Dependence of pH Variation on the Structural, Morphological, and Magnetic Properties of Sol-Gel Synthesized Strontium Ferrite Nanoparticles

In this research work, an attempt of regulating the pH as a sol-gel modification parameter during preparation of SrFe12O19 nanoparticles sintered at a low sintering temperature of 900°C has been presented. The relationship of varying pH (pH 1–14) on structural microstructures and magnetic behaviors of SrFe12O19 nanoparticles was characterized by X-ray diffraction (XRD), field emission scanning microscope (FESEM), thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR), and vibrating-sample magnetometer (VSM). The single-phase SrFe2O19 with optimum magnetic properties can be obtained at pH 1 with a sintering temperature of 900°C. As pH values increase, the presence of impurity Fe2O3 was observed. TGA data-varying pH shows that the total weight loss of most samples was at 30.44% which corresponds to the decomposition process. The IR spectra showed three main absorption bands in the range of 400–600 cm−1 corresponding to strontium hexaferrite. SEM micrographs exhibit a circular crystal type of strontium ferrite with an average crystal size in the range of 53–133 nm. A higher saturation magnetization Ms, remanent magnetization Mr, and hysteresis Hc were recorded to have a large loop of 55.094 emu/g, 33.995 emu/g, and 5357.6 Oe, respectively, at pH 11, which make the synthesized materials useful for high-density recording media and permanent magnets

Preparation and characterization of Sr1−xNdxFe12O19 derived from steel-waste product via mechanical alloying

Steel waste product had been used as the main source of raw material in the preparation of permanent magnets ferrites. Steel waste product is an impure material that contains the iron oxide and impurities. The steel waste product is a form of flakes is grinding for several hours to form a fine powder. The iron oxide powder is separated from magnetic and non-magnetic particle using magnetic particle separation. The magnetic particle was again been purified by using the Curie temperature separation technique. The magnetic powder was carried out from the purification and oxidize at 500 °C for 6 hours at 2 °C/ mins to form the hematite, Fe2O3, used as a raw powder to prepare SrFe12O19. Microstructure of Nd-doped strontium ferrites, Sr1-xNdxFe12O19, with x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5, were prepared through a mechanical alloying technique. Several characterizations have been done, such as X-ray Diffraction (XRD) and Field emission scanning electron microscopy (FESEM). The magnetic properties of coercivity (Hc) and the energy product BHmax of samples are carried out. The magnetic properties of samples were investigated with an expectation of enhancing the magnetic properties by substitutions of Nd3+ ions on Fe3+ ion basis sites. The saturation magnetization Ms revealed magnetic behavior with respect to Nd3+ doping concentration, showing a decrease. The coercivity Hc increased with increasing Nd3+ doping concentration

Evolution of dielectric ceramic Ba6-3xNd8+2xTi18O54 (x=0.15) with microstructure at different sintering temperatures

The doping mechanism of neodymium ion on barium titanate could be promising a new material for applications in miniature microwave technology and mobile communication systems. Microstructural of Ba6-3xNd8+2xTi18O54, with x=0.15 ceramics at different sintering temperatures were investigated. The samples were prepared by the magnetic stirring method and sintered at a temperature range from 600°C to 1300°C. Sintering effects on the crystallite structure and surface morphology were studied and characterized by XRD and FESEM. The transformation of majority of the phase in the system from barium titanate to barium neodymium titanate was confirmed by XRD pattern due to change in sintering temperature. The change in sample densities was determined using Archimede’s method. Two activation energies of grain growth were observed by using estimated diffusion process. The activation energies were 0.0698 and 0.3348 eV for low sintering and high sintering temperatures respectively

Magnetic phase transition of mechanically alloyed single sample Co0.5Ni0.5Fe2O4

The parallel evolutional relationship between microstructural properties and magnetic and electrical properties was elucidated through this study. A Co0.5Ni0.5Fe2O4 rod sample was prepared via high energy ball milling and subsequent moulding into a nano-sized compacted powder. This single sample was sintered through 10 cycles at different sintering temperatures in the range of 500 °C–1400 °C. After each sintering, the sample was characterized for its phase, microstructural, density, magnetic and electrical properties using XRD, SEM, B-H tracer, Curie temperature measurement and two probes method. An integrated study of microstructural properties with elevating sintering temperature would point to the existence of three stages of sintering, which involved atomic, interfaces (lattice and boundaries), and volume diffusions respectively. Three distinct shape-differentiated groups of B–H hysteresis loops were observed. The existence of these groups was associated with microstructural properties such as phase purity, volume fraction of disordered phase or grain boundaries, and grain size. In terms of average grain size, from 48.25 nm to 71.93 nm, a weak paramagnetic behaviour was observed; while from 83.65 nm to 374.79 nm, a relatively square-shaped hysteresis loops with moderate ferromagnetic behaviours were observed. The occurrences of erect and well-defined sigmoid-shape were observable when there were sufficiently high single-phase purity and crystallinity, where the average grain size was in the range of 964.73 nm–11215.91 nm. The critical grain size of 186.75 nm was found by plotting average grain size against coercivity, suggesting the number of single-domain particles was reduced, and the number of multi-domain particles was increased by increasing sintering temperature. The electrical resistivity variations were strongly related to the microstructural properties

