Density, Refractive Index, and Ultrasound Speed in Mixtures of Active

Article pubs.acs.org/jced

Density, Refractive Index, and Ultrasound Speed in Mixtures of Active Carbon and Exfoliated Graphite Nanoplatelets Dispersed in N,N‑Dimethylformamide at Temperatures from (293.15 to 318.15) K Ion Ion,† Florinela Sirbu,‡,* and Alina Catrinel Ion† †

Faculty of Applied Chemistry and Material Science, ”Politehnica” University of Bucharest, 1-7 Polizu Strasse, 011061, Bucharest, Romania ‡ ”Ilie Murgulescu” Institute of Physical Chemistry of Romanian Academy, 202 Splaiul Independentei Strasse, 060021, Bucharest, Romania ABSTRACT: The density and refractive index of diluted binary mixtures of active carbon and exfoliated graphite nanoplatelets dispersed in N,N-dimethylformamide were measured at different temperatures, and the ultrasound speed through these materials was determined. From the experimental results, acoustic parameters such as the acoustic impedance, isentropic compressibility, specific refraction, space-filling factor, and relaxation strength were estimated for all compositions and temperatures. The results were used to identify molecular interactions in the mixtures, including structural changes of exfoliated graphite nanoplatelets in polar solvents.

■

INTRODUCTION Investigations on thermodynamic and acoustic properties contribute to our understanding of the physicochemical behavior of binary and multicomponent liquid mixtures. Experimental data on thermodynamic and thermophysical properties combined with other analytical data on liquid mixtures are fundamentally important for the analysis of chemicals and the chemical industry. Moreover, S. S. Ubarhande et al. showed that these properties influence the dispersion of nanostructures in solvents, providing new information on the structure and interactions of mixed solvents.1 Single−layer graphene, which has interesting properties such as ballistic conductivity, high elasticity, high mechanical strength, high surface area, and heterogeneous electron transfer2 was first isolated in 2004 by Novoselov et al.3 Because single−layer graphene sheets are finite and dimensional limitations influence the electronic properties of graphene, graphene-based materials can be categorized according to the dimensions of sheets that are parallel and perpendicular to the layers.4 The properties of graphite nanoplatelets (10−100 graphene layers, 3−30 nm thick), also known as exfoliated graphite nanoplatelets (xGnP), are independent of the number of layers and show similar electrochemical behavior.5 Although the number of articles on xGnP has increased,6 data on their thermodynamic properties, thermophysical description, and molecular modeling properties are relatively scarce. In some previous studies, the stabilization of graphene dispersed in polar solvents, such as DMSO and DMF,7 was reported. It was observed that DMSO can break polymerized structures of oxygenated compounds,8 and this has been used in recent years for the dispersion of xGnP. N,N-Dimethylformamide (DMF) is a polar solvent that is used in a variety of industrial applications because it is a stable © 2013 American Chemical Society

compound with strong electron-pair donating and accepting abilities. The negative pole in DMF is an oxygen atom and a hydrogen-bond acceptor. The positive pole is a nitrogen atom that is located inside the molecule and is an electron pair donor.9 To characterize the type and magnitude of molecular interactions between DMF and xGnP, the density, ultrasound speed, and refractive index of the pure solvent and mixtures of DMF and xGnP were determined. In the present study xGnP dispersed in DMF can be used in environmental and agricultural applications10 such as composite nanomaterials for sensors4 (in-field sensing systems to monitor environmental stresses) and sorbents (enabling the delivery of drugs11 or the removal of contaminants from mixtures of solutions12). With respect to water quality, xGnP dispersed in DMF can be used in a variety of applications, such as desalination or the removal of heavy metals. In the detection and sensing of pollutants and impurities, the detection level in the laboratory and field applications is usually parts per billion (ppb). In the field of nanotechnology, the prototyping of sensors and sorbents based on nanomaterials is highly advanced; however, the basic level of knowledge concerning interactions at the molecular level is not sufficient. As a continuation of our research on mixtures of solutions, the thermophysical properties of binary systems of active carbon (AC)/exfoliated graphite nanoplatelets (xGnP) in N,N-dimethylformamide (DMF), for which experimental data are not available, were obtained in the present study. The effect of the studied parameters on the composition was determined to understand the nature and extent of interactions between unlike molecules. Received: December 19, 2012 Accepted: March 29, 2013 Published: April 12, 2013 1212

dx.doi.org/10.1021/je301343n | J. Chem. Eng. Data 2013, 58, 1212−1222

Journal of Chemical & Engineering Data

■

Article

EXPERIMENTAL SECTION Materials and Methods. xGnP containing a mass fraction more than 0.95 carbon was provided from XG Sciences, Lansing, MI, USA, and was characterized in our laboratory. KBr, and N,Ndimethylformamide (DMF) were purchased from Merck. Activated carbon (AC) was supplied by Sigma Aldrich. These chemicals were used without further purification because their mass fraction purity is higher than 0.99. The details of the chemical compounds used for samples preparation are given in the Table 1. Working solutions with different (AC) or (xGnP) +

The air was expelled from the syringe before each measurement in order to inject the correct volume of the sample. The internal calibration of the instrument was confirmed by measuring the density and ultrasound speed through atmospheric air and doubly distilled deionized water, according to the recommendations of the manufacturer. Similar to the results described in the literature, the density of water was measured as 0.99704 g·cm3 at 298.15 K.13−15 The values of ρ and c were reproducible within ± 0.000005 g·cm−3 and ± 0.05 m·s−1, respectively. The refractive indices were measured using an Anton Paar GmbH Abbe automatic refractometer with a precision of ± 0.000001, and the temperature of the samples was controlled within ± 0.01 K. The refractometer was calibrated by measuring the refractive index of doubly distilled water. The refractive index of water was measured as 1.33249 at 298.15 K, which is similar to the value mentioned in the literature of 1.33250.14,16 The samples were introduced into the cell (prism assembly) using a syringe. At least three independent measurements were taken for each sample at each temperature to ensure the effectiveness of the measurement. For each sample, all of the measurements were repeated at least three times and were repeatable within the level of precision quoted for the

Table 1. Specification of Active Carbon, Exfoliated Graphite Nanoplatelets, and N,N-Dimethylformamide Compounds Used in Samples chemical name ACa xGnPb DMFc KBrd

source Sigma Aldrich XG Sciences, Lansing, MI, USA E. Merck E. Merck

initial mass purification fraction purity method

final mass fraction purity

0.99 0.95

none none

0.99 0.95

p.a. 0.99

none none

p.a. 0.99

a c

AC = active carbon. bD-Glu = exfoliated graphite nanoplatelets. DMF = N,N-dimethylformamide. dKBr = potassium bromide.

