Nano echnology
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An e ec i e o maldehyde gas senso based on
oxygen- ich h ee-dimensional g aphene
To ci e his a icle: Shu Zhang e al 2022 Nano echnology 33 185702
View he a icle online o upda es and enhancemen s.
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An e ec i e o maldehyde gas senso based
on oxygen- ich h ee-dimensional g aphene
Shu Zhang
1,2,17
, Jinbo Pang
1,17,∗
, Yu en Li
1,17
, Be goi Iba lucea
3,4,17
,
Yu Liu
5,6
, Ting Wang
7,8
, Xiaoyan Liu
1
, Songang Peng
9,10
,
Thomas Gemming
11
, Qilin Cheng
1
, Hong Liu
1,12,∗
, Jiali Yang
1
,
Gianau elio Cunibe i
3,4,13,14,∗
, Weijia Zhou
1
and Ma k H Rümmeli
5,6,11,15,16,∗
1
Collabo a i e Inno a ion Cen e o Technology and Equipmen o Biological Diagnosis and The apy in
Uni e si ies o Shandong, Ins i u e o Ad anced In e disciplina y Resea ch (iAIR), Uni e si y o Jinan,
Shandong, Jinan 250022, People’s Republic o China
2
School o Chemis y and Chemical Enginee ing, Uni e si y o Jinan, Jinan, Shandong, Jinan 250022,
People’s Republic o China
3
Ins i u e o Ma e ials Science and Max Be gmann Cen e o Bioma e ials, Technische Uni e si ä
D esden, D esden D-01069, Ge many
4
Cen e o Ad ancing Elec onics D esden, Technische Uni e si ä D esden, D esden D-01069, Ge many
5
College o Ene gy, Soochow Ins i u e o Ene gy and Ma e ials Inno a ions, Soochow Uni e si y, Suzhou
215006, People’s Republic o China
6
Key Labo a o y o Ad anced Ca bon Ma e ials and Wea able Ene gy Technologies o Jiangsu P o ince,
Soochow Uni e si y, Suzhou 215006, People’s Republic o China
7
S a e Key Labo a o y o Biobased Ma e ial and G een Pape making, Qilu Uni e si y o Technology,
Shandong Academy o Sciences, No.3501 Daxue Road, Jinan 250353, People’s Republic o China
8
School o Bioenginee ing, Qilu Uni e si y o Technology, Shandong Academy o Science, Jinan 250353,
People’s Republic o China
9
High-F equency High-Vol age De ice and In eg a ed Ci cui s R&D Cen e , Ins i u e o Mic oelec onics,
Chinese Academy o Sciences, Beijing, 100029, People’s Republic o China
10
Key Labo a o y o Mic oelec onic De ices & In eg a ed Technology, Ins i u e o Mic oelec onics,
Chinese Academy o Sciences, Beijing, 100029, People’s Republic o China
11
Ins i u e o Complex Ma e ials, Leibniz Ins i u e o Solid S a e and Ma e ials Resea ch D esden,
PO Box 270116, D esden, D-01171 Ge many
12
S a e Key Labo a o y o C ys al Ma e ials, Cen e o Bio & Mic o/Nano Func ional Ma e ials, Shandong
Uni e si y, 27 Shandanan Road, Jinan 250100, People’s Republic o China
13
D esden Cen e o Compu a ional Ma e ials Science, Technische Uni e si ä D esden, D esden
D-01062, Ge many
14
D esden Cen e o In elligen Ma e ials (GCL DCIM), Technische Uni e si ä D esden, D esden
D-01062, Ge many
15
Cen e o Polyme and Ca bon Ma e ials, Polish Academy o Sciences, M. Cu ie Sklodowskiej 34,
Zab ze 41-819, Poland
16
Ins i u e o En i onmen al Technology (CEET),VŠB-Technical Uni e si y o Os a a, 17. Lis opadu 15,
Os a a 708 33, Czech Republic
E-mail: [email p o ec ed],[email p o ec ed],[email p o ec ed] and m.
