Effect of anionic surfactant sodium dodecyl sulfate on the reaction of hexacyanoferrate (III) oxidation of levothyroxine in aqueous medium: a kinetic and mechanistic …

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  Effect of anionic surfactant sodium dodecyl sulfate on the reaction of hexacyanoferrate (III) oxidation of levothyroxine in aqueous medium: a kinetic and mechanistic …
  See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/257658930 Effect of anionic surfactant sodium dodecylsulfate on the reaction of hexacy anoferrate(III)oxidation of...  Article   in  Research on Chemical Intermediates · July 2012 DOI: 10.1007/s11164-012-0764-x CITATIONS 2 READS 33 7 authors , including: Some of the authors of this publication are also working on these related projects: High Efficiency Perovskite Sensitized Solar Cell (PSC)   View projectAbdullah M. AsiriKing Abdulaziz University 1,681   PUBLICATIONS   9,948   CITATIONS   SEE PROFILE Anish KhanKing Abdulaziz University 80   PUBLICATIONS   502   CITATIONS   SEE PROFILE Naved AzumKing Abdulaziz University 79   PUBLICATIONS   626   CITATIONS   SEE PROFILE Mohammed M. RahmanKing Abdulaziz University 252   PUBLICATIONS   3,139   CITATIONS   SEE PROFILE All content following this page was uploaded by Abdullah M. Asiri on 01 May 2014. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the srcinal documentand are linked to publications on ResearchGate, letting you access and read them immediately.  Temperature Gradient Measurements by UsingThermoelectric Effect in CNTs-Silicone AdhesiveComposite Muhammad Tariq Saeed Chani 1,2 * , Kh. S. Karimov 3,4 , Abdullah M. Asiri 1,2 , Nisar Ahmed 3 , MuhammadMehran Bashir 3 , Sher Bahadar Khan 1,2 , Malik Abdul Rub 1,2 , Naved Azum 1,2 1 Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz University, Jeddah, Saudi Arabia,  2 Department of Chemistry, Faculty of Science, KingAbdulaziz University, Jeddah, Saudi Arabia,  3 GIK Institute of Engineering Science and Technology, Topi, Swabi, Khyber Pakhtunkhwa, Pakistan,  4 Physical TechnicalInstitute of Academy of Sciences, Dushanbe, Tajikistan Abstract This work presents the fabrication and investigation of thermoelectric cells based on composite of carbon nanotubes (CNT)and silicone adhesive. The composite contains CNT and silicon adhesive 1:1 by weight. The current-voltage characteristicsand dependences of voltage, current and Seebeck coefficient on the temperature gradient of cell were studied. It wasobserved that with increase in temperature gradient the open circuit voltage, short circuit current and the Seebeck coefficient of the cells increase. Approximately 7 times increase in temperature gradient increases the open circuit voltageand short circuit current up to 40 and 5 times, respectively. The simulation of experimental results is also carried out; thesimulated results are well matched with experimental results. Citation:  Chani MTS, Karimov KS, Asiri AM, Ahmed N, Bashir MM, et al. (2014) Temperature Gradient Measurements by Using Thermoelectric Effect in CNTs-Silicone Adhesive Composite. PLoS ONE 9(4): e95287. doi:10.1371/journal.pone.0095287 Editor:  Vipul Bansal, RMIT University, Australia Received  October 31, 2013;  Accepted  March 25, 2014;  Published  April 18, 2014 Copyright:    2014 Chani et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permitsunrestricted use, distribution, and reproduction in any medium, provided the srcinal author and source are credited. Funding:  This project was funded by the Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz University, Jeddah, under grantno. CEAMR-434-03. The authors have full rights to publish this article. The funders had no role in study design, data collection and analysis, decision to publish, orpreparation of the manuscript. Competing Interests:  The authors have declared that no competing interests exist.