Lanthanum cobaltite perovskite supported on zirconia as an efficient heterogeneous catalyst for activating Oxone in water

LaCoO3/SBA-15 as a high surface area catalyst to activate peroxymonosulfate for degrading atrazine in water

An efficient perovskite-based heterogeneous catalyst is highly desired to activate peroxymonosulfate (PMS) for removing organic pollutants in water. A high surface area PMS-activator was fabricated by loading LaCoO3 on SBA-15 to degrade atrazine (ATR) in water. The LaCoO3/SBA-15 depicted better textural properties and higher catalytic activity than LaCoO3. In 6.0 min, atrazine (ATZ) degradation in the selected LaCoO3/SBA-15/PMS system, LaCoO3, adsorption by LaCoO3/SBA-15, sole PMS processes reached approximately 100%, 55.15%, 12.80%, and 16.65 % respectively. Furthermore, 0.04 mg L-1 Co was leached from LaCoO3/SBA-15 during PMS activation by LaCoO3/SBA-15. The LaCoO3/SBA-15 showed stable catalytic activity after reuse. The use of radical scavengers and electron paramagnetic resonance spectroscopy (EPR) demonstrated that ROS such as 1O2, O2•-, •OH, and SO4•- were generated by PMS activated by LaCoO3/SBA-15 owing to redox reactions [Co2+/Co3+, and O2-/O2]. EPR, XPS, ATR-FTIR, EIS, LSV, and chronoamperometric measurements were used to explain the catalytic mechanism for PMS activation. Excellent atrazine degradation was due to high surface area, porous nature, diffusion-friendly structure, and ROS. Our investigation proposes that perovskites with different A and B metals and modified perovskites can be loaded on high surface area materials to activate PMS into ROS.

Hollow-Architected Heteroatom-Doped Carbon-Supported Nanoscale Cu/Co as an Enhanced Magnetic Activator for Oxone to Degrade Toxicants in Water

Even though transition metals can activate Oxone to degrade toxic contaminants, bimetallic materials possess higher catalytic activities because of synergistic effects, making them more attractive for Oxone activation. Herein, nanoscale CuCo-bearing N-doped carbon (CuCoNC) can be designed to afford a hollow structure as well as CuCo species by adopting cobaltic metal organic frameworks as a template. In contrast to Co-bearing N-doped carbon (CoNC), which lacks the Cu dopant, CuCo alloy nanoparticles (NPs) are contained by the Cu dopant within the carbonaceous matrix, giving CuCoNC more prominent electrochemical properties and larger porous structures and highly nitrogen moieties. CuCoNC, as a result, has a significantly higher capability compared to CoNC and Co3O4 NPs, for Oxone activation to degrade a toxic contaminant, Rhodamine B (RDMB). Furthermore, CuCoNC+Oxone has a smaller activation energy for RDMB elimination and maintains its superior effectiveness for removing RDMB in various water conditions. The computational chemistry insights have revealed the RDMB degradation mechanism. This study reveals that CuCoNC is a useful activator for Oxone to eliminate RDMB.

Degradation of tartrazine by Oxone® in the presence of cobalt based catalyst supported on pillared montmorillonite - Efficient technology even in extreme conditions

The catalytic degradation of hazardous organic contaminants in industrial wastewater is a promising technology. Reactions of tartrazine, the synthetic yellow azo dye, with Oxone® in the presence of catalyst in strong acidic condition (pH 2), were detected by using UV-Vis spectroscopy. In order to extend the applicability profile of Co-supported Al-pillared montmorillonite catalyst an investigation of Oxone® induced reactions were performed in extreme acidic environment. The products of the reactions were identified by liquid chromatography-mass spectrometry (LC-MS). Along with the catalytic decomposition of tartrazine induced by radical attack (confirmed as unique reaction path under neutral and alkaline conditions), the formation of tartrazine derivatives by reaction of nucleophilic addition was also detected. The presence of derivatives under acidic conditions slowed down the hydrolysis of tartrazine diazo bond in comparison to the reactions in neutral environment. Nevertheless, the reaction in acidic conditions (pH 2) is faster than the one conducted in alkaline conditions (pH 11). Theoretical calculations were used to complete and clarify the mechanisms of tartrazine derivatization and degradation, as well as to predict the UV-Vis spectra of compounds which could serve as predictors of certain reaction phases. ECOSAR program, used to estimate toxicological profile of compounds to aquatic animals, indicated an increase in the harmfulness of the compounds identified by LC-MS as degradation products from the reaction conducted for 240min. It could be concluded that an intensification of the process parameters (higher concentration of Oxone®, higher catalyst loading, increased reaction time, etc.) is needed in order to obtain only biodegradable products.

