Autonomously Propelled Motors for Value-Added Product Synthesis and Purification

Article abstract of DOI:10.1002/chem.201600923

A proof-of-concept design for autonomous, self-propelling motors towards value-added product synthesis and separation is presented. The hybrid motor design consists of two distinct functional blocks. The first, a sodium borohydride (NaBH₄) granule, serves both as a reaction prerequisite for the reduction of vanillin and also as a localized solid-state fuel in the reaction mixture. The second capping functional block consisting of a graphene–polymer composite serves as a hydrophobic matrix to attract the reaction product vanillyl alcohol (VA), resulting in facile separation of this edible value-added product. These autonomously propelled motors were fabricated at a length scale down to 400 μm, and once introduced in the reaction environment showed rapid bubble-propulsion followed by high-purity separation of the reaction product (VA) by the virtue of the graphene–polymer cap acting as a mesoporous sponge. The concept has excellent potential towards the synthesis/isolation of industrially important compounds, affinity-based product separation, pollutant remediation (such as heavy metal chelation/adsorption), as well as localized fuel-gradients as an alternative to external fuel dependency.

Full text of DOI:10.1002/chem.201600923

DOI: 10.1002/chem.201600923
Communication
&
Hybrid Micromotors
Autonomously Propelled Motors for Value-Added Product
Synthesis and Purification
Sarvesh K. Srivastava* and Oliver G. Schmidt[a]
propelling the spatially confined asymmetric microstructures in
Abstract: A proof-of-concept design for autonomous, self-
propelling motors towards value-added product synthesis
and separation is presented. The hybrid motor design
consists of two distinct functional blocks. The first,
a sodium borohydride (NaBH4) granule, serves both as a re-
action prerequisite for the reduction of vanillin and also as
a localized solid-state fuel in the reaction mixture. The
second capping functional block consisting of a gra-
phene–polymer composite serves as a hydrophobic matrix
to attract the reaction product vanillyl alcohol (VA), result-
ing in facile separation of this edible value-added product.
These autonomously propelled motors were fabricated at
a length scale down to 400 mm, and once introduced in
the reaction environment showed rapid bubble-propul-
sion followed by high-purity separation of the reaction
product (VA) by the virtue of the graphene–polymer cap
acting as a mesoporous sponge. The concept has excel-
lent potential towards the synthesis/isolation of industrial-
ly important compounds, affinity-based product separa-
tion, pollutant remediation (such as heavy metal chela-
tion/adsorption), as well as localized fuel-gradients as an
alternative to external fuel dependency.
its aqueous reaction environment.[13,14] This has been achieved
with the incorporation of certain heterogeneous catalytic
layers (Pt, Pd, Ru) in presence of an external fuel (for example,
peroxides or hydrazine) to propel these micromotors. A classic
example is the oxygen evolution reaction via dissociation of
H2O2 in the presence of Pt metal catalysts.[15–17] Therefore, there
is a constant need to innovate newer reactions and associated
materials/design to actively propel these micromotors with an
aim to explore novel applications. Recently, Sen et al.[18] report-
ed autonomous motion by a depolymerization-based mecha-
nism of poly(2-ethyl cyanoacrolyte) polymer in aqueous
medium. Similarly, studies have been reported for preferential
dissolution of magnesium to propel certain microstructures in
aqueous environment.[19,20]
The quest for newer reaction mechanisms not only facilitates
innovative material/design parameters but is also important in
exploring newer applications for such chemically-propelled
motor systems. In several of the above mentioned micromotor
studies, one may notice that an external fuel gradient is
merely required to facilitate the propulsion. Recently, we have
reported the wastewater mediated activation of micromotors
for pollutant degradation, in which the pollutant mixture itself
served as a fuel, thereby limiting external fuel or addition of
surfactants.[21] This study happens to be the first scientific
report confirming highly efficient pollutant degradation by au-
tonomously propelled micromotors in the volume range of mL
along with the absence of surfactants/pH control or addition
of external fuel for propulsion. Another interesting study re-
ported by Gao et al[22] demonstrated the Zn-coated micromo-
tor propulsion inside the mouse stomach. Apart from the fact
that this may have been the first study reporting an in vivo mi-
cromotor application, the very reaction centered around the
H2 evolution by oxidation of Zn metals in presence of HCl war-
rant its application under acidic conditions (like digestive
