Ching-cheh Hung, Janet Hurst, Diana Santiago, and Richard B. Rogers

Glenn Research Center, Cleveland, Ohio

Exfoliation of Hexagonal Boron Nitride via

Ferric Chloride Intercalation

NASA/TM—2014-218125

April 2014
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Ching-cheh Hung, Janet Hurst, Diana Santiago, and Richard B. Rogers

Glenn Research Center, Cleveland, Ohio

Exfoliation of Hexagonal Boron Nitride via

Ferric Chloride Intercalation

NASA/TM—2014-218125

April 2014

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
Acknowledgments

The authors thank NASA Aeronautical Sciences Project for supporting this research and Momentive Performance Materials, Inc., 

of Strongsville, Ohio, for supplying the original hBN powder samples.

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at the NASA Glenn Research Center.

Level of Review: This material has been technically reviewed by technical management. 

This report is a formal draft or working 

paper, intended to solicit comments and 

ideas from a technical peer group.
NASA/TM—2014-218125 1 

Exfoliation of Hexagonal Boron Nitride via 

Ferric Chloride Intercalation 

Ching-cheh Hung, Janet Hurst, Diana Santiago, and Richard B. Rogers 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Summary 

NaF was used as an activation agent to successfully intercalate FeCl3 into hexagonal boron nitride 

(hBN). This reaction caused the hBN mass to increase by ~100 percent, the lattice parameter c to decrease 

from 6.6585 to between 6.6565 and 6.6569 Ǻ, the x-ray diffraction (XRD) (002) peak to widen from 

0.01° to 0.05° of the full width half maximum value, the Fourier transform infrared (FTIR) spectrum’s 

broad band (1277 cm–1 peak) to change shape, and new FTIR bands to emerge at 3700 to 2700 and 

1600 cm–1. This indicates hBN’s structural and chemical properties are significantly changed. The 

intercalated product was hygroscopic and interacted with moisture in the air to cause further structural 

and chemical changes (from XRD and FTIR). During a 24-h hold at room temperature in air with 

100 percent relative humidity, the mass increased another 141 percent. The intercalated product, hydrated 

or not, can be heated to 750 °C in air to cause exfoliation. Exfoliation becomes significant after two 

intercalation-air heating cycles, when 20-nm nanosheets are commonly found. Structural and chemical 

changes indicated by XRD and FTIR data were nearly reversed after the product was placed in HCl, 

resulting in purified, exfoliated, thin hBN products. 

1.0 Introduction 

The structural similarity between hexagonal boron nitride (hBN) and graphite is highlighted by the 

widespread use of the term “white graphite” for boron nitride (BN). This similarity has led to the efforts 

of using carbon chemistry and technology as guidance for research in BN chemistry and technology. Such 

efforts resulted in the synthesis of cubic boron nitride (cBN) based on the structure of diamond (Ref. 1), 

and boron nitride nanotubes (BNNT) based on the structure of carbon nanotubes (Ref. 2). 

On the other hand, the differences in chemical bonding between graphite and hBN leads to 

differences in properties such as electrical conductivity and reactivity to air at high temperature. The ionic 

interlayer bonding in hBN is much stronger than the Van der Waals force between the graphite layers, 

causing differences in the reactivity in intercalation. This also leads to differences in the efficiencies of 

mass production of their respective exfoliated products for engineering applications. 

1.1 Intercalation and Exfoliation for Exfoliated Products and Graphene 

A layered material is “intercalated” when other chemicals are inserted into the layers. A layered 

material is “exfoliated” when the layered structure splits into thinner layers. Graphite can easily be 

intercalated (Ref. 3) and then exfoliated by driving intercalates out of the layers quickly and/or 

explosively. The process of intercalation-exfoliation of graphite has been applied for engineering 

applications. Fabrication of flexible graphite, or grafoil, is an example (Ref. 4). Recently there are reports 

that this process has been used to split graphite into graphene in large quantities (Ref. 5). 

The similarity between carbon and BN suggest the possibility that BN can easily be intercalated and 

exfoliated as well (Ref. 6). However, this is not the case. Starting from hBN instead of graphite, the 

above process to produce a large quantity of exfoliated hBN or “white graphene” has not been successful 

(Ref. 7). Intercalation of hBN is difficult. Alkali metals (Li, Na, and K) (Refs. 8 and 9) and fluorosulfate 

(S2O6F2) (Ref. 10) are among the few intercalates that were successfully intercalated into hBN. Doing this 
NASA/TM—2014-218125 2 

involves highly reactive chemicals and reactions. The feasibility of using these chemicals for mass 

producing exfoliated hBN or white graphene was not studied or discussed in these reports. The less 

reactive intercalates for graphite, such as metal chloride, was found to be unreactive to hBN. Most 

notably among them is ferric chloride (FeCl3). After examining the claims and counter claims, it is 

generally believed that intercalation of hBN with FeCl3 in particular or metal chloride in general is not 

likely (Refs. 3, 10, and 11). For producing exfoliated hBN, the less-efficient method of functionalization, 

sonication, and centrifuge is commonly used (Ref. 7). For white graphene, either plasma etching (Ref. 12) 

or micromechanical cleavage is used for minute quantities (Ref. 7). 

1.2 BN Nanotechnology: BNNT Intercalation and Exfoliation 

Although hBN exfoliation by way of intercalation with metal chloride has not been successful, recent 

efforts in BN nanotechnology suggests this can be done. Figure 1 shows the walls from two exfoliated 

BNNTs resulting from removing iron nanoparticles and other impurities from BNNTs during purification 

(Ref. 13). Also, although BNNTs cannot be intercalated by direct exposure to molten FeCl3, the wetting 

and cleaning effects of BNNTs by FeCl3 has been observed (Ref. 14). In addition, BNNTs intercalated 

with potassium and then exfoliated by reacting to water was successfully demonstrated (Ref. 15). This led 

to a hypothesis that if hBN may be chemically activated similar to BNNTs, intercalation of hBN with 

FeCl3 and subsequent exfoliation may be possible. 

This hypothesis is in parallel with the experience in carbon intercalation: Some of the graphite 

intercalation reactions need to be “activated” in order to proceed. For example, graphite cannot be 

intercalated with iodine unless the graphite is “activated” by bromine or HBr (Ref. 16). 
NASA/TM—2014-218125 3 

2.0 Methods and Experiments 

2.1 General Experimental Approach 

This research examines two processes to produce exfoliated hBN. 

