Palm oil mill effluent (POME) is a serious and expensive environmental problem in Malaysia. In this paper, CaFe2O4 is introduced as a novel photocatalyst for the degradation of POME under visible light irradiation. Two synthesis routes, auto-combustion and co-precipitation, and two calcination temperatures 550 °C and 700 °C were used to produce four CaFe2O4 catalysts AC550, AC700, CP550 and CP700. CP550 exhibited the greatest photocatalytic degradation at 56% chemical-oxygen-demand (COD) removal after 8 h of irradiation which dropped to 49% after three consecutive cycles indicating reasonable conversion and high recyclability. BET analysis indicated CP550 had the highest SBET (27.28 m2/g) and pore volume (0.077 cm3/g) which dropped precipitously for CP700 upon increasing the calcination temperature to an SBET of 9.73 m2/g and pore volume of 0.025 cm3/g due to annealing which created a smoother surface area as evidenced by the SEM images. UV-Vis DRS indicated CP550 had the highest band-gap (1.52 eV) which is likely due to the presence of a highly crystalline pure CaFe2O4 phase compared to the other products which existed as a mixture of Fe oxidation states evidenced by the XRD data. The PL spectra for all catalysts indicated significantly lower recombination rate for both CP550 and CP700. Introduction of IPA into the reaction mixture to eliminate hydroxyl radicals resulted in a diminishing of COD removal from 56% to 7% proving hydroxyl radicals to be the primary reactive species responsible for photodegradation of POME.
Over the last few decades, the application of nanoparticles (NPs) gained immense attention towards environmental and biomedical applications. NPs are ultra-small particles having size ranges from 1 to 100 nm. NPs loaded with therapeutic or imaging compounds have proved a versatile approach towards healthcare improvements. Among various inorganic NPs, zinc ferrite (ZnFe2O4) NPs are considered as non-toxic and having an improved drug delivery characteristics . Several studies have reported broader applications of ZnFe2O4 NPs for treating carcinoma and various infectious diseases. Additionally, these NPs are beneficial for reducing organic and inorganic environmental pollutants. This review discusses about various methods to fabricate ZnFe2O4 NPs and their physicochemical properties. Further, their biomedical and environmental applications have also been explored comprehensively.
The spatiotemporal accuracy of microscale magnetophoresis has improved significantly over the course of several decades of development. However, most of the studies so far were using magnetic microbead composed of nanosphere particle for magnetophoretic actuation purpose. Here, we developed an in-house method for magnetic sample analysis called quadrupole magnetic steering control (QMSC). QMSC was used to study the magnetophoretic behavior of polystyrene microbeads decorated with iron oxide nanospheres-coated polystyrene microbeads (IONSs-PS) and iron oxide nanorods-coated polystyrene microbeads (IONRs-PS) under the influence of a quadrupole low field gradient. During a 4-s QMSC experiment, the IONSs-PS and IONRs-PS were navigated to perform 180° flip and 90° turn formations, and their kinematic results (2 s before and 2 s after the flip/turn) were measured and compared. The results showed that the IONRs-PS suffered from significant kinematic disproportion, translating a highly uneven amount of kinetic energy from the same magnitude of magnetic control. Combining the kinematic analysis, transmission electron microscopy micrographs, and vibrating sample magnetometry measurements, it was found that the IONRs-PS experienced higher fluid drag force and had lower consistency than the IONSs-PS due to its extensive open fractal nanorod structure on the bead surface and uneven magnetization, which was attributed to its ferrimagnetic nature.
