On the role of functionalization in graphene-moisture interaction

Cu en Opinion in Solid S a e and Ma e ials Science 27 (2023) 101122 A ailable online 16 No embe 2023 1359-0286/© 2023 The Au ho (s). Published by Else ie L d. This is an open access a icle unde he CC BY license (h p://c ea i ecommons.o g/licenses/by/4.0/). On he ole o unc ionaliza ion in g aphene-mois u e in e ac ion Zhijian Cao a , Xinyue Wen a , Vanesa Quin ano a , b , * , Rakesh Joshi a , * a School o Ma e ials Science and Enginee ing, Uni e si y o New Sou h Wales, Sydney, NSW 2052, Aus alia b Ca alan Ins i u e o Nanoscience and Nano echnology (ICN2), CSIC and BIST, Campus UAB, Bella e a, 08193 Ba celona, Spain ARTICLE INFO Keywo ds: G aphene oxide Func ionaliza ion Mois u e de ec ion A mosphe ic wa e ha es ing ABSTRACT G aphene-based ma e ials such as g aphene oxide (GO) ha e demons a ed ex ao dina y sensi i i y owa ds wa e molecules due o he hyd ophilic na u e. The hyd ophilici y o GO can be u he imp o ed ia addi ional unc ionaliza ion. P e ious s udies sugges ha he in e ac ion be ween GO and wa e molecules esul s in he o ma ion o a hyd ogen bond ne wo k and modi ies he in e laye s uc u e o GO lamina es. Based on he ecen de elopmen s, we p esen ou opinion on he in e ac ion be ween mois u e and g aphene oxide and how his in e ac ion can be u ilized o en i onmen al applica ions such as mois u e de ec ion and a mosphe ic wa e ha es ing. G aphene has been widely known as he i s disco e ed 2D ca bon- based ma e ial [1,2], which is a omically hin and composed o sp 2 - hyb idized ca bon a oms ha a e densely packed in he honeycomb la ice [3–5], as shown in Fig. 1 (a). P is ine g aphene has g ea he mal conduc i i y, heo e ical speci ic su ace a ea [6], adso p ion capaci y, elec ical conduc i i y [7], and op ical anspa ency. G aphene can be chemically modi ied by he a ached unc ional g oups on o he su ace. Such a g aphene-based sys em, known as g aphene oxide, is widely used in memb anes o sepa a ion and pu i ica ion [8,9] as well as o chemical sensing [10,11]. As shown in Fig. 1 (b) [12], compa ed wi h g aphene, GO is composed o sp 2 - and sp 3 -hyb idized ca bon a oms, wi h oxygen- con aining unc ional g oups: hyd oxyl, epoxy, ca boxyl, and ke one [13,14], p o iding he hyd ophilic na u e o g aphene oxide [15]. These wa e -induced changes in g aphene oxide o e huge po en ial o mois u e- ela ed en i onmen al applica ions such as humidi y senso s [16–19], and a mosphe ic wa e ha es ing[20–25]. T adi ionally, he e ha e been se e al epo s on he a ious ypes o humidi y senso s ha a e ab ica ed based on me al oxide nanopa icles [26], ca bon nano ubes (CNTs)[27,28], ce amics, and polyme s[29]. Howe e , i has been demons a ed ha oxide-based humidi y senso s equi e ex e nal hea ing o main ain hei sensi i i y [30,31], and CNTs- based humidi y senso s a e commonly subjec o s ong es ic ions om he low sensi i i y owa ds wa e molecules [32,33]. Mo eo e , GO adso bs mois u e om he en i onmen like a adi ional desiccan ma e ial [20]. Due o he s ong wa e adso p ion and deso p ion ki- ne ics [34], GO can be used as a po en ial a mosphe ic wa e ha es ing (AWH) applica ion [35]. AWH is de ined as a mois u e-cap u ing p o- cess ha applies hyd ophilic ma e ials as ha es e s o induce spon a- neous adso p ion o ap he wa e molecules in he o m o apou om he ai and hen deso b as liquid wa e [36,37]. This opinion ocuses on discussing how unc ionaliza ion imp o es he in e ac ion be ween g aphene oxide and mois u e o imp o e he pe o mance in mois u e de ec ion and AWH applica ions using hyd ophilic c osslinke s. The lamina ed o m o GO has an in e laye s uc u e ha p o ides a unique pa h o mass anspo [38] and ac s like a po ous ma e ial. The in e laye egion o GO is gene ally di ided in o p is ine a oma ic e- gions and oxidized non-a oma ic egions [8,39]. In con as , p is ine egions e ain he a oma ici y owing o he sp 2 ca bon a oms-conjuga ed sys ems. The oxidized egions o GO a e de ined as he hyd ophilic si es o in e ac