We present here the multitasking capabilities of Ag-embedded ZnO nanocomposites (Ag-ZnO NCs), which include the photocatalytic degradation of organic dyes, bacterial inhibition, and cancer ...therapeutics. Ag-embedded ZnO nanocomposites (Ag-ZnO NCs) of mesoporous spherical morphology (size ∼ 150 ± 50 nm) are successfully synthesized by a facile and single step soft-chemical approach. To understand the effect of Ag loading on multitasking properties, Ag-ZnO NCs are synthesized with different wt% of Ag. It was found that Ag
-ZnO NCs (5 wt% of Ag) showed excellent solar light-induced photocatalytic degradation properties against both cationic as well as anionic dyes. In addition, the presence of Ag in these NCs makes them strongly antibacterial, and kills 100% Escherichia coli (E. coli) cells within 2 hours (under dark), and within 30 min (under solar light). The enhanced photocatalytic and antibacterial activity of Ag-ZnO NCs is due to the anchoring of Ag NPs onto ZnO as well as minor substitution of Ag ions in the lattice of ZnO. This produces abundant charge carriers and generates significantly enhanced reactive oxygen species (ROS), which seem responsible for the multitasking properties. Furthermore, the cytotoxic study shows that Ag
-ZnO NCs kill oral carcinoma (KB) cells under visible light irradiation, and work as photosensitizers towards the photodynamic therapy of cancer due to the excellent photocatalytic activity. The high ROS concentration depolarizes the mitochondrial membrane potential, which in turn initiates apoptosis in oral carcinoma (KB) cells inducing cell death. Therefore, the as-prepared mesoporous Ag-ZnO NCs show great promise in waste water treatment, and cancer therapeutics.
An efficient magnetic resonance imaging (MRI) contrast agent with a high R2 relaxivity value is achieved by controlling the shape of iron oxide to rod like morphology with a length of 30-70 nm and ...diameter of 4-12 nm. Fe3O4 nanorods of 70 nm length, encapsulated with polyethyleneimine show a very high R2 relaxivity value of 608 mM(-1) s(-1). The enhanced MRI contrast of nanorods is attributed to their higher surface area and anisotropic morphology. The higher surface area induces a stronger magnetic field perturbation over a larger volume more effectively for the outer sphere protons. The shape anisotropy contribution is understood by calculating the local magnetic field of nanorods and spherical nanoparticles under an applied magnetic field (3 Tesla). As compared to spherical geometry, the induced magnetic field of a rod is stronger and hence the stronger magnetic field over a large volume leads to a higher R2 relaxivity of nanorods.
Localized heat induction using magnetic nanoparticles under an alternating magnetic field is an emerging technology applied in areas including, cancer treatment, thermally activated drug release and ...remote activation of cell functions. To enhance the induction heating efficiency of magnetic nanoparticles, the intrinsic and extrinsic magnetic parameters influencing the heating efficiency of magnetic nanoparticles should be effectively engineered. This review covers the recent progress in the optimization of magnetic properties of spinel ferrite nanoparticles for efficient heat induction. The key materials factors for efficient magnetic heating including size, shape, composition, inter/intra particle interactions are systematically discussed, from the growth mechanism, process control to chemical and magnetic properties manipulation.
Synthesis and functionalization of monodisperse carbon nano-onions (CNOs) for glucose sensing applications.
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•A simple, scalable and inexpensive metal catalyzed synthesis of CNOs is ...reported.•The CNOs based enzymatic glucose sensor shows a sensitivity value of 26.5 µA cm−2 mM−1.•A non-enzymatic sensor is designed by decorating 2.5 nm Pt NPs on the surface of CNOs.•The non-enzymatic sensor has good sensitivity, a wide linear range and low detection limit.
A high sensitive glucose sensing characteristic has been realized in carbon nano-onions (CNOs). The CNOs of mean size 30 nm were synthesized by an energy-efficient, simple and inexpensive combustion technique. These as-synthesized CNOs could be employed as an electrochemical sensor by covalently immobilizing the glucose oxidase enzyme on them via carbodiimide chemistry. The sensitivity achieved by such a sensor is 26.5 µA mM−1 cm−2 with a linear response in the range of 1–10 mM glucose. Further to improve the catalytic activity of the CNOs and also to make them enzyme free, platinum nanoparticles of average size 2.5 nm are decorated on CNOs. This sensor fabricated using Pt-decorated CNOs (Pt@CNOs) nanostructure has shown an enhanced sensitivity of 21.6 µA mM−1 cm−2 with an extended linear response in the range of 2–28 mM glucose. Through these attempts we demonstrate CNOs as a versatile biosensing platform.
Abstract Magnetic materials at the nanometer scale can demonstrate highly tunable properties as a result of their reduced dimensionality. While significant advancements have been made in the ...production of magnetic oxide nanoparticles over the past decades, maintaining the magnetic and electronic phase stabilities in the nanoscale regime continues to pose a critical challenge. Finite-size effects modify or even eliminate the strongly correlated magnetic and electronic properties through strain effects, altering density and intrinsic electronic correlations. In this review, we examine the influence of nanoparticle size, shape, and composition on magnetic and tunneling magnetoresistance (TMR) properties, using magnetite (Fe 3 O 4 ) as an example. The magnetic and TMR properties of Fe 3 O 4 nanoparticles are strongly related to their size, shape, and synthesis process. Remarkably, faceted nanoparticles exhibit bulk-like magnetic and TMR properties even at ultra-small size-scale. Moreover, it is crucial to comprehend that TMR can be tailored or enhanced through chemical and/or structural modifications, enabling the creation of ‘artificially engineered’ magnetic materials for innovative spintronic applications.
