Tóm tắt luận án Tiến sĩ Vật lý: Nghiên cứu các tính chất động học và phát triển hệ laser rắn tử ngoại sử dụng vật liệu pha tạp ion Ce3+

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Luận văn tiến hành nhằm nghiên cứu các quá trình động học phát xạ cho laser rắn tử ngoại Ce:LiCAF băng rộng, có khả năng phát đơn xung ngắn dưới nano giây. Đánh giá ảnh hưởng của năng lượng laser bơm, thông số BCH lên độ rộng xung laser lối ra. Mời các bạn cùng tham khảo nội dung chi tiết.

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Nội dung Text: Tóm tắt luận án Tiến sĩ Vật lý: Nghiên cứu các tính chất động học và phát triển hệ laser rắn tử ngoại sử dụng vật liệu pha tạp ion Ce3+

MINISTRY OF EDUCATION VIETNAM ACADEMYOF AND TRAINING SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY ---------------------------- NGUYEN THI MAI THO STUDY ON USING PHOTOTCATALYST BASED ON LAYERED DOUBLE HYDROXIDES ZnBi 2 O 4 /GRAPHIT AND ZnBi 2 O 4 /Bi 2 S 3 FOR TREATMENT OF ORGANIC DYES Major: Inorganic Chemistry Code: 9440113 SUMMARY OF CHEMISTRY DOCTORAL THESIS Ha Noi - 2021
0 The dissertation was completed at: Industrial University of Ho Chi Minh City, Korea Instite of Toxicology – Gajeong-ro, Yuseong-gu, Daejeon; The Department of Chemistry - Changwon National University; HoChiMinh City Institute of Resources Geography. Graduate University of Sciences and Technology, Vietnam Academy of Science and Technology; Institute of Applied Materials Science. Scientific Supervisors: 1. Assoc. Prof. Dr. Nguyen Thi Kim Phuong 2. Dr. Bui The Huy 1 st Reviewer: ........................................................................... 2nd Reviewer: .......................................................................... 3 rd Reviewer:........................................................................... The dissertation will be defended at Institute of Applied Materials Science, Graduate University of Science And Technology, Vietnam Academy of Science and Technology, 01A, Thanh Loc 29, Thanh Loc ward, 12 District, Ho Chi Minh City. At ….. hour….. date….. month …..2021. The dissertation can be found in: - National Library of Vietnam and the library of Graduate University of Science And Technology - Vietnam Academy of Science and Technology
1 INTRODUCTION 1. The necessity of the thesis Currently, environmental pollution is at an alarming level, especially pollution of textile industry wastewater. Therefore, the research and development of materials as well as the textile and dyeing wastewater treatment methods are essential requirements. The removal of harmful organic pollutants through advanced oxidation processes (AOPs) photocatalytic oxidation is attracting an increasing attention. Heterojunctions in photocatalysts has been proved to be one of the most promising ways for the preparation of advanced photocatalysts because of its feasibility and effectiveness for the spatial separation of electron–hole pairs. 2. Objectives Study on treatment of RhB (Rhodamine B) and IC (Indigo carmine) dyes by photocatalytic ZnBi2O4/x.0Graphite, ZnBi2O4/x.0Bi2S3 under visible light. 3. Research scope and content. ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 composites have signifcance to find cost-effective and advanced heterojunction photocatalysts for environmental remediation. 4. Structure of the thesis The dissertation has 116 pages, including the Preface, Chapter 1: Overview, Chapter 2: Experiment, Chapter 3: Results and discussions, Conclusions, publications with 44 images, 32 tables and 153 references. Chapter 1. OVERVIEW A heterojunction, in general, is defned as the interface between two different semiconductors with unequal band structure, which can
2 result in band alignments. The heterojunction photocatalyst should fulft several requirements, such as visible-light activity, high solar- conversion effciency, proper bandgap structure for redox reactions, high photostability for long-term applications, and scalability for commercialization. Many semiconductors have been investigated and developed for various photocatalytic such as ZnO/Al-Mg-LDHs, RGO/Bi-Zn-LDHs,Ti/ZnO-Cr2O3. Recently, mixed-metal oxides, which are prepared by the calcination treatment of layered double hydroxides (LDHs), have been used as photocatalysts for the elimination of toxic organic compounds in aqueous solutions. LDHs are two-dimensional layered anionic clays that are generally expressed as [M1-x 2+Mx3+ (OH)2]x+ (An-)x/n.yH2O as one of the simplest mixed-metal oxides derived from LDHs, ZnBi2O4 is a promising, highly efﬁcient, visible-light active photocatalyst, with advantages of small optical band gap, high stability, and low conduction band edges. There have been many studies of the photocatalysts application based on Bi3+ to remove organic pollutants. Graphite is a carbon allotrope with a layered structure of stacked graphene sheets. It is commonly available and widely used as an adsorbent for organic pollutants and several studies on the photocatalytic performance of graphite have been reported so far. Bismuth sulfide (Bi2S3) has a typical lamellar structure with a narrow bandgap, especially as a potential visible light photocatalyst through combination with other semiconductors material. In the present work, ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 composites were obtained through a simple co-precipitation method which exhibited effective photocatalysis for the decomposition of RhB and IC under visible light.
