Bivalent Cobalt Research Articles

A Graded Redox Interfacial Modifier for High-Performance Perovskite Solar Cells.

Perovskite solar cells have emerged as a potential competitor to the silicon photovoltaic technology. The most representative perovskite cells employ SnO2 and spiro-OMeTAD as the charge-transport materials. Despite their high efficiencies, perovskite cells with such a configuration show unsatisfactory lifespan, normally attributed to the instability of perovskites and spiro-OMeTAD. Limited attention was paid to the influence of SnO2, an inorganic material, on device stability. Here we show that improving SnO2 with a redox interfacial modifier, cobalt hexammine sulfamate, simultaneously enhances the power-conversion efficiency (PCE) and stability of the perovskite solar cells. Redox reactions between the bivalent cobalt complexes and oxygen lead to the formation of a graded distribution of trivalent and bivalent cobalt complexes across the surface and bulk regions of the SnO2. The trivalent cobalt complex at the top surface of SnO2 raises the concentration of (SO3NH2)- which passivates uncoordinated Pb2+ and relieves tensile stress, facilitating the formation of perovskite with improved crystallinity. Our approach enables perovskite cells with PCEs of up to 24.91%. The devices retained 93.8% of their initial PCEs after 1000 hours of continuous operation under maximum power point tracking. These findings showcase the potential of cobalt complexes as redox interfacial modifiers for high-performance perovskite photovoltaics.

A Graded Redox Interfacial Modifier for High‐Performance Perovskite Solar Cells

Perovskite solar cells have emerged as a potential competitor to the silicon photovoltaic technology. The most representative perovskite cells employ SnO2 and spiro‐OMeTAD as the charge‐transport materials. Despite their high efficiencies, perovskite cells with such a configuration show unsatisfactory lifespan, normally attributed to the instability of perovskites and spiro‐OMeTAD. Limited attention was paid to the influence of SnO2, an inorganic material, on device stability. Here we show that improving SnO2 with a redox interfacial modifier, cobalt hexammine sulfamate, simultaneously enhances the power‐conversion efficiency (PCE) and stability of the perovskite solar cells. Redox reactions between the bivalent cobalt complexes and oxygen lead to the formation of a graded distribution of trivalent and bivalent cobalt complexes across the surface and bulk regions of the SnO2. The trivalent cobalt complex at the top surface of SnO2 raises the concentration of (SO3NH2)‐ which passivates uncoordinated Pb2+ and relieves tensile stress, facilitating the formation of perovskite with improved crystallinity. Our approach enables perovskite cells with PCEs of up to 24.91%. The devices retained 93.8% of their initial PCEs after 1000 hours of continuous operation under maximum power point tracking. These findings showcase the potential of cobalt complexes as redox interfacial modifiers for high‐performance perovskite photovoltaics.

Bivalent Cobalt as Efficient Catalyst Intercalation Layer Improves Polysulfide Conversion in Lithium-Sulfur Batteries.

Herein, we investigated in detail the effect of metal valences in different cobalt-based organic framework compounds on the kinetics of sulfur reaction in lithium-sulfur batteries (LSBs). On this basis, two organic framework compounds of zeolite-imidazole-based cobalt organic framework compound (Co-ZIF) and tetrakis(4-benzoic acid) porphyrinato-CoIII chloride [Co-TBP(III)] with different valences were constructed as the functional intercalation separators of LSBs, and explored the effects of different valences on improving the reaction kinetics of polysulfides and inhibiting the shuttle effect. Experiments and theoretical calculations prove that CoII exhibits the best catalytic activity. This is mainly due to the fact that +2 valence shows a strong adsorption energy for polysulfides and a higher Fermi level compared with +3 valence, thus improving the efficiency of the rapid catalytic conversion of sulfur species. As expected, the discharge specific capacity of Co-ZIF as the catalytic layer of the LSBs reached 772.7 mAh g-1 at a high current density of 5 C. More importantly, the initial specific capacity is 839.6 mAh g-1 at high current 3 C, and after 720 cycles, the attenuation rate of per cycle is only 0.092 %, and the coulombic efficiency remains above 92 %.

