Characterization of partially inverse spinel ZnFe2O4 with high saturation magnetization synthesized via soft mechanochemically assisted route

ZnFe₂O₄ was prepared by a soft mechanochemical route from two starting combinations of powders: (1) Zn(OH)₂/α-Fe₂O₃ and (2) Zn(OH)₂/Fe(OH)₃ mixed in a planetary ball mill. The mechanochemical treatment provoked reaction leading to the formation of the ZnFe₂O₄ spinel phase that was monitored by XRD, TEM, IR and Raman spectroscopy. The spinel phase was first observed after 4 h of milling and its formation was completed after 18 h in both the cases of starting precursors. The synthesized ZnFe₂O₄ has a nanocrystalline structure with a crystallite size of about 20.3 and 17.6 nm, for the cases (1) and (2), respectively. In the far-infrared reflectivity spectra are seen four active modes. Raman spectra suggest an existence of mixed spinel structure in the obtained nanosamples. In order to confirm phase formation and cation arrangement, Mössbauer measurements were done. Estimated degree of inversion is about 0.58 for both starting mixtures. The magnetic properties of the prepared ZnFe₂O₄ powders were also studied. The results show that the samples have a typical superparamagnetic-like behavior at room temperature. Higher values of magnetization in the case of samples obtained with starting mixture (2) suggest somewhat higher degree of cation inversion.     

Topochemical polymerization of a diarylbutadiyne derivative in the gel and solid states

A diarylbutadiyne derivative was synthesized using a few steps and gelified in aromatic solvents. The gel prepared at low concentration is made of micrometers-long nanofibrils as shown by scanning electron microscopy. XRD of the dried gel shows sharp features, revealing a well-organized material. A topochemical reaction was performed on the dried gel, and a polydiacetylene presenting reversible thermochromism properties was obtained.     

Density-dependent liquid nitromethane decomposition: molecular dynamics simulations based on ReaxFF

The decomposition mechanism of hot liquid nitromethane at various compressions was studied using reactive force field (ReaxFF) molecular dynamics simulations. A competition between two different initial thermal decomposition schemes is observed, depending on compression. At low densities, unimolecular C-N bond cleavage is the dominant route, producing CH(3) and NO(2) fragments. As density and pressure rise approaching the Chapman-Jouget detonation conditions (～30% compression, >2500 K) the dominant mechanism switches to the formation of the CH(3)NO fragment via H-transfer and/or N-O bond rupture. The change in the decomposition mechanism of hot liquid NM leads to a different kinetic and energetic behavior, as well as products distribution. The calculated density dependence of the enthalpy change correlates with the change in initial decomposition reaction mechanism. It can be used as a convenient and useful global parameter for the detection of reaction dynamics. Atomic averaged local diffusion coefficients are shown to be sensitive to the reactions dynamics, and can be used to distinguish between time periods where chemical reactions occur and diffusion-dominated, nonreactive time periods.     

Large conformal metrics with prescribed sign-changing Gauss curvature

Let \((M,g)\) be a two dimensional compact Riemannian manifold of genus \(g(M)>1\). Let \(f\) be a smooth function on \(M\) such that

$$\begin{aligned} f \ge 0, \quad f\not \equiv 0, \quad \min _M f = 0. \end{aligned}$$

Let \(p_1,\ldots ,p_n\) be any set of points at which \(f(p_i)=0\) and \(D^2f(p_i)\) is non-singular. We prove that for all sufficiently small \(\lambda >0\) there exists a family of “bubbling” conformal metrics \(g_\lambda =e^{u_\lambda }g\) such that their Gauss curvature is given by the sign-changing function \(K_{g_\lambda }=-f+\lambda ^2\). Moreover, the family \(u_\lambda \) satisfies

$$\begin{aligned} u_\lambda (p_j) = -4\log \lambda -2\log \left( \frac{1}{\sqrt{2}} \log \frac{1}{\lambda }\right) +O(1) \end{aligned}$$

and

$$\begin{aligned} \lambda ^2e^{u_\lambda }\rightharpoonup 8\pi \sum _{i=1}^{n}\delta _{p_i},\quad \text{ as } \lambda \rightarrow 0, \end{aligned}$$

where \(\delta _{p}\) designates Dirac mass at the point \(p\).

