Flower-Like Molybdenum Disulfide for Polarity-Triggered

Sep 25, 2017 - Department of Electrical & Computer Engineering and Materials Science and Engineering Program, University of Houston, Houston, Texas 77...
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Flower-Like Molybdenum Disulfide for Polarity-Triggered Accumulation/Release of Small Molecules Qizhang Huang,†,§ Yueyun Fang,†,§ Jifu Shi,*,†,‡ Yanliang Liang,*,∥ Yanqing Zhu,† and Gang Xu*,†,⊥ †

Guangzhou Institute of Energy Conversion, Key Laboratory of Renewable Energy, Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development, Chinese Academy of Sciences, Guangzhou 510640, China ‡ Siyuan Laboratory, Department of Physics, Jinan University, Guangzhou 510632, Guangdong, China § University of Chinese Academy of Sciences, Beijing 100049, China ∥ Department of Electrical & Computer Engineering and Materials Science and Engineering Program, University of Houston, Houston, Texas 77204, United States ⊥ Tibet New Energy Research and Demonstration Centre, Lhasa, Tibet 850000, China S Supporting Information *

ABSTRACT: Flower-like molybdenum disulfide (MoS2) with rich edge sites has been prepared by the hydrothermal method. The edge sites possess polarity due to the noncentrosymmetric Mo−S on exposed (100) facets and thus show a strong electrostatic attraction toward polar species. The flower-like MoS2 can be used as small-molecule carriers for the model drug, Rhodamine B (RhB). The results prove that flower-like MoS2 have fast adsorption kinetics and perform a switchable accumulation/release with response to the solvent polarity. An outstanding reusability can be found in flower-like MoS2 due to little cargo retention, and the recycle of adsorption can be repeated 100 times with above 88.5% of the adsorption capacity retained. The flower-like MoS2 with solvent polarity-triggered loading/release can be extended to controlled release and color switch of display. KEYWORDS: molybdenum disulfide, polarity, reusability, adsorption, solvents

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change, and considerable retention of cargos upon release.3 Surface-adsorbing materials such as reduced graphene oxide− ferrite hybrids and polymeric adsorbents, on the other hand, show fast adsorption kinetics (92% of Rhodamine B can be removed within 2 min) due to few obstacles for adsorbate diffusion, but they have generally low adsorption capacity (20− 50 mg g−1) because of the lack of multilayer adsorption capability.7,8 High-surface-area-activated carbon nanotubes have higher adsorption capacity of 100−400 mg g−1 but at the same time insufficient reusability and slow adsorption kinetics due to a long diffusion distance of adsorbates.9 It seems that the balance between adsorption kinetics and capacity needs to be

INTRODUCTION Smart materials with reversible adsorption−release capabilities in response to the external environment are crucial for a wide variety of applications such as controlled drug release, protein immobilization, biosensors, matter recycling, and water treatment.1,2 Ideally, the material should rapidly adsorb the target molecules (e.g., drugs) for efficient accumulation and later release the adsorbed molecules under the desired condition.3 For these purposes, materials like carbon nanocapsules,4 gelatin microgels,5 ionically cross-linked polymer networks,3 and polyelectrolyte/silica composites6 have been recently developed as small-molecule carriers. The controlled release capability of these materials mainly stems from their steric hindrance that traps cargo molecules and retards them from diffusing out. However, the complicated architecture can lead to limited adsorption/release kinetics, slow response to environment © XXXX American Chemical Society

Received: August 10, 2017 Accepted: September 25, 2017 Published: September 25, 2017 A

DOI: 10.1021/acsami.7b11940 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

Figure 1. Morphology analysis of MoS2: (a) XRD patterns of flower-like MoS2 (red) and commercial MoS2 (black); SEM images of (b) commercial MoS2 and (c) flower-like MoS2 with insets of water contact angle test; (d) TEM image of flower-like MoS2 with insets of amplified selected area (top right); (e) HRTEM image of the MoS2 petal; and (f) SAED image of the whole area in (d).

