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The ole o guanidine hyd ochlo ide
in g aphi ic ca bon ni ide syn hesis
Ane a Smýkalo á1,2, K yš o Foniok1, Daniel C ejn2,3, Kamil Maciej Gó ecki2 & Pe P aus1,2*
G aphi ic ca bon ni ide (CN) was syn hesized om guanidine hyd ochlo ide (G), melamine (M) and
dicyandiamide (DCDA). The CN ma e ials syn he ized om he pu e p ecu so s and hei mix u es
we e cha ac e ized by common me hods, including he mal analysis, and hei pho oca aly ic
ac i i ies we e es ed by he deg ada ion o selec ed o ganic pollu an s, such as amoxicillin, phenol,
Rhodamine B (RhB). Rema kable changes in hei ex u e p ope ies in e ms o pa icle sizes, speci ic
su ace a eas (SSA) and consequen ly hei pho oca aly ic ac i i y we e explained by he ole o
guanidine hyd ochlo ide in hei syn hesis. The SSA inc eased due o he elease o NH3 and HCl and
i s complex eac ions wi h melamine and DCDA o ming s uc u e impe ec ions and dis up ions. The
pho oca aly ic ac i i y o he CN ma e ials was ound o be dependen on hei SSA.
G aphi ic ca bon ni ide is a me al- ee polyme ic semiconduc o which has been a ac ing he a en ion o
scien is s o he las decade because o i s abili y o abso b isible ligh (band gap ene gy abou 2.7eV), high
he mal and chemical s abili y, low cos syn hesis, e c. The his o y, p ope ies and possible applica ions o his
ma e ial ha e been al eady desc ibed in many comp ehensi e e iew pape s, o ins ance in Re s.1–7. The majo -
i y o i s applica ions we e ocused on he e ogenous pho oca alysis bu i is also used o sola cells ab ica ion8,
imaging, bio he apy, and he sensing o some compounds9–12. Besides physical and chemical apou deposi ion,
CN has been mos ly p epa ed by he hea ing o a ious ni ogen- ich o ganic p ecu so s, such as melamine13,
u ea14, hiou ea15, iazines16, cyanamide17, dicyandiamide18, cyanu ic chlo ide19 and guanidine hyd ochlo ide20
o hiocyana e21. The chemical syn hesis is based on he polycondensa ion o melamine in o melem/melam,
melon and inally a polyme ic ne wo k o ca bon and ni ogen7,22,23. The o he p ecu so s o m melamine which
u he polyme izes o CN h ough he a o emen ioned ou e.
In his wo k, he syn hesis o CN based on he polyme iza ion o guanidine hyd ochlo ide wi h melamine
and guanidine hyd ochlo ide wi h dicyandiamide has no been published ye . The mix u e o guanidine hyd o-
chlo ide and melamine was ound o p o ide CN wi h he highes speci ic su ace a ea (wi hou u he ex olia-
ion) and consequen ly he highes pho oca aly ic ac i i y. The pho oca aly ic ac i i y was es ed using h ee
di e en kinds o o ganic compounds ep esen ing a ious en i onmen al pollu an s: amoxicillin, Rhodamine
B and phenol.
Ma e ials and me hods
Chemicals. All chemicals used o he syn hesis o all ma e ials, pho oca aly ic deg ada ion and he de e mi-
na ion o phenol we e o analy ical- eagen g ade (p o analysis) and used as ob ained. Melamine, dicyandiamide,
guanidine hyd ochlo ide, 4-ni oaniline and amoxicillin we e pu chased om Sigma-Ald ich (Da ms ad , Ge -
many). Phenol and Rhodamine B we e ob ained om The mo Fishe Scien i ic (Wal ham, MA, USA). Sodium
ca bona e, sodium ni a e, e hylenediamine e aace ic acid (EDTA), p-benzoquinone and -bu anol we e pu -
chased om Pen a (Ch udim, Czech Republic). Dis illed wa e was used o he p epa a ion o solu ions and
expe imen s.
Syn hesis o CN ma e ials. The CN ma e ials we e syn he ized by a acile me hod o he di ec hea ing o
melamine, dicyandiamide and guanidine hyd ochlo ide o hei mix u es a 550°C o 4h wi h a hea ing a e
o 3°C min−1. Typically, 5g o indi idual p ecu so s o hei mix u es o a pa icula mass a io, which we e
manually mixed in an aga e mo a , we e placed in a ce amic c ucible wi h a lid in a mu le u nace. The c ucible
was hen cooled down o oom empe a u e ou o u nace and g ound in a labo a o y mill in o a ine powde .
