Metavalent Bonding in 2D Chalcogenides: Structural Origin and Chemical Mechanisms.

An unusual set of anomalous functional properties of rocksalt crystals of Group IV chalcogenides were recently linked to a kind of bonding termed as metavalent bonding (MVB) which involves violation of the 8-N rule. Precise mechanisms of MVB and the relevance of lone pair of Group IV cations are still debated. With restrictions of low dimensionality on the possible atomic coordination, 2D materials provide a rich platform for exploration of MVB. Here, we present first-principles theoretical analysis of the nature of bonding in five distinct 2D lattices of Group IV chalcogenides MX (M: Sn, Pb, Ge and X: S, Se, Te), in which the natural out-of-plane expression of the lone pair versus in-plane bonding can be systematically explored. While their honeycomb lattices respecting the 8-N rule are shown to exhibit covalent bonding, their square and orthorhombic structures exhibit MVB only in-plane, with cationic lone pair activating the out-of-plane structural puckering that controls their relative stability. Anomalies in Born-effective charges, dielectric constants, Grüneisen parameters occur only in their in-plane behaviour, confirming MVB is confined strictly to 2D and originates from p-p orbital interactions. Our work opens up directions for chemical design of MVB based 2D materials and their heterostructures.

A new precursor route for the growth of NbO2thin films by chemical vapor deposition.

Niobium dioxide (NbO2) exhibits metal-insulator transition (Mott transition) and shows the potential for application in memristors and neuromorphic devices. Presently growth of NbO2thin films requires high-temperature reduction of Nb2O5films using H2or sophisticated techniques such as molecular beam epitaxy and pulsed laser deposition. The present study demonstrates a simple chemical route of the direct growth of crystalline NbO2films by chemical vapor deposition using a freshly prepared Nb-hexadecylamine (Nb-HDA) complex. X-ray diffraction studies confirm the NbO2phase with a distorted rutile body-centered-tetragonal structure and the film grown with a highly preferred orientation onc-sapphire. X-ray photoelectron spectroscopy confirms the +4 oxidation state. The present method offers facile growth of NbO2films without post-reduction steps which will be assumed to be a cost-effective process for NbO2based devices.

Inter-individual Variation in Pain Sensitivity among Healthy Young Indian Adults- a pilot study.

Background Pain perception, with inter-individual variability, is a challenge for both patients and clinicians. Distribution of pain sensitivity parameters being less explored in Indian population can vary with reports from outside India. Objective To describe distribution of pain sensitivity parameters using cold pressor test in healthy adults and to explore relationship of pain sensitivity with gender, vascular reactivity and parental history of hypertension. Method Pain was induced with non-dominant hand immersed in cold water (30 C to 50 C) in 150 subjects (75 males and 75 females) selected as per inclusion and exclusion criteria. Pain sensitivity (pain threshold, tolerance and unpleasantness), vascular reactivity (Δ change in blood pressure and pulse rate) were measured. Result Subjects demonstrated pain threshold [17.6 s (10.7, 26.6)], tolerance [40.2 s (30.0, 59.2)] and unpleasantness [7.0 (6.1,8.0)]. Pain unpleasantness showed a weak negative correlation with pain threshold and tolerance (p < 0.001). Pain threshold had moderate positive correlation with tolerance (p < 0.001). Males had significantly higher pain threshold and tolerance than females (p=0.004). Significant rise in posttest systolic and diastolic blood pressure (p < 0.001), decrease in pulse rate (p=0.007) were found compared to resting values. Pain tolerance showed a weak positive correlation with Δ systolic blood pressure (p=0.039). Subjects with positive parental history of hypertension showed higher pain unpleasantness scores (p=0.02). Conclusion The study demonstrated a wide range of pain sensitivity for narrow age and body mass index. Gender difference was observed for pain threshold and tolerance. Vascular reactivity was demonstrated. Subjective pain perception was higher in subjects with parental history of hypertension.

