Dye sensitization of a large band gap semiconductor by an iron(III) complex

The Fe(III) complex, [Fe^III(HQS)₃] (HQS = 8-hydroxyquinoline-5-sulfonic acid), is found to effect sensitization of the large band gap semiconductor, TiO₂. The role of interfacial electron transfer in sensitization of TiO₂ nanoparticles by surface adsorbed [Fe^III(HQS)₃] was studied using femtosecond time scale transient absorption spectroscopy. Electron injection has been confirmed by direct detection of the electron in the conduction band. A TiO₂-based dye-sensitized solar cell (DSSC) was fabricated using [Fe^III(HQS)₃] as a sensitizer, and the resulting DSSC exhibited an open-circuit voltage value of 425 mV. The value of the short-circuit photocurrent was found to be 2.5 mA/cm². The solar to electric power conversion efficiency of the [Fe^III(HQS)₃] sensitized TiO₂-based DSSC device was 0.75 %. The results are discussed in the context of sensitization of TiO₂ by other Fe(II)-dye complexes.     

Preparation and Characterization of Room-temperature Ferromagnetic Ni-doped TiO2 Nanobelts

Ni-doped anatase TiO₂ nanobelts (NBs) with different Ni²⁺ contents were simply prepared by combining ion-exchange with hydrothermal treatment. They were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), and magnetic measurement techniques. The results showed that Ni²⁺ cations doped into the TiO₂ lattice and no metallic nickel clusters or nanoparticles could be found. The magnetic results demonstrated that the prepared Ni-doped TiO₂ samples had complex magnetic mechanism including room-temperature ferromagnetic and paramagnetic behaviors, and with the increase of Ni²⁺ content, the magnetization also increased under the same applied field owing to uniform distribution of Ni²⁺ ions in TiO₂ nanobelts.     

CdSe量子点敏化纳米二氧化钛太阳电池的电化学交流阻抗谱

量子点敏化纳米TiO2太阳电池(QDSSCs)具有诱人的发展前景,但是与传统的染料敏化太阳电池(DSSCs)相比,其目前的光电转换效率还非常低(仅为3%左右).为了寻找QDSSCs光电转换效率低的原因,本文主要采用外加偏压下的交流阻抗谱技术对通常以S2-/S-x离子对为电解质的CdSe胶体量子点敏化纳米TiO2电极的准...     

CdSe/ZnS量子点敏化太阳能电池电子注入与光伏性能表征

合成了CdSe/ZnS核壳结构量子点(QDs), 将其作为光敏剂吸附在TiO2纳米晶薄膜上, 组装成量子点敏化太阳能电池(QDSSCs), 从电子注入速率和电池性能两方面对QDSSCs进行了表征. 为了定量研究ZnS层包覆对电子注入的影响, 运用飞秒瞬态光谱技术, 测试了包覆ZnS前后, CdSe-TiO₂体系的电子注入速率. 实验测得ZnS包覆前后电子注入速率分别为7.14×10¹¹s^-1和2.38×10^-11s^-1, 可以看出包覆后电子注入速率明显降低, 仅为包覆前的1/3. 电池器件J-V性能测试表明, ZnS作为绝缘层包覆在CdSe的表面有效提高了QDSSCs的填充因子和稳定性, 但同时也导致了效率的降低. 上述结果说明了电子注入速率的降低是导致电池电流和效率下降的重要原因, 为今后优化核壳结构QDSSCs的电流和效率提供了依据.     

Au/TiO<Subscript>2</Subscript>/Graphene Composite with Enhanced Photocatalytic Activity Under Both UV and Visible Light Irradiation

Au/TiO₂/graphene composite was synthesized by the combination of electrostatic attraction and photo-reduction method. In the composite, graphene sheets act as an adsorption site for dye molecules to provide a high concentration of dye near to the TiO₂ and Au nanoparticles (NPs), and work as an excellent electron transporter to separate photoinduced e ^?/h ⁺ pairs. Under UV irradiation, photogenerated electrons of TiO₂ are transferred effectively to Au NPs and graphene sheets, respectively, retarding the recombination of electron–hole pairs. Under visible light irradiation, the Au NPs are photo-excited due to the surface plasmon resonance effect, and charge separation is accomplished by the interfacial electron injection from the Au NPs to the conduction band of TiO₂ and then transfer further to graphene sheets. As a result, compared with pure TiO₂, Au/TiO₂/graphene composite exhibited much higher photocatalytic activity for degradation of methylene blue under both UV and visible light irradiation, based on the synergistic effect of Au, graphene in contact with TiO₂, allowing response to the visible light, effective separation of photoinduced charges, and better adsorption of the dye molecules.     

