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Original article
13 (
1
); 1386-1396
doi:
10.1016/j.arabjc.2017.11.010

Chemically functionalized activated carbon with 8-hydroxyquinoline using aryldiazonium salts/diazotization route: Green chemistry synthesis for oxins-carbon chelators

,
 Department of Chemistry, College of Science, Taibah University, 41477 AlMedinah AlMunwarah, Saudi Arabia

⁎Corresponding author. asuhaimi@taibahu.edu.sa (Awadh O. AlSuhaimi)

Received: , Accepted: ,
© The Author(s) 2017
Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

The past few years witnessed the emergence of aryldiazonium salts as versatile coupling agents for the functionalization of carbon and other substrates. Although the approach has demonstrated extensive applications in many fields, its use for the synthesis of chelating resins has not been explored. In this work, the concept has been exploited to develop an ecofriendly synthetic method for carbon based chelators. Herein, the p-nitroanline aryldiazonium salt was generated (in situ) in presence of hypophosphorous acid and covalently grafted onto activated carbon (AC) to allow addition of 8-hydroxyquinoline (8-HQ) via diazo coupling. The successfulness of the functionalization was confirmed by DRIR, XPS, and TGA. The risen was packed into cartridges and used with standard solid phase extraction (SPE) apparatus for the extraction of trace metals; Cd(II), Ni(II), Mn(II), Zn(II) and Pb(II) from groundwater samples prior to their measurement by ICPMS. The resin exhibited more 50% enhancement in capacity exchange relative to the plain AC. Under the optimum conditions the sorption capacity of the sorbent was 0.393, 0.170, 0.345, 0.092, 0.314 mmol g−1 for Mn(II), Cd(II), Ni(II), Pb(II) and Zn(II) respectively. The sorbent showed efficient performance when applied for SPE of trace metals from groundwater certified reference materials BCR-609 and groundwater real samples from AlMadinah AlMumnawarah, Saudi Arabia.

Keywords

Aryldiazonium salts
Chemical modification
Green chemistry
Chelating resin
Solid phase extraction
Activated carbon
ICP-MS and groundwater
1

1 Introduction

The accurate determination of trace elements from complex matrices, such as soils, sediments, groundwater, wastewaters and seawaters, is a challenging task due to the low concentrations of the targeted ions and the substantial matrix effects (Biniak et al., 1997; Castillo et al., 2012; Chang et al., 2008; Mohammadifar et al., 2015). Therefore, this type of analysis always requires a laborious sample preparation stage (Nema et al., 2010; Tokalioğlu et al., 2009). There are several methods for sample preparation including liquid–liquid extraction (Salgado et al., 2003), solvent extraction (Preston, 1985), membrane extraction (Jönsson and Mathiasson, 1999), chemical precipitation and co-precipitation (Boyle and Edmond, 1975) … etc. However, these methods are mostly time consuming, entail relatively large volumes of high purity solvents, suffer from matrix effect and can also give erroneous results at trace levels (Gao et al., 2009; Garg et al., 1999). Among the various methods available for sample preparation, solid phase extraction (SPE) techniques have received considerable attention during last years, and gained increased popularity owing to their selectivity and enhanced sensitivity for trace metals (Ahmadi et al., 2009; Ensafi and Shiraz, 2008; Mohammadifar et al., 2015; Zhang et al., 2010).

SPE became a convenient method for separation and enrichment of various inorganic and organic analytes, i.e., metal ions from broad range of matrices (Amin and AL-Attas, 2012; Gao et al., 2009; Soleimani et al., 2013; Tian et al., 2010; Zhang et al., 2010; Zougagh et al., 2005). This is due to its congenital advantages over other sample preparation techniques, such as simplicity, rapidity (Vereda Alonso et al., 2016; Zhang et al., 2010), stability and reusability of the sorbents, high enrichment factor (Gao et al., 2009; Tu et al., 2009), flexibility for integration with many analytical instruments, low cost, consumption of less organic solvents (Albishri and Marwani, 2016) and safety with respect to hazardous reagents/samples (Marahel et al., 2011; Zougagh et al., 2005). Conceivably, one of the potential advantages of SPE is the availability of large number of highly selectivity sorbent materials (Donia et al., 2014; Hatay et al., 2008; Marahel et al., 2011).