Process 1:

hBN + FeCl A (intercalated product) Activation agent

3    (1) 

To determine the stability of the intercalated product in dry air, a portion of the intercalated product A 

was stored in dry air for 4 months and characterized twice during this period. The rest was used to 

synthesize the exfoliated hBN material: 

A B* B(exfoliated product) Heat Rinsewithwater   (2) 

The chemical reaction experiments conducted in this research for possible intercalation reactions are 

similar to those described in previous reports (Refs. 11 and 17), except in this report, sodium fluoride 

(NaF) was added to the original reactants. NaF was considered as a possible activating agent for 

intercalation because its aqueous solution with hydrochloric acid (HCl) was previously observed to attack 

and/or activate BNNTs (Ref. 13). The products of Reactions (1) and (2), A and B, were then further 

examined for evidence of intercalation and exfoliation. 

The processes of intercalation and exfoliation described above were repeated in order to see if the 

additional effort would cause further exfoliation. That is, 

B FeC1 C (intercalation) Activationagent  3    (3) 

C D (exfoliation) Heat Rinsewithwater (4) 

The products A to D were then further treated chemically. They were rinsed with HCl at room 

temperature to remove impurities and intercalates: 

A,B,C,or D HC1EA,EB,EC ,ED (5) 

Process 2:

The intercalated products (A or C) were exposed to room-temperature moist air for a period of time 

and characterized several times during this period to study the water-adsorbing characteristics of the 

apparently hygroscopic intercalated product: 

AorC A' or C'(hydration) wetair (6) 

The hydrated products were placed into a high-temperature furnace, and the moisture violently boiled off 

at a temperature much higher than 100 C. This was found to induce exfoliation to a greater extent. 

A'orC' B'orD'(exfoliation) Heat Rinsewithwater (7) 

Heat

Heat
NASA/TM—2014-218125 4 

The products A' to D' were then rinsed with HCl at room temperature to remove impurities and 

intercalates: 

HC1 ' ' ' ' A', B',C',or D' EA , EB , EC , ED (8) 

2.2 Chemicals, Apparatus, and Experimental Procedures 

Two different kinds of commercially available hBN powder were used in this research. One 

comprises large platelets mostly 20 to 80 m wide and 5 to 10 m thick. The other one comprises mostly 

small platelets, 200 to 800 nm wide and 80 to 200 nm thick. Both of them are well crystallized, as 

indicated by their significant x-ray diffraction (XRD) peaks for hBN. 

FeCl3 (98 percent) and NaF (99.98 percent) used in the experiments were purchased from Alfa Aesar. 

NaF was used as purchased. FeCl3, however, was distilled once immediately before being used in the 

intercalation reaction because it is highly hygroscopic. Its melting point and boiling point are 306 and 

315 °C, respectively. When it evaporates/sublimates, a fraction simultaneously decomposes into FeCl2

and Cl2. For distillation conducted in this research, FeCl3 was sublimated/evaporated at about 260 to 

330 °C and then condensed at about 30 °C lower. Based on the vapor pressure (as a function of 

temperature) during decomposition for FeCl3 (Ref. 18), the vapor pressure for Cl2 during distillation was 

4.4 torr at 260 C and 72 torr at 330 C. The FeCl3 pressure was 51 torr at 260 C and 688 torr at 

330 C under a system total pressure of 1 atm. 

The detailed experimental procedures are as follows: Precalculated quantities of hBN, distilled FeCl3, 

and NaF were weighed and mixed into a 50-ml test tube. The test tube was sealed using 

polytetrafluoroethylene (PTFE) tape, and then placed into a 500-ml reactor kettle, which is then sealed air 

tight. Pure nitrogen was then allowed to flow through valves into and out of the kettle to purge air and 

keep the system in an inert environment during the entire reaction period. The sample at the bottom of the 

test tube was heated to a temperature slightly below the melting point of FeCl3 (306 °C) for intercalation, 

and eventually to a temperature slightly above the boiling point of FeCl3 (315 °C) for letting the excess 

FeCl3 boil off from the product in the bottom of the test tube and then condense at the top of the tube 

where the temperature is lower due to the lighter thermal insulation. After the reaction and the system 

cooled, the product was removed from the test tube and stored in dry environment. Results of the 

procedure described in this paragraph are products A or C in Reactions (1) to (5). 

Samples of product A were then placed in a quartz watchglass, weighed, and placed into a furnace 

heated to 600 to 750 °C for a period ranged from 2 to 4 h using a preprogramed temperature schedule. 

After heating, the product is removed from the furnace, cooled, and rinsed with water. This is product B, 

described previously, from Reaction (2). This product was then further treated for intercalation according 

to the procedure described previously in Reaction (3) to form product C. In this research, some, but not 

all, of the product C was exposed to moist air, either at ambient humidity or at 100 percent relative 

humidity to form product C'. Both products C and C' were then placed in a quartz watchglass, weighed, 

put into a furnace heated to 600 to 750 °C for a period ranging from 2 to 4 h using a preprogramed 

temperature schedule, cooled, and then rinsed with water to result in products D (Reaction (4)) or D' 

(Reaction (7)), respectively. 

Concentrated (35 wt%) HCl was used to remove intercalates (Reactions (5) and (8)). 

Detailed reactant and product mass data and temperature schedule of the experimental runs used for 

this report are described in Table I. 

 
NASA/TM—2014-218125 5 

TABLE I.—SUMMARY OF INTERCALATION OF AS-PURCHASED COMMERCIAL hBN 

WITH FeCl3

Reactantsa

 Reaction temperature 

during two or three 

steps of sequential 

heating in nitrogen, 

temperature (C)/duration (h) 

Productsb

hBN 

type 

Mass ratio hBN mass 

content, 

percent 

Labeld

NaF 

to hBN 

FeCl3 

to hBNc 

L 0.120 2.7 315/12 340/2 --- 55 A1 

L 0.141 2.8 320/23 340/19 --- 45 A2 

L 0.115 2.3 290/14 320/30 355/16 54 A3 

L 0.190 1.7 240/25 285/22 330/21 42 A4 

S 0.14 2.7 290/3 330/38 --- 45 A5 a

Reactants were hBN, NaF, and excess FeCl3. L indicates large platelets, mostly 20 to 80 μm wide and 5 to10 μm thick, 

and S indicates small platelets, mostly 200 to 800 nm wide and 80 to 200 nm thick. b

Products of the intercalation reaction were not washed. They included hBN, FeClx where 2  x  3 (the intercalated 

chemicals), FeOCl, and NaCl. The presence of NaCl and absence of NaF or fluorine atoms were confirmed by XRD 

and EDS data. c

Boiling point of FeCl3 is 315 C. At this temperature, iron chloride vapor is in dimer form and is partially decomposed to 

gaseous Cl2 and solid FeCl2. At one atmosphere under this condition, the equilibrium partial pressures for Fe2Cl6 and 

Cl2 are 718 and 42 mmHg, respectively. d

These labels were used to identify the products described in text. 

