Enhanced photocatalytic activity of ZnO microflower arrays synthesized by one-step etching approach

doi:10.1016/j.molcata.2013.05.013

Journal of Molecular Catalysis A: Chemical

Volume 378, 1 November 2013, Pages 1-6

https://doi.org/10.1016/j.molcata.2013.05.013 Get rights and content

Highlights

•
ZnO microflower arrays were synthesized by a one-step etching route.
•
ZnO microflowers exhibit higher photocatalytic activity than other samples.
•
The superior photocatalytic activity of ZnO microflowers was analyzed.
•
The formation mechanism of ZnO microflowers was proposed.

Abstract

A new type of ZnO microflower arrays was successfully synthesized via a one-step etching route based on chemical bath disposition (CBD) method without any assistant reagents. The inner and outer wall surfaces of ZnO microflowers are quite smooth with the average thickness of 50 nm. The formation mechanism is proposed that ZnO microflowers were evolved from microrods by preferential etching in reaction solution. ZnO microrod arrays and microcandle arrays were also obtained by varying reaction time. Photoluminescence and photocatalysis properties of ZnO samples were investigated at room temperature. Superior photocatalytic activity of ZnO microflower arrays in the degradation of RhB compared to other samples under identical conditions has been demonstrated, and the origin is mainly ascribed to the increasing surface area and higher oxygen vacancies density of ZnO microflower with partial hollow structure.

Graphical abstract

Introduction

Water contamination and shortages are becoming more and more serious with the development of industry and economy. Photocatalysis, with semiconductor-assisted, has attracted more concern for complete elimination of pollutants in the waste water due to its efficiency and broad applicability [1], [2], [3]. Photocatalysis reaction is a complicated process and the photocatalyst activity of semiconductor materials is influenced by many factors [4], [5], [6], such as size [7], morphology [8], [9], orientation [10], [11], defects [12], [13], [14] and exposed crystal facets [15], [16]. Usually, the photocatalysis reaction occurs at the interface between catalyst and organic pollutants [17], so photocatalytic performance are strongly dependent on the surface structure of materials. And a large surface/volume (S/V) ratio of material is required to improve the activity [18], [19]. For example, decreasing particle size is an effective way to enhance surface area of materials. Alternatively, hollow structure material is considered the most promising morphology used in the fields of photocatalysis because of its high surface area. Therefore, exploring the fabrication of hollow structure catalysts whose active surfaces are extended to the inner surfaces is essential for the development of advanced photocatalysts.

ZnO with a wide band gap of 3.37 eV and a large exciton binding energy of 60 meV is an important semiconductor material and has been widely used as photocatalyst for photodegradation organic pollutants in waste water [20], [21], [22]. Various synthesis routes, such as thermal evaporation [23], [24], sonochemical [25], electrochemical [26], hydrothermal oxidation [27] and sol–gel method [28], have been developed to fabricate ZnO with various morphologies. Recently, a great quantity of ZnO tubes with different sizes has been prepared by various chemical methods [29], [30], [31]. Generally, ZnO tubes have been synthesized by a two-step etching process. However, most of the synthesis techniques are demand complicated controlling processes and those methods are unfavorable for low-cost and large-scale production. Therefore, how to fabricate a new type ZnO hollow architectures with desired functionality by a simply and low-cost synthetic strategy still remains a great challenge in the area of materials research. Moreover, understanding of the relationship between microstructure and the photocatalytic activity of ZnO is also significant.

In this paper, a new type of ZnO microflower arrays with partial hollow structure was synthesized via a novel one-step etching route in reaction solution without any assistant reagents. The formation mechanism of ZnO microflowers was analyzed, and the photocatalytic performance was studied for the degradation of dyes. ZnO microflowers exhibited the superior photocatalytic activity in the degradation of rhodamine B (RhB) compared to other samples in our experiments.

Section snippets

Materials

All reagents, including zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O), methenamine (C₆H₁₂N₄), rhodamine B (RhB) and absolute propanol, were analytical grade, purchased from Sinopharm Chemical Regent Co., Ltd., and used without further purification.

