inorganics
Article
Nano-ZrO2@C, Nano-(ZrC, ZrO2)@C and Nano-ZrC@C
Composites Prepared by Plasma-Assisted Carbonization of
Zr-Loaded Iminodiacetate-Functionalized
Styrene-Divinylbenzene Copolymers
Alejandro Martiz 1,2 , Zoltán Károly 1 , Attila Domján 1 , Miklós Mohai 1 , Laura Bereczki 1 , László Trif 1 ,
Attila Farkas 3 , Krisztina László 2 , Alfréd Menyhárd 2 and László Kótai 1,4, *
1
2
3
4
*
Citation: Martiz, A.; Károly, Z.;
Domján, A.; Mohai, M.; Bereczki, L.;
Trif, L.; Farkas, A.; László, K.;
Menyhárd, A.; Kótai, L.
Nano-ZrO2 @C, Nano-(ZrC, ZrO2 )@C
and Nano-ZrC@C Composites
Prepared by Plasma-Assisted
Carbonization of Zr-Loaded
Iminodiacetate-Functionalized
Styrene-Divinylbenzene Copolymers.
Inorganics 2022, 10, 77. https://
doi.org/10.3390/inorganics10060077
Academic Editor:
Carlos Martínez-Boubeta
Received: 21 April 2022
Accepted: 31 May 2022
Published: 2 June 2022
Publisher’s Note: MDPI stays neutral
Research Centre for Natural Sciences, Institute of Materials and Environmental Chemistry,
Magyar Tudósok krt. 2, H-1117 Budapest, Hungary; josalmar20@gmail.com (A.M.);
karoly.zoltan@ttk.hu (Z.K.); domjan.attila@ttk.hu (A.D.); mohai.miklos@ttk.hu (M.M.);
nagyne.bereczki.laura@ttk.hu (L.B.); trif.laszlo@ttk.hu (L.T.)
Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics,
Műegyetem rakpart 3, H-1111 Budapest, Hungary; laszlo.krisztina@vbk.bme.hu (K.L.);
menyhard.alfred@vbk.bme.hu (A.M.)
Department of Organic Chemistry, Budapest University of Technology and Economics, Műegyetem rakpart 3,
H-1111 Budapest, Hungary; farkas.attila@vbk.bme.hu
Deuton-X Ltd., Selmeci u. 89, H-2030 Érd, Hungary
Correspondence: kotai.laszlo@ttk.hu
Abstract: We have developed an easy route to prepare (nano-ZrO2 ,nano-ZrCx )@C composites with
varying ZrO2 /ZrCx content. The process consists of preparing a zirconium-loaded, iminodiacetatefunctionalized styrene-divinylbenzene (STY-DVB) copolymer, and its subsequent carbonization in
a tube furnace and/or a thermal plasma reactor. Depending on the zirconium salt used (zirconyl
chloride, zirconyl nitrate or zirconium (IV) sulfate) in the Zr loading, the Zr-loaded resins resulted in
ZrO2 @C pre-pyrolizates with C to Zr molar ratios of 5.8, 6.8 and 6.60. This carbon surplus is sufficient
for the partial or even complete reduction of ZrO2 into ZrC0.58 at 1400 ◦ C. The reaction products
also contain 5 to 55 mass% residual free carbon. The plasma processing of the ZrO2 @C composite
formed at 1000 ◦ C in a tube furnace led to ZrC0.94 @C composites. The transformation of amorphous
carbon content during the plasma treatment strongly depended on the atmosphere (He or H2 ) in
the reactor and the anion type of the Zr salt. In the presence of He, amorphous carbon could be
completely transformed into graphite. In the presence of H2 , amorphous carbon and graphite were
found at roughly the same ratio. No ZrO2 could be detected in the plasma-treated samples, whilst
different ZrO2 polymorphs were found in the samples prepared in the tube furnace, depending on
the synthesis conditions.
Keywords: zirconium carbide; zirconium dioxide; imino-diacetate functionalization; styrenedivinylbenzene copolymer; thermal decomposition; evolved gas analysis; nanocomposites
with regard to jurisdictional claims in
published maps and institutional affiliations.
1. Introduction
Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Composites containing zirconium carbide, amorphous carbon or graphite and
some or no ZrO2 are important strategic materials for the nuclear industry due to their
advantageous mechanical properties, neutron absorption cross-section and radiolytic
stability [1–4]. A recently developed method of synthesizing (nano-ZrC,nano-ZrO2 )@C
composites is the high-temperature or plasma-assisted carbonization of Zr-loaded functionalized polymers. This can be achieved with polyacrylonitrile-ZrCl4 composites [3]
and quaternary ammonium salt or styrene-divinylbenzene copolymers containing a
sulfonate group and loaded with anionic [4] and cationic zirconium species [5], respectively, as precursors. The homogeneous distribution of the functional groups allows
Inorganics 2022, 10, 77. https://doi.org/10.3390/inorganics10060077
https://www.mdpi.com/journal/inorganics
Inorganics 2022, 10, 77
2 of 27
for zirconium to be bound at an atomic level, enhancing the distribution of ZrC in the
carbon matrix after carbonization.
The chemical nature of functional groups (sulfonate or iminodiacetate) and DVB
content in the STY-DVB copolymer have a significant influence on the chemical nature
of metal compounds embedded in the carbon matrix during the carbonization of metalloaded, functionalized, styrene-divinylbenzene (STY-DVB) copolymers, [6–8]. In fact, ZrC
could be prepared by the carbonization of the quaternary ammonium group-containing
and anionic Zr-loaded STY-DVB resins at 1350 ◦ C [3], whereas only ZrO2 @C composites
were formed from the sulfonated resins [5]. Due to the moderate reactivity of ZrO2 in these
composites, their subsequent RF plasma treatment in either a He or H2 atmosphere [5] only
resulted in a partial conversion of ZrO2 into ZrC.
Our goal was to study the effect of functional groups on the formation and composition
of zirconium carbide using STY-DVB copolymer precursors functionalized with groups
that differed from sulfonate or quaternary ammonium. Since no information is available on
the carbonization reactions of Zr-loaded iminodiacetate-functionalized STY-DVB resins, we
studied the formation of ZrC in the carbonization process of these resins in both a tubular
furnace and/or a thermal plasma-assisted process.
It is known that STY-DVB resins functionalized with iminodiacetate groups and loaded
with a polyvalent element such as iron(III) have special properties due to the divalent
selective iminodiacetate groups and the presence of a third, outer counter-ion neutralizing
the third valence of iron(III) (X=Cl, nitrate or sulfate) [7,9,10]. Therefore, we conducted a
detailed study of the influence of counter-ions such as chloride, nitrate, or sulfate on the
chemical form of Zr in Zr-loaded iminodiacetate-functionalized STY/DVB copolymers.
Hereinafter, the prepared materials are referred to as L-X, L-Zr-X, L-Zr-X-T-t, where
L stands for the Lewatite resin skeleton, X stands for the anion in the mineral acid or Zr
salt used in H or Zr loading, respectively. T corresponds to the pyrolysis temperatures
(1000, 1200, 1400 ◦ C), whereas t represents reaction time (2 or 8 h). The L-Zr-X-1000-2
samples subjected to subsequent RF plasma processing in a H2 and He atmosphere
were labeled as L-Zr-X-1000-2-P-H2 /He, as summarized in Table 1. Sulfate and nitrate
ions were given the abbreviations S and N, respectively, in the L-Zr-X, L-Zr-X-T-t and
L-Zr-X-100-2-P-H2 /He formulas.
Table 1. Labels for samples.
Label
L-X
L-X-Zr
L-X-Zr-T-t
L-Zr-X-1000-2-P-H2 /He
Description of Sample
H-form of iminodiacetate-functionalized STY-DVB copolymers
containing 2 mass% DVB.
Zirconium-loaded iminodiacetate-functionalized STY-DVB
copolymer samples containing 2 mass% DVB with ZrOX2 (X=Cl
NO3 ) and Zr(SO4 )2 (X=S) salts.
Samples obtained by carbonizing L-X-Zr resins at the given T
temperature and for a carbonization time of t.
Plasma-treated samples from L-Zr-X-1000-2 samples containing
ZrO2 @C in a H2 or He atmosphere.
In this paper, we present the preparation conditions and properties of nano(ZrCx ,ZrO2 )@C composites made in a tube furnace (1000–1400 ◦ C for 2–8 h) from
Zr-loaded iminodiacetate-functionalized STY-DVB resins, and nano-ZrCx @C samples
from L-Zr-X-1000-2 samples containing ZrO2 . The method we used was RF thermal
plasma treatment. We also conducted a detailed study of the chemical nature of Zr in
the L-Zr-X samples, the number of iminodiacetate groups in the STY-DVB polymer
chain, and the influence of the degree of Zr saturation and the anion of the Zr salt used
during Zr loading on the properties of the forming nano-(ZrO2 , ZrC)@C.
