Physical and arsenic adsorption properties of maghemite and magnetite sub-microparticles

•To study the magnetite to maghemite topotactic transformation is a challenge.•The adsorptive properties of the submicroparticles were increased.•Maghemite sub-microparticles efficiently decrease the As-content in water below the WHO guideline. The topotactic transformation from magnetite to maghemite sub-microparticles was demonstrated by a variety of techniques that include X-ray diffraction, Raman spectroscopy, electron microscopy, Mössbauer spectroscopy, magnetic measurements, and vis-NIR diffuse reflectance. The physical, chemical, and morphological properties of the particles were correlated with their adsorptive properties in water with respect to arsenic (V). The adsorptive properties of the iron oxide are increased by changing the crystal phases involved, specifically, the transformation of magnetite to maghemite. Maghemite sub-microparticles are capable of efficiently decreasing the arsenic content in water from 100 ppb to below the World Health Organization (WHO) guideline of 10 ppb.