Preparation

Si (1 0 0) wafers were used as the substrate. Before deposited ZnO films, ZnO seed layers were spin coated onto Si wafers according to the literature [32]. In a typical ZnO films preparation, the seed-coated substrate was immersed into a solution of 0.1 M

Characterizations

Fig. 1 presents SEM images of the as-prepared ZnO arrays grown on Si substrate when the reaction time was fixed at 5 h. As shown in Fig. 1a–c, ZnO microflower arrays grow in large-scale and exhibit high orientation perpendicular to the substrate. The high-magnification image in Fig. 1d of a single microflower reveals that the inner and outer wall surfaces are quite smooth with the average thickness of 50 nm. However, a small quantity of microrods and partial tubular microstructure (like morning

Conclusions

In summary, major ZnO microflowers structure on Si substrate have been successfully synthesized via a simple one-step etching route based on chemical bath disposition (CBD) method by employing the propanol/deionized water as solvent. It is found that the reaction time play the most important role in the formation of microflowers, and the formation is mainly due to the preferential etching along c-axis. ZnO with different morphologies such as microrods and microcandles can be obtained by

Acknowledgements

This work is supported by the National Natural Science Foundation of China (Grant No. 61178074, 61008051, 11204104 and 11254001), program for the development of Science and technology of Jilin province (Item No. 201115219, 201105084, 20100113, 201215225 and 201215222), the Twentieth Five-Year Program for Science and Technology of Education Department of Jilin Province (Item No. 20110170, 20110169, 20120174 and 20130447), program for the master students’ scientific and innovative research of

References (44)

M.N. Chong et al.
Water Res.
(2010)
G. Colón et al.
Appl. Catal. B: Environ.
(2008)
G. kenanakis et al.
Appl. Catal. A: Gen.
(2010)
R. Shi et al.
Appl. Catal. B: Environ.
(2010)
X.L. Xu et al.
Catal. Commun.
(2010)
B. Subash et al.
J. Mol. Catal. A: Chem.
(2013)
W. Liu et al.
J. Mol. Catal. A: Chem.
(2013)
R. Yousefi et al.
Ceram. Int.
(2012)
F. Jamali-Sheini et al.
Ceram. Int.
(2013)
R. Yousefi et al.
Ceram. Int.
(2013)

J.H. Zeng et al.

Chem. Phys. Lett.

(2009)

Y.X. Wang et al.

Sep. Purif. Technol.

(2008)

C. McCullagh et al.

J. Chem. Technol. Biotechnol.

(2011)

A.D. Paola et al.

J. Hazard. Mater.

(2012)

S.H.S. Chan et al.

J. Chem. Technol. Biotechnol.

(2011)

G.R. Li et al.

J. Phys. Chem. C

(2008)

A. Selloni

Nat. Mater.

(2008)

L.P. Xu et al.

Chem. Mater.

(2009)

N. Kislov et al.

Lamgmuir

(2009)

J.C. Wang et al.

Langmuir

(2009)

M. D’Arienzo et al.

J. Am. Chem. Soc.

(2011)

S.W. Liu et al.

J. Am. Chem. Soc.

(2010)

Cited by (31)

