Ultrafast Nanocrystals Decorated Micromotors for On-Site Dynamic

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Ultrafast Nanocrystals Decorated Micromotors for On-site Dynamic Chemical Processes Beatriz Jurado-Sanchez, Joseph Wang, and Alberto Escarpa ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b05824 • Publication Date (Web): 07 Jul 2016 Downloaded from http://pubs.acs.org on July 18, 2016

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ACS Applied Materials & Interfaces

Ultrafast Nanocrystals Decorated Micromotors for On-site Dynamic Chemical Processes B. Jurado-Sánchez,*† J. Wang,§ A. Escarpa,*† †

Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, University

of Alcala, Alcala de Henares E-28871, Madrid, Spain §

Department of Nanoengineering, University of California, San Diego, La Jolla, USA

KEYWORDS. Micro/nanomotors; self-propulsion; nanocrystals; quantum dots; cationexchange; photocatalytic degradation

ABSTRACT. CdS-polyaniline-Pt and ZnS-polyaniline-Pt micromotors have been synthetized and characterized. The nanocrystals are generated “in-situ” during the template electrosynthesis of the micromotors while simultaneously trapped in the polymeric network, generating a hybrid structure. The presence of nanocrystal “edges” in the inner polyaniline layer result in a rough Pt catalytic surface and enhanced electron transfer for highly efficient bubble propulsion at remarkable speeds of over 2500 µm/s. The incorporation of CdS and ZnS nanocrystals impart several attractive functions, including cation-exchange based chemical transformation capabilities and enhanced photocatalytic performance. The remarkable ion-exchange properties of ZnS-PANI-Pt micromotors are illustrated for the cation exchange of heavy metals cations. The superior photocatalytic performance of CdS-PANI-Pt micromotors is used for the enhanced photocatalytic oxidation of bisphenol A. Such self-propelled micromotors act as highly efficient

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dynamic platforms that offer significantly shorter and more efficient processes as compared with common static operations. The attractive properties of these micromotors will pave the way for diverse sensing, decontamination, energy generation or electronic applications


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INTRODUCTION Transition-metal chalcogenides, also known as semiconductor nanocrystals (NCs) or quantum dots, are subject of great research interest because of their excellent luminescent and photochemical properties.1,2 The small dimensions of such ‘nanosized’ particles (1-100 nm) results in a strong quantum mechanical behavior, with size-dependent color tunability. In connection with their narrow bandwidth, NCs have emerged as novel candidates for a wide range of applications, including solar cells,3 bioimaging,4,5 multiplexed chemical analyses,6 photocatalyst,7 etc. For example, CdS NCs can act as visible light catalyst to degrade hazardous compounds or to produce hydrogen.8,9 Of particular interest, CdS, ZnS or PbS calchogenides can undergo cationic exchange transformation with several species such as Ag, Pb or Hg.10-12 Scientifics take further advantage of such features to use NCs for novel synthesis processes.10,13,14 Recent trends in material synthesis are directed to integrate nanoparticles (such as NCs) into host structures, leading to multifunctional entities with new collective properties that are different from those displayed by individual nanoparticles and bulk samples.15-17 Controlled “in-situ” synthesis of NCs on the surface of different templates is a very advantage route to avoid the inherent NCs aggregation in aqueous solutions towards homogeneous coating while avoiding its corrosion in oxygen-containing rich media.18,19 Herein we will show a new synthetic route for the “in-situ” growth of CdS and ZnS NCs on the surface of tubular micromotors via template-assisted electrochemical deposition, leading to new multifunctional structures with unpreceded capabilities. Chemically powered micromotors offer an ideal template for the controlled assembly and growth of nanoparticles towards multifunctional materials with the ability to propel autonomously.20-24 Recent efforts in the field are directed to the fabrication of micromotors for


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i.e., drug delivery,25,26 sensing27-29, environmental remediation30,31 or value added products synthesis and purification.32 New fabrication schemes involve the controlled self-assembly of functional nanoparticles into several templates by bottom-up approaches.33,34 The template layerby-layer self-assembly (LBL) technique also allow for the self-consecutive assembly of nanoparticles into the pores of the membrane templates or the surface of the micromotors.35 Our group already described the preparation of highly efficient mobile microsensors through the incorporation of pre-formed CdTe QDs on the surface of tubular micromotors via LBL.36 Polymer stomatiocytes or red blood cells are also excellent candidates for the encapsulation of nanoparticles towards the design on novel micromotors for cancer cell sensing and therasnostics applications, respectively.37,38 Electrodeposition is also a favorable method for creating multifunctional motors due its low cost and scalability.39,40 For example, zirconia-graphene-Pt hybrid tubular micromotors, prepared by simultaneous electrochemical deposition of zirconia and reduced graphene oxide, are considerable attractive for nerve agents removal.41 In the following sections, we will describe for the first time the synthesis and applications of NCs-polyaniline (PANI)-Pt multifunctional micromotors. The new process involves the “in-situ” formation of CdS and ZnS NCs, which are simultaneously trapped within the polymeric network, ultimately generating a hybrid structure. Compared to our previously developed CdTemicromotors -which propels at diminished speed of 201 µm/s (5 % H2O2)- the new micromotors do not require additional LBL immobilization steps for further functionalization that can hinder its efficient propulsion for practical applications. Thus, the template prepared NCs-based micromotors moves at remarkably high speed of up to 2500 µm/s (5 % H2O2), due to a synergetic effect between the “built-in” Pt roughness imparted by the NCs deposited over the polymer and a larger active area for faster hydrogen peroxide decomposition. This speed is


