Photoelectrochemical oxidation of hydrazine on TiO2 modified titanium electrode: its application for detection of hydrazine

Despite extensive investigations on the photoelectrochemical properties of TiO₂-based electrodes, it is surprising that no photoelectrochemical investigation has been done for the case of hydrazine oxidation. In this paper, TiO₂ modified titanium (Ti/TiO₂) electrode was fabricated by anodization process under a constant applied potential. The morphological and microstructural characterization of the Ti/TiO₂ electrode was performed by scanning electron microscopy (SEM). The electrochemical and photoelectrochemical behavior of Ti/TiO₂ electrode in the absence and presence of hydrazine was examined by cyclic voltammetry and linear sweep voltammetry. Experimental results indicated that the photocurrent response of photoelectrode was highly increased in the presence of hydrazine especially at lower potentials. It can be due to hole scavenging effect of hydrazine which decreases the recombination of photogenerated electrons and holes. Based on these perceptions, a simple photoelectrochemical sensor for detection of hydrazine was obtained. The sensor showed high reproducibility, stability, and selectivity properties. This photoelectrode was successfully applied for direct determination of hydrazine in tap water.     

SrTiO3/TiO2 Hybridstructure as Photoanode in Dye‐Sensitized Solar Cell

In dye‐sensitized solar cells (DSSCs), the charge recombination at the TiO₂/dye/electrolyte interface greatly influences the photoelectron conversion efficiency. Hybrid semiconductor materials with matched band potentials are designed to reduce the charge recombination. In this study, SrTiO₃/TiO₂ hybridstructure was synthesized by using TiO₂ nanoparticles as template in a hydrothermal, showing a negative shift in the flat band potential. The DSSC with the SrTiO₃/TiO₂ anode exhibits an increased photovoltage and a reduced photocurrent. The suppression of charge recombination at the TiO₂/dye/electrolyte interface was observed in the electrochemical impedance spectroscopy, causing an improvement in the photovoltage. However, the SrTiO₃/TiO₂ system shows an obstructed electrons injection from the dye to SrTiO₃/TiO₂, limiting the photocurrent performance. The photoelectrochemical properties of the SrTiO₃/TiO₂ system are discussed in detail herein.     

CdS/TiO2–SrTiO3 heterostructure nanotube arrays for improved solar energy conversion efficiency

TiO₂–SrTiO₃ heterostructure nanotube arrays have been utilized as a novel oxide substrate for CdS quantum dot sensitized solar cells (QDSCs). SrTiO₃ on TiO₂ surface passivates surface states of TiO₂ and builds cascade-structured band alignment, which significantly reduces charge recombination at electrode surface. CdS/TiO₂–SrTiO₃ electrode exhibits a superior photoelectrochemical performance than CdS/TiO₂ electrode with ～ 70% increase in external quantum efficiency. This study suggests that the suppression of charge recombination at electrode surface is critical to efficient solar energy conversion.     

Effect of calcination temperature on the photocatalytic activity of carbon‐doped titanium dioxide revealed by photoluminescence study

Carbon‐doped titania (C‐TiO₂) nanoparticles were synthesized by the sol–gel method at different calcination temperatures (300–600°C) employing titanium tetraisopropoxide (TTIP) as the titanium source and polyoxyethylene sorbitan monooleate (Tween 80) as the carbon source. The physical properties of C‐TiO₂ samples were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic activities were checked through the photodegradation of phenolphthalein (PHP) under ultraviolet irradiation. The UV spectrum showed that the carbon doping extends the absorption range of TiO₂ to the visible region. However, the photocatalytic activity is affected by the electron–hole recombination phenomenon, as revealed by the photoluminescence (PL) study. According to the PL spectra, carbon doping reduces the edge‐to‐edge electron–hole recombination. Nevertheless, the number of defect sites is greatly influenced by the calcination temperature of C‐TiO₂. C‐TiO₂ that was calcined at 400°C showed the highest photodegradation percentage of PHP, which was mainly attributed to the synergic effect of the low direct edge‐to‐edge electron–hole recombination, high content of defect sites, and retention of active electrons on the surface hydroxyl group.     

