Core-shell nanohybrids have wide applications in pollutant degradation. In this study, core-shell nanohybrid was formed through heteroaggregation between neutral nanoparticles (i.e., hematite nanoparticles or HemNPs) and charged nanoparticles (i.e., carboxylated polystyrene nanoparticles or PSNPs). In the dispersant solution of 1 mM NaCl at pH 6.3, HemNPs were neutral and underwent favorable homoaggregation, whereas PSNPs were negatively charged and underwent no homoaggregation. When the two types of particles were mixed, homoaggregation of HemNPs and heteroaggregation between HemNPs and PSNPs took place simultaneously, forming HemNPs-PSNPs heteroaggregates. The transmission electron microscopy images of heteroaggregates show that HemNPs and PSNPs formed core-shell structure in which HemNPs were the cores and PSNPs were the shells. The size of the core-shell nanohybrids can be controlled by varying the concentration ratio of HemNPs to PSNPs. The increase of the size of charged nanoparticles resulted in larger nanohybrids. This new method has lower energy footprint than existing ones. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Polymer nanocomposites are a going part of Materials Science and Engineering. These new composite materials exhibit dimensional and thermal stability of inorganic materials and toughness and dielectric properties of polymers. Development of nanocomposites become an important approach to create high-performance composite materials. In this study silica, fly ash, silica nanotubes and carbon black particles have been added to modify polyurethane foam and thermoplastic polyurethanes. It has been found that the addition of silica can diminish the size of foam bubbles, resulting in an increased stiffness of the material, increase of the compressive strength, and greater resistance to deformation. However, the uniformity of bubbles is reduced, resulting in increased friction of the material. Fly ash added to the foam can make bubbles smaller and improve uniformity of cells. Therefore, the material stiffness and compressive strength, resistance to deformation, and has little impact on the dynamic friction of the material. Adding nanotubes make bubble size unequal, and the arrangement of the bubble uneven, resulting in decreased strength of the material, while the friction increases. After the addition of carbon black to the polyurethane foam, due to the special surface structure of the carbon black, the foam generates more bubbles during the foaming process changing the foam structure. Therefore, the material becomes soft, we obtain a flexible polyurethane foam. The results of mechanical properties determination of the thermoplastic polyurethane that adding particles may increase the stiffness and wear resistance of the thermoplastic polyurethane, while the tensile properties of the material are reduced. This phenomenon may be due to agglomeration of particles during the mixing process. Possibly the particles cannot be uniformly dispersed in the thermoplastic polyurethane.

Chapter I: This chapter briefly gives an introduction about microorganisms, their varieties, growth, reproduction etc. In particular, about bacterial function. A sincere attempt is made to review this briefly, including an account of the studies already reported in the literature. Chapter II deals with the antimicrobial activity of Ag/agar film on Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Candida albicans (C. albicans). In particular, films were repeatedly cycled for its antimicrobial activity. The antimicrobial activity of Ag/agar film was found to be in the order, C. albicans > E. coli > S. aureus. Chapter III describes the synthesis of Ag@AgI NPs in agarose matrix. A detailed antibacterial studies including repetitive cycles are carried out on E. coli and S. aureus bacteria. EPR and TEM studies are carried out on the Ag@AgI/Agarose and the bacteria, respectively, to elucidate a possible mechanism for killing of the bacteria. The hybrid could be recycled for the antibacterial activity many times and is found to be non toxic towards human cervical cancer cell (HeLa cells). Chapter IV reports the antibacterial efficacy of silver nanoparticles (Ag NPs) deposited alternatively layer by layer (LBL) on chitosan polymer in the form of a thin film over a quartz plate and stainless steel strip against E. coli. AFM studies are carried out on the microbe to know the morphological changes affected by the hybrid film. The hybrid films on aging (3 months) are found to be as bioactive as before. Cytotoxicity experiments indicated good biocompatibility. Chapter V describes the fabrication of carbon foam porous electrode modified with reduced graphene oxide-Ag nanocomposites. The device can perform sterilization by killing pathogenic microbes with the aid of just one 1.5V battery with very little power consumption. Chapter VI Here we have studied in particular a property say the influence of surface defect in the production of ROS by ZnO NPs and in turn the bactericide activity. Secondly, a homogeneous ZnO and ZnO/Ag nanohybrid has been synthesized by employing chitosan as mediator. The synergistic antibacterial effect of ZnO/Ag nanohybrid on bacteria is found to be more effective, compared to the individual components (ZnO and Ag). A possible mechanism has been proposed for the death of bacteria by ZnO/Ag nanohybrid, based on EPR studies and TEM studies.

