Mechanically Activated Solvent-Free Assembly of Ultrasmall Bi2S3

Article pubs.acs.org/cm

Mechanically Activated Solvent-Free Assembly of Ultrasmall Bi2S3 Nanoparticles: A Novel, Simple, and Sustainable Means To Access Chalcogenide Nanoparticles Michael Y. Malca,† Huizhi Bao,† Thomas Bastaille,†,§ Nadim K. Saadé,† Joseph M. Kinsella,‡,∥ Tomislav Frišcǐ ć,† and Audrey Moores*,† †

Centre for Green Chemistry and Catalysis, Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec H3A 0B8, Canada ‡ Department of Bioengineering, McGill University, Montreal, Quebec H3A 0C3, Canada § Faculté des Sciences et Technologies, Université de Lorraine, BP 70239, 54506 Vandœuvre-les-Nancy Cedex, France ∥ Department of Biomedical Engineering, McGill University, Montreal, Quebec H3A OC5, Canada S Supporting Information *

ABSTRACT: Nanosized Bi2S3 particles are one of the most promising nanomaterials for biomedical imaging, due to a unique combination of low toxicity and the high electron count of bismuth. However, the study and use of nano-sized Bi2S3 have been prevented by major synthetic challenges, including sensitivity to air and harsh solvothermal conditions. Herein, we describe a novel and surprisingly simple pathway, based on solid-state bottom-up self-assembly, to access the elusive Bi2S3 nanoparticles functionalized with surface ligands that allow dispersion in either organic or aqueous media. This one-pot, room-temperature synthesis utilizes mechanical activation in the solid state, either by milling or even manual grinding, to induce the spontaneous assembly of monodisperse 2 nm diameter nanoparticles applicable for CT imaging in physiological media. This solvent-free methodology utilizes readily available precursors to provide unprecedented one-step access to monodisperse nano-Bi2S3 in multigram amounts, including polyethylene glycol (PEG)-coated nanoparticles, without the need for controlled atmospheres or solvothermal treatment.

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INTRODUCTION

has yet to be deployed for more complex binary or ternary systems such as chalcogenides. The importance of the latter materials for emerging technologies, for instance, those related to energy22 or medical diagnostics,23 calls for this development. Whereas solvent-free milling has previously been used to access diverse types of nanosized materials (including supported metal NPs;17,21,24−27 metal oxide, nitride, and sulfide NPs;28−31 carbon-based NPs;32−34 and porous nanocomposites)35,36 such work has been largely based on top-down mechanochemical routes, i.e., through energy-demanding particle size reduction of bulk materials. Such comminution techniques can yield particles in the size range 10−50 nm, but they cannot provide the required level of size and shape control required for high end applications.37,38 Bismuth sulfide (Bi2S3) is a V−VI semiconductor that has attracted much attention for applications in photoconducting materials,39,40 lithium ion batteries,41,42 solar cells,43,44 electrochemical hydrogen storage,45,46 and thermoelectric devices.47,48 Due to the large atomic number of bismuth, Bi2S3 NPs are also

Nanomaterials are emerging as highly attractive candidates for solving some of the most daunting scientific and technological problems in the domains of energy, health, and electronics.1−4 However, accessing these materials in a scalable fashion, from abundant resources and with good control of their properties, remains a major challenge, which significantly impacts the prospect for their commercialization. In recent years, significant attention has been given to creating new and more efficient and sustainable routes to molecules and materials,5−7 with particular focus on reduction of waste and energy input, as well as the use of safe reagents.8,9 Nanoparticle (NP) synthesis is intrinsically complicated by their metastable nature, necessitating the use of high dilution and presence of surface capping ligands to achieve uniform sample features, e.g., size and shape.10−13 These constraints imply that the development of scalable approaches to NPs with well-defined features remains a challenge for low waste and energy-efficient synthesis.14−16 Recently, mechanochemistry was featured as a highly promising, simple, bottomup methodology for producing gram amounts of highly monodisperse NPs from simple molecular precursors, with significant improvements in atom- and energy-economy.17−21 This methodology was validated for metal nanoparticles, but © 2017 American Chemical Society

