Theoretical study of adsorption of water vapor on surface of metallic uranium

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田志坚_物理吸附和催化剂的宏观物性测定

吸附量与吸附曲线
V = f ⎡⎣ p,T ,u ( g ), w(s)⎤⎦
Adsorption Isotherms
T1 T2
T3
Adsorption Isosteres
V3s V2s V1s
T1 < T2 < T3
Pressure
P3 P2
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Adsorption Isobars
V1s < V2s < V3s
恒温、恒容和恒定吸附剂表面积时，吸附量恒定条件下，相当于吸附1mol气体的热效应。(与覆盖度有关）
Qd
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⎛ ⎜⎝
∂ΔU ∂n
⎞ ⎟⎠T ,V ,A
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2013-7-1
吸附热的测定
z 直接用实验测定在高真空体系中，先将吸附剂脱附干净，然后用精密的量热计测量吸附一定量气体后放出的热量。这样测得的是积分吸附热。
2013-7-1
物理吸附和催化剂的宏观物性测定
田志坚
洁净能源国家实验室化石能源与应用催化研究部中科院大连化学物理研究所 2013年7月1日
催化剂的宏观物性与物理吸附
z 多相催化研究的一个根本问题就是固体催化剂的催化性能与它的物理和化学性质的关联。催化剂的物理性质主要包括其表面积、孔结构和机械性质等。
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物理吸附和催化剂的宏观物性测定
物理吸附
z 物理吸附
z 气固界面上的吸附
z 物理吸附 z 比表面（BET）和孔结构的表征
z 催化剂的宏观物性测定
z 孔容及孔分布测定 z 催化剂的颗粒分析 z 密度测定 z 催化剂的机械强度测定
z 吸附现象以及有关的概念 z 吸附的理论基础 z 物理吸附和化学吸附 z 吸附曲线