[email p o ec ed]
Recei ed 15 Decembe 2021, e ised 20 Janua y 2022
Accep ed o publica ion 24 Janua y 2022
Published 10 Feb ua y 2022
Nano echnology
Nano echnology 33 (2022)185702 (12pp)h ps://doi.o g/10.1088/1361-6528/ac4eb4
17
These au ho s con ibu ed equally.
∗
Au ho s o whom any co espondence should be add essed.
O iginal con en om his wo k may be used unde he e ms
o he C ea i e Commons A ibu ion 4.0 licence. Any
u he dis ibu ion o his wo k mus main ain a ibu ion o he au ho (s)and
he i le o he wo k, jou nal ci a ion and DOI.
0957-4484/22/185702+12$33.00 P in ed in he UK © 2022 The Au ho (s). Published by IOP Publishing L d1
Abs ac
Th ee-dimensional (3D)g aphene wi h a high specific su ace a ea and excellen elec ical
conduc i i y holds ex ao dina y po en ial o molecula gas sensing. Gas molecules adso bed
on o g aphene se e as elec on dono s, leading o an inc ease in conduc i i y. Howe e , se e al
challenges emain o 3D g aphene-based gas senso s, such as slow esponse and long eco e y
ime. The e o e, esea ch in e es emains in he p omo ion o he sensi i i y o molecula gas
de ec ion. In his s udy, we ab ica e oxygen plasma- ea ed 3D g aphene o he high-
pe o mance gas sensing o o maldehyde. We syn hesize la ge-a ea, high-quali y, 3D g aphene
o e Ni oam by chemical apo deposi ion and ob ain ees anding 3D g aphene oam a e Ni
e ching. We compa e h ee ypes o s a egies—non- ea men , oxygen plasma, and e ching in
HNO
3
solu ion— o he pos ea men o 3D g aphene. E en ually, he s a egy o oxygen
plasma- ea ed 3D g aphene exceeds expec a ions, which may highligh he gene al gas sensing
based on chemi esis o s.
Supplemen a y ma e ial o his a icle is a ailable online
Keywo ds: 3D g aphene, chemical apo deposi ion, chemi esis o s, oxygen plasma ea men s,
gas sensing
In oduc ion
G aphene is an ideal wo-dimensional (2D)ma e ial wi h
unique elec ical and chemical p ope ies [1]. These include
ex emely high Young’s modulus and ac u e s ess [2], high
elec ical conduc i i y [3,4], excellen he mal conduc i i y
[5], low con ac esis ance [6], high mobili y [7], la ge spe-
cific su ace a ea, and high ligh ansmi ance and flexibili y
[8]. The e o e, g aphene can be de eloped and applied in
a ious fields [9], such as high-quali y composi e ma e ials
[10], biomedical and d ug deli e y [11], ansis o s [12,13],
in eg a ed ci cui s [14],flexible elec onics [15]and ene gy
s o age de ices [16].
Owing o he excellen p ope ies o 2D g aphene [17], i s
h ee-dimensional (3D)coun e pa is widely used in gas
molecula senso s owing o i s unique 3D nanopo ous s uc-
u e [18], and easible su ace unc ionaliza ion [19]. The
esis ance o he g aphene-based chemi esis o [20]changes
wi h he in oduc ion o gases, which is he gas-sensing
mechanism.
Compa ed wi h o he ca bon nanoma e ials [21], g a-
phene has he ad an ages o high conduc i i y and a la ge,
heo e ical, specific su ace a ea (3523 m
2
g
−1
)[22]. These
acili a e he e ec i e adso p ion o gas molecules. G aphene
shows excellen p ospec s o gas-sensing applica ions [23].
Th ee-dimensional g aphene in e ac s wi h di e en compo-
si ions and s uc u es o gas adso ben s [24]in di e se ways.
The gaseous molecule adso bs on o g aphene by weak Van
de Waals in e ac ions; hence, he esis ance o g aphene can
be moni o ed by uncomplica ed elec ical equipmen [25].
Owing o i s high-quali y la ice s uc u e [26], 3D g aphene
possesses inhe en ly low elec ical noise, which a oids la ge
cha ge fluc ua ions compa ed wi h ca bon nano ubes [27].In
addi ion, chemi esis o -based sensing o ma s possess he
ad an ages o simple equipmen , easy ab ica ion, and di ec
measu emen [28].