3 Chapter 2. EXPERIMENT 2.1 Synthetic of ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 Synthesized ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 heterojunction by in-situ coprecipitation (Figure 2.1). The as-prepared materials were labeled as ZnBi2O4, ZnBi2O4/x.0Graphite (x = 1, 2, 5, 10, and 20), ZnBi2O4/x.0Bi2S3(x = 1, 2, 6, 12, and 20), x is the percentages of graphite and Bi2S3 in ZnBi2O4. Figure 2.1. The synthesis process a) ZnBi2O4/x.0Graphit and (b) ZnBi2O4/x.0Bi2S3 The ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 were characterized using various methods, including XRD, IR, XPS, UV-VIS, SEM, TEM, UV-Vis DRS... 2.2 Applications of ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 photocatalytic systems. The photocatalytic activity of the ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 was assessed using IC and RhB under visible light irradiation. The catalytic process consists of two phases. QT1: the dark adsorption equilibrium was established for 60 min. QT2: visible-light
4 irradiation by A 300 W halogen lamp (Osram, Germany) was used to provide a full spectrum emission without the use of a filter. Chapter 3. RESULTS AND DISCUSSIONS 3.1 ZnBi2O4/x.0Graphite comsposite. 3.1.1 Characterization of ZnBi2O4/x.0Graphite. Figure 3.1 shows the XRD patterns of graphite, ZnBi2O4 and ZnBi2O4/x.0Graphite. The XRD pattern of ZnBi2O4 showed several strong peaks corresponding to tetragonal zinc bismuth oxide and pure hexagonal zinc oxide. Pristine graphite typically shows a strong diffraction peak at around 26.6°. The diffraction pattern of ZnBi2O4/20.0Graphite was characterized by a new stronger peak at 27.3° as compared to that of pristine ZnBi2O4, indicating hybridization between graphite and ZnBi2O4. The main diffraction peaks of ZnBi2O4/xGraphite were similar to those of ZnBi2O4 and graphite. Figure 3.1 XRD and IR patterns of the samples: ZnBi2O4 and ZnBi2O4/xGraphite (x = 1, 2, 5, 10 and 20).
