Crystallization of Disordered Nanosized ZnO Formed by Thermal Decomposition of Nanocrystalline Hydrozincite

Abstract

The formation and crystallization of disordered nanosized ZnO resulting from the thermal decomposition of nanocrystalline hydrozincite [Zn5(CO3)2(OH)6] has been observed and investigated during pulse annealing experiments up to 625 °C in air or vacuum by electron paramagnetic resonance of trace amounts of substitutional Mn2+ impurity ions, in correlation with X-ray diffraction and transmission electron microscopy measurements. The mesoporous structure of the disordered ZnO, which initially forms in air and vacuum at 225 and 175 °C, respectively, further transforms into nanocrystalline ZnO of increasing particle size and improved lattice quality at higher annealing temperatures. The crystallization process, which does not affect the concentration of the substitutional impurity ions, as well as the simultaneous presence of both disordered and crystalline phases, should be considered in further applications of the resulting nanosized ZnO.

Novel photocatalysts based on Cd1−Zn S/Zn(OH)2 for the hydrogen evolution from water solutions of ethanol

“…The higher thermostability of 2D b-Zn(OH) 2 can be explained by the fact that it exists as a surface phase, probably on top of mixed CdeZn sulfide. The thermally induced decomposition of the Zn(OH) 2 surface phase is known to proceed in a broad temperature range, which is explained by a gradual, three-step dehydration [28]. In contrast, the decomposition of bulk polycrystalline ε-Zn(OH) 2 is single-step and proceeds in a narrow temperature range.…”

Origin and evolution of paramagnetic states in mixtures of ZnO and carbon nanoparticles during intensive mechanical treatment

“…The sextet lines can be seen in the EPR spectra of Mn-doped ZnO nanoparticles, prepared by different methods (see Norberg et al 2004;Toloman et al 2013;Romeiro et al 2013), but these lines were not interpreted at all. Nistor et al (2011) attributed the presence of the sextet to the EPR spectra of Mn 2? in disordered ZnO (Mn 2?…”

EPR detection of sphalerite ZnO in mechanically treated ZnO+0.1C nanosystem

“…Thus the Mn 2 þ EPR sextet S(II) observed in the sample ZnO þ0.1% C cannot be assigned to any of these phases. Also, the observed sextet S(II) cannot be attributed to the Mn 2 þ ions localized in a highly disordered ZnO Wt phase (Mn 2 þ -d state) [34].…”

“…The sextet lines can be seen in EPR spectra of colloidal Mn 2 þ :ZnO Wt quantum dots after a thermal treatment at 100°C [29]; in annealed Mn-doped ZnO Wt nanoparticles [30]; or in the Zn 1 À x Mn x O nanostructures synthesized via the microwave-assisted hydrothermal method [31]. In previous studies [34][35][36], Mn 2 þ EPR sextets (like S(II)) were attributed to highly disordered nanocrystalline ZnO Wt (Table 1).…”

“…In polycrystalline samples with a wide spread of the axial distortion parameter D, (ΔD or s(D) in [34][35][36]), a singularity of finestructure transitions75/2, m2 7 3/2, m and 73/2, m2 7 1/2, m (m is components of nuclear spin I) is broaden and has recorded only the central singularity transitions À 1/2,m2 þ 1/2,m. These singularities in the polycrystalline EPR spectrum of Mn 2 þ ions in ZnO Wt occur at θ 1 ¼90°and θ 2 ¼57°(in the general case, the θ 2 value can be determined using the expressions (2)).…”