Inorganics 2022, 10, 77
3 of 27
2. Results and Discussion
2.1. Preparation and Properties of Zr-Loaded Ion-Exchangers (L-Zr-X, X=Chloride (Cl), Nitrate
(N) and Sulfate (S))
The iminodiacetate-functionalized styrene-divinylbenzene copolymer was prepared
via chloromethylation of STY-DVB copolymer containing 2% DVB exclusively at the metaposition of STY rings [11] with subsequent coupling with iminodiacetic acid diethyl ester
and by alkaline hydrolysis (ESI Scheme S1). The sodium salt of the resin containing
the iminodiacetate group was activated with 10% HCl, HNO3 and H2 SO4 (Scheme 1a),
resulting in L-X resins as starting materials.
Scheme 1. (a) Synthesis route of Zr-loaded iminodiacetate functionalized STY-DVB copolymers;
(b) the structure of chelating (a), neutralizing (a) and surplus (b) iminodiacetate groups in the
L-Zr-X complexes.
Inorganics 2022, 10, 77
4 of 27
The Zr-loading of L-X resins was performed with zirconium salts containing X anions, namely 0.5% zirconyl chloride (ZrOCl2 .8H2 O in a 3 M HCl solution), 0.5% zirconyl
nitrate (in 3 M HNO3 ) and 0.5% zirconium (IV) sulfate (in 1.5 M H2 SO4 ) (Scheme 1a).
Due to their acidic pH, the formal chemical species of zirconium (IV) was the “zirconyl”
ion, ZrO2+ [12–14]. Therefore, the CHNS elemental analysis data of L-Zr-X resins, the
zirconium content of the solution eluted during Zr loading, and the amounts of L-X
resins/salts containing zirconium used provide sufficient information for the calculation of the Zr/iminodiacetate group ratio (loading rate), water content and the Zr/C
ratios according to the method given by Dunlop CJ et al. [15] (Supplementary Materials,
Table S1).
The ratio of N content (x mole of iminodiacetate is located on the DVB and STY
rings) and carbon content (x mole of methylene-iminodiacetic acid groups and the polymer
chain consisting of DVB and STY) suggests that almost exactly one -CH2 N(CH2 COO)2 2group is located on every aromatic (STY or DVB) ring (Table S1). This means that during
chloromethylation of the base polymer (STY-DVB) [16] (and consecutive coupling with
iminodiacetic acid ester), only one chloromethyl group (iminodiacetate group) was inserted
into every aromatic ring and, according to the synthesis conditions, it was built exclusively
into the meta-position (see the IR results below and Supplementary Materials Figure S1)
(Supplementary Materials, Scheme S1).
Knowing the ratio of STY/DVB/-CH2 N(CH2 COO)2 2- groups, we calculated the number of hydrogens belonging to these building elements. The ratio of Zr loading and the
amount of iminodiacetate groups in L-Zr-X samples was easy to calculate from the molar
ratio of nitrogen and zirconium contents. Zr loading was 34.8%, 27.0% and 22.8% for
the samples produced from zirconyl chloride, zirconyl nitrate and zirconium (IV) sulfate, respectively. The difference between the calculated and measured hydrogen content
may be attributed to the presence of swelling water, whose amounts were around ~20%
(Supplementary Materials Table S1).
2.2. The Chemical Nature of Zirconium in the L-Zr-X Samples
The chelate-forming ability of the iminodiacetate group resulting in the coordination
of a nitrogen lonely electron pair to the zirconium d orbitals stabilizes the chelate structure.
In this way, the protonation possibility of a tertiary nitrogen atom with HX acids in the
chelate ring is lost. Therefore, the presence of foreign anions (chloride, nitrate and sulfate)
due to the protonation of tertiary N atoms cannot be expected. The iminodiacetate group is
a divalent-ion selective group; thus, one iminodiacetate group neutralizes only two charges
of a multivalent cation, and one or more foreign ions neutralize the surplus charges, as was
observed in the case of L-Fe-X complexes containing Fe(III) ions [6–9]. In principle, the
counter-ions in the salts used for Zr loading (chloride, nitrate or sulfate) may neutralize
foreign anions. However, the elemental analysis data and IR spectroscopy results on L-Zr-X
compounds show the absence of any foreign anion; thus, the tertiary amino group of the
-CH2 N(CH2 COOH)2 part must be self-protonated with one of its carboxylic acid group
(-CH2 NH(CH2 COO)(CH2 COOH) (Scheme 1b)).
The almost identical N content in the three L-Zr-X samples or the lack of sulfur
indicates the absence of nitrate or sulfate anions (Supplementary Materials, Table S1). The
matching IR patterns for L-Zr-X samples (X=Cl, N and S, Supplementary Materials, Figure
S2) confirm that the chemical nature of these samples is practically the same. Most of the
sulfate and nitrate IR bands would coincide with the IR bands of the iminodiacetate group
and STY-DVB skeleton. A comparison of the IR spectra of the HCl, HNO3 and H2 SO4 salts
of the iminodiacetic acid (Supplementary Materials, Figure S3) and L-Zr-Cl (Supplementary
Materials, Figure S2) resins showed that the νas (S-O) and νd (N-O) modes of sulfate and
nitrate ions could be identified in the IR spectra of [HN(CH2 COOH)2 ].HX (X=NO3 and
1
−1 and a singlet at 1057 cm−1 , respectively. These
2 SO4 ) salts as a doublet at 1143/1042 cm
bands should appear in these spectral ranges to show the presence of sulfate and nitrate
Inorganics 2022, 10, 77
5 of 27
ions in the IR spectra of L-X and L-Zr-X resins if the tertiary N atom of the iminodiacetate
fragment is protonated with the HX (X=N or S) acids.
However, a comparison of the L-X and L-Zr-X compounds (Supplementary Materials,
Figures S4–S6) showed that neither the L-X compounds nor the L-Zr-X compounds contain
foreign anions (Cl- , NO3 - or SO4 2- ). The presence of the Zr=O group or its hydrated form
(Zr(OH)2 ) with oxide- or hydroxide-neutralizing anions cannot be confirmed because
of the absence of a strong and wide band at 1020–870 cm−1 characterizing the zirconyl
ion [14–17]. Yuchi et al., assumed the presence of Zr species of the type L-Zr(OH)2 in
a Zr-saturated IDA resin, but we did not observe any strong and sharp bands of ionic
OH [17,18] above 3500 cm−1 in the IR spectra of our L-Zr-X resins (Figure 1). Therefore, a
similar chemical environment of the N atom is expected in all six L-X and L-Zr-X (X=Cl, N
and S) compounds.
Figure 1. IR spectra of IDA-S, L-S and L-Zr-S samples.
The IR spectra of L-X and L-Zr-X resins showed the typical C-H (aromatic and aliphatic)
and C-C (aromatic ring) and other vibrational modes of the polystyrene-divinylbenzene
copolymers [5,19,20], and the typical normal modes of iminodiacetate groups as well [21].
The evaluation of the spectra imposes a challenge due to the substantial overlaps of the
polystyrene network and iminodiacetate group modes. The most critical peaks agree with
the reference values [5,14,22–28] given for polystyrene-DVB samples. There is no peak
at 1680 cm−1 associated with the free vinyl groups of the crosslinker. Thus, there are
no pendant vinyl groups in the samples. The lack of a peak at 833 cm−1 and the steric
Inorganics 2022, 10, 77
6 of 27
hindrance of the ortho positions due to the steric demand of iminodiacetate groups confirm
the meta-substitutions on the STY rings [24].
Even when we used a significant excess of zirconium salt, we could not saturate the
iminodiacetate groups—the ratio of uncomplexed/chelated iminodiacetate groups in the
L-Zr-X samples was ~2:1, ~3:1 and ~4:1 for X=Cl, N and S, respectively. Since the iminodiacetic acid groups forming in the acidic environment during Zr loading rearrange into
an N-protonated form with the formation of a carboxylate group, a “free” iminodiacetic
group can act as a monovalent acid. It can be considered as only a monovalent anion,
[HN(CH2 COO)2 ]- . Thus, the counter-ions of zirconium (IV) used to neutralize the excess
of two charges of zirconium (IV) may be two ionic unchelated iminodiacetate groups
(Scheme 1b). Due to intramolecular self-protonation, a minimum of two free iminodiacetate groups need to neutralize one chelated iminodiacetate-coordinated zirconium.
Thus, the Zr-loading of iminodiacetate groups in the L-Zr-X samples may not be higher
than 1/3 due to the 2:1 ratio of monovalent anionic and chelated iminodiacetate groups,
respectively, as was found in the case of the zirconyl chloride-loaded L-Zr-Cl sample
(Scheme 1b).
To confirm the presence of the protonated/Zr-coordinated nitrogen atoms in the L-ZrX samples, we used solid-state 15 N and 13 C CP MAS NMR spectroscopy. Deconvolution
of the broad 15 N CP-MAS NMR signal of the iminodiacetate nitrogen resulted in two
components for both samples, L-N and L-Zr-N (315/330 and 317/332 ppm, Figure 2a,b,
respectively). The signal at 315 ppm may be attributed to the protonated N-atom, whereas
the signal at 317 ppm can be attributed to the protonated and Zr-coordinated N-atom. This
latter signal is broadened by the quadrupolar magnetic nature of the Zr. A weak 15 N signal
of the unprotonated tertiary N atom (due to the equilibrium character of the protonation
reaction) also appears in both spectra.
