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Processable dispersions of graphitic carbon nitride based nanohybrids and application in polymer nanocomposites Yongqian Shi, Bibo Wang, Lijin Duan, Yulu Zhu, Zhou Gui, Richard K.K. Yuen, and Yuan Hu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b01237 • Publication Date (Web): 24 Jun 2016 Downloaded from http://pubs.acs.org on June 26, 2016

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Industrial & Engineering Chemistry Research

Processable dispersions of graphitic carbon nitride based nanohybrids and application in polymer nanocomposites Yongqian Shi

a,b

, Bibo Wang (equal contribution) a, Lijin Duan a, Yulu

Zhu a, Zhou Gui a*, Richard K.K. Yuen b, and Yuan Hu a** a

State Key Laboratory of Fire Science, University of Science and

Technology of China, 96 Jinzhai Road, Hefei 230026, PR China. b

Department of Architecture and Civil Engineering, City University of

Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong 999077, PR China. E-mail: [email protected]; yuanhu@ustc. edu.cn; Fax: +86-551-3601669, +86-551-63601664; Tel: +86-551-3601288, +86-551-63601664 Abstract Graphitic carbon nitride (g-C3N4) nanosheets are endowed with extraordinary chemical and thermal stability, and good optical and photoelectrochemical properties and expected to use in a wide range of fields. The direct dispersion of hydrophobic g-C3N4 nanosheets in water or organic solvents without the assistance of dispersing agents is considered to be a great challenge. Here we report novel g-C3N4/organic modified montmorillonite (OMMT) nanohybrids, which were synthesized through electrostatic interaction and then introduced into polystyrene (PS) matrix to fabricate nanocomposites by a simple solvent blending-precipitation method. Hybridizing the g-C3N4 with OMMT could easily form stable aqueous colloids through electrostatic stabilization. These nanohybrids were evenly dispersed in PS and showed strong interfacial interactions with the polymer matrix. It is noted that the generation of total gaseous products was dramatically inhibited by combining g-C3N4 with OMMT. Moreover, flame retardancy was improved upon incorporation of the nanohybrids into PS host. These improvements were due to the strong interactions at interface of ternary systems, synergism between g-C3N4 and OMMT, and physic barrier effect of

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the two components. This work provides a new pathway to manufacture well-dispersed polymeric materials with enhanced fire safety.

1. Introduction Graphitic carbon nitride (g-C3N4), the most stable allotrope of carbon nitride with a stacked two-dimensional (2D) structure, has attracted increasing attention due to its fascinating properties such as thermal and chemical stability and optical and photoelectrochemical properties.1,2 There are residual −NH2 or −NH groups presenting in g-C3N4, and the amount of these groups increases with the decrease of polycondensation degree.3 The g-C3N4 and its various derivatives have been widely studied in a wide variety of fields, including catalysts, hydrogen devices, lithium ion storage, optoelectronic device and bioimaging.4-10 Moreover, g-C3N4-based polymer composites

have

also

been

investigated.

Yan

et

al.

prepared

the

poly(3-hexylthiophene)/g-C3N4 composites with enhanced the hydrogen production from water.11 Myllymaa et al. revealed that surface hydrophilicity of polypropylene was improved by addition of silicon-doped carbon nitride coating.12 Our group studied thermal stability, flame retardancy and mechanical properties of polymer nanocomposites containing g-C3N4 or its modifications. Introduction of g-C3N4 into sodium alginate resulted in enhanced thermal and mechanical properties.13 Moreover, the incorporation of g-C3N4/CuCo2O4 led to markedly reduced peak of heat release rate (pHRR) and total heat release (THR) of thermoplastic polyurethane.14 Comparative study was carried out for g-C3N4 and functionalized layered double hydroxides (LDH) filled polypropylene-grafted maleic anhydride (PP-g-MA) nanocomposites.15 The results showed that the g-C3N4 could contribute to more significant improvements in flame-retardant, thermal, mechanical and UV-shielding properties of PP-g-MA, compared to modified LDH. It was demonstrated that these improvements were attributed to catalytic effect and barrier effect of g-C3N4, and synergistic effect between g-C3N4 and other compounds. However, there are two important issues left to solve: the first is that g-C3N4 is poorly distributed in polymer matrix, and the other is that these modifications mentioned above partly destroy the