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critical for highly efficient operation in real media, as will be also demonstrated. The resulting nanostructures exhibit cation-exchange based chemical transformation capabilities and enhanced photo and electrical activities. Such remarkable ion-exchange properties are illustrated here for heavy metals cations. The superior photocatalytic performance is further used for the enhanced photocatalytic oxidation of bisphenol A (BPA). On both applications, the greatly increased fluid transport and micromotor enhanced mixing leads to a greatly improved removal-degradation yield (~100 %) compared to the use of the sedimented counterpart structures (~20 %). The novelty of the present work lies in the incorporation of NCs with multiple functions on the outer polymeric layer itself, leading to new micromotors with multiple functionalities. Compared with previous reports, such protocol is highly versatile, allowing to tailor made the composition of the nanocrystal for a myriad of applications, ranging from sensing, decontamination, energy generation, electronics, etc. EXPERIMENTAL SECTION Reagents. Aniline, CdCl2, H2SO4, Na2S, Zn (CH3COO)2, hydrogen peroxide, sodium dodecyl sulfate, bisphenol A (water solubility, 381 mg/L at 25 ºC), methylene chloride, isopropanol, methanol and ethanol were purchased from Sigma-Aldrich (Madrid, Spain). Mercury, silver, cadmium, lead, uranium and gold standard for AAS (1000 mg/L ) either in water in nitric acid were obtained from Sigma-Aldrich. Platinum RTP plating solution was supplied by Technic Inc (Anaheim, CA). Screen-printed carbon electrodes (DS-110) were purchased from DropSens (Llanera, Spain). Milli-Q ultrapure water (18.2 MΩ cm) was used for all experiments. Equipment. Template electrochemical deposition of micromotors and electrochemical experiments were carried out using an Autolab PGSTAT 12 (Eco Chemie, The Netherlands).


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Scanning electron microscopy (SEM) images were obtained with a Phillips XL30 ESEM instrument, using an acceleration voltage of 20 kV. Energy-dispersive X-ray mapping analysis was performed using an Oxford EDX detector attached to SEM instrument and operated by INCA software. UV-VIS and fluorescence spectroscopy were performed using a Lambda 35 ES UV/VIS spectrophotometer (Perkin Elmer) and a LS 55 Fluorescense Spectrometer (Perkin Elmer), respectively. For UV−vis and fluorescence spectroscopy, quartz cuvettes of 1 cm path length were used. A Zeiss Axiovert inverted optical microscope coupled with a DAPI filter was used to capture fluorescence images of the micromotors. The autonomous motion of the micromotors was recorded using an inverted optical microscope (Nikon Eclipse Instrument Inc. Ti-S/L100), coupled 20X objective and Zyla sCMOS camera controlled by NIS Elements AR 3.2 software. The speed of the micromotors was tracked using a NIS Elements tracking module. Preparation of CdS and ZnS nanocrystals decorated tubular micromotors. For micromotors preparation, a polycarbonate membrane containing 2 µm diameter conical pores (Catalog No. 7060-2511; Whatman, Maidstone, UK) was employed as the template. A thin gold film (75 nm) was first sputtered on the branched side of the membrane to serve as a working electrode. A platinum wire and an Ag/AgCl electrode were used as counter and reference electrode, respectively. The membrane was assembled in a Teflon plating cell with aluminum foil serving as an electrical contact for the subsequent electrodeposition. Aniline monomer was freshly distilled before used at a vapor temperature of 100 ºC. PANI-CdS micromotors were electropolymerized in two steps: first, a PANI layer containing the Cd2+ was electrodeposited from a 10 mL platting solution containing 18 mg of CdCl2 and 0.05 M of aniline in 1 M of H2SO4 by applying a constant current of 60 µA for 300 s. This solution was then discarded and the cell was washed 3 times with ultrapure water. Secondly, the platting cell was filled with a 10


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mL platting solution containing 25 mg of Na2S and 0.05 M of aniline in 1 M of H2SO4. CdS NCs were generated “in-situ” and trapped in the PANI surface by applying a constant current of 120 µA for 300 s. Thirdly, the catalytic Pt layer was deposited galvanostatically at -2 mA for 500 s from the commercial platinum plating solution. PANI-ZnS micromotors were electropolymerized similarly in two steps: first a PANI layer containing the Zn2+ was electrodeposited from a 10 mL platting solution containing 21 mg of Zn (CH3COO)2 and 0.04 M of aniline in 1 M of H2SO4 by applying a constant current of 60 µA for 300 s. The second PANIS2- layer was deposited as previously described leading to the generation of ZnS nanocrystals; following by deposition of the catalytic Pt layer. Control PANI micromotors were electropolymerized from a 10 mL platting solution containing 0.1 M of aniline in 1 M of H2SO4 by applying a constant current of 120 µA for 600 s, following by deposition of the Pt catalytic layer. In each case, the sputtered gold layer was completely removed by hand polishing with 3-4 µm alumina slurry and the resulting micromotors were released from the template by dissolving the membrane in methylene chloride for 15 min (two times). Micromotors were then collected by centrifugation at 8000 rpm for 30 s and washed with isopropanol, ethanol and ultrapure water (3 times). These micromotors can be stored for four weeks without any decrease in its properties. UV-VIS and electrochemical characterization of CdS and ZnS nanocrystals decorated tubular micromotors. UV-VIS spectra of CdS and ZnS micromotors (10 x 105 micromotors/mL) was used to calculate the direct optical band gap by simply plotting (αhν)2 versus (hν), according to the Tauc relation: = ( − )


