TiO2 Interface Research Articles

Plasmonic Pt nanoparticles triggered efficient charge separation in TiO2/GaN NRs hybrid heterojunction for the high performance self-powered UV photodetectors

Solar radiation, especially the UV-A light rays (320–400 nm) exposure causes severe health hazard such as skin-related cancer and premature aging. Owing to the significance of UV-A photodetection, a high-performance UV-A photodetectors (PD) with high sensitivity, large detectivity and fast response time, have attracted great attention in various optoelectronic applications. Herein, we report a self-powered (SP) UV PD based on Pt nanoparticles (NP) decorated TiO2/GaN nanorods (NRs) hybrid heterojunction. The proposed Pt NP@TiO2/GaN NRs hybrid device demonstrates pronounced photoelectric performances including a large responsivity (44.6 A/W), superior detectivity (1.57 × 1014 Jones) and high electronic quantum efficiency (8.65 × 103 %) under the UV light intensity (λ = 382 nm, 1.32 mW/cm2) at zero bias, which are relatively much higher as compare to the pristine counterparts. In addition, the hybrid PD showed a short response/recovery times of 180 ms/200 ms, with a remarkable reproducibility and long-term stability towards the UV light. The impressive photoresponse properties of the hybrid SP PD are ascribed to the large photon absorption endorsed by the localized surface plasmonic resonance effect of Pt NP and the adequate built-in potential at the TiO2 and GaN NRs heterojunction interface, which further endows the effective separation and transport of photogenerated charge carriers. Furthermore, the plausible mechanism for the high-performances of hybrid UV PD is demonstrated in detailed using the energy band diagram. Our work reveals that the integral advantages of hybrid heterostructures, have a significant potential for the practical applications of advanced optoelectronics and high-performance SP UV-A PD.

A DFT+U approach: Superior charge transfer characteristics and optoelectronic properties of GQD@TiO2 rutile (110) surface for improved hydrogen evolution

The understanding on complex electronic structure and charge transfer characteristics is crucial in the development of heterostructure-based photocatalyst such as graphene quantum dots (GQD) and titanium dioxide (TiO2). Simulation studies will be useful in gaining valuable insight on the complex system at atomistic level. Herein, for the first time, a theoretically designed heterogeneous GQD modified TiO2 (110) interface model using Hubbard's modified first-principles density functional theory (DFT+U) is presented. The structural properties were simulated with Perdew–Burke–Ernzerhof assisted generalized gradient approximation (GGA+PBE) and optoelectronic properties with Hubbard's modified (GGA+U) exchange correlation functional. The addition of GQD reduces the bandgap energy of the TiO2 rutile (110) surface from 2.95 eV to 1.86 eV, thereby improving the visible light response as it reduces the electron transition energy. Charge density difference map and Mulliken population analysis demonstrate frequent transfer of charges from GQD to the TiO2 surface, resulting in reduction of charge recombination rate. Moreover, the energy band edge estimation confirms a suitable band edge position in accordance with the redox potential of water. The collective effect of the heightened absorption of visible light and effective charge separation led to a significant photocatalytic performance of the hybrid photocatalyst.

Impacts of plasmonic nanoparticles incorporation and interface energy alignment for highly efficient carbon-based perovskite solar cells

This work utilizes a realistic electro-optical coupled simulation to study the (i) impact of mesoporous TiO2 removal; (ii) the embedding of Ag@SiO2 and SiO2@Ag@SiO2 plasmonic nanoparticles; (iii) utilization of solution-processed inorganic p-type copper(I) thiocyanate (CuSCN) layer at the perovskite/carbon interface; and (iv) the increase of the work function of carbon electrodes (via incorporation of suitable additives/binders to the carbon ink) on the performance of carbon-based PSCs. Removal of mesoporous TiO2 increased the power conversion efficiency (PCE) of the device from 14.83 to 16.50% due to the increase in exciton generation rate and charge carriers’ mobility in the vicinity of the perovskite-compact TiO2 interface. Subsequently, variable mass ratios of Ag@SiO2 and SiO2@Ag@SiO2 plasmonic nanoparticles are embedded in the vicinity of the perovskite-compact TiO2 interface. In the optimum cases, the PCE of the devices increased to 19.72% and 18.92%, respectively, due to light trapping, scattering, and strong plasmonic fields produced by the plasmonic nanoparticles. Furthermore, adding the CuSCN layer remarkably increased the PCE of the device with a 0.93% mass ratio of Ag@SiO2 nanoparticles from 19.72 to 26.58% by a significant improvement of Voc and FF, due to the proper interfacial energy band alignment and the reduction of the recombination current density. Similar results were obtained by increasing the carbon work function, and the cell PCE was enhanced up to 26% in the optimal scenario. Our results pave the way to achieve high efficiencies in remarkably stable printable carbon-based PSCs.

