Superparamagnetic ZnFe2O4 Nanoparticles-Reduced Graphene Oxide-Polyurethane Resin Based Nanocomposites for Electromagnetic Interference Shielding Application

nanoma e ials A icle Supe pa amagne ic ZnFe2O4Nanopa icles-Reduced G aphene Oxide-Polyu e hane Resin Based Nanocomposi es o Elec omagne ic In e e ence Shielding Applica ion Ragh end a Singh Yada 1,* , Anju 1, Thaiskang Jama ia 1, I o Kuˇ i ka 1, Ja mila Vilˇcáko á1, Da id Škoda 1, Pa el U bánek 1, Michal Macho ský1, Milan Masaˇ 1, Michal U bánek 1, Lukas Kalina 2and Ja omi Ha lica 2   Ci a ion: Yada , R.S.; Anju; Jama ia, T.; Kuˇ i ka, I.; Vilˇcáko á, J.; Škoda, D.; U bánek, P.; Macho ský, M.; Masaˇ , M.; U bánek, M.; e al. Supe pa amagne ic ZnFe2O4 Nanopa icles-Reduced G aphene Oxide-Polyu e hane Resin Based Nanocomposi es o Elec omagne ic In e e ence Shielding Applica ion. Nanoma e ials 2021,11, 1112. h ps:// doi.o g/10.3390/nano11051112 Academic Edi o s: Yu ii K. Gun’ko, Geo ge C. Hadjipanayis and Cesa De Julian Fe nandez Recei ed: 30 Ma ch 2021 Accep ed: 23 Ap il 2021 Published: 25 Ap il 2021 Publishe ’s No e: MDPI s ays neu al wi h ega d o ju isdic ional claims in published maps and ins i u ional a il- ia ions. Copy igh : © 2021 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/). 1Cen e o Polyme Sys ems, Uni e si y Ins i u e, Tomas Ba a Uni e si y in Zlín, T ida Tomase Ba i 5678, 760 01 Zlín, Czech Republic; [email p o ec ed] (A.); [email p o ec ed] (T.J.); [email p o ec ed] (I.K.); [email p o ec ed] (J.V.); [email p o ec ed] (D.Š.); [email p o ec ed] (P.U.); [email p o ec ed] (M.M.); [email p o ec ed] (M.M.); [email p o ec ed] (M.U.) 2 Ma e ials Resea ch Cen e, B no Uni e si y o Technology, Pu kyˇno a 464/118, 61200 B no, Czech Republic; [email p o ec ed] (L.K.); [email p o ec ed] (J.H.) *Co espondence: [email p o ec ed]; Tel.: +420-576031725 Abs ac : Supe pa amagne ic ZnFe 2 O 4 spinel e i e nanopa icles we e p epa ed by he sonochemi- cal syn hesis me hod a di e en ul a-sonica ion imes o 25 min (ZS25), 50 min (ZS50), and 100 min (ZS100). The s uc u al p ope ies o ZnFe 2 O 4 spinel e i e nanopa icles we e con olled ia sono- chemical syn hesis ime. The a e age c ys alli e size inc eases om 3.0 nm o 4.0 nm wi h a ise o sonica ion ime om 25 min o 100 min. The change o physical p ope ies o ZnFe 2 O 4 nanopa icles wi h he inc ease o sonica ion ime was obse ed. The p epa ed ZnFe 2 O 4 nanopa icles show supe pa amagne ic beha io . The p epa ed ZnFe 2 O 4 nanopa icles (ZS25, ZS50, and ZS100) and educed g aphene oxide (RGO) we e embedded in a polyu e hane esin (PUR) ma ix as a shield agains elec omagne ic pollu ion. The ul a-sonica ion me hod has been used o he p epa a ion o nanocomposi es. The o al shielding e ec i eness (SE T ) alue o he p epa ed nanocomposi es was s udied a a hickness o 1 mm in he ange o 8.2–12.4 GHz. The high a enua ion cons an ( α ) alue o he p epa ed ZS100-RGO-PUR nanocomposi e as compa ed wi h o he samples ecommended high abso p ion o elec omagne ic wa es. The exis ence o elec ic-magne ic nano ille s in he esin ma ix deli e ed he inclusi e ac s o magne ic loss, dielec ic loss, app op ia e a enua ion cons an , and e ec i e impedance ma ching. The syne gis ic e ec o ZnFe 2 O 4 and RGO in he PUR ma ix led o high in e acial pola iza ion and, consequen ly, signi ican abso p ion o he elec omagne ic wa es. The ou comes and me hods also assu e an in en i e and compe en app oach o de elop ligh weigh and lexible polyu e hane esin ma ix-based nanocomposi es, consis ing o supe pa amagne ic zinc e i e nanopa icles and educed g aphene oxide as a shield agains elec omagne ic pollu ion. Keywo ds: sonochemical syn hesis; spinel e i e; nanopa icles; nanocomposi es; elec omagne ic in e e ence shielding 1. In oduc ion Recen ly, he apid p og ess in elec onic de ices and in o ma ion echnology has endo sed he widesp ead u iliza ion o high-powe elec omagne ic wa es in scien i ic, com- me cial, ci il, and mili a y applica ions [ 1 , 2 ]. The abundan elec omagne ic in e e ence (EMI) in he en i onmen has in luenced he wo king o elec onic de ices [ 3 ]. Exposu e o elec omagne ic adia ion has also in luenced human heal h [ 4 ]. Elec omagne ic shielding o abso p ion has been demons a ed o be one o he ope a i e app oaches o add ess elec omagne ic pollu ion [ 5 ]. The e o e, elec omagne ic shielding o abso p ion ma e ial is one o he bes p ocedu es o en i onmen and heal h de ense [ 6 ]. A ligh weigh , lexible, Nanoma e ials 2021,11, 1112. h ps://doi.o g/10.3390/nano11051112 h ps://www.mdpi.com/jou nal/nanoma e ials Nanoma e ials 2021,11, 1112 2 o 25 and cos -e icien ad anced nanocomposi e shielding ma e ial is equi ed o a enua e he de imen al elec omagne ic wa e in e e ence [7]. The EMI-shielding mechanism consis s o mainly he wo-loss ac o s: (i) e lec ion loss and (ii) abso p ion loss. A single componen , i.e., an only elec ic conduc i e ma e ial o magne ic ma e ial, has less compe ence o pay bo h he mechanism o e lec ion and ab- so p ion. The abso p ion loss-dominan shielding ma e ial is mo e desi able because i can p e en he second e lec ion pollu ion in compa ison wi h he e lec ion-dominan ma e- ial. In ecen yea s, esea che s and academicians ha e comp ehended ha he in en ion o nanocomposi es consis ing o bo h elec ic and magne ic cons i uen s is a p uden choice o cul i a e p o icien EMI-shielding ma e ial [ 8 ]. Such delibe a e shielding ma e ial is an ici- pa ed o close he gap be ween pe mi i i y and pe meabili y. In ecen imes, ca bon-based ma e ials, including ca bon nano ubes, nano ibe s, and educed g aphene oxide, ha e es ablished signi ican conside a ion o e icien elec omagne ic in e e ence shielding ma e ial [9]. Reduced g aphene oxide pa ades a high speci ic su ace a ea wi h plen eous unc ional g oups and s uc u al de ec s on i s su ace. The e o e, i can deli e copious in e acial pola iza ion and de ec dipole pola iza ion [ 10 ]. Reduced g aphene oxide also exhibi s ou s anding dielec ic cha ac e is ics and highe elec ical conduc i i y [ 11 ]. In ecen yea s, i is also pe cei ed ha he in oduc ion o magne ic nanopa icles, including spinel e i e in he p esence o educed g aphene oxide, can mode a e i s impedance ma ching condi ion and obus a enua ion capabili y o he shielding nanocomposi e [ 12 ]. The mic owa e abso p ion cha ac e is ics also depend on he ac ion o nanopa icles and educed g aphene oxide [ 13 ]. Fu he , supe pa amagne ic spinel e i e nanopa icles ha e es ablished a b oad applica ion due o hei compe ence o has ily espond o an applied magne ic ield, which is concomi an wi h negligible emanence and coe ci i y [ 14 , 15 ]. Fo ha eason, he e is an in ensi e esea ch subjec o de elop supe pa amagne ic spinel e i e nanopa icles and u he hei applica ion as elec omagne ic in e e ence shield- ing [ 16 ]. A esea ch g oup, Honglei Yuan e al. [ 17 ] epo ed he supe pa amagne ic Fe 3 O 4 /MWCNTs nanocomposi es displayed ema kably enhanced mic owa e abso p ion cha ac e is ics in a high- equency ange (Ku-band). This esea ch g oup p o ided an app oach o imp o e he esonance equency b eak o he Snoek limi , which conside ably boos s he mic owa e abso p ion cha ac e is ics a high- equency applica ions. T adi ional shielding ma e ials, such as me als and me allic composi es, ha e d awbacks, including chemical esis ance, weak lexibili y, co osion, hea y weigh , and ha d p ocessibili y, e c. Polyme composi es as an al e na i e candida e o EMI shielding can p o ide ligh weigh , esis ance o co osion, lexibili y, easy a ailabili y, p ocessabili y, and cos -e ec i eness. ZnFe 2 O 4 is one o he mos in es iga ed spinel e i e sys ems. An in e es ing cha ac e is ic o ZnFe 2 O 4 is he possibili y o con olling he magne ic p ope ies wi h pa icle/c ys alli e size. The a ia ion o magne ic p ope y om pa amagne