CO Molar Ratio Research Articles

Direct methanol fuel cell with enhanced oxygen reduction performance enabled by CoFe alloys embedded into N-doped carbon nanofiber and bamboo-like carbon nanotube

The exploration of cost-effective electrocatalysts with high catalytic activity and methanol tolerance to replace precious metal catalysts in the oxygen reduction reaction (ORR) is highly desirable for direct methanol fuel cells (DMFCs). Herein, we report a novel complex composed of a CoFe alloy with a modulated electronic structure confined to nitrogen-doped carbon nanofiber (NCNF) and bamboo-like carbon nanotube (BCNT) by tuning the molar ratio of Co and Fe (CoFe@NCNF/BCNT). The synthetized catalysts possess one-dimensional (1D) mesoporous structure, high specific surface area, and rich pyridinic-N content. Notably, the Co1Fe1@NCNF/BCNT and Co1Fe3@NCNF/BCNT (Co:Fe ≈ 1:1 and 1:3) exhibited enhanced oxygen reduction activity and methanol tolerance, compared to unmodified samples. In addition, alkaline DMFCs containing Co1Fe1@NCNF/BCNT and Co1Fe3@NCNF/BCNT presented high power density (29.10 and 31.11 mW cm−2), exceeding that of Pt/C-modified DMFC (27.23 mW cm−2). Furthermore, the Co1Fe1@NCNF/BCNT-catalyzed DMFC exhibited high stability. This improved catalytic activity can be attributed to the rich surface area, controllable alloy composition, optimized N configuration, and favorable electronic interaction. The as-developed CoFe@NCNF/BCNT with multifunctional components may open a new avenue for designing highly active cathode catalysts for various fuel cells.

Bimetallic Co3V2O8 microstructure: A versatile bifunctional electrode for supercapacitor and electrocatalysis applications

Our research focuses on hydrothermally synthesizing a bimetallic cobalt vanadium oxide Co3V2O8 (CVO) microstructure, tailoring it for use in both bifunctional supercapacitor and electrolysis applications. We carefully optimized the molar ratio of Co and V to achieve a hexagonal microstructure for Co3V2O8, confirming it through field emission scanning electron microscopy (FESEM) and High resolution transmission electron microscopy (HRTEM) studies. The optimized electrode exhibited exceptional electrochemical characteristics when utilized in a supercapacitor application. It demonstrated a superior areal capacitance of 3.76 F/cm2 at a current density of 1 mA/cm2. Subsequently, we utilized the optimized electrode in an asymmetric supercapacitor configuration with activated carbon (AC), resulting in an areal capacitance of 126.1 mF/cm2 and an energy density of 29.6 mWh/cm2 at a power density of 2.6 W/cm2. To assess the stability of this configuration, we conducted 5000 cycles at 5 mA/cm2 and observed a retention rate of 87%. Additionally, we investigated the effectiveness of the optimized electrode as an electrocatalyst for water oxidation in a 1 M KOH electrolyte. In this setup, the CVO-4 electrode exhibited a lower overpotential of 226 mV for the hydrogen evolution reaction (HER) and a Tafel slope of 178 mV/dec for HER. Overall, our findings indicate that the as-prepared optimized electrode operates highly efficiently in bifunctional applications, positioning it as a promising candidate for energy conversion and storage operations.

Insights into the simultaneously enhanced activity, selectivity, and H2O resistance of cobalt modified MnCeOx/TiO2 catalyst for selective catalytic reduction of NOx with NH3