CdS nanoparticles with highly exposed (1 1 1) facets decorated on Pt/TiO2 nanotubes for highly efficient photocatalytic H2 evolution

Photocatalytic water splitting is a prospective strategy to solve the shortage of human fossil fuel energy. In this work, we designed and synthesized the Pt as co-catalyst decorated on TiO2 nanotubes/metastable zinc-blende (ZB) CdS nanoparticles (NPs) with highly exposed (111) facets (HPTCA3) via the electrospinning-solvothermal and chemical deposition methods. The H2 evolution rate of HPTCA3 was 15025.38 μmol·g−1·h−1, which was about 111.3 and 2.4 times stronger than that of pure CdS power and Pt-TiO2/CdS hollow nanotubes (HPTC). The XRD patterns showed the presence of acetate promoted the growth of ZB CdS (111) crystal facets, and the photogenerated electrons were easily tended to accumulate on the CdS (111) facets, whichwas conducive to the transmission of electrons on the CdS and TiO2 interface. The type II heterojunction can broaden the visible light response range and accelerate the separation and transfer of photo-generated electrons and holes which can be supported by the Optical and Electrochemical characterizations. Band structure calculations and XPS spectrum indicated that the composite catalyst had an efficient electron transfer mechanism, which was beneficial for the spatial separation of photogenerated carriers. The work provides a rational photocatalyst design to improve the performance of photocatalytic splitting of water into hydrogen.

Modulating the Ferroelectricity of Hafnium Zirconium Oxide Ultrathin Films via Interface Engineering to Control the Oxygen Vacancy Distribution

AbstractHafnium oxides‐based ferroelectric materials are promising for applications in nonvolatile memory devices. To control the ferroelectricity of such materials, it is necessary to tune their polymorphism, interfacial features, and defect (oxygen vacancy) distribution. A strategy is described for enhancing the ferroelectric properties of polycrystalline hafnium zirconium oxide (HZO) ultrathin films by modifying the oxygen pressure during the device preparation stage, which involves thermal annealing of TiN electrodes that serve as oxygen reservoirs. Microstructural and chemical characterizations along with theoretical analysis reveal that interfacial layers of TiO2−x (or TiOxNy) can characteristically form between the TiN electrode and the HZO thin film, depending on the oxygen treatment conditions. These interfacial layers directly affect the polymorphic distribution of the as‐deposited HZO. In particular, the engineered interfacial TiO2−x layer facilitates the generation and stabilization of ferroelectric orthorhombic phase HZO by promoting the uniform distribution of oxygen vacancies. Electric field cycling tests further highlight the enhanced ferroelectric polarization and coercive voltage following interfacial engineering. The results presented herein demonstrate successful tuning of the structural and interfacial properties of polycrystalline HZO devices, thus enabling control over their ferroelectric characteristics, which is critical for the fabrication of devices with designed functionality.

Characterizing Interfacial Structures of Dye-Sensitized Solar Cell Working Electrodes.

