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 : 8440112.03 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 hồn thành luận văn Em xin chân thành cảm ơn thầy mơn Hóa phân tích, anh, chị, em bạn phịng thí nghiệm Hóa phân tích ln nhiệt tình giúp đỡ em suốt 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 6000C 41 3.2.2 Vật liệu nung 12000C 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 Tiếng Anh Tiếng Việt BET Brunauer - Emmett - Teller Phương pháp BET CHĐBM Surfactant Chất hoạt động bề mặt HPLC High Performance Liquid Chromatography Sắc ký lỏng hiệu cao LOD Limit Of Detection Giới hạn phát LOQ Limit Of Quantity Giới hạn định lượng MB Methylene Blue Xanh metyelen RhB Rhodamine B Rhodamin B SDS Sodium Dodecyl Sulfate Natri dodecyl sufphat SEM Scanning Electron Microscope Kính hiển vi điện tử quét Transmission Electron Kính hiển vi điện tử Microscope truyền qua TEM UV-Vis Ultral Violet – Visible Phổ hấp phụ phân tử vùng tử ngoại, khả kiến 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-Al2O3 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 6000C 42 Hình 3.5 Phổ FT-IR vật liệu nano Al2O3 nung 6000C 42 Hình 3.6 Ảnh TEM vật liệu nano Al2O3 nung 6000C 43 Hình 3.7 Đường đẳng nhiệt hấp phụ N2 vật liệu nano Al2O3 nung 6000C 43 Hình 3.8 Phổ XRD vật liệu nano Al2O3 nung 12000C 44 Hình 3.9 Phổ FT-IR vật liệu nano Al2O3 nung 12000C 44 Hình 3.10 Ảnh TEM vật liệu nano Al2O3 nung 12000C 45 Hình 3.11 Đường đẳng nhiệt hấp phụ N2 vật liệu nano Al2O3 nung 12000C 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 Al2O3 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 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 biến tính khơng biến tính SDS A Mẫu M1; B Mẫu M2 M2 thêm 10-5M RhB; C Mẫu M3 M3 thêm 10-5M RhB……………………………………… 66 MỞ ĐẦU Công 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 Al2O3 có nhiều pha cấu trúc khác như: α, β, γ, η, θ, κ, and χ [34] Vật liệu Al2O3 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) materials Article Synthesis, Characterization, and Modification of Alumina Nanoparticles for Cationic Dye Removal Thi Phuong Minh Chu , Ngoc Trung Nguyen , Thi Lan Vu , Thi Huong Dao , Lan Chi Dinh , Hai Long Nguyen , Thu Ha Hoang , Thanh Son Le 1, * and Tien Duc Pham 1, * * Faculty of Chemistry, VNU-University of Science, Vietnam National University, Hanoi, 19 Le Thanh Tong, Hoan Kiem, Hanoi 10000, Vietnam; minhxndpvp@gmail.com (T.P.M.C.); trungnn.hus@gmail.com (N.T.N.); vuthilan_t59@hus.edu.vn (T.L.V.); daohuongk56a1993@gmail.com (T.H.D.) HUS High School for Gifted Students, VNU-University of Science, Vietnam National University, Hanoi, 182 Luong The Vinh, Thanh Xuan, Hanoi 10000, Vietnam; dinhchi55@gmail.com (L.C.D.); ceonguyenhailong@gmail.com (H.L.N.) High School of Education Sciences, University of Education, Vietnam National University, Hanoi, Kieu Mai, Phuc Dien, Bac Tu Liem, Hanoi 10000, Vietnam; hoangthuha0105@yahoo.com Correspondence: sonlt@vnu.edu.vn (T.S.L.); tienduchphn@gmail.com or tienducpham@hus.edu.vn (T.D.P.); Tel.: +84-243-825-3503 (T.S.L & T.D.P.); Fax: +84-243-824-1140 (T.S.L & T.D.P.) Received: 27 December 2018; Accepted: 30 January 2019; Published: February 2019 Abstract: In the present study, alumina nanoparticles (nano-alumina) which were successfully fabricated by solvothermal method, were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Transmission Electron Microscopy (TEM), and Brunauer–Emmett–Teller (BET) methods The removal of cationic dye, Rhodamine B (RhB), through adsorption method using synthesized nano-alumina with surface modification by anionic surfactant was also investigated An anionic surfactant, sodium dodecyl sulfate (SDS) was used to modify nano-alumina surface at low pH and high ionic strength increased the removal efficiency of RhB significantly The optimum adsorption conditions of contact time, pH, and adsorbent dosage for RhB removal using SDS modified nano-alumina (SMNA) were found to be 120 min, pH 4, and mg/mL respectively The RhB removal using SMNA reached a very high removal efficiency of 100% After four times regeneration of adsorbent, the removal efficiency of RhB using SMNA was still higher than 86% Adsorption isotherms of RhB onto SMNA at different salt concentrations were fitted well by a two-step model A very high adsorption capacity of RhB onto SMNA of 165 mg/g was achieved Adsorption mechanisms of RhB onto SMNA were discussed on the basis of the changes in surface modifications, the change in surface charges and adsorption isotherms Keywords: Alumina nanoparticles; Rhodamine B; SDS; Adsorption isotherm; Two-step model Introduction Removal of organic dye from a water environment is important in environmental remediation Organic dye is one kind of popular pollutant that is can released from many industrial activities related to cosmetic, paint, pigments, textile, paper, etc [1] Almost charged organic dyes (ionic dye) are colored and highly toxic [2] Nowadays, numerous techniques have been used ionic dye treatment like adsorption [3–6], degradation using photocatalyst [7,8], electrochemical oxidation [9,10], coagulation/flocculation [11], and biodegradation [12] Among them, adsorption is one of the most effective methods for ionic dye treatment Adsorption technique also is suitable for the developing countries by using low cost adsorbents [13,14] Metal oxides are main components of natural soil that are a cheap adsorbent Materials 2019, 12, 450; doi:10.3390/ma12030450 www.mdpi.com/journal/materials Materials 2019, 12, 450 of 15 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 α, β, γ, η, θ, κ, and χ [15] It is found that gamma alumina (γ-Al2 O3 ) has high specific surface area, especially nano γ-Al2 O3 , which is powerful