result in plenty of thin petals and high polarity on the edge sites.20 Some have shown the adsorption behavior of the as-prepared flower-like MoS2 toward Rhodamine B (RhB) whose maximum adsorption capacity was about 49.2 mg g−1.21 Furthermore, by introducing porosity into the flower-like MoS2 adsorbent, the adsorption capacity for RhB can be increased to 163 mg g−1. Unfortunately, it takes an interval lasting 420 min to accomplish the adsorption which is a time-consuming process.22 Recently, Han et al. have prepared flower-like MoS2 as a regenerable dye adsorbent.23 They proposed that the negative surface charges play an important role in cationic dye adsorption, and the MoS2 adsorbent can be recovered to some extent by alkaline solution. However, more effort is still needed to be made for further exploration of the adsorption mechanism, increase of adsorption kinetics, and enhancement of stimuli response. Herein, we have synthesized flower-like MoS2 with rich edge sites by using an easily scalable one-pot hydrothermal method, where high concentrations of precursors and excessive thiourea to the stoichiometric ratio were employed (see experiment in SI). Because of the polarity at the edge sites, the flower-like MoS2 attract polar species and adsorb multiple layers of small molecules, showing a satisfactory adsorption capacity of 231.3 mg g−1 for Rhodamine B (RhB), a representative model drug in release studies,24−26 and a rapid loading speed of 42.4 mg g−1 min−1. More importantly, reversible and repeatable loading/ release of RhB is realized through controlling the polarity of the solvent, which can show an immediate response to the solvent environment within seconds and stably perform ten consecutive times of accumulation/release of RhB. To the best of our knowledge, this is the first demonstration of polarity-triggered reversible accumulation/release. It adds to the previously reported triggers including pH value,27 cations,28 irradiation,29 ultrasound,30 and temperature31 and opens the door to new

compromised. To overcome these limitations, carriers with strong multilayer adsorbing capabilities and readily switchable accumulation/release behaviors are highly desirable. Molybdenum disulfide (MoS2) possesses a unique sandwiched three-atom (S−Mo−S) lamellar layer structure with strong in-plane covalent bonds but weak interlayer van der Waals interaction.10 Unlike layer-structured graphitized carbon that consists of nonpolar covalent bonds, MoS2 possesses polar Mo−S covalent bonds at the edges of the lamellar layers11 which is capable of multilayer adsorption.12,13 The surface adsorption by MoS2 differs from the trapping mechanism for capsule architectures, in which the adsorption-active edges can offer fast response to the change of the external environment due to the absence of buffer shell layers, and cargo retention will be minimized. Flower-like MoS2 with much surfaces (petals) are very favorable in adsorption, when compared with those of sphere and wire shapes which can, respectively, be prepared by hydrothermal growth directed by additive agents (templates14 or pH adjustion15) and low-temperature sulfuration of MoO3.16 With regard to the preparation of flower-like MoS2, chemical vapor deposition (CVD) has been reported.17 However, the hydrothermal method is the most common synthesis method of flower-like MoS2 because of its relatively easy operation and mass production.18,19 In addition, the formation of an edge dislocation and sheet curve do easily occur by hydrothermal synthesis of MoS2, which can lead to petal growth in different directions and increase the exposed edge sites of flower-like MoS2. On the other hand, the concentration and stoichiometric ratio of the starting materials (Mo and S sources) in hydrothermal can influence the growth of flower-like MoS2 (by growth rates and morphologies). High concentration and disproportionality of the starting materials are beneficial for increasing the defect richness of flower-like MoS2 that may B

DOI: 10.1021/acsami.7b11940 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

Figure 2. Interaction between MoS2 and RhB: (a) EDS mapping of the distribution of the N element (orange dots) on the surface of flower-like MoS2; (b) isotherm sorption of RhB by flower-like MoS2 and commercial MoS2; (c) adsorption kinetic profile of a solution of RhB (0.01 mg/mL, 100 mL) in the presence of flower-like MoS2 (20 mg) at different time intervals (second) of 0, 2, 5, 10, 15, 30, 45, and 60 s; and (d) illustration of RhB adsorbed in flower-like MoS2.

