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MINISTRY OF EDUCATION AND TRAINING MINISTRY OF NATIONAL DEFENCE ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY TRAN VAN CHINH STUDY ON THE FABRICATION OF SPINEL FERRITE-BASED MATERIALS AND THEIR APPLICATIONS FOR THE REMOVAL OF HEAVY METAL IONS AND TOXIC ORGANIC DYE FROM AQUEOUS MEDIUM Specialization: Chemical engineering Code: 52 03 01 SUMMARY OF TECHNICAL DOCTORAL THESIS Ha Noi - 2022 THE DISSERTATION HAS BEEN COMPLETED AT ACADEMY OF MILITARY SCIENCE AND TECHNOLOGYMINISTRY OF NATIONAL DEFENCE Scientific supervisors: Assoc Prof Dr Nguyen Thi Hoai Phuong Prof Dr Vu Thi Thu Ha Reviewer 1: Prof Dr Dang Kim Chi Vietnam Association for Conservation of Nature and Environment Reviewer 2: Prof Dr Le Quoc Hung Vietnam Academy of Science and Technology Reviewer 3: Prof Dr Nguyen Viet Bac Academy of Military Science and Technology This doctoral dissertation has been defended at the Doctoral Evaluating Council at Academy level held at Academy of Military Science and Technology at , date .2022 This doctoral dissertation can be found at: - Library of Academy of Military Science and Technology - Viet Nam National Library INTRODUCTION The rationale of the thesis: In recent years, economic development has brought many good values to social life However, along with that development, people face the risk of the living environment being polluted due to many factors: The emission of industrial zones, factories producing chemicals, fertilizers, thermal power plants, textiles, dyeing, and battery industry wastewater which pollutes water and soil by heavy metal ions and organic dyes To deal with these conditions, it often requires expensive solutions and can cause secondary pollution Therefore, it is urgent to find an effective technique and materials to treat these pollutants Among the focused methods, adsorption and photocatalysis has been considered a cost-effective solution to remove the heavy metals and organic dye from the aqueous solution Recently, spinel ferrites (MFe2O4, M = Mg, Cu, Co, Ni, Zn,…), advanced materials, have been extensively studied as an adsorbent to remove the pollutants from wastewater These materials have chemical stability, favorable active sites to interact with the pollutants leading to the large adsorption capacity Additionally, spinel ferrites have magnetic properties, so they can be easily recovered from the solution by an external magnetic field, minimizing the secondary pollution and increasing recyclability It has been widely known that TiO2 is widely used as a photocatalyst in many processes, including environmental treatment However, several limitations, such as the rapid recombination of the generated e- and h+ pairs, difficulty recovering and reusing from solution, and only absorbing light in the ultraviolet (UV) region, have limited its practical performance application Tuning the energy band to absorb photon energy from a wide range of solar spectrums and improving charge separation of the photocatalyst has received attention from scientists worldwide In addition, material recyclability plays an essential role in feasibility for practical wastewater treatment Magnetic spinel ferrites were commonly incorporated to form the MFe2O4/TiO2 composite to solve this problem Along with magnetic properties, spinel ferrite also exhibits good harvesting capability for low-energy photons due to its bandgap energy of about 2eV, thus improving organic dyes' photocatalytic efficiency and quickly recovering after treatment by an external magnetic field Based on that rationale, the candidate focused on the “Study on the fabrication of spinel ferrite-based materials and their applications for removing heavy metal ions and toxic organic dye from aqueous medium." The main objectives of the thesis: - Synthesis of spinel ferrite Cu1-xMgxFe2O4 (x = 0; 0,5; 1) - Synthesis of TiO2 and Cu0.5Mg0.5Fe2O4/TiO2 composite - Characterizations of the prepared materials - Study on the effect of the factors on Pb2+ adsorption of Cu0.5Mg0.5Fe2O4 spinel ferrite Study on the photocatalytic performance of Cu0.5Mg0.5Fe2O4/TiO2 composite for the RhB degradation Research methodology used in the thesis: The thesis uses the literature review technique and experimental methodology to synthesize spinel ferrite materials and spinel ferrite/TiO2 composite by co-precipitation and sol-gel techniques Modern physicochemical analysis techniques were