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RESEARCH PRODUCT

Chromium oxide nanoparticles with controlled size prepared from hydrothermal chromium oxyhydroxide precursors

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Abstract This work reports the preparation of morphologically well-defined chromium oxide nanoparticles with controlled sizes of 20–30 nm. The synthetic procedure encompass two stages, the first one refers to the preparation of chromium oxyhydroxide nanoparticles by a hydrothermal approach of previously precipitated xerogels, followed by a thermal transformation of CrOOH nanoparticles to Cr2O3. The series of chromium oxyhydroxide particles sized over the range 15–50 nm were prepared through the control of the pH of precipitation of the xerogels and the water/xerogel ratio of the hydrothermal aging. Results showed the formation of non-aggregated oxyhydroxide nanoparticles with two different trends: xerogels precipitated at pH 5 showed smaller particles for the higher amount of water (water/xerogel ratio in weight of 60/1); on the contrary, at pH 10 the size of oxyhydroxide nanoparticles increased with increasing the amount of water. The transformation from CrOOH to Cr2O3 took place at around 450 °C; well-defined, non-aggregated crystalline nanoparticles of Cr2O3 with similar sizes, regardless of the precursors, were observed after treating the different oxyhydroxides at 600 °C for one hour. Chromia nanocrystals obtained from precipitates at pH 10 displayed intense and better-defined absorption bands than those prepared at pH 5. Remarkable high reflectance intensity was shown by chromia nanocrystals prepared at pH 10 and the larger 60/1 water/xerogel ratio. The mechanisms of formation of both the CrOOH –grimaldite- and the Cr2O3 –eskolaite- nanoparticles by the two subsequent steps have been proposed based on the results arisen from the different characterization techniques.