Competitive Doping Chemistry for Nickel-Rich Layered Oxide Cathode Materials.

Chemical modification of electrode materials by heteroatom dopants is crucial for improving storage performance in rechargeable batteries. Electron configurations of different dopants significantly influence the chemical interactions inbetween and the chemical bonding with the host material, yet the underlying mechanism remains unclear. We revealed competitive doping chemistry of Group IIIA elements (boron and aluminum) taking nickel-rich cathode materials as a model. A notable difference between the atomic radii of B and Al accounts for different spatial configurations of the hybridized orbital in bonding with lattice oxygen. Density functional theory calculations reveal, Al is preferentially bonded to oxygen and vice versa, and shows a much lower diffusion barrier than BIII . In the case of Al-preoccupation, the bulk diffusion of BIII is hindered. In this way, a B-rich surface and Al-rich bulk is formed, which helps to synergistically stabilize the structural evolution and surface chemistry of the cathode.

Ultrasound-assisted dispersive solid phase extraction for promoting enrichment of ng L-1 level Hg2+ on ionic liquid coated magnetic materials.

Herein, we investigated the enrichment behavior of inorganic mercury (Hg2+) on magnetic adsorbent with different ultrasound (US) energy field input. The enrichment rate of 0.10 µg L-1 mercury is increased by 4.5 times after US instead of stirring as dispersion mode. The input of higher frequency and power ultrasound can accelerate the enrichment of magnetic ionic liquid adsorbent and reduce the Hg2+ residue, importantly, which has not been reported. The positive correlation between cavitation effect and acoustic frequency and power in imaging experiments documents that US parameters are the key factors affecting the magnetic solid phase extraction. In addition, in-situ desorption and detection of adsorbate and recovery of adsorbent can be realized by slurry vapor generation (SVG) technology. The recovery of Hg2+ in four cycles is more than 90%, which indicates that the structure and properties of the material are not affected by the application of US. Hence, the degradation of adsorption properties caused by agglomeration of magnetic materials can be improved by introducing dispersion methods such as US. At the same time, 95% enrichment efficiency and 0.01-1.0 µg L-1 linear calibration range corresponding to 150 mL sample documents that magnetic ionic liquid adsorbent combined with US and sensitive spectral detector can meet the needs of ng L-1 level Hg2+ analysis in natural water samples.

Highly efficient electrochemical gas reduction on a three-dimensional foam electrode: mechanism and application for the determination of hazardous mercury in complex matrix.

For the first time a nickel foam electrode (NFE) is applied in the field of electrochemical vapor generation (EVG) to carry out the electrochemical vapor phase conversion of mercury. Systematical electrochemical and morphological research has demonstrated that the specific surface area of the NFE was several times larger than that of the metal/non-metal electrode with the same geometric size. At the same time, the 3D porous channel composed of multi-layer nickel wire ensures the full contact between reactant and interface. The evident enhancement of spectral signals on a Ni electrode (283%), compared with Pt (27%) and graphite (109%), confirmed that the NFE effectively enhances the yield of mercury reduction. The NFE exhibits low limit of detection (0.017 µg L-1) and a wide linear range (0.2-20 µg L-1) with recoveries of actual samples in the range 87.8-117% towards Hg2+. Although the NFE has no advantage in electronic transmission and catalytic performance, its excellent stability, especially anti-interference and other characteristics, is sufficient for the analysis of hazardous mercury in complex matrix including certified reference materials and real samples.

Dual-frequency ultrasound assisted-enzyme digestion coupled with atomic fluorescence spectrometry as a green and efficient tool for cadmium detection in rice flour samples.

