An amino acid derived ionic liquid, Fe3O4 nanoparticles and graphene oxide (GO) were used to prepare a material for the magnetic solid phase extraction (MSPE) of the ions Al(III), Cr(III), Cu(II) and Pb(II). The material was characterized by Fourier transform infrared spectral (FT-IR), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), magnetic analysis and isoelectric point (pI) analysis. It is shown to be a viable sorbent for the separation of these metal ions. Single factor experiments were carried out to optimize adsorption including pH values, ionic strength, temperature and solution volume. Following desorption with 0.1 M HCl, the ions were quantified by inductively coupled plasma optical emission spectrometry. Under the optimum conditions, the method provides a linear range from 10 to 170 μg· L?1 for Al(III); from 4.0 to 200 μg· L?1 for Cr(III); from 5.0 to 170 μg· L?1 for Cu(II); and from 5.0 to 200 μg· L?1 for Pb(II). The limits of detection (LOD) are 6.2 ng L?1 for Al(III); 1.6 ng L?1 for Cr(III); 0.52 ng L?1 for Cu(II); and 30 ng L?1 for Pb(II). Method performance was investigated by determination of these ions in (spiked) environmental water and gave recoveries in the range of 89.1%–117.8%.
Graphical abstract The graph shows that Al(III), Cr(III), Cu(II), Pb(II) are not adsorbed quantitatively by Fe3O4-SiO2. On the other hand, Cr(III) and Pb(II) are adsorbed quantitatively by Fe3O4-SiO2-GO while Al(III) and Cu(II) are not quantitatively retained. However, 3D–Fe3O4-SiO2-GO-AAIL adsorb all these 4 metal ions quantitatively.
This study describes an amperometric sensor for hydrogen peroxide (H2O2) that uses an ITO glass electrode which was modified with a nanocomposite consisting of electrochemically reduced graphene oxide and gold nanoclusters (AuNCs). The sensor was used to quantify extracellular H2O2 released from human neuroblastoma cells of type SH-SY5Y. The calibration plot, established best at a working voltage of ?0.4 V (vs. Ag/AgCl) is linear in the 40 nmol?L?1 to 2 μmol?L?1 concentration range, and the detection limit is 20 nmol?L?1 (at a signal-to-noise ratio of 3). The method was further applied to study bupivacaine-induced cell damage and the protective effects of α-lipoic acid. The study indicated that pretreatment of the cells with lipoic acid retards cell damage induced by bupivacaine. The sensor can be easily fabricated, is disposable and highly sensitive. The sensor is perceived to represent an alternative for studying the interactions of drugs with cells, and as an effective tool to quantify cell-secreted H2O2.
Graphical abstract One-step electrochemical synthesis of graphene oxide and gold nanoclusters on an ITO electrode for studying the release of H2O2 from SH-SY5Y cells and for evaluation of drug-induced cell damage
A temperature-responsive biosensing film consisting of the temperature-responsive block co-polymer poly (N-isopropylacrylamide)-b-poly(2-acrylamidoethyl benzoate) (referred to as PNIPAM-b-PAAE), graphene oxide (GO), and hemoglobin (Hb) was fabricated and used to modify a glassy carbon electrode (GCE). The film provides a favorable micro-environment for Hb to facilitate the electron transfer to the GCE. Hb at PNIPAM-b-PAAE/GO/Hb (PGH) film exhibits a couple of well-defined redox peaks with a formal potential of ?0.371 V (vs. SCE) and displays intrinsic electro-catalytic activity toward H2O2. The sensing film also shows temperature-tunable catalytic activity toward H2O2 that can be stimulated by temperature. Large peak currents can be seen in amperometry at 0.4 V (vs. SCE) in pH 7.0 phosphate buffer only if the temperature is above the lower critical solution temperature (LCST) of 32 °C. The response of the modified GCE is linear in the 0.1 to 3.7 μmol L?1 concentration range if operated at above 32 °C, but in the 0.2 to 3.7 μmol L?1 concentration range at below 30 °C. This behavior is attributed to the temperature-dependent phase transition of PNIPAM-b-PAAE and cooperative effect of GO. The strategy presented here in our perception meets the requirements of switchable sensors for use in bioscience and biotechnology.
Graphical abstract A temperature-responsive biosensing film consisting of temperature-responsive polymer, graphene oxide and hemoglobin has been fabricated. This film displays favorable electrochemical property and good electro-catalytic activity toward H2O2. It also exhibits catalytic activity change upon temperature stimuli.