Received: May 24, 2017 Revised: August 15, 2017 Published: August 16, 2017 7766

DOI: 10.1021/acs.chemmater.7b02134 Chem. Mater. 2017, 29, 7766−7773

Article

Chemistry of Materials well-suited as contrast agents in computed tomography (CT) and have shown equal or superior efficacy compared to currently used iodinated CT compounds.49−51 However, the development of bismuth-based CT contrast agents has been hampered by synthetic challenges.52 Hydrothermal methods, which are commonly employed in Bi2S3 NP syntheses, typically require high temperatures, an extended heating period, inert atmospheres, and copious amounts of solvents in order to access monodisperse nanomaterials.49,51,53,54 In all cases, these approaches lead to the synthesis of nanomaterials readily suspendable in organic solvent, implying that, for any biological or medicinal application, an extra functionalization step is required to render them water-suspendable. One solvent-free room-temperature synthesis of Bi2S3 NPs has also been reported by Dutkova et al.,38 and it relies on a top-down approach, using as starting materials metallic bismuth and sulfur powder under an argon atmosphere, affording polydisperse products. We now describe a completely novel and surprisingly simple synthesis of Bi2S3 NPs suitable for CT imaging applications, which is based on solid-state reaction and self-assembly induced by brief mechanical activation. Remarkably, the formation of nanosized Bi2S3 proceeds at room temperature and in air, yielding gram amounts of NPs with well-defined average diameters that can be modulated between 2 and 8 nm, depending on the reaction conditions. This opens access to unprecedently small nanoparticles of this material, irrespective of the synthetic method. The approach directly yields NPs capped by either oleylamine (OA) or sodium 6-aminohexanoate (AHA). The OA-modified Bi2S3 NPs are readily suspended in organic solvent, while using AHA gives access to NPs compatible with aqueous media. Furthermore, this new and simple technique also allows one-step, solvent-free assembly of Bi2S3 NPs modified by poly(ethylene glycol)methyl-ether-amine (mPEG-NH2, MW = 5000 g/mol), a polymer typically used to functionalize biotargeted agents.49 The herein presented methodology is readily scalable for generating grams of NP materials suitable as bioimaging contrast agents, as demonstrated by evaluating the radiodensity of the AHA-capped NPs, as well as their PEGylated counterparts in physiological buffer medium.

Scheme 1. Overview of Herein Developed Synthesis of Bi2S3 NPs Capped with Oleylamine (OA), Sodium 6Aminohexanoate (AHA), and Poly(ethylene glycol)-methylether-aminea

a

mPEG-NH2 MW = 5000 g/mol. All steps are performed at ambient conditions in air.

