Evaluation of ultrasonically ZnO loading effect on photocatalytic self-cleaning, UV protection and antibacterial activity of plasma/citric acid-activated cotton fabric

Ci a ion: I an, M.; Hussain, H.; Saleem, B.; Saleem, M.; Shuk ullah, S.; Legu ko, S.; Pe ˚u, J.; Naz, M.Y.; Pagáˇc, M.; Rahman, S.; e al. E alua ion o Ul asonically ZnO Loading E ec on Pho oca aly ic Sel -Cleaning, UV P o ec ion and An ibac e ial Ac i i y o Plasma/ Ci ic Acid-Ac i a ed Co on Fab ic. Nanoma e ials 2022,12, 2122. h ps:// doi.o g/10.3390/nano12122122 Academic Edi o s: Rodica Vlădoiu, Milan Tichy and Sil iu Polosan Recei ed: 17 May 2022 Accep ed: 17 June 2022 Published: 20 June 2022 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 : © 2022 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/). nanoma e ials A icle E alua ion o Ul asonically ZnO Loading E ec on Pho oca aly ic Sel -Cleaning, UV P o ec ion and An ibac e ial Ac i i y o Plasma/Ci ic Acid-Ac i a ed Co on Fab ic Muhammad I an 1, Humai a Hussain 2, Bisma Saleem 3, Muhammad Saleem 3, Shazia Shuk ullah 3,*, S anislaw Legu ko 4, Jana Pe ˚u 5, Muhammad Yasin Naz 3,*, Ma ek Pagáˇc 5, Sai u Rahman 1 and Rehan Khan 6 1Elec ical Enginee ing Depa men , College o Enginee ing, Naj an Uni e si y Saudi A abia, Naj an 61441, Saudi A abia; [email p o ec ed] (M.I.); [email p o ec ed] (S.R.) 2Depa men o Chemis y, Uni e si y o Oka a, Oka a 56300, Pakis an; [email p o ec ed] 3Depa men o Physics, Uni e si y o Ag icul u e Faisalabad, Faisalabad 38040, Pakis an; [email p o ec ed] (B.S.); [email p o ec ed] (M.S.) 4Facul y o Mechanical Enginee ing, Poznan Uni e si y o Technology, 3 Pio owo S ee , 60-965 Poznan, Poland; s anislaw[email p o ec ed] 5Depa men o Machining, Assembly and Enginee ing Me ology, Mechanical Enginee ing Facul y, VŠB-Technical Uni e si y o Os a a, 17. Lis opadu 2172/15, 708 00 Os a a, Czech Republic; [email p o ec ed] (J.P.); ma [email p o ec ed] (M.P.) 6Depa men o Mechanical Enginee ing, College o Elec ical and Mechanical Enginee ing, Na ional Uni e si y o Sciences and Technology, Islamabad 44000, Pakis an; [email p o ec ed] *Co espondence: [email p o ec ed] (S.S.); [email p o ec ed] (M.Y.N.) Abs ac : Zinc oxide (ZnO) nanopa icles we e loaded o e non- he mal plasma (P1) and ci ic acid (P2)- unc ionalized co on ab ics using a oom empe a u e soni ica ion p ocess. The co on samples we e p e ea ed wi h dielec ic ba ie discha ge (DBD) plasma and ci ic acid o in oduce some eac i e moie ies on he ab ic o enhance he adhesion powe o ZnO nanopa icles wi h an a e age pa icle size o 41 nm. The nanopa icles we e dispe sed homogeneously on he su ace o he P1 sample, which enhanced he an ibac e ial, UV p o ec ion and pho oca aly ic sel -cleaning cha ac e is ics o ZnO-loaded ab ic. The sel -cleaning e iciency o P1 and P2 samples was measu ed o be abou 77% and 63%, espec i ely. The inhibi ion zones o 5.5 mm and 5.4 mm we e p oduced by sample P1 agains E. coli and S. au eus bac e ia, espec i ely, which we e sligh ly highe han he inhibi ion zones p oduced by sample P2. The inhibi ion zone o he samples oughly dec eased by 17% a e pe o ming 10 wash cycles. The unloaded co on ab ic had a UPF alue o 70.02 uni s and blocking pe cen age o 70.92% and 76.54% o UVA and UVB adia ions, espec i ely. The UVA-blocking capaci y o samples P1 and P2 was 95.27% and 91.22, espec i ely. Simila ly, he UVB blocking capaci y was 94.11% and 92.65%, espec i ely. The p e-coa ing plasma ea men was ound o be help ul in imp o ing he UV-blocking abili y o ZnO-loaded co on ab ic. Keywo ds: co on ab ic; ZnO nanopa icles; DBD plasma; sel -cleaning; UV p o ec ion; soni ica ion p ocess; an ibac e ial ac i i y 1. In oduc ion The as - ising en i onmen al pollu ion index o Sou h Asian coun ies is pu ing human heal h a se ious isk. Pollu ion occu s when dange ous chemicals a e eleased in o ce ain sec ions o he ecosys em. This could be he ash o med by a na u ally e up ed olcano, o i could be ha m ul umes eleased h ough he combus ion o ossil uels. I is di icul o simul aneously ea he en i onmen o all ypes o pollu an s [ 1 ]. Pakis an is among he op ga men -manu ac u ing and expo ing coun ies. The ga men sec o con ibu es o 80% o he o al expo s o he coun y. In he ex ile p ocessing indus y, a Nanoma e ials 2022,12, 2122. h ps://doi.o g/10.3390/nano12122122 h ps://www.mdpi.com/jou nal/nanoma e ials Nanoma e ials 2022,12, 2122 2 o 14 numbe o physical and chemical p ocesses a e ca ied ou o he inishing o ab ics [2,3] . Abou 98% o ex iles a e dyed a ea ly o la e s ages be o e hi ing he ma ke . A con- side able po ion o he dye is los o he was ewa e s eam du ing he colo ing p ocess because i does no adhe e o he ab ic [ 4 ]. The abso p ion and e lec ion o sunligh in o aqua ic bodies is a majo en i onmen al haza d caused by syn he ic dyes. Because algae a e a he bo om o he ood chain, ligh abso p ion educes hei pho osyn he ic ac i i y, which has majo consequences o he ood chain. One