Exfoliated graphite was prepared by chemical route and then further subjected to thermal oxidation and sonication for size reduction and increased interlayer spacing in natural flake graphite. Exfoliated graphite/ABS ...Exfoliated graphite was prepared by chemical route and then further subjected to thermal oxidation and sonication for size reduction and increased interlayer spacing in natural flake graphite. Exfoliated graphite/ABS composites were pre-pared with varying filler concentration by solution casting method. Exfoliated graphite and composites were character-ised by scanning electron microscopy and energy dispersive X-ray analysis, Fourier transform infrared spectroscopy and X-ray diffractometry techniques. After thermal exfoliation significant peak of graphite at 2? = 26.4? disappeared completely, confirming successful exfoliation of graphite. SEM images revealed homogeneous dispersion of exfoliated graphite in the matrix and EDAX confirmed successful reduction of graphite oxide.展开更多
[Objective] The aim was to develop a rapid,simple method for determination of cadmium and lead in sugarcane samples by graphite furnace atomic absorption spectrometry.[Method] The method for determination of Cd and Pb...[Objective] The aim was to develop a rapid,simple method for determination of cadmium and lead in sugarcane samples by graphite furnace atomic absorption spectrometry.[Method] The method for determination of Cd and Pb in sugarcane by combined graphite furnace atomic absorption spectrometry and microwave digestion was used.[Result] The concentration curve was linear within the range of 0-0.80 μg/L the detection limits of Cd and Pb was 0.015 and 0.030 μg/L,respectively.The precision for elevenfold determination of Cd and of Pb at the 0.40 μg/L level were 1.8% and 2.3%（RSD）,respectively.Recoveries of 96.7%-98.2% for Cd and 104.6%-106.7% for Pb were obtained for two sugarcane samples and one certified reference material.[Conclusion] The proposed method has the advantages of simple operation,high sensitivity,and high efficiency;it was successfully used for determination of Cd and Pb in sugarcane samples.展开更多
We adopted the solution impregnation route with aluminum dihydrogen phosphate solution as liquid medium for effective surface modification on graphite substrate.The mass ratio of graphite to Al(H_(2)PO_(4))_(3) change...We adopted the solution impregnation route with aluminum dihydrogen phosphate solution as liquid medium for effective surface modification on graphite substrate.The mass ratio of graphite to Al(H_(2)PO_(4))_(3) changed from 0.5:1 to 4:1,and the impregnation time changed from 1 to 7 h.The typical composite phase change thermal storage materials doped with the as-treated graphite were fabricated using form-stable technique.To investigate the oxidation and anti-oxidation behavior of the impregnated graphite at high temperatures,the samples were put into a muffle furnace for a cyclic heat test.Based on SEM,EDS,DSC techniques,analyses on the impregnated technique suggested an optimized processing conditions of a 3 h impregnation time with the ratio of graphite:Al(H_(2)PO_(4))_(3) as 1:3 for graphite impregnation treatment.Further investigations on high-temperature phase change heat storage materials doped by the treated graphite suggested excellent oxidation resistance and thermal cycling performance.展开更多
As an alternative to lithium-ion batteries,aqueous zinc-graphite batteries(ZnGBs)are being explored as safer and low-cost options with the expectation of scalability to large energy storage systems.However,the current...As an alternative to lithium-ion batteries,aqueous zinc-graphite batteries(ZnGBs)are being explored as safer and low-cost options with the expectation of scalability to large energy storage systems.However,the currently adopted polyatomic and metal complex anion intercalation process at the graphite electrode in ZnGB exhibits poor electrochemical performances.Alternatively,incorporating halogen anions offers exceptional electrochemical performance to graphite electrodes due to their redox process.In this work,ZnGBs are assembled using a LiCl/ZnCl2/KBr^(-)based water-in-salt electrolyte,which efficiently supplies bromide(Br^(−))ions for conversion into Br_(x)^(−)and facilitates Br_(2)intercalation at the graphite electrode.The conversion and intercalation of bromine together enable the ZnGB to achieve a discharge capacity of 2.73 mAh/cm^(2)with 91.0%of coulombic efficiency(CE)while supporting high current density operations of up to 150 mA/cm^(2).With high energy density(4.56 Wh/cm^(2)),high power density(199.5 mW/cm^(2)),and excellent rate capability(∼93.0%CE at 150 mA/cm^(2)),the ZnGB is shown to operate efficiently for as much as 800 cycles.Beguilingly,an anode-free ZnGB offers enhanced stability for up to 1100 cycles without performance decay,matching the electrochemical performance of Zn metal electrodes.This work provides insights into the bromine reaction mechanism at graphite electrodes and the role of surface exfoliation in enabling efficient Br_(x)^(−)formation,along with Br_(2)intercalation,for achieving high-performance ZnGBs.展开更多
