotube layer immersed in a potassium iodide (KI) solution acting as an iodine precursor. A number of endeavors were undertaken in order to optimize the doping conditions. Electrolyte concentration, reaction voltage, and time/duration were the main factors that influenced the iodine (I)-doping effect on the photoactivity. The parameters of electrochemical doping that result in a material characterized by the highest photocurrent density are as follows: reaction voltage of 1.5 V, duration of 15 min, and 0.1 M KI. Different spectroscopic techniques, i.e., UV–Vis spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the absorbance capability and the crystalline phase, to confirm the presence of iodine atoms and to study the nature of chemical compounds. The morphology inspection performed by means of scanning electron microscopy shows that the doping process does not affect the ordered tubular architecture. The photocurrent densities of the I-doped sample were six times higher in comparison to those generated by the pure titania nanotube electrode. Moreover, doped samples act as a much better catalyst in the photodegradation process of methylene blue and formation of hydroxyl radicals (•OH) than undoped samples.
The increasing consumption of fossil fuels and the exacerbation of environmental pollution have made the development of sustainable clean energy conversion technologies an urgent priority. Piezo-photocatalytic technology, which integrates piezoelectric...
TiO2 is an important material for reasons that are related to fundamental research, as well as to existing and potential technological applications. There is no aspect of the chemistry and physics of TiO2, which is not decisively affected by the presence of defects. An increase in the present state of understanding of the science of TiO2-based material interfaces is essential for progress in this area; such progress is possible thanks to high purity TiO2 single crystals which are ideal for basic investigation of and on titanium dioxide surfaces under carefully controlled laboratory conditions. Surface functionalization through precise control of the nature of the defects, their concentration and arrangement, allows the modification and optimization of the material, or even the generation of completely new targeted properties of the surfaces independent from the bulk. A new generation of TiO2 surfaces with enhanced functionality and performance limits has been successfully created by the use of surface engineering. In Part I of this review, a brief description of the results is given of the experimental and theoretical investigations on the influence of the defect states on the correlation between crystallographic, electronic and atomic geometrical structures of the most technically important single low Miller index titania surfaces and their physical properties. In addition, the formation and detection techniques for surface oxygen vacancies are also considered. Special attention in this area is given to the behaviour of the electrons remaining in the system upon vacancy formation and the ability of current quantum-mechanical modelling methods to provide a precise description of the electronic structure of non-stoichiometric TiO2. These fundamental studies allow scientists to create real functional TiO2 surfaces, such as the targeted nanostructured thin films with predefined structure and properties required for the development of high-performance devices in the fields of energy, environment and health.
In this study, undoped, boron doped and graphene oxide doped TiO2 nanotubes (TNT) were synthesized on Cp-Ti (commercially pure titanium) samples. The aim of this research is to investigate the structural properties, surface wettability, corrosion resistance and tribocorrosion behavior of boron and graphene oxide doped TNT. XRD, Micro-Raman, XPS, SEM and a surface tension meter were used to characterize the nanotubes. It was found that the increasing surface roughness and contact area of the synthesized nanotubes improved the surface wettability. By preventing the SBF liquid from reaching the substrate material, the anodic films formed in all TNT-synthesized samples improved the corrosion resistance. The ceramic TiO2 structure formed on the surface increased the surface hardness and consequently, wear resistance improved. The best tribocorrosion resistance was obtained from the graphene oxide doped TNT, which has the longest tubular architecture.
Titanium and its alloys have many advantages such as acceptable biocompatibility and good corrosion resistance and these advantages make them a widely preferred biomaterial. However, it is also known
that they have some disadvantages such as poor wear resistance and insufficient surface wettability. Therefore, to overcome this disadvantages, boric/sulfuric anodic films with different anodization
time was formed on the surface of Ti6Al4V. The morphological and structural properties of anodic films were evaluated by XRD, XPS, SEM, Raman spectra, micro-hardness tester, 3D profilometer, and surface tension-meter. Also, the tribological behavior of them was analyzed by a pin-on-disk tribotester. The average coefficient of friction (CoF) of the untreated Ti6Al4V alloy is 0.37, while the CoF of boron containing TiO2 anodic films is in the range of 0.04–0.15. Also, the anodic films reduced the wear rate by about 30% compared to the untreated Ti6Al4V. In addition to all these, it was observed that the anodic films changed the surface morphology. It was determined that the produced anodic films were in porous structures and with the increase of the applied anodizing time, the possibility of contacting the liquid with the surface increased.
Photocatalytic (PC) / Photoelectrochemical (PEC) water splitting under solar light irradiation is considered as a prospective technique to support the sustainable and renewable H2 economy and to reach the ultime goal of carbon neutral. TiO2 based photocatalysts with high chemical stability and excellent photocatalytic properties have great potential for solar-to-H2 conversion. To conquer the challenges of the large band-gap and rapid recombination of photo generated electron-holepairs in TiO2, non-metal doping turns out to be economic, facile, and effective on boosting the visible light activity. The localized defect states such as oxygen vacancy and Ti³⁺ generated by non-metal doping are located in the band-gap of TiO2, which result in the reduction of band-gap, thus a red-shift of the absorption edge. The hetero doping atoms such as B³⁺, I⁷⁺, S⁴⁺/S⁶⁺, P⁵⁺ can also act as electron donors or trap sites which facilitate the charge carrier separation and suppress the recombination of electron-hole pairs. In this comprehensive review, we present the most recent advances on non-metal doped TiO2 photocatalysts in terms of fundamental aspects, origin of visible light activity and the PC / PEC behaviours for water splitting. In particular, the characteristics of different non-metal elements (N, C, B, S, P, Halogens) as dopants are discussed in details focusing on the synthesis approaches, characterization as well as the efficiency of PC and PEC water splitting. The present review aims at guiding the readers who want quick access to helpful information about how to efficiently improve the performance of photocatalysts by simple doping strategies and could stimulate new intuitive into the new doping strategies.
Generation of controlled intrinsic defects such as oxygen deficiencies is the best method for modulating optical as well as electronic properties of metal oxide semiconductor nanostructures. The present chapter describes recent studies about different approaches for introducing oxygen vacancies in the chemically prepared metal oxide thin films and their useful contribution in the photocatalytic applications. Semiconductor metal oxide thin films with oxygen vacancies such as TiO2 and WO3 exhibit substantially improved photocatalytic activities in water splitting, CO2 photoreduction, and photodegradation of organic pollutants. The increased photo-activities are reflected by increased intrinsic properties by the production of oxygen deficiencies as shallow donor sites in the forbidden band gap of metal oxide semiconductors. Also, the discussion is extended to the current progress on the preparation of different metal oxides with oxygen deficiencies and their role for the improvement of photocatalytic activities of metal oxides.