Principally, solid phase extractors have been prepared either by physical loading (impregnation) or chemical binding of selected moieties (e.g., chelating agents for metals) to various solid supports (Ensafi and Shiraz, 2008; Jain et al., 2007). The process usually referred to as post synthesis modification. Many substances, such as silica gel (Didukh et al., 2016; Hatay et al., 2008), activated carbon (Biniak et al., 1997), cellulosic derivatives (Donia et al., 2014), ion exchange resins (Leinonen and Lehto, 2000), naphthalene (Caro et al., 2004), alumina (Ezoddin et al., 2010), zeolite (Al-Degs et al., 2008), polyurethane foam (Ferreira et al., 1999), C18 (Otero-Romaní et al., 2005), fiber (Lee et al., 2004), recycled sludge (Chu, 1999), manganese oxides (Lion et al., 1982), nanomaterials such as carbon nanotubes (Paszkiewicz et al., 2017; Sahmetlioglu et al., 2014) and XAD resins, are useful substrate for the synthesis of SPE materials (Marahel et al., 2011; Rajesh et al., 2008; Tokalıoğlu et al., 2017).

Activated carbon (AC) is a favorite materials for extraction/preconcentration of trace elements (Ahmadi et al., 2009) because of its simple usage, large internal surface area, high porosity, large adsorption capacity, and ecologically friendly (Dhelipan et al., 2016; Gao et al., 2009; Saha et al., 2001; Tu et al., 2009; Yin et al., 2007). Many examples overviewing its applications are well documented in many reviews (Bhatnagar et al., 2013; Dabrowski et al., 2005; Dias et al., 2007; Hennion, 2000; Herrera-Herrera et al., 2012; Ioannidou and Zabaniotou, 2007; Mohan and Pittman, 2006; Pyrzyńska and Bystrzejewski, 2010; Yang et al., 2007; Yin et al., 2007).

The chemical modification of AC materials are adaptable methods to enhance their selectively toward certain analytes. The modifications are expected to change the nature of surface and the interfacial region by increasing surface functional groups (Albishri and Marwani, 2016). Thus, it is useful to produce materials tailorated for specific applications such as chelating resins (Rios et al., 2003). Most frequently, COOH and aromatic groups are utilized in the modification procedures.

The carboxylic acid groups are usually utilized in chemical modifications throughout amide linkage (Rios et al., 2003). Ordinarily, the activated carbon is treated with NH-R, in the presence of catalytic additives, commonly N,N′-dicyclohexylcarbodiimide (DCC) (Albishri and Marwani, 2016; Hatami and Faghihian, 2015; Li et al., 2011; Tu et al., 2009). The surface-COOH also can be converted into a more reactive intermediate; acyl chloride groups, AC-OCl, which is a proper function to attach moieties encompassing alcohol or amine groups (Cui et al., 2011; Hwang et al., 2005; Pittman et al., 1997; Rios et al., 2003; Zhu et al., 2009a, 2009b; Zhu et al., 2009d). The secondary —OH groups within carbon surface also can be exploited to link organosilane onto surface using silylation reactions (Zhu et al., 2009c).

The recently introduced modification via radical addition with aryldiazonium salts route is a very useful ecofriendly approach for the covalent attachment of various moieties onto carbonic materials (Pandurangappa and Raghu, 2011; Scheuerman and Tumelty, 2000). This reaction, which is catalyzed by hypophosphorous acid, is simple and convenient for the preparation of gram quantities of modified carbon and offers high degree of grafting which results in bulk modified carbon substrate material (Pandurangappa and Raghu, 2011). The obtained intermediate from radical addition reaction is suitable for the attachment of enormous moieties making use of various approaches like the versatile azo coupling method. A comprehensive overview of the methodology along with scope of the surface modification strategies of a wide range of graphite surface nanomaterials are well documented in recent reviews, and the cited references therein (Barrière and Downard, 2008; Mohamed et al., 2015).