The CN ma e ials om he mix u es o guanidine hyd ochlo ide, melamine and dicyandiamide we e labelled
CN-GM Y and CN-GD Y espec i ely, whe e Y is a numbe and ep esen s he mass a io o guanidine and he
OPEN
1Depa men o Chemis y, VSB-Technical Uni e si y o Os a a, 17. lis opadu 15, 708 00 Os a a-Po uba, Czech
Republic. 2Ins i u e o En i onmen al Technology, CEET, VSB-Technical Uni e si y o Os a a, 17. lis opadu 15, 708
00 Os a a-Po uba, Czech Republic. 3ENET Cen e, CEET, VSB-Technical Uni e si y o Os a a, 17. lis opadu 15,
708 00 Os a a-Po uba, Czech Republic. *email: pe [email p o ec ed]
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o he p ecu so (melamine o DCDA). The syn he ized CN ma e ials used o compa ison we e labelled as CN-M
(CN p epa ed solely om melamine), CN-D (CN p epa ed solely om dicyandiamide) and CN-G (CN p epa ed
solely om guanidine hyd ochlo ide). The heo e ical composi ion o he ma e ials is summa ized in Table1.
UV–Vis DR spec ome y. The UV–Vis di use e lec ance spec a (DRS) we e eco ded using a Shimadzu
UV-2600 spec opho ome e (IRS-2600Plus, Shimadzu, Kyo o, Japan) a oom empe a u e. The di use e lec-
ance da a ob ained we e ans o med using he Kubelka–Munk equa ion24 as ollows
whe e R∞ is he di use e lec ance om a semi-in ini e laye .
X‑ ay di ac ion analysis. The X- ay di ac ion (XRD) pa e ns we e eco ded using a Rigaku Sma -
Lab di ac ome e (Rigaku, Tokyo, Japan) equipped wi h a de ec o D/ eX Ul a 250. A Co ube (CoKα,
λ1 = 0.178892nm, λ2 = 0.179278nm) ope a ed a 40kV and 40mA was used as a sou ce o X- ay i adia ion.
The pa e ns we e eco ded be ween 5° and 90° o 2θ wi h a s ep size o 0.01° and speed o 0.5deg min−1. The
c ys alli e size (L) was calcula ed using Sche e ’s equa ion25 o b oadening B(2θ) in adians a a hal maximum
in ensi y (FWHM) o a di ac ion band as
whe e θ is B agg’s angle, λ is he wa eleng h o X- ays and K is a cons an equal o 0.94 o cubic and 0.89 o
sphe ical c ys alli es. In his wo k K = 0.90.
Fou ie ans o m in a ed spec oscopy. The Fou ie ans o m in a ed (FTIR) spec a we e eco ded
using a Nicole iS50 de ice (The mo Fishe Scien i ic, Wal ham, MA, USA). A small amoun , app oxima ely
200mg, o he CN ma e ial was mixed and homogenized wi h KB and p essed o ob ain a anspa en able .
Each spec um consis ed o 64 scans a a minimum.
Speci ic su ace a ea measu emen . The speci ic su ace a ea o he syn he ized ma e ials was de e -
mined by he adso p ion and deso p ion o ni ogen a 77K a e sample degassing a oom empe a u e o
24h unde less han 1Pa acuum. The SSA was e alua ed by means o he B unaue –Emme –Telle (BET)
heo y o he p/p0 = 0.05–0.25. Fo his pu pose, a de ice SORPTOMATIC 1990 se ies (The mo Fishe Scien-
i ic, Wal ham, MA, USA) was employed. The mesopo e olumes we e calcula ed based on he Ba e , Joyne
and Halenda (BJH) heo y.
Elemen al analysis. The elemen al composi ion o he syn he ized ma e ials was de e mined by a Flash
2000 Elemen al analyse (The mo Fishe Scien i ic, Wal ham, MA, USA). The con en o ca bon, ni ogen and
hyd ogen was measu ed, and he con en o oxygen was calcula ed as a di e ence o 100%. The chlo ine con en
in he CN ma e ials was de e mined by an X- ay luo escence spec ome e (XRF) SPECTRO Xepos (SPECTRO
Analy ical Ins umen s GmbH, Kle e, Ge many).
Pho oca aly ic deg ada ion. The pho oca aly ic ac i i y o he CN ma e ials was es ed using Rhoda-
mine B, phenol and amoxicillin in he concen a ions o 10mg L−1, 30mg L−1 and 20mg L−1, espec i ely. Each
suspension p epa ed o he pho oca aly ic deg ada ion con ained 45mg o he CN ma e ial and 150mL o he
(1)
F
(R∞)=
(1−R∞)
2
2
R∞
,
(2)
B
(2θ)=
K
Lcos θ,
Table 1. Mass and mola a io o CN ma e ials. *X s ands o melamine (M) and dicyandiamide (D).