For hydration (Reaction (6)), the products A or C were placed on either a glass slide or watchglass 

and exposed either to ambient air with known humidity or to an enclosed container containing liquid 

water for 100 percent relative humidity. 

2.3 Characterization Instruments 

The samples were characterized using Fourier transform infrared spectroscopy (FTIR), XRD, and 

field emission scanning electron microscopy (FESEM). 

An Agilent Cary 660 FTIR with an attenuated total reflectance (ATR) accessory was used to 

characterize IR bands near 1380 and 755 cm–1 for BN in the products. 

A Bruker D8 Advance X-Ray Diffractometer was used to find XRD peaks for hBN and identify the 

impurities in the products. The samples were normally scanned at 0.02° (2Ɵ value) per step unless 

otherwise stated when extra precision was required (0.005° per step in that case). The full width at half 

maximum (FWHM) values as the width for hBN’s (002) peak were calculated using the split-Pearson VII 

empirical fitting function. The (004), (006), and in some cases (008) peaks for hBN were used to 

accurately calculate the lattice parameter c using the fundamental parameters approach (Ref. 19) and the 

Pawley fitting method (Ref. 20) as implemented in the Bruker TOPAS software program. It is therefore a 

sensitive method to evaluate the state of intercalation. Nonhygroscopic samples, typically 10 mg in mass, 

were mounted as a thin layer on a flat “zero” background holder (ZBH), which consisted of a polished 

silicon wafer cut on a nondiffracting, high-index plane. Hygroscopic intercalated samples were mounted 

in a 0.5-mm deep well ZBH holder. The iron and chlorine concentrations for those samples were such that 

their x-ray penetration depths (95 percent contribution to the diffracted beam) were typically near 60 m. 

Under these conditions, the FWHM values were not affected by the thickness of the samples being 

scanned. 

A Hitachi S–4700II FESEM was used to study the morphology throughout the reactions studied in 

this research. Energy dispersive x-ray spectroscopy (EDS) was used to identify the chemical elements in 

the products. 
NASA/TM—2014-218125 6 

3.0 Results and Discussions 

3.1 XRD: Crystalline Lattice Structure and Phase Identification 

The large hBN platelets (mostly 20 to 80 m wide and 5 to 10 m thick) were highly crystalline as 

seen by sharp and intense XRD peaks. Once intercalated, their layered lattice structure changes, with their 

XRD peaks becoming lower and wider, and their lattice parameters, especially the c parameter (a measure 

of the interlayer spacing), will also change. Observation of lattice structure changes at hBN’s interior 

some distance away from the surface, at the reaction temperature of 240 to 360 C, signals that the 

chemicals surrounding the platelets may have entered the interior (i.e., intercalated). 

Figure 2 shows the experiments conducted in this research where large hBN platelets were 

intercalated and exfoliated for the first time. Note that the sample labels A1, A2, and A3correspond to the 

same labels in both Table 1 and the chemical label A in Reaction (1). The labels B*1, B*2, and B*3 

(heated but not rinsed) correspond to the intermediate product in Reaction (2). The labels EA3 and EB*3

correspond to the chemical label E (HCl treated) in Reaction (5) or (8). The hBN’s (002) peak width 

(FWHM) and the c parameters for the hBN reactant and all intermediate and final products were also 

included. We estimate the precision of the FWHM to be in the range of 0.01° based on observation of 

sample repetitions. This is compared to the 0.01 to 0.05° of the FWHM values and 0.02° scanning step 

value during data collection. The lattice parameter data were based on analysis of (004) and (006) peaks. 

We estimate the accuracy and precision to be in the range of 0.0005 Ǻ based on observation of sample 

repetitions and comparison to results with an internal standard. Even though the analysis program 
NASA/TM—2014-218125 7 

generates estimated standard deviations for the lattice parameter results, it is well known that the 

estimated standard deviation can be over an order of magnitude smaller than the true error (Ref. 21). 

Therefore, we prefer to state the above estimation of error, which is more conservative. After reacting to 

FeCl3 and NaF, changes in hBN’s lattice structures were observed. These changes, however, were mostly 

restored after the final rinse with 35 wt% HCl to result in pure, exfoliated hBN. According to the 

reasoning in the previous paragraph, this result indicates that the hBN was most likely intercalated, and 

mostly if not completely deintercalated, to become a thinner product having lattice structure similar to the 

original reactant as HCl removed all intercalates. 

The (002) peak width, as expected, becomes wider because intercalation introduced disorder into the 

lattice. Explanations of the changes of the lattice parameter c (and therefore the interplanar spacings 

between the BN layers) due to intercalation are beyond the scope of this research. It was slightly 

decreased during intercalation, then increased to a value slightly larger than the original hBN reactant 

during exfoliation in 750 °C air, and eventually returned to the original hBN value after HCl treatment. 

Note FeCl3 intercalation also causes the interplanar spacings between graphite layers to change. The 

changes, however, are small and only between graphite layers adjacent to the intercalate layer (Ref. 22). 

The similarity between the hBN reactant and its intercalated-then-deintercalated product (EB*3 in 

Fig. 2) observed here suggests that most—if not all—intercalates in the hBN layers were removed. This 

phenomenon is very different from graphite. Completely removing intercalate from graphite layers is very 

difficult. The “residue compound” left after the incomplete deintercalation of graphite exhibits XRD peak 

widths and c parameters generally larger than those of their precursor (Ref. 3). This difference is likely 

because that ionic forces are between the hBN layers, but Van der Waal’s force are between graphite 

layers. The stronger ionic force between the hBN layers could be sufficient to control the distances 

between the neighboring BN layers and reach the lowest energy state by driving out the chemicals in it. 

The graphite layers, with the weaker Van der Waal’s force between them, will reshape and eventually 

tightly enclose a small amount of intercalates in its structure. 

