Novel graphitic carbon nitride/KTaO3 (g-C3N4/KTaO3) nanocomposite photocatalysts have been successfully synthesized via a facile and simple ultrasonic dispersion method. Compared to either g-C3N4 or KTaO3, the composite photocatalysts show significantly increased photocatalytic activity for degradation of Rhodamine B (RhB) under visible light irradiation. The increased photocatalytic performance of the composite could be attributed to the enhanced photogenerated charge carrier separation capacity. Moreover, it is observed that
Semiconductor photocatalysis has been regarded as an ideal green chemistry technology in dealing with the globally concerned energy shortage and environment pollution issues. In view of practical application, developing highly active photocatalysts has drawn great attention in recent years. Among the various photocatalytic materials, KTaO3 has been reported as a unique photocatalyst for hydrogen generation as well as organic pollutant degradation [
Recently, Wang and coworkers discovered that the graphitic carbon nitride (g-C3N4), a conjugative
Since the conduction band bottom of g-C3N4 (−1.13 eV) [
The g-C3N4 powder sample was synthesized by directly heating melamine under 550°C according to the previously reported procedure [
The typical process for preparation of g-C3N4/KTaO3 (CN/KTO) composites was as follows: an appropriate amount of g-C3N4 was added into methanol and then ultrasonically treated in an ultrasonic bath for 30 min. After KTaO3 powder was added, the solution was stirred in the fume hood for 24 h. Finally the mixture was dried at 100°C overnight and then heated to 300°C for 2 h. The CN/KTO composites with different ratios of g-C3N4 to KTO were prepared and denoted as gcn30, gcn50, and gcn70, respectively, in which the number indicates percentage (mass%) of g-C3N4 in the composite.
Crystal structures of the synthesized samples were examined by a powder X-ray diffractometer (XRD, Rigaku D/MAX 2500 with Cu K
Photocatalytic activities of CN/KTO samples were evaluated by Rhodamine B (RhB) degradation in aqueous solution under visible light irradiation. 100 mL aqueous solution of RhB (4 mg/L) was put in a glass beaker, and 0.1 g photocatalyst was then added. In order to establish the adsorption-desorption equilibrium, the suspension was ultrasonically treated and stirred in the dark for 60 min, respectively. Photocatalytic activity was evaluated under irradiation from a 300 W Xenon lamp with a UV cutoff filter, which provides the visible light ranging from 420 to 700 nm. At each given irradiation time interval, 3 mL of the mixture was collected and then the slurry sample was centrifuged to separate the photocatalyst particles. The concentration of RhB was analyzed by measuring the maximum absorption at 553 nm using Shimadzu UV2700 spectrophotometer.
The XRD patterns of KTO, g-C3N4, and their composites are shown in Figure
XRD patterns of KTO, g-C3N4, and their composites.
From the UV-Vis diffuse reflectance spectra of KTO, g-C3N4, and their composites as shown in Figure
UV-Vis DRS of KTO, g-C3N4, and their composites.
The microstructures of KTO, g-C3N4, and their composites were observed on a transmission electron microscope (TEM). As shown in Figure
TEM images of (a) KTO, (b) g-C3N4, and (c) gcn70. The scale bar for (a) and (b) is 100 nm; the scale bar for (c) is 200 nm.
As shown in Figure
Photocatalytic degradation of RhB over g-C3N4, KTO, and their composites under visible light irradiation.
It is known that
As shown in Figure
Photocatalytic degradation of RhB with different scavengers under visible light irradiation.
Repeatability of the photocatalytic activity was tested by running several cycles of photocatalytic degradation for RhB over gcn70. Each cycle ran for the same time of 90 min, and the photocatalyst was filtered to use for next cycle. As shown in Figure
(a) Cycling test for the degradation of RhB by gcn70 sample and (b) XRD patterns of gcn70 before and after the cycling test.
Figure
Photoluminescence (PL) spectra of g-C3N4 and gcn70.
As mentioned above, the composites CN/KTO have shown much better photocatalytic activity than either KTO or g-C3N4 under visible light irradiation. It is known that under visible light irradiation, g-C3N4 can be excited due to the appropriate band gap (2.7 eV), whereas KTO is inert owing to its wide band gap. Since the conduction band bottom of g-C3N4 (−1.13 eV) [
Proposed mechanism for the photodegradation of RhB on CN/KTO composite.
The novel g-C3N4/KTaO3 composites were successfully prepared by a facile and simple ultrasonic dispersion method. The resulting g-C3N4/KTaO3 composites showed an enhanced photocatalytic activity for degradation of RhB under visible light irradiation, and the optimal mass ratio of g-C3N4/KTaO3 was 70/30. Owing to the well-aligned energy band edges and interface between g-C3N4 and KTaO3, effective photogenerated charge carrier transfer and separation was evidenced by photoluminescence, which suppressed the recombination of electrons and holes. As a consequence, the photocatalytic activity of the g-C3N4/KTaO3 composite was significantly improved.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This work was supported by the National Basic Research Program of China (973 Program, Contract no. 2014CB239301). Zhiqing Yong is grateful to Dr. Naoto Umezawa and Professor Jinhua Ye (NIMS) for hosting his internship visit to NIMS. Dr. Hua Tong, Dr. Haiying Jiang (NIMS), and Dr. Xianguang Meng (NIMS) are appreciated for their valuable discussion and/or assistance in photocatalytic evaluation.