The chelating resins encompassing oxine derivatives i.e., 8-Hydroxyquinoline are much preferable due to their superb extractability for many transaction metals. Until now, the attachment of oxins moieties onto carbon has been accomplished via diazotization of p-phenylenediamine which is previously attached to carbon surface via an amide linkage with C—COOH (Hatami and Faghihian, 2015; Tian et al., 2010). In this approach, the modification efficiency depends on the number of activated carboxylic groups.

In this work, the versatile radical addition reaction was proposed as green chemistry tactic for the syntheses of carbon based chelators, for the first time. Herein, the diazonium salt, p-nitroaniline was generated in situ and anchored onto AC surface. Subsequently, this intermediate can be used to attach 8-HQ via the prominent diazo coupling. In this approach, surface aryl groups of AC have been exploited, thus the surface C-COOH can still contribute in extraction, and hence a potential enhancement in resin capacity is expected. The chelating resin applicability as SPE materials for sample preparation of trace metals from groundwater samples investigated.

2

2 Experimental

2.1

2.1 Chemicals and materials

All plastic and glassware cleaned with water, hot solution of 5% nitric acid and soaked in 10% v/v nitric acid overnight. Before use, they were rinsed several times with water Milli-Q water 18 M Ω cm−1.

All reagents used in the immobilization or analytical process were of analytical grade. The solid support AC (mesh size −100) and sodium nitrite (NaNO2) were purchased from LobalCheme (Mumbai, India). The 4-nitroanline was obtained from Acros Organics (Geel, Belgium), 8-Hydroxyquinoline, toluene and ethanol from Scharlau (Barcelona, Spain), hydrochloric acid from Philip Harris (Birmingham, UK), and nitric acid from Chem-Lab NV (Zedelgem, Belgium). Element stock solutions 1 mg/ml, Acros Organics, (Geel, Belgium) were used in the preparation of standard solutions of the studied metals. Ammonium acetate and sodium hydrosulfite were purchased from Sigma Aldrich, (England, UK). The pH was adjusted to the required value with acetic acid or liquid ammonia solution.

2.2

2.2 Instrumentation and apparatus

ICP-MS 7500 series from Agilent technologies (Santa Clara, CA, USA) was employed for the determination of metal ions at the manufacturer standard operating conditions. The measurement of solution pH performed using Basis pH meter HI22111 pH/ORP meter from HANNA Instrument Company (Bedfordshire LU, UK). Diffuse Reflection Infrared Spectroscopy (DRIR) from Perkin-Elmer 100 series (Beaconsfield, Bucks, UK), used to scan samples in the range of 200–4000 cm−1. X-ray photoelectron spectroscopy (XPS) analysis for C1s, N1s, and O1s were performed on VG ESCALab250 (Thermo Scientific, MA, USA) equipped with an Al Kα Twin Anode source at 1486.68 eV A pass energy of 20 eV with a step size of 0.05 eV. Thermogravimetric analysis (TGA) was carried out under nitrogen atmosphere at a heating rate 10 °C min−1 using TA instrument, model SDT600 (New Castle, DE, UK).

2.3

2.3 Preparation of activated carbon 8-hydroxyquinoline chelating resin

The chemical functionalization of AC with 4-nitroanaline diazonium intermediate was adapted from literature (Regitz, 1968; Saylam et al., 2014). Briefly, 10 g of activated carbon was stirred into 50 ml of 4-nitroanaline to which 50 ml of hypophosphorous acid (H3PO2, 50% V/V in water) was added slowly. Subsequently, the solution was left to stand at 5 °C for 1 h with gentle stirring. After which the solution was filtered and washed with deionized water thoroughly to remove any excess acid and finally with acetonitrile to remove any unreacted diazonium salt from the reaction mixture. The functionalized AC was then air dried by placing it inside a fume hood for a period of 24 h and prior to use for next step (Abiman et al., 2008; Kempegowda and Malingappa, 2013; Wildgoose et al., 2005).