Wi h he imp o emen in human li ing s anda ds and
inc easing a en ion o en i onmen al p o ec ion, ai quali y,
and a mosphe ic pollu ion, mo e significan equi emen s o
gas moni o ing ha e been in oduced [29]. Ai pollu ion
indoo s and inside ehicles h ea ens human heal h and has
become a common conce n wo ldwide. Among he exis ing
haza dous gases, o maldehyde is a common ep esen a i e
example [30]. I is a colo less and soluble i i an gas, which
is ola ile in adhesi e deco a ion ma e ials such as wallpape .
High concen a ions o 20 o 100 ppm a e de imen al o
heal h and well-being [31,32], while long- e m exposu e o
lowe le els can cause alle gies, ca cinogenesis, and mu a-
ions [33,34]. Among all con ac s, child en (leukemia a e)
and p egnan women (abo ion a e)a e pa icula ly sensi i e.
The e o e, an e ec i e o maldehyde gas senso is an
immedia e sa e y equi emen . Among he exis ing o -
maldehyde senso s, some o hem ely on ampe ome ic
echniques, equi ing ei he UV i adia ion [35]o enzymes
[36]as ecep o s, which a e p one o con o ma ional changes
and, he e o e, show poo long- e m s abili y o equi e spe-
cial s o age condi ions.
Indeed, con en ional semiconduc o senso equi es high
ope a ion empe a u e [37–39]o ex e nal UV-ligh ac i a ion
[35]. The g aphene has he ad an age o high conduc i i y a
low ope a ion empe a u e, which o en was blended wi h
semiconduc ing oxides o imp o ing he su ace a ea and
conduc i i y. Indeed, g aphene/me al oxides based compo-
si es could imp o e he sensi i i y o o maldehyde senso
because o he elec on ans e channels p o ided by he
me al oxide such as SnO [40], SnO
2
[39,41,42], TiO
2
[43–45], and ZnO [46–48]and ZnSnO
3
[49]. Besides, he
g aphene has o med composi es wi h polyme s [50–52],Si
nanowi es [53]and MoS
2
[54,55] o se e as o maldehyde-
sensing ma e ials. Howe e , he oxygen plasma ea ed 3D
g aphene has ye applied in o maldehyde sensing.
The e o e, we employed 3D g aphene wi h di e en
ea men s and compa ed hei s uc u e-pe o mance ela-
ionships. In his s udy, we applied h ee s a egies o ea 3D
g aphene, including un ea ed, HNO
3
e ching, and oxygen
plasma ea men and hei applica ion in chemi esis o s o
gas sensing using o maldehyde as an example.
2
Nano echnology 33 (2022)185702 S Zhang e al
Expe imen al de ails
Syn hesis o 3D g aphene by chemical apo deposi ion (CVD)
The Ni oam was washed wi h HCl (19 ol%), hen washed
wi h deionized wa e . The p e- ea ed Ni oam was placed in a
qua z boa and deposi ed in he cen e o he u nace (figu e
S1 (a ailable online a s acks.iop.o g/NANO/33/185702/
mmedia)). Fi s , he ubula u nace was acuum pumped o
10 Pa o emo e ai and wa e . Second, he fixed ca ie gas
a e was 270/30 ml min
−1
A /H
2
a e high-speed cleaning
wi h a la ge flow o A /H
2
o a mosphe ic p essu e. I was
hea ed a 70 °C min
−1
and annealed a 1028 °C o 15 min.
Fu he , 20 sccm CH
4
as g ow h gas was injec ed o 1 h, hen
apidly cooled o oom empe a u e.
