Ag2S quantum dots-sensitized TiO2 nanotube array photoelectrodes

Ag₂S quantum dots (QDs) were deposited on ordered TiO₂ nanotube arrays (TNTAs) using a sequential chemical bath deposition (S-CBD) approach. AgNO₃ and thiourea were used as the precursor materials of Ag⁺ and S²⁻ ions, respectively. The decoration of Ag₂S QDs significantly shifted the absorption spectrum of the TNTAs to visible light region. As a result, Ag₂S QDs-sensitized TNTAs exhibited much higher photocurrent density than pure TNTAs under visible light irradiation.     

Light‐Induced Motion of Microengines Based on Microarrays of TiO2 Nanotubes

An electrochemical approach for manufacturing light‐driven nanostructured titanium dioxide (TiO₂) microengines with controlled spatial architecture for improved performance is reported. The microengines based on microscale arrays of TiO₂ nanotubes with variable (50–120 nm) inner diameter show a quasi‐ordered arrangement of nanotubes, being the smallest tubular entities for catalytic microengines reported to date. The nanotubes exhibit well defined crystalline phases depending upon the postfabrication annealing conditions that determine the microengines' efficiency. When exposed to UV‐light, the microarrays of TiO₂ nanotubes exhibiting conical internal shapes show directed motion in confined space, both in the presence and absence of hydrogen peroxide. In the former case, two different motion patterns related to diffusiophoresis and localized nanobubble generation inside of the tubes due to the photocatalytic decomposition of H₂O₂ are disclosed. Controlled pick‐up, transport, and release of individual and agglomerated particles are demonstrated using the UV light irradiation of microengines. The obtained results show that light‐driven microengines based on microarrays of TiO₂ nanotubes represent a promising platform for controlled micro/nanoscale sample transportation in fluids as well as for environmental applications, in particular, for the enhanced photocatalytic degradation of organic pollutants due to the improved intermixing taking place during the motion of TiO₂ microengines.     

From UV to Near‐Infrared Light‐Responsive Metal–Organic Framework Composites: Plasmon and Upconversion Enhanced Photocatalysis

The exploitation of photocatalysts that harvest solar spectrum as broad as possible remains a high‐priority target yet grand challenge. In this work, for the first time, metal–organic framework (MOF) composites are rationally fabricated to achieve broadband spectral response from UV to near‐infrared (NIR) region. In the core–shell structured upconversion nanoparticles (UCNPs)‐Pt@MOF/Au composites, the MOF is responsive to UV and a bit visible light, the plasmonic Au nanoparticles (NPs) accept visible light, whereas the UCNPs absorb NIR light to emit UV and visible light that are harvested by the MOF and Au once again. Moreover, the MOF not only facilitates the generation of “bare and clean” Au NPs on its surface and realizes the spatial separation for the Au and Pt NPs, but also provides necessary access for catalytic substrates/products to Pt active sites. As a result, the optimized composite exhibits excellent photocatalytic hydrogen production activity (280 µmol g^?1 h^?1) under simulated solar light, and the involved mechanism of photocatalytic H₂ production under UV, visible, and NIR irradiation is elucidated. Reportedly, this is an extremely rare study on photocatalytic H₂ production by light harvesting in all UV, visible, and NIR regions.     

Single‐Component TiO2 Tubular Microengines with Motion Controlled by Light‐Induced Bubbles

In this work, light‐controlled bubble‐propelled single‐component metal oxide tubular microengines have for the first time been demonstrated. For such a simple single‐component TiO₂ tubular microengine in H₂O₂ aqueous solution under UV irradiation, when the inner diameter and length of the tube are regulated, the O₂ molecules will nucleate and grow into bubbles preferentially on the inner concave surface rather than on the outer surface, resulting in a vital propulsion of the microengine. More importantly, the motion state and speed can be modulated reversibly, fast (the response time is less than 0.2 s) and wirelessly by adjusting UV irradiation. Consequently, the as‐developed TiO₂ tubular microengine promises potential challenged applications related to photocatalysis, such as “on‐the‐fly” photocatalytic degradation of organic pollutes and photocatalytic inactivation of bacteria due to the low cost, single component, and simple structure, as well as the facile fabrication in a large‐scale.     

