Metal Oxide Nanostructures: Synthesis, Properties, and ApplicationsView this Special Issue
Synthesis and Application of Magnetic Photocatalyst of Ni-Zn Ferrite/TiO2 from IC Lead Frame Scraps
IC lead frame scraps with about 18.01% tin, 34.33% nickel, and 47.66% iron in composition are industrial wastes of IC lead frame production. The amount of thousand tons of frame scraps in Taiwan each year is treated as scrap irons. Ni-Zn ferrites used in high frequent inductors and filters are produced from Ni-Zn ferrite powders by pressing and sintering. The amount of several ten thousand tons of ferrites of in compositions is consumed annually in the whole world. Therefore, these IC lead frame scraps will be used in this research as raw materials to fabricate magnetic ferrite powders and combined subsequently with titanium sulfate and urea to produce magnetic photocatalysts by coprecipitation for effective waste utilization. The prepared Ni-Zn ferrite powder and magnetic photocatalyst (Ni-Zn ferrite/TiO2) were characterized by ICP, XRF, XRD, EDX, SEM, SQUID, and BET. The photocatalytic activity of synthesized magnetic photocatalysts was tested by FBL dye wastewater degradation. TOC and ADMI measurement for degradation studies were carried out, respectively. Langmuir-Hinshelwood kinetic model of the prepared magnetic TiO2 proved available for the treatments. Wastes are transformed to valuable magnetic photocatalysts in this research to solve the separation problem of wastewater and TiO2 photocatalysts by magnetic field.
Wastewaters from textile and dyeing industries are highly colored by various nonbiodegradable dyes which cause serious environmental problems . Advanced oxidation processes such as UV/H2O2 , ozonation [3–5], Fenton processes [5–8], ozone/Fenton , and TiO2 and modified TiO2 [10–17] are promising alternatives for the mineralization of textile dyes or other pollutants. Among them, semiconductor TiO2’s simultaneous photocatalytic oxidation and reduction show significant potential due to being photoreactive, nontoxic, chemically and biologically inert, photostable, and lower in cost. Among different advanced oxidation processes (AOPs), a brand new AOP, sonolysis or hybrid AOP, combined with sonolysis has drawn increasing attention as it generates free radical through transient cavitation by ultrasound irradiation [18–20]. Cavitation is essentially the nucleation, growth, and transient implosive collapse of gas bubbles driven by ultrasound wave.
The well-known nickel-zinc ferrite is of special technological significance, particularly at high frequencies, because of its high resistivity and low eddy current losses. Several methods are conventionally used for the synthesis of these nanosized ferrites such as ceramic [21, 22], sol-gel [23, 24], coprecipitation , hydrothermal method [26, 27], citrate precursor method [28, 29], and autocombustion method [29, 30]. Sonochemical approach is considerably new to synthesize ferrite in which ferrite nanoparticles are prepared by ultrasound irradiation or sonication of the reaction mixture .
Despite existing technologies, separation difficulty of nanosized TiO2 particles from treated wastewater still remains. Fixed-film-TiO2 systems are undermined due to immobility while magnetic TiO2 offers to overcome this limitation. For example, Chen and Zhao  reported a magnetically separable photocatalyst of TiO2/SiO2/-Fe2O3 prepared by solid phase synthesis. The addition of a SiO2 membrane between the -Fe2O3 core and the TiO2 shell weakened the adverse effects of -Fe2O3 on the photocatalysis of TiO2. Photocatalysts in Chen and Zhao’s article showed good photocatalytic activity and could be separated from the solution with magnetic field. Gao et al.  synthesized a magnetically separated photocatalyst of TiO2/-Fe2O3 by sol-gel method. The sample sintered at 500°C displayed the highest degradation activity for acridine dye aqueous solution, with the optimal TiO2 supporting amount approximating 50%. Fu et al.  successfully prepared TiO2/NiCuZn ferrite composite powder as a magnetic photocatalyst. The core NiCuZn ferrite powder was synthesized with the waste material from steel and electroplating industries. TiO2 nanocrystal shell was prepared by sol-gel hydrolysis of titanium isopropoxide with NiCuZn ferrite powder followed by heat treatment. In their study, the optimum dosage of the magnetic photocatalyst was 2.67 g/L to treat methylene blue solution.
Recently we produced MnZn ferrite powders , which are used in power transformers and inductors, from spent alkali-manganese batteries in order to solve their heavy metal contamination problem. Comparing with MnZn ferrite, Ni-Zn ferrite is easier to be prepared. Lower temperature and no protecting atmosphere are needed during sintering. Therefore Ni-Zn ferrite was chosen to produce magnetic photocatalysts from IC lead frame scrap and waste pickling acid. Both ferrites solve the different heavy metals pollution problems and transform into useful magnetic photocatalysts.