By loading nanometer anatase onto exfoliated graphite with the sol-gel method, exfoliated graphite-TiO2 composite （EG-TiO2） can be prepared, which can adsorb oil and can also degrade oil. In a technologic condition ...By loading nanometer anatase onto exfoliated graphite with the sol-gel method, exfoliated graphite-TiO2 composite （EG-TiO2） can be prepared, which can adsorb oil and can also degrade oil. In a technologic condition for preparing EG-TiO2, the impregnated number of times is the most important factor to influence oil-adsorbing capability, that is, when the impregnated number of times increases, the amount of saturation-adsorbed oil decreases. The study of EG-TiO2 photocatalytic degradation of machine oil based on the weight-loss method and infrared spectrum method indicates that EG-TiO2 has obvious effect of photocatalytic degradation for machine oil. Its performance is superior to pure nanometer TiO2 powder because nanometer TiO2 in EG-TiO2 has three-dimension laminar structure and comparatively high adsorption capability.展开更多
Graphitic carbon nitride(g-C_(3)N_(4))has garnered significant attention due to its remarkable advantages such as lightweight,exceptional chemical stability and defect-rich surface.Nevertheless,its inadequate electric...Graphitic carbon nitride(g-C_(3)N_(4))has garnered significant attention due to its remarkable advantages such as lightweight,exceptional chemical stability and defect-rich surface.Nevertheless,its inadequate electrical conductivity and impedance matching hindered the practical implementation in the electromagnetic wave absorption(EMWA)field.To address these challenges,we developed a composites system of carbon spheres/g-C_(3)N_(4)(CCN)through a supramolecular self-assembly strategy,subsequently integrated with reduced graphene oxide(RGO)via a water bath method.Systematic investigation revealed that the EMWA performance of CCN/RGO composites exhibited a distinct dependence(a trend of first increasing and then decreasing)on RGO content.Especially,when the mass ratio of RGO to CCN was 20%,the CCN/RGO composite brought a minimum reflection loss value of-45.40 dB at 13.44 GHz and a broad effective absorbing bandwidth of 6.32 GHz at 2.19 mm.First-principles calculations based on density functional theory suggested that the constructed heterostructure effectively facilitated electron mobility and charge redistribution,boosting both conductive loss and polarization loss mechanisms.The exceptional absorption performance was ascribed to the synergistic effects of conductive loss,relaxation loss,and suitable impedance matching.As a results,this work provided a rational design strategy for high-performance g-C_(3)N_(4)-based EMWA materials.展开更多
A new method based on the cloud point extraction（CPE） for separation and preconcentration of nickel（Ⅱ） and its subsequent determination by graphite furnace atomic absorption spectrometry（GFAAS） was proposed, 8-...A new method based on the cloud point extraction（CPE） for separation and preconcentration of nickel（Ⅱ） and its subsequent determination by graphite furnace atomic absorption spectrometry（GFAAS） was proposed, 8-hydroxyquinoline and Triton X-100 were used as the ligand and surfactant respectively. Nickel（Ⅱ） can form a hy-drophobic complex with 8-hydroxyquinoline, the complex can be extracted into the small volume surfactant rich phase at the cloud point temperature（CPT） for GFAAS determination. The factors affecting the cloud point extraction, such as pH, ligand concentration, surfactant concentration, and the incubation time were optimized. Under the optimal conditions, a detection limit of 12 ng/L and a relative standard deviation（RSD） of 2.9% were obtained for Ni（Ⅱ） determination. The enrichment factor was found to be 25. The proposed method was successfully applied to the determination of nickel（Ⅱ） in certified reference material and different types of water samples and the recovery was in a range of 95%―103%.展开更多
Various experimental conditions were described for the vanadium determinationby graphite furnace atomic absorption spectroscopy (GFAAS). The experiments showed that whenatomization took place under the conditions wher...Various experimental conditions were described for the vanadium determinationby graphite furnace atomic absorption spectroscopy (GFAAS). The experiments showed that whenatomization took place under the conditions where the combination of a pyrolytic coating graphitetube and fast raising temperature were used and the temperature was stable, the signal peak shapescould be improved, the sensitivity was enhanced, and the memory effect was removed. The vanadium infood and traditional Chinese medicinal herbs can be accurately determined using the standard curvemethod.展开更多
