Tóm tắt Luận án Nghiên cứu biến tính diatomit phú yên ứng dụng trong hấp phụ và xúc tác

rên bề mặt diatomit xuất hiện nhiều lỗ xốp và có thể thấy những “vầng” sáng (light inclusion) phủ lên bề mặt mao quản diatomit. Hình 3.7. Ảnh SEM của diatomit tự nhiên (a) và Fe-Mn/D63 (b) 3.3.2. Nghiên cứu phản ứng oxy hoá phenol dùng xúc tác Fe-Mn/D trong hệ CWHO 3.3.2.1. Phản ứng oxy hóa phenol trong hệ CWHO dùng chất xúc tác diatomit tự nhiên và các diatomit biến tính Sự đóng góp hoạt tính xúc tác của các ion kim loại hòa tan từ xúc tác rắn trên toàn bộ hoạt tính xúc tác rắn là một vấn đề quan trọng trong việc ứng dụng xúc tác dị thể trong pha lỏng. Thí nghiệm đánh giá sự hòa tan của xúc tác khẳng định rằng vật liệu Fe-Mn/D63 là xúc tác dị thể trong phản ứng phân hủy phenol. 0 20 40 60 80 100 120 140 160 180 200 0 20 40 60 80 100 § é c h u y Ó n h ã a P N ( % ) Thêi gian (phót) Diatomit TN Fe/D Fe-Mn/D Mn/D (a) 0 50 100 150 200 250 0.0 0.1 0.2 N å n g ® é H P (m o l/ L ) Thêi gian (phót) Diatomit TN Fe/D Fe-Mn/D Mn/D (b) Hình 3.8. Độ chuyển hóa phenol (a) và sự phân hủy HP (b) trên các xúc tác khác nhau. (b) (a) 16 0 50 100 150 200 250 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0.0035 N å n g ® é C T (m o l/ L ) Thêi gian (phót) Diatomite tù nhiªn Fe-D Fe-Mn/D63 (a) 0 50 100 150 200 250 0.0000 0.0004 0.0008 0.0012 0.0016 N å n g ® é H Q ( m o l/ L ) Thêi gian (phót) Diatomite tù nhiªn Fe/D Fe-Mn/D63 (b) Hình 3.9. Sự tạo thành và phân hủy CT (a) và HQ (b) trên các chất xúc tác khác nhau. Hình 3.8a trình bày sự biến đổi nồng độ phenol theo thời gian trên diatomit tự nhiên và diatomit biến tính. Sự chuyển hóa của tác chất H2O2 và các chất trung gian chủ yếu catechol và hydroquinon lần lƣợt đƣợc trình bày trên hình 3.8b và hình 3.9. 3.3.2.2. Động học phân hủy phenol trên xúc tác Fe-Mn/D63 Sắc đồ HPLC, cho thấy rằng phản ứng oxi hóa PN trên xúc tác Fe-Mn/D63 chủ yếu tạo ra hai sản phẩm chính là CT và HQ, hai sản phẩm này tiếp tục bị oxi hóa hoàn toàn tạo ra CO2 và nƣớc nhƣ minh họa trong sơ đồ 3.1. Sơ đồ 3.1. Sơ đồ phản ứng oxi hóa PN bằng HP trên xúc tác Fe-Mn/D63 Mô hình tổng quát động học xúc tác phản ứng lƣỡng tâm, lƣỡng phân tử trình bày trên sơ đồ 3.2. Theo đó, chất xúc tác tồn hai 17 tâm xúc tác S1 và S2 độc lập. Tác chất A và B hấp phụ độc lập trên từng tâm và tạo ra dạng hấp phụ hoạt tính, các dạng hấp phụ hoạt tính này phản ứng với nhau tạo ra sản phẩm. A A B B S1 S2 Sơ đồ 3.2. Mô hình phản ứng lưỡng tâm lưỡng phân tử Kết quả so sánh cặp đôi các giá trị hệ số cân bằng ở các nồng độ khác nhau đƣợc trình bày ở bảng 3.10. Bảng 3.10. So sánh cặp đôi của các giá trị hệ số cân bằng K ở các nồng độ khác nhau Cặp so sánh t df Giá trị p K-200 - K-500 -1.061 7 0,324 K-200 - K-1000 -1,136 7 0,294 K-500 - K-1000 1,308 7 0,232 Bảng 3.11. Giá trị hằng số tốc độ (k(5)) được tính trên hai mô hình với ba dãy số liệu PN 200, 500 và 1000 mg/L k-200 k-500 k-1000 kPN 5809 1097 119,0 kHQ 5795 1079 113,88 kCT 5767 1081 113,98 kHQ* 1448000 273500 19280 kCT* 735845 76600 4790 Hằng số tốc độ đƣợc tính ở các nồng độ khác nhau đƣợc trình bày ở bảng 3.11. Kết quả cho thấy giá trị hằng số tốc độ của sự biến 18 đổi PN, CT, và HQ giảm dần theo sự tăng của nồng độ. Tốc độ chuyển hóa PN xấp xỉ với tốc độ tạo ra HQ và CT và tốc độ phân hủy phân hủy HQ nhanh hơn CT. 3.4. NGHIÊN CỨU HẤP PHỤ ASEN TRÊN VẬT LIỆU Fe- Mn/D65 3.4.1. So sánh khả năng hấp phụ As(III) của một số vật liệu Kết quả cho thấy, vật liệu biến tính Fe-Mn/D có khả năng hấp phụ cao hơn các vật liệu khác. Khả năng hấp phụ tăng dần theo chiều diatomit tự nhiên, Fe/D, Mn/D và các vật liệu Fe-Mn/D. pH ảnh hƣởng không đáng kể đến khả năng hấp phụ As(III) (chỉ dao động từ 60-65% hấp phụ As(III)). Tuy nhiên, xu hƣớng cho thấy, khi pH tổng hợp vật liệu càng tăng, khả năng hấp phụ As(III) càng có xu hƣớng giảm. Khi tăng dần tỷ lệ mol Fe/Mn thì khả năng hấp phụ tăng, nhƣng sau đó giảm. Sự hấp phụ cao nằm trong khoảng tỷ lệ Fe/Mn ban đầu từ 4:1-6:1 và đạt cao nhất ở tỷ lệ 5:1. 3.4.2. Khảo sát quá trình hấp phụ asen của vật liệu Fe-Mn/D65 3.4.2.1. Sự hấp phụ/oxyhóa As(III) thành As(V) trên vật liệu Fe- Mn/D65 Kết quả ở bảng 3.26 cho thấy bề mặt Fe-Mn/D65 sau khi hấp phụ As(III) tạo ra hai dạng As(V) và As(III) với tỷ lệ tƣơng đƣơng nhau, trong khi đó, thành phần của các trạng thái của oxy hóa của Fe2p3/2 và Mn2p3/2 thay đổi so với ban đầu. 3.4.2.2. Ảnh hưởng của pH đến khả năng hấp phụ As(III) và As(V) của vật liệu Fe-Mn/D65 Hình 3.10 cho thấy rằng độ chuyển hóa hấp phụ As(III) tăng, ngƣợc lại độ chuyển hóa hấp phụ As(V) giảm đáng kể khi pH tăng. 19 Hình 3.10. Ảnh hưởng của pH đến khả năng hấp phụ As(V) và As(III) 3.4.3. Đẳng nhiệt hấp phụ Kết quả nghiên cứu đẳng nhiệt cho thấy mô hình Freundlich biến đổi có hệ số xác định R2 cao, mô hình này mô tả tốt kết quả thực nghiệm. 3.4.4. Ảnh hƣởng của lực ion 3.4.4.1. Ảnh hưởng của lực ion NaCl Hình 3.11. Ảnh hưởng của lực ion NaCl đến hấp phụ asen Hình 3.11 trình bày ảnh hƣởng của lực ion NaCl đến khả năng hấp phụ asen. Lực ion NaCl ít ảnh hƣởng đến chuyển hóa hấp phụ, thực tế có sự tăng nhẹ độ chuyển hóa hấp phụ As(III) từ 32% đến 40% và độ chuyển hóa hấp phụ As(V) tăng từ 80% đến 83,8% khi nồng độ NaCl tăng từ 0 đến 100 mg/L. Điều này cho thấy ion Cl- ít cạnh trạnh với các anion của asen. 0 20 40 60 80 1.56 2.9 4.99 6 8.3 10.4% H ấp p h ụ A s( II I) pH 0 20 40 60 80 1 .8 3 .1 4 .1 5 .4 6 .6 7 .5 1 0 .1 1 1 .0% H ấp p h ụ A s( V ) pH 76 78 80 82 84 86 0 10 20 40 60 80 100% H ấp p h ụ A s( V ) Nồng độ NaCl (mg/L) 0 20 40 60 0 10 20 40 60 80 100% H ấp p h ụ A s( II I) Nồng độ NaCl (mg/L) 20 3.4.4.2. Ảnh hưởng của lực ion Na2CO3 Khác với NaCl, lực ion Na2CO3 ảnh hƣởng nhiều đến độ chuyển hóa hấp phụ asen. Độ chuyển hóa hấp phụ As(III) tăng từ 31% đến 71% nhƣng độ chuyển hóa hấp phụ As(V) lại giảm từ 80% đến 42% khi hàm lƣợng CO3 2- tăng từ 0 đến 100 mg/L nhƣ trình bày ở hình 3.12. Hình 3.13. Ảnh hưởng của lực ion Na2CO3 đến quá trình hấp phụ asen 3.4.4.3. Ảnh hưởng của lực ion Na3PO4 