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.     

Electron Transfer in Dye‐Sensitised Semiconductors Modified with Molecular Cobalt Catalysts: Photoreduction of Aqueous Protons

A visible‐light driven H₂ evolution system comprising of a Ru^II dye ( RuP ) and Co^III proton reduction catalysts ( CoP ) immobilised on TiO₂ nanoparticles and mesoporous films is presented. The heterogeneous system evolves H₂ efficiently during visible‐light irradiation in a pH‐neutral aqueous solution at 25 °C in the presence of a hole scavenger. Photodegradation of the self‐assembled system occurs at the ligand framework of CoP , which can be readily repaired by addition of fresh ligand, resulting in turnover numbers above 300 mol H₂ (mol CoP )^?1 and above 200,000 mol H₂ (mol TiO₂ nanoparticles)^?1 in water. Our studies support that a molecular Co species, rather than metallic Co or a Co‐oxide precipitate, is responsible for H₂ formation on TiO₂. Electron transfer in this system was studied by transient absorption spectroscopy and time‐correlated single photon counting techniques. Essentially quantitative electron injection takes place from RuP into TiO₂ in approximately 180 ps. Thereby, upon dye regeneration by the sacrificial electron donor, a long‐lived TiO₂ conduction band electron is formed with a half‐lifetime of approximately 0.8 s. Electron transfer from the TiO₂ conduction band to the CoP catalysts occurs quantitatively on a 10 μs timescale and is about a hundred times faster than charge‐recombination with the oxidised RuP . This study provides a benchmark for future investigations in photocatalytic fuel generation with molecular catalysts integrated in semiconductors.     

Enhanced hydrogen production activity over BiO_X–TiO_2 under solar irradiation:Improved charge transfer through bismuth oxide clusters

A series of titania nanoparticles and nanotubes deposited with various quantities of bismuth(Bi) were prepared via sol-gel and hydrothermal methods, respectively. They were then characterized using X-ray diffraction spectroscopy(XRD), X-ray photo electron spectroscopy(XPS), UV–Vis diffused reflectance spectra(DRS), photoluminescence spectra(PLS), transmission electron microscopy(TEM), energy dispersive analysis of X-rays(EDAX), and BET surface analysis. These catalysts were employed for the photocatalytic production of hydrogen from a mixture of pure water and glycerol under solar light irradiation. The presence of the Bi~((3+x)+) species was found to play a vital role in enhancing activity while minimizing electron hole recombination(relative to bare TiO_2). The nanotubes exhibited better activity than the nanoparticles of Bi-deposited TiO_2, showing the significance of the morphology; however, photocatalytic activity is predominantly dependent on the deposition of bismuth. The activity increased by approximately an order of magnitude at the optimum concentration of Bi deposited over TiO_2(2 wt%). The presence of the Bi~((3+x)+) species played a vital role in minimizing electron hole recombination, resulting in higher activity compared to bare TiO_2.     

Effect of the support calcination temperature on selective hydrodesulfurization of TiO2 nanotubes supported CoMo catalysts

TiO₂ nanotubes (TiO₂-NTs) were synthesized by the hydrothermal method. Co and Mo active components were supported on a series of the as-prepared TiO₂-NTs samples which were calcined at different temperatures. The effects of support calcination temperature of CoMo/TiO₂-NTs catalysts on their catalytic performance were investigated for selective hydrodesulfurization (HDS). The samples were characterized by means of the scanning electron microscopy (SEM), the transmission electron microscopy (TEM), N₂ adsorption-desorption, X-ray diffraction (XRD), Raman spectroscopy and H₂ temperature-programmed reduction (H₂-TPR). The experimental results revealed that TiO₂-NTs support calcined under 500 °C can maintain the nanotubular structure with higher surface area and pore volume. Meanwhile, the obtained supported CoMo/TiO₂-NTs catalysts exhibited weak metal-support interaction, more octahedral Mo⁶⁺ species and high catalytic performance in selective HDS.     

