Carbon dot/TiO2nanocomposites as photocatalysts for metallaphotocatalytic carbon-heteroatom cross-couplings

Article abstract of DOI:10.1039/d1gc01284c

Carbon dots have been previosly immobilized on titanium dioxide to generate photocatalysts for pollutant degradation and water splitting. Here we demonstrate that these nanocomposites are valuable photocatalysts for metallaphotocatalytic carbon-heteroatom cross-couplings. These sustainable materials show a large applicability, high photostability, excellent reusability, and broadly absorb across the visible-light spectrum.

Full text of DOI:10.1039/d1gc01284c

Green Chemistry
View Article Online
View Journal | View Issue
PAPER
Carbon dot/TiO2 nanocomposites as photocatalysts
for metallaphotocatalytic carbon–heteroatom
cross-couplings†
Cite this: Green Chem., 2021, 23,
4524
Zhouxiang Zhao,a,b Susanne Reischauer,a,b Bartholomäus Pieber *a and
a
Martina Delbianco
*
Received 13th April 2021,
Accepted 3rd June 2021
Carbon dots have been previosly immobilized on titanium dioxide to generate photocatalysts for pollutant
degradation and water splitting. Here we demonstrate that these nanocomposites are valuable photocatalysts
for metallaphotocatalytic carbon–heteroatom cross-couplings. These sustainable materials show a large
applicability, high photostability, excellent reusability, and broadly absorb across the visible-light spectrum.
DOI: 10.1039/d1gc01284c
rsc.li/greenchem
have long-lived triplet excited states.25–27 To overcome the pro-
blems associated with the short-lived excited states, CDs can
Introduction
Carbon dots (CDs) are quasi-spherical fluorescent carbon- be immobilized on heterogeneous semiconductors, such as
based materials with a size of typically less than 10 nm.1–5 CDs titanium dioxide, to generate a composite material that
are easily prepared through top-down or bottom-up absorbs visible-light and generates a long-lived charge-separ-
approaches from a variety of carbon sources that permit to ated species.28–30 Still, the applications of such composites
adjust their chemical compositions and tune their photo- remained limited to water splitting, CO2 reduction, and pollu-
luminescence (PL) properties.6,7 Their chemical inertness and tant degradation (Fig. 1A).31–33
biocompatibility has prompted applications in sensing, bio-
The combination of a photo- and a nickel catalyst (termed
imaging, and nanomedicine.7–11 Moreover, the surface func- metallaphotocatalysis) triggers many important carbon–
tional groups enabled applications as sustainable nano- heteroatom and carbon–carbon cross-couplings using light as
organocatalysts for synthetic transformations. The superficial sustainable energy source.34 Suitable photocatalysts for these
carboxylic acid, hydroxy, or amino functionalities were reactions range from ruthenium and iridium polypyridyl com-
exploited in acid–base, hydrogen bond, or amine-catalysed
reactions.12–15
CDs are also promising metal-free photocatalysts for pollu-
tant degradation, H2 evolution and CO2 conversion, owing to
their photostability, light-harvesting ability and electron-trans-
fer efficiency.16–19 The high solubility of CDs in water makes
them a suitable alternative to hydrophobic organic materials,
such as carbon nitride and graphite.20 This feature permitted
to use CDs in combination with nickel catalysis for H2 evol-
ution in aqueous solution.21,22
However, due to their short PL lifetimes,23,24 examples of
CDs as photocatalysts for selective organic synthesis are
scarce14,15 when compared to common photocatalysts, such as
ruthenium (Ru) and iridium (Ir) polypyridyl complexes that
aDepartment of Biomolecular Systems, Max Planck Institute of Colloids and
Interfaces, Am Mühlenberg 1, 14476 Potsdam, Germany.
E-mail: martina.delbianco@mpikg.mpg.de, bartholomaeus.pieber@mpikg.mpg.de
bDepartment of Chemistry and Biochemistry, Freie Universität Berlin, Arnimallee 22,
14195 Berlin, Germany
Fig. 1 Schematic representation of CD/TiO2 nanocomposites as photo-
catalysts for water splitting, pollutant degradation (A) and metallaphoto-
catalytic carbon–heteroatom cross-couplings (B).
