Structurally designed porous polymer monoliths as probe-anchoring templates as benign and fast responsive solid-state optical sensors for the sensing and recovery of copper ions

Sustainable and reusable probe-encapsulated porous poly(AMST-co-TRIM) monolithic sensor for the selective and ultra-sensitive detection of toxic cadmium(II) from industrial/environmental wastewater

This study focuses on a new type of fast responsive solid-state visual colorimetric sensor, custom engineered with dual-entwined porous polymer imbued with chromoionophoric 4-(sec-butyl)- 2-((5-mercapto-1,3,4-thiadiazol-2-yl)diazenyl)phenol (SMDP) probe for selective and ultra-sensitive colorimetric sensing of Cd(II). The polymer monolith, i.e., poly(aminostyrene-co-trimethylolpropanetrimethacrylate) denoted as poly(AMST-co-TRIM), is designed through a stoichiometric blending of monomer, crosslinker, and porogens leading to superior surface area, pore and adsorption properties for the voluminous incorporation of SMDP probe for target specific ion sensing. The porosity, surface and structural characteristics of the poly(AMST-co-TRIM)monolith and poly(AMST-co-TRIM)SMDP sensor are investigated using p-XRD, XPS, TG-DTA, FT-IR, BET/BJH, FE-SEM, HR-TEM, EDAX, and SAED techniques. The poly(AMST-co-TRIM)SMDP sensor reveals a frozen geometrical orientation of SMDP molecules to bind selectively with Cd(II), forming stable charge-transfer complexes by exhibiting transitional visible color shifts from light yellow to dark green (λmax 608 nm). The sensor imposes a linear response from 0-200 ppb, with quantification and detection limits of 0.95 and 0.28 ppb. The fabricated sensor material is cost-effective and versatile in its solid-state naked-eye sensing, with excellent reusability. The sensor performance has been verified using various environmentally contaminated water and commercial cigarette samples, with a recovery of ≥ 99.12% and an RSD of ≤ 1.95%, thus reflecting exceptional data reproducibility/reliability.

Chromogenic probe adhered porous polymer monolith as real-time solid-state sensor for the detection of ultra-trace toxic mercury ions

The escalating predicament of water pollution has spurred the development of new chromogenic materials for the efficient detection/screening of toxic mercuric (Hg2+) ions. In this study, we report a simple and efficient detection stratagem by infusing a chromogenic ion-receptor (BTDA), i.e., 4-(benzothiazol-2-yl)-N, N-dimethylaniline onto a structurally intertwined meso-/macro-pore polymer template for the target-specific sensing of ultra-trace Hg2+. The structural/surface features of the monolithic polymer template, prepared from glycidyl methacrylate (GMA) monomer crosslinked with ethylene glycol dimethacrylate (EGDMA), facilitate voluminous infusion and uniform decoration of ion-receptor molecules across the continuous porous poly(GMA-co-EGDMA) framework, resulting in a solid-state colorimetric sensory system. The bimodal polymer network's intriguing surface and structural morphology of the chromogenic sensor material are interpreted using scanning/transmission electron microscopy, X-ray diffraction, photoelectron spectroscopy, energy dispersive X-ray spectrometry, optical spectroscopy, surface area, porosity and thermal analysis. The proposed Hg2+ sensor offers a linear response range of 1-150 μg/L, with a detection and quantification limit of 0.29 and 0.97 μg/L, respectively. The poly(GMA-co-EGDMA)-BTDA sensor exhibits a quick ion-sensing response (40 s) with distinct color transitions from pastel yellow to olive as a function of increasing Hg2+ concentration. The matrix tolerance studies for the proposed sensory system reveal high selectivity for Hg2+, with a recovery of ≥99.2% in on-site environmental samples. The sensor material exhibits excellent data reproducibility and reliability up to seven cycles of reusability.

Fabrication of reusable probe impregnated polymer monolithic sensor for the visual detection of Cd2+ in natural waters and cigarette samples

This work demonstrates the fabrication of a simple, low-cost naked-eye colorimetric solid-state sensor model for selective sensing of Cd2+. The sensor was developed using a polymer monolithic architect; namely, poly(n-allylthiourea-co-ethyleneglycol dimethacrylate) (poly(ATU-co-EGD) imbued with the chromophoric probe, 3-(quinoline-8-yldiazenyl)quinoline-2,4-diol (QYQD). The concocted indigenous perforated structural assemblies were studied through various microscopic, spectroscopic, and diffraction techniques. The template possessed a uniform arrangement of interconnected macro/mesoporous networks available for the maximum hooking of the QYQD probe moieties for the rapid and enhanced Cd2+ sensing process. The developed sensor offered an enhanced solid-state color transition response from yellow to dark meron for a proportional concentration increase of Cd2+ exhibiting precise absorption spectra with λmax at 475 nm. The relative stoichiometric binding ratio of the QYQD probe with Cd2+ was observed to be 2:1. The enhanced working conditions of the developed poly(ATU-co-EGD)QYQD sensor were tuned by validating various analytical conditions. The sensor exhibited a linear response signal from 2 to 150 ppb of Cd2+, and the corresponding LOD and LOQ values were 0.31 and 1.03 ppb, respectively. The efficacious performance drive of the sensor was validated in real water and cigarette samples that showed excellent data accuracy with a recovery value of ≥ 99.72% (n = 3).

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.

Probe tethered monolithic architectures as facile solid-state chemosensors for the on-site colorimetric recognition of Co(II) in aqueous and industrial samples

In this work, we report two novel solid-state opto-chemosensors that proffer exclusive selectivity and excellent sensitivity for the naked-eye detection of ultra-trace Co²⁺ ions. The opto-chemosensors are concocted using structurally engineered porous silica and polymer monolith templates that are uniformly arranged with a chromoionophoric probe i.e., (Z)-2-mercapto-5-(quinolin-8-yldiazenyl)pyrimidine-4,6-diol (AQTBA). The probe anchored monolithic opto-chemosensors induces sequential color transitions, from yellowish-orange to dark brown, with incremental addition of Co²⁺ ions. The optimized ground state structure of the AQTBA probe and its AQTBA-Co²⁺ complex are analyzed using a gaussian 16 program at B3LYP level, with a 6-311+ G (d, p) basis set. The structural and surface morphology of the opto-sensors are characterized using various microscopic, spectroscopic, and diffraction techniques, which discloses a uniform pattern of pore network that proffers rapid ion diffusion kinetics to the probe chelating sites. The proposed monolithic sensors exhibit a high degree of tolerance towards various foreign cations and anions, thus revealing its exclusive selectivity in targeting ultra-trace concentrations of Co²⁺. The silica and polymer monolithic sensors exhibit a broad linear response range of 0-200 ppb, with a detection limit of 0.35 and 0.07 ppb for Co²⁺ ions, respectively. The unique features of the proposed sensors are their faster response kinetics (120 s), greater reusability (nine cycles), excellent chemical and thermal durability (pH ≤ 12.0; T ≤ 200 °C), with reliable data reproducibility (recovery ≥99.3 %; RSD ≤2.3 %). The proposed solid-state opto-chemosensors paves way for maximum waste reduction strategy, along with the feasibility for real-time monitoring of environmental and industrial water samples.

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.

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%).