ABSTRACT:
In this study, MIL-53(Fe) and Ni-doped MIL-53(Fe) has been successfully synthesized under an appropriate solvothermal condition and characterized by XRD, FE-SEM, FT-IR, nitrogen physisorption measurements (BET). We also investigated the photocatalytic activity of these materials for the decomposition of Rhodamine B under visible light irradiation. From XRD and FTIR results, doping of the Ni ion in the crystal lattice did not change the high crystallinity of the MIL-53(Fe) structure, and all the metal ions were incorporated into the structures of MIL-53(Fe) as well as replaced Fe ion or located at the interstitial site. The Ni-doped MIL-53(Fe) sample expressed the highest photocatalytic degradation capacity of organic dyes due to a small-particle-size effect.
Keywords: Photocatalytic Decomposition of Rhodamine B, MIL-53(Fe), Ni-doped MIL-53(Fe), visible light irradiation.
1. Introduction
Metal-organic frameworks (MOFs) are a new class of high surface area and crystalline porous materials made of metal ions and organic linkers1. They have received considerable attention in recent years, due to their high resistance, high surface area, large pore volume, low density and easily tunable framework. Among the MOFs, the MIL-53(Fe) have attracted extensive interests for applications in gas storage2,3, adsorption and separation of heavy metal4, sensors5 and in the biomedical field such as drug delivery6.
Recently, another important direction is using MIL-53(Fe) as a catalyst carrier or modification of MIL-53(Fe) as a catalyst for chemical reactions7. One of the sites of interest in the structure of MIL-53 (Fe) is the transition metal center, which has the potential to act as Lewis acid in many organic reactions8. There has been a great deal of research on the potential use of Fe concentration in MIL-53 (Fe) as a photochemical catalyst for some organic decomposition reactions such as methylene blue (MB)9-11, rhodamine B (RhB)7-11 and p-nitrophenol (PNP)7 gives good decomposition results, so this is a very potential application direction of MIL-53(Fe) in the removal of pollutants.
Yuan et al. have shown that MIL-53(Fe) has high photocatalytic degradation capacity of dye under visible light irradiation. However, the decomposition rate of photosynthesis is not high, due to the recombination of photogenerated holes and electrons, resulting in the reduced holes for decolorization of organic dyes 6. To limit the recombinant process, inorganic oxidants such as H2O2, KBrO3, and (NH4)2S2O8 have been introduced in this process and they act as electron acceptors, thus increasing the photocatalytic efficiency of the material. According to research by Yuan et al., H2O2 is the efficient electron acceptor in the photocatalytic decomposition process of organic pigments by MIL-53(Fe) under visible light irradiation6. In addition, in order to improve the efficiency of materials for existing applications and open up new applications, MIL-53(Fe) have been doped or combined with one or more metals have attracted much attention in recent years, due to this combination can enhance their activity12–15. For this study, Qiao Sun et al. modified the MIL-53(Fe) by adding Mn, Co, and Ni metal into the MIL-53(Fe) network of MIL-53(Fe) material. Results show that the catalytic performance of these materials is high in liquid-phase degradation of phenol16.
In this work, we synthesized MIL-53(Fe) and Ni-doped MIL-53(Fe) photocatalysts by solvothermal method. This compound was characterized by XRD, Raman, FE-SEM, FT-IR, and nitrogen physisorption measurements (BET) and was used for photocatalytic degradation of Rhb from aqueous solution under different experimental conditions.
2. Materials and Methods
MIL-53(Fe) was prepared through a solvothermal method similar to MIL-53(Fe) in the literature[17]. In a typical synthesis, terephthalic acid (9 mmol, 1.525 g) and FeCl36H2O (6 mmol, 1.637 g) were dissolved in 60 mL DMF (with a Fe/TPA/DMF molar ratio of 1:1.5:130). Then the solution was transferred into a 100 mL Teflon-lined autoclave. Then, the autoclave was kept in an oven at 100oC for 3 days. After being cooled to room temperature in air, the remaining terephthalic acid was removed by distillation method with DMF for 24h at 100oC. Finally, the sample was obtained by centrifugation and washed with DMF, ethanol, and water. The product was dried for 12h at 60oC. Moreover, Ni-doped MIL-53(Fe) (Ni-MOF-0.3, with 0.3 was the molar ratio of Ni2+/Fe3+) was synthesized based on the above procedures.
X-ray diffraction patterns were recorded in a D8 Advance Bruker powder diffractometer with a Cu Ká excitation source. The surface morphologies and particle size of MIL-53(Fe) and Ni-doped MIL-53(Fe) samples were analyzed by a JSM 7401F instrument (Jeol, United States). FT-IR was recorded on an EQUINOX 55 spectrometer (Bruker, Germany) by means of the KBr pellet technique. The textural properties of the adsorbents were determined by N2 adsorption/desorption measurement at 77 K in a TriStar 3000 V6.0.
