Ứng dụng các phương pháp phân tích quang phổ hiện đại nghiên cứu đặc tính hấp phụ bề mặt của thuốc nhuộm mang điện trên vật liệu nano nhôm oxit biến tính

ĐẠI HỌC QUỐC GIA HÀ NỘI TRƯỜNG ĐẠI HỌC KHOA HỌC TỰ NHIÊN CHU THỊ PHƯƠNG MINH ỨNG DỤNG CÁC PHƯƠNG PHÁP PHÂN TÍCH QUANG PHỔ HIỆN ĐẠI NGHIÊN CỨU ĐẶC TÍNH HẤP PHỤ BỀ MẶT CỦA THUỐC NHUỘM MANG ĐIỆN TRÊN VẬT LIỆU NANO NHƠM OXIT BIẾN TÍNH LUẬN VĂN THẠC SỸ KHOA HỌC Hà Nội – 2019 ĐẠI HỌC QUỐC GIA HÀ NỘI TRƯỜNG ĐẠI HỌC KHOA HỌC TỰ NHIÊN CHU THỊ PHƯƠNG MINH ỨNG DỤNG CÁC PHƯƠNG PHÁP PHÂN TÍCH QUANG PHỔ HIỆN ĐẠI NGHIÊN CỨU ĐẶC TÍNH HẤP PHỤ BỀ MẶT CỦA THUỐC NHUỘM MANG ĐIỆN TRÊN VẬT LIỆU NANO NHƠM OXIT BIẾN TÍNH Chun ngành: Hóa phân tích Mã số LUẬN VĂN THẠC SỸ KHOA HỌC NGƯỜI HƯỚNG DẪN KHOA HỌC: PGS.TS LÊ THANH SƠN TS PHẠM TIẾN ĐỨC Hà Nội – 2019 LỜI CẢM ƠN Với lòng biết ơn sâu sắc, em xin trân trọng cảm ơn PGS.TS Lê Thanh Sơn TS Phạm Tiến Đức giao đề tài tận tình hướng dẫn, bảo để em hoàn thành luận văn Em xin chân thành cảm ơn thầy cô mơn Hóa phân tích, anh, chị, em bạn phịng thí nghiệm Hóa phân tích ln nhiệt tình giúp đỡ em suốt q trình thực luận văn Em gửi lời cảm ơn đến gia đình, bạn bè, đồng nghiệp người thân yêu tạo điều kiện giúp đỡ em suốt thời gian học tập hoàn thành luận văn Hà Nội, ngày tháng năm 2019 Học viên Chu Thị Phương Minh MỤC LỤC MỞ ĐẦU CHƯƠNG TỔNG QUAN 1.1 Giới thiệu nhôm oxit 1.1.1 Cấu tạo nhôm oxit 1.1.2 Tính chất nhơm oxit 1.1.3 Các thành phần pha Al2O3 1.1.4 Các phương pháp tổng hợp vật liệu nano nhôm oxit 1.1.5 Ứng dụng nhôm oxit 1.2 Giới thiệu thuốc nhuộm mang điện Rhodamine B 1.2.1 Thuốc nhuộm Rhodamine B tính chất 1.2.2 Ứng dụng Rhodamine B 1.2.3 Tác hại RhB 10 1.2.4 Phương pháp xác định RhB 11 1.2.5 Các phương pháp xử lý thuốc nhuộm RhB 13 1.3 Tổng quan hấp phụ 17 1.3.1 Giới thiệu hấp phụ 17 1.3.2 Hấp phụ đẳng nhiệt 19 1.3.3 Động học hấp phụ 21 1.4 Chất hoạt động bề mặt 22 CHƯƠNG NỘI DUNG VÀ PHƯƠNG PHÁP NGHIÊN CỨU 25 2.1 Mục tiêu nghiên cứu nội dung nghiên cứu 25 2.1.1 Mục tiêu nghiên cứu 25 2.1.2 Nội dung nghiên cứu 25 2.2 Thiết bị, dụng cụ, hóa chất 26 2.2.1 Thiết bị 26 2.2.2 Dụng cụ 26 2.2.3 Hóa chất 26 2.3 Phương pháp nghiên cứu 27 2.3.1 Phương pháp tổng hợp vật liệu nano nhơm oxit 27 2.3.2 Biến tính nano Al2O3 chất hoạt động bề mặt 28 2.3.3 Các phương pháp nghiên cứu cấu trúc, thành phần, đặc tính bề mặt vật liệu 30 2.3.4 Phương pháp nghiên cứu hấp phụ 33 2.3.5 Phương pháp UV-Vis 33 2.3.6 Lấy mẫu, bảo quản xử lý RhB mẫu nước thải dệt nhuộm 34 2.3.7 Phương pháp xử lý số liệu 35 CHƯƠNG KẾT QUẢ VÀ THẢO LUẬN 38 3.1 Đánh giá phương pháp xác đinh RhB UV–Vis 38 3.1.1 Chọn bước sóng đo phổ 38 3.1.2 Khảo sát khoảng tuyến tính 39 3.1.3 Xây dựng đường chuẩn 39 3.1.4 Đánh giá phương trình hồi quy 41 3.1.5 Giới hạn phát (LOD) giới hạn định lượng (LOQ) đường chuẩn 41 3.2 Đặc tính cấu trúc bề mặt nano Al2O3 41 3.2.1 Vật liệu nung 600 C 41 3.2.2 Vật liệu nung 1200 C 44 3.3 Khảo sát điều kiện hấp phụ RhB vật liệu nano Al2O3 tổng hợp 46 3.3.1 Ảnh hưởng pH đến khả hấp phụ RhB 46 3.3.2 Ảnh hưởng lực ion đến khả hấp phụ RhB 47 3.3.3 Khảo sát lượng vật liệu 50 3.3.4 Khảo sát thời gian cân hấp phụ 52 3.4 Hấp phụ đẳng nhiệt 54 3.5 Động học hấp phụ 58 3.6 So sánh khả hấp phụ vật liệu biến tính khơng biến tính .61 3.7 Cơ chế hấp phụ 62 3.8 Khảo sát khả tái sử dụng vật liệu 64 3.9 Xử lý mẫu thực 65 KẾT LUẬN 68 TÀI LIỆU THAM KHẢO 70 PHỤ LỤC 78 CÁC KÝ HIỆU VIẾT TẮT Ký hiệu viết tắt BET CHĐBM HPLC LOD LOQ MB RhB SDS SEM TEM UV-Vis DANH MỤC CÁC BẢNG Bảng 1.1 So sánh hấp phụ vật lý hấp phụ hóa học 18 Bảng 3.1 Độ hấp thụ quang xác định RhB nồng độ khác bước sóng 554nm 40 Bảng 3.2 Kết khảo sát ảnh hưởng pH 46 Bảng 3.3 Kết khảo sát ảnh hưởng lực ion 48 Bảng 3.4A Kết khảo sát lượng vật liệu γ-Al 2O3 50 Bảng 3.4B Kết khảo sát lượng vật liệu α-Al2O3 51 Bảng 3.5 Kết khảo sát thời gian cân hấp phụ 52 Bảng 3.6 Kết khảo sát ảnh hưởng nồng RhB ban đầu tới khả hấp phụ RhB lên vật γ-M1 nồng độ muối NaCl 54 Bảng 3.7 Kết khảo sát ảnh hưởng nồng RhB ban đầu tới khả hấp phụ RhB lên vật α-M1 nồng độ muối NaCl 55 Bảng 3.8 Các thông số sử dụng mơ hình bước hấp phụ mơ tả hấp phụ RhB lên vật liệu nano Al2O3 biến tính SDS 58 Bảng 3.9 Thơng số mơ hình động học giả bậc bậc mô tả hấp phụ RhB lên vật liệu nano Al2O3 biến tính SDS 61 Bảng 3.10 Kết hấp phụ xử lý RhB mẫu nước thải dệt nhuộm vật liệu α-M0 α-M1 67 DANH MỤC CÁC HÌNH Hình 1.1 Cấu trúc tinh thể nhôm oxit Hình 1.2 Sơ đồ mơ tả q trình chuyển pha nhơm oxit theo nhiệt độ Hình 1.3 So sánh cấu trúc tinh thể α-Al2O3 γ-Al2O3 Hình 1.4 Cấu trúc phân tử Rhodamine B Hình 1.5 Hình họa mơ tả phân tử CHĐBM bề mặt phân cách nước-khơng khí 22 Hình 1.6 Hình ảnh minh họa Phân tử CHĐBM Mixen CHĐBM 23 Hình 1.7 Cơng thức cấu tạo SDS 24 Hình 2.1 Quy trình tổng hợp vật liệu nano-Al2O3 28 Hình 2.2 Biến tính bề mặt Al2O3 SDS 29 Hình 2.3 Thiết bị UV-1650PC, Shimadzu, Nhật Bản 34 Hình 3.1 Phổ UV-Vis dung dịch RhB 38 Hình 3.2 Khảo sát khoảng tuyến tính phương pháp UV-Vis xác định RhB 39 Hình 3.3 Đường chuẩn xác định RhB UV-Vis 40 Hình 3.4 Phổ XRD vật liệu nano Al2O3 nung 600 C 42 Hình 3.5 Phổ FT-IR vật liệu nano Al2O3 nung 600 C 42 Hình 3.6 Ảnh TEM vật liệu nano Al2O3 nung 600 C 43 Hình 3.7 Đường đẳng nhiệt hấp phụ N2 vật liệu nano Al2O3 nung 600 C 43 Hình 3.8 Phổ XRD vật liệu nano Al2O3 nung 1200 C 44 Hình 3.9 Phổ FT-IR vật liệu nano Al2O3 nung 1200 C 44 Hình 3.10 Ảnh TEM vật liệu nano Al2O3 nung 1200 C 45 Hình 3.11 Đường đẳng nhiệt hấp phụ N2 vật liệu nano Al2O3 nung 1200 C 45 Hình 3.12 Kết khảo sát ảnh hưởng pH đến hiệu suất hấp phụ RhB 47 Hình 3.13 Kết khảo sát ảnh hưởng lực ion đến hiệu suất hấp phụ RhB 49 Hình 3.14 Kết khảo sát lượng vật liệu 51 Hình 3.15 Kết khảo sát thời gian cân hấp phụ 53 Hình 3.16 Đường đẳng nhiệt hấp phụ RhB vật liệu nano Al 2O3 biến tính với SDS nồng độ muối khác Các điểm thực nghiệm, đường kết thu từ mơ hình bước hấp phụ: A.γ-M1; B.α-M1 56 Hình 3.17 Đường động học theo mơ hình giả bậc q trình hấp phụ RhB vật liệu nano-Al2O3 biến tính với SDS nồng độ RhB khác nhau: A γ-M1 B α-M1 59 Hình 3.18 Đường động học theo mơ hình giả bậc trình hấp phụ RhB vật liệu nano-Al2O3 biến tính với SDS nồng độ RhB khác nhau: A γ-M1 B α-M1 60 Hình 3.19 So sánh khả hấp phụ RhB pha vật liệu nano Al2O3 61 Hình 3.20 Thế ζ vật liệu nano γ-Al2O3 tổng hợp, sau biến tính với SDS sau hấp phụ RhB dung dịch NaCl 1mM (pH = 4,0) 62 Hình 3.21A Phổ FT-IR vật liệu γ-M1 63 Hình 3.21B Phổ FT-IR vật liệu γ-M1sau hấp phụ RhB 64 Hình 3.22.Kết khảo sát tái sử dụng vật liệu 64 Hình 3.23 Kết xử lý RhB mẫu nước thải dệt nhuộm vật liệu α-Al2O3 -5 biến tính khơng biến tính SDS A Mẫu M1; B Mẫu M2 M2 thêm 10 M -5 RhB; C Mẫu M3 M3 thêm 10 M RhB……………………………………… 66 MỞ ĐẦU Cơng nghiệp hóa-hiện đại hóa đem lại nhiều thành tựu cho phát triển kinh tế, nâng cao chất lượng sống Tuy nhiên, nguy ô nhiễm nguồn nước chất thải hữu từ ngành công nghiệp ngày cao Vì vậy, xử lý chất gây ô nhiễm nước quan trọng việc bảo vệ mơi trường sống Thuốc nhuộm tổng hợp có nguồn gốc hữu sử dụng phổ biến