DMF compositions were prepared at 298.15 K using N,Ndimethylformamide of analytical purity (p.a.). The mixtures were prepared by mixing known compositions of stock and pure DMF solutions in narrow-mouth, ground glasses. All precautions were taken to minimize losses due to evaporation. The binary mixtures were kept in special airtight glass bottles to avoid evaporation. A volume of 100 cm3 stock solution of activated carbon and exfoliated graphite nanoplatelets (solutes) with a concentration of 0.001 g·cm−3 at 293.15 K was prepared by directly weighing the materials using an A&D GH-252 (Japan) electronic balance with a precision of ± 0.0001 g. The initial concentration of the solutions was prepared with an accuracy of ± 0.0002 g·cm−3. For each solute, six samples with different specific concentrations ranged from (0 to 100) kg·m−3 in increments of 20 kg·m−3 were prepared from a stock solution. For uniformity, all of the liquid mixtures were dispersed using an ultrasonic bath. The uncertainty of sample preparation was 0.002 cm3 for the micropipet, and the potential error in the composition was estimated to be less than ± 0.0001 g·cm−3. Each sample was sonicated for 30 min at 303.15 K and was measured immediately. The morphological structure of as-received xGnP was characterized by scanning electron microscopy (SEM). The samples were directly coated on conductive surfaces, and SEM images were taken with a SEM microscope coupled to an energy dispersive X-ray spectroscope (Philips Quanta Inspect F). The images were obtained at 30 kV and a magnification of 2000×. Fourier transform infrared (FTIR) measurements were performed using a Shimadzu 8400 FTIR spectrophotometer equipped with a KBr beam splitter (KBr, FTIR grade). Spectra were acquired in the (4000 up to 400) cm−1 range at a resolution of 4 cm−1. The background spectrum of KBr was recorded under the same conditions. The density and ultrasound speed of stock binary mixtures were measured with an Anton Paar DSA 5000 digital (Austria) analyzer with a precision of ± 0.000001 g·cm−3. The temperature for the density measurements was controlled at a precision of ± 0.001 K, and several Peltier units were used.

Figure 1. FEG images of the as-grown xGnP dispersion in DMF (N,Ndimethylformamide) solvent.

Figure 2. SEM images of the as-grown xGnP dispersion in DMF (N,N-dimethylformamide) solvent. 1213



Article

Figure 3. FT-IR absorption spectra (transmittance A) of xGnP in DMF (N,N-dimethylformamide) solvent.

Table 2. Comparison of Experimental Values of the Density ρ, Ultrasound Speed c, and Refractive Index nD at Various Temperatures T, for the Pure N,N-Dimethylformamide with Corresponding Literature Valuesa ρ/kg·m−3

c/m·s−1

nD

T/K

expt

lit

Δρ %

expt

lit

293.15

949.81

1402.035

945.02

1463.76

303.15

940.25

308.15

935.46

313.15

930.67

318.15

925.89

−0.23 −0.55 −0.53 0.08 −0.10 0.00 −0.18 0.25 −0.03 −0.47 −0.20 0.45 −0.61 −1.31

1483.36

298.15

952.035 955.136 950.136 944.337 946.038 943.839 941.936 937.940 935.736 939.938 932.536 926.540 931.638 938.241

Δc %

expt

lit

ΔnD %

5.80

1.43035

1465.238

−0.10

1.42805

1.427035 1.428536 1.429037 1.426736

0.23 0.13 −0.07 0.09

1444.15

1459.639

−1.06

1.42576

1.424036

0.12

1424.58

1434.740

−0.71

1.42347

1405.10

1420.839

−1.11

1.42120

1.422136 1.428537 1.420536

0.10 −0.35 0.05

1385.74

1379.641

0.44

1.41887

1.427837

−0.63

Standard uncertainties u are u(T) = 0.001 K for ρ and c; u(T) = 0.01 K for nD and the combined expanded uncertainties Uc are Uc(ρ) = 0.01 kg·m−3, Uc(c) = 0.1 m·s−1; (level of confidence = 0.95, k = 2) and Uc(nD) = 0.00001; The relative deviation Δy %: Δy = ((yexpt − ylit)/ylit)100. a

where K is the bulk modulus of the solution. According to the method of Gerecze21 and Lorentz− Lorenz,20 the space-filling factor (S) was computed from refractive index (sodium D line) data using the following relation:23,24

apparatus. Uncertainties associated with the experimental data such as density, ultrasonic speed, and refractive index were estimated based on the uncertainty in measurement17 and presented together with the experimental results in the tables. Theory and Calculation. The following thermodynamic acoustical and optical parameters were calculated using the standard relations employed in previous studies.18−31 The acoustic impedance (Z) was calculated using the following relation:18

Z = ρc

S=

(1)

where ρ is the density (kg·m ), and c is the ultrasound speed (m·s−1) in the mixture. The isentropic (adiabatic) compressibility coefficient kS for the pure solvent and liquid mixtures was calculated from the density ρ and the ultrasound speed c using the Laplace equation:19 1 1 = 2 K ρc

(3)

where B is the effective volume occupied by molecules per mole, V is the molecular volume, and nD is the refractive index of the mixed solution. The specific refraction (rD) was calculated from the density (ρ) and space-filling factor (S) using the Lorentz and Lorenz equation, which is based on the electromagnetic theory of light, whereas the other equations are of empirical origin:25,26

−3

kS =

n2 − 1 B = D2 V nD + 2

rD =

(2) 1214

nD2 − 1 1 nD2 + 2 ρ

(4)



Article

Table 3. Experimental Values of the Density ρ, Ultrasound Speed c, and Refractive Index at Various Temperatures T and Specific Concentrations C of AC, for the System AC + DMFa T/K

ρ/kg·m−3

c/m·s−1

ρ/kg·m−3

nD

−3

293.15 298.15 303.15 308.15 313.15 318.15

949.81 945.02 940.25 935.46 930.67 925.89

293.15 298.15 303.15 308.15 313.15 318.15

950.08 945.32 940.55 935.77 930.98 926.16

293.15 298.15 303.15 308.15 313.15 318.15

950.05 945.30 940.52 935.75 930.94 926.15

C/kg·m = 0 1483.36 1463.76 1444.15 1424.58 1405.10 1385.74 C/kg·m−3 = 40 1484.12 1464.62 1445.03 1425.49 1406.02 1386.69 C/kg·m−3 = 80 1483.99 1464.49 1444.96 1425.39 1406.01 1386.57

1.43035 1.42805 1.42576 1.42347 1.42120 1.41887

950.00 945.23 940.46 935.69 930.87 926.06

1.43030 1.42805 1.42578 1.42349 1.42123 1.41891

950.09 945.34 940.58 935.82 930.99 926.20

1.43030 1.42807 1.42580 1.42354 1.42129 1.41897

945.00 945.23 940.45 935.66 930.86 926.05

c/m·s−1 C/kg·m−3 = 20 1483.81 1464.27 1444.79 1425.22 1405.62 1386.37 C/kg·m−3 = 60 1484.21 1464.71 1445.19 1425.61 1406.17 1386.81 C/kg·m−3 = 100 1483.94 1464.42 1444.76 1425.18 1405.68 1386.26

nD 1.43029 1.42805 1.42577 1.42349 1.42122 1.41891 1.43030 1.42808 1.42580 1.42353 1.42126 1.41894 1.43035 1.42814 1.42589 1.42365 1.42137 1.41904

C/kg·m−3 is the specific concentration of AC in the DMF solvent. Standard uncertainties u are u(T) = 0.001 K for ρ and c; u(T) = 0.01 K for nD and the combined expanded uncertainties Uc are Uc(ρ) = 0.01 kg·m−3, Uc(c) = 0.05 m·s−1; (level of confidence = 0.95, k = 2) and Uc(nD) = 0.00001. a