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chemical structure of g-C3N4. Therefore, it is of significance to develop other modification methods for improving the distribution of g-C3N4 in polymer matrix without changing its chemical structure. It is well known that dispersion of nanoscale additives in polymers can enhance the mechanical, barrier, flammability properties as well as the thermal stability of the polymer matrix, even at low loadings (typically less than 10 wt%).16-19 In the case of polymer/g-C3N4 nanocomposites, the g-C3N4 stacks into aggregations upon being incorporated into polymer matrix, leading to slight improvements in the fire resistance, thermal stability and smoke suppression properties of the nanocomposites. If we can enhance the dispersion of g-C3N4 nanosheets in polymer matrix, it is anticipated that the macroscopic properties of the polymer/g-C3N4 nanocomposites will be further improved. The g-C3N4 nanosheets dispersed in aqueous solution can be stored stably for several months under room temperature owing to the vast negative charges at the surfaces.20 As reported in previous work, the colloidal stability of an electrostatically stabilized dispersion was strongly dependent on pH, the electrolyte concentration, and the content of dispersed particles.21-23 By controlling these parameters, it is easy to find that chemically converted graphene sheets could form stable colloids through electrostatic stabilization. Moreover，it is demonstrated that the electrostatic repulsion mechanism that makes graphene colloids stable could also enable the formation of well-dispersed graphene colloids. Inspired by the electrostatic repulsion, g-C3N4 nanosheets can be stably dispersed in aqueous or organic solution by combination of other compounds with negative charges. The naturally occurring clays such as commonly utilized montmorillonite (MMT) have the 2:1 layered silicate/aluminum oxide structure which consists of two tetrahedron sheets sandwiching an edge-shared octahedral sheet.16,24 The surface of MMT is endowed with amounts of negative charges, whereas many metal ion species existing in its interlayer are exchangeable with organic salts to increase silicate-gallery spacing. Furthermore, our previous research reported that g-C3N4 nanosheets were successfully intercalated into interlayers of Na-MMT, and then adding the g-C3N4/MMT nanohybrids into sodium alginate led to improved thermal



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stability.25 Therefore, combination of g-C3N4 and organic modified MMT (OMMT) is expected to improve the dispersion of g-C3N4 and fire safety of polystyrene (PS). In the present work, a series of g-C3N4/OMMT nanohybrids were synthesized through electrostatic interaction, and subsequently incorporated into PS matrix to prepare nanocomposites by a simple solvent blending-precipitation method. The pyrolysis gaseous product suppression of PS nanocomposites was measured by thermogravimetric analysis/infrared spectrometry. Moreover, their flame retardancy was evaluated by using a microscale combustion calorimeter. The mechanism to illustrate reduced fire hazards of PS was also discussed.

2. Experimental section 2.1 Raw materials Urea, N,N-dimethyl formamide (DMF), anhydrous ethanol and cetyl trimethyl ammonium bromide (CTAB) were provided by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Benzyldimethylhexadecylammonlum chloride (HDBAC) was purchased from Aladdin Industrial Corporation. Na-montmorillonite (Na-MMT) was obtained from Zhejiang Fenghong New Materials Co., Ltd. (Zhejiang, China). The cation exchange capacity of the sample was 100 mmol/100 g. Polystyrene (PS, 158 K) was provided by BASF-YPC Co., Ltd. (China). All reagents were used without further purification. 2.2 Preparation of OMMT The CTAB-modified MMT (ABMMT) was obtained by dispersing 10 g of Na-MMT in 800 mL of deionized water under ultrasound-assisted agitation for 30 min, and subsequently stirring at 80 °C for 2 h, followed by adding 6 g of CTAB into the suspension. Finally, the products were filtered, washed several times with deionized water and anhydrous ethanol, and dried overnight. The same procedure was also performed to prepare the HDBAC-modified MMT (BACMMT). 2.3 Preparation of g-C3N4/OMMT nanohybrids The bulk g-C3N4 was synthesized according to the previous work.26 Then, a desired amount of bulk g-C3N4 was added into deionized water to obtain the g-C3N4


