1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Selected Papers from the 2nd Radiocarbon in the Environment Conference, Debrecen, Hungary, 3-7 July 2017
© 2018 by the Arizona Board ofRegents on behalf o f the University of Arizona
ISOTOPE ANALYTICAL CHARACTERIZATION OF CARBON-BASED NANOCOMPOSITES
T ib o r S zab ó • Ja n o v ic s R ó b e r t1 • M a ria n n a T ú r i1 • Is tv á n F u t ó 1 • Is tv á n P a p p 1 M ih á ly B r a u n • K ris z tiá n N é m e th 3 • G e rg ő P é te r S z e k e re d • A n ik ó K in k a 3 • A n n a S z a b ó 3 • K lá r a H e r n á d i • K a ta H a jd u 1,2 • L ász ló N a g y 2 • L ász ló R in y u 1
'isotope Climatology and Environmental Research Centre (ICER), Institute for Nuclear Research, Hungarian Academy of Sciences, Bem tér 18/c, Debrecen 4026, Hungary.
2Department of Medical Physics and Informatics, University of Szeged, Rerrich B. tér 1, Szeged 6720, Hungary.
d e p a rtm e n t of Applied and Environmental Chemistry, University of Szeged, Rerrich B. tér 1, Szeged 6720, Hungary.
ABSTRACT. Carbon-based nanomaterials of different dimensions (1-3D, tubes, bundles, films, papers and sponges, graphene sheets) have been created and their characteristic properties are discussed in the literature. Due to their unique advantageous, tunable properties these materials became promising candidates in new generations of applica
tions in many research laboratories and, recently, in industries as well. Protein-based bio-nanocomposites are referred to as materials of the future, which may serve as conceptual revolution in the development of integrated optical devices, e.g. optical switches, microimaging systems, sensors, telecommunication technologies or energy harvesting and biosensor applications. In our experiments, we designed various carbon-based nanomaterials either doped or not doped with nitrogen or sulfur during catalytic chemical vapor deposition synthesis. The amounts of heteroatoms in the composites were determined by radioanalytical and isotope analytical methods and their physico-/chemical prop
erties were compared. Based on 14C-analytics the yield of protein functionalization was also evaluated.
KEYWORDS: 14C analytics, carbon nanotubes, nanocomposites, N- and S-doping, reaction center protein.
INTRODUCTION
R e c e n t d e v e lo p m e n ts in in fo rm a tio n /c o m p u te r te ch n o lo g ies, in fo rm a tic s, o p to e le c tro n ic s a n d m o le c u la r b io lo g y m a d e it p o ssib le to m a n ip u la te m a te ria ls o n n a n o m e te r scales, o r even a t th e level o f m o lecu les, w h ich led to new disciplines o f th e 2 1 st ce n tu ry , su ch as “ N a n o te c h n o lo g y ” (see e.g. B h u s h a n 2004; W o lf 2004), “ N a n o - b io n ic s ” (see e.g. W o n g e t al. 2017; G ir a ld o e t al.
2014), “ (B io -)p h o to n ic s” (see e.g. W ilso n e t al. 2005; G e rd 2016; K n e ip p 2017), etc. T h a n k s to th e a c h ie v em e n ts o f th e se te ch n o lo g ie s new ty p e s o f m a te ria ls, n a n o m a te ria ls , are p ro d u c e d , w h ich offer new g e n e ra tio n s o f p ra c tic a l a p p lic a tio n s (S hoseyov a n d L ev y 2008;
C a rm e li e t al. 2007; D a r d e r e t al. 2007; F á b iá n e t al. 2010; S choles e t al. 2011; M a g y a r e t al.
2013; N a g y e t al. 2014).
A m o n g th e n a n o m a te ria ls , th e n a n o c o m p o s ite s are o f special in te re st b ec au se th e a d v a n ta g e o u s p ro p e rtie s o f th e c o m p o n e n ts c a n be c o m b in e d a n d /o r new c h a ra c te ristic s c a n a p p e a r w ith th e p o ssib ility o f tu n a b le , p red e fin e d m a n n e r (K a m ig a ito 1991; E v a n g e lo s 2007; N e m e th e t al.
2017). T h e special class o f n a n o c o m p o s ite s is th e b io -n a n o c o m p o site s, w h ich are co n sid ered as m a te ria ls o f th e fu tu re ( D a rd e r e t al. 2007; S ho sey o v a n d L ev y 2008; R u iz -H itz k y e t al. 2010;
N a g y e t al. 2014). A lth o u g h th e e x p lo ita tio n o f th e b io -n a n o c o m p o site m a te ria ls is m a in ly a w ish a t p re se n t, th e re is in te n siv e re se a rc h in m a n y la b o ra to rie s aim in g to ex p lo re th e ir fu n d a m e n ta l p ro p e rtie s o r to d e v e lo p th e ir p o ssib le p ra c tic a l a p p lic a tio n s. T h e ex tre m ely h ig h specificity, sensitivity, a n d effectiveness o f th e b io lo g ica l c o m p o n e n t o ffer p ro m isin g a p p lic a tio n s e.g. in activ e e lem e n ts o f b io se n so rs (Li e t al. 2011; C resp ilh o 2013; H o u e t al. 2016; S zabó e t al. 2017), in te g ra te d o p tic a l ( F á b iá n e t al. 2010, 2011), a n d o p to e le c tro n ic ( F la n a g a n e t al.
1988) devices. M a n y a tte m p ts h a v e b e e n m a d e fo r c re a tin g lig h t energy c o n v e rtin g (e.g. p h o to v o lta ic ) b io -n a n o c o m p o site devices (K ie tz k e 2007; Lee e t al. 2014; H a r tm a n n e t al. 2014;
S zekeres e t al. 2015; S z ab ó e t al. 2015). A d d itio n a lly , th e p ro ce sses h a p p e n in g a t th e in te rfa ce
*Corresponding author. Email: szabo.tibor@med.u-szeged.hu.