ic o supe pa amagne ic o e i- magne ic in ZnFe 2 O 4 nanopa icles is a ibu ed o ca ion edis ibu ion a oc ahed al and e ahed al si es [ 18 ]. The mixed ca ion dis ibu ion in nanosized ZnFe 2 O 4 spinel e i e also depends on he syn hesis me hod [ 19 ]. Qui e a lo o syn hesis app oaches ha e been u ilized o he p epa a ion o nanopa icles and hei nanocomposi es [ 20 ]. Sonochemis y is an inno a i e and po en syn hesis me hodology o he de elopmen o nanopa icles and nanocomposi es. This echnique a o ds no ewo hy ewa ds, such as well dispe sion, size educ ion, pa icle de-agglome a ion, homogeniza ion, and emulsi ica ion, e c. [ 21 ]. The ad an age o he sonochemical syn hesis app oach is cos -e ec i eness, s ong eac ion a e, con ollable syn hesis, na ow pa icle size dis ibu ion, high pu i y, and nonpollu - ing [ 22 , 23 ]. Unde ex eme sonochemical syn hesis condi ions, nanoma e ials wi h he equi ed size can be designed a con olled chemical eac ions and physical changes [24]. In he p esen wo k, s uc u al and physical p ope ies o supe pa amagne ic ZnFe 2 O 4 spinel e i e nanopa icles ha e been con olled by he sonochemical syn hesis app oach wi h inc eased sonochemical syn hesis ime. To he bes o he au ho s’ knowledge, his is he i s epo on supe pa amagne ic ZnFe 2 O 4 spinel e i e nanopa icles- educed g aphene oxide (RGO)-polyu e hane esin (PUR) nanocomposi es as a shield agains elec- Nanoma e ials 2021,11, 1112 3 o 25 omagne ic pollu ion. RGO exhibi ed high speci ic su ace a ea and excellen elec ical con- duc i i y. Howe e , non-magne ic RGO exhibi ed s ong dielec ic loss and also impedance misma ching issues. The e o e, he combina ion o magne ic spinel e i e wi h he elec i- cally conduc i e RGO can imp o e EMI-shielding pe o mance wi h balanced impedance ma ching condi ions. Addi ionally, he EMI-shielding pe o mance can be imp o ed wi h nanopa icles/nanos uc u es due o i s excellen elec omagne ic p ope ies and high su ace a ea. The s uc u al and elec omagne ic p ope ies/pa ame e s o de eloped supe pa amagne ic ZnFe 2 O 4 nanopa icles and RGO embedded PUR-based nanocom- posi es we e examined in de ail. The con i ma ion o s uc u al o ma ion o p epa ed nanopa icles and nanocomposi es was ca ied ou by X- ay di ac ome y (XRD), in a ed spec ome y (FTIR), and Raman spec ome y. Mic os uc u al ea u es we e s udied by ansmission elec on mic oscopy (TEM) and ield emission-scanning elec on spec oscopy (FE-SEM). The sonochemical syn hesis app oach can also be used o he indus ial-scale o ma ion o a ious spinel e i e nanopa icles. The de eloped ligh weigh and lexi- ble EMI-shielding nanocomposi e can ind po en ial applica ion in he ield o po able elec onics and wea able de ices ha need o be ligh weigh , hin, and lexible ma e ial. 2. Ma e ials and Me hods 2.1. Ma e ials Sodium hyd oxide, zinc ni a e, and i on ni a e we e acqui ed om Al a Aesa GmbH & Co KG, Ge many. Po assium pe mangana e and g aphi e lakes we e p ocu ed om Sigma-Ald ich, Ge many. Fu he , sodium ni a e was p ocu ed om Lach-Ne , he Czech Republic. The educing agen , Vi amin C (Li sane), o he educ ion o g aphene oxide, was ob ained om D . Kleine Pha ma GmbH, Biele eld, Ge many. Polyu e hane esin (PUR) was selec ed as a polyme elas ome ic cas ing ma ix o e y low sh inkage and lexibili y. PUR ma ix was p epa ed by using Bi esin ® U1404 elas ome ic cas ing esin o mold-making om Sika Ad anced Resins GmbH, Bad U ach, Ge many, which has a desc ip ion as a basis: wo-componen PUR sys em; Componen A: Bi esin ® U1404, isocyana e p epolyme , colo less- anspa en , un illed; Componen B: Bi esin ® U1404, amine, eddish- anspa en , un illed; Componen B: Bi esin ® U1434, amine, beige, illed. I p o ides p oduc bene i s, such as insensi i e o mois u e, e y so , high elonga ion a b eak, good ensile s eng h, and elas ici y, wi h componen B Bi esin ® U1404 o sho e ha dness o A 40, wi h componen B Bi esin ® U1434 o sho e ha dness o A 55, and e y low sh inkage. The PUR ma ix o ZnFe 2 O 4 and RGO as nano ille s was ob ained in liquid o m wi h isocyana e p epolyme (componen A, Bi esin ® U1404) and amine (componen B, Bi esin ® U1434) as a cu ing agen (ha dene ) wi h a densi y o 1.3 g/cm 3 ; iscosi y o ~3700 mPa-s; sho e ha dness o 55A; ea s eng h o 9 N/mm; ensile s eng h o 4 MPa; elonga ion a b eak >600%; linea sh inkage in e nal <0.02%. 2.2. Sonochemical P epa a ion o ZnFe2O4Nanopa icles ZnFe 2 O 4 nanopa icles we e syn hesized by he sonochemical syn hesis echnique. Fi s , 2.63 g Zn(NO 3 ) 2· 6H 2 O and 7.56 g Fe(NO 3 ) 3· 9H 2 O we e mixed in 60 mL o deionized wa e . Addi ionally, aqueous 1.6 M sodium hyd oxide (NaOH) was mixed in he abo e se solu ion wi h con inuous s i ing by a magne ic s i e . Mo eo e , he a ained mixed solu ion was placed o high-in ensi y ul asonic wa es o 25 min, 50 min, and 100 min wi h he use o he UZ SONOPULS HD 2070 Ul asonic homogenize (Be lin, Ge many) a 70 W powe and 20 kHz equency. The achie ed p oduc was washed by u ilizing deionized wa e and e hanol o elimina e unwan ed chemical impu i y. Finally, hese washed nanopa icles we e d ied a 60 ◦ C o 18 h. The p epa ed ZnFe 2 O 4 nanopa icles we e designa ed as ZS25, ZS50, and ZS100 acco ding o hei sonochemical syn hesis ime o 25 min, 50 min, and 100 min, espec i ely. Nanoma e ials 2021,11, 1112 4 o 25 2.3. P epa a ion o Reduced G aphene Oxide (RGO) Fi s , g aphene oxide (GO) was p epa ed om na u al g aphi e powde s by u ilizing he Humme s’ me hod. Typically, he mix u e comp ised o g aphi e powde (1.5 g) and sodium ni a e (1.5 g) was added slowly o concen a ed H 2 SO 4 (75 mL). The beake , which con ains he abo e eac ion mix u e, was placed on an ice ba h, and po assium pe mangana e (9 g) was added g adually wi hin 20 min, and his mixed solu ion was s i ed u he o 30 min unde an ice ba h ( empe a u e in he ange o 0–5 ◦ C). This solu ion was s i ed o an addi ional 48 h a oom empe a u e. A e wa d, 138 mL o deionized wa e was g adually added in o he abo e mix u e and s i ed o 10 min. In his achie ed mix u e, 420 mL wa m deionized wa e was hen pou ed and kep unde a con inuous s ong s i ing. Mo eo e , H 2 O 2 (30 mL) was mixed in o he abo e eac ion mix u e o elimina e he emaining KMnO 4 and s i ed un il he colo o he p oduc ans o med in o b igh yellow, which signaled he o ma ion o g aphi e oxide om g aphi e. Finally, he ob ained b igh yellow p oduc suspension was cen i uged and washed wi h e hanol and deionized wa e un il he pH ~7 was eached. The ob ained p oduc was annealed a 60 ◦C in a acuum o en o 24 h. Vi amin C (10 g) was u ilized as a educing agen in he de elopmen o educed g aphene oxide (RGO) om 3 g o g aphene oxide (GO). Fo his, he abo e-p epa ed GO was mixed in deionized wa e and addi ionally placed o high-in ensi y ul asonic wa es o 15 min wi h he use o UZ SONOPULS HD 2070 Ul asonic homogenize . Then, in his a ained solu ion, i amin C was added g adually, and hen he ob ained suspension was con inuously s i ed o he ime o 3 h a empe a u e 90 ◦ C. Addi ionally, he achie ed p oduc suspension was cen i uged and washed wi h e hanol and deionized wa e . Finally, he washed p oduc was d ied in a acuum o en a 60 ◦C o 15 h. 2.4. Ul asonic P epa a ion o Nanocomposi es Nanocomposi es o polyu e hane esin (PUR) (50 w .%) wi h nano ille s (40 w .% zinc e i e nanopa icles and 10 w .