Converting solar energy into fuel via photo-assisted water splitting to generate hydrogen or drive CO₂ reduction is an attractive scientific and technological goal to address the increasing global demand for energy and to reduce the impact of energy production on climate change. Engineering an efficient, low-cost photocatalyst is necessary to achieve this technological goal. A photocatalyst combines a photosensitiser and an electrocatalyst to capture light and accelerate the chemical reactions in the same device. In this perspective paper, we first describe the recent developments of some families of semiconductors that are attractive candidates for engineering photocatalysts. We then discuss the use of semiconductors as light harvesting agents, combined with a bio-catalyst, synthetic bio-mimetic molecular catalyst or synthetic all-inorganic catalyst, in photocatalytic hybrid systems for water splitting and CO₂ reduction. To highlight the advantages of semiconductors for engineering efficient and robust photocatalysts, we compare these systems to examples of homogeneous photocatalytic systems constructed from molecular photosensitisers (dyes). We conclude that all-inorganic catalysts coupled to appropriate semiconductors look more promising for the construction of robust photocatalytic hybrid systems for producing solar fuels.

The recent developments of hetero-nanostructures for photocatalytic H₂production and CO₂reduction are reviewed in detail, based on material compositions that form heterojunctions.

The use of nanomaterials has raised safety concerns, as their small size facilitates accumulation in and interaction with biological tissues. Here we show that exposure of endothelial cells to TiO₂ nanomaterials causes endothelial cell leakiness. This effect is caused by the physical interaction between TiO₂ nanomaterials and endothelial cells’ adherens junction protein VE-cadherin. As a result, VE-cadherin is phosphorylated at intracellular residues (Y658 and Y731), and the interaction between VE-cadherin and p120 as well as β-catenin is lost. The resulting signalling cascade promotes actin remodelling, as well as internalization and degradation of VE-cadherin. We show that injections of TiO₂ nanomaterials cause leakiness of subcutaneous blood vessels in mice and, in a melanoma-lung metastasis mouse model, increase the number of pulmonary metastases. Our findings uncover a novel non-receptor-mediated mechanism by which nanomaterials trigger intracellular signalling cascades via specific interaction with VE-cadherin, resulting in nanomaterial-induced endothelial cell leakiness.