o he main easons ha aqua ic li e su e s in egions whe e dyes a e dumped is a lack o algae. The syn he ic dyes a e also oxic hemsel es [5]. The sel -cleaning and UV p o ec ion ac o s o ab ics a e also among he ising human heal h conce ns. UV adia ion is p ima ily emi ed by sunligh . UV adia ions o di e en kinds each he ea h in di e en amoun s. UVA pho ons accoun o app oxima ely 95% o UV ays ha each he ea h, wi h UVB pho ons accoun ing o he emaining 5%. UV exposu e can cause p ema u e skin ageing and sun damage signs such as lea he y skin, li e spo s, w inkles, ac inic ke a osis and sola elas osis [ 6 ]. UV adia ions can also cause co neal in lamma ion o bu ns, as well as he p oduc ion o ca a ac s and p e ygium, bo h o which can impai ision. Some people a e mo e ulne able o he ha m ul e ec s o UV ays. Some d ugs can make people mo e sensi i e o UV ays, inc easing hei chances o being bu n unde sunligh [ 7 ]. The goal o ex ile inishing is o shield he skin om he e ec s o sun adia ion because he ex ile does no always p o ide app op ia e p o ec ion. Tex iles’ speci ic p o ec i e p ope ies agains a wide ange o impac s ha e gained inc easing a en ion. Un inished clo hes ha e a limi ed ligh e a ding capaci y ha p e en s hem om p o iding sui able p o ec ion o he human body om UV adia ion [ 3 ]. As a esul , UV s abilize s o p o ec i e coa ings a e used o o e an ex a laye o sun p o ec ion. Tex iles’ UV p o ec ion ac o is de e mined by hei a chi ec u e, ya n spacing, ibe ype, ex ile imp egna ion, colo , and he p esence o UV abso be s and op ical b igh ene s. The ul a iole p o ec ion ac o (UPF) o na u al ibe s is lowe han ha o syn he ic ibe s. Among na u al ibe s, co on ab ic in a g ey s a e has a g ea e UPF due o na u al colo s, pec ins, and waxes. Undyed and bleached co on ab ics ha e a low UPF, while dyed co on ab ics ha e a high UPF [ 8 ]. UV abso be s a e o ganic o ino ganic subs ances ha show s ong abso p ion in he wa eleng h ange o 290–360. Elec onic exci a ion ene gy is con e ed o he mal ene gy ia UV abso be s embedded wi hin he ibe s. They ac as oxygen sca enge s and adical sca enge s [ 9 ]. High-in ensi y UV ays s imula e he UV abso be , causing i o abso b a la ge amoun o ene gy, which is hen dispe sed as longe -wa e adia ion. Isome iza ion, on he o he hand, can occu , causing UV abso be s o agmen in o non-abso bing isome s. This s udy ocused on he p o ec i e coa ing o me al nanopa icles on he ab ic su ace o impa sel -cleaning and UV blocking ai s. A g een syn hesis me hod, coupled wi h he soni ica ion p ocess, was conside ed o he concu en syn hesis o nanopa icles and coa ings o e ab ic. G een syn hesis is an e ec i e and eco- iendly way o p oduc- ing nanoma e ials ha o e economic and en i onmen al iendly solu ions compa ed o chemical and physical me hods [ 10 ]. G een syn hesis is a simple, low-cos , and en i on- men ally iendly p ocess ha does no equi e high empe a u e, p essu e, ene gy, and ha m ul chemicals. The bioac i e p oduc s o plan s, bac e ia, ungi and yeas s can be an excellen sou ce o he syn hesis o nanopa icles. In his s udy, we syn hesized me al oxides o zinc wi h a g een me hod using he ex ac o Azadi ach a indica and s udied hei pho oca aly ic [ 11 ], UV p o ec ion and an ibac e ial ac i i ies by coa ing hem on o an a mosphe ic p essu e plasma- ea ed co on ab ic. Azadi ach a indica, also called Neem, is an indigenous ee, which belongs o he mahogany amily Meliaceae. The medicinal bene i s o Azadi ach a indica a e ou s anding. Azadi ach a indica lea es con ain a a ie y o biologically ac i e phy ocons i uen s, including la onoids, alkaloids, e penoids and polyphenols, which can be u ilized o educe me al ions in o hei nanopa icles [12]. Wi h a band gap o 3.37 eV and a la ge exci on binding ene gy o 60 meV, ZnO is a good n- ype semiconduc o which can be used in biosenso s, sola cells, gas senso s, ligh Nanoma e ials 2022,12, 2122 3 o 14 de ec o s, he ex ile indus y and cosme ics [ 13 ]. Because o i s compa able band gap alue and low cos , ZnO is conside ed as an e ec i e al e na i e pho oca alys o TiO 2. Hence, nanopa icles o ZnO and TiO 2 could be employed as he bes pho oca aly ic ma e ial o he deg ada ion o o ganic pollu an s. In o de o ea in ec ions due o an ibio ic- esis an bac e ia, i is becoming inc easingly i al o de elop no el an ibac e ial nanoma e ials [ 14 ]. Pho oca aly ic ac i i y, an ibac e ial ac i i y and o he applica ions o ZnO nanopa icles make hem impo an ma e ials in he medical and ene gy indus ies. ZnO nanopa icles ha e been used by se e al esea che s o de i e pho oca aly ic eac ions o he deg ada ion o o ganic pollu an s and compounds in bo h isible and UV egions o he elec omagne ic spec um. Pho oca alysis occu s when a semiconduc o pho oca alys is subjec ed o UV adia ions, which exci es he elec ons and causes hem o mo e o he conduc ion band by c ea ing holes in he alence band [ 15 , 16 ]. These elec ons and holes