Sorption kinetics of 1,3,5-trinitrobenzene to biochars produced at various temperatures

Sorption kinetics of organic compounds on biochars is important for understanding the retardation of mobility and bioavailability of organic compounds.Herein,sorption kinetics of 1,3,5-trinitrobenzene on biochars prepared from 200 to 700℃was investigated to explore the sorption process.Loose partition matrix and condensed partition matrix were formed at relatively low and moderate temperatures,respectively.However,biochars produced at relatively high temperatures formed rich pore structures.Therefore,sorption equilibrium time of 1,3,5-trinitrobenzene increased with increasing preparation temperature from 200 to 350℃due to the slower diffusion rate in the more condensed matrix,and then decreased when preparation temperature was higher than 400℃because of the faster adsorption rate in the greater number of pores.Linear positive relationship between matrix diffusion rates of 1,3,5-trinitrobenzene on biochars prepared at 200,250,300,350℃and H/C ratios of biochars was observed,suggesting that the inhibition of partition process was caused by the condensed matrix in biochars.Linear positive relationships between adsorption rates(i.e.,fast outer diffusion rate and slow pore diffusion rate)of 1,3,5-trinitrobenzene on biochars prepared at 400,450,550,700℃and graphite defects of biochars were observed,because the increase of graphite defects of biochars could promote the adsorption by increasing the quantity of fast diffusion channels and sorption sites.This study reveals the underlying mechanisms of sorption kinetics for organic compounds with relatively large size on biochars,which has potential guidance for the application of biochars and prediction of the environmental risks of organic compounds.

Using dynamic dewpoint isotherms to determine the optimal storage conditions of inert dust-treated hard red winter wheat

Water-solid interactions play a key role in determining the efficacy of inert dusts. The critical water activity(Awc) for phase transition in amorphous materials is an important characteristic of amorphous inert dusts used as grain protectants. As water activity(Aw) rises above Awc, amorphous dusts undergo a transition from glassy or vitreous state to rubbery state. Such a transition induces dramatic changes in material properties, texture and structure, and hence impact their performance as grain protectants. Full Dynamic Dewpoint Isotherms(DDI) of a synthetic amorphous zeolite intended for grain protection were generated using the Vapor Sorption Analyzer(VSA) to determine Awcby investigating the relationship between moisture content and Awat constant temperatures. Sorption experimental data was fitted using three sorption isotherm models: Guggenheim-Anderson-de Boer(GAB), Double Log Polynomial(DLP),and Brunauer-Emmet-Teller(BET). DLP model was the best model to estimate zeolite and wheat sorption isotherms. Full sorption isotherms of zeolite and wheat obtained at 25, 35, and 45 °C clearly showed the hysteresis phenomenon. The hysteresis loops were of type H3 for wheat, and of type H4 for zeolite powder. The intensity of hysteresis remained unchanged for wheat. However, the intensity of hysteresis decreased with increasing temperatures during water adsorption by porous zeolite powder. Monolayer moisture content values for each sorption direction were provided only by GAB and BET models and indicated a decrease in monolayer moisture content with an increase in temperature. The net isosteric heats of sorption and the differential enthalpy of zeolite estimated by the Clausius–Clapeyron equation and determined graphically decreased with increasing moisture content. Conversely, differential entropy of zeolite decreased with increasing zeolite moisture content. The optimal moisture content of inert dust for grain treatment was dependent on wheat moisture content and wheat storage temperature. This is the first time that a synthetic amorphous dust is being investigated for grain protection.Our results recommend the application of inert dusts at the optimal moisture content to mitigate moisture migration within the system "wheat-dust", thus ensuring dust maximal efficacy.

A Quantitative LC-MS/MS Study of the Partitioning, Transport, and Fate of Pesticide Residues on Soil

Titration of pesticides onto sorption sites can determine sorption capacities on soils. Previous studies have tracked the sorption capacities and detailed kinetics of the uptake of atrazine and its decomposition byproduct hydroxyatrazine on different soils, including measurements made using LC-MS/MS. These studies have now been extended to explore sorption-desorption equilibria for a mixture of pesticides from soil using LC-MS/MS. Desorption of sorbed pesticide residues has environmental regulatory implications for pesticide levels in runoff, or for longer term sequestration, partitioning, and transport. The uptake of pesticides by the soil at equilibrium was measured for a number of different concentrations, and sorption capacities were estimated. Pesticide-soil interaction studies were conducted by exposing standard stock solutions of pesticide mixtures to a characterized Nova Scotia soil. The mixture contained atrazine and dicamba. Initial aqueous mixture concentrations ranging from 5 × 10-9 to 10-5 M or greater were exposed to 25 mg aliquots of soil and allowed to reach equilibrium. The total uptake of each pesticide was measured indirectly, by measuring the concentration remaining in solution using an IONICS 3Q 120 triple quadrupole mass spectrometer. These sorption capacities have been supplemented by studies examining equilibrium recovery rates from soil aliquots with different initial uptakes. This gives insight into the fraction of easily recoverable (reversibly sorbed) pesticides on the soil. Proper quantification of equilibrium constants and kinetic rate coefficients using high performance LC-MS/MS facilitates the construction of accurate, predictive models. Predictive kinetic models can successfully mimic the experimental results for solution concentration, labile sorption, and intra-particle diffusion, and could be used to guide regulatory practices.

Solid-State Hydrogen Storage Properties of Ti-V-Nb-Cr High-Entropy Alloys and the Associated Effects of Transitional Metals(M=Mn,Fe,Ni)

Recently,high-entropy alloys(HEAs)designed by the concepts of unique entropy-stabilized mechanisms,started to attract widespread interests for their hydrogen storage properties.HEAs with body-centered cubic(BCC)structures present a high potential for hydrogen storage due to the high hydrogen-to-metal ratio(up to H/M=2)and vastness of compositions.Although many studies reported rapid absorption kinetics,the investigation of hydrogen desorption is missing,especially in BCC HEAs.We have investigated the crystal structure,microstructure and hydrogen storage performance of a series of HEAs in the Ti-V-Nb-Cr system.Three types of TiVCrNb HEAs(Ti_(4)V_(3)NbCr_(2),Ti_(3)V_(3)Nb2Cr_(2),Ti_(2)V_(3)Nb_(3)Cr_(2))with close atomic radii and different valence electron concentrations(VECs)were designed with single BCC phase by CALPHAD method.The three alloys with fast hydrogen absorption kinetics reach the H/M ratio up to 2.Particularly,Ti_(4)V_(3)NbCr_(2)alloy shows the hydrogen storage capacity of 3.7 wt%,higher than other HEAs ever reported.The dehydrogenation activation energy of HEAs’hydride has been proved to decrease with decreasing VEC,which may be due to the weakening of alloy atom and H atom.Moreover,Ti_(4)V_(3)NbCr_(2)M(M=Mn,Fe,Ni)alloys were also synthesized to destabilize hydrides.The addition of Mn,Fe and Ni lead to precipitation of Laves phase,however,the kinetics did not improve further because of their own excellent hydrogen absorption.With increasing the content of Laves phase,there appear more pathways for hydrogen desorption so that the hydrides are more easily dissociated,which may provide new insights into how to achieve hydrogen desorption in BCC HEAs at room temperature.