Porous covalent electron-rich organonitridic frameworks as highly selective sorbents for methane and carbon dioxide

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1 Received 9 My 2011 Accepted 20 Jun 2011 Pulished 19 Jul 2011 DOI: /ncomms1405 Porous covlent electron-rich orgnonitridic frmeworks s highly selective sorents for methne nd cron dioxide Pritosh Mohnty 1,, Lilin D. Kull 1 & Ki Lndskron 1 Cron dioxide cpture from point sources like col-fired power plnts is considered to e solution for stilizing the CO 2 level in the tmosphere to void glol wrming. Methne is n importnt energy source tht is often highly diluted y nitrogen in nturl gs. For the seprtion of CO 2 nd CH 4 from N 2 in flue gs nd nturl gs, respectively, sorents with high nd reversile gs uptke, high gs selectivity, good chemicl nd therml stility, nd low cost re desired. Here we report the synthesis nd CO 2, CH 4, nd N 2 dsorption properties of hierrchiclly porous electron-rich covlent orgnonitridic frmeworks (PECONFs). These were prepred y simple condenstion rections etween inexpensive, commercilly ville nitridic nd electron-rich romtic uilding units. The PECONF mterils exhiit high nd reversile CO 2 nd CH 4 uptke nd exceptionl selectivities of these gses over N 2. The mterils do not oxidize in ir up to temperture of 400 C. 1 Deprtment of Chemistry, Lehigh University, Bethlehem, Pennsylvni 18015, USA. Present ddress: Discipline of Chemistry, Deprtment of Pper Technology, IIT Roorkee, Shrnpur Cmpus, Shrnpur , UP, Indi. Correspondence nd requests for mterils should e ddressed to K.L. (emil: kl205@lehigh.edu).

2 nture communictions DOI: /ncomms1405 Flue gs emitted from col-fired power plnts constitutes 15 16% CO 2, 6 7% H 2 O, 3 4% O 2, nd out 70% N 2 (ref. 1). Cron dioxide cpture from col-fired power plnt emitters is currently considered s possile technology to stilize the CO 2 level in the tmosphere to void climte chnges 2. A vriety of sorent mterils re currently under investigtion for cron dioxide cpture. The key fetures of suitle sorents for cron dioxide cpture re high selective uptke of CO 2, fcile regenertion of the sorent t low-energy penlty, low cost of the sorent mteril, chemicl stility towrds H 2 O, O 2, SO x, nd NO x, s well s good therml stility. Porous mterils hve een discussed s promising sorents for cron dioxide cpture. Severl clsses of porous mterils re currently under investigtion, predominntly metl orgnic frmeworks (MOFs) 3 11, ctivted crons 12 14, moleculr orgnic solids 15, nd mine-functionlized silics More recently, lso reports on CO 2 sorption in porous covlent orgnic frmeworks nd polymers hve een pulished Generlly, sorents which physisor CO 2 (for exmple, MOFs nd crons) tend towrd lower selectivity nd gs uptke t low CO 2 pressure ( 1 tm) ut exhiit fcile reversiility, while strongly chemisoring mterils such s mine-functionlized silics tend towrds higher selectivities nd cpcities ut typiclly show less fcile reversiility. Recently, mine-functionlized MOFs hve een reported tht exhiit incresed CO 2 sorption t low pressure s well s significntly improved selectivity 4,5. Still, MOFs tend towrd chemicl instility (oxidtion, hydrolysis) due to the dtive nture of the metl lignd onds. It is pprent tht sorents with enhnced chemicl stilities nd hets of dsorption t the orderline etween strong physisorption nd wek chemisorption (c kj mol 1 ) re n ttrctive trget to rech good trde-off etween selectivity nd reversiility. Here we produce novel porous electron-rich covlent orgnonitridic frmeworks (PECONFs) s potentil sorents for cron cpture. In PECONFs, inorgnic nitridic uilding units re interconnected vi electron-rich romtic units to form porous covlent frmeworks. Cron dioxide sorption is expected to occur ecuse of the Lewis-cid Lewis-se interctions etween the electron-rich romtic constituents nd the electron-poorer cron dioxide molecules. In ddition, wek Lewis cid-se interctions etween the lone pirs t the nitridic uilding units nd CO 2 could contriute. Both types of interctions re likely stronger thn simple dispersion forces (5 20 kj mol 1 ) ut weker thn strong chemisorptive interctions ( > 50 kj mol 1 ), ecuse