Synthesis of titanium dioxide magnesium ferritereduced graphene oxide photocatalyst materials for removal p nitrophenol from water

ĐẠI HỌC QUỐC GIA THÀNH PHỐ HỒ CHÍ MINH TRƯỜNG ĐẠI HỌC BÁCH KHOA -o0o - NGUYỄN TẤN TIẾN NGHIÊN CỨU TỔNG HỢP VẬT LIỆU XÚC TÁC QUANG TITAN DIOXIT-FERRIT MAGIE /GRAPHENE OXIT DẠNG KHỬ ĐỂ LOẠI p-NITROPHENOL TRONG NƯỚC (Synthesis of titanium dioxide-magnesium ferrite/reduced graphene oxide photocatalyst materials for removal p-nitrophenol from water) Chuyên ngành: KỸ THUẬT HÓA HỌC Mã số: 60520301 LUẬN VĂN THẠC SĨ TP HỒ CHÍ MINH, tháng 09 năm 2020 Cơng trình hoàn thành tại: Trường Đại Học Bách Khoa – ĐHQG – HCM Cán hướng dẫn khoa học: PGS TS Nguyễn Hữu Hiếu (Ghi rõ họ, tên, học hàm, học vị, chữ ký) Cán hướng dẫn khoa học: TS Đoàn Thị Yến Oanh (Ghi rõ họ, tên, học hàm, học vị, chữ ký) Cán chấm nhận xét 1: (Ghi rõ họ, tên, học hàm, học vị, chữ ký) Cán chấm nhận xét 2: (Ghi rõ họ, tên, học hàm, học vị, chữ ký) Luận văn thạc sĩ bảo vệ Trường Đại học Bách Khoa, ĐHQG Tp HCM, ngày tháng năm 2020 Thành phần Hội đồng đánh giá luận văn thạc sĩ gồm: Xác nhận Chủ tịch Hội đồng đánh giá LV Trưởng Khoa quản lý chuyên ngành sau luận văn sửa chữa (nếu có) i ĐẠI HỌC QUỐC GIA TP.HCM CỘNG HÒA XÃ HỘI CHỦ NGHĨA VIỆT NAM TRƯỜNG ĐẠI HỌC BÁCH KHOA Độc lập - Tự - Hạnh phúc NHIỆM VỤ LUẬN VĂN THẠC SĨ Họ tên học viên: NGUYỄN TẤN TIẾN MSHV: 1770456 Ngày, tháng, năm sinh: 18/06/1993 Chuyên ngành: Kỹ thuật Hóa học Nơi sinh: Đồng Nai Mã số : 60520301 I TÊN ĐỀ TÀI: Tên tiếng Việt: Nghiên cứu tổng hợp vật liệu xúc tác quang titan dioxit-ferrit magie/graphene oxit dạng khử để loại p-nitrophenol nước Tên tiếng Anh: Synthesis of titanium dioxide-magnesium ferrite/graphene oxide photocatalyst materials for removal p-nitrophenol from water II NHIỆM VỤ VÀ NỘI DUNG: 2.1 Tổng quan Hợp chất phenolic, vật liệu titan dioxit, ferrit magie, graphene oxit dạng khử, titan dioxit-ferrit magie/graphene oxit dạng khử, chế xúc tác quang phân hủy 2.2 Thực nghiệm - Tổng hợp thử nghiệm khả xúc tác quang phân hủy p-nitrophenol vật liệu titan dioxit/graphene oxit dạng khử; - Tổng hợp thử nghiệm khả xúc tác quang phân hủy p-nitrophenol vật liệu titan dioxit-ferrit magie/graphene oxit dạng khử; - Khảo sát ảnh hưởng yếu tố thời gian chiếu sáng, thể tích hydro peroxit, pH, lượng chất xúc tác đến khả xúc tác quang titan dioxit-ferrit magie/graphene oxit dạng khử đánh giá động học trình; - Thử nghiệm khả thu hồi tái sử dụng vật liệu titan dioxit-ferrit magie/graphene oxit dạng khử III NGÀY GIAO NHIỆM VỤ : 02/2020 IV NGÀY HOÀN THÀNH NHIỆM VỤ: 06/2020 V CÁN BỘ HƯỚNG DẪN : PGS TS Nguyễn Hữu Hiếu TS Đoàn Thị Yến Oanh Tp HCM, ngày tháng năm 2020 CÁN BỘ HƯỚNG DẪN CHỦ NHIỆM BỘ MÔN ĐÀO TẠO (Họ tên chữ ký) (Họ tên chữ ký) TRƯỞNG KHOA KỸ THUẬT HÓA HỌC (Họ tên chữ ký) ii LỜI CẢM ƠN Đầu tiên, tác giả xin gửi lời cảm ơn đến gia đình người thân ln quan tâm, động viên tạo điều kiện thuận lợi cho tác giả suốt thời gian thực luận văn Tác giả xin cảm ơn quý Thầy/Cô Khoa Kỹ Thuật Hóa Học nhiệt tình giúp đỡ tác giả tạo điều kiện thuận lợi cho tác giả q trình học tập hồn thành luận văn tốt nghiệp Đặc biệt, tác giả xin bày tỏ lòng biết ơn sâu sắc đến thầy PGS TS Nguyễn Hữu Hiếu TS Đồn Thị Yến Oanh trực tiếp hướng dẫn, định hướng nghiên cứu, tận tình giúp đỡ thực nghiên cứu khoa học tạo điều kiện thuận lợi cho tác giả hoàn thành luận văn Cuối cùng, tác giả xin cảm ơn tập thể anh, chị, em Phịng Thí nghiệm Trọng điểm Đại học Quốc gia TP HCM Cơng nghệ Hóa học Dầu khí (CEPP Lab), Trường Đại học Bách Khoa giúp đỡ tác giả suốt thời gian học tập thực luận văn Tác giả Nguyễn Tấn Tiến iii TÓM TẮT LUẬN VĂN Trong luận văn này, vật liệu titan dioxit-ferrit magie/graphene oxit dạng khử (TiO2MFO/rGO) tổng hợp kết hợp phương pháp đồng kết tủa phương pháp phối trộn huyền phù có hỗ trợ siêu âm Cấu trúc-hình thái-đặc tính vật liệu