Phenolic pollutants as highly toxic and hazardous organics are widely generated from industrial and domestic process. Phenolic pollutants with different hydroxyl position (catechol, resorcinol, hydroquinone, phenol) were preferentially and efficiently oxidized in photocatalytic process (PC) by designing boron-doped TiO2 (B-TiO2).The key role for enhancing the photocatalytic activity of B-TiO2 was the formation of abundant Ti³⁺ species. The formation of Ti³⁺-O weakened the competitive adsorption of H2O in aqueous solution and favored the formation of cooperative hydrogen bond on the surface of B-TiO2, leading to enhanced adsorption of phenolic pollutants. The degradation rate constant of B-TiO2 (kB-TiO2) was regardless of the corresponding oxidation potential of phenolic pollutants. The kB-TiO2 for catechol in photocatalytic process was as high as 3.46 min⁻¹, which was 18.2, 1.6 times higher than that of biodegradation and ozonation methods, respectively. Of note, the preferential removal mechanism of phenolic pollutants was elucidated by in-situ attenuated total reflectance (ATR)-IR and density functional theory calculation (DFT). The results were helpful for developing new preferential oxidation technologies in HO∙-mediated process for selectively removing low concentration but highly toxic pollutants.
A simple anodic oxidation method was used to prepare TiO2 nanotubes (TNTs), and calcined at 500 °C with urea to prepare g-C3N4/TNTs (CN/TNTs) composites. The photocatalytic activity of TNTs was improved by constructing a Z-scheme transfer mechanism. The results show that 2 g CN/TNTs greatly improves the separation efficiency of electron-hole pairs and reduces its recombination efficiency, and the visible light absorption also undergoes a significant redshift. The degradation of rhodamine B can reach 96.3%, and the degradation rate is 0.0195min⁻¹. The sample has good stability and can be used repeatedly without losing activity. In the CN/TNTs system, h⁺, O2- and OH are active species.
Photoelectrochemical (PEC) water splitting offers the capability of harvesting, storing, and converting solar energy into clean and sustainable hydrogen energy. Metal oxides are appealing photoelectrode materials because of their easy manufacturing and relatively high stability. In particular, metal oxides prepared by electrochemical anodization are typical of ordered nanostructures, which are beneficial for light harvesting, charge transfer and transport, and the adsorption and desorption of reactive species due to their high specific surface area and rich channels. However, bare anodic oxides still suffer from low charge separation and sunlight absorption efficiencies. Accordingly, many strategies of modifying anodic oxides have been explored and investigated. In this review, we attempt to summarize the recent advances in the rational design and modifications of these oxides from processes before, during, and after anodization. Rational design strategies are thoroughly addressed for each part with an aim to boost overall PEC performance. The ongoing efforts and challenges for future development of practical PEC electrodes are also presented.
Anode materials are crucial to anodic oxidation for wastewater treatment. In this regard, stable boron and cobalt co-doped TiO2 nanotube (B, Co-TNT) was prepared for the first time, and its lifetime was found increased significantly while electrocatalytic activity decreased with the increase of Co(NO3)2 in preparation from 1 to 10 mM. Characterized by scanning electron microscope (SEM), X-Ray Diffraction (XRD) and X-ray Photo-electronic Spectroscopy (XPS), B and Co content were optimized and successfully doped on TNT, which was more smooth without ripple with Co content of 0.038 mg/cm² in a valence of +2, and B atomic content of 2.17 at.% in form of Ti-B-O. This optimized anode enhanced electrode lifetime 122.8 times while the electrochemical activity decreased slightly when compared to the undoped TNT. The effects of current density, initial pH and initial 2,4-dichlorophenoxyacetic acid (2,4-D) concentration were investigated, and the mainly responsible radical for degradation was confirmed to be the surface OH on B, Co-TNT anode. This anode had better performance on the TOC removal, mineralization current density (MCE) and energy consumption (Ec) when compared with BDD, PbO2, DSA and Pt anodes, and it also presented a very stable degradation for 10 cycles oxidation of 20 mg/L 2,4-D with allowable Co leaching. Therefore, B, Co-TNT anode is a promising, stable, safety and cost-effective anode for application in electrochemical advanced oxidation processes (EAOPs).
Boron‐doped anatase TiO2 particles were effectively coupled with carbon nitride (CN) forming nanocomposites. The materials were fully characterized by DR‐UV‐Vis, N2 adsorption‐desorption isotherms, XRD, Raman, FTIR, TGA, XPS, TEM, electron energy loss spectroscopy, photoluminescence, and electron paramagnetic spectroscopy (EPR) spectroscopy. The developed heterojunctions were applied as photocatalysts for hydrogen (H2) evolution by the photoreforming process of ethanol under solar irradiation, using minimal amount of Pt nanoparticles (0.1 wt. %) as co‐catalyst. The effects of boron addition and CN content were evaluated and optimized nanocomposite presented 85 % increase in H2 evolution compared with the pure anatase TiO2 catalyst. The observed higher H2 evolution rates were ascribed to improvements in charge formation and separation efficiency due to the B‐dopant and the presence of CN.
Non-metals B, N, P and I were doped into titanium dioxide (TiO2) to form photocatalyst particles. TiO2 doped with various ratios of B, N, P and I were thus formed and these photocatalyst particles were bonded to fix each other in a column system under sunlight as a result of the photocatalytic degradation of bisphenol A (BPA). The doped TiO2 was characterized by X-ray diffraction (XRD), UV-visible absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS) to elucidate the mechanism of doping reaction. Doping with B, N, P and I to form the photocatalyst greatly red-shifted the absorption wavelength, increasing the effectiveness of the photocatalyst in reducing BPA. XPS analysis following doping revealed the bonding of B, N, P, I and other functional groups of the surface of the photocatalyst. Results of an experiment that involved the photocatalysts revealed that BPA degradations of 88%, 94%, 93% and 100% in 66.5 minutes under sunlight using B, N, P, and I-doped titanium dioxide, respectively. The doped photocatalysts were all superior to the undoped titanium dioxide.
The photocatalytic activity of TiO2-nanotubes can be improved through the construction of a Z-scheme composite, where photogenerated electrons from TiO2 recombine with the photogenerated holes in a coupled semiconductor. This arrangement allows for improved oxidation due to the residual holes of TiO2, and better chemical reduction due to the greater availability of the photogenerated electrons of the coupled semiconductor. Efficient Z-scheme porous-g-C3N4/TiO2-nanotubes (PCN/TNTs) composites were developed here using a solid sublimation and transition approach, with Al-O links added by an impregnation method to increase interfacial linkages between the PCN and TNTs. The best results for photocatalytic CO2 conversion were obtained using 0.7PCN/0.4Al/TNTs, as shown by production of 54.9±0.70 mg L−1 h−1 of acetic acid, 42.7±0.54 mg L−1 h−1 of formic acid, and 45.4±0.55 mg L−1 h−1 of methanol, which were about 3.8, 4.3 and 4.2 times that produced with bare TNTs. Photocatalytic 2,4-dichlorophenol decomposition with 0.7PCN/0.4Al/TNTs showed a 40% enhancement compared to bare TNTs in 1.5 h. This Z-scheme composite photocatalyst therefore provides an improved method for more efficient CO2 conversion or pollutant degradation based on the improved charge separation and linkage of the PCN/TNTs using Al-O.