Table 4. Experimental Values of the Density ρ, Ultrasound Speed c and Refractive Index at Various Temperatures T and Specific Concentration C of (xGnP), for the System xGnP + DMFa T/K

ρ/kg·m−3

c/m·s−1

ρ/kg·m−3

nD

−3

293.15 298.15 303.15 308.15 313.15 318.15

949.81 945.02 940.25 935.46 930.67 925.89

293.15 298.15 303.15 308.15 313.15 318.15

950.37 945.60 940.84 935.98 931.28 926.47

293.15 298.15 303.15 308.15 313.15 318.15

950.48 945.77 940.98 936.23 931.44 926.61

C/kg·m = 0 1483.36 1463.76 1444.15 1424.58 1405.10 1385.74 C/kg·m−3 = 40 1484.47 1464.94 1445.46 1425.74 1406.23 1386.86 C/kg·m−3 = 80 1483.59 1464.57 1444.96 1425.47 1405.98 1386.64

c/m·s−1

nD

−3

1.43035 1.42805 1.42576 1.42347 1.42120 1.41887

950.16 945.37 940.62 935.81 931.01 926.23

1.43021 1.42765 1.42557 1.42280 1.42065 1.41826

950.49 945.78 941.01 936.20 931.40 926.62

1.43006 1.42694 1.42438 1.42195 1.41912 1.41690

950.43 945.69 940.88 936.08 931.32 926.55

C/kg·m = 20 1484.27 1464.68 1445.04 1425.46 1405.87 1386.55 C/kg·m−3 = 60 1484.29 1464.90 1445.33 1425.81 1406.34 1386.97 C/kg·m−3 = 100 1482.78 1463.62 1444.01 1424.54 1405.12 1385.65

1.42994 1.42776 1.42595 1.42374 1.42139 1.41897 1.42812 1.42628 1.42366 1.42176 1.41896 1.41650 1.42771 1.42581 1.42358 1.42150 1.41879 1.41738

C/kg·m−3 is the specific concentration of AC in the DMF solvent. Standard uncertainties u are u(T) = 0.001 K for ρ and c; u(T) = 0.01 K for nD and the combined expanded uncertainties Uc are Uc(ρ) = 0.01 kg·m−3, Uc(c) = 0.1 m·s−1; (level of confidence = 0.95, k = 2) and Uc(nD) = 0.00001. a

■

The relaxation strength (r) was calculated using the following equation:23,27−30 c2 r=1− 2 cct

RESULTS AND DISCUSSIONS

Prior to the experiments, dispersed xGnP was characterized via scanning electron microscopy (SEM) and Fourier infrared spectroscopy (FTIR). As shown in Figures 1 and 2, the SEM film is densely packed, which confers conductive properties to it. Most of the nanoplatelets

(5)

where c is the ultrasound speed in the experimental solution, and cct is a constant with a value of 1600 m·s−1.29 1215



Article

Figure 5. Comparative representation of the ultrasound speed of binary AC + DMF and xGnP + DMF systems versus concentration of solute at various temperatures, T/K: ⧫, 293.15; ■, 298.15; ▲, 303.15; ×, 308.15; ∗, 313.15; ●, 318.15 for AC; ◊, 293.15; □, 298.15; Δ, 303.15; +, 308.15; boxed ×, 313.15; ○, 318.15 for xGnP; , polynomial correlated values.

Figure 4. Comparative representation of the density of binary AC + DMF and xGnP + DMF systems versus concentration of solute at various temperatures, T/K: ⧫, 293.15; ■, 298.15; ▲, 303.15; ×, 308.15; ∗, 313.15; ●, 318.15 for AC; ◊, 293.15; □, 298.15; Δ, 303.15; +, 308.15; boxed ×, 313.15; ○, 318.15 for xGnP; , polynomial correlated values.

laid flat on the surface of the film; however, some of the platelets stuck out from the surface of the material. Multilayer structures of xGnP edges were observed. Figures 1 and 2 show that the xGnP surfaces were approximately 10 nanometers in width and they were irregular and porous in nature. SEM micrographs indicated that the graphene nanoplatelets presented a curled morphology. The graphene sheets overlapped, which was consistent with the results described in the literature.30 As suggested by other authors, FTIR analysis31 can be useful for xGnP characterization.32 Figure 3 shows several significant bands indicating the presence of acidic functional groups, including carbonyl groups (1400 cm−1), carboxyl groups (1650 cm−1), and hydroxyl groups (3500 cm−1), were observed on the surface of xGnP. These functional groups are produced on the internal and external surface of xGnP, which increases the surface polarity and alters the surface charges. The peak at 3413 cm−1 was attributed to O−H stretching vibrations of structural O−H groups. The peak at 1626 cm−1 is assigned to CC skeletal vibrations of unoxidized domains.33,34 The presence of carboxyl groups was detected at (1735 and 1053) cm−1. The peak at 1543 cm−1 in both spectra reflected the skeletal vibrations of graphene sheets. The thermophysical properties of pure DMF products were verified by measuring the density (ρ), ultrasound speed (c), and refractive index (nD). Table 2 presents the experimental results obtained and relative deviation, (ΔY) between the measured data in this paper (Y) and literature values.30−32,35−41 The relative percentage deviation is calculated as follows: yexpt − ylit Δy = 100 ylit (6)

Figure 6. Comparative representation of the refractive indices of binary AC−DMF and xGnP−DMF systems versus concentration of solute at various temperatures, T/K: ⧫, 293.15; ■, 298.15; ▲, 303.15; x, 308.15; ∗, 313.15; ●, 318.15 for AC; ◊, 293.15; □, 298.15; Δ, 303.15; +, 308.15; boxed ×, 313.15; ○, 318.15 for xGnP; , smoothed line.

where yexpt and ylit. are the values of the experimental data and that available in literature, respectively. The relative deviations were calculated for the density values in the range between (−1.31 and 0.45) %, on ultrasound speed values ranging between (−1.11 and 5.80) %, and on refractive index values ranging between (−0.63 and 0.23) % for pure DMF solvent at temperatures from (293.15 to 318.15) K. 1216



Article

exfoliated graphite nanoplatelets and activated carbon. Adsorbed molecules of DMF may form two hydrogen bonds on the adsorption centers. The layers of graphene sheets are covered by a layer of hydrogen atoms; thus, DMF molecules interact with the nonoxidized carbon surface, depending on the degree of dispersion of AC and xGnP. The dependence of the ultrasound speed on the concentration of (AC) + DMF and (xGnP) + DMF is presented in Figure 5, along with the correlated values. As shown in Figure 5, the ultrasound speed values of the binary (AC or xGnP) + DMF system decrease by increasing the temperature at the same the concentration of the solute for