juices in the stomach with pH 1.5–3.5). Likewise, Soler et al[23]
utilized the Fenton reaction for the degradation of Rhoda-
mine 6G in water. The reaction utilizes H2O2 in the presence of
the Pt-incorporated micromotor structure (along with a Fe
layer to execute the Fenton reaction under acidic conditions),
thereby providing an autonomous propulsion. These bench-
mark studies illustrate that the potential application for micro-
motors can be combined with autonomous propulsion by the
virtue of their reaction mechanism. Therefore, it is important
to combine the external fuel dependency as an intricate part
of the reaction mechanism (if not completely avoidable) to ex-
ecute/innovate newer applications for such chemical micro
Since the onset of industrial age, motors have played a key
role in the advancement of the human society by converting
one form of energy into another. The trend towards greater
miniaturization[1] presents a case for autonomously powered
micromotors that are capable of converting the energy of
chemical fuels or external fields into mechanical motion.[2,3]
These microswimmers[4] (with different propulsion mechanisms,
such as self-electrophoresis,[5] diffusophoresis,[6] catalytic
random fluctuation,[7] or bubble propulsion,[8,9] have been of
considerable interest owing to their wide variety of applica-
tions in drug delivery,[10] cargo delivery,[11] and next-generation
medibots (a multi-specialty microbot for advanced biomedical
applications).[12]
The working principle behind bubble-propelled micromotors
in particular is to generate a thrust of gases in liquid medium
by catalyzing a gas evolution reaction (such as O2, H2), thereby
[a] Dr. S. K. Srivastava, Prof. Dr. O. G. Schmidt
Institute for Integrative Nanosciences, IFW Dresden
Helmholtzstrasse 20, 01069 Dresden (Germany)
E-mail: sarvesh.kumar@ifw-dresden.de
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201600923.
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swimmers. This trend was well-captured by a recent study
done by Yamamoto et al.[24] showing aerobic oxidation of non-
toxic alcohols and aldehydes for autonomous propulsion.
In this study, we present the first proof of concept for food-
producing micromotors (value-added product synthesis) based
on the autonomous propulsion of our hybrid motor setup fab-
ricated both at the macroscopic (1-4 mm) and microscopic (ca.
400 mm) length scale. We synthesized vanillyl alcohol (4-(hy-
droxymethyl)-2-methoxyphenol) by reduction of vanillin (3-me-
thoxy-4-hydroxy benzaldehyde), which is an important food
additive.[25] Vanillin is a phenolic aldehyde extracted from Vanil-
la beans (Vanilla planifolia) as the natural source.[26,27] Several
biological and chemical methods have been reported to
obtain vanillyl alcohol (VA) from vanillin.[28–30] However, these
share an inherent disadvantage of resource intensive extrac-
tion, elaborate purification/downstream-processing, or selec-
tion/culturing of microbiological strains. Chemical reduction of
vanillin with NaBH4 has emerged as a viable alternative (as
compared to LiBH4 or Al(BH4)3) owing to relatively safe han-
dling under industrial conditions.[31] It should be noted that
even with NaBH4 mediated reduction, formation of by-prod-
ucts such as borates together with VA requires the use of re-
peated distillation/downstream processing to obtain a pure
product.
hyde group in vanillin, creating a partial positive charge on the
carbon of the aldehyde group owing to the greater electrone-
gativity of the oxygen atom, resulting in formation of oxygen–
boron bonds (equation of Figure 1a). Therefore, upon intro-
duction of the motor in the vanillin containing reactant
medium, rapid dissociation of NaBH4 results in the reduction of
vanillin along with simultaneous propulsion of our bifunctional
motors. Once the NaBH4 granule is consumed, in the next
phase of the reaction, the oxygen–boron bonds are hydrolyzed
in presence of HCl, thereby forming our desired product, vanil-
lyl alcohol (Figure 1b). Addition of HCl (pH 2.5) not only hydro-
lyzes the OÀB bond in the intermediate but also destroys
excess NaBH4 that may be present in the reaction mixture. Fi-
nally, as shown in Figure 1c, owing to the hydrophobic nature
of our polymer coating, the resulting product VA was attracted
and adhered to it on the top-layer of the reaction mixture pro-
moting easy separation. This can be understood by the fact
that the resulting product VA has higher electron density re-
tained by the virtue of the attached aromatic OH groups (lone
pairs on the oxygen overlaps with the delocalized ring electron
system). Upon completion of the reduction reaction, this ena-
bles the product to become attracted towards the graphene–
polymer composite (referred hereafter as mesoporous sponge),
thereby promoting rapid separation of the high-purity product.
