Cu2OTiO2heterostructure nanotube arrays prepared by an.docx

1、Cu2OTiO2heterostructure nanotube arrays prepared by anCu2O/TiO2 heterostructure nanotube arrays prepared by an electrodeposition method exhibiting photocatalytic activity for CO2 reduction to methanolJunyi Wang a, Guangbin Ji a, *, Yousong Liu a, M. A. Gondal b, Xiaofeng Changaa. College of Material

2、s Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 211100, China;b. Physics Department, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia.* The corresponding author: Prof. Dr. Guangbin JiTel: +86-25-52112902; Fax: +86-25-52112900E-mail addre

3、ss: gbjiPreparation of Cu2O/TNTsThe Cu2O/TNTs composites were obtained by Cu2O electrochemical deposition in a conventional three-electrode cell, using the TNTs, Ag/AgCl and Pt as the working, reference, and counter electrodes, respectively. The electrolyte was prepared by dissolving 0.4 M CuSO4 in

4、3 mol L1 lactic acid solution, and was adjusted to pH=11.0 with NaOH solution with the existence of lactic acid which can stabilize the copper ions in alkaline solution to form copper lactate complex 1-2. The electrochemical deposition was carried out at a potential of -0.8V referenced to Ag/AgCl. T

5、he electrolyte was kept at a constant temperature of 25C, magnetically stirred during the deposition process. Three types of samples were obtained by varying the concentration of electrodeposition charges: 0.5 C, 1.0 C and 1.5 C. After the electrodeposition process, the samples were washed with deio

6、nized water, placed in a vacuum and annealed in a tubular furnace at 200C for 10 min in N2 atmosphere.Details about Photoelectrochemical measurements The photoelectrochemical measurements were carried out with CHI 660D in a three-electrode cell in 0.05 M Na2SO4 electrolyte solution with Cu2O/TNTs sa

7、turation mercury electrode were used as the working electrode, counter electrode and reference electrode, respectively. A 500 W Xenon lamp with a light intensity of 400 mW/cm2 was used as the light source. The wavelengths of the incident light were greater than 400 nm using a 400 nm cut-off lter.Det

8、ails about photocatalytic reduction of CO2The laser used as the light source of excitation in this study was the third harmonic of the pulsed Nd:YAG laser (Model Spectra Physics GCR 25010) laser. The photo-catalytic reactor is a cylindrical stainless steel cell with quartz windows on the top to enab

9、le the transmission of both UV and Visible light radiation. At the bottom of the cell, there is a gas inlet with a needle valve that lets the CO2 gas pass through the distilled water and almost at the same level, in order to dispense the sample through the syringe there is an outlet fixed with the r

10、ubber septum at the opposite side. The whole cell is kept on a magnetic stirrer that constantly replenishes the photo-catalyst in the path of laser radiations. Attention was paid to have a better interaction of incident radiations with the photocatalyst and keep the water level above the catalyst to

11、 be minimum (almost to the level of the catalyst platform). Since the quantity of the sample taken for gas chromatographic analysis at each time was around 4.0 l, the water level did not decrease due to the sample withdrawal from the reaction cell. The reaction cell was cleaned and dried, and 3 cm 3

12、 cm catalyst was loaded along with 100 ml distilled water and then tightly closed and checked for leaks up to 50 psi pressure. High purity CO2 gas (99.99%) was introduced through reactor inlets and the reactor pressure was maintained at 50 psi. Prior to turning on the pulsed laser, CO2 gas was purge

13、d into 100 ml water containing 3 cm 3 cm catalyst for 30 min to saturate the aqueous solution of the reactor with CO2. After a predetermined irradiation time, the liquid samples were withdrawn from the reactor using syringe without opening the reactor and were subjected to GC analysis.The liquid sam

14、ples were analyzed for the end products like methanol and other hydrocarbons using a gas chromatograph equipped with flame ionization detector 0FID). The separation of the components was carried out on Rtx-Wax column (dimensions: 30 m x 0.32 mm x 0.32 mm) obtained from Restek using temperature-progr

15、ammed conditions. For the analysis, 4.0 l product sample was injected into the gas chromatograph and the operating conditions were as follows: Oven temperature was set at 40 oC, increased to 90 oC at heating rate of 5 oC/min and then increased to 180 oC at the rate of 50 oC/min to elute all the comp

16、onents before injecting another sample. The injector and detectors were both set at 200 oC and helium was used as a carrier gas. The total analysis run time was 11.8 min. A calibration plot was developed using a standard methanol solution in distilled water for calculating the amount of methanol pro

17、duced as a function of irradiation time.Analysis and quantification of methanol productGas chromatography (GC) technique was employed to verify and quantify the methanol as an end product from the CO2 reduction over Cu2O/TNTs nanocomposite. It is depicted in Fig.S-1 (a) that the retention time of st

