Irreversible Amide-Linked Covalent Organic Framework for Selective and Ultrafast Gold Recovery

Article abstract of DOI:10.1002/anie.202006535

Design of stable adsorbents for selective gold recovery with large capacity and fast adsorption kinetics is of great challenge, but significant for the economy and the environment. Herein, we show the design and preparation of an irreversible amide-linked covalent organic framework (COF) JNU-1 via a building block exchange strategy for efficient recovery of gold. JNU-1 was synthesized through the exchange of 4,4′-biphenyldicarboxaldehyde (BA) in mother COF TzBA consisting of 4,4′,4′′-(1,3,5-triazine-2,4,6-triyl)trianiline (Tz) and BA with terephthaloyl chloride. The irreversible amide linked JNU-1 gave good stability, unprecedented fast kinetics, excellent selectivity and outstanding adsorption capacity for gold recovery. X-ray photoelectron spectroscopy along with thermodynamic study and quantum mechanics calculation reveals that the excellent performance of JNU-1 for gold recovery results from the formation of hydrogen bonds C(N)?H???Cl and coordinate interaction of O and Au. The rational design of irreversible bonds as both inherent linkage and functional groups in COFs is a promising way to prepare stable COFs for diverse applications.

Full text of DOI:10.1002/anie.202006535

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Accepted Article
Title: Irreversible amide-linked covalent organic framework for selective
and ultrafast gold recovery
Authors: Hai-Long Qian, Fan-Lin Meng, Cheng-Xiong Yang, and Xiu-
Ping Yan
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202006535
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10.1002/anie.202006535
Angewandte Chemie International Edition
RESEARCH ARTICLE
Irreversible amide-linked covalent organic framework for
selective and ultrafast gold recovery
Hai-Long Qian,*[a,c] Fan-Lin Meng,[c] Cheng-Xiong Yang,[e] and Xiu-Ping Yan*[a,b,c,d]
Abstract: Design of stable adsorbents for selective gold recovery
with large capacity and fast kinetics is of great challenge, but
significant for economy and environment. Here, we show the design
and preparation of an irreversible amide-linked covalent organic
framework (COF) JNU-1 via a building block exchange strategy for
efficient recovery of gold. JNU-1 was synthesized through the
exchange of 4,4'-biphenyldicarboxaldehyde (BA) in mother COF
TzBA consisting of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)trianiline (Tz) and
BA with terephthaloyl chloride. The irreversible amide linked JNU-1
gave good stability, unprecedented fast kinetics, excellent selectivity
and outstanding adsorption capacity for gold recovery. X-ray
photoelectron spectroscopy along with thermodynamic study and
quantum mechanics calculation reveals that the excellent
performance of JNU-1 for gold recovery results from the formation of
hydrogen bonds C(N)-HCl and coordinate interaction of O and Au.
The rational design of irreversible bonds as both inherent linkage
and functional groups in COFs is a promising way to prepare stable
COFs for diverse applications.
extraction and ion exchange have been developed to recover
gold from aqueous solution.[3] The adsorption approach with
porous adsorbents attracts wide attention on account of its eco-
friendship, low cost, and easy operation.
As the core of adsorption, various functional adsorbents have
been designed to meet the demands of gold recovery, such as
metal organic frameworks (MOFs), organic polymers, and
biomass materials.[3d,4] However, a majority of these adsorbents
suffer from terrible kinetics with several hours or even days to
reach equilibrium.[4b-4d] Additionally, the poor selectivity, low
loading capacity and lacking stability also go against the efficient
recovery of gold. Consequently, it is essential to design novel
stable adsorbents with large capacity and rapid kinetics for
selective gold recovery.
Typical covalent organic frameworks (COFs) are known as a
kind of crystalline porous materials linked with reversible
covalent bonds such as boronate ester, boroxine, azine,
hydrazone and imine, showing wide potential in gas storage,
catalysis, sensing and separation.[5] The relatively stable imine-
linked COFs reveal greater promise in diverse fields than the
easily hydrolyzed boronate esters or boroxines-linked COFs,
indicating the stability plays a pushing role in the application of
COFs.[6] However, typical COFs are formed on the basis of
dynamic covalent chemistry.[5b,7] The reversible covalent linkage
is the nub of the formation of crystallinity as well as the inherent
limitation for the stability of COFs.
Construction of COFs with irreversible bonds is crucial in
developing stable COFs, but remains challenging. Few efforts
have been devoted to explore this likelihood. Polyarylether-
based COFs (also called dioxin-linked COFs) have been
synthesized with irreversible nucleophilic aromatic substitution
reaction.[6a,8] The irreversible benzoxazole- and amide-linked
COFs have been prepared via chemical conversion[9] or under
high-temperature and high-pressure.[10] However, the available
synthetic strategies and the number of irreversible COFs are
nowhere near enough for the wide applications.
