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Visible light driven recyclable micromotors for “on-the-fly” water remediation
Journal Pre-proofs Visible Light Driven Recyclable Micromotors for “On-the-fly” Water Remediation Ziheng Zhan, Fanan Wei, Jianghong Zheng, Chao Yin, Wenguang Yang, Ligang Yao, Songsong Tang, Dong Liu PII: DOI: Reference:
S0167-577X(19)31456-9 https://doi.org/10.1016/j.matlet.2019.126825 MLBLUE 126825
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
23 September 2019 12 October 2019 15 October 2019
Please cite this article as: Z. Zhan, F. Wei, J. Zheng, C. Yin, W. Yang, L. Yao, S. Tang, D. Liu, Visible Light Driven Recyclable Micromotors for “On-the-fly” Water Remediation, Materials Letters (2019), doi: https://doi.org/ 10.1016/j.matlet.2019.126825
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
Visible Light Driven Recyclable Micromotors for “On-the-fly” Water Remediation Ziheng Zhana, Fanan Wei*a, b, Jianghong Zhenga, Chao Yina, Wenguang Yangc, Ligang Yao*a, Songsong Tangd, Dong Liua
a. School of Mechanical Engineering and Automation, Fuzhou University, Fuzhou, Fujian, 350108, China.
b. State Key Laboratory of Robotics, Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang, Liaoning, 110016,
China.
c. School of Electromechanical and Automotive Engineering, Yantai University, Yantai, Shandong, 264005, China.
d. Research Center for Bioengineering and Sensing, Technology University of Science and Technology Beijing, Beijing, 100083,
China.
Abstract Organic pollutant, originating from both industry and domestic waste, has been greatly threatening the waters all over the world. Micromotors, integrated with photocatalysis, provide a promising solution to this critical challenge. In this work, by taking advantage of the positive motion of the micromotors and visible light response of photocatalysis, we fabricated BiOI microspheres based micromotors and applied them into organic pollutant removal in water. The motion characterization and dye degradation tests demonstrate that "On-the-fly” water remediation is realized under visible light irradiation. What’s more, with the iron oxide nanoparticles embedded, the micromotors are recycled using magnet and reused in organic pollutant degradation. Keyword: micromotor, water remediation, visible light, BiOI 1. Introduction Environment problems, especially the organic wastewater pollution [1], have turned to be a 1
worldwide challenge. Due to the efficient catalytic performance, rich supplies of light energy as well as the environment-friendly merit, some photocatalytic materials have gained tremendous attention recently [2, 3]. So far, the application of photocatalysts in water remediation still suffers from low catalytic efficiency [4] and the limitation of passive work mode. Micromotors have come into our sights due to their rapid development and the potential functions in various applications [5, 6]. While combining with photocatalysts, they are promising to enhance the photocatalytic performance by increasing the probability of contact between the organic pollutant and the catalysts through the so-called “on-the-fly” working mode [7, 8]. With the outstanding merits including abundant storage, remote propagation and clean energy input, light has been acknowledged to be a promising energy source to propel micromotors [9].. Considering the great potential of light driven micromotors in environment remediation, much efforts have been devoted to the combination of photocatalysts with micromotors [10, 11]. Then, a various light driven micromotors, such as Au-WO3@C Janus micromotor [12], Si-Au based micromotor [13], have been successfully synthesized and used in organic pollutants remediation. Such micromotors can lead to a propulsion under light irradiation and combine with dye molecule in the water. But several challenges are still faced before the large mass application of photocatalytic micromotors such as the unsuitable wavelength of light irradiation, the low degradation efficiency and the recollection of micromotors [14]. In this paper, in order to overcome the challenges mentioned above, we fabricated BiOI/AgI/Fe3O4/Au micromotors through a simple hydrothermal method, and apply them into the degradation of Rhodamine B (RhB). By introducing AgI into the micromotor, we attempt to enhance the photocatalytic performance, and subsequently increase the motion speed and raise the organic pollutant degradation performance. Finally, with the integration of Fe3O4, the recyclability and reusability of the
