Highly selective ammonia sensors based on Co1−xNixFe2O4/multi-walled carbon nanotubes nanocomposites

Co1−xNixFe2O4/multi-walled carbon nanotubes (MWCNTs) nanocomposites (x = 0.2, 0.4, 0.5, 0.6, 0.8) were synthesized via an in situ solvothermal method using ethylene glycol as solvent. X-ray diffraction analysis result confirmed that MWCNTs and high purity Co1−xNixFe2O4 nanocrystallites coexisted in the nanocomposites. Transmission electron microscopy revealed that 50-60 nm Co1−xNixFe2O4 nanoparticles (NPs) were densely clustered along the length of the MWCNTs. Substitution of the Co2+ by Ni2+ at octahedral sites was verified by vibrating sample magnetometry. Co1−xNixFe2O4/MWCNTs nanocomposites have a high selectivity for ammonia vapor, with a sensitivity greater than that observed for either bare MWCNTs or Co1−xNixFe2O4 NPs.