Conventional techniques to remove Fe impurities in kaolin typically involve high environmental impact and cost. Alternative methods have been focused on the use of bioleaching where Fe in kaolin is reduced with microorganisms. Early results established a noticeable effect of the bacteria on the redox state of Fe, but knowledge gaps persist such as details on the bacterial-kaolin interactions during attachment of bacteria onto kaolin surface, the metabolites produced by bacteria, and changes in Fe(II)/Fe(III) ion equilibria in solution. To bridge these gaps, this study was conducted to determine the detailed physicochemical changes in bacteria and kaolin during bioleaching through surface, structural, and chemical analysis. Bioleaching experiments were conducted for 10 days where each of the three Bacillus sp. was put in contact (at 9 × 108 CFU) with 20 g of kaolin powder using 200 mL of 10 g/L glucose solution. All samples treated with bacteria showed increasing trends in Fe(III) reduction up until day 6 or 8 followed by a slight decrease towards the end of the ten-day period. Examination of scanning electron microscope (SEM) images suggests that bacterial activity damaged the edges of kaolin particles during bioleaching. Ion chromatography (IC) results showed that during bioleaching, Bacillus sp. produced organic acids such as lactic acid, formic acid, malic acid, acetic acid, and succinic acid. EDS analysis of kaolin before and after bioleaching showed Fe removal efficiencies of up to 65.3%. Analyses of color properties of kaolin before and after bioleaching showed an improvement in whiteness index of up to 13.6%. KEY POINTS: • Dissolution of iron oxides by Bacillus species proven with phenanthroline analysis. • Organic acid type and concentration unique to species detected during bioleaching. • Whiteness index of kaolin is improved after bioleaching.
Magnetophoresis of iron oxide magnetic nanoparticle (IOMNP) under low magnetic field gradient (<100 T/m) is significantly enhanced by particle shape anisotropy. This unique feature of magnetophoresis is influenced by the particle concentration and applied magnetic field gradient. By comparing the nanosphere and nanorod magnetophoresis at different concentration, we revealed the ability for these two species of particles to achieve the same separation rate by adjusting the field gradient. Under cooperative magnetophoresis, the nanorods would first go through self- and magnetic field induced aggregation followed by the alignment of the particle clusters formed with magnetic field. Time scale associated to these two processes is investigated to understand the kinetic behavior of nanorod separation under low field gradient. Surface functionalization of nanoparticles can be employed as an effective strategy to vary the temporal evolution of these two aggregation processes which subsequently influence the magnetophoretic separation time and rate.
Colloidal Fe3O4 nanoparticles were synthesized using a gamma-radiolysis method in an aqueous solution containing iron chloride in presence of polyvinyl alcohol and isopropanol as colloidal stabilizer and hydroxyl radical scavenger, respectively. Gamma irradiation was carried out in a 60Co gamma source chamber at different absorbed doses. Increasing the radiation dose above a certain critical dose (100 kGy) leads to particle agglomeration enhancement, and this can influence the structure and crystallinity, and consequently the magnetic properties of the resultant particles. The optimal condition for formation of Fe3O4 nanoparticles with a uniform and narrow size distribution occurred at a dose of 100 kGy, as confirmed by X-ray diffractometry and transmission electron microscopy. A vibrating sample magnetometry study showed that, when radiation dose increased, the saturation and remanence magnetization decreased, whereas the coercivity and the remanence ratio increased. This magnetic behavior results from variations in crystallinity, surface effects, and particle size effects, which are all dependent on the radiation dose. In addition, Fourier transform infrared spectroscopy was performed to investigate the nature of the bonds formed between the polymer chains and the metal surface at different radiation doses.
Fe3O4/talc nanocomposite was used for removal of Cu(II), Ni(II), and Pb(II) ions from aqueous solutions. Experiments were designed by response surface methodology (RSM) and a quadratic model was used to predict the variables. The adsorption parameters such as adsorbent dosage, removal time, and initial ion concentration were used as the independent variables and their effects on heavy metal ion removal were investigated. Analysis of variance was incorporated to judge the adequacy of the models. Optimal conditions with initial heavy metal ion concentration of 100, 92 and 270 mg/L, 120 s of removal time and 0.12 g of adsorbent amount resulted in 72.15%, 50.23%, and 91.35% removal efficiency for Cu(II), Ni(II), and Pb(II), respectively. The predictions of the model were in good agreement with experimental results and the Fe3O4/talc nanocomposite was successfully used to remove heavy metals from aqueous solutions.