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
d1gc01284c
4524 | Green Chem., 2021, 23, 4524–4530
This journal is © The Royal Society of Chemistry 2021

View Article Online
Green Chemistry
Paper
plexes and organic dyes to heterogeneous semiconductors.34 with β-alanine (β-Ala) ensured a high amount of surface car-
Moreover, nickel complexes and photocatalysts were combined boxylic acid groups (Fig. S6 and S7†).42 The zeta potential in
in bifunctional heterogeneous materials, such as metal– the range of −11.1 to +18.7 mV suggested the presence of
organic frameworks,35,36 or organic polymers.37
several functional groups (carboxylic acids, alcohols, and
Titanium dioxide can be sensitized with organic dyes to amino groups) on the surface of CD1 (Fig. S8†).42,43
serve as a visible light photocatalyst for selective organic Transmission electron microscopy (TEM) confirmed
a
transformations.38,39 Recently, it was shown that the immobil- spherical shape of the CD nanoparticles with a diameter of
ization of a Ni(II) catalyst and an organic dye on the surface of about 4 nm (Fig. 2B and Fig. S2†). The X-ray diffraction (XRD)
metal oxides provides a heterogeneous catalytic system for profile showed a single broad peak (2θ = 23°), indicating the
metallaphotocatalytic carbon–carbon and carbon–heteroatom amorphous structure of CD1 (Fig. S9†). A colloidal solution of
cross-couplings that overcomes the problems associated with CD1 in H2O emitted blue light under UV light irradiation (λex
=
short-lived singlet excited states of organic dyes.40 Following 366 nm) (Fig. S3†). Spectroscopic analysis showed an absorp-
this seminal work, we show that CDs are a valuable alternative tion peak at 276 nm (Fig. S5†) and a PL emission maximum at
to organic dyes in such catalytic systems due to (i) their low ∼460 nm (λex = 360 nm, Fig. S4†). A PL lifetime of 4.45 ns was
economic cost and toxicity, (ii) their facile immobilization on measured by fitting the PL decay curve of CD1 (Fig. S10†).
semiconductors, (iii) their broad absorption across the visible-
CD1 was immobilized on the surface of TiO2 P25 by stirring
light spectrum, and (iv) their superior photo- and chemical a mixture of the two components in water (mass ratio 1 : 1;
stability (Fig. 1B).21,30
Fig. 2A). The resulting brown powder (CD1/TiO2) was analysed
by scanning electron microscopy (SEM) and energy dispersive
X-ray spectroscopy (EDX) (Fig. S15†). The morphology and size
of the nanocomposites remained similar to unfunctionalized
TiO2. The increased carbon content confirmed the immobiliz-
ation of CD1. UV-Vis spectroscopy of the resulting material
confirmed its extended absorption in the visible-light region
(Fig. 2C).
Results and discussion
Preparation of CD1/TiO2 nanocomposite
Carbohydrates are an attractive carbon source for CD synthesis
owing to their low cost, high solubility in water, easy carbonis-
ation at relatively low temperatures, and presence of hetero-
atoms.41 We therefore began our investigations by preparing
Applicability of CD1/TiO2 as photocatalyst
CD1 from glucosamine hydrochloride (GlcN·HCl), following a The applicability of CD1/TiO2 as photocatalyst for metallapho-
microwave-based carbonisation method (Fig. 2A).42 Doping tocatalytic cross-couplings was tested for the C–O arylation of
Fig. 2 Schematic representation of the preparation of CD1 and CD1/TiO2 nanocomposite (A). TEM image of CD1 (B). UV-Vis absorption (solid state)
and photographs of TiO2 and CD1/TiO2 nanocomposite (C). GlcN·HCl = Glucosamine hydrochloride. β-Ala = β-Alanine.
This journal is © The Royal Society of Chemistry 2021
Green Chem., 2021, 23, 4524–4530 | 4525

View Article Online
Paper
Green Chemistry
Fig. 3 Optimized conditions and control experiments for the cross-coupling of Boc-Pro-OH with methyl 4-iodobenzoate using CD1/TiO2 nano-
composite (A). Application of CD1/TiO2 as photocatalyst for C–O, C–S, and C–N cross-couplings (B).
N-(tert-butoxycarbonyl)-L-proline (Boc-Pro-OH) with methyl
To our delight, CD1/TiO2 served as an active photocatalyst
4-iodobenzoate using visible-light (Fig. 3A).40,44
A
Ni(II) for a range of metallaphotocatalytic carbon–heteroatom cross-
complex that contains carboxylic acid groups was employed to couplings.34 Moderate to excellent yields were obtained for the
bind to the nanocomposite. The selective formation of 83% of coupling of aryl halides with an alcohol, a thiol, a sodium sul-
the desired ester product (1) was observed when the reaction fonate, and a sulfonamide using slightly adapted conditions
was irradiated with blue (440 nm) light for 24 h (entry 1). (Fig. 3B).
