C-, N-, S-, and F-Doped Anatase TiO2 (101) with Oxygen Vacancies: Photocatalysts Active in the Visible Region

Anatase TiO2 presents a large bandgap of 3.2 eV, which inhibits the use of visible light radiation (λ > 387 nm) for generating charge carriers. We studied the activation of TiO2 (101) anatase with visible light by doping with C, N, S, and F atoms. For this purpose, density functional theory and the Hubbard U approach are used. We identify two ways for activating the TiO2 with visible light. The first mechanism is broadening the valence or conduction band; for example, in the S-doped TiO2 (101) system, the valence band is broadened. A similar process can occur in the conduction band when the undercoordinated Ti atoms are exposed on the TiO2 (101) surface. The second mechanism, and more efficient for activating the anatase, is to generate localized states in the gap: N-doping creates localized empty states in the bandgap. For C-doping, the surface TiO2 (101) presents a “cleaner” gap than the bulk TiO2, resulting in fewer recombination centers. The dopant valence electrons determine the number and position of the localized states in the bandgap. The formation of charge carriers with visible light is highly favored by the oxygen vacancies on TiO2 (101). The catalytic activity of C-doping using visible radiation can be explained by its high absorption intensity generated by oxygen vacancies on the surface. The intensity of the visible absorption spectrum of doped TiO2 (101) follows the order: C > N > F > S dopant.

Download Full-text

Visible-light photocatalysis on C-doped ZnO derived from polymer-assisted pyrolysis

RSC Advances ◽

10.1039/c4ra17227b ◽

2015 ◽

Vol 5 (35) ◽

pp. 27690-27698 ◽

Cited By ~ 93

Author(s):

Ahmad S. Alshammari ◽

Lina Chi ◽

Xiaoping Chen ◽

Abdulaziz Bagabas ◽

Denis Kramer ◽

...

Keyword(s):

Photocatalytic Activity ◽

Visible Light ◽

Light Absorption ◽

Oxygen Vacancies ◽

Charge Carriers ◽

Visible Light Photocatalysis ◽

Visible Light Absorption ◽

C Doping ◽

Doped Zno

Heavy C-doping can effectively enhance visible-light absorption yet exhibited lower visible-light-responsive photocatalytic activity due to significant recombination of photogenerated charge carriers caused by C-dopant and oxygen vacancies.

Download Full-text

First–Principles Investigation of the Structural, Elastic, Electronic, and Optical Properties of α– and β–SrZrS3: Implications for Photovoltaic Applications

Materials ◽

10.3390/ma13040978 ◽

2020 ◽

Vol 13 (4) ◽

pp. 978

Author(s):

Henry Igwebuike Eya ◽

Esidor Ntsoenzok ◽

Nelson Y. Dzade

Keyword(s):

Optical Properties ◽

First Principles ◽

Density Functional ◽

Visible Region ◽

Charge Carriers ◽

Band Gaps ◽

Strong Light ◽

Electronic And Optical Properties ◽

Optical Absorbance ◽

Effective Masses

Transition metal perovskite chalcogenides are attractive solar absorber materials for renewable energy applications. Herein, we present the first–principles screened hybrid density functional theory analyses of the structural, elastic, electronic and optical properties of the two structure modifications of strontium zirconium sulfide (needle–like α–SrZrS3 and distorted β–SrZrS3 phases). Through the analysis of the predicted electronic structures, we show that both α– and β–SrZrS3 materials are direct band gaps absorbers, with calculated band gaps of 1.38, and 1.95 eV, respectively, in close agreement with estimates from diffuse–reflectance measurements. A strong light absorption in the visible region is predicted for the α– and β–SrZrS3, as reflected in their high optical absorbance (in the order of 105 cm−1), with the β–SrZrS3 phase showing stronger absorption than the α–SrZrS3 phase. We also report the first theoretical prediction of effective masses of photo-generated charge carriers in α– and β–SrZrS3 materials. Predicted small effective masses of holes and electrons at the valence, and conduction bands, respectively, point to high mobility (high conductivity) and low recombination rate of photo-generated charge carriers in α– and β–SrZrS3 materials, which are necessary for efficient photovoltaic conversion.

