Cobalt Nitrate Research Articles

Grapefruit Oil and Cobalt Nitrate-Loaded Polyurethane Hybrid Nanofibrous Scaffold for Biomedical Applications

The goal of this work is to fabricate a new composite based on polyurethane (PU), grapefruit (GP) oil, and cobalt nitrate [Co(NO3)2] using an electrospinning technique. Morphology results revealed the reduction in the fiber diameter of the composites compared to pristine PU control. The interaction of PU with GP and Co(NO3)2 was confirmed by hydrogen bond formation evident in infrared analysis. The fabricated PU/GP composites depicted a more hydrophobic behavior, while PU/GP/Co(NO3)2 showed a hydrophilic behavior than the pristine PU. Atomic force micrographs (AFM) revealed that the developed composites showed a decrease in the surface roughness (Ra) compared to PU. The addition of GP and Co(NO3)2 improved the mechanical strength of the pristine PU. The blood compatibility assays concluded not only the increase in blood clotting levels but also the less toxic nature of the fabricated composites compared to the pristine PU. Hence, the newly designed composites possessing outstanding physicochemical and biological properties may be used as a potential candidate for scaffolding in tissue engineering applications.

Restructuring morphology and surface-electronic-structure of Pt-Co3O4-δ-carbon toward ultra-highly efficient hydrogen production

Although Pt has been verified as the most active catalyst for hydrogen production, it is highly desirable to minimize the usage of Pt while boost the catalytic performance of catalysts considering the low availability and high price of Pt. Herein, we propose a morphology and surface-electronic-structure reconstruction strategy to realize the anchoring of Pt nanoparticles (NPs) on Co3O4-δ-carbon matrix via the co-reduction of Pt precursor and Co3O4-carbon formed by direct pyrolysis of an aerogel composed of cobalt nitrate, chitosan, and urea. The transformation of the porous-network to hierarchically porous structure consisted of Co3O4-δ-carbon nanosheets, deposition of electron-rich Pt NPs, and generation of abundant oxygen-vacancy are facilely achieved through flexible co-reduction of Pt(IV) ions and Co3O4-carbon with ammonia borane (AB). The achieved Pt/Co3O4-δ-UC with an ultralow Pt loading (0.1 wt%) exhibits an ultrahigh activity for hydrolytic AB dehydrogenation with turnover frequencies of 7700 min−1 in aqueous solution at 25 ℃. This catalyst also has a high durability with 71.3% remained activity after ten repetitive cycles. The morphology and surface-electronic-structure reconstruction engaged formation of electron-efficient Pt species could accelerate the oxidative cleavage of O − H bond in H2O and greatly boost the hydrogen generation from hydrolytic AB dehydrogenation. This strategy presented herein offers a new pathway for constructing ultra-highly active supported metal NPs toward hydrogen evolution reaction.

Facile one-pot solvothermal approach to produce inorganic hybrid TiO2@CoTiO3 green nano-pigment: structural, optical and photocatalytic properties

ABSTARCT Herein, we report the synthesis of TiO2@CoTiO3 green nano-pigment by means of simple one-pot solvothermal process. The adapted solvothermal protocol involves the use of (Cobalt(II) nitrate, Titanium(IV) butoxide) and dimethyl sulfoxide (DMSO) as metals precursors and solvent respectively. A thermal treatment is necessary to produce high crystalline structure. The ideal calcination temperature was established to 600 °C in which the hybrid nanocomposite was completely crystalized. The obtained powder is green, characteristic color of cobalt titanate (CoTiO3) pigment. This structure was further confirmed by X-ray powder diffraction (XRD) technique. On the other hand, the morphology of the designed material was observed via Scanning Electron Microscopy (SEM). The prepared TiO2@CoTiO3 shows interesting optical properties in both UV and visible domains, which make it a promising photocatalyst under solar energy. The preliminary photocatalytic test against Methylene Blue (MB) prove high efficiency of the hybrid TiO2@CoTiO3 compared to pristine TiO2 probably due to the extension of the absorption region from UV (pristine TiO2) to UV/Visible region (hybrid material).

