Prospects for the incorporation of cobalt into α-Fe2O3 nanorods during hydrothermal synthesis

Abstract

A feasibility study on the incorporation of cobalt into a-Fe 2 O 3 nanorods (NRs) during hydrothermal synthesis (HS) is presented as a function of FeCl 3 and CoCl 2 concentration, phosphate surfactant concentration and pH value, with samples assessed using X-ray diffractometry, transmission electron microscopy, selected area electron diffraction and energy dispersive X-ray analysis. No evidence was found for the incorporation of cobalt into a-Fe 2 O 3 NRs at low pH, whilst synthesis at intermediate and high pH values favoured the formation of CoFe 2 O 4

Application of surface complexation modeling on modification of hematite surface with cobalt cocatalysts: a potential tool for preparing homogeneously distributed catalysts

“…1b, a low initial Co 2+ concentration prevents the formation of Co(OH) 2 precipitates, whereas a neutral pH guarantees the deprotonation of hydroxyl groups on hematite surface so that they are available for Co 2+ accommodation. 11,12 In these cases, following thermal treatment transforms Co(OOH) precipitates into coarse Co 3 O 4 clusters and thus enhanced photocatalytic activity was achieved. 10,27 This is very important since the charge transfer from hematite to Co 3 O 4 clusters is much kinetically favorable when they are located inside the Helmholtz layer of the hematite surfaces.…”

“…Therefore, the possible mechanism responsible for these successful studies through the hydrothermal reaction is by the consideration of the deposition of hydrolysis product of Co(OOH) on hematite surface. 11,12 In these cases, following thermal treatment transforms Co(OOH) precipitates into coarse Co 3 O 4 clusters and thus enhanced photocatalytic activity was achieved.…”

“…2,3 Several methods have been proposed to prepare SACs, including impregnation or ion-exchange techniques, coprecipitation, colloidal deposition method, templates, and adsorption of metal complexes followed by thermal treatment. [10][11][12][13] Several methods were proposed to associate cobalt cocatalyst onto hematite surface, including atomic layer deposition (ALD), 14 (photo)electrodeposition, 13,[15][16][17][18] thermal hydrolysis, 10-12 and post treatment. However this preparation route strongly relies on the knowledge regarding the interaction between metal complexes and the support surface, which leads to limited success in the literature.…”

“…By associating with a few weight percentage of cobalt-based cocatalyst, its photocatalytic performance is demonstrated greatly improved as a result of the reduction in the recombination losses and thus more photogenerated holes are able to participate in water oxidation. [10][11][12][13] Several methods were proposed to associate cobalt cocatalyst onto hematite surface, including atomic layer deposition (ALD), 14 (photo)electrodeposition, 13,[15][16][17][18] thermal hydrolysis, [10][11][12] and post treatment. 19 These preparation methods, except ALD and thermal hydrolysis, are conducted in a solution containing different concentrations of Co 2+ , sometimes along with some structure directing agents.…”