% RGO) we e p epa ed. Fo he PUR ma ix, componen A and componen B we e used in he a io o 100–50. Fo he p epa a ion o nanocomposi es, in a 25-mL beake , isocyana e p epolyme (componen A, Bi esin U1404) we e mixed wi h nano ille s (ZnFe 2 O 4 (90%) + RGO (10%)) by using a EURO-ST-D mechanical s i e o 30 min and hen sonica ed by using a UP 400S ul a p obe (Hielsche Ul asonics GmbH, Tel ow, Ge many) ( equency: 24 kHz, powe : 400 W) o 30 min in an ice ba h. Fu he , amine (componen B) as a cu ing agen was mixed o he abo e mix u e and hen sonica ed a ano he 10 min by using a UP 400S ul a p obe ( equency: 24 kHz, powe : 400 W). Finally, he p epa ed sample was closed and e ained in a d ying o en, whe e he composi e ma e ial was cu ed a 25 ◦ C o 5 days. Th ee PUR-based nanocomposi e using zinc e i e nanopa icles (ZS25, ZS50, o ZS100) and RGO as nano ille s, namely, (i) ZS25- RGO-PUR, (ii) ZS50-RGO-PUR, and (iii) ZS100-RGO-PUR, we e p epa ed. Addi ionally, ec angle-shaped samples 22.86 ×10.16 ×1 mm3we e p oduced by cas molding. 2.5. Cha ac e iza ion Techniques The sonochemically p epa ed zinc e i e nanopa icles X- ay Di ac ion (XRD) was pe o med using an X- ay powde di ac ion om Rigaku Co po a ion, Tokyo, Japan. The Raman spec oscopy o PUR-based nanocomposi es was pe o med on a Raman spec- ome e o The mo Fishe Scien i ic, Wal ham, MA, USA. XPS s udy o g aphene oxide and educed g aphene oxide was pe o med on an X- ay pho oelec on spec oscope o K a os Analy ical L d. (Manches e , UK). The FTIR spec oscopy o ZnFe 2 O 4 nanopa i- cles and PUR-based nanocomposi es was pe o med on Nicole 6700 (The mo Scien i ic, Wal ham, MA, USA). The high- esolu ion ansmission elec on mic oscope (JEOL JEM 2100) (JEOL, Peabody, MA, USA) was u ilized o in es iga e he mo phology and la ice inges o ZnFe 2 O 4 nanopa icles. The su ace mo phology and s uc u e o he PUR nanocomposi es we e in es iga ed wi h an FE-SEM o FEI NanoSEM450 (The Ne he land, FEI Company). Magne ic hys e esis cu es o sonochemically p epa ed supe pa amagne ic Nanoma e ials 2021,11, 1112 5 o 25 ZnFe 2 O 4 nanopa icles we e s udied u ilizing a VSM 7407, Lake Sho e, Wes e ille, OH, USA. ZFC and FC empe a u e-dependen magne iza ion s udy o he sonochemically p epa ed zinc e i e nanopa icles we e in es iga ed using a SQUID magne ome e o Quan um Design MPMS XL-7. The elec omagne ic in e e ence shielding e ec i eness o he de eloped PUR-based nanocomposi e wi h zinc e i e nanopa icles and RGO as nano ille s was s udied by using a ec o ne wo k analyze (Agilen N5230A, Agilen Technologies, San a Cla a, CA, USA) in 8.2–12.4 GHz (X band). 3. Resul s 3.1. X- ay Di ac ion S udy The X- ay di ac ion pa e n o he sonochemically syn hesized ZnFe 2 O 4 spinel e i e nanopa icles a sonica ion imes o 25 min, 50 min, and 100 min is displayed in Figu e 1. The obse ed di ac ion peaks co espond o he e lec ion o (220), (311), (222), (400), (331), (422), (511), (440), (531), and (442) planes o an Fd 3 m spinel c ys al s uc u e. Addi ionally, he e is no p esence o an impu i y peak, which designa es he high pu i y o spinel e i e ma e ial. I is wo h no ing ha as he sonica ion syn hesis ime inc eased, he in ensi y o di ac ion peaks inc eased, and he wid h o he di ac ion peak dec eased, which sugges s g ain g ow h wi h an inc ease o sonica ion ime. The a e age c ys alli e size o syn hesized ZnFe2O4nanopa icles was s udied by u ilizing he Debye–Sche e equa ion [25]: D=(0.9)λ βcosθ(1) Nanoma e ials 2021, 11, x FOR PEER REVIEW 6 o 25 ZS100 samples, espec i ely (Table 1). Thus, an inc ease o sonica ion ime o 25 min, 50 min, and 100 min dec eased he densi y o he p epa ed spinel e i e nanopa icles. 20 30 40 50 60 70 0 50 100 150 20 30 40 50 60 70 0 500 1000 1500 20 30 40 50 60 70 0 500 1000 1500 20 30 40 50 60 70 0 500 1000 1500 (311) C ys alli e Size = 3.0 nm (331) (442) (531) JCPDS: 01-070-3384 Ul asonica ion ime = 25 min (440) (511) (400) (222) (311) (220) 2 θ (deg ee) ZS25 (442) (531) (440) (511) (422) (331) (400) (222) (311) (220) ZS50 In ensi y ( cps ) (442) (531) (440) (511) (422) (331) (400) (222) (311) (220) Ul asonica ion ime = 50 min (422) C ys alli e Size = 4.0 nm C ys alli e Size = 3.6 nm (442) (531) (440) (511) (422) (331) (400) (222) (220) Ul asonica ion ime = 100 min ZS100 Figu e 1. X- ay di ac ion pa e n o sonochemically p epa ed ZnFe2O4 spinel e i e nanopa icles. Table 1. C ys alli e size, La ice Pa ame e , X- ay Densi y, and Ionic Radii ( A, B) o he p epa ed ZnFe2O4 spinel e i e nanopa icles by he sonochemical syn hesis app oach. Sample C ys alli e Size (nm) La ice Pa ame e , a (Å) X- ay Densi y dx (g/cm3) Ionic Radii A (Å) Ionic Radii B (Å) ZS 25 3.0 7.219 8.51 0.2757 1.4026 ZS 50 3.6 7.245 8.42 0.2816 1.4087 ZS 100 4.0 7.248 8.41 0.2822 1.4093 Addi ionally, s uc u al pa ame e s, such as ionic adii, hopping leng h o he oc a- hed al and e ahed al si e, e ahed al and oc ahed al bond leng h, e ahed al edge, and he sha ed and unsha ed oc ahed al edge, o p epa ed ZnFe2O4 nanopa icles we e as- sessed [29,30]. The a ia ion in hese pa ame e s wi h sonica ion imes o 25 min, 50 min, and 100 min was no iced, as men ioned in Tables 1 and 2. The inc ease in ionic adii, hop- ping leng h o he oc ahed al and e ahed al si e, e ahed al and oc ahed al bond leng h, e ahed al edge, and he sha ed and unsha ed oc ahed al edge o p epa ed ZnFe2O4 nanopa icles wi h an inc ease o sonica ion ime was no iced. Mic os uc u e and ul asonic-ac i a ed o de ing/ eo de ing o ca ions in ZnFe2O4 nanopa icles was as- socia ed wi h an inc ease in sonica ion ime, which can a ec he physical p ope ies o he ma e ial [31]. Table 2. S uc u al pa ame e s o p epa ed ZnFe2O4 nanopa icles syn hesized by sonochemical app oach: hopping leng h o he oc ahed al and e ahed al si e, e ahed al and oc ahed al bond leng h, e ahed al edge, and he sha ed and unsha ed oc ahed al edge. Sample Hopping Leng h o Te ahed al Si e dA (Å) Hopping Leng h o Oc ahed al si e dB (Å) Te ahed al Bond Leng h, dAx (Å) Oc ahed al Bond Leng h, dBx (Å) Te ahed al Edge, dAxE (Å) Sha ed Oc ahed al Edge, dBxE (Å) Unsha ed Oc ahed al Edge, dBxEU (Å) ZS 25 3.1263 2.5526 1.6757 1.7424 2.7364 2.3688 2.5559 Figu e 1. X- ay di ac ion pa e n o sonochemically p epa ed ZnFe 2 O 4 spinel e i e nanopa icles. He ein, λ , β , and θ a e he wa eleng h o X- ay, he ull-wid h a hal maximum (FWHM), and he B agg angle, espec i ely. The a e age c ys alli e size inc eases om 3.0 nm o 4.0 nm wi h an inc ease in sonica ion ime, as shown in Table 1. The g ow h o spinel e i e nanoc ys als was associa ed wi h an inc ease in ul asonic ime [26]. Nanoma e ials 2021,11, 1112 6 o 25 Table 1. C ys alli e size, La ice Pa ame e , X- ay Densi y, and Ionic Radii ( A , B ) o he p epa ed ZnFe 2 O 4 spinel e i e nanopa icles by he sonochemical syn hesis app oach. Sample C ys alli e Size (nm) La ice Pa ame e , a (Å) X- ay Densi y dx(g/cm3)Ionic Radii A(Å) Ionic Radii B(Å) ZS 25 3.0 7.219 8.51 0.2757 1.4026 ZS 50 3.6 7.245 8.42 0.2816 1.4087 ZS 100 4.0 7.248 8.41 0.2822 1.4093 The la ice pa ame e was de e mined by u ilizing he ollowing ela ion [25]: a2= λ2h2+k2+l21/2 4sin2θ(2) He ein, θ is he B agg angle, and (hkl) a e he Mille indices o he planes. The la ice pa ame e inc eases om 7.219 Å o 7.248 Å wi h an inc ease in sonica ion ime om 25 min o 100 min, as shown in Table 1. The obse ed inc ease in he la ice cons an wi h sonica ion ime ollows Vega d’s law [ 27 ]. Gene ally, he la ice cons an in he case o spinel e i e co ela es wi h mic os uc u e, o de ing/ eo de ing o ca ions, alence s a es, and de ec s, e c. [ 28 ]. In he p esen wo k, he a ia ion in he la ice cons an can be a ibu ed o changes in mic os uc u e and ul asonic-ac i a ed o de ing/ eo de ing o ca ions in ZnFe2O4spinel e i e nanopa icles. The X- ay densi y (d x ) o p epa ed spinel e i e nanopa icles is e alua ed by he ollowing ela ion [25]: dx=ZM NV (3) He ein, Z, M, N, and V a e he numbe o he nea es neighbo , he molecula weigh , he A ogad o numbe , and he olume o he uni cell (V = a 3 ), espec i ely. The e alua ed alue o he X- ay densi y was 8.51 g/cm 3 , 8.42 g/cm 3 , and 8.41 g/cm 3 o ZS25, ZS50, and ZS100 samples, espec i ely (Table 1). Thus, an inc ease o sonica ion ime o 25 min, 50 min, and 100 min dec eased he densi y o he p epa ed spinel e i e nanopa icles. Addi ionally, s uc u al pa