Self-supporting NiCoP for hydrogen generation via hydrolysis of ammonia borane

Ammonia borane (NH3BH3) is being widely used as a hydrogen (H2) storage material. Hydrogen storage content of NH3BH3 is suitable to produce H2 at room temperature in the presence of an efficient catalyst. Herein, cobalt doped nickel phosphide catalyst is developed to improve NH3BH3 hydrolysis by two steps. In first step, cobalt doped nickel hydroxide nanosheets are developed on the surface of nickel foam (NF) by immersing the NF in different concentrations of cobalt nitrate solution. In second step, self-supported cobalt doped nickel phosphide on NF is prepared by phosphidation at 300 °C. The partial positive charge of Ni and partial negative charge of P produce the charged polarization at the surface of NF. The catalyst optimization shows that 4-NiCoP/NF (0.01 M concentration of cobalt nitrate solution) produces the highest H2 production among all prepared samples. Same procedure is adopted to produce FeNiP/NF to determine the authenticity of the method. The reaction kinetics are calculated for both 4-NiCoP/NF and 4-FeNiP/NF best catalysts. The energy of activations 58.95 kJ·mol−1 for NiCoP/NF and 60.26 kJ·mol−1 NiFeP/NF are calculated via Arrhenius Equation. High activation energy of NiFeP/NF reveals that NiCoP/NF is better for H2 production. The on/off characteristics of the catalyst is unique for H2 evolution.

Synthesis, Structural Characterization, and Biological Activities of Organically Templated Cobalt Phosphite (H2DAB)[Co(H2PO3)4]·2H2O

A novel hybrid cobalt phosphite, (H2DAB)[Co(H2PO3)4] 2H2O, was synthesized by using a slow evaporation method in the presence of cobalt nitrate, phosphorous acid, and 1,4-diaminobutane (DAB = 1,4-diaminobutane) as a structure-directing agent. Single-crystal X-ray diffraction analysis showed that the compound crystallizes in the triclinic system (space group P-1(n.2)) with the following unit cell parameters (Å, °) a = 5.4814 (3), b = 7.5515 (4), c = 10.8548 (6), α = 88.001 (4), β = 88.707 (5), γ = 85.126 (5), and V = 447.33 (4) Å3. The crystal structure is built up from corner-sharing [CoO6] octahedra, forming chains parallel to [001], which are interconnected by H2PO3− pseudo-tetrahedral units. The diprotonated cations, residing between the parallel chains, interact with the inorganic moiety via hydrogen bonds, thus leading to the formation of the 3D crystal structure. The Fourier transform infrared spectrum showed characteristic bands corresponding to the phosphite group and the organic amine. The thermal behavior of the compound mainly consisted of the loss of its organic moiety and the water molecules. The biological tests exhibited significant activity against Candida albicans and Escherichia coli strains at different concentrations, while less inhibitory activity was pronounced against Staphylococcus epidermidis and Saccharomyces cerevisiae, and in the case of multi-cellular organisms, no activity against the nematode model Steinernema feltiae was detected.

Facile fabrication of surface vulcanized Co-Fe spinel oxide nanoparticles toward efficient 4-nitrophenol destruction

Developing efficient modulation strategies to boost the degradation efficiencies of non-noble metal catalysts for toxic phenolic compounds involving peroxymonosulfate (PMS)-based oxidation processes is essential but remains an arduous challenge. This study reports the one-pot construction of in-situ surface vulcanized CoFe2O4 @carbon (Sx-CF@C) to boost the PMS activation for 4-nitrophenol (4-NP) destruction. The direct pyrolysis of an aerogel precursor consisted of cobalt nitrate, ferric nitrate, melamine, and thiourea enables the as-formed Sx-CF@C with hierarchical structure, rich oxygen vacancies, and electron/mass transfer, thereby considerably promoting PMS activation performance of Sx-CF@C toward 4-NP degradation. Specifically, the optimal S0.2-CF@C can achieve a removal efficiency of 99% for 4-NP destruction (20 mg/L) through PMS activation. Meanwhile, the catalyst also has generality to degrade a variety of antibiotic and dye organic pollutants. The radical quenching and electron paramagnetic resonance tests reveal the radical and non-radical activation mechanism in the S0.2-CF@C/PMS system. The degradation pathway for 4-NP destruction over the S0.2-CF@C/PMS system is proposed. This study provides an efficient approach to modulate the PMS activation performance of ferrite spinel materials toward the degradation of acute phenolic compounds.

