Water pollution, especially by inorganic and organic substances, is considered as a critical problem worldwide. Several governmental agencies are listing an increasing number of compounds as serious problems in water because of their toxicity, bioaccumulation, and persistence. In recent decades, there has been considerable research on developing analytical methods of heavy metal ions and organic pollutants from water. Ionic liquids, as the environment-friendly solvents, have been applied in the analytical process owing to their unique physicochemical properties. This review summarizes the applications of ionic liquids in the determination of heavy metal ions and organic pollutants in water samples. In addition, some sorbents that were modified physically or chemically by ionic liquids were applied in the adsorption of pollutants. According to the results in all references, the application of new designed ionic liquids and related sorbents is expected to increase in the future
From the industrial revolution to today, environmental pollutions caused by heavy metals and toxic organic compounds are an enormous problem worldwide [
For example, lead (Pb) is a heavy metal found widely in nature that was also commonly used for several centuries. The development of the civilization and related products increased the amount of lead emissions and caused an obvious increase in concentration in the environment [
Wastewater released from industrial process contains many heavy metals. Cadmium (Cd) is a nonessential element and a health hazard, even at very low concentrations in water [
In addition to heavy metal toxicity, there are other issues: (1) their high affinity for water makes them difficult to remove using conventional solvents; (2) common filtration methods cannot remove them because of the minimal structures; (3) they are unaffected by natural processes, and hence, their concentration is reduced only by dilution; and (4) biological accumulation. These features can also be found in organic pollutants. Phenols, pesticides, and endocrine disrupting compounds (EDCs) are three major types of pollutants in water samples. Phenol is an organic substance used in several industrial processes, such as the production of phenolic resin and other phenol derivative chemicals. The compound is also used as a solvent, as an antiseptic, and as an additive in disinfectants [
However, the concentrations of all pollutants in the water sample are normally quite low. In order to detect and analyze the properties in detail, assistant techniques are involved to concentrate the pollutants from water samples and can be increased the accuracy of analysis. Although traditional techniques (evaporation, extraction, crystallization, and so on) are frequently used for treating aqueous solutions, the high operational cost or difficulty in treating wastewater limits the application of most techniques, particularly when the pollutants are dissolved in large volumes of solutions. Despite the considerable improvements in modern instrumental analysis of heavy metal ions and organic pollutants, their detection is still difficult because of the low levels in samples and the high complexity of sample matrices. Although some common organic solvents were associated, the toxicity and low selectivity are one of the problems in further analysis.
In this case, a range of preconcentration processes can be used and combined with several extraction and separation methods which include liquid-liquid extraction (LLE) [
Recently, ionic liquids (IL), which are recognized as green solvents, have been used in efficient extraction or sorbent modification. This type of solvents are salts and liquids over a wide temperature range including room temperature and are prepared by the combination of organic cations with various anions. IL has some unique physicochemical properties, such as negligible vapor pressure, wide chemical and electrochemical windows, nonflammability, tunable viscosity and miscibility with water and organic solvents, as well as good extractability for a range of organic compounds, which make them potential replacements for organic solvents in the several areas [
In this case, IL as a unique solvent can solve the problems in association with analytical techniques. First, as an environment-friendly solvent [
A large amount of research work applied IL on the analysis of pollutants. Hence, we provide an overview of recent applications of IL and IL-modified sorbents in determination of heavy metal ions and organic pollutants in various water samples.
Before the analysis of heavy metal ions and organic pollutants, pretreatment or concentration of water samples can efficiently increase the precision, sensitivity, and limit of detection. Liquid extraction and its derivative methods are the typical assistant techniques used in pretreatment process. Since the first use of an IL as an alternative to traditional volatile organic solvents for two phase liquid-liquid extraction, many ionic liquids have shown several advantages (solvent power, viscosity, possibility to adjust the solubility by the choice of the anion and cation to improve and the transport properties, provide ion exchange interactions, electrostatic interactions and
Full names of anion/cation and abbreviations of all ionic liquids.
