Ci a ion: Teijido, R.; Zhang, Q.;
Blanco, M.; Pé ez-Ál a ez, L.;
Lance os-Méndez, S.; Vilas-Vilela, J.L.;
Ruiz-Rubio, L. G aphene-Enhanced
Me hac yla ed Algina e Gel Films o
Sus ainable Dye Remo al in Wa e
Pu i ica ion. Gels 2024,10, 25.
h ps://doi.o g/10.3390/
gels10010025
Academic Edi o : Yi Cao
Recei ed: 20 No embe 2023
Re ised: 24 Decembe 2023
Accep ed: 26 Decembe 2023
Published: 27 Decembe 2023
Copy igh : © 2023 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/).
gels
A icle
G aphene-Enhanced Me hac yla ed Algina e Gel Films o
Sus ainable Dye Remo al in Wa e Pu i ica ion
Rubén Teijido 1,2 , Qi Zhang 2, Mi en Blanco 3, Ley e Pé ez-Ál a ez 1,2 , Senen xu Lance os-Méndez 2,
JoséLuis Vilas-Vilela 1,2,* and Lei e Ruiz-Rubio 1,2,*
1
Mac omolecula Chemis y G oup (LQM), Physical Chemis y Depa men , Facul y o Science and Technology,
Uni e si y o he Basque Coun y (UPV/EHU), 48940 Leioa, Spain; [email p o ec ed] (R.T.);
ley e.pe [email p o ec ed] (L.P.-Á.)
2BCMa e ials, Basque Cen e o Ma e ials, Applica ions and Nanos uc u es, UPV/EHU Science Pa k,
48940 Leioa, Spain; [email p o ec ed] (Q.Z.); [email p o ec ed] (S.L.-M.)
3Teknike , Basque Resea ch and Technology Alliance (BRTA), 20600 Eiba , Spain; mi en.blanco@ eknike .es
*Co espondence: [email p o ec ed] (J.L.V.-V.); [email p o ec ed] (L.R.-R.)
Abs ac : Sel -s anding nanocomposi e ilms we e p epa ed by h ee-dimensional UV-induced adical
copolyme iza ion o me hac yla ed algina e (MALG) wi h ac ylic acid (AA) and ein o ced wi h
g aphene oxide (GO) o imp o e bo h mechanical s eng h and dye adso p ion capaci y in was ewa e
decon amina ion ope a ions. Dynamic mechanical– he mal analysis e ealed a ia ions in s o age
modulus: he highe he GO con en , he highe he s o age modulus (E
′
) alues. Also, he highe he
empe a u e (associa ed wi h a lowe and lowe wa e con en o ilms), he la ge alues o E
′
o
he ilms o he same composi ion (E
′
(25
◦
C) = 676.6–1538.7 MPa; E
′
(100
◦
C) = 886.9–2066.6 MPa),
p o iding insigh s in o he compa ibili y be ween GO and he MALG/AA ma ix, as well as, assessing
he imp o emen in he nanocomposi e’s inal mechanical p ope ies. These c osslinked ilms in a d y
s a e exhibi ed apid wa e up ake and ela i ely sho d ying imes (ca. 30 min a oom empe a u e
o he MALG/AA/GO composi es) esul ing om he swelling–d ying s udies and wa e con ac
angle measu emen s. The e icacy o me hylene blue emo al om wa e assessed ia UV–VIS
spec ome y e ealed excellen esul s, exp essed as an adso p ion yield o 70–80% and 85–98% a e
30 h and 258 h, espec i ely, o imme sion ime o ilms in o an MB aqueous solu ion o 12.5 mg/L
(as he con amina ed wa e model). The eusabili y o he same ilms was e alua ed by consecu i e
ex ac ion p ocesses o MB om he composi e memb anes when he con en o deso bed dye was
also spec opho ome ically moni o ed and conduc ed in acidic condi ions (HCl aqueous solu ions o
pH 2). O e all, he in oduc ion o GO in he de eloped sel -s anding MALG/AA nanocomposi e
ilms exhibi ed enhanced mechanical p ope ies and inc eased e iciency o dye emo al applica ions.
Thei g ea eu iliza ion po en ial was highligh ed by low d ying imes and a good abili y o elease
he dye ini ially adso bed. Thus, he p epa ed ilms could be sui able ma e ials o sus ainable and
e ec i e wa e ea men echnologies.
Keywo ds: me hac yla ed algina e; hyd ogels; ilms; g aphene oxide; dye adso p ion; wa e pu i ica ion
1. In oduc ion
Polysaccha ides s and ou as biopolyme s wi h conside able po en ial applica ions [
1
–
3
]
based on hei widesp ead a ailabili y, ela i ely low cos s, and eco- iendliness. In ecen
yea s, he e has been a g owing in e es in algina e, a na u ally occu ing subs ance abun-
dan ly ound in he cell walls o nume ous algae species, p o iding ema kable lexibili y
and oughness, enabling hese algae o wi hs and he elen less o ces o con inuous wa es
and idal ac i i ies [
4
]. S uc u ally, algina e is a linea copolyme o
β
-d-mannu onic acid
(M) and i s C-5 epime
α
-l-gulu onic acid (G) linked by e he 1
→
4 bonds. Each algina e
species can be cha ac e ized by i s M/G a io, as i may g ea ly in luence he ma e ial’s inal
mechanical cha ac e is ics [
5
,
6
]. The dis inc i e cha ac e is ics o algina e a e ela ed o i s
Gels 2024,10, 25. h ps://doi.o g/10.3390/gels10010025 h ps://www.mdpi.com/jou nal/gels
Gels 2024,10, 25 2 o 13
chemical s uc u e, wi h an abundance o ca boxyl and hyd oxyl g oups. This cha ac e is ic
signi ican ly inc eases hei ange o po en ial applica ions and allows a b oad spec um
o modi ica ions and physical blending wi h di e en ma e ials o de elop non-soluble 3D
ne wo ks as a pla o m, gi ing o m o no el bio-composi es. Examples o applica ions in-
clude (a) he use o algina es as he mal ba ie s in highly ene ge ic Li-ion ba e ies, blended
wi h ca boxyme hyl cellulose and u he c osslinked wi h Ca
2+
ions [
7
]; (b) hei iono opic
gela ion wi h s a ch in o nanobeads o d ug deli e y applica ions [
8
]; o (c) many possibili ies
o hei di e en ypes o unc ionaliza ion and composi ional o mula ions in was ewa e
ea men applica ions [9].
When i comes o pollu an emo al om was ewa e , algina e-based ma e ials migh
be a p omising pH-sensi i e adso ben , e ec i e in he adso p ion o a ious species o
hyd ophilic and/o ca ionic a oma ic compounds ound in con amina ed en i onmen al
wa e [10].
