(4)--2022High-efficiency radon adsorp核化学与放射化学.pdf

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1、9222|New J.Chem.,2022,46,92229228This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2022Cite this:New J.Chem.,2022,46,9222High-efficiency radon adsorption by nickelnanoparticles supported on activated carbonXiangyuan Deng,abcBo Yu,abHaibiao Wu,abZheng

2、zhong He,abMeng Wang*aandDetao Xiao*abRadon(Rn)is a universally known indoor radioactive gas that poses a significant threat to human health.Activated carbon(AC)is the only commercial Rn adsorbent;its adsorption performance is extremelylimited due to too few micropores.A series of nickel nanoparticl

3、es supported on AC(Ni/AC)composites,combining abundant micropores with open metal sites,is rationally designed for adsorbing Rn via a two-stepprocess consisting of impregnation and high-temperature reduction.The Rn adsorption performance of the Ni/AC composites is obviously improved due to the intro

4、duction of nickel nanoparticles.The adsorptioncoefficient of Ni/AC calcined at 800 1C reaches 6.56?0.14 m3kg?1at 25 1C and 1 bar,48%higher than thatof AC.The Ni/AC Rn adsorption coefficient is similar over five cycles.The fine and homogeneous dispersion ofnickel nanoparticles,the appropriate chemica

5、l state of nickel and the high content of Ni0synergisticallypromote Rn adsorption on Ni/AC.Experiments verify that Ni/AC composites are a promising candidate for theadsorption of Rn in the atmospheric environment.1.IntroductionRn,as the second leading cause of lung cancer(after smoking)listed by the

6、 World Health Organization,1is the main source ofnatural radiation to human beings.In the United States,radonis considered to be responsible for about 21000 lung cancerdeaths per year.2Therefore,attention needs to be paid to thehealth hazards of radon to the public.3,4To date,manymethods5havebeenuse

7、dtoremoveRn,suchasventilation,6,7plugging,8,9and adsorption.1012However,venti-lation consumes a considerable amount of energy and is notsuitable for maintaining comfort in extreme weather.Due tothe aging of anti-radon materials,plugging cannot easilyachieve long-term effectiveness,especially in unde

8、rgroundbuildings.Thus,adsorption is the most effective method toreduce indoor Rn concentrations.13In particular,it can beapplied in inconveniently ventilated places such as under-ground facilities.An adsorptive material is the key factor toachieve efficient Rn removal.To date,it has been proven that

9、zeolite,14silicagel,15metalorganicframeworkmaterials(MOFs),16,17activated carbon,18etc.,can adsorb Rn.Amongthem,the adsorption performance of zeolites and silica gels isnot as good as that of activated carbon.Several MOFs showsuperior performance of Rn adsorption by Grand CanonicalMonte Carlo(GCMC)s

10、imulations.16,17,19There are few experi-mental studies on Rn adsorption by MOFs,because of theradioactivity of Rn.As the only commercial Rn adsorbent,activated carbon has been a research hotspot.One of theimportant factors affecting the radon absorption of activatedcarbon is the proportion of microp

11、ores.20Various physical andchemical methods have been applied to increase the number ofmicropores.2123However,through these physical or chemicalmodification methods,the original micropores in activatedcarbon are destroyed during the formation of new micropores,thus preventing effective improvements

12、in the adsorptioncapacity of Rn.Therefore,it is necessary to develop effectiveradon absorbents based on new principles.In recent years,it has been found that nanometal particleshave strong adsorption sites.24,25Supported nanometal porousmaterials,which possess abundant micropores and open metalsites

13、 conducive to the adsorption of gases,26,27have shownexcellent adsorption properties for gases,such as CO2,28,29HCHO,30,31H2,32CH433,34and xenon.35,36However,to the bestof our knowledge,the use of nickel nanoparticles supported onactivated carbon for the removal of Rn has never been reported.In this