Anion abbr. | Full name | Cation abbr. | (Full name) | ILs |
---|---|---|---|---|
[BA] | Benzoate | [A336] | Tricaprylmethylammonium or aliquat | [A336][BA] |
[BF4] | Tetrafluoroborate | [MIM] | Methylimidazolium | [MIM][BF4] |
[C2MIM] or [EMIM] | 1-Ethyl-3-methylimidazolium | [C2MIM][BF4] | ||
[C4MIM] or [BMIM] | 1-Butyl-3-methylimidazolium | [C4MIM][BF4] | ||
[C6MIM] or [HMIM] | 1-Hexyl-3-methylimidazolium | [C6MIM][BF4] | ||
[C8MIM] or [OMIM] | 1-Octyl-3-methylimidazolium | [C8MIM][BF4] | ||
Br | Bromide | [C2MIM], [C4MIM], | [C2MIM]Br, [C4MIM]Br, | |
[C6MIM], [C8MIM] | [C6MIM]Br, [C8MIM]Br | |||
[CH3CO2] | Acetate | [C4MIM] | [C4MIM][CH3CO2] | |
[Cl] | Chloride | [C2MIM], [C4MIM], | [C2MIM]Cl, [C4MIM]Cl, | |
[C6MIM], [C8MIM] | [C6MIM]Cl, [C8MIM]Cl | |||
[A336] | [A336]Cl or Aliquat 336 | |||
[AMIM] | 1-Allyl-3-methylimidazolium | [AMIM]Cl | ||
[BDMIM] | 1-Butyl-2,3-dimethylimidazolium | [BDMIM]Cl | ||
[C4MPIP] or [BMPIP] | 1-Butyl-1-methylpiperidinium | [C4MPIP]Cl | ||
[C4MPYR] or [BMPYR] | 1-Butyl-1-methylpyrrolidinium | [C4MPYR]Cl | ||
Cyphos 101 | Trihexyl(tetradecyl)phosphonium | Cyphos IL 101 | ||
Cyphos 167 | Tributyl(tetradecyl)phosphonium | Cyphos IL 167 | ||
[VBIM] | 1-Vinyl-3-butylimidazolium | [VBIM]Cl | ||
3-(anthracen-9-ylmethyl)-1-vinyl-1H-imidazol-3-ium | — | |||
[BnSAc] | Benzylsulfanyl acetate | [N1888] | Methyltrioctylammonium | [N1888][BnSAc], [P1888][BnSAc]; |
[C4SAc] | Butylsulfanyl acetate | [P1888] | Methyltrioctylphosphonium | [N1888][C4SAc], [P1888][C4SAc], |
[C5SAc] | Pentylsulfanyl acetate | [N1888][C5SAc], [P1888][C5SAc], | ||
[C6SAc] | Hexylsulfanyl acetate | [N1888][C6SAc], [P1888][C6SAc], | ||
FAP | Tris(pentafluoroethyl)trifluorophosphate | [C4MIM] | [C4MIM][FAP] | |
Gly | Glycine | [C6MIM] | [C6MIM]Gly | |
[Hex] | Hexanoate | [A336] | [A336][Hex] | |
P | Propionate | TOA | Tri- |
TOAP |
[MTBA] | 2-(Methylthio)benzoate | [A336] | [A336][MTBA] | |
[PR4] | Trihexyl(tetradecyl)phosphonium | [PR4][MTBA] | ||
[N(CN)2] | Dicyanamide | [C4MIM] | [C4MIM][N(CN)2] | |
NO3 | Nitrate | [C4MIM], TOMA | [C4MIM]NO3, TOMAN | |
[PF6] | Hexafluorophosphate | [C4MIM], [C6MIM], | [C4MIM][PF6], [C6MIM][PF6], | |
[C8MIM] | [C8MIM][PF6] | |||
[NH4] | Ammonium | [NH4][PF6] | ||
[SCN] | Thiocyanate | [A336], [C4MIM] | [C4MIM][SCN], [A336][SCN] | |
[SAl] | Salicylate | [PR4], TOMA | [PR4][Sal], TOMAS | |
[Tf2N] | Bis(trifluoromethylsulfonyl)imide | [C2MIM], [C4MIM], | [C2MIM][Tf2N], [C4MIM][Tf2N], | |
[C6MIM], [C8MIM] | [C6MIM][Tf2N], [C8MIM][Tf2N] | |||
[CNC3MIM] | 1-(3-Cyanopropyl)-3-methylimidazolium | [CNC3MIM][Tf2N] | ||
[BMP] | 1-Butyl-1-methylpyrrolidinium | [BMP][Tf2N] | ||
[C6MPY] | 1-Hexyl-4-methylpyridinium | [C6MPY][Tf2N] | ||
[ClPr] | Chlorpromazine hydrochloride | [ClPr][Tf2N] | ||
[R4P] | Bis(2,4,4-trimethylpentyl) phosphinate | Cyphos 104 | Trihexyl(tetradecyl)phosphonium | Cyphos IL 104 |
[TDI] | 2,4-Diisocyanate | [BIM] | 1-Benzylimidazole | [BIM][TDI] |
[TOS] | Tosylate | [C4MIM] | [C4MIM][TOS] | |
[TS] | Thiosalicylate | [A336], [PR4] | [A336][TS], [PR4][TS] |
In traditional liquid extraction, the solvent is a hydrophobic phase compared with an aqueous metal ion solution. The hydration environment of the metal ion needs to be changed either using organic ligands that provide a more hydrophobic region around the metal, or with inorganic anions that form softer, more extractable anionic complexes with the metal [
Determination of heavy metal ions in real water samples using IL.
