Phase Transition Behavior and Oriented Aggregation During Precipitation of In(OH)₃ and InOOH Nanocrystals

Abstract

The phase transition behavior and oriented aggregation (OA) during colloidal synthesis of In(OH) 3 nanocrystals in water are investigated by TEM, SEM, Xray diffraction, and density functional theory (DFT) calculations. Besides the cubic In(OH) 3 phase, also orthorhombic InOOH is formed in a precipitation route using indium acetate as the In 3+ source. Well-developed nano-and microcuboids are observed that consist solely of In(OH) 3 . In contrast, the InOOH phase remains semicrystalline even for long reaction (refluxing) times. The irregular growth of the InOOH phase is explained by proton transfers from hydroxyl groups to oxygen ions within the InOOH lattice that lead to OH disorder and lattice strain. DFT calculations of the surface energies of ideal and water-saturated low-index InOOH and In(OH) 3 surfaces predict that the In(OH) 3 phase becomes energetically more favorable than InOOH above a critical crystallite size. This explains why InOOH is formed before the In(OH) 3 phase, which is an unusual pathway for a hydrothermal process. Once InOOH has transformed to In(OH) 3 by incorporation of water, the crystallites can grow without restriction due to the disappearance of OH-disorder-induced strain. Finally, for the In(OH) 3 cuboids a three-step formation process is suggested: In the first step, one-dimensional OA under formation of nanorods occurs. In the second step, parallel bundles are formed from the nanorods. In the third step these bundles merge into cuboids by three-dimensional OA.

First Combined Electron Paramagnetic Resonance and FT-IR Spectroscopic Evidence for Reversible O2Adsorption on In2O3–xNanoparticles

“…In addition, in its cubic form In 2 O 3 is well known as the active layer of resistive gas sensors which are particularly sensitive to oxidizing gases and at the same time nearly insensitive to reducing gases. [6][7][8] A variety of methods for the preparation of In 2 O 3 thin films and powders such as electronbeam deposition 3 , metal organic chemical vapor deposition 1,8 , dc magnetron sputtering 9 , vacuum evaporation 4 and -last but not least -solution based methods [10][11][12][13][14] have been reported. There is, however, only little information about the fundamental surface properties of In 2 O 3 in its various forms, ranging from single crystals with well-defined planar surfaces 15 , to sputtered thin polycrystalline films or particle based high surface area coatings.…”

Sensing Molecules with Metal–Organic Framework Functionalized Graphene Transistors

“…As a reference, in ambient conditions, the water chemical potential is μ W (293 K, 1 bar) = 0.57 eV. [ 65 ] The environment favoring alcohol chemisorption is possible in the experiment when the flow of dry air (nitrogen) is still saturated with alcohol vapor at ambient pressure. The chemisorption of alcohol on alumina causes the alcohol to split into H + and negatively charged alkoxy groups (alkoxy − such as ethoxy C 2 H 5 O − ).…”

“…This can be seen from the higher binding energy/exothermic chemisorption of water compared to any alcohols. [ 65 ] As a result, depending on the interplay of the protonation and the removal efficiency of the anions, the surface of alumina can acquire some positive charge density. During the exposure of the GFET with alcohol gas, the positive net charge is caused by the remaining H + at the alumina surface, when alkoxy − is released and drifts away.…”

Porous corundum-type In2O3 nanoflowers: controllable synthesis, enhanced ethanol-sensing properties and response mechanism

“…At the early stage, the XRD pattern was in good agreement with the cubic InIJOH) 3 phase, and small amounts of the orthorhombic InOOH phase were existent, which was consistent with previous references. 29,41 As the reaction proceeds, the peaks corresponding to InOOH became apparent. These peaks were significantly broader than the peaks corresponding to InIJOH) 3 , indicating the change from cubic to orthorhombic.…”

“…From our experiments, it became evident that the InOOH phase was present at short reaction times, which was in accordance with the results obtained by Lin et al 29 The formation of InOOH can be described as the obtained InIJOH) 3 nuclei eliminating water molecules from their core while maintaining a hydroxide shell because of the lower water/solid interface energy of InOOH. 41 In general, as the reaction proceeds, InOOH particles could transform to InIJOH) 3 by incorporation of water, and the particles can grow without restriction and frustration because of the regular cubic crystal structure. However, under our experimental conditions, there was not enough water to generate InOOH, and there was less OH − in the solution (less water) to combine with In 3+ due to the strong acidity of the reaction solution with a pH value of 4-5.…”