TiO2, MFO, TiO2/rGO, TiO2-MFO/rGO phân tích phương pháp: phổ hồng ngoại biến đổi Fourier, nhiễu xạ tia X, phổ Raman, kính hiển vi điện tử quét, kính hiển vi điện tử truyền qua, phổ tán xạ lượng tia X, diện tích bề mặt riêng theo phương pháp Brunauer-Emmett-Teller, phân tích nhiệt trọng lượng, phổ UV-vis Ảnh hưởng yếu tố thời gian chiếu sáng, thể tích H2O2, pH, lượng chất xúc tác đến khả xúc tác quang phân hủy p-nitrophenol (PNP) TiO2-MFO/rGO khảo sát Khả xúc tác quang phân hủy động học trình xúc tác phân hủy p-nitrophenol vật liệu TiO2-MFO/rGO nghiên cứu so sánh với TiO2/rGO, TiO2, MFO Thêm vào đó, khả thu hồi, tái sử dụng, chế xúc tác quang phân hủy PNP thử nghiệm iv ABSTRACT In this thesis, titanium dioxide-ferrite magnesium/reduced graphene oxide (TiO2MFO/rGO) was prepared by in-situ method and ultrasound-assisted ex-situ method The characteristics of the catalyst material (TiO2, MFO, TiO2/rGO, and TiO2-MFO/rGO) were confirmed by Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, Scanning electron microscope, Transmission electron microscopy, Energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller specific surface area, Thermal gravimetric analysis, and UV-vis spectroscopy The effects of factors including the illumination time, H2O2 volume, pH, and the amount of catalyst on the p-nitrophenol (PNP) photodegradation of TiO2-MFO/rGO were investigated The photodegradation p-nitrophenol ability and kinetic catalytic process of TiO2-MFO/rGO materials was compared with TiO2/rGO, TiO2, and MFO In addition, The catalyst recovery, reusability, and photodegradation PNP mechanism of the TiO2-MFO/rGO were also study v LỜI CAM ĐOAN Tác giả xin cam đoan luận văn nghiên cứu cá nhân tác giả thực hướng dẫn thầy PGS TS Nguyễn Hữu Hiếu-Phịng TN Trọng điểm ĐHQG-HCM Cơng nghệ Hóa học Dầu khí (CEPP Lab), Trường Đại học Bách Khoa TS Đồn Thị Yến Oanh-Nhà xuất Khoa học tự nhiên Công nghệ, Viện hàn lâm Khoa học Công nghệ Việt Nam Số liệu, kết nghiên cứu, kết luận luận văn hoàn toàn trung thực, chưa cơng bố cơng trình khác trước Tác giả xin chịu trách nhiệm nghiên cứu Tác giả Nguyễn Tấn Tiến vi MỤC LỤC NHIỆM VỤ LUẬN VĂN THẠC SĨ ii LỜI CẢM ƠN iii TÓM TẮT LUẬN VĂN iv ABSTRACT v LỜI CAM ĐOAN vi MỤC LỤC vii DANH MỤC HÌNH x DANH MỤC BẢNG xii DANH MỤC CÁC TỪ VIẾT TẮT xiii ĐẶT VẤN ĐỀ CHƯƠNG 1: TỔNG QUAN 1.1 Tình hình nhiễm phương pháp xử lý hợp chất phenolic 1.1.1 Tình hình chung nhiễm 1.1.2 Hợp chất phenolic 1.1.3 Ứng dụng hợp chất phenolic 1.1.4 Hiện trạng ô nhiễm hợp chất phenolic nước 1.1.5 Ảnh hưởng hợp chất phenolic đến sức khỏe người sinh vật 1.1.6 Các phương pháp xử lý 1.1.6.1 Phương pháp ozon hóa 1.1.6.2 Phương pháp điện hóa 1.1.6.3 Phương pháp sinh học 1.1.6.4 Phương pháp hấp phụ 1.1.6.5 Phương pháp xúc tác quang 1.2 Vật liệu xúc tác quang phân hủy 1.2.1 Titan dioxit 1.2.2 Ferrit magie 10 1.2.3 Graphene oxit dạng khử 12 1.3 Vật liệu composite titan dioxit-ferrit magie/graphene oxit dạng khử 13 1.3.1 Giới thiệu 13 1.3.2 Phương pháp tổng hợp TiO2-MFO/rGO 14 vii 1.3.2.1 Phương pháp đồng kết tủa 14 1.3.2.2 Phương pháp phối trộn huyền phù 15 1.3.2.3 Ứng dụng 16 1.3.2.4 Cơ chế xúc tác quang phân hủy 16 1.4 Đánh giá khả xúc tác quang phân hủy TiO2-MFO/rGO 17 1.4.1 Năng lượng vùng cấm vật liệu 17 1.4.2 Hiệu suất xúc tác quang phân hủy 17 1.4.3 Động học trình 17 1.5 Tình hình nghiên cứu trong/ngồi nước tính cấp thiết đề tài 18 1.5.1 Tình hình nghiên cứu nước 18 1.5.1.1 Trong nước 18 1.5.1.2 Ngoài nước 18 1.5.2 Tính cấp thiết 19 1.6 Mục tiêu, nội dung, phương pháp nghiên cứu 19 1.6.1 Mục tiêu 19 1.6.2 Nội dung 19 1.6.3 Phương pháp nghiên cứu 20 1.6.3.1 Phương pháp tổng hợp vật liệu 20 1.6.3.2 Phương pháp phân tích cấu trúc-hình thái-đặc tính vật liệu 20 CHƯƠNG 2: THỰC NGHIỆM 27 2.1 Nguyên liệu, hoá chất, dụng cụ, thiết bị, địa điểm thực 27 2.1.1 Hóa chất 27 2.1.2 Dụng cụ thiết