Boron (a metalloid) has been chosen as the doping agent in the titanium dioxide structure via in situ anodizing method in this work. FE-SEM, XPS, Raman spectroscopy, XRD, EDX and UV–visible techniques were used to investigate the morphology, structure and optical properties of the samples prepared. XPS and UV–visible techniques were used to confirm the presence of boron in the nanotubes and the reduction in band gap, respectively. Afterward, the impact of the concentration of the doping agent on the photoelectrocatalytic and anticorrosion properties of the nanotubes was studied through different electrochemical techniques such as linear sweep voltammetry, chronoamperometry, open-circuit potential and Tafel under visible light. Better photocatalytic performance and anticorrosion properties are shown by nanotubes modified by boron compared with bare titanium dioxide nanotubes, according to the results. The photo-response increases dramatically as boric acid concentration in anodizing electrolyte is increased from samples BT1 to BT10 and slowly decreases for samples BT10-BT25. The best photoelectrocatalytic performance in photoelectrochemical water splitting studies was shown by samples BT10 and BT15. Ultimately, the photo-generated cathodic protection of 403 stainless steel (403SS) has been studied in a corrosion cell using a 3.5% NaCl solution under visible light by the photocatalysts prepared. The photocatalytic activity of TiO 2 under visible light illumination was enhanced by doping of boron, based on the results.
In this work we show the impact of applied potential on network vibrations and photoelectrochemical properties of a composite material containing hydrogenated titania nanotubes and poly (3,4-ethylenedioxythiophene) with iron hexacyanoferrate (H-TiO2/pEDOT:Fehcf) acting as a redox centre. For this purpose, Raman spectroscopy measurements under the working electrode (WE) polarization were carried out, allowing investigation of changes in the structure of the obtained heterojunction. The photoelectrochemical behaviour of the H-TiO2/pEDOT:Fehcf composite was also studied at different potentials of WE. Both, in-situ Raman spectroelectrochemical and transient photocurrent measurements were performed in aqueous 0.1 M K2SO4 electrolyte. The reduction and oxidation of the electrode material enabled control of the organic matrix doping level and in consequence processes occurring at the electrode/electrolyte interface. The intensity of bands typical for the organic part of the junction strongly depends on the applied potential: the highest intensity of Raman bands characteristic for the pEDOT chain was observed in the cathodic potential range, whereas under anodic polarization pEDOT signals diminish. On the contrary, the intensity and the positions of anatase active modes remain almost unchanged independently of the applied potential. Furthermore, the effect of various polarization conditions within the anodic and cathodic potential ranges on the photocurrents was also observed. The maximum value of the photocurrent is reached at +0.8 V vs. Ag/AgCl/0.1 M KCl and equals 290 μA/cm².
The paper discusses the synthesis, photoelectrochemical and electrochemical behaviour of titania nanotube arrays modified by a pyrolyzed metal-organic framework (MOF). A poly(3,4–ethylenedioxyphene) (PEDOT) matrix with an embedded inorganic network of iron hexacyanoferrate (BP) covering TiO2 nanotubes (TNT) is used as a MOF for the further sintering procedure, resulting in a novel, thin film of carbonaceous wrap supported Fe catalytic centers: TNT@C:Fe. UV–Vis and Raman spectroscopies were utilized to characterize the absorbance capability and the crystalline phase of titania, respectively. XPS was used for identification of the valence stage of iron Fe(0), Fe(II), Fe(III) in the shell part of the novel composite TNT@C:Fe. The electrochemical performance of the modified nanotubular TiO2 electrodes has been monitored by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge cycles in an aqueous electrolyte. TNT@C:Fe exhibited the capacitance of 9.1 mF cm−2 even after 5000 cycles, being much higher than pure titania (2.1 mF cm−2). The photocurrent density reached 304 μA cm−2 for TNT@C:Fe, whereas only 32 μAcm−2 was registered for pure titania nanotubes under simulated solar light illumination at a potential of +0.5 V. An improved decolorization rate of methylene blue in water confirms enhanced photoactivity of TNT@C:Fe in comparison with pristine titania nanotubes.
A practical large-scale energy storage should deliver a high capacitance/capacity under an ultrahigh rate and do so economically over cycles. Existing electrode materials, however, have fallen short of these requirements in one measure or another. Here we discovered a surface confined titania redox couple on black TiO2 nanotube arrays (B-TNAs). Such rapid Ti3+/Ti4+ conversion provides an outstanding rate for B-TNAs of 400 mA cm-2 in supercapacitors (SCs) and 200 C in lithium ion batteries (LiBs), with a negligible capacitance/capacity fading up to 15000 cycles. The ultrafast pseudocapacitive behaviour from black titania suggests a new family of electrode materials, which may offer a way for overcoming the present difficulties of SCs and LiBs in grid-scale energy storage systems.
High quality ternary-alloyed CdTeSe quantum dots (QDs) have been synthesized via a simple one-pot approach in aqueous phase. CdTeSe QDs show an average size of 3.0 nm with good crystallinity, excellent monodispersity and relatively narrow size distribution. TiO2 nanotubes (TNTs) were prepared by hydrothermal method with larger specific surface area (364.2 m² g⁻¹), and CdTeSe@TNTs were synthesized by in situ process. The absorption edge of CdTeSe@TNTs is red shifted significantly toward 697 nm. After sensitized with CdTeSe, the photoluminescence (PL) emission of CdTeSe@TNTs is significantly quenched, and the fluorescence lifetime of the composites is drastically decayed from 105.82 ns to 0.13 ns with a high photoinduced electron transfer rate (ket = 7.98 × 10⁹ s⁻¹) because of their high matchable lattice constant. In addition, under visible-light irradiation, the photocatalytic efficiency of rhodamine B (RhB) with CdTeSe@TNTs reaches 90% for 80 min. And the photocatalytic reaction rate constant for CdTeSe@TNTs is 0.0272 min⁻¹, which is 5.4 and 3.4 times larger than that of pure TNTs and CdTeSe QDs, respectively. It is due to the broad visible absorption of CdTeSe@TNTs and the faster photoinduced electron transfer from CdTeSe QDs to TNTs.
Titanium dioxide is a well-known photoactive semiconductor with a variety of possible applications. The procedure of pollutant degradation is mainly performed using TiO2 powder suspension. It can also be exploited an immobilized catalyst on a solid support. Morphology and chemical doping have a great influence on TiO2 activity under illumination. Here we compare photoactivity of titania nanotube arrays doped with non-metal atoms: nitrogen, iodine and boron applied for photodegradation of organic dye - methylene blue and terephtalic acid. The doped samples act as a much better photocatalyst in the degradation process of methylene blue and lead to the formation of much higher amount of hydroxyl radicals (•OH) than undoped TiO2 nanotube arrays. The use of a catalyst active under solar light illumination in the form of thin films on a stable substrate can be scaled up for an industrial application.
