Pentachlorophenol Sorption in the Cetyltrimethylammonium Bromide

Aug 29, 2013 - Bromide/Bentonite One-Step Process in Single and Multiple Solute .... wastewater treatment process, due to their environmental toxicity...
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Pentachlorophenol Sorption in the Cetyltrimethylammonium Bromide/Bentonite One-Step Process in Single and Multiple Solute Systems Zhongjian Li, Min Yao, Jun Lin, Bin Yang, Xingwang Zhang, and Lecheng Lei* Key Laboratory of Biomass Chemical Engineering of Ministry of Education, Department of Chemical and Biological Engineering, Yuquan Campus, Zhejiang University, Hangzhou, Zhejiang 310027, China ABSTRACT: The selective sorption of pentachlorophenol (PCP) in a multiple solute system provides the possibility of using the cetyltrimethylammonium bromide (CTMAB)/bentonite one-step process as a promising technique for hydrophobic organics removal from wastewater. The PCP sorption mechanism, especially the effects of coexisting solutes, was studied. Compared to raw bentonite and conventional CTMAB modified organobentonite, the one-step process exhibited higher PCP removal efficiency. In a single solute system, the PCP sorption isotherm implied that the dominating sorption mechanism is a partition mechanism. The logarithms of sorption coefficients (Kd) for different organics are linearly related to the logarithm of their octanol−water partition coefficients (Kow). In a multiple solutes system, phenol and 2,4-dichlorophenol (2,4-DCP) could effectively enhance PCP sorption. The PCP sorption coefficient increases in the order: PCP/phenol < PCP/2,4-DCP < PCP/phenol/2,4-DCP. The PCP sorption enhancement is likely resulted from the interlayer space expansion and the organic carbon content increase. On the basis of the comparison between the single and the multiple solute systems, phenol and 2,4-DCP sorption coefficients decrease in the order: Kd of a single solute system > Kd of a binary solute system > Kd of a ternary solute system, and no enhancement for phenol and 2,4-DCP sorption was observed.

1. INTRODUCTION Bentonite has been proved to be a promising adsorbent due to its sheet-like structure and high specific surface area.1 For example, bentonite exhibits very good sorption performance for heavy metal ions.2,3 However, its sorption performance for anionic and nonionic pollutants from water is very poor, owing to its negative charged and hydrophilic surface.4 To improve its sorption capacity for anionic and nonionic pollutants, modified natural bentonite was developed and is known as organobentonite.5 Organobentonite can be produced by adding ion exchanging quaternary ammonium cationic surfactants onto the bentonite external surface as well as sheet-like inner layers.6 Modification with quaternary ammonium cationic surfactants effectively makes the surface properties more hydrophobic, which dramatically increases the anionic and nonionic organic compound sorption capacity.7−10 The partition mechanism usually describes chemical transfer from one phase to another. For example, chemicals transfer from water to soil and eventually reach equilibrium at the water−soil interface. In this work, it specifically means that organics transfer from the water phase to the organic layer at the bentonite surface. Researchers have intensively studied the sorption mechanisms of different adsorbates onto organobentonite, for example, heavy metal ions and organic compounds.11−14 In addition to single solute systems, organobentonite sorption has also been studied in multiple solute systems, because coexisting solutes might have a promotion or an inhibition effect on the target © 2013 American Chemical Society

adsorbate sorption through competitive effect or synergistic effect.13−16 The sorption mechanism might be different from that with the existence of coexisting solutes. On the other hand, organobentonite sorption is believed to be a very promising technology for wastewater treatment.10,17,18 Thus it is desirable to study the sorption mechanism in a multiple solute system. Conventional organobentonite preparation processes are complicated and energy/resource-consuming. This includes pulverizing bentonite, mixing bentonite−surfactant, separation, drying, and grinding products.14,19 Additionally, poor settling performance and distribution capacity in the liquid phase, caused by exchanging quaternary ammonium cationic surfactants onto its surface, are additional limiting factors for employing organobentonite as an adsorbent in wastewater treatment applications.20,21 To overcome the above-mentioned disadvantages, the surfactant/bentonite one-step process has been developed. This process combines the two independent steps (organobentonite assembling and pollutant sorption) into a one-step process by dosing raw bentonite and cationic surfactant into wastewater simultaneously. The surfactant/ bentonite one-step process has been proved to be an efficient wastewater treatment process, such as for persistent organic pollutant (POP) removal.22 Compared to traditional organoReceived: May 25, 2013 Accepted: August 21, 2013 Published: August 29, 2013 2610

