It is found in this work that variation of laser power density in low-pressure plasma spectrochemical analysis of hydrogen affects sensitively the hydrogen emission intensity from the unwanted and yet ubiquitous presence of ambient water. A special experimental setup has been devised to allow the simple condition of focusing/defocusing the laser beam on the sample surface. When applied to zircaloy-4 samples prepared with various hydrogen impurity concentrations using low-pressure helium surrounding gas, good-quality hydrogen emission lines of very high signal to background ratios were obtained with high reproducibility under weakly focused or largely defocused laser irradiation. These measurements resulted in a linear calibration line with nonzero intercept representing the residual contribution from the recalcitrant water molecules. It was further shown that this can be evaluated and taken into account by means of the measured intensity ratio between the oxygen and zirconium emission lines. We have demonstrated the applicability of this experimental approach for quantitative determination of hydrogen impurity concentrations in the samples considered.

Hydrogen emission has been studied in laser plasma by focusing a Nd-YAG laser (1,064 nm, 50 mJ, 8 ns) on various types of samples, such as copper plate, zinc plate and glass plate. Several parameters influencing the emission were varied, such as the type of gas (air, nitrogen and helium), gas pressures (ranging from 2 up to 760 Torr) and laser power density. It was found that H emission with a narrow spectral width occurs with high efficiency when the laser plasma is produced in the low-pressure region. It was also confirmed that the conventional well-known laser-induced breakdown spectroscopy (LIBS), which usually carried out at atmospheric air pressure, cannot be applied for the analysis of hydrogen as impurity. This specific characteristic of the pressure dependence of hydrogen is interpreted based on our shock wave model, taking account of the fact that the hydrogen mass is extremely light compared to that of the host elements.

Global pollution from toxic metal waste has resulted in increased research on toxic metal adsorption. A cellulose acetate–polyurethane (CA–PU) film adsorbent was successfully prepared in this research. The cellulose acetate–polyurethane film adsorbent was prepared with a polycondensation reaction between cellulose acetate and methylene diphenyl diisocyanate. The CA–PU bond formation was confirmed by functional group analysis obtained from Fourier transform infrared (FTIR) spectroscopy. The obtained film was characterized for improved tensile and thermal properties with the addition of methylene diphenyl diisocyanate (MDI). The adsorption ability of the obtained film was evaluated with laser-induced breakdown spectroscopy (LIBS). The best film adsorbent from the LIBS was selected and studied for adsorption isotherm. The FTIR analysis confirmed the formation of the CA–PU bond from the polycondensation between cellulose acetate and the methylene diphenyl diisocyanate. The result showed that the addition of methylene diphenyl diisocyanate (MDI) resulted in the urethane network’s growth. The characterization result showed an improvement in the morphology, thermal stability, and tensile strength of the film. The LIBS studies showed improvement in the adsorption of Pb2+ with CA–PU compared with the neat CA. The isotherm studies revealed that Pb2+ adsorption by cellulose acetate–polyurethane film adsorbent was heterogeneously dependent on the Freundlich isotherm model (R2 = 0.97044). Overall, the polycondensation method proposed by this study enhanced the Pb2+ removal, and was comparable to those reported in previous studies.

An experimental study has been carried out on the dynamical process taking place in the laser plasma generated by Transversely Excited Atmospheric CO2 laser (100 mJ, 50 ns) irradiation of a soft sample at surrounding helium pressure of 1 atm. It is shown that the presence of a copper subtarget behind the soft sample is crucial in raising the gushing speed of the atoms to the level adequate for the generation of shock wave laser plasma even at atmospheric pressure. It is also found that the time profiles of spatially integrated emission intensity of the target's atoms and gas atoms exhibit a characteristic dynamical process that consists of successive excitation and cooling stages even at such a high pressure, which is typical of shock wave laser plasma. It is therefore suggested that the generation of the laser plasma at atmospheric pressure is more likely due to the shock wave mechanism than to the widely known breakdown mechanism. Initial spectrochemical analysis of water from the blow off of a boiler system was also carried out, showing a detection limit of as low as 5 ppm for calcium.

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