O ganic dyes a e some o he mos impo an indus ially p oduced pollu an s in
ex ile, pain s, p in ing, cosme ics, and ood p ocessing and packaging indus ies, among
o he s. I no con olled, hese non-biodeg adable subs ances may cause se e e and long-
e m con amina ion in wa e s eams. Me hylene blue (MB) is one o he mos signi ican
dyes, aking in o accoun i s p e alence, and is ound in a ious indus ies such as he
ex ile o ab ics like co on and wool and as a colo ing agen in he p oduc ion o pape ,
plas ics, cosme ics, o pha maceu ical p oduc s, o highligh only a ew examples [
11
].
MB’s main pe nicious e ec s, when accumula ed, ange om blocking he sunligh and
de aining he pho osyn he ic ac i i y o aqua ic species (cyanobac e ia, mic oalgae, algae),
o ca cinogenic, mu agenic, and o he highly oxic e ec s (eye bu n, issue nec osis) in
animal species ha li e in o use wa e [12,13].
Di e en s a egies ha e been commonly employed in he decon amina ion o o ganic
dyes, including physicochemical me hods such as p ecipi a ion, loccula ion, elec odialysis,
pho oca alysis, o memb ane sepa a ion [
12
,
14
]. Howe e , adso p ion me hodologies ha e
p o en o be he mos e ec i e due o hei high dye emo al capabili ies, applica ion
simplici y, compa ibili y wi h high wa e lows, and economic implemen a ion [
15
,
16
].
Recen ly, polyme ic memb anes and, in pa icula , hose ab ica ed om biopolyme s
(algina e, chi osan) ha e gained ele ance o e o he ma e ials, such as he conside ably
cos ly po ous ce amics [
17
–
19
] due o hei en i onmen al iendliness, low cos , and
a ailabili y. Polysaccha ide modi ica ion, unc ionaliza ion, o combina ion wi h o he
ma e ials in o high adso p ion pe o mance nanocomposi es ha e la ely ga he ed abundan
esea ch e o s [
12
,
20
,
21
]. Despi e he high adso p ion po en ial al eady e idenced by
hese biopolyme s, such a p ope y is s ongly in luenced by he chemical s uc u e o he
adso ben , which in u n may be u he modi ied in acco dance wi h a p e-se pu pose.
As an example, he adso p ion capabili y o ALG owa ds MB is mainly based on i s
abundan ca boxylic g oups [
22
], which a e able o in e ac a o ably wi h MB molecules
and immobilize hem on o he biopolyme ne wo k. Thus, chemically modi ying ALG wi h
a p ocess ha deple es he inal s uc u e om hese unc ional g oups could diminish i s
adso p ion capaci y ega ding such a ca ionic dye.
This esea ch wo k p oposes a chemical unc ionaliza ion o algina e wi h me hac ylic
g oups by means o a me hac ylic anhyd ide eac ion wi h he hyd oxyl g oups in C-2 on
e e y gulu onic acid uni (G), hus lea ing he ca boxylic g oups unal e ed. Besides he
chemical s uc u e, a iables such as mechanical s eng h and swelling/d ying beha io ,
among o he s, need o be op imized o each speci ic applica ion [
21
]. The me hac ylic
unc ionali ies enable a UV-induced c osslinking p ocess (in ac , a h ee-dimensional
homopolyme iza ion o MALG o a h ee-dimensional copolyme iza ion o MALG and AA
when AA was used), esul ing in a hyd ogel-like s uc u e o he ab ica ed ilms.
G aphene oxide nanopla ele s could be excellen ille s in biopolyme -based nanocom-
posi es o a la ge a ie y o applica ions. This ino ganic 2D-laye ed ma e ial is well-known
o i s compa ibili y wi h biopolyme s [
23
,
24
] due o he abundance o oxygen-bea ing
unc ionali ies on pla ele su aces. These may a o ably in e ac wi h mos pola ma ixes,
Gels 2024,10, 25 3 o 13
hus ein o cing he global s uc u e and p o iding addi ional adso p ion si es in he GO
shee s’ in e laye ed space. Based on he ela i ely high ma ke p ice o GO, only wo GO-
con aining o mula ions ha e been chosen, de eloped, and s udied, MALG/AA/GO1.25
and MALG/AA/GO5, whe e 1.25 and 5 deno e he pe cen ages o GO wi h espec o he
MALG componen in he o mula ions a o emen ioned.
The di e en amoun s o g aphene oxide (GO) we e inco po a ed in o me hac yla ed
algina e/ac ylic acid (MALG/AA) ilms o e alua e hei impac on he esul ing mechani-
cal p ope ies and MB adso p ion e iciency. The o e all e iciencies and capaci ies we e
quan i ied h ough UV–VIS spec opho ome ic analysis o aqueous MB solu ions in which
he ab ica ed ilms we e imme sed. In esponse o he demand o enhanced adso p ion
p ope ies o ma e ials conce ning wa e pollu an s, a s udy o he eu iliza ion po en ial
o he ab ica ed ilms was ca ied ou in ol ing he cha ac e iza ion o swelling–d ying
beha io and associa ed ime ames, as well as he e alua ion o he ex ac ion e iciency o
adso bed MB (as pollu an model in was ewa e ) unde acidic condi ions.
2. Resul s and Discussion
2.1. Syn hesis and Cha ac e iza ion o Algina e and I s Me hac yla ed De i a i e
The M/G a io o he algina e in luences he inal mechanical p ope ies o he ma e i-
als [
5
,
6
]. Conside ing his, he M/G a io o he used algina e was de e mined by
1
H-NMR.
The yield o he syn hesis o me hac yla ed algina e was 78%. Fo he de e mina ion o he
me hac yla ion deg ee (%MD), as sugges ed by Jensen e al. [
25
], MALG samples
1
H-NMR
spec a we e acqui ed a an ele a ed empe a u e o 80
◦
C o wo main easons. Fi s ly, a
80
◦
C, he sample iscosi y dec eased, esul ing in na owe signal wid hs. Secondly, he
wa e esonance signal shi ed ou o he spec al egion o in e es (Figu e 1), o iginally
posi ioned be ween 4.5–5 ppm. This shi is e y ele an as i esol es he o e lap wi h
signals om he anome ic p o ons in algina e G and M uni s, hinde ing he de e mina ion
o %MD h ough hese in eg a ion me hodologies.
Gels 2024, 10, x FOR PEER REVIEW 4 o 14
Figu e 1. MALG
1
H-NMR spec a showing he displacemen o wa e esonance signal in he expe -
imen pe o med a 80 °C.
Figu e 2. MALG
1
H-NMR spec a wi h he in eg a ed signals used in he cha ac e iza ion o he G
and M uni s in MALG.
2.2. Con ac Angle Measu emen s
The wa e we abili y o he indi idual ilms is highly dependen on he su ace
oughness bu also on hei chemical unc ionali ies and possible addi i es in ol ed in
hei o mula ions. Wa e con ac angle (WCA) esul s we e ob ained as he mean alues
o i e measu emen s, and some ep esen a i e images o sessile wa e d ops a e p e-
sen ed in Figu e 3.
