Solid-state ion recognition strategy using 2D hexagonal mesophase silica monolithic platform: a smart two-in-one approach for rapid and selective sensing of Cd2+ and Hg2+ ions

pH Modulation of Super-Assembled Heteromembranes for Sustainable Chiral Sensing

Enantioselective sensing and separation represent formidable challenges across a diverse range of scientific domains. The advent of hybrid chiral membranes offers a promising avenue to address these challenges, capitalizing on their unique characteristics, including their heterogeneous structure, porosity, and abundance of chiral surfaces. However, the prevailing fabrication methods typically involve the initial preparation of achiral porous membranes followed by subsequent modification with chiral molecules, limiting their synthesis flexibility and controllability. Moreover, existing chiral membranes struggle to achieve coupled-accelerated enantioseparation (CAE). Here, we report a replacement strategy to controllably produce mesoscale and chiral silica-carbon (MCSC) hybrid membranes that comprise chiral pores by interfacial superassembly on a macroporous alumina (AAO) membrane, in which both ion- and enantiomers can be effectively and selectively transported across the membrane. As a result, the heterostructured hybrid membrane (MCSC/AAO) exhibits enhanced selectivity for cations and enantiomers of amino acids, achieving CAE for amino acids with an isoelectric point (pI) exceeding 7. Interestingly, the MCSC/AAO system demonstrates enhanced pH-sensitive enantioseparation compared to chiral mesoporous silica/AAO (CMS/AAO) with significant improvements of 78.14, 65.37, and 14.29% in the separation efficiency, separation factor, and permeate flux, respectively. This work promises to advance the synthesis of two or more component-integrated chiral nanochannels with multifunctional properties and allows a better understanding of the origins of the homochiral hybrid membranes.

Selenium-transition metal supported on a mixture of reduced graphene oxide and silica template for water splitting

Exploration of economical, highly efficient, and environment friendly non-noble-metal-based electrocatalysts is necessary for hydrogen and oxygen evolution reactions (HER and OER) but challenging for cost-effective water splitting. Herein, metal selenium nanoparticles (M = Ni, Co & Fe) are anchored on the surface of reduced graphene oxide and a silica template (rGO-ST) through a simple one-pot solvothermal method. The resulting electrocatalyst composite can enhance mass/charge transfer and promote interaction between water molecules and electrocatalyst reactive sites. NiSe2/rGO-ST shows a remarkable overpotential (52.5 mV) at 10 mA cm-2 for the HER compared to the benchmark Pt/C E-TEK (29 mV), while the overpotential values of CoSeO3/rGO-ST and FeSe2/rGO-ST are 246 and 347 mV, respectively. The FeSe2/rGO-ST/NF shows a low overpotential (297 mV) at 50 mA cm-2 for the OER compared to RuO2/NF (325 mV), while the overpotentials of CoSeO3-rGO-ST/NF and NiSe2-rGO-ST/NF are 400 and 475 mV, respectively. Furthermore, all catalysts indicate negligible deterioration, indicating better stability during the process of HER and OER after a stability test of 60 h. The water splitting system composed of NiSe2-rGO-ST/NF||FeSe2-rGO-ST/NF electrodes requires only ∼1.75 V at 10 mA cm-2. Its performance is nearly close to that of a noble metal-based Pt/C/NF||RuO2/NF water splitting system.

Colorimetric detections of iodide and mercuric ions based on a regulation of an Enzyme-Like activity from gold nanoclusters

A simple colorimetric method was developed for sensitive and selective detections of I^- and Hg²⁺. Histidine stabilized gold nanoclusters (His-AuNCs) were synthesized and catalyzed the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product. As a strong ligand toward gold, iodide (I^-) attached to the surface of the His-AuNCs and significantly enhanced the oxidase-like activity of the His-AuNCs. Based on this enhancement, a sensitive colorimetric response toward I^- was obtained. Furthermore, the strong interaction between Hg²⁺ and I^- was adopted for an indirect Hg²⁺ detection. Under the optimal conditions, the platform presented high selectivity for the determinations of I^- and Hg²⁺ in the ranges 0.02-1 µM and 0.05-0.8 µM, with detection limits as 3.3 nM and 8 nM respectively. This colorimetric assay was successfully applied for analysis of real samples.

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%).