Photocatalysis

A single crystalline phase of strontium carbonate (SrCO 3) was successfully obtained from solvothermal treatments of hydrated strontium hydroxide in ethanol (EtOH) at 100 • C for 2 h, using specific Sr:EtOH mole ratios of 1:18 or 1:23. Other solvothermal treatment times (0.5, 1.0 and 3 h), temperatures (80 and 150 • C) and different Sr:EtOH mole ratios (1:13 and 1:27) led to formation of mixed phases of Sr-containing products, SrCO 3 and Sr(OH) 2 xH 2 O. The obtained products (denoted as 1:18 SrCO 3 and 1:23 SrCO 3), containing a single phase of SrCO 3 , were further characterized in comparison with commercial SrCO 3 , and each SrCO 3 material was employed as a photocatalyst for the degradation of methylene blue (MB) in water under visible light irradiation. Only the 1:23 SrCO 3 sample is visible light responsive (E g = 2.62 eV), possibly due to the presence of ethanol in the structure, as detected by thermogravimetric analysis. On the other hand, the band gap of 1:18 SrCO 3 and commercial SrCO 3 are 4.63 and 3.25 eV, respectively, and both samples are UV responsive. The highest decolourisation efficiency of MB solutions was achieved using the 1:23 SrCO 3 catalyst, likely due to its narrow bandgap. The variation in colour removal results in the dark and under visible light irradiation, with radical scavenging tests, suggests that the high decolourisation efficiency was mainly due to a generated hydroxyl-radical-related reaction pathway. Possible degradation products from MB oxidation under visible light illumination in the presence of SrCO 3 are aromatic sulfonic acids, dimethylamine and phenol, as implied by MS direct injection measurements. Key findings from this work could give more insight into alternative synthesis routes to tailor the bandgap of SrCO 3 materials and possible further development of cocatalysts and composites for environmental applications.

In this work, TiO2 photocatalysts were synthesized using a conventional
sol-gel and hydrothermal synthesis methods with steam pressure treatment.
Photocatalysts were characterized by X-ray diffraction (XRD), diffuse
reflectance spectra (DRS) and N2 adsorption-desorption. The photoactivity of
the samples was analyzed towards the photooxidation of the azo dye Orange
II (Or-II) and phenol using different illumination set-ups to compare the
activity features of photocatalysts. The effect of the synthesis variables such
as the synthesis route, water/alcoxide and alcohol/alcoxide ratios, as well as
the alcohol type was analyzed. TiO2 photocatalysts obtained by hydrothermal
synthesis have a better photoactivity than the particles synthesized by the
chosen sol-gel route, reaching the Or-II degradation photoactivity of the
commercial TiO2 P25. On the other hand, the water/alcoxide ratio and
alcohol type have a marked effect on the photoactivity of the hydrothermal
synthesized TiO2, whereas the alcohol/alcoxide ratio does not have a relevant
effect on the Or-II degradation photoactivity.

In this study, synthesis of novel binary chitosan-SnO 2 nanocomposites is reported. Different physical and chemical techniques were used to characterize and analyze the characteristics of the chitosan-SnO 2 nanocomposites as photocatalysts. The prepared novel photocatalysts were used to degrade the model dyes such as methyl orange (MO) and rhodamine B (RhB) under different wavelengths (254, 310 and 365 nm) of UV light. The photocatalytic degradation results suggest that the prepared binary chitosan-SnO 2 (50:50) nanocomposite shows superior degradation efficiency compared with pure SnO 2 and binary chitosan-SnO 2 (75:25) nanocomposite owing to its high crystallinity, high surface area, and small particle size. It was also observed that chitosan-SnO 2 (50:50) nanocom-posite under different wavelengths (254 nm, 310 nm, and 365 nm) of UV light showed highest photocatalytic degradation of methyl orange and rhodamine B at 365 nm irradiation.