Synthesis of hydrogen-substituted graphdiynes via dehalogenative homocoupling reactions

Article abstract of DOI:10.1039/d1cc00453k

A new method is introduced to prepare hydrogen-substituted graphdiynes (HsGDYs) via the dehalogenative homocoupling of terminal alkynyl bromides. Compared with previous synthetic strategies, the reaction conditions are moderate and the time is shortened. HsGDYs exhibit porous structures and hydrogen/oxygen evolution reaction (HER/OER) catalytic activity, endowing applications in electrochemical catalysis.

Full text of DOI:10.1039/d1cc00453k

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Synthesis of hydrogen-substituted graphdiynes via
dehalogenative homocoupling reactions†
Cite this: DOI: 10.1039/d1cc00453k
Jiasheng Wu, Jizhe Liang, Yijie Zhang, Xiaoli Zhao* and Chunxue Yuan
*
Received 26th January 2021,
Accepted 14th April 2021
DOI: 10.1039/d1cc00453k
rsc.li/chemcomm
A new method is introduced to prepare hydrogen-substituted graph- the homocoupling reaction of monomers with terminal alkynyl
diynes (HsGDYs) via the dehalogenative homocoupling of terminal groups. Among them, Glaser, Glaser–Hay and Eglinton coupling
4,16,18–23
alkynyl bromides. Compared with previous synthetic strategies, the reactions are the most commonly utilized.
However, due to
reaction conditions are moderate and the time is shortened. HsGDYs the high reactivity, such monomers face the risk of oxidative
exhibit porous structures and hydrogen/oxygen evolution reaction deterioration during the whole process and extra heating is usually
(HER/OER) catalytic activity, endowing applications in electrochemical required. The homocoupling of terminal alkynylsilane groups is the
catalysis.
other type. As a protection group, trimethylsilyl can significantly
enhance the stability and directly yield the coupling products
24,25
Graphdiyne and its analogues (GDYs), as a rising star of the without deprotection (like Hiyama coupling).
However, for
carbon family, are a series of artificial two-dimensional nano- the preparation of GDYs via the homocoupling reaction of
2
materials which contain sp and sp hybridized carbon atoms. hexakis[(trimethylsilyl)ethynyl]benzene, the efficiency is low and
17,24
Different from graphene, the introduction of alkynyl bonds various byproducts are generated.
Thus, exploiting new pre-
renders GDYs unique physical and chemical properties. This cursors with both great stability and high reactivity is highly
extended p-conjugated system endows GDYs with a natural desirable.
4
band gap of 0.44 to 1.47 eV and a high carrier mobility of 10
Beyond wet chemistry, dry chemistry is another powerful
5
2
ꢀ1 ꢀ1 1
to 10 cm V
with diacetylenic bonds, dictating a flat structure with evenly deposition.
dispersed pores. Combining the uniform nanoscale porosity constructed two-dimensional molecular networks with acetyle-
s . GDYs consist of aromatic rings connected approach, such as the explosion approach and chemical vapor
2
6,27
We recently designed tBEP and successfully
2
8
and exceptional electronic properties, GDYs show great nic scaffoldings on Au(111) under ultrahigh vacuum. During
potential in the fields of energy storage, catalysis, sewage the synthesis process, the terminal alkynyl bromides of tBEP
2
–8
treatment, etc.
More than that, by altering precursors, the revealed higher stability than terminal alkynyl and dehalogena-
pore size can be precisely controlled and GDYs with different tive C–C coupling yielded higher selectivity and fewer bypro-
3
,4,6,9–14
heteroatoms (such as Cl, F, N, and H) can be obtained.
ducts than the dehydrogenative ones. Naturally, this interesting
Compared with GDY, HsGDY has lower atom density and larger phenomenon raised our curiosity about the possibility of con-
pore size which facilitate ion diffusion parallel and perpendi- structing HsGDYs with terminal alkyne bromides via the deha-
cular to the basal plane. The vicinity of these extra hydrogen logenative homocoupling reaction in the solution phase.
atoms also leads to the promotion of ion storage capacity.
Herein, we successfully prepared HsGDY films in solution
Though Baughman predicted the existence of graphyne in 1987, via the dehalogenative homocoupling reaction of terminal
the preparation remained a challenge until Li and co-workers’ alkynyl bromide molecules. HsGDY is a free-standing film with
15,16
ground-breaking work in 2010.
So far, the synthetic strategies continuous large area not only from the view of the macroscopic
for GDYs have been classified into wet chemistry and dry chemistry. morphology but also well-organized gauze-like membrane struc-
For wet chemistry approaches, the reactions related can be divided tures in the micronic scale. HsGDY consists of aromatic rings
17
into two types according to the functional groups. The first type is connected with a conjugated diyne linkage, as confirmed by a
series of measurements. Besides, HsGDY shows an electrochemical
7,29
catalytic performance comparable with previous reports.
