GRAPHENE AS A TEMPLATE AND STRUCTURAL SCAFFOLD FOR THE SYNTHESIS OF 3D POROUS BIO-ADSORBENT

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1 Procdings of th 4 th Intrnational Confrnc on Environmntal Scinc and Tchnology Rhods, Grc, 3-5 Sptmbr 205 GRAPHENE AS A TEMPATE AND STRUCTURA SCAFFOD FOR THE SYNTHESIS OF 3D POROUS BIO-ADSORBENT ZHUANG Y., YU F. 3, MA J. and CHEN J.,2 Stat Ky aboratory of Pollution Control and Rsourc Rus, School of Environmntal Scinc and Enginring, Tongji Univrsity, 239 Siping Road, Shanghai , P. R. of China, 2 Dpartmnt of Mchanical Enginring, Univrsity of Wisconsin Milwauk, Milwauk, WI 532, USA, 3 Collg of chmistry and nvironmntal nginring, Shanghai Institut of Tchnology, Shanghai 20048, China jma@tongji.du.cn, jhchn@tongji.du.cn ABSTRACT Graphn-soy protin (GS) arogl was prpard by a simpl thrmal rduction mthod and thn usd as an adsorbnt for th rmoval of antibiotics. Th GS arogl wr charactrizd by optical contact angl mtr, scanning lctron microscopy (SEM), transmission lctron microscopy (TEM), X-ray diffraction (XRD), Raman, Branaur-Emmtt-Tllr (BET) and Fourir transform infrard spctroscopy (FTIR). In GS, graphn acts as a tmplat that loads onto th surfac of protin through hydrogn bonds to form a layrd bulk unit and intracts with ach othr to form slf-assmbld hydrogls. Morovr, graphn intracts wll with protin without obvious structural damag and dos not agglomrat. In Raman, thr is a slight incras of th intnsity ratio of th D pak to G pak (ID/IG) for th GS compard with GN which dmonstratd th succssful incorporation of graphn into protin without obvious structural damag. Th rsulting GS has a high spcific ara of m 2 /g with abundant microspors and xcllnt hydrophilic proprtis. Th macropor, msopor, and micropor of GS ar 0.009, 0.74, and 0.20 cm 3 /g, rspctivly. Th avrag por siz of GS is 0.23 nm. GS has xcllnt adsorption proprtis for ttracyclin (500.0 mg/g) and ciprofloxacin (500.0 mg/g). This rsult suggsts that th small quantity of graphn assistd th protin to form an xcllnt bioadsorbnt. Kywords: graphn, protin, adsorption, antibiotics. Introduction In th past svral yars, fr-standing two-dimnsional monolayr graphn with xcllnt proprtis has caught global attntion and has bn adoptd for various applications (Yu, Bo t al. 20, Wn, Cui t al. 202, Vadahanambi, t al. 203). Graphn has bn considrd as an xcllnt adsorbnt in nvironmntal applications du to thir high SSA (2630 m 2 /g). With its dlocalizd π bonds, graphn can potntially adsorb organic contaminants, spcially thos with molculs containing π-lctrons that can intract with th polarizd graphn surfac via π-π lctron coupling or van dr Waals intractions (in, Xu t al. 203, Chn, Gao t al. 204). Compard with polymrs, graphn composits may hav bttr hydrophilicity, biological compatibility, and lowr cytotoxicity; morovr, gls can b prpard at a larg scal by a facil glation procss in a short priod of tim. Howvr, graphn nanoshts tnd to aggrgat du to intrplanar intractions (Chowdhury and Balasubramanian 204). In addition, most forms of graphn matrials ar not wll disprsibl or solubl in most common solvnts du to thir low hydrophilicity, poor biocompatibility and fw functional groups, and high cost. Ths abov factors limit thir applications as adsorbnts. Th us of biocompatibl hydrophilic biopolymrs may improv watr solubility proprtis of nanomatrials. Thrfor, it is rasonabl to prdict that th biopolymr-mdiatd graphn gls may function as porous adsorbnts with satisfactory adsorption capacity and limitd toxicity for applications in wastwatr tratmnt (Chng, Dng t al. 203). As an adsorbnt, thr-dimnsional (3D)