Download Full-text

Phase transition-induced band edge engineering of BiVO4 to split pure water under visible light

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1509674112 ◽

2015 ◽

Vol 112 (45) ◽

pp. 13774-13778 ◽

Cited By ~ 52

Author(s):

Won Jun Jo ◽

Hyun Joon Kang ◽

Ki-Jeong Kong ◽

Yun Seog Lee ◽

Hunmin Park ◽

...

Keyword(s):

Phase Transition ◽

Visible Light ◽

Band Gap ◽

Conduction Band ◽

Density Functional ◽

Density Functional Theory Calculation ◽

Pure Water ◽

Volume Growth ◽

Band Edge ◽

Conduction Band Edge

Through phase transition-induced band edge engineering by dual doping with In and Mo, a new greenish BiVO4 (Bi1-XInXV1-XMoXO4) is developed that has a larger band gap energy than the usual yellow scheelite monoclinic BiVO4 as well as a higher (more negative) conduction band than H+/H2 potential [0 VRHE (reversible hydrogen electrode) at pH 7]. Hence, it can extract H2 from pure water by visible light-driven overall water splitting without using any sacrificial reagents. The density functional theory calculation indicates that In3+/Mo6+ dual doping triggers partial phase transformation from pure monoclinic BiVO4 to a mixture of monoclinic BiVO4 and tetragonal BiVO4, which sequentially leads to unit cell volume growth, compressive lattice strain increase, conduction band edge uplift, and band gap widening.

Download Full-text

Femtosecond Spectroscopy of Au Hot-Electron Injection into TiO2: Evidence for Au/TiO2 Plasmon Photocatalysis by Bactericidal Au Ions and Related Phenomena

Nanomaterials ◽

10.3390/nano9020217 ◽

2019 ◽

Vol 9 (2) ◽

pp. 217 ◽

Cited By ~ 11

Author(s):

Marina Radzig ◽

Olga Koksharova ◽

Inessa Khmel ◽

Vladimir Ivanov ◽

Khursand Yorov ◽

...

Keyword(s):

Visible Light ◽

Tio2 Nanoparticles ◽

Conduction Band ◽

Light Absorption ◽

Au Nanoparticles ◽

Visible Region ◽

Electron Injection ◽

Femtosecond Spectroscopy ◽

Hot Electron ◽

Resonance Band

In the present work, we provide evidence for visible light irradiation of the Au/TiO2 nanoparticles’ surface plasmon resonance band (SPR) leading to electron injection from the Au nanoparticles to the conduction band of TiO2. The Au/TiO2 SPR band is shown to greatly enhance the light absorption of TiO2 in the visible region. Evidence is presented for the light absorption by the Au/TiO2 plasmon bands leading to the dissolution of Au nanoparticles. This dissolution occurs concomitantly with the injection of the hot electrons generated by the Au plasmon into the conduction band of TiO2. The electron injection from the Au nanoparticles into TiO2 was followed by femtosecond spectroscopy. The formation of Au ions was further confirmed by the spectral shift of the transient absorption spectra of Au/TiO2. The spectral changes of the SPR band of Au/TiO2 nanoparticles induced by visible light were detected by spectrophotometer, and the morphological transformation of Au/TiO2 was revealed by electron microscopy techniques as well. Subsequently, the fate of the Au ions was sorted out during the growth and biofilm formation for some selected Gram-negative bacteria. This study compares the bactericidal mechanism of Au ions and Ag ions, which were found to be substantially different depending on the selected cell used as a probe.

Download Full-text

Contrasting Photo-Switching Rates in Azobenzene Derivatives: How the Nature of the Substituent Plays a Role

Polymers ◽

10.3390/polym12051019 ◽

2020 ◽

Vol 12 (5) ◽

pp. 1019

Author(s):

Domenico Pirone ◽

Nuno A. G. Bandeira ◽

Bartosz Tylkowski ◽

Emily Boswell ◽

Regine Labeque ◽

...