Our
College of Materials Science and Engineering, Tongji University, Shanghai, 201804,
China. E-mail: cxyuan@tongji.edu.cn, zxl36@tongji.edu.cn
strategy is substantially efficient and facile compared with previous
ones, demonstrated by the shortened reaction time and room
temperature conditions. This work proposed a novel path for the
†
Electronic supplementary information (ESI) available: Experimental details and
additional experimental results. See DOI: 10.1039/d1cc00453k
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preparation of HsGDYs under mild solution conditions, recon-
structing the fascinating result which could only be attained under
severe ultrahigh vacuum conditions reported previously.
The synthetic routes of monomer tBEP and HsGDY are
shown in Scheme S1 (ESI†). The detailed synthesis of tBEP
was modified based on our previous work to shorten the
reaction period and save costs without reducing the yield of
2
8
tBEP. Copper foils were washed and sonicated with 1 M HCl,
acetone and ethanol for 15 min successively, dried under a flow
of nitrogen, and used immediately. To a three-necked flask, the
pre-treated copper foil and tBEP (10 mg) were added. Then the
flask was sealed and filled with nitrogen. 10 mL pyridine was
added into the flask and stirred for 2 minutes. After that, 1 mL
NaOH aqueous solution (0.1 M) was added dropwise into the
mixture. Without extra heating, the mixture was stirred under a
Fig. 2 SEM and EDS mapping images of HsGDY. (a, b) SEM images of the
top side of a HsGDY film. (c) The SEM image of the bottom side of a HsGDY
nitrogen atmosphere at r.t. for 12 h. The copper foils were taken film. (d–g) EDS mapping images of C + O (e), C (f), and O (g) of HsGDY.
out and washed with acetone and ethanol in turn. A nearly
transparent light-yellow film was obtained on the copper foils.
We also conducted this reaction with (bromoethynyl)benzene (Fig. 2c). In this reaction, the copper foil acts as not only the
0
and 3-(bromoethynyl)-1,1 -biphenyl and both reactions occurred catalyst source but also the substrate for the formation of
16
smoothly under the same conditions with high yields (ESI†).
HsGDYs. At the beginning, the surface of the copper foil is
Through the dehalogenative homocoupling reaction of tBEP, entirely exposed to the system and HsGDY forms and spreads over
the HsGDY film was successfully grown on copper foils in pyridine the surface along with the dehalogenative homocoupling of tBEP.
and NaOH aqueous solutions (Fig. 1a). The colour of the copper As the reaction proceeds, the coverage of HsGDYs goes up and the
foils turns light yellow and the surface is no longer shiny after proportion of the bare copper surface goes down. At some point,
HsGDY growth. When removed from copper foils, this free- the formed HsGDYs would become the obstacle of the subsequent
standing film is light yellow and nearly transparent with an area reaction and eventually cause the irregularity of the film.
2
of 7 cm (Fig. 1b). SEM was employed to observe the morphology
Since the structure of HsGDY can be regarded as replacing
details of the as-prepared HsGDY film. The thickness of this film half of the acetylene bonds in GDY with hydrogen atoms,
is about 600 nm according to the cross-sectional SEM image HsGDY theoretically possesses only two elements (carbon and
(
Fig. S6, ESI†). As shown in Fig. 2a, the surface of the sample hydrogen) and two kinds of hybridized carbon atoms (sp and
2
30
contains abundant pores with different sizes. The pore diameter sp ). Thus, an energy dispersive spectrometer (EDS) was
ranges from several micrometres to tens of nanometres. With employed to analyze the element composition of the sample.
further magnification, densely dispersed smaller pores of about As depicted in Fig. 2e, the film is mainly composed of two
several nanometres in diameter are observed (Fig. 2b). These open elements: carbon and oxygen, mostly carbon. The oxygen is
hierarchical pores give the HsGDY film a three-dimensional mainly concentrated on the external impurity particles (Fig. 2g)
porous structure with high surface accessibility. For an efficient like the unreacted NaOH and the by-products, while the carbon
reaction and ion storage, this macro/mesoporous second-order spreads all over the film underneath in high density (Fig. 2f).
11,12
structure provides abundant channels and vacancies.
Com- The result of EDS proves the fact that the as-prepared HsGDY is
paring the morphology of the bottom and the top surface, it can a carbon-rich material. Fig. 3a shows the XRD patterns of the
be found that the side close to the copper foil (Fig. 2b) is clearly sample. The peak at 23.31 corresponds to an interlayer spacing
flatter and more regular than the side away from the copper foil of 3.81 Å. Due to the conformational fluctuation of HsGDY, the
Fig. 1 (a) Schematic diagram of the dehalogenative homocoupling reaction and the chemical structure of HsGDY. (b) A photograph of the HsGDY film.
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1,34
ꢀ1
film we obtained is amorphous.
As depicted in Fig. 3b, the of aromatic rings in the sample. The peak at 2200 cm is
solid-state NMR of HsGDY indicates the existence of four types assigned to the typical stretching vibration of the alkynyl bond,
of carbon atoms. The peaks at 130.6, 123.5, 80.2, and 75.0 ppm which is also parallel to the Raman spectrum, indicating the
2
16,32
correspond to aromatic C–C, aromatic C–H, C(sp)–C(sp ) and formation of a conjugated diyne linkage.
C(sp)–C(sp), respectively.