2 graphn adsorbnts can b asily sparatd in th aquous solution. Dvloping hydrophilic and biocompatibl 3D bio-adsorbnts with a larg SSA and uniqu msoporosity will xpand thir significanc in nvironmntal applications (Zhao, Wang t al. 204). Chng t al. (Chng, Dng t al. 203) prpard thr typical graphn oxid (GO)-biopolymr gls (bovin srum albumin, chitosan, and doubl-strandd DNA) for th first tim and invstigatd th adsorption capabilitis of dys and havy mtals. Th GO-biopolymr gls displayd an adsorption capacity as high as 00 mg/g for mthyln blu dy and 350 mg/g for mthyl violt dy, rspctivly. Thus, it can b sn that graphn and polymrs can form gls to b usd as bioadsorbnts; howvr, th combination ways of graphn with polymrs and th charactristics of th rsulting matrials still nd furthr study. In this papr, a graphn assistd 3D porous soy protin arogl (GS) is prpard by a simpl thrmal rduction mthod, and thn th GS is usd as an adsorbnt for th rmoval of antibiotics from aquous solutions. This mthod is inxpnsiv, simpl, and faturs a highyild. In th synthsis procss of GS, graphn acts as a tmplat that is loadd onto th surfac of th protin to form a layrd bulk unit. Mor importantly, graphn also acts as a structural scaffold to form 3D hydrogls through slf-assmbly, which can b turnd into porous arogls aftr frz drying. Th protin combins wll with graphn in th GS, and th rsulting GS posssss high hydrophilicity and xcllnt adsorption proprtis for antibiotics. 2. Exprimntal 2.. Matrials All chmicals wr purchasd from Sinopharm Chmical Ragnt Co., td. (Shanghai, China) in analytical purity and wr usd in th xprimnts without any furthr purification. All solutions wr prpard using dionizd watr Prparation of graphn-soy protin arogls Graphit oxid was obtaind using th modifid Hummrs mthod (Hummrs and Offman 958, Hirata, Gotou t al. 2004, Mao, Pu t al. 202), disprsd in dionizd watr, and sonicatd in an ultrasound bath for 2 h. Soy protin and ascorbic acid wr addd to th GO disprsion and placd into an ultrasound bath for 5 h to form a uniform solution. Th mass ratio of graphn to soy protin was :6; th rsulting products wr dnotd as GS. Th mixtur was hatd in a watr bath undr 90 for 2 h to form hydrogls. Th arogls wr synthsizd aftr th hydrogls wr washd with distilld watr for svral tims and thn frz-drid for 24 h. For comparison, graphn arogl (GN) without protin was also prpard as dscribd abov Charactrization mthods Th surfac morphologis of GN and GS wr visualizd using a fild-mission SEM (Hitachi, S-4800), AFM (NanoScop III a MultiMod) and TEM (JEO, JEM-200). Th hydrophilicitis wr charactrizd by an optical contact angl mtr (Dataphysics, OCA-20). Masurmnts of micro-raman spctra wr carrid out using a Raman Scop systm (abram, B) with a 532 nm wavlngth incidnt lasr light and 20 mw powr. XRD wr collctd on a Bragg-Brntano diffractomtr (Rigaku, D/Max-2200) with monochromatic Cu Kα radiation (λ =.548 Å) of a graphit curv monochromator, and th data wr collctd from 2θ = 2-40 at a continuous scan rat of 2 / min for phas idntification. Th BET isothrms wr masurd by an Acclratd Surfac Ara and Porosimtry systm (Micromritics, ASAP 2020). A UV-visibl absorption-basd approach is usd for a dirct valuation of th protin contnt rlasd from GS (Attal, Thiruvngadathan t al. 2006, Jong, Kim t al. 2007). A calibration plot is thn mad by monitoring th intnsity of th pak as a function of th tru concntration of th CNTs. Earlir rfrnc statd that th adsorption pak at 280 nm is a signatur of th soy protin Batch sorption xprimnts Batch xprimnts wr conductd to valuat th adsorption prformanc of antibiotics on th adsorbnts. GN and GS wr slctd as adsorbnts for antibiotics adsorption in an aquous solution. Th rsidual concntrations in th solution wr dtrmind by an ultraviolt spctrophotomtr (Tianmi UV-230(II)) at 360 nm for ttracyclin and 270 nm for