These differences in relative deviations could be attributed to the purity of solvent, but especially, to the different experimental methods used. Nevertheless, a good agreement between our results and those reported by Shukla et al.36 for density at (303.15 and 308.15) K and refractive index at 313.15 K, respectively, and Roy et al.38 for ultrasound speed at 298.15 K was observed. The experimental data of densities (ρ), ultrasound speed (c), and refractive indices (nD) as a function of specific concentration of active carbon (AC) in N,N-dimethylformamide mixtures at various temperatures between (293.15 to 318.15) K are shown in Table 3. Also, Table 4 displayed experimental results for the same thermodynamic properties measured as a function of specific concentration of exfoliated graphite nanoplatelets (xGnP) in N,N-dimethylformamide mixtures at the same temperatures. AC and xGnP are miscible with high dielectric liquids; thus, these materials are completely miscible with DMF, a high dielectric solvent. The density, ultrasound speed, and refractive index values as a function of specific concentration of active carbon (AC) and exfoliated graphite nanoplatelets (xGnP) are shown in Figures 4, 5, and 6, respectively, by comparison between both binary (AC) + DMF and (xGnP) + DMF systems, along with polynomial correlated values (ρ, c). The specific concentration dependence on density and on ultrasound speed obtained in the both systems was correlated by a polynomial type equation:

Table 5. Calculated Values of the Acoustic Impedance Z, Adiabatic Compressibility kS, Space Filling Factor S, Specific Refraction rD, and Relaxation Strength r at Various Temperatures T, Specific Concentration C of (AC), for the System AC + DMF T K

n

F (Y ) =

∑ Ai C i − 1 i=1

Z

ks

105 kg·m−2·s−1 10−9·m2·N−1

293.15 298.15 303.15 308.15 313.15 318.15

14.08910 13.83287 13.57858 13.32640 13.07678 12.83037

293.15 298.15 303.15 308.15 313.15 318.15

14.09622 13.84076 13.58769 13.33560 13.08451 12.83865

293.15 298.15 303.15 308.15 313.15 318.15

14.10030 13.84540 13.59126 13.33929 13.08970 12.84302

293.15 298.15 303.15 308.15 313.15 318.15

14.10132 13.84643 13.59321 13.34116 13.09125 12.84469

293.15 298.15 303.15 308.15 313.15 318.15

14.09871 13.84385 13.59009 13.33807 13.08907 12.84165

293.15 298.15 303.15 308.15 313.15 318.15

14.09736 13.84206 13.58725 13.33481 13.08493 12.83745

(7)

where Y represents the properties measured in general (ρ, c) and C represents the specific concentration. Figure 4 presents the experimental and correlated density values as a function of the solute concentration (active carbon and exfoliated graphite nanoplatelets) of binary systems containing DMF. As can be observed, the density values of the binary (AC or xGnP) + DMF systems decrease by increasing the temperature at the same concentration of the solute. Also, the density values increase by increasing AC and xGnP concentrations, up to C = 60 kg·m−3 for (AC) + DMF and (xGnP) + DMF mixtures, respectively, then decrease slowly at the same temperature for both systems. For (xGnP) + DMF mixture, at temperature of 313.15 K, density values increase by increasing xGnP concentration up to C = 80 kg·m−3, then slowly decrease. The density values of (xGnP) + DMF mixture are higher than those obtained for the system (AC) + DMF, and the difference is more pronounced at higher temperatures (308.15 to 318.15) K. Slight differences were observed between the two systems, indicating that the solute changes the structure of DMF−xGnP more strongly than DMF−AC. These differences may be due to a different density of xGnP and AC themselves or to the number and position of oxygen-containing groups on the surface of xGnP, which improve the dispersion of the nanomaterial in DMF. These results support the conclusion that a hydrogen bonding interaction occurs between carbon-based nanomaterials and DMF, which increases the density by increasing the concentration of solute in the mixture. In previous studies42 the adsorption of polar molecules was assumed to occur at model centers, which exist on the graphene atomic layer. These groups are not evenly distributed over the carbon surface but are located at the junctions of faces on 1217

rD S

C/kg·m−3 = 0 47.8487 0.25851 49.3876 0.25730 50.9957 0.25610 52.6745 0.25489 54.4242 0.25369 56.2444 0.25247 C/kg·m−3 = 20 47.8100 0.25848 49.3422 0.25730 50.9389 0.25611 52.6145 0.25490 54.3719 0.25371 56.1826 0.25248 C/kg·m−3 = 40 47.7862 0.25848 49.3139 0.25730 50.9171 0.25611 52.5900 0.25490 54.3349 0.25371 56.1505 0.25249 C/kg·m−3 = 60 47.7799 0.25848 49.3072 0.25732 50.9041 0.25612 52.5782 0.25492 54.3227 0.25373 56.1383 0.25250 C/kg·m−3 = 80 47.7958 0.25848 49.3238 0.25731 50.9239 0.25612 52.5985 0.25493 54.3379 0.25374 56.1613 0.25252 C/kg·m−3 = 100 47.8020 0.25851 49.3325 0.25735 50.9416 0.25617 52.6191 0.25499 54.3679 0.25379 56.1923 0.25256

10−3·m3·kg−1

r

0.27217 0.27227 0.27237 0.27248 0.27259 0.27268

0.14049 0.16305 0.18532 0.20725 0.22879 0.24989

0.27208 0.27221 0.27232 0.27242 0.27255 0.27264

0.13996 0.16247 0.18460 0.20654 0.22822 0.24921

0.27207 0.27218 0.27230 0.27240 0.27252 0.27262

0.13960 0.16207 0.18433 0.20624 0.22778 0.24886

0.27206 0.27220 0.27230 0.27241 0.27254 0.27262

0.13950 0.16200 0.18415 0.20610 0.22761 0.24873

0.27207 0.27220 0.27232 0.27243 0.27257 0.27265

0.13976 0.16221 0.18441 0.20635 0.22779 0.24899

0.272118 0.272263 0.272386 0.272522 0.272635 0.272725

0.13981 0.16229 0.18464 0.20659 0.22815 0.24933



Article

Table 6. Calculated Values of the Acoustic Impedance Z, Adiabatic Compressibility kS, Space Filling Factor S, Specific Refraction rD, and Relaxation Strength r at Various Temperatures T, Specific Concentration C of (xGnP), for the System xGnP + DMF T K

Z

ks

rD

105 kg·m−2·s−1 10−9·m2·N−1

S

10−3·m3·kg−1

r

0.27217 0.27227 0.27237 0.27248 0.27259 0.27268

0.14049 0.16305 0.18532 0.20725 0.22879 0.24989

0.27208 0.27221 0.27232 0.27242 0.27255 0.27264

0.13996 0.16247 0.18460 0.20654 0.22822 0.24921

−3

293.15 298.15 303.15 308.15 313.15 318.15

14.08910 13.83287 13.57858 13.32640 13.07679 12.83037

293.15 298.15 303.15 308.15 313.15 318.15

14.09622 13.84076 13.33560 13.33663 13.08451 12.83865

293.15 298.15 303.15 308.15 313.15 318.15

14.10792 13.85244 13.59942 13.34467 13.09598 12.84887

293.15 298.15 303.15 308.15 313.15 318.15

14.10809 13.85467 13.60067 13.34840 13.09868 12.85198

293.15 298.15 303.15 308.15 313.15 318.15

14.10126 13.85151 13.59680 13.34566 13.09580 12.84880

293.15 298.15 303.15 308.15 313.15 318.15

14.09279 13.84123 13.58639 13.33489 13.08615 12.83874

C/kg·m = 0 47.8487 0.25851 49.3876 0.25730 50.9957 0.25610 52.6745 0.25489 54.4242 0.25369 56.2444 0.25247 C/kg·m−3 = 20 47.7726 0.25848 49.3073 0.25730 50.9125 0.25611 52.5901 0.25490 54.3445 0.25371 56.1580 0.25248 C/kg·m−3 = 40 47.7491 0.25844 49.2781 0.25709 50.8714 0.25600 52.5596 0.25454 54.3007 0.25341 56.1180 0.25214 C/kg·m−3 = 60 47.7544 0.25734 49.2715 0.25637 50.8713 0.25500 52.5423 0.25400 54.2853 0.25251 56.1000 0.25121 C/kg·m−3 = 80 47.8000 0.25835 49.2939 0.25672 50.8988 0.25537 52.5656 0.25409 54.3111 0.25260 56.1272 0.25142 C/kg·m−3 = 100 47.8549 0.25713 49.3625 0.25612 50.9713 0.25495 52.6424 0.25385 54.3844 0.25242 56.2114 0.25167

