Ci a ion: T azzi, P.A.; Vashish ha, M.;
Najse , J.; Schmalenbe ge , A.;
Kannuchamy, V.K.; Leahy, J.J.;
Kwapinski, W. Adso p ion o
Ammonium, Ni a e, and Phospha e
on Hyd ocha s and Biocha s. Appl.
Sci. 2024,14, 2280. h ps://doi.o g/
10.3390/app14062280
Academic Edi o s: Luca Fio i and
Filomena De Leo
Recei ed: 5 Decembe 2023
Re ised: 2 Ma ch 2024
Accep ed: 5 Ma ch 2024
Published: 8 Ma ch 2024
Copy igh : © 2024 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/).
applied
sciences
A icle
Adso p ion o Ammonium, Ni a e, and Phospha e on
Hyd ocha s and Biocha s
Paulo And éT azzi 1,2 , Mayank Vashish ha 2, Jan Najse 3, Achim Schmalenbe ge 4,
Vasan h Kuma Kannuchamy 5, James J. Leahy 2and Wi old Kwapinski 2,*
1PPG Ci lo , Uni e sidade Fede al do Ac e, UFAC, BR 364 km 04, Bai o Dis i o Indus ial,
Rio B anco 69920-900, B azil
2Chemical Sciences Depa men , Uni e si y o Lime ick, V94 T9PX Lime ick, I eland
3ENET Cen e, VSB—Technical Uni e si y o Os a a, 708 00 Os a a, Czech Republic; [email p o ec ed]
4Biological Sciences Depa men , Uni e si y o Lime ick, V94 T9PX Lime ick, I eland
5School o Chemis y and Chemical Enginee ing, Facul y o Enginee ing and Physical Sciences,
Uni e si y o Su ey, Guild o d GU2 7XH, UK; .kannuchamy@su ey.ac.uk
*Co espondence: [email p o ec ed]
Abs ac : Biocha (BC) and hyd ocha (HC) ha e a ac ed conside able a en ion owing o hei
e sa ile cha ac e is ics and p o en e ec i eness in di e se echnical ields. Solid BC is gene a ed
as a esul o he d y ca bonisa ion p ocess o py olysis, in con as o he slu y HC, which is
p oduced du ing he hyd o he mal ca bonisa ion p ocess. In his s udy, we e alua ed he adso p ion
po en ial o wo hyd ocha samples (HCs) and h ee biocha samples (BCs) p oduced om suga
cane bagasse. The adso p ion capaci y o hese samples was es ed o ammonium, ni a e, and
phospha e ions unde a ious condi ions. The BCs and HCs we e subjec ed o cha ac e isa ion using
a CHNS/O analyse , he ze a po en ial, and Fou ie ans o m in a ed (FTIR). Ele a ing he py olysis
empe a u e o he biocha esul ed in changes in he ixed ca bon and ash con en s, while he ola ile
ma e and H/C and O/C a omic a ios dec eased. As he esidence ime inc eased, he H/C a io and
ola ile ma e con en o he hyd ocha s (HCs) dec eased. Howe e , he ixed ca bon con en , ash
con en , and O/C and C/N a ios exhibi ed an inc ease. The modynamics, adso p ion iso he ms, and
pH we e also aken in o conside a ion. The FTIR spec a analysis indica ed ha he ca boxyl and es e
unc ional g oups p esen in bo h he BCs and HCs displayed educed peak in ensi ies subsequen o
he adso p ion o he h ee ions. While he adso p ion was exo he mic, we no iced ha he adso p ion
capaci y inc eased wi h empe a u e. The esul s indica e ha so p ion was homogenous ac oss
all binding si es, as e idenced by he op imal i o he Langmui iso he m. The esea ch indings
indica e ha he adso p ion capaci y o a ious BC and HC adso ben s is signi ican ly in luenced by
he su ace a ea o he adso ben s in he case o ni a e and phospha e, bu in he case o ammonia,
adso p ion is dic a ed by he unc ional pola g oups p esen on he adso ben su ace.
Keywo ds: biocha ; hyd ocha ; ca bonisa ion; py olysis; hyd o he mal; adso p ion; iso he ms;
he modynamics
1. In oduc ion
The nomencla u e employed o e e o he esidual ma e ial de i ed om he slow
py olysis o biowas e, which is p ima ily composed o ca bon, is biocha (BC). Con e sely,
he esidual ma e ial ob ained om he hyd o he mal ca bonisa ion (HTC) p ocess, also
called we py olysis, is e e ed o as hyd ocha (HC). Bo h o he a o emen ioned p oduc s
ha e ga ne ed signi ican a en ion owing o hei po en ial applica ions in a a ie y o
enginee ing and indus ial ields [
1
]. The p oduc ion o BC in ol es a py olysis p ocess
ha necessi a es an ex a ene gy inpu o d y he eeds ock. Con e sely, he p oduc ion
o HC enables he u ilisa ion o we eeds ock ha does no equi e d ying du ing he
Appl. Sci. 2024,14, 2280. h ps://doi.o g/10.3390/app14062280 h ps://www.mdpi.com/jou nal/applsci
Appl. Sci. 2024,14, 2280 2 o 19
p ocess. The biomass unde goes a high- empe a u e ea men in he p esence o wa e ,
which se es as a ca alys [2].
BC and HC exhibi p omising cha ac e is ics and s uc u es ha make hem sui able
o u ilisa ion as soil enhance s. These ea u es include he capaci y o enhance c op yield,
acili a e he il a ion o pe cola ing soil wa e , and assimila e a mosphe ic ca bon in
soil [
3
]. The a iances in he cha ac e is ics and unc ions o BC ha ha e been obse ed
a e subjec o he in luence o a ious p ocess pa ame e s [
4
–
8
]. These pa ame e s include
he eeds ock, p ocessing empe a u e, hea ing a e, and esidence ime. The syn hesis o
HC can be achie ed h ough he u ilisa ion o wa e as he eac ion medium a a lowe
empe a u e, esul ing in a mo e cos -e ec i e p ocess compa ed o py olysis. The eac ion
condi ions commonly obse ed in he li e a u e include empe a u es anging om 180 o
260
◦
C, au ogene ic p essu es anging om 2 o 6 MPa, and eac ion imes anging om
30 o 240 min [
9
]. The su ace o HC exhibi s a highe concen a ion o unc ional g oups
con aining oxygen and molecules ha ha e unde gone a oma isa ion. The inco po a ion
o unc ional g oups in o he molecule enhances i s hyd ophilici y, he eby ende ing i
sui able o augmen ing he wa e e en ion capaci y o soil [10].
