Valence Band Of TiO2 Research Articles

Rational design of nitrogen and carbon co-decorated mesoporous TiO2 composites for photocatalytic selective oxidation of alcohols

Photocatalytic organic synthesis has attracted much attention in recent years. Herein, a N and C co-decorated mesoporous TiO2 (mp-NCT) photocatalyst was synthesized for selective oxidation of alcohols. Notably, the as-prepared mp-NCT composites possess large specific surface areas and mesoporous structures, which could provide sufficient active sites and improve mass transfer. Furthermore, the co-doping of N and C species could not only extend the light absorption, but also tune the valence band of TiO2. Meanwhile, numerous oxygen vacancies and intra-band could be introduced, which helps to reduce the combination of the photogenerated carriers. As a result, the mp-NCT composites show excellent photocatalytic performance towards selective oxidation of benzyl alcohol and its derivatives to corresponding aldehydes under simulated sunlight irradiation. Mechanism studies revealed that the photogenerated electrons, holes and high dynamic equilibrium concentration of O2•- radicals were responsible for the efficient conversion of alcohols to aldehydes.

Polymer blending and nanophotocatalyst loading synergy in visible light‐driven photocatalytic PES/SPSf mixed matrix membranes

AbstractThe synergy of polymer blending and loading photocatalytic titania–amorphous carbon nanotubes (TiO2–aCNT) in tailoring the morphological, surface, and optoelectrical properties of membranes is investigated. High energy band gap (Eg) polyethersulfone (PES), and low Eg sulfonated polyethersulfone (SPSf) polymer blends were loaded with TiO2–aCNT nanocomposite fillers. SEM reveals membranes consisting of a selective layer, a dense sublayer and a spongy layer with the latter two consisting of a network of nanofibers whose diameters decrease with increasing TiO2–aCNT loading. The downshifting in the wavenumbers of sulfonyl and sulfone peaks in Fourier transform infrared and Raman spectra confirms bonding of TiO2–aCNT with PES/SPSf via these groups. Blending PES with SPSf decreases the Eg of the membranes while loading TiO2–aCNT produces a second band edge corresponding to = 2.8 eV. Suppression of charge recombination in membranes is realized at 1.2 filler wt.%. Charge separation occurrs via shuttling of the positive holes to the aCNTs and valence band of TiO2 while electrons are shuttled to the conduction bands of PES and SPSf. Electron impedance spectroscopy shows TiO2–aCNT loading reduces polymer membrane resistance to charge transport. Dye degradation up to 85% is realized under direct sunlight irradiation accompanied by mineralization.

Study on the treatment of oily wastewater with non equilibrium plasma synergistic catalysts

Petroleum is currently a highly demanded power fuel, but oil fields produce oily wastewater during production. If not treated in a timely manner, it can cause serious ecological problems. To solve this issue, this article utilizes the non-equilibrium plasma generated by Dielectric Barrier Discharge (DBD) technology to treat diesel simulated oily wastewater under the synergistic effect of AC/Mn + TiO2 catalyst. The results indicate that: After 180 min of DBD treatment, the degradation rates of diesel and Tween-80 were 60.9% and 53.2%, respectively; after 180 min of synergistic DBD treatment with AC/Mn + TiO2 catalyst, the degradation rates of diesel and Tween-80 were 76.0% and 71.7%, respectively, with a significant increase in degradation rates. The SEM characterization of the catalyst before and after the reaction was compared, and it was found that the surface of the crystal after the reaction was smooth. XPS characterization showed that Mn electron migration leads to the generation of positively charged holes on the valence band of TiO2. These all demonstrate that the synergistic effect of DBD and catalyst promotes the degradation of oily wastewater.