Adsorption of uranium(VI) from aqueous solution

Adsorption of uranium(VI)from aqueous solutionby diethylenetriamine-functionalized magnetic chitosanJinsheng Xu •Mansheng Chen •Chunhua Zhang •Zhengji YiReceived:16February 2013/Published online:12June 2013ÓAkade´miai Kiado ´,Budapest,Hungary 2013Abstract In this paper,the modiﬁed magnetic chitosan resin containing diethylenetriamine functional groups (DETA-MCS)was used for the adsorption of uranium ions from aqueous solutions.The inﬂuence of experimental conditions such as contact time,pH value and initial ura-nium(VI)concentration was studied.The Langmuir,Fre-undlich,Sips and Dubinin–Radushkevich equations were used to check the ﬁtting of adsorption data to the equilib-rium isotherm.The best ﬁt for U(VI)was obtained with the Sips model.Adsorption kinetics data were tested using pseudo-ﬁrst-order and pseudo-second-order models.Kinetic studies showed that the adsorption followed the pseudo-second-order kinetic model,indicating that the chemical adsorption was the rate-limiting step.The present results suggest that DETA-MCS is an adsorbent for the efﬁcient removal of uranium(VI)from aqueous solution.Keywords Uranium ÁAdsorption ÁDiethylenetriamine-functionalized magnetic chitosan (DETA-MCS)ÁIsothermIntroductionUranium is not only a main raw material for nuclear industry,but also a radioactivity element,which is one of metal ions such as cesium and strontium are highly toxic,causes progressive or irreversible renal injury and in acutecases may lead to kidney failure and death [1–5].For this reason,the recovery,accumulation,and removal of ura-nium are of great importance.Nowadays,recovery of uranium(VI)from dilute aqueous solution commonly includes coagulation,chromatographic extraction,chemi-cal precipitation,ion exchange,membrane dialysis,etc.[3,4],but they have several disadvantages,like clogging,high cost and ineffectiveness when uranium(VI)ions are present in the wastewater at low concentrations,especially in the range of 1–100mg/L [6,7].Therefore,the above methods have limitation in application.In recent years,much attention has been focused on various adsorbents with metal-binding capacities and low cost,such as chitosan,zeolites,clay or certain waste products [8].As well known,chitosan and its derivatives have great potential application in the areas of biotech-nology,biomedicine,food ingredients,and cosmetics.Furthermore,chitosans are the most important materials examined for the removal of toxic metal ions due to their inexpensive and effective in natures [9,10].Magnetic chitosan resins (MCR)have been widely used in various applications such as enzyme puriﬁcation,cell separation,and waste treatment [11,12].On the other hand,as we know,one of the promising methods is the use of chelating resins that have suitable functional groups capable of interaction with metal ions.And the number of chelate rings can increase the stability of complex formed by poly amine,furthermore,the diethylenetriamine can exhibit different kinds of coordination modes of interaction of the U(VI)ions by ﬁve-memberd chelating rings in order to increase the adsorption capacity.Based on the above dis-cussion,in this study,the diethylenetriamine-modiﬁed magnetic chitosan resins (DETA-MCS)were synthesized.It was expected that DETA-MCS should be efﬁcient for the removal of U(VI)ions,owing to the strong adsorptionJ.Xu (&)ÁM.Chen ÁC.Zhang ÁZ.YiDepartment of Chemistry and Material Sciences,KeyLaboratory of Functional Organometallic Materials of Hengyang Normal University,College of Hunan Province,Huangbai Road No.165,Hengyang 421008,Hunan,China e-mail:hynuxujs@J Radioanal Nucl Chem (2013)298:1375–1383DOI 10.1007/s10967-013-2571-2capacity for the target ions and quick separation from aqueous by the magnetism.The different factors affecting the uptake behavior such as pH,initial concentration of the U(VI)ions,and contact time were investigated.Moreover, the adsorption isotherms,kinetics and regeneration studies were also identiﬁed.Materials and methodsChitosan with40mesh,90%degree of deacetylation(DD) and molecular weight of1.39105,and diethylenetriamine were purchased from Shanghai Medicine Company.0.45l m polypropylene membrane(PPM)ﬁlter was pur-chased from Sinopharm Chemical Reagent Co.Ltd.(ori-ginal from Kenker Company,US).A stock solution of U(VI)(1,000mg/L)was prepared by dissolving U3O8in a mixture of HCl,H2O2and HNO3.The U3O8was provided by School of Nuclear Resources and Nuclear Fuel Engi-neering,University of South China.All working solutions of different U(VI)concentrations were obtained by diluting the stock solution with distilled and deionized water at room temperature.All other reagents and solvents used in this study were of analytical grade.Uranium adsorption experimentsBatch sorption experiments of U(VI)were conducted in a series of250mL conicalﬂasks.Generally speaking, 100mL U(VI)solution was mixed with a known amount of DETA-MCS powder.The pH of the U(VI)solution was adjusted as desired using1.0mol/L NaOH and1.0mol/L HCl before mixing with the adsorbent(20mg DETA-MCS powder).A sample of solution was collected at suitable time intervals andﬁltered through a0.45l m PPMﬁlter which does not adsorb uranyl cations.Then theﬁltrates were analyzed for U(VI)concentration in the supernatants using a standard method given by Xie et al.[13].The U(VI)removal efﬁciency and adsorption capacity of U(VI) onto the DETA-MCS were calculated using the following equations:removal efficiencyð%Þ¼C0ÀC fC0Â100ð1Þq e¼ðC0ÀC fÞVWð2Þwhere q e denotes the adsorption capacity of U(VI)onto the DETA-MCS(mg/g);C0and C f the concentrations of the U(VI)in the solution before and after adsorption(mg/L), respectively;V the volume of the aqueous solution(L);and W is the mass of dry adsorbent used(g).Results and discussionPreparation and characterizationThe magnetic chitosan microspheres(MCS)were prepared according to the literature[14].The MCS(10.0g)were suspended in120mL isopropyl alcohol to which10mL epichlorohydrine(125mmol)dissolved in200mL ace-tone/water mixture(1:1v/v)was added.The solid which is modiﬁed MCS with epichlorohydrine(MCS-ECH)was ﬁltered and washed by ethanol followed by water for three times.Then the MCS-ECH obtained were suspended in 200mL ethanol/water mixture(1:1v/v),then diethylene-triamine(10mL)was added.The reaction mixture was stirred at60°C for12h,and the solid products DETA-MCS wereﬁltered and successively washed with acetone, demineralized water,and methanol,and dried in a vacuum oven at60°C.The resins studied were synthesized as shown in Fig.1.Figure2shows the FTIR spectra of DETA-MCS and MCS,The peaks at560–660cm-1were assigned to Fe–O bond vibration of Fe3O4.The absorption band around 3,380cm-1,revealing the stretching vibration of N–H group and–OH group in magnetic chitosan,and at 1,588cm-1conﬁrms the N–H scissoring from the primary amine,due to the free amino groups in the cross-linked chitosan.But in DETA-MCS,the peak becomes broad because of the existence of–NH2.The increasing intensity at1,667and1,082cm-1in the spectrum of DETA-MCS indicates that DETA-MCS has more amine groups than the unmodiﬁed magnetic chitosan(MCS).Effect of contact timeSince the contact time between the adsorbate and adsorbent is a key parameter for the adsorption process,the contact time required for the sorption equilibrium experiments was ﬁrst determined.Under the conditions of50mL solution contain20mg adsorbent amount,pH 3.5,298K and 50mg/L U(VI),the adsorption experiments were carried out for contact times ranging from20to180min.The results are shown in Fig.3.The sorption capacity increased with increasing contact time and a larger amount of ura-nium was removed by DETA-MCS in theﬁrst60min of contact time.Then the U(VI)sorption process proceeded slowly and reached saturation levels gradually at about 120min.After120min,the change of adsorption capaci-ties for U(VI)did not show notable effects.In our study,a contact time of120min was selected to guarantee an optimum U(VI)uptake.Effect of initial pH valuesIt is known that the medium pH has an inﬂuence upon the uranium sorption process because it controls the solubility of metals as well as the dissociation state of some func-tional groups,such as carboxyl,hydroxyl and amino on the adsorbent surface [15–17].In order to search for the opti-mum pH for the adsorption process as well as to ﬁnd out whether the DETA-MCS was able to show a good U(VI)uptake at extreme pH values,metal uptake was studied at pH ranging from 1.0to 6.0.The dependence of adsorption percentage of U(VI)ions on the pH of solution was given in Fig.4.The adsorption percentage of the U(VI)ions adsorbed on the DETA-MCS indicated a marked inﬂuencewith increasing pH of solution from 1.0to 3.5then started to decrease slightly with further increase in the pH of solution after reaching a maximum of 96.1%at pH 3.5.In strong acidic solutions (pH \3.5),more protons will be available to protonate amine groups to form groups –NH 3?,reducing the number of binding sites for the adsorption of UO 22?,therefore,the removal efﬁciency of uranium is lower in strong acidic solutions (pH \3.5).However,the availability of free U(VI)ions is maximum at pH 3.5and hence maximum adsorption,when pH value increase beyond 3.5,hydrolysis precipitation starts because of the formation of complexes in aqueous solution [18].The hydrolysis of uranyl ions play signiﬁcant role in deter-mining the equilibrium between U(VI)in solution and on adsorbent.Hydrolysis products occur,includingUO 2(OH)?,(UO 2)2(OH)22?,(UO 2)3(OH)53?,which results in decline of adsorption removal efﬁciency of U(VI),similar results were also observed [19].The hydrolysis equilibria are as follows:UO 2þ2þ2H 2O UO 2ðOH ÞþþH 3O þpK 1¼5:82UO 2þ2þ4H 2O ðUO 2Þ2ðOH Þ2þ2þ2H 3O þpK 2¼5:623UO 2þ2þ10H 2O ðUO 2Þ3ðOH Þþ5þ5H 3OþpK 3¼15:63where pKs are the logarithms of the equilibrium constants.When the pH becomes low enough,the divalent free UO 22?becomes the dominant ion form in the solution.Along with increasing pH,the percentage of UO 22?in the solution decreases,whereas the percentage oftheFig.1Scheme for the synthesis ofDETA-MCSFig.2FT-IR spectra MCS andDETA-MCSFig.3Effect of contact time on the adsorption of uranium (VI)([UO 22?]