The promotional effect of cobalt (Co) modification on MnCeOx/TiO2 catalyst for selective catalytic reduction of NO with NH3 (NH3-SCR) was investigated extensively in this study. A series of CoMnCeOx/TiO2 catalysts with different Co contents were prepared by the facile impregnation method and characterized by XRD, N2 sorption, XPS, H2-TPR, NH3/NO-TPD, and in situ DRIFT spectroscopy. The results indicate that the modification of MnCeOx/TiO2 by Co could significantly improve its low-temperature activity and N2 selectivity, and broaden operation temperature window (>95% NO conversion at 100–225 °C), and that the optimal mole ratio of Co to Ti in the catalyst is 0.4. Furthermore, the introduction of Co to MnCeOx/TiO2 could obviously enhance H2O resistance. The characterization results reveal that the addition of Co to the MnCeOx/TiO2 catalyst could enhance the dispersion of MnOx and CeOx, and increase the relative ratio of Mn4+ and Ce3+ on the catalyst surface. In addition, the surface area of MnCeOx/TiO2 is enlarged evidently after doping of Co. From the results of H2-TPR, NH3/NO-TPD, and NO oxidation, CoMnCeOx/TiO2 exhibits stronger reducibility, larger adsorption capacity for NH3 and NO, and higher NO to NO2 conversion than MnCeOx/TiO2, thus obtaining the higher SCR activity, N2 selectivity, and H2O tolerance. In situ DRIFT spectroscopy tests indicate that the NH3-SCR reaction on both MnCeOx/TiO2 and CoMnCeOx/TiO2 follow simultaneously the Langmuir-Hinshelwood and Eley-Rideal mechanisms.

Experimental and theoretical study on the photocatalytic degradation of brilliant green dye by N-doped Zn2GeO4

In this study, experimental and theoretical insights on the photocatalytic degradation of BG in an N-doped Zn2GeO4/UV irradiation system were explored. Kinetic experiments, degradation mechanisms analysis, and toxicity evaluation of intermediates were involved. The catalytic performance of N-doped Zn2GeO4 was optimum when the molar ratio of CO(NH2)2 and GeO2 is 1: 1. BG was almost 100% degraded within 10 min. Catalyst dosage and initial concentration had effects on the photodegradation of BG. Materials Studio calculations indicated that the nitrogen atoms are interstitially doped into Zn2GeO4 in the form of Zn–N–Ge. The N 2 s orbital contributes more than the N 2p orbital to the PDOS of N-doped Zn2GeO4, suggesting the difficult recombination of e- and h+. According to mass spectrometry analysis, de-ethylation, hydroxylation, condensation, carboxylation, and ring-opening were the main photocatalytic degradation pathways of BG. ∙OHs and O2∙-s played important roles in the Hg lamp/N-doped Zn2GeO4 reaction system, while h+ was existed in this system using quenching experiments. The 2FED2HOMO and (FED2HOMO + FED2LUMO) values implied the locations vulnerable to attack by free radicals of BG, which validated the reasonableness of the LC-MS/MS analysis result. Toxicity evaluations by the ECOSAR program suggested that photocatalytic degradation can exacerbate the aquatic toxicity of BG in the initial stage.

Operating performance characteristics and analysis of a high temperature fuel cell system integrated with a methanol steam reformer

A high temperature proton exchange membrane fuel cell system integrated with a methanol steam reformer is developed in this study. A system model considering thermal-coupled balance-of-plant components and several temperature constraints is established. The hydrogen production performance of the reformer is evaluated and experimentally validated. A high methanol conversion rate above 90.1% with a low CO content below 1.5% are obtained with the reformer temperature of 573 K at a steam to carbon ratio of 1.3. Besides, CO poisoning effect on the stack is inhibited with an increase in the operating temperature. The fuel cell voltage increases 35% with variation of the operating temperature from 160 °C to 180 °C at the current density of 0.4 A/cm2 and CO molar ratio of 1%. Furthermore, model-based analysis is conducted to investigate impacts of various input parameters on system operating performance. The proposed system presents a maximum electrical efficiency of 37.8%, and increasing the current density and decreasing air excess ratio are favorable for improving the net power output, but also increasing the heat duties of components and resulting in a reduced safety operating region. Finally, an optimal operating strategy with maximum system efficiency is proposed for variable output powers ranging from 15 to 55 W.

