The Application of Modified SBA-15 as a Chemosensor

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The Santa Barbara Amorphous (SBA-15), with a large surface area covered with abundant Si-OH active groups on the walls of its pores, can be modified with various organic compounds to build organic-inorganic hybrid materials, which can be used as a catalyst in organic reactions, drug delivery systems, nano sorbent due to its high capacity for removing heavy metals in waste water and as chemosensors for ions. Tunable and straight channels of SBA-15 facilitate the entrance and diffusion of ions through the channels. This paper presents a review of the past five years of literature covering the application of SBA-15 as an ions chemosensor in the liquid and gaseous media.

SBA-Pr-Is-TAP Functionalized Nanostructured Silica as a Highly Selective Fluorescent Chemosensor for Fe3+ and Cr2O72- Ions in Aqueous Media

SBA-Pr-Is-TAP was synthesized via functionalization of SBA-15. The synthesized hybrid nanomaterial was characterized by various techniques including FT-IR, TGA, XRD, SEM, and BET. SBA-Pr-Is-TAP could precisely bind Fe3+ and Cr2O72- ions among a range of different species in aqueous media, consequently acting as a nanoporous chemosensor of Fe3+ and Cr2O72- ions. An excellent linear relation was observed between the nanoporous chemosensor and ion concentrations, with acceptable detection limits of 2.43 × 10-6 M and 3.96 × 10-7 M for Fe3+ and Cr2O72- ions respectively.

Discriminatory behavior of a rhodamine 6G decorated mesoporous silica based multiple cation sensor towards Cu2+ and Hg2+vis-à-vis Al3+, Cr3+ and Fe3+: selective removal of Cu2+ and Hg2+ from aqueous media

Selective identification of metal ions as well as their removal is possible when a sensing unit is anchored to a solid support. In this paper, functionalized mesoporous silica with a pendant rhodamine 6G moiety (R6FMS) has been obtained by successive grafting of an aldehyde derivative of bisphenol A followed by rhodamine 6G over a 3-aminopropyl anchored mesoporous silica framework. The materials have been characterized by powder X-ray diffraction, nitrogen sorption and electron microscopy studies, FT-IR and solid state MAS NMR spectral studies, and thermal analysis. In ethanol, the colorless silica material gives pink coloration in the presence of Al3+, Cr3+, Fe3+ and Cu2+ which is also clearly evident from the generation of an absorption peak at 525 nm. Upon excitation at 500 nm, the fluorescence intensity of the probe increases by 36-, 17-, 40- and 89-fold in the presence of Al3+, Cr3+, Fe3+ and Cu2+ ions, respectively. This suggests that R6FMS is a colorimetric and fluorescent chemosensor for these cations in ethanol. However, when the solvent is changed from ethanol to water, it becomes a selective chemosensor only for Cu2+ and Hg2+, by the generation of a pink color and strong fluorescence at ca. 550 nm, thereby discriminating the trivalent cations. Cations induce the opening of the spirolactam ring resulting in pink coloration and strong fluorescence. The quantum yield and lifetime of the probe have been increased considerably in the presence of these cations in ethanol as well as in aqueous media. The detection limit values for these cations range from 10-6 to 10-8 M. R6FMS has been used to remove Hg2+ and Cu2+ from their aqueous solution with a maximum adsorption capacity of 35 mg g-1 and 148 mg g-1 for Cu2+ and Hg2+, respectively.

8-Hydroxyquinoline Fluorophore for Sensing of Metal Ions and Anions

Among various known hydroxyquinolines, 8-hydroxyquinoline (8-HQ) is the most prevalent moiety due to excellent property for the formation of the complex with different metal ions and anions, and utilized in a wide variety of applications in pharmacological and medicinal fields. 8-Hydroxyquinoline moiety and its analogues acts as fluorophoric ligands on complex formation with alkali and alkaline as well as transition metal ions and anions, thus, considered as an ideal building block in metallo-supramolecular chemistry for recognition, separation, and quantitative investigation of cations. 8-Hydroxyquinoline moiety is also used in various applications for the advancement of novel fluorescent chemosensors in a wide variety of areas viz., material chemistry, bioorganic chemistry, molecular imaging, analytical chemistry, molecular recognition, medical and biological science communities. The present review emphasises on the progress of sensing properties of 8-HQ centred small-molecule fluorescent chemosensors towards several metal ions viz., Fe³⁺ , Al³⁺ , Ag⁺ , Hg²⁺ , Cu²⁺ , Pd²⁺ , Zn²⁺ , Cr³⁺ , Cd²⁺ , Mn²⁺ , Ca²⁺ , and K⁺ and anions such as F^- , CN^- and PPi, from 2008 to 2020, because of their sensitivity and selectivity in terms of diverse colour changes for different species. This critical and comprehensive review might facilitate the improvement of more prevailing chemosensors for future exciting and broad applications.

Effective removal of Cr(VI) from aqueous solution based on APTES modified nanoporous silicon prepared from kerf loss silicon waste

Recently, the recycling of kerf loss silicon waste has trigged much attention due to the rapid growth of PV market. In this study, 3-aminopropylethoxysilane (APTES)-functionalized nanoporous silicon (NPSi) hybrid materials were prepared by nanosilver-assisted chemical etching (Ag-ACE) of kerf loss silicon waste derived from diamond-wire saw cutting silicon ingot process. The resulting APTES-NPSi indicated high-effective adsorption ability of Cr(VI) from aqueous solution, which was highly pH dependent, and the maximum adsorption capacity reached up to 103.75 mg/g after 60 min at room temperature. The adsorption kinetics and adsorption isotherms were in good agreement with pseudo-second-order model and Langmuir isotherm. Additionally, the Cr(VI) up-take mechanism was carefully investigated and ascribed to the Cr(VI) adsorption on the protonated anime groups by chemical chelating reaction in which the Cr(VI) was reduced to Cr(III). It was worth mentioning that the APTES-NPSi maintained excellent adsorption capacity after five successive regenerated cycles. Therefore, the work would pave the way for recycling of silicon cutting waste and the potential of Cr(VI) removal from aqueous solution based on the modified NPSi.