Ma e ial Mass a io G:X* Mola a io G:X*
CN-G – –
CN-M – –
CN-D – –
CN-GM 0.5 0.5:1 0.4:1
CN-GM 1 1:1 0.7:1
CN-GM 2 2:1 1.5:1
CN-GM 3 3:1 2.2:1
CN-GM 4 4:1 3.0:1
CN-GD 0.5 0.5:1 0.6:1
CN-GD 1 1:1 1.1:1
CN-GD 2 2:1 2.2:1
CN-GD 3 3:1 3.3:1
CN-GD 4 4:1 4.4:1
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model pollu an solu ion. Be o e he pho oca aly ic deg ada ion, each mix u e was s i ed in a glass cylind ical
essel o 200mL wi h 80mm in heigh and a diame e o 57mm in he da k o 60min o each adso p ion–
deso p ion equilib ium and hen was i adia ed om he op wi h an LED sou ce (420nm, in ensi y o 7.1 mW
cm−2) o 120min; he eac ion suspension empe a u es we e kep a 20°C. The aliquo s o 2mL we e aken a
egula in e als and il e ed using sy inge il e s Ch oma il GF/RC-20/25 ( he po e size o 0.2–1µm).
The pho oca aly ic ac i i y es ed on Rhodamine B was e alua ed by measu ing he abso bance a 554nm
using a Helios Alpha spec ome e (The mo Fishe Scien i ic, Wal ham, MA, USA). The amoun o decomposed
amoxicillin was de e mined using a high-pe o mance liquid ch oma og aph (HPLC) Wa e s 2996 (Wa e s
Co po a ion Mil o d, MA, USA) wi h a PDA de ec o . Fo he HPLC sepa a ion a Syne gi 4µm Pola -RP 80Å
(100 × 3mm) column was used. The mobile phase consis ed o he me hanol solu ion o 5mmol L−1 ammonium
o ma e and he wa e solu ion o 5mmol L−1 ammonium o ma e (30:70, / ) wi h he 0.5mL min−1 low.
Fo he de e mina ion o phenol 1mL o he decomposed phenol solu ion and 9mL o dis illed wa e we e pu
in a beake , 4mL o 5% solu ion o sodium ca bona e was added and mixed. Then, 4mL o a diazo ized solu ion
o 4-ni oaniline was added, mixed and a e 15min he abso bance was measu ed a 470nm. The diazo ized
colou less solu ion o 4-ni oaniline was p epa ed by adding 8–10 d ops o he sa u a ed sodium ni a e solu ion
o a 40mL o 5mmol L−1 4-ni oaniline dissol ed in he dilu ed HCl solu ion (1:9).
Applica ion o sca enge s. In a ypical expe imen wi h sca enge s, he ini ial concen a ion o Rhodamine B
and he pho oca alys s we e iden ical o he pho oca aly ic ac i i y es . EDTA was used as he sca enge o he
holes, p-benzoquinone as he sca enge o supe oxide adicals and e c-bu anol as he sca enge o hyd oxyl
adicals. The concen a ion o e e y sca enge in a s o age bo le was 1mmol L−1. An aliquo o 25mL o e e y
sca enge was added o 125mL o he ca alys suspension and Rhodamine B.
Pho oluminescence spec oscopy. S eady-s a e and ime- esol ed pho oluminescence (PL) measu e-
men s we e ca ied ou using a FLS980 luo escence spec ome e (Edinbu gh Ins umen s, UK) equipped wi h
a 450W xenon a c lamp and an EPL-375ps pulsed diode lase (λem = 372nm wi h a pulse wid h o 66.5ps, a
epe i ion a e o 10MHz and an a e age powe o 75µW (Edinbu gh Ins umen s, UK) as exci a ion sou ces.