Preparation and dye separation performance of ZIF-67/mesoporous silica ceramic nanofiltration membrane by liquid phase epitaxy (LPE) growth method

Ceramic membrane plays an important role in separation process with advantages of high thermal and chemical resistances, but its applications on the nanofiltration are restricted because of the limitation of pore size. In this study, a commercial tubular ceramic membrane with pore diameter of 0.1 μm was firstly coated with mesoporous silica substrates, in which ZIF-67 nanocrystals were generated layer-by-layer inside the mesochannels via liquid phase epitaxy growth method. The open pore size of ceramic membrane can be precisely controlled by increasing the growth cycles of ZIF-67 nanocrystals. The influence of preparation conditions on the dye separation was investigated, including growth cycles, precursor concentration, and molar ratio of Co2+/2-methylimidazole (Co2+/Hmim). Under the optimized conditions, the rejection of methylene blue, methyl orange, chromium black T, rhodamine B, acid fuchsin, and Congo red were in the range of 92–99 % with membrane fluxes of 0.45–0.73 L m−2 h−1. Bovine serum albumin solution was used to evaluate the anti-fouling abilities of the ceramic membrane. The flux recovery ratio, which was calculated according to the ratio between the water permeance after washing and before filtration, was 52.3 % with the flux decline rate of 66.3 %.

Effect of the hydrogen/kerosene blend on the combustion characteristics and pollutant emissions in a mini jet engine under CDC conditions

In this CFD study conducted with the geometry of a mini gas turbine engine using kerosene as fuel, colorless distributed combustion conditions were achieved by increasing the N2 ratio in the air. Then, H2 was added to the kerosene fuel in order to increase the combustion performance and the combustion chamber temperature distributions, NOx, CO, and CO2 values were examined. In the simulations using the simplified GTM-120 geometry, the combustion chamber outlet temperatures at 80 k, 100 k, and 120 k rpm were compared with the experimental results in the literature by changing the ratio of fuel and air for the validation study. Standard k-ε and Discrete Ordinates were chosen for turbulence and radiation models, respectively. In the study conducted with the non-premixed combustion model, simulations were made at O2 rates of 21%, 19%, 17%, and 15% for the formation of colorless distributed combustion conditions. For enrichment with hydrogen, H2 was added from 0% to 50% with 10% increments. HEF (Hydrogen energy fraction) has been used as the hydrogen addition rate. In light of the analyses made, it was seen that the colorless distributed combustion regime reduced the flame temperature from 2292 K to 1912 K and the NOx amount from 2.85 ppm to 0.0086 ppm. On the other hand, it is seen that this regime increased the CO emissions from 6.9 ppm to 38.67 ppm and the mole ratio of CO2 from 6.25% to 6.94%. It was observed that these findings prepared the ground for increasing the amount of hydrogen in the fuel, which increases the flame temperature and, accordingly, NOx emissions. By adding 50% H2 to kerosene under standard atmospheric conditions, the average NOx emission at the combustion chamber outlet increased from 2.85 ppm to 7.97 ppm, while the average CO emission decreased from 6.9 ppm to 1.08 ppm. As a matter of fact, by the addition of 50% H2 to the kerosene with air that contains 15% O2, which is the most extreme combustion situation in this study, the flame temperature decreased to 1912 K, and NOx rose to 0.0713 ppm. However, the CO emissions at the combustion chamber outlet decreased to 1.83 ppm and the CO2 ratio to 3.48%. Thus, with this study, it has become possible to use hydrogen as an alternative fuel in a real engine geometry by using CDC and hydrogen enrichment together, both in terms of pollutant emissions and combustion performance.

