Nano-sized TiO 2 photocatalytic water-splitting technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy. Presently, the solar-to-hydrogen energy conversion efficiency is too low for the technology to be economically sound. The main barriers are the rapid recombination of photo-generated electron/hole pairs as well as backward reaction and the poor activation of TiO 2 by visible light. In response to these deficiencies, many investigators have been conducting research with an emphasis on effective remediation methods. Some investigators studied the effects of addition of sacrificial reagents and carbonate salts to prohibit rapid recombination of electron/hole pairs and backward reactions. Other research focused on the enhancement of photocatalysis by modification of TiO 2 by means of metal loading, metal ion doping, dye sensitization, composite semiconductor, anion doping and metal ion-implantation. This paper aims to review the up-to-date development of the above-mentioned technologies applied to TiO 2 photocatalytic hydrogen production. Based on the studies reported in the literature, metal ion-implantation and dye sensitization are very effective methods to extend the activating spectrum to the visible range. Therefore, they play an important role in the development of efficient photocatalytic hydrogen production.

A review and recent developments in photocatalytic water-splitting using TiO2 for hydrogen production

1. Setting the Scope of the Challenge 6474 1.1. The Need for Solar Energy Supply and Storage 6474 1.2. An Imperative for Discovery Research 6477 1.3. Scope of Review 6478 2. Large-Scale Centralized Energy Storage 6478 2.1. Pumped Hydroelectric Energy Storage (PHES) 6479 2.2. Compressed Air Energy Storage (CAES) 6480 3. Smaller Scale Grid and Distributed Energy Storage 6481 3.1. Flywheel Energy Storage (FES) 6481 3.2. Superconducting Magnetic Energy Storage 6482 4. Chemical Energy Storage: Electrochemical 6482 4.1. Batteries 6482 4.1.1. Lead-Acid Batteries 6483 4.1.2. Alkaline Batteries 6484 4.1.3. Lithium-Ion Batteries 6484 4.1.4. High-Temperature Sodium Batteries 6484 4.1.5. Liquid Flow Batteries 6485 4.1.6. Metal-Air Batteries 6485 4.2. Capacitors 6485 5. Chemical Energy Storage: Solar Fuels 6486 5.1. Solar Fuels in Nature 6486 5.2. Artificial Photosynthesis and General Considerations of Water Splitting 6486

Solar Energy Supply and Storage for the Legacy and Nonlegacy Worlds

ZnS nanostructures: From synthesis to applications

The remarkable achievement by Fujishima and Honda (1972) in the photo-electrochemical water splitting results in the extensive use of TiO 2 nanomaterials for environmental purification and energy storage/conversion applications. Though there are many advantages for the TiO 2 compared to other semiconductor photocatalysts, its band gap of 3.2 eV restrains application to the UV-region of the electromagnetic spectrum ( λ  ≤ 387.5 nm). As a result, development of visible-light active titanium dioxide is one of the key challenges in the field of semiconductor photocatalysis. In this review, advances in the strategies for the visible light activation, origin of visible-light activity, and electronic structure of various visible-light active TiO 2 photocatalysts are discussed in detail. It has also been shown that if appropriate models are used, the theoretical insights can successfully be employed to develop novel catalysts to enhance the photocatalytic performance in the visible region. Recent developments in theory and experiments in visible-light induced water splitting, degradation of environmental pollutants, water and air purification and antibacterial applications are also reviewed. Various strategies to identify appropriate dopants for improved visible-light absorption and electron–hole separation to enhance the photocatalytic activity are discussed in detail, and a number of recommendations are also presented.