Impacts of Metal-Support Interaction on Hydrogen Evolution Reaction of Cobalt-Nitride-Carbide Catalyst.

Cobalt-nitride-carbide (Co-N-C) catalysts are promising cost-efficient transition metal catalysts for electrocatalytic hydrogen evolution, but few works investigate the metal–support interaction (MSI) effect on hydrogen evolution reaction (HER) performance. Herein, efficient Co-N-CX catalysts with controllable MSI between encapsulated Co nanoparticles and nitrogen-doped graphitic carbon nanosheets were synthesized via a facile organic–inorganic hybridization method. Results demonstrate that the Co-N-C0.025M catalyst with the coexistence of single-atom Co sites and Co nanoparticles prepared by 0.025 M cobalt nitrate shows excellent HER performance, achieving a low overpotential of 145 mV to reach 10 mA cm−2 in 0.5 M sulfuric acid, which is mainly because the optimal MSI, which leads to a moderate hydrogen adsorption energy and improved electroactive sites, not only facilitates the charge transfer to improve the HER kinetics, but also improves the durability of the catalyst by Co-N bond anchoring and encapsulation of active Co species. This work provides guidance to further reveal the influence of MSI on their catalytic activity.

Preparation and Photo-Catalytic Performance of ZIF-67@F-Ta<sub>2</sub>O<sub>5</sub> Hetero-Structure

ZIF-67@Ta2O5 graded hetero-structure material was designed and prepared using F-Ta2O5 as a raw material and Zeolite imidazole ester(ZIF-67) as framework structure material. The hetero-structure Ta2O5 and ZIF-67@Ta2O5 were annealing 6 hours at 900°C in nitrogen ambience. The photolysis properties of the Ta2O5 and ZIF-67@Ta2O5 materials as catalysts for photocatalytic decomposition of water to hydrogen were characterized. The results show that the heterogeneous composite structure formed by cobalt-tantalum oxide and tantalum pentoxide can significantly improve the hydrogen production performance of tantalum pentoxide samples, and the properties of samples obtained under nitrogen atmosphere are better. Among them, the N-50 sample (F-Ta2O5 is 50mg, Cobalt nitrate dosage is 6ml, annealing 6 hours at 900°C in nitrogen ambience) has the best hydrogen production performance, and the hydrogen production rate is 116μmol/g/h.

Bulk Co3O4 for Methane Oxidation: Effect of the Synthesis Route on Physico-Chemical Properties and Catalytic Performance

The synthesis of bulk pure Co3O4 catalysts by different routes has been examined in order to obtain highly active catalysts for lean methane combustion. Thus, eight synthesis methodologies, which were selected based on their relatively low complexity and easiness for scale-up, were evaluated. The investigated procedures were direct calcination of two different cobalt precursors (cobalt nitrate and cobalt hydroxycarbonate), basic grinding route, two basic precipitation routes with ammonium carbonate and sodium carbonate, precipitation-oxidation, solution combustion synthesis and sol-gel complexation. A commercial Co3O4 was also used as a reference. Among the several examined methodologies, direct calcination of cobalt hydroxycarbonate (HC sample), basic grinding (GB sample) and basic precipitation employing sodium carbonate as the precipitating agent (CC sample) produced bulk catalysts with fairly good textural and structural properties, and remarkable redox properties, which were found to be crucial for their good performance in the oxidation of methane. All catalysts attained full conversion and 100% selectivity towards CO2 formation at a temperature of 600 °C while operating at 60,000 h−1. Among these, the CC catalyst was the only one that achieved a specific reaction rate higher than that of the reference commercial Co3O4 catalyst.