Effects of different zinc oxide morphologies on photocatalytic desulfurization of thiophene
2022, Journal of Alloys and Compounds
Citation Excerpt :
In fact, by prolonging the processing period, it could decrease the growth rate and then cease due to insufficient supply of Zn2+ and OH- ions, resulting in a shorter structure of ZnO [38]. Moreover, the advantage of applying higher temperatures during the growth process could increase the reaction rate and contribute to higher production of ZnO particles compared to lower temperatures [42]. Thus, it can be inferred that the CBD method could synthesize flower-like morphology in a 3-dimensional structure better than the hydrothermal method.
Zinc oxide (ZnO) nanoparticles are superior photocatalysts for pollutant degradation due to their stability, low hazard, and high photosensitivity. The morphology of this material is one of the key factors influencing the performance of pollutant degradation. In fact, studies on the effects of different ZnO morphologies on thiophene desulfurization via photocatalysis process are limited. Thus, this study focuses on the performance of different ZnO morphologies for thiophene desulfurization. Nine ZnO nanoparticles were synthesized and categorized into two groups, namely flower-like and non-flower-like ZnO. Flower-like ZnO included flakes, clusters, rods, and needles, while the non-flower-like ZnO comprised nanoballs, short-nanorods, nanocubes, and nanoporous. The physical properties of all ZnO morphologies were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and Fourier-transform infrared (FTIR), and compared with commercial ZnO. From the findings, flower-like ZnO flakes showed the highest performance in thiophene desulfurization (30%). High pH and turbidity reduction in the permeate confirmed that the thiophene compound in the solution was highly degraded after treatment. Moreover, all ZnO morphologies applied to pseudo-second-order models due to higher linear regression (R²) values. Greater thiophene desulfurization was indicated by the highest Ce value of ZnO flakes (909.09 mg/g). The optimum conditions for thiophene desulfurization were at pH 7 and 0.05 g/L ZnO flakes loading for 90 min contact time.
Highly efficient and Reusable ZnO microflower photocatalyst on stainless steel mesh under UV–Vis and natural sunlight
2020, Optical Materials
The photocatalytic process is used to remove organic contaminants, dyes, industrial sewage from wastewater before reusing it for human consumption again. Here a simple cost-effective ultrasonic spray pyrolysis (USP) technique is used to deposit ZnO microflower on glass and stainless steel (SS) mesh in a single step. X-Ray Diffraction (XRD) and Raman spectroscopy indicate the polycrystalline wurtzite nature of ZnO. Field emission scanning electron microscope (FESEM) shows the ZnO microflower structure. PL and XPS studies show the oxygen defect in the films. Photocatalytic degradation results show that methylene blue (MB) dye with 1 × 10⁻⁵ M concentration can be degraded around 97.94% and 85% in 120min and 210 min with a degradation rate of 0.03035 min⁻¹ and 0.00917 min⁻¹ respectively using ZnO deposited on SS mesh and glass substrate in both UV–Vis and sunlight condition. ZnO deposited on SS mesh shows high repeatability performance to degrade the MB and it can degrade 96% of MB at 10th cycle. Degradation rate at base medium is higher than acidic medium. A plausible photocatalysis mechanism is also explained.
Modification of photocatalyst with enhanced photocatalytic activity for water treatment
2020, Advanced Water Treatment: Advanced Oxidation Processes
Increasing demand and shortage of energy resources and clean water due to the rapid development of industry, population growth, and long-term droughts have become an issue worldwide. As a result, global warming, long-term droughts, and pollution-related diseases are becoming more and more serious. The traditional technologies, such as precipitation, neutralization, sedimentation, filtration, and waste immobilization, cannot prevent the pollution but restrict the waste chemicals only after the pollution emission. Meanwhile, most of these treatments cannot thoroughly degrade the contaminants and may generate toxic secondary pollutants into ecosystem.
Heterogeneous photocatalysis as the innovative wastewater technology attracts many attention, because it is able to generate highly reactive transitory species for total degradation of organic compounds, water pathogens, and disinfection by-products. Semiconductors as photocatalysts have demonstrated their efficiency in degrading a wide range of organics into readily biodegradable compounds and eventually mineralized them to innocuous carbon dioxide and water. But, the efficiency of photocatalysis is limited, and hence, it is a crucial issue to modify photocatalyst to enhance photocatalytic activity.
In this thesis, first of all, two literature views are conducted. A survey of materials for photocatalysis has been carried out to summarize the properties and the applications of photocatalysts that have been developed in this field. Meanwhile, the strategy for the improvement of photocatalytic activity has been explicitly discussed.
Furthermore, all the raw material and chemicals used in this work have been listed as well as a specific experimental process and characterization method has been described. The synthesize methods of different photocatalysts have been depicted step by step. Among these cases, different modification strategies have been used to enhance the efficiency of photocatalyst on degradation of organic compounds (methylene blue or phenol). For each case, photocatalytic experiments have been done to exhibit their photocatalytic activity. The photocatalytic experiments have been designed, and its process has been explained and illustrated in detailed.