Ions | Sample | Used ILs | Analysis condition | Operation method | Added ( |
Found ( |
Recovery (%) | Type of interference ions | Ref. |
---|---|---|---|---|---|---|---|---|---|
Co2+ | Tap, lake, and rain water (5.0 mL) | 25.0 mg of [HMIM][BF4] with 80.0 mg of NaPF6 | R.T.; FAAS | ISFME | 0.0–50.0 | 0.0–71.1 | 94.1–101.4 | Na+, K+, Ca2+, Mg2+, Ba2+, Fe2+, Fe3+, Mn2+, Cd2+, Ni2+, Zn2+, Pb2+, NO3−, Cl−, SO42−, Br−, and Cu2+ | [ |
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Co2+ | Mineral, tap, and river water (10.0 mL) | 64.0 mg of [HMIM][PF6] with 5.0 mg of [HMIM][Tf2N] | 35°C; FAAS | DLLME | 0.0–100.0 | 0.0–100.9 | 98.0–102.5 | Ag+, Hg2+, Na+, K+, Mg2+, NH4+, Ca2+, Ni2+, Mn2+, Cu2+, Zn2+, Cd2+, Fe3+, Al3+, Rh2+, Sn2+, Pb2+, Cr3+, HPO42−, CO32−, NO3−, H2PO4−, F−, SO42−, and PO43− | [ |
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Cd2+ | Lake and waste water (15.0 mL) | 100.0 |
R.T.; FAAS | DLLME | 0.0–20.0 × 106 | 13.2–37.1 × 106 | 97.6–101.0 | Fe3+, Zn2+, Pb2+, Na+, K+, Ca2+ and Mg2+ | [ |
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Cr4+ | Mineral, sea, and river water (10.0 mL) | 150.0 |
R.T.; FAAS | LLME | 0.0–10.0 | 0.0–13.2 | 97.6–99.2 | Li+, Na+, Ca2+, Mg2+, Ba2+, Ag+, Mn2+, Zn2+, Co2+, Cu2+, Ni2+, Cd2+, Bi3+, Al3+, Pb2+, Fe3+, and Hg2+ | [ |
Pb2+ | Ground and surface water (10.0 mL) | 125.0 |
50°C; FAAS | UA-ILDME | 0.0–4.0 | 1.7–5.7 | 97.3–99.3 | Na+, K+, Ca2+, Mg2+, Al3+, Fe3+, Mn2+, Co2+, Ni2+, Zn2+, Cr3+, and Cd2+ | [ |
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Ag+ | Photographic waste, mineral, and lake water (10.0 mL) | 60.0 |
0°C; UV-Vis | M-CIAME | 0.0–50.0 | 0.0–107.3 | 98.4–104.8 | Li+, Na+, Pb2+, Cd2+, Al3+, Ba2+, Ca2+, Co2+, Zn2+, Mg2+, Pd2+, Cu2+, Ni2+, Cr3+, Mn2+, Cr4+, Bi3+, Fe3+, and Hg2+ | [ |
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Al3+, Ga3+, and In3+ | Tap, mineral, and well water (10.0 mL) | 75.0 |
R.T.; UV-Vis | UA-ILDME | 0.0–50.0 | 6.7–54.3 | 86.0–120.5 | Li+, Na+, K+, Cl−, NO3−, Ca2+, Mg2+, Ba2+, SO42−, Pb2+, Ag+, Hg2+, Co2+, Zn2+, Cr3+, Mn2+, Cd2+, Ni2+, Fe2+, and Cu2+ | [ |
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Co2+ and Ni2+ | Tap and mineral water (10.0 mL) | 65.0 mg of [HMIM][Tf2N] with 1.0 × 10−3 mol/L PAN | R.T.; UV-Vis | DLLME | 0.0–10.0 | 0.0–14.5 | 94.0–102.0 | Na+, K+, Ag+, F−, Cl−, Br−, NO3−, SO42−, PO43−, SCN−, CH3COO−, Mg2+, Ca2+, Ba2+, Pb2+, Cr3+, Cr3+, Al3+, Sb3+, Cu2+, Cd2+, Pd2+, and Fe2+ | [ |
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Cd2+ and Pb2+ | Tap, river, and well water (15.0 mL) | 120.0 |
R.T.; FAAS | UA-MR- il-DLLME | 0.0–15.0 | 0.0–18.9 | 97.1–101.6 | Na+, K+, Ca2+, Mg2+, Mn2+, Cu2+, Zn2+, Cl−, and SO42− | [ |
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Ni2+, Co2+, Cd2+, Cu2+, and Pb2+ | River and lake water (15.0 mL) | Cyphos IL 104 | R.T.; LC | IL-UADLLME-SAP | 0.2–62.4 | 0.3–15.3 | 97.0–102.0 | — | [ |
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Ag+, As3+, Cd2+, Cr3+, Cu2+, Hg+, Ni2+, Pb2+, Pt4+, Sn2+, and Zn2+ | Communal and industrial wastewater (20.0 mL) | 120.0 |
20°C; LC-MS | LLME | (Extraction efficiency: 5.0–100.0) | — | [ |
R.T.: room temperature; FAAS : flame atomic absorption spectrometer; LC-MS : liquid chromatography-mass spectrometry.
Cadmium is a nonessential element that has no positive nutritional or biometallic role in humans or animals [
