Resonance Detection Research Articles

Development of magnetical Wells-Dawson polyoxometalates with defects for the highly effective oxidative desulfurization of fuel oil

Developing high-performance and recyclable catalysts for the oxidation desulfurization of fuel oils remains largely a challenge. Herein, the Wells-Dawson phosphotungstic acid (P2W18) with oxygen vacancy (OV) defects was embedded into the carbon shell of magnetic microspheres (Fe3O4) encapsulated by the carbon matrix, developing the Fe3O4@C@P2W18 catalyst. The as-prepared Fe3O4@C@P2W18 catalyst was applied in the oxidation desulfurization (ODS) reaction of model fuels with H2O2 as oxidant. Under Fe3O4@C@P2W18 catalyst, fuel oil (2000 ppm S) could reach 100 % of sulfur removal in 15 min at 70 ℃ with a theoretical O/S molar ratio of 2, collaborating its extraordinary ODS performance. The eminent catalyst activity is mainly given the credit to the intrinsically high activity of Wells-Dawson P2W18 with OV defects, more accessible active sites induced by the highly even dispersion of P2W18, and the microenvironment effect of the carrier. Moreover, Fe3O4@C@P2W18 shows facile separation through external magnetic field as well as excellent reusability with a negligible reduction of sulfur removal after twelve cycles. Additionally, according to the free radical experiments and electron paramagnetic resonance (EPR) detection, a •OH radical mechanism is disclosed to be responsible for the current catalytic ODS reaction of fuel oils. Therefore, the catalyst developed by this study holds great promise for highly efficient and deep oxidation desulfurization of fuel oils.

Covalent triazine frameworks as particle electrode for three-dimensional photoelectrocatalytic degradation of oxytetracycline: Synergy effects, pathway, and mechanism.

Photoelectrocatalysis has been widely employed for degrading antibiotics due to its high efficiency. However, the application is significantly impeded by the rapid recombination of photogenerated charge carriers and the limited surface areas of photoelectrodes. In the study, high crystallinity covalent triazine frameworks were fabricated at low temperature of 150°C and firstly used as particle photoelectrode in the three-dimensional photoelectrochemical reactor to degrade oxytetracycline (OTC). SEM, TEM, XRD, XPS, and FT-IR confirmed the successful synthesis of high crystallinity covalent triazine frameworks. Compared to CTF-120 (71.2%) and CTF-180 (46.9%), CTF-150 exhibited excellent OTC removal. Electrochemical impedance, UV-vis absorption spectra, and Mott-Schottky tests showed that CTF-150 demonstrated more wide light absorption range of 501nm and narrow bandgap of 2.52eV, and smaller Rct value under illumination, in comparing to CTF-120 and CTF-180. When the initial concentration of OTC was 50mgL-1, the 86.2% of OTC removal and 62.7% of mineralization were obtained under light irradiation (λ>420nm), current of 10mA, pH of 6.4, electrolyte of 0.1M Na2SO4. The synergy effect between photocatalytic and electrocatalytic processes of CTF-150 not only enhanced by 38.5% current efficiency but also reduced energy consumption to 1.90 kWh m-3. CTF-150 had a wide range of acid-base application and displayed resistance on coexisting ions. Electron spin resonance detection, quenching experiments, and probe experiments illustrated that h+, •O2-, 1O2, and •OH contributed to the degradation of OTC and the generation pathways of •O2-, 1O2, and •OH were verified. Moreover, •O2-, 1O2, and h+ were the main reactive species responsible for OTC removal, while 1O2 was for OTC mineralization. Based on high-performance liquid chromatography-tandem mass spectrometry detection, OTC with benzene ring was decomposed to opening ring products. The acute toxicity, developmental toxicity, bioaccumulation factor and mutagenicity of OTC and its intermediates using T.E.S.T. showed the toxicity of 82.35% degradation products decreased.

