The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has been the hotspot in the materials science as a metal-free and visible-light-responsive photocatalyst. Pure g-C3N4 suffers from the insufficient sunlight absorption, low surface area and the fast recombination of photo-induced electron-hole pairs, resulting in low photocatalytic activity. Element doping is known to be an efficient method to tune the unique electronic structure and band gap of g-C3N4, which considerably broaden the light responsive range and enhance the charge separation. This review summarizes the recent progress in the development of efficient and low cost doped g-C3N4 systems in various realms such as photocatalytic hydrogen evolution, reduction of carbon dioxide, photocatalytic removal of contaminants in wastewater and gas phase. Typically, metal doping, nonmetal doping, co-doping and heterojunction based on doped g-C3N4 have been explored to simultaneously tune the crystallographic, textural and electronic structures for improving photocatalytic activity by enhancing the light absorption, facilitating the charge separation and transportation and prolonging the charge carrier lifetime. Finally, the current challenges and the crucial issues of element doped g-C3N4 photocatalysts that need to be addressed in future research are presented. This review presented herein can pave a novel avenue and add invaluable knowledge to the family of element doped g-C3N4 for the develop of more effective visible-light-driven photocatalysts.

Doping of graphitic carbon nitride for photocatalysis: A reveiw

Novel porous P-doped graphitic carbon nitride (g-C3N4) nanosheets were for the first time fabricated by combining P doping and thermal exfoliation strategies. The as-prepared P-doped g-C3N4 nanosheets show a high visible-light photocatalytic H2-production activity of 1596 μmol h−1 g−1 and an apparent quantum efficiency of 3.56% at 420 nm, representing one of the most highly active metal-free g-C3N4 nanosheet photocatalysts. This outstanding photocatalytic performance originates from the P-doped conjugated system and novel macroporous nanosheet morphology. Particularly, the empty midgap states (−0.16 V vs. standard hydrogen electrode) created by P doping are for the first time found to greatly extend the light-responsive region up to 557 nm by density functional theory and experimental studies, whilst the novel macroporous structure promotes the mass-transfer process and enhances light harvesting. Our study not only demonstrates a facile, eco-friendly and scalable strategy to synthesize highly efficient porous g-C3N4 nanosheet photocatalysts, but also paves a new avenue for the rational design and synthesis of advanced photocatalysts by harnessing the strong synergistic effects through simultaneously tuning and optimizing the electronic, crystallographic, surface and textural structures.

Porous P-doped graphitic carbon nitride nanosheets for synergistically enhanced visible-light photocatalytic H2 production

Bull. Chem. Soc. Jpn. への投稿のすすめ

Self-cleaning materials have gained considerable attention for both their unique properties and practical applications in energy and environmental areas. Recent examples of many TiO2-derived materials have been illustrated to understand the fundamental principles of self-cleaning hydrophilic and hydrophobic surfaces. Various models including those proposed by Wenzel, Cassie-Baxter and Miwa-Hashimoto are discussed to explain the mechanism of self-cleaning. Examples of semiconductor surfaces exhibiting the simultaneous occurrence of superhydrophilic and superhydrophobic domains on the same surface are illustrated, which can have various advanced applications in microfluidics, printing, photovoltaic, biomedical devices, anti-bacterial surfaces and water purification. Several strategies to improve the efficiency of photocatalytic self-cleaning property have been discussed including doping with metals and non-metals, formation of hetero-junctions between TiO2 and other low bandgap semiconductors, and fabrication of graphene based semiconductor nano-composites. Different mechanisms such as band-gap narrowing, formation of localized energy levels within the bandgap and formation of intrinsic defects such as oxygen vacancies have been suggested to account for the improved activity of doped TiO2 photocatalysts. Various preparation routes for developing efficient superhydrophilic–superhydrophobic patterns have been reviewed. In addition, reversible photo-controlled surfaces with tuneable hydrophilic/hydrophobic properties and its technological applications are discussed. Examples of antireflective surfaces exhibiting self-cleaning properties for the applications in solar cells and flat panel displays have also been provided. Discussion is provided on TiO2 based self-cleaning materials exhibiting hydrophilic and underwater superoleophobic properties and their utilities in water management, antifouling applications and separation of oil in water emulsions are discussed. In addition, ISO testing methods (ISO 27448: 2009, ISO 10678: 2010 and ISO 27447: 2009) for analysing self-cleaning activity and antibacterial action have also been discussed. Rapid photocatalytic self-cleaning testing methods using various photocatalytic activity indicator inks such as resazurin (Rz), basic blue 66 (BB66) and acid violet 7(AV7) for a broad range of materials such as commercial paints, tiles and glasses are also described. Various commercial products such as glass, tiles, fabrics, cement and paint materials developed based on the principle of photo-induced hydrophilic conversion of TiO2 surfaces have also been provided. The wide ranges of practical applications of self-cleaning photocatalytic materials suggest further development to improve their efficiency and utilities. It was concluded that a rational fabrication of multifunctional photocatalytic materials by integrating biological inspired structures with tunable wettability would be favorable to address a number of existing environmental concerns.