Interface engineering-induced perovskite/spinel LaCoO3/Co3O4 heterostructured nanocomposites for efficient peroxymonosulfate activation to degrade levofloxacin

Conventional perovskite oxides (ABO₃) tend to suffer from their inactive surfaces and limited active sites that reduce their catalytic activity and stability, while interface engineering is a facile modulating technique to boost the catalyst's inherent activity by constructing heterogeneous interfaces. In this study, perovskite/spinel LaCoO₃/Co₃O₄ nanocomposites with heterogeneous interfaces were synthesized via sol-gel and in-situ gradient etching methods to activate peroxymonosulfate (PMS) for degrading levofloxacin (LEV). LaCoO₃ on the surface was etched into spinel Co₃O₄, and LaCoO₃/Co₃O₄ nanocomposites with two crystal structures of perovskite and spinel were successfully formed. The surface-modified LaCoO₃/Co₃O₄ exhibited superior catalytic performance with a reaction rate constant more than 2 times that of the original LaCoO₃, as well as excellent pH adaptability (3-11) and reusability (more than 6 recyclings) for LEV degradation. Besides, multiple characterization techniques were carried out to find that LaCoO₃/Co₃O₄ possessed a larger specific surface area and richer oxygen vacancies after surface modification, which provided more active sites and accelerated mass transfer rate. The mechanism of reactive oxygen species involved in the reaction system was proposed that LaCoO₃/Co₃O₄ not only reacted with PMS directly to produce SO₄^•- and ^•OH but also its surface hydroxyl group helped to form the [≡Co(Ⅲ)OOSO₃]⁺ reactive complex with PMS to produce O₂^•- and ¹O₂. In addition, electrochemical experiments demonstrated that the surface electronic structure of LaCoO₃/Co₃O₄ was effectively regulated, exhibiting a faster electron transfer rate and facilitating the redox process. By detecting and identifying degradation intermediates, three degradation pathways for LEV were proposed. Our work provided profound insights into the design of efficient and long-lasting catalysts for advanced oxidation processes.

La2CoO4+δ perovskite-mediated peroxymonosulfate activation for the efficient degradation of bisphenol A

Sulfate radical-based technology has been considered as an efficient technology to remove pharmaceuticals and personal care products (PPCPs) with heterogeneous metal-mediated catalysts for the activation of peroxymonosulfate (PMS). In this study, La₂CoO_4+δ perovskite with Ruddlesden-Popper type structure was synthesised by the sol-gel method, which was employed in PMS activation. Different characteriazation technologies were applied for the characterization of La₂CoO_4+δ , such as SEM-EDX, XRD, and XPS technologies. A common organic compound, bisphenol A (BPA), is used as a target contaminant, and the effect impactors were fully investigated and explained. The results showed that when the dosage of La₂CoO_4+δ was 0.5 g L^-1 and the concentration of PMS was 1.0 mM in neutral pH solution, about 91.1% degradation efficiency was achieved within 25 minutes. Quenching experiments were introduced in the system to verify the catalytic mechanism of PMS for the BPA degradation, proving the existence of superoxide, hydroxyl radicals and sulfate radicals, which are responsible for the catalytic degradation of BPA. Moreover, the reusability and stability of the catalyst were also conducted which showed good stability during the reaction. This work would improve the applications of A₂BO₄-type perovskites for activating PMS to degrade BPA.