Doping level effect on visible-light irradiation W-doped TiO2–anatase photocatalysts for Congo red photodegradation

A series of W-modified TiO₂ (W–TiO₂) photocatalysts were synthesized by a simple sol–gel method. The new photocatalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis-diffuse reflectance spectroscopy (DRS), and Brunauer, Emmett and Teller (BET) surface area analyzer. The photoactivity of the W–TiO₂ photocatalysts was evaluated by the photocatalytic oxidation of Congo red (CR) dye. It was found that the average size of the prepared photocatalysts is 10 nm. Moreover, they have high surface areas (∼ 216 m² g⁻¹) and their light-absorption extends to the visible region compared to pure TiO₂. The effects of W-loading and of the calcination temperature of the prepared photocatalysts on their photocatalytic activity were also studied. The obtained results show that the W_0.5–TiO₂ photocatalyst calcined at 350 °C is much highly photoactive than non-doped or highly doped TiO₂. The enhanced photocatalytic activity of the weakly doped TiO₂ may be attributed to the increase in the charge separation efficiency and the presence of surface acidity on the W_0.5–TiO₂ photocatalyst.     

A New Mussel‐Inspired Polydopamine Sensitizer for Dye‐Sensitized Solar Cells: Controlled Synthesis and Charge Transfer

The efficient electron injection by direct dye‐to‐TiO₂ charge transfer and strong adhesion of mussel‐inspired synthetic polydopamine (PDA) dyes with TiO₂ electrode is demonstrated. Spontaneous self‐polymerization of dopamine using dip‐coating (DC) and cyclic voltammetry (CV) in basic buffer solution were applied to TiO₂ layers under a nitrogen atmosphere, which offers a facile and reliable synthetic pathway to make the PDA dyes, PDA‐DC and PDA‐CV, with conformal surface and perform an efficient dye‐to‐TiO₂ charge transfer. Both synthetic methods led to excellent photovoltaic results and the PDA‐DC dye exhibited larger current density and efficiency values than those in the PDA‐CV dye. Under simulated AM 1.5 G solar light (100 mW cm^?2), a PDA‐DC dye exhibited a short circuit current density of 5.50 mW cm^?2, corresponding to an overall power conversion efficiency of 1.2 %, which is almost 10 times that of the dopamine dye‐sensitized solar cell. The PDA dyes showed strong adhesion with the nanocrystalline TiO₂ electrodes and the interface engineering of a dye‐adsorbed TiO₂ surface through the control of the coating methods, reaction times and solution concentration maximized the overall conversion efficiency, resulting in a remarkably high efficiency.     

Preparation of Anatase Hollow TiO2 Spheres and Their Photocatalytic Activity in the Photodegradation of Chlorpyrifos

Hollow anatase titania (TiO₂) spheres were synthesized using fructose and tetrabutyl titanate (Ti(OC₄H₉)₄, TBT) as the precursors via the conventional hard template method. The morphological, structural and thermal properties of the products were characterized using scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG‐DTA), Brunauer? Emmett? Teller (BET) surface area analysis and diffuse reflectance ultraviolet visible (DR UV? Vis) spectroscopy. XRD revealed that the hollow TiO₂ prepared was in the anatase phase and the BET surface area measured was about 22 m² g^?1. The photocatalytic activity of the synthesized hollow anatase TiO₂ in the photodecomposition of chlorpyrifos was 18.67 % higher than that obtained using commercial TiO₂.     

Investigation of Electron Behavior in Nano‐TiO2 Photocatalysis by Using In Situ Open‐Circuit Voltage and Photoconductivity Measurements

The in situ open‐circuit voltages (V_oc) and the in situ photoconductivities have been measured to study electron behavior in photocatalysis and its effect on the photocatalytic oxidation of methanol. It was observed that electron injection to the conduction band (CB) of TiO₂ under light illumination during photocatalysis includes two sources: from the valence band (VB) of TiO₂ and from the methanol molecule. The electron injection from methanol to TiO₂ is slower than that directly from the VB, which indicates that the adsorption mode of methanol on the TiO₂ surface can change between dark and illuminated states. The electron injection from methanol to the CB of TiO₂ leads to the upshift of the Fermi level of electrons in TiO₂, which is the thermodynamic driving force of photocatalytic oxidation. It was also found that the charge state of nano‐TiO₂ is continuously changing during photocatalysis as electrons are injected from methanol to TiO₂. Combined with the apparent Langmuir–Hinshelwood kinetic model, the relation between photocatalytic kinetics and electrons in the TiO₂ CB was developed and verified experimentally. The photocatalytic rate constant is the variation of the Fermi level with time, based on which a new method was developed to calculate the photocatalytic kinetic rate constant by monitoring the change of V_oc with time during photocatalysis.     