We also analyse the
1
1
Raman and FT-IR spectra of the tBEP monomer. An obvious
ꢀ
1
In characterizing carbon materials, Raman spectroscopy has intensity decrease of the peak at 994 cm can be observed in the
proven itself to be a versatile tool. It shows accurate and acute Raman spectrum (Fig. S7, ESI†). As for the FT-IR spectra (Fig. 3d),
ꢀ
1
detection of the symmetrical vibration of skeleton and func- the intensity of the peak at 617 cm , belonging to the stretching
3
1
tional groups. Meanwhile, as a complement, Fourier trans- vibration of C–Br, significantly decreases after the reaction. Com-
form infrared spectroscopy (FT-IR) shows incredible sensitivity bined with the spectra mentioned, the variations of these two
to absorption signals generated from the asymmetrical vibra- signal peaks indicate the occurrence of the dehalogenative homo-
tion of functional groups. Combining the merits of both coupling reaction and the formation of HsGDYs.
approaches, we are capable of having a clear vision of the
product and the reaction. As depicted in Fig. 3c and Fig. S10 electron spectroscopy (XPS) was conducted. As shown in Fig. 3e,
ESI†), three major peaks can be found in the Raman spectra of the as-prepared HsGDY film contains three major elements: C
To identify the hybridization status of carbon, X-ray photo-
(
ꢀ
ꢀ
1
HsGDY. The D-band located at 1359 cm is assigned to the (78.9%), O (14.3%) and Cu (2.73%), among which Cu mainly
defects/edges, and the G-band at 1603 cm is attributed to the comes from the copper foil. The C 1s peak can be deconvoluted
vibration of the abundant benzene rings. The peak at 2227 cm
corresponds to the vibration of alkynyl bonds. The FT-IR spectra (Fig. 3f). The peaks at 284.5 eV and 285.3 eV refer to C–C (sp )
of HsGDY in Fig. 3d present four obvious peaks. Among them, the and C–C (sp) respectively and the area ratio of sp /sp is nearly 1.
peak at 1579 cm is caused by the skeletal vibrations of benzene This number is consistent with the theoretical structure of
rings and is parallel to the G-band of the Raman spectrum HsGDY (Fig. 1a) and demonstrates the successful formation of
1
ꢀ
1
into four subpeaks: 284.5 eV, 285.3 eV, 286.7 eV and 289.3 eV
30
2
2
ꢀ1
1
1,12,16
(
Fig. 3c). The stretching and bending vibrations of the C–H bonds HsGDYs.
On the other hand, the peaks at 286.7 eV and
289.3 eV refer to C–O and CQO and the O1s peak can be
respectively. These three signal peaks demonstrate the existence additionally assigned to carbonyl (CQO), ester (OQC–O) and
ꢀ1
ꢀ1
of the benzene rings lead to peaks at 2923 cm and 875 cm
,
3
3,34
hydroxyl (O–H) (Fig. S8, ESI†).
The appearance of these
bonds indicates that oxygen slightly dopes HsGDY, which may
partly alter the localized electronic structures and eventually
3
4
affect the properties.
Due to the extended p-conjugated system and the macro/
mesoporous second-order structure, HsGDY provides a huge
number of tunnels and interspaces for ion transmission and
1
1,12,35
storage.
The HER and OER catalytic performances of
HsGDYs were investigated with a typical three-electrode system
in 1M KOH. The as-prepared HsGDY on copper foil was directly
used as the working electrode without further treatment.
As depicted in Fig. 4a and b, the overpotential required for
ꢀ
2
HsGDYs to reach a current density ( j) of 10 mA cm is 531 mV
ꢀ1
and the Tafel slope is 363 mV dec . As for the OER, HsGDY
ꢀ
2
exhibits an overpotential of 646 mV at 10 mA cm with a Tafel
ꢀ
1
slope of 128 mV dec (Fig. 4c and d). HsGDY we obtained
exhibits a similar HER/OER activity to that in previous studies,
like exfoliated graphdiyne (690 mV for the HER) and GDY
7
,36
(445 mV for the OER).
The small number of O-containing
functional groups in our sample may somewhat decrease the
continuity of the planar p-conjugation system and decrease the
3
7
charge carrier mobility and electrical conductivity. We sug-
gest that HsGDY can achieve much better catalytic performance
7
,12,36
when combined with other metal atoms.
In contrast to the
stability of graphene, the sp hybridized linkages (–CRC–) of
HsGDYs possess higher reactivity, which can chelate metal atoms
5,6,29
more firmly and thus boost the catalytic performance.
Fig. 3 The structure of HsGDY. (a) XRD patterns of HsGDY. (b) The
C solid-state NMR spectrum of HsGDY. (c) Raman spectra of three
In summary, combining the traditional synthesis strategy of
GDY and our previous result of surface chemistry, we utilized a
new monomer tBEP and successfully prepared the HsGDY film
on copper foils via the dehalogenative homocoupling reaction.
13
random spots on a HsGDY film. (d) FT-IR spectra of the monomer and
HsGDY film. (e and f) XPS total spectrum (e) and high resolution C 1s
spectrum (f) of HsGDY.
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