Introduction
Though best-known as jewelry, gold actually possesses wide
application in our daily life including electronics, medicine, and
catalysis due to its superb physical and chemical properties.[1]
The huge consumption of gold leads to the low abundance of
this raw metal recourse and massive risk in ecology. Hence, the
recovery of gold from secondary resources such as the waste of
electrical and electronic equipment demonstrates extreme
importance in view of the economy and environment.[2] Plenty of
technologies involving adsorption, precipitation, solvent
[a]
Dr. H.-L. Qian, Prof. Dr. X.-P. Yan
State Key Laboratory of Food Science and Technology
Jiangnan University
Herein, we report the design and synthesis of a highly stable
and irreversible amide-linked COF JNU-1 for selective gold
recovery via building block exchange (BBE). A BBE strategy is
developed for the synthesis of JNU-1 owing to its great potential
in preparing de novo unreachable COFs.[11] Amide linkage is
designed as both inherent linkage and functional groups since it
is irreversible and selective for gold.[3b,12] The proposed amide-
linked JNU-1 is prepared from terephthaloyl chloride (TaCl) and
the mother COF TzBA consisting of 4,4',4''-(1,3,5-Triazine-2,4,6-
triyl)trianiline (Tz) and 4,4'-biphenyldicarboxaldehyde (BA) via
the BBE strategy. The design of such a BBE strategy for the
preparation of JNU-1 and its application for gold recovery are
studied via detail experimental characterization in combination
with quantum mechanics calculations. The prepared JNU-1
gives unprecedented fast kinetics, high selectivity as well as
large capacity for gold recovery. This work shows the high
potential of introducing irreversible bonds as both inherent
linkage and functional groups in preparation of stable COFs for
wide significant applications.
Wuxi 214122, China
E-mail: xpyan@jiangnan.edu.cn
hlqian@jiangnan.edu.cn
Prof. Dr. X.-P. Yan
International Joint Laboratory on Food Safety
Jiangnan University
[b]
[c]
Wuxi 214122, China
Dr. H.-L. Qian, F.-L. Meng, Prof. Dr. X.-P. Yan
Institute of Analytical Food Safety, School of Food Science and
Technology
Jiangnan University
Wuxi 214122, China
Prof. Dr. X.-P. Yan
Key Laboratory of Synthetic and Biological Colloids, Ministry of
Education
Jiangnan University
Wuxi 214122, China
[d]
[e]
Dr. C.-X. Yang
Research Center for Analytical Sciences, College of Chemistry
Nankai University
Tianjin 300071, China
Supporting information for this article is given via a link at the end of
the document.
1
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RESEARCH ARTICLE
Figure 1. (a) Design of a BBE strategy for the synthesis of JNU-1. (b) Diagram for computed HOMO–LUMO interactions of Tz with BA and TaCl. (c) Space-filling
model of TzBA. (d) Space-filling model of JNU-1 (gray, C; blue, N; red, O; white, H).
amine monomer, as confirmed by the powder X-ray diffraction
(PXRD) (Figure S1a, c and d). So, in the present designed BBE
Results and Discussion
strategy (Figure 1a), Tz was firstly condensed with BA to
prepare the crystalline mother COF TzBA. Note that
scandium(III) trifluoromethanesulfonate (Sc(OTf)3) was used to
replace typical aqueous acetic acid as the catalyst due to the
negative influence of H2O in aqueous acetic acid on the chloride
monomer in next BBE step. Terephthaloyl chloride (TaCl) with
higher nucleophilicity was chosen to exchange the BA block of
TzBA to produce the daughter JNU-1 as the easiness of a
chemical reaction is mainly determined by the electron
delocalization between the HOMO and LUMO based on the
frontier orbit theory.[13] As shown in Figure 1b, the energy gap
between the HOMO of Tz and the LUMO of TaCl (ΔEHOMO(Tz)-
LOMO(TaCl)) is lower than ΔEHOMO(Tz)-LOMO(BA), so the electron is
easier to flow from the HOMO of Tz to the LUMO of TaCl than to
the LUMO of BA
Design and preparation of amide-linked COFs via BBE.
Dynamic covalent chemistry is thought to be the fundamental of
forming typical crystalline COFs, where the reversible reaction is
the key of the process.[5b,7] However, the formed reversible
linkage inherently limits the stability of COFs. Fabrication of
COFs based on irreversible bonds is an effective way to obtain
stable COFs, but hard to access via conventional de novo
approach. BBE strategy is a promise way to synthesize de novo
inaccessible COFs,[11] but has never been designed for the
preparation of irreversible COFs. Here we show the design and
synthesis of highly stable COF based on irreversible linkage via
BBE. We took amide-linked COF JNU-1 as a proof-of-concept
(Figure 1a). The irreversible amide with high selectivity for
gold[3b,12] was selected as the linkage, which is a prerequisite to
form stable COFs. However, it is impossible to prepare amide-
linked COF JNU-1 via direct condensation of acyl chloride and
Control of reaction rate is essential for BBE. Rapid reaction is
unfavorable for the formation of high crystallinity,[14] so we
2
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RESEARCH ARTICLE
investigated the effect of the amount of TaCl, reaction
temperature and time on the crystallinity of the prepared JNU-1.