ngành công nghiệp như: dệt vải, thuộc da, giấy, cao su, nhựa, thực phẩm,…để tạo màu Nước thải công nghiệp chứa thuốc nhuộm hữu mối đe dọa lớn sức khỏe hệ sinh thái chứa nhiều hóa chất độc hại chất rắn lơ lửng [9, 26], gây ung thư đột biến gen [13] Hiện nay, nhiều phương pháp xử lý nước thải chứa thuốc nhuộm hữu nghiên cứu như: keo tụ [39, 46], màng lọc [22], phương pháp phân hủy quang xúc tác [65], điện hóa [2, 4] hấp phụ [29, 42] Trong đó, hấp phụ số phương pháp hiệu để xử lý thuốc nhuộm mang điện tích mơi trường nước Phương pháp hấp phụ phù hợp nước phát triển sử dụng vật liệu hấp phụ sẵn có, rẻ tiền [62] Các oxit kim loại thành phần vật liệu hấp phụ tự nhiên giá rẻ Vật liệu nano phát triển mạnh mẽ thập kỷ qua Ưu điểm trội vật liệu hấp phụ nano so với vật liệu hấp phụ thơng thường kích thước hạt nhỏ, diện tích bề mặt lớn hơn, dễ hoạt hóa thay đổi điện tích bề mặt đặc biệt dễ điều chỉnh đặc tính hình thái, kích thước, lỗ xốp, làm tăng hiệu xử lý chất ô nhiễm môi trường nước [28] Nhôm oxit (Al2O3) biết đến vật liệu oxit kim loại ứng dụng phổ biến làm vật liệu hấp phụ kỹ thuật mơi trường Al 2O3 có nhiều pha cấu trúc khác như: α, β, γ, η, θ, κ, and χ [34] Vật liệu Al 2O3 có diện tích bề mặt lớn, cấu trúc xốp, đặc biệt chế tạo kích thước nano phù hợp làm vật liệu hấp phụ xử lý hiệu thuốc nhuộm mang điện Tuy nhiên, tỷ trọng điện tích vật liệu Al2O3 pH trung tính khơng cao, nên khả xử lý trực tiếp thuốc nhuộm mang điện tích dương thấp Vì vậy, việc biến tính bề mặt vật liệu Al2O3 để nâng cao hiệu suất xử lý cần thiết Natri dedocyl sulfat (SDS) Alumina is a well-known metal oxide material that is one of the most common adsorbents used in environmental engineering Alumina has numerous structural phases, namely , , , , , , and [ 15] It is found that gamma alumina ( -Al2O3) has high specific surface area, especially nano -Al 2O3, which is powerful enough to be an effective adsorbent for ionic dye Nevertheless, -Al 2O3 has low negative charge density in the neutral pH [16] Thus, it is hard to remove cationic dye due to small electrostatic attraction between cationic dye and negatively charged alumina surface In this case, surface modification of alumina is necessary Many studies focused on the modification of alumina by using ionic surfactants to enhance removal efficiency of both organic and inorganic pollutants [1,17–20] Rhodamine B (RhB), which is a cationic dye, is widely used in many industrial activities Rhodamine B is also well known to occur in wastewater [21–23] To our best knowledge, the adsorptive removal of RhB using surfactant modified synthesized alumina nanoparticles has not been reported In order to understand adsorption process systematically, isothermal condition is basically evaluated by modeling Langmuir and Freundlich isotherms are the most common models for adsorption [24,25] Nevertheless, these isotherms are not applicable for surfactant adsorption Interestingly, a two-step adsorption derived by Zhu et al [26] successfully described various adsorption systems of surfactants, polymers, and antibiotics [6,26–32] Thus, this model could be suitable for RhB adsorption onto surfactant modified alumina The aim of this work is to investigate the removal of RhB by adsorption technique using sodium dodecyl sulfate (SDS) modified nano -Al 2O3 (SMNA) after surface modification of -Al 2O3 with SDS solution Some effective parameters for RhB removal using after characterization of -Al 2O3 by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Transmission Electron Microscopy (TEM), and Brunauer–Emmett–Teller (BET) methods were also studied The adsorption isotherms of RhB adsorption onto SMNA were investigated by both experimental and modeling Adsorption mechanisms of RhB onto SMA are discussed on the basis of adsorption isotherms, the surface charge changes of nano -Al2O3 after adsorption by potential and the changes of surface functional groups by Fourier transform infrared spectroscopy (FT-IR), respectively The regeneration of SMNA was carried out in the present study to evaluate the reuse adsorbent Materials and Methods 2.1 Materials Aluminum nitrate Al(NO3)3 9H2O and NaOH pellets which were pure analytical reagents, were purchased from Merck, Darmstadt, Germany Cationic dye, Rhodamine B (CAS 81-88-9) for microscopy (with purity > 95.0%), with a molecular weight of 479.02 g/mol, was delivered from Merck (Darmstadt, Germany) An anionic surfactant, sodium dodecyl sulfate (SDS) (with purity greater 95%) supplied from Scharlau (Barcelona, Spain, EU), was used without further purification to modify synthesized nano-alumina Figure shows the chemical structures of RhB (A) and SDS (B) The cationic dye, methylene blue (with purity > 98.5%) and organic solvent chloroform CHCl3 (HPLC grade) from Merck (Darmstadt, Germany) were used to quantify the concentrations of SDS Ionic strength and pH were adjusted by the addition of NaCl (p.A, Merck, Darmstadt, Germany), HCl and NaOH (volumetric analysis grade, Merck, Darmstadt, Germany) Solution pH was conducted using an HI 2215 pH meter (Hanna, Woonsocket, RI, USA) The glass pH electrode was checked for calibration with three standard buffers of 4.01, 7.01, and 10.01 (Hanna, Woonsocket, RI, USA) Other chemicals with analytical grade were purchased from Merck (Darmstadt, Germany) Ultrapure water was taken from ultrapure water system (Labconco, Kansai, MO, USA) with resistivity 18.2 MW cm was used in preparing all aqueous solution Materials 2019, 12, 450 Materials 2019, 12, x FOR PEER REVIEW (A) (B) Figure Chemical structures of Rhodamine B (RhB)) ((A)) and sodium dodecyl sulfate (SDS)S) ((BB)) 2.2 Fabrication of Alumina Nanoparticles 2.2 Fabrication of Alumina Nanoparticles AluminaAlumina nanoparticlesnanoparticles werewere fabricatedfabricated accordingaccording toto previousprevious studystudy withwith aa modificationmodification [33].[33] The solutions of Al(NO ) and NaOH were used to synthesize alumina The 4M NaOH solution was The solutions of Al(NO33)3 and NaOH were used to synthesize alumina The 4M NaOH solution was prepared by dissolving 12.2449 g NaOH pellets in 75.0 mL ultrapure water A solution of M Al(NO ) prepared by dissolving 12.2449 g NaOH pellets in 75.0 mL ultrapure water A solution of 3M3 was prepared by dissolving 37.50 g of Al(NO ) 9H O in 100.0 mL ultrapure water Aluminum 33 Al(NO3)3 was prepared by dissolving 37.50 g of Al(NO 3)3·9H2O in 100.0 mL ultrapure water hydroxide was obtained by slowly adding M Al(NO ) with M NaOH in a plastic vessel White Aluminum hydroxide was obtained by slowly adding3 13 M Al(NO3)3 with M NaOH in a plastic precipitation of aluminum hydroxide formed from this state was then separated by using a centrifuge vessel White precipitation of aluminum hydroxide formed from this state was then separated by at 6000 rpm (Digisytem, Taiwan) After that, the samples were dried in thermal oven at 80 C for 24 h using a centrifuge at 