Dis inguishable a ia ions exis in he physical and chemical cha ac e is ics o BCs and
HCs. The s udy by Takaya and colleagues [
11
] e ealed ha BC and HC exhibi adso p ion
capaci ies anging om a ound 0 o 30 mg
·
g
−1
and 105 o 146 mg
·
g
−1
o phospha e and
ammonium, espec i ely. This obse ed phenomenon can be a ibu ed p ima ily o he
unique physicochemical cha ac e is ics o he subjec in ques ion. The in es iga ion o
he p ope ies and in e ac ion mechanisms o BC and HC adso p ion is c ucial o he
u ilisa ion o soil e ilise s in o de o mi iga e po en ial en i onmen al consequences.
Eu ophica ion is a phenomenon ha occu s in es ua ies and coas al wa e s as a esul o
an o e abundance o ni ogen and phospha e. This p ocess leads o an escala ion in he
g ow h o plan and oxic algae [
12
]. The applica ion o syn he ic e ilise s has been ound
o ha e a posi i e co ela ion wi h he elease o ammonium, ni a e, and phospho us in o
wa e bodies om ag icul u al land [
13
,
14
]. Resea ch [
15
,
16
] indings indica e ha BC and
HC ha e he abili y o impede he up ake o ni ogen and phospho us by he soil. The
u ilisa ion o suga cane bagasse BC has been obse ed o enhance he e en ion ime o
ni a e in he icini y o plan oo s, he eby acili a ing i s up ake by he plan s [
17
]. The
op imal condi ions we e iden i ied o ammonium adso p ion on bamboo cha coal, which
esul ed in he emo al o up o 82.4% o ammonium om an aqueous solu ion [
18
]. As
pe exis ing esea ch, i has been obse ed ha BC has he abili y o solubilise phospha e.
I has also been no ed ha modi ying he concen a ion o BC p esen in soil can lead o
imp o ed ag onomic pe o mance [
19
]. As pe he indings o a p e ious s udy [
20
], i can
be in e ed ha HC exhibi s po en ial as an adso ben o he pu pose o emo ing and
eco e ing phospho us om was ewa e . This is suppo ed by he ac ha HC has shown
o be ema kably e icien in adso bing phospha e ions unde di e en pH condi ions, e en
in he p esence o compe ing anions.
The in es iga ion o he so p ion cha ac e is ics o BC and HC is cu en ly in i s nascen
phase. The majo i y o esea ch in es iga ions ha e concen a ed on he ion adso p ion
capabili ies o BC, whe eas he published indings ega ding HC ha e been no ably limi ed.
Unde s anding he cha ac e is ics o bo h BCs and HCs and hei impac on he adso p ion
mechanisms o ammonium, ni a e, and phospha e is c ucial o he imp o ed managemen
o ni ogen and phospho us in soil and ag onomic p ac ices. The aim o his in es iga ion
is o examine he impac o bio-based eeds ock-de i ed BCs and HCs, p oduced unde
a ious d y and hyd o he mal ca bonisa ion condi ions, on he adso p ion o ammonium,
ni a e, and phospha e.
2. Ma e ials and Me hods
2.1. BC and HC P epa a ion
BC and HC we e ob ained h ough he py olysis and he mal hyd olysis o suga cane
bagasse, espec i ely. The biomass unde wen an ini ial sh edding p ocess esul ing in
Appl. Sci. 2024,14, 2280 3 o 19
agmen s measu ing be ween 2 and 3 cm in leng h. The s udy in ol ed he implemen a ion
o slow py olysis a 300
◦
C, 500
◦
C, and 700
◦
C o a du a ion o 60 min wi hin a ixed-bed
eac o . The BC p oduced a hese empe a u es was labelled as BC300, BC500, and BC700,
espec i ely. The expe imen al se up comp ised a empe a u e con olle cabine , a qua z
ube eac o wi h an inne diame e o 2.5 cm, and an elec ic u nace hea e . The BCs ha
we e acqui ed unde wen a g inding p ocess and we e subsequen ly insed wi h deionised
wa e . A e wa d, hey we e d ied in a u nace a a empe a u e o 105
◦
C o a du a ion o
24 h. The BCs we e hen s o ed in ai igh con aine s a oom empe a u e un il hey we e
eady o u he use.
HC was p oduced by means o a 2G Pa agi a ed p essu e eac o ea u ing a emo -
able glass line . The expe imen al p ocedu e in ol ed he addi ion o 200 g o suga cane
bagasse and 1 L o dis illed wa e in o he glass line , ollowed by ho ough mixing o
a du a ion o 30 min. The essel was he me ically sealed and subjec ed o a con inuous
low o ni ogen gas o a du a ion o 10 min. The expe imen in ol ed subjec ing he
essel and i s con en s o a empe a u e o 250
◦
C while simul aneously agi a ing hem
o 30 and 180 min. This p ocess yielded wo dis inc samples, namely, HC30 and HC180.
Subsequen ly, he essel along wi h i s con en s unde wen apid cooling in a cold-wa e
ba h main ained a oom empe a u e. The HCs we e isola ed h ough he p ocess o
acuum il a ion, ollowed by mul iple washes wi h dis illed wa e . The esul ing HCs
we e hen subjec ed o d ying in an o en se a 105
◦
C o a pe iod o 24 h. Finally, he HCs
we e s o ed in plas ic ecep acles o u he use.
Ac i a ed ca bon (AC) om Sigma-Ald ich was subjec ed o cha ac e isa ion and
subsequen ly employed in so p ion expe imen s o acili a e a compa ison be ween he BCs
and HCs.
2.2. Cha ac e isa ion o BCs and HCs
The BC, HC, and AC samples we e subjec ed o analysis u ilising a CHNS/O analyse ,
speci ically he Elemen a Va ian LE Cube. The mois u e con en o he cha samples was
de e mined in acco dance wi h he ICS 75.160.10, DD CEN/TS 14774-3:2009 s anda d [
21
].