Since their first observation in 1991, carbon nanotubes (CNTs) have attracted a lot of attention owing to their exceptional properties. Their excellent electrical and thermal conducting performances combined with their high toughness and transverse flexibility allow their use in a large range of varied applications. Offering at the same time a high aspect ratio (length-to-diameter) and a low density, carbon nanotubes show strong application potential in reinforced composite materials. Unfortunately, CNTs have the strong tendency to form bundles very difficult to dissociate and disperse in a majority of polymer matrices. Without efficient CNTs dispersion, nanocomposites can not present optimal mechanical, thermal and electrical properties. To overcome this drawback, one solution consists to graft polymer chains on the carbon nanotubes surface in order to disaggregate bundles and, in few cases, to improve interaction between the polymer matrix and nanotubes. The thesis work can be divided into three parts. The first is the one-step amination of multi-walled carbon nanotubes (MWNTs) via an original microwave plasma process. The MWNTs, placed in the post-discharge chamber in presence of H2, are subjected to a reactive flow of atomic nitrogen produced by the plasma. The results give evidence for efficient covalent grafting of primary amine groups along the sidewalls of MWNTs, avoiding any structural damage and alteration of properties. The so-grafted amine groups have been further consider as initiation sites for promoting the ring opening polymerization of lactone monomers yielding polyester-grafted MWNT nanohybrids. Finally, these nanohybrids have been used as highly filled masterbatches to be dispersed in the molten state within several polymer matrices, such as polycaprolactone (PCL) and high density polyethylene (HDPE), to obtain nanocomposites with largely improved properties. For instance, electrical measurements and morphological characterizations showed that the polyester surface-grafting allows for improving the dispersion state of the nanotubes in the different polymer matrices leading to enhanced electrical properties as well as thermal and mechanical performances.

Abstract Transition metal dichalcogenide (TMD) materials crystalize in a layered structure with a stoichiometry MX₂ where M is a transition metal (Mo, W, Tc, Re, V, Nb, Ta, Ti, Zr, Hf) and X is a chalcogen (S, Se, Te). While there is a strong covalent bond between the chalcogen and the metal atoms in each 2-dimensional (2D) sheet, the bulk 3-dimensional crystals are held together by weak van der Waals forces acting on the adjacent 2D sheets allowing for micromechanical and liquid phase exfoliation into nanostructures composed of either a single layer or a few layers. Since the electronic band structure depends not only on the chemistry but also on the number of layers, a whole new range of metal, semimetal and semiconductor materials may be achieved. These properties, among many other advantages (e.g. tunable band structure, high mobility of carriers, easy intercalation with ions), make TMDs appealing and timely for applications in solar cells and photodetectors, heterogeneous catalysis, electrocatalytic electrodes, energy storage and in (electro) chemical sensing. Motivated by the anticipated fascinating properties of TMDs, this research work focuses on the synthesis, characterization and application of a novel hybrid WS₂ nanomaterial. While the original goal of the research work was to develop a simple method to synthesize WS₂ nanowires, it became clear that instead of nanowires a hybrid nanowire-nanoflake (NW-NF) structure could be synthesized by a simple thermal sulfurization of hydrothermally grown WO₃ nanowires. The structure, morphology and composition of the new materials were analyzed by X-ray diffraction, Raman spectroscopy, electron microscopy and X-ray photoelectron spectroscopy. Temperature dependent electrical measurements