6000 rpm (Digisytem, Taiwan) After that, the samples were dried in thermal The obtained powder was then calcined at 600 C for 12h in thermal furnace before cooling to room oven at 80 °C for 24 h The obtained powder was then calcined at 600 °C for 12h in thermal furnace temperature in a dessicator Finally, alumina particles were stored in a polyethylene container before cooling to room temperature in a dessicator Finally, alumina particles were stored in a polyethylene container 2.3 Characterization Methods 2.3 CharacterizationThesynthesizedMethodsalumina was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Transmission Electron Microscopy (TEM), Brunauer–Emmett–Teller The synthesized alumina was characterized by X-ray diffraction (XRD), Fourier transform (BET) methods and potential measurements infrared spectroscopy (FT-IR), Transmission Electron Microscopy (TEM), Brunauer–Emmett–Teller The XRD pattern was performed on a Bruker D8 Advance X-ray Diffractometer (Karlsruhe, (BET) methods and ζ potential measurements German) with CuK radiation ( l = 1.5418 Å) The XRD pattern was recorded in a range of 20–80 (2 ) The XRD pattern was performed on a Bruker D8 Advance X-ray Diffractometer with a step size of 0.03 The FT-IR spectra was collected with an Affinity-1S spectrometer (Shimadzu, (Karlsruhe, German) with CuKα radiation (λ = 1.5418 Å) The XRD pattern was recorded in a range Kyoto, Japan) The FTIR spectra of nano-alumina particles, SDS modified nano-alumina (SMNA) at the of 20–80° (2θ) with a step size of 0.03° The FT-IR spectra was collected with an Affinity-1S plateau adsorption level, SMNA after RhB adsorption and RhB salt were obtained with a resolution of1 spectrometer (Shimadzu, Kyoto, Japan) The FTIR spectra of nano-alumina particles, SDS modified cm at atmospheric pressure (25 C) nano-alumina (SMNA) at the plateau adsorption level, SMNA after RhB adsorption and RhB salt BET method was used using a surface area and pore size Analyzer surface area analyzer were obtained with a resolution of cm−1 at atmospheric pressure (25 °C) Micromerities (TriStar 3000, Norcross, GA, USA) The adsorption isotherm of nitrogen (N2) was BET method was used using a surface area and pore size Analyzer surface area analyzer conducted in a mL cell with outgas condition of 150 C in 90 The particle size distribution of Micromerities (TriStar 3000, Norcross, GA, USA) The adsorption isotherm of nitrogen (N2) was synthesized nano-alumina which was evaluated by TEM, was performed by using Hitachi (H7650, conducted in a mL cell with outgas condition of 150 °C in 90 The particle size distribution of Tokyo, Japan) with Olympus camera (Veleta 2000 2000) The operating conditions were accelerating synthesized nanoalumina which was evaluated by TEM, was performed by using Hitachi (H7650, condition of 80 kV and exposure time of s Tokyo, Japan) with Olympus camera (Veleta 2000 × 2000) The operating conditions were accelerating The surface charge of synthesized nano-alumina, SMNA and SMNA after RhB adsorption in condition of 80 kV and exposure time of sec mM NaCl, at pH were examined by using Zetasizer Nano ZS (Malvern, Worcestershire, UK) The surface charge of synthesized nano-alumina, SMNA and SMNA after RhB adsorption in Dynamic Light Scattering (DLS) for particle size characterization in the solutions of nano-alumina mM NaCl, at pH were examined by using Zetasizer Nano ZS (Malvern, Worcestershire, UK) and SMNA was also conducted with Zetasizer Nano ZS by applying backscattering detection (173 Dynamic Light Scattering (DLS) for particle size characterization in the solutions of nano-alumina and SMNA was also conducted with Zetasizer Nano ZS by applying backscattering detection (173° Materials 2019, 12, 450 detection optics) at 22 C A cleaned plastic cuvette containing mL of the sample was used in each DLS measurement The zeta ( ) potential was calculated from electrophoretic mobility using Smoluchowski’s equation [34] ueh = # # rs where is the potential (mV), ue is the electrophoretic mobility ( m cm/sV), h is the dynamic viscosity of the liquid (mPa s), #rs is the relative permittivity constant of the electrolyte solution, and #0 is the 12 electric permittivity of the vacuum (8.854 10 F/m) All adsorption experiments were conducted by batches in 15mL Falcon tubes at 25 C controlled by an air conditioner All adsorption of SDS and RhB onto synthesized nano-alumina were carried out in triplicates For SDS adsorption onto synthesized nano-alumina, a fixed 50 mg/mL of synthesized nano-alumina was mixed with 10 mL of different SDS concentrations at 10 and 100 mM NaCl for h to form SDS modified nano-alumina (SMNA) The concentrations of SDS were quantified by an extractive spectrophotometric method using the ion paired formation complex of SDS and methylene blue in chloroform solvent Detail of the procedure was published in our previously published paper [30] For RhB adsorption, a known amount of adsorbent was thoroughly mixed with 10 mL aqueous RhB in different NaCl concentration The effective conditions (pH, adsorption time, adsorbent dosage, ionic strength) on adsorption RhB were studied The concentrations of RhB were determined by using Ultraviolet Visible (UV-Vis) spectroscopy at a wavelength of 554 nm with a quartz cuvette with a cm optical path length using a spectrophotometer (UV-1650 PC, Shimadzu, Kyoto, Japan) The molar absorbance coefficient of RhB determined by experiment is 105,456 734 cm 1 1 M that is very good agreement with the value of 106,000 cm M for standard RhB The adsorption capacities of SDS onto nano-alumina and RhB onto SMNA were determined by the following equation G= Ci m Ce M 1000 where G is the adsorption capacity of SDS or RhB (mg/g), Ci is the initial concentration of SDS or RhB (mol/L), Ce is the equilibrium concentration of SDS or RhB (mol/L), M is molecular weight of SDS or RhB (g/mol), and m is the adsorbent dosage (mg/mL) The removal efficiency (%) of RhB was calculated by Equation (3) Removal efficiency (%) = where Ci and Ce are initial concentration and equilibrium concentration of RhB (mol/L), respectively The obtained isotherms were fitted by general isotherm equation that could be applied to describe adsorption isotherms of RhB onto SMNA The general isotherm equation [26] is: G= where G is the amount of adsorbed RhB at concentration C, G¥ is the maximum adsorption at high concentrations, k1 and k2 are equilibrium constants involved in the first and second step, respectively, and n is clusters of multilayer C is the equilibrium concentrations of RhB Materials 2019, 12, 450 ResultsMaterials2019and,12Discussion,xFORPEERREVIEW , 12, x 3.13.3 1Char1 CharacterizationaofofofSynthesizedAluminaNanoparticles of TheTheXRDXRDpatternofofthethealuminananoparticlesticles oobbtainedbytheesolvothermalmethodis isshown in Figurein 2The sharp peaks alumina The gamma phase of in Figure The sharp peakswithhighintensityity at 2θ = 38° and 67° indicatethe high crystalline of θ alumina The gamma phase ofofalumina was confirmedd dueduetotothepresencepresenceofof the peaks atat 46° and ° d confi 6161°[35[35][35] FacultyofofChemistry,HUS,VNU,D8D8ADVANCE Bruker 800L1 600 600 500 500 400 200 d=2.393 300 d=2.3 93 (Cps) 300 200 d=2.798 Lin Lin (Cps) 400 thehighcrystallineof of of the peaks at 46 and d=2.798 100 100 0 20 20 File: HuongPT 800L1.raw - Type: 2Th/Th locked - Start: 20.000 ? - End: 80.000 ? - Step: 0.030 ? - Step time: 0.3 s - Temp.: 25 癈 (Room) - Time Started: 13 s - -Theta: 20.000 ? - Theta File: HuongPT 800L1.raw - Typ e: 2Th/Th locked - Start: 20 000 ? - End: 80 000 ?