ake pa in edox eac ions o deg ade dye molecules and neu alize bac e ia. The adhesion and binding o nanopa icles emains an impo an issue in he ex ile indus y. Nou bakhsh e al. [ 17 ] unc ionalized polyes e ab ic wi h NaOH o inc ease he s abili y and binding abili y o ab ic o ZnO. The chemical alkaline ea men o ab ic can damage i s s uc u e and weakens he s eng h o he ibe . Addi ionally, i p oduces wa e pollu ion by discha ging chemicals. The co osi e na u e and high concen a ion o NaOH p oduce he bulk o was ewa e , which causes he insing o ea ed ex iles. The e o e, a d y, en i onmen ally iendly and cos -e ec i e app oach is sough o he su ace modi ica ion o ab ic wi hou damaging i s bulk s uc u e. The ea men o co on wi h non- he mal plasma can imp o e i s a ious p ope ies. The su ace p ope ies o co on can be imp o ed by gene a ing plasma in he p esence o non-polyme izing gases. A mosphe ic p essu e plasma can emo e non-cellula impu i ies om he su ace o co on h ough a physical e ching p ocess. Plasma ea men enhances hyd ophilici y as well as sizing, dyeing, adhesion and su ace oughness [ 2 ]. In plasma ea men , he su ace o co on ab ic is inco po a ed wi h plasma-gene a ed ee adicals, which ac as g a ing o c oss-linking agen s. So, he ac i a ion o co on wi h plasma esul s in be e we abili y, an is a ic beha io , adhesion o non-coa ings dyeing, p in abili y, cleaning, disin ec ion o su ace and elec ical p ope ies [ 18 ]. The main objec i e o his esea ch was o ind he bes echnique o enhancing he adhesion p ope y o ZnO nanos uc u es on a co on subs a e. Two echniques we e used o unc ionalize he co on ab ic. The i s was o ea he co on wi h ci ic acid binde and he second was o ea he co on wi h dielec ic ba ie discha ge plasma. 2. Ma e ials and Me hods 2.1. P ecu so Ma e ials Chemicals o an analy ical eagen g ade, including we ing agen , Ci ic acid (C 6 H 8 O 7 ), Zinc ni a e (Zn(NO 3 ) 2· 6H 2 O), sodium chlo ide, and sodium hyd oxide we e supplie o Me ck (Bu ling on, VT, USA). The comme cial-g ade me hylene blue was pu chased om a local scien i ic s o e in Faisalabad, Pakis an. The unp ocessed wo en co on ab ic was p ocu ed om Sapphi e Tex ile limi ed, Sheikhupu a, Punjab, Pakis an. The wo en ab ic had 100 ends, 85 picks and a densi y o 118 g/m 2 . The aw ab ic was desized o emo e s a ch, di , and o he con aminan s be o e he coa ing es s. 2.2. Desizing o Co on Samples The wo en co on was cu in o pieces o 10 × 10 cm 2 dimensions and desized in ho dis illed wa e wi h 2 g/L sodium chlo ide, 3.5 g/L enzyme and 2 g/L we ing agen . Desizing was conduc ed o 2 h. The desized samples we e hea ea ed in an o en a 90 ◦ C and s o ed o he plasma ea men and nanocoa ing o ZnO nanopa icles. 2.3. P epa a ion o Neem Ex ac G een lea es o Neem plan wi h he scien i ic name “Azadi ach a indica” we e aken om a local bo anical ga den in Faisalabad, Pakis an. The esh lea es we e washed wi h Nanoma e ials 2022,12, 2122 4 o 14 DI wa e se e al imes o emo e dus pa icles and o he impu i ies. The washed lea es we e d ied in an open en i onmen o 7 days unde shade. The lea es we e hen g ound in o a ine powde . Abou 20 g o Neem powde was aken in a glass beake . Abou 150 mL o e hanol was added o he glass con aine , ollowing which i was co e ed wi h aluminum oil and placed in a da k oom o e nigh . A e ha , he solu ion was hea ed on a magne ic ho pla e o 2 h a 70 ◦ C unde con inuous s i ing. The solu ion was hen cooled and il e ed o ob ain he lea ex ac o use in he g een syn hesis o ZnO. 2.4. Ac i a ion o Co on wi h DBD Plasma and Ci ic Acid A desized sample o co on was pas ed on o a mo able elec ode o he DBD plasma sys em, as illus a ed in Figu e 1. The ab ic-ca ying elec ode was o a ed a 100 pm unde plasma exposu e. The plasma was gene a ed be ween an in e elec ode gap o 2 mm. The DBD mic odischa ge was gene a ed in an open gap wi h ai as he sou ce gas. A schema ic o he DBD plasma sys em o he unc ionaliza ion o he co on su ace is shown in Figu e 1. The ope a ing condi ions o he plasma p oduced we e as ollows: inpu powe o 106 W, discha ge cu en 3.8 mA and discha ge ol age o 26 kV. The co on sample was ac i a ed om bo h sides wi h plasma o he op imum exposu e ime o 70 s, as epo ed in ou p e ious wo k [10]. In he p e-coa ing ci ic acid ea men , he co on ab ic was unc ionalized wi h 0.5% dilu e solu ion o ci ic acid in o de o inc ease he adhesion o ZnO pa icles. Equa ions (1) and (2) show ha when he co on ibe s and ci ic acid a e placed in deion- ized wa e , bo h become ionized. In p ocessing eac ions, he hyd oxyl g oups (OH) on co on a e a ached wi h he ca boxylic g oups o acid using he ollowing Equa ion (3) [ 19 ]. H2O+C6H8O7↔C6H7O− 7+H3O+(1) Cellulose −OH +H2O↔Cellulose −O−+H3O+(2) C6H8O7+Cellulose −OH +H2O↔Cellulose −CA +H3O+(3) Nanoma e ials 2022, 12, 2122 4 o 15 2.3. P epa a ion o Neem Ex ac G een lea es o Neem plan wi h he scien i ic name “Azadi ach a indica” we e aken om a local bo anical