Selective Optical Sensing of Hg(II) in Aqueous Media by H-Acid/SBA-15: A Combined Experimental and Theoretical Study

Coumarin derivative-functionalized nanoporous silica as an on-off fluorescent sensor for detecting Fe3+ and Hg2+ ions: a circuit logic gate

A highly efficient fluorescent sensor (S-DAC) was easily created by functionalizing the SBA-15 surface with N-(2-Aminoethyl)-3-Aminopropyltrimethoxysilane followed by the covalent attachment of 7-diethylamino 3-acetyl coumarin (DAC). This chemosensor (S-DAC) demonstrates selective and sensitive recognition of Fe3+ and Hg2+ in water-based solutions, with detection limits of 0.28 × 10-9 M and 0.2 × 10-9 M for Hg2+ and Fe3+, respectively. The sensor's fluorescence characteristics were examined in the presence of various metal ions, revealing a decrease in fluorescence intensity upon adding Fe3+ or Hg2+ ions at an emission wavelength of 400 nm. This sensor was also able to detect ferric and mercury ions in spinach and tuna fish. The quenching mechanism of S-DAC was investigated using UV-vis spectroscopy, which confirmed a static-type mechanism for fluorescence quenching. Moreovre, the decrease in fluorescence intensity caused by mercury and ferric ions can be reversed using trisodium citrate dihydrate and EDTA as masking agents, respectively. As a result, a circuit logic gate was designed using Hg2+, Fe3+, trisodium citrate dihydrate, and EDTA as inputs and the quenched fluorescence emission as the output.

Design of a new polyethersulfone nanofiltration membrane with anti-fouling properties using supported protic ionic liquid modification for dye/salt removal

Facile techniques to fabricate the nanofiltration membranes with ideal molecular sieving is one of the most interesting subjects in membrane separation technology. In this study, the application of modified graphene oxide (GO) with triethylenetetramine (TETA), CuFe₂ O₄ , and acetic acid (AC) (supported GO-TETA-CuFe₂ O₄ @AC) as a supported protic ionic liquid (PIL) modifier for polyethersulfone (PES) membrane was evaluated to approve the improvement of anti-fouling properties and wastewater rejection of the fabricated membranes. To enhance the key properties of graphene oxide, it was modified by hydrophilic nanomaterials (TETA-CuFe₂ O₄ ). High flux and promising flux recovery ratio (up to 95% compared to the unmodified membrane) can be observed in the modified membranes. The modified membranes by GO-TETA-CuFe₂ O₄ @AC were studied at optimum concentrations (0.5 wt.%) for salt rejection and different dyes. The obtained data indicated that the modified membranes by GO-TETA-CuFe₂ O₄ @AC indicated higher salt removal (up to 97% for BaCl₂ than the unmodified membrane), which was related to the efficient modification. The obtained pure water flux (PWF) for bare and optimal modified membrane from 13.11 to 27.87 kg/m² ·h, respectively. To exact evaluate the effect of membrane modification on performance examination, the modified membranes were evaluated for chlorine resistance testing. This study aimed to develop cost-effective nanofiltration (NF) membranes with high anti-fouling properties and to determine the maximum filtration capacity of in-time dyes and salts in effluents. PRACTITIONER POINTS: A GO-TETA-CuFe2O4 mixed matrix membrane was prepared for removal of salts and dyes. The effect of GO-TETA-CuFe2O4 enhanced the hydrophilicity and porosity. The membrane exhibited superior antifouling properties and ions rejection.

Synthesis of SBA-Pr-NHC as a selective fluorescent sensor for the detection of Ag+ ion in aqueous media

SBA-Pr-NHC as a novel silica-based chemosensor was synthesized through the functionalization of mesoporous silica SBA-15 material with 4-hydroxy-2-oxo-2H-chromene-3-carbaldehyde, which was successfully immobilized to the surface of mesoporous silica, and its hexagonal mesoporous structure has been preserved. Photoluminescence spectroscopy was applied to study the sensing behavior of SBA-Pr-NHC, which displayed high selectivity for sensing Ag⁺ ion in aqueous media. After the addition of trace amounts of Ag⁺ ions into the aqueous solution, a significant enhancement of fluorescence emission has occurred with the detection limits of 2.4 × 10^-5 M.

Terthiophene-functionalized mesoporous silica-based fluorescence sensor for the detection of trace methyl orange in aqueous media

A terthiophene-functionalized mesoporous SBA-15 silica, i.e., TTU-SBA-15, was successfully developed and used as a highly selective and ultrasensitive fluorescence sensor for methyl orange (MO) detection. When the concentration of MO was increased, the fluorescence emission intensity of TTU-SBA-15 suspensions at 452 nm gradually decreased at an excitation wavelength of 368 nm, and the color of the suspension solutions changed obviously from blue to dark under 365 nm UV light. The fluorescence intensity at 452 nm was linearly proportional to the concentration of MO in the range 0.20 - 2.0 μM, with a detection limit of 0.092 μM. Competitive pollutants, variations in pH, and sample recycling had subtle or negligible effects on the detection of MO. TTU-SBA-15 was applied to the determination of MO in tap water, and recoveries from spiked samples were in the range 98.3 - 103.0%. This study provides a convenient and effective strategy to realize highly sensitive and selective sensors that could target dyes via the functional modification of mesoporous materials.

