Water Disinfection Using Chitosan Microbeads With N-, C-, C-N/TiO2 By Photocatalysis Under Visible Light

Co, Cu, Fe, and Ni Deposited over TiO2 and Their Photocatalytic Activity in the Degradation of 2,4-Dichlorophenol and 2,4-Dichlorophenoxyacetic Acid

Pure TiO2 synthesized by the sol-gel method and subsequently deposited at 5% by weight with Co, Cu, Fe, and Ni ions by the deposition–precipitation method were studied as photocatalysts. The nanomaterials were analyzed by SEM, TEM, UV-Vis DRS, DRX, Physisorption N2, and XPS. The SEM and TEM images present a semi-spherical shape with small agglomerations of particles and average size between 63 and 65 nm. UV-Vis results show that a reduction below 3.2 eV exhibits a redshift displacement and increment in the optical absorption of the nanoparticles promoting the absorption in the UV-visible region. XRD spectra and analysis SAED suggest the characteristic anatase phase in TiO2 and deposited materials according to JCPDS 21-1272. The specific surface area was calculated and the nanomaterial Ni/TiO2 (21.3 m2 g−1) presents a slight increment when comparing to TiO2 (20.37 m2g−1). The information generated by the XPS spectra present the deposition of metallic ions on the support and the presence of different valence states for each photocatalyst. The photocatalytic activity was carried out in an aqueous solution with 80 mg L−1 of 2,4-D or 2,4-DCP under UV light (285 nm) with 100 mg L−1 of each photocatalysts for 360 min. The nanomaterial that presented the best efficiency was Ni/TiO2, obtaining a degradation of 85.6% and 90.3% for 2,4-D and 2,4-DCP, respectively. Similarly, this material was the one that presented the highest mineralization, 68.3% and 86.5% for 2,4-D and 2,4-DCP, respectively. Photocatalytic reactions correspond to the pseudo-first-order Langmuir–Hinshelwood model.

Acesulfame K Photodegradation over Nitrogen-Doped TiO2

Acesulfame K is a zero-calorie alternative to sugar used worldwide. There is contradictory information on the toxicity of the compound, but its accumulation in the aquatic environment is undeniable. In this study, one-pot sol-gel synthesis was used to obtain nitrogen-doped TiO2 photocatalysts. Doping up to 6.29 wt % of nitrogen caused an increase in the surface area of the catalysts (48.55–58.23 m2∙g−1) and a reduction of the pHPZC value (5.72–5.05). Acesulfame K photodegradation was tested at the initial concentration of 20–100 ppm and the catalyst concentration at the level of 1 g∙L−1. Compared to the pure anatase, 4.83–6.29 wt % nitrogen-doped TiO2 showed an effective photodegradation of Acesulfame K. Ninety percent molecule removal was obtained after ~100 min, ~90 min, and ~80 min for initial concentrations of 20 ppm, 50 ppm, and 100 ppm, respectively. The increased activity of the catalysts is due to the modification of the TiO2 lattice structure and probably the limitation of the photogenerated electron/hole charge carrier recombination. It was shown that the electrostatic interactions between Acesulfame K and the catalyst surface play an important role in the photodegradation efficiency.