Preparation and application of KCC-1@ZIF-8 for the solid extraction of tetracycline with high adsorption capacity

In this study, three different materials were prepared: dendritic fiber-type silica (KCC-1), zeolitic imidazolate framework-8 (ZIF-8), and a new composite material called KCC-1@ZIF-8. These materials were synthesized using microemulsion, stirring, and coating methods, respectively. The properties of the materials were characterized using various techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), TGA and X-ray diffraction (XRD). The results showed that KCC-1@ZIF-8 exhibited a significant increase in the BET surface area and pore size compared to the individual components KCC-1 and ZIF-8. These improved properties of the composite material were beneficial for enhancing the adsorption capacity. The effects of initial concentrations, solution pH and reaction time on the adsorption capacity were investigated. The adsorption kinetics and isothermal data of ZIF-8 and KCC-1@ZIF-8 fitted well with pseudo-second-order and Langmuir isotherm models. The results of adsorption thermodynamics show that the adsorption process is spontaneous and endothermic. KCC-1@ZIF-8 exhibited a very high adsorption capacity (751.46 mg g-1) at an initial TC hydrochloride concentration of 80 mg L-1 in an aqueous solution at 301.15 K, and the value was higher than that of ZIF-8 (549.80 mg g-1) under the same conditions. KCC-1 exhibited a relatively lower capacity (37.860 mg g-1). Based on these findings, KCC-1@ZIF-8 was considered a promising adsorbent for the treatment of wastewater contaminated with TC hydrochloride. Additionally, the composite material, when combined with high-performance liquid chromatography (HPLC), could be used as a solid-phase extraction adsorbent for the adsorption of TC hydrochloride in animal foodstuff samples. The calibration curves showed a linear range of 20-500 μg L-1, and the recovery rate ranged from 85.216% to 90.717%. No one has made adsorbents with this new structure before, and KCC-1@ZIF-8 possessed excellent adsorption properties, which make it a potential candidate for environmental remediation and analytical applications involving TC hydrochloride.

Defects tune the acidic strength of amorphous aluminosilicates

Crystalline zeolites have high acidity but limited utility due to microporosity, whereas mesoporous amorphous aluminosilicates offer better porosity but lack sufficient acidity. In this work, we investigated defect engineering to fine-tune the acidity of amorphous acidic aluminosilicates (AAS). Here we introduced oxygen vacancies in AAS to synthesize defective acidic aluminosilicates (D-AAS). 1H, 27Al, and 17O solid-state nuclear magnetic resonance (NMR) studies indicated that defects induced localized structural changes around the acidic sites, thereby modifying their acidity. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy studies substantiated that oxygen vacancies alter the chemical environment of Brønsted acidic sites of AAS. The effect of defect creation in AAS on its acidity and catalytic behavior was demonstrated using four different acid-catalyzed reactions namely, styrene oxide ring opening, vesidryl synthesis, Friedel-Crafts alkylation, and jasminaldehyde synthesis. The defects played a role in activating reactants during AAS-catalyzed reactions, enhancing the overall catalytic process. This was supported by in-situ FTIR, which provided insights into the molecular-level reaction mechanism and the role of defects in reactant activation. This study demonstrates defect engineering as a promising approach to fine-tune acidity in amorphous aluminosilicates, bridging the porosity and acidity gaps between mesoporous amorphous aluminosilicates and crystalline zeolites.

Rational Design of Dinitroxide Polarizing Agents for Dynamic Nuclear Polarization to Enhance Overall NMR Sensitivity

We evaluate the overall sensitivity gains provided by a series of eighteen nitroxide biradicals for dynamic nuclear polarization (DNP) solid-state NMR at 9.4 T and 100 K, including eight new biradicals. We find that in the best performing group the factors contributing to the overall sensitivity gains, namely the DNP enhancement, the build-up time, and the contribution factor, often compete with each other leading to very similar overall sensitivity across a range of biradicals. NaphPol and HydroPol are found to provide the best overall sensitivity factors, in organic and aqueous solvents respectively. One of the new biradicals, AMUPolCbm, provides high sensitivity for all three solvent formulations measured here, and can be considered to be a "universal" polarizing agent.