Graphdiyne-hybridized N-doped TiO<Subscript>2</Subscript> nanosheets for enhanced visible light photocatalytic activity

In this study, graphdiyne (GD)-hybridized nitrogen-doped TiO₂ nanosheets with exposed (001) facets (GD-NTNS) have been prepared via a hydrothermal reaction and utilized as photocatalyst for the photodegradation of rhodamine B (RhB) under visible light illumination. The resultant GD-NTNS composites exhibit superior visible light photocatalytic activity than that of the bare TiO₂ nanosheets (TNS) and nitrogen-doped TiO₂ nanosheets (NTNS). The enhanced photoactivity can be attributed to the synergistic effects of GD and nitrogen doping with efficient electron transfer and strong visible light absorption. It has been revealed that ^·O^2? and h⁺ are the major species for the enhanced photoactivity under visible light. Our work will facilitate the potential for future design of hybrid materials for practical applications beyond photocatalysts.     

Light‐Activated,Multi‐Semiconductor Hybrid Microswimmers

Using a dynamic fabrication process, hybrid, photoactivated microswimmers made from two different semiconductors, titanium dioxide (TiO₂) and cuprous oxide (Cu₂O) are developed, where each material occupies a distinct portion of the multiconstituent particles. Structured light‐activated microswimmers made from only TiO₂ or Cu₂O are observed to be driven in hydrogen peroxide and water most vigorously under UV or blue light, respectively, whereas hybrid structures made from both of these materials exhibit wavelength‐dependent modes of motion due to the disparate responses of each photocatalyst. It is also found that the hybrid particles are activated in water alone, a behavior which is not observed in those made from a single semiconductor, and thus, the system may open up a new class of fuel‐free photoactive colloids that take advantage of semiconductor heterojunctions. The TiO₂/Cu₂O hybrid microswimmer presented here is but an example of a broader method for inducing different modes of motion in a single light‐activated particle, which is not limited to the specific geometries and materials presented in this study.     

Microwave assisted hydrothermal synthesis and characterization of ZnO–TNT composites

TiO₂ nanotubes with different contents of ZnO (3–40 wt.% ZnO) have been successfully synthesized by microwave assisted hydrothermal process by using commercial TiO₂-P25 as a precursor. The phase and crystallinity of the obtained ZnO–TNT were analyzed by X-ray Diffraction (XRD). The surface area of the ZnO–TNT was determined by BET method. The effect of the different contents of ZnO on morphology of TiO₂ nanotubes was investigated by SEM and TEM. Optical properties and band gap energy of ZnO–TNT were calculated by using UV–vis DRS spectroscopy and modified Kubelka–Munk equation. Photocatalytic performance of ZnO–TNT was investigated by degradation of rhodamine B (RhB) dye under UV and visible light irradiation. Increasing ZnO content in TNT gradually decreased the diameter and length of nanotubes. Furthermore, addition of 40 wt.% ZnO into the TNT exceeded the saturation limit of ion exchangeability of Zn²⁺ and Na⁺ ions and aggregation of finely dispersed ZnO particles on the surface of TNT were observed. The ZnO–TNT has shown relatively larger band gap energies than that of TiO₂-P25. However, ZnO–TNT has shown considerable increase in photo-activity for degradation of RhB dye in visible light as compared to UV light irradiation.     