2
BiOI/AgI/Fe3O4/Au micromotor were tested and evaluated. 2. Materials and methods As illustrated in Fig. 1a, BiOI based micromotors used in this work were synthesized through a hydrothermal approach. Details of the synthesis recipe are presented in Supplementary Information. a Autoclave BiOI/Fe3 O4
200 °C, 12 h Fe3 O4
FeCl3 + EG + DEG + PVP + NaAc
Autoclave, 160 °C, 24 h
Bi(NO3 )3 + DEG + KI AgNO 3 solution
Au deposition
BiOI/AgI/Fe3 O4 /Au micromotor
b
c
BiOI/AgI/Fe3 O4
d
f
e
g b a a
b
Fig. 1 Synthesis schematic and SEM images of micromotors. (a) Schematic of Fe3O4 nanoparticles and BiOI/AgI/Fe3O4/Au
micromotors synthesis. (b-f) show the SEM images of the synthesized BiOI, BiOI/AgI, BiOI/Fe3O4, BiOI/Fe3O4/AgI
and BiOI/Fe3O4/AgI/Au microstructures, respectively. (g) The distribution of Au element along the line ab in Fig. 1f.
Scale bars in (b-f) are 2 μm.
3. Results and discussions 3.1 Characterizations and analysis of synthesized microstructures Scanning electron microscope (SEM) characterization results indicate that pure BiOI microspheres have flower-like structures with the average diameter of 3-4 μm (Fig. 1b). Sheet-like AgI microplates are 3
well decorated on the surface of BiOI microspheres (Fig. 1c-e). And after modification with Fe3O4, the surface of BiOI sphere is covered by Fe3O4 nanoparticles, whose size is around 200 nm. After half coating the BiOI/AgI/Fe3O4 particle with gold layer, the Janus structure of the BiOI/AgI/Fe3O4/Au micromotor is formed and verified in Fig. 1f-g. 3.2 Micromotors motion under visible light Significant motion of the micromotors under light irradiation is essential for “on-the-fly” pollutant removal. Based on the previous research [15], we presented the visible light powered BiOI/AgI/Fe3O4/Au micromotor and conducted the motion test for the synthesized micromotors. As displayed in Fig. 2a, the micromotor kept almost still in the dark. Once the light was on, the motion started immediately. In Fig 3b, under the visible light irradiation, the photogenerated electrons will travel from the BiOI/AgI/Fe3O4 conduction band (CB) to the gold layer. Meanwhile, the holes will be transported to the surface of BiOI/AgI/Fe3O4 and react to generate H+ and ·OH. The depletion and generation of H+ at the two sides cause the ion gradient around the micromotor, creating a self-generated electrical field and thus propelling the BiOI/AgI/Fe3O4/Au micromotor to move towards the BiOI side. Velocity of micromotors increased as the light intensity ramped up gradually (Fig. 2c). Besides, without the gold layer coating, the non-Janus BiOI/AgI/Fe3O4 microspheres just moved randomly. Compared with pure BiOI/Au micromotor, the addition of AgI can improve the photon absorption of the micromotor and subsequently increase the velocity. Besides, light intensity can also tune the motion mode. As the light intensity increased further, the motion of the micromotor changed from Brownian motion into directional
4
a
b
Vis light
h+ h+
H2 O H+ OH
Propulsion OH
O2
c
H+
e- e-
d
motion (Fig. 2d). Figure 2. Visible light actuated micromotor motion. (a) Micromotor motion trajectories without (upper) and with (lower) light. The
scale bar is 20 μm. (b) The schematic diagram of the motion of micromotor based on the self-eletrophoresis mechanism. (c) Motion
velocities of micromotors under different light intensities. (d) The motion trajectories of the micromotor with varied light intensities.