employed to study the structure and properties of materials such as TGA, XRD, EDX, FT-IR, SEM, TEM, XPS, BET, PL, UV-Vis DRS, VSM Atomic absorption spectroscopy (AAS) and UV-Vis spectrophotometric methods were utilized to determine Pb2+ and RhB concentrations in solution during the treatment The scientific and practical significance of the thesis: - The thesis has successfully synthesized magnetic spinel ferrite Cu1-xMgxFe2O4 (x = 0; 0.5; 1) and Cu0.5Mg0.5Fe2O4/TiO2 composite for the Pb2+ adsorption and the RhB photodegradation in aqueous media - Synthesized materials can be utilized in practical environmental treatment because they could be facilely recovered after an external magnetic field treatment, thereby reducing the generation of secondary pollution sources The structure of the thesis: The thesis has 158 pages, which has been divided into parts following: abstract, pages; chapter - literature review, 41 pages; chapter - experiments, 15 pages; chapter - results and discussion, 59 pages; conclusion, pages; list of published articles, pages and 32 pages of references (242 references) Chapter LITERATURE REVIEW 1.1 Spinel ferrite material This section introduced the structural characteristics, properties, synthesis techniques, and applications of spinel ferrite materials 1.2 TiO2 material This section introduced the properties, structures, and photocatalytic mechanism and applications of TiO2 and TiO2-based materials 1.3 Current status and approaches for the treatment of heavy metals and organic dyes in aqueous medium Analysis of the situation and status of water pollution by heavy metals and toxic organic dyes Theoretical foundations of adsorption and photocatalysis 1.4 Related research situation in Vietnam and worldwide This section analyzed and evaluated the research situation in Vietnam and worldwide on the application of spinel ferrite-based materials in heavy metal adsorption and photodegradation of organic dyes From there, set the scientific basis and orientation for the implementation of the research content of the thesis were drawn and carried out Chapter EXPERIMENTS 2.1 Chemicals, equipment and laboratory instruments Chemicals were used in the thesis, including FeCl3.6H2O; MgCl2.6H2O; CuCl2.2H2O; Ti(BuO)4; Pb(NO3)2; RhB; HCl, NaOH; C2H5OH, The equipments employed in the thesis consist of Heating magnetic stirrers Joanlab, Drying oven Ketong 101, Hightemperature furnaces HT 16/18 Nobertherm, Centrifuge UNIVERSAL 320/ 20 R, Overhead stirrer IKA RW16, Analytical balance PA 213 OHAUS, pH meter Hanna and the photocatalytic reactor uses a lamp simulating sunlight (wavelength from UV to IR range) xenon AHD350 of Shenzhen Anhonda and UV B light (wavelength from 280÷320 nm) 2.2 Synthesis of spinel ferrite Cu1-xMgxFe2O4 The spinel ferrite Cu1-xMgxFe2O4 (x = 0; 0,1; 0,3; 0.5; 0,7; 0,9; 1) were prepared using a chemical co-precipitation method The molar ratio of Fe3+:M2+ = 2:1 (M2+ = Cu2+ + Mg2+) FeCl3.6H2O, CuCl2.2H2O, MgCl2.6H2O were dissolved in a glass beaker containing 50 mL distilled water with the (Fe3+)/(Cu2++Mg2+) molar ratio of 1:2 The solution was stirred and heated to 90 °C with a magnetic stirrer for h before adding NaOH M solution to pH of 9-10 The solution was cooled down to the room temperature, and then was filtered and washed several times with distilled water and ethanol until pH of The washed samples were dried at 100 oC for 12 hours and then calcined at 400 ÷ 1000 oC for h 2.3 Synthesis of TiO2 and Cu0.5Mg0.5Fe2O4/TiO2 composite - TiO2 was synthesized by the sol-gel method, using titanium butoxide (Ti(BuO)4) as a precursor, and calcined at 450 ◦C for h - Cu0.5Mg0.5Fe2O4/TiO2 composite was synthesized by the solgel method as follows: 0,5 g of Cu0.5Mg0.5Fe2O4 was gradually added to the mixed solution of Ti(BuO)4 : Ethanol : H2O with different ratios The solution was mixed at 50 °C for h using a mechanical stirrer The precipitates were filtered, thoroughly washed, dried, and calcined at 450 ◦C for h in the air to obtain Cu0.5Mg0.5Fe2O4/TiO2 composite The mass ratio between Cu0.5Mg0.5Fe2O4 and TiO2 in the composite was adjusted by changing the Ti(BuO)4 proportion in the reaction mixture The symbols of the samples with various mass ratios of Cu0.5Mg0.5Fe2O4:TiO2 are shown in Table 2.2 Table 2.2 Symbols for samples under different conditions Parameters Mass of spinel (g) Volume of Ti(BuO)4 (mL) Mass ratio of Spinel:TiO2 Cu0.5Mg0.5Fe2O4 0,5 - 1:0 TiO2 - 0:1 