Figu e 3. Values o he con ac angle measu ed by he me hod o sessile wa e d ops deposi ed on
he ilm su aces o (a) ALG, (b) MALG, (c) MALG/AA, (d) MALG/AA/GO1.25 and (e)
MALG/AA/GO5.
The wa e con ac angle esul s e idenced he dec ease in he hyd ophilici y o hese
polysaccha ide-based ilms (Figu e 3) ela ed o he GO inc ease in he o mula ion. The
39.2 ± 6.1° 52.4 ± 3.2° 69.4 ± 4.1° 59.0 ± 4.7° 62.6 ± 3.7°
Figu e 1. MALG
1
H-NMR spec a showing he displacemen o wa e esonance signal in he
expe imen pe o med a 80 ◦C.
All calcula ions o he M/G a io and %MD we e ca ied ou ollowing equa ions 1 and 2
and conside ing he in eg a ion o he signals o he anome ic p o ons in G(I
G
= 4.9–5.0 ppm)
and M(I
M
= 4.55–4.6 ppm) uni s, as well as he signals o inylic p o ons in he me hac yla ed
uni s (IA= 5.6–5.7, IB= 6.0–6.1 ppm) (Figu e 2):
%G=IG
IM+IG
×100% (1)
Gels 2024,10, 25 4 o 13
%MDA=%G×
IA+IB
2
IG
×100% (2)
Gels 2024, 10, x FOR PEER REVIEW 4 o 14
Figu e 1. MALG
1
H-NMR spec a showing he displacemen o wa e esonance signal in he expe -
imen pe o med a 80 °C.
Figu e 2. MALG
1
H-NMR spec a wi h he in eg a ed signals used in he cha ac e iza ion o he G
and M uni s in MALG.
2.2. Con ac Angle Measu emen s
The wa e we abili y o he indi idual ilms is highly dependen on he su ace
oughness bu also on hei chemical unc ionali ies and possible addi i es in ol ed in
hei o mula ions. Wa e con ac angle (WCA) esul s we e ob ained as he mean alues
o i e measu emen s, and some ep esen a i e images o sessile wa e d ops a e p e-
sen ed in Figu e 3.
Figu e 3. Values o he con ac angle measu ed by he me hod o sessile wa e d ops deposi ed on
he ilm su aces o (a) ALG, (b) MALG, (c) MALG/AA, (d) MALG/AA/GO1.25 and (e)
MALG/AA/GO5.
The wa e con ac angle esul s e idenced he dec ease in he hyd ophilici y o hese
polysaccha ide-based ilms (Figu e 3) ela ed o he GO inc ease in he o mula ion. The
39.2 ± 6.1° 52.4 ± 3.2° 69.4 ± 4.1° 59.0 ± 4.7° 62.6 ± 3.7°
Figu e 2. MALG
1
H-NMR spec a wi h he in eg a ed signals used in he cha ac e iza ion o he G
and M uni s in MALG.
A e analysing i e samples, he p opo ion o Guni s was ound o be 65
±
1%,
esul ing in an M/G a io o 0.539 and a %MD = 44.4 ±2.9%.
2.2. Con ac Angle Measu emen s
The wa e we abili y o he indi idual ilms is highly dependen on he su ace
oughness bu also on hei chemical unc ionali ies and possible addi i es in ol ed in
hei o mula ions. Wa e con ac angle (WCA) esul s we e ob ained as he mean alues o
i e measu emen s, and some ep esen a i e images o sessile wa e d ops a e p esen ed in
Figu e 3.
Gels 2024, 10, x FOR PEER REVIEW 4 o 14
Figu e 1. MALG
1
H-NMR spec a showing he displacemen o wa e esonance signal in he expe -
imen pe o med a 80 °C.
Figu e 2. MALG
1
H-NMR spec a wi h he in eg a ed signals used in he cha ac e iza ion o he G
and M uni s in MALG.
2.2. Con ac Angle Measu emen s
The wa e we abili y o he indi idual ilms is highly dependen on he su ace
oughness bu also on hei chemical unc ionali ies and possible addi i es in ol ed in
hei o mula ions. Wa e con ac angle (WCA) esul s we e ob ained as he mean alues
o i e measu emen s, and some ep esen a i e images o sessile wa e d ops a e p e-
sen ed in Figu e 3.
Figu e 3. Values o he con ac angle measu ed by he me hod o sessile wa e d ops deposi ed on
he ilm su aces o (a) ALG, (b) MALG, (c) MALG/AA, (d) MALG/AA/GO1.25 and (e)
MALG/AA/GO5.
The wa e con ac angle esul s e idenced he dec ease in he hyd ophilici y o hese
polysaccha ide-based ilms (Figu e 3) ela ed o he GO inc ease in he o mula ion. The
39.2 ± 6.1° 52.4 ± 3.2° 69.4 ± 4.1° 59.0 ± 4.7° 62.6 ± 3.7°
Figu e 3. Values o he con ac angle measu ed by he me hod o sessile wa e d ops de-
posi ed on he ilm su aces o (a) ALG, (b) MALG, (c) MALG/AA, (d) MALG/AA/GO1.25 and
(e) MALG/AA/GO5.
The wa e con ac angle esul s e idenced he dec ease in he hyd ophilici y o hese
polysaccha ide-based ilms (Figu e 3) ela ed o he GO inc ease in he o mula ion. The
lowes alue o WCA (39.2
◦
) was ob ained o pu e algina e ilms. Fu he mo e, due o
he poo physical c osslinking o his highly hyd ophilic biopolyme , he sessile d op was
apidly abso bed by he ilm (local dissolu ion o algina e), lea ing a hole on he su ace.
The s abili y p oblem o wa e d ops was sol ed once chemical c osslinking was in oduced
in o hese sys ems. A i s c osslinking app oach consis ed o h ee-dimensional adical
homopolyme iza ion o me hac yla e algina e induced by UV-i adia ion, which allowed
o ob ain highe WCA alues (52.40
◦
), bu wi h he pe sis ence o pa ial dissolu ion o
he subs a e on which he wa e d ops we e placed. On he o he hand, by using a
small amoun o AA, he c osslinking p ocess consis ing o h ee-dimensional adical
copolyme iza ion o me hac yla ed algina e wi h AA mos likely led o highe c osslinking
densi y, wi h a di ec consequence in inc easing he alue o con ac angle up o 69.40
◦
( he
highes alue). Ins ead, inco po a ing 1.25 w .% o g aphene oxide (GO) as a hyd ophilic
ille o enhance mechanical p ope ies and dye adso p ion capaci y de e mined a educ ion
Gels 2024,10, 25 5 o 13
o wa e con ac angle (WCAs) o 59
◦
. A he same ime, inc easing GO con en om 1.25 o
5% wi h espec o he MALG amoun led o highe alues o con ac angle o 62.60
◦
, due
o he po en ial o physical c osslinking o hese ma e ials wi h he algina e-based ma ix
and he ba ie e ec o he impe meable GO nanopla ele s.