no covlent onds re formed etween the sorent nd CO 2. The covlent nd inert nture of the onds in PECONFs suggests high chemicl stility. Results Synthesis. We hve produced rchetypes of porous electron-rich covlent orgnonitridic frmeworks (PECONFs) from inexpensive 3,3 -diminoenzidine (DAB) nd hexchlorocyclotriphosphzene (Fig. 1) in simple polycondenstion rections using dimethylsulphoxide (DMSO) s the solvent. DAB cts s the electron-rich romtic uilding lock due to its four mino groups while hexchlorocyclotriphosphzene hs the role of the nitridic uilding unit. These uilding locks re significntly less expensive thn those used for covlent orgnic frmeworks nd polymers typiclly used so fr The mterils were otined s monoliths, which could e solventexchnged nd dried without crcking or disintegrtion (Supplementry Fig. S1). The microstructures of the monoliths could e modulted y systemticlly decresing the mount of the solvent (DMSO) in the rection mixture (see Supporting Informtion). Electron microscopy nd X-ry diffrction. The scnning electron microscopy (SEM) (Fig. 2) nd trnsmission electron microscopy (TEM) (Supplementry Fig. S2) imges of the PECONFs show tht the mterils re composed of intergrown, nerly sphericl prticles. Cl Cl P N N Cl Cl P P N Cl Cl + H 2 N NH 2 NH 2 NH 2 NH HN HN NH HN P NH N N P P N NH HN Figure 1 Rection scheme for the synthesis of PECONFs. Hexchlorocyclotriphosphzene nd diminoenzidine rect in polycondenstion rections from DMSO solutions to form PECONF mterils. c The dimeter of the spheres is function of the rectnt concentrtion., which ws synthesized t the highest concentrtions, showed the lrgest spheres with dimeters round 600 nm. nd, which were synthesized t decresed rectnt concentrtions, exhiited decresed sphere dimeters of round 400 nd 200 nm, respectively. The moderte intergrowth of the spheres produced mcropores etween the spheres., which ws prepred t the lowest rectnt concentrtions, hs polygrnulr structure with grin sizes in the order of few tens of nnometers. As consequence, does not exhiit mcroporosity. All mterils were non-crystlline, ccording to powder X-ry diffrction (Supplementry Fig. S3) nd selective re electron diffrction (Supplementry Fig. S4). MAS NMR spectroscopy. To investigte the structure of the mterils in more detil, we hve studied the 31 P MAS NMR nd 13 C CP MAS NMR spectr of the PECONFs. Figure 3 shows the 13 C spectr of PECONFs. Strong signls round 141 nd 131 p.p.m. with shoulder t 121 p.p.m. nd smll wek signl t 106 p.p.m. were oserved in the 13 C CP MAS spectr. The chemicl shifts re consistent with the presence of the DAB uilding lock. This confirms H N H N HN NH Figure 2 Scnning electron microscopy imges of PECONFs. (), (), (c), nd (d)., 2, nd 3 exhiit mcroporous structures of wekly intergrown sphericl prticles with tunle dimeters. does not show ny mcroporosity. Scle r equls one micrometer. d

3 nture communictions DOI: /ncomms1405 ARTICLE 240 Side nds # DMSO # Chemicl shift (p.p.m.) Chemicl shift (p.p.m.) Figure 3 Cross-polriztion mgic ngle spinning nucler mgnetic resonnce (CPMAS NMR) of PECONFs. () 13 C CPMAS NMR spectr nd () 31 P CPMAS NMR spectr of,,, nd re in ccordnce with structures composed of interconnected cyclotriphosphzene nd diminoenzidine uilding locks. Side nds re indicted y str. tht the electron-rich romtic DAB unit ws incorported into the PECONF mterils. An dditionl signl ws oserved round 39 p.p.m., which cn e ssigned to residul DMSO tht ws used s the solvent for the synthesis. The 31 P MAS NMR spectr (Fig. 3) of the PECONFs showed signls in the rnge from 0 to 25 p.p.m. which re typicl for P(V)N 4 tetrhedr 25,26,28. In, two strong, nd one wek signl were oserved t 0.4, 10.4, nd 22.5 p.p.m., respectively. In, 3, nd 4 three signls t lmost identicl chemicl shifts were seen. All the signls were stonishingly shrp given tht ll the mterils were non-crystlline indicting comprtively high degree of order. The oservtion of three signls suggests tht three different phosphorus environments re present in the frmeworks. This my e explined y the fct the P toms cn e surrounded y ridging s well s terminl DAB units in the frmework. Fourier trnsform