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140 mg·kg−1 (100 mg·kg−1 raw bentonite modified by 40 mg· kg−1 CTMAB before dosing). The method of organobentonite preparation has been reported in our previous paper.4 In CTMAB/bentonite one-step sorption experiments, the bentonite dosage is 100 mg·kg−1, and the CTMAB dosage is 40 mg·kg−1 (100% CEC). In all sorption experiments, the solution weight was 50 g, and the initial pH of the solution was adjusted to 7 with 6 mol·kg−1 HCl or NaOH solution. The pH value can be maintained around 7 during the whole sorption experiment process, due to the buffer capacity of bentonite. In experiments measuring isotherm data for phenol, 2,4-DCP, and PCP sorption in a single solute system, the initial concentrations of these three solutes were controlled at eight levels, which are 0.01 mmol·kg−1, 0.02 mmol·kg−1, 0.025 mmol·kg−1, 0.03 mmol· kg−1, 0.035 mmol·kg−1, 0.04 mmol·kg−1, 0.045 mmol·kg−1, and 0.05 mmol·kg−1. For measuring PCP isotherm data in a binary solute system, PCP was chosen as the main solute, and the initial concentrations were controlled at 0.01 mmol·kg−1, 0.02 mmol·kg−1, 0.025 mmol·kg−1, 0.03 mmol·kg−1, 0.035 mmol· kg−1, 0.04 mmol·kg−1, 0.045 mmol·kg−1, and 0.05 mmol·kg−1. Under all these eight different conditions, the concentration of coexisting solute, phenol, or 2,4-DCP was controlled at two different levels, which were 0.01 mmol·kg−1 or 0.025 mmol· kg−1. For PCP isotherm data measurements in a ternary solute system, the PCP concentration was varied from 0.01 mmol·kg−1 to 0.05 mmol·kg−1 (eight different levels mentioned above). The concentrations of the two coexisting solutes (phenol and 2,4-DCP) in each batch sorption experiment were identical, and they were either 0.01 mmol·kg−1 or 0.025 mmol·kg−1, that is, PCP + 0.01 mmol·kg−1 phenol + 0.01 mmol·kg−1 2,4-DCP and PCP + 0.025 mmol·kg−1 phenol + 0.025 mmol·kg−1 2,4DCP. For phenol and 2,4-DCP isotherm data measurement in single and multiple solute systems, the concentrations of all solutes were identical and varied from 0.01 mmol·kg−1 to 0.05 mmol·kg−1 (eight levels as mentioned above). In all of the isotherm data measurement experiments, the solution volume was 50 mL, and the initial pH of the solution was adjusted to 7 with 6 mol·kg−1 HCl or NaOH solution. After adding solutes and adsorbents (raw bentonite, organobentonite, or bentonite with CTMAB), the reactors were kept shaking at 200 rpm, 298 K for 4 h to make sure the sorption reached equilibrium (preliminary experiments showed one hour was enough for reaching equilibrium stage, data not shown). Then, the mixed solution was centrifuged at 8000 rpm, 298 K for 5 min, and the supernatant was used for analysis. Equilibrium sorption (qe) was calculated as follows:

bentonite sorption processes, the surfactant/bentonite process has the following advantages: (1) lower cost, (2) better dispersion properties, and (3) faster sedimentation.23 All of these advantages make the surfactant/bentonite one-step process more suitable for wastewater treatment. Although great attention has been paid to the surfactant/ bentonite one-step process, its sorption mechanism is still not certain, especially in regard to the interactions between different coexisting solutes in a multiple solute system. Most reported work only focuses on the sorption behavior in a single solute system.1,23,24 In addition, only a few published papers assessed the one-step process performance for pollutant removal in real wastewater.4,22 Nevertheless, the effects of coexisting solutes on target adsorbate sorption are still lacking in this field. This results in the circumstance that the effect of coexisting solutes on target adsorbate sorption is still unclear for the surfactant/bentonite one-step process. Thus further work on the sorption mechanism in complicated environments is essential. The aim of this paper is to reveal the sorption mechanism in a multiple solutes system and examine the effects of the interactions between coexisting solutes on their sorption behaviors in surfactant/bentonite one-step process. In this study, a nonionic POP, PCP, was chosen as the model nonpolar solute for sorption mechanism study. Two other organics, phenol and 2,4-dichlorophenol (2,4-DCP), were chosen as the coexisting solutes due to their different polarity. Phenol and 2,4-DCP were used as examples of polar and weak polar compounds since they are also very common pollutants in real wastewater. But they are not chosen to be additives for wastewater treatment process, due to their environmental toxicity. First, PCP sorption performance was evaluated by comparing to other two conventional sorption processes. Then the PCP sorption isotherm was studied in a single solute system to reveal the sorption mechanism in the surfactant/bentonite one-step process. In addition, the PCP sorption mechanism is further studied in a multiple solute system to examine the effects of polar/weak polar coexisting solutes on the PCP sorption. Finally, the effect of PCP on phenol and 2,4-DCP sorption was also studied to further clarify the interaction between coexisting solutes.

2. EXPERIMENTAL SECTION 2.1. Material and Methods. The raw bentonite (Cabentonite) used in this study was obtained from Huate Co., Ltd. (Hangzhou, China). Its cationic exchange capacity (CEC) was 1.084 mmol·g−1, and the organic carbon content was 0.14 mass fraction. The bentonite sample was gently ground to 0.074 mm size. The purity and sources of the chemicals are listed in Table 1. 2.2. Sorption Experiments. In raw bentonite sorption experiments, the bentonite dosage was 100 mg·kg−1. In organobentonite sorption experiments, organobentonite was 100% CEC CTMAB modified bentonite, and the dosage was

qe =

where C0 (mg·kg−1) is the initial concentration of target solute, Ce (mg·kg−1) is the concentration at equilibrium, W (kg) is the solution weight, and m (mg) is the adsorbent mass. 2.3. Analytical Methods. The PCP, 2,4-DCP, and phenol were analyzed by high-performance liquid chromatography using an Agilent 1260 series system with a XDB C18 column (Eclipse XDB C18, 250 mm × 5 μm × 4.6 mm (i.d.), Agilent Technologies, USA) and a UV detector (G1314F, Agilent Technologies, USA). The mobile phase was 75 % acetonitrile/ 25 % H2O with a flow rate of 1.0 mL·min−1. The column oven was set at 308 K, and the injection volume was 10 μL. The PCP, 2,4-DCP, and phenol were quantified by the UV detector set at 220 nm. All data presented in this work was measured in duplicate, and the estimated error is less than 5 %.

Table 1. Purity of the Chemicals Studied chemical name PCP 2,4-DCP phenol CTMAB

source Feixiang Chemical Aladdin J&K Tianyu Chemical

initial mass fraction purity

purification method

> 0.985

none

> 0.98 0.99 > 0.99

none none none

(C0 − Ce)W m

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3. RESULTS AND DISCUSSION 3.1. Comparison of PCP Removal between Different Bentonite Sorption Processes. The PCP sorption performance in the CTMAB/bentonite one-step process was compared with both the raw bentonite and the conventional CTMAB modified organobentonite processes respectively. As can be seen from Figure 1, the sorption process with conventional

Figure 1. Comparison of PCP removal efficiencies in different bentonite sorption processes.

CTMAB modified organobentonite and the CTMAB/bentonite one-step process can achieve significantly higher PCP removal efficiency than the sorption process with raw bentonite. This increase is attributed to CTMAB modification, which formed a microscopic organic phase by exchanging CTMAB quaternary ammonium cations onto the external and inner-layer surface of raw bentonite. The long chain alkyl group in the quaternary ammonium cation converts the hydrophilic bentonite surface to a hydrophobic surface. Due to the similar hydrophobic properties of PCP and CTMAB modified bentonite surface, PCP sorption on modified bentonite is significantly higher than that on raw bentonite surface, which is hydrophilic. Moreover, the high PCP removal efficiency (97.8 %) in the CTMAB/bentonite one-step process can also be a convictive evidence that organobentonite self-assembly and PCP sorption can be achieved simultaneously. The CTMAB/ bentonite one-step process could simplify the operation of organobentonite preparation and bentonite sorption process significantly. Furthermore, the CTMAB/bentonite one-step process is proven to be a selective sorption technique for hydrophobic organics. 3.2. Single Solute Sorption Mechanism in CTMAB/ Bentonite One-Step Process. To have a more comprehensive understanding of the sorption mechanism of different solutes in CTMAB/bentonite one-step process, sorption isotherms of PCP, phenol, and 2,4-DCP were investigated in a single solute system, respectively (Figure 2). A linear sorption model was used to fit the sorption isotherm data: qe = KdCe + b

