Facile Ionic-Liquid-Assisted Synthesis of Nanopowder Ammonium

Article pubs.acs.org/IECR

Facile Ionic-Liquid-Assisted Synthesis of Nanopowder Ammonium Cadmium Phosphate with Highly Efficient Lead-Ion Removal from Glucose Solution Mingyu Xu, Ping Yin,* Wei Liu, Chunping Liu, Qinghua Tang, Rongjun Qu,* and Qiang Xu School of Chemistry and Materials Science, Ludong University, Yantai 264025, P. R. China S Supporting Information *

ABSTRACT: Heavy-metal uptake by plants growing in contaminated soil poses a potential harm to human health because of its transition into the food chain, and the removal of heavy metals from beverages has attracted considerable attention. In the present article, a facile ionic-liquid-assisted synthesis of nanopowder ammonium cadmium phosphate (NPACP) using an ionic liquid with a large anion, namely, 1-butyl-3-methyl imidazolium tetraphenylborate, [BMIM][BPh4], as a template is reported. This simple one-step method can suitably be scaled up for large-scale synthesis. The adsorption properties of the nanopowder were evaluated, NPACP was used as an adsorbent for lead ions from glucose solution, and it was found that NPACP has excellent adsorption properties for Pb(II). The feasibility of using NPACP for lead removal was confirmed, and the film diffusion mechanism was found to dominate the adsorption process of Pb(II) ions on NPACP. Its adsorption kinetics were modeled by a pseudo-second-order rate equation. Therefore, the present research work has provided an effective method for lead-ion removal from drinks, and NPACP can be used as a promising adsorbent with high efficiency for heavy-metal-ion uptake in the beverage industry.

■

INTRODUCTION In recent years, pollution of the environment with toxic heavy metals is spreading through the world along with industrial progress. These heavy-metal ions are nonbiodegradable and ubiquitous in the global environment, and they are derived from both natural sources and industrial activities. They can accumulate in the food chain, which poses a severe danger to human health.1−3 Therefore, heavy-metal pollution has attracted considerable attention. Heavy-metal uptake by plants growing in contaminated soil poses a potential harm. Williams et al. found that the concentration of Pb in lemon juice in Nigeria was beyond the local permissible levels.4 Many treatment processes, such as chemical precipitation, reverse osmosis, and adsorption, are currently used. Of these methods, adsorption is highly effective and economical and is a promising and widely applied method.5 Thus, it is very important to prepare effective adsorbents with strong affinities and high loading capacities for targeted heavy-metal ions. Wu et al. tried to utilize thiol-modified biomass to adsorb Pb(II) from glucose solution and provided a method for lead-ion removal from drinks.6 Recently, research on nanopowders has received considerable attention because of their interesting properties originating from quantum size effects and surface effects.7,8 Control over particle size, shape, and thus the dimensionality of nanoparticles is of great interest with respect to specific applications of materials such as nanodevices.9 Ionic-liquid-assisted nanomaterials have recently been developed.7,8 Ionic liquids (ILs) are a class of materials composed entirely of ions that are liquids below 373 K. ILs have many fascinating properties, including negligible vapor pressure, high stability, and large electrochemical windows. In addition, the physicochemical properties of ILs, such as viscosity, hydrophobicity, density, and © 2013 American Chemical Society

solubility, can be tuned by simply selecting different combinations of cations and anions, as well as attaching substituents to customize ILs for many specific demands. ILs are usually regarded as greener solvents and designer solvents because of their negligible vapor pressure, which avoids atmospheric pollution.10 Transition-metal phosphates have received increased attention during the past few decades because of their potential applications in the fields of catalysis, separation, absorption, and ion exchange. A large number of transition-metal phosphates have been developed, and divalent metal phosphates are of particular interest because they are soluble in acid solution and, therefore, are more easily crystallized than those containing tetravalent metal ions. Moreover, these divalent transition metals contain potentially active lone pairs, and their phosphate compounds can be used in ion exchange and catalysis. In contrast to zinc phosphate compounds, those involving cadmium phosphates are relatively few, although they exhibit structural features similar to those of zinc phosphates. So far, to our knowledge, there have been no reports on the synthesis of nanopowder ammonium cadmium phosphate in the presence of ILs and the related utilization in heavy-metal removal from beverages. The objective of the present work was to explore nanopowder ammonium cadmium phosphate with excellent adsorption properties using the ionic-liquid-assisted synthesis method. This method is facile and environmentally friendly, and this simple one-step method can be suitably scaled up for large-scale synthesis. The as-synthesized nanopowder ammoReceived: Revised: Accepted: Published: 14752