infrred spectroscopy. The PECONF mterils were further studied y Fourier trnsform infrred spectroscopy (Supplementry Fig. S5). All the spectr show rod nd round 3,420 cm 1 nd shrp nd round 1,617 cm 1. These nds cn e ttriuted to the N H stretching nd ending virtions, respectively. Furthermore, severl rod nds re oserved in the region from 1,500 to 500 cm 1. The nds t ~1,090 nd ~950 cm 1 cn e ttriuted to the ν s (P NH P) virtions. The nds t 1,218 nd 1,420 cm 1 re due to the ν s (P = N P) virtions. The nd round 520 cm 1 cn e ssigned to the δ(p = N P) virtions. Similr nds re lso oserved in phosphorus nitride, nitride imides, nd oxynitrides The shrpness of the nds in the fingerprint region suggests reltively high degree of order in the mterils which corroortes the results from 31 P MAS NMR spectroscopy. Therml nd chemicl properties. We further studied the therml ehviour nd the oxidtive stility of the PECONFs. Supplementry Figure S6 shows the thermogrvimetric nlysis (TGA) nd differentil thermogrvimetry (DTG) thermogrms of PECONFs. The mterils re thermlly stle up to temperture of 400 C in ir. The thermogrms demonstrte tht mss loss occurs in four steps. The first two steps (mss loss ~20%) elow 300 C re ttriuted to the desorption of smll mounts of wter nd occluded DMSO (the presence of DMSO ws confirmed from the 13 C MAS NMR). Only ove 400 C, continuous mss loss ws oserved tht cn e ttriuted to oxidtion nd frmework decomposition (Supplementry Fig. S6). The mss loss t ~500 C cn e ssigned to the oxidtion of the orgnic units. Furthermore, shoulder ws oserved t ~700 C which is due to the decomposition of the P N Volume (cc g 1 ) c Gs uptke (mmol g 1 ) Volume dsored (mmol g 1 ) Reltive pressure P/P 0 Pressure (r) mesured t 273 K CH 4 uptke (mmol g 1 ) units. The TGA thermogrms of the smples heted in N 2 environment re shown in Supplementry Figure S7. All the thermogrms show three-step mss loss with totl mss loss of out 60%. The first two steps were oserved elow 300 C nd re due to desorption of smll mount of wter nd occluded DMSO. Unlike the smple heted in ir, no significnt mss loss ws oserved etween 400 to 600 C. This confirmed tht the mss loss t ~500 C in ir is due to the oxidtion of the orgnic units 28. The mterils re thermlly stle up to temperture of 600 C in N 2 tmosphere. The decomposition of the P-N units did not occur elow 800 C in N 2. Gs dsorption. To proe for porosity in the PECONFs, we recorded N 2 isotherms of little monolithic pieces (~2 3 mm dimeter) t 77 K. Figure 4 shows the N 2 sorption isotherms of,, nd. All of these mterils show type-i isotherm, which is typicl for microporous mterils. The surfce re of these smples increses systemticlly from to. The Lngmuir surfce res were estimted to e 583, 742 nd 969 m 2 g 1 for, nd, respectively (Tle 1). These vlues re further comprle with the cumultive surfce res (559, 717, nd 939 m 2 g 1 for, nd, respectively) clculted y density functionl theory (DFT) & Monte-Crlo nlysis (Tle 1). The clculted Brunuer Emmett Teller surfce res (499, 637, nd 851 m 2 g 1 for, nd, respectively) hve somewht lower vlues compred with the corresponding Lngmuir surfce res. The pore volumes estimted t p/p 0 = 0.95 re 0.29, 0.35 nd 0.43 cm 3 g 1 for, nd, respectively. Detils out the physicochemicl properties re given in Tle 1. No hysteresis ws oserved etween p/p 0 of 0.40 nd 0.85 in these mterils confirming the sence of mesopores. The shrp N 2 uptke ove p/p 0 = 0.95 confirms the mcroporosity, which ws lredy seen y TEM nd SEM. The isotherms re not completely closed yet t p/p 0 = A similr non-closed isotherm for non-crystlline covlent orgnic frmework ws recently oserved y Hupp et l. 21 d Pressure (r) Pressure (r) Figure 4 Isotherms of PECONF mterils. () N 2 nd () CO 2 sorption of PECONFs (monolithic form) mesured t 77 nd 273 K, respectively. N 2 nd CO 2 uptke increses from to. (c) N 2 nd CO 2 sorption isotherms of monoliths. Due to the sence of mcropores, the gs diffusion into the micropores is ssocited with slow kinetics which leds to very low N 2 uptke. (d) Methne sorption isotherms of,,, nd (powder form) mesured t 273 K. Isotherms of nd re very similr nd not distinguishle.