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where α is the absorption coefficient, hν is the photon energy (calculated as ℎ = 1240/ℎ), Eg is the direct band gap energy, and B is a constant. The absorption coefficient (α) was determined by using a relation deduced from Beer–Lambert’s relation, =

. ! "

, where d is the path length of the quartz cuvette and A is the absorbance determined

from the UV–VIS spectrum. The average band gap was estimated from the intercept of linear portion of the (αhν)2 vs. hν plots on hν axis. The particle size of CdS and ZnS nanocrystals (r) was calculated using the bandgap (Eg) with the following equation: 42

# ( ) =

$. %& − &. ' ( − %. )' & (%. * − )

Chronocoulometric charge (Q) time plots of ZnS-PANI-Pt, CdS-PANI-Pt and control PANIPt micromotors were obtained in 0.5 M H2SO4 under inert nitrogen atmosphere for 10 min. To this end, 10 µL of each micromotor solution (10 x 105 micromotors/mL) were dropped on the active area of a glassy-carbon electrode and let it dry for 1h. Then, 10 µL of a 5 % nafion solution were dropped in the same area and let dry for another hour. Prior use and in order to remove any potential interference, the glassy carbon electrode was polished with 0.02 µm alumina slurry and washed with concentrated HNO3 under gentle sonication. The corresponding electrochemical surface areas were estimated based on the slope of the plot of Q vs. t1/2 and using the following equation:

+ (,) =

&-./0 √23 √4

+ +6 + +7

Where A is the effective electrochemical surface area of the working electrode (cm2), c is the concentration of the electroactive species (mol/cm3), n is the number of transfer electrons, F is


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the Faraday constant, and D is the diffusion coefficient. Qd is the double layer charge, which could be eliminated by background subtraction, and Qi is the Faradaic charge. Heavy metal experiments. Cation-exchange of Hg and control experiments with different metals were performed by immersing a suspension of the ZnS-PANI-Pt micromotors (10 x 105 micromotors /mL) in 0.5 mL samples containing various levels of the different metals. The motors were propelled in the contaminated solution for 5 min in the presence of 0.5 % H2O2 fuel and 0.1 % sodium dodecyl sulfate. The addition of Hg resulted in the immediate appearance of bright yellow color, which was monitored by UV-VIS spectrophotometry. Fluorescent spectra of the micromotors before and after addition of each metal were recorded at an excitation wavelength of 315 nm. Photoelectrocatalytic degradation of bisphenol A. Experiments were performed under visible light irradiation (sunlight) by using 100 µL solutions containing different concentrations of BPA in 0.05 M NaCl, 1 % H2O2, 0.1 % sodium dodecyl sulfate and 10 x 105 micromotors /mL CdS-PANI-Pt, and PANI-Pt micromotors. In order to monitor the extend of removal; experiments were performed on screen-printed electrodes coupled to differential pulse voltammetry (DPV). DPVs of 10 cycles (reaching a constant peak height) between 0.30 V and 0.90 V were recorded, with pulse width of 0.05 s, step potential of 4 mV and amplitude of 25 mV. RESULTS AND DISCUSSION Figure 1 depicts the schematic of the templated-based preparation of CdS-PANI-Pt and ZnSPANI-Pt micromotors; which involves the “in-situ” growth of the nanocrystals along surface and through the micromotors. Cyclopore carbonate membranes (pore diameter, 2 µm) are used as


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templates for the synthesis of ~12 µm long conical micromotors. PANI-CdS and PANI-ZnS composite formation is triggered by Cd2+ or Zn2+ aggregation on the polymeric core followed by the corresponding nanocrystal generation. Polyaniline was chosen as supporting polymer due to its excellent stability and straightforward synthesis. Thus, aniline tend to polymerize fast and preferentially growth on the sides of the membrane for rapid entrapment of the generated NCs. As shown in Figure 1A, a first aniline layer is co-electrodeposited with the corresponding cation (Cd2+ or Zn2+). Due to solvophobic and electrostatic interactions, the monomer rapidly formed a PANI mesh on the inner wall of the membrane, with the cations entrapped into and along the backbone. The simultaneous addition of S2- anions during the electropolymerization of a second PANI layer leads to the rapid an uniform generation of the corresponding NCs along the polymeric backbone. A third catalytic Pt layer is then platted inside the PANI-CdS or PANI-ZnS micromotors for efficient bubble propulsion in H2O2 solutions. The epifluorescense microscopy images of Figure 1B reveals the uniform distribution of the NCs on the microtubular structure, which exhibit strong and uniform blue fluorescence emission (λex, 300 nm, λem, 438 nm). For comparison, no apparent fluorescence emission is observed for control PANI-Pt micromotors. In addition, the side view SEM image of Figure 1B, c reveals the rough surface of the CdS-PANIPt micromotor, with multiple NCs distributed along the micromotors, as compared with the flat surface of control PANI micromotors (Figure 1B, d). Figure 1C show cross-view SEM images of CdS-PANI-Pt (a), ZnS-PANI-Pt (b) and control PANI-Pt (c) micromotors. The micromotors have a defined structure with a thin outer polymeric layer of ~ 115 nm thickness and an inner, rough Pt layer of ~ 700 nm thickness (Fig. 1 C, d). It should be pointed out here that the NCs imparts some roughness and porosity to the inner polymeric layer for Pt deposition, resulting in a granular Pt structure. Note also the slight different on the Pt patch in both micromotors and the