enough to be an effective adsorbent for ionic dye Nevertheless, γ-Al2 O3 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 γ-Al2 O3 (SMNA) after surface modification of γ-Al2 O3 with SDS solution Some effective parameters for RhB removal using after characterization of γ-Al2 O3 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 γ-Al2 O3 after adsorption by ζ 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 ·9H2 O 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 MΩ·cm was used in preparing all aqueous solution Materials 2019, 12, 450 of 15 Materials 2019, 12, x FOR PEER REVIEW of 16 (A) (B) (A) and sodium sodium dodecyl dodecyl sulfate sulfate (SDS) (SDS) (B) (B) Figure Chemical structures of Rhodamine B (RhB) (A) 2.2 2.2 Fabrication Fabrication of of Alumina Alumina Nanoparticles Nanoparticles Alumina were fabricated according to to previous previous study study with with aa modification modification [33] [33] Alumina nanoparticles nanoparticles were fabricated according The and NaOH NaOH were were used used to The solutions solutions of of Al(NO Al(NO33))33 and to synthesize synthesize alumina alumina The The 4M 4M NaOH NaOH solution solution was was prepared by dissolving 12.2449 g NaOH pellets in 75.0 mL ultrapure water A solution of M Al(NO )3 prepared by dissolving 12.2449 g NaOH pellets in 75.0 mL ultrapure water A solution of 3M was prepared by dissolving 37.50 g of Al(NO ) · 9H O in 100.0 mL ultrapure water Aluminum 3of Al(NO Al(NO3)3 was prepared by dissolving 37.50 g 3)3·9H2O in 100.0 mL ultrapure water hydroxide was obtained by slowly adding M Al(NO ) with M NaOH in4aM plastic vessel White 3 Aluminum hydroxide was obtained by slowly adding M Al(NO 3)3 with 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 6000arpm (Digisytem, Taiwan) After that, the samples were dried thermalwere oven dried at 80 ◦in C for 24 h using centrifuge at 6000 rpm (Digisytem, Taiwan) After that, theinsamples 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 atodessicator Finally, alumina particles were stored in a polyethylene container before cooling room temperature in a dessicator Finally, alumina particles were stored in a polyethylene container 2.3 Characterization Methods 2.3 Characterization Methods The synthesized alumina 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 ζ 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 CuKα radiation (λ = 1.5418 Å) The XRD pattern was recorded in a range of 20–80◦ (2θ) 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 of spectrometer (Shimadzu, Kyoto, Japan) The FTIR spectra of nano-alumina particles, SDS modified cm−1 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 GA, USA) adsorption isotherm surface of nitrogen ) was BET method was 3000, used Norcross, using a surface area The and pore size Analyzer area (N analyzer ◦ C in 90 The particle size distribution of conducted in a mL cell with outgas condition of 150 Micromerities (TriStar 3000, Norcross, GA, USA) The adsorption isotherm of nitrogen (N2) was synthesized which wascondition evaluatedofby TEM, by using (H7650, conducted innano-alumina a mL cell with outgas 150 °C inwas 90 performed The particle sizeHitachi distribution of Tokyo, Japan) with Olympus camera (Veleta 2000 × 2000) The operating conditions were accelerating synthesized nano-alumina which was evaluated by TEM, was performed by using Hitachi (H7650, condition of 80with kV and exposure time(Veleta of s 2000 × 2000) The operating conditions were accelerating Tokyo, Japan) Olympus camera The surface charge of synthesized SMNA and SMNA after RhB adsorption in condition of 80 kV and exposure time ofnano-alumina, sec mMThe NaCl, at pH were examined by using Zetasizer Nano ZSSMNA (Malvern, surface charge of synthesized nano-alumina, SMNA and afterWorcestershire, RhB adsorptionUK) 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 Scattering also conducted Zetasizer Nano ZS by applying backscattering (173◦ Dynamic Light (DLS)with for particle size characterization in the solutions ofdetection nano-alumina and SMNA was also conducted with Zetasizer Nano ZS by applying backscattering detection (173° Materials 2019, 12, 450 of 15 detection optics) at 22 ◦ C A cleaned plastic cuvette containing mL of the sample was used in each DLS measurement The zeta (ζ) potential was calculated from electrophoretic mobility using Smoluchowski’s equation [34] ue η ζ= (1) ε rs ε where ζ is the ζ potential (mV), ue is the electrophoretic mobility (µm cm/sV), η is the dynamic viscosity of the liquid (mPa·s), εrs is the relative permittivity constant of the electrolyte solution, and ε0 is the electric permittivity of the vacuum (8.854 × 10−12 F/m) 2.4 Adsorption Studies 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 ·M−1 that is very good agreement with the value of 106,000 cm−1 ·M−1 for standard RhB The adsorption capacities of SDS onto nano-alumina and RhB onto SMNA were determined by the following equation Ci − Ce Γ= × M × 1000 (2) m where Γ 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 (%) = Ci − Ce × 100% Ci (3) 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: Γ= Γ∞ k1 C n + k C n−1 + k C (1 + k C n−1 ) (4) where Γ is the amount of adsorbed RhB at concentration C, Γ∞ 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 of 15 Materials xxFOR Results and12, Discussion Materials2019, 2019, 12, FORPEER PEERREVIEW REVIEW 55 of of 16 16 Characterization Synthesized Alumina Nanoparticles 3.1.3.1 Characterization ofofof Synthesized 3.1 Characterization SynthesizedAlumina AluminaNanoparticles Nanoparticles The XRD pattern the alumina nanoparticles is shown The XRD pattern of thealumina aluminananoparticles nanoparticles obtained obtained by by