Atomic Layer Deposited Ti2 O3 Thin Films.

Ti2 O3 thin films have been prepared through atomic layer deposition and subjected to electrical resistivity measurements as a function of temperature. The as-prepared films were stable for up to three weeks. In Ti2 O3 thin films, the insulator-metal transition is observed at ∼80 K, with nearly 3-4 orders of magnitude change in resistivity. The anomalous increase in electrical resistivity in the films is in accordance with the two-band model. However, the energy interval between the bands depending on the crystallographic c/a ratio leads to a change in electrical resistivity as a function of temperature.

ZrO2-Ag2O nanocomposites encrusted porous polymer monoliths as high-performance visible light photocatalysts for the fast degradation of pharmaceutical pollutants.

This work reports a unique ZrO2-Ag2O heterojunction nanocomposite uniformly dispersed on a macro-/meso-porous polymer monolithic template to serve as simple and effective visible light-driven heterogeneous plasmonic photocatalysts for water decontamination. The monolithic photocatalysts' structural properties and surface morphology are characterized using various surface and structural characterization techniques. The photocatalytic performance of the proposed photocatalysts is evaluated by optimizing multiple operational parameters. The photocatalytic properties of the fabricated monolithic nanocomposite are monitored through time-dependent photocatalytic disintegration of norfloxacin drug, a widely employed antimicrobial, with considerable aquatic persistence. The analytical results conclude that a (60:40) ZrO2-Ag2O nanocomposite embedded polymer monolith exhibits superior photocatalytic activity for the complete mineralization of norfloxacin molecules under optimized conditions of solution pH (3.0), photocatalyst quantity (100 mg), pollutant concentration (15 mg/L), photosensitizers (2.0 mM KBrO3), visible light intensity (300 W/cm2 tungsten lamp) and irradiation time (≤ 1 h). The proposed new-age inorganic-organic hybrid visible light photo-catalysts with superior structural and surface properties exhibit brilliant performance and fast responsiveness for water decontamination applications, in addition to their excellent chemical stability, high durability, multi-reusability, and cost-effectiveness.

Enteroviruses in gastrointestinal diseases.

Gastrointestinal diseases including diarrhoea constitute a major cause of morbidity and mortality in infants and young children especially in developing countries. Worldwide deaths among all ages due to diarrhoea during 2015 were estimated to be about 1.31 million, diarrhoeal deaths in children below 5 years of age being 499 000. Rotavirus accounted for about 200 000 deaths. Although diarrhoeal deaths decreased significantly during the last two decades, they still represent the third largest cause of infantile deaths. Several bacterial, viral, parasitic, fungal and non-infectious diarrhoea causing agents have been identified, but 30% to 40% of diarrhoeal cases remain undiagnosed. Enteroviruses transmit by the faecal-oral route and replicate first in intestinal cells before spreading to the target organ. They have been associated with diarrhoea in a few studies, but their causative role in diarrhoea in humans has not been systematically demonstrated. In view of the recent demonstration that enteroviruses cause diarrhoea in newborn mice pups, thus validating Koch's postulates, the purpose of this review is to emphasise the importance of recognising enteroviruses as major gastrointestinal pathogens associated with acute and persistent diarrhoea and non-diarrhoeal increased frequency of bowel movements in infants, young children and adults. Our studies and several other subsequent studies reported from different countries should stimulate strategies to reduce the burden of infantile gastrointestinal disease, which has hitherto remained unaddressed.

Ultrasound assisted one-pot synthesis of rosuvastatin based novel azaindole derivatives via coupling-cyclization strategy under Pd/Cu-catalysis: Their evaluation as potential cytotoxic agents.