78.5° than the 140.3° for commercial MoS2 (insets in Figure 1b and c).33 The much increased surface polarity of flower-like MoS2 will lead to affinity toward polar solvents and good dispersion in water. Transmission electron microscopy (TEM) reveals more structural details of the flower-like MoS2 (Figure 1d). The MoS2 bouquets have several flower-like MoS2 consisting of interleaved, elliptical, and primary sheets (socalled petals) with a thickness of about 30 nm (Figure 1e). Aiming at identifying the spatial distribution of the phases, high-resolution transmission electron microscopy (HRTEM) images of the petals are measured (Figure 1e). Interplanar spacing of 0.26 and 0.65 nm is observed at the plane and the edge, respectively, corresponding to those of (100) and (002) planes.11 Combined with the XRD results, morphologies observed from SEM and TEM images can confirm that the active (100) facets exist on the edge of the MoS2 petals. The selective area electronic diffraction (SAED) image of the whole area in Figure 1d shows that the synthesized flower-like MoS2 are polycrystalline (see Figure 1f). The polar edge of MoS2 can cause an electric field and attract bipolar molecules.11 RhB with a zwitterionic form can interact with the polar edge of MoS2 in this way. To verify the existence of the interaction, flower-like MoS2 were dispersed in RhB solution, collected by centrifugation, and dried. The distribution of RhB adsorbed on the surface of flower-like MoS2 was investigated with energy-dispersive X-ray spectrometry (EDS) mapping analysis. Figure 2a reveals that the N element signal

applications including solvent-controlled release and solvatochromic apparatus. The reusability, a property rarely investigated for molecule carriers, of MoS2 is found to be excellent with an adsorption capacity of 88.5% remaining after 100 recycles for RhB loading.

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RESULTS AND DISCUSSIONS The black powders (MoS2) were obtained by a one-pot hydrothermal reaction between hexaammonium heptamolybdate tetrahydrate and thiourea. The X-ray diffraction (XRD) patterns of flower-like MoS2 and commercial MoS2 are shown in Figure 1a. All the diffraction peaks are in a good agreement with the standard pattern of hexagonal MoS2 (JCPDS card No. 73-1508). The intensity ratio of (100) and (002) diffraction peaks is 0.48 and 0.15 for flower-like MoS2 and commercial MoS2, respectively. It indicates that MoS2 nanoflowers have more (100) facet exposed, compared with commercial MoS2. The SEM image in Figure 1b shows that the commercial MoS2 nanosheets have a lamellar structure with the base plane occupying most of the surface, hence the dominant (002) diffraction peak in the XRD pattern. In contrast, a large amount of edge sites are observed for flower-like MoS2 (Figure 1c), which contributes to the higher (100) ratio. The noncentrosymmetric Mo−2S structure on the (100) facets renders the edge sites inherently polar.11,32 The effect of such polarity on the surface property of MoS2 is quantified via water contact angle: flower-like MoS2 show a smaller water contact angle of C

DOI: 10.1021/acsami.7b11940 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Figure 3. High-resolution XPS spectra of (a) Mo 3d and (b) S 2p and (c) Raman spectra of MoS2 (the upper lines: MoS2 loaded with RhB, the lower line: pristine MoS2).