The chemical shifts in the nitrogen atoms in protonated and coordinated forms
(Scheme 1b) are similar—the electron-shielding environment is similar. In other words,
the strength of the coordination of Zr to the nitrogen atom in the iminodiacetate group of
L-Zr-X samples is close to the strength of the proton binding to the protonated nitrogen
atoms in -HN(CH2 COOH)(CH2 COO) or -HN(CH2 COO)2 - groups (Scheme 1b).
When X= sulfate and nitrate, the chelated/unchelated iminodiacetate group ratios
were 1:4 and 1:3, respectively. The free iminodiacetate groups are in their acidic form
according to the low pH used during Zr loading and, due to self-protonation, these are
in the [-CH2 -NH(CH2 COO)(CH2 COOH) (Scheme 1b) form [29]. The asymmetric nature
of these iminodiacetate groups results in two C=O carbonyl signals [28] in the 13 C NMR
spectra of the L-X-Zr samples (Supplementary Materials, Figure S7).
Due to the lack of foreign neutralizing ions in the L-Zr-X samples, a question arises:
why is Zr loading so different depending on the chemical form of the zirconium salt used
in the loading experiments?
The zirconium(IV) ion easily hydrolyzes/polymerizes in aqueous solutions, even
under highly acidic conditions [12]. The exclusive form of zirconium(IV) in aq. solutions
above pH > 0 are zirconyl ions (ZrO2+ ), but the counter-ions have an enormous influence
on the chemical nature of the species containing Zr. For example, solid zirconyl nitrate,
ZrO(NO3 )2·5H2 O, consists of H2 [ZrO(NO3 )4 ].H2 O anionic species. It completely dissociates in its aqueous solutions with the formation of a neutral ZrO(OH)NO3 , which could
not be loaded on a cationic (Amberlite IR 100) ion exchanger [13].
Zirconium sulfate strongly hydrolyzes in water. Basic zirconium sulfates are formed,
including zirconyl sulfate, given the affinity of zirconium to sulfate, which is higher than
the affinity to water. Thus, the sulfate ion is bound to zirconium strongly even in aq.
solutions. For example, the electrolysis of aqueous Zr(SO4 )2 solutions results in hydrogen
evolution on the cathode, and H2 [ZrO(SO4 )2 ·3H2 O] was identified in the solution [30],
which contains the zirconium in an anionic species.
Inorganics 2022, 10, 77
7 of 27
Figure 2.
15 N
CP MAS solid-state NMR spectra of L-NO3 (a) and L-Zr-NO3 (b) samples.
Solid zirconyl chloride (ZrOCl2 .8H2 O) is a tetramer, [Zr4 (OH)8 (H2 O)16 ]Cl8 [12], and
the zirconyl ion is the dominant form in its aqueous solutions. Zirconium (IV) ions would
form only in >12 M HCl solutions and at a very low (0.0001 M) zirconium concentration [12].
We used a 0.055 M zirconyl chloride solution in 10% aq. HCl, thus, this solution contained
only ZrO2+ and not Zr4+ ions.
The solution-phase zirconium species form complex equilibriums with the resin-phase
iminodiacetate group. The difference between the chemical forms of zirconium in the
solutions of the three zirconium salts may be attributed to the differences in Zr loading on
the L-X resin under identical Zr loading conditions.
Inorganics 2022, 10, 77
8 of 27
2.3. Thermal Studies on Compounds L-Zr-X
During the heat-induced carbonization of STY-DVB copolymers—with or without functionalization with functional groups—a part of the carbon content turns into volatile compounds such as hydrocarbons and the cracking products of the functional groups [6,9]. The
iminodiacetate group is expected to be cracked into fragments of the CH2 N(CH2 COOH)2
group, including H2 O (from dehydration) or CO2 (from decarboxylation) and various
fragments containing N [31]. The evolution of H2 O, CO2 , STY, DVB, some aromatic hydrocarbons, and the expected fragmentation products of the iminodiacetate group containing
N is illustrated as a function of temperature (Figures 3 and 4 and Supplementary Materials,
Figures S8–S10).
Figure 3. TG-MS curves for H2 O and CO2 evolution during decomposition of L-Zr-X samples.
The ratio of solid to volatile carbon compounds strongly depends on the decomposition
temperature, heating rate, and DVB content and is influenced by the presence of metal
ions and the extent of metal loading [6,9]. Generally, the higher the metal or DVB content,
the more solid carbon products are formed [6,32–34]. Either the 2% DVB content or the
incomplete saturation of functional groups by zirconium is a favorable condition for low
solid carbon content in the decomposition products [5,6], increasing the Zr/C ratio in the
carbonized material. Therefore, first, we studied the mass loss ratio of volatiles (H2 O, CO2 ,
and organic decomposition products)/solids (ZrC, ZrO2 and carbon) at 800 and 1400 ◦ C.
The measured C/ZrO2 ratios in the pre-pyrolyzed products of L-Zr-X samples formed
at 800 ◦ C (after eliminating all organic volatiles) were ~5.8, ~6.8 and 6.64 for X=Cl, N
and S, respectively. Thus, the C/Zr ratio ensures that there is enough carbon content to
form ZrC from ZrO2 /C intermediates. The free carbon contents of the decomposition
Inorganics 2022, 10, 77
9 of 27
products formed at 1400 ◦ with a 10 ◦ C/min heating rate were ~10, ~5 and ~45 mass% for
the composites prepared from L-Zr-X resins (X=Cl, N and S), respectively.
Figure 4. TG-MS decomposition curves of iminodiacetate group (a) and STY-DVB skeleton fragments,
depolymerization products (b), and aromatics (c) of L-Zr-Cl sample.
Inorganics 2022, 10, 77
10 of 27
The thermal decomposition of the L-Zr-X samples (X=Cl, N and S) started similarly,
by losing the swelling water and some adsorbed organic materials from the pores of the
hydrophilic STY-DVB polymer network below 200 ◦ C (Figure 3). The TG-MS curves first
showed the elimination of water. Loss of the iminodiacetate functional groups occurred
with the evolution of CO2 , H2 O and CH2 COO fragments (Figures 3 and 4, Supplementary
Materials, Figures S8 and S9) at around ~220 and ~320 ◦ C. Depolymerization first
occurred around ~320 ◦ C, with the formation of STY and DVB. Complete cracking of
the organic residues occurred with the formation of aromatic compounds between 400
and 500 ◦ C. The TG-MS curves of decarboxylation, dehydration, depolymerization and
cracking are given for L-Zr-X samples in Figure 4 and Supplementary Materials, Figures
S8 and S9. The TG-DSC curves of the L-Zr-X systems are attached as Supplementary
Materials, Figure S10.
Water elimination, depolymerization and cracking are endothermic, whereas the
decomposition of the iminodiacetate functional groups was exothermic for L-Zr-X (X=Cl,
N) samples. For X=S, all when the lower amount of Zr is adsorbed on the resin, all the
reactions are endothermic (Supplementary Materials, Figure S8a–c). For X=N, zirconium
carbide formed as an endothermic process, starting at 1180 and completed at 1321 ◦ C.
2.4. The Composition of Carbonization Products
Carbonization was first studied in a tubular furnace at 1000, 1200 and 1400 ◦ C for 2 h.
The effect of reaction time was examined at 1400 ◦ C—holding time was increased up to 8 h.
Orthorhombic and tetragonal ZrO2 were detected as primary decomposition products at
1000 ◦ C. The orthorhombic/tetragonal ratio strongly depended on Zr loading and was 1.36,
0.77 and 0 for the samples with X=Cl, N and S, respectively. Furthermore, the crystallite
sizes of ZrO2 particles ranged between 5 and 10 nm for these samples (Table 2).
Table 2. Composition and properties of (ZrC0.58 , ZrO2 )@C composites prepared from L-Zr-Cl, L-Zr-N
and L-Zr-S resins in a tubular furnace.
Composite
ZrC,
(wt%)
(Size in nm)
L-Zr-Cl-1000-2
-
L-Zr-Cl-1200-2
L-Zr-Cl-1400-2
L-Zr-Cl-1400-8
75 (10)
80 (10)
85 (14)
L-Zr-N-1000-2
-
L-Zr-N-1200-2
L-Zr-N-1400-2
L-Zr-N-1400-8
L-Zr-S-1000-2
65 (10)
95 (17)
95 (18)
-
L-Zr-S-1200-2
50 (8)
L-Zr-S-1400-2
30(13)
L-Zr-S-1400-8
50 (56)
ZrO2
(wt%)
(Size in nm)
65 (5)
Ortho/tetra = 1.36
15 (11) tetra
10 (12) tetra
5 (26) tetra/mono = 1.92
80(5)
ortho/tetra = 0.77
25 (7) tetra
10 (8)
10 (8)
ortho/tetra = 0.26
15 (8) tetra
5 (31)
mono/cubic = 1.05
Carbon
(wt%)
BET Surface Area
(m2 /g)
35
140
10
10
10
311
310
245
20
278
10
5
5
90
447
430
438
33
40
41
55
54
55
35
As carbonization temperature was increased to 1200 ◦ C, a cubic ZrC0.58 (a = 4.6690 Å,
Fm3m) appeared as the main reaction product (75, 65 and 50 mass% ZrC and 15, 25 and
10 mass% ZrO2 content for X=Cl, N and S, with a crystallite size of ~10 nm in every
case (Table 2)). The exact composition of ZrC was calculated from the lattice constants
determined by XRD (Figure 5 and Supplementary Materials, Figure S11), with the Gusev
equation [35], which was valid for ZrCx samples with 0.5 < x < 1.0. Senczyk’s equation [36]
valid for samples 0.65 < x < 01.0 did not give results in this range, which shows that x is
out of the validity range of the equation. Residual amorphous carbon content would be
Inorganics 2022, 10, 77
11 of 27
enough to form stoichiometric ZrC by incorporating carbon into the ZrC0.58 structure at
high-temperature heat treatment [37,38]. Thus, two sets of heat-treatment tests were carried
out at 1400 ◦ C with treatment times of 2 h and 8 h, and an RF plasma treatment was also
performed in an H2 and He atmosphere on nano-ZrO2 @C samples with Zr/C atomic ratios
of ~5.8, ~6.8 and 6.64.
