Huiping Zhao
Abstract:
To overcome the issue of UV-light response character of Bi2O2CO3 due to its wide band gap, we primarily attempted to understand the possibility of improving the photocatalytic activity of Bi2O2CO3 via g-C3N4 surface decoration by the theoretical calculation. Subsequently, g-C3N4 surface-decorated Bi2O2CO3 was successfully prepared via a facile hydrothermal method. It was found that the g-C3N4 surface-decorated Bi2O2CO3 samples exhibited enhanced activities for the photo degradation of tetracycline compared with pure Bi2O2CO3 upon simulated solar light irradiation. Among them, the 10 wt% g-C3N4 surface-decorated Bi2O2CO3 sample showed the highest photo catalytic efficiency. First principle calculation and experimental data confirmed that the charge transfer at the interface between g-C3N4 and Bi2O2CO3 could significantly suppress the recombination of photogenerated electron-holes pairs, thus improving the photocatalytic performance. The proposed mechanism for the enhanced photocatalytic activity was also discussed. Moreover, the photodegradation of antibiotics over g-C3N4 surface-decorated Bi2O2CO3 was also performed in actual water matrix.
1. Introduction
The harmful e�?¯�?¬�?�?�ects of antibiotics in ecosystems have been widely studied in recent years. Among them, tetracycline is one of the most common and widely used antibiotics due to its broad antibacterial spectrum and cheap price. Like other antibiotics, tetracycline residue in waste water could produce potential risks for aquatic and terrestrial ecosystems. Consequently, exploring e�?¯�?¬�?�?cient methodology for the antibiotic tetracycline treatment in waste water has been received particular research attention. There are numbers of traditional techniques for wastewater treatment including biological process, adsorption process, membrane processes and chemical oxidation methods. Correspondingly, some advanced oxidation technologies for water puri�?¯�?¬�?cation are mostly concerned in recent years, which majorly involve electrochemical, photochemical, Fenton, and some combinational processes of them in energy devices. Compared with all the other methods, semi-conductor photo catalysis emerges as a most powerful and cost e�?¯�?¬�?�?�ective alternative for antibiotics removal in waste water owing to the mineralization of organics by highly e�?¯�?¬�?�?�ective active species generated in the process
2. Experimental
2.1. Chemicals: Bismuth nitrate pentahydrate (Bi(NO3)3·5H2O), tetracycline (TC),tetracycline hydrochloride (TC·HCl), oxytetracycline (OTC), congo red(CR), methyl orange (MO), malachite green (MG) and methylene blue(MB) were purchased from Aladdin. Urea and melamine were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).All the chemicals were of analytical reagent grade and used without further puri�?¯�?¬�?cation.
2.2. Preparation: Graphitic carbon nitride (g-C3N4) was prepared according to the literature. Typically, 10 g melamine were placed into a semi-closed combustion boat, which was heated in a program-controlled mu�?¯�?¬�?�??e furnace to 500 °C at a rate of 5 °C min−1and then kept at that temperature for 2 h. Subsequently, the obtained sample was collected by cooling naturally to room temperature
2.3. Characterization: Powder X-ray di�?¯�?¬�?�?�raction (XRD) was carried on Bruker axs D8Discover (Cu Ka = 1.5406 Å). The scanning rate was 1° min−1in the 2θrange from 10° to 80°. Scanning electron microscopy (SEM) images were taken on Hitachi S4800 scanning electron microscope operating at5 kV. Transmission electron microscopy (TEM) images were recorded on a Philips Tecnai 20 electron microscope at an accelerating voltage of200 kV. More experimental conditions are Photocatalytic activity evaluation, electrochemical measurement and First-principle calculation
3. Results and discussion
3.1. First principle calculation and band structure analysis In order to understand the possibility of the improved photocatalytic properties of Bi2O2CO3 via g-C3N4 surface-decoration, the thermodynamic stability and the charge transfer at the interface between g-C3N4 and Bi2O2CO3 were primarily investigated. The optimal calculation results of different random initial models all end up with g-C3N4 lying on Bi2O2CO3 (0 0 1) facet. The interface formation energy was calculated according to the following equation: E E F g C N BOC = 3 4/ (001) E E g C N BOC 3 4 (001) where EF is the formation energy, Eg C N BOC 3 4/ (001), Eg C N3 4 and EBOC (001) represent the total energy of the optimized g-C3N4/BOC(0 0 1) model, monolayer g-C3N4 and Bi2O2CO3 (0 0 1) slab, respectively.
3.2. Characterization of g-C3N4/ Bi2O2CO3 samples Based on the theoretical calculation, surface-decorated Bi2O2CO3 samples with different g-C3N4 amount (4.8, 10, and 33.3 wt%) were prepared. XRD patterns of g-C3N4 surface-decorated Bi2O2CO3 samples. All the diffraction peaks of g-C3N4 decorated Bi2O2CO3 samples could be well matched to the standard diffraction data of tetragonal Bi2O2CO3 (JCPDS card No. 41-1488), indicative of the formation of tetragonal Bi2O2CO3 phase. In order to confirm the presence of g-C3N4 in the surface-decorated Bi2O2CO3 sample, FT-IR spectra of g-C3N4, Bi2O2CO3, and g-C3N4 surface-decorated Bi2O2CO3 samples were characterized.
3.3. Photocatalytic activity evaluation
The variations of TC concentrations (Ct/Co) with irradiation time during the photocatalytic process, where Co is the initial TC concentration and Ct is the TC concentration at t time. Direct photolysis of TC could be negligible upon solar light irradiation. It was found that all the g-C3N4 surface-decorated Bi2O2CO3 samples exhibited higher photocatalytic activity than that of bare Bi2O2CO3. The good linear relationship indicates that the process follows the traditional Langmuir-Hinshelwood (L-H) mechanism.
4. Conclusion
In summary, we clarified the charge transfer process at the interface of g-C3N4 surface-decorated Bi2O2CO3 photocatalyst through the first principle simulation and band match analysis, which confirmed the possibility of enhancing the photocatalytic activity of Bi2O2CO3 through g-C3N4 surface-decoration. The g-C3N4 surface-decorated Bi2O2CO3 samples were prepared via a facile hydrothermal method. Based on the electrochemical measurement and PL spectra, the relatively faster charge transfer rate combined with the deeply suppressed recombination of photo-generated electron-hole pairs greatly facilitate the enhancement of photocatalytic efficiency of the g-C3N4 surface-decorated Bi2O2CO3 photocatalyst. Moreover, the photocatalytic activity of the gC3N4 surface-decorated Bi2O2CO3sample for TC degradation in actual water matrix was also evaluated. This work not only provides a new route to fabricate g-C3N4 surface-decorated Bi2O2CO3 photocatalyst, but also develops a strategy to improve the photocatalytic performance for UV light response semiconductor photocatalysts.
Note: This work is partly presented at 5th International Conference on Organic and Inorganic Chemistry on July 12-13, 2018 at Paris, France