5 The ZnBi2O4/x.0Graphite sample exhibited characteristic vibrational peaks at 1480 cm-1 and 1028 cm-1 corresponding to the stretching modes of C=C and C–O groups, respectively. The bands at 1384 and 843 cm-1 in the pristine ZnBi2O4, ZnBi2O4/x.0Graphite samples are typically attributed to Bi–O and Bi–O–Bi stretching modes, respectively. The C 1s XPS spectrum of graphite for the ZnBi2O4/1.0Graphite sample is shown in Figure 3.2. A dominant peak at 284.4 eV and a weak peak at 288.1 eV are observed in the graphite spectrum corresponding to C-C (or C=C) and C=O, respectively. The binding energies decreasing Zn 2p (0.4 eV), Bi 4f (0.8eV) O 1s (0.3eV) compare the ZnBi2O4/1.0Graphite and ZnBi2O4 sample. The strong electronic coupling between ZnBi2O4 and Graphite would likely accelerate the electron-hole separation. Figure 3.2. XPS spectra of ZnBi2O4 and ZnBi2O4/1.0Graphite
6 Figure 3.3 SEM image of as- prepared samples (a) Graphite, (b) ZnBi2O4, and (c-f) ZnBi2O4/x.0Graphite (x = 1, 5, 10 and 20); (g) TEM image ZnBi2O4/1.0Graphite sample. Figure 3.4. The absorption edges of the samples, and band gap energy of Graphite, ZnBi2O4, and ZnBi2O4/x.0Graphite. The SEM of ZnBi2O4/x.0Graphite samples, ZnBi2O4 tends to grow on the graphite sheet. Figure 3.3 shows the typical TEM images of the ZnBi2O4/1.0Graphite composite; it was found that the graphite sheets were densely covered by the ZnBi2O4 plates.
7 Bảng 3.1 Band gap energy Eg of ZnBi2O4, Graphit, ZnBi2O4/x.0Graphit. Graphit 768 1.5 400 2.9 ZnBi2O4 535 2.2 ZnBi2O4/x.0Graphit 400 2.9 (x = 1, 2, 5, 10). 535 2.2 ZnBi2O4/20.0Graphit 420 3.10 The pristine ZnBi2O4 material exhibited visible-light response with the absorption edges at 400 and 535 nm, indicating the presence of a small amount of the ZnO phase, while graphite showed intense absorption over the visible range that extended even to the infrared region (Figure 3.4). The absorption edges of ZnBi2O4/x.0Graphite (x = 1, 2, 5, 10) were similar to that of ZnBi2O4 and blue-shifted in comparison with those of graphite. However, the ZnBi2O4/20.0Graphite composites exhibited a mixed absorption at 420 nm. This change indicated a strong interaction between graphite and ZnBi2O4 in the resulting ZnBi2O4/x.0Graphite photocatalysts, which strongly affected the light energy absorption region. 3.1.2 Photocatalytic Degradation of IC by ZnBi2O4/x.0Graphite Effect of Graphite content in ZnBi2O4/x.0Graphite composites. The order of the RhB degradation rate for as-prepared photocatalysts was ZnBi2O4/1.0Graphite (0.0141 min–1) > ZnBi2O4/2.0Graphite (0.0077 min–-1) > ZnBi2O4/5.0Graphite (0.0074 min–1) > –1 –1 ZnBi2O4/10.0Graphite (0.0043 min ) > ZnBi2O4 (0.0032 min ) > ZnBi2O4/20.0Graphite (0.0018 min–1). The kinetic data of the photodegradation were a good approximation to pseudo-first-order
8 kinetic behavior (r2 = 0.9121–0.9945). The photodegradation rate of RhB on ZnBi2O4/1.0Graphite was significantly higher (~4.5-fold) than that of ZnBi2O4. Thus, ZnBi2O4/1.0Graphite structure increased the rate of RhB oxidation in comparison with pristine ZnBi2O4 (figure 3.5) Figure 3.5. Photodegradation of RhB using ZnBi2O4/xGraphite catalysts under visible light irradiation. Effect of the loading of ZnBi2O4/1.0Graphite When the concentration of ZnBi2O4/1.0Graphite was increased from 0.5 to 1.0 g/L, the rate constant k of RhB degradation increased significantly from 0.0053 to 0.0141 min–1 (Figure 3.6a). Beyond the ZnBi2O4/1.0Graphite loading of 1.0 g/L, the value of k decreased (0.0137–0.0059 min–1), which may be due to the excessive catalyst causing opacity of the solution, there by hindering light passing through the solution and consequently interfering with the RhB degradation reaction. Effect of initial RhB concentration The effect of initial RhB concentration on the degradation kinetics was investigated in range 15–60 mg/mL. It can be seen that the rate constant k of RhB degradation was greatly decreased from 0.0519 to 0.0089 min–1 with the increasing initial RhB concentration from 15 to 60 mg/L. This might be explained by the fact that a high concentration
9 of RhB lowered the penetration of photons into the solution and this consequently decreased the photodegradation efficiency. Figure 3.6. Photodegradation of RhB over ZnBi2O4/1.0Graphite under visiblbe light (a) Effect of the loading of ZnBi2O4/1.0Graphite, (b) Effect of initial RhB concentration, (c) Effect of pH solution, and (d) Reusability of ZnBi2O4/1.0Graphite catalyst under visible light. Effect of pH solution Figure 3.6c shows that the maximum degradation of 50 mg/L of RhB over ZnBi2O4/1.0Graphite was more than 93% for a duration of 150 min at pH 2.0 (k = 0.0141), while ~72% and 66% of RhB was degraded at pH 4.5 (k = 0.0070) and pH 7.0 (k = 0.0059). Stability and reusability of ZnBi2O4/1.0Graphit ZnBi2O4/1.0Graphite exhibited high photochemical stability, even though the photocatalyst had been recycled four times successively.