0.27193 0.27189 0.27210 0.27195 0.27210 0.27216

0.13920 0.16170 0.18385 0.20596 0.22755 0.24868

0.27074 0.27107 0.27100 0.27130 0.27111 0.27110

0.13941 0.16175 0.18399 0.20589 0.22742 0.24856

0.27181 0.27144 0.27139 0.27140 0.27119 0.27133

0.14022 0.16212 0.18441 0.20626 0.22782 0.24892

0.27054 0.27083 0.27097 0.27119 0.27104 0.27163

0.14116 0.16321 0.18548 0.20730 0.22876 0.24999

Figure 7. Comparative representation of the isentropic compressibility of binary AC−DMF and xGnP−DMF systems versus concentration of solute at various temperatures, T/K: ⧫, 293.15; ■, 298.15; ▲, 303.15; x, 308.15; ∗, 313.15; ●, 318.15 for AC; ◊, 293.15; □, 298.15; Δ, 303.15; +, 308.15; boxed ×, 313.15; ○, 318.15 for xGnP; , polynomial correlated values.

both systems. Also, ultrasound speed values increase by increasing AC concentration, up to C = 60 kg·m−3 for (AC) + DMF mixture, then decreases slowly at the same temperature. The ultrasound speed values increase by increasing xGnP concentration, up to C = 40 kg·m−3 for (xGnP) + DMF mixture, then decrease slowly at temperatures of (293.15, 298.15 and 303.15) K. The ultrasound speed varies at the other three temperatures, is similarly as binary (AC) + DMF system. The ultrasound speed values of (xGnP) + DMF mixture are higher than those obtained for the system (AC) + DMF up to approximately C = 60 kg·m−3, then are smaller. The difference between both systems is higher at lower temperatures of (293.15, 298.15, and 303.15) K and then it diminishes.

Figure 8. Comparative representation of the relaxation strength of binary AC−DMF and xGnP−DMF systems versus concentration of solute at various temperatures, T/K: ⧫, 293.15; ■, 298.15; ▲, 303.15; x, 308.15; ∗, 313.15; ●, 318.15 for AC; ◊, 293.15; □, 298.15; Δ, 303.15; +, 308.15; boxed ×, 313.15; ○, 318.15 for xGnP; , polynomial correlated values.

The behavior of ultrasound speed values by increasing concentration of the solute (AC and xGnP) indicates the presence 1218



Article

Table 7. Fitting Parameters Ai, Correlation Coefficient (R2) Obtained for Density ρ, Ultrasonic Speed c, Isentropic Compressibility kS, and Relaxation Strength r along with the Absolute Average Percentage Deviation (AAD %) for Binary (AC) in DMF Mixturesa T/K

C/kg·m−3

A1/kg·m−3

A2/kg0·m0

A3/kg−1·m

R2

AAD %

−0.0000758 −0.0000864 −0.0000908 −0.0000980 −0.0000900 −0.0000895 A3/kg2·m−7·s

0.97128 0.98035 0.97722 0.98384 0.98211 0.99684 R2

0.002 0.002 0.001 0.001 0.002 0.000 AAD %

−3

293.15 298.15 303.15 308.15 313.15 318.15 T/K 293.15 298.15 303.15 308.15 313.15 318.15 T/K

0−100 0−100 0−100 0−100 0−100 0−100 C/kg·m−3 0−100 0−100 0−100 0−100 0−100 0−100 C/kg·m−3

949.83 945.04 940.26 935.47 930.68 925.89 A1/kg0·m−1·s

ρ/kg·m 0.0091448 0.0103941 0.0108102 0.0115436 0.0106959 0.0105236 A2/kg·m−4·s

1483.38 1463.78 1444.19 1424.62 1405.08 1385.76 A1/10−9·kg0·m2·N−1

c/m·s−1 0.0256679 0.0289107 0.0324571 0.0329089 0.0350018 0.0357250 A2/10−9·kg−1·m5·N−1

−0.0002062 −0.0002312 −0.0002714 −0.0002772 −0.0002897 −0.0003098 A3/10−9·kg−2·m8·N−1

0.95231 0.96024 0.97558 0.97881 0.99513 0.99173 R2

0.003 0.003 0.003 0.003 0.001 0.002 AAD %

0.0000171 0.0000201 0.0000241 0.0000260 0.0000277 0.0000306 A3/kg−2·m−6

0.96192 0.96905 0.97627 0.98014 0.99739 0.99300 R2

0.007 0.008 0.008 0.007 0.003 0.004 AAD %

0.0000002 0.0000003 0.0000003 0.0000003 0.0000003 0.0000003

0.94871 0.96245 0.97602 0.97962 0.99467 0.99221

0.106 0.104 0.028 0.028 0.033 0.055

293.15 298.15 303.15 308.15 313.15 318.15 T/K

0−100 0−100 0−100 0−100 0−100 0−100 C/kg·m−3

47.8468 49.3900 50.9924 52.6712 54.4251 56.2430 A1/kg0·m0

kS/10−9·m2·N−1 −0.0021146 −0.0024914 −0.0028751 −0.0030803 −0.0033345 −0.0035362 A2/kg−1·m3

293.15 298.15 303.15 308.15 313.15 318.15

0−100 0−100 0−100 0−100 0−100 0−100

0.14047 0.16302 0.18528 0.20721 0.22881 0.24987

r −0.0000299 −0.0000323 −0.0000366 −0.0000368 −0.0000385 −0.0000388

Ai and R2 were obtained from eq 7. AAD %: AAD(Y) = 100/N∑ni |Yexpt − Ycalcd|/Yexpt, where N = 6 number of experimental data at each temperature.

a

The temperature dependence of refractive index obtained in both systems from this work was correlated using a polynomial equation of the first-order. As can be observed, the refractive index values of the binary (xGnP) + DMF system present a correlation with a correlation coefficient R2 of (0.996 to 1), very slightly lower than that one obtained from the correlation data of the (AC) + DMF system of R2 between (0.999 and 1). At a concentration of C = 80 kg·m−3, the value of the refractive index and the space-filling factor increased, suggesting that dispersion considerably improves for a specific concentration of xGnP in DMF. In comparison, variations of the refractive index were not detected with AC at this concentration. Thus, above a specific concentration of xGnP in solution, the degree of dispersion will not improve, and the optimized concentration in each solvent must be determined for future applications. The location of possible functional groups on the surface of xGnP plays a major role; however, the precise location is impossible to be determined with atomic resolution. Nevertheless, these groups are located at the edges of the xGnP sheets, and a specific concentration of xGnP in solution has a significant effect on the properties of the material. The amount of edges, planes, and defects and the crystallite size of xGnP induce major differences compared to the simpler carbon material (AC).

