Hierarchical Mesoporous In₂O₃ with Enhanced CO Sensing and Photocatalytic Performance: Distinct Morphologies of In(OH)₃ via Self Assembly Coupled in Situ Solid–Solid Transformation

Abstract

The present investigation details our interesting findings and insights into the evolution of exotic hierarchical superstructures of In(OH)3 under solvothermal conditions. Controlled variation of reaction parameters such as, reactant concentration, solvent system, crystal structure modifiers, water content along with temperature and time, yielded remarkable architectures. Diverse morphologies achieved for the first time includes (i) raspberry-like hollow spheres, (ii) nanosheet-assembled spheres, (iii) nanoparticle-assembled spheres, (iv) nanocube-assembled hollow spheres, (v) yolk-like spheres, (vi) solid spheres, (vii) nanosheets/flakes, and (viii) ultrafine nanosheets. A plausible mechanism is proposed based on the evidence gathered from a comprehensive analysis aided by electron microscopy and X-ray diffraction studies. Key stages of morphological evolution could be discerned and rationally correlated with nucleation, growth, oriented attachment, and Ostwald ripening mediated by dissolution-redeposition mechanism coupled with solid evacuation. Remarkably phase-pure bcc-In2O3 with retention of precursor morphology could be realized postcalcination at 400 °C, which underlines the advantage of this strategy. Two typical hierarchical structures (raspberry-like hollow spheres and nanoparticles assembled spheres) were investigated for their gas sensing and photocatalytic performances to highlight the advantages offered by nanostructuring. An impressive sensor response, Smax ≈ 7340 and 4055, respectively for the two structures along with appreciably fast response/recovery times over a wide concentration range and as low as 1 ppm exhibits the superior sensitivity toward carbon monoxide (CO). When compared to commercial In2O3, estimated rate constant indicates ∼3-4 times enhancement in photocatalytic activity of the substrates toward Rhodamine-B.

Low-Temperature H2S Detection with Hierarchical Cr-Doped WO3 Microspheres

“…In addition, SEM observations also reveal that hollow Cr-doped WO 3 microspheres were assembled in a more complex manner (Figure d and Figure S2b). These findings corresponding to the related publications, − which confirm that Cr-doped WO 3 hierarchical surface and mesoporous morphology well promote the diffusion and transport of gases into sensing layer, thus obtaining better sensor performance.…”

Realization of ppm-level CO detection with exceptionally high sensitivity using reduced graphene oxide-loaded SnO2 nanofibers with simultaneous Au functionalization

“…To date, significant amount of research studies have been reported on the sensing of CO gas (Table S1, ESI †). First, very high sensor responses, in the range of 29-480, was attained by means of using various material systems, including Au and SnO 2 nanocrystals on CNTs, 18 Co 3 O 4 nanowires, 19 In 2 O 3 raspberry hollow spheres, 20 Au-doped SnO 2 -In 2 O 3 nanocomposites, 21 Pt/SnO 2 , 22,23 and Sm 2 O 3 -doped Pt/SnO 2 . 23 However, the concentration of CO gas was set to 100-1000 ppm.…”

Structure and Photocatalytic Properties of In(OH)₃/InOOH Natural Heterojunction Nanocrystals Prepared by Hydrothermal Synthesis

“…InOOH is a metastable oxide; therefore, the phase transformation of In(OH) 3 to InOOH is a non-equilibrium system. However, as shown in the TGA curve of In(OH) 3 in Figure 2, the weight loss in the temperature range of 50-150°C is slow with a weight loss rate is about 2.41%, which corresponds to the physical evaporation of adsorbed water on the sample surface (Shanmugasundaram et al, 2015). e weight loss rate is 2.97% in the temperature range of 150-200°C, which is due to the chemical dehydration of In(OH) 3 [2In(OH) 3 =2InOOH+H 2 O].…”