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%