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suspension (1 mg/mL) through the ultrasound-assisted stirring for 4 h. Similarly, the ABMMT dispersion (1 mg/mL) was achieved by introducing the certain amounts of ABMMT into deionized water under the ultrasonic assisted stirring for 30 min. The g-C3N4/ABMMT hybrids could be prepared by mixing g-C3N4 suspension with ABMMT dispersion at room temperature and further stirring for 2 h. Finally, the as-prepared products were filtered, and washed several times with deionized water and anhydrous ethanol, and dried. These obtained samples were labelled as CABMχ, where χ represented the percentage of g-C3N4 in CABM, when the ABMMT was used. The same strategy was also conducted to prepare CBACMχ when the BACMMT was added. The schematic representation for the formation of g-C3N4/OMMT nanohybrids s is illustrated in Figure 1. 2.4 Fabrication of PS/g-C3N4/OMMT nanocomposites The PS solution was obtained by dissolving PS grains in DMF at 80 °C. The desired concentration of CABMχ hybrids (2 wt% in this work) dispersed in DMF under sonication for 10 min was added to the PS solution above. The mixture was further treated under sonication-assisted stirring for 1 h. Then, the hot mixture was poured into deionized water to precipitate PS/CABMχ. This obtained PS/CABMχ nanocomposites were separated by filtration, and dried, followed by melt blending. The PS/CBACMχ nanocomposites were also fabricated by substituting CBACMχ for CABMχ in above-described procedure. For comparison, the same procedure was performed to prepare PS/g-C3N4, PS/ABMMT and PS/BACMMT nanocomposites containing 2 wt% g-C3N4, ABMMT and BACMMT, respectively. 2.5 Characterization X-ray diffraction (XRD) patterns were obtained by a Japan Rigaku Dmax X-ray diffractometer equipped with graphite monochromatized high-intensity Cu Kα radiation (λ = 1.54178 Å). Fourier transform infrared (FTIR) spectra were obtained using a Nicolet 6700 FTIR (Nicolet Instrument Company, USA) with scanning from 500 to 4000 cm-1. Zeta-potential values were recorded using a Zeta Sizer 3000 HS, Malvern Instruments, as a function of samples. All the samples were dispersed in DMF. Transmission electron microscopy (TEM) was provided by a JEOL 2010



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instrument with an acceleration voltage of 200 kV. The dispersions of g-C3N4, OMMT and their nanohybrids were treated through sonication, and then dripped onto copper grids before observation. The distribution of these nanoadditives in PS matrix was observed from their ultrathin sections using an Ultratome (Model MT-6000, Du Pont Company, USA). The morphology of PS nanocomposites was investigated by scanning electron microscopy (SEM) (AMRAY1000B, Beijing R&D Center of the Chinese Academy of Sciences, China). These samples were fractured in liquid nitrogen and sputter coated with a gold layer for observation. Thermogravimetric analysis/infrared spectrometry (TG-IR) of PS sphere and its nanocomposites was carried out through a TL-9000 device. Thermal analyzer was conducted in the range from room temperature to 750 °C with a heating rate of 20 °C/min in helium atmosphere. Pyrolysis products content per gram of the samples was measured. Small scale combustion properties were evaluated using a microscale combustion calorimeter (MCC) (GOVMARK, New York). Approximately 5 mg of samples were heated to 750 °C at a heating rate of 1 °C/s in a nitrogen stream flowing (80 mL/min). The gaseous pyrolysis products were mixed with oxygen (20 mL/min) and then raised into a combustion furnace (900 °C). Each of these samples was repeated three times, and results were averaged.

3. Results and discussion 3.1 Structure and morphology characterization of g-C3N4/OMMT nanohybrids The well-resolved FTIR absorption bands in Figure 2 reveal a typical molecular structure of g-C3N4. The absorption band at ca. 811 cm-1 is attributed to the characteristic breathing vibration of tri-azine ring, while the bands at 1000–1800 cm-1 correspond to stretching vibration of connected units of C–N(–C)–C or C–NH–C. Furthermore, the broad peaks between 3000 and 3500 cm-1 are contributed by the presence of incompletely condensed secondary and primary amines associated with their stretching vibration models.27-29 The typical Na-MMT bands corresponding to the Si–O bonds are found in the region below 1200 cm-1. A sharp peak near 3600 cm-1 and a broad band at 3400 cm-1, corresponding to O–H stretches, are present in