In this feature article, we discuss the fundamental use of materials-characterization methods that directly determine structural information on the dye···TiO2 interface in dye-sensitized solar cells (DSCs). This interface is usually buried within the DSC and submerged in solvent and electrolyte, which renders such metrological work nontrivial. We will show how ex-situ X-ray reflectometry (XRR), atomic-force microscopy (AFM), grazing-incidence X-ray scattering (GIXS), pair-distribution-function analysis of X-ray diffraction data (gaPDF), and in-situ neutron reflectometry (NR) can be used to deliver specific structural information on the dye···TiO2 interface regarding dye anchoring, dye aggregation, molecular dye orientation, intermolecular spacing between dye molecules, interactions between the dye molecules and the TiO2 surface, and interactions between the dye molecules and the electrolyte components and precursors. Some of these materials-characterization techniques have been developed specifically for this purpose. We will demonstrate how the direct acquisition of such information from materials-characterization experiments is crucial for assembling a holistic structural picture of this interface, which in turn can be used to develop DSC design guidelines. Moreover, we will show how these methodologies can be used in the experimental-validation process of "design-to-device" pipelines for big-data- and machine-learning-based materials discovery. We conclude with an outlook on further developments of this design-to-device approach as well as the materials characterization of more dye···TiO2 interfacial structures that involve known DSC dyes using the methods described herein. In addition, we propose to combine these formally disparate metrologies so that their complementary merits can be exploited simultaneously. New metrologies of this kind could serve as a "one-stop-shop" for the materials characterization of surfaces, interfaces, and bulk structures in DSCs and other devices with layered architectures.

Effects of Carbon Incorporation on Electrical Characteristics and Thermal Stability of Ti/TiO2/n-Ge MIS Contact

The effects of carbon incorporation on the thermal stability of the interfacial TiO₂ layer and the electrical characteristics of Ti/TiO₂/<i>n</i>-Ge contacts were investigated. The improved thermal stability and contact characteristics of Ti/TiO₂/<i>n</i>-Ge contacts were characterized in terms of Schottky barrier height (SBH) and specific contact resistivity (&#x03C1;_<i>c</i>) using the Schottky diode and circular transmission line model (CTLM). The values of SBH and &#x03C1;_<i>c</i> increased after the rapid thermal annealing (RTA) above 550 &#x00B0;C. The current density&#x2013;bias voltage (<i>J&#x2013;V</i>) curves of the Schottky diode showed a change of contact characteristics from Ohmic-like behavior to rectifying. This thermal instability was mainly caused by the decomposition of the interfacial TiO₂ layer after high-temperature annealing. The structural degradation was confirmed by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) analyses. When carbon ions were incorporated into the interfacial TiO₂ layer, the SBH and &#x03C1;_<i>c</i> values showed relatively stable characteristics as the RTA temperature increased up to 600 &#x00B0;C. The EELS mapping showed that the diffusion of oxygen from the interfacial TiO₂ layer was effectively suppressed thanks to the incorporation of carbon. Thus, the carbon incorporation can improve the thermal stability of the interfacial TiO₂ layer and the metal&#x2013;insulator&#x2013;semiconductor contact characteristics for Ge-based device applications.

UV-selective organic absorbers for the cosensitization of greenhouse-integrated dye-sensitized solar cells: synthesis and computational study.

Molecular cosensitization is favorable for manipulating solar radiation through the judicious choice of cosensitizers having complementary absorption spectra. For greenhouse-integrated dye-sensitized solar cells (DSCs), the manipulation of solar radiation is crucial in order to maximize the flow of photosynthetically active radiation (PAR) for the effectual photosynthetic activity of plants; meanwhile, non-PAR is utilized in agrivoltaics for generating electricity. In this study, we report the synthesis of novel four UV-selective absorbers, based on the diimide scaffold, functionalized with carboxylate and pyridyl anchoring groups, for adequate adsorption onto the TiO2 electrode in DSC. The UV/Vis absorption spectra of the DMF solution-based free dyes were measured experimentally. Basic photophysical and energetics requirements for operating greenhouse-integrated DSCs were examined at the molecular level via (time-dependent) density functional theory-based calculations. The computational results revealed the outperformance of the biphenyldiimide-structured DI-CA1 dye, especially for maximum charge transferred to its anchor, lower thermodynamic barrier for dissociating the photogenerated exciton, largest Stokes' shift, strong electronic coupling with TiO2 nanoparticles, and higher degree of charge separation at the DI-CA1/TiO2 interface. PDOS showed deeper existence for the LUMO level in the CB of TiO2, which expedites the electron injection process. The chemical and optical compatibility of DI-CA1 were then investigated as a potential cosensitizer of a reference BTD–DTP1, a green light-absorbing dye. Considerable overlap between the fluorescence spectrum of DI-CA1 and absorption spectrum of the reference BTD–DTP1 advocated the opportunity of excitation energy transfer via the radiative trivial reabsorption mechanism, which confirms the cosensitization functionality. Energy decomposition analysis and reduced density gradient maps estimated the chemical compatibility owing to weak dispersion interactions as the dominant stabilizing attractive force. This noncovalent functionalization retains the chemical compatibility without distorting the π–π conjugation and the associated physicochemical properties of the individual dye molecules. Along with the expanded consumption of non-photosynthetically active solar radiation, an improved power conversion efficiency of greenhouse-integrated DSC is accordingly expected.

