Effects of pH and particle size on kinetics of nitrobenzene reduction by zero-valent iron

Nitrobenzene has been considered as a significant groundwater contaminant due to its wide usage in explosives, insecticides, herbicides, pharmaceuticals and dyes. Nitrobenzene is of environmental concern because of its toxicity. In the presence of zero-valent iron （ZVI）, reduction of the nitro group is the dominant transformation process for nitrobenzene. A series of experiments were carried out to investigate the kinetics of nitrobenzene reduction by ZVI and the effects of pH and ZVI particle size on nitrobenzene removal in groundwater. The results indicated that nitrobenzene could be reduced to aniline by ZVI; the reduction of nitrobenzene by ZVI followed a pseudo first-order kinetics; the observed nitrobenzene reduction rate constant （k obs ） was 0.0006 min^-1 and the half-life of nitrobenzene （t 1/2 ） was 115.5 min; the mass balance achieved 87.5% for nitrobenzene reduction by the 1 mm ZVI particle and the final removal efficiency was 80.98%. In addition, the pH and ZVI particle size were found to exhibit significant influences on the nitrobenzene reduction. The observed nitrobenzene reduction rate constant linearly decreased with increase pH and the data fitted on polynomial regression equation for the observed nitrobenzene reduction rate constant and ZVI particle size. Therefore, use of ZVI based permeable reactive barrier technology to remedy nitrobenzene contaminated groundwater was feasible.

A MoS_2 nanocatalyst with surface-enriched active sites for the heterogeneous transfer hydrogenation of nitroarenes

A highly efficient and reusable plane‐curved and interlayer‐expanded MoS2nanocatalyst with increased exposure of active sites was prepared.The catalyst was used for the heterogeneous hydrogen transfer reaction of nitroarenes with hydrazine monohydrate as a reductant under mild reaction conditions without pressure and base,which was different from other hydrogen transfer systems that require the presence of a base(e.g.,propan‐2‐ol/KOH).The sandwiching of carbon between the MoS2nanosheets increased the distance between the layers of MoS2and exposed more Mo sites,resulting in superior catalytic performance compared with that of bulk MoS2catalyst.The active hydrogen(H*)generated from N2H4could directly transfer to the–NO2groups of nitrobenzene to form aniline followed by N2emission,which was confirmed by detecting the gas emission with mass spectrometry during the decomposition of hydrazine or the co‐existence of nitrobenzene and hydrazine.?2018,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published by Elsevier B.V.All rights reserved.

Kinetics of nitrobenzene degradation coupled to indigenous microorganism dissimilatory iron reduction stimulated by emulsified vegetable oil

Widespread contamination by nitrobenzene（NB） in sediments and groundwater requires better understanding of the biogeochemical removal process of the pollutant. NB degradation, coupled with dissimilatory iron reduction, is one of the most efficient pollutant removal methods. However, research on NB degradation coupled to indigenous microorganism dissimilatory iron reduction stimulated by electron donors is still experimental. A model for remediation in an actual polluted site does not currently exist.Therefore, in this study, the dynamics was derived from the Michaelis–Menten model（when the mass ratio of emulsified vegetable oil and NB reached the critical value 91：1）. The effect of SO4^（2-）, NO3^-, Ca^（2＋）/Mg^（2＋）, and the grain size of aquifer media on the dynamics were studied, and the NB degradation dynamic model was then modified based on the most significant factors. Utilizing the model, the remediation time could be calculated in a contaminated site.

Direct transformation of ZIF-8 into hollow porous carbons and hollow carbon composites

Hollow porous carbons(HPCs)are a class of porous materials with advantages of high surface to volume ratio,large interior cavities,low density,and short diffusion length,which are promising in various applications.Direct carbonization of carbon precursors is the simplest and the most cost-effective method to prepare porous carbons,however,it often leads to non-hollow structures.Herein,we demonstrate the preparation of HPCs through a direct carbonization method with a two-step heating process of zeolitic imidazolate framework-8(ZIF-8)and tetrafluoroterephthalonitrile(TFTPN).During the carbonization,ZIF-8 nanoparticles first react with TFTPN at low temperature to create polymer coatings on the surface,which are then converted into HPCs at elevated temperature.The obtained HPCs show hierarchically porous structure with high specific surface areas and pore volumes.Additionally,this method has been adopted to fabricate Au@HPCs yolk–shell composites,exhibiting good catalytic performance in nitrobenzene reduction.The developed synthesis strategy can enrich the toolbox for the preparation of novel HPCs and their composites.

Ultrasmall Pd nanoclusters: facile synthesis and versatile catalytic application

A simple and efficient method for the synthesis of ultrasmall Pd nanoclusters(NCs) has been developed. The as-obtained Pd NCs displayed uniform size with an average diameter of 1.8±0.2 nm. The ultrasmall Pd NCs and carbon nanotubes(CNTs)-supported Pd NCs also showed outstanding catalytic activity for nitrobenzene reduction and Suzuki coupling reactions. Notably, the reactions were conducted under mild conditions with high yield and selectivity.