* E-mail: tariqchani1@gmail.com Introduction With the expanding human population, the demand for energyis increasing continuously, and the sustainable energy supply isarising as one of major problems of 21 st century. By the year 2050,the expected world population will be 10.6 billion and the energydemand will also become double because of industrialization of societies and better life standard. But, the currently serving fossilfuel resources are limited and causing global warming andenvironmental issues, so, the scientific society is trying to exploreenvironmental friendly energy resources. Now, the efficientproduction of clean and sustainable energy is the most provoking challenge of coming few decades [1 – 4]. To meet the future energy challenges, the thermoelectric phenomena can play an importantrole, which involve the conversion of heat to electricity and endowwith the methods for materials heating and cooling [1]. Thesustainability of the electricity can also be improved by scavenging of waste heat from industrial processes, factories, power plants,automotive exhaust computers, home heating and even from thehuman body by the use of thermoelectric generators [4 – 6]. Use of waste heat for the generation of electric power is of primeimportance to meet the world’s future energy requirements [7].The devices that are used for the conversion of heat energy intoelectricity are the semiconductor thermoelectric cells, which arealso used for the cooling at thermoelectric refrigerators. Thermo-electric cells work on the principle of Seebeck effect [8] and theirefficiency (Z) is determined by the following expression [9]: Z  ~ a 2 s = k  tot  ð 1 Þ where  a  and  s  are the Seebeck coefficient and electricalconductivity, respectively, while k  tot  is the total thermal conduc-tivity, which is equal to sum of the electron (k  el  ) and phonon (k  ph  )thermal conductivities. The increase in efficiency of thermoelectricgenerators depends, first of all on decrease in phonon thermalconductivity (k  ph  ). In this way, the layered chalcogenides withcomplex crystal structure are investigated intensively [10]. During the last years, thermoelectric cells based on 11  m m thick layers of n-Si/SiGe-p-B 4 C/B 9 C deposited on the silicon substrate has beenfabricated, which showed high efficiency of 15% [11]. At the sametime the thermoelectric effect is used not only for the conversion of energy, but also for the measurements of temperature gradient ininstrumentation, which in turn is used for the measurement of concentration of gases (like CO, CH 4  and C 2 H 5 OH,etc) [12] bythe use of thermoelectric cells on the base of oxides of tin andindium. In ref. [13] the Bi 2 Te 3  –Sb 2 Te 3  (p-type) and Bi 2 Te 3  – Bi 2 Se 3  (n-type) based thermoelectric cells for the measurement of temperature gradient are shown. It is also reported that these cellshave high thermoelectric figure of merit (ZT) and can be used todetermine the velocities of gas flow.In addition to chalcogenides, the transition metal oxides are also very attractive thermoelectric materials. These materials haveexcellent mechanical, chemical and electronic properties along with fascinating thermoelectric characteristics like tunable phonon PLOS ONE | www.plosone.org 1 April 2014 | Volume 9 | Issue 4 | e95287  and electronic transport properties, high electrical conductivityand Seebeck coefficient, high temperature stability and well-known synthesis processes. Some representative thermoelectricmetal oxides are the MnO 2 , TiO 2 , ZnO and WO 3  [10,14–16].Recently, Walia et al. implemented ZnO and MnO 2  for thefabrication of wave-based thermo-power energy generationdevices; the concept of thermo-power waves demonstrates greatpotential for the miniaturization of power sources by maintaining their capabilities of energy generation. These devices have beenfabricated by sequential deposition of thermoelectric material(ZnO or MnO 2  ) and solid fuel (nitrocellulose) on Al 2 O 3  substrate.The thermo-power waves are generated by solid fuel’s exothermicreaction and then propagated through thermoelectric material.This self propagation of waves resulted in very high output voltageof 500 mV and 1.8 V in case of ZnO and MnO 2  based devices,respectively, while, their corresponding room temperature See-beck coefficients are  2 360  m VK 2 1 and  2 460  m VK 2 1 [15,16].Presently, not only inorganic but also organic materials basedthermoelectric sensors and generators are investigated on the baseof Seebeck effect. Sumino et al. [17] investigated the properties of organic thin film thermoelectric cells based on semiconductive bi-layer structures in which C 60  and Cs 2 CO 3  were used as n-typeelements, while, pentacene and F 4 -TCNQ (tetracyanoquinodi-methane) as a p-type elements. It is reported that the Seebeck coefficient for n-type and p-type elements was respectivelymeasured as 0.19 and 0.39 mV/ u C and it is also concluded thatthe bi-layer structures allow to increase conductivity and efficiencyof the thermoelectric cells.Investigations on the thermoelectric properties of the