Solgel-hydrothermal synthesis of Tb/Tourmaline/TiO2 nano tubes and enhanced photocatalytic activity

In this study, we synthesized Tb/Tourmaline/TiO₂ nano tubes (NTs) through a solgel-hydrothermal method. The as-prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectromicroscope, scanning electron microscopy, transmission electron microscopy and UV-vis diffuse reflectance spectroscopy. The resulting Tb/Tourmaline/TiO₂ NTs exhibited higher photocatalytic activity than pure TiO₂ and TiO₂ nano particles (NPs) in the degradation of menthyl orange under UV-light. Results revealed that doping rare earth element Tb could narrow the wide band gap of TiO₂ and tourmaline could trap the photogenerated electron of TiO₂ to inhibit the recombination of photogenerated electron-hole pairs.     

CdSeTe@CdS@ZnS Quantum‐Dot‐Sensitized Macroporous Tio2 Film: A Multisignal‐Amplified Photoelectrochemical Platform

A macroporous TiO₂ film (M‐TiO₂), which was prepared by burning off the polystyrene microsphere (PS) template from a PS/TiO₂ composite film, can provide a large active surface, improve electron‐transport performance, and increase the photocurrent. Furthermore, core–shell–shell CdSeTe@CdS@ZnS quantum dots (QDs) were introduced to sensitize the M‐TiO₂ film, which can efficiently broaden the absorption spectra range, separate and transfer charge carriers, reduce recombination loss, and improve photovoltaic response, with a sensitization shell of CdS and a passivation shell of ZnS. A multisignal‐amplified photoelectrochemical platform was fabricated by further modifying this film with a combination of biotin–DEVD–peptide (Biotin–Gly–Asp–Gly–Asp–Glu–Val–Asp–Gly–Cys) (which is specifically cleaved by caspase‐3) and streptavidin‐labeled alkaline phosphatase (SA‐ALP). Under the enzymatic catalysis of ALP with the substrate 2‐phospho‐L ‐ascorbic acid trisodium salt (AAP), ascorbic acid (AA) was generated as a better electron donor, leading to increased photocurrent output. The activity of caspase‐3, which depends on the amount of residual peptide on the electrode, was inversely proportional to the amount of AA. By monitoring the variation of photocurrent caused by AA, caspase‐3 activity and the therapeutic effect of nilotinib (a special medicine of chronic myeloid leukemia, CML) were indirectly detected and evaluated. The photoelectrochemical platform can be used as a potential evaluation system for monitoring caspase‐3 activity and drug effects.     

FeO(OH)-TiO2/CoPi复合光阳极的制备及其光电催化氧化水性能

采用溶胶-凝胶法制备了TiO₂ 纳米晶, 并通过浸渍技术在其表面引入了FeO(OH). 采用紫外-可见(UV-Vis)吸收光谱确定了引入FeO(OH)的最佳Fe³⁺浓度. 通过电化学法在FeO(OH)-TiO₂光阳极上沉积了催化水分解制备氧气的钴基催化剂(CoPi), 得到了FeO(OH)-TiO₂/CoPi 复合光阳极. 利用透射电镜(TEM), 高分辨透射电镜(HRTEM), X射线衍射(XRD), 扫描电镜(SEM)对TiO₂纳米晶, FeO(OH)-TiO₂以及FeO(OH)-TiO₂/CoPi复合光阳极进行了表征, 采用电化学和光电化学技术研究了中性条件下FeO(OH)-TiO₂/CoPi 复合光阳极的光电催化分解水性能. 结果表明, TiO₂纳米晶为梭形的锐钛矿, 其表面修饰的FeO(OH)为针铁矿型, 且当前驱体溶液中Fe³⁺与TiO₂的质量比为0.05%时得到的FeO(OH)-TiO₂具有最佳的光吸收效果. 形成FeO(OH)-TiO₂/CoPi复合光阳极后, 在光照条件下CoPi 电催化分解水制备氧气的过电位显著降低. TiO₂表面FeO(OH)的引入增加了光阳极对可见光的吸收能力, 同时光阳极表面沉积的CoPi有效地利用了FeO(OH)-TiO₂产生的光生空穴, 将水氧化形成氧气, 从而在光照条件下显著提高了CoPi催化氧化水的效率.     