14、 work,nickel nanoparticles supported on activatedcarbon composites,combining abundant micropores withopen metal sites,were rationally designed for the adsorptionand separation of Rn in the atmospheric environment at roomtemperature.Impregnation followed by a high-temperatureaSchool of Nuclear Scienc

15、e and Technology,University of South China,Hengyang 421001,Hunan,China.E-mail:bRadon Key Laboratory of Hunan Province,University of South China,Hengyang 421001,Hunan,China.E-mail:cSchool of Mathematics and Physics,University of South China,Hengyang 421001,Hunan,China Electronic supplementary informa

16、tion(ESI)available.See DOI:https:/doi.org/10.1039/d2nj00862aReceived 19th February 2022,Accepted 8th April 2022DOI:10.1039/d2nj00862arsc.li/njcNJCPAPERThis journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2022New J.Chem.,2022,46,92229228|9223reduction me

17、thod was adopted to synthesize nickel nano-particles supported on activated carbon(Ni/AC).The effect ofcalcination temperature on the structure was studied in detail.Static Rn adsorption experiments were conducted to analyzethe relationship between the Rn adsorption performance andthe structure of t

18、he samples.The mechanism of the Ni/ACcomposite with high Rn adsorption performance for Rn waselucidated and discussed.2.Methods2.1.MaterialsCommercial coconut shell active carbon was obtained fromHongshen Co.,Ltd(China).Ni(NO3)?6H2O(99.99%)was pur-chased from Shanghai Aladdin Biochemical Technology

19、Co.,Ltd(China).Ultrahigh-purity grade N2(499.99%)was pur-chased from Dongxing Co.,Ltd(China).All chemicals wereused as received without further purification.2.2.SynthesisThe adsorbents were prepared by impregnation and a high-temperature reduction method.In a typical run,the coconutshell active carb

20、on was washed with deionized water and driedin an oven at 120 1C for 12 h.Ni(NO3)?6H2O(1.98 g)wasdissolved in 100 ml of deionized water,and then 20 g of driedcoconut shell active carbon was added.The mixed solution wasstirred for 30 min at room temperature.After the AC wasimpregnated with aqueous ni

21、ckel nitrate solution for 8 h,themixed solution was then ultrasonicated for 2 h at 60 1C.The excess liquid was vaporized by heating to 75 1C withstirring.The mixture was further dried at 120 1C for 3 h in avacuum oven.The obtained solid was calcined in a N2flow of200 ml min?1at a heating rate of 3 1

22、C min?1to the targettemperatures(600,700,800 and 900 1C)with a holding time of2 h and then cooled to room temperature in a tube furnace in aN2atmosphere.These adsorbents were then instantly stored ina dryer.The obtained samples were denoted as Ni/AC-T(T=600900 1C,representing the calcination tempera

23、ture ofthe active carbon).2.3.CharacterizationThe morphology of the samples was observed by field emissionscanning electron microscopy(SEM,Quanta 400 FEG,FEI)andtransmission electron microscopy(TEM,JEM-2100,JEOL).Theobtained TEM image was then analyzed by using Nano Mea-surer analysis software to es

24、timate the particle size of the nickelnanoparticles.The content of Ni in Ni/AC was determined byinductively coupled plasma optical emission spectrometry(ICP-OES,Agilent ICPOES720).Nitrogen adsorptiondesorption iso-therm experiments were performed using a Mack 3Flex at 77 Kto measure the BrunauerEmme

25、ttTeller(BET)specific areaand pore size distribution(deformation isotherms,nonlocaldensity functional theory(NLDFT)model).X-ray diffraction(XRD)patterns of the samples were recorded using a SmartLabusing a Cu Ka radiation source with a scanning angle(2y)rangeof 51901 and operated at 40 kV and 30 mA.