Addressing the increasing incidences of cancer worldwide along with the multifaceted problem of drug resistance via development of new anticancer agents has become an essential goal. Due to the known cytotoxic effects and reported Akt inhibitory potential of azaindoles we designed a new framework incorporating the structural features of rosuvastatin and 5- or 7-azaindole. The framework was used to construct a library of small molecules for further pharmacological evaluation. The design was supported by the docking studies of two representative molecules in silico. A one-pot sonochemical approach was established for the synthesis of these rosuvastatin based azaindoles that involved the coupling-cyclization of a rosuvastatin derived terminal alkyne with appropriate 3-iodopyridine derivatives under Pd/Cu-catalysis. When tested using an MTT assay, some of the synthesized compounds showed desirable cytotoxic effects against three cancer cell lines e.g. HCT 116, Hep G2 and PA-1 but no significant effects against the non-cancerous HEK cell line. According to the SAR the 5-azaindole ring appeared to be marginally better than the 7-azaindole whereas the activity was varied with the variation of sulfonamide moiety attached to the N-1 atom of the azaindole ring. Among all the groups present in the sulfonamide moiety the p-MeC6H4 group appeared to be most effective in terms of activity. While 3b and 5b were identified as initial hit molecules the compound 5b (in addition to 3b) also showed significant inhibition of Akt1 in vitro that was reflected by its strong interaction with Akt1 in silico (with the docking score -11.7 kcal/mol) involving two H-bonding interactions with Ser7 and Asp439 residues. Further, a reasonable ADME was predicted for 5bin silico. Being a potent inhibitor (MIA Paca-2 IC50 = 18.79 ± 0.17 nM) and with NOAEL (No Observed Adverse Effect Level) > 100 µM in Zebrafish, 5b emerged as a promising compound.

A Bibliometric Analysis of Robotic Surgery From 2001 to 2021.

INTRODUCTION: Bibliometric analyses are a method of evaluating the quality of research output in a certain domain. Robotic surgery has made vast leaps during the past 20 years and this paper aimed to assess some of the main areas of research using this method. METHODS: A search was undertaken for documents published between 2001 and 2021 from the World of Science database, using the keywords 'robotic surgery', 'robotic assisted surgery' and 'robotic-assisted surgery. Results were compared using numerous bibliometric methodologies, and stratified by source-specific metrics, author-specific metrics and country-specific metrics. RESULTS: The search yielded 3839 documents, from 879 different sources. Only 2% of sources were found to be within Bradford's Zone 1 of research and the most relevant sources were from the field of urology. The Journal of Urology and Surgical Endoscopy and other Techniques ranked highly among metrics such as H, G, M index and total citations. The top-rated authors had a H index of 15 in the field of robotic surgery and the total citations reached a peak at 1342. The USA, Japan and Italy were the most productive nations and increased collaborative research is leading to a greater number of multiple-centre publications. CONCLUSION: Research into robotic surgery is still in its infancy with further reviews of the literature and greater output through large randomised controlled trials in multiple centres through collaborative research needed.

Lhb-/-Lhr-/- Double Mutant Mice Phenocopy Lhb-/- or Lhr-/- Single Mutants and Display Defects in Leydig Cells and Steroidogenesis.

In the mouse, two distinct populations of Leydig cells arise during testis development. Fetal Leydig cells arise from a stem cell population and produce T required for masculinization. It is debated whether they persist in the adult testis. A second adult Leydig stem cell population gives rise to progenitor-immature-mature adult type Leydig cells that produce T in response to LH to maintain spermatogenesis. In testis of adult null male mice lacking either only LH (Lhb-/-) or LHR (Lhr-/-), mature Leydig cells are absent but fetal Leydig cells persist. Thus, it is not clear whether other ligands signal via LHRs in Lhb null mice or LH signals via other receptors in the absence of LHR in Lhr null mice. Moreover, it is not clear whether truncated LHR isoforms generated from the same Lhr gene promoter encode functionally relevant LH receptors. To determine the in vivo roles of LH-LHR signaling pathway in the Leydig cell lineage, we generated double null mutant mice lacking both LH Ligand and all forms of LHR. Phenotypic analysis indicated testis morpho-histological characteristics are identical among double null and single mutants which all showed poorly developed interstitium with a reduction in Leydig cell number and absence of late stage spermatids. Gene expression analyses confirmed that the majority of the T biosynthesis pathway enzyme-encoding mRNAs expressed in Leydig cells were all suppressed. Expression of thrombospondin-2, a fetal Leydig cell marker gene was upregulated in single and double null mutants indicating that fetal Leydig cells originate and develop independent of LH-LHR signaling pathway in vivo. Serum and intratesticular T levels were similarly suppressed in single and double mutants. Consequently, expression of AR-regulated genes in Sertoli and germ cells were similarly affected in single and double mutants without any evidence of any additive effect in the combined absence of both LH and LHR. Our studies unequivocally provide genetic evidence that in the mouse testis, fetal Leydig cells do not require LH-LHR signaling pathway and a one-to-one LH ligand-LHR signaling pathway exists in vivo to regulate adult Leydig cell lineage and spermatogenesis.

