9.24.3
De e mina ion o Pho o he mal and
EMI Shielding E iciency o
G aphene–Sil e Nanopa icle
Composi es P epa ed unde Low-
Dose Gamma I adia ion
Andjela S e ano ić, Dejan Kepić, Miloš Momčilo ić, James L. Mead, Mi osla Huskić,
Kamel Haddadi, Mohamed Sebbache, Biljana Todo o ić Ma ko ić and S e lana Jo ano ić
A icle
h ps://doi.o g/10.3390/nano14110912
Ci a ion: S e ano i´c, A.; Kepi´c, D.;
Momˇcilo i´c, M.; Mead, J.L.; Huski´c,
M.; Haddadi, K.; Sebbache, M.;
Todo o i´c Ma ko i´c, B.; Jo ano i´c, S.
De e mina ion o Pho o he mal and
EMI Shielding E iciency o
G aphene–Sil e Nanopa icle
Composi es P epa ed unde
Low-Dose Gamma I adia ion.
Nanoma e ials 2024,14, 912.
h ps://doi.o g/10.3390/
nano14110912
Academic Edi o : Li Cao
Recei ed: 25 Ap il 2024
Re ised: 15 May 2024
Accep ed: 19 May 2024
Published: 23 May 2024
Copy igh : © 2024 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
nanoma e ials
A icle
De e mina ion o Pho o he mal and EMI Shielding E iciency o
G aphene–Sil e Nanopa icle Composi es P epa ed unde
Low-Dose Gamma I adia ion
Andjela S e ano i´c 1,2, Dejan Kepi´c 1,*, Miloš Momˇcilo i´c 1, James L. Mead 3, Mi osla Huski´c 4,
Kamel Haddadi 5, Mohamed Sebbache 5, Biljana Todo o i´c Ma ko i´c 1and S e lana Jo ano i´c 1
1Vinˇca Ins i u e o Nuclea Sciences, Na ional Ins i u e o he Republic o Se bia, Uni e si y o Belg ade,
P.O. Box 522, 11001 Belg ade, Se bia
2Facul y o Chemis y, Uni e si y o Belg ade, S uden ski g 12-16, 11158 Belg ade, Se bia
3Depa men o Compu ing Science, Uni e si y o Oldenbu g, D-26129 Oldenbu g, Ge many
4Facul y o Polyme Technology, Oza e 19, 2380 Slo enj G adec, Slo enia
5Uni e si y o Lille, CNRS, Uni e si y Poly echnique Hau s-de-F ance, UMR 8520-IEMN-Ins i u
d’élec onique de mic oélec onique e de nano echnologie, F-59000 Lille, F ance;
[email p o ec ed] (K.H.)
*Co espondence: [email p o ec ed]; Tel.: +381-(0)11-34-08-582
Abs ac : Sil e nanopa icles (Ag NPs) ha e been p oduced by low-dose (1–20 kGy) gamma i adia-
ion o sil e ni a e in he p esence o g aphene-based ma e ial (g aphene oxide o elec ochemically
ex olia ed g aphene). The la ge su ace a ea o hose g aphene-based ma e ials combined wi h he
p esence o oxygen-con aining unc ional g oups on he su ace p o ided success ul nuclea ion and
g ow h o Ag nanopa icles, which esul ed in a uni o mly co e ed g aphene su ace. The ob ained
Ag nanopa icles we e sphe ical wi h a p edominan size dis ibu ion o 10–50 nm o g aphene oxide
and 10–100 nm o elec ochemically ex olia ed g aphene. The pho o he mal e iciency measu emen
showed a empe a u e inc ease upon exposu e o a 532 nm lase o all samples and he highes
pho o he mal e iciency was measu ed o he g aphene oxide/Ag NP sample p epa ed a 5 kGy.
Elec omagne ic in e e ence (EMI) shielding e iciency measu emen s showed poo shielding o he
composi es p epa ed wi h g aphene oxide. On he o he hand, all composi es p epa ed wi h elec o-
chemically ex olia ed g aphene showed EMI shielding o some ex en , and he bes pe o mance was
measu ed o he samples p epa ed a 5 and 20 kGy doses.
Keywo ds: sil e nanopa icles; gamma i adia ion; g aphene oxide; elec ochemically ex olia ed
g aphene; pho o he mal e iciency; EMI shielding
1. In oduc ion
G aphene, a one-a om- hick ca bon shee , has been a ac ing he a en ion o many
esea che s since i s disco e y in 2004 because o i s unique s uc u e. A pe ec honeycomb
c ys al s uc u e o g aphene is composed o a ca bon–ca bon (C-C) sp
2
hyb idized ne wo k
ha o ms a 2D plana shee . In he ca bon amily, g aphene has become a ising s a
due o i s excep ional physicochemical cha ac e is ics, such as high su ace a ea, low
densi y, ou s anding elec ical conduc i i y, he mal s abili y, mechanical s eng h, and
biocompa ibili y. In addi ion o i s o iginal ea u es, g aphene’s su ace modi ica ion
can p o ide addi ional unc ions and expand i s ange o applica ions. The ma e ial can
be modi ied in e ms o i s physical and chemical cha ac e is ics, such as i s p e e ed
in e ac ion wi h nea by species, imp o ed mechanical s eng h, magne ic capabili ies,
ca aly ic quali ies, and semiconduc ing beha io [
1
]. Howe e , due o he dis up ion
o i s conjuga ed s uc u e, he chemical modi ica ion o g aphene a ec s i s elec ical
conduc i i y [
2
]. To make g aphene mo e wa e -dispe sible, s ong oxidan s a e o en
used o co alen ly modi y g aphene o p oduce g aphene oxide (GO), which can la e
Nanoma e ials 2024,14, 912. h ps://doi.o g/10.3390/nano14110912 h ps://www.mdpi.com/jou nal/nanoma e ials
Nanoma e ials 2024,14, 912 2 o 13
be educed o ob ain educed g aphene oxide ( GO) [
3
–
5
]. S ong oxidan s co alen ly
al e g aphene’s s uc u e o in oduce a ious pola unc ional g oups. The g aphene-
based la ice and exis ence o a ious oxygen-con aining g oups enable GO’s abundan
ascina ing p ope ies. Fi s , he unc ional g oups on he GO su ace se e as s ong
ancho ing si es o immobilize a a ie y o ac i e species. Typically, GO is insula ing
due o he la ge po ion o sp
3
hyb idized ca bon a oms domains and he p esence o
oxygen-con aining g oups. Howe e , a e he educ ion o GO, he ma e ial u ns in o
a semiconduc o o e en a semime al simila o g aphene [
6
]. Ano he way o p oduce
g aphene oxide is elec ochemical ex olia ion o g aphi e, which is a p omising subs i u e
since i dec eases g aphene’s deg ee o oxida ion while main aining i s s uc u al and
elec ical cha ac e is ics [
7
,
8
]. B ie ly, he an de Waals o ces in g aphi e a e weakened
by hyd oxyl ions o med om he educ ion o wa e du ing he elec ochemical p ocess,
which bind o he edges o g aphene and allow o he in e cala ion o elec oly e ions
be ween g aphene laye s. In he ollowing s age, in e cala ed ions a e educed, gas bubbles
expand, and g aphene laye s sepa a e. Wi h his me hod, i is easible o p oduce single-
and ew-laye g aphene wi h a high yield and big lake size [9].