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smooth Pt patch of PANI micromotors. As will be described below, such structure exert a strong influence for the enhanced movement of the micromotors. EDX mapping analysis of Figure 2A and Figure 2B further confirm the presence and uniform distribution of Zn, Cd and S within the conical micromotors. CdS and ZnS nanocrystals decorated tubular micromotors were further characterized by recording its absorption spectrum (10 x 105 micromotors/mL). Direct optical band gap was calculated by simply plotting (αhν)2 vs (hν), according to the Tauc relation described in the experimental section (not shown). The bandgap was calculated to be 3.8 eV and 2.9 eV for ZnS-PANI-Pt and CdS-PANI-Pt, respectively; yielding particles sizes of over 5.3 and 5 nm. The time lapse-microscopy images of Figure 3A-B (taken for SI Videos 1 and 2) illustrate the efficient propulsion of ZnS-PANI-Pt and CdS-PANI-Pt micromotors. A long tail of oxygen bubbles generated from the catalytic decomposition of H2O2 by the rough Pt inner layer is released from the rear large-opening side of the micromotors, which reached average speeds of 2500 ± 397 µm/s and 1900 ± 468 µm/s, in 5 % H2O2. As can be also seen, the speed depend on the concentration of peroxide fuel. The greatly increased speed of ZnS-PANI-Pt and CdS-PANIPt micromotors at 5 % peroxide levels reﬂects the higher pressure experienced by the bubbles. The radius and frequency of the generated oxygen bubbles are inﬂuenced by the level of peroxide fuel. The bubble frequency increases greatly upon raising the peroxide level from 1 to 5%, with subsequent decrease in the bubble size, as show in the time-lapse images. Smaller bubbles with higher frequencies led to such dramatical speed increase.39 Compared with previously LBL prepared CdTe-PEDOT-Pt micromotors,36 which propel at speeds of 201 µm/s in 5 % H2O2, the new micromotors exhibit nearly 9-fold acceleration, due to our preparation protocol do not require additional functionalization steps that can hinder the efficient propulsion


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of the micromotors. Such speed is also higher than that reported for similar size (2 µm), smooth PANI-Pt micromotors (1410 µm/s in 5 % H2O2) or PPy-Pt micromotors (1120 µm/s in 5 % H2O2). This nearly 1.5-fold acceleration of ZnS-PANI-Pt and CdS-PANI-Pt micromotors reflects its larger electrochemical active surface areas and enhanced catalytic properties along with improved fuel accessibility. The presence of NCs in the polymeric layer also enhances the catalytic properties of the resulting micromotors, enhancing the mass transport for fuel decomposition.43 The increased electrochemical active surface area of the micromotors, associated with its enhanced electrocatalytic activity is also reflected in the chronocoulometric charge-time plots of Figure 3C. The corresponding active electrochemical areas, estimated from Anson plots,44 were 0.02, 0.03, 0.06 and 0.09 cm2 for bare electrode, PANI-Pt, CdS-PANI-Pt and ZnS-PANI-Pt micromotors; indicating that the NCs-based micromotors has a nearly 3-fold increase in the active area when compared with control PANI micromotors. Such improved surface area is of great importance for future practical applications, as will be described below. To demonstrate the practical utility of the hybrid ZnS-PANI-Pt micromotors, associated with their cation-exchange capacity and enhanced mixing, we examined its ability for the dynamic exchange of toxic Hg ions in water. Figure 4 display the results obtained before and after treatment of Hg2+ contaminated solutions (0, 200, 300 and 500 ppm) with the ZnS-PANI-Pt micromotors (10 x 105 micromotors /mL). Such highly efficient exchange capacity is clearly demonstrated in the EDX mapping of two ZnS-PANI-Pt micromotors (Figure 4A, top part) and one HgS-PANI-Pt micromotor (Figure 4A, down part) after 5 min exposure to Hg. The images revealed the full completion of the exchange reaction, with all the Zn2+ (a) replaced by Hg2+ (b) after treatment. The UV-VIS absorption spectra of different micromotor dispersions after treatment with variable concentrations of Hg2+ of Figure 4B further demonstrated the successful


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transformation of the micromotors. Clear changes in the UV-VIS adsorption spectra are noted with increased Hg2+ concentrations (100- 500 ppm), with the appearance of an absorption edge at ~420 nm, which was attributed to the successful conversion into HgS-PANI-Pt micromotors. Such conversion also induce a color of the solution, which turned to light yellow, enabling the visible identification of Hg2+ pollution. No color development or distinct absorption spectrum was noted in additional control experiments performed with PANI-Pt and sedimented (precipitated) ZnS-PANI-Pt micromotors (under the absence of peroxide fuel). To estimate the mixing capacity and the power input of the micromotors, the cationic-exchange behavior was compared with that obtained with sedimented motors under forced convection conditions. Thus, mixing Hg contaminated solution (200-500 ppm Hg) containing the static/sedimented ZnSPANI-Pt microengines with a magnetic stirrer resulted in rapid color development and UV-VIS spectra comparable to that obtained with moving micromotors. The remarkable performance and accelerated heavy metal removal achieved by the motor-induced self-stirring of the remediation solution can be attributed to the large-scale collective motion of the micromotors, as hydrodynamic interactions lead to an enhanced mixing. The continuous bubble generation by the micromotors is also expected to contribute to the solution mixing and to have profound effects on the accelerated decontamination. These results revealed that the enhanced movement and fluid mixing induced by the micromotor, in combination with ZnS NCs, play a critical role in such micromotor unique behavior. We also perform a series of experiments to study the possible effect of time upon color appearance during Hg removal. Color appearance is almost instantaneous ( @ ? + B& C → B + CB (&) ∗ > @ ? + CB → CB (%) @ ? + B& C& → ∗CB + CB> ())