Localized surface plasmon resonance effect of bismuth nanoparticles in Bi/TiO2 catalysts for boosting visible light-driven CO2 reduction to CH4

Herein, the photocatalysts of metallic Bi-modified TiO2 microsphere (namely BTO) were synthesized by one-pot solvothermal method. The localized surface plasmon resonance (LSPR) effect of introduced metallic Bi nanoparticles is beneficial to improve the absorption efficiency for visible light, and its surface hot electrons can donate to the valence band of TiO2 for boosting the separation efficiency of light generated electron-hole pairs. BTO catalysts exhibit the super catalytic activity for visible light-driven CO2 reduction with H2O to CH4. The formation amount and selectivity of CH4 product over BTO-2 catalyst are 49.12 μmol g−1 and 85.48 % for 4 h, respectively. Based on the results of in-situ DRIFTS and density functional theory calculation, the mechanism for photocatalytic CO2 reduction is proposed: the visible light-driven LSPR effect on BTO catalyst can boost the key step of CO2* -to-HCO* for promoting selective generation of CH4 product. It inspires the design of efficient photocatalysts for CO2 conversion.

Doping TiO2 with sludge-derived activated carbon by UV light irradiation method: Molecular dynamic simulation and experimental study

Sludge-derived activated carbon (SDAC) is prepared from sewage sludge and can be used to treat pollutants. SDAC can also be used to dope catalytic materials to improve their pollutant degradation ability. However, there needs to be more research on doping TiO2 with SDAC. In this study, TiO2 was doped with SDAC by Ultraviolet light irradiation method under room temperature. The doping process saved a large amount of energy. The TiO2 doped with SDAC had the ability to degrade dyes under visible light. The results showed that the removal rates of SDAC-doped TiO2 for methyl orange (MO) and methylene blue (MB) were over 90% and 94% under visible light conditions. After five cycles, the removal rate of MO was 75%, while the removal rate of MB decreased to 45%. Molecular dynamics simulation results showed that the valence band and conduction band of SDAC-doped TiO2 shifted downward, and three apparent impurity levels appeared near the Fermi level after SDAC doping.

Photocatalytic hydrogen production from seawater by TiO2/RuO2 hybrid nanofiber with enhanced light absorption

Compared to hydrogen production through pure water photocatalysis, the direct utilization of seawater for hydrogen production aligns better with the principles of sustainable development. Seawater, however, contains impurity ions like Na+ and Cl−, which pose higher demands on photocatalysts. It is widely acknowledged that RuO2 and TiO2 demonstrate excellent stability in seawater. Consequently, this study focuses on the model system of RuO2-modified TiO2 for investigating hydrogen production in simulated seawater. TiO2/RuO2 nanofibers (NFs) were synthesized via a one-step electrospinning method, ensuring intimate contact between the two components. The hydrogen production activity of TiO2/RuO2 NFs in simulated seawater nearly matches that in pure water. Remarkably, RuO2 serves as an oxidation cocatalyst, effectively scavenging holes from the valence band of TiO2 and enhancing the separation efficiency of electrons and holes. Interestingly, Cl− ions, similar to RuO2, contribute to reducing excess holes. This study lays the groundwork for future research into hydrogen production from seawater.

Effect of thiophene rings rigidity on dye-sensitized solar cell performance. Dithienothiophene versus terthiophene as [formula omitted] donor moiety

Solar cells are fabricated based on two new dyes. Dye acts as an additive to thin layer interface. The effect of the π-conjugated rigidity of the thiophene rings on the photovoltaic characteristics has been investigated. The structures of the dye 1 was based on dithieno [3,2-b:2′,3′-d] thiophene-2-cyanoacrylic acid, while dye 2 was based on [2,2':5′,2″-terthiophene]-5-cyanoacrylic acid and were confirmed by elemental analysis, mass spectrometry, 1H NMR and 13C NMR spectral data. The P3HT/dye 1/nc-TiO2 solar cell produced the highest efficiency of 0.3 % with an open circuit voltage of 0.7 V compared to dye 2 solar cell. This has been attributed to the difference in energy levels of the dyes and location of their HOMO relative to conduction and valence bands of nc-TiO2. The dye 1 has rigid fused thiophene rings and its HOMO is located between valence band of TiO2 and HOMO of P3HT which leads to improve the charge carrier separation and increase the current density to reach 1.2 mA/cm2.

