Synthesis of Ag and Cu nanoparticles by plasma discharge in inorganic salt solutions

Resea ch A icle Jakub Ho ák*, An on Niki o o , F an išek K čma, Ma ějBřezina, Zdenka Kozáko á, LukášDos ál, Michal Kalina, and LukášKalina Syn hesis o Ag and Cu nanopa icles by plasma discha ge in ino ganic sal solu ions h ps://doi.o g/10.1515/n e -2022-0549 ecei ed Oc obe 17, 2022; accep ed Ap il 21, 2023 Abs ac : In ecen yea s, nanopa icles ha e eme ged as an impo an playe in a b oad ange o applica ions, espe- cially hanks o ecen ad ances in hei syn hesis. The sil e and coppe nanopa icles a e o en used due o hei an ibac e ial and ungicidal ac i i ies, and his a icle p e- sen s he esul s o he nanopa icle syn hesis using elec- ical glow discha ge gene a ed di ec ly in a olume o hei sal solu ions. The e o e, he e is no influence o ai (i.e. eac i e ni ogen species) as i is usual in o he com- monly used app oaches. Nanopa icles we e p epa ed unde a ious expe imen al condi ions, and hey we e cha - ac e ized by ul a iole / isible spec ome y, dynamic ligh sca e ing, X- ay pho oelec on spec oscopy, and high- eso- lu ion scanning elec on mic oscopy. Pa icles we e p o- duced wi hou any su ac an o s abilizing agen , and some o hem showed highe esis ance agains agglome a- ion du ing hei sho - e m (days) s o age. The nanopa icle o ma ion mechanism was confi med by he as came a imaging. Thus, he de eloped app oach can be applied o simple en i onmen ally iendly nanopa icle p oduc ion o a ious applica ions. Keywo ds: nanopa icle, plasma discha ge, sil e nanopa - icles, coppe nanopa icles, discha ge in liquids, i ual ca hode in liquid, su ace plasmon esonance 1 In oduc ion Pa icles wi h specific size be ween 10 −9 and 10 −8 m in dia- me e a e called nanopa icles. Ma e ials o hese dimen- sions ha e diffe en p ope ies om he bulk ma e ial. Such pa icles ha e e y high specific su ace a ea ha is impo an o many applica ions, including ca alysis [1,2] and medicine [3,4]. Nanopa icle p ope ies a e dependen no only on he selec ed ma e ial (pu e me al, semicon- duc o , alloy) bu also on he size, shape, and c ys allo- g aphic pa ame e s. All hese p ope ies a e s ongly depen- den on he enginee ing p ocedu e. Thus, nanopa icles made o he same ma e ial can ha e e y diffe en p ope - ies [5,6]. Sil e nanopa icles a e used in many applica ion fields such as pho o ol aics (diagnos ics senso s, sola cells) [7], conduc i e applica ions (conduc i e inks) [8], o cos- me ics [9,10]. Coppe nanopa icles can be used in simila applica ions such as sil e nanopa icles [10,11], and a big in e es is in hei ca aly ic p ope ies [1,12,13]. The e is also a g owing in e es in he use o sil e and coppe nanopa icles in heal h ca e [14–16]. Such applica ions equi e nanopa icles in well-defined shapes and especially, a size dis ibu ion uni- o mi y.Thesmalle henucleio Ag, hehighe an ibac e ial ac i i y [17]. Nowadays, he sil e nanopa icles a e al eady used o biomedical de ices (ca he e s, join implan s, e c.), o wound and bone healing, and o he s [3]. Sil e nanopa i- cles con ained in hese p oduc s a e con inuously eleasing a small amoun o sil e ions o p o ide a p o ec ion agains bac e ia. Howe e , coppe nanopa icles show lowe an ibac- e ial efficiency compa ed o sil e nanopa icles [15,18], bu hei g een and cos -effec i e syn hesis leads o hei applica- ion in ag icul u e [19]. Nanopa icle p epa a ion can be ca ied ou by wo gen- e ally diffe en