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
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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
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