26、The Ni of Ni/AC wasdetected by X-ray photoelectron spectroscopy(XPS,ThermoEscalab 250XI).The high temperature thermal stability of Ni/AC was investigated using a thermo gravimetric/differentialscanning calorimeter(TG/DSC,3+Switzerland Mettler Toledo).2.4.Rn adsorption measurementsThe radon adsorptio

27、n performance of the sample was testedusing the static equilibrium method.27,37The K parameter wasdefined as the adsorption coefficient of activated carbontowards Rn by eqn(1):K C2C1(1)where C2and C1are the concentrations of Rn in the activatedcarbon(units:Bq m?3)and the concentration of Rn in the g

28、asphase after the adsorption equilibrium of activated carbon toRn(units:Bq m?3).The K parameter reflects the adsorptioncapacity of the material to Rn.In a typical experiment,approximately 2 g of the sample wasdried before being packed into a stainless steel adsorption tank(volume 1 L).One milliliter

29、 of radon gas was pumped from theradon source into the adsorption tank.Another 1 ml of radongas was pumped from the radon source into the scintillationchamber(model ST203,volume 0.51 L).After the scintillationchamber was left for 3 h and the radon and its short-livedsubstrates reached decay equilibr

30、ium,the activity of radon wasmeasured by a FD125 Rn and thorium analyzer(Fig.S1,ESI),and this activity was the initial activity A0(Bq)of the radoninjected into the adsorption tank.After the adsorption tankinjected with radon was stored for 15 h to reach adsorptionequilibrium(Fig.S2,ESI),the radon co

31、ncentration C1in theair inside the adsorption tank was measured,and the corres-ponding radon activity was A1(Bq).Because of the decaycorrection of radon,the activity of radon adsorbed in theadsorption material(A2)can be estimated using eqn(2):A2=A0e?lt?A1(2)where l(2.1 10?6s?1)is the decay constant

32、of radon;t(s)istime for storing the sample reach adsorption equilibrium;m(kg)is the mass of the sample;V(m3)is the effective volume ofthe stainless steel adsorption tank.K C2C1A2mA1VA0e?lt?A1A1?Vm(3)3.Results and discussion3.1.Morphology and structure analysisThe morphologies and microstructures of

33、the synthesizedadsorbents were characterized by SEM/EDS.AC has abundantpores dozens of nanometers in size,which is beneficial for Rnadsorption and support of the nickel nanoparticles.The roughsurface of Ni/AC-800,showed nickel nanoparticles evenly dis-tributed on the surface of AC(Fig.1a and b).Furt

34、hermore,thePaperNJC9224|New J.Chem.,2022,46,92229228This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2022elemental mapping of Ni/AC-800 shows that the distribution ofNi element follows those of C and O,which further signifies thehomogeneous distribu

35、tion of nickel nanoparticles on AC.Thecontents of C,O and Ni are 92.3,5.1 and 2.6 wt%,respectively(Fig.1c and d).The content of Ni in Ni/AC-800 determined byICP-OES was 1.96 wt%.All of these results demonstrate thesuccessful impregnation of nickel onto the surface of AC.The effect of the calcination

36、 temperature on the structuralchange of Ni/AC composites was investigated.Fig.2 shows thestructural evolution of the samples prepared at temperaturesranging from 600 to 900 1C.The average particle sizes ofmetallic nickel in Ni/AC determined by TEM analysis were41.2?11.1,36.9?9.6,20.9?7.6,and 45.6?14

37、.8 nm,respectively.Ni/AC-800 showed the finest and most homoge-neous dispersion of nickel nanoparticles.However,nickelnanoparticles were not well dispersed in Ni/AC-900,and thepercentage of Ni metal particles in the range of 7090 nmincreased compared to those of other Ni/AC samples.Thereason may be

38、that the high reaction temperature induces theagglomeration of nickel nanoparticles.38In the HRTEM image(Fig.3a),it can be clearly seen that Nihas a lattice width of 0.20 nm,further verifying the presence ofNi in Ni/AC-800.As seen in the selected area electron diffraction(SAED)pattern(Fig.3b),the ni