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Na-MMT.30,31 The former arises from intra-sheet O–H and the latter originates from H2O adsorbate or intercalate. After modification, the IR absorption spectra for the OMMT reveal the presence of peak at 2900 cm-1 that can be attributed to the vibration of the C–H bond.32 The weak peak at around 720 cm-1 is originated from adsorption band of (CH2)n. For g-C3N4/OMMT nanohybrids, it is found that peaks appearing are assigned to both g-C3N4 and ABMMT or BACMMT. XRD technique was widely used to dissect the structural phase of materials. XRD patterns of g-C3N4, Na-MMT, OMMT and the nanohybrids are shown in Figure 3, and the related XRD data are recorded in Table S1 (Supporting information). It is observed from Figure 3a and c that there exist two diffraction peaks at 2θ= 27.72° and 13.18°, assigned to the stacking of the conjugated aromatic system, and the in-planar repeating unit with a period of 0.671 nm, respectively for g-C3N4. In the case of Na-MMT, its typical XRD reflections occur at 2θ= 7.08° corresponding to basal spacing d001 of 12.5 Å. After the organophilic treatment, the interlayer spacing shifts to 33.8 Å for ABMMT and 34.6 Å for BACMMT. However, after hybridization, the interlayer spacing is decreased gradually with increasing proportion of g-C3N4 to OMMT (Figure 3b and d, Table S1 (Supporting Information)). In addition, the peak at 2θ= 13.18° becomes weak at low loadings of g-C3N4, indicating the increased in-planar interlayer spacing of g-C3N4. These phenomena can be attributed to the explanations that the g-C3N4 nanosheets with negative charges inserted into the interlayers of OMMT induce the interlayered shrinkage.20 It can be clearly seen from Figure 4 that g-C3N4 or Na-MMT alone causes occurrence of precipitation upon being dispersed into DMF solvent. The same result is obtained when the original MMT is organo-functionalized. However, hybridizing the g-C3N4 with OMMT achieves the stable dispersions in DMF solvent. It is supposed that stable g-C3N4/OMMT dispersions are formed through electrostatic stabilization. The assumption can be supported by our zeta potential analysis, as shown in Figure 5. Zeta-potential measurement results show that the g-C3N4/OMMT nanohybrids have an overall negative surface charge, and the absolute values of their zeta potential



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exceed 30 mV. It is widely reported that zeta potential values less than –30 mV are generally considered to represent sufficient mutual repulsion to ensure the stability of a dispersion.22,33 These results indicate that the dispersions of the nanohybrids are stable in DMF solvent. However, the zeta potential of the nanohybrids decreases with increasing proportion of g-C3N4. This is due to the fact that re-stacking is driven by redundant g-C3N4 nanosheets, leading to occurrence of precipitation, which can be confirmed by the result of CABM50 in Figure 4. The morphology of the obtained samples was observed by TEM, as shown in Figure 6. The virgin g-C3N4 shows a rippled 2D profile and paper-like structure (Figure 6a). For pure Na-MMT, 10–20 stacked layers occur when the MMT is dispersed in DMF solvent (Figure 6b). After ultrasound-assisted organic intercalation, the MMT layers are destroyed into pieces and still show the stacked structure, as depicted in Figure 6c and d. However, g-C3N4 nanosheets exhibit two types of dispersions for g-C3N4/OMMT nanohybrids. It is noted that the part of g-C3N4 nanosheets are inserted into interlayers of MMT; on the other hand, the part of g-C3N4 nanosheets start to stack on the OMMT layers (Figure 6e and f). These results are well accordant with those obtained from Figure 4 and 5. 3.2 Structure characterization of PS/g-C3N4/OMMT nanocomposites The XRD traces of PS nanocomposites are plotted in Figure 7, and the corresponding XRD data are given in Table S2 (Supporting Information). As can be observed from Figure 7 and Table S2 (Supporting Information), a similar value in d001 to that of OMMT is observed, suggesting the typical intercalated structure for PS/OMMT nanocomposites. It is noted that the slight increase in interlayered spacing is visible after incorporating the g-C3N4/OMMT nanohybrids into PS matrix. For instance, 0.43 and 0.37 nm increase in d001 are found in PS/CABM20 and PS/CBACM40, respectively. Interestingly, the values of d001 decrease as the percentage of g-C3N4 in the CABMχ increases, whereas the opposite results are obtained with increasing addition of g-C3N4 in CBACMχ. This may be due to the explanations that formed π–π conjugation between tri-azine ring of g-C3N4 nanosheets and benzene ring of PS chains is beneficial to intercalation of PS chains into the interlayers of OMMT during