nano-materials show that their Seebeck coefficient and ZT as a rule arehigher than that of traditional thermoelectric materials [18]: forexample, maximum figure of merit of nano-BiSbTe and BiSbTeapproximately were equal to 1.5 and 1.0. Theoretical investiga-tions show that the ZT of CNT based thermoelectric cells can belarger than 2 [19,20]. However, experimental results show that ZTis in the range of 10 2 3 to 10 2 2 , Seebeck coefficient is around of 40  m V/ u C (at room temperature) [20]. The value of ZT can beincreased up to 0.4 by plasma treatment of CNT in argonatmosphere, which causes to increase Seebeck coefficient anddecrease thermal conductivity of the material. Nevertheless thefigure of merit is low for utilization of the CNT for conversion of the heat energy into electricity [20]. The thermoelectric propertiesof ultra small single-wall carbon nanotubes showed that ZT can beincreased by surface design, formation of bundles, increasing thetube length, and so on, which significantly reduce the phonon andelectron-derived thermal conductance [21].Investigation of thermoelectric properties of single-wall carbonnanotube/ceramic nanocomposites (3Y-TZP/Al 2 O 3  ) produced byspark-plasma-sintering showed that the thermoelectric power andZT of the composites increase with increase in temperature. Thethermoelectric power changed from 28.5  m V/K to 50.4  m V/K onchange in temperature from 345 K to 644 K, while the value of ZT is  , 0.02 at 850 K, which is double than that of SWCNT (inpure form). These factors indicate the potential of CNTS for theiruse as a thermoelectric material [22]. Seebeck coefficient increasedlinearly with increase of temperature. The conductivity of thecomposite decreased with temperature showing the metallicbehavior. The effect of single (SWCNTs), few (FWCNTs) andmulti-walled CNTs (MWCNTs) on the thermoelectric perfor-mance of CNT/polymer (Nafion) nanocomposites was studied byChoi et al. [7]. It was found that the electrical properties of theCNT/Nafion nanocomposites were primarily affected by theCNTs since the Nafion acts as an electrically non-conducting matrix. The thermal conductivity of the nanocomposites wasdominated by the Nafion mainly due to weak van der Waalsinteraction. The electrical conductivity and Seebeck coefficientincreased as the concentration of CNTs was increased. It wasfound that for thermoelectric applications FWCNTs andMWCNTs are preferred over SWCNTs in CNT/Nafionnanocomposites. In polyaniline/carbon nanotube (PANI/CNT)composites in which PANI coats CNT networks, the enhancedSeebeck coefficients and figure of merits were obtained [23]. It wasfound that the thermoelectric parameters are several times largerthan those of either of the individual components. It is alsoconsidered that this new approach has potential for synthesizing high-performance thermoelectric materials. Therefore, it would bereasonable to investigate the possibilities to use CNTs in thethermoelectric cells because of their relatively low cost andcommercial availability. In this paper, the results of theinvestigation of thermoelectric cells fabricated on the base of CNT-silicone adhesive composites are presented. Experimental Commercially available (Sun Nanotech Co Ltd., China) multi-walled carbon nanotubes (MWNTs) powder and liquid siliconadhesives (Hero Gum) were used for the fabrication of composites.The diameter of MWNTs varied between 10–30 nm. For thefabrication of thermoelectric cells, the composite was prepared bymixing the multi-walled carbon nanotubes powder with siliconeadhesive. The ratio of components was 1:1 by weight. The medicalglass slides were used as substrate. Before deposition of compositelayer on glass substrates, the substrates were cleaned by methanoland dried. The layers of composite were deposited by sequentialuse of drop-casting and doctor blade technologies. The length,width and total thickness of the composites layers were equal to45 mm, 10 mm and 100  m m respectively. The thickness of theCNT composite layers was controlled by screen and measured byoptical microscope. After deposition, the samples were dried forone day in room temperature conditions and then for 2hrs at 90 u C. Figure 1 shows SEM image of the CNT-silicone adhesivecomposite layer at various magnification. The composite layerconsisted of grains, which are in the range of 1 to 4 micron.For the measurement of temperature, the thermocouples wereused, which also played the role of electrodes as well for