Copper-assisted growth of high-purity carbon nanofiber networks with controllably tunable wettabilities†
The controlled growth of high-purity three-dimensional carbon nanofiber (CNF) networks is achieved on the outer surfaces of ceramic boats via chemical vapor deposition (CVD) after placing copper nitrate in ceramic boats. During CVD, the copper-nitrate-derived copper nanoparticles in the ceramic boats dramatically improve the yield of these CNF networks on the inherently rough outer surfaces of the ceramic boats, which act as weak catalytic sites for the growth of CNF networks. This approach can be extended to various commonly used ceramic substrates. The free-standing CNF networks, peeled off from the outer surfaces of the ceramic boats, exhibit superior properties, including hydrophobicity, porosity and excellent flexibility, and hence have high absorption capacity for various oils. Furthermore, Janus CNF networks are prepared using selective plasma modification or ammonia annealing of the free-standing CNF networks to produce areas of different wettabilities on their obverse and reverse surfaces. The hydrophobic areas on the obverse and reverse surfaces of the Janus CNF networks exhibit different patterns, which are reversibly switched between invisibility and visibility via alternately dropping and removing water. The Janus CNF networks can also act as bifunctional sorbent materials for the simultaneous removal of oils and dyes from water.