app oaches. The fi s one, physical (called also as op-down), is based on he bulk ma e ial b eaking down in o smalle pa icles. The mos o en me hods a e he e a- po a ion–condensa ion o he lase abla ion, bo h o en in he liquid en i onmen . The second app oach is a chemical me hod (also called as bo om-up), mainly based on he educ- ion om he me al sal solu ions (Ag + and Cu 2+ o Ag 0 and  * Co esponding au ho : Jakub Ho ák, Facul y o Chemis y, B no Uni e si y o Technology, Pu kyňo a 464/118, 612 00 B no, Czech Republic, e-mail: [email p o ec ed] An on Niki o o : Depa men o Applied Physics, Ghen Uni e si y, Sain -Pie e snieuws aa 41 B4, 9000 Ghen , Belgium F an išek K čma, Ma ějBřezina, Zdenka Kozáko á, Michal Kalina, LukášKalina: Facul y o Chemis y, B no Uni e si y o Technology, Pu kyňo a 464/118, 612 00 B no, Czech Republic LukášDos ál: Facul y o Elec ical Enginee ing and Communica ion, B no Uni e si y o Technology, Technická 3058/10, 616 00 B no, Czech Republic Nano echnology Re iews 2023; 12: 20220549 Open Access. © 2023 he au ho (s), published by De G uy e . This wo k is licensed unde he C ea i e Commons A ibu ion 4.0 In e na ional License. Cu 0 , espec i ely) by using a ious educing agen s (sodium ci a e, hyd azine, sodium bo ohyd ide, and o he s) [12,13,15,20]. The main disad an age o bo h physical and chemical me hods is ha p epa ed nanopa icles end o agglom- e a equickly,and hus, hei p ope ies a e significan ly changed. To p e en his, diffe en s abilizing agen s such as N,N′-dime hyl o mamide [20], poly inyl py olidone [12,14,20], and polye hylene glycol [12] a e commonly used. Thei applica ion leads o he pa icle g ow h s abi- liza ion (in many cases by hei su ace coa ing wi h a hin o ganic laye ), and hus, pa icles a e p e en ed om a loss o hei unique p ope ies [12–15,17,20]. The applica ion o hese addi i es can be a he isky in case o hei use in medicine whe e hei esidues can be non- accep able because o hei side effec s. A specific nanopa icle o ma ion p ocess was ecen ly p oposed based on he combina ion o plasmas wi h liquid en i onmen . Such me hods a e ope a ing a a mosphe ic p essu e and in he p esence o liquid (mainly wa e solu- ions) and p e en he o ma ion o bigge pa icles and agglome a es. Mo eo e , pa icles can be co e ed by hin laye o oxides, OH g oups, o ca bon-con aining laye s dependen on he used liquid du ing he o ma ion o immedia ely a e i . Thus, no addi ional su ac an s a e necessa y o p e en nanopa icles om hei agglome a- ion [21]. The p oposed me hod is an efficien example o he chemical app oach whe e he p ecu so solu ion i sel se es as a nanopa icle’s ma e ial sou ce. Many s udies we e ocused on he liquid su ace ea men by a ious gas- eous discha ges (mos ly a ious je s) o by mic oplasmas. These discha ges a e usually o med be ween he high- ol- age (HV) elec ode in he gaseous phase (abo e liquid) and he su ace o he g ounded solu ion [22–26]. The applica ion o a c o lase -induced plasmas di ec ly in he liquid phase a e he example o he physical app oach o he efficien nanopa icle p oduc ion wi hou su ac an s [27,28]. A special way is also he combina ion o chemical and physical p ocesses o he nanopa icle o ma ion in he liquid phase. The fi s es s we e pe o med using he lase - induced plasma applied o colloidal nanopa icle solu ions [29] o he a c discha ge ope a ion in nanopa icle-s abi- lizing solu ions [30]. Some pilo s udies o he pu e chemical app oach