Molybdenum disulphide (MoS ₂ ) is a layered material with interesting photocatalytic properties.

In present work, we examine the photocatalytic properties of S-doped TiO₂ (S1, S2) compared to bare TiO₂ (S0) in present work. The photocatalytic tests were performed in alkaline aqueous solutions (pH = 10) of three differently substituted phenols (phenol (I), 4,4′-isopropylidenebisphenol (II), and 4,4′-isopropylidenebis(2,6-dibromophenol) (III)). The activity of the catalysts was evaluated by monitoring I, II, III degradation in the reaction mixture. The physicochemical properties (particle size, ζ-potential, E_bg, Eu, E⁰_cb, E⁰_vb, σ_o, K_L) of the catalysts were established, and we demonstrated their influence on degradation reaction kinetics. Substrate degradation rates are consistent with first-order kinetics. The apparent conversion constants of the tested compounds (k_app) in all cases reveal the sulfur-loaded catalyst S2 to show the best photocatalytic activity (for compound I and II S1 and S2 are similarly effective). The different efficiency of photocatalytic degradation I, II and III can be explained by the interactions between the catalyst and the substrate solution. The presence of bromine substituents in the benzene ring additionally allows reduction reactions. The yield of bromide ion release in the degradation reaction III corresponds to the Langmuir constant. The mixed oxidation-reduction degradation mechanism results in higher degradation efficiency. In general, the presence of sulfur atoms in the catalyst network improves the degradation efficiency, but too much sulfur is not desired for the reduction pathway.

The literature shows that both in laboratory and in industrial conditions, the photocatalytic oxidation method copes quite well with degradation of most environmental toxins and pathogenic microorganisms. However, the effective utilization of photocatalytic processes for environmental decontamination and disinfection requires significant technological advancement in both the area of semiconductor material synthesis and its application. Here, we focused on the presence and “photocatalytic capability” of photocatalysts among soil minerals and their potential contributions to the environmental decontamination in vitro and in vivo. Reactions caused by sunlight on the soil surface are involved in its normal redox activity, taking part also in the soil decontamination. However, their importance for decontamination in vivo cannot be overstated, due to the diversity of soils on the Earth, which is caused by the environmental conditions, such as climate, parent material, relief, vegetation, etc. The sunlight-induced reactions are just a part of complicated soil chemistry processes dependent on a plethora of environmental determinates. The multiplicity of affecting factors, which we tried to sketch from the perspective of chemists and environmental scientists, makes us rather skeptical about the effectiveness of the photocatalytic decontamination in vivo. On the other hand, there is a huge potential of the soils as the alternative and probably cheaper source of useful photocatalytic materials of unique properties. In our opinion, establishing collaboration between experts from different disciplines is the most crucial opportunity, as well as a challenge, for the advancement of photocatalysis.

: In this mini-review, the problem of effective elimination of perfluorinated organic micropollutants from aquatic environment has been touched. The extraordinary chemical stability of common perfluorinated organic surfactants results in unsatisfactory efficiency of conventional treatment processes, which opens perspectives for photocatalytic methods - especially for reductivedehalogenation. To tackle this challenge by photocatalysis one have to be aware of objective, physical limits set by very nature of the reduction process, electronic structure chemical stability, and formulation of the catalyst as well as emission characteristic of the light source. The paper provides some clues for rational design of reductive-dehalogenation oriented photolytic systems, which are derived on the basis of physical principles, and, rather sparse, experimental examples.

Background: Tetrabromobisphenol A (4,4’-isopropylidenebis(2,6-dibromophenol), TBBPA) is one of the most widely used brominated flame retardants. Due to its widespread use, high lipophilicity, and persistence, it has been detected in various environmental samples. Therefore, it is of great significance to develop methods to efficiently remove TBBPA from the contaminated environment. Objective: The aim of our study was to examine photocatalytic dehalogenation of TBBPA on microand nano-sized Fe3O4 exposed to the visible light. The Fe3O4 catalyst was chosen due to its indisputable low impact on the environment. Methods: A solution of TBBPA (1.84 × 10-4 mol dm-3) with a pH = 8 with suspended catalyst was illuminated (light intensity about 1.1x1017 photons per second, spectrum range 200-600 nm) for 1 hour. Analysis of the reaction progress was carried out by HPLC measurements of TBBPA decay and potentiometric measurements of an increase in bromide concentration. Results: The degradation process seems to be the most effective for TBBPA in the reaction mixture containing the n-Fe3O4 (t0.5 ≈ 2 min). Slightly lower degradation efficacy is observed for TBBPA degradation in the presence of the μ-Fe3O4 (decay within the first 5 min). TBBPA decomposition of both n-Fe3O4 and μ-Fe3O4 is accompanied by different bromide concentrations time-profile. Conclusion: The photogenerated electron-induced degradation by dissociative-attachment to the aromatic ring was followed by bromine ion expulsion. The micro-magnetite showed a strong tendency for adsorption of bromide anions during the process, which could be adventurous for the overall waste-decontamination process.