bị 28 2.1.3 Địa điểm thực luận văn 28 2.2 Thí nghiệm 28 2.2.1 Tổng hợp TiO2/rGO 28 2.2.1.1 Giai đoạn 1: Tổng hợp GO 28 2.2.1.2 Giai đoạn 2: Tổng hợp TiO2/rGO 29 2.2.2 Tổng hợp vật liệu TiO2-MFO/rGO 30 2.2.2.1 Giai đoạn 1: Tổng hợp MFO 30 2.2.2.2 Giai đoạn 2: Tổng hợp TiO2-MFO/rGO 30 2.2.3 Phân tích cấu trúc-hình thái-đặc tính vật liệu 31 viii 2.2.4 Khảo sát khả phân hủy PNP vật liệu xúc tác 32 2.2.5 Khảo sát khả thu hồi tái sử dụng TiO2-MFO/rGO 33 CHƯƠNG 3: KẾT QUẢ VÀ BÀN LUẬN 34 3.1 Tổng hợp vật liệu TiO2/rGO 34 3.2 Tổng hợp vật liệu TiO2-MFO/rGO 36 3.2.1 Cấu trúc vật liệu TiO2-MFO/rGO 36 3.2.2 Hình thái vật liệu 39 3.2.3 Đặc tính vật liệu 41 3.3 Khả xúc tác quang phân hủy PNP vật liệu 43 3.3.1 Các yếu tố ảnh hưởng đến khả xúc tác quang phân hủy PNP TiO2-MFO/rGO 43 3.3.2 So sánh khả xúc tác quang phân hủy PNP TiO2-MFO/rGO với vật liệu TiO2/rGO, TiO2, MFO động học phản ứng 46 3.4 Khả thu hồi số lần tái sử dụng TiO2-MFO/rGO 49 3.5 Cơ chế hấp phụ xúc tác quang phân hủy PNP TiO2-MFO/rGO 51 CHƯƠNG 4: KẾT LUẬN VÀ KIẾN NGHỊ 54 4.1 Kết luận 54 4.2 Kiến nghị 54 TÀI LIỆU THAM KHẢO PHỤ LỤC CƠNG TRÌNH ĐÃ CƠNG BỐ ix exhibited no impact because the diffraction peak has overlapped with the crystal surface of (101) of the anatase phase [14] Intensity (a.u.) : MFO à: Anatase MFO-TiO2/rGO    à  TiO2/rGO TiO2 MFO 10 Figure FTIR spectra of research materials 20 30 40 50 2 (deg) 60 70 80 Figure XRD patterns of research materials Raman spectra of GO, TiO2, and MFO are shown in Figure The G-band represents characteristic of sp2 hybridized carbon materials, which can provide the information on the in-plane vibration of sp2 bonded carbon domains while the D-band relates to the disorder band associated with structural defects in graphene [15] As shown in Table 1, the doping of MFO in the TiO2/rGO nanocomposite shown no significant in D and G band-shift of ternary composite, but higher in intensity, which confirm the enhancing in the photocatalytic property Moreover, the Raman spectrum shows a strong signal localized at 164 cm-1 corresponding to the E1g vibrational modes, which is caused by the external vibration of the TiO2 anatase structure In MFO-TiO2/rGO, the peaks of 554 and 681 cm-1 reveal the attribution of F2g and A1g vibration mode of the tetrahedral nanocrystalline site of MFO, respectively [16] The increase in ID/IG value of TiO2/rGO and MFO-TiO2/rGO implied a high level of sp2 domains in the rGO layer via the disorder in the structure of ternary nanocomposite during the hydrothermal [10, 11] Eg D TiO2 Intensity (a.u.) B1g MFO F2g 200 400 G A1g 600 MFO-TiO2/rGO TiO2/rGO 500 1000 1500 Raman shift (cm-1) 2000 Figure Raman spectra of research materials In the SEM image of GO as shown in Figure 4a, the sheets contained a large amount of platelet displaying a smooth and fluffy morphology The SEM images of TiO2/rGO and MFO-TiO2/rGO (Figure 4b and c, respectively) revealed that the oxide adaptors were homogeneously distributed on the surface of the carrier In TiO2/rGO, the aggregation of TiO2NPs could not be observed due to the one-pot synthesis so that the formation and boundary of TiO2 onto the rGO sheets occur concomitantly, making the binary composite [17] Regarded to MFO-TiO2/rGO, the slight agglomeration in MFO-TiO2/rGO could be explained as high magnetic property containing in MFO which creates the magnetic dipoledipole interaction between its molecular and the Van der Waals force between TiO and MFO However, the anchoring with MFO and hydrothermal method has intensively created a mesoporous structure of the material (Figure 4c), which attributed to high adsorption capacity toward the organic contaminants [18] In TiO2/rGO, Ti constituted 44.65 %, but when loading MFO onto the binary nanocomposite, the mass fraction reduced insignificantly (38.83%) The constituent of Fe