the solvothermal method is is shown The XRD pattern ofof the obtained bythe thesolvothermal solvothermalmethod method shown ◦ ◦ The sharp peaks with high intensity crystalline of in Figure Figure The sharppeaks peakswith withhigh highintensity intensity at at 2θ 2θ === 38° 38° and and 67° indicate the high crystalline of of in in Figure 2 The sharp 38 and67° 67 indicate indicatethe thehigh high crystalline ◦ and alumina The gamma phase of alumina was at 46° alumina The gammaphase phaseof ofalumina aluminawas was confirmed confirmed due due to the presence ofofthe the peaks atat 46° and alumina The gamma confirmed dueto tothe thepresence presenceof thepeaks peaks 46and [35] 61° [35] 61◦61° [35] Faculty Facultyof ofChemistry, Chemistry,HUS, HUS,VNU, VNU,D8 D8ADVANCE-Bruker ADVANCE-Bruker 800L1 800L1 600 600 500 500 Lin (Cps) (Cps) Lin 400 400 d=1.976 d=1.976 d=2.393 d=2.393 d=1.526 d=1.526 d=2.285 d=2.285 d=2.798 d=2.798 200 200 d=1.399 d=1.399 300 300 100 100 00 20 20 30 30 4040 5050 6060 7070 88 2-Theta 2-Theta Scale Scale File: File:HuongPT HuongPT800L1.raw 800L1.raw- -Type: Type:2Th/Th 2Th/Thlocked locked- -Start: Start:20.000 20.000? ?- -End: End:80.000 80.000?-?-Step: Step:0.030 0.030? ?- -Step Steptime: time:0.3 0.3s s- -Temp.: Temp.:2525癈癈(Room) (Room)- -Time TimeStarted: Started:1313s s- -2-Theta: 2-Theta:20.000 20.000? ?- -Theta: Theta:10.000 10.000? ?- -Chi: Chi:0.00 0.00? ?- -Phi: Phi:0.00 0.00? ?- -XX 00-050-0741 00-050-0741(I)(I)- -Aluminum AluminumOxide Oxide- -gamma-Al2O3 gamma-Al2O3- -Y:Y:100.00 100.00%%- -d dx xby: by:1.1.- -WL: WL:1.5406 1.5406- -Cubic Cubic- -a a7.93900 7.93900- -b b7.93900 7.93900- -c c7.93900 7.93900- -alpha alpha90.000 90.000- -beta beta90.000 90.000- -gamma gamma90.000 90.000- -Face-centered Face-centered- -Fd-3m Fd-3m(227) (227)- -11 11- -500.3 500.3 Figure 2.2.2 XRD γ-Al O333nanoparticles nanoparticles Figure XRD pattern of synthesized Figure XRDpattern patternof ofsynthesized synthesizedγ-Al γ-Al222O O nanoparticles The FT-IR spectra ofof the Figure indicatedthat thatthe thepeaks peaks appearing The FT-IR spectra the nano-alumina shown appearing at The FT-IR spectra of thenano-alumina nano-aluminashown shown in in Figure Figure 333indicated indicated that the peaks appearing at at −1 are assigned 3657.04, 3550.95, and 3622.32 cm assignedfor for–OH –OHstretching stretchingvibration vibration aluminum hydr(oxide) 3657.04, 3550.95, and 3622.32 cm in aluminum hydr(oxide) 3657.04, 3550.95, and 3622.32 cm−1−1are for –OH stretching vibration inin aluminum hydr(oxide) − −1,1 structure The peaks appeared 1031.92, 520.78, and 426.27 to Al-O bending structure The peaks appeared corresponding Al-O bending structure The peaks appearedatat at1031.92, 1031.92,520.78, 520.78,and and426.27 426.27 cm cm−1 , ,corresponding corresponding toto Al-O bending −1 −1 −1 − − −1 −1 −1−1 vibration of Al-OH group [36] The broader peaks between 1000 cm , 981.77 cm , and 520.78 vibration of Al-OH group [36] The broader peaks between1000 1000cm cm , 981.77 981.77 cm cm , ,and cm vibration of Al-OH group [36] The broader peaks between and520.78 520.78cm cm confirmed the bending vibration Al-O bond [35] confirmed the bending vibrationofof ofAl-O Al-Obond bond[35] [35] confirmed the bending vibration Figure 3.3.3 The γ-Al O333nanoparticles nanoparticles Figure The FT-IR spectra of synthesized Figure TheFT-IR FT-IRspectra spectraof ofsynthesized synthesizedγ-Al γ-Al22O O nanoparticles Transmission electron performed tocharacterize characterizethe themorphology morphology and Transmission electron microscopy (TEM) and Transmission electronmicroscopy microscopy(TEM) (TEM) was was performed performed to to characterize the morphology and particle size ofof alumina TEM image shownin inFigure Figure444shows shows that alumina particle size alumina powers (Figure 4) that alumina particle size of aluminapowers powers(Figure (Figure4) 4) The The TEM TEM image image shown shown in Figure shows that alumina particles particlesare aresphered spheredones oneswith withthe thesize sizein inthe therange rangeof of30–40 30–40nm, nm,indicating indicatingthat thatsynthesized synthesizedalumina alumina Materials 2019, 12, 450 of 15 Materials 2019, 12, x FOR PEER REVIEW of 16 Materials 12, x FOR PEERwith REVIEW of 16 particles are2019, sphered ones the size in the range of 30–40 nm, indicating that synthesized6 alumina is aisnanosized powder TheThe DLS datadata (not shown in detail) indicates that the Z-average indicates thathydrodynamic thehydrodynamic hydrodynamic isa ananosized nanosizedpowder powder The DLS DLS data (not (not shown shown in in detail) detail) indicates that the Z-Zdiameter of nano-alumina was about 410–450nm at pH 4atthat much higher than the particle size of average diameter of nano-alumina was about 410–450 nm 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 nano-alumina due to thedue aggregation of nano-alumina in NaClin concentration The Z-average diameter size totothe NaCl concentration concentration TheZ-average Z-average sizeofofnano-alumina nano-aluminadue theaggregation aggregation of of nano-alumina nano-alumina in NaCl The of diameter SMNA was about 924–958 nm, indicating that the formation of SMNA aggregates in the presence the formation formation of ofSMNA SMNAaggregates aggregatesininthe the of diameterofofSMNA SMNAwas wasabout about924–958 924–958nm, nm, indicating indicating that that the presence ofofSDS aggregation of SMNA did induce significantly significantly toRhB RhBadsorption adsorption SDS However, theHowever, aggregation SMNA did induce significantly to RhB adsorption presence SDS However,the theof aggregation ofnot SMNA did not not induce to 200 200 nm nm Figure TEMimage imageof ofsynthesized