Grape-like mesostructured silica nanoparticle-decorated single-walled carbon nanotubes: Silica growth and dye adsorptivity

Single-walled carbon nanotube (SWCNT)-mesostructured silica nanoparticle (MSN) adsorbents (S-MSNs) were prepared through a simple one-step method with various loadings of SWCNTs. Their surface properties were characterized by XRD, TEM, N₂ physisorption, and FTIR spectroscopy. A grape-like S-MSN was produced, for which the growth of MSNs became intense with increasing CNT loading. A bimodal pore structure also developed, which increased the average pore size and pore volume, but decreased the surface area. The increasing amount of CNTs was found to provide more sites for silica growth that enhanced the adsorptivity of the S-MSNs toward methylene blue (MB) dye. Accordingly, 0.1 g L^-1 5 wt% S-MSN was able to adsorb 478 mg g^-1 (q_m) of 50 mg L^-1 MB at pH 7 and 323 K. The equilibrium data were evaluated using the Langmuir, Freundlich, Redlich-Peterson, and Dubinin-Radushkevich isotherm models, with the Langmuir and Redlich-Peterson models affording the best fit to the adsorption data. The adsorption was best described by a pseudo-second-order kinetics model and thermodynamically favored the endothermic chemisorption process. These results indicated the potential of S-MSN as an effective new adsorbent for dye adsorption.