2.3. Mechanical P ope ies o MALG/AA and MALG/AA/GO Films
Dynamic mechanical he mal analysis (DMTA) was conduc ed on he sel -s anding
ilms composed o MALG/AA, wi h a ious quan i ies o g aphene oxide (GO) in hei
o mula ions. The esul s a e p esen ed in Figu e 4, wi h he de e mined s o age modulus
alues a wo pa icula empe a u es ga he ed in Table 1.
Gels 2024, 10, x FOR PEER REVIEW 5 o 14
lowes alue o WCA (39.2°) was ob ained o pu e algina e ilms. Fu he mo e, due o he
poo physical c osslinking o his highly hyd ophilic biopolyme , he sessile d op was
apidly abso bed by he ilm (local dissolu ion o algina e), lea ing a hole on he su ace.
The s abili y p oblem o wa e d ops was sol ed once chemical c osslinking was in o-
duced in o hese sys ems. A i s c osslinking app oach consis ed o h ee-dimensional
adical homopolyme iza ion o me hac yla e algina e induced by UV-i adia ion, which
allowed o ob ain highe WCA alues (52.40°), bu wi h he pe sis ence o pa ial dissolu-
ion o he subs a e on which he wa e d ops we e placed. On he o he hand, by using
a small amoun o AA, he c osslinking p ocess consis ing o h ee-dimensional adical
copolyme iza ion o me hac yla ed algina e wi h AA mos likely led o highe c osslink-
ing densi y, wi h a di ec consequence in inc easing he alue o con ac angle up o 69.40°
( he highes alue). Ins ead, inco po a ing 1.25 w .% o g aphene oxide (GO) as a hyd o-
philic ille o enhance mechanical p ope ies and dye adso p ion capaci y de e mined a
educ ion o wa e con ac angle (WCAs) o 59°. A he same ime, inc easing GO con en
om 1.25 o 5% wi h espec o he MALG amoun led o highe alues o con ac angle o
62.60°, due o he po en ial o physical c osslinking o hese ma e ials wi h he algina e-
based ma ix and he ba ie effec o he impe meable GO nanopla ele s.
2.3. Mechanical P ope ies o MALG/AA and MALG/AA/GO Films
Dynamic mechanical he mal analysis (DMTA) was conduc ed on he sel -s anding
ilms composed o MALG/AA, wi h a ious quan i ies o g aphene oxide (GO) in hei
o mula ions. The esul s a e p esen ed in Figu e 4, wi h he de e mined s o age modulus
alues a wo pa icula empe a u es ga he ed in Table 1.
Figu e 4. DMTA he mog ams o he p epa ed MALG/AA ilms wi hou and wi h he inco po a-
ion o diffe en GO con en s.
Table 1. S o age modulus (E*, MPa) alues o MALG/AA, MALG/AA/GO 1.25, and MCHI/AA/GO
5 a he speci ied empe a u es.
Film Fo mula ion E* (MPa) a 25 °C E* (MPa) a 100 °C
MALG/AA 676.6 886.9
MALG/AA/GO1.25 1178.2 1305.3
MALG/AA/GO5 1538.7 2066.6
Due o he high hyd ophilici y o hese sys ems, i was no iced ha he ambien hu-
midi y abso bed by he ilms be o e he DMTA expe imen s in luenced hei mechanical
p ope ies. This was e idenced by an inc ease in he s o age modulus om 25 o 100 °C
o all samples as he wa e con en diminished. Fo his eason, wo esul s o he s o age
modulus a e p esen ed, one a 25 °C and one a 100 °C. The la e alues a e conside ed
25 50 75 100 125 150 175 200 225
0
250
500
750
1000
1250
1500
1750
2000
2250
MALG_AA75
MALG_AA75_GO 1.25
MALG_AA75_GO 5
S o age Modulus (E*) (MPa)
Tempe a u e (ºC)
Figu e 4. DMTA he mog ams o he p epa ed MALG/AA ilms wi hou and wi h he inco po a ion
o di e en GO con en s.
Table 1. S o age modulus (E*, MPa) alues o MALG/AA, MALG/AA/GO 1.25, and MCHI/AA/GO
5 a he speci ied empe a u es.
Film Fo mula ion E* (MPa) a 25 ◦C E* (MPa) a 100 ◦C
MALG/AA 676.6 886.9
MALG/AA/GO1.25 1178.2 1305.3
MALG/AA/GO5 1538.7 2066.6
Due o he high hyd ophilici y o hese sys ems, i was no iced ha he ambien
humidi y abso bed by he ilms be o e he DMTA expe imen s in luenced hei mechanical
p ope ies. This was e idenced by an inc ease in he s o age modulus om 25 o 100
◦
C
o all samples as he wa e con en diminished. Fo his eason, wo esul s o he s o age
modulus a e p esen ed, one a 25
◦
C and one a 100
◦
C. The la e alues a e conside ed
indica i e o comple ely d ied ilms, e lec ing he obse ed maximum s o age modulus. I
could be obse ed ha he in oduc ion o he ille s in luenced he mechanical p ope ies
o he ilms. A subs an ial inc ease in he s o age modulus was measu ed o ilm specimens
bea ing GO when compa ed o hose wi hou i . This e ec was mo e e iden a highe
GO p opo ions, wi h alues almos h ee imes highe han hose o he p is ine polyme
a he wo p esen ed empe a u es. The high compa ibili y o GO unc ionali y wi h he
biopolyme ic ma ix acili a ed mo e in ima e ille -ma ix in e ac ions, he eby ein o cing
he inal s uc u e o he ma e ial.
2.4. Dye Adso p ion On o MALG/AA and MALG/AA/GO Films
The po en ial applicabili y o hese ilms o dye decon amina ion was moni o ed by
UV–VIS spec oscopy. Thus, allowing o he calcula ion o he adso p ion capaci y pe
g am o ma e ial and he o al amoun o dye adso bed o adso p ion yield, he esul s a e
p esen ed in Figu e 5.
Gels 2024,10, 25 6 o 13
Gels 2024, 10, x FOR PEER REVIEW 6 o 14
indica i e o comple ely d ied ilms, e lec ing he obse ed maximum s o age modulus.
I could be obse ed ha he in oduc ion o he ille s in luenced he mechanical p ope -
ies o he ilms. A subs an ial inc ease in he s o age modulus was measu ed o ilm spec-
imens bea ing GO when compa ed o hose wi hou i . This effec was mo e e iden a
highe GO p opo ions, wi h alues almos h ee imes highe han hose o he p is ine
polyme a he wo p esen ed empe a u es. The high compa ibili y o GO unc ionali y
wi h he biopolyme ic ma ix acili a ed mo e in ima e ille -ma ix in e ac ions, he eby
ein o cing he inal s uc u e o he ma e ial.