F ees anding 3D g aphene wi hou Ni
Fi s , 3D g aphene ab ica ed by CVD was soaked in 2M
FeCl
3
mixed solu ion o emo e he Ni subs a e. The ully
e ched 3D g aphene was hen ans e ed o deionized wa e
(mixed wi h HCl acid) o 2 h. He e, he HCl solu ion was
dilu ed o 0.37 w % wi h deionized wa e . Then, he soaking
in dilu ed HCl was epea ed o h ee imes o ho oughly
emo ing he esidual Fe species. Indeed, he i e by he
ans e ecipe has been well es ablished in ou g oup o
ho ough emo al o Fe emo al, i.e. no eme gence o Fe
a oms o e g aphene in TEM images [17,56], which ha e
been commonly obse ed by he Cs-co ec ed a omic eso-
lu ion TEM imaging [57,58]. E en ually, he ees anding 3D
g aphene was d ied na u ally a 25 °C o s o age, cha -
ac e iza ions, and de ice ab ica ions.
Pos ea men o 3D g aphene
Th ee app oaches we e employed o g aphene pos ea men
(Table S1). Fi s , non- ea men was conduc ed on he 3D
g aphene. The second ea men was he HNO
3
e ching o 3D
g aphene. The syn hesized 3D g aphene was subme ged in
HNO
3
(34 w %) o 24 h. Thi d, he 3D g aphene was ea ed
wi h oxygen plasma (Diene Elec onic, model: A o-BLS).
Ini ially, he chambe was acuumed a 20 Pa. Then, oxygen
a a flow a e o 10 ml min
−1
was in oduced in o he
chambe . Fu he , he oxygen plasma was gene a ed a an RF
powe (13.56 MHz)o 90 W and ea ed o 5–30 min. The
plasma-induced de ec s in 3D g aphene we e cha ac e ized
using Raman spec oscopy. E en ually, 15 min was ound o
be op imal o comple ely unc ionalizing g aphene wi h
oxygen.
Ma e ial cha ac e iza ion
Op ical mic oscopy (Olympus BX53MRF-S)wasused oob ain
snapsho op ical mic og aphs. Raman spec a and mapping we e
pe o med using 532 nm exci a ion wa eleng h Raman
spec oscopy (Ho iba Lab am HR800). The p esen chemical
bonds o unc ional g oups we e de e mined using a Fou ie
ans o m in a ed spec ome e (B uke VERTEX 70 FT-IR).
The phase s uc u e was es ed using x- ay di ac ome y
(The mo Fishe ARL Equlnox 3000). The su ace mo phologies
we e in es iga ed using a scanning elec on mic oscope (Hi achi
Regulus8100). The la ice s uc u e, selec ed a ea elec on di -
ac ion, and elemen al analysis we e conduc ed using a ans-
mission elec on mic oscope (JEOL JEM-2100)in eg a ed wi h
ene gy-dispe si e x- ay spec oscopy.
De ice ab ica ion
Th ee ypes o pos - ea ed 3D g aphene (2×2cm
2
)we e
ans e ed o glass slides wi h pa e ned Au elec odes (50 nm
Au). Gold elec odes we e ab ica ed on glass slides using
an elec on-beam e apo a o (HHV ATS 500). The 3D g a-
phene was aligned and adhe ed o b idge o wo adjacen Au
elec odes (figu e S9).
Gas-sensing examina ion
A simple gas chambe was used o es o he p esence o
absence o esis i e 3D g aphene based senso s. A 25 ml
o maldehyde solu ion (Sigma-Ald ich, 38%)was d opped
on o a ho pla e (30 °C) o gene a e o maldehyde apo . The
ela i e humidi y was main ained a 30%, and he empe a u e
was main ained a 25 °C.
The concen a ion o he a ge ed gas molecule was
measu ed om he mean o he s a ic liquid dis ibu ion,
which was calcula ed using he ollowing equa ion:
=´´´
´
´CV
MV
22.4 1000 ppm,
1
2
Ф
whe e C(ppm)is he concen a ion o he a ge gas, Фis he
olume ac ion o he a ge gas molecule, ρ(gml
−1
)is he
densi y o he liquid, V
1
(ml)is he olume o he es liquid,
V
2
(l)is he olume o he es chambe , and M(g mol
−1
)is
he molecula weigh o he es liquid.
The ime-dependen cu en cu es o he gas senso we e
collec ed using a sou ce measu emen uni (Kei hley 2400).
