Preparation and thermal properties of palmitic acid/polyaniline/copper nanowires form-stable phase change materials

Form-stable phase change materials (PCMs) with high thermal conductivity are essential for thermal energy storage systems, which in turn are indispensible in solar thermal energy applications and efficient use of energy. In this paper, a new palmitic acid (PA)/polyaniline (PANI) form-stable PCMs were prepared by surface polymerization. The highest loading of PA in the form-stable PCMs was 80 mass% with the phase change enthalpy (ΔH _melting) of 175 J g^?1. Copper nanowires (Cu NWs) were introduced to the form-stable PCM by mixing the Cu NWs with PA and ethanol prior to the emulsifying of PA in surfactant solution. The Cu NWs would remain intact in case the ethanol was eliminated before the PA/Cu NWs mixture was mixed with surfactant solution. Otherwise, the Cu NWs would be partially oxidized under the attack of ethanol and ammonium persulfate. The ΔH _melting of the form-stable PCMs containing Cu NWs decreased linearly with the increasing of Cu NWs loading. The ΔH _melting of the form-stable PCMs doped with 11.2 mass% Cu NWs was 149 J g^?1. The thermal conductivity of the form-stable PCMs could be effectively improved by Cu NWs. By adding 11.2 mass% Cu NWs, the thermal conductivity of the form-stable PCM could attain 0.455 W m^?1 K^?1.     

Selective detection of dopamine in the presence of ascorbic acid by use of glassy-carbon electrodes modified with both polyaniline film and multi-walled carbon nanotubes with incorporated β-cyclodextrin

A simple, sensitive, and reliable method based on a combination of multi-walled carbon nanotubes with incorporated β-cyclodextrin (β-CD-MWNTs) and a polyaniline (PANI) film-modified glassy-carbon (GC) electrode has been successfully developed for determination of dopamine (DA) in the presence of ascorbic acid (AA). The PANI film had good anti-interference properties and long-term stability, because of the permselective and protective properties of the conducting redox polymer film. The acid-treated MWNTs with carboxylic acid functional groups promoted the electron-transfer reaction of DA and inhibited the voltammetric response of AA. Sensitive detection of DA was further improved by the preconcentration effect of formation of a supramolecular complex between β-CD and DA. The analytical response of the β-CD-MWNTs/PANI film to the electrochemical behavior of DA was, therefore, better than that of a MWNTs/PANI film, a PANI film, or a bare glassy-carbon (GC) electrode. Under the conditions chosen a linear calibration plot was obtained in the range 1.0 × 10⁻⁷–1.0 × 10⁻³ mol L⁻¹ and the detection limit was 1.2 × 10⁻⁸ mol L⁻¹. Interference from AA was effectively eliminated and the sensitivity, selectivity, stability, and reproducibility of the electrodes was excellent for determination of DA.     

Thermal conductivity enhancement of Ag nanowires on an organic phase change material

One of the greatest challenges in the application of organic phase change materials (PCMs) is to increase their thermal conductivity while maintaining high phase change enthalpy. 1-Tetradecanol/Ag nanowires composite PCM containing 62.73 wt% (about 11.8 vol%) of Ag nanowires showed remarkably high thermal conductivity (1.46 W m⁻¹ K⁻¹) and reasonably high phase change enthalpy (76.5 J g⁻¹). This behavior was attributed to the high aspect ratio of Ag nanowires, few thermal conduct interfaces, and high interface thermal conductivity of Ag nanowires in the composite PCM. These results indicated that Ag nanowires might be strong candidates for thermal conductivity enhancement of organic PCMs.     

