A review of some papers published in the last fifty years that focus on the semiconducting metal oxide (SMO) based sensors for the selective and sensitive detection of various environmental pollutants is presented.

A new composite electrode has been fabricated using multiwall carbon nanotubes (MWCNT) and the ionic liquid n-octylpyridinum hexafluorophosphate (OPFP). This electrode shows very attractive electrochemical performances compared to other conventional electrodes using graphite and mineral oil, notably improved sensitivity and stability. One major advantage of this electrode compared to other electrodes using carbon nanotubes and other ionic liquids is its extremely low capacitance and background currents. A 10% (w/w) loading of MWCNT was selected as the optimal composition based on voltammetric results, as well as the stability of the background response in solution. The new composite electrode showed good activity toward hydrogen peroxide and NADH, with the possibility of fabricating a sensitive biosensor for glucose and alcohol using glucose oxidase and alcohol dehydrogenase, respectively, by simply incorporating the specific enzyme within the composite matrix. The marked electrode stability and antifouling features toward NADH oxidation was much higher for this composite compared to a bare glassy carbon electrode. While a loading of 2% MWCNT showed very poor electrochemical behavior, a large enhancement was observed upon gentle heating to 70 degrees C, which gave a response similar to the optimum composition of 10%. The ease of preparation, low background current, high sensitivity, stability, and small loading of nanotubes using this composite can create new novel avenues and applications for fabricating robust sensors and biosensors for many important species.

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The synthesis of a novel biphenol from phenolphthalein that contains an anhydride group is described. The biphenol readily undergoes further reactions. Two biphenols that contain the 1,2-benzoylenebisbenzimidazole or phthaloperin-12-one moiety, respectively, were prepared from the biphenol anhydride by reaction with aromatic diamines, o-phenylenediamine, and 1,8-diaminonaphthalene. Two series of poly(arylene ether)s were synthesized from these heterocyclic containing biphenols. The polymers and copolymers synthesized exhibited extremely high glass transition temperatures and excellent thermooxidative stability. The highest T g and 5% weight loss temperatures of these polymers were almost 360 and 600°C, respectively. The two series of poly(arylene ether)s were yellow and orange in color, respectively. These poly(arylene ether)s have good solubility and can be cast from solution into tough films. The glass transition temperatures of the copolymers increased with increasing heterocycle content, while the solubilities decreased. We have also synthesized, utilizing a biphenol containing the dicyanoarylene moiety, a polymer that contains the phthalocyanine copper(II) moiety that has a blue color. Copolymers containing all three moieties have been synthesized that have a permanent black color since they absorb over the entire visible spectral region from 300 to 750 nm. All of the polymers were highly fluorescent materials with emission wavenumbers ranging from 400 to 750 nm.