The esponse and eco e y imes we e de e mined om he
ime-dependen cu en cu es o he gas senso s. The
esponse ime o he senso was de e mined when he esis -
ance (in gas)d opped o 90% o he p is ine esis ance (in ai )
du ing he adso p ion p ocess. The eco e y ime was de e -
mined when he esis ance d opped o 90% upon he deso-
p ion o gas molecules.
Resul s and discussion
Th ee di e en ea men s o 3D g aphene a e g ow h we e
in es iga ed and compa ed in his s udy. These labels a e
p o ided in Table S1, and each expe imen in he ex and
g aphics employs he same label. The 3D g aphene ea men s
we e non- ea men , oxygen plasma, and e ching in HNO
3
solu ion.
We fi s discuss he appea ance and mo phology o he
3D g aphene obse ed by op ical mic oscopy (figu e 1) o
confi m he homogenei y o he la ge a ea o he syn hesized
3D g aphene.
3
Nano echnology 33 (2022)185702 S Zhang e al
The 3D g aphene syn hesized by CVD had a la ge 3D
amewo k s uc u e (figu e 1(a)) and high su ace uni o mi y
(figu e 1(b)). The 3D g aphene ea ed by oxygen plasma
main ained he in insic 3D amewo k p ope y (figu e 1(d))
and homogeneous su ace uni o mi y (figu e 1(e)). This illu-
s a ed ha he pos ea men o oxygen plasma did no a ec
he mo phology o 3D g aphene. Besides, he HNO
3
ea -
men has caused negligible changes in mo phology and
s uc u e o 3D g aphene (figu e S6).
Raman spec oscopy is a powe ul ool o explo ing he
p ope ies o g aphene. The quali y and pu i y o he syn-
hesized 3D g aphene was de e mined by Raman spec osc-
opy. I was also used o analyze he numbe o laye s o he
g own g aphene films on he subs a e o he Ni oam. The
Raman spec um illus a ed he monolaye p ope y h ough
peaks a ca. 1580 cm
−1
o he G mode and ca. 2700 cm
−1
o
he 2D mode (figu e 1(c)). The eme gence o he D mode (ca.
1350 cm
−1
)indica ed g aphene de ec s (figu e 1( )). Hence,
3D g aphene ea ed by oxygen plasma may lead o de ec s
due o su ace unc ionaliza ion.
A e he pos ea men wi h oxygen plasma, 3D g a-
phene possessed oxygen-con aining g oups. Fo example,
ca bonyl and epoxy g oups, his is u he discussed wi h he
in a ed spec a. These s uc u al de ec s we e de e mined by
Raman spec oscopy. The Raman spec a o 3D g aphene
wi h di e en oxygen plasma ea men imes a e shown in
figu e 1(g). Oxygen unc ionaliza ion o en occu ed a he
su ace and he edges o he 3D g aphene [59]upon he
in oduc ion o plasma. Specifically, no oxygen was inco -
po a ed in o he in e laye spacing o ew-laye g aphene [60].
The e o e, su ace oxygen unc ionaliza ion could achie e a
sa u able condi ion on he g aphene su aces. We used he
D/G a io in he oxygen-plasma- ea ed g aphene o de e -
mine he sa u a ion o oxygen unc ionaliza ion. Oxygen
Figu e 1. Mo phology and Raman spec a o 3D g aphene wi h and wi hou oxygen plasma ea men . (a),(b)The op ical mic oscopic images
o non- ea ed 3D g aphene (o e Ni oam)wi h di e en magnifica ions. (c)The Raman spec um o non- ea ed 3D g aphene. The peak
posi ions we e assigned o D mode (ca. 1350 cm
−1
), G mode (ca. 1580 cm
−1
)and 2D mode (ca. 2700 cm
−1
).(d),(e)The op ical
mic oscopic g aphs and ( )Raman spec um o 3D g aphene a e ea men wi h oxygen plasma. The Raman spec a and D/G a io o
oxygen plasma- ea ed 3D g aphene. (g)The Raman spec a o oxygen plasma- ea ed 3D g aphene o di e en du a ions o ( om bo om o
op)0, 5, 10, 15, 20 min. (h)S a is ics o he D/G a io o he oxygen plasma- ea ed 3D g aphene a e di e en ea men imes.