The Effect of Heavy Atoms on Photoinduced Electron Injection from Nonthermalized and Thermalized Donor States of MII–Polypyridyl (M=Ru/Os) Complexes to Nanoparticulate TiO2 Surfaces: An Ultrafast Time‐Resolved Absorption Study

We have synthesized ruthenium(II)– and osmium(II)–polypyridyl complexes ([M(bpy)₂ L ]²⁺, in which M=Os^II or Ru^II, bpy=2,2′‐bipyridyl, and L =4‐(2,2′‐bipyridinyl‐4‐yl)benzene‐1,2‐diol) and studied the interfacial electron‐transfer process on a TiO₂ nanoparticle surface using femtosecond transient‐absorption spectroscopy. Ruthenium(II)‐ and osmium(II)‐based dyes have a similar molecular structure; nevertheless, we have observed quite different interfacial electron‐transfer dynamics (both forward and backward). In the case of the Ru^II/TiO₂ system, single‐exponential electron injection takes place from photoexcited nonthermalized metal‐to‐ligand charge transfer (MLCT) states. However, in the case of the Os^II/TiO₂ system, electron injection takes place biexponentially from both nonthermalized and thermalized MLCT states (mainly ³MLCT states). Larger spin–orbit coupling for the heavier transition‐metal osmium, relative to that of ruthenium, accounts for the more efficient population of the ³MLCT states in the Os^II‐based dye during the electron‐injection process that yields biexponential dynamics. Our results tend to suggest that appropriately designed Os^II–polypyridyl dye can be a better sensitizer molecule relative to its Ru^II analogue not only due to much broader absorption in the visible region of the solar‐emission spectrum, but also on account of slower charge recombination.     

Catalysis of redox reactions by Ag@TiO<Subscript>2</Subscript> and Fe<Superscript>3+</Superscript>-doped Ag@TiO<Subscript>2</Subscript> core–shell type nanoparticles

Ag nanoparticles encapsulated by TiO₂ shells have the ability to catalyze redox reactions on their surface. By continually monitoring by use of UV–visible spectroscopy it was found that the surface charge of both TiO₂-coated and uncoated colloidal silver particles changed after chemical electron injection. The charging and discharging process of Ag@TiO₂ vary, depending on the different Ag content of the core–shell nanoparticles. In order to enhance the stability of Ag@TiO₂ colloids, Fe³⁺ was doped into the lattice of the TiO₂ shells. The experimental results showed that the Fe³⁺ ions have the capacity to store and transfer electrons. Furthermore, the charging and discharging rate can be controlled by changing the thickness of the TiO₂ shells, because they are limited by the diffusion distance of electrons through the TiO₂ shells.     

The influence of noncovalent interactions in metal‐free organic dye molecules to augment the efficiency of dye sensitized solar cells: A computational study

The efficiency of dye sensitized solar cells (DSSCs) can be enhanced with achieving better planarity of metal‐free organic dye molecules and thinning of their aggregation on the semiconductor surface. We report that the subtle noncovalent N^…S interaction between the substituted phosphazene group and thiophene spacer unit in dye molecule which induces the desired planarity and avoid aggregation of such molecules on the TiO₂ surface using DFT calculations. DFT results show that phosphazene group increases the maximum absorption wavelength (λ_max), driving force for electrons injection (ΔG_injection), singlet excited state lifetime (τ), dipole moments (μ_normal), and number of electrons transferred from dye to TiO₂ surface (Δq), which are known to augment the efficiency of DSSCs. Further, the lower ΔG_regeneration value of phosphazene containing dyes (e.g., –.37 eV, dye 2 ) than the reported dyes (e.g., –.81 eV, dye 1 ) indicate the faster electron injection rate from the former dye to the semiconductor TiO₂. The role of phosphazene group to prevent the aggregation of dye molecules on the TiO₂ anatase surface was also examined with GGA‐PBE/DNP level of theory. The calculated results suggest that the dye molecules on 1 ‐(TiO₂)₃₈ and 2 ‐(TiO₂)₃₈ anatase clusters avoids the aggregation due to the steric congestion induced by phosphazene group. This work reports to accomplish dual properties with subtle noncovalent interactions in dye molecules to augment the efficiency in DSSCs.     