and Mg in MFO-TiO2/rGO was 5.07 and 0.22 %, respectively, which roughly indexed to MFO preparation as shown in Table and Figure Figure SEM images of (a) GO, (b) TiO2/rGO, and (c) MFO-TiO2/rGO a b Figure Energy-dispersive X-ray spectroscopy mapping images of (a) TiO2/rGO and (b) MFO-TiO2/rGO Those stated results were further supported by the TEM image (Figure 6a) The ferrite and TiO2 particles nanosized with an average diameter of 5-14 nm were scattered uniformly on the most surface of the rGO sheet (Figure 6b) Interestingly, TiO2 contained the clear lattice fringes with interplanar space (d) of 0.342 nm while the lattice fringe of the spherical MFO nanocrystalline was 0.290 and 0.251 nm, which was attributed to d(220) and d(311), respectively (as shown in Figure 6c) The rGO in the role of the oxide-loading matrix was revealed with wrinkle and during the hydrothermal and sonication process, the stacking of rGO was restrained enough to let the oxide crystal densely attached on its surface [19] The selected area electron diffraction (SAED) was expressed in Figure 6d, where the rings are associated with (101), (004), (112), and (224) crystalline plane of anatase phase; (311) and (511) of the spinel MFO The SAED further confirms the crystallinity of the composite and well-indexed to XRD patterns Figure TEM image of MFO-TiO2/rGO Table Morphology data of researching carbonaceous catalysts Raman bands (cm -1) TiO2/rGO MFOTiO2/rGO Band D Band G Intensity ratio ID/IG 7137 6447 1.11 Specific surface area (m2/g) 160.002 11350 9936 1.14 259.620 % mass Pore volume (cm3/g) Pore diameter (Å) 0.265 16.266 14.46 40.89 44.65 0.218 20.060 14.47 41.41 38.83 C O Ti Fe Mg 5.07 0.22 The BET data of nanomaterials were listed in Table The highest specific surface area containing in MFO-TiO2/rGO could be explained as once MFO has uniformly occupied on the rGO sheets, the magnetic particle repulsed each other by the dipole-dipole interaction, indeed reduce the wrinkles in rGO and stretch among the sheets, which was highly agreed with TEM and SEM images The imposing surface area and mesoporous structure contained in our nanocomposites have played a key role in heightening the photocatalytic property of materials [55,64] According to the TGA curve of MFO-TiO2/rGO (Figure 7a), the first weight loss of the above materials up to 200 oC was indexed to the evaporation of water and organic compound on the surface of materials In the second step (200 – 500 oC), the sample exhibited a considerable weight loss attributed to the decomposition of oxygenfunctionalizing groups in rGO and C element in rGO was started to break out to CO and CO above 500 oC Altogether, the residue mass ratio of the ternary was 83.15 wt.% [21] The optical bandgap for direct bandgap semiconductor of our material was investigated by following Tauc equation (4): αhν = k(hν − Eg )1/2 (4) where α is an absorption coefficient, k is a constant, and Eg (eV) is the bandgap of the material By linearly expressing the relationship between hν and (αhν)2 , the bandgap shall be determined [14] The bandgap value (Figure 7b) of TiO2/rGO (2.81 eV) was relatively smaller than pristine TiO2 due to the Ti-O-C bond formed would narrow the bandgap and create more electron transportation in TiO2 Similarly, the MFO in-doped material shows smaller bandgap (2.46 eV) compared with binary material, which demonstrated that the introduction of ferrite nanoparticles towards TiO2/rGO could enhance the photocatalytic performance in the visible region [22] 100 MFO TiO2 TiO2/rGO MFO-TiO2/rGO  = 5.88% 98 2.81 eV 94  = 5.03% 92 2.01 eV (ahn)2 Weight (%) 96 2.46 eV 90 3.04 eV 88  = 5.94% 86 84 82 100 200 300 400 500 600 700 800 2.0 2.5 3.0 hn (eV) Temperature (°C) (a) (b) Figure (a) TGA curve, (b) Bandgap of as-prepared materials 3.5 4.0 3.2 PNP