The detailed structural, magnetic, and cryogenic magneto-caloric properties of chromium-substituted gadolinium iron garnet (Gd3Fe5-xCrxO12) nanocrystalline powders were studied using the facile ...autocombustion method and a calcination temperature of 1100 °C. The X-ray diffraction pattern showed that all samples were single-phase with cubic Ia3d symmetry. The temperature and field-dependent magnetization data of Gd3Fe5-xCrxO12 samples revealed a ferrimagnetic ordering at low temperatures. Upon Cr3+ substitution, the Curie temperature reduced by 7% at x = 0.25 from 560 K for x = 0.00 sample. In a field up to 5 T, the maximum magnetic entropy change was observed as ΔSM ∼ 3.8 J K−1 kg−1 for x = 0.00 and −ΔSM ∼ 3.9 J K−1 kg−1 for x = 0.25 sample, while the maximum relative cooling power, RCP, value of 420 J kg−1 was measured for x = 0.25 sample, which is 10% larger than the x = 0.00 (RCP ∼ 380 J kg−1). Therefore, Cr3+ substituted Gd3Fe5-xCrxO12 samples exhibit promising magneto-caloric performance and have potential low-temperature magnetic refrigeration applications.
We demonstrate magnetic and hyperthermia properties of CoxFe3-xO4 (x = 0, 0.1, 0.3 and 0.5) nanoparticles synthesized via a simple cation exchange reaction of ∼12 nm Fe3O4 nanoparticles. The ...substitution of Fe cations with Co2+ ions leads to enhanced magnetocrystalline anisotropy and coercivity of the pristine superparamagnetic Fe3O4 nanoparticles. Hyperthermia measurement shows that by controlling the Co content (x = 0 to 0.5) in CoxFe3-xO4 nanoparticles, their specific absorption rate (SAR) can be greatly improved from 132 to 534 W/g. The strong enhancement in SAR value is attributed to the increased anisotropy and coercivity. Moreover, with the increase of ac magnetic field from 184 to 491 Oe, the SAR values of Fe3O4 and Co0.5Fe2.5O4 nanoparticles increase from 81 to 132 W/g and 220 to 534 W/g, respectively.
A surfactant- and template-free approach is described for the synthesis of mesoporous α-Fe 2 O 3 , Fe 3 O 4 and α-Fe nanowires (NWs). In this approach, α-FeOOH NWs (length 550 nm and diameter 30 nm) ...were first prepared by hydrolysis of FeCl 3 . On subsequent thermal treatment in a fluidized bed reactor in the presence of a forming gas (Ar 93% + H 2 7%), α-FeOOH transformed to mesoporous NWs of ɑ-Fe 2 O 3 , Fe 3 O 4 and ɑ-Fe by controlling the process parameters such as reaction time and temperature. The obtained NWs of α-Fe 2 O 3 , Fe 3 O 4 and α-Fe were ferromagnetic at room temperature with a coercive field ( H c ) of 412, 583 and 628 Oe respectively. The aligned NWs showed 1.6 to 2 times-enhanced remanence in the parallel direction relative to the perpendicular direction due to magnetic anisotropy. These mesoporous magnetic NWs with a high specific surface area (82 m 2 g −1 for α-Fe 2 O 3 NWs) were used in photocatalysis due to the high adsorptivity of three probe dye molecules. The as-prepared α-Fe 2 O 3 NWs exhibited only modest photocatalytic activity; however, the catalytic activity could be further enhanced by decorating the mesoporous ɑ-Fe 2 O 3 NWs with 10 nm sized ZnO nanoparticles. The developed ɑ-Fe 2 O 3 /ZnO nanowire nanohybrids could eliminate 100% of the probe dyes: methylene blue, Rhodamine B and methyl orange within 90 min irradiation with solar light, underlining the high photocatalytic degradation efficiency of the nanohybrid. The nanowire nanohybrids could be easily recovered by applying an external magnetic field and reused for at least 4 times without significant loss of their photocatalytic activity.
We have observed large tunneling Magnetoresistance (TMR) in amine functionalized octahedral nanoparticle assemblies. Amine monolayer on the surface of nanoparticles acts as an insulating barrier ...between the semimetal Fe3O4 nanoparticles and provides multiple tunnel junctions where inter-granular tunneling is plausible. The tunneling magnetoresistance recorded at room temperature is 38% which increases to 69% at 180 K. When the temperature drops below 150 K, coulomb staircase is observed in the current versus voltage characteristics as the charging energy exceeds the thermal energy. A similar study is also carried out with spherical nanoparticles. A 24% TMR is recorded at room temperature which increases to 41% at 180 K for spherical particles. Mössbauer spectra reveal better stoichiometry for octahedral particles which is attainable due to lesser surface disorder and strong amine coupling at the facets of octahedral Fe3O4 nanoparticles. Less stoichiometric defect in octahedral nanoparticles leads to a higher value of spin polarization and therefore larger TMR in octahedral nanoparticles.
The magnetic properties of single crystalline hcp Co nanowire (NW) assemblies with different packing densities are investigated. The compacted assemblies exhibit an unusual increase in coercivity ...(HC) from 5.5 kOe to 6.1 kOe with the increase of the packing density from 2.1 to 4.5 g/cm3. While Hc decreases with further increase in packing density. A similar trend in Hc value variation with density has also been noticed at different temperatures. The initial increase in HC values is ascribed to magnetostatic interaction between the nanowires, which became stronger with the increased packing density. However, above the density of 4.5 g/cm3, the Hc decreases due to the proximity effect as shown in the δM plot. The δM plot shows a negative peak at high field and it becomes prominent with the increased density. Moreover, it has been found that the variation of HC with the packing density is also related to diameter of Co NWs. A larger diameter of the nanowires gives a negative dependence of the Hc value with the density in the whole investigated region.
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