This is also important as, in absence of this hydrophobic pull/
interaction (keeping other reaction conditions constant), the
resulting VA product also contains borates/metaborates as the
reaction by-product thereby requiring further downstream
processing. The presence of graphene polymer composite in
the reaction medium results in faster assimilation of the prod-
uct (VA) compared to the control sample (Supporting Informa-
tion, video S4). This can also be understood by the fact that
the oxygenated moieties (carbonyl and carboxyl groups) pres-
ent over the graphene surface acting as a platform for the
loading of resulting product via p–p stacking. This warrants
the use of graphene polymer composite together with the
solid-state fuel for the product synthesis and isolation. Similar
motion mechanism was deployed by Ismagilov et al.[36] for arti-
ficial millimeter-scale catalytic boat, which can glide across the
surface of a liquid via combination of catalytic decomposition
of H2O2 and relative motion caused by capillary interactions at
the fluid–air interface. It is important to note that although ki-
netic/quantitative analysis may yield greater information about
the conversion efficiency and product recovery, it is beyond
Herein, we fabricated autonomously propelled motors capa-
ble of converting vanillin into vanillyl alcohol and also promot-
ing their rapid separation (Figure 1). We observed that both
the macroscopic (1–4 mm) and microscopic (ca. 400 mm) ver-
sion of our fabricated micromotor followed similar propulsion
characteristics.
We utilized the solvent-dissolved parafilm to create a func-
tional hydrophobic coating (due to the presence of olefin
waxes together with graphene) on NaBH4 lumps comprising
our motor structure as shown in Figure 1a. The idea to utilize
parafilm was based on the fact that it is readily available along
with facile motor fabrication by a polymer dissolution ap-
proach.[32] Inclusion of graphene with the parafilm polymer
composite was made to utilize the inherent hydrophobic at-
traction of such mesoporous materials[33] for adsorbing the re-
action product, vanillyl alcohol.[34] The resulting reaction in-
volves the reduction of the aldehyde group in vanillin where
for every one equivalent of NaBH4, there are four equivalents
of hydride.[35] The reduction mechanism involves the transfer
of hydride ions from NaBH4 to the carbonyl carbon of the alde-
Figure 1. The conversion of vanillin into vanillyl alcohol by autonomously propelled motors.
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the rationale of our current proof of concept study. Likewise,
in another study by Ikezoe et al.[37] they utilized a peptide–
MOF (metal–organic framework) for functional microelectric
generators. This was achieved by reorganization of hydropho-
bic peptides, which could create the large surface tension gra-
dient around the MOF and efficiently powered the translation
motion of MOFs. Therefore, we can see that the difference in
hydrophobicity/supramolecular interactions towards material
synthesis can find a wide range of applications for these micro-
motors. This is further important to understand that the pro-
pulsion of the motors is at the air–liquid interface, that is, es-
sentially 2D. However, to realize the value-added product syn-
thesis and purification, a two-step process takes place: a) prod-
uct synthesis via complete dissolution of NaBH4 granule in con-
tact with the solution; b) once the NaBH4 granule has reacted
completely (dissolved), the graphene–polymer composite inter-
face is in contact with the reaction medium, facilitating prod-
uct separation.
note that although this satisfies the criteria for being autono-
mously propelled, in absence of any meaningful functionality,
this limits the application of the resulting swimmer system
(and micromotors in general). However, incorporation of gra-
phene together with the parafilm polymer matrix (mesoporous
sponges) facilitated rapid product separation (via adsorption)
once the reaction gets completed (Figure 2e,f). Upon extract-
ing and drying these mesoporous sponges, we can clearly see
the pure product vanillin alcohol (as yellow–orange amber-like
product) in Figure 2 f. The product can then be separated by
a simple physical separation method, such as gentle crushing.