Enhanced syngas production from waste lubricant oil reforming with transition metal catalysts

Waste lubricant oil (WLO) which is a spent oil from vehicles, and machinery is often incinerated or landfilled, leading to environmental pollution and heavy metal-contaminations. At the same time WLO can converted to synthesis gas using steam reforming. In this study, catalytic steam reforming of WLO was performed in a micro fixed bed reactor at atmospheric pressure. Ni and Fe metals were loaded in a ratio of 5% and 10% on dolomite and olivine catalysts through impregnation method. The effects of equivalent ratio (ER) and metal (Ni and Fe) loadings on dolomite and olivine supported catalysts were investigated. Carbon-hydrogen conversions were significantly affected by ER with the optimum data at 0.88, which resulted in low CH4, and high H2 and CO. Nonetheless, the 5%Ni/dolomite exhibited superior overall activity with the highest overall conversion and hydrogen yield. In this case, hydrogen and carbon conversions were 65.71% and 66.38%, respectively, while H2 to CO molar ratio was 1.05 and the lower heating value was 6.76 MJ/m3. Hence, this suggests that the surface-active site of Ni on dolomite has high activity for C–C cleavage and water gas shift reaction. The conversion to H2 and CO was improved through methane and hydrocarbon steam reforming on the catalyst surface. Catalytic reforming of WLO not only enhanced synthesis gas generation which can be readily used as energy, a partial source of H2 or chemical feedstock but also as an appealing, sustainable, and economical waste management alternative.

Preparation of CoFe2O4-Doped TiO2 Nanofibers by Electrospinning and Annealing for Oxygen Electrocatalysis.

In this paper, catalyst precursor fibers were prepared by a sol gel method combined with an electrospinning method using tetrabutyl titanate as a titanium source, cobalt acetylacetonate as a cobalt source, and iron acetylacetonate as an iron source. CoFe@TiO2 nanofibers (NFs) with a bimetallic spinel structure were formed after thermal annealing, which have dual-functional catalytic activity. With the molar ratio of Co and Fe coming to 1:1, a typical spinel CoFe2O4 structure was generated in Co1Fe1@TiO2 NFs. At a load of only 28.7 μg·cm-2, Co1Fe1@TiO2 NFs not only have a low overpotential (284 mV) and Tafel slope (54 mV·dec-1) in the oxygen evolution reaction but also show a high initial potential (0.88 V) and limiting current density (6.40 mA·cm-2) in the oxygen reduction reaction. Meanwhile, Co1Fe1@TiO2 NFs exhibit good durability, cycle stability, and dual-function catalysis.

Solvothermal synthesis and characterization of cobalt blue pigment

A novel low-cost solvent-thermal method was proposed for the preparation of cobalt blue (CoAl2O4) pigments. The effects of solvent composition, reaction time, reactant molar ratio, and reaction temperature on the structure and tone of the synthesized pigments were investigated. The results revealed that the optimal process conditions for the synthesis of uniform, vibrant cobalt blue pigments were obtained when the volume ratio of alcohol-water was 1:1, the molar ratio of Co2+ to Al3+ was 1:3, the reaction time was 4 ​h, and the reaction temperature was 200 ​°C. This solvothermal synthesis method is mild, cost-effective, and easily controllable, thus making it highly suitable for industrial applications.

Influence of Oxygen/Steam Addition on the Quality of Producer Gas during Direct (Air) Gasification of Residual Forest Biomass

Biomass gasification is a relevant option to produce a gaseous fuel, it faces, however, several barriers regarding its quality for energetic applications. Therefore, in this study, air-steam and O2-enriched air mixtures were used as gasification agents during the gasification of residual biomass from eucalyptus to improve the producer gas quality. The steam addition promoted an increase in CO2 and H2 concentrations, whilst decreasing the CO and CH4 concentrations. The steam addition had no evident impact on the lower heating value of the dry producer gas and a positive effect on gas yield and the H2:CO molar ratio, attaining the later values up to 1.6 molH2∙mol−1CO. The increase in O2 concentration in the gasification agent (φ) promoted an increase in all combustible species and CO2 concentrations. The lower heating value of the dry producer gas underwent an increase of 57%, reaching a value of 7.5 MJ∙Nm−3dry gas, when the φ increased from 20 to 40 %vol.O2, dry GA. The gas yield had a significant decrease (33%) with φ increase. This work showed that the addition of steam or O2 during air gasification of residual biomass improved producer gas quality, overcoming some of the barriers found in conventional air gasification technology.