carried out on random networks of the nanostructures showed nonlinear characteristics and a negative temperature coefficient of resistance indicating that the hybrids were semiconducting. Resistive gas sensors were prepared and exposed to H₂S, CO, NH₃, H₂ and NO and to which the devices displayed ultra-high sensitivity (0.043 ppm⁻¹) towards H₂S with a detection limit of 20 ppb. The results suggest further exploration of gas sensing with TMDs as potential competitive alternatives to the classical metal oxide based devices. Moreover, photodetector devices with excellent visible light response were also demonstrated using an individual WS₂ NW-NF hybrid as well as its random networks having photoresponsivity of up to 400 mAW⁻¹. This was two orders of magnitude higher than that measured for other 2D materials based devices. Overall, the WS₂ nanowire-nanoflake hybrid is a truly multipurpose and multifunctional semiconductor making it a promising material for advanced micro, nano and optoelectronics devices. / Tiivistelmä Siirtymämetallidikalkogenidistä (transition metal dichalcogenide, TMD) olevat materiaalit kiteytyvät kerroksittaisiksi rakenteiksi, joiden stoikiometria on MX₂, missä M on siirtymämetalli (Mo, W, Tc, Re, V, Nb, Ta, Ti, Zr, Hf) ja X on kalkogeeni (S, Se, Te). 2-ulotteisessa (2D) tasossa kalkogeenin ja metallin välillä on voimakas kovalenttinen sidos, mutta suuremmassa kolmiulotteisessa kiteessä viereisiä tasoja sitoo toisiinsa vain heikot van der Waals-voimat, jolloin tasot on mahdollista erottaa mikromekaanisesti ja nestefaasikuorinnalla yksittäisiksi tai muutamasta kerroksesta koostuvaksi nanorakenteeksi. Koska elektronivyörakenne ei riipu ainoastaan kemiallisesta koostumuksesta vaan myös kerrosten lukumäärästä, voidaan muodostaa täysin uusia metallisia, puolimetallisia tai puolijohdemateriaaleja. Nämä ominaisuudet monien muiden lisäksi (esim. räätälöity vyörakenne, korkeanliikkuvuuden varauksen kuljettajat, helppo ionien interkelaatio) tekevät TMD-materiaaleista kiinnostavia ja ajankohtaisia aurinkokennoihin, valokennoihin, heterogeeniseen katalyysiin, sähkökatalyyttisiin elektrodeihin, energiavarastoihin ja sähkökemiallisiin antureihin. TDM-materiaalien oletettavasti kiehtovien ominaisuuksien motivoimana tämä tutkimus keskittyy uusien hybridi-WS₂-nanomateriaalien synteesiin, karakterisoimiseen ja sovellutuksiin. Tutkimuksen alkuperäinen tavoite oli kehittää yksinkertainen menetelmä WS₂-nanolankojen syntetisoimiseksi, mutta kävi ilmi että nanolankojen sijaan syntyi nanolanka-nanohiutale -hybridirakenne (nanowire-nanoflake, NW-NF), kun hydrotermisesti kasvatettuja WO₃-nanolankoja rikitettiin termisesti. Näiden uusien materiaalien rakenne, morfologia ja koostumus on analysoitu röntgendiffraktiolla, Raman-spekstrokopialla, elektronimikroskoopilla ja röntgenfotoelektronispektroskopialla. Valikoimattomista nanorakenteista koostuvien verkostojen lämpötilasta riippuvien sähköisten ominaisuuksien mittaukset osoittavat epälineaarisia piirteitä ja negatiivinen resistanssin lämpötilakerroin viittaa hybridien puolijohtavuuteen. Materiaalista valmistettiin resistiivisiä kaasuantureita, jotka altistettiin H₂S:lle, CO:lle, NH₃:lle, H₂:lle ja NO:lle, näistä anturi osoitti erittäin suurta herkkyyttä H₂S:lle (0.043 ppm) havaintorajan ollessa 20 ppb. Tulokset kannustavat TMD-materiaalien kaasuanturisovellutusten jatkotutkimukseen tarjoten potentiaalisesti kilpailukykyisen vaihtoehdon perinteisille metallioksidi-pohjaisille laitteille. Lisäksi, yksittäisillä WS₂-nanolanka-nanohiutalepartikkeleilla sekä valikoimattomilla nanolanka-nanohiutalehybridiverkostoilla demonstroitiin valokenno, jonka vaste näkyvään valoon oli jopa 400 mAW⁻¹ ollen kaksi kertaluokkaa korkeampi kuin muilla 2D-materiaaleihin perustuvilla kennoilla. Kaiken kaikkiaan, WS₂-nanolanka-nanohiutalehybridi on todella monikäyttöinen ja monipuolinen puolijohde ollen lupaava materiaali kehittyneille mikro-, nano- ja optoelektronisille laitteille.