Synthesis, spectroscopic characterization and photophysical properties of transition metal complexes of 4-((3-fluoro-2-methylbenzylidene)amino)-5-methyl-4H-1,2,4-triazole-3-thiol

This study focused on the synthesis and spectral investigation of divalent transition metal complexes of novel ligand 4-((3-fluoro-2-methylbenzylidene)amino)-5-methyl-4H-1,2,4-triazole-3-thiol (FMMT). Extensive physical, spectroscopic and theoretical investigations are performed on the ligand and its complexes, and the results are compatible with their expected compositions. Based on IR and NMR spectral data, metal complexes with coordination number of 6 and 4 were proposed, with FMMT functioning as a bidentate ligand. The metal complexes display an octahedral geometry around bivalent cobalt, nickel and zinc centers, and for copper and palladium tetrahedral environment was suggested and also optimized by Avogadro program. The polarity of the solvent used promoted the complex solvatochromism. Furthermore, optical bandgap was calculated with the help of Tauc's plot. Thermogravimetric study was employed to estimate the thermal stability and coordinated H2O in the complexes. CV endorsed a reversible one electron transfer Cu(II)/Cu(I) redox reaction. In vitro antibacterial and antifungal studies of compounds exhibited modest to substantial activity against different microbial strains. The bio-efficacy data proved that the complexation of ligand with metal centers leads to enhanced bio–activity which could be elucidated by chelation and Overton’s theory.

Degradation mechanism and eco-toxicity assessment of bisphenol S based on peroxymonosulfate activated with Co3O4 surfaces

In this paper, the degradation mechanism and eco-toxicity assessment of bisphenol S (BPS) was studied in the aqueous environment based on the heterogeneous activation of peroxymonosulfate (PMS) through spinel tricobalt tetraoxide (Co3O4) catalyst using density functional theory (DFT) and computational toxicology methods. The result indicates that (100) and (311) surfaces have the higher proportion of bivalent cobalt, the increase of charge transfer, negative adsorption energy, and the lower surface energy. They can more effectively promote the decomposition of PMS to generate reactive oxide species. When generated oxidants react with BPS, HO•-addition reaction at the ortho-C atom-sites plays a dominant role in the system Co3O4/PMS. The presence of SO4•-, HO•, and O2 promotes the formation of transformation intermediates and products. The formation pathways of important experimental intermediates hydroquinone, p-hydroxybenzenesulfonic acid, and 3, 4-dihydroxybenzenesulfonic acid are identified. And, some hydroxylation products that are not identified in the experiment are determined. The eco-toxicity evaluation shows that most of the decomposition products are completely harmless or significantly reduced compared to BPS. This study not only provides insights into the degradation mechanism of BPS in Co3O4/PMS system, but also is expected to be a guide for further experimental research and the design and optimization of the activated catalysts in sulfate radical-based advanced oxidation technologies.

Preparation of New Complexes of Bivalent Manganese, Iron, Cobalt, and Nickel with Mixed Ligands of Ciprofloxacin (Cip) and Metronidazole (Met) or 4-Aminoantipyrine (4AAP) with Study of Their Chemical, Physical Properties and Antibacterial Activity

Preparation of New Complexes of Bivalent Manganese, Iron, Cobalt, and Nickel with Mixed Ligands of Ciprofloxacin (Cip) and Metronidazole (Met) or 4-Aminoantipyrine (4AAP) with Study of Their Chemical, Physical Properties and Antibacterial Activity

Amorphous cobalt oxide decorated halloysite nanotubes for efficient sulfamethoxazole degradation activated by peroxymonosulfate