2 T Szabo et al.
b etw e en th e b io lo g ic a l a n d n o n -b io lo g ic a l c o m p o n e n ts c a n be a useful m o d e l to av o id
u n w a n te d re a c tio n s a g a in st th e h isto c o m p a tib ility o f artificial tissues, o rg a n s o r o th e r im p la n ts 44
in living beings. 45
T o im prove th e electrical properties o f M W C N T s, d o ping o f lattice o f c a rb o n n an o tu b es w ith 46
Q 5 different h etero ato m s (N , B, o r S) (D uclaux 2002; L iu et al. (2017); S h arm a e t al. (2017) via chem ical 47 Q 6 v ap o r deposition technique is a very p o p u la r m e th o d in th e field o f c a rb o n n an o tu b e science. 48 T h e re are several fields w h ere iso to p e a n a ly tic s a n d r a d io a n a ly tic s p ro v id e useful in sig h ts to 49 design, c re a te a n d ap p ly n a n o m a te ria ls (also (b io -)n a n o c o m p o site s) in e n v iro n m e n ta l sciences 50 as w ell ( G e r a n io e t al. 2010; F ei e t al. 2012; K i m e t al. 2 0 1 3 ,2 0 1 4 ; M a g y a r e t al. 2013; R o i g e t al. 51 2016; Y e d r a e t al. 2016; G o ttse lig e t al. 2017). E x a m p le s are as follow s: 52 I. D e te r m in a tio n o f ty p e s/so u rce s o f p re c u rso rs ( c a rb o n so u rces fro m d iffe re n t e n v iro n m e n t), 53 h e te ro a to m s (e.g. N o r S c o n te n t) w h e n c a r b o n m a te ria ls a re p ro d u c e d . 54 II. D e te r m in a tio n o f elem e n t c o n te n t vs. p h y sic o -/ch e m ic al c h a ra c te ristic s o f ( c a rb o n b a se d as 55 w ell) n a n o m a te ria ls . W e are fo cu sin g o n th e effects o f d o p in g (N , S d o p in g ), c o v e rin g w ith 56 m e ta l oxides o r fu n c tio n a liz a tio n o n th e o p tic a l a n d electric p ro p e rtie s. 57 III. F u n c tio n a liz a tio n w ith b io lo g ic a l m a te ria ls le a d s to th e c re a tio n o f b io -n a n o h y b rid 58 m a te ria ls w h ich are m a te ria ls o f th e fu tu re . Is o to p e a n a ly tic s h elp s in d e te rm in a tio n o f 59 yield o f fu n c tio n a liz a tio n , a b s o lu te q u a n tity o f c o m p o n e n ts a n d en z y m e activity. 60 O u r aim s w ere to p re p a re n itro g e n a n d su lfu r d o p e d c a rb o n n a n o tu b e s a n d to d e te rm in e th e 61 h e te r o a to m a n d 14C c o n te n t fo r fu rth e r c h a ra c te riz in g th e b io h y b rid m a te r ia l fo r fu tu re use. 62 T h e h e te r o a to m c o n ta in in g M W C N T s will be used as c a rrie rs a n d re a c tio n c e n te r p ro te in s 63
(R C s) as sensitizer m a tric e s. 64
MATERIALS AND METHODS 65
Preparation of Nitrogen and Sulfur Doped CNTs 66
D u rin g th e e x p e rim e n ts e ith e r F e (III)-C o (II)/c a lc iu m c a r b o n a te o r n ic k el(II)-o x id e c a ta ly sts 67 w ere used. In th is stu d y , a c a ta ly s t c o n ta in in g 5 m /m % F e a n d 5 m /m % C o w as p re p a re d b y 68 th e im p re g n a tio n te c h n iq u e . C a lc u la te d a m o u n ts o f C o (II)-a c e ty la c e to n a te , F e (III)- 69 a c e ty la c e to n a te a n d C a C O 3 w ere m ix e d in a b e a k e r w ith distilled w a te r. A fte r th a t a sh o rt 70 so n ic a tio n p ro ce ss w as ap p lie d to p re v e n t th e a g g re g a tio n o f solid p re c u rso r p article s. 71 A m m o n ia w as a d d e d to th e system to set th e p H to 9, a n d th e n th e d isp e rsio n w as p la ce d o n a 72 m a g n e tic stirre r a n d w as h e a te d a n d stirred in te n se ly a t 70°C u n til m o s t o f th e so lv e n t h a d 73 e v a p o ra te d . A fte r th e e v a p o ra tio n , th e p o w d e r c a ta ly st w as d rie d a t 100°C fo r 24 h r. In th e case 74 o f th e n ic k el(II)-o x id e c a ta ly st, c a lc u la te d a m o u n t o f N iO w as d issolved in a c e to n e a n d th e 75
su sp e n sio n w as d r o p p e d o n to a Si-sheet. 76
In this study, cataly tic chem ical v a p o r d ep o sitio n (C C V D ) m e th o d w as applied to synthesize 77 n itro g e n a n d sulfur d o p e d m u ltiw alled c a rb o n n a n o tu b e s (M W C N T s). N itro g e n a n d h y d ro g en 78 gases w ere passed th ro u g h th e re a c to r to m a in ta in a n in e rt a tm o sp h e re d u rin g the synthesis th a t 79 prev en ts M W C N T s fro m o x id a tio n a t h igher te m p eratu re s. T h e elem ental n itro g e n gas did n o t 80 ta k e p a r t in th e d o p in g process itself. T herefore, acetylene gas, th io p h e n e, a n d trip ro p y la m in e 81 (T P A ) w ere used as c a rb o n , sulfur a n d n itro g e n precursors, respectively. A cetylene a n d n itro g e n 82 gases w ere in tro d u c e d in to th e system b y passing th ro u g h a Y -sh ap ed ju n c tio n , w hile th e liquid- 83 p h ase T P A o r th io p h e n e w ere ad d e d b y th e b u b b lin g technique, w here the gases w ere co n d u c te d 84
Syringe pump or bubbling system
- * o —
exhaust
quartz boat with sample
Figure 1 Schematic image of the CCVD reactor
in to liquid T P A o r th io p h e n e, b efore the rea cto r, th u s th e gas b ubbles carried th e T P A o r th io ph en e to th e rea ctio n site (F igure 1). F o r m o re intense T P A feed, in jection m e th o d using a syringe p u m p w as also applied; fo r fu rth e r exp erim en tal details see Szekeres e t al. (2015).