synthesized γ-Al γ-Al Figure TEM image of synthesized OO33 nanoparticles Figure 4.4.4 TEM γ-Al222O nanoparticles 3nanoparticles The specific surface area thenano nanoγ-Al γ-Al22O O3 by BET was from N adsorption isotherm The specific surface area ofofof the byBET BETwas wascalculated calculated from isotherm The specific surface area the nano γ-Al calculated from N2N adsorption isotherm 33 by adsorption 2/g (Figure 5) and found to be around 221.3 m and found totobebearound (Figure5) 5) and found around221.3 221.3mm2/g /g (Figure Volume Adsorbed Volume Adsorbedcc/g(STP) cc/g(STP) 100 100 80 80 60 60 40 40 20 20 0 0 0.2 0.4 0.6 0.8 0.2 Relative 0.4 Pressure 0.6 P /P 0.8 s o 1 Relative Pressure Ps/Po Figure Adsorption isotherm of N2 onto synthesized nano-alumina Figure5.5.Adsorption Adsorption isotherm isotherm of N22 onto Figure ontosynthesized synthesizednano-alumina nano-alumina The specific surface area in our work is similar to the results of alumina published by Khataee specific surface areasynthesized work is similar the results of published alumina published The specific surface inin ourour work is similar to3 has the to results of alumina bygood Khataee etThe al [37] It implies thatarea the nano γ-Al 2O high specific surface area that is for by Khataee et al [37] It implies synthesized nano γ-Al has high specific that etadsorptive al [37] It implies that the that synthesized nano 2O high specific surface areasurface that is area good for is removal of ionic dye.the However, in γ-Al order to3 has enhance removal efficiency of RhB using O3the nano γ-Alremoval 2O3, theremoval surface modification is needed because theremoval electrostatic interaction is more adsorptive of ioniccharge dye However, in order toorder enhance the efficiency of RhB using good for adsorptive of ionic dye However, in to enhance the removal efficiency of RhB important ionic dyesurface adsorption [1] modification nano γ-Alγ-Al 2Ofor 3, the chargecharge modification is needed becausebecause the electrostatic interaction is more is using nano , the is needed the electrostatic interaction O3surface important for ionic dye adsorption [1] [1] more important for ionic dye adsorption 3.2 Modification of Synthesized Nano-Alumina by SDS Adsorption Modification Synthesized Nano-Alumina 3.2.3.2 Modification ofofSynthesized Nano-Alumina by SDS Adsorption The synthesized nano γ-Al 2O3 was modified byAdsorption SDS pre-adsorption of at two salt concentration atThe pH 4.synthesized At pH 4, thenano surface charge of γ-Al 2O3 is highly positive due to theof point of zero charge 8.5 of The nanoγ-Al γ-Al 2O3 was modified by pre-adsorption salt concentration synthesized by SDS SDS pre-adsorption ofatattwo two salt concentration 2O was modified alumina [16] Atthe pH < 4, the dissolution of alumina could occur sotothat the characteristics may8.5beof at pH At pH 4, surface charge of γ-Al O is highly positive due the point of zero charge at pH At pH 4, the surface charge of γ-Al2 O3 is highly positive due to the point of zero charge changed[16] [38].At Figure shows that adsorption SDS onto nanooccur γ-Al2O grew up with an increasemay of saltbe 4, the dissolution of of alumina could so3 occur that the 8.5alumina of alumina [16].pHAt< pH < 4, the dissolution of alumina could so characteristics 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].6 Figure shows that adsorption of SDS onto nano γ-Al2 O3 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, x FOR PEER REVIEW Materials 2019, 12,12, 450 77 of of 16 15 SDS onto activated beads of Al2O3 in which the electrostatic attraction is main driving force [39] In of 16 this case, SDSfrom adsorption γ-Al2O3of is anionic controlled both electrostatic and ishydrophobic increase of salt 10 to 100onto mM.nano Adsorption SDSby onto nano γ-Al2 O3 here different to interactions The maximum adsorption capacity was obtained at 10 mM NaCl when SDS adsorption of SDS onto activated beads of Al O in which the electrostatic attraction is main driving SDS onto activated beads of Al2O3 in which the [39] In 3electrostatic attraction is main driving force the concentration was greater than 0.01 M It should be noted that the micelles are surely formed in the force [39] SDS In this case, SDSonto adsorption onto γ-Al2 O3by is both controlled by bothand electrostatic and this case, adsorption nano γ-Al 2O3 nano is controlled electrostatic hydrophobic solution with 0.01 M SDS its concentration is much higher thewhen critical micelle hydrophobic interactions Thebecause maximum adsorption capacity wasthe obtained 10 mM NaCl when the interactions The maximum adsorption capacity was obtained at 10 mMatthan NaCl the SDS concentration (CMC) Thethan admicelle of ItSDS completely γ-Al 2formed O3 surface that concentration was greater 0.01 0.01 M should be noted that the areon surely in the SDS concentration was greater than M Itmolecules should beare noted thatmicelles theformed micelles are surely formed in the charge reversal is occurred The plateau adsorption capacity of SDS onto γ-Al O reaches to 450 solution with 0.010.01 MM SDS because itsits concentration is is much the solution with SDS because concentration muchthe thehigher higherthan thanthe thecritical criticalmicelle micelle mg/g that is similar theadmicelle SDS adsorption onto alumina the previous paper [40] the presence concentration ofofSDS molecules arein completely formed on γ-Al 2O3 surface that concentration (CMC).toThe The admicelle SDS molecules are completely formed onWith γ-Al O surface of a high number of admicelles on γ-Al 2O3,adsorption the removal of cationic dye RhB using highly negative the charge reversal is occurred The plateau capacity of SDS onto γ-Al O reaches to 450 that