ame e s, such as ionic adii, hopping leng h o he oc- ahed al and e ahed al si e, e ahed al and oc ahed al bond leng h, e ahed al edge, and he sha ed and unsha ed oc ahed al edge, o p epa ed ZnFe 2 O 4 nanopa icles we e assessed [ 29 , 30 ]. The a ia ion in hese pa ame e s wi h sonica ion imes o 25 min, 50 min, and 100 min was no iced, as men ioned in Tables 1and 2. The inc ease in ionic adii, hopping leng h o he oc ahed al and e ahed al si e, e ahed al and oc ahed al bond leng h, e ahed al edge, and he sha ed and unsha ed oc ahed al edge o p epa ed ZnFe 2 O 4 nanopa icles wi h an inc ease o sonica ion ime was no iced. Mic os uc u e and ul asonic-ac i a ed o de ing/ eo de ing o ca ions in ZnFe 2 O 4 nanopa icles was associa ed wi h an inc ease in sonica ion ime, which can a ec he physical p ope ies o he ma e ial [31]. Table 2. S uc u al pa ame e s o p epa ed ZnFe 2 O 4 nanopa icles syn hesized by sonochemical app oach: hopping leng h o he oc ahed al and e ahed al si e, e ahed al and oc ahed al bond leng h, e ahed al edge, and he sha ed and unsha ed oc ahed al edge. Sample Hopping Leng h o Te ahed al Si e dA(Å) Hopping Leng h o Oc ahed al Si e dB(Å) Te ahed al Bond Leng h, dAx (Å) Oc ahed al Bond Leng h, dBx (Å) Te ahed al Edge, dAxE (Å) Sha ed Oc ahed al Edge, dBxE (Å) Unsha ed Oc ahed al Edge, dBxEU (Å) ZS 25 3.1263 2.5526 1.6757 1.7424 2.7364 2.3688 2.5559 ZS 50 3.1374 2.5617 1.6816 1.7486 2.7461 2.3772 2.5650 ZS 100 3.1384 2.5625 1.6822 1.7491 2.7470 2.3780 2.5658 Nanoma e ials 2021,11, 1112 7 o 25 3.2. TEM S udy TEM measu emen s we e ca ied ou o in es iga e he s uc u al ea u es o p epa ed ZnFe 2 O 4 spinel e i e nanopa icles. Figu e 2 ep esen s TEM and HRTEM images o p epa ed nanopa icles, namely ZS25, ZS50, and ZS100. The TEM image o ZS25 is depic ed in Figu e 2a, which shows pa icles in he ange o 2–4.5 nm (Figu e S1 in supplemen a y ma e ial). The HRTEM image o ZS25 is shown in Figu e 2b, which displays he la ice o (220) planes (d spacing 0.29 nm), (311) planes (d spacing 0.25 nm), and (400) planes (d spacing 0.21 nm) o ZnFe 2 O 4 spinel e i e [ 32 ]. Fu he , Figu e 2c depic s a low- esolu ion TEM image o he ZS50 sample, which illus a ed ha he p oduc consis ed o pa icles wi h sizes o 2.5–5 nm. Figu e 2d shows la ice inges wi h an in e plana spacing o 0.29 nm, which is consis en wi h (220) planes o spinel e i e. Addi ionally, he TEM image o ZS100 is depic ed in Figu e 2e, which demons a ed ha he p epa ed nanopa icles exhibi ed size 3–12 nm. Figu e 2 depic s he HRTEM image o ZS100. The in es iga ion o he HRTEM image depic s he in e plana spacing o 0.25 nm, 0.21 nm, and 0.17 nm o la ice inges co esponding o (311), (400), and (422) plane o ZnFe 2 O 4 spinel e i e. Nanoma e ials 2021, 11, x FOR PEER REVIEW 7 o 25 ZS 50 3.1374 2.5617 1.6816 1.7486 2.7461 2.3772 2.5650 ZS 100 3.1384 2.5625 1.6822 1.7491 2.7470 2.3780 2.5658 3.2. TEM S udy TEM measu emen s we e ca ied ou o in es iga e he s uc u al ea u es o p e- pa ed ZnFe2O4 spinel e i e nanopa icles. Figu e 2 ep esen s TEM and HRTEM images o p epa ed nanopa icles, namely ZS25, ZS50, and ZS100. The TEM image o ZS25 is de- pic ed in Figu e 2a, which shows pa icles in he ange o 2–4.5 nm (Figu e S1 in supple- men a y ma e ial). The HRTEM image o ZS25 is shown in Figu e 2b, which displays he la ice o (220) planes (d spacing 0.29 nm), (311) planes (d spacing 0.25 nm), and (400) planes (d spacing 0.21 nm) o ZnFe2O4 spinel e i e [32]. Fu he , Figu e 2c depic s a low- esolu ion TEM image o he ZS50 sample, which illus a ed ha he p oduc consis ed o pa icles wi h sizes o 2.5–5 nm. Figu e 2d shows la ice inges wi h an in e plana spac- ing o 0.29 nm, which is consis en wi h (220) planes o spinel e i e. Addi ionally, he TEM image o ZS100 is depic ed in Figu e 2e, which demons a ed ha he p epa ed na- nopa icles exhibi ed size 3–12 nm. Figu e 2 depic s he HRTEM image o ZS100. The in es iga ion o he HRTEM image depic s he in e plana spacing o 0.25 nm, 0.21 nm, and 0.17 nm o la ice inges co esponding o (311), (400), and (422) plane o ZnFe2O4 spinel e i e. (b) (c) (d) (e) ( ) (a) Figu e 2. Con . Nanoma e ials 2021,11, 1112 8 o 25 Nanoma e ials 2021, 11, x FOR PEER REVIEW 8 o 25 Figu e 2. (a) TEM image o ZS25, (b) HRTEM image o ZS25, (c) TEM image o ZS50, (d) HRTEM image o ZS50, (e) TEM image o ZS100, and ( ) HRTEM image o ZS100. 3.3. FE-SEM S udy Figu e 3 depic s he ypical SEM image o RGO and p epa ed polyu e hane esin- based nanocomposi es. W inkled and cu led g aphene shee s can be no iced in Figu e 3a. Fu he , he p esence o RGO and p epa ed ZnFe 2 O 4 nanopa icles in polyu e hane esin can be no iced in SEM images o he su aces o he PUR-based nanocomposi es, as shown in Figu e 3b–d. The inc ease in he hickness o RGO may be due o he agglome a ion o RGO du ing he p ocessing and o ma ion o polyme nanocomposi e [33]. (a) (b) (c) ZS100 PUR RGO RGO (e) ( ) Figu e 2. ( a ) TEM image o ZS25, ( b ) HRTEM image o ZS25, ( c ) TEM image o ZS50, ( d ) HRTEM image o ZS50, ( e ) TEM image o ZS100, and ( ) HRTEM image o ZS100. 3.3. FE-SEM S udy Figu e 3depic s he ypical SEM image o RGO and p epa ed polyu e hane esin- based nanocomposi es. W inkled and cu led g aphene shee s can be no iced in Figu e 3a. Fu he , he p esence o RGO and p epa ed ZnFe 2 O 4 nanopa icles in polyu e hane esin can be no iced in SEM images o he su aces o he PUR-based nanocomposi es, as shown in Figu e 3b–d. The inc ease in he hickness o RGO may be due o he agglome a ion o RGO du ing he p ocessing and o ma ion o polyme nanocomposi e [33]. Nanoma e ials 2021, 11, x FOR PEER REVIEW 8 o 25 Figu e 2. (a) TEM image o ZS25, (b) HRTEM image o ZS25, (c) TEM image o ZS50, (d) HRTEM image o ZS50, (e) TEM image o ZS100, and ( ) HRTEM image o ZS100. 3.3. FE-SEM S udy Figu e 3 depic s he ypical SEM image o RGO and p epa ed polyu e hane esin- based nanocomposi es. W inkled and cu led g aphene shee s can be no iced in Figu e 3a. Fu he , he p esence o RGO and p epa ed ZnFe 2 O 4 nanopa icles in polyu e hane esin can be no iced in SEM images o he su aces o he PUR-based nanocomposi es, as shown in Figu e 3b–d. The inc ease in he hickness o RGO may be due o he agglome a ion o RGO du ing he p ocessing and o ma ion o polyme nanocomposi e [33]. (a) (b) (c) ZS100 PUR RGO RGO (e) ( ) Figu e 3. Con . Nanoma e ials 2021,11, 1112 9 o 25 Nanoma e ials 2021, 11, x FOR PEER REVIEW 9 o 25 Figu e 3. FE-SEM image o RGO (a), and FE-SEM image o he ac u e su ace o ZS100-RGO-PUR (b), ZS50-RGO-PUR (c), and ZS25-RGO-PUR (d). 3.4. X- ay Pho oelec on Spec oscopy The p epa ed GO and RGO we e examined by X- ay pho oelec on spec oscopy (XPS). Figu e 4 shows he XPS spec a o p epa ed g aphene oxide (GO) and educed g a- phene oxide (RGO). Figu e 4a,c signi ies he su ey scan spec a o GO and RGO, which display he exis ence o ca bon and oxygen. Figu e 4b depic s he high- esolu ion XPS spec a o he C 1s egion o GO. The decon olu ed C 1s peak displays he peak binding ene gy o 284.1 eV, 284.7 eV, 286.5 eV, 288.4 eV, and 290.0 eV, which esembles C=C (sp 2 ca bon), C-C (sp 3 ca bon), C-O, C=O, and O-C=O bonds, espec i ely [34]. Addi ionally, Figu e 4d deno es he high- esolu ion XPS spec a o C 1s o RGO. I displays he peak binding ene gy o 284.4 eV, 285.9 eV, 287.7 eV, 289.1 eV, and 290.6 eV ela ed o C=C, C- OH, C=O, O-C=O, and π-π* sa elli e bonds, espec i ely [35]. The XPS in es iga ion demons a ed ha a e educ ion ea men , he unc ional g oup o GO is educed, and he sp 3 ca bon is al e ed o sp 2 ca bon. 1,200 1,000 800 600 400 200 0 0 50000 100000 150000 200000 250000 GO C 1s O 1s O KLL ( a ) In ensi y ( cps ) Binding Ene gy ( eV ) 292 290 288 286 284 282 280 0 1000 2000 3000 4000 5000 6000 7000 O-C=O C=O C-O C-C (sp 3 ) C=C (sp 2 ) GO ( b ) In ensi y ( cps ) Binding Ene gy ( eV ) (d) RGO PUR ZS50 PUR ZS25 RGO (c) Figu e 3. FE-SEM image o RGO ( a ), and FE-SEM image o he ac u e su ace o ZS100-RGO-PUR ( b ), ZS50-RGO-PUR ( c ), and ZS25-RGO-PUR (d). 