High yield boron based nanosheets from layered magnesium boride in water

1. Supporting Information
Simple, Green, and High-Yield Production of Boron-Based
Nanostructures with Diverse Morphologies by Dissolution
and Recrystallization of Layered Magnesium Diboride
Crystals in Water
Harini Gunda, Saroj Kumar Das, and Kabeer Jasuja*[a]
cphc_201701033_sm_miscellaneous_information.pdf

2. 1. TEM/HR-TEM/EDX/EELS/STEM analysis of magnesium boride nanostructures of the
filtrate sample at different aging times obtained with ultrasonication
The formation of dispersed phase in the filtrate sample upon aging was studied by performing TEM analysis of the sample at
different aging times (viz. 0 h, 24 h, 48 h, and 72 h) is shown in Figure S1(i). TEM analysis of the nascent filtrate sample
shows the presence of nanodots (Figure S1 (ii)), filtrate sample aged for 24 hours shows nanograins (suggesting the
transformation of nanodots into nanograins), and the coalescence of nanograins resembles bridged nanostructures (Figure S2).
Sample aged for 48 hours displays nanograins with a higher degree of coalescence as well as mesocrystals (Figure S3 (i)).
Sample aged for 72 hours shows the presence of flake-like nanostructures with embedded thicker regions and few
nanostructure resembling nano garlands (Figure S4 (i)). The respective HR-TEM images, TEM/EDX, EELS, and STEM analysis for
the nanostructures prepared from different aging times (t=0, 24, 48, and 72 h) are presented in Figures S1 (iii), S3 (ii), and S4 (ii)
respectively.
Figure S1 (i). Transmission Electron Microscopy (TEM) images of the filtrate at different aging times deposited on a 300 mesh size copper grid coated with a lacey
carbon film: (a)-(b) are the images of the filtrate at zero hour showing the presence of nanodots (<20 nm); (c)-(d) dispersion aged for 24 hours shows the presence
of nanograins and their coalescence with two-dimensional (2D) oriented attachment resembling bridged nanostructures; (e)-(f) dispersion aged for 48 hours shows
higher degree of coalescence of nanograins resembling bridged nanostructures as well as mesocrystals; (g)-(i) dispersion aged for 72 hours shows the presence of
nanoflakes and few resemble like a nanogarland.

3. TEM images of the nascent filtrate sample
Figure S1 (ii). TEM images of the nanostructures (resembling nanodots) immobilized from the nascent filtrate sample.

4. Figure S1 (iii). TEM/HR-TEM/EDX/EELS/STEM analysis of a pre-nucleation clusters obtained at 0 h of aging the filtrate sample: (a) Typical TEM image of pre-
nucleation clusters prepared by aging the filtrate sample for 0 h and (b) HR-TEM image of the selected dashed white box in (a); (c-f) STEM image and the
corresponding elemental mapping; (g) TEM/EDX; (h) Boron EELS spectrum (192−214 eV).

5. TEM images of the filtrate sample aged for 24 hours
Figure S2. TEM images of the nanostructures (resembling nanograins) immobilized from the dispersion aged for 24 hours.
TEM images of the filtrate sample aged for 48 hours
Figure S3 (i). TEM images of the nanostructures (resembling bridged nanostructures/mesocrystals) immobilized from the dispersion aged for 48 hours.

6. Figure S3 (ii). TEM/HR-TEM/EDX/EELS/STEM analysis of nanostructures obtained at 48 h of aging the filtrate sample: (a) Typical TEM image of the nanostructure
prepared by aging the filtrate sample for 48 h and (b-c) HR-TEM image of the selected dashed white box in (a); (d-g) STEM image and the corresponding elemental
mapping; (h) Boron EELS spectrum (192−214 eV); (i) TEM/EDX.

7. TEM images of the filtrate sample aged for 72 hours
Figure S4 (i). TEM images of the nanoflakes (some resemble nano garlands) immobilized from the dispersion aged for 72 hours.

