**2. Preparation and catalytic properties of some functionalized graphene nanocomposites**

Recently, our group has reported the design and fabrication of hybrid organogels by selfassembly of composites containing cationic compounds and GO [33]. It is interesting to note that the obtained gelation performances can be regulated via different functional substituted headgroups in used compounds. The experimental data indicated that ammonium headgroup in molecular skeletons seemed more favorable for the composite gelation than pyridinium segment. The obtained results suggested that the self-assembly modes in present GO-based composites could be manipulated by controlling efficient headgroup effect. In addition, various weak forces between present building blocks seemed also responsible for the forma‐ tion of different nanostructures. Based on the obtained results data in present composite gel system, a reasonable mechanism about self-assembly modes in gels is shown in Figure 1. For the prepared CTAB-GO gel, various organized building blocks are obtained in different solvents because of the van der Waals force of substituent chains and the strong electrostatic interaction of ammonium headgroups with oxygen-containing functional groups at GO surface. In addition, for the cases of C16Py-GO and BPy-GO composite gels, the strong π–π stacking between carbon net in GO plane and additional pyridine headgroups showed as more competitive with other forces, such as electrostatic interaction and van der Waals force. Thus, the present research work demonstrates new exploration for the design of GO-based composite gels and self-assembled soft matters.

In addition, we have also demonstrated the formation of organogels by self-assembly of cationic gemini amphiphile–GO composites [34]. Their gelation behaviors in various organic solvents can be controlled by regulating molecular symmetry. The obtained data indicated that the designed functional groups and molecular symmetry could change the self-assembly modes and produce different self-assembled nanostructures. It seemed that longer alkyl chains in molecular skeletons could be helpful to enhance the intermolecular hydrophobic force in the process of self-assembly. So the changes of building blocks and stacking modes between present GO-based composites and different solvents are responsible for the formation of various nanostructures, as seen in Figure 2. It clearly indicated that the formed nanostructures in present composite materials were obviously different, such as nano-wrinkle, nano-lamella, and nano-belt. The obtained different morphologies in self-assembled gels can be mainly due to various formation mechanisms upon special self-assembly modes via weak interactive forces between building blocks. Finally, a reasonable self-assembled mechanism for symmetry effects in formation of present organized nanostructures is demonstrated. Thus, the present GO-based composite gel materials will give a helpful clue for the design and preparation of functional GO composite nanomaterials.

**Figure 1.** Scheme of different assembly modes in cationic amphiphiles–graphene oxide gels. CTAB-GO (a), C16Py-GO (b), and BPy-GO (c).

Preparation of Functionalized Graphene and Gold Nanocomposites – Self-assembly and Catalytic Properties http://dx.doi.org/10.5772/62166 251

**Figure 2.** SEM images of xerogels for GO sheet, C18-6-6/GO gels, C18-6-12/GO gels, and C18-6-18/GO gels in different solvents.

**Figure 3.** SEM and TEM images for the RGO/PEI and RGO/PEI/Ag hydrogels.

**Figure 1.** Scheme of different assembly modes in cationic amphiphiles–graphene oxide gels. CTAB-GO (a), C16Py-GO

(b), and BPy-GO (c).

250 Advanced Catalytic Materials - Photocatalysis and Other Current Trends

In another composite system, we have reported the design and preparation of silver nanopar‐ ticle-containing RGO-based composite hydrogel materials via an in situ reduction process [35]. The obtained experimental data indicated that the prepared composite gels were composed of 3D net-like nanostructures, as seen in Figure 3. In addition, the used preparation method included the in situ reduction of GO and silver acetate in hydrogel structures to fabricate present RGO-based composite hydrogel. So the formed silver nanoparticles were uniformly anchored on RGO surface in composite gel. Moreover, the photocatalytic behaviors for removing dye pollutants are also characterized for the silver nanoparticle-containing RGObased composite hydrogel, as seen in Figure 4. It is interesting to note that the obtained photocatalytic composite materials can be reused from an aqueous degradation system, indicating the important and potential applications for dye removal and wastewater treatment.

**Figure 4.** Degradation kinetics curves of as-prepared RGO/PEI/Ag nanocomposites on MB (a, b) and RhB (c, d) at 298 K.

In order to investigate the mechanism of hybrid graphene composites, we have also synthe‐ sized some LaMnO3–graphene composites as photocatalysts by a sol–gel method [36]. It is found that LaMnO3 perovskite phase was successfully fixed on graphene surface with welldispersion capacity, as seen in Figure 5. The data indicated that the photocatalytic capacity of as-formed LaMnO3–graphene composite materials were better than pristine LaMnO3 material, with the detailed results in Figure 6. The enhancement of photocatalytic properties can be mainly due to the high separation efficiency of photo-induced electron–hole pairs originated from the excellent conductivity of graphene in composite and the large interfacial contact between components, which is helpful to increase the dyes adsorption and improve the transfer efficiency in photocatalytic process. This research demonstrated new inspiration for designing photocatalytic graphene-based hybrid materials.

included the in situ reduction of GO and silver acetate in hydrogel structures to fabricate present RGO-based composite hydrogel. So the formed silver nanoparticles were uniformly anchored on RGO surface in composite gel. Moreover, the photocatalytic behaviors for removing dye pollutants are also characterized for the silver nanoparticle-containing RGObased composite hydrogel, as seen in Figure 4. It is interesting to note that the obtained photocatalytic composite materials can be reused from an aqueous degradation system, indicating the important and potential applications for dye removal and wastewater treatment.

