Insigh in o he TiO
2
nanos uc u es s abilized wi h cashew ee gum o
emo e eme ging con aminan s as a g een echnology
Ma celo Xis o Ribei o
a
, F ancisca P. A aujo
a
, Edson Ca alcan i da Sil a-Filho
a
,
Luciano C. Almeida
b
, Du cilene Al es da Sil a
a
, Ram´
on R. Pe˜
na Ga cia
a,c
,
Juan An onio Cecilia
d
, Ma celo Ba bosa Fu ini
a
, Josy A. Osajima
a,*
,
Ma ia Del Ma O a Cue as
e,*
a
Fede al Uni e si y o Piauí, In e disciplina y Labo a o y Ad anced Ma e ials, Te esina, PI, B azil
b
Fede al Uni e si y o Pe nambuco, Chemical Enginee ing Depa men , Reci e, PE, B azil
c
Fede al Uni e si y o Pe nambuco, Cabo de San o Agos inho Academic Uni , Cape S . Augus ine, PE, B azil
d
Depa men o Ino ganic Chemis y, C ys allog aphy, and Mine alogy, Facul y o Sciences, Uni e si y o M´
alaga, M´
alaga 29071, Spain
e
Depa amen o de Química Analí ica, Facul ad de Fa macia, Uni e sidad de Se illa, C/P o eso Ga cía, Gonz´
alez 2, Se illa 41012, Spain
ARTICLE INFO
Keywo ds:
Plan polysaccha ide
S abilize
Nanos uc u es
Dye
D ugs
ABSTRACT
Sea ching o echnologies o comba eme ging pollu an s such as dyes and pha maceu icals is a duous. Plan
polysaccha ides ha e been used o syn hesize pho oca alys s as s a egies o g een echnology. The p esen s udy
aimed o syn hesize TiO
2
nanos uc u e pho oca aly ic using cashew ee gum. S uc u al, mo phological, and
op ical cha ac e iza ion was ca ied ou o e i y he gum’s e ec on he g ow h o nanos uc u es. Pho o-
ca aly ic es s we e pe o med wi h Me hylene dye (MB) and Ibup o en (IBP) pollu an s unde UV i adia ion.
S uc u al cha ac e iza ion demons a ed he o ma ion o ana ase- ype TiO
2
, wi h a band gap a 3.15 eV.
Pho oca aly ic assays using CGT showed ha he ma e ial was mo e e icien in emo ing MB (43.17 %) when
compa ed o IBP (29.86 %). In addi ion, sca enge s udies indica ed ha elec ons a e he species in ol ed in dye
deg ada ion. The e o e, he esul s a e p omising o using TiO
2
nanopa icles ob ained wi h gum o emo e
pollu an s.
1. In oduc ion
The excessi e and inadequa e elease o ma e ials o ene gy has
caused high pollu ion le els in all he plane ’s ecosys ems. Some p e-
dic ions ha e es ima ed ha a ound 9 millon people die due o pollu ion
yea ly [1]. Rega ding wa e esou ces, pollu ion le els ha e wo sened
due o he high pe cen age o un ea ed was ewa e discha ged in o
su ace wa e bodies and he high a es o chemical con amina ion in
d ainage wa e in some egions o he plane [2]. Among he p ima y
pollu an s a e dyes, pes icides, medicines, beau y p oduc s, ag ances,
and ho mones [3], now known as eme ging pollu an s. Thei p esence
and pe sis ence in wa e , e en in low concen a ions, pose se e e isks o
human heal h and he gene al well-being o o he species in he en i-
onmen [4].
In B azil, ini ial esea ch da es o he 1990s, when pes icides, d ugs,
and ho mones we e iden i ied in di e en aqua ic ma ices [5].
