In this paper, thermogravimetric analyses, Fourier transform infrared spectra, X-ray powder diffraction, photoluminescence, electron paramagnetic resonance, and superconducting quantum interference device magnetometer are applied to observe the thermal decomposition of Zn5(OH)8Ac2·2H2O to ZnO for understanding the origin of room temperature ferromagnetism in ZnO porous microspheres. The results show that both zinc vacancies and shallow donors induced by hydrogen may play an important role in triggering magnetic order in ZnO samples fabricated by annealing the precursor Zn5(OH)8Ac2·2H2O at temperature above 400 °C.

Novel and extended ZnO/Zn 5 (OH) 8 Ac 2 3 2H 2 O architectures are desirable for many applications. Here we report on the design and growth of the novel ZnO/Zn 5 (OH) 8 Ac 2 3 2H 2 O architectures by a hydrothermal synthesis approach. ZnO microrods and/or columnar film are grown in the aqueous solution containing Zn(Ac) 2 3 2H 2 O and hexamethylenetetramine, while Zn 5 (OH) 8 Ac 2 3 2H 2 O microspheres and/or porous film are formed when enough citrate anions are added into the solution. The citrate anions not only modify the morphology but also decide the phase of the grown zinc compounds. The ZnO thin layer coated on glass substrate is used to control the nucleation event and finally modifies the morphology of the grown ZnO. Our work provides an effective and facile approach to design and selectively grow the novel ZnO/Zn 5 (OH) 8 Ac 2 3 2H 2 O architectures at a low temperature of 95 °C.

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Hydrangea-like hollow microspherical ZnO has been synthesized via a transformation from layered basic zinc acetate (LBZA) and characterized using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Investigation of the early stages of the crystal growth revealed a non-classic growth mechanism. With increasing reaction time, (1) amorphous spherical aggregates formed initially, followed by (2) surface multiple nucleation, (3) crystallization into LBZA nanosheets which are vertical to the microspheres' surface, (4) surface condensation leading to the formation of hollow microspheres, (5) extension of the crystallization both inwards and outwards, and ( 6) transformation to zinc oxide during annealing in air. The detailed formation mechanism of the hydrangea-like microspheres, consisting of thin (y5.4 nm) LBZA nanosheets, is proposed. The hydrangea-like ZnO exhibited superior photocatalytic performance in dye degradation due to its unique construction and high specific surface area. This work may shed light on crystal engineering of porous microspheres, hollow crystals and thin nanosheets of other materials.

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