3.3 Photodegradation of organic pollutant with the micromotors The photocatalytic activity micromotors were tested through the degradation of RhB, as shown in Fig. 3. The capability of degradation was calculated according to Eqa. 1. 𝐶
k𝑡 = ―ln𝐶0
(1)
where k represents the apparent pseudo-first-order rate constant (min-1), C is the concentration of RhB at time t, and C0 is the original concentration of RhB. Under dark, all the micromotors showed weak photocatalytic performance. After the light was introduced, photocatalytic activities of the micromotors were significantly enhanced. It was found that pure BiOI could hardly purify the RhB and the BiOI/AgI/Au micromotors have the highest RhB degradation performance. The BiOI/AgI/Fe3O4/Au micromotors presented degradation performance a little lower than that of the BiOI/AgI/Au micromotors. Owing to the extremely narrow band gap (~0.1 eV), Fe3O4 nanoparticles, embedded into the micromotors, will serve as the recombination center for
5
photogenerated electrons and holes, causing a quick recombination of active electrons and holes, thus hinder the generation rate of · OH around the micromotors, and therefore weaken the degradation performance and decrease the velocity of micromotor. Despite this, we cannot ignore the excellent magnetic performance of Fe3O4 nanoparticles, which will be discussed later in details. As indicated from Fig. 3b, the rate constant (k) of BiOI/AgI/Au and BiOI/AgI/Fe3O4/Au micromotors were much higher than the others. The highest degradation speed (0.0271 min-1) was achieved by BiOI/AgI/Au micromotors.
Figure 3. Photodegradation of RhB solution with different micromotors and the mechanism of photocatalytic process in
BiOI/AgI/Fe3O4/Au micromotor. (a) The degradation performance of different kinds of micromotors. (b) The degradation
efficiencies calculated from (a). (c) Mechanism of photocatalytic process in BiOI/AgI/Fe3O4/Au micromotor. (d) The recycling
process of micromotors through a magnet. (e) The photodegradation performance evaluated through four cycles. (f) The RhB
degradation rate of each cycle in (e).
The possible mechanism of photocatalytic process was presented in Fig. 3c. Under visible light 6
irradiation, the electron holes (h+) can be generated on the VB side of both BiOI and AgI. Since the positions of VB and CB of AgI are higher than BiOI, the photogenerated electrons (e-) can be easily transferred from the CB of AgI to the CB of BiOI; and assist to enhance the photodegradation activity. Moreover, the recycling and reusing of the micromotor were also discussed. After the remediation of RhB, micromotors were easily collected using a magnet (Fig. 3d). After rinse and dry, the recollected micromotors were applied in the same photo-degradation experiments again. As presented in Fig. 3e and Fig. 3f, the degradation rate of RhB decreased from 53.2% to 44.3% after three times recycles. Despite the loss of micromotors in each recycle, it can be obviously found that the micromotors can still keep a relatively high photodegradation efficiency, demonstrating their stability. 