Reduction of silver nitrate by polyaniline nanotubes to produce silver-polyaniline composites

Polyaniline (PANI) nanotubes were prepared by oxidation of aniline in 0.4 M acetic acid. They were subsequently used as a reductant of silver nitrate in 1 M nitric acid, water or 1 M ammonium hydroxide at various molar ratios of silver nitrate to PANI. The resulting PANI-silver composites contained silver nanoparticles of 40–60 nm size along with macroscopic silver flakes. Under these experimental conditions, silver was always produced outside the PANI nanotubes. Changes in the molecular structure of PANI were analyzed by FTIR spectroscopy. Silver content in the composites was determined as a residue by thermogravimetric analysis, and confirmed by density measurements. The highest conductivity of a composite, 68.5 S cm⁻¹, was obtained at the nitrate to PANI molar ratio of 0.67 in water. Also, the best reaction yield was obtained in water. Reductions performed in an acidic medium gave products with conductivity of 10⁻⁴–10⁻² S cm⁻¹, whereas the reaction in alkaline solution yielded non-conducting products.     

A new amperometric H<Subscript>2</Subscript>O<Subscript>2</Subscript> biosensor based on nanocomposite films of chitosan–MWNTs,hemoglobin, and silver nanoparticles

A new H₂O₂ biosensor was fabricated on the basis of nanocomposite films of hemoglobin (Hb), silver nanoparticles (AgNPs), and multiwalled carbon nanotubes (MWNTs)–chitosan (Chit) dispersed solution immobilized on glassy carbon electrode (GCE). The immobilized Hb displayed a pair of well-defined and reversible redox peaks with a formal potential (E ^θ′) of −22.5 mV in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k _s) in the Chit–MWNTs film was evaluated as 2.58 s⁻¹ according to Laviron’s equation. The surface concentration (Γ*) of the electroactive Hb in the Chit–MWNTs film was estimated to be (2.48 ± 0.25) × 10⁻⁹ mol cm⁻². Meanwhile, the Chit–MWNTs/Hb/AgNPs/GCE demonstrated excellently electrocatalytical ability to H₂O₂. Its apparent Michaelis–Menten constant (K _M^app) for H₂O₂ was 0.0032 mM, showing a good affinity. Under optimal conditions, the biosensors could be used for the determination of H₂O₂ ranging from 6.25 × 10⁻⁶ to 9.30 × 10⁻⁵ mol L⁻¹ with a detection limit of 3.47 × 10⁻⁷ mol L⁻¹ (S/N = 3). Furthermore, the biosensor possessed rapid response to H₂O₂ and good stability, selectivity, and reproducibility.     

Facile preparation of polyethylene glycol/wood-flour composites as form-stable phase change materials for thermal energy storage

Journal of Thermal Analysis and Calorimetry - The polyethylene glycol/wood-flour (PEG/WF) composites were synthesized as novel form-stable phase change materials (PCMs) using PEG as phase change...     

Electrochemical performance of Co–Al layered double hydroxide nanosheets mixed with multiwall carbon nanotubes

Regular hexagonal Co–Al layered double hydroxides (Co–Al LDH) were synthesized by urea-induced homogeneous precipitation. This material proved to be nanosheets by scanning electron microscopy and X-ray diffraction measurements. The electrochemical capacitive behavior of the nanosheets in 1 M KOH solution were evaluated by constant current charge/discharge and cyclic voltammetric measurements, showing a large specific capacitance of 192 F·g⁻¹ even at the high current density of 2 A·g⁻¹. When multiwall carbon nanotubes (MWNTs) were mixed with the Co–Al LDH, it was found that the specific capacitance and long-life performance of all composite electrodes at high current density are superior to pure LDH electrode. When the added MWNTs content is 10 wt%, the specific capacitance increases to 342.4 F·g⁻¹ and remains at a value of 304 F·g⁻¹ until the 400th cycle at 2 A·g⁻¹, showing that this is a promising electrode material for supercapacitors working at heavy load. According to the electrochemical impedance spectra, MWNTs greatly increase the electronic conductivity between MWNTs and the surface of Co–Al LDH, which consequently facilitates the access of ions in the electrolyte and electrons to the electrode/electrolyte interface.     