10 This implied that the progressive reduction after fourth consecutive cycles was very small. Approximately 84.14% of RhB had been successfully degraded after four runs, indicating that the loss in photocatalytic performance of ZnBi2O4/1.0Graphite was insignificant after four recycling runs. These results indicate that h+ and O2– are the major active species responsible for the complete photocatalytic mineralization of RhB, whereas the contribution of the OH radicals is minor. TOC removal reached 77.7% after visible-light irradiation for 150 min. Figure 3.7. (a) Photodegradation of RhB and (b) The rate constant k of photodegradation of RhB over ZnBi2O4/1.0Graphite under visible light with addition of h+; O2- and OH radical scavengers and (c) The mechanisms of the RhB photodegradation over ZnBi2O4/1.0Graphite under visible light. The enhancement of photocatalytic activity of ZnBi2O4/1.0Graphite could be mainly attributed to the effective transfer of photogenerated e- at the heterojunction interface of ZnBi2O4 and graphite, which reduced the recombination of the e- - h+ pairs.
11 The mechanism for photodegradation of RhB by the ZnBi2O4/1.0Graphite catalyst under visible-light irradiation can be described by the following reactions: ZnBi2O4+ h  ZnBi2O4 (e–, h+) RhB + h  RhB+ + e– ZnBi2O4 (h+) + RhB/RhB+  CO2 + H2O Graphite + e–  Graphite (e–) Graphite (e–) + O2  O2– O2– + RhB/RhB+  CO2 + H2O O2– + 2H2O  2OH + 2OH– ZnBi2O4 (h+) + 2H2O  OH + H+ OH + RhB/RhB+  CO2 + H2O h+ + e–  (e–, h+) (negligible recombination) 3.1.3 Photocatalytic Degradation of IC by ZnBi2O4/x.0Graphite The order of the rate constants of the IC decomposition of the catalysts is as follows: ZnBi2O4/5.0Graphite (0.0032 min-1)> ZnBi2O4/2.0Graphite (0.0027 min-1)> ZnBi2O4/1.0Graphit (0.0021 min-1)> ZnBi2O4/10.0Graphit (0.0016 min-1)> ZnBi2O4 (0.0012 min- 1 )> ZnBi2O4/20.0Graphit (0, 0007 min-1). Figure 3.8. Photodegradation of IC over ZnBi2O4/x.0Graphite (1, 2,5, 10, 20) under visiblbe light.