Due o i s high su ace a ea, g aphene and i s de i a i es a e g ea ma e ials o ancho
me al nanopa icles [
10
]. Those nanopa icles show unique op ical, elec onic, and chemical
p ope ies ha a e signi ican ly dis inc i e om hei bulk me al coun e pa s. The mos
ex ensi ely s udied nanopa icles a e noble me al nanopa icles ha show p omising
esul s o be applied as senso s, ungicidal and bac e icidal agen s, in diagnos ics and
he apeu ics, and in d ug deli e y, o lis some [
11
–
13
]. An impo an cha ac e is ic o hese
nanopa icles is he exis ence o localized su ace plasmon esonance (LSPR) phenomenon.
B ie ly, when he ligh o a speci ic wa eleng h in e ac s wi h elec ons a he su ace
o he nanopa icle, hei collec i e oscilla ion esul s in s ong abso p ion o ligh as
well as sca e ing. The kine ic ene gy o he oscilla ing elec ons is hen con e ed o
hea h ough elec on–phonon and phonon–phonon in e ac ions and dissipa ed o he
su ounding medium h ough pa icle–medium in e aces [
14
]. This phenomenon pa ed
he way o he use o me al nanopa icles in wa e emedia ion, pho o he mal ca alysis, and
pho o he mal cance he apy [
15
]. Ano he eme ging applica ion o hese nanos uc u es
is he de elopmen o elec omagne ic in e e ence (EMI) shielding ma e ials owing o
hei high elec ic conduc i i y and la ge speci ic su ace a ea. Fo his pu pose, hese
nanos uc u es a e o en used as illing ma e ial wi h di e en polyme s o ca bon-based
nanoma e ials such as ca bon nano ubes o g aphene. Fo example, Kim e al. p epa ed a
s e chable EMI shielding ma e ial o sil e nanopa icles inco po a ed in o mic opo ous
poly(s y ene-b-bu adiene-b-s y ene) [
16
]. Zhang e al. inco po a ed Ag nanopa icles in o a
ca bon nano ube sponge and epo ed he maximum EMI shielding e iciency o o e
90 dB
in he X-band wi h a 3 w .% loading o Ag [
17
]. Li e al. co e ed a e lec i e laye o Al ilm
wi h g aphene/Ag nanopa icles coa ing and measu ed an EMI shielding e ec i eness
o 92.29 dB [
18
]. Nanowi es o Ag we e also in es iga ed o EMI shielding applica ions,
ei he sandwiched be ween g aphene laye s [
19
] o aligned and w apped in g aphene [
20
].
Apa om p o iding al e na i e pa hways o elec on ans e , g aphene shee s ac as
ba ie s ha block he con ac o he Ag nanos uc u e wi h oxygen, which leads o a be e
s abili y o Ag nanos uc u es and a p olonged li e ime o he shielding ma e ial.
Ag nanopa icles can be p epa ed by se e al me hods: chemical educ ion [
21
], sp ay
py olysis [
22
], lase abla ion [
23
], mic owa e plasma me hod [
24
], o UV ligh o elec-
on i adia ion [
25
,
26
]. Al hough he chemical educ ion me hod is cheap and simple,
i equi es he p esence o a s abilizing (capping) agen ha p e en s he o e g ow h o
agglome a ion o nanopa icles and ensu es hei long- e m s abili y. Ul asonic sp ay py-
olysis p o ides con ol o e pa icle size bu demands high empe a u es o up o 1000
◦
C.
The physical me hods o Ag nanopa icle syn hesis ha e d awbacks such as high ene gy
consump ion and equi e high concen a ions. Because i is s aigh o wa d, quick, and
a o dable, gamma i adia ion o e s an al e na i e o he adi ional me hods o c ea ing
sil e nanopa icles [
27
]. I does no equi e high empe a u es o ex a educ an s; hus, i is
Nanoma e ials 2024,14, 912 3 o 13
ene gy-e icien and en i onmen ally iendly. Addi ionally, by pe o ming he syn hesis o
Ag nanopa icles in he p esence o g aphene, he oxygen-con aining g oups on g aphene’s
shee s se e as loca ions whe e me al nanopa icles can be ancho ed [
28
]. G aphene hen
inhibi s hei oxida ion and p e en s nanopa icle agglome a ion, hus making he use o
s abilizing agen s supe luous. To da e, Ag nanopa icles we e syn hesized in he p es-
ence o g aphene oxide o educed g aphene oxide. Ha eesh e al. p epa ed a Ag- GO
nanocomposi e wi h poly inyl py olidone employing gamma i adia ion doses o 29, 58,
86, and 115 kGy [
29
]. A Ag- GO nanocomposi e wi h Roselle ex ac was p epa ed unde
80 kGy and in es iga ed o symme ic supe capaci o applica ions [
30
]. Liu e al. used he
elec on beam o he simul aneous educ ion o GO and Ag
+
ions employing doses om
70 o 500 kGy [
31
]. Ka i ha e al. used lowe doses o 2, 5, and 10 kGy o inco po a e he Ag-
GO composi e in o a glu a aldehyde (GA) c osslinked PVA ma ix o adia ion-sensi i e
op oelec onic applica ions [
32
]. Howe e , he use o low doses o gamma i adia ion o
he p epa a ion o Ag nanopa icles di ec ly syn hesized on g aphene shee s and wi hou
addi ional s abilizing agen s is insu icien ly desc ibed in he li e a u e.