Anatomy of high-uniform unidirectional volatile switching behavior in SiO2/TiO2-based selection device

Unidirectional volatile switching behavior is a typical resistive switching phenomenon in oxides, which has been proposed as attractive candidates for selection devices for high density memory and neuromorphic systems applications with cross-point arrays. However, the microscopic origin of the underlying mechanism is still unclear due to the lack of direct experimental evidence. Here, a high performance selection device with a low forming voltage, low OFF-state current, high nonlinearity, and excellent uniformity is proposed in SiO2/TiO2 stacked structure. The underlying nature of the unidirectional volatile switching behavior in the Pt/Ag/SiO2/TiO2/Ti selection device is revealed by using scanning electron microscope and energy-dispersive X-ray spectroscopy analysis in planar structure devices, which can be attributed to the unstable conductive filament (CF) consisting of Ag nanoparticles formed in the SiO2 layer, and the Schottky contact formed between the Ag CF and TiO2 interface. This work provides clearly experimental evidence to deepen understanding of themechanism for unidirectional volatile switching behavior, which can provide a guide to further improve the device performances for high density memory and neuromorphic systems applications.

Fabrication of a stable light-activated and p/n type AgVO3/V2O5-TiO2 heterojunction for pollutants removal and photoelectrochemical water splitting

In this study, we fabricated TiO2 nanorod arrays (TiO2), which were decorated with AgVO3 quantum dots (QDs) on and a layer of V2O5 film, forming a heterojunction material for removal pollutants and photoelectrochemical (PEC) water splitting. The AgVO3/V2O5-TiO2 nanorod arrays (AgVO3/V2O5-TiO2) synthesized by the secondary hydrothermal method were grown on conductive glass to form one-dimensional (1D) nanorod and p-n junction structures. Through experimental characterisation and testing, optical, morphological photocatalysis and PEC characteristics of the materials were measured and studied. The TiO2 modified with AgVO3 and V2O5 can significantly improve the visible light optical absorption, the reduce the electron-hole pair binding rate and shorten the band gap (3.07–1.41 eV) of TiO2. The resulting photocurrent density (116 uA/cm2) and photodegradation efficiency (rate constant, k = 0.025 min−1) of AgVO3/V2O5-TiO2 are approximately 20 (6 uA/cm2) and 5 times (0.005 min−1) higher than those of bare TiO2, respectively. The AgVO3/V2O5-TiO2 achieved a current density of 10 mA at an overpotential of 246.2 mV and exhibited excellent oxygen evolution reaction (OER) performance. The systematic PEC experiments concluded that the optimized of the TiO2 interface by AgVO3 and V2O5 could promote the separation and transport of charge carriers.

Origin of Kinetic Dispersion in Eosin-Sensitized TiO2: Insights from Single-Molecule Spectroscopy

By removing the effects of ensemble averaging and molecular aggregation, we untangle the factors that govern the dispersive electron transfer kinetics of eosin-sensitized TiO2, focusing on the impact of environmental heterogeneity versus injection from multiple excited states. The blinking dynamics of single eosin Y chromophores on nanocrystalline TiO2 films are analyzed using a change point detection algorithm for binned data. Robust statistical analysis based on maximum likelihood estimation, Kolmogorov–Smirnov tests, and log likelihood ratio tests is used to determine the functional form that best fits the resulting on- and off-time distributions and to distinguish between mechanisms for dispersive electron transfer. Using this approach, we find that the on- and off-time distributions for eosin Y on TiO2 are best fit to lognormal distributions corresponding to μon = −0.64 ± 0.04, σon = 1.52 ± 0.02, μoff = −0.23 ± 0.04, and σoff = 1.96 ± 0.03, respectively. Monte Carlo simulations based on the Albery model for dispersive electron transfer (i.e., where the median rate constant κ is modified by the exponential of a parameter, x, that is normally distributed, k = κ e–γx) successfully reproduce this behavior using a median rate constant for injection and back electron transfer of ∼1010 and ∼104 s–1, respectively, and a corresponding energetic dispersion, γ, of ∼200–350 meV. To examine how injection from both the singlet and triplet excited states contributes to this dispersion, we studied two rhodamine sensitizers, R123 and 5ROX, that inject only from their singlet excited state. Surprisingly, when access to the T1 state is minimized in going from EY to R123 and 5ROX, kinetic dispersion actually increases. Collectively, these observations support the interpretation that static and dynamic inhomogeneities at the EY–TiO2 interface govern kinetic dispersion, with dynamic fluctuations in binding configuration and/or vibrational motion playing a decisive role.