copy (XPS, Figures S1 and S2, and detailed characterization in Supporting Information), which revealed the presence of Bi, S, O, N, and C. Detection of N confirms the presence of a ligand shell surrounding the NPs, and the appearance of O is attributed to adsorbed moisture. In the two samples, the Bi 4f7/2, Bi 4f5/2, Bi 4d5/2, and Bi 4d3/2 signals were all consistent with Bi3+ ions, while the S 2p and S 2s signals matched S2−. The Bi 4f7/2 binding energy found at 158.4 eV in all the samples is ca. 1.0 eV lower than that of Bi2O3,56 signifying the exclusive formation of Bi2S3. The integration of Bi 4d and S 2s signals indicated an average Bi/S atomic ratio between 0.5 and 0.6, thus implying a slight excess of sulfur. Structures of 5OA@Bi2S3-90-MM and 10OA@Bi2S3-90MM were further analyzed by transmission electron microscopy (TEM, Figure 1A,B). In both cases, very small NPs were observed, with narrow size distributions that were independent of the OA/bismuth ratio. Specifically, the OA/bismuth ratios of either 5:1 or 10:1 both gave NPs with average diameters of 2.09 ± 0.29 and 2.08 ± 0.32 nm, respectively. Overall, these results reveal the successful assembly of pure Bi2S3 NPs despite the absence of an inert atmosphere, which is a requirement in most reported syntheses.38,49 Next, thermogravimetric analysis (TGA) was performed on samples 5OA@Bi2S3-90-MM and 10OA@Bi2S3-90-MM in order to gain insight into the organic ligand shell. Increasing the ligand/bismuth stoichiometric ratio during synthesis from 5:1 to 10:1 afforded no significant change in the OA surface coating (Figure S3), and the loss of organic matter upon thermolysis of the final product was very similar in both cases (17.5% and 17.6% by weight, respectively). These results indicate that the NP surface is already saturated with organic ligand at the 5:1 stoichiometric ratio, and that any additional ligand will likely be washed away during workup. We also tested the possibility to produce NPs using a 3:1 stoichiometric ratio of the OA and bismuth, respectively, but these attempts failed to produce NPs even after 5 days of aging. Surprisingly, milling time did not have a notable effect on the resulting material, indicating that the principal role of milling treatment is mechanical activation. For example, the XPS and TEM analysis results are virtually identical for 5OA@Bi2S3-5MM, obtained using a milling period of 5 min and featuring NPs of a 2.09 ± 0.31 nm mean diameter, and for 5OA@Bi2S390-MM, which was obtained after 90 min of milling and 12 h of aging (Figure S1 and Figure 1A). To further investigate the

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RESULTS AND DISCUSSION Organo-Suspendable Bi2S3 Nanoparticles. We first explored the possibility of a mechanochemically accessible synthesis of Bi2S3 NPs by mixer ball milling (MM) of Bi(NO3)3·5H2O and L-cysteine55 as sources of bismuth and sulfur, respectively, in the presence of oleyamine (OA) as the capping agent. After 90 min of milling, TEM analysis of the resulting pale yellow paste did not reveal any sign of NP formation. However, it was observed that the sample after milling began to darken without external manipulation. After 12 h in air at room temperature, the paste became completely black and was then purified through several washing and centrifugation cycles (Scheme 1). Throughout this study, the bismuth-to-sulfur ratio in all cases was chosen to match the stoichiometry of Bi2S3, while the OA to bismuth stoichiometric ratio was set to either 5:1 (sample 5OA@Bi2S3-90-MM) or 10:1 (sample 10OA@Bi2S3-90-MM) (Table 1). The resulting materials were readily suspendable in hexanes and toluene after brief sonication, and remained so for at least 7 days. Purified 5OA@Bi2S3-90-MM and 10OA@Bi2S3-90-MM samples were first analyzed by X-ray photoelectron spectros7767


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Chemistry of Materials Table 1. Summary of Synthetic Parameters and Mean Particle Diameters for the Resulting Bi2S3 NP Samples xligand@NP-t-millingH2O

liganda

ligand/bismuth molar ratio

milling time (min)

milling methodc

5OA@Bi2S3-90-MM 10OA@Bi2S3-90-MM 5OA@Bi2S3-5-MM 5OA@Bi2S3-MG 5OA@Bi2S3-90-PM 5AHA@Bi2S3-90-MM0 5AHA@Bi2S3-90-MM50 10AHA@Bi2S3-90-MM50 5AHA@Bi2S3-90-MM100 10AHA@Bi2S3-90-MM100 5AHA@Bi2S3-90-PM 5AHA&PEG@Bi2S3-90-MM50

OA OA OA OA OA AHA AHA AHA AHA AHA AHA AHA and mPEG-NH2

5:1 10:1 5:1 5:1 5:1 5:1 5:1 10:1 5:1 10:1 5:1 4.5:1 and 0.5:1

90 90 5 NAb 90 90 90 90 90 90 90 90

MM MM MM MG PM MM MM MM MM MM PM MM

water (μL)

mean diameter (nm)