The photocatalytic activities of MIL-53(Fe) and Ni-doped MIL-53(Fe) photocatalysts were evaluated by the photodegradation of RhB dye under a 40W lamp irradiation (Philips). In a typical photodegradation experiment, 2 mg of MIL-53(Fe) photocatalyst was put into 100 mL of RhB aqueous solution (3×10-5 mol/L) in a 250 mL beaker followed by addition of H2O2. Samples were withdrawn at the same intervals and immediately centrifuged for 15 min to separate photocatalysts for analysis. The RhB concentration was monitored by measuring the absorption intensity at its maximum absorbance wavelength of λ = 554 nm using a UV-visible spectrophotometer (Model Evolution 60S, Thermo Fisher Scientific).
3. Results and Discussion
Figure 1(A) shows the XRD pattern for MIL-53 (Fe) and Ni-doped MIL-53(Fe). Result XRD spectrum shows that the MIL-53(Fe). DMF sample had the characteristic peaks of MIL-53 (Fe), as previously reported in the literature 17. The Ni-doped MIL-53(Fe) displayed the same XRD patterns as MIL-53(Fe) with little increase in intensity implying the increase of its crystallinity. The results show that there was no change in the crystal structure after the incorporation of Ni. In case of the MIL-53(Fe). H2O and Ni-MOF-0.3.H2O samples, the main peaks position of the XRD patterns were changed. They can be explained by the formation of hydrogen bondings between the water molecules and the inorganic hydrophilic parts of the pore.
FTIR spectroscopic studies were performed for MIL-53(Fe).DMF, Ni-MOF-0.3.DMF, MIL-53 (Fe).H2O and Ni-MOF-0.3.H2O in the wave range of 400-4000 cm-1 (Figure 2(B). In the case of Ni-MIL-53(Fe).DMF, two strong vibrational bands around 1657, 1601, 1391, 1017 and 749 cm-1 confirms the presence of dicarboxylate linker within the sample and are identical to those of reported data in the literature2,16,18. The strong bands at 547 cm-1 are attributed to Fe-O vibrations19. Analysis of FTIR spectra for the material was again washed once time with ethanol, and thrice with H2O showed that adsorbed water molecules in MIL-53(Fe). H2O and Ni-MOF-0.3.H2O material account for the spectral band observed at 1601 cm-1.
The morphology of the crystals MIL-53(Fe) and Ni-doped MIL-53(Fe) catalyts was analyzed using SEM. The crystals of MIL-53(Fe) (Figure 1(C)) is not so homogeneous (probably due to concomitant nucleation and crystal growth under solvothermal method20) and the surface morphology of MIL-53 (Fe) looks like octahedral shaped crystals and similar to the images presented in the literature 4,6,20. The SEM image of Ni-MOF-0.3 shows that the Fe3O and FexNiyO clusters are not distributed separately in two kinds of crystals MIL-53(Fe) and Ni-MOF, respectively.
Figure 1: XRD patterns (A), FT-IR spectra (B), and SEM images (C) of the MIL53 and Ni-MOF-0.3
The N2 adsorption–desorption isotherms of MIL-53(Fe) and Ni-doped MIL-53(Fe), as shown in Figure 2a, displayed an intermediate mode between type I and type IV, which is associated with mesoporous and microporous materials, respectively21. The Brunauer–Emmett–Teller (BET) surface area, total pore volume and pore width of MIL-53(Fe) and Ni-doped MIL-53(Fe) samples were shown in Table 1.
Figure 2: (A) Nitrogen adsorption-desorption isotherms of MIL-53(Fe). DMF (a), MIL-53(Fe)H20 (b), Ni-MOF-0.3.DMF (c) and Ni-MOF-0.3.H20 (d). (B) The Barrett-Joyner-Halenda (BJH) mesoporous size distribution of MIL-53(Fe).DMF (a), MIL-53(Fe).H20 (b), Ni-MOF-0.3.DMF(c) and Ni-MOF-0.3.H20 (d)
The photocatalytic activities of MIL-53(Fe) and Ni-doped MIL-53(Fe) photocatalysts were evaluated by the photodegradation of RhB dye. (Figure 3a). displays the photocatalytic degradation of RhB under different experimental conditions. For the degradation of RhB in visible light/H2O2 system. After visible light irradiation for 180 min, no observation of the photolysis of RhB reflects that the RhB was quite stable under visible light irradiation. While the presence of MIL-53(Fe) could enhance the degradation efficiency of RhB up to 81.46% by photolysis process in MIL-53 (Fe)/visible light/H2O2 catalytic system. With Ni-MOF-0.3/visible light/H2O2 catalytic system, the degradation efficiency of RhB was remarkably enhanced, about 91.14% RhB removal was achieved. The Ni-MOF-0.3 exhibits much higher activity than that of MIL-53(Fe) can be clearly indicated by the change of the UV–vis absorption spectra of the solution in the course of the RhB degradation (Figure 3b and 3c). The photodegradation of RhB over MIL-53(Fe) and Ni-MOF-0.3 photocatalysts approximately followed pseudo-first-order kinetics model. The presence of Ni-MOF-0.3 promotes the photodegradation rate, the rate constants were 0.888×10-2 min-1 for MIL-53(Fe) and 1.115×10-2 min-1 for Ni-MOF-0.3.