May 30, 2013 September 20, 2013 September 27, 2013 September 27, 2013 dx.doi.org/10.1021/ie401727w | Ind. Eng. Chem. Res. 2013, 52, 14752−14759

Industrial & Engineering Chemistry Research

Article

ground for another 30 min, and the reactants cadmium chloride and ammonium phosphate were mixed in a molar ration of 1.0:1.0. The resultant materials were washed with ethanol and distilled water and collected using the centrifugation method, and the product was dried in air. Yield: 95.7%. Computational Details. Density functional theory calculations of [BMIM][BPh4] were performed with the Gaussian 03 program12 using the B3LYP/6-31G(d) basis set to obtain the optimized molecular structure and vibrational wavenumbers. The frequencies for the required structure were evaluated at the B3LYP/6-31G(d) level to ascertain the nature of stationary points, and harmonic vibrational wavenumbers were calculated using the analytic second derivatives to confirm the convergence to the minimum of the potential surface. Pb(II) Adsorption Kinetics Experiments from Glucose Solution. Batch adsorption kinetics experiments were carried out by shaking 2.0 mg of the adsorbent NPACP with 10.0 mL of Pb(II) glucose solution [0.6 mmol/L Pb(II) ions in 5.0 mmol/L glucose solution] in a series of flasks at 15−35 °C and pH 5.0. The adsorption amount was calculated according to the equation

nium cadmium phosphate (NPACP) was characterized and utilized for heavy-metal removal from simulated juice beverage solution. Moreover, relevant adsorption kinetics experiments were carried out, and it was found that NPACP might be a promising and excellent adsorbent for lead-ion uptake in the beverage industry.

■

EXPERIMENTAL SECTION Materials and Methods. All reagents were of analytical grade and were used without further purification. IR spectra (KBr pellets) were recorded on a Magna-IR 550 (series II) Fourier transform spectrometer (Nicolet Instrument Corporation, Madison, WI). Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker AV500 spectrometer and calibrated with tetramethylsilane as an internal reference. Powder X-ray diffraction (XRD) data were obtained using a Rigaku MAX-2500VPC diffractometer with Cu Kα1 radiation (λ = 1.54056 Å). Porous structure parameters were characterized using an ASAP 2020 automatic physisorption analyzer (Micromeritics Instruments Corporation, Norcross, GA) by the Brunauer−Emmett−Teller (BET) and Barrett− Joyner−Halenda (BJH) methods through N2 adsorption at 77 K. The morphologies of the compounds were examined on a JSF5610LV scanning electron microscope (JEOL Co., Tokyo, Japan) and a JEOL JEM-1230 transmission electron microscope (JEOL Co., Tokyo, Japan). Inductively coupled plasma (ICP) analysis was carried out on a Jarrell-Ash Mark III 1100 spectrometer. The concentrations of Pb(II) solutions were determined on a GBC-932 atomic absorption spectrophotometer made in Australia that was equipped with an air− acetylene flame. Synthesis of an Ionic Liquid with a Large Anion, [BMIM][BPh4]. The ionic liquid [BMIM]Br was synthesized according to the methods outlined in ref 11, carried out through the microwave-assisted reaction of 1-methylimidazole with an excess of bromohexane. Charged into a round-bottom flask equipped with a reflux condenser and a thermometer were 0.02 mol of [BMIM]Br and 50 mL of water; a solution of 0.02 mol of sodium tetraphenylborate in 150 mL of water was added dropwise with stirring. Then, the reaction was allowed to proceed for 1 h at room temperature. The product [BMIM][BPh4] was washed with distilled water until there no bromide ion was present in the effluent. Yield: 93.1%. 1H NMR (500 MHz, CDCl3): δ (ppm) = 7.49 (s, 8H), 6.92 (m, 12H) [−BPh4], 5.91 (d, 2H), 5.05 (s, 1H), 2.73 (s, 3H), 3.14 (t, 2H), 1.30 (m, 2H), 1.10 (m, 2H), 0.86 (t, 3H). The IR wave numbers were at ν (cm−1) = 3435 (C−H stretching vibration of imidazole ring), 3143 (C−H stretching vibration of imidazole ring), 2956 (C−H stretching vibration of alkyl group on the side chain), 2935 (C−H stretching vibration of tetraphenylborate), 2852 (C−H stretching vibration of alkyl group on the side chain), 1647 (CC stretching vibration of benzene ring), 1571 (skeletal vibration of imidazole ring), 1430 (skeletal vibration of imidazole ring), 1168 (CC stretching vibration of benzene ring), 1075 (out-of-plane swing of C−H on benzene ring), 869 (B−C stretching vibration), 746 (C−H stretching vibration of CH2 in long chain), 708 (B−C stretching vibration) (Figure S1, Supporting Information). Synthesis of Nanopowder Ammonium Cadmium Phosphate, NPACP. In a typical procedure for the synthesis of NPACP, quantitative [BMIM][BPh4] and cadmium chloride were mixed and ground for 30 min at ambient temperature. Fed with ammonium phosphate, the mixture was continually