Khan et al. [
Although chromium is an essential material for humans and plays an important role in the physiological metabolism, Cr4+ is a very toxic ion to humans and living organisms [
Cobalt and its compounds are used in the metallurgical industry, electroplating, nuclear technology, fertilizers, medicine, and colored pigments. On the other hand, cobalt is harmful when an excess cobalt metal (more than 40.0
Lead is a heavy metal found widely in nature. The element cannot be biodegraded in the environment, so it accumulates in the tissues of living organisms and is a high health risk. The concentration of lead in wastewater should be less than 50.0
Silver is one of the precious metals that is used widely in accessories, tableware, and coins. With its high antibacterial activity, it is used as a disinfectant in drinking water, foods, and cosmetics. Silver in such products diffuses gradually to the environment, and excess amounts in the human body cause skin diseases and blood disorders. The regulation value of silver in water has been set to 100.0
Aluminum, gallium, and indium are used widely in human life and industry, such as packaging materials, semiconductors, and photodetectors. The safe level of the three metal ions in drinking water is less than 0.20 mg/L, and an excess amount of these ions has been implicated in several human diseases. In this case, the three metal ions should be removed from water samples. Ghasemi and Zolfonoun [
Nickel and cobalt are nutritionally essential trace metals for at least several animal species, microorganisms, and plants. Large amounts of these metals are toxic and can cause an allergic reaction in the human body. The EPA recommends that the drinking water levels should be no higher than 100.0
Yao et al. [
Werner [
Fischer et al. [
Several studies investigated the extraction effects of interfering metal ions that were common coexistence ions in water samples. Although they had a competitive interaction with the chelating agent, selective extraction can be adjusted using different IL interacting with functional groups on metal ion-chelating agent complex. In addition, pH is a significant factor in metal-chelate-IL formation and is a key parameter for extraction. Therefore, the selected IL can extract the target metal ions with high recoveries under the optimized pH.
In the concentration and determination process of organic pollutants, based on different interactions between the receptor and dispersing solvent, the pollutants could be concentrated in different phases. Therefore, when IL was used in aqueous systems, the hydrophilic/hydrophobic properties of IL could affect the extraction efficiency. To reveal the interaction mechanism and chemical bonds, Gao et al. [
From the results of previous research, the hydrophilic/hydrophobic properties and chemical bonds of IL are two major mechanisms to promote the concentration of organic compounds. On the other hand, one of the IL characteristics exploited is their ability to dissolve a variety of solutes by modifying and combining suitable cations and anions. Therefore, IL is a novel, environmentally benign solvent for the analysis of organic pollutants [
Determination of organic pollutants in real samples by IL solutions.