8. Figure S4 (ii). TEM/HR-TEM/EDX/EELS/STEM analysis of nanostructures obtained at 72 h of aging the filtrate sample: (a & e) Typical TEM image of the
nanostructure prepared by aging the filtrate sample for 72 h and (b-d) HR-TEM image of the selected dashed white box in (a); (f-i) STEM image and the
corresponding elemental mapping; (j) TEM/EDX; (k) Boron EELS spectrum (192−214 eV).
2. ICP-AES analysis with sample calculation:
From ICP-AES analysis of the filtrate sample that was allowed to age for different times, we obtained the concentrations of Mg
and B (mg/L), and calculated their stoichiometric ratios and summarized in Table 1 (main file).
Formula for stoichiometric ratio calculation:
concentration of Mg obtained from ICP − AES
Atomic weight of Mg
∶
concentration of B obtained from ICP − AES
Atomic weight of B
Sample stoichiometric ratio calculation for the filtrate sample aged for zero hour =
377.31
24.30
∶
817.72
10.81
= 0.41: 2
The average stoichiometric ratio of Mg and B in the filtrate at different aging times is Mg: B ≈ 0.41:2, comparing with the
standard MgB2 (Mg: B = 0.99:2), shows the reduction in the stoichiometric value of Mg, indicating that the filtrate sample at
different aging times is rich in boron. The nascent filtrate sample appears golden yellow in color. To check if any contamination
is yielding golden yellow color to the filtrate, we also conducted full scan elemental analysis (using ICP-AES) (See Table S1). Full

9. scan elemental analysis shows that the DI water that we used as a solvent for the synthesis does not contain any elements,
suggesting 100% purity of the solvent. For the standard MgB2 powder it shows the elements Ti, Cr, Fe, Co, Ni, Cu, Ba, and Hg in
very trace amounts, which agrees well with the quality of the MgB2 powder used (≥99% purity). The residue left at the bottom
of the vessel also showed the trace amounts of similar elements as shown in MgB2. The liquid residue contains the trace
amount of Hg, but the solid residue (vacuum dried form of the residue left on the filter paper after vacuum filtration) does not
contain even trace amounts of Hg. This suggests that vacuum drying eliminated the trace amounts of Hg. Golden yellow color
filtrate shows the absence of the elements Ti and Cr, suggesting that vacuum filtration eliminated the elements Ti and Cr but
added As and Bi in trace amounts. Therefore, even though the full scan elemental analysis showed the presence of elements
other than Mg and B but as they are all in very negligible amounts, we anticipate that the golden yellow color of the filtrate is
not due to any of the other elements. Therefore, the golden yellow color of the nascent filtrate can be attributed to the
presence of nanodots derived from MgB2, which becomes colorless upon aging can be attributed to the presence of thicker
nanoflakes.
Table S1: Full scan elemental analysis of various samples using ICP-AES
Sample Name Elements
B Mg Ti Cr Fe Co Ni Cu As Ba Hg Bi
DI Water (L) - - - - - - - - - - - -
≥ 99% purity MgB2
(S)
        -   -
Residue (L)         -   -
Residue (S)         -  - -
Filtrate (L)   - -        