2.4. Dye Adso p ion On o MALG/AA and MALG/AA/GO Films
The po en ial applicabili y o hese ilms o dye decon amina ion was moni o ed by
UV–VIS spec oscopy. Thus, allowing o he calcula ion o he adso p ion capaci y pe
g am o ma e ial and he o al amoun o dye adso bed o adso p ion yield, he esul s a e
p esen ed in Figu e 5.
(a) (b)
Figu e 5. Me hylene blue adso p ion capaci y (a) and o e all adso p ion yield (b) o he p epa ed
MALG ilms as a unc ion o ime o exposu e o MB aqueous solu ions.
The capaci y o MB adso p ion appea ed o be ela ed o he o al wa e inco po a-
ion capaci y o he ab ica ed ilms, ollowing he same end as in he swelling beha io
(Figu e 6). MALG/AA ilms showed highe capaci ies (17 mg MB/g ilm). In con as , he
capaci ies o he mo e in ica e s uc u es o MALG/AA/GO ilms we e 10 mg MB/g ilm
o 1.25 w .% GO con aining ilms and 12 mg MB/g ilm o ilms wi h 5 w .% o GO,
e idencing a compensa ion effec due o he MB molecules inco po a ed h ough in e ac-
ions inbe ween he GO laye ed s uc u e. The appa en low ep oducibili y, as shown by
la ge e o ba s (Figu e 5a), was ound o be mos likely due o he signi ican in luence o
ilm hickness (o mass) exe ed on his pa ame e . Thus, he ep oducibili y o he hick-
ness o he ilms was low du ing he diffe en sample ab ica ions due o he ad hoc molds
used and he e apo a ion o he sol en du ing he c osslinking eac ion. In o he wo ds,
samples wi h diffe en hicknesses p oduced a b oad dispe sion o adso p ion capaci y
esul s, so ha a be e con ol o e ilm hickness is expec ed o imp o e he consis ency
o measu emen s. Howe e , he o al efficiency o MB adso p ion was inc eased in ilms
wi h GO con en om 88% o MALG/AA ilms o 90% on hose bea ing 1.25 w .% o GO
and 97% on hose wi h a 5 w .% o GO. Such an ascending endency o MB adso p ion
wi h inc easing GO con en could be due o he g ea affini y o his dye o GO ia mul iple
in e ac ion ypes (hyd ogen bonding, elec os a ic in e ac ions, π–π s acking), as sug-
ges ed in Figu e 7 [26].
0 20406080100120
0
5
10
15
20
25
30
35
Adso p ion capaci y (mg MB/g ilm)
ime (h)
MALG/AA
MALG/AA/GO 1.25
MALG/AA/GO 5
0 20406080100120
0
20
40
60
80
100
Adso p ion yield (%)
ime (h)
MALG/AA
MALG/AA/GO 1.25
MALG/AA/GO 5
Figu e 5. Me hylene blue adso p ion capaci y (a) and o e all adso p ion yield (b) o he p epa ed
MALG ilms as a unc ion o ime o exposu e o MB aqueous solu ions.
The capaci y o MB adso p ion appea ed o be ela ed o he o al wa e inco po a-
ion capaci y o he ab ica ed ilms, ollowing he same end as in he swelling beha io
(Figu e 6). MALG/AA ilms showed highe capaci ies (17 mg MB/g ilm). In con as , he
capaci ies o he mo e in ica e s uc u es o MALG/AA/GO ilms we e 10 mg MB/g ilm
o 1.25 w .% GO con aining ilms and 12 mg MB/g ilm o ilms wi h 5 w .% o GO, e i-
dencing a compensa ion e ec due o he MB molecules inco po a ed h ough in e ac ions
inbe ween he GO laye ed s uc u e. The appa en low ep oducibili y, as shown by la ge
e o ba s (Figu e 5a), was ound o be mos likely due o he signi ican in luence o ilm
hickness (o mass) exe ed on his pa ame e . Thus, he ep oducibili y o he hickness
o he ilms was low du ing he di e en sample ab ica ions due o he ad hoc molds
used and he e apo a ion o he sol en du ing he c osslinking eac ion. In o he wo ds,
samples wi h di e en hicknesses p oduced a b oad dispe sion o adso p ion capaci y
esul s, so ha a be e con ol o e ilm hickness is expec ed o imp o e he consis ency
o measu emen s. Howe e , he o al e iciency o MB adso p ion was inc eased in ilms
wi h GO con en om 88% o MALG/AA ilms o 90% on hose bea ing 1.25 w .% o GO
and 97% on hose wi h a 5 w .% o GO. Such an ascending endency o MB adso p ion
wi h inc easing GO con en could be due o he g ea a ini y o his dye o GO ia mul iple
in e ac ion ypes (hyd ogen bonding, elec os a ic in e ac ions,
π
–
π
s acking), as sugges ed
in Figu e 7[26].
Gels 2024, 10, x FOR PEER REVIEW 7 o 14
Figu e 6. Weigh a ia ions du ing swelling–d ying o he specified films.
Figu e 7. A possible adso p ion mechanisms o GO o MB, a posi i e cha ge is alloca ed in he S
a om, as i is one o he possible esonance o ms o he MB molecule. (Red: Fun ional g oups p esen
in GO)
Fo compa ison and a be e unde s anding o his p ocess o MB adso p ion, a b ie
collec ion o composi es accompanied by specific mechanical p ope ies and co espond-
ing MB adso p ion yields is lis ed in Table 2.
Table 2. Published esul s on diffe en mechanical p ope ies and MB adso p ion yields o some
algina e-based sys ems.
Composi e
Mechanical P ope ies
Adso p ion Yield (%)
Re .
Algina e/Ca2+/fil e pape
Elas ic modulus
773 (1 w .% ALG) MPa
1907 (4 w .% ALGSA) MPa
93.9 [27]
Algina e/Ca
2+
/g aphene
oxide
No p o ided 91.3 [28]
Algina e/poly(ac ylic
acid)/TiO2 NPs
S o age modulus (G′)
971 MPa
80 (no TiO
2
NPs)
94.1 (0.05 g TiO2NPs)
99.4 (0.2 g TiO
2
NPs)
[29]
Me hac yla ed Algi-
na e/poly(ac ylic
acid)/g aphene oxide
S o age modulus (E′)
677 (no GO) MPa
1158 (1.25 w .% GO) MPa
1539 (5 w .% GO) MPa
88 (no GO)
90 (1.25 w .% GO)
97 (5 w .% GO)
Cu en
wo k
010 20 30 40 50
0
50
100
150
200
weigh a ia ion (%)
ime (min)
MALG/AA
MALG/AA/GO1.25
MALG/AA/GO5
Swelling D ying
Figu e 6. Weigh a ia ions du ing swelling–d ying o he speci ied ilms.
