Co esponding au ho : Nguyễn Đình Thuấ
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P epa a ion and cha ac e iza ion o ac i a ed ca bon om b own algae (Sa gassum
sp.) using phospho ic acid ac i a ion o hea y me al adso p ion
Lê Xuân Sơn 1, Nguyễn Đình Thuấ 2, * and Dang Xuan Cuong 3
1 Phu Yen Voca ional College, Tuy Hoa awa d, Đăk Lăk 560000, Vie nam.
2 Ins i u e o Oceanog aphy, VAST, 650000 Khanh Hoa, Vie nam.
3 Ho Chi Minh Ci y Uni e si y o Indus y and T ade, 700000 Ho Chi Minh, Vie nam.
GSC Biological and Pha maceu ical Sciences, 2025, 33(01), 073-079
Publica ion his o y: Recei ed on 25 Augus 2025; e ised on 05 Oc obe 2025; accep ed on 07 Oc obe 2025
A icle DOI: h ps://doi.o g/10.30574/gscbps.2025.33.1.0381
Abs ac
Keywo ds: B own seaweed; Ac i a ed ca bon; Zinc chlo ide ac i a ion; C ⁶⁺ adso p ion; Hea y me als; Sus ainable
wa e ea men ; Mic opo osi y; Bio-based adso ben
1 In oduc ion
The inc easing con amina ion o wa e esou ces by hea y me als such as lead (Pb²⁺), cadmium (Cd²⁺), and me cu y
(Hg²⁺) has aised se ious en i onmen al and public heal h conce ns globally. Unlike o ganic pollu an s, hea y me als
a e non-biodeg adable, pe sis in ecosys ems, and end o bioaccumula e in he ood chain, leading o se e e
oxicological e ec s in humans and animals [1,4]. Con en ional emedia ion echnologies such as chemical p ecipi a ion,
ion exchange, and memb ane il a ion a e o en cos ly, ine icien a low concen a ions, and gene a e seconda y was e
[6].
Ac i a ed ca bon (AC) has been widely ecognized as a highly e ec i e adso ben o hea y me al emo al due o i s
high su ace a ea, po osi y, and su ace unc ional g oups [2]. Howe e , comme cial ac i a ed ca bons a e ypically
de i ed om non- enewable sou ces like coal o pe oleum-based ma e ials, leading o conce ns abou sus ainabili y
and p oduc ion cos .
In ecen yea s, he e has been g owing in e es in he de elopmen o bio-based ac i a ed ca bons om ag icul u al o
ma ine was e, aligning wi h ci cula economy p inciples and sus ainable de elopmen goals. Among ma ine biomass
esou ces, b own seaweed (Sa gassum spp.) is pa icula ly p omising due o i s abundance in opical and sub opical
egions, high ca bon con en , and na u al composi ion o polysaccha ides such as algina e, ucoidan, and lamina in,
which can se e as e icien ca bon p ecu so s [3,5].
This s udy p esen s he success ul p epa a ion and e alua ion o ac i a ed ca bon de i ed om b own seaweed
(Sa gassum sp.) was e using chemical ac i a ion wi h zinc chlo ide (ZnCl₂) and he mal ea men . The esul ing
bioso ben was cha ac e ized by i s iodine numbe , su ace mo phology, and adso p ion e iciency o hexa alen
ch omium (C ⁶⁺) ions in aqueous solu ions. The ac i a ed ca bons exhibi ed high mic opo osi y, wi h iodine numbe s
eaching 290 mg/g a 800 °C, closely compa able o comme cial ac i a ed ca bon. SEM analysis e ealed a po ous
su ace s uc u e, suppo ing i s high adso p ion capaci y.
Ba ch adso p ion expe imen s demons a ed ha C ⁶⁺ emo al e iciency was s ongly in luenced by solu ion pH,
ini ial ion concen a ion, and con ac ime. Op imal emo al (>90%) was achie ed a pH 2, low me al concen a ions,
and a con ac ime o 120 minu es. The bio-based ac i a ed ca bon showed p omising po en ial as a cos -e ec i e and
en i onmen ally iendly ma e ial o hea y me al emedia ion. This app oach con ibu es o sus ainable was e
alo iza ion and suppo s ci cula economy p ac ices.