4
Nano echnology 33 (2022)185702 S Zhang e al

sa u a ion occu ed when he D/G a io ceased o inc ease
wi h p olonged plasma ea men . A e 15 min o oxygen
plasma he D/G a io (0.10)o g aphene s abilized
(figu e 1(h)).
P is ine 3D g aphene does no show D mode in Raman
spec um (figu e 1(c)). Wi h 5 min oxygen plasma ea men ,
he g aphene exhibi s significan D mode (figu e 1(g)). A e
ex ending he oxygen plasma du a ion om 5 min o 20 min,
he D/G in ensi y a io inc eases o 0.1 (figu e 1(h)). Fu he
oxygen plasma ea men , i.e. o 30 min, does no induce
la ge D/G a io. The e o e, we selec ed an oxygen plasma
du a ion o 15 min o he g aphene ea men and subsequen
de ice ab ica ion.
To show he c ys al quali y, we compa ed pu e 3D g a-
phene and Ni-suppo ed 3D g aphene by x- ay di ac ion
(figu e 2).
The pu i y o he 3D g aphene was analyzed a e e ch-
ing. The 3D g aphene suppo ed by he Ni amewo k
(figu e 2(a)) showed an ob ious ace-cen e ed cubic peak o
Ni me al a ca. 2θ=44.4°(111), ca. 2θ=51.7°(200), and ca.
2θ=76.3°(220), espec i ely. The XRD g aph o he pu e
3D g aphene (figu e 2(b)) a e e ching exhibi s one peak
(002). This confi med he success o e ching as no Ni esidue
o o he impu i ies emained.
The XRD pa e n o he syn hesized 3D g aphene
showed a di ac ion peak a 2θ=26.6°(figu e 2(b)). The
es ima ed laye spacing o g aphene was 0.335 nm by he
B agg equa ion 2dsin θ=nλ, which was he esul o he
p e e ed o ien a ion o he g aphene eflec ion. A no iceable
eflec ion o he (002)peak demons a ed ha he g own 3D
g aphene was a anged egula ly along he s acking di ec ion.
Compa ed wi h he non- ea men o 3D g aphene, he
3D g aphene a e oxygen plasma ea men (figu e 2(c))
showed he same single s eng h peak a he c ys al plane o
(002), which indica ed ha he pos ea men o oxygen
plasma did no des oy he ini ial c ys al s uc u e. In addi ion,
we did no see he eme gence o he GO peak a a ound 10
deg ees [61]. Again, he oxygen-plasma ea men does no
change he c ys al s uc u e o g aphene, i.e. wi hou he
o ma ion o g aphene oxide. In addi ion, he HNO
3
ea men
did no cause change in c ys al s uc u e o g aphene (figu e
S8)as XRD da a show.
To u he s udy he su ace mo phology cha ac e is ics
o 3D g aphene, scanning elec on mic oscopy (SEM)was
used o mo e de ailed obse a ion and cha ac e iza ion. A e
e ching he Ni amewo k, 3D g aphene e ained he in e -
connec ed 3D suppo ing s uc u e o he o iginal Ni oam
empla e (figu e 2(d)) and a la ge hollow ube (figu e 2( )).
The po e size o he 3D g aphene was mainly dis ibu ed in
he ange o 300–500 μm(figu e 2(e)), which was consis en
wi h he diame e o he hole o he Ni oam. The e o e, he
syn hesized 3D g aphene possessed s uc u al in eg i y and
size s abili y.
The c ys al s uc u e and cha ac e is ics o he syn he-
sized 3D g aphene a e ea men wi h oxygen plasma we e
analyzed h ough imaging and elec on di ac ion o he
ans e ed 3D g aphene (figu e 3).