Fluorescence study of 5-nitroisatin Schiff base immobilized on SBA-15 for sensing Fe3+

N’-(5-nitro-2-oxoindolin-3-ylidene) thiophene-2-carbohydrazide (NH) was successfully synthesized as a ligand, then grafted onto the surface of mesoporous silica SBA-15via an aminopropyl bridge. The successful grafting of ligand NH onto the hybrid nanomaterial (SBA-15/APTES-NH) was confirmed by infrared spectroscopy. On excitation at 276 and 370 nm, the ligand NH and the hybrid nanomaterial SBA-15/APTES-NH showed a strong and narrow emission peak centered at 533 nm. By dispersing SBA-15/APTES-NH in an aqueous solution containing metal ions, the resulting solid materials showed a higher binding of NH sensing site to Fe3+ ions as compared to the others with a quench of the emission intensity up to 84%. This result showed that the hybrid nanomaterial is a potential chemosensor that requires development for the detection of metal ions.

Triazole-based novel bis Schiff base colorimetric and fluorescent turn-on dual chemosensor for Cu2+ and Pb2+: application to living cell imaging and molecular logic gates

A triazole-based novel bis Schiff base colorimetric and fluorescent chemosensor (L) has been designed, synthesized and characterized by elemental analysis, ¹H-NMR, ESI-MS, FTIR spectra and DFT studies. The receptor L showed selective and sensitive colorimetric sensing ability for Cu²⁺ and Pb²⁺ ions by changing color from colorless to yellow and light yellow respectively in CH₃OH–tris-buffer (1 : 1, v/v). However, it displayed strong fluorescence enhancement upon the addition of both Cu²⁺ and Pb²⁺ ions, attributed to the blocking of PET. The fluorometric detection limits for Cu²⁺ and Pb²⁺ were found to be 12 × 10⁻⁷ M and 9 × 10⁻⁷ M and the colorimetric detection limits were 3.7 × 10⁻⁶ M and 1.2 × 10⁻⁶ M respectively; which are far below the permissible concentration in drinking water determined by WHO. Moreover, it was found that chemosensor L worked as a reversible fluorescence probe towards Cu²⁺ and Pb²⁺ ions by the accumulation of S²⁻ and EDTA respectively. Based on the physicochemical and analytical methods like ESI-mass spectrometry, Job plot, FT-IR, ¹H-NMR spectra and DFT studies the detection mechanism may be explained as metal coordination, photoinduced electron transfer (PET) as well as an internal charge transfer (ICT) process. The sensor could work in a pH span of 4.0–12.0. The chemosensor L shows its application potential in the detection of Cu²⁺ and Pb²⁺ in real samples, living cells and building of molecular logic gate.

A novel triazole-based bis Schiff base colorimetric and fluorescent chemosensor (L) has been designed, synthesized and characterized. The chemo-sensor L shows its application potential in the detection of Cu²⁺ and Pb²⁺ in living cells and building molecular logic gate.

A hybrid magnetic core–shell fibrous silica nanocomposite for a chemosensor-based highly effective fluorescent detection of Cu(ii)

Herein, a novel hybrid magnetic core–shell fibrous silica nanocomposite (RhB–Fe₃O₄/MnO₂/SiO₂/KCC-1) probe-based chemosensor was designed and its behaviour towards Cu(ii) metal ion was investigated using a fluorescence spectrometer.

A new macrocyclic ligand as a turn-on fluorescent chemosensor for the recognition of Pb2+ions

The chemosensor L has a detection limit of 9.63 nM for Pb²⁺in an acetonitrile/H₂O (9 : 1, v/v) mixture.

Highly Selective and Sensitive Detection of Nitroaromatic Compounds and Metal Ions by Supramolecular Assemblies of 3,3',5,5'-Azobenzenetetracarboxylic Acid and 4,4'-Bipyridine

A supramolecular compound, (H₄L)(4,4'-bpy)₂ (1) (H₄L = 1,2-bis(3,5-dicarboxyphenyl)diazene oxide, 4,4'-bpy = 4,4'-bipyridine) with 2D + 2D → 2D 3-fold parallel interpenetrated layer feature, has been prepared which was investigated as selective sensing material for detection of nitroaromatic compounds (NACs) and metal ions, and exhibits significant fluorescence quenching toward NACs and high selectivity for detection of Fe³⁺ ion. The result indicates that 1 is a promising multi-functional fluorescence probe for detecting and recognizing NACs and metal ions with high sensitivity and selectivity.

One-pot synthesis of sulfur-doped graphene quantum dots as a novel fluorescent probe for highly selective and sensitive detection of lead(ii)

A facile strategy was developed for the one-step synthesis of S-GQDs with a monolayer-graphene crystal structure. The change of surface chemistry by S-doping resulted in selective and sensitive detection of Pb²⁺.

Fluorometric sensing of Pb2+and CrO42−ions through host–guest inclusion for human lung cancer live cell imaging

The formation of an inclusion complex between 1,5-dihydroxyanthraquinone (1,5-DHAQ;1) and β-cyclodextrin (β-CD) in aqueous media has been studied by UV-visible and fluorescence spectroscopy.