An effective formaldehyde gas sensor based on oxygen-rich three-dimensional graphene

Nano echnology PAPER • OPEN ACCESS 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. You may also like Me al-assis ed-chemical-e ching o silicon nanowi es o empla ing 3D g aphene g ow h owa ds ene gy s o age in mic osys ems Jinhua Li, Nguyen Van Toan, Zhuqing Wang e al. - Op imiza ion o CVD pa ame e s on 3D g aphene oam s uc u es wi h esponse su ace me hodology (RSM) Sibel Kasap, Mehme Bahad Aca and Dilek Çak olu - Ad ances in esea ch on 2D and 3D g aphene-based supe capaci o s Johannes Ph. Mensing, Cha wa in Poochai, Sadanan Ke dpocha e al. - This con en was downloaded om IP add ess 158.196.184.115 on 08/07/2022 a 06:47 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. 5 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). 6 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. 7 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. 8 Nano echnology 33 (2022)185702 S Zhang e al