39、ckel nanoparticles exhibit goodcrystalline behavior,and the distinct diffraction rings matchthose of cubic Ni(ICDD 04-850).The XRD patterns of the samples were analyzed to furtherinvestigate the effect of temperature on the structural change ofthe Ni/AC composites.As shown in Fig.4,the broad peaks a

40、t2y=241 are attributed to amorphous activated carbon.39Threemajor peaks at 44.61,51.81 and 76.41 are attributed to Ni(111),Ni(200)and Ni(220),respectively.40,41The average crystallinesizes of Ni/AC-600,Ni/AC-700,Ni/AC-800 and Ni/AC-900 calcu-lated by the Scherrer equation were 38.7 nm,35.7 nm,26.9 n

41、m,and 40.1 nm,respectively.Notably,Ni/AC-800 has the smallestcrystallite dimension among all the samples.This result isconsistent with that of the TEM measurements.More impor-tantly,it was found that the diffraction peak intensity of nickelfirst increased and then decreased with increasing tempera-t

42、ure,and Ni/AC-800 presented the largest diffraction peakintensity of nickel,suggesting that it possesses the highestcontent of nickel.These phenomena might derive from the factthat the temperature at 800 1C favors reaction of activatedFig.1SEM images of(a)activated carbon and(b)Ni/AC-800;(c)ele-ment

43、al mapping of Ni/AC-800;and(d)EDS spectrum of Ni/AC-800.Fig.2TEM images of(a)Ni/AC-600,(b)Ni/AC-700,(c)Ni/AC-800,and(d)Ni/AC-900.Fig.3(a)HRTEM image of Ni/AC-800;and(b)SAED of Ni/AC-800.NJCPaperThis journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2022Ne

44、w J.Chem.,2022,46,92229228|9225carbonwithnickelnitratetoformcrystallizednickelnanoparticles.Studies show that the loaded metal valence has an impor-tant influence on the adsorption of noble gases.25,42DFTcalculations showed that Ni atoms strongly adsorb onto xenonatoms.43To further investigate the e

45、ffect of the calcinationtemperature of Ni/AC on the valence state of nickel metal,XPSwas adopted to analyze the surface valence of nickel.Thechemical states of nickel in Ni/AC are shown in Fig.5.Clearly,there are three chemical states of nickel.44The first peak atapproximately 853.0 eV is attributed

46、 to Ni0,the second peak at855.8 eV with a satellite peak at 861.1 eV is attributed to Ni2+,and the third peak at 857.5 eV is ascribed to Ni3+.40,45Thedivalent and trivalent nickel components may be due to theincomplete reduction of Ni in the precursor.The content ofnickel in different valence states

47、 is directly proportional to theintensity of the peaks.The peak intensity is characterized bycorresponding integration of the area,and the area ratiorepresents the ratio of nickel content of different valence states.The surface composition of Ni/AC is shown in Table 1.Ni/AC-800 has the highest conte

48、nt of Ni0on the adsorbent surface,which is very significant for Rn uptake.Nitrogenadsorptionanddesorptionisothermswereobtained to evaluate the porosity levels of the AC and Ni/ACadsorbents.All samples exhibited IUPAC type I isotherms.Steep N2adsorption at a very low relative pressure(p/p0o0.01)indic

49、ates that the pores of these samples are mainlycomposed of micropores.Furthermore,in the range of 0.450.9(p/p0),an obvious hysteresis loop was observed for allsamples,indicating the presence of very few mesopores.Meso-pores could provide the mass transfer channel for the gases(Fig.S3a,ESI).The pore

50、size distribution curves can furtherconfirmthedistributioncharacteristicsofmicropores(Fig.S3b,ESI)and mesopores(Fig.S3c,ESI).The supportednickel nanoparticles do not change the pore distribution ofactivated carbon.All samples have a very sharp peak at approxi-mately 0.55 nm.The micropore size compar