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.
Trang 1MINISTRY OF EDUCATION
AND TRAINING
VIETNAM ACADEMYOF SCIENCE AND TECHNOLOGY
GRADUATE UNIVERSITY SCIENCE AND
TECHNOLOGY -
NGUYEN THI MAI THO
STUDY ON USING PHOTOTCATALYST BASED
O N L A Y E R E D D O U B L E H Y D R O X I D E S ZnBi2O4/GRAPHIT AND ZnBi2O4/Bi2S3 FOR
Trang 2The 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
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
Trang 3INTRODUCTION
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
Trang 4result 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-x2+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
Trang 5Chapter 2 EXPERIMENT
2.1 Synthetic of ZnBi 2 O 4 /x.0Graphite and ZnBi 2 O 4 /x.0Bi 2 S 3
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) ZnBi 2 O 4 /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 ZnBi 2 O 4 /x.0Graphite and ZnBi 2 O 4 /x.0Bi 2 S 3 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
Trang 6irradiation 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 ZnBi 2 O 4 /x.0Graphite comsposite
3.1.1 Characterization of ZnBi 2 O 4 /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: ZnBi 2 O 4 and
ZnBi 2 O 4 /xGraphite (x = 1, 2, 5, 10 and 20)
Trang 7The 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-1in the pristine ZnBi2O4, ZnBi2O4/x.0Graphitesamples 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 ZnBi 2 O 4 and ZnBi 2 O 4 /1.0Graphite
Trang 8Figure 3.3 SEM image of
as-prepared samples (a) Graphite,
(b) ZnBi 2 O 4 , and (c-f)
ZnBi 2 O 4 /x.0Graphite (x = 1, 5,
10 and 20); (g) TEM image
ZnBi 2 O 4 /1.0Graphite sample
Figure 3.4 The absorption edges of the samples, and band gap
energy of Graphite, ZnBi 2 O 4 , and ZnBi 2 O 4 /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
Trang 9Bảng 3.1 Band gap energy E g of ZnBi 2 O 4 , Graphit,
(x = 1, 2, 5, 10)
400
535
2.9 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 ZnBi 2 O 4 /x.0Graphite
Effect of Graphite content in ZnBi 2 O 4 /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) > ZnBi2O4/10.0Graphite (0.0043 min–1) > ZnBi2O4 (0.0032 min–1) > ZnBi2O4/20.0Graphite (0.0018 min–1) The kinetic data of the photodegradation were a good approximation to pseudo-first-order
Trang 10kinetic behavior (r 2 = 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 ZnBi 2 O 4 /xGraphite
catalysts under visible light irradiation
Effect of the loading of ZnBi 2 O 4 /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
Trang 11of RhB lowered the penetration of photons into the solution and this consequently decreased the photodegradation efficiency
Figure 3.6 Photodegradation of RhB over ZnBi 2 O 4 /1.0Graphite under visiblbe light (a) Effect of the loading of ZnBi 2 O 4 /1.0Graphite, (b) Effect of initial RhB concentration, (c) Effect of pH solution, and (d) Reusability of ZnBi 2 O 4 /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 ZnBi 2 O 4 /1.0Graphit
ZnBi2O4/1.0Graphite exhibited high photochemical stability, even though the photocatalyst had been recycled four times successively
Trang 12This 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 ZnBi 2 O 4 /1.0Graphite under visible light with addition of h + ; O 2- and OH radical scavengers and (c) The mechanisms of the RhB photodegradation over
ZnBi 2 O 4 /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
Trang 13The mechanism for photodegradation of RhB by the ZnBi2O4/1.0Graphite catalyst under visible-light irradiation can be described by the following reactions:
OH + RhB/RhB+ CO2 + H2O
h+ + e– (e–, h+) (negligible recombination)
3.1.3 Photocatalytic Degradation of IC by ZnBi 2 O 4 /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 ZnBi 2 O 4 /x.0Graphite (1,
2,5, 10, 20) under visiblbe light
Trang 14It 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 ZnBi 2 O 4 /x.0Bi 2 S 3 comsposite
3.2.1 Characterization of ZnBi 2 O 4 /x.0Bi 2 S 3
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: ZnBi 2 O 4
and ZnBi 2 O 4 /x.0Bi 2 S 3 (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
Trang 15843 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 ZnBi 2 O 4 and ZnBi 2 O 4 /12.0 Bi 2 S 3
Figure 3.11 UV-Vis spectra, and band gap energy of pristine
ZnBi 2 O 4 , pristine Bi 2 S 3 , and ZnBi 2 O 4/ Bi 2 S 3 composites