Nanometer-sized zinc oxide (ZnO) has been synthesized through sol-gel method with natural cellulose substance (commercial filter paper) as template. The structure of zinc oxide nanomaterial was characterized by nitrogen adsorption-desorption and XRD. The morphology was observed by SEM and TEM. The results show that the hexagonal wurtzite phase is actually the only crystal phase in the sample and the product faithfully inherits the hierarchical morphology and the complex network structure of the original filter paper, which is composed of many randomly intersecting zinc oxide microfibers and nanosheets with lots of close stacked particles adsorbed on the surface. Moreover, these zinc oxide nanomaterials possess abundant mesoporous structure with an average pore diameter of
In recent years, the environmental pollution has been increasing. The photocatalytic processes in polluted air and water through photocatalytic oxidation of semiconductor catalysts have been studied extensively in recent years [
Synthesis by using natural materials as template is a facile strategy to yield functional materials with complex and hierarchical natural structures, which are generally difficult to prepare even through the most advanced synthetic methods. Among these biotemplates, natural cellulosic substances such as the common filter paper possess a macroscopic-to-nanoscopic random morphological hierarchy. Using these common and low-cost natural cellulose substances as the structural templates, many nanomaterials with complex functional nanostructures can be formed. With the natural cellulosic materials as structural templates, unique and intricate morphologies originated from nature substances become the choice for the design and preparation of zinc oxide nanomaterials, which extensively expands the structural varieties of ZnO materials.
In this paper, we synthesized nanometer-sized zinc oxide through sol-gel method with natural cellulose substance (commercial filter paper) and polyethylene glycol (PEG) as dual templates, Zn(CH3COO)2·2H2O as precursor, ethanol as solvent, and NH(C2H2OH)2 as chelating agent. The resulting zinc oxide nanomaterials faithfully inherit the hierarchical morphologies and the complex network structures of the initial cellulose substance and exhibit relatively high photocatalytic activity.
Pure cellulosic fiber from commercial ashless quantitative filter paper (GB/T1914-93) was used for the entire process. Polyethylene glycol [
Zinc oxide sol was prepared in the following way: Firstly, zinc acetate [Zn(CH3COO)2·2H2O] was dissolved in 50 mL of absolute ethanol and stirred with a magnetic stirrer (70°C) to be mixed thoroughly. When the solution changed into an emulsion, an amount of diethanolamine [NH(C2H2OH)2; DEA] as chelating agent was added to the emulsion (the molar ratio of DEA/zinc acetate was 1 : 1). When the emulsion became clear after a period of stirring, 0.7 g polyethylene glycol (PEG) was added and continually stirred for 2 h until a transparent sol was obtained. After the sol solution was cooled to the room temperature, 150 mg precutted squared filter paper fractions of
The morphologies of samples were observed by a field emission scanning electron microscope (FE-SEM, Hitachi, S-4800), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HR-TEM, FEI Tecnai G20/JEM 2010, operated at 200 kV). To prepare the specimens for SEM and TEM observation, a small piece of the sample sheet specimen was suspended in ethanol by ultrasonication for several seconds. The suspension was dropped onto silicon wafer followed by sputtering with gold or platinum to increase conductivity for SEM observation or onto copper mesh for TEM observation, and the specimens were dried in air. Crystal phase of the obtained materials was determined by powder X-ray diffraction (XRD) recorded on a Dandong TD3500 Advanced Diffractometer with Cu-K
Methyl orange (C14H14N3NaO3S), a widely used dye, was employed as a representative dye pollutant to evaluate the photocatalytic activity of zinc oxide nanomaterials under UV light. Firstly, 100 mL aqueous solution of zinc oxide catalyst (0.2 g) was treated with ultrasonication for 30 min to promote dispersion uniformity and 400 mL dye aqueous solution of MO (30 mg/L) was prepared for subsequent photocatalytic activity test. Then, the two prepared solutions above were mixed in a quartz tube. Before irradiation, the above mixed solution was stirred for 30 min in the dark to ensure the establishment of adsorption-desorption equilibrium. Under ambient conditions and stirring, the quartz tube was exposed to the UV irradiation produced by a 500 W Hg arc lamp equipped with a band-pass light filter (365 ± 15 nm). At selected time intervals, about 3 mL of the suspension was withdrawn for analysis on a Varian UV-vis spectrophotometer (Cary-50, Varian Co.). The percentage of residual dye is reported as
The XRD pattern of the obtained zinc oxide nanomaterials demonstrates that hexagonal wurtzite phase is actually the only crystal phase in the product (Figure
X-ray diffraction pattern of the prepared filter paper inspired zinc oxide nanomaterial.
The widening XRD peak enables estimation of the crystallite size via the Scherrer equation as below:
The morphology of zinc oxide product was investigated by SEM and TEM, and typical images are shown in Figure
Micromorphology observation of prepared zinc oxide nanomaterials. (a) FE-SEM image, (b) further magnified SEM image, (c) typical TEM image of zinc oxide nanosheet, and (d) HR-TEM image and SAED pattern (insert).
The nitrogen adsorption and desorption curve of the synthesized zinc oxide nanomaterials is shown in Figure
N2 adsorption/desorption isotherms of the prepared zinc oxide nanomaterials and BJH pore size distribution plot (insert).
The UV-vis adsorption spectrum of the prepared zinc oxide nanomaterials was measured by UV-vis optical absorbance pattern (Figure
(a) UV-vis absorption spectra of the prepared zinc oxide nanomaterials and (b) the plots of
The results above indicate that our zinc oxide samples possess stronger capability of absorption than commercial zinc oxide semiconductor in the ultraviolet light range.
The photocatalytic activity of our porous zinc oxide sample was further evaluated by monitoring the degradation of methyl orange (MO) under UV irradiation (Figure
(a) Photographs of MO under UV irradiation at different times, (b) liquid-phase photocatalytic degradation of MO under the irradiation of UV light, and (c) kinetics of photocatalytic degradation of MO under UV for filter paper inspired zinc oxide nanomaterials.
The kinetics of photocatalytic degradation of MO can be depicted by pseudo-first-ordered kinetics equation as below [
Figure
In this paper, ZnO porous thin films were prepared on natural cellulose substance (commercial filter paper) by sol-gel method with polyethylene glycol (PEG) as organic template, Zn(CH3COO)2·2H2O as precursor, ethanol as solvent, and NH(C2H2OH)2 as chelating agent. The obtained material was characterized by XRD, SEM, TEM, SAED, N2 adsorption/desorption, and UV-vis. From the results of the XRD and SAED, we can deduce that hexagonal wurtzite phase is actually the only crystal phase in the sample. The SEM results show that the product faithfully inherits the hierarchical morphologies of the initial cellulose substances and consists of many randomly intersecting zinc oxide microfibers and nanosheets with lots of particles adsorbed on the surface. With further magnification, we can observe that the solid zinc oxide microtubes and nanosheets are composed of lots of closely packing zinc oxide particles. Analysis of TEM and N2 adsorption/desorption isotherm plots show that these zinc oxide nanomaterials possess the mesoporous structure with an average pore diameter of
The authors declare that there are no competing interests regarding the publication of this paper.
This work was financially supported by the National Natural Science Foundation of China (21101136, 21401015), Project of International Cooperation and Exchanges NSFC (no. 21310102011), the Key Project of Chinese Ministry of Education (212144), Natural Science Foundation Project of CQ CSTC (cstc2012jjA50037, cstc2014jcyjA50012), and Chongqing University of Arts and Sciences (nos. R2012CJ15, R2013CJ04).