A theoretical exploration of catechol sensitization of C-doped bronze TiO2 surfaces for photochemical systems

Doping with atom impurities is currently an attractive mechanism to enhance the optical absorption capacity of TiO2 and other inorganic oxide semiconductors. In this work, the electronic and optical properties of carbon-doped TiO2(B) (100) ultrathin surfaces were investigated using density functional theory (DFT) calculations, with the aim of evaluating their potential as photoelectrode for dye-sensitized solar cells (DSSCs). Carbon impurities were introduced onto oxygen sites located in the proximity of the surface and catechol was employed as a sensitizer model, focusing our study mainly on the evolution of the semiconductor’s electronic structure. The reduction of the band gap energy resulting from impurity states within the valence band of C-doped TiO2(B) was confirmed. Moreover, our findings suggest that C doping not only induces a stronger interaction between the catechol molecule and the surface but also, could increase the light absorption capacity of the material. Thus, carbon-doped TiO2(B) could act as a promising semiconductor for DSSCs and other photochemical systems.

Enhanced photocatalytic hydrogen production of S-scheme TiO2/g-C3N4 heterojunction loaded with single-atom Ni

S-scheme heterostructure photocatalysts can achieve highly efficient solar energy utilization. Here, single-atom Ni species were deposited onto TiO2/g-C3N4 (TCN) composite photocatalyst with an S-scheme heterojunction for highly efficient photocatalytic water splitting to produce hydrogen. Under solar irradiation, it realized the hydrogen production activity of 134 µmol g–1 h–1, about 5 times higher than the TCN without atomic Ni. In-situ Kelvin probe force microscopy characterization and the density functional calculation certify that by forming the S-scheme heterojunction, the photo-excited electrons from the TiO2 combine with the photogenerated holes at the coupled g-C3N4 driven by a built-in electric field. More importantly, the single-atom Ni species stabilized the photogenerated electrons from the g-C3N4 could effectively enhance the charge separation between the holes on the valence band of TiO2 and electrons at the conduction band of g-C3N4. Meanwhile, the Ni atoms act as the surface catalytic centers for the water reduction reaction, which greatly improves the reactivity of the photocatalyst. The present work provides a new approach for developing noble metal-free heterojunctions for high-efficiency photocatalysis.

Ti3C2 MXene-induced interface charge transferred in Z-scheme heterojunction for efficient photocatalytic removal of nitric oxide

Currently, NO pollution is an urgent challenge for us to face, and photocatalytic degradation has been recognized as one of the most promising methods to reduce it. As a representative photocatalyst, g-C3N4 has attracted researchers because of its low cost and excellent performance. In this work, a new triphasic Z-scheme heterostructure was built, TiO2/Ti3C2 MXene/g-C3N4, to improve the visible-light irradiation-induced NO removal efficiency of g-C3N4. In this Z-scheme heterostructure, Ti3C2 MXene could form a directional electron transfer thoroughfare between g-C3N4 and TiO2 to accelerate the electronic transmission rate, meanwhile, due to the specificity of the band structure, electrons on conduction band of g-C3N4 and holes on valence band of TiO2 can be well separated and react with the adsorbed species to achieve good photocatalytic performance. Because of the triphasic heterostructure formed by TiO2, Ti3C2 MXene and g-C3N4, the efficiency of this compound for visible-light irradiation-induced NO removal improves from 32% to 56%. This work provides a new strategy to improve NO removal efficiency and shows a broader application prospect of photocatalysts with a triphasic structure.

Density functional theory of Ca/F co-doped anatase TiO2

In order to understand the improved photocatalytic activity of Ca/F co-doped TiO2, the lattice parameters, energy band structures, density of states and absorption spectra of pure, Ca doped, F doped and Ca/F co-doped anatase TiO2 were calculated by first principles based on the density functional theory. It was found that the doping can result in lattice distortion of TiO2, especially the biggest lattice distortion was generated by the Ca/F co-doping. The forbidden energy band width of anatase TiO2 was broadened by Ca or F doping, while it was reduced by Ca/F co-doping. The calculated electronic density of states indicated that Ca doping provided contribution to the valence band of TiO2, and F doping resulted in the highest energy level occupied by electrons appeared in the conduction band. The energy band of TiO2 almost kept unchanged after Ca/F co-doping except the reduction of forbidden band width. Therefore, the experimentally obtained photocatalytic activity improvement of TiO2 co-doped with Ca and F may have resulted from the reduction of forbidden band width of TiO2.