Functionalized mesoporous silica as a fluorescence sensor for selective detection of Hg2+ in aqueous medium

We combined the virtues of mesoporous silica and organic functional groups to develop a hybrid fluorescent sensor, PyU-SBA-15, with excellent ability to detect Hg²⁺ in aqueous medium with high selectivity. In this sensor, the pyrene fluorophore acts as the reporter and the urea unit acts as the receptor during Hg²⁺ determination. The control material, PyH-SBA-15, which lacks a carbonyl group in the receptor portion, did not display metal-ion selectivity, thereby demonstrating that introducing an additional metal-chelating unit is necessary to improve the metal-ion selectivity of the hybrid sensor. When the concentration of Hg²⁺ was increased, the fluorescence emission intensities of PyU-SBA-15 at 379, 398, and 476 nm gradually decreased. The emission intensity at 379 nm was linearly proportional to Hg²⁺ concentrations in the range of 0-1.0 × 10^-4 M, and the sensor was determined to have a detection limit of 9.92 × 10^-8 M. This work provides an effective strategy for improving or modulating the metal-ion selectivity of fluorescent sensors based on organic-inorganic hybrid mesoporous silica systems.

Aggregation induced emission active fluorescent sensor for the sensitive detection of Hg2+ based on organic-inorganic hybrid mesoporous material

We report the preparation of an organic-inorganic hybrid mesoporous material, PHC-SBA-15, derived from the coupling of a pyrene-based derivative PHC and mesoporous SBA-15 silica. Compared with the stable aggregation-induced emission (AIE) properties of PHC, those of PHC-SBA-15 were more promoted and active due to the fixation of PHC and the space limitation in mesoporous SBA-15. The aggregation and disaggregation activities can be tuned by controlling the concentrations in aqueous media and changing the fluorescence color from yellow to blue. In addition to the controllable AIE properties, PHC-SBA-15 was applied for the highly selective and sensitive detection of Hg²⁺ through the fluorescence quenching of monomeric pyrene in aqueous media. The fluorescence intensity at 395 nm was linearly proportional to that of Hg²⁺ in the concentration ranges of 0-1.0 × 10^-5 and 1.0 × 10^-5-10 × 10^-5 M, showing a low detection limit of 1.02 × 10^-7 M. This work provides an effective strategy for modulating the AIE properties from non-active to active by introducing AIE stable molecule into mesoporous silica material. This method also favors the development of fluorescent sensors for detecting targets with high sensitivity and selectivity in aqueous media with less synthetic difficulties.

Dual-Emission Fluorescent Microspheres for the Detection of Biothiols and Hg2

Dual-emission nanosensor for Hg²⁺ detection was prepared by coupling CA-AEAPMS on the surface of RBS-doped modified silica microspheres. The CA-AEAPMS was synthesized by using N-(β-aminoethyl)-γ-aminopropyl methyldimethoxysilane (AEAPMS) and citric acid as the main raw material. The obtained nanosensor showed characteristic fluorescence emissions of Rhodamine B (red) and CA-AEAPMS (blue) under a single excitation wavelength (360 nm). Upon binding to Hg²⁺, only the fluorescence of CA-AEAPMS was quenched, resulting in the ratiometric fluorescence response of the dual-emission silica microspheres. This ratiometric nanosensor exhibited good selectivity to Hg²⁺ over other metal ions, because of the amide groups on the surface of CA-AEAPMS serving as the Hg²⁺ recognition sites. The ratio of F₄₅₀/F₅₈₀ linearly decreased with the increasing of Hg²⁺ concentration in the range of 0 to 3 × 10^-6 M, and a detection limit was as low as 97 nM was achieved. Then, the addition of three thiol-containing amino acids (Cys, Hcy, GSH) to the quenched fluorescence solution with Hg²⁺ can restore the fluorescence, and the detection limits of the three biothiols (Cys, Hcy, GSH) are 0.133 μM, 0.086 μM, and 0.123 μM, respectively.

