Selective online solid-phase extraction of copper using p-morpholino-methylcalix[4]arene appended silica-based column

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Selective online solid-phase extraction of copper

using p-morpholino-methylcalix[4]arene appended

silica-based column

Naeem A. Memon, Fakhar N. Memon, Hatice K. KARA, Hüseyin KARA, Sayed

T. H. Sherazi, Ayaz A. Memon, Shahabuddin Memon & Muhammad K.

Leghari

To cite this article: Naeem A. Memon, Fakhar N. Memon, Hatice K. KARA, Hüseyin KARA, Sayed T. H. Sherazi, Ayaz A. Memon, Shahabuddin Memon & Muhammad K. Leghari (2020) Selective online solid-phase extraction of copper using p-morpholino-methylcalix[4]arene appended silica-based column, Separation Science and Technology, 55:9, 1650-1655, DOI: 10.1080/01496395.2019.1600551

To link to this article: https://doi.org/10.1080/01496395.2019.1600551

Published online: 03 Apr 2019. _{Submit your article to this journal}

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Selective online solid-phase extraction of copper using

p-morpholino-methylcalix

[4]arene appended silica-based column

Naeem A. Memona_{, Fakhar N. Memon}b_{, Hatice K. KARA}c_{, Hüseyin KARA}c_{, Sayed T. H. Sherazi}a_{, Ayaz A. Memon}a_,

Shahabuddin Memona_{, and Muhammad K. Leghari}a

a_{National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan;}b_{Department of Chemistry, University of}

Karachi, Karachi, Pakistan;c_{Department of Chemistry, Selçuk University, Konya, Turkey}

ABSTRACT

This study deals with investigation of selectivity of p-morpholino-methylcalix[4]arene appended silica from a group of metal ions having similar charge and radii. The values of distribution ratio revealed that modified silica possess higher selectivity for Cu2+. In addition, relative selectivity coefficients of modified silica were found to be 24.1, 13.8, 8.6 and 4.01 for Cu2+_/Ni2+_{, Cu}2+_/Co2+_,

Cu2+_/Cd2+_{, Cu}2+_/Pb2+_{, respectively. The maximum adsorption capacity was 1.5 mmolg}−1_{. The}

reusability data suggested no any loss of adsorption capacity of this material up to 10 cycles. The developed material was also applied for determination of copper in lake water samples with satisfactory results.

ARTICLE HISTORY

Received 15 October 2018 Accepted 25 March 2019

KEYWORDS

Calix[4]arene; silica resin; copper; solid-phase extraction; HPLC; atomic absorption spectroscopy

Introduction

In recent years, heavy metals are pragmatic source of wastewater contamination due to some industrial activ-ities and increased population growth. Improper hand-ling and less efficient process for waste management allow a large quantity of heavy metals to enter in the environment. Among all the heavy metals, copper has attracted much attention due to its presence in indus-trial, environmental as well as biological samples. Its maximum contamination level goal (MCLG) in drink-ing water is 1.3 mgL−1according to USEPA.[1]When its presence exceeds that limit, it poses severe hazard to human health. The two diseases, which are profoundly related to copper metabolism in humans, are Menkes and Wilson diseases.[2]Furthermore, its long-time expo-sure leads to the damage of liver and kidney along with gastrointestinal distress. Consequently, for the remedia-tion of this noxious pollutant a number of techniques are in under consideration and some of them have been applied successfully such as coprecipitation,[3] ion exchange,[4] dispersive liquid–liquid micro extraction,[5] liquid–liquid extraction,[3,6] cloud point extraction,[7–9]voltametric and adsorptive stripping.[10] However, these techniques are useful but are applic-able only at higher concentration and require more pre-concentration times and huge amount of solvents.