Another difference between graphite and hBN intercalation is the lack of staging phenomenon for 

hBN. In graphite, there are a certain number (n) of carbon layers between two intercalate layers. The 

regular insertion of intercalate layers into graphite results in a “stage n intercalated product” and new 

intercalation XRD peaks (Ref. 3). In hBN, the intercalate insertion seems to be random, as no new XRD 

peaks can be accounted for as “intercalation peaks.” 

Even though the very large (002) peaks were obtained, analyzing the implications of this XRD peak 

heights (or its total integrated intensity) is complicated because measured peak values are affected by 

many parameters, some of which are either not well known or difficult to control, such as chemical 

composition and preferred orientation of the samples being measured. Consequently, the XRD peak 

heights were not closely examined other than the general observations that hBN’s (002) peak heights 

were reduced during intercalation, and they were mostly restored after the subsequent exfoliation 

reactions by 750 °C air and cleaning by HCl. This is illustrated in Figure 3(a), which shows the relative 

heights of (002) peaks from samples of hBN reactant, A3, B*3, and EB*3, described in Figure 2. The full 

XRD scans of these four samples are shown in Figures 3(b) to (e). In these figures, no chemicals other 

than hBN were detected in the original hBN (Fig. 3(b)) and in the final product after HCl cleaning (EB*3

in Fig. 3(e)). In the intercalated sample (Fig. 3(c)), the major intercalate (iron chlorides) are not visible 

and are believed to be amorphous, but small impurity peaks of FeOCl and NaCl were detected. After the 

intercalated samples were heated in 750 °C in air, Fe2O3 (major intercalate) and NaCl were detected 

(see Fig. 3(d)). The presence of NaCl in A3 and B*3 is believed to be the result of reactions of NaF and 

FeCl3 during the intercalation reaction. The presence of FeOCl in A3 is caused by a trace of oxygen in the 

reaction system, as reported previously (Ref. 11). The oxygen may come from water that remained in the 

once-distilled FeCl3. It may also come from the reaction between NaF and the glass container. The 

presence of Fe2O3 is believed to be the oxidation product of FeCl3 and FeOCl. 

 
NASA/TM—2014-218125 8 

3.2 FTIR: Changes in Chemical Properties 

The hBN is much less chemically reactive than the intercalates. By inserting reactive chemicals into 

the hBN layers, the atoms/molecules of the intercalates will be brought into the proximity of individual 

hBN layers, and the chemical properties of hBN may be affected. The possible changes of hBN’s 

chemical properties can be probed by examining the FTIR data. 

Typically for hBN, there are two characteristic FTIR peaks: a relatively broad band at 1700 to 

900 cm–1, and a relatively narrow band at 850 to 700 cm–1, which are associated with the in-plane B–N 

bond stretching vibration and the out-of-plane B–N–B bending vibration, respectively (Refs. 23 and 24). 

The FTIR data of hBN used in this research is consistent with this (curve i of Fig. 4). After reacting with 

FeCl3, the product has large and broad new FTIR bands in the 3700 to 3050 cm–1 range, which includes 

double bands at 3555 and 3480 cm–1. 

Figure 4(a) compares FTIR spectra of the original hBN (curve i), intercalated hBN containing FeCl3

(curves ii and iv), and the pure FeCl3 (curve vii) at the wavenumber range 3800 to 3000 cm–1. The 

original hBN does not have a band in this range, but the other two do. The broad band from the 

intercalated product is therefore thought to be the band from FeCl3. However, this band’s (curve ii) 

positions and shapes are different than that of the pure FeCl3 (curve vii). The FTIR differences between 

pure FeCl3 and intercalated FeCl3 indicate the intercalated FeCl3 is affected by hBN. That is, there are 

interactions between hBN and FeCl3. 

 
NASA/TM—2014-218125 9 

Figure 4(b) is the FTIR data in the 2000 to 500 cm–1 region. It shows the shape changes of the broad 

hBN bands during the entire process. That is, from the original hBN reactant (curve i) it was sequentially 

treated by (1) heating in a FeCl3-NaF mixture for intercalation (curve ii), (2) heating in 750 °C air for 

exfoliation followed by rinsing in deionized water to removing NaCl (curve iii), (3) heating in the FeCl3-

NaF mixture again for intercalation the second time (curve iv), (4) heating in 750 °C air for exfoliation 

followed by deionized water rinse for removing NaCl the second time (curve v), and (5) finally placing in 

35 wt% HCl to remove the intercalates (curve vi). 

For the broad 1700 to 900 cm–1 band, its shape changed during the intercalation-oxidationdeintercalation process. The peak position of this band shifted from 1383 to 1277 cm–1 during the process 

(Fig. 4(b), curves ii, iii, iv, and v), but returned to the original 1277 cm–1 after all intercalates are removed 

(Fig. 4(b), curve vi). Changes of the 850 to 700 cm–1 band, on the other hand, remained in the narrow 760 

to 755 cm–1 range. This suggests a change of the B–N stretching vibration, but not much change of the 

B–N–B bending vibration. A discussion of this difference is beyond the scope of this report. 

In addition to the above-described bands, new FTIR peaks at about 1600 cm–1 are observed in the 

intercalated samples (curves ii and iv). A close look shows they are double-peaks. One of them was from 

an intercalate (FeCl3), which will be described in more detail later in this report. The other was believed 

to be due to stretching in the direction that is comparable to BNNT’s tangential stretching vibration. It is 

noted such a peak does not show up in regular hBN, but showed up in BNNT because the tube curvature 
NASA/TM—2014-218125 10 

induces a strain on the hBN network (Ref. 25). The observation of such a band in the hBN sample here 

suggests strain on the hBN, possibility due to the presence of the intercalates in the hBN network. 

The band near 500 cm–1 is believed to be from Fe2O3, which was from oxidation of FeCl3. 

Similar to the XRD data, all changes in the FTIR data during the process were nearly completely 

reversed, and the peaks returned to the original shape, after the final HCl treatment where the intercalates 

and other impurities were removed. 

The overall changes of the hBN’s vibration modes during the entire process indicates interactions 

between hBN and an intercalate (hBN-FeCl3 or hBN-Fe2O3) result in changes of hBN’s chemical 

properties, and such changes can be reversed by removing the intercalates. 

3.3 FESEM, EDS, and Mass Data on Overall Morphology and Chemical Changes 

The mass ratio of the original reactant mixture was hBN:FeCl3:NaF ≈ 1:2:0.2. After heating the 

mixture of hBN (large platelets), FeCl3, and NaF and then boiling off excess FeCl3, the as-synthesized 

products were brown in color and had a mass gain over the original hBN by about 100 percent. EDS data 

obtained from FESEM operated at 15 kV indicated that the overall mole ratio of Fe:Cl:Na for this assynthesized product was about 1:2.8:0.45. It is noted that EDS did not detect fluorine, which was in the 

original reactant in the form of NaF. 