This is a distinct advantage over conventional synthesis meth-
ods where formation of borates as byproduct together with
the VA always requires further processing and treatment. Also,
in the presence of NaBH4 alone, the resulting product mixture
was rather turbid as compared to the visually distinguishable
top-layer of the product which gets adsorbed around the me-
soporous sponges , thereby requiring subsequent product pu-
rification (Supporting Information, Figure S1).
SEM imaging was carried out to visualize the surface of our
polymer matrix (Figure 2). Figure 2a shows the polymer film
without any mesoporous graphene, highlighting a compara-
tively smooth surface. In contrast, Figure 2b shows the surface
of the polymer–graphene composite with remarkable changes
in terms of surface morphology, with an irregular/rough sur-
face as is the case with mesoporous materials.[38] This gra-
phene–polymer matrix was analyzed post-adsorption of the re-
action product VA (Figure 2c). We were able to visualize vanill-
yl alcohol globules adhered to the surface of the graphene
polymer matrix, clearly highlighting their role as mesoporous
sponge. Figure 2d shows a representative image for polymer
film coated NaBH4 without any inclusion of graphene, corre-
sponding to the SEM surface imaging observed in Figure 2a.
From the Supporting Information, video S4, it is important to
The product adsorption on graphene can be greatly influ-
enced by reaction parameters such as pH and the presence/
absence of ionizable species, especially on the adsorption of
hydrophobic compounds.[39,40] Furthermore, the ubiquitous
natural organic matter (NOM) present in the reaction medium
can directly affect product adsorption by decreasing the ad-
sorption sites through competition and pore blockage or in-
creasing adsorption sites owing to its better dispersibility.[41]
These properties have in fact made carbon-based adsorbents
a lucrative choice for the adsorption and separation of organic
compounds such as dyes or pollutants.[42,43] Similarly, we utilized
the tendency of polycyclic aromatic units present in the gra-
phene sheets[44] to aggregate our product vanillyl alcohol into
columnar stacks, which is due to non-covalent interactions.
Figure 2. a)–c) SEM surface imaging of a) polymer composite without graphene, b) polymer–graphite composite, and c) polymer–graphite composite after ad-
sorption of the VA product (inset: false color image showing VA globules in green adhered to the graphene polymer surface). d)–f) Representative optical
images of d) polymer composite without graphene in its reaction medium, e) polymer–graphite composite with the product VA in the reaction medium, and
f) the dried polymer–graphene composite motor covered with pure VA product.
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gion IV of Figure 3b. Finally, we obtained the FTIR spectra of
vanillyl alcohol adsorbed graphite sponge (Figure 3c) showing
comparable peak positions as compared to vanillyl alcohol
(Figure 3b) with distinct absence of the aldehyde group (re-
gion II). The peaks were further amplified after the extraction
and drying of the top layer of the reaction mixture comprising
of VA adsorbed onto the mesoporous sponge showing high
purity product separation (Supporting Information, Figure S2).
As expected, no major peak was observed for vanillin or VA in
case of the graphene–polymer control sample (Figure 3a).
Finally, autonomous motion of food producing motors was
studied as shown in Figure 4. The motor design comprised of
a bifunctional setup where the lower portion consisting of
NaBH4 reacts with the vanillin containing reaction mixture and
once it is dissolved, the top hydrophobic graphene–polymer
layer comes in contact with the reaction mixture and acts like
a mesoporous sponge promoting facile separation of VA. We
observed varying velocities in case of graphite deposited and
non-deposited motors as shown in Figure 4a,b. When the
graphite containing bifunctional NaBH4 lumps were introduced
in the vanillin reaction medium, an average velocity of
1.3 mmsÀ1 (Supporting Information, video S1) was observed.