In these ex p e rim en ts, 150 m g o f c a ta ly st w as m e a su re d in to a q u a rtz b o a t. A fte r 15 m in o f leach in g , th e q u a r tz b o a t w as p la c e d in to th e o v en h e a te d u p to 720°C . In th e follo w in g step, a fte r th e r e a c to r w as h e a te d , ac ety len e flow w as set to 35 L h r-1 a n d th e M W C N T g ro w in g p ro ce ss sta rte d . T o finalize th e sy nthesis, th e ac ety len e flow ra te w as set to zero , a n d a fte r a sh o rt-tim e o f le ac h in g , th e re a c to r w as co o led d o w n to ro o m te m p e ra tu re to co llect th e M W C N T sam ples. I n all cases T P A o r th io p h e n e w as fed in to th e re a c to r d u rin g th e w hole re a c tio n tim e (30 m in).
Preparation of MWCNT/RC Complexes
RC Purification
T h e c a ro te n o id le ss R -2 6 s tra in o f R h o d o b a c te r ( R b . ) s p h a e r o id e s p u rp le b a c te riu m w as g ro w n p h o to -h e te ro tro p h ic a lly u n d e r a n a e ro b ic c o n d itio n s in a S istro m -m e d iu m su p p le m e n te d w ith p o ta ssiu m su c cin a te (S istro m 1960). R C s w ere p re p a re d by L D A O (la u ry ld im e th ila m in e N -o x id e , F lu k a ) so lu b iliz a tio n a n d s ta n d a r d p r o te in p u rific a tio n m e th o d s (a m m o n iu m su lfate p re c ip ita tio n , D E A E S ep h acell (S igm a) c o lu m n c h ro m a to g ra p h y a n d u ltra filtra tio n ) as d escrib ed p rev io u sly (M a r o ti a n d W r a ig h t 1988).
Functionalzation of MWCNTs with -CO O H Group
M W C N T s w ere fu n c tio n a liz e d w ith ca rb o x y l g ro u p s in a q u e o u s n itric acid so lu tio n w ith a c o n c e n tra tio n o f 1 0 m /m % fo r 1 hr. A fte r fu n c tio n a liz a tio n , th e sa m p le s w ere w a sh e d w ith distilled w a te r a n d p u t in a d rie r a t 90°C fo r 2 hr.
Binding RC to MWCNTs
R C w as b o u n d to c a rb o x y l-fu n c tio n a liz e d M W C N T s by E D C /N H S ch e m istry p ro c e d u re . C N T w as a c tiv a te d b y th e a d d itio n o f c ro sslin k ers N -h y d ro x y su c c in im id e (N H S ) a n d
85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101
102 103 104 105
106 107 108
4 T Szabó et al.
Primary amine of RC
Stable MWCNT/RC complex (amide
; binding) Carboxyl functionalized
MWCNT
0 Hydrolysis
O -a c il iso u r e a
(unstable intermedier)
Amin-reactive
NHS ester Primary amine
of RC
Figure 2 Schematic representation of binding reaction center to -CO O H functionalized MWCNTs by the EDC/
NHS method.
l-[3 -d im e th y la m in o p ro p y l]-3 -e th y l-c a rb o d iim id e (E D C ). A fte r a c tiv a tio n , th e m ix tu re w as d ia ly ze d in p o ta s s iu m p h o s p h a te b u ffe r (O .lM , p H 7.0) to re m o v e th e u n b o u n d cro sslin k ers.
T h e n , th e c a lc u la te d a m o u n t o f R C so lu tio n (ty p ically ca. l0 0 p M ) w as a d d e d to th e ac tiv a te d M W C N T a n d it w as stirre d a t 4 °C fo r 3 hr. F in a lly , th e sa m p le w as se p a ra te d a n d w ash e d by an u ltra c e n trifu g e u n til th e ste a d y -sta te a b s o rp tio n sp e c tru m o f th e s u p e rn a ta n t d id n o t show th e c h a ra c te ristic p e a k s o f th e R C in th e n e a r in fra re d . T h e re a c tio n schem e is su m m a riz e d in F ig u re 2.
Electron Microscopy
E a c h sa m p le w as c h a ra c te riz e d b y tra n sm issio n e le c tro n m ic ro sc o p y (T E M , F E I , T e c h n a i G 2 20 X -T W IN , 200kV ) to stu d y th e ir m o rp h o lo g y , w h ich p la y s a key ro le in th e u n d e rs ta n d in g o f th e M W C N T d o p in g . T h e sa m p le s w ere p re p a re d as follow s: first a sm all a m o u n t o f sa m p le w as d isp ersed in a b s o lu te e th a n o l b y u ltra s o n ic a tio n (35 k H z) in a n u ltra s o n ic a tio n b a th (T ra n sso n ic T 5 7 0 /H ), th e n a few d ro p s o f th e d isp e rsio n w ere p la c e d o n a 200 m e sh C u T E M g rid w ith c a r b o n layer.