Lực ion Na3PO4 ảnh hƣởng đáng kể đến khả năng hấp phụ As(V) nhƣ trong trƣờng hợp CO3 2- (hình 3.14). Độ chuyển hóa hấp phụ giảm từ 91% đến 45% khi nồng độ ion phosphat tăng từ 0 đến 100 mg/L. Tuy nhiên lực ion Na3PO4 ít ảnh hƣởng đến khả năng hấp phụ As(III), độ chuyển hóa hấp phụ chỉ tăng từ 30% đến 39% khi hàm lƣợng phosphat tăng từ 0 đến 100 mg/L. Hình 3.14. Ảnh hưởng của lực ion Na3PO4 đến quá trình hấp phụ asen 0 10 20 30 40 50 0 10 20 40 60 80 100 % H ấp p h ụ A s( II I) Nồng độ Na3PO4 (mg/L) 0 20 40 60 80 0 10 20 40 60 80 100 % H ấp p h ụ A s( II I) Nồng độ Na2CO3 (mg/L) 0 50 100 0 10 20 40 60 80 100 % h ấp p h ụ A s( V ) Nồng độ Na2CO3 (mg/L) 0 20 40 60 80 100 0 10 20 40 60 80 100% H ấp p h ụ A s( V ) Nồng độ Na3PO4 (mg/L) 21 3.4.4.4. Ảnh hƣởng của ion CaCl2, MgCl2 Ảnh hƣởng lực ion của các muối CaCl2 và MgCl2 đƣợc trình bày ở hình 3.15 và hình 3.16. Lực ion các muối này ít ảnh hƣởng đến khả năng hấp phụ asen. Hình 3.15. Ảnh hưởng của lực ion CaCl2 đến quá trình hấp phụ asen Hình 3.16. Ảnh hưởng của lực ion MgCl2 đến quá trình hấp phụ asen Từ kết quả trên cho thấy vật liệu Fe-Mn/D65 có khả năng hấp phụ cao As(III) và As(V), đặc biệt khả năng hấp phụ/oxy hóa chuyển hóa As(III) có độc tính cao thành As(V) có độc tính thấp hơn, làm cho vật liệu này có nhiều tiềm năng ứng dụng trong công nghệ xử lý nƣớc. 87 88 89 90 91 92 93 0 10 20 40 60 80 100 % H ấp p h ụ A s (V ) Nồng độ CaCl2 (mg/L) 63 64 65 66 67 68 69 70 0 10 20 40 60 80 100 % H ấp p h ụ A s (I II ) Nồng độ CaCl2 (mg/L) 62 64 66 68 70 72 0 10 20 40 60 80 100% H ấp p h ụ A s( II I) Nồng độ MgCl2 (mg/L) 82 84 86 88 90 92 94 0 10 20 40 60 80 100% H ấp p h ụ A s( V ) Nồng độ MgCl2 (mg/L) 22 KẾT LUẬN 1. Diatomit Phú Yên tự nhiên có thành phần hóa học chủ yếu là silic, nhôm và một lƣợng khá lớn tạp chất sắt. Diatomit tự nhiên có cấu trúc vô định hình với diện tích bề mặt riêng lớn và dễ bị chuyển thành tinh thể quart. Với tính chất xốp cao, diatomit tự nhiên có thể ứng dụng vào lĩnh vực hấp phụ và xúc tác. Diatomit có khả năng hấp phụ cao phẩm nhuộm cation, cụ thể với phẩm nhuộm AB dung lƣợng trung bình qm = 602 mg/g, có tiềm năng sử dụng ở qui mô công nghiệp. Quá trình khuếch tán phẩm nhuộm AB vào diatomit là quá trình phức tạp với bƣớc quyết định tốc độ hấp phụ là giai đoạn khuếch tán màng (hấp phụ hóa học). 2. Trong hệ hấp phụ phẩm nhuộm AB trên diatomit, các tham số phƣơng trình Langmuir và Freundlich thay đổi khi thay đổi nồng độ chất ban đầu thay đổi. Điều này bản chất của xốp của vật liệu giới hạn sự khuếch tán và kích thƣớc lớn của chất bị hấp phụ nên hệ chỉ đạt đến trạng thái gần cân bằng. Các hệ số này trở thành các hệ số thực nghiệm và mất ý nghĩa hoá lý nhƣ khi ban đầu thiết lập nên nó. 3. Diatomit xử lý nhiệt trong khoảng 100-300 0C là thuận lợi cho biến tính diatomit. Thời gian hydrat hóa diatomit ảnh hƣởng đến đáng kể đến việc gắn kết MPTMS lên diatomit. Lƣợng MPTMS kết gắn lớn nhất khi hydrat hóa trong 3 giờ. Vật liệu MPTMS-diatomit có khả năng biến tính trên điện cực GCE để xác định đồng thời Cd(II) và Pb(II) bằng phƣơng pháp von-ampe hòa tan anot với kỹ thuật xung vi phân (DP-ASV). Các dòng đỉnh hòa tan tƣơng quan tuyến tính với nồng độ Cd(II) trong khoảng 20-300 ppb (i (μA) = - 23 0,0202 + 0,0036 C (ppb), R 2 = 0,9997) và nồng độ Pb(II) trong khoảng 20-150 ppb (i (μA) = -0,1179 + 0,0069 C (ppb), R2 = 0,994. Giới hạn phát hiện với Cd(II) và Pb(II) lần lƣợt là 15,9 ppb và 6,9 ppb. Theo sự hiểu biết của chúng tôi đây là kết quả lần đầu tiên đƣợc công bố về sử dụng vật liệu MPTMS-diatomit để biến tính điện cực xác định đồng thời Cd(II) và Pb(II) bằng phƣơng pháp DP-ASV. 4. Lƣỡng oxit sắt và mangan có thể đƣợc phân tán đồng nhất lên bề mặt diatomit bằng phản ứng oxy hóa khử giữa KMnO4 và FeSO4 trong môi trƣờng pH = 3-8. Lớp lƣỡng oxit sắt mangan tồn tại trạng thái đa hóa trị (Mn(III), Mn(VI), Fe(III) và Fe(II)) và có tỉ lệ xấp xỉ Mn:Fe xấp xỉ 1:10 bất kể pH, hay tỉ lệ mol Mn:Fe khác nhau. Fe-Mn/D63 có hoạt tính xúc tác oxy hóa hoàn toàn phenol và các chất trung gian chính (catechol và hydroquinon). Xúc tác điều chế đƣợc có thể hoạt động trong môi trƣờng pH từ 4,7-7. Hoạt tính oxy hóa phenol là do tính cộng lực xúc tác của oxit sắt và mangan phân tán điều trên bề mặt diatomit. Vật liệu diatomit biến tính bằng lƣỡng oxit sắt và mangan là một xúc tác tiềm năng cho việc xử lý phenol và các chất hữu cơ nói chung trong hệ CWHO. Đây cũng là điểm mới của luận án. 5. Vật liệu diatomit đƣợc biến tính bằng lƣỡng oxit sắt và mangan (Fe-Mn/D65) có khả năng hấp phụ cao As(III) và As(V) trong dung dịch nƣớc. Quá trình hấp phụ As(III) xảy ra sự oxy hóa As(III) thành As(V) do Mn(IV). Khả năng hấp phụ asen tuân theo cả hai cơ chế tạo phức cầu nội và cầu ngoại giữa các anion và các nhóm hydroxyl (Mn-OH, Fe-OH). Khả năng hấp phụ As(III) tăng khi pH dung dịch tăng, ngƣợc lại khả năng hấp phụ As(V) lại giảm khi pH 24 dung dịch tăng. Lực ion NaCl, Na2CO3, Na3PO4 ảnh hƣởng đáng kể đến khả năng hấp phụ asen, khi lực ion tăng khả năng hấp phụ As(III) tăng nhƣng khả năng hấp phụ As(V) lại giảm. Lực ion CaCl2, MgCl2 hầu nhƣ ảnh hƣởng không đáng kể đến khả năng hấp phụ asen. 1 DANH MỤC CÁC CÔNG TRÌNH LIÊN QUAN ĐẾN LUẬN ÁN 1. Bui Hai Dang Son, Vo Quang Mai, Dang Xuan Du, Le Cong Nhan, Tran Thai Hoa, Dinh Quang Khieu (2013), “Freundlich and Langmuir adsorption isotherms for removal astrazon black AFDL dye onto Phu Yen diatomite from aqueous solution”, Vietnam Journal of chemistry, Vol. 59(2AB), 296-301. 2. Bui Hai Dang Son, Vo Quang Mai, Dang Xuan Du, Le Cong Nhan, Tran Thai Hoa, Dinh Quang Khieu (2013), “A kinetic study on astrazon black AFDL dye adsorption onto Phu Yen diatomite”, Vietnam Journal of chemistry, Vol. 51(3AB), pp. 1-5. 3. Bùi Hải Đăng Sơn, Võ Quang Mai, Đặng Xuân Dự, Lê Công Nhân, Trần Thái Hòa, Đinh Quang Khiếu (2013), “Nghiên cứu tổng hợp mercaptopropyl-diatomite”, Tạp chí Xúc tác và Hấp phụ, số 2, tr. 136-141. 