Epigenetics in NAFLD/NASH: Targets and therapy.

Recently non-alcoholic fatty liver disease (NAFLD) has grabbed considerable scientific attention, owing to its rapid increase in prevalence worldwide and growing burden on end-stage liver diseases. Metabolic syndrome including obesity, diabetes, and hypertension poses a grave risk to NAFLD etiology and progression. With no drugs available, the mainstay of NAFLD management remains lifestyle changes with exercise and dietary modifications. Nonselective drugs such as metformin, thiazolidinediones (TZDs), ursodeoxycholic acid (UDCA), silymarin, etc., are also being used to target the interrelated pathways for treating NAFLD. Considering the enormous disease burden and the unmet need for drugs, fresh insights into pathogenesis and drug discovery are required. The emergence of the field of epigenetics offers a convincing explanation for the basis of lifestyle, environmental, and other risk factors to influence NAFLD pathogenesis. Therefore, understanding these epigenetic modifications to target the primary cause of the disease might prove a rational strategy to prevent the disease and develop novel therapeutic interventions. Apart from describing the role of epigenetics in the pathogenesis of NAFLD as in other reviews, this review additionally provides an elaborate discussion on exploiting the high plasticity of epigenetic modifications in response to environmental cues, for developing novel therapeutics for NAFLD. Besides, this extensive review provides evidence for epigenetic mechanisms utilized by several potential drugs for NAFLD.

CuCl2-catalyzed inexpensive, faster and ligand/additive free synthesis of isoquinolin-1(2H)-one derivatives via the coupling-cyclization strategy: Evaluation of a new class of compounds as potential PDE4 inhibitors.

In spite of possessing a wide range of pharmacological properties the anti-inflammatory activities of isoquinolin-1(2H)-ones were rarely known or explored earlier. PDE4 inhibitors on the other hand in addition to their usefulness in treating inflammatory diseases have been suggested to attenuate the cytokine storm in COVID-19 especially TNF-α. In our effort, a new class of isoquinolin-1(2H)-ones derivatives containing an aminosulfonyl moiety were designed and explored as potential inhibitors of PDE4. Accordingly, for the first time a CuCl2-catalyzed inexpensive, faster and ligand/additive free approach has been developed for the synthesis of these predesigned isoquinolin-1(2H)-one derivatives via the coupling-cyclization strategy. Thus, the CuCl2-catalyzed reaction of 2-iodobenzamides with appropriate terminal alkynes proceeded with high chemo and regioselectivity affording the desired compounds in 77-84% yield within 1-1.5 h. The methodology also afforded simpler isoquinolin-1(2H)-ones devoid of aminosulfonyl moiety showing a broader generality and scope of this approach. Several of the synthesized compounds especially 3c, 3k and 3s showed impressive inhibition (83-90%) of PDE4B when tested at 10 µM in vitro whereas compounds devoid of aminosulfonyl moiety was found to be less active. In spite of high inhibition showed at 10 µM these compounds did not show proper concertation dependent inhibition below 1 µM that was reflected in their IC50 values e.g. 2.43 ± 0.32, 3.26 ± 0.24 and 3.63 ± 0.80 µM for 3k, 3o and 3s respectively. The anti-inflammatory potential of these compounds was indicated by their TNF-α inhibition (60-50% at 10 µM). The in silico docking studies of these molecules suggested good interactions with PDE4B and selective inhibition of PDE4B by 3k over PDE4D that was supported by in vitro assay results. These observations together with the favorable ADME and safety predicted for 3kin silico not only suggested 3k as an interesting hit molecule for further studies but also reveal the first example of isoquinolin-1(2H)-one based inhibitor of PDE4B.

