Aerogels are 3D network porous, and lightweight structure gels formed typically with sol-gel chemistry, a process that encompasses the transformation of molecular precursors into highly cross-linked inorganic or organic gels. Then, the special driving techniques (e.g., supercritical drying, freeze drying, etc.) will be employed to replace the liquid components of the wet gels with a gas (typically air). The aerogels consist of three-dimensional networks of interconnector nanometer sized primary particles, and can be called solid smoke. The aerogels have ultra-low density (as low as 1 Kg m -3 ), 3D interconnected porosity and high surface area (1000 m g -2 ), high strength and heat resistance, and are the lightest solid in the world so far. In aqueous solution, the aerogels can expand rapidly, and can maintain a large volume of water without dissolving. The aerogels with these properties find a solid role in the fields of energy storage, environmental remediation, sensors, thermal insulators, and biomedicine, etc. . Rhodamine B for three days with a concentration of 1.0 g L -1 . The BC/dye hybrid aerogels were obtained by freeze-dried method, followed by sublimation at a temperature of -50 ˚C, and a pressure of 0.04 mbar. The BC/dye hybrid aerogels were further pyrolyzed under N2 atmosphere, at different temperature varying from 500 to 900 ˚C for 1 h to obtain the N-Sdoped CNF aerogels. The N-S-CNF aerogels had a 3D network structure with a fiber diameter of 10-20 nm with numerous interconnected pores. The XPS analysis revealed the presence of N and S heteroatoms with 4.64, and 0.91 at%, respectively. The prepared doped CNF aerogels were found to be promising electrocatalysts for ORR, and as electrode materials for supercapacitor studies. Ye et al. demonstrated the preparation of a "vein-leaf"-type 3D complex with CNF @ nitrogen-doped graphene through calcination of a mixture of urea, and BC . Urea was used as the source of nitrogen, and also as the precursor of layered g-C3N4, which was served as a sacrificial template for the formation of graphene nanosheets in the interlayer voids. BC pellicles was employed as the precursor for in-situ carbonization into CNF. The CNF@NG 3D network was obtained at 900 ˚C, since the g-C3N4 template undergoes complete thermolysis at 680 ˚C. The SBET of CNF@NG was found to 206 m g -2 , which was higher than that of bare CNF (132.9 m g -2 ) due to the presence of graphene with high SBET (782 m g -2 ). The XPS analysis showed nitrogen atoms into the structure of CNF@NG with 9.82 at%. The prepared CNF@NG 3D network revealed superior activity, and stability in ORR in alkaline media attributed to the robust porous 3D structure, which favored both electron, and mass transfer for ORR. increased pyrolytic temperature (600-1000 ˚C), whereas the mesopores content in the CNF aerogel structure was found to be increased, and a slight fall in the SBET (845.68 m g -2 ) was recorded at 1100 ˚C (Fig. ). The authors stated that, the mesopores performed a dual role;