3.4. X- ay Pho oelec on Spec oscopy The p epa ed GO and RGO we e examined by X- ay pho oelec on spec oscopy (XPS). Figu e 4shows he XPS spec a o p epa ed g aphene oxide (GO) and educed g aphene oxide (RGO). Figu e 4a,c signi ies he su ey scan spec a o GO and RGO, which display he exis ence o ca bon and oxygen. Figu e 4b depic s he high- esolu ion XPS spec a o he C 1s egion o GO. The decon olu ed C 1s peak displays he peak binding ene gy o 284.1 eV, 284.7 eV, 286.5 eV, 288.4 eV, and 290.0 eV, which esembles C=C (sp 2 ca bon), C-C (sp 3 ca bon), C-O, C=O, and O-C=O bonds, espec i ely [ 34 ]. Addi ionally, Figu e 4d deno es he high- esolu ion XPS spec a o C 1s o RGO. I displays he peak binding ene gy o 284.4 eV, 285.9 eV, 287.7 eV, 289.1 eV, and 290.6 eV ela ed o C=C, C-OH, C=O, O-C=O, and π - π * sa elli e bonds, espec i ely [ 35 ]. The XPS in es iga ion demons a ed ha a e educ ion ea men , he unc ional g oup o GO is educed, and he sp 3 ca bon is al e ed o sp2ca bon. Nanoma e ials 2021, 11, x FOR PEER REVIEW 9 o 25 Figu e 3. FE-SEM image o RGO (a), and FE-SEM image o he ac u e su ace o ZS100-RGO-PUR (b), ZS50-RGO-PUR (c), and ZS25-RGO-PUR (d). 3.4. X- ay Pho oelec on Spec oscopy The p epa ed GO and RGO we e examined by X- ay pho oelec on spec oscopy (XPS). Figu e 4 shows he XPS spec a o p epa ed g aphene oxide (GO) and educed g a- phene oxide (RGO). Figu e 4a,c signi ies he su ey scan spec a o GO and RGO, which display he exis ence o ca bon and oxygen. Figu e 4b depic s he high- esolu ion XPS spec a o he C 1s egion o GO. The decon olu ed C 1s peak displays he peak binding ene gy o 284.1 eV, 284.7 eV, 286.5 eV, 288.4 eV, and 290.0 eV, which esembles C=C (sp 2 ca bon), C-C (sp 3 ca bon), C-O, C=O, and O-C=O bonds, espec i ely [34]. Addi ionally, Figu e 4d deno es he high- esolu ion XPS spec a o C 1s o RGO. I displays he peak binding ene gy o 284.4 eV, 285.9 eV, 287.7 eV, 289.1 eV, and 290.6 eV ela ed o C=C, C- OH, C=O, O-C=O, and π-π* sa elli e bonds, espec i ely [35]. The XPS in es iga ion demons a ed ha a e educ ion ea men , he unc ional g oup o GO is educed, and he sp 3 ca bon is al e ed o sp 2 ca bon. 1,200 1,000 800 600 400 200 0 0 50000 100000 150000 200000 250000 GO C 1s O 1s O KLL ( a ) In ensi y ( cps ) Binding Ene gy ( eV ) 292 290 288 286 284 282 280 0 1000 2000 3000 4000 5000 6000 7000 O-C=O C=O C-O C-C (sp 3 ) C=C (sp 2 ) GO ( b ) In ensi y ( cps ) Binding Ene gy ( eV ) (d) RGO PUR ZS50 PUR ZS25 RGO (c) Figu e 4. Con . Nanoma e ials 2021,11, 1112 16 o 25 inc eased wi h he inc ease o he size o supe pa amagne ic ZnFe 2 O 4 nanopa icles in p epa ed nanocomposi es. Nanoma e ials 2021, 11, x FOR PEER REVIEW 16 o 25 The ela ion be ween elec ical conduc i i y (σAC) and imagina y pe mi i i y (ε″) can be s a ed as [70]: σ =εε󰆒󰆒2π (10) He ein, εo is he dielec ic cons an o ee space; is he equency o he elec omag- ne ic wa e. The abo e ela ion signi ies ha he elec ical conduc i i y will inc ease wi h an inc ease in he alue o imagina y pe mi i i y. The e o e, he enhanced alue o he complex pe mi i i y can be associa ed wi h he inc ease in he elec ical conduc i i y o he p epa ed nanocomposi es wi h an inc ease in he size o embedded supe pa amag- ne ic e i e nanopa icles. Figu e 9c ep esen s he change in elec ical conduc i i y wi h he equency o p epa ed nanocomposi es. The elec ical conduc i i y is in he ange o 1.9 × 10−3 o 3.9 × 10−3 S/cm, 2.5 × 10−3 o 4.3 × 10−3 S/cm, 2.9 × 10−3 o 7.5 × 10−3 S/cm o ZS25- RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, espec i ely. Fu he , in epo ed li e a u e by o he esea che s, he Debye heo y is gene ally u i- lized o cla i y he elaxa ion p ocess o dipoles [71,72]. Acco ding o he Debye heo y o dielec ic loss cha ac e is ics, he eal pe mi i i y (ε′) and imagina y pe mi i i y (ε″) can be w i en as [73]: ε󰆒=ε+ε−ε 1+(ωτ) ε󰆒󰆒 =ε 󰆒󰆒 +ε 󰆒󰆒 =ε−ε 1+(ωτ)ωτ + σ ωε (11) He ein, εs and ε∞ a e he s a ic and in ini e pe mi i i y; ω = 2π is he angula e- quency; τ is he elaxa ion ime; σ is he conduc i i y. I can be seen om he abo e ela ion ha he ε′ and ε″ a e he unc ions o ωτ. Hence, bo h he ε′ and ε″ a e mu ually dependen on one ano he . A ela ionship be ween ε′ and ε″ can be in e ed a e igno ing he con i- bu ion o σ and by elimina ing ωτ [74]: ε󰆒−ε+ε 2+(ε󰆒󰆒)=󰇡ε−ε 2󰇢 (12) F om he abo e ela ion, i is easy o ecognize ha he cu es o ε′ and ε″ would be a semi-ci cle, which is known as he Cole–Cole semici cle [75]. 8G 9G 10G 11G 12G 5 6 7 8 9 10 ( a ) ε′ F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR 8G 9G 10G 11G 12G 0.4 0.6 0.8 1.0 1.2 1.4 ( b ) ε″ F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR Nanoma e ials 2021, 11, x FOR PEER REVIEW 17 o 25 8G 9G 10G 11G 12G 2.0x10 -3 3.0x10 -3 4.0x10 -3 5.0x10 -3 6.0x10 -3 7.0x10 -3 8.0x10 -3 ( c ) σ AC (S/cm) F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR 6.8 6.9 7.0 7.1 7.2 7.3 0.4 0.6 0 . 8 7.6 7.7 7.8 7.9 0.6 0.8 8.4 8.6 8.8 9.0 0.8 1.0 1.2 ZS100-RGO-PUR ZS50-RGO-PUR ZS25-RGO-PUR ε″ ( d ) ε″ ε′ ε′ ε″ ε′ Figu e 9. (a) F equency dependence o he eal pe mi i i y (ε′), (b) equency dependence o he imagina y pe mi i i y (ε”), (c) equency dependence o he ac conduc i i y, and (d) Cole–Cole plo s o nanocomposi es. Figu e 9d depic s he Cole–Cole plo s o he de eloped PUR-based nanocomposi es. In gene al, he elaxa ion is associa ed wi h a delay in pola iza ion conce ning he change in he elec ical ield. Some ob ious Cole–Cole semici cles can be no iced in Figu e 9d, which signi ies ha he elaxa ion con ibu ed o he dielec ic loss. Addi ionally, one Cole–Cole semici cle ep esen s a Debye dipola elaxa ion, and he exis ence o mo e semici cles is a ibu ed o mul iple elaxa ion p ocesses [76]. These o he semici cles a e associa ed wi h Maxwell–Wagne elaxa ion, elec on/ion pola iza ion, and in e acial po- la iza ion [77]. The mul iple dielec ic losses we e esponsible o he imp o emen o he abso p ion cha ac e is ics o PUR-based nanocomposi es. I is well-known ha he eal pe meabili y (µ′) ep esen s he s o age abili y o mag- ne ic ene gy, and he imagina y pe meabili y (µ″) signi ies he magne ic loss. Figu e 10a ep esen s he equency dependence o he eal pe meabili y (µ′) o PUR-based nanocom- posi es. The µ′ is in he ange o 0.86 o 0.96, 0.91 o 0.99, and 0.90 o 1.09 o nanocompo- si es ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, espec i ely. The alue o eal pe meabili y (µ′) was inc eased wi h an inc ease o g ain size o u ilized supe pa a- magne ic ZnFe2O4 spinel e i e nanopa icles. Fu he , he alue o µ″ is in he ange o - 0.06 o 0.03, −0.01 o 0.07, and 0.03 o 0.19 o he p epa ed composi es ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, espec i ely, as shown in Figu e 10b. Rema ka- bly, i is no iced ha he µ″ exhibi ed nega i e alue also o some PUR-based nanocom- posi es, which is associa ed wi h he mo ion o cha ges [78]. 