GSC Biological and Pha maceu ical Sciences, 2025, 33(01), 073-079
74
This s udy aims o de elop a cos -e ec i e and en i onmen ally iendly ac i a ed ca bon om Sa gassum spp. collec ed
om Vie namese coas al a eas. Using chemical ac i a ion wi h phospho ic acid (H₃PO₄) and subsequen he mal
ca boniza ion, he esul an bioso ben was cha ac e ized o i s physicochemical p ope ies (su ace a ea, po e
s uc u e, and unc ional g oups) and e alua ed o i s e iciency in emo ing hea y me als (Pb²⁺ and Cd²⁺) om
aqueous solu ions. The esea ch no only con ibu es o sus ainable wa e ea men echnologies bu also alo izes
ma ine biomass was e, hus p omo ing bo h en i onmen al p o ec ion and esou ce eco e y.
2 Ma e ial and me hods
2.1 P epa a ion o seaweed esidue biomass
B own seaweed was e (Sa gassum sp.) was collec ed om he p ocessing si e, ho oughly washed i s wi h ap wa e
and hen wi h dis illed wa e o comple ely emo e sal s and o he impu i ies. The cleaned biomass was ai -d ied unde
ambien condi ions, g ound o a ine powde , and hen sie ed o ob ain wo pa icle-size ac ions: ma e ial MA wi h
pa icle size less han 0.5 mm and ma e ial MB wi h pa icle size g ea e han 0.5 mm. Bo h ac ions we e placed in
ai igh con aine s o p e en mois u e up ake and s o ed o subsequen expe imen s.
2.2 Chemical ac i a ion and ca boniza ion
Twen y g ams (20 g) o d ied seaweed powde om each ac ion was soaked in 200 mL o 20% (w/ ) zinc chlo ide
(ZnCl₂) solu ion. The mix u e was s i ed con inuously o 2 hou s o ensu e uni o m imp egna ion. A e soaking, he
excess ZnCl₂ solu ion was decan ed, and he imp egna ed biomass was d ied in a ho -ai o en a 100 ± 2 °C o 24 hou s.
The d ied, ZnCl₂-imp egna ed biomass was hen ans e ed in o ce amic c ucibles and subjec ed o py olysis in a
mu le u nace unde limi ed ai supply. Two ca boniza ion empe a u es we e es ed: 600 °C and 800 °C, wi h a
esidence ime o 2 hou s. The u nace empe a u e was inc eased apidly om oom empe a u e o he a ge
empe a u e.
2.3 Pos - ea men and washing
A e ca boniza ion, he ac i a ed ca bon was allowed o cool and hen washed wi h 0.5 N HCl o emo e esidual ZnCl₂.
The sample was u he insed wi h wa m dis illed wa e un il he washings eached neu al pH (~7.0), indica ing he
comple e emo al o ee Zn²⁺ ions. The cleaned ca bon was d ied a 105 °C o 12 hou s in a ho -ai o en. The inal
p oduc was weighed o de e mine he ca bon yield.
2.4 De e mina ion o Iodine Numbe
The iodine numbe , which e lec s he mic opo osi y and adso p ion capaci y o ac i a ed ca bon, was de e mined using
he s anda d iodine adso p ion me hod. In his p ocedu e, 0.1 g o ac i a ed ca bon was accu a ely weighed in o a
200 mL E lenmeye lask and mixed wi h 40 mL o a s anda d iodine solu ion o known ini ial concen a ion (C₁, mol/L).