Maghemite (γ-Fe2O3) nanoparticles have been synthesized using a chemical coprecipitation method at different nitric acid concentrations as an oxidizing agent. Characterization of all samples performed by several techniques including X-ray diffraction (XRD), transmission electron microscopy (TEM), alternating gradient magnetometry (AGM), thermogravimetric analysis (TGA), dynamic light scattering (DLS), and zeta potential. The XRD patterns confirmed that the particles were maghemite. The crystallite size of all samples decreases with the increasing concentration of nitric acid. TEM observation showed that the particles have spherical morphology with narrow particle size distribution. The particles showed superparamagnetic behavior with decreased magnetization values at the increasing concentration of nitric acid. TGA measurement showed that the stability temperature decreases with the increasing concentration of nitric acid. DLS measurement showed that the hydrodynamic particle sizes decrease with the increasing concentration of nitric acid. Zeta potential values show a decrease with the increasing concentration of nitric acid. The increasing concentration of nitric acid in synthesis of maghemite nanoparticles produced smaller size particles, lower magnetization, better thermal stability, and more stable maghemite nanoparticles suspension.
Hematite (α-Fe2O3) nanoparticles were synthesized by the solid transformation of ferrous hydroxide and ferrihydrite in hydrothermal condition. The as-prepared α-Fe2O3 nanoparticles were characterized by UV-vis, PL, XRD, Raman, TEM, AFM, FESEM, and EDX analysis. The experimental results indicated the formation of uniform hematite nanoparticles with an average size of 45 nm and perfect crystallinity. The electrochemical behavior of a GC/α-Fe2O3 electrode was studied using CV and EIS techniques with an electrochemical probe, [Fe(CN)6](3-/4-) redox couple. The electrocatalytic activity was investigated toward DA oxidation in a phosphate buffer solution (pH 6.8) by varying different experimental parameters. The chronoamperometric study showed a linear response in the range of 0-2 μM with LoD of 1.6 μM for DA. Square wave voltammetry showed a linear response in the range of 0-35 μM with LoD of 236 nM for DA.
The cladded conductor is broadly utilized in engineering fields, such as aerospace, energy, and petrochemical; however, it is vulnerable to thickness loss occurring in the clad layer and nonconductive protection coating due to abrasive and corrosive environments. Such a flaw severely undermines the integrity and safety of the mechanical structures. Therefore, evaluating the thickness loss hidden inside cladded conductors via reliable nondestructive evaluation techniques is imperative. This paper intensively investigates the pulse-modulation eddy current technique (PMEC) for the assessment of thickness loss in a cladded conductor. An analytical model of the ferrite-cored probe is established for analyzing PMEC signals and characteristics of lift-off intersection (LOI) in testing signals. Experiments are conducted for evaluation of the thickness loss in cladded conductors. An inverse scheme based on LOI for estimation of the thickness-loss depth is proposed and further verified. Through simulations and experiments, it is found that the influences of the thickness loss in the clad layer and protective coating on the PMEC signals can be decoupled in virtue of the LOI characteristics. Based on LOI, the hidden thickness loss can be efficiently evaluated without much of a reduction in accuracy by using the PMEC probe for dedicated inspection of the cladded conductor.
We employ complementary field and laboratory-based incubation techniques to explore the geochemical environment where siderite concretions are actively forming and growing, including solid-phase analysis of the sediment, concretion, and associated pore fluid chemistry. These recently formed siderite concretions allow us to explore the geochemical processes that lead to the formation of this less common carbonate mineral. We conclude that there are two phases of siderite concretion growth within the sediment, as there are distinct changes in the carbon isotopic composition and mineralogy across the concretions. Incubated sediment samples allow us to explore the stability of siderite over a range of geochemical conditions. Our incubation results suggest that the formation of siderite can be very rapid (about two weeks or within 400 hr) when there is a substantial source of iron, either from microbial iron reduction or from steel material; however, a source of dissolved iron is not enough to induce siderite precipitation. We suggest that sufficient alkalinity is the limiting factor for siderite precipitation during microbial iron reduction while the lack of dissolved iron is the limiting factor for siderite formation if microbial sulfate reduction is the dominant microbial metabolism. We show that siderite can form via heated transformation (at temperature 100°C for 48 hr) of calcite and monohydrocalcite seeds in the presence of dissolved iron. Our transformation experiments suggest that the formation of siderite is promoted when carbonate seeds are present.