4. Conclusions In this work, we applied visible light driven micromotors based on BiOI into organic water pollution degradation. Through the cost-effective hydrothermal method, BiOI/AgI/Fe3O4/Au micromotors are synthesized. Significant motion of the micromotor was observed with visible light irradiation. Moreover, the micromotor exhibited better RhB degradation performance than the pure BiOI photocatalyst. Besides, the micromotors can be recollected and reused through a magnet and still showed relatively high photocatalytic activity after three times recycle. Acknowledgments Thanks to the financial support from the National Natural Science Foundation of China (No.61803088), the Natural Science Foundation of Fujian Province, China (No. 2017J01748), the Open Project Programs from the State Key Laboratory of Robotics, Shenyang Institute of Automation, Chinese Academy of Sciences (Grant No: 2017-O02) , the State Key Laboratory of Photocatalysis on Energy and Environment (Grant No. SKLPEE-KF201718) and Fuzhou University Testing Fund of precious apparatus
7
(No. 2018T016 and No. 2019T015). We would also like to thank Prof. Mingdeng Wei and Mr. Minghuang Guo for assistance at Au deposition. Conflict of Interest None. References [1] C.H. Neoh, Z.Z. Noor, N.S.A. Mutamim, C.K. Lim, Green technology in wastewater treatment technologies: Integration of membrane bioreactor with various wastewater treatment systems, Chem. Eng. J. 283 (2016) 582-594. [2] L.J. Bao, Maruya, K. A., Snyder, S. A., & Zeng, E. Y, China's water pollution by persistent organic pollutants, Environ. Pollut. 163 (2012) 100-108. [3] A.Y. Hoekstra, M.M. Mekonnen, The water footprint of humanity, Proc Natl Acad Sci U S A 109(9) (2012) 3232-3237. [4] L. Ye, Y. Su, X. Jin, H. Xie, C. Zhang, Recent advances in BiOX (X = Cl, Br and I) photocatalysts: synthesis, modification, facet effects and mechanisms, Environmental Science: Nano 1(2) (2014) 90-112. [5] T. Li, X. Chang, Z. Wu, J. Li, G. Shao, X. Deng, J. Qiu, B. Guo, G. Zhang, Q. He, L. Li, J. Wang, Autonomous Collision-Free Navigation of Microvehicles in Complex and Dynamically Changing Environments, ACS Nano 11(9) (2017) 9268-9275. [6] T. Li, A. Zhang, G. Shao, M. Wei, B. Guo, G. Zhang, L. Li, W. Wang, Janus Microdimer Surface Walkers Propelled by Oscillating Magnetic Fields, Adv. Funct. Mater. 28(25) (2018). [7] Z. Zhan, F. Wei, J. Zheng, W. Yang, J. Luo, L. Yao, Recent advances of light-driven micro/nanomotors: toward powerful thrust and precise control, Nanotechnol Rev 7(6) (2018) 555-581. [8] S. Shklyaev, Janus droplet as a catalytic micromotor, EPL 110(5) (2015) 54002. [9] L. Xu, F. Mou, H. Gong, M. Luo, J. Guan, Light-driven micro/nanomotors: from fundamentals to applications, Chem. Soc. Rev. 46(22) (2017) 6905-6926. [10] M. Safdar, J. Simmchen, J. Jänis, Light-driven micro- and nanomotors for environmental remediation, Environmental Science: Nano 4(8) (2017) 1602-1616. [11] X. Chang, W. Tang, Y. Feng, H. Yu, Z. Wu, T. Xu, H. Dong, T. Li, Coexisting Cooperative Cognitive Micro-/Nanorobots, Chem Asian J 14(14) (2019) 2357-2368. [12] Q. Zhang, R. Dong, Y. Wu, W. Gao, Z. He, B. Ren, Light-Driven Au-WO3@C Janus Micromotors for Rapid Photodegradation of Dye Pollutants, ACS Appl Mater Interfaces 9(5) (2017) 4674-4683. [13] D. Zhou, Li, Y. C., Xu, P., Ren, L., Zhang, G., Mallouk, T. E., & Li, L, Visible-light driven Si–Au micromotors in water and organic solvents, Nanoscale 9(32) (2017) 11434-11438. [14] H. Yu, W. Tang, G. Mu, H. Wang, X. Chang, H. Dong, L. Qi, G. Zhang, T. Li, Micro-/Nanorobots Propelled by Oscillating Magnetic Fields, Micromachines (Basel) 9(11) (2018). [15] R. Dong, Y. Hu, Y. Wu, W. Gao, B. Ren, Q. Wang, Y. Cai, Visible-Light-Driven BiOI-Based Janus Micromotor in Pure Water, J. Am. Chem. Soc. 139(5) (2017) 1722-1725.
Highlights
Successful synthesis of BiOI based Janus micromotors through hydrothermal approach.
8
“On-the-fly” pollutant remediation achieved with light-driven micromotors.
Micromotors can be easily recollected and retain a high photocatalytic activity.