Enhanced photoelectrochemical properties of visible light-responsive TiO2 photoanode for separate-type Pt-free photofuel cells by Rh3+ addition

Visible light-responsive TiO₂ (Vis-TiO₂) electrode has been applied for the Pt-free separate-type photofuel cell (SPFC) where two different electrolytes containing various biomass derivatives and a I₃ ^?/I^? redox solution were employed for the anode and cathode sides, respectively. This new SPFC exhibits good photoelectrochemical performance under simulated solar-light irradiation. It was found that the Rh³⁺ loading on Vis-TiO₂ electrode enhanced the photoelectrochemical performance of the SPFC through the increase in the visible light absorption as well as the increase in the electron conductivity of Vis-TiO₂ electrode.     

Enhancing Electron Collection Efficiency and Effective Diffusion Length in Dye‐Sensitized Solar Cells

Intensity‐modulated photocurrent spectroscopy and intensity‐modulated photovoltage spectroscopy are employed to measure the dynamics of electron transport and recombination in the ZnO nanowire (NW) array‐ZnO/layered basic zinc acetate (LBZA) nanoparticle (NP) composite dye‐sensitized solar cells (DSSCs). The roles of the vertical ZnO NWs and insulating LBZA in the electron collection and transport in DSSCs are investigated by comparing the results to those in the TiO₂–NP, horizontal TiO₂–NW and vertical ZnO–NW‐array DSSCs. The electron transport rate and electron lifetime in the ZnO NW/NP composite DSSC are superior to those in the conventional TiO₂–NP cell due to the existence of the vertical ZnO NWs and insulating LBZA. It indicates that the ZnO NW/NP composite anode is able to sustain efficient electron collection over much greater thickness than the TiO₂–NP cell does. Consequently, a larger effective electron diffusion length is available in the ZnO composite DSSC.     

Chemical synthesis of Ni/TiO<Subscript>2</Subscript> nanophotocatalyst for UV/visible light assisted degradation of organic dye in aqueous solution

The Ni/TiO₂ nanoparticles with different Ni dopant content were prepared by a modified sol–gel method. The structure and photoinduced charge properties of the as-prepared catalysts were determined using X-ray diffraction, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy and surface photovoltage spectroscopy techniques, and the photocatalytic efficiency of these catalysts was tested using an organic dye. It was shown that Ni modification could greatly enhance the photocatalytic efficiency of these nanocomposite catalysts by taking the photodegradation of methyl orange as a model reaction. With appropriate ratio of Ni and TiO₂, Ni/TiO₂ nanocomposites showed the superior photocatalytic activity than the single TiO₂ nanoparticles. Surface photovoltage spectra demonstrated that Ni modification could effectively inhibit the recombination of the photoinduced electron and holes of TiO₂. This electron–hole pair separation conditions are responsible for the higher photocatalytic performance of Ni/TiO₂ nanocomposites in the visible region of electromagnetic spectrum.     

Correlation between Energy and Spatial Distribution of Intragap Trap States in the TiO2 Photoanode of Dye‐Sensitized Solar Cells

The energy and spatial distribution of intragap trap states of the TiO₂ photoanode of dye‐sensitized solar cells and their impact on charge recombination were investigated by means of time‐resolved charge extraction (TRCE) and transient photovoltage (TPV). The photoanodes were built from TiO₂ nanospheroids with different aspect ratios, and the TRCE results allowed differentiation of two different types of trap states, that is, deep and shallow ones at the surface and in the bulk of the TiO₂ particles, respectively. These trap states exhibit distinctly different characteristic energy with only a slight variation in the particle size, as derived from the results of the density of states. Analyses of the size‐dependent TPV kinetics revealed that in a moderate photovoltage regime of about 375–625 mV, the dynamics of electron recombination are dominated by shallow trap states in the bulk, which can be well accounted for by the mechanism of multiple‐trap‐limited charge transport.     