In his pape , we employed gamma i adia ion a low doses (1–20 kGy) o ob ain Ag
nanopa icles ancho ed on o g aphene shee s in a one-s ep syn he ic p ocedu e. Di e -
en mic oscopy and spec oscopy cha ac e iza ion echniques we e used o examine he
gene a ed g aphene/Ag NP composi es, wi h a ocus on he mo phological and s uc u al
al e a ions b ough on by gamma i adia ion. The pho o he mal p ope ies o he compos-
i es we e de e mined by measu ing he empe a u e changes unde a 532 nm lase exposu e.
Fu he mo e, we measu ed he complex e lec ion and ansmission o elec omagne ic
adia ion up o 18 GHz and in es iga ed hei e iciency in EMI shielding.
2. Ma e ials and Me hods
2.1. Ma e ials
G aphi e powde (Sigma-Ald ich, S . Louis, MO, USA), highly o ien ed py oly ic
g aphi e ods (Vinˇca Ins i u e o Nuclea Sciences, Belg ade, Se bia), concen a ed sul u ic
acid (Ca lo E ba Reagen s, Milano, I aly), sodium ni a e (Lach-Ne , Ne a o ice, Czech
Republic), po assium pe mangana e (Me ck, Da ms ad , Ge many), hyd ogen pe oxide
(Mac on Fine Chemicals, Radno , PA, USA), ammonium pe sul a e (Al a Aesa , Wa d Hill,
MA, USA), and sil e ni a e (Al a Aesa ) we e used in his wo k. All eagen s we e used
as ecei ed.
2.2. Syn hesis o GO/Ag NP and EEG/Ag NP Composi es
As a s a ing g aphene ma e ial, we used g aphene oxide (GO) ob ained by modi ied
Humme s’ me hod and elec ochemically ex olia ed g aphene (EEG) ob ained by elec o-
chemical ex olia ion. To p epa e GO, 2 g o g aphi e powde was mixed wi h 46 mL o
concen a ed H
2
SO
4
and 1 g o NaNO
3
and cooled o 0
◦
C. Then, 6 g o KMnO
4
was added
while he solu ion was con inuously s i ed in a wa e ba h o keep he empe a u e below
20
◦
C. A e 30 min o s i ing, he empe a u e o he eac ion mix u e was aised o
35 ◦C
and 100 mL o dis illed wa e was added, a e which he empe a u e was aised o 98
◦
C
and main ained o 2 h. A e ha ime, 400 mL o wa e was added o dilu e he eac ion
mix u e, and 2 mL o 30% H
2
O
2
was added be o e allowing he liquid o cool o oom
empe a u e. The syn hesized GO was pu i ied by se e al cycles o cen i uga ion and
washing wi h dis illed wa e un il he supe na an ’s pH was neu al. Finally, he wa e
was e apo a ed and emo ed, and GO was d ied o e nigh a 60
◦
C in he o en. EEG
was p epa ed in a wo-elec ode sys em using highly o ien ed py oly ic g aphi e ods as
bo h he coun e and he wo king elec ode, wi h a cons an dis ance o 4 cm be ween
he elec odes. Ammonium pe sul a e was dissol ed in wa e o a concen a ion o
0.1 M
o make he elec oly e solu ion. A di ec cu en (DC) ol age o +12 V was applied,
and he ol age was kep cons an un il he ex olia ion p ocess was inished, which was
indica ed by he o al consump ion o he wo king elec ode. The ex olia ed p oduc was
collec ed by acuum il a ion and ho oughly cleaned wi h deionized wa e o lush ou
Nanoma e ials 2024,14, 912 4 o 13
any emaining sal . The p oduc was hen dispe sed in wa e using an ul asonic ba h. The
dispe sion was cen i uged a 2575
×
g o emo e any non-ex olia ed g aphi ic ma e ial,
and he supe na an was hen u ilized o he u he s eps. G aphene (GO o EEG) was
dispe sed in deionized MilliQ wa e using an ul asonic ba h o achie e s able dispe sion
wi h a g aphene concen a ion o 1 mg/mL. Then, sil e ni a e was added o a speci ic
olume o he g aphene dispe sions o achie e an AgNO
3
concen a ion o 0.001 M. As a
sca enge o oxida i e species p oduced du ing he adiolysis o wa e , isop opyl alcohol
was added o he eac ion mix u e in a olume a io o 1:10. Addi ionally, a gon was pu ged
h ough he eac ion mix u e be o e i adia ion o 15 min o emo e dissol ed oxygen.
The ials we e hen he me ically sealed and exposed o gamma adia ion. Gamma- ay
lux om he
60
Co nuclide was used o he i adia ions, wi h a dose a e o 8.8 kGy/h.
Samples we e exposed o he gamma i adia ion sou ce, ecei ing 1, 5, 10, and 20 kGy
doses. A e he i adia ion, he samples we e il e ed (0.2
µ
m po e size, Isopo e Memb ane
Fil e s, Da ms ad , Ge many), insed wi h deionized wa e , and d ied a 60 ◦C.