Figure 4. (a) FTIR spectra of RhB, RhB dissolved in water, RhB dissolved in THF, and THF, and (b) adsorption/desorption mechanism of MoS2 toward RhB with an inset of UV−vis absorption spectra of RhB in water and THF/water (9:1 v/v).

solution after different time intervals of adsorption are shown in Figure S2. In addition to loading, the release behavior is equally important for the reusability of the carriers. As will be discussed below, RhB exists in different forms in solution as the polarity of the solvent changes. A change in solvent polarity will hence change the polarity of the RhB molecule, thus triggering the release of RhB from MoS2. After dispersing RhB-loaded flowerlike MoS2 in a mixture of tetrahydrofuran (THF) and water (9:1 v/v), the color of the solution changed from colorless to violet within 2 s, indicating a quick response to the solution environment and rapid release kinetics. More than 90% of the adsorbed RhB can be released (evaluated by the concentrations of the released RhB, Figure S3), which represents a noticeably low cargo retention when compared with those of complexstructural adsorbents (∼20%).4 We went on to scrutinize the origin of the adsorption and desorption behaviors of MoS2. The surface charge of flower-like MoS2 was characterized by a zeta potential of −20.6 mV, denoting the capability of electrostatic attraction toward cations and polar organics. Thus, the positively charged CN+ group in the RhB molecule will be electrostatically attracted by the negatively charged S atoms in the polar Mo−2S dipoles. The interaction between S and CN+ is expected to cause a decreased electron cloud density within the Mo−2S dipoles, which is detectable by X-ray photoelectron spectroscopy

corresponding to adsorbed RhB mainly appears at around the edge sites of the petals. This result proves that the edge sites are responsible for the adsorption of RhB (as shown in Figure 2d). We then studied the adsorption model and kinetics of RhB on flower-like MoS2. The Sips model (Supporting Information S1) was employed to evaluate the adsorption behaviors of flower-like MoS2 and commercial MoS2. The relationship between the residual amount of RhB (Ce) and the adsorbed RhB amount per unit mass of adsorbent (Qe) is well fitted by the Sips model with a correlation coefficient R2 of 0.984, and the fitted value of heterogeneity ns is 1.5 (Figure 2b), indicating a multilayer adsorption. After a contact time of 60 min, the fitted maximum adsorption capacity (qm) of flower-like MoS2 and commercial MoS2 is 231.3 and 14.5 mg g−1, respectively. The significant difference in qm can be interpreted as the result of different richness of edge sites between the two samples, which reconfirms the role of edge sites in adsorption. The polarity of the edge sites also favors high loading speed. Figure 2c shows the progressive adsorption of RhB with flower-like MoS2. The increase of loading amount (left y-axis) and the decrease of the corresponding normalized concentration (right y-axis) of RhB versus time show a high loading speed of 42.4 mg g−1 min−1 and a high RhB removal efficiency of 90% within 60 s, respectively. This is much more rapid than that of reduced graphene oxide−ferrite hybrids (3.32 mg g−1 min−1 within the first 2 min).7 Absorbance spectra and a digital photo of RhB D

DOI: 10.1021/acsami.7b11940 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

Figure 5. (a) Recycling of MoS2 carriers for loading of RhB in water 100 times; (b) release of RhB controlled by THF volume ratio in water solution; and (c) loading/release switch of RhB for ten consecutive times.