Intriguing 3D micro-flower structure of Co1.11Te2 deposited on Te nanosheets showing an efficient bifunctional electrocatalytic property for overall water splitting

The development of efficient and low-cost bifunctional catalysts for electrochemical water splitting is important for future sustainable hydrogen energy deployment. In this paper, a series of composition-controlled hybrid catalysts (Co1.11Te2/Te) were successfully constructed by introducing different proportions of Co source into the precursor solutions during the hydrothermal synthesis of Te nanosheets(Te NSs). The experimental results show that the content of Co3+active species in the hybrid materials can be adjusted by controlling the molar ratio of Co to Te, thereby significantly improving the electrocatalytic performance of the samples. Benefiting from the highest content of Co3+, the large specific surface area, and the great charge transfer ability, the Te-Co-3 electrode exhibited the best catalytic activity and durability among all samples. The hydrogen evolution reaction(HER) and oxygen evolution reaction(OER) overpotentials of the electrode were only 135 and 261 mV, respectively, to drive a current density of 10 mA cm−2 in an alkaline environment (1 M KOH). Furthermore, it required only a cell potential of 1.56 V to achieve overall water splitting at 10 mA cm−2. This work should be useful for the design and preparation of non-noble metal bifunctional catalysts.

CO2 hydrogenation over cubic yttrium oxide support: Effect of metal type

CO2 methanation is an effective strategy for making full use of waste gases and converting them into valuable chemicals. Nowadays, the key challenge is the design of efficient catalysts to enhance low-temperature catalytic performance. The present work studies the effect of metal type on the catalytic performance of yttrium oxide-supported catalysts for CO2 methanation reaction. Ru/Y2O3, Ni/Y2O3, and Co/Y2O3 catalysts were prepared by wetness incipient impregnation method, characterized using N2-adsorption/desorption isotherm, XRD, FTIR, and H2-TPR and TGA techniques to evaluate the surface, crystal phase, and thermal stability. The catalytic test was conducted with the use of a fixed-bed reactor under atmospheric pressure. The temperature of catalytic performance was 350 °C with a supply of H2: CO2 molar ratio of 4 and a total flow rate of 200 mL/min. The main products of the reaction were CH4, and traces of carbon monoxide were present among the products. The methane yield reached 64.67%, 60.03%, and 50.82% over Ru/Y2O3, Ni/Y2O3, and Co/Y2O3 catalysts, respectively.

Oxygen vacancies rich Co-Mo metal oxide microspheres as efficient oxidase mimetic for colorimetric detection of sulfite

Modulation of surface oxygen vacancies (Ov) by defect engineering is an attractive strategy for designing high performance transition metal oxide nanozymes. In this work, we reported the fabrication of the CoMoO4 oxidase-like nanozyme, i.e. CoMo-300r, by first pyrolyzing the CoMo layered double hydroxide precursor in an air atmosphere at 300 °C and subsequent NaBH4 reduction strategy. Various characterization outcomes confirm the mesoporous structures of both CoMo-300r and no NaBH4 treated CoMo-300, while the specific surface area of CoMo-300 is significantly increased from 103.54 m2·g−1 to 165.24 m2·g−1 after NaBH4 reduction. Also, NaBH4 reduction treatment leads to the formation of Ov rich CoMoO4 and reduced metal ion species on the surface, promoting the redox reaction kinetics. The CoMo-300r prepared at a molar ratio of Co to Mo of 1:2, pyrolysis temperature of 300 °C and 10 mM NaBH4 exhibited the best oxidase-like activity. The oxidase-like activity of CoMo-300r is 2.6-fold times that of no NaBH4 treated optimal CoMo-300. The CoMo-300r can effectively promote TMB oxidation to produce blue color and has the Michaelis-Menten constant of 0.0428 mM, which was lower than most cobalt-based oxide nanozymes and indicated a higher affinity for TMB. In terms of inhibition of SO32− on the CoMo-300r/TMB system, a sensitive SO32− colorimetric sensing platform was established. The linear range and limit of detection for sulfite determination were 0.2–40 μM and 0.09 μM, respectively. The relative standard deviation for the determination of 10 μM sulfite was 1.41% (n = 11). The method was successfully applied to the detection of sulfite in white wine. This work provides a new strategy to fabricate high activity oxidase mimetic for food analysis.