High-efficiency microwave absorbers with broadband absorption are strongly desired for electromag-netic protection.Herein,we successfully synthesized a hybrid microwave absorbing material with two-dimensional layered ...High-efficiency microwave absorbers with broadband absorption are strongly desired for electromag-netic protection.Herein,we successfully synthesized a hybrid microwave absorbing material with two-dimensional layered structure,which consisted of expanded graphite(EG)and boron nitride(BN).The introduction of BN is to regulate the conductivity of EG and also to improve the thermal stability of the composite material.The ultrathin BN nano-sheets were uniformly wrapped on the EG sheets via chemi-cal vapor deposition.Attributed to the dielectric loss and conductive loss,the as-prepared hybrid material exhibited high performance for microwave absorption.The effective absorbing bandwidth(reflection loss value<-10 dB)was achieved up to 9.37 GHz with the thickness of 2.4 mm in the frequency range of 5.75-6.98 GHz and 9.86-18 GHz.And the minimum reflection loss was-51.58 dB at the thickness of 3 mm.The excellent performance of microwave absorption was attributed to the dielectric loss,interfacial polarization loss and optimized impedance matching.Moreover,compared to pure EG,the thermal de-composition temperature of EG/BN composite materials had increased by about 100℃which was up to 714℃.Taking the advantages of high thermal stability of BN as well as the fine microwave absorbability of EG,the EG/BN composites would be applied in high-temperature microwave absorbing fields.展开更多
The expandable graphite(EG)modified TiO_(2) nanocomposites were prepared by the high shearmethod using the TiO_(2) nanoparticles(NPs)and EG as precursors,in which the amount of EG doped in TiO_(2) was 10 wt.%.Followed...The expandable graphite(EG)modified TiO_(2) nanocomposites were prepared by the high shearmethod using the TiO_(2) nanoparticles(NPs)and EG as precursors,in which the amount of EG doped in TiO_(2) was 10 wt.%.Followed by the impregnation method,adjusting the pH of the solution to 10,and using the electrostatic adsorption to achieve spatial confinement,the Pt elementswere mainly distributed on the exposed TiO_(2),thus generating the Pt/10EG-TiO_(2)-10 catalyst.The best CO oxidation activity with the excellent resistance to H_(2)O and SO_(2) was obtained over the Pt/10EG-TiO_(2)-10 catalyst:CO conversion after 36 hr of the reaction was ca.85%under the harsh condition of 10 vol.%H_(2)O and 100 ppm SO_(2) at a high gaseous hourly space velocity(GHSV)of 400,000 hr−1.Physicochemical properties of the catalystswere characterized by various techniques.The results showed that the electrostatic adsorption,which riveted the Pt elements mainly on the exposed TiO_(2) of the support surface,reduced the dispersion of Pt NPs on EG and achieved the effective dispersion of Pt NPs,hence significantly improving CO oxidation activity over the Pt/10EG-TiO_(2)-10 catalyst.The 10 wt.%EG doped in TiO_(2) caused the TiO_(2) support to form a more hydrophobic surface,which reduced the adsorption of H_(2)O and SO_(2) on the catalyst,greatly inhibited deposition of the TiOSO_(4) and formation of the PtSO4 species as well as suppressed the oxidation of SO_(2),thus resulting in an improvement in the resistance to H_(2)O and SO_(2) of the Pt/10EG-TiO_(2)-10 catalyst.展开更多
A method is described for the direct determination of iron in high purity sodium fluoride using graphite furnace atomic absorption spectrometry. Interferences caused by the matrix are investigated. It is shown that th...A method is described for the direct determination of iron in high purity sodium fluoride using graphite furnace atomic absorption spectrometry. Interferences caused by the matrix are investigated. It is shown that the ashing temperature can be increased to 1 400°C and matrix interferences eliminated, the sensitivity of iron increased in 1. 27 fold by the addition of nickel nitrate. The method is applied to the determination of iron in sodium fluoride and satisfactory results are obtained.展开更多