Gels 2024,10, 25 7 o 13
Gels 2024, 10, x FOR PEER REVIEW 7 o 14
Figu e 6. Weigh a ia ions du ing swelling–d ying o he speci ied ilms.
Figu e 7. A possible adso p ion mechanisms o GO o MB, a posi i e cha ge is alloca ed in he S
a om, as i is one o he possible esonance o ms o he MB molecule. (Red: Fun ional g oups p esen
in GO)
Fo compa ison and a be e unde s anding o his p ocess o MB adso p ion, a b ie
collec ion o composi es accompanied by speci ic mechanical p ope ies and co espond-
ing MB adso p ion yields is lis ed in Table 2.
Table 2. Published esul s on diffe en mechanical p ope ies and MB adso p ion yields o some
algina e-based sys ems.
Composi e Mechanical P ope ies Adso p ion Yield (%) Re .
Algina e/Ca2+/ il e pape
Elas ic modulus
773 (1 w .% ALG) MPa
1907 (4 w .% ALGSA) MPa
93.9 [27]
Algina e/Ca2+/g aphene
oxide No p o ided 91.3 [28]
Algina e/poly(ac ylic
acid)/TiO2 NPs
S o age modulus (G′)
971 MPa
80 (no TiO2NPs)
94.1 (0.05 g TiO2NPs)
99.4 (0.2 g TiO2NPs)
[29]
Me hac yla ed Algi-
na e/poly(ac ylic
acid)/g aphene oxide
S o age modulus (E′)
677 (no GO) MPa
1158 (1.25 w .% GO) MPa
1539 (5 w .% GO) MPa
88 (no GO)
90 (1.25 w .% GO)
97 (5 w .% GO)
Cu en
wo k
0 1020304050
0
50
100
150
200
weigh a ia ion (%)
ime (min)
MALG/AA
MALG/AA/GO1.25
MALG/AA/GO5
Swelling D ying
Figu e 7. A possible adso p ion mechanisms o GO o MB, a posi i e cha ge is alloca ed in he S
a om, as i is one o he possible esonance o ms o he MB molecule. (Red: Fun ional g oups p esen
in GO).
Fo compa ison and a be e unde s anding o his p ocess o MB adso p ion, a b ie
collec ion o composi es accompanied by speci ic mechanical p ope ies and co esponding
MB adso p ion yields is lis ed in Table 2.
Table 2. Published esul s on di e en mechanical p ope ies and MB adso p ion yields o some
algina e-based sys ems.
Composi e Mechanical P ope ies Adso p ion Yield (%) Re .
Algina e/Ca2+/ il e pape
Elas ic modulus
773 (1 w .% ALG) MPa
1907 (4 w .% ALGSA) MPa
93.9 [27]
Algina e/Ca2+/g aphene oxide No p o ided 91.3 [28]
Algina e/poly(ac ylic acid)/TiO2NPs S o age modulus (G′)
971 MPa
80 (no TiO2NPs)
94.1 (0.05 g TiO2NPs)
99.4 (0.2 g TiO2NPs)
[29]
Me hac yla ed Algina e/poly(ac ylic
acid)/g aphene oxide
S o age modulus (E′)
677 (no GO) MPa
1158 (1.25 w .% GO) MPa
1539 (5 w .% GO) MPa
88 (no GO)
90 (1.25 w .% GO)
97 (5 w .% GO)
Cu en wo k
2.5. MALG/AA/GO Films Reusabili y
2.5.1. Swelling–D ying Tes s o he P epa ed MALG Films
In addi ion, swelling–d ying beha io was also e alua ed, he esul s o each o mu-
la ion being displayed in Figu e 7.
The swelling–d ying esul s e idenced good s abili y o he ilms, ba ely losing mass
due o an almos negligible b eaking o decomposi ion o he sample du ing he p ocess.
Addi ionally, he ilms p esen ed a ema kable abili y o spon aneously d y a ambien
empe a u e, losing weigh du ing he d ying s age conside ably as e , hin ing a a good
eusabili y in wa e - ela ed applica ions. The inco po a ion o GO in he MALG/AA
ilms had he e ec o hinde ing he wa e adso p ion, which led o he mos subs an ial
dec ease o he equilib ium swelling o he ilms wi h 1.25% GO by ca. 33% compa ed
o he equilib ium swelling o he ilms de oid o GO (Figu e 7). This e ec was sligh ly
compensa ed by inc easing he GO con en o 5% and, as a esul o he hyd ophilic na u e o
he ille , he educ ion in he equilib ium swelling o hese sys ems compa ed o ha o he
ilms wi hou GO was only 17%. Du ing he d ying s age, he ilms wi hou GO we e able
o eco e hei ini ial weigh in 30 min a ambien empe a u e in a en ila ed oom. Also,
he same ilms showed sho e d ying imes, being 20 min o MALG/AA/GO1.25 ilms
and only 15 min o MALG/AA/GO5 ilms. Fo his las case, he d ying ime o 15 min
was equal o ha cha ac e is ic o he en i e swelling phase. The esul s e ealed highe
Gels 2024,10, 25 8 o 13
e apo a ion a es o wa e molecules physically bonded o he GO ille -con aining ilms
han hose bonded o he algina e–ac ylic acid ma ix, he e ec being mo e p onounced a
an ele a ed ille con en .
2.5.2. Abso bed MB Ex ac ion om MALG Films in Acidic Condi ions
To con inue wi h he eusabili y cha ac e iza ion o he ab ica ed ilms, he pos-
sibili y o ex ac ing he abso bed MB was s udied. MB bea s ionizable e ia y amine
unc ionali ies in i s chemical s uc u e unde acidic condi ions (Figu e 8) [
30
]. Thus,
he selec ed expe imen al condi ions o MB ex ac ion include subme ging he ilms in
HCl solu ions (0.01 M, pH = 2) o p ede ined pe iods o ime when he dye posi i ely
cha ged is less and less adso bed on an algina e ma ix wi h an elec ical cha ge inc eas-
ingly close o ze o in such an acidic medium, as epo ed by O hman e al. [
31
] and also
employed by Fang e al. [32].
Gels 2024, 10, x FOR PEER REVIEW 8 o 14
2.5. MALG/AA/GO Films Reusabili y
2.5.1. Swelling–D ying Tes s o he P epa ed MALG Films
In addi ion, swelling–d ying beha io was also e alua ed, he esul s o each o mu-
la ion being displayed in Figu e 7.
The swelling–d ying esul s e idenced good s abili y o he ilms, ba ely losing mass
due o an almos negligible b eaking o decomposi ion o he sample du ing he p ocess.