In this study, a new hollow nanotube material, 30% Co–CHNTs was prepared by the impregnation–chemical reduction–calcination method. This material can be used as a peroxymonosulfate (PMS) activator to catalyse the degradation of sulfamethoxazole (SMX). The best reaction conditions that correspond to the degradation rate of SMX, up to 97.5%, are as follows: the concentration of SMX is 10 mg L−1, the amount of catalyst is 0.20 g L−1, the dosage is 1.625 mM, and the solution pH is 6.00. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectrometry (ICP-OES) show that the calcined composites mainly stimulate an increase in the content of bivalent cobalt in PMS and reduce the leaching of cobalt ions after the reaction. Additionally, the 30% Co–CHNTs + PMS reaction system exhibits a reasonable SMX degradation rate in a natural organic matter solution and excellent stability after three repeated experiments. Furthermore, the possible degradation mechanism in the 30% Co–CHNTs + PMS reaction system was analysed through electron paramagnetic resonance (EPR) and free-radical capture experiments, and it was observed that the non-radical degradation of 1O2 plays a leading role in SMX degradation. Finally, according to the nine degradation intermediates detected by liquid chromatography-mass spectrometry (LC–MS), four possible SMX degradation routes were proposed. This study proved that a 30% Co–CHNTs heterogeneous catalyst is easily prepared, inexpensive, and environmentally friendly and has potential application in antibiotic wastewater treatment.

Cobalt doped nano-hydroxyapatite incorporated gum tragacanth-alginate beads as angiogenic-osteogenic cell encapsulation system for mesenchymal stem cell based bone tissue engineering

Angiogenic-osteogenic cell encapsulation system is a technical need for human mesenchymal stem cell (hMSC)-based bone tissue engineering (BTE). Here, we have developed a highly efficient hMSC encapsulation system by incorporating bivalent cobalt doped nano-hydroxyapatite (HAN) and gum tragacanth (GT) as angiogenic-osteogenic components into the calcium alginate (CA) beads. Physico-chemical characterizations revealed that the swelling and degradation of HAN incorporated CA-GT beads (GT-HAN) were 1.34 folds and 2 folds higher than calcium alginate (CA) beads. Furthermore, the diffusion coefficient of solute molecule was found 2.5-fold higher in GT-HAN with respect to CA bead. It is observed that GT-HAN supports the long-term viability of encapsulated hMSC and causes 50% less production of reactive oxygen species (ROS) in comparison to CA beads. The expression of osteogenic differentiation markers was found 1.5–2.5 folds higher in the case of GT-HAN in comparison to CA. A similar trend was observed for hypoxia inducible factor 1 alpha (HIF-1α) and vascular endothelial growth factor (VEGF). The soluble secretome from hMSC encapsulated in the GT-HAN induced proliferation of endothelial cells and supported tube formation (2.5-fold higher than CA beads). These results corroborated that GT-HAN could be used as an angiogenic-osteogenic cell encapsulation matrix for hMSC encapsulation and BTE application.

Thermal reduction-assisted electronic structure tuning of perovskite oxide as catalyst for efficient advanced oxidation

Development of efficient and green heterogeneous catalyst is a challenging goal in peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) for wastewater remediation. Perovskite-type oxides with rich physicochemical properties and flexible structure are one of the most promising categories of heterogeneous catalysts to activate PMS, while appropriate structural tuning is key to develop highly active perovskite oxides for efficient wastewater treatment. Here, we propose a simple strategy based on facile high-temperature quenching to significantly improve activity of perovskite oxide LaCoO3-δ (LCO) for PMS activation. Such quenching process improves bivalent cobalt over the surface of LCO, enhances electron transfer rate, and increases surface oxygen defects, consequently improving the decomposition rate of PMS. Specifically, compared with LCO prepared from naturally cooling at 600 °C (LCO-600-C), directly quenched LCO sample (LCO-600-Q + C) shows more than 50% improvement in catalytic activity for phenol degradation. Sulfate radical and singlet oxygen are identified as the dominating reactive oxygen species (ROS) by in-situ electron paramagnetic resonance spectroscopy and radical scavenging experiments, but a different generating rate of SO4·- over LCO-600-Q + C and LCO-600-C. Such a strategy may be suitable for the design and development of other type of materials.

