3.1 Organic Linkers
Organic Linkers refers to category of complexes which are organic ligands, for
example, polyacrylonitrile (PAN) or coordinated to organic ligands like metal
organic frameworks (MOFs). These organic ligands are defined as molecules that
can bind to, and form a stable complex with, trace metals in the aquatic dissolved
(typically <0.2 µm) phase. They have always been an attractive complexing agent
in trace metals detection by virtue of the selective chelating ability of their heteroatoms such as oxygen, sulphur, nitrogen, etc. In general, the formed selective
complex is either a chelate or a ring. They often used in conjugation with metallic
nanoparticles and quantum dots. Further, previously discussed sensing mechanisms
can be employed for the detection of desired analytes. Here, recently discovered or
utilized organic linkers in the area of colorimetric sensing of inorganic water pollutants are discussed.
Recently Tian et al. recognises the potential of small organic molecules in field
of colorimetric detection of multiple inorganic metals ions and utilized them for the
detection of Hg(II), Co(II), Fe(II), and Fe(III) well below the prescribed WHO
limits [7]. To achieve this, Terpyridine (Tpy), a heterocyclic compound having
three nitrogen elements results in strong chelating effects and ability to shows color
changes and change in absorption spectra on interacting with metal ions. To
improve the hydrophobicity of Tpy molecule quinolinium iodide (QL) and
Table 1 (continued)
Material
Heavy
metals
Analytical details
Water matrix
Other chromogenic materials
ZIF-8/GO [24]
Ag(I)
LOD = 153 ppt
River water;
Human
serum
PAN fibre [25]
Hg(II), Cu
(II)
Screening only
Distilled
water
Curcumin based NFs [26]
Pb(II)
LOD: 207 ppm
Distilled
water
PAR onto PAN fibre [27]
Hg(II)
LOD = 35 ppb
Distilled
water
BSA bovine serum albumin, Cys cysteine, GO graphene oxide, HCFI 3(5-hydroxy-4-carboxyphenylimino)-5-fluoro indol-2(H)one reagent, LOD limit of detection LR
linear range, MOF metal-organic framework, MPA mercapto-propanoic acid, NC nanocluster, NF
nanofiber, NP nanoparticle, PAR 4-(2-pyridylazo)-resorcinol, PAN polyacrylonitrile, PEG
polyethylene glycol, P(DHB-a-DHBDT) poly(2, 3-dihydroxybutylene-alt-2,3-dihydroxybutylenedithioether),
PST
2-(5-bromopyridine-2-yl)-3′,6′-bis(diethylamino)-spiro[isoindoline-1,9′-xanthene]-3-thione,
PyDPP
2-(2-(2-methoxyethoxy)-ethyl)-3,6-di(pyridin-2-yl)2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, QD quantum dots, RS rhodamine hydrazide, Tpy-BZ
terpyridine benzo thiazolium iodide, Tpy-QL terpyridine quinolinium iodide, ZIF zeolite
imidazolate frameworks
Materials in Colorimetric Detection of Water Pollutants
133
Organic Linkers refers to category of complexes which are organic ligands, for
example, polyacrylonitrile (PAN) or coordinated to organic ligands like metal
organic frameworks (MOFs). These organic ligands are defined as molecules that
can bind to, and form a stable complex with, trace metals in the aquatic dissolved
(typically <0.2 µm) phase. They have always been an attractive complexing agent
in trace metals detection by virtue of the selective chelating ability of their heteroatoms such as oxygen, sulphur, nitrogen, etc. In general, the formed selective
complex is either a chelate or a ring. They often used in conjugation with metallic
nanoparticles and quantum dots. Further, previously discussed sensing mechanisms
can be employed for the detection of desired analytes. Here, recently discovered or
utilized organic linkers in the area of colorimetric sensing of inorganic water pollutants are discussed.
Recently Tian et al. recognises the potential of small organic molecules in field
of colorimetric detection of multiple inorganic metals ions and utilized them for the
detection of Hg(II), Co(II), Fe(II), and Fe(III) well below the prescribed WHO
limits [7]. To achieve this, Terpyridine (Tpy), a heterocyclic compound having
three nitrogen elements results in strong chelating effects and ability to shows color
changes and change in absorption spectra on interacting with metal ions. To
improve the hydrophobicity of Tpy molecule quinolinium iodide (QL) and
Table 1 (continued)
Material
Heavy
metals
Analytical details
Water matrix
Other chromogenic materials
ZIF-8/GO [24]
Ag(I)
LOD = 153 ppt
River water;
Human
serum
PAN fibre [25]
Hg(II), Cu
(II)
Screening only
Distilled
water
Curcumin based NFs [26]
Pb(II)
LOD: 207 ppm
Distilled
water
PAR onto PAN fibre [27]
Hg(II)
LOD = 35 ppb
Distilled
water
BSA bovine serum albumin, Cys cysteine, GO graphene oxide, HCFI 3(5-hydroxy-4-carboxyphenylimino)-5-fluoro indol-2(H)one reagent, LOD limit of detection LR
linear range, MOF metal-organic framework, MPA mercapto-propanoic acid, NC nanocluster, NF
nanofiber, NP nanoparticle, PAR 4-(2-pyridylazo)-resorcinol, PAN polyacrylonitrile, PEG
polyethylene glycol, P(DHB-a-DHBDT) poly(2, 3-dihydroxybutylene-alt-2,3-dihydroxybutylenedithioether),
PST
2-(5-bromopyridine-2-yl)-3′,6′-bis(diethylamino)-spiro[isoindoline-1,9′-xanthene]-3-thione,
PyDPP
2-(2-(2-methoxyethoxy)-ethyl)-3,6-di(pyridin-2-yl)2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, QD quantum dots, RS rhodamine hydrazide, Tpy-BZ
terpyridine benzo thiazolium iodide, Tpy-QL terpyridine quinolinium iodide, ZIF zeolite
imidazolate frameworks
Materials in Colorimetric Detection of Water Pollutants
133