Copper benzene-1,3,5-tricarboxylate (HKUST-1) – graphene oxide pellets for methane adsorption

Microporous and Mesoporous Materials 316 (2021) 110948

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Microporous and Mesoporous Materials
journal homepage: />
Copper benzene-1,3,5-tricarboxylate (HKUST-1) – graphene oxide pellets
for methane adsorption
n a, Janos Madar
ărgy Sa
fran c, Ying Wang d, Krisztina La
´szlo
´ a, *
Andrea Doma
asz b, Gyo
a

Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics, Budafoki út 8., Budapest, H, 1521, Hungary
Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, Szt. Gell´ert t´er 4., Budapest, H, 1521, Hungary
c
Research Institute for Technical Physics and Materials Science, Eă
otvă
os Lor
and Research Network, Konkoly Thege M. út 29-33., H-1121, Budapest, Hungary
d
College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, China
b

A R T I C L E I N F O

A B S T R A C T

Keywords:
MOF
MOF-GO composite
Adsorption
XRD
Compression
Gas storage

Copper benzene-1,3,5-tricarboxylate (HKUST-1) is one of the materials holding the greatest potential for clean
energy gases among microporous storage materials. Although this material is commercially available as a powder
with particle size 10–20 μm, for easier handling adsorbents are preferentially employed as pellets or monoliths.
Even under binder free conditions there could be a high price to pay for compacting: loss in crystallinity and in
porosity. To determine the protection potential of graphene oxide (GO) a HKUST-1@GO composite was studied.
The material of 16% GO was obtained in a single step solvothermal synthesis. The pristine HKUST-1 as well as
HKUST1@GO formed consistent, integrated pellets when compressed at 25 and 50 bar without any binder.
PowderXRD and N2 adsorption were used to monitor the changes in crystallinity and pore structure. It was found
that GO has a protective effect against the 25 or 50 bar applied pressure, as 75% of the pore volume and the
apparent surface area is saved in HKUST1@GO (vs. 43% and 47%, respectively, in HKUST-1) after compression.
Presumably, the flexible GO sheets with high mechanical stability act as compressible spacers between the
crystals thus preventing their amorphisation. Comparison of the adsorption properties of the HKUST-1 and
HKUST-1@GO powders and pellets revealed that the performed compression deteriorated the structure of the
MOF and thus reduced the CH4 uptake. Further studies are needed to optimize the compression pressure for a
more reasonable loss in the gas uptake capacity.

1. Introduction
Cleaner combustion natural gas and bio gas as alternative fuels could
significantly reduce environmental stress from carbon dioxide and other
emissions [1]. Current high-pressure and cryogenic gas storage methods
however are not economically ideal for the storage and transport of

these gases. Adsorption gas storage may offer attractive solutions for
their capture and portable storage. For cost effective implementation of
this technology suitable nanoporous adsorbents are required [2,3]. The
American Department of Energy (DOE) has established the gravimetric
and/or volumetric methane adsorption capacities necessary for adsor­
bents (263 cm3 CH4/cm3 adsorbent) [4,5].
Metal organic frameworks (MOFs) with outstanding gas adsorption
properties are among the most promising materials for this purpose,
thanks to their permanent microporosity and outstanding apparent

surface area. Their hybrid three dimensional open framework with or­
dered open pore structure is constructed from multivalent metal ions or
clusters connected by organic ligands via coordination bonds [6–8].
Copper benzene-1,3,5-tricarboxylate or HKUST-1 (named after
Hong-Kong University of Science and Technology) [9] attracts special
attention among MOFs because its volumetric methane adsorption ca­
pacity has actually reached the DOE target [10]. HKUST-1 is composed
of copper (II) ions and benzene-1,3,5-tricarboxylate (btc3− ) organic li­
gands. In its paddle-wheel secondary building unit (SBU) two copper (II)
ions form coordination bonds with one of the carboxylate groups of four
btc3− ligands, leaving one unsaturated open metal site on each copper. It
is commercially available as Basolite C300. However, the sensitivity of
the as received HKUST-1 in its powder form to humid environment and
its moderate thermal conductivity present a formidable technical chal­
lenge to its applications as an adsorption gas storage vehicle.

* Corresponding author.
E-mail addresses: (A. Dom´
an), (J. Madar´
asz), (G. S´

afr´
an), yingwang@tongji.
edu.cn (Y. Wang), , (K. L´
aszl´
o).
/>Received 25 September 2020; Received in revised form 31 January 2021; Accepted 2 February 2021
Available online 6 February 2021
1387-1811/© 2021 The Authors.
Published by Elsevier Inc.
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A. Dom´
an et al.

