Tailored crystal growth of two dimensional (2D) structured BiOCl photocatalyst is a quite challenging area and prerequisite for achieving superior photoreactivity. In this work, the constrained growth of ultrasmall BiOCl nanodiscs (similar to 65 nm in diameter) with a low percentage of exposed {001} facets (as low as similar to 59%) has been achieved through a facile hydrolysis route at normal temperature and pressure, by using sodium bismuthate (NaBiO3) and hydroxylammonium chloride (HONH2 center dot HCl) aqueous solution as the bismuth source and "four-in-one" reaction media, respectively. By means of diverse characterization techniques and density functional theory (DFF) method, it was found that hydroxylammonium chloride solution not only acts as a kind of solvent, reductant and chloride donator, but also plays a crucial role on the constrained growth of {001} facets in BiOCl nanodiscs via the two-stage growth mechanism. Additionally and more importantly, the as-prepared BiOCl nano discs exhibit superior sorption capacity and visible-light-induced photodegradation performance of Rhodamine B contaminant, to the conventional BiOCl nanosheets dominated with {001} facets. (C) 2015 Elsevier B.V. All rights reserved.