4. Bui Hai Dang Son, Vo Quang Mai, Dang Xuan Du, Le Cong Nhan, Phan Thi Chi, Dinh Quang Khieu (2014), “Mn-Fe binary oxide incorporated into diatomite: an efficient catalyst for phenol oxidation reaction”, Journal of Science and Technology, 52(5B), pp. 490-495. 5. Bùi Hải Đăng Sơn, Võ Quang Mai, Đặng Xuân Dự, Lê Công Nhân, Đinh Quang Khiếu (2015), “Hấp phụ cadimi trong dung dịch bằng mercaptopropyl/diatomit”, Tạp chí Hóa học, số 53(3E12), tr. 238-241. 6. Bùi Hải Đăng Sơn, Nguyễn Thị Ngọc Trinh, Nguyễn Đăng Ngọc, Đinh Quang Khiếu (2015), “So sánh đặc trƣng hóa lý của hai loại diatomic Phú Yên và diatomit Merck”, Tạp chí Xúc tác và Hấp phụ, Số 4(4A), tr. 115-119. 7. Bui Hai Dang Son,Vo Quang Mai, Phan Thi Chi, Nguyen Thi Ngoc Trinh, Dang Xuan Du, Le Cong Nhan, Dinh Quang Khieu (2014), “Study on synthesis of Mn-Fe @ diatomite”, Journal of Catalysis and Adsorption, 3, pp. 127-133. 8. Bùi Hải Đăng Sơn, Mai Xuân Tịnh, Trần Thanh Minh, Nguyễn Đăng Ngọc (2016), “Nghiên cứu khả năng hấp phụ As(III) và As(V) bằng vật liệu diatomite biến tính lƣỡng oxit sắt-mangan”, Tạp chí Đại Học Huế, Số 3, tr.117-124. 9. Bui Hai Dang Son, Vo Quang Mai, Dang Xuan Du, Nguyen Hai Phong, Dinh Quang Khieu (2016), “A Study on Astrazon Black AFDL Dye Adsorption onto Vietnamese Diatomite”, Journal of Chemistry, pp. 1-11, dx.doi.org/10.1155/2016/8685437. (I.F. = 0.996, ISSN = 2090-9071). 10. Bui Hai Dang Son, Vo Quang Mai, Dang Xuan Du, Nguyen Hai Phong, Nguyen Duc Cuong, Dinh Quang Khieu (2016), “Catalytic wet peroxide oxidation of phenol solution over Fe-Mn binary oxides diatomit composite”, Journal of Porous Material,pp.1-11,DOI 10.1007/s10934-016-0296-7. (I.F. = 1.4, ISSN: 1380-2224). 11. Dinh Quang Khieu, Bui Hai Dang Son, Vo Thi Thanh Chau, Pham Dinh Du, Nguyen Hai Phong, Nguyen Thi Diem Chau (2017), “3-mercaptopropyltrimethoxysilane modified diatomite: preparation and application for voltammetric determination of lead (II) and cadmium (II)” Journal of Chemistry, pp. 1-10 (I.F. = 0.996, ISSN: 2090-9071) 2 MINISTRY OF EDUCATION AND TRAINING HUE UNIVERSITY COLLEGE OF SCIENCE PhD candidate: BUI HAI DANG SON Dissertation title: PHU YEN DIATOMITE: MODIFICATION AND ITS APPLICATION TO CATALYST AND ADSORPTION Major: Theoretical Chemistry and Physical Chemistry Code: 62.44.01.19 PhD DISSERTATION ABSTRACT Hue, 2017 3 INTRODUCTION 1. Research motivation Activated carbon is the most employed adsorbent for toxic species removal from aqueous solution because of well-developed pore structures and a high internal surface area that leads to its excellent adsorption properties. However, the high cost of activated carbon and recycle ability sometimes restrict its applicability for dye removal. Therefore, in recent years, a considerable number of studies have investigated into low cost and efficient alternative materials such as clay, diatomite, zeolite. Catalytic Wet Air Oxidation (CWAO) is an efficient and promising oxidative pollution removal process that has been proved successful in the research on wastewater treatment. However, the CWAO usually requires rather critical conditions including high pressure and temperature, and the implementation of this technology is not cost-effective. The process of catalytic wet peroxide oxidation (CWPO) has provided an alternative for the treatment of wastewater with high-poisonous organic compounds. Heavy metals (Hg(II), Pb(II), Cd(II), Cu(II), Co(II), Ni(II), Zn(II) etc.), which are commonly found in wastewaters discharged from chemical manufacturing, mining, extractive metallurgy, nuclear and other industries, cause danger to humans and aquatic animals and plants and therefore must be controlled urgently. The detection of heavy metal ions in water samples has received much attention over the past few years. Anodic stripping voltammetry (ASV) is a useful electrochemical method for detecting trace metals because of its wide linear dynamic range and low detection limit which results from a pre-concentration step performed directly in the 4 voltammetric cell. Several porous materials have been utilized as electrode modifiers with the aim of pre-concentrating the analyte at the electrode surface via a selective reaction due to special function groups grafted to electrode surface. Diatomite has received considerable attention for its unique combination of physical and chemical properties including large porosity, fine particle size, and chemical inertness. With the aim of improving catalyst and adsorption activities of diatomite, the modification of diatomite by active ground was needed. The diatomite in combination with surface coated functional groups offers a potential materials for adsorption and modifying electrodes to determine the dye. To the best of our knowledge, the use of a 3- mercaptopropyl trimethoxysilane (MPTMS) grafted diatomite for modifying electrode in connection to the electrochemical analysis of Pb (II) and Cd (II) has not yet been reported. Although diatomite modified by manganese oxide, iron oxide or binary manganese and iron oxide has been extensively studied as adsorbent of arsenide/arsenate from aqueous solution, little research has been done into the use of Fe-Mn binary oxides diatomite as an oxidation catalyst. 2. The aims and contents of dissertation 2.1. The aims The aim of this study was modification of Phu Yen diatomite by organic or inorganic group to obtain modified diatomite with high activity of catalyst and adsorption. 2.2. Content 2.1. Physical chemistry characterization of Phu yen diatomite and its application to dye removal. 5 2.3. Synthesis of Fe-Mn binary oxides coating on diatomite and Catalytic wet peroxide oxidation of phenol solution 2.3. 