A Conductive Network and Dipole Field for Harnessing Photogenerated Charge Kinetics.

Photogenerated charge separation and directional transfer to active sites are pivotal steps in photocatalysis, which limit the efficiency of redox reactions. Here, a conductive network and dipole field are employed to harness photogenerated charge kinetics by using a Ti3 C2 /TiO2 network (TTN). The TTN exhibits a prolonged charge-carrier lifetime (1.026ns) and an 11.76-fold increase in hexavalent chromium photoreduction reaction kinetics compared to TiO2 nanoparticles (TiO2 NPs). This super photocatalytic performance is derived from the efficient photogenerated charge kinetics, which is steered by the conductive network and dipole field. The conductivity enhancement of the TiO2 network is achieved by continuous chemical bonds, which promotes electron-hole (e-h) separation. In addition, at the interface of Ti3 C2 and TiO2 , band bending induced by the dipole field promotes photogenerated electron spatially directed transfer to the catalytic sites on Ti3 C2 . This study demonstrates that a conductive network and dipole field offer a new concept to harness charge kinetics for photocatalysis.

New emerging magnetic, optical and photocatalytic properties of Tb doped TiO2 interfaced with CoFe2O4 nanoparticles

The CoFe2O4/TiO2:Tb composite nanoparticles were prepared by a two-stage chemical route. The composites were characterized by using X-Ray Diffraction, Transmission Electron Microscopy, X-ray and UV Photoelectron Spectroscopies, FT-IR, Raman and UV–Vis spectroscopies.There is a polarized spin transfer at the interface between the cobalt ferrite into the TiO2 conduction band. As a result, the magnetic moments of oxygen vacancies in TiO2 becomes (ferro) magnetically ordered. The magnetic moments sublattice of Tb ions may have an either “ferro” or “antifero” coupling depending on the dopant concentration. The magnetic semiconductor intensifies the optical absorption in the visible. There is a band-to-band absorption assisted by single-occupied oxygen vacancies coupled to some local crystal lattice relaxations.The lifetime of the photoexcited electrons in the conduction band increases due to their coupling with magnetically ordered interface transferred states. Also, the trapping of electrons into multiplet states of Tb3+ reduces the recombination rate. The photocatalytic efficiency of the magnetically ordered titania increases with respect to bare TiO2. The reactive oxygen species produced at the solid–liquid interface of TiO2 were identified by Electron Spin Resonance coupled with spin-trapping technique. The results were correlated to the presence of the magnetic order inside the titania.

Facilitated interfacial charge separation using triphenylamine-zinc porphyrin dyad-sensitized TiO2 nanoparticles for photocatalysis

Three triphenylamine (TPA) substituted dichromophoric zinc porphyrins XZP1–3 and a single zinc porphyrin ZP1 have been rationally designed to construct dye-sensitized TiO2 nanoparticles to explore the feasibility of dichromophoric dye design for photocatalysis. TPA, N,N-diphenyl-(1,1′-biphenyl)− 4-amine and a carbazole-diphenylaniline derivative are attached to the meso-position of porphyrin core as the second chromophore. The electronic structure of the porphyrins is studied by density functional theory (DFT) calculations and the dye-sensitized composites are investigated using couples of spectral and electrochemical techniques. XZP2/TiO2 exhibits the smallest charge transfer resistance and the longest electron lifetime among the investigated composites. The same catalyst performs the highest efficiency in photodegradation of both acid black (AB1) and tetracycline (TC) polluted water samples. Electronic paramagnetic resonance and radical quenching experiments reveal that the priority reactive species are superoxide radicals (•O2−) and holes (h+), suggesting the efficient charge separation at the porphyrin-sensitized TiO2 interface. This work demonstrates the facilitated interfacial charge separation using dichromophoric dye-sensitized semiconductor particles for photodegradation and, the insights should aid in dyad design for photocatalysis application.