Microporous and Mesoporous Materials 316 (2021) 110948

Fig. 1. Characterisation of HKUST-1 and HKUST-1@GO samples: (a) powder XRD pattern of the air-dried material; (b) TG and (d) DTG curves from the thermal
analysis of the samples up to 800 ◦ C in air flow (130 cm3/min) at heating rate 10 ◦ C/min; (c) low temperature (− 196 ◦ C) nitrogen adsorption/desorption isotherms
and (d) TEM image of HKUST-1 powder.

route to prepare HKUST-1 pellets is by densification of pre synthetized
HKUST-1 powder. Pelletisation has further potential advantages, like
enhancement in mechanical strength, thermal conductivity, chemical
stability, packing and volumetric density. Mechanochemically assisted
methods were found effective in the synthesis of carbon materials with
enhanced gas uptake capacity [15–17]. However, the most commonly
observed response of HKUST-1 under high external pressure is
amorphisation, which results in an unfavourable reduction of surface
area and pore volume [10,18–25]. For instance, Kim et al. compacted
activated (100 ◦ C, 5 h) HKUST-1 powder (1737 m2/g) at 25–340 bar for
10 min and found a decrease in crystallinity and surface area with
increasing pressure. The loss in SBET was 34% already at 25 bar. While
partial structural damage through collapse was observable only above
100 bar, 340 bar resulted in almost total collapse of the pore system
[21]. Addition of polyvinyl alcohol (PVA) binder in the HKUST-1 pellets
led to a moderate surface area of 963 m2/g, probably because the PVA
molecules partially occupied the pore system of HKUST-1 [20]. This
result supports the standpoint that, although binders can enhance the
mechanical or even the thermal stability, free pellets are more desirable
to preserve the excellent adsorption properties of MOFs. Dhainaut et al.
pelletised HKUST-1 (and also UiO-66, UiO-67, UiO-66-NH2) powders
with 1 and 2 wt% expanded natural graphite (ENG) binder at up to 1210
bar. Obviously, simply mixing HKUST-1 with ENG resulted in a limited
decrease of SBET from 1288 m2/g (no ENG added) to 1246 m2/g (1 wt%
ENG) and 1105 m2/g (2 wt% ENG), since the surface area of graphite

lags behind that of HKUST-1. The surface area of the composite systems
decreased further with increasing pressure. Maximum losses of ca. 25,
23 and 26% were observable at the highest pressures in the binder free
pellets and in samples with 1 wt% and 2 wt% ENG content, respectively
[23]. Various groups report contradictory findings regarding the level of
pressure induced amorphisation either in lab made HKUST-1 [10,19,21,
23] or in commercially available Basolite C300 powder [22,24,25].
Dhainaut et al. suggested that the amorphisation depends at least partly
on the compression protocol. Therefore results obtained in an uncon­
trolled or poorlycontrolled densification manner should be interpreted
with care [23]. However, Terracina et al. prepared tablets from com­
mercial Basolite C300 powder using a pill maker, operating with a hy­
draulic press. They found that 400 bar is required to form mechanically
stable tablets. In a unique way, they have observed, that the specific

Fig. 2. Effect of water vapour on HKUST-1 powder; (a) water vapour adsorp­
tion/desorption isotherm (20 ◦ C) of HKUST-1. SEM images of the (b) as
received and (c) the aged (85% relative humidity RH. 20 ◦ C. 21 days) samples.

Fig. 3. HKUST-1 and HKUST-1@GO (16 wt% GO) pellets formed under 25 or
50 bar.

Several attempts have been made to form more desirable HKUST-1
monoliths such as by sol-gel synthesis [11], Cu(OH)2 monolith conver­
sion [12], 3D printing [13] or powder packing [14]. The most common
2


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an et al.

Microporous and Mesoporous Materials 316 (2021) 110948

Fig. 4. Comparison of the XRD pattern of the powder and compressed (a) HKUST-1 and (b) HKUST-1@GO.