Figure 5. XRD pattern of L-Zr-X-1400-8 and L-Zr-X-1000-2-P-He (X=Cl, N and S) samples.
The heating time of 2 h at 1400 ◦ C resulted in ZrC0.58 @C (X=N) and (ZrC0.58 ,ZrO2 )@C
composites with a ZrC0.58 /ZrO2 molar ratio of 8 and 2 (Table 2). ZrO2 was only detected
as its tetragonal modification in these samples. Increasing the heating time to 8 h resulted
in an increasing ZrC0.58 content and a partial transformation of ZrO2 into its monoclinic
form (the tetragonal/monoclinic ratio was 2 and 5 for X=Cl and S, respectively). The
crystallite sizes of ZrC0.58 ranged between 10 and 20 nm. Neither graphite nor Zr3 C2
was found in these samples. Even under prolonged heating, additional carbon atoms
were not incorporated into the ZrC0.58 structure. The reactivity of ZrO2 and carbon
species in composites prepared from various Zr-loaded resins with various zirconium
content was different in the carbonization reactions, despite the lack of foreign anions
in the L-Zr-X samples. Therefore, we studied the behavior of all three L-Zr-X-1000-2
Inorganics 2022, 10, 77
12 of 27
composites (containing ZrO2 ) (X=Cl, N and S) in RF plasma under an inert (He) and a
reducing (H2 ) atmosphere.
Due to the high temperature that prevailed in the RF thermal plasma, the carbonization reaction between the ZrO2 and C species took place rapidly and zirconium carbide
crystallized with a composition of ZrC0.94 (a = 4.6930, Fm3m) could be prepared. The ZrC
stoichiometry in ZrCx was determined from the lattice constants of the particular samples
(Figure 5) with the Senczyk equation [36]. The composition of samples did not depend on
the counter-ion of the loading Zr salt, but the amount of ZrC/amorphous carbon/graphite
ratio strongly depended on this.
The main features of ZrC0.94 @C samples are the complete transformation of ZrO2
into ZrC. The amorphous carbon is expected to transform into graphite during the plasma
treatment [37]. The average size of ZrC crystallites ranged between 35 and 62 nm, which is
higher than that of the samples made in a tube furnace. This may be attributed to the effect
of high temperature, resulting in fast diffusion and growing crystallites.
In general, the low DVB content (2%) of L-Zr-X samples resulted in a relatively high
ratio of organic volatiles during carbonization, resulting in high ZrO2 /C and high ZrC/C
ratios in the precursor and product samples. The incorporation of iminodiacetate functional
groups for Zr loading instead of sulfonyl groups [37] increased ZrC content in the ZrC@C
composites. The composition of ZrC in the RF plasma-treated samples was almost the same,
Zr0.93 and Zr0.94 , for the samples prepared from sulfonated [37] and iminodiacetate-loaded
resins, respectively. However, the ZrC0.94 content and ZrC0.94 /ZrO2 ratio were far higher
in the case of iminodiacetate-loaded than the sulfonated resins [37].
2.5. Surface Characterization of the Carbon Composites Containing Nano-ZrO2 and Nano-ZrC
We characterized the surface of the carbonized samples containing carbon balls decorated with nano-ZrO2 polymorphs, nano-ZrC or their mixture by N2 BET surface area
analysis (Tables 2 and 3), X-ray photoelectron spectroscopy (XPS) and high-resolution
transmission electron microscopy (HRTEM). The surface area of nano-ZrO2 @C composites prepared at 1000 ◦ C for 2 h was 140, 278 and 33 m2 /g for the samples with X=Cl, N
and S, respectively. We found the same tendency for the samples containing ZrC and
ZrO2 + ZrC prepared in a tubular furnace as the ZrO2 @C samples. The highest values
were found for X=N and the lowest values for X=S. Increasing the temperature from 1200
to 1400 ◦ C had no critical effect on the surface area, whereas heating time (8 h instead
of 2 h at 1400 ◦ C) only had a considerable influence in the case of the X=Cl resin. The
plasma treatment brought about significant sintering, resulting in a decreased surface
area (Table 3).
Table 3. Composition and properties of ZrC0.94 @C composites prepared in RF plasma.
Sample
ZrC,
(wt%)
(Size in nm)
Carbon (wt%)
BET Surface Area
(m2 /g)
Total Pore Volume
(cm3 /g)
L-Cl-1000-2-P-He
L-Cl-1000-2-P-H2
L-N-1000-2-P-He
L-N-1000-2-P-H2
L-S-1000-2-P-He
L-S-1000-2-P-H2
95 (49)
90 (40)
95 (62)
90 (35)
80 (40)
75 (42)
5
10
5
15
20
20
50
62
52
82
52
58
0.21
0.26
0.22
0.22
0.20
0.22
The surface composition of some nano-ZrO2 @C, nano-(ZrC0.58 , ZrO2 )@C and nanoZrC0.94 @C composites were determined by XPS, and the Zr3d , C1s and O1s spectra are given
in Figures 6–9 and Supplementary Materials, Figures S12 and S13. The calculated surface
concentrations are given in Supplementary Materials, Tables S2–S5.
Inorganics 2022, 10, 77
13 of 27
Figure 6. X-ray photoelectron spectra of the Zr3d lines of the composites containing nano-ZrO2 @C
and nano-(Zr0.58 C,ZrO2 )@C.
The surface of the L-Zr-X-T-t samples with X=Cl and S contains approximately
85–95% graphite. Zr0.58 C (Zr3d5 BE ≈ 179.9 ± 0.5 eV) was found only in samples heated
above 1200 ◦ C in low concentration, but its presence was undoubtedly detected based
on the zirconium spectra (Figure 6). Increasing the temperature to 1400 ◦ C or applying
prolonged heating had no significant effect on the concentration of ZrC on the surface.
The surface concentration of ZrC in the L-Zr-Cl samples is approximately double that
of the L-Zr-S samples. Zirconium was present in the samples in two other forms: ZrO2
(Zr3d5 BE ≈ 183.8 ± 0.5 eV) and presumably some kind of zirconium oxycarbide (Zr3d5
BE ≈ 182.5 ± 0.5 eV) (Tables S2 and S3, Figures 6–9, Supplementary Materials, Figures
S12 and S13). Oxidized carbon derivatives are also detectable on the surface in a few
percentages. The line positions of the corresponding oxygen, O1s 531.2 eV and carbon,
C1s 182.0 eV agreed with the literature data [39]. The appearance of the ZrO2 minor
phase can be attributed to the high affinity between Zr and O [37,38]. Some of the oxygen
is chemically bound to carbon (O1s 533.0 ± 0.2 eV, C1s 286.7 ± 0.2 eV). In the carbon
Inorganics 2022, 10, 77
14 of 27
spectra, the quantity of the oxidized carbon species can only be determined with an error
due to the presence of the high graphite peak. The graphite peak was fitted with an
asymmetric peak shape with AS(40;0.6) parameters. π-π* satellites were also present in
the spectra at a binding energy of approximately 290 eV. Chlorine or sulfur could not be
detected in the L-Zr-Cl-T-t and L-Zr-S-T-t samples.
Figure 7. X-ray photoelectron spectra of the C1s lines of the composites containing nano-ZrO2 @C
and nano-(Zr0.58 C,ZrO2 )@C.
The surface of RF-plasma-treated samples also contained 80–90 atomic% graphite
and 1–8 atomic% ZrC0.94 . The quantity of ZrC0.94 is the highest in the L-Zr-N samples
and the lowest in the L-Zr-S samples. In the case of H2 plasma treatment, the surface
ZrC0.94 contents are always higher than in the case of He plasma treatment. The ZrC0.94
content vs. the zirconium oxide content on the surface is the highest in the L-Zr-N
samples. ZrO2 and zirconium oxycarbide concentrations varied between 2 and 11
atomic% (Supplementary Materials, Table S5), and a low percentage of oxidized carbon
derivatives were also detected.
Inorganics 2022, 10, 77
15 of 27
Figure 8. X-ray photoelectron spectra of the Zr3d lines of the composites containing zirconium carbide
prepared in RF plasma at various conditions.
Inorganics 2022, 10, 77
16 of 27
Figure 9. X-ray photoelectron spectra of the C1s lines of the composites containing zirconium-carbide
prepared in RF plasma.