A high-photoactivity boric acid-doped titanium dioxide (B-doped TiO2) photocatalyst of the degradation of aqueous bisphenol A (BPA) under sunlight was synthesized and characterized by scanning electron microscope, X-ray photoelectron spectroscopy and UV-vis diffuse reflectance. The band gap energies of TiO2 and B-doped TiO2 (B/Ti mole ratio = 0.2%) were 3.01 and 2.98, showing that B-doped TiO2 could narrow the band gap of pure TiO2. In the photocatalytic kinetics of the photodegradation, the BPA photodegradation rate constants were 1.67 and 1.08 h⁻¹, respectively. The BPA removal rate satisfies pseudo-first-order kinetics. Results showed that photocatalysts doped with boron displayed greater photodegradation (88% BPA removal) than pure TiO2 (65% BPA removal). Experimental results indicated that B-doped TiO2 not only was an effective photocatalyst, but also had considerable mineralization effects. The recycling test revealed that the photocatalyst remained effective after 10 uses, revealing the stability and reusability.
The paper discusses the synthesis and performance of iodine doped titania nanotube arrays exhibited under irradiation. The doping procedure was performed as an additional, electrochemical process carried out after formation of nanotube arrays via anodization of Ti substrate. The optical and structural properties were characterized using Raman, UV-vis, photoluminescence and X-ray photoelectron spectroscopy. The surface morphology and cross-section studies performed by means of the scanning electron microscopy show that the ordered tubular architecture is not influenced by any doping methods. However, iodine doping causes a reduction of bandgap energy and photoluminescence intensity. The nanotubular TiO2 electrodes have been monitored by electrochemical (using cyclic voltammetry and electrochemical impedance spectroscopy) and in-situ UV-vis spectroelectrochemical measurements in contact with an aqueous electrolyte. Collected results show significant differences in electrochemical activity between pure and doped titania exhibited as i.e. change of Mott-Schottky relation or shift in onset potential when a decrease in reflectance is initiated. The photocurrent density reached 155.2 and 142.2 µA cm-2 for iodine doped materials when KI and HIO4 were used as iodine precursors whereas only 25.6 µA cm-2 was registered for pure titania nanotubes under UV-vis illumination. Moreover, doped samples are far more efficient at the photodegradation progress than undoped material leading to decomposition of over 70% of methylene blue used as model organic pollution. Reported studies demonstrate for the first time the detailed optical, electrochemical and photoelectrochemical studies of iodine doped nanotube arrays.
Nitrogen doped titania nanotubes were successfully sensitized by electrochemical method, i.e. as-anodized titania was immersed in different amine (diethyleneamine-DETA, triethyleneamine-TEA, ethylenediamine-EDA) and urea (U) solution and a constant potential was applied. The highly ordered morphology of fabricated N-TiO2 was investigated by using scanning electron microscopy. Spectroscopic techniques, i.e. UV-Vis spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and photoluminescence spectroscopy were utilized to characterize absorbance capability and the crystalline phase, to confirm the presence of nitrogen atoms and to study charge recombination, respectively. The highest photocurrent under both UV-Vis and visible illumination (λ > 420 nm) was registered for N-TiO2 sample obtained from diethylenetriamine solution, used as a nitrogen precursor. The photocurrent density exhibited during UV-Vis irradiation by the most active nitrogen doped titania was 2.83 times higher compared to pure TiO2 nanotubes. The photocatalytic activity studies, demonstrated a significant improvement when N-TiO2-DETA (52 %) and N-TiO2-U samples (49 %) where used instead of undoped TiO2 (27 %). The presented results show that electrochemical doping with 0.5 M amine or urea solutions is a simple, cheap and effective strategy to introduce nitrogen atoms into the titania structure without affecting its morphology.
Two types of TiO2 nanotubular arrays were obtained by anodisation of a titanium foil, in two different solutions containing fluoride ions. For the first type which has rough tube walls, impedance measurements in the dark showed the presence of a localised surface state which was related to adsorbed molecular water. Under UV illumination, this adsorbed molecular water was photo-dissociated. Moreover, an increase of 2 orders of magnitude for the limiting capacitance of the space charge layer was observed, simultaneously with the disappearance of the localised state and with a 100-time increase of the carrier density associated with hydrogen insertion. The second type of layer was characterised by smoother tube walls, a high doping level (1020 cm−3) in the dark, a lack of localised states and no long-lasting photo-induced effect. In this case, the width of the space charge layer became rapidly higher than the half-thickness of the tube walls, when the applied potential increased. Therefore, the walls were progressively depleted under anodic polarisation, passing from a situation where the tubes were totally active in the cathodic range towards a situation where the contribution of the tube walls could be neglected.
B-doped TiO2 nanotubes (B/TiO2 NTs) were prepared by the combination of sol–gel process with hydrothermal treatment. The prepared catalysts were characterized
by XRD, TEM and XPS. The photocatalytic activity of B/TiO2 NTs was evaluated through the photodegradation of aqueous methyl orange. The results demonstrated that the 1.5% B/TiO2 NTs calcined at 300°C possessed the best photocatalytic activity. Compared with pure TiO2 nanotubes, the doping with B significantly enhanced the photocatalytic efficiency.
KeywordsB-doped TiO2
-Nanotubes-Photocatalytic activity
A review of patents on the application of titanium dioxide photocatalysis for air treatment is presented. A comparison between water treatment and air treatment reveals that the number of scientific publications dedicated to photocatalytic air treatment is significantly lower than the number of scientific manuscripts dedicated to photocatalytic water treatment, yet the situation is reversed upon comparing relevant patents. This indicates a growing interest in the implementation of photocatalysis for air treatment purposes, which surpasses that of water treatment.This manuscript analyzes the various patents in the area of air treatment, while differentiating between indoor air treatment and outdoor air treatment. Specific efforts were made to characterize the main challenges and achievements en-route for successful implementation, which were categorized according to mass transport, adsorption of contaminants, quantum efficiency, deactivation, and, no less important, the adherence and the long term stability of the photocatalyst.
Second-generation TiO(2)-(x)D(x) photocatalysts doped with either anions (N, C, and S mostly) or cations have recently been shown to have their absorption edge red-shifted to lower energies (longer wavelengths), thus enhancing photonic efficiencies of photoassisted surface redox reactions. Some of the studies have proposed that this red-shift is caused by a narrowing of the band gap of pristine TiO(2) (e.g., anatase, E(bg) = 3.2 eV; absorption edge ca. 387 nm), while others have suggested the appearance of intragap localized states of the dopants. By contrast, a recent study by Kuznetsov and Serpone (J. Phys. Chem. B, in press) has proposed that the commonality in all these doped titanias rests with formation of oxygen vacancies and the advent of color centers (e.g., F, F(+), F(++), and Ti(3+)) that absorb the visible light radiation. This article reexamines the various claims and argues that the red-shift of the absorption edge is in fact due to formation of the color centers, and that while band gap narrowing is not an unknown occurrence in semiconductor physics it does necessitate heavy doping of the metal oxide semiconductor, thereby producing materials that may have completely different chemical compositions from that of TiO(2) with totally different band gap electronic structures.