of solute−solvent interactions via hydrogen bonding, which can produce displacements of electrons and nuclei in the range of specific concentrations. These interactions are improved in xGnPDMF system. It slightly decreases with the temperature, much more for the (xGnP) + DMF system. As the temperature is increased, the thermal energy leads to the breaking of the bonds and it weakens the molecular forces which decrease the ultrasound speed. The dependence of the refractive indices on the concentration of the solute (active carbon and exfoliated graphite nanoplatelets) in DMF is presented in Figure 6. The refractive indices values of the binary (AC or xGnP) + DMF system decreased by increasing the temperature at the same concentration of the solute for both systems. Also, the refractive indices values increase by increasing AC concentration in the (AC) + DMF mixture at the same temperature. In the (xGnP) + DMF mixture, variation of the refractive index values at increase concentration of the xGnP is about constant up to C = 40 kg·m−3, then it decreases abruptly up to C = 60 kg·m−3. The difference between both systems are higher at the temperatures of (293.15, 298.15, and 303.15) K and lower at the other temperatures. The refractive index dependence on the temperature reported for exfoliated graphite nanoplatelets in DMF mixture is higher than in the (AC) + DMF system. 1219



Article

Table 8. Fitting Parameters Ai, Correlation Coefficient (R2) Obtained for Density ρ, Ultrasonic Speed c, Isentropic Compressibility kS, and Relaxation Strength r along with the Absolute Average Percentage Deviation (AAD %) for Binary (xGnP) in DMF Mixturesa T/K

C/kg·m−3

A1/kg·m−3

A2/kg0·m0

A3/kg−1·m3

R2

AAD %

−0.0001289 −0.0001385 −0.0001497 −0.0001351 −0.0001456 −0.0001358 A3/kg2·m−7·s

0.99742 0.99764 0.99705 0.9855 0.99876 0.99855 R2

0.001 0.001 0.001 0.003 0.001 0.001 AAD %

−3

293.15 298.15 303.15 308.15 313.15 318.15 T/K 293.15 298.15 303.15 308.15 313.15 318.15 T/K

0−100 0−100 0−100 0−100 0−100 0−100 C/kg·m−3 0−100 0−100 0−100 0−100 0−100 0−100 C/kg·m−3

949.82 945.02 940.25 935.45 930.66 925.88 A1/kg0·m−1·s

ρ/kg·m 0.0188898 0.0205454 0.0212661 0.0200689 0.0212180 0.0201930 A2/kg·m−4·s

1483.43 1463.79 1444.17 1424.59 1405.08 1385.72 A1/10−9·kg0·m2·N−1

c/m·s−1 0.0471500 0.0507482 0.0536500 0.0513304 0.0500125 0.0515071 A2/10−9·kg−1·m5·N−1

−0.0005446 −0.0005228 −0.0005518 −0.0005147 −0.0004924 −0.0005161 A3/10−9·kg−2·m8·N−1

0.98111 0.98962 0.99592 0.99076 0.99355 0.9853 R2

0.005 0.003 0.002 0.003 0.002 0.004 AAD %

0.0000416 0.0000425 0.0000470 0.0000456 0.0000466 0.0000501 A3/kg−2·m−6

0.98045 0.99316 0.99829 0.98773 0.99576 0.99111 R2

0.010 0.006 0.003 0.008 0.006 0.007 AAD %

0.0000006 0.0000006 0.0000006 0.0000006 0.0000005 0.0000005

0.95724 0.95754 0.97813 0.98047 0.95942 0.97263

0.088 0.100 0.046 0.088 0.061 0.085

293.15 298.15 303.15 308.15 313.15 318.15 T/K

0−100 0−100 0−100 0−100 0−100 0−100 C/kg·m−3

47.8436 49.3857 50.9945 52.6745 54.4263 56.2463 A1/kg0·m0

kS/10−9·m2·N−1 −0.0039888 −0.0044912 −0.0049336 −0.0049179 −0.0051075 −0.0054015 A2/kg−1·m3

293.15 298.15 303.15 308.15 313.15 318.15

0−100 0−100 0−100 0−100 0−100 0−100

0.14057 0.16317 0.18539 0.20733 0.22890 0.24998

r −0.0000546 −0.0000579 −0.0000603 −0.0000570 −0.0000549 −0.0000557

Ai and R2 were obtained from eq 7. AAD %: AAD(Y) = 100/N∑ni |Yexpt − Ycalcd|/Yexpt, where N = 6 number of experimental data at each temperature.

a

component molecules. It gradually increases by increasing the concentration of the solute up to 60 kg·m−3, then it decreases up to 100 kg·m−3. Isentropic compressibility is inversely proportional to the square of the ultrasonic speed, and its deviation can be attributed to the loss of dipolar association and differences in the size and shape of component molecules, which increases the speed and reduces the compressibility. This hypothesis can explain the observed dependences because graphite nanoplatelets have larger particle areas than active carbon. The nanostructure of the material was conferred by the nanometer thicknesses of the platelets. Dipole− dipole interactions or hydrogen-bonded complex formation between unlike molecules decreased the ultrasound speed and increased the compressibility. The dependence of the relaxation strength on the temperature of both systems did not show significant differences, as evidenced in Figure 8. In the (AC) + DMF binary mixture, the relaxation strength increased with an increase in the temperature and decreased with an increase in the concentration to C = 40 kg·m−3 and C = 60 kg·m−3 at T = (293.15, 298.15 and 303.15) K and T = (308.15, 313.15 and 318.15) K, respectively, then increased. As the concentration of DMF gradually increased, various interactions such as H-bonding, dipole−dipole, and dipole induced

On the basis of the measured properties, the derived thermophysical parameters as acoustic impedance Z (eq 1), isentropic compressibility kS (eq 2), space filling factor S (eq 3), specific refraction rD (eq 4), and relaxation strength r (eq 5) values as function of specific concentration fraction C of (AC) in DMF at various temperatures T were calculated and presented in Table 5. In the (AC) + DMF system, the isentropic compressibility decreases with increasing the concentration up to 60 kg·m−3, then increases for (80 and 100) kg·m−3, as observed in Table 5. Similarly, Table 6 shows the same thermophysical parameters, calculated for binary exfoliated graphite nanoplatelets (xGnP) in DMF mixtures under the same conditions. The isentropic compressibility kS and relaxation strength r values as a function of specific concentration have been plotted and shown in Figures 7 and 8 by comparative representations between binary (AC) + DMF and (xGnP) + DMF systems. The dependence of the isentropic compressibility on the concentration of the solute is presented in Figure 7. As shown in Figure 7, the isentropic compressibility of the two binary systems increases by increasing the temperature. The observed decrease up to about 60 kg·m−3 and increase in the isentropic compressibility as a function of the concentration in the (xGnP) + DMF binary mixture might indicate interactions between 1220