Pollutants | Samples | Used IL | Analysis condition | Operation method | Added ( |
Found ( |
Recovery (%) | LOD ( |
RSD (%) | Ref. |
---|---|---|---|---|---|---|---|---|---|---|
o,p’-DDT, p,p’-DDT, p,p’-DDD, and p,p’-DDE | Snow, rain, lake, and tap water (5.0 mL) | 300.0 |
R.T.; HPLC | DLLME | 5.0 | — | 85.7–106.8 | 0.2–0.5 | 6.0–8.5 | [ |
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17- |
Lake, well, tap, and river water (160.0 mL) | 80.0 |
R.T.; HPLC | DLLME | 0.2–0.9 | — | 95.5–114.6 | 0.04–0.05 | 4.2–8.0 | [ |
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Phenol, CP, DCP, TCP, and PCP | Aqueous emulsion (10.0 mL) | 0.02% (v/v) of [BMIM][PF6] in TBP | R.T.; UV-vis | Liquid membranes | Extraction efficiency: 96.9%–99.5% | [ | ||||
0.2% (v/v) of aliquat 336 in TBP | Extraction efficiency: 90.1%–99.3% | [ | ||||||||
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Phenol, o-cresol, 2-chlorophenol, and resorcinol | Aqueous solution | 5.0 mg/mL of [BMIM][Tf2N], [HMIM][Tf2N], and [PMIM][Tf2N] | 33°C; color reaction | Liquid extraction | — | — | 99.99 | — | — | [ |
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Gallic acid, vanillic acid, and vsyringic acid | Salty aqueous solution (20.0 mL) | 5 wt% of [BMIM](SCN), [BMIM][TOS], [BMIM][N(CN)2], [BMIM][CH3CO2], [BMIM]Cl, [BMPIP]Cl, and [BMPYR]Cl | R.T.; UV-vis | ATP | Extraction efficiency: 66.0%–94.6% | — | [ | |||
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NT, DNT, and TNT | Tap and lake water (5.0 mL) | 26.0 mg of [HMIM][Tf2N] and [C6MPY][Tf2N] | R.T.; HPLC | DLLME | 5.0–20.0 | 4.7–20.0 | 93.2–101.0 | 0.7–1.1 | 3.1–4.3 | [ |
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BPA, 4-CP, t-BP, OP, t-OP, and NP | Deionized and sea water (20.0 mL) | 10.0 |
R.T.; HPLC | DLLME | — | — | 67.6–114.0 | 0.8–4.8 | 2.8–11.0 | [ |
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BPA and 2-naphthol | Tap, lake, and river water (5.0 mL) | 35.0 |
R.T.; HPLC | CIA-ME | 20.0 | — | 97.1–108.1 | 0.6–0.9 | 2.3–4.1 | [ |
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BPA | Tap, reservoir, and beach water (0.05 mL) | 5.0 |
20°C; HPLC | ATPM | 100.0–1500.0 | 95.5–1559.0 | 95.5–109.9 | 4.3–4.6 | 2.9–4.5 | [ |
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TCL, DOX, BPA, TCS, and MTCS | Sea, WRTR, and tap water (5.0 mL) | 115.0 |
R.T.; HPLC | SILM-DS | 8.0–50.0 | 6.3–47.7 | 74.5–106.9 | 0.1–0.8 | 2.2–6.5 | [ |
Phenolic compounds are common organic compounds used in many manufacturing processes and chemical solvents. On the other hand, because of the carcinogenic effect, they are toxic to humans and the environment [
Almeida et al. [
Nitroaromatic compounds are quite toxic, even at low concentrations. They can be released into the environment through waste from the chemical industry and other industries. Berton et al. [
Some studies compared the influences of different cations or anions of IL on the analysis of pesticides. DDT is a pesticide that was used all over the world several decades ago and can still be found in the environment. Wang et al. [
BPA is a widely used EDC in the plastic industry and can influence the generative function of humans at low concentration in the wastewater system. López-Darias et al. [
17-
Gao et al. [
Overall, IL can detect the heavy metal ions and organic pollutants in water samples efficiently. The hydrated nature of the metal ions explains their affinities to water. Therefore, the hydration state needs to be altered using a chelating agent to form a complex and provide a more hydrophobic structure from water samples. In addition, metal ions are positively charged in aqueous solution. With designed anions, for example, eight IL with different anions in Fischer’s research [
From the literature related to the organic pollutants, it was found that IL is strongly solvated by hydrogen-bonding solvents, principally by forming hydrogen bonds with the anions. On the other hand, hydrophobic interactions between the cation of IL and benzene/phenol functional group on the phenolic compounds and EDCs are also very important. Based on these results from the literature, the organic pollutants that can be bound to IL by hydrogen bonding and hydrophobic interactions are transferred easily from aqueous solution to the IL phases.