ga den in Faisalabad, Pakis an. The esh lea es we e washed wi h DI wa e se e al imes o emo e dus pa icles and o he impu i ies. The washed lea es we e d ied in an open en i onmen o 7 days unde shade. The lea es we e hen g ound in o a ine powde . Abou 20 g o Neem powde was aken in a glass beake . Abou 150 mL o e hanol was added o he glass con aine , ollowing which i was co e ed wi h alu- minum oil and placed in a da k oom o e nigh . A e ha , he solu ion was hea ed on a magne ic ho pla e o 2 h a 70 °C unde con inuous s i ing. The solu ion was hen cooled and il e ed o ob ain he lea ex ac o use in he g een syn hesis o ZnO. 2.4. Ac i a ion o Co on wi h DBD Plasma and Ci ic Acid A desized sample o co on was pas ed on o a mo able elec ode o he DBD plasma sys em, as illus a ed in Figu e 1. The ab ic-ca ying elec ode was o a ed a 100 pm unde plasma exposu e. The plasma was gene a ed be ween an in e elec ode gap o 2 mm. The DBD mic odischa ge was gene a ed in an open gap wi h ai as he sou ce gas. A schema ic o he DBD plasma sys em o he unc ionaliza ion o he co on su ace is shown in Figu e 1. The ope a ing condi ions o he plasma p oduced we e as ollows: inpu powe o 106 W, discha ge cu en 3.8 mA and discha ge ol age o 26 kV. The co - on sample was ac i a ed om bo h sides wi h plasma o he op imum exposu e ime o 70 s, as epo ed in ou p e ious wo k [10]. In he p e-coa ing ci ic acid ea men , he co on ab ic was unc ionalized wi h 0.5% dilu e solu ion o ci ic acid in o de o inc ease he adhesion o ZnO pa icles. Equa ions (1) and (2) show ha when he co on ibe s and ci ic acid a e placed in deionized wa e , bo h become ionized. In p ocessing eac ions, he hyd oxyl g oups (OH) on co on a e a ached wi h he ca boxylic g oups o acid using he ollowing Equa ion (3) [19]. H  O + C  H  O  ↔ C  H  O   + H  O  (1) Cellulose − OH + H  O ↔ Cellulose − O  + H  O  (2) C  H  O  + Cellulose − OH + H  O ↔ Cellulose − CA + H  O  (3) Figu e 1. Illus a ion o DBD plasma sys em o ac i a ion o co on ab ic in open ai . Figu e 1. Illus a ion o DBD plasma sys em o ac i a ion o co on ab ic in open ai . 2.5. Syn hesis and Coa ing o ZnO Nanopa icles on Ac i a ed Fab ic The ZnO nanopa icles we e syn hesized using a g een me hod. Abou 150 mL o Neem lea ex ac was hea ed on a magne ic s i e a 60 ◦ C o 10 min. A e ha , 0.1 M solu ion o zinc ni a e (50 mL) and 0.2 M solu ion o sodium hyd oxide (20 mL) we e added Nanoma e ials 2022,12, 2122 5 o 14 o 100 mL o he ex ac in he s i ing mode. NaOH is a basic educing agen o me al sal s. I eac s exo he mically and o en iolen ly wi h oxidizing agen s o all ypes. Neem ex ac was used because i is a low-cos ac i e biological componen ha can unc ion as a educing, s abilizing, and capping agen . When coupled wi h NaOH, i expedi es he eac ion a e by cu ing down he eac ion ime. Neem ex ac con ains e penoids and la anones, which help in s abilizing nanopa icles. He e, a one-po eac ion, acile, sa e and eco- iendly co-p ecipi a ion app oach ha u ilized Azadi a cha Indica ex ac along wi h NaOH as he alkaline medium was pe o med [ 20 ]. Only 30 min was equi ed o he comple e con e sion o me al ions in o nanopa icles a oom empe a u e. In he absence o neem ex ac , 2 h was equi ed o comple e he eac ion. The mix u e u ned in o c eam-colo ed p ecipi a es o ZnO a e 30 min o con inuous s i ing. The p ecipi a es we e cen i uga ed a 3000 pm and washed wi h dis illed wa e . A e d ying in an o en, he powe was g ound o p oduce ine nanopa icles o ZnO. The nanopa icles we e calcina ed in an elec ic u nace o 1 h a 300 ◦C. The DBD plasma- ea ed and ci ic acid- ea ed samples we e placed in a 3% solu ion o ZnO in sepa a e beake s o i e minu es. The solu ions and ab ic we e hen sonica ed o 15 min a 75 ◦ C. Then, he samples we e emo ed om he sonica ion ba h, ai -d ied and cu ed a 140 ◦ C. The samples we e insed 5 imes o wash ou he impu i ies and unbounded nanopa icles. The p e-ci ic acid- ea ed ZnO-coa ed sample was named as P1 and he pos -ci ic acid- ea ed ZnO-coa ed sample was named as P2. Finally, he p oduced samples we e d ied, cha ac e ized and used o an ibac e ial ac i i y. The samples we e also es ed o UV p o ec ion and he emo al o me hylene blue om he solu ion exposed o UV ligh . UV- isible spec oscopy in he 300–700 nm egion was used o in es iga e he op ical cha ac e is ics o ZnO pa icles. XRD pa e ns o he P1 and P2 samples we e ob ained by using X- ay di ac ome e Cu-K α adia ions in he ange o 20 ◦ o 80 ◦ . The pa icle size, mo phology and shape o ZnO coa ings we e analyzed by SEM. The a ached unc ional g oups du ing DBD plasma ea men we e de ec ed in he FTIR spec a in a se ies o abso bance peaks in 500–4500 cm−1 ange. 2.6. An ibac e ial and Sel -Cleaning Ac i i ies o ZnO-Coa ed Samples ZnO-coa ed samples we e es ed o an ibac e ial ac i i y agains E. coli and S. au eus s ains. The well-di usion me hod was used o de e mine he ac i i y o ZnO agains selec ed bac e ia. Mulle –Hin on aga