X-Ray Powder Diffractometry (XRD)
T h e g ra p h itic p ro p e rtie s o f M W C N T s w as in v e stig a ted b y X R D m e th o d (R ig a k u M iniflex I I D iffra c to m e te r) utilizin g c h a ra c te ristic X -ra y (C u , Kot) r a d ia tio n (angle ra n g e 0 = 2 0 -7 0 °).
Raman Spectroscopy
G ra p h itic p ro p e rtie s o f M W C N T s w ere also verified b y R a m a n sp e ctro sc o p y m e a su re m e n ts (T h e rm o Scientific D X R R a m a n m ic ro sc o p e ) usin g 532 n m la se r e x c ita tio n , 2 0 x objective,
l 0 m W la ser p o w e r a n d l 5 m i n m e a su rin g tim e Measurements of the Radiocarbon Contents
T h e c a r b o n c o n te n t o f th e sa m p le s w as lib e ra te d b y sealed tu b e c o m b u s tio n m e th o d . T h e sam p le a n d th e M n O 2 o x id a n t w ere w eig h ted in to a g lass tu b e . W h e n th e in itia l sa m p le w as in a liq u id m a trix it w as w eig h ted in to th e c o m b u s tio n tu b e a n d d rie d w ith th e h e lp o f a freeze d ry er
109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
u n it. T h e q u a n tity o f th e sa m p le w as c a lc u la te d fro m th e c o m b u stio n tu b e w ith th e d rie d sam p le
a n d th e e m p ty m a ss o f th a t. T h e tu b e s w ere e v a c u a te d to < 5 .1 0 _3 m b a r a n d sealed by a to rc h . 133 T h e sa m p le s w ere c o m b u ste d to C 0 2 in a m uffle fu rn a c e a t 550°C fo r 48 h r. T h e g a in e d C 0 2 w as 134 pu rified using a d e d ic a te d g as h a n d lin g system eq u ip p e d w ith cry o g en ic tr a p s in o rd e r to rem o v e 135 th e o th e r c o m b u ste d g a s c o m p o n e n ts . T h e q u a n tity o f th e p u re C 0 2 w as d e te rm in e d in a k n o w n 136 v o lu m e b y h ig h -p re c isio n p ressu re se n so r (Jan o v ic s 2016). T h e yield o f th e c a r b o n e x tra c tio n 137 c a n be c a lc u la te d fro m th e q u a n tity o f th e p u re C 0 2. T h e tr a p p e d a n d c lea n ed C 0 2 w ere 138 co n v e rte d to g ra p h ite by zinc re d u c tio n sealed tu b e g ra p h itiz a tio n m e th o d (R in y u e t al. 2013; 139 0 r s o v s z k i a n d R in y u 2015). In th e case o f less th a n 100 m ic ro g ra m s c a rb o n , zinc m ic ro - 140
g ra p h itiz a tio n te c h n iq u e w as used (R in y u e t al. 2015). 141
T h e m e a su re m e n ts o f th e 14C c o n te n ts w ere c a rrie d o u t o n a M I C A D A S ty p e a c c e le ra to r 142 m a ss s p e c tro m e te r (S ynal e t al. 2004, 2007) in th e In s titu te fo r N u c le a r R e se a rc h , D e b re c e n , 143 H u n g a ry (M o ln a r e t al. 2013). In o rd e r to tr a c k p o ssib le m o d e rn c a r b o n c o n ta m in a tio n 144 d u rin g th e p r e tr e a tm e n t a n d c o m b u stio n p ro cess, we h a v e e x tra c te d c h e m ic al s ta n d a rd s w ith 145 w ell-k n o w n 14C a c tiv ity (IA E A C 7 a n d C8; L e C le rc q e t al. 1998) o n th e sa m e tr e a tm e n t line 146 a n d m e a su re d th e m to g e th e r w ith th e sa m p le s in th e sam e m e a su re m e n t m a g az in es. B A T S 147 A M S d a t a e v a lu a tio n so ftw a re w as used to tre a t, p ro ce ss a n d an a ly z e all o f th e 14C d a t a 148
(L u k a s 2010). 149
Measurement of Stable Isotope Ratios 150
S tab le iso to p es w ere m e a su re d b y a T h e rm o F in n ig a n D e lta plusX P iso to p e r a tio m a ss spec- 151 tro m e te r a tta c h e d to a n e le m e n ta l a n a ly z e r (F is o n s N A 1 5 0 0 N C S ). T h is E A -I R M S m e th o d is 152 b ased o n th e ra p id o x id a tio n o f th e sa m p le b y flash c o m b u stio n , w h ich c o n v e rts all th e o rg a n ic 153 a n d in o rg a n ic su b sta n c e s in to c o m b u stio n p ro d u c ts, th e n th e re su lte d gases are se p a ra te d in a 154 c h ro m a to g ra p h ic c o lu m n a n d d e te c te d b y th e m a ss sp e c tro m e te r (M a jo r e t al. 2017). T h e 155 m e a su re d v alu es are expressed in d e lta n o ta tio n like 8 13C a n d 8 15N , w h ich d e lta v alu es are 156 de n ed as follow s: 8 ( I ) = (R / R - 1) x 1000, w h ere R is th e 13C /12C , 15N / 14N 157 ra tio in th e sam p le o r in th e in te rn a tio n a l referen ce m a te ria l as in d ic a te d . T h e u n c e rta in ty o f th e 158
m e a su re m e n ts is 0 . 2 I fo r S 13C a n d ± 0 . 3 I fo r 8 15N . 159
Measurement of Sulfur Content 160
C a rb o n n a n o tu b e sa m p le s w ere dig ested usin g a M a rs 5 m ic ro w a v e system . 50 m g o f th e sa m p le 161 w as w eig h ted in to th e T eflo n b o m b s a n d w as dig ested by 2 m L 67% (m /m ) n itric acid (su p ra - 162 p u re , V W R C hem icals). T h e ap p lie d p o w e r w as 800 W , 2 0 0 °C w as re a c h e d w ith in 20 m in , a n d 163 it w as h e ld fo r 30 m in . T h e sa m p le s w ere tra n s fe rre d in to 50 m L v o lu m e tric flasks a n d filled u p 164
w ith u ltra p u re w ate r. 165
T h e an a ly sis o f su lfu r w as p e rfo rm e d b y A g ile n t 8800 IC P -Q Q Q -M S system , u sin g M S /M S 166 m o d e . C h e m ic a l re a c tio n cell (C R C ) w as o p e ra tin g w ith o xygen re a c tio n gas. T h e su lfu r w as 167 m e a su re d w ith m a ss-sh ift, m e a su re d o n m /z 48 (cf. E q u a tio n 1): 168
32S + + 32 0 2 = 32S 160 + + 160 (1)
RESULTS AND DISCUSSIONS 169
Structural Characterizations of MWCNTs 170
By c o m p a rin g th e T E M im ag es o f u n d o p e d (F ig u re 3), N -d o p e d (F ig u re 4) a n d S -d o p e d 171 (F ig u re 5), m o rp h o lo g ic a l c h a n g e s c a n be clea rly identified. T h e m ic ro g ra p h o f N -d o p e d 172 M W C N T s (F ig u re 4) rev e ale d th a t th e re a c tio n p r o d u c t w as a c a r b o n d e p o s it c o n ta in in g