2.3. Cha ac e iza ion
T ansmission elec on mic oscope (TEM) examina ion o he samples was ca ied ou
using a JEOL (Tokyo, Japan) JEM-2100F using an accele a ion ol age o 200 kV. The samples
we e dispe sed in e hanol using an ul asound ba h and a d op o he mix u e was placed
on lacey ca bon coppe g ids (200 mesh) and d ied in he ai . The pa icle size dis ibu ions
we e calcula ed using SemA o e so wa e e sion 5.21. Scanning elec on mic oscopy
(SEM) analyses we e pe o med on JEOL JSM-6390LV (Tokyo, Japan) mic oscope a oom
empe a u e. Powde samples we e ixed on ca bon adhesi e ape. EDS measu emen s
we e pe o med on Ox o d Ins umen s Az ec X-max (Abingdon, UK) ene gy-dispe si e
spec oscope. The LLG-uniSPEC 2 spec opho ome e was used o eco d he UV–Vis
abso p ion spec a. To ca y ou he measu emen s, a small quan i y o he d ied ma e ial
was dispe sed in wa e , and spec a we e eco ded in qua z cu e es a oom empe a u e.
Fou ie - ans o m in a ed spec oscopy (FTIR) was eco ded on an A a a 370 The mo
Nicole spec ome e in he o m o a KB pelle . The mog a ime ic analysis (TGA) es s
we e pe o med on a TGA/DSC 3+ (Me le Toledo ins umen s, G ei ensee, Swi ze land)
unde ni ogen (20 mL/min) a a hea ing a e o 5
◦
C/min, om 25 o 700
◦
C. Con ac angle
measu emen s we e ca ied ou by using he sessile d op me hod on he The a Li e con ac
angle me e (Biolin Scien i ic, Go henbu g, Sweden). Thin ilms we e made by passing
15 mL
o composi e wa e dispe sion (concen a ion 1 mg/mL) h ough Me ck Millipo e
0.2
µ
m polyca bona e memb ane using a acuum. Fo da a acquisi ion,
∼
6
µ
L o deionized
wa e (MilliQ 18.2 m
Ω
/cm) was ca e ully d opped on he samples using a mic o sy inge.
All measu emen s we e pe o med a ambien condi ions (25
◦
C) and immedia ely a e
d ople s abili y. The da a we e analyzed using OneA ension so wa e ( e sion 4.0.3).
2.4. Pho o he mal Con e sion E iciency De e mina ion
Pho o he mal con e sion e iciency measu emen s we e pe o med in 1
×
1
×
4.5 cm
spec ome e qua z cu e es a oom empe a u e (22.3
◦
C). S able homogeneous dispe -
sions o he samples in wa e wi h a concen a ion o 1 mg/mL we e exposed o 532 nm
con inuous wa e (CW) lase adia ion. The lase powe was 180 mW, he lase powe
densi y was 1.38 W/cm
2
, and he beam was ci cula wi h 1.5 mm in diame e . To ensu e
he pe pendicula inciden lase beam o he cu e e wall, a special cu e e holde was
used (Figu e 1). The cen e o he lase spo was placed a a ixed posi ion in he cen e o
he cu e e. The empe a u e e olu ion was eco ded by a he mocouple (accu acy
0.1 ◦C
)
e e y 30 s. The samples we e i adia ed o 10 min (hea ing cycle) un il hey eached
he mal equilib ium. Then, he lase was swi ched o o allow he sample o cool down o
oom empe a u e and he empe a u e was moni o ed o he ollowing 15 min (cooling
cycle). The pho o he mal e iciency o he samples was calcula ed using Rope ’s me hod as
p e iously desc ibed [33,34].
Nanoma e ials 2024,14, 912 5 o 13
(Figu e 1). The cen e o he lase spo was placed a a ixed posi ion in he cen e o he
cu e e. The empe a u e e olu ion was eco ded by a he mocouple (accu acy 0.1 °C)
e e y 30 s. The samples we e i adia ed o 10 min (hea ing cycle) un il hey eached he -
mal equilib ium. Then, he lase was swi ched o o allow he sample o cool down o
oom empe a u e and he empe a u e was moni o ed o he ollowing 15 min (cooling
cycle). The pho o he mal e iciency o he samples was calcula ed using Rope ’s me hod
as p e iously desc ibed [33,34].
Figu e 1. Expe imen al se up o he pho o he mal e iciency measu emen s.
2.5. EMI Shielding E iciency Measu emen s
Samples we e p epa ed by passing 15 mL o 1 mg/mL wa e dispe sions h ough 0.2
µm PC memb ane using a acuum. EMI shielding e iciency measu emen s we e con-
duc ed using a Vec o Ne wo k Analyze (VNA) om Keysigh Technologies (S eamline
P5008A, San a Rosa, CA, USA) ope a ing in he equency ange 150 kHz–53 GHz. The
VNA was connec ed h ough highly s able coaxial cables o a dedica ed coaxial se -up o
measu e he complex e lec ion (S11) and ansmission (S21) up o 18 GHz. The EMIs o he
di e en samples a e ela ed o he esidual RF signals ansmi ed h ough he shield. In
o he wo ds, he ampli ude o he ansmission coe icien co esponds o RF signals ha
a e nei he e lec ed no abso bed by he samples. P elimina y o he mic owa e cha ac-
e iza ion o he samples, ec o calib a ion was pe o med a he ou pu o he coaxial
cables o emo e sys ema ic e o s. Inpu RF powe was se o −15 dBm, and in e media e
equency (IF) bandwid h was se o 100 Hz, esul ing in a ime pe equency o 10 ms.
All measu emen s we e conduc ed a oom empe a u e. Each sample was sandwiched
be ween wo hin ilms o cellulose (named ‘’pape ’’ in he ollowing) o a oid any con-
amina ion o he coaxial lange.