Control experiments confirmed the necessity of TiO2, CD1,
and the carboxylic acid functionalized ligand 2,2′-bipyridine-
Photostability and recyclability studies
4,4′-dicarboxylic acid (dcbpy) (entries 2–5).
Next, we sought to compare the photostability of the CD1/TiO2
A previous report that used molecular dyes with short nanocomposite with TiO2 that was functionalized with the
excited state lifetimes instead of CD1 showed that insulating organic dye fluorescein (Fluo/TiO2) (Fig. 4). The functionalized
materials, such as SiO2, can be used instead of TiO2 for the semiconductors were pre-irradiated with blue light for a defined
same reaction.40 In this case, it was proposed that the close amount of time and subsequently used as photocatalysts in the
proximity between dye molecules and the nickel complex is metallaphotocatalytic C–O arylation of Boc-Pro-OH. The photo-
responsible for productive catalysis. Using a CD1/SiO2 nano- catalytic performance of CD1/TiO2 remained unchanged even
composite, we only observed a modest yield of 7% of the after 72 h exposure to light. In contrast, Fluo/TiO2 produced sig-
desired product (entry 6), suggesting that an electronic com- nificantly lower yields after 6 h irradiation. The yield obtained
munication between the excited CD and the immobilized with the Fluo/TiO2 photocatalyst did not decrease linearly with
nickel complex “through”
a
semiconducting material is the irradiation time, but seemed to reach a plateau after 6–12 h
crucial.
pre-irradiation. We assume that the prolonged irradiation could
Using CD1/TiO2 an almost quantitative formation of 1 promote the formation of fluorescein degradation products that
required 40 h (entry 7). The broad absorption of the nano- still serve as a sensitizer.45,46
composite also enabled cross-coupling at longer wavelengths
The CD1/TiO2 nanocomposite was characterized before and
(525 nm), albeit with longer reaction times (entry 8). It is after the catalytic reaction (Table S3†). Inductively coupled
worth noting that CD1/TiO2 is also highly active using very low plasma - optical emission spectrometry (ICP-OES) revealed the
loadings (Table S6†), and that the nanocomposite is bench- presence of nickel in the CD1/TiO2 nanocomposite after the
stable and does not lose its catalytic activity upon storage at C–O cross-coupling (Fig. 3A, entry 7). This indicated that the
room temperature for 26 weeks (Table S5†).
nickel complex remained immobilized on CD1/TiO2, prompt-
4526 | Green Chem., 2021, 23, 4524–4530
This journal is © The Royal Society of Chemistry 2021

View Article Online
Green Chemistry
Paper
Fig. 4 Photobleaching experiments to compare the photostability of CD1/TiO2 and Fluo/TiO2. The two photocatalysts were pre-irradiated with
blue light and then used in the metallaphotocatalytic C–O arylation. Yields were determined via 1H-NMR using 1,3,5-trimethoxybenzene as internal
standard. Fluo = fluorescein.
Fig. 5 Reusability of CD1/TiO2 nanocomposite decorated with a nickel complex in the metallaphotocatalytic C–O arylation.
ing us to explore the recyclability of the bifunctional hetero- different carbon sources and doping agents on the photo-
geneous catalyst (Fig. 5). Recyclability experiments were per- catalytic reaction (Fig. 6A). A first set of CDs was synthesized
formed using the reaction conditions reported in Fig. 3A (entry 1). maintaining GlcN·HCl as the carbon source and screening
After each cycle, the heterogeneous material was separated, different doping agents. 1,3-Diaminobenzene, l-cysteine
washed, and reused in the next C–O cross-coupling. Excellent (l-Cys), poly(ethylene glycol) (average Mn 400) (PEG), and
catalytic performances were observed even after four recycling glycine (Gly) were tested. Each compound was selected to
cycles. Importantly, the addition of nickel salt or nickel introduce respectively aromatic groups,48 sulphur atoms, poly-
complex after each cross-coupling cycle, which was previously mers to enhance surface passivation,49 or amino acid ana-
required in a related approach,40 was not only unnecessary, logues of β-Ala. A second set of CDs was based on β-Ala as
but significantly decreased the catalytic activity. This may be doping agent and different carbon sources. Three mono-
ascribed to Ni accumulation and formation of nickel-black saccharides (glucose (Glc), N-acetyl-glucosamine (GlcNAc), galac-
upon irradiation by high-energy light (Fig. S28†).47
tose (Gal)), a disaccharide (D-lactose (Lac)) and a polysacchar-
Overall, these results underscore the potential of CD1/TiO2 ide (pullulan) were tested to explore the influence of chain
nanocomposites as a robust, cheap, and green photocatalyst length and sugar structure on the photocatalytic performance.
for applications in organic chemistry.