Highly effective Fe-doped TiO2 nanoparticles for removal of toxic organic dyes under visible light illumination

This article addresses the synthesis of Fe3+ doped TiO2 nanoparticles with variations of molar concentrations of Fe3+ and their adequate use as potential photocatalysts for Photocatalysis applications. Synthesized photocatalysts were characterized thoroughly by different analytical techniques in terms of morphological, chemical, structural, crystalline, optical, electronic structure, surface area etc properties. The occurrence of red shift phenomenon of the energy band gap attributes to the transfer of charges and transition between the d electrons of dopant and conduction band (CB) or valence band (VB) of TiO2. The doping of Fe3+ ions generates more trap sites for charge carriers with the surface trap sites. Thorough experimental conclusions revealed that the Fe3+ ions necessarily regulate the catalytic property of TiO2 nanomaterial. The obtained total degradation efficiency rate of Methylene Blue (MB) was 93.3% in the presence of 0.1 M Fe3+ in the host material and for Malachite Green Oxalate the efficiency was 100% in the presence of 0.05 M and 0.1 M Fe3+in the host material. In both the cases the total visible light irradiation time was 90 min. The adsorption properties of the photocatalysts have been also performed in a dark for 90 min in the presence of MB dye. However, till now there are hardly reported photocatalysts which shows complete degradation of these toxic organic dyes by visible light driven photocatalysis. of potential values of valence and conduction band shows the production of active oxidizing species for hydrogen yield and the possible mechanism of the Schottky barrier has been proposed. A schematic diagram of visible light driven Photocatalysis has been pictured showing degradation activity of Fe3+-TiO2 catalysts sample.

Map of 20 reactions that take place during vapor–solid phase photocatalytic dehydrogenation of ethanol on metal‐loaded TiO2

AbstractWe report the map of 20 reactions that take place during vapor‐phase photochemical dehydrogenation of ethanol on four metal‐doped TiO2 (Mn/TiO2, Mn = nanoparticles of Pd, Pt, Au, and Cu) under solar simulated light. The reactions are sensitively affected by the moisture amount and the nature of the carrier gas. To construct the above map, we also used CH3CHO, CH3CO2H, (C2H5O)2CHCH3, and CH3CO2C2H5, respectively, as an independent starting reagent. Amazingly, Mn/TiO2 not only serves as photocatalysts but also as thermocatalysts for various reactions that appear in the above map. The reaction is proposed to proceed by a radical mechanism in which photoinduced electron transfer from the valence band to the conduction band of TiO2 is the initial step and the subsequent electron injection from organic reactants to the hole in the TiO2 valence band. This report also features highly valuable unprecedented reactions, which bear great potential to be commercialized.

Direct Interfacial Excitation from TiO2 to Cu(II) Nanoclusters Enables Cathodic Photoresponse for Hydrogen Evolution under Visible-Light Irradiation.

The titaniumdioxide(TiO2 )photocatalyst is only active under UV irradiation due to its wide-gap nature. A novel excitation pathway denoted as interfacial charge transfer (IFCT) has been reported to activate copper(II) oxide nanoclusters-loaded TiO2 powder (Cu(II)/TiO2 )under visible-light irradiation for only organic decomposition (downhill reaction) so far. Here, the photoelectrochemical study shows that the Cu(II)/TiO2 electrode exhibits a cathodic photoresponse under visible-light and UV irradiation. It originates from H2 evolution on the Cu(II)/TiO2 electrode, while O2 evolution takes place on the anodic side. Based on the concept of IFCT, a direct excitation of electrons from the valence band of TiO2 to Cu(II) clusters initiates the reaction. This is the first demonstration of a direct interfacial excitation-induced cathodic photoresponse for water splitting without any addition of a sacrificial agent. This study is expected to contribute to the development of abundant visible-light-active photocathode materials for fuel production (uphill reaction).

Synthesis of a Gold-Inserted Iron Disilicide and Rutile Titanium Dioxide Heterojunction Photocatalyst via the Vapor-Liquid-Solid Method and Its Water-Splitting Reaction.

