Abstract
Some perovskites exhibit catalytic activity in the abatement of organic pollutants in water. However, their performance decreases over time, possibly due to forms of poisoning, such as carbonate formation. Here, we present the kinetics of carbonate formation on a Ce-doped SrFeO3 perovskite with formula Sr0.85Ce0.15FeO3−δ (SCF), which can act as a thermocatalyst for the degradation of organic pollutants. The carbonate formation was studied in air, in deionized water, and during degradation of bisphenol A. The formation of SrCO3 occurred for perovskites in aqueous environments, i.e., when dispersed in water or used as catalysts in the degradation of bisphenol A, while no SrCO3 was detected for samples stored in air for up to 195 days. SrCO3 formation was detected using both XRD and ATR-FT-IR, and from the XRD, the crystallite size was found to decrease when carbonates formed. The samples containing SrCO3 showed an increasing mass loss at >610 °C with increasing time used as catalysts or dispersed in water, showing that SCF reduces its own efficiency during catalytic use. The kinetics of carbonate formation based on the TGA measurements showed that SrCO3 forms approximately three times faster during the degradation of organic compounds in water compared to SCF dispersed in water. The formation of SrCO3 in SCF is thermally reversible; thus, the catalyst can resume its activity after heat treatment at 900 °C for 1 h.
Highlights
Perovskite-like materials have the formula ABX3 and are structurally similar to the original perovskite, CaTiO3 [1]
The crystallite size was similar for all the samples stored in air, approximately 514 Å, while a significant reduction in crystallite size was found for the samples dispersed in water or used as catalysts (Table 1)
SrCO3 formation was detected by X-ray diffraction (XRD) and ATR-FT-IR for the SCF dispersed in water or used as a catalyst in water, but not when the SCF was stored in air for up to 195 days
Summary
Perovskite-like materials have the formula ABX3 and are structurally similar to the original perovskite, CaTiO3 [1]. Srilakshmi et al [19] only observed carbonate formation when SrFeO3 was used as a catalyst for the degradation of nitrobenzene in water, and no carbonate formation was reported while SrFeO3 was stored in air This might be attributed to the formation of carbonate species due to the dissolved CO2 in the water, which can form carbonates on the surface of SCF and related perovskites, such as SrO parts. A systematic investigation of the formation of carbonates on Sr0.85Ce0.15FeO3−δ (SCF) was carried out to understand the decreasing efficiency of the catalytic activity over time. This was investigated by storing the SCF in air, dispersing the SCF in deionized water, and using the SCF in the thermocatalytic degradation of bisphenol A. The carbonate formation was studied using XRD and ATR-FT-IR, and the kinetics of carbonate formation were determined using TGA measurements
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