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In this article, we have reported a one-step scalable synthesis of MgCo2O4 nanostructures as efficient anode material for Li-ion batteries and investigated the role of post-synthesis calcination temperature (400, 600 and 800 °C) on its physiochemical properties and electrochemical performances. The XRD pattern of the calcinated sample at 400 °C (MC 400) indicates a pure phase of MgCo2O4. However, on increasing the calcination temperature to 600 °C (MC 600), an additional phase corresponding to MgO was detected and the corresponding XRD peak intensity further increased on increasing the calcination temperature to 800 °C (MC 800 °C). This was accompanied by a morphological transformation from flake and rod-like nanostructures, to an agglomerated dense flake-like morphology. Electrochemical studies revealed that the calcination temperature plays an important role in determining the electrochemical performance of the MgCo2O4 as anode material. In a half cell, the MC 600 showed the best electrochemical performance with high discharge capacity of 980 mA h g−1 (2nd discharge at 60 mA g−1) and a reversible discharge capacity of 886 mA h g−1 at the end of 50 cycles with high coulombic efficiency of 98%. Long term stability was carried out at 0.5C which showed a capacity retention of 358 mA h g−1 at the end of 500 cycles. The superior electrochemical performance of the MC600 can be attributed to the presence of the small amount of MgO, which is believed to provide the anode materials better structural stability during cycling. The claim was further supported by ex-situ TEM analysis of the anode material of a cycled cell (50 cycles).

We report a simple and scalable synthesis of MnCo2O4/MWCNT nanocomposite by a simple precipitation method and its application as a high capacity anode material for Li-ion batteries. X-ray diffraction analysis showed a pure phase of MnCo2O4 and morphological analysis revealed a uniform decoration of MnCo2O4 nanoparticles along MWCNT backbone. As an electrode material, MnCo2O4 showed a high initial discharge capacity of 1431 mA h g−1 with a capacity retention of 444 mA h g−1 at the end of 30 cycles. With a small addition of MWCNT to MnCo2O4, the stability of the composite increased with a reversible capacity of 871 mA h g−1 at the end of 30 cycles. The inclusion of MWCNT as a conductive matrix resulted in a significant improvement in rate capability and cyclic stability.

In this paper, we show that magnesium and cobalt doped SnO2 (Mg-SnO2 and Co-SnO2) nanostructures have profound influence on the discharge capacity and coulombic efficiency of lithium ion batteries (LIBs) employing pure SnO2 and zinc doped SnO2 (Zn-SnO2) as benchmark materials. The materials were synthesized via sol-gel technique. The structural, chemical and morphological characterization indicates that the Zn, Mg and Co dopants were effectively implanted into the SnO2 lattice and that Co doping significantly reduced the grain growth. The electrochemical performances of the nanoparticles were investigated using galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The Co-SnO2 electrode delivered a reversible capacity of around 575 mAh g−1 at the 50th cycle with capacity retention of ∼83% at 60 mA g−1current rate. A capacity of ∼415 mAh g−1 when cycling at 103 mA g−1and >60% improvement in coulombic efficiency compared to the pure compound clearly demonstrate the superiority of Co-SnO2 electrodes. The improved electrochemical properties are attributed to the reduction in particle size of the material up to a few nanometers, which efficiently reduced the distance of lithium diffusion pathway and reduction in the volume change by alleviating the structural strain caused during the Li+ intake/outtake process. The EIS analyses of the electrodes corroborated the difference in electrochemical performances of the electrodes: the Co-SnO2 electrode showed the lowest resistance at different voltages during cycling among other electrodes.

In this article, we report simple and scalable one-pot molten salt synthesis of CoFe2O4 as electrode material for Lithium ion batteries. X-ray diffraction studies along with Rietveld analysis showed a pure phase of CoFe2O4 with space group Fd-3m and crystallite size of 54 nm. As an anode material CoFe2O4 showed high initial discharge/charge capacity of 1556/1093 mA h g−1 and a reversible capacity of 926 mA h g−1 after 30 cycles with columbic efficiency of 99%. A relatively high reversible capacity of 594 mA h g−1 was observed at high current density of 1C (916 mA g−1) which shows the better reversibility of CoFe2O4 at high current density. As the current was reduced to 0.1C reversible capacity of 899 mA h g−1 was retained suggesting high rate performance of CoFe2O4. The long-term stability test, carried out using galvanostatic charge/discharge (GC) at a current density of 0.5C, showed a reversible capacity of 369 mA h g−1 at the end of 200th cycle. The structural and morphological evaluation of the sample after cycling, using ex-situ X-ray diffraction and ex-situ transmission electron microscopy, confirmed structural degradation and formation of metal nanoparticles, Li2O and amorphous nature of electrode material. The one-pot molten salt synthesis approach is quite simple and can be extended for large-scale production of electrode materials.

In this article, we investigated the role of potassium and Lithium hydroxide (KOH & LiOH) as precipitating agents on the physiochemical properties and electrochemical performance of MgCo2O4. Uniform cubic particles were obtained using lithium hydroxide. When LiOH was used as precipitating agents, discrete nanoparticles with uniform particle size were obtained. Whereas KOH as precipitating agent resulted in more agglomerated particles with non-uniform size distribution. After testing, we found that MgCo2O4 nanostructures prepared with LiOH showed high initial discharge/charge capacity of 1384/1013 mA h g−1 at current density of 60 mA g−1, and retained a high reversible capacity of 899 mA h g−1 over 50 cycles, which was superior in comparison to the electrochemical performance of the MgCo2O4 prepared using KOH as precipitating agent. The high electrochemical performance can be attributed to the small particle size and crystallinity of MgCo2O4 obtained using LiOH.