12 It can be seen that the ZnBi2O4/1.0Graphite hasn't an good photocatalytic activity for the degradation of RhB under visible light irradiation, on which more than 42,5% of IC had been degraded within 180 min. 3.2. ZnBi2O4/x.0Bi2S3 comsposite. 3.2.1 Characterization of ZnBi2O4/x.0Bi2S3 The XRD pattern of pristine ZnBi2O4 sample is in good accordance with the standard card of tetragonal ZnBi2O4 (JCPDS No. 043-0449) and the formation of pure hexagonal ZnO (JCPDS No. 079- 0207). The main diffraction peaks of ZnBi2O4/x.0Bi2S3 composites were similar to those of the ZnBi2O4 samples. However, the patterns of the ZnBi2O4/x.0Bi2S3 composites showed a low-intensity and wide diffraction peaks, especially the peak at 2 = 28.1, indicating the presence of an amorphous phase after coupling took place between Bi2S3 and ZnBi2O4. Figure 3.9. XRD and FT- IR patterns of the samples: ZnBi2O4 and ZnBi2O4/x.0Bi2S3 (x = 1, 2, 6, 12 and 20). The peak at 3460, 1630 cm-1 in the ZnBi2O4, ZnBi2O4/x.0Bi2S3 spectrum can be referred to OH bonding (FT-IR). The bands at 1384 and
13 843 cm-1 in the pristine ZnBi2O4, ZnBi2O4/x.0Bi2S3 samples are typically attributed to Bi–O and Bi–O–Bi stretching modes, respectively. The higher the amount of Bi2S3 in ZnBi2O4/x.0 Bi2S3, the more obvious the shift in the number of Bi-O bonds at the 832 cm-1, proving that there is a chemical interaction that changes the number of characteristic waves of the bond. Figure 3.10. XPS spectra of ZnBi2O4 and ZnBi2O4/12.0 Bi2S3 Figure 3.11. UV-Vis spectra, and band gap energy of pristine ZnBi2O4, pristine Bi2S3, and ZnBi2O4/Bi2S3 composites.
14 XPS spectra of Zn 2p, O 1s, 4f5/2 and Bi 4f7/2 two samples ZnBi2O4 and ZnBi2O4/12.0Bi2S3 showed difference in energy level. The lower binding energy shift of Zn 2p that reduces the charge density of Zn is due to the chemical interaction of ZnBi2O4 and Bi2S3 that stimulates the electron transfer between Zn and Bi via an oxygen (Zn-O-Bi). The energy difference Bi-O at 4f5/2 and Bi 4f7/2 also changes with chemical interaction between Bi2S3 and ZnBi2O4 in ZnBi2O4/12.0B Bi2S3. The pristine ZnBi2O4 material exhibited visible light response with the absorption edges at 400 and 535 nm while Bi2S3 showed intense absorption over the visible range that extended even to the infrared region. However the ZnBi2O4/x.0Bi2S3 (x = 6, 12) composites exhibited a mixed absorption edge between Bi2S3 and ZnBi2O4 and were significantly red shifted as compared to that of ZnBi2O4. This change was attributed to the strong interaction between Bi2S3 and ZnBi2O4 in the resulting ZnBi2O4/x.0Bi2S3 photocatalysts, which strongly affected the energy profile. The band gap energy (E g) of the as-prepared materials was estimated in Table 3.2. Table 3.2: Band gap energy (Eg) of the as-prepared materials. Material max (nm) Eg (eV) Bi2S3 900 1,20 400 2,9 ZnBi2O4 535 2,2 ZnBi2O4/x.0Bi2S3 (x = 1, 2) 400 2,9 ZnBi2O4/x.0Bi2S3 400 2,9 (x = 6, 12, 20) 900 1,39 The SEM micrographs revealed that as-prepared ZnBi2O4 and Bi2S3 consisted of stacked particles with an irregular morphology because
