Magnetic photocatalyst solves the separation problem between wastewater and TiO2 photocatalysts by the application of magnetic field. This research investigates the treatment of simulated FBL dye wastewater using Mn-Zn ferrite/TiO2 magnetic photocatalyst. The magnetic Mn-Zn ferrite powder was first produced by a chemical coprecipitation method from spent dry batteries and spent pickling acid solutions. These two scraps comprise the only constituents of Mn-Zn ferrite. The as-synthesized Mn-Zn ferrite was then suspended in a solution containing Ti(SO4)2 and urea. Subsequently a magnetic photocatalyst was obtained from the solution by chemical coprecipitation. The prepared Mn-Zn ferrite powder and magnetic photocatalyst (Mn-Zn ferrite/TiO2) were characterized using XRD, EDX, SEM, SQUID, BET, and so forth. The photocatalytic activity of the synthesized magnetic photocatalysts was tested using degradation of FBL dye wastewater. The adsorption and degradation studies by the TOC and ADMI measurement were carried out, respectively. The adsorption isotherm and Langmuir-Hinshelwood kinetic model for the prepared magnetic TiO2 were proved to be applicable for the treatment. This research transforms waste into a valuable magnetic photocatalyst.
Wastewaters from textile and dyeing industries are highly colored by various nonbiodegradable dyes which cause serious environmental problems [
Manganese zinc ferrites are important ferrimagnetic materials because of their high magnetic permeability and low magnetic hysteresis loss [
Despite existing technologies, nanosized TiO2 particles remain difficult to separate from treated wastewater. Fixed-film-TiO2 systems are undermined by their own immobility, while magnetic TiO2 systems offer to overcome this limitation. For example, Ma et al. [
In this research, a simple magnetic photocatalyst preparation method was undertaken. First, Mn-Zn magnetic ferrite powder was prepared from spent Mn-Zn dry batteries and ferrous sulfate containing spent acid solution from steel plants by using coprecipitation method. Then, the magnetic powder was added to a titanium sulfate solution and the hydroxides of titanium were precipitated at desired pH using urea solution. After filtration, drying, and grinding, the precipitates were sintered at 500°C under N2 atmosphere to form the magnetic photocatalyst, Mn-Zn ferrite/TiO2. The adsorption and degradation of simulated FBL (Everdirect Supra Turquoise Blue) dye wastewater were carried out by applying self-prepared magnetic photocatalysts under dark as well as under solar irradiation. The adsorption isotherm and L-H kinetic model were also studied.
The flow diagram for preparing the Mn-Zn ferrite powder and ferrite is shown in Figure
Flow chart for preparation of Mn-Zn ferrite by coprecipitation process from zinc-carbon waste dry batteries and waste sulfuric acid.
The magnetic photocatalyst was prepared by adding Mn-Zn ferrite magnetic powder 10 g and urea (N2H4CO) of 150 g into 92 mL of Ti(SO4)2 solution. The ratio of Mn-Zn ferrite powder to TiO2 was 1 : 1 (wt%). The flow chart for the preparation of the magnetic photocatalyst of Mn-Zn ferrite/TiO2 is shown in Figure
Flow chart for the preparation of magnetic photocatalyst of Mn-Zn ferrite/TiO2.
The crystalline structure of both magnetic powder and magnetic photocatalyst was 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). The chemical compositions of the particles were analyzed by XRF (X-ray fluorescence, XEPOS/XEPO1, Spectro Co., Germany). Their microstructure was observed by SEM (scanning electron microscopy, S-3000N, Hitachi, Japan). The specific area was measured by BET (Brunauer-Emmett-Teller, Model-ASAP 2012, Micromeritics, USA).
The adsorption and photocatalytic reaction were carried out by mixing 1 L of a FBL dye solution with 5 g of magnetic Mn-Zn ferrite/TiO2 photocatalysts inside a 2 L photoreactor beaker, using a teflon agitator under dark and under solar irradiation for 8 hrs, respectively. The structure of the FBL dye was shown in [
The XRF analysis of Mn-Zn ferrite powder and Mn-Zn ferrite/TiO2 is shown in Table
XRF analysis of magnetic powder and magnetic photocatalyst.