The significance of NaF in the reaction is observed when comparing the above mass data to those in 

preliminary experiments where the same heating and boiling process was conducted without the presence 

of NaF. In those cases, the as-made products were white in color and had a mass gain over the original 

hBN of less than 10 percent. 

Figure 5(a) is a FESEM image of the as-synthesized product obtained from secondary electrons. 

Figure 5(b) shows the same image of hBN platelets, except the FESEM detected backscattered electrons, 

which highlights the heavy element (iron) as bright areas. Comparing these two images, it can be seen 

that iron is concentrated more at the sides and edges of the platelets. These data suggest that the mass 

increases during the reactions resulted from FeCl3 entering the layered structures of the hBN from the side. 

 
NASA/TM—2014-218125 11 

Figures 6(a) and (b) are FESEM micrographs of the above intercalated sample after it was slowly 

oxidized by oxygen in air at high temperature to become Fe2O3 nanoparticles (i.e., B*1 in Fig. 2). The 

heating rate was 5 C per minute from room temperature to 750 C with a holding time of 2 h at 300 C. 

It was sufficiently slow so that the iron chloride intercalates were in solid phase and did not change 

location when they became Fe2O3. The presence of Fe2O3 in the sample was confirmed by XRD. 

Figure 6(a) shows a top view of alternating layers of hBN and Fe2O3 nanoparticles. Figure 6(b) is the side 

view of a relatively thick hBN layer about 1 m thick. It can be seen that this layer is split into numerous 

thin layers about 20 to 30 nm thick. Both pictures suggest that hBN was intercalated with nanoparticle’s 

precursor (i.e., FeCl3). 

Figure 7 shows FESEM micrographs from a sample treated similarly to that in Figure 6, except this 

intercalated sample was quickly oxidized by placing it into the preheated 750 C furnace (i.e., B*2 in 

Fig. 2). The fewer but much larger, micron-sized Fe2O3 particles are believed result from some FeCl3

intercalates melting, coagulating, moving out of the lattice, and then oxidizing. This sample also shows 

intercalation and a limited degree of exfoliation. Figure 7(b) shows exfoliated hBN in this sample. 

The above-mentioned figures show signs that by using NaF as an activating agent, hBN was indeed 

intercalated with FeCl3. Furthermore, subsequent heating of this intercalated product in air at 750 °C 

appeared to result in some degree of exfoliation. However, the exfoliation shown in both Figures 5(b) and 

6(b) was the minority among a large number of platelets in the samples. Although 20-nm exfoliation 
NASA/TM—2014-218125 12 

thicknesses were found, some platelets were not exfoliated, and the thicknesses of most of the exfoliated 

hBN platelets were in 0.5 to 2.0 m range. Nevertheless, although overall thinner than the original hBN 

reactant platelets (mostly 5 m thick), this is far from the goal of fabricating white graphene. For the 

purpose of generating further exfoliation, Reactions (3) to (7) were carried out in two similar processes 

with one incorporating hydration before exfoliation: 

I. The intercalated and then air-heated product (hBN containing micron-sized Fe2O3 particles 

described in Fig. 7) was rinsed with water to remove sodium chloride to form product B in 

Reaction (2) (from EDS data), intercalated (mixed with FeCl3 and NaF and heated) to form 

product C (Reaction (3)), exfoliated (heated in 750 °C air and rinsed with water) for the second 

time to form product D (Reaction (4)), and then cleaned in 35 wt% HCl to form product ED

(Reaction (5)). The result is more complete and pronounced exfoliation, where 20-nm nanosheets of 

pure hBN and pores can commonly be seen (Fig. 8(a)). This result also demonstrates that, with 

additional cycles of intercalation and exfoliation, more extensive exfoliation into even thinner 

nanosheets is possible. 

II. The hBN was intercalated and exfoliated for the second time in a way similar to process I, except 

 The intermediate intercalated product (product C) was placed in ambient air for 50 h 

(product C', Reaction (6)) before it was exfoliated for the second time in a 750 °C preheated 

furnace (see Reaction (7)). 

 The sample was covered by a quartz lid during the above 750 °C heating to exfoliate the 

sample for the second time. 

Ambient air (about 30 percent relative humidity) exposure caused the hygroscopic intercalated hBN 

to adsorb water 10 percent of its own mass. The subsequent 750 °C heating caused the water and 

then FeCl3 to violently boil off, resulting in exfoliation and producing steam that carried away some 

exfoliated BN layers. These BN layers were then deposited on the quartz lid and, after the system 

was cooled to room temperature, picked up by a piece of carbon tape for FESEM examination. 

FESEM micrographs show they were nanosheets, about 10 to 20 nm thick and separated by a space 

of about 10 to 60 nm (Fig. 8(b)). The hBN not carried away by the steam is rinsed (product D' in 

Reaction (7)). 

Exfoliation of hBN as observed in this research, suggests that the original hBN was intercalated. 

Repeating these processes causes additional exfoliation, supporting this suggestion. 
NASA/TM—2014-218125 13 

3.4 Reactions to Moisture in Ambient Air 

The apparent enhancement of exfoliation after the hygroscopic intercalated compound picked up 

moisture in air calls for additional study on the reactions between the intercalated compound and water. In 

a preliminary test, an intercalated sample A3 described in Table I was exposed to the ambient 

environment (24 C, 59 to 63 percent relative humidity) overnight after it was stored in dry air for 

23 days. This resulted in a 20 percent mass increase. The XRD data indicate that its lattice parameter c 

and hBN (002) peak width (FWHM) changed from 6.6584 Ǻ and 0.059° to 6.6569 Ǻ and 0.056°, 

respectively, during the overnight ambient air exposure. 

A more detailed study of the effects of moisture in air on the same intercalated hBN was conducted after 

it was stored in dry air for 4 to 5 months. In this study, samples were exposed to room-temperature air at 

different relative humidities and analyzed using three different types of data (mass, FTIR, and XRD). 

