Periodic mesoporous organosilica films: Key components of fiber-optic-based heavy-metal sensors

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Volumn 6, Issue 11, 2010, Pages 1168-1172

  Du, Jenny ^a   Cipot Wechsler, Judy ^a   Lobez, Jose M ^a   Loock, Hans Peter ^a   Crudden, Cathleen M ^a  

^a QUEEN S UNIVERSITY   (Canada)

Author keywords

Fiber optics; Lead; Periodic mesoporous organosilica; Refractive index; Sensors

Indexed keywords

BATCH PROCESS; ELECTRIC AND MAGNETIC FIELDS; EVANESCENT WAVE SENSORS; KEY COMPONENT; ORGANOSILICAS; PARTS PER BILLION; PERIODIC MESOPOROUS ORGANOSILICAS; REFRACTIVE INDEX SENSOR; RELAY INFORMATION; REMOTE LOCATION; REMOTE SITES; SENSOR PLATFORM;

BATCH DATA PROCESSING; FIBER OPTICS; FIBERS; INDUSTRIAL PLANTS; LEAD; LIGHT REFRACTION; MAGNETIC FIELDS; REFRACTIVE INDEX; REFRACTOMETERS; SENSORS;

FIBER OPTIC SENSORS;

HEAVY METAL; LEAD; ORGANIC COMPOUND; SILICON DIOXIDE;

ARTICLE; ARTIFICIAL MEMBRANE; CHEMISTRY; EQUIPMENT; EQUIPMENT DESIGN; FIBER OPTICS; INSTRUMENTATION; POROSITY; REFRACTOMETRY; TRANSDUCER;

EQUIPMENT DESIGN; EQUIPMENT FAILURE ANALYSIS; FIBER OPTIC TECHNOLOGY; LEAD; MEMBRANES, ARTIFICIAL; METALS, HEAVY; ORGANIC CHEMICALS; POROSITY; REFRACTOMETRY; SILICON DIOXIDE; TRANSDUCERS;

EID: 77953166977     PISSN: 16136810     EISSN: 16136829     Source Type: Journal    
DOI: 10.1002/smll.201000269     Document Type: Article

References (38)

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4. f). This results in a spectrum, exemplified in Figure 1, in which the resonant wavelengths appear as attenuation peaks. For more details, see References [2] and [3].
5. As the RI of the external environment approaches that of the cladding (1.44), the LPG's sensitivity to RI changes is maximized due to increased extension of the evanescent wave past the cladding-ambient interface into the external medium. For example, changing the external medium from air (RI=1.000) to a solution of RI=1.372 (Delta;RI=0.372 at 1550 nm) results in a resonant peak shift towards shorter wavelengths of 4.2 nm. However, a more pronounced shift of 24.6nm is observed for a much smaller change in RI from 1.372 to 1.417 (Delta;RI=0.045) as the external index approaches the RI of the fiber cladding (see Figure 1).
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28. Ellipsometric porosimetry experiments were attempted on PMO films dip coated onto silicon substrates in order to further characterize the material's porous properties. Unfortunately, these thick films did not give satisfactory isotherms - likely due to the film nonuniformity exceeding the tolerance of this characterization technique. However, the nitrogen porosimetry data for the large batch of scraped films (presented in Figure S2) are expected to be a reasonable alternative to the ellipsometric porosimetry data.
29. Higher tetrasulfide loadings did not provide increased sensitivity.
30. Although the ellipsometric porosimetry yielded unsatisfactory results for the thick films, the modeled RI of a thin film (average thickness of 500 nm) prepared using a sol of the same composition as the thick films was averaged over three experiments with different adsorbates to be 1.391 (at 633 nm).
31. DMSO was chosen as the modifying solvent due to its high water miscibility and its relatively high RI, which allows for the evaluation and calibration of the sensor responsivity over a larger RI range.
32. This is due to the fact that the RI of the area surrounding the LPG is now a composite RI of both the condensed matrix of the coating and the solution medium. In contrast, the RI of the area surrounding an uncoated grating comprises only the solution RI, which is often lower than the RI of the skeleton of the film. Thus a higher RI solution is required to induce significant peak shifts in the attenuation spectra for the uncoated LPG.
33. This particular set of Pb(II) uptake data was collected in aqueous DMSO solutions with RI 1/4 1.402 (at 1550 nm) (28 mol% DMSO).
34. Although the sensor selectivity remains to be explored in greater detail, under identical conditions, no response was observed to a mixture of metals including 10 ppm each of Cd(II), Co(II), Ni(II), Fe(II), and Zn(II). Hg(II) could not be tested under the same conditions due to its limited solubility in the solution medium. However, under acidic conditions, the optical response to Hg(II) was less than 10% of that observed for Pb(II). The effects of pH, metal-ligand binding affinity, and metal polarizability are currently under investigation.
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37. In an ideal scenario, this Pb(II) detection could be carried out in a purely aqueous medium. However, a predilution of a test sample with the requisite amount of DMSO could easily be accomplished in the field with a simple pump, which we argue is easier than currently employed off-site measurement techniques such as inductively coupled plasma mass spectrometry (ICP-MS).
38. Due to the inherently low degree of silica condensation in these amorphous silica sol-gel films (see Reference [20]), we anticipate that the material is unstable to acid over prolonged periods of time. It is also possible that the ligand may break down with repeated exposure to the acidic solution since a reduced capacity for metal binding by a siliceous powder incorporating this ligand after exposure to acid was previously reported (see Reference [15]).