Hierarchical ZnO Microspheres Research Articles

Engineering polarization surface of hierarchical ZnO microspheres via spray-annealing strategy for wide-frequency electromagnetic wave absorption

• Hierarchical ZnO microspheres were successfully synthesized via spray-annealing strategy. • Pure dielectric loss ZnO materials were assembled by nanorods and nanoparticles with adjusting different aspect ratios, defects and polar faces. • Hierarchical ZnO-1 materials shown the widest efficient absorption region from 9.9 to 18.0 GHz at 2.4 mm. Regulating orientation growth plays a dominant role in enhancing dielectric properties for the electromagnetic (EM) functional materials, which faces a huge challenge in the synthesis method. By spray-annealing strategy, hierarchical ZnO microspheres assembled by ZnO nanorods and nanoparticles were successfully fabricated. With confined microsphere space and controlling crystal growth, oriented ZnO nanorods possess rich defects, Zn-polar, O-polar faces, and high permittivity. Meanwhile, temperature-dependency of exposed polarization surfaces is discovered in the semiconductor ZnO nanoparticles with evolved aspect ratios. As pure dielectric EM wave absorption material, the hierarchical ZnO microsphere exhibits adjustable complex permittivity and polarization behaviors. When the thickness is 2.4 mm, the hierarchical ZnO-1 absorber shows the widest efficient absorption (RL ≤ –10 dB) region from 9.9 to 18.0 GHz (8.1 GHz, ∼50.6% testing frequency). The minimum reflection loss (RL) of ZnO-1 can reach –31.5 dB at only 2.0 mm. Because of the outstanding dielectric loss ability and wide absorption frequency, large-scale hierarchical ZnO microspheres can be a potential EM absorption candidate.

Morphologically Controllable Hierarchical ZnO Microspheres Catalyst and Its Photocatalytic Activity.

The degradation of pollutants in wastewater using abundant resources and renewable energy sources, such as light, is attractive from an environmental perspective. ZnO is a well-known photocatalytic material. Therefore, in this study, a hierarchical ZnO microsphere precursor was prepared using a hydrothermal method. The precursor was subsequently annealed at different temperatures, which enabled the production of a ZnO catalyst having a controllable morphology. Specifically, as the annealing temperature increased, the precursor crystallized into hexagonal wurtzite and the crystallinity also increased. The catalysts were tested for their photocatalytic activity for the degradation of dye molecules (methylene blue and rhodamine B), and the catalyst sample annealed at 400 °C showed the best photocatalytic activity. The origin of this activity was studied using electron paramagnetic resonance spectroscopy and transient photocurrent measurements, and the structure of the optimal catalyst was invested using electron microscopy measurements, which revealed that it was formed of two-dimensional nanosheets having smooth surfaces, forming a 2D cellular network. Thus, we have presented a promising photocatalyst for the mineralization of organic contaminants in wastewater.

Influence of Ag Photodeposition Conditions over SERS Intensity of Ag/ZnO Microspheres for Nanomolar Detection of Methylene Blue.

Surface enhanced Raman spectroscopy (SERS) is considered a versatile and multifunctional technique with the ability to detect molecules of different species at very low molar concentration. In this work, hierarchical ZnO microspheres (ZnO MSs) and Ag/ZnO MSs were fabricated and decorated by hydrothermal and photodeposition methods, respectively. For Ag deposition, precursor molar concentration (1.9 and 9.8 mM) and UV irradiation time (5, 15, and 30 min) were evaluated by SEM, TEM, X-ray diffraction and Raman spectroscopy. X-ray diffraction showed a peak at 37.9° corresponding to the (111) plane of Ag, whose intensity increases as precursor concentration and UV irradiation time increases. SEM images confirmed the formation of ZnO MSs (from 2.5 to 4.5 µm) building by radially aligned two-dimensional ZnO nanosheets with thicknesses below 30 nm. The Raman spectra of Ag/ZnO MSs exhibited a vibration mode at 486 cm−1 which can be directly associated to Ag deposition on ZnO MSs surface. The performance of SERS substrate was evaluated using rhodamine 6G. The SERS substrate grown at 9.8 mM during 30 min showed the best SERS activity and the ability to detect methylene blue at 10−9 M.