3. Resul s and Discussion
The la ge speci ic a ea o g aphene in he o m o g aphene oxide (GO) o elec o-
chemically ex olia ed g aphene (EEG) was used as a suppo o he nuclea ion and
g ow h o sil e nanopa icles (Ag NPs) p epa ed by gamma i adia ion a low doses (1–
20 kGy). As a sou ce o gamma i adia ion, 60Co nuclide was used, which p o ides su i-
cien ene gy o cause he adiolysis o wa e and he eme gence o eac i e oxida i e and
educ i e species. The p ima y educ i e species ha o igina e om he adiolysis o wa-
e such as hyd a ed elec on (e−(aq)) and hyd ogen adical (H•) ha e s anda d po en ials
o −2.9 V e sus s anda d hyd ogen elec ode (SHE) and −2.4 V/SHE, espec i ely [35].
The in oduc ion o isop opyl alcohol ha ac s as a sca enge o oxida i e species helps in
c ea ing he p edomina ely educ i e en i onmen , ans o ming he isop opanol mole-
cule in o a seconda y adical α-me hyl-hyd oxye hyl adical [36]. Bo h p ima y and
Figu e 1. Expe imen al se up o he pho o he mal e iciency measu emen s.
2.5. EMI Shielding E iciency Measu emen s
Samples we e p epa ed by passing 15 mL o 1 mg/mL wa e dispe sions h ough
0.2 µm
PC memb ane using a acuum. EMI shielding e iciency measu emen s we e con-
duc ed using a Vec o Ne wo k Analyze (VNA) om Keysigh Technologies (S eamline
P5008A, San a Rosa, CA, USA) ope a ing in he equency ange 150 kHz–53 GHz. The
VNA was connec ed h ough highly s able coaxial cables o a dedica ed coaxial se -up o
measu e he complex e lec ion (S
11
) and ansmission (S
21
) up o 18 GHz. The EMIs o
he di e en samples a e ela ed o he esidual RF signals ansmi ed h ough he shield.
In o he wo ds, he ampli ude o he ansmission coe icien co esponds o RF signals
ha a e nei he e lec ed no abso bed by he samples. P elimina y o he mic owa e
cha ac e iza ion o he samples, ec o calib a ion was pe o med a he ou pu o he
coaxial cables o emo e sys ema ic e o s. Inpu RF powe was se o
−
15 dBm, and
in e media e equency (IF) bandwid h was se o 100 Hz, esul ing in a ime pe equency
o 10 ms. All measu emen s we e conduc ed a oom empe a u e. Each sample was
sandwiched be ween wo hin ilms o cellulose (named ‘’pape ” in he ollowing) o a oid
any con amina ion o he coaxial lange.
3. Resul s and Discussion
The la ge speci ic a ea o g aphene in he o m o g aphene oxide (GO) o elec ochem-
ically ex olia ed g aphene (EEG) was used as a suppo o he nuclea ion and g ow h o
sil e nanopa icles (Ag NPs) p epa ed by gamma i adia ion a low doses (1–20 kGy). As
a sou ce o gamma i adia ion,
60
Co nuclide was used, which p o ides su icien ene gy
o cause he adiolysis o wa e and he eme gence o eac i e oxida i e and educ i e
species. The p ima y educ i e species ha o igina e om he adiolysis o wa e such as
hyd a ed elec on (e
−(aq)
) and hyd ogen adical (H
•
) ha e s anda d po en ials o
−2.9 V
e sus s anda d hyd ogen elec ode (SHE) and
−
2.4 V/SHE, espec i ely [
35
]. The in o-
duc ion o isop opyl alcohol ha ac s as a sca enge o oxida i e species helps in c ea ing
he p edomina ely educ i e en i onmen , ans o ming he isop opanol molecule in o a
seconda y adical
α
-me hyl-hyd oxye hyl adical [
36
]. Bo h p ima y and seconda y species
can educe sil e ions o a ze o alen s a e conside ing ha he s anda d edox po en ial
o Ag+/Ag is 0.7996 V/SHE.
The p esence o oxygen moie ies on g aphene’s s uc u e is esponsible o he nu-
clea ion and g ow h o Ag nanopa icles [
37
–
39
], as well as o hei s abiliza ion a e
g ow h [
40
]. I is specula ed ha ca boxyl and ca bonyl g oups a e p edominan ly localized
a he edges o shee s on sp
2
hyb idized C a oms, while hyd oxyl and epoxy g oups a e
placed on he basal plane on sp3hyb idized ca bon [41]. In his wo k, we used wo o ms
o g aphene—GO ob ained using s ong oxidan s by Humme s’ me hod and EEG p epa ed
unde mild condi ions om highly o ien ed py oly ic g aphi e. To inspec he p esence and
ype o oxygen unc ional g oups a ached o g aphene shee s be o e and a e he i adia-
ion, FTIR analysis was pe o med. As can be seen om Figu e 2, bo h ypes o g aphene
Nanoma e ials 2024,14, 912 6 o 13
show simila abso p ion bands ha can be a ibu ed o a ious oxygen-con aining unc-
ional moie ies on he g aphene’s su ace. The b oad band a 3420–3450 cm
−1
o igina es
om he O-H s e ching ib a ions o he C-OH g oups and adso bed wa e molecules,
while he bands a 1717, 1635, 1385, and 1060 cm
−1
co espond o he s e ching ib a ions
om ca bonyl g oups, s e ching ib a ion o C=C bond, s e ching ib a ions o hyd oxyl
o ca boxyl g oups, and s e ching ib a ions o C-O g oups, espec i ely. A e he i a-
dia ion, in he spec um o GO/Ag NPs, bands a 1385 and 1060 cm
−1
a e no de ec able,
while he band a 1717 cm
−1
om ca bonyl g oups has dec eased in ensi y. On he o he
hand, he spec um o EEG/Ag NPs shows he same bands as he s a ing EEG. This migh
be an indica ion o a be e suscep ibili y o he educ ion o GO unde gamma- ay lux in
compa ison o EEG.
seconda y species can educe sil e ions o a ze o alen s a e conside ing ha he s and-
a d edox po en ial o Ag+/Ag is 0.7996 V/SHE.