This thesis aims at presenting the use and development of original catalytic systems based on lipases immobilized on clays which are efficient for the synthesis of biopolyesters and allowing the preparation of organic/inorganic nanohybrids based on clay nanoparticles (sepiolite and montmorillonite) grafted with such polyesters. These nanoclays were used as lipase supports and the clay-immobilized forms of Candida antarctica lipase B (CALB) were tested for ε-caprolactone and lactide isomers polymerization. Polymerization kinetics and characterization of resulting materials have shown that lipases immobilized on montmorillonite show better performances compared to the ones immobilized on sepiolite. Clay surface organo-modification has proved to greatly enhance the catalytic activity of the corresponding systems. CALB immobilized on montmorillonite allowed the elaboration of organic/inorganic nanohybrids as evidenced by the effective grafting of polyester chains from the clay surface. Finally, random PCL/PLA copolyesters were successfully obtained by lipase-catalyzed copolymerization of D-lactide with ε-caprolactone.

L'objectif de ce travail est de développer des catalyseurs originaux et performants à base de lipases immobilisées sur argiles pour la synthèse de biopolyesters et d’obtenir des nanohybrides organique/inorganique par greffage de chaînes polyesters sur les nanoparticules d'argiles. Deux argiles (sépiolite et montmorillonite) ont été utilisées pour l'immobilisation de Candida antarctica lipase B (CALB) et les catalyseurs obtenus ont été testés en polymérisation de l'ε-caprolactone et des isomères de lactide. Les cinétiques de polymérisation et la caractérisation des polyesters ont montré que les lipases immobilisées sur montmorillonite sont plus performantes que celles immobilisées sur sepiolite. L’organo-modification de ces argiles améliore l’activité catalytique des systèmes obtenus. L'utilisation de CALB immobilisée sur montmorillonite a permis l’élaboration de nanohybrides organique/inorganique via le greffage et la croissance des chaînes polyesters à partir de la surface de l’argile. Finalement, des copolyesters statistiques PCL/PLA ont été obtenus avec succès par polymérisation enzymatique du D-lactide avec l'ε-caprolactone. / This thesis aims at presenting the use and development of original catalytic systems based on lipases immobilized on clays which are efficient for the synthesis of biopolyesters and allowing the preparation of organic/inorganic nanohybrids based on clay nanoparticles (sepiolite and montmorillonite) grafted with such polyesters. These nanoclays were used as lipase supports and the clay-immobilized forms of Candida antarctica lipase B (CALB) were tested for ε-caprolactone and lactide isomers polymerization. Polymerization kinetics and characterization of resulting materials have shown that lipases immobilized on montmorillonite show better performances compared to the ones immobilized on sepiolite. Clay surface organo-modification has proved to greatly enhance the catalytic activity of the corresponding systems. CALB immobilized on montmorillonite allowed the elaboration of organic/inorganic nanohybrids as evidenced by the effective grafting of polyester chains from the clay surface. Finally, random PCL/PLA copolyesters were successfully obtained by lipase-catalyzed copolymerization of D-lactide with ε-caprolactone.