All CD precursors resulted in spherical nanoparticles with dia-
meters smaller than 10 nm (Fig. S11†). Most CDs showed
similar photophysical properties, with the exception of CD2
Screening of different CD photosensitizers
Having demonstrated the potential of CD1 as photosensitizer that emitted bright green light under UV light irradiation (λex
=
for dual photoredox/Ni catalysis, we assessed the effect of 366 nm) (Fig. S12 and S13†) and had an absorption maximum
This journal is © The Royal Society of Chemistry 2021
Green Chem., 2021, 23, 4524–4530 | 4527

View Article Online
Paper
Green Chemistry
Fig. 6 Chemical structures of carbon sources and doping agents used for CD synthesis (A). UV-Vis absorption spectra (solid state) of CD/TiO2
nanocomposites (B). Evaluation of different CD/TiO2 nanocomposites as photocatalyst for the metallaphotocatalytic C–O arylation of Boc-Pro-OH
with methyl 4-iodobenzoate (C).
4528 | Green Chem., 2021, 23, 4524–4530
This journal is © The Royal Society of Chemistry 2021

View Article Online
Green Chemistry
Paper
at 363 nm (Fig. S14†). All CDs were immobilized on TiO2 P25 German Federal Ministry of Education and Research (BMBF, grant
to prepare nine CD/TiO2 nanocomposites able to absorb light number 13XP5114) and the China Scholarship Council. S.R. and
in the visible region (Fig. 6B and Fig. S18†). While most UV-Vis B.P. acknowledge financial support by a Liebig Fellowship of the
spectra share a similar profile, CD2/TiO2 nanocomposites German Chemical Industry Fund (Fonds der Chemischen
exhibit a strong absorption band with a maximum at 466 nm. Industrie, FCI). B.P. thanks the Deutsche Forschungsgemeinschaft
The photocatalytic performances of all nanocomposites were (DFG, German Research Foundation) for financial support
compared (Fig. 6C). Despite the broad and intense absorption (PI 1635/2-1). Open Access funding provided by the Max Planck
in the visible range, CD2/TiO2 resulted in low yields, whereas Society.
all other nanocomposites showed good to excellent results. For
a fair comparison it should be noted that, even though all
nanocomposites were prepared starting with an initial
1 : 1 mass ratio of CD : TiO2, differences in immobilization
Notes and references
might play a role in the photocatalytic results.
1 X. Xu, R. Ray, Y. Gu, H. J. Ploehn, L. Gearheart, K. Raker
and W. A. Scrivens, J. Am. Chem. Soc., 2004, 126, 12736.
2 G. A. M. Hutton, B. C. M. Martindale and E. Reisner, Chem.
Soc. Rev., 2017, 46, 6111.
3 Z. L. Wu, Z. X. Liu and Y. H. Yuan, J. Mater. Chem. B, 2017,
5, 3794.
4 J. Zhan, B. Geng, K. Wu, G. Xu, L. Wang, R. Guo, B. Lei,
F. Zheng, D. Pan and M. Wu, Carbon, 2018, 130, 153.
5 L. Vallan, E. P. Urriolabeitia, F. Ruiperez, J. M. Matxain,
R. Canton-Vitoria, N. Tagmatarchis, A. M. Benito and
W. K. Maser, J. Am. Chem. Soc., 2018, 140, 12862.
6 S. Y. Lim, W. Shen and Z. Gao, Chem. Soc. Rev., 2015, 44, 362.
7 K. Jiang, S. Sun, L. Zhang, Y. Lu, A. Wu, C. Cai and H. Lin,
Angew. Chem., Int. Ed., 2015, 54, 5360.
These results show that the system is highly flexible and
that CD photosensitizers can be prepared from several starting
materials, without affecting the catalytic performances. For
example, excellent results were obtained for CD9 and CD10
prepared using lactose and pullulan as carbon source, respect-
ively. These materials are highly abundant and cheap (lactose
is a waste product of the dairy industry that is produced at
>6 million ton scale every year) suggesting the possibility of
turning naturally sourced polysaccharides from waste
materials into valuable catalysts. Fine tuning of the elemental
composition and its effect on the photocatalytic reaction will
be explored in follow up studies.