6 T Szabo et al.
Figure 3 Representative TEM image of undoped CNTs.
Figure 4 Representative TEM image of N-doped MWCNTs, visualizing the structural degenerations caused by the dopant, e.g. the bamboo structure.
h o llo w M W C N T s w ith b a m b o o -lik e segm ents. D iffe re n t fro m th e N -d o p e d n a n o s tru c tu re s , S -d o p e d n a n o s tru c tu re s sho w ed a special coiled m o rp h o lo g y , w h ich is o v era ll re p re se n ta tiv e fo r th e sam ples. T h e stru c tu ra l v a rie tie s fo u n d in th e N -d o p e d a n d S -d o p e d sa m p le s ca n
173
Figure 5 Representative TEM image of S-doped MWCNTs, showing the coiled morphology.
Figure 6 XRD diffractograms of undoped and N-doped CNTs.
p o ssib ly in d ic a te th e p rese n ce o f d o p a n ts , as sim ila r re a c tio n c o n d itio n s w ith d iffe ren t
h e te r o a to m resu lted in d istin c t s tru c tu ra l ch an g es. T h e stru c tu ra l d ifferen ces c a n re su lt fro m th e 174 m a n y fo rm s th e d o p a n ts c a n in c o rp o ra te in to th e M W C N T la ttic e (Szekeres e t al. 2015; Y a n g 175
e t al. 2015). 176
P o w d e r X R D m e a su re m e n ts w ere p e rfo rm e d to d e te rm in e , w h e th e r th e sy n th esized sa m p le s 177 possess a g ra p h itic stru c tu re . T h e d iffra c to g ra m s in F ig u re 6 show th e c h a ra c te ristic reflec tio n s 178 o f th e g ra p h itic la ttic e a t 20 = 26.11° a n d 44.65°, b u t w ith d iffe re n t rela tiv e in te n sities to e a ch 179 o th e r in th e tw o d a ta se ts, w h ich is th e re su lt o f th e significantly c h a n g e d stru c tu re s. T h e resu lts, 180 h o w ev e r, assu re th a t th e severe s tru c tu ra l d e g e n e ra tio n u p o n d o p in g d o es n o t n ecessarily re su lt 181
8 T Szabo et al.
uridaped MWCNT --- N-doped MWCNT
0.66 -
0.44 -
0.00 -
500 1000 1500 2000 2500 3000 3500 Raman shift (cm’ )
Figure 7 Raman spectra of undoped and N-doped CNTs.
in th e loss o f g ra p h itic p ro p e rtie s, a n d th e re fo re in th e exclu sio n o f u n iq u e electrical ch a racteristics.
R a m a n sp e c tra o f u n d o p e d a n d d o p e d M W C N T s a re sh o w n in F ig u re 7. G ra p h itic p ro p e rtie s are o fte n e x p lain e d b y th e in te n sity ra tio s o f th e D -b a n d (1341 cm -1 , assig n ed to th e p resen ce o f d efe ct sites) a n d th e G -b a n d (1527 c m 1, assig n ed to th e g ra p h itiz a tio n level). T h e in c re ase d D -b a n d in te n sity , as w ell as th e d e c re m e n t in th e G -b a n d in te n sity su g g est th a t th e c o n tin u o u s g ra p h itic la ttic e is significantly c o rru p te d in th e N -d o p e d sam ple. H o w e v e r, th e p resen ce o f th e G - a n d G ’-b a n d s in d ic a te th a t th e sam p le d id n o t lose its o v era ll g ra p h itic id e n tity , o n ly its h o m o g e n e ity — d u e to th e a lte re d re a c tio n c o n d itio n s c a u se d b y in tro d u c in g a d o p a n t— is low er.
S im ilar c o n c lu sio n s c a n be d ra w n fro m th e X R D a n d R a m a n in v e stig a tio n s o f th e S -d o p ed M W C N T s.
Isotope Analytical Investigations of CNTs
N in e d iffe re n t ty p e o f c a r b o n n a n o tu b e s w ere an a ly z e d b y iso to p e a n a ly tic a l m e th o d s a n d th e sam p le id e n tific a tio n w ith c h a ra c te ristic s (T a b le 1) a n d resu lts o f sta b le N a n d C c o n te n t (T a b le s 2, 3) a n d 14C c o n te n t (T a b le 4) are su m m a riz e d .