using sys em-gene a ing plasmas di ec ly in liquids we e also comple ed ecen ly [31]. Gene al no el y o ou syn hesis app oach is he ac ha hanks o he plasma gene a ion below he solu ion su ace, he o ma- ion o eac i e ni ogen species is negligible. Ni ogen is coming only om dissol ed ai and he used sal , and i s o al concen a ion is many o de s lowe han ha o oxygen ( om deionized wa e en i onmen ). Thus, only eac i e oxygen species, a omic hyd ogen, and elec ons can be conside ed du ing he nanopa icle o ma ion in ou no el sys em whe e ca hode and anode spaces a e sepa a ed by ba ie wi h small o ifice. Two special ca hode cons uc ions [32–35] we e used o he discha ge gene a- ion. Thus, elec ochemical p ocesses unning a he me allic (pla inum) anode do no play a ole in he nanopa icle o ma ion p ocess. Whole p ocess is unning as single s ep and cos -effec i e app oach using he DC elec ical discha ge di ec ly gene a ed in he p ecu so solu ion wi hou he addi ion o any haza dous compounds. The discha ge gen- e a ion di ec ly in liquid phase leads o he o ma ion o nanopa icles wi h supp essed agglome a ion. Whole sys em can also be easily scalable (e.g. heuseo amul i- elec ode sys em). All hese ea u es a e impo an o he g eene nanopa icle p oduc ion in applicable amoun s. Simplici y o he used powe supply and he use o common cheap p ecu so s b ings addi ional economic benefi s. A gon in oduc ion in o he discha ge olume leads o he lowe ini ial powe needed o a b eakdown, and hus, lowe ini ial sal concen a ions can be used. This leads o he o ma ion o smalle nanopa icles. The as came a mo ies we e used o e i y he nano- pa icle o ma ion p ocess. The ole o a gon in oduced in o he discha ge on he nanopa icle gene a ion was also in es iga ed. The sil e and coppe nanopa icles we e p epa ed unde selec ed discha ge pa ame e s om hei sulpha e and ni a e sal s, espec i ely, and hey we e cha ac e ized by he ul a iole / isible (UV/Vis) spec o- me y, dynamic ligh sca e ing (DLS), X- ay pho oelec on spec oscopy (XPS), and scanning elec on mic oscopy (SEM). Finally, he Tauc plo [36,37] p ocedu e was applied o calcula e he band gap ene gy o he p epa ed nanopa - icles because hei su ace was oxidized jus a e hei o ma ion in wa e solu ions. 2 Ma e ials and me hods The no el y o his esea ch is in he use o an expe i- men al de ice depic ed in Figu e 1, which was used in his wo k. In gene al, i is simila as o he discha ge gene a ion in he pin-hole configu a ion [38], whe e wo chambe s (elec ode spaces) o he glass appa a us a e di ided by a Teflon diaph agm wi h he o ifice filled by he wo king solu ion. The diaph agm is used o sepa a e he anode pa and elec ochemical p ocesses aking place a he anode su ace om he ca hode compa men whe e nanopa icles a e syn hesized. No discha ge is c ea ed a he o ifice, only a he ip o he used ca hode. The whole glass eac o is cons uc ed wi h a double wall o wa e cooling. 2Jakub Ho ák e al. Two diffe en g ounded ca hode configu a ions we e used (Figu e 2). Configu a ion A consis s o an elec ode head made om Maco ce amics o 10 mm in diame e wi h a s ainless-s eel capilla y (ou e diame e o 1 mm; inne diame e o 0.7 mm). This capilla y ends 1 mm be o e he Maco edge, and hus, a pin-hole is o med in he Maco nozzle [32–34]. A gon a a flow a e o 42 sccm is blown o he elec ode ip. Thus, he discha ge is gene a ed in a gon bubbles con aining wa e apou coming om he bulk solu ion. Configu a