Cobalt-embedded carbon nanofiber derived from a coordination polymer as a highly efficient heterogeneous catalyst for activating oxone in water

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.

Single cobalt atom anchored on carbon nitride with cobalt nitrogen/oxygen active sites for efficient Fenton-like catalysis

As one of the tactics to produce reactive oxygen radicals, the Fenton-like process has been widely developed to solve the increasingly severe problem of environmental pollution. However, establishing advanced mediators with sufficient stability and activity for practical application is still a long-term objective. Herein, we proposed a facile strategy through polymeric carbon nitride (pCN) in-situ growth single cobalt atom for efficient degradation of antibiotics by peroxymonosulfate (PMS) activation. X-ray absorption spectroscopy and high-angle annular dark field-scanning transmission electron microscopy prove the single cobalt atoms are successfully anchored on pCN. Moreover, extended X-ray absorption fine structure analysis shows that the embedded cobalt atoms are constructed by covalently forming the Co-N bond and Co-O bond, which endow the single-atom cobalt catalyst with high stability. Experiment results indicate that the prepared single-atom cobalt catalyst can be used for efficient PMS activation catalytic degradation of tetracycline with a high degradation rate of 98.7 % in 60 min. And the CoN/O sites with single cobalt atoms serve as the active site for generating active radical species (singlet oxygen) from PMS activation. This work may expand the strategy for constructing single-atom catalysts and extend its application for the advanced oxidation process.

Syntheses, crystal structures, and fluorescent properties of three coordination polymers with 5-sulfoisophthalic acid anion and 4-phenylpyridine

Three coordination polymers—{[Ag2(SIP)(4-pp)]·[Ag(4-pp)2]·H2O}n, [Pb4(SIP)2( μ3-OH)2(H2O)2]n, and {[Zn2(SIP)2(4-pp)4][Zn(4-pp)2(H2O)4]·4H2O}n (SIP = 5-sulfoisophthalic acid anion, 4-pp = 4-phenylpyridine)—are constructed under hydrothermal or solvothermal conditions using sodium m-phthalate 5-sulfonate (NaH2SIP) and 4-phenylpyridine as ligands. The structures of the three complexes are determined by single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analyses, Fourier-transform infrared analysis, and photoluminescence. The fluorescent properties of the complexes in the solid state are investigated at room temperature, and the results indicate that they all show photoluminescent properties.

Recent advances in cobalt-activated sulfate radical-based advanced oxidation processes for water remediation: A review

Sulfate radical-based advanced oxidation processes (SR-AOPs) have attracted increasing attention for the degradation of organic contaminants in water. The oxidants of SR-AOPs could be activated to generate different kinds of reactive oxygen species (ROS, e.g., hydroxyl radicals (OH), sulfate radicals (SO₄^-), singlet oxygen (¹O₂), and superoxide radicals (O₂^-)) by various catalysts. As one of the promising catalysts, cobalt-based catalysts have been extensively investigated in catalytic activity and stability during water remediation. This article mainly summarizes recent advances in preparation and applications of cobalt-based catalysts on peroxydisulfate (PDS)/peroxymonosulfate (PMS) activation since 2016. The review covers the development of homogeneous cobalt ions, cobalt oxides, supported cobalt composites, and cobalt-based mixed metal oxides for PDS/PMS activation, especially for the latest nanocomposites such as cobalt-based metal-organic frameworks and single-atom catalysts. This article also discussed the activation mechanisms and the influencing factors of different cobalt-based catalysts for activating PDS/PMS. Finally, the future perspectives on the challenges and applications of cobalt-based catalysts are presented at the end of this paper.

Carbon nanofibers supported Co/Ag bimetallic nanoparticles for heterogeneous activation of peroxymonosulfate and efficient oxidation of amoxicillin

The carbon nanofibers supported Co/Ag bimetallic nanoparticles (Co@CNFs-Ag) were synthesized for heterogeneous activation of peroxymonosulfate and efficient oxidation of amoxicillin in this work. Co nanoparticles with a diameter of 20-30 nm were encapsulated in the carbon nanofibers to reduce the loss of Co during the preparation and catalysis processes. Ag nanoparticles (5-10 nm) were distributed on the surface of CNFs. Complete removal of amoxicillin could be achieved within 30 min by Co@CNFs-Ag activated peroxymonosulfate system. The high catalytic performance could be attributed to the large aspect ratio (> 10,000) of the carbon nanofibers and the mutual reaction of the Co/Ag bimetallic nanoparticles with peroxymonosulfate. The optimal mass ratio of oxidant and catalyst was 10 and the optimized pH was 7. Co@CNFs-Ag exhibited stable catalytic activity and minimal metal leakage over a period of 5 cycles. The activation energy of the system was 29.51 kJ/mol derived by the Arrhenius equation. Both hydroxyl and sulfate radicals contributed to amoxicillin degradation and the latter were key to the degradation. Finally, the reaction mechanism of bimetallic synergistic catalytic system and possible amoxicillin degradation pathways were elucidated. The results of this study provide novel insights for application of sulfate radical-based advanced oxidation processes in environmental remediation.

