Synthesis of copper catalysts for click chemistry from distillery wastewater using magnetically recoverable bionanoparticles

Article abstract of DOI:10.1039/c9gc00270g

Copper recovered from a whisky distillery waste stream is shown to be an effective catalyst for a range of azide-alkyne "click" reactions. Biogenic nanomagnetite (BNM), produced under mild conditions, was used to rapidly recover and subsequently support t

Full text of DOI:10.1039/c9gc00270g

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Synthesis of copper catalysts for click chemistry
from distillery wastewater using magnetically
recoverable bionanoparticles†
Cite this: DOI: 10.1039/c9gc00270g
Received 23rd January 2019,
Accepted 22nd May 2019
Richard L. Kimber, *‡a Fabio Parmeggiani, ‡b Nimisha Joshi,a
Alexander M. Rakowski,c Sarah J. Haigh, c Nicholas J. Turner b and
DOI: 10.1039/c9gc00270g
a
Jonathan R. Lloyd
rsc.li/greenchem
Copper recovered from a whisky distillery waste stream is shown demonstrated that under mild aqueous conditions, metal-redu-
to be an effective catalyst for a range of azide–alkyne “click” reac- cing bacteria can act as both reductant and support for CuAAC
tions. Biogenic nanomagnetite (BNM), produced under mild con- catalysts.20 Producing these catalysts with Cu sourced from
ditions, was used to rapidly recover and subsequently support the waste streams would greatly enhance their green credentials,
Cu catalyst which could be separated and recycled easily.
offering numerous advantages over traditional synthesis using
Cu salts. Cu recovery from waste provides a low-cost, renewable
source of Cu, minimises or actively reduces waste volumes, and
recycles and valorises waste metal into highly useful catalysts.
Magnetic iron nanoparticles offer a promising method for
simple recovery of metals from waste solutions.21,22 In
addition, they have gained increased attention as supports for
CuAAC catalysts due to their ease of separation, recovery and
reuse.23–25 However, the chemical synthesis of these magnetic
nanoparticles often requires high temperature, non-aqueous
solvents, stabilizing agents or hazardous chemicals. Microbial
metabolism can be harnessed to provide simple, inexpensive,
scalable and tunable processes for the synthesis of magnetic
nanoparticles under mild conditions.26,27
Herein, we present the first synthesis of a CuAAC catalyst
using copper recovered from an industrial waste source
(Fig. 1). We also demonstrate that the copper can be recovered
and subsequently supported using biogenic nanomagnetite
(BNM), synthesised under very mild conditions. Due to the
magnetic nature of the BNM, the catalyst could easily be separ-
The uncatalysed Huisgen 1,3-dipolar cycloaddition of organic
azides and alkynes is a slow, high temperature process that
affords a mixture of 1,4 and 1,5-disubstitution products.1 In
2002, the groups of Sharpless2 and Meldal3 discovered that
copper(I) can greatly accelerate the reaction and markedly
improve its regioselectivity. Since then, Cu(I)-catalysed azide–
alkyne cycloaddition (CuAAC) has become almost synonymous
with “click chemistry”, with applications in drug discovery,4,5
bioconjugation,6,7 materials science,8 and polymer chemistry.9
Click chemistry, a concept introduced by Sharpless in 2001,
describes a set of highly efficient reactions which are high
yielding, wide in scope, use benign solvents, generates only
inoffensive byproducts and are regio/stereospecific.10 Despite
the green credentials of click chemistry, the synthesis of
CuAAC catalysts often does not follow these same stringent
criteria.
There is much interest in the use of supported Cu catalysts
due to their increased robustness, ease of recovery and
improved reusability, compared to their unsupported
counterparts.11,12 To this end, efforts have been made to
immobilize CuAAC catalysts on polymers,13 zeolites,14
charcoal,15,16 graphene,17,18 and clay.19 Our previous work
aSchool of Earth and Environmental Sciences and Williamson Research Centre for
Molecular Environmental Science, University of Manchester, Manchester, UK.
E-mail: richard.kimber@manchester.ac.uk
bSchool of Chemistry, Manchester Institute of Biotechnology (MIB), University of
Manchester, Manchester, UK
cSchool of Materials, University of Manchester, Manchester, UK
†Electronic supplementary information (ESI) available: Supplementary figures
and tables, experimental methods, product characterisation data, copies of NMR
and HRMS spectra. See DOI: 10.1039/c9gc00270g
Fig. 1 Overview of the Cu-BNM catalyst preparation procedure and
‡These authors contributed equally.
application to CuAAC.