10. 3. TEM, HR-TEM, SAED, and FE-SEM/EDX studies at different aging times of the filtrate
sample obtained with ultrasonication
Figure S5. TEM and SAED patterns of the nanostructures present in the filtrate sample at different aging times.
From the TEM and SAED patterns of the filtrate sample at different aging times, we found that the nanodots and
nanograins are amorphous in nature (Figure S5 a-c). While the thicker nanostructures are crystalline and
polycrystalline in nature (Figure S5 d and f) and the thinner crumpled, nanosheets are amorphous in nature (Figure S5
e). Some more HR-TEM images and their respective SAED patterns and Inverse FFT along with the line profiling are
shown in the Figure S6. The micrograph (Figure S6 a) indicates the HR-TEM of the nanostructure obtained after aging
for 48 h, which shows polycrystalline nature as indicated by its SAED pattern (see inset of Figure S6 a). The Inverse FFT
of the selected region of Figure S6 a, is shown in the Figure S6 d, and the line profiling of the marked line is shown as
inset (i) indicating the d spacing as 0.19 nm. We also observed the presence of multilamellar structures, which are
hollow centrally, and merging up in the form of a dumbbell shape (Figure S6 b). Liu et al. earlier reported similar kind
of structures and termed them as Multi-Walled Boron Nanotubes (MWBNTs).[1] The selected area electron diffraction
pattern (SAED) of the dumbbell shaped MWBNTs shows ring-like patterns indicating that they are polycrystalline in
nature (see inset of Figure S6 b). The d spacing between the layers in MWBNTs is 0.43 nm, and at the point of merging
of the two MWBNTs, it is 0.33 nm respectively and is shown in Figure S6 b. It is pertinent to note that the interlayer
spacing at the point of the merging of the MWBNTs matches with the value shown by Liu et al. (~0.32 nm).[1] The
micrograph in Figure S6 c shows the presence of a single nanodots/quantum dot embedded in a thicker nanosheet

11. and the selected region Inverse FFT is shown in Figure S6 e. Also, the selected line profile is shown as inset (ii)
indicating its d spacing as 0.29 nm, which does not match with any of the d spacing values of the MgB2 crystal
indicating a constitutional modification.
Figure S6. HR-TEM, IFFT, line profiling and, SAED patterns of the thicker nanostructures: (a) HR-TEM image showing the fringes and the SAED shown in the inset
indicate its polycrystalline nature and the selected region IFFT is shown in the fig. (d) where the selected line profile is shown in the inset (i) indicating a d spacing of
0.19 nm; (b) HR-TEM image showing the merging of multilamellar structures ((or) Multi-Walled Boron Nanotubes (MWBNTs)) in the form of double dumbbell shape
and its SAED in the inset shows it is in polycrystalline in nature; (c) HR-TEM image showing the presence of a single nanodots/quantum dot in the thicker
nanostructure and the selected region IFFT is shown in the fig. (e) where the selected line profile is shown in the inset (ii) indicating a d spacing of 0.29 nm.
FE-SEM/EDX:
We have performed FE-SEM analysis on the liquid drop cast and powder samples of the filtrate samples at different aging
times. FE-SEM images at zero hour (Figure S7) shows the presence of the pre nucleation clusters (<10 nm), up on aging the
filtrate sample to 24 hours (Figure S7) shows the oriented attachment of the nanodots to form nanograins like structures. The
filtrate sample aged for 48 hours (Figure S7) shows the fusing of nanograins to form nanoflakes. The sample aged for 72 hours
(Figure S7) shows the presence of the nano flakes and nanosheets. The composition of these nanostructures is characterized
through the EDX analysis, which is shown in Figure S8.

12. Figure S7. FE-SEM images of the filtrate sample at different aging times: (a) filtrate sample at 0h shows the presence of nanodots; (b and c) filtrate sample at 24h
shows the oriented attachments of the nanodots to grow into nanograins like structures; (d-f) 48 h aged filtrate sample clearly shows the oriented attachment of
the nanograins and (g) shows the transformation of nanograins to nanoflakes through the oriented attachment; (h and i) filtrate sample at 72h of aging shows the
presence of nanosheets or nanoflake like structures.
FE-SEM/EDX analysis of the samples was performed to qualitatively identify the elemental composition. Figure S8 shows the FE-
SEM images of the nanostructures at different aging times and the qualitative elemental composition of the parent MgB2 and
the boron-based nanostructures. The EDX analysis of boron-based nanostructures reported here is the average qualitative
elemental composition of the filtrate samples at different aging times. FE-SEM/EDX analysis suggests the presence of elements
boron, oxygen, and Mg indicating that these are functionalized magnesium boride nanostructures, which are rich in boron.