9
Under the visible light irradiation, the self-propelled BiOI/AgI/Fe3O4/Au micromotors show significant motion in the polluted water, and facilitate the “on-the-fly” organic pollutant removal. The micromotors can be easily recycled using a magnet and reused into Rhodamine B degradation.
10
S0167-577X(19)31456-9 https://doi.org/10.1016/j.matlet.2019.126825 MLBLUE 126825
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
23 September 2019 12 October 2019 15 October 2019
Please cite this article as: Z. Zhan, F. Wei, J. Zheng, C. Yin, W. Yang, L. Yao, S. Tang, D. Liu, Visible Light Driven Recyclable Micromotors for “On-the-fly” Water Remediation, Materials Letters (2019), doi: https://doi.org/ 10.1016/j.matlet.2019.126825
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
Visible Light Driven Recyclable Micromotors for “On-the-fly” Water Remediation Ziheng Zhana, Fanan Wei*a, b, Jianghong Zhenga, Chao Yina, Wenguang Yangc, Ligang Yao*a, Songsong Tangd, Dong Liua
a. School of Mechanical Engineering and Automation, Fuzhou University, Fuzhou, Fujian, 350108, China.
b. State Key Laboratory of Robotics, Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang, Liaoning, 110016,
China.
c. School of Electromechanical and Automotive Engineering, Yantai University, Yantai, Shandong, 264005, China.
d. Research Center for Bioengineering and Sensing, Technology University of Science and Technology Beijing, Beijing, 100083,
China.
Abstract Organic pollutant, originating from both industry and domestic waste, has been greatly threatening the waters all over the world. Micromotors, integrated with photocatalysis, provide a promising solution to this critical challenge. In this work, by taking advantage of the positive motion of the micromotors and visible light response of photocatalysis, we fabricated BiOI microspheres based micromotors and applied them into organic pollutant removal in water. The motion characterization and dye degradation tests demonstrate that "On-the-fly” water remediation is realized under visible light irradiation. What’s more, with the iron oxide nanoparticles embedded, the micromotors are recycled using magnet and reused in organic pollutant degradation. Keyword: micromotor, water remediation, visible light, BiOI 1. Introduction Environment problems, especially the organic wastewater pollution [1], have turned to be a 1
worldwide challenge. Due to the efficient catalytic performance, rich supplies of light energy as well as the environment-friendly merit, some photocatalytic materials have gained tremendous attention recently [2, 3]. So far, the application of photocatalysts in water remediation still suffers from low catalytic efficiency [4] and the limitation of passive work mode. Micromotors have come into our sights due to their rapid development and the potential functions in various applications [5, 6]. While combining with photocatalysts, they are promising to enhance the photocatalytic performance by increasing the probability of contact between the organic pollutant and the catalysts through the so-called “on-the-fly” working mode [7, 8]. With the outstanding merits including abundant storage, remote propagation and clean energy input, light has been acknowledged to be a promising energy source to propel micromotors [9].. Considering the great potential of light driven micromotors in environment remediation, much efforts have been devoted to the combination of photocatalysts with micromotors [10, 11]. Then, a various light driven micromotors, such as Au-WO3@C Janus micromotor [12], Si-Au based micromotor [13], have been successfully synthesized and used in organic pollutants remediation. Such micromotors can lead to a propulsion under light irradiation and combine with dye molecule in the water. But several challenges are still faced before the large mass application of photocatalytic micromotors such as the unsuitable wavelength of light irradiation, the low degradation efficiency and the recollection of micromotors [14]. In this paper, in order to overcome the challenges mentioned above, we fabricated BiOI/AgI/Fe3O4/Au micromotors through a simple hydrothermal method, and apply them into the degradation of Rhodamine B (RhB). By introducing AgI into the micromotor, we attempt to enhance the photocatalytic performance, and subsequently increase the motion speed and raise the organic pollutant degradation performance. Finally, with the integration of Fe3O4, the recyclability and reusability of the
2
BiOI/AgI/Fe3O4/Au micromotor were tested and evaluated. 2. Materials and methods As illustrated in Fig. 1a, BiOI based micromotors used in this work were synthesized through a hydrothermal approach. Details of the synthesis recipe are presented in Supplementary Information. a Autoclave BiOI/Fe3 O4
200 °C, 12 h Fe3 O4
FeCl3 + EG + DEG + PVP + NaAc
Autoclave, 160 °C, 24 h
Bi(NO3 )3 + DEG + KI AgNO 3 solution
Au deposition
BiOI/AgI/Fe3 O4 /Au micromotor
b
c
BiOI/AgI/Fe3 O4
d
f
e
g b a a
b
Fig. 1 Synthesis schematic and SEM images of micromotors. (a) Schematic of Fe3O4 nanoparticles and BiOI/AgI/Fe3O4/Au
micromotors synthesis. (b-f) show the SEM images of the synthesized BiOI, BiOI/AgI, BiOI/Fe3O4, BiOI/Fe3O4/AgI
and BiOI/Fe3O4/AgI/Au microstructures, respectively. (g) The distribution of Au element along the line ab in Fig. 1f.