In the results of all above-mentioned techniques, the research studies using in association with the ionic liquid showed relatively low LODs, high recovery, and high efficiency. In addition, the overall precision of the current method in terms of RSD was better or comparable than other methods. Hence, the IL with the appropriate anion and cation will enhance the facility for determination.
Determination methods are necessary to evaluate the removing efficiency of heavy metal ions and organic pollutants from water samples. The most commonly used techniques for determining the amount of cadmium ions in aqueous solution include UV-visible spectrometry, atomic fluorescence spectrometry (AFS) [
In this case, preconcentration methods such as the classical LLE and SPE are proposed. On the other hand, these methods require large quantities of organic solvents that are still harmful to the environment [
Among the treatments to concentrate heavy metal ions and organic pollutants, adsorption is the simplest and most dynamic physicochemical process that has been employed for the removal of a range of toxic pollutants present in water systems [
Although IL is considered as efficient liquid extractants and can interact with metal ions or organic pollutants through hydrophobic,
In the preparation of sorbents, two modified methods, such as impregnation and chemical modification, were used. In the preparation of an impregnated sorbent, IL and substrate were mixed and stirred in a solvent for several hours. The operation and process were quite simple and convenient. On the other hand, the chemical bonds between the IL and substrates were mainly van der Waals force or hydrogen bonds, which were neither strong nor stable enough. Therefore, some researchers chemically immobilized IL groups on substrates by covalent bonding to increase the stability and efficiency of the sorbents. Table
Preparation methods of IL-modified sorbents.
Substrate | Used IL | Preparation process | Method | Ref. |
---|---|---|---|---|
Graphene, CNT | (BMP)[Tf2N] | Impregnation | 57.0% graphite powder, 14.0% (BMP)[Tf2N], 10.0% MWCNTs and 13.0% macrocyclic ligand, and 6.0% paraffin oil (weight ratio) | [ |
Activated carbon | TOMAS | 0.18 g of PSAC and 0.12 g of TOMAS | [ | |
Three resins | Cyphos IL 101 | 0.5 g of Cyphos IL 101, 1.0 g of amberlite XAD-4, XAD-16, and XAD-1180, mixing in 5.0 mL of ethanol for 6 h | [ | |
XAD-4 | (BMP)[Tf2N] | 1.0 g of XAD-4 and 100.0 |
[ | |
Silica | [NH2EBIM][PF6] | 3.0 mL of [NH2EBIM][PF6] and 10.0 g of silica, mixing in methanol for 2.5 h | [ | |
Silica | [EMIM][Tf2N], [OMIM][Tf2N] | 10.0 g of Sil-NH2, 5.0 mL of [EMIM][Tf2N], or 7.2 g of [OMIM][Tf2N], mixing in toluene at room temperature (RT) | [ | |
Graphene, CNT | [BMIM][PF6] | 20.0% [BMIM][PF6], 18.0% ionophore, 49.0% graphite powder, 10.0% MWCNT, and 3.0% nanosilica (weight ratio) | [ | |
Graphene oxide | [BMIM][PF6] | 500.0 |
[ | |
Graphene oxide | [HMIM]Gly | 0.1 g of IL and 0.1 g of Fe-GO, mixing in 10 mL of methyl alcohol for 2 h | [ | |
MOF | [BMIM]Cl | 0.5 g of [BMIM]Cl and 10.0 mL of MIL-100(Fe), mixing in aqueous solution for 15 h at RT | [ | |
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Silica | [ClPr][Tf2N] | Chemical modification | 2.0 g of [ClPr][Tf2N], 6.0 g of silica, 5.0 ml of tetraethoxysilane, and 1.0 ml of 25.0% aqueous ammonia solution, mixing in 60.0 mL of toluene at 25°C for 5 h | [ |
Silica | [CNC3MIM][Tf2N] | 20.0 g of silica and 20.0 mL of 3-aminopropyltrimethoxysilane, reacting in 150.0 mL of toluene | [ | |
5.0 g of the aminated silica and 3.0 g of [CNC3MIM][Tf2N], reacting in 100.0 mL of toluene | ||||
|
[BIM][TDI] | First, |
[ | |
Third, 1.0 g of | ||||
Silica | [BMIM]Br | 400.0 mg of silica and 462.3 mg of [C4MIM]Br, reacting in 50.0 mL methanol at 30°C for 4 h | [ | |
1.9 mL of ethylene dimethacrylate and 10.0 mg of azobisisobutyronitrile were added and shaked at 60°C for 24 h | ||||
MIPIL | 3-(Anthracen-9-ylmethyl)-1-vinyl-1h-imidazol-3-ium chloride | 1-vinylimidazole (0.94 g) and 9-chloromethylanthracene (1.133 g), reacting in acetonitrile (30 mL) at 70°C for 12 h. Then, the obtained IL monomer (64 mg), EGDMA (198 mg), p-NA (7 mg), and AIBN reacting at 60°C for 12 h | [ | |
MIP | [VBIM]Cl | CS (1.5 mmol), [VBIM]Cl (3.6 mmol), EDMA (8.0 mmol), and AIBN (20.0 mg), reacting in 2.5 mL N,N-dimethylformamide and 4.0 mL toluene and 1.0 mL methanol at 60°C for 24 h | [ |
Adsorption of pollutants in real water samples by IL-modified sorbents.