ion B is simila , bu he s ainless-s eel capilla y is eplaced by a ungs en od o he same dia- me e (i.e. 1 mm) ha also ends 1 mm be o e he Maco edge [35]. This allows he discha ge gene a ion in wa e apou bubbles gene a ed by he Joule hea ing. De ails abou his special discha ge can be ound in he p e ious s udy [35]. Bo h discha ge configu a ions we e sus ained o 3 min by DC ol age o abou 1.3 kV co esponding o 50 W supplied powe . A plana pla inum anode ( he ac i e a ea in he liquid o 15 ×25 mm 2 ) connec ed o he HV sou ce was used o bo h coppe and sil e nanopa icle p epa a ion. Coppe nanopa icles we e syn he ized in he wo king solu ion o coppe sulpha e (CuSO 4 ) as a p ecu so . The ini ial concen- a ions o 25, 50, 75, and 100 mg/l we e es ed. Sil e nano- pa icles we e syn hesized in he wo king solu ion o sil e ni a e (AgNO 3 ) wi h ini ial concen a ions o 1, 10, 25, 50, and 100 mg/l. To p epa e ou wo king solu ions, deionized wa e wi h conduc i i y adjus ed by app op ia e elec o- ly e was used. S ock solu ion o NaNO 3 (o Na 2 SO 4 , espec- i ely) in deionized wa e was p epa ed wi h a conduc- i i y o 950 µS/cm ( he concen a ion o such solu ion was 560 mg/l NaNO 3 and 460 mg/l Na 2 SO 4 ). This s ock solu- ion was used ins ead o pu e deionized wa e o dissol e he p ecu so sal s, which inc eased i s final conduc i i y by abou 50 µS/cm. The conduc i i y adjus men was pe o med o lowe he DC ol age needed o plasma gene a ion and o main- ain he s abili y o he discha ge as was also done in he p e ious s udy [39] wi h one-chambe eac o . Solu ions we e mixed by sel -mixing as shown in he supplemen a y mo ies p esen ed in he s udy by K čma e al. [35]. The nanopa icle o ma ion p ocess was obse ed by ul a as came a mo ies using he Pho on FASTCAM SA-X2 pe pendicula ly o he ca hode axis. An addi ional cubic polyca bona e essel wi h a qua z window o 50 mm in diame e was used o his pu pose. The discha ge essel was illumina ed by wo Dedoligh halogen lamps Dedocool ins alled pe pendicula ly one o he o he and o he op ical axis. The ame exposu e ime o 80 μs a 10,000 ames pe second and he ull chip image we e used. The discha ge ime e olu ion was isualized wi h he high space esolu ion o 50 mic ons pe pixel. The p epa ed colloid solu ions o nanopa icles we e cha - ac e ized by UV/Vis spec ome e Helios Omega (The moFishe Scien ific). Ob ained abso p ion spec a o coppe nanopa i- cles we e used o calcula e he di ec band gap ene gy using he Tauc plo me hod. This gi es ela ion (αhν) 2 o he pho on ene gy (αis he abso bance, his he Planck cons an , and νis he adia ion equency). Mo phology, size, and su ace Figu e 1: Double-ba ch plasma eac o : 1) HV powe supply, 2) g ounded ca hode, 3) anode, 4) gaske , 5) eflon diaph agm, 6) cooling wa e inle , 7) cooling wa e ou le , 8) anode chambe , and 9) ca hode chambe . Figu e 2: Schemes o ca hode configu a ions: 1) Maco body, 2) s ainless-s eel capilla y a) o ungs en wi e b), 3) plasma in bubble in liquid, 4) silicone glue, 5) glass ube, and 6) gas inle . Syn hesis o Ag and Cu nanopa icles by plasma discha ge 3 opog aphy o nanopa icles we e s udied by he DLS (Ze asize Nano ZS, Mal e n Panaly ical), XPS (K a os AXIS ULTRA DLD), and he high- esolu ion scanning elec on mic oscope JEOL JSM-7600F. XPS analyses we e ca ied ou wi h Axis Ul a DLD spec ome e using a monoch o- ma ic Al Kα(hν=1486.7 eV) X- ay sou ce ope a ing a 75 W (5 mA, 15 kV). The spec a we e ob ained using