Heavy Metal Detection in Soils by Laser Induced Breakdown Spectroscopy Using Hemispherical Spatial Confinement

Spatial confinement has great potential for Laser Induced Breakdown Spectroscopy （LIBS） instruments after it has been proven that it has the ability to enhance the LIBS signal strength and repeatability. In order to achieve in-situ measurement of heavy metals in farmland soils by LIBS, a hemispherical spatial confinement device is designed and used to collect plasma spectra, in which the optical fibers directly collect the breakdown spectroscopy of the soil samples. This device could effectively increase the stability of the spectrum intensity of soil. It also has other advantages, such as ease of installation, and its small and compact size. The relationship between the spectrum intensity and the laser pulse energy is studied for this device. It is found that the breakdown threshold is 160 cm-2, and when the laser fluence increases to 250 J/cm2, the spectrum intensity reaches its maximum. Four different kinds of laser pulse energy were set up and in each case the limits of detection of Cd, Cu, Ni, Pb and Zn were calculated. The results show that when the laser pulse fluence was 2.12 GW/cm2, we obtained the smallest limits of detection of these heavy metals, which are all under 10 mg/kg. This device can satisfy the needs of heavy metal in-situ detection, and in the next step it will be integrated into a portable LIBS instrument.

Effect of cylindrical cavity height on laserinduced breakdown spectroscopy with spatial confinement

In this paper, we present a study on the spatial confinement effect of laser-induced plasma with a cylindrical cavity in laser-induced breakdown spectroscopy （LIBS）. The emission intensity with the spatial confinement is dependent on the height of the confinement cavity. It is found that, by selecting the appropriate height of cylindrical cavity, the signal enhancement can be significantly increased. At the cylindrical cavity （diameter = 2 mm） with a height of 6 mm, the enhancement ratio has the maximum value （approximately 8.3）, and the value of the relative standard deviation （RSD） （7.6%） is at a minimum, the repeatability of LIBS signal is best. The results indicate that the height of confinement cavity is very important for LIBS technique to reduce the limit of detection and improve the precision.

Effect of distances between lens and sample surface on laser-induced breakdown spectroscopy with spatial confinement

Spatial confinement can significantly enhance the spectral intensity of laser-induced plasma in air. It is attributed to the compression of plasma plume by the reflected shockwave. In addition,optical emission spectroscopy of laser-induced plasma can also be affected by the distance between lens and sample surface. In order to obtain the optimized spectral intensity, the distance must be considered. In this work, spatially confined laser-induced silicon plasma by using a Nd：YAG nanosecond laser at different distances between lens and sample surface was investigated.The laser energies were 12 mJ, 16 mJ, 20 mJ, and 24 mJ. All experiments were carried out in an atmospheric environment. The results indicated that the intensity of Si（I） 390.55 nm line firstly rose and then dropped with the increase of lens-to-sample distance. Moreover, the spectral peak intensity with spatial confinement was higher than that without spatial confinement. The enhancement ratio was approximately 2 when laser energy was 24 mJ.

Spatial confinement effects of laser-induced breakdown spectroscopy at reduced air pressures

Spatial confinement is a simple and cost-effective method for enhancing signal intensity and improving the detection sensitivity of laser-induced breakdown spectroscopy(LIBS).However,the spatial confinement effects of LIBS under different pressures remains a question to be studied,because the pressure of the ambient gas has a significant influence on the temporal and spatial evolution of plasma.In this study,spatial confinement effects of LIBS under a series of reduced air pressures were investigated experimentally,and the plasma characteristics under different air pressures were studied.The results show that the reduced air pressure can lead to both earlier onset and weakening of the enhancement effect of the spatial confinement on the LIBS line intensity.When the air pressure drops to 0.1 kPa,the enhancement effect of the emission intensity no longer comes from the compression of the reflected shock wave on the plasma,but from the cavity’s restriction of the plasma expansion space.In conclusion,the enhancement effect of spatial confinement technology on the LIBS is still effective when the pressure is reduced,which further expands the research and application field of spatial confinement technology.

Synthesis of cycloparaphenylene under spatial nanoconfinement

Suzuki coupling reactions between symmetrical monomers were conducted in various mesoporous silica nanoreactors grafted with palladium catalysts,enabling the selective formation of[12]cycloparaphenylene precursor with separate yield up to 25%in one-pot reactions,much higher than that in homogeneous reaction.The spatial nanoconfinement of the nanoreactors promotes the macrocyclization while limits the concomitant linear oligomer formation,offering more possibilities for the synthesis of macrocycles from symmetrical monomers in one-pot reaction.

Okra‑Like Multichannel TiO@NC Fibers Membrane with Spatial and Chemical Restriction on Shuttle‑Effect for Lithium–Sulfur Batteries

It is especially important to coordinately design the structure and composition of the host in lithium–sulfur batteries(LSBs)for improving its physicochemical adsorption and conversion of lithium polysulfide,which can alleviate the harmful shuttle effect.Herein,a self-supporting multichannel nitrogen-doped carbon fibers membrane embedded with TiO nanoparticles(TiO@NC)was constructed as the electrode for LSBs.The inner channels and the embedded TiO nanoparticles offer spatial confinement and chemical binding for polysulfides,respectively.Moreover,the TiO nanoparticles have abundant oxygen vacancies that promote the conversion of polysulfides.In addition,the nitrogen-doped carbon skeleton can not only serve as highly conductive transportation paths for electrons,but also integrate with the inner channels to sustain the morphology and bear volume expansion during cycling processes.Therefore,the fabricated self-supporting quadruple-channel TiO@NC ultrathin fibers electrode exhibits a high initial specific capacity of 1342.8 mAh g^(-1)at 0.5 C and high-rate capability of 505.8 mAh g^(-1)at 4.0 C.In addition,it maintains 696.0 mAh g^(-1)over 500 cycles with only 0.059%capacity decay per cycle at the high current density of 2.0 C.The multichannel configuration combined with TiO nanoparticles provides a synergetic design strategy for fabricating high-performance electrodes in LSBs.

Spatial confinement of zeolitic imidazolate framework deposits by porous carbon nanospheres for dual-atom catalyst towards high-performance oxygen reduction reaction

Dual atom catalysts(DACs),are promising electrocatalysts for oxygen reduction reaction(ORR)on account of the potential dual-atom active sites for the optimized adsorption of catalytic intermediates and the lower reaction energy barriers.Herein,spatial confinement strategy to fabricate DACs with well-defined Fe,Co dual-atom active site is proposed by implanting zeolitic imidazolate frameworks inside the pores of highly porous carbon nanospheres(Fe/Co-SAs-Nx-PCNSs).The atomically dispersed dual-atom active sites facilitate the adsorption/desorption of intermediates.Furthermore,the spatial confinement effect protects metal atoms aggregating.Benefiting from the rich accessible dual-atom active sites and boosted mass transport,we achieve remarkable ORR performance with half-wave potential up to 0.91 and 0.8 V(vs.reversible hydrogen electrode(RHE)),and long-term stability up to 10 h in both alkaline and acidic electrolytes.The remarkably enhanced ORR catalytic property of our as-developed DACs is in the rank of excellence for 1%.The as-developed rechargeable Zn-air battery(ZAB)with Fe/Co-SAs-Nx-PCNSs air cathode delivers ultrahigh power density of 216 mW·cm^(−2),outstanding specific capacity of 813 mAh·g^(−1),and promising cycling operation durability over 160 h.The flexible Zn-air battery also exhibits excellent specific capacity,cycling stability,and flexibility performance.This work opens up a new pathway for the multiscale design of efficient electrocatalysts with atomically dispersed multiple active sites.