Composite films of polyaniline and molybdenum oxide formed by electrocodeposition in aqueous media

Composite films of polyaniline (PANI) and molybdenum oxide (MoO_x) were afforded through a convenient route of electrocodeposition from aniline and (NH₄)₆Mo₇O₂₄. The composite films showed characteristic redox behaviors of PANI and MoO_x, respectively, on the cyclic voltammograms. Chlorate and bromate were catalytically electroreduced with an enlarged current on the composite film at a potential ca. 0.2 V more positive than that on MoO_x. The potential window for the composite film to display pseudocapacitive properties in 1.0 mol·dm⁻³ NaNO₃ was −0.6 ∼ 0.6 V vs SCE. The cathodic potential limit shifted at least 0.4 V negatively from that of polyaniline (PANI)-based materials reported so far. The specific capacitance was 363.6 F·g⁻¹ when the composite film was charged–discharged at 1.5 mA·cm⁻², about two times of that of the similarly prepared PANI. The composite film was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Molybdenum existed in a mixed state of +5 and +6 in the composite film based on XRD and XPS investigations. Figure PANI and (MoO_x) were electrocodeposited in aqueous solutions from aniline and (NH₄)₆Mo₇O₂₄. The composite film obtained displayed catalytic activities toward the electroreduction of oxoanions. The pseudocapacitance of the composite film is nearly two times of that of PANI with the potential window extended negatively up to −0.6 V vs SCE     

The preparation of PANI/CA composite electrode material for supercapacitors and its electrochemical performance

Polyaniline (PANI)/carbon aerogel (CA) composite electrode materials were prepared by chemical oxidation polymerization. The morphology of PANI/CA composite was examined by scanning electron microscopy. The results showed that PANI was uniformly deposited onto the surface of porous CA and filled big inner pores of the CA. Electrochemical performance of the composite electrode was studied by cyclic voltammograms and galvanostatic charge/discharge measurements. The results indicated that the PANI/CA composite electrode had much better electrochemical performance, high reversibility, and high charge/discharge properties than CA. Moreover, the results based on cyclic voltammograms showed that the composite material has a high specific capacitance of 710.7 F g⁻¹, while the capacitance of CA electrode was only 143.8 F g⁻¹. Besides, the supercapacitor using the PANI/CA composite as electrode active material showed a stable cycle life in the potential range of −0.2–0.8 V.     

A kinetic analysis of thermal decomposition of polyaniline/ZrO<Subscript>2</Subscript> composite

Synthesis, characterization and thermal analysis of polyaniline (PANI)/ZrO₂ composite and PANI was reported in our early work. In this present, the kinetic analysis of decomposition process for these two materials was performed under non-isothermal conditions. The activation energies were calculated through Friedman and Ozawa-Flynn-Wall methods, and the possible kinetic model functions have been estimated through the multiple linear regression method. The results show that the kinetic models for the decomposition process of PANI/ZrO₂ composite and PANI are all D₃, and the corresponding function is ƒ(α)=1.5(1−α)^2/3[1−(1-α)^1/3]−1. The correlated kinetic parameters are E _a=112.7±9.2 kJ mol⁻¹, lnA=13.9 and E _a=81.8±5.6 kJ mol⁻¹, lnA=8.8 for PANI/ZrO₂ composite and PANI, respectively.     

Preparation of polyaniline grafted multiwalled carbon nanotubes and conductive application in polyetherimide