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Self-Cleaning Applications of TiO2 by Photo-Induced Hydrophilicity and Photocatalysis

TiO2 is one of the most promising candidate materials for clean-energy generation and environmental remediation. However, the larger-than 3.1 eV bandgap of perfectly crystalline TiO2 confines its application to the ultraviolet (UV) range. In this study, the electronic and the optical properties of undoped mixed-phase TiO2 nanoparticles were investigated using UV and inverse photoemission, low intensity X-ray photoelectron (XP), and diffused reflectance spectroscopy methods. The facile solution-phase synthesized nanoparticles exhibited a midgap-states-induced energy gap of only ∼2.2 eV. The diffused reflectance spectrum showed sub-bandgap absorption due to the existence of a large Urbach tail at 2.2 eV. The UV photoemission spectrum evidenced the presence of midgap states. The 2.2 eV energy gap enables the nanoparticles to be photoactive in the visible energy range. The gas-phase CO2 photoreduction test with water vapor under visible light illumination was studied in the presence of the synthesized TiO2 na...

Toward a Visible Light-Driven Photocatalyst: The Effect of Midgap-States-Induced Energy Gap of Undoped TiO2 Nanoparticles

A developed route to form TiO 2 self cleaning coatings on polycarbonate substrates is reported. TiO 2 coatings on plastics may find widespread application in auto and construction industries if possess desired photocatalytic and mechanical properties. A chemical surface treatment method was used to create hydrophilic groups on the surface. X-ray photoelectron spectroscopy showed the treatment led to the oxidation of surface groups. TiO 2 deposition was based on wet coating using an anatase sol of TiO 2 nanoparticles of 30 nm size. The sol was synthesized using a sol–gel route. A pre-coat of peroxotitanium complex was employed to improve adhesion and inhibit the substrate degradation. The coating reduced the transparency for 10–15%. The photocatalytic activity was found linearly dependent on the thickness. The reaction rate constant for methylene blue degradation was estimated 0.024 s − 1 for films of 150 nm thickness. The mechanical properties were also improved after coating, as demonstrated by nano-indentation and nano-scratch tests. The hardness and scratch resistance were improved by 2.5 and ∼6.4 folds.

Self cleaning TiO2 coating on polycarbonate: Surface treatment, photocatalytic and nanomechanical properties

Post-deposition annealing effects on nanomechanical properties of granular TiO2 films on soda-lime glass substrates were studied. In particular, the effects of Na diffusion on the films’ mechanical properties were examined. TiO2 photocatalyst films, 330 nm thick, were prepared by dip-coating using a TiO2 sol, and were annealed between 100 °C and 500 °C. Film’s morphology, physical and nanomechanical properties were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, differential thermo-gravimetric analysis, and nanoindentation. Contrary to expectations, the maximum film hardness was achieved for 300°C annealing, with a value of 0.69 ± 0.05 GPa. Higher annealing temperatures resulted in inferior mechanical properties. No pile-up or sink-in effects were observed with minimal creep for the 300 °C annealed sample. Considerable decrease in the amount of chemisorbed water was found with increasing annealing temperature, causing gel films densification, explaining the i...

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Nanomechanical properties of TiO2 granular thin films.

Application of poly (p-phenylene oxide) as blocking layer to reduce self-discharge in supercapacitors

Large photocurrent response and external quantum efficiency in biophotoelectrochemical cells incorporating reaction center plus light harvesting complexes.

Houman Yaghoubi

Papers

Toward a Visible Light-Driven Photocatalyst: The Effect of Midgap-States-Induced Energy Gap of Undoped TiO2 Nanoparticles

Self cleaning TiO2 coating on polycarbonate: Surface treatment, photocatalytic and nanomechanical properties

Nanomechanical properties of TiO2 granular thin films.

Application of poly (p-phenylene oxide) as blocking layer to reduce self-discharge in supercapacitors

Large photocurrent response and external quantum efficiency in biophotoelectrochemical cells incorporating reaction center plus light harvesting complexes.