Influence of calcination temperature on photocatalytic H2O2 productivity of hierarchical porous ZnO microspheres

Photocatalytic production of H2O2 from water and atmospheric oxygen has been recognized as a green and sustainable chemical process, due to the abundance of raw materials and sustainable solar energy. Herein, flower-like hierarchical ZnO microspheres were prepared by hydrothermal method followed by calcination at different temperatures, and their photocatalytic performance in H2O2 production was examined under simulated sunlight irradiation. The calcination temperature plays a vital role in the structure, morphology, and surface area of the final ZnO products as well as their optical and electrochemical properties, which are determining factors in their photocatalytic activity. The ZnO calcined at 300 °C (Zn-300) exhibits the highest activity and optimal stability, showing productivity of 2793 μmol l−1 within 60 min of irradiation, which was 6.5 times higher than that of uncalcined ZnO precursor. The remarkable photocatalytic activity is attributed to enhanced light utilization, large surface area, abundant exposed active sites, improved separation efficiency, and prolonged carrier lifespan. Moreover, the results from cycling experiments indicate the as-prepared ZnO samples exhibit good stability and long-time performance. This work provides useful information for the preparation of hierarchical ZnO photocatalysts.

Triethylamine gas sensor based on Pt-functionalized hierarchical ZnO microspheres

Abstract Monitoring and detection of triethylamine (TEA) gas are indispensable to environmental and human safety. However, TEA gas sensor suffers from low response. Herein, unique nanosized-Pt-decorated hierarchical ZnO microspheres were prepared. Compared with pristine ZnO microspheres and Pt-c-ZnO (Pt nanoparticles deposited on commercial ZnO), the obtained Pt-ZnO exhibited the best TEA gas sensing behaviors, in terms of lower working temperature (200 °C), better selectivity and long-term stability. Notably, the response value of Pt-ZnO sensor towards 100 ppm TEA was up to 242, which was 50 and 16-fold higher than those of pristine ZnO and Pt-c-ZnO sensor, respectively. The superior properties were attributed to structural advantages as well as the synergistic effect between Pt and ZnO. The sensing mechanism was thoroughly clarified by the electron-sinker effect of Pt. It was further corroborated by Kelvin probe and density function theory (DFT) simulation. Moreover, higher surface adsorption oxygen activity and lower TEA adsorption energy of this optimal sample were demonstrated by temperature programmed desorption (O2-TPD) and DFT simulation. Based on the aforementioned advantages, Pt-ZnO becomes a satisfactory candidate for TEA gas sensors. Significantly, this work opens a new avenue for the understanding the mechanism for performance enhancement under.

Template-free synthesis and photocatalytic activity of hierarchical hollow ZnO microspheres composed of radially aligned nanorods

In this work, hierarchical hollow ZnO microspheres with an average diameter of 3.5 μm are successfully synthesized via a simple template-free solvothermal route. And these microspheres are constructed by anisotropic single-crystalline ZnO nanorods which grows along the [0001] c-axis direction because of the selective adsorption of ethylene glycol. It is noted that ethylene glycol plays a crucial role in promoting the growth and aggregation of nanorod by comparing the effect of other solvents, such as water, ethanol, isopropanol and glycerol. Furthermore, the photocatalytic activity of as-obtained hollow ZnO microspheres is evaluated by the degradation of methylene blue (MB) in aqueous solution. The photocatalytic performance reveals that these hollow ZnO microspheres can not only efficiently degradate the dye, but also show good stability during the cycling photodegradation.

Pd-based catalysts promoted by hierarchical porous Al2O3 and ZnO microsphere supports/coatings for ethyl acetate highly active and stable destruction

Developing economical and active materials is of great significance for VOC purification. Here, hierarchical porous Al2O3 and ZnO microspheres (Al2O3-pm and ZnO-pm) were synthesized by a facile hydrothermal strategy. The urchin-like Al2O3-pm and flower-like ZnO-pm possess high specific surface area (especially; external surface area) obviously boost the dispersion of Pd with 29.3 % and 30.1 % over Pd/Al2O3-pm and Pd/ZnO-pm, respectively, over 3.4 times higher than those of commercial Al2O3- and ZnO-supported counterparts. Pd/Al2O3-pm possesses excellent activity and CO2 yield in ethyl acetate (EA) degradation, with TOF reaches 7.76 × 10−3 s−1 at 160 °C under GHSV of 50,000 h-1. Moreover, Pd/Al2O3-pm exhibits satisfied performance in EA-contained binary VOCs oxidation and has high long-term stability under both dry and humid conditions. Both Pd sites and Brønsted acid sites participated in reaction process and initially react with EA to form ethylene and ethanol, respectively. Larger amount Brønsted acid sites over Pd/Al2O3-pm promote ethanol formation and C-C cleavage, resulting in different CO2 yields and EA activation mechanisms. The coating greatly enhances Pd dispersion over Pd supported monolithic catalyst, endowing its desired activity and stability even with a much lower Pd loading. This work promotes the potential application of noble-metal-based monolithic materials in VOC degradation.