8 Z. Shen, C. Zhang, X. Yu, J. Li, Z. Wang, Z. Zhang and
B. Liu, J. Mater. Chem. C, 2018, 6, 9636.
9 B. Zhi, Y. Cui, S. Wang, B. P. Frank, D. N. Williams,
R. P. Brown, E. S. Melby, R. J. Hamers, Z. Rosenzweig,
D. H. Fairbrother, G. Orr and C. L. Haynes, ACS Nano, 2018,
12, 5741.
10 S. Sri, R. Kumar, A. K. Panda and P. R. Solanki, ACS Appl.
Mater. Interfaces, 2018, 10, 37835.
11 H. Zhao, J. Duan, Y. Xiao, G. Tang, C. Wu, Y. Zhang, Z. Liu
and W. Xue, Chem. Mater., 2018, 30, 3438.
12 B. Majumdar, S. Mandani, T. Bhattacharya, D. Sarma and
T. K. Sarma, J. Org. Chem., 2017, 82, 2097.
13 X. Pei, D. Xiong, H. Wang, S. Gao, X. Zhang, S. Zhang and
J. Wang, Angew. Chem., Int. Ed., 2018, 57, 3687.
14 Y. Han, H. Huang, H. Zhang, Y. Liu, X. Han, R. Liu, H. Li
and Z. Kang, ACS Catal., 2014, 4, 781.
15 G. Filippini, F. Amato, C. Rosso, G. Ragazzon, A. Vega-
Peñaloza, X. Companyó, L. Dell’Amico, M. Bonchio and
M. Prato, Chem, 2020, 6, 3022.
Conclusions
Carbohydrate-based CDs were immobilized on TiO2 to prepare
nanocomposites, offering a cheap and robust alternative to
organic dyes. This approach allowed us to overcome the issues
associated with the short excited state lifetime of CDs. We
demonstrated that CDs are valuable photocatalysts for metalla-
photocatalytic carbon–heteroatom cross-couplings. High conver-
sions were observed under irradiation by either blue or green
light. Photobleaching experiments confirmed that the catalytic
performances of the CD/TiO2 nanocomposites are not affected by
long-time light irradiation prior to their use in catalytic reactions.
Recycling experiments showed the excellent reusability of this
catalytic system in C–O cross-coupling reactions. CDs could be
prepared from different carbohydrate sources and doping agents,
without significant difference in the catalytic performance. This
is particularly important in the perspective of using polysacchar-
ide waste materials to generate valuable photocatalysts.
16 S. Hu, R. Tian, L. Wu, Q. Zhao, J. Yang, J. Liu and S. Cao,
Chem. – Asian J., 2013, 8, 1035.
17 P. Yang, J. Zhao, J. Wang, H. Cui, L. Li and Z. Zhu,
Chemphyschem, 2015, 16, 3058.
18 J. Wu, S. Ma, J. Sun, J. I. Gold, C. Tiwary, B. Kim, L. Zhu,
N. Chopra, I. N. Odeh, R. Vajtai, A. Z. Yu, R. Luo, J. Lou,
G. Ding, P. J. Kenis and P. M. Ajayan, Nat. Commun., 2016,
7, 13869.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We gratefully acknowledge the Max-Planck Society for generous 19 L. Cao, S. Sahu, P. Anilkumar, C. E. Bunker, J. Xu,
financial support. M.D. and Z.Z. acknowledge financial support
from the MPG-FhG Cooperation Project Glyco3Dysplay, the
K. A. S. Fernando, P. Wang, E. A. Guliants, K. N. Tackett, II
and Y. P. Sun, J. Am. Chem. Soc., 2011, 133, 4754.
This journal is © The Royal Society of Chemistry 2021
Green Chem., 2021, 23, 4524–4530 | 4529

View Article Online
Paper
Green Chemistry
20 H. Li, X. He, Z. Kang, H. Huang, Y. Liu, J. Liu, S. Lian, 35 G. Lan, Y. Quan, M. Wang, G. T. Nash, E. You, Y. Song,
C. H. Tsang, X. Yang and S. T. Lee, Angew. Chem., Int. Ed.,
2010, 49, 4430.
S. S. Veroneau, X. Jiang and W. Lin, J. Am. Chem. Soc., 2019,
141, 15767.