- Step: 030 ? - Step time: s - Temp.: 25 癈 (Room) - Time Started: 13 s - 2-Theta: 20.000 ? - Theta: 10.000 ? - Chi: 0.00 ? - Phi: 0.00 ? - X 00-050-0741 (I) - Aluminum Oxide - gamma-Al2O3 - Y: 100.00 % - d x by: - WL: 1.5406 - Cubic - a 7.93900 - b 7.93900 - c 7.93900 - alpha 90.000 - beta 90.000 - gamma 90.000 00-050-0741 (I) - Aluminum Oxide - gamma-Al2O3 - Y: 100.00 % - d x by: - WL: 1.5406 - Cubic - a 7.93900 - b 7.93900 - c 7.93900 - alpha 90.000 - beta 90.000 - gamma 90.000 - Figure 2XRD The FT-IR3657.04, 3550.95, 3657.04,3550.95,and 3622.32cm structure.The.Thepeaksapappearedatat1031.92,.520.78,.and426 27cm of vibrationvibrationof AlofAl-OH-OHgroupgroup[36[36].The.Thebroaderpeaksbetween10100000cmcm ,, 9811 77 cm , and,and520520.78.78cmcm confirmed the bending confirmed the bending vibrationof Al-O bond[[35]35 Figure 3.3The F igure The FT- IRs pe ctra of synthesized γ-Al 2O33na nopa rtic les Transmission particle particle electron size to electronmicroscopy(TEM) was performedto characterizethe of perfo the morphologyand and to size ofofaluminapowers(Figure 4)4) The TTEM in that iimageieshowninin Figure44 showsthat alumina particlesare sphered oneswith the sizeinin the rarange ofof 30––40 nm,indicating thatsynthesizedalumina Materials 2019, 12, 450 Materials 2019, 12, x FOR PEER REVIEW Mater ials 019 , 12, x FOR PEER RE VIEW particles are sphered ones with the size in the range of 30–40 nm, indicating that synthesized alumina is a nanosized powder The DLS data (not shown in detail) indicates that the hydrodynamic Z-average is a nanosized powder The DLS data (not shown in detail) indicates that the hydrodynamic Z- is a nanosized powder The DLS data (not shown in detail) indicates that the hydrodynamic Zdiameter of nano-alumi nano was about 410–45 0nm at pH   that much higher than the particle size of average diameter of -alumina was about 410–450 nm at pH that much higher than the particle average diameter of nano-alumina was about 410–450 nm at pH that much higher than the particle nanosize-alumiofnanoa-duealuminatothedueaggregationtotheaggregationofnano-ofaluminanano-aluminaNaClinconcentrationNaClconcentration.TheZ-.averageTheZ-averagdiameter size of ofnano-alumina due to the aggregation of nano-alumina in NaCl concentration The Z-average diameterSMNAwasof SMNAabout 924was–958aboutnm,924indicating–958nm, indicatingthattheformationthatthe formationSMNA ofaggregatesSMNAaggregatesinthepresenceinth of diameter of SMNA was about 924–958 nm, indicating that the formation of SMNA aggregates in the SDSpresencepresence.However,ofofSDSSDS.the.However,aggregationHowever,thetheofaggregationaggregationSMNAdidofofnotSMNASMNAinducediddid notnotsignificantlyinduceinducesignificantlysignificantlytoRhBadstotoRhBrptionRhBadsorption.adsorption 200 nm 200 nm Figure TEM image of synthesized γ-Al2O3 nanoparticles Figure 4.TEMimage of synthesized γ-Al O nanoparticles s - l22O33 The specific surface area of the nano γ-Al2O3 by BET was calculated from N adsorption isotherm The specific surface area of the The specific surface a rea of the nano γ-Al2 O3 by BETwas calcula te dfrom N and found to be around 221.3 m22/g (Figure 5) andandfoundfoundtotobebearound2221.3.3mm2/g (Figure5)5) 100 cc/g(STP) 100 cc/g(STP) 80 80 Adsorbed 60 60 40 Adsorbed 40 Volume Volume 20 20 0 Figure Adsorption isotherm of N2 onto synthesized nano-alumina Figure5.5.Adsorption isotherm of N22 ontosynthesizednanonano-alumina- The specific surface area in our work is similar to the results of alumina published by Khataee etThealThe.[37]specificspecific.Itmpliesurfathatceareathesynthesizedininourourworkworknanoissimilarγis-AlsimilarOtohasthe tohighresultsthespecificofresultsaluminasurfaceofpublishedaluminaareatt publishedbygoodKhataeefor by Khataeeetadsorptivel.[37]et.alIt implies[removal37].Itimpliesthatofionicthethatsynthesizeddye.However,synthesizednanoinγorder-Alnano2Oto3hasenhance-AlhighO thespecifichasremovalhighsurfacespecificefficiencyareasurfacethatofRhBisareagoodusingthatfor is goodananosorptiveforadsorptiveγ-Alremoval2O3,theremovalsurfaceofionichargeofdyeionic.However,modificationdye.However,inordeisnrededintoorderenhancebecausetoenhancetheremovalelectrostatictheremovalefficiencyinteractionefficiencyofRhBismusingofreRhB usingnanoimportantnanoγ-AlOAlfor,theionicOsurface,thedyesurfaceadsochageptionchargemodification[1].modificationisneededisnebecausededbecausetheelectherostaticelectrostaticinteractioninteractionismore is im portant for ionic dye adsorpti adsorption [1] 3 more important for ionic dye [1] 3.2 Modification of Synthesized Nano-Alumina by SDS Adsorption 3.23 2Modification.ModificationofofSynthesizedNano Aluminai by SDS Adsorption The synthesized nano γ-Al2O3 was modified by SDS pre-adsorption of at two salt concentration at pH At pH 4, the surface charge of γ -Al O is highly positive due to the point of zero charge 8.5 of The synthesized nano γ-Al O was modified2ified3 by SDS pre-adsorptionof at two salt concentration The synthesized nano -Al2O233 pre- of at two salt concentration alumina [16] At pH < 4, the dissolution of alumina could occur so that the characteristics may be at pH At pH 4, the surface charge of γ-Al O is highly positive due to the point of zero charge 8.5 of at pH At pH 4, the surface charge of -2Al32O3 is highly positive due to the point of zero charge changed [38] Figure shows that adsorption of SDS onto nano γ-Al 2O3 grew up with an increase of salt alumina [16] At pH < 4, the dissolution of alumina could occur so that the characteristics may be 8.5 of alumina [16 ] At pH < 4, the dissolution of alumina could occur so that the characteristics from 10 to 100 mM Adsorption of anionic SDS onto nano γ-Al 2O3 here is different to adsorption of changed [38] Figure shows that adsorption of SDS onto nano γ- Al 2O3 grew up with an increase of salt may be changed [38] Figure shows that adsorption of SDS onto nano -Al2O3 grew up with an from 10 to 100 mM Adsorption of anionic SDS onto nano γ-Al2O3 here is different to adsorption of Materials 2019, 12, x FOR PEER REVIEW Materials 2019, 12, 450 SDS onto activated beads of Al2O3 in which the electrostatic attraction is main driving force [39] In Materials 2019, 12, x FOR PEER REVIEW of 16 increasethiscase,of