Figure 3: Degradation of RhB under different conditions (a), the UV–vis spectral changes of RhB in Ni-MOF-0.3/visible light/H2O2 catalytic system (b) and in MIL-53(Fe)/visible light/H2O2 catalytic system (c)
4. Conclusions
We have successfully prepared MIL-53(Fe) and Ni-MIL-53(Fe) via a direct solvothermal method. The Structure characterization results with XRD and FT-IR confirmed the incorporation of Ni into the MIL-53(Fe) structures was no change in the crystal structure. The photocatalytic activities of these materials were studied in the photodegradation of RhB dye. The results have demonstrated that the incorporation of Ni could promote the photocatalytic degradation capacity of organic dye. After 180 min of visible light irradiation, about 91.14% and 81.46% of RhB was photocatalytically degraded on Ni-MOF-0.3/visible light/H2O2 and MIL-53(Fe)/visible light/H2O2 catalytic system, respectively. These results suggest that the best photocatalytic degradation result was achieved on the Ni-MOF-0.3.
Acknowledgements. This research is funded by NTTU Foundation for Science and Technology Development under grant number 2017.01.13/HĐ-KHCN.
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Nghiên cứu tổng hợp vật liệu khung hữu cơ kim loại
MIL-53 (Fe) và MIL-53 (Fe) biến tính và ứng dụng trong
xử lý hợp chất hữu cơ sử dụng ánh sáng nhìn thấy
● NGUYỄN HỮU VINH
Viện Kỹ thuật Công nghệ cao NTT, Trường Đại học Nguyễn Tất Thành
Khoa Hóa học, Trường Đại học Khoa học Tự nhiên, Đại học Quốc gia Hồ Chí Minh
● BẠCH LONG GIANG
Viện Kỹ thuật Công nghệ cao NTT, Trường Đại học Nguyễn Tất Thành
● TRẦN VĂN THUẬN
Viện Kỹ thuật Công nghệ cao NTT, Trường Đại học Nguyễn Tất Thành
● TRẦN VĂN MẪN
Khoa Hóa học, Trường Đại học Khoa học Tự nhiên, Đại học Quốc gia Hồ Chí Minh
● NGUYỄN DUY TRINH
Viện Kỹ thuật Công nghệ cao NTT, Trường Đại học Nguyễn Tất Thành
TÓM TẮT:
Trong nghiên cứu này, MIL-53(Fe) và MIL-53(Fe) biến tính với Ni đã được tổng hợp thành công thông qua phương pháp dung nhiệt. Vật liệu được đặc trưng cấu trúc bằng các phương pháp phân tích hiện đại như XRD, FE-SEM, FT-IR, đẳng nhiệt hấp phụ-giải hấp phụ khí nitơ (BET). Hoạt tính quang xúc tác của vật liệu được đánh giá thông qua phản ứng quang phân hủy hợp chất hữu cơ (Rhodamine B) sử dụng ánh sáng nhìn thấy. Kết quả XRD và FTIR cho thấy, khi biến tính với Ni không làm thay đổi cấu trúc tinh thể của vật liệu MIL-53(Fe) và tất cả các ion kim loại được xen chèn bên trong cấu trúc của vật liệu cũng như thay thế các ion Fe trong nút mạng tinh thể. Vật liệu MIL-53(Fe) biến tính với Ni cho hiệu quả quang xúc tác phân hủy chất màu hữu cơ cao dưới ánh sáng nhìn thấy.
Từ khóa: Quang xúc tác phân hủy Rhodamine B, MIL-53(Fe), Ni-doped MIL-53(Fe), chiếu xạ ánh sáng nhìn thấy.
Xem tất cả ấn phẩm Các kết quả nghiên cứu khoa học và ứng dụng công nghệ số 10 tháng 09/2017 tại đây