Magnetic paper were prepared via the in situ synthesis method with ferrites in the presence of polyethylenimine (PEI). In this work, the thermomechanical pulp (TMP) fibers were used due to low percentage of collapse lumen and the large lumen size for optimum loading degree. Four cycles of the reaction were performed on the TMP fibers with pH values of 4-10. It was found that variation of pH value played an important role in the loading degree of pulp during synthesis process. The magnetic, morphological and structural properties of the magnetic paper obtained were reported. At the
optimum pH of 6.0, saturation magnetization was found to be 3.08 emu/g, remainance magnetization was 0.11 emu/g and coercive force was 12.64 Oe. The optimum loading degree was found to be 23.25%.
Sampels of Mnx-zMgzZn1-xFe2O4 ferrites, with x = 0.5, 0 < z < 0.5; x = 0.6, 0 < z 0.6 and x = 0.7, 0 < z < 0.7, were prepared by solid state reaction. For all samples, magnetization as a function of applied magnetic field was measured at room temperature (TR) and several temperatures above TR but below the Neel temperature (TN); while magnetic hysteresis was obtained at TR and 373 K using a vibrating sample magnetometer (VSM). Electrical resistivity at TR was measured by a two terminal method. The three series of Mn-Mg-Zn ferrite indicate a maximum ,agnetization at certain substitution of Mg. TN increased with the increase of Mg content while resistivity varied in the opposite manner. The variation of magnetization is interpreted as due to Mg started to replace the Mn at the tetrahedral sites (A) so that the resultant magnetic moment increased. However further substitution occurred at the octahedral sites (B), thus lowering the magnetic moment. A small coercivity indicates that the samples are soft ferrites with a small energy loss. A reduction in the electrical resistivity with Mg content probably due to an increase in the mobility of charge hopping between the Fe2+ and Fe3+ ions and also between Mn2+ and Mn3+ ions.
Sampel ferit Mnx-zMgzZn1-xFe2O4 dengan x = 0.5, 0 < z < 0.5; x = 0.6, 0 < z 0.6 dan x = 0.7, 0 < z < 0.7, disediakan dengan tindak balas keadaan pepejal. Pengukuran pemagnetan sebagai fungsi medan magnet dilakukan pada suhu bilik (TR) dan suhu-suhu yang lebih tinggi tetapi di bawah suhu Neel bilik (TR) dan suhu-suhu yang lebih tinggi tetapi di bawah suhu Neel (TN) serta histerisis magnet pada suhu bilik dan 373 K diperolehi untuk semua sampel menggunakan magnetometer sampel bergetar (VSM). Kerintangan elektrik pada suhu bilik diperolehi dengan kaedah dua terminal. Ketiga-tiga siri ferit Mn-Mg-Zn itu masing-masing menunjukkan suatu pemagnetan maksimum pada suatu kadar penggantian Mn oleh Mg. TN meningkat dengan kandungan Mg tetapi kerintangan elektrik berubah sebaliknya. Perubahan pemagnetan seperti yang tersebut disebabkan Mg mula menggantikan Mn pada tapak tetrahedron (A) menyebabkan momen magnet paduan meningkat. Penambahan Mg seterusnya menyebabkan Mn pada tapak oktahedron pula diganti, sehingga momen magnet paduan mengurang. Koersiviti yang kecil menunjukkan sampel bersifat magnet lembut dengan kehilangan tenaga yang sangat kecil. Pengurangan kerintangan dengan penambahan Mg mungkin disebabkan oleh peningkatan kelincahan pembawa cas yang melompat di antara ion-ion Fe2+ dan Fe3+ dan juga di antara Mn2+ dan Mn3+.