The 4-nitrobenzyl-AC was added to 50 ml of 5% sodium hydrosulfite (Na2S2O4) in a sealed flask at 45 °C for 24 h, to reduce —NO2 group to —NH2. The product was then filtered and washed with cold distilled water to remove any access of salt and used to next step (Fan et al., 2007; Scheuerman and Tumelty, 2000). The aminobenzyl AC was diazotized for 1.5 h at 0–5 °C using 50 ml of 2% w/v 8-HQ solution in ethanol, which added dropwise into the mixture for 4 h under stirring. The resulting solid was filtered, washed with ethanol and deionized water until the filtrate was colorless and transparent, and finally dried under vacuum at 70 °C for 3 h (Daneshfar et al., 2012; Li et al., 2013; Tian et al., 2010). The resin was stored in a dissector until use.

2.4

2.4 SPE procedure

A 12-way standard SPE manifold from Ato Science (China) employed for the solid- phase extraction process. The SPE cartridges (bond straight barrel; Agilent Technologies, Santa Clara, CA, USA) packed with 200 mg of washed resin to make discs 5–10 mm in height between two porous Teflon filters. The manifold operated with a vacuum pump AP-9950 (Ato Science, China). For the SPE process, the SPE cartridges were conditioned with a passing buffer at a flow rate of 1 ml/min, and then the samples were loaded at a flow rate of 0.5 ml/min. The cartridges were flushed with water to remove any trapped metals and matrices, and then the chelated metals were eluted with 1.5 M nitric acid at 2 ml/min (Liu et al., 2014; Zhao et al., 2011). The eluted metals were collected into 10 ml PTFE sample tubes and analyzed using ICP-MS. This procedure was followed for the standards, certified reference material and the real samples.

3

3 Results and discussion

3.1

3.1 Synthesis of 8-HQ-AC chelating resin

The proposed chemical transformation for the synthesis of 8-HQ-AC resin is illustrated schematically in Fig. 1. In the first step, 4-nitroanaline moiety was introduced to the activated carbon surface using the chemically activated one-electron reduction of the 4-nitrobenzenediazonium intermediate in the presence of hypophosphorous acid as a catalyst (Masheter et al., 2007; Scheuerman and Tumelty, 2000). The second step in the sequence involved the reduction of nitro groups into amines using Na2S2O4 in order to allow the diazotization coupling for 8-HQs. In the third step, 8-HQ was anchored onto the AC surface via diazo addition (see Table 1).

Scheme for the preparation of 8-HQ-AC chelating resin.
Fig. 1 Scheme for the preparation of 8-HQ-AC chelating resin.
Table 1 Figure of merits from the modified matrix with 8-HQ-AC resin.
Calibration parameters Metal ions (ng ml−1)
Pb2+ Mn2+ Cd2+ Ni2+ Zn2+
Conc. range (ng ml−1), (n = 7) 0–50 0–50 0–50 0–50 0–50
% RSD at 2 ng ml−1 (n = 4) 1.130 1.210 1.090 1.870 1.140
% RSD at 10 ng ml−1 (n = 4) 1.420 1.360 1.870 2.010 1.830
Correlation coefficient, R2 0.9976 0.9976 0.9952 0.9979 0.9954
Sensitivity, CPS ratio/ng ml−1 4446.60 2421.30 502.64 569.06 488.56
LOD/ng ml−1 0.029 0.079 0.012 0.091 0.034

3.2

3.2 Characterization of 8-HQ-AC resin

3.2.1

3.2.1 DRIR Characterization

The successfulness of 8-HQ-AC resin synthesis has been confirmed by DRIR analysis. The main functional groups present in 8-HQ-AC were indicated by the characteristic band at 3254.48 cm−1 attributed to the phenolic hydroxyl group (O-H) (Fig. 2a). The stretching of bands appeared at 3047.99, 1549 and 1503 cm−1 confirmed the presence of aromatic proton and carbon respectively. The band shown around 1631.72 cm−1 assigned for carbonyl group (C⚌O). In the interim, the peaks at 1466.62 and 1255.81 cm−1 confirm the existence of (C⚌N) and the (C—O) (Li et al., 2013; Tian et al., 2010; Tu et al., 2009; Vuković et al., 2009). These peaks could not be recognized in IR spectra of bare AC (Fig. 2b).