photodegradation The amount of H2O2 poured in the solution before irradiation has played a vital role in removing PNP from aqueous media, which is conducted in a range from 0.125 mL to mL as shown in Figure 7a After 50 min, the photocatalytic yield reached 73.94, 85.89, 91.51, and 94.47 % corresponding to 0.125, 0.25, 0.5, and mL of H2O2, respectively It was proved that the amount of reactive oxygen species (ROS), particularly •OH radical has a crucial impact on enhancing the degradation yield of the organic compound [23] Therefore, substituting a small amount of H2O2 to the reaction system is one of the most effective and eco-friendly methods to increase this radical bulk and reaction yield, hence improve the operation condition (cost, time) of reaction The cleavage of H2O2 to produce •OH radical with the help of electron and superoxide species originated from the conduction band of TiO and MFO as followed: H2O2 + ℎ𝜈 H2O2 + e−cb H2O2 + •O2−    •OH •OH + OH− •OH + OH− + O2 (5) (6) (7) The enhancement in ROS was also described by Fenton-like reaction [22], where H2O2 acts as the oxidant and Fe3+ in MFO matrix was reduced as: H2O2 + Fe3+ H2O2 + Fe2+ + HOO•   Fe2+ + HOO• + H+ Fe3+ + •OH + OH− (8) (9) Catalyst dosage was claimed as an important parameter in improving the photo elimination efficiency for decomposing PNP The results of the investigation about the number of catalysts from 10 to 40 mg were expressed in Figure 8b With the increase in weight of MFO-TiO2/rGO, there was a corresponding increase in the yield from 82.52 to 94.45 % This can be explained as once the more in catalysts added, there witnessed an enlargement in reaction site for PNP and also photon adsorption, indeed aid in the decomposition of PNP under UV light control [1, 24] The impact of pH on the photocatalytic yield was conducted by levels: pH 5, 7, and 9, as shown in Figure 8c The pH of the solution was adjusted by HCl and NaOH 0.1 M before UV irradiation Owning to the results, the changing pH from to would provide a slight advance in the efficiency of 92.44 to 94.47%, as under the acidic environment, the agglomeration of the material occurs strongly, which lead to the decrease in reaction site and also the adsorption capacity PNP undergoes a 99.53 % degradation in basic solution PNP is claimed to be moderately acidic in water with pKa = 7.15 In lower pH, it can be adsorbed on the rGO layer by π- π interaction by the benzene ring in PNP and delocalized conjugated π electrons and oxygen-containing groups in rGO When the solution is altered by the basic solution (pH > pKa), PNP dissociated to negatively charged nitrophenolate anion It was stated that the surface of rGO is negative when pH due to the increase in OH − concentration, the electrostatic repulsion eventually prevented the PNP from contacting with rGO sheets [25] However, the high interaction of the material, particularly the functional groups in rGO with OH−, which is enriched by the alkaline solution can lead to a greater amount of •OH radical yielded under UV light and enhance the photodegradation yield Figure Effect of amount of (a) H2O2, (b) amount of catalyst, and (c) pH on MFO-TiO2/rGO photocatalyst, the comparison of photodegradation yield (d) and the kinetic studies among the catalysts (e) The comparison of PNP photodegradation between the ternary nanocomposite with the binary one and MFO and TiO2 alone was performed via 40 mg catalyst, mL H2O2 substituted, and pH The results in Figure 7d indicated that the types of catalyst achieved the overall photodegradation yield > 90% after 50 irradiation The mono-oxide held up 86.27 and 84.96 % PNP decomposition corresponding to TiO2 and MFO, respectively The TiO2, with a wider bandgap, results in the higher recombination of electron-hole pair, thus restricts the photocatalytic