Paramagnetic Surface Research Articles

Role of Paramagnetic Impurities and Surface Roughness on NMR Relaxation Times: Insights from Molecular Dynamics Simulations

Role of Paramagnetic Impurities and Surface Roughness on NMR Relaxation Times: Insights from Molecular Dynamics Simulations

N-Hydroxysuccinamide functionalized iron oxide nanoparticles conjugated with 5-flurouracil for hyperthermic therapy of malignant liver cancer cells by DNA repair disruption

Magnetized iron oxide nanoparticles are ideal materials for biological and biomedical applications due to their biocompatibility, super paramagnetic behavior, surface capability, and chemical stability. This research article is narrating the overview of methodologies of preparation, functionalization, characterization and applications of Fe3O4 nanoparticles. Super paramagnetic nanoparticles are studied for their hyperthermia properties. The proposed mechanism behind the hyperthermia was damaging the proteins responsible for DNA repair thereby, directly accelerating the DNA damages on cancer cells by increasing the temperature in the vicinity of the cancer cells. In this study, super paramagnetic iron oxide (Fe3O4) nanoparticles (SPIONs) and anti-cancer drug, 5-fluorouracil, functionalized with N-Hydroxysuccinimide organic molecules. A specific absorption rate at 351 nm can be achieved using UV analysis. The magnetic Fe3O4 nanoparticles had a cubic crystalline structure. FE-SEM(field emission scanning Electron microscopy) with EDAX(energy dispersive X-ray analysis) analysis shows that the size of the SPION was about 30–100 nm range and the percentage of chemical compositions was higher in the order of Fe, O, C. for particle size analysis, the SPION were positively charged derived at +9.9 mV and its conductivity is measured at 0.826 mS/cm. In-vitro anti-cancerous activity analysis in Hep-G2 cells (liver cancer cells) shows that the 5-fluorouracil functionalized SPIONs have higher inhibition rate than the bare Fe3O4 nanoparticles. The Fe3O4 nanoparticles were studied for their hyperthermic abilities at two different frequencies such as 3.05 × 106 kAm−1s−1 and 4.58 × 106 kAm−1s−1.The bare Fe3O4 at low magnetic field, 10 mg was required to raise the temperature above 42°- 45 °C and at high magnetic field, 6 mg was enough to raise the same temperature. The 5-fluorouracil functionalized Fe3O4 shows that at low magnetic field, 6 mg is required to raise the hyperthermia temperature and at high magnetic field, 3 mg is required to raise the temperature above 42°- 45 °C. the rate of heating and the temperature achieved with time can be tuned with concentrations as well as magnetic component present in the Fe3O4 nanoparticles. Beyond this concentration, the rate of cell death was observed to increase. The saturation and low residual magnetization were revealed by the magnetization analysis, making them well suited for clinical applications

Impact on the Photocatalytic Dye Degradation of Morphology and Annealing-Induced Defects in Zinc Oxide Nanostructures.

In this study, three different morphologies, nanoflower (NF), nano sponge (NS), and nano urchin (NU), of zinc oxide (ZnO) nanostructures were synthesized successfully via a mild hydrothermal method. After synthesis, the samples were annealed in the atmosphere at 300, 600, and 800 °C. Although annealing provides different degradation kinetics for different morphologies, ZnO NS performed significantly better than other morphologies for all annealing temperatures we used in the study. When the photoluminescence, electron paramagnetic resonance spectroscopy, BET surface, and X-ray diffraction analysis results are examined, it is revealed that the defect structure, pore diameter, and crystallinity cumulatively affect the photocatalytic activity of ZnO nanocatalysts. As a result, to obtain high photocatalytic activity in rhodamine B (RhB) degradation, it is necessary to develop a ZnO catalyst with fewer core defects, more oxygen vacancies, near band emission, large crystallite size, and large pore diameter. The ZnO NS-800 °C nanocatalyst studied here had a 35.6 × 10-3 min-1 rate constant and excellent stability after a 5-cycle photocatalytic degradation of RhB.

