Short-wavelength (λ < 160 nm) Raman spectroscopy offers an advantage of a generally higher sensitivity than Raman spectroscopy in the visible range. An application with high potential is its use for environmental water analysis targeting archetypal compounds that are present in industrial and urban sewage water. However, this application is feasible only if specific performance benchmarks are met. We validate the applicability of a simple and cost-effective deep-UV Raman spectrometer (λexc = 236.5 nm). The analysis brings to the fore that the experimentally derived detection limits the studied archetypal compounds are to high by several orders of magnitude. We outline potential further development and associated limitations. These are the deterioration of the analysed species by photolysis as a consequence of the high photon energy and intensity, and the self absorption of the UV radiation. These effects are explained and partially corrected along a simple mathematical model from which a general limit of detection is estimated.
The standard approach to surface analysis is X-ray photoelectron spectroscopy (XPS), which is used to follow electronic structure changes of the catalyst material TiO2 upon hydrogenation, however, without conclusion whether the effect can be traced back to the hydrogen treatment. Resonant photoemission experiments using a tunable synchrotron X-ray source yields further insights. The integration of the electron yield over all kinetic energies results in X-ray absorption spectra (XAS). Furthermore, in resonant conditions, electrons are excited from a core level to the conduction band and can subsequently be trapped by specific defect states. From this, the observed shallow trap states can be identified as Ti3+ states. We quantify the Ti3+/Ti4+ ratio both from XPS and XAS and the oxygen to titanium elemental ratio. The correlation of the results from resonant and non-resonant photoemission reveals that hydrogen defects serve as trap centers, while defects associated with oxygen vacancies serve as recombination centers suppressing trap state emission. The main effect of hydrogen in TiO2 is the increased disorder in the material.
Deep-UV Raman spectroscopy is a promising method for the analysis of nitrates and nitrites in water at ppm (mg/l) concentrations. In addition to the high sensitivity, the tunability of the laser source allows to deeper investigate the photoinduced reactions taking place under deep-UV illumination. Under these conditions, nitrate ions decompose into oxygen and nitrite through different reaction pathways. Analysis of the evolution of nitrate and nitrite Raman modes as a function of the excitation wavelength allows for estimating the photo-energy dependent quantum yield of the photolysis process. The results highlight the limits and capabilities of deep UV Raman as a on-line nitrate and nitrite monitoring method.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.