q=

(C i − Ce)V W

(1)

where q is the adsorption amount (mmol/g); CI and Ce are the initial and equilibrium concentrations, respectively, of Pb(II) ions (mmol/mL) in solution; V is the volume of the solution (mL); and W is the weight of NPACP (g). At different time intervals, the adsorbent was filtered, and the concentrations of Pb(II) in glucose solution were determined by atomic adsorption spectrophotometer (GBC-932A). The resulting kinetics plots for the adsorption of Pb(II) onto NPACP are provided in the next section of the article.

■

RESULTS AND DISCUSSION Ionic-Liquid-Assisted Synthesis and Characterization of NPACP. ILs are environmentally friendly, and they are increasingly finding applications in mateials secience. The potential application of ILs in the synthesis of metal architectures and metal compounds is particularly interesting because their electrostatic and coordination effects should influence, and might even facilitate, this synthesis.13 The physicochemical properties of ILs can be changed by selecting the appropriate combination of cations and anions. In particular, 1-alkyl-3-methylimidazolium-type ILs combined with specific anions are known to self-organize in a way that is adaptable to the fabrication of nanoparticles, and novel nanostructures can be developed by choosing suitable IL systems.14 In the present work, we synthesized an ionic liquid with a large anion, [BMIM][BPh4]. To design the ionic liquid, we theoretically calculated [BMIM][BPh4] at the B3LYP/631G(d) level in advance. In Figure 1, the optimized structure of [BMIM][BPh4] is displayed. The corresponding selected bond lengths, bond angles, and dihedral angles are presented in Table S1 (Supporting Information). The absence of an imaginary wavenumber in its calculated vibrational spectrum confirms that the structure deduced corresponds to the minimum energy. The IL [BMIM][BPh4] is a “green” organic salt and has the large anion. It has a tendency to self-assemble into ordered structures and, accordingly, can be used as a kind of template in the synthesis of NPACP. 14753

dx.doi.org/10.1021/ie401727w | Ind. Eng. Chem. Res. 2013, 52, 14752−14759


Article

mesoporousity was mainly due to interparicle porosity rather than intraparticle porosity. Figure 2c shows the energydispersive X-ray (EDX) spectrum, it is obvious that there are peaks for Cd, P, O, and N and the atomic ratio of P to Cd is 1.00:1.05, which very close to the anticipated 1:1 stoichiometric composition. The ICP results for the studied sample show that cadmium made up 46.21%, which is also consistent with the chemical composition of ammonium cadmium phosphate (46.17%). Figure 3 shows the powder XRD pattern of

Figure 1. Optimized structure of the ionic liquid with a large anion, [BMIM][BPh4].

The size and morphology of the as-synthesized NPACP were examined by TEM and SEM analyses. The TEM image of NPACP demonstrates that the product consisted of nanoplates with radii ranging from ca. 10 to 40 nm (Figure 2a), and the SEM image of NPACP indicates that the product aggregated to the level of the micrometer scale (Figure 2b). As seen from the TEM and SEM images, the particles were somewhat platelike in shape, and pores were observed throughout the particles, which was further confirmed by the N2 adsorption analysis and discussed later in this article. A disordered wormlike porous structure could clearly be observed, and the accessible pores were connected at random, lacking discernible long-range order in the pore arrangement among the nanopowder particles. During the air-drying process, the particles accumulated together to form porous aggregates. This indicates that the

Figure 3. XRD pattern of NPACP.

NPACP, and the diffraction peaks correspond well in position with the standard pattern (JCPDS No. 33-0048), indicating the phase purity of the as-synthesized sample. The strong peaks (2θ) included 10.06°, 31.04°, 25.54°, 38.63°, 20.36°, and 23.46°, whose d values were 8.79, 2.88, 3.48, 2.33, 4.36, and 3.79 Å, respectively. These peaks correspond to the (010), (121), (111), (131), (011), and (101) crystal planes, respectively. The nitrogen adsorption−desorption isotherm and the corresponding pore size distribution curves of NPACP are