4 nture communictions DOI: /ncomms1405 Tle 1 Physicochemicl properties of PECONF monoliths. Smple ID Surfce re from N 2 sorption t 77 K (m 2 g 1 ) DFT & Monte-Crlo Cumultive surfce re (m 2 g 1 ) DFT & Monte-Crlo Cumultive pore volume (cm 3 g 1 ) Totl pore volume (N 2 t 77 K) (cm 3 g 1 ) BET Lngmuir N 2 t 77 K CO 2 t 273 K N 2 t 77 K CO 2 t 273 K The microporous nture nd the high surfce re of PENCONF-1, 2, nd 3 prompted us to study their CO 2 sorption properties. Figure 4 shows the CO 2 sorption isotherms of,, nd mesured t 273 K. For ll mterils, the CO 2 sorption ws completely reversile nd no significnt hysteresis ws oserved. The CO 2 uptke of,, nd reches vlues of 1.86, 2.85, nd 3.49 mmol g 1, respectively, t 1 tm. The cumultive surfce res clculted from the CO 2 isotherm t 273 K using DFT & Monte-Crlo nlysis show vlues of 438, 670, nd 827 m 2 g 1 for,, nd, respectively (Supplementry Tle S1). These vlues re somewht lower compred with the surfce res clculted from the N 2 sorption dt of these mterils using the Lngmuir eqution (Tle 1). The results indicte tht the CO 2 gs uptke scles with the surfce re of the mteril nd is inversely proportionl to the rectnt concentrtion in the synthesis. dsored only very smll mounts of N 2 t 77 K (Fig. 4c) nd ppered prcticlly non-porous for N 2. Surprisingly, however, it hd reltively lrge CO 2 uptke of 1.81 mmol g 1 t 273 K (Fig. 4c). The surfce re nd the pore volume clculted from the CO 2 sorption isotherm of this mteril using DFT showed vlues of 433 m 2 g 1 nd 0.14 cm 3 g 1, respectively (Tle 1). The CO 2 uptke is remrkle given the smll pore volume of only 0.14 mmol g 1. In fct, hs the highest gs uptke to pore volume rtio of ll PECONF mterils. The pore size distriutions of to estimted from the CO 2 sorption using DFT theory re shown in Supplementry Figure S8. nd hve nrrow monomodl pore size distriution centred on 0.55 nm. egins to exhiit imodl pore-size distriution. is trimodl with smll dditionl smll mximum is oserved t 0.62 nm. The smll N 2 uptke in cn e explined y the slow mss trnsport of N 2 into the strictly microporous monoliths t 77 K. In contrst, t 273 nd 298 K, mss trnsport is lrge enough to llow for significnt CO 2 gs uptke in. To confirm tht mss trnsport hs n importnt role in monoliths, we pulverized monoliths nd remesured the CO 2 isotherms t 273 nd 298 K nd the N 2 isotherms t 77 K. As expected, the PECONF- 4 mteril showed t type I N 2 isotherm (Supplementry Fig. S9). The CO 2 cpcity incresed to vlue of 2.95 mmol g 1 (Supplementry Fig. S10). This effect ws sent for pulverized forms of, 2, nd 3 demonstrting tht their hierrchicl microporous mcroporous structures provide effective mss trnsport into the monoliths (Supplementry Fig. S11). We hve further studied the methne sorption ehviour of the PECONF mterils in powder form. Figure 4d shows the CH 4 sorption isotherms of the to. All the isotherms re reversile with high mximum uptke of 1.07 mmol g 1 oserved for nd t 1 r nd 273 K. The dsors somewht smller mount (1.00 mmol g 1 ) of methne. hs the lowest CH 4 gs uptke of 0.83 mmol g 1. The methne uptke cpcities of these smples re still high t 298 K with the mximum uptke of 0.67 mmol g 1 t pressure of 1 r oserved for Het of dsorption (kj mol 1 ) CO 2 dsored (mmol g 1 ) CH 4 dsored (mmol g 1 ). This methne uptke (15 cc g 1 ) is higher compred with the methne sorption (0.8 wt % or 11.1 cc g 1 ) of microporous tris-o-phenylenedioxycyclotriphosphzene vn der Wls crystls 34 reported y Sozzni et l. 35 ut somewht smller thn those of covlent orgnic cges reported y Tozw et l. 36 However, the ltter cn only e mde y n expensive synthesis procedure. The methne sorption cpcities of,, nd re 0.53, 0.63, nd 0.58 mmol g 1, respectively t 