3-mercaptopropyltrimethoxysilane modified diatomite: preparation and application for voltammetric determination of Lead(II) and Cadmium(II) 3. New contributions A study on physical chemistry properties of Phu yen diatomite and its modification by Fe-Mn binary oxides, mercaptopropyl silane as well as their application to dye and toxic metal removal or phenol oxidation were studied systematically for very first time in Vietnam. The Vietnamese diatomite, which is composed of amorphous silica, has high porosity and surface area. It was studied as an adsorbent for the removal of Astrazon Black AFDL dye (AB) from aqueous solution. Experimental isothermal data were fitted well to both Langmuir and Freundlich model. However, parameters of these equations were effected remarkably on the initial AB concentrations. Both value of qmom and qm increases with the increasing initial AB concentration. Piecewise linear regression as a statistical method for the analysis of experimental adsorption data by the Webber’s intraparticle-diffusion models provide the time periods for each diffusion. Mn-Fe binary oxides has been homogeneously incorporated into diatomite by redox reaction of KMnO4 and FeSO4. The redox products consist of multiple oxidation state oxides (Mn(III), Mn(VI), Fe(III) and Fe(II)). For the first time, the Fe-Mn binary oxides was tested as catalysts for CWPO of phenol. The catalyst demonstrated well in the aqueous medium the wide range of pH 4.7-7. The high catalytic activity for phenol oxidation is due to catalytically 6 synergized properties of iron and manganese oxide highly dispersed on pores of diatomite. Fe-Mn binary oxides modified diatomite materials are promising catalysts for complete oxidation of phenol with hydrogen peroxide in aqueous solutions. Electrochemical sensors of mercaptopropyl-diatomite modified glassy carbon electrode (GC/mecarptopropyl-diatomite) has been developed for the determination of Pb(II) and Cd(II) for the first time in Vietnam. The contents of the dissertation consist of 131 pages, 31 tables, 59 figures, 207 references. The layout of the thesis is as follows: Introduction: 2 pages Chapter 1. Literature review: 27 pages Chapter 2. Objectives, content, research methods and experimental methods: 25 pages Chapter 3. Results and Discussion: 78 pages Chapter 4. Conclusions: 2 pages CHAPTER 1. LITERATURE REVIEW Dyes are a kind of organic compounds with a complex aromatic molecular structures that can cause bright and firm color to other materials. These molecules lead to high chemical oxygen demand, and they exhibit low biodegradability. Many treatment systems have been proposed for the removal of synthetic dyes from aqueous solution. Methods based on adsorption, biological treatments, coagulation, electrochemical techniques, membrane processes, and oxidation/ozonation, photochemical oxidation are known to be effective for the removal of this type of dyes from polluted water. Adsorption is considered to be competitive and economically cost effective and efficient process for removal of dyes 7 and heavy metals. Therefore, in recent years, a considerable number of studies have investigated into low cost and efficient alternative materials such as clay, diatomite, zeolite. In the present study, the adsorption of AB dye onto Vietnam diatomite has demonstrated. Catalytic Wet Air Oxidation (CWAO) is an efficient and promising oxidative pollution removal process that has been proved successful in the research on wastewater treatment. However, the CWAO usually requires rather critical conditions including high pressure and temperature, and the implementation of this technology is not cost-effective. The process of catalytic wet peroxide oxidation (CWPO) has provided an alternative for the treatment of wastewater with high-poisonous organic compounds. In the study, the incorporation of manganese and iron oxides into a diatomite to form Fe-Mn binary oxides diatomite was studied. Fe-Mn binary oxides diatomite as a Fenton-like catalyst was tested for CWPO of phenol. Anodic stripping voltammetry (ASV) is a useful electrochemical method for detecting trace metals because of its wide linear dynamic range and low detection limit which results from a pre-concentration step performed directly in the voltammetric cell. In this study, the preparation of MPTMS modified diatomite was demonstrated. The effects of thermal treatment of diatomite and the humidity of diatomite on MPTMS functionalization and the possible proposed mechanisms of MPTMS grafting diatomite surface were discussed. The MPTMS-diatomite was used to modify electrode for simultaneous determination of Pb(II) and Cd(II) in aqueous solution by differential pulse anodic stripping voltammetry method (DP-ASV) was also studied. 8 CHAPTER 2. AIMS, CONTENTS AND EXPERIMENTAL METHODS 2.1.AIMS The aim of this study was modification of Phu Yen diatomite by organic or inorganic group to obtain modified diatomite with high activity of catalyst and adsorption. 2.2 . CONTENTS 2.1. Physical chemistry characterization of Phu yen diatomite and its application to dye removal. 2.2.3-mercaptopropyltrimethoxysilane modified diatomite: preparation and application for voltammetric determination of Lead (II) and Cadmium (II) 2.3. Synthesis of Fe-Mn binary oxides diatomite and Catalytic wet peroxide oxidation of phenol solution 2.3. RESEARCH METHODS 2.3.1. Physical and chemistry methods - X-ray diffraction method (XRD), Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM),Energy dispersive X-ray (EDX ), Nitrogen adsorption/desorption isotherms, Diffuse reflectance ultraviolet visible Spectroscopy (UV - Vis), High performance liquid chromatography (HPLC), Methods of analysis hydroperoxide, Methods of statistical analysis CHAPTER 3. RESULTS AND DISCUSSION 3.1. Physical chemistry characterization of Phu yen diatomite and its application to dye removal Table 1. Chemical composition of diatomite analyzed by EDS Oxide Al2O3 SiO2 TiO2 Fe2O3 Others %, wt 20.72 68.35 0.92 9.21 0.80 9 Figure 1. FTIR spectrum (a) and nitrogen adsorption/desorption isotherms (b) of diatomite. The sample of diatomite was mainly formed by centric type frustules which were characterized by notable pores as discs or as cylindrical shapes indicating that there is a good possibility for dyes to be