Element-specific X-Ray detection of electron paramagnetic resonance in thin films of quantum bits

Element-specific magnetism accessible by synchrotron-based X-ray spectroscopy has proven to be valuable to study spin and orbital moments of transition metals and lanthanides in technologically relevant thin-film and monolayer samples. The access to coherent spin superposition states relevant for emergent quantum technologies remains, however, elusive with ordinary X-ray spectroscopy. Here, we approach the study of such quantum-coherent states via the X-ray detection of microwave-driven electron paramagnetic resonance, which involves much smaller signal levels than X-ray detected ferromagnetic resonance on classical magnets. We demonstrate the feasibility of this approach with thin films of phthalocyanine-based metal complexes containing copper or vanadium centers. We also identify X-ray specific phenomena that we relate to charge trapping of secondary electrons resulting from the decay of the X-ray excited core-hole state. Our findings pave the way toward the element-specific X-ray detection of coherent superposition states in monolayers of atomic and molecular spins on virtually arbitrary surfaces.

Graphene-Enabled Multiresonator Metasurfaces for Ultrasensitive Surface Plasmon Resonance Detection of Waterborne Bacteria Across Multiple Frequencies with Machine Learning Optimization

Graphene-Enabled Multiresonator Metasurfaces for Ultrasensitive Surface Plasmon Resonance Detection of Waterborne Bacteria Across Multiple Frequencies with Machine Learning Optimization

Concept for a geometry-insensitive high-field magnetic resonance detector

AbstractWe introduce an inverse design methodology for a new class of eigenfrequency-invariant metamaterial-resonators, targeting nuclear magnetic resonance detection at ultra-high $$\mathbf {B_0}$$ B 0 field, and operating at two specified frequencies selected from within the 100-1500 MHz range. The primary optimisation goal is to maximise the magnetic field intensity and uniformity within a liquid sample, while the electric energy should be kept to a minimum level to reduce dielectric heating or quadrupolar moment excitation effects. Due to the symmetric geometry requirement of the cavity, a demultiplexer is also designed to direct each discrete resonant signal to another predetermined output port of the resonator. In order to reduce the geometrical dependency of the resonance frequency, a bespoke metamaterial is used for the cavity host. Therefore, an additional optimisation problem for a unit cell domain is defined to seek a proper material layout for the host region of the resonators. Given the sensitivity of the frequency domain, the optimisation process is effectively regulated through the utilisation of both a Helmholtz filter and a projection method. It is found that considerable improvements of the resonator quality factor can be obtained through this optimisation process.

Detection of electron paramagnetic resonance of two electron spins using a single NV center in diamond

An interacting spin system is an excellent testbed for fundamental quantum physics and applications in quantum sensing and quantum simulation. For these investigations, detailed information on the interactions, e.g., the number of spins and their interaction strengths, is often required. In this study, we present the identification and characterization of a single nitrogen vacancy (NV) center coupled to two electron spins. In the experiment, we first identify a well-isolated single NV center and characterize its spin decoherence time. Then, we perform NV-detected electron paramagnetic resonance (EPR) spectroscopy to detect surrounding electron spins. From the analysis of the NV-EPR signal, we precisely determine the number of detected spins and their interaction strengths. Moreover, the spectral analysis indicates that the candidates of the detected spins are diamond surface spins. This study demonstrates a promising approach for the identification and characterization of an interacting spin system for realizing entangled sensing using electron spin as quantum reporters.