The ash and ola ile ma e con en s we e de e mined using ICS 75.160.10, DD CEN/TS
14775:2009 [
22
] and ICS 75.160.10, DD CEN/TS 15148:2009 [
23
], espec i ely. The pH
alues o he BCs and HCs we e measu ed by means o a pH me e (PHM 84, Radiome e ,
Denma k) equipped wi h glass REF 451 and calomel pHG 201-8 elec odes. The a io o BC
o HC o dis illed wa e was main ained a 1:20 (m/ ) du ing he pH de e mina ion p ocess.
The s udy employed a Fou ie ans o m in a ed (FTIR) spec ome e , speci ically he Ca y
630 FTIR spec ome e om Agilen Technologies Inc. (San a Cla a, CA, USA). Spec a
we e ob ained wi hin he 400–4000 cm
−1
ange, using a esolu ion o 4 cm
−1
and 64 scans
pe sample. The biocha su ace a ea and po e olume we e de e mined by using he
B unaue –Emme –Telle (BET) me hod, using a Gemini 2375 V5.01 su ace a ea analyse
(Mc ome i ics Ins umen Co., No c oss, GA, USA).
The ze a po en ials o he BCs, HCs, and AC we e de e mined. The expe imen al
p ocedu e in ol ed mixing 0.5 g o each sample wi h 100 mL o deionised wa e a a pH
o 7. The impac o NH
4+
, NO
3−
, and PO
43−
adso p ion on he ze a po en ial was assessed
by in oducing 0.5 g o each cha sample o a solu ion con aining 100 mg
·
dm
−3
o NH
4+
,
NO
3−
, and PO
43−
. P io o his, he pH o he suspensions was adjus ed o a ange be ween
4.0 and 9.0 using 0.1 mol
·
dm
−3
o HCl o NaOH. The solu ions unde in es iga ion we e
subjec ed o mechanical agi a ion a a a e o 250 e olu ions pe minu e o a du a ion
o 30 min. The suspensions unde wen ul asonic dispe sion o a du a ion o 1 h a a
empe a u e o 30
◦
C, u ilising a ba h- ype sonica o wi h a equency o 40 kHz and a
ol age o 300 W. Subsequen ly, he solu ion unde wen il a ion using il e pape o he
Wha man 42 a ie y. The ze a po en ial o each supe na an solu ion was de e mined by
means o a Mal e n Ze asize Nano ins umen (Mal e n Ins umen s, Mal e n, UK). The
eplicabili y o all analyses was ensu ed.
Appl. Sci. 2024,14, 2280 4 o 19
2.3. Adso p ion o NH4+, NO3
−, and PO43−
Ini ial analyses we e pe o med o de e mine he mos e ec i e adso be dosage.
Adso p ion expe imen s we e conduc ed o e a ange o adso ben masses, speci ically
be ween 0.1 and 1 g wi h inc emen s o 0.1 g. The concen a ion o he adso ba e used was
100 mg
·
dm
−3
. A no able a iance in he adso be ma e ial dosage was obse ed a 0.5 g,
which was u ilised in subsequen expe imen al ials.
2.3.1. Analysis o NH4+, NO3−, and PO43−
An analysis o NH
4+
was pe o med u ilising a Va ian Spec opho ome e (UV-Vis-
4000) in acco dance wi h he phena e me hod [
24
]. The de e mina ion o NO
3−
and PO
43−
was ca ied ou using ion ch oma og aphy equipmen (Dionex DX-120 Ion and ICS1100,
Manasquan, NJ, USA). The analysis poin s we e ob ained by calcula ing he mean o h ee
dis inc pa allel sample solu ions. S a is ical signi icance was de e mined a a le el o
p< 0.05.
2.3.2. pH E ec
In o de o de e mine he e ec o pH, 0.5 g o an adso ben ma e ial was mixed
wi h 100 cm
3
o a solu ion con aining 100 mg
·
dm
−3
o ei he NH
4+
, NO
3−
, o PO
43−
.
Be o e adding he biocha , he pH o he solu ions was adjus ed o lie wi hin he ange o
3 o 9. Using a PHM 84 pH me e equipped wi h glass REF 451 and calomel pHG 201-8
elec odes, his was accomplished. Fo e e y pH measu emen , a unique expe imen al
se up was es ablished. The suspensions we e agi a ed o 24 h on an agi a o ope a ing a
250 e olu ions pe minu e and a empe a u e o 25
◦
C. Each sample was il e ed using
a pape il e wi h a po e size o 0.5 mic ome es. The pH o he subsequen il a e was
hen measu ed. The concen a ions o NH4+, NO3−, and PO43−we e measu ed using he
p e iously desc ibed me hod.
Equa ion (1) was u ilised o de e mine he equilib ium adso p ion capaci y:
qe=V(C0−Ce)
m(1)
whe e q
e
is he adso p ion capaci y a equilib ium (mg
·
g
−1
); Vis he olume o he solu-
ion (dm
3
); C
0
and C
e
a e he ini ial and equilib ium concen a ions o NH
4+
, NO
3−
, and
PO43−(mg·dm−3); and mis he weigh o he adso ben (g).
2.3.3. Adso p ion Iso he ms
In his expe imen , we added he BCs, HCs, and AC (0.5 g) o 250 cm
3
E lenmeye
lasks con aining NH
4+
, NO
3−
, and PO
43−
solu ions. The solu ions had a ying concen-
a ions o 25, 50, 100, 200, and 500 mg dm
−3
, and he pH was kep cons an a 7. The
suspensions unde wen agi a ion on a shake ope a ing a 200 o a ions pe minu e and
a empe a u e o 25
◦
C o a du a ion o 24 h. The il a ion p ocess in ol ed he use o a
pape il e wi h a po e size o 0.5 mic ome es o il e he suspensions. The il a es we e
subjec ed o he measu emen o NH4+, NO3−, and PO43−concen a ions.
The adso p ion da a o he NH
4+
, NO
3−
, and PO
43−
on he BCs, HCs, and AC we e
analysed using he Langmui and F eundlich iso he m models. The Langmui model is
desc ibed in Equa ion (2) [25]:
Ce
qe
=1
KLqm
+Ce
qm(2)
whe e C
e
is he equilib ium concen a ion (mg
·
dm
−3
), and cons an q
m
(mg
·
g
−1
) and K
L
a e he cha ac e is ics o he Langmui equa ion (dm
3·
mg
−1
) and can be de e mined om
he linea ised o m (plo s o C
e
/q
e
s. C
e
). The F eundlich model is exp essed acco ding o
Equa ion (3) [26]:
lnqe=lnKF+1
nlnCe(3)
Appl. Sci. 2024,14, 2280 5 o 19
whe e K
F
is he F eundlich adso p ion capaci y (mg
·
g
−1
), and 1/n is he F eundlich cons an .