Photo-reduction of nitrate to nitrite in aqueous solution in presence of CaO: Selectivity, mechanism and application

Nitrate (NO3−) photolysis leads to various nitrogenous products, which depends on the reaction conditions and solution properties. How to regulate the composition of products is an important issue. Herein, we found that the involvement of CaO in the NO3− photolysis could selectively reduce NO3− to nitrite (NO2−). Almost 100 % NO2− selectivity was achieved in CaO/UV/NO3− system at initial pH (3–10), initial NO3− concentration (5–45 mg N/L) and CaO dosage (1–6 g/L). The high NO2− selectivity in CaO/UV/NO3− system was attributed to the rich basic sites and paramagnetic surface species of CaO, which captured nitrogen oxides (NOX) and promoted the conversion of NOX to NO2−, respectively. The two-step reduction strategy of CaO/UV coupled with H2NSO3H was used to remove NO3− in wastewater, in which NO3− was firstly reduced to NO2−, then the produced NO2− was further reduced to N2 by H2NSO3H. As for secondary effluent of municipal wastewater with initial NO3− concentration of 30 mg N/L, 93 % removal of NO3− and 100 % of N2 selectivity were achieved at CaO dosage of 2 g/L and H2NSO3H dosage of 0.4 g/L.

Synthesis and Applications of Biopolymer /FeO Nanocomposites: A Review

Magnetic oxide nanoparticles have engaged most consideration due to their rare character, such as easy separation, surface-to- volume ratio, paramagnetic and high surface area. Natural biopolymers, namely, (Chitosan, Guar-Gum, Tamarind, Alginate, Dextran, Pectin) have posed as an incredible host for the preparation of magnetic nanoparticles. Biopolymer based magnetic nanocomposites have been fabricated from long time using method like co-precipitations, green synthesis, in-situ, hydrothermal and wet chemical method. Properties of biopolymer magnetic nanocomposites draw attention to the researchers towards fabricating at the nano level for various applications like as adsorptions inorganic metal, organic impurity, targeted drug-delivery, bio-sensing, catalysis activity, antimicrobial activity, antifungal activity, antioxidant activity, anti-cancer activity, energy, environmental remediation, waste water treatment and textiles. This review is designed to report very firstly reported biopolymer magnetic nanoparticles (BMNPs) in last ten years and attractive approach in various applications.

FeOOH@MoS2 as a highly effective and stable activator of peroxymonosulfate-based advanced oxidation processes for pollutant degradation

Fe-based materials are widely used as activators in advanced oxidation processes (AOPs) for the degradation of persistent organic pollutants because of their high activity and environmental friendliness. The continuous consumption of Fe2+ and the generation of excessive Fe3+, however, lead to the formation of sludge (iron cement) and the degradation of material performances. In this work, we report MoS2 with a self-assembled ultrathin Fe (oxy)hydroxide layer on the surface (FeOOH@MoS2) as a highly effective and stable activator for peroxymonosulfate (PMS)-based AOPs system. The FeOOH@MoS2/PMS system performed exceptionally for removing antibiotics from aquatic environment under both acidic and basic conditions, with function pH condition from 4 to 10. The stability of FeOOH@MoS2 was also outstanding, with only 10.1% decrease after 5 cycles under pH 8, which is much better than conventional heterogeneous Fe-based activator for PMS based AOPs. The combination of quenching experiments, electron paramagnetic resonance (EPR) tests and surface analysis suggest that such high performance is attributed to high catalytic activity of MoS2 as the co-catalyst and the strong interface interaction between MoS2 and FeOOH. While the Fe2+FeOOH in FeOOH effectively activate PMS to produce SO4•− and •OH radical to remove antibiotics, the produced Fe3+FeOOH is reduced back to Fe2+FeOOH by MoS2 co-catalyst, enabling the recycle of Fe2+. Our results provide a facile strategy for improving the activity and stability of heterogeneous Fe-based catalysts for AOP systems, particularly under basic environment, which contribute towards the large-scale implementation.