an analysis a ea o ∼300 ×700 µm. The high- esolu ion spec a we e measu ed wi h he s ep size o 0.1 and a pass ene gy o 20 eV. Ins umen base p essu e du ing he measu emen s was cons an a 2 ×10 −8 Pa. Spec a we e analysed using CasaXPS so wa e ( e sion 2.3.15) and ha e been cha ge-co - ec ed o he main line o he ca bon C 1s spec al componen (C–C, C–H) se o 284.8 eV. A s anda d Shi ley backg ound was used o all sample spec a. 3 Resul s and discussion The bubble o ma ion occu s independen ly on he used ca hode configu a ion (wi h [33] o wi hou [35] a gon flow). In case o he discha ge wi hou a gon flow, he bubble is c ea ed due o he ex ensi e Joule hea ing loca- lized close o he ca hode ip. In case o he configu a ion wi h a gon flow, he e a e wo mechanisms coupled o each o he –bubble is o med no only due o he a gon flow, bu also due o he Joule hea ing like in he p e ious case. The discha ge s a s o p opaga e inside he bubble, i.e. in he gaseous phase (in pu e wa e apou o in a gon wi h sa u a ed wa e apou , espec i ely). The bubble is enla ged in bo h cases up o he poin whe e he bubble collapses and he discha ge is swi ched off. Then, he p o- cess epea s again, so he discha ge ope a ion is sel -pulsing as confi med by he cu en – ol age eco ds. Examples o ypical cu en – ol age wa e o ms a e p esen ed in Figu e 3. The pe iod o he discha ge on is abou 100 µs. In case o he ope a ion wi hou a gon, he e is one cu en peak seen pe each pe iod. Bu i he sys em is ope a ing wi h a gon, he seconda y peak can be seen a e he p ima y peak, i.e. when he bubble collapses. We suppose ha he e a e some ions emaining in he elec ode icini y ha can ini ia e an addi ional smalle discha ge, which is no significan due o insufficien powe ou pu . This seconda y discha ge is obse ed wi h a ypical delay o abou 50 µs. Addi ionally, he equency o he discha ge sel -pulsing is highe in he case when a gon is used. Due o he wo-chambe sys em, we obse ed an effec o ion sepa a ion due o elec olysis –no such hing can be seen in case o common je ea men s in one-chambe se ups [31,39,40]. We obse ed simila ends as in he p e- iously published s udy [41], whe e he pin-hole sys em in he diaph agm configu a ion was used. While conduc i i y sligh ly ose in bo h ca hode and anode pa s, we obse ed s ong diffe ence in pH alues. Fo Ag nanopa icles p e- pa ed in 50 mg/l solu ion, an inc ease o pH in he ca hodic pa om pH 5.5 o pH 10.7 (wi h A ) o pH 10.1 (wi hou A ) was ound, while i d opped o pH 2.6 (wi h A ) o pH 2.4 (wi hou A ) in he anode pa . In case o solu ion o Cu nanopa icles p epa ed om 75 mg/l solu ion, he change om pH 5.3 o pH 6.3 (wi h A ) o pH 7.0 (wi hou A ) and a dec ease o pH 2.6 (A ) o pH 2.6 (wi hou A ) in he anode pa was de e mined. The diffe ence in he pH inc ease in he ca hodic pa s o Cu and Ag is e y p obably caused by hei diffe en ionic mobili y. On he o he hand, acidic pH in he anodic pa was caused by highe H + ion mobili y. The highe pH alue o Ag nanopa icles no only co e- sponds wi h he p e ious findings, bu i can also suppo inc eased Ag nanopa icle o ma ion (as was also published in he p e ious s udies [42,43]). Fo Cu nanopa icles, pH Figu e 3: Cu en – ol age wa e o ms o he sys em wi h and wi hou a gon flow. 4Jakub Ho ák e al. plays an impo an ole in he con ol o pa icle size (e.g.in e . [44]). In es iga ion o he pH effec on p epa ed nanopa - icles and hei p ope ies will be a pa o ou nex wo k. Thus, he plasma