Micro Electro Discharge Machining (micro-EDM) is widely used for producing different types of micro features and micro components. Tool wear rate (TWR) is an important factor that affects the accuracy of machining as well as the productivity of micro-EDM process. This study examines the effects of process parameters and the use of Maghemite (γ-Fe2O3) nano-powder mixed dielectric medium on tool wear rate when micro-EDM Co-Cr-Mo. A Copper electrode with 300 μm diameter and positive polarity was used to evaluate the machining process by focusing on TWR. Two different concentrations of nano-powder (i.e., 2 g/l and 4 g/l) were added to the dielectric. Results showed that increasing the discharge current and voltage leads to a corresponding increase in TWR, while the presence of γ-Fe2O3 nano-powder in the dielectric liquid decreases TWR. Mixed micro-EDM with 2 g/l of nano-powder achieved a lower TWR.
The fabrication of an electrochemical sensor based on an iron oxide/graphene modified glassy carbon electrode (Fe3O4/rGO/GCE) and its simultaneous detection of dopamine (DA) and ascorbic acid (AA) is described here. The Fe3O4/rGO nanocomposite was synthesized via a simple, one step in-situ wet chemical method and characterized by different techniques. The presence of Fe3O4 nanoparticles on the surface of rGO sheets was confirmed by FESEM and TEM images. The electrochemical behavior of Fe3O4/rGO/GCE towards electrocatalytic oxidation of DA was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) analysis. The electrochemical studies revealed that the Fe3O4/rGO/GCE dramatically increased the current response against the DA, due to the synergistic effect emerged between Fe3O4 and rGO. This implies that Fe3O4/rGO/GCE could exhibit excellent electrocatalytic activity and remarkable electron transfer kinetics towards the oxidation of DA. Moreover, the modified sensor electrode portrayed sensitivity and selectivity for simultaneous determination of AA and DA. The observed DPVs response linearly depends on AA and DA concentration in the range of 1-9 mM and 0.5-100 µM, with correlation coefficients of 0.995 and 0.996, respectively. The detection limit of (S/N = 3) was found to be 0.42 and 0.12 µM for AA and DA, respectively.
A detailed study on the conflicting role that colloid stability plays in magnetophoresis is presented. Magnetic iron oxide particles (MIOPs) that were sterically stabilized via surface modification with poly(sodium 4-styrene sulfonate) of different molecular weights (i.e., 70 and 1000 kDa) were employed as our model system. Both sedimentation kinetics and quartz crystal microbalance with dissipation (QCM-D) measurements suggested that PSS 70 kDa is a better stabilizer as compared to PSS 1000 kDa. This observation is mostly attributed to the bridging flocculation of PSS 1000 kDa decorated MIOPs originated from the extended polymeric conformation layer. Later, a lab-scale high gradient magnetic separation (HGMS) device was designed to study the magnetophoretic collection of MIOPs. Our experimental results revealed that the more colloidally stable the MIOP suspension is, the harder it is to be magnetically isolated by HGMS. At 50 mg/L, naked MIOPs without coating can be easily captured by HGMS at separation efficiency up to 96.9 ± 2.6%. However, the degree of separation dropped quite drastically to 83.1 ± 1.2% and 67.7 ± 4.6%, for MIOPs with PSS 1000k and PSS 70k coating, respectively. This observation clearly implies that polyelectrolyte coating that was usually employed to electrosterically stabilize a colloidal system in turn compromises the magnetic isolation efficiency. By artificially destroying the colloidal stability of the MIOPs with ionic strength increment, the ability for HGMS to recover the most stable suspension (i.e., PSS 70k-coated MIOPs) increased to >86% at 100 mM monovalent ion (Na(+)) or at 10 mM divalent ion (Ca(2+)). This observation has verified the conflicting role of colloidal stability in magnetophoretic separation.