252 Advanced Catalytic Materials - Photocatalysis and Other Current Trends

**Figure 4.** Degradation kinetics curves of as-prepared RGO/PEI/Ag nanocomposites on MB (a, b) and RhB (c, d) at 298 K.

In order to investigate the mechanism of hybrid graphene composites, we have also synthe‐ sized some LaMnO3–graphene composites as photocatalysts by a sol–gel method [36]. It is found that LaMnO3 perovskite phase was successfully fixed on graphene surface with welldispersion capacity, as seen in Figure 5. The data indicated that the photocatalytic capacity of as-formed LaMnO3–graphene composite materials were better than pristine LaMnO3 material, with the detailed results in Figure 6. The enhancement of photocatalytic properties can be mainly due to the high separation efficiency of photo-induced electron–hole pairs originated from the excellent conductivity of graphene in composite and the large interfacial contact between components, which is helpful to increase the dyes adsorption and improve the In another work, organized La1-xSrxMnO3/graphene thin films were prepared by both sol–gel and spin-coating methods [37]. In experimental process, the formed sol nanoparticles were adsorbed on graphene surface via electrostatic force in aging time. Then, the formed LaM‐ nO3 nanoparticles increase sizes and form crystal domains on graphene surface in the next calcination step. Present obtained nanostructures and morphology were investigated during various characterization techniques. Figure 7 shows the XRD patterns of graphene, LaMnO3, LaMnO3/graphene, and La0.9Sr0.1MnO3/graphene thin film. The diffraction peak of graphene appeared in the vicinity of 23°, which was similar to the diffraction peak position of graphite. However, this peak broadened and weakened because the size of the graphite sheet decreased, the integrity of the crystal structure declined, and the degree of disorder increased. The pattern of LaMnO3 is in agreement with PDF33-0713, indicating its perovskite structure with complete crystal shape. In the process of acid red 3GN photodegradation, LaMnO3/graphene thin film had sound stability and better photocatalytic ability than LaMnO3 thin film. As shown in Figure 8, a mild photodecomposition effect was observed in the degradation of dye. The absorption peak of acid red 3GN dye solution at 509 nm was from the initial 0.5446 to 0.5138 after irradiating for 48 h without photocatalysts. The experimental results indicated that graphene enhanced the dye adsorption, inhibiting the reunion of light-induced e<sup>−</sup> –h+ and improving photocatalytic capacity. In addition, it should be noted that a red shift of absorption edge was found by doping Sr, which seemed helpful to increase the photocatalytic performance of the obtained composite film.

In addition, another new LaMn1–xCoxO3/graphene composite material as photocatalyst had been designed and prepared by sol–gel method [38]. The experimental data indicated that LaMnO3 perovskite phase was anchored on graphene surface with the special perovskite structure. In addition, the photocatalytic capacity was characterized by the degradation of diamine green B. In the photodegradation process, the graphene component in composite can accelerate the dye adsorption, while doping Co component improves the photocatalytic performance. Thus, the reasonable charge transfer mechanism that occurred in the obtained LaMnO3/graphene composite during photocatalytic process is demonstrated in Figure 9. Firstly, diamine green B molecules could shift to the active surface of prepared composites from solution and organized in self-assembled face-to-face mode via π–π stacking with aromatic graphene net. Due to the effect of these holes and electron transfers, charge recom‐ bination is pushed in obtained LaMnO3/graphene composite and improves the efficiency of photocatalytic capacity.

Moreover, we have also reported the preparation of some graphene-based LaNiO3 composite films by both sol–gel method and spin-coating technique [39]. The obtained experimental results indicated that the size of formed LaNiO3 nanoparticles was about 20 nm, well dispersed on graphene surface. The photocatalytic capacity of present hybrid films had been demon‐ strated by degradation of acid red A. In comparison with pure LaNiO3 films, the designed LaNiO3/graphene composite films showed better photocatalytic behavior. It is interesting to

**Figure 5.** (a) AFM image of the as-synthesized graphene; (b) SEM image of graphene; (c, d, e) SEM, HRTEM, and SA‐ ED images of LaMnO3–graphene composites.

note that when the content of graphene shifted to the value of about 4%, the photocatalytic efficiency of the obtained composite films was double that of pure LaNiO3 films.