Therefore, solid-phase extraction (SPE) is considered as an alternative to all these techniques with a benefit of less consumption of solvents, less extraction time and less disposal costs along with its ability to combine instrumental and analytical methods together including HPLC.[11]However, batch wise SPE has very limited applications due to its small scale remediation. Therefore, to tackle the large-scale application column SPE-based agreement is considered as highly successful and reliable tools to achieve the desired goal. Furthermore, for effective SPE, the choice of sorbent is very important which is based on the functional groups attached on its periphery and their interaction with analyte. In this regard, calixarenes (the third-generation supramolecular system after cyclodextrins and crown ethers) are considered as highly efficient materials to trap the variety of pollutants[11] as there is a great possibility to attach a wide variety of different functional groups. Furthermore, their attachment with different solid supports such as XAD and silica has proved their enhanced trapping efficiency for metals as well as neutral molecules.[12–14]

The current study is extension of our previous work,[15]in which central composite design has been applied for optimization purposes. In the present work, same resin, i.e., p-morpholino-methylcalix[4] arene (p-MMC4)appended silica has been used in the CONTACTFakhar N. Memon fakhar_memon2@yahoo.com;fakhar.nisa@uok.edu.pk Department of Chemistry, University of Karachi, Karachi 75270, Pakistan

Color versions of one or more of the figures in the article can be found online atwww.tandfonline.com/lsst. 2020, VOL. 55, NO. 9, 1650_–1655

https://doi.org/10.1080/01496395.2019.1600551

column agreement for selective online SPE of copper from aqueous solutions. In addition, the matrix ions effect was also evaluated and the material was success-fully applied to real samples. In addition, it has been compared with other solid-phase extractors for its effi-ciency. From the results, it has been revealed that due to excellent mechanical strength and good sorption capacity, p-MMC4-based silica could be used repeat-edly without any significant loss of adsorption capacity.

Experimental

Materials

All the reagents and solvents used in present study were of analytical grade and all the solutions were prepared by using double distilled water. All the salts of copper, nickel, cobalt, cadmium, and lead were used in their nitrate form, whereas for magnesium, calcium and sodium their chlor-ide salts were used. All the salts were procured from Merck (Darmstadt, Germany). Stock solution of each metal ion was diluted up to desired level to obtain the corresponding standard solution for AAS calibration. The pH of the solutions was adjusted with 5% HCl and 5% NaOH solu-tions. Compounds 1–3 [Scheme 1] were synthesized according to previously reported methods.[16,17] Silica gel having 60 Å pore size, 40–63 μm particle size, 230–400 mesh size and 500 m2/g surface area was used for immo-bilization and purchased from Sigma-Aldrich (Germany).

Instrumentation

To record the FT-IR spectra Thermo Nicollet AVATAR 5700 FT-IR spectrometer was used with KBr pellets in spectral range from 4000 to 400 cm−1. Scanning elec-tron microscopic (SEM) studies were performed by using a JSM-6380 instrument. For SPE operations Agilent 1100 series HPLC system was used. This system consisted of a G1311C model quaternary pump, a G1314F model variable wavelength UV detector, and a G1329B model Rheodyne auto injector system with 20-μL loop. The solutions and solvents were degassed with a G1379A model degasser. The tempera-ture of the column was controlled by means of a G1316A model thermostatted column compartment. A UNICAM 929 model Atomic Absorption was used for quantitative metal analysis.

Online solid-phase extraction of copper

For online SPE, the packed column was conditioned with UPW for 5 min followed by loading of the corre-sponding metal ion solution with appropriate concen-tration at pH 4.5 with flow rate of 4.5 mL min−1until the signal verified saturation of column. Consequently, the unloaded metal ion was washed out from the col-umn by the passage of UPW for 10 min at flow rate of 0.5. Finally, the loaded metal ion was stripped out using appropriate stripping agent and that solution

O H HCHO + OHOHOHHO 2 OH HO OH OH OHOHOHHO N N N O O O O N 3 SiCl4 Si O O Si O Si O Si O Cl Cl Cl Si O O Si O Si O OH O HO O O N _N O N O O O N O Si Si O O Si O Si O 1 + 4 Scheme 1.Synthetic pathway forp-morpholino-methylcalix[4]arene (3) appended silica (4).

containing stripped metal ion was collected in a separate bottle and was subjected to AAS for its quantitative analysis.