PL decay cu es we e i ed using a mul i-exponen ial unc ion:
whe e I( ) is he in ensi y o pho oluminescence, is he ime, Bi coe icien s a e he ime-in a ian cons an s and
τi a e he decay imes (decay cons an s). A mean decay ime τm was calcula ed as
Scanning elec on mic oscopy. Fo he mic oscopic in es iga ions o he syn he ized ma e ials a scan-
ning elec on mic oscope Tescan Vega (Tescan O say Holding, B no, Czech Republic) wi h a ungs en ca hode
and an ene gy-dispe si e X- ay spec ome e (EDAX, Ame ex, PA, USA) was used. Mic og aphs we e ob ained
using a mix o he signals o seconda y elec ons (SE) and backsca e ed elec ons (BSE) mode o ge he bene i
o bo h echniques (SE + BSE) while educing he impac o hei d awbacks. The pa icles sized we e e alua ed
om he SEM mic og aphs by means o he ee so wa e Image J (Na ional Ins i u es o Heal h, Ma yland,
USA).
The mog a ime ic analysis wi h di e en ial scanning calo ime y. A de ice NETZSCH STA 449
F3 Jupi e wi h an S- ype measu emen holde was use o he mog a ime ic analysis (TGA) simul aneously
wi h di e en ial scanning calo ime y (DSC). App oxima ely 10mg o he p ecu so s and hei mix u es was pu
in o an Al2O3 c ucible wi hou a lid. Be o e hei hea ing, he inne space o a u nace was lushed a 20°C wi h
high pu i y a gon wi h a low o 240mL min−1 o one hou . A sample o he pu e p ecu so o hei mix u e was
hea ed up o 900°C wi h a linea hea ing a e o 5°C min−1. The cons an a gon low o 70mL min−1 was kep
du ing he whole analysis.
S a is ical da a analysis. The s a is ical da a analysis was pe o med a he α = 0.05 signi icance le el using
he so wa e package QC.Expe (T iloby e, Czech Republic).
Resul s and discussion
UV–Vis spec oscopy. A e he syn hesis and g ounding he e we e no signi ican isible di e ences
be ween he CN ma e ials (see Supplemen a y ma e ials, Fig.S1). The UV–Vis DRS spec a we e eco ded o
obse e ligh abso p ion p ope ies (Fig.1) and mainly o de e mine he op ical band gap ene gies o he syn-
he ized ma e ials.
The op ical band gap ( u he only band gap) ene gies (Eg) lis ed in Table2 a e andomly changing in he
ange o 2.67eV o 2.73eV. These alues (n = 13) we e s a is ically es ed: hei no mali y was con i med (skew-
ness = − 0.701, ku osis = 3.05, p = 0.454 o he momen es , p = 0.184 o he Kolmogo o –Smi no es , p = 0.458
o he D’Agos ino es ). The band-gap ene gies we e de e mined using he well-known Tauc me hod26 as ollows
(3)
I
( )=
3

i=1
Bie− /τi
,
(4)
τ
m=
B1τ
2
1+B2τ
2
2+B3τ
2
3
B1τ1
+
B2τ2
+
B3τ3
.
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whe e ε is he mola ex inc ion coe icien , hν is he ene gy o inciden pho ons, C is a cons an and p is powe
depending on he ype o elec on ansi ion. The powe p = 2 and p = ½ a e o di ec and indi ec semiconduc-
o s, espec i ely. In his wo k, p = ½ was used27. The Tauc plo s a e shown in Fig.S2.
Physiso p ion o ni ogen. The speci ic su ace a ea o syn he ized ma e ials was measu ed by he phy-
siso p ion o ni ogen and was e alua ed using he BET me hod, see Table2. The adso p ion–deso p ion iso-
he ms o all ma e ials a e shown in Fig.S3. The hys e esis loops demons a e he exis ence o mesopo es in
hese ma e ials.
(5)
ε
hν=C(hν−E
g
)
p,
Figu e1. UV–Vis di use e lec ance spec a o CN ma e ials.
Table 2. Band gap ene gy, speci ic su ace a ea and mesopo e olume o CN ma e ials.
Ma e ial Eg (eV) SSA (m2 g−1) Mesopo e olume (cm3g−1) × 10–3
CN-G 2.71 23 9.00
CN-M 2.67 12 5.73
CN-D 2.69 8 2.62
CN-GM 0.5 2.69 25 9.52
CN-GM 1 2.73 29 11.3
CN-GM 2 2.73 54 16.2
CN-GM 3 2.72 23 8.67
CN-GM 4 2.71 23 7.95
CN-GD 0.5 2.71 20 7.95
CN-GD 1 2.72 34 11.8
CN-GD 2 2.71 35 10.7
CN-GD 3 2.70 23 7.35
CN-GD 4 2.71 25 8.47
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The SSA o CNs p epa ed om he single p ecu so dec eased in he sequence CN-G > CN-M > CN-D. The
ma e ials syn he ized om he mix u e o wo pa s o guanidine hyd ochlo ide and one pa o melamine (CN-
GM 2) and dicyandiamide (CN-GD 2) had he highes alues o SSA wi hin he CN-GM se ies and CN-GD
se ies, espec i ely. The ma e ial CN-GM 2 had he highes mesopo e olume ollowed by CN-GD 1; CN-GM
1 and CN-GD 2. A s ong co ela ion ( = 0.966) be ween he SSA and he mesopo e olume was ound which
indica es he domina ing mesopo e s uc u e o hese ma e ials.