Figure 2. (a) Sorption isotherms of phenol, 2,4-DCP, and PCP in the CTMAB/bentonite one-step process. (b) Relationships between log Kow and log Kd of PCP, 2,4-DCP, and phenol: ■, phenol; ●, 2,4-DCP; ▲, PCP.

other researchers, the hydrophilic property of target solute has a significant effect on the sorption coefficient in the partition mechanism dominated sorption processes.26 This is also confirmed by our results (Kd = 0.8 kg·g−1 for phenol, Kd = 10.7 kg·g−1 for 2,4-DCP and Kd = 28.5 kg·g−1 for PCP, Kd values were derived from the linear sorption model). Phenol is a polar organic molecule, which is usually considered as hydrophilic. This attributes to the lowest Kd value for phenol. The introduction of either weak polar organic molecule, 2,4DCP, which is less hydrophilic, or nonpolar organic hydrophobic molecule PCP leads to the Kd value sequence for these three solutes. To further reveal the relationship between the hydrophilic property and Kd, the octanol−water partition coefficient (Kow) was employed to quantificationally describe the organic hydrophilic property. Organics with high Kow values usually are considered to be more hydrophobic than those with low Kow. The sorption coefficient was plotted to Kow (Figure 2 insert). The result indicated that log Kow and log Kd are linearly related (R2 > 0.99). This positive relationship between log Kow and log Kd implied that the organic phase at the bentonite surface formed by quaternary ammonium cations modification has a stronger uptake capacity for more hydrophobic organics. 3.3. PCP Sorption Mechanism in a Multiple Solute System. Results obtained from the single solute systems demonstrated the CTMAB/bentonite one-step process has a higher sorption capacity for hydrophobic organics than hydrophilic organics. Then, we tried to confirm the above results in multiple solute systems. The effects of other coexisting solutes on target solute sorption were examined. Here, PCP was chosen as the target solute. The sorption isotherms of PCP were first measured in binary solute systems

(1)

−1

where qe (mg·g ) is the adsorbed amount at equilibrium, Kd (kg·g−1) is the sorption coefficient, and Ce (mg·kg−1) is the equilibrium concentration.13 As shown in Figure 2, the linear sorption model has a very good agreement with all the isotherms data (R2 > 0.99). The Langmuir mode was also applied to fit the data. But the fitting was not good (R2 < 0.9). This indicates that the dominant sorption mechanism is the partition mechanism. As reported by 2612

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solute systems (Figure 3c). The Kd for PCP sorption with different coexisting solutes are listed in Table 2. It can be

using phenol or 2,4-DCP as the coexisting solute separately. Figure 3a,b shows that either phenol or 2,4-DCP can increase

Table 2. Partition Coefficient for PCP Sorption in the CTMAB/Bentonite One-Step Process in a Multiple Solute Systema

a

main solute

coexisting solutes (concentration)

Kd (kg·g−1)

PCP PCP PCP PCP PCP PCP PCP

PCP single phenol (0.01 mmol·kg−1) phenol (0.025 mmol·kg−1) 2,4-DCP (0.01 mmol·kg−1) 2,4-DCP (0.025 mmol·kg−1) phenol + 2,4-DCP (0.01 mmol·kg−1) phenol + 2,4-DCP (0.025 mmol·kg−1)

28.5 36.0 43.5 61.8 58.2 127.3 112.7

Standard uncertainties u are ur(qe) = 0.005 and ur(Ce) = 0.005.