50 50 100 100 2000d 50

2.09 ± 0.29 2.08 ± 0.32 2.09 ± 0.31 1.96 ± 0.24 1.88 ± 0.27 NA 7.9 ± 2.1 8.2 ± 2.3 7.6 ± 4.0 7.8 ± 1.9 3.0 ± 0.41 2.9 ± 1.2

a

OA, oleylamine; AHA, sodium 6-aminohexanoate; mPEG-NH2, poly(ethylene glycol)-methyl-ether-amine. bManual grinding was performed until the reaction mixtures appeared homogeneous. cMM, mixer ball milling; PM, planetary ball milling; MG, manual grinding. d2 mL water was added to the PM scale-up vessel, equivalent to 75 μL of water in the MM procedure.

monodisperse and water-soluble Bi2S3 NPs by replacing OA with the sodium salt of 6-aminohexanoic acid in the milling procedure. However, attempts to synthesize such NPs by 90 min milling of Bi(NO3)3·5H2O, L-cysteine, and sodium 6aminohexanoate (AHA), followed by aging up to 5 days, were not successful. Next, we turned to liquid-assisted grinding (LAG), a technique that utilizes catalytic, substoichiometric amounts of liquid to facilitate mechanochemical transformations.20 Milling in the presence of 50 μL of water (sample nAHA@Bi2S3-90-MM50, with the AHA/Bi ratios n = 5 and 10) provided, after 24 h aging at room temperature, highly uniform NPs of 7.6−8.2 nm in diameter (Figure 3, Table 1). The XPS spectra revealed similar binding energies for each element as previously seen for OA-capped NPs (Figures S8 and S9). Just like the OA-capped NPs, the as-prepared AHA-functionalized samples diffracted poorly (Figure S10). The amount of water introduced into the reaction mixture in LAG also did not significantly affect the final NP size, although doubling the amount of water additive from 50 to 100 μL allowed for a shorter aging time of 12 h.20 The characterization was completed with UV−vis on the 5AHA@Bi2S3-90-MM50. An absorbance edge around 395 nm was measured, which is blueshifted with respect to bulk Bi2S3, consistent with the nanoscale of the material (Figure S11).63 The use of AHA provided larger NPs than OA, which may be explained by the relative sizes of the two capping agents, the aliphatic chain of AHA being 3 times shorter than that in OA. Indeed, the earlier study on mechanosynthesis of gold NPs showed that longer chain lengths lead to smaller NP sizes,18 due to a more limited access of precursors to the NP surface protected by larger capping agents. The result suggests that nanoparticle stabilization models based on micellar arrangements64 cannot be applied for the reported particles made under mechanochemical conditions. Multigram Scale Synthesis of OA- and AHA-Capped Bi2S3 NPs. The described mechanical activation and aging approach to monodisperse Bi2S3 NPs is readily scalable to multigram scales. In particular, both the 5OA@Bi2S3 and 5AHA@Bi2S3 syntheses were linearly scaled-up (using 2.5 and 2.0 g of reactant Bi(NO3)3·5H2O, respectively) by 90 min of mechanical activation using a planetary ball mill (PM) operating at 500 rpm. Sample analysis by TEM demonstrated the formation of uniform NPs of 1.88 ± 0.27 and 3.0 ± 0.41