2.6. TEM Analysis of the L-Zr-S-1400-8 and L-Zr-N-1000-P-H2 Samples
We studied HRTEM samples containing ZrC0.58 and ZrC0.94 prepared from the L-Zr-N
and L-Zr-S copolymers in RF plasma and tubular furnace. The L-Zr-S-1400-8 sample shows
a crystalline ZrO2 monoclinic phase (ESI Figure S14) together with the ZrC cubic phase.
(Figure 10).
Inorganics 2022, 10, 77
17 of 27
Figure 10. Images (a,c), SAED pattern identifying the presence of cubic ZrC (b) and HAADF image
(d) of L-Zr S-1400-8 sample, together with the elemental distribution maps for zirconium (yellow),
oxygen (red) and carbon (blue).
The HAADF image and elemental maps show the distribution of Zr and O to be very
similar. This may be partly attributed to the presence of ZrO2 and partly to the ZrC0.58
phase embedded in a carbon matrix containing a homogeneous oxidized surface. The
zirconium-rich ZrC0.58 phase surface may contain some amount of oxygen, as oxycarbide
species were detected by XPS as well.
A cubic ZrC0.94 (Fm3m) main phase was identified in L-Zr-N-1000-P-H2 sample
by the selected area electron diffraction (SAED) pattern (Figure 11b). Oxygen mainly
appears in the smallest particles, which might be attributed to the oxidation of the
carbon surface.
The plasma-treated L-Zr-N-1000-P-H2 sample mainly contains ZrC0.94 (Figure 5),
which may be attributed to the reaction of zirconium dioxide particles passing through the
plasma flame, evaporating, and reacting with carbon. The appropriate residence time for
particles in the hottest zone of the plasma varied depending on the particle sizes and the
actual thermal trajectory of the individual particles.
Inorganics 2022, 10, 77
18 of 27
Figure 11. Images (a,c), SAED pattern identifying the presence of cubic ZrC (b) and HAADF image
(d) of L-Zr-N-1000-P-H2 sample, together with the elemental distribution maps for zirconium (red),
oxygen (green) and carbon (blue).
2.7. Raman Studies on ZrO2 @C, ZrC@C and (ZrC,ZrO2 )@C Composites
Powder XRD analysis is inadequate when exactly determining the ratio of amorphous
carbon/graphite components in the nano-(ZrO2, ZrC)@C composites [40]. However, the
Raman spectroscopy is suitable for following the quantitative changes in amorphous carbon,
graphite and distorted graphite structures and the graphitization processes [27–32]. Highly
ordered monocrystalline graphite (ideal graphite lattice) has two first-order Raman bands,
G (E2g , degenerated optical mode at the center of the Brillouin zone) and G1 (2D) (harmonic
in-plane transverse optical mode close to the zone boundary K point) at around 1580 cm−1
and 2687 cm−1 , respectively [33,34]. The disordered graphitic lattice has a band D1 (D) (A1g ,
phonon of the in-plane longitudinal optical branch close to the zone center) and D2 (D’)
Inorganics 2022, 10, 77
19 of 27
(E2g , in-plane acoustic branch close to the K point), or graphene layer edges and surfaces,
at around 1350 and 1620 cm−1 , respectively [37,40–42].
The amorphous carbon D3 band (D” or A) is at ca. 1500 cm−1 , whereas the D4 (D*)
band at ca. 1200 cm−1 contains mixed modes, including a mode of the disordered graphite
lattice (A1g ), and polyenes or ionic impurities induced modes [27,30,40,41]. Moreover, the
Raman spectra of carbonaceous materials contain bands belonging to weak combination
(D + D”) and harmonic overtone (2D’) modes as well [42–44].
The Raman spectra of composites prepared from L-Zr-X samples between 1000 and
1400 ◦ C for various times for X=Cl, N and S are given in Supplementary Materials, Table S6 and illustrated in Supplementary Materials, Figures S15–S17. The spectra and
peak positions/intensities for plasma-treated samples are given in Figures 12 and 13 and
Table 4, respectively.
Table 4. Raman shifts peak positions (in cm−1 ) and their intensities (in arbitrary units) for the
plasma-treated samples.
Sample
L-Zr-Cl-1000-2-P-H2
L-Zr-Cl-1000-2-P-He
L-Zr-N-1000-2-P-H2
L-Zr-N-1000-2-P-He
L-Zr-S-1000-2-P-H2
L-Zr-S-1000-2-P-He
R shift
[cm−1 ]
Intensity
FWHM
R shift
[cm−1 ]
Intensity
FWHM
R shift
[cm−1 ]
Intensity
FWHM
R shift
[cm−1 ]
Intensity
FWHM
R shift
[cm−1 ]
Intensity
FWHM
R shift
[cm−1 ]
Intensity
FWHM
D*
D
D”
G
D’
2D
D + D’
1100
1340
1572
1592
1614
2676
2929
0
0
2650
53.53
1552
44.38
784
29.40
585
23.47
1313
71.72
173
40.98
1100
1339
1488
1574
1603
2675
2930
0
0
1647
81.88
259
115.5
1012
52.17
705
35.59
305
79.04
110
54.11
1100
1340
1480
1574
1606
2680
2933
0
0
2762
57.92
206
88.54
2907
40.51
802
29.73
2070
60.06
157
35.56
1100
1339
1481
1574
1607
2679
2933
0
0
2581
80.57
475
109.4
2670
46.94
1004
30.00
1343
62.47
178
57.14
1100
1339
1517
1582
2078
2671
2925
0
0
1943
65.45
60.55
0.113
1349
64.27
0
0
387
79,9
127
59.33
1100
1340
1494
1575
1604
2676
2934
0
0
2128
97.33
392
109.5
1511
51.36
1068
35.97
558
80.13
143
75.83
ID/IG
I2D/IG
3.38
1.68
1.63
0.30
0.95
0.71
0.97
0.50
1.44
0.29
1.41
0.37
For the L-Zr-Cl-T-t samples, the intensity ratio of the peaks belonging to amorphous/graphitic components (D”/(D+G)) gradually decreases with an increasing reaction
temperature, suggesting an advance in graphitization. The D and G bands become sharper
due to the formation of more crystalline phases. The intensities of D* and D’ bands decrease
with increasing temperature, showing the partial decomposition of organic polyene structures and surface graphene layers, respectively. Increasing the reaction time does not have a
considerable effect. The I2D /IG ratio, related to the thickness or separation of the monolayer
carbon sheets, slightly and irregularly changes with increasing reaction temperature and
time, indicating that Zr atoms are not incorporated into the carbon network to a great
extent [45]. The formation of graphite may also be attributed to the increased temperature
and the catalytic effect of ZrC [46] forming above 1200 ◦ C. The more ZrC is formed, the
more graphite/disordered graphite was detected.
Inorganics 2022, 10, 77
20 of 27
Figure 12. Raman spectra of plasma-treated L-Zr-X-P-H2 samples (X=Cl, N and S).
Inorganics 2022, 10, 77
21 of 27
Figure 13. Raman spectra of plasma-treated L-Zr-X-P-He samples (X=Cl, N and S).
Inorganics 2022, 10, 77
22 of 27
For the samples L-Zr-N-T-t, the catalytic effect of ZrC on graphitization might be more
pronounced than the effect of temperature, whereas, for the L-Zr-S-t-t samples, the increase
in temperature and reaction time resulted in regular improvements in the graphitization
process (Supplementary Materials, Table S6). For the samples made from zirconyl nitrate,
the ratio of amorphous carbon to graphite decreases with increasing temperature. The
amorphous phase and polyenes completely disappear at 1400 ◦ C in 2 h. Amorphous carbon
remains in another experiment conducted at the same temperature but with a longer time
(8 h). This shows that there are some differences between the two processes in terms
of graphitization. This effect does not directly depend on heating time, but some other
unknown factor(s), e.g., activation of some catalytic processes to increase nucleation or
crystal growth, might play a role in its appearance.
The Raman spectra of all plasma-treated samples show the complete disappearance
of the D* bands due to the thermal decomposition of polyene structures and the transformation of surface graphene layers. The amount of defective graphite and amorphous
carbon is the highest in the X=Cl sample made in H2 , and when the atmosphere was
changed to He, the ID/IG and ID”/(ID+G) ratios decreased from 0.45 to 0.097 and from
3.38 to 1.63, respectively. For the samples with X=N, the ID/IG and ID”/(ID+G) ratios
are close to each other. For the samples with X=N, less amorphous carbon is found, and
the ratio of defective/regular graphitic structures is almost the same (ID/IG = 0.95 and
0.97 in H2 and He, respectively). A considerable influence of the atmosphere in ABAB
stacking and the separation of the monolayer sheets (I2D /IG ratio) was only found for
the X=Cl sample [47–49].
3. Materials and Methods
Chemical-grade resins and other chemicals (HCl, sulfuric acid, nitric acid, zirconyl
nitrate, zirconyl chloride, zirconium(IV) sulfate, sodium hydroxide, calcium oxide and
other analytical reagents), were supplied by Deuton-X Ltd., Hungary.
3.1. Experimental
3.1.1. Preparation of L-X-Zr Samples
The iminodiacetate functionalized STY-DVB copolymer containing 2% DVB (Lewatit
TP-207, BASF, Lanxess, Germany) was soaked in a 10% aq. acid (HCl, H2 SO4 and HNO3 )
solution for 24 h and the beads that swelled were filled into a 20-cm-long glass column.