Journal of Chemical & Engineering Data dipole interactions occurred between molecules. The relaxation strength decreased in pure DMF, similar to the region where only H-bonding was present. In the (xGnP) + DMF binary mixture, the relaxation strength values decreased at a solute concentration of approximately 60 kg·m−3 at the same temperature and increased after by increasing the solute concentration, suggesting the predominance of molecular interactions. Also, at the same the concentration of the solute, the relaxation strength values in the binary (xGnP) + DMF system increased by increasing the temperature. In the (xGnP) + DMF mixture, the relaxation strength values are lower in comparison with those from (AC) + DMF up to C = 60−80 kg·m−3, then they increase. The differences of the relaxation strength values between both systems are higher at lower temperatures of (293.15, 298.15, and 303.15) K and then diminish. Correlations of ρ, c, kS, and r as a function of concentration (eq 7) along with the absolute average percentage deviation (AAD) were analyzed. The absolute average percentage deviation (AAD %) was determined using the following relationship: AAD(Y ) =

100 N

n

∑ i

CONCLUSIONS

■

AUTHOR INFORMATION

In the present investigation, the density, refractive index and ultrasound speed binary mixtures of activated carbon (AC) + DMF and exfoliated graphite nanoplatelets (xGnP) + DMF over the composition range from (0 to 100) kg·m−3 at temperatures between (293.15 and 318.15) K were measured. The results indicated that the studied parameters depend on the temperature and on the composition of the mixture, which is indicative of the presence of molecular interactions. A comparison between the two studied systems activated carbon (AC) + DMF and exfoliated graphite nanoplatelets (xGnP) + DMF show that the values of the absolute percentage deviations are comparable for the calculated thermodynamic properties. The absolute average percentage deviation (AAD %) for calculated thermodynamic properties of the binary (AC) + DMF system, as density, ultrasound speed, isentropic compressibility, and relaxation strength are less than (0.002, 0.003, 0.008, and 0.106) %, thus it can be concluded to be well correlated by this equation. For binary (xGnP) in DMF mixtures the absolute average percentage deviation (AAD %) for the same calculated thermodynamic parameters are less than (0.003, 0.005, 0.01, and 0.100) %, respectively. In the present research, differences between the behavior of (AC) and (xGnP) were observed; however, the behavior of these materials was not dependent on the number of layers of nanostructured carbon-based nanomaterials. Thus, graphite nanoplatelets can be fabricated and used instead of active carbon in a variety of applications, using considerably reduced amounts of nanomaterials. Unlike exfoliated graphite nanoplatelets, the number of edge-plane sites per gram of nanomaterial is not such an important parameter in active carbon.

Yexpt − Ycalc Yexpt

■

Article

(8)

where N is the number of experimental data points. The subscripts “expt” and “calc” represent the values of the experimental and calculated property, respectively. Fitting parameters Ai and absolute average percentage deviation results are reported in Table 7 for binary AC in DMF mixtures at all temperatures studied. The absolute average percentage deviation (AAD %) for calculated thermodynamic properties as density, ultrasonic speed, isentropic compressibility, and relaxation strength with eq 8 are less than (0.002, 0.003, 0.008, and 0.106) %, thus the properties of the binary (AC) + DMF system can be concluded to be well correlated by this equation. As can be observed, the density of (AC) + DMF mixture increases as the specific concentration of AC increases at the same temperature. Its density decreases as temperature increases at the same concentration of AC. Also, Table 8 summarized the calculated values of the Ai parameters, correlation coefficient (R2) obtained from eq 7, along with the absolute average percentage deviation (AAD %) by eq 8 for binary (xGnP) in DMF mixtures. The absolute average percentage deviation (AAD %) for calculated thermodynamic properties as density, ultrasound speed, isentropic compressibility, and relaxation strength based on eq 8 are less than (0.003, 0.005, 0.01, and 0.100) %, thus the properties of the binary (xGnP) + DMF system can be concluded to be well correlated by this equation. AAD absolute average percentage deviation values of the thermodynamic properties presented are of the same order of magnitude for binary (AC) + DMF and (xGnP) + DMF mixtures obtained at several temperatures. The isentropic compressibility (kS) increases by an increase in the temperature but it decreases by an increase of the composition. AAD of the calculated isentropic (adiabatic) compressibility was reliable within (0.003 and 0.01) % for both systems studied. As shown in Tables 7 and 8, and in Figures 4 to 8, the experimentally values were correlated with good accuracy based on polynomial equation (eq 7). Therefore, it is observed that the polynomial expression reproduces the main properties of the experimental data using three parameters to describe the mixtures.

Corresponding Author

*E-mail: sfl[email protected]. Funding

The present study was carried out within the research programme Chemical Thermodynamics of Ilie Murgulescu Institute of Physical Chemistry, which was financed by the Romanian Academy of Sciences. Support from the EU (ERDF) and Romanian Government, which allowed for the acquisition of the research infrastructure under POS-CCE O 2.2.1 project INFRANANOCHEM - Nr. 19/01.03.2009 is gratefully acknowledged. Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Ubarhande, S. S.; Burghate, A. S.; Berad, B. N.; Turak, J. D. Studies on refractive index of 1,3-diaryl carbamides in different percentage of binary liquid mixture. Rasayan J. Chem. 2011, 4, 585− ̅ 587. (2) Dreyer, D. R.; Ruoff, R. S.; Bielawski, C. W. From conception to realization: An historial account of graphene and some perspectives for its future. Angew. Chem., Int. Ed. 2010, 49, 9336−9344. (3) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric field effect in atomically thin carbon films. Science 2004, 306, 666−669. (4) Pumera, M. Graphene-based nanomaterials and their electrochemistry. Chem. Soc. Rev. 2010, 39, 4146−4157. (5) Goh, M. S.; Pumera, M. The electrochemical response of graphene sheets is independent of the number of layers from a single graphene sheet to multilayer stacked graphene platelets. Chem. Asian J. 2010, 5, 2355−2357.