Change in the structural and characteristic of the anodic oxide on pure Ti with the duration of anodization time was investigated. With the progress of the anodization, the phase of the formed TiO2 successively changed from anatase phase to rutile phase. In the transition process, peak intensities of rutile TiO2 1 0 1, 1 1 1 and 2 1 1 planes of X-ray diffraction characteristically increased. The contact angles of water droplets on the anodize TiO2 were monotonously decreased with the progress of the anodization except on the characteristically oriented rutile surface. In the evaluations of acetaldehyde photocatalysis under UV illumination, the anatase TiO2 anodized for short period exhibited high activities. On the other hand, when illuminated with visible light (>422 nm), rutile-structured TiO2 formed by anodization with a long duration exhibited superior photocatalytic activities probably due to high rutile fraction and sulfur incorporation from the electrolyte.
In the present study, chemical vapour deposition (CVD) was applied to dope boron into TiO2 nanotubes anodized Ti in C2H2O4·2H2O + NH4F electrolyte with the goal of improving the photocatalytic (PC) activity under visible light. The undoped TiO2 nanotubes had a highly self-organized structure. However, after doping through CVD, TiO2 nanotubes suffered from an observable disintegration of morphological integrity. X-ray diffraction (XRD) results confirmed that annealing temperature had an influence on the phase structure and boron impurities could retard anatase–rutile phase transition. Diffuse reflectance absorption spectra (DRS) analysis indicated that B-doped samples displayed stronger absorption in both UV and visible range. B-doped TiO2 nanotubes electrode annealed at 700 °C through CVD showed higher photoelectrocatalytic (PEC) efficiency in methyl orange (MO) degradation than that annealed at 400 °C and 550 °C. MO degradation was substantially enhanced with the increasing applied bias potential. Moreover, there was a synergetic effect between the electrochemical and photocatalytic processes, and the synergetic factor R reached 1.45. B-doped TiO2 nanotubes electrode showed good stability after 10 times by repeating photoelectrocatalysis of MO.
Addition of NaBF4 during anodic synthesis of TiO2 nanotube arrays (TNTAs) photocatalyst
and its application for generating hydrogen from glycerolewater solution has been
investigated. The TNTAs were synthesized by anodic oxidation of titanium metal in glycerol
electrolyte solution containing NH4F. During the process, the NaBF4 with different
concentrations were added to the solution. Annealing of the formatted TNTAs were performed
at 500 �C for 3 h under 20% H2 in argon atmosphere, to produce crystalline phase
photocatalyst. FESEM analysis showed that self-organized and well ordered TNTAs have
range of inner diameters, wall thicknesses and lengths approximately 62e130 nm, 27 nm
and 1.53 mm, respectively. FTIR analysis indicated that carbon, nitrogen and boron were
incorporated into the TNTAs lattice. Refer to UVeVis DRS and XRD analysis, the TNTAs
photocatalysts prepared have the band gap range of 2.70e3.10 eV, with mostly have
anatase phase. The NaBF4 addition during synthesis, resulted modified TNTAs that can
reduce the recombination of photo-induced electrons-holes. Photocatalytic hydrogen
production test, from glycerolewater solution, indicated that TNTAs with the addition of
NaBF4 during anodic synthesis process showed higher hydrogen production comparing to
the one without NaBF4 addition. Among them the TNTAs,b (with the addition 5 mM of
NaBF4) showed up to 32% improvement in the hydrogen production and can be considered
as the optimum condition.
Boron(B)-doped TiO2 (BT) materials are synthesized through a simple one-pot process using a sol-gel method, and are employed as anode materials in Li-ion batteries. The increase of B-dopant concentration up to 10.4 wt.% in BT samples increases the interplanar spacing between TiO2 lattices from 3.33 Å to 4.33 Å, and the BET surface area from 27.7 m2 g-1 to 90.6 m2 g-1. Additionally, the BT sample containing a relatively large amount of B possesses cylindrical pores that are favorable for lithium-ion transfer, leading to the highest diffusion coefficient. Consequently, the BT anodes with high B-dopant concentration exhibit significantly-improved cyclic capacities at 100 cycles: 166.9 mAh g-1 at 1C and 119.4 mAh g-1 at 10 C, whereas the non-doped BT sample, TiO2, exhibits 107.7 mAh g-1 at 1C and 19.9 mAh g-1 at 10 C at 100 cycles.
Sol-gel dip-coating was used to grow ZnO thin films doped with
various concentrations of B ranging from 0 to 2.5 at.% on quartz
substrates. The effects of B doping on the absorption coefficient
(α), optical band gap (Eg), Urbach energy
(EU), refractive index (n), refractive index at infinite
wavelength (n∞), extinction coefficient (k),
single-oscillator energy (Eo), dispersion energy
(Ed), average oscillator strength (So), average
oscillator wavelength (λo), moments
M-1 and M-3, dielectric constant
(ɛ), optical conductivity (σ), and electrical resistivity
(ρ) of the BZO thin films were investigated. The transmittance
spectra of the ZnO and BZO thin films show that the transmittance of the
BZO thin films was significantly higher than that of the ZnO thin films
in the visible region of the spectrum and that the absorption edge of
the BZO thin films was blue-shifted. The BZO thin films exhibited higher
Eg, EU, and Eo and lower Ed,
λo, M-1 and M-3
moments, So, n∞, and ρ than the ZnO thin
films.
Highly ordered tungsten doped TiO2 nanotube arrays (W-TiO2NTs) were prepared in glycerol/fluoride electrolyte solution containing sodium tungstate via the electrochemical oxidation of a Ti substrate. The resulting arrays were characterized by XRD, SEM, and XPS. The 15 mM W-TiO2NTs exhibited better photoelectrochemical activity than the TiO2NTs and W-TiO2NTs fabricated using other W concentrations under Xe illumination. The W ion was successfully introduced into the TiO2 crystal lattice in the W6 + form according to the XPS analysis, which enhanced the photoelectrocatalytic activity of the W-TiO2NTs, as indicated by the efficient removal of Rhodamine B and the production of hydrogen.
Boron and phosphor co-doped TiO2 nanotube arrays (BP–TNTs) were prepared in an electrolyte containing triethyl borate and tributyl phosphate via an anodization process on a Ti sheet, and were characterized by the field-emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and UV–Vis diffusion reflectance spectroscopy. The photoelectrochemical properties and photocatalytic activities of obtained-samples were tested under visible light irradiation. The results showed that the photoelectrochemical and photocatalytic activities of B–TNTs, P–TNTs and BP–TNTs were higher than those of pure TiO2 nanotube arrays (TNTs). The synergistic effect of B and P co-doping was absent.