the charge reversal is occurred The plateau adsorption capacity of SDS onto γ-Al2 O3 reaches charge γ-Al O particles can increase significantly Therefore, the adsorption of initial 0.01 M mg/g is similar to the SDS adsorption onto alumina in the previous paper [40].paper With [40] the presence to 450 that mg/g that is similar to the SDS adsorption onto alumina in the previous WithSDS the onto γ-Al O was fixed to modify the γ-Al O surface that was carried out at 100 mM NaCl (pH 4) of a highofnumber admicelles on γ-Al2O 3, the of cationic dye RhB using highly negative presence a high of number of admicelles on γ-Alremoval O , the removal of cationic dye RhB using highly charge γ-Al 2O3 γ-Al particles can increase significantly Therefore, the adsorption of initial 0.01 M0.01 SDSM negative charge can increase significantly Therefore, the adsorption of initial O3 particles 500 ontoonto γ-Alγ-Al 2O3 was fixed to modify the γ-Al2O3 surface that was carried out at 100 mM NaCl (pH 4) SDS O3 was fixed to modify the γ-Al2 O3 surface that was carried out at 100 mM NaCl (pH 4) Materials 2019, 12, x FOR PEER REVIEW ΓSDS (mg/g) Γ (mg/g) 400 500 300 400 SDS 200 300 100mM 10mM 100 200 100mM 1000 0.000 0.002 0.004 0.006 10mM 0.008 CSDS (mo/L) 0.004 0.006 0.008concentrations Figure Adsorption0.000 of SDS onto 0.002 synthesized nano-alumina at different NaCl CSDS (mo/L) 3.3 Adsorptive of RhB Using (NA) without andconcentrations with SDS Figure Adsorption of SDS ontoSynthesized synthesizedNano-Alumina nano-aluminaat atdifferent different NaCl concentrations Figure6 6.Removal Adsorption synthesized nano-alumina NaCl 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 The removal of RhB using synthesized nano γ-Al O3 isthe strongly influenced by pH because pH 3.3.1 Effect of pH highly affects to the charging behavior of nano γ-Al2O32 and desorption of SDS [30,32] The effects Removal Efficiency (%) (%) Removal Efficiency highly affects adsorptive to the charging behavior γ-Al desorption of SDS [30,32] Thewith effects of O3 and the nano of pH of of RBnano using synthesized γ-Al 2O3 without and SDS The on removal of RhBremoval using synthesized nano γ-Al2O3 is strongly influenced by pH because pH pH on adsorptive removal of RB using synthesized nano γ-Al O without and with SDS modification modification were in the pH rangeγ-Al 3–10 mM with contact of 180 and highly affects to the conducted charging behavior of nano 2Oin and the2NaCl desorption of SDStime [30,32] Themin effects were conducted in the pH range 3–10 in mM NaCl with contact time of 180 and adsorbent dosage of mg/mL ofadsorbent pH on adsorptive removal(Figure of RB7).using synthesized nano γ-Al2O3 without and with SDS dosage of mg/mL (Figure 7) modification were conducted in the pH range 3–10 in mM NaCl with contact time of 180 and adsorbent dosage of mg/mL (Figure 7) 100 80 100 60 80 40 60 20 40 with SDS 200 with SDS without SDS without SDS 10 12 pH 10 12 Figure Theeffect effectofofpH pHon onRhB RhBremoval removalusing usingsynthesized synthesizednano nanoγ-Al γ-Al22O O33 without SDS modification Figure 7.The pH −6−6 M M and and with with SDS SDS modification (Ci (RhB) == 10 (RhB) (Ci(Ci (RhB) = =1010 10−4−4M) M) 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 of 16 of 15 Figure indicates that the removal efficiency decreased with increasing pH from to 10 for synthesized γ-Althat 2O3 without while the removal reduced from pH to 10 At pH 3, the Figure nano indicates the removal efficiency decreased with increasing pH from to 10 for dissolution of alumina occurred so that the property may bepH changed When solution synthesized nano γ-Al2 Ois without while the removal reduced from to 10.[41] At pH 3, thepH dissolution increases, positive charge nano γ-Al2Omay is decreased whereas RhB is cationic dye in such range of aluminathe is occurred so thatofthe property 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 γ-Al2 O3 is decreased whereas RhB is cationic dye in such range of pH For SDS negativelynano charge modified alumina is occurred [32] It should be noted that the initial modified γ-AlSDS O3 (SMNA), the SDS desorption may be enhanced so that the less negatively −4 M RhB using SMNA is greater than that for the case without SDS (10−6 M) concentration of 10 charge SDS modified alumina is occurred [32] It should be noted that the initial concentration of Nevertheless, the SMNA removal efficiency RhB SMNA is SDS always than that using −4 M RhB using M) Nevertheless, 10 is greater thanofthat forusing the case without (10−higher the synthesized nano γ-Al 2O3 It implies that the removal efficiency increased significantly using removal efficiency of RhB using SMNA is always higher than that using synthesized nano γ-Al2 O3 nanothe γ-Al 2O3 (SMNA) compared without SDS modification Maximum removal efficiency Itmodified implies that removal efficiency increased significantly using modified nano γ-Al2 O3 (SMNA) achieved 97.7% at pH for SMNA At the sameremoval RhB concentration of 10−4 M, the at removal efficiency compared without SDS 4modification Maximum efficiency achieved 97.7% 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 3.3.2 Effect Effect of of Adsorption Adsorption Time Time 3.3.2 Adsorption time time affects affectsthe thecompleteness completenessof ofadsorption adsorptionequilibration equilibration The The effect effect of of contact contact time time Adsorption on the the adsorptive adsorptive removal of RhB using with and SDS from 1010 to on using synthesized synthesizednano nanoγ-Al γ-Al2O andwithout without SDS from 2O with 240 is presented in Figure Figure shows that the adsorption reaches equilibrium 90 and to 240 is presented in Figure Figure shows that the adsorption