A new method is proposed for the preconcentration of vanadium(Ⅴ) with crosslinked chitosan (CCTS) and determination by graphite furnace atomic absorption spectrometry (GFAAS). The adsorption rate of vanadium(Ⅴ) by C...A new method is proposed for the preconcentration of vanadium(Ⅴ) with crosslinked chitosan (CCTS) and determination by graphite furnace atomic absorption spectrometry (GFAAS). The adsorption rate of vanadium(Ⅴ) by CCTS was 97% at pH 4.0, and vanadium(Ⅴ) was eluted from crosslinked chitosan with 2 mL 2.0 mol·L -1 chlorhydric acid and determined by GFAAS. The detection limit (3σ,n=7) for vanadium(Ⅴ) was 4.8×1 0 -12g and the relative standard deviation (R.S.D) at concentration level of 2.6 μg·L -1 is less than 3.6%. The method shows a good selectivity and high sensitivity, and it was applied to determination of vanadium(Ⅴ) in oyster and water samples. The analytic recoveries are (97±5)%.展开更多
The liquid phase microextraction (LPME) was combined with the modified Graphite furnace atomic absorption spectrometry (GF-AAS) for determination of lead in the water and solid samples. In a preconcentration step, lea...The liquid phase microextraction (LPME) was combined with the modified Graphite furnace atomic absorption spectrometry (GF-AAS) for determination of lead in the water and solid samples. In a preconcentration step, lead was extracted from a 2 ml of its aqueous sample in the pH = 5 as lead-Pyrimidine-2-thiol cationic complex into a 4 μl drop of 1,2 dichloroethane and ammonium tetraphenylborate as counter ion immersed in the solution. In the drop, the lead-Pyrimidine-2-thiol ammonium tetraphenylborate ion associated complex was formed. After extraction, the microdrop was retracted and directly transferred into a graphite tube modified by [W.Pd.Mg] (c). Some effective parameters on extraction and complex formation, such as type and volume of organic solvent, pH, concentration of chelating agent and counter ion, extraction time, stirring rate and effect of salt were optimized. Under the optimum conditions, the enrichment factor and recovery were 525% and 94%, respectively. The calibration graph was linear in the range of 0.01 - 12 μg?L–1 with correlation coefficient of 0.9975 under the optimum conditions of the recommended procedure. The detection limit based on the 3Sb criterion was 0.0072 μg?L–1 and relative standard deviation (RSD) for ten replicate measurement of 0.1 μg?L–1 and 0.4 μg?L–1 lead was 4.5% and 3.8% respectively. The characteristic concentration was 0.0065 μg?L–1 equivalent to a characteristic mass of 26 fg. The results for determination of lead in reference materials, spiked tap water and seawater demonstrated the accuracy, recovery and applicability of the presented method.展开更多
Mixed polyanion phosphate Na_(4)Fe_(3)(PO_(4))_(2)P_(2)O_(7)(NFPP)is regarded as the most promising cathode material for sodium-ion batteries(SIBs),due to its high structural stability and low-cost environmental frien...Mixed polyanion phosphate Na_(4)Fe_(3)(PO_(4))_(2)P_(2)O_(7)(NFPP)is regarded as the most promising cathode material for sodium-ion batteries(SIBs),due to its high structural stability and low-cost environmental friendliness.However,its intrinsic low conductivity and sluggish Na^(+)diffusion restricted the fast-charge and low-temperature sodium storage.Herein,an NFPP composite encapsulated by in-situ pyrolytic carbon and coupled with expanded graphite(NFPP@C/EG)was constructed via a sol-gel method followed by a ballmill procedure.Due to the dual-carbon modified strategy,this NFPP@C/EG only enhanced the electronic conductivity,but also endowed more channels for Na^(+)diffusion.As cathode for SIBs,the optimized NFPP(M-NFPP@C/EG)delivers excellent rate capability(capacity of~80.5 mAh/g at 50 C)and outstanding cycling stability(11000 cycles at 50 C with capacity retention of 89.85%).Additionally,cyclic voltammetry(CV)confirmed that its sodium storage behavior is pseudocapacitance-controlled,with in-situ electrochemical impedance spectroscopy(EIS)further elucidating improvements in electrode reaction kinetics.At lower temperatures(0℃),M-NFPP@C/EG demonstrated exceptional cycling performance(8800 cycles at 10 C with capacity retention of 95.81%).Moreover,pouch cells also exhibited excellent stability.This research demonstrates the feasibility of a dual carbon modification strategy in enhancing NFPP and proposes a low-cost,high-rate,and ultra-stable cathode material for SIBs.展开更多
It is of important significance to make studies on the sur-face electric characteristics of flake graphite and their variation law for strengthening the floatation of flake graphite.In this paper, DPM type microelectr...It is of important significance to make studies on the sur-face electric characteristics of flake graphite and their variation law for strengthening the floatation of flake graphite.In this paper, DPM type microelectrophoresis apparatus is used to de-termine the surface Zeta-potential of flake graphite pure mineral, study the affection of pulp pH value, seueral kinds of inorganic salt ions and anion surface activation agent (petroleum sodium sulfonate ) on flake graphite surface Zeta-potential,and explore the surface absorption charac-teristics of graphite.The floatation experiment of flake graphite pure mineral shows that both the petroleum sodium sulfonate and inorganic salt can strengthen the conventional floatation of flake graphite. The surface characteristic varia-tion caused by them is also an important factor to promote graphite floata-tion.展开更多