Table 1
Data from low temperature (− 196 ◦ C) nitrogen adsorption isotherms and
methane uptake values of HKUST-1 and HKUST-1@GO powder and pellets at
1000 mbar.
Sample

Nitrogen
SBET
2

HKUST-1
powder
HKUST-1_25
HKUST-1_50
HKUST1@GO
powder
HKUST1@GO_25
HKUST1@GO_50

Methane uptake at 1000 mbar
Vtot

Vmicro

3

0 ◦C

− 8 ◦C

cm
(STP)/g

mg/
g

cm3
(STP)/g

mg/
g

0.55

32.6

23.3

39.6

28.3

0.39
0.25
0.65

0.36
0.24
0.57

28.1
23.8
30.6

20.1
17.0
21.8

32.9
27.4
37.8

23.5
19.6
27.0

1110

0.46

0.41

28.5

20.3

34.6

24.7

1130

0.47

0.42

27.0

19.3

31.8

22.7

m /
g

cm /g

1500

0.62

970
620

1550

3

group [29]. The effect of the external pressure (25–200 bar) was
compared in a physical HKUST-1+CA mixture to HKUST-1@CA (both
with a mass ratio 1:1). In the latter the MOF crystals were grown on CA
under solvothermal conditions.
The nanoscale structure of HKUST-1+CA is more sensitive to the
external pressure, but at higher compressions HKUST-1 loses its crys­
talline structure also in the composite sample. No significant difference
was found between the corresponding CH4 adsorption isotherms of the
composites, either in the as-prepared samples or after compression at
100 bar. After exposure to higher external pressure the CH4 uptake
seems to be governed by the MOF.
Graphene oxide (GO) was found to improve the methane adsorption
properties of HKUST-1 [30,31]. GO is a single or oligo-layer graphene
decorated with various oxygen containing functional groups (e.g. hy­
droxyl, carboxyl, epoxide groups) [32]. The functional groups make it
possible to produce stable aqueous graphene oxide suspensions, which,
furthermore, can be reactive [33].
In this paper, we report a new synthesis route to prepare HKUST1@GO composites. Although HKUST-1 - GO systems were studied
earlier, e.g., by Xu et al. [34], we propose a novel synthesis route by
circumventing the drying step at the end of the improved Hummers
exfoliation. The copper salt was directly mixed with the diluted GO
suspension instead of using dry GO. Using this technique the ultrasound
assisted tedious re-suspension step of the GO can also be avoided. The
protective effect of GO during the pelletisation HKUST-1@GO is inves­
tigated. Methane adsorption properties of the HKUST-1 and
HKUST-1@GO powders and pellets are compared.

Fig. 5. Low temperature (− 196 ◦ C) nitrogen adsorption/desorption isotherms
of the powder and compressed HKUST-1 and HKUST-1@GO samples. Red circle
highlights the fine structure of the corresponding isotherms. (For interpretation
of the references to colour in this figure legend, the reader is referred to the
Web version of this article.)

surface area increased in the pelletising process by 15% from 1620 to
1935 m2/g [26].
Nanostructured carbon support can potentially improve the me­
chanical stability and the thermal conductivity, and moreover enhance
the water resistance and/or gas adsorption capacity by a synergistic
effect [27,28].
The protective effect of a resorcinol – formaldehyde based carbon
aerogel (CA) support was studied earlier in two different forms by our
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Microporous and Mesoporous Materials 316 (2021) 110948

Fig. 6. Integral (a, b) and differential (c, d) pore size distributions calculated from the adsorption branch of the nitrogen adsorption isotherms.

Fig. 7. SEM images of the HKUST-1@GO sample. Powder (a); surface (b) and inside (c) after compression at 25 bar; surface (d) and inside (e) after compression at
50 bar.

4

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an et al.

Microporous and Mesoporous Materials 316 (2021) 110948

Fig. 8. Atmospheric (up to 1000 mbar) methane adsorption isotherms of HKUST-1 and HKUST-1@GO powders and pellets (a) at 0 ◦ C and (b) at − 8 ◦ C.

Approximately 100 mg non-activated samples were placed in a 13 mm
diameter sample holder and kept at the required pressure for 10 min.
The compressed samples were designated by sample name and applied
pressure. HKUST-1_25 thus refers to HKUST-1 compressed at 25 bar.
2.2. Methods
Scanning electron microscopy (SEM, JEOL JSM 6380LA) was used to
characterize the morphology of the samples. Gold coating was applied to
increase the conductivity of the samples. Conventional and high reso­
lution transmission electron microscopy (200 kV Philips CM20 TEM and
300 kV JEOL 3010 HRTEM) were used to image the morphology, grain
and grain size distribution of the samples. For TEM and HRTEM imaging
the samples were drop-dried on carbon-coated microgrids.
XRD patterns were obtained in the range 2θ = 4◦ –84◦ with an X’pert
Pro MPD (PANalytical Bv., The Netherlands) X-ray diffractometer using
an X’celerator type detector, Cu Kα radiation with a Ni filter foil (λ =
1.5408 Å) and a “zero-background" Si single crystal sample holder.
Phase identification was assisted by the Search&Match algorithm of the
HighScore Plus (PANalytical Bv., The Netherlands) software, based on
either the international Powder Diffraction File (PDF4+, Release 2020,
International Centre of Diffraction Data, ICDD, Pennsylvania, USA), or
The Cambridge Structural Database (CSD-Enterprise, version 5.42,
Cambridge Crystallographic Data Centre, CCDC [41]) using the built-in