The mix u e was shaken o 15 minu es o ensu e comple e adso p ion equilib ium. A e equilib a ion, he esidual
iodine in he solu ion was i a ed wi h 0.05 M sodium hiosul a e (Na₂S₂O₃) using s a ch as an indica o . The iodine
numbe (Q, mg/g) was hen calcula ed om he ini ial and inal iodine concen a ions and olumes acco ding o he
ollowing ela ionship:
Q=mAC(C1V1−C2V2)×mI
𝑄 = (𝐶1𝑉1− 𝐶2𝑉2)𝑚𝐼
𝑚𝐴𝐶
whe e C1 and C2 a e he ini ial and equilib ium iodine concen a ions (mol/L), V1 and V2 a e he ini ial and inal olumes
(mL), mI is he molecula weigh o iodine (254 g/mol), and mAC is he mass o ac i a ed ca bon used (g).
2.5 Cha ac e iza ion o Ac i a ed Ca bon
Su ace Mo phology: The mo phological s uc u e o he ac i a ed ca bon was obse ed using Scanning Elec on
Mic oscopy (SEM), which e ealed he de elopmen o po ous ca i ies a e ac i a ion.
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2.6 Da a analysis
Da a was analysed wi h desc ip i e s a is ics and emo ed ou lie s using he Duncan me hod.
3 Resul s and discussion
3.1 Iodine numbe o ac i a ed ca bon
The iodine numbe , an impo an indica o o mic opo osi y and adso p ion capaci y o ac i a ed ca bon, was used o
e alua e he quali y o he p epa ed bio-based ac i a ed ca bons. As shown in Table 1, he iodine numbe a ied wi h
ac i a ion empe a u e and ype o ca bon:
Table 1 Iodine numbe o ac i a ed ca bons a di e en ac i a ion empe a u es
Type o Ac i a ed Ca bon
Iodine Numbe (mg/g)
Ac i a ed ca bon om seaweed a 800 °C
290
Ac i a ed ca bon om seaweed a 600 °C
276
Comme cial ac i a ed ca bon (con ol)
303
Among he h ee ypes, comme cial ac i a ed ca bon exhibi ed he highes iodine numbe (303 mg/g), indica ing i s
supe io mic opo osi y. Howe e , he ac i a ed ca bons p oduced om Sa gassum sp. was e a bo h 800 °C and 600 °C
also showed high iodine alues (290 mg/g and 276 mg/g, espec i ely), demons a ing ha seaweed biomass can be
e ec i ely con e ed in o po ous adso ben s.
No ably, he sample ac i a ed a 800 °C achie ed a highe iodine numbe han ha a 600 °C, sugges ing ha ele a ed
ac i a ion empe a u es enhance he de elopmen o mic opo ous s uc u e, he eby imp o ing he adso p ion
capabili y. This esul is consis en wi h p e ious indings whe e he mal ac i a ion a highe empe a u es o en
inc eases su ace a ea and po e de elopmen .
3.2 E ec o pH on C ⁶⁺ adso p ion capaci y
To u he e alua e he adso p ion pe o mance o he ac i a ed ca bon, he emo al e iciency o hexa alen ch omium
(C ⁶⁺) om aqueous solu ion (10 mg/L) was assessed as a unc ion o pH a e 60 minu es o con ac ime (Figu e 1).
Figu e 1 E ec o pH on C ⁶⁺ adso p ion capaci y
GSC Biological and Pha maceu ical Sciences, 2025, 33(01), 073-079
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As obse ed, he adso p ion e iciency was highly dependen on he solu ion pH. The emo al pe cen age was highes
in acidic condi ions, eaching a peak a a ound pH 2, wi h an e iciency exceeding 70%. As he pH inc eased, he
adso p ion e iciency sha ply declined and pla eaued a pH 5–9, wi h alues below 40%.
This beha io can be a ibu ed o he specia ion o C ⁶⁺ and he su ace cha ge o he ac i a ed ca bon. Unde acidic
condi ions, C ⁶⁺ p ima ily exis s as HC O₄⁻, which in e ac s mo e e ec i ely wi h posi i ely cha ged unc ional g oups
on he ca bon su ace. As pH inc eases, he su ace becomes less p o ona ed and C ⁶⁺ con e s o C O₄²⁻ o C ₂O₇²⁻,
leading o elec os a ic epulsion and educed adso p ion.
