Controlling the morphological evolution in nanostructures is essential for improving their functionality, for example, in catalysis. Here, we demonstrate, using chromium oxide as a model system, that morphologies of functional binary oxide particles can be tailored by an efficient template-free synthetic approach. We construct a morphological "phase diagram" for chromium oxide spheres that shows the evolution of size and surface roughness as a function of the precursor and urea concentrations. It is notable that these chromium oxide spheres show an exceptional ability to remove azo-dye pollutant in water treatment. Thus, the porous chromium oxide spheres with very good dye absorptions are expected to be useful in alternative absorption technologies.