The effects of background absorption of TmCl 3 and Tm(NO 3) 3 matrices in graphite furnace atomic absorption spectrometry(GFAAS) were inverstigated. The experiments demonstrated that the background absorption of Tm...The effects of background absorption of TmCl 3 and Tm(NO 3) 3 matrices in graphite furnace atomic absorption spectrometry(GFAAS) were inverstigated. The experiments demonstrated that the background absorption of Tm matrices is obviously wavelength dependent. The background absorption of TmCl 3 is larger than that of Tm(NO 3) 3, especially in short wavelength region. The background absorption of TmCl 3 is decreased significantly as the ashing temperature increases and that of Tm matrices is eliminated completely at about 1900 ℃. The time distribution of background signal is related to the atomization temperature and the heating mode of atomization HNO 3 can be used to reduce the background absorption of TmCl 3 matrix.展开更多
In general, biological organisms have the ability to absorb a specific element selectively. Holcombe and his co-workers reported that copper, nickel and cobalt could be separated from riverine and sea-water samples an...In general, biological organisms have the ability to absorb a specific element selectively. Holcombe and his co-workers reported that copper, nickel and cobalt could be separated from riverine and sea-water samples and cadmium from river water samples by unicellular green algae and were determined by slurry GFAAS. Dar-展开更多
文摘Exfoliated graphite was prepared by chemical route and then further subjected to thermal oxidation and sonication for size reduction and increased interlayer spacing in natural flake graphite. Exfoliated graphite/ABS composites were pre-pared with varying filler concentration by solution casting method. Exfoliated graphite and composites were character-ised by scanning electron microscopy and energy dispersive X-ray analysis, Fourier transform infrared spectroscopy and X-ray diffractometry techniques. After thermal exfoliation significant peak of graphite at 2? = 26.4? disappeared completely, confirming successful exfoliation of graphite. SEM images revealed homogeneous dispersion of exfoliated graphite in the matrix and EDAX confirmed successful reduction of graphite oxide.
基金Supported by Fund of Guangxi Sugarcane Research Institute(G2008011)~~
文摘[Objective] The aim was to develop a rapid,simple method for determination of cadmium and lead in sugarcane samples by graphite furnace atomic absorption spectrometry.[Method] The method for determination of Cd and Pb in sugarcane by combined graphite furnace atomic absorption spectrometry and microwave digestion was used.[Result] The concentration curve was linear within the range of 0-0.80 μg/L the detection limits of Cd and Pb was 0.015 and 0.030 μg/L,respectively.The precision for elevenfold determination of Cd and of Pb at the 0.40 μg/L level were 1.8% and 2.3%（RSD）,respectively.Recoveries of 96.7%-98.2% for Cd and 104.6%-106.7% for Pb were obtained for two sugarcane samples and one certified reference material.[Conclusion] The proposed method has the advantages of simple operation,high sensitivity,and high efficiency;it was successfully used for determination of Cd and Pb in sugarcane samples.
基金Funded by Scientific and Technological Innovation Project of Carbon Emission Peak and Carbon Neutrality of Jiangsu Province(No.BE2022028-4)。
文摘We adopted the solution impregnation route with aluminum dihydrogen phosphate solution as liquid medium for effective surface modification on graphite substrate.The mass ratio of graphite to Al(H_(2)PO_(4))_(3) changed from 0.5:1 to 4:1,and the impregnation time changed from 1 to 7 h.The typical composite phase change thermal storage materials doped with the as-treated graphite were fabricated using form-stable technique.To investigate the oxidation and anti-oxidation behavior of the impregnated graphite at high temperatures,the samples were put into a muffle furnace for a cyclic heat test.Based on SEM,EDS,DSC techniques,analyses on the impregnated technique suggested an optimized processing conditions of a 3 h impregnation time with the ratio of graphite:Al(H_(2)PO_(4))_(3) as 1:3 for graphite impregnation treatment.Further investigations on high-temperature phase change heat storage materials doped by the treated graphite suggested excellent oxidation resistance and thermal cycling performance.