We obtained a higher velocity in case of the parafilm polymer
coating without graphene (v=1.92 mmsÀ1), suggesting that
certain surface interactions[47,48] can be responsible for slowing
down the polymer-graphene motor (Supporting Information,
video S2). This is expected, as graphene tends to interact with
the vanillyl alcohol reaction product owing to p–p interactions
resulting in its separation. Also, given the fact that our autono-
mous hybrid motor is operational at the air–water interface,
surface tension effects will influence the motor movement
(along with the hydrogen evolution reaction as the main pro-
pelling mechanism), as observed in case of camphor boats[49,50]
and solvent-driven gels.[51] The propulsion concept may draw
some parallels to a study done by Jin et al.,[52] where they
demonstrated a new type of Marangoni propulsion promoting
steady velocity for a prolonged period of time owing to the
constant supply of fuel vapor through the membrane.
Figure 3. FTIR spectra of a) graphene–polymer control, b) vanillyl alcohol
standard, c) graphene–polymer with vanillyl alcohol as adsorbed product,
and d) vanillin standard. Regions I–IV highlight different functional groups:
I) C=C aromatic ring stretching; II) aldehyde group HC=O; III) phenolic hy-
droxy and associated alkyl CH3 group; IV) substituted OH on the benzene
ring.
The synthesis and separation of vanillyl alcohol was con-
firmed by FTIR analysis (Figure 3). Both vanillin and vanillyl al-
cohol are structurally similar but with a major difference where
the C=O stretch of the aldehyde (region II) in vanillin is re-
duced to OH (region IV) in VA. Figure 3d shows FTIR spectra
for vanillin standard, with characteristic absorption of the C=C
benzene ring stretching of in the range 1510–1600 cmÀ1 (re-
gion I) followed by the HC=O peak of the aldehyde group at
about 1660 cmÀ1 (region II).[45] Further, the phenolic ring along
with CÀH stretching in the methoxy (OÀCH3) associated with
the aromatic ring can be attributed to the 2800–3200 cmÀ1
broad stretch (region III), while the ring-associated OH peak is
highlighted at about 3400 cmÀ1 (region IV).[46] Compared to
this, FTIR spectra for vanillyl alcohol (Figure 3b) showed the
C=C peaks for the benzene ring structure (region I) except for
the HC=O (aldehyde group, region II). As stated above, this al-
dehyde group was replaced with the ring-associated OH
group, with a characteristic absorption peak observed in re-
Similar propulsion behavior was observed for the micro-
scaled version (400 mm), as shown in Figure 4c. We observed
Figure 4. Autonomous propulsion pattern as observed in: a) NaBH4–polymer composite (without graphene), b) NaBH4–graphene–polymer composite, and
c) NaBH4–graphene polymer composite at the microscale.
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a propulsion speed of 0.4Æ0.24 mmsÀ1 when the micromotor
was introduced into its reactant environment (Supporting In-
formation, video S3). This is comparatively slower than its mac-
roscopic variant probably due to the fact that at macroscopic
length scale or large Reynolds numbers, the phoretic effects
that power the micromotor motion no longer play an impor-
tant role. Also, microscale propulsion for a reactant-to-product
system may not be as effective as the corresponding larger an-
alogue owing to enhanced viscous, thermal, and interfacial mi-
croscale effects.[53,54] Therefore, we observed higher velocity as
compared to the phoretic mechanisms in micromotile objects.
This also justifies the use of a macroscale architecture for au-
tonomous propulsion based upon its intended application and
imparted functionalities. Finally, we believe that such reactant-
to-product type micromotors can find interesting applications
in production of valuable compounds, removal of pollutants
(such as POPs, heavy metals) in water, and may even be ex-
tended to biological systems for adsorption of toxins or the
sustained release of drugs. Incorporation of high-specificity ad-
sorbents to efficiently trap/purify the compound of interest
will greatly influence the development of such autonomous
motors from a proof-of-concept study to viable industrial solu-
tion in future.
[16] W. F. Paxton, K. C. Kistler, C. C. Olmeda, A. Sen, S. K. St. Angelo, Y. Cao,
T. E. Mallouk, P. E. Lammert, V. H. Crespi, J. Am. Chem. Soc. 2004, 126,
13424–13431.
[17] F. Mou, D. Pan, C. Chen, Y. Gao, L. Xu, J. Guan, Adv. Funct. Mater. 2015,
25, 6173–6181.
[18] H. Zhang, W. Duan, L. Liu, A. Sen, J. Am. Chem. Soc. 2013, 135, 15734–
15737.
