Enhancement of Photoexcited Charge Transfer by {001} Facet-Dominating TiO₂ Nanoparticles

The recent discovery of a synthetic method for chemically reactive {001} facet-dominating TiO₂ nanoparticles using hydrofluoric acid provided a new aspect of interfacial chemistry in photo catalysts, batteries, and photoelectrochemical cells using TiO₂. We reveal the effects of the reactive {001} facet on the photoexcited charge transfer from organic fluorophores, 9-substituted anthracene derivatives (An–X; X = H and COOH) and tetracene, to TiO₂ nanoparticles by differing the fraction of {001} facet. The kinetic analysis of the fluorescence quenching by TiO₂ nanoparticles based on Stern–Volmer relation is employed to estimate the quenching rate constant as a function of the fraction of {001} facet. The results imply a significant enhancement of the photoexcited charge transfer from fluorophores to TiO₂ nanoparticles by the reactive {001} facet with a factor of more than 10 in the quenching rate constant at maximum

Sequential Coupling Approach to the Synthesis of Nickel(II) Complexes with <i>N</i>‑aryl-2-amino Phenolates

A sequential multicomponent coupling approach is a powerful method for the construction of combinatorial libraries because structurally complex and diverse molecules can be synthesized from simple materials in short steps. In this paper, an efficient synthesis of nickel­(II) complexes with <i>N</i>-aryl-2-amino phenols via a sequential three-step coupling approach is described, for potential use in nonlinear optical materials, bioinspired catalytic systems, and near-infrared absorbing filters. Seventeen <i>N</i>-aryl-2-amino phenolates were successfully synthesized in high yields based on the coupling of 3,5-di-<i>tert</i>-butylbenzene-1,2-diol with a pivotal aromatic scaffold, 4-bromo-2-iodo-aniline, followed by sequential Suzuki–Miyaura coupling with aryl boronates. A total of 16 analytically pure nickel­(II) complexes with <i>N</i>-aryl-2-amino phenolates were obtained from 17 complexation trials. The procedure allowed us to assemble 4 components in high yields without protection, deprotection, oxidation or reduction steps. Various building blocks that included electron-donating, electron-withdrawing, and basic were used, and readily available, nontoxic and environmentally benign substrates and reagents were employed with no generation of toxic compounds. No strict anhydrous or degassed conditions were required. Absorption spectroscopic measurement of the synthesized nickel­(II) complexes revealed that the <i>ortho</i>-substituent Ar¹ exerted more influence on the absorption wavelength of the complexes than the <i>para</i>-substituent Ar². On the other hand, both substituents Ar¹ and Ar² influenced the molar absorptivity values. These observations should be useful for the design of new and useful nickel­(II) complexes as near-infrared chromophores

Precise Control of Photoinduced Electron Transfer in Alternate Layered Nanostructures of Titanium Oxide–Tungsten Oxide

The alternate layered structure was synthesized by the thiol–ene click reaction between the alkylthiol-modified tungsten oxide layer and the alkene-modified titanium oxide layer. The interlayer distances between the titanium oxide layer and the tungsten oxide layer were controlled to 0.72, 0.94, 1.01, and 1.14 nm by changing the carbon number of the functional groups. Photoinduced electron transfer from the titanium oxide layer to the tungsten oxide layer depends on the interlayer distance of the titanium oxide–tungsten oxide alternate layers from 0.7 to 1.1 nm. The alternate layers of narrow interlayer distance showed high photocatalytic activity in decomposition of methylene blue. The amount of the photoexcited electron transfer from titanium oxides to tungsten oxides was quantitatively measured by the reduction of Ag ions with the electrons stored in tungsten oxide. Because the rate of photoinduced electron transfer should be proportional to the amount of electron transfer, the tunneling decay constant β was estimated to be 0.63 Å^–1 in the alternate layer samples, indicating that electrons transfer from titanium oxide to tungsten oxide by through-space tunneling

Effects of energetics with {001} facet-dominant anatase TiO2 scaffold on electron transport in CH3NH3PbI3 perovskite solar cells

The anatase titania with large fraction of {001} facet on the mesoscopic anatase titania scaffold in the hybrid perovskite solar cells exhibited higher photocurrent and open-circuit voltage. The higher performance with {001}-dominant anatase titania with the fraction of 74% were discussed with the characteristic electron transport properties in addition to the energy levels of trap states and conduction band as compared with those properties of conventional anatase titania scaffold. The resulted higher photocurrent and open-circuit voltage were attributed to the enhancement of the electron injection and suppression of the carrier recombination, respectively, at the titania/perovskite semiconductor interface.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore)Accepted versio

Electromagnetic and Heat-Transfer Simulation of the Catalytic Dehydrogenation of Ethylbenzene under Microwave Irradiation

Electromagnetic and heat-transfer simulations were used to study the effects of microwave-generated nonuniform temperature distributions in a catalyst bed on the rate enhancement of a fixed-bed flow reaction. We used the dehydrogenation of ethylbenzene over a magnetite catalyst as a model reaction. During the microwave reaction, a temperature gradient was generated in the catalyst bed; the highest temperature occurred at the core of the catalyst bed, and it parabolically decreased toward the surface. Using these simulation results and Arrhenius parameters, the reaction rates were estimated by considering the nonuniform temperature distribution. The measured reaction rate was 36% larger than the simulated value, indicating that the rate enhancement under microwaves can not only be attributed to the nonuniform temperature distribution in the catalyst bed. This could be due to nonequilibrium local heating (the so-called hot spot) in the very small region around the catalyst particle

Microwave Effects on Co–Pi Cocatalysts Deposited on α‑Fe₂O₃ for Application to Photocatalytic Oxygen Evolution

We analyze the effects of microwave applied in the process of photoelectrochemical deposition of cobalt-based cocatalysts, Co–Pi, onto well-orientated flat α-Fe₂O₃ thin films, which were fabricated by pulsed laser deposition. As compared with conventional heating, microwave significantly affects the morphology, chemical composition, and photocatalytic activity of Co-Pi/α-Fe₂O₃ composite. A significant enhancement in photocurrent related to photocatalytic water oxidation is achieved by the Co–Pi catalyst prepared under microwave irradiation. This, along with its interfacial electron-transfer properties, is studied by means of electrochemical impedance spectroscopy