A methodology for improving antistatic property of polyetherimide (PEI) composite using polyaniline (PANI) grafted multi‐walled carbon nanotubes (MWNTs) as conductive medium was proposed. First, the MWNTs grafted with PANI (PANI‐g‐MWNTs) were prepared by in‐situ polymerization in an emulsion system. Subsequently, PANI‐g‐MWNTs were blended with PEI using N‐methyl‐2‐pyrrolidone as solvent. After removing the solvent, the PEI/PANI‐g‐MWNT composite was prepared. As assisted conductive medium, the grafted PANI molecular chains on MWNT surface were dispersed in the PEI matrix to decrease the percolation value of the antistatic composites. The structure and morphology of PANI‐g‐MWNTs were characterized by Fourier transform infrared spectroscopy, transmission electron microscope, thermogravimetric analysis, and X‐ray powder diffraction, respectively. The dispersion of PANI‐g‐MWNTs in PEI matrix was studied by scanning electron microscope. The electrical performance was characterized by highly resistant meter. The volume resistivity of the conductivity percolation threshold was 1.781 × 10^?8 S/cm when the loading of PANI‐g‐MWNTs was 1.0 wt%. The conductivity of PANI‐g‐MWNTs/PEI composites was found to be higher than that of pristine MWNTs/PEI composite. Copyright © 2012 John Wiley & Sons, Ltd.     

Chemometrics to evaluate the quality of water sources for human consumption

Multilayer films of multiwalled carbon nanotubes (MWNTs) were homogeneously and stably assembled on a glassy carbon (GC) electrode using the layer-by-layer (LBL) method based on electrostatic interaction between MWNTs (negatively charged) and a biopolymer chitosan (CHIT) (positively charged). Scanning electron microscopy (SEM) image of the resulting {CHIT/MWNTs}₉ film indicated that the substrate was mostly covered with MWNTs in the form of small bundles or single nanotubes. The multilayer film was used to study the electrocatalytic oxidation of NADH. The assembled {CHIT/MWNTs}₉/GC electrode could decrease the oxidation overpotential of NADH by more than 350 mV. The {CHIT/MWNTs}₉/GC electrode exhibited a wide linear response range of 8 × 10⁻⁷ to 1.6 × 10⁻³ mol · L⁻¹ with a correlation coefficient of 0.997 for the detection of NADH. The response time and detection limit (S/N = 3) were determined to be 3 s and 0.3 × 10⁻⁶ mol · L⁻¹, respectively. Another attractive characteristic was that the method was simple and the assembled {CHIT/MWNTs}₉/GC electrode was highly stable.     

Effects of MWNTs on phase change enthalpy and thermal conductivity of a solid-liquid organic PCM

The effects of multi-walled carbon nanotubes (MWNTs) on the phase change enthalpy (ΔH) and the thermal conductivity (κ) of a solid-liquid phase change materials (PCM), palmitic acid (PA), have been investigated. The results showed that both the ΔH and the κ of the composite were lower than that of PA when the loading of MWNTs was small. As the concentration of MWNTs in the composites increased, the ΔH of the composites was slightly improved and then decreased linearly. However, the κ of the composites was monotonously increased from the minimum value. When the loading of MWNTs increased to 5% and no surfactant was added, the κ of the composite was enhanced to be 26% higher than that of PA. The κ of the composite could be enhanced by CTAB instead of SDBS when the loading of MWNTs was small, as SDBS showed no obvious effect on the κ of the composites. Furthermore, the effects of surface modification of MWNTs on the ΔH and the κ of the composites have also been investigated.     

Polyaniline-coated cellulose fibers decorated with silver nanoparticles

Cellulose fibers of 20 μm in diameter and aspect ratio of 2 or 10 were coated with protonated polyaniline (PANI) during the oxidation of aniline hydrochloride with ammonium peroxydisulfate in an aqueous medium. The presence of PANI has been proved by FTIR spectroscopy. The conductivity increased from 4.0 × 10⁻¹⁴ S cm⁻¹ to 0.41 S cm⁻¹ after coating the fibers with PANI. The percolation threshold in the mixture of original uncoated and PANI-coated fibers was reduced from 10 mass % PANI to 6 mass % PANI, as the aspect ratio changed from 2 to 10. The subsequent reaction with silver nitrate results in the decoration of PANI-coated cellulose fibers with silver nanoparticles of about 50 nm average size. The content of silver of up to 10.6 mass % was determined as a residue in thermogravimetric analysis. FTIR spectra suggest that the protonated emeraldine coating changed to the pernigraniline form during the latter process and, consequently, the conductivity of the composite was reduced to 4.1 × 10⁻⁴ S cm⁻¹, despite the presence of silver.     