Pollution | Source of water samples | Analytical method | Added ( |
Found ( |
Recovery (%) | LOD ( |
RSD (%) | Ref. |
---|---|---|---|---|---|---|---|---|
Hg2+ | Sea and waste | Potentiometer | 0.0–0.08 | 0.02–0.1 | 98.6–103.2 | 0.008 | 2.8 | [ |
Cd2+ | Drinking | Potentiometer | 1.4 × 107 | — | 97.8–104.6 | 14.4 | 1.6–3.2 | [ |
Hg2+ | Mineral, tap, and river | SPE | 0.0–1.0 | 0.03–1.1 | 96.2–103.0 | 2.3 × 10−3 | 2.7 | [ |
Cd2+ | Tap and lake | SPE | 0.0–1.0 | 0.0–1.2 | 97.0–104.0 | 8.9 × 10−3 | 2.3 | [ |
Cd2+ | Tap and waste | Adsorption in vitro | 1.0–2.0 × 103 | — | 97.8–98.8 | — | — | [ |
Pb2+ | Tap, river, and waste | Potentiometer | 26.7–1.3 × 104 | 24.9–1.6 × 104 | 95.0–102.0 | 0.4 | <1.0 | [ |
Cu2+, Co2+, Cr2+, Ni2+, Zn2+, and Cd2+ | Waste, river, and mineral | Adsorption in vitro | 20.0 | 19.1–91.0 | 90.5–107.5 | 0.1–1.0 | <3.2 | [ |
Al3+, Cr3+, Cu2+, and Pb2+ | Lake and waste | Adsorption in vitro | 0.0–100.0 | 0.0–170.9 | 88.4–117.8 | 0.5–30.0 × 10−3 | 1.4–6.0 | [ |
Pb2+ and Cd2+ | Tap, domestic, and industrial | Adsorption | 2.0–12.0 × 103 | 1.1–19.2 × 103 | 97.4–99.8 | — | — | [ |
DBP | River and canal | Adsorption in vitro | 1.0–10.0 | — | 80.0–87.0 | 0.15 | 4.3–7.8 | [ |
4-CP | Drinking, ground, lake, sea, and waste | Adsorption in vitro | 25.0–75.0 × 103 | 0.5–8.5 × 103 | 88.6–98.1 | 9.8 × 103 | — | [ |
12 PAHs | Mineral, river, and sea | SPE | 2.0–20.0 | 1.9–20.1 | 97.0–103.5 | 2.0–5.5 × 10−3 | 3.0–4.9 | [ |
6 phenols | Tap and river | SPE | 0.5–1.0 × 103 | — | 87.0–116.3 | 0.2–0.4 | 1.0–3.4 | [ |
2,4-DCP, BPA, and 2,4-DNP | Industrial, dyeing, textile, river, and plant effluent | SPE | 6.0–500.0 | — | 71.1–115.7 | — | 1.1–11.3 | [ |
|
River, tap, and lake | Adsorption in vitro | 5.0–45.0 × 103 | — | 89.0–114.0 | — | — | [ |
CS | Surface | SPE | 1.0–5.0 | — | 81.0–110.1 | 1.0 × 10−3 | 1.2–7.6 | [ |
Because of the excellent stability of inorganic substrates, several studies applied these sorbents, particularly carbon-based materials and silica, to adsorb pollutants from water samples. Activated carbon, carbon nanotubes (CNT), and graphene are three of the most important carbon-based materials with a large specific surface area, and they provide high efficiency to extract various metal ions. Ismaiel et al. [
Afkhami et al. [
Rofouei et al. [
Silica also has a large specific surface area, and a large number of –OH groups on its surface, making it easy to be modified by IL groups. Wen et al. [
Organic substrates have other advantages, such as various functional groups and controllable porous structure. Hence, they are also applied to prepare IL-modified sorbents. Cyphos IL 101 was already applied in metal ion extraction, and Navarro et al. [
IL-modified silica sorbent was also applied to the adsorption of organic pollutants. Marwani and Bakhsh [
Considering the various groups in organic pollutants, researchers paid more attention to IL-modified organic substrates. Two IL-impregnated organic sorbents were prepared to adsorb dibutyl phthalate (DBP) and polycyclic aromatic hydrocarbons (PAH). Phthalates (PAE) are classified as EDCs and priority pollutants with dibutyl phthalate (DBP) being one of the most common PAE present in environmental samples. Qureshi et al. [
Furthermore, IL were chemically modified as sorbents to increase the adsorption efficiencies. Raoov et al. [
p-Nitroaniline (p-NA) is an aromatic amine, and it is important for the synthesis of chemical products. On the other hand, it may poison the blood of humans and even cause cancer. Lu et al. [