Bi‐Reforming of Biogas for Hydrogen Production with Sulfur‐Resistant Multimetallic Catalyst

AbstractA multimetallic sample, NiCeSnRh/Al2O3, was tested in methane reforming with a CH4:H2O:CO2 molar ratio equal to 3:2:1. A very stable methane conversion with the time‐on‐stream was achieved during 20 h. Dimethyl sulfide served as a model sulfur molecule and a sulfurized sample was also tested. This achieved slightly lower conversion with a stable performance for more than 10 h and a minor but continuous decrease of its activity, after this period. The carbon dioxide conversion was always higher than the methane conversion in agreement with the lower H2/CO ratio observed with respect to the theoretical value, 2/1, indicating the sulfur might block the active sites for H2O activation. The analysis of the used catalysts showed graphitic and disordered carbon deposits.

Facile synthesis of neuronal nickel–cobalt-manganese sulfide for asymmetric supercapacitors with excellent energy density

A neuronal nickel–cobalt–manganese sulfide material with a large surface area and high porosity can be homogeneously grown along a nickel foam via a simple one-step hydrothermal procedure. An optimal molar ratio of Ni, Co, Mn, and thiourea of 3:1:1:5 was obtained by adjusting the molar ratio of thiourea. This binder-free composite material supported by a nickel foam can be directly used as a battery-type electrode for supercapacitors. Under the optimal hydrothermal conditions, the battery-type electrode exhibited excellent electrochemical properties with a favorable specific capacitance (2805.3F/g, 1 A/g) and good rate properties (87.7 %, 10 A/g) because of the synergistic effect of the multiple transition metals. Furthermore, the battery-type electrode exhibited a remarkable capacitance retention rate (82.9 %, 10 A/g) after 10,000 cycles of electric charging and discharging owing to the addition of Mn, which suggests excellent cycle stability. Furthermore, an asymmetric supercapacitor (ASC) device prepared using the battery-type electrode material and activated carbon electrode exhibited a considerable energy density (86.9 W h kg−1) at a high power density (799.1 W kg−1). After charging for 26 s to 3.2 V, two ASC devices in series could light two red-light-emitting diodes for at least 300 s. Thus, a simple and effective synthesis scheme can be designed to prepare high-performing supercapacitors.

Dynamic simulation of a solar-autothermal hybridized gasifier: Model principle, experimental validation and parametric study

Solar thermochemical fuel production technologies, such as biomass gasification, are confronted to the intermittency of solar irradiance. The development of dynamic simulation tools is thus required to design around-the-clock control strategies. An innovative model was developed here, based on unsteady mass and energy conservation equations, considering gas-phase thermodynamic equilibrium and heterogeneous char oxidation kinetics. The char accumulation and gas species production rates were therefore tracked throughout operation, giving insight into the reactor dynamics with optimized computational cost. The model was validated via a comparison with experimental results, regarding both thermal and chemical reactor performances. Simulations reliably predicted the evolution of reactor temperatures and syngas production rates, under both solar-only and hybridized (solar-autothermal) operation. Parametric studies regarding the impact of reactants injection rates on steady-state performances were finally proposed. Steam addition (0.22 to 0.60 g/min) increased the syngas H2:CO molar ratio significantly (1.13 to 1.47). Biomass addition (1 to 3 g/min) boosted the solar-to-fuel efficiency (0.22 to 0.47), but altered the reactor temperature. Finally, oxygen addition kept the reactor running despite fluctuations of solar power, while decreasing the total H2 + CO production and cold-gas efficiency linearly. A constant H2 + CO production (2.17 NL/min) could however be achieved by feeding additional biomass and oxygen during hybridization, thus limiting the cold-gas efficiency decrease and improving the reactor energy efficiency (0.29 to 0.40). Such a dynamic reactor model can be further applied to hybridized gasification process optimization and dynamic control under real fluctuating solar irradiation conditions.

