Porous silica and polymer monolith architectures as solid-state optical chemosensors for Hg2+ ions

Chromophoric Ion Receptor-Decorated Porous Monolithic Polymer for the Solid-State Naked Eye Sensing of Hg(II): An Experimental and Theoretical Approach

The current work presents a perspective to obliterate toxic Hg(II) from an aqueous environment, a strategic environmental remediation and decontamination measure. We report a simple, efficient, and reusable solid-state visual sensing strategy for the selective detection and quantitative recovery of ultratrace Hg(II). The capture of Hg(II) ions was effectuated using a macro-/mesoporous polymer monolith uniformly decorated with an azo-based chromophoric ion receptor, i.e., 7-((1H-benzo[d]imidazol-2-yl)diazenyl)quinolin-8-ol (BIDQ). The porous polymer template was synthesized through free radical polymerization of gylcidylmethacrylate and ethylene glycol dimethacrylate, leading to distinct structural and surface properties that offer exclusive solid-state colorimetric selectivity for Hg(II) upon restricted spatial dispersion of the ion receptor. The sensor provides a broad linear response range of 1-200 μg/L, with an outstanding detection limit of 0.2 μg/L for Hg(II) ions, thus effectuating reliable and reproducible sensing. Optimizing analytical parameters such as solution pH, receptor concentration, sensor quantity, kinetics, temperature, and matrix interference proved to be promising for the real-time monitoring of toxic mercury ions from aqueous/industrial systems, with maximum response in the pH range of 7.5-8.0, with a response time of ≤80 s. Density functional theory (DFT) calculations were employed to study the electronic structure of BIDQ upon chelating with Hg(II) ions, using 6-311G and LAND2Z basis sets.

Probe decorated porous silica and polymer monoliths as solid-state optical sensors and preconcentrators for the selective and fast recognition of ultra-trace arsenic ions

In this work, we manifested a new approach in designing solid-state colorimetric sensors for the selective optical sensing of As³⁺. The sensor fabrication is modulated using, (i) a cubic mesopores of ordered silica monolith, and (ii) a bimodal macro-/meso-porous polymer monolith, as hosting templates that are immobilized with a tailor-made chromoionophoric probe (DFBEP). The surface morphology and structural dimensions of the monolith templates and the sensor materials are characterized using p-XRD, XPS, FE-SEM-EDAX, HR-TEM-SAED, FT-IR, TGA, and BET/BJH analysis. The sensing components such as pH, probe content, sensor dosage, kinetics, temperature, analyte concentration, linear response range, selectivity, and sensitivity are optimized to arrive at the best sensing conditions. The silica and polymer-based monolithic sensors show a linear spectral response in the concentration range of 2-300 and 2-200 ppb, with a detection limit of 0.87 and 0.75 ppb for As³⁺, respectively. The real-time ion-monitoring propensity of the sensors is tested with spiked synthetic and real water samples, with a recovery efficiency of ≥99.1% (RSD ≤1.57%). The sensors act as both naked-eye optical sensors and preconcentrators, with a response time of ≤2.5 min. The molecular and photophysical properties of the DFBEP-As³⁺ complex are studied by TD-DFT calculations, using the B3LYP/6-31G (d,p) method.

Porous carbon-based polymer monolithic template implanted with an ion-receptor molecular probe as a solid-state ocular sensor for the selective targeting and capturing of cobalt ions

Polymer monolithic solid-state optical sensor offers exclusive selectivity and a faster response for ultra-trace Co(ii) ions, with excellent reusability and data reproducibility.

Fluorescence Based Comparative Sensing Behavior of the Nano-Composites of SiO2 and TiO2 towards Toxic Hg2+ Ions

We have synthesized sulfonamide based nano-composites of SiO2 and TiO2 for selective and sensitive determination of toxic metal ion Hg2+ in aqueous medium. Nano-composites (11) and (12) were morphologically characterized with FT-IR, solid state NMR, UV-vis, FE SEM, TEM, EDX, BET, pXRD and elemental analysis. The comparative sensing behavior, pH effect and sensor concentrations were carried out with fluorescence signaling on spectrofluorometer and nano-composites (11) and (12), both were evaluated as "turn-on" fluorescence detector for the toxic Hg2+ ions. The LODs were calculated to be 41.2 and 18.8 nM, respectively of nano-composites (11) and (12). The detection limit of TiO2 based nano-composites was found comparatively lower than the SiO2 based nano-composites.

Fabrication of target specific solid-state optical sensors using chromoionophoric probe-integrated porous monolithic polymer and silica templates for cobalt ions

The article demonstrates the design of two solid-state sensors for the capturing of industrially relevant ultra-trace Co(II) ions using porous monolithic silica and polymer templates. The mesoporous silica reveals high surface area and voluminous pore dimensions that ensures homogeneous anchoring of 4-((5-(allylthio)-1,3,4-thiadiazol-2-yl)diazenyl)benzene-1,3-diol, as the chromoionophore. We report a first of its kind solid-state macro-/meso-porous polymer monolithic optical sensor from a monomeric chromoionophore, i.e., 2-(4-butylphenyl)diazenyl)-2-hydroxybenzylidene)hydrazine-1-carbothioamide. The monolithic solid-state sensors are characterized using HR-TEM-SAED, FE-SEM-EDAX, p-XRD, XPS, ²⁹Si/¹³C CPMAS NMR, FT-IR, TGA, and BET/BJH analysis. The electron microscopic images reveal a highly ordered hexagonal mesoporous network of honeycomb pattern for silica monolith, and a long-range macroporous framework with mesoporous channels for polymer monolith. The sensors offer exclusive ion-selectivity and sensitivity for trace cobalt ions, through a concentration proportionate visual color transition, with a response kinetics of ≤ 5 min. The optimization of ion-sensing performance reveals an excellent detection limit of 0.29 and 0.15 ppb for Co(II), using silica- and polymer-based monolithic sensors, respectively. The proposed sensors are tested with industrial wastewater and spent Li-ion batteries, which reveals a superior cobalt ion capturing efficiency of ≥ 99.2% (RSD: ≤ 2.07%).

Mercury Toxicity and Detection Using Chromo-Fluorogenic Chemosensors

Mercury (Hg), this non-essential heavy metal released from both industrial and natural sources entered into living bodies, and cause grievous detrimental effects to the human health and ecosystem. The monitoring of Hg2+ excessive accumulation can be beneficial to fight against the risk associated with mercury toxicity to living systems. Therefore, there is an emergent need of novel and facile analytical approaches for the monitoring of mercury levels in various environmental, industrial, and biological samples. The chromo-fluorogenic chemosensors possess the attractive analytical parameters of low-cost, enhanced detection ability with high sensitivity, simplicity, rapid on-site monitoring ability, etc. This review was narrated to summarize the mercuric ion selective chromo-fluorogenic chemosensors reported in the year 2020. The design of sensors, mechanisms, fluorophores used, analytical performance, etc. are summarized and discussed.