Visible light-driven selective oxidative transformation of vicinal diols using ZnS-based photocatalyst in the presence of molecular oxygen

The heterogeneous photocatalysis for the oxidative cleavage of C–C bond is significant to the transformation of biomass feedstock. In this work, a heterojunction photocatalyst based on the conductor ZnS and C3N4 (CN) material is prepared and employed in the aerobic oxidative cleavage reaction of vicinal diol under visible light irradiation. As a result, it is found that 3ZnS/CN catalyst obtained by a mechanical grinding method shows a high photocatalytic activity. In the photocatalytic oxidative cleavage process of 1-phenyl-1,2-glycol, more than 98.7% conversion of substrate with a 96.2% selectivity of benzaldehyde was attained using O2 as oxidant. In addition, the photocatalyst recycling experiments exhibited that the 3ZnS/CN catalyst still kept a good activity and stability even after being recycled for 5 times. Finally, the active reaction intermediates were investigated by the control experiments and the relative electron paramagnetic resonance (EPR) detection. According to the obtained results and photocatalytic principle, the mechanism for the selective oxidative transformatioin of 1-phenyl-1,2-glycol has been proposed. It gives a promising approach for the catalytic utilization of biomass-based lignin and cellulose.

Sensing force gradients with cavity optomechanics while evading backaction

We study force-gradient sensing with a coherently driven mechanical resonator and phase-sensitive detection of motion through the two-tone backaction evading measurement of cavity optomechanics. The response of the optomechanical system, solved by numerical integration of the classical equations of motion, shows an extended region which is monotonic to changes in force gradient. We use Floquet theory to model the fluctuations, which rise only slightly above that of the usual backaction evading measurement in the presence of the mechanical drive. The monotonic response and minimal backaction are advantageous for applications such as atomic force microscopy. Published by the American Physical Society 2024

Detection of electron spin resonance of a single nitrogen-vacancy center in diamond using the excited-state lifetime

We demonstrated a high precision lifetime-based magnetometry with a single NV center in the bulk diamond. The magnetometry precision in long-time measurements under this scheme outperformed that in the conventional intensity-based method, showing precision robustness neglecting the accumulation of technical noises such as sample drifts or laser power fluctuations. A magnetic field sensitivity of 7.8 μT Hz−1/2 with a single NV center was achieved, which is 13 times improvement of previously demonstrated lifetime-based magnetometry with π-pulses. In addition, the lifetime-based electron spin detection method provides time-resolved spin dynamic information, can be further combined with recently reported continuous measurement protocols towards higher precision.

Cumulative damage characteristics of rock samples under cyclic low energy inclined plane impact

The ore pass wall in underground mines is often damaged by the impact and wear caused by unloaded ores. Studying the mechanisms of rock damage and failure under different impact angles can provide technical insights for the design and maintenance of the ore passes. This study employed an inclined impact experimental device along with a drop hammer loading test machine to perform cyclic low-energy impact tests on sandstone samples at five different inclined plane angles. The porosity of the rock samples was measured using a nuclear magnetic resonance (NMR) detection system, which provided data on porosity, T2 spectrum distribution, and NMR images of the samples after different numbers of impacts at different slope angles. The results indicate that: (1) Under cyclic inclined plane impact loading, an increase in the inclination angle, leads to reduced damage to the rock sample. The rock sample impacted at a 45° inclined plane exhibited the most severe damage. Rock samples with large inclination angles are more prone to experience rupture fractures at the tip of the inclined plane, primarily due to shear-tensile failure. The porosity changes dramatically at initially slope angles, resulting in greater damage. (2) As the number of impacts increases, the porosity of the samples first decreases, then increases, and subsequently decreases again. This progression corresponds to the closure of large pores following the first impact, followed by the expansion of micropores into macropores after 5 impacts, ultimately leading to gradual degradation of the samples until failure. (3) As the number of impacts increases, new cracks form within the rock sample and small cracks expand. Despite an increase in the number of micropores, the macropores still exert a significant influence on the rock samples, with the macropore spectrum area accounting for over 95%.

