The most widely used oxide for photocatalytic applications owing to its low cost and high activity is TiO₂. The discovery of the photolysis of water on the surface of TiO₂ in 1972 launched four decades of intensive research into the underlying chemical and physical processes involved. Despite much collected evidence, a thoroughly convincing explanation of why mixed-phase samples of anatase and rutile outperform the individual polymorphs has remained elusive. One long-standing controversy is the energetic alignment of the band edges of the rutile and anatase polymorphs of TiO₂ (ref. ). We demonstrate, through a combination of state-of-the-art materials simulation techniques and X-ray photoemission experiments, that a type-II, staggered, band alignment of ~ 0.4 eV exists between anatase and rutile with anatase possessing the higher electron affinity, or work function. Our results help to explain the robust separation of photoexcited charge carriers between the two phases and highlight a route to improved photocatalysts.

Specialized computational chemistry packages have permanently reshaped the landscape of chemical and materials science by providing tools to support and guide experimental efforts and for the prediction of atomistic and electronic properties. In this regard, electronic structure packages have played a special role by using first-principle-driven methodologies to model complex chemical and materials processes. Over the past few decades, the rapid development of computing technologies and the tremendous increase in computational power have offered a unique chance to study complex transformations using sophisticated and predictive many-body techniques that describe correlated behavior of electrons in molecular and condensed phase systems at different levels of theory. In enabling these simulations, novel parallel algorithms have been able to take advantage of computational resources to address the polynomial scaling of electronic structure methods. In this paper, we briefly review the NWChem computational chemistry suite, including its history, design principles, parallel tools, current capabilities, outreach, and outlook.

Photocatalytic hydrogen evolution may provide one of the solutions to the shift to a sustainable energy society, but the quantum efficiency of the process still needs to be improved. Precise control of the composition and structure of the metal nanoparticle cocatalysts is essential, and we show that fine-tuning the Au-Pd nanoparticle structure modifies the electronic properties of the cocatalyst significantly. Specifically, Pd(shell)-Au(core) nanoparticles immobilized on TiO2 exhibit extremely high quantum efficiencies for H2 production using a wide range of alcohols, implying that chemical byproducts from the biorefinery industry can be used as feedstocks. In addition, the excellent recyclability of our photocatalyst material indicates a high potential in industrial applications. We demonstrate that this particular elemental segregation provides optimal positioning of the unoccupied d-orbital states, which results in an enhanced utilization of the photoexcited electrons in redox reactions. We consider that the enhanced activity observed on TiO2 is generic in nature and can be transferred to other narrow band gap semiconductor supports for visible light photocatalysis.

In this review, we discuss selected examples from recent literature on the role of the support on directing the nanostructures of Au-based monometallic and bimetallic nanoparticles. The role of support is then discussed in relation to the catalytic properties of Au-based monometallic and bimetallic nanoparticles using different gas phase and liquid phase reactions. The reactions discussed include CO oxidation, aerobic oxidation of monohydric and polyhydric alcohols, selective hydrogenation of alkynes, hydrogenation of nitroaromatics, CO2 hydrogenation, C–C coupling, and methane oxidation. Only studies where the role of support has been explicitly studied in detail have been selected for discussion. However, the role of support is also examined using examples of reactions involving unsupported metal nanoparticles (i.e., colloidal nanoparticles). It is clear that the support functionality can play a crucial role in tuning the catalytic activity that is observed and that advanced theory and characterization add greatly to our understanding of these fascinating catalysts.

We report that the valence and conduction band energies of TiO 2 can be tuned over a 4 eV range by varying the local coordination environments of Ti and O. We examine the electronic structure of eight known polymorphs and align their ionization potential and electron affinity relative to an absolute energy reference, using an accurate multi-scale quantum-chemical approach. For applications in photocatalysis, we identify the optimal combination of phases to enhance activity in the visible spectrum. The results provide a coherent explanation for a wide range of phenomena, including the performance of TiO 2 as an anode material for Li-ion batteries, allow us to pinpoint hollandite TiO 2 as a new candidate transparent conducting oxide, and serve as a guide to improving the efficiency of photoelectrochemical water splitting through polymorph engineering of TiO 2 .