saltSDSfromadsorption10to100ontomMnano.Adsorptionγ-Al2O3 ofis anioniccontrolledSDSbyontobothnanoelectrostatic-AlO interactions The maximum adsorption capacity adsorption of SDS onto activ a te d beads of Al O SDS onto activated beads of Al O in which the2 concentration was greater than 0.01 M It should be noted that the force [39] In this case, SDS adsorption onto23 this ase, SDS adsorption onto nano γ-Al O nanoisc solution with 0.01 M SDS because its concentration is much the higher than the critical micelle hydrophinteractiobicns interactionsThemaxim um.Theadsorptionmximum adsorptioncapacitywascapacityobtainedwas atobtained10m Mat NaC l10mMwhenNaCl thewhenSDSthe (CMC) The admicelle of SDS molecules are SDSconcentrationwas wasgreatergreaterthanthan0.01 0M.01.ItMshould.Itshouldbenotedbenotedthatcompletelythatmicellesthemicellaressuaresurelyformedformedinthein the charge reversal is occurred The plateau adsorption capacity of SDS onto γ-Al O reaches to 450 thesolutionsolutionwithwith0.01.01M MSDSSDSbecauseitsitsconcentrationis ismuchmuchthethehigherthanthethe2critical3micelle mg/g that is similar to the SDS adsorption onto alumina in the previous paper [40] With the presence concentration (CMC) The admicelleofofSDSSDSmoleculesarearecompletelyformedformedonγon-Al2OAl3surfaceOsurfthatce of a high number of reachesto450 admicelles on γ-Al O , the removal of cationic dye RhB using highly negative thatthe cthargechargerevereversalisoccurrisoccurred.The plateauThe2plateau3adsorptionadsorptioncapacitycapacityofSDSofontoSDSγ-ontoAl2O3 -reachesAlO charge γ-Al O particles can increase significantly Therefore, the adsorption of initial 0.01 M SDS tomg/g450 thatmg/gis similarthat23is similartotheSDStotheadsorptionSDSontorptionaluminaonto aluminathepreviousinthe paperrevious[40]paper.With [the40].presenceWiththe onto γAl O was fixed to modify the γ-Al O surface AlremovalO,theofremovalcationicofdyecationicRhBusingdyeRhBhighlyusinegativehighly that was carried out at 100 mM NaCl (pH 4) negative 3 chargeγ charge -AlO particles -AlO particles canincrease significantly can increase significantly Therefore, theadsorption Therefore, ofinitial theadsorption 0.01M SDS of initial ofnumberadmicellesofadmicellesonγ-Al2Oon32, presenceofahighofnumber a high the3- 01M 500 SDSontoontoγ-Al2-OAl3wasO wasfixedfixedtomodifytomodifythe γthe-Al2O-Al3surfaceOsurfacethat thatwas wascarriedcarriedout atout100at mM100mMNaClNaCl(pH (pH4) 4) 23 Γ SD (mg/ S g) Γ (mg/g) 23 Figure Adsorption of SDS onto synthesized nano-alumina at different NaCl concentrations CSDS (mo/L) 3.3 Adsorptive Removal of RhB Using Synthesized Nano-Alumina (NA) without and with SDS Figure 66 Adsorption of SDS onto synthesized nano aalumina at diffferentNaClconcentrations Modification 3.3 Adsorptive Removal of RhB Using Synthesized Nano-Alumina (NA) without and with SDS Modification 3.3 Adsorptive Removal of RhB Using Synthesized Nano-Alumina (NA) without and with SDS 3.3.1 Effect of pH Modification 3.3.1 Effect of pH The removal of RhB using synthesized nano γ-Al2O3 is strongly influenced by pH because pH 3.3.1The.EffectremovalofpH of RhB using synthesized nano -Al2 O3 is strongly influenced by pH because pH highly affects to the charging behavior of nano γ-Al2O3 and the desorption of SDS [30,32] The effects highly affects to the charging behavior of nano -Al2O3 and the desorption of SDS [30,32] The effects of of pH on adsorptive removal of RB synthesized nano γ-Al2O3 without and with SDS The removal of RhB using synthesizedusingano γ-Al2O3 is strongly influenced by pH because pH pH on adsorptive removal of RB using synthesized nano -Al2O3 without and with SDS modification modification were conducted in the pH range 3–10 in mM NaCl with contact time of 180 and highly affects to the charging behavior of nano γ-Al2O3 and the desorption of SDS [30,32] The effects were conducted in the pH range 3–10 in mM NaCl with contact time of 180 and adsorbent adsorbent dosage of mg/mL (Figure 7) of pH on adsorptive removal of RB using synthesized nano γ-Al 2O3 without and with SDS dosage of mg/mL (Figure 7) modification were adsorbent dosage of Figure Figure TheTheeffectof pH on RhB removal using synthesizednano (Ci (RhB) = 10 (Ci (RhB) = 10 Figure The effect of pH on RhB removal using synthesized nano γ-Al2O3 without SDS modification (Ci (RhB) = 10−6 M and with SDS modification (Ci (RhB) = 10−4 M) Materials 2019, 12, x FOR PEER REVIEW Materials 2019, 12, 450 Figure indicates that the removal efficiency decreased with increasing pH from to 10 for synthesized nano γ-Al2O3 without while the removal reduced from pH to 10 At pH 3, the Figure indicates that the removal efficiency decreased with increasing pH from to 10 for dissolution of alumina is occurred so that the property may be changed [41] When pH solution synthesized nano -Al2O3 without while the removal reduced from pH to 10 At pH 3, the dissolution increases, the positive charge of nano γ-Al 2O3 is decreased whereas RhB is cationic dye in such range of alumina is occurred so that the property may be changed [41] When pH solution increases, the of pH For SDS modified nano γ-Al 2O3 (SMNA), the SDS desorption may be enhanced so that the less positive charge of nano -Al 2O3 is decreased whereas RhB is cationic dye in such range of pH For SDS negatively charge SDS modified alumina is occurred [32] It should be noted that the initial modified nano -Al2O3 (SMNA), the SDS desorption may be enhanced so that the less negatively concentration of 10−4 M RhB using SMNA is greater than that for the case without SDS (10 −6 M) charge SDS modified alumina is occurred [32 ] It should be noted that the initial concentration of Nevertheless,4 the removal efficiency of RhB using SMNA is always higher than that using 10 M RhB using SMNA is greater than that for the case without SDS (10 M) Nevertheless, the synthesized nano γ-Al2O3 It implies that the removal efficiency increased significantly using removal efficiency of RhB using SMNA is always higher than that using synthesized nano -Al2O3 modified nano γ-Al2O3 (SMNA) compared without SDS modification Maximum removal efficiency It implies that the removal efficiency increased significantly using modified nano -Al 2O3 (SMNA) achieved 97.7% at pH for SMNA At the same RhB concentration of 10−4 M, the removal efficiency compared without SDS modification Maximum removal efficiency achieved 97.7% at pH for SMNA of RhB using alumina is smaller than 40% Therefore, pH is chosen for further adsorption study of At the same RhB concentration of 10 M, the removal efficiency of RhB using alumina is smaller than RhB onto two adsorbents 40% Therefore, pH is chosen for further adsorption study of RhB onto two adsorbents 3 Effect of of Adsorption Time of of on Adsorption time affects the completeness of adsorption equilibration The effect of contact time on the adsorptive removal of RhB γ- Al O with and without