Loading capacity

The loading capacity of the p-MMC4 appended silica-based column was calculated for copper by loading the required concentrations of copper at least three times for each experiment and after desired treatment process and consequent stripping the solutions were analyzed using AAS. The AAS analyses were performed using standard solutions of copper ion with the linear con-centration range (R2 = 0.99). All calculations were performed by using the data obtained from AAS ana-lysis. The amount of the sorbed metal ion was calcu-lated using following equation:

Q¼ðC0 CfÞV

m (1)

where Q (mmol g−1) is the loaded metal ion, Co(mmol L−1) and Cf(mmol L−1) are the concentration of metal ion before and after loading, respectively. V (mL) is the volume of the solution passed through the column and m (g) is the amount of the p-MMC4 appended silica filled in the column.

Selectivity experiments

The selectivity of p-MMC4 appended silica was evalu-ated by competitive adsorption of different ion such as Ni2+, Co2+,Cd2+ andPb2+ which were selected on the basis of same charge and similar ionic radius as Cu2+ and most often are found to exist with copper in natural sources. The binary solutions of these metals with copper (Cu2+/Ni2+, Cu2+/Co2+, Cu2+/Cd2+, Cu2 +_/Pb2+_{) were passed through the column at pH 4.5} and 27°C and consequently were eluted using appro-priate stripping agent by simultaneous analysis using AAS. The values of distribution ratios D (mL g−1) and the selectivity factor of Cu2+with respect to other metal ions αCu2þ=M2þwere used to calculate the selectivity of p-MMC4 appended silica. The distribution ratios and selectivity factor values are calculated as follows:

D¼Ci Cf Cf V m (2) αCu2þ_=M2þ ¼DCu 2þ DM2þ (3) where Ciand Cfare the initial and final concentrations of each metal, V is the volume of the solution and m is

the amount in grams of p-MMC4 appended silica used to fill the column. However, DCu2þand D_M2þ are

distri-bution ratios of copper and other metal ions.

Real sample analysis

The lake water sample was collected from the vicinity of Konya, Turkey. Before analysis, the water sample was filtered with 0.45 μm membrane filter. For pre-concentration procedure, a volume of 300 mL was passed through the column at optimum conditions and was eluted with the appropriate stripping agent and subjected to AAS for quantitative analysis. This experiment was repeated for three times.

Results and discussion

Sorption capacity of p-MMC4 appended silica

In order to estimate maximum sorption capacity of p-MMC4 appended silica, the experiments were per-formed with increasing the concentration of copper with a fixed amount of p-MMC4 appended silica in a column agreement using optimum conditions. Consequently, the adsorbed metal was stripped out with appropriate stripping agent and was quantitavely analyzed using AAS. It was observed that the moles of copper ions adsorbed on p-MMC4 appended silica were increased linearly with increased initial concentration of copper ions. The concentration of copper ions was increased till the maximum sorption capacity achieved. The maximum capacity of p-MMC4 appended silica was found to be 1.5 mmolg−1for copper ions.

Selectivity of p-MMC4 appended silica

The selectivity of p-MMC4 appended silica was evalu-ated from the competitive sorption of Cu2+/Ni2+, Cu2+/Co2+, Cu2+/Cd2+, Cu2+/Pb2+. The distribution ratios and selectivity coefficients of copper with respect to other heavy metals are given in Table 1. It can be evaluated from the distribution value of p-MMC4 appended silica for each metal that the value is much higher (24 mL/g) for copper as compared to other heavy metal ions (< 10 mL/g) which proves that the

Table 1.Selective adsorption properties of the p-MMC4 appended silica.

Ions Distribution ratio (D mL/g) Selectivity coefficients (αCu/M)

Cu2+ 24.0 –

Ni2+ _{9.9 24.1}

Co2+ _{8.6 13.8}

Cd2+ 4.0 8.6

p-MMC4 appended silica is highly selective for the efficient removal of copper as compared to other heavy metal ions. Furthermore, the selectivity coeffi-cients for each heavy metal ions are greater than 1. These observations can be attributed to three possible factors. One is the inherent selectivity behavior of the morpholino-methyl attached on the moiety of calix[4] arene. Since morpholine possess the basic character due to presence of amine; hence, it will not prefer to inter-act with alkali metal and alkali earth metal ions that are classified as hard acids. Secondly, cavity size selectivity is possible. That is, the size of Cu2+exactly fits with the cavity size of p-MMC4 appended silica sorbent. The third is the coordination-geometry selectivity since p-MMC4 appended silica sorbent can provide the ligand groups arranged in a suitable way required for coordination of Cu2+ion. Although, Cu2+, Ni2+, Co2+, Cd2+and Pb2+have similar charge and ionic radius but still p-MMC4 appended silica sorbent show high selec-tivity toward Cu2+. These results suggest that the coor-dination geometry selectivity may dominate in the selectivity enhancement. As demonstrated later, the present online solid-phase extraction system allowed the interference-free extraction of Cu2+in real sample.