medium was used o make he wells on pla es. The pla es we e hen seeded wi h wo ypes o bac e ia using a s e ilized swab. Gel punc u e was used o c ea e ou wells in each pla e. Each well was illed wi h samples o ZnO-coa ed ab ics. To obse e he zones o inhibi ion, he seeded pla es we e placed in an incuba o a 35 ◦C o 24 h. The deg ada ion o me hylene blue (MB) molecules unde UV ligh exposu e was s udied using a 380 nm cu o il e and a Xenon lamp. The P1 and P2 samples we e added indi idually o 0.05% w/ MB dye solu ion o es hei pho oca aly ic ac i i y. The solu- ions wi h P1 and P2 samples we e kep in he da k o p oduce he adso p ion–deso p ion equilib ium be ween he dye and he coa ed sample. A e ha , he P1-con aining solu ion was i adia ed wi h UV ligh o di e en ime in e als. Fo di e en hou s o he i adia- ion o UV ligh , he UV- isible spec a o he samples we e eco ded. The abso p ion o ligh by MB solu ion was obse ed a 665 nm and i s UV–Visible abso p ion spec a we e eco ded o es ima e he a e o dye b eakdown. The Bee –Lambe law (A = εm CL) was used o calcula e he dye concen a ion in he solu ion. The pho oca aly ic e iciency o ZnO-coa ed co on ab ic owa ds MB was de e mined using he ollowing o mula: Deg ada ion e iciency (%) = [1−C Co]×100 (4) whe e, C o is he ini ial dye concen a ion in solu ion and C is inal dye concen a ion. Simila ly, he pho oca aly ic e iciency o he P2 sample was also measu ed. Nanoma e ials 2022,12, 2122 6 o 14 2.7. Ul a iole P o ec ion The Va ian CARY UV-Vis ins umen (Agilen Technologies, San a Cla a, CA, USA) was employed o in es iga e he UV p o ec ion abili y o he de eloped ab ic samples. A spec opho ome e consis ing o sola sc een so wa e and an in eg a ing sphe e wi h a wa eleng h ange o 280–400 nm was ope a ed unde a s anda d AATCC 183–2000. Using his s anda d, he pe cen age o ansmission and blocking o UV adia ion h ough he ab ic samples we e de e mined. The samples we e handled a s anda d empe a u e condi ions (25 ± 2 ◦ C) and a ela i e humidi y o 66 ± 2%. The a e age alue o he i e measu emen s was aken. The ollowing Equa ion (5) was used o de e mine UPF [21]: UPF =∑400 nm 280 nm EλSλ∆λ ∑400 nm 280 nm EλSλTλ∆λ (5) whe e, Eλ is he sola i adiance, Sλ spec al esponse o ela i e e y hemal, ∆λ is wa e- leng h in nm and Tλis pe cen age ansmi ance. 3. Resul s and Discussion 3.1. FTIR Analysis o DBD Plasma T ea ed Co on FTIR spec a (Agilen Technologies, San a Cla a, CA, USA) o aw co on, and as- p oduced ZnO nanopa icles a e epo ed in Figu e 2. The FTIR spec um in Figu e 2a e ealed he hemicellulose, lignin and cellulosic bands in he spec um o aw co on. The band a 3330 cm −1 co esponds o a cha ac e is ic peak o cellulosic hyd oxyl g oups, wa e and lignin. A pa ially s ong peak a 2895 cm −1 co esponds o he s e ching ib a ion o cellulosic C-H. The p esence o wa e in co on ab ic co esponds o he 1622 cm−1 band. The band a 1315 cm −1 co esponds o he bending ib a ional mode o he hyd oca bon s uc u e. The bands a 1365 cm −1 and 1428 cm −1 e e o he cellulosic molecule’s o igina ed symme ic s e ching o ca boxyla es (CH 2 and C-H). A s ong peak a he 1032 cm −1 band appea ed due o he s e ching ib a ion o he polysaccha ide o cellulose. On he o he hand, he FTIR spec um in Figu e 2b shows a band be ween 500 cm−1 and 1000 cm −1 , which is he cha ac e is ic mode o ZnO nanopa icles. The Zn-O bending ib a ion was con i med by a medium band a 670 cm−1[22]. Nanoma e ials 2022, 12, 2122 6 o 15 Deg ada ion e iciency (%) = [ 1 −    ] × 100 (4) whe e, Co is he ini ial dye concen a ion in solu ion and C is inal dye concen a ion. Sim- ila ly, he pho oca aly ic e iciency o he P2 sample was also measu ed. 2.7. Ul a iole P o ec ion The Va ian CARY UV-Vis ins umen (Agilen Technologies, San a Cla a, CA, USA) was employed o in es iga e he UV p o ec ion abili y o he de eloped ab ic samples. A spec opho ome e consis ing o sola sc een so wa e and an in eg a ing sphe e wi h a wa eleng h ange o 280–400 nm was ope a ed unde a s anda d AATCC 183–2000. Using his s anda d, he pe cen age o ansmission and blocking o UV adia ion h ough he ab ic samples we e de e mined. The samples we e handled a s anda d empe a u e con- di ions (25 ± 2 °C) and a ela i e humidi y o 66 ± 2%. The a e age alue o he i e meas- u emen s was aken. The ollowing Equa ion (5) was used o de e mine UPF [21]: UPF = ∑ E  S  ∆      ∑ E  S  T      ∆  (5) whe e, E is he sola i adiance, S spec al esponse o ela i e e y hemal, ∆ is wa e- leng h in nm and T is pe cen age ansmi ance. 3. Resul s and Discussion 3.1. FTIR Analysis o DBD Plasma T ea ed Co on FTIR spec a (Agilen Technologies, San a Cla a, CA, USA) o aw co on, and as- p oduced ZnO nanopa icles a e epo ed in Figu e 2. The FTIR spec um in Figu e 2a e ealed he hemicellulose, lignin and cellulosic bands in he spec um o aw co on. The band a 3330 cm−1 co esponds o a cha ac e is ic peak o cellulosic hyd oxyl g oups, wa e and lignin. A pa ially s ong peak a 2895 cm−1 co