基金The authors acknowledge the University of Sharjah for financial support through a competitive research project grant(project number:23020406277)。
文摘As an alternative to lithium-ion batteries,aqueous zinc-graphite batteries(ZnGBs)are being explored as safer and low-cost options with the expectation of scalability to large energy storage systems.However,the currently adopted polyatomic and metal complex anion intercalation process at the graphite electrode in ZnGB exhibits poor electrochemical performances.Alternatively,incorporating halogen anions offers exceptional electrochemical performance to graphite electrodes due to their redox process.In this work,ZnGBs are assembled using a LiCl/ZnCl2/KBr^(-)based water-in-salt electrolyte,which efficiently supplies bromide(Br^(−))ions for conversion into Br_(x)^(−)and facilitates Br_(2)intercalation at the graphite electrode.The conversion and intercalation of bromine together enable the ZnGB to achieve a discharge capacity of 2.73 mAh/cm^(2)with 91.0%of coulombic efficiency(CE)while supporting high current density operations of up to 150 mA/cm^(2).With high energy density(4.56 Wh/cm^(2)),high power density(199.5 mW/cm^(2)),and excellent rate capability(∼93.0%CE at 150 mA/cm^(2)),the ZnGB is shown to operate efficiently for as much as 800 cycles.Beguilingly,an anode-free ZnGB offers enhanced stability for up to 1100 cycles without performance decay,matching the electrochemical performance of Zn metal electrodes.This work provides insights into the bromine reaction mechanism at graphite electrodes and the role of surface exfoliation in enabling efficient Br_(x)^(−)formation,along with Br_(2)intercalation,for achieving high-performance ZnGBs.
文摘By loading nanometer anatase onto exfoliated graphite with the sol-gel method, exfoliated graphite-TiO2 composite （EG-TiO2） can be prepared, which can adsorb oil and can also degrade oil. In a technologic condition for preparing EG-TiO2, the impregnated number of times is the most important factor to influence oil-adsorbing capability, that is, when the impregnated number of times increases, the amount of saturation-adsorbed oil decreases. The study of EG-TiO2 photocatalytic degradation of machine oil based on the weight-loss method and infrared spectrum method indicates that EG-TiO2 has obvious effect of photocatalytic degradation for machine oil. Its performance is superior to pure nanometer TiO2 powder because nanometer TiO2 in EG-TiO2 has three-dimension laminar structure and comparatively high adsorption capability.
基金supported by the National Natural Science Foundation of China(No.52173267)the Key Laboratory of High Temperature Electromagnetic Materials and Structure of MOE(No.KB202402).
文摘Graphitic carbon nitride(g-C_(3)N_(4))has garnered significant attention due to its remarkable advantages such as lightweight,exceptional chemical stability and defect-rich surface.Nevertheless,its inadequate electrical conductivity and impedance matching hindered the practical implementation in the electromagnetic wave absorption(EMWA)field.To address these challenges,we developed a composites system of carbon spheres/g-C_(3)N_(4)(CCN)through a supramolecular self-assembly strategy,subsequently integrated with reduced graphene oxide(RGO)via a water bath method.Systematic investigation revealed that the EMWA performance of CCN/RGO composites exhibited a distinct dependence(a trend of first increasing and then decreasing)on RGO content.Especially,when the mass ratio of RGO to CCN was 20%,the CCN/RGO composite brought a minimum reflection loss value of-45.40 dB at 13.44 GHz and a broad effective absorbing bandwidth of 6.32 GHz at 2.19 mm.First-principles calculations based on density functional theory suggested that the constructed heterostructure effectively facilitated electron mobility and charge redistribution,boosting both conductive loss and polarization loss mechanisms.The exceptional absorption performance was ascribed to the synergistic effects of conductive loss,relaxation loss,and suitable impedance matching.As a results,this work provided a rational design strategy for high-performance g-C_(3)N_(4)-based EMWA materials.
基金Supported by the National Natural Science Foundation of China(No.20075009)
文摘A new method based on the cloud point extraction（CPE） for separation and preconcentration of nickel（Ⅱ） and its subsequent determination by graphite furnace atomic absorption spectrometry（GFAAS） was proposed, 8-hydroxyquinoline and Triton X-100 were used as the ligand and surfactant respectively. Nickel（Ⅱ） can form a hy-drophobic complex with 8-hydroxyquinoline, the complex can be extracted into the small volume surfactant rich phase at the cloud point temperature（CPT） for GFAAS determination. The factors affecting the cloud point extraction, such as pH, ligand concentration, surfactant concentration, and the incubation time were optimized. Under the optimal conditions, a detection limit of 12 ng/L and a relative standard deviation（RSD） of 2.9% were obtained for Ni（Ⅱ） determination. The enrichment factor was found to be 25. The proposed method was successfully applied to the determination of nickel（Ⅱ） in certified reference material and different types of water samples and the recovery was in a range of 95%―103%.
文摘Various experimental conditions were described for the vanadium determinationby graphite furnace atomic absorption spectroscopy (GFAAS). The experiments showed that whenatomization took place under the conditions where the combination of a pyrolytic coating graphitetube and fast raising temperature were used and the temperature was stable, the signal peak shapescould be improved, the sensitivity was enhanced, and the memory effect was removed. The vanadium infood and traditional Chinese medicinal herbs can be accurately determined using the standard curvemethod.