Figure 9 shows the percent mass increase of two intercalated samples during the ambient air 

exposure. One of them was weighed several times during an exposure time of 66 min (Fig. 9(a)). The 

relative humidity was 26 to 27 percent during the time of this experiment. The results show the sample 

mass increased rapidly during the first 20 min and reached a peak in 30 to 40 min of exposure time, to an 

11 percent mass gain. The other sample was tested similarly, but over a long exposure time of 165 h 

(Fig. 9(b)). The relative humidity schedule was also shown (Fig. 9(c)). It was in the 15 to 28 percent 

range. It can be seen that after the mass reached a peak value within an hour, it began to decrease 

continuously for days during the ambient air exposure. Despite the initial mass increase, the overall mass 

during this ambient air exposure experiment actually decreased. The data suggests that the samples picked 

up moisture from air quickly. The moisture then reacted with intercalates, resulting in gas products, 

possibly HCl or Cl2, during the conversion of FeCl3 to Fe2O3. 
NASA/TM—2014-218125 14 

For XRD analysis, a sample of the same product (A3 in Table I) was mounted and filled in a 0.5-mm 

deep well ZBH holder and scanned for XRD 12 times during an 85-h period of ambient air exposure. All 

of the 12 datasets were obtained from a 10° to 90° scan followed by high-resolution scans of the (002), 

(004), (006), and (008) peaks. The sample surface turned dark, but remained intact during data acquisition. 

Table II shows the 12 datasets of lattice parameter c, the (002) peak width (FWHM), and the relative 

(002) peak height acquired during the course of the 85 h of ambient-air exposure. These values were 

obtained from the XRD data scanned at 0.005° per step. We estimate the lattice parameter c and the 

FWHM relative accuracy to be 0.0002 Å and 0.002°, respectively, with these scans that were longer in 

duration and to higher angles than data previously discussed. It can be seen that both the height and the 

width of the (002) peak continue to decrease throughout the process, indicating a decrease of the 

crystalline content in the sample. It appears that water absorbed by (and possibly intercalated into) the 

sample causes some crystallites to become amorphous and that the reaction would continue for several 

days or more. 

At the beginning, the lattice parameter c was in a decreasing trend. This trend leveled at about 40 h of 

ambient air exposure, which suggests that, among the crystallites in the sample the hBN crystallites that 

become amorphous during this process of humid air exposure are those with larger lattice parameter c 

(and therefore larger interplanar spacing). 

The FTIR spectra of the same intercalated product (A3 in Table I exposed to ambient air at 15 to 

30 percent relative humidity for 6 min, 64 h, and 189 h, respectively, were obtained and shown in 

Figure 10(a). For comparison, the FTIR spectra of the original hBN reactant and the intercalated product 

before the ambient air exposure are also included in Figure 10(a), and FTIR spectra of dry (distilled) and 

wet (ambient-air-exposed) FeCl3 are shown in Figure 10(b). 

TABLE II.—XRD ANALYSIS OF INTERCALATED hBN A3a (TABLE I AND FIG. 2): LATTICE PARAMETER c, 

(002) PEAK WIDTH (FWHM), AND (002) PEAK HEIGHT IN THE 85 h DURING WHICH SAMPLE 

WAS EXPOSED TO AMBIENT AIR (HUMIDITY SCHEDULE OF AIR IS INCLUDED) 

XRD 

scanning 

dataset 

Total ambient exposure 

time at beginning and 

end of scanning, 

h 

Relative humidity at 

beginning and end 

of scanning, 

percent 

Lattice parameter c 

from scanning 

dataset,b 

Å 

FWHM from 

scanning 

dataset,c 

deg 

Relative 

(002) peak 

height 

 Beginning End Beginning End 

Pure hBN 

reactant 

--- --- --- --- 6.6585 0.014 --- 

1 0.03 2.2 15 16 6.6585 0.064 1.00 

2 2.2 4.3 16 17 6.6581 0.066 0.90 

3 4.3 6.4 17 18.5 6.6580 0.066 0.89 

4 6.4 8.6 18.5 20.5 6.6579 0.066 0.88 

5 13.6 19.4 25.5 17.5 6.6579 0.065 0.88 

6 24.4 30.2 14.5 14.5 6.6579 0.062 0.84 

7 35.2 41.1 13.5 13.5 6.6578 0.058 0.80 

8 46.0 51.9 11 13.5 6.6582 0.053 0.74 

9 56.9 62.7 11.5 12.5 6.6579 0.05 0.67 

10 67.7 73.5 11 13.5 6.6579 0.047 0.61 

11 73.6 79.4 13.5 22.5 6.6582 0.047 0.59 

12 79.4 85.3 22.5 31 6.6582 0.048 0.58 a

Sample had been stored in dry air for 123 days at beginning of experiment. b

Error is estimated to be ±0.0002 Å for c values. c

Error is estimated to be ±0.002° for FWHM values. 

 
NASA/TM—2014-218125 15 

Figure 10(a) shows the intercalated hBN has five prominent FTIR bands: 1600, 1370, 1250, and 

750 cm–1 bands and a broad 3700 to 2700 cm–1 band. The 1370 and 1250 cm–1 bands do not seem to be 

affected by moisture absorption when exposed to ambient air. The other three bands, however, have 

changes in shape, position, and size as the intercalated hBN absorb moisture during ambient air exposure. 

Comparing to these five bands, Figure 10(b) shows pure FeCl3 has three prominent FTIR bands, all of 

them changes during moisture absorption, and all of them are near the wavenumbers of the three bands in 

Figure 10(a) that change during moisture absorption. It is therefore believed that the FTIR changes for the 

intercalated hBN result from moisture absorption, as seen in Figure 10(a), and are due to the interaction 

between water and the intercalated FeCl3. 

Furthermore, it is observed that the shape, position, and/or size of the three bands in Figure 10(a) that 

change during moisture absorption have noticeable differences from the three prominent bands in 

Figure 10(b). Their change patterns during moisture absorption were also different. This indicates 

intercalated FeCl3 is not the same as pure FeCl3, and suggests the possibility that there are interactions 

between hBN and FeCl3, and their interactions change during moisture absorption. 
NASA/TM—2014-218125 16 

The double-band near 1600 cm–1 (described earlier as the peaks for strained hBN layers and FeCl3, 

respectively) was again observed in the FTIR of the intercalated hBN without hydration (curve ii of 

Fig. 10(a)). The fact that this double band became single after the sample begin to pick up moisture 

suggests water causes the intercalated FeCl3 to rearrange during hydration, and hence reduces the internal 

stress and strain. 