Howe e , s udies ha e been epo ed mo e in ensi ely since 2012 [6],
jus i ied by he ange o oxic subs ances ha we e ound in he a ious
egions o he coun y, om mo e de eloped a eas whe e a high con-
sump ion o pes icides has always been used in ensi ely in ex ensi ely
cul i a ed a eas, o less de eloped a eas plagued by p eca ious basic
sani a ion. Al hough B azil does no ha e o icial me hodologies o
g ouping hese subs ances, egula o y bodies and sani a ion companies
such as he En i onmen al Company o he S˜
ao Paulo S a e and he
B azilian Associa ion o Sani a y and En i onmen al Enginee ing ha e
based hei decisions on academic esea ch [5].
CONAMA Resolu ions, No. 357/2005 [7] and No. 396/2008 [8], as
well as O dinance MS 2914/2011 o he Minis y o Heal h [9], a e he
p incipal egula ions o dealing wi h eme ging pollu an s and a he
same ime ein o ce he weakness o B azilian legisla ion because,
among he housands o eme ging pollu an s iden i ied, only 7 % o all
pes icides au ho ized o use in he coun y a e co e ed by hese
* Co esponding au ho s.
E-mail add esses: [email p o ec ed] (J.A. Osajima), [email p o ec ed] (M.D.M. O a Cue as).
Con en s lis s a ailable a ScienceDi ec
Nano-S uc u es & Nano-Objec s
jou nal homepage: www.else ie .com/loca e/nanoso
h ps://doi.o g/10.1016/j.nanoso.2024.101362
Recei ed 24 June 2024; Recei ed in e ised o m 12 Sep embe 2024; Accep ed 22 Sep embe 2024
Nano-S uc u es & Nano-Objec s 40 (2024) 101362
A ailable online 25 Sep embe 2024
2352-507X/Published by Else ie B.V. This is an open access a icle unde he CC BY license ( h p://c ea i ecommons.o g/licenses/by/4.0/ ).
documen s. I is, he e o e, impe a i e o lea n abou he sou ces,
ans o ma ion, and a e o hese con aminan s using cleane and mo e
economically sound echnologies ha make i possible o p o ec he
en i onmen [5].
De eloping low-cos emedia ion echniques p io i izing he en i-
onmen al componen is essen ial and has mobilized se e al esea ch
g oups. Pho oca alysis is a popula and highly e icien me hod o
emo ing ecalci an compounds om wa e bodies. I consis s o using
sui able ca alys s o accele a e he deg ada ion o o ganic con aminan s
and con e hem om oxic o ha mless o ms [10]. This echnology is
based on ac i a ing a semiconduc o using elec omagne ic adia ion
(UV o isible), which is p eceded by he o ma ion o cha ge ca ie s.
F om his, di e en oxygen adical species can be o med, which des oy
he s uc u e o he a ge molecule h ough oxida ion eac ions. As a
esul , mine aliza ion o he pollu an is expec ed [11–14].
Among some ma e ials wi h pho oca aly ic p ope ies, TiO
2
is a
e e ence semiconduc o in wa e decon amina ion due o i s low cos ,
good s abili y, and high e iciency. Howe e , di icul ies such as he
apid ecombina ion o cha ge ca ie s and he wide in insic band gap
(E
g
=3.2 eV) ha e been epo ed as some o he obs acles o a supe io
pho oca aly ic pe o mance [15]. The e o e, syn hesis s a egies ha e
been sugges ed o e he yea s as al e na i es o inc easing he pho o-
ca aly ic po en ial o TiO
2
, such as la ice doping using me allic and
non-me allic elemen s, immobiliza ion in ma e ials wi h high su ace
a ea, and ob aining he e ojunc ions wi h di e en ca alys s and ma e-
ials [16,17]. Howe e , he p ocess can become expensi e due o he
high cos o some me allic eagen s and he me allic lixi ia ion p ocess
ha can agg a a e he con amina ion scena io [16].
