| In recent years, marine environmental pollution of Chinese sea has become increasingly serious, most of which is induced by inorganic nitrogen and phosphate, therefore long-term, effective and real-time monitoring of the oceanic nutritive salts is need to be solved urgently. The traditional nutrient detection using the method of analytical chemistry, which turns to be a relatively complicated and time-consuming method.Surface-enhanced infrared absorption (SEIRA) of nano-material is expected to effectively probe the vibrational modes with the various molecular bonds in a sample, achieving the information of the low concentration of nutrient salts, which has become one of the main approaches to gain the oceanic ecological environmental information. As we all know, Ag film received its share of attention by the remarkably SEIRA effect and diamond has many exceptional properties, such as extreme hardness, high chemical stability and high optical transmittance, therefore is suitable for infrared window.Silver/diamond powder (Ag/DP) composites were prepared via pyrolysis of silver nitrate (AgNO3) on silicon substrate. Parameters like nAg:nc and diameter of the diamond were controlled to create materials with better infrared strengthen effect. The composites were identified and characterized by Raman spectroscopy, Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS). It turns out to be that when nAg:nc=2:1 & d=1μm, the Ag nanoparticles were well-dispersed on the surface of DP, forming Ag/DP core shell stable structure.Fourier transform infrared (FTIR) spectrum is used to study infrared absorption of nitrate (NO3-) enhanced by the as-grown composites. It shows that Ag/DP composites not only improve the NO3- vibration strength considerably, but also lead to frequency blue-shifted between the two individual antisymmetric stretching modes of NO3-. It is concluded that NO3- get rid of H2O, combined with Ag/DP composites and affected by its short distance interactions. The infrared absorption of ammonium and phosphate, both have certain effect, but not as nitrates strong.When electric field is applied, the antisymmetric stretching absorption of NO3- is enhanced markedly by the presence of the Ag/DP composites, and further enhancement is achieved due to the polarization effect of hydrated NC3- caused by certain applied electric field. The significant enhancement achieved by exploiting electric field is mainly attributed to Vlow vibrational mode, which can be interpreted as that the majority of hydrated NO3- polarize in accordance with Vlow vibrational direction. Additionally the force constant is increased by external electric field, and hence the absorption band of antisymmetric stretching vibration appears blue-shifted. Lastly, Ag/DP composites is synthesized on zinc selenide (ZnSe) and employed to detect infrared absorption of NO3-. Similarly, notably infrared absorption enhancement of NO3- is observed and lay the foundation of nutrient salts detection to develop devices in seawater environment. |
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