Structural, magnetic and adsorptive properties of nano spinel of cobalt aluminate doped with nickel for Cr(VI) removal

Nanocrystallines of cobalt aluminate spinel doped with Nickel (MAl2O4; M = Co+2, Ni+2) were synthesized by sol-gel method. The MAl2O4 samples were prepared by using aluminum nitrate; cobalt nitrate, nickel nitrate, citric acid and diethylene glycol mono ethyl ether as precursor materials. The nanocrystallines spinel were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction(XRD), Thermal gravimetric (TGA), Scanning electron microcopy (SEM) with the energy dispersive X-ray spectroscopy (EDX) methods. The Specific surface area of the synthesized powders was measured with a Brunauer-Emmet-Teller (BET) apparatus using N2 adsorption. According to obtained XRD patterns the formation of single phase MAl2O4 completed up 800 °C. The average crystallite's sizes spinel and specific surface area at 800 °C were estimated about 11.07 nm and 154 m2 g−1, respectively. The results of SEM analysis show that the nanoparticles shape are as spherical shape, uniform and a little agglomerated. The magnetic behavior of spinels showed the magnetization decreased with increasing nickel ions. Adsorption of Cr(VI) by as prepared spinels were considered. The highest percent of Cr(VI) adsorption was occurred at contact time of 45 min, pH 7.0, and adsorbent dose of 2 g L−1. The order of adsorption capacity of sorbent samples for Cr(VI) removal was as follow: Ni0.5Cu0.5Al2O4 >Ni0.7Cu0.3Al2O4 >Ni0.3Cu0.7Al2O4>NiAl2O4> CoAl2O4. Kinetic studies indicated that the adsorption process follows by pseudo second-order model. Thermodynamic results revealed that the adsorption of Cr(VI) is endothermic, spontaneously process and feasible in the range of 298–338 K.

Facile precipitation microfluidic synthesis of Monodisperse and inorganic hollow microspheres for Photocatalysis

AbstractBACKGROUNDHollow microspheres have potential applications for wide‐range fields, especially photocatalysis, attracting tremendous attention in material science. However, conventional synthesis of hollow microspheres involves complicated procedures, high cost and poor yields, greatly impeding their development. Due to the limitations of raw material for the polymerization or hydrolysis routes so far the hollow materials prepared in a microfluidics chip were limited to some specific substances.RESULTSHerein, a controllable precipitating reaction strategy in droplets was presented to form the hollow structure from easily accessible industrial chemical materials (such as nitrates of Zinc, Copper and Cobalt, and Ferrous sulfate). After generating monodisperse droplets and followed introducing precipitant into the droplets in a microfluidics chip, the spherical shell was constructed through the accumulation of precipitated particles at the oil/water interface of droplets and further particle growth on the inner shell. As a result, hollow microspheres with a Janus shell of different inner and outer morphology were formed. The photocatalytic activities of these hollow microspheres were evaluated for RhB photodegradation oxidation based on heterogeneous photo‐Fenton. The photocatalytic activities of the fresh hollow samples showed better than their solid samples or their oxidized hollow samples.CONCLUSIONWith microfluidic technology, the transition‐metallic inorganic hollow microspheres can be rapid, low‐costly manufactured through direct precipitation reaction in droplets. The prepared α‐Co(OH)2 hollow microspheres showed promising photocatalytic activity. © 2021 Society of Chemical Industry (SCI).

