Evaluating lithium diffusion mechanisms in the complex spinel Li2NiGe3O8.

Lithium-ion diffusion mechanisms in the complex spinel Li2NiGe3O8 have been investigated using solid-state NMR, impedance, and muon spectroscopies. Partial occupancy of migratory interstitial 12d sites is shown to occur at lower temperatures than previously reported. Bulk activation energies for Li+ ion hopping range from 0.43 ± 0.03 eV for powdered samples to 0.53 ± 0.01 eV for samples sintered at 950 °C for 24 h, due to the loss of Li during sintering at elevated temperatures. A lithium diffusion coefficient of 3.89 × 10-12 cm2 s-1 was calculated from muon spectroscopy data for Li2NiGe3O8 at 300 K.

Mechanism of Hydrogen-Bonded Complex Formation between Ibuprofen and Nanocrystalline Hydroxyapatite.

Nanocrystalline hydroxyapatite (nanoHA) is the main hard component of bone and has the potential to be used to promote osseointegration of implants and to treat bone defects. Here, using active pharmaceutical ingredients (APIs) such as ibuprofen, we report on the prospects of combining nanoHA with biologically active compounds to improve the clinical performance of these treatments. In this study, we designed and investigated the possibility of API attachment to the surface of nanoHA crystals via the formation of a hydrogen-bonded complex. The mechanistic studies of an ibuprofen/nanoHA complex formation have been performed using a holistic approach encompassing spectroscopic (Fourier transform infrared (FTIR) and Raman) and X-ray diffraction techniques, as well as quantum chemistry calculations, while comparing the behavior of the ibuprofen/nanoHA complex with that of a physical mixture of the two components. Whereas ibuprofen exists in dimeric form both in solid and liquid state, our study showed that the formation of the ibuprofen/nanoHA complex most likely occurs via the dissociation of the ibuprofen dimer into monomeric species promoted by ethanol, with subsequent attachment of a monomer to the HA surface. An adsorption mode for this process is proposed; this includes hydrogen bonding of the hydroxyl group of ibuprofen to the hydroxyl group of the apatite, together with the interaction of the ibuprofen carbonyl group to an HA Ca center. Overall, this mechanistic study provides new insights into the molecular interactions between APIs and the surfaces of bioactive inorganic solids and sheds light on the relationship between the noncovalent bonding and drug release properties.

In situ or Ex situ Synthesis for Electrochemical Detection of Hydrogen Peroxide-An Evaluation of Co2SnO4/RGO Nanohybrids.

Nowadays, there is no doubt about the high electrocatalytic efficiency that is obtained when using hybrid materials between carbonaceous nanomaterials and transition metal oxides. However, the method to prepare them may involve differences in the observed analytical responses, making it necessary to evaluate them for each new material. The goal of this work was to obtain for the first time Co2SnO4 (CSO)/RGO nanohybrids via in situ and ex situ methods and to evaluate their performance in the amperometric detection of hydrogen peroxide. The electroanalytical response was evaluated in NaOH pH 12 solution using detection potentials of -0.400 V or 0.300 V for the reduction or oxidation of H2O2. The results show that for CSO there were no differences between the nanohybrids either by oxidation or by reduction, unlike what we previously observed with cobalt titanate hybrids, in which the in situ nanohybrid clearly had the best performance. On the other hand, no influence in the study of interferents and more stable signals were obtained when the reduction mode was used. In conclusion, for detecting hydrogen peroxide, any of the nanohybrids studied, i.e., in situ or ex situ, are suitable to be used, and more efficiency is obtained using the reduction mode.

Synthesis and characterization of Li11Nd18Fe4O(39-δ).

Li(11)Nd(18)Fe(4)O(39-δ) has been synthesized by the solid-state reaction of pellets, covered with powder of the same composition to avoid lithium loss, with a final reaction temperature of 950 °C. This phase has been reported previously to have various stoichiometries: Li(5)Nd(4)FeO(10), Li(8)Nd(18)Fe(5)O(39), and Li(1.746)Nd(4.494)FeO(9.493). The crystal structure of Li(11)Nd(18)Fe(4)O(39-δ) is closely related to that reported previously for two of the other three compositions but contains extra Li and differences in Li/Fe site occupancies. Fe is present in a mixture of 3+ and 4+ oxidation states, as confirmed by Mössbauer spectroscopy. The oxygen content of 39 - δ is variable, depending on the processing conditions. Samples slow-cooled in air from 800 °C are semiconducting, attributed to the presence of Fe(4+) ions, whereas samples quenched from 950 °C in N(2) are insulating.

Unchartered waters: the unintended impacts of residual chlorine on water quality and biofilms.

Disinfection residuals in drinking water protect water quality and public heath by limiting planktonic microbial regrowth during distribution. However, we do not consider the consequences and selective pressures of such residuals on the ubiquitous biofilms that persist on the vast internal surface area of drinking water distribution systems. Using a full scale experimental facility, integrated analyses were applied to determine the physical, chemical and biological impacts of different free chlorine regimes on biofilm characteristics (composition, structure and microbiome) and water quality. Unexpectedly, higher free chlorine concentrations resulted in greater water quality degredation, observable as elevated inorganic loading and greater discolouration (a major cause of water quality complaints and a mask for other failures). High-chlorine concentrations also reduced biofilm cell concentrations but selected for a distinct biofilm bacterial community and inorganic composition, presenting unique risks. The results challenge the assumption that a measurable free chlorine residual necessarily assures drinking water safety.