X‑ ay di ac ion analysis. The XRD pa e ns o syn he ized CN ma e ials we e e y simila o CN ones
syn he ized om single p ecu so s (Fig.2). The ypical g aphi ic ca bon s uc u es wi h he main di ac ions a
31.9° (002) and 14.8° (100) a ibu ed o in e laye s acking o he (002) melem planes and in-plane o de ing o
he ni ogen-linked hep azine uni s28 we e obse ed.
Roughly speaking, he size o c ys alli e L(002) calcula ed om he (002) di ac ions diminished wi h he
ising amoun o guanidine hyd ochlo ide in he mix u es (Table3). The d(002) spacings we e simila indica ing
no changes in he CN laye s ackings in dependence on he used p ecu so s.
FTIR spec oscopy. The s uc u e o he p epa ed ma e ials was s udied by FTIR spec ome y and
hei spec a a e displayed in Fig.3. Two egions A and B, which a e ypical o g aphi ic ca bon ni ide, we e
obse ed29–31. The bands a ound 3500 cm−1 a e ela ed o he s e ching ib a ions o –OH g oups. The bands in
egion A a e ela ed wi h he s e ching ib a ions o N–H bonds and he bands in egion B a e ela ed wi h he
s e ching ib a ions o he C=N and C–N bonds o he e ocyclic ings. The b ea hing mode o iazine uni s is
isible a ound 810 cm−1. The FTIR spec a o all he CN ma e ials we e simila and no e ec o he used p ecu -
so s was obse ed. The small bands a ound 710 cm−1 obse ed in he CN-GM3 and CN-GD3 we e explained by
he p esence o some labo a o y con aminan s.
Figu e2. XRD pa e ns o CN ma e ials (Co Kα).
Table 3. Selec ed XRD cha ac e is ics o CN ma e ials.
Ma e ial 2 The a (deg) FWHM (deg) L(002) (nm) d(002) (nm)
CN-G 31.82 1.96 4.71 0.326
CN-M 31.93 1.23 7.50 0.325
CN-D 31.77 1.69 5.46 0.327
CN-GM 0.5 31.93 1.43 6.45 0.325
CN-GM 1 31.88 1.88 4.91 0.326
CN-GM 2 31.93 1.82 5.07 0.325
CN-GM 3 31.86 2.02 4.57 0.326
CN-GM 4 31.84 1.98 4.66 0.326
CN-GD 0.5 31.96 1.50 6.15 0.325
CN-GD 1 31.91 1.84 5.01 0.325
CN-GD 2 31.89 1.70 5.43 0.326
CN-GD 3 31.84 2.16 4.27 0.326
CN-GD 4 31.91 1.96 4.71 0.325

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Elemen al analysis. The esul s o elemen al analysis o he CN ma e ials a e summa ized in Table4. The
C, H and N con en s we e de e mined by he elemen al analyse and he con en o O was calcula ed up o 100%.
The C/N mola a io was simila (a ound 0.66) o all he ma e ials which indica es hei simila inal s uc u es.
The e we e di e ences in he con en s o hyd ogen and oxygen. CN-G was mo e oxidized by ai oxygen (4.51
w %) han CN-M (1.88 w %) and CN-D (0.87%) likely due o he oxida ion endency o guanidine hyd ochlo-
ide. In he case o he CN-GM and CN-GD ma e ials (n = 10) he con en o oxygen changed andomly om
1.34 o 3.92 w %. Thei no mali y was con i med by he Kolmogo o –Smi no es (p = 0.633), he momen es
(p = 0.866) and he D’Agos ino es (p = 0.470). The p esence o chlo ine was no de ec ed by XRF.
Pho oca aly ic deg ada ion o o ganic compounds. The pho oca aly ic deg ada ions o RhB, phenol
and amoxicillin we e pe o med unde he LED i adia ion o 420nm. The pho olysis o hese compounds was
no obse ed. Figu e4 shows he deg ada ion e iciency o di e en CN ma e ials a e 120min. The maximal
pho oca aly ic ac i i y o CN-GM 2 and CN-GD 2 can be explained by hei maximal speci ic su ace a eas. The
selec ed kine ic cu es o he pho oca aly ic deg ada ion o RhB, phenol and amoxicillin a e shown in Fig.5.
