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Gas sensors based on metal oxide nanoparticles and their application for environmentally hazardous gases detection – a mini-review

Jońca Justyna, Sówka Izabela

Zeszyty Naukowe SGSP / Szkoła Główna Służby Pożarniczej

2023

Nr 85

7—27

Hazardous gases have adverse effects on living organisms and the environment. They can be classified into two categories, i.e. toxic gases (e.g. H2 S, SO2 , CO, NO2 , NO and NH3 ) and greenhouse gases (e.g. N2 O, CH4 and CO2 ). Moreover, their presence in confined areas may lead to fire accidents, cause serious health problems or even death. Therefore, monitoring of these substances with gas sensors allows assessing the quality of the atmosphere, helps avoiding accidents and saves lives. Metal oxide semiconductor gas sensors (MOS) are one of the most popular choices for these applications owing to their numerous advantages, i.e. high sensitivity, long lifetime and short response time. However, these devices have their limitations as well. They exhibit baseline drift, sensor poisoning and poor selectivity. Although much has been done in order to deal with those problems, the improvement of MOS sensors continues to attract researchers’ attention. The strict control of gas sensing materials preparation is one of the approaches that helps to improve MOS sensors performance. Nanomaterials have been found to be more suitable candidates for gas detection than materials designed at microscale. Moreover, it was found that the regular and ordered morphology of metal oxide nanostructures, their loading with noble metals, or the formation of heterojunctions can exert additional influence on the properties of these nanostructures and improve their gas sensing performance, which will be described in the following sections of this paper. Following a discussion of the operation principle of MOS sensors, a comprehensive review of the synthesis and application of metal oxide nanoparticles in the construction of the MOS sensors dedicated for environmentally hazardous gases is presented. The paper discusses also present issues and future research directions concerning application of nanotechnology for gas sensing.

Niebezpieczne gazy mają niekorzystny wpływ na organizmy żywe i środowisko. Zaliczamy do nich gazy toksyczne (np. H2 S, SO2 , CO, NO2 , NO i NH3 ), gazy cieplarniane (np. N2 O, CH4 i CO2 ). Co więcej, ich obecność w zamkniętych pomieszczeniach może doprowadzić do pożarów, spowodować poważne problemy zdrowotne, a nawet doprowadzić do śmierci. Monitorowanie tych substancji za pomocą czujników gazowych może pomóc uniknąć wypadków i uratować życie. Półprzewodnikowe czujniki gazowe na bazie tlenków metalu (MOS) są jednymi z najpopularniejszych w tych zastosowaniach ze względu na swoje liczne zalety, takie jak wysoka czułość, długa żywotność i krótki czas odpowiedzi. Urządzenia te mają również swoje ograniczenia, tj. wykazują dryft odpowiedzi w czasie, mogą ulec dezaktywacji i charakteryzują się słabą selektywnością, dlatego nadal prowadzone są badania nad poprawą parametrów czujników MOS. Ścisła kontrola procesu przygotowania materiałów czułych jest jedną z metod pozwalających na poprawę wydajności czujników MOS. Stwierdzono, że nanomateriały są bardziej odpowiednie do wykrywania gazów niż ich odpowiedniki zaprojektowane w mikroskali. Stwierdzono również, że regularna i uporządkowana morfologia nanostruktur tlenków metali, pokrywanie ich nanocząstkami metali szlachetnych lub tworzenie heterozłączy może poprawiać skuteczność wykrywania gazów. W przedstawionej pracy dokonano przeglądu metod syntezy i zastosowania nanocząstek tlenków metali w konstrukcji czujników gazów niebezpiecznych dla środowiska. W artykule omówiono również aktualne problemy i przyszłe kierunki badań nad zastosowaniem nanotechnologii do detekcji gazów.

Współczesne podejścia elektrochemiczne do oznaczania arsenu

Ozimek W., Rutkowska I. A., Cox J. A., Kulesza P. J.

Wiadomości Chemiczne

2015

[Z] 69, 9-10

809--822

There has been growing interest in development of new methods for the determination of arsenic due to its high toxity and increasing population in the environment. At present, chromatographic (separation) and spectroscopic (detection) approaches are the most common. Although, they are characterized by high sensitivity and low detection limits, the experimental procedures often require generation of toxic AsH3. Electrochemical methods for the determination of arsenic can be considered as complimentary because they are fairly simple and they are subject to different selectivity criteria. In this respect, various stripping voltammetric procedures are becoming popular. The actual stripping voltammetric measurement consists of two steps in which preconcentration of an analyte at the electrode surface is followed by the so called „stripping” step involving electrode reaction recorded in a form of the voltammetric peak. A representative approach involves reduction of the analyte anions upon application of the sufficiently negative potential to form As(0) on the electrode (e.g. gold) surface; this step is followed by voltammetric oxidation (anodic stripping) of the deposit (to As(III)). In a case of so called cathodic stripping voltammetry, the stationary Hanging Mercury Drop Electrode (HMDE) is often used. During the preconcentration step, an insoluble salt is produced on the electrode surface. To facilitate its formation, copper or selenium species are used as mediators. Under such conditions, insoluble Cu3As2 is generated together with copper amalgam on the surface of HMDE. Because sensitivity and detection limit in electroanalytical determinations strongly depend on the current densities measured, there is a need to search for specific catalytic materials that would induce otherwise highly slow and irreversible redox processes of As(III) (oxidation) and, in particular, As(V) (reduction). Designing effective electrocatalytic materials would be of importance to the development of more sensitive stripping methods and monitoring of arsenic under chromatographic and flow conditions. Representative examples of catalytic systems are provided and discussed here. Some attention is also paid to application of enzymes to sensing of arsenic. Electrochemical determination of arsenic(III) is generally better described in literature. Direct determination of As(V) typically requires its binding into chemical compounds. It is reasonable to expect intense research in future aiming at the developing of new electroanalytical methods for direct selective determination of As(V).