Targeting the paracrine hormone-dependent guanylate cyclase/cGMP/phosphodiesterases signaling pathway for colorectal cancer prevention.

Colorectal cancer (CRC) is one of the leading causes of cancer related-deaths. The risk of development of CRC is complex and multifactorial, and includes disruption of homeostasis of the intestinal epithelial layer mediated though dysregulations of tumor suppressing/promoting signaling pathways. Guanylate cyclase 2C (GUCY2C), a membrane-bound guanylate cyclase receptor, is present in the apical membranes of intestinal epithelial cells and maintains homeostasis. GUCY2C is activated upon binding of paracrine hormones (guanylin and uroguanylin) that lead to formation of cyclic GMP from GTP and activation of downstream signaling pathways that are associated with normal homeostasis. Dysregulation/suppression of the GUCY2C-mediated signaling promotes CRC tumorigenesis. High-calorie diet-induced obesity is associated with deficiency of guanylin expression and silencing of GUCY2C-signaling in colon epithelial cells, leading to tumorigenesis. Thus, GUCY2C agonists, such as linaclotide, exhibit considerable role in preventing CRC tumorigenesis. However, phosphodiesterases (PDEs) are elevated in intestinal epithelial cells during CRC tumorigenesis and block GUCY2C-mediated signaling by degrading cyclic GMP to 5`-GMP. PDE5-specific inhibitors, such as sildenafil, show considerable anti-tumorigenic potential against CRC by amplifying the GUCY2C/cGMP signaling pathway, but cannot achieve complete anti-tumorigenic effects. Hence, dual targeting the elevation of cGMP by providing paracrine hormone stimuli to GUCY2C and by inhibition of PDEs may be a better strategy for CRC prevention than alone. This review delineates the involvement of the GUCY2C/cGMP/PDEs signaling pathway in the homeostasis of intestinal epithelial cells. Further, the events are associated with dysregulation of this pathway during CRC tumorigenesis are also discussed. In addition, current updates on targeting the GUCY2C/cGMP/PDEs pathway with GUCY2C agonists and PDEs inhibitors for CRC prevention and treatment are described in detail.

Chemical Route to Twisted Graphene, Graphene Oxide and Boron Nitride.

The recently discovered twisted graphene has attracted considerable interest. A simple chemical route was found to prepare twisted graphene by covalently linking layers of exfoliated graphene containing surface carboxyl groups with an amine-containing linker (trans-1,4-diaminocyclohexane). The twisted graphene shows the expected selected area electron diffraction pattern with sets of diffraction spots out with different angular spacings, unlike graphene, which shows a hexagonal pattern. Twisted multilayer graphene oxide could be prepared by the above procedure. Twisted boron nitride, prepared by cross-linking layers of boron nitride (BN) containing surface amino groups with oxalic acid linker, exhibited a diffraction pattern comparable to that of twisted graphene. First-principles DFT calculations threw light on the structures and the nature of interactions associated with twisted graphene/BN obtained by covalent linking of layers.

Metals and non-metals in the periodic table.

