Characterization of Ti-doped CaFe₂O₄ prepared from a malic acid complex

Abstract

Ti-doped and undoped CaFe 2 O 4 powders were prepared from a malic acid complex and their properties were evaluated using analytical instruments. According to an XRD measurement, there were no traces of impurity phases in 5 mol % Ti-doped CaFe 2 O 4 powder, while impurity phases such as ¡-Fe 2 O 3 and CaTiO 3 were observed for 10 mol % Ti-doped CaFe 2 [Received September 16, 2013; Accepted December 3, 2013] For several decades, the physical and chemical properties of calcium ferrite (CaFe 2 O 4 ) crystal have been researched widely because of its useful applications such as in gas absorbers, in electrochemical devices for high-temperature use, and as an oxidation catalyst.1)3) CaFe 2 O 4 has recently attracted considerable attention as a new photocatalyst material owing to its excellent photoreductive property for H 2 O and CO 2 . 4)9) In general, CaFe 2 O 4 is prepared by a solid-state reaction. Although a solidstate reaction is most frequently used because of ease and convenience, it has several problems such as changes in stoichiometric ratio and the ease of formation of impurity phases.10) This is because the starting materials must be repeatedly ground and calcined many times to prepare the intended crystal phase. As a result, the specific surface area of the product decreases and the catalytic activity has inevitably falls. Needless to say, a high surface area is an important property of surface functionality materials such as catalysts.Marcilly and co-workers have reported a new preparation method employing organic acids (citric, malic, tartaric, glycolic acids etc.) to obtain metal oxides. 11) They showed that H + in an organic acid with -OH or -COOH groups is replaced by the metal ion in the solution and the organic acid complex is easily formed. This complex is available for a precursor to prepare the objective material. Therefore, it is expected that the precursor is transformed to objective oxide at lower calcination temperature than the case of a solid-state reaction method and the resulting final product has a large surface-area and a high homogeneity.In the present study, we have examined the preparation of CaFe 2 O 4 powder with high specific surface area from a malic acid complex, instead of employing a solid-state reaction, and characterized the powder by X-ray diffractometry (XRD), X-ray photoelectron spectrometry (XPS), fluorescence X-ray spectrometry (XRF), scanning electron microscopy (SEM), surface area measurement, and UVvis spectrometry. Furthermore, the effect of Ti addition on the crystal phase, microstructure, specific surface area, and optical properties of CaFe 2 O 4 was investigated.CaFe 2 O 4 powder was synthesized by a malic acid complex method. Ca(NO 3 ) 2 ·4H 2 O, Fe(NO 3 ) 3 ·9H 2 O, and malic acid in a 1:2:3 molar ratio were dissolved in deionized water. The addition of Ti to CaFe 2 O 4 carried out using Ti[OCH(CH 3 ) 2 ] 4 . The amount of Ti doped set to 5 and 10 mol % to Fe. The solution was dehydrated and heated on a hot plate to prepare the precursor powder of CaFe 2...

Formation of CaFe₂O₄ porous structure by addition of Zr in malic acid complex

“…As for the preparation of CaFe 2 O 4 , the forming temperature could be lower at least 200°C results in 700°C by adopting organic acid complex method, and the specific surface area (SSA) of the obtained CaFe 2 O 4 powder was approximately five times larger than that of the product obtained by a solid-state reaction. 10) On the other hand, however, microstructure control of the malic acid complex derived products has not been examined. There are some strategies for microstructure control of CaFe 2 O 4 , i.e., the selection of complex formable acids, the addition of another element, and so on.…”

“…Although our research group has examined some addition of another element in CaFe 2 O 4 preparation procedure, drastic changes in microstructure could not be obtained. 10) However, recently, zirconium (Zr) addition was found to be a candidate for morphological control of CaFe 2 O 4 . Thus, the effect of Zr addition on the microstructure, morphology, and SSA of CaFe 2 O 4 was intensively investigated and the characteristics of the products were examined in the present study.…”

Oxygen deficient perovskites: effect of structure on electrical conductivity, magnetism and electrocatalytic activity.

“…In addition, a satellite peak appearing at about 7-9 eV higher than the 2P3/2 peak is the signature of trivalent Fe. [103][104] The XPS data for Ca2Fe0.5Ga1.5O5 ( Figure 5.4) show the 2P3/2 peak for Fe at ~710 eV followed by a satellite peak at ~718 eV, confirming that Fe is primarily in trivalent state. There is also a sight shoulder on the right side of the Fe 2P2/3 peak, which indicates the presence of a small amount of tetravalent Fe.…”

“…investigated by X-ray photoelectron spectroscopy (XPS). The 2P3/2 peaks for trivalent and tetravalent Fe are expected to appear at ~710-711 eV [103][104] and ~712-713 eV, 44,105 respectively. In addition, a satellite peak appearing at about 7-9 eV higher than the 2P3/2 peak is the signature of trivalent Fe.…”

“…The 2P3/2 peak for trivalent Fe is expected to appear at about 710 -711.5 eV followed by its satellite peak at about 8 -9 eV higher in binding energy. [43][44][104][105] The satellite peak position is particularly important, as it is the signature of trivalent Fe. The XPS data are shown in Figure 7.6.…”