SDS from 10 to 240 is presented in using synthesized nano - Al2 2O33 with and without SDS from 10 to 240 ispresented Figure Figure 8shows the adsorption reaches equilibrium 90min and 180 in Figure 8.Figure 8showsthathat the adsorption reaches equilibrium 90min and for SMNA and without SDS modification, re The γ180 for SMNA and without SDS modification, respectively Theadsorption time of RhB onto nano Al It is on Al 22O33 with SDS modificatifion is much fastert than that without SDS It is also faster than RhB adsorption on traditional activated carbon is fixed for (120 min) [[42]42 The adsorption timee of 90 is fixed for RhB adsorption and 180 is for one onto nano γ -Al O ontoSMNAand 180 is selectedfor one onto synthesizednano -Al 22O 33 Removal Efficiency (%) the with SDS 40 Figure The effect of contact time ±2 modification(Temperature25 on without SDS 80 120 160 200 240 280 Contact time (min) on RhBB removal using synthesized nano C, C (RhB) = 10 M and with SDS modification(C (RhB) = 10 M) nano γ 25 °C, iCi (RhB) = 10−6 M and with SDS -Al O -Al2 O3 without SDS (iCi (RhB) = 10−4 M) 3.3.3 The Effect of Adsorbent Dosage 3.3.3 The Effect of Adsorbent Dosage The adsorbent dosage highly affects to the adsorption process because it can induce the total The adsorbent dosage highly affects to the adsorption process because it can induce the total specific surface area of adsorbent and number of binding sites [43] The amounts of synthesized specific surface area of adsorbent and number of binding sites [43] The amounts of synthesized nano nano -Al2O3 with and without SDS were varied from 0.5 to 30 mg /mL (Figure 9) As can be γ-Al2O3 with and without SDS were varied from 0.5 to 30 mg /mL (Figure 9) As can be seen in Figure seen in Figure 9, the removal of RhB using synthesized nano -Al2 O3 without SDS increased with 9, the removal of RhB using synthesized nano γ-Al2O3 without SDS increased with increasing increasing adsorbent dosage, while SDS modified nano -Al2O3 required much smaller amount When adsorbent dosage, while SDS modified nano γ-Al 2O3 required much smaller amount When using using SMNA, the amount of adsorbent is economical comparing with nano -Al 2O3 without SDS SMNA, the amount of adsorbent is economical comparing with nano γ-Al 2O3 without SDS For For removal of RhB using SMNA, the adsorbent dosage mg/mL is good enough to achieve the removal of RhB using SMNA, the adsorbent dosage mg/ml is good enough to achieve the efficiency efficiency of approximately 100% Thus, optimum adsorbent dosage is found to be mg/mL of approximately 100% Thus, optimum adsorbent dosage is found to be mg/mL Because the removal efficiency of RhB using SMNA is much higher than nano -Al 2O3 without SDS, we only focus on the adsorption mechanisms of RhB onto SMNA in the next section Materials 2019, 12, x FOR PEER REVIEW (% ) Materials 2019, 12, 450 Materials 2019, 12, x FOR PEER REVIEW Efficiency(%) EfficiencyRemoval Remov al Figure The effect of 0adsorbent dosage on RhB removal using synthesized nano γ-Al2O3 without SDS modification (Ci (RhB) 0= 10−6 M) and with10 SDS modification20 (Ci (RhB)30 = 10−4 M) 40 Adsorbent dosage (mg/mL) Because the removal efficiency of RhB using SMNA is much higher than nano γAl2O3 without Figure 99 The effectfect of adsorbent dosage on RhBremovalusingsynthesizednano γ-Al-AlO2O3 without SDS, we only focus on the adsorption mechanisms of RhB onto SMNA in the next section 23 SDSS modification odification ((Ci ((RhB)==1010M) M) and and withwith SDSSDS modification modification (Ci ( RhB)(C(RhB)=10 i 3.4 Adsorption Isotherms of RhB on SDS Modified Nano-Alumina (SMNA) 3.4 Adsorption Isotherms of RhB on SDS Modified Nano-Alumina (SMNA) Because the removal efficiency of RhB using SMNA is much higher than nano γ-Al 2O3 without The effect of ionic strength on adsorption of RhB onto SDS modified nan SDS, only focus the Thwe effect of ionic strengthadsorptionadsorption of RhB onto SDS modified nano -Al2O3 clearly observed on the isotherms (Figure 10) At pH 4, the adsorption of RhB decreases with is clearly observed on the isotherms (Figure 10) At pH 4, the adsorption of RhB decreases with increasing3.4.AdsorptionNaClIsothermsconcentrationofRhB onat SDSlow RhBModifiedconcentrationNano-Alumina.Nevertheless,(SMNA) increasing NaCl concentration at low RhB concentration Nevertheless, at high RhB concentration at high RhB concentration adsorption increases with an increase of ionic strength At low RhB adsorption, an increase in salt adsorption increases with an increase of ionic strength At low RhB adsorption, an increase in salt The effect of ionic strength on adsorption of RhB onto SDS modified nano γ-Al 2O3 (SMNA) is concentration increased the number of cation + concentration increased the number of cation Na clearly observed on the isotherms (Figure 10) At pH 4, the adsorption of RhB decreases with decreasing the electrostatic effect of RhB on negatively charged SMNA The electrostatic attraction the electrostatic effect of RhB on negatively charged SMNA The electrostatic attraction between increasing NaCl concentration at low RhB concentration Nevertheless, at high RhB concentration between the positive charge of RhB and negatively charge of alumina is significantly screened by the positive charge of RhB and negatively charge of alumina is significantly screened by increasing adsorption increases with an increase of ionic strength At low RhB adsorption, an increase in salt increasing salt concentrations However, other interactions such as surface complexation and Van salt concentrations However, other interactions such + concentration increased the number of cation der Waals interactions and hydrogen bonding can induce adsorption at high RhB concentration It is interactions and hydrogen bonding can induce adsorption at high RhB concentration It is suggested decreasing the electrostatic effect of RhB on negatively charged SMNA The electrostatic attraction suggested that adsorption of RhB onto SMNA is controlled by both electrostatic and non- electrostatic that adsorption of RhB onto SMNA is controlled by both electrostatic and non-electrostatic interactions between the positive charge of RhB and negatively charge of alumina is significantly screened by interactions The isotherms of RhB show a common intersection point (CIP) in which the electrostatic The isotherms of RhB show a common intersection point (CIP) in which the electrostatic contribution increasing salt concentrations However, other interactions such as surface complexation and Van contribution to the adsorption vanishes and the salt effect disappears [30] to the adsorption vanishes and the salt effect disappears [30] der Waals interactions and hydrogen bonding can induce adsorption at high RhB concentration It is suggested that adsorption of RhB onto SMNA is controlled by both electrostatic and nonelectrostatic 200.0 interactions The isotherms