Huijie Zhao, 1,2 Xiufeng Song, 1 Haibo Zeng 1,2
1 Institute of Optoelectronics & Nanomaterials, College of Materials Science and
Engineering, Nanjing University of Science and Technology, Nanjing, China.
2 College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing, China.
Corresponding author: Professor H. Zeng, School of Materials Science and
Engineering, Nanjing University of Science and Technology, 200# Xiaolingwei Street,
Nanjing, Jiangsu 210094, China.
E-mail: zeng.haibo@njust.edu.cn
1

Figure S1.
Photograph of the sample before (a) and after (b) heating. Photograph of a piece of superlight 3D WGs with a size of 4.2×3×2.5cm
3 on the balance (only 64.5 mg) (c) and standing on a dandelion (d), indicating its ultralight property.
After the reaction, the sample expanded several hundred times. The obtained 3D
WGs present the scale of about 30cm and weight of about of 1.2g. We realize a large scale and gram yield though the gas-form technique.
2

Figure S2.
(a) Low- and (b) high-magnification TEM image of BN nanosheet, three dark stripes meaning three layers of BN nanosheet. (b) Intensity line profile of the bright stripes along the line in Figure S2(a), the measured distance of interlayer spacing is 0.33nm.
3

Figure S3 XRD patterns of the as-prepared 3D WG. prepared at 1300°C, (a) without vesicants, (b) with thiourea, (c) with thiosemicarbazide. The characteristic peaks matches well with h-BN (JCPDS 34-0421), which suggests that the as-prepared white products have a dominant h-BN structure. The peaks at 2θ=26.56° and 41.98° could be assigned to the (002) and (100) lattice planes of h-BN. The broad peaks and less intensity indicate the products are not well-crystallized, which is due to a relatively lower synthetic temperature (1400°C) that is not enough to form well-crystallized h-BN.
Figure S4 XPS survey of the obtained BN, inset: N 1s (right) and B 1s (left) XPS spectra, respectively.
The B 1s and N 1s XPS peaks are centered at 188.9 eV and 396.7 eV, respectively. The additional oxygen and carbon peaks might result from the atmospheric exposure or residual carbon. The XPS spectra indicate the presence of elements B and N, and the configuration for B and atoms is the B-N bonding. The
B/N ratio calculated from XPS spectra (inset of Figure S4) is 2.7/2.57=1.05, which is similar to that of EELS.
4

Figure S5 Raman spectrum of the 3D WGs. The characteristic peak at 1372cm -1 is attributed to the B-N vibrational mode (E
2g
) within h-BN layers. The peak of obtained h-BN nanosheets is red-shift about 5cm -1 compared with 1367cm -1 of bulk h-BN.
Figure S6 FTIR spectrum of the 3D WGs, (a) without vesicants, (b) with thiourea, (c) with thiosemicarbazide. There are two strong vibrations at 1328 and 771 cm -1 . The broad peak at 1328 cm -1 results from the in-plane B−N transverse optical modes (E
1u
) of the sp2-bonded h-BN; while weaker peak at 771 cm -1 could be ascribed to B-N-B bending vibration mode (A
2u
) parallel to the c-axis. The peak around 3217 cm -1 can be attributed to the water molecules absorbed on the surface of the samples. No obvious
5

absorption peaks associated with the starting materials and carbon are observed.
Without adding vesicants, the FTIR spectrum is identical with that of adding thiourea or thiosemicarbazide, which indicated that the vesicants have no effects on the crystal structure and phase components of the BN.
Figure S7 (a)UV-visible absorption spectrum. (b) calculation of the optical of band-gap by plotting (aE)2 as a function of E. the extrapolation of the straight region and its intersection with the E axis, gives an estimation of the band-gap energy. There is a strong absorption edge at about 202 nm (6.13eV). The optical band gap is estimated from absorption spectrum to be around 5.89eV.
6

Figure S8 Adsorption isotherms of MO on 3D WGs after heating at 400 °C for 2h in air. The removal capacity for MO was calculated to be 461 mg/g.
7

Figure S9 Adsorption properties of the typical 3D WGs. (a) Absorption spectra of an aqueous solution of MO in the presence of 3D WGs at different time. (b) Adsorption rate of MO on the as-prepared WGAs. The inset shows the corresponding photographs of the MB aqueous solution with WGAs at different time. (c)Adsorption isotherms of MO on 3D WGs. The inset shows the photographs of the process of recycling 3D WGs with MO by heating at 400 °C for 2h in air. The removal capacity for MO was calculated to be 384.7 mg/g.
8

Figure S10 Pump oil adsorption recyclability of 3D WGs. Pump oil can be removed by direct combustion in air for repeated recycle tests. The removal efficiency is still maintained about 85% even after five cycles.
9