Moreover, the experimental results have been shown and discussed. All the findings have been demonstrated in detail and discussed case by case. Eventually, the mechanisms on the improvement of photocatalytic activities have been clarified by characterization of samples and analysis of results. As a conclusion, the photocatalytic activities of selected semiconductors have been successfully enhanced via choosing appropriate strategy for the modification of photocatalysts.
Facile preparation of ZnO/Ag<inf>2</inf>CO<inf>3</inf> heterostructured nanorod arrays with improved photocatalytic activity
2019, Journal of Physics and Chemistry of Solids
Citation Excerpt :
Recently, semiconductor-assisted photocatalysis has aroused extensive interest due to its ability to degrade various organic dyes effectively and produce clean products [6–10]. Among various semiconductor materials, ZnO with wide direct band gap energy of 3.2 eV has been extensively used as a fascinating photocatalyst to degrade various organic contaminants in wastewater because of its relatively high photocatalytic activity, low cost and nontoxic nature [11–13]. Nevertheless, the quick recombination of electron-hole pairs resulting in the poor photocatalytic activity, which restricts the practical application of ZnO [14,15].
ZnO nanorod arrays (NRAs) are successfully decorated with Ag₂CO₃ nanoparticles via the successive ionic layer adsorption and reaction (SILAR) technique. The content of Ag₂CO₃ is controlled by changing the times of SILAR. The average diameter of ZnO is about 200 nm, and the sizes of Ag₂CO₃ nanoparticles vary from 50 to 100 nm. Comparison with pure ZnO NRAs, ZnO/Ag₂CO₃ NRAs show an enhancement of absorption in the visible region, and the absorption intensity in the visible region enhances with the increasing of Ag₂CO₃ content. The photocatalytic result shows that ZnO/Ag₂CO₃ NRAs exhibit superior photocatalytic activity than pure ZnO in degrading of rhodamine B (RhB) water solution under simulated sunlight illumination. When the molar ratio of Ag/Zn is about 3.65%, ZnO/Ag₂CO₃ NRAs exhibit the highest photocatalytic activity.
A novel stellerite-based photocatalytic composite and its enhanced disinfection application
2018, Journal of Photochemistry and Photobiology B: Biology
The aim of this work was to prepare, characterize and evaluate the potential of novel ZnO/stellerite composite photocatalysts against Staphylococcus aureus (S. aureus). SEM/EDS studies employed to study the surface morphological properties revealed stellerite as the catalysts carrier played a role of dispersant for ZnO nanoparticles. The XRD patterns of the ZnO/stellerite indicated hexagonal crystal structure with 20–30 nm size. It was found that the crystallite size of ZnO/stellerite was much smaller as compared to pure ZnO and increased with increasing ZnO loading amount. The results of optical properties of ZnO/stellerite showed smaller band gap in contrast to pure ZnO, investigated by UV–vis absorption. Due to the optimum ZnO loading, the as-prepared ZnO-20 composite had the highest BET surface area and the pore volume. Using the TG-DSC measurement, the high thermal stability of the product was studied for different temperature values. Antibacterial activity of ZnO/stellerite affected by the ZnO loading, concentration of samples and light conditions (under dark and UV irradiation conditions) was examined by disinfection of S. aureus. The as-prepared ZnO-20 composite with 100 mg/L was found to exhibit excellent inactivation efficiencies (87.65% in the dark and 97.67% under UV illumination) towards S. aureus. Compared with pure ZnO, the obtained composite photocatalysts showed significantly better antibacterial performance by studying the disinfection kinetics of S. aureus. Thus, the present study reveals that the novel ZnO/stellerite shows great potential for its use in the targeted disinfection applications.
Multifunctional zinc-based hollow nanoplatforms as a smart pH-responsive drug delivery system to enhance in vivo tumor-inhibition efficacy
2018, Materials and Design
Novel multifunctional ZnO@ (Fe₃O₄/ZnS:Mn²⁺) nanocomposites as a pH-responsive drug delivery system were designed and successfully synthesized by a self-assembling method. The as-prepared ZnO@(Fe₃O₄/ZnS:Mn²⁺) possess porous hollow structure with strong orange fluorescence and faster magnetic response, which is beneficial for the functions of drug loading, fluorescence labeling and magnetic targeting simultaneously. Both in vitro and in vivo experiments testify that the ZnO@(Fe₃O₄/ZnS:Mn²⁺) nanocomposites own a good biocompatibility without obvious side effects on both cells and mice. After 24 days of treatment on the mice, ZnO@(Fe₃O₄/ZnS:Mn²⁺) nanocomposites greatly inhibited the tumor growth without causing both body weight change and any obvious pathological changes in major organs. The better antitumor efficacy than free DOX can be ascribed to both the accumulation of DOX-ZnO@(Fe₃O₄/ZnS:Mn²⁺) inside tumor and a sustained DOX release due to the dissociation of ZnO@(Fe₃O₄/ZnS:Mn²⁺) in acidic environment.

View all citing articles on Scopus

View full text

Enhanced photocatalytic activity of ZnO microflower arrays synthesized by one-step etching approach

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Preparation

Characterizations

Conclusions

Acknowledgements

Water Res.

Appl. Catal. B: Environ.

Appl. Catal. A: Gen.

Appl. Catal. B: Environ.

Catal. Commun.

J. Mol. Catal. A: Chem.

J. Mol. Catal. A: Chem.

Ceram. Int.

Ceram. Int.

Ceram. Int.

Chem. Phys. Lett.

Sep. Purif. Technol.

J. Chem. Technol. Biotechnol.

J. Hazard. Mater.

J. Chem. Technol. Biotechnol.

J. Phys. Chem. C

Nat. Mater.

Chem. Mater.

Lamgmuir

Langmuir

J. Am. Chem. Soc.

J. Am. Chem. Soc.