Addi ionally, he ilms p esen ed a ema kable abili y o spon aneously d y a ambien
empe a u e, losing weigh du ing he d ying s age conside ably as e , hin ing a a good
eusabili y in wa e - ela ed applica ions. The inco po a ion o GO in he MALG/AA ilms
had he effec o hinde ing he wa e adso p ion, which led o he mos subs an ial de-
c ease o he equilib ium swelling o he ilms wi h 1.25% GO by ca. 33% compa ed o he
equilib ium swelling o he ilms de oid o GO (Figu e 7). This effec was sligh ly com-
pensa ed by inc easing he GO con en o 5% and, as a esul o he hyd ophilic na u e o
he ille , he educ ion in he equilib ium swelling o hese sys ems compa ed o ha o
he ilms wi hou GO was only 17%. Du ing he d ying s age, he ilms wi hou GO we e
able o eco e hei ini ial weigh in 30 min a ambien empe a u e in a en ila ed oom.
Also, he same ilms showed sho e d ying imes, being 20 min o MALG/AA/GO1.25
ilms and only 15 min o MALG/AA/GO5 ilms. Fo his las case, he d ying ime o 15
min was equal o ha cha ac e is ic o he en i e swelling phase. The esul s e ealed
highe e apo a ion a es o wa e molecules physically bonded o he GO ille -con aining
ilms han hose bonded o he algina e–ac ylic acid ma ix, he effec being mo e p o-
nounced a an ele a ed ille con en .
2.5.2. Abso bed MB Ex ac ion om MALG Films in Acidic Condi ions
To con inue wi h he eusabili y cha ac e iza ion o he ab ica ed ilms, he possibil-
i y o ex ac ing he abso bed MB was s udied. MB bea s ionizable e ia y amine unc-
ionali ies in i s chemical s uc u e unde acidic condi ions (Figu e 8) [30]. Thus, he se-
lec ed expe imen al condi ions o MB ex ac ion include subme ging he ilms in HCl
solu ions (0.01 M, pH = 2) o p ede ined pe iods o ime when he dye posi i ely cha ged
is less and less adso bed on an algina e ma ix wi h an elec ical cha ge inc easingly close
o ze o in such an acidic medium, as epo ed by O hman e al. [31] and also employed by
Fang e al. [32].
Figu e 8. Acid-base equilib ia o me hylene blue.
The MB deso p ion (assessed ia UV–Vis spec ome y) was conduc ed unde acidic
condi ions (Figu e 9), de e mining he MB con en in deso p ion solu ions, namely, HCl
aqueous solu ions o pH 2, o e a pe iod o ime o 258 h by using MALG/AA/GO5 ilms.
This speci ic o mula ion was chosen due o i s demons a ed highe adso p ion efficiency
wi hin he same ime ame (Figu e 5). These es s ound good s abili y o he ilms in acidic
media (pH = 2) du ing exposu e ime. Howe e , as can be seen in Figu e 10, only 42% o
he o al MB adso bed by he MALG/AA/GO5 ilm was ex ac ed o e 258 h o imme sion
wi h a p onounced ex ac ion du ing he i s 24 h (ca. 26%), which indica es ha a u he
imp o emen o hese me hodology needs o be achie ed o a mo e efficien ex ac ion o
he ini ially adso bed dye.
Figu e 8. Acid-base equilib ia o me hylene blue.
The MB deso p ion (assessed ia UV–Vis spec ome y) was conduc ed unde acidic
condi ions (Figu e 9), de e mining he MB con en in deso p ion solu ions, namely, HCl
aqueous solu ions o pH 2, o e a pe iod o ime o 258 h by using MALG/AA/GO5 ilms.
This speci ic o mula ion was chosen due o i s demons a ed highe adso p ion e iciency
wi hin he same ime ame (Figu e 5). These es s ound good s abili y o he ilms in acidic
media (pH = 2) du ing exposu e ime. Howe e , as can be seen in Figu e 10, only 42% o
he o al MB adso bed by he MALG/AA/GO5 ilm was ex ac ed o e 258 h o imme sion
wi h a p onounced ex ac ion du ing he i s 24 h (ca. 26%), which indica es ha a u he
imp o emen o hese me hodology needs o be achie ed o a mo e e icien ex ac ion o
he ini ially adso bed dye.
Gels 2024, 10, x FOR PEER REVIEW 9 o 14
Figu e 9. Image o he deso p ion solu ions du ing he cou se o MB deso p ion om
MALG/AA/GO5 ilms in HCl (0.01 M, pH = 2) aqueous solu ions.
Figu e 10. Accumula ed MB ex ac ion om a MALG/AA/GO5 used ilm du ing 258 h o i s imme -
sion in diffe en HCl aqueous solu ions o pH 2.
2.6. Addi ional Nanocomposi e MALG/AA/GO Films Cha ac e iza ions
Addi ional cha ac e iza ion echniques employed du ing he s udy o he ab ica ed
ilms, such as c oss-sec ional SEM images and powde XRD diff ac og ams, a e p o ided
in he suppo ing in o ma ion. The XRD diff ac og am o a me hac yla ed algina e ilm
(Figu e S1) shows a cha ac e is ic highly amo phous signal o algina e wi h a maximum
o a ound 26° wi h a shoulde o his le a ound 12–15°, co esponding o he GO maxi-
mum peak. This diff ac og am is simila o o he s epo ed in he li e a u e o algina e-
based ilms con aining GO [28]. Meanwhile, in he c oss-sec ional SEM images p o ided
in Figu e S2, he hickness o wo ilm samples can be measu ed, esul ing in 21 µm o
p is ine MALG ilm and 29 µm o a MALG ilm con aining 5 w .% o GO. Addi ionally,
he pla elle s o GO, mos ly o ien ed pa allel o he ilm su aces, can be obse ed in he
images o he MALG/GO5 ilms.
3. Conclusions
This esea ch wo k p obed he possibili y o easily ab ica ing algina e-based hyd o-
gel-like ilms o ea dye-con amina ed was ewa e . The use o hese adso p ion echnol-
ogies has al eady shown high efficiencies o dye emo al, which, oge he wi h hei com-
posi ion based on abundan and inexpensi e biopolyme s, may p oduce new solu ions
ha a e affo dable e en o de eloping coun ies whe e hese p oblems end o be mo e
acu e. Howe e , algina e ilms lack he mechanical p ope ies o wi hs and hei manipu-
la ion and in eg a ion in complex wa e ea men sys ems. Thus, his esea ch showed
how he inclusion o g aphene oxide in algina e-based ilms can g ea ly imp o e hei
mechanical p ope ies, leading o s o age modulus alues inc eased by a ac o o 2.5. This
imp o emen may allow, o example, he use o hese sel -s anding ilms in applica ions
0 25 50 75 100 250 275
0
20
40
60
80
100
MB ex ac ed (%)
ime (h)
Figu e 9. Image o he deso p ion solu ions du ing he cou se o MB deso p ion om
MALG/AA/GO5 ilms in HCl (0.01 M, pH = 2) aqueous solu ions.