reaches equilibrium 90 180 180 minmin for for SMNA andand without SDS modification, onto and SMNA without SDS modification,respectively respectively.The Theadsorption adsorption time time of RhB onto nano γ-Al γ-Al22O33 with SDS modification is much faster than that without without SDS SDS It It is is also also faster faster than than RhB RhB nano adsorption on traditional activated carbon (120 min) [42] The adsorption time of 90 is fixed for adsorption on traditional activated carbon (120 min) [42] The adsorption time of 90 is fixed for RhBadsorption adsorptiononto ontoSMNA SMNAand and180 180min minisisselected selectedfor forone oneonto ontosynthesized synthesizednano nanoγ-Al γ-Al22O O33 RhB Removal Efficiency (%) 100 80 60 40 20 with SDS without SDS 0 40 80 120 160 200 240 Contact time (min) 280 Figure Figure 8.8 The effect of contact contact time time on on RhB RhB removal removal using using synthesized synthesizednano nanoγ-Al γ-Al2 2OO33 without without SDS SDS ◦ − −4−4M) modification 2525 ± ±2 2C, = =1010−6M = =1010 i (RhB) M and andwith withSDS SDSmodification modification(C(C i (RhB) M) modification(Temperature (Temperature °C,CiC(RhB) i (RhB) 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 γ-Al2 O3 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 γ-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 γ-Al2 O3 required much smaller amount When adsorbent dosage, while SDS modified nano γ-Al2O3 required much smaller amount When using using SMNA, the amount of adsorbent is economical comparing with nano γ-Al2 O3 without SDS SMNA, the amount of adsorbent is economical comparing with nano γ-Al2O3 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 γ-Al2 O3 without SDS, we only focus on the adsorption mechanisms of RhB onto SMNA in the next section Materials 2019, 12, x FOR PEER REVIEW of 16 100 Removal (%) Efficiency (%) Removal Efficiency Materials 2019, 12, 450 Materials 2019, 12, x FOR PEER REVIEW of 15 of 16 80 100 60 80 40 60 20 with SDS without SDS 40 20 10 20 30 with SDS Adsorbent dosage (mg/mL) without SDS 40 Figure The effect of 0adsorbent dosage on RhB removal using synthesized nano γ-Al2O3 without (Ci (RhB) SDS modification (Ci (RhB) 0= 10−6 M) and with 10 SDS modification 20 30 = 10−4 M) 40 Adsorbent dosage (mg/mL) Because the removal efficiency of RhB using SMNA is much higher than nano γ-Al2O3 without Figure The effect ofadsorbent adsorbent dosage onRhB RhBremoval removal usingsynthesized synthesized nano γ-Al 2O without 9.9 The effect of dosage on nano γ-Al 2O 33 without SDS,Figure we only focus on the adsorption mechanisms of RhBusing onto SMNA in the next section −6 M) −6 M) SDS with modification (Ci (RhB) 10−4 M) (Cii ((RhB) RhB) ==1010 andand with SDSSDS modification (Ci (RhB) = 10−4 = M) SDS modification modification(C 3.4 Adsorption Adsorption Isotherms Isotherms of of RhB RhB on on SDS SDS Modified Modified Nano-Alumina Nano-Alumina (SMNA) (SMNA) 3.4 Because the removal efficiency of RhB using SMNA is much higher than nano γ-Al2O3 without ΓRhB (mg/g) ΓRhB (mg/g) The effectfocus of ionic ionic strength on of onto SDS modified nano 2O3 (SMNA) is SDS,The we only on the adsorption mechanisms of RhB onto SMNA in the nextγ-Al section effect of strength on adsorption adsorption of RhB RhB onto SDS modified nano γ-Al O3 (SMNA) 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 increasing NaCl concentration at low low RhB RhB concentration concentration Nevertheless, at high high RhB RhB concentration concentration 3.4 Adsorption Isotherms of RhB on SDS Modified Nano-Alumina (SMNA) at increasing NaCl concentration at Nevertheless, adsorption increases with an increase of ionic strength At low RhB adsorption, an increase in salt salt adsorption increases with an increase of ionic strength At low adsorption, an increase in The effect of ionic strength on adsorption of RhB onto SDSRhB modified nano γ-Al 2O3 (SMNA) is + on the negatively charge layer of SMNA, concentration increased the number of cation Na + concentration increased theisotherms number of(Figure cation Na charge layer SMNA, decreasing clearly observed on the 10) on Atthe pHnegatively 4, the adsorption of 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 thecharge positive charge ofnegatively RhB and negatively charge ofis alumina is significantly by the positive of with RhB and charge of alumina screened byscreened increasing adsorption increases an increase of ionic strength At lowsignificantly RhB adsorption, an increase in salt increasing salt concentrations However, other interactions such as surface complexation and Van salt concentrations However, other interactions as surface complexation and Van of derSMNA, Waals concentration increased the number of cation such Na+ on the negatively charge layer der Waals interactions andbonding hydrogen bonding can induce adsorption atconcentration high RhB concentration It is interactions and hydrogen can induce adsorption at high RhB 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 charge onto SMNA is controlled by both electrostatic and non-electrostatic interactions between the positive 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 the saltbonding effect disappears [30] der Waals interactions andand hydrogen can induce adsorption at high RhB concentration It is suggested that adsorption of RhB onto SMNA is controlled by both electrostatic and non-electrostatic 200.0 interactions The isotherms of RhB show a common intersection point (CIP) in which the electrostatic contribution to the adsorption vanishes and the salt effect disappears [30] 160.0 200.0 120.0 160.0 80.0 mM 120.0 40.0 80.0 0.0 0.0000 40.0 100 mM 0.0005 mM 0.0015 CRhB(mol/L) 100 mM 0.0010 0.0020 Figure 10 