Figure S11 Nitrogen adsorption and desorption isotherms of the obtained 3D WGs.
By analysis the nitrogen sorption characterization, the calculated
Brunauer–Emmmett–Teller (BET) surface area of the 3D WG is 32 m 2 /g. According to IUPAC classification, the obtained isotherm can be classified as a type-IV isotherm, and exhibits an H3 type hysteresis loop at p/p o
range of 0.4-0.9. The isotherm is not obvious change at the relative pressure range of 0-0.6, and increases steeply at a high relative pressure (p/p o
=0.8-0.99). This result is attributed to the change of the vesicular structure of 3D WGs at high pressure. As shown in Figure
2c-2f, the bubbles of the obtained 3D WGs are hierarchical pore distribution and the walls of bubbles are composed of single or several layers, which strongly urge the 3D
WGs to present enormous superiority for adsorb pollutants of organic solvent or metal ions.
10

Table 1 Comparison of various sorbent materials.
Sorbent materials Aborbed substances
Sorption capacity (g g -1 )
Synthesis
Process
Polymers oils and organic solvents
5-25 simple
Actived carbons
Exfoliated graphene
Graphene-based aerogel benzene,toluene heavy oil oils
<1
60-90
28-40 simple simple simple
Carbon fiber aerogel
Graphene-based sponges
Spongy graphene
Carbon nanotube sponges
Carbon nanofiber aerogels
N-doped graphene framework
Ultra-flyweight carbon aerogels
Porous BN nanosheets
3D WGs oils and organic solvents oils and organic solvents oils and organic solvents oils and organic solvents oils and organic solvents oils and organic solvents oils and organic solvents oils and organic solvents oils and organic solvents
50-192
54-165
20-86
80-180
106-312
200-600
215-913
20-33
70-190 simple simple complex complex complex very complex very complex simple simple
Ref.
[S1]
[S2]
[S3]
[S4]
[S5]
[S6]
[S7]
[S8]
[S9]
[S10]
[S11]
[S12] this work
11

Without foaming agents, the as-prepared BN displayed sheet structure with many fluctuations and ripples (Figure S12a). By adding foaming agents, the obtained BN displayed a vesicular structure with super-thin walls (Figure 2a, b and Figure S12b). For this gas-foaming strategy, the match between thermal decomposition kinetics of the foaming agents and precursor plays a crucial role in the foaming process.
In order to investigate the thermal decomposition kinetics for the forming process of 3D WGs, thermogravimetry (Tg) and differential thermal analysis
(DTA) were employed. As shown in Figure S13a, below 200 °C the mass of
AB lost about 55%, which is mainly due to the decomposing of AB. In this period, H
2
, NH
2
=BH
2
, N
3
B
3
H
6
were released, and the B–N–H polymeric forms
(PAB and PIB) were produced. When the temperature increases to 200 °C, the
BN sponges formed and the crystalline increased. According to this forming process of BN, the introduced foaming agents should start to release gases at the beginning stage of BN crystalline. Thiourea and thiosemicarbazide present the decomposed temperature between 200 °C and 740 °C, which is corresponding to crystalline of BN (Figure 6a). This decomposed process is of benefit to the foaming of BN. At the same time, the DTA curves indicate that the reaction of AB is an exothermic reaction after 200 °C, and that of thiourea is similar with AB (Figure S13b). Therefore, there exists a synergistic reaction between AB and thiourea, which promoted the generation of BN bubbles, so
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the vesicular structural 3D WGs were achieved. However, the reaction of aminothiourea is an endothermic reaction (Figure S13b), which is not synergistic with AB, leading to affect the crystalline of BN and suppress the bubble foaming (Figure S12b). Urea was also selected to adding into the AB to prepare BN foams. However, the decomposition stops at about 400 °C and the reaction is an endothermic reaction above 400 °C, which is not consistent with that of AB (Figure S13). There is not a vesicular structural 3D WG but a BN network with fiber obtained. (Figure S14).
Reaction temperature is also a critical factor in the synthetic processes to form the 3D WGs. At low temperature of 1100 °C, a large number of small bubbles with the size of several to several tens microns were found (Figure
S15a, S16). The inner structure of the bubble was hollow, which is observed from the cracked bubbles. These small bubbles were the protuberances growing on the sheets of BN. At 1200 °C, the bubbles became bigger, huddled and connected together. The congregation of the bubbles created the skeletons at the joint of bubbles (Figure 2a, 2b). The interface of two bubbles is one or several layered BN sheets. This microstructure can supply thermal or electrical continuous conducting passages, which is of benefit to the transports of electricity and heat for the whole networks. The vesicular structures of WGs were formed. Further increasing the temperature to 1300 °C, the surface-tension creased, the sheets of BN shrank, and broke off from the skeletons. The bubbles were destroyed (Figure S15b).
13

Figure S12 SEM image of BN products (a)without foaming agents and (b)with thiosemicarbazide.
Figure S13 Tg(c) and DTA (d) curves of the raw materials with and without foaming agents in N
2
environment. The heating rate is 5°C/min.
14

Figure S14 SEM image of BN products at 1300°C with urea.
Figure S15 SEM image of BN products with different reaction temperature: (a) 1100
°C; (b)1300 °C.
Figure S16 Closed pore structure of 3D WGs synthesized at 1100°C for 3h with aminothiourea as the vesicants. The pore diameter is in the range of 500nm to 5  m.
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