adsorbed into these pores. The chemical analysis by EDS (Table 1) showed that silica represents the major composition (68 % wt) and metallic oxides contribute to the rest. FTIR analyses were performed in the range 400 - 4000 cm -1 as shown in Figure 1. The bands at 3695, 3622 and 2858 are attributed to the free silanol group (Si–O–H) and the band at 1639 cm-1 corresponds to H–O–H bending vibration of water. The bands at 1153 and 1022 are assigned to the siloxane (–Si–O–Si–) group stretching and the 914 cm -1 band represents Si–O stretching of silanol group. The absorption peaks around 528 and 443 cm -1 are attributed to the Si–O–Si bending vibration. Figure 1b shows the nitrogen adsorption/desorption isotherm of diatomite. The diatomite with BET surface area around 51 m 2 g -1 and pore volume of 0.0952cm³ g -1 is rather higher than those of reported diatomite. The present diatomite, which is composed of 500 1000 1500 2000 2500 3000 3500 4000 0 20 40 60 80 100 T ra n sm is si o n ( % ) Wavelength (cm-1) 3695 3622 2858 1639 11531022 914 798 690 528 443 3421 (a) 0.0 0.2 0.4 0.6 0.8 1.0 10 20 30 40 50 60 70 V o lu m e ( c m 3 g -1 ) p/p 0 (relative pressure) Adsorption Desorption (b) (a) 10 amorphous silica, has properties such as high porosity and high surface area indicating a potential absorbent for adsorption. Table 2. The isotherm parameters of Langmuir and Freundlich models at various concentrations from 400 -1400 mg L -1 C (mg L-1) Langmuir model Freundlich model qmom KL R 2 RL p 1/n Kf qm R 2 p 400 357.1 0.0244 0.955 0.0930 0.000 0.429 34.2607 447.3 0.975 0.000 500 416.7 0.0123 0.947 0.1402 0.001 0.480 24.2060 476.5 0.987 0.000 600 526.3 0.0098 0.957 0.1450 0.000 0.478 27.1669 578.8 0.978 0.000 800 625.0 0.0046 0.968 0.2132 0.000 0.499 20.5672 579.0 0.991 0.000 900 666.7 0.0033 0.975 0.2507 0.000 0.494 19.4608 560.1 0.977 0.000 1200 625.0 0.0020 0.986 0.3431 0.000 0.541 22.7250 539.3 0.961 0.001 1400 625.0 0.0021 0.946 0.2528 0.001 0.379 30.7288 477.5 0.931 0.002 As can be seen in Table 2 both models have the very close to coefficients of determination (R 2 ) and favorable characteristic parameters (i.e. RL for Langmuir isotherm and 1/n for Freundlich isotherm). These results confirmed that the equilibrium data of AB adsorption onto the diatomite could be well fitted by the two adsorption isotherm models. The high correlation to both Langmuir and Freundlich isotherms implies a monolayer adsorption and the existence of heterogeneous surface in the adsorbents, respectively. For Langmuir model, the KL was known as equilibrium constant which should be constant at specified temperature. The qmon is the maximum monolayer adsorption capacity which is thought to be specified for each absorbent. However, the data show that the KL and qmon are not constant at specified temperature but tend to increase as the initial concentration increases. In similar manner, the parameters of Freundlich model were also varied monotonically with the increase in initial concentration in the range of 400-900 mg L -1 . 11 In the range of initial concentration from 400-900 mg L -1 , the qmon and qm are as a function of initial concentration. Pair sample t-test were conducted to compare the difference of qm and qmom. Since p- value is larger than 0.05 significant level the difference between the average value of qm (M = 518.0 ± 13.2 mg g -1 ) and the average value of qmom (M = 528 ± 62 mg g -1 ) is not statistically significant (t(4) = - 0.269, p = 0.801). It means the value calculated from both isotherm models is statistically similar. The data of maximum adsorption capacity shows that diatomite possesses very high capacity of dye adsorption compared to other minerals as adsorbents. The large and positive value of H0 indicates that adsorption is endothermic process and chemical sorption by nature. The positive value of S0 indicates the increasing randomness at the solid–liquid interface during the adsorption of AB molecules on the diatomite .The negative values of Gibbs free energy for AB adsorption on diatomite, Go, the more negative at higher temperature, which implies that the spontaneity increases with the increase in the temperature. As the Gibbs free energy change is negative accompanied by the positive standard entropy change, the adsorption reaction is spontaneous with high affinity. Based on the values of ΔH, the suggest that the AB adsorption using diatomite probably involved a chemical mechanism. In the present paper, the diffusion kinetics was studied by using Webber’s model. Because the plots of this model often have a multi-linear nature, and in general, the graphical method is employed to analyze the data in which the linear segments are determined visually. These results strongly suggests that the AB adsorption on diatomite are controlled by film diffusion or chemical reaction 12 control the adsorption rate (e.g., surface adsorption and liquid film diffusion) instead of intraparticle diffusion In order to determine the rate-limiting step, kinetic models such as pseudo first-order, and pseudo second-order equation were employed to evaluate the experimental data. The R 2 could be used to compare pseudo first-order and pseudo second-order models for the goodness of fit because both models have the same parameters and experimental points. For initial concentration from 200 to 400 the experimental points of the pseudo-second-order kinetic model reflected high correlation coefficients (R 2 = 0.804 - 0.999) and qe,cal values agreed with the value qe,exp indicating that the adsorption may be governed by a pseudo-second-order mechanism. This suggests that the rate-limiting step is a chemical adsorption which might be involved the formation of covalent bonds between AB molecules and diatomite through enabled sharing or exchange of electrons. A chemisorption mechanism only allows for a monolayer adsorption, which is in good agreement with Langmuir model that describes well the equilibrium adsorption data. The pseudo-second order kinetic rate coefficient decreases from 0.040 to 0.009 mg g -1 min -1 when the initial AB concentration increase from 150 to 600 mg L-1. This behavior was observed by various authors. This could be attributed to the fact that increasing the dye concentration might reduce the diffusion of dye molecules in the boundary layer and enhance the diffusion in the solid. 