High response methane sensor based on Au-modified hierarchical porous nanosheets-assembled ZnO microspheres

Detecting methane (CH4) gas is very important owing to its widely use as a fossil fuel with an explosive hazard in modern society. In this study, a CH4 gas sensor was prepared, which is based on hierarchical porous nanosheets-assembled Au/ZnO microspheres with diameters of 10–12 μm. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the textural properties and morphology of the nanocomposites. In addition, the gas sensing properties of the sensors basedon pure ZnO and Au/ZnO nanomaterials were systematically investigated. By modifier Au nanoparticles, the characteristics of ZnO based sensor for CH4 detection were significantly enhanced. Especially, the Au/ZnO based sensor with an Au content of 1.0 at.% exhibited the best sensing performances (4.16) of 100 ppm CH4 at 250 °C. Furthermore the sensor also exhibited a good linear relation (10–2000 ppm CH4 concentration), excellent repeatability, satisfactory stability and a low detection limit of detection (1.83 ppm). The possible enhanced sensing mechanism could be attributed to the synergism between the unique hierarchical porous nanosheets-assembled microspheres structure and the sensitizing actions utilized by the Au nanoparticles.

WO<sub>3</sub>/Nb<sub>2</sub>O<sub>5</sub> Nanoparticles-Decorated Hierarchical Porous ZnO Microspheres for Enhanced Photocatalytic Degradation of Palm Oil Mill Effluent and Simultaneous Production of Biogas

Conventionally, palm oil mill effluent (POME) was treated using open ponding system, which nevertheless long retention times and large treatment areas were required. In this report, heterogeneous photocatalysis was used to degrade the POME and simultaneously assessed the biogas formation. Characterization of the chemically prepared hierarchical porous ZnO microspheres showed that wurtzite was the predominant crystalline phase with a band gap energy of 3.22 eV. Moreover, the as-prepared ZnO were assembled by large numbers of interleaving nanosheets and formed an open porous structure. Under UV irradiation, the as-prepared ZnO demonstrated photocatalytic property on POME degradation. The WO3 and Nb2O5 decorated ZnO photocatalysts (WO3/ZnO and Nb2O5/ZnO) with improved photocatalytic performances were also prepared using a simple and rapid way. Significantly, in the presence of WO3/ZnO and Nb2O5/ZnO composites, the degradation of POME achieved 68.3% and 91.7%, respectively after 240 min irradiation. Interestingly, the assessment of the biogas formation showed that the photocatalytic reactions over Nb2O5/ZnO and WO3/ZnO composites generated higher amount of biogas products (CH4 + CO2) compared to that of ZnO. The photocatalytic enhancement was attributed to the high separation efficiency of photogenerated electron–hole pairs based on the formation of heterojunction structures between the WO3/Nb2O5 and ZnO. The observed findings also revealed that the photocatalytic technology using hierarchical WO3/ZnO and Nb2O5/ZnO composites had the potential to efficiently treat wastewater.

Insights into charge transfer and solar light photocatalytic activity induced by the synergistic effect of defect state and plasmon in Au nanoparticle-decorated hierarchical 3D porous ZnO microspheres

