Comparative catalytic properties of Ni(OH)₂ and NiO nanoparticles towards the degradation of nitrite (NO₂^-) and nitric oxide (NO)

Nitrite (NO₂^-) and nitric oxide (NO) have been identified as an environmentally hazardous analytes from discharged industrial effluents. Thus in this study, nickel oxide (NiO) and nickel hydroxide (Ni(OH)₂) nanoparticles were synthesized using the complexation-precipitation method and their catalytic properties towards NO₂^- and NO investigated. The success of the synthesised nanoparticles was confirmed using characterisation techniques, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and the Fourier transformed infrared (FTIR) spectroscopy. The sizes of the synthesized NiO and Ni(OH)₂ nanoparticles were estimated to be 5.39 and 5.07 nm respectively. The catalytic behaviour of NiO and Ni(OH)₂ nanoparticles towards the oxidative degradation of NO and NO₂^- in acidic and neutral media respectively was studied using UV-Vis spectrophotometer. Result indicated that NiO nanoparticles demonstrated better catalytic properties at different reaction time towards NO₂^- and NO oxidation compared to Ni(OH)₂, while NiO and Ni(OH)₂ at nano scale showed enhanced catalysis towards the analytes compared with the bulk Ni salt. The bulk Ni salt did not show any sensing properties towards NO₂^-. However in NO, the absorbance intensity due to the generation of nitrate (NO₂^-) was five times higher in the presence of NiO nanoparticles compared with the bulk Ni salt. The improved catalysis of Ni(OH)₂ and NiO nanoparticles in this study was attributed to effective pore sizes and large surface area which expose the analytes to more catalytic site. The nanoparticles are simple to prepare, therefore can be used for the fabrication of a simple, portable, miniaturized nitrite and nitric oxide nanosensor for potential clinical and analytical application.