Matrix ion effect

Pre-concentration methods for the trace determination of heavy metals are highly affected due to the presence of some matrix constituents of the sample. Hence, to examine the reliability of the proposed method, the experiments were performed to evaluate the effect of most common matrix ions such as Mg2+, Ca2+and Na2 + _{on the adsorption capacity of p-MMC4 appended} silica for copper. The results are presented in [Fig. 1] which revealed that up to 100 mg L−1for Mg2+, 100 mg

L−1 Ca2+ and 10 mg L−1 Na2+have no any significant effect on the sorption of 0.005 moles L−1 of copper.

Analytical application of the method

The p-MMC4 appended silica was successfully applied for the determination of copper in lake water samples. The standard addition method was used for the analysis of water sample and the values of % Recovery are presented in Table 2. It can be seen from Table 2 that the % recovery is greater than 98% indicating the usability of p-MMC4 appended silica for selective SPE and determination in real water samples.

Reusability study

In order to evaluate the reusability and stability of the p-MMC4 appended silica, the experiments were per-formed repeatedly up to 10 times under optimum con-ditions. The results are compiled in [Fig. 2], which shows that up to 10 experiments the % recovery is greater than 98% suggesting the suitability and repeat-ability of the p-MMC4 appended silica that can be reused again and again without the loss of adsorption capacity.

Comparative study

The distinct features of the proposed material (i.e., oper-ating parameters and their adsorption capacity) were compared with a number of recently reported methods for the sorption of copper ions. The comparison data is given inTable 3. As the adsorption capacity is compared to previously reported SPE materials such as calcined clay (0.3 mmolg−1), SG-INDP (0.99 mmolg−1), DTO-coated activated carbon (0.0074 mmolg−1), APPS-CA

0 0.02 0.04 0.06 0.08 0.1 0.12 g/l o m m Ma gnesium Ca lcium Sodium

Figure 1.Effect of matrix ions on the sorption of copper onp-MMC4 appended silica.

(0.54 mmolg−1), ion-imprinted polymer (IIP) (0.076 mmolg−1), insolubilized humic acid (IHA) (0.048 mmolg−1), and APS-ImHA (0.021 mmolg−1), p-MMC4 appended silica is found to be highly efficient and reusable with greater adsorption capacity (1.5 mmolg−1) for the removal of copper.

Conclusion

In this study, the selectivity of p-morpholino-methylcalix[4]arene appended silica was investigated for Cu2+, Ni2+, Co2+, Cd2+and Pb2+ions in a column agreement. From the selectivity experiments, it was observed that the distribution ratio values for Cu2+ are higher, while the distribution ratio values for Ni2+, Co2+, Cd2+and Pb2+decrease significantly. The relative selectivity factors (α) are found to be greater than 1.

This means that Cu2+ions can be adsorbed more selec-tively than other ions with similar charge and ionic radii. Furthermore, to examine the reliability of the proposed method, different foreign ions were added to the fixed concentration of copper ions. The results showed that there is no any significant effect of foreign ions on the adsorption capacities of the p-morpholino-methylcalix[4]arene appended silica for copper. The new material was also successfully applied for the removal of copper from real lake water samples and was found to be highly efficient and reusable as com-pared to previously reported SPE materials.

Acknowledgments

The authors thank the National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro and Scientific and Technological Research Council of Turkey

(TÜBİTAK) for financial support to Dr. Fakhar-un-Nisa

Memon, Post-doc. fellow under 2216program in Selçuk University, Faculty of Science, Department of Chemistry, Konya, Turkey.

Conflicts of interest

No potential conflict of interest was reported by the author.

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