The abo e equa ion can be linea ised o calcula e he pa ame e s K
F
and n(plo s o log q
e
s. log Ce).
S udies o he he modynamics and he e ec o empe a u e a e p esen ed in
Sec ion 3.6
.
The expe imen s we e conduc ed as ollows: he BCs and HCs we e s udied a 20, 35, and
50
◦
C using ini ial NH
4+
, NO
3−
, and PO
43−
concen a ions o 100 mg
·
dm
−3
a pH 7. Each
sample was il e ed h ough a 0.5
µ
m pape il e , and he concen a ions o NH
4+
, NO
3−
,
and PO43−we e measu ed.
3. Resul s and Discussion
3.1. BC and HC Cha ac e is ics
Ul ima e and p oxima e analyses o he BC and HC samples p oduced unde a ious
condi ions a e p esen ed in Table 1. The esul s indica e ha an inc ease in esidence ime
led o a co esponding inc ease in he ixed ca bon and ash con en s, as well as in he O/C
and C/N a ios, o he HCs. Con e sely, he ola ile ma e and H/C a io dec eased wi h
an inc ease in esidence ime. The esul s sugges ha he esidence imes o 30 and 180 min
did no signi ican ly a ec he p oduc ion o hyd oca bons, as he alues ob ained we e
closely aligned. The obse ed di e ence in he C/N a io can be a ibu ed o he inc ease
in N losses ha occu s wi h longe esidence imes. The indings ob ained a e consis en
wi h he ou comes and pa e ns documen ed in p io esea ch [
27
–
29
]. The BET me hod
was applied o de e mine he po e s uc u e. The BET su ace a ea and po e olume o
he BCs p oduced a a low empe a u e and he HCs a e simila , and he alues o bo h
pa ame e s inc eased signi ican ly as he py olysis empe a u e inc eased, as con i med
in o he s udies [
30
,
31
]. The su ace a ea o he BC s ayed a a s able le el a e passing
500 ◦C, as p esen ed in Table 1.
Table 1. Ul ima e and p oxima e analyses o BC and HC samples p oduced unde di e en py olysis
and hyd o he mal ca bonisa ion condi ions.
Ul ima e Analysis
w .% A omic Ra ios
BET Su ace A ea
m2/g
Po e Volume
cm3/g
P oxima e Analysis
w .%
Ma e ial N C H S O
C/N H/C O/C
Ash
Vola ile
Ma e
Fixed
Ca bon
HC30 0.49 67.2 6.15 0.0 19.9 138
0.092 0.297
1.4 0.004 4.83 48.8 46.4
HC180 0.36 65.2 5.77 0.0 21.2 179
0.088 0.325
1.8 0.004 6.30 45.9 47.8
BC300 0.39 56.4 5.67 0.0 28.3 145
0.100 0.502
2.4 0.003 6.30 58.7 35.0
BC500 0.57 69.1 2.96 0.0 13.7 121
0.043 0.199
80.4 0.032 10.1 15.8 74.2
BC700 0.54 76.3 1.37 0.0 0.97 142
0.018 0.013
84.3 0.030 17.8 5.72 76.5
AC 0.48 86.1 0.30 0.0 6.51 179
0.003 0.076
400 1.365 3.60 4.44 92.0
The esul s indica e ha an inc ease in ca bonisa ion empe a u e led o an inc ease
in he concen a ions o ixed ca bon and ash, while he ola ile ma e and a omic a ios
(H/C and O/C) dec eased o he BCs. The ob ained esul s a e consis en wi h hose
p e iously epo ed in he scien i ic li e a u e [
16
,
32
] o a ious ca bonisa ion empe a u es.
Acco ding o he indings o p e ious esea ch, he py olysis p ocess p ima ily esul s in
he ans o ma ion o hemicelluloses and cellulose in o gaseous p oduc s, whe eas lignin is
p edominan ly ans o med in o cha a ele a ed empe a u es. The esul s o his s udy
sugges ha inc easing he py olysis empe a u e can inc ease he deg ee o ca bonisa ion
o BC. Acco ding o p e ious esea ch [
16
], his inding sugges s ha he BCs p oduced
by his p ocess may ha e po en ial bene i s o ca bon seques a ion. Compa ed o he
BCs and HCs, he AC was ound o ha e he highes concen a ion o ixed ca bon and he
lowes concen a ions o ash and ola ile ma e [33].
An FTIR spec al analysis plays a c ucial ole in he iden i ica ion o dis inc unc ional
g oups esponsible o ion adso p ion [
18
]. As shown in Figu e 1, he FTIR spec a o HC30,
HC180, BC300, BC500, BC700, and AC we e collec ed and analysed in he p esence and
absence o NH4+, NO3−, and PO43−adso p ion.

Appl. Sci. 2024,14, 2280 6 o 19
Appl. Sci. 2024, 14, x FOR PEER REVIEW 6 o 22
sugges ha inc easing he py olysis empe a u e can inc ease he deg ee o ca bonisa ion
o BC. Acco ding o p e ious esea ch [16], his inding sugges s ha he BCs p oduced
by his p ocess may ha e po en ial bene i s o ca bon seques a ion. Compa ed o he BCs
and HCs, he AC was ound o ha e he highes concen a ion o ixed ca bon and he
lowes concen a ions o ash and ola ile ma e [33].
An FTIR spec al analysis plays a c ucial ole in he iden i ica ion o dis inc unc-
ional g oups esponsible o ion adso p ion [18]. As shown in Figu e 1, he FTIR spec a
o HC30, HC180, BC300, BC500, BC700, and AC we e collec ed and analysed in he p es-
ence and absence o NH4+, NO3−, and PO43− adso p ion.
Figu e 1. The FTIR spec a o (a) HC30, (b) HC180, (c) BC300, (d) BC500, (e) BC700, and ( ) AC be o e
and a e NH4+, NO3−, and PO43− adso p ion.
