One-pot synthesis of carbon fiber/carbon nanotube hybrid using lanthanum (III) chloride for tensile property enhancement of epoxy composites

• A facile one-pot method for CF/CNT hybrid preparation. • The eco-friendly LaCl 3 -urea-ethanol solution is used to synthesize CF/CNT hybrid. • La (III)/urea on CF and CNT surface play the role of bridge to connect them. • Tensile strength of CF/CNT/Ep composites was enhanced by 59.0%. • Strengthening mechanism was revealed based on La (III), urea and CNT on CF surface. This study presents a one-pot method for facile synthesis of carbon fiber (CF) / carbon nanotube (CNT) hybrid, which is achieved by the surface reaction of CF and carboxylated carbon nanotubes (CNT-COOH) in the eco-friendly lanthanum (III) chloride (LaCl 3 )-urea-ethanol solution. The control variate method is utilized to investigate the formation mechanism of the CF/CNT hybrid. Based on the scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared and X-ray photoelectron spectroscopy results, it is found that La (III) coordinates with two or more atoms from different material surface so as to link different material, and urea serves as lone electron pair donor to provide extra binding sites for La (III), then both La (III) and urea play the role of bridge to connect CF and CNT-COOH. The prepared CF/CNT hybrid improves the tensile strength (modulus) of epoxy composites by 59.0% (78.5%), and corresponding improving mechanism has been revealed. The one-pot synthesis of CF/CNT hybrid is convenient, eco-friendly and thus suitable for green industrial application.