CO2-assisted template synthesis of porous hollow bi-phase gamma-/alpha-Fe2O3 nanoparticles with high sensor property

In this contribution, monodisperse porous hollow bi-phase gamma-/alpha-Fe O-2(3) nanoparticles were successfully fabricated based on hard-template method with using carbon colloids as sacrificial templates. A new concept of assembling one kind of metal oxide with different crystalline structures into a single shell was presented for the first time. The critical procedure of coating carbon cores with a uniform layer of oxide was performed in CO2-expanded ethanol, which is a versatile way to produce high-quality hollow oxide nanoparticles. The formation of the novel bi-phase shell was achieved through combining the reduction ability of carbon cores under inert calcination atmosphere and the unique chemical composition of intermediate-shell formed in CO2-expanded ethanol. The porous hollow gamma-/alpha-Fe2O3 nanoparticles with an average diameter of 99 nm not only possess combined properties of gamma-Fe2O3 and alpha-Fe2O3, but also have a large specific surface area of 93.7 m(2) g(-1) and a high pore volume of 1.056 cm(3) g(-1), enabling them to have widespread applications in sensors, catalysis, magnetic and electrochemical areas, etc. Herein, such hollow bi-phase gamma-/alpha-Fe2O3 nanoparticles were utilized to prepare a sensor device, and intriguingly it shows higher sensitivity and selectivity to ethanol than gamma-Fe2O3 powders and many other porous alpha-Fe2O3 materials reported recently. The probable sensor mechanism of hollow gamma-/alpha-Fe2O3 nanoparticles was discussed in detail.