esponds o he s e ching ib a ion o cellulosic C-H. The p esence o wa e in co on ab ic co esponds o he 1622 cm−1 band. The band a 1315 cm−1 co esponds o he bending ib a ional mode o he hyd oca bon s uc u e. The bands a 1365 cm−1 and 1428 cm−1 e e o he cellulosic molecule’s o igina ed symme ic s e ching o ca boxyla es (CH2 and C-H). A s ong peak a he 1032 cm−1 band appea ed due o he s e ching ib a ion o he polysaccha ide o cellulose. On he o he hand, he FTIR spec um in Figu e 2b shows a band be ween 500 cm−1 and 1000 cm−1, which is he cha ac e is ic mode o ZnO nanopa icles. The Zn-O bending ib a ion was con- i med by a medium band a 670 cm−1 [22]. Figu e 2. FTIR spec a o (a) aw co on and (b) as-p oduced ZnO nanopa icles. Figu e 2. FTIR spec a o (a) aw co on and (b) as-p oduced ZnO nanopa icles. 3.2. UV-Vis Analysis o ZnO Nanopa icles Va ian ca y 500 was used o ob ain he UV- isible spec um o he solu ions con aining ZnO nanopa icles, as shown in Figu e 3. The peaks in he spec um a e he esul o su ace plasmon esonance o nanopa icles [ 23 ]. The elec on’s collec i e exci a ion in he conduc ion band close o he su ace o he nanopa icles is called su ace plasmon esonance. A 250 nm, a p ominen UV ligh abso p ion peak can be no iced. The Tauc-Plo Nanoma e ials 2022,12, 2122 7 o 14 me hod was used o disce n he band gap ene gy o ZnO nanopa icles. The ma hema ic o m o he Tauc ela ion is [24]: αhυ=A(hυ−Eg)n(6) whe e, E g , is he band gap, h υ is he ene gy o inciden pho ons, α is he abso p ion coe icien , and Ais he ansi ion p obabili y cons an . The cons an ncan be 1/2 o 2 based on di ec o indi ec ansi ions. The ene gy band gap lies be ween 3.35 eV o 3.4 eV. I is wo h no ing ha he pe cei ed blue shi abso p ion is di e en om ha o bulk ZnO, which has an abso p ion peak a a ound 355 nm due o he quan um con inemen e ec o ZnO nanos uc u es. The peaks change wi hin he ange o 250 nm o 350 nm. So, i was con i med ha he Neem lea es con ain all he s abilizing and educing agen s essen ial o he syn hesis o nanopa icles. When Neem ex ac was added o he solu ion, he solu ion u ned o c eam-colo ed p ecipi a es in jus 30 min compa ed o he solu ion con aining NaOH. A as change in colo indica ed he o ma ion o ZnO nanopa icles due o he educ ion o zinc sal . The apid educ ion o Zinc sal in o nanopa icles can be a ibu ed o e penoids and la anones compounds in he Neem ex ac [ 25 ]. A peak a ound 250 nm was due o he exci a ion o su ace plasmon ib a ions in ZnO nanopa icles. Nanoma e ials 2022, 12, 2122 7 o 15 3.2. UV-Vis Analysis o ZnO Nanopa icles Va ian ca y 500 was used o ob ain he UV- isible spec um o he solu ions con- aining ZnO nanopa icles, as shown in Figu e 3. The peaks in he spec um a e he esul o su ace plasmon esonance o nanopa icles [23]. The elec on’s collec i e exci a ion in he conduc ion band close o he su ace o he nanopa icles is called su ace plasmon esonance. A 250 nm, a p ominen UV ligh abso p ion peak can be no iced. The Tauc- Plo me hod was used o disce n he band gap ene gy o ZnO nanopa icles. The ma he- ma ic o m o he Tauc ela ion is [24]: α h υ =   h υ −     (6) whe e, Eg, is he band gap, hυ is he ene gy o inciden pho ons, α is he abso p ion coe - icien , and A is he ansi ion p obabili y cons an . The cons an n can be ½ o 2 based on di ec o indi ec ansi ions. The ene gy band gap lies be ween 3.35 eV o 3.4 eV. I is wo h no ing ha he pe cei ed blue shi abso p ion is di e en om ha o bulk ZnO, which has an abso p ion peak a a ound 355 nm due o he quan um con inemen e ec o ZnO nanos uc u es. The peaks change wi hin he ange o 250 nm o 350 nm. So, i was con i med ha he Neem lea es con ain all he s abilizing and educing agen s essen ial o he syn hesis o nanopa icles. When Neem ex ac was added o he solu ion, he so- lu ion u ned o c eam-colo ed p ecipi a es in jus 30 min compa ed o he solu ion con- aining NaOH. A as change in colo indica ed he o ma ion o ZnO nanopa icles due o he educ ion o zinc sal . The apid educ ion o Zinc sal in o nanopa icles can be a ibu ed o e penoids and la anones compounds in he Neem ex ac [25]. A peak a ound 250 nm was due o he exci a ion o su ace plasmon ib a ions in ZnO nanopa - icles. 200 300 400 500 600 700 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Abso bance (a.u) Wa eleng h (nm) ZnO Figu e 3. UV- is p o ile o as-p oduced ZnO nanopa icles be o e coa ing o e co on ab ic. 3.3. XRD Analysis o ZnO-Coa ed Co on The sui able me hod o s udy he c ys alline na u e o coa ed nanopa icles is X- ays di ac ion. XRD pa e ns o blank co on and ZnO nanopa icles, aken a a cu en o 20 mA and ol age o 40 kV in he 2θ ange o 0° o 80°, a e shown in Figu e 4. Figu e 4a con i ms he c ys alline na u e o he cellulose in co on. A majo XRD peak a 2θ o 22.6° is he cha ac e is ic peak o cellulose, desc ibes he (002) c ys alline plane. Some addi ional XRD peaks a 2θ o 14.9° and 16.5° co espond o he (101) c ys alline plane. Figu e 4b, on he o he hand, e ealed he