1. Full name: Nguyen Thi Phuong Le Chi                         2. Sex: female

3. Date of birth: 02/02/1989                                                        4. Place of birth: Phu Yen

5. Admission decision number: No. 3972/ QD-DHKHTN 24/11/2016 of the President of Vietnam National University, Hanoi.

6. Changes in academic process:

7. Official thesis title: Research on synthesis of photocatalytic materials contain tantalum nitride and application in environmental treatment.

8. Major: Environmental Chemistry                                             9. Code: 9440112.05

10. Supervisors: Main instruction: Prof. Dr. Nguyen Van Noi

                           Additional guidance: Assoc.Prof. Dr. Nguyen Minh Phuong

11. Summary of the new findings of the thesis:

- We successfully synthesized the Ta3N5 (Ebg = 2,1 eV), BiVO4 (Ebg = 2,19 eV) và g-C3N4 (Ebg = 2,52 eV) using solid phase thermal method/combining with sonification, hydrothermal.

- We successfully synthesized seven the Ta3N5/BiVO4 materials under different conditions. The obtained resuls show that, optimum conditions to synthesize Ta3N5/BiVO4: the optimal Ta3N5/BiVO4 ratio in the heterojunction system was 5 %, temperature 600 oC (TB-5-600). The band gap energy of Ta3N5/BiVO4 was approximately 1.82 eV and degradation of RhB dye using TB-5-600 in aqueous environment is 89.30% under visible light (after 6 hours).

- We successfully synthesized eight the Ta3N5/g-C3N4 materials under different conditions. The obtained resuls show that, optimum conditions to synthesize Ta3N5/g-C3N4: the optimal Ta3N5/g-C3N4 ratio in the heterojunction system was 2 %, temperature 550 oC (TCN-2-550). The band gap energy of Ta3N5/g-C3N4 was approximately 1.91 eV and degradation of RhB dye using TCN-2-550 in aqueous environment is 90,26% under visible light (after 3 hours).

- Three V doped Ta3N5 (V-Ta3N5) materials was synthesized. The optimal V doping ratio in the V/Ta was 2 % (2%V-Ta3N5). The V dopants, which existed in the Ta3N5 lattice, could act as an intermediate band (V 3d) between the valence band (N 2p) and the conduction band (Ta 5d) of the Ta3N5 to increase electron – hole separation efficiency of the photocatalysts. Thus, the photocatalytic activity of the V-Ta3N5 was much higher than that of the Ta3N5. Degradation of RhB dye using V-Ta3N5 in aqueous environment is 75,15% under visible light (after 6 hours).

- The reaction rate of RhB on Ta3N5/BiVO4, Ta3N5/g-C3N4 and V-Ta3N5 were found to obey pseudo first-order kinetics represented by the Langmuir-Hinshelwood model. The value of reaction rate constants for RhB degradation are 0,42160 h-1 (after 6 hours); 0,74572 h-1; (after 3 hours) and 0,2213 h-1 (after 6 hours), respectively.

- Proposed possible mechanism of our established Ta3N5/BiVO4 (HO• radical - main factor) and Ta3N5/g-C3N4 (O2•- radical - main factor) systems for photocatalytic degradation of RhB pollutants under light visible region. 

- Used the V-Ta3N5 and Ta3N5/BiVO4 for the CO2 conversion to produce valuable solar fuels. The production rates of CH4 generated from the photocatalytic reduction of CO2 by 2% V/Ta and Ta3N5/BiVO4 under visible light are 425 and  322 (µmol. g-1cat. h-1), respectively.

- Evaluated the ability to convert CO2 into CH4 into renewable fuels on Ta3N5/BiVO4 and V-Ta3N5 materials.

12. Practical applicability, if any:

Thesis researching and preparing modified materials Ta3N5/BiVO4, Ta3N5/g-C3N4,

V-Ta3N5 from tantalum nitride to catalyze the decomposition of some toxic organic compounds in water environment is a direction High scientific and practical significance.

The results obtained from the assessment of the ability to convert CO2 into renewable

fuels on Ta3N5/BiVO4 and V-Ta3N5 materials show the potential for application of these materials in CO2 conversion reaction, aiming to solve two current heating issues are global warming and fuel scarcity.

13. Further research directions, if any

 Evaluate the ability to convert CO2 into renewable fuels on Ta3N5/g-C3N4 materials.

