ZnO Microflowers Grown by Chemical Bath Deposition: A Low-Cost Approach for Massive Production of Functional Nanostructures

Abstract

The massive production of nanostructures with controlled features and high surface area is a challenging and timely task in view of developing effective materials for sensing and catalysis. Herein, functional ZnO nanostructures, named microflowers (MFs) have been prepared by a facile and rapid chemical bath deposition. ZnO MFs show an intriguing sheets-composed spheroidal shape, with diameters in the range 0.2–2.5 µm, whose formation is achieved by a complexing action by F in an aqueous solution of zinc nitrate hexahydrate and hexamethylenetetramine. The evolution of the physical and structural properties of the material, following post-deposition thermal annealing, has been investigated by scanning electron microscopy (SEM), energy dispersive X-ray analyses (EDX), photoluminescence (PL) and X-ray diffraction (XRD) techniques. The effectiveness of ZnO MFs in UV detection has also been tested to account for the potentiality of these nanostructures.

Optical and Structural Characteristics of Rare Earth-Doped ZnO Nanocrystals Prepared in Colloidal Solution

“…In the PL spectra of the ZnO NCs, a narrow near-band edge emission (NBE) around 380 nm and a broad band deep-level emission (DLE) between 450 nm to 700 nm were generally observed [5][6][7][8]27]. Figure 3 shows the spectra normalized to the absorbance at λex = 290 nm.…”

“…The stronger suppression of the NBE band compared to the DLE band most likely indicated that RE ions acted as non-radiative defects, the origin of which was different from the radiative defects responsible for the DLE band. In the PL spectra of the ZnO NCs, a narrow near-band edge emission (NBE) around 380 nm and a broad band deep-level emission (DLE) between 450 nm to 700 nm were generally observed [5][6][7][8]27]. Figure 3 shows the spectra normalized to the absorbance at λ ex = 290 nm.…”

“…Due to the size effects, ZnO nanostructures offer exciton-related ultra-violet (UV)/blue light emission at room temperature [5]. In addition, the presence of deep centers stemming from intrinsic and/or extrinsic defects allows ZnO nanostructures to emit light in the violet-red spectral range, covering almost the entire visible spectral range [6].…”

Low-Cost, High-Yield ZnO Nanostars Synthesis for Pseudocapacitor Applications

“…ZnO nanostars (NSs) were synthesized by means of chemical bath deposition (CBD). Starting from an aqueous solution of zinc nitrate and hexamethylenetetramine (HMTA) [ 34 ], the ZnO NSs production was attained by adding ammonium fluoride to the bath [ 26 ]. Three solutions (50 mL each) were separately prepared with deionized water (MilliQ, 18 MΩ cm): (i) 25 mM zinc nitrate hexahydrate ( , purum p.a., crystallized, ≥99.5%, Sigma Aldrich, Milan, Italy); (ii) 25 mM HMTA ( ≥ 99.5%, Sigma Aldrich, Milan, Italy); and (iii) 16 mM ammonium fluoride ( , ≥99.99%, Sigma-Aldrich, Milan, Italy).…”

“…Owing to its eco-friendly nature and good electrochemical activity, ZnO also became a promising electrode material for supercapacitors [ 19 , 20 , 21 ]. Moreover, ZnO can be easily nanostructured in a multitude of morphologies by employing many different methods [ 22 , 23 , 24 , 25 , 26 ]. Solution routes for ZnO nanostructure synthesis have a multitude of advantages, such as cost containment, a simple laboratory setup, low-temperature processes, and fast kinetics growth [ 27 ].…”