=50mg/L,DETA-MCS =20mg,pH =3.5,and T =298K)Fig.4Effect of initial pH on the adsorption of uranium (VI)([UO 22?]=50mg/L,DETA-MCS =20mg,and T =298K)monovalent hydrolyzed species,UO 2(OH)?,(UO 2)3(OH)5?,increases.At higher pH [5.5,dissolved solid schoepite (4UO 3Á9H 2O)exist in the solution.In view of the above result,all subsequent experiments were performed at pH 3.5.Effect of initial uranium(VI)concentrationThe percentage removal and adsorption capacity of U(VI)by contacting a ﬁxed mass of DETA-MCS (20mg)at the temperature (298K)and initial pH (3.5)using a range of initial U(VI)concentrations were shown in Fig.5.It was found that the adsorption removal efﬁciency of U(VI)decreased with increasing the initial U(VI)concentration in the aqueous solution.On one hand,this is because more mass of uranium is put into the system with increasing the initial U(VI)concentration in the aqueous solution.On the other hand,because of the higher mobility of uranyl ions (UO 2)2?in the diluted solutions,the interaction of this ion with the adsorbent also increases slowly.All in all,the adsorption capacity of DETA-MCS for uranium increased with increase in the initial uranium concentration.Similar results on the inﬂuence of the U(VI)biosorption has beenreported by Ku¨tahyal ıet al.[20]in their study using acti-vated carbon prepared from charcoal by chemical activation.Adsorption isothermThe adsorption isotherm is the most important information,which indicates how the adsorbent molecules distribute between the liquid and the solid phase when the adsorption process reaches an equilibrium state [21].The parameters of Langmuir,Freundlich,Sips and Dubinin–Radushkevich(D–R)models obtained are given in Table 1.In the research,the sorption data have been subjected to different sorption isotherms,namely the Langmuir,Freundlich,Sips and D–R isotherm models.Figure 6shows the adsorption isotherm of uranium(VI)on the DETA-modiﬁed MCR from the non-linear models.The Langmuir equation assumes that:(i)the solid surface presents a ﬁnite number of identical sites which are energetically uniform;(ii)there is no interactions between adsorbed species,meaning that the amount adsorbed has no inﬂuence on the rate of adsorption and (iii)a monolayer is formed when the solid surface reaches saturation.The Langmuir isotherm con-siders the adsorbent surface as homogeneous with identical sites in terms of energy.Equation (3)represents the Langmuir isotherm:q e ¼q m K L C e 1þK L C eð3Þwhere C e is the concentration of the adsorbate in solution at equilibrium (mg/g),q e is the adsorption capacity at equilibrium (mg/g),q m is the maximum adsorption capacity of the adsorbent (mg/g),and K L is the Langmuir adsorption constant related to the energy of adsorption (L/mg).The empirical Freundlich equation based on adsorption on a heterogeneous surface is given as follows:q e ¼K F C 1=neð4Þwhere q e denotes the equilibrium adsorption capacity (mg/g);C e the residual U(VI)concentration in the solution at equilibrium (mg/g);K F the Freundlich constant related to the adsorption capacity of sorbent (mg/g);n the Freundlich exponent related to adsorption intensity.To resolve the problem of continuing increase in the adsorbed amount with a rising concentration as observed for Freundlich model (Fig.6),an expression was proposed as Sips isotherm model [22,23],which is a combined form of Langmuir and Freundlich expressions deduced for predict-ing the heterogeneous adsorption systems.It is given as:q e ¼q s K s C 1=me1þK s C 1=með5Þwhere q s (mg/g)is the Sips maximum uptake of U(VI)per unit mass of DETA-MCS,K S (L/mg)is Sips constant related to energy of adsorption,and parameter m could be regarded as the Sips parameter characterizing the system heterogeneity.Figure 6shows the equilibrium adsorption of U(VI)ions onto the DETA-MCS and the ﬁtting plot of the three iso-therm models.For the studied system,the Sips isotherm correlates best (R =0.998)with the experimental data from adsorption equilibrium of U(VI)ions by DETA-MCS in these models.The phenomenon also suggeststheFig.5Effect of initial concentration on the adsorption of ura-nium(VI)(DETA-MCS =20mg,pH =3.5,and T =298K)heterogeneity of the adsorption,which may be attributed to the complicated form of U(VI)ions at the acid pH regions and the heterogeneous distribution of the active sites on DETA-MCS surface.The maximum adsorption capacity of DETA-MCS for U(VI)ions obtained by Sips isotherm model is 69.68mg/g.Dubinin–Radushkevich isotherm is more general than the Langmuir isotherm because it does not assume a homogeneous surface or constant sorption potential [24].Therefore,in this paper,the D–R isotherm is also used to analyze the experimental isotherm data.The linearized form of the D–R isotherm may be written as:ln C ads ¼ln q m ÀKE 2ð6Þwhere C ads is the amount of metal ions adsorbed on per unit weight of adsorbent,q m is the maximum sorption capacity and K is the activity coefﬁcient related to the mean adsorption energy and E is the Polanyi potential which is equal to:E ¼RT ln ð1þ1=C e Þð7ÞThe values of q m and K deduced by plotting ln C ads versus E 2(Fig.7),and the mean energy of adsorption (E )was calculated from the equation,according to the D–R isotherm,as:E ¼1=ðÀ2K Þ1=2ð8ÞThe plot of ln C ads versus E 2as shown in Fig.7is a straight line.From the slope and intercept of this plot the values of K =-5.9983910-9mol 2/kJ 2and q m =70.52mg U(VI)/g have been estimated.As we know,the adsorption value of the mean sorption energy is in the range of 1–8kJ/mol and in that of 9–16kJ/mol predicted the physical adsorption and the chemical adsorption,respectively [25].The value of E is calculated to be E =9.13kJ/mol and evaluated in the range of 9–16kJ/mol for composite adsorbent.The value of E is expected for chemical adsorption.It is assumed to be heterogeneous in the structure of composite.The results of linearized equations are shown in Table 1,the Langmuir model effectively described the sorption data with all R values [0.99.The adsorption isotherms of U(VI)ions exhibit Langmuir behavior which indicates a mono-layer paring the four isotherm models described above,Sips isotherm is most suitable to char-acterize the uranium-sorption behavior of DETA-MCS according to the values of R .Adsorption kineticsIn order to investigate the kinetic mechanism,which con-trols the adsorption process,the pseudo-ﬁrst-order andTable 1Isotherm constants and values of R for DETA-MCS ParameterValue R Langmuir isotherm q m (mg/g)65.160.991K L (L/mg)1.24Freundlich isotherm K F (mg/g)36.350.898n3.36Sips isotherm q s (mg/g)69.680.998Ks (L/mg) 1.27m2.74Dubinin–Radushkevich (D–R)isotherm K (mol 2/kJ 2)-5.998391090.955q m (mg/g)70.52Eads (kJ/mol)9.13Fig.6Plots of q e versus C e for the adsorption of uranium(VI)on DETA-MCS (DETA-MCS =20mg,pH =3.5,and T =298K)Fig.7Dubinin–Radushkevich isotherm of sorption U(VI)onto DETA-MCS adsorbentpseudo-second-order models were used to test the experi-ment data [26,27].The pseudo-ﬁrst-order kinetic model is given as:ln ðq e Àq t Þ¼ln q e Àk 1tð9Þwhere q e is the amounts of adsorbed metal per unit mass (mg/g)at equilibrium and k 1is the rate constant of pseudo ﬁrst-order sorption (min -1).The value of the rate constant k 1and q e for the pseudo-ﬁrst-order sorption reaction can be obtained by plotting ln (q e -q t )versus t as well as further linear regression analysis (Fig.8).A series of parameters,including kinetic constants,correlation coefﬁcients and q e values,were obtained via linear regression analysis and shown in Table 2.The calculated q e value of ﬁrst-order kinetic model (54.35mg/L)cannot give reasonable values,which was lower greater than experimental value Q exp (62.75mg/L).Hence,this equation cannot provide an accurate ﬁt of the experimental data.The pseudo-second order kinetic model deﬁnes that the rate controlling mechanism formed by chemical reaction for the sorption of metal ions on adsorbents [28–31].In order to describe U(VI)sorption on the DETA-MCS resin for the initial U(VI)concentrations at constant temperature (298K),the kinetic data obtained from batch adsorption experiments have been analyzed using the pseudo-second order kinetic equation given below.t q t ¼t q e þ1k 2q eð10Þwhere k 2is the rate constant of pseudo-second-order adsorption (g/mg min).The pseudo-second-order plot (Fig.9)is also linear with correlation coefﬁcient of 0.994(Table 2),however the calculated value of adsorption capacity,q e ,cal (61.33mg/g)is close to the value of experimental adsorption capacity,q e,exp (62.75mg/g).Therefore,the pseudo-second-order rate kinetic model best described the experimental data.In other words,U(VI)sorption by DETA-MCS followed the pseudo-second-order kinetic reaction.The goodness of the ﬁt to the pseudo-second-order kinetic model indicates that U(VI)adsorption on the DETA-MCS resin occurred by chemical adsorption [32].Comparison of U(VI)sorption capacity with other adsorbentsTo evaluate the potential application prospect of DETA-MCS,the prepared magnetic adsorbent can be well dis-persed in the water and can be easily separated magneti-cally from the medium after adsorption.These unique features present this adsorbent as a novel,promising and feasible alternative for uranium removal as compared with other adsorbents [33–45](Table 3).This paper emphasizes the material of DETA-MCS as a novel adsorbent in envi-ronmental remediation.Although a direct comparison of DETA-MCS with other adsorbents is very difﬁcultowingFig.8Pseudo-ﬁrst-order kinetics of uranium(VI)adsorption on DETA-MCS ([UO 22?]=50mg/L,DETA-MCS =20mg,pH =3.5,and T =298K)Table 2Kinetic parameters of uranium(VI)adsorbed onto DETA-MCSPseudo-ﬁrst-order Pseudo-second-orderExperimental Q e valuek 1(min -1)Q e 1(mg/g)R k 2(g/(mg min))Q e 2(mg/g)R Q exp (mg/g)0.0326554.350.9490.004461.330.99462.75Fig.9Pseudo-second-order kinetics of uranium(VI)adsorption on DETA-MCS ([UO 22?]