of RhB show a common intersection point (CIP) in which the electrostatic Γ RhB Γ(mg/g) Rh B (mg/g) contribution to the adsorption vanishes and the salt effect disappears [30] 160.0 0.0 Figure 10 Adsorption isotherms of RhB onto SDS modified nano -Al2O3 (SMNA) at different Figure 10 Adsorption isotherms of RhB onto SDS modified nano γ-Al2O3 (SMNA) at different NaCl NaCl concentrations The0.0000points are 0experimental.00050.data0010while 0solid.0015lines are0.0020fitted by a two-step concentrations The points are experimental data while solid lines are fitted by a two-step adsorption adsorption model model CRhB(mol/L) Figure 10 also shows that at different NaCl concentrations, the experimental results of RhB Figure 10 Adsorption isotherms of RhB onto SDS modified nano γ- Al2O3 (SMNA) at different NaCl onto SMNA can be represented well by general isothermal equation, Equation (4), with the fitting concentrations The points are experimental data while solid lines are fitted by a two-step adsorption model Materials 2019, 12, x FOR PEER REVIEW Figure 10 also shows that at different NaCl concentrations, the experimental results of RhB onto Materials 2019, 12, 450 10 of 15 SMNA can be represented well by general isothermal equation, Equation (4), with the fitting parameters in Table At different salt concentrations, the maximum adsorption capacity of RhB at parameters in Table At different salt concentrations, the maximum adsorption capacity of RhB at 100 mM is higher than that at mM Table also shows that we can use the same fitting parameters mM is higher than that at mM Table also shows that we can 1002 (k and n) for isotherms at and 100 mM NaCl However, the value of k at mM NaCl is 10 times and n) for isotherms at and 100 mM NaCl However,1 greater than that at 100 mM It suggests that k is a valuable parameter to evaluate electrostatic than that at 100 mM It suggests that k1 is a valuable parameter to evaluate electrostatic interaction1 interaction at low RhB concentration The higher the salt concentration, the higher value k is obtained low RhB concentration The higher the salt concentration, the higher value k is obtained Table The fit parameters for adsorption RhB onto SDS modified nano γ-Al2O3 (SMNA) Table The fit parameters for adsorption RhB onto SDS modified nano -Al2O3 (SMNA) C 3.5 Adsorption Mechanisms of RhB onto SDS Modifiified Nano gγ-Al2O3 (SMNA)) In this section,, adsorption mechanisismss of RhB onto SSDS modifiedodifiednano γ Al2O3 is discussed in detail based on the change in surface charge by monitoring ζ potential and the change in ffunctional groups by FT IR and aadsorption isothermss of RhB onto SSMNA The ζ potential in Figure 1111 showss that the ζ potential ofof synthesized nano γ Al2O3 is highly positive at pH (ζ = +47.5.55mV) AftersurfacemodificationficationwithwithSDSSDStotoformformSDSSDSmodifiedmodifiednananoγAl-Al2O3O(SMNA),thethesurfacesurfacechargechargeof ofadsorbentchangedfromfrompositivetotonegative(ζ( = =−13.1395.95mV)mV).It 3 Itimpliesthatthatthetheadmicelleswereocccuurrredontonano γ All22OO33surfaceandthe charge was taken place in the presencese ce of anion DS− [30,32]30,32] Nevertheless, afterr adsorption of cationic dye RhB, the negative charge of SMNA changed from negative to slightt positive ((ζ = +2.85 mV) The results of ζ potential suggest that RhB adsorption onto SMNA is due to electrostatic interaction 50.0 ζ potential (mV) 40.0 30.0 20.0 10.0 0.00 -10.00 -13.95 -20.00 Figure 11 The potential of synthesized nano Figure 11 The ζ potential of synthesized nano γ-Al O , SDS modified nano γ-Al O (SMNA), and -Al2O3, SDS modified nano SMNA after RhB adsorption in mM NaCl (pH 4) -Al2O3 (SMNA), and SMNA after RhB adsorption in mM NaCl (pH 4) FTIR is powerful tool to evaluate the change in functional groups after adsorption [44] Figure 12 showsFTIRthe FTispowerful-IRspectrumtooloftotheevaluateFT-IR spectrumthechangeof inSMNAfunction(A)alndgroupsSMNAafterafteradsorptionRhBadsorption[44].Figure(B)in the12showswavenumbertheFT-IRrangespectrum400–4000of thecm FT1.-IR spectrum of SMNA (A) and SMNA after RhB adsorption (B) inWethecanwavseenumberthattherangestrong400 –band4000 cmof−1stretching of –OH appear in the wavelength of about 3658.We96cmcan 1seeforthatSMNAthestrong(Figureband12A)of stretchingissimilar ofto -FTOH-IRapspectrumarintheofwavelengthsynthesizedofnanoabout 3658-AlO.96 (Figurecm−1for3SMNA).Figure(Figure12Aalso12A)showsissimilarthatFTto-IRFTspectra-IRspectrumofaluminaofsynthesizedafterSDS adsorptionnanoγ-Al2Oare3(Figuresimilar 3)to theFigureraw12Aone also(Figureshows3) Inthatadditive,FT-IRspecttherelativeofaluminaintensityafterof SDSasymmetadsorptionicalandaresymmetricalsiilartothestretchingawo of(Figure–CH23)– presented.Inadditive,at2920the.23relativend2850intensity.79cmof1asymmetricalappearedwithandverysymmetricalhighintensityretchingFT-IRofspectra–CH2– ofpresentedSMNA [at452920].This.23 confirmsand2850 that79cmthe−1 appearedhydrophobicwithintveractionyhigh occurredintensity onin FTtheIRsurfaspecetraofofaluminaSMNA In[45]addition,.ThisconfirmsthecharacteristicsthatthehydrophobicofSO2 interactionatabout1226occurred.73cmon1 theappearsufaceveryofstronglyaluminain.Inspectraaddition,of SDS while all bands disappear in the spectra of alumina [39] It suggests that SDS has a sulfate head Materials 2019, 12, x FOR PEER REVIEW the characteristics of SO42− at about 1226.73 cm−1 appear very strongly in spectra of SDS while all Materials 2019, 12, 450 11 of 15 bands disappear in the spectra of alumina [39] It suggests that SDS has a sulfate head group in contact with the surface of alumina nanoparticles via electrostatic attraction at high salt concentration (100 group in contact with the surface of alumina nanoparticles via electrostatic attraction at high salt mM NaCl) In other words, the modification of alumina was successful due to the presence of bilayer concentration (100 mM NaCl) In other words, the modification of alumina was successful due to the or admicelles, or both, on the surface of alumina o f presenceOnthe oneofbilhand,yer theoradmicelles,peakof–CHor2–both,presentedontheatsurface2061.90ofcmalumina.−1ofSMNA disappears in the spectra SMNAOn aftertheoneRhBhand,adsorption.thepeakTheof –CHpeaks2– inpresentedarangeatof2061.901591.27cmcm−1oftoSMNA1651.07disappearscm−1ofRhBinthe spectra of SMNA after RhB adsorption The peaks surfaceinrange of 1591.27 cm to 1651.07 cm of RhB characterizing for N–H bonds [46] appeared on the of SMNA The FT-IR spectra of SMNA characterizing for N–H bonds [46] appeared on the surface of SMNA The FT-IR spectra of SMNA after after RhB adsorption suggest that RhB mainly adsorb the surface of Al 2O3 by both electrostatic attractions RhBadsorption suggest aswell ashydrophobic thatRhBmainly interaction adsorb These thesurface results ofAl O by are2 3in good both electrostatic agreement with attractions RhB as adsorptionwellashydrophobicisothermin whichinteractionRhB.adsorptionTheseresultsontoareSMNAingood is agreementcontrolled bywithbothRhBelectrostaticadsorptionandisothermnon- in electrostaticwhichRhBinteractionsadsorption onto SMNA is controlled by both electrostatic and non-electrostatic interactions (A) (B) FigureFigure12 12.TheTheFT-FTIR-spectraIRspectraofSDSofSDSmodifiedmodifiednanonanoγ-Al-2AlO32(OA3) (andA)andSMNASMNAafterafterRhBRhBadsorptionadsorption(B).