Keyword(s):

Visible Light ◽

Smart Materials ◽

Density Functional ◽

Molecular Design ◽

Visible Region ◽

Building Blocks ◽

Stimuli Responsive ◽

Order Of Magnitude ◽

Azo Derivatives ◽

Commercial Polymers

A molecular design approach was used to create asymmetrical visible light-triggered azo-derivatives that can be good candidates for polymer functionalization. The specific electron–donor substituted molecules were characterized and studied by means of NMR analyses and UV-visible spectroscopy, comparing the results with Time Dependent Density Functional (TD-DFT) calculations. A slow rate of isomerization (ki = 1.5 × 10−4 s−1) was discovered for 4-((2-hydroxy-5methylphenyl) diazenyl)-3-methoxybenzoic acid (AZO1). By methylating this moiety, it was possible to unlock the isomerization mechanism for the second molecule, methyl 3-methoxy-4-((2-methoxy-5-methylphenyl) diazenyl)benzoate (AZO2), reaching promising isomerization rates with visible light irradiation in different solvents. It was discovered that this rate was heightened by one order of magnitude (ki = 3.1 × 10−3 s−1) for AZO2. A computational analysis using density functional (DFT/PBE0) and wavefunction (QD-NEVPT2) methodologies provided insight into the photodynamics of these systems. Both molecules require excitation to the second (S2) excited state situated in the visible region to initiate the isomerization. Two classic mechanisms were considered, namely rotation and inversion, with the former being energetically more favorable. These azo-derivatives show potential that paves the way for future applications as building blocks of functional polymers. Likewise, they could be really effective for the modification of existing commercial polymers, thus transferring their stimuli responsive properties to polymeric bulky structures, converting them into smart materials.

Download Full-text

ELECTRONIC STRUCTURES OF S-DOPED ANATASE AND RUTILE TiO2

Journal of Theoretical and Computational Chemistry ◽

10.1142/s0219633607002903 ◽

2007 ◽

Vol 06 (01) ◽

pp. 23-32 ◽

Cited By ~ 5

Author(s):

XIN-GUO MA ◽

CHAO-QUN TANG ◽

XIAO-HUA YANG

Keyword(s):

Photocatalytic Activity ◽

Visible Light ◽

Valence Band ◽

Visible Light Irradiation ◽

Electronic Structures ◽

Density Functional ◽

Visible Region ◽

Light Irradiation ◽

Band Shift ◽

Deep Impurity

The electronic structures of S -doped TiO 2 have been carried out by first-principles calculations based on density functional theory with plane-wave ultrasoft pseudopotential method. Comparing anion doping with cation doping in anatase and rutile, we found different energy band structures and origins of photoactivity of S -doped TiO 2. For anion-doped TiO 2, new S –3p bands appear and which lie slightly above the top of the O –2p valence band. It plays a significant role in increasing absorbance in the visible region, resulting in improvement in photocatalytic activity under visible-light irradiation. For cation-doped TiO 2, the potential of the O –2p valence band shift much downwards, yielding the stronger oxidative power than that of undoped and S anion-doped TiO 2. Nevertheless, the deep impurity states in BG (bond gap) that originate from the S -dopant have negative effects on the recombination of the photoexcited electrons and holes. From our calculated results, we can explain their differences in photocatalytic activity under visible-light irradiation.

Download Full-text

Rendering Visible-Light Photocatalytic Activity to Undoped ZnO via Intrinsic Defects Engineering

Catalysts ◽

10.3390/catal10101163 ◽

2020 ◽

Vol 10 (10) ◽

pp. 1163

Author(s):

Lan-li Chen ◽

Bao-gai Zhai ◽

Yuan Ming Huang

Keyword(s):