(XPS). We have compared the XPS spectra of flower-like MoS2 before and after RhB adsorption. Once loaded with RhB, signals for C 1S (268.3 eV), O 1S (530.5 eV), and N 1S (399.1 eV) belonging to RhB were detected in addition to pristine MoS2 (Figure S4a and b). The high-resolution XPS spectra show that the binding energies for Mo 3d 3/2, Mo 3d 5/2, S 2p1/2, and S 2p 3/2 all shifted by 0.3−0.4 eV toward lower energy (Figure 3a and b), evidencing the interaction between RhB and Mo−2S dipoles. More insights into the interaction between RhB and MoS2 were obtained via Raman and Fourier transformed infrared (FTIR) spectroscopy. The two Raman peaks at 379.0 and 403.8 cm−1 can be, respectively, assigned to the E12g and A1g vibration modes of Mo−S bonds (Figure 3c). In E12g mode, Mo and S atoms vibrate along the in-plane direction (opposite to each other) of the lamellar structure, where the Mo−2S dipoles introduce additional polarity orientating the in-plane direction. In A1g mode, S atoms vibrate in the perpendicular-to-plane direction, which is a centrosymmetric excursion without introducing additional polarity. After the loading of RhB, the A1g mode stayed at 402.1 cm−1, while the E12g mode shifted to the lower wavenumbers of 376.4 cm−1, which may be attributed to decreased electron cloud density as was observed from XPS results. Figure S5 shows the FTIR spectra of flower-like MoS2 before and after loading RhB. The peak at 461 cm−1 corresponding to the Mo−S vibration13 shifted to 458 cm−1 after the loading of RhB, again confirming the weakening of the Mo−S bonds. The new peak located at 593 cm−1 can be attributed to the vibration of N−Cl bonds of the loaded RhB. RhB exists in different forms in solutions, including zwitterionic, cationic, and lactonic forms depending on the solvents.34 Thereby, changing the composition of the solvent will result in a form transition of RhB. In a highly polar solvent such as water (ET(30) = 63.1 kcal/mol),35 RhB molecules have a strong tendency to separate the charges and exhibit a zwitterionic form.36 As shown in Figure 4a, the FTIR spectrum of water-solvated RhB shows a significant strengthening of the peak for CN+ (1645 cm−1) with other peaks drastically diminished, indicating the predominant presence of the zwitterionic form. In the FTIR spectrum of RhB solvated by THF (whose ET(30) is equal to 37.4 kcal/mol),35 the peaks at 1086 and 919 cm−1 attributable to the vibration of C−O−C become the strongest. The UV−vis absorption peak of RhB in water and THF/water (9:1 v/v) locates at 553 and 556 nm, respectively, whose values agree with those for the zwitterionic and cationic forms measured in aqueous solution, respectively (Figure 4b).36 These results show that the molecular form of

RhB undergoes a solvent polarity-induced transition between zwitterionic and cationic forms. Based on the above analysis, the adsorption/release mechanism can be summarized and explained as follows (see Figure 4b): (1) Driven by the electrostatic attraction, zwitterionic RhB molecules in water are adsorbed on the polar edge sites of flower-like MoS2. (2) Due to the polarity of the zwitterionic RhB, further adsorption of RhB occurs on top of the previous layer of RhB in a head-to-tail way; the process repeats and finally forms RhB aggregates.37,38 This multilayer adsorption can be fit by the Sips model as discussed above. (3) When exposed to a low-polarity solvent system such as a THF/ H2O mixture, protonation of the carboxylate group of RhB occurs, and RhB switches from the zwitterionic to cationic form. Consequently, the RhB aggregates fall apart due to the insufficient polarity or even repulsion between the positively charged molecules. The adsorbed RhB cannot be completely released due to the residual RhB monolayer directly adhered to the polar edge sites, which explains the ∼10% cargo retention mentioned above. The switchable response of RhB-loaded flower-like MoS2 to the solution environment translates into excellent reusability of the carrier. After 100 times of recycle loading, the flower-like MoS2 retain a loading efficiency of 88.5% for RhB solution (5 mL, 0.01 mg/mL) (Figure 5a). Meanwhile, the sensitive loading/release of flower-like MoS2 carriers loaded with RhB (42.4 mg g−1) is presented by changing the concentration of THF as a stimulus in water, which can alter the equilibrium of RhB content distributing between the polar edge sites and the liquid phase. The stimulus for release can be extended to ethanol, acetone, and other water-soluble species with polarity lower than that of water. As shown in Figure 5b, with increasing THF volume concentration, the release amount of RhB gradually becomes larger, while the released RhB can be reloaded once the THF concentration is decreased. The absorbance ratio of the liquids, which is, respectively, extracted from the mixture of 5 mg loaded MoS2 (42.4 mg g−1) in THF solution (20 vol %) and water, equals to approximately 37 (1.12/0.03), denoting an obvious color distinction. This color switch caused by THF concentration can be performed for a consecutive ten times without performance degradation (Figure 5c). Such stability implies a promising application potential in solvent-controlled release and color display.