These indings sugges ha he adso p ion o C ⁶⁺ on o he bio-based ac i a ed ca bon is mos e ec i e in acidic
en i onmen s, wi h pH 2 being op imal o emo al.
3.3 E ec o C ⁶⁺ concen a ion on he adso p ion e iciency o ac i a ed ca bon
Figu e 2 E ec o C ⁶⁺ concen a ion on he adso p ion e iciency o ac i a ed ca bon
The in luence o he ini ial C ⁶⁺ concen a ion on he adso p ion e iciency o ac i a ed ca bon a pH 2, using 0.6 g o
adso ben , was e alua ed ac oss a concen a ion ange om 10 o 60 ppm. The esul s a e illus a ed in Figu e 2. A clea
dec easing end in adso p ion e iciency was obse ed wi h inc easing me al ion concen a ion.
A he lowes es ed concen a ion (10 ppm), he emo al e iciency eached a maximum o app oxima ely 92%,
indica ing a highly e ec i e in e ac ion be ween he C ⁶⁺ ions and he a ailable adso p ion si es on he ac i a ed ca bon
su ace. Howe e , as he ini ial concen a ion inc eased, he adso p ion e iciency s eadily declined, wi h he lowes
e iciency o a ound 79% eco ded a 60 ppm.
This phenomenon can be explained by he sa u a ion o ac i e si es on he su ace o he adso ben . A low
concen a ions, he numbe o C ⁶⁺ ions is su icien ly small compa ed o he numbe o a ailable adso p ion si es,
acili a ing e ec i e adso p ion. As he concen a ion inc eases, he compe i ion be ween C ⁶⁺ ions o he limi ed
numbe o ac i e si es in ensi ies, leading o a g adual educ ion in emo al e iciency.
Addi ionally, highe me al ion concen a ions may inc ease he ionic s eng h o he solu ion, po en ially in e e ing
wi h he elec os a ic in e ac ions be ween C ⁶⁺ ions and he adso ben su ace. Fu he mo e, a high concen a ions,
di usion limi a ions may a ise, educing he access o C ⁶⁺ ions o in e nal po es o he ac i a ed ca bon.
These indings a e consis en wi h p e ious s udies, which also epo ed a nega i e co ela ion be ween ini ial me al
ion concen a ion and adso p ion e iciency when using a ixed amoun o adso ben unde cons an pH condi ions.
GSC Biological and Pha maceu ical Sciences, 2025, 33(01), 073-079
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3.4 E ec o con ac ime on he adso p ion o C ⁶⁺ Ions
Figu e 3 E ec o con ac ime on he adso p ion o C 6+ ions
Figu e 3 demons a es he signi ican impac o con ac ime on he adso p ion e iciency o C ⁶⁺ ions using 0.6 g o
ac i a ed ca bon a pH 2. The s udy explo ed ini ial concen a ions o C ⁶⁺ anging om 10 o 60 ppm and e alua ed
adso p ion a h ee ime in e als: 15, 60, and 120 minu es. A clea end was obse ed whe ein he emo al e iciency
imp o ed ma kedly wi h inc eased con ac ime. Fo ins ance, a a C ⁶⁺ concen a ion o 10 ppm, he emo al e iciency
inc eased om app oxima ely 53% a 15 minu es o a ound 80% a 120 minu es. This enhancemen can be a ibu ed
o he g adual occupa ion o adso p ion si es as he p ocess p og esses. No ably, he adso p ion capaci y a e 120
minu es consis en ly su passed ha a 60 and 15 minu es ac oss all es ed concen a ions. Howe e , a pla eau in he
emo al e iciency a 120 minu es sugges s ha equilib ium was achie ed, indica ing sa u a ion o mos accessible
adso p ion si es on he ac i a ed ca bon. Beyond his poin , u he inc eases in con ac ime yielded only ma ginal
imp o emen s in adso p ion, implying limi ed a ailabili y o unoccupied o ene ge ically a o able binding si es.
