water. [1] Furthermore, looking into the future, increasing amounts of fresh water will be required to account for population growth, greenhouse gas induced climate change, contamination of freshwater resources, industrial expansion, and agricultural activities. It has been reported that the only methods capable of meeting the increasing demands for freshwater supply are desalination and water reuse. [2] Of these, seawater and brackish water desalination offers a seemingly unlimited and high-quality water supply since 71% of the planet's surface is covered by ocean. Presently, two of the most successful commercialized technologies for water desalination are the multistage flash (MSF) distillation and reverse osmosis (RO) processes. [3] The MSF process is being gradually replaced by the RO process since it produces large quantities of fresh water while consuming less electric energy and having a smaller CO 2 footprint. [4] In the past two decades, numerous large-scale seawater desalination plants based on the RO processes have been built worldwide to harvest available water resources, and the global water production by desalination is projected to exceed 38 billion m 3 per year in 2016. [5] Compared to conventional drinking water treatment processes (coagulation, sedimentation, filtration, and disinfection), seawater desalination consumes a greater amount of electric energy, and thus emits a larger quantity of greenhouse gases. [4] Moreover, a large number of marine organisms, especially juvenile-stage fish, are killed during the seawater intake process. [6] In addition, electric power and centralized water desalination maybe unavailable for the RO process in some remote and rural areas.To overcome these two disadvantages of the RO process, a new concept, named "Air-Water Interface Solar Heating" (AWISH), has been employed for seawater desalination by modifying the old "Solar Distillation Seawater Desalination" (SDSD) process. [7,8] In this conceptually new process, black materials that are capable of efficiently absorbing the solar irradiance and converting it to heat energy are coated on meshes, gauzes or other floating supports. To date, black materials that have been investigated to function as solar-thermal absorbers in AWISH desalination apparatuses include Fe 3 O 4 /C, [8] carbon nanoparticles, [9] black gold, [10] polypyrrole, [7] aluminum nanoparticles, [11] hollow TiO x (x < 2) nanoparticles with tunable colors from white to gray to bluegray to black are synthesized by magnesium (Mg) reduction of white P25 TiO 2 nanocrystals followed by removal of excess Mg with aqueous HCl and distilled water. Increasing amounts of Mg smoothly decrease the oxygen content in TiO x which is responsible for the gradual increase in light absorption and concomitant darkening of its color from white to black with decreasing values of x. The as-synthesized TiO x nanoparticles are spin-coated onto the surface of a stainless steel mesh followed by surface superhydrophobization in order to test their performance as a solar water...

The solar‐to‐chemical energy conversion of greenhouse gas CO2 into carbon‐based fuels is a very important research challenge, with implications for both climate change and energy security. Herein, the key attributes of hydroxides and oxygen vacancies are experimentally identified in non‐stoichiometric indium oxide nanoparticles, In2O3‐x(OH)y, that function in concert to reduce CO2 to CO under simulated solar irradiation.

Think thin! Colloidally stable ultrathin Bi2S3 nanowires (see picture), which display strong excitonic features never before seen in bismuth chalcogenides and extremely high extinction coefficients, have been synthesized on a gram‐scale. Nanostructures such as this are of very high technological potential for thermoelectric applications.

Gaseous CO2 is transformed photochemically and thermochemically in the presence of H2 to CH4 at millimole per hour per gram of catalyst conversion rates, using visible and near‐infrared photons. The catalyst used to drive this reaction comprises black silicon nanowire supported ruthenium. These results represent a step towards engineering broadband solar fuels tandem photothermal reactors that enable a three‐step process involving i) CO2 capture, ii) gaseous water splitting into H2, and iii) reduction of gaseous CO2 by H2.

Silicon constitutes 28% of the earth's mass. Its high abundance, lack of toxicity and low cost coupled with its electrical and optical properties, make silicon unique among the semiconductors for converting sunlight into electricity. In the quest for semiconductors that can make chemicals and fuels from sunlight and carbon dioxide, unfortunately the best performers are invariably made from rare and expensive elements. Here we report the observation that hydride-terminated silicon nanocrystals with average diameter 3.5 nm, denoted ncSi:H, can function as a single component heterogeneous reducing agent for converting gaseous carbon dioxide selectively to carbon monoxide, at a rate of hundreds of μmol h−1 g−1. The large surface area, broadband visible to near infrared light harvesting and reducing power of SiH surface sites of ncSi:H, together play key roles in this conversion. Making use of the reducing power of nanostructured hydrides towards gaseous carbon dioxide is a conceptually distinct and commercially interesting strategy for making fuels directly from sunlight.

