Optimization of synthesis conditions of carbon nanotubes via ultrasonic-assisted floating catalyst deposition using response surface methodology

Abstract

The growing use of carbon nanotubes (CNTs) in a plethora of applications has provided to us a motivation to investigate CNT synthesis by new methods. In this study, ultrasonic-assisted chemical vapor deposition (CVD) method was employed to synthesize CNTs. The difficulty of controlling the size of clusters and achieving uniform distribution—the major problem in previous methods—was solved by using ultrasonic bath and dissolving ferrocene in xylene outside the reactor. The operating conditions were optimized using a rotatable central composite design (CCD), which helped optimize the operating conditions of the method. Response surface methodology (RSM) was used to analyze these experiments. Using statistical software was very effective, considering that it decreased the number of experiments needed to achieve the optimum conditions. Synthesis of CNTs was studied as a function of three independent parameters viz. hydrogen flow rate (120–280 cm3/min), catalyst concentration (2–6 wt %), and synthesis temperature (800–1200°C). Optimum conditions for the synthesis of CNTs were found to be 3.78 wt %, 184 cm3/min, and 976°C for catalyst concentration, hydrogen flow rate, and synthesis temperature, respectively. Under these conditions, Raman spectrum indicates high values of (IG/ID), which means high-quality CNTs.