8G 9G 10G 11G 12G 0.85 0.90 0.95 1.00 1.05 1.10 ( a ) μ′ F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR 8G 9G 10G 11G 12G -0.05 0.00 0.05 0.10 0.15 0.20 ( b ) μ″ F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR Figu e 9. ( a ) F equency dependence o he eal pe mi i i y ( ε0 ), ( b ) equency dependence o he imagina y pe mi i i y (ε00), (c) equency dependence o he ac conduc i i y, and (d) Cole–Cole plo s o nanocomposi es. The ela ion be ween elec ical conduc i i y ( σAC ) and imagina y pe mi i i y ( ε00 ) can be s a ed as [70]: σAC =εoε00 2π (10) He ein, εo is he dielec ic cons an o ee space; is he equency o he elec o- magne ic wa e. The abo e ela ion signi ies ha he elec ical conduc i i y will inc ease wi h an inc ease in he alue o imagina y pe mi i i y. The e o e, he enhanced alue o he complex pe mi i i y can be associa ed wi h he inc ease in he elec ical conduc i i y o he p epa ed nanocomposi es wi h an inc ease in he size o embedded supe pa am- agne ic e i e nanopa icles. Figu e 9c ep esen s he change in elec ical conduc i i y wi h he equency o p epa ed nanocomposi es. The elec ical conduc i i y is in he ange o 1.9 ×10−3 o 3.9 × 10 −3 S/cm, 2.5 × 10 −3 o 4.3 × 10 −3 S/cm, 2.9 × 10 −3 o 7.5 ×10−3S/cm o ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, espec i ely. Fu he , in epo ed li e a u e by o he esea che s, he Debye heo y is gene ally u ilized o cla i y he elaxa ion p ocess o dipoles [71,72]. Acco ding o he Debye heo y Nanoma e ials 2021,11, 1112 17 o 25 o dielec ic loss cha ac e is ics, he eal pe mi i i y ( ε0 ) and imagina y pe mi i i y ( ε00 ) can be w i en as [73]: ε0=ε∞+εs−ε∞ 1+(ωτ)2 ε00 =ε00 elax +ε00 σ=εs−ε∞ 1+(ωτ)2ωτ +σ ωεo (11) He ein, εs and ε∞ a e he s a ic and in ini e pe mi i i y; ω = 2 π is he angula equency; τ is he elaxa ion ime; σ is he conduc i i y. I can be seen om he abo e ela ion ha he ε0 and ε00 a e he unc ions o ωτ . Hence, bo h he ε0 and ε00 a e mu ually dependen on one ano he . A ela ionship be ween ε0 and ε00 can be in e ed a e igno ing he con ibu ion o σand by elimina ing ωτ [74]: ε0−εs+ε∞ 22 +(ε00 )2=εs−ε∞ 22(12) F om he abo e ela ion, i is easy o ecognize ha he cu es o ε0 and ε00 would be a semi-ci cle, which is known as he Cole–Cole semici cle [75]. Figu e 9d depic s he Cole–Cole plo s o he de eloped PUR-based nanocomposi es. In gene al, he elaxa ion is associa ed wi h a delay in pola iza ion conce ning he change in he elec ical ield. Some ob ious Cole–Cole semici cles can be no iced in Figu e 9d, which signi ies ha he elaxa ion con ibu ed o he dielec ic loss. Addi ionally, one Cole–Cole semici cle ep esen s a Debye dipola elaxa ion, and he exis ence o mo e semici cles is a ibu ed o mul iple elaxa ion p ocesses [ 76 ]. These o he semici cles a e associa ed wi h Maxwell–Wagne elaxa ion, elec on/ion pola iza ion, and in e acial pola iza ion [ 77 ]. The mul iple dielec ic losses we e esponsible o he imp o emen o he abso p ion cha ac e is ics o PUR-based nanocomposi es. I is well-known ha he eal pe meabili y ( µ0 ) ep esen s he s o age abili y o mag- ne ic ene gy, and he imagina y pe meabili y ( µ00 ) signi ies he magne ic loss. Figu e 10a ep esen s he equency dependence o he eal pe meabili y ( µ0 ) o PUR-based nanocom- posi es. The µ0 is in he ange o 0.86 o 0.96, 0.91 o 0.99, and 0.90 o 1.09 o nanocomposi es ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, espec i ely. The alue o eal pe meabili y ( µ0 ) was inc eased wi h an inc ease o g ain size o u ilized supe pa am- agne ic ZnFe 2 O 4 spinel e i e nanopa icles. Fu he , he alue o µ00 is in he ange o − 0.06 o 0.03, − 0.01 o 0.07, and 0.03 o 0.19 o he p epa ed composi es ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, espec i ely, as shown in Figu e 10b. Rema kably, i is no iced ha he µ00 exhibi ed nega i e alue also o some PUR-based nanocomposi es, which is associa ed wi h he mo ion o cha ges [78]. Nanoma e ials 2021, 11, x FOR PEER REVIEW 17 o 25 8G 9G 10G 11G 12G 2.0x10 -3 3.0x10 -3 4.0x10 -3 5.0x10 -3 6.0x10 -3 7.0x10 -3 8.0x10 -3 ( c ) σ AC (S/cm) F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR 6.8 6.9 7.0 7.1 7.2 7.3 0.4 0.6 0 . 8 7.6 7.7 7.8 7.9 0.6 0.8 8.4 8.6 8.8 9.0 0.8 1.0 1.2 ZS100-RGO-PUR ZS50-RGO-PUR ZS25-RGO-PUR ε″ ( d ) ε″ ε′ ε′ ε″ ε′ Figu e 9. (a) F equency dependence o he eal pe mi i i y (ε′), (b) equency dependence o he imagina y pe mi i i y (ε”), (c) equency dependence o he ac conduc i i y, and (d) Cole–Cole plo s o nanocomposi es. Figu e 9d depic s he Cole–Cole plo s o he de eloped PUR-based nanocomposi es. In gene al, he elaxa ion is associa ed wi h a delay in pola iza ion conce ning he change in he elec ical ield. Some ob ious Cole–Cole semici cles can be no iced in Figu e 9d, which signi ies ha he elaxa ion con ibu ed o he dielec ic loss. Addi ionally, one Cole–Cole semici cle ep esen s a Debye dipola elaxa ion, and he exis ence o mo e semici cles is a ibu ed o mul iple elaxa ion p ocesses [76]. These o he semici cles a e associa ed wi h Maxwell–Wagne elaxa ion, elec on/ion pola iza ion, and in e acial po- la iza ion [77]. The mul iple dielec ic losses we e esponsible o he imp o emen o he abso p ion cha ac e is ics o PUR-based nanocomposi es. I is well-known ha he eal pe meabili y (µ′) ep esen s he s o age abili y o mag- ne ic ene gy, and he imagina y pe meabili y (µ″) signi ies he magne ic loss. Figu e 10a ep esen s he equency dependence o he eal pe meabili y (µ′) o PUR-based nanocom- posi es. The µ′ is in he ange o 0.86 o 0.96, 0.91 o 0.99, and 0.90 o 1.09 o nanocompo- si es ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, espec i ely. The alue o eal pe meabili y (µ′) was inc eased wi h an inc ease o g ain size o u ilized supe pa a- magne ic ZnFe2O4 spinel e i e nanopa icles. Fu he , he alue o µ″ is in he ange o - 0.06 o 0.03, −0.01 o 0.07, and 0.03 o 0.19 o he p epa ed composi es ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, espec i ely, as shown in Figu e 10b. Rema ka- bly, i is no iced ha he µ″ exhibi ed nega i e alue also o some PUR-based nanocom- posi es, which is associa ed wi h he mo ion o cha ges [78]. 8G 9G 10G 11G 12G 0.85 0.90 0.95 1.00 1.05 1.10 ( a ) μ′ F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR 8G 9G 10G 11G 12G -0.05 0.00 0.05 0.10 0.15 0.20 ( b ) μ″ F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR Figu e 10. Con . Nanoma e ials 2021,11, 1112 18 o 25 Nanoma e ials 2021, 11, x FOR PEER REVIEW 18 o 25 8G 9G 10G 11G 12G 0.04 0.06 0.08 0.10 0.12 0.14 0.16 ( c ) anδε F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR 8G 9G 10G 11G 12G -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 ( d ) anδμ F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR Figu e 10. (a) F equency dependence o he eal pe meabili y (µ′), (b) equency dependence o he imagina y pe meabili y (µ″), (c) dielec ic loss angen , and (d) magne ic loss angen o nanocomposi es. Addi ionally, he Globus equa ion is exp essed as [79]: μ∝ (M D K  ⁄) ⁄ (13) This equa ion signi ies ha o ge a highe complex pe meabili y, a highe sa u a ion magne iza ion (MS), la ge g ain size (D), and smalle magne oc ys alline aniso opy con- s an (K1) a e needed. The inc eased magne iza ion and la ge g ain size o he ZS100 sam- ple may add o he la ge pe meabili y o p epa ed ZS100-RGO-PUR nanocomposi es, as compa ed wi h ZS25-RGO-PUR and ZS50-RGO-PUR nanocomposi es. Fu he , based on he ollowing ela ions [80]: =󰆒󰆒 󰆒 =μ󰆒󰆒 μ󰆒 (14) and u ilizing elec omagne ic pa ame e s o ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR nanocomposi es, he dielec ic loss angen ( anδε) and magne ic loss angen ( anδµ) we e e alua ed. Figu e 10c ep esen s dielec ic loss angen s. equency cu es o p epa ed PUR-based nanocomposi es. The dielec ic loss angen ( anδε) o samples ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, luc ua ed wi h an in- c ease o equency o elec omagne ic wa e be ween 0.05 o 0.10, 0.06 o 0.11, and 0.07 o 0.15, espec i ely. Addi ionally, he dielec ic loss is ela ed o dipole pola iza ion and in- e acial pola iza ion a highe equencies [81]. I can be also no iced ha he dielec ic loss (ε″) alue o he ZS100-RGO-PUR sample is much highe han he o he wo samples (i.e., ZS25-RGO-PUR, and ZS50-RGO-PUR). The highe dielec ic loss in he ZS100-RGO- PUR sample is associa ed wi h enhanced elec ical conduc i i y and dielec ic cons an induced by mic o-cu en s and pola iza ion in nanocomposi es [82]. The magne ic loss angen a ia ion wi h he equency o an elec omagne ic wa e o p epa ed PUR-based nanocomposi es is p esen ed in Figu e 10d. I can be pe cei ed ha he magne ic loss angen luc ua ed be ween −0.06 o 0.03, −0.01 o 0.07, and 0.03 o 0.19 