B-doped TiO2 was synthesized by a direct hydrolyzation of n-tetrabutyl titanate in a solution of boric acid, and was treated by hydro-thermal synthesis. The powder was characterized by X-ray diffraction (XRD), FT-IR, scanning and transmission electron microscopy (SEM and TEM), surface photoviolet spectra, UV–visible absorption spectra and X-ray photoelectron spectroscopy (XPS). Rhodamine B (RhB) degradation was used as a probe reaction to evaluate the photocatalytic activity of B-doped TiO2 under simulate sunlight, and excellent photocatalytic performance was achieved.
a b s t r a c t We report a modification of nanostructured WO 3 films by doping with boron. The films were obtained by a direct one-step sol–gel route involving tungstic acid/polyethelene glycol precursor. Raman spec-troscopy and X-ray photoelectron spectroscopy (XPS) showed that the incorporation of boron results in the retention of a substantial amount of water and/or hydroxyl groups in the WO 3 lattice and at the surface of nanoparticles occurring despite high temperature (550 • C) annealing of the films. Another con-sequence of boron doping is the largely increased roughness factor revealed by atomic force microscopy (AFM) imaging. Both kinds of films are highly porous and consist of partly sintered particles with sizes in the range of tens of nanometers. The photoelectrochemical (PEC) studies performed under simulated solar AM 1.5 illumination showed significantly enhanced water oxidation photocurrents for B-WO 3 pho-toanodes, by about 25% higher than those for the undoped WO 3 films of similar thickness. The low extent of recombination of photogenerated charges was confirmed by incident photon-to-current conversion efficiencies (IPCEs) reaching 70% in the region of visible wavelengths at 420 nm. The improved PEC prop-erties were attributed to the increased surface hydroxylation of B-WO 3 nanoparticles favoring water photo-oxidation reaction and to the larger surface area of the film exposed to the electrolyte.
Decoration of TiO2 by metal nanoparticles allows for the fabrication of a new nanocomposite electrode with enhanced performance in photo-electrochemical applications. In this article, we report a facile way to synthesize free-standing, highly orientated TiO2nanotube (TiO2-NT) arrays by a new kind of two-step electrochemical anodization method, and an efficient decoration of uniform sized Agnanoparticles onto the outer and inner surface of TiO2nanotubes through a wetting-thermal decomposition route. In particular, compared with pure TiO2-NT arrays, the testing of nanoelectrode made with Ag/TiO2-NTs composite arrays presents enhanced efficiency in photocatalytic degradation of methylene blue dye and organic pollutant of pentachlorophenol, and improved electrochemical responses as results of the suppression of electron/hole pairs from recombination and acceleration of surface charge transfer by Agnanoparticles.
An efficient photoelectrode is fabricated by sequentially assembled CdS and CdSe quantum dots (QDs) onto a ZnO-nanowire film. As revealed by UV–vis absorption spectrum and scanning electron microscopy (SEM), CdS and CdSe QDs can be effectively adsorbed on ZnO-nanowire array. Electrochemical impedance spectroscopy (EIS) measured demonstrates that the electron lifetime for ZnO/CdS/CdSe (13.8ms) is calculated longer than that of ZnO/CdS device (6.2ms), which indicates that interface charge recombination rate is reduced by sensitizing CdSe QDs. With broader light absorption range and longer electron lifetime, a power conversion efficiency of 1.42% is achieved for ZnO based CdS/CdSe co-sensitized solar cell under the illumination of one Sun (AM 1.5G, 100mWcm−2).
This study investigates the adsorption and reactions of the monomer and dimer of B(OH)3 on a TiO2 anatase (101) surface by first-principles calculations based on the density functional theory and pseudopotential method. On the clean surface, the most stable adsorption structure for B(OH)3 is a molecular monodentate configuration with one hydrogen bonded to a neighboring surface bridging oxygen. The adsorbed B(OH)3 molecule can dissociate into the bidentate adsorption configuration, Ti−OB(OH)O−Ti(a), in which the −OB(OH)O− moiety binds to the surface through two Ti−O bonds with the two dissociated H atoms on neighboring bridged surface oxygen atoms following two successive H migrations. The overall exothermicity is 10.8 kcal/mol; significantly the adsorption energy for Ti−OB(OH)O−Ti(a) with 2 H’s on two O2c surface atoms is 140.1 kcal/mol. In the case of the dimer, there are two identical molecules like the monodentate configuration of B(OH)3 adsorbed on two 5-fold-coordinated Ti atoms of the surface. The Ti−OB(OH)OB(OH)O−Ti binding with 2 H’s on two neighboring O2c surface atoms is very strong like the monomer case, with 150.0 kcal/mol of adsorption energy. Thus, both Ti−OB(OH)O−Ti and Ti−OB(OH)OB(OH)O−Ti adsorbates can be employed as strong linkers between semiconductor quantum dots such as InN and TiO2 nanoparticles. The energeties and mechanisms of these surface reactions have also been explicitly predicted with the computed potential energy surfaces. Most of the B(OH)3 reactions on the anatase surface are exothermic.
The structures and local environments of boron species in B-doped and (B, N)-codoped TiO2 photocatalysts have been investigated by solid-state 11B NMR spectroscopy in conjunction with density functional theory (DFT) calculations. Up to seven different boron sites were identified in the B-doped anatase TiO2, which may be classified into three categories, including interstitial, bulk BO3/2 polymer, and surface boron species, and has been supported by results obtained from FT-IR and XPS spectroscopy as well as from DFT calculations. Two types of interstitial borons, namely the tricoordinated (T*)- and pseudotetrahedral-coordinated (Q*) borons, were observed in addition to the two types of bulk BO3/2 polymer and three types of surface B, in good agreement with experimental data. Further density of state analyses revealed that, compared to undoped TiO2, the T* species in boron-doped TiO2 are solely responsible for the observed increase in energy band gap, whereas the presence of Q* species tend to lead to a decrease in band gap and hence are more favorable for the absorption in the visible-light region. In comparison with B- and N-doped TiO2, (B, N)-codoped TiO2 tends to exhibit a much higher visible-light photocatalytic activity for the oxidation of rhodamine B. Accordingly, a photochemical mechanism of the (B, N)-codoped TiO2 under visible-light irradiation is proposed.
Boron-doped TiO2 nanotube arrays were produced by forming a nanotube-like TiO2 film in an anodization process on a Ti sheet, followed by chemical vapor deposition treatment using trimethyl borate as the boron source with N2 as the carrier gas, and were characterized by ESEM, XPS, XRD, and UV−vis methods. The highly ordered vertically oriented nanotube arrays were obtained, and the nanotubes were open at the top end with an average diameter of approximately 80 nm. Analysis by XPS indicated that the introduced boron was probably incorporated into TiO2 and that the chemical environmental surrounding boron might be Ti−B−O. The boron-doped sample with a mixture of anatase and rutile was identified by X-ray diffraction. A shift of the absorption edge to a lower energy in the spectrum of the UV−vis absorption was observed. Under both UV and 400−620 nm visible light irradiation, the B-doped TiO2 nanotube array electrode exhibited a higher photoconversion efficiency than the non-doped one, a notable photoconversion efficiency of 31.5% was achieved under high-pressure mercury lamp irradiation, and a photoconversion efficiency of 15.1% on the B-doped electrode was obtained under λ > 290 nm light irradiation. The photoelectrocatalytic activity of the prepared electrode was evaluated using pentachlorophenol as a test substance under UV and visible light irradiation.