Activation of persulfate by LaFe1-xCoxO3 perovskite catalysts for the degradation of phenolics: Effect of synthetic method and metal substitution

The presence of resistant organic pollutants in environmental substrates requires the development and finding of novel decontamination methods. Advanced oxidation processes are among the most effective methods used for degradation of these pollutants through their oxidation and degradation into non-toxic and harmless, for the environment, final products. Ιn this research, a series of perovskites of ABO₃-type, with La and Fe and/or Co in A and B positions respectively, LaFe_1-xCo_xO₃ (x = 0, 0.25, 0.5, 0.75, 1), were synthesized with two different methods, a soft template method using anionic surfactant and by glycine combustion method and studied for their catalytic activity towards the degradation of phenolic compounds, a major class of environmental pollutants, through persulfate activation. The catalytic activity depended both by the B metal ion of perovskites and their ratio as well as by the synthesis method. LaCoO₃ prepared with the anionic surfactant method, showed the highest catalytic activity with a rate constant of 0.024 min^-1. Furthermore, the synthesis method also influenced the stability of perovskites as metal leaching studies showed that perovskites synthesized with the anionic surfactant showed greater stability. Quenching experiments were also used in order to shed light on the catalytic activation mechanism of persulfate for the degradation of phenolics. Overall, the results showed that the synthesis method can significantly affect the catalytic activity of the materials and their stability since the same materials synthesized with different methods show significantly different catalytic properties.

ZrO2 supported perovskite activation of peroxymonosulfate for sulfamethoxazole removal from aqueous solution

In this study, A- and B-site doped perovskite La_0.5Sr_0.5Co_0.8Ni_0.2O₃ （LSCN) was prepared by sol-gel method. On this basis, ZrO₂ supported LSCN used to maintain high catalytic activity while inhibit the leaching of toxic Co ions. Compared with the non-doped LaCoO₃, the ZrO₂@La_0.5Sr_0.5Co_0.8Ni_0.2O₃ (Z@LSCN82)/PMS system could almost completely degrade SMX in 30 min. In addition, the leaching amount of Co ions was only 0.303 mg L^-1. Free radical quenching experiments and electron paramagnetic resonance experiments proved that active species SO₄^•-, •OH and ¹O₂ existed in the Z@LSCN82/PMS system, and SO₄^•- played a major role. Besides, the catalyst had high efficiency for SMX degradation in a wide pH range. In addition, co-existing anions in water such as HPO₄^- and Cl^- also showed slight inhibition of the system. It was indicated that the Z@LSCN82/PMS system had huge potential applications for practical wastewater treatment.

Critical review of perovskite-based materials in advanced oxidation system for wastewater treatment: Design, applications and mechanisms

Perovskite has been widely concerned in the field of modern environmental catalysis due to its low price, high stability, excellent catalytic activity, diverse structure and strong conversion adaptability. In recent years, people have been working on the coupling of perovskite catalysts and advanced oxidation processes (AOPs) on the removal of organic pollutants from wastewater. In this review, we classified perovskites of different designs and summarized the application and basic reaction mechanisms of each perovskite in different AOPs. This review helps scientists selecting and designing more effective perovskite catalysts for AOPs by summarizing the applications and reaction mechanisms of perovskite in AOPs. At the end of the review, the challenges and future directions of perovskite in removing organic pollutants from wastewater are discussed.

The synergistic effect of PMS activation by LaCoO3/g-C3N4 for degradation of tetracycline hydrochloride: performance, mechanism and phytotoxicity evaluation

A LaCoO3/g-C3N4 catalyst with high stability was designed and used for PMS activation to degrade TC.

Reduced alkaline earth metal (Ca, Sr) substituted LaCoO3 catalysts for succinic acid conversion

Surface distribution and particle size play a key role in the catalytic activity of substituted La1−xAxCoO3 (A = Ca/Sr, x = 0.2–0.4) perovskites.

Degradation of organic contaminants in marine sediments by peroxymonosulfate over LaFeO3 nanoparticles supported on water caltrop shell-derived biochar and the associated microbial community responses

Sediment is an important final repository of persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs). Herein, a novel catalyst of LaFeO₃ nanoparticles supported on biochar was synthesized from water caltrop shell by chemical precipitation. The composite (LFBC) was used as peroxymonosulfate (PMS) activator to oxidize PAHs in real marine sediments. Systematic surface characterization confirmed the immobilization of well crystalline nano LaFeO₃ particles onto the biochar surface. Under optimal conditions, i.e., [PMS] = 3 × 10^-4 M, [LFBC] = 0.75 g/L, pH 6.0, and seawater, the total PAH degradation efficiency was 90%, while that of 2-, 3-, 4-, 5-, and 6-ring PAHs was 52%, 61%, 66%, 56%, and 29%, respectively, in 24 h. The Langmuir-Hinshelwood equation better predicted the PAHs degradation kinetics over LFBC by PMS. Interactions between surface oxygen species at LaFeO₃ defective sites and the graphitized biochar network facilitated the PAHs degradation. Furthermore, changes in the bacterial community during the LFBC/PMS treatment were highlighted to assess the sustainable development of the sediment ecosystem. The LFBC/PMS process enhanced the biological richness and diversity of sediment eco-systems. The major phylum was Proteobacteria initially, while Hyphomonas was the genera after LFBC/PMS treatment of the sediment.