DRIR spectra of 8-HQ-AC (a) and AC (b).
Fig. 2 DRIR spectra of 8-HQ-AC (a) and AC (b).

3.2.2

3.2.2 XPS characterization

XPS spectrum of 8-HQ-AC resin displays three different peaks for C1s, N1s, and O1s obtained by wide scans for the regions of the spectra corresponding for these atoms (Fig. 3). The XPS spectrum shows an intense peak in the C1s region centered the asymmetric strong peaks at a binding energy of 284.1, 285.2 and 285.9 eV, resolved into three components for C1s. The first peak at 283.8–286.5 eV could be attributed to the carbon from AC. Meanwhile the second peak at 284.3–285.5 eV more likely to be assigned to the carbon present in carboxylic acid (COOH), aromatic (C⚌C) in the phenyl and pyridine groups from both AC and 8- HQ. The third peak at 284.0–285.9 eV, on the other hand, confirms the presence of carbon C attached to nitrogen groups C⚌N from 8-HQ as seen in Fig. 3a (Biniak et al., 1997; Kosa et al., 2012; Li et al., 2013).

XPS of C1s region (a), XPS of N1s region (b), XPS of O1s region (c) for 8-HQ-AC.
Fig. 3 XPS of C1s region (a), XPS of N1s region (b), XPS of O1s region (c) for 8-HQ-AC.

The nitrogen XPS spectrum N 1s as displayed in Fig. 3b shows the two components peaks of pyridinic N (398.5 eV), N⚌N (400.3 eV). Noticeably, the smaller peak signal observed at 405.5 eV is assumed to be assigned for N and the tiny fraction of residual nitro groups which is expected to be absorbed physically onto the AC surface (Chingombe et al., 2005; Li et al., 2015; Masheter et al., 2007; Moulder et al., 1995).

O1s XPS spectra as shown in Fig. 3c reveals the presence of peaks at 530.4–535.8 eV corresponding to C⚌O groups, and small peak for OH groups in phenyl ring at 530.4–533.1 eV. In the interim, the peak allocated to OH in carboxylic acid appeared at 529.5–538.1 eV. In addition the characteristic peak at 530.5–540.1 eV indicating that the O atoms that attached onto the surface might be as nitro groups (Biniak et al., 1997; Moulder et al., 1995; Silva et al., 2002).

Overall, the XPS survey shows a strong indication that both N and O from the 8-HQ are present. The estimated ratio from peak area for C:N:O = 15:3:1. This conceded with the ratio of atoms that assumed from the structure. Thus, it is clear that 8-HQ is covalently bonded to the AC.

3.2.3

3.2.3 TGA characterization

The prepared 8-HQ-AC chelating resin was also characterized with TGA. The samples were heated at a rate of 10 °C/min from room temperature to 900 in flow of N2. The TGA curves of the raw carbon together with the 8-HQ-AC resin are shown in Fig. 4.

TGA Thermogram of AC and 8-HQ-AC resin.
Fig. 4 TGA Thermogram of AC and 8-HQ-AC resin.

The thermogram of raw AC showed a minor drop in mass appeared entirely at 40 °C due to the dehydration of the physisorbed water and the degradation of carbon start from 450 to 650. Apparently, the thermogram of 8-HQ-AC resin shows more loss in weight in comparison to the raw AC (Fig. 4). The thermogram curve of 8-HQ-AC displays three distinct mass loss steps. The first one below 120 °C (3.7%) is ascribed to the evaporation of organic and solvent residual as well as the physisorbed water on the surface of the carbon. The second mass reduction of (12.5%) between 140 °C and 500 °C is corresponding to detachment of organic molecules, because most organic functional moieties are thermally unstable in this range. The last mass loss of 82.62% between 500 and 650 °C is attributed to the decomposition of AC (Hu et al., 1999; Vuković et al., 2009; Zhou et al., 2008; Zhu et al., 2009d).