Iron–molybdenum bimetals incorporated montmorillonite-based catalytic ceramic membrane for heterogenous Fenton reaction towards the degradation of micropollutants in water

This study developed an innovative material approach that integrated Fenton catalysis with membrane filtration in a single system using iron–molybdenum bimetal oxides (FeMoO) incorporated montmorillonite (MMT)-based ceramic membrane (FeMoMMTCM) to achieve continuous Fenton reaction for water purification. The embedded bimetallic FeMoO catalyst created abundant active Fe(II) sites on the external and internal surfaces of the ceramic membrane (CM) for H2O2 activation. Using naproxen (NPX) as a model micropollutant in water, the FeMoMMTCM/H2O2 system achieved a 98.6 % removal of NPX (10 mg/L) within a filtration period of 3.4 min through the membrane, in comparison to a 17.5 % removal by FeMoMMTCM filtration with no H2O2 dosing and a 21.1 % removal by the FeMoO-less MMTCM/H2O2 system. The catalytic membrane demonstrated its high NPX removal efficiency over multiple cycles, retaining its effectiveness even in the presence of co-existing ions and organic matter in the water matrix. Furthermore, the FeMoMMTCM/H2O2 system was able to remove nearly 70 % of residual organic pollutants from the actual secondary wastewater effluent. The quenching tests and electro-paramagnetic resonance (EPR) detection confirmed the generation of hydroxyl (OH) and superoxide (O2−) radicals from H2O2. The excellent catalytic performance can be attributed to the Fe-Mo bimetallic catalyst, in which the active Mo(VI)/Mo(IV) cycle can facilitate the Fe(II)/Fe(III) cycle for continuous Fenton reaction. The cost analysis indicates that the low-cost MMT and its low sintering temperature for ceramics would greatly decrease the cost of MMTCM (243.1 US$/m2 vs. 541.5 US$/m2 of alumina-based CM). Overall, the research presents a technical strategy for the fabrication of highly cost-effective catalytic membranes with Fenton reaction for removing micropollutants from water.

Study on photocatalytic degradation and antibacterial properties of conjugated microporous polymers/TiO2 composite membranes

Conjugated microporous polymers (CMPs) are widely used in the field of photocatalysis due to their unique conjugated structures and various synthesis methods. Herein, we report the design and synthesis of conjugated microporous polymers hollow spheres (CMPs-HS) superhydrophilic modified by acetylcysteine (CMPs-HS-S) and compounded with the inorganic semiconductor material titanium dioxide (CMPs-HS-S/TiO2) for efficient photocatalytic degradation. To facilitate recycling, the composite membrane material was prepared by combining the materials mentioned above with PVDF membrane. The composite membrane materials had good hydrophilic and photocatalytic properties. Under visible light, the degradation rate of tetracycline (TC) (10 mg/L 180 min) reached 90 %, and the bactericidal rates for Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were 89 % and 99.99 %, respectively. The efficient photocatalytic performance of the composite membranes could be attributed to the hollow sphere structure of CMPs and the role of TiO2 as a photogenic electron transfer platform. Additionally, the hydrophilicity of the membrane also helped to accelerate the occurrence of photocatalytic reactions. After electron paramagnetic resonance (EPR) detection, h+, 1O2 and O2− were proved to be important reactive substances, which played a major role in degradation. These studies reflect the versatility of CMPs-based photocatalysts and provide a new idea for the future development of CMPs-based photocatalysts.

Near-infrared light enhanced oxygen vacancies on metal organic frameworks through photothermal effect for peroxydisulfate activation to remove organic pollutants

Peroxydisulfate (PDS)-based advanced oxidation processes (AOPs) are a promising strategy for addressing the challenges of contamination in aqueous environment. Taking advantage of solar energy based photocatalysis showed great potential on PDS activation for pollution control. However, the limited usage of near-infrared (NIR) region by photocatalysts restricted the realization of using full sunlight energy. Herein, zeolitic imidazolate frameworks derived materials (ZNC) with oxygen vacancies (VO) are designed and obtained, which can efficiently activate PDS under NIR light due to the photothermal effect, exhibiting superior carbamazepine (CBZ) degradation performance (84 % of CBZ within 60 min). Further quenching tests and electron paramagnetic resonance detection demonstrate that the photothermal effect can enhance the concentration of oxygen vacancies on the surface and facilitate charge separation of ZNC, which effectively activate PDS to generate O2−, 1O2, and h+, thus significantly enhancing the photocatalytic degradation of CBZ. Additionally, combining the results of intermediates analysis and DFT calculation, a systematic CBZ degradation pathway by two tracks is proposed. Moreover, the overall potential risks of CBZ are expected to be weakened in the ZNC/PDS/NIR process through photothermal catalytic degradation. Thus, a new strategy is provided for optimizing the use of solar energy to boost PDS activation for water purification.

