The design of multidirectional porous metal oxide catalysts has attracted extensive attention because such materials have potential for environmental applications. To satisfy the requirements of these applications, large-scale production, low-cost manufacturing, and efficient transformation reactions are needed. The present paper reports the fabrication of hierarchical nickel oxide nanocrystals (NiO NCs) with hexagonal nanoplatelets and micro-, meso-, and macropore cavities through an eco-friendly method. The controlled size and shape of the NiO platelets in condensed orientation sequence "tesserae blocks" led to the formation of a hexagonal mosaic-like morphology. The NiO NCs could be recovered and reused without lost of activity over a number of batch reactions. In addition, theoretical models to predict the molecular structures of both the intermediate and transition states within the chemical transformation reactions were developed. The theoretical findings in the current study provide insight into the key factors that control the changes in the molecular structure throughout the transformation mechanism of the phenolic pollutants using NiO platelet nanocatalysts. (C) 2012 Elsevier B.V. All rights reserved.