The authors report on the preparation of a hollow-structured cobalt ferrite (CoFe2O4) nanocomposite for use in a non-enzymatic sensor for hydrogen peroxide (H2O2). Silica (SiO2) nanoparticles were exploited as template for the deposition of Fe3O4/CoFe2O4 nanosheets, which was followed by the removal of SiO2 template under mild conditions. This leads to the formation of hollow-structured Fe3O4/CoFe2O4 interconnected nanosheets with cubic spinel structure of high crystallinity. The material was placed on a glassy carbon electrode where it acts as a viable sensor for non-enzymatic determination of H2O2. Operated at a potential of ?0.45 V vs. Ag/AgCl in 0.1 M NaOH solution, the modified GCE has a sensitivity of 17 nA μM?1 cm?2, a linear response in the range of 10 to 1200 μM H2O2 concentration range, and a 2.5 μM detection limit. The sensor is reproducible and stable and was applied to the analysis of spiked urine samples, where it provided excellent recoveries.
Graphical abstract Schematic of a cobalt ferrite (CoFe2O4) hollow structure for use in electrochemical determination of H2O2. The sensor shows a low detection limit, a wide linear range, and excellent selectivity for H2O2.
The authors describe a 3-component nanoparticle system composed of a silica-coated magnetite (Fe3O4) core and a layered double (Cu-Cr) hydroxide nanoplatelet shell. The sorbent has a high anion exchange capacity for extraction anionic species. A simple online system, referred to as "on-line packed magnetic-in-tube solid phase microextraction" was designed. The nanoparticles were placed in a stainless steel cartridge via dry packing. The cartridge was then applied to the preconcentration acidic drugs including naproxen and indomethacin from urine and plasma. Extraction and desorption times, pH values of the sample solution and flow rates of sample solution and eluent were optimized. Analytes were then quantified by HPLC with UV detection. Under optimal conditions, the limits of detection range from 70 to 800 ng L?1, with linear responses from 0.1–500 μg L?1 (water samples), 0.6–500 μg L?1 (spiked urine), and 0.9–500 μg L?1 (spiked plasma). The inter- and intra-assay precisions (RSDs, for n?=?5) are in the range of 2.2–5.4%, 2.8–4.9%, and 2.0–5.2% at concentration levels of 5, 25 and 50 μg L?1, respectively. The method was applied to the analysis of the drugs in spiked human urine and plasma, and good results were achieved.
Graphical abstract Fe3O4@SiO2@CuCr-LDH magnetic nanoparticles were synthesized and packed in to a stainless steel column. The column was applied to solid phase microextraction of acidic drugs from biological samples.
The authors describe an electrochemical sensor for hydrogen peroxide (H2O2). It was constructed by consecutive, selective modification of a glassy carbon electrode (GCE) with Prussian Blue (PB), layered molybdenum disulfide (MoS2), and reduced graphene oxide (rGO). The properties of the modified GCE were characterized via high-resolution transmission electron microscopy, UV-vis spectroscopy and X-ray diffraction. The electrochemical properties of the electrode were studied using cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibits excellent electrocatalytic activity for the reduction of hydrogen peroxide in comparison to GCEs modified with MoS2-rGO or PB only. Response is linear in the 0.3 μM to 1.15 mM H2O2 concentration range at a working analytical voltage of 0.1 V, with a 0.14 μM detection limit. The electrochemical sensitivity is 2883.5 μA·μM?1·cm?2, and response is fast (<10 s). The sensor is selective, stable and reproducible. This is attributed to the efficient electron transport properties of the MoS2-rGO composite and the high loading with PB.
Graphic abstract Prussian Blue nanoparticles were deposited on MoS2-rGO modified glassy carbon electrode by electrochemical method. This sensor was used for the detection of H2O2 in tap water and river water.
The authors describe a cataluminescence (CTL) based sensing method via signals generated at the surface of In3LaTi2O10 nanoparticles for simultaneous determination of trimethylamine, formaldehyde and benzene in air. The analytical wavelengths are 340 nm, 440 nm and 600 nm, and the best surface temperature of the catalytic material is 275 °C. The limits of detection of this method are 0.3 mg?m?3 for trimethylamine, 0.07 mg?m?3 for formaldehyde, and 0.2 mg?m?3 for benzene. The linear ranges of CTL intensity versus gas/vapor concentration are from 1.0 to 65.1 mg?m?3 for trimethylamine, from 0.2 to 72.5 mg?m?3 for formaldehyde, and from 0.5 to 77.5 mg?m?3 for benzene. The recoveries after testing 10 standard samples ranged from 98.1% to 102.6% for trimethylamine, from 98.1% to 102.6% for formaldehyde, and from 97.7% to 103.8% for benzene. Gaseous ammonia, acetaldehyde, toluene, ethylbenzene, ethanol, sulfur dioxide and carbon dioxide do not interfere. The relative deviation of the CTL signals after 200 h of continuous detection of trimethylamine, formaldehyde and benzene is <3%.