3.2. Synthesis of Fe-Mn binary oxides diatomite and catalytic wet peroxide oxidation of phenol solution (a) 13 Figure 2. TEM observation (a) and PXRD (b) of FM-diatomite prepared at pH 6. TEM observations of FM-diatomite prepared at pH shows that many pores around several nanometers can be seen on the surface of diatomite suggesting that a porous structure still remains; even the surface of diatomite was covered by Mn-Fe binary oxides; PXRD patterns of FM-diatomite were also similar to those of raw diatomite suggesting that Fe-Mn-binary oxides in nanoscales particles were dispersed highly on diatomite surfaces. For XPS spectra the bending energies of 723 and 709 eV corresponding to Fe 3+ and Fe 2+ and those of 648 and 640 eV for Mn 3+ and Mn 4+ were observed. pH value seems to affect significant oxidation state. The Fe 2+ was oxidized partly to Fe 3+ while the majority of Mn 6+ was reduced to Mn 3+ and a minority to Mn 4+ . 10 20 30 40 50 60 70 20 40 60 80 100 120 In te n s it y ( c p s ) 2 theta (degree) (b) 14 Figure 3. XPS Fe2p3/2 and Mn2p3/2 core level of FM-diatomite. pH 6 pH 6 pH 4 p pH 4 pH 9 pH 9 pH 7 p H pH 9 pH 7 15 The reaction occurred rather deeply at pH = 6 in which around 91 % Fe 2+ was converted into Fe 3+ . The molar ratio of Mn to Fe around 0.1 (a range of 0.09-0.14) for FM-diatomite compared with an initial molar ratio of 0.3 seems to be unchangeable despite pH change . Table 4. The elemental compositions of Fe-Mn/D Catalyst Al (%) Si (%) Ti (%) Mn (%) Fe (%) Molar ratio Mn:Fe Fe-Mn/D61 11.38 77.83 0,57 0.70 7.58 0.09 ± 0.034 Fe-Mn/D63 10.48 76.36 0.39 1.31 9.36 0,14 ± 0.019 Fe-Mn/D65 9.33 75.41 0.37 0.95 12.38 0,08 ± 0.04 The obtained FM-diatomite as Fenton-like catalyst was tested for CWPO of phenol. FM-diatomite prepared at an initial pH of 6 exhibited the highest catalytic activity for total phenol oxidation in comparison with others. The total degradation of phenol and other main intermediates (catechol and hydroquinone) was obtained under 50 minutes. The combination of both iron oxide and manganese oxide into diatomite has a drastic impact on catalytic performance. Total conversion of phenol and dihydroxyl benzene were obtained after only 50 minutes of reaction time. The present Fe-Mn binary oxides modified diatomite performs a promising catalytic activity for total phenol oxidation in mild conditions. 3.3. 3-mercaptopropyltrimethoxysilane modified diatomite: preparation and application for voltammetric determination of Lead (II) and Cadmium (II) Figure 1 shows XRD patterns of diatomite calcinated at 100 °C, 300 °C, 500 °C and 700 °C. The raw diatomite (dried at 100 °C) consisted of mainly amorphous structure. At 300 °C, the 16 characterized peak of quartz was observed indicating that the silica in amorphous form was crystallized to form quartz crystallites. The diffraction intensity of quartz phase increases with an increase in calcinated temperature. Thermal analysis of diatomite functionalized by MPTMS at dried conditions show that the DSC and TG curves were similar for all samples. The exothermic peak, together with no any ignition loss at around 300°C should be attributed to the crystallization of amorphous silica to quartz. The result also agrees with the fact that the crystallization of quartz was detected at 300°C by XRD analysis. However, even for sample 300D-700D which was calcinated at 300°C for 3hours before functionalization, this peak is also observed. This can be explained by a reconstruction to form amorphous silica during silane treatment. The exothermic peaks and ignition losses at around 520°C should be assigned to the decomposition and oxidation of MPTMS incorporated into diatomite. The hydrolysis of MPTMS into silanols occurs in water. The silane incorporated into diatomite is due to the condensation of silanols of diatomite and silane. In this work, it is suggested that the silane is strongly bonded to diatomite surface as silane is not removed by washing chloroform, dispersed in water, or heated at 100 °C. Then the amount of MPTMS incorporated into diatomite is proportional to the amount of ignition loss in range 100 °C to 700 o C calculated by TG. Therefore, the ignition loss (100-700 o C) was assumed as MPTMS loading to diatomite. The amount of MPTMS seems to increase slightly from 5.6% to 6.3% for D100 and D300 and decrease remarkably with a 17 further increase in thermal treatment temperature (see Table 2). TG-DSC diagrams of functionalized diatomite under humid conditions show that the curves were similar to all samples. The thermal behaviors were also similar to the case of samples under dried conditions except for ignition loss together exothermic peaks at around 300°C observed for most cases. From Table 2, the amount of MPTMS incorporated into diatomite seems to be higher in the samples in dried conditions and the diatomite thermal treated at 100 °C -300 °C is most favorable for MPTMS functionalization. Table 2. The amount of MPTES incorporated into diatomite estimated by TG Dried condition Humid condition 100D 300D 500D 700D 100H 300H 500H 700H Ignition loss at ca. 100°C (%) 5.67 0.00 0.00 0.00 3.71 2.45 0 0.00 Ignition loss at ca. 300°C (%) 0.00 0.00 0.00 0.00 0.00 2.02 1.31 0.80 Ignition loss at ca.520°C (%) 5.44 3.76 2.55 1.82 6.99 5.69 1.70 0.97 Total ignition loss >100°C (%) 5.44 3.76 2.55 1.82 6.99 7.71 3.01 1.77 There are two types of silanols, isolated and H-bonded silanols on diatomite surface . At room temperature, both types of silanols are H-bonded with water. With