The demarcation of the chemical elements into metals and non-metals dates back to the dawn of Dmitri Mendeleev's construction of the periodic table; it still represents the cornerstone of our view of modern chemistry. In this contribution, a particular emphasis will be attached to the question 'Why do the chemical elements of the periodic table exist either as metals or non-metals under ambient conditions?' This is perhaps most apparent in the p-block of the periodic table where one sees an almost-diagonal line separating metals and non-metals. The first searching, quantum-mechanical considerations of this question were put forward by Hund in 1934. Interestingly, the very first discussion of the problem-in fact, a pre-quantum-mechanical approach-was made earlier, by Goldhammer in 1913 and Herzfeld in 1927. Their simple rationalization, in terms of atomic properties which confer metallic or non-metallic status to elements across the periodic table, leads to what is commonly called the Goldhammer-Herzfeld criterion for metallization. For a variety of undoubtedly complex reasons, the Goldhammer-Herzfeld theory lay dormant for close to half a century. However, since that time the criterion has been repeatedly applied, with great success, to many systems and materials exhibiting non-metal to metal transitions in order to predict, and understand, the precise conditions for metallization. Here, we review the application of Goldhammer-Herzfeld theory to the question of the metallic versus non-metallic status of chemical elements within the periodic system. A link between that theory and the work of Sir Nevill Mott on the metal-non-metal transition is also highlighted. The application of the 'simple', but highly effective Goldhammer-Herzfeld and Mott criteria, reveal when a chemical element of the periodic table will behave as a metal, and when it will behave as a non-metal. The success of these different, but converging approaches, lends weight to the idea of a simple, universal criterion for rationalizing the instantly-recognizable structure of the periodic table where …the metals are here, the non-metals are there … The challenge of the metallic and non-metallic states of oxides is also briefly introduced. This article is part of the theme issue 'Mendeleev and the periodic table'.

Photoelectrochemical OER activity by employing BiVO4 with manganese oxide co-catalysts.

The structure-activity relationship in the electrochemical OER has been studied widely, but aspects of the photoelectrochemical (PEC) O2 evolution activity with different manganese oxides are not fully explored. In the present study different manganese oxides (MnO2, MnOx (a mixture of Mn3+ and Mn4+ ions), Mn2O3, and Mn3O4) have been electrodeposited onto the BiVO4 photoanode as co-catalysts for PEC water splitting. We find that BiVO4-MnOx shows the lowest onset potential of 0.33 V vs. RHE and the highest activity among the manganese oxides. Annealing at different temperatures results in the improvement of the OER kinetics at the interface with some detrimental effect on the activity of BiVO4. Such a study may lead to useful changes in the fabrication of semiconductor thin film photoelectrodes useful for PEC water splitting.

Anderson localization of IR light in 1D nanosystems.

This contribution reports on the observation of a strong light localization of Anderson type in 1D systems consisting of ship-shaped carbon nanotubes. Such a localization of infrared (IR) light was observed using Fourier transform infrared spectroscopy under attenuated total reflection geometry within the spectral range of 2-20 µm. Such an IR light localization manifests itself in the form of a significant interference profile of the optical transmission over the full wavenumber range of 400-4000cm-1.

Solar thermochemical splitting of water to generate hydrogen.

Solar photochemical means of splitting water (artificial photosynthesis) to generate hydrogen is emerging as a viable process. The solar thermochemical route also promises to be an attractive means of achieving this objective. In this paper we present different types of thermochemical cycles that one can use for the purpose. These include the low-temperature multistep process as well as the high-temperature two-step process. It is noteworthy that the multistep process based on the Mn(II)/Mn(III) oxide system can be carried out at 700 °C or 750 °C. The two-step process has been achieved at 1,300 °C/900 °C by using yttrium-based rare earth manganites. It seems possible to render this high-temperature process as an isothermal process. Thermodynamics and kinetics of H2O splitting are largely controlled by the inherent redox properties of the materials. Interestingly, under the conditions of H2O splitting in the high-temperature process CO2 can also be decomposed to CO, providing a feasible method for generating the industrially important syngas (CO+H2). Although carbonate formation can be addressed as a hurdle during CO2 splitting, the problem can be avoided by a suitable choice of experimental conditions. The choice of the solar reactor holds the key for the commercialization of thermochemical fuel production.