Porous ZrO2 encapsulated perovskite composite oxide for organic pollutants removal: Enhanced catalytic efficiency and suppressed metal leaching

Cobalt-based perovskite material, an effective activator of PMS, is widely employed for wastewater remediation, but still affected by the leakage of the cobalt ions. In this study, a porous core-shell structured perovskite LaFe_0.1Co_0.9O_3-λ/SiO₂ core @ZrO₂ shell (LFCS@ZrO₂) was fabricated and partially etched to enlarge channels to further enhance mass transfer ability. The well-designed core-shell structure can not only restrain metal ion leaching by changing the surface microenvironment but also provide an additional driving force attributed to the enriched concentration gradient, thus enhancing the catalytic oxidation performance. Results showed that the partially etched LFCS@ZrO₂ (eLFCS@ZrO₂) particles exhibited an increased pore size and showed an attractive catalytic performance as well as a suppressed cobalt ion leaching (3.61 to 0.67 mg/L). Over 99% of tetracycline hydrochloride (20 mg/L) could be degraded in 15 min, and the reaction rate increased 2 folds compared with pristine LaFe_0.1Co_0.9O_3-λ. Besides, quenching test and electron paramagnetic resonance analysis proved that sulfate radicals and singlet oxygen were the two predominant reactive oxygen species during the catalytic oxidation. This work provides a novel perspective for the fabrication of an environmentally friendly perovskite catalyst, which has a great potential application in organic pollutant degradation.

Perovskite and Spinel Catalysts for Sulfate Radical-Based Advanced Oxidation of Organic Pollutants in Water and Wastewater Systems

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.

Carbamazepine degradation by heterogeneous activation of peroxymonosulfate with lanthanum cobaltite perovskite: Performance, mechanism and toxicity

The widely used carbamazepine (CBZ) is one of the most persistent pharmaceuticals and suffers insufficient removal efficiency by conventional wastewater treatment. A synthesized Co-based perovskite (LaCoO₃) was used to activate peroxymonosulfate (PMS) in order to degrade CBZ. Results showed that LaCoO₃ exhibited an excellent performance in PMS activation and CBZ degradation at neutral pH, with low cobalt leaching. The results of FT-IR and XPS verified the high structurally and chemically stability of LaCoO₃ in PMS activation. Electron spin resonance (ESR) analysis suggested the generation of radical species, such as sulfate radicals (SO₄^-) and hydroxyl radicals (OH). Radical quenching experiments further revealed the responsibility of SO₄^- as the dominant oxidant for CBZ oxidation. Ten products were detected via the oxidation of CBZ, with the olefinic double bond attacked by SO₄^- as the initial step. Hydroxylation, hydrolysis, cyclization and dehydration were involved along the transformation of CBZ. The toxicity of CBZ solution was significantly reduced after treating by PMS/LaCoO₃.

Enhanced activation of peroxymonosulfte by LaFeO3 perovskite supported on Al2O3 for degradation of organic pollutants

In this study, the effect of various supports on activation of peroxymonosulfate and consequent degradation of Acid Orange 7 (AO7) in aqueous solutions was examined at the presence of LaFeO₃ perovskite as catalyst. Results showed that the AO7 degradation efficiency by LaFeO₃ supported on different supports was in an order of LaFeO₃/Al₂O₃ (86.2%) > LaFeO₃ (70.8%) > LaFeO₃/CeO₂ (59.0%) > LaFeO₃/SiO₂ (52.3%) > LaFeO₃/TiO₂ (32.2%). Moreover, the pseudo first-order rate constant for AO7 degradation by LaFeO₃/Al₂O₃ was 3.2 times than that by LaFeO₃. The enhancement was attributed to its large surface area, abundant chemisorbed surface-active oxygen, redox property and faster electron transfer. AO7 degradation and the leaching of iron ions decreased with the increase of pH. Data of electron spin resonance spectroscopy and quenching experiments revealed that sulfate and hydroxyl radicals were generated on LaFeO₃/Al₂O₃ surface, while sulfate radicals were identified to be the main reactive species responsible for AO7 degradation. Mechanisms for peroxymonosulfate activation were consequently proposed. Furthermore, LaFeO₃/Al₂O₃ catalyst exhibited a superior stability after five cycles. This work provides a new approach for design of iron-based perovskite catalysts with high and stable catalytic activity for removal of organic pollutants from aqueous solutions.