Cobalt Doped Titanium Dioxide Nanoparticles: Synthesis,Characterization and Electrocatalytic Study

In this work, green synthesis of cobalt doped titanium dioxide (Co‐TiO₂) has been carried out in aqueous medium using gelatin. The Co‐TiO₂ particles have been characterized using transmission electron microscopy (TEM), X‐ray diffraction (XRD), energy dispersive X‐ray (EDAX), FT‐IR spectroscopy and voltammetry techniques. XRD results show pure Co‐TiO₂ and TiO₂ powders with average crystallite size about 12 nm and 15 nm, respectively. Co loaded in TiO₂ hasn't influence crystalline structure. Moreover, efficient Co‐TiO₂‐based anode was fabricated by casting of the Co‐TiO₂ solution on glassy carbon electrode (Co‐TiO₂/GCE). The electrocatalysis of oxygen evolution reaction (OER) at Co‐TiO₂/GCE has been examined using linear scanning voltammetry (LSV) in alkaline media. The OER is significantly enhanced at Co‐TiO₂/GCE, as demonstrated by a negative shift in the LSV curve at the Co‐TiO₂/GCE compared to that obtained at the unmodified one. The value of energy saving of oxygen gas at a current density of 5 mA cm^?2 is 12.6 kW h kg^?1. The low cost as well as the marked stability of the modified electrode make it promising candidate in industrial water electrolysis process.     

Solar active nano-TiO2 for mineralization of Reactive Red 120 and Trypan Blue: 1st Nano Update

Nano-TiO₂ was synthesized by sol–gel method. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) images, transmission electron microscope (TEM), BET surface area measurement and DRS analysis. The formation of anatase phase nano-TiO₂ was confirmed by XRD measurements and its crystalline size is found to be 15.2 nm. SEM images depict the crystalline nature of prepared TiO₂. The BET surface area of prepared TiO₂ is found to be 86.5 m² g^?1 which is higher than that of commercially available TiO₂–P25. The photocatalytic activity of prepared anatase phase TiO₂ has been tested for the degradation of two azo dyes: Reactive Red 120 (RR 120) and Trypan Blue (TB) using solar light. The photocatalytic activity of nano-TiO₂ is higher than TiO₂–P25 under solar light. The mineralization of dyes has been confirmed by chemical oxygen demand (COD) measurements.     

Structural characterization and photocatalytic activity of hollow binary ZrO2/TiO2 oxide fibers

The formation of hollow binary ZrO₂/TiO₂ oxide fibers using mixed precursor solutions was achieved by activated carbon fibers templating technique combined with solvothermal process. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N₂ adsorption, X-ray photoelectron spectroscopy (XPS), UV-vis, and infrared (IR) spectroscopy. The binary oxide system shows the anatase-type TiO₂ and tetragonal phase of ZrO₂, and the introduction of ZrO₂ notably inhibits the growth of TiO₂ nanocrystallites. Although calcined at 575 °C, all hollow ZrO₂/TiO₂ fibers exhibit higher surface areas (>113 m²/g) than pure TiO₂ hollow fibers. The Pyridine adsorption on ZrO₂/TiO₂ sample indicates the presence of stronger surface acid sites. Such properties bring about that the binary oxide system possesses higher efficiency and durable activity stability for photodegradation of gaseous ethylene and trichloromethane than P25 TiO₂. In addition, the macroscopic felt form for the resulting materials is more beneficial for practical applications than traditional catalysts forms.     

Effect of Surface Protonation on Device Performance and Dye Stability of Dye-sensitized TiO2 Solar Cell

A flat thin TiO₂ film was employed as the photo-electrode of a dye sensitized solar cell (DSSC), on which only a geometrical mono-layer of dye was attached. The effect of sur-face protonation by HCl chemical treatment on the performance of DSSCs was studied. The results showed that the short-circuit current Jsc increased significantly upon the HCl treatment, while the open-circuit voltage Voc decreased slightly. Compared to the untreated DSSC, the Jsc and energy conversion efficiency was increased by 31% and 25%, respectively, for the 1 mol/L HCl treated cell. TiO₂ surface protonation improved electronic coupling between the chemisorbed dye and the TiO₂ surface, resulting in an enhanced electron in-jection. The decreased open-circuit voltage after TiO₂ surface protonation was mainly due to the TiO₂ conduction band edge downshift and was partially caused by increased electron recombination with the electrolyte. In situ Raman degradation study showed that the dye stability was improved after the TiO₂ surface protonation. The increased dye stability was contributed by the increased electron injection and electron back reaction with the electrolyte under the open-circuit condition.