CoFe-based layered double hydroxide for high removal capacity of hydrogen sulfide under high humid gas stream

Although the adsorption method was considered as the most realistic way in the removal of gaseous hydrogen sulfide (H2S), finding an efficient sorbent at low temperature with the high humid condition is still desired. A layered double hydroxide (LDH) of CoFe bimetal was prepared by co-precipitation of bivalent cobalt and trivalent iron and applied to H2S gas stream treatment. CoFe-LDH was optimally synthesized under 3:1 of Co/Fe molar ratio, pH 10 of a mixing solution of precipitating reagents, and 60 °C of aging temperature, which allowed high breakthrough capacity (0.209 g H2S/g) in H2S removal. XPS and spectral analyses on spent CoFe-LDH proved that the H2S removal proceeded through two reaction processes: formed intermediate HS− from dissociated H2S which finally replaced with the hydroxide on the metal surface; and formed HS− through carbonate counter ion at interlayer. This resulted in the formation of CO2 as a gaseous product with CoFeS2 and CoFeSO4 as solid products after the treatment of H2S. Environmental application evidenced the prepared CoFe-LDH more efficient in high humid (90% relative humidity (RH) at room temperature) condition and even at high concentrated H2S source (3333 ppm).

Polyfunctional Ionochromic 1,3-Dihydroxy-6-oxo-6H-benzo[c]chromene-2,4-dicarbaldehyde Aroylhydrazones

Bisaroylhydrazones of a novel 1,3-dihydroxy-6-oxo-6H-benzo[c]chromene-2,4-dicarbaldehyde have been synthesized. The obtained compounds represent multifunctional chemosensors capable of detecting fluoride, cyanide, and acetate anions as well as transition metal cations. The formation of complexes with anions has led to a change in the color of the solution in DMSO from light yellow to orange-red. The addition of bivalent nickel, cobalt, or zinc chlorides has changed the solution color to orange. At the same time, the initial fluorescence has been significantly quenched.

Understanding the relationship between the local crystal structure and the ferrimagnetic ordering of CoxMn3-xO4 (x = 0–0.5) solid solutions

The local crystal structure alterations in the tetrahedral positions of the hausmannite Mn3O4 structure by Co2+ ions and its consequence on the magnetic ordering are studied in detail. The cation composition, bond distance and bond angle of the CoxMn3-xO4 series (x = 0.0. 0.1, 0.3 and 0.5) is determined by XRD Rietveld refinement. The charge state of the elements Co, Mn and O are investigated using XPS measurements, which confirm the bivalent cobalt ion occupation in the tetrahedral lattice. Considerable reduction in tetrahedral and axial octahedral bonds with the introduction of Co2+ ions dramatically increased the Curie temperature (TC) from 43 K (Mn3O4) to 62 K (Co0.5Mn2.5O4). The Lotgering-Srinivasan-Seehra model is employed to study the canted spin arrangement and the exchange interactions of Co0.5Mn2.5O4. The presence of cluster glass transition at TP = 42 K in Co0.3Mn2.7O4 is well-established through the AC susceptibility measurements and it is further substantiated by Vogel-Fulcher law and dynamic scaling power law. The origin of the cluster glass state is confirmed by the calculated strong geometric frustration factor (f = 19.5), due to the inhomogeneous distribution of cobalt ions in the intermediate concentrations. Field cooled isothermal magnetic measurements corroborated the exchange bias phenomenon in the Co0.3Mn2.7O4 sample, because of the interaction between ferrimagnetic-cluster glass phases occurring below the spin freezing temperature TP.

Treatment of Sb(V) and Co(II) containing wastewater by electrocoagulation and enhanced Sb(V) removal with Co(II) presence

Antimony (Sb) and cobalt (Co) are toxic to human if present in high concentrations. The existence of Sb and Co pollution in some mining areas has generated the need for an effective Sb and Co treatment method. In this work, the removal of pentavalent antimony (Sb(V)) and bivalent cobalt (Co(II)) by iron (Fe) electrocoagulation (EC) was investigated. The interaction between Sb(V) removal and Co(II) removal in Fe EC was studied. Results indicated that both Sb(V) and Co(II) can be effectively removed in Fe EC process. At the current density of 5 mA cm−2, the concentration of Sb(V) and Co(II) can be reduced from 60 mg/L and 29 mg/L to below 0.1 mg/L within 20 min by EC process. Interestingly, the existence of Co(II) ions has promoted the removal of Sb(V) in EC. Through the characterization of the precipitates by Raman and XRD techniques, it was found that layered double hydroxides (LDHs) can be more steadily formed with the existence of Co(II) in EC, which has facilitated the removal of Sb(V). During the EC process, Co was primarily removed through precipitation (95.2%) and electrodeposition onto the cathode (4.8%), and Sb was mainly removed by the formed flocs from water.