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the ultrasonically assisted fabrication of PS/OMMT nanocomposites. Moreover, the intercalated effect is more obvious for PS/BACMMT, resulting from formation of additional π–π conjugation between benzene ring of HDBAC molecules and benzene ring of PS chains. 3.3 Morphology characterization and dispersion evaluation of PS/g-C3N4/OMMT nanocomposites In order to clarify the interfacial adhesion between nanoadditives and polymer host, SEM were employed to dissect the micro-morphology of brittle failure surfaces of polymeric materials. Figure 8 illustrates the SEM images of the fractured surfaces of the PS/CABMχ and PS/ABMMT. In the case of PS/CABMχ, the protruding CABMχ nanohybrids indicate the presence of enhanced interfacial force in host-guest, as compared to the findings of previous work (Figure 8a-e and Figure S1a-e (Supporting Information)).34 Furthermore, there is no obviously different change of morphology observed in the PS nanocomposites when the concentration of g-C3N4 in CABMχ is increased. Investigating the fracture surface of PS/ABMMT (Figure 8f and Figure S1f (Supporting Information)) reveals a similar result to PS/CABMχ systems in host-guest. The buckling ABMMT layers also demonstrate strong interactions at PS/ABMMT interface. For PS/CBACMχ systems, the similar results are also observed, as shown in Figure 9 and Figure S2 (Supporting Information). In addition, the protruding CBACMχ nanohybrids thickly coated with the polymeric material reveal stronger interfacial interactions than CABMχ. The exfoliation and distribution of these nanoadditives in the polymer host were further evaluated by TEM technique. Figure 10a presents the TEM ultrathin profiles of the PS/g-C3N4. The thin sections are exfoliated g-C3N4 layers, while the dark sections manifest the presence of aggregation due to the strong hydrogen bonding between g-C3N4 nanosheets. Nevertheless, combining g-C3N4 with OMMT enables good dispersion of the g-C3N4 in the polymeric material. The thickness of the g-C3N4 nanosheets is 3.63 nm in PS/CABM50 (Figure 10b), indicating few g-C3N4 nanolayers (10 layers); thickness of the g-C3N4 nanosheets is 3.26 nm, indicative of fewer g-C3N4 nanolayers (9 layers).1 The results are in agreement with those obtained



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from Figure 7-9. Thus, it can be concluded that the organic modifier is the key to exfoliation and dispersion, which is related to the interactions with g-C3N4. It is expected that excellent dispersion of g-C3N4/OMMT nanohybrids is conducive to significant improvement in fire safety of PS. 3.4 Pyrolytic volatile gaseous products detection of PS/g-C3N4/OMMT nanocomposites The TG-IR technique was widely used to simultaneously detect the time-dependent evolution of pyrolysis gases and the change of the residual content, which can greatly contribute to the understanding of the thermal decomposition mechanism of materials. The evolution of total pyrolysis gaseous products is presented in Figure 11. It is found that incorporation of OMMT into PS leads to reduced generation of pyrolytic gas products. In comparison with BACMMT, g-C3N4 shows poor performance in suppression of released gaseous products, which is attributed to the reason that BACMMT exhibits better distribution than g-C3N4, thus improving the physical barrier effect. Surprisingly, when g-C3N4 is combined with OMMT, the total pyrolysis gaseous products released from decomposition of PS are decreased remarkably. It is evident that the nanohybrids, especially CBACM50 has tremendous advantages in suppression of gaseous product generation, compared to the single counterpart. To further highlight the difference between PS and its nanocomposites, the principal pyrolysis products as a function of temperature at different wavenumbers are plotted in Figure 12. Wilkie et al. demonstrated that pure PS primarily decomposes into monomer, dimer and trimer of phenyl alkenyl.35 Hence, the total organic volatiles are principally assigned to aromatic compounds, observed at bands of 698, 772, 1496 and 3072 cm-1. It can be clearly seen that addition of g-C3N4 or OMMT alone into PS matrix can reduce evolution of the aromatic compounds. Furthermore, the amount of combustible gaseous products evolved from PS nanocomposites can be further decreased by combining g-C3N4 with OMMT. It is apparent that the amount of combustible volatile products for PS/CBACM50 is much less than that for PS/CABM50. Decrease in these combustible gases can be attributed to the synergistic effect and the physical barrier effect of the nanohybrids.