Scale bars in (b-f) are 2 μm.
3. Results and discussions 3.1 Characterizations and analysis of synthesized microstructures Scanning electron microscope (SEM) characterization results indicate that pure BiOI microspheres have flower-like structures with the average diameter of 3-4 μm (Fig. 1b). Sheet-like AgI microplates are 3
well decorated on the surface of BiOI microspheres (Fig. 1c-e). And after modification with Fe3O4, the surface of BiOI sphere is covered by Fe3O4 nanoparticles, whose size is around 200 nm. After half coating the BiOI/AgI/Fe3O4 particle with gold layer, the Janus structure of the BiOI/AgI/Fe3O4/Au micromotor is formed and verified in Fig. 1f-g. 3.2 Micromotors motion under visible light Significant motion of the micromotors under light irradiation is essential for “on-the-fly” pollutant removal. Based on the previous research [15], we presented the visible light powered BiOI/AgI/Fe3O4/Au micromotor and conducted the motion test for the synthesized micromotors. As displayed in Fig. 2a, the micromotor kept almost still in the dark. Once the light was on, the motion started immediately. In Fig 3b, under the visible light irradiation, the photogenerated electrons will travel from the BiOI/AgI/Fe3O4 conduction band (CB) to the gold layer. Meanwhile, the holes will be transported to the surface of BiOI/AgI/Fe3O4 and react to generate H+ and ·OH. The depletion and generation of H+ at the two sides cause the ion gradient around the micromotor, creating a self-generated electrical field and thus propelling the BiOI/AgI/Fe3O4/Au micromotor to move towards the BiOI side. Velocity of micromotors increased as the light intensity ramped up gradually (Fig. 2c). Besides, without the gold layer coating, the non-Janus BiOI/AgI/Fe3O4 microspheres just moved randomly. Compared with pure BiOI/Au micromotor, the addition of AgI can improve the photon absorption of the micromotor and subsequently increase the velocity. Besides, light intensity can also tune the motion mode. As the light intensity increased further, the motion of the micromotor changed from Brownian motion into directional
4
a
b
Vis light
h+ h+
H2 O H+ OH
Propulsion OH
O2
c
H+
e- e-
d
motion (Fig. 2d). Figure 2. Visible light actuated micromotor motion. (a) Micromotor motion trajectories without (upper) and with (lower) light. The
scale bar is 20 μm. (b) The schematic diagram of the motion of micromotor based on the self-eletrophoresis mechanism. (c) Motion
velocities of micromotors under different light intensities. (d) The motion trajectories of the micromotor with varied light intensities.