In-situ growth behavior of FAPbBr3 on two-dimensional materials for photocatalytic reaction to controllable products

Constructing mixed dimensional materials have been regarded as an outstanding approach to maximum the advantages from materials of different dimensions. In this work, we prepared a mixed dimensional photocatalyst based on Formamidinium lead bromide (FAPbBr3) perovskite and 2D materials (2DMs). The aim of this work is to utilize distributions of the active sites in 2DMs, through growing FAPbBr3 on the different position of 2DMs, the concentration of photogenerated charges is manipulated, thus conducting different reactions. A pre-treatment using HBr to increase the unsaturated bonds in MoS2 presents significant influence on the FAPbBr3 growth and its photocatalytic product. The scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) confirm that the perovskite nanoparticles were well loaded on the 2D materials. The photocatalytic process and the heterojunction arrangement are demonstrated by X-ray photoelectron spectroscopy (XPS), time-resolved photoluminescence (TRPL), electron paramagnetic resonance (EPR) and surface photovoltage microscopy (SPVM). By adjusting the weight ratios and growth of FAPbBr3 on the top of 2DMs, the optimized composite photocatalyst (with 30 wt% of FAPbBr3) exhibits remarkable photoactivity for oxidation of benzyl alcohol into benzaldehyde (30 wt% FAPbBr3@WS2 performed 75.9% conversion in 4 h, approximately 9-fold than the pure 2DMs). Meanwhile, by growing FAPbBr3 on the edge of 2DMs, benzoic acid is obtained as the product. Although longer reaction time is needed, the photocatalyst performs outstanding activity (30 wt% FAPbBr3@MoS2 reached 84.5% conversion in 5 h).

Activation of peroxydisulfate by carbon nanotube for the degradation of 2,4-dichlorophenol: Contributions of surface-bound radicals and direct electron transfer

Carbon materials have been used to activate peroxydisulfate (PDS) for the degradation of organic pollutants. The mechanism involved, especially whether radicals are formed in these processes, is still under debate. In this research, multi-walled carbon nanotube (MWCNT) was employed to activate PDS for the removal of 2,4-dichlorophenol (2,4-DCP). The effects of solution pH, PDS concentration, 2,4-DCP concentration, and MWCNT loading on the degradation of 2,4-DCP were investigated. The mechanism was explored via radical scavenging experiments, electron paramagnetic resonance (EPR) and MWCNT surface characterization. The results showed that the rate of 2,4-DCP degradation increased with the increasing solution pH, PDS concentration and MWCNT loading. The presence of OH and SO4− signals in EPR studies, no inhibitory effect in radical scavenging experiments, and the chlorination of MWCNT observed by X-ray photoelectron spectroscopy (XPS) suggested that surface reactions involving both surface-bound radicals and direct electron transfer were responsible for 2,4-DCP degradation. Reusability tests showed that the surface sites responsible for surface-bound radical formation were poisoned after PDS activation, while those responsible for direct electron transfer remained active after five cycles. This research provided the first in-depth insights for the dual roles of MWCNT in the PDS activation process.

Effect of Dusty Particles on Darcy-Brinkman Gravity-Driven Ferro-Thermal-Convection in a Ferrofluid Saturated Porous Layer with Internal Heat Source: Influence of Boundaries

In the present work, penetrative ferro-thermal-convection (FTC) via internal heating in a ferrofluid-saturated porous layer for different types of velocity, temperature and magnetic potential bounding surfaces, is investigated theoretically. A Galerkin-type based on weighted residual method has been used to obtain the eigenvalue problem. The stability of the system is notably influenced on porous medium via internal heating. It is demonstrated that paramagnetic surface with large magnetic susceptibility $$ (\chi > 0) $$ delay the FTC as compared to very low magnetic susceptibility $$ (\chi = 0) $$ as well as ferromagnetic ones. Increase in heat source strength, non-linearity of magnetization, dust particles and magnetic number hasten, while increase in viscosity ratio, concentration parameter and inverse Darcy number delay the onset. The rigid paramagnetic surfaces induct more stabilizing effect on FTC compared to very low magnetic susceptibility as well as ferromagnetic surfaces. In limiting cases, some results published previously are recovered from the present results.