2.6. Addi ional Nanocomposi e MALG/AA/GO Films Cha ac e iza ions
Addi ional cha ac e iza ion echniques employed du ing he s udy o he ab ica ed
ilms, such as c oss-sec ional SEM images and powde XRD di ac og ams, a e p o ided
in he suppo ing in o ma ion. The XRD di ac og am o a me hac yla ed algina e ilm
(Figu e S1) shows a cha ac e is ic highly amo phous signal o algina e wi h a maximum o
a ound 26
◦
wi h a shoulde o his le a ound 12–15
◦
, co esponding o he GO maximum
peak. This di ac og am is simila o o he s epo ed in he li e a u e o algina e-based
ilms con aining GO [
28
]. Meanwhile, in he c oss-sec ional SEM images p o ided in
Figu e S2, he hickness o wo ilm samples can be measu ed, esul ing in 21
µ
m o
p is ine MALG ilm and 29
µ
m o a MALG ilm con aining 5 w .% o GO. Addi ionally,
he pla elle s o GO, mos ly o ien ed pa allel o he ilm su aces, can be obse ed in he
images o he MALG/GO5 ilms.
Gels 2024,10, 25 9 o 13
Gels 2024, 10, x FOR PEER REVIEW 9 o 14
Figu e 9. Image o he deso p ion solu ions du ing he cou se o MB deso p ion om
MALG/AA/GO5 ilms in HCl (0.01 M, pH = 2) aqueous solu ions.
Figu e 10. Accumula ed MB ex ac ion om a MALG/AA/GO5 used ilm du ing 258 h o i s imme -
sion in diffe en HCl aqueous solu ions o pH 2.
2.6. Addi ional Nanocomposi e MALG/AA/GO Films Cha ac e iza ions
Addi ional cha ac e iza ion echniques employed du ing he s udy o he ab ica ed
ilms, such as c oss-sec ional SEM images and powde XRD diff ac og ams, a e p o ided
in he suppo ing in o ma ion. The XRD diff ac og am o a me hac yla ed algina e ilm
(Figu e S1) shows a cha ac e is ic highly amo phous signal o algina e wi h a maximum
o a ound 26° wi h a shoulde o his le a ound 12–15°, co esponding o he GO maxi-
mum peak. This diff ac og am is simila o o he s epo ed in he li e a u e o algina e-
based ilms con aining GO [28]. Meanwhile, in he c oss-sec ional SEM images p o ided
in Figu e S2, he hickness o wo ilm samples can be measu ed, esul ing in 21 µm o
p is ine MALG ilm and 29 µm o a MALG ilm con aining 5 w .% o GO. Addi ionally,
he pla elle s o GO, mos ly o ien ed pa allel o he ilm su aces, can be obse ed in he
images o he MALG/GO5 ilms.
3. Conclusions
This esea ch wo k p obed he possibili y o easily ab ica ing algina e-based hyd o-
gel-like ilms o ea dye-con amina ed was ewa e . The use o hese adso p ion echnol-
ogies has al eady shown high efficiencies o dye emo al, which, oge he wi h hei com-
posi ion based on abundan and inexpensi e biopolyme s, may p oduce new solu ions
ha a e affo dable e en o de eloping coun ies whe e hese p oblems end o be mo e
acu e. Howe e , algina e ilms lack he mechanical p ope ies o wi hs and hei manipu-
la ion and in eg a ion in complex wa e ea men sys ems. Thus, his esea ch showed
how he inclusion o g aphene oxide in algina e-based ilms can g ea ly imp o e hei
mechanical p ope ies, leading o s o age modulus alues inc eased by a ac o o 2.5. This
imp o emen may allow, o example, he use o hese sel -s anding ilms in applica ions
0 25 50 75 100 250 275
0
20
40
60
80
100
MB ex ac ed (%)
ime (h)
Figu e 10. Accumula ed MB ex ac ion om a MALG/AA/GO5 used ilm du ing 258 h o i s
imme sion in di e en HCl aqueous solu ions o pH 2.
3. Conclusions
This esea ch wo k p obed he possibili y o easily ab ica ing algina e-based hyd ogel-
like ilms o ea dye-con amina ed was ewa e . The use o hese adso p ion echnologies
has al eady shown high e iciencies o dye emo al, which, oge he wi h hei composi-
ion based on abundan and inexpensi e biopolyme s, may p oduce new solu ions ha
a e a o dable e en o de eloping coun ies whe e hese p oblems end o be mo e acu e.
Howe e , algina e ilms lack he mechanical p ope ies o wi hs and hei manipula ion
and in eg a ion in complex wa e ea men sys ems. Thus, his esea ch showed how he
inclusion o g aphene oxide in algina e-based ilms can g ea ly imp o e hei mechanical
p ope ies, leading o s o age modulus alues inc eased by a ac o o 2.5. This imp o e-
men may allow, o example, he use o hese sel -s anding ilms in applica ions wi h
highe wa e low a es. Fu he mo e, he a ini y o GO o some dyeing p oduc s, such
as me hylene blue, ha can be apped on o/be ween GO laye s, has he e ec o g ea ly
inc easing hei adso p ion e iciency. Al hough some s udies ha e been made o he
po en ial eusabili y o hese ilms, wi h good esul s o hei d ying imes (35 min) once
unsubme ged, imp o emen s on he abso bed dye ex ac ion s a egy need o be achie ed,
as he ea men wi h acidic solu ions p o ed no o be enough by ex ac ing ba ely hal o
he amoun o he abso bed dye.
4. Ma e ials and Me hods
4.1. Ma e ials and P oduc s
Sodium algina e (SA), me hac ylic anhyd ide (MA,
≥
94%), sodium hyd oxide pelle s
(99%), glacial ace ic acid (HAc), ac ylic acid (AA), I gacu e-2959 pho o-ini ia o and me hy-
lene blue (MB) we e pu chased om Sigma-Ald ich (S . Louis, MI, USA). G aphene oxide
(GO) powde was p o ided by G aphenea (San Sebas ian, Spain).
4.2. Me hac yla ion o Polysaccha ides
Me hac yla ed algina e was syn hesized h ough es e i ica ion o hyd oxyl g oups
o algina e wi h MA. B ie ly, a 2% w/ SA solu ion in deionized wa e was p epa ed and
adjus ed o pH = 8 using 5 M aqueous solu ion o NaOH. In he cou se o he i s wo hou s
o eac ion ime, MA a 20- old excess was added slowly, while main aining he empe a u e
a 4
◦
C unde igo ous s i ing. Du ing his ime, pH was con inuously moni o ed o be
o e a alue o 8, adjus ing when necessa y by adding 5 M NaOH. Then, he solu ion was
kep in a e ige a o o 22 h a 40
◦
C o he eac ion o comple e. Modi ied algina e was
pu i ied by dialysis (cellulose memb anes, molecula weigh cu -o
−
3.5 kDa, Medicell
Memb anes L d., London, UK) agains 2 L o deionized wa e , wi h wa e pe iodically
changed 8 imes o e 96 h o emo e un eac ed MA. By eeze-d ying he dialyzed MA