property In MFO, although can have higher efficiency due to its lowest bandgap (2.01 eV), the higher agglomeration capacity due to the dipole-dipole interaction and Van der Waals force can lead to the decrease in reaction site, thus decrease the photon adsorption [22] When anchoring the TiO2 on the rGO sheet, which acts as an outstanding charge carrier, the charge transportation among the molecule and also the separation of electron and hole were remarkably improved The rapid charge transfer from TiO2 to rGO via the promoted photoinduced charges consequently could lead to enhance photodegradation of the organic contaminants under UV light Consequently, TiO 2/rGO has promoted the efficiency of 91.08 % after 50 mins in comparison to TiO2 Furthermore, the doping of MFO to TiO2/rGO gave an extraordinary effect in enhancing the yield (up to 99.53 %) The narrower bandgap of MFO-TiO2/rGO (2.46 eV) could assist in the enlargement of a lifetime in photo-induced electron and hole, so utilized the separation of them under irradiation and showed a synergistic effect in increasing the PNP photodegradation [26] Besides, MFO was uttered to give photoelectron a strong reducing ability due to its high energy of conduction band (CB) and the bandgap capable to absorb visible light By the virtue of its crystal lattice, MFO also improves the catalyst site in TiO2/rGO, therefore, optimize the photodegradation yield in ternary material [27] Furthermore, under UV light control, the photoinduced electron can easily transfer through the rGO layers, then to the TiO particles nearby; therefore improve the photo-reacting capacity These results were agreed with to kinetic studies in Figure 8e and Table 2, which demonstrated that the photodegradation of PNP using MFO-TiO2/rGO as catalyst follows pseudo-first-order reaction with the highest rate constant (0.1011 min1 ) compared to others Table The kinetic parameters of research material of PNP photodegradation Type of Catalyst TiO2 MFO TiO2/rGO MFO-TiO2/rGO Rate constant k (min-1) 0.0348 0.0386 0.0437 0.1011 Correlation coefficient R2 0.9923 0.9947 0.9926 0.9939 The comparing the impact of catalytic morphology and reaction condition in Table also intended to address the role of particle diameter, specific surface area, and the H2O2 added to the reaction system in enhancing the photocatalytic property Purely, the crystal size had a vital correlation to photocatalytic performance in enlarging the interaction with the contaminants The larger size will lead to the light absorbance mostly in the outer plane of the particle and prevent the penetration of light through the activated site inside the catalyst, hence reduce its photocatalytic property [28] Besides, the high surface area and mesoporous structure facilitated the pollutant adsorption capacity on catalyst surface via the reaction site between the catalyst and photogenerated radicals As mentioned above, the amount of H2O2 poured to the reaction would increase the radical generation under UV condition, indeed improved the PNP removal in water Furthermore, the rate constant was also improved under the incidence of H 2O2, which ultimately shortened the time of decomposition Table Comparison of PNP photodegradation yield Average diameter (nm) SBET (m2/g) Condition Yield (%) References 5-14 259.620 PNP 20 ppm, catalyst 40 mg, mL H2O2, pH = 9, 30 adsorption, 50 irradiation 99.53 This research Coprecipitation - - PNP 0.02 g/L, catalysts 0.05 g, 90 irradiation 95.6 [29] H-TiO2 Mixing - 74.81 PNP 10 ppm, catalyst 100 mg, 180 irradiation 95 [30] Ag-TiO2 Sol-gel 30-50 69.29 PNP mg/L, catalyst 0.05 g, 1h adsorption, 60 irradiation 90 [31] Bi2O3 Coprecipitation 42 2.00 PNP 25 ppm, 100 mg of catalyst, 90 irradiation ~100 [32] Zn0.94Fe0.04S/g-C3N4 Microwave hydrothermal 16.6 32.0442.56 PNP 10mg/L, catalyst 