3.3

3.3 Study of pH effect

Since the solution pH has tremendous impact on the extent of complexation, which in turn determines the percentage of metal retained by the resin, the influence of the pH of 0.2 M ammonium acetate buffer on the recovery of the selected metals was studied in the range from 2 to 8. The results calculated as the average of three determinations are presented in Fig. 5. Obviously, the relative amount of metal taken up by resin increases as a function of medium pH.

pH effect studies for 8-HQ-AC chelating resin.
Fig. 5 pH effect studies for 8-HQ-AC chelating resin.

Metal sorption initiates when the pH rises to the range where most acidic ion exchange sites start to exchange hydronium ions (H+) for metals and the capacity reaches maximum value in the pH range where all the ion exchange sites take part in the reaction and the functional groups able to form chelate rings with metal cations (Hatami and Faghihian, 2015; Kosa et al., 2012).

As can be seen in Fig. 5, nearly all ions exhibited linear upward trends before reaching the maximum recovery, because the degree of dissociation increases and the concentration of H+ in solution decrease (Tian et al., 2010). The minimum adsorption observed at low pH values might have been due to the fact that the higher concentration and mobility of hydrogen ions (H+) present at lower pH proton competes with metal ions for binding to ligand that leads to a decrease in the extraction efficiency so; it favored the preferential adsorption of hydrogen ions than metal ions.

Meanwhile the increasing of pH to around 6, probably due to dissociation of sorbent functional group enhances the tendency for retention of metal ions following their complexation. However, at pH higher than 6, probably due to the precipitation of M(OH)n, the extraction efficiency is decreased, so that the pH 6 was chosen throughout the subsequent experiments (Daneshfar et al., 2012).

Noticeably, a preference recovery for Pb+2 is observed in all the investigated pH values. The acidity seems to play a negligible role on Pb+2 complexation. However, this finding match previous result by other investigators with many carbon based resins such as: aminoethylamino)-2-chlorobut-2-enoate- AC (Tu et al., 2011), aminoethylamino-methyl-phenol-AC (He et al., 2010). This phenomena might ascribed to the fact that ionic interaction is contributed in the adsorption of Pb+2, and oxygen atoms on bulky carbon may also subsidize to the adsorption according to the hard/soft acid/base theory (HSAB) (Alfarra et al., 2004; Kołodyńska, 2010; Mladenova et al., 2012). However, the recoveries of all other ions appear to be dependent on pH of medium and the maximum sorption attained around pH 6. At this pH value, the recovered value for the studied metals ranged from 92 to 98% for Ni+2 and Zn+2, and 80 to 88% for Pb+2, Cd+2 and Mn+2.

3.4

3.4 Studies of exchange capacity

The adsorption capacity is a key factor demonstrating resin performance, because it helps in estimating the required amount of sorbent to quantitatively extract/concentrate the analytes from a given solution. The calculated static capacity values of this resin for Mn, Cd, Ni, Pb and Zn were shown in 3 replicates at pH 6 and compared with exchange capacity for unmodified AC, under the same condition as seen in Fig. 6. Clearly, the capacity exchange for 8-HQ-AC resin was imp improved by more than 50% in comparison with the bare AC for all the investigated ions. The lower values for Cd and Pb might be attributed to the size of ions or to the ion behaviors as stated in the hard and soft acids and bases theory (HSAB) (Alfarra et al., 2004; Kołodyńska, 2010; Mladenova et al., 2012).

Exchange capacities (mmol g−1) of 8-HQ-AC resin.
Fig. 6 Exchange capacities (mmol g−1) of 8-HQ-AC resin.

3.5

3.5 Method validation: Analysis of groundwater reference materials

To verify the accuracy of the proposed procedure, groundwater Certified Reference Material BCR-609 was processed using the SPE manifold described before preceding to the determination of the targeted ions by ICPMS. For assessing the method performance, the measured values of the CRMs were well compared with the certified values and it was observed that the obtained values agreed with the certified ones Table 2.

