Using the common natural cellulose substance (filter paper) and triblock copolymer (Pluronic P123) micelles as dual templates, porous titania nanotubes with enhanced photocatalytic activity have been successfully synthesized through sol-gel methods. Firstly, P123 micelles were adsorbed onto the surfaces of cellulose nanofibers of filter paper, followed by hydrolysis and condensation of tetrabutyl titanate around these micelles to form titania layer. After calcination to remove the organic templates, hierarchical titania nanotubes with pores in the walls were obtained. The sample was characterized by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption/desorption, Fourier Transform Infrared Spectroscopy (FT-IR), Ultraviolet-Visible Diffuse Reflectance Spectroscopy (UV-Vis DRS), and X-ray photoelectron spectroscopy (XPS). As compared with commercial P25 catalyst, the porous titania nanotubes prepared by this method displayed significantly enhanced photocatalytic activity for degrading methyl orange under UV irradiation. Within 10 minutes, the porous titania nanotubes are able to degrade over 70% of the original MO, while the value for the commercial Degussa P25 is only about 33%.
As the most promising photocatalyst, titania materials (TiO2) have been expected to play an important role in a wide range of fields including environmental pollution control, photocatalyst, and high effect solar cell due to their excellent physicochemical properties such as relatively high photocatalytic activity, thermal and chemical stability, nonphoto corrosive, being nontoxic, being capable of photooxidative destruction of most organic pollutants, and low cost [
In this paper, we synthesized titania nanotubes through sol-gel method with employed natural cellulose substance (filter paper) as template. The resulting titania nanotubes truly inherit the complex network structures and hierarchical morphologies of the initial cellulose substance and exhibit obviously enhanced photocatalytic activity compared with commercial P25.
Commercial ashless quantitative filter paper (GB/T1914-93) was used throughout the work. Triblock copolymer Pluronic P123 (PEG-PPG-PEG) and titanium
The synthetic procedure of hierarchical titania nanotubes is schematically illustrated in Scheme
Schematic illustration of the preparation process for hierarchical titania nanotubes templated by filter paper.
The micromorphologies of obtained hierarchical titania nanotubes sample were examined by S-4800 field emission scanning electron microscope (FE-SEM) from Hitachi, 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 electron microscope observation, a small piece of the nanotubular titania sheet specimen was suspended in ethanol by supersonic dispersion. Then some of the suspension was dropped onto silicon wafer and sputtered with gold or platinum for SEM observation. And some are dropped onto copper mesh for TEM observation. The crystal phase of the obtained hierarchical titania nanotubes materials was determined by powder X-ray diffraction (XRD) recorded on a Dandong TD3500 Advanced diffractometer (Cu-K
A widely used dye methyl orange (C14H14N3NaO3S), which can act as a representative dye pollutant, was chosen to evaluate the photocatalytic performance of TiO2 nanotubes under UV light. Firstly, 100 mL aqueous solution of TiO2 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 for establishing the adsorption-desorption equilibrium. Then under ambient conditions and stirring, the mixture 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 every 2-minute interval, about 3 mL suspension was withdrawn from the mixture for analysis on a Varian Cary-50 UV-Vis spectrophotometer. The initial concentration of dye solution before photodegradation experiment is noted as
The XRD pattern in Figure
Characteristic XRD pattern of (a) P25; (b) the prepared hierarchical TiO2 nanotubes sample; and (c) JCPDF card number 73-1764 of anatase TiO2.
The morphology of obtained TiO2 sample was observed by SEM and TEM. Figure
Micromorphology observations of prepared porous TiO2 nanotubes. (a) FE-SEM image. (b) Further magnified SEM image. (c) TEM image of individual titania nanotube and magnified TEM image of tube wall (insert). (d) HR-TEM image and SAED pattern (insert).
According to the IUPAC classification of porous materials, the nitrogen adsorption and desorption curve of the obtained hierarchical porous TiO2 nanotubes material in Figure
(a) N2 adsorption/desorption isotherms of the prepared TiO2 nanotubes and BJH pore-size distribution plot (insert). (b) FT-IR spectrum of the obtained porous TiO2 nanotubes.
Band gaps (
Figure
(a) UV-Vis absorption spectra of the TiO2 nanotubes and P25. (b) The plots of
Using X-ray photoelectron spectroscopy (XPS), we examined the surface chemical state and element composite of our porous TiO2 nanotubes. The XPS full spectrum shown in Figure
(a) XPS full spectrum of TiO2 sample. (b) High resolution XPS of C 1s and subpeak fitting chart. (c) High resolution XPS of Ti 2p and subpeak fitting chart. (d) High resolution XPS of O 1s and subpeak fitting chart.
TiO2 material is the most promising photocatalyst because of its high photosensitivity and wide band gap. Here, we evaluate the photocatalytic performance of the as-prepared porous TiO2 nanotubes by monitoring the degradation of methyl orange (MO) under UV irradiation. Before UV irradiation, the mixture of MO solution and the catalyst was stirred in the dark for 30 min to ensure that MO was adsorbed to saturation on the surface of catalyst. Figure
(a) Photographs and (b) adsorption spectra of MO solutions in the presence of porous TiO2 nanotubes irradiated by UV lamp at different periods of time.
Figure
Photodegradation kinetics of methyl orange in the presence of porous TiO2 nanotubes. (a) Plot for the degradation percentage (
Figure
It has been reported that the photodegradation activity of TiO2 material is mainly attributed to the factors including surface area, absorptive capacity, grain size, crystalline, and morphology. Generally, high surface area and small grain size are most important for promoting the photocatalytic performance of titania materials [
Figure
(a) Low magnified and (b) large magnified SEM images of porous TiO2 nanotubes after photocatalytic reaction for MO. (c) XRD patterns of porous TiO2 nanotubes before and after photocatalytic degradation for MO.
In summary, hierarchical porous TiO2 nanotubes were successfully synthesized through a facile and efficient template synthesis strategy with the natural cellulose substance (filter paper) and triblock copolymer (Pluronic P123) micelles as dual templates. The resultant porous TiO2 nanotubes really inherited the hierarchical morphologies of the initial cellulose substances and consisted of many randomly intersecting titania microfibers with high aspect ratios. The further microstructure observation shows that the product was endowed with not only the tubular structure with tube wall thickness of 30–40 nm but also abundant intergranular pores with a diameter of
The authors declare that they have no competing financial interests.
This work was financially supported by the National Natural Science Foundation of China (21101136 and 21401015), the Key Project of Chinese Ministry of Education (212144), Natural Science Foundation Project of CQ CSTC (cstc2012jjA50037 and cstc2014jcyjA50012), the Natural Science Foundation of Yongchuan (Ycstc, 2014nc4001), and Chongqing University of Arts and Sciences (R2012CJ15, R2012CJ19, and R2013CJ04).