(B) 3.6 Comparison of Effectiveness of Surfactant-Modified Nano -Al O (SMNA) and Other Adsorbents for g 3.6 Comparison of Effectiveness of Surfactant-Modified Nano γ-Al 2O32(SMNA)3 and Other Adsorbents for RhB Removal and Other Nano g-Al2O3 RhB Removal and Other Nano γ-Al2O3 The synthesized nano -Al2 O3 is a novel adsorbent for RhB removal after surface modification The synthesized nano γ- Al2O3 is a novel adsorbent for RhB removal after surface modification with with SDS The removal efficiency is about 100% and very high adsorption capacity of 165 mg/g is SDS The removal efficiency is about 100% and very high adsorption capacity of 165 mg/g is achieved achieved at the optimum adsorption conditions We found that various scientific papers reported the at the optimum adsorption conditions We found that various scientific papers reported the removal removal of RhB using many kinds of adsorbents To our best knowledge, the removal of RhB using Materials 2019, 12, 450 SMNA has not been investigated Furthermore, the SMNA used in the present study achieved highest adsorption capacity and absolute removal efficiency compared to other adsorbents (Table 2) Table Adsorption capacity and removal efficiency of surfactant-modified nano -Al2O3 (SMNA) and other absorbents for removal of Rhodamine B (RhB) In order to emphasize the high performance of SMNA for dye removal, let us discuss the potential in term of removal of cationic dye, methylene blue (MTB) The previously published paper by Ali el al [51] successfully synthesized nano -Al2O3 by a precipitant method in the presence of nonionic surfactant Tween-80 This procedure required the ultrasonication and washing with ethanol before calcination at 550 C In our case, the nano -Al 2O3 was easily synthesized by titrating NaOH into Al(NO3)3 without any other chemicals The nano -Al 2O3 in this study achieved better morphology and much higher specific surface area than that in the paper [51] For cationic dye adsorption, MTB was removed with removal efficiency of 98% while the removal efficiency of RhB using SMNA in this paper reached to 100% for the similar initial concentration of cationic dye It implies that nano -Al 2O3 is an excellent adsorbent for MTB removal while SMNA is a novel adsorbent for RhB removal For removal of pollutants by adsorption technique, the regeneration cycles of adsorbent is necessary to evaluate reuse potential and stability of SMNA adsorbent Figure 13 shows the removal efficiency of OTC using SMA after four times of regeneration A small decrease in removal efficiency is observed but it is insignificant The RhB removal efficiency is still about 87% after four reused times The error bars show that the standard deviations xFOR SMNA four reused PEERREVIEW time experiments are very small, demonstrating Materials2019,12, isnot only a novel adsorbent but also applicable for regeneration 13 of 16 Removal Efficiency (%) that after Number of regeneration Figure1313 RemovalefficiencyefficiencyofofRhBusingSMNAafterfoururregenerations Errrorbarsshows tandard deviationofofthreeereplicates Conclusions We successfully synthesized γ-Al 2O3 nanoparticles and modified the surface of γ-Al 2O3 by adsorption of anionic surfactant sodium dodecyl sulfate (SDS) The nano γ-Al 2O3 has a mean particle size distribution of 40 nm while the functional surface groups of nano γ-Al 2O3 was confirmed by Fourier transform infrared spectroscopy (FT-IR) A high specific surface area of nano γ-Al2O3 was Materials 2019, 12, 450 Conclusions We successfully synthesized -Al2O3 nanoparticles and modified the surface of -Al 2O3 by adsorption of anionic surfactant sodium dodecyl sulfate (SDS) The nano -Al 2O3 has a mean particle size distribution of 40 nm while the functional surface groups of nano -Al 2O3 was confirmed by Fourier transform infrared spectroscopy (FT-IR) A high specific surface area of nano -Al 2O3 was found to by 221.3 m /g The SDS adsorption onto nano -Al 2O3 was done at 100 mM NaCl forming bilayer of admicelles to enhance the removal of Rhodamine B dye Under optimum adsorption conditions of RhB onto SDS modified nanoalumina (SMNA) including contact time 120 min, pH 4, and adsorbent dosage of mg/mL, the removal efficiency reached 100% and adsorption capacity was 165.0 mg/g After reuse four times, the removal efficiency of RhB using SMNA was higher than 86% At different NaCl concentration, adsorption isotherms of RhB onto SMNA were in good agreement with the two-step model Adsorption mechanisms of RhB onto SMNA were electrostatic attraction between cationic dye molecules and negatively charged SMNA surface at low RhB concentrations, while hydrophobic interaction was important controlled adsorption at high RhB concentrations We indicate that SMNA is a smart nanomaterial for RhB removal from water environment Author Contributions: Conceptualization, T.D.P and T.S.L.; Methodology, T.D.P and T.S.L.; Software, T.D.P., N.T.N; Validation, T.H.H, T.S.L and T.D.P; Formal Analysis, T.P.M.C, N.T.N, T.L.V, T.H.D, L.C.D and H.L.N.; Investigation, T.D.P and T.S.L; Resources, T.P.M.C, N.T.N.; Data Curation, T.P.M.C, N.T.N, T.L.V, T.H.D, L.C.D and H.L.N; Writing-Original Draft Preparation, T.D.P; Writing-Review & Editing, T.D.P and T.S;L; Visualization, T.H.H and T.S.L.; Supervision, T.D.P and T.S.L.; Project Administration, T.D.P.; Funding Acquisition, T.D.P All authors reviewed and approved the manuscript Funding: This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 104.05-2016.17 Acknowledgments: The authors would like to thank Mr Atsushi Yamaguchi at University of Tsukuba for kind help in TEM measurements Conflicts of Interest: The authors declare no conflict of interest References Adak, A.; Bandyopadhyay, M.; Pal, A Removal of crystal violet dye from 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Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/) ... sử dụng linh hoạt Trên sở đó, chúng tơi lựa chọn đề tài: ? ?Ứng dụng phương pháp phân tích quang phổ đại nghiên cứu đặc tính hấp phụ bề mặt thuốc nhuộm mang điện vật liệu nano nhơm oxit biến tính? ??...ĐẠI HỌC QUỐC GIA HÀ NỘI TRƯỜNG ĐẠI HỌC KHOA HỌC TỰ NHIÊN CHU THỊ PHƯƠNG MINH ỨNG DỤNG CÁC PHƯƠNG PHÁP PHÂN TÍCH QUANG PHỔ HIỆN ĐẠI NGHIÊN CỨU ĐẶC TÍNH HẤP PHỤ BỀ MẶT CỦA THUỐC NHUỘM MANG ĐIỆN... tiêu nghiên cứu tổng hợp nano Al2O3 với hai pha tinh thể gamma (γ) anpha (α) Al 2O3 Ứng dụng phương pháp phân tích vật lý đại nghiên cứu đặc tính vật liệu tổng hợp đặc tính hấp phụ, chế hấp phụ thuốc