The linea ela ionships o c/c0 e sus ime desc ibing he ze o-o de eac ions we e ound o all he o ganic
compounds and can be de i ed om he de ini ion o he ze o-o de eac ion a e as
whe e k is he kine ic cons an and c is he ac ual concen a ion o he o ganic compounds. One can see ha he
pho oca aly ic ac i i y dec eased in he sequence CN-GM 2 > CN-GD 2 > CN-M ≈ CN-G > CN-D in consis ency
wi h hei SSA which is in ag eemen wi h he esul s displayed in Fig.4.
The kine ic cons an s o all he es ed o ganic compounds and all he CN ma e ials a e summa ised in Table5.
F om his da a we can see ha (i) CN-GM 2 and CN-GD 2 we e he mos ac i e pho oca alys s (CN-GM 2 was
be e han CN-GD 2), (ii) he p esence o guanidine hyd ochlo ide in he p ecu so mix u es mos ly imp o ed
(6)
=−
dc
d
=k
,
Figu e3. FTIR spec a o CN ma e ials.
Table 4. Elemen al composi ion o CN ma e ials.
Ma e ial C (w %) H (w %) N (w %) O (w %) C/N mola a io
CN-G 34.00 1.39 60.10 4.51 0.660
CN-M 34.93 1.72 61.47 1.88 0.663
CN-D 34.70 3.43 61.00 0.87 0.664
CN-GM 0.5 34.73 3.04 60.89 1.34 0.665
CN-GM 1 34.80 1.44 61.50 2.26 0.660
CN-GM 2 34.64 2.62 60.79 1.95 0.665
CN-GM 3 34.41 2.47 60.48 2.64 0.664
CN-GM 4 34.10 1.48 60.50 3.92 0.658
CN-GD 0.5 34.45 2.50 60.56 2.49 0.664
CN-GD 1 34.40 1.68 61.10 2.82 0.657
CN-GD 2 34.52 2.50 60.69 2.29 0.664
CN-GD 3 34.05 2.66 59.81 3.48 0.664
CN-GD 4 34.70 1.51 61.10 2.69 0.663
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he pho oca aly ic ac i i ies o he inal CN ma e ials and (iii) he deg ada ion e iciency o he o ganic com-
pounds dec eased in he sequence RhB > amoxicillin > phenol likely due o hei di e en deg ada ion mecha-
nisms. The pho oca aly ic deg ada ion o RhB is di ec h ough ch omopho e clea age wi hou any isible ligh
abso bing p oduc s37. The pho oca aly ic deg ada ion o amoxicillin leads h ough wo pa hways38 and he com-
plex deg ada ion o phenol leads h ough ca echol, hyd oquinone and benzoquinone o a ious in e media es
which a e u he deg aded39,40.
Figu e4. Pho oca aly ic deg ada ion o RhB, phenol (Phe) and amoxicillin (Amox) a e 120min o isible
ligh i adia ion.
Figu e5. Kine ics cu es o pho oca aly ic deg ada ion o amoxicillin, RhB and phenol (CN-G, CN-M,
CN-D, CN-GM 2 and CG-GD 2) (The LED i adia ion o 420nm and he in ensi y o 7.1 mW cm−2). The
pho oca alys s concen a ion was 0.3g L−1.
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The s a is ically signi ican co ela ions o he kine ics cons an s and he SSA, such as = 0.916 o amoxi-
cillin, = 0.898 o RhB and = 0.886 o phenol, indica es he pho oca aly ic ac i i y depends on he speci ic
su ace a ea o hese CN ma e ials. The esul s ob ained in his wo k we e b ie ly compa ed wi h hose ound
in he li e a u e, see Table6. I is ob ious, o example, ha he pho oca aly ic e iciency o 54% o CN-GM 2
is compa able wi h hose o he o he au ho s and is lowe han 75% published in he pape 35. Howe e , in his
wo k a lowe loading o he pho oca alys and a sho e i adia ion ime we e used.
The s abili y o he CN ma e ials was es ed in 5 cycles o he pho oca aly ic deg ada ion o amoxicillin
(Fig.6). A e e e y cycle he ma e ials we e il e ed, washed wi h dis illed wa e and d ied a 105°C un il hei
cons an weigh . The deg ada ion e iciency o CN-GM 2 dec eased mo e, abou 9%, han o CN-GD 2 a e
he i s un. Howe e , he e iciency o bo h ma e ials s ayed nea ly cons an o he o he uns. The i s un
dec ease was likely caused by he loss o small pa icles du ing he i s il a ion. Mo eo e , he s abili y was
also con i med by he XRD analysis o he mos ac i e ma e ials CN-GD 2 and CN-GM 2 a e he i h un. No
Table 5. Kine ic cons an s o he deg ada ion o amoxicillin, RhB and phenol and mean decay imes o CN
ma e ials.