Co2+ anchored on surface-functionalized PET non-woven fabric and used as high efficiency monoatom-like catalyst for activating Oxone in water

Fenton-like processes have emerged as most promising techniques for generating reactive oxygen-containing radicals to deal with increasing levels of environmental pollution. Developing novel catalysts with simple manufacturing requirements, excellent activity levels, and stability remains a long-term goal in terms of practical application. So herein, a new polyethylene terephthalate (PET) non-woven fabric based composite catalyst has been fabricated, using radiation-induced graft polymerization of a functionalized group to chelate Co²⁺ ions as heterogeneous catalysts in peroxymonosulfate (Oxone) activation. Several impact factors, including catalyst dosage, Oxone concentration, reaction temperature, pH value, Co²⁺ precipitation ratio (of Co@PET at different pH values), and highly concentrated NaCl have been investigated here. Notably, Co@PET has shown the lowest activation energy of any reported catalyst, for degrading RhB by activating Oxone. Interestingly, as experimental RhB and Oxone solutions were passed through single Co@PET sheets, the RhB was decomposed into a colorless solution in the penetration process. Based on radical trapping and quenching experiments, a channel was determined to dominate RhB degradation, and furthermore, Co@PET could be re-used for RhB degradation by activating Oxone. These results showed that Co@PET effectively provided improved Fenton-like catalytic performance and stability, and was suitable for practical applications.

N-doped hierarchically porous carbon for highly efficient metal-free catalytic activation of peroxymonosulfate in water: A non-radical mechanism

Metal-free carbo-catalyst has recently emerged as a promising candidate as a substituent for tradition-metal based heterogeneous catalyst for catalytic activation of peroxymonosulfate (PMS). However, most reported carbo-catalysts suffer from low catalytic efficiency and poor stability, thus a high-performance catalyst is urgently desired. In this study, a novel carbo-catalyst (NHPC-800), prepared by using tannic acid and dicyandiamide as renewable carbon/nitrogen feedstocks via a simple pyrolysis route, is reported as an activator of PMS with highly efficient catalytic ability and stability. The as-prepared NHPC-800 possesses as high as 22.4 atom% of nitrogen dopants and a hierarchically porous structure with abundant meso/macropores, accompanied by the abundant edges and wrinkles, which supply sufficient exposed catalytically active centers and fast electrons/mass transportations. Using rhodamine B as a model pollutant, the NHPC-800 shows a highly efficient catalytic ability which is superior to most reported carbo-catalysts and even some state-of-the-art metal catalysts. Based on competitive quenching experiments and electron paramagnetic resonance (EPR) results, a non-radical pathway involving the generation of ¹O₂ is responsible for the degradation of pollutants. Given that the NHPC-800 shows good recycling performance and strong resistance to adventitious interference such as anions and natural organic matters, we believe NHPC-800 can be a promising candidate for practical applications, and this study can provide inspirations for the further development of highly efficient carbo-catalysts.

Implementation of martite nanoparticles prepared through planetary ball milling as a heterogeneous activator of oxone for degradation of tetracycline antibiotic: Ultrasound and peroxy-enhancement

The aim of the present study was to employ martite nanoparticles synthesized through planetary ball milling instead of conventional sources of iron for the activation of Oxone in order to decompose tetracycline (TC) antibiotic in the aquatic phase. Accordingly, martite nanoparticles-activated Oxone exhibited a remarkable improvement in degrading TC molecules up to 87%. The results indicated an increased decomposition rate of TC with increasing Oxone concentration, martite nanoparticles dosage, and initial pH. In the absence of ultrasound, the decomposition rate of TC was 0.0481 min^-1 within 30 min, while the implementation of ultrasound at 320 W and addition of hydrogen peroxide at 40 mM led to increase in the decomposition rate up to 0.0770 and 0.0907 min^-1, respectively. The presence of carbonate and even persulfate ions suppressed the decomposition rate. Inversely, the addition of chloride and carbon tetrachloride enhanced the reactor performance in terms of TC degradation. Within four consecutive experimental runs, only 10.8% was dropped in the decomposition rate, indicating the appropriate reusability potential of martite nanoparticles. The results confirmed the appropriate ability of the treatment process in degrading and mineralizing the target pollutant but a longer exposure time is required for an efficient mineralization.

Synthesis of cerium and nickel doped titanium nanofibers for hydrolysis of sodium borohydride

A recyclable titanium nanofibers, doped with cerium and nickel doped was successfully synthesized by using sol-gel and electrospinning method for hydrogen generation from alkali free hydrolysis of NaBH₄. The resultant nanocomposite was characterized to find out the structural and physical-chemical properties by a series of analytical techniques such as FT-IR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), SEM (scanning electron microscope), EDX (energy-dispersive X-ray spectroscopy),N₂ adsorption-desorption and BET (Brunauer-Emmett-Teller), etc. The results revealed that cerium and nickel nanoparticles were homogeneously distributed on the surface of the TiO₂ nanofibers due to having similar oxidation state and atomic radium of TiO₂nanofibers with CeO₂ and NiO for the effective immobilization of metal ions. The NiO doped catalyst showed superior catalytic performance towards the hydrolysis reaction of NaBH₄ at room temperature. These catalysts have ability to produce 305 mL of H₂ within the time of 160 min at room temperature. Additionally, reusability test revealed that the catalyst is active even after five runs of hydrolytic reaction, implying the as-prepared NiO doped TiO₂ nanofibers could be considered as a potential candidate catalyst for portable hydrogen fuel system such as PEMFC (proton exchange membrane fuel cells).