wi h he wa e molecules by o ming a hyd ogen bonds ne wo k [40–43]. Fu he mo e, he hyd ophilic na u e o GO suppo s i s applicabili y o wa e pu i ica ions [44–47] and ion sie ing [48]. Simila ly, in mois u e de ec ion and AWH applica ions, he le el o hyd ophilici y di ec ly de e mines he sensi i i y o he ma e ial owa ds he apou , indica ing how apidly he ma e ial could induce he in e ac ion wi h wa e molecules [49]. Fu he mo e, i is wo h men ioning he e ha he oxygen-con aining unc ional g oups no only con ibu e hyd ophilici y o GO bu also p o ide s abili y o he lamina ed s uc u e, ha is, he in e laye spacing (d-space). Hence, uning he unc ional g oups in GO will di ec ly impac he in e laye space and he elec ical beha iou [50]. In mois u e de ec ion applica ions, pa icula ly he sensing ma e- ial should ini ially exhibi high elec ical esis ance in he d y s a e * Co esponding au ho s a : School o Ma e ials Science and Enginee ing, Uni e si y o New Sou h Wales, Sydney, NSW 2052, Aus alia (V. Quin ano). E-mail add esses: [email p o ec ed] (V. Quin ano), [email p o ec ed] (R. Joshi). Con en s lis s a ailable a ScienceDi ec Cu en Opinion in Solid S a e & Ma e ials Science jou nal homepage: www.else ie .com/loca e/cossms h ps://doi.o g/10.1016/j.cossms.2023.101122 Recei ed 26 Oc obe 2023; Recei ed in e ised o m 7 No embe 2023; Accep ed 9 No embe 2023 Cu en Opinion in Solid S a e & Ma e ials Science 27 (2023) 101122 2 [51]. A e wa ds, in he we s a e, he sensing ma e ial would be capable o g adually al e ing he espec i e elec ical esis ance on in e ac ing wi h wa e molecules[52–54]. The in e ac ion be ween hyd ophilic ma e ial, GO in his case, and mois u e can be unde s ood in e ms o adso p ion o abso p ion, depending on whe he he wa e molecules pene a e he hyd ophilic ma e ial h ough he ac i e si es on i s su ace o induce u he a ia ions in he chemical s uc u e[55,56]. A mosphe ic wa e ha es ing is a collec ing p ocess ha u ilizes he in e ac ion be ween wa e and hyd ophilic ma e ials[57]. The key mechanism o adso p ion and he associa ed physical deso p ion o GO can be unde s ood by ailo ing he hyd ogen bonds ne wo k in he p esence o wa e [34]. As he amoun o physically adso bed wa e molecules inc eases, he ela i e humidi y (RH%) be ween he in e - laye o GO lakes would ise[39,58]. A e wa ds, due o he e e s- ibili y, he associa ed deso p ion esul s in he de achmen o wa e molecules om he ac i e binding si es o GO. Wang e al.[59] ecen ly epo ed a liquid-so ben a mosphe ic wa e gene a o based on sal - esis an GO-based ae ogel, which e ains as high as 66.9 % deso p ion e iciency wi h he inpu o sola ene gy. The au ho s used 50 w % CaCl 2 solu ion as he so ben o adso b wa e molecules om he apou in he ai hen p ocessed in e acial sola hea ing on he GO-based ae ogels o deso b he wa e molecules om he so ben ia e apo a ion. As a esul , Wang e al. demons a ed a 2.89 kgm -2 day −1 daily wa e gene a ion a 70 % RH le el[59]. As illus a ed in Fig. 2 (a) o (c), he p ocedu e o AWH examined by he au ho s can be summa ized in o h ee s eps: (i) open he lid, physically adso b he wa e molecules om we ai by 50 w % CaCl 2 , (ii) close he lid, e apo a e he cap u ed wa e ia he in e acial hea ing p o ided by sunligh on he sal - esis an GO-based ae ogel, and (iii) condense he e apo a ed wa e apou , calcium ca ions, and chlo ine anions back in o eshwa e o collec . Simila o he a mosphe ic wa e ha es ing (AWH) echnology, he mechanism o GO-based humidi y sensing is also di ec ly based on he physiso p ion o wa e molecules. Among he in insic cha ac e is ics o GO discussed ea lie , he p esence o unc ional g oups on GO dis up s he p o bi als on he join ed sp 2 hyb idized ca bon a oms[60], esul ing in inc eased elec ical esis i i y in he d y s a e. Howe e , in he we s a e, he in e ac ion be ween GO and wa e molecules gi es a ise in he densi y o cha ge ca ie s, leading o a simul aneous dec ease in elec- ical esis ance and an inc ease in capaci ance[61,62]. Based on he p e ious discussions, i is unde s