The preparation and performance of flocculent polyaniline/carbon nanotubes composite electrode material for supercapacitors

Polyaniline (PANI)/carbon nanotubes (CNTs) composite electrode material was prepared by in situ chemical polymerization. The structure and morphology of PANI/CNTs composite are characterized by Fourier infrared spectroscopy, scanning electron microscope, and transmission electron microscopy. It has been found that a flocculent PANI was uniformly deposited on the surface of CNTs. The supercapacitive behaviors of the PANI/CNTs composite materials are investigated with cyclic voltammetry, galvanostatic charge/discharge, impedance, and cycle life measurements. The results show that the PANI/CNTs composite electrodes have higher specific capacitances than CNT electrodes and better stability than the conducting polymers. The capacitance of PANI/CNTs composite electrode is as high as 837.6 F g⁻¹ measured by cyclic voltammetry at 1 mV s⁻¹. Besides, the capacitance retention of coin supercapacitors remained 68.0% after 3,000 cycles.     

Fabrication of polyaniline/carbon nanotube composite modified electrode and its electrocatalytic property to the reduction of nitrite

A polyaniline (PANI)/carbon nanotubes (CNTs) composite modified electrode was fabricated by galvanostatic electropolymerization of aniline on multi-walled carbon nanotubes (MWNTs)-modified gold electrode. The electrode thus prepared exhibits enhanced electrocatalytic behavior to the reduction of nitrite and facilitates the detection of nitrite at an applied potential of 0.0 V. Although the amperometric responses toward nitrite at MWNTs/gold and PANI/gold electrodes have also been observed in the experiments, these responses are far less than that obtained at PANI/MWNTs/gold electrode. The effects of electropolymerization time, MWNTs concentration and pH value of the detection solution on the current response of the composite modified electrode toward sodium nitrite, were investigated and discussed. A linear range from 5.0 × 10⁻⁶ to 1.5 × 10⁻² M for the detection of sodium nitrite has been observed at the PANI/MWNTs modified electrode with a sensitivity of 719.2 mA M⁻¹ cm⁻² and a detection limit of 1.0 μM based on a signal-to-noise ratio of 3.     

Preparation and characterization of form-stable tetradecanol–palmitic acid expanded perlite composites containing carbon fiber for thermal energy storage

In this study, tetradecanol–palmitic acid/expanded perlite composites containing carbon fiber (TD-PA/EP-CF CPCMs) were prepared by a vacuum impregnation method. Binary eutectic mixtures of PA and TD were utilized as thermal energy storage material in the composites, where EP behaved as supporting material. X-ray diffraction demonstrated that crystal structures of PA, TD, EP, and CF remained unchanged, confirming no chemical interactions among raw materials besides physical combinations. The microstructures indicated that TD-PA was sufficiently absorbed into EP porous structure, forming no leakage even in molten state. Differential scanning calorimetry estimated the melting temperature of TD-PA/EP-CF CPCM to 33.6 °C, with high phase change latent heat (PCLH) of 138.3 kJ kg⁻¹. Also, the freezing temperature was estimated at 29.7 °C, with PCLH of 137.5 kJ kg⁻¹. The thermal cycling measurements showed that PCM composite had adequate stability even after 200 melting/freezing cycles. Moreover, the thermal conductivity enhanced from 0.48 to 1.081 W m⁻¹ K⁻¹ in the presence of CF. Overall, the proposed CPCMs look promising materials for future applications due to their appropriate phase change temperature, elevated PCLH, and better thermal stability.