A solid-state Z-scheme system is constructed whereby rutile titania (TiO2) and beta-iron disilicide (β-FeSi2) were combined to act as oxygen (O2)- and hydrogen (H2)-evolution photocatalysts, respectively, connected by gold (Au). β-FeSi2 island grains with diameters in the 0.5-2 μm range were formed on the surface of Au-coated TiO2 powder by the co-sputtering method. On the surface of TiO2 powder, the Au-Si liquidus phase was obtained via a Au-Si eutectic reaction, which contributed to the selective deposition and crystallization of β-FeSi2 island grains onto Au. After the loading of the H2-evolution cocatalysts platinum and chromium oxide onto β-FeSi2, the system obtained catalyzed the evolution of H2 and O2 in a stoichiometric ratio from pure water under ultraviolet light irradiation. The transfer of photoexcited electrons in the conduction band (CB) of β-FeSi2 to Pt causes the reduction of protons to H2, and the photogeneration of holes in the valence band (VB) of TiO2 causes the oxidation of water to O2. In addition, the photogenerated holes in the VB of β-FeSi2 and the photoexcited electrons in the CB of TiO2 combined with each other in the Au layer, affording the completion of the overall photocatalytic water-splitting.

Ru/In Dual‐Single Atoms Modulated Charge Separation for Significantly Accelerated Photocatalytic H2 Evolution in Pure Water

AbstractPhotocatalytic hydrogen production is a prospective technology to solve the energy crisis and environmental problems. However, it is still challenging to produce hydrogen from photocatalytic water splitting on a large scale without a sacrificial agent and cocatalyst. Here, it is demonstrated that the dual doping of Ru/In single atoms on TiO2 (Ru‐In SA/TiO2) can modulate the separation of photogenerated carriers during the photocatalytic splitting of pure water. Impressively, the H2 evolution rate of Ru‐In SA/TiO2 reaches 174.1 µmol h−1, which is 6, 18, and 53 times higher than those of the Ru single‐atom decorated TiO2, In single‐atom decorated TiO2, and pristine TiO2, respectively. More importantly, Ru‐In SA/TiO2 outperforms most of the reported photocatalysts for photocatalytic water splitting in the absence of a sacrificial agent. Detailed investigations reveal that the decoration of Ru/In dual‐single atoms leads to the remarkable increase of Ti3+ and enrichment of oxygen vacancies, which accelerate the charge separation. In particular, the femtosecond transient absorption spectroscopy suggests that the doping of Ru single atom promotes the transfer of photogenerated electrons from TiO2 into Ru, while the doping of In single atom enhances the transfer of photogenerated holes from the TiO2 valence band to In single atoms, as a result of an efficient electron‐hole separation. This work not only provides an efficient photocatalyst for H2 production through pure water splitting in the absence of a sacrificial agent, but also promotes fundamental research on catalyst design and modification.

Correlation between optical and structural properties of nitrogen doped anatase TiO2 thin films

Raman spectroscopy, grazing incidence X-ray diffractometer (GIXRD), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), atomic force microscopy (AFM) and photoluminescence spectroscopy (PL) were performed on TiO2 thin films exposed to a nitrogen N2+ ion beam at different temperatures from 45 °C to 585 °C. The crystalline structure, the thickness, the dielectric functions, the band gap and the Urbach energies were studied. The obtained results show a strong change of physical properties of TiO2 after exposing to N2+ ion beam. Raman modes and diffracted peaks show the anatase structure for all the deposited N-doped films. The presence of nitrogen doping into the TiO2 layer is confirmed by XPS measurements. The substitutional nitrogen defects promote a decrease of the band gap for N-doped TiO2 by 150 meV at the doping temperature 585 °C. This reduction was explained by the increase in valence band extremity caused by the hybridization of the N 2p states and the O 2p states of the valence band of TiO2. The Raman, GIXRD, XPS, SE, AFM, and PL results are consistent and provide an invaluable complementary information about the nitrogen diffusion within the TiO2 lattice at different temperatures.