In ecen yea s, he scien i ic communi y’s in e es in de eloping
mo e ecological syn hesis me hods has g own, gi en he need o
a ional use o na u al esou ces and as an al e na i e o minimize isks
o human heal h [18–20]. These me hods a e inse ed in o a se o
p inciples and p ac ices ha encou age he design o p oduc s and
p ocesses ha educe ha m ul e ec s on man and he en i onmen . In
his con ex , using plan -based subs a es o eplace chemical sol en s o
s abilize s is highly ele an , as hey signi ican ly educe he oxici y o
he p ocess [21]. When syn hesizing nanopa icles ha gene ally ha e a
solid endency o agglome a e, plan subs a es s and ou o he p o-
ec i e and s abilizing ac ion o nanopa icles [22].
Gum polysaccha ides a e na u al polyme s exploi ed o ob ain
semiconduc o nanos uc u es due o hei unique s uc u e and unc-
ionali y. I is possible o use a ious ypes o gums wi h di e en
unc ional and s uc u al p ope ies o syn hesize a a ie y o nano-
s uc u es om di e en sou ces wi h s uc u al and unc ional cha -
ac e iza ion sui able o speci ic applica ions, as well as p o iding access
o a ious me al oxides [23,24]. S udies ha e shown ha using gums o
ob ain oxide nanos uc u es di ec ly impac s p ope ies such as
mo phology, su ace a ea, and op ics. All hese pa ame e s can be
decisi e in he pho oca aly ic pe o mance o semiconduc o ma e ials.
The di e si y o B azilian lo a allows egional species o be explo ed as
po en ial subs i u es o hese comme cial gums. The cashew ee
(Anaca dium occiden ale) is a la ge ee common in no heas e n B azil,
and he gum ob ained om he exuda e o he plan unk – Cashew Gum
(CG) – has been men ioned as a possible al e na i e o eplace A abic
gum [25]. CG polysaccha ide is o med om galac ose in i s main chain
(72 %) plus side chains wi h glucose (14 %), a abinose (4.6 %), ham-
nose (3.2 %), and u onic acid (4.7 %) [26]
In o de o expand he use o Anaca dium occiden ale exuda e and
coope a e wi h he de elopmen o wa e emedia ion echnologies
using ecological me hods, his wo k p oposes he syn hesis o TiO
2
using
CG polysaccha ide o emo e Me hylene Blue (MB) dye.
2. Expe imen al pa
2.1. Reagen s
In he syn hesis p ocess we e used he ollowing eagen s: E hyl
alcohol 99.8 % (Ald ich), Ti anium isop opoxide 97 % (Ald ich), CG
gum was collec ed in Pa naiba ci y (Piauí S a e), and ul apu e wa e .
All he eagen s we e analy ical g ade used wi hou p io pu i ica ion.
The cashew ee is egis e ed in SisGen numbe ABD61DA.
2.2. Sample p epa a ion
CG-s abilized TiO
2
nanopa icles we e ob ained by he sol-gel
me hod, acco ding o a p e ious s udy [27,28]. An illus a i e scheme
o he syn hesis is shown in Fig. 1. CG polysaccha ide (2 % w/ ela i e
o he i anium p ecu so - TTIP) was ini ially added o 100.0 mL o he
e hyl alcohol. The mix u e was kep unde magne ic s i ing o 30 min
o comple e homogeniza ion o he gum. Then, a olume (6.0 mL) o
me allic p ecu so was d opped in o he sys em. A e 30 min, an equal
olume o ul apu e wa e was slowly added o he eac ion. The sys em
was s i ed o ano he 30 minu es, and he gel ob ained was aged o
24 h. A e ha , he ma e ial was d ied o e nigh in an o en a 75 ◦C and
calcined a 400 ◦C in an o en o 2 h. The sample was named a CGT.