In another system, La1-xCaxMnO3 perovskite–graphene composites are synthesized as catalysts for Zn–air cell cathodes [40]. The results indicated that perovskite phase adhered on the surface of graphene sheets, and adding graphene significantly improved the electrochemical per‐ formance of LaMnO3. The XPS spectrum of La0.6Ca0.4MnO3–graphene composite is shown in Figure 10. The peak contained all the elements of La0.6Ca0.4MnO3. In addition, the obtained graphene showed gauze-like fold nanostructures, mainly originated from the oxygenic functional groups and the surface defects during preparation process. So the formed porous

**Figure 6.** (a) UV–Vis spectral changes of the degradation of acid red A by LaMnO3–graphene and LaMnO3; (b) photo‐ catalytic activities of LaMnO3–graphene composite and LaMnO3; (c) kinetics of photocatalytic degradation by the LaM‐ nO3 and LaMnO3–graphene.

note that when the content of graphene shifted to the value of about 4%, the photocatalytic

**Figure 5.** (a) AFM image of the as-synthesized graphene; (b) SEM image of graphene; (c, d, e) SEM, HRTEM, and SA‐

In another system, La1-xCaxMnO3 perovskite–graphene composites are synthesized as catalysts for Zn–air cell cathodes [40]. The results indicated that perovskite phase adhered on the surface of graphene sheets, and adding graphene significantly improved the electrochemical per‐ formance of LaMnO3. The XPS spectrum of La0.6Ca0.4MnO3–graphene composite is shown in Figure 10. The peak contained all the elements of La0.6Ca0.4MnO3. In addition, the obtained graphene showed gauze-like fold nanostructures, mainly originated from the oxygenic functional groups and the surface defects during preparation process. So the formed porous

efficiency of the obtained composite films was double that of pure LaNiO3 films.

ED images of LaMnO3–graphene composites.

254 Advanced Catalytic Materials - Photocatalysis and Other Current Trends

**Figure 7.** XRD pattern of graphene, LaMnO3, LaMnO3/graphene, and La0.9Sr0.1MnO3/graphene.

**Figure 8.** UV–Vis absorb spectrums of acid red-3GN under different conditions: (a) raw dye solution, (b) irradiation 48 h without catalyst, (c) LaMnO3 thin film adsorb dye 4 h without irradiation, (d) LaMnO3/graphene or La0.9Sr0.1MnO3/ graphene thin film adsorb dye 4 h without irradiation, (e) irradiation 4 h with LaMnO3 thin film as catalyst, (f) irradia‐ tion 4 h with LaMnO3/graphene thin film as catalyst.

Preparation of Functionalized Graphene and Gold Nanocomposites – Self-assembly and Catalytic Properties http://dx.doi.org/10.5772/62166 257

**Figure 9.** Proposed mechanism for photocatalytic degradation of diamine green B over graphene-based perovskite photocatalysts under light irradiation.

**Figure 7.** XRD pattern of graphene, LaMnO3, LaMnO3/graphene, and La0.9Sr0.1MnO3/graphene.

256 Advanced Catalytic Materials - Photocatalysis and Other Current Trends

**Figure 8.** UV–Vis absorb spectrums of acid red-3GN under different conditions: (a) raw dye solution, (b) irradiation 48 h without catalyst, (c) LaMnO3 thin film adsorb dye 4 h without irradiation, (d) LaMnO3/graphene or La0.9Sr0.1MnO3/ graphene thin film adsorb dye 4 h without irradiation, (e) irradiation 4 h with LaMnO3 thin film as catalyst, (f) irradia‐

tion 4 h with LaMnO3/graphene thin film as catalyst.

3D nanostructure can obviously enhance the three-phase domains and improve the mass transfer process as catalyst materials of air electrode. The experimental data indicated that the voltage plateau was superior with 10 wt% ratio value of graphene. Moreover, Ca doping maintained the perovskite structure and obviously enhanced the electrocatalytic activity for ORR, and La0.6Ca0.4MnO3–graphene composite demonstrated the best catalytic capacity. Thus, the obtained research work indicates that the prepared graphene-based La1−xCaxMnO3 composites are important material for design of air electrodes catalysts.

Recently, we have also reported the preparation of LaMnO3/graphene thin films with the perovskite-type as new photocatalyst via sol–gel process and spin-coating method [41]. The obtained results indicated that the addition of graphene did not change the perovskite structure, with formed LaMnO3 particles at about 22 nm well dispersed on graphene surface. Figure 11 displays the nitrogen adsorption–desorption isotherms and pore size distribution curves calculated by BJH method for LaMnO3 and LaMnO3/graphene powders. The larger surface area can effectively absorb the dye, thus increasing the contact probability of pollutant molecular and catalyst. Determination of contact angle indicated that the contact angle of glass substrate decreased and the hydrophilicity improved after treating with H2SO4 and APTES. The UV–Vis photocatalytic activity of the photocatalysts was evaluated by the degradation of diamine green B. LaMnO3/graphene thin films had better photocatalytic ability than LaM‐ nO3 and TiO2 films.

**Figure 10.** XPS spectrum of La0.6Ca0.4MnO3–graphene composite. (a) Overall spectrum, high-resolution curves of (b) O 1s region, (c) Ca 2p region, and (d) Mn 2p region.

**Figure 11.** N2 adsorption–desorption isotherms (a) and pore size distributions of samples (b).
