A method of producing a composite product is provided. The method includes providing a fluidized bed of carbon-based particles in a fluidized bed reactor, providing a catalyst or catalyst precursor in the fluidized bed reactor, providing a carbon source in the fluidized bed reactor for growing carbon nanotubes, growing carbon nanotubes in a carbon nanotube growth zone of the fluidized bed reactor, and collecting a composite product comprising carbon-based particles and carbon nanotubes.