Citric Acid Assisted Synthesis

Pd-doped catalysts have been produced by USS [82]. The fingerprint of Pd adopting the octahedral coordination of Fe in LaFeo,95Pdo,o503 has been observed in the XANES spectra of the material prepared by spray synthesis (27m /g) similarly to the preparation by the amorphous citrate method (14m /g) [17,82]. In contrast, the flame-made material of the same composition (22m /g) exposed metallic Pd particles on LaFeOs similarly to preparation by solution combustion. The different nature of the Pd species obtained by changing the synthesis method dramatically influences their catalytic performance, since PdO nanoparticles exposed at the surface of the mixed oxide exhibit catalytic activity, whereas Pd—O species in the bulk of the mixed oxide are inactive, at least in the case of methane oxidation [27]. In contrast to LaFeOs, LaMnOs did not allow Pd to adopt the octahedral coordination irrespective of synthesis method. Therefore, the coordination of Pd strongly depends on both the composition of the perovskite-type oxide and the synthesis method. 

Pereniguez et al. [101] have prepared LaNiOs as precursor of Ni/La20s for methane reforming reactions upon reduction and compared USS preparation with solution combustion and hydrothermal synthesis. The citric acid-assisted synthesis of LaNiOs, named spray pyrolysis -F combustion, produced a material with intrinsically improved catalytic activity compared to the other synthesis methods. As described above, the combustion of the citric acid induced a larger specific surface area and the smallest LaNiOs crystallites (12 nm, XRD). By comparison, the synthesis in the absence of citric acid produced average crystallites 

A final example demonstrates the improved textural properties of USS products compared to the citric acid route. Smaller SrFeOs-s nanoparticles (20-30 nm against 70-100 nm determined by electron microscopy) were produced by USS that exhibited a larger fraction of surface defect from interpretation of the XPS data [102]. As a result of the defects and particle structure, the band gap of the material shifted toward longer wavelength making the USS-SrFeOs-s sample a more efficient photocatalyst upon visible light irradiation. 

In conclusion, the few examples provided above show that powder perovskite-type oxides prepared by USS demonstrate in general enhanced structural properties compared to more conventional synthesis methods. However, a rational synthesis by design is desirable that should be based on a systematic research of the effect of synthesis parameters on structural and morphological properties of the product 

39 Marina, OA. and Pederson, L.R. (2002) Proc. 5th European SOFC Forum, European Solid Oxide Fuel Cell Forum 2002. 

---

V. Subramanian, D.-W. Jeong, W.-B. Han, W.-J. Jang, J.-O. Shim, H.-S. Roh, Ha production from high temperature shift of the simulated waste derived synthesis gas over magnetite catalysts prepared by citric acid assisted direct synthesis method, Int. J. Hydrogen Energy 38 (2013) 8699-8703. 

Citric acid assisted solvothermal synthesis of BiFeOa microspheres with high visible-light photocatalytic activity. 

Julien C, El-Farh L, Rangan S, Massot M (1999) Synthesis of LiNii yCoy02 cathode materials prepared by a citric acid-assisted sol-gel method for lithium batteries. J Sol Gel Sci Technol 15 63-72... 

Table 8.1 shows properties and physiological functions of some essential blood plasma proteins used here to study their interaction with gold NPs decorated with citric acid (the most common surface coating for gold NPs since it assists in their synthesis and promotes NPs solubility in water). 

---