Actuellement, l'élaboration de matériaux nanohybrides organiques/inorganiques suscite l'engouement de nombreux chercheurs du fait de leurs diverses applications potentielles. Le but de ce projet de thèse a été de préparer et caractériser de nouveaux éléments inorganiques et organiques permettant la conception de nanohybrides multi-fonctionnels possédant des propriétés répondant aux problématiques actuelles. Dans cet objectif, nous avons préparé des nanoparticules d'oxyde de zinc (ZnO) en tant que composant inorganique par ablation laser. La surface de ces NPs peut être modifiée par des composés organiques possédant un groupe d'ancrage acide carboxylique. Nous avonssynthétisé et caractérisé des dérivés viologènes, bien connu comme de forts accepteurs d'électron, possédant le groupe d'ancrage. Les nanohybrides de ZnO/viologènes ont été préparés et caractérisés par diverses techniques de spectroscopie. Nous avons développé des voies de synthèse efficaces permettant d'obtenir une série de nouveaux hétérocycles possédant des propriétés de donneur d'électron : dérivés de dibenzo[2,3:5,6]pyrrolizino[1,7-bc]indolo[1,2,3-lm]carbazole. Ces nouvelles molécules présentent une forte stabilité thermique et une forte fluorescence dans le domaine du visible. Leurs propriétés d'absorption à un et deux photons (Proche-infrarouge) ainsi que leur habilité de donneur d'électron ont été étudiés expérimentalement et à l'aide de calculs de mécanique quantique. Les éléments organiques et inorganiques étudiés sont des motifs de choix pour l'élaboration future de nanohybrides utilisables pour diverses applications comme dans le domaine de l'énergie photovoltaïque ou encore l'imagerie médicale. / Currently, the development of organic/inorganic nanohybrid materials arouses the enthusiasm of many researchers owing to their potential applications. The aim of this thesis was to prepare and characterize new inorganic and organic components for the future design of new multi-functional nanohybrids with properties responding to the current challenges. For this purpose, we have prepared nanoparticles of zinc oxide (ZnO) as the inorganic component by laser ablation. The surface of these nanoparticles can be modified by an organic component bearing the carboxylic group as an anchor. We synthesized and characterized a number of viologen derivatives, well known as strong electron acceptors, involving the anchoring groups. The nanohybrids of ZnO/viologens were prepared and characterized by various spectroscopic techniques. We have developed efficient synthetic routes toward a series of new heterocycles possessing the electron donating properties: derivatives of dibenzo[2,3:5,6]pyrrolizino[1,7-bc]indolo[1,2,3-lm]carbazole. These new molecules exhibit high thermal stability and strong fluorescence in the visible range. Their one- and two-photon (Near-infrared) absorption properties and electron donor ability were investigated experimentally and by means of quantum mechanical calculations. The studied organic and inorganic components can serve as promising building blocks of choice for the future development of nanohybrids used in various application domains such as in the fields of photovoltaics and medical imaging.

Controlling the morphology of nanocrystals provides provides a possible pathway to tune properties and hence has been explored in depth. However, to obtain a wider spectrum of properties or for multi-functionality. Other strategies need to be devised. Combining different functional nanostructures to obtain a functional hybrid is one such strategy that holds promise for a wide range of applications. While this is simple in principle, there are no simple and general protocols for synthesis of such functional heterostructure. The challenge lies in producing a hybrid with good control over the structure and chemistry of the interfaces in the system. The use of molecular linkers or physical forces to form the hybrid has several drawbacks in terms of interface quality and stability. In this dissertation, a rational basis is developed for the evolution of symmetry forbidden FCC nanocrystals via wet chemical route which relies on appropriate choice of reagents and the reaction conditions for nucleation and growth. The concept is extended to devise general synthetic strategies for functional nanoheterostrcutres in solution via economic, facile and environment friendly routes. Electron microscopy and X-ray photoelectron spectroscopy has been used as the major tools for structural characterization of the materials and to investigates the reaction/formation mechanism. The properties of the synthesized materials are investigated primarily targeting the nanoelectronic and catalytic applications. The entire study reported in the thesis is organized as follow: chapter I leads to a general introduction of nanocrystals and role in different fields of application. It describes the motivation behind controlling the shape of nanocrystals and combining two or more nanostructures to obtain a functional heterostructure. The existing methodologies to achieve shape control and nanoscale hybrid/heterostructure with active interfaces are elaborated while indicating the role of morphology, interfaces and composition for enhanced activity/performance. The information on the chemical used for synthesis, routers adopted for synthesizing and the basic techniques utilized to characterize the materials in study are detailed in the respective chapters. Chapter 2 provides a study by which one can easily select an appropriate reductant for a metal couple to achieve the desired morphology. Moreover, the role of kinetics and the factors driving the kinetics in obtaining the symmetry breaking shapes like 2-D and I-D for Ag and Au nanocrystals is discussed in detail and