themeasurement of voltage. The thermocouples were fixed at thecell’s surface by silver paste. Figure 2 shows schematic diagram of the thermoelectric cell. The temperature, voltage and current weremeasurement by using FLUKE 87 multimeter, while, the Seebeck coefficients were obtained as a ratio of the voltage developedbetween ‘‘hot’’ and ‘‘cold’’ thermocouples (Fig. 2) and temperaturegradient (  D T). Figure 1. SEM image of the CNT-silicone adhesive compositelayer at lower (a) and higher (b) magnifications. doi:10.1371/journal.pone.0095287.g001Temperature Gradient Measurements by Using Thermoelectric EffectPLOS ONE | www.plosone.org 2 April 2014 | Volume 9 | Issue 4 | e95287  Results and Discussion Figure 3 shows current-voltage characteristics of the thermo-electric cell at different values of temperature gradient (  D T) and atdifferent values of load resistance of the cell. It can be seen that as D T increases the open circuit voltages and short circuit currents of the cell also increase. Figure 4 shows open-circuit voltage andshort circuit current-temperature gradient relationships. Theserelationships are quasi-linear, that make application of the cellsmore suitable. As the temperature gradient increases approxi-mately 7 times, the open circuit voltage and short circuit currentincrease up to 40 and 5 times respectively. The Seebeck coefficient(  a  )-temperature relationship is shown in Fig. 5. It can be seen thatinitially  a  increases with temperature and shows saturationbehavior. Usually, the CNT composite samples are the blend of semiconductor and metallic phases. The temperature dependenceof the Seebeck coefficient of the CNTs can be described by thefollowing expression [24] a ~ p 2 3 k  2 B  T ed  ( DOS  ( E  F  )) dE  F  ð 2 Þ where T is temperature, DOS(E F  ) is density of states on the Fermienergy level (E F  ). In the case of metallic and semiconductivenanotubes, the derivative d(DOS(E F  ))/dE F  is equal to zero or non-equal, respectively [24]. In the case of the metallic or degeneratesemiconductor behavior of the CNTs, the following expressionmay be more relevant [4,15,25]: a ~ 8 m  p 2 k  2 B  3 eh 2  T   p 3 n   2 = 3 ð 3 Þ where  n  and  m * are the carrier concentration and the effective massof the carriers, respectively. It means that metallic behavior of theinvestigated CNT composite observed in Seebeck coefficient (  a  )-temperature relationship shown in Fig. 5 shows that ‘‘metallicphase’’ is dominating over of ‘‘semiconducting phase’’ in this case.Under the temperature gradient, the measurements of the polarityof open-circuit voltage, in particular, positive potential of the‘‘cold’’ side of the sample with respect of the ‘‘hot’’ side revealedthat the CNT-silicone adhesive composite is a p-type material.Previously, it was stated that limitation in the sizes of particlesled to the increase in efficiency of the thermoelectric cells. Thecells fabricated on the base of nanomaterials were more efficient ascompared to the ordinary materials of the same composition.However, it was observed that in the case of intrinsic undoped-nano-materials, the thermoelectric effect was relatively low due tosymmetrical contribution of the electrons and holes [18].Therefore, due to the increase in thermoelectric parameters likefigure of merit and efficiency, the practical application of the nano-materials may be realized by doping them with n-type and p-typeimpurities. As the electronic properties are concerned, it is well known thatCNTs show metallic or semi-conductive (small band gap) behaviordepending on the orientation of the graphene lattice with respectof CNT axis [26]. This idea is also supported by the resistancetemperature relationships investigated by us: it is found that withincrease in temperature from 29 u C to 72 u C, the resistance of thecells decreases from 662 V to 586 V , i.e. temperature coefficient of the resistance is equal to  2 0.27%/ u C.The conductivity of charges in the composite can be attributedto percolation theory [27,28]. According to this theory, theaverage conductivity can be calculated using this expression: s ~ 1 LZ   ð 4 Þ Figure 2. Schematic diagram of the thermoelectric cell basedon CNT-silicone adhesive composite. doi:10.1371/journal.pone.0095287.g002 Figure 3. Current-voltage characteristics of the thermoelectriccell at different values of temperature gradient ( D T). doi:10.1371/journal.pone.0095287.g003 Figure 4. Open-circuit voltage and short circuit current-temperature gradient