Electrocatalytic hydrogen evolution reaction activity comparable to platinum exhibited by the Ni/Ni(OH)2/graphite electrode.

Electrochemical dual-pulse plating with sequential galvanostatic and potentiostatic pulses has been used to fabricate an electrocatalytically active Ni/Ni(OH)2/graphite electrode. This electrode design strategy to generate the Ni/Ni(OH)2 interface on graphite from Ni deposits is promising for electrochemical applications and has been used by us for hydrogen generation. The synergetic effect of nickel, colloidal nickel hydroxide islands, and the enhanced surface area of the graphite substrate facilitating HO-H cleavage followed by H(ad) recombination, results in the high current density [200 mA/cm2 at an overpotential of 0.3 V comparable to platinum (0.44 V)]. The easy method of fabrication of the electrode, which is also inexpensive, prompts us to explore its use in fabrication of solar-driven electrolysis.

The Future of Neurocritical Care Research: Proceedings and Recommendations from the Fifth Neurocritical Care Research Network Conference.

The Fifth Neurocritical Care Research Network (NCRN) Conference held in Boca Raton, Florida, in September of 2018 was devoted to challenging the current status quo and examining the role of the Neurocritical Care Society (NCS) in driving the science and research of neurocritical care. The aim of this in-person meeting was to set the agenda for the NCS's Neurocritical Care Research Central, which is the overall research arm of the society. Prior to the meeting, all 103 participants received educational content (book and seminar) on the 'Blue Ocean Strategy®,' a concept from the business world which aims to identify undiscovered and uncontested market space, and to brainstorm innovative ideas and methods with which to address current challenges in neurocritical care research. Three five-member working groups met at least four times by teleconference prior to the in-person meeting to prepare answers to a set of questions using the Blue Ocean Strategy concept as a platform. At the Fifth NCRN Conference, these groups presented to a five-member jury and all attendees for open discussion. The jury then developed a set of recommendations for NCS to consider in order to move neurocritical care research forward. We have summarized the topics discussed at the conference and put forward recommendations for the future direction of the NCRN and neurocritical care research in general.

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.

The possibility of a multifunctional and reversible solid-state colorimetric sensor is described for the identification and quantification of ultra-trace Cd2+ and Hg2+ ions, using a honeycomb-structured mesoporous silica monolith conjoined with an indigenous chromoionophoric probe, i.e., 4-hexyl-6-((5-mercapto-1,3,4-thiadiazol-2-yl)diazenyl)benzene-1,3-diol (HMTAR). The amphiphilic probe is characterized using NMR, FT-IR, HR-MS, and CHNS elemental analysis. The structural and surface properties of the monolithic template have been characterized using p-XRD, XPS, TEM-SAED, SEM-EDAX, FT-IR, TG-DTA, and N2 isotherm analysis. The unique structural features and distinct analytical properties of the solid-state sensor proffer a strong response in selectively signaling the target analytes. The probe (HMTAR) exhibits a 1:1 stoichiometric binding ratio with the target ions (Cd2+ & Hg2+), with a visual color change from pale orange to dark red for Cd2+ (525 nm, λmax), and to purple for Hg2+ (530 nm, λmax), respectively, in the pH range 7.0-8.0. The influence of various analytical criteria such as pH, temperature, response kinetics, critical probe concentration, sensor quantity, matrix tolerance, linear response range, reusability, the limit of detection (LOD), and quantification (LOQ) has been investigated to validate the sensor performance. The proposed method displays a linear signal response in the concentration range 5-100 µg/L, with a LOD value of 2.67 and 2.90 µg/L, for Cd2+ and Hg2+, respectively. The real-world efficacy of the sensor material has been tested with real and synthetic water samples with a significant recovery value of ≥ 99.2%, to authenticate its data reliability and reproducibility (RSD ≤ 3.53%). Graphical abstract.