The crystallographic properties of two titanium dioxide (TiO₂) photocatalysts, P25, and commercial C1-TiO₂ reactive grade, were analyzed by X-ray diffraction (XRD) and the band-gap was calculated with UV–Vis spectrometry with integration sphere. Then, their performance was tested in the degradation of 6-mercaptopurine (6-MP) by heterogeneous photocatalysis with solar radiation under different pH conditions and the addition of hydrogen peroxide (H₂O₂); the degradation efficiency was monitored by UV–Vis spectrophotometry. The XRD analysis showed that both photocatalysts studied have anatase phase, while only P25 contains rutile; the band gap values were lower, in both catalysts, than those reported for catalysts obtained by the sol-gel method. With both photocatalysts, degradation experiments showed efficiency greater than 98% in experiments in the presence of H₂O₂ regardless of pH. The properties of the photocatalysts, along with the data obtained from the experimentation, helped determine the best semiconductor for the degradation of 6-MP with these operating conditions in this work.

The performance of a photocatalytic fibre reactor (UBE Chemical Europe), made of cartridges of fine particles of TiO₂ dispersed within silicon fibres and irradiated by ultraviolet light, for the removal of organic pollutants from synthetic waters was evaluated. In the sensitivity analysis carried out, the factors catalytic surface area, fibre state, temperature and initial substrate concentration were studied using 4-chlorophenol as a test compound. The percentage of titanium in the fibre remained practically invariable after a series of experiments and cleaning procedures. Furthermore, the kinetics of removal of pyrene, phenol, 4-chlorophenol and bisphenol A (BPA) from water were evaluated by means of HPLC, UV-absorption and fluorescence techniques. Kinetic operational parameters were determined from a mathematical model proposed by Langmuir–Hinshelwood. Results show that catalytic surface, initial substrate concentration and temperature directly affect the degradation rate of organic compounds, whereas fibre state does not have a significant effect on that. It is proposed that removal of organic compounds from water mainly depends on the adsorption of the specific pollutant on the photocatalytic fibre and on the physical diffusion of the substrate towards the photocatalytic TiO₂ active sites on the fibre, with the heterogeneous phase reaction prevailing over the homogeneous phase reaction.

The degradation mechanism of NH₄⁺/NH₃ in aqueous solutions by heterogeneous photocatalysis (TiO₂/SiO₂) and photolysis in UV-C pilot photoreactor has been studied. Under the conditions used, NH₄⁺/NH₃ can be decomposed both by photolytically and photocatalytically, without disregarding stripping processes. The greatest degradation is achieved at the highest pH studied (pH 11.0) and at higher lamp irradiation power used (25 W) with degradation performances of 44.1% (photolysis) and 59.7% (photocatalysis). The experimental kinetic data fit well with a two parallel reactions mechanism. A low affinity of ammonia for adsorption and surface reaction on the photocatalytic fiber was observed (coverage not higher than 10%), indicating a low influence of surface phenomena on the reaction rate, the homogeneous phase being predominant over the heterogeneous phase. The proposed reaction mechanism was validated, confirming that it is consistent with the photocatalytic and photolytic formation of nitrogen gas, on the one hand, and the formation of nitrate, on the other hand. At the optimal conditions, the rate constants were k₃ = 0.154 h⁻¹ for the disappearance of ammonia and k₁ = 3.3 ± 0.2 10⁻⁵ h⁻¹ and k₂ = 1.54 ± 0.07 10⁻¹ h⁻¹ for the appearance of nitrate and nitrogen gas, respectively.

This review provides a descriptive analysis of metformin, highlighting its environmental presence and classification as an emerging contaminant. It examines the risks associated with metformin and evaluates advanced oxidation processes (AOPs) for its degradation, including photolysis, photocatalysis, electrolysis, and ozonation. Metformin, a widely used biguanide for type 2 diabetes, is increasingly detected in aquatic environments due to its incomplete metabolism in humans, raising ecological concerns. While certain AOPs, such as ultraviolet (UV) photocatalysis and ozonation, achieve high degradation rates of 99.9% and 100%, respectively, they produce toxic by-products harmful to aquatic systems. Solar photocatalysis, despite a lower degradation rate (74.22%), stands out for operating without artificial energy and generating fewer hazardous by-products. The review identifies gaps in current degradation strategies and underscores the need for clean, sustainable methods. Future research directions include advancing biological and photocatalytic technologies to improve AOPs’ efficiency while minimizing environmental risks.

Methylthionine chloride (MTC) is a compound with several applications both in the clinical and medical industries. Nevertheless, such compounds can become an environmental problem, as they are not properly treated by wastewater treatment plants. This objective of this work was to study MTC degradation in a flat plate reactor through solar photolysis and heterogeneous photocatalysis processes with TiO₂ as a catalyst. In addition to the processes, three pH (3.5, 6.5, and 9) and the effect of H₂O₂ addition (no dose, 0.5, and 1 mM/L) were tested. The results show that acidic pH is the most appropriate for MTC degradation, which ranged between 56% and 68.7% for photolysis and between 76% and 86.7% in photocatalysis. The H₂O₂ addition resulted in lower degradation in all cases, leading the authors to conclude that the presence of peroxide actually hinders degradation in solar photolysis and photocatalysis processes. Statistical analysis showed that the constant rate reactions calculated for every process, under the same conditions of pH and H₂O₂ addition, are significantly different from one another, and the three factors considered for experimental design (process, pH, and H₂O₂) have a statistically significant effect on MTC degradation. The collector area per order confirmed higher efficiency for photocatalysis when compared to photolysis processes.

6-Mercaptopurine (6-MP) is a commonly used cytostatic agent, which represents a particular hazard for the environment because of its low biodegradability. In order to degrade 6-MP, four processes were applied: Photolysis (UV-C), photocatalysis (UV-C/TiO₂), and their combination with H₂O₂, by adding 3 mM H₂O₂/L (UV-C/H₂O₂ and UV-C/TiO₂/H₂O₂ processes). Each process was performed with variable initial pH (3.5, 7.0, and 9.5). Pilot scale reactors were used, using UV-C lamps as radiation source. Kinetic calculations for the first 20 min of reaction show that H₂O₂ addition is of great importance: in UV-C experiments, highest k was reached under pH 3.5, k = 0.0094 min⁻¹, while under UV-C/H₂O₂, k = 0.1071 min⁻¹ was reached under the same initial pH; similar behavior was observed for photocatalysis, as k values of 0.0335 and 0.1387 min⁻¹ were calculated for UV-C/TiO₂ and UV-C/TiO₂/H₂O₂ processes, respectively, also under acidic conditions. Degradation percentages here reported for UV-C/H₂O₂ and UV-C/TiO₂/H₂O₂ processes are above 90% for all tested pH values. Ecotoxicity analysis of samples taken at 60 min in the photolysis and photocatalysis processes, suggests that contaminant degradation by-products present higher toxicity than the original compound.