Ma e ial k(amoxicillin) × 10–3 (mol L−1 min−1)k(RhB) × 10–3 (mol L−1 min−1)k(phenol) × 10–3 (mol L−1 min−1) τm (ns)
CN-G 1.28 ± 0.08 1.87 ± 0.24 0.871 ± 0.057 9.1
CN-M 1.57 ± 0.21 1.64 ± 0.24 0.795 ± 0.031 8.0
CN-D 0.612 ± 0.075 0.737 ± 0.055 0.267 ± 0.025 8.8
CN-GM 0.5 1.98 ± 0.11 2.15 ± 0.10 0.754 ± 0.123 9.4
CN-GM 1 2.34 ± 0.13 2.87 ± 0.16 1.53 ± 0.16 9.2
CN-GM 2 5.05 ± 0.15 4.63 ± 0.51 2.05 ± 0.09 10.2
CN-GM 3 2.10 ± 0.18 2.68 ± 0.13 1.21 ± 0.08 9.5
CN-GM 4 1.56 ± 0.14 2.22 ± 0.13 0.928 ± 0.115 9.1
CN-GD 0.5 0.994 ± 0.223 1.70 ± 0.06 0.678 ± 0.027 8.9
CN-GD 1 2.20 ± 0.14 2.11 ± 0.11 1.39 ± 0.07 9.1
CN-GD 2 3.54 ± 0.75 3.14 ± 0.09 1.92 ± 0.08 9.3
CN-GD 3 1.55 ± 0.26 2.78 ± 0.10 0.900 ± 0.048 9.9
CN-GD 4 1.47 ± 0.26 2.72 ± 0.07 0.819 ± 0.049 9.4
Table 6. Compa ison o ob ained esul s wi h da a published in li e a u es.
P ecu so Me hod o syn hesis SSA (m2 g−1)
Compound,
concen a ion (mg
L−1)Concen a ion o
pho oca alys (g L−1)I adia ion ime
(min) E iciency (%) Re e ences
Guanidine hyd ochol-
o ide 5g, calcina ion in ai
550°C, 3°C/min, 4h 23 Rhodamine B
10 0.3 120 22 CN-G ( his wo k)
Melamine 5g, calcina ion in ai
550°C, 3°C/min, 4h 12 Rhodamine B
10 0.3 120 19 CN-M ( his wo k)
Dicyandiamide 5g, calcina ion in ai
550°C, 3°C/min, 4h 8Rhodamine B
10 0.3 120 9 CN-D ( his wo k)
Guanidine hyd ochlo-
ide and melamine 5g, calcina ion in ai
550°C, 3°C/min, 4h 54 Rhodamine B
10 0.3 120 54 CN-GM 2 ( his wo k)
Guanidine hyd o-
chlo ide
and dicyandiamide
5g, calcina ion in ai
550°C, 3°C/min, 4h 35 Rhodamine B
10 0.3 120 38 CN-GD 2 ( his wo k)
Guanidine hyd o-
chlo ide 4g, calcina ion in ai
550°C, 3°C/min, 3h 16 Rhodamine B
50.5 20 52 32
Guanidine ca bona e calcina ion in ai
550°C, 6°C/min, 3h 19 Me hyl o ange
20 4 120 24 23
Dicyandiamide calcina ion in ai
550°C; 6°C/min; 3h 18 Me hyl o ange
20 4 120 13 23
Melamine calcina ion in ai
550°C, 6°C/min, 3h 10 Me hyl o ange
20 4 120 30 23
Melamine calcina ion in ai
550°C, 3°C/min; 3h 7Me hyl o ange
20 1 300 24 33
Melamine 5g; calcina ion in ai
560°C, 4.5°C/min, 2h –Rhodamine B
10 0.3 60 25 34
Dicyandiamide 3g; calcina ion in ai
550°C, 4h 10 Rhodamine B
10 1 180 75 35
Dicyandiamide 2g; calcina ion in ai
550°C, 5°C/min, 4h 14 Rhodamine B
10 1 90 60 36
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s uc u al changes we e obse ed as shown in Fig.S4. The s abili y es s showed ha he CN ma e ials a e s able
agains pho oca aly ic deg ada ion.