13. Figure S8. FE-SEM/EDX analysis of filtrate sample at different aging times: (a-d) shows the FES-SEM images of the filtrate sample at 0h, 24h, 48h, and 72h of aging
respectively; (e and f) shows the EDX analysis of the parent MgB2 and boron-based nanostructures.
4. Customized vessel for the collection of gasses during ultrasonication
Figure S9. Experimental setup designed for the collection of gases during ultrasonication: (a) Full view of the flat-bottomed double walled jacketed vessel,
covered with a customized disc-shaped cap carrying a 90° vent on the side (for exiting any evolved gases) and a circular aperture in the middle (for allowing in
the ultrasonicator probe); (b) Closer view of the customized cap showing the collection of gases in a syringe; (c) Storing of collected gases in a screw-cap valve
Supel-Inert foil gas sampling bag connected through a small flexible polyethylene tube with a flow controller. The gas can be retained in the sampling bag for
~ five days.
During the process of ultrasonication of standard MgB2 with water at 25°C, we the observed evolution of gasses from the
mixture. To obtain insights into the possible interactions between MgB2 and water during ultrasonication, we need to collect
and analyze the evolving gasses. To collect the evolving gasses, we customized the flat-bottomed jacketed glass vessel (with
coolant circulating at 25°C) consisting of a flat neck with a lid. The customized lid consists of a central aperture for
ultrasonicator and a 90-degree hole to enable the exit of any evolved gasses (see Figure S9). We also observed the evolution of
gases even at lower temperatures of 5, 10, 15, and 20°C. At all the temperatures mentioned above, we collected the evolved
gasses through a syringe and stored in a gas sampling bag (Supel-inert foil with Thermogreen LB-2 Septa) for the further
analysis (See main file GC-MS section for the analysis results). Thus, the synthesis of boron-based nanostructures by

14. ultrasonication was carried out in this customized setup. The temperature of the suspension during ultrasonication is measured
at regular intervals and the data is presented in table S2.
Table S2: Temperature of the suspension during ultrasonication at regular intervals
Ultrasonication on time (minutes) Suspension temperature (ᵒC)
5 minutes 27
10 minutes 26
15 minutes 26
20 minutes 29
25 minutes 28
30 minutes 28
5. Zeta Potential Analysis:
Zeta potential analysis of the filtrate sample at different aging times is observed to know the stability of the sample. The zeta
potential values of the filtrate sample are plotted against the aging time (days) for seven days (see Figure S10). From the zeta
potential values, it confirms that the stability of these boron-based nanostructures is on the verge of incipient instability and
thus we observed a moderate degree of coalescence between these nanostructures (see TEM images).
Figure S10. Stability analysis of the filtrate sample for one week using zeta potential: The filtrate sample shows an increasing trend in the potential values for the
initial three days and later shows a fluctuating trend. The negative zeta potential indicates the presence of negative surface charge and their magnitude specifies
that the nanostructures be mostly in the stage of incipient instability.