Graphical abstract Schematic of a cataluminescence (CTL) based method for simultaneous determination of trimethylamine (TMA), formaldehyde (HCHO) and benzene (C6H6) in air. The linear ranges of CTL intensity versus gas/vapor concentration are from 1.0 to 65.1 mg?m?3 for TMA, from 0.2 to 72.5 mg?m?3 for HCHO, and from 0.5 to 77.5 mg?m?3 for C6H6.
The authors have prepared organized assemblies of a hemoglobin-chitosan(CS)@Fe3O4 composite on glassy carbon electrodes (GCEs) via three strategies with the aim of preparing tunable Hb-coated GCEs with good stability and long-term oxygen storage capability. The formation and morphology of the Hb-CS@Fe3O4 composite was characterized by scanning electrochemical microscopy, XRD and UV–vis spectroscopy. It is shown that Hb is fully integrated into the CS@Fe3O4 and can be manipulated by a magnetic field whilst maintaining its biological activity. In the absence of oxygen, a surface-controlled electrode process occurs with an interfacial electron transfer rate (ks) of 2.14 s?1. The modified GCE also has a favorable oxygen storage lifetime (almost 6 h). One Hb-CS@Fe3O4 film on the electrode displays particularly good electrocatalytic reduction activity towards oxygen. The linear range for detection of O2 is 1.2?×?10?7?~?2.0?×?10?4 mol L?1 with a detection limit of 4.0?×?10?8 mol L?1. In our opinion, this method has great potential in terms of enhanced oxygen storage capability of Hb, which can be applied in special situations such as space operations, down hole mining, mountaineering and diving.
Graphical Abstract Hb-CS@Fe3O4 composites were prepared by three strategies, and oxygen carrying capability was studied. The corresponding modified electrode constructed on the basis of the magnetic field environment was superior in terms of stability, sensitivity and O2 storage time, showing wider linear range and lower detection limit.
A porous, hollow, microspherical composite of Li2MnO3 and LiMn1/3Co1/3Ni1/3O2 (composition: Li1.2Mn0.53Ni0.13Co0.13O2) was prepared using hollow MnO2 as the sacrificial template. The resulting composite was found to be mesoporous; its pores were about 20 nm in diameter. It also delivered a reversible discharge capacity value of 220 mAh g?1 at a specific current of 25 mA g?1 with excellent cycling stability and a high rate capability. A discharge capacity of 100 mAh g?1 was obtained for this composite at a specific current of 1000 mA g?1. The high rate capability of this hollow microspherical composite can be attributed to its porous nature.
The synthesis of rattle-type nanostructured Fe3O4@SnO2 is described along with their application to dispersive solid-phase extraction of trace amounts of mercury(II) ions prior to their determination by continuous-flow cold vapor atomic absorption spectrometry. The voids present in rattle-type structures make the material an effective substrate for adsorption of Hg(II), and also warrant high loading capacity. The unique morphology, large specific surface, magnetism property and the synergistic effect of magnetic cores and SnO2 shells render these magnetic nanorattles an attractive candidate for solid-phase extraction of heavy metal ions.The sorbent was characterized by transmission electron microscopy, scanning electron microscopy, FTIR, energy-dispersive X-ray spectroscopy and by the Brunnauer-Emmett-Teller technique. The effects of pH value, adsorption time, amount of sorbent, volume of sample solutions, concentration and volume of eluent on extraction efficiencies were evaluated. The calibration plot is linear in the 0.1 to 40 μg·L?1 concentration range, and the preconcentration factor is 49. The detection limit is 28 ng·L?1. The sorbent was applied to the analysis of (spiked) river and sea water samples. Recoveries ranged from 97.2 to 100.5%.
Graphical abstract A yolk-shell structure based on a Fe3O4 core and SnO2 shell was developed as an efficient MSPE sorbent. A middle silica layer was etched by alkaline solution. The resulting sorbent was utilized for preconcentration of mercury ions from aqueous media.
