A new sensor for the detection of hydrogen sulfide (H2S) gas has been developed to replace commercial lead(II) acetate-based test papers. The new sensor is a wet, porous, paper-like substrate coated with Bi(OH)3 or its alkaline derivatives at pH 11. In contrast to the neurotoxic lead(II) acetate, bismuth is used due to its nontoxic properties, as Bi(III) has been a reagent in medications such as Pepto-Bismol. The reaction between H2S gas and the current sensor produces a visible color change from white to yellow/brown, and the sensor responds to ≥ 30 ppb H2S in a total volume of 1.35 L of gas, a typical volume of human breath. The alkaline, wet coating helps the trapping of acidic H2S gas and its reaction with Bi(III) species, forming colored Bi2S3. The sensor is suitable for testing human bad breath and is at least 2 orders of magnitude more sensitive than a commercial H2S test paper based on Pb(II)(acetate)2. The small volume of 1.35-L H2S is important, as the commercial Pb(II)(acetate)2-based paper requires large volumes of 5 ppm H2S gas. The new sensor reported here is inexpensive, disposable, safe, and user-friendly. A simple, laboratory setup for generating small volumes of ppb-ppm of H2S gas is also reported.
A pyridine-functionalized thin film has been fabricated to selectively preconcentrate Cr(VI) anions for electrochemical detection in the 5-300 μg L−1 range. Glassy carbon electrodes were modified through physical deposition of single-walled carbon nanotubes (SWNTs) on the electrode surface, followed by electrochemical deposition of a sol-gel containing a 2-pyridine functional group. The use of SWNTs has increased sensitivity for Cr(VI) detection in aqueous solutions, providing a detection limit of 0.8 μg L−1.
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