Dynamic Nuclear Polarization of Inorganic Halide Perovskites

The intrinsic low sensitivity of nuclear magnetic resonance (NMR) experiments limits their utility for structure determination of materials. Dynamic nuclear polarization (DNP) under magic angle spinning (MAS) has shown tremendous potential to overcome this key limitation, enabling the acquisition of highly selective and sensitive NMR spectra. However, so far, DNP methods have not been explored in the context of inorganic lead halide perovskites, which are a leading class of semiconductor materials for optoelectronic applications. In this work, we study cesium lead chloride and quantitatively compare DNP methods based on impregnation with a solution of organic biradicals with doping of high-spin metal ions (Mn²⁺) into the perovskite structure. We find that metal-ion DNP provides the highest bulk sensitivity in this case, while highly surface-selective NMR spectra can be acquired using impregnation DNP. The performance of both methods is explained in terms of the relaxation times, particle size, dopant concentration, and surface wettability. We envisage the future use of DNP NMR approaches in establishing structure-activity relationships in inorganic perovskites, especially for mass-limited samples such as thin films.

Role of fiber density of amine functionalized dendritic fibrous nanosilica on CO2 capture capacity and kinetics

Textural properties of the solid sorbents are critical to tuning their CO2 capture performance. In this work, we studied the effect of fiber density (in turn, pore size, distribution, and accessibility) on CO2 capture capacity and kinetics. CO2 solid sorbents were prepared by physisorption of tetraethylenepentamine (TEPA) molecules on dendritic fibrous nanosilica (DFNS) with varying fiber density. Among the various DFNS, the DFNS with moderate fiber density [DFNS-3] showed the best CO2 capture capacity under the flue gas condition. The maximum CO2 capture capacity achieved was 24.3 wt % (5.53 mmol/g) at 75 °C for DFNS-3 under humid gas conditions. Fiber density also played a role in the kinetics of CO2 capture. DFNS-1 with dense fiber density needed ∼10.4 min to reach 90 % capture capacity, while DFNS-3 (moderate fiber density) needed only 6.4 min, which further decreased to 5.9 min for DFNS-5 with lightly dense fibers. The DFNS-impregnated TEPA also showed good recyclability during 21 adsorption and desorption cycles under humid and dry conditions. The total CO2 capture capacity of DFNS-3 (14.7) in 21 cycles was 108.9 and 105.0 mmol/g under humid and dry conditions, respectively. Adsorption lifetime calculation and recyclability confirmed the fiber density-dependent CO2 capture performance.

Dendritic Fibrous Nanosilica: Discovery, Synthesis, Formation Mechanism, Catalysis, and CO2 Capture-Conversion

ConspectusSilica-based mesoporous nanomaterials have been widely used for a range of applications. Although mesopore materials (such as MCM-41 and SBA-15) possess high surface area, due to their tubular pore structures, pore accessibility is restricted, which causes limitations in mass transport. A new nanosilica was needed to overcome these challenges, including better accessibility, controllable particle size, and good stability. In 2010, my group invented dendritic fibrous nanosilica (DFNS), which has now become a family of novel nanosilicas. DFNS has several unique properties: (i) Tunable particle sizes (50 to 1200 nm), (ii) high surface area (500 to 1200 m²/g), (iii) tunable pore volume (0.32 to 2.18 cm³/g), (iv) wide pore size distribution (3.7 to 25 nm) characterized by radially oriented pores, (v) controllable fiber density (number of fibers per sphere), (vi) variable pore size and pore volume, (vi) high thermal (∼800 °C) and hydrothermal stability, and (vii) mechanical stability (∼130 MPa). DFNS possesses unique dendritic fibrous morphology, and hence can be reached from all sides and easily accessible. DFNS can now be synthesized using a open refluxing protocol, which allowed the scale-up of the process with a sustainable E-factor. In the last 12 years, the DFNS family of materials has been extensively studied for their formation mechanism and range of applications such as catalysis, solar energy harvesting, CO₂ capture, CO₂ conversion, sensing, biomedicine, energy storage and many more.This Account discusses the invention of DFNS, its synthesis with tunable particle size, textural properties (surface area, pore volume, and pore size), and fiber density. In addition, the DFNS formation mechanism via the complex interplay of self-assembly, the dynamics, and coalescence of bicontinuous microemulsion droplets (BMDs) is discussed. Finally, applications of DFNS in a range of fields, that include catalysis, photocatalysis, synthesis of plasmonic black gold, nanosponges of aluminosilicates, CO₂ capture, and CO₂ conversion to fuel, are presented.

Dendritic Mesoporous Nanoparticles: Structure, Synthesis and Properties

Recently, a new family of "dendritic" mesoporous silica nanoparticles has attracted great interest with widespread applications. Despite a large number of publications (>800), the terminology of "dendritic" is ambiguous. Understanding what possible "dendritic structures" are, their formation mechanisms and the underlying structure-property relationship is fundamentally important. With the advance of characterization techniques such as electron tomography, two types of tree branch-like and flower-like structures can be distinguished, both described as "dendritic" in literature. In this review, we start with the definition of "dendritic", then provide critical analysis of reported dendritic silica nanoparticles according to their structural classification. We also update the understandings of the formation mechanisms of two types of "dendritic" nanoparticles, with a focus on how to control different structural parameters. Various applications of dendritic mesoporous nanoparticles are also reviewed with a focus in biomedical field, providing new insights into the structure-property relationship in this family of nanomaterials.

