A solvothermal transformation of α-Fe₂O₃ nanocrystals to Fe₃O₄ polyhedrons

Abstract

The transformation process of α-Fe2O3 to cubic Fe3O4 through “dissolution–reduction–recrystallization”.

Sunlight-Induced photochemical synthesis of Au nanodots on α-Fe2O3@Reduced graphene oxide nanocomposite and their enhanced heterogeneous catalytic properties

“…The FTIR spectra for the Au@α-Fe 2 O 3 @RGO ternary nanocomposite, Fig. 4(c), exhibits six intense peaks at 570, 1630, 1710, 2850–2925 and 3430 cm −1 corresponds to Fe-O vibration in α-Fe 2 O 3 , stretching vibration of C=C, stretching of C=O in COOH groups, C-H stretch vibrations of the methylene groups and stretching vibration of water molecules, respectively 7,8,31,32 . Significance of this studies clearly attributed to the regeneration of electronic holes in the VB of α-Fe 2 O 3 from excited chlorophyll photoelectrons and there were no observed chemical changes to the α-Fe 2 O 3 in the ternary nanocomposites following the chlorophyll mediated reduction of Au 3+ ions.

Figure 4FTIR spectra of ( a ) GO, ( b ) RGO, ( c ) α-Fe 2 O 3 , ( d ) α-Fe 2 O 3 @RGO and ( e ) Au@α-Fe 2 O 3 @RGO ternary nanocomposites.

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“…The FeOOH monomers are connected by hydrogen bonds until dehydration occurs between the molecules, following the hydrothermal (180 °C) step. Consequently, crystalline α-Fe 2 O 3 nanospheres are obtained without any further calcination (Equation 4) 23,32 .

Figure 7Schematic illustration for the synthesis of α-Fe 2 O 3 @RGO nanocomposites synthesized by hydrothermal process at 180 °C for 12 h and photochemical synthesis of Au@α-Fe 2 O 3 @RGO ternary nanocomposites.

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“…7 illustrate the entire synthesis of α-Fe 2 O 3 @RGO nanocomposite based on electrostatic-interaction induced self-assembling mechanisms. Following the mixing of FeCl 2 .4H 2 O and GO suspensions, the Fe 2+ ions are attracted by negatively charged oxygen-containing functional groups (carboxyl, hydroxyl, and epoxy groups) on GO through electrostatic interaction, creating nucleation site 32 . The Fe 2+ ions are uniformly attached on the GO surface is further hydrolysed by sodium acetate, which releases OH − ions which result in the formation of FeOOH on the GO sheets surface.…”

“…When the entire mixed solution was transferred to the Teflon-lined stainless steel autoclave and heated at 180 °C for 12 h, the FeOOH phase grows and decomposes to α-Fe 2 O 3 nanoparticles with sphere-like morphology. Meanwhile, the GO nanosheets are hydrothermally partially reduced into RGO 32 . This method does not use any hazardous reducing agent like ethylenediamine, ammonia, hydrazine hydrate, etc .…”

“…Meanwhile, the electronic vacancy in the VB holes of α-Fe 2 O 3 was regenerated through the excess of photoelectron transfer to prevent the structural loses of α-Fe 2 O 3 . The following chemical reactions (Equations 7–10) expressed the formation of ternary nanocomposites using chlorophyll 28,32,33 .

Figure 8Schematic illustrations of Au 3+ ions reduction process ( a ) α-Fe 2 O 3 @RGO, ( b ) Chlorophyll-α-Fe 2 O 3 @RGO under visible light irradiation, ( c and d ) I-V characteristic of the chlorophyll film.

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