15 of the collapse of the layered structure. The individual plates of ZnBi2O4 were flat and the edges of the plates appeared rounded. Another interesting observation was made in the case of the ZnBi2O4/x.0Bi2S3 composites; the SEM images showed that Bi2S3 tended to grow on the plates of ZnBi2O4 in the composites. Figure 3.12. SEM image of as-prepared samples ZnBi2O4/x.0Bi2S3 (x = 1, 2, 6; 12 and 20); (g) TEM image ZnBi2O4/x.0Bi2S3 sample. 3.2.2 Photocatalytic Degradation of IC by ZnBi2O4/x.0Bi2S3 Effect of Bi2S3 content in ZnBi2O4/x.0Bi2S3 composites The efficacy of the photocatalysts under visible light was evaluated by comparing the values of k and followed the decreasing order of ZnBi2O4/12.0Bi2S3 (0.0540 min–1) > ZnBi2O4/20.0Bi2S3 (0.0266 min– 1 ) > ZnBi2O4/6.0Bi2S3 (0.0254 min–1) > ZnBi2O4/2.0Bi2S3 (0.0203 min–1) > ZnBi2O4/1.0Bi2S3 (0.0180 min–1) > ZnBi2O4 (0.0028 min–1). The values of r2 ranged from 0.9562 to 0.9920 and indicated that the
16 photocatalytic experimental results were a good approximation to first-order kinetic behavior. Figure 3.13. Photocatalytic IC degradation efficiencies of the ZnBi2O4-xBi2S3 catalysts under visible-light irradiation. Effect of the loading of ZnBi2O4/12.0Bi2S3 Figure 3.14a illustrates the degradation of 50 mg/L of IC under visible light irradiation with various loads of ZnBi2O4/12.0Bi2S3 at pH 6.3. When the concentration of ZnBi2O4/12.0Bi2S3 was increased from 0.2 to 1.0 g/L, the rate constant k of IC degradation was greatly increased from 0.0059 to 0.0540 min–1. Beyond the ZnBi2O4/12.0Bi2S3 loading of 1.0 g/L, the value of k decreased to 0.0198 min–1. Effect of initial IC concentration. The rate constant k of IC degradation by ZnBi2O4/12.0Bi2S3 was greatly decreased from 0.0854 to 0.0380 min–1 with increasing initial Indigo carmine concentration from 15 to 60 mg/L. Effect of pH solution Figure 3.14a shows that the maximum degradation of 50 mg/L of Indigo carmine over ZnBi2O4/12.0Bi2S3 was more than 97% in 1 h at
17 pH 6.3 (k=0.0540 min–1), while the degradation of IC at pH 4.0 and pH 7.0 was 90% (k=0.0385 min–1) and 82% (k= 0.0262 min–1), respectively. Approximately 94.1% of IC was degraded after four runs, indicating that the loss in photocatalytic performance of ZnBi2O4/12.0Bi2S3 was insignificant after four recycling runs. These results indicate that O2– radicals are the major active species responsible for the complete photocatalytic degradation/mineralization of IC. The TOC removal reached 81.1% in the presence of ZnBi2O4/12.0Bi2S3 catalyst after visible light irradiation for 1 h, which confirmed that the outstanding mineralization performance of composite under visible light. Figure 3.14. Photodegradation of IC over ZnBi2O4/12.0Bi2S3 under visiblbe light (a) Effect of the loading of ZnBi2O4/12.0Bi2S3, (b) Effect of initial IC concentration, (c) Effect of pH solution, and (d) Reusability of ZnBi2O4/12.0Bi2S3 catalyst under visible light.
18 Thus, the likely mechanism for the photodegradation of IC using the ZnBi2O4/12.0Bi2S3 catalyst under visible light irradiation can be described by the following reactions: ZnBi2O4/12.0Bi2S3 + h  ZnBi2O4/12.0Bi2S3 (e–, h+) ZnBi2O4/12.0Bi2S3 (e–) + O2  O2– O2– + IC  CO2 + H2O ZnBi2O4/12.0Bi2S3 (h+) + IC  CO2 + H2O ZnBi2O4/12.0Bi2S3 (h+) + 2H2O  OH + H+ OH + IC  CO2 + H2O h+ + e–  (e–, h+) (negligible recombination) This strong synergistic effect is ascribed to the promotion of heterogeneous catalysis in ZnBi2O4/12.0Bi2S3 by the irradiation of visible light as a result of improved transfer of the photogenerated electron and h+ at the heterojunction interface between ZnBi2O4 and 0Bi2S3, which reduces the recombination of e- and h+ pairs. Figure 3.15 Photodegradation of Indigo carmine over ZnBi2O4- 12.0Bi2S3 under visible light with addition of h+; O2–, and OH radical scavengers; Proposed mechanism of the IC photodegradation over ZnBi2O4/12.0Bi2S3 under visible light. 3.2.3 Photocatalytic Degradation of RhB by ZnBi2O4/x.0Bi2S3 Effect of Bi2S3 content in ZnBi2O4/x.0Bi2S3 composites