Fe(III)-citrate enhanced sunlight-driven photocatalysis of aqueous Carbamazepine

New aspects of the photodegradation of iron(III) citrate: spectroscopic studies and plant-related factors

“…In our case, the observed similarity of Mössbauer parameters of the new Fe II compound and the synthesized Fe II citrate confirmed the formation of the ferrous citrate complex as the only product of photoreduction at pH > 3. The presence of a stable complex between Fe II and organic radical at all pH values is in a good agreement with the calculations [14], small variation in the region of low pH is probably caused by different Fe to citrate molar ratio and final Fe concentration. The inconsistency with the results obtained by laser flash photolysis [49,50] may be caused by the intensity of the laser overcoming the intensity of the lamps used in the plant growth chambers.…”

“…Results of laser flash photolysis described in [49,50] reported the formation of long-lived radical complexes with lifetimes in the order of only a millisecond, followed by the dissociation to the organic radical and an Fe II aqua complex. In the meantime, calculations performed by Ghoul et al [14] showed simultaneous presence of Fe II aqua and Fe II citrato complexes, while the ratio depends on the pH of the solution. In our case, the observed similarity of Mössbauer parameters of the new Fe II compound and the synthesized Fe II citrate confirmed the formation of the ferrous citrate complex as the only product of photoreduction at pH > 3.…”

“…The quantum yield and the final products highly depend on the pH of the solution, ligand-to-metal ratio and the type of the light source. Since the 1910s until now [14,15], studies of ferric citrate photodegradation have been performed by means of different methods involving detection of the organic products of the carboxylate degradation. The organic intermediates were found to be acetonedicarboxylic acid (3-oxoglutaric acid) and acetoacetic acid, which further decay into acetone and carbon dioxide [16][17][18].…”

“…In most of the works, the coordination of ferric ions in the final state is not specified, while others suggest cyclic formation of the Fe III citrate complex [21]. However, most of these studies are devoted to determining the quantum yield of HO• radical formation [14,23,24]. The only characterization of the Fe III form obtained after total photoreduction of Fe III citrate solution was performed by Dodge and Francis [18] using X-ray diffraction analysis of the precipitate, which was identified as ferrihydrite.…”

“…Some studies suggest a nearly complete transformation of Fe III to Fe II and the formation of a stable long-lived ferrous complex [16,25,26]. This contradiction might occur because the measurement of Fe II was performed by adding o-phenanthroline [14,17,21,22,25], bathophenanthroline disulfonate (BPDS) [26] or ferrozine…”