21 B. C. Martindale, G. A. Hutton, C. A. Caputo and 36 Y.-Y. Zhu, G. Lan, Y. Fan, S. S. Veroneau, Y. Song,
E. Reisner, J. Am. Chem. Soc., 2015, 137, 6018.
D. Micheroni and W. Lin, Angew. Chem., Int. Ed., 2018, 57,
22 Y. Liu, Y. Zhao, Q. Wu, X. Wang, H. Nie, Y. Zhou,
14090.
H. Huang, M. Shao, Y. Liu and Z. Kang, Chem. Eng. J., 37 Y. Pan, N. Zhang, C.-H. Liu, S. Fan, S. Guo, Z.-M. Zhang
2021, 409, 128184. and Y.-Y. Zhu, ACS Catal., 2020, 10, 11758.
23 Z. Zhou, P. Tian, X. Liu, S. Mei, D. Zhou, D. Li, P. Jing, 38 D. Franchi and Z. Amara, ACS Sustainable Chem. Eng., 2020,
W. Zhang, R. Guo, S. Qu and A. L. Rogach, Adv. Sci., 2018,
5, 1800369.
8, 15405.
39 S. Gisbertz and B. Pieber, ChemPhotoChem, 2020, 4, 456.
24 S. Li, K. Ji, M. Zhang, C. He, J. Wang and Z. Li, Nanoscale, 40 S. Reischauer, V. Strauss and B. Pieber, ACS Catal., 2020,
2020, 12, 9533.
10, 13269.
25 D. M. Schultz and T. P. Yoon, Science, 2014, 343, 1239176.
26 C. K. Prier, D. A. Rankic and D. W. MacMillan, Chem. Rev.,
2013, 113, 5322.
27 L. Marzo, S. K. Pagire, O. Reiser and B. Konig, Angew.
Chem., Int. Ed., 2018, 57, 10034.
28 Y. X. Weng, L. Li, Y. Liu, L. Wang and G. Z. Yang, J. Phys.
Chem. B, 2003, 107, 4356.
29 S. Agrawal, N. J. English, K. R. Thampi and J. M. MacElroy,
Phys. Chem. Chem. Phys., 2012, 14, 12044.
41 S. Hill and M. C. Galan, Beilstein J. Org. Chem., 2017, 13,
675.
42 S. A. Hill, D. Benito-Alifonso, S. A. Davis, D. J. Morgan,
M. Berry and M. C. Galan, Sci. Rep., 2018, 8, 12234.
43 S. A. Hill, D. Benito-Alifonso, D. J. Morgan, S. A. Davis,
M. Berry and M. C. Galan, Nanoscale, 2016, 8, 18630.
44 B. Pieber, J. A. Malik, C. Cavedon, S. Gisbertz, A. Savateev,
D. Cruz, T. Heil, G. Zhang and P. H. Seeberger, Angew.
Chem., Int. Ed., 2019, 58, 9575.
30 L. Xu, X. Bai, L. Guo, S. Yang, P. Jin and L. Yang, Chem. 45 U. Kriiger and R. Memming, Ber. Bunsenges. Phys. Chem.,
Eng. J., 2019, 357, 473. 1974, 78, 670.
31 R. Shi, Z. Li, H. Yu, L. Shang, C. Zhou, G. I. N. Waterhouse, 46 Q. Zheng and L. D. Lavis, Curr. Opin. Chem. Biol., 2017, 39,
L. Z. Wu and T. Zhang, ChemSusChem, 2017, 10, 4650. 32.
32 J. Zhang, X. Zhang, S. Dong, X. Zhou and S. Dong, 47 S. Gisbertz, S. Reischauer and B. Pieber, Nat. Catal., 2020,
J. Photochem. Photobiol., A, 2016, 325, 104. 3, 611.
33 M. Li, M. Wang, L. Zhu, Y. Li, Z. Yan, Z. Shen and X. Cao, 48 S. A. Hill, S. Sheikh, Q. Zhang, L. Sueiro Ballesteros,
Appl. Catal., B, 2018, 231, 269.
34 C. Zhu, H. Yue, J. Jia and M. Rueping, Angew. Chem., Int.
Ed., 2021, 60, 2.
A. Herman, S. A. Davis, D. J. Morgan, M. Berry, D. Benito-
Alifonso and M. C. Galan, Nanoscale Adv., 2019, 1, 2840.
49 L. Li and T. Dong, J. Mater. Chem. C, 2018, 6, 7944.
4530 | Green Chem., 2021, 23, 4524–4530
This journal is © The Royal Society of Chemistry 2021