Highly ordered boron-doped TiO2 nanotube arrays were fabricated via a facile electrodeposition method. X-ray photoelectron spectroscopy (XPS) analysis revealed incorporated B atoms in the lattice of a TiO2 nanotube array. The X-ray diffraction (XRD) spectrum indicated improved crystallinity of boron-doped TiO2 nanotube arrays, relative to undoped TiO2 nanotube arrays. A shift of the absorption edge toward the visible region and a new absorption shoulder (380–510 nm) of boron-doped TiO2 nanotube arrays were observed via diffuse reflectance spectroscopy (DRS). In photoelectrochemical measurements, under either ultraviolet (UV) or visible-light irradiation, the photocurrent conversion efficiency was enhanced because of boron doping. The photoelectrocatalysis of phenol under simulated solar irradiation was performed using boron-doped or undoped TiO2 nanotube arrays, and the kinetic constant of a boron-doped TiO2 nanotube array photoelectrode was increased by ca. 28%, compared to that of an undoped TiO2 nanotube array photoelectrode.
Boron-doped TiO2 nanoparticles were prepared by the sol−gel method and characterized by XRD, TEM, XPS, FT-IR, and UV−vis spectroscopy. XRD results showed that the doping of boron ions could efficiently inhibit the grain growth and facilitate the anatase-to-rutile transformation prior to the formation of diboron trioxide phase. FT-IR and XPS results revealed that the doped boron was present as the form of B3+ in B-doped TiO2 samples, forming a possible chemical environment like Ti−O−B. The lattice parameters at different boron contents and calcination temperatures indicated that B3+ was likely to weave into the interstitial TiO2 structure. The photocatalytic activity of the B-doped TiO2 nanoparticles was evaluated by the photoregeneration of reduced nicotinamide adenine dinucleotide (NADH). All B-doped TiO2 nanoparticles calcined at 500 °C showed higher photocatalytic activity than pure TiO2 sample in the photocatalytic reaction of NADH regeneration under UV light irradiation. When the molar ratio of B to Ti was 5%, the TiO2 nanoparticles could photocatalytically reproduce 94% NADH.
The aim of this review is to offer an overview of the evolution in the use of different anchors (supports) for the immobilisation of a semiconductor photocatalyst, which is titanium dioxide (TiO2). Several supports and immobilisation techniques that are commonly used for the removal of contaminants in wastewater are discussed. Generally, the immobilisation of a photocatalyst onto supporting material has largely been carried out via one of two major routes; physical (the thermal treatment method) route or chemical (the sol–gel method, chemical vapour deposition, electrodeposition, etc.) route. The benefits and drawbacks of various immobilisation techniques to obtain a high surface area TiO2 support are also discussed.
Boron doped TiO2 thin films have been successfully deposited on glass substrate and silicon wafer at 30°C from an aqueous solution of ammonium
hexa-fluoro titanate and boron trifluoride by liquid phase deposition technique. The boric acid was used as an F
− scavenger. The resultant films were characterized by XRD, EDAX, UV and microstructures by SEM. The result shows the deposited
film to be amorphous which becomes crystalline between 400 and 500°C. The EDAX and XRD data confirm the existence of boron
atom in TiO2 matrix and a small peak corresponding to rutile phase was also found. Boron doped TiO2 thin films can be used as photocatalyst for the photodegradation of chlorobenzene which is a great environmental hazard.
It was found that chlorobenzene undergoes degradation efficiently in presence of boron doped TiO2 thin films by exposing its aqueous solution to visible light. The photocatalytic activity increases with increase in the
concentration of boron.
In this work impedance spectroscopy technique was employed in order to characterize the gas-sensing behavior of undoped titanium dioxide (TiO2) polycrystalline thin films. The electrical measurements were performed in a sensor-testing chamber that allows independent control of temperature, pressure, gas composition and flow rate. Frequency measurements, in the range from 40 Hz to 110 MHz, were performed in order to evaluate the gas sensor response of the samples as a function of temperature (50–350 °C) and surrounding atmosphere (vacuum or air at atmospheric pressure). Impedance spectroscopy is a very useful and important technique due to the possibility of using this method for discriminating between grain boundary capacitance (Cgb) and grain boundary resistance (Rgb) contributions. Therefore, a simple model taking into account variations in the intergranular potential barriers is proposed in this work.
The boron-doped TiO2 nanotube arrays were fabricated by potentiostatic anodization of titanium in an aqueous electrolyte containing fluoride ion and sodium fluoroborate (NaBF4). The highly ordered nanotube arrays with an inner pore diameter of approximately 80 nm and a length of 1.4 μm are obtained. X-ray photoelectron spectroscopy (XPS) data indicate that the boron atoms are successfully incorporated into the TiO2 matrix, forming Ti–B–O bond in the sample with small amount of boron (1.5 at.%), and the chemical environment surrounding boron is more similar to that in B2O3 in the samples with larger amounts of boron (3.1 and 3.8 at.%). The B-doped TiO2 nanotube arrays with a mixture of anatase phase and very little rutile phase upon thermal annealing at 500 °C for 2 h were identified by X-ray diffraction (XRD). Red shifts and enhanced absorption intensities in both UV and visible light regions are observed in the spectra of UV–vis absorption of B-doped samples. The B-doped nanotube arrays show improved photochemical capability under both simulated sunlight and UV irradiation. By comparison, the sample with 3.1 at.% of boron exhibits the best photoelectrochemical properties, and its photocurrent densities under simulated sunlight and UV irradiation are approximately 1.17 and 1.27 times of those of TiO2 nanotube arrays, respectively. The visible photoelectrocatalytic (PEC) activities of the prepared electrodes were evaluated using atrazine as a test substance under simulated sunlight irradiation. The kinetic constant of PEC degradation of atrazine using B-doped electrode with 3.1 at.% of boron is 53% higher than that using non-doped one. A synergetic effect of the photocatalytic (PC) and electrochemical (EC) processes is observed.
Synthesis of new boron-containing TiO2 powders (B-TiO2) and their activity under UV and visible light are reported. The catalysts were prepared by the sol-gel method and by grinding anatase powder with a dopant. Boric acid triethyl ester and boric acid were used as boron sources in both catalysts preparation procedures. The photocatalytic activity of obtained powders in UV and visible light was estimated by measuring the decomposition rate of phenol (0.21 mmol/dm(3)) in an aqueous solution. Carbon and boron presence in all prepared photocatalysts was confirmed by the XPS technique. The oxidation state of B atoms incorporated in TiO2 particles was mainly B3+, as determined from the X-ray photoelectron spectra (XPS). It was confirmed that boron-doped TiO2 was activated by visible light and used as effective catalyst in photooxidation reactions.
TiO(2) is one of the most studied compounds in materials science. Owing to some outstanding properties it is used for instance in photocatalysis, dye-sensitized solar cells, and biomedical devices. In 1999, first reports showed the feasibility to grow highly ordered arrays of TiO(2) nanotubes by a simple but optimized electrochemical anodization of a titanium metal sheet. This finding stimulated intense research activities that focused on growth, modification, properties, and applications of these one-dimensional nanostructures. This review attempts to cover all these aspects, including underlying principles and key functional features of TiO(2), in a comprehensive way and also indicates potential future directions of the field.
