Maghemite/ZnO nanocomposites: A highly efficient, reusable and non-noble metal catalyst for reduction of 4-nitrophenol

Abstract

Maghemite/ZnO nanocomposites synthesized by a two step process were used for catalytic reduction of p-nitrophenol. Maghemite nanoparticles were synthesized by hydrothermal technique followed by deposition of ZnO on it via co-precipitation process. X-ray diffraction analysis suggested formation of Maghemite and ZnO with tetragonal and hexagonal close packed structure respectively whereas electron microscopy images indicated the formation of near spherical nanocomposites with a size range of 30–50 nm. Maghemite/ZnO calcined at 300 °C is investigated as heterogeneous catalyst for reduction of p-nitrophenol and its catalytic activity is compared with that of Maghemite and ZnO nanoparticles. The parameters responsible for reduction of p-nitrophenol over Maghemite/ZnO were scrutinized using Response Surface Methodologyand the predicted values of reduction efficiency were found to be in a good agreement with the experimental findings (R2 > 0.9). The highest achievable percentage of reduction of target molecular species was noted to be of 98.6%. Optimization study showed that maximum reduction efficiency was observed at optimum conditions: p-NP concentration = 0.2 mM, Maghemite/ZnO loading = 200 ppm, reaction time = 6 min. Maghemite/ZnO has shown noticeably higher catalytic activity than pure oxides which remained almost unaltered for five consecutive cycling suggesting possible commercial potential of the developed material.