Thermodynamics of Fe3O4–Co3O4 and Fe3O4–Mn3O4 spinel solid solutions at the bulk and nanoscale

Greigite (Fe3S4) is thermodynamically stable: Implications for its terrestrial and planetary occurrence

Iron sulfide minerals are widespread on Earth and likely in planetary bodies in and beyond our solar system. Using measured enthalpies of formation for three magnetic iron sulfide phases: bulk and nanophase Fe₃S₄ spinel (greigite), and its high-pressure monoclinic phase, we show that greigite is a stable phase in the Fe-S phase diagram at ambient temperature. The thermodynamic stability and low surface energy of greigite supports the common occurrence of fine-grained Fe₃S₄ in many anoxic terrestrial settings. The high-pressure monoclinic phase, thermodynamically metastable below about 3 GPa, shows a calculated negative P-T slope for its formation from the spinel. The stability of these three phases suggests their potential existence on Mercury and their magnetism may contribute to its present magnetic field.

On the elaboration of the next generation of thermodynamic models of solid solutions

Thermodynamic models of solid solutions used in computational thermochemistry have not been modernized in recent years. With the advent of fast and cheap computers, it is nowadays possible to add, at a minimal computational cost, physical ingredients such as coordination numbers, inter-atomic distances and classical interatomic potentials to the function describing the energetics of ordered and disordered solid solutions. As we show here, the integration of these elements into a robust statistical thermodynamic model of solution establishes natural connections with other deterministic and stochastic atomistic methods such as Monte Carlo and molecular dynamics simulations. Ultimately, all these numerical approaches need to be self-consistent and generate complementary sets of numerical thermo-physical properties. The present work proposes a new formalism to define the Gibbs free energy of ordered and disordered solid solutions. It allows for a complete prediction of the thermal, volumetric and compositional dependence of the Gibbs free energy by solving a constrained minimization problem. As a proof of concept, we explore the energetic behavior of pure face-centered cubic gold as well as the AuCu L1₀ ordered solution as a function of both temperature and pressure. We finally compare these results with the average properties obtained from classical molecular dynamics simulations and explain the origin of the existing differences between the two approaches based on how the temperature is accounted for in each method.

Loading and release of doxorubicin hydrochloride from iron(iii) trimesate MOF and zinc oxide nanoparticle composites

A significant amount of work has been done in recent years for the development of metal organic framework (MOF) based drug delivery vehicles. Often, nanomaterials such as iron oxide (Fe3O4), zinc oxide (ZnO), and other metal oxides like graphene oxide etc. are incorporated into the structures to impart additional functionality. In this work, an iron(iii) trimesate metal organic framework i.e. MIL-100(Fe) and its composites with ZnO nanoparticles i.e. ZnO@MIL-100(Fe) were investigated as delivery agents for anticancer drug doxorubicin hydrochloride (DOX). The synthesis of the composites was done by two routes viz. a conventional HF route (in the presence of HF as a crystallizing agent) and another one in the absence of HF. The resultant MOF and its composites significantly differ in DOX loading capacity and release rates. The results obtained in this work indicate that the DOX loading capacity increases upon addition of nanoparticles when the original MOF has lower mesopore volume (as in the sample obtained via the HF route). Surprisingly, this increase in the DOX loading was comparable to that of Fe3O4@MIL-100(Fe), although the two pure nanoparticles (ZnO and Fe3O4) have widely different loading capacities. On the other hand, the addition of ZnO nanoparticles reduces the DOX loading capacity, if the MOF has higher mesopore volume (as for the sample obtained via the HF free route). The composites synthesized by the HF route with enhanced loading capacity exhibit slower DOX release rates due to the stronger interaction of the drug with the composite.

Large scale and facile sonochemical synthesis of magnetic graphene oxide nanocomposites and their dual electro/magneto-stimuli responses

Magnetic Fe₃O₄/GO nanocomposites have been prepared via an effective electrostatic strategy under ultrasonic waves. Their appealing dual electro/magnetorheological (ER/MR) performances were investigated under applied electric or magnetic fields.

Soft-templated synthesis of Mn3O4 microdandelions for the degradation of alizarin red under visible light irradiation

A soft-templated strategy has been developed for the synthesis of self-assembled Mn₃O₄ microdandelions that exhibit potential photocatalytic activity towards the degradation of alizarin red under visible light irradiation.

Hysteresis phenomenon in a reaction system of nanocrystalline iron and a mixture of ammonia and hydrogen

In a nanoFe/NH₃/H₂ system a hysteresis phenomenon occurs and two phases coexist, according to the extended phase rule of Gibbs due to a degree of freedom associated with the nanocrystallite size.