A nitrogen-doped TiO(2) (N-TiO(2)) photocatalyst was prepared by calcination of the hydrolysis precipitate of Ti(SO(4))(2) with aqueous ammonia. The prepared N-TiO(2) was treated with NH(4)F (F-N-TiO(2)) by an impregnation-calcination method. The photocatalyst (F-N-TiO(2)) was characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR), UV-vis diffusive reflectance spectroscopy (DRS), BET and X-ray photoelectron spectroscopy (XPS). With blue light-emitting diode (LED) as the light source, its photocatalytic activity for the degradation of formaldehyde was investigated. NH(4)F treatment enhances markedly photocatalytic activity of N-TiO(2). The treatment increases the visible absorption of N-TiO(2), decreases its specific surface area and influences the concentration of oxygen vacancies in N-TiO(2). Photocatalytic activity of F-N-TiO(2) depends on the visible absorption, the specific surface area, and the concentration of oxygen vacancies. The preparation conditions, such as the calcination temperature and the initial molar ratio of NH(4)F to N-TiO(2), have a significant influence on the photocatalytic activity. The doping mechanism of NH(4)F was investigated.
Self-organized nitrogen and fluorine co-doped titanium oxide (TiONF) nanotube arrays were created by anodizing titanium foil in a fluoride and ammoniate-based electrolyte, followed by calcination of the amorphous nanotube arrays under a nitrogen protective atmosphere for crystallization. TiONF nanotube arrays were found to have enhanced visible light absorption capability and photodegradation efficiency on methylene blue under visible light illumination over the TiO(2) nanotube arrays. The enhancement was dependent on both the nanotube structural architecture and the nitrogen and fluorine co-doping effect. TiONF nanotube arrays promise a wide range of technical applications, especially for environmental applications and solar cell devices.
Dye-sensitized solar cells consist of a random network of titania nanoparticles that serve both as a high-surface-area support for dye molecules and as an electron-transporting medium. Despite achieving high power conversion efficiencies, their performance is limited by electron trapping in the nanoparticle film. Electron diffusion lengths can be increased by transporting charge through highly ordered nanostructures such as titania nanotube arrays. Although titania nanotube array films have been shown to enhance the efficiencies of both charge collection and light harvesting, it has not been possible to grow them on transparent conducting oxide glass with the lengths needed for high-efficiency device applications (tens of micrometres). Here, we report the fabrication of transparent titania nanotube array films on transparent conducting oxide glass with lengths between 0.3 and 33.0 microm using a novel electrochemistry approach. Dye-sensitized solar cells containing these arrays yielded a power conversion efficiency of 6.9%. The incident photon-to-current conversion efficiency ranged from 70 to 80% for wavelengths between 450 and 650 nm.
To promote efficient use of solar energy, many studies have focused on the modification of TiO2 to extend its spectral response to visible region. Here we report a combined modification of TiO2 by two components: the nonmetal element boron and the metal oxide Ni2O3. The photocatalyst presents high photocatalytic activity in the visible region, which can efficiently degrade and mineralize toxic organic pollutants such as trichlorophenol (TCP), 2,4-dichlorophenol (2,4-DCP), and sodium benzoate. The dechlorination and mineralization results indicate the photocatalytic pathway via visible light excitation. The study demonstrates that the modification of TiO2 both to extend its spectral response to the visible region and to improve its catalytic efficiency can be achieved by doping with boron, a nonmetal, and Ni2O3, a metal oxide.
The photocatalytic splitting of water into hydrogen and oxygen using solar light is a potentially clean and renewable source for hydrogen fuel.(1,2) There has been extensive investigation into metal-oxide semiconductors such as TiO(2), WO(3), and Fe(2)O(3), which can be used as photoanodes in thin-film form.(3-5) Of the materials being developed for photoanodes, TiO(2) remains one of the most promising because of its low cost, chemical inertness, and photostability.(6) However, the widespread technological use of TiO(2) is hindered by its low utilization of solar energy in the visible region. In this study, we report the preparation of vertically grown carbon-doped TiO(2) (TiO(2-x)C(x)) nanotube arrays with high aspect ratios for maximizing the photocleavage of water under white-light irradiation. The synthesized TiO(2-x)C(x) nanotube arrays showed much higher photocurrent densities and more efficient water splitting under visible-light illumination (> 420 nm) than pure TiO(2) nanotube arrays. The total photocurrent was more than 20 times higher than that with a P-25 nanoparticulate film under white-light illumination.
We describe the use of highly ordered transparent TiO(2) nanotube arrays in dye-sensitized solar cells (DSCs). Highly ordered nanotube arrays of 46-nm pore diameter, 17-nm wall thickness, and 360-nm length were grown perpendicular to a fluorine-doped tin oxide-coated glass substrate by anodic oxidation of a titanium thin film. After crystallization by an oxygen anneal, the nanotube arrays are treated with TiCl(4) to enhance the photogenerated current and then integrated into the DSC structure using a commercially available ruthenium-based dye. Although the negative electrode is only 360-nm-thick, under AM 1.5 illumination the generated photocurrent is 7.87 mA/cm(2), with a photocurrent efficiency of 2.9%. Voltage-decay measurements indicate that the highly ordered TiO(2) nanotube arrays, in comparison to nanoparticulate systems, have superior electron lifetimes and provide excellent pathways for electron percolation. Our results indicate that remarkable photoconversion efficiencies may be obtained, possibly to the ideal limit of approximately 31% for a single photosystem scheme, with an increase of the nanotube-array length to several micrometers.
Boron- and cerium-codoped TiO2 photocatalysts were synthesized using modified sol-gel reaction process and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), particle size distribution (PSD), diffuse reflectance spectra (DRS), and Brunauer-Emmett-Teller (BET). The photocatalytic activities were evaluated by monitoring the degradation of dye Acid Red B (ARB). The results showed that the prepared photocatalysts were mixed oxides mainly consisting of titania, ceria, and boron oxide. The structure of TiO2 could be transformed from amorphous to anatase and then to rutile by increasing calcination temperature; the transformation being accompanied by the growth of particle size without any obvious change in phase structure of CeO2. The XPS of B(1.6)Ce(1.0)-TiO2 prepared at 500 degrees C showed that a few boron atoms were incorporated into titania and ceria lattice, whereas others existed as B2O3. Cerium ions existed in two states, Ce3+ and Ce4+, and the atomic ratio of Ce3+/Ce4+ was 1.86. When boron and cerium were doped, the UV-Vis adsorption band wavelength showed an obvious shift toward the visible range (< or =526 nm). As the atomic ratio of Ce/Ti increased to 1.0, the absorbance edge wavelength increased to 481 nm. The absorbance edge wavelength decreased for higher cerium doping levels (Ce/Ti = 2.0). The particles size ranged from 122 to 255 nm with a domain at 168 nm (39.4%). The degradation of ARB dye indicated that the photocatalytic activities of boron- and cerium-codoped TiO2 were much higher than those of P25 (a standard TiO2 powder). The activities increased as the boron doping increased, whereas decreased when the Ce/Ti atomic ratio was greater than 0.5. The optimum atomic ratio of B/Ti and Ce/Ti was 1.6 and 0.5, respectively.
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