Morphology Transition Engineering of ZnO Nanorods to Nanoplatelets Grafted Mo8O23-MoO2 by Polyoxometalates: Mechanism and Possible Applicability to other Oxides

Abstract

A new fundamental mechanism for reliable engineering of zinc oxide (ZnO) nanorods to nanoplatelets grafted Mo8O23-MoO2 mixed oxide with controlled morphology, composition and precise understanding of the nanoscale reaction mechanism was developed. These hybrid nanomaterials are gaining interest due to their potential use for energy, catalysis, biomedical and other applications. As an introductory section, we demonstrate a new expansion for the concept ‘materials engineering’ by discussing the fabrication of metal oxides nanostructures by bottom-up approach and carbon nanoparticles by top-down approach. Moreover, we propose a detailed mechanism for the novel phenomenon that was experienced by ZnO nanorods when treated with phosphomolybdic acid (PMA) under ultra-sonication stimulus. This approach is expected to be the basis of a competitive fabrication approach to 2D hybrid nanostructures. We will also discuss a proposed mechanism for the catalytic deposition of Mo8O23-MoO2 mixed oxide over ZnO nanoplatelets. A series of selection rules (SRs) which applied to ZnO to experience morphology transition and constitute Abdelmohsen theory for morphology transition engineering (ATMTE) will be demonstrated through the article, besides a brief discussion about possibility of other oxides to obey this theory.

Influence of Salinity and Pb on the Precipitation of Zn in a Model System

“…The changing intensity of the three main peaks of ZnO in low and medium AQs is a strong indication for a changed morphology of the ZnO particles [19,35]. In the presence of foreign atoms, the preferential growth of the ZnO nanostructure can be modified [36]. Furthermore, the low intensity of the reflexes in medium saline AQ is interpreted as a decrease of the crystallinity or size of the phases.…”

Theory for Morphology Engineering of Solid Compounds (ATMESC): Facts, Predictions and Experimental Evidences

“…The ability of zinc oxide (ZnO), and expected similar behaviour of cuprous oxide (Cu 2 O) and other binary compounds that exhibit (d 10 ) orbitals to experience morphology transition when react with phosphomolybdic acid (PMA), has initiated the idea of the ability of other solid chemical compounds to acquire polar surfaces to experience morphology transition under certain conditions. Facts, predictions and some experimental evidences are discussed which support the theory.Abdelmohsen theory for morphology transition engineering (ATMTE) has paved the way towards a general theory that may govern the morphology transition of nearly all solid compounds under specific conditions [1]. The morphology transition of zinc oxide was explained physically by attributing the inducing of polarity to the repulsion force between electron clouds of surface ions and polyoxometalates anions (POMs anions) which induces relaxation of outer surface atoms [1,2].…”

“…The contribution of chemical etching was considered and supported by the ability of molybdates to form intermediate compounds like Zn-molybdates (ZM) or/and Zn phosphomolybdate (ZMP) (pigments) when react with zinc cations. Intermediate compound mechanism (ICM) was supposed which may involve dissolution and re-crystallization of zinc oxide to facilitate solid-state fusion [1][2][3].From a point of view of a chemist, the concept of materials engineering [4] was expanded to include "controlling and designing the oriented structures of materials by rescaling their dimensions [5][6][7] or varying their external morphologies [8][9][10], favorably with functionalization [11][12][13], decoration [14][15][16][17], doping [18][19][20][21] or mixing [22,23] with other materials to attend the synergistic effect [24][25][26] which enhance their properties". There are two main methods used for nanofabrication; Top-down and bottom-up approaches.…”

“…ATMTE states that "Binary compounds especially amphoteric/ diamagnetic pure and doped metal-oxides like (ZnO, Cu 2 O) that have appropriate energy difference between their LUMO (acid site/ cation) and HOMO (base site/anion), may experience morphology transition to various dimensions (1D, 2D and 3D) when reacts with polyoxometalates under specific conditions, with a possibility to manipulate their surface catalytic properties" [1]. ATMTE has expected similar behviour for all binary compounds that acquire (d 10 ) electronic configuration.…”

“…The contribution of chemical etching was considered and supported by the ability of molybdates to form intermediate compounds like Zn-molybdates (ZM) or/and Zn phosphomolybdate (ZMP) (pigments) when react with zinc cations. Intermediate compound mechanism (ICM) was supposed which may involve dissolution and re-crystallization of zinc oxide to facilitate solid-state fusion [1][2][3].…”