In this paper, the LiNi0.5Mn1.5O4 cathode materials of lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining process. The use of a spray-drying process to form particles, followed by a calcination treatment at the optimized temperature of 750 °C to produce spherical LiNi0.5Mn1.5O4 particles with a cubic crystal structure, a specific surface area of 60.1 m2 g?1, a tap density of 1.15 g mL?1, and a specific capacity of 132.9 mAh g?1 at 0.1 C. The carbon nanofragment (CNF) additives, introduced into the spheres during the co-precipitation spray-drying period, greatly enhance the rate performance and cycling stability of LiNi0.5Mn1.5O4. The sample with 1.0 wt.% CNF calcined at 750 °C exhibits a maximum capacity of 131.7 mAh g?1 at 0.5 C and a capacity retention of 98.9% after 100 cycles. In addition, compared to the LiNi0.5Mn1.5O4 material without CNF, the LiNi0.5Mn1.5O4 with CNF demonstrates a high-rate capacity retention that increases from 69.1% to 95.2% after 100 cycles at 10 C, indicating an excellent rate capability. The usage of CNF and the synthetic method provide a promising choice for the synthesis of a stabilized LiNi0.5Mn1.5O4 cathode material.
Graphical Abstract Micro/nanostructured LiNi0.5Mn0.5O4 cathode materials with enhanced electrochemical performances for high voltage lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining routine and using carbon nanofragments (CNFs) as additive.
Hydrothermally synthesized Co3O4 microspheres were anchored to graphite oxide (GO) and thermally reduced graphene oxide (rGO) composites at different cobalt weight percentages (1, 10, and 100 wt%). The composite materials served as the active materials in bulk electrodes for two-electrode cell electrochemical capacitors (ECCs). GO/Co3O4–1 exhibited a high energy density of 35 W kg?1 with a specific capacitance (Csp) of 196 F g?1 at a maximum charge density of 1 A g?1. rGO/Co3O4-100 presented high specific power output values of up to 23.41 kW h kg?1 with linear energy density behavior for the charge densities applied between 0.03 and 1 A g?1. The composite materials showed Coulombic efficiencies of 96 and 93 % for GO/Co3O4–1 and rGO/Co3O4–100 respectively. The enhancement of capacitive performance is attributed to the oxygenated groups in the GO ECC and the specific area in the rGO ECC. These results offer an interesting insight into the type of carbonaceous support used for graphene derivative electrode materials in ECCs together with Co3O4 loading to improve capacitance performance in terms of specific energy density and specific power.
A nanocomposite composed of graphene oxide and magnetite (Fe3O4) was coated with the ionic liquid (IL) 1,3-didecyl-2-methylimidazolium chloride and used to capture and separate hemin from serum samples. The critical parameters affecting the extraction of analyte, such as pH, surfactant and adsorbent amounts, and desorption conditions were studied and optimized. Following magnetic separation and desorption with a 5:1 mixture of acetic acid and acetone, hemin (an iron porphyrin complex) was quantified by FAAS of iron. Under optimum conditions, the enrichment factor was 96. The calibration curve was linear in the 4.8 to 730 μg L?1 concentration range, the limit of detection was 3.0 μg L?1, and the relative standard deviations (RSDs) for single-sorbent repeatability and sorbent-to-sorbent reproducibility were less than 3.9 % and 10.2 % (n = 5), respectively. The adsorbent displayed adsorption capacity as high as 200 mg g?1, indicating IL-coated Fe3O4/GO to be a good sorbent for the adsorption of hemin. The method was validated by determining serum hemin in the presence of a large excess (480-fold) of Fe3+ without considerable interference. The results compare well to those obtained with a commercial hemin assay kit. The results show that this method can be successfully applied to the enrichment and determination of hemin in acid digested serum samples of breast cancer patients.
Graphical abstract Fe3O4/GO nanocomposites were coated with the ionic liquid 1,3-didecyl-2-methylimidazolium chloride and used as the sorbent for the separation and preconcentration of hemin from blood serum samples prior to determination using by flame AAS.
