Structure-catalytic functionality of size-facet-performance in pentlandite nanoparticles

As one of the pentlandites,Fe5Ni4S8(FNS) based materials have attracted increasing attention due to their excellent catalytic properties and promising applicability.The control over the catalyst surface structure often benefits its heterogeneous catalytic activity.However,this has not been investigated for FNS materials at the nanoscale regarding the catalytic activity related to high-index facets.Herein,FNS nanoparticles(FNSNPs) with enclosed continuous tunable high-index facets were prepared and studied to clarify the relationship between the structure and catalytic functionality.The results suggested strong dependence between exposed facets of FNSNPs and their sizes.The decline in the average size to5.8 nm led to enclosing by high-index facets(422) and(511) to yield optimal electrocatalytic activities toward the hydrogen evolution reaction.The catalytic activity of FNSNPs was closely related to the surface energy of the main exposed facets.These findings clarified the relationship between high-index-facet and high-surface-energy FNSNPs,as promising approaches in crystal surface control engineering.

Isothermal Kinetics of the Pentlandite Exsolution from mss/Pyrrhotite Using Model-Free Method

The pentlandite exsolution from monosulfide solid solution （mss）/pyrrhotite exsolution is a complex multi-step process, including nucleation, new phase growth and atomic diffusion, and lamellae coarsening. Some of these steps occur in sequence, others simultaneously. These make its kinetic analysis difficult, as the mechanisms cannot be elucidated in detail. In mineral reactions of this type, the true functional form of the reaction model is almost never known, and the Arrhenius parameters determined by the classic Avrami method are skewed to compensate for errors in the model. The model-free kinetics allows a universal determination of activation energy. Kinetic study of pentlandite exsolution from mss/pyrrhotite was performed over the temperature range 200 to 300℃. For mss/pyrrhotite with bulk composition （Fe0.77Ni0.19）S, activation energy of pentlandite exsolution, Ea, varies from 49.6 kJ · mol^-1 at the beginning of reaction （nucleation is dominant） to 20.7 kJ · mol^-1 at the end （crystal growth is dominant）. In general, the activation energy varies during the course of solid reaction with the extent of reaction. The surrounding environment of reactant atoms affects the atom＇s activity and more or less accounts for changes of activation energy Ea.

Enhanced reconstruction of Fe_(5)Ni_(4)S_(8) by implanting pyrrolidone to unlock efficient oxygen evolution

During oxygen evolution reaction(OER),complex changes have been reported on surfaces of bimetallic Fe-Ni-based catalysts,and regulating the dynamic evolution could improve their electrocatalytic performances.Herein,a pyrrolidone-promoted reconstruction of pentlandite was investigated to uncover the correlation between the reconstructed surface and the OER performance.The theoretical calculations indicated the preferential implantation of pyrrolidone at Fe atoms,useful for regulating the electronic structures of pentlandite.The vale nce state of Ni increased,suggesting the promotion of the in-situ reconstruction of pentlandite via strengthening hydroxyl adsorption to generate highly active NiOOH.The electron-rich pentlandite was also found conducive to charge transfer under applied voltages.The Operando Raman and various quasi-in-situ characterizations confirmed the realization of more delocalized electronic structures of pentlandite by introducing pyrrolidone.This,in turn,promoted the accumulation of hydroxyl groups on the pentlandite surface,thereby boosting the formation of highly active NiOOH at lower OER potentials.Consequently,the adsorption energies of intermediates were optimized,conducive to enhanced OER reaction kinetics.As a proof of concept,the pentlandite decorated by pyrrolidone exhibited an overpotential as low as 265 mV at 10 mA cm^(-2) coupled with stable catalysis for 1000 hours at a high current density of 100 mA cm^(-2).In sum,new insights into unlocking the high catalytic activity of bimetallic Fe-Ni-based catalysts were provided,promising for future synthesis of advanced catalysts.

Application of Microwave Radiation to Extractive Metallurgy

In applying the microwave radiation to extractive me- tallurgy,it is essential first of all to find the extent of microwave energy absorbed by various minerals experi- mentally.In this paper,more than 25 kinds of common useful minerals have been individually irradiated by a 500 W,2450 MHz microwave source in an enclosed quartz crucible to ascertain their heating temperature in a definite time.In addition,the reduction and cbloridization tests were also carried out on the titanomagnetite concentrate and pentlandite with microwave heating,respectively. These experiments indicate potential applications of util- izing microwave energy in extractive metallurgy.

A study of self-heating characteristics of a pyrrhotite-rich sulphide ore stockpile

Original surface chemistry of sulphidesis altered upon contact with air, leading to ''oxidation'', which is accompanied by evolution of heat. The current study reports results of an investigation on extent of exothermicity of an experimental nickel-copper sulphide stockpile that was formed at a mining site in Sudbury, Canada. The ore contained pentlandite and chalcopyrite that are accompanied by a large quantity of pyrrhotite. The self-heating characteristics were recorded by temperature sensors placed inside the stockpile. Ambient conditions such as temperature, humidity, and wind velocity were simultaneously recorded. The inner temperature of the stockpile indicated significant fluctuations due to rapid changes, particularly in the outside temperature. The minimum and maximum temperatures recorded in the outside and inside were 5 and 10.5, 44.3 and 32 ℃, respectively. The self-heating capacity of the sulphide ore stockpile observed represents a mild case compared to that experienced by coals. Possible reasons are discussed.