2.3. Cha ac e iza ion
The ma e ial powde ob ained was s uc u ally cha ac e ized by X-
ay di ac ion (XRD) using a B uke di ac ome e (D8 Ad anced) wi h
Cu-K
α
adia ion and a scan a e 2◦min
−1
. F om he XRD da a, he alues
o c ys alli e size (D) and la ice s ain (
ε
) we e calcula ed using he
Williamson and Hall me hod, exp essed by Eq. 1:
βhklcos(θ) = Kλ
D+4
ε
sinθ(1)
whe e β co esponds o line b oadening a hal maximum in ensi y
(FWHM), θ is B agg’s angle, K is Sche e ’s cons an ha admi s a alue
o 0.9 o he sphe oid o ma , λ is he wa eleng h o Cu K-
α
o he X-
ays used (1.540 Å), D is c ys alli e size, and
ε
ep esen he la ice
s ain. Using a linea adjus men o he da a, he c ys alline size was
es ima ed om he in e cep , and he la ice s ain was es ima ed om
Fig. 1. Schema ic diag am o he syn hesis o TiO
2
by sol-gel me hod.
M.X. Ribei o e al.
Nano-S uc u es & Nano-Objec s 40 (2024) 101362
2
he slope o he linea adjus men .
Di use e lec ance analysis was pe o med using a Shimadzu UV-Vis
spec opho ome e , model UV-3600 wi h di use e lec ance accesso y,
moni o ing he egion be ween 200 and 800 nm. The op ical band gap
(E
g
) was de e mined using Kubelka - Munk unc ion F(R)exp essed in
Eq. 2:
F(R) = (1−R))2
2R=K
S(2)
Whe e he unc ion F(R) co esponds o he abso bance, R is he absolu e
e lec ance, K is he abso p ion coe icien , and S is he sca e ing co-
e icien
The unc ion F(R) is di ec ly p opo ional o he abso p ion coe i-
cien
α
, as demons a ed in Eq. 3:
F(R)h
υ
≈ (h
ν
−Eg)n(3)
whe e: h is he Planck cons an , ʋ is he equency, and n co esponds o
he di e en ansi ions (di ec o indi ec ). The band gap ene gies (E
g
)
can be es ima ed om a plo ing (
α
h
ν
)2 e sus he pho on ene gy (h
ν
),
conside ing he in e sec ion o he ex apola ed linea pa .
Su ace mo phology was ob ained h ough Scanning Elec on Mi-
c oscopy using TESCAN MIRA3 FIB-SEM equipmen , and a semi-
quan i a i e analysis o he su ace o he sample was pe o med using
an Ene gy Dispe si e Spec oscopy (EDS) analyze coupled o SEM
equipmen .
2.4. Pho oca aly ic expe imen
The pho oca aly ic ac i i y o TiO
2
was in es iga ed h ough he
deg ada ion o MB (1.0×10
−5
mol.L
−1
) unde UV i adia ion. Thus,
0.5 g.L
−1
o he pho oca alys was added o 200 mL o pollu an solu-
ion. The adso p ion equilib ium was eached in 30 min in he da k. The
es s we e conduc ed in a bo osilica e eac o unde magne ic s i ing
and s ic empe a u e con ol (25◦C ±1◦C). The ligh sou ce was a
comme cial lamp (160 W) whose po ency was moni o ed using a adi-
ome e (HANNA – HI 97500 – Luxme e ). Du ing he pho oca aly ic es ,
aliquo s we e emo ed a di e en imes 0, 5, 10, 15, 30, 45, 60, 90 and
120 min). A e i adia ion, he samples we e immedia ely cen i uged,
and he abso bance measu emen s we e ca ied ou in a CARY 300
model spec opho ome e . The deg ada ion a e was de e mined by he
Eq. 4:
Deg ada ion =(C0−C)
C0x100 (4)
C
0
and C ep esen he ini ial concen a ion o he pollu an a e he
de e mined i adia ion ime, espec i ely. The ecyclabili y o CGT in
consecu i e cycles o pho oca alysis was also in es iga ed, and emo al
capaci y was de e mined in each case. The ole o eac i e species p o-
duced by CGT in he pho oca alysis o con aminan s was s udied in an
inhibi o es . Thus, he eagen s e hylenediamine acid – EDTA
(2.4×10
−6
mol L
−1
), Isop opyl alcohol - IPA (1.6×10
−6
mol L
−1
), o
sil e ni a e (5.0×10
−4
mol L
−1
), inhibi o s o he hole (h
+
), hyd oxyl
adical (
•
OH) and elec ons (e
-
), espec i ely, we e added o he eac ion
medium and he deg ada ion a e de e mined in each case.