Selective oxidation of alcohols to high value-added carbonyl compounds using air over Co-Co3O4@NC catalysts

The sustainable catalytic transformation of alcohols to high value-added fine chemicals is a significant and challenging research topic. Herein, a set of nitrogen-doped carbon encapsulated Co-based catalysts (Co-Co3O4@NC-T) were prepared by using low-cost dicyandiamide, glyoxal and cobalt nitrate as precursors. The obtained catalysts were utilized for the selective oxidation of alcohols to high value-added esters and carboxylic acids with air as the oxygen source and displayed wide applicability for the oxidation of both aromatic and aliphatic alcohols. Based on the controlled experiments, the protective effect of N-doped carbon structure and the synergistic effect between Co core and Co3O4 species guaranteed the high reaction conversion and selectivity. Benefitting from heterogeneity and magnetism of the catalyst, it can be easily recycled and reused for long-term stability. Reasonable mechanisms of selective oxidation reaction were proposed through EPR analysis and controlled experiments. The present work provides a facile strategy for potential large-scale preparation of heterogeneous catalyst for sustainable and green catalytic transformations.

Gas-solid two-phase flow method for preparing trimesic acid series MOFs for catalytic thermal decomposition of ammonium perchlorate.

The Zn-BTC, Co-BTC and Zn-Co-BTC series metal-organic frameworks were successfully prepared by a gas-solid two-phase flow (GSF) method with zinc nitrate, cobalt nitrate, and 1,3,5-benzenetricarboxylic acid (H3BTC) as raw materials. Single-crystal structures were obtained by the solvothermal method, and the structure and thermal stability of the target materials were characterized by FT-IR, XRD, SEM, energy-dispersive X-ray spectroscopy and DTA. The three obtained target substances were applied to catalyze the thermal decomposition of ammonium perchlorate (AP), and the performance was longitudinally compared. Testing and calculation results showed that when 10 wt% of the sample was added, monometallic Zn-BTC and Co-BTC lowered the AP pyrolysis temperature by 64.1 °C and 92.3 °C, respectively, and their activation energies decreased from 215.96 kJ mol-1 to 136.27 kJ mol-1 and 125.29 kJ mol-1, respectively. Bimetallic Zn-Co-BTC lowered the AP pyrolysis peak by 103.1 °C and the activation energy to 115.56 kJ mol-1, indicating that the series of samples exhibited good catalytic performance, and the catalytic effect of the bimetallic sample was significantly better than those of the monometallic samples.

Synthesis, Characterization and Magnetic properties of Nanoparticles of Cobalt Doped Ferrite

Ferrites are ceramic like material having magnetic properties which are being utilized for several applications. Cobalt ferrites are hard magnetic material with high coercivity. In our study Crystalline, Magnetic nanoparticles of Cobalt ferrite Co0.8Fe2.2O4 were synthesized by Sol Gel Method using ferric chloride and cobalt nitrate with NaOH as a reactant. Structural characteristics of samples were determined by X-Ray diffraction, FESEM and TEM. Particle size found 14.26nm by using Debye Scherrer method. Scanning electron microscopic (SEM) studies revealed nano-crystalline nature of the sample. AFM showed surface roughness. Magnetic properties were investigated using VSM (vibrating sample magnetometer). Various magnetic parameters such as saturation magnetization (Ms) and remanence (Mr) and coercivity (Hc) are obtained from the hysteresis loops. The calculated value of saturation magnetization in our study for Cobalt ferrite was found lower than the value reported for the bulk. The coercivity was found very high which indicate that the nanoparticles exhibit ferromagnetic behavior.

Смешанно-лигандный комплекс тримезината никеля с 1,10-фенантролином как адсорбент для органических красителей и прекурсор наноструктурированных материалов

Metal-organic frameworks based on nickel and cobalt trimesinates were synthesized according to a modified procedure by the interaction of nickel acetate or cobalt nitrate and trimesic acid in the presence of alkali. They have been used to extract the organic Congo red and methylene blue dyes from their aqueous solutions. The degree of adsorption depends on temperature and reaches 97 % for Congo red, while for methylene blue it is about 83 %. The mechanisms and characteristic parameters of the adsorption process are analyzed using empirical models of the isotherms of Langmuir, Temkin, and Freundlich, of which the most optimal adsorption process is described by the Freundlich model. The calculated thermodynamic parameters indicate a spontaneous process in the case of nickel trimesinate, while for cobalt trimesinate the adsorption of Congo red is spontaneous, and the adsorption of methylene blue is a forced process.