T h e m ass sp e ctru m o f the sam ple n a n o tu b e is co m p a re d to th e reference m a te ria l o f k n o w n c a rb o n a n d n itro g e n c o n te n t a n d all o f these calcu latio n s o f w eight p erc en t d e te rm in a tio n refer to the so-called signfiicant p eak . T h ere are sam ples w ith som e n itro g e n c o n te n t betw een 2.61% an d 5.3 m /m % (1/1466/9,10,13,14). T h e c a rb o n c o n te n t o f different sam ples is fairly different how ever, it ran g es betw een 33 a n d 67%. T h e sam ples w ith n itro g e n c o n te n t h a s a 8 15N value betw een 4 . 2 5 1 a n d 6 . 0 9 1 a n d th e stable c a rb o n iso to p e results cover a w ider ran g e betw een - 2 0 . 5 7 ! an d - 2 9 . 5 7 ! .
By using th io p h e n e , we fo u n d th a t th e in c re ase o f C V D synthesis te m p e ra tu re resu lted in h ig h e r c a r b o n d e p o s it th u s h ig h e r c a r b o n (m /m % ) (T a b le 2). O n th e o th e r h a n d , in c re asin g te m p e r a tu re is n o t a d v a n ta g e o u s fo r th e in c o rp o r a tio n o f h e te ro a to m s in to g ra p h itic stru c tu re s th e re th ro u g h th e b u ilt-in a m o u n t o f su lfu r is so m e w h a t lo w er a t 800°C .
T h e b u b b lin g m e th o d used fo r th e p r e p a ra tio n o f S -d o p e d C N T w as fo u n d to be m u c h less effective in th e sy n th esis o f N -d o p e d m a te ria ls, w hile u sin g T P A as d o p a n t. T h e sta b le N c o n te n t o f sam p les 11, 12, a n d 15 w as n o t d e te c ta b le (see T a b le 2), h o w ev e r, T E M
182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208
T a b le 1 Id e n tific a tio n a n d d e s c rip tio n o f d iffe re n t ty p e s o f n a n o tu b e s u sed fo r th e analysis.
S a m p le d e sc rip tio n
R e a c tio n tim e /
S am p le ID M e th o d L iq u id d o p in g tim e [min] T [°C]
I/1466/1 S -dop. B u b b lin g T h io p h e n e 30/30 700
I/1466/2 B u b b lin g T h io p h e n e 30 30 800
I/1466/9 N -d o p e d In je c tio n T P A - fe rro c e n e -a c e to n e 10 2 720
I/1466/10 In je c tio n T P A - fe rro c e n e -a c e to n e 20 5 720
I/1466/11 B u b b lin g T P A 40 40 720
I/1466/12 B u b b lin g T P A - a c eto n e 40 40 720
I/1466/13 In je c tio n T P A 20 5 720
I/1466/14 In je c tio n T P A 20 10 720
I/1466/15 B u b b lin g T P A 40 40 750
T a b le 2 S tab le n itro g e n , su lfu r a n d c a r b o n iso to p e resu lts o f in v e stig a te d n a n o tu b e species.
T h e sa m p le I D refers to th e sa m p le s listed in T a b le 1.
Sample ID
N ( 1 , A IR)
o ( 1 , A IR)
N itrogen (m/m%)
C ( 1 , VPDB)
o
( 1 , VPDB)
C arbon
(m m%) S ((mg/kg) o ((mg/kg)
I/1466/1 — — — -2 6 .7 9 0.16 33.30 318 3
I/1466/2 — — — -2 5 .8 9 0.04 41.94 256 4
I/1466/9 6.09 0.03 5.30 -2 4 .2 2 0.09 66.43 — —
I/1466/10 4.25 0.33 2.61 -2 7 .5 5 0.11 66.35 — —
I 1466 11 — — — -2 5 .0 5 0.16 45.41 — —
I/1466/12 — — — -2 6 .0 3 0.24 41.34 — —
I/1466/13 5.13 0.01 2.84 -2 9 .5 7 0.08 58.79 — —
I/1466/14 5.96 0.39 3.47 -2 9 .5 0 0.27 55.78 — —
I/1466/15 — — — -2 0 .5 7 0.04 37.56 — —
T a b le 3 14C c o n te n t o f th e in v e stig a te d n a n o tu b e s.
T h e sa m p le I D refers to th e sam p les listed in T a b le 1.
S am p le ID
C o m b u s tio n yield (%)
14C c o n te n t (p M C )
I/1466/9 56.0 18.0
I/1466/10 44.0 6.2
I/1466/11 63.0 4.0
I/1466/12 73.0 3.0
I/1466/13 59.0 13.6
I/1466/14 58.0 13.4
I/1466/15 33.0 34.1
Q7
in v e stig a tio n s rev e ale d som e b a m b o o -lik e c h a r a c te r o f th e se c a r b o n n a n o tu b e s , to o . S am p le 15
d e m o n s tra te d th a t in c re a sin g re a c tio n te m p e ra tu re is n o t a so lu tio n fo r g e ttin g h ig h e r N -d o p - 209 ing. F o r th e sy n th esis o f sam p le 12 th e liq u id used fo r b u b b lin g w as c h a n g e d , n a m e ly T P A w as 210 m ix e d w ith a c e to n e (1:9 r a tio ), w h ich p ro v id e d b e tte r v o la tility . H o w ev er, th is m o d ific a tio n d id 211
n o t re su lt in h ig h e r N -d o p in g eith er. 212
10 T Szabo et al.
T a b le 4 S u m m a ry o f d a ta o b ta in e d d u rin g d e te rm in a tio n o f th e 14C q u a n tity . S istro m m e d iu m is th e g ro w in g m e d iu m o f th e b a c te ria , R C is re a c tio n c e n te r p ro te in , f -M W C N T COOH is th e - C O O H fu n c tio n a liz e d 1/1466/11 sa m p le , a n d f -M W C N T COOH/R C is th e c a r b o n n a n o tu b e / re a c tio n c e n te r n a n o c o m p o site , respectively.