Mechanis ically, he apid up ake in he ini ial phase (15–60 minu es) is likely d i en by he high numbe o a ailable
ac i e si es and a s eep concen a ion g adien , acili a ing as mass ans e . As he si es become p og essi ely illed,
s e ic hind ance, epulsi e elec os a ic o ces, and di usion limi a ions con ibu e o a slowe adso p ion a e. These
indings ha e p ac ical implica ions o he design o ba ch adso p ion sys ems, pa icula ly in was ewa e ea men .
They indica e ha a con ac ime o app oxima ely 120 minu es is op imal o maximize C ⁶⁺ emo al unde he speci ied
condi ions, enabling e ec i e p ocess planning and esou ce u iliza ion.
3.5 Su ace mo phology o ac i a ed ca bon de i ed om b own seaweed was e
The su ace mo phology o he ac i a ed ca bon syn hesized om b own seaweed esidue was examined using
Scanning Elec on Mic oscopy (SEM), as shown in Figu e 4. The mic og aph e eals a ough, ac u ed s uc u e wi h a
highly po ous su ace, cha ac e ized by nume ous i egula c acks, lakes, and ca i ies. This mo phological pa e n
sugges s a well-de eloped ne wo k o mic o- and mesopo es, which is ypical o biocha ma e ials de i ed om
lignocellulosic biomass a e py olysis and chemical ac i a ion.
The po ous ex u e signi ican ly inc eases he su ace a ea a ailable o adso p ion, he eby enhancing he ma e ial’s
capaci y o cap u e C ⁶⁺ ions om aqueous solu ions. The ac u ed laye s and open po e channels acili a e bo h su ace
adso p ion and in e nal di usion o me al ions, which is c ucial o achie ing high emo al e iciency. The o ma ion o
such s uc u es is likely a ibu ed o he decomposi ion o o ganic ma e and elease o ola ile compounds du ing
he mal ea men , esul ing in he expansion and collapse o cellula walls in he seaweed ma ix.
These mo phological ea u es no only con i m he success ul ac i a ion o he seaweed biomass bu also di ec ly
co ela e wi h he high adso p ion pe o mance obse ed in ba ch expe imen s. The abundance o accessible adso p ion
si es, coupled wi h he in e connec ed po e ne wo k, makes his ma e ial a p omising candida e o low-cos , eco-
iendly wa e ea men applica ions, especially in he emo al o oxic hea y me als like C ⁶⁺.
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Figu e 4 Ac i a ed ca bon om b own algae was e unde scanning elec on mic oscope
3.6 P epa a ion p ocessing o ac i a ed ca bon om b own seaweed was e
The p epa a ion o ac i a ed ca bon (AC) om b own seaweed was e was conduc ed ollowing a mul is ep p o ocol
in ol ing size sepa a ion, chemical p e ea men wi h zinc chlo ide, d ying, ca boniza ion, and ac i a ion, as ou lined
below.
3.6.1 Raw ma e ial p epa a ion and ac iona ion
D ied b own seaweed was i s cleaned and milled o emo e impu i ies and educe pa icle size. The milled seaweed
was hen sie ed in o wo size ac ions:
• MA ac ion: pa icles smalle han 0.5 mm (150 g)
• MB ac ion: pa icles la ge han 0.5 mm (160 g)
3.6.2 Imp egna ion wi h ZnCl₂
Each ac ion was subjec ed o chemical ac i a ion ia imp egna ion wi h a 20% w/ solu ion o zinc chlo ide (ZnCl₂):
• MA: mixed wi h 1,500 mL o 20% ZnCl₂
• MB: mixed wi h 1,600 mL o 20% ZnCl₂
The mix u es we e allowed o soak o 24 hou s o ensu e su icien ZnCl₂ pene a ion. Subsequen ly, he imp egna ed
biomass was d ied in a ho -ai o en a 100°C o 24 hou s o emo e mois u e and pa ially ix he ac i a ing agen .