Accurate structural descriptor enabled screening for nitrogen and oxygen vacancy codoped TiO2 with a large bandgap narrowing

• An accurate structural descriptor to represent the doping configurations of N/V O -codoped anatase TiO 2 is constructed. • Machine learning assisted electronic properties screening for the optimal doping configurations is enabled by the structural descriptor. • Two types of doping configurations featured by a linear and corner-sharing TiO 5 N 1 /TiO 4 N 2 octahedron chain with a large bandgap narrowing are identified. • The spatial ordering of N-dopants has been uncovered as the intrinsic reason for a large bandgap narrowing in N/V O -codoped TiO 2 . Nitrogen (N) doping has been widely adopted to improve the light absorption of TiO 2 . However, the newly introduced N-2 p states are largely localized thus barely overlap with O-2 p states in the valence band of TiO 2 , resulting in a shoulder-like absorption edge. To realize an apparent overlap between N-2 p and O-2 p states, charge compensation between N 3− and O 2− via electron transfer from oxygen vacancies (V O ) to N dopants is one possible strategy. To verify this, in numerous doping configurations of N/V O -codoped anatase TiO 2 , we identified two types of V O position independent N-dopant spatial orderings by efficient screening enabled with a newly designed structural descriptor. Compared with others, these two types of the N-dopant spatial orderings are highly beneficial for charge compensation to produce an apparent overlap between N-2 p and O-2 p states, therefore achieving a large bandgap narrowing. Furthermore, the two types of the N-dopant spatial orderings can also be generalized to N/V O -codoped rutile TiO 2 for bandgap narrowing.

Constructing mesoporous Zr-doped SiO2 onto efficient Z-scheme TiO2/g-C3N4 heterojunction for antibiotic degradation via adsorption-photocatalysis and mechanism insight

Novel modified-TiO2/Zr-doped SiO2/g-C3N4 ternary composite is fabricated via an in-situ grow of porous Zr–SiO2 layer to TiO2/g-C3N4 heterojunction, which exhibits well adsorption-photocatalytic performance under simulated solar light irradiation. The nano-size mesoporous TiO2 are dispersed on the lamellar g-C3N4, and the Zr–SiO2 is in-situ fabricated onto the surface of g-C3N4 sheets. The adsorption occurs on the SiO2 layers, and doping Zr element to SiO2 enhances the adsorption of pollutants, while the photocatalytic reaction occurs on the valence band (VB) of TiO2 and conduction band (CB) of g-C3N4, which gives reactive oxygen species of ∙O2−, h+, and ∙OH for high efficient decomposition of antibiotics, i.e. berberine hydrochloride (98.11%), tetracycline (80.76%), and oxytetracycline (84.84%). The excellent adsorption capacity and Z-scheme photoinduced charge carrier migration behavior endowed the novel material with enhanced berberine hydrochloride (BH) removal in water, which approximately 2.5 and 3.8 folds than that of pure g-C3N4 and sole TiO2, respectively. Three degradation pathways are unraveled by LC-MS and theoretical calculations. Furthermore, the toxicity of intermediates was evaluated by the Toxicity Estimation Software Tool (T.E.S.T.), the result demonstrated a good application potential of M-TiO2/Zr–SiO2/g-C3N4 as an novel adsorptive photocatalyst.

Designs of composite photocatalysts for their enhanced performance based on photoinduced charge transfer

The author and coworkers focused on the fabrication of composite photocatalysts and charge transfer between composite constituents for increased activity and sensitivity to visible light, aiming at developing materials for environmental preservation through the oxidative decomposition of organic pollutants and clean energy production through water splitting for hydrogen generation. Cu2+ ion-grafted titanium dioxide (TiO2) was designed on the basis of visible-light-induced interfacial charge transfer from the valence band (VB) of TiO2 to Cu2+, generating high oxidative decomposition activity owing to the utilization of photogenerated holes in the VB of TiO2. Cu+ produced by electron injection was converted back to Cu2+ by oxygen (O2) reduction through multi-electron O2 reduction reaction. As for water splitting, zinc rhodium oxide (ZnRh2O4) and bismuth vanadate (Bi4V2O11) as H2 and O2 evolution photocatalysts, respectively, were connected with silver (Ag), acting as a solid-state electron mediator, to prepare a composite photocatalyst that is sensitive to red light. The key function of the heterojunction photocatalyst is the transfer of photoexcited electrons from the conduction band (CB) of Bi4V2O11 to the VB of ZnRh2O4 via Ag. Thus, the photoexcited electrons in the CB of ZnRh2O4 and the holes in the VB of Bi4V2O11 effectively reduced and oxidized water, respectively, thereby splitting water and liberating H2 and O2 at a stoichiometric ratio.