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3.5 Flame retardancy assessment of PS/g-C3N4/OMMT nanocomposites MCC was widely used to evaluate the polymeric material and its nanocomposites related to their fire-retardant performances. The HRR and THR of PS and its nanocomposites are portrayed in Figure 13, and the corresponding data are given in Table S3 (Supporting Information). For monobasic components, there is a distinct difference in pHRR reduction. For instance, the pHRR of PS/g-C3N4 is slightly increased as compared to that of pure PS, whereas that of the PS/OMMT is found to be lower than that of neat PS. These results can be due to these reasons that active sites located in the g-C3N4 are easily oxidized into inert compounds, and that OMMT layers display a better layered barrier effect than g-C3N4. Fortunately, a dramatic decrease in pHRR is observed for PS/g-C3N4/OMMT systems. The pHRR values decrease from 1120 W/g of neat PS to 1025 and 830 W/g in PS/CABM50 and PS/CBACM50, respectively, indicating that the flame retardancy of PS has been improved significantly. Also, reduction in THR can be observed in the PS/CBACM50 and PS/BACMMT nanocomposites. The improvement in flame retardancy can be explained by synergism between g-C3N4 and BACMMT, meaning that the two 2D materials show enhanced layered barrier effect that retards the permeation of heat and the escape of volatile gaseous products, which are in good consistence with published work.36-39

4. Conclusions In the work, novel g-C3N4/OMMT nanohybrids were synthesized through electrostatic interaction, and subsequently incorporated into PS matrix to fabricate nanocomposites by a simple solvent blending-precipitation method. Structural, morphological and electrochemical analyses indicated that g-C3N4 nanosheets with negative charges inserted into the interlayers of OMMT induced the interlayered shrinkage, and hybridizing the g-C3N4 with OMMT achieved the stable dispersions in DMF solvent, which was generally considered to represent sufficient mutual repulsion to ensure the stability of g-C3N4/OMMT dispersion. These nanohybrids were well-dispersed in PS and showed strong interfacial interactions with the polymer matrix. Results obtained



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from TG-IR indicated that the generation of total gaseous products was also distinctly inhibited by combination of g-C3N4 and OMMT. Moreover, the ternary systems showed improved flame retardancy. These enhancements were attributed to the strong interactions at interface of PS/g-C3N4/OMMT, enhanced synergism between g-C3N4 and OMMT, and physic barrier effect of the two components. This work creates a paradigm to design well-dispersed polymeric materials for fire safety.

Acknowledges This work was supported by the National Basic Research Program of China (973 Program) (Grant No. 2012CB719701), the National Basic Research Program of China (973 Program) (Grant No. 2012CB922002), National Natural Science Foundation of China (Grant No. 51303167), Fundamental Research Funds for the Central Universities (WK2320000027) and the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. CityU 122612).

Supporting Information The Supporting Information includes two figures (Figure S1. SEM images of the fractured surface of (a) PS/CABM10, (b) PS/CABM20, (c) PS/CABM30, (d) PS/CABM40, (e) PS/CABM50, and (f) PS/ABMMT at high magnification; Figure S2. SEM images of the fractured surface of (a) PS/CBACM10, (b) PS/CBACM20, (c) PS/CBACM30, (d) PS/CBACM40, (e) PS/CBACM50, and (f) PS/BACMMT at high magnification) and three tables (Table S1. XRD data of both CABM and CBACM with respect to d-spacing (d001); Table S2. XRD data of PS nanocomposites with respect to d001;Table S3. The related MCC data of PS and its nanocomposites).