Photocatalytic Activity ◽

Methyl Orange ◽

Visible Light ◽

Density Functional Calculations ◽

Density Functional ◽

Oxygen Vacancies ◽

Intrinsic Defect ◽

Visible Light Photocatalytic Activity ◽

Zno Nanocrystals ◽

Visible Light Photocatalytic

It is significant to render visible-light photocatalytic activity to undoped ZnO nanostructures via intrinsic defect engineering. In this work, undoped ZnO nanocrystals were derived via co-precipitation synthesis. The resulting ZnO nanocrystals were characterized by means of X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy, and ultraviolet-visible absorption spectroscopy, respectively. The visible-light photocatalytic activity of the products were characterized by monitoring the decomposition of methyl orange in water under visible-light illumination of a 300 W halogen lamp. It is found that undoped ZnO nanocrystals exhibit visible-light photocatalytic activity with their first-order rate constant up to 4.6 × 10−3 min−1. Density functional calculations show that oxygen vacancies create deep energy levels at EV + 0.76 eV in the bandgap of ZnO. In conjunction with the density functional calculations, the photocatalytic degradation of methyl orange under visible-light irradiation provides direct evidence that oxygen vacancies in ZnO nanocrystals yield the visible-light photocatalytic activity. Our results demonstrate that visible-light photocatalytic activity can be endowed to undoped ZnO nanocrystals by manipulating the intrinsic defects in ZnO. Intrinsic defect-modulated ZnO photocatalysts thus represent a powerful configuration for further development toward visible-light responsive photocatalysis.

Download Full-text

DFT Study of Se and Te Doped SrTiO 3 for Enhanced Visible-Light Driven Phtocatalytic Hydrogen Production

10.21203/rs.3.rs-415517/v1 ◽

2021 ◽

Author(s):

Hakim BENTOUR ◽

Mourad Boujnah ◽

Mohamed Houmad ◽

Mourad El Yadari ◽

Abdelilah BENYOUSSEF ◽

...

Keyword(s):

Visible Light ◽

Band Gap ◽

Water Splitting ◽

Density Functional ◽

Hydrogen Generation ◽

Visible Region ◽

Solar Spectrum ◽

Photogenerated Electron ◽

Generalized Gradient ◽

Light Activity

Abstract The pure STiO3 has been experimentally demonstrated to catalyze H2 production using water splitting, but the reaction can only be driven by Ultraviolet (UV) radiation due to the large band gap of SrTiO3. This motivated us to search efficient strategy to tune its band gap, so that it can function in the visible region of the solar spectrum. In this study, the electronic, optical and photocatalytic properties of Se-doped, and Te-doped SrTiO3 has been investigated using density functional theory (DFT) within the generalized gradient approximation (GGA). Our results reveal that the effect of doping can lead to band gap narrowing without introducing any isolated mid-gap states. This improves greatly the visible light activity of SrTiO3 and depresses the recombination of photogenerated electron-hole pairs. Furthermore, the locations of calculated band edges relative to the water reduction and oxidation levels for doped systems meet the water-splitting requirements. Consequently, our results show that the performance of SrTiO3 for hydrogen generation by photocatalytic water splitting is significantly enhanced with Se and Te doping. In particular, Te doping can enhance greatly the visible light photocatalytic activity of SrTiO3. We expect this study can provide a theoretical basis for a prospective experimental works.

Download Full-text

Defect-Pairs of Titanium and Carbon in Iron Oxide Film for Efficient Visible Light Driven Water Splitting

ECS Meeting Abstracts ◽

10.1149/ma2018-01/31/1910 ◽

2018 ◽

Vol MA2018-01 (31) ◽

pp. 1910-1910

Author(s):

Il Yong Choi ◽

Donghun Kim ◽

Tae Hwa Jeon ◽

Byeong-Gyu Chae ◽

Kug-Seung Lee ◽

...

Keyword(s):