The p esence o oxygen moie ies on g aphene’s s uc u e is esponsible o he nucle-
a ion and g ow h o Ag nanopa icles [37–39], as well as o hei s abiliza ion a e g ow h
[40]. I is specula ed ha ca boxyl and ca bonyl g oups a e p edominan ly localized a he
edges o shee s on sp2 hyb idized C a oms, while hyd oxyl and epoxy g oups a e placed
on he basal plane on sp3 hyb idized ca bon [41]. In his wo k, we used wo o ms o g a-
phene—GO ob ained using s ong oxidan s by Humme s’ me hod and EEG p epa ed un-
de mild condi ions om highly o ien ed py oly ic g aphi e. To inspec he p esence and
ype o oxygen unc ional g oups a ached o g aphene shee s be o e and a e he i adi-
a ion, FTIR analysis was pe o med. As can be seen om Figu e 2, bo h ypes o g aphene
show simila abso p ion bands ha can be a ibu ed o a ious oxygen-con aining unc-
ional moie ies on he g aphene’s su ace. The b oad band a 3420–3450 cm−1 o igina es
om he O-H s e ching ib a ions o he C-OH g oups and adso bed wa e molecules,
while he bands a 1717, 1635, 1385, and 1060 cm−1 co espond o he s e ching ib a ions
om ca bonyl g oups, s e ching ib a ion o C=C bond, s e ching ib a ions o hyd oxyl
o ca boxyl g oups, and s e ching ib a ions o C-O g oups, espec i ely. A e he i a-
dia ion, in he spec um o GO/Ag NPs, bands a 1385 and 1060 cm−1 a e no de ec able,
while he band a 1717 cm−1 om ca bonyl g oups has dec eased in ensi y. On he o he
hand, he spec um o EEG/Ag NPs shows he same bands as he s a ing EEG. This migh
be an indica ion o a be e suscep ibili y o he educ ion o GO unde gamma- ay lux in
compa ison o EEG.
Figu e 2. FTIR spec a o (a) GO ( e e ence) and GO/Ag NP composi e i adia ed a 20 kGy and (b)
EEG ( e e ence) and EEG/Ag NP composi e i adia ed a 20 kGy.
The nuclea ion and g ow h o Ag NPs depend on he numbe o oxygen-con aining
unc ional g oups ha ha e he ole o nuclea ion si es. The high densi y o hese g oups
a o s nuclea ion o e g ow h, which consequen ly leads o a highe numbe o Ag nano-
pa icles [37]. In he opposi e case, he low densi y o hese g oups is ad an ageous o
g ow h, which yields a smalle numbe o hese nanopa icles bu compa ably bigge . To
p o ide a be e insigh in o Ag nanopa icle size, we eco ded TEM images o he GO/Ag
NPs and EEG/Ag NPs samples i adia ed by he lowes and he highes applied dose (Fig-
u e 3). TEM p o ides Z-con as images which enable a clea dis inc ion be ween Ag (Z =
47) ha appea s as da k spo s compa ed o pale g ay a eas o C (Z = 6). Fo bo h GO and
EEG, he ob ained Ag nanopa icles a e p edominan ly sphe ical and uni o mly co e he
su ace o g aphene shee s. Bo h ypes o g aphene success ully p e en ed he agglome -
a ion and c ea ion o la ge agg ega es o Ag nanopa icles ha commonly occu when Ag
nanopa icles a e syn hesized wi hou addi ional s abilize s. Fo GO, he majo i y o ob-
ained Ag nanopa icles (~75%) ha e sizes be ween 10 and 50 nm, while o he applied
dose o 20 kGy, we no iced only a mino inc ease in he 50–100 nm pa icle size ange and
Figu e 2. FTIR spec a o (a) GO ( e e ence) and GO/Ag NP composi e i adia ed a 20 kGy and
(b) EEG ( e e ence) and EEG/Ag NP composi e i adia ed a 20 kGy.
The nuclea ion and g ow h o Ag NPs depend on he numbe o oxygen-con aining
unc ional g oups ha ha e he ole o nuclea ion si es. The high densi y o hese g oups
a o s nuclea ion o e g ow h, which consequen ly leads o a highe numbe o Ag nanopa -
icles [
37
]. In he opposi e case, he low densi y o hese g oups is ad an ageous o g ow h,
which yields a smalle numbe o hese nanopa icles bu compa ably bigge . To p o ide a
be e insigh in o Ag nanopa icle size, we eco ded TEM images o he GO/Ag NPs and
EEG/Ag NPs samples i adia ed by he lowes and he highes applied dose (Figu e 3).
TEM p o ides Z-con as images which enable a clea dis inc ion be ween Ag (Z = 47)
ha appea s as da k spo s compa ed o pale g ay a eas o C (Z = 6). Fo bo h GO and
EEG, he ob ained Ag nanopa icles a e p edominan ly sphe ical and uni o mly co e he
su ace o g aphene shee s. Bo h ypes o g aphene success ully p e en ed he agglom-
e a ion and c ea ion o la ge agg ega es o Ag nanopa icles ha commonly occu when
Ag nanopa icles a e syn hesized wi hou addi ional s abilize s. Fo GO, he majo i y o
ob ained Ag nanopa icles (~75%) ha e sizes be ween 10 and 50 nm, while o he applied
dose o
20 kGy
, we no iced only a mino inc ease in he 50–100 nm pa icle size ange and
a dec ease in big pa icles (>100 nm). On he o he hand, only 45% o Ag nanopa icles
p epa ed on EEG ha e sizes be ween 10 and 50 nm and a signi ican po ion o Ag nanopa -
icles is la ge . This dissimila i y in Ag nanopa icle size dis ibu ion migh be due o he
di e ence in he numbe o oxygen-con aining unc ional g oups be ween GO and EEG.
Addi ionally, o EEG, a conside able inc ease in 50–100 nm pa icles and a dec ease in
>100 nm pa icles could be no iced a e he 20 kGy dose i adia ion.