powder pattern generator algorithm of the Mercury program [42].
The thermal behaviour of the samples was investigated by simulta­
neous thermogravimetry/differential thermal analysis (TG/DTA; STD
2960 Simultaneous DTA-TGA, TA Instruments). The measurements were
carried out in dry air flow of 130 cm3/min (heating rate 10 ◦ C/min).
Nitrogen adsorption/desorption isotherms were measured at
− 196 ◦ C by a NOVA 2000e (Quantachrome, USA) volumetric computercontrolled surface analyser. All the samples were outgassed in vacuum at
110 ◦ C (activation) prior to the nitrogen adsorption measurements. The
apparent surface area SBET was calculated using the Brunauer-EmmettTeller (BET) model [43]. The total pore volume Vtot was derived from
the amount of N2 adsorbed at relative pressure p/p0 → 1, assuming that
the pores were filled with liquid adsorbate. The micropore volume Vmicro
was obtained from the Dubinin-Radushkevich (DR) plot [44]. The pore
size distribution was calculated with the Barett-Joyner-Halenda (BJH)
method. The validity of this process is limited to the range 2–50 nm.
Transformation of the primary adsorption data was performed with the
Quantachrome ASiQwin software (version 3.0).
Water vapour adsorption/desorption isotherms were measured by a

Fig. 9. Comparison of the methane uptake of HKUST-1 and HKUST-1@GO
powders and pellets at 0 ◦ C and − 8 ◦ C at 1000 mbar.

2. Experimental
2.1. Materials
The improved Hummers’ method was used to prepare the GO [35,
36]. After thorough purification a 1.1w/w% aqueous suspension was
obtained [37]. The GO was used in this suspended form.
HKUST-1 (C18H6Cu3O12, M: 604.87 g/mol) was synthesized under
solvothermal conditions following Wang et al. [38,39]. The benzene-1,
3,5-tricarboxylic acid (H3BTC) was dissolved in ethanol and then
mixed with the stoichiometric amount of Cu(NO3)2⋅3H2O dissolved in

MilliQ water. After 10 min argon gas was bubbled through the mixture
for 5 min to eliminate air from the autoclave prior to sealing. The
mixture was kept at 80 ◦ C for 24 h. The obtained turquoise crystals were
washed with ethanol three times and dried in air at ambient conditions
for 24 h. The samples were stored for further use in a desiccator filled
with freshly activated silica. The HKUST-1@GO composites were pre­
pared in the same way, but instead of pure water a 2 g/dm3 GO sus­
pension was used as solvent for the copper salt and as GO source [40].
Air-dried samples were homogenized in a mortar before further
measurements.
HKUST-1 and HKUST-1@GO samples were compressed under 25 and
50 bar using an OL57 hydraulic press (Manfredi, Pinerolo, Italy).
5


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Microporous and Mesoporous Materials 316 (2021) 110948

Hydrosorb-1 (Quantachrome, USA) volumetric computer-controlled
surface analyser at 20 ◦ C, up to 1000 mbar. The samples were out­
gassed in vacuum at 180 ◦ C prior to the measurement.
Methane adsorption/desorption isotherms were measured at 0 and
− 8 ◦ C with an AUTOSORB-1 (Quantachrome, USA) computer-controlled
analyser.