A sample treatment technique based on a duel frequency ultrasonic device for enzymatic digestion of rice is reported. The ultrasonic device combines a high intensity ultrasonic probe and the temperature control function of ultrasonic water bath, which can effectively extract cadmium from rice within only 160 s under the optimized conditions. Compared with the traditional ultrasonic assisted enzymatic digestion, the new method not only shortens the time significantly (e.g., from the 90 min of ultrasonic water bath to the present few minutes), but also increases the extraction efficiency of cadmium (such as ~ 75% from ultrasonic probe to app. 100%). Through the optimization of ultrasonic mode, ultrasonic frequency, power and the type of enzyme, we found that enzyme played a dominant role in ultrasound assisted enzymatic digestion. Compared with a-amylase and pepsin, trypsin is more suitable for the extraction of cadmium from rice. Furthermore, ultrasound energy is beneficial to enzymatic hydrolysis of bimolecular, and this promotion is related to the frequency of ultrasound. The reliability of this method was evaluated by analyzing the content of cadmium in the certified reference materials (CRMs, GBW10045, GBW08510, GBW08511 and GBW08512) based on atomic fluorescence spectrometry combined with a modified chemical vapor generation. The proposed method has been applied satisfactorily in the determination of Cd in several rice samples.

Sensitive determination of Se(IV) and tSe in rice and water samples using L-cysteine modified carbon paste electrode-based electrolytic hydride generation and atomic fluorescence spectrometry analysis.

This work illustrates an accurate method for determination of Se by electrolytic hydride generation technique based on a novel carbon paste electrode for sample introduction combined with atomic fluorescence spectral analysis. The studies show that Se(IV) can be converted efficiently to SeH2 on an L-cysteine modified carbon paste electrode (CMCPE), which has never been reported before. Significantly, generation from Se(IV) implies that the use of carbon paste electrode-based electron-induced hydride generation system to achieve efficiency is almost 90% to that obtained by chemical hydride generation, and the response obtained from CMCPE is 2 and 3 times of that from the Pb and graphite electrode, respectively. Results also display that the lifetime and the stability of the CMCPE is superior to that of L-cysteine ornamented graphite electrode fabricated by covalently bonding. Under the optimal conditions, a low concentration limit of detection 0.065µgL-1 of Se(IV) is achieved. The repeatability denoted as % RSD is 2.2% for 1.0µgL-1 Se(IV). The utility of the studied method is compared with certified reference materials as well as several edible samples. The advantages and limitations of this method, compared with existing techniques, are also discussed.

Selective and sensitive determination of As(III) and tAs in Chinese herbal medicine samples using L-cysteine modified carbon paste electrode-based electrolytic hydride generation and AFS analysis.

A novel non-chromatographic speciation technique for ultra-trace arsenite [As(III)] and total arsenic (tAs) in Chinese herbal medicine (CHM) is developed and validated by electrolytic hydride generation (EHG) coupled with atomic fluorescence spectrometry (AFS). The studies show that As(III) can be converted efficiently to AsH3 on an L-cysteine modified carbon paste electrode (CMCPE), which has never been reported before. Significantly, other arsenic species such as arsenate [As(V)], monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) do not form any or only less volatile hydrides at low applied current mode (<1.0 A). The results also demonstrate that L-cysteine and graphite powder play different roles in the electrolytic generation of AsH3. Comparing with the traditional graphite electrode, CMCPE has better stability, sensitivity and interference tolerance. Under the optimal conditions, the limit of detection (LOD) of tAs and As(III) for this method are 0.087µgL-1 and 0.095µgL-1 respectively. The accuracy of the method is verified through the analysis of reference materials (CRM 08231 and SRM1568a), and the proposed method has been applied satisfactorily to the determination of As(III) and tAs in several CHM samples.

Selective determination of four arsenic species in rice and water samples by modified graphite electrode-based electrolytic hydride generation coupled with atomic fluorescence spectrometry.