Chlorsulfuron (CS) is a widely used herbicide that is found frequently in environmental water samples. Guo et al. [
Overall, the selectivity of sorbents increased with specially designed anion/cation IL. The adsorption of metal ions and organic pollutants was largely dependent on their hydrophilicity and the pH of the solution. With the exception of the properties of IL, such as H-bonding and polarity, ionic bonds had major impacts on adsorption. The IL-modified sorbents preferred to form ionic bonds between metal ions and anions on IL and between negative charge organic ions and cations on IL. On the other hand, because of the stronger ionic bonds between the metal ions and IL, the adsorption efficiency of metal ions on the sorbents was higher than that of organic pollutants. Therefore, researchers preferred to evaluate the adsorption of metal ions in water than organic pollutants. In addition, the substrates can greatly enhance the adsorption capacity because of their high specific surface area and tunable pore sizes. In the literature, the substrates were normally inorganic (such as silica and carbon) and organic (such as polymer and MOF) materials. Inorganic substrates have a huge surface area and provided large numbers of functional sites for IL modification. The structure of organic substrates can be adjusted easily by porogens or templates. Furthermore, without volatile organic solvents, the adsorption method using the IL-modified sorbent is simple, rapid, reproducible, and environmentally friendly. Also, the sensitivity is satisfactory and comparable to other reported methods.
When IL was used as a green solvent to detect pollutants, according to properties of the target substances, IL with different types of cations and anions were selected according to the different hydrogen bond basicity strength, viscosity, hydrophilicity, and hydrophobicity. On the other hand, heavy metal ions in water samples were hardly combined by pure IL because the hydrated ions preferred the aqueous phase, and conventional IL have no selectivity. To increase the analysis accuracy, two methods in the above studies were adopted. First, the ions could be successfully concentrated into IL-complexed ion-pairing agent with the associated methods. Second, functionalized IL that contains metal ion coordinating groups incorporated covalently into the cation or anion were designed. The hydrophilicity/hydrophobicity of IL is the main interaction in determination of organic pollutants. The methods with assistance of IL proved to be a rapid, simple, sensitive, precise, and accurate analytical approach. Although the analysis using low volumes of IL provided a simple, economic, and environmentally friendly operation process, there were still some drawbacks, such as the lower selectivity for metal ions, difficulty in phase separation, and entraining loss of ionic liquid to the aqueous phase. IL-modified sorbents can solve these problems, and in the adsorption process, the sorbents could obviously improve the adsorption capacity. Nevertheless, additional agents and low efficiency on sorbent modification limited the application of IL in the determination process. Therefore, in the future, newly designed IL may provide considerable assurance for applying them as an effective approach for determination of pollutants in complicated and variable water samples.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
This work was supported by the Program of China Scholarships Council (no. 201808420038) and the National Research Foundation of Korea (NRF) grant funded by the Korean government MSIT (no. NRF-2019R1A2C1010032).