A glassy carbon electrode (GCE) was modified with a nanocomposite consisting of tetraoctylammonium bromide (TOAB), C60 fullerene, and palladium nanorods (PdNRs). The PdNRs were hydrothermally prepared and had a typical width of 20 ± 2 nm. The nanocomposite forms stable films on the GCE and exhibits a reversible redox pair for the C60/C60? system while rendering the surface to be positively charged. The modified GCE was applied to fabricate an electrochemical biosensor for detecting acetylcholinesterase (AChE) by measurement of the amount of thiocholine formed from acetylthiocholine, best at a working voltage of ?0.19 V (vs. SCE). The detection scheme is based on (a) measurement of the activity of ethyl paraoxon-inhibited AChE, and (b) measurement of AChE activity after reactivation with pralidoxime (2-PAM). Compared to the conventional methods using acetylthiocholine as a substrate, the dual method presented here provides data on the AChE activity after inhibition and subsequent reactivation, thereby yielding credible data on reactivated enzyme activity. The linear analytical range for AChE activity extends from 2.5 U L?1 to 250 kU·L?1, and the detection limit is 0.83 U L?1.
Graphical abstract Cyclovoltammetric acetylcholinesterase (AChE) activity assay is constructed based on the palladium nanorods composited with functionalized C60 fullerene (PdNR/C60 + TOAB), which aims to measure the signal change between ethyl paraoxon-inhibited and subsequent pralidoxime (2-PAM)-reactivated AChE activity.
Li[Ni1/3Co1/3Mn1/3]O2 (NCM 111) is a promising alternative to LiCoO2, as it is less expensive, more structurally stable, and has better safety characteristics. However, its capacity of 155 mAh g?1 is quite low, and cycling at potentials above 4.5 V leads to rapid capacity deterioration. Here, we report a successful synthesis of lithium-rich layered oxides (LLOs) with a core of LiMO2 (R-3m, M?=?Ni, Co) and a shell of Li2MnO3 (C2/m) (the molar ratio of Ni, Co to Mn is the same as that in NCM 111). The core–shell structure of these LLOs was confirmed by XRD, TEM, and XPS. The Rietveld refinement data showed that these LLOs possess less Li+/Ni2+ cation disorder and stronger M*–O (M*?=?Mn, Co, Ni) bonds than NCM 111. The core–shell material Li1.15Na0.5(Ni1/3Co1/3)core(Mn1/3)shellO2 can be cycled to a high upper cutoff potential of 4.7 V, delivers a high discharge capacity of 218 mAh g?1 at 20 mA g?1, and retains 90 % of its discharge capacity at 100 mA g?1 after 90 cycles; thus, the use of this material in lithium ion batteries could substantially increase their energy density.
Graphical Abstract Average voltage vs. number of cycles for the core–shell and pristine materials at 20 mA g?1 for 10 cycles followed by 90 cycles at 100 mA g?1
The authors describe a sensitive surface-enhanced Raman scattering (SERS)-based aptasensor for the detection of the food pathogen Vibrio parahaemolyticus. Nanostructures consisting of Fe3O4@Au particles wrapped with graphene oxide (GO) were used both as SERS substrates and separation tools. A first aptamer (apt 1) was immobilized on the Fe3O4@Au/GO nanostructures to act as a capture probe via the affinity binding of aptamer and V. parahaemolyticus. A second aptamer (apt-2) was modified with the Raman reporter molecule TAMRA to act as a SERS sensing probes that binds to the target the same way as the Fe3O4@Au/GO-apt 1. The sandwich formed between Fe3O4@Au/GO-apt 1/V. parahaemolyticus and apt 2-TAMRA can be separated with the aid of a magnet. The concentration of V. parahaemolyticus can be quantified by measurement of the SERS intensity of TAMRA. Under optimal conditions, the signal is linearly related to the V. parahaemolyticus concentration in the range between 1.4 × 102 to 1.4 × 106 cfu·mL?1, with a detection limit of 14 cfu·mL?1. Recoveries ranging from 98.5% to 105% are found when analyzing spiked salmon samples. In our perception, the assay described here is a useful tool for quantitation of V. parahaemolyticus in real samples.
Graphical abstract GO wrapped Fe3O4@Au nanostructures were synthesized as the substrate and modified with with a first aptamer (apt 1) to capture V. parahaemolyticus. TAMRA labelled aptamer 2 was then used as signal probe. The V. parahaemolyticus concentrations are closely related to the Raman intensity of TAMRA.