The low-magnifica ion TEM g aph (figu e 3(a)) demon-
s a ed he smoo h homogenei y o he su ace o he 3D
Figu e 2. Di ac ion spec a and su ace mo phology o 3D g aphene. (a)The x- ay di ac ion (XRD)spec um o he 3D g aphene
suppo ed by Ni oam. The XRD spec a o (b)3D g aphene (a e Ni emo al)and (c)3D g aphene (a e Ni e ching) ea ed by oxygen
plasma. (d)–( )SEM mic og aphs o oxygen ea ed 3D g aphene (a e Ni emo al). In panel ( ), a hollow ube o 3D g aphene was
p esen ed.
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Nano echnology 33 (2022)185702 S Zhang e al
g aphene a e ea men wi h oxygen plasma. The SAED
(figu e 3(b)) exhibi ed a [100]la ice plane wi h six- old sym-
me y o he 3D g aphene c ys al. The TEM mic og aph o
g aphene wi h inges (figu e 3(c)) showed he 3D g aphene
laye s (ca. 8–10), which was illus a ed by he mic o-nano-
c ys alline su ace (figu e 3(d)). The su ace a omic diag am o
he mul ilaye g aphene demons a ed he dis ibu ion o he
epoxy and ca bonyl g oups (figu e 3(e)). The TEM da a show
negligible di e ence o p is ine 3D g aphene (figu e S2)and
HNO
3
ea ed 3D g aphene (figu e S3), compa ed o he oxygen
plasma ea ed sample.
Now we come o discuss he de ec s and he oxygen
con en s o g aphene by h ee ypes o ea men s. CVD-
g own g aphene o e Ni oam was ee o de ec s, i.e. none D
mode in Raman spec um. The oxygen plasma seems o
in oduce sp
3
ype de ec s, e.g. hyd oxyl o epoxy g oups in
ou expe imen s (figu e 3(e)). Indeed, he ib a ional modes
and chemical en i onmen s o hese oxygen- ela ed bonds
we e confi med la e as FT-IR (figu e 4)and XPS da a
(figu es S4 and S5)indica e. The s uc u e diso de in g a-
phene, o en e med de ec s, e.g. sp
3
ype, could be induced
wi h plasma ea men s [62,63]. Indeed, he plasma could
in oduce de ec s bo h a edges and on he basal planes as ip-
enhanced Raman spec oscopy mapping shows [64]. Besides,
acancy- ype de ec s we e o en obse ed wi h hea ily ions-
i adia ed g aphene su aces [65–68]. The g aphene edges
con ibu e o he D modes unde Raman spec oscopic cha -
ac e iza ions [69–71].
Figu e 3. S uc u al, elemen al, and di ac ion analysis o he oxygen-plasma- ea ed 3D g aphene. (a)Low-magnifica ion ansmission
elec on mic oscope g aph o g aphene ( ans e ed)o e a Quan i oil g id. (b)Selec ed a ea elec on di ac ion (SAED)pa e n o he
g aphene. (c)TEM mic og aph o g aphene wi h inges and (d)high-magnifica ion TEM mic og aphs showing he laye s acks o he
g aphene. (e)The su ace a omic diag am o he mul ilaye g aphene. ( )Ene gy-dispe si e x- ay spec um o he oxygen plasma- ea ed 3D
g aphene. (g)TEM g aph showing he s acked laye s o ew-laye 3D g aphene. (h)The in ensi y p ofile o he in e laye spacing o g aphene
in panel (g).
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Nano echnology 33 (2022)185702 S Zhang e al
The p is ine 3D g aphene con ains he minimum oxygen
con en (0.4 a %)as EDX da a show (figu e S2(e)), which
co esponding o hyd oxyl g oup (figu e 4(a)). Then, he 3D
g aphene ea ed by oxygen plasma is less (figu e 3( )), i.e.
0.7 a %, co esponding o he hyd oxyl g oups as indica ed by
in a ed spec a (figu e 4(b)). In addi ion, he oxygen con en
o h ee-dimensional g aphene e ched by ni ic acid is he
highes (0.8 a %),(figu e S3(e)) which co esponds o he
enhancemen o C–O g oup in he peak shown by in a ed
ansmi ance spec um (figu e S7(a)). The hyd oxyl g oups
a e p e e ed o he apid esponse o o maldehyde gas
molecules compa ed o o he oxygen-con aining g oups
(discussed la e in he sec ion o sensing mechanism).