In this research, a simple magnetic photocatalyst preparation was undertaken. First, Ni-Zn magnetic ferrite powder was prepared from IC lead frame scraps and ferrous sulfate containing spent acid solution from steel plants by coprecipitation. Then, the magnetic powder was added to a titanium sulfate solution and the hydroxides of titanium were precipitated at desired pH with urea solution. After filtration, drying, and grinding, the precipitates were sintered at 500°C under N2 atmosphere to form the magnetic photocatalyst, Ni-Zn ferrite/TiO2. The degradations of simulated FBL (Everdirect Supra Turquoise Blue) dye wastewater were carried out by applying self-prepared magnetic photocatalysts under UVA irradiation. Also L-H kinetic model was studied.
2. Materials and Methods
2.1. Preparation of Magnetic Ni-Zn Ferrite Powder and Magnetic Photocatalyst
Nitric acid was added sequentially to the small piece of lead frame scraps to dissolve nickel and iron. When hydrolysis was complete, tins were all precipitated as Sn(OH)4 and the filtrate contained Ni+2 and Fe+2 ions. After detinning and according to the nickel concentration, waste acids from steel industry containing iron and reagent of zinc nitrate were added to the solution to adjust the solution composition as , where is chosen as 0.5. NaOH solution is then added to adjust the solution pH value to alkali. Subsequently, all Fe, Ni, and Zn ions in the solution were transformed into hydroxide forms and suspended in the solution. The solution was pumped with air to oxidize ferrous ion and heated for several hours. All hydroxides were reacted and precipitated from the solution as ferrite powders. Ni-Zn ferrite powders were filtered, washed, calcined, and dried. The designed composition was Ni : Zn : Fe = 0.5 : 0.5 : 2.0 by moles and Ni : Zn : Fe = 16.9 : 18.8 : 64.3 by weight percentages or NiO : ZnO : Fe2O3 = 9.4 : 10.2 : 80.4 by weight. Corresponding reactions are shown in the following:Experimental treatment with photocatalyst-TiO2 alone for dye wastewater is proved to be very efficient. Besides, the secondary pollution by other advanced treatment methods can be eliminated. But there still exists the separation problem of solids (TiO2) and liquids (wastewater). Therefore, used in this study were titanium sulfate, urea, and Ni-Zn ferrite powder to produce modified titanium dioxide photocatalyst by coprecipitation. The ratio of Ni-Zn ferrite powder to TiO2 was 1 : 1 (wt%). Finally magnetic photocatalyst powder was obtained by filtration, drying, grinding, and calcination at 500°C. The same procedure was used for the preparation of TiO2 except the step of no addition of magnetic Ni-Zn ferrite powder. Related reactions were
The characterizations of the prepared Ni-Zn ferrite powders and modified magnetic photocatalysts, Ni-Zn ferrite/TiO2, were investigated by ICP, XRF, XRD, SEM, SQUID, and BET measurements. TOC and ADMI values can be applied for the treatment of dye wastewater under UVA irradiation with the self-prepared TiO2 and Ni-Zn ferrite/TiO2 magnetic photocatalysts.
The crystalline structures of both magnetic powder and magnetic photocatalyst were examined by XRD (X-ray diffractometer, XRD-6000, Shimadzu, Japan). Their M-H loops were measured by SQUID (superconducting quantum interference device, MPM57, Quantum Design, USA). Particle chemical compositions were analyzed by ICP (ICAP 9000, USA) and XRF (X-ray fluorescence, XEPOS/XEPO1, Spectro Co., Germany). Their microstructures were observed by SEM (scanning electron microscopy, S-3000N, Hitachi, Japan). The specific area was measured by BET surface area analyzer (Brunauer-Emmett-Teller, Model-ASAP 2012, Micromeritics, USA).
2.3. Photocatalytic Degradation
Photocatalytic reactions were carried out by mixing 1 L of FBL dye solution and 5 g of magnetic Ni-Zn ferrite/TiO2 photocatalysts inside a 2 L photoreactor with a Teflon agitator under UVA irradiation for 8 hrs. The structure of the FBL dye was shown in . The initial dye concentrations were COD = 100, 200, 300, and 400 mg/L for each experiment. After photoreaction and filtration by 0.45 μm MFS, TOC (total organic carbon, Model 1010, O.I. Analytical, USA) and ADMI color values (American Dye Manufacturers Institute, Model DR/4000V, HACH, USA) were measured for each sample. COD was determined by potassium dichromate titration as described in Standard Methods . UVA intensities were measured by a radiometer (Lutron Co., Taiwan) and expressed as (mW/cm2).
3. Results and Discussion
3.1. Characterization of Magnetic Photocatalyst of Ni-Zn Ferrite/TiO2
XRF analyses of Ni-Zn ferrite powders and Ni-Zn ferrite/TiO2 are shown in Table 3. It is clear that the experimental values of magnetic powders from wastes are close to the quantity of the predetermined value. SEM micrographs suggest that particles of magnetic Ni-Zn ferrite powders agglomerate. The particle size is around 0.3 μm by DLS (dynamic light scattering) analysis . TiO2 is precipitated on the surface of the secondary particle and its size is approximately 469.7 nm as shown in Figure 1. EDX diagrams of Ni-Zn ferrite powders and Ni-Zn ferrite/TiO2 photocatalyst indicate the presence of Ni, Zn, Fe, and titanium as shown in Figure 2. X-ray diffraction patterns of Ni-Zn ferrite powders and magnetic photocatalysts in Figure 3 reveal the spinel cubic ferrites and the anatase form of TiO2. All peaks in the pattern match well with the Joint Committee of Powder Diffraction Standard (JCDDS). A small amount of hematite also exists in the specimens. The surface area of Ni-Zn ferrite powder by BET measurement is 17 m2/g and that of Ni-Zn ferrite/TiO2 rises to 61 m2/g, which shows more active sites for photoreaction.
