THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THIS INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED FIELD OF INVENTION The present disclosure relates to nanoscale shell of metal oxide/hydroxide on an organic-templated-boehmite-nanoarchitecture, along with methods of preparation and its use for water purification. PRIOR ART: Aluminum based compositions have been exhaustively studied for the removal of inorganic anions from drinking water (e.g., fluoride/arsenate). Use of aluminum based compositions is more pertinent for fluoride adsorption from water due to its relatively higher fluoride adsorption capacity vis-a-vis other adsorbents as well as no additional requirement of pre/post-filtration. Improvement in the capacity of aluminum based compositions has been looked at from various approaches. It is also important to understand that practically all aluminum based compositions in the field use require frequent regeneration, largely to reduce the cost of water purification. However, traditionally followed practice of regeneration (alkali treatment followed by acidification) leads to secondary contamination of water sources such as high fluoride concentration in the sludge, leaching of aluminum in water and high dissolved salt content of the sludge. Prior art related to fluoride removal using aluminum based compositions and associated challenges are covered in detail in our previous patent application (1529/CHE/2010). Some of the most recent prior art on fluoride removal using aluminum and/or chitosan based compositions are highlighted here. (a) Miretzky P., Cirelli A. F., Fluoride removal from water by chitosan derivatives and composites: A review, Journal of Fluorine Chemistry 132 (2011) 231-240 (b) Jagtap S., Yenkie M. K., Das S., Rayalu S., Synthesis and characterization of lanthanum impregnated chitosan flakes for fluoride removal in water, Desalination 273 (2011) 267-275 (c) Fluoride removal from water by adsorption—A review, Bhatnagar A., Kumar E., Mika Sillanpaa M., Chemical Engineering Journal, 171 (2011) 811-840 (d) Liu R., Gong W., Lan H., Gao Y., Liu H., Qu J., Defluoridation by freshly prepared aluminum hydroxides, 175 (2011) 144-149 BACKGROUND OF THE INVENTION The motivation of our research group is to solve the problem of fluoride removal from drinking water, considering the following boundary conditions: (i) Adsorbent composition should be implementable at the household level (i.e., high adsorption kinetics and low empty bed contact time) (ii) Adsorbent composition requires no regeneration, thereby generating no secondary contamination (iii) Adsorbent composition should be easy-to-use and maintain (i.e., requiring no pre/post-filtration) (iv) Adsorbent dose should be able to reduce any input concentration <10 ppm to below 1 ppm (National Sanitation Foundation norm for challenge water to be used for fluoride removal claim: 8 ppm as input concentration for the challenge water and <1 ppm for output water). (iv) Most importantly, cost of water purification should not exceed