Isatin functionalized nanoporous SBA-15 as a selective fluorescent probe for the detection of Hg(II) in water

A highly ordered mesoporous silica material functionalized with isatin (SBA-Pr-IS) was designed and synthesized. Characterization techniques including XRD, TGA, BET, SEM, and FT-IR were employed to characterize the pore structure, textural properties, microscopic morphology, and molecular composition of grafted organic moieties of SBA-Pr-IS. The successful attachment of the organic moiety (0.34 mmol g^-1) without the SBA-15 structure collapsing after the modification steps was confirmed. Fluorescence characterization of SBA-Pr-IS was examined upon addition of a wide variety of cations in aqueous medium and it showed high sensitivity toward Hg²⁺ ions. During testing in an ion competition experiment, it was observed that the fluorescence changes of the probe were remarkably specific for Hg²⁺ ions. Furthermore, a good linearity between the fluorescence intensity of this material and the concentration of Hg²⁺ ions was constructed with a suitable detection limit of 3.7 × 10^-6 M. Finally, the applicability of the proposed method was successfully evaluated for the determination of Hg²⁺ ions in real samples. Therefore, SBA-Pr-IS can be used as an efficient fluorescence probe for Hg²⁺ ions. Graphical Abstract A novel organic-inorganic hybrid material was designed and synthesized by functionalization of SBA-15 mesoporous silica material with isatin. The evaluation of the sensing ability of SBA-Pr-IS using fluorescence spectroscopy revealed that the SBA-Pr-IS was a selective fluorescent probe for Hg²⁺ ion in water in the presence of a wide range of metal cations.

A Fluorescent Sensor for Al(III) and Colorimetric Sensor for Fe(III) and Fe(II) Based on a Novel 8-Hydroxyquinoline Derivative

A novel 8-hydroxyquinoline-based fluorescent and colorimetric chemosensor was designed, synthesized and fully characterized. The sensor showed high selectivity and sensitivity toward Al(3+) over other tested cations in EtOH/H2O (1:99, v/v) medium. The increase in fluorescence intensity was linearly proportional to the concentration of Al(3+) with a detection limit of 7.38 × 10(-6) M. Moreover, the sensor exhibited an obvious color change from yellow to black in the presence of Fe(2+) and Fe(3+) in EtOH/THF (99:1, v/v) solution. The absorbance changes showed a linear response to iron ions with the detection limits of 4.24 × 10(-7) M and 5.60 × 10(-7) M for Fe(2+) and Fe(3+), respectively. Thus, this chemosensor provides a novel approach for selectively recognition of Al(3+), Fe(3+) and Fe(2+) among environmentally relevant metal ions.

SBA-15 Functionalized with Naphthalene Derivative for Selective Optical Sensing of Cr2O7(2-) in Water

A novel organic-inorganic hybrid optical sensor (NUS) was designed and prepared in two steps: the grafting of 3-(isocyanatopropyl)trimethoxysilane onto the surface of SBA-15, and then the attachment of naphthalene-1-amine. The obtained materials were characterized using low-angle XRD, N2 adsorption-desorption, TGA, FT-IR, and TEM techniques. A fluorescence study revealed that the NUS was a highly selective optical sensor for the detection of Cr2O7(2-) among various anions, including F(-), I(-), Cl(-), Br(-), CO3(2-), HCO3(-), NO3(-), H2PO4(-), CH3COO(-), and NO2(-) with a good linearity between the fluorescence intensity and the concentration of Cr2O7(2-) as well as a detection limit of 1.2 × 10(-7) M in a 100% aqueous medium. Moreover, the applicability of real samples of the sensor is also discussed.

Fluorescence chemosensors based on functionalized SBA-15 for detection of Pb2+ in aqueous media

A highly ordered mesoporous silica material (SBA-15) functionalized with 5-(4-carboxy-phenylazo)-8-hydroxyquinoline (CPA-8-HQL) for use as a fluorescence chemosensor for Pb²⁺ detection has been reported in this study.

A single hybrid optical sensor based on nanoporous silica type SBA-15 for detection of Pb2+and I−in aqueous media

Simple two-steps post synthesis procedure achieved the functionalized nanoporous SBA-15 as a single hybrid optical sensor for detecting Pb²⁺and I⁻ions in aqueous media.

Theoretical assessment of the selective fluorescence quenching of 1-amino-8-naphthol-3,6-disulfonic acid (H-Acid) complexes with Zn(2+), Cd(2+), and Hg(2+): A DFT and TD-DFT study

Density functional theory (DFT) and time-dependent (TD)-DFT calculations at the PBE0/6-31++G** aug-cc-PVDZ (along with corresponding ECP for metal ions) level of theory were carried out to investigate the differences in structure, bonding, and fluorescence behavior of 1-amino-8-naphthol-3,6-disulfonic acid (H-acid) (1) when coordinated to Zn(2+) (2), Cd(2+) (3), and Hg(2+) (4) in a simulated continuous aqueous media (PCM). Ground and excited state calculations were performed on all compounds in order to gain insight on their bonding properties, as well as on their photochemical behavior, since we previously reported that complexation of Hg(2+) quenches the fluorescence properties of ligand (1), while at the same time exhibits a different coordination pattern than the two other remaining complexes. Changes in the excited states' radiative lifetime upon coordination to different metals account for this selective quenching.

Conjugation-induced fluorescence labelling of mesoporous silica nanoparticles for the sensitive and selective detection of copper ions in aqueous solution

A newly developed fluorescent “on–off” chemosensor presents high selectivity towards Cu²⁺ with detection limit as low as 0.28 μM.