15. 6. Raman Analysis:
Raman spectra of the samples were acquired from the range of 100 cm-1 to 800 cm-1 with an excitation wavelength of
785 nm. For the standard MgB2 powder, the spectra were recorded using varying laser powers (5%, 10%, 50%, and 100%). The
presence of peaks is apparent when 50% laser power source is used. At 100% laser power, we could not acquire any data due
to overheating of the sample. Therefore, the Raman spectra for all the samples were further acquired only by using 50% laser
power source. The Raman microscopic images are presented in the Figure S11 (b-f).
Figure S11. Raman microscopic images of standard MgB2 powder and filtrate samples and A2umode in FTIR analysis of the samples: (a) shows a representative image
for the powder form of the nanostructures; (b) Raman microscopic image showing the overheating of standard MgB2 powder resulted due to the usage of 100%
laser power source; (c)-(f) Shows the Raman microscopic images of the lyophilized filtrate samples at 0, 24, 48, and 72 hours of aging; (g) shows the FTIR spectra of
the samples indicating the A2u mode in the range of 400 cm-1 to 410 cm-1, indicating the presence of boron and Mg planes moving against each other.
7. IR Active A2u mode from FTIR Analysis:
Standard MgB2 powder shows a broad band at 405.59 cm-1 indicating the presence of IR active A2u mode (that is indicative of B
and Mg planes moving against each other)[2,3]. Whereas lyophilized filtrate samples of 24, 48, and 72 hours shows A2u mode
bands at 404.08 cm-1
, 402.71 cm-1, and 408.95 cm-1 respectively also indicates the out-of-plane boron vibrations.[3] A2u mode is
also reported at ~394 cm-1 [4], which could not be detected in the spectrum range of 400 cm-1 to 4000 cm-1 and this could be the
reason for the absence of A2u mode for the filtrate sample of zero hours in the given spectral range.
8. XRD Analysis:
XRD analysis of the parent MgB2 powder and the powder form of the filtrate samples at different aging times were
performed to understand the crystalline nature and the phase of the materials. As shown in Figure S12, the parent MgB2
powder shows sharp diffraction peaks indicating its crystalline nature and the peaks match well with the reported values
for standard MgB2 in the PDF 00-038-1369 from ICDD data. The powder form of the filtrate sample at different aging times
shows three broad peaks indicating the weak crystalline nature of the nanostructures and suggests that the growth of the
nanostructures is in lateral directions only. The phase analysis of the nanostructures obtained at different aging times
shows that two of the broad peaks matches with the (101) and (100) peaks of parent MgB2 and a peak at ~17°, which is not
present in the parent MgB2, matches with the reported value for the borane (B20H26) in the PDF-03-066-0038 from ICDD
data. We observed that with increasing the aging time the intensity of the peak at ~17° is increasing while the intensity of
(100) peak is decreasing suggesting that the borane functionality increases with aging. The presence of borane

16. functionality can also be corroborated with the FTIR analysis as shown in Figure 7b (main file). Thus, the XRD analysis
suggests that these are weakly ordered-functionalized magnesium boride nanostructures.
Figure S12. XRD analysis of the standard MgB2 powder and the filtrate sample at different aging times: XRD of standard MgB2 indicates crystalline nature, whereas
XRD of the powder form of the filtrate sample at different aging times indicates weak crystallinity.
XRD analysis of the precipitate:
To obtain the insights about the precipitate, we carried out the XRD analysis of the dried precipitate. The phase analysis of the
precipitate matches well (~99%) with the magnesium diboride of the form Mg0.92B2 having the PDF 01-079-6150 from the ICDD
data is as shown in Figure S13. In addition to the peaks of Mg0.92B2, we found the presence of impurities like MgO [PDF 01-071-

17. 3631], Mg(OH)2 [PDF 01-078-3956 and PDF 01-082-2453, Syn], and B20H26 [PDF 03-066-0038] (heavier boron hydride), which are
labelled with different symbols is shown in the Figure S13. From the XRD analysis, it is evident that the precipitate is mostly of
the form magnesium diboride but partly functionalized with hydrides, oxides, and hydroxide functional groups.
Figure S13. XRD analysis of the precipitate obtained after filtration: the XRD analysis of the precipitate matches well (~99%) with the magnesium diboride (Mg0.92B2)
compound and the other impurities present are found to be MgO, Mg(OH)2, and B20H26 that are labelled with various symbols on the peaks.
9. Processing of an HRTEM image using Gatan DigitalMicrograph:
The obtained HR-TEM image is loaded into the Gatan software and calibrated by choosing “calibrate image” option
from the Microscope menu. To find the FFT of the HR-TEM image, we select an area by using square option (ROI-Region of
Interest) and then select “LIVE-FFT” option from the process menu. Get the diffraction pattern by adjusting display control
options. Compare the obtained diffraction pattern with the standard pattern (by drawing all possible lines passing through the
reflection points and measure angle values and distance values from the diffraction pattern) and finally obtain the beam
direction (hkl) matching with the standard pattern. Then index the obtained diffraction pattern.