an increase in temperature, dehydration occurs. At first, the desorption of water and the exposure of more and more isolated silanols were favorable for the silanols of silane adsorbing onto diatomite surfaces. This accounts for the fact that the high amount of MPTMS was incorporated into diatomite cacinated in the range of 100 - 300°C. The calcinated diatomite exposed to water-saturated medium could create more silanols, which 18 consequently adsorb MPTMS more strongly than the diatomite under dried conditions. As the temperature increases to more than 300°C, the silanols begin to condense to form siloxane bridges that are not favorable for coupling reactions. In the case of hydrated diatomite, two decompositions of silane incorporated into diatomite are observed at around 320°C and 520 o C in TG- DSC curves instead of only 520°C in the case of the dried diatomite. Based on the results reported by Johansson et al. about adsorption of silane coupling agents onto kaolin surfaces, we suggest two possible mechanisms by which MPTMS react with diatomite surface. The first proposed mechanism involves four steps: (1) MPTMS was converted to the reactive silanol formed by hydrolysis SH-(CH2)3Si(OCH3)3 + 3H2O  SH-(CH2)3Si(OH)3 + 3HOCH3 (2) Condensation of the organosilan to oligomers (3) Formation of hydrogen bonds between the oligomers and the OH groups on the diatomite surface Si OH HO SH Si OH SH O OH n n + 1 SH-(CH2)3Si(OH)3 + n H2O 19 (4) Finally, a covalent linkage is formed under drying The second proposed mechanism involves only two steps: (1) MPTMS is converted to the reactive silanol form by hydrolysis (R: CH2-CH2-CH2-SH; X: OCH3) SH-(CH2)3Si(OCH3)3 + 3H2O  SH- (CH2)3Si(OH)3 + 3HOCH3 (2) The silanol groups react directly with hydroxyl groups on the diatomte surface It is assumed that silane incorporated in diatomite by the first mechanism is more stable than one by the second mechanism. It means that it will be decomposed at higher temperature with the silane incorporated by the latter. For silane treatment with dried diatomite, the only ignition loss and exothermic peak at around 520°C could be assigned to the decomposition of silane grafting through the first mechanism. When diatomite is hydrated before silane treatment, the incorporation of MPTMS might occur through both mechanisms. Then, ignition loss and exothermic peak at around 300°C in TG-DSC for 100-700H might be assigned to decomposition of silanes in which MPTMS is grafted through the second 20 mechanism. 3.2. Voltammetric characteristics of Cd(II) and Pb(II) on MPTMS-diatomite/GCE and limit of detection (LOD) The thiol group binds Cd(II) and Pb(II) to surface complexes because of its high affinity to metal ions. The metals were accumulated in electrode due to reduction reaction, and then dissolved in solution through oxidation reaction. The electrochemical reaction occurred as follows: Complex step Accumulation step Stripping step Electrochemical process of Pb(II) and Cd(II) on electrodes modified by MPTMS-diatomite was illustrated by Figure 4. Figure 4. Proposed representation of preconcentration and stripping mechanism of Cd(II) and Pb(II) on MPTMS-diatomite/GCE. 21 Figure 5 shows the DP-ASV of Cd(II) and Pb(II) with different concentrations. An obvious anodic peak at around -0.82 and at -0.61 V. These observations can be attributed to the oxidation species of Cd(II) and Pb(II), respectively that have been deposited into the surface of MPTMS-diatomite/GCE during reduction processes. The intensity of anodic peak increased with an increase in Cd(II) and Pb(II) concentration from 20 to 300 ppb. A calibration plot of the anodic current response versus Cd(II) concentration and Pb(II) are presented in the insets of Figure 5. The results show that the current peak response was linear to the Cd(II) concentration with a R 2 of 0.999 in the range of 20-300 ppb and the Pb(II) concentration with R 2 of 0.994 in the range of 20-150 ppb. The limit of detection (LOD) was calculated on the basis of (3.3 Sa/b) criteria (Sa represents the standard deviation of the intercept while b represents the slope of the calibration curve defined for the LOD concentration range (20-300 ppb)). The LOD for Cd(II) and Pb(II) calculated was 15.9 ppb and 6.9 ppb, respectively. A comparison of MPTMS-diatomite-GCE developed with other GCEs modified with other nanoparticles for simultaneous determination of Pb(II) and Cd(II) shows that the GCE modified with MPTMS-diatomite developed in the present work shows good LOD compared with other similar materials/GCE reported previously in the literature. This indicates that MPTMS-diatomite is a potential material for electrode modifiers. 22 Figure 5. The DP-ASV voltammograms of Cd(II) and Pb(II): Conditions: the concentrations in the range of 20 to 300 ppb of the Cd(II) and Pb(II); other conditions: 0.1 M ABS (pH 4.5); Eacc = –1.2 V; tacc = 60 s; pulse amplitude (E) = 50 mV; pulse time = 40 ms; potential step = 6 mV; v = 20 mV s –1 ;  = 2000 rpm. (inset (left): a plot of stripping peak current with concentration of Cd(II); inset (right): a plot of stripping peak current with concentration of Pb(II)). CONCLUSION 1.The Vietnamese diatomite, which is composed of amorphous silica, has high porosity and surface area. It was studied as an adsorbent for the removal of AB dye from aqueous solution. Solution pH has a significant influence in the adsorption of AB, where the capacity of the adsorbents increases with increasing pH from 4.0 to 11.0. Experimental isothermal data were fitted well to both Langmuir and Freundlich model in the large range of 400-1400 mg L -1 . The U(V) -0.4-0.5-0.6-0.7-0.8-0.9-1 j( u A ) 3.6 3.4 3.2 3 2.8 2.6 2.4 2.2 2 0 100 200 300 400 0.0 0.4 0.8 1.2 I P ,C d (  A ) CCd(II), ppb 0 40 80 120 160 0.0 0.3 0.6 0.9 1.2 I P , P b , ( A ) CPb(II), (ppb) 23 maximum adsorption capacity, qm = 518.0 ± 13.2 mg g -1 , calculated from Freundlich equation and qmom = 528 ± 62 