The self-prepared TiO2 follows the same coprecipitation without the addition of Ni-Zn ferrite powder and the corresponding SEM and EDX diagrams are shown in Figures 4 and 5. The particle size is around 1 μm–4.8 μm and BET is 116 (m2/g) while BET of commercial TiO2 (7 nm) is 231 (m2/g).
3.2. Magnetic Property
Magnetic properties of Ni-Zn ferrite powders and Ni-Zn ferrite/TiO2 are presented in Figure 6 as magnetic hysteresis loops by SQUID. The saturation magnetization (Ms) of Ni-Zn ferrite powder and Ni-Zn ferrite/TiO2 is 64.43 and 17.05 emu/g and the corresponding coercive forces (Hc) are 6.13 and 7.66 Oe, respectively. Due to the minimal hysteresis and small Hc, the prepared magnetic materials are all soft magnetic and the magnetic photocatalysts made up from wastes can be recycled by applied magnetic field because of the magnetic property. The small coercivity of the ferrite mainly comes from the soft magnetic properties of the Ni-Zn ferrite, which has very low crystal and shape anisotropy constant, and is not due to size effect . The saturation magnetization of the ferrite (Ni0.5Zn0.5Fe2O4) prepared here is 64.43 emu/g, and the literature values are about 70 emu/g , depending on the preparation conditions. They are quite comparable.
Photodegradations of simulated FBL dye wastewater at initial CODs of 100, 200, 300, and 400 mg/L under UVA irradiation with self-produced magnetic photocatalysts from wastes are shown in Figures 7 and 8. The degradation efficiencies increase as the pollutant concentrations decrease. For dilute pollution of FBL dye (COD = 100 ppm), TOC removal can reach 84.22% and color or ADMI removal reaches 81.68%. The photodegradations by self-prepared TiO2, commercial TiO2, and Ni-Zn ferrite/TiO2 are also summarized and compared in Table 4. Ni-Zn ferrite/TiO2 from wastes is very close to the commercial TiO2 (20 nm) in treatment efficiency by treating dilute simulated dye wastewater. The treatment efficiency of the self-prepared TiO2 is better than that of the commercial TiO2 (20 nm).
3.4. Langmuir-Hinshelwood Kinetic Model (L-H Model)
L-H model can be expressed by the following equation: where is the photocatalytic reaction constant [mg/(L-min)], is the apparent degradation rate constant (min−1), and is the dye concentration, TOC (mg/L). Combining zero-order and first-order reactions, L-H model becomes Let C = 0.715C0, t = t0.715; the equation becomesPlotting t0.715 against 0.285C0 brings about a straight line as shown in Figure 9. From the slope and intercept, kinetic constants can be calculated.
Constants obtained from L-H model are (mg/L min), (min−1), and . The result shows that L-H kinetic model fits well for the photodegradation of FBL simulated dye wastewater with the self-prepared Ni-Zn ferrite/TiO2.
The following conclusions can be drawn:(1)Magnetic ferrite powder of Ni0.5Zn0.5Fe2O4 was successfully prepared by coprecipitation from industrial wastes of IC lead frame and waste acids of steel industry.(2)Magnetic photocatalyst of Ni-Zn ferrite/TiO2 was also successfully fabricated from prepared magnetic ferrite powder, Ti (SO4)2, and urea by the same coprecipitation. By XRD analysis, TiO2 in magnetic photocatalyst shows the crystal structure of anatase form.(3)By SQUID analysis, the saturation magnetism (Ms) of the prepared magnetic photocatalysts is 17.05 emu/g with the coercive force (Hc) of 7.66 Oe, which proves that the magnetic photocatalyst is soft magnetic material and can be recycled by magnetic field.(4)The degradation of FBL dye shows that TOC and ADMI removal efficiencies are quite close for the prepared Ni-Zn ferrite/TiO2 and the commercial 20 (nm) TiO2. The magnetic photocatalysts can solve the separation problem between wastewater and TiO2 photocatalysts by magnetic field.(5)L-H kinetic model fits well for the self-prepared magnetic photocatalysts of Ni-Zn ferrite/TiO2, which can be used successfully in AOP.(6)Quite consequential is the transformation of hazardous wastes to valuable magnetic ferrite powders and magnetic photocatalysts and the processes studied not only recycle wastes to solve the global pollution problem but also tell the possibility of turning profits.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
This project was supported by National Science Council, Taiwan, and Yeou Hung Material Technology Co., Ltd., Taiwan, under Contract no. NSC 100-2622-E-159-001-CC3. The authors express sincere gratitude for the financial support for this research.
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