ST0 0,5 0,5 4,4:1 ST1 0,5 2,2:1 ST2 0,5 1,1:1 ST3 0,5 1:1,4 ST4 0,5 1:2,8 Samples 2.4 Research methodologies and techniques - The physicochemical properties of the catalysts were determined by several methods such as TGA-DTA, XRD, EDX, FTIR, BET, solid sample UV-Vis, PL, SEM, TEM, and XPS - UV-vis spectrophotometry, Liquid chromatography-mass spectrometry (LC-MS)/MS spectra and the total organic carbon (TOC) were utilized for evaluation of the RhB degrading process - Atomic absorption spectroscopy (AAS) was employed to determine the concentration of metal ions in solution - Determination of the point of zero charge (pHpzc): 0,1 g of materials were added into flasks containing 25 mL of NaCl 0,1M solution with different initial pH values (pHi) from to 12 pH values were adjusted using HCl 0,1M and NaOH 0,1M solutions The flasks were closed tightly before being shaken for 24 h, then the final pH value (pHf) was measured Finally, the pHpzc value was estimated by plotting the ΔpH (pHi - pHf) against the pHi 2.5 Study on Pb2+ adsorption of Cu0.5Mg0.5Fe2O4 For each experiment, 0,1 g of Cu0.5Mg0.5Fe2O4 were added into flasks containing 50 mL of Pb2+ solution The flasks were placed on the shaker for 180 minutes at 100 rpm and they were kept at room temperature Then, the material was separated from the solution by a magnet and the concentration of Pb2+ in the solution after adsorption was determined 2.5.1 Effect of substitution of Cu2+ by Mg2+ on the adsorption capacity The adsorption process was carried out as above with Cu1-xMgxFe2O4 materials (x = 0; 0.1; 0.3; 0.5; 0.7; 0.9, 1), the initial concentration of Pb2+ solution was 23 mg/L, and pH of 2.5.2 Effect of pH on Pb2+ adsorption The adsorption process was carried out as above with the initial concentration of Pb2+ solution was 20 mg/L, pH of 3, 5, 7, 9, 11 (pH values were adjusted using HCl 0,1M and NaOH 0,1M solutions) 2.5.3 Adsorption isotherm` The adsorption process was carried out as above with Pb2+ concentration varying from ÷ 85 mg/L, and pH of 2.5.4 Adsorption kinetics The adsorption process was carried out as above with the initial concentration of Pb2+ solution of 80 mg/L, pH of at time points of 10, 30, 45, 60, 120, 240, and 360 minutes 2.5.5 The reusability of Cu0.5Mg0.5Fe2O4 The adsorption process was carried out as above, with the initial concentration of Pb2+ solution being 20 mg/L and pH of After each cycle, the adsorbent was separated and washed with 10 mL of HCl 0,1M solution After 60 minutes, the adsorbent was separated from the solution and washed again with water, then dried at 100 oC for hours and reused for the next cycles with the same adsorption process as mentioned above 2.5.6 The selective adsorption by Cu0.5Mg0.5Fe2O4 Cu0.5Mg0.5Fe2O4 was studied for selective adsorption toward Pb2+, Mg2+, Ca2+, Na+, and K+ with the same initial concentration of 20 mg/L, and pH of 2.6 Study on photodegradation of RhB solution by Cu0.5Mg0.5Fe2O4/TiO2 composite Figure 2.4 Photocatalytic reactor using xenon lamp AHD350 The photocatalytic performances of prepared photocatalysts were evaluated for the degradation of the RhB dye as a simulated pollutant under visible light using a 350 W xenon lamp, which simulated sunlight irradiation The photocatalytic performance was tested using a multitube photocatalytic reactor The distance between the light source and the reactor was 20 cm In a typical photocatalytic test, 20 mg of the photocatalyst was added to 20 mL of a 10 ppm RhB solution with pH of (the catalyst dose of g/L) Before carrying out the photocatalytic degradation experiment, the solutions were kept in the dark for h to establish an absorptiondesorption equilibrium The solution was taken out at certain times, and an external magnet was used to collect the photocatalysts The photocatalytic degradation process was monitored by measuring the characteristic absorption peak at 552 nm using a UV-vis spectrophotometer 2.6.1 Effect of TiO2 content on photocatalytic activity The samples denoted in Table 2.1, including TiO2, ST0, ST1, ST2, ST3, ST4, were calcined at 450 oC for hours, and Cu0.5Mg0.5Fe2O4 was studied for photocatalytic performance as above Determination of RhB concentration after 90 minutes of light irradiation and the results were compared between different samples 2.6.2 Effect of calcination temperature The Cu0.5Mg0.5Fe2O4/TiO2 composite (with optimal TiO2 content) were calcined at 450 oC, 550 oC, 650 oC and 750 