Perovskites as Catalysts in Advanced Oxidation Processes for Wastewater Treatment

Advanced oxidation processes (AOPs), based on the formation of highly reactive radicals are able to degrade many organic contaminants present in effluent water. In the heterogeneous AOPS the presence of a solid which acts as catalyst in combination with other systems (O3, H2O2, light) is required. Among the different materials that can catalyse these processes, perovskites are found to be very promising, because they are highly stable and exhibit a high mobility of network oxygen with the possibility of forming vacancies and to stabilize unusual oxidation states of metals. In this review, we show the fundaments of different kinds of AOPs and the application of perovskite type oxides in them, classified attending to the oxidant used, ozone, H2O2 or peroxymonosulfate, alone or in combination with other systems. The photocatalytic oxidation, consisting in the activation of the perovskite by irradiation with ultraviolet or visible light is also revised.

Efficient removal of organic and bacterial pollutants by Ag-La0.8Ca0.2Fe0.94O3-δ perovskite via catalytic peroxymonosulfate activation

Removal of toxic organics and bacterial disinfection are important tasks in wastewater treatment. Most heavy metal-based catalysts for degradation of aqueous organic pollutants in heterogeneous Fenton-like processes suffer from the toxicity of leached metals. The present work reports environmentally benign systems for both degradation of organics and bacterial disinfection. Calcium substituted LaFeO_3-δ perovskite was demonstrated as an efficient catalyst to activate peroxymonosulfate (PMS) for degradation of phenol, methylene blue and rhodamine 6 G. Compared to LaFeO_3-δ and nanocrystal Fe₃O₄, the lattice oxygen vacancies in B-site cation-deficient perovskite of La_0.8Ca_0.2Fe_0.94O₃-_δ (LaCaFeO_3-δ) particles renders this material a greatly improved catalytic performance. Electron paramagnetic resonance (EPR) suggested that both sulfate (SO₄-) and hydroxyl radicals (OH) played critical roles in the advanced oxidation processes. Moreover, silver doped perovskite (Ag-LaCaFeO_3-δ)/PMS successfully inhibited the growth of waterborne pathogen Escherichia coli and Methicillin-resistant Staphylococcus aureus (MRSA) at a lower dose than silver ions, proving a synergetic effect between free radicals and Ag⁺ in killing the bacteria. Therefore, Ag-LaCaFeO_3-δ/PMS would be promising for practical wastewater treatment.

Nanostructured Co-Mn containing perovskites for degradation of pollutants: Insight into the activity and stability

The efficient oxidative removal of persistent organic components in wastewater relies on low-cost heterogeneous catalysts that offer high catalytic activity, stability, and recyclability. Here, we designed a series of nanostructured Co-Mn containing perovskite catalysts, LaCo_1-xMn_xO_3+δ (LCM, x = 0, 0.3, 0.5, 0.7, and 1.0), with over-stoichiometric oxygen (δ > 0) to show superior catalytic activity for the degradation of a variety of persistent aqueous organic pollutants by activating peroxymonosulfate (PMS). The nature of LCM for catalysis was comprehensively investigated. A "volcano-shaped" correlation was observed between the catalytic activity and electron filling (e_g) of Co in LCM. Among these compounds, LaCo_0.5Mn_0.5O_3+δ (LCM55) exhibited an excellent activity with e_g = 1.27. The high interstitial oxygen ion diffusion rate (D_O^2- = 1.58 ± 0.01 × 10^-13 cm² s^-1) of LCM55 also contributes to its catalytic activity. The enhanced stability of LCM55 can be ascribed to its stronger relative acidity (3.22). Moreover, an increased solution pH (pH ≥ 7) generated a faster organic degradation rate and a decrease in metal leaching (0.004 mM) for LCM55 perovskite, justifying it as a potential material for environmental remediation.