S udy o pho oca aly ic mechanisms. The pho oca aly ic mechanisms o he pho oca aly ic deg ada ion we e
s udied using sui able sca enge s. Holes, supe oxide and hyd oxyl adicals we e sca enged wi h EDTA, p-ben-
zoquinone and -bu anol, espec i ely. The changes in he pho oca aly ic ac i i y a e shown in Fig.7. I is ob i-
12345
0
10
20
30
40
50
60
70
E iciency (%)
Numbe o cycle
CN-GM 2
CN-GD 2
Figu e6. S abili y es s o CN-GM 2 and CN-GD 2 ma e ials.
53 50
5
52
37 36
2
35
no sca . EDTA p-benzoquinone -bu anol
0
10
20
30
40
50
60
70
E iciency (%)
CN-GM 2
CN-GD 2
Figu e7. Pho oca aly ic decomposi ion o RhB in he p esence o CN-GM 2 and CN-GD 2 using sca enge s
o holes (EDTA), supe oxide adicals (p-benzoquinone) and hyd oxyl adicals ( -bu anol). The decomposi ion
ime was 120min. The RhB concen a ion was 10mg L−1.
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beha iou o all he p ecu so s which con ibu ed o an explana ion o he eac ion pa hways o guanidine
hyd ochlo ide and melamine/DCDA and he sugges ions o he inal dis up i e CN s uc u e o ma ions.
One ma e ial om each se ies consis ing o wo mass pa s o guanidine hyd ochlo ide and one pa o
melamine ( he GM se ies) o DCDA ( he GD se ies) possessed he highes speci ic su ace a ea o 54 m2 g−1
and 35 m2 g−1, espec i ely, and he highes pho oca aly ic ac i i y conce ning he deg ada ion o amoxicillin,
Rhodamine B and phenol. The ze o-o de kine ics o all he CN ma e ials and he o ganic compounds we e
obse ed. Supe oxide adicals we e ound o be he main pho oca aly ic agen s. The pho oca aly ic s abili y o
he CN ma e ials was p o ed by he 5 epea ed deg ada ions o amoxicillin. The PL decay s udy e ealed ha
he li e imes o pho oinduced elec ons and holes we e independen o he CN ma e ials’ composi ion and hese
cha ge ca ie s ecombined wi h localised luminescence cen es. The signi ican co ela ions be ween he pho-
oca aly ic eac ion a e cons an s and he SSAs indica ed he pho oca aly ic ac i i ies o he CN ma e ials we e
dependen on hei speci ic su ace a eas ( = 0.916 o amoxicillin, = 0.898 o RhB and = 0.886 o phenol).
The main ole o guanidine hyd ochlo ide in he syn hesis o g aphi ic ca bon ni ide was ound in e ms
o a ec ing i s speci ic su ace a eas. The SSA inc eased due o he c ea ion o po es as a esul o he eleasing
o NH3 and HCl and due o he HCl complex eac ions o ming s uc u e impe ec ions and dis up ions. The
ob ained esul s e ealed how he pho oca aly ic p ope ies o g aphi ic ca bon ni ide can be changed and
employed o he deg ada ion o o ganic en i onmen al pollu an s.
Recei ed: 23 July 2021; Accep ed: 21 Oc obe 2021
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Acknowledgemen s
This wo k was suppo ed by he Czech Science Founda ion (P ojec No. 19-15199S), EU s uc u al unding in
Ope a ional P og am Resea ch, De elopmen and Educa ion (P ojec s No. CZ.02.1.01/0.0/0.0/16_019/0000853
and CZ.02.1.01/0.0/0.0/17_049/0008419) and by VŠB-TU Os a a (P ojec No. SP 2021/46). The au ho s also
hank he La ge Resea ch In as uc u e ENREGAT (P ojec No. LM2018098). The au ho s hank p o . D . B.
Sme ana (VŠB-TU Os a a) o he measu emen o TGA/DSC and D . A. Ma aus (CEET; IET) o he XRD
measu emen .
Au ho con ibu ions
A.S. and P.P. analysed he expe imen al da a and w o e he manusc ip , A.S. and K.F. syn he ized CN ma e ials,
pe o med some cha ac e iza ions and pho oca aly ic expe imen s, K.G. ook SEM mic og aphs, D.C. d ew
s uc u es and eac ions and w o e he manusc ip . All au ho s discussed he esul s. All au ho s ha e ead and
ag eed wi h his manusc ip e sion.
Compe ing in e es s
The au ho s decla e no compe ing in e es s.
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