oC for hours Then, the experiment was conducted as in section 2.6 after 90 minutes of irradition 2.6.3 Effect of photocatalysts The experiment was conducted with Cu0.5Mg0.5Fe2O4; TiO2 and Cu0.5Mg0.5Fe2O4/TiO2 photocatalysts The concentration of RhB solution was determined after each time point of 30 minutes 2.6.4 Effect of pH The experiment was performed as in section 2.6 at pH values of 3, 5, 7, 9, and 11 after 180 minutes of irradiation 2.6.5 The reusability of Cu0.5Mg0.5Fe2O4/TiO2 composite The stability and reusability of the Cu0.5Mg0.5Fe2O4/TiO2 photocatalyst were studied for five cycles of RhB degradation under simulated sunlight irradiation after 180 minutes The photocatalyst was recovered using an external magnetic field after each cycle of the photocatalytic reaction and dried at 100 oC for hours for the next cycle with the same photocatalytic conditions 2.6.6 Comparison of photocatalytic performance of Cu0.5Mg0.5Fe2O4/TiO2 composite under different light sources Photodegradation of RhB solution by Cu0.5Mg0.5Fe2O4/TiO2 photocatalyst was performed under different light sources: simulated sunlight, sunlight (irradiation time from 11 am to 14 pm of 24/7/2021, outdoor temperature of about 34 oC), and ultraviolet light (UVB lamp 280 ÷ 320 nm, power 26 W) Determination of RhB concentration after 180 minutes of irradiation to compare the photocatalytic performance under different light sources 2.6.7 Effect of the scavengers on the photodegradation of RhB 1,4-benzoquinon 10 mM (BQ), isopropanol (IPA), amonium oxalate 10 mM (AO), and AgNO3 10 mM (SN) were used as , * OH, h+ and e scanvengers, respectively 0,5 mL of BQ, IPA, AO, SN solutions were added into photocatalytic reactors containing 20 mL of a 10 ppm RhB solution (the catalyst dose of g/L) Determination of RhB concentration after 180 minutes of irradiation to evaluate role of the free radicals in the degraradation reactions 2.6.8 Evaluation of photodegradation products and mineralization The intermediates during the photodegradation of RhB over the Cu0.5Mg0.5Fe2O4/TiO2 photocatalyst were monitored by LC-MS/MS of the samples after illumination at time points min, 60 min, 120 min, and 180 TOC of the samples determined the mineralization after illumination at time points min, 30 min, 60 min, 90 min, 120 min, 150 min, and 180 Chapter RESULTS AND DISCUSSION 3.1 Synthesis of spinel ferrite Cu1-xMgxFe2O4 (x= 0; 0.5; 1) Thermogravimetric analysis (TGA) was carried out for Cu0.5Mg0.5Fe2O4 precursor to investigate the phase formation of spinel ferrite As shown in Figure 3.1, the weight loss of from 40 to 400 oC is about 22,7%, corresponding to the loss of moisture and decomposition of Cu(OH)2, Mg(OH)2, Fe(OH)3 hydroxides to form CuO, MgO, Fe2O3 oxides At above 400 oC, a negligible mass loss of about 3% is attributed to the complete decomposition of hydroxides and the formation of a spinel structure Figure 3.2 XRD patterns of Cu0.5Mg0.5Fe2O4 calcined at diffirent temperatures The X-ray diffraction (XRD) patterns of Cu0.5Mg0.5Fe2O4 samples calcined at different temperatures are shown in Figure 3.2 The intensities of characteristic peaks of the spinel structure could be observed as the temperature increased, and a single spinel phase was Figure 3.1 TGA-DTA curves for the Cu0.5Mg0.5Fe2O4 precursor 11 Figure 3.9: Magnetic hysteresis lop of Figure 3.10: Tauc plot of the samples the samples 3.2 Synthesis of TiO2 and Cu0.5Mg0.5Fe2O4/TiO2 composite The XRD pattern of TiO2 displayed diffraction peaks of the anatas phase (JCPDS 01-071-1167) The characteristic diffraction peaks of Cu0.5Mg0.5Fe2O4 (S) and TiO2 (A) also appeared in the XRD pattern of the Cu0.5Mg0.5Fe2O4/TiO2 compsite, indicating the successful fabrication of the Cu0.5Mg0.5Fe2O4/TiO2 composite (Figure 3.12) The chemical natures of TiO2, Cu0.5Mg0.5Fe2O4, and Cu0.5Mg0.5Fe2O4/TiO2 were studied using FTIR spectroscopy, as shown in Figure 3.13 Figure 3.12: XRD patterns of the Figure 3.13: FT-IR spectra the samples samples Figure 3.14 shows the EDX spectra of Cu0.5Mg0.5Fe2O4/TiO2 with all elements of Cu, Mg, Fe, Ti, and O appear in the EDX spectra Figure 3.14: EDX spectra of Cu0.5Mg0.5Fe2O4/TiO2 12 The XPS spectrums of the Cu0.5Mg0.5Fe2O4/TiO2 composite are shown in Figure 3.15 As shown in Figure 3.15, the characteristic peak for Fe 2p, Mg 1s, Cu 2p, Ti 2p, and O 1s reveal the oxidation state of Fe3+, Mg2+, Cu2+, Ti4+ and O2-, respectively in Cu0.5Mg0.5Fe2O4/TiO2 SEM images of the