[19] W. Gao, X. Feng, A. Pei, Y. Gu, J. Li, J. Wang, Nanoscale 2013, 5, 4696–
4700.
[20] F. Mou, C. Chen, H. Ma, Y. Yin, Q. Wu, J. Guan, Angew. Chem. Int. Ed.
2013, 52, 7208–7212; Angew. Chem. 2013, 125, 7349–7353.
[21] S. K. Srivastava, M. Guix, O. G. Schmidt, Nano Lett. 2016, 16, 817–821.
[22] W. Gao, R. Dong, S. Thamphiwatana, J. Li, W. Gao, L. Zhang, J. Wang,
ACS Nano 2015, 9, 117–123.
[23] L. Soler, V. Magdanz, V. M. Fomin, S. Sanchez, O. G. Schmidt, ACS Nano
2013, 7, 9611–9620.
[24] D. Yamamoto, T. Takada, M. Tachibana, Y. Iijima, A. Shioi, K. Yoshikawa,
Nanoscale 2015, 7, 13186–13190.
[25] N. J. Walton, M. J. Mayer, A. Vanillin, Phytochemistry 2003, 63, 505–515.
[26] M. D. Sharp, N. A. Kocaoglu-Vurma, V. Langford, L. E. Rodriguez-Saona,
W. J. Harper, J. Food Sci. 2012, 77, C284–C292 .
[27] A. K. Sinha, U. K. Sharma, N. Sharma, Int. J. Food Sci. Nutr. 2008, 59,
299–326.
[28] A. S. Ranadive, J. Agric. Food Chem. 1992, 40, 1922–1924.
[29] T. Li, J. P. N. Rosazza, Appl. Environ. Microbiol. 2000, 66, 684–687.
[30] J. Overhage, H. Priefert, A. Steinbüchel, Appl. Environ. Microbiol. 1999,
65, 4837–4847.
[31] M. V. Nora De Souza, T. R. A. Vasconcelos, Appl. Organomet. Chem. 2006,
20, 798–810.
[32] B. A. Miller-Chou, J. L. Koenig, Progress in Polymer Science (Oxford) 2003,
28, 1223–1270.
[33] H. Bi, X. Xie, K. Yin, Y. Zhou, S. Wan, L. He, F. Xu, F. Banhart, L. Sun, R. S.
Ruoff, Adv. Funct. Mater. 2012, 22, 4421–4425.
Acknowledgements
[34] O. Leenaerts, B. Partoens, F. M. Peeters, Phys. Rev. B 2009, 79, 235440 .
[35] M. R. Johnson, B. Rickborn, J. Org. Chem. 1970, 35, 1041–1045.
[36] R. F. Ismagilov, A. Schwartz, N. Bowden, G. M. Whitesides, Angew. Chem.
Int. Ed. 2002, 41, 652–654; Angew. Chem. 2002, 114, 674–676.
[37] Y. Ikezoe, J. Fang, T. L. Wasik, T. Uemura, Y. Zheng, S. Kitagawa, H.
Matsui, Adv. Mater. 2015, 27, 288–291.
[38] P. Innocenzi, L. Malfatti, D. Carboni, Nanoscale 2015, 7, 12759–12772.
[39] F. Liu, J. Zhao, S. Wang, P. Du, B. Xing, Environ. Sci. Technol. 2014, 48,
13197–13206.
[40] X. Wang, J. Lu, B. Xing, Environ. Sci. Technol. 2008, 42, 3207–3212.
[41] L. L. Ji, W. Chen, Z. Y. Xu, S. R. Zheng, D. Q. Zhu, J. Environ. Qual. 2013,
42, 191–198.
[42] P. M. Budd, B. S. Ghanem, S. Makhseed, N. B. McKeown, K. J. Msayib,
C. E. Tattershall, Chem. Commun. 2004, 230–231.
[43] P. M. Budd, E. S. Elabas, B. S. Ghanem, S. Makhseed, N. B. McKeown, K. J.
Msayib, C. E. Tattershall, D. Wang, Adv. Mater. 2004, 16, 456–459.
[44] N. B. McKeown, P. M. Budd, Chem. Soc. Rev. 2006, 35, 675–683.