hexagonal phase o as-p oduced ZnO nanopa icles. Some Figu e 3. UV- is p o ile o as-p oduced ZnO nanopa icles be o e coa ing o e co on ab ic. 3.3. XRD Analysis o ZnO-Coa ed Co on The sui able me hod o s udy he c ys alline na u e o coa ed nanopa icles is X- ays di ac ion. XRD pa e ns o blank co on and ZnO nanopa icles, aken a a cu en o 20 mA and ol age o 40 kV in he 2 θ ange o 0 ◦ o 80 ◦ , a e shown in Figu e 4. Figu e 4a con i ms he c ys alline na u e o he cellulose in co on. A majo XRD peak a 2 θ o 22.6 ◦ is he cha ac e is ic peak o cellulose, desc ibes he (002) c ys alline plane. Some addi ional XRD peaks a 2 θ o 14.9 ◦ and 16.5 ◦ co espond o he (101) c ys alline plane. Figu e 4b, on he o he hand, e ealed he hexagonal phase o as-p oduced ZnO nanopa icles. Some p ominen XRD peaks we e obse ed a 2 θ o 31.54 ◦ , 34.40 ◦ , 36.71 ◦ , 47.45 ◦ , 56.36 ◦ , and 62.82 ◦ , co esponding o (100), (002), (101), (102), (110), (103) planes, espec i ely [ 26 ]. The in ensi y o he cha ac e is ic peak a 2 θo 34.40 ◦ was sha p as compa ed o o he peaks in he (101) c ys alline plane. A simila plane was obse ed in he c ys alline s uc u e o cellulose. The c ys alli e size o nanopa icles was measu ed by conside ing he ull wid h a hal maximum (FWHM) o he selec ed XRD peaks. The lowe FWHM shows a la ge c ys alli e size. In con as , la ge FWHM deno es a smalle c ys alli e size. The Sche e equa ion was used o de e mine he size o c ys alli es. Nanoma e ials 2022,12, 2122 8 o 14 Nanoma e ials 2022, 12, 2122 8 o 15 p ominen XRD peaks we e obse ed a 2θ o 31.54°, 34.40°, 36.71°, 47.45°, 56.36°, and 62.82°, co esponding o (100), (002), (101), (102), (110), (103) planes, espec i ely [26]. The in ensi y o he cha ac e is ic peak a 2θ o 34.40° was sha p as compa ed o o he peaks in he (101) c ys alline plane. A simila plane was obse ed in he c ys alline s uc u e o cellulose. The c ys alli e size o nanopa icles was measu ed by conside ing he ull wid h a hal maximum (FWHM) o he selec ed XRD peaks. The lowe FWHM shows a la ge c ys alli e size. In con as , la ge FWHM deno es a smalle c ys alli e size. The Sche e equa ion was used o de e mine he size o c ys alli es. 0 10 20 30 40 50 60 0 100 200 300 400 500 600 (a) In ensi y (a.u.) 2 (Deg ee) Raw co on (101) (101) (002) 20 30 40 50 60 0 2000 4000 6000 8000 10000 12000 14000 16000 (b) (100) (002) (101) In ensi y (a.u.) 2(Deg ee) ZnO (110) Figu e 4. XRD spec a o (a) aw co on and (b) as-p oduced ZnO nanopa icles be o e coa ing o e co on ab ic. 3.4. SEM Analysis o ZnO-Coa ed Co on The su ace mo phology o ZnO nanopa icles and coa ed co on samples was ana- lyzed by gene a ing SEM and STEM images, as shown in Figu e 5. The size and mo phol- ogy o ZnO nanos uc u es a e ou lined in Figu e 5a, which shows almos a sphe ical shape o he nanopa icles. The a e age pa icle size was measu ed o be abou 40 nm. Figu e 5b shows he STEM image o he nanopa icles. The STEM image e eals he low agglome a ion o he nanopa icles. The dispe sed nanopa icles make a s ong bond wi h he ab ic su ace and show high s abili y o e mul iple wash cycles. Figu e 5c,d e eal he SEM mo phology o he ZnO-coa ed co on samples (P1 and P2). ZnO nanopa icles dispe sed homogeneously on he su ace o plasma unc ionalized ab ic (P1), which p o- mo ed he an ibac e ial and pho oca aly ic cha ac e is ics o he coa ed ab ic. The coa ing on sample P2, on he o he hand, was dense in some places. The nanopa icles in he dense pa s did no make s ong con ac wi h he su ace and showed sligh ly lowe s abili y o e mul iple wash cycles compa ed o he plasma unc ionalized sample. Fo he plasma- ea ed sample, P1, he quan i y o ZnO coa ing was highe han he ci ic acid- ea ed P2 sample. This was due o he ac ha plasma induced some impo an moie ies (COOH, NO3, NH2, O, OH) on he su ace o co on. These g oups made a s ong in e ac ion wi h he nanopa icles. The occu ence o acous ic ca i a ion du ing he ul asonic-assis ed coa ing p ocedu e p oduces sho ly li ed localized ho zones. The high empe a u e and p essu e zones cause he sonolysis o wa e by p oducing hyd ogen and hyd oxyl adicals. The ai apped by he ab ic u ns in o bubbles in he ab ic. The ansien bubbles cause powe ul con ec ion when hey mo e nea he ab ic su ace. This phenomenon in ensi- ies he ans e and adso p ion o nanopa icles o he ab ic su ace. The nanopa icles also e ealed a s ong a ini y o he hyd oxyl adicals p oduced du ing sonolysis o wa e . The hyd oxyl adicals o m s ong in e acial bonding o he i m in e ac ion o nanopa - icles wi h he ab ic su ace. Figu e 4. XRD spec a o ( a ) aw co on and ( b ) as-p oduced ZnO nanopa icles be o e coa ing o e co on ab ic. 3.4. SEM Analysis o ZnO-Coa ed Co on The su ace mo phology o ZnO nanopa icles and coa ed co on samples was ana- lyzed by gene a ing SEM and STEM images, as shown in Figu e 5. The size and mo phology o ZnO nanos uc u es a e ou lined in Figu e 5a, which shows almos a sphe ical shape o he nanopa icles. The a e age