3. Resul s and discussion
3.1. Cha ac e iza ion
The s uc u al cha ac e iza ion o he CGT samples using XRD ana-
lyses and di ac og ams is shown in Fig. 2. Peaks we e iden i ied a 2θ =
25.7◦, 37.9◦, 47.7◦, 54.6◦, 62.8◦, 69.9◦, 75.6◦and 82.5◦ ha co e-
sponding o planes (101), (004), (200), (211), (204), (116), (215) and
(224), espec i ely, conside ing JCPDS (21–1272) ca d o TiO
2
in
ana ase phase [29,30]. Addi ional peaks ela i e o o he phase we e no
iden i ied in he di ac og am. This esul indica es ha he syn hesis
me hod allowed c ys alline s uc u es o ana ase TiO
2
o be ob ained.
Based on he XRD esul , he c ys alli e size was es ima ed using he
Williamson-Hall me hod [31], ob aining he alues a 0.48309 nm o
he c ys alli e size and 0.12443 o la ice s ain. He ein, gum poly-
saccha ide plays a hole p o ec i e du ing he g ow h o nanopa icles,
s abilizing hem and hinde ing he diso de ly g ow h o hese s uc u es
[32–34]. The possible mechanism in ol ed in he g een syn hesis o
TiO
2
nanopa icles in ol es he educ ion o he i anium p ecu so by
bioac i e educing g oups, o ming nuclei and g ow h o TiO
2
, and
s abilizing he nanopa icles by he g een agen used [35]. In he i s
case, he Ti
4+
p esen in he me al p ecu so unde goes hyd olysis,
o ming i anium hyd oxide species (Ti(OH)
4
). The dona ion o elec ons
o Ti(IV) by he educing agen s allows he educ ion o Ti(IV) o lowe
oxida ion s a es, such as Ti(III). Then, nuclei a e o med, which g ow
and o igina e TiO
2
nanopa icles. Du ing his p ocess, polysaccha ides
can be adso bed on he su ace o he nanopa icles, s abilizing hem and
inhibi ing he diso de ed g ow h o he s uc u es [36]. FTIR echnique
was used o in es iga e he unc ional g oups in he CGT s uc u e, as
shown by he spec um in Fig. 3. The band a 3336 cm
−1
is a ibu ed o
s e ching ib a ion in he O-H bond [37]. The band obse ed a
Fig. 2. XRD di ac og am o he CGT syn hesized by sol-gel me hod and cal-
cina ed a 400
◦C.
Fig. 3. FTIR analysis CGT sample.
M.X. Ribei o e al.
Nano-S uc u es & Nano-Objec s 40 (2024) 101362
3
1632 cm
−1
may be ela ed o ib a ion in he C
–
–
O bond, p esen in he
u onic g oups ound in he gum [34]. O he bands iden i ied in 1390 and
1145 cm
−1
a e due o O-H ib a ion in he acid g oups and C–O
s e ching ib a ions, espec i ely [38,39]. In gene al, bands associa ed
wi h ib a ions o Ti-O and Ti-O-Ti bands a e ound in he egion below
800 cm
−1
[40]. Thus, i is possible o a i m ha he band ound a
665 cm
−1
in he CGT spec um is ypical o ib a ion in he
me al-oxygen bond.