文摘High-efficiency microwave absorbers with broadband absorption are strongly desired for electromag-netic protection.Herein,we successfully synthesized a hybrid microwave absorbing material with two-dimensional layered structure,which consisted of expanded graphite(EG)and boron nitride(BN).The introduction of BN is to regulate the conductivity of EG and also to improve the thermal stability of the composite material.The ultrathin BN nano-sheets were uniformly wrapped on the EG sheets via chemi-cal vapor deposition.Attributed to the dielectric loss and conductive loss,the as-prepared hybrid material exhibited high performance for microwave absorption.The effective absorbing bandwidth(reflection loss value<-10 dB)was achieved up to 9.37 GHz with the thickness of 2.4 mm in the frequency range of 5.75-6.98 GHz and 9.86-18 GHz.And the minimum reflection loss was-51.58 dB at the thickness of 3 mm.The excellent performance of microwave absorption was attributed to the dielectric loss,interfacial polarization loss and optimized impedance matching.Moreover,compared to pure EG,the thermal de-composition temperature of EG/BN composite materials had increased by about 100℃which was up to 714℃.Taking the advantages of high thermal stability of BN as well as the fine microwave absorbability of EG,the EG/BN composites would be applied in high-temperature microwave absorbing fields.
基金supported by the National Key R&D Program of China (No.2017YFC0210303).
文摘The expandable graphite(EG)modified TiO_(2) nanocomposites were prepared by the high shearmethod using the TiO_(2) nanoparticles(NPs)and EG as precursors,in which the amount of EG doped in TiO_(2) was 10 wt.%.Followed by the impregnation method,adjusting the pH of the solution to 10,and using the electrostatic adsorption to achieve spatial confinement,the Pt elementswere mainly distributed on the exposed TiO_(2),thus generating the Pt/10EG-TiO_(2)-10 catalyst.The best CO oxidation activity with the excellent resistance to H_(2)O and SO_(2) was obtained over the Pt/10EG-TiO_(2)-10 catalyst:CO conversion after 36 hr of the reaction was ca.85%under the harsh condition of 10 vol.%H_(2)O and 100 ppm SO_(2) at a high gaseous hourly space velocity(GHSV)of 400,000 hr−1.Physicochemical properties of the catalystswere characterized by various techniques.The results showed that the electrostatic adsorption,which riveted the Pt elements mainly on the exposed TiO_(2) of the support surface,reduced the dispersion of Pt NPs on EG and achieved the effective dispersion of Pt NPs,hence significantly improving CO oxidation activity over the Pt/10EG-TiO_(2)-10 catalyst.The 10 wt.%EG doped in TiO_(2) caused the TiO_(2) support to form a more hydrophobic surface,which reduced the adsorption of H_(2)O and SO_(2) on the catalyst,greatly inhibited deposition of the TiOSO_(4) and formation of the PtSO4 species as well as suppressed the oxidation of SO_(2),thus resulting in an improvement in the resistance to H_(2)O and SO_(2) of the Pt/10EG-TiO_(2)-10 catalyst.
文摘A method is described for the direct determination of iron in high purity sodium fluoride using graphite furnace atomic absorption spectrometry. Interferences caused by the matrix are investigated. It is shown that the ashing temperature can be increased to 1 400°C and matrix interferences eliminated, the sensitivity of iron increased in 1. 27 fold by the addition of nickel nitrate. The method is applied to the determination of iron in sodium fluoride and satisfactory results are obtained.
文摘A new method is proposed for the preconcentration of vanadium(Ⅴ) with crosslinked chitosan (CCTS) and determination by graphite furnace atomic absorption spectrometry (GFAAS). The adsorption rate of vanadium(Ⅴ) by CCTS was 97% at pH 4.0, and vanadium(Ⅴ) was eluted from crosslinked chitosan with 2 mL 2.0 mol·L -1 chlorhydric acid and determined by GFAAS. The detection limit (3σ,n=7) for vanadium(Ⅴ) was 4.8×1 0 -12g and the relative standard deviation (R.S.D) at concentration level of 2.6 μg·L -1 is less than 3.6%. The method shows a good selectivity and high sensitivity, and it was applied to determination of vanadium(Ⅴ) in oyster and water samples. The analytic recoveries are (97±5)%.