Coordinating Polymers Based on Nickel(II) and Cobalt(II) Trimesinates as Promising Adsorbents of Organic Dyes

Metal-organic frameworks (MOFs) are crystalline compounds consisting of metal ions coordinated by bridg-ing organic ligands. Depending on the coordination geometry of the metal and the direction of the bond of donor atoms, as well as on the geometry of the bridging ligand, 1D, 2D, or 3D polymer structures are formed. The characteristic features of metal-organic frameworks are low density, high porosity and crystallinity, and large specific surface. Wide attention is paid to the technological aspects of creating such materials and their integration into various devices. To obtain MOFs, various synthetic approaches have been developed based on precipitation reactions at room temperature and under convective heating, including hydrothermal and solvothermal syntheses. In this work, metal organic framework structures based on nickel and cobalt trimesinates were synthesized by a modified procedure by reacting nickel acetate and cobalt nitrate with trimesic acid in the presence of alkali. The obtained compounds were used to study the adsorption of Congo Red and Methylene blue organic dyes from their aqueous solutions. The degree of adsorption depends on temperature and reaches a value of 97% for Congo Red, while for Methylene blue it is 83%. The mechanisms and characteristic parameters of the adsorption process were analyzed using empirical models of Langmuir, Temkin, and Freundlich isotherms, of which the adsorption process was optimally described by the Freundlich model. The calculated thermodynamic parameters indicate the spontaneity of the process and its insignificant endothermic character.

Терапевтический эффект наноалмазов взрывного синтеза при кобальтиндуцированном дерматите

The aim of the research. To evaluate the therapeutic eff ect of modifi ed nanodiamonds (MND) of explosive synthesis for treatment of allergic contact dermatitis induced by cobalt ions. Material and methods. Th e study was performed on guinea pigs. Th e animals were divided into 3 groups (6 animals in each group). Allergic contact dermatitis was initiated using 2% aqueous solution of cobalt nitrate applied to the animals’ skin for 14 days according to the common procedure. For allergic contact dermatitis treatment, glycerol and MND suspension with the nanoparticle concentration of 5g · l-1 prepared in glycerol were used. MND with high colloidal stability in water suspensions and the average nanoparticle cluster size of d50 = 50nm was used in the work. Th e animals of group I were controls: aft er allergic contact dermatitis development, their skin was not treated by any means for 7 days. Th e animals in groups II and III were experimental: aft er allergic contact dermatitis initiation, their skin was treated for 7 days using glycerol and MND suspension, respectively. Upon experiment completion, biopsy of skin sample was performed on all animals for histological and spectral examination. The content of cobalt in skin samples was determined through atomic adsorption spectroscopy. Results. The results of histological and morphometric analysis indicate that, in the case with dermatitis modelled in guinea pigs using cobalt ions, treatment of the animals’ skin with MND suspension reduces allergic inflammation intensity. Th e therapeutic effect of MND is caused by adsorption of cobalt ions onto nanoparticles and their subsequent elimination from the skin, which complies with the atomic adsorption spectroscopy data. Conclusion. Th e prospects of MND as a new therapeutic agent for binding and elimination of chemical allergens (particularly, cobalt ions inducing the allergic contact dermatitis development) are discussed.

