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A two-dimensional layer of oxide reveals itself as a essential element to drive the photocatalytic activity in a nanostructured hybrid material, which combines high-quality epitaxial graphene and titanium dioxide nanoparticles. In particular, it has been revealed that the addition of a 2D Ti oxide layer sandwiched between graphene and metal induces a p-doping of graphene and a consistent shift in the Ti d states. These modifications induced by the interfacial oxide layer induce a reduction of the probability of charge carrier recombination and enhance the photocatalytic activity of the heterostructure. This is indicative of a capital role played by thin oxide films in fine-tuning the properties of heterostructures based on graphene and pave the way to new combinations of graphene/oxides for photocatalysis-oriented applications.

Generally adopted design strategies for enhancing the photocatalytic activity are aimed at tuning properties such as the visible light response, the exposed crystal facets, and the nanocrystal shape. Here, we present a different approach for designing efficient photocatalysts displaying a substrate-specific reactivity upon defect engineering. The defective anisotropic brookite TiO2 photocatalyst functionalized with Pt nanocrystals are tested for alcohol photoreforming showing up to an 11-fold increase in methanol oxidation rate, compared to the unreduced one, whilst presenting much lower ethanol or isopropanol specific oxidation rates. We demonstrate that the alcohol oxidation and hydrogen evolution reactions are tightly related, and when the substrate-specific alcohol oxidation ability is increased, the hydrogen evolution is significantly boosted. The reduced anisotropic brookite shows up to twenty-six-fold higher specific photoactivity with respect to anatase and brookite with isotropic nanocrystals, reflecting the different type of defective catalytic sites formed depending on the TiO2 polymorph and its crystal shape. Advanced in-situ characterizations and theoretical investigations reveal that controlled engineering over oxygen vacancies and lattice strain produces large electron polarons hosting the substrate-specific active sites for alcohol photo-oxidation.

Visible light-driven production of fuels and value-added chemicals is currently one of the most intensely investigated research topics across various scientific disciplines, due to its potential to ease the World s dependence on fossil fuels. In this perspective, we recapitulate some of the main features of dye-sensitized photocatalytic systems aimed at solar H$_2$ production, focusing in particular on TiO$_2$-based three-component assemblies with organic sensitizers. Relevant aspects include the structural and electronic properties of the sensitizers, the nature of the semiconductor and the hydrogen evolution catalysts, the role of the sacrificial donor and the effect of the reaction parameters on H$_2$ production rate and stability. Besides presenting the most significant recent developments of the field, we also analyse some of its common practices in terms of experimental design, laboratory procedures and data presentation, trying to highlight their weaknesses and suggesting possible improvements. We then conclude with a short paragraph discussing the possible future development of this exciting research area.

Electrocatalytic CO$_2$RR is an interfacial process, involving a minimum of three phases at the contact point of gaseous CO$_2$ with the electrodic surface and the liquid electrolyte. As a consequence, surface chemistry at composite interfaces plays a central role for CO$_2$RR selectivity and catalysis. Each interface defines a functional boundary, where active sites are exposed to a unique environment with respect to distal sites in the bulk or organic and inorganic materials. While the individual role of each component-type is hardly predictable a-solo, the interface ensemble works via a strategic interplay of individual effects, including: (i) enhanced electrical conductivity, (ii) high surface area and exposure of the interfacial catalytic sites, (iii) favorable transport and feeding of reactants, (iv) complementary interactions for the on/off stabilization of cascade intermediates, (v) a secondary sphere assistance to lower the activation energy of bottleneck steps, (vi) a reinforced robustness and long-term operation stability by mutual protection and/or healing mechanisms. Selected CO$_2$RR case studies are compared and contrasted to highlight how the organic domains of carbon nanostructures merge with metal and metal-oxide active sites to separate tasks but also to turn them into a cooperative asset of mutual interactions, thus going beyond the classic Divide et Impera rule.

The shape-controlled synthesis of cuprous oxide (Cu$_2$O) photocatalysts with both low or high index crystal planes has received increasing attention due to their unique facet-dependent properties. Since they are cheap and earth abundant, these well-defined Cu$_2$O nanostructures are extensively used for different photocatalytic reactions, also because of their strong visible light absorption capability. However, further development will be still needed to enhance the efficiency and photostability of Cu$_2$O, which still limits its industrial application. We start this review by summarizing the synthetic advancement in the facet engineering of Cu$_2$O and other associated hybrid Cu$_2$O-based heterostructures with a special emphasis put on their growth mechanism. We then discuss different facet-dependent properties, which are relevant to photocatalysis. In the subsequent section, we present a critical discussion on the photocatalytic performance of faceted Cu$_2$O nanostructures during organic synthesis, hydrogen production, and carbon dioxide photoreduction. The relation between photocatalytic efficiency and product selectivity with exposed crystal facets or with different composition of hybrid nanostructures is also discussed. Finally, important strategies are proposed to overcome the photostability issue, while outlining the course of future development to further boost the technological readiness of well-defined Cu$_2$O-based photocatalysts.