     

Simultaneous Square‐Wave Voltammetric Determination of Paracetamol,Caffeine and Orphenadrine in Pharmaceutical Formulations Using a Cathodically Pretreated Boron‐Doped Diamond Electrode

An electroanalytical method for the simultaneous determination of paracetamol (PAR), caffeine (CAF), and orphenadrine (ORPH) using the square‐wave voltammetry (SWV) and a cathodically pretreated boron‐doped diamond electrode was developed. The method exhibits linear responses to PAR, CAF, and ORPH in the concentration ranges 5.4×10^?7–6.1×10^?5 M, 7.8×10^?7–3.5×10^?5 M, and 7.8×10^?7–3.5×10^?5 M, respectively, with detection limits of 2.3×10^?7 M, 9.6×10^?8 M, and 8.4×10^?8 M, respectively. The proposed method was successfully applied in the simultaneous determination of these analytes in pharmaceutical formulations.     

Comprehensive description of the photodegradation of bromophenols using chromatographic monitoring and chemometric tools

A general procedure for the study of complex photodegradation processes of environmental pollutants based on chromatographic monitoring and chemometric method is proposed. The procedure consists of multiset data analysis of aliquots collected at different reaction times and injected in High-Performance Liquid Chromatography coupled to diode array detection and mass spectrometry (HPLC-DAD-MS). In this study, photodegradation of six bromophenols with different degrees of bromination has been investigated in order to find out their photodegradation pathways and kinetics and to show the potential of the procedure proposed. Multivariate curve resolution-alternating least squares (MCR-ALS) has been used to resolve chromatographic elution profiles and pure spectra of species involved in the photodegradation process and, hence, to elucidate the photodegradation mechanism and to propose the chemical structure of the main photoproducts. This study shows that chromatographic monitoring is the preferred option when photochemical systems with large number of components with similar spectra and kinetic evolution are analyzed. This work reveals the advantages of the double DAD and MS detection to provide mechanistic and structural information about these complex photodegradation processes.     

Morphological, structural, and magnetic properties of Co nanoparticles in a silicon oxide matrix

We present a morphological, structural, and magnetic characterization of Co nanoparticles (mean diameter of 10.3 ± 1.8 nm) grown using a gas aggregation source and embedded in a silicon oxide matrix by sequential deposition of nanoparticles and silicon oxide. We show that the Co nanoparticles ??soft-land?? on the substrates and suffer a moderate oxidation in contact with the silicon oxide. Despite this moderate oxidation, it is found that, at room temperature, the magnetic volume of the resulting nanoparticles is below the superparamagnetic limit. The results presented in this article are compatible with the presence of an assembly of magnetically independent particles that also display a moderate exchange bias at low temperature.     

Spin-assisted photoluminescence of polycrystalline α-MnSe

We have studied photoluminescence of α-MnSe in the antiferromagnetic and paramagnetic phases. Two broad, possibly multi-component emission bands centred at about 1.53 and 1.66 eV are observed at 20 K. The frequencies and intensities of these bands show step-like shift in the vicinity of T_N. On the basis of difference in peak energies at T=1.8 K and T_N the d-p-d superexchange interaction in excited state is estimated to be J_2g(exc)=0.918 meV.     

Towards sustainable micro-pollutants’ removal from wastewaters: caffeine solubility,self-diffusion and adsorption studies from aqueous solutions into hydrochars

ABSTRACT

Hydrochars obtained via hydrothermal carbonisation of pistachio shells are both a sustainable and an efficient alternative to commercial activated carbons for the removal of micro-pollutants from wastewaters that are difficult to handle by conventional treatments. Here a combined experimental and molecular simulation approach is adopted for the study of the caffeine/hydrochars aqueous systems. This case study serves to tune a general framework for the rational customisation of surface functional groups on hydrochars for the selective adsorption of micro-pollutants from wastewaters. Caffeine’s solubility, self-diffusion and adsorption results from aqueous solutions at relevant conditions are presented. Insights about the role of surface functional groups over the caffeine adsorption mechanism into hydrochars are gained and discussed.