298 K (Supplementry Fig. S12). Hets of dsorption. To further understnd the pore surfce chrcteristics of the mterils nd the dsorption process, we hve clculted the isosteric hets of dsorption ( H) for CO 2 nd CH 4. H ws clculted using the Clusius Clpeyron eqution from the sorption dt collected t 273, 298, nd 323 K (refs 4,37). The H vlue cn e otined from the plot of ln p versus the reciprocl of the temperture. Figure 5 shows H of CO 2 for to. At the dsorption onset, the H vlues for,,, nd re 29, 31, 26, nd 34 kj mol 1, respectively. Remrkly, the isosteric het of dsorption is nerly independent from the mount of CO 2 dsored. The het of dsorption drops only y 30% () nd 25% (PECONF 3 nd 4), respectively. This suggests tht if the pore volumes of the mterils cn e further incresed significntly higher CO 2 gs uptke cn proly e chieved even t low CO 2 pressure. We further clculted the isosteric het of dsorption of methne for ll the smples. Figure 5 shows H of to PECONF- 4. At the dsorption onset,,,, nd show high vlues of 22, 27, 25, nd 22 kj mol 1, respectively. The het of dsorption only wekly decreses with incresed methne loding. It is noteworthy, tht with the exception of the methne gs uptke is incresing with incresing het of dsorption, while the CO 2 gs uptke increses with the surfce re. Apprently, in the cse of methne dsorption the het of dsorption is more importnt thn the surfce re. The generlly high Het of dsorption (kj mol 1 ) Figure 5 Isosteric het of dsorption of PECONF mterils. () Isosteric hets of dsorption for CO 2 () nd CH 4 () hve een clculted from CO 2 nd CH 4 isotherms collected t 273, 298, nd 323 K. Hets of dsorption wekly decrese with incresed gs loding.

5 nture communictions DOI: /ncomms1405 ARTICLE methne uptke for ll PECONFs my e explined y H-π interctions. Such interctions hve een oserved in Vn der Wls crystls of tris-o-phenylenedioxycyclotriphosphzene molecules, tht re structurlly relted to the uilding units of the PECONF mterils 35. Gs selectivity. In ddition to the high CO 2 uptke nd the reversiility, high selectivity for CO 2 over N 2 is one of the necessry properties for mteril to e used s CO 2 dsorent. The selectivity for the PECONF monoliths ws estimted using the rtios of the Henry lw constnts 4. These constnts cn e clculted from the initil slopes of the isotherms. This method is one of the most common methods to clculte gs selectivities nd hs een pplied extensively to determine gs selectivities of metl orgnic frmeworks, crons, nd covlent orgnic frmeworks. The clculted CO 2 :N 2 selectivity of is the highest mong the PECONF mterils reching vlues of 109:1 t 273 K nd 51:1 t 298 K (Supplementry Tle S1; Supplementry Figs. S13 nd S14). The vlue is much higher compred with the next-higher vlue reported so fr (81:1 t 273 K) 4. Be et l. 38 reported CO 2 /N 2 selectivity of 95 t 298 K for crorne-sed metl orgnic frmework. However, this mteril ppers to e more expensive thn our mterils. The CO 2 :N 2 selectivities for (Supplementry Figs S13 nd S15) nd (Supplementry Figs S13 nd S16) re still high (: 74:1 nd 44:1 t 273 nd 298 K, : 77:1 nd 41:1 t 273 nd 298 K). The higher selectivity of compred with, nd 3 cn e ttriuted to its higher het of dsorption. hs selectivity of 83:1 nd 51:1 t 273 nd 298 K, respectively (Supplementry Figs S13 nd S17). We further clculted the selectivity of CO 2 :CH 4 nd CH 4 :N 2 of these smples t 273 nd 298 K (Supplementry Tle S1; Supplementry Figs S13 S17). hs the highest CO 2 :CH 4 selectivity of 12 t 273 K mong ll the mterils. However, the CH 4 : N 2 selectivity of 16 is mximum for t 273 K. Sorents with high selectivity for CH 4 over N 2 re of high prcticl interest, ecuse methne is often highly diluted y N 2 in nturl gs