3.6.3 Ca boniza ion and ac i a ion
The d ied, imp egna ed seaweed samples we e subjec ed o ca boniza ion unde he ollowing condi ions:
• Fu nace empe a u e: 600°C
• Hea ing du a ion: 30 minu es
• A mosphe e: limi ed oxygen (semi-closed sys em o a oid comple e combus ion)
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A e ca boniza ion, he esul an cha was washed ho oughly wi h ho dis illed wa e un il he il a e eached neu al
pH, indica ing he emo al o esidual ZnCl₂ and soluble by-p oduc s. The cha was hen o en-d ied a 100°C and
weighed o de e mine yield.
3.6.4 Yield o ac i a ed ca bon
• F om 150 g o MA ac ion, 36 g o ac i a ed ca bon was ob ained (yield: 24%).
• F om 160 g o MB ac ion, 34 g o ac i a ed ca bon was ob ained (yield: 21%).
These esul s sugges ha smalle pa icle size (MA < 0.5 mm) led o sligh ly highe ca boniza ion yield unde he same
ac i a ion condi ions, po en ially due o imp o ed ZnCl₂ pene a ion and mo e e icien hea ans e du ing py olysis.
4 Conclusion
This esea ch demons a ed he success ul p epa a ion o ac i a ed ca bon om b own seaweed was e using ZnCl₂
chemical ac i a ion and con olled he mal ea men . The p ocess p oduced ac i a ed ca bons wi h good yields (24%
o MA and 21% o MB ac ions) and a well-de eloped po ous s uc u e, as con i med by SEM imaging. The ma e ials
exhibi ed high adso p ion e iciency o C ⁶⁺ ions, wi h pe o mance s ongly in luenced by pH, ini ial me al ion
concen a ion, and con ac ime.
These indings indica e ha b own seaweed, a enewable ma ine biomass, can be e ec i ely con e ed in o alue-added
adso ben s o hea y me al emo al om was ewa e . The app oach con ibu es o sus ainable was e managemen and
suppo s ci cula economy p inciples while o e ing a low-cos al e na i e o comme cial ac i a ed ca bons o
en i onmen al emedia ion.
Compliance wi h e hical s anda ds
Disclosu e o con lic o in e es
No con lic o in e es o be disclosed.
Re e ences
[1] Ali H., Khan E., & Ilahi I. (2019). En i onmen al chemis y and eco oxicology o haza dous hea y me als:
En i onmen al pe sis ence, oxici y, and bioaccumula ion. Jou nal o Chemis y 2019; A icle ID 6730305.
h ps://doi.o g/10.1155/2019/6730305
[2] Babel S., & Ku niawan T. A. Low-cos adso ben s o hea y me als up ake om con amina ed wa e : A e iew.
Jou nal o Haza dous Ma e ials 2003; 97(1–3), 219–243. h ps://doi.o g/10.1016/S0304-3894(02)00263-7
[3] Dawood S., & Sen T. K. Remo al o anionic dye Congo ed om aqueous solu ion by aw pine and acid- ea ed
pine cone powde as adso ben : Equilib ium, he modynamic, kine ics, mechanism and p ocess design. Wa e
Resea ch 2012; 46(6), 1933–1946. h ps://doi.o g/10.1016/j.wa es.2012.01.009
[4] Jaishanka M, Tse en T, Anbalagan N, Ma hew BB, Bee egowda KN. Toxici y, mechanism and heal h e ec s o
some hea y me als. In e discip Toxicol 2014; 7(2):60-72. doi: 10.2478/in ox-2014-0009.
[5] Fi o J, Tibebu S, Nkambule TTI. Op imiza ion o C (VI) emo al om aqueous solu ion wi h ac i a ed ca bon
de i ed om Eichho nia c assipes unde esponse su ace me hodology. BMC Chem 2023; 17(1):4. doi:
10.1186/s13065-023-00913-6.
[6] Fu F., & Wang Q. Remo al o hea y me al ions om was ewa e s: A e iew. Jou nal o En i onmen al
Managemen 2011; 92(3), 407–418. h ps://doi.o g/10.1016/j.jen man.2010.11.011
