Titanium dioxide (TiO₂), one of the most frequently used materials in general, has emerged as an excellent photocatalytic material for environmental applications. In this review, principles and mechanisms of the photocatalytic activity of TiO₂ have been analyzed. Structural and physical specificities of TiO₂ nanoparticles, such as morphology, crystal structure, and electronic and optical properties, have been considered in the context of photocatalytic applications. A review of the influence of several factors, such as the type and dimensions of photocatalyst particles, pH of the solution, the influence of oxidants/electron acceptors, and light intensity on photocatalytic properties of TiO₂, has been provided. Superhydrophilicity as an intrinsic property of the TiO₂ surface was discussed through surface reconstruction on TiO₂ during the reversible hydrophilic changes. Additionally, attention was paid to improving the photocatalytic properties of TiO₂ particles through aggregation and agglomeration.

Metoprolol (MET) belongs to a group of frequently used β₁-blockers, which often occur in waste waters. The objective of this work was to employ liquid chromatography (LC) and total organic carbon methods to study the photocatalytic degradation of MET in UV irradiated aqueous suspensions of TiO₂ (Wackherr's “Oxyde de titane standard” and Degussa P25), in the presence of different electron acceptors such as molecular oxygen, hydrogen peroxide, potassium bromate, and ammonium persulfate. The degradation rates were found to be strongly influenced by the kind of electron acceptor and the type of catalyst. The optimal amount of hydrogen peroxide and potassium bromate was investigated as well. MET photocatalytic degradation was the fastest in the presence of O₂ and potassium bromate with TiO₂ Degussa P25, while mineralization was most efficient in the presence of molecular oxygen alone. In all investigated cases, degradation followed a pseudo-first order kinetics. Reaction intermediates of MET degradation in the presence of different electron acceptors with both catalysts were studied in detail and a number of them were indentified using LC-ESI-MS/MS. The interactions with MET of reactive radical species relevant to this study (O₂˙⁻, ˙OH, BrO₂˙, and SO₄˙⁻) were theoretically investigated by means of density functional theory (DFT) computations.