Sensitization of Mn with CdS nanoparticles via electrochemical deposition technique for photocurrent enhancement of nanomaterial’s-sensitized photoelectrochemical cells

A photoconversion efficiency of 2.12% was obtained under visible light illumination by nanostructure-sensitized photoelectrochemical cells using Mn/CdS as sensitizer loaded on TiO₂ nanotube arrays (NTAs) (Mn/CdS/TiO₂). Sensitization of Mn on CdS nanoparticles pre-loaded on TiO₂ NTAs was carried out by a two-step electrodeposition method. Compared with unsensitized TiO₂ NTAs, the photocurrent had increased from 0.03 to 4.12 for Mn/CdS/TiO₂ prepared at 1 min. The effects of deposited Mn on the physical, chemical, and photoelectrochemical properties of the CdS/TiO₂ NTAs nanostructure were investigated by using UV–visible diffuse reflectance spectroscopy, X-ray diffractometry, and field-emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The photoelectrochemical analysis was examined in a three-electrode system under a halogen illumination by using the prepared film as the photo-anode.     

Single‐Walled TiO2 Nanotubes: Enhanced Carrier‐Transport Properties by TiCl4 Treatment

In the present work we report significant enhancement of the photoelectrochemical properties of self‐ organized TiO₂ nanotubes by a combined “de‐coring” of classic nanotubes followed by an appropiate TiCl4 treatment. We show that, except for the expected particle decoration, a key effect of the TiCl4 treatment is that the electron transport characteristics in TiO₂ nanotubes can be drastically improved, for example, we observe an enhancement of up to 70 % in electron‐transport times.     

An Efficient Strategy for Boosting Photogenerated Charge Separation by Using Porphyrins as Interfacial Charge Mediators

Surface recombination at the photoanode/electrolyte junction seriously impedes photoelectrochemical (PEC) performance. Through coating of photoanodes with oxygen evolution catalysts, the photocurrent can be enhanced; however, current systems for water splitting still suffer from high recombination. We describe herein a novel charge transfer system designed with BiVO₄ as a prototype. In this system, porphyrins act as an interfacial‐charge‐transfer mediator, like a volleyball setter, to efficiently suppress surface recombination through higher hole‐transfer kinetics rather than as a traditional photosensitizer. Furthermore, we found that the introduction of a “setter” can ensure a long lifetime of charge carriers at the photoanode/electrolyte interface. This simple interface charge‐modulation system exhibits increased photocurrent density from 0.68 to 4.75 mA cm^?2 and provides a promising design strategy for efficient photogenerated charge separation to improve PEC performance.     

掺杂纳米金粒子的火焰氧化TiO2膜的光电化学性质的研究

A nano-Au modified TiO2 electrode was prepared via the oxidation of Ti sheet in flame and subsequent modification with gold nanoparticles. The results of SEM and TEM measurements show that the Au nanoparticles are well dispersed on TiO2 surface. A near 2-fold enhancement in photocurrent was achieved upon the modification with Au nanoparticles. From the results of photocurrent and electrochemical impedance experiments it was found that the flatband potential of nano-Au/TiO2 electrode negatively shifted about 100 mV in 0.5 mol/L Na2SO4 solutions compared with that of bare TiO2 electrode. The improvement of photoelectrochemical performance was explained by the inhibition for charge recombination of photo-induced electrons and holes, and the promotion for interracial charge-transfer kinetics at nano-Au/TiO2 composite film. Such nanometal-semiconductor composite films have the potential application in improving the performance of photoelectrochemical solar cells.     

Cu2O/reduced graphene oxide/TiO2 nanomaterial: An effective photocatalyst for azide-alkyne cycloaddition with benzyl halides or epoxide derivatives under visible light irradiation

Cu₂O/reduced graphene oxide/TiO₂ (Cu₂O/rGO/TiO₂) photocatalyst was synthesized under ultrasonic irradiation. The nanomaterial was identified by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, UV–vis absorption, and inductively coupled plasma optical emission spectroscopy (ICP-OES). The Cu₂O/rGO/TiO₂ photocatalyst was utilized in “click” reaction for the preparation of 1,4-disubstituted 1,2,3-triazoles via one pot multicomponent reaction of benzyl halide or epoxide derivatives with alkynes in presence of NaN₃ and triethylamine under visible light irradiation. The “click” reaction was performed under mild conditions affording good to excellent yields of the triazole compounds using low catalyst loading in short reaction times. The nanocomposite was recovered and recycled for five successive runs without a major diminution in its catalytic performance.     