The mo phology o he CGT ma e ial was in es iga ed using he SEM
echnique, and he image is shown in Fig. 4a. As seen, an agglome a ion
o nanopa icles was obse ed. Addi ionally, semi-quan i a i e analysis
was pe o med using he EDS echnique (Fig. 4b), whe e he p esence o
peaks associa ed wi h Ti anium (Ti) and Oxygen (O), which a e ela ed
o TiO
2
was no ed. O he peaks iden i ied, such as Ca bon (C) and Gold
(Au), a e due o he sample p epa a ion p ocess and ca bon ape ixa ion
in he sample holde .
The UV–Vis e lec ance analysis was pe o med o de e mine he
op ical band gap ene gy (Eg), an essen ial measu emen o ma e ials
wi h pho oca aly ic p ope ies. These esul s a e demons a ed in Fig. 5.
An Eg alue a 3.15 eV was ound om he da a, and successi e ma h-
ema ical ans o ma ions showed in 2.3 sec ion. The sligh dec ease in
he band gap ene gy alue has been epo ed in o he s udies in ol ing
Fig. 4. (a) CGT mo phology in es iga ed by SEM demons a ing he p esence o TiO
2
nanopa icles and (b) semi-quan i a i e analysis o he ma e ial pe o med
by EDS.
Fig. 5. (a) Band gap ene gy (Eg) calcula ed om he Kubelka-Munk me hod
and (b) size dis ibu ion.
Fig. 6. (a) Ni ogen adso p ion and (b) po e olume o he CGT sample.
M.X. Ribei o e al.
Nano-S uc u es & Nano-Objec s 40 (2024) 101362
4
he p oduc ion o TiO
2
nanopa icles using ma e ials o na u al o igin
[27,35,41,42]. Fo example, using Ka aya Gum, [26] obse ed an Eg
alue g ea e han 3.20 eV o TiO
2
nanopa icles syn hesized wi h
Ka aya gum. In ano he s udy epo ed in he li e a u e, he syn hesis o
TiO
2
using plan ex ac esul ed in a ma e ial wi h a band ene gy o
3.13 eV [35]. This beha io is due o he o ma ion o su ace de ec s in
TiO2 ha ac as elec on aps and hinde he elec on-hole pai ’s
ecombina ion. Fo pho oca aly ic applica ions, his is ad an ageous
because he cha ge ca ie s o med become mo e a ailable o igge
edox eac ions ha will cause he deg ada ion o he pollu an .
N
2
adso p ion-deso p ion iso he m o he p epa ed CGT sample is
shown in Fig. 6a. The iso he m pa e n demons a ed o be ype IV,
conside ing he In e na ional Union o Pu e and Applied Chemis y
(IUPAC) classi ica ion, wi h an H3 hys e esis loop [43,44]. I indica es
ha CGT has a mesopo ous s uc u e [28,40]. Based on he iso he ms,
he speci ic su ace a ea (S
BET
) was 110 m
2
.g
−1
. This esul is supe io o
ha demons a ed in a s udy in which TiO
2
was syn hesized using
Ka aya Gum [27]. A high su ace a ea indica es g ea e a ailabili y o
eac i e si es. Thus, eac ions ha occu in he su ace egion, such as
pho oca alysis, can bene i ma e ials wi h an inc ease in his pa ame e .
The inse g aph o Fig. 6b shows he size dis ibu ion. The nanopa icles
showed a concen a ed size dis ibu ion be ween 5 and 20 nm, con-
i ming he exis ence o mesopo es [45].
3.2. Pho oca aly ic es
The pho oca aly ic esponse o he CGT sample unde UV i adia ion
was es ed agains MB dye and IBP d ug, conside ed a model pollu an in
se e al pho oca alysis s udies [28,46–48]. Va ia ions in concen a ion
a MB e IBP due o he pho oca aly ic ac i i y o CGT we e moni o ed by
UV– is analysis, and he esul s a e shown in Fig. 7a-b. As seen, he
ypical band o each pollu an dec eased du ing he pho oca alysis es .