Adsorption0.0 isotherms of RhB onto SDS modified nano γ-Al2 O3 (SMNA) at different Figure 10 Adsorption isotherms of RhB onto SDS modified nano γ-Al2O3 (SMNA) at different NaCl 0.0000 0.0020 NaCl concentrations The points are 0.0005 experimental0.0010 data while 0.0015 solid lines are fitted by a two-step concentrations The points are experimental data while solid lines are fitted by a two-step adsorption adsorption model C (mol/L) RhB model 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 10 of 16 Figure 10 450 also shows that at different NaCl Materials 2019, 12, concentrations, the experimental results of RhB 10onto 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 saltTable concentrations, the maximum adsorption of RhB at 100 mM is higher than that at mM also shows that we can use the samecapacity fitting parameters 100 mM is higher than that at mM Table also shows that we can use the same fitting parameters (k2 (k2 and n) for isotherms at and 100 mM NaCl However, the value of k1 at mM NaCl is 10 times and n) for isotherms and 100ItmM NaCl that However, value ofparameter k1 at mMto NaCl is 10 times greater greater than that atat100 mM suggests k1 is athevaluable evaluate electrostatic than that at 100 mM It suggests that k is a valuable parameter to evaluate electrostatic interaction at interaction at low RhB concentration The higher the salt concentration, the higher value k1 is obtained low RhB concentration The higher the salt concentration, the higher value k1 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 γ-Al2 O3 (SMNA) 𝜞 CNaCl k1 k2 g/mg)n−1 C(mM) Γ (mg/g) (104 g/mg) k1 (104 g/mg) k2 (10n−1 (103 g/mg) NaCl (mM) (mg/g) 100 100 11 165 165 120 120 10 100 20 20 10 100 20 20 n n 2.2 2.2 2.2 2.2 Modified Nano Nano γ-Al γ-Al22O33 (SMNA) 3.5 Adsorption Mechanisms of RhB onto SDS Modified (SMNA) section, adsorption adsorption mechanisms mechanisms of of RhB RhB onto onto SDS SDS modified modifiednano nanoγ-Al γ-Al22O O33 is discussed in In this section, change in surface surface charge by by monitoring monitoring ζ potential potential and the change change in functional functional detail based on the change groups by FT-IR and adsorption isotherms of RhB onto SMNA groups by FT-IR and adsorption isotherms of RhB onto SMNA potential in in Figure Figure 11 11 shows shows that that the the ζζ potential potential of of synthesized synthesized nano nano γ-Al γ-Al22O O33 is highly The ζ potential SDS toto form SDS modified nano γpositive at pH (ζ (ζ ==+47.55 +47.55mV) mV).After Aftersurface surfacemodification modificationwith with SDS form SDS modified nano Al2O23O(SMNA), thethe surface charge of of adsorbent changed from positive mV) It γ-Al surface charge adsorbent changed from positivetotonegative negative(ζ(ζ= =−13.95 −13.95 mV) (SMNA), implies It impliesthat thatthe theadmicelles admicelleswere wereoccurred occurredonto ontonano nano γ-Al γ-Al22OO33surface surfaceand andthe thecharge charge was was taken place the presence presence of of anion anion DS DS−− [30,32] in the [30,32] Nevertheless, Nevertheless, after after adsorption adsorption of cationic dye RhB, the negative SMNA changed changed from from negative negative to to slight slight positive positive (ζ (ζ == +2.85 +2.85 mV) The results of ζζ potential potential charge of SMNA adsorption onto onto SMNA SMNA is is due due to to electrostatic electrostatic interaction interaction suggest that RhB adsorption ζ potential (mV) 50.00 40.00 30.00 47.55 nano γ-Al2O3 SDS modified nano γ-Al2O3 After RhB adsorption 20.00 10.00 2.85 0.00 -10.00 -20.00 -13.95 Figure 11 The ζ potential of synthesized nano γ-Al2 O3 , SDS modified nano γ-Al2 O3 (SMNA), and Figure after 11 The potential ofinsynthesized γ-Al2O3, SDS modified nano γ-Al2O3 (SMNA), and SMNA RhBζ adsorption mM NaClnano (pH 4) 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 FTIR is powerful tooloftothe evaluate the change functional groups after [44] Figure shows the FT-IR spectrum FT-IR spectrum of in SMNA (A) and SMNA afteradsorption RhB adsorption (B) in − 12 shows the FT-IR spectrum of the spectrum of SMNA (A) and SMNA after RhB adsorption the wavenumber range 400–4000 cm FT-IR (B) inWe thecan wavenumber range 400–4000 see that the strong band cm of −1stretching of –OH appear in the wavelength of about Wecm can−1see the strong band of stretching in theofwavelength aboutγ-Al 3658.96 3658.96 forthat SMNA (Figure 12A) is similar of to -OH FT-IRappear spectrum synthesizedofnano O3 −1 cm for3) SMNA 12A) is similar to FT-IR spectrum of synthesized nano γ-Al2O (Figure (Figure Figure(Figure 12A also shows that FT-IR spectra of alumina after SDS adsorption are similar 3) to Figure shows that FT-IR spectra of alumina after adsorption aresymmetrical similar to the raw one the raw12A one also (Figure 3) In additive, the relative intensity of SDS asymmetrical and stretching −1asymmetrical (Figure In additive, the relative intensity and symmetrical stretching ofspectra –CH2– of –CH23) –presented at 2920.23 and 2850.79 cmof appeared with very high intensity in FT-IR −1 presented at 2920.23 and 2850.79 withinteraction very high occurred intensity on in FT-IR spectra SMNA of SMNA [45] This confirms thatcm the appeared hydrophobic the surface ofof alumina −1 the [45] This confirms that the hydrophobic occurred surface alumina.inInspectra addition, In addition, the characteristics of SO4 2− interaction at about 1226.73 cmon appear veryofstrongly 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 11 of 16 theMaterials characteristics of SO42− at about 1226.73 cm−1 appear very strongly in spectra of SDS while 11 allof 15 2019, 12, 450 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 inIn contact with the of alumina