S am ple
S am p le q u a n tity (m g)
M e a su re d c a rb o n (m g)
Y ield
(%) p M C
S istro m -m e d iu m 9.93 2.07 21% 31.9 ± 0.5
R C 2.78 1.49 54% 66.1 ± 0.3
f-M W C N T 1.15 0.85 74% 6.4 ± 0 .1
f -M W C N T COOH/R C F
0.39 38.0 ± 2.0%
0.28 73% 29.1 ± 0 .1
A re a so n a b le e x p la n a tio n fo r th is sig n ifican t d iffe ren ce b etw e en th io p h e n e a n d T P A d o p a n ts c a n be fo u n d in th e ir v a p o r p ressu re v alu es a t ro o m te m p e ra tu re , w h ich d iffer b y 2 o rd e rs o f m a g n itu d e (T P A : 1.51 m m H g , th io p h e n e : 79.7 m m H g ). T h is ex p erien ce in sp ire d us to so m e w h a t m o d ify o u r C V D se tu p a n d b u ild a syringe p u m p in to th e system .
N -d o p e d sam ples p re p a re d w ith th e injection tech n iq u e (9, 10, 13, 14) resulted in signfficantly h igher stable N c o n te n t o f C N T sam ples (T able 2). I f we co m p a re th e N m /m % d a ta fo r sam ples 13 a n d 14, we c a n conclu d e th a t increasing d o p in g tim e fro m 5 to 10 m in (applying 20 m in rea ctio n tim e) c a n resu lt in a slightly h igher a m o u n t o f in c o rp o ra te d N . I t is k n o w n fro m literary d a ta (Y a d av e t al. 2005) th a t ferrocene is able to b lo c k the n itro g e n in c o rp o ra tio n in to th e c a rb o n n a n o tu b e structure, th e re fo re sam ples 9 a n d 10 w ere p re p a re d w ith ferrocene feed. S table iso to p e m easu rem en ts also revealed th a t th e in h ib itio n effect o f ferrocene a p p e ars only after a n in d u c tio n p eriod. 2 m in “T P A - ferrocene - a c eto n e” feed is n o t sufficient to b lo c k n itro g e n in c o rp o ratio n , hence th e stable N co n te n t value fo r sam ple 9 is sim ilar to th a t o f o th e r sam ples p re p a re d by injection. In creasin g ferrocene injection to 5 m in , th e block ag e c a n be alread y d etected (approx.
50% low er N -c o n te n t in T ab le 2) w hich is in ac co rd an c e w ith fo rm e r E M observations.
T h e 14C c o n te n t o f th e n a n o tu b e s w as also e x a m in e d a n d th e resu lts a re su m m a riz e d in T a b le 3. W e d id n o t g e t a v alid re s u lt in tw o sa m p le s (I/1466/1 a n d 2). T h e c o m b u stio n efficiency flu c tu a te s significantly fo r th e d iffe re n t sam ples. I t seem s th a t th is efficiency is h ig h ly d e p e n d e n t o n th e c a r b o n c o n te n t o f th e sam p le, w h ich is d e te rm in e d b y th e ap p lie d c a rrie rs a n d p re c u rso rs.
R e su lts in d ic a te th a t th e 14C c o n te n t o f th e n a n o tu b e s p ro d u c e d b y th e v a rio u s p r e p a ra tio n m o d e s v arie s w idely (fro m 3.0 p M C u p to 34.1 p M C ). Iso to p ic a n a ly tic a l studies h av e sh o w n th a t th e used sta rtin g m a te ria ls, p re c u rso rs a n d c a rrie rs h av e a stro n g iM u e n c e on th e c h a ra c te ristic s o f th e p ro d u c e d n a n o tu b e s . F o r b in d in g stu d ies, it is im p o r ta n t fo r th e 14C c o n te n t o f th e n a n o tu b e a n d th e p ro te in h a s to be significantly d iffe ren t. A s th e 14C c o n te n t o f th e in v e stig a te d p ro te in is d e te rm in e d by th e c a r b o n so u rce fro m w h ich th e p r o te in is d ev elo p ed , one asp ec t w as th e selectio n o f th o se n a n o tu b e ty p e s, w h ich h a v e th e lo w est 14C c o n te n t d u rin g th e analysis. E v e n tu a lly , th e tw o sa m p le c a n d id a te s fo r fu rth e r in v e stig a tio n s w ere I/1466/11 a n d I/1466/12 (cf. T a b le 4). W e used sa m p le I/1466/11 fo r n a n o c o m p o s ite p re p a ra tio n . A low 14C c o n te n t o f th e n a n o -tu b e is re q u ire d in o rd e r to b e tte r d e te rm in a tio n o f 14C c o n c e n tra tio n ch a n g e c a u se d by re a c tio n c e n te r co m p lex b in d in g (w hich is rec en t). T h is c a n be used to m o re a c c u ra te ly d e te rm in e th e b o n d e d R C ra tio .
In th e case o f th e re a c tio n ce n te r, th e p rim a ry c a r b o n so u rce is su p p lied b y th e S istro m -m e d iu m (31.9 ± 0.5 p M C , cf. T a b le 4). H o w e v e r, th e re c e n t a tm o sp h e ric c a rb o n -d io x id e (a ro u n d
100 p M C ) as se c o n d a ry so u rce also iM u e n c e s th e 14C c o n te n t o f th e b a c te riu m cells.