is obse ed be ween he poin ca hode and he i ual anode o med by he expanding bubble su - ace ( o i s isualiza ion, see in e . [35]). Me allic ca ions om he dissocia ed p ecu so in liquid a e a ac ed o he bubble su ace ha plays a ole o i ual ca hode whe e solid ma e ial is deposi ed. The p ocess o his deposi ion akes place only du ing a e y sho ime pe iod when he discha ge is on, and hus, nanopa icles a e o med. The sho p ocess du a ion limi s he nuclea ion ime and esul s in he o ma ion o small nanopa icles wi h he size o ens o nm. When he bubble ca i a es, he o med nanopa icles a e sp ead in o he bulk liquid and disappea om he elec- ode icini y due o he liquid sel -mixing. The whole p o- cess is well isible on he mo ie shown in supplemen a y ma e ials; wo selec ed pic u es om he supplemen a y ma e ials a e shown in Figu e 4. The p ocess is epea ing wi h he discha ge sel -oscilla ion. Schema ics o he whole p ocess a e shown in Figu e 5. 3.1 Syn hesis o sil e nanopa icles In he cu en expe imen s, we decided o use conduc i i y adjus men s in o de o keep he discha ge ope a ion s able [35]. The 3 min ea ed solu ions we e analysed immedia ely by he UV/Vis spec ome y. The samples we e aken ou om he ca hode pa only, because no nanopa icle p oduc ion was obse ed in he anode pa o he eac o excep negligible diffusion h ough he sepa a ing o ifice. The abso p ion spec a (Figu e 6) o he sys em wi h o wi hou he a gon flow show he main abso p ion peak a he wa eleng h o abou 425 nm, which indica es he p esence o sil e nanopa icles. The peak posi ion a ies be ween app oxima ely 413 and 450 nm, which was caused by he su ace plasmon eso- nance effec . This is also well isible by he naked eye as i is shown in Figu e 7. O he co esponding pic u es can be ound in he supplemen a y ma e ials. The DLS analysis ( h ee independen eplica ions) showed ha he pa icle size o p epa ed Ag nanopa icles is a he consis en wi h excep ion o he lowes (wi hou A ) and he Figu e 4: a) Nanopa icles (in he ed ci cle) dissol ed in o he bulk liquid a e he discha ge bubble ca i a ion; b) nanopa icles in he bulk liquid a e 5 s o he discha ge ope a ion. To see he whole p ocess in he eal ime, he mo ie is p o ided in he supplemen . Figu e 5: Schema ics o he nanopa icle syn hesis p ocess: a) me al ions a e a ac ed o he edge o he i ual ca hode; b) he bubble ca i a es and syn he ized nanopa icles a e sp ead in o he bulk liquid due o sel -mixing. Syn hesis o Ag and Cu nanopa icles by plasma discha ge 5 highes (wi h A ) concen a ions o AgNO 3 (Table 1 and Figu e 8). O e all, DLS shows an in e es ing concen a ion effec on nanopa icle size – he highe he sal concen a- ion, he bigge he pa icle size (Figu e 8). These esul s we e confi med by he SEM analysis as i is shown in Figu e 9. Sil e o med he sphe ical-like shaped pa icles wi h he size a ying in he ange o 10–80 nm and agglom- e a es as obse ed by SEM images. This could be he effec o he d ying p ocess du ing he p epa a ion. The XPS su ace analysis was pe o med on selec ed samples. Resul s o Ag nanopa icles a e p esen ed in Figu e 10 whe e he signal co esponding o he oxidic s a e o sil e as well as a esidual signal om he used ino ganic sal was de ec ed. The p esence o oxygen in he sil e nanopa icles was no obse ed in SEM by EDS as significan ly as in he case o Cu nanopa icles, and he e- o e, we assume mainly he su ace oxida ion, as confi med by XPS. Toge he wi h plasmonic band in