ability to assemble uniform Bi2S3 NPs with minimum mechanical activation, we explored manual grinding (MG), using a mortar and pestle, which generated the sample 5OA@ Bi2S3-MG. In this case again, TEM revealed an average NP diameter of 1.96 ± 0.24 nm (Figure 1D), and XPS showed binding energies similar to those for 5OA@Bi2S3-90-MM (Figure S1). Consequently, using OA as the capping agent leads to reproducible assembly of Bi2S3 NPs with a preferred size of ca. 2 nm, as long as intimate mixing is achieved. To the best of our knowledge, these are the smallest NPs of Bi2S3 ever reported. Powder X-ray diffraction (PXRD) analysis of all samples involving OA, prepared either by milling or manual grinding, revealed only broad, featureless diffractograms (Figure S4), indicating either very small particle sizes and/or an amorphous nature. PXRD of annealed samples was used as a means to prove the absence of bismuth oxide in the produced samples (Supporting Information). UV−vis was performed on the 5OA@Bi2S3-90-MM sample and reveals a broad band edge at 405 nm (Figure S5). Characterization was completed by mass spectrometry, a method previously used in analysis of nanoclusters and smallsized nanocrystals.18,57−61 Matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF MS) characterization of Bi2S3 NPs revealed clear fragmentation patterns of Bi and S loss, with peaks separated by 209.2 and 32.0 units, respectively (Figure 2, Figures S6 and S7, and Table S1), consistent with the laser beam-induced decomposition of Bi2S3 NPs into Bin and BinSm clusters (n = 3−7, m = 1−4). The peaks of highest Bi mass were measured as 1463.6 for all the OA-capped samples, corresponding to bare Bi7 clusters (Table S1). Importantly, no oxygen species were detected, validating the formation of bismuth sulfide under aerobic synthetic conditions. Water-Suspendable Bi2S3 Nanoparticles. While the NPs produced in the presence of OA are readily suspendable in a poorly polar solvent such as toluene, consistent with the presence of NPs capped with hydrophobic long chain amine ligands,54,62 direct functionalization of Bi2S3 NPs with watercompatible ligands would be critical for their use as in vivo injectable contrast agents. In classic syntheses, an extra phasetransfer reaction step is required to reach such species.49 Consequently, we explored the possibility of synthesizing 7768


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Figure 2. MALDI-TOF MS measurements for 5OA@Bi2S3-90-MM.

Figure 1. TEM images and size distribution histograms of OA-capped Bi2S3 NPs: (A1 and A2) 5OA@Bi2S3-90-MM (n = 250); (B1 and B2) 10OA@Bi2S3-90-MM (n = 250); (C1 and C2) 5OA@Bi2S3-5-MM (n = 250); (D1 and D2) 5OA@Bi2S3-MG (n = 250). Scale bars represent 20 nm.

nm in diameter, for 5OA@Bi2S3-90-PM and 5AHA@Bi2S3-90PM, respectively, after milling and 48 h of aging (Figure S12). Switching from a mixer to a planetary mill resulted in a limited size change for OA-derived materials (1.88 ± 0.27 nm for 5OA@Bi2S3-90-PM vs 2.09 ± 0.29 nm for 5OA@Bi2S3-90MM), while a marked drop in average NP diameter from 7.9 nm (5AHA@Bi2S3-90-MM50) to 3.0 nm (5AHA@Bi2S3-90PM) was observed with AHA samples. Amounts of 1.70 and 0.936 g of purified product were obtained for the OA and AHA samples, corresponding to a respective yield in bismuth of 95% and 72% (based on TGA analysis, Figures S3 and S13). Besides being done in the absence of hazardous solvents or external heating, these synthesis are also economically efficient, with the cost for scale-up reactions being approximately $2.61 CDN per gram of purified 5OA@Bi2S3-90-PM and $4.56 CDN per gram

Figure 3. TEM images and size distribution histograms of AHAcapped Bi2S3 NPs: (A1 and A2) 5AHA@Bi2S3-90-MM50 (n = 120); (B1 and B2) 5AHA@Bi2S3-90-MM100 (n = 150); (C1 and C2) 10AHA@Bi2S3-90-MM50 (n = 75); (D1 and D2) 10AHA@Bi2S3-90MM100 (n = 150); (E1 and E2) 5AHA/PEG@Bi2S3-90-MM50 (n = 250). Scale bars represent 50 nm.

of purified 5AHA@Bi2S3-90-PM (see Supporting Information for experimental details and cost analysis). 7769


