Terahertz (THz) wave, which lies in the frequency gap between infrared and microwave, has an electromagnetic spectrum conventionally defined in the range from 0.1 to 30 THz. [1][2][3] Because its corresponding photon energy has a scale of milli-electron volt (meV) coinciding with the energy scale of many collective excitations in materials, [1] it has a great potential in fundamental scientific research, [4][5][6][7] THz imaging [8,9] and security applications [3] . Driven by these scientific and technological prospects, many efforts have thus been directed towards the development of new THz sources which are powerful,
Titanium dioxide (TiO2) as a common photothermal material usually faces with low photothermal conversion efficiency, mainly owing to the little utilization of visible (Vis) and near-infrared (NIR) light in the solar spectrum. Introducing oxygen vacancies is an effective strategy for narrowing its bandgap and thus enhancing the light absorption capacity. However, traditional approaches are always not energy-efficient or unable to create enough oxygen vacancies. Herein, laser ablation in liquid (LAL) was successfully employed to prepare rutile TiO2 nanoparticles (NPs) with abundant oxygen vacancies in one step, which were then assembled into the self-floating evaporator. Our experimental results demonstrate that the existence of oxygen vacancies narrows the bandgap and forms conduction band tail states, leading to significant improvements of light absorbance and photothermal conversion efficiency. Moreover, the light trapping structure of nickel foam (NF) support also contributes to the high solar absorption of laser TiO2 (L-TiO2)/NF. Eventually, the L-TiO2/NF evaporator realizes an excellent water evaporation rate of 1.25 kg m–2 h–1 and light-to-water evaporation efficiency of 78.5% under one-sun irradiation, which are both 1.81 times than those of commercial TiO2 (C-TiO2)/NF and even surpass those of most recently reported titanium oxide-based evaporators.
The detection of dissolved gases in seawater plays an important role in ocean observation and exploration. As a potential technique for oceanic applications, Raman spectroscopy has already proved its advantages in the simultaneous detection of multiple species during previous deep-sea explorations. Due to the low sensitivity of conventional Raman measurements, there have been many reports of Raman applications on direct seawater detection in high-concentration areas, but few on undersea dissolved gas detection. In this work, we have presented a highly sensitive Raman spectroscopy (HSRS) system with a special designed gas chamber for small amounts of underwater gas extraction. Systematic experiments have been carried out for system evaluation, and the results have shown that the Raman signals obtained by the innovation of a near-concentric cavity was about 21 times stronger than those of conventional side-scattering Raman measurements. Based on this system, we have achieved a low limit of detection of 2.32 and 0.44 μmol/L for CO2 and CH4, respectively, in the lab. A test-out experiment has also been accomplished with a gas-liquid separator coupled to the Raman system, and signals of O2 and CO2 were detected after 1 h of degasification. This system may show potential for gas detection in water, and further work would be done for the improvement of in situ detection.
Multiple reflection has been proven to be an effective method to enhance the gas detection sensitivity of Raman spectroscopy, while Raman gas probes based on the multiple reflection principle have been rarely reported on. In this paper, a multi-reflection, cavity enhanced Raman spectroscopy (CERS) probe was developed and used for in situ multi-component gas detection. Owing to signal transmission through optical fibers and the miniaturization of multi-reflection cavity, the CERS probe exhibited the advantages of in situ detection and higher detection sensitivity. Compared with the conventional, backscattering Raman layout, the CERS probe showed a better performance for the detection of weak signals with a relatively lower background. According to the 3σ criteria, the detection limits of this CERS probe for methane, hydrogen, carbon dioxide and water vapor are calculated to be 44.5 ppm, 192.9 ppm, 317.5 ppm and 0.67%, respectively. The results presented the development of this CERS probe as having great potential to provide a new method for industrial, multi-component online gas detection.
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