samples in Figure 3.16 show that TiO2 has a spherical shape with a diameter in the 10÷20 nm range Cu0.5Mg0.5Fe2O4 has a cube-like shape with an average particle size of approximately 30 nm The SEM and TEM images of the Cu0.5Mg0.5Fe2O4/TiO2 (Fig 3.16c and d, respectively) reveal the hybrid morphologies of both TiO2 and Cu0.5Mg0.5Fe2O4 These particles tend to aggregate, which might result from the high static affinities of the surfaces of the TiO2 and Cu0.5Mg0.5Fe2O4 particles Figure 3.15: (a) XPS survey spectrum of the Cu0.5Mg0.5Fe2O4/TiO2 and the core-level XPS profiles of (b) Fe 2p, (c)Mg 1s, (d) Cu 2p, (e)Ti 2p and (f) O 1s 13 Figure 3.16: SEM images and the size distribution histogram of (a) TiO2; (b) Cu0.5Mg0.5Fe2O4; (c) Cu0.5Mg0.5Fe2O4/TiO2, and (d) HR-TEM of Cu0.5Mg0.5Fe2O4/TiO2 The saturation magnetizations of Cu0.5Mg0.5Fe2O4 and Cu0.5Mg0.5Fe2O4/TiO2 is shown in the figure 3.18 with the value of 23,1 and 11,2 emu/g, respectively The lower saturation magnetization value of Cu0.5Mg0.5Fe2O4/TiO2 compared with that of Cu0.5Mg0.5Fe2O4 results from the presence of nonmagnetic TiO2 in the composite material The saturation magnetization value of Cu0.5Mg0.5Fe2O4/TiO2 is close to the saturation magnetization value of MgFe2O4 (Ms = 13,1 emu/g) 14 Figure 3.19: Tauc plot of the Figure 3.18 Magnetic hysteresis samples lop of the samples From the Tauc plot, the bandgap energies of Cu0.5Mg0.5Fe2O4/TiO2, and TiO2 were calculated to be 2,86, and 3,25 eV, respectively The PL spectrum of Cu0.5Mg0.5Fe2O4/TiO2 highlights a lower PL intensity than that of TiO2 and Cu0.5Mg0.5Fe2O4 This indicates that the recombination of photoinduced electron-hole pairs was significantly reduced Figure 3.20: PL spectra of the samples 3.3 Study on Pb2+ adsorption of Cu0.5Mg0.5Fe2O4 Figure 3.21: Adsorption Figure 3.22: Effect of pH on behavioour of the Cu-Mg ferrite Pb2+ adsorption 2+ toward Pb with various degrees of Mg substitution As shown in Figure 3.21, it is obvious that the relative 15 adsorption capacities of Cu-Mg ferrite toward Pb(II) increase along with the increase of Mg substitution degree However, after the Mg substitution degree reaches 0,5, the further increase of Mg substitution witnessed an insignificant increase of adsorption capacities Thus, hereafter, the Cu0.5Mg0.5Fe2O4 spinel ferrite are considered as the optimized composition for the following investigation Pb(II) adsorption significantly increased when solution pH increase from to 7, and its high adsorption capacity was maintained at pH from to 11 (Figure 3.22) The increase in adsorption capacity with solution pH from to is ascribed to the presence of lead species in the acidic solution and surface functional groups of the adsorbent Even though the high Pb(II) adsorption on Cu0.5Mg0.5Fe2O4 was observed until a pH of 11, pH will be used for all later experiments to eliminate any possible influence caused by Pb(OH)2 precipitation The linear plots of experimental data based on the Langmuir and Freundlich models are shown in Figure 3.25 The The Langmuir model is fitted for the adsorption behaviour indicating the adsorption process of the material follows the heterogeneous mechanism The maximum adsorption capacity of the sample calculated from the Langmuir model is 57,44 mg/g This indicates that the Pb(II) ions are adsorbed on Cu0.5Mg0.5Fe2O4 as a monolayer and each active site can only adsorb one Pb2+ cation Figure 3.25: Alinear plot of isotherm data based on (a) Langmuir, and (b) Freundlich models The linearized plots of the adsorption kinetics are shown in Figure 3.28 The results revealed that the pseudo-second-order kinetic model described well the Pb(II) adsorption onto Cu0.5Mg0.5Fe2O4 spinel ferrite 16 Figure 3.28: Linearized plot of log(qe-qt) vs time (t) in the pseudofirst-order kinetic model (a) and t/qt vs time (t) in the pseudo-second-order kinetics model (b) The Cu0.5Mg0.5Fe2O4 were removed from treated the solution using an external magnet and regenerated before the next testing cycle by washing the adsorbent with 10 mL of 0,1M HCl solution and water It can be clearly seen that only less than 10% in the decrease of removal efficiency was observed after cycles, which indicates that the Cu0.5Mg0.5Fe2O4 spinel ferrite is durable for the Pb(II) removal The Cu0.5Mg0.5Fe2O4 spinel ferrite showed a good selectivity against common contaminated ions in water including Ca2+, Mg2+, K2+, and Na2+ ions (Figure 3.30) The results revealed