1221



Article

(6) Zhu, Y.; Murali, S.; Cai, W.; Li, X.; Suk, J. W.; Potts, J. R.; Ruoff, R. S. Graphene and graphene oxide: synthesis, properties, and applications. Adv. Mater. 2010, 22, 3906−3924. (7) Shih, C. J.; Lin, S.; Strano, M. S.; Blankschtein, D. Understanding the stabilization of liquid-phase-exfoliated graphene in polar solvents: Molecular dynamics simulations and kinetic theory of colloid aggregation. J. Am. Chem. Soc. 2010, 132, 14638−14648. (8) Tamura, K.; Murakami, S.; Akagi, Y.; Fukumori, M.; Kawasaki, Y. Thermodynamic properties of binary mixtures: Hexamethylphosphoric triamide + a polar liquid at 25°C. J. Solution Chem. 1994, 23, 263−273. (9) Attri, P.; Madhusudhan, R. P; Venkatesu, P. Density and ultrasonic sound speed measurements for N,N-dimethylformamide with ionic liquids. Indian J. Chem. 2010, 49A, 736−742. (10) Chen, H.; Yada, R. Nanotechnologies in agriculture: New tools for sustainable development. Trends Food Sci. Technol. 2011, 22, 585− 594. (11) Emerich, D. F.; Tahnos, C. G. The pinpoint promise of nanoparticle-based drug delivery and molecular diagnosis. Biomol. Eng. 2006, 23, 171−184. (12) Farmen, L. Nanotechnology applications for clean water; William Andrew Inc.: New York, Norwich, 2009. (13) Wagner, W.; Pruss, A. The IAPWS Formulation 1995 for the thermodynamic properties of ordinary water substance for general and scientific use. J. Phys. Chem. Ref. Data. 2002, 31, 387−535. (14) Rayer, A. V.; Sumon, K. Z.; Henni, A.; Tontiwachwuthikul, P. Physicochemical properties of {1-methyl piperazine (1) + water (2)} system at T = (298.15 to 343.15) K and atmospheric pressure. J. Chem. Thermodyn. 2011, 43, 1897−1905. (15) Malham, I. B.; Turmine, M. Viscosities and refractive indices of binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate with water at 298 K. J. Chem. Thermodyn. 2008, 40, 718−723. (16) Riddick, J. A.; Bunger, W. B.; Sakano, T. K. Organic Solvents: Physical Properties and Methods of Purification, 4th ed.; Wiley: New York, 1986. (17) Evaluation of measurement data-guide to the expression of uncertainty in measurement. Report of Working Group 1 of the Joint Committee for Guides in Metrology, 2008. (18) Gonzalez, C.; Resa, J. M.; Lanz, J.; Iglesias, M. Intermolecular interactions in soybean oil + different organic solvents by ultrasonic velocity measurements. J. Food Eng. 2006, 77, 152−161. (19) Rowlinson, J. S.; Swinton, F. L. Liquid and Liquid Mixtures, 3rd ed.; Butterworths: London, 1982. (20) Spierings, G. A. C. M.; Melis, G. P. Refractive index and density of alkali lime borogermanosilicate glasses. J. Mater. Sci. 1981, 16, 1059−1062. (21) Gerecze, N. G. Ultrasonic studies in solution of poly(ethylene glycol). Acoustica 1977, 38, 51−57. (22) Pinotti, A.; Bevilacqua, A.; Zaritzky, N. Optimization of the flocculation state in a model system of a food emulsion waste using chitosan and polyelectrolyte. J. Food Eng. 1997, 32, 69−81. (23) Reddy, V. N.; Rao, K. S. W. K.; Subha, M. C. S.; Rao, K. C. Miscibility behaviour of dextrin/PVA blends in water at 35 °C. Intl. Conf. Adv. Polym. Technol., India 2010, Feb. 26−27, 356−368. (24) Naidu, S. V.; John, K.; Brahmam, P. V.; Challa, P. K. Ultrasonic studies of poly(vinyl acetate) solution in dimethylformamide. Int. J. Polym. Anal. Char. 2004, 9, 351−359. (25) Allen, R. D. A new equation relating index of refraction and specific gravity. Am. Mineral. 1956, 41, 245−257. (26) Larsen, E. S.; Berman, H. The microscopic determination of the nonopaque minerals. U.S. Geol. Survey Bull. 1934, 848, 30−32. (27) Baluja, S.; Vekariya, N.; Movaliya, J. Acoustical studies of some derivatives of 4-amino benzoic acid in 1, 4-dioxane and dimethyl formamide at 308.15 K. Iran. J. Chem. Chem. Eng., Res. Note. 2008, 27, 129−135. (28) Azhagiri, S.; Jayakumar, S.; Padmanaban, R.; Gunasekaran, S.; Srinivasan, S. Acoustic and thermodynamic properties of binary liquid mixtures of benzaldehyde in hexane and cyclohexane. J. Sol. Chem. 2009, 38, 441−448.

(29) Venkateswara, R. A.; Raman, G. K.; Varada, R. A. Acoustical parameters of polystyrene in binary mixture. Asian J. Chem. 1993, 5, 582−592. (30) Kovtyukhova, N. I.; Ollivier, P. J.; Martin, B. R.; Mallouk, T. E.; Chizhik, S. A.; Buzaneva, E. V.; Gorchinskiy, A. D. Layer-by-layer assembly of ultrathin composite films from micron-sized graphite oxide sheets and polycations. Chem. Mater. 1999, 11, 771−778. (31) Malard, L. M.; Pimenta, M. A.; Dresselhaus, G.; Dresselhaus, M. S. Raman spectroscopy in graphene. Phys. Reports 2009, 473, 51−87. (32) Ion, I.; Ion, A. C. Differential pulse voltammetric analysis of lead in vegetables using a surface amino-functionalized exfoliated graphite nanoplatelet chemically modified electrode. Sens. Actuators B 2012, 166−167, 842−847. (33) Pan, Y.; Wu, T.; Bao, H.; Li, L. Green fabrication of chitosan films reinforced with parallel aligned graphene oxide. Carbohydr. Polym. 2011, 83, 1908−1915. (34) Guo, H. L.; Wang, X. F.; Qian, Q. Y.; Wang, F. B.; Xia, X. H. A green approach to the synthesis of graphene nanosheets. ACS Nano 2009, 3, 2653−2659. (35) Regmi, S. Study and estimation of temperature dependent physical parameters of poly(vinylidene fluoride) and poly(1,4-butylene adipate) dissolved in N,N-dimethyl formamide. Kathmandu Univ. J. Sci. Eng. Tech. (KUSET) 2007, 1, 1−6. (36) Shukla, R. K.; Kumar, A.; Awasthi, N.; Srivastava, U.; Gangwar, V. S. Density, viscosity and refractive index of binary liquid mixtures at 293.15, 298.15, 303.15, 308.15 and 313.15 K. Exp. Therm. Fluid Sci. 2012, 37, 1−11. (37) El-Dossoki, F. I. Refractive index and density measurements for selected binary protic−protic, aprotic−aprotic, and aprotic−protic systems at temperatures from 298.15 to 308.15 K. J. Chin. Chem. Soc. 2007, 54, 1129−1137. (38) Roy, M. N.; Chanda, R.; Ghosh, G. Molar volumes, viscosity, and isentropic compressibility of some primary monoalkanols in aqueous N,N-dimethylformamide solutions. Russ. J. Phys. Chem. A. 2009, 83, 1331−1341. (39) García-Giménez, P.; Martınez-López, J. F.; Blanco, S. T.; Velasco, I.; Otín, S. Densities and isothermal compressibilities at pressures up to 20 MPa of the Systems N,N-dimethylformamide or N,N-dimethylacetamide + 1-chloroalkane. J. Chem. Eng. Data 2007, 52, 1693−1699. (40) Xu, L.; Lin, G.; Wang, X.; Lin, R. Densities and volumetric properties of 2-chloroethanol with N,N-dimethylformamide and water at different temperatures. J. Mol. Liq. 2006, 123, 130−133. (41) Baluja, S.; Shah, A. Acoustical studies of some derivatives of 4amino antipyrene in 1,4-dioxane and dimethylformamide at 318.15 K. Fluid Phase Equilib. 2004, 215, 55−59. (42) Tarasevich, Y. I.; Aksenenko, E. V. Interaction of water, methanol and benzene molecules with hydrophilic centres at a partially oxidised model graphite surface. Colloids Surf. A: Physicochem. Eng. Aspects 2003, 215, 285−291.

1222


Density, Refractive Index, and Ultrasound Speed in Mixtures of Active

Recommend Documents