ood ha in mois u e de ec ion, he in insic hyd ophilici y o GO is a c ucial ac o . Highe hyd ophilici y makes GO mo e sensi i e owa d wa e molecules; hence, enhancing hyd ophilici y has been he p ima y means o imp o ing he mois u e de ec ion pe o mance o GO in he pas decade[63–65]. The unc ionaliza ion o GO has become a widely used modi ica ion app oach o u he imp o ing he in insic cha ac e is ics o GO, which in ol es he applica ion o eac i e c oss-linking eagen s o o m chemical bonds wi h he oxygen-con aining unc ional g oups o GO [66–70]. Func ionaliza ion o GO can be ca ego ized in o co alen and non- co alen unc ionaliza ion[71,72]. The co alen unc ionaliza ion o GO includes he in oduc ion o oxygen-con aining unc ional g oups on GO such as ca boxyl, epoxy, hyd oxyl, and ke one[73,74], whe eas he non-co alen unc ionaliza ion o GO elies on in e molecula in- e ac ions be ween he ac i e si es o GO and he c oss-linking eagen s, such as he π − π in e ac ion, pola i y-induced hyd ogen bonding, and elec os a ic in e ac ions[75]. Consequen ly, i can be unde s ood ha Fig. 1. (a) P is ine g aphene lamina e. (b) He e ocyclic chemical s uc u e and unc ional g oups dis ibu ion o g aphene oxide (GO). Ca boxyl, hyd oxyl, ke one, and epoxy g oups a e highligh ed in ed, blue, g een, and pu ple, espec i ely. Fo he s uc u e o g aphene oxide shown in Fig. 1 (b), we e e o he Le -Klinowski model[12]. Z. Cao e al. Cu en Opinion in Solid S a e & Ma e ials Science 27 (2023) 101122 3 he co alen unc ionaliza ion o GO, by o ming o ganic co alen bonding be ween unc ional g oups, ob ains signi ican ly g ea e s a- bili y bu equi es mo e s ingen and complex eac ion condi ions and ac i a ion p ocesses[76–79]. On he o he hand, he non-co alen unc ionaliza ion o GO, while no as s able as co alen unc ionaliza- ion does no equi e ex ensi e ac i a ion eagen s[79,80]. Among he mos used humidi y senso s a e he epoxy- ich, e hyl- enediamine (EA) and polye hyleneimine unc ionalized GO-based sen- so s. EA has wo amine g oups which ob ain he eac i i y owa d he epoxy and ca boxy g oups on GO[81–83], dis ibu ed a bo h ends o i s ca bon chain in one uni o EA molecule. The e o e, EA is commonly applied as he amine-con aining c oss-linking agen in he ca boxyl unc ionaliza ion o GO, whe e he amine g oups induce nucleophilic subs i u ion o eac wi h he ac i a ed ca boxyl g oups o gene a e amide linkages[84]. Howe e , because o he eac ion ene gy ba ie s and s e ic hind ance e ec s[85–87], di ec c oss-linking h ough amine g oups induced by ca boxyl unc ionaliza ion is no easible; hus, i is ypically necessa y o apply ca bodiimide coupling eagen s o p e- ac i a e he ca boxyl g oups on he edges o GO lakes[88–91], gene - a ing highly eac i e in e media es o amida ion[92–94]. Ho e al.[95] epo ed an EA-deco a ed GO-based humidi y senso . In hei wo k au ho s deposi ed he ca boxyl unc ionalized EA-GO on o qua z c ys al mic obalance (QCM) elec odes, which shows a much as e mois u e-de ec ing speed han he amine- ee GO/QCM-based humidi y senso . Be o e es ing and compa ing he di e ences in mois- u e de ec ion pe o mances, he au ho s measu ed he con ac angles o bo h EA-GO and p is ine GO[95]. As shown in Fig. 3 (a) and (b), a e he EA-induced amida ion eac ion be ween amine and ac i a ed ca boxyl g oups, he con ac angle o EA-GO was ound o be 2 deg ees smalle han ha o pu e GO[95], which di ec ly indica es ha he success ul c oss-linking wi h EA has led o a signi ican imp o emen in he hyd ophilici y o GO. Fig. 3 (c) illus a es he mois u e de ec ion se ups in which he au ho s used di e en sal solu ions o adjus he es ing RH% and deposi ed he EA-GO ilm on o QCM elec odes o examine he mois u e-de ec ing pe o mance unde he con olled ope a ing equency (15 MHz)[95]. Fig. 3 (d) clea ly demons a es ha , compa ed o pu e GO, al hough pu e GO exhibi s he abili y o adso b mo e wa e molecules (75 RH%), EA-GO ilms display signi ican ly sho e esponse and eco e y imes when in e ac ing wi h mois u e unde 23 % RH. In ano he s udy, Liu