=50mg/L,DETA-MCS =20mg,pH =3.5,and T =298K)to different experimental conditions adopted,it is con-cluded that U(VI)sorption capacity of DETA-MCS is higher than that of chitosan grafted MWCNTs,magnetic Fe3O4@SiO2and Fe3O4/GO,but lower than that of ion-imprinted MCR.The lower uptake values observed may be attributed to the increased extent of protonation of amino groups in the acidic solution.All in all,it is noteworthy that DETA-MCS-bound U(VI)can be favorably and quickly separated from a solution by using the external magnetic ﬁeld and it is a prospective adsorbent for application in the ﬁeld of U(VI)removal.Resins regenerationTo make the process more effective and economically feasible,sorbent regeneration and U(VI)recovery must be evaluated.Regeneration of the DETA-MCS resins was carried out using0.5M HNO3.Adsorption/desorption cycles were carried out repeatedly.The regeneration efﬁ-ciency was calculated using equation[46,47].Regeneration efficiencyð%)¼Uptake of UðVIÞin the second cycleUptake of UðVIÞin the first cycleÂ100ð11ÞRegeneration efﬁciency of94.4%was achieved for DETA-MCS over three cycles with a standard deviation of ±1.1%.On the other hand,the DETA-MCS after being used for three cycles could still be aggregated very fast from the solution by a3,000G magnet.This higher regeneration efﬁciency along with easy separation from adsorption medium using external magneticﬁeld indicate promising application in theﬁeld of U(VI)removal.ConclusionsThe U(VI)adsorption capacity by DETA-MCS was strongly dependent on contact time,pH,and initial ura-nium(VI)concentration.The adsorption capacity of U(VI) onto DETA-MCS increases with an increase of contact time and reaches adsorption equilibrium within120min, the adsorption removal efﬁciency increased with increasing pH to a maximum value(pH3.5)and then declines slowly with further increase in pH.Four adsorption models were used for the mathematical description of the adsorption equilibrium.It is found that the equilibrium isotherm data wereﬁtted well by Sips isotherm and pseudo-second-order equation.In summary,DETA-MCS could be used as an effective adsorbent for U(VI)removal from aqueous solution.The resins loaded by U(VI)are easily regenerated for repeated use using HNO3.Acknowledgments This study was supported by the Key Project of Science and Technology Plan of Hunan Province(No.2012FJ2002), the Innovation Platform Open fund of Hunan Provincial Education Department(No.11K009),the Hunan Provincial Natural Science Foundation of China(No.13JJ6069)and the Hunan Provincial Key Discipline Construction.References1.Mellah A,Chegrouche S,Barkat M(2006)The removal of ura-nium(VI)from aqueous solutions onto activated carbon:kinetic and thermodynamic investigations.J Colloid Interface Sci 296:434–4412.Anirudhan TS,Bringle CD,Rijith S(2010)Removal of ura-nium(VI)from aqueous solutions and nuclear industry efﬂuents using humic acid-immobilized zirconium-pillared clay.J Environ Radioact101:267–2763.Donia AM,Atia AA,Moussa EMM,El-Sherif AM,Abd El-Magied MO(2009)Removal of uranium(VI)from aqueous solutions using glycidyl methacrylate chelating resins.Hydro-metallurgy95:183–1894.Kulkarni PS,Mukhopadhyay S,Bellary MP,Ghosh SK(2002)Studies on membrane stability and recovery of uranium(VI)fromTable3Reported values of adsorption capacities of U(VI)by dif-ferent adsorbentsAdsorbents Adsorptioncapacity(mg/g)ReferencesChitosan22.3[33] Cross-linked chitosan with citric acid191[33] Cross-linked chitosan withepichlorohydrin49.05[32] Chitosan/amine resin493.2[12] Chitosan-tripolyphosphate236.9[34] Chitosan grafted MWCNTs39.2[35]Ion-imprinted magnetic chitosanresins(IMCR)187.26[36]Non-imprinted magnetic chitosanresins160.77[36]Magnetic chitosan grafted withSaccharomyces Cerevisiae72.4[37] Magnetic chitosan42[38] Glycidyl methacrylate(GMA)withdivinylbenzene/magnetite460.3[3]Ion-imprinted cross-linked chitosanHQ-type(IIC-HQ-CTS)218[39]Attapulgite/iron oxide magnetic(ATP/IOM)8.31[40] Magnetic Schiff base94.30[41] Magnetic Fe3O4@SiO252.36[42] Ethylenediamine-modiﬁed magneticchitosan82.83[43]Fe3O4/GO69.49[44] Magnetite nanoparticles5[45]aqueous solutions using a liquid emulsion membrane process.Hydrometallurgy64:49–585.Wang JS,Hu XJ,Liu YG,Xie SB,Bao ZL(2010)Biosorption ofuranium(VI)by immobilized Aspergillus fumigatus beads.J Environ Radioact101:504–5086.Sangi MR,Shahmoradi A,Zolgharnein J,Azimi GH,Ghorban-doost M(2008)Removal and recovery of heavy metals from aqueous solution using Ulmus carpinifolia and Fraxinus excelsior tree leaves.J Hazard Mater155:513–5227.Xie SB,Yang J,Chen C,Zhang XJ,Wang QL,Zhang C(2008)Study on biosorption kinetics and thermodynamics of uranium by Citrobacter freudii.J Environ Radioact99:126–1338.Babel S,Kurniawan TA(2003)Low-cost adsorbents for heavymetals uptake from contaminated water:a review.J Hazard Mater 97:219–2439.Merriﬁeld JD,Davids WG,MacRae JD,Amirbahman A(2004)Uptake of mercury by thiol-grafted chitosan gel beads.Water Res 38:3132–313810.Wan Ngah WS,Kamari A,Koay YJ(2004)Equilibrium andkinetics studies of adsorption of copper(II)on chitosan and chitosan/PVA beads.Int J Biol Macromol34:155–16111.Justi KC,Favere VT,Laranjeira MC,Neves A,Peralta RA(2005)Kinetics and equilibrium adsorption of Cu(II),Cd(II),and Ni(II) ions by chitosan functionalized with2[bis-(pyridylmethyl)ami-nomethyl]-4-methyl-6-formylphenol.J Colloid Interface Sci 291:369–37412.Atia AA(2005)Studies on the interaction of mercury(II)and ura-nyl(II)with modiﬁed chitosan resins.Hydrometallurgy80:13–22 13.Xie SB,Zhang C,Zhou XH,Yang J,Zhang XJ,Wang JS(2009)Removal of uranium(VI)from aqueous solution by adsorption of hematite.J Environ Radioact100:162–16614.Zhou LM,Wang YP,Liu ZR,Huang QW(2009)Characteristicsof equilibrium,kinetics studies for adsorption of Hg(II),Cu(II), and Ni(II)ions by thiourea-modiﬁed magnetic chitosan micro-spheres.J Hazard Mater161:995–100215.O¨zerog˘lu C,Kece˛li G(2011)Investigation of Cs(I)adsorption ondensely crosslinked poly(sodium methacrylate)from aqueous solutions.J Radioanal Nucl Chem289:577–58616.O¨zerog˘lu C,Kece˛li G(2009)Kinetic and thermodynamic studieson the adsorption of U(VI)ions on densely crosslinked poly(methacrylic acid)from aqueous solutions.Radiochim Acta 97:709–71717.Venkatesan KA,Shymala KV,Antony MP,Srinivasan TG,RaoPRV(2008)Batch and dynamic extraction of uranium(VI)from nitric acid medium by commercial phosphinic acid resin,Tulsion CH-96.J Radioanal Nucl Chem275:563–57018.Li WC,Victor DM,Chakrabarti CL(1980)Effect of pH anduranium concentration on interaction of uranium(VI)and ura-nium(IV)with organic ligands in aqueous solutions.Anal Chem 52:520–53419.Parab H,Joshi S,Shenoy N,Verma R,Lali A,Sudersanan M(2005)Uranium removal from aqueous solution by coir pith: equilibrium and kinetic studies.Bioresour Technol96:1241–1248 20.Ku¨tahyalıC,Eral M(2004)Selective adsorption of uranium fromaqueous solutions using activated carbon prepared from charcoal by chemical activation.Sep Purif Technol40:109–11421.Hasan M,Ahmad AL,Hameed BH(2008)Adsorption of reactivedye onto crosslinked chitosan/oil palm ash composite beads.Chem Eng J136:164–17222.Ncibi MC(2008)Applicability of some statistical tools to predictoptimum adsorption isotherm after linear and non-linear regres-sion analysis.J Hazard Mater153:207–21223.Foo KY,Hameed BH(2010)Insights into the modeling ofadsorption isotherm systems.Chem Eng J156:2–1024.Oguz E(2005)Thermodynamic and kinetic investigations ofPO43-adsorption on blast furnace slag.J Colloid Interface Sci 28:62–6725.Saeed MM(2003)Adsorption proﬁle and thermodynamicparameters of the preconcentration of Eu(III)on2-thenoyltri-ﬂuoroacetone loaded polyurethane(PUR)foam.J Radioanal Nucl Chem256:73–8026.Chiou MS,Li HY(2002)Equilibrium and kinetic modeling ofadsorption of reactive dye on cross-linked chitosan beads.J Hazard Mater93:233–24827.Ho S,Mckay G(1999)Pseudo-second order model for sorptionprocess.Process Biochem34:451–46528.Ho YS,McKay G(2002)Application of kinetic models on thesorption of copper(II)on to peat.Adsorpt Sci Technol20: 797–81529.Liu Y,Liu Y,Cao X,Hua R,Wang Y,Pang C,Hua M,Li X(2011)Biosorption study of uranium(VI)on crosslinked chitosan: isotherm,kinetic and thermodynamic aspects.J Radioanal Nucl Chem290:231–23930.Wu FC,Tseng RL,Juang RS(2001)Enhanced abilities of highlyswollen chitosan beads for color removal and tyrosinase immo-bilization.J Hazard Mater81:166–17731.Ho YS(2004)Citation review of Lagergren kinetic rate equationon adsorption reactions.Scientometrics59:171–17732.Wang GH,Liu JS,Wang XG,Xie ZY,Deng NS(2009)Adsorption of uranium(VI)from aqueous solution onto cross-linked chitosan.J Hazard Mater168:1053–105833.Suc NV,Yeu Ly HT(2011)Adsorption of U(VI)from aqueoussolution onto modiﬁed chitosan.Int J ChemTech Res3: 1993–200234.Sureshkumara MK,Dasb D,Malliac MB,Gupta PC(2009)Adsorption of uranium from aqueous solution using chitosan-tripolyphosphate(CTPP)beads.J Hazard Mater184:65–72 35.Shao DD,Hu J,Wang XK(2010)Plasma induced graftingmultiwalled carbon nanotube with chitosan and its application for removal of UO22?,Cu2?,and Pb2?from aqueous solutions.Plasma Process Polym7:977–98536.Zhou LM,Shang C,Liu ZR,Huang GL,Adesina AA(2012)Selective adsorption of uranium(VI)from aqueous solutions using the ion-imprinted magnetic chitosan resins.J Colloid Interface Sci366:165–17237.Saifuddin N,Sultanbayeva D(2012)Immobilization of Saccha-romyces cerevisiae onto cross-linked chitosan coated with mag-netic nanoparticles for adsorption of uranium(VI)ions.Adv Nat Appl Sci6:249–26738.Stopa LCB,Yamaura M(2010)Uranium removal by chitosanimpregnated with magnetite nanoparticles:adsorption and desorption.Int J Nucl Energy Sci Technol5:283–28939.Liu YH,Cao XH,Le ZG,Luo MB,Xu WY,Huang GL(2010)Pre-concentration and determination of trace uranium(VI)in environments using ion-imprinted chitosan resin via solid phase extraction.J Braz Chem Soc21:533–54040.Fan QH,Li P,Chen YF,Wu WS(2011)Preparation and appli-cation of attapulgite/iron oxide magnetic composites for the removal of U(VI)from aqueous solution.J Hazard Mater 192:1851–185941.Zhang XF,Jiao CS,Wang J,Liu Q,Li RM,Yang PP,Zhang ML(2012)Removal of uranium(VI)from aqueous solutions by magnetic Schiff base:kinetic and thermodynamic investigation.Chem Eng J198–199:412–41942.Fan FL,Qin Z,Bai J,Rong WD,Fan FY,Tian W,Wu XL,ZhaoL(2012)Rapid removal of uranium from aqueous solutions using magnetic Fe3O4@SiO2composite particles.J Environ Radioact 106:40–46。