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ated and reused for up to three cycles. The industrial waste
source selected for this study was the spent lees from a whisky
distillery located in Scotland. Spent lees are the residues left in
the spirit still following the second distillation phase of whisky
production, and contain elevated Cu concentrations in
addition to a range of fermentation products creating a
complex waste source (see ESI†). The lees are normally treated
in an effluent plant before being discharged to the environ-
ment or applied to land as a soil conditioner. The presence of
copper increases the treatment levels required and limits the
potential for application to land.
To produce the BNM, cells of the metal-reducing bacterium
Geobacter sulfurreducens were added to amorphous ferrihydrite
and supplied with acetate as an electron donor. The reaction
proceeded at 30 °C and the only solvent used was water. After
synthesis, the BNM was easily recovered using a magnet and
washed 3 times in water to remove residual biomass. Previous
characterization revealed an average particle size of 13.3
0.6 nm.28
Inductively coupled plasma atomic emission spectroscopy
(ICP-AES) confirmed the Cu content in the spent less was
49 mg L−1. A BNM concentration of 2.8 mg mL−1 spent lees
was chosen for Cu recovery and catalyst synthesis in order to
provide sufficient Fe2+ on the BNM surface for potential Cu2+
reduction, and to demonstrate catalytic activity at a relatively
low Cu loading. Rapid removal of Cu following BNM addition
was confirmed by ICP-AES which revealed >97% of Cu was
removed in less than 1 minute. The BNM was then magneti-
cally recovered. Scanning transmission electron microscopy
(STEM) and energy-dispersive X-ray spectroscopy (EDX)
mapping confirmed the recovered Cu was supported on the
BNM (CuleesBNM) with clear evidence of the Cu associated
with the Fe signal of the BNM (Fig. 2). Digestion of the recov-
ered CuleesBNM revealed a Cu loading of 2 wt%.
Fig. 2 High-angle annular dark field (HAADF) images and corres-
ponding elemental maps of Fe and Cu of the CuleesBNM catalyst.
Characterisation of the CuleesBNM was performed using
X-ray photoelectron spectroscopy (XPS). Interestingly, XPS ana-
lysis of the spent lees suggested the presence of two Cu
species. The Cu 2p3/2 peak at 934.2 eV is characteristic of Cu(II)
whereas the peak at 932.8 eV suggests the presence of reduced
Cu (Fig. 3a).
However, distinguishing between Cu(I) and Cu(0) is not
accurate with this technique.29 After recovery of the Cu by the
BNM, only one peak at 932.7 eV was present, suggesting
reduction of the Cu(II) had occurred, most likely mediated by
Fig. 3 XPS surface analysis of (a) CuleesBNM and (b) CusaltBNM catalysts.
Data is displayed as black solid lines whilst fits are displayed as red
dotted lines.
the Fe(II) present within and on the surface of the BNM.30,31
A
catalyst prepared by the addition of reagent grade CuSO4 (dis-
solved in water) to BNM (CusaltBNM), giving an identical Cu
loading of 2 wt%, was also prepared and characterised (Fig. 3b applied, both the CuleesBNM and CusaltBNM were found to be
and ESI†). A similar Cu 2p3/2 peak at 932.8 eV suggested that poorly active (Table 1, entries 3 and 4), likely due to the pres-
reduction of Cu(II) by BNM also occurred in the synthesis of ence of some residual Cu(II) on the surface of the nano-
the CusaltBNM catalyst (Fig. 3b).
material. Addition of ascorbate to the reaction mixture,
To investigate the potential for using Cu recovered from leading to reduction of Cu(II) to Cu(I), afforded complete con-
waste for click reactions, we began by testing the CuleesBNM version to the corresponding 1,2,3-triazole product 3a (>95%,
catalyst in the cycloaddition of benzyl azide 1a and phenyl- Table 1, entries 5 and 6). However, ascorbate addition also
acetylene 2a (Table 1). The activity was compared against the resulted in dissolution of the CuleesBNM catalyst after pro-
CusaltBNM catalyst. When no additional reducing agent was longed incubation, precluding any potential recyclability, as
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Table 1 Performance of CuleesBNM and CusaltBNM catalysts for
CuAACa
Entry
Catalyst
Reducing agent
Time [h]
Yieldb [%]
1
2
3
4
5
6
7
8
9
None
BNM
None
None
None
12
12
12
12
12
12
5
12
5
12
n.d.
n.d.
