Facile fabrication of flower like self-assembled mesoporous hierarchical microarchitectures of In(OH)3 and In2O3: In(OH)3 micro flowers with electron beam sensitive thin petals
Introduction
Micro structured materials show a clear correlation between their morphology and function, which in turn decides their applications. Micro/superstructures with good interconnectivity and conductivity are useful in several fields [1]. As size and shape of materials are controlling factors, thereby influencing to the physical and chemical properties, it is natural that the synthesis of materials with fascinating morphologies is of researchers' interest. In particular, porous hierarchical architectures with interesting applications are materials of wide importance. Synthesis methods based on a hydrothermal process are especially beneficial due to its simplicity and modifiability, and also it is environmentally benign. In surfactant-free, simple hydrothermal process crystals as large as a few micrometers can be obtained simply by extending the reaction period under controlled conditions.
In2O3 is an n-type semiconductor with the band gap of 3.6 eV, and has applications in optoelectronics [2], touch screens [3] and in photocatalysis [4]. It is also used as a sensor for H2 [5], [6], Cl2 [7], O3 [8], CO2 [5] and NO2 [6] gases. Since the conversion of In(OH)3/InOOH to In2O3 was found to proceed with a retention of morphology, the morphological regulation of In2O3 depends on its precursors [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. Furthermore, research on metal hydroxides is still relatively limited compared to metal oxides and sulfides. In an attempt to prepare morphologically interesting In(OH)3 and In2O3 structures, herein we report template and capping-reagent free hydrothermal synthesis of flower like In(OH)3 microstructures and its conversion to In2O3. To the best of our knowledge this is the first report on the synthesis of mesoporous hierarchical microarchitectures with a flower-like morphology for both In(OH)3 and In2O3.
Section snippets
Hydrothermal synthesis and calcination
Milli Q-Plus water (resistance = 18.2 M Ω) was used for all experimental work. In(OH)3 microstructures with a flower-like morphology were prepared using indium nitrate (3 g, 10 mmol) and biuret (6.2 g, 60 mmol). Both were separately dissolved in about 100 mL of water and heated to the boiling point. The hot solutions were mixed under stirring (200 rpm), and after 30 min the mixture was transferred into a 250 mL Teflon cup. The sealed Teflon vessel was put into a stainless steel flask and kept
SEM and TEM studies
The hydrothermal reaction products present flower-like morphology in the diameter range of 2–3.5 μm, as evidenced by SEM images (Fig. 1). These microstructures are 3D hierarchical structures assembled from nano-sized flakes with the thickness of about 30–50 nm (Fig. 1d). The results from the EDX spectrum (Fig. SM1) suggest formation of In(OH)3 as the determined In/O ratio is close to 1:3; which is further confirmed unambiguously by the powder X-ray diffraction (see following sections). TEM
Conclusions
Hydrothermal fabrication of mesoporous hierarchical microarchitectures of In(OH)3 with a flower like morphology using indium nitrate and biuret is reported. Biuret is expected to have a triple role as alkaline media, chelating agent and surface anchored organic molecule. The plausible mechanism for the formation of hierarchical architectures of In(OH)3 might be Ostwald ripening. Calcination of In(OH)3 results in mesoporus In2O3 hierarchical architectures. For In2O3 the average crystal size is
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