尿素在ZnO_1010_表面的吸附

[Article]物理化学学报(Wuli Huaxue Xuebao )Acta Phys.-Chim.Sin .,2010,26(5)：1373-1377May Received:October 19,2009;Revised:February 5,2010;Published on Web:March 19,2010.*Corresponding authors.Email:weiwei@,yhsun@;Tel:+86-351-4053801.The project was supported by the Key Technology R&D Program for 11th Five -Year Plan,China (07ZCU11691)and the Key Project of Knowledge Innovation Program of Chinese Academy of Sciences (08YCA21691).“十一五”国家科技支撑计划重大项目(07ZCU11691)和中国科学院知识创新重要方向性项目(08YCA21691)资助鬁Editorial office of Acta Physico -Chimica Sinica尿素在ZnO(101軈0)表面的吸附唐文东1,2高阳艳1,2魏伟1,*孙予罕1,3,*(1中国科学院山西煤炭化学研究所,太原030001;2中国科学院研究生院,北京100049;3中国科学院上海高等研究院低碳能源研究中心,上海201203)摘要：运用VASP(Vienna ab -initio simulation package),采用基于密度泛函理论(DFT)的第一原理计算,研究了尿素在ZnO(101軈0)表面的吸附行为.计算结果表明:尿素分子在ZnO(101軈0)表面主要发生分子吸附,稳定的吸附产物通过尿素分子中的氮原子或氧原子与表面锌原子之间的键合作用而形成,吸附能分别为-1.48和-1.41eV;表面吸附的尿素分子也可以发生解离,生成表面吸附的异氰酸根、氨气和一个表面羟基,吸附能为-1.66eV.关键词：吸附;尿素;ZnO;碳酸二甲酯;VASP 中图分类号：O641Adsorption of Urea onto a ZnO(101軈0)Surface TANG Wen -Dong 1,2GAO Yang -Yan 1,2WEI Wei 1,*SUN Yu -Han 1,3,*(1Institute of Coal Chemistry,Chinese Academy of Sciences,Taiyuan 030001,P.R.China ;2Graduate University ofChinese Academy of Sciences,Beijing 100049,P.R.China ;3Low Carbon Energy Center,Shanghai AdvancedResearch Institute,Chinese Academy of Sciences,Shanghai 201203,P.R.China )Abstract ：First -principles calculations based on density functional theory (DFT)were used to investigate theadsorption of urea onto a nonpolar ZnO(101軈0)surface with the VASP (Vienna ab -initio simulation package)code.The calculation results indicated that urea was favorably adsorbed onto the ZnO(101軈0)surface molecularly,and that stable adsorption products were formed through the reaction between nitrogen atom or oxygen atom from urea and zinc atom on the surface.The adsorption energy was -1.48and -1.41eV,respectively.The adsorbed urea can dissociate to form an isocyanic radical,an ammonia molecule,and a surface hydroxyl,all of which adsorb onto the surface.The adsorption energy was -1.66eV.Key Words ：Adsorption;Urea;ZnO;Dimethyl carbonate;VASP近年来,人们为了克服合成碳酸二甲酯传统工艺的缺点,如有毒性、易爆炸性、反应工艺复杂和低转化率等,发展了一种满足“绿色化学”要求[1]的新型合成方法,即以尿素和甲醇为原料合成碳酸二甲酯[2-5](图1).为了提高反应的转化率,人们研究了包括碱、有机锡化合物、金属氧化物、含锌化合物在内的一系列催化剂[2,6-15],结果表明,在这一系列催化剂中,ZnO 由于其低毒性,高催化活性和易于分离的优点而被认为是最具潜力的催化剂[2,16].为了对该尿素甲醇化反应有一个清晰的认识,人们设计了许多实验来研究反应的机理,并且提出了几种机理模型[2,17-18].Wang 等[2]认为,ZnO 对第二步反应具有很高的活性,并且把这种高活性归因于氧化锌的酸碱性质.祁增忠等[17]则认为,在反应过程中,首先是氧化锌吸附甲醇,吸附的甲醇再与尿素作用生成中间产物氨基甲1373Acta Phys.-Chim.Sin.,2010Vol.26酸甲酯,该中间产物再和另一分子的甲醇反应生成终产物碳酸二甲酯.Zhao 等[18]则做了更进一步的研究:他们比较了分别从尿素和氨基甲酸甲酯为原料合成碳酸二甲酯的醇解反应,发现氧化锌对第二条路线即氨基甲酸甲酯和甲醇合成碳酸二甲酯几乎没有催化活性,而它却是第一条路线的决速步骤.因此,他们认为氧化锌只是催化剂的前驱体,真正的催化剂是由氧化锌转变成的另外一种物质.通过对该物质的提取和表征,他们建议该物质的化学式为Zn(NH 3)2(NCO)2,该物质通过三步过程生成:尿素首先分解成HNCO 和NH 3,接着HNCO 和ZnO 作用生成Zn(NCO)2,该物质再和NH 3通过配合作用生成Zn(NH 3)2(NCO)2.然而整个反应的机理仍然没有搞清楚.要认识非均相反应的机理,首先要认识非均相催化剂在反应过程中的催化行为,而考察反应分子在催化剂表面的吸附则是第一步.对于我们的反应体系,反应物为尿素和甲醇,催化剂为氧化锌,由于Raj 等[19]对甲醇在氧化锌表面的吸附行为已做了相关研究,因此本文工作主要研究尿素在氧化锌表面的吸附行为.这对认识整个反应过程的反应机理具有很重要的意义.本文中我们只研究了尿素在ZnO(101軈0)表面的吸附行为.这是因为在室温下纤维锌矿(wurtzite)结构的氧化锌是最稳定的[20],它包含大量的低米勒指数的表面[21],其中,四个低指数表面是该形态的氧化锌的特征表面:即非极性表面(101軈0)和(112軈0)表面,极性表面(0001)-Zn 和(0001)-O 表面[22].非极性表面(101軈0)和(1120)表面是主要的,大约占粉末中所有表面的80%[23],而且(1010)表面的表面能比(112軈0)表面的表面能小0.1J ·m -2[22],即表明(1010)表面比(112軈0)表面更稳定.所以在本文中我们只研究了尿素在ZnO(101軈0)表面的吸附行为,在下一步工作中我们将研究更普遍的情况.1计算方法和模型本文中的所有计算都是通过VASP(Vienna ab -initio simulation package)[24]完成的.采用由Bl 觟chl [25],Kresse 和Joubert [26]发展的缀加投影波函数(PAW)方法来描述电子-离子的相互作用(electron-ion inter -actions),交换相关能采用广义梯度函数(GGA)PW91[27]进行计算,紧束缚芯电子采用PAW -GGA 赝势进行描述.所有计算中平面波截断能(plane -wave basis cutoff energy)和布里渊区k 点分别设置为350eV 和2×2×1,除了在模拟尿素时采用了5×5×5的布里渊区k 点设置.经过结构优化的氧化锌元胞的晶格参数为a =b =0.32493nm,c =0.52054nm,该结果和Sawada 等[28]的实验值,a =b =0.32490nm,c =0.52052nm,非常吻合.表1中还列出了其他一些理论计算结果[29-32],均表明我们的结果与实验值符合得比较好.对于ZnO(101軈0)表面,我们采用一个(3×2)的超晶胞来模拟.该超晶胞包含6个原子层和一个1.5nm 的真空层.在对ZnO(101軈0)表面进行结构优化的过程中,我们固定了模型中的下面四个原子层,只对表面的两个原子层进行了结构弛豫.计算结果表明,经过弛豫后,表面的Zn —O 键均有所变短(Zn 1—O 1键从0.1988nm 缩短为0.1867nm,Zn 2—O 1键从0.1974nm 缩短为0.1931nm,其中Zn 1,Zn 2和O 1分别代表第一层的锌原子,第二层的锌原子和第一层的氧原子),该计算结果和Cooke 等[32]的研究结果相符合;表面能为1.063J ·m -2,该结果与Nyberg 等[33](1.1J ·m -2)和Wander 等[34](1.16J ·m -2)的结果符合得很好.ZnO(101軈0)表面的起始构型和优化构型见图2.2结果与讨论尿素可以在ZnO(101軈0)表面发生分子吸附和解离吸附.我们首先设计了尿素分子在氧化锌表面发生分子吸附的可能构型,进行结构优化以确定最稳定的分子吸附模型,然后再以最稳定的分子吸附模(1)(2)图1尿素和甲醇合成碳酸二甲酯的反应方程式Fig.1Reactions of dimethyl carbonate (DMC)synthesis from urea and methanol表1ZnO 元胞的晶格参数Table 1Crystal lattice parameters of ZnO unit cella =ba /nmc /nm X -ray [28]0.324900.52052present work 0.324930.52054Ref.[29]0.32530.5207Ref.[30]0.32710.5138Ref.[31]0.3200.5152Ref.[32]0.319590.515851374No.5唐文东等：尿素在ZnO(1010)表面的吸附型出发,进一步研究解离吸附.本文中我们只计算了各种可能吸附构型的吸附能,以此来确定最稳定的吸附构型,并且期望能从中得到一些关于催化行为的信息.所有的吸附能由以下公式计算所得:E ads=E urea/slab-E urea-E slab其中,Eurea/slab 表示吸附复合物的总能,Eurea表示尿素分子的总能,Eslab则表示ZnO(1010)表面所在的超晶胞的总能.Eads为负值时就表明该吸附是一放热过程.2.1分子吸附所有可能的分子吸附构型的优化结构和其相应的吸附能列于图3中.计算结果表明,尿素分子不能通过其氢原子和ZnO(1010)表面的氧原子发生键合作用，而是倾向于通过氢原子和表面氧原子之间的氢键作用而发生吸附.在这两种构型中,尿素分子的结构几乎和未发生吸附分子的结构相同,除了形成氢键的氢原子所在的N—H键有所增长;两个氢键的形成使构型2比构型1更稳定,因为它具有更大的吸附能(构型2的为-0.53eV,构型1的为-0.43eV,图3).计算结果指出,尿素分子倾向于通过其氮原子和表面的锌原子发生键合作用而形成相对比较稳定的吸附复合物(图3,构型3和4).在这两种吸附构型中,和表面锌原子发生作用的氮原子所在的C—图2ZnO(1010)表面的超晶胞模型Fig.2Supercell models of the ZnO(1010)surface(a)unrelaxed surface structure,(b)relaxed surface structure;The numbers1to6in Fig.1(a)represent the atomic layers1to6,respectively.bond length in nm图3尿素在ZnO(1010)表面发生分子吸附的优化构型及其相应的吸附能Fig.3Optimized structures and adsorption energies of the molecular adsorption modes ofurea on the ZnO(1010)surfaceWe used the top two layers of the ZnO(1010)supercell for short.bond length in nm1375Acta Phys.-Chim.Sin.,2010Vol.26N键变长,C襒O键变短;构型3新形成两个N—Zn键和两个氢键;构型4中则只形成一个N—Zn和一个氢键.吸附的发生也使表面结构发生了变化,在这两种构型中,表面的O1—Zn1和O2—Zn1键都有明显的增长(此处的Zn1原子是表示和氮原子相连接的锌原子),使得表面的锌原子有从表面离开的趋势.构型3中两个N—Zn键和两个氢键的形成使其比构型4更稳定,二者的吸附能分别为-1.48和-0.85eV.另一种比较稳定的吸附构型是尿素分子通过其羰基中的氧原子和表面锌原子发生键合作用的情况.O—Zn键的生成减弱了C襒O键的作用,C襒O键键长变长;两个氢键的形成也减弱相应的N—H键的作用,键长变长;表面结构也因吸附作用的发生而发生改变,表面的O1—Zn1和O2—Zn1都有所增长.在该构型中,由于分子和表面之间形成了一个O—Zn键和两个氢键,使得该吸附构型也相对比较稳定,吸附能高达-1.41eV.从我们的计算结果来看,所有的分子吸附过程都是放热反应.这表明,它们都是热力学上有利的吸附构型,吸附能绝对值越大,其相应的吸附复合物就越稳定.因此,这些吸附复合物的稳定性和被吸附的机会具有相同的顺序:即3＞5＞4＞2＞1.如果把吸附能作为产率的粗略近似,根据吸附能Eads之间较大的差异,通过假设平衡的粗略估算可以得知,在ZnO(101軈0)表面上,吸附复合物1、2和4几乎不会存在,而吸附复合物3和5则是最多的.这就意味着在整个分子吸附过程中,吸附复合物3和5是主要的分子吸附产物.2.2解离吸附在表面原子的作用下,表面吸附的分子可以发生解离作用.我们以2.1节中得到的两种主要分子吸附产物为起始点,进一步研究尿素在ZnO(101軈0)表面的解离吸附情况.解离吸附的优化构型及相应的吸附能列于图4中.在我们的结果中只得到了一种解离吸附复合物,来源于分子吸附复合物3.我们用同样的符号标记解离吸附复合物以表明它们的来源(即分子吸附复合物).该解离吸附复合物来自于尿素分子中的N—H键的断裂,形成了一个表面羟基和一个H2NCONH自由基,该自由基的两个氮原子和表面的锌原子键合在一起.通过对吸附能的比较,我们发现,解离吸附复合物没有其相应的分子吸附复合物稳定.解离吸附复合物的吸附能为-1.37eV,而其相应的分子吸附复合物的吸附能为-1.48eV,解离需吸热0.11eV.这表明,尿素分子在ZnO(101軈0)表面倾向于发生分子吸附.研究发现,初次解离吸附产物可以发生进一步的解离.计算结果表明,解离吸附复合物3可以通过C—N键的断裂,生成表面吸附的氨气、异氰酸根和一个表面羟基,形成更稳定的二次解离吸附复合物3(Eads=-1.66eV),放出0.29eV的能量(图5).3结论采用VASP研究了尿素分子在ZnO(1010)表面的吸附行为，计算结果表明:(1)尿素分子在ZnO(101軈0)表面主要发生分子吸附反应,稳定的吸附产物通过表面锌原子与尿素分子中氮原子或氧原子之间的键合作用而生成.(2)吸附在ZnO(101軈0)表面的尿素分子也可以发生解离作用,生成表面吸附的异氰酸根、氨气和一图5尿素在ZnO(1010)表面二次解离吸附的优化构型Fig.5Optimized structure of the secondarydissociative adsorption mode of urea on theZnO(1010)surfaceWe used the top two layers of the ZnO(1010)slab for short.bond length in nm图4尿素在ZnO(1010)表面解离吸附的优化构型Fig.4Optimized structure of the dissociative adsorption mode of urea on the ZnO(1010)surface We used the top two layers of the ZnO(1010)slab for short.bond length in nm1376No.5唐文东等：尿素在ZnO(1010)表面的吸附个表面羟基.致谢：感谢中国科学院山西煤炭化学研究所霍春芳副研究员的有益讨论和帮助.References1Tundo,P.;Selva,M.Accounts Chem.Res.,2002,35(9):7062Wang,M.H.;Zhao,N.;Wei,W.;Sun,Y.H.Ind.Eng.Chem.Res., 2005,44(19):75963Yang,B.L.;Wang,D.P.;Lin,H.Y.;Sun,J.J.;Wang,X.P.Catal.Commun.,2006,7(7):4724Wang,M.H.;Wang,H.;Zhao,N.;Wei,W.;Sun,Y.H.Catal.Commun.,2006,7(1):65Sun,J.J.;Yang,B.L.;Wang,X.P.;Wang,D.P.;Lin,H.Y.J.Mol.Catal.A-Chem.,2005,239(1-2):826Cho,T.;Tamura,T.;Cho,T.;Suzuki,K.Process for preparing dialkyl carbonates:US,5534649[P].1996-10-157Lin,H.Y.;Yang,B.L.;Sun,J.J.;Wang,X.P.;Wang,D.P.Chem.Eng.J.,2004,103(1-3):218Saleh,R.Y.;Michaelson,R.C.;Suciu,E.N.;Kuhlmann,B.Process for manufacturing dialkyl carbonate from urea and alcohol: US,5565603[P].1996-10-159Ryu,J.Y.;Gelbein,A.P.Process and catalyst for making dialkyl carbonates:US,6392078[P].2002-05-2110Wu,C.C.;Zhao,X.Q.;Wang,mun.,2005,6(10): 69411Bhanage,B.M.;Fujita,S.;Ikushima,Y.;Arai,M.Green Chem., 2003,5(4):42912Li,Q.B.;Zhang,W.Y.;Zhao,N.;Wei,W.;Sun,Y.H.Catal.Today,2006,115(1-4):11113Zhao,X.Q.;Zhang,Y.;Wang,Y.J.Ind.Eng.Chem.Res.,2004, 43(15):403814Suciu,E.N.;Kuhlmann,B.;Knudsen,G.A.;Michaelson,R.C.anomet.Chem.,1998,556(1-2):4115Wang,D.P.;Yang,B.L.;Zhai,X.W.;Zhou,L.G.Fuel Process.Technol.,2007,88(8):80716Zhao,W.B.;Wang,F.;Peng,W.C.;Zhao,N.;Li,J.P.;Xiao,F.K.;Wei,W.;Sun,Y.H.Ind.Eng.Chem.Res.,2008,47(16):5913 17Qi,Z.Z.;Wang,H.B.;Xia,D.K.Industrial Catalysis,2006,14(1):26[祁增忠,王洪波,夏代宽.工业催化,2006,14(1):26] 18Zhao,W.B.;Peng,W.C.;Wang,D.F.;Zhao,N.;Li,J.P.;Xiao,F.K.;Wei,W.;Sun,mun.,2009,10(5):65519Raj,G.S.P.;Horia,M.J.Catal.,2008,254(2):32520Jan,W.;Jacek,P.Solid State Commun.,2008,146(7-8):32421Gay,R.R.;Nodine,M.H.;Henrich,V.E.;Zeiger,H.J.;Solomon,E.I.J.Am.Chem.Soc.,1980,102(22):675222Marana,N.L.;Longo,V.M.;Longo,E.;Martins,J.B.L.;Sambrano,J.R.J.Phys.Chem.A,2008,112(38):895823Sarano,D.;Spoto,G.;Bordiga,S.;Zecchina,A.;Lamberti,C.Surf.Sci.,1992,276(1-3):28124Kresse,G.;Furthmuller,put.Mater.Sci.,1996,6(1):1525Bl觟chl,P.E.Phys.Rev.B,1994,50(24):1795326Kresse,G.;Joubert,D.Phys.Rev.B,1999,59(3):175827Perdew,J.P.;Chevary,J.A.;Vosko,S.H.;Jackson,K.A.;Pederson,M.R.;Singh,D.J.;Fiolhais,C.Phys.Rev.B,1992,46(11):667128Sawada,H.;Wang,R.P.;Sleight,A.W.J.Solid State Chem., 1996,122(1):14829Beltran,A.;Andres,J.;Calatayud,M.;Martins,J.B.L.Chem.Phys.Lett.,2001,338(4-6):22430Binks,D.J.;Grimes,R.W.J.Am.Ceram.Soc.,1993,76(9):2370 31Gopal,P.;Spaldin,N.A.J.Electron.Mater.,2006,35(4):53832Cooke,D.J.;Arnaud,M.;Stephen,C.P.J.Phys.Chem.B,2006, 110(15):798533Nyberg,M.;Nygren,M.A.;Pettersson,L.G.M.;David,H.G.;Rohl,A.L.J.Phys.Chem.,1996,100(21):905434Wander,A.;Harrison,N.M.Surf.Sci.,2000,457(1-2):3421377。

Adsorption

• In order to obtain a direct measurement of the values of kL and kG the measurement of the concentration at the interface would be necessary. These values can only be obtained in very special circumstances, and it has been found of considerable value to use two overall coefficients KG and KL defined by: • KG and KL are known as the overall gas and liquid phase coefficients, respectively.
• Writing PBm as the log mean of the partial pressures PB1 and PB2, then:
Gas-film transfer coefficient
• Hence the rate of absorption of A per unit time per unit area is given by:
• Thus, from the figure,1/V’ = 13,902 and: V’ = 71.9×10−6m3/kg. which agrees with the value from the BET isotherm. • It may be noted that areas calculated from the isotherm are some 20 per cent greater than the geometric surface, probably due to the existence of some internal surface within the particles.