An Ultrasensitive Molecular Detector for Direct Sensing of Spin Currents at Room Temperature.

The experimental analysis of pure spin currents at interfaces is one major goal in the field of magnonics and spintronics. Complementary to the established Spin-Hall effect using the spin-to-charge conversion in heavy metals for information processing, we present a novel approach based on spin pumping detection by an interfacial, resonantly excited molecular paramagnet adsorbed to the surface of the spin current generating magnet. Here, we show that the sensitivity of this electron paramagnetic resonance (EPR) detector can be enhanced by orders of magnitude through intramolecular transfer of spin polarization at room temperature. Our proof-of-principle sample consists of octahedral-shaped ferrimagnetic Fe3O4 nanoparticles covered by oleic acid (OA) which has two paramagnetic centers, S1 and S2. S1 arises from the chemisorption of OA and is located directly at the interface to Fe3O4. S2 originates from radical formation at the center of the molecule close to the double bond of oleic acid and is not influenced by chemisorption. Using ferromagnetic resonance (FMR) excitation of the Fe3O4 nanoparticles to pump spins into S1, a population inversion of the spin-split levels of S2 is formed, vastly enhancing the detection sensitivity on the atomic scale.

X-Band Single Chip Integrated Pulsed Electron Spin Resonance Microsystem.

We report on the design and characterization of a single chip integrated pulsed electron spin resonance detector operating at 9.1 GHz. The microsystem consists of an excitation microcoil, a detection microcoil, a low noise microwave preamplifier, a mixer, and an intermediate frequency (IF) amplifier. The chip area is about 0.7 mm2. To exemplify its possible applications, we report the results of single pulse, Rabi nutation, Hahn echo, two echoes, Carr-Purcell, and inversion recovery echo experiments performed on 0.02 and 0.05 nL samples of α, γ-bisdiphenylene-β-phenylallyl (BDPA) and 1% BDPA in polystyrene (BDPA:PS) at room temperature. The measured spin sensitivity is about 8 × 107 spins/Hz1/2 on a sensitive volume of about 0.1 nL. The microsystem power consumption is less than 100 mW, the radio frequency (RF) input bandwidth is 8.8 to 9.8 GHz, the IF output bandwidth is DC to 350 MHz, and the deadtime is less than 30 ns.

Large-enhancement nanoscale dynamic nuclear polarization near a silicon nanowire surface.

Dynamic nuclear polarization (DNP) has revolutionized the field of nuclear magnetic resonance spectroscopy, expanding its reach and capabilities to investigate diverse materials, biomolecules, and complex dynamic processes. Bringing high-efficiency DNP to the nanometer scale would open exciting avenues for studying nanoscale nuclear spin ensembles, such as single biomolecules, virus particles, and condensed matter systems. Combining pulsed DNP with nanoscale force-detected magnetic resonance measurements, we demonstrated a 100-fold enhancement in the Boltzmann polarization of proton spins in nanoscale sugar droplets at 6 kelvin and 0.33 tesla. Crucially, this enhancement corresponds to a factor of 200 reduction in the averaging time compared to measurements that rely on the detection of statistical fluctuations in nanoscale nuclear spin ensembles. These results substantially advance the capabilities of force-detected magnetic resonance detection as a practical tool for nanoscale imaging.