Evaluate the ability to decompose some toxic organic compounds in the water environment by V-Ta3N5 material to choose the most suitable materials for practical application.

14. Thesis-related publications:

1. Thi Dieu Cam Nguyen, Thi Phuong Le Chi Nguyen, Hung Thanh Tung Mai, Van-Duong Dao, Minh Phuong Nguyen, Van Noi Nguyen (2017), "Novel photocatalytic conversion of CO2 by vanadium-doped tantalum nitride for valuable solar fuel production", Journal of Catalysis, 352, pp.67–74 (Q1, IF = 7,732).

2. Nguyễn Thị Phương Lệ Chi, Mai Hùng Thanh Tùng, Nguyễn Thị Diệu Cẩm, Trương Thanh Tâm, Trần Thị Thu Phương, Nguyễn Thị Minh Thư, Nguyễn Minh Phương, Nguyễn Văn Nội (2017), "Tổng hợp vật liệu Ta3N5 và đánh giá hoạt tính quang xúc tác khử CO2 trong vùng ánh sáng khả kiến", Tạp chí Hóa học, tập 55(5E1,2), tr.17-21.

3. Nguyễn Thị Phương Lệ Chi, Lê Quỳnh Như, Trương Thanh Tâm, Nguyễn Thị Diệu Cẩm, Nguyễn Tấn Lâm, Nguyễn Thị Minh Thư, Trần Thị Thu Phương, Nguyễn Minh Phương, Mai Hùng Thanh Tùng (2018), "Tổng hợp vật liệu composit Ta3N5/BiVO4 có hoạt tính quang xúc tác cao trong vùng ánh sáng khả kiến", Tạp chí Hóa học, tập 56(3), tr.350-354.

4. Lê Quỳnh Như, Nguyễn Thị Phương Lệ Chi, Nguyễn Thị Diệu Cẩm (2019), "Điều chế vật liệu xúc tác quang BiVO4 bằng phương pháp thủy nhiệt", Tạp chí Phân tích Lý, Hóa và Sinh học, tập 24, tr.60-65.

5. Nguyễn Thị Phương Lệ Chi, Cao Văn Hoàng, Bùi Thị Ngọc Trúc, Nguyễn Tiến Trung, Phạm Thanh Đồng, Nguyễn Thị Diệu Cẩm, Nguyễn Minh Phương, Nguyễn Văn Nội (2020), " Tổng hợp, đặc trưng và hoạt tính quang xúc tác của vật liệu bán dẫn hữu cơ g-C3N4 trong vùng ánh sáng nhìn thấy", Tạp chí Phân tích Lý, Hóa và Sinh học (đã nhận đăng ngày 2/12/2019).

6. Nguyễn Thị Phương Lệ Chi, Nguyễn Thị Diệu Cẩm, Cao Văn Hoàng, Mai Hùng Thanh Tùng, Phạm Thanh Đồng, Nguyễn Minh Phương, Nguyễn Văn Nội (2020), "Ảnh hưởng của nhiệt độ tổng hợp đến hoạt tính quang xúc của vật liệu Ta3N5/g-C3N4", Tạp chí Phân tích Lý, Hóa và Sinh học (đã nhận đăng ngày 11/11/2019).

Other thesis-related publications:

1. Van-Duong Dao, Nguyen Thi Phuong Le Chi, Doan Van Thuan, Thanh-Dong Pham, Dinh-Trinh Tran, Minh Phuong Nguyen, Phuong Thao, Minh Viet Nguyen, Nguyen Thi Dieu Cam, Nguyen Manh Tuong, Nhat Minh Dang, Ho-Suk Choi (2019), "Superior stability and photocatalytic activity of Ta3N5 sensitized/protected by conducting polymers for water splitting", Journal of Alloys and Compounds, 775, pp.942-949.

2. Nguyen Thi Thanh Truc, Nguyen Thi Hanh, Minh Viet Nguyen, Nguyen Thi Phuong Le Chi, Nguyen Van Noi, Dinh Trinh Tran, Minh Ngoc Ha, Do Quang Trung, Thanh-Dong Pham (2018), "Novel direct Z-scheme Cu2V2O7/g-C3N4 for visible light photocatalytic conversion of CO2 into valuable fuels", Applied Surface Science, 457, pp.968–974.