Ag<Subscript>2</Subscript>S/Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> co-sensitized TiO<Subscript>2</Subscript> nanorod arrays prepared on conductive glass as a photoanode for solar cells

TiO₂ nanorod arrays (TiO₂ NRAs) were synthesized through a hydrothermal method. Ag₂S and Bi₂S₃ were then grown on the surface of TiO₂ NRAs with successive ionic layer adsorption and reaction method. The pristine rutile TiO₂ NRAs, Ag₂S/TiO₂, Bi₂S₃/TiO₂, and Bi₂S₃/Ag₂S/TiO₂ electrodes were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible absorption spectroscopy, and electrochemical analysis. According to photoelectrochemical (PEC) measurement, an enhanced short circuit current density was obtained for the co-sensitized TiO₂ NRAs under simulated sunlight illumination, which was 10.7 times higher than that of the TiO₂ NRAs. Appropriate potential positions of conduction band and valence band of Bi₂S₃ that match well those of rutile TiO₂ NARs and Ag₂S lead to the improved PEC performance. In addition, the PEC property of the co-sensitized TiO₂ NRAs under visible light irradiation was also investigated and showed a dramatically enhanced photocurrent response.     

Synthesis of N-doped titanium oxide by hydrothermal treatment

N-doped TiO₂ nanoparticles have been prepared by continuous or batch treatment of the colloidal TiO₂ nanoparticles under hydrothermal conditions with formamide, nitric acid, ammonia or triethylamine. The optical absorption tail of the obtained photocatalysts near the band gap extended to the visible region around λ = 500 nm. The efficiency of nitrogen doping was strongly dependent on the kind of nitrogen compounds, treatment method as well as treatment temperature. The most effective N-doping could be accomplished by the batch treatment with a small amount of triethylamine, which showed the efficient photocatalytic activity for both the reduction of Ag⁺ ions and the degradation of methylene blue under visible light irradiation.     

TiO2@Perylene Diimide Full‐Spectrum Photocatalysts via Semi‐Core–Shell Structure

A semi‐core–shell structure of perylene diimide (PDI) self‐assembly coated with TiO₂ nanoparticles is constructed, in which nanoscale porous TiO₂ shell is formed and PDI self‐assembly presented 1D structure. A full‐spectrum photocatalyst is obtained using this structure to resolve a conundrum—TiO₂ does not exhibit visible‐light photocatalytic activity while PDI does not exhibit ultraviolet photocatalytic activity. Furthermore, the synergistic interaction between TiO₂ and PDI enables the catalyst to improve its ultraviolet, visible‐light, and full‐spectrum performance. The interaction between TiO₂ and PDI leads to formation of some new stacking states along the Π–Π stacking direction and, as a consequence, electron transfer from PDI to TiO₂ suppresses the recombination of e^?/h⁺ and thus improves photocatalytic performance. But the stronger interaction in the interface between TiO₂ and PDI is not in favor of photocatalytic performance, which leads to rapid charge recombination due to more disordered stacking states. The study provides a theoretical direction for the study of core–shell structures with soft materials as a core, and an idea for efficient utilization of solar energy.     

Sn<Superscript>4+</Superscript> and La<Superscript>3+</Superscript> co doped TiO<Subscript>2</Subscript> nanoparticles and their optical,photocatalytic and antibacterial properties under visible light

Sn⁴⁺ and La³⁺ co-doped TiO₂ photocatalytic material with nanoparticle structure have been successfully prepared using SnCl₂·2H₂O and La(NO₃)₃·6H₂O as precursors. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy and UV–visible spectroscopy have been used to for the characterization of the morphology, crystal structure, particle size and optical properties of the samples. The photocatalytic properties of sample with various amount of La doped TiO₂ have been studied by photo degradation of methyl orange (MO) in water under visible light. XRD patterns showed both rutile and anatase phases for 5 mol% of Sn and 5–10 mol% of La. But anatase phase with a little rutile phase was formed for 5 mol%Sn and 10 mol%La. The prepared Sn and La co doped TiO₂ photo-catalyst showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of MO solution under visible irradiation. Antibacterial behavior towards E. coli was then studied under visible irradiation. The synthesized T-5%Sn-10%La powder exhibited superior antibacterial activity under visible irradiation compared to the pure TiO₂.     