that over 99% of Pb(II) was removed, while the material negligibly absorbed the others Figure 3.29: Recyclability of the Figure 3.30: Adsorption Cu0.5Mg0.5Fe2O4 for the selective of the sample removal of Pb2+ 3.4 Study on photodegradation of RhB solution by Cu0.5Mg0.5Fe2O4/TiO2 composite The photocatalytic activities of the as-prepared samples were investigated through the degradation of RhB under simulated sunlight irradiation Before the photocatalytic degradation experiment, the solutions were kept in the dark for h to establish 17 absorption-desorption equilibrium The absorption behavior of the photocatalysts was negligible 3.4.1 Effect of TiO2 content on photocatalytic activity Figure 3.31: UV-Vis absorption spectra of the RhB photodegradation over the samples (Vdd = 20 mL; Co(RhB) = 10 mg/L; mxt = 0,02 g; irradiation time 90 minutes; pH = 7) The content of TiO2 in the composite is shown in Table 2.2 As shown in Figure 3.31, the photocatalytic activity of the samples with diffirent TiO2 contents are in the order of Cu0.5Mg0.5Fe2O4 < TiO2 < ST0 < ST1 < ST4 < ST3 < ST2 The ST2 sample provides the highest efficiency for photodegradation of RhB solution Thus, the ST2 sample (Cu0.5Mg0.5Fe2O4/TiO2 composite) are considered as the optimized composition for the following investigation 3.4.2 Effect of calcination temperature The Cu0.5Mg0.5Fe2O4/TiO2 composites were calcined at 450 oC, o 550 C, 650 oC, and 750 oC for hours The sample calcinated at 450 o C had the maximum degradation performance (Figure 3.32) Figure 3.32: UV-Vis absorption spectra of the RhB photodegradation over Cu0.5Mg0.5Fe2O4/TiO2 calcined at diffirent temperatures (Vdd = 20 mL; Co(RhB) = 10 mg/L; mxt = 0,02 g; irradiation time 90 minutes; pH = 7) 3.4.3 Effect of photocatalysts It is clear that the photocatalytic performance of TiO2 was better 18 than that of Cu0.5Mg0.5Fe2O4 but lower than that of the Cu0.5Mg0.5Fe2O4/TiO2 composite While the RhB removal efficiencies of TiO2 and Cu0.5Mg0.5Fe2O4 were 52,7% and 21,5%, respectively, the removal efficiency of Cu0.5Mg0.5Fe2O4/TiO2 was almost 100% after 180 of simulated sunlight irradiation This strongly suggests that the TiO2 and Cu0.5Mg0.5Fe2O4 composite significantly improves the photocatalytic performance Figure 3.35: The kinetics of the Figure 3.33: The photocatalytic samples for RhB degradation performance curve of the samples (Vdd = 20 mL; Co(RhB) = 10 for RhB degradation (Vdd = 20 mL; mg/L; mxt = 0,02 g; irradiation Co(RhB) = 10 mg/L; mxt = 0,02 g; time 180 minutes; pH = 7) pH = 7) The kinetics of the photocatalytic reaction were determined using a pseudo-first-order kinetics model Ln(C/Co) = -kt The results are presented in Figure 3.35 and Table 3.10 Bảng 3.10: Apparent reaction rate constant (k) and photodegradation efficiency of the samples for RhB initial concentration of 10 ppm Photodegradation Catalysts k (10-3.min-1) efficiency, % TiO2 3,24 52,7 Cu0.5Mg0.5Fe2O4 1,06 21,5 Cu0.5Mg0.5Fe2O4-TiO2 13,96 98,4 The values of the photodegradation rate constant (k) of TiO2, Cu0.5Mg0.5Fe2O4 Cu0.5Mg0.5Fe2O4/TiO2 were 3,24.10-3 min-1; 1,06.10-3 min-1, and 13,96.10-3 min-1, respectively The rate constants of Cu0.5Mg0.5Fe2O4/TiO2 are 4,3 and 13,2 times higher than those of the free-standing TiO2 and Cu0.5Mg0.5Fe2O4 These results demonstrate that the Cu0.5Mg0.5Fe2O4/TiO2 composite remarkably improved the photocatalytic activity of both TiO2 and Cu0.5Mg0.5Fe2O4 19 3.4.3 The reusability of Cu0.5Mg0.5Fe2O4/TiO2 composite Figure 3.38: Recyclability of Cu0.5Mg0.5Fe2O4/TiO2 photocatalyst for RhB degradation (Vdd = 20 mL; Co(RhB) = 10 mg/L; mxt = 0,02 g; irradiation time 180 minutes; pH = 7) The figure 3.38 clearly shows that the removal efficiency of RhB when using the Cu0.5Mg0.5Fe2O4/TiO2 photocatalyst negligibly reduces after five cycles of photocatalytic reaction with a reduction of only 6,8% This indicates that the synthesized Cu0.5Mg0.5Fe2O4/TiO2 composite has high photocatalytic activity with good stability and reusability, which is promising for treating dyes-contaminted wastewater 3.4.4 Comparison of photocatalytic activity of Cu0.5Mg0.5Fe2O4/TiO2 composite under different light sources Figure 3.40: Photocatalytic activities of Cu0.5Mg0.5Fe2O4/TiO2 under irradiation of different light sources (Vdd = 20 mL; Co(RhB) = 10 mg/L; mxt = 0,02 g; irradiation time 180 min; pH = 7) In order to evaluate the capability of the prepared material for the practical application, a