The ib a ional spec a o he HCs and BCs we e compa ed, and i was obse ed ha
he numbe o ib a ional peaks was signi ican ly g ea e in he HC spec a han in he BC
spec a. The ib a ional peaks a 2850 cm−1, 1698 cm−1, and 1206 cm−1 we e a ibu ed o C-
H s e ching, a oma ic C=O, and C-O s e ching ib a ions, espec i ely, as depic ed in
Figu e 1. The echniques o hyd olysis and py olysis exhibi ed dis inc diffe ences in
e ms o chemical s uc u e. The obse ed peaks in he spec a can be a ibu ed o he
p esence o ca boxyl and es e unc ional g oups, as p e iously epo ed [34]. The s udy
in [35] epo ed compa able ansmi ance alues in he ange o 4000 o 650 cm−1 o wo
Figu e 1. The FTIR spec a o (a) HC30, (b) HC180, (c) BC300, (d) BC500, (e) BC700, and ( ) AC be o e
and a e NH4+, NO3−, and PO43−adso p ion.
The ib a ional spec a o he HCs and BCs we e compa ed, and i was obse ed ha
he numbe o ib a ional peaks was signi ican ly g ea e in he HC spec a han in he BC
spec a. The ib a ional peaks a 2850 cm
−1
, 1698 cm
−1
, and 1206 cm
−1
we e a ibu ed o
C-H s e ching, a oma ic C=O, and C-O s e ching ib a ions, espec i ely, as depic ed in
Figu e 1. The echniques o hyd olysis and py olysis exhibi ed dis inc di e ences in e ms
o chemical s uc u e. The obse ed peaks in he spec a can be a ibu ed o he p esence
o ca boxyl and es e unc ional g oups, as p e iously epo ed [
34
]. The s udy in [
35
]
epo ed compa able ansmi ance alues in he ange o 4000 o 650 cm
−1
o wo samples
o HCs. This sugges s ha he e we e no signi ican chemical s uc u al modi ica ions
esul ing om an inc ease in he esidence pe iod.
A co ela ion was obse ed be ween he py olysis empe a u e and he p esence
o unc ional g oups in he BCs, wi h a dec ease in he numbe o unc ional g oups
as he empe a u e inc eased. The ob ained spec a exhibi ed dis inc peaks a speci ic
wa enumbe s, namely, 2907 cm
−1
o me hyl CH s e ching ib a ions, 1703 cm
−1
o
a oma ic ca bonyl/ca boxyl C=O, 1595 cm
−1
o a oma ic C=C and C=O, 1028 cm
−1
o alipha ic COC and OH, and 814 cm
−1
o a oma ic CH [
36
]. The obse ed shi s in
he appea ance o he bands a e consis en wi h he indings o p e ious s udies [
37
,
38
]
and we e a ibu ed o he inc ease in py olysis empe a u e. Acco ding o Zhou and
colleagues [
18
], he peaks obse ed in he ange o 1000 o 600 cm
−1
a e associa ed wi h
Appl. Sci. 2024,14, 2280 7 o 19
he undula ing ib a ion o a oma ic C-H. Wi h an inc ease in py olysis empe a u e, a
educ ion in he pola unc ional g oups (OH and C-O) was obse ed, as indica ed by
he smalle peaks in hei espec i e spec a [
16
]. Upon he adso p ion o NH
4+
, NO
3−
,
and PO
43−
, bo h he biocha s (BCs) and hyd ocha s (HCs) exhibi ed compa able peaks.
Ne e heless, he peaks obse ed in he BC spec a we e ela i ely eeble, whe eas hose
in he HC spec a we e ela i ely obus . Consis en wi h p e ious s udies [
16
,
39
,
40
], ou
FTIR spec a analysis e ealed he absence o a signi ican band subsequen o phospha e
adso p ion. Upon analysing he wa eleng hs o pa icula peaks depic ed in Figu e 1, sligh
de ia ions we e obse ed, consis en wi h indings epo ed p e iously [
41
,
42
]. The p esen
s udy demons a es he complexa ion phenomenon be ween ammonium ions and ionised
-OH g oups, as well as he bonded -OH bands o ca boxylic acids. This was e idenced
by a disce nible shi in he wa enumbe o mul iple peaks wi hin he ange o 3500 o
3200 cm
−1
. The con i ma ion o he ion-exchange phenomenon be ween he p o ons o
alipha ic C-H and he symme ic s e ching ib a ion o CH
2
wi h ammonium ions has been
es ablished h ough shi s obse ed a 2920 and 2860 cm−1, as p e iously epo ed [42].
3.2. Ze a Po en ial
The ze a po en ial alues o he HCs, BCs, and AC we e measu ed a e he adso p ion
o NH
4+
, NO
3−
, and PO
43−
, as p esen ed in Figu e 2. The samples we e analysed o
hei ze a po en ial a pH 7, which was ound o ange om
−
18.7 o
−
32.6 mV. This
sugges s ha he pa icles p esen in he samples possessed nega i ely cha ged su aces.
The esul s o his s udy indica e ha he AC exhibi ed he highes a e age ze a po en ial,
while he HC displayed he lowes . An inc ease in he pH o he suspension esul ed in
an ele a ed disc epancy in he ze a po en ial be ween he sys ems. The indings o his
s udy indica e ha HCs, BCs, and AC ha e he abili y o selec i ely adso b NH
4+
, NO
3−
,
and PO
43−
. Mo eo e , i was obse ed ha he in luence o speci ic adso p ion became
mo e p onounced a ele a ed suspension pH le els. Simila indings [
16
,
43
] we e epo ed
in s udies on he u ilisa ion o c op s aw eeds ock-based biocha o he adso p ion o
coppe and phospha e, espec i ely.
Appl. Sci. 2024, 14, x FOR PEER REVIEW 8 o 22
Figu e 2. Ze a po en ial o HCs, BCs, and AC a e NH
4+
, NO
3−
, and PO
43−
adso p ion.