Green synthesis of cerium oxide, Co-doped cerium oxide nanoparticles and its dielectric properties

In this article, we have synthesized CeO2 and Co-doped CeO2 nanoparticles (NPs) using the sol–gel method in a greener route by using Acacia Concinna fruit extract as a natural surfactant. Different doping concentrations of Ce1-xCoxO2 (where x = 0.02, 0.04, and 0.06 w/w) were prepared by adding varying concentrations of cobalt nitrate to ceric ammonium nitrate in a stoichiometric ratio. The characterizations were done by different techniques like XRD, SEM, Raman spectroscopy, and FT-IR. XRD pattern shows a single-phase cubic fluorite type structure for the CeO2 and Co-doped CeO2 NPs. The crystallite sizes calculated from the XRD pattern were 22.7 nm for CeO2 NPs and for Co-doped CeO2 NPs, it increased from 38.15 nm to 46.04 nm, when the concentration of cobalt doping was increased from 2 % to 6 %. The formation of the cubic phase of CeO2 in both pure and Co-doped CeO2 NPs was further confirmed through Raman spectroscopy, which signified the vibrational mode of cubic fluorite type structure of CeO2 NPs at 462 cm−1. SEM images illustrated a porous structure for both the doped and un-doped NPs, the porosity being more for Co-doped CeO2 NPs. FT-IR analysis showed characteristic absorption bands for Co-O-Ce and CO at 1118 cm−1 and 2924 cm−1, respectively. The effects of the composition of the dopant on the dielectric properties of Co-doped CeO2 NPs were studied. The dielectric properties of the as-synthesized NPs vary with the percentage of cobalt doping.

Crystal Sizes and Energy Gaps of Cerium Oxide Using Co-Precipitation Method

Co-precipitation was used to prepare cerium oxide nano-particles. The effects of aging temperature and concentration of cobalt ion on the optical property, morphology, and particle size were investigated. The cerium oxide was prepared by adding ammonia solution into a mixed solution of cerium nitrate with cobalt nitrate solutions to obtain a large amount of precipitates and then aged further. Subsequently, the precipitates were kept in an oven for calcination keeping the temperature at 400?C for lasting 24 h. The average size of cerium oxide particles was obtained from the (111) peak in the X-ray diffraction pattern using the Scherrer equation. The crystal sizes obtained were found to be in the range of 11.82 - 13.47 nm. The results showed that the particle size decreased with an increase in the Co ion concentration and decreased with an increase in temperature. The SEM pictures show that the morphology for cerium oxide is granular and/or columnar. It can be seen from UV/Vis absorption spectrum that the maximum absorption peaks were in the range of 334 - 390 nm, depending on the operating conditions. The corresponding energy gaps were observed in the range of 3.18 - 3.71 eV. Subsequently, the Brus equation for the energy gap was discussed. Finally, particle size was correlated with the aging temperature and Co ion concentration.

Fluorescence Quenching Probe Based on Graphene Quantum Dots for Detection of Copper Ion in Water

Heavy metal contamination in water is a serious issue causing adverse effects on health, ecosystem, and environment. To monitor this contamination, fluorescence quenching probe based on the graphene quantum dots (GQDs) was used for detection of metal compounds. The effect of metal compounds on the fluorescence quenching efficiency of the GQDs was investigated. A typical sample of metal compounds was selected from copper acetate, copper chloride, copper nitrate, copper sulfate, cobalt nitrate, cobalt chloride, and zinc nitrate. It was found that the GQDs exhibited high selectivity for copper acetate. The quantity of copper acetate was obtained using Stern-Volmer plot. It was found that the plot exhibited a linear behavior for the fluorescence quenching of the GQDs by copper acetate. This analytical method could be developed for the determination of copper acetate in the concentration range of 0–2.5 mM with the Stern-Volmer quenching constant of 2445 M−1. To understand an occurring interaction between metal compounds and the GQDs in the system, redox characteristics of the GQDs mixed metal compounds were investigated. Noticeably, electrochemical potential gap (ΔE) of the GQDs mixed copper acetate with UV irradiation seems higher than that of the GQDs mixed copper acetate without UV irradiation, implying better electron transfer behavior from the GQDs to copper acetate. This result was in good agreement with the fluorescence quenching of the GQDs by copper acetate. Accordingly, the nonradiative recombination of the GQDs could be explained in terms of the fluorescence quenching. The fluorescence quenching efficiency was proportional to the amount of the copper acetate. These results can be further explored for a novel graphene quantum dots-based fluorescent probe and this method could be more widely applied in water resources.