Figure 2. (a) TEM image, (b) SEM image, and (c) EDX spectrum of NPACP. 14754



Article

liquid. During the nucleation process, [BMIM][BPh4] provided a multitude of nucleation centers for cadmium phosphate. The continuing condensation led to the formation of ammonium cadmium phosphate nanoparticles, and interparticle pores were formed by the agglomeration of ammonium cadmium phosphate nanoparticles. When the templates were washed out, mesoporous cadmium phosphate was produced, as confirmed by the BJH model. The sidewalls of the ammonium cadmium phosphate nanoplates with a round shape are more prone to intercept cadmium phosphate than the {010} faces. Subsequently, based on the diffusion-limited-aggregation (DLA) model, ammonium cadmium phosphate crystals assembled in a round plate. As viewed from the chemical kinetics angle, the above-mentioned reactive procedures using ILs as a template at room temperature rather than in an aqueous state or at high temperature could be advantageous to the product being prevented from further growth and being kept at the nanoscale. Kinetics of Pb(II) Adsorption from Glucose Solution onto NPACP. Heavy-metal pollution has attracted considerable attention, and heavy-metal uptake by plants growing in contaminated soil poses a potential harm. Therefore, it is very important to develop effective adsorbents with strong affinities and high loading capacities for toxic heavy-metal ions from foods and beverages. In the present work, the ionic liquid [BMIM][BPh4] was used as the template to prepare nanopowder ammonium cadmium phosphate (NPACP) that was utilized as an adsorbent for Pb(II) from simulated juice beverage solution. The as-synthesized sample is a layered cadmium phosphate material, in which the structure is a (CdPO4−) polyanion framework with ammonium ions and water species residing in the space between the layers and cadmium ions coordinated by the phosphate oxygen atoms. The cadmium ions are located in the frame structure of NPACP, and they cannot leach out of the adsorbent material. Moreover, ICP and atomic absorption spectrometry detection did not find cadmium ions in the simulated beverage solution after the adsorption process. Therefore, it is safe to use NPACP to remove lead ions from beverage solutions. The adsorption kinetics that describes the solute uptake rate governing the contact time of adsorption is an important characteristics defining the efficiency of adsorption.16 The adsorption kinetics of NPACP for Pb(II) ions from glucose solution was investigated at different temperatures, and Figure 6a shows the adsorption kinetics of NPACP for Pb(II) from simulated juice beverage solution at 15−35 °C. It is clear that the as-synthesized NPACP had a high adsorption rate: It could reach the adsorption saturation capacity within 1 h, which is shorter than the time required to reach adsorption equilibrium on silica-gel-supported hyperbranched poly(amidoamine) (PAMAM) dendrimers (SiO2-G0−SiO2-G4.0).3 It is obvious

displayed in Figure 4. It can be seen that the nitrogen adsorption−desorption isotherm should be classified as type IV

Figure 4. N2 adsorption−desorption isotherm and corresponding pore size (inset) of NPACP.

according to the IUPAC classification, and it has a hysteresis loop that is representative of mesopores. The volume adsorbed increased steeply at a medium relative pressure (p/p0), indicating capillary condensation of nitrogen within the mesoporous structure. The inset of Figure 4b displays the BJH desorption pore size distributions of NPACP. As illustrated in the figure, the pore size distribution curve shows a wide range, with pores around 40 nm being dominant for the product. The porous structure parameters of the sample were derived from the nitrogen adsorption data, and the values of BET surface area, BJH desorption average pore radius, and BJH desorption cumulative volume of pores for NPACP were found to be 31.1 m2/g, 40.85 nm, and 0.16 cm3/g, respectively. The loop at a relative pressure of p/p0 = 0.9 represents ink-bottleshaped pores. On the basis of these results, a possible synthesis mechanism of round-plate-shaped nanocrystals cadmium phosphate is schematically presented in Figure 5, assuming that [BMIM][BPh4] functioned as a template. Templates are employed for controlling the production of materials with specific structures and desired properties. In the synthesis, it was found that [BMIM][BPh4] played a crucial role in the final morphology of the products. It is known that anion adsorption on the surface of metal salt crystals influences their growth and, consequently, their shape.15 The large [BPh4]− anions could attract cadmium cations driven by the Coulomb force. After ammonium phosphate was added to the reaction system, cadmium phosphate crystal nuclei formed around the ionic

Figure 5. Schematic view of the formation of NPACP with an ionic liquid with a large anion, namely, [BMIM][BPh4], as the template. 14755



Article

Figure 6. (a) Kinetic adsorption of Pb(II) onto NPACP at different glucose solution temperatures. (b) Pseudo-first-order kinetic model of NPACP for Pb(II). (c) Pseudo-second-order kinetic plots for the adsorption of Pb(II) onto NPACP at various glucose solution temperatures. (d) Bt vs time plots at different solution temperatures for Pb(II) reported onto NPACP from glucose solution.