3.3. Adso p ion o Ammonium
The impac o ca bonisa ion empe a u e and esidence du a ion on he adso p ion
capaci y and su ace a ea o he cha s was highly signi ican . The equilib ium iso he ms
and he adso p ion capaci y a ia ion as a unc ion o he cha used and he ini ial NH
4+
concen a ion a e illus a ed in Figu e 3. The esul s o his s udy indica e ha HC180 ex-
hibi ed a highe adso p ion capaci y compa ed o HC30. Howe e , BC700 demons a ed
a lowe adso p ion capaci y in compa ison o BC500 and BC300. The esul s indica e ha
BC300 exhibi ed he mos signi ican NH
4+
adso p ion capaci y, while HC30 demons a ed
he leas . Upon inc easing he ini ial concen a ion o NH
4+
om 25 o 500 mg·dm
−3
, he
obse ed mean alues o he HCs exhibi ed a ange o 0.63 o 2.67 mg·g
−1
, while he mean
alues o he BCs anged om 2.59 o 9.05 mg·g
−1
. In e ms o NH
4+
adso p ion capaci y,
he AC was su passed only by BC300.
The adso p ion beha iou o he BCs was obse ed o be in luenced by he ini ial
concen a ion o NH
4+
in he solu ion, as well as he empe a u e o ca bonisa ion. The
esul s o he obse a ions indica e an in e se ela ionship be ween NH
4+
adso p ion ca-
paci y and ca bonisa ion empe a u e. Speci ically, as he empe a u e o ca bonisa ion
inc eased, he capaci y o NH
4+
adso p ion dec eased. Compa able esul s we e ob ained
by Wang e al. [14] on biocha s de i ed om oak sawdus h ough py olysis a empe a-
u es be ween 300 °C and 600 °C. The esul s o his s udy indica e ha he adso p ion o
NH
4+
is augmen ed by BCs ha a e gene a ed a lowe empe a u es. As pe p io e-
sea ch, i can be obse ed in Figu e 1 ha he BC p oduced a a highe py olysis empe -
a u e lacked he p esence o a oma ic C=O and C=C, -CH
2
-, CO, and CC unc ional g oups.
As a esul , i was obse ed ha he unc ional pola g oups p esen in he ma e ial un-
de wen a eac ion wi h NH
4+
du ing he adso p ion p ocess. This led o a signi ican in-
c ease in he adso p ion capaci y o he BC ha was p oduced a lowe empe a u es, e en
i s su ace a ea was g ea ly lowe han ha p oduced a highe empe a u es.
Figu e 2. Ze a po en ial o HCs, BCs, and AC a e NH4+, NO3−, and PO43−adso p ion.
Fu he mo e, he ze a po en ial o he HCs, BCs, and AC became mo e nega i e
wi h inc eased pH alues, sugges ing ha he amoun o nega i e cha ge inc eased wi h
he inc ease in pH and ha he adso p ion capaci y should be lowe . The elec os a ic
adso p ion o ions on solid cha ged su aces does no end o a ec he su ace cha ge o
su ace po en ial o colloidal pa icles, as he adso bed ions exis in he di use laye o
he elec ic double laye s on he pa icles. Ne e heless, he speci ic adso p ion o ions
Appl. Sci. 2024,14, 2280 8 o 19
changes he su ace cha ge and he su ace po en ial o colloidal pa icles, since hese ions
go in o he S e n laye o he elec ic double laye s and o m chemical bonds wi h he
solid pa icle su aces. In addi ion, du ing he p ocess o ca ion speci ic adso p ion, some
posi i e cha ges a e ans e ed o he su ace o biocha s. This p ocess could lead o a less
nega i e su ace cha ge o e en a ne posi i e cha ge [
44
]. Acco dingly, he ze a po en ial
o he BCs became less nega i e o changed om nega i e o posi i e.
3.3. Adso p ion o Ammonium
The impac o ca bonisa ion empe a u e and esidence du a ion on he adso p ion
capaci y and su ace a ea o he cha s was highly signi ican . The equilib ium iso he ms
and he adso p ion capaci y a ia ion as a unc ion o he cha used and he ini ial NH
4+
concen a ion a e illus a ed in Figu e 3. The esul s o his s udy indica e ha HC180
exhibi ed a highe adso p ion capaci y compa ed o HC30. Howe e , BC700 demons a ed
a lowe adso p ion capaci y in compa ison o BC500 and BC300. The esul s indica e ha
BC300 exhibi ed he mos signi ican NH
4+
adso p ion capaci y, while HC30 demons a ed
he leas . Upon inc easing he ini ial concen a ion o NH
4+
om 25 o 500 mg
·
dm
−3
, he
obse ed mean alues o he HCs exhibi ed a ange o 0.63 o 2.67 mg
·
g
−1
, while he mean
alues o he BCs anged om 2.59 o 9.05 mg
·
g
−1
. In e ms o NH
4+
adso p ion capaci y,
he AC was su passed only by BC300.
Appl. Sci. 2024, 14, x FOR PEER REVIEW 9 o 22
Figu e 3. Equilib ium iso he m plo s a 20 °C o NH4+ so p ion on BCs, HCs, and AC. Solid and
dashed lines ep esen he Langmui and F eundlich iso he m da a models, espec i ely.
The obse ed esul s indica e ha he e was no signi ican a ia ion in he NH4+ ad-
so p ion capaci y o he HCs ha we e assessed. The esul s sugges ha a ying he es-
idence ime be ween 30 and 180 min does no signi ican ly impac he NH4+ adso p ion
capaci y. In hei s udy, Takaya e al. [11] conduc ed hyd o he mal ca bonisa ion a 250 °C
o syn hesise HC and compa ed i wi h BCs ob ained om diffe en biomass sou ces a
low and high py olysis empe a u es (400–450 °C and 600–650 °C, espec i ely). The s udy
ound ha he e we e a ia ions in he physicochemical p ope ies o he cha and he
e ining condi ions. Howe e , he NH4+ so p ion capaci ies anged be ween 105.8 and
146.4 mg·g−1. As pe he indings o he s udy, i can be in e ed ha he NH4+ adso p ion
capaci y is no p ima ily in luenced by he su ace a ea [11,45].
The p esen s udy employed he Langmui and F eundlich iso he m models o in-
es iga e he adso p ion beha iou o NH4+, NO3−, and PO43− on a ious samples o BCs,
HCs, and AC. The esul s o he analysis a e p esen ed in Table 2. Acco ding o he exis ing
li e a u e, he Langmui iso he m model posi s ha so p ion occu s uni o mly ac oss all
binding si es. Con e sely, he F eundlich iso he m model sugges s ha he su ace is he -
e ogeneous, wi h an une en dis ibu ion o adso p ion capaci y o e he su ace [46]. The
Langmui model demons a es supe io desc ip i e capabili ies o he adso p ion p o-
cess o NH4+, NO3−, and PO43− on he BCs, HCs, and AC, as e idenced by he highe R2
alues. Th ough he u ilisa ion o bo h BCs and HCs, i was ound in he s udy in [11] ha
he Langmui iso he m model exhibi ed a highe deg ee o accu acy in desc ibing NH4+
adso p ion in compa ison o he F eundlich iso he m model.