Samples | Fe2O3 (wt%) | MnO (wt%) | ZnO (wt%) | TiO2 (wt%) |
---|---|---|---|---|
Mn-Zn ferrite powder |
70.55% | 20.89% | 8.56% | — |
Mn-Zn ferrite powder |
66.2% | 26.2% | 7.5% | — |
Mn-Zn ferrite/TiO2 (N2 500°C) |
28.4% | 8.5% | 2.9% | 60.1% |
SEM images of self-prepared magnetic photocatalyst of Mn-Zn ferrite/TiO2 (a) ×10000, (b) ×25000.
EDX of Mn-Zn ferrite powder (a) and Mn-Zn ferrite/TiO2 (b).
XRD pattern of Mn-Zn ferrite powder (a), Mn-Zn ferrite sintered at 1200°C (N2) (b), and Mn-Zn ferrite/TiO2 (N2, 500°C) (c).
The magnetic properties of Mn-Zn ferrite powder, Mn-Zn ferrite, and Mn-Zn ferrite/TiO2 are presented by magnetic hysteresis loops using SQUID as shown in Figure
Hysteresis loop of Mn-Zn ferrite calcined at 1200°C (a), Mn-Zn ferrite powder without calcinations (b), and Mn-Zn ferrite/TiO2 calcined at 500°C (c).
The TOC and color ADMI removal percentage through the adsorption of Mn-Zn ferrite/TiO2 from FBL simulated dye wastewater, having initial dye COD concentrations of 100, 200, 300, or 400 mg/L and the weight ratio of ferrite powder : TiO2 maintained at 1 : 1, are shown in Figures
TOC removal % versus time by adsorption of magnetic photocatalyst of Mn-Zn ferrite/TiO2 (N2, 500°C) (FBL, COD = 100–400 ppm).
ADMI removal % versus time by adsorption of magnetic photocatalyst of Mn-Zn ferrite/TiO2 (N2, 500°C) (FBL, COD = 100–400 ppm).
The photodegradation for simulated FBL dye wastewater with initial COD of 100, 200, 300, and 400 mg/L under solar irradiation by using self-produced magnetic photocatalysts from waste and also TiO2 prepared is shown in Figures
TOC removal % versus time by using Mn-Zn ferrite/TiO2 (
ADMI removal % versus time by using Mn-Zn ferrite/TiO2 (
The Langmuir adsorption isotherm has the following equation [
Langmuir adsorption isotherm for Mn-Zn ferrite/TiO2.
The L-H model can be expressed by the following equation [
L-H kinetic model for the magnetic photocatalysts of Mn-Zn ferrite/TiO2.
The constants obtained from adsorption isotherm and L-H model were summarized in Table
Adsorption constant for Langmuir isotherm and constants for L-H model.
Constants | Langmuir | Langmuir-Hinshelwood |
---|---|---|
|
— | 3.1614 |
|
— | 0.3212 |
|
0.1014 | 0.1016 |
Mn-Zn ferrite magnetic powder and the sintered Mn-Zn ferrite were successfully prepared from spent dry batteries and steel picking sulfuric waste acid. The composition obtained is close to the designed value as molar ratio of ZnO : MnO : Fe2O3 = 12.5 : 35 : 52.5. The sintered Mn-Zn ferrite can be used directly in magnetic industry. The magnetic photocatalyst of Mn-Zn ferrite/TiO2 was also successfully produced by using magnetic powder, titanium sulfate, and urea as raw material and then followed by simple coprecipitation method. Comparing with JCPDS data, the XRD patterns of the photocatalyst contain Mn-Zn ferrite, anatase TiO2, and a small amount of hematite. The magnetic photocatalyst falls into the category of soft-magnetic materials by SQUID study which can be recycled by the application of magnetic field. The treatment efficiency by magnetic photocatalyst of Mn-Zn ferrite/TiO2 for dilute simulated FBL dye wastewater can reach 87.85% of TOC removal and 96.17% of color removal and is very close to the efficiency of using TiO2 alone. The Mn-Zn ferrite and magnetic photocatalyst produced from waste not only solve the pollution problems but also create the possibility of the benefits for the commercial applications. Both the Langmuir adsorption isotherm and L-H model fit well for the prepared magnetic photocatalyst and can be used successfully in AOP.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This project was supported by the Ministry of Education, Taiwan, and Rui Da Hung Technology Materials Co., Ltd., Taiwan, under Contract no. 99G-39-03. The authors express sincere gratitude to the financial support for this research.