that the adsorption was rapid in the first 20 min and then slowed considerably. The reason perhaps is that, in the initial fast adsorption step, Pb(II) ions might enter the accessible pore sites easily. The increased number of active sites available at the initial stage might lead to an increased concentration gradient between adsorbate in solution and adsorbate in the adsorbent.17 Then, slower adsorption would follow as the number of available adsorption sites gradually decreases.18 Figure 6a also displays the effect of temperature on the adsorption of Pb(II) by NPACP, demonstrating that temperature generally has a positive effect on the adsorption capacity. The adsorption capacity of Pb(II) on NPACP exhibited some changes at different temperatures, being 5.59, 6.21, and 6.68 mmol/g at 15, 25, and 35 °C, respectively. The saturation capacity also increased with increasing temperature over the range of 15−35 °C. As the adsorption kinetic data show, the adsorption process could be carried out perfectly with smaller reactor volumes, ensuring efficiency and economy at the desired processing temperature. Under the same experimental conditions, it was found that the adsorption capacity of NPACP was higher than that of calcium phosphate (Figure S2, Supporting Information). Moreover, as we compared the adsorption capacity of different types of adsorbents used for lead ions adsorption in the literature, it was clear that the adsorption capacity of NPACP

was significantly higher than those of other reported adsorbents (Table 1).19−22 Adsorption kinetics parameters, which can control the residence time of the adsorbate uptake at the solution−solid interface and provide valuable insight into water-treatment process design, are of great importance for the application of Table 1. Adsorption Capacities of Different Adsorbents

adsorbent

14756

ref

NPACP

present work

thiol-functionalized cotton thiol-functionalized wood sawdust thiol-functionalized buckwheat hull N-methylimidazole modified palygorskite Typha angustifolia biomass modified by SOCl2activated EDTA low-silica nanozeolite X Ni-doped bamboo charcoal

6

adsorption capacity (mg/g)

19 20

1158.25 (15 °C) 1286.71 (25 °C) 1384.10 (35 °C) 28.67 43.14 44.84 714.29 263.9

21 22

909.09 142.7



Article

Table 2. Kinetic Parameters for the Adsorption of Pb(II) onto NPACP from Glucose Solution pseudo-first-order kinetics

pseudo-second-order kinetics

T (°C)

qe(exp) (mg/g)

K1 (min−1)

qe(cal) (mg/g)

R12

K2 × 10−3 (g/mg·min)

qe(cal) (mg/g)

R22

15 25 35

1157.06 1284.67 1383.43

0.02539 0.02421 0.02494

404.58 479.11 523.82

0.7713 0.7778 0.7771

0.2415 0.1951 0.1811

1172.82 1302.80 1404.26

0.9996 0.9995 0.9997

adsorbents. Both pseudo-first-order23 and pseudo-secondorder24 equations were used to express the adsorption process of NPACP for Pb(II), as expressed by eqs 2 and 3, respectively ln(qe − qt ) = ln qe − k1t t 1 t = + qt qe k 2qe 2

assumed to be spherical. F is the fractional attainment of equilibrium at time t, and it is obtained by the expression q F= t q0 (7)

(2)

where qt is the amount of adsorbate taken up at time t and q0 is the maximum equilibrium uptake. Values of Bt can be obtained from the corresponding values of F. Bt values for each given F value are plotted in Figure 6d, and the fitting results are listed in Table 3. Plots of Bt versus

(3)

where qe is the amount of metal adsorbed at equilibrium per unit weight of adsorbent (mg/g); qt is the amount of metal ion adsorbed at time t (mg/g); and k1 (min−1) and k2 (g/mg·min) are the rate constants of pseudo-first-order and pseudo-secondorder adsorption, respectively. The experimental and calculated qe, k1, k2, and regression coefficient (R2) values are presented in Table 2. Pseudo-first-order and pseudo-second-order kinetic plots and kinetic parameters for the sorption of Pb(II) onto NPACP at different temperatures are shown in panels b and c, respectively, of Figure 6. As can be seen from Table 2, The obtained regression coefficient values of the pseudo-secondorder model (>0.9995) were better than those of the pseudofirst-order model (0.7713−0.7778), suggesting that the pseudosecond-order model is more suitable for describing the adsorption kinetics of NPACP for Pb(II). Therefore, the adsorption kinetics can be well approximated more favorably by a pseudo-second-order kinetic model for the adsorption of Pb(II) onto NPACP from glucose solution. In general, the adsorption process of metal ions onto porous media can be described by the following three steps: (1) mass transfer from the fluid phase to the particle surface across the boundary layer (film diffusion), (2) diffusion within the porous particle (intraparticle diffusion), and (3) adsorption onto the solid surface.25 The third stage is generally recognized as rapid and is not supposed to the rate-controlling step in the adsorption. To determine the rate-controlling step and adsorption mechanism and to distinguish film-diffusion- from particle-diffusion-controlled adsorption, kinetics experimental results are usually analyzed by thr Boyd equation26 and thr Reichenberg equation.27 The relevant equations are 6 F=1− 2 π