concluded from Table 2 that the PCP sorption increases in the order: PCP/phenol < PCP/2,4-DCP < PCP/phenol/2,4-DCP. Compared to the single solute system, the existence of polar and weak polar solutes effectively enhances the PCP sorption coefficient. This is mainly because the delocalized π-bond systems in phenol and 2,4-DCP interact strongly with the cationic ammonium center and alkyl chains of CTMAB. This interaction can result in a reorientation of the alkyl substituent to a more orthogonal position and thus allows PCP interaction with the revealed mineral surfaces. A more orthogonal position of alkyl chain expands the CTMAB modified bentonite interlamellar region, which makes more interlayer region accessible for PCP sorption and eventually increases the PCP sorption capacity.20,25,26 Besides this reason, the sorption of phenol and 2,4-DCP also increased the organic carbon content of CTMAB modified bentonite. Higher organic carbon content also could increase the PCP sorption capacity.27 From the viewpoint of pollutant removal, the positive correlation between hydrophobicity and sorption capacity makes the CTMAB/bentonite one-step process a promising technology for selective removal of different pollutants in wastewater, depending on their different hydrophobicities. The phenomenon of phenol and 2,4-DCP enhancing PCP sorption provides us with the idea of adding some polar or weak polar compound to enhance the hydrophobic organics sorption during the bentonite/surfactant self-assembling process. But phenol and 2,4-DCP are typical pollutants, and their incomplete sorption or desorption might cause danger to the environment. Here, these two compounds were used as examples of polar and weak polar solutes for studying their effects on PCP sorption and are not additives. Finding some polar but nontoxic organics and using them as the additive for surfactant/bentonite one-step process would be valuable for improving the sorption performance of the CTMAB/bentonite one-step process in wastewater treatment. Furthermore, from the aspect of practical application, for some complex real wastewater (e.g., dyeing wastewater) containing both surfactants and various POPs, our work provides the possibility of removing these pollutants simultaneously. This would significantly reduce the wastewater treatment cost and simplify the processes. 3.4. Sorption Mechanism of Phenol and 2,4-DCP in a Multiple Solute System. The partition mechanism of phenol and 2,4-DCP in multiple solute systems was also studied by measuring the isotherms (Figure 4). According to the comparison among single, binary, and ternary solute systems, it is suggested that both phenol and 2,4-DCP sorption

Figure 3. (a) Sorption isotherms of PCP in the CTMAB/bentonite one-step process with phenol: ■, PCP single; ●, with 0.01 mmol·kg−1 phenol; ▲, with 0.025 mmol·kg−1 phenol. (b) Sorption isotherms of PCP in the CTMAB/bentonite one-step process with 2,4-DCP: ■, PCP single; ●, with 0.01 mmol·kg−1 2,4-DCP; ▲, with 0.025 mmol· kg−1 2,4-DCP; (c) Sorption isotherms of PCP in the CTMAB/ bentonite one-step process with phenol and 2,4-DCP: ■, PCP single; ●, with 0.01 mmol·kg−1 phenol and 2,4-DCP; ▲, with 0.025 mmol· kg−1 phenol and 2,4-DCP.

the PCP sorption coefficient. After conducting the sorption experiments in binary system, PCP sorption was further investigated in a ternary solute system with both phenol and 2,4-DCP as coexisting solutes. Similar phenomena can be observed (Figure 3c). The linear sorption model has a good agreement with all of the isotherm data, which implies that the dominating sorption mechanism of PCP sorption in CTMAB/ bentonite one-step process is a partition mechanism in multiple 2613

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4. CONCLUSION The PCP sorption mechanism in the CTMAB/bentonite onestep process was studied in single solute systems and multiple solute systems. The CTMAB/bentonite one-step process exhibited slightly higher PCP removal efficiency (97.8%) than two-step processes. In a single solute system, the linear sorption model showed a very good agreement to the PCP sorption isotherm data, which implied the dominating sorption mechanism is the partition mechanism. The partition coefficient, Kd for CTMAB/bentonite one-step process, derived from the isotherm curve is 28.54 kg·g−1, slightly higher than the Kd for the conventional two-step organobentonite sorption process (Kd = 28.24 kg·g−1). Also, partition coefficients for organics were positively linearly related with their hydrophilic properties. In a multiple solute system, phenol and 2,4-DCP could effectively enhance the PCP sorption. PCP sorption decreased in the order: PCP/phenol/2,4-DCP > PCP/2,4-DCP > PCP/phenol. The reasons for the effect of enhancement are: (1) phenol and 2,4-DCP sorption expands the CTMAB modified bentonite interlamellar region and makes more interlayer region accessible for PCP sorption; (2) phenol and 2,4-DCP sorption increased the organic carbon content. As for phenol and 2,4-DCP sorption in a multiple solute system, the comparison among single, binarym and ternary solute systems suggested that both phenol and 2,4-DCP sorption coefficients decreased in the order: Kd of the single solute system > Kd of the binary solutes system > Kd of the ternary solutes system. This decrease is mainly because PCP competitive sorption reduced phenol and 2,4-DCP sorption amount. Based on our results, the CTMAB/bentonite one-step process can be a promising technique for low concentration, nonpolar, and hydrophobic organics selective removal from wastewater.