EF + ∗CB → G#HI7J HJ7K → =C& + B& C (*) As can be seen, the active oxygen species such as OH- and superoxide are the key active intermediates for the efficient BPA degradation. On a first step (1), photons with energy higher than CdS are absorbed onto its surface. Thus, the valence band electrons (hVB) are excited to the conduction band (eCB), leaving a positive charged hole in the valence band. Subsequently, valence (hVB) and conduction band (eCB) electrons can react with water (2), hydroxyl group (3) and to a lower extent with the hydrogen peroxide fuel to propel the rockets (4) to produce *OH and OH-. Finally, such species reacts with BPA to produce organic acid intermediates and complete degrade the compound (5). Figure 5A shows the DPV voltammograms obtained after of 10 min treatment of 25 µg/L of BPA with moving CdS-PANI-Pt micromotors (red line 1),


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sedimented (precipitated) CdS-PANI-Pt micromotors (blue line 2) and control PANI-Pt micromotors (black line 3). For comparison, the figure also include the DPV corresponding to 25 µg/L of BPA in bare SPE (orange line 4), which exhibit a distinct anodic peak at ~0.51 V corresponding to the electrochemical oxidation of BPA. Such peak remains almost constant in the experiments performed with moving PANI micromotors (without CdS) and only a negligible decrease is observed after 10 min treatment with sedimented CdS-PANI-Pt micromotors. However, a drastic decrease is observed after 10 min treatment with the moving CdS-PANI-Pt micromotors, due to the complete degradation of BPA. Thus, efficient micromotor movement and associated fluid mixing improve the kinetic of reaction for highly efficient BPA degradation while avoding at the same time corrosion or inactivation of the CdS catalyst. To estimate the mixing capacity and the power input of the micromotors, BPA removal efficiencies were compared to that obtained with sedimented motors under forced convection conditions. To this end, contaminated solutions spiked with 70 µg/L of BPA and CdS-PANI-Pt microengines (in the absence of H2O2) were mixed using a magnetic stirrer for 10 min. The removal efficiencies obtained with moving micromotors were higher (80 %) than the obtained under stirring conditions (70 %). As previously described with Hg removal experiments, the accelerated BPA removal achieved by the motor-induced self-stirring of the remediation solution can be attributed to the large-scale collective motion and enhanced mixing induced by the micromotors. The graphics in Figure 5B and 5C testified the high efficiency of our CdS-based micromotors for the degradation of different concentrations of BPA. Thus, percent degradation rates of ~80 and 100 %, were obtained after 10 min treatment of 25 and 70 µg/L of BPA, respectively, with CdSPANI-Pt micromotors. In contrast, negligible BPA degradation is obtained with control PANI-Pt micromotors, sedimented CdS-PANI-Pt micromotors (in the absence of H2O2) or with bare GCE,


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with further testified the crucial role of the micromotors movement -in connection with CdS NCs- for the successful degradation of BPA. CONCLUSION We have described the preparation and behavior of self-propelled tubular micromotors based on ZnS and CdS nanocrystals. The new synthetic route involves the “in-situ” growth of the NCs along the surface and through the PANI micromotors, leading to new multifunctional structures with “built-in” recognition and avoiding the need for further functionalization. Compared to our previously developed CdTe micromotors, the new micromotors propels at speed up to 9 times higher. Such improved propulsion performance can be also attributed to the presence of a microporous Pt surface (on the rough NCs-PANI surface) and larger electrochemical active areas that offers a greatly enhanced catalytic activity and efficient bubble evolution. The practical utility of the hybrid ZnS-PANI-Pt micromotors, associated with their cation-exchange capacity and enhanced mixing, has been demonstrated using toxic Hg ions in water. Efficient Hg exchange allow for the removal of high concentrations of such toxic ion (100-500 ppm), with the simultaneous appearance of a light yellow color in the solution, enabling also the visible identification of Hg2+ pollution. The applicability of CdS-PANI-Pt micromotors has been also demonstrated for the highly efficient photocatalytic degradation of the endocrine disruptor BPA. The continuous movement of multiple CdS micromotros across, along with the high-density tail of microbubbles, results in a greatly enhanced fluid dynamics, leading to the complete degradation of BPA after 10 min treatment under solar light irradiation. Active oxygen species such as OH- and superoxide are the key active intermediates for the efficient BPA degradation. The new combination of CdS nanocrystal with the autonomous micromotor movement avoid common problems associated with the use of common nanoparticles such as agglomeration, loss


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of efficiency or the requirement for UV light irradiation. Micromotor speed have strong implications upon the overall Hg removal and BPA degradation efficiency. We have demonstrated here that even at relative low peroxide levels (0.5-1 %) and propulsion speeds, remarkably high Hg removal and BPA degradation efficiencies (~100 %) can be achieved. However, the speed dependence on the concentration of peroxide fuel and fastest speed is extremely important for future in real-life environments. The high viscosity of such real media along with co-existing molecules that can passivate the catalytic Pt surface can prevent the efficient micromotor movement, lowering its efficiency.47 Hence, due the initial record-breaking speed and peroxide-speed dependence, our CdS-PANI-Pt and ZnS-PANI-Pt micromotors can tolerate such diminished speed in raw viscous real-life media while still display a highly efficient propulsion and pollutant removal efficiencies”. These micromotors can be easily recovered by incorporating a magnetic Ni layer (that allows also magnetic guidance).41, 48 While peroxidedriven motors are used for proof-of-concept here, practical environmental applications can be achieved by the replacement of the Pt catalyst by a Mg or Zn catalytic layer for water driven propulsion.