comparision of the photocatalytic activity of Cu0.5Mg0.5Fe2O4/TiO2 composite was carried out under irradiation of simulated light, sunlight, and ultraviolet light (UV) The experimental results are shown in Figure 3.40 Photodegradation efficiency of the catalyst under UV light is lowest with the RhB 20 removal percentage of about 42,6 % after 180 While under both simulated light and sunlight, photocatalytic performance of the catalyst reveals high removal efficiency of 98,4%; 90,1%, respectively 3.4.5 Proposed photodegradation mechanism of RhB To investigate the role of free radicals ( , *OH, h+, and e-) generated during the photodegradation of RhB by the Cu0.5Mg0.5Fe2O4/TiO2 photocatalyst, trapping experiments were carried out with 1,4-benzoquinone (BQ) for scavenging, isopropyl alcohol (IPA) for *OH scavenging, ammonium oxalate (AO) for h+ scavenging, and silver nitrate (SN) for e- scavenging As shown in Figure 3.41, *OH is the main active species participating in the photodegradation of RhB dye by the Cu0.5Mg0.5Fe2O4/TiO2 photocatalyst Figure 3.41: Effect of a series of scavengers on the degradation efficiency of RhB over Cu0.5Mg0.5Fe2O4/TiO2 The intermediates during the photodegradation of RhB over the Cu0.5Mg0.5Fe2O4/TiO2 photocatalyst were monitored by LC-MS/MS, as shown in Figure 3.42 Figure 3.42: LC-MS/MS spectra of RhB during photodegradation process by the Cu0.5Mg0.5Fe2O4/TiO2photocatalyst, (a) RhB, (b) DER and (c) DR or EER 21 Figure 3.44: Removal efficiency of TOC durring photodegradation of RhB The m/z peak values at approximately 443, 415, 387, and 359 were assigned to RhB, N,N-diethyl-N’-ethylrhodamine (DER), N,Ndiethylrhodamine (DR) or N-ethyl-N’-ethylrhodamine (EER), and N’-ehthylrhodamine (ER), respectively After N-deethylation, the small aromatic molecules further experience a ring-opening process before mineralizing to form CO2 and H2O environmentally friendly products The mineralization of small aromatic compounds to form CO2 and H2O was confirmed by total organic carbon analysis (Figure 3.44) Possible pathways of RhB photodegradation over Cu0.5Mg0.5Fe2O4/TiO2 catalyst was presented in Figure 3.44, including four processes: N-deethylation, cleavage chromophore, opening-ring, and mineralization RhB 443 N-de-ethylation EER 387 DER 415 ER 359 DR 387 Cleavage chromophore 22 Axit benzoic Phenol Opening-ring Small aromatic molecules Mineralization CO2 + H2O Figure 3.45: Possible pathways of RhB photodegradation over Cu0.5Mg0.5Fe2O4/TiO2 under simulated irradiation condition Based on the above results and discussion, the possible mechanisms of the photodegradation activity of the Cu0.5Mg0.5Fe2O4/TiO2 can be proposed as follows (Figure 3.46) Cu0.5Mg0.5Fe2O4/TiO2 + hυ → Cu0.5Mg0.5Fe2O4/TiO2 ( + ) * eCB O2 O2 O2* H 2O *OH OOH hVB H 2O *OH H OH RhB CO2 H 2O * Figure 3.46: Plausible mechanism concerning photocatalytic activity of Cu0.5Mg0.5Fe2O4/TiO2 photocatalyst for RhB degradation under simulated sunlight irradiation When the Cu0.5Mg0.5Fe2O4/TiO2 photocatalyst was irradiated under simulated sunlight, electron-hole pairs were generated from the Cu0.5Mg0.5Fe2O4 and TiO2 semiconductors The photogenerated electrons were transferred from the conductive band of Cu0.5Mg0.5Fe2O4 to the conductive band of TiO2 through the interface 23 and reduced O2 in water to Conversely, the photogenerated holes in TiO2 were transferred to the valence band of Cu0.5Mg0.5Fe2O4 and participated in the redox reactions by forming * OH radicals and oxidizing RhB to CO2 and H2O CONCLUSSIONS The results - Successful synthesis of magnetic spinel ferrite Cu1-xMgxFe2O4 (x = 0; 0,5; 1) by co-precipitation method The saturation magnetization for Cu0.5Mg0.5Fe2O4 is 23,1 emu/g The particles of Cu0.5Mg0.5Fe are relatively uniform with an average particle size of approximately 29,5 nm with a single-phase spinel structure at 900 o C The surface area and porosity of Cu0.5Mg0.5Fe2O4 are higher than that of CuFe2O4 and MgFe2O4 spinel ferrites - Study on Pb2+ adsorption of Cu0.5Mg0.5Fe2O4 spinel ferrite When replacing Mg2+ into the structure of CuFe2O4, the Pb2+ adsorption capacity of CuFe2O4 improved Adsorption behaviour of the Cu0.5Mg0.5Fe2O4 toward Pb2+ was found to be Langmuir model and pseudo-second order The maximum adsorption capacity of the sample calculated from the Langmuir model is 57,44 mg/g at pH of and 25 oC The Cu0.5Mg0.5Fe2O4 material is stable and effective for the removal of lead ions - Successful synthesis of TiO2 and Cu0.5Mg0.5Fe2O4/TiO2 composite by the sol-gel method The bandgap energy of Cu0.5Mg0.5Fe2O4/TiO2 is 2,86 After TiO2 was loaded on Cu0.5Mg0.5Fe2O4, the recombination of photo-induced electron-hole pairs was significantly reduced, which in turn enhanced the photocatalytic performance The saturation magnetization for Cu0.5Mg0.5Fe2O4/TiO2 composite is 11,2 emu/g - The photodegradation of RhB (10 mg/L) by Cu0.5Mg0.5Fe2O4/TiO2 composite was 98,4% after 180 of simulated sunlight irradiation - Photodegradation mechanism and pathway of RhB wer proposed *OH is the main active species participating in the photodegradation of RhB dye by the Cu0.5Mg0.5Fe2O4/TiO2 photocatalyst The RhB degradation by the material experiences four stages: N-deethylation, cleavage chromophore, opening-ring, and mineralization 24 New contributions of the thesis - Successful synthesis of spinel ferrite nanoparticles containing two divalent metal ions (Cu2+ and Mg2+) by co-precipitation method with single-phase spinel structure and uniform distribution of particle sizes - The spinel ferrite-based nanoparticles prepared by replacing Mg2+ into the structure of CuFe2O4 showed enhanced adsorption capacity toward Pb2+ ions The adsorption mechanism of Cu0.5Mg0.5Fe2O4 for the Pb2+ was proposed, which indicates that the improved adsorption capability of the material is ascribed to the increase in pore volume and the decrease in the particle size - Successful fabrication of Cu0.5Mg0.5Fe2O4/TiO2 composite material and employed as a photocatalyst for the Rhodamine B degradation With low bandgap energy, the new photocatalyst could harvest the energy in the visible light region The prepared composite material exhibited high photocatalytic performance toward Rhodamine B The plausible photocatalytic mechanism was proposed and discussed The photocatalyst is facilely separated using an external magnet and showed high recyclability, thereby reducing secondary pollution source emissions THE SCIENTIFIC PUBLICATIONS [CT1] Trần Văn Chinh, Nguyễn Thị Hoài Phương, Nguyễn Hoài Phương, (2019): “Nghiên cứu chế tạo vật liệu spinel ferrite CuxMg1-xFe2O4 (x = 0,5) ứng dụng xử lý kim loại nặng nước” Tạp chí Hấp phụ Xúc tác, số 8, tập 2, tr - 11 [CT2] Tran Van Chinh, Nguyen Huong Lan, Nguyen Thi Hoai Phuong, Vu Thi Thu Ha, (2020): “Photocatalytic degradation of MB over MgFe 2O4-TiO2 composite material under simulated sunlight irradiation” Vietnam journal of Chemistry, V.58 (5E12), pp 359-365 [CT3] Chinh Van Tran, Dang Viet Quang, Hoai Phuong Nguyen Thi, Tuan Ngoc Truong, Duong Duc La, (2020): “Effective Removal of Pb (II) from Aqueous Media by a New Design of Cu–Mg Binary Ferrite” ACS Omega, V.5, Is.13, pp 7298-7306 [CT4] Tran Van Chinh, Nguyen Thi Hoai Phuong, Vu Thi Thu Ha, Phan Thanh Xuan, Phung Khac Nam Ho (2021): “Structure, morphological, magnetic and optical properties of CuxMg1-xFe2O4 (x = 0, 0.5, 1) nano ferrites synthesized by co-precipitation method” Journal of Military Science and Technology Special Issue - No.72A [CT5] Chinh Van Tran, La Duc Duong, Hoai Phuong Nguyen Thi, Ha Duc Ninh, Phuong Nguyen Thi Hong, Thu Ha Thi Vu, Ashok Kumar Nadda, X Cuong Nguyen, Dinh Duc Nguyen, Ngo Huu Hao, (2021): “A new TiO 2-doped Cu-Mg spinel ferrite based photocatalyst for degrading highly toxic Rhodamine B dye in wastewater” Journal of Hazardous Materials, V.420, p.126636 [CT6] D Duong La, Chinh V Tran, Nhung TT Hoang, M Duyen Doan Ngoc, TH Phuong Nguyen, H Tung Vo, P Hien Ho, T Anh Nguyen, Sheshanath V Bhosale, X Cuong Nguyen, S Woong Chang, Woo J Chung, D Duc Nguyen, (2020): Efficient photocatalysis of organic dyes under simulated sunlight irradiation by a novel magnetic CuFe2O4@porphyrin nanofiber hybrid material fabricated via self-assembly Fuel, V.281, pp 118655 ... Nguyễn Thị Hoài Phương, Nguyễn Hoài Phương, (2019): ? ?Nghiên cứu chế tạo vật liệu spinel ferrite CuxMg1-xFe2O4 (x = 0,5) ứng dụng xử lý kim loại nặng nước? ?? Tạp chí Hấp phụ Xúc tác, số 8, tập 2, tr -... spinel structure at 900 o C The surface area and porosity of Cu0.5Mg0.5Fe2O4 are higher than that of CuFe2O4 and MgFe2O4 spinel ferrites - Study on Pb2+ adsorption of Cu0.5Mg0.5Fe2O4 spinel ferrite. .. UV to IR range) xenon AHD350 of Shenzhen Anhonda and UV B light (wavelength from 280÷320 nm) 2.2 Synthesis of spinel ferrite Cu1-xMgxFe2O4 The spinel ferrite Cu1-xMgxFe2O4 (x = 0; 0,1; 0,3; 0.5;
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