Iron Oxide ◽

Electrical Properties ◽

Visible Light ◽

Water Splitting ◽

Density Functional ◽

Photocurrent Density ◽

Band Alignment ◽

Charge Carriers ◽

Charge Carrier Density ◽

Pec Water Splitting

Solar-powered photoelectrochemical (PEC) water splitting has been a promising candidate for producing hydrogen in a clean and renewable way. Photoelectrodes are key components in PEC cells for efficient and stable hydrogen generation because they play crucial roles in absorption of photons, the separation and transportation of photo-generated charge carriers, as well as the chemical reactions with water. A variety of metal oxides for efficient photoelectrode have been intensively explored, but it is still challenging to find desirable materials to satisfy lots of requirements for PEC water splitting. Iron oxide (hematite, Fe2O3) has recently attracted much attention due to its earth abundance, low cost as well as desirable material properties for PEC water oxidation including narrow band gap energy of 2.0~2.2eV for visible light absorption and proper energy band alignment, etc. However, Fe2O3 has very short hole diffusion length and low carrier mobility, which causes considerable recombination of photo-generated electrons and holes. A lot of approaches such as nanostructures, heterojunction with other materials, surface modification, etc. have been reported to prevent the recombination of charge carriers and improve electrical properties of Fe2O3; however, these require complex manufacturing processes. In the present work, we found a much simpler way to improve the electrical properties of Fe2O3 film, namely defect-pairs due to co-doping. Titanium (Ti) and carbon (C) co-doped thin Fe2O3 film (i.e. (Ti,C)-Fe2O3) has been realized via a combination of simple solution-based spin-coating and tube furnace annealing process. This film turns out to lead significantly enhanced PEC performance when used as a photoanode: an impressively high photocurrent density of more than 4.5mAcm-2 was achieved at 1.23VRHE under AM1.5G solar spectrum and 1 sun illumination. This is compared to the value of Ti-doped Fe2O3 film, which is only about 2.6mAcm-2 photocurrent density at 1.23VRHE even though the optical properties of each film are similar. The origin for such substantial enhancement was revealed using a series of experimental and computational spectroscopies. X-ray absorption spectroscopy, electrochemical impedance measurements and density-functional-theory calculations both indicate that C atoms can be more deeply and heavily doped under the existence of Ti dopants in Fe2O3 film and then the defect-pairs of Ti and C increase not only charge carrier density but also electron’s mobility. An emphasis should be placed on the fact that this achievement was not assisted by co-catalysts and complex nanostructuring methods; hence even higher performance is expected when the film is further treated with extra-cares.

Download Full-text

Theoretical insights of codoping to modulate electronic structure of $$\hbox {TiO}_2$$ and $$\hbox {SrTiO}_3$$ for enhanced photocatalytic efficiency

Scientific Reports ◽

10.1038/s41598-020-72195-0 ◽

2020 ◽

Vol 10 (1) ◽

Cited By ~ 1

Author(s):

Manish Kumar ◽

Pooja Basera ◽

Shikha Saini ◽

Saswata Bhattacharya

Keyword(s):

Electronic Structure ◽

Visible Light ◽

Band Gap ◽

Density Functional ◽

Low Cost ◽

Visible Region ◽

Photocatalytic Efficiency ◽

Large Shift ◽

Realistic Condition ◽

Charged Defects

Abstract $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 are well known materials in the field of photocatalysis due to their exceptional electronic structure, high chemical stability, non-toxicity and low cost. However, owing to the wide band gap, these can be utilized only in the UV region. Thus, it’s necessary to expand their optical response in visible region by reducing their band gap through doping with metals, nonmetals or the combination of different elements, while retaining intact the photocatalytic efficiency. We report here, the codoping of a metal and a nonmetal in anatase $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 for efficient photocatalytic water splitting using hybrid density functional theory and ab initio atomistic thermodynamics. The latter ensures to capture the environmental effect to understand thermodynamic stability of the charged defects at a realistic condition. We have observed that the charged defects are stable in addition to neutral defects in anatase $$\hbox {TiO}_2$$ TiO 2 and the codopants act as donor as well as acceptor depending on the nature of doping (p-type or n-type). However, the most stable codopants in $$\hbox {SrTiO}_3$$ SrTiO 3 mostly act as donor. Our results reveal that despite the response in visible light region, the codoping in $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 cannot always enhance the photocatalytic activity due to either the formation of recombination centers or the large shift in the conduction band minimum or valence band maximum. Amongst various metal-nonmetal combinations, $$\hbox {Mn}_\text {Ti}\hbox {S}_\text {O}$$ Mn Ti S O (i.e. Mn is substituted at Ti site and S is substituted at O site), $$\hbox {S}_\text {O}$$ S O in anatase $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {Mn}_\text {Ti}\hbox {S}_\text {O}$$ Mn Ti S O , $$\hbox {Mn}_\text {Sr}\hbox {N}_\text {O}$$ Mn Sr N O in $$\hbox {SrTiO}_3$$ SrTiO 3 are the most potent candidates to enhance the photocatalytic efficiency of anatase $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 under visible light irradiation.

Download Full-text