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CONCLUSION In summary, flower-like MoS2 with rich edge sites have been synthesized using a facile one-pot hydrothermal method. The E

DOI: 10.1021/acsami.7b11940 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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(7) Bai, S.; Shen, X. P.; Zhong, X.; Liu, Y.; Zhu, G. X.; Xu, X.; Chen, K. M. One-pot Solvothermal Preparation of Magnetic Reduced Graphene Oxide-ferrite Hybrids for Organic Dye Removal. Carbon 2012, 50 (6), 2337−2346. (8) Huang, J. H.; Huang, K. L.; Liu, S. Q.; Wang, A. T.; Yan, C. Adsorption of Rhodamine B and Methyl Orange on a Hypercrosslinked Polymeric Adsorbent in Aqueous Solution. Colloids Surf., A 2008, 330 (1), 55−61. (9) Ma, J.; Yu, F.; Zhou, L.; Jin, L.; Yang, M. X.; Luan, J. S.; Tang, Y. H.; Fan, H. B.; Yuan, Z. W.; Chen, J. H. Enhanced Adsorptive Removal of Methyl Orange and Methylene Blue from Aqueous Solution by Alkali-Activated Multiwalled Carbon Nanotubes. ACS Appl. Mater. Interfaces 2012, 4 (11), 5749−5760. (10) Shanmugam, M.; Durcan, C. A.; Yu, B. Layered Semiconductor Molybdenum Disulfide Nanomembrane Based Schottky-barrier Solar Cells. Nanoscale 2012, 4 (23), 7399−7405. (11) Wu, J. M.; Chang, W. E.; Chang, Y. T.; Chang, C. K. PiezoCatalytic Effect on the Enhancement of the Ultra-High Degradation Activity in the Dark by Single- and Few-Layers MoS2 Nanoflowers. Adv. Mater. 2016, 28 (19), 3718−3725. (12) Geng, X. M.; Zhang, Y. L.; Han, Y.; Li, J. X.; Yang, L.; Benamara, M.; Chen, L.; Zhu, H. L. Two-Dimensional Water-Coupled Metallic MoS2 with Nanochannels for Ultrafast Supercapacitors. Nano Lett. 2017, 17 (3), 1825−1832. (13) Massey, A. T.; Gusain, R.; Kumari, S.; Khatri, O. P. Hierarchical Microspheres of MoS2 Nanosheets: Efficient and Regenerative Adsorbent for Removal of Water-Soluble Dyes. Ind. Eng. Chem. Res. 2016, 55 (26), 7124−7131. (14) Luo, H.; Zhang, L. Z.; Yue, L. Synthesis of MoS2/C Submicrosphere by PVP-Assisted Hydrothermal Method for Lithium Ion Battery. Adv. Mater. Res. 2012, 531, 471−477. (15) Tan, Y. H.; Yu, K.; Yang, T.; Zhang, Q. F.; Cong, W. T.; Yin, H. H.; Zhang, Z. L.; Chen, Y. W.; Zhu, Z. Q. The Combinations of Hollow MoS2Micro@nano-spheres: One-step Synthesis, Excellent Photocatalytic and Humidity Sensing Properties. J. Mater. Chem. C 2014, 2 (27), 5422−5430. (16) Chen, Z. B.; Cummins, D.; Reinecke, B. N.; Clark, E.; Sunkara, M. K.; Jaramillo, T. F. Core-shell MoO3-MoS2 Nanowires for Hydrogen Evolution: A Functional Design for Electrocatalytic Materials. Nano Lett. 2011, 11 (10), 4168−4175. (17) Zhu, H.; Du, M. L.; Zhang, M.; Zou, M. L.; Yang, T. T.; Fua, Y. Q.; Yao, J. M. The Design and Construction of 3D Rose-petal-shaped MoS2 Hierarchical Nanostructures with Structure-sensitive Properties. J. Mater. Chem. A 2014, 2 (21), 7680−7685. (18) Tang, G. G.; Sun, J. R.; Chen, W.; Tang, H.; Wang, Y. J.; Li, C. S. Surfactant-assisted Hydrothermal Synthesis and Tribological Properties of Flower-like MoS2 Nanostructures. Micro Nano Lett. 2013, 8 (3), 164−168. (19) An, J. H.; Jang, J. A Highly Sensitive FET-type Aptasensor using Flower-like MoS2 Nanospheres for Real-time Detection of Arsenic(iii). Nanoscale 2017, 9 (22), 7483−7492. (20) Xiong, J. H.; Liu, Y. H.; Wang, D. K.; Liang, S. J.; Wu, W. M.; Wu, L. An Efficient Cocatalyst of Defect-decorated MoS2 Ultrathin Nanoplates for the Promotion of Photocatalytic Hydrogen Evolution over CdS Nanocrystal. J. Mater. Chem. A 2015, 3 (24), 12631−12635. (21) Wang, X. H.; Ding, J. J.; Yao, S. W.; Wu, X. X.; Feng, Q. Q.; Wang, Z. H.; Geng, B. Y. High Supercapacitor and Adsorption Behaviors of Flower-like MoS2 Nanostructures. J. Mater. Chem. A 2014, 2 (38), 15958−15963. (22) Li, H.; Xie, F.; Li, W.; Fahlman, B. D.; Chen, M. F.; Li, W. J. Preparation and Adsorption Capacity of Porous MoS2 Nanosheets. RSC Adv. 2016, 6 (107), 105222−105230. (23) Han, S.; Liu, K.; Hu, L.; Teng, F.; Yu, P.; Zhu, Y. Superior Adsorption and Regenerable Dye Adsorbent Based on Flower-Like Molybdenum Disulfide Nanostructure. Sci. Rep. 2017, 7, 43599. (24) Tangso, K. J.; Patel, H.; Lindberg, S.; Hartley, P. G.; Knott, R.; Spicer, P. T.; Boyd, B. J. Controlling the Mesostructure Formation within the Shell of Novel Cubic/Hexagonal Phase Cetyltrimethylammonium Bromide-Poly(acrylamide-acrylic acid) Capsules for pH