This study provides insights into the charge transfer and solar light photocatalytic activity induced by the synergistic effect between defect state and plasmon in Au nanoparticle-decorated hierarchical 3D porous ZnO microspheres. Photoluminescence emission shows that the photogenerated electrons of ZnO are efficiently transferred from its defect level to the conduction band (CB) induced through the coupling action of the defect state and plasmon. Compared with the pure ZnO microsphere photocatalysts, the fabricated Au/ZnO microsphere photocatalysts show remarkably enhanced activity for the decomposition of methylene blue dyes under solar-light illumination. Moreover, the photocatalytic performance of the Au/ZnO microspheres was manipulated by tuning the size of the Au nanoparticles (NPs). When decorated with 10 nm Au NPs, the Au/ZnO microsphere photocatalyst achieves a rate constant of 0.09846 min−1, 26 and 8.5 times higher than those of the pure ZnO microsphere photocatalysts (0.00378 min−1) and the Au/ZnO microsphere photocatalysts decorated with 30 nm Au NPs (0.01154 min−1), respectively.. The enhanced photocatalytic performance of the Au/ZnO microsphere photocatalysts is ascribed to the defect state-plasmon coupling-induced efficient transfer of photogenerated electrons from the defect level to the CB of ZnO. This work enhances the understanding of the defect state-plasmon coupling-induced enhanced photocatalytic activity in metal/semiconductor heterostructure photocatalysts.

Conductometric acetone vapor sensor based on the use of gold-doped three-dimensional hierarchical porous zinc oxide microspheres.

A versatile nanoprobe for acetone vapor was designed and fabricated. It is based on the use of gold-doped three-dimensional (3D) hierarchical porous zinc oxide microspheres (Au/ZnO HPMSs). The nanoprobe was synthesized by annealing zinc hydroxide carbonate precursor (obtained by a hydrothermal method) doped with gold nanoparticles. The resulting products possess a 3D open framework structure built of 2D porous nanosheets with a nanoporous wormhole-like shape. The microspheres doped with 0.5mol% gold display a good selectivity towards acetone. The conductometric nanoprobe, typically operated at a voltage of 5V, can detect sub-ppm levels of acetone, and the detection limit is as low as 0.2ppm. The response (at a level of up to 100ppm of acetone at 325°C) was high (74 ± 1.9), and the response and recovery time are 6 and 3s, respectively. This superior performance is ascribed (a) to the hierarchical porous ZnO architecture that warrants a large surface area; and (b) to the presence of gold nanoparticles that facilitate the chemisorption and dissociation of gas molecules. Graphical abstract Gold-doped 3D hierarchical porous ZnO microspheres (Au/ZnO HPMSs) architectures assembled by interconnected 2D porous nanosheets structures. The resistive sensor using these Au/ZnO HPMSs demonstrates outstanding acetone vapor sensing behaviors and 0.2ppm detection limits.

Hierarchical ZnO Microspheres Embedded in TiO2 Photoanode for Enhanced CdS/CdSe Sensitized Solar Cells

Control of structural and compositional characteristics of photoanodes is a crucial step toward rapid transport of charges and high-efficiency loading of dye or quantum dots in the case of solar cell application. Hierarchical ZnO microspheres (ZMS) and TiO2 hybrid photoanode film were prepared for improved CdS/CdSe quantum dot sensitized solar cells (QDSCs). The addition of ZMS into TiO2 electrode films resulted in both increased short circuit current density (Jsc) and open circuit voltage (Voc). Such an improvement is ascribed to the increased light harvesting owing to scattering by ZMS and the reduced charge recombination due to the surface modification. TiO2/ZMS hybrid photoanode displays superior charge injection/transport performance due to the ZMS with unique hierarchical structure, providing charge transfer continuity and multiple electron transport channels for timely electron transport. As a result, the Jsc, Voc, and the photovoltaic conversion efficiency (PCE) were all remarkably enhanced with t...

Facile synthesis of three-dimensional ZnO hierarchical microspheres composed of well-ordered nanorods by hydrothermal method

Abstract Three-dimensional (3D) ZnO hierarchical microspheres composed of well-ordered nanorods were synthesized by a facile one-step hydrothermal method without any surfactants. The effects of reaction conditions including reaction temperature, reaction time on the microstructure of hierarchical microspheres were investigated. The results demonstrated that the reaction conditions played an important role in the morphology of 3D ZnO hierarchical microspheres. A three-stage reaction mechanism of 3D ZnO hierarchical microspheres was proposed. Firstly, Zn2+ reacts with OH− and NH4+ to produce nanoparticles. Then the nanoparticles are self-assembled into nucleis. Finally is the formation and growth of the hierarchical structure on the nuclear surface. When the as-synthesized ZnO were used as the anode of the dye sensitization solar cells (DSSCs), the 3D ZnO hierarchical microspheres composed of well-ordered nanorods exhibits the best photoelectric properties, which was attributed to the increased surface area and advantageous electronic transmission path.