Fu he mo e, an inc ease in abso p ion in he egion be ween 240 and
300 nm o he IBP spec um was e idenced. This beha io is expec ed in
IBP deg ada ion and has been epo ed in p e ious s udy [49]. Unde a
quan i a i e app oach, he C/C
0
a io was ob ained, shown in Fig. 7c,
and MB and IBP emo al capaci y by CGT sample was de e mined
du ing he expe imen . Fo MB, in da k adso p ion, dye emo al was
37.08 %. A e 120 min o UV i adia ion, he pe cen age o MB
emo ed was 43.17 %. Fo he es pe o med in he IBP solu ion, CGT’s
adso p ion by his pollu an is i ele an , sugges ing ha CGT has a
g ea e a ini y o MB. A e 120 min o i adia ion, he capaci y o IBP
emo al was 29.86 %. The deg ada ion kine ics we e in es iga ed using
he pseudo- i s -o de model. Plo ing ln C/C
0
e sus ime i adia ion
and ob aining he linea i o he da a, as seen in Fig. 7d, whe e he
slope ep esen s he eac ion a e cons an s (k) o he con aminan so-
lu ion i adia ed [50]. The alues ound we e 4.71×10
−3
and
3.75×10
−3
min
−1
o MB and IBP deg ada ion, espec i ely.
When TiO
2
is i adia ed wi h adequa e wa eleng h, holes (h
+
) a e
o med in he alence band (VB) due o he elec onic jump om hem o
Fig. 7. Pho oca aly ic ac i i y in an expe imen using CGT sample: spec al a ia ion o (a) MB and (b) IBP, (c) C/C
0
a io, and (d) kine ic a e.
M.X. Ribei o e al.
Nano-S uc u es & Nano-Objec s 40 (2024) 101362
5

he conduc ion band (CB). Thus, pho ogene a ed cha ge ca ie s eac
wi h molecules ado ed on he su ace o he semiconduc o . Fo
example, in VB, he holes p omo e he oxida ion o H
2
O molecules,
p oducing hyd oxyl adicals (
•
OH). Simul aneously, elec ons in CB
cause he educ ion o O
2
molecules, o ming supe oxide anions. A e
successi e eac ions,
•
OH adicals a e also gene a ed. The powe o
•
OH
adicals in pho oca aly ic sys ems has been epo ed in he deg ada ion
o di e en pollu an s [51,52]. The deg ada ion o MB on he TiO
2
su ace has been epo ed in he li e a u e h ough he classical mech-
anism as shown in he Eqs. (5–8) below [50,53,54]:
TiO
2
+h
ν
→ h
+(VB)
+e
- (CB)
(5)
h
+(VB)
+H
2
O
(adso bed)
→Н
+
+ΟН
•
(adso bed)
(6)
e
- (CB)
+O
2
→ O
2
•

(7)
MB +OH
•
→ In e media e pho op oduc s (8)
Sca enge s udies we e pe o med o iden i y eac i e species
in ol ed in he pho oca aly ic ac i i y o CGT pho oca alys s. Thus,
AgNO
3
, EDTA, o IPA eagen s we e added o he sys em as inhibi o s o
elec ons, holes, and hyd oxyl adicals. As seen in Fig. 8, a e
120 minu es o i adia ion, he MB emo al capaci y was 51.4, 24.6, and
18.2 % in he es s pe o med wi h EDTA, IPA, and AgNO
3
, espec i ely.