3 ciprofloxacin. Th adsorption isothrm was studid at ph=6, and th initial concntration was st from mg/ to 50 mg/. Th adsorption capacity (mg/g) was calculatd using Equation () V qt ( C0 Ct ) m whr C 0 and C t ar th initial concntration and th concntration aftr a priod of tim t (mg/); V is th initial solution volum (); and m is th adsorbnt dosag (g). Adsorption isothrms wr fittd using angmuir and Frundlich modls, which wr usd to valuat th adsorption quilibrium, as shown in Equations (2) and (3). Anothr important paramtr, R, calld th sparation factor or quilibrium paramtr, can b usd to dtrmin th fasibility of adsorption in a givn concntration rang ovr adsorbnt, as shown by Equation (4) (i, iu t al. 203). C q Inq R ( ) C K K InK F K C InC n 0 whr K (/g) and α (/mg) ar th angmuir isothrm constants, and α rlats to th nrgy of adsorption. Whn C /q is plottd against C, a straight lin will b obtaind. Th valu of K can b obtaind from th intrcpt, which is /K, and th valu of α can b obtaind from th slop, which is α /K. Th maximum adsorption capacity of th adsorbnt, q m,cal, i.., th quilibrium monolayr capacity or saturation capacity, is numrically qual to K /α ; K F is th adsorption constant of th Frundlich modl, and n is th Frundlich linarity indx. Th angmuir modl is idal, as it posssss a prfct adsorbnt surfac and monolayr molcul adsorption. As an mpirical modl, th Frundlich modl is usd widly in th fild of chmistry. 3. Rsults and discussion 3.. Morphological and microstructur of GN and GS Digital imags of graphit oxid, protin, GS, and GN hydrogls ar shown in Fig. (a). It can b obsrvd that both GN and GS hydrogls hav uniform structurs; howvr, th GN hydrogl is much loosr than th GS hydrogl, and th GN hydrogl floats whil th GS hydrogl rmains at th bottom. () (2) (3) (4) Figur: Morphology and microstructur of GN and GS: (a) photographs of GN and GS hydrogls, (b) SEM of GS, (c) TEM of GN, and (d) TEM of GS..

4 Schmatic : Prparation procss of GS. To vrify th combination of graphn and protin, w invstigatd th microstructur of GN and GS arogls. An SEM of GS is shown in Fig. b, and it can b asily sn that GS has a rough structur with layrs, indicating por intractions btwn nanofillrs and th matrix (Rodríguz-Gonzálz, Martínz-Hrnándz t al. 202, Huang, i t al. 203). As a rsult, th protins ar sparatd into layrs of graphn. From Fig. d, it can b sn that in GS th protin (as pointd by th arrow in Fig. d) xists on th dg of graphn, and in GS th graphn around th protin appars to b much closr togthr than in GN as shown in Fig. c Composition and structur analysis XRD spctra of GN and GS ar prsntd in Fig. 2a, and Raman spctra of GN and GS ar prsntd in Fig. 2b. In Fig. 2a, no pak appars at 2θ of 0.6 dgr, proving that graphn oxid is partially rducd during th hydrogl prparation for both GN and GS. In Fig. 3c, 2θ of around 25 dgr of GN is th charactristic pak of frz-drid graphn arogl (Xu, Shng t al. 200), which furthr provs that th nanosht in this biocomposit is graphn rathr than graphn oxid. Morovr, th charactristic pak in GS is to th lft of that of GN. Sinc th lattic paramtrs of GS ar largr than GN, this furthr provs that th protin prvntd th graphn from agglomration. In Fig. 2b, th slight incras of th intnsity ratio of th D pak to G pak (I D/I G) for th GS compard with GN dmonstratd th succssful incorporation of graphn into protin without obvious structural damag (Gao, iu t al. 204). Fig. 2c shows th N 2 adsorption-dsorption isothrms of GS and protin. Th isothrms of GN xhibit a typical typ-i curv and a hystrsis loop at a rlativ prssur of 0.4, indicating th prsnc of slitshapd pors btwn paralll layrs of graphn (Frrari 2007). Th spcific aras of GS and GN ar m 2 /g and 9.7 m 2 /g rspctivly, whil th protin spcific ara is about 0 m 2 /g. Th por siz distribution of GS is also shown in Fig. 2d. Th macropor, msopor, and micropor of GS ar 0.009, 0.74, and 0.20 cm 3 /g, rspctivly. Th avrag por siz of GS is 0.23 nm. (a) (b) D G GN Intnsity GS Intnsity D G' GN G GS G' (dgr) Raman shift (cm - ) Quality adsorbd (cm 3 /g) (c) Adsorption-GS Dsorption-GS Adsorption-Protin Dsorption-Protin Por Volum (cm 3 /g) (d) Rlativ prssur (P/P 0 ) Por diamtr (nm) Figur 2: Composition and structur analysis (a) XRD of GN and GS, (b) Raman of GN and GS, (c) N 2 adsorption and dsorption curvs of GS and protin, (d) por siz distribution of GS.