Magnetic collection of the microalgae Chlorella sp. from culture media facilitated by low-gradient magnetophoretic separation is achieved in real time. A removal efficiency as high as 99% is accomplished by binding of iron oxide nanoparticles (NPs) to microalgal cells in the presence of the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA) as a binder and subsequently subjecting the mixture to a NdFeB permanent magnet with surface magnetic field ≈6000 G and magnetic field gradient <80 T m(-1) . Surface functionalization of magnetic NPs with PDDA before exposure to Chlorella sp. is proven to be more effective in promoting higher magnetophoretic removal efficiency than the conventional procedure, in which premixing of microalgal cells with binder is carried out before the addition of NPs. Rodlike NPs are a superior candidate for enhancing the magnetophoretic separation compared to spherical NPs due to their stable magnetic moment that originates from shape anisotropy and the tendency to form large NP aggregates. Cell chaining is observed for nanorod-tagged Chlorella sp. which eventually fosters the formation of elongated cell clusters.
The effect of pH and redox potential on the redox equilibria of iron oxides in aqueous-based magnetite dispersions was investigated. The ionic activities of each dissolved iron species in equilibrium with magnetite nanoparticles were determined and contoured within the Eh-pH framework of a composite stability diagram. Both standard redox potentials and equilibrium constants for all major iron oxide redox equilibria in magnetite dispersions were found to differ from values reported for noncolloidal systems. The "triple point" position of redox equilibrium among Fe(II) ions, magnetite, and hematite shifted to a higher standard redox potential and an equilibrium constant which was several orders of magnitude higher. The predominant area of magnetite stability was enlarged to cover a wider range of both pH and redox potentials as compared to that of a noncolloidal magnetite system.
Calcium sulfate-bioactive glass (CSBG) composites doped with 5, 10 and 20 mol% Fe were synthesized using quick alkali sol-gel method. X-ray diffraction (XRD) data of samples heated at 700 °C revealed the presence of anhydrite, while field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) characterization confirmed the formation of nano-sized CSBGs. The UV-vis studies confirmed that the main iron species in 5% Fe and 10% Fe doped CSBGs were tetrahedral Fe(III) whereas that in 20% Fe doped CSBG were extra-framework FeOx oligomers or iron oxide phases. Measurement of magnetic properties of the samples by vibrating sample magnetometer (VSM) showed very narrow hysteresis loop with zero coercivity and remanence for 10% Fe and 20% Fe doped CSBG, indicating that they are superparamagnetic in nature. All samples induced the formation of apatite layer with Ca/P ratio close to the stoichiometric HA in simulated body fluid (SBF) assessment.
In this work, heterogeneous photocatalysis was used to treat pulp and paper mill effluent (PPME). Magnetically retrievable Fe2O3-TiO2 was fabricated by employing a solvent-free mechanochemical process under ambient conditions. Findings elucidated the successful incorporation of Fe2O3 into the TiO2 lattice. Fe2O3-TiO2 was found to be an irregular and slightly agglomerated surface morphology. In comparison to commercial P25, Fe2O3-TiO2 exhibited higher ferromagnetism and better catalyst properties with improvements in surface area (58.40 m2/g), pore volume (0.29 cm3/g), pore size (18.52 nm), and band gap (2.95 eV). Besides, reusability study revealed that Fe2O3-TiO2 was chemically stable and could be reused successively (five cycles) without significant changes in its photoactivity and intrinsic properties. Additionally, this study demonstrated the potential recovery of Fe2O3-TiO2 from an aqueous suspension by using an applied magnetic field or sedimentation. Interactive effects of photocatalytic conditions (initial effluent pH, Fe2O3-TiO2 dosage, and air flow-rate), reaction mechanism, and the presence of chemical oxidants (H2O2, BrO3-, and HOCl) during the treatment process of PPME were also investigated. Under optimal conditions (initial effluent pH = 3.88, [Fe2O3-TiO2] = 1.3 g/L, and air flow-rate = 2.28 L/min), the treatment efficiency of Fe2O3-TiO2 was 98.5% higher than the P25. Based on Langmuir-Hinshelwood kinetic model, apparent rate constants of Fe2O3-TiO2 and P25 were 9.2 × 10-3 and 2.7 × 10-3 min-1, respectively. The present study revealed not only the potential of using magnetic Fe2O3-TiO2 in PPME treatment but also demonstrated high reusability and easy separation of Fe2O3-TiO2 from the wastewater.