mg.g -1 calculated from Langmuir equation are statistically similar. However, parameters of these equations were effected remarkably on the initial AB concentrations. Both value of qmom and qm increases with the increasing initial AB concentration. The free energy of AB adsorption on diatomite is more negative at higher temperature, which demonstrates that the spontaneity increases with the rise of temperature. Piecewise linear regression as a statistical method for the analysis of experimental adsorption data by the Webber’s intraparticle-diffusion models provide the time periods for each diffusion and results show that the AB adsorption onto diatomite was film diffusion controlled. The rate-limiting step is effected on the initial AB concentration. The adsorption processes obey the pseudo- second-order process in the range of 150-400 mg L -1 and the pseudo- first order one in range of 400-900 mg L -1 . 2. Mn-Fe binary oxides have been homogeneously incorporated into diatomite by means of redox reaction of KMnO4 and FeSO4. The redox products consist of multiple oxidation state oxides (Mn 3+ , Mn 4+ , Fe 3+ and Fe 2+ . The binary oxides dispersed highly into the diatomite surface, forming a Mn-Fe oxides thin layer covering the diatomite surface. Oxide thin layer possesses approximate 1:10 molar ratio of Mn/Fe in composition regardless of the samples prepared in different pH media. The Fe-Mn binary oxides were tested as catalysts for CWPO of phenol. The catalyst demonstrated well in the aqueous medium with a wide range of pHs 4.7-7. The phenol (1000 mg L -1 ) and intermediates of dihydroxyl benzene were degraded completely after 50 minutes. The high catalytic activity for 24 phenol oxidation is due to catalytically synergized properties of iron and manganese oxide highly dispersed on pores of diatomite. Fe-Mn binary oxides modified diatomite materials are promising catalysts for complete oxidation of phenol with hydrogen peroxide in aqueous solutions. 3. The effects of functionalization conditions on the loading of MPTMS in diatomite were investigated. Diatomite from Phu Yen consists of mainly amorphous structure. The crystallization to form quartz occurs at more than 300°C. The diatomite with thermal treatment in the range of 100-300°C is favorable for functionalization. The humidity of diatomite also affects the functionalization level significantly. The MPTMS loading around 9.8% peaked as diatomite was hydrated for 3hours. We have demonstrated that MPTMS-diatomite is useful to prepare chemically modified glassy carbon electrodes. The electrode modified by MPTMS-diatomite exhibited potential for the use of the simultaneous determination of cadmium and lead by DP-ASV. The stripping peak currents of the two metal ions had linear relationships with the concentrations in the range of 20 to 300 ppb (i (µA) = ‒ 0.0202 + 0.0036 C (ppb), R 2 = 0.9997) for Cd(II) and 20 to 150 ppb (i (µA) = ‒0.1179 + 0.0069 C (ppb), R2 = 0.9943) for Pb(II). The LOD for Cd(II) and Pb(II) calculated was 15.9 ppb and 6.9 ppb. 25 List of articles related to dissertation 1. Bui Hai Dang Son, Vo Quang Mai, Dang Xuan Du, Le Cong Nhan, Tran Thai Hoa, Dinh Quang Khieu (2013), “Freundlich and Langmuir adsorption isotherms for removal astrazon black AFDL dye onto Phu Yen diatomite from aqueous solution”, Vietnam Journal of chemistry, Vol. 59(2AB), 296-301. 2. Bui Hai Dang Son, Vo Quang Mai, Dang Xuan Du, Le Cong Nhan, Tran Thai Hoa, Dinh Quang Khieu (2013), “A kinetic study on astrazon black AFDL dye adsorption onto Phu Yen diatomite”, Vietnam Journal of chemistry, Vol. 51(3AB), pp. 1-5. 3. Bui Hai Dang Son, Vo Quang Mai, Dang Xuan Du, Le Cong Nhan, Tran Thai Hoa, Dinh Quang Khieu (2013), “Study on synthesis of mercaptopropyl- functionalized diatomite”, Journal of Catalysis and Adsorption, vol 2, pp. 136-141. 4. Bui Hai Dang Son, Vo Quang Mai, Dang Xuan Du, Le Cong Nhan, Phan Thi Chi, Dinh Quang Khieu (2014), “Mn-Fe binary oxide incorporated into diatomite: an efficient catalyst for phenol oxidation reaction”, Journal of Science and Technology, 52(5B), pp. 490-495. 5. Bui Hai Dang Son, Vo Quang Mai, Dang Xuan Du, Le Cong Nhan, Dinh Quang Khieu (2015), “Study on the cadimium adsorption over 3- mercaptopropymethosilane modified diatomite from aqueous solution”, Vietnam Journal of chemistry, vol 53(3E12), pp. 238-241. 6. Bui Hai Dang Son, Nguyen Thi Ngoc Trinh, Nguyen Dang Ngọc, Dinh Quang Khieu (2015), “A comparison of physicochemical properties of Phu Yen diatomite and Merck diatomite”, Journal of Catalysis and Adsorption, vol 4(4A), pp. 115-119. 7. Bui Hai Dang Son,Vo Quang Mai, Phan Thi Chi, Nguyen Thi Ngoc Trinh, Dang Xuan Du, Le Cong Nhan, Dinh Quang Khieu (2014), “Study on synthesis of Mn-Fe @ diatomite”, Journal of Catalysis and Adsorption, 3, pp. 127-133. 8. Bui Hai Đang Son, Mai Xuan Tinh, Tran Thanh Minh, Nguyen Dang Ngoc (2016), “Arsenite and arsenate adsorption by Fe-Mn binary oxides modified diatomite”, Hue University Journal of Science, vol 3, pp.117-124. 9. Bui Hai Dang Son, Vo Quang Mai, Dang Xuan Du, Nguyen Hai Phong, Dinh Quang Khieu (2016), “A Study on Astrazon Black AFDL Dye Adsorption onto Vietnamese Diatomite”, Journal of Chemistry, pp. 1-11; dx.doi.org/10.1155/2016/8685437. (I.F. = 0.996, ISSN = 2090-9071). 10. Bui Hai Dang Son, Vo Quang Mai, Dang Xuan Du, Nguyen Hai Phong, Nguyen Duc Cuong, Dinh Quang Khieu (2016), “Catalytic wet peroxide oxidation of phenol solution over Fe-Mn binary oxides diatomit composite”, Journal of Porous Material,pp.1-11;doi 10.1007/s10934-016-0296-7. (I.F. = 1.4, ISSN: 1380-2224). 11. Bui Hai Dang Son, Dinh Quang Khieu, Vo Thi Thanh Chau, Pham Dinh Du, Nguyen Hai Phong, Nguyen Thi Diem Chau (2017), “3- mercaptopropyltrimethoxysilane modified diatomite: preparation and application for voltammetric determination of lead (II) and cadmium (II)” Journal of Chemistry; pp.1-10, doi.org/10.1155/2017/9560293. (I.F. = 0.996, ISSN = 2090- 9071). 26