Nanocrystalline titania xerogels doped by metal precursors in the photocatalytic degradation of 2,4-D sodium salts

Photocatalytic degradation of acid yellow 36 with calcined titania-hydroxyapatite-CuO xerogels

“…OH), which are very powerful oxidizing agents that can break azo bonds and thereby discolor this type of dyes. Among the AOPs those using semiconductors agents such as titanium oxide (TiO 2 ) as a photocatalyst and dopants such as copper, iron, and zinc have been studied [ 11 ]. The process allows the generation of electron-hole pairs when illuminated with light of wavelength equal to or greater than their band gap.…”

“…The process allows the generation of electron-hole pairs when illuminated with light of wavelength equal to or greater than their band gap. Electrons and holes allow the generation of hydroxyl radicals and reactive oxygen species that are responsible for the degradation of many pollutants, as they are not selective [ 11 , 12 ]. The photogenerated carriers could also be used in the direct oxidation/reduction of the pollutants, but this process is highly selective and requires adsorption near the active site, a good match between the redox potentials of the pollutant and the semiconductor band positions, among other factors [ 11 ].…”

“…Electrons and holes allow the generation of hydroxyl radicals and reactive oxygen species that are responsible for the degradation of many pollutants, as they are not selective [ 11 , 12 ]. The photogenerated carriers could also be used in the direct oxidation/reduction of the pollutants, but this process is highly selective and requires adsorption near the active site, a good match between the redox potentials of the pollutant and the semiconductor band positions, among other factors [ 11 ]. Furthermore, adsorption of the dye or its degradation subproducts on the hetero-doped SC surface, could cause the obstruction of active sites where hydroxyl radicals are catalytic or photocatalytic generated.…”

“…Anatase is the crystalline phase of TiO 2 is a SC that is considered photocatalytically active (band gap of 3.2 eV). It can be decorated with metal oxides such as CuO, that is a SC with band gap of ∼1.5–2.2 eV [ 11 , 13 ], and materials with an abundance of oxygen such as hydroxyapatite (HA), to increase its catalytic and/or photocatalytic activity and, at the same time, promote the interaction and adsorption of the aqueous pollutant onto HA. Additionally, the combination of various SC can avoid electron-hole recombination if coupled properly [ 4 , 13 ].…”

“…Additionally, the combination of various SC can avoid electron-hole recombination if coupled properly [ 4 , 13 ]. CuO has been shown to be a very active photocatalyst when supported in anatase [ 11 , 13 ], as well as economic and abundant in nature. On the other hand, HA [Ca 10 (PO 4 ) 6 (OH) 2 ] is a n environmentally friendly phosphate material widely used in biomedicine, especially for the manufacture of bone implants, due to its biocompatibility.…”