validated by experiments. Chapter 3 describes the methodology to attach ultrafine Au nanowires to different nanosubstrates ranging from oxides to carbon (CNT/graphene) where the key step is heteronucleation of the Au (I) precursor on the substrate. Chapter 4 deals with the growth of ultrafine Au nanowires on various substrates and between pre-defined contacts to fabricate nanodevices. The mechanistic investigation directs to the controlled heterogeneous nucleation of the building units (Au nanoparticles) on substrate as the key step followed by its subsequent growth into wires in presence of Au nanoparticles in the medium. Kinetic control of the nucleation and growth step enabled precise control over the population and length of the wires. This is of immense importance for application like catalysis, sensors and nanoelectronics. Moreover, the method enabled the first time electrical transport studies on these wires which revealed an insulating behavior in such metallic wires on progressive lowering of temperature down to few kelvins. The concept of heterogeneous nucleation is extended to design nanoscale heterogeneous in the following three chapters where primarily a precursor coating is formed on a nanosubstrate, viz. ZnO nanorods and graphene, and converted to the phase of interest in a controlled manner to obtain the desired morphology. In each of the chapters the mechanisms of formation of the heterostructure are discussed in detail. Chapter 5 deals with formation of semiconductor based heterostructure like ZnO/CdS in solution by aqueous route. The material has been demonstrated as a potential visible light catalyst for dye degradation with enhanced activity. The interfacial chemistry could be tuned appropriately to achieve high activity in the catalyst by simple wet chemical route. In chapter 6, an ultrafast, facile, green route to obtain oxide supported metal catalyst has been demonstrated. ZnO/Au heterostructures were designed with well defined morphology and studied for low temperature CO oxidation reaction. Detail investigation reveals the surface doping of ZnO with Au the nucleation process leading to active ionic sites for CO oxidation. Chapter 7 demonstrate a rapid and economically viable route to graphene based pt catalysts where a synergistic co-reduction mechanism operates between the metal precursor and the graphic oxide to from the heterostructure. The obtained G-Pt heterostructure exhibits high catalytic activity for methanol oxidation reaction and hydrogen convention at ambient conditions. Finally a conclusion is drawn, highlighting the possibilities and prospects that the study leads to.

This thesis deals with the research work carried out for the development of novel applications by integrating biomolecules with various nanostructures. The thesis is organized as follows: Chapter 1 reviews the properties of nanomaterials which are important to consider while developing them for various biological and other applications. It discusses the factors which affect the cytotoxicity of nanocrystals towards living cells, photocatalytic mechanisms of nanocrystals that work behind the inactivation of bacterial cells and gas sensing properties of nanocrystals. It also mentions about the integration of biomolecules with nanomaterials which is useful for the development of biosensors, materials that are presently used for fabricating biosensors and the challenges associated with designing successful biosensors. Chapter 2 presents the antibacterial and anticancer properties of ZnO/Ag nanohybids. In this study a simple route to synthesize ZnO/Ag nanohybrids by microwave synthesis has been established where ZnO/Ag nanohybrids have shown synergistic cytotoxicity towards mammalian cells. The observed synergism in the cytotoxicity of ZnO/Ag nanohybrids could lead to the development of low dose therapeutics for cancer treatment. Chapter 3 presents photocatalytic inactivation of bacterial cells by pentavalent bismuthates class of materials. AgBiO3 which was obtained from KBiO3 by ion-exchange method was investigated for its photocatalytic inactivation properties towards E.coli and S.aureus cells under dark and UV illumination conditions. Chapter 4 presents the integration of DNA molecules with ZnO nanorods for the observation of Mott-Gurney characteristics. In this study, ZnO nanorods were synthesized hydrothermally and were characterized by TEM and XRD analysis. DNA molecules were immobilized over ZnO nanorods which were confirmed by UV-Vis spectroscopy and confocal florescence microscopy. Solution processed devices were fabricated by using these DNA immobilized nanostructures and I-V characteristics of these devices were taken in dark and under illumination conditions at different wavelengths of light at fixed intensity. Interestingly, Mott-Gurney law was observed in the I-V characteristics of the devices fabricated using DNA immobilized ZnO nanorods. Chapter 5 presents the chemical synthesis of molecular scale ultrathin Au nanowires. These nanostructures were then used for fabricating electronic biosensors. In this study, the devices were fabricated over Au nanowires by e-beam lithography and a methodology to functionalize Au nanowires and then characterize them by florescence microscopy as well as AFM has been established. The fabricated biosensors were employed for the label free, electrical detection of DNA hybridization process. Chapter 6 presents a simple, cost effective and solution processed route to fabricate devices using ultrathin Au nanowires. The devices were then used for sensing ethanol, H2 and NH3. An important property of these devices is that they can sense these gases at room temperature which reduce their operation cost and makes them desirable to use under explosive conditions.