Preparation and doping modification of cerium oxide photosensitizers applied to photosensitive glass ceramics

CeO₂ nanoparticles doped with different types of Pr, Y, W and CaF₂ are prepared via a facile one-pot combustion method. Their crystallinity, particle size and absorption spectrum are investigated by X-ray diffraction (XRD), grading analysis and ultraviolet–visible spectroscopy (UV–Vis) absorption spectrum. Among the doped samples, W-doped CeO₂ (Ce_0.9W_0.1O₂) is selected out, which exhibits obvious red-shift of the absorption band as compared with the undoped CeO₂, achieving good match between the ceria absorption peak and the industrial 365 nm light source. Consequently, under the 365 nm exposure, the W-doped CeO₂ show more efficient reduction ability for Ag⁺ to Ag. The results indicate that W-doped CeO₂ is a very promising photosensitizer for photosensitive glass ceramics under industrial 365 nm light exposure, which can better absorb photons under UV light and then reduce Ag⁺ to elemental Ag.

     

La<Subscript>1−x</Subscript>Ag<Subscript>x</Subscript>FeO<Subscript>3</Subscript>/halloysites nanocomposite with enhanced visible light photocatalytic performance

La_1?xAg_xFeO₃/halloysites nanotubes (HNTs) nanocomposite was synthesized by sol–gel method. It was characterized by X-ray diffraction, transmission electron microscope, Fourier transform infrared spectroscopy and UV–visible diffused reflectance spectroscopy measurements. The photo-activity of the La_1?xAg_xFeO₃/HNTs nanocomposite was evaluated via degradation of methylene blue (MB) under visible-light irradiation. The results showed that the HNTs with unique pore structure favored the adsorption of organic molecules. Adequate Ag⁺ doping improved the absorption ability for visible light. The La_0.95Ag_0.05FeO₃/HNTs demonstrated the best photocatalytic performance, which achieved as high as 99 % for MB degradation exposed 2 h irradiation. However,further increasing of Ag⁺ doping gradually reduced the photocatalytic activity. The nanocomposite catalyst showed outstanding recyclability after eight cycles which still remained up to 90 %.     

Effects of samarium dopant on photocatalytic activity of TiO<Subscript>2</Subscript> nanocrystallite for methylene blue degradation

Sm³⁺-doped TiO₂ nanocrystalline was synthesized by a sol–gel auto-combustion method and characterized by X-ray diffraction, Brunauer-Emmett-Teller method (BET), UV–vis diffuse reflectance spectroscopy (DRS), and also photoluminescence (PL) emission spectroscopy. The photocatalytic activity of Sm³⁺–TiO₂ catalyst was evaluated by measuring degradation rates of methylene blue (MB) under either UV or visible light. The results showed that doping with the samarium ions significantly enhanced the photocatalytic activity for MB degradation under UV or visible light irradiation. This was ascribed to the fact that a small amount of samarium dopant simultaneously increased MB adsorption capacity and separation efficiency of electron-hole pairs. The results of DRS showed that Sm³⁺-doped TiO₂ had significant absorption between 400 nm and 500 nm, which increased with the increase of samarium ion content. The adsorption experimental demonstrated that Sm³⁺–TiO₂ had a higher MB adsorption capacity than undoped TiO₂ and adsorption capacity of MB increased with the increase of samarium ion content. It is found that the stronger the PL intensity, the higher the photocatalytic activity. This could be explained by the points that PL spectra mainly resulted from surface oxygen vacancies and defects during the process of PL, while surface oxygen vacancies and defects could be favorable in capturing the photoinduced electrons during the process of photocatalytic reactions, so that the recombination of photoinduced electrons and holes could be effectively inhibited.     

