Brookite is the least studied TiO₂ photocatalyst due to the difficulties usually encountered in order to obtain it as a pure phase. In this review, a comprehensive survey of the different methods available for preparing brookite powders and films is reported. Attention has been paid both to the most traditional methods, such as hydrothermal processes at high temperatures and pressures, and to environmentally benign syntheses using water soluble compounds and water as the solvent. Papers reporting the photocatalytic activity of pure and brookite-based samples have been reviewed.

The influence of bromide ions on systems containing highly reactive radical species is of great interest for environmental remediation, atmospheric chemistry, and the synthesis of high-added-value compounds. In this regard, irradiated TiO₂ suspensions are simple and suitable systems to highlight some mechanisms of general validity in the aforementioned research fields. In this work the spin-trapping technique has allowed highlighting the concurrent action of hydroxyl and superoxide radicals toward bromide ions. In fact, hydroxyl radicals oxidize bromide ions to bromine atoms, which in turn can be reduced back to bromide ions by superoxide radicals. The results suggest that this relay mechanism, mainly based on secondary redox products (such as reactive oxygen species, ROS) rather than on direct interfacial electron transfer, is responsible for the generally observed constant concentration of bromide ions in irradiated TiO₂ suspensions. The presence of nitrate ions in the system significantly alters this equilibrium. In fact, nitrate radicals generated by hole-induced oxidation of nitrate ions selectively oxidize bromide ions to elemental bromine even under anoxic conditions, but in the presence of bromate as an opportune electron scavenger. This result not only reveals the importance of nitrate radicals toward the photocatalytic production of elemental bromine but also confirms the active role of nitrate ions in irradiated photocatalytic suspensions.

Limonene epoxide (1,2-limonene oxide) readily reacts with carbon dioxide inserted in a ring-opening copolymerization reaction and forms polycarbonates of exceptional chemical and physical properties. Both poly(limonene carbonate) and poly(limonene dicarbonate) can be synthesized using low-cost Zn or Al homogeneous catalysts. This study addresses selected relevant questions concerning the technical and economic feasibility of limonene and carbon dioxide polymers en route to the bioeconomy.