Hierarchical In(OH)₃ as a Precursor to Mesoporous In₂O₃ Nanocubes: A Facile Synthesis Route, Mechanism of Self-Assembly, and Enhanced Sensing Response toward Hydrogen

Abstract

Mesoporous In 2 O 3 nanocubes were achieved in this present work following a transformation from hierarchical structures of mesoporous In(OH) 3 nanocubes synthesized hydrothermally. Appreciable control on the morphology of In(OH) 3 nanostructures was attained by optimizing the reactant concentration, ratio of structure directing agent in the reaction medium (water/PEG ratio), the reaction temperature, and time. The synthesized samples were characterized extensively by XRD, TG-DTA, micro-Raman, and UV-DRS. Surface area and pore size distribution were determined from N 2 adsorption and desorption isotherms. Morphological evaluations carried out using electron microscopy in scanning (FE-SEM) and transmission (TEM) mode not only provided information on the size and shape of the materials but also revealed the hierarchical assembly consisting of primary and secondary structures. Controlled studies as a function of various reaction parameters and the morphological evolution observed are rationally correlated to propose a plausible formation mechanism. Further, hydrogen gas sensing properties (sensitivity, sensor response, and recovery time) of the asprepared In 2 O 3 nanostructures (nanocubes, nanobricks, nanoflakes, and nanoparticles) were investigated to demonstrate the influence of morphology. Owing to the porous structures and large surface area, In 2 O 3 nanocubes exhibit superior sensitivity with short response/recovery times at concentrations as low as 100 ppb. Surface decoration with Pd nanoparticles activates these nanocubes, promoting excellent sensing response and selectivity toward hydrogen at room temperature.

Metastable γ-Bi2O3 tetrahedra: Phase-transition dominated by polyethylene glycol, photoluminescence and implications for internal structure by etch

“…7) indicate that they both have pure monoclinic phase of Bi 2 O 3 (JCPDS 41-1449). General, polyethylene glycol (PEG) is a nonionic surfactant with uniform and ordered chain structure and easily adsorbed on different crystal faces to confine the growth rate of crystal in some certain directions which leads into anisotropic growth of crystals during material synthesis [34][35][36][37][38]. In this reaction, the uniform and ordered chains of PEG play a crucial role not only in the morphology, even more important in phase-transition of Bi 2 O 3 .…”

Monodispersed In2O3 mesoporous nanospheres: One-step facile synthesis and the improved gas-sensing performance

“…Thus, porous micro-/nanostructures can cause the enhancement of both sensing sensitivity and response rate [22]. For obtaining porous In 2 O 3 , one method is through precursor-mediated route [23][24][25]. In this case, In(OH) 3 [26], InOOH [27,28], or similar precursors were firstly prepared.…”

“…For example, Lee et al demonstrated the synthesis of porous In 2 O 3 hollow spheres through a sucrose-mediated precursor [29]. Mesoporous In 2 O 3 nanocubes were prepared from hierarchical In(OH) 3 nanocubes synthesized hydrothermally [23]. Recently, Zhang et al synthesized porous In 2 O 3 micro-/nanoflowers from In(OH) 3 precursor.…”

Pd-loaded In2O3 nanowire-like network synthesized using carbon nanotube templates for enhancing NO2 sensing performance

“…CNTs are ideal templates to synthesize quasi-1D metal oxides, because of their excellent acid and alkali resistance. [27][28][29][30][31] Pd-loaded In 2 O 3 may theoretically improve sensing performance. In earlier studies, Ning Du et al 21 prepared porous In 2 O 3 nanotubes with polyelectrolytes using layer-by-layer assembly/deposition on CNTs, followed by calcination.…”