45
CusaltBNM
CuleesBNM
CusaltBNM
CuleesBNM
CusaltBNM
CusaltBNM
CuleesBNM
CuleesBNM
None
43
Ascorbatec
>95
>95
56
>95
47
Ascorbatec
d
NaBH4 d
NaBH4 d
NaBH4 d
NaBH4
10
>95
a Reaction conditions: 0.25 mmol 1a, 0.25 mmol 2a, 500 µL Cu-BNM
suspension, 5 mL H2O/t-BuOH (8 : 2), 25 °C. b Calculated by 1H NMR
(n.d. = product not detected). c 50 mM sodium ascorbate added to the
click reaction mixture. d Treatment of the Cu-BNM with 10 mM
sodium borohydride prior to click reaction.
has been reported previously.24 In order to alleviate this issue,
the Cu-BNM catalysts were pre-treated with NaBH4 as the redu-
cing agent. This resulted in a shift in the Cu 2p3/2 peaks of the
nanocatalysts of between 0.4 and 0.8 eV (Fig. 3), likely due to
reduction of any residual Cu(II). This enabled excellent cata-
lytic yields whilst also preserving the integrity of the catalyst so
that it could be easily separated magnetically for potential
reuse. The CuleesBNM catalyst prepared from the spent lees
waste gave complete conversion after 12 hours and was only
slightly less efficient over a shorter incubation time compared
to the CusaltBNM catalyst (Table 1, entries 7 and 9). Therefore,
all subsequent preparative scale experiments were carried out
using the CuleesBNM catalyst.
We next investigated the CuAAC of an expanded range of
azides (1a–c) and alkynes (1a–h) using the CuleesBNM catalyst,
to produce a variety of 1,2,3-triazole products (Scheme 1). The
reactions were conducted on a 5 mL scale, with 0.25 mmol of
each reagent and 500 µL of the CuleesBNM suspension, at
25 °C for 12 h, and the products were isolated by extraction
with ethyl acetate. The catalytic system proved very efficient in
all cases, affording almost quantitative conversion and very
good isolated yields (81–97%) for 12 different triazoles 3a–l.
This also highlights the broad tolerance of this procedure
towards different functional groups such as esters, ethers,
alcohols, ketones and heterocycles.
Scheme 1 Preparative scale synthesis of triazoles 3a–l using the
CuleesBNM catalyst.
Table 2 Recyclability of the CuleesBNM catalyst for the synthesis of 3aa
Furthermore, the recyclability of the CuleesBNM was
assessed by simple magnetic separation and recovery of the
catalyst, before being applied to a new reaction cycle. The
recyclability test was performed for the synthesis of 3a, by
extracting the product and/or leftover starting materials with
ethyl acetate, magnetically recovering the particles, rinsing
them twice with H2O/EtOH 9 : 1, and resuspending them in
water for a new reaction cycle (Table 2). The recovered catalyst
Cycle
Yield [%]
1
2
3
4
5
>95
90
71
27
<5
a Reaction conditions for CuAAC: 0.25 mmol 1a, 0.25 mmol 2a, 500 µL
CuleesBNM suspension, 5 mL H2O/t-BuOH (8 : 2), 25 °C, 12 h.
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demonstrated good yields for the first three cycles, before a support (grants BB/L013711/1 and BB/R010412/1). SJH and
significant decrease in activity at cycle 4. This highlights the AMR thank the EPSRC U.K (grants EP/M010619/1, EP/
advantage of supporting the copper on a magnetic nano- P009050/1, and the NoWNano CDT), and the ERC under the
material that can be recovered easily. Further optimisation to EU’s
Horizon
2020
program
(ERC-2016-
improve recyclability is being investigated. STG-EvoluTEM-715502). We gratefully acknowledge Ronald
Lastly, in order to prove the scalability of this protocol, a Daalmans and Chivas Brothers for supplying the spent lees.
gram-scale synthesis of 3a from 5 mmol of 1a and 2a was per- The authors would also like to thank P. Lythgoe, B. Spencer
formed (employing slightly increased substrate concentrations and R. Spiess (University of Manchester) for ICP-AES, XPS and
and decreased catalyst loading, see ESI† for details). Triazole HRMS analyses, respectively.
3a was obtained in 82% isolated yield after extraction and
recrystallisation, demonstrating the usefulness of the
CuleesBNM as a preparative-scale catalyst for CuAAC reactions.
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Herein, we report for the first time CuAAC reactions using
copper recovered from an industrial waste stream. In addition,
we demonstrate the first use of biogenic magnetic nano-
particles as a simple, green method for recovering and sub-
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Recovery from Waste program (NE/L014203/1) and BBSRC for
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