Solar-driven water splitting provides a leading approach to store the abundant yet intermittent solar energy and produce hydrogen as a clean and sustainable energy carrier. A straightforward route to light-driven water splitting is to apply self-supported particulate photocatalysts, which is expected to allow solar hydrogen to be competitive with fossil-fuel-derived hydrogen on a levelized cost basis. More importantly, the powder-based systems can lend themselves to making functional panels on a large scale while retaining the intrinsic activity of the photocatalyst. However, all attempts to generate hydrogen via powder-based solar water-splitting systems to date have unfortunately fallen short of the efficiency values required for practical applications. Photocatalysis on photocatalyst particles involves three sequential steps: (i) absorption of photons with higher energies than the bandgap of the photocatalysts, leading to the excitation of electron-hole pairs in the particles, (ii) charge separation and migration of these photoexcited carriers, and (iii) surface chemical reactions based on these carriers. In this review, we focus on the challenges of each step and summarize material design strategies to overcome the obstacles and limitations. This review illustrates that it is possible to employ the fundamental principles underlying photosynthesis and the tools of chemical and materials science to design and prepare photocatalysts for overall water splitting.

Particulate Photocatalysts for Light-Driven Water Splitting: Mechanisms, Challenges, and Design Strategies

Challenges in photocatalytic reduction of nitrate as a water treatment technology

Au–pd bimetallic alloy nanoparticle-decorated BiPO4 nanorods for enhanced photocatalytic oxidation of trichloroethylene

The paper reviews the state of the art in the synthesis of multinary (ternary, quaternary and more complex) metal chalcogenide nanocrystals (NCs) and their applications as a light absorbing or an auxiliary component of light-harvesting systems. This includes solid-state and liquid-junction solar cells and photocatalytic/photoelectrochemical systems designed for the conversion of solar light into the electric current or the accumulation of solar energy in the form of products of various chemical reactions. The review discusses general aspects of the light absorption and photophysical properties of multinary metal chalcogenide NCs, the modern state of the synthetic strategies applied to produce the multinary metal chalcogenide NCs and related nanoheterostructures, and recent achievements in the metal chalcogenide NC-based solar cells and the photocatalytic/photoelectrochemical systems. The review is concluded by an outlook with a critical discussion of the most promising ways and challenging aspects of further progress in the metal chalcogenide NC-based solar photovoltaics and photochemistry.

Solar light harvesting with multinary metal chalcogenide nanocrystals

Activation of amorphous bismuth oxide via plasmonic Bi metal for efficient visible-light photocatalysis

Bi2Ga4O9: An undoped single-phase photocatalyst for overall water splitting under visible light

An open-framework gallium borate with intrinsic photocatalytic activities to water splitting has been discovered. Small inorganic molecules, H3BO3 and H3B3O6, are confined inside structural channels by multiple hydrogen bonds. It is the first example to experimentally show the structural template effect of boric acid in flux synthesis.

Open-Framework Gallium Borate with Boric and Metaboric Acid Molecules inside Structural Channels Showing Photocatalysis to Water Splitting

Borate particulate photocatalysts for photocatalytic applications: A review

Borates are well-known candidates for optical materials, but their potentials in photocatalysis are rarely studied. Ga3+-containing oxides or sulfides are good candidates for photocatalysis applications because the unoccupied 4s orbitals of Ga usually contribute to the bottom of the conducting band. It is therefore anticipated that Ga4B2O9 might be a promising photocatalyst because of its high Ga/B ratio and three-dimensional network. Various synthetic methods, including hydrothermal (HY), sol–gel (SG), and high-temperature solid-state reaction (HTSSR), were employed to prepare crystalline Ga4B2O9. The so-obtained HY-Ga4B2O9 are micrometer single crystals but do not show any UV-light activity unless modified by Pt loading. The problem is the fast recombination of photoexcitons. Interestingly, the samples obtained by SG and HTSSR methods both possess a fine micromorphology composed of well-crystalline nanometer strips. Therefore, the excited e– and h+ can move to the surface easily. Both samples exhibit ex...

Ga4B2O9: an efficient borate photocatalyst for overall water splitting without cocatalyst.

Band structure engineering is an efficient technique to develop desired semiconductor photocatalysts, which was usually carried out through isovalent or aliovalent ionic substitutions. Starting from a UV-activated catalyst ZnGa2S4, we successfully exploited good visible light photocatalysts for H2 evolution by In3+-to-Ga3+ and (Cu+/Ga3+)-to-Zn2+ substitutions. First, the bandgap of ZnGa2–xInxS4 (0 ≤ x ≤ 0.4) decreased from 3.36 to 3.04 eV by lowering the conduction band position. Second, Zn1–2y(CuGa)yGa1.7In0.3S4 (y = 0.1, 0.15, 0.2) provided a further and significant red-shift of the photon absorption to ∼500 nm by raising the valence band maximum and barely losing the overpotential to water reduction. Zn0.7Cu0.15Ga1.85In0.3S4 possessed the highest H2 evolution rate under pure visible light irradiation using S2– and SO32– as sacrificial reagents (386 μmol/h/g for the noble-metal-free sample and 629 μmol/h/g for the one loaded with 0.5 wt % Ru), while the binary hosts ZnGa2S4 and ZnIn2S4 (synthesized usin...

ZnGa(2-x)In(x)S4 (0 ≤ x ≤ 0.4) and Zn(1-2y)(CuGa)(y)Ga(1.7)In(0.3)S4 (0.1 ≤ y ≤ 0.2): optimize visible light photocatalytic H2 evolution by fine modulation of band structures.

Jia Yang

Papers

Bi2Ga4O9: An undoped single-phase photocatalyst for overall water splitting under visible light

Open-Framework Gallium Borate with Boric and Metaboric Acid Molecules inside Structural Channels Showing Photocatalysis to Water Splitting

Borate particulate photocatalysts for photocatalytic applications: A review

Ga4B2O9: an efficient borate photocatalyst for overall water splitting without cocatalyst.

ZnGa(2-x)In(x)S4 (0 ≤ x ≤ 0.4) and Zn(1-2y)(CuGa)(y)Ga(1.7)In(0.3)S4 (0.1 ≤ y ≤ 0.2): optimize visible light photocatalytic H2 evolution by fine modulation of band structures.