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Visible-light activation of TiO2 photocatalysts: Advances in theory and experiments

Environmental problems associated with organic pollutants and toxic water pollutants provide the impetus for sustained fundamental and applied research in the area of environmental remediation. Semiconductor photocatalysis offers the potential for complete elimination of toxic chemicals through its efficiency and potentially broad applicability. [1] Various new compounds and materials for photocatalysis have been synthesized in the past few decades. A successful example is TiO2, a metal oxide often used as a catalyst in photochemistry, electrochemistry, environmental protection, and in the battery industry. [2] Recently, transition-metal sulfides, in particular ZnS and CdS, have been intensively studied because of their unique catalytic functions compared to those of TiO2. [2, 3] These studies have revealed that ZnS nanocrystals (NCs) are good photocatalysts as a result of the rapid generation of electron– hole pairs by photoexcitation and the highly negative reduction potentials of excited electrons. The photocatalytic properties occur not only in the photoreductive production of H2 from water and the photoreduction of CO2, [4] but also in the phototransformation of various organic substrates such as the oxidative formation of carbon–carbon bonds from organic electron donors, cis–trans photoisomerization of alkenes, and the photoreduction of aldehydes and their derivatives. [5] The notable finding in nonmetalized ZnS photocatalysis is an irreversible two-electron-transfer photoreduction of organic substrates. [6] A favorable shift of the optical response into the visible region occurs subsequent to the doping of transition metal or rare-earth metal ions, such as Ni 2+ and Cu 2+ ; therefore, ZnS NCs can also be used as effective catalysts for photocatalytic evolution of H2 and photoreduction of toxic ions under visible-light irradiation. [7] An important application of ZnS is as a photocatalyst in environmental protection through the removal of organic

Mass Production and High Photocatalytic Activity of ZnS Nanoporous Nanoparticles

Selective heavy metal receptor functional phthalocyanines bearing thiophenes: Synthesis, characterization, spectroscopy and electrochemistry

Synthesis, H- or J-type aggregations, electrochemistry and in situ spectroelectrochemistry of metal ion sensing lead(II) phthalocyanines

A new electrochemical sensor electrode was constructed with a new electrode modification technique, “click electrochemistry” (CEC) based on a functional cobalt phthalocyanine. In this newly constructed modified electrode (GCE/PANI-N 3 /TA-CoPc (CEC)), a terminal-alkynyl (TA) substituted cobalt phthalocyanine (CoPc-TA) was electrochemically bonded to the azido end of electro-polymerized 4-azidoaniline (PANI-N 3 ), which was electropolymerized on the GCE electrochemically previously. GCE/PANI-N 3 /TA-CoPc (CEC) electrode was characterized with voltammetric, electrochemical impedance spectroscopy (EIS), UV–vis spectroscopy, and scanning electron microscopy (SEM) techniques. GCE/PANI-N 3 /TA-CoPc electrode gave three redox couples assigned to the CoPc and PANI in nonaqueous and aqueous electrolyte systems, which is a desired factor for the application of a modified electrode in various electrochemical applications such as electrocatalytic and electrosensing fields. Pesticide sensing responses of GCE/ PANI-N 3 /TA-CoPc (CEC) electrode were tested with SWV method for usability as an electrochemical pesticide sensor for eserine. Basic sensor parameters, calibration lines, and detection limits (LOD) of GCE/ PANI-N 3 /TA-CoPc (CEC) electrode were derived from SWV responses of the electrode. Amperometric sensing analyses of SVW responses of the electrode give a linear range between 1.56 × 10 −7 and 2.45 × 10 −6  mol dm −3 eserine with a sensitivity of 1.15 A dm 3  mol −3 and LOD of 1.75 × 10 −7  mol dm −3 .

Atıf Koca

Papers

Selective heavy metal receptor functional phthalocyanines bearing thiophenes: Synthesis, characterization, spectroscopy and electrochemistry

Synthesis, H- or J-type aggregations, electrochemistry and in situ spectroelectrochemistry of metal ion sensing lead(II) phthalocyanines

Electrode modification based on “click electrochemistry” between terminal-alkynyl substituted cobalt phthalocyanine and 4-azidoaniline

Synthesis, Electrochemistry, Spectroelectrochemistry and Electrocolorimetry of Phthalocyanine-Anthraquinone Hybrids

Electrocatalytic hydrogen evolution reaction with metallophthalocyanines modified with click electrochemistry