18. For finding the d spacing of the generated FFT, add a spot mask on the reflection points of the FFT image and then select
“apply mask-keep the masked area” from the process menu. Then select “Inverse FFT” from the process menu, and a scale bar
can be generated by selecting “Add a new scale-mark” from the toolbar options. The line profiling of the obtained Inverse FFT
(IFFT) can be generated by choosing “line profile” from the toolbar options and then select the ROI on the IFFT. Select the
desired peak midpoints (let us say ‘Y’), and Y peaks correspond to a distance of X nm then calculate the distance for one peak
then that gives the d spacing value.
10. UV-Vis Absorption Spectroscopy:
The UV-Vis spectra of boron-based nanostructures are recorded for different aging times. We found that these boron-based
nanostructures, exhibit strong absorption in the UV regime (see Figure. S14 a). The obtained absorption spectrum for zero
hours was deconvoluted to four daughter spectra using the fityk software. The peaks of daughter spectra are located at ~191
nm (~6.49 eV), ~211 nm (~5.87 eV), ~254.7 nm (~4.86 eV), and ~302 nm (~4.10 eV), we expect the introduction of various
functional groups results in new electron states as shown in our earlier study.[5] The ability of these boron-based
nanostructures to absorb strongly in the UV regime makes these nanostructures as prospective candidates for making
transparent UV absorbing materials.
Figure S14. UV-Vis absorption spectra of filtrate sample at various hours: (a) shows the UV-Vis absorption spectra of filtrate sample at 0, 24, 48, and 72 hours
indicating the strong absorption in the UV regime; (b) deconvolution of UV-Vis spectra of the zero hour filtrate sample shows the presence of four daughter peaks at
191, 211, 254.7, and 302 nm respectively.

19. 11. TEM images at different aging times of the filtrate sample obtained without
ultrasonication
Knowing the occurrence of the chemical reaction of the MgB2 crystals with water at room temperature, we carried out the
experiment by simply putting the MgB2 crystals in water and leaving the suspension for 24 hours at room temperature followed
by filtration using 0.22µm filter paper. Similar to the case with ultrasonication, the filtrate we obtained without ultrasonication
is also in golden yellow color and observed the similar physical changes in the color upon aging the filtrate, and finally, it
appeared colorless at the end of 72 hours of aging. This physical change in color and the formation of dispersed phase (from
strong Tyndall effect) similar to the case with ultrasonication suggests the growth of nanostructures by oriented attachment
following the non-classical crystallization pathway. From the TEM, HRTEM, and SAED patterns (see Figures. S15 – S17) it
confirms that the boron-based nanodots, nanograins, and nanoflakes form upon aging the filtrate sample for 72 hours. We also
observed more of crumpled nanoflakes (nano garlands) in the case when ultrasonication is used, whereas mostly flat
nanoflakes in the case without ultrasonication.

20. Figure S15. TEM images of the nanostructures obtained without ultrasonication immobilized on an ultrathin carbon film on a lacey carbon coated on a 400-
mesh copper grid.

21. 12. TEM, HR-TEM, and SAED studies at different aging times of the filtrate sample
obtained without ultrasonication
Figure S16. TEM, HR-TEM, and SAED patterns of the nanograins and neck formation between nanograins obtained at zero and 24 hours of aging shows the
amorphous nature of the nanostructures.
Figure S17. TEM, HR-TEM, and SAED patterns of the nanostructures obtained at 48 and 72 hours of aging shows crystalline nature of the nanostructures. Panel i,
shows the presence of honeycomb lattice arrangement with a d spacing value of 0.27 nm.

22. References:
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[2] J. Kortus, I. I. Mazin, K. D. Belashchenko, V. P. Antropov, L. L. Boyer, Physical Review Letters 2001, 86, 4656–4659.
[3] J. a. Alarco, A. Chou, P. C. Talbot, I. D. R. Mackinnon, Phys. Chem. Chem. Phys. 2014, 16, 24443–24456.
[4] K. P. Bohnen, R. Heid, B. Renker, Physical Review Letters 2001, 86, 5771–5774.
[5] S. K. Das, A. Bedar, A. Kannan, K. Jasuja, Scientific Reports 2015, 5, 10522.