o samples ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, espec i ely. I is well-known ha na u al esonance, exchange esonance, and eddy cu en a e he main con ibu o s o he magne ic loss o nanopa icles [83]. The eddy cu en loss can be s a ed by he ollowing ela ion when he size o magne ic nanopa icle (D) is smalle han he skin dep h (δ) [84]: μ󰆔 μ󰆒αμ󰆒 D ⍴ (15) Figu e 10. ( a ) F equency dependence o he eal pe meabili y ( µ0 ), ( b ) equency dependence o he imagina y pe meabili y (µ00), (c) dielec ic loss angen , and (d) magne ic loss angen o nanocomposi es. Addi ionally, he Globus equa ion is exp essed as [79]: µ∝M2 sD/K11/2 (13) This equa ion signi ies ha o ge a highe complex pe meabili y, a highe sa u a ion magne iza ion (M S ), la ge g ain size (D), and smalle magne oc ys alline aniso opy cons an (K 1 ) a e needed. The inc eased magne iza ion and la ge g ain size o he ZS100 sample may add o he la ge pe meabili y o p epa ed ZS100-RGO-PUR nanocomposi es, as compa ed wi h ZS25-RGO-PUR and ZS50-RGO-PUR nanocomposi es. Fu he , based on he ollowing ela ions [80]: anδε=ε00 ε0 anδµ=µ00 µ0 (14) and u ilizing elec omagne ic pa ame e s o ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100- RGO-PUR nanocomposi es, he dielec ic loss angen ( an δε ) and magne ic loss angen ( an δµ ) we e e alua ed. Figu e 10c ep esen s dielec ic loss angen s. equency cu es o p epa ed PUR-based nanocomposi es. The dielec ic loss angen ( an δε ) o samples ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, luc ua ed wi h an inc ease o equency o elec omagne ic wa e be ween 0.05 o 0.10, 0.06 o 0.11, and 0.07 o 0.15, espec i ely. Addi ionally, he dielec ic loss is ela ed o dipole pola iza ion and in e acial pola iza ion a highe equencies [ 81 ]. I can be also no iced ha he dielec ic loss ( ε00 ) alue o he ZS100-RGO-PUR sample is much highe han he o he wo samples (i.e., ZS25-RGO-PUR, and ZS50-RGO-PUR). The highe dielec ic loss in he ZS100-RGO-PUR sample is associa ed wi h enhanced elec ical conduc i i y and dielec ic cons an induced by mic o-cu en s and pola iza ion in nanocomposi es [82]. The magne ic loss angen a ia ion wi h he equency o an elec omagne ic wa e o p epa ed PUR-based nanocomposi es is p esen ed in Figu e 10d. I can be pe cei ed ha he magne ic loss angen luc ua ed be ween − 0.06 o 0.03, − 0.01 o 0.07, and 0.03 o 0.19 o samples ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, espec i ely. I is well-known ha na u al esonance, exchange esonance, and eddy cu en a e he main con ibu o s o he magne ic loss o nanopa icles [ 83 ]. The eddy cu en loss can be s a ed by he ollowing ela ion when he size o magne ic nanopa icle (D) is smalle han he skin dep h (δ) [84]: µ00 µ0αµ0 D ρ(15) whe e is he elec omagne ic wa e equency; ρ is he elec ic esis i i y o he nanopa - icles. Based on his abo e ela ion, C o = −1 ( µ0 ) −2µ00 should be cons an , i he magne ic Nanoma e ials 2021,11, 1112 19 o 25 loss is mainly con ibu ed om he eddy cu en loss. I can be seen in Figu e 11a ha he alue C o is no cons an o all he p epa ed PUR-based nanocomposi es. I signi ies ha he eddy cu en loss would no be a dominan con ibu o o magne ic loss. Nanoma e ials 2021, 11, x FOR PEER REVIEW 19 o 25 whe e is he elec omagne ic wa e equency; ⍴ is he elec ic esis i i y o he nanopa - icles. Based on his abo e ela ion, Co = −1(µ′)−2µ″ should be cons an , i he magne ic loss is mainly con ibu ed om he eddy cu en loss. I can be seen in Figu e 11a ha he alue Co is no cons an o all he p epa ed PUR-based nanocomposi es. I signi ies ha he eddy cu en loss would no be a dominan con ibu o o magne ic loss. 8G 9G 10G 11G 12G -0.010 -0.005 0.000 0.005 0.010 0.015 0.020 ( a ) C o ( ns ) F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR 8G 9G 10G 11G 12G 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13 0.14 ( b ) δ (mm) F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR 8G 9G 10G 11G 12G 0 20 40 60 80 100 ( c ) A enua ion Cons an , α F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR 8G 9G 10G 11G 12G 0.32 0.33 0.34 0.35 0.36 0.37 0.38 ( d ) Impedance Ma ching Coe icien (η) F equency ( Hz ) ZS25-RGO-PUR ZS50-RGO-PUR ZS100-RGO-PUR Figu e 11. F equency dependence o (a) he eddy cu en loss, (b) skin dep h, (c) a enua ion cons an , and (d) impedance ma ching coe icien o p epa ed PUR-based nanocomposi es. Besides dielec ic and magne ic losses, skin dep h (δ) is ano he impo an ac o ha s imula es he abso p ion o elec omagne ic wa es. Skin dep h s a es he dis ance a which he ield d ops o 1/e o he inciden alue and s a ed as [85]: δ=1  π μσ ⁄ (16) He ein, is he equency; σ is he elec ical conduc i i y; µ is he pe meabili y. This ela ion signi ies ha skin dep h educes wi h an inc ease in equency, pe meabili y, and conduc i i y. Figu e 11b depic s he equency dependence a ia ion o skin dep h o he p epa ed PUR-based nanocomposi es. A smalle skin dep h s a es a s onge abso p ion capaci y [86]. The skin dep h o samples ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100- RGO-PUR luc ua ed wi h an inc ease in he equency o elec omagne ic wa es be ween 0.08 o 0.14 mm, 0.08 o 0.12 mm, and 0.06 o 0.11 mm, espec i ely. The p epa ed ZS100- RGO-PUR nanocomposi e exhibi s smalle skin dep h and, he e o e, s onge abso p ion. Figu e 11. F equency dependence o ( a ) he eddy cu en loss, ( b ) skin dep h, ( c ) a enua ion cons an , and ( d ) impedance ma ching coe icien o p epa ed PUR-based nanocomposi es. Besides dielec ic and magne ic losses, skin dep h ( δ ) is ano he impo an ac o ha s imula es he abso p ion o elec omagne ic wa es. Skin dep h s a es he dis ance a which he ield d ops o 1/e o he inciden alue and s a ed as [85]: δ=1/pπ µσ (16) He ein, is he equency; σ is he elec ical conduc i i y; µ is he pe meabili y. This ela ion signi ies ha skin dep h educes wi h an inc ease in equency, pe meabili y, and conduc i i y. Figu e 11b depic s he equency dependence a ia ion o skin dep h o he p epa ed PUR-based nanocomposi es. A smalle skin dep h s a es a s onge abso p ion capaci y [ 86 ]. The skin dep h o samples ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100- RGO-PUR luc ua ed wi h an inc ease in he equency o elec omagne ic wa es be ween 0.08 o 0.14 mm, 0.08 o 0.12 mm, and 0.06 o 0.11 mm, espec i ely. The p epa ed ZS100- RGO-PUR nanocomposi e exhibi s smalle skin dep h and, he e o e, s onge abso p ion. The a enua ion cons an ( α ) is an impo an ac o ha go e ns he elec omagne ic wa e abso p ion capabili ies o shielding nanocomposi es. I can be assessed by he ollowing ela ion [87]: α=√2π c (µ00 ε00 −µ0ε0)+q(µ0ε00 +µ00ε0)2+(µ00ε00 −µ0ε0)2(17) Nanoma e ials 2021,11, 1112 20 o 25 Figu e 11c displays he equency dependence a ia ion o he a enua ion cons an ( α ) o p epa ed PUR-based nanocomposi es. The high a enua ion cons an ( α ) alue o he p epa ed ZS100-RGO-PUR nanocomposi e compa ed wi h o he samples demons a ed high abso p ion o elec omagne ic wa es. Ano he key ac o ha go e ns elec omagne ic wa e abso p ion is impedance ma ching. I is s a ed by he modulus o he no malized cha - ac e is ic impedance (Z), which can be calcula ed by u ilizing he ollowing ela ion [88]: Z=|Z1/Zo|(18) whe e Z1=Zopµ /ε ; Zo is he impedance in ee space; ε is he alue o complex pe - mi i i y; µ is he alue o complex pe meabili y. Figu e 11d shows he a ia ion o he impedance ma ching coe icien o p epa ed PUR-based nanocomposi es wi h equency. The alues o Z a e below one, and he ZS100-RGO-PUR nanocomposi e has a lowe Z alue compa ed o o he samples. A high a enua ion cons an and mode a e Z alue o ZS100- RGO-PUR nanocomposi e p o ided he high alue o EMI-shielding e ec i eness [ 89 ]. The schema ic illus a ion o he elec omagne ic in e e ence shielding mechanism in he p epa ed nanocomposi e is shown in Figu e 12. When elec omagne ic wa es in e ac