relationships for the thermoelectric cellbased on CNT-silicone adhesive composite. doi:10.1371/journal.pone.0095287.g004Temperature Gradient Measurements by Using Thermoelectric EffectPLOS ONE | www.plosone.org 3 April 2014 | Volume 9 | Issue 4 | e95287  where  L   is the characteristic length between sites and  Z   is theaverage resistance of the connecting path between sites. Here totalconduction can be considered as a conduction of both layers.Probably, the contribution of the CNT layer is considerably larger,as the change in the thickness of the CNT layer and concentrationof CNT influences much to the total conduction of the composite.The adhesive in the composite plays a vital role in making theCNT layers firm, so that these layers could provide stableproperties. This effect was practically observed during the currentstudy. Another expected role of adhesive is that it may affect thethermoelectric properties of the composite. But, the comparison of the Seebeck coefficients of the investigated composite withdifferent CNTs and CNT-composites [7,20 – 23] shows that the effect of adhesive to the thermoelectric properties was reallynegligible as the value of the main parameter, Seebeck coefficient,measured by us was in the similar range as presented in therelevant references.Unlike to thermoelectric generators, where the efficiency orfigure of merit are most important parameters, the most importantparameters for the temperature gradient sensors are the Seebeck coefficient, linearity of the voltage-temperature gradient and therange of the temperature gradient. In principle, both organic orinorganic semiconductors can be used for the temperaturegradient sensors. For example, as organic semiconductors thequasi-one dimensional crystals of tetracyanoquino-dimethanecomplexes could be used, where the Seebeck coefficient is aroundof 1000  m V/ u C [29]. At the same time, for practical applications,the growth of sufficiently large sized crystals is difficult. Therefore,utilization of the thin film thermoelectric cells on the base of theCNT composites seems reasonable. During last few years, theproperties of thin films based cells have been improved [18].The simulation of current-voltage behavior is carried out byusing the following mathematical relationship [30]  f  ( x ) ~ ax z b  ð 5 Þ The modified form of above relationship for the current-voltageis the following  I  ~ kV  z C   ð 6 Þ where I is the short circuit current, V is open circuit voltage and k is current-voltage factor. The value of k for the data presented inFig. 3 is calculated as  2 1.4 6 10 2 4  A/V. The comparison of experimental and simulated results is given in Fig. 6 and it isevident from the graphs that the experimental and simulatedresults are in good agreement.For the simulation of open-circuit voltage and short circuitcurrent-temperature gradient relationships the following exponen-tial function is used [30]:  f  ( x ) ~ e x ð 7 Þ The Eq.4 has been modified for open circuit voltage-temper-ature gradient relationship as follows: V  oc ( V  oc ) o ~ e k  1 D ( D T  )(4 D T m z D T  ) = (5 D T  ) ð 8 Þ where  (V  oc   ) o  is initial open circuit voltage at minimal temperaturegradient (  D T=10 u C),  V  oc   is open circuit voltage at instantaneoustemperature gradients (  D T   ) and k  1  is voltage-temperature gradientfactor. The value of voltage-temperature gradient factor is6.4 6 10 2 2 / u C. For the simulation of short circuit current-temperature gradient relationship the Eq.7 is modified as I  sc ( I  sc ) o ~ e k  2 D ( D T  )( D T m z 2 D T  ) = (3 D T  ) ð 9 Þ where  (I  sc   ) o  and  I  sc   are initial short circuit current at minimaltemperature gradient (  D T=10 u C) and instantaneous values of short circuit current, respectively, while  D T   and  D T  m   aretemperature gradient and maximum temperature gradientaccordingly. The k  2  is current-temperature gradient factor andits value is calculated as is 2.8 6 10 2 2 / u C. The comparison of experimental and simulated results of voltage-temperature gradi- Figure 5. Seebeck coefficient ( a )-temperature relationship of the cell. doi:10.1371/journal.pone.0095287.g005 Figure 6. Comparison of experimental and simulated results of current-voltage behavior of the cells. doi:10.1371/journal.pone.0095287.g006Temperature Gradient Measurements by Using Thermoelectric EffectPLOS ONE | www.plosone.org 4 April 2014 | Volume 9 | Issue 4 | e95287
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