Fabrication of Heterostructured Fe2TiO5–TiO2 Nanocages with Enhanced Photoelectrochemical Performance for Solar Energy Conversion

Photocatalysts with well-designed compositions and structures are desirable for achieving highly efficient solar-to-chemical energy conversion. Heterostructured semiconductor photocatalysts with advanced hollow structures possess beneficial features for promoting the activity towards photocatalytic reactions. Here we develop a facile synthetic strategy for the fabrication of Fe₂TiO₅–TiO₂ nanocages (NCs) as anode materials in photoelectrochemical (PEC) water splitting cells. A hydrothermal reaction is performed to transform MIL-125(Ti) nanodisks (NDs) to Ti–Fe–O NCs, which are further converted to Fe₂TiO₅–TiO₂ NCs through a post annealing process. Owing to the compositional and structural advantages, the heterostructured Fe₂TiO₅–TiO₂ NCs show enhanced performance for PEC water oxidation compared with TiO₂ NDs, Fe₂TiO₅ nanoparticles (NPs) and Fe₂TiO₅–TiO₂ NPs.     

Fabrication of Heterostructured Fe2TiO5–TiO2 Nanocages with Enhanced Photoelectrochemical Performance for Solar Energy Conversion

Photocatalysts with well‐designed compositions and structures are desirable for achieving highly efficient solar‐to‐chemical energy conversion. Heterostructured semiconductor photocatalysts with advanced hollow structures possess beneficial features for promoting the activity towards photocatalytic reactions. Here we develop a facile synthetic strategy for the fabrication of Fe₂TiO₅–TiO₂ nanocages (NCs) as anode materials in photoelectrochemical (PEC) water splitting cells. A hydrothermal reaction is performed to transform MIL‐125(Ti) nanodisks (NDs) to Ti–Fe–O NCs, which are further converted to Fe₂TiO₅–TiO₂ NCs through a post annealing process. Owing to the compositional and structural advantages, the heterostructured Fe₂TiO₅–TiO₂ NCs show enhanced performance for PEC water oxidation compared with TiO₂ NDs, Fe₂TiO₅ nanoparticles (NPs) and Fe₂TiO₅–TiO₂ NPs.     

Structural and photoelectrochemical characterization of MWCNT-TiO2 matrices sensitized with Bi2S3

Structural and photoelectrochemical characterization of multiwall carbon nanotubes–titanium oxide (MWCNT-TiO₂) matrices, sensitized with bismuth sulfide (Bi₂S₃), are presented as a function of MWCNT-TiO₂ annealing temperature and Bi₂S₃ deposition time. Random matrices of multiwall carbon nanotubes were grown on stainless steel substrates by spray pyrolysis and then functionalized with a thin layer of TiO₂. Air annealing modifies the morphology and C/TiO₂ ratio in the hybrid materials, from MWCNT-TiO₂ core and shell structures at 400 °C to carbon-doped TiO₂ (C-TiO₂) at 550 °C. Both matrices increase the amount of Bi₂S₃ deposited by the chemical bath, but the best photoelectrochemical performance is observed in electrodes based on C-TiO₂. Electrodes based on core–shell structures of MWCNT-TiO₂ show large capacitive currents that interfere with photocurrent generation, demonstrating the storage potential of MWCNT and the critical role of MWCNT/TiO₂ ratio for photoelectrochemical applications. Regardless of the superior properties of C-TiO₂ photoanodes, the power conversion efficiency of Bi₂S₃-sensitized C-TiO₂ is limited by the appearance of an electron collection barrier at the substrate/film interface.     

Formation of anodic TiO2 nanotube or nanosponge morphology determined by the electrolyte hydrodynamic conditions

The present work studies the effect of hydrodynamic conditions on the growth of anodic TiO₂ nanostructures on Ti in a glycerol/water/NH₄F electrolyte. Parameter screening for fluoride content, anodization voltage and rotation rate (Reynolds number) of a rotating anode showed that two distinctly different TiO₂ morphologies could be obtained: the classic ordered nanotubes or a nanoscale sponge layer. We present conditions for TiO₂ sponge formation and growth to several micrometers of thickness, and show that in specific cases sponge layers can be superior to tube morphologies, as illustrated for photoelectrochemical water-splitting under standard AM 1.5 conditions.