SEM-EDS analyses we e pe o med o explo e he dis ibu ion o he cons i uen
elemen s o he p epa ed composi es (Figu e 4). In he s a ing g aphene ma e ials (GO and
EEG), we de ec ed only C and O wi h aces amoun o sul u and sodium ha emained
om he syn he ic p ocedu e. Elemen al analysis showed ha GO has a highe O con en
han EEG (Table 1). All composi es o GO and EEG showed homogeneous co e age o
g aphene shee s by Ag nanopa icles.
Nanoma e ials 2024,14, 912 7 o 13
a dec ease in big pa icles (>100 nm). On he o he hand, only 45% o Ag nanopa icles
p epa ed on EEG ha e sizes be ween 10 and 50 nm and a signi ican po ion o Ag nano-
pa icles is la ge . This dissimila i y in Ag nanopa icle size dis ibu ion migh be due o
he di e ence in he numbe o oxygen-con aining unc ional g oups be ween GO and
EEG. Addi ionally, o EEG, a conside able inc ease in 50–100 nm pa icles and a dec ease
in >100 nm pa icles could be no iced a e he 20 kGy dose i adia ion.
Figu e 3. TEM images o (a) GO/Ag NPs p epa ed a 1 kGy i adia ion dose, (b) GO/Ag NPs p e-
pa ed a 20 kGy i adia ion dose, (c) pa icle size dis ibu ion o GO/Ag NPs, (d) TEM images o
EEG/Ag NPs p epa ed a 1 kGy i adia ion dose, (e) EEG/Ag NPs p epa ed a 20 kGy i adia ion
dose and ( ) pa icle size dis ibu ion o EEG/Ag NPs.
SEM-EDS analyses we e pe o med o explo e he dis ibu ion o he cons i uen ele-
men s o he p epa ed composi es (Figu e 4). In he s a ing g aphene ma e ials (GO and
EEG), we de ec ed only C and O wi h aces amoun o sul u and sodium ha emained
om he syn he ic p ocedu e. Elemen al analysis showed ha GO has a highe O con en
han EEG (Table 1). All composi es o GO and EEG showed homogeneous co e age o
g aphene shee s by Ag nanopa icles.
The di e ence in oxygen-con aining unc ional g oup abundance be ween GO and
EEG is well depic ed in he TGA cu es (Figu e 5). The samples we e i s ly hea ed o 700
°C in a ni ogen a mosphe e. The TGA g aphs showed h ee empe a u e zones wi h dis-
inc i e mass loss s eps: egion (100 °C) associa ed wi h he loss o adso bed mois u e,
egion (100–360 °C) associa ed wi h he b eakdown o he mally labile oxygen-con aining
g oups, and egion (360–700 °C) associa ed wi h he decomposi ion o he ca bon la ice
[42,43]. EEG shows g ea e he mal s abili y and main ains 65.8% o he weigh a 700 °C
compa ed o GO (48.5% o he weigh a 700 °C). This is a consequence o a g ea e po ion
o he mally labile oxygen-con aining g oups in GO han in EEG. In addi ion, o bo h GO
and EEG, weigh loss is mos p ominen o non-i adia ed samples, and wi h he inc ease
in he i adia ion dose, his weigh loss g adually dec eases. This is an indica ion o he
pa ial es o a ion o g aphene’s conjuga ed s uc u e and he elimina ion o oxygen-con-
aining unc ionali ies caused by he educ ion unde gamma i adia ion [27].
Figu e 3. TEM images o (a) GO/Ag NPs p epa ed a 1 kGy i adia ion dose, (b) GO/Ag NPs
p epa ed a 20 kGy i adia ion dose, (c) pa icle size dis ibu ion o GO/Ag NPs, (d) TEM images o
EEG/Ag NPs p epa ed a 1 kGy i adia ion dose, (e) EEG/Ag NPs p epa ed a 20 kGy i adia ion
dose and ( ) pa icle size dis ibu ion o EEG/Ag NPs.
Figu e 4. SEM image and EDS maps o he co esponding a ea o ca bon, oxygen, and sil e o (a)
GO, (b) GO/Ag NPs p epa ed a 5 kGy, (c) GO/Ag NPs p epa ed a 20 kGy, (d) EEG, (e) EEG/Ag
NPs p epa ed a 5 kGy, and ( ) EEG/Ag NPs p epa ed a 20 kGy.
Table 1. Elemen al composi ion o GO, EEG, and hei composi es wi h Ag nanopa icles p epa ed
a di e en i adia ion doses.
Sample W .% Sample W .%
C O Ag C O Ag
GO 70.9 29.1 EEG 76.7 23.3
GO/Ag NP 1 kGy 62.6 28.7 8.7 EEG/Ag NP 1 kGy 84.9 14.3 0.8
GO/Ag NP 5 kGy 63.0 29.0 8.0 EEG/Ag NP 5 kGy 82.5 13.0 4.5
GO/Ag NP 10 kGy 60.6 25.8 13.6 EEG/Ag NP 10 kGy 74.4 16.9 8.7
GO/Ag NP 20 kGy 63.3 21.9 14.8 EEG/Ag NP 20 kGy 78.0 15.2 6.8
Figu e 4. SEM image and EDS maps o he co esponding a ea o ca bon, oxygen, and sil e o
(a) GO, (b) GO/Ag NPs p epa ed a 5 kGy, (c) GO/Ag NPs p epa ed a 20 kGy, (d) EEG, (e) EEG/Ag
NPs p epa ed a 5 kGy, and ( ) EEG/Ag NPs p epa ed a 20 kGy.
Nanoma e ials 2024,14, 912 8 o 13
Table 1. Elemen al composi ion o GO, EEG, and hei composi es wi h Ag nanopa icles p epa ed a
di e en i adia ion doses.