3.3 Photodegradation of organic pollutant with the micromotors The photocatalytic activity micromotors were tested through the degradation of RhB, as shown in Fig. 3. The capability of degradation was calculated according to Eqa. 1. 𝐶
k𝑡 = ―ln𝐶0
(1)
where k represents the apparent pseudo-first-order rate constant (min-1), C is the concentration of RhB at time t, and C0 is the original concentration of RhB. Under dark, all the micromotors showed weak photocatalytic performance. After the light was introduced, photocatalytic activities of the micromotors were significantly enhanced. It was found that pure BiOI could hardly purify the RhB and the BiOI/AgI/Au micromotors have the highest RhB degradation performance. The BiOI/AgI/Fe3O4/Au micromotors presented degradation performance a little lower than that of the BiOI/AgI/Au micromotors. Owing to the extremely narrow band gap (~0.1 eV), Fe3O4 nanoparticles, embedded into the micromotors, will serve as the recombination center for
5
photogenerated electrons and holes, causing a quick recombination of active electrons and holes, thus hinder the generation rate of · OH around the micromotors, and therefore weaken the degradation performance and decrease the velocity of micromotor. Despite this, we cannot ignore the excellent magnetic performance of Fe3O4 nanoparticles, which will be discussed later in details. As indicated from Fig. 3b, the rate constant (k) of BiOI/AgI/Au and BiOI/AgI/Fe3O4/Au micromotors were much higher than the others. The highest degradation speed (0.0271 min-1) was achieved by BiOI/AgI/Au micromotors.
Figure 3. Photodegradation of RhB solution with different micromotors and the mechanism of photocatalytic process in
BiOI/AgI/Fe3O4/Au micromotor. (a) The degradation performance of different kinds of micromotors. (b) The degradation
efficiencies calculated from (a). (c) Mechanism of photocatalytic process in BiOI/AgI/Fe3O4/Au micromotor. (d) The recycling
process of micromotors through a magnet. (e) The photodegradation performance evaluated through four cycles. (f) The RhB
degradation rate of each cycle in (e).
The possible mechanism of photocatalytic process was presented in Fig. 3c. Under visible light 6
irradiation, the electron holes (h+) can be generated on the VB side of both BiOI and AgI. Since the positions of VB and CB of AgI are higher than BiOI, the photogenerated electrons (e-) can be easily transferred from the CB of AgI to the CB of BiOI; and assist to enhance the photodegradation activity. Moreover, the recycling and reusing of the micromotor were also discussed. After the remediation of RhB, micromotors were easily collected using a magnet (Fig. 3d). After rinse and dry, the recollected micromotors were applied in the same photo-degradation experiments again. As presented in Fig. 3e and Fig. 3f, the degradation rate of RhB decreased from 53.2% to 44.3% after three times recycles. Despite the loss of micromotors in each recycle, it can be obviously found that the micromotors can still keep a relatively high photodegradation efficiency, demonstrating their stability. 4. Conclusions In this work, we applied visible light driven micromotors based on BiOI into organic water pollution degradation. Through the cost-effective hydrothermal method, BiOI/AgI/Fe3O4/Au micromotors are synthesized. Significant motion of the micromotor was observed with visible light irradiation. Moreover, the micromotor exhibited better RhB degradation performance than the pure BiOI photocatalyst. Besides, the micromotors can be recollected and reused through a magnet and still showed relatively high photocatalytic activity after three times recycle. Acknowledgments Thanks to the financial support from the National Natural Science Foundation of China (No.61803088), the Natural Science Foundation of Fujian Province, China (No. 2017J01748), the Open Project Programs from the State Key Laboratory of Robotics, Shenyang Institute of Automation, Chinese Academy of Sciences (Grant No: 2017-O02) , the State Key Laboratory of Photocatalysis on Energy and Environment (Grant No. SKLPEE-KF201718) and Fuzhou University Testing Fund of precious apparatus