18、andard methanol is 2.46 mins for the GC selected parameters and the used column. The relationship between GC peak area and methanol concentration was confirmed by using standard concentrations of methanol for calibration as mentioned earlier and depicted in Fig. S-1 (b), which exhibits clearly a lin

19、ear trend.Fig.S-1 (a). GC peak positions using standard methanol; (b). Calibration curve of methanol concentration vs GC peak area.Details about photocatalytic degradation of TNTs and Cu2O/TNTs Photodegradation experiments were carried out in a 100 mL conical ask containing 50 mL, dye Acid orange (A

20、O) solution with initial concentration of 1 ppm under stirring conditions. The prepared Cu2O/TNTs composites were kept in a quartz device and the reaction system was illuminated under visible light after the samples reached adsorption equilibriums according to previous report 3. 4 mL of the suspensi

21、on was withdrawn throughout the experiment after every 20 min. The samples were analyzed by a UV-Vis spectrophotometer (SHIMADZU UV-3600).Photocatalytic activity for the degradation of AOIn order to further prove the construction of Cu2O/TNTs heterojunction, the photocatalytic activity of the TNTs a

22、nd Cu2O/TNTs samples were evaluated by the degradation of AO dye molecules in water under illumination with a 300 W Xe arc lamp having an output intensity of 400 mW/cm2. With a wide optical absorption wavelength range and high absorption intensity, the Cu2O/TNTs samples are expected to be highly des

23、irable and potential materials for photocatalytic applications. Visible light photocatalytic activities of Cu2O/TNTs and TNTsAs depicted in Fig. S-2, the dark absorption process lasts for 60 minutes duration before Xe arc lamp was on. The typical absorption peak of AO was decreased with the extensio

24、n of irradiation time by TNTs and Cu2O/TNTs with different electrodeposition charges under visible light irradiation. It is obvious from figure that the typical absorption peak of AO after degradation by TNTs decreases less rapidly than that for Cu2O/TNTs samples, indicating that Cu2O/TNTs samples e

25、xhibit better photocatalytic activity than that of TNTs.Fig. S-3 depicts the comparison of adsorption and photocatalytic result of TNTs and Cu2O/TNTs with different electrodeposition charge under visible light irradiation. These results show that 88% of the AO was photocatalytically degraded after 2

26、 h irradiation using the Cu2O/TNTs with the charge of 0.5 C. The Cu2O/TNTs with the charge of 1.0 C exhibit higher photocatalytic degradation rate than that of Cu2O/TNTs with the charge of 0.5 C. The photocatalytic activity of the Cu2O/TNTs with the charge of 1.5 C for AO degradation is much lower t

27、han that of two samples with only 60%. For comparison, the TNTs function as the photocatalyst, the degradation of the AO was extremely slow (only 20% of the AO was decolorized after 2 h of irradiation). UV light photocatalytic activities of Cu2O/TNTs and TNTsFig.S-4 depicts a series of absorption sp

28、ectra of AO aqueous solution after degradation by Cu2O/TNTs and TNTs exposed to Xe arc lamp for various time durations under UV and visible light irradiation. The typical absorption peak gradually diminishes, suggesting the degradation of AO assisted by Cu2O/TNTs and TNTs. Fig.S-5 depicts the compar

29、ison of adsorption and photocatalytic result of TNTs and Cu2O/TNTs with different electrodeposition charges under UV and visible light irradiation after 1 h Xe arc lamp irradiation. These results clearly demonstrate that all three kinds of Cu2O/TNTs samples could be effective photocatalysts under li

30、ght irradiation. They all exhibit a better photocatalytic performance than that of the bare TNTs. The Cu2O/TNTs with the charge of 1.0 C exhibits the highest photocatalytic decomposition efciency (the Cu2O/TNTs with the charge of 0.5 C is lower and 1.5 C is the worst). The repeated photocatalytic de

31、gradation of an aqueous AO solution under visible light irradiation was conducted to study the stability of the Cu2O/TiO2 composite nanotube arrays. Cu2O/TiO2 was used for five successive AO degradation experiments. As shown in the Fig.S-6, the photocatalytic activity of Cu2O/TiO2 is relatively stab

32、le. Although some photocatalytic activity losses were observed in five successive runs. The results show that 90 % of the AO was degraded after 2 h irradiation using the Cu2O/TNTs with the charge of 1.0 C in the first run and 74.6% of the AO was degraded in the fifth run.The photocatalytic degradati

33、on of the aqueous AO solution led to a signicant reduction when the Cu2O/TNTs photocatalyst was present. The enhanced catalytic activity of Cu2O/TNTs could be attributed to the heterojunction construction and the separation of the photogenerated electron and hole in the heterojunction structure to improve