Exploiting Free-Standing p-CuO/n-TiO2 Nanochannels as a Flexible Gas Sensor with High Sensitivity for H2S at Room Temperature.

Hydrogen sulfide (H2S) is an extremely hazardous gas and is harmful to human health and the environment. Here, we developed a flexible H2S gas-sensing device operated at room temperature (25 °C) based on CuO nanoparticles coated with free-standing TiO2-nanochannel membranes that were prepared by simple electrochemical anodization. Benefiting from the modulated conductivity of the CuO/TiO2 p-n heterojunction and a unique nanochannel architecture, the traditional thermal energy was innovatively replaced with UV irradiation (λ = 365 nm) to provide the required energy for triggering the sensing reactions of H2S. Importantly, upon exposure to H2S, the p-n heterojunction is destroyed and the newly formed ohmic contact forms an antiblocking layer at the interface of CuS and TiO2, thus making the sensing device active at room temperature. The resulting CuO/TiO2 membrane exhibited a notable detection sensitivity for H2S featuring a minimum detection limit of 3.0 ppm, a response value of 46.81% against 100 ppm H2S gas, and a rapid response and recovery time. This sensing membrane also demonstrated excellent durability, long-term stability, and wide-range response to a concentration of up to 400 ppm in the presence of 40% humidity as well as outstanding flexibility and negligible change in electrical measurements under various mechanical stability tests. This study not only provides a new strategy to design a gas sensor but also paves a universal platform for sensitive gas sensing.

Manipulating Intermediates at the Au–TiO2 Interface over InP Nanopillar Array for Photoelectrochemical CO2 Reduction

Manipulating Intermediates at the Au–TiO₂ Interface over InP Nanopillar Array for Photoelectrochemical CO₂ Reduction

INVESTIGATION ON DRY SLIDING WEAR BEHAVIOR OF TITANIUM DIOXIDE-REINFORCED MAGNESIUM MATRIX COMPOSITE

In this work, the dry sliding wear behaviors of pure monolithic magnesium and magnesium–titanium dioxide (Mg–TiO2) composites were studied using pin-on-disc tribometer against an oil-hardened nonshrinking die steel (OHNS) counter-disc with a normal load of 0.5–2[Formula: see text]kg and a sliding velocity of 1.5–2.5[Formula: see text][Formula: see text] with the sliding distance and wear track diameter of 1500[Formula: see text]m and 90[Formula: see text]mm, respectively. The pin samples were characterized for their microstructural, nanomechanical and tribological properties such as wear rate, coefficient of friction and wear fractographs. Scanning electron microscopy (SEM) was used to analyze the worn-out surfaces of each pin sample in order to identify the different types of wear and wear mechanisms and the chemical constituents of each element were quantified by energy-dispersive spectroscopy. The influence of TiO2 reinforcements on the nanomechanical behavior was studied by nanoindentation technique. As compared with pure Mg, the nanoindentation strengths of Mg–1.5TiO2, Mg–2.5TiO2 and Mg–5TiO2 composites were found to increase by 11.9%, 22.2% and 35.8%, respectively, which was due to the addition of TiO2 particles and also due to the good bonding at the interface of TiO2 and magnesium particles. From the wear test results, a significant change in wear rate was observed with the change in normal load than that of sliding speed, whereas a significant change in coefficient of friction was noticed with the changes in both normal load and sliding velocity. The dominant wear mechanisms involved under the testing conditions were identified through plotting the contour maps and SEM fractographs. Also, from the fractographs it was noticed that delamination and plowing effect have been the significant wear mechanisms observed during low wear rate of samples, whereas melting, delamination and oxidation wear have been observed during high wear rate of pure Mg and its composites.