After 189 h of ambient air exposure, both hydration-related bands (3700 to 2700 cm–1 and 757 cm–1) 

were reduced, but the 1380 to 1280 cm–1 band, which was not effected by hydration, still did not change 

much. It appears that water caused some reactions and consequently was consumed. However, no new 

compounds were detected by FTIR or XRD during this period. 

To further study the effects of water, a new intercalated product (A4 in Table I) was exposed to 

100 percent relative humidity, room-temperature air for 24 h to gain as much water as possible. The fully 

hydrated product gained 141 percent mass and became viscous and pastelike. It was further treated in 

300 °C air for 3 h and eventually in 35 wt% HCl for 24 h to remove all intercalates. Figure 10(c) shows 

its FTIR data and the FTIR data of the products obtained during this process. The large quantity of water 

mass increase was reflected by the complete overlap of the hBN 760 cm–1 band and the hydrated FeCl3

679 cm–1 band. The water was tightly bounded to the product, as the large and broad water-related 3700 

to 2700 cm–1 band could not be completely removed during the subsequent 300 °C air heating. However, 

both the intercalation effects and the hydration effects were completely reversed to the state of the 

original reactant after the final HCl treatment to remove all intercalate. 

In summary, upon exposing the hBN intercalated with FeCl3 to ambient air, it adsorbed moisture in 

air quickly, between 1 and 2 h. The moisture in the sample is in the form of iron chloride hydrate (from 

FTIR data) and is likely to be in the hBN layers (from XRD data). The amount of moisture adsorbed 

depends on the humidity of the air. Data in this research showed 11 percent mass gain at room 

temperature and 26 to 27 percent relative humidity. Upon continuous ambient air exposure, water in the 

sample is believed to cause some reactions and consequently was consumed. If the ambient air is close to 

100 percent humidity, the changes are similar in trend, but are extreme. In that case the adsorbed water 

was measured to be 141 percent of the sample’s dry mass. During ambient air exposure, the lattice 

structures change, but are not irreversibly destroyed, as the original hBN FTIR data can be largely 

restored by treating this product with 35 wt% HCl. 

3.5 Stability in Dry Air 

A sample of an intercalated product (A3 in Table I) was scanned by XRD immediately after it was 

synthesized. Two samples of the same product were stored in dry air for 23 and 185 days, respectively, and 

then scanned. Table III shows the lattice parameter c and the peak width from these three scans. It appears 

that the intercalated hBN underwent a slow change in dry air. The mass data, however, shows the changes in 

the chemical compositions during this period were within experimental error. 

TABLE III.—XRD ANALYSIS OF INTERCALATED hBN SAMPLE A3a (TABLE I 

AND FIG. 2): LATTICE PARAMETER c AND (002) PEAK WIDTH (FWHM) 

MEASURED AT THREE DIFFERENT STORAGE TIMES DURING WHICH 

THE SAMPLES WERE IN DRY AIR 

XRD scanning 

dataset 

Storage time, 

days 

Lattice parameter c from 

scanning dataset,b 

Å 

FWHM from scanning 

dataset,c 

deg 

Pure hBN 

reactant 

--- 6.6585 0.01 

1 0 6.6565 0.05 

2 23 6.6584 0.06 

3 123 6.6585 0.06 a

Samples were prepared in ambient air for about 5 min before XRD scanning. b

Error estimated to be ±0.0005 Å for c values. 

c

Error estimated to be ±0.01° for FWHM values. 
NASA/TM—2014-218125 17 

3.6 Toward White Graphene Fabrication 

The exfoliated hBN layers obtained in this research are still much thicker than white graphene. 

Further exfoliation is needed if producing white graphene is the long-term scientific and engineering goal. 

For additional exfoliation, results in this research point to the direction of adding more water into the 

intercalated products, heating the intercalated-hydrated product to higher temperature at higher rate, and 

conducting more cycles of intercalation-hydration-heating for exfoliation. In addition, smaller platelets, 

with fewer layers and less area to split, may exfoliate more extensively than the larger ones. To test these 

suggestions, hBN with small platelets was intercalated (A5 in Table I), exfoliated, rinsed, intercalated 

again, hydrated, exfoliated again, and then rinsed with HCl according to Reactions (2), (3), (6), (7), and 

(8). For a high heating rate in Reaction (7), the exfoliation was conducted by heating the sample at 750 C 

where both the furnace and the sample holder were preheated. For a high degree of hydration, the sample 

was placed in 100 percent relative humidity environment for 7.5 h, resulting in a 36.4 percent mass gain. 

The final product was the most extensively exfoliated so far in this research (Fig. 11). Observed from the 

FESEM operated at 6 kV, all hBN platelets that can be examined for exfoliation show that the exfoliated 

layers are about 20 nm thick or less. 

 
NASA/TM—2014-218125 18 

Using carbon adhesive tape, a sample was peeled to remove the top layer and then examined under 

FESEM at 0.5 kV (Fig. 12). The top view of an exfoliated platelet shows multiple semitransparent layers. 

Based on the Kanaya-Okayama penetration depth formula, the total thickness of the multiple 

semitransparent layers need to be less than 5.5 nm in order to let the 0.5-kV electrons give them a 

semitransparent appearance.1

Producing even thinner exfoliated layers or nanosheets seems likely with additional cycles of 

intercalation and exfoliation. However, further research is needed in order to evaluate the potential of 

using these reactions to mass produce white graphene. 

4.0 Conclusion 

After treating a mixture of hexagonal boron nitride (hBN), FeCl3, and NaF at 290 to 355 °C in a 

nitrogen environment, a new product was obtained and examined. The changes of the lattice parameter, 

the widening of the hBN (002) peak in x-ray diffraction (XRD), the shape and size changes of the hBN 

peaks in Fourier transform infrared (FTIR) spectra at 1383 and 1277 cm–1, the appearance of new fourier 

transform infrared peaks at 3700 to 2700 and 1600 cm–1, the mass increase data, the observed iron 

 1

 Let the average atomic weight (A) be 12.5, atomic number (Z) be 6, and density (ρ) be 2 g/cm3 in the formula 

H = (0.0276 A V1.67)/(Z 0.89 ρ), for the hBN, where H and V are penetration depth in μm and voltage in kV, 

respectively. The electrons need to travel through the layers, hit the subject underneath, and travel through the layers 

back to be detected in order to give the layers a semitransparent appearance in the FESEM micrograph. 
NASA/TM—2014-218125 19 

distribution in the micrographs and energy dispersive x-ray spectroscopy (EDS) of field emission 

scanning electron microscopy, and the fact that the hBN can be exfoliated to 20 nm after heating this 

product to 750 °C, collectively make a strong case that FeCl3 was located between the hBN layers in this 

product. That is, the hBN was likely intercalated with FeCl3. The fact that these changes were extended 

and exfoliation was enhanced after the product adsorbs moisture from air suggest the adsorbed water was 

also intercalated into the hBN layers. The difference between this experiment and the previous ones 

where intercalation was unsuccessful is that NaF was used as the activation chemical. 