Sample W .% Sample W .%
C O Ag C O Ag
GO 70.9 29.1 EEG 76.7 23.3
GO/Ag NP 1 kGy 62.6 28.7 8.7 EEG/Ag NP 1 kGy 84.9 14.3 0.8
GO/Ag NP 5 kGy 63.0 29.0 8.0 EEG/Ag NP 5 kGy 82.5 13.0 4.5
GO/Ag NP 10 kGy 60.6 25.8 13.6 EEG/Ag NP 10 kGy 74.4 16.9 8.7
GO/Ag NP 20 kGy 63.3 21.9 14.8 EEG/Ag NP 20 kGy 78.0 15.2 6.8
The di e ence in oxygen-con aining unc ional g oup abundance be ween GO and
EEG is well depic ed in he TGA cu es (Figu e 5). The samples we e i s ly hea ed
o 700
◦
C in a ni ogen a mosphe e. The TGA g aphs showed h ee empe a u e zones
wi h dis inc i e mass loss s eps: egion (100
◦
C) associa ed wi h he loss o adso bed
mois u e, egion (100–360
◦
C) associa ed wi h he b eakdown o he mally labile oxygen-
con aining g oups, and egion (360–700
◦
C) associa ed wi h he decomposi ion o he
ca bon la ice [
42
,
43
]. EEG shows g ea e he mal s abili y and main ains 65.8% o he
weigh a 700
◦
C compa ed o GO (48.5% o he weigh a 700
◦
C). This is a consequence
o a g ea e po ion o he mally labile oxygen-con aining g oups in GO han in EEG. In
addi ion, o bo h GO and EEG, weigh loss is mos p ominen o non-i adia ed samples,
and wi h he inc ease in he i adia ion dose, his weigh loss g adually dec eases. This is an
indica ion o he pa ial es o a ion o g aphene’s conjuga ed s uc u e and he elimina ion
o oxygen-con aining unc ionali ies caused by he educ ion unde gamma i adia ion [
27
].
Figu e 5. TGA cu es o (a) GO ( e e ence) and GO/Ag NPs p epa ed a di e en i adia ion doses
and (b) EEG ( e e ence) and EEG/Ag NPs p epa ed a di e en i adia ion doses.
The pa ial es o a ion o g aphene’s conjuga ed s uc u e can be ollowed by UV–
Vis spec oscopy (Figu e 6). The spec um o GO displays wo di e en ea u es: a s ong
peak a 230 nm esul ing om he a oma ic C=C bonds’ π-π* ansi ion, and a shoulde a
~300 nm esul ing om he C=O bonds’ n-π* ansi ion, while he spec um o EEG shows
only π-π* ansi ion o a oma ic C=C bonds a 270 nm. The peak om he a oma ic C=C
bonds shows a g adual edshi wi h he inc ease in he i adia ion dose, while he shoul-
de a ~300 nm in he GO/Ag NPs samples g adually dec eases un il i comple ely an-
ishes a he highe applied doses o 10 and 20 kGy. In addi ion, Ag NPs a e cha ac e ized
by he p esence o a localized su ace plasmon esonance (LSPR) peak as a consequence
o he collec i e oscilla ion o elec ons om he conduc ion band wi h espec o he la ice
o posi i e nuclei. This LSPR peak appea s as one b oad peak a ~420 nm in GO/Ag NPs
samples and ~400 nm in EEG/Ag NPs samples, and i is mos dis inguishable o he high-
es applied dose. The di e ence in he LSPR peak posi ion migh be induced by he a i-
a ion in Ag nanopa icle sizes p epa ed wi h GO and EEG.
Figu e 6. UV–Vis spec a o (a) GO ( e e ence) and GO/Ag NPs p epa ed a di e en i adia ion
doses and (b) EEG ( e e ence) and EEG/Ag NPs p epa ed a di e en i adia ion doses.
The we abili y o composi e hin ilms p epa ed by acuum il a ion was in es i-
ga ed by measu ing he con ac angle o wa e d ople s (Figu e 7). As expec ed, bo h p is-
ine GO and EEG show hyd ophilic beha io wi h con ac angles o 26.5° and 53.5°, e-
spec i ely. The highe measu ed con ac angle o p is ine EEG compa ed o GO is a esul
o he lowe abundance o pola oxygen-con aining g oups on i s su ace. GO/Ag NP com-
posi es show a sligh inc ease in con ac angle un il eaching he maximum o 51.2° o he
composi e i adia ed wi h he highes dose. In con as , EEG/Ag NP composi es show a
dec eased con ac angle compa ed o p is ine EEG, and, simila ly o GO, he highes alue
Figu e 5. TGA cu es o (a) GO ( e e ence) and GO/Ag NPs p epa ed a di e en i adia ion doses
and (b) EEG ( e e ence) and EEG/Ag NPs p epa ed a di e en i adia ion doses.
The pa ial es o a ion o g aphene’s conjuga ed s uc u e can be ollowed by UV–Vis
spec oscopy (Figu e 6). The spec um o GO displays wo di e en ea u es: a s ong
peak a 230 nm esul ing om he a oma ic C=C bonds’
π
-
π
* ansi ion, and a shoulde a
~300 nm
esul ing om he C=O bonds’ n-
π
* ansi ion, while he spec um o EEG shows
only
π
-
π
* ansi ion o a oma ic C=C bonds a 270 nm. The peak om he a oma ic C=C
bonds shows a g adual edshi wi h he inc ease in he i adia ion dose, while he shoulde
a ~300 nm in he GO/Ag NPs samples g adually dec eases un il i comple ely anishes
a he highe applied doses o 10 and 20 kGy. In addi ion, Ag NPs a e cha ac e ized by
he p esence o a localized su ace plasmon esonance (LSPR) peak as a consequence o
he collec i e oscilla ion o elec ons om he conduc ion band wi h espec o he la ice
o posi i e nuclei. This LSPR peak appea s as one b oad peak a ~420 nm in GO/Ag NPs
samples and ~400 nm in EEG/Ag NPs samples, and i is mos dis inguishable o he