     

Selective solid-phase extraction of Cu(II) using freshly precipitated lead diethyldithiocarbamate and its spectrophotometric determination

A new solid-phase extraction method has been developed for the selective extraction of Cu(II) in an aqueous system using freshly precipitated lead diethyldithiocarbamate (Pb(DDTC)₂) as a reagent. The method is based on the quantitative replacement of Pb(II) ions in the solid Pb(DDTC)₂ phase by Cu(II) ions present in aqueous phase. The obtained solid Cu(DDTC)₂ phase was dissolved in chloroform and determined spectrophotometrically at 435 nm. Beer’s law was obeyed over the concentration range of 0.2–5 mg dm⁻³. The molar absorptivity and the Sandell’s sensitivity coefficients of the solutions were 1.0689 × 10⁴ dm³ mol⁻¹ cm⁻¹ and 0.0060 μg cm⁻², respectively. The optimum conditions for each parameter were experimentally determined and possible interferences of various salts were also studied. The method has been validated and applied to determine Cu(II) in various alloys and water samples.     

Adsorption properties of BEA zeolites and their aluminum phosphate extrudates for purification of isomaltose

The disaccharide isomaltose is produced via an enzymatic reaction and is adsorbed to BEA zeolite. This reaction integrated adsorption can be achieved as fluidized bed as well as fixed bed. We investigated isotherms, adsorption enthalpies and sorption kinetics of BEA zeolite and extrudates with a novel aluminum phosphate sintermatrix. These extrudates contain 50% (w/w) of BEA 150 zeolites (Si/Al = 75) as primary crystals. BET-surface for extrudates is 245 m²⋅g⁻¹ and 487 m²⋅g⁻¹ for zeolite. Extrudates show a monomodal macropore structure with a maximum at 90 nm. All isotherms show a type I shape. For lower equilibrium concentrations, which occur during the enzymatic reaction, Henry’s law is applied and compared to a Langmuir model. Adsorption equilibrium constant K _i,L calculated from Langmuir for extrudates at 4 °C is 64.7 mL⋅g⁻¹ and more than twice as high as obtained from Henry’s law with K _i is 26.8 mL⋅g⁻¹. Adsorption on extrudates at 4 °C is much stronger than on zeolite crystals where the Henry coefficient K _i is 17.1 mL⋅g⁻¹. Adsorption enthalpy Δh _Ad calculated from van’t Hoff plot with the Henry equation is −44.3 kJ⋅mol⁻¹ for extrudates and −29.6 kJ⋅mol⁻¹ for zeolite crystals. Finally, the kinetics for ad- and desorption were calculated from the initial slope. The diffusion rate for ad- and desorption on extrudates were in the same range while adsorption on zeolites is three orders of magnitudes faster than desorption.     

Form-stable electrospun nanofibrous mats as a potential phase change material

A series of Poly vinyl butyral–Poly (acrylic acid) (PVB-PAA) based form-stable phase change materials (PCMs) have been prepared for the use of thermal energy storage applications. Six types of formulations containing five different fatty alcohols were prepared by adding PVB to PAA. Using electrospinning to fabricate nanofibrous mats, our aim was to investigate their properties as form-stable PCMs. Fatty alcohols, 1-Tetradecanol, 1-Hexadecanol, 1-Octadecanol, 1-Eicosanol and 1-Docosanol, were added separately to base formulation. The structural characterization tests were performed by ATR-FTIR spectroscopy. Morphological tests were conducted using Scanning Electron Microscope (SEM). Thermal performances and phase change behaviors were tested by thermogravimetric analysis system (TGA) and differential scanning calorimetry (DSC). The heating cycle phase change enthalpy is measured between 223 and 241?J/g, and the freezing cycle phase change enthalpy is found between 215 and 239?J/g. The main decomposition PVB-PAA based PCMs started at 220?°C. This study suggested that PVB-PAA based PCMs possess well phase change properties and they were found to have an applicable temperature range. With the presented results these materials promise a great potential in thermal energy storage applications.