三种微生物对铀的吸附行为研究

三种微生物对铀的吸附行为研究马佳林;龚运军;聂小琴;董发勤;代群威;张东;杨杰;周娴;黄荣;龚俊源【摘要】To compare the similarities and differences of adsorption properties and adsorption properties during interaction of microorganisms with uranium, we selected Bacillus subtilis (bacteria), yeast (fungus), chlorella (algae) as objects and studied the adsorption performance and a variety of microbial factors by using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The results indicated that three types of microorganisms in water uranium has good effect on uranium adsorption. The best adsorption rate of uranium by yeast and chlorella and Bacillus subtilis were 97.19%、97.13% and 98.03%, respectively. And the maximum adsorption capacity of uranium by yeast and chlorella and Bacillus subtilis were 341.2、356.5、512.5mgU/g(DW) , respectively. The adsorption process and mechanism for uranium adsorption by three kinds of microbe was different, yeast and chlorella in line with the Langmuir model, bacillus subtilis is more suitable for the Freundlich model. The results of Scanning electron microscope and energy spectrum indicated that the uranium is adsorbed onto the cell surface at the beginning with no precipitation or mineral. Then, the sheet and clumps of uranium-phosphorus crystallization were formed on the surface of yeast after12hours.however, There were not found the similar crystals on the surface of chlorella and bacillus subtilis. Interaction of microorganisms with uranium will cause changes in cell morphology, especially for bacillussubtilis and chlorella.%开展了酵母菌(真菌)、枯草芽孢杆菌(细菌)、小球藻(藻类)对水体中铀(Ⅵ)的吸附性能及机理研究.结果表明：3种微生物对铀都具有较好的吸附效果.酵母菌,小球藻,枯草芽孢杆菌对铀的最佳吸附率分别为97.19%、97.13%、98.03%；且最大吸附量分别达到341.2、356.5、512.5mgU/g(DW).3种微生物对铀的吸附过程和机理有所不同,酵母菌和小球藻符合Langmuir模型,枯草芽孢杆菌更适合Freundlich模型,吸附至12h,酵母菌表面逐渐出现铀和磷的片状结晶及含铀沉积物堆积,小球藻和枯草芽孢杆菌与铀(50mgU/L)作用后细胞出现明显变形,菌体表面未出现铀的结晶物.【期刊名称】《中国环境科学》【年(卷),期】2015(000)003【总页数】8页(P825-832)【关键词】铀;微生物;吸附;机理【作者】马佳林;龚运军;聂小琴;董发勤;代群威;张东;杨杰;周娴;黄荣;龚俊源【作者单位】西南科技大学，核废物与环境安全国防重点学科实验室，四川绵阳621010;西南科技大学，核废物与环境安全国防重点学科实验室，四川绵阳621010;西南科技大学，核废物与环境安全国防重点学科实验室，四川绵阳621010;西南科技大学，核废物与环境安全国防重点学科实验室，四川绵阳621010;西南科技大学，核废物与环境安全国防重点学科实验室，四川绵阳621010;中国工程物理研究院核物理与化学研究所，四川绵阳 621900;西南科技大学，核废物与环境安全国防重点学科实验室，四川绵阳 621010;西南科技大学，核废物与环境安全国防重点学科实验室，四川绵阳 621010;西南科技大学，核废物与环境安全国防重点学科实验室，四川绵阳 621010;西南科技大学，核废物与环境安全国防重点学科实验室，四川绵阳 621010【正文语种】中文【中图分类】X591随着核工业的不断发展以及核设施的退役，由此产生的含铀放射性废水种类和数量越来越多，通过地表径流和地下迁移、渗透而进入土壤和水体的铀污染问题对人类健康和自然环境造成潜在的威胁［1-3］.近20 年来，国内外学者针对铀污染环境的原位生物修复开展了大量的研究工作［4-9］.有研究表明在放射性废物库附近的土壤和地下水中，通过微生物菌毛原位传递电子获取提供生存能量并促进可溶性U （Ⅵ）原位还原成溶解性小的U（Ⅳ），或者通过还原酶的分泌及胞外代谢产物进行铀的沉淀和矿化等作用可以有效的阻滞或延缓铀的迁移［6-9］.关于微生物原位修复铀污染环境，研究对象主要包括细菌、真菌、藻类等三大类［1-2，12］，不同种类微生物对铀存在着不同的吸附性能和作用机制，主要表现为离子交换，络合沉淀，胞内赋存，生物矿化，氧化还原等等［10-16］.微生物与铀的相互作用受介质成分、环境条件、细胞结构和代谢过程等多种因素的影响，表现出的作用方式也不尽相同.因此，本研究选取酵母菌、小球藻、枯草芽孢杆菌为几类微生物的典型代表为研究对象，在相同条件下，比较分析不同种类微生物对铀的吸附性能及机理，旨在为生物修复铀污染环境的研究提供参考依据.1.1 试验材料1.1.1 菌株及试剂酵母菌为市售安琪面包酵母；小球藻和枯草芽孢杆菌由西南科技大学生命科学与工程学院实验中心提供.铀溶液的配置：准确称取2.1092g的硝酸铀酰［UO2（NO3）2·6H2O］，少量水溶解后，加入10mL硝酸，移入1000mL容量瓶中，用水稀释至刻度，摇匀，即为铀浓度为1g/L的铀溶液.通过去离子水稀释得到其他浓度的铀溶液，采用0.1mol/L HNO3、10g/L Na2CO3和5g/L NaHCO3的缓冲液调节溶液pH值.1.1.2 主要试验仪器紫外可见分光光度计（UV-1600，上海美谱达仪器有限公司）；离心机（LD5-2B，北京雷勃尔离心机有限公司）；场发射扫描电子显微镜（Ultra55，德国蔡司仪器公司）；能谱仪（Oxford IE450，英国Oxford公司）.1.3 实验方法1.3.1 菌体制备将活化后的菌体种子液接入到液体培养基中，于35℃，150r/min 恒温振荡培养箱中振荡培养48h.培养后以4000r/min离心10min.取沉淀的菌体，用0.9%的生理盐水稀释为所需菌悬液（吸光度值OD600=0.5）.1.3.2 吸附实验准确移取20mL一定浓度的铀溶液于50mL锥形瓶中，取20mL预培养好的菌悬液离心（4000r/min）10min，将离心后的湿菌体（干重2.5～5.0mg）分别加入上述50mL锥形瓶中，置于空气恒温摇床内进行恒温振荡吸附0.5～72h，离心后取5mL上清液，测溶液中残余铀浓度，每组设置3个平行样，以铀溶液作为对照.1.4 分析测试1.4.1 铀的分析水样中铀含量的检测按照偶氮胂Ⅲ分光光度法［2］进行.1.4.2 SEM-EDS分析供试微生物与50mgU/L铀溶液作用一定时间（0～72h）后，离心，经去离子水清洗、离心、制备成菌悬液，在盖玻片上点样，自然干燥，加入2.5%戊二醛固定10h，去掉戊二醛溶液，依次用30%、50%、70%、90%、100%乙醇溶液逐级脱水（每次脱水20min），最后自然晾干，备用.样品经过喷金处理后进行样品形貌观察和微区元素分布分析.1.5 数据处理式中：R为吸附率，%；C0为初始铀浓度， mgU/L；Ct为t时刻的铀浓度，mgU/L；q为吸附量， mgU/g（DW）；V为溶液初始体积，L；m为微生物的干重，g.2.1 溶液初始pH值对微生物吸附铀的影响溶液pH值通过改变微生物表面电位电荷分布、结合位点以及溶液中铀酰离子的络合形态，从而影响微生物对溶液中铀的吸附行为［1］.在强酸性溶液中，铀主要以形式存在，当pH＞4时逐渐水解，溶液中出现一定量的UO2OH+络合阳离子.当pH值接近6时，溶液中则主要以等络阴离子形式存在［1］.由图1可以看出，当pH值在1.0～6.0时，随着溶液pH值不断升高，酵母菌和小球藻对铀的吸附量逐渐增加，在pH=6.0时吸附量分别240.7mgU/g（DW）、206.9mgU/g（DW）；枯草芽孢杆菌在pH=5.0时吸附量为107.6mgU/g （DW）.结合后面的扫描电镜结果可以推断，在初始浓度为100mgU/L 的条件下，枯草芽孢杆菌细胞受到严重损伤，在作用24h时细胞处于死亡状态，因此枯草芽孢杆菌与铀的作用过程可以看作是生物吸附剂对铀的吸附.生物吸附剂对溶液中离子吸附的最佳pH值通常是由吸附剂表面的等电点（pK=3～5）决定［1］，当溶液pH值超过等电点的pH值时，铀酰络阴离子与吸附剂表面的负电荷产生静电斥力，在本研究中表现为枯草芽孢杆菌在pH=6时吸附能力下降（图1）.有研究表明，酵母菌［4］和小球藻［1］细胞在大于100mgU/L的条件下仍能很好地存活.推断该类吸附行为是以依赖代谢的生物吸附为主的过程，在越适宜生存的pH值条件下，对溶液中的铀酰离子吸附作用越有利.本研究结合微生物的生长条件及含铀废水的实际情况，主要考察微生物在弱酸性环境下的最佳吸附条件，故未设置pH ＞6的条件开展实验.本文选择pH=5开展后续实验.2.2 初始铀浓度对微生物吸附铀的影响由图2可以看出，在初始铀浓度为10mgU/L时，3种微生物对铀均有较好地吸附效果，吸附率在60%～80%之间.与高浓度铀溶液相比，相同接菌量的微生物在低浓度的铀溶液中，吸附位点相对充足能与微生物细胞表面充分接触，吸附率较高，当C0=50mgU/L时，酵母菌表现最佳吸附能力，吸附率达93.0%，小球藻、枯草芽孢杆菌均在10mgU/L时取得最大吸附率，分别为：77.8%、66.1%.随着溶液中初始铀浓度的增加，3种微生物对铀的吸附率整体下降，吸附量逐渐增高，当C0≥200mgU/L 后，酵母菌、小球藻吸附量趋于平衡，有研究表明［4-5］细胞壁上的吸附位点是有限的，当吸附达到平衡时，吸附位点达到饱和，此时铀的初始浓度再提高，吸附量基本接近稳定；3种微生物均在本实验中设置的最高铀浓度时获得最大吸附量，酵母菌最高，达325.5mgU/ g（DW），小球藻和枯草芽孢杆菌分别为294.9和215.0mgU/g（DW）.从对铀的吸附率和吸附量来看，总体表现为：酵母菌＞小球藻＞枯草芽孢杆菌.2.3 接触时间对微生物吸附铀的影响由图3可知，吸附的初始阶段（5min～12h）吸附速率很快，吸附位点充足，在1h时，酵母菌、小球藻和枯草芽孢杆菌对铀的吸附率分别为50.4%、51.7%和79.5%.随着吸附的进行，吸附速率减缓，有效吸附位点逐渐减少；24h之后，枯草芽孢杆菌对铀的吸附达到稳定，而酵母菌和小球藻经历过一段平衡时期（12～48h）之后，吸附率进一步升高.在72h时，酵母菌、小球藻和枯草芽孢杆菌对铀的吸附率分别为：75.3%、74.6%和94.7%.关于微生物对铀的吸附过程［5-10］，可以归纳为：初始阶段起主导作用的快速、可逆且无需能量的被动吸附，将铀酰离子吸附到微生物表面；第二阶段起主导作用的主动吸附，将细胞表面吸附的铀酰离子沉淀矿化或者转移至细胞内部，缓慢、不可逆，此阶段需要能量并且与细胞的代谢有关.死体微生物对铀的吸附通常仅表现为第一阶段，而活体微生物对铀的吸附还有第二阶段的进行.