e al. p epa ed he epoxy-GO (EGO) samples ia modi ied Humme ’s me hod[96]. Subsequen ly, hey deposi ed ilms by spin-coa ing GO and EGO on o he elec odes. The au ho s employed a ious sa u a ed sal solu ions in ai - igh essels o adjus di e en RH % o examining he mois u e de ec ion pe o mances[96]. A e wa ds, he au ho s es ed he esponse speed o epoxy- ich unc ionalized GO samples, as shown in Fig. 4 (a), as he olume o added wa e inc eases, he slope o he cu e di ec ly inc eases, which means he esponse ime o senso s o eac becomes sho e . In Fig. 4 (a), he sample which was unc ionalized wi h he la ges amoun o wa e du ing Humme ’s me hod e ained he g ea es slope, he e o e i ob ained he highes sensi i i y owa ds wa e molecules. Addi ionally, Liu e al. es ed ou Fig. 2. Schema ic g aph o he ope a ing mechanism o in e acial sola -hea ing-assis ed a mosphe ic wa e gene a o based on GO-based ae ogel. (a) Vapou so p ion by using 50 w % CaCl 2 . (b) Vapou deso p ion by e apo a ing he cap u ed wa e on GO-based ae ogel. (c) Wa e gene a ion by condensing he e apo a ed apou . Figu es we e ep oduced wi h he pe missions om ( e .[59]). Copy igh (2019), wi h pe mission om John Wiley and Sons. Fo de ailed in o ma ion, we e e o scheme 1 in he e .[59]. Z. Cao e al. Cu en Opinion in Solid S a e & Ma e ials Science 27 (2023) 101122 4 samples wi h ixed RH le els wi hin 60 s[96]. As shown in Fig. 4 (b), as he added wa e amoun inc eased, he esponse ime g adually dec eased, and he EGO-W-5 sample exe ed an ex emely sha p esponse cu e om 10 s o 30 s owa ds 32.8 % RH, which also p o ed ha epoxy- ich unc ionalized GO would e ain highe hyd ophilici y [96]. The ole o epoxy- ich unc ionaliza ion can be explained as imp o ing he e ec i e su ace a ea o in e ac ion and modi ying he hyd ophilici y by adding mo e ac i e si es[96,97]. Table 1 summa izes he ole o unc ionaliza ion in g aphene-based mois u e de ec ion and AWH applica ions. Fo de ailed in o ma ion abou he c oss-linke s, ma e ials used and pe o mance we e e o he ci ed e e ences in Table 1. In summa y, he in insic cha ac e is ics o GO, such as in e laye spacing and elec ical esis i i y, can be modi ied when i is exposed o he mois u e en i onmen . This wa e -induced change can be u ilized o humidi y sensing and a mosphe ic wa e gene a ion. Fu he mo e, owing o he exis ence o oxygen-con aining unc ional g oups, GO is Fig. 3. Con ac angles o (a) TCGO and (b) TCGO EA examined by Ho e al. (TCGO means he pu e GO ab ica ed unde con olled empe a u e, TCGO EA ep esen s he unc ionalized GO). (c) Mois u e de ec ion se ups applied by Ho e al. on EA-GO and GO ilms. (d) Response and eco e y ime examina ions o EA-GO, pu e GO, and QCM elec odes unde 23% RH o 75% RH. (RTGO means he esis i i y- ab ica ed GO). Figu es we e ep in ed wi h pe mission om ( e .[95]). Copy igh (2020), wi h pe mission om Else ie . Fo de ailed in o ma ion, we e e o igu e 5 (a), igu e 5 (c), igu e 8 (a), and g aphical abs ac o e .[95]. Fig. 4. (a) S a ic esponse cu es o EGO samples unde inc easing RH%. (b) Dynamic esponse cu es o EGO samples in 32.8% RH. The igu es we e ep oduced wi h pe mission om ( e .[96]). Copy igh (2020), wi h pe mission om Else ie . Fo de ailed in o ma ion, we e e o igu e 6 in e .[96]. Z. Cao e al. Cu en Opinion in Solid S a e & Ma e ials Science 27 (2023) 101122 5 eac i e o a ious o ganic c oss-linking eagen s and, hence, a good pla o m o unc ionaliza ion o enhance he applica ion po en ial. The ole o unc ionaliza ion is o p o ide addi ional ac i e adso p ion si es o su ace-dependen applica ions based on he o ma ion o he hyd ogen bond ne wo k; hence, unc ionaliza ion s ill holds g ea po- en ial in GO-based AWH and mois u e de ec ion applica ions. Decla a ion o Compe ing In e es The au ho s decla e ha hey ha e no known compe ing inancial in e es s o pe sonal ela ionships ha could ha e appea ed o in luence he wo k epo ed in his pape . Da a a ailabili y No da a was used o he esea ch desc ibed in he a icle. 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