∞

∑ n−1

2 2 1 ⎛ −Di tπ n ⎞ ⎜ ⎟ n2 ⎝ r0 2 ⎠

Table 3. Bt versus Time Linear Equations and R2 Coefficients for NPACP Adsorbent T (°C)

linear equation

R2

15 25 35

Bt = 0.02181t + 0.9127 Bt = 0.01858t + 0.8617 Bt = 0.01926t + 0.8519

0.9647 0.9573 0.9073

time of Pb(II) adsorption onto NPACP from simulated juice beverage solution at 15−35 °C were used to distinguish between film-diffusion- and particle-diffusion-controlled adsorption. If the plots are straight lines passing through the origin, then the adsorption process should be dominated by particle-diffusion mechanism; otherwise, it might be governed by film diffusion. As can be seen in Figure 6d, all of the lines of the Bt versus time plots did not pass through the origin in the cases studied, indicating that film diffusion, not particle diffusion, dominated the adsorption process of Pb(II) onto NPACP from glucose solution. Determination of the Thermodynamic Parameters for Pb(II) Adsorption from Glucose Solution and the Recycling Properties of NPACP. The thermodynamic parameters of the adsorption process, such as the free energy of adsorption ΔG, enthalpy of adsorption ΔH, and entropy of adsorption ΔS, were determined using the equations28,29 Kc =

CAe Ce

log Kc =

(4)

(8)

ΔS ΔH − 2.303R 2.303RT

ΔG = −RT ln Kc

or F=1−

6 π2

∞

∑ n−1

1 exp( −n2Bt ) n2

π 2Di r0 2

(10)

where Ce and CAe are the equilibrium concentration in solution (mg/L) and the solid-phase concentration at equilibrium (mg/ L), respectively. Kc is the partition coefficient at each temperature. R is the gas constant (8.314 J/mol·K), and T is the temperature in kelvin. From the slope and y intercept of the linear plot of ln Kc versus 1/T (shown in Figure S3, Supporting Information), the changes of enthalpy and entropy could be obtained. The thermodynamic parameters are listed in Table 4. The positive values of ΔH (8.44 kJ·mol−1) indicate that the adsorption of Pb(II) ions onto NPACP from glucose solution is endothermic. This result is consistent with the above-

(5)

and B=

(9)

= time constant (6)

where n is an integer that defines the infinite-series solution; Di is the effective diffusion coefficient of metal ions in the adsorbent phase; and r0 is the radius of the adsorbent particle, 14757



■

Table 4. Thermodynamic Parameters of NPACP for Pb(II) Adsorption from Glucose Solution T (K)

ΔG (kJ/mol)

ΔH (kJ/mol)

ΔS (J/K·mol)

288 298 308

−4.09 −4.38 −4.96

8.44

43.37

Article

ASSOCIATED CONTENT

S Supporting Information *

Figures S1−S4 and Table S1 as mentioned in the text. This material is available free of charge via the Internet at http:// pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Authors

*Tel.: + 86-535-6696162. Fax: + 86-535-6697667. E-mail: [email protected]. *E-mail: [email protected].