0 100 200 300 400 500
0
2
4
6
8
10
12
0 100 200 300 400 500
BC 300
BC 500
BC 700
HC 30
HC 180
AC
q
e
, mg·g-
1
C
e
, mg·dm
-3
F eundlich
Langmui
Figu e 3. Equilib ium iso he m plo s a 20
◦
C o NH
4+
so p ion on BCs, HCs, and AC. Solid and
dashed lines ep esen he Langmui and F eundlich iso he m da a models, espec i ely.
The adso p ion beha iou o he BCs was obse ed o be in luenced by he ini ial
concen a ion o NH
4+
in he solu ion, as well as he empe a u e o ca bonisa ion. The
esul s o he obse a ions indica e an in e se ela ionship be ween NH
4+
adso p ion
capaci y and ca bonisa ion empe a u e. Speci ically, as he empe a u e o ca bonisa ion
inc eased, he capaci y o NH
4+
adso p ion dec eased. Compa able esul s we e ob ained
by Wang e al. [
14
] on biocha s de i ed om oak sawdus h ough py olysis a empe a u es
be ween 300
◦
C and 600
◦
C. The esul s o his s udy indica e ha he adso p ion o NH
4+
is augmen ed by BCs ha a e gene a ed a lowe empe a u es. As pe p io esea ch,
Appl. Sci. 2024,14, 2280 9 o 19
i can be obse ed in Figu e 1 ha he BC p oduced a a highe py olysis empe a u e
lacked he p esence o a oma ic C=O and C=C, -CH
2
-, CO, and CC unc ional g oups. As a
esul , i was obse ed ha he unc ional pola g oups p esen in he ma e ial unde wen a
eac ion wi h NH
4+
du ing he adso p ion p ocess. This led o a signi ican inc ease in he
adso p ion capaci y o he BC ha was p oduced a lowe empe a u es, e en i s su ace
a ea was g ea ly lowe han ha p oduced a highe empe a u es.
The obse ed esul s indica e ha he e was no signi ican a ia ion in he NH
4+
adso p ion capaci y o he HCs ha we e assessed. The esul s sugges ha a ying he
esidence ime be ween 30 and 180 min does no signi ican ly impac he NH
4+
adso p ion
capaci y. In hei s udy, Takaya e al. [
11
] conduc ed hyd o he mal ca bonisa ion a 250
◦
C
o syn hesise HC and compa ed i wi h BCs ob ained om di e en biomass sou ces a
low and high py olysis empe a u es (400–450
◦
C and 600–650
◦
C, espec i ely). The s udy
ound ha he e we e a ia ions in he physicochemical p ope ies o he cha and he
e ining condi ions. Howe e , he NH
4+
so p ion capaci ies anged be ween 105.8 and
146.4 mg
·
g
−1
. As pe he indings o he s udy, i can be in e ed ha he NH
4+
adso p ion
capaci y is no p ima ily in luenced by he su ace a ea [11,45].
The p esen s udy employed he Langmui and F eundlich iso he m models o in es-
iga e he adso p ion beha iou o NH
4+
, NO
3−
, and PO
43−
on a ious samples o BCs,
HCs, and AC. The esul s o he analysis a e p esen ed in Table 2. Acco ding o he exis ing
li e a u e, he Langmui iso he m model posi s ha so p ion occu s uni o mly ac oss all
binding si es. Con e sely, he F eundlich iso he m model sugges s ha he su ace is
he e ogeneous, wi h an une en dis ibu ion o adso p ion capaci y o e he su ace [
46
].
The Langmui model demons a es supe io desc ip i e capabili ies o he adso p ion
p ocess o NH
4+
, NO
3−
, and PO
43−
on he BCs, HCs, and AC, as e idenced by he highe
R
2
alues. Th ough he u ilisa ion o bo h BCs and HCs, i was ound in he s udy in [
11
]
ha he Langmui iso he m model exhibi ed a highe deg ee o accu acy in desc ibing
NH4+adso p ion in compa ison o he F eundlich iso he m model.
Table 2. Langmui and F eundlich iso he m pa ame e s o he adso p ion o ammonium, ni a e,
and phospha e on BCs, HCs, and AC.
Sys em Ma e ial
BC300 BC500 BC700 HC30 HC180 AC
Ammonium
F eundlich
KF1.177 1.016 0.755 0.192 0.186 1.117
n 2.737 2.700 2.502 2.187 2.134 2.778
R20.886 0.846 0.896 0.866 0.944 0.886
Langmui
q09.833 8.183 8.137 2.970 3.434 9.050
KL0.028 0.032 0.020 0.016 0.012 0.029
R20.968 0.946 0.980 0.975 0.993 0.967
Ni a e
F eundlich
KF0.036 0.073 0.091 0.033 0.093 0.093
n 1.565 1.583 1.632 1.971 1.523 1.539
R20.688 0.674 0.651 0.826 0.748 0.708
Langmui
q01.637 3.051 3.261 0.698 1.399 4.529
KL0.008 0.009 0.010 0.013 0.007 0.008
R20.879 0.880 0.871 0.953 0.902 0.893
Phospha e
F eundlich
KF0.119 0.272 0.301 0.033 0.098 0.477
n 1.992 2.147 2.193 1.971 2.107 2.092
R20.829 0.809 0.860 0.826 0.805 0.832
Langmui
q02.413 4.184 4.699 0.698 1.615 8.292
KL0.013 0.017 0.014 0.013 0.016 0.014
R20.955 0.948 0.956 0.953 0.947 0.943
Appl. Sci. 2024,14, 2280 16 o 19
Table 3. Con .
Ca bonaceous
Ma e ials
Condi ions o he
Adso ben Adso bed Ion
Solu ion
Concen a ion
mg dm−3
Adso p ion
Capaci y
mg g−1
Re .