edge sites are noticeably polar and show a strong attraction toward RhB. The flower-like MoS2 can be used as smallmolecule carriers with fast adsorption kinetics and fulfill a switchable accumulation/release by responding to the solvent environment. The recycle of adsorption can be repeated 100 times without significant performance degradation, revealing an outstanding reusability. The flower-like MoS2 capable of solvent polarity-triggered loading/release depict a picture of the broad application of controlled release and color switch.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b11940. Experimental procedures; interpretation of Sips model; EDS mapping of flower-like MoS2 after adsorption of RhB; absorbance spectra and digital photo of RhB solution after different time intervals of adsorption; digital photo of desorption of RhB in THF solution (90 vol %); XPS spectra of flower-like MoS2; FTIR spectra of flower-like MoS2; and other two forms of Rhodamine B (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. ORCID

Qizhang Huang: 0000-0002-6576-7064 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (21673243), Guangdong-Hong Kong Joint Innovation Project of Guangdong Province, China (2014B050505015), Special Support Program of Guangdong Province, China (2014TQ01N610), Project of Science and Technology Service Network initiative, Chinese Academy of Sciences (KFJ-STS-QYZD-010), and Tibet Autonomous Region Major Special Projects (ZD20170017).

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REFERENCES

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DOI: 10.1021/acsami.7b11940 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

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DOI: 10.1021/acsami.7b11940 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX