Structure directing agent assisted solvothermal synthesis of octahedral WO3?nH2O large microcrystals: Study of electrochemical and optical properties

In the present study, the growth of tungsten trioxide crystals by solvothermal method was investigated in the presence of polyethylene glycol (PEG) and L-3,4-dihydroxyphenylalanine (L-dopa) as the structure directing agents in acetonitrile solution. The change of crystal faces consisting of stacked layers to very smooth facets is attributed to the change of the crystal growth mechanism from a three-step mechanism in the absence of PEG and L-dopa to a two-step mechanism in their presence. The rate of formation and growth of crystals in the presence of 5 w% of PEG increases significantly compared to those grown in the absence of PEG. The crystals solvothermally grown in the presence of L-dopa were of the octahedral WO3 center dot 0.5H2O with fully smooth faces, and those grown in the presence of PEG were the octahedral and rectangular microcrystals of WO3 center dot H2O The transparency and electro-optical properties of the prepared crystal layers are improved in the presence of PEG. The dynamic po-tential electropolymerization of aniline and the formation of a thin layer of polyaniline on tungsten trioxide crystals were performed and the properties of the obtained core-shell hybrid film were studied. It was shown that covering the crystals with a very thin layer of polyaniline helps to stabilize their electrochemical and optical properties.