Novel UV–Visible Photodetector in Photovoltaic Mode with Fast Response and Ultrahigh Photosensitivity Employing Se/TiO2 Nanotubes Heterojunction

A feasible strategy for hybrid photodetector by integrating an array of self‐ordered TiO₂ nanotubes (NTs) and selenium is demonstrated to break the compromise between the responsivity and response speed. Novel heterojunction between the TiO₂ NTs and Se in combination with the surface trap states at TiO₂ help regulate the electron transport and facilitate the separation of photogenerated electron–hole pairs under photovoltaic mode (at zero bias), leading to a high responsivity of ≈100 mA W^?1 at 620 nm light illumination and the ultrashort rise/decay time (1.4/7.8 ms). The implanting of intrinsic p‐type Se into TiO₂ NTs broadens the detection range to UV–visible (280–700 nm) with a large detectivity of over 10¹² Jones and a high linear dynamic range of over 80 dB. In addition, a maximum photocurrent of ≈10⁷ A is achieved at 450 nm light illumination and an ultrahigh photosensitivity (on/off ratio up to 10⁴) under zero bias upon UV and visible light illumination is readily achieved. The concept of employing novel heterojunction geometry holds great potential to pave a new way to realize high performance and energy‐efficient optoelectronic devices for practical applications.     

An Unusual Strong Visible‐Light Absorption Band in Red Anatase TiO2 Photocatalyst Induced by Atomic Hydrogen‐Occupied Oxygen Vacancies

Increasing visible light absorption of classic wide‐bandgap photocatalysts like TiO₂ has long been pursued in order to promote solar energy conversion. Modulating the composition and/or stoichiometry of these photocatalysts is essential to narrow their bandgap for a strong visible‐light absorption band. However, the bands obtained so far normally suffer from a low absorbance and/or narrow range. Herein, in contrast to the common tail‐like absorption band in hydrogen‐free oxygen‐deficient TiO₂, an unusual strong absorption band spanning the full spectrum of visible light is achieved in anatase TiO₂ by intentionally introducing atomic hydrogen‐mediated oxygen vacancies. Combining experimental characterizations with theoretical calculations reveals the excitation of a new subvalence band associated with atomic hydrogen filled oxygen vacancies as the origin of such band, which subsequently leads to active photo‐electrochemical water oxidation under visible light. These findings could provide a powerful way of tailoring wide‐bandgap semiconductors to fully capture solar light.     

Au Nanoclusters Sensitized Black TiO2−x Nanotubes for Enhanced Photodynamic Therapy Driven by Near‐Infrared Light

The low reactive oxygen species production capability and the shallow tissue penetration of excited light (UV) are still two barriers in photodynamic therapy (PDT). Here, Au cluster anchored black anatase TiO_2?x nanotubes (abbreviated as Au₂₅/B‐TiO_2?x NTs) are synthesized by gaseous reduction of anatase TiO₂ NTs and subsequent deposition of noble metal. The Au₂₅/B‐TiO_2?x NTs with thickness of about 2 nm exhibit excellent PDT performance. The reduction process increased the density of Ti³⁺ on the surface of TiO₂, which effectively depresses the recombination of electron and hole. Furthermore, after modification of Au₂₅ nanoclusters, the PDT efficiency is further enhanced owing to the changed electrical distribution in the composite, which forms a shallow potential well on the metal–TiO₂ interface to further hamper the recombination of electron and hole. Especially, the reduction of anatase TiO₂ can expend the light response range (UV) of TiO₂ to the visible and even near infrared (NIR) light region with high tissue penetration depth. When excited by NIR light, the nanoplatform shows markedly improved therapeutic efficacy attributed to the photocatalytic synergistic effect, and promotes separation or restrained recombination of electron and hole, which is verified by experimental results in vitro and in vivo.     

Iron promotion of the TiO2 photosensitization process towards the photocatalytic oxidation of azo dyes under solar-simulated light irradiation