Activation was conducted using a 10% aq. HCl, H2 SO4 and HNO3 solutions, respectively,
with a flow rate of 5 mL min−1 , and Zr loading was performed using a zirconyl chloride
solution containing 0.5 mass% Zr in 3 M HCl until the maximum possible loading with
zirconium was reached [5]. Similarly, 0.5 mass% of zirconyl nitrate in 3 M HNO3 and 0.5 M
Zr(SO4 )2 in 1.5 M H2 SO4 were used under the same conditions as ZrOCl2.8H2 O.
The L-X-Zr samples that swelled during Zr loading were dried at 90 and 110 ◦ C for
3 h and 2 h, respectively, in ambient air at atmospheric pressure with a heating rate of
10 ◦ C/min. The beads were left to cool in a desiccator filled with freshly prepared CaO.
3.1.2. Carbonization Experiments
The Zr-loaded L-Zr-X resins were subsequently ground in a planetary ball mill
(225 rpm, 30 min; Idar-Oberstein, Germany) until their size was reduced to ~63 µm. In
each case, ca. 1.6 g of the sample was put into a quartz boat, and the carbonization
process (pyrolysis) was performed in a tubular furnace under an Ar atmosphere (alumina
tube) at temperatures of 1000, 1200 and 1400 ◦ C for 2 h and 8 h. The heating rate
(15 ◦ C min−1 ) and the volume flow rate of the gas (1.5 L·min−1 ) were kept the same for
all the experiments.
3.1.3. RF Plasma Processing
Due to the ~20% swelling water content in the resins (Table S1) and the short
residence time of the particles within the RF plasma, the L-Zr-X samples could not be
Inorganics 2022, 10, 77
23 of 27
sufficiently directly carbonized. Therefore, we exposed the sample L-Zr-1000-2 prepared
with the carbonization of the L-Zr-X samples at 1000 ◦ C for 2 h and containing only ZrO2
and elemental carbon (Table 2). These samples were exposed to in-flight thermal plasma
treatment both in an inert (He) and a redutive (H2 ) atmosphere. The experimental setup
is described in [5,28,37]. This consisted of a reactor chamber supplied with a radiofrequency, inductively coupled plasma torch (PL-35, TEKNA Ltd., Sherbrooke, Canada,
mounted on the top) and an RF generator (LEPEL, Waukesha, USA) with a maximum
power of 30 kW at 4–5 MHz, together with a cyclone, a filter unit and a vacuum pump [5].
The solid samples were delivered into the plasma as described in [5] via a Praxair feeder
(Danbury, Connecticut, USA) with He as carrier gas (flow rate of 5 L·min−1 ). The feeding
probe was coaxially in the middle of the induction coil. The feeding rate of the powdered
resins was 3 g·min−1 . The plasma gas was a mixture of 11 L·min−1 Ar and 6 L·min−1
He, whereas the sheath gas was a mixture of 35 L·min−1 Ar and 5 L·min−1 He. The same
experiments were performed with hydrogen in sheath gas instead of He with a flow
rate of 5 L·min−1 . The most important operating conditions for the particular tests were
adapted from [5] (70 kPa and 25 kW of power).
3.1.4. Elemental Analysis
The CHS analysis of the L-Zr-X samples were carried out after drying them in
glass vials in a vacuum oven (Thermo Electron, Karlsruhe, Germany) at 140 ◦ C for 19 h
(tightly capped under N2 and sealed with a plastic film) was performed with a Carlo Elba
1106 instrument.
3.1.5. Specific Surface Area Measurements
We calculated the surface area using the Brunauer–Emmett–Teller (BET) equation
from nitrogen adsorption data collected at −196 ◦ C (Autosorb 1C, Quantachrome, Boynton
Beach, Florida, USA). The samples were evacuated for 24 h at 100 ◦ C prior to measurements.
3.1.6. Transmission Electron Microscopy
Transmission Electron Microscopy (TEM) was carried out with a 200 keV (Talos
Thermo Scientific, Santa Clara, CA, USA) transmission electron microscope. Grains were
crushed in EtOH and deposited onto Cu grids covered by Lacey carbon. We obtained
bright-field TEM (BFTEM), high-resolution TEM (HRTEM), and high-angle annular darkfield (HAADF) scanning TEM images as well as selected-area electron diffraction (SAED)
patterns. In TEM mode, the current was ~600 pA and the SAED patterns were obtained
with a camera length of 520 mm [5]. In addition, we performed elemental mapping in STEM
mode to study the grains’ chemical composition and heterogeneity. In STEM mode, the
current was ~200 pA. Beam convergence was 10.5 mrad. The camera length was 125 mm.
Dwell time was 10 µs. We used a “Super-X” detector system with 4 silicon drift detectors
built into the microscope column. Fast Fourier transforms (FFTs) were calculated from the
HRTEM images with the Digital Micrograph 3.6.1 software (Gatan Inc., Pleasanton, CA,
USA). The details of TEM spectroscopy are given in [32].
3.1.7. Thermal Studies
We performed simultaneous thermogravimetric analysis (TGA), differential scanning
calorimetry (DSC) and mass spectrometric evolved gas analysis (MS-EGA) using a SETARAM Labsys Evo and a Pfeiffer Vacuum OmniStar instrument, under a high-purity He
gas stream (6.0) with a heating rate of 10 ◦ C/min from 25 ◦ C to 1600 ◦ C. The details of
thermal measurements are given in [31,32]
3.1.8. Powder X-ray Diffraction
A Philips Bragg–Brentano parafocusing goniometer was used to acquire powder XRD
patterns (Cu weighted Kα radiation, 1.5406/1.5444 Å) in the range of 4–70◦ 2θ (with a
step size of 0.02◦ and an interval time of 1 s). Although the unit cell dimensions of the
Inorganics 2022, 10, 77
24 of 27
phases were well-determined, the composition (in mass%) of phases should be considered
an estimate rather than an accurate value. Due to the amorphous carbon content, problems
occurred when determining the background. Thus, no goodness-of-fit parameters are given.
The details of the XRD measurements are given in [32].
3.1.9. Vibrational Spectroscopy
The analytical IR and far-IR range spectra were collected on a Bruker Alpha FT-IR
(Bruker, Ettingen, Germany) and a Biorad-Digilab FTS-30-FIR far-IR instrument (Hercules,
CA, USA) with a Smart Attenuated Total Reflectance (ATR) accessory, respectively. All
spectra were recorded from 16 scans and acquired with a resolution of 4 cm−1 [33–35].
A Horiba Jobin–Yvon LabRAM micro-spectrometer (Longjumeau, France) was used,
with an external Nd-YAG laser source of 532 nm for Raman spectroscopy. We focused the
laser beam on an objective (20X, numerical aperture = 0.4) using a D0.3 or D0.6 optical filter,
which reduced the intensity of the laser to avoid degradation. A total of 1000 µm of the
confocal hole was used, with a grating monochromator of 1800 mm−1 for light dispersion.
The wavenumbers were scanned with a resolution of 3 cm−1 , with an accumulation time of
90–120 s per point for all the spectra in a range of 200–3400 cm−1 . After baseline correction,
the first- and second-order regions of the spectra were deconvoluted into Lorentzian
functions using the fitting tool available in the Origin software.
3.1.10. X-ray Photoelectron Spectroscopy
The X-ray photoelectron spectra (XPS) of the RF plasma-treated samples were
recorded with a Kratos XSAM 800 instrument (Manchester, UK) in fixed analyzer transmission mode, with a pass energy of 40 eV, Mg Kα1,2 (1253.6 eV) excitation and an
analysis chamber pressure of < 1·10−7 Pa. Survey spectra were recorded for both samples in the 100–1300 eV kinetic energy range. High-resolution spectra of the characteristic
photoelectron lines of zirconium, oxygen, and carbon were recorded with 0.1 eV steps
and a dwell time of 1 s. Quantitative analysis (after removal of the Shirley background)
was performed with the XPS MultiQuant program (Version 7.8, M. Mohai, Budapest,
Hungary) with experimentally determined photoionization cross-section data and asymmetry parameters [39].
3.1.11. Solid-State NMR Measurements
15 N
NMR magic angle spinning (MAS) spectra were recorded on a Varian System
spectrometer operating at a 1 H frequency of 600 MHz with a Chemagnetics 6.0-mm narrowbore triple resonance T3 probe in double resonance mode. 15 N cross-polarization spectra
were recorded with 5 ms contact time at 18 ◦ C with a spinning rate of 1.6 kHz. 13 C magic
angle spinning (MAS) spectra were recorded on a Varian System spectrometer operating at
a 1 H frequency of 400 MHz with a Chemagnetics 4.0 mm narrow-bore double resonance T3
probe. 13 C cross-polarization spectra were recorded with 2 ms contact time at 18 ◦ C with a
spinning rate of 8.0 kHz. A repetition delay of 20 s and TPPM decoupling were used in all
the measurements. For the 15 N and 13 C measurements, glycine and adamantane were used
as a chemical shift reference.
4. Conclusions
(1)
(2)
Due to the low (2%) divinylbenzene content of the Zr-loaded iminodiacetate functional
groups containing styrene-divinylbenzene (L-Zr-X) copolymers samples, a significant
loss of the organic volatiles was observed during the carbonization reaction of the
L-Zr-X samples, which resulted in high ZrO2 /C and ZrC/C ratios in the precursor
and product samples, respectively.