mentioned case that the adsorption capacities of Pb(II) ions increased with increasing temperature. The negative value of ΔG (−4.09 kJ·mol−1 at 15 °C, −4.38 kJ·mol−1 at 25 °C, and −4.96 kJ·mol−1 at 35 °C) for Pb(II) adsorption onto NPACP indicate the feasibility of the adsorption process and the spontaneous nature of the adsorption of Pb(II) onto the surface of NPACP. In addition, the values of ΔG became more negative with increasing temperature, which indicates that the adsorption process was more favorable at higher temperatures. The positive value of ΔS (43.37 J· K−1·mol−1) resulted from the increased randomness due to the adsorption of Pb(II) ions, which suggests good affinity of lead ions toward the adsorbent NPACP and increased randomness at the solid−solution interface during the fixation of Pb(II) ions on the active sites of the adsorbent NPACP. The XRD patterns of NPACP before and after Pb(II) adsorption are shown in Figure S4 (Supporting Information). As seen in this figure, some characteristic peaks of NPACP became diminished, and some new peaks appeared, indicating that the treatment of the glucose solution containing Pb(II) ions with NPACP allowed lead ions to be adsorbed in the interior pores of NPACP and form complexes. Therefore, Pb(II) adsorption onto NPACP was mainly driven through electrostatic attraction, ion exchange, and inner-pore complex formation. In the present investigation, studies on the repeated availability of NPACP adsorbent were conducted to illustrate its stability and potential recovery. Lead-ion-loaded NPACP samples were treated with KCl-saturated solution to remove the lead ions, leached, and then subjected to another round of metal-ion adsorption testing. The results for lead-ion adsorption using the regenerated adsorbents showed that a slight decrease of the adsorption efficiency was observed in the second use, and the samples retained 88.68% of their lead removal capacities after three adsorption−desorption processes. Therefore, the high adsorption capacity and good reproducibility give NPACP significant potential for removing lead ions from beverage solutions using the adsorption method.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The support provided by the National Natural Science Foundation of China (51102127, 51073075, 51373074, 51302127, and 51143006), Natural Science Foundation of Shandong Province (Nos. 2009ZRB01463, 2008BS04011, and Y2007B19), Nature Science Foundation of Ludong University (Nos. 08-CXA001, 032912, 042920, and LY20072902), Educational Project for Postgraduate of Ludong University (Nos. YD05001 and Ycx0612), and Program for Scientific Research Innovation Team in Colleges and Universities of Shandong Province is greatly appreciated.

■

REFERENCES

(1) Mouflih, M.; Aklil, A.; Sebti, S. Removal of lead from aqueous solutions by activated phosphate. J. Hazard. Mater. 2005, 119, 183− 188. (2) Stephen, B.; Inbaraj, J.; Wang, S.; Lu, J. F.; Siao, F. Y.; Chen, B. H. Adsorption of Toxic Mercury(II) by an Extracellular Biopolymer Poly(γ-glutamic acid). Bioresour. Technol. 2009, 100, 200−207. (3) Niu, Y. Z.; Qu, R. J.; Sun, C. M.; Wang, C. H.; Chen, H.; Ji, C. N.; Zhang, Y.; Shao, X.; Bu, F. L. Adsorption of Pb(II) from aqueous solution by silica-gel supported hyperbranched polyamidoamine dendrimers. J. Hazard. Mater. 2013, 244−245, 276−286. (4) Williams, A. B.; Ayejuyo, O. O.; Ogunyale, A. F. Trace metal levels in fruit juices and carbonated beverages in Nigeria. Environ. Monit. Assess. 2009, 156, 303−306. (5) Li, Y.; Di, Z.; Ding, J.; Wu, D.; Luan, Z.; Zhu, Y. Adsorption thermodynamic, kinetic and desorption studies of Pb2+ on carbon nanotubes. Water Res. 2005, 39, 605−609. (6) Wu, Z.; Cheng, Z.; Ma, W. Adsorption of Pb(II) from glucose solution on thiol-functionalized cellulosic biomass. Bioresour. Technol. 2012, 104, 807−809. (7) Zhai, Y. A.; Zhang, Q.; Liu, F. Q.; Gao, G. Synthesis of nanostructure rutile TiO2 in a carboxyl-containing ionic liquid. Mater. Lett. 2008, 62, 4563−4565. (8) Zhou, W.; He, W.; Zhang, X.; Yan, S.; Sun, X.; Tian, X.; Han, X. Biosynthesis of iron phosphate nanopowders. Powder Technol. 2009, 194, 106−108. (9) Kanthimathi, M.; Dhathathreyan, A.; Nair, B. U. Nanosized nickel oxide using bovine serum albumin as template. Mater. Lett. 2004, 58, 2914−2917. (10) Yan, H.; Wu, J.; Dai, G.; Zhong, A.; Chen, H.; Yang, J.; Han, D. Interaction mechanisms of ionic liquids [Cnmim]Br (n = 4, 6, 8, 10) with bovine serum albumin. J. Lumin. 2012, 132, 622−628. (11) Pal, A.; Kumar, H.; Kumar, B.; Sharma, P.; Kaur, K. Thermophysical properties of ionic liquid {1-butyl-3-methylimidazolium bromide [bmim][Br] in alkoxyalkanols + water} mixtures at different temperatures. J. Chem. Thermodyn. 2013, 57, 182−188. (12) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;

■

CONCLUSIONS In the present work, nanopowder ammonium cadmium phosphate (NPACP) has been successfully synthesized using the ionic liquid [BMIM][BPh4] as a template. [BMIM][BPh4] provides nucleation sites and induces growth of cadmium phosphate. Such a simple synthesis method could have potential applications in physics and chemistry. Moreover, it was found that NPACP has excellent absorption capacities for Pb(II) ions from glucose solution and that the adsorption equilibrium can be reached within 1 h by an adsorption process that follows a pseudo-second-order model with film diffusion as the rate-controlling step. Therefore, the results suggest that NPACP might be used as a promising adsorbent with high efficiency for lead-ion uptake in the beverage industry. 14758



Article

aqueous solutions onto L-lysine modified crosslinked chitosan resin. J. Hazard. Mater. 2007, 146, 39−50.

Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03; Gaussian, Inc.: Pittsburgh, PA, 2003. (13) Ren, L.; Meng, L.; Lu, Q.; Fei, Z.; Dyson, P. J. Fabrication of gold nano- and microstructures in ionic liquidsA remarkable anion effect. J. Colloid Interface Sci. 2008, 323, 260−266. (14) Li, X.; Gao, Y.; Yu, L.; Zheng, L. Template-free synthesis of CdS hollow nanospheres based on an ionic liquid assisted hydrothermal process and their application in photocatalysis. J. Solid State Chem. 2010, 183, 1423−1432. (15) Liu, X.; Liu, R.; Chen, S.; Liang, B. Hythothermal synthesis of CdSe hierarchical dendrites using ionic liquid as template. Mater. Lett. 2012, 66, 264−266. (16) Tuzen, M.; Sari, A.; Mendil, D.; Soylak, M. Biosorptive removal of mercury(II) from aqueous solution using lichen (Xanthoparmelia conspersa) biomass: Kinetic and equilibrium studies. J. Hazard. Mater. 2009, 169, 263−270. (17) Wang, Y.; Mu, Y.; Zhao, Q. B.; Yu, H. Q. Isotherms, kinetics and thermodynamics of dye biosorption by anaerobic sludge. Sep. Purif. Technol. 2006, 50, 1−7. (18) Singh, V.; Singh, S. K.; Maurya, S. Microwave induced poly(acrylic acid) modification of Cassia javanica seed gum for efficient Hg(II) removal from solution. Chem. Eng. J. 2010, 160, 129− 137. (19) Chang, Y.; Liu, H.; Zha, F.; Chen, H.; Ren, X.; Lei, Z. Adsorption of Pb(II) by N-methylimidazole modified palygorskite. Chem. Eng. J. 2011, 167, 183−189. (20) Liu, W.; Zeng, F.; Jiang, H.; Zhang, X. Adsorption of lead (Pb) from aqueous solution with Typha angustifolia biomass modified by SOCl2 activated EDTA. Chem. Eng. J. 2011, 170, 21−28. (21) Rasouli, M.; Yaghobi, N.; Hafezi, M.; Rasouli, M. Adsorption of divalent lead ions from aqueous solution using low silica nano-zeolite X. J. Ind. Eng. Chem. 2012, 18, 1970−1976. (22) Wang, Y.; Wang, X.; Wang, X.; Liu, M.; Wu, Z.; Yang, L.; Xia, S.; Zhao, J. Adsorption of Pb(II) from aqueous solution to Ni-doped bamboo charcoal. J. Ind. Eng. Chem. 2013, 19, 353−359. (23) Razvigorova, M.; Budinova, T.; Petrov, N.; Minkova, V. Purification of water by activated carbons from apricot stones, lignites and anthracite. Water Res. 1998, 32, 2315−2139. (24) Ho, Y. S.; McKay, G. Pseudo-second order model for sorption processes. Process. Biochem. 1999, 34, 451−465. (25) Wang, X. J.; Xu, X. M.; Liang, X.; Wang, Y.; Liu, M.; Wang, X.; Xia, S. Q.; Zhao, J. F.; Yin, D. Q.; Zhang, Y. L. Adsorption of copper(II) onto sewage sludge-derived materials via microwave irradiation. J. Hazard. Mater. 2011, 192, 1226−1233. (26) Boyd, G. E.; Adamson, A. W.; Myers, L. S. The exchange adsorption of ions from aqueous solutions by organic zeolites. II. Kinetics. J. Am. Chem. Soc. 1947, 69, 2836−2848. (27) Reichenberg, D. Properties of ion-exchange resins in relation to their structure. III. Kinetics of exchange. J. Am. Chem. Soc. 1953, 75, 589−597. (28) Anirudhan, T. S.; Radhakrishnan, P. G. Thermodynamics and kinetics of adsorption of Cu(II) from aqueous solutions onto a new cation exchanger derived from tamarind fruit shell. J. Chem. Thermodyn. 2008, 40, 702−709. (29) Fujiwara, K.; Ramesh, A.; Maki, T.; Hasegawa, H.; Ueda, K. Adsorption of platinum (IV), palladium (II) and gold (III) from 14759


Facile Ionic-Liquid-Assisted Synthesis of Nanopowder Ammonium

Recommend Documents