Structural and superconducting properties of Y(Ba1-xKx)2Cu3O7-δ ceramics

Y(Ba1-xKx)2Cu3O7-δ ceramics (x = 0.00, 0.03, 0.05 and 0.08) were synthesized by thermal treatments of aqueous solution of metals nitrates and polyvinyl pyrrolidone (PVP) that acts as a capping agent. The effects of K-substitution on the crystal structure, microstructure and electrical resistance of samples were investigated. The X-ray diffractions results indicated an improvement of crystallinity and variation of lattice constant, a, b and c of YBa2Cu3O7-δ (Y123) phase with K-substitution. The K-substitution resulted in increasing of orthorhombicity factor compared to pure Y123. Microstructural observation using scanning electron microscopy showed that K-substitution promotes the grain growth of Y123. The superconducting transitions (Tc) of the substituted-samples were higher than that of the pure Y123. The Tc (onset) were 93, 97, 95, 95 K for the samples with x = 0.00, 0.03, 0.05 and 0.08, respectively. Comparing with pure sample, the substituted-samples showed sharper superconducting transition (ΔTc). The best superconducting properties was observed for sample with x = 0.03

Structure development in sol-gel derived yttrium aluminium oxide, yttrium gallium oxide and their solid solutions

The structural study of the garnet system Y3Al5O12 (YAG) prepared by different sample preparations (solid-state sintering and sol-gel) is reported. Different sample preparations were investigated to find a suitable method for obtaining pure YAG. 27Al and 89Y MAS NMR were used to investigate the short range structure and results are compared to long-range order information from x-ray diffraction (XRD). These two techniques are comlementary in detecting phase composition and disorder in samples. There is a challenge in preparing pure Y3Al5O12 since intermediate phases easily grow when sintered at high temperature, i.e. YAlO3 (YAP), Y4Al2O9 (YAM), Y2O3 (Yttria) and Al2O3 (Corundum). Therefore structural information on these impurity phases was obtained to compare with samples under study. Different sample preparations were also used to try to obtain pure YAP and YAM. Since it is difficult to obtain pure YAG by high temperature solid-state sintering, the sol-gel technique was used to produce pure YAG at low temperature. In this work, pure YAG has been obtained at temperatures as low as 800oC using a sol-gel citrate-nitrate with combustion process (SGCNCT). Other sol-gel syntheses used are: sol-gel glycolate (SGG), citrate-nitrate (SGCN) and modification of the citrate-nitrate ratio with combustion process (SGCNCT). The modification of the citrate to nitrate ratio and controlling the mixing temperature as low as 50- 60oC is a novel route to produce pure YAG at low as 800oC. This technique was then used to prepare different garnet systems, i.e. Y3Ga5O12 (YGG) and also garnet solid solution system, Y3Al5-xGaxO12. Again, information from NMR was compared with results from XRD to determine different phase distribution and disorder. The 27Al chemical shift range for different structural units (e.g. AlO4, AlO5 and AlO6) in YAG allowed the aluminium distribution in these materials to be refined. This is important when dealing with low temperature amorphous phases. For example, the AlO5 site cannot be traced using XRD. The work was extended to study different nuclei, i.e. 89Y and 71Ga NMR. 27Al and 71Ga is a quadrupolar nuclei with spin, I=5/2 and 3/2, respectively. Extensive broadening of the NMR signal was observed at some sites due to the quadrupolar interaction and the effect of this on the quantitation of 27Al and 71Ga NMR is discussed. The substitution of Al and Ga in the garnet system was investigated. The different distribution of next nearest neighbour atom (nnn) produces a peak shift in 27Al, 71Ga NMR and also XRD

Complex Permittivity and Electromagnetic Interference Shielding Effectiveness of OPEFB Fiber-Polylactic Acid Filled with Reduced Graphene Oxide