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FIGURES

Figure 1. (A) Schematic of the fabrication of the CdS-PANI-Pt and ZnS-PANI-Pt micromotors. (a) Deposition of a thin PANI layer containing Cd2+ or Zn2+ (b) electrochemical deposition of a second PANI S2- layer and “in-situ” generation of the corresponding nanocrystals and (c) deposition of a catalytic Pt catalytic layer (c). (B) Epifluorescence microscopy images of CdSPANI-Pt (a) and control PANI-Pt micromotors (b) and corresponding SEM images showing the surfaces of a NCs based micromotor (c) compared to the control micromotors (d). (C) SEM images of the top view of a CdS-PANI-Pt (a), ZnS-PANI-Pt (b) and control PANI-Pt (c)


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micromotors and high magnification SEM image showing the thickness of the CdS-PANI layer (d). Scale bars, 1 µm.

Figure 2. SEM and EDX images showing the distribution of Zn, Cd, and S in the ZnS-PANI-Pt (A) and CdS-PANI-Pt (B) micromotors. Scale bars, 1 µm.


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Figure 3. Enhanced catalytic activity of the nanocrystal-based micromotors. Time-lapse images (taken from SI Video 1 and 2) illustrating the ultrafast propulsion of (A) ZnS-PANI-Pt and (B) CdS-PANI-Pt micromotors in 1, 2, 3 and 5 % H2O2 (a-d) and 0.1 % sodium dodecyl sulfate surfactant. (C) Chronocoulometric charge-time plots of PANI-Pt (red line, 2), CdS-PANI-Pt (green line, 3) and ZnS-PANI-Pt (blue line, 4) in N2 saturated 0.5 M H2SO4. Black line shows the signal corresponding to bare gassy carbon electrode. Scale bars, 10 µm.


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Figure 4. Mercury ions removal and sensing by ZnS micromotors. (A) EDX analysis showing the distribution Zn, Hg and S in the micromotors before (top) and after being exposed 5 min to 500 ppm Hg (bottom) (B) UV-Vis spectra of PANI-Pt control micromotors (black dotted line), sedimented ZnS-PANI-Pt under the presence of 500 ppm of Hg (red line, 1), ZnS-PANI-Pt + 200 ppm Hg (blue line, 2), ZnS-PANI-Pt + 300 ppm Hg (pink line, 3) and ZnS-PANI-Pt + 500 ppm Hg (olive line, 4). Top inset show the increase of the yellow color of the solution at increasing Hg concentrations (0-500 ppm, from 1 to 5). (C) Fluorescence spectra of ZnS micromotors (black line, 4), ZnS + 500 ppm of Cu (II) (red line, 3), ZnS + 500 ppm of Ag (II) (pink line, 2) and ZnS+ 500 ppm of Hg (II) (blue line, 1). Left inset shows the appearance of the different ZnS solutions after addition of 500 ppm of Cu (1), Hg (2), Cd (3) Ag (4), Pb (5), U (6) and Au (7). Scale bars, 2 µm.


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Figure 5. Photoelectrocatalytic degradation of bisphenol A (BPA) by CdS-PANI-Pt micromotors. (A) DPVs obtained after 10 min treatment of 25 µg/L of BPA with CdS-PANI-Pt micromotors (red line 1), sedimented CdS-PANI-Pt micromotors (blue line 2), PANI-Pt micromotors (black line 3) and 25 µg/L of BPA in bare carbon electrodes (orange line 4). Dotted green line correspond to the blank signal. Conditions: 0.05 M NaCl, 1 % H2O2 (except in the experiment with sedimented micromotors) and 0.1 % SDS. (B, C) Degradation and percent removals of different BPA concentrations (25-70 µg/L) using CdS-PANI-Pt micromotors, control PANI-Pt micromotors and bare carbon screen-printed electrodes.


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ASSOCIATED CONTENT Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org. Ultrafast propulsion of ZnS-PANI-Pt micromotors in H2O2 solutions (AVI) Ultrafast propulsion of CdS-PANI-Pt micromotors in H2O2 solutions (AVI) AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] (Dr. Beatriz Jurado-Sánchez) *E-mail: [email protected] (Prof. Alberto Escarpa) Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT B. J-S acknowledges support from the People Programme (Marie Curie Actions) of the EU 7th Framework Programme (FP7 2007-2013) under REA Grant PIOF-GA-2012-326476. AE acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (CTQ2014-58643-R) and the NANOAVANSENS program (S2013/MIT-3029) from the Community of Madrid.