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Chemistry of Materials Synthesis of PEG-Functionalized NPs. Finally, we explored another strategy to obtain water-soluble biocompatible Bi2S3 NPs through milling and aging, by direct surface ligand conjugation with poly(ethylene glycol) (PEG) polymers. Namely, PEG polymers are often used to make NPs pharmaceutically relevant by reducing surface protein adsorption,65−67 avoiding NP recognition by the mononuclear phagocyte system and increasing their circulation time in vivo.65−67 To afford directly biocompatible PEGylated Bi2S3 NPs by mechanochemistry, the amino-terminated polymer mPEG-NH2 (MW = 5000 mg/mol, 10 mol % NH2-content) was added into the reaction mixture ahead of a typical AHAcapped Bi2S3 NP synthesis. TEM images (Figure 3E) of the product revealed NPs 3 nm in diameter, which is ca. half the size of pure AHA-capped Bi2S3 NPs obtained under the same conditions, suggesting that attachment of the mPEG-NH2 hinders NP growth. An infrared analysis of the synthesized NPs (Figure S14 and Table S2) clearly revealed the characteristic adsorption bands of AHA in 5AHA@Bi2S3-90MM50, while 5AHA&PEG@Bi2S3-90-MM50 exhibited all the characteristic bands of both AHA and mPEG-NH2. We conclude that the synthesized Bi2S3 NPs are stabilized by a composite of mPEG-NH2 and AHA. UV−vis of 5AHA&PEG@Bi2S3-90-MM50 also reveals an absorbance edge observed at 305 nm. It is blue-shifted with respect to its AHA-only counterparts, consistent with the smaller NP sizes obtained (Figure S11). Bi2S3 NP Solubility and μCT Analysis. In order to establish that ultrasmall Bi2S3 NPs produced by mechanical activation would be viable as contrast probes for CT imaging, we explored their solubility and solution μCT contrast generation. Solubility was evaluated in water and phosphate buffered saline (PBS) solution, a physiologically representative buffer used as a solvent for NP intravenous injection formulations, a medium relevant for contrast agents.68 For 5AHA@Bi2S3-90-MM50 and 5AHA&PEG@Bi2S3-90-MM50 saturated suspensions samples in water, the measured concentrations were 14.8 and 24.3 mM, respectively, and were stable for at least 2 h. In PBS, the corresponding values were 74.7 and 74.7 mM, respectively. Importantly, the PBS suspensions were stable for over 24 h and were used to evaluate radiodensity as a function of concentration. The concentration of bismuth in each suspension was evaluated by ICP (Figure 4 and Table S3). Two parallel results were collected for each sample, and the mean concentration of bismuth was expressed with corresponding Hounsfield unit (HU) values, calibrated for each dilution by referencing to air (HU = −1000) and PBS (HU = 0). For both 5AHA&PEG@Bi2S3-90-MM50 and 5AHA@Bi2S3-90-MM50 samples, the concentrated samples of 0.075 M showed good radiodensity reponses, of 1437 ± 0.0 HU and 1335 ± 33.8 HU, respectively, on par with the best reports in the literature.49 For all explored concentrations, the HU values for both NPs were very close to the concentration values determined by ICP, demonstrating that the herein generated Bi2S3 NPs can be reliably used as PBS-suspended contrast agents over an order of magnitude of concentrations.

Figure 4. Experimental radiodensity for the Bi2S3 NP samples 5AHA@Bi2S3-90-MM50 and 5AHA&PEG@Bi2S3-90-MM50 as a function of bismuth concentration (M) measured by ICP. Error bars represent standard deviation of the CT value (in Hounsfield units) for 20 random measurements (circular regions of 2r = 3.0 mm, 11.1 pixels/mm) about the μCT images of each sample. Opacities of PBS and air were calibrated to HU = 0 and HU = −1000, respectively. Inset: μCT images of 0.075 M 5AHA@Bi2S3-90-MM50 and 5AHA&PEG@Bi2S3-90-MM50 samples with PBS for comparison.