Table 2 Analysis of reference materials BCR-609 using 8-HQ-AC resin.
Cd2+ Pb2+ Mn2+ Zn2+ Ni2+
Certified 0.164 1.630 – – 9.110
Fund 0.145 ± 0.018 1.710 ± 0.050 2.810 ± 0.120 6.470 ± 0.200 9.840 ± 0.101
Recovery% 88.41% 104.91% – – 108.01%

3.6

3.6 Method application: The analysis of groundwater samples

The proposed method was used for the determination of trace metals in groundwater real samples (TDS 534–742 mg/l) collected from several wells in AlMedinah Almunawwara, Hamra' Al'Asad district. All the samples were filtered and acetified to pH 2 in site and stored in clean plastic bottle at 4 °C in icebox, and immediately transported to laboratory. As with standards, 0.2 M ammonium acetate was used to buffer the samples before the SPE processing. The concentrations of the analyzed metals in real samples, along with the recovery from spiked samples are presented in Table 3. The recoveries as estimated from the addition of different concentrations of spikes to water samples were in the range of 98.6–102.0%,97.6 102.6%,87.8−105.2%,97.8–101.0% and 100–100.6% for Cd, Pb, Mn, Zn and Ni respectively. Thus, the proposed method proved to be an adequate simple analytical procedure for the simultaneous analysis of heavy/transition elements in groundwater and other environmental real samples.

Table 3 Analysis of real samples using 8-HQ-AC Result are mean ± RSD (ng ml−1).
Sample Metals Added (ng ml−1) Fund ± RSD (ng ml−1) Recovery (%)
G1 Cd2+ 0 1.340 ± 0.110 98.6
5 6.270 ± 0.120
Pb2+ 0 1.390 ± 0.300 97.6
5 6.270 ± 0.840
Mn2+ 0 8.500 ± 1.290 87.8
5 12.890 ± 1.640
Zn2+ 0 10.840 ± 1.90 97.8
5 15.730 ± 2.150
Ni2+ 0 2.420 ± 0.580 100
5 7.420 ± 1.520
G2 Cd2+ 0 1.310 + 0.160 100.4
5 6.330 ± 0.170
Pb2+ 0 1.550 ± 0.270 97.6
5 6.390 ± 0.760
Mn2+ 0 6.270 ± 1.270 110
5 11.770 ± 1.050
Zn2+ 0 12.410 ± 2.240 89.2
5 16.870 ± 2.170
Ni2+ 0 3.640 ± 0.680 106.8
5 8.980 ± 1.740
G3 Cd2+ 0 1.350 + 0.150 102.9
5 6.497 ± 0.130
Pb2+ 0 1.580 ± 0.230 102.6
5 6. 710 ± 0.610
Mn2+ 0 8.50 ± 1.640 105.2
5 13.760 ± 1.430
Zn2+ 0 11. 970 ± 2.060 101.0
5 17.020 ± 1.840
Ni2+ 0 0.890 ± 0.790 103.6
5 6.076 ± 1.080

3.7

3.7 Resin stability and reusability

The prepared chelating resin exhibited excellent stability upon multiple used in cartridges. It has been used for more than 60 SPE cycles without noticeable deterioration in capacity exchange values. However, the nature of AC as fragile material makes the resin inadequate for batch applications that required shaking as black colouration can be observed when the resin is shacked for extended time. In addition, no change in performance noticed during storing for extended time up to one year.

4

4 Conclusion

The developed ecofriendly chemical grafting reported in this article enabled the synthesis of AC- 8-HQ chelating resin via covalent attachment of 8-HQ moieties onto AC surfaces. ATR-IR, XPS and TGA analysis confirmed the success of the proposed functionalization. The investigation of the most influencing parameters on SPE processes e.g., the effect of pH, showed that the resin behave similar to other 8-HQ based chelating resins. As expected, the efficiency of the resin is relatively higher at neutral and marginally acidic or basic media. The preferred common pH range to the studied metals was 5.5–6.5. At optimum conditions, the recovery values for Ni and Zn were 92% and 98% respectively and for the others metals were at least 82–88%. Therefore, the resin is ideal for SPE in dynamic mode such as with SPE manifold. This has been established by application of the new resin as SPE materials for sample preparation of trace metals from groundwater CRM and groundwater real samples.

Acknowledgments

The authors appreciate the generous financial support from King Abdulaziz city for Science and Technologies (KACST) for financial support (grant No: P-S-36-158).

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