Changing the anion in the zirconium salt used to load the chelate-forming resin
resulted in ZrO2 @C precursors with varying reactivity levels towards carbonization
and alterable Zr content.
Inorganics 2022, 10, 77
25 of 27
(3)
(4)
ZrC0.54 @C samples can be prepared with or without ZrO2 in a tubular furnace, with
nanosize ZrC and ZrO2 content.
The RF plasma treatment of ZrO2 @C samples led to ZrC0.94 @C samples with high
(75–95%) nanosized ZrC0.94 content and a pore volume of 0.20–0.26 cm3 /g, with or
without graphite content.
Supplementary Materials: The following supporting information can be downloaded at: https:
//www.mdpi.com/article/10.3390/inorganics10060077/s1. ESI Scheme S1. Synthesis of the sodium
salt of iminodiacetate functionalized STY-DVB copolymers. ESI Table S1. Elementary analyses result
on L-Zr-X Zr-loaded iminodiacetate-functionalized styrene-divinylbenzene copolymers. ESI Table S2.
Surface composition of composites prepared by heat treatment of L-Zr-Cl resins at 1000 and 1200 ◦ C
for 2 h, or at 1400 ◦ C for 2 and 4 h. ESI Table S3. Surface composition of composites prepared
by heat treatment of L-Zr-N resins at 1000 and 1200 ◦ C for 2 h, or at 1400 ◦ C for 2 and 4 h. ESI
Table S4. Surface composition of composites prepared by heat treatment of L-Zr-S resins at 1000
and 1200 ◦ C for 2 h, or at 1400 ◦ C for 2 and 4 h. ESI Table S5. Surface composition of composites
prepared by RF plasma treatment of L-Zr-X-1000-2 resins in H2 and He atmosphere. ESI Table
S6. Raman band positions (cm−1 ) and band intensities (arbitrary units) in the Raman spectra of
L-Zr-X-T-t composites. ESI Figure S1. IR spectrum of the iminodiacetate functionalized STY-DVB
copolymer. ESI Figure S2. IR patterns for L-Zr-X samples for X= S, Cl and N between the intervals
4000–3000 cm−1 and 2000–400 cm−1 . ESI Figure S3. IR spectra of iminodiacetic acid (IDA) salts
with H2 SO4 (IDA-S), HNO3 (IDA-N), and HCl (IDA-Cl) between the intervals 4000–3000 cm−1 and
2000–400 cm−1 . ESI Figure S4. IR spectra of L-S and L-Zr-S compounds between 2000 and 400 cm−1 .
ESI Figure S5. IR spectra of L-N and L-Zr-N compounds between 2000 and 400 cm−1 . ESI Figure S6.
IR spectra of L-Cl and L-Zr-Cl compounds between 2000 and 400 cm−1 . ESI Figure S7. 13 C CP MAS
solid state NMR spectra of L-X and L—Zr-X samples (X=Cl (Top), N(Middle) and S(Botton)). ESI
Figure S8. TG-MS curves of iminodiacetate groups (a) and STY-DVB skeleton fragments (b,c) in the
decomposition of L-Zr-N sample. ESI Figure S9. TG-MS curves of iminodiacetate groups (a) and STYDVB skeleton fragments (b,c) in the decomposition of L-Zr-S sample. ESI Figure S10. TG-DSC curves
of the decomposition of L-Zr-X sample (X=Cl (green), N (Blue), S (Red)). ESI Figure S11. Complete
XRD pattern of L-Zr-X-1400-8 and L-Zr-X-1000-2-P-He (X=Cl, N and S) samples. ESI Figure S12. X-ray
photoelectron spectra of the O1s lines of the nano-ZrO2 @C and nano-(Zr0.58 C,ZrO2 )@C containing
composites. ESI Figure S13. X-ray photoelectron spectra of the O1s lines of the RF-plasma treated
nano Zr0.94 C@C containing composites. ESI Figure S14. Identification of crystalline monoclinic ZrO2
in The L-Zr-S-1400-8 sample. ESI Figure S15. Raman spectra of L-Zr-Cl-T-t samples. ESI Figure S16.
Raman spectra of L-Zr-N-T-t samples. ESI Figure S17. Raman spectra of L-Zr-S-T-t samples.
Author Contributions: Conceptualization, A.M. (Alejandro Martiz), Z.K. and L.K.; methodology,
Z.K., L.K.; software, A.M. (Alejandro Martiz); formal analysis, M.M.; investigation, A.M. (Alejandro
Martiz), Z.K., A.D., L.B., L.T., A.F., K.L.; resources, Z.K., A.M. (Alejandro Martiz), data curation, A.M.
(Alejandro Martiz), Z.K. and L.K.; writing—original draft preparation, A.M. (Alejandro Martiz), Z.K.
and L.K.; writing—review and editing, A.M. (Alejandro Martiz), Z.K. and L.K.; visualization, A.M.
(Alejandro Martiz), L.B., A.F.; supervision, L.K.; project administration, A.M. (Alfréd Menyhárd);
funding acquisition, Z.K. All authors have read and agreed to the published version of the manuscript.
Funding: Alejandro Martiz thanks to Tempus Public Foundation for the financial support granted
through the Stipendium Hungaricum scholarship program.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Acknowledgments: TEM studies were performed at the electron microscopy laboratory of the
University of Pannonia, established using grant no. GINOP-2.3.3-15-2016-0009 from the European
Structural and Investments Funds and the Hungarian Government.
Conflicts of Interest: The authors declare no conflict of interest.
Inorganics 2022, 10, 77
26 of 27
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
Pierson, H.O. Handbook of Refractory Carbides and Nitrides: Properties, Characteristics, Processing and Applications, 1st ed.; Noyes
Publication: Westwood, NJ, USA, 1997.
Liu, G.; Cheng, L.; Li, K.; Chen, Z.; Xiong, X.; Luan, X. Damage behavior of atomic oxygen on zirconium carbide coating modified
carbon/carbon composite. Ceram. Int. 2020, 3, 3324–3331. [CrossRef]
Scales, N.; Chen, J.; Aughterson, R.D.; Karatchevtseva, I.; Stopic, A.; Lumpkin, G.R.; Luca, V. Porous ZrC-carbon microspheres as
potential insoluble target matrices for production of 188W/188Re. J. Radioanal. Nucl. Chem. 2018, 318, 835–847. [CrossRef]
Scales, N.; Chen, J.; Hanley, T.L.; Riley, D.P.; Lumpkin, G.R.; Luca, V. Hierarchically porous carbon–zirconium carbide spheres as
potentially reusable transmutation targets. Microporous Mesoporous Mater. 2015, 212, 100–109. [CrossRef]
Martiz, A.; Károly, Z.; Bódis, E.; Fazekas, P.; Mohai, M.; Bertóti, I.; Keszler, A.M. In-flight Synthesis of Nanosized ZrC Particles
from Various Precursors in RF-Thermal Plasma. Period. Polytech.-Chem. 2021, 65, 331–342. [CrossRef]
Cheng, W.; Campolongo, M.J.; Tan, S.J.; Luo, D. Freestanding ultrathin nano-membranes via self-assembly. Nano Today. 2009, 4,
482–493. [CrossRef]
Byrappa, K.; Ohara, S.; Adschiri, T. Nanoparticles synthesis using supercritical fluid technology towards biomedical applications.
Adv. Drug Deliv. Rev. 2008, 60, 32714. [CrossRef]
Hussain, I.; Jalil, A.A.; Hamid, M.Y.S.; Hassan, N.S. Recent advances in catalytic systems in the prism of physicochemical
properties to remediate toxic CO pollutants: A state-of-the-art review. Chemosphere 2021, 277, 130285. [CrossRef]
Kocsis, T.; May, Z.; Czégény, Z.; Sreedhar, B.; Pawar, R.P.; Kótai, L. Perspectives of magnetic and nanosized metal-containing
amorphous carbon composite chemosorbents and catalysts. Nano Stud. 2016, 14, 7–35.
Dou, B.; Wang, C.; Song, Y.; Chen, H.; Jiang, B.; Yang, M.; Xu, Y. Solid sorbents for in-situ CO2 removal during sorption-enhanced
steam reforming process: A review. Renew. Sust. Energy Rev. 2016, 53, 536–546. [CrossRef]
Ciddor, L.; Bennett, J.A.; Hunns, J.A.; Wilson, K.; Lee, A.F. Catalytic upgrading of bio-oils by esterification. J. Chem.
Technol. Biotechnol. 2015, 90, 780–795. [CrossRef]
Wang, C.; Cheng, R.; Liao, L.; Duan, X. High-performance thin-film electronics based on inorganic nanostructures and composites.
Nano Today 2013, 8, 514–530. [CrossRef]
Basumatary, S. Transesterification with heterogeneous catalyst in production of biodiesel: A review. J. Chem. Pharm. 2013, 5, 1–7.
