Citrate Sol–Gel Method

The citrate sol–gel method is usually used to prepare nanosized materials. Although its application is limited due to stability of its precursor system, it is difficult to control the chemical composition of complex oxides. The sol–gel procedure in aqueous medium uses inorganic salts and a chelating agent of carboxylic acid such as citric acid as a precursor. This technique has widely been used in making thin films with low temperature. Chu et al. (2018) reported a B site–deficient perovskite prepared via the classic sol–gel calcination method. In these methods, the nitrates of the metal ions were dissolved in deionized water, citric acid, and ethylene glycol to form a homogeneous solution at a certain pH, calcination temperature, and time. The XRD pattern showed that pure perovskite was successfully formed. SEM images revealed that most of the nanoparticles are non-agglomerated due to low calcination temperature. The prepared photocatalyst displayed a good photocatalytic property.

In another report, LaMg_xFe_x-1O_3-δ perovskite prepared via sol–gel route showed a formation of well-crystallized perovskite. LaMgFe₃ and LaMgFe₄ photocatalysts presented a particle size of around 100–150 nm with a well-defined size. The photocatalytic efficiency of LaMgFe₄ was higher than that of other prepared catalysts owing to its smaller particle size distribution and higher surface area (Teresita et al., 2016). Zhang Y. et al. (2019) prepared SrFe_xNi_1xO₃-_δ (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) via the citrate sol–gel method (Figure 3). They recorded their optimum catalyst with good electrocatalytic performance for water treatment was prepared at a reaction time of 120 min, a calcination temperature of 700°C, and Fe-doping content of x = 0.3.

Schematic diagram of the fabrication process of the SrFe_xNi_1-xO₃-_δ perovskites (Zhang Y. et al., 2019).