References (1) Wang, X.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen, K.; Antonietti, M. A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat. Mater. 2009, 8, 76-80. (2) Wang, Y.; Wang, X.; Antonietti, M. Polymeric graphitic carbon nitride as a


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Figure captions Figure 1. Schematic illustration for facile preparation of g-C3N4/OMMT nanohybrids: (a) preparation process; (b) dispersions. Figure 2. FTIR spectra of g-C3N4, Na-MMT, (a) CABMχ and ABMMT, and (b) CBACMχ and BACMMT. Figure 3. XRD patterns of g-C3N4, Na-MMT, (a, b) CABMχ and ABMMT, and (c, d) CBACMχ and BACMMT. Figure 4. Digital photos of g-C3N4, Na-MMT, OMMT and the nanohybrids dispersions in DMF: (a) CABM10, (b) CABM20, (c) CABM30, (d) CABM40, (e) CABM50, (f) CBACM10, (g) CBACM20, (h) CBACM30, (i) CBACM40, (j) CBACM50, (k) ABMMT, (l) BACMMT, (m) Na-MMT and (n) g-C3N4. Figure 5. Zeta potential vs. various g-C3N4/OMMT nanohybrids. Figure 6. TEM images of (a) g-C3N4, (b) Na-MMT, (c) ABMMT, (d) BACMMT, (e) CABM50, and (f) BACM50. Figure 7. XRD patterns of PS/g-C3N4, (a) PS/ABMMT and PS/CABMχ, and (b) PS/BACMMT and PS/CBACMχ. Figure 8. SEM images of the fractured surface of (a) PS/CABM10, (b) PS/CABM20, (c) PS/CABM30, (d) PS/CABM40, (e) PS/CABM50, and (f) PS/ABMMT. Figure 9. SEM images of the fractured surface of (a) PS/CBACM10, (b)



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PS/CBACM20, (c) PS/CBACM30, (d) PS/CBACM40, (e) PS/CBACM50, and (f) PS/BACMMT. Figure 10. TEM images of (a) PS/g-C3N4, (b) PS/CABM50 and (c) PS/CBACM50. Figure 11. Gram–Schmidt curves of PS and its nanocomposites. Figure 12. Intensities of characteristic peaks for pyrolysis gaseous products of PS and its nanocomposites at: (a) 698, (b) 772, (c) 1496 and (d) 3072 cm-1. Figure 13. (a) HRR and (b) THR curves of PS and its nanocomposites.

Figure 1. Schematic illustration for facile preparation of g-C3N4/OMMT nanohybrids: (a) preparation process; (b) dispersions..


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Figure 2. FTIR spectra of g-C3N4, Na-MMT, (a) CABMχ and ABMMT, and (b) CBACMχ and BACMMT.



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Figure 3. XRD patterns of g-C3N4, Na-MMT, (a, b) CABMχ and ABMMT, and (c, d) CBACMχ and BACMMT.


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Figure 4. Digital photos of g-C3N4, Na-MMT, OMMT and the nanohybrids dispersions in DMF: (a) CABM10, (b) CABM20, (c) CABM30, (d) CABM40, (e) CABM50, (f) CBACM10, (g) CBACM20, (h) CBACM30, (i) CBACM40, (j) CBACM50, (k) ABMMT, (l) BACMMT, (m) Na-MMT and (n) g-C3N4.



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Figure 5. Zeta potential vs. various g-C3N4/OMMT nanohybrids.


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Figure 6. TEM images of (a) g-C3N4, (b) Na-MMT, (c) ABMMT, (d) BACMMT, (e) CABM50, and (f) BACM50.



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Figure 7. XRD patterns of PS/g-C3N4, (a) PS/ABMMT and PS/CABMχ, and (b) PS/BACMMT and PS/CBACMχ.


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Figure 8. SEM images of the fractured surface of (a) PS/CABM10, (b) PS/CABM20, (c) PS/CABM30, (d) PS/CABM40, (e) PS/CABM50, and (f) PS/ABMMT.



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Figure 9. SEM images of the fractured surface of (a) PS/CBACM10, (b) PS/CBACM20, (c) PS/CBACM30, (d) PS/CBACM40, (e) PS/CBACM50, and (f) PS/BACMMT.


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Figure 10. TEM images of (a) PS/g-C3N4, (b) PS/CABM50 and (c) PS/CBACM50.



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Figure 11. Gram–Schmidt curves of PS and its nanocomposites.


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Figure 12. Intensities of characteristic peaks for pyrolysis gaseous products of PS and its nanocomposites at: (a) 698, (b) 772, (c) 1496 and (d) 3072 cm-1.



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Figure 13. (a) HRR and (b) THR curves of PS and its nanocomposites.


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Graphic abstract



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Processable Dispersions of Graphitic Carbon ... - ACS Publications

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