Photocatalytic water splitting using sunlight is a promising technology capable of providing high energy yield without pollutant byproducts. Herein, we review various aspects of this technology including chemical reactions, physiochemical conditions and photocatalyst types such as metal oxides, sulfides, nitrides, nanocomposites, and doped materials followed by recent advances in computational modeling of photoactive materials. As the best-known catalyst for photocatalytic hydrogen and oxygen evolution, TiO 2 is discussed in a separate section, along with its challenges such as the wide band gap, large overpotential for hydrogen evolution, and rapid recombination of produced electron-hole pairs. Various approaches are addressed to overcome these shortcomings, such as doping with different elements, heterojunction catalysts, noble metal deposition, and surface modification. Development of a photocatalytic corrosion resistant, visible light absorbing, defect-tuned material with small particle size is the key to complete the sunlight to hydrogen cycle efficiently. Computational studies have opened new avenues to understand and predict the electronic density of states and band structure of advanced materials and could pave the way for the rational design of efficient photocatalysts for water splitting. Future directions are focused on developing innovative junction architectures, novel synthesis methods and optimizing the existing active materials to enhance charge transfer, visible light absorption, reducing the gas evolution overpotential and maintaining chemical and physical stability.

We report a facile synthetic protocol to prepare mesoporous FeS without the aid of hard template as an electrocatalyst for the hydrogen evolution reaction (HER). The mesoporous FeS materials with high surface area were successfully prepared by a sol-gel method following a sulfurization treatment in an HS atmosphere. A remarkable HER catalytic performance was achieved with a low overpotential of 96 mV at a current density of 10 mA·cm and a Tafel slope of 78 mV per decade under alkaline conditions (pH 13). The theoretical calculations indicate that the excellent catalytic activity of mesoporous FeS is attributed to the exposed (210) facets. The mesoporous FeS material might be a promising alternative to the Pt-based electrocatalysts for water splitting.

A unique approach for the synthesis of nonstoichiometric, mesoporous molybdenum oxide (MoO 3-x ) with nanosized crystalline walls by using a soft template (PEO-b -PS) synthesis method is introduced. The as-synthesized mesoporous MoO 3-x is very active and stable (durability > 12 h) for the electrochemical hydrogen evolution reaction (HER) under both acidic and alkaline conditions. The intrinsic MoO 3 serves as an HER electrocatalyst without the assistance of carbon materials, noble metals, or MoS 2 materials. The results from transmission electron microscopy and N 2 sorption techniques show that the as-synthesized mesoporous MoO 3-x has large accessible pores (20-40 nm), which are able to facilitate mass transport and charge transfer during HER. In terms of X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed oxidation, and diffusive refl ectance UV-vis spectroscopy, the mesoporous MoO 3-x exhibits mixed oxidation states (Mo 5+ , Mo 6+ ) and an oxygen-defi cient structure. The as-synthesized MoO 3-x only requires a low overpotential (≈0.14 V) to achieve a 10 mA cm −2 current density in 0.1 M KOH and the Tafel slope is as low as 56 mV dec −1 . Density functional theory calculations demonstrate a change of electronic structure and the possible reaction pathway of HER. Oxygen vacancies and mesoporosity serve as key factors for excellent performance.

We investigate the Hamiltonian formulation of f (T ) gravity and find that there are five degrees of freedom. The six first class constraints corresponding to the local Lorentz transformation in Teleparallel gravity become second class constraints in f (T ) gravity, which leads to the appearance of three extra degrees of freedom and the violation of the local Lorentz invariance in f (T ) gravity.In general, there are D − 1 extra degrees of freedom for f (T ) gravity in D dimensions, and this implies that the extra degrees of freedom correspond to one massive vector field or one massless vector field with one scalar field. * Electronic address: mli@itp.ac.cn † Electronic address:

The high photocatalytic activity of mixed phase (80% anatase and 20% rutile) titanium dioxide (Degussa P25) has attracted a great deal of interest in recent years. However, its low efficiency in visible light and nonporous nature limits the potential use and capabilities. Here, we report a novel preparation method for crystalline, thermally stable (up to 800 °C) TiO2 materials with tunable anatase/rutile phase compositions (0–100%) and monomodal mesoporosity. The control of the phase compositions was achieved by framework vanadium doping and various applied heat treatments. Vanadium (0% to 10% doping) decreased the anatase–rutile transformation temperature (from 1000 to 600 °C) and shifted the absorption band to the visible light region (narrowed the band gap). The mesopore structure was preserved in mixed phase TiO2. These materials are members of the recently discovered University of Connecticut (UCT) mesoporous materials family. The UCT materials are randomly packed nanoparticle aggregates and mesopores that are formed by connected intraparticle voids. The synthesis of UCT materials relies on controlling the sol–gel chemistry of inorganic sols in inverse surfactant micelles and NOx (nitric oxides) chemistry. The visible light (>400 nm) photocatalytic activity of mixed phase mesoporous titania samples was studied. The highest photocatalytic activity was obtained by mesoporous titania with 61% anatase and 39% rutile composition. The catalyst can totally remove (100% conversion) methylene blue dye (MB) under visible light irradiation in 2 h, whereas commercial P25 was only able to remove 28% under the same reaction conditions. The mixed phase mesoporous material also shows high photocatalytic activity for degrading phenol and 4-chlorophenol under visible light irradiation. Moreover, the good crystallinity, high surface area (94 m2/g), and monomodal mesoporosity (around 5 nm) can be preserved even after three cycles of photocatalytic reactions.