Oak-based hyd ocha Hyd o he mal ca bonisa ion
a 250 ◦CPO43−400 26.6 [11]
Oak-based BC Slow py olysis a 450 ◦C 5.5
Slow py olysis a 650 ◦C 3.6
Poul y manu e BC slowly py olysed a 350 ◦C
a e Al doping PO43−3000 701 [71]
Suga cane BC slowly py olysed a 350 ◦C
a e Al doping 759
Based on he da a in Table 3, i appea s ha he BCs and HCs employed in his s udy sha e
simila so p ion capaci ies wi h o he adso ben s used in ea lie in es iga ions. Highe NH
4+
adso p ion was obse ed in HCs de i ed om oak [
11
] and HCs ac i a ed wi h KOH [
62
]
compa ed o HCs de i ed om o he biomass sou ces. Ou HC30s om suga cane bagasse
adso bed a less ammonium han hose in Table 3. When compa ed o whea s aw BC [
34
],
BC500 was a leas en imes mo e e icien in emo ing ni a es om he en i onmen .
The so p ion capaci ies o he BCs and HCs examined he e a e compa able o hose
o p e iously in es iga ed adso ben s, as shown in Table 3. Compa ed o HCs gene a ed
om o he biomass sou ces, HCs ac i a ed wi h KOH and HCs de i ed om oak exhibi ed
much g ea e NH
4+
adso p ion. Table 3displays he ammonium adso p ion capaci ies o
se e al HCs. Suga cane bagasse HC30 exhibi ed he lowes alue. BC500 was shown o be
a leas en imes mo e e ec i e han whea s aw BC a adso bing ammonium.
Table 3shows ha he BCs and HCs used he e compa e a ou ably o o he adso ben s
in e ms o hei so p ion capaci ies. KOH-ac i a ed HC and oak HC we e shown o ha e
much g ea e NH
4+
adso p ion han HCs gene a ed om o he biomass sou ces. Table 3
shows ha , compa ed o he o he HCs, suga cane bagasse HC30 was much less e ec i e a
adso bing ammonium. BC500 was a leas 10 imes mo e e ec i e a adso bing ammonium
han BC p oduced om whea s aw.
Fo he bes NO
3−
adso p ion esul s, use BC [
55
] p oduced om e ined suga cane
bagasse. In acidic solu ions, adso p ion was shown o be mo e e icien han in basic ones.
Table 3sugges s ha , among he BCs, BC500 had he highes ni a e adso p ion a e.
The highes PO
43−
adso p ion capaci y o he modi ied suga cane BC was achie ed
h ough slow py olysis a 350
◦
C wi h Al en ichmen , simila o wha was ca ied ou
in a p io wo k [
66
]. The BCs’ imp o ed P adso p ion capaci y can be a ibu ed o he
ma e ial being doped wi h Al ca ions, which acili a e bonding be ween ions and ca boxylic
g oups. Su ace i egula i y and speci ic su ace a ea a e p o en o ha e a majo impac on
BCs’ adso p ion pe o mance [
67
]. Acco ding o Table 3, al e na i e HCs, such as sewage
sludge HC, KOH-ac i a ed sewage sludge HC, and oak-based HC, a e mo e e icacious
han he suga cane bagasse HC30 used in he p esen s udy [
66
]. As a esul , he adso p ion
capaci y di e s subs an ially depending on he ype o biomass, he deg ee o which i was
p e- ea ed o ac i a ed, and he condi ions unde which i was manu ac u ed.
4. Conclusions
The u ilisa ion o BCs and HCs has expe ienced a signi ican su ge owing o hei
demons a ed e icacy and e sa ili y in a ious in e disciplina y domains. In he p esen
s udy, suga cane bagasse unde wen py olysis and hyd o he mal ca bonisa ion a a ious
empe a u es o yield BC and HC. As he py olysis empe a u e was ele a ed o he BCs,
he e was a no iceable inc ease in he ixed ca bon, su ace a ea, po e olume, and ash
con en , whe eas he ola ile ma e and he H/C and O/C a omic a ios expe ienced a
dec ease. The obse ed end indica ed an inc ease in he ixed ca bon con en , ash con en ,
and O/C and C/N a ios, as well as ola ile ma e and H/C a ios, wi h an inc ease in
esidence ime o he hyd oca bons. Upon he adso p ion o NH
4+
, NO
3−
, and PO
43−
, a

Appl. Sci. 2024,14, 2280 17 o 19
educ ion in he in ensi ies o ca boxyl and es e unc ional g oups was obse ed in he
FTIR spec a o bo h he BCs and HCs. Fu he mo e, he esea ch indings demons a e
ha he Langmui iso he m model exhibi ed a ma ginally be e con o mi y han he
F eundlich iso he m model, implying ha he adso p ion p ocess was homogeneous ac oss
all adso p ion si es. A ele a ed empe a u es, he exo he mic eac ion pe aining o he
adso p ion o he h ee ions was expedi ed. The adso p ion capaci y o he BC and HC
adso ben s was obse ed o be signi ican ly in luenced by he ype o biomass employed,
he ex en o p e- ea men o ac i a ion o he cha s, and he p epa a ion pa ame e s.
Howe e , in he case o ammonia adso p ion on he BCs, he unc ional pola g oups
p esen in he ma e ial unde wen a eac ion wi h NH
4+
du ing he adso p ion p ocess and
had a much s onge e ec han he su ace a ea.
Au ho Con ibu ions: Concep ualiza ion, P.A.T. and W.K.; Me hodology, A.S. and J.J.L.; Fo mal
analysis, A.S.; In es iga ion, J.N.; W i ing—o iginal d a , P.A.T. and M.V.; W i ing— e iew & edi ing,
J.N., V.K.K. and W.K.; Supe ision, W.K. All au ho s ha e ead and ag eed o he published e sion
o he manusc ip .
Funding: This esea ch ecei ed no ex e nal unding.
Da a A ailabili y S a emen : The o iginal con ibu ions p esen ed in he s udy a e included in he
a icle, u he inqui ies can be di ec ed o he co esponding au ho .
Con lic s o In e es : The au ho s decla e no con lic s o in e es .
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Disclaime /Publishe ’s No e: The s a emen s, opinions and da a con ained in all publica ions a e solely hose o he indi idual
au ho (s) and con ibu o (s) and no o MDPI and/o he edi o (s). MDPI and/o he edi o (s) disclaim esponsibili y o any inju y o
people o p ope y esul ing om any ideas, me hods, ins uc ions o p oduc s e e ed o in he con en .