wells. Currently, N 2 /CH 4 seprtions re still eing done cryogeniclly ecuse of the sence of solid sorents with high methne sorption cpcities nd suitle selectivities. To verify the vlidity of the selectivities estimted from Henry s constnt rtios, we hve dditionlly clculted the selectivities y n independent method. We hve used idel dsored solution theory (IAST) which llows for the determintion of the selectivities s function of pressure. Becuse vlues clculted from Henry constnt rtios represent selectivities close to zero pressure, IAST selectivities t zero pressure should mtch with selectivities clculted from Henry s lw constnts. Our clcultions show tht the IAST selectivities re in resonle greement with the vlues otined from Henry s constnt rtios (Supplementry Figs S18 S23). The CO 2 /N 2 selectivity of t 273 is even somewht higher (135) compred with the vlue otined from Henry s constnts (109). It should e noted though tht rel selectivites cn only e determined y mesurements tht mimic the proposed sorption conditions. For exmple, in post-comustion CO 2 cpture, the contct time with the sorent would likely to e of the order of seconds; s such, ny equilirium sorption mesurements hve the potentil to e misleding, nd in this regrd pore size nd kinetic mss trnsport effects re lso importnt. Discussion In conclusion, we hve synthesized microporous electron-rich covlent orgnonitridic frmeworks in fcile condenstion rections from commercilly ville, reltively inexpensive uilding locks. The structures re tunle despite their non-crystllinity nd exhiit remrkle degree of mid-rnge order. The hierrchicl micromcroporosity is further dvntgeous feture of the mterils due to the enefits of hierrchicl porosity for the mss trnsport in porous mterils. The tunility of the structures trnsltes to their gs sorption properties. The mterils dsor high mounts of CO 2 (up to 3.5 mmol g 1 t 1 tm nd 273 K) which is exceeded y only few other sorents, nmely the mine-functionlized silic MBA- 2 (3.8 mmol) 33, nd the mine-functionlized MOFs io-mof-11 (6.0 mmol g 1 ), Zn 2 (C 2 O 4 )(C 2 N 4 H 3 ) 2 (H 2 O) 0.5 (4.35 mmol g 1 ) 4,5, nd Mg/DOBDC (7.2 mmol g 1 ) 39,40. exhiits one of the highest selectivities (CO 2 over N 2 ) for sorent with reversile CO 2 dsorption desorption isotherm. The high isosteric het of dsorption nd the high selectivity for CO 2 over N 2 cn e explined y Lewis cid se interctions etween the electronpoor CO 2 nd the electron-rich sorent. The hets of dsorption do not decline significntly even t high CO 2 lodings. Similrly, high isosteric hets of dsorption hve een oserved only for metlorgnic frmeworks ut not for covlent frmework mterils composed exclusively from non-metls 41. The strong covlent P N, N C, nd C C onds in the frmework provide the mterils with high chemicl roustness compred with MOFs s seen y the high oxidtive stility t tempertures s high s 400 C. The comintion of high therml nd oxidtive stility, high gs uptke, low cost, nd exceptionl selectivity for CO 2 over N 2 mke these mterils interesting cndidtes for CO 2 cpture pplictions. Furthermore, the PECONF mterils show high sorption cpcities nd hets of dsorption for methne s well s high selectivities of CH 4 over N 2 which is of high interest for the purifiction of nturl gs tht is frequently diluted with N 2. The mechniclly very stle monolithic structure s well s the hierrchicl micro-mcroporosity suggests further pplictions, for exmple in monolithic chromtogrphy. The successful synthesis of the PECONF mterils in monolithic shpe nd the strictly microporous nture of suggests tht this mteril cn lso e mde s gs-selective memrnes. Methods Mterils. Hexchlorocyclotriphosphzene, Alf Aesr, 98%. DAB, AK Scientific, 99%. Anhydrous dimethyl