Spreading a water droplet through filter paper on the metal substrate for surface-enhanced laser-induced breakdown spectroscopy

Improving the Laser-Induced Breakdown Spectroscopy for Highly Efficient Trace Measurement of Hazardous Components in Waste Oils

Improper disposal of waste oils containing hazardous components damages the environment and the ecosystem, posing a significant threat to human life and health. Here, we present a method of discharge-assisted laser-induced breakdown spectroscopy combined with filter paper sampling (DA-LIBS-FPS) to detect hazardous components and trace the source of polluting elements. DA-LIBS-FPS significantly enhances spectral intensity by 1-2 orders of magnitude due to the discharge energy deposition into the laser-induced plasma and the highly efficient laser-sample interaction on the filter paper, when compared to single-pulse LIBS with silica wafer sampling (SP-LIBS-SWS). Additionally, the signal-to-noise ratio and the signal-to-background ratio are both significantly increased. Resultantly, indiscernible lines, such as CN and Cr I, are well distinguished. In contrast with DA-LIBS combined with silica wafer sampling (DA-LIBS-SWS), the spectral signal fluctuations in DA-LIBS-FPS are reduced by up to 33%, because of the homogeneous distribution of the oil layer on the filter paper in FPS. Further examination indicates that the limit of detection for Ba is reduced from a several parts per million level in SP-LIBS-SWS to a dozens of parts per billion level in DA-LIBS-FPS, i.e., nearly 2 orders of magnitude enhancement in analysis sensitivity. This improvement is attributed to the extended plasma lifespan in DA-LIBS and the increasing electron density and plasma temperature in FPS. DA-LIBS-FPS provides a low-cost, handy, rapid, and highly sensitive avenue to analyze the hazardous components in waste oils with great potential in environmental and ecological monitoring.

A Review on Pulsed Laser Fabrication of Nanomaterials in Liquids for (Photo)catalytic Degradation of Organic Pollutants in the Water System

The water pollution caused by the release of organic pollutants has attracted remarkable attention, and solutions for wastewater treatment are being developed. In particular, the photocatalytic removal of organic pollutants in water systems is a promising strategy to realize the self-cleaning of ecosystems under solar light irradiation. However, at present the semiconductor-based nanocatalysts can barely satisfy the industrial requirements because their wide bandgaps restrict the effective absorption of solar light, which needs an energy band modification to boost the visible light harvesting via surface engineering. As an innovative approach, pulsed laser heating in liquids has been utilized to fabricate the nanomaterials in catalysis; it demonstrates multi-controllable features, such as size, morphology, crystal structure, and even optical or electrical properties, with which photocatalytic performances can be precisely optimized. In this review, focusing on the powerful heating effect of pulsed laser irradiation in liquids, the functional nanomaterials fabricated by laser technology and their applications in the catalytic degradation of various organic pollutants are summarized. This review not only highlights the innovative works of pulsed laser-prepared nanomaterials for organic pollutant removal in water systems, such as the photocatalytic degradation of organic dyes and the catalytic reduction of toxic nitrophenol and nitrobenzene, it also critically discusses the specific challenges and outlooks of this field, including the weakness of the produced yields and the relevant automatic strategies for massive production.

Micro-hole array sprayer combined with an organic membrane to assist LIBS (MASOM-LIBS): A novel highly sensitive detection method for dissolved trace heavy metals in water

The development of highly sensitive and rapid detection technology for heavy metal elements in water is of great significance to the monitoring of water environmental pollution, sewage discharge control and other application fields. As an alternative detection method with great potential in the above fields, LIBS technology still has some problems that need to be solved. To improve the sensitivity and efficiency of LIBS detection of trace metals in water, a new method Micro-hole Array Sprayer combined with an Organic Membrane to assist LIBS (MASOM-LIBS) was proposed in this study. In this method, water samples were transformed into a large number of micrometer droplets by a micro-hole array injection device and were sprayed onto a rotating polypropylene organic film. After natural drying, LIBS analysis was performed. The test results of the mixed solution show that plasma with lower electron density and higher electron temperature can be obtained after full drying, the signal intensity will be stronger, and the stability can be reduced to less than 1%. The experimental results of Cu, Cd, Mn, Pb, Cr and Sr as target elements show that the LODs of the MASOM-LIBS method for most elements is less than 0.1 mg/L when the detection time is less than 3 min, which has certain advantages over similar LIBS methods. If the detection time is increased appropriately, the LODs of this method is even expected to be reduced to less than 0.01 mg/L. These results indicate that MASOM-LIBS is a feasible method to improve the sensitivity and speed of the detection of trace heavy elements in liquid samples and can facilitate the wide application of LIBS in water quality monitoring. In view of the short detection time, high sensitivity and low LODs of MASOM-LIBS, this method is expected to be developed into a water trace heavy metal detection technology with fully automatic, real-time, highly sensitive and multi-element detection technology in the future.

Diagnosis of HLB-asymptomatic citrus fruits by element migration and transformation using laser-induced breakdown spectroscopy

Huanglongbing (HLB) is one of the most devastating bacterial diseases in citrus growth and there is no cure for it. The mastery of elemental migration and transformation patterns can effectively analyze the growth of crops. The law of element migration and transformation in citrus growth is not very clear. In order to obtain the law of element migration and transformation, healthy and HLB-asymptomatic navel oranges collected in the field were taken as research objects. Laser-induced breakdown spectroscopy (LIBS) is an atomic spectrometry technique for material component analysis. By analyzing the element composition of fruit flesh, peel and soil, it can know the specific process of nutrient exchange and energy exchange between plants and the external environment, as well as the rules of internal nutrient transportation, distribution and energy transformation. Through the study of elemental absorption, the growth of navel orange can be effectively monitored in real time. HLB has an inhibitory effect on the absorption of navel orange. In order to improve the detection efficiency, LIBS coupled with SVM algorithms was used to distinguish healthy navel oranges and HLB-asymptomatic navel oranges. The classification accuracy was 100%. Compared with the traditional detection method, the detection efficiency of LIBS technology is significantly better than the polymerase chain reaction method, which provides a new means for the diagnosis of HLB-asymptomatic citrus fruits.

Sensitive Quantitative Analysis of Strontium in Microdroplet by Surface-enhanced Laser-induced Breakdown Spectroscopy Using Porous Silicon

Surface-enhanced laser-induced breakdown spectroscopy (SELIBS) is a promising method for microanalysis of liquid samples. We previously demonstrated that the SELIBS signal was significantly enhanced by using porous silicon (Si) instead of flat Si. In this work, we dried aqueous droplets containing 1 - 200 ppb strontium (Sr) on porous Si substrates and evaluated the quantitative performance by analyzing the dry residues. A linear calibration curve for the Sr quantification (R² = 0.998) was obtained and an LOD was 0.67 ppb.