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(No. 2018T016 and No. 2019T015). We would also like to thank Prof. Mingdeng Wei and Mr. Minghuang Guo for assistance at Au deposition. Conflict of Interest None. References [1] C.H. Neoh, Z.Z. Noor, N.S.A. Mutamim, C.K. Lim, Green technology in wastewater treatment technologies: Integration of membrane bioreactor with various wastewater treatment systems, Chem. Eng. J. 283 (2016) 582-594. [2] L.J. Bao, Maruya, K. A., Snyder, S. A., & Zeng, E. Y, China's water pollution by persistent organic pollutants, Environ. Pollut. 163 (2012) 100-108. [3] A.Y. Hoekstra, M.M. Mekonnen, The water footprint of humanity, Proc Natl Acad Sci U S A 109(9) (2012) 3232-3237. [4] L. Ye, Y. Su, X. Jin, H. Xie, C. Zhang, Recent advances in BiOX (X = Cl, Br and I) photocatalysts: synthesis, modification, facet effects and mechanisms, Environmental Science: Nano 1(2) (2014) 90-112. [5] T. Li, X. Chang, Z. Wu, J. Li, G. Shao, X. Deng, J. Qiu, B. Guo, G. Zhang, Q. He, L. Li, J. Wang, Autonomous Collision-Free Navigation of Microvehicles in Complex and Dynamically Changing Environments, ACS Nano 11(9) (2017) 9268-9275. [6] T. Li, A. Zhang, G. Shao, M. Wei, B. Guo, G. Zhang, L. Li, W. Wang, Janus Microdimer Surface Walkers Propelled by Oscillating Magnetic Fields, Adv. Funct. Mater. 28(25) (2018). [7] Z. Zhan, F. Wei, J. Zheng, W. Yang, J. Luo, L. Yao, Recent advances of light-driven micro/nanomotors: toward powerful thrust and precise control, Nanotechnol Rev 7(6) (2018) 555-581. [8] S. Shklyaev, Janus droplet as a catalytic micromotor, EPL 110(5) (2015) 54002. [9] L. Xu, F. Mou, H. Gong, M. Luo, J. Guan, Light-driven micro/nanomotors: from fundamentals to applications, Chem. Soc. Rev. 46(22) (2017) 6905-6926. [10] M. Safdar, J. Simmchen, J. Jänis, Light-driven micro- and nanomotors for environmental remediation, Environmental Science: Nano 4(8) (2017) 1602-1616. [11] X. Chang, W. Tang, Y. Feng, H. Yu, Z. Wu, T. Xu, H. Dong, T. Li, Coexisting Cooperative Cognitive Micro-/Nanorobots, Chem Asian J 14(14) (2019) 2357-2368. [12] Q. Zhang, R. Dong, Y. Wu, W. Gao, Z. He, B. Ren, Light-Driven Au-WO3@C Janus Micromotors for Rapid Photodegradation of Dye Pollutants, ACS Appl Mater Interfaces 9(5) (2017) 4674-4683. [13] D. Zhou, Li, Y. C., Xu, P., Ren, L., Zhang, G., Mallouk, T. E., & Li, L, Visible-light driven Si–Au micromotors in water and organic solvents, Nanoscale 9(32) (2017) 11434-11438. [14] H. Yu, W. Tang, G. Mu, H. Wang, X. Chang, H. Dong, L. Qi, G. Zhang, T. Li, Micro-/Nanorobots Propelled by Oscillating Magnetic Fields, Micromachines (Basel) 9(11) (2018). [15] R. Dong, Y. Hu, Y. Wu, W. Gao, B. Ren, Q. Wang, Y. Cai, Visible-Light-Driven BiOI-Based Janus Micromotor in Pure Water, J. Am. Chem. Soc. 139(5) (2017) 1722-1725.
Highlights
Successful synthesis of BiOI based Janus micromotors through hydrothermal approach.
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“On-the-fly” pollutant remediation achieved with light-driven micromotors.
Micromotors can be easily recollected and retain a high photocatalytic activity.
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Under the visible light irradiation, the self-propelled BiOI/AgI/Fe3O4/Au micromotors show significant motion in the polluted water, and facilitate the “on-the-fly” organic pollutant removal. The micromotors can be easily recycled using a magnet and reused into Rhodamine B degradation.
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