Core-Shell Prussian Blue Analogs with Compositional Heterogeneity and Open Cages for Oxygen Evolution Reaction.

Here, a reduction‐cation exchange (RCE) strategy is proposed for synthesizing Fe–Co based bimetallic Prussian blue analogs (PBAs) with heterogeneous composition distribution and open cage nanocage architecture. Specially, bivalent cobalt is introduced into a potassium ferricyanide solution containing hydrochloric acid and polyvinyl pyrrolidone. The uniform PBAs with opened cages are formed tardily after hydrothermal reaction. Time‐dependent evolution characterization on composition elucidating the RCE mechanism is based on the sequential reduction of ferric iron and cation exchange reaction between divalent iron and cobalt. The PBA structures are confirmed by electron tomography technology, and the heterogeneous element distribution is verified by energy‐dispersive X‐ray spectroscopy elemental analysis, leading to the formation of core–shell PBAs with compositional heterogeneity (Fe rich shell and Co rich core) and open cage architecture. When the PBA catalysts are used to boost the oxygen evolution reaction (OER), superior OER activity and long‐term stability (low overpotential of 271 mV at 10 mA cm−2 and ≈5.3% potential increase for 24 h) are achieved, which is attributed to the unique compositional and structural properties as well as high special surface areas (576.2 m2 g−1). The strategies offer insights for developing PBAs with compositional and structural multiplicity, which encourages more practical catalytic applications.

The role of different network modifying cations on the speciation of the Co2 + complex in silicates and implication in the investigation of historical glasses

In the last decades the speciation of the cobalt complex in a glass matrix has been extensively studied. Bivalent cobalt ions in glasses of different composition commonly adopt a tetrahedral coordination, though hexa- or penta-coordinated species are also possible. Changes in the absorbance spectrum of Co-doped glasses were attested in previous studies according to the introduction of different modifying cations. A shifting of the first sub-band characterizing the typical triplets of tetrahedral Co2+ ions in both the visible and near infrared regions was observed, but discrepancies in literature suggested a relevant role of glass composition on the definition of the optical signature of cobalt. Co-doped glasses with different composition (soda-lime, potash-lime, mixed alkali and ZnO-Na2O-CaO-SiO2) were studied via Fiber Optic Reflectance Spectroscopy (FORS). Pseudo-Voigt functions were used for the deconvolution of the absorbance spectra and the features of the bands characteristic of each cobalt complex were investigated. The structural role played by each modifying cation and the fundamental implications of glass basicity on the speciation of different Co-complexes were stressed. Changes in glass structure resulted in different equilibria between the three absorbing species whose specific optical signatures in the 480–530nm region interact to determine the resulting absorbance spectrum.

Role of Water in Diethyl Ether Dehydration Reaction

The study examined catalytic conversion of diethyl ether in a gas phase in the static system on the synthetic mordenite (NaM) and the mordenite which the bivalent cobalt cation was introduced into (CoM). The reaction was observed in the temperature range from 424 K to 653 K, and the reaction products on both catalysts were ethene and water, and on NaM a small quantity of butene.The reaction of diethyl ether dehydration in the observed temperature interval is accelerate in time. The initial reaction is registered at the very beginning of the reaction followed by the water occurrence. The water originating from the reaction is generated on the surface of the zeolite catalyst the active centers that is favorable for the dehydration reaction. With the temperature growth the initial period on NaM catalyst gradually disappears and the reaction becomes the first order reaction (temperature is 653 K), while on CoM catalyst the initial period is registered at all observed temperatures. The explanation of the role of water in the occurrence of active centers needed for diethyl ether hydrolysis was obtained by experiments in which water was also added to the reaction mixture of diethyl ether – catalyst.