many cases that application of high external pressure to MOFs can result
in anomalous mechanical behaviour [18,47]. For this reason the
HKUST-1@GO composite was compressed to reveal the mechanical

behaviour of the associated system during the compression. The pristine
HKUST-1, as well as the GO derivative, formed consistent, integrated
pellets when compressed at 25 and 50 bar (Fig. 3).
The characteristic XRD pattern of HKUST-1 is clearly retained after
the compression of the powders (Fig. 4a and b). The peak positions in the
compressed materials are slightly shifted to higher angles, implying a
decreased interplanar distance. Peak widening and baseline increase
however indicate a certain level of structural damage. These phenomena
were not observed in HKUST-1@GO_25. Instead, the increased relative
intensity of the (222) reflection at 2θ = 12◦ of this sample implies that
during the compression individual HKUST-1 crystals rotated into a
preferred direction due to GO.
The adsorption isotherms show that the microporous character of all
the samples is preserved after the compression, in spite of the significant
decrease in the apparent surface area (SBET), total and micro pore vol­
ume (Vtot and Vmicro, respectively) (Fig. 5, Table 1). The linear range of
the BET representation was located with the procedure proposed by
Rouquerol et al. [48]. The main criteria of the procedure were met in the
p/p0 = 0–0.02 range. As no kernel files necessary for DFT based calcu­
lations are available for the HKUST-1@GO systems, the BJH method,
limited to the mesopore range, was employed to calculate the pore size
distributions (PSDs) (Fig. 6). The uncompressed samples show a bimodal
pore size distribution as implied by the fine distinct structure high­
lighted in the isotherms. Both the isotherms and the PSDs reveal that the
addition of GO moderates the effects of the compression. In the iso­
therms of the pellets the fine structure at p/p0 < 0.1 disappears. This
phenomenon results in the simplification of the distribution functions in
Fig. 6 c and d. The SEM images in Fig. 7 confirm that the surface and the
internal morphology of the HKUST-1 and its composites are altered after
the compression.

On comparing the parameters that characterize the pore structure
(SBET, Vtot and Vmicro in Table 1) of HKUST-1 powder and pellets the
overall loss in porosity increases linearly with the pressure. By contrast,
in the associated system the loss is notably smaller and is not influenced
by the compression pressure. Presumably, the flexible GO sheets with
high mechanical stability act as compressible spacers between the
crystals thus preventing their degradation.

3. Results and discussion
3.1. Characterisation of the samples
The pristine HKUST-1 powder was obtained with a yield of 84%
(solvent free MOF). The crystalline structure of the turquoise product
was identified by powder XRD phase analysis (Fig. 1a). Its thermal
decomposition in oxidative atmosphere (Fig. 1b) shows three well
distinguishable mass loss steps. The first up to 150 ◦ C corresponds to
water release from the pore network, the second (150–250 ◦ C) to the
exile of strongly bonded water and the thermal decomposition of the
ester groups decorating the carboxylic groups not bonded to the copper,
and the third, around 300 ◦ C, to thermal degradation of the organic
linker [39]. The low temperature nitrogen adsorption/desorption
isotherm is of Type Ib according to the recent IUPAC classification [45],
characteristic of exclusively microporous systems (Fig. 1c). The nano­
sized crystalline particles of HKUST-1 are clearly recognisable on the
HRTEM image (Fig. 1d).
Although HKUST-1 is an outstanding candidate for methane and
natural gas storage, this application is seriously challenged by its
vulnerability to the presence of water either in liquid or vapour form
(Fig. 2). The water uptake of HKUST-1 substantially exceeds that of
nitrogen, and part of the water remains irreversibly sorbed under the
condition of the last point of the desorption branch (vacuum, 20 ◦ C). The

air dried HKUST-1 contains ca. 9.4 mol/unit water. Part of this water
fills the pores as “bulk” water and 3 mol/unit is related to the free Cu
sites. The presence of the water results in a slow decomposition of the
MOF with an estimated half-life of about 33 months. Exposure to high
relative humidity accelerates the degradation (Fig. 2 inset) [46].
In our previous work, we reported that graphene oxide is able to
improve the water resistance of HKUST-1 when used in combination
[40]. It was reported earlier that acidic surface groups are advantageous
for the formation of HKUST-1 [29]. Therefore HKUST-1@GO compos­
ites were prepared in water – ethanol binary solvent. It was found that
the GO can, at least partially, save the metal – linker coordination bonds
by sacrificing the ester groups, formed between ethanol and the carboxyl
groups on the GO sheets during the solvothermal synthesis.
The XRD pattern of the HKUST-1@GO system confirmed that the
octahedral HKUST-1 crystals were successfully formed also in the
presence of 2 g/dm3 GO (Fig. 1a) with a yield of 82%. The GO content in
the solvent-free HKUST-1@GO system was 16 wt%. The thermal
behaviour of the composites is similar to that of pristine HKUST-1
(Fig. 1b). Since GO adheres well to HKUST-1 crystals and is well
distributed in the system, the thermal decomposition of the MOF also
facilitates the disintegration of GO. GO therefore burns out simulta­
neously with HKUST-1 at around 300 ◦ C, at a much lower temperature
than when it is alone. The highly microporous nature of HKUST-1 is
preserved even after its association with GO (Fig. 1c). However, the
adsorption/desorption isotherm of HKUST-1@GO exhibits a flat, elon­
gated hysteresis loop of Type H4 [45]. This indicates a certain degree of
mesopore formation, presumably in the interface of aggregated
compounds.