sulfoxide (DMSO), Alf Aesr, 99.8%. Synthesis of PECONFs. In typicl synthesis, out 1.5 mmol of DAB nd 0.5 mmol of PNC were dissolved in 3, 7.5, 15 nd 20 ml of DMSO for the synthesis of,,, nd, respectively. The resulting solution ws stirred for 30 min t RT. It ws then heted t temperture of 125 C. Geltion strts s erly s 5 min. After 30 min the smple cooled down to room temperture nd solid monoliths were collected. All the experiments were crried out in N 2 tmosphere using Schlenk s pprtus. The DMSO from the s-synthesized monoliths ws removed y soxhlet extrction using diethyl ether. The otined solid monoliths were sonicted in 30 ml of wter, wshed severl times with wter, nd dried in vcuum t 100 C. The sonictor used in the present reserch ws Cvittor Ultrsonic ME 11 (Mettler Electronics) with mximum power output of 200 W t 67 khz. Mesurements. The microstructures of the specimens were studied y SEM nd trnsmission electron microscopy (TEM). The SEM imges of the specimens were tken on Hitchi S-4300 SEM. The TEM imges were tken on JEOL JEM-2000 electron microscope operted t 200 kv. X-ry diffrction ws crried out using Rigku Rotflex diffrctometer with Cu Kα rdition source (λ = nm). The thermogrvimetric nlysis experiments were crried out oth in ir nd nitrogen using TA TGA 2950 instrument with heting rte of 10 C per minute. 31 P nd 13 C CP MAS NMR spectr were otined t MHz on Generl Electric NMR Instrument model GN-300 equipped with Doty Scientific 7 mm MAS proe. 13 C NMR chemicl shifts were referenced to the downfield line of dmntine t p.p.m., nd for 31 P NMR, the chemicl shift of 85% H 3 PO 4 ws set to zero using externl reference stndrds. The formtion of the microporous frmework structures were studied y nitrogen nd cron dioxide sorption using n Autosor-1 instrument (Quntchrome). Before nlysis, ll the smples were out-gssed overnight t 150 C in vcuum. The Brunuer Emmett Teller surfce re nlysis ws crried out using 5 dt points in the pressure rnge etween 5 nd 0.35 tm. Before IAST clcultions, ll isotherms were fitted into Lngmuir Freundlich isotherm. In ll cses, fit > 99% ws reched. IAST clcultions were performed using the softwre pckge ChromWorks. References 1. White, C. M., Strzisr, B. R., Grnite, E. J., Hoffmn, J. S. & Pennline, H. W. Seprtion nd cpture of CO 2 from lrge sttionry sources nd sequestrtion in geologicl formtions-coleds nd deep sline quifers. J. Air Wste Mnge. Assoc. 53, (2003).

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Commun. 46, (2010). 39. M, X., Wng, X. & Song, C. Moleculr sket sorents for seprtion of CO 2 nd H 2 S from vrious gs strems. J. Am. Chem. Soc. 131, (2009). 40. Cskey, S., Wong-Foy, A. & Mtzger, A. Drmtic tuning of cron dioxide uptke vi metl sustitution in coordintion polymer with cylindricl pores. J. Am. Chem. Soc. 131, (2008). 41. Dwson, R., Adms, D. & Cooper, A. I. Chemicl Tuning in CO 2 sorption in roust nnoporous orgnic polymers. Chem. Sci. 2, (2011). Acknowledgements The present work ws supported y Lehigh University strt-up funds nd fculty grnts. Dr Norm Zheng is grtefully cknowledged for MAS NMR mesurements. We thnk Mr Wde H. Biley who supported our therml nlysis experiments. Author contriutions K.L. nd P.M. designed experiments. P.M. nd L.K. performed the experiments. K.L. nd P.M. wrote the pper. Additionl informtion Supplementry Informtion ccompnies this pper t nturecommunictions Competing finncil interests: The uthors declre no competing finncil interests. Reprints nd permission informtion is ville online t reprintsndpermissions/ How to cite this rticle: Mohnty, P. et l. Porous covlent electron-rich orgnonitridic frmeworks s highly selective sorents for methne nd cron dioxide. Nt. Commun. 2:401 doi: /ncomms1405 (2011).