pa icle size was measu ed o be abou 40 nm. Figu e 5b shows he STEM image o he nanopa icles. The STEM image e eals he low agglome a- ion o he nanopa icles. The dispe sed nanopa icles make a s ong bond wi h he ab ic su ace and show high s abili y o e mul iple wash cycles. Figu e 5c,d e eal he SEM mo phology o he ZnO-coa ed co on samples (P1 and P2). ZnO nanopa icles dispe sed homogeneously on he su ace o plasma unc ionalized ab ic (P1), which p omo ed he an ibac e ial and pho oca aly ic cha ac e is ics o he coa ed ab ic. The coa ing on sample P2, on he o he hand, was dense in some places. The nanopa icles in he dense pa s did no make s ong con ac wi h he su ace and showed sligh ly lowe s abili y o e mul iple wash cycles compa ed o he plasma unc ionalized sample. Fo he plasma- ea ed sample, P1, he quan i y o ZnO coa ing was highe han he ci ic acid- ea ed P2 sample. This was due o he ac ha plasma induced some impo an moie ies (COOH, NO 3 , NH 2 , O, OH) on he su ace o co on. These g oups made a s ong in e ac ion wi h he nanopa icles. The occu ence o acous ic ca i a ion du ing he ul asonic-assis ed coa ing p ocedu e p oduces sho ly li ed localized ho zones. The high empe a u e and p essu e zones cause he sonolysis o wa e by p oducing hyd ogen and hyd oxyl adicals. The ai apped by he ab ic u ns in o bubbles in he ab ic. The ansien bubbles cause powe ul con ec- ion when hey mo e nea he ab ic su ace. This phenomenon in ensi ies he ans e and adso p ion o nanopa icles o he ab ic su ace. The nanopa icles also e ealed a s ong a ini y o he hyd oxyl adicals p oduced du ing sonolysis o wa e . The hyd oxyl adicals o m s ong in e acial bonding o he i m in e ac ion o nanopa icles wi h he ab ic su ace. 3.5. Pho oca aly ic Ac i i y The pho oca aly ic ac ion o ZnO nanopa icles, coa ed on samples P1 and P2, was assessed by measu ing he in ensi y o he UV- is spec a o he MB solu ion a e adminis- e ing UV ligh exposu e o di e en in e als o ime. The mechanism o he pho oca aly ic sel -cleaning ac ion o a coa ed ab ic in ol es he pho oexci a ion o he ZnO pho oca alys and p oduc ion o elec on-hole pai s by he mig a ion o elec ons in o he conduc ion band om he alance band [ 27 ]. The elec ons and holes de i e he edox eac ions a he coa ed su ace o deg ade dye molecules, as illus a ed in Figu e 6. Nanoma e ials 2022,12, 2122 9 o 14 Nanoma e ials 2022, 12, 2122 9 o 15 Figu e 5. (a) SEM mic og aph o as-p oduced ZnO, (b) STEM mic og aph o as-p oduced ZnO, (c) SEM mic og aph o ZnO-coa ed P1 sample and (d) SEM mic og aph o ZnO-coa ed P2 sample. 3.5. Pho oca aly ic Ac i i y The pho oca aly ic ac ion o ZnO nanopa icles, coa ed on samples P1 and P2, was assessed by measu ing he in ensi y o he UV- is spec a o he MB solu ion a e admin- is e ing UV ligh exposu e o di e en in e als o ime. The mechanism o he pho o- ca aly ic sel -cleaning ac ion o a coa ed ab ic in ol es he pho oexci a ion o he ZnO pho oca alys and p oduc ion o elec on-hole pai s by he mig a ion o elec ons in o he conduc ion band om he alance band [27]. The elec ons and holes de i e he edox eac ions a he coa ed su ace o deg ade dye molecules, as illus a ed in Figu e 6. Figu e 6. Mechanism o pho oca aly ic sel -cleaning ac ion o ZnO nanopa icles. Figu e 5. ( a ) SEM mic og aph o as-p oduced ZnO, ( b ) STEM mic og aph o as-p oduced ZnO, (c) SEM mic og aph o ZnO-coa ed P1 sample and (d) SEM mic og aph o ZnO-coa ed P2 sample. Nanoma e ials 2022, 12, 2122 9 o 15 Figu e 5. (a) SEM mic og aph o as-p oduced ZnO, (b) STEM mic og aph o as-p oduced ZnO, (c) SEM mic og aph o ZnO-coa ed P1 sample and (d) SEM mic og aph o ZnO-coa ed P2 sample. 3.5. Pho oca aly ic Ac i i y The pho oca aly ic ac ion o ZnO nanopa icles, coa ed on samples P1 and P2, was assessed by measu ing he in ensi y o he UV- is spec a o he MB solu ion a e admin- is e ing UV ligh exposu e o di e en in e als o ime. The mechanism o he pho o- ca aly ic sel -cleaning ac ion o a coa ed ab ic in ol es he pho oexci a ion o he ZnO pho oca alys and p oduc ion o elec on-hole pai s by he mig a ion o elec ons in o he conduc ion band om he alance band [27]. The elec ons and holes de i e he edox eac ions a he coa ed su ace o deg ade dye molecules, as illus a ed in Figu e 6. Figu e 6. Mechanism o pho oca aly ic sel -cleaning ac ion o ZnO nanopa icles. Figu e 6. Mechanism o pho oca aly ic sel -cleaning ac ion o ZnO nanopa icles. Figu e 7shows UV- is spec a o he dye-con aining solu ion a e UV i adia ion o di e en ime pe iods in he p esence o ZnO-coa ed P1 and P2 samples. The concen a ion o dye dec eased wi h he UV exposu e ime. The mola abso p i i y o he dye solu ion was measu ed by d awing a linea i o he abso bance o dye agains a ange o dye concen a ion, as shown in Figu e 8. Dye deg ada ion inc eases wi h he exposu e ime, which was con i med by a dec ease in ligh abso p ion by he solu ion. The sample P1 showed be e sel -cleaning ac i i y han sample P2. The sel -cleaning e iciency was 77%