Magnetic field noise analyses generated by the interactions between a nitrogen vacancy center diamond and surface and bulk impurities

We investigated the mechanism of magnetic noise due to both surface and bulk impurities. For surface noise, we apply the Langevin method to spin fluctuation theory to calculate the noise for paramagnetic surface impurities absorbed in a thin layer of water. We find that the mechanisms generating noise are spin flip and spin precession which depend on impurity spin relaxation and spin precession time. For the bulk noise, we consider carbon-13 and nitrogen as impurities and employ the correlated-cluster expansion to calculate noise. Carbon-13 noise is a few orders of magnitude larger than nitrogen due to the higher impurity density in the typical NV center diamond system. We also find that the noise in the secular approximation underestimates noise under low applied magnetic field. Overall, the major source of magnetic field noise is spin precession noise, which is more than five orders of magnitude larger than the spin flip noise.

Facile synthesis of kermesinus BiOI with oxygen vacancy for efficient hydrogen generation

Many studies have been devoted to enhancing photocatalytic activity of hydrogen generation by water splitting in recent years. Herein, a well-defined 3D flowerlike mesoporous photocatalyst (kermesinus BiOI, K-BiOI) was successfully prepared through UV–Vis-Light driving method. The X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and surface photovoltage (SPV) tests confirmed that the oxygen vacancies (OVs) were introduced onto the surface of BiOI, which resulted that the color of BiOI changed from normal orange to kermesinus. The successful introduction of OVs led to the absorption range of K-BiOI stretched. Although the OVs are introduced on the surface, the main body of the material is still BiOI. Furthermore, K-BiOI exhibited a remarkably improved hydrogen production rate of 6.51 mmol g−1 h−1 under UV–Vis-light irradiation, which was 21-fold higher than that of BiOI under UV light irradiation. The OVs on the K-BiOI surface could form a defect state lying near the conduction band minimum of the photocatalyst and act as an electron scavenger delaying the photogenerated carrier recombination during the photoreaction process. The present work provides a new approach to introduce OVs on the surface of BiOI, which can provide a new strategy of catalyst preparation for the efficient H2 production.

Characterisation and reactivity of oxygen species at the surface of metal oxides

Surface reactive oxygen species play a fundamental role in selective oxidation and combustion reactions catalyzed by metal oxides. Unravelling the nature of these transient species, and understanding the details of both their electronic structure and reactivity has been for decades one of the prime research areas of surface and catalytic chemistry. The longstanding activity of Michel Che in this area has been a source of inspiration for generation of researchers, and constitute his outstanding and enduring scientific legacy. Present review provides a survey of the surface oxygen species on oxide materials, which moving on from the Che’s pioneering works includes noteworthy results obtained during the years by other researchers. In particular, applications of two powerful techniques such as electron paramagnetic resonance (EPR) and photoluminescence (PL) for detailed characterization of paramagnetic (O−, O2−, O3−) and diamagnetic surface oxygen varieties (O2−surf), respectively, are addressed here. Classification and insights into the formation pathways of these species on various oxide surfaces, as well as their involvement in model and real gas/solid and liquid/solid reactions of catalytic and photocatalytic relevance is also considered. Finally, the relationship between the thermodynamic and kinetic Bronsted basicity of low coordinated O2−Lc anions is discussed, on the basis of Che’s fundamental studies and on recent developments.