本研究表明，枯草芽孢杆菌对铀的吸附过程以被动吸附为主，同时又异于一般死体微生物，因为在铀溶液的胁迫下，枯草芽孢杆菌体内过氧化程度加重，壁膜破坏，将分泌和释放大量的代谢或者胞外产物，这些产物与菌体表面的活性位点一并与溶液中的铀酰离子发生络合、离子交换或者沉淀矿化等作用，部分铀酰离子也可能直接快速地穿透细胞壁膜进入到体内.而酵母菌和小球藻则表现为活体微生物对铀的吸附过程，通过菌毛［6］和表面活性官能团［7-8］将溶液中的铀酰离子优先聚集在细胞表面，随着吸附的进行，可能在细胞表面发生电子转移引起氧化还原反应，将部分U（Ⅵ）还原为U（Ⅳ）［10-11］，离子交换［12］，络合沉淀［13］，结晶矿化［14-15］，胞内沉积［16］等生物物理化学多种作用.2.4 接菌量对微生物吸附铀的影响由图4可知，随着接菌量的增加，3种微生物对铀的吸附率也逐渐上升，当接菌量达0.4g/L时，吸附率均达90%以上.在最小接种量时，枯草芽孢杆菌表现出最大的吸附率，吸附量超过500mgU/g（DW）.随着接菌量继续增大，吸附率有较小幅度的上升，吸附量逐渐降低.分析其原因可能是随着吸附的进行，溶液中铀浓度不断下降，溶液中游离的铀酰离子减少，铀结合到吸附微生物表面的几率减小，大量的微生物在溶液中共存造成一定的空间位阻效应.在本实验中，酵母菌、小球藻、枯草芽孢杆菌的最大吸附率分别为：97.19%、97.13%、98.03%.2.5 吸附等温模线Langmuir 吸附等温线假设吸附剂对金属离子的吸附为均一的单分子层吸附，且被吸附的离子间无相互作用.Freundlich 吸附等温线假设吸附剂对金属离子的吸附为非均一的多分子层吸附，被吸附的离子的量随着溶液浓度的增加而增大.本文采用Langmuir和Freundlich两种吸附等温模型来对3种微生物在不同U（Ⅵ）浓度下的等温吸附过程进行拟合，相关参数见表1.由拟合结果可知，Langmuir模型能较好地描述酵母菌和小球藻对铀的吸附过程，R2分别为0.988和0.991，拟合所得的酵母菌和小球藻最大吸附量分别为344.8mgU/g（DW）和355.9mgU/g（DW），与实验所得的最大吸附量（341.2mgU/g（DW）和356.5mgU/g（DW））吻合较好，表明酵母菌和小球藻对铀的吸附过程表现为单层吸附.枯草芽孢杆菌对铀的吸附过程更适合Freundlich模型，R2=0.961，该吸附过程并不完全是单层分子的表面吸附，1/n=0.23小于0.5，吸附容易自发进行.2.6 SEM-EDS结果与分析酵母菌与50mgU/L作用不同时间（0.5～72h）后的扫描电镜结果如图5所示.未进行吸附的菌体（图5a）多数表面光滑、形态完好；0.5h后（图5b），形态基本完好，表面未见异常. 12h后（图5c）菌体有轻微塌陷，在菌体表面出现明显的片状沉积物堆积，JIANG等［14-15］研究表明，微生物在对核素进行短期吸附后，细胞壁上金属离子的结合位点可能会成为晶体的成核点.24h后，菌体出现一定的塌陷和扭曲形变，在菌体表面能观察到明显的铀结晶体出芽（图5d），该形貌与Toshihiko等［13］报道的关于铀磷无机纳米矿化体在酵母菌表面沉积图片有高度的相似性，EDS分析结果可以很好地支撑这一推断.同时在菌体附近同样出现团状结晶（图5e），分析团状沉积物堆簇出现的原因，可能是由于在制样过程中，先经过去离子水反复清洗并离心，作用力强度过大，导致部分在菌体表面的沉淀物与菌体表面分离，并在离心力下粘附在菌体表面或脱离菌体束缚的聚集成一团；因为铀对酵母细胞的胁迫作用，导致壁膜受损，引起磷脂分解或ATP水解导致无机磷释放到溶液中，从而引起溶液中的铀酰离子与无机磷结合沉淀.酵母菌吸附铀前后能谱分析结果如图6所示.吸附后菌体表面出现了U的吸收峰，结合能为2.0～4.0KeV；Na，Mg，Ca元素的含量明显下降，但P元素的含量明显增加.由此表明，酵母菌对溶液中铀酰离子吸附过程中，细胞中的P参与了与铀酰离子的相互作用， JIANG等［15］认为细胞表面含磷部位在铀沉淀过程中起重要作用，既是络合官能团的载体，又作为底物来诱导磷酸盐的结晶.由此推断，酵母菌表面的结晶物主要来源于菌体本身释放的磷在细胞表面上与铀的成矿作用；吸附前细胞元素含量表中有较多的Si元素，而吸附后几近没有，可能是待测样品在盖玻片上，吸附前的样品较为稀薄、分散，X-射线穿过细胞缝隙打到玻璃片上，而出现的Si吸收峰.研究结果表明，随着吸附的进行，酵母菌表面逐渐开始出现铀-磷片状结晶、菌体附近有含铀的团状沉积物堆积，菌体之间发生粘连，菌体表面出现凹陷、皱缩，接触时间越长，细胞受到的破坏越严重.枯草芽孢杆菌的SEM结果如图7所示，未进行吸附的菌体表面光滑、形态完好（图7a）；在吸附30min后，菌体的形态发生很大变化，呈短节状，随着吸附的进行，在24h时，菌体形态的破坏程度加重，未见修复的迹象，推测菌体基本死亡，在一些菌体表面可以见到一些片状沉积物堆积.能谱分析与细胞成分接近，C、O含量占70%以上，不含铀，疑为菌体分泌物（结果未在本文中给出）.在72h时，只观察到残缺断裂的菌体，未见酵母菌吸附后出现的铀片状结晶或沉积物.小球藻的扫描电镜（图7e）和能谱分析结果表现为在吸附后期细胞出现明显塌陷，表面出现褶皱，并且出现粘连，整体形貌也发生了严重变化，未观察到铀的结晶物出现.菌体形态的变化可能由于铀进入细胞内部结构，对菌体的毒害作用增强，使细胞质生物大分子遭破坏，细胞内产生空壳结构，而导致脱水时细胞壁内陷.研究结果表明，3种微生物与铀作用的机制不同.铀结合到细胞表面后，酵母菌以无机微沉淀和生物矿化为主，严重受损的活性小球藻及死亡的枯草芽孢杆菌可能主要是通过与壁膜的活性位点络合配位，以及进入到胞内赋存的方式，未见胞外沉淀和矿化产物，微生物与铀作用过程和产物有多种方式，推测这可能与3种微生物的壁膜结构［8］和代谢过程［7］有关.3.1 3种微生物对水体中铀（Ⅵ）都具有较好的吸附效果.在pH=5.0，初始铀浓度为10～350mgU/ L，投加量在0.06～1.12mgU/L（DW），25℃下吸附24h，酵母菌，小球藻，枯草芽孢杆菌对铀的最佳吸附率分别为97.19%、97.13%、98.03%；最大吸附量分别达到341.2、356.5、512.5mgU/g （DW）.3.2 在等温吸附模型中，Langmuir模型可较好地描述酵母菌和小球藻对铀的吸附过程，相关系数分别为0.988、0.991，最大吸附量的理论值与实验值吻合较好，枯草芽孢杆菌对铀的吸附过程更适合Freundlich模型，R2=0.961，表明酵母菌和小球藻对铀的吸附属于单分子层吸附，枯草芽孢杆菌为多层吸附.3.3 SEM-EDS分析表明，3种微生物对铀的吸附作用机理不同.随着吸附时间的延长，铀会在酵母菌表面和周围出现铀和磷的纳米片状矿化体及沉积物，小球藻和枯草芽孢杆菌则未在表面或周围产生铀的纳米结晶或沉淀；3种微生物与铀作用后均会引起细胞形态的变化，而枯草芽孢杆菌的形态被破坏得最早最严重，表明枯草芽孢杆菌对铀的耐受性最弱.【相关文献】［1］Vogel M，Günther A， Rossberg A， et al. Biosorption of U （VI） by the green algae Chlorella vulgaris in dependence of pH value and cell activity ［J］. Science of the total environment， 2010，409（2）：384-395.［2］Liu M X， Dong F Q， Yan X Y， et al. Biosorption of uranium by Saccharmyces cerevisiae and surface interactions under culture conditions ［J］. Bioresource Technolgy，2010，101：8573-8580.［3］冯颖思，宋刚，祝秋萍，等.某铀矿下游水系沉积物剖面的放射性核素分布特征［J］. 中国环境科学， 2013，33（8）：1442-1446.［4］彭国文，丁德馨，胡南，等.纳米Fe3O4负载啤酒酵母菌对铀的吸附性能与机理［J］. 中国有色金属学报， 2012，22（2）：604-610.［5］LI J， ZHANG Y. Remediation technology for the uranium contaminated environment： a review ［J］. Procedia Environmental Sciences， 2012，13：1609-1615. ［6］Mukherjee A， Wheaton Gh， Blum Ph， et al. Uranium extremophily is an adaptive，rather than intrinsic， feature for extremely thermoacidophilic Metallosphaera species ［J］. PNAS，2012，109：16702-16707.［7］Bargar J R， Williams Kh， Campbell K M， et al. Uranium redox transition pathwaysin acetate-amended sediments ［J］. PNAS 2013，110：4506-4511.［8］Cologgi D L， Pastirk S L， Speers A M， et al. Extracellular reduction of uranium via Geobacter conductive pili as a protective cellular mechanism ［J］. PNAS， 2011，108：15248-15252.［9］Rashmi V， Shylajanaciyr M， Rajalakshmi R， et al. Siderophore mediated uranium sequestration by marine cyanobacterium Synechococcus elongatus BDU 130911 ［J］. Bioresour Technol.，2013，130：204-210.［10］Lovley D R. Bioremediation. Anaerobes to the rescue ［J］. Science，2001，293（5534）：1444-1446.［11］Lovley D R， Phillips E J P， Gorby Y A et al. Microbial reduction of uranium ［J］. Nature， 1991，350（6317）：413-416.［12］Toshihiko O， Takahiro Y， Takuo O， et al. Interactions of uranium with bacteria and kaolinite clay ［J］. Chemical Geology，2005，220（3/4）：237-243.［13］Toshihiko O， Takuo Ozaki， Takahiro Y， et al. Mechanisms of uranium mineralization by the yeast Saccharomyces cerevisiae ［J］. Geochimica et Cosmochimica Acta， 2005，69（22）：5307-5316.［14］Jiang M Y， Ohnuki T， Tanaka K， et al. Post-adsorption process of Yb phosphate nano-particle formation by Saccharomyces cerevisiae ［J］. Geochimica et Cosmochimica Acta， 2012，93：30-46.［15］Jiang M Y， Ohnuki T， Kozai N， et al. Biological nanomineralization of Ce phosphate by Saccharomyces cerevisiae ［J］. Chemical Geology， 2010，277（1/2）：61-69.［16］Toshihiko O， Naofumi K， Fuminori S， et al. Association of actinides with microorganisms and clay： Implications for radionuclide migration from waste-repository sites ［J］. Geomicrobiology Journal， 2010，27（3）：225-230.。