213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245
Measurements on MWCNT/RC Hybrid System
F o r p re p a rin g M W C N T /R C b io h y b rid system M W C N T s fu n c tio n a liz e d b y - C O O H g ro u p s w ere used, h e re a fte r referre d as f -M W C N T COOH. I n o rd e r to d e te rm in e th e a b s o lu te q u a n tity o f th e R C in th e f -M W C N T COOH/R C c o m p lex th e a m o u n t o f th e p r o te in b o u n d to th e f -M W C N T w as d e te rm in e d . F o r th is re a so n , th e p M C u n it w as d e te rm in e d f o r th e R C , f -M W C N T a n d f -M W C N T /R C sam ples. T h e R C fra c tio n o f th e f -M W C N T / R C co m p lex is o b ta in e d b y 14C b a la n c e e q u a tio n . 14C c o n te n t o f th e tw o -c o m p o n e n t m ix tu re is defined as E q u a tio n 2:
p M Cf _ m w c n tcooh / r c = Fr c ■ ° M Cr c + ( 1 - Fr c) - p M Cf _ m w c n tcooh (2)
w here p M C RC, p M C a n d p M C is th e m e a su re d 14C c o n te n t o f th e R C , f -M W C N T a n d f -M W C N T /R C co m p lex , respectively. F RC is th e R C fra c tio n o f th e 14C c o n te n t o f th e f -M W C N T /R C co m p lex . T h e R C f ra c tio n o f th e m ix tu re is o b ta in e d a fte r th e re a rra n g e m e n t o f 14C b a la n c e e q u a tio n (E q u a tio n 3):
Fr c =p M C f - MWCNTcooh / RC _ p M C f _ m w c n t cooh p M C RC _ p M C f _ MWCNTc
100
% . (3)By u sin g th e d a t a o b ta in e d d u rin g th e d e te rm in a tio n o f 14C q u a n tity a n d su m m a riz e d in T a b le 4, Fr c = 38.0 ± 2.0% c a n be c a lc u la te d . F in a lly , th e to ta l R C /f -M W C N T r a tio a n d th e a m o u n t o f R C (m /m ) b y th e k n o w n m o le c u la r w eig h t (M W : 80 k D a , 48% c a r b o n c o n te n t) c a n be c a lc u la te d using th e R C fra c tio n c o n s ta n t a n d th e c a r b o n e x tra c tio n yields o f th e a p p r o p r ia te c o m p o n e n ts . C a r b o n c o n te n t w as e s tim a te d b y th e R C stru c tu re o f 2 W X 5 .p d b d e p o site d in th e B ro o k h a v e n P ro te in D a ta B a n k (h ttp s ://w w w .rc sb .o rg /p d b /h o m e /h o m e .d o ) a fte r o m ittin g th e w a te r m o lecu les. T h e c a lc u la te d a m o u n t o f th e p h o to sy n th e tic re a c tio n c e n te r b o u n d to M W C N T s fo u n d 53 m /m % R C w h en th e p r o te in b o u n d b y th e E D C - N H S ch em ical b in d in g m e th o d .
CONCLUSIONS
F o r s u m m a ry , we c a n c o n c lu d e th a t b y a p p ly in g a specific c h a n g e in th e e le m e n t c o m p o sitio n o f th e p re c u rs o rs d u rin g N W C N T sy n th e sis specific d o p in g c a n b e ac h ie v e d , fo r e x a m p le N a n d S c a n be in se rte d in th e C N T s tru c tu re . T h e yield o f th e d o p in g w as p ro v e d b y th e is o to p e a n a ly tic a l in v e stig a tio n s. D o p in g th e M W C N T s b y N a n d S re su lte d in specific s tr u c tu ra l c h a n g e s w ith th e a p p e a r a n c e o f “ b a m b o o -lik e ” o r sp ira l s tru c tu re s, resp ectiv ely .
T h e iso to p e c o n s titu tio n o f b io h y b rid m a te r ia ls p r e p a re d f ro m th e b a r e a n d /o r d o p e d c a r rie r C N T s a n d e n z y m e s p ro v e d th a t iso to p e a n a ly tic s is a u se fu l to o l f o r d e te rm in in g th e q u a n ti
ta tiv e b in d in g o f th e b io lo g ic a l m a te r ia ls to th e c a r rie r m a tric e s. A fte r d e te rm in in g th e q u a n tita tiv e a m o u n t o f th e en z y m e th e specific a c tiv ity o f th e sa m p le c a n b e d e te rm in e d . T h e a m o u n t o f th e p h o to s y n th e tic r e a c tio n c e n te r b o u n d to M W C N T s c a n b e d e te rm in e d in a sen sitiv e w a y a n d fo u n d 53 m /m % R C w h e n th e p r o te in b o u n d by th e E D C - N H S ch e m ic al b in d in g m e th o d . D e ta ile d in v e s tig a tio n o f th e effec t o f d iffe re n t c a r b o n so u rce s u n d e r th e g r o w th c o n d itio n s a re b e y o n d th e sc o p e o f th is p u b lic a tio n , h o w e v e r, th is c a n b e a m a tte r o f f u rth e r in v e stig a tio n .
246 247 248 249 250 251 252
253 254 255 256 257
258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283
12 T Szabó et al.
ACKNOWLEDGMENTS
T h e re se a rc h w as su p p o rte d b y th e E u ro p e a n U n io n a n d th e S ta te o f H u n g a ry , co -fin an ced b y 284 th e E u ro p e a n R e g io n a l D e v e lo p m e n t F u n d in th e p ro je c t o f G IN O P -2 .3 .2 .-1 5 -2 0 1 6 - 285 00009 “ I C E R ” a n d fro m th e N a tio n a l R e se a rc h , D e v e lo p m e n t a n d I n n o v a tio n ( N K F I ) F u n d 286 (O T K A P D 1 1 6 7 3 9 ), a n d K .N . a c k n o w led g e s th e fin a n c ia l s u p p o r t o f O T K A N N 1 1 4 4 6 3 287
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