Figure 4. (a) Sorption isotherms of phenol in the CTMAB/bentonite one-step process in multiple solute system: ■, phenol single; ●, with PCP; ▲, with PCP and 2,4-DCP. (b) Sorption isotherms of 2,4-DCP in the CTMAB/bentonite one-step process in multiple solutes system: ■, 2,4-DCP single; ●, with PCP; ▲, with PCP and phenol.

coefficients decreased in the order: Kd of single solute system > Kd of binary solute system > Kd of ternary solute system (Table 3). The reason for the Kd decrease is that the nonpolar

■

Table 3. Parameters for Sorption Isotherms of Phenol and 2,4-DCP on Bentonite in the CTMAB/Bentonite One-Step Process in Multiple Solute Systema

a

Corresponding Author

*Tel.: +86 571 87952525; fax: +86 571 87952525. E-mail address: [email protected].

−1

main solute

coexisting solutes

Kd (kg·g )

phenol phenol phenol 2,4-DCP 2,4-DCP 2,4-DCP

phenol single PCP (0.01−0.05 mmol·kg−1) PCP/2,4-DCP (0.01−0.05 mmol·kg−1) 2,4-DCP single (0.01−0.05 mmol·kg−1) PCP PCP/phenol (0.01−0.05 mmol·kg−1)

0.8 0.5 0.7 10.7 5.8 3.6

AUTHOR INFORMATION

Funding

The authors would like to acknowledge financial support for this work provided by MOST project of China (no. 2008BAC32B06). Notes

The authors declare no competing financial interest.

■

Standard uncertainties u are ur(qe) = 0.005, ur(Ce) = 0.005.

molecule, PCP, occupied a larger bentonite surface, which decreased the phenol and 2,4-DCP sorption site amount and eventually resulted in the decrease of phenol and 2,4-DCP sorption. By comparing Figure 4a to b, it reveals that the phenol sorption amount on the bentonite in the one-step process is one magnitude lower than that of 2,4-DCP. This implied that the great 2,4-DCP sorption amount enhancement is caused by very small amount of phenol (1−3 mg·g−1). This enhancement also attributes to the higher sorption capacity due to the expand bentonite interlamellar region and stronger partition ability due to the higher organic carbon content.20,26 As for the phenol sorption isotherm, the sorption amount at equilibrium in the single, binary, and ternary solute systems is very close. This is mainly because phenol is hydrophilic and thus has very low sorption amount on bentonite in the CTMAB/bentonite one-step process.

REFERENCES

(1) Ma, J. F.; Zhu, L. Z. Removal of phenols from water accompanied with synthesis of organobentonite in one-step process. Chemosphere 2007, 68, 1883−1888. (2) Alvarez-Ayuso, E.; Garcia-Sanchez, A. Removal of heavy metals from waste waters by natural and Na-exchanged bentonites. Clays Clay Miner. 2003, 51, 475−480. (3) Kapoor, A.; Viraraghavan, T. Use of immobilized bentonite in removal of heavy metals from wastewater. J. Environ. Eng.: ASCE 1998, 124, 1020−1024. (4) Yao, M.; Zhang, X. W.; Lei, L. C. Removal of Reactive Blue 13 from Dyeing Wastewater by Self-Assembled Organobentonite in a One-Step Process. J. Chem. Eng. Data 2012, 57, 1915−1922. (5) Boyd, S. A.; Lee, J. F.; Mortland, M. M. Attenuating organic contaminant mobility by soil modification. Nature 1988, 333, 345− 347. (6) Zhu, L. Z.; Chen, B. L. Use of Bentonite-Based Sorbents in Organic Pollutant Abatements. Prog. Chem. 2009, 21, 420−429.

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dx.doi.org/10.1021/je400505j | J. Chem. Eng. Data 2013, 58, 2610−2615