The field of solar fuels seeks to harness abundant solar energy by driving useful molecular transformations. Of particular interest is the photodriven conversion of greenhouse gas CO2 into carbon-based fuels and chemical feedstocks, with the ultimate goal of providing a sustainable alternative to traditional fossil fuels. Nonstoichiometric, hydroxylated indium oxide nanoparticles, denoted In2O3-x(OH)y, have been shown to function as active photocatalysts for CO2 reduction to CO via the reverse water gas shift reaction under simulated solar irradiation. However, the relatively wide band gap (2.9 eV) of indium oxide restricts the portion of the solar irradiance that can be utilized to ∼9%, and the elevated reaction temperatures required (150-190 °C) reduce the overall energy efficiency of the process. Herein we report a hybrid catalyst consisting of a vertically aligned silicon nanowire (SiNW) support evenly coated by In2O3-x(OH)y nanoparticles that utilizes the vast majority of the solar irradiance to simultaneously produce both the photogenerated charge carriers and heat required to reduce CO2 to CO at a rate of 22.0 μmol·gcat(-1)·h(-1). Further, improved light harvesting efficiency of the In2O3-x(OH)y/SiNW films due to minimized reflection losses and enhanced light trapping within the SiNW support results in a ∼6-fold increase in photocatalytic conversion rates over identical In2O3-x(OH)y films prepared on roughened glass substrates. The ability of this In2O3-x(OH)y/SiNW hybrid catalyst to perform the dual function of utilizing both light and heat energy provided by the broad-band solar irradiance to drive CO2 reduction reactions represents a general advance that is applicable to a wide range of catalysts in the field of solar fuels.

The development of strategies for increasing the lifetime of photoexcited charge carriers in nanostructured metal oxide semiconductors is important for enhancing their photocatalytic activity. Intensive efforts have been made in tailoring the properties of the nanostructured photocatalysts through different ways, mainly including band-structure engineering, doping, catalyst-support interaction, and loading cocatalysts. In liquid-phase photocatalytic dye degradation and water splitting, it was recently found that nanocrystal superstructure based semiconductors exhibited improved spatial separation of photoexcited charge carriers and enhanced photocatalytic performance. Nevertheless, it remains unknown whether this strategy is applicable in gas-phase photocatalysis. Using porous indium oxide nanorods in catalyzing the reverse water-gas shift reaction as a model system, we demonstrate here that assembling semiconductor nanocrystals into superstructures can also promote gas-phase photocatalytic processes. Transient absorption studies prove that the improved activity is a result of prolonged photoexcited charge carrier lifetimes due to the charge transfer within the nanocrystal network comprising the nanorods. Our study reveals that the spatial charge separation within the nanocrystal networks could also benefit gas-phase photocatalysis and sheds light on the design principles of efficient nanocrystal superstructure based photocatalysts.

Thermal treatment of ultrathin films of hematite (α-Fe2 O3 ) under an atmosphere of 5 % H2 in Ar is presented as a means of activating α-Fe2 O3 towards the photoelectrochemical splitting of water. Spin-coated films annealed in air exhibited no photoactivity, whereas films treated in hydrogen exhibited a photocurrent response. X-ray photoelectron spectroscopy and UV/Vis absorption spectroscopy results showed that the H2 -treated films contain oxygen vacancies, which suggests improved charge transport. However, Tafel slopes, scan-rate dependent measurements, and kinetic analyses performed by using H2 O2 as a hole scavenger suggested that surface modification may also contribute to their induced photoactivity. Electrochemical impedance spectroscopy results revealed the buildup of a surface trap capacitance at the point of photocurrent onset for the hydrogen-treated films under illumination. A decrease in charge trapping resistance was also observed, which suggests improved transport of charges away from the surface.