0.8g/L, H2O2 0.1mM, pH = 6.1, 20 adsorption, 60 irradiation 96 [33] 93 [94] No Catalyst Method MFO-TiO2/rGO Ultasoundassisted hydrothermal SnO2/rGO SiO2/Fe3O4/C@TiO2 Mixing - 44.62 mL PNP, catalyst 20 mg, 0.8 mL H2O2, pH = 7, 40 adsorption, 260 irradiation FeVO4CeO2 Hydrothermal 78 27.50 PNP 20 ppm, catalyst 0.1g/L, H2O2 10 mM, pH = 10, 1h irradiation ~99 [95] Cu2O NCs/TiO2 PC Hydrothermal reduction 10 88.47 pH = 6, 30 adsorption, 240 irradiation 60 [36] 3.3 Catalyst recovery and reusability The catalyst recovery and reusability of the ternary composite were also investigated under the as-mentioned conditions: 40 mg catalyst, mL H2O2 substituted, and pH The process of PNP photodegradation under UV light control using TiO2/rGO material was claimed to be inadequate since the inconvenience to separate to residue out of the aqueous media after the reaction Thus, the doping with MFO, a spinel magnetic ferrite, within the binary material not only enhances the photocatalytic property but also makes a simple pathway for recover the catalyst by conveniently using an external magnet (Figure 9a) This was in good accordance with Figure 9b where there is just minor loss in weight of the catalyst after recovering from the reacting solution after each time run Through 5-consecutive recycle run, the ternary nanocomposite exhibited an insignificant decline in its photodegradation yield Particularly, the catalyst was well-remained in its yields ranging from 99.53 to 98.09 % The overall chance was probably associated with the human error, the loss of catalyst in the washing and drying process after the reaction, or the reduction of Fe3+ in MFO to Fe2+ in the presence of H2O2 during the reaction [22] Figure (a) The catalytic recovery, (b) PNP Photodegradation via time-runs of MFO-TiO2/rGO, the SEM image (c), and EDX mapping (d) of MFO-TiO2/rGO at initial and 5th recycle run These results were further proved by SEM (as shown in Figure 9d), revealed that the morphology as well as the element component (Figure 9c) of the nanocomposite was highly maintained Besides, there was no mapping detection in the nitrogen element in the material for both cases, which stated the entire photodegradation of PNP on its surface According to Table 4, the nanocomposite exhibited a high reusing capacity due to its insignificant change in the specific surface area after a 5-time recycle run of photodegradation The mentioned result confirmed that MFO-TiO2/rGO could preserve its photocatalytic properties, durability as well as its structure and morphology after a 5-time run, which was claimed to create an economical and sustainable pathway for treating with organic contaminants in the eluent Table BET parameters of catalyst at initial and 5th recycle run Specific surface area (m2/g) Pore volume (cm3/g) Pore diameter (Å) Initial 259.620 0.218 20.060 th After recycle run 248.810 0.216 20.080 3.4 PNP adsorption and photodegradation mechanism For the FTIR spectra of MFO-TiO2/rGO (Figure 10), it is observed that before and after UV irradiation, there was no significant change in the broadband of oxygen-containing group stretching, which indicated that the photodegradation showed no effect to the structure of the nanocomposite As compared with others, the absorption bands of ternary material when reaching the adsorption-desorption equilibrium in the dark showed higher intensity at 1630 and 3400 cm1 originated from the stretching C=C and –OH, respectively which indicated the existence of organic pollutant on the surface of the materials This could respond to the following: (1) The benzene ring in PNP and delocalized conjugated electrons and oxygen-containing groups in rGO possibly promoted the π- π interaction (2) The H-bond between the hydroxyl group in rGO and phenolic proton of PNG (3) The NO2 