The TEM g aph exhibi ed ypical g aphi ic inges along
smoo h edges, which indica ed mul ilaye g aphene ea u es
(figu e 3(g)). The measu emen o he in e laye spacing o
he 3D g aphene was ca. 0.33 nm (figu e 3(h)).
We compa ed he in a ed spec a o he 3D g aphene
wi h and wi hou oxygen plasma. The s ong abso p ion peak
o O–H was a ca. 3450 cm
−1
(figu e 4(a)). This was caused
by he hyd ogen bond adhe ing o he g aphene su ace du ing
he plasma e ching. This was caused by he hyd ogen bond
adhe ing o he g aphene su ace du ing he plasma e ch-
ing [59,72].
Compa ed o he non- ea ed 3D g aphene, he pos -
ea men wi h oxygen plasma sample showed an abso p ion
peak a ca. 2700 cm
−1
(−CHO), and a s onge s e ching
ib a ion peak o C=O a 1625 cm
−1
(figu e 4(b)) [73].In
addi ion, he abso p ion peaks eme ge a ca. 2900 cm
−1
(including wo peaks a 2920 and 2850 cm
−1
), which a e
assigned as he C–H s e ching modes [74,75]. The e o e,
oxygen-con aining unc ional g oups we e in oduced ac oss
he su ace o 3D g aphene (figu e 4(e)). These oxygen-con-
aining g oups we e mo e likely o adso b o maldehyde gas
Figu e 4. In a ed spec a o 3D g aphene wi hou (a)and wi h (b)oxygen plasma ea men . Oxygen plasma leads o he o ma ion o epoxy
g oups and ca bonyl adicals a he edges and on he su ace o g aphene. The a omic configu a ion o g aphene du ing plasma ea men (c)
p is ine g aphene, (d)ini ial oxygen plasma, and (e)comple e plasma ea men . The oxygen-con aining g oups a e dis ibu ed o e he
su ace o g aphene, such as he ca bonyl, aldehyde, and epoxy g oups. ( )A ypical SEM mic og aph o he oxygen plasma- ea ed 3D
g aphene.
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Nano echnology 33 (2022)185702 S Zhang e al
molecules, which was consis en wi h he pe o mance es s
o he de ec ion o o maldehyde molecules (discussed la e ).
We examined he gas-sensing pe o mance o he h ee
ypes o pos - ea ed 3D g aphene. The elec ic cu en o he
senso was es ed a a fixed ol age (0.1 V). Liquid o -
maldehyde was injec ed and d opped on o a ho pla e (30 °C)
(figu e S10). A high empe a u es, o maldehyde ola ilized
in o gaseous molecules, which filled he gas es chambe
(figu e 5). A la ge specific su ace a ea and high quali y o 3D
g aphene ha e been demons a ed in he de ec ion o gas
molecules. The analysis o esponse and eco e y confi med
he gas sensi i i y o he 3D g aphene-based gas senso a a
o maldehyde concen a ion o 11 ppm a 25 °C.
The un ea ed 3D g aphene exhibi ed a s able esponse
and excellen epea abili y o exposu e o a o maldehyde
concen a ion o 11 ppm. This demons a ed ha he senso
Figu e 5. Gas-sensing pe o mances o 3D g aphene wi h and wi hou oxygen plasma ea men . (a)The gas senso es ing pla o m
schema ic includes a es chambe , elec ic measu emen equipmen (sou ce measu emen uni ), and a gas in oducing uni . (b)The
pho og aph o he gas senso based on he oxygen plasma- ea ed 3D g aphene b idging wo Au elec odes. (c),(d)Response cu e o he gas
senso based on he un ea ed 3D g aphene. The esponse is he quo ien o he Ra/Rg. Ra deno es he esis ance o 3D g aphene in open ai .
Rg deno es he esis ance o 3D g aphene wi h in oducing he a ge gas. (e),( )The esponse pe o mances o he gas senso based on
oxygen plasma- ea ed 3D g aphene. Di e en concen a ions o o maldehyde molecules we e in oduced du ing he senso examina ion.
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Nano echnology 33 (2022)185702 S Zhang e al