The photocatalytic oxidation of the azo dye Orange-II (Or-II) using Fe loaded TiO₂ (Fe–TiO₂) was studied under ultraviolet (UV), visible (vis) and simultaneous UV–vis irradiations using a solar light simulator. Photocatalysts were characterized by means of XRD, SEM-EDX, FTIR and DRS. Fe³⁺ species, identified in XPS analyses, were responsible of the increased absorption of visible light. Moreover, DRS analyses showed a decrease in the bandgap due to Fe³⁺ loading. Photocatalystic tests proved that Fe modification enhanced the TiO₂ photocatalytic activity towards Or-II photodegradation under simultaneous UV–vis irradiation. Even so, the performance of the Fe–TiO₂ samples towards the photodegradation of phenol, under UV irradiation, was lower than TiO₂ suggesting the recombination of the UV photogenerated electron–hole pair. Therefore, results evidence a Fe³⁺ promotion of the electron caption in the photosensitization process of TiO₂ by Or-II acting as a sensitizer. Such process leads to the Or-II photooxidation under UV–vis irradiation by losing energy in electron transferring processes to sensitize TiO₂, and, the formation of reactive oxygen species promoted by the injected electron to the TiO₂ conduction band.     

Enhancement of photocatalytic activity and stability of Ag2CO3 by formation of AgBr/Ag2CO3 heterojunction in mordenite zeolite

Two serious problems for semiconductor photocatalysts are their poor photocatalytic activity and low stability. In this work, Ag₂CO₃ nanoparticles incorporated in mordenite zeolite (MOR) by a facile precipitation method. Silver bromide (AgBr) with different weight percentage (20%, 40% and 50%) was coupled into Ag₂CO₃-MOR composite and producing a series of novel AgBr/Ag₂CO₃-MOR nanocomposites. The effects of AgBr on the Ag₂CO₃–MOR catalyst for the photocatalytic degradation of methyl blue (MB) under visible light irradiation have been investigated. The structure, composition and optical properties of nanocomposites were investigated by UV–Visible diffuse reflectance spectroscopy (UV–Vis DRS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM). The prepared AgBr/Ag₂CO₃-MOR photocatalyst with the optimal content of AgBr (50 wt%) indicated higher photocatalytic activity than that of the Ag₂CO₃-MOR and Ag₂CO₃ for degradation of methylene blue (MB) under visible light irradiation. For studying of stability of nanocomposites, Fe⁺³ ions, as a cheap and available cocatalyst, was inserted into mordenite matrix (Fe³⁺/MOR) by impregnation method. The hybrid material (AgBr/Ag₂CO₃) was synthesized in the Fe³⁺/MOR matrix by precipitation method. The cycle experiments on the AgBr/Ag₂CO₃-Fe/MOR nanocomposite indicated that cocatalyst, not only to improve photocatalytic activity, but also enhance photoinduced stability of photosensitive silver compounds in all cycles with respect to MOR. On the basis of the experimental results, a possible mechanism for the enhanced photocatalytic activity and photoinduced stability of silver compounds by Fe³⁺ cocatalyst was proposed. The mordenite support played an important role in decreases of recombination of photogenerated electrons-holes and increases of MB absorption. The Fe cocatalyst reduced photocorrosion of silver compounds.     

Fabrication of Ag<Subscript>3</Subscript>PO<Subscript>4</Subscript>-AgBr-PTh composite loaded on Na<Subscript>2</Subscript>SiO<Subscript>3</Subscript> with enhanced visible-light photocatalytic activity

A novel Ag₃PO₄-AgBr-PTh composite loaded on Na₂SiO₃ was synthesized for enhanced visible-light photocatalytic activity. The photocatalytic activity of the samples was evaluated by photodegrading rhodamine B (RhB) under visible light irradiation. The main reactive species and possible photocatalytic mechanism were also discussed. As a result, the Ag₃PO₄-AgBr-PTh composite loaded on Na₂SiO₃ exhibited enhanced photocatalytic activity for RhB compared with Ag₃PO₄ under visible-light irradiation. Additionally, it was demonstrated that the hole (h⁺) and superoxide radical (?O ₂ ^? ) were the major reactive species involving in the RhB degradation. PTh played vital role for the enhanced photocatalytic activity of Ag₃PO₄-AgBr-PTh-Na₂SiO₃ composite, which offered an electron transfer expressway and accelerated the transfer of the electrons from the CB of AgBr into Ag₃PO₄. This work could provide a new perspective for the synthesis of Ag₃PO₄-based composites and the improvement of photocatalytic activity of Ag₃PO₄.