Extending the Quantum Coherence of a Near-Surface Qubit by Coherently Driving the Paramagnetic Surface Environment.

Surfaces enable useful functionalities for quantum systems, e.g., as interfaces to sensing targets, but often result in surface-induced decoherence where unpaired electron spins are common culprits. Here we show that the coherence time of a near-surface qubit is increased by coherent radio-frequency driving of surface electron spins, where we use a diamond nitrogen-vacancy (NV) center as a model qubit. This technique is complementary to other methods of suppressing decoherence and, importantly, requires no additional materials processing or control of the qubit. Further, by combining driving with the increased magnetic susceptibility of the double-quantum basis, we realize an overall fivefold sensitivity enhancement in NV magnetometry. Informed by our results, we discuss a path toward relaxation-limited coherence times for near-surface NV centers. The surface-spin driving technique presented here is broadly applicable to a wide variety of qubit platforms afflicted by surface-induced decoherence.

Paramagnetic surface defects in LiMgPO4

The samples of LiMgPO4 were synthesized by the solid state reaction and melting methods. The EPR spectra obtained at 300 K and 115 K are indicative of the existence of charged defects in LiMgPO4. The main imperfections are identified as a radical CO−3 (g = 2) and a singly charged oxygen vacancy (g1 = 2.45, g2 = 2.20, g3 = 2.00). The presence of carbon-containing groups is proved by Raman spectroscopy. The assumption is made that the defects are located mainly on the surface of the grains. Thermoluminescent characteristics of LiMgPO4 annealed in atmospheres with different pO2 demonstrate that the surface defects impair the efficiency of LiMgPO4 as a dosimetric material.

Carbon Quantum Dots: Elegant Surface of CoNi Alloys toward Efficient Magnetorheological Performances Realized with Carbon Quantum Dots (Adv. Mater. Interfaces 15/2018)

A series of CoNi based hierarchical microspheres with different surface morphologies, including litchi-like, seed of plane tree-like and waxberry-like shapes, are obtained via surface nucleation of carbon quantum dots (CQDs). Taking both the synergistic benefits of paramagnetic CoNi microspheres and surface architecture, the resulting CoNi microspheres exhibit enhanced interparticle friction for enhancing their MR effects compared with smooth surface microspheres. This work is reported by Wen Ling Zhang, Jingquan Liu and co-workers in article number 1800164.

Paramagnetic Surface Active Ionic Liquids: Interaction with DNA and MRI Application

Paramagnetic surface active ionic liquids (PMSAILs) have been synthesized wherein long alkyl chain bearing imidazoilium, pyridinium or isoquinolinium are cationic and bromotrichloroferrate (III) is paramagnetic counterion constituents. PMSAILs have been investigated for their aggregation properties using surface tension, conductivity, and dynamic light scattering (DLS). Interaction of PMSAILs with DNA in aqueous solutions has been examined through CD, fluorescence, ITC, DLS, zeta potential, and agarose gel electrophoresis. DNA compaction has been observed upon interaction with PMSAILs in dilute solutions. PMSAIL with isoquinolinium cation was found more efficient towards the DNA compaction. Decompaction of DNA could be achieved simply with the addition of NaCl. Further, the application of PMSAILS as MRI contrast materials has been explored. All the investigated PMSAILS exhibited excellent dual mode T1 & T2 contrast property in low concentration regime. To improve the real-time practical importance, MRI results have been compared with clinically available Gd-BOPTA based MRI contrast agent.

Low-Coordinated Titanium(III) Alkyl-Molecular and Surface-Complexes: Detailed Structure from Advanced EPR Spectroscopy.

The structure of paramagnetic surface species is notoriously difficult to determine. For TiIII centers related to Ziegler-Natta catalysis, we demonstrate here that detailed structural information can be obtained by advanced EPR spectroscopy and DFT computations, benchmarked on molecular analogs. The hyperfine sublevel correlation (HYSCORE) spectra obtained after reaction with 13 C-labeled ethylene provides information about the coupling with a proton in the first coordination sphere of TiIII as well as significant 13 C hyperfine coupling and thereby allows structural assignment of the surface species.