Hierarchical S-scheme titanium dioxide@cobalt-nickel based metal-organic framework nanotube photocatalyst for selective carbon dioxide photoreduction to methane.

Efficient photocatalysts are of great importance for the photochemical conversion of CO2 into fuels. Herein, S-scheme titanium dioxide@cobalt-nickel based metal-organic framework (TiO2@CoNi-MOF) heterojunction photocatalysts with high surface area and porosity are designed and fabricated by a multi-step controllable strategy. The photocatalytic activity of the composites can be optimized by adjusting the loading content of CoNi-MOF in TiO2@CoNi-MOF and molar ratios of Co2+ and Ni2+ in CoNi-MOF. The optimized hybrid photocatalyst showed a much higher CO2 photoreduction activity than the control single-component samples (TiO2 and CoNi-MOF) with a high CH4 yield (41.65μmolg-1h-1) and selectivity (93.2%). The accelerated charge carrier separation induced by the S-scheme heterojunction significantly promoted the photocatalytic performance of TiO2@CoNi-MOF NTs. Meanwhile, the introduction of bimetallic CoNi-MOF nanosheets significantly resulted in the increase of active sites, CO2 adsorbability, visible-light utilization, and CH4 selectivity. Moreover, the S-scheme photoinduced charge transfer model of the TiO2@CoNi-MOF NTs photocatalyst was confirmed by photoluminescence spectroscopy, free radical trapping tests, and work function calculated from Kelvin probe. The work aims to design and fabricate heterojunction photocatalysts with high efficiency for solar fuel production.

Efficient separation of uranium(VI) from aqueous solution using magnetic Co/Al layered double oxides coated with carbon dots.

Herein, magnetic layered double oxides coated with carbon dots (MLCs) were synthesized through introducing sodium dodecylbenzene sulfonate and FeCl2 into Co/Al LDH for capturing uranium from aqueous solution. When the molar ratio of Co to Al was 4 : 1, the MLC composite possessed the strongest affinity to uranium(VI) in solution with short equilibrium time (<160 min), high adsorption efficiency (94.31%) and large removal capacity (513.85 mg g-1). The adsorption behavior of MLCs for uranium(VI) was well fitted with Langmuir and pseudo-second-order models, suggesting that the monolayer chemical adsorption was the rate-limiting step. Besides, MLC-3 could be reused by using 0.15 mol L-1 ethylene diamine tetraacetic acid as an eluent and the removal percentage still remained at a high level (>83.3%) after 5 adsorption/desorption cycles. Redox reaction, chemical complexation and electrostatic attraction were proved to play significant roles in uranium(VI) separation. Therefore, MLC-3 could be used as a potential adsorbent in uranium(VI)-containing wastewater treatment due to its excellent adsorption performance for uranium(VI).

3D flower-shape Co/Cu bimetallic nanocomposites with excellent wideband electromagnetic microwave absorption

Electromagnetic wave (EMW) absorbing materials prepared by Metal-organic-frameworks (MOFs) derived two-dimensional sheet carbon materials and magnetic metal composites have been widely studied because of their advantages of low density and large specific surface area. However, it is still a challenge to design the microstructure and composition of materials effectively to obtain the best EMW absorption properties. In this work, 3D flower-shape Co/Cu bimetallic nanocomposites were synthesized by calcination of MOFs precursors. By tuning the ratio of Co and Cu salts, nanocomposites with different morphology, size and pore structure were obtained. Impedance matching can be improved by adjusting the synergistic effect of magnetic loss and dielectric loss. When the molar ratio of Co and Cu salts was 4:1, the best EMW absorption performance of the CoCu-CNF-10 composite was achieved. The minimum reflection loss reaches − 51.7 dB at 12.6 GHz with a thin thickness of 2.7 mm, while the effective absorption bandwidth is as broad as 6.4 GHz (9.7–16.1 GHz). This work provides a new idea for the rational design of MOFs-derived materials with excellent EMW absorption properties.