he Ag UV/Vis spec a, hese findings sugges ha Ag nanopa icles e y p obably exhibi a co e–shell cha ac e (Ag/Ag 2 O) because he XPS echnique is sensi i e up o abou 5 nm, only, so only a hin su ace con ibu es o he signal. The UV/Vis measu e- men is no su ace-sensi i e, only, so he inne pa o nano- pa icles con ibu es, oo. And he inne pa is in he me allic o m. Figu e 6: Abso p ion spec a o he ea ed sil e solu ions wi h and wi hou a gon flow. Figu e 7: Sil e solu ions ea ed wi h a gon flow (a e 40 days, mixed). Table 1: A e age diame e esul s o he DLS analysis o he p epa ed Ag nanopa icles Concen a ion (mg/l) 1 10 25 50 100 A e age diame e (nm) A 48 ± 11 38 ± 1 50 ± 1 65 ± 3 145 ± 6 NoA 186 ± 8 39 ± 1 50 ± 1 50 ± 3 59 ± 1 6Jakub Ho ák e al. Thanks o i s su ace composi ion, he p epa ed Ag nano- pa icles a e conside ed o be semiconduc ing [45–47]. Thus, he Tauc diag ams based on he UV/Vis spec a we e con- s uc ed o ge he alue o he di ec op ical band gap ene gy. The simplified s ep-by-s ep p ocedu e is depic ed in he sup- plemen a y ma e ials; de ailed desc ip ions can be ound in p e ious s udies [36,37,48,49]. The calcula ed op ical gap ene - gies o he p epa ed Ag nanopa icles a e p esen ed in Table 2. Obse ed alues a e in a good ag eemen wi h he published esul s, which a e in he ange o 1.2–3.4 eV [45,46,50]. The op ical band gap alues do no exhibi any changes dependen on concen a ion, and hey a e simila o bo h nanopa icles’p epa a ion modes. This indica es ha he su ace chemical composi ion and su ace p ope - ies o he same nanopa icles a e independen o he p e- cu so concen a ion. 3.2 Syn hesis o coppe nanopa icles Coppe nanopa icles we e syn he ized by he same app oach as in he sil e nanopa icle case. The 3 min ea ed solu ions we e analysed immedia ely by he UV/Vis spec ome y (Figu e 11). The b oade abso p ion peaks we e measu ed wi h maximum abso bance close o 300 nm. This eflec s ha he size o he p epa ed coppe nanopa icles is bigge han in case o Ag nanopa icles as i is confi med also by he DLS analysis (Table 3 and Figu e 12). The samples Figu e 8: Ag nanopa icle a e age size dis ibu ion o solu ions ea ed wi h a gon. Figu e 9: Ag nanopa icles p epa ed in 100 mg/l solu ion wi h (le ) and wi hou ( igh ) a gon flow. Table 2: Op ical band gaps o Ag nanopa icles Concen a ion [mg/l] (αhν) 2 [eV 2 /cm 2 ] A NoA 1 2.23 2.16 10 2.21 2.33 25 2.34 2.20 50 2.42 2.29 100 2.17 2.01 Syn hesis o Ag and Cu nanopa icles by plasma discha ge 7 we e fil e ed wi h a 0.45 µm fil e o emo e he bigges agglome a es p io o he DLS analysis. Acco ding o he DLS esul s, a gon p esence in he discha ge leads o he bigge pa icles o ma ion. The SEM analysis has showed ha Cu nanopa icles a e nano- whiske s in shape (Figu e 13); he e o e, DLS analysis o Figu e 10: XPS da a o Ag pa icles syn hesized wi h (le ) and wi hou ( igh ) a gon flow. Figu e 11: Abso p ion spec a o he ea ed coppe solu ions wi h (le ) and wi hou ( igh ) a gon flow. Table 3: A e age diame e esul s o he DLS analysis o he p epa ed Cu nanopa icles Concen a ion (mg/l) 50 75 100 A e age diame e (nm) A 310 ± 20 290 ± 70 240 ± 10 NoA 240 ± 30 200 ± 60 260 ± 30 Figu e 12: Cu nanopa icle a e age size dis ibu ion o solu ions ea ed wi h a gon. 8Jakub Ho ák e al. Figu e 13: Cu nanopa icles p epa ed in 75 mg/l solu ion wi h (le ) and wi hou ( igh ) a gon flow. Figu e 14: SEM and EDS images o Cu pa icles. Syn hesis o Ag and Cu nanopa icles by plasma discha ge 9