aqueous, or physiological media. Thorough characterization by XPS, TEM, MALDI-TOF, and XRD revealed that the pure Bi2S3 NPs with well-defined, monodisperse sizes, ranging from 2 to 8 nm in diameter, were easily accessed, in contrast to previous mechanochemical techniques that led to NP sizes in the range 100−300 nm, with a mean crystallite size of 26 nm.38 The effects of the ligand nature, the milling duration, the ligand/bismuth ratio, and the grinding technique (mixer milling, planetary milling or manual grinding) were extensively studied, and the use of planetary milling devices enabled the scale-up to yield multigram quantities of each product. Further distinguishing this methodology from those conventionally employed to generate similar NPs, all syntheses were performed without solvents, without heating, and under aerobic conditions. This, combined with herein demonstrated excellent X-ray attenuation properties of selected NP systems in physiological media, provides a clear illustration of how unconventional and solvent-free approaches can lead to novel inexpensive, materials- and energy-efficient routes to advanced nanomaterials. Future research will focus on the use of these materials for in vivo applications. In particular, the behavior of the produced nanoparticles in suspension, the potential formation of aggregates, and their ability to cross biological barriers will be thoroughly evaluated. While this method is so far unique for Bi2S3, we believe it may develop into a novel, more general pathway to access ultrasmall and monodisperse metal chalcogenides and binary species, in a size range that conventional techniques do not allow researchers to explore.

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CONCLUSIONS Mechanical activation enabled the unprecedented solvent-free, room-temperature bottom-up assembly of small, monodisperse Bi2S3 NPs from solid reagents. This operationally simple process enabled the synthesis of a variety of Bi2S3 NPs, differently functionalized for suspension in either organic, 7770


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ASSOCIATED CONTENT

S Supporting Information *

REFERENCES

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.7b02134. Materials and methods, characterization, additional materials characterization, synthesis cost analysis, XPS spectra, TGA spectra, PXRD diffractograms, expanded MALDI-TOF windows, scale-up TEM images, IR spectra and their assignments, experimental radiodensity table, and UV−vis results (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Phone: +1 (514) 398-4564. Fax: +1 (514) 398-1689. E-mail: [email protected]. ORCID

Tomislav Frišcǐ ć: 0000-0002-3921-7915 Audrey Moores: 0000-0003-1259-913X Author Contributions

M.Y.M. and H.B. designed, performed, and characterized all experiments. M.Y.M. and H.B contributed equally. T.B. designed, performed, and characterized preliminary experiments. N.K.S. developed the method for the MALDI-TOF characterization. J.M.K., T.F., and A.M. supervised M.Y.M., H.B., and T.B. M.Y.M., H.B., A.M., and T.F. cowrote the manuscript, and J.M.K. edited the manuscript. Funding

We acknowledge the Natural Science and Engineering Research Council of Canada (NSERC) Discovery Grant program, the NSERC-Collaborative Research and Training Experience (CREATE) in Green Chemistry, the Canada Foundation for Innovation (CFI), the Canada Research Chairs (CRC), the Fonds de Recherche du Québec-Nature et Technologies (FRQNT) Equipe program, the Centre for Green Chemistry and Catalysis (CGCC), and McGill University for their financial support. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Dr. David Liu and Dr. Lihong Shang for their technical help and discussions on TEM and XPS, respectively. Dr. Monika Rak and Mary Bateman are thanked for training on mechanochemistry and ICP-OES techniques, respectively. Dr. Madhu Kaushik is thanked for insightful comments on the manuscript.

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ABBREVIATIONS NP, nanoparticle; Bi2S3, bismuth sulfide; OA, oleylamine; AHA, sodium 6-aminohexanoate; PEG, poly(ethylene glycol); MG, manual grinding; PM, planetary ball milling; MM, mixer ball milling; LAG, liquid assisted grinding; CT, computed topography; TEM, transmission electron miscroscopy; XPS, X-ray photoelectron spectroscopy; TGA, thermogravimetric analysis; PXRD, powder X-ray diffraction; MALDI-TOF MS, matrixassisted laser desorption/ionization time-of-flight mass spectroscopy; HU, Hounsfield unit; UV−vis, ultraviolet−visible spectroscopy 7771


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Mechanically Activated Solvent-Free Assembly of Ultrasmall Bi2S3

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