5 3.3. Antibiotics adsorption Th adsorption isothrms wr calculatd by angmuir and Frundlich modls, as shown in Fig. 3a and 3b, rspctivly. Basd on th R 2 valus, it can b sn from Tabl that th adsorption isothrms fit wll by both th angmuir and th Frundlich modls. It could b calculatd from th angmuir isothrm quation that th maximum thortical adsorption capacitis of th two antibiotics on GS wr both mg/g. C /q (a) Ttracyclin Ciprofloxacin C (mg/) In q 7 (b) Ttracyclin Ciprofloxacin In C Figur 3: Antibiotics adsorption proprtis, antibiotics adsorption capacitis (a) of protin, GS and GN, adsorption isothrm (b), angmuir isothrm (c) and Frundlich isothrms (d) of antibiotics on GS. 4. Conclusions A graphn-assistd 3D porous soy protin arogl (GS) is prpard by a simpl mthod and thn usd as an adsorbnt for th rmoval of antibiotics. Th GS arogl has good hydrophilicity and abundant functional groups. Morovr, unlik protin which dos not contain any nano-pors, th GS has a larg spcific surfac ara. Th graphn in GS turnd out to b sparatd by protin and was prvntd from aggrgation. Th rsulting GS posssss xcllnt adsorption proprtis. As protin is inxpnsiv and nontoxic, th porous biocomposit arogl has significant potntial for us as an adsorbnt for biological applications. REFERENCES. Attal, S., R. Thiruvngadathan and O. Rgv (2006). "Dtrmination of th concntration of singlwalld carbon nanotubs in aquous disprsions using UV-visibl absorption spctroscopy." Analytical Chmistry 78(23): Chn, H., B. Gao and H. i (204). "Functionalization, ph, and ionic strngth influncd sorption of sulfamthoxazol on graphn." J. Environ. Chm. Eng. 2(): Chng, C. S., J. Dng, B. i, A. H, X. Zhang,. Ma, S. i and C. Zhao (203). "Toward 3D graphn oxid gls basd adsorbnts for high-fficint watr tratmnt via th promotion of biopolymrs." Journal of Hazardous Matrials 263 Pt 2: Chowdhury, S. and R. Balasubramanian (204). "Rcnt advancs in th us of graphn-family nanoadsorbnts for rmoval of toxic pollutants from wastwatr." Adv Colloid Intrfac Sci 204: Frrari, A. C. (2007). "Raman spctroscopy of graphn and graphit: Disordr, lctron phonon coupling, doping and nonadiabatic ffcts." Solid Stat Communications 43(-2): Gao, C., T. iu, C. Shuai and S. Png (204). "Enhancmnt mchanisms of graphn in nano-58s bioactiv glass scaffold: mchanical and biological prformanc." Sci Rp 4: Hirata, M., T. Gotou, S. Horiuchi, M. Fujiwara and M. Ohba (2004). "Thin-film particls of graphit oxid." Carbon 42(4): Huang,., C. i, W. Yuan and G. Shi (203). "Strong composit films with layrd structurs prpard by casting silk fibroin-graphn oxid hydrogls." Nanoscal 5(9): Hummrs, W. S. and R. E. Offman (958). "Prparation of graphitic oxid." J. Am. Chm. Soc. 80(3): Jong, S. H., K. K. Kim, S. J. Jong, K. H. An, S. H. and Y. H. (2007). "Optical absorption spctroscopy for dtrmining carbon nanotub concntration in solution." Synthtic Mtals 57(3-5): i, R.,. iu and F. Yang (203). "Prparation of polyanilin/rducd graphn oxid nanocomposit and its application in adsorption of aquous Hg(II)." Chmical Enginring Journal 229:

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