a he su ace o he p epa ed nanocomposi e, a pa o i is e lec ed, ano he pa is abso bed, and he emaining pa has mul iple e lec ions and sca e ing [ 90 ]. The e lec ion is associa ed wi h mo ing cha ge ca ie s in e ac ed wi h elec omagne ic wa es [ 91 ]. The abso p ion signi ies he dissipa ion o ene gy o he elec omagne ic wa es due o he in e ac ion o elec omagne ic wa es wi h he elec ic and magne ic dipoles [ 92 ]. The mul iple e lec ions a e e lec ions a di e en su aces o in e aces p esen due o inhomogenei y wi hin he p epa ed nanocomposi e. The p epa ed nanocomposi es consis ed o conduc i e RGO shee s and ZnFe 2 O 4 magne ic nanopa icles no only imp o e impedance ma ching bu also c ea es a mic o-cu en ne wo k and a ains in e acial pola iza ion [ 93 ]. The app op ia e conduc i i y o RGO shee s gi ed he p epa ed nanocomposi es exhibi ed a mode a e conduc i i y loss. Residual unc ional g oups and de ec s in RGO shee s and ZnFe 2 O 4 o igi- na ed dipole pola iza ion and de ec pola iza ion [ 94 ]. The in e ac ion o elec omagne ic wa es also c ea es hopping and mig a ing elec ons ac oss he de ec s o RGO shee s. Nanoma e ials 2021, 11, x FOR PEER REVIEW 21 o 25 Figu e 12. Schema ic illus a ion o he elec omagne ic in e e ence shielding mechanism in p e- pa ed nanocomposi es. 4. Conclusions In summa y, supe pa amagne ic ZnFe 2 O 4 spinel e i e nanopa icles we e p epa ed success ully by he sonochemical syn hesis app oach a a ious ul a-sonica ion imes o 25 min (ZS25), 50 min (ZS50), and 100 min (ZS100). The a e age c ys alli e size inc eased om 3.0 nm o 4.0 nm wi h an inc ease in sonica ion ime. The la ice pa ame e inc eased om 7.219 Å o 7.248 Å wi h an inc ease in sonica ion ime om 25 min o 100 min. The inc ease in ionic adii, hopping leng h o he oc ahed al and e ahed al si e, e ahed al and oc ahed al bond leng h, e ahed al edge, and sha ed and unsha ed oc ahed al edge o p epa ed ZnFe 2 O 4 nanopa icles wi h an inc ease in sonica ion ime is associa ed wi h ca ion edis ibu ion in ZnFe 2 O 4 nanopa icles wi h an inc ease in sonica ion ime. The p epa ed spinel e i e nanopa icles exhibi ed ze o emanen and ze o coe ci i y, which is associa ed wi h supe pa amagne ic cha ac e is ics. The p epa ed magne ic ZnFe 2 O 4 na- nopa icles (ZS25, ZS50, and ZS100) and elec ically conduc i e educed g aphene oxide (RGO) we e embedded in a polyu e hane esin (PUR) ma ix o de elop ligh weigh and lexible nanocomposi es o elec omagne ic in e e ence shielding applica ion. The max- imum o al shielding e ec i eness (SE T ) alue o de eloped nanocomposi es o hickness 1 mm in he ange o 8.2–12.4 GHz equency was 12.7 dB, 13.8 dB, and 16.7 dB, o ZS25- RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, espec i ely. The highe a enua ion cons an (α) alue o in p epa ed ZS100-RGO-PUR nanocomposi e as compa ed wi h o he samples demons a ed high abso p ion o elec omagne ic wa es. This wo k demons a ed an ingenious and e ec i e s a egy o de elop polyu e hane esin-based nanocomposi es consis ing o supe pa amagne ic ZnFe 2 O 4 spinel e i e nanopa icles wi h RGO o shielding elec omagne ic pollu ion. Supplemen a y Ma e ials: The ollowing a e a ailable online a www.mdpi.com/xxx/s1, Figu e S1: (a) TEM image o ZS25, (b) size dis ibu ion o ZS25, (c) TEM image o ZS50, (d) size dis ibu ion o ZS50, (e) TEM image o ZS100, ( ) size dis ibu ion o ZS100. Au ho Con ibu ions: A. and T.J. pe o med he expe imen s; D.Š., P.U., M.M. (Michal Macho ský), M.M. (Milan Masař), M.U., and L.K. pe o med he cha ac e iza ions; R.S.Y., I.K., J.V. and J.H. analyzed he da a and w o e he manusc ip . All au ho s ha e ead and ag eed o he pub- lished e sion o he manusc ip . Funding: We hank he inancial suppo o he Czech Science Founda ion (GA19-23647S) p ojec a he Cen e o Polyme Sys ems, Tomas Ba a Uni e si y in Zlin, Czech Republic. One au ho , Anju, Figu e 12. Schema ic illus a ion o he elec omagne ic in e e ence shielding mechanism in p epa ed nanocomposi es. The magne ic cha ac e is ics o he supe pa amagne ic ZnFe 2 O 4 nanopa icles com- ponen in he de eloped nanocomposi es p o ided a deg ee o magne ic loss such as na u al esonance and eddy cu en loss. I imp o es he impedance ma ching be ween complex pe mi i i y and pe meabili y, which p o ides well abso p ion condi ion o elec- Nanoma e ials 2021,11, 1112 21 o 25 omagne ic wa es [ 95 ]. The imp o ed elec omagne ic wa e shielding cha ac e is ics o he ZS100-RGO-PUR nanocomposi e can be p ima ily a ibu ed o he inclusi e ac s o magne ic loss, dielec ic loss, and app op ia e a enua ion cons an de i ed om a ious nano ille s in he ma ix. 4. Conclusions In summa y, supe pa amagne ic ZnFe 2 O 4 spinel e i e nanopa icles we e p epa ed success ully by he sonochemical syn hesis app oach a a ious ul a-sonica ion imes o 25 min (ZS25), 50 min (ZS50), and 100 min (ZS100). The a e age c ys alli e size inc eased om 3.0 nm o 4.0 nm wi h an inc ease in sonica ion ime. The la ice pa ame e inc eased om 7.219 Å o 7.248 Å wi h an inc ease in sonica ion ime om 25 min o 100 min. The inc ease in ionic adii, hopping leng h o he oc ahed al and e ahed al si e, e ahed al and oc ahed al bond leng h, e ahed al edge, and sha ed and unsha ed oc ahed al edge o p epa ed ZnFe 2 O 4 nanopa icles wi h an inc ease in sonica ion ime is associa ed wi h ca ion edis ibu ion in ZnFe 2 O 4 nanopa icles wi h an inc ease in sonica ion ime. The p epa ed spinel e i e nanopa icles exhibi ed ze o emanen and ze o coe ci i y, which is associa ed wi h supe pa amagne ic cha ac e is ics. The p epa ed magne ic ZnFe 2 O 4 nanopa icles (ZS25, ZS50, and ZS100) and elec ically conduc i e educed g aphene ox- ide (RGO) we e embedded in a polyu e hane esin (PUR) ma ix o de elop ligh weigh and lexible nanocomposi es o elec omagne ic in e e ence shielding applica ion. The maximum o al shielding e ec i eness (SE T ) alue o de eloped nanocomposi es o hick- ness 1 mm in he ange o 8.2–12.4 GHz equency was 12.7 dB, 13.8 dB, and 16.7 dB, o ZS25-RGO-PUR, ZS50-RGO-PUR, and ZS100-RGO-PUR, espec i ely. The highe a en- ua ion cons an ( α ) alue o in p epa ed ZS100-RGO-PUR nanocomposi e as compa ed wi h o he samples demons a ed high abso p ion o elec omagne ic wa es. This wo k demons a ed an ingenious and e ec i e s a egy o de elop polyu e hane esin-based nanocomposi es consis ing o supe pa amagne ic ZnFe 2 O 4 spinel e i e nanopa icles wi h RGO o shielding elec omagne ic pollu ion. Supplemen a y Ma e ials: The ollowing a e a ailable online a h ps://www.mdpi.com/a icle/10 .3390/nano11051112/s1, Figu e S1: (a) TEM image o ZS25, (b) size dis ibu ion o ZS25, (c) TEM image o ZS50, (d) size dis ibu ion o ZS50, (e) TEM image o ZS100, ( ) size dis ibu ion o ZS100. Au ho Con ibu ions: A. and T.J. pe o med he expe imen s; D.Š., P.U., M.M. (Michal Macho ský), M.M. (Milan Masaˇ ), M.U., and L.K. pe o med he cha ac e iza ions; R.S.Y., I.K., J.V. and J.H. analyzed he da a and w o e he manusc ip . All au ho s ha e ead and ag eed o he published e sion o he manusc ip . Funding: We hank he inancial suppo o he Czech Science Founda ion (GA19-23647S) p ojec a he Cen e o Polyme Sys ems, Tomas Ba a Uni e si y in Zlin, Czech Republic. One au ho , Anju, also acknowledges he inancial suppo by he in e nal g an no. IGA/CPS/2020/003 o speci ic esea ch om Tomas Ba a Uni e si y in Zlín. Ins i u ional Re iew Boa d S a emen : No applicable. In o med Consen S a emen : No applicable. Da a A ailabili y S a emen : Da a can be a ailable upon eques om he co esponding au ho . Acknowledgmen s: Au ho s acknowledge Old ich Schneeweiss, Ins i u e o Physics o Ma e ials, Academy o Sciences o he Czech Republic, Zizko a 22, 616 62 B no, Czech Republic, o he ze o- ield-cooled (ZFC) and ield-cooled (FC) empe a u e-dependen magne iza ion measu emen . 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