group is an electron-withdrawing group, so it reduces the e− density in the aromatic ring, which links to rGO surface by cation- π bonding [37] The adsorption mechanism could be concretized in Figure 11 Figure 10 FTIR spectra of the ternary nanocomposite during the PNP photodegradation Under light irradiation, the photogenerated electrons from the valence band (VB) of MFO and TiO were excited to the conduction band (CB) Since rGO can act as an electron acceptor, so this e− can migrate from MFO through its surface, then into TiO2 nearby to join in the reducing of molecular adsorbed oxygen to form superoxide anion radical (•O2−) Meanwhile, the valence holes (h+) photogenerated on the TiO2 surface could react with water molecules to form •OH− and •HO2 radicals [27, 38] Those radicals are the primary oxidant and completely degrade adsorbed PNP The reaction was expressed as followed: MFO + ℎ𝜈 TiO2 + ℎ𝜈 MFO (e−) + O2 MFO (e−) + rGO rGO (e−) + TiO2 TiO2 (e−) + O2 TiO2 (e−) + rGO rGO (e−) + O2 TiO2 (h+) + H2O MFO (h+) + H2O H2O2 + ℎ𝜈 H2O2 + e−cb H2O2 + •O2− H2O2 + Fe3+ H2O2 + Fe2+ + HOO• •OH + •O2− + PNP                 MFO (e− + h+) TiO2 (e− + h+) MFO + •O2− MFO + rGO (e−) rGO + TiO2 (e−) TiO2 + •O2− TiO2 + rGO (e−) rGO + •O2− TiO2 + H+ + •OH MFO + H+ + •OH •OH •OH + OH− •OH + OH− + O2 Fe2+ + HOO• + H+ Fe3+ + •OH + OH− CO2 + H2O (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) Under UV light, the photodegradation reaction generates the strong electrophilic radicals such as •OH and •O2− from the nanocomposites [39, 40] The attack of these radicals preferentially occurs at the high electron area of the aromatic ring of PNP, at the ortho and para position with respect to –OH group, resulting in the formation of phenolic radical and hydroxylate products Besides, nitrite ion released further reacts with radicals to yield nitrate ion The interaction of phenolic intermediates with radicals led to the open of aromatic ring, the cleavage of the carbon chain, and the mineralization eventually to form CO2 and H2O [41, 42, 43] Figure 11: Adsorption and photodegradation mechanism Conclusions The ternary MFO-TiO2/rGO material was successfully prepared via a hydrothermal and ultrasonic method MFO and TiO2 nanocrystals have uniformly arranged on the GO sheet The substitution of magnesium ferrite and together with large surface area (259.620 m2/g) and average diameter of 5-15 nm has played the key role in collaborative adsorption and eradication of antibiotics in UV light control, hence made it more effective photocatalyst Particularly, under UV light after 80 with 40mg amount of catalysts, mL H2O2 substitution and pH of 9, 99.53 % of PNP was eliminated out of aqueous media and the reaction by using MFO-TiO2/rGO as photocatalyst and exhibited the greater yield than binary nanocomposite (TiO2/rGO) or MFO and TiO2 alone Moreover, it could be easily separated by an external magnet and the 5-run-reusing test showed catalytic stability without significant change in photodegradation yield Certainly, the use of this magnetic catalyst is a green, economical, and effective pathway for micro-pollutants in the aqueous phase in the future mass scale Acknowledgments This research was financially supported by the Vietnam National University HoChiMinh City (VNU-HCM) under grant number C2020-20-44 References [1] Li, 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p-nitrophenol from water. .. Graphite oxide Graphite oxit GO Graphene oxide Graphene oxit Gr Graphene Graphene rGO Reduced graphene oxide Graphene oxit dạng khử MFO Magnesium ferrite Ferrit magie TiO2- Titanium dioxide-magnesium. .. ferrite/reduced graphene oxide magie /graphene oxit dạng khử TiO2-rGO Titanium dioxide/reduced graphene oxide Titan dioxit graphene PNP p-nitrophenol p-nitrophenol TIP Titanium isopropoxide Titan