A High-Performance Primary Nanosheet Heterojunction Cathode Composed of Na0.44 MnO2 Tunnels and Layered Na2 Mn3 O7 for Na-Ion Batteries.

Owing to its large capacity and high average potential, the structure and reversible O-redox compensation mechanism of Na2 Mn3 O7 have recently been analyzed. However, capacity fade and low coulombic efficiency over multiple cycles have also been found to be a problem, which result from oxygen evolution at high charge voltages. Herein, a Na0.44 MnO2 ⋅Na2 Mn3 O7 heterojunction of primary nanosheets was prepared by a sol-gel-assisted high-temperature sintering method. In the nanodomain regions, the close contact of Na0.44 MnO2 not only supplies multidimensional channels to improve the rate performance of the composite, but also plays the role of pillars for enhancing the cycling stability and coulombic efficiency; this is accomplished by suppressing oxygen evolution, which is confirmed by high-resolution (HR)TEM, cyclic voltammetry, and charge/discharge curves. As the cathode of a Na-ion battery, at 200 mA g-1 after 100 cycles, the Na0.44 MnO2 ⋅Na2 Mn3 O7 heterojunction retains an 88 % capacity and the coulombic efficiency approaches 100 % during the cycles. At 1000 mA g-1 , the Na0.44 MnO2 ⋅Na2 Mn3 O7 heterojunction has a discharge capacity of 72 mAh g-1 . In addition, the average potential is as high as 2.7 V in the range 1.5-4.6 V. The above good performances indicate that heterojunctions are an effective strategy for addressing oxygen evolution by disturbing the long-range order distribution of manganese vacancies in the Mn-O layer.

Co2TiO4/Reduced Graphene Oxide Nanohybrids for Electrochemical Sensing Applications.

For the first time, the synthesis, characterization, and analytical application for hydrogen peroxide quantification of the hybrid materials of Co2TiO4 (CTO) and reduced graphene oxide (RGO) is reported, using in situ (CTO/RGO) and ex situ (CTO+RGO) preparations. This synthesis for obtaining nanostructured CTO is based on a one-step hydrothermal synthesis, with new precursors and low temperatures. The morphology, structure, and composition of the synthesized materials were examined using scanning electron microscopy, X-ray diffraction (XRD), neutron powder diffraction (NPD), and X-ray photoelectron spectroscopy (XPS). Rietveld refinements using neutron diffraction data were conducted to determine the cation distributions in CTO. Hybrid materials were also characterized by Brunauer-Emmett-Teller adsorption isotherms, Scanning Electron microscopy, and scanning electrochemical microscopy. From an analytical point of view, we evaluated the electrochemical reduction of hydrogen peroxide on glassy carbon electrodes modified with hybrid materials. The analytical detection of hydrogen peroxide using CTO/RGO showed 11 and 5 times greater sensitivity in the detection of hydrogen peroxide compared with that of pristine CTO and RGO, respectively, and a two-fold increase compared with that of the RGO+CTO modified electrode. These results demonstrate that there is a synergistic effect between CTO and RGO that is more significant when the hybrid is synthetized through in situ methodology.

Spinel-rock salt transformation in LiCoMnO4-δ.

The transformation on heating LiCoMnO4, with a spinel structure, to LiCoMnO3, with a cation-disordered rock salt structure, accompanied by loss of 25% of the oxygen, has been followed using a combination of diffraction, microscopy and spectroscopy techniques. The transformation does not proceed by a topotactic mechanism, even though the spinel and rock salt phases have a similar, cubic close-packed oxygen sublattice. Instead, the transformation passes through two stages involving, first, precipitation of Li2MnO3, leaving behind a Li-deficient, Co-rich non-stoichiometric spinel and, second, rehomogenization of the two-phase assemblage, accompanied by additional oxygen loss, to give the homogeneous rock salt final product; a combination of electron energy loss spectroscopy and X-ray absorption near edge structure analyses showed oxidation states of Co2+ and Mn3+ in LiCoMnO3. Subsolidus phase diagram determination of the Li2O-CoO x -MnO y system has established the compositional extent of spinel solid solutions at approximately 500°C.

Synthesis and characterisation of Li11RE18M4O39-δ: RE = Nd or Sm; M = Al, Co or Fe.

Four new phases of general formula, Li11RE18M4O39-δ: REM = NdAl, NdCo, SmCo, SmFe, have been synthesised and characterised. The NdAl phase, and probably the others, is isostructural with the NdFe analogue, but some cation disorder and partial site occupancies prevent full structural refinement of powder neutron diffraction data. The NdCo phase also forms a solid solution with variable Li content (and charge compensation by either oxygen vacancies or variable transition metal oxidation state). The NdAl phase is a modest conductor of Li(+) ions whereas the other three phases are electronic conductors, attributed to mixed valence of the transition metal ions. Subsolidus phase diagrams for the systems Li2O-Nd2O3-Al2O3, 'CoO' have been determined and an additional new phase, LiCoNd4O8, which appears to have a K2NiF4-related superstructure, identified.