Fedorov, P.P.; Yarotskaya, E.G. Zirconium dioxide. Review. Kondens. Sredy Mezhfaznye Granitsy Condens. Matter Interphases 2021, 23,
169–187. [CrossRef]
Dunlap, C.J.; Mcneff, C.V.; Stoll, D.; Carr, P.W. Zirconia stationary phases for extreme separations. Anal. Chem. 2001, 73,
599A–607A. [CrossRef] [PubMed]
Camps, M.; Chatzopoulos, M.; Camps, J.M.; Montheards, J.P. Chloromethylation of Polystyrenes and Styrene Copolymers.
Applications. JMS-Rev. Macromol. Chem. Phys. 1987, 27, 505–557.
Yuchi, A.; Yoshida, N. Adsorption of tetravalent metal ions chelating resins containing iminodiacetic acid groups. Bull. Chem.
Soc. Jpn. 2000, 73, 1841–1842. [CrossRef]
Auer, B.M.; Skinner, J.L. IR and Raman spectra of liquid water: Theory and interpretation. J. Chem. Phys. 2008, 128, 224511.
[CrossRef]
Ikawa, K.; Iwamoto, K. Coating microspheres with zirconium carbide-carbon alloy. J. Nucl. Mater. 1974, 52, 128–130. [CrossRef]
Ikawa, K. Vapor deposition of zirconium carbide-carbon composites by the chloride process. JCOMA 1972, 29, 233–239. [CrossRef]
González Vílchez, M.C.; Puerta Vizcaíno, M.F.; Gargallo, E. Thermal behavior of iminodiacetic acid and its disodium salt.
Thermochim. Acta 1980, 42, 295–303. [CrossRef]
Li, F.; Huang, X.; Zhang, G.J. Scalable foaming assisted synthesis of ZrC nanopowder by carbothermal reduction. Ceram Int. 2015,
41, 3335–3338. [CrossRef]
Sacks, M.D.; Wang, C.A.; Yang, Z.; Jain, A. Carbothermal reduction synthesis of nanocrystalline zirconium carbide and hafnium
carbide powders using solution-derived precursors. J. Mat. Sci. 2004, 39, 6057–6066. [CrossRef]
Byun, H.S.; Burford, R.P.; Fane, A.G. Sulfonation of crosslinked asymmetric membranes based on polystyrene and divinylbenzene.
J Appl. Polym. Sci. 1994, 52, 825–835. [CrossRef]
Dobson, K.D.; McQuillan, A.J. An Infrared Spectroscopic Study of Carbonate Adsorption to Zirconium Dioxide Sol-Gel Films
from Aqueous Solutions. Langmuir 1997, 13, 3392–3396. [CrossRef]
Jiang, J.; May, I.; Sarsfield, M.J.; Ogden, M.; Fox, D.O.; Jones, C.J.; Mayhew, P. Spectroscopic Study of the Dissolution of Cesium
Phosphomolybdate and Zirconium Molybdate by Ammonium Carbamate. J. Sol. Chem. 2005, 34, 443–468. [CrossRef]
Fitzgerald, J.J.; Weiss, R.A. Cation-Anion and Cation-Cation Interactions in Sulfonated Polystyrene Ionomers Spectroscopic
Studies of the Effects of Solvents. ACS 1986, 302, 35–53.
El-NahhalI, I.M.; Zaggout, F.R.; Nassar, M.A.; El-Ashgar, N.M.; Maquet, J.; Babonneau, F.; Chehimi, M. Synthesis, Characterization
and Applications of Immobilized Iminodiacetic Acid-Modified Silica. J Sol-Gel Sci. Technol. 2003, 28, 255–265. [CrossRef]
Jiang, J.; Renshaw, J.C.; Sarsfield, M.J.; Livens, F.R.; Collison, D.; Charnock, J.M.; Eccles, H. Solution Chemistry of Uranyl Ion
with Iminodiacetate and Oxydiacetate: A Combined NMR/EXAFS and Potentiometry/Calorimetry Study. Inorg. Chem. 2003, 42,
1233–1240. [CrossRef]
Busca, G.; Lorenzelli, V. Infrared spectroscopic identification of species arising from reactive adsorption of carbon oxides on metal
oxide surfaces. Mater. Chem. 1982, 7, 89–126. [CrossRef]
Inorganics 2022, 10, 77
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
27 of 27
Kawashiro, K.; Morimoto, S.; Yoshida, H. Mass spectra of butyl esters and N-trifluoroacetyl butyl esters of some iminodicarboxylic
acids upon electron impact. Bull. Chem. Soc. Jpn. 1984, 57, 1097–1103. [CrossRef]
Fazekas, P.; Czégény, Z.; Mink, J.; Bódis, E.; Klébert, S.; Németh, C.; Keszler, A.M.; Károly, Z.; Szépvölgyi, J. Decomposition of
poly(vinyl chloride) in inductively coupled radiofrequency thermal plasma. Chem. Eng. J. 2016, 302, 163–171. [CrossRef]
Komarov, V.S.; Yatsevskaya, M.I.; Sycheva, O.A. Properties of activated carbon produced from spent ion-exchange resins.
Dokl. Akad. Nauk. BSSR 1985, 29, 1010–1023.
Chinthaka Silva, G.W.; Kercher, A.A.; Hunn, J.D.; Martin, R.C.; Jellison, G.E.; Meyer, H.M. Characterization of zirconium carbides
using electron microscopy; optical anisotropy; Auger depth profiles, X-ray diffraction and electron density calculated by charge
flipping method. J. Solid State Chem. 2012, 194, 91–99. [CrossRef]
Gusev, A.I. Structural stability boundaries for nonstoichiometric compounds. Phys. Status Solidi A 1989, 111, 443–450. [CrossRef]
Senczyk, D. The lattice parameters of MeC-type carbides; nitrides and carbonitrides of transition metals of IV and V groups
of the periodic system. In Proceedings of the 11th Conference of Applied Crystallography, Kozubnik, Poland; 1984; Volume 1,
pp. 234–240.
Martiz, A.; Károly, Z.; Trif, L.; Mohai, M.; Bereczki, L.; Németh, P.; Molnár, Z.; Menyhárd, A.; Pawar, R.P.; Tekale, S.; et al. Plasmaassisted preparation of nano-(ZrC; ZrO2 )@carbon composites from Zr-loaded sulfonated styrene–divinylbenzene copolymers.
J. Therm. Anal. Calorim. 2022, 1–13, in press. [CrossRef]
Pechishcheva, N.V.; Shunyaev, K.Y.; Melchakova, O.V. Zirconium in modern analytical chemistry. Rev. Anal. Chem. 2018, 37, 1–26.
[CrossRef]
Reilman, R.F.; Msezane, A.; Manson, S.T. Relative intensities in photoelectron spectroscopy of atoms and molecules. J. Electron.
Spectr. Relat. Phenom. 1976, 8, 389–394. [CrossRef]
Martiz, A.; Farkas, A.; Karoly, Z.; Franguelli, F.P.; Samaniego, S.K.; Menyhard, A.; Kotai, L. Raman studies on carbon-containing
phases in nanosized-ZrO2/C and nanosized-(ZrC; ZrO2 )/C composites. Nano Stud. 2022, 10, 21–22.
Devia, D.H.; Sykes, A.G. Aqueous solution chemistry of zirconium(IV). 1. Kinetic studies on hydrogen ion and general acid (HX)
induced dissociations of the tetrameric ion [Zr4(OH)8(H2O)16]8+. Inorg. Chem. 1981, 20, 910–913. [CrossRef]
Lokshin, E.P.; Tareeva, O.A. Sorption of Zirconium from Nitrate and Sulfate Solutions. Theor. Found. Chem. Eng. 2019, 53, 688–692.
[CrossRef]
Clearfield, A. Structural aspects of zirconium chemistry. Rev. Pure Appl. Chem. 1964, 14, 91–108.
Fathy, M.; Moghny, T.A.; Awadallah, A.E.; El-Bellihi, A.H. Nano Composites of Polystyrene Divinyl Benzene Resin Based on
Oxidized Multi-Walled Carbon Nanotubes. Int. J. Mod. Org. Chem. 2013, 2, 67–80.
Shishlov, N.M.; Khurasan, S.L. Effect of ion interactions on the IR spectrum of benzenesulfonate ion. Restoration of sulfonate ion
symmetry in sodium benzenesulfonate dimer. J. Mol. Struct. 2016, 1123, 360–366.
De, R.; Lee, H.; Das, B. Exploring the interactions in binary mixtures of polyelectrolytes: Influence of mixture composition;
concentration; and temperature on counter-ion condensation. J. Mol. Liq. 2018, 251, 94–99. [CrossRef]
Claramunt, S.; Varea, A.; Lopez-Diaz, D.; Velazquez, M.; Cornet, A.; Cirera, A. The Importance of Interbands on the Interpretation
of the Raman Spectrum of Graphene Oxide. J. Phys. Chem. C 2015, 119, 10123–10129. [CrossRef]
Vollebregt, S.; Ishihara, R.; Tichelaar, F.D.; Hou, Y.; Beenakker, C.I.M. Influence of the growth temperature on the first and
secondorder Raman band ratios and widths of carbon nanotubes and fibers. Carbon 2012, 50, 3542–3554. [CrossRef]
Cuesta, A.; Dhamelincourt, P.; Laureyns, J. Raman Microprobe studies on carbon materials. Carbon 1994, 8, 1523–1532. [CrossRef]