Insights into Photocatalytic Selective Dehydrogenation of Ethanol over Au/Anatase–Rutile TiO2

Selective dehydrogenation of ethanol under mild conditions is of great significance for the conversion of ethanol into high-value chemicals. This work reports Au/anatase–rutile TiO2 photocatalysts for the targeted activation of O–H and α–H bonds and provides deep insights into the ethanol photocatalytic mechanism. In situ EPR, in situ FT-IR, and XPS were performed on Au/anatase–rutile TiO2 to explore the photocatalytic selective dehydrogenation process of ethanol. Under UV irradiation, O–H and α–H bonds of ethanol can be activated on TiO2 at the same time. Detailed investigations verified that Au/rutile TiO2 dominates the activation of O–H and facilitates the generated CH3CH2O• and CH3CH(OH)• diffused in the liquid phase for their subsequent reaction to 1,1-diethoxyethane (DEE). While radicals formed on Au/anatase TiO2 can not only react directly for DEE formation, they can also further dehydrogenate to acetaldehyde due to the strong adsorption on the surface of the catalyst and then produce DEE by condensation with ethanol. Au nanoparticles distributed at the anatase–rutile TiO2 interface show a significant electron–hole separation efficiency; therefore, the photocatalytic activity of ethanol selective dehydrogenation was improved. This study is of vital importance to the understanding of the reaction mechanism of photocatalytic ethanol conversion.

Dual-channel D-(π-A)2 phenoxazine/phenothiazine dyes with an auxiliary N-alkoxy benzoic acid anchor for fabrication of dye-sensitized solar cells

Research and exploitation of metal free organic photosensitizers with multi-electron transfer channels have attracted extensive attention in recent decade because of these chromophores possess obvious merits comparing to the single electron transfer channel analogues. Herein, four dual-channel D-(π-A)2 dyes (OT6, OT12, TT6, and TP6) with an auxiliary N-alkoxy benzoic acid anchor in side chain have been synthesized and characterized. The variation of structural segments such as donor phenoxazine/phenothiazine, π-bridge thiophene/benzene, and the different length of alkyl branch chain n-hexyl/n-dodecyl embedded in the skeleton of dyes exerts a conspicuous influence on the photophysical, electrochemical, and photoelectrochemical properties of the pristine dyes. The rich electron-donating unit of phenoxazine or thiophene employed as donor or π-bridge is beneficial to broaden the absorption spectra, increase the light-harvesting efficiency, reduce the electron injection voltage loss, and diminish the torsion dihedral angle between donor and π-bridge. These aforesaid factors are conducive to generate a relatively superior short-circuit current for the corresponding devices. Meantime, the longer alkyl side chain of n-dodecyl amalgamated with the auxiliary benzoic acid anchor helps in dominating the adsorption of dyes and hindering the charge recombination processes at the TiO2 interface and thus to achieve the higher open circuit-voltage which derived from the longer excited electron lifetime of the cells. Consequently, a maximal power conversion efficiency of 5.74% for OT12 is attributed to the comparatively higher short-circuit current and open circuit-voltage of the cells in liquid iodide/triiodide redox couple.

Light-induced osteogenic differentiation of BMSCs with graphene/TiO2 composite coating on Ti implant

Light-induced surface potential have been demonstrated as an effective bone marrow mesenchymal stem cells (BMSCs) osteogenic differentiation regulator. However, traditional bone repair implants almost were weak or no light-responsive. Fortunately, surface modification was a feasible strategy to realize its light functionalization for bone implants. Herein, a graphene oxide (GO)/titanium dioxide (TiO2) nanodots composite coating on the surface of titanium (Ti) implant was constructed, and GO was reduced to reduced graphene oxide (rGO) with the method of UV-assisted photocatalytic reduction. After rGO deposited on the surface of TiO2, a heterojunction formed at the interface of rGO and TiO2. With visible light illumination, positive charges accumulated on the surface of rGO/TiO2 film, and performed as a positive surface potential change. The light-induced surface potential which was generated under proper light intensity is harmless to the cell adhesion and proliferation behavior, but presented a good BMSCs osteogenic differentiation promoting effect, and the activation of the voltage-gated calcium channels through surface potential and the promotion of the adsorption of osteogenic growth factors could be the reason. This work given a new insight of the modification for Ti implant with a light-induced surface potential, and shows potential application for bone regeneration on the clinical practice through light stimulation.