This study was aimed at fabricating composites of polylactic acid (PLA) matrix-reinforced oil palm empty fruit bunch (OPEFB) fiber filled with chemically reduced graphene oxide (rGO). A total of 2–8 wt.% rGO/OPEFB/PLA composites were characterized for their complex permittivity using an open-ended coaxial probe (OEC) technique. The shielding efficiency properties were calculated using the measured transmission (S21) and the reflection (S11) coefficient results. All the measurements and calculations were performed in the 8–12 GHz frequency range. The morphological and microstructural study included X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Fourier transform infrared spectroscopy (FTIR). The results indicated that the incorporation of rGO as filler into the composites enhanced their complex permittivity properties. The composites showed a total shielding efficiency (SET) of about 31.2 dB at a frequency range of 8–12 GHz, which suggests their usefulness for microwave absorption.</jats:p

The Effect of MWCNTs Filler on the Absorbing Properties of OPEFB/PLA Composites Using Microstrip Line at Microwave Frequency

Oil palm empty fruit bunch (OPEFB) fiber/polylactic acid (PLA)-based composites filled with 6–22 wt.% multi-walled carbon nanotubes (MWCNTs) were prepared using a melt blend method. The composites were analyzed using X-ray diffraction (XRD), Fourier transforms infrared (FTIR), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) of the MWCNTs. The composites were characterized for complex permittivity using the coaxial probe at 8–12 GHz range and the transmission/reflection coefficients were measured through micro strip line. The dielectric permittivity measurements carried out at X-band frequency revealed that 22 wt.% MWCNTs nanocomposite display higher dielectric constant (ε′) and dielectric loss (ε″) values of 4.23 and 0.65, respectively. A maximum absorption loss of 15.2 dB was obtained for the 22 wt.% nanocomposites at 11.75 GHz. This result suggests that PLA/OPEFB/MWCNTs composites are a promising cheap and lightweight material for the effective microwave absorption in the X-band frequency range.</jats:p

Recent advances in the rejection of endocrine-disrupting compounds from water using membrane and membrane bioreactor technologies: a review

Water is a critical resource necessary for life to be sustained, and its availability should be secured, appropriated, and easily obtainable. The continual detection of endocrine-disrupting chemicals (EDCs) (ng/L or µg/L) in water and wastewater has attracted critical concerns among the regulatory authorities and general public, due to its associated public health, ecological risks, and a threat to global water quality. Presently, there is a lack of stringent discharge standards regulating the emerging multiclass contaminants to obviate its possible undesirable impacts. The conventional treatment processes have reportedly ineffectual in eliminating the persistent EDCs pollutants, necessitating the researchers to develop alternative treatment methods. Occurrences of the EDCs and the attributed effects on humans and the environment are adequately reviewed. It indicated that comprehensive information on the recent advances in the rejection of EDCs via a novel membrane and membrane bioreactor (MBR) treatment techniques are still lacking. This paper critically studies and reports on recent advances in the membrane and MBR treatment methods for removing EDCs, fouling challenges, and its mitigation strategies. The removal mechanisms and the operating factors influencing the EDCs remediation were also examined. Membranes and MBR approaches have proven successful and viable to eliminate various EDCs contaminants

An Insight into a Sustainable Removal of Bisphenol A from Aqueous Solution by Novel Palm Kernel Shell Magnetically Induced Biochar: Synthesis, Characterization, Kinetic, and Thermodynamic Studies

Recently Bisphenol A (BPA) is one of the persistent trace hazardous estrogenic contaminants in the environment, that can trigger a severe threat to humans and environment even at minuscule concentrations. Thus, this work focused on the synthesis of neat and magnetic biochar (BC) as a sustainable and inexpensive adsorbent to remove BPA from aqueous environment. Novel magnetic biochar was efficiently synthesized by utilizing palm kernel shell, using ferric chloride and ferrous chloride as magnetic medium via chemical co-precipitation technique. In this experimental study, the influence of operating factors comprising contact time (20–240 min), pH (3.0–12.0), adsorbent dose (0.2–0.8 g), and starting concentrations of BPA (8.0–150 ppm) were studied in removing BPA during batch adsorption system using neat biochar and magnetic biochar. It was observed that the magnetically loaded BC demonstrates superior maximum removal efficiency of BPA with 94.2%, over the neat biochar. The functional groups (FTIR), Zeta potential, vibrating sample magnetometer (VSM), surface and textural properties (BET), surface morphology, and mineral constituents (FESEM/EDX), and chemical composition (XRD) of the adsorbents were examined. The experimental results demonstrated that the sorption isotherm and kinetics were suitably described by pseudo-second-order model and Freundlich model, respectively. By studying the adsorption mechanism, it was concluded that π-π electron acceptor–donor interaction (EAD), hydrophobic interaction, and hydrogen bond were the principal drives for the adsorption of BPA onto the neat BC and magnetic BC.</jats:p