nanoparticles via electrostatic high salt mM NaCl) other words, thesurface modification of alumina was successful due to the attraction presence ofatbilayer 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 −1 of SMNA disappears in the spectra presence of bilayer or admicelles, or2–both, on theatsurface alumina On the one hand, the peak of –CH presented 2061.90ofcm −1 On the one hand, the peak of –CH – presented at 2061.90 in the in a range of 1591.27cm of SMNA after RhB adsorption The peaks cm−1oftoSMNA 1651.07disappears cm−1 of RhB −1 to 1651.07 cm−1 of RhB spectra of SMNA after RhB adsorption The peaks in a range of 1591.27 cm characterizing for N–H bonds [46] appeared on the surface of SMNA The FT-IR spectra of SMNA characterizing for N–H bondsthat [46]RhB appeared on adsorb the surface SMNA.ofThe of SMNA after after RhB adsorption suggest mainly the of surface Al2FT-IR O3 byspectra both electrostatic RhB adsorption suggest that RhB mainly adsorb the surface of Al O by both electrostatic attractions 3in good agreement with attractions as well as hydrophobic interaction These results are RhB as well as hydrophobic interaction These results areSMNA in good with RhB adsorptionand isotherm adsorption isotherm in which RhB adsorption onto is agreement controlled by both electrostatic non- in which RhBinteractions adsorption onto SMNA is controlled by both electrostatic and non-electrostatic interactions electrostatic (A) (B) Figure 12 12 TheThe FT-IR spectra of SDS modified nano γ-Al 2O3 (A) andand SMNA afterafter RhBRhB adsorption (B).(B) Figure FT-IR spectra of SDS modified nano γ-Al SMNA adsorption O3 (A) Comparison of Effectiveness of Surfactant-Modified Nano γ-Al O3 (SMNA) Other Adsorbents 3.6.3.6 Comparison of Effectiveness of Surfactant-Modified Nano γ-Al 2O32(SMNA) and and Other Adsorbents for for RhB Removal and Other Nano γ-Al O RhB Removal and Other Nano γ-Al2O3 synthesized nano γ-Al O3 is aadsorbent novel adsorbent RhB removal after modification surface modification TheThe synthesized nano γ-Al2O3 is a2 novel for RhBfor removal after surface with with SDS The removal efficiency is about 100% and very high adsorption capacity of 165 mg/g SDS The removal efficiency is about 100% and very high adsorption capacity of 165 mg/g is achieved is achieved at the optimumconditions adsorptionWe conditions Wevarious found that various scientific papers at the optimum adsorption found that scientific papers reported thereported removalthe removal of RhB using many kinds of adsorbents To our best knowledge, the removal of RhB using Materials 2019, 12, 450 12 of 15 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 γ-Al2 O3 (SMNA) and other absorbents for removal of Rhodamine B (RhB) Adsorbent Adsorption Capacity (mg/g) Removal Efficiency (%) References Monodispersed mesoporous nanosilica Polyamide grafted carbon microspheres Polymeric nanotubes Kaolinite Sago waste activated carbon Hypercross linked polymeric adsorbent Surfactant-modified coconut coir pith Surfactant-modified nano γ-Al2 O3 (SMNA) 23.0 19.9 35.58 46.1 16.1 25.0 14.9 165.0 96 100 99 83 100 97 97 100 [47] [46] [23] [48] [42] [49] [50] This study 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 γ-Al2 O3 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 γ-Al2 O3 was easily synthesized by titrating NaOH into Al(NO3 )3 without any other chemicals The nano γ-Al2 O3 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 γ-Al2 O3 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 after four reused time experiments are very small, Materials 2019, 12, that x FOR PEER REVIEW demonstrating SMNA is not only a novel adsorbent but also applicable for regeneration 13 of 16 Removal Efficiency (%) 100 80 60 40 20 Number of regeneration Figure13 13.Removal Removalefficiency efficiencyofofRhB RhBusing usingSMNA SMNAafter afterfour fourregenerations regenerations.Error Errorbars barsshow showstandard standard Figure deviationofofthree threereplicates replicates deviation Conclusions We successfully synthesized γ-Al2O3 nanoparticles and modified the surface of γ-Al2O3 by adsorption of anionic surfactant sodium dodecyl sulfate (SDS) The nano γ-Al2O3 has a mean particle size distribution of 40 nm while the functional surface groups of nano γ-Al2O3 was confirmed by Fourier transform infrared spectroscopy (FT-IR) A high specific surface area of nano γ-Al2O3 was Materials 2019, 12, 450 13 of 15 Conclusions We successfully synthesized γ-Al2 O3 nanoparticles and modified the surface of γ-Al2 O3 by adsorption of anionic surfactant sodium dodecyl sulfate (SDS) The nano γ-Al2 O3 has a mean particle size distribution of 40 nm while the functional surface groups of nano γ-Al2 O3 was confirmed by Fourier transform infrared spectroscopy (FT-IR) A high specific surface area of nano γ-Al2 O3 was found to by 221.3 m2 /g The SDS adsorption onto nano γ-Al2 O3 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 nano-alumina (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 wastewater by surfactant-modified alumina Sep Purif Technol 2005, 44, 139–144 [CrossRef] Wong, Y.C.; Szeto, Y.S.; Cheung, W.H.; McKay, G Equilibrium Studies for Acid Dye Adsorption onto Chitosan Langmuir 2003, 19, 7888–7894 [CrossRef] Almeida, M.R.; Stephani, R.; Dos Santos, H.F.; de Oliveira, L.F.C Spectroscopic and Theoretical Study of the “Azo”-Dye E124 in Condensate Phase: Evidence of a Dominant Hydrazo Form J Phys Chem A 2009, 114, 526–534 [CrossRef] [PubMed] Dogan, ˘ M.; Alkan, M.; Türkyilmaz, A.; Özdemir, Y Kinetics and mechanism of removal of methylene blue by adsorption onto perlite J Hazard Mater 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Al2O3 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