After the reaction of FeCl3 and NaF to form the intercalation compound, shape changes of the hBN 

broad FTIR band (peaked at 1277 cm–1) and the appearance of the new band at 1600 cm–1 were observed. 

The new FTIR band at 3700 to 2700 cm–1 is similar to the pure FeCl3 FTIR band at the same wavenumber 

range. However, some of their differences suggest the intercalated FeCl3 is different from the pure one 

and there are hBN-FeCl3 interactions in the intercalated product. Overall, the FTIR data suggest a change 

in the chemical properties of the intercalated product from the precursor hBN. These new chemical 

properties may be further developed to make products such as composites with special electrical, thermal, 

and mechanical properties. 

This result brings into focus the comparison between hBN and graphite: Both materials can be 

intercalated with FeCl3, and both can be exfoliated after intercalation, although the mechanisms behind 

their respective intercalation and exfoliation may have some differences. The comparison between 

graphite and hBN can now be moved to a new level: Graphite intercalation and exfoliation has been 

scaled up for engineering and industrial applications such as Grafoil or graphene. Can hBN use the 

graphite technology as the reference to do the same? 

References 

1. Wentorf, R.H.: Cubic Form of Boron Nitride. J. Chem. Phys., vol. 26, 1957, p. 956. 

2. Chopra, N.G., et al.: Boron Nitride Nanotubes. Science, vol. 269, 1995, pp. 966‒967. 

3. Rudorff, W.: Graphite Intercalation Compounds. Advances in Inorganic Chemistry and 

Radiochemistry, H.J. Emeleus and A.G. Sharpe, eds., Vol. 1, Academic Press Inc., New York, NY, 

1959, pp. 223‒266. 

4. Inagaki, M.; Kang, F.; and Toyoda, M.: Exfoliation of Graphite via Intercalation Compounds. 

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pp. 1‒69. 

5. Jacoby, M.: Graphene Moves Toward Applications. Chem. Eng. News, vol. 89, no. 47, 2011, pp. 

10‒15. 

6. Dailly, A., et al.: Methods for Purifying Carbon Materials. U.S. Patent 7,537,682, May 2009. 

7. Lin, Y.; Williams T.V.; and Connell, J.W.: Soluble, Exfoliated Hexagonal Boron Nitride 

Nanosheets. J. Phys. Chem. Lett., vol. 1, 2010, pp. 277‒283. 

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1989, pp. 2554‒2558. 

9. Sumiyoshi, A.; Hyodo, H.; and Kimura, K.: Li-Intercalation Into Hexagonal Boron Nitride. J. Phys. 

Chem. Solids, vol. 71, 2010, pp. 69–571. 

10. Shen, C., et al.: Intercalation of Hexagonal Boron Nitride by Strong Oxidizers and Evidence for the 

Metallic Nature of the Products. J. Solid State Chem., vol. 147, 1999, pp. 74‒81. 

11. Ohashi, K.; and Shinjo, T.: On the Existence of Intercalation Compound of Boron Nitride With 

Ferric Chloride. Bull. Inst. Chem. Res., Kyoto Univ., 1977, vol. 55, pp. 441‒446. 

12. Zeng, H., et al.: “White Graphenes”: Boron Nitride Nanoribbons via Boron Nitride Nanotube 

Unwrapping. Nano. Lett., vol. 10, 2010, pp. 5049‒5055. 

13. Hung, C.; and Hurst, J.: Exfoliation of Boron Nitride Nanotubes Prepared From a Solid-Gas 

Chemical Reaction. 240th American Chemical Society National Meeting and Exposition, Boston, 

MA, 2010. 
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14. Hung, C.; and Hurst, J.: Use of Ferric Chloride as a Solvent To Purify Boron Nitride Nanotube. 

240th American Chemical Society National Meeting and Exposition, Boston, MA, 2010. 

15. Erickson, K., et al.: Longitudinal Splitting of Boron Nitride Nanotubes for the Facile Synthesis of 

High Quality Boron Nitride Nanoribbons. Nano. Lett., vol. 11, 2011, pp. 3221‒3226. 

16. Hung, C.; and Kucera, D.: Graphite Intercalation Compound With Iodine as the Major Intercalate. 

Carbon, vol. 32, 1994, pp. 1441–1448. 

17. Freeman, A.G.; and Larkindale, J.P.: Preparation, Mössbauer Spectra, and Structure of Intercalation 

Compounds of Boron Nitride With Metal Halides. J. Chem. Soc. A, 1969, pp. 1307‒1308. 

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Chem., 1958, vol. 62, pp. 433‒437. 

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Exfoliation of Hexagonal Boron Nitride via Ferric Chloride Intercalation

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

Sodium fluoride (NaF) was used as an activation agent to successfully intercalate ferric chloride (FeCl3) into hexagonal boron nitride

(hBN). This reaction caused the hBN mass to increase by ~100 percent, the lattice parameter c to decrease from 6.6585 to between 6.6565

and 6.6569 Ǻ, the x-ray diffraction (XRD) (002) peak to widen from 0.01° to 0.05° of the full width half maximum value, the Fourier

transform infrared (FTIR) spectrum’s broad band (1277 cm-1 peak) to change shape, and new FTIR bands to emerge at 3700 to 2700 and

1600 cm-1. This indicates hBN’s structural and chemical properties are significantly changed. The intercalated product was hygroscopic and

interacted with moisture in the air to cause further structural and chemical changes (from XRD and FTIR). During a 24-h hold at room

temperature in air with 100 percent relative humidity, the mass increased another 141 percent. The intercalated product, hydrated or not, can

be heated to 750 °C in air to cause exfoliation. Exfoliation becomes significant after two intercalation-air heating cycles, when 20-nm

nanosheets are commonly found. Structural and chemical changes indicated by XRD and FTIR data were nearly reversed after the product

was placed in hydrochloric acid (HCl), resulting in purified, exfoliated, thin hBN products.

15. SUBJECT TERMS

Hexagonol boron nitride (hBN); Ferric chloride; Graphite; Intercalation; Exfoliation; White graphene

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