Preparation of Nb2O5-decorated hierarchical porous ZnO microspheres with enhanced photocatalytic degradation of palm oil mill effluent

In the present work, Nb2O5-decorated hierarchical porous ZnO microspheres (ZnO/Nb2O5) were successfully prepared through a facile surfactant-free method. The as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectroscopy and Brunauer–Emmett–Teller surface area analyses. Under UV light irradiation, the ZnO/Nb2O5 composites degraded palm oil mill effluent (POME) efficiently and demonstrated much higher photocatalytic activity compared to those of pure ZnO and Nb2O5. The enhanced photocatalytic degradation performance of ZnO/Nb2O5 composites was attributed to the high charge separation efficiency and hydroxyl radical generation ability as verified by the photoluminescence spectra. Phytotoxicity test upon the POME degradation over ZnO/Nb2O5 photocatalysis considerably decreased through the measurement of radicle lengths of Vigna radiata. Moreover, the ZnO/Nb2O5 composites were reused several times without appreciable loss of activity. This work revealed that the as-prepared ZnO/Nb2O5 composites have great potential for practical applications in the field of wastewater treatment.

Hierarchical ZnO microspheres photoelectrodes assembled with Zn chalcogenide passivation layer for high efficiency quantum dot sensitized solar cells

The power conversion efficiency of quantum dot sensitized solar cells with ZnO as photoelctrode is relatively low, largely due to high charge recombination rate at the ZnO surface. This paper reports high-efficiency hierarchical ZnO microspheres photoelectrodes with appropriate Zn chalcogenide passivation layers (ZnO@ZnS and ZnO@ZnSe) were constructed for reducing charge recombination of the resultant QDSCs. They were fabricated via a facile chemical solution route without any template or high temperature condition followed with controlled ion exchange. ZnS or ZnSe serves as passivation layer in CdS/CdSe QDSCs and their influences on the charge recombination as well as the light absorption were investigated. It was found that the ZnS or ZnSe passivation layer can effectively reduce charge recombination and significantly enhance the fill factor and open circuit voltage of the resulting QDSCs. Both of ZnS and ZnSe passivation layers enhanced the overall performance of the resultant QDSCs, which generated high power conversion efficiency of 5.13% and 5.20%, present 52% and 55% enhancement compared with 3.36% for the solar cell with hierarchical ZnO microspheres photoelectrode. ZnSe appears more favoring the deposition of QDs and enhancing the light absorbance than ZnS, resulting in an increased photocurrent density.

Direct Z-scheme PDA-modified ZnO hierarchical microspheres with enhanced photocatalytic CO2 reduction performance

To extend the light utilization of ZnO from UV to visible light, polydopamine (PDA) was introduced. The PDA-modified ZnO hierarchical microsphere was prepared through self-assembled method taking advantage of the functional groups on dopamine. The hybridization endowed the material with better light-to-fuel harvesting efficiency, which can be ascribed to the eximious light utilization and direct Z-scheme charge transfer mechanism (DZCTM). Importantly, the DZCTM between them was confirmed by in-situ X-ray photoelectron spectroscopy (ISI-XPS) characterization. This mechanism kept the strong redox abilities of the overall photocatalyst. Besides, abundant functional groups on PDA boosted CO2 adsorption. The research highlights the feasibility of loading organic molecule on inorganic substance for photocatalytic CO2 conversion.

On the high response towards TEA of gas sensors based on Ag-loaded 3D porous ZnO microspheres

In this paper, an ultra-high response and fast response/recovery triethylamine (TEA) gas sensor is fabricated by growing Ag nanoparticles on the surface of hierarchical 3D porous ZnO microspheres (Ag-ZnO) via a green and facile precipitation method. The morphological characterizations reveal that the hierarchical 3D ZnO microspheres are assembled by large numbers of thin and porous nanosheets. The sizes of the microspheres are 3–5 μm and the thickness of these porous nanosheets is about 20 nm. Gas sensing measurements show that the Ag-ZnO gas sensor exhibits superior TEA sensing performance. Its response to 100 ppm TEA is 6043, which is 14.8 times higher than that of pure ZnO sensor. Besides, its optimal working temperature decreases from 230 to 183.5 °C compared with the pure one. And the Ag-ZnO gas sensor also exhibits fast response/recovery rate (about 1 s and 60 s, respectively). Furthermore, the Ag-ZnO gas sensor shows no obvious degradation through a testing period of 30 days. The superior TEA sensing performances could be attributed to the structural advantage of hierarchical 3D porous microsphere, as well as the synergistic effects of Ag nanoparticles and ZnO microspheres.