Low‐Coordinated Titanium(III) Alkyl—Molecular and Surface—Complexes: Detailed Structure from Advanced EPR Spectroscopy

AbstractThe structure of paramagnetic surface species is notoriously difficult to determine. For TiIII centers related to Ziegler–Natta catalysis, we demonstrate here that detailed structural information can be obtained by advanced EPR spectroscopy and DFT computations, benchmarked on molecular analogs. The hyperfine sublevel correlation (HYSCORE) spectra obtained after reaction with 13C‐labeled ethylene provides information about the coupling with a proton in the first coordination sphere of TiIII as well as significant 13C hyperfine coupling and thereby allows structural assignment of the surface species.

Elegant Surface of CoNi Alloys toward Efficient Magnetorheological Performances Realized with Carbon Quantum Dots

AbstractDesigning and fabricating a rational surface architecture is one of the critical factors to achieve desirable physical and chemical properties and still remains an immense challenge. Herein, a series of CoNi‐based hierarchical microspheres with different surface morphologies, including litchi‐like, seed‐of‐plane‐tree‐like, and waxberry‐like shapes, are obtained via surface nucleation of carbon quantum dots (CQDs) with different concentrations in liquid polyol. Microstructure investigations suggest that all the CoNi microspheres are uniformly with enhanced surface roughness with the increasing concentration of CQDs. This study provides insight into the surface dominant magnetorheological (MR) behaviors of these CoNi‐based suspensions. Taking both the synergistic benefits of paramagnetic CoNi microspheres and surface architecture, the resulting CoNi microspheres exhibit enhanced interparticle friction for enhancing their MR effects compared with smooth surface microspheres, opening up the possible mechanism for revealing the MR effect. Moreover, this facile strategy can be extended as an effective path to achieve high‐performance MR behaviors for engineering applications.

Compact Micellization: A Strategy for Ultrahigh T1 Magnetic Resonance Contrast with Gadolinium-Based Nanocrystals.

Paramagnetic gadolinium (Gd(3+))-based nanocrystals (NCs) with a large number of confined gadolinium ions can be expected to heavily enhance the longitudinal (T1) relaxation of water protons compared to clinical gadolinium complexes with only a single paramagnetic center. However, paramagnetic Gd(3+)-NCs reported to date show only a modest T1 relaxivity of ∼10 mM(-1) s(-1) per Gd(3+) at 1.5 T, only about 3-times higher than clinical Gd(3+) complexes. Here we demonstrate a strategy that achieves ultrahigh T1 relaxivity that is about 25-times higher than clinical Gd(3+) complexes by controlling the proximity of water protons to a paramagnetic NC surface. Using NaGdF4 NCs (∼3 nm) coated with PEG-ylated phospholipid (DSPE-PEG) micelles, we show that the distance of water protons to the NCs surface can be tuned by controlling the NC-micelle sizes. Increasing the ratio of DSPE-PEG to NCs during micellization decreases the size of NC-micelles, enhancing the proximity of water to the NC surface. Using this strategy, we have achieved compact NC-micelles (hydrodynamic diameter, HD ∼ 5 nm) with ultrahigh T1 relaxivity of ∼80 mM(-1) s(-1) per Gd(3+) at 1.41 T. The findings reported here demonstrate a nanostructured Gd(3+)-contrast agent (CA) that simultaneously achieves an ultrahigh T1 relaxivity approaching theoretical predictions, extremely compact size (HD < 5 nm), and a biocompatible surface. Our results show the hitherto unknown ultrahigh T1 relaxation enhancement of water protons in close proximity to a colloidal gadolinium-NC surface that is achievable by precise control of their surface structure.