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REFERENCES (1) Yu, J.; Zhang, J.; Liu, S. Ion-Exchange Synthesis and Enhanced visible-Light Photoactivity Of Cus/Zns Nanocomposite Hollow spheres. J. Phys. Chem C 2010, 114, 13642−13649. (2) Heine, T. Transition Metal chalcogenides: Ultrathin Inorganic Materials with Tunable Electronic Properties. Acc. Chem. Res. 2015, 48, 65−72. (3) Kamat, P. V. Quantum Dots Solar cells. Semiconductor Nanocrystals As Light harvesters. J. Phys. Chem C 2008, 112, 18737−18753. (4) Medintz, I. L.; Uyeda, H. T.; Goldman, E. R.; Mattoussi, H. Quantum Dots Bioconjugates for Imaging, Labelling and sensing. Nat. Mater. 2005, 4, 435−436. (5) Wang, Y.; Hu, R.; Lin, G.; Roy, I.; Yong, K. T. Functionalized Quantum Dots for Biosensing and Bioimaging and Concerns on toxicity. ACS App. Mater. Interfaces 2013, 5, 2786−2799. (6) Xiong, L. H.; Cui, R.; Zhang, Z. L.; Yu, X.; Xie, Z.; Shi, Y. B.; Pang, D. W. Uniform Fluorescent Nanobioprobes for Pathogen Detection. ACS Nano 2014, 15, 5116−5124. (7) Xiao, F. X.; Miao, J.; Liu, B. Layer-By-Layer Self-Assembly of Cds Quantum Dots/Graphene Nanosheet Hybrid Films for Photoelectrochemical and Photocatalytic Applications. J. Am. Chem. Soc. 2014, 136, 1559−1569. (8) Pan, B.; Xie, Y.; Zhang, S.; Lu, Lv.; Zhang, W. Visible Light Photocatalytic Degradation of Rhb by Polymer-Cds Nanocomposites: Role of The Host Functional Group. ACS Appl. Mater. Interfaces 2012, 4, 3938−3943. (9) Shi, Y.; Li, H.; Wang, L.; Shen, W.; Chen, H. Novel α-Fe2O3/Cds Cornlike Nanorods with Enhanced Photocatalytic Performance. ACS Appl. Mater. Interfaces 2012, 4, 4800−4806.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 31

(10) Robinson, R. D.; Sadtler, B.; Demchenko, D. O.; Erdomez, C. K.; Wang, L. W.; Alivisatos, A. P. Spontaneous Supperlattice Formation in Nanorods Through Partial Cation Exchange. Science 2014, 317, 355−358. (11) Justo, Y.; Sagar, L. K.; Flamee, S.; Zhao, Q.; Vantomme, A.; Hens, Z. Less Is More: Cation Exchange and The Chemistry Of The Nanocrystal Surface. ACS Nano 2014, 8, 7948−7957. (12) Jaiswal, A.; Ghosh, S. S.; Chattopadhyay, A. Quantum Dot Impregnated-Chitosan Film For Heavy Metal Ion Sensing and Removal. Langmuir 2012, 28, 15687−15696. (13) Qu, Z.; Yan, L.; Li, L.; Xu, J.; Liu, M.; Li, Z.; Yan. N. Ultraeffective Zns Nanocrystal Sorbent For Mercury (II) Removal Based On Size-Dependant Cation Exchange. ACS Appl. Mater. Interfaces 2014, 6, 18026−18032. (14) Son, D. H.; Hughes, S. M.; Yin, Y.; Alivisatos, A. P. Cation Exchange Reactions in Ionic Nanocrystals. Science 2004, 306, 1009−1012. (15) Nie, Z.; Petukhova, A.; Kumacheva, A. Properties and Emerging Applications of SelfAssembled Structures Made from Inorganic Nanoparticles. Nature Nanotech. 2010, 5, 15−25. (16) Lu, Z.; Gao, C.; Zhang, Q.; Chi, M.; Howe, J. Y.; Yin, Y. Direct Assembly of Hydrophibic Nanoparticles To Multifunctional Structures . Nano Lett. 2011, 11, 3404−3412. (17) Shan, F.; Lu, X.; Zhang, Q.; Su, B.; Lu, Q. Anisotropy Property of Cds and Pbs Quantum Dots Encapsulated in Silica Film with Uniformly Oriented Mesochannel. Langmuir 2012, 28, 812−817. (18) Antony, J. V.; Kurian, P.; Vadakkedathu, N. P. N.; Kochimoolayil, G. E. In Situ Synthesis of Cds Quantum Dot-Partially Sulfonated Polystyrene Composite: Characterization and Optical Properties. Ing. Eng. Chem. Res. 2014, 53, 2261−2269.


26

Page 27 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(19) Banerjee, S.; Wong, S. S. In Situ Quantum Dot Growth on Multiwalled Carbon Nanotubes. J. Am. Chem. Soc. 2003, 125, 10342−10350. (20) Paxton, W. F.; Kistler, K. C.; Olmeda, C. C.; Sen, A.; St. Angelo, S. K.; Cao, Y.; Mallouk, T. E.; Lammert, P. E.; Crespi, V. H. Catalytic Nanomotors: Autonomous Movement of Striped Nanorods. J. Am. Chem. Soc. 2004, 126, 13424−13431. (21) Ozin, G. A.; Manners, I.; Fournier-Bidoz, S.; Arsenault, A. Dream Nanomachines. Adv. Mater. 2005, 17, 3011−3018. (22) Wang, J. Nanomachines: Fundamentals and Applications, Wiley-VCH, Weinheim, Germany, 2013, ISBN 978-3-527-33120-8. (23) Mei, Y.; Solovev, A. A.; Sanchez, S.; Schmidt, O. G. Rolled-Up Nanotech on Polymers: From Basic Perception to Self-Propelled Catalytic Microengines. Chem. Soc. Rev. 2011, 40, 2109−2119. (24) Sanchez, S.; Soler, L.; Katuri, J. Chemically Powered Micro- and Nanomotors. Angew. Chem. Int. Ed. 2015, 54, 1414−1444. (25) Srivastava, S. K.; Medina-Sánchez, M.; Koch, B.; Schmidt, O. G. Medibots: Dual-Action Biogenic Microdaggers for Single-Cell Surgery and Drug Release. Adv. Mater. 2015, 28, 832−837. (26) Peng, F.; Tu, Y.; van Hest, J. C. M.; Wilson, D. A. Self-Guided Supramolecular Anticancer Drug Loaded Polymeric Nanomotors With Chemotactic Behavior. Angew. Chem. Int. Ed. 2015, 54, 11662−11665. (27) Wang, J. Self-Propelled Affinity Biosensors: Moving the Receptor Around the Sample. Biosens. Bioelectron. 2016, 15, 234−242.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 31