Compa ing hese esul s wi h each o he , he ac i i y o he species
in ol ed in he CGT pho oca aly ic esponse is in he ollowing o de : e
-
>
•
OH >h
+
. The ab up dec ease in he deg ada ion a e o MB in he
p esence o AgNO
3
indica es ha elec ons a e he main species in ol ed
in he pho oca aly ic ac i i y o CGT. I is known ha he Ag
+
ions ac by
seques e ing he pho ogene a ed elec ons du ing semiconduc o ac i-
a ion [55]. Thus, he inhibi ion o elec ons caused a d ama ic educ-
ion in he a e o MB deg ada ion. Simila beha io was obse ed o
modi ied TiO
2
nanopa icles [48]. Based on hese esul s, a p oposed
mechanism in ol ed in he pho oca aly ic ac i i y o MB is shown in
Fig. 9.
Pho oca alys euse expe imen s we e pe o med o e i y he s a-
bili y o he ma e ial in consecu i e pho oca aly ic es s. These esul s
a e p esen ed in Fig. 10. The abili y o CGT o emo e he pollu an
du ing euse es s was 32.3, 27.4, 23,.7, and 19.5 % a e he i s , sec-
ond, hi d, and ou h cycles, espec i ely. The dec ease in pho o-
ca aly ic e iciency du ing euse can be explained by he pa ial
deac i a ion o he ma e ial su ace due o accumula ed in e media es,
as epo ed in o he s s udies [56,57].
Fig. 8. Inhibi o es in pho oca alysis media ed by CGT ma e ial.
Fig. 9. Mechanism in ol ed in he MB emo al by CGT pho oca alysis.
Fig. 10. Pe cen age o pho o discolo a ion o MB solu ion a e consecu-
i e cycles.
M.X. Ribei o e al.
Nano-S uc u es & Nano-Objec s 40 (2024) 101362
6
4. Conclusion
TiO
2
nanos uc u es ana ase ype can be syn hesized by using s a-
bilized cashew gum. The pho oca alys demons a ed an excellen abil-
i y o emo e MB dye pollu an emo al. The su ace a ea mus ha e
con ibu ed o he pollu an emo al because hese p ocesses occu a
he solid-liquid in e ace. In he pho oca aly ic emo al o MB by CGT,
elec ons a e an impo an species, as obse ed in inhibi o es s. In-
e media e pho op oduc s om MB deg ada ion can accumula e on he
CGT su ace, dec easing he ma e ial’s deg ada ion e iciency. Finally,
TiO
2
syn hesized wi h na u al polysaccha ides may be a candida e o
pollu an emo al.
CRediT au ho ship con ibu ion s a emen
Ma celo Xis o Ribei o Xis o Ribei o: W i ing – o iginal d a ,
In es iga ion, Da a cu a ion. Ma ía del Ma O a Cue as: Resou ces,
Funding acquisi ion. Josy A. Osajima: Supe ision, P ojec adminis-
a ion. Ma celo Ba bosa Fu ini: W i ing – e iew & edi ing. Juan
An onio Cecilia: W i ing – e iew & edi ing. Ram´
on R. Pe˜
na Ga cia:
Fo mal analysis. Du cilene Al es da Sil a: W i ing – e iew & edi ing.
Luciano C. Almeida: Me hodology. Edson Ca alcan i da Sil a-Filho:
Visualiza ion. F ancisca P. A aújo: Fo mal analysis.
Decla a ion o Compe ing In e es
The au ho s decla e ha hey ha e no known compe ing inancial
in e es s o pe sonal ela ionships ha could ha e appea ed o in luence
he wo k epo ed in his pape .
Da a a ailabili y
No da a was used o he esea ch desc ibed in he a icle.
Acknowledgmen s
The au ho s hank he CAPES, CNPq, FAPEPI and hei ins i u es:
UFPI, UFRPE, UFPB, Uni e sidad de Malaga, Uni e sidad de Se illa, and
In e disciplina y Labo a o y o Ad anced Ma e ials - LIMAV o
p o iding wo k esea ch condi ions and he Fundacíon Ca olina o
ellowship.
INCT/ Polysaccha ides (Na ional Technology-Science Ins i u e o
Polysaccha ides. This wo k was pa ially suppo ed by B azilian
agencies CNPq, CAPES and FAPEPI.
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