吸附解析等温线

吸附等温线的类型及特点物理吸附仪是微孔材料样品分析的常用设备之一，常被用于多孔材料比表面积和孔隙度的表征，能够提供比表面积、孔容及孔径分布等关键物性参数。

其工作原理所采用的气体吸附法（BET法）是在朗格缪尔(Langmuir)单分子层吸附理论的基础上，经南勃鲁纳尔（Brunauer）、爱曼特（Emmett）和泰勒（Teller）等三人推广得出的多分子层吸附理论（BET理论）。

「单分子层吸附理论」1916年，Langmuir 根据分子运动理论和一些假定提出单分子层吸附理论，基于一些明确的假设条件，得到简明的吸附等温式——Langmuir方程，既可应用于化学吸附，也可以用于物理吸附，因而普遍应用于现阶段多相催化研究中。

假定①：吸附剂表面存在吸附位，吸附质分子只能单层吸附于吸附位上；假定②：吸附位在热力学和动力学意义上是均一的（吸附剂表面性质均匀），吸附热与表面覆盖度无关；假定③：吸附分子间无相互作用，无横向相互作用；假定④：吸附-脱附过程处于动力学平衡。

式中，θ为表面覆盖度，V为吸附量，V m表示单分子层吸附容量，p为吸附质蒸汽吸附平衡时的压力，a为吸附系数/吸附平衡常数。

通过测定恒定温度下，不同吸附质压力所对应的气体吸附量，可以得到一条相对压力（P/P0）和吸附量的关系曲线，即吸附等温线。

由于Langmuir方程是一个理想的吸附公式，对应的是Brunauer定义的五种吸附等温线中的第一种——Langmuir型等温线，它代表了在均匀表面，吸附分子彼此没有作用，且吸附是单分子层情况下吸附达到平衡时的规律，但在实践中不乏与其相符的实验结果，这可能是实际非理想的多种因素互相抵消所致。

Type I：单分子层吸附等温线I类等温线呈现出一定压力后接近饱和的情况，又称Langmuir型等温线。

除单分子层吸附表现出I类等温线外，沸石、活性炭、硅胶等具有2-3 nm以下的微孔吸附剂，其吸附等温线也呈现第I类型。

这是因为相对压力由零增加时，微孔吸附剂在发生多层吸附的同时也发生了毛细孔凝聚，使吸附量急剧增加，所有微孔被迅速填满后，吸附量便不再随相对压力而增加，呈现出吸附饱和。

纯锡在铝—钢层状复合材料上的润湿行为及界面结构

623K、673K及723K时正视方向最终接触角分别为59°、35°与 32°,而侧视方向的铺展受到抑制。体系铺展过程中Al层界面的溶解不仅改变了熔体的表面张力,且溶质Al与复合界面中的Fe发生反应并形成Fe2Al5。
整个实验中得到的最终接触角均不满足Cassie方程,通过计算得到不同温度下的表面张力,将Naidich模型与表面张力耦合后得到修正后的Naidich模型能够较好地符合实验结果。最后,利用 Fluent流体动力学软件对流体在复合界面上的铺展进行数值模拟,得到的模拟结果验证了实验结果。
Байду номын сангаас
首先,研究了623K-723K高真空条件下纯Sn在Q235钢与纯Al基板表面的润湿行为（即典型的反应润湿与溶解润湿体系）并分析了界面结构。研究表明:Sn在钢表面的最终接触角受温度影响较小,为39°;界面上有金属间化合物（Fe Sn,Fe Sn2）生成,三相线处有前驱膜的出现,铺展机制为反应过程中生成的金属间化合物破除了基板表面的氧化膜促进铺展。
然而利用钎焊方法连接层状复合材料,钎料要与被连接材料有较好的润湿性（即θ f<90°）。因此,本课题通过研究熔体锡在纯铝、Q235钢及铝-钢层状复合材料上的润湿行为, 探讨润湿体系中复合界面与界面反应耦合时对其最终润湿性的影响,研究内容不仅可对金属层状复合材料的钎焊连接提供理论指导,也可丰富冶金熔体在异质表面的反应润湿理论。
纯锡在铝—钢层状复合材料上的润湿行为及界面结构

膨润土对铀的吸附研究

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随着全球核电站数量不断增加，废料对自然核
环境的威胁越来越大。如何安全永久地处理核废料
Ｋｏ，．；失量，０。其吸蓝量和阳离子交换容２１３烧８１量分别为１４８ｑ１００．／０ｇ和８．ｑ１０。ｍｅ１ｍｅ／０ｇ７
离地表深约５０１０ｍ的地质体中，之永久与人０￣００使
１试剂与仪器－２
试剂：硝酸铀酰（ＯｆＯ６２）Ｕ：Ａ・Ｈ０，Ｎ
分析纯。设备仪器：ＪⅢ型微量铀分析仪，州ＷＧ一杭
大吉光电仪器有限公司；０２型离心沉淀机（８－转速
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8-Adsorption

results in decrease in G
Types of adsorption: 1)Lack of solvent-solute interactions (hydrophobicity –surfactants) 2)Specific solid-solute interaction
• Exchange adsorption (ion exchange)– electrostatic due to charged sites on the surface. Adsorption goes up as ionic charge goes up and as hydrated radius goes down. • Physical adsorption: Van der Waals attraction between adsorbate and adsorbent. The attraction is not fixed to a specific site and the adsorbate is relatively free to move on the surface. This is relatively weak, reversible, adsorption capable of multilayer adsorption.
There are several ways to look at surface excess. One is to view it as the amount of solute adsorbed at the surface per unit surface area in excess of bulk concentration (units = moles/cm2). As shown in this figure this "surface excess" could be viewed as a concentration in a small volume near the surface.

co在金属cu上的吸附能

co在金属cu上的吸附能
CO在金属Cu表面的吸附能是一个重要的物理化学参数，它对
于理解CO在Cu表面的吸附行为以及相关催化反应具有重要意义。

吸附能可以通过实验方法或理论计算来确定。

从实验角度来看，科学家们可以利用表面科学技术，如吸附质
谱（Adsorption Mass Spectrometry）和透射红外光谱（Transmittance Infrared Spectroscopy）等手段来测定CO在金
属Cu表面的吸附能。

这些实验方法可以提供关于CO在Cu表面的吸
附构型和吸附能的重要信息。

另一方面，从理论计算的角度来看，密度泛函理论（Density Functional Theory，DFT）等计算方法可以用来预测CO在金属Cu
表面的吸附能。

通过计算电子结构和相互作用能，可以得出CO在
Cu表面吸附的能量。

此外，吸附能的大小还受到各种因素的影响，包括CO的结构、Cu表面的晶格结构、表面缺陷等。

因此，研究人员需要从实验和理
论两方面综合考虑，以获得对CO在金属Cu表面吸附能的全面理解。

总之，CO在金属Cu表面的吸附能是一个复杂而重要的研究课题，需要实验和理论相结合的方法来全面揭示其吸附行为及相关的催化反应机理。

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第19卷第4期原子与分子物理学报Vol.19，(.4

)**)年1*月+,-./0/1234.56275829-+5.:926/+3654;,<0-+02=>.，)**)

ArticleID：1***?*@A4（)**)）*4?*B1C?*B

Theoreticalstudyofadsorptionofwatervaporonsurfaceofmetallicuranium*

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*收稿日期：)**)?*B?14

作者简介：熊必涛（19CC\），男，湖南武冈人，中国工程物理研究院硕士研究生，研究方向：核化学化工。/?RHGl：XZG>aUGMH.=oR（4K=KGWKL

RHQ14，)**)，4KWGUKL1VlQ1，)**)，5==KY>KL0KY>KRZKT4，)**)）.coreelectrons（1s2，2s2，2p6，3s2，3p6，3d10，4s2，4p6，4d10，4f14，5s2，5p6，5d10）.Thereforethereis14（6s26p65f36d17s2）valenceelectrons.ThegeometricparametersandgroundstateenergyoftheadsorbedintermediatesubstanceUOH2（5A1）intheinitialoxidationwhenwatervaporwasadsorbedontouraniumwasoptimizedbyB3LYPmethodofDFTintheGaussian98，whereuraniumatomwasused14（6s26p65f36d17s2）valenceelectronsRECPandcontractedvaluedbasissets（6s5p2d4f）/［3s3p2d2f］［5］andforhydrogenandoxygenatomsallwere6-311G**basissets.2THERESULTSANDDISCUSSIONS2.1TheadsorptionmodeofwateronmetallicuraniumBothphysicalandchemicaladsorptionwouldtakeplaceonthesurfaceofmetallicuraniumintheinitialstageofuranium-watervaporreaction.Reactionontheecleanuraniumsurfaceinvolvestheadsorptionofwatermoleculesontothesurfacethroughametal-oxygenbond.That’sakindofchemisorption.ChemisorptionbreaksoneoftheO-Hbondsinadissociativereactiontoleaveastrong

chemisorbedOH-andanHweaklyboundtothe

surfacehydroxylion［1］.Otherwatermolecules

hydrogen-bondtotheoxygenatomformingwateradsorptionofmultiplayer.Adsorptionmodesdiagrammaticallyshowbelow：

ainly，onewatermoleculeisadsorbedtooneoxygenbond，anditsgeometryandgrouVC2VEnergy（a.u.）De（kJ.mol-1）DipoleRUO（Å）ROH（Å

）

∠UOH（deg）∠HOH（deg

）

1A1-127.8266353700.32503.70642.68680.9718126.5337106.9326

3B2-127.8439375659.11042.94142.61600.9787125.9865108.0271

5A1-127.9226322865.71323.16922.80050.9717126.9056106.1889

7A1-127.9114656836.40554.53722.71350.9655126.4192107.1616

9A2-127.6661021192.20363.65002.70731.847664.6831230.6338

Frontable1，UOH2inthestateof5A1isthegroundelectronicstatewiththeminimumenergy.Andthecalculationresultsindicatedthatitsdissociationenergyisthelowest.Thegroundelectronicstateofuraniumatom5LuwouldbereducedtoC2VofconfigurationwhentheintermediatesubstanceUOH2formed.Thedirectsumof5Luintermofirreduciblerepresentationof

C2Vgroupis：55A1⊕45A2⊕55B1⊕55B2….AndH2O’sirreduciblerepreentationis1A1.Theirdirectproductsare：