This work describes a novel non-chromatographic approach for the accurate and selective determining As species by modified graphite electrode-based electrolytic hydride generation (EHG) for sample introduction coupled with atomic fluorescence spectrometry (AFS) detection. Two kinds of sulfydryl-containing modifiers, l-cysteine (Cys) and glutathione (GSH), are used to modify cathode. The EHG performance of As has been changed greatly at the modified cathode, which has never been reported. Arsenite [As(III)] on the GSH modified graphite electrode (GSH/GE)-based EHG can be selectively and quantitatively converted to AsH3 at applied current of 0.4A. As(III) and arsenate [As(V)] on the Cys modified graphite electrode (Cys/GE) EHG can be selectively and efficiently converted to arsine at applied current of 0.6A, whereas monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) do not form any or only less volatile hydrides under this condition. By changing the analytical conditions, we also have achieved the analysis of total As (tAs) and DMA. Under the optimal condition, the detection limits (3s) of As(III), iAs and tAs in aqueous solutions are 0.25µgL(-1), 0.22µgL(-1) and 0.10µgL(-1), respectively. The accuracy of the method is verified through the analysis of standard reference materials (SRM 1568a).

Efficient generation of volatile species for cadmium analysis in seafood and rice samples by a modified chemical vapor generation system coupled with atomic fluorescence spectrometry.

A vapor generation procedure to determine Cd by atomic fluorescence spectrometry (AFS) has been established. Volatile species of Cd are generated by following reaction of acidified sample containing Fe(II) and L-cysteine (Cys) with sodium tetrahydroborate (NaBH4). The presence of 5 mg L(-1) Fe(II) and 0.05% m/v Cys improves the efficiency of Cd vapor generation substantially about four-fold compared with conventional thiourea and Co(II) system. Three experiments with different mixing sequences and reaction times are designed to study the reaction mechanism. The results document that the stability of Cd(II)-Cys complexes is better than Cys-THB complexes (THB means NaBH4) while the Cys-THB complexes have more contribution to improve the Cd vapor generation efficiency than Cd(II)-Cys complexes. Meanwhile, the adding of Fe(II) can catalyze the Cd vapor generation. Under the optimized conditions, the detection limit of Cd is 0.012 µg L(-1); relative standard deviations vary between 0.8% and 5.5% for replicate measurements of the standard solution. In the presence of 0.01% DDTC, Cu(II), Pb(II) and Zn(II) have no significant influence up to 5 mg L(-1), 10 mg L(-1)and 10 mg L(-1), respectively. The accuracy of the method is verified through analysis of the certificated reference materials and the proposed method has been applied in the determination of Cd in seafood and rice samples.

Speciation of inorganic- and methyl-mercury in biological matrixes by electrochemical vapor generation from an L-cysteine modified graphite electrode with atomic fluorescence spectrometry detection.

A novel nonchromatographic speciation technique for ultratrace inorganic mercury (Hg(2+)) and methylmercury (CH(3)Hg(+)) in biological materials is developed and validated by electrolytic vapor generation (EVG) coupled with atomic fluorescence spectrometry (AFS). The studies show that CH(3)Hg(+) and Hg(2+) can be converted to Hg vapor efficiently on an l-cysteine modified graphite cathode, which has never been reported before. We observe that only Hg(2+) can be converted efficiently to Hg vapor at low current mode (0.2 A). While at high current mode (2.2 A), both CH(3)Hg(+) and Hg(2+) can be reduced efficiently. As a result, we successfully establish an exact and sensitive method based on the current control to detect mercury speciation for the first time. The factors of electrolytic conditions have been optimized, and the potential mechanism is discussed. Under the optimal conditions, the detection limits (3s) of Hg(2+) and CH(3)Hg(+) in aqueous solutions are 0.098 and 0.073 µg L(-1), respectively. The relative standard deviations for 6 replicate determinations of 2 µg L(-1) Hg are determined as 3.2% and 4.7% for Hg(2+) and CH(3)Hg(+). The accuracy of the method is verified through the analysis of certified reference materials (CRM, NRC-DORM-2), and the proposed method has been applied satisfactorily to the determination of mercury speciation in several seafood samples by calibration curve mode.