Alternative energy technologies are greatly hindered by significant limitations in materials science. From low activity to poor stability, and from mineral scarcity to high cost, the current materials are not able to cope with the significant challenges of clean energy technologies. However, recent advances in the preparation of nanomaterials, porous solids, and nanostructured solids are providing hope in the race for a better, cleaner energy production. The present contribution critically reviews the development and role of mesoporosity in a wide range of technologies, as this provides for critical improvements in accessibility, the dispersion of the active phase and a higher surface area. Relevant examples of the development of mesoporosity by a wide range of techniques are provided, including the preparation of hierarchical structures with pore systems in different scale ranges. Mesoporosity plays a significant role in catalysis, especially in the most challenging processes where bulky molecules, like those obtained from biomass or highly unreactive species, such as CO₂ should be transformed into most valuable products. Furthermore, mesoporous materials also play a significant role as electrodes in fuel and solar cells and in thermoelectric devices, technologies which are benefiting from improved accessibility and a better dispersion of materials with controlled porosity.

Mesoporous silica, which shows well-defined pore systems, tunable pore diameters (2–30 nm), narrow pore size distributions and high surface areas (>600 m² g⁻¹), is frequently modified using different methodologies (including in situ and post-synthetic strategies) to introduce various chemical functionalities useful in applications like catalysis, separation, drug delivery, and sensing. This contribution aims to provide a critical overview of the various strategies to incorporate chemical functionalities in mesoporous silica highlighting the advantages of the in situ methods based on the bottom-up construction of mesoporous silica containing various chemical functionalities in its structure.

Novel magnetically separable TiO₂-guanidine-(Ni,Co)Fe₂O₄ nanomaterials were prepared and characterised by a series of techniques including XRD, SEM, TEM, N₂ physisorption as well as XPS and subsequently tested for their photocatalytic activities in the selective transformation of malic acid in aqueous solution. The modification with guanidine, which remarkably decreases the band gap of the metal oxide, was found to have a significant effect in the photocatalytic activity of the materials under visible light, showing a remarkably superior activity to that of the commercial Degussa P25. These materials are also envisaged to have interesting photocatalytic activities under sunlight.