Abstract
Since environmental pollution by emerging organic contaminants is one of the most important problems, gaining ground year after year, the development of decontamination technologies of water systems is now imperative. Advanced oxidation processes (AOPs) with the formation of highly reactive radicals can provide attractive technologies for the degradation of organic pollutants in water systems. Among several AOPs that can be applied for the formation of active radicals, this review study focus on sulfate radical based-AOPs (SR-AOPs) through the heterogeneous catalytic activation of persulfate (PS) or peroxymonosulfate (PMS) using perovskite and spinel oxides as catalysts. Perovskites and spinels are currently receiving high attention and being used in substantial applications in the above research area. The widespread use of these materials is based mainly in the possibilities offered by their structure as it is possible to introduce into their structures different metal cations or to partially substitute them, without however destroying their structure. In this way a battery of catalysts with variable catalytic activities can be obtained. Due to the fact that Co ions have been reported to be one of the best activators of PMS, special emphasis has been placed on perovskite/spinel catalysts containing cobalt in their structure for the degradation of organic pollutants through heterogeneous catalysis. Among spinel materials, spinel ferrites (MFe2O4) are the most used catalysts for heterogeneous activation of PMS. Specifically, catalysts with cobalt ion in the A position were reported to be more efficient as PMS activators for the degradation of most organic pollutants compared with other transition metal catalysts. Substituted or immobilized catalysts show high rates of degradation, stability over a wider pH area and also address better the phenomena of secondary contamination by metal leaching, thus an effective method to upgrade catalytic performance.
Highlights
The contamination of aquatic resources by both organic and inorganic compounds, especially by the most resistant or continuously emitted ones, is one of the most important environmental problems in recent years
Luo et al [73] focused on the targeted synthesis of a mesopore double perovskite catalyst, La2 CoMnO6−δ (MLCMO), performed via a facile method of transformation-induced self-assembly (EISA) using PEO-b-PS as the template and its activity was evaluated for the degradation of atrazine and other organic pollutants
CoFe2 O4 -rGO catalyst as well as CoFe2 O4 -Gr was synthesized by hydrothermal treatment and the results showed that they had a high PMS activation efficiency and organic pollutants removal
Summary
The contamination of aquatic resources by both organic and inorganic compounds, especially by the most resistant or continuously emitted ones, is one of the most important environmental problems in recent years. The common commercialized form of PMS, the so-called Oxone® , a triple potassium salt of formula (2KHSO5 ·KHSO4 ·K2 SO4 ) [15], is dissolved in water as its solubility is greater than 250 g L−1 (20 ◦ C), is very stable in a broad pH range, non-toxic with a comparable cost to other chemical oxidants (e.g., oxone cost $2.2 per kg vs H2 O2 cost $1.5 per kg) [16] It is a relatively strong oxidant itself, (PMS oxidation potential 1.82 V), it cannot be used alone for the degradation of organic pollutants due to low reaction rates, an activation method is required [9].
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