A facile route for fabrication of hierarchical porous Nb2O5/ZnO composites with enhanced photocatalytic degradation of palm oil mill effluent

A facile route was demonstrated for the synthesis of hierarchical porous ZnO microspheres based on a surfactant-free chemical solution method. The as-synthesized ZnO were assembled by large numbers of interleaving nanosheets and formed an open porous structure. Under UV irradiation, the as-synthesized ZnO exhibited photocatalytic property on the degradation of palm oil mill effluent (POME) solution. The Nb2O5 decorated ZnO photocatalysts (Nb2O5/ZnO) with enhanced photocatalytic performances were also synthesized via a facile and rapid route. Compared with ZnO, the Nb2O5(3 wt%)/ZnO exhibited the best POME degradation and colour removal efficiencies of 91.7% and 100%, respectively after 240 min irradiation. Phytotoxicity of the POME after Nb2O5/ZnO photocatalysis was significantly reduced via the measurement of radicle lengths of Vigna radiata. The observed results demonstrated the photocatalytic technology using hierarchical Nb2O5/ZnO composites had the potential to effectively purify wastewater.

Synthesis of hierarchical 3D porous ZnO microspheres decorated by ultra-small Au nanoparticles and its highly enhanced acetylene gas sensing ability

In this paper, ultra-small Au nanoparticles (1–2 nm) were successfully decorated on the surface of three-dimensional porous wool like ZnO microspheres through a facile, surfactant-free and green precipitation manner. The ZnO microspheres were synthesized via a hydrothermal method. The crystal structure and morphology of the samples as-synthesized were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results showed that quantities of Au nanoparticles of which the diameter ranged about 1–2 nm were distributed evenly on the surface of ZnO microspheres. Gas sensing measurements revealed that the ZnO microspheres decorated with ultra-small Au nanoparticles (Au-ZnO microspheres) showed ultrasensitive and selective detection to acetylene. The Au-ZnO microspheres exhibited ultra-higher response to acetylene (311.3–100 ppm acetylene) at a lower optimal working temperature (183.5 °C) compared with pure ZnO microspheres. Meanwhile, The Au-ZnO microspheres displayed a fast response/recovery speed (about 1 s and 20 s, respectively). Besides, the Au-ZnO microspheres also showed good stability and repeatability over a two-month testing period. Furthermore, the formation of schottky junction, the catalytic effect of Au nanoparticles and the physical advantages of the nanomaterial in size and structure could be three dominant factors to the superior acetylene sensing performance.

A novel exposed facet dependent topological transformation mechanism from hydrozincite microspheres into hierarchical mesoporous ZnO structures

Distinct from normal hierarchical mesoporous ZnO structures exposed with (2−1−10) facets derived from polycrystal hydrozincite precursors exposed with (010) facets, single-crystal hydrozincite precursors with exposed (001) facets were prepared by a hydrothermal method assisted with sodium citrate and then topologically transformed into hierarchical mesoporous ZnO microspheres with exposed (0001) facets by calcination. To reveal the transformation process, a novel exposed facet dependent topological transformation mechanism was proposed as follows. Firstly, CO bonds and OH bonds in Zn5(CO3)2(OH)6 were broken with H2O and CO2 gases releasing; secondly, the remaining Zn atoms and O atoms rearranged their positions, leading to a transformation from a unit cell of monoclinic hydrozincite into eight unit cells of wurtzite ZnO based on their relationship of crystal lattice parameter. As a result, the (010) and (001) facets of hydrozincite can be transferred into the (2−1−10) and (0001) facets of wurtzite ZnO, respectively. In this sense, the exposed facets of hydrozincite precursors determined the exposed facets of ZnO micro/nano structures. Therefore, the transformation mechanism can be also used to synthesize other metal oxide structures with special exposed facets.