Synthesis and electrochemical properties of Co3O4 nanoparticles by hydrothermal method at different temperatures

In this work, Co3O4 nanoparticles were synthesized by hydrothermal method at different temperatures. The synthesized Co3O4 nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS) and nitrogen adsorption-desorption. The Co3O4 nanoparticles prepared at the hydrothermal temperature of 140 °C and at the annealing temperature of 350 °C have a shorter crystal spacing distance associated to the (220) crystal planes, larger BET surface area and more bivalent cobalt on the surface than these of Co3O4 nanoparticles prepared at higher hydrothermal temperature or higher annealing temperature. The supercapacitor performances of synthesized Co3O4 nanoparticles were analysed by cyclic voltammograms (CVs), Galvano static charge/discharge (GCD) and the electrochemical impedance spectroscopy (EIS) in 6 M KOH aqueous electrolyte solution. The Co3O4 nanoparticles produced at lower temperatures exhibit good pseudo capacitance behaviour. Also, owning to the low hydrothermal temperature and the annealing temperature of Co3O4 nanoparticles, they can be relatively low cost in favour of a promising candidate for electrochemical supercapacitors.

Shape-dependent enzyme-like activity of Co3O4 nanoparticles and their conjugation with his-tagged EGFR single-domain antibody

In this study, Co3O4 nanopolyhedrons, nanocubes, nanoplates and nanorods were synthesized and characterized. Furthermore, the peroxidase- and catalase-like activities of these Co3O4 nanoparticles (NPs) were studied and influence of the exposed crystal planes was explored. According to their morphology and peroxidase-like activity, dimercaptosuccinic acid (DMSA) modified Co3O4 nanopolyhedrons synthesized via coprecipitation method (Co3O4 NHs) were selected as a proper candidate for the immunohistochemical (IHC) detection of epidermal growth factor receptor (EGFR) expression in non-small cell lung cancer (NSCLC) tissues. Bivalent cobalt ions were coupled to the carboxyls on the surface of the obtained Co3O4 NHs so as to chelate the hexahistidine residues (His-Tags) at the C-terminal of EGFR single-domain antibodies (EGFR sdAbs). Finally, the as-obtained EGFR sdAbs-binding Co3O4 NHs (Co3O4 nanoprobes) were successfully applied to the detection of EGFR expression in NSCLC tissues.

Oxidation of Co(II) by ozone and reactions of Co(III) in solutions of sulfuric acid

Reactions of the oxidation of bivalent cobalt ions by ozone, of the spontaneous decomposition of trivalent cobalt, and of interactions between Co(III) and chloride ions in solutions of sulfuric acid are studied. The order and rate constant of the process of decomposition of Co(III) are determined. Information on the kinetics of the interaction between Co(III) and Cl– is obtained. Kinetic patterns of the accumulation of Co(III) during the ozonation of solutions of CoSO4 in sulfuric acid are explained. Molar absorption coefficients of Co(III) and Co2+ ions in the visible range of wavelengths are determined.

Hydrosoluble 50% N-acetylation-thiolated chitosan complex with cobalt as a pH-responsive renal fibrosis targeting drugs

About 50% N-acetylation-thiolated chitosan possessing good water solubility was modified from commercial low-molecular-weight chitosan. Chitosan performed obvious target toward renal tubular epithelial cells, and bivalent cobalt ions improved the renal fibrosis inflammation significantly. There were many complexation sites on chitosan after being modified with sulfydryl. So sulfydryl played a role of connecting bridge between chitosan and cobalt ions. Then, this N-acetylation-thiolated chitosan cobalt (NTCC) nanocomplex was designed. The nanocomplex showed excellent stability under normal physiological conditions, and cobalt would be released from the biomaterials in acidic environment. As it was affected by inflammation, the pH in renal fibrosis lesion region was acidic. So there was a specific drug release process happening in lesion region. And drug release efficiency was determined by acidity, which demonstrated that lower the acidity, the faster and more the cobalt ion release. When this nanocomplex was intraperitoneally injected into ureter-obstructed mice, obvious attenuation of fibrotic progression was shown. It was demonstrated that NTCC exhibited special renal-targeting capacity and could be chosen as drug for treating renal fibrosis.