The results show that 87.1% of TzBA was converted into high-
crystalline JNU-1 with 1 equiv TaCl for BBE in the absence of
triethylamine (TEA) at low temperature (0 and 4 C) for 2 days
(Figures S2-S6).
The transformation of TzBA to designable JNU-1 in the
presence of TaCl was further verified by FTIR and 13C solid-state
nuclear magnetic resonance (SNMR) spectroscopy. The
appearance of
a
distinct stretching band at 1656 cm-1
(corresponding to the C=O of amide) in accompany with the
absence of the C=N stretching band at 1621 cm-1 in the FTIR
spectra of the as-prepared JNU-1 indicate the conversion of
imine into amide after BBE (Figure 3a, Figure S12). The mother
COF TzBA gave a wide peak at 156 ppm for imine carbon in the
13C SNMR spectra (Figure S13). In contrast, the BBE product
JNU-1 gave a new peak for amide carbon at 168 ppm instead of
imine carbon, which was verified by the amide carbon peak at
166 ppm in 13C SNMR spectra of model compound (Figure 3b,
Figures S14-S17). All the above evidences further confirm the
formation of amide-linkage.
Characterization of amide-linked COF. The simultaneous
disappearance of amino and aldehyde stretching bands for the
starting monomers as well as the appearance of imine stretching
band for TzBA in Fourier transform infrared (FTIR) spectra
indicate the successful condensation of Tz and BA (Figure S7).
The prepared mother COF TzBA gave the XRD pattern with
several main diffraction peaks at 2.41, 4.11 and 6.09, in good
agreement with the corresponding simulated one (Figures S8
and S9, Table S1). These results show the designable
crystallinity and structure of TzBA. Compared to its mother COF
TzBA, the BBE product JNU-1 exhibited an extraordinary
improvement in crystallinity as the intensity of main peak at
2.40 increased about 10 times (Figure 2a). The as-prepared
JNU-1 also gave several diffraction peaks at 4.10, 4.69, 6.14
and 26.07 (Figure S1b). The PXRD pattern of the as-prepared
JNU-1 coincided well with that of simulated AA stacking unite
cell of JNU-1 (a = b = 43.0452 Å, c = 3.3639 Å, α = β =90° and γ
= 120°) with Rwp of 6.79% and Rp of 5.35% after Pawley
refinement, rather than that of simulated AB stacking model
(Figure 2b-2d and Figure S10). The unit cell parameters of JNU-
1 show little change after the BBE of TaCl, revealing the overall
structure retained (Tables S1-S2). In addition, the PXRD pattern
of control COF exhibited no improvement without addition of
TaCl (Figure. S11). The above PXRD data confirm the
transformation of TzBA to JNU-1 after BBE with TaCl.
Scanning electron microscopy (SEM) images demonstrate no
clear change in morphology during the transformation of TzBA to
JNU-1. Both TzBA and JNU-1 exhibited the aggregation of
spheres (Figure S18). Transmission electron microscopy (TEM)
images show typical layer-like structure of the two COFs,
coinciding with the simulated stacking layer structure (Figure
S19). TzBA and JNU-1 gave Brunauer–Emmett–Teller (BET)
surface area of 156 and 261 m2 g-1 with the pore size of ca. 40
and 39 Å, and the pore volume of 0.36 and 0.70 cm3 g-1,
respectively (Figure S20). The increase of the BET surface area
may come from the improvement of the crystallinity, the
decrease of the pore size and the increased pore volume due to
the reduction in the building unit size after BBE. On the contrary,
the TzTaCl prepared from the direct condensation of TaCl and
Tz gave the BET surface area of only 33 m2 g-1 with no obvious
pores (Figure S20).
Figure 2. (a) PXRD patterns of the mother COF TzBA and its BBE product
JNU-1. (b) Experimental and simulated PXRD patterns (AA stacking) of JNU-1.
(c) Pawley refinement of JNU-1. (d) Eclipsed AA unit cell of JNU-1.
Figure 3. (a) FTIR spectra of TzBA and its BBE product JNU-1. (b) Liquid 13C
NMR spectra of model compound and the 13C SNMR spectrum of TzBA and
its BBE product JNU-1. (c) PXRD patterns and (d) FTIR spectra of JNU-1 after
treatment with various solvents.
3
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