A series of field sampling and controlled laboratory experiments were undertaken to quantify the role of trace metals found in ambient fine particulate matter and metal-rich primary sources in the heterogenous catalytic conversion of SO2 gas into sulfate particulate matter (PM) in the atmosphere. Analysis produced source profiles of three primary source materials, fluidized-bed catalytic cracking catalyst, coal-fired combustion fly ash, and paved road dust, featuring 33 elements including rare earth metals, which are not commonly reported in the literature. Subsequently three sets of experiments were conducted exposing 1) source materials, 2) ambient PM, and 3) ambient PM augmented with approximately an equal amount of source material to SO2 gas and measuring sulfate formation. Source material experiments revealed that the greatest extent of reaction was on the surface of coal fly ash with sulfate formation of 19 ± 5 mg sulfate g−1 material. Ambient fine particulate matter (PM) experiments showed sulfate formation ranging from negligible amounts to 180 ± 10 mg sulfate g−1 PM. It was much more difficult to quantify the sulfate formation on ambient filters augmented with the source materials. In these experiments, sulfate formation ranged from negligible amounts to 40 ± 8 mg sulfate g−1 of particles (ambient + augmented material). These three sets of experiments shows that heterogenous sulfate formation is often negligible but, under some conditions can contribute 10% or more to the total sulfate concentrations when exposed to high SO2 concentrations such as those found in plumes. Factor analysis of the source material experiments grouped metals into two categories, crustal components and anthropogenically emitted metals representative of catalyst material, with the former showing the strongest correlation with sulfate formation. Subsequent analysis of data collected from the ambient PM experiments showed a much weaker correlation of sulfate formation with the crustal components, including iron and titanium, remaining clustered with sulfate formation. Independent research has been previously reported in the literature establishing mechanisms for the iron and titanium catalyzed conversion of S(IV) to S(VI) suggesting there may be other metals within these crustal type metal components that behave similarly. Additional experiments spanning a wider range of variables including more sources, SO2 concentrations and exposure times, ambient PM locations, as well as more individual samples may be necessary to obtain more conclusive evidence into the role of various metals in catalyzing the conversion of S(IV) to S(VI).

In the absence of a certified reference material, a robust microwave-assisted acid digestion procedure followed by inductively coupled plasma - mass spectrometry (ICP-MS) was developed to quantify rare earth elements (REEs) in fluidized-bed catalytic cracking (FCC) catalysts and atmospheric fine particulate matter (PM2.5). High temperature (200 C), high pressure (200 psig), acid digestion (HNO3, HF, and H3BO3) with 20 minute dwell time effectively solubilized REEs from six fresh catalysts, a spent catalyst, and PM2.5. This method was also employed to measure 27 non-REEs including Na, Mg, Al, Si, K, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Zr, Mo, Cd, Cs, Ba, Pb, and U. Complete extraction of several REEs (Y, La, Ce, Pr, Nd, Tb, Dy, and Er) required HF indicating that they were closely associated with the aluminosilicate structure of the zeolite FCC catalysts. Internal standardization using 115In quantitatively corrected non-spectral interferences in the catalyst digestate matrix. Inter-laboratory comparison using ICP-optical emission spectroscopy (ICP-OES) and instrumental neutron activation analysis (INAA) demonstrated the applicability of the newly developed analytical method for accurate analysis of REEs in FCC catalysts. The method developed for FCC catalysts was also successfully implemented to measure trace to ultra-trace concentrations of La, Ce, Pr, Nd, Sm, Gd, Eu, and Dy in ambient PM2.5 in an industrial area of Houston, TX.

A study was conducted in Houston, TX focusing on rare earth elements (REEs) in atmospheric fine particles and their sources. PM2.5 samples were collected from an ambient air quality monitoring site (HRM3) located in the proximity of a large number of oil refineries and petrochemical industries to estimate the potential contributions of emissions from fluidized-bed catalytic cracking operations to ambient fine particulate matter. The elemental composition of ambient PM2.5, several commercially available zeolite catalysts, and local soil was measured after microwave assisted acid digestion using inductively coupled plasma—mass spectrometry. Source identification and apportionment was performed by principal component factor analysis (PCFA) in combination with multiple linear regression. REE relative abundance sequence, ratios of La to light REEs (Ce, Pr, Nd, and Sm), and enrichment factor analysis indicated that refining and petrochemical cat cracking operations were predominantly responsible for REE enrichment in ambient fine particles. PCFA yielded five physically meaningful PM2.5 sources: cat cracking operations, a source predominantly comprised of crustal material, industrial high temperature operations, oil combustion, and sea spray. These five sources accounted for 82% of the total mass of atmospheric fine particles (less carbon and sulfate). Factor analysis confirmed that emissions from cat cracking operations primarily contributed to REE enrichment in PM2.5 even though they comprised only 2.0% of the apportioned mass. Results from this study demonstrate the need to characterize catalysts employed in the vicinity of the sampling stations to accurately determine local sources of atmospheric REEs.