[45] H. Peng, H. Xiong, J. Li, M. Xie, Y. Liu, C. Bai, L. Chen, Food Chem. 2010,
121, 23–28.
[46] F. Kayaci, T. Uyar, J. Agric. Food Chem. 2011, 59, 11772–11778.
[47] E. Lauga, A. M. J. Davis, J. Fluid Mech. 2012, 705, 120–133.
[48] K. Ichimura, Science 2000, 288, 1624–1626.
[49] S. Nakata, Y. Iguchi, S. Ose, M. Kuboyama, T. Ishii, K. Yoshikawa, Lang-
muir 1997, 13, 4454–4458.
[50] H. Kitahata, S. Hiromatsu, Y. Doi, S. Nakata, R. M. Islam, Phys. Chem.
Chem. Phys. 2004, 6, 2409–241.
S.K.S. would like to thank Deutscher Akademischer Austausch-
dienst (DAAD)–Leibniz for funding. Also, S.K.S. expresses sin-
cere gratitude to Dr. Mariana Medina-Sµnchez and Tony Jau-
mann for helpful discussions. The authors thank Yan Chen for
help with SEM.
Keywords: food production · graphene · hybrid micromotors ·
polymers · vanillin
[1] P. Peercy, Nature 2000, 406, 1023–1026.
[2] T. E. Mallouk, A. Sen, Sci. Am. 2009, 300, 72–77.
[3] G. A. Ozin, I. Manners, S. Fournier-Bidoz, A. Arsenault, Adv. Mater. 2005,
17, 3011–3018.
[4] S. Sengupta, M. E. Ibele, A. Sen, Angew. Chem. Int. Ed. 2012, 51, 6378;
Angew. Chem. 2012, 124, 6484.
[5] Y. Wang, R. M. Hernandez, D. J. Bartlett, J. M. Bingham, T. R. Kline, A.
Sen, T. E. Mallouk, Langmuir 2006, 22, 10451–10456.
[6] Y. Shi, L. Huang, D. W. Brenner, J. Chem. Phys. 2009, 131, 014705 .
[7] D. Yamamoto, A. Mukai, N. Okita, K. Yoshikawa, A. Shioi, J. Chem. Phys.
2013, 139, 034705 .
[8] Y. Mei, A. A. Solovev, S. Sanchez, O. G. Schmidt, Chem. Soc. Rev. 2011,
40, 2109–2119.
[9] M. Manjare, B. Yang, Y. P. Zhao, Phys. Rev. Lett. 2012, 109, 128305 .
[10] F. Mou, C. Chen, Q. Zhong, Y. Yin, H. Ma, J. Guan, ACS Appl. Mater. Inter-
faces 2014, 6, 9897–9903.
[11] A. K. Singh, K. K. Dey, A. Chattopadhyay, T. D. Mandal, K. Bandyopadhyay,
Nanoscale 2014, 6, 1398–1405.
[12] S. K. Srivastava, M. Medina-Sµnchez, B. Koch, O. G. Schmidt, Adv. Mater.
2016, 28, 832–837.
[51] R. Sharma, S. T. Chang, O. D. Velev, Langmuir 2012, 28, 10128–10135.
[52] H. Jin, A. Marmur, O. Ikkala, R. H. A. Ras, Chem. Sci. 2012, 3, 25–26.
[53] Y. Hong, D. Velegol, N. Chaturvedi, A. Sen, Phys. Chem. Chem. Phys.
2010, 12, 1423–1435.
[54] Y. G. Tao, R. Kapral, J. Chem. Phys. 2009, 131, 024113 .
[13] A. A. Solovev, Y. Mei, E. B. UreÇa, G. Huang, O. G. Schmidt, Small 2009,
5, 1688–1692.
Received: February 26, 2016
Revised: April 3, 2016
[14] W. Gao, A. Pei, J. Wang, ACS Nano 2012, 6, 8432–8438.
[15] D. L. Hitt, C. M. Zakrzwski, M. A. Thomas, Smart Mater. Struct. 2001, 10,
1163–1175.
Published online on May 24, 2016
Chem. Eur. J. 2016, 22, 9072 – 9076
www.chemeurj.org
9076
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