3.3. Adsorption of methane

The effect of pelletisation on the methane adsorption capacity is of
primary importance for gas storage application. The methane adsorption
performance of the powders and the compressed pellets was measured at
0 ◦ C and − 8 ◦ C. Fig. 8 compares the atmospheric methane isotherms of
the various samples. The shape of all the isotherms reflects reversible
adsorption. The adsorption capacities at 1000 mbar equilibrium pres­
sure are compared in Fig. 9. Table 1 also reports these capacities in mg/g
units. The volumes found for the associated systems exceed those of the
pristine HKUST-1 pellets at both temperatures in the whole pressure
range.
The loss in methane uptake is proportional to the applied pressure
not only for HKUST-1 but also for HKUST-1@GO. At both temperatures
the effect of pressure is about twice as great for the pristine MOF. The
added GO enhances the pressure tolerance particularly at the higher
compression applied. As already proposed, the flexible GO sheets act as
compressible spacers thus preventing amorphisation of the crystals.

3.2. Compression

4. Conclusions

For easier handling, adsorbents are preferentially employed as pel­
lets or monoliths. The compression step is intended to reduce the space
between individual crystals without destroying their structure and, if
possible, to increase the adsorption capacity. It has been reported in

HKUST-1 is one of the outstanding candidates for adsorption gas
storage on account of its excellent methane uptake, but its powder re­
quires compaction to allow it to be easily handled. During the pellet­
isation process, however, a significant part of the pore volume is lost.

6


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an et al.

Microporous and Mesoporous Materials 316 (2021) 110948

This article describes how HKUST-1@GO (with 16% GO) was prepared
in powder form with solvothermal self-assembly of the MOF using a ca
1% aqueous GO suspension as solvent for the copper salt. Pristine
HKUST-1 and HKUST-1@GO were pelleted and the effect of the external
pressure (25 and 50 bar) was investigated.
Both the pristine HKUST-1 as well as the GO derivative are able to
form consistent, integrated pellets without a binder. The nitrogen
adsorption isotherms show that the microporous character of all the
samples is preserved after the compression, but the porosity decreases
significantly. Nevertheless, GO has a protective effect against the 25 or
50 bar applied pressure, as 75% of the pore volume and the apparent
surface area is saved in HKUST 1@GO, while only 43% and 47%,
respectively, in HKUST-1 after compression. XRD diffractograms indi­
cate a certain level of structural damage. XRD, nitrogen and methane
adsorption data concomitantly imply that the incorporated GO moder­
ates the effect of the external pressure. The flexible GO sheets may act as
compressible spacers thus inhibiting amorphisation of the MOF crystals.
The methane uptake decreases proportionally to the applied pressure,
but for HKUST-1@GO the effect is about half as strong: GO enhances the
pressure tolerance particularly at the higher compression applied.
Further experiments are needed to optimize the pelletisation pressure in
order to reduce the loss in the methane uptake capacity.

[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]

Funding

[19]

This research was supported by the OTKA grant K 128410 from
National Research, Development and Innovation Office (NKFIH),
Hungary and by the BME-Nanotechnology and Materials Science (BME
IE-NAT) TKP2020 IE grant.

[20]

CRediT authorship contribution statement

[23]

´n: Investigation, (sample preparation, sample char­
Andrea Doma
acterisation, adsorption measurements), Writing - review & editing.
sz: Investigation, (XRD data, Formal analysis. Gyo
ă rgy
Janos Madara
fra
n: Investigation, (TEM imaging). Ying Wang: Writing - review &
Sa
´szlo
´ : Conceptualization, Writing editing, commentary. Krisztina La
review & editing, Resources.

[24]

[21]
[22]

[25]
[26]
[27]

Declaration of competing interest

[28]

The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.

[29]
[30]
[31]

Acknowledgments

[32]

The authors are grateful to Prof. K. Kaneko for fruitful discussions.
We also extend our warm thanks to G. Bosznai and B. Pinke (BME) for
their invaluable technical assistance.

[33]

References

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[34]

[36]

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