Ultrasonic Synthesis of Carbon Nanotube-Titanium Dioxide Composites: Process Optimization via Response Surface Methodology.

In this study, the central composite design of response surface methodology was applied to optimize the ultrasonic synthesis of multiwalled carbon nanotube-titanium dioxide (MWNT-TiO) composites. Twenty composites were prepared by adjusting three parameters (MWNT concentration in water, sonication to disperse/exfoliate MWNTs in water, and sonication to attach TiO onto MWNTs) at five levels. On the basis of the experimental design, semiempirical expressions were developed, analyzed, statistically assessed, and subsequently applied to predict the impact of the studied parameters on composite synthesis. The composite synthesis process was optimized to capture the experimental conditions favoring the highest productivity (i.e., MWNT-TiO formation or percent TiO attachment) utilizing minimal resources. The synthesis process optimization results showed that, to make a MWNT-TiO composite in 10 mL of water, 23.2 mg (∼99% of 23.4 mg) of TiO can be attached to 2.6 mg of MWNTs. This process requires only 727 J sonication energy, of which 592 J is invested to exfoliate MWNTs (Sonication 1) and 135 J to attach TiO (Sonication 2) to MWNTs. Finally, the optimally synthesized composite was extensively characterized using SEM, surface area and porosity analysis, TGA, and ζ-potential analysis/DLS. Also, this composite was tested for stability under variable pH and solvent polarity. The approach developed in this study could be used to optimize the synthesis process of other similar composites.