A dual-responsive sandwich-type immunosensor is described for the detection of interleukin 6 (IL-6) by combining electrochemiluminescent (ECL) and electrochemical (EC) detection based on the use of two kinds of TiO2 mesocrystal nanoarchitectures. A composite was prepared from TiO2 (anatase) mesocages (AMCs) and a carboxy-terminated ionic liquid (CTIL) and then placed on a glassy carbon electrode (GCE). In the next step, the ECL probe Ru(bpy)3(II) and antibody against IL-6 (Ab1) were immobilized on the GCE. Octahedral anatase TiO2 mesocrystals (OAMs) served as the matrix for immobilizing acid phosphatase (ACP) and secondary antibody (Ab2) labeled with horseradish peroxidase (HRP) to form a bioconjugate of type Ab2-HRP/ACP/OAMs. It was self-assembled on the GCE by immunobinding. 1-Naphthol, which is produced in-situ on the surface of the GCE due to the hydrolysis of added 1-naphthyl phosphate by ACP, is oxidized by HRP in the presence of added H2O2. This results in an electrochemical signal (typically measured at 0.4 V vs. Ag/AgCl) that increases linearly in the 10 fg·mL?1 to 90 ng·mL?1 IL-6 concentration range with a detection limit of 0.32 fg·mL?1. Secondly, the oxidation product of 1-naphthol quenches the ECL emission of Ru(bpy)32+. This leads to a decrease in ECL intensity which is linear in the 10 ag·mL?1 to 90 ng·mL?1 concentration range, with a detection limit of 3.5 ag·mL?1. The method exhibits satisfying selectivity and good reproducibility which demonstrates its potential in clinical testing and diagnosis.
Graphical abstract A dual-responsive sandwich-type immunosensor was fabricated for the detection of interleukin 6 by combining electrochemiluminescence and electrochemical detection based on the use of two kinds of TiO2 mesocrystal nanoarchitectures.
In this work, Bi3.64Mo0.36O6.55 nanoparticles (NPs) were successfully prepared by a facile hydrothermal method and utilized in pseudocapacitor for the first time. Within a redox potential range from ?1.0 to 0 V vs. Hg/HgO in a 1 M aqueous KOH solution by cyclic voltammetry (CV), chronopotentiometry (CP) and AC impendence, the specific capacitance could reach 998 F g?1 at 1 A g?1, which is possibly ascribed to the higher Bi content of Bi3.64Mo0.36O6.55 NPs. Furthermore, the Bi3.64Mo0.36O6.55 NP electrode exhibited good cycle stability maintaining over 85 % after 5000 cycles. These results demonstrated Bi3.64Mo0.36O6.55 NPs might be a promising electrode material for pseudocapacitor.
Graphical abstract The fabrication of uniform Bi3.64Mo0.36O6.55 nanoparticles with a diameter of 100 nm were succefully reported by a facial hydrothermal method, which exhibits a extraordinary electronic performance with 998 F g-1 at 1 A g-1 and cycling stability
The authors describe magnetic nanoparticles consisting of an Fe3O4 core and a poly(methacrylic acid) coating for dispersive solid phase extraction (DSPE) of arsenic prior to its determination by hydride-generation microwave plasma AES (HG-MP-AES). The particles have an average size of 25 nm, can be prepared at low costs, and provide improved operational safety in combination with plasma generation. The methods allows arsenic to be determined with detection limits (at 3σ/m) of 3.0 ng?L?1 for As(III) and of 10.0 ng?L?1 of As(V). Recoveries of (spiked) samples range from 99.0 to 102%. This is the first report on the use of HG-MP-AES for speciation and preconcentration of arsenic using DSPE. The method displays detection limits that come close to those of ICP-OES and ICP-MS.
Graphical abstract A core/shell Fe3O4@poly(methacrylic acid) coated sorbent was synthesised and employed to the speciation of arsenic prior to its determination by hydride-generation microwave plasma atomic emission spectrometry.
LiMn2O4 is one of the most promising cathode materials due to its high abundance and low cost. However, the practical application of LiMn2O4 is greatly limited owing to its low volumetric energy density. Therefore, increasing its energy density is an urgent problem to be resolved. Herein, using the simple and mass production preferred solid-state reaction, surficial Nb-doped LiMn2O4 composed of the truncated octahedral or spherical-like primary particles are successfully synthesized. Auger electron spectroscopy (AES) and X-ray diffraction (XRD) characterizations confirm that most of Nb5+ enrich in the surficial layer of the particles to form a LiMn2-xNbxO4 phase. This kind of doping can increase the specific discharge capacity of LiMn2O4 materials. Contrast with the pristine LiMn2O4, the discharge capacity of LiMn1.99Nb0.01O4-based 18650R-type battery increases from 1497 to 1705 mAh with the volumetric energy density increasing by ~?13.9%, benefiting from the joint increments of the specific discharge capacity from 119.5 to 123.7 mAh g?1 and the compacted density from 2.81 to 3.10 g cm?3. Furthermore, the capacity retention after 500 cycles at 1 C (1500 mA) is also improved by 17.1%.