Resonant switching current detector based on underdamped Josephson junctions

Current-biased Josephson junctions can act as detectors of electromagnetic radiation. At optimal conditions, their sensitivity is limited by fluctuations causing stochastic switching from the superconducting to the resistive state. This work provides a quantitative description of a stochastic switching current detector, based on an underdamped Josephson junction. It is shown that activation of a Josephson plasma resonance can greatly enhance the detector responsivity in proportion to the quality factor of the junction. The ways of tuning the detector for achieving optimal operation are discussed. For realistic parameters of Nb/AlOx/Nb tunnel junctions, the sensitivity and noise-equivalent power (NEP) can reach values of S≃5×1012 (V/W) and NEP≃2×10−23 (WHz−1/2), respectively. These outstanding characteristics facilitate both bolometric and single-photon detection in microwave and terahertz ranges. Published by the American Physical Society 2024

Electrical Detection of Acoustic Antiferromagnetic Resonance in Compensated Synthetic Antiferromagnets.

Compensated synthetic antiferromagnets (SAFs) stand out as promising candidates to explore various spintronic applications, benefitting from high precession frequency and negligible stray field. High-frequency antiferromagnetic resonance in SAFs, especially the optic mode (OM), is highly desired to attain fast operation speed in antiferromagnetic spintronic devices. SAFs exhibit ferromagnetic configurations above saturation field; however in that case, the intensity of OM is theoretically zero and hard to be detected in well-established microwave resonance experiments. To expose the hidden OM, the exchange symmetry between magnetic layers must be broken, inevitably introducing remanent magnetization. Here, we experimentally demonstrate a feasible method to break the symmetry via surface acoustic waves with the maintenance of compensated SAF structure. By introducing an out-of-plane strain gradient inside the Ir-mediated SAFs, we successfully reveal the hidden OM. Remarkably, the OM intensity can be effectively modulated by controlling strain gradients in SAFs with different thicknesses, confirmed by finite-element simulations. Our findings provide a feasible scheme for detecting the concealed OM, which would trigger future discoveries in magnon-phonon coupling and hybrid quasiparticle systems.

Crown ethers: Small organic molecules unexpectedly hidden in nuclear magnetic resonance

The new class of ten macrocyclic compounds, lactic acid derived crown ethers, was designed and synthesized. They mainly composed of lactic acid and benzene or iodobenzene skeletons, and the introduction of iodine on the benzene ring was crucial to the formation of more regular crown ether conformation, starting from the diacid precursor. They possessed stable and larger cavities than classical macrocycles such as cyclodextrins. These crown ethers were discovered hiding function onto small molecules such as ethyl lactate, methanol, ethanol, aniline and phenol in nuclear magnetic resonance detection.

Highly sensitive terahertz polarization biosensor utilizing chiral metasurface

In order to achieve a highly sensitive biosensor with a simple structure, we propose a chiral metasurface polarization sensor. Using immunological surface plasmon resonance (SPR) detection, the antigen or antibody is fixed as a probe on the SPR metasurface to detect the corresponding antibody or antigen. Through the change of the refractive index of the analyte on the surface facial mask, the terahertz signal changes, and finally the sensing detection of avian influenza virus can be achieved. The designed metasurface adopts a hollow split sector chiral structure to generate chiral surface current, which can convert linearly polarized incident waves as elliptical polarized waves. The structure achieves the high sensitivity of 401 deg/RIU at frequency of 0.8 THz, and the avian influenza virus (H1N1, H5N2 and H9N2) with the same real part of the refractive index can also be distinguished. Influenza viruses belong to the family Orthomyxoviridae of RNA viruses, divided into three types: A, B, and C. In this article, avian influenza viruses belong to type A influenza viruses. It can clearly identify different Avian Influenza Viruses by the two polarization characteristic parameters of the reflection spectrum PEA (Polarization Ellipse Angle) and PRA (Polarization Rotation Angle). This method has a significant application prospect in the fields of biomedicine and food industries.