文摘The liquid phase microextraction (LPME) was combined with the modified Graphite furnace atomic absorption spectrometry (GF-AAS) for determination of lead in the water and solid samples. In a preconcentration step, lead was extracted from a 2 ml of its aqueous sample in the pH = 5 as lead-Pyrimidine-2-thiol cationic complex into a 4 μl drop of 1,2 dichloroethane and ammonium tetraphenylborate as counter ion immersed in the solution. In the drop, the lead-Pyrimidine-2-thiol ammonium tetraphenylborate ion associated complex was formed. After extraction, the microdrop was retracted and directly transferred into a graphite tube modified by [W.Pd.Mg] (c). Some effective parameters on extraction and complex formation, such as type and volume of organic solvent, pH, concentration of chelating agent and counter ion, extraction time, stirring rate and effect of salt were optimized. Under the optimum conditions, the enrichment factor and recovery were 525% and 94%, respectively. The calibration graph was linear in the range of 0.01 - 12 μg?L–1 with correlation coefficient of 0.9975 under the optimum conditions of the recommended procedure. The detection limit based on the 3Sb criterion was 0.0072 μg?L–1 and relative standard deviation (RSD) for ten replicate measurement of 0.1 μg?L–1 and 0.4 μg?L–1 lead was 4.5% and 3.8% respectively. The characteristic concentration was 0.0065 μg?L–1 equivalent to a characteristic mass of 26 fg. The results for determination of lead in reference materials, spiked tap water and seawater demonstrated the accuracy, recovery and applicability of the presented method.
基金supported by the National Key Research and Development Program of China(No.2022YFB2502000)the National Natural Science Foundation of China(Nos.U21A20332,51771076,U21A200970,52301266)the Science and Technology Planning Project of Guangzhou(No.2024A04J3332)。
文摘Mixed polyanion phosphate Na_(4)Fe_(3)(PO_(4))_(2)P_(2)O_(7)(NFPP)is regarded as the most promising cathode material for sodium-ion batteries(SIBs),due to its high structural stability and low-cost environmental friendliness.However,its intrinsic low conductivity and sluggish Na^(+)diffusion restricted the fast-charge and low-temperature sodium storage.Herein,an NFPP composite encapsulated by in-situ pyrolytic carbon and coupled with expanded graphite(NFPP@C/EG)was constructed via a sol-gel method followed by a ballmill procedure.Due to the dual-carbon modified strategy,this NFPP@C/EG only enhanced the electronic conductivity,but also endowed more channels for Na^(+)diffusion.As cathode for SIBs,the optimized NFPP(M-NFPP@C/EG)delivers excellent rate capability(capacity of~80.5 mAh/g at 50 C)and outstanding cycling stability(11000 cycles at 50 C with capacity retention of 89.85%).Additionally,cyclic voltammetry(CV)confirmed that its sodium storage behavior is pseudocapacitance-controlled,with in-situ electrochemical impedance spectroscopy(EIS)further elucidating improvements in electrode reaction kinetics.At lower temperatures(0℃),M-NFPP@C/EG demonstrated exceptional cycling performance(8800 cycles at 10 C with capacity retention of 95.81%).Moreover,pouch cells also exhibited excellent stability.This research demonstrates the feasibility of a dual carbon modification strategy in enhancing NFPP and proposes a low-cost,high-rate,and ultra-stable cathode material for SIBs.
文摘It is of important significance to make studies on the sur-face electric characteristics of flake graphite and their variation law for strengthening the floatation of flake graphite.In this paper, DPM type microelectrophoresis apparatus is used to de-termine the surface Zeta-potential of flake graphite pure mineral, study the affection of pulp pH value, seueral kinds of inorganic salt ions and anion surface activation agent (petroleum sodium sulfonate ) on flake graphite surface Zeta-potential,and explore the surface absorption charac-teristics of graphite.The floatation experiment of flake graphite pure mineral shows that both the petroleum sodium sulfonate and inorganic salt can strengthen the conventional floatation of flake graphite. The surface characteristic varia-tion caused by them is also an important factor to promote graphite floata-tion.
文摘The effects of background absorption of TmCl 3 and Tm(NO 3) 3 matrices in graphite furnace atomic absorption spectrometry(GFAAS) were inverstigated. The experiments demonstrated that the background absorption of Tm matrices is obviously wavelength dependent. The background absorption of TmCl 3 is larger than that of Tm(NO 3) 3, especially in short wavelength region. The background absorption of TmCl 3 is decreased significantly as the ashing temperature increases and that of Tm matrices is eliminated completely at about 1900 ℃. The time distribution of background signal is related to the atomization temperature and the heating mode of atomization HNO 3 can be used to reduce the background absorption of TmCl 3 matrix.
文摘In general, biological organisms have the ability to absorb a specific element selectively. Holcombe and his co-workers reported that copper, nickel and cobalt could be separated from riverine and sea-water samples and cadmium from river water samples by unicellular green algae and were determined by slurry GFAAS. Dar-