(28) Jurado-Sánchez, B.; Escarpa, A. Milli, Micro and Nanomotors: Novel Analytical Tools for Real-World Applications. Trends Anal. Chem. 2016, doi:10.1016/j.trac.2016.03.009. (29) Yi, Y.; Sanchez, L.; Gao, Y.; Yu, Y. Janus Particles for Biological Imaging and Sensing. Analyst, 2016, 141, 3526–3539. (30) Teo, W. Z.; Zboril, R.; Medrik, I.; Pumera, M. Fe0 Nanomotors in Ton Quantities (1020 Units) for Environmental Remediation. Chem. Eur. J. 2016, 22, 4789–4793. (31) Singh, V. V.; Wang, J. Nano/Micromotors for Security/Defense Applications. A review. Nanoscale, 2015, 7, 19377–19389. (32) Srivastava, S. K..; Schimdt, O. Autonomously Propelled Motors for Value-Added Products Synthesis and Purification. Chem. Eur. J., 2016, 22, 9072–9076. (33) Lin, X.; Wu, Z.; Wu, Y.; Xuan, M.; He, Q. Self-Propelled Micro-/Manomotors Based on Controlled Assembled Architectures. Adv. Mater. 2016, 28, 1060–1072. (34) Dong, B.; Zhou, T.; Zhang, H.; Li, C. Y. Direct Self-Assembly of Nanoparticles for Nanomotors. ACS Nano, 2013, 7, 5192–5198. (35) Wu, Z.; Lin, X.; Si, T.; He, Q. Recent Progress on Bioinspired Self-Propelled Micro/Nanomotors via Controlled Molecular Self-Assembly. Small, 2016, 12, 3080–3093. (36) Jurado-Sánchez, B.; Escarpa, A.; Wang, J. Lighting-Up Micromotors with Quantum Dots for Smart Chemical Sensing. Chem. Commun., 2015, 51, 14088–14091. (37) Wilson, D. A.; Nolte, R. J. M.; van Hest, J. C. Autonomous Movement of PlatinumLoaded Stomatocytes. Nat. Chem., 2012, 4, 268–274. (38) Wu, Z.; Esteban-Fernández de Ávila, B.; Martín, A. ; Christianson, C.; Gao, W.; Thamphiwatana, S. K.; Escarpa, A.; He, Q.; Zhang, L.; Wang, J. RBC Micromotors Carrying Multiple Cargos Towards Potential Theranostic Applications. Nanoscale, 2015, 7, 13680–13686.


28

Page 29 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(39) Gao, W.; Sattayasamitsathit, S.; Orozco, J.; Wang, J. Highly Efficient Catalytic Microengines: Template Electrosynthesis of Polyaniline/Platinum Microtubes. J. Am. Chem. Soc. 2011, 133, 11862–11864. (40) Wang, H.; Pumera, M. Fabrication of Micro/Nanoscale Motors. Chem. Rev. 2015, 115, 8704–8735. (41) Singh, V. V.; Martin, A., Kaufmann, K.; de Oliveira, S. D. S.; Wang, J. Zirconia/Graphene Oxide Hybrid Micromotors for Selective Capture of Nerve Agents. Chem. Mater. 2015, 27, 8162–8169. (42) Isarov, A. V.; Chrysochoos, J. Optical And Photochemical Properties of Nonstoichiometric Cadmium Sulfide Nanoparticles: Surface Modification with Copper (II) Ions. Langmuir 1997, 13, 3142–3149. (43) Zhai, C.; Zhu, M.; Pang, F.; Bin, D.; Lu, C.; Goh, M. C.; Yang, P.; Du, Y. High Efficiency Photoelectrocatalytic Methanol Oxidation on Cds Quantum Dots Sensitized Pt Electrode. ACS Appl. Mater. Interfaces 2016, 8, 5972−5980. (44) Martín, A.; Hernández-Ferrer, J.; Vázquez, L.; Martínez, M. T.; Escarpa, A. Controlled Chemistry of Tailored Graphene Nanoribbons for Electrochemistry: A Rational Approach yo Optimizing Molecule Detection. RSC Adv. 2014, 4, 132–139. (45) Luo, J. Y.; Chen, L. L.; Liang, X. H.; Zhao, Q. W.; Li, H. Anodic Deposition-Assisted Photoelectrocatalytic Degradation Of Bisphenol A At A Cadmium Sulfide Modified Electrode Based on Visible Light-Driven Fuel Cells. Electrochim. Acta 2015, 186, 420–426. (46) Samadi-Maybodi, A.; Sadeghi-Maleki, M. R. In-Situ Synthesis of High Stable CdS Quantum Dots and Their Application for Photocatalytic Degradation of Dyes. Spectrochim Acta A Mol. Biomol. Spectrosc. 2016, 152, 156–164.


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(47) Gao, W.; Sattayasamitsathit, S.; Orozco, J.; Wang, J. Efficient Bubble Propulsion of Polymer-Based Microengines in Real-Life Environments. Nanoscale 2013, 5, 8909–8914. (48) Vilela, D.; Parmar, J.; Zeng, Y.; Zhao, Y.; Sánchez, S. Graphene-Based Microbots for Toxic Heavy Metal Removal and Recovery from Water. Nano Lett. 2016, 16, 2860–2866.


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TOC 58x36mm (150 x 150 DPI)


Ultrafast Nanocrystals Decorated Micromotors for On-Site Dynamic

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