This critical review shows the basis of photocatalytic water splitting and experimental points, and surveys heterogeneous photocatalyst materials for water splitting into H2 and O2, and H2 or O2 evolution from an aqueous solution containing a sacrificial reagent Many oxides consisting of metal cations with d0 and d10 configurations, metal (oxy)sulfide and metal (oxy)nitride photocatalysts have been reported, especially during the latest decade The fruitful photocatalyst library gives important information on factors affecting photocatalytic performances and design of new materials Photocatalytic water splitting and H2 evolution using abundant compounds as electron donors are expected to contribute to construction of a clean and simple system for solar hydrogen production, and a solution of global energy and environmental issues in the future (361 references)

Heterogeneous photocatalyst materials for water splitting

Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2

http://pubs.acs.org/doi/pdf/10.1021/cr1002326

Solar Water Splitting Cells

Boron-doped silicon nanowires (SiNWs) were used to create highly sensitive, real-time electrically based sensors for biological and chemical species. Amine- and oxide-functionalized SiNWs exhibit pH-dependent conductance that was linear over a large dynamic range and could be understood in terms of the change in surface charge during protonation and deprotonation. Biotin-modified SiNWs were used to detect streptavidin down to at least a picomolar concentration range. In addition, antigen-functionalized SiNWs show reversible antibody binding and concentration-dependent detection in real time. Lastly, detection of the reversible binding of the metabolic indicator Ca2+ was demonstrated. The small size and capability of these semiconductor nanowires for sensitive, label-free, real-time detection of a wide range of chemical and biological species could be exploited in array-based screening and in vivo diagnostics.

/pdf/nanowire-nanosensors-for-highly-sensitive-and-selective-4f3aqhtkwe.pdf

Nanowire Nanosensors for Highly Sensitive and Selective Detection of Biological and Chemical Species

Photoinduced reactivity of titanium dioxide

The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .

An overview of semiconductor photocatalysis

Strontium titanate photoelectrodes. Efficient photoassisted electrolysis of water at zero applied potential

Ferrofluids are colloidal suspensions of surfactant-coated magnetic particles in a liquid medium. This paper describes a simple synthesis of an aqueous-based ferrofluid that may be used in an introductory science or engineering laboratory. Magnetite (Fe3O4) particles are precipitated by combining FeCl3 and FeCl2 in a 2:1 stoichiometric ratio in aqueous ammonia solution. The resulting particles, ~10-20 nm in diameter based on powder X-ray diffraction, are then treated with aqueous tetramethylammonium hydroxide, which acts as a surfactant. When the resulting ferrofluid is placed near a magnet, it forms conical spikes. This paper also describes a method for repelling both oil- and water-based ferrofluid from solid surfaces that would otherwise be stained by the fluid. Finally, a demonstration of the interaction between ferrofluid and magnetic fields, in which ferrofluid is induced to leap upward by a stack of magnets, is described.

/pdf/preparation-and-properties-of-an-aqueous-ferrofluid-4xkud6hpl1.pdf

Preparation and properties of an aqueous ferrofluid

Surface Chemistry of Prototypical Bulk II-VI and III-V Semiconductors and Implications for Chemical Sensing.

Studies of CdX-based photoelectrochemical cells in X/sup 2 -//X/sup 2 -//sub n/ electrolytes are reported for X = S, Se, and Te. For eight of the nine electrode/electrolyte combinations we have demonstrated that the n-type semiconducting single-crystal CdX photoelectrodes are stable to anodic dissolution. Only for CdTe in S/sup 2 -//S/sup 2 -//sub n/ do we find that oxidation of the added chalcogenide does not quench the decomposition of CdX typically found in aqueous electrolytes. For all eight remaining elecrolyte/electrode combinations the added chalcogenide is oxidized at the photoelectrode at a rate which precludes anodic dissolution of the CdX. For the stable combinations each electrolyte is capable of being oxidized at the photoelectrode and subsequently reduced at the dark counter electrode to complete a cycle where no net chemical change obtains. For all nine electrolyte/electrode combinations and for the CdX in alkaline H/sub 2/O, the redox level associated with the oxidation of X/sup 2 -/ or with O/sub 2/ evolution is between the valence band and conduction band positions at the semiconductor--electrolyte interface. Thus, energetic requirementsfor X/sup 2 -/ oxidation or O/sub 2/ evolution from H/sub 2/O are met in all cases, but apparently kinetic factors control whether oxidation ofmore » X/sup 2 -/ or of H/sub 2/O will be fast compared to anodic dissolution, which is also energetically feasible. For the stable electrode/electrolyte combinations, conversion of optical to electrical energy can be accomplished with efficiencies of > 10 percent for monochromatic visible light. For CdTe or CdSe in the Te/sup 2 -//Te/sub 2//sup 2 -/ electrolyte input power densities of >500 mW/cm/sup 2/ can be converted with a few percent efficiency with no deterioration of properties. Output voltages at maximum power conversion efficiency are of the order of 0.4 V.« less

Arthur B. Ellis

Papers

Strontium titanate photoelectrodes. Efficient photoassisted electrolysis of water at zero applied potential

Preparation and properties of an aqueous ferrofluid

Surface Chemistry of Prototypical Bulk II-VI and III-V Semiconductors and Implications for Chemical Sensing.

Study of n-type semiconducting cadmium chalcogenide-based photoelectrochemical cells employing polychalcogenide electrolytes

Visible light to electrical energy conversion. Stable cadmium sulfide and cadmium selenide photoelectrodes in aqueous electrolytes