Indirectly Detected DNP-Enhanced 17 O NMR Spectroscopy: Observation of Non-Protonated Near-Surface Oxygen at Naturally Abundant Silica and Silica-Alumina

Recent studies have shown that dynamic nuclear polarization (DNP) can be used to detect ¹⁷ O solid-state NMR spectra of naturally abundant samples within a reasonable experimental time. Observations using indirect DNP, which relies on ¹ H mediation in transferring electron hyperpolarization to ¹⁷ O, are currently limited mostly to hydroxyls. Direct DNP schemes can hyperpolarize non-protonated oxygen near the radicals; however, they generally offer much lower signal enhancements. In this study, we demonstrate the detection of signals from non-protonated ¹⁷ O in materials containing silicon. The sensitivity boost that made the experiment possible originates from three sources: indirect DNP excitation of ²⁹ Si via protons, indirect detection of ¹⁷ O through ²⁹ Si nuclei using two-dimensional ²⁹ Si{¹⁷ O} D-HMQC, and Carr-Purcell-Meiboom-Gill refocusing of ²⁹ Si magnetization during acquisition. This ²⁹ Si-detected scheme enabled, for the first time, 2D ¹⁷ O-²⁹ Si heteronuclear correlation spectroscopy in mesoporous silica and silica-alumina surfaces at natural abundance. In contrast to the silanols showing motion-averaged ¹⁷ O signals, the framework oxygens exhibit unperturbed powder patterns as unambiguous fingerprints of surface sites. Along with hydroxyl oxygens, detection of these moieties will help in gaining more atomistic-scale insights into surface chemistry.

Characterization of Functional Groups in Estuarine Dissolved Organic Matter by DNP-enhanced 15 N and 13 C Solid-State NMR

Estuaries are key ecosystems with unique biodiversity and are of high economic importance. Along the estuaries, variations in environmental parameters, such as salinity and light penetration, can modify the characteristics of dissolved organic matter (DOM). Nevertheless, there is still limited information about the atomic-level transformations of DOM in this ecosystem. Solid-state NMR spectroscopy provides unique insights into the nature of functional groups in DOM. A major limitation of this technique is its lack of sensivity, which results in experimental time of tens of hours for the acquisition of ¹³ C NMR spectra and generally precludes the observation of ¹⁵ N nuclei for DOM. We show here how the sensitivity of solid-state NMR experiments on DOM of Seine estuary can be enhanced using dynamic nuclear polarization (DNP) under magic-angle spinning. This technique allows the acquisition of ¹³ C NMR spectra of these samples in few minutes, instead of hours for conventional solid-state NMR. Both conventional and DNP-enhanced ¹³ C NMR spectra indicate that the ¹³ C local environments in DOM are not strongly modified along the Seine estuary. Furthermore, the sensitivity gain provided by the DNP allows the detection of ¹⁵ N NMR signal of DOM, in spite of the low nitrogen content. These spectra reveal that the majority of nitrogen is in the amide form in these DOM samples and show an increased disorder around these amide groups near the mouth of the Seine.

Biomedical applications of dendritic fibrous nanosilica (DFNS): recent progress and challenges

Dendritic fibrous nanosilica (DFNS), with multi-component and hierarchically complex structures, has recently been receiving significant attention in various fields of nano-biomedicine. DFNS is an emerging class of mesoporous nanoparticles that has attracted great interest due to unique structures such as open three-dimensional dendritic superstructures with large pore channels and highly accessible internal surface areas. This overview aims to study the application of DFNS towards biomedical investigations. This review is divided into four main sections. Sections 1–3 are related to the synthesis and characterization of DFNS. The biomedical potential of DFNS, such as cell therapy, gene therapy, immune therapy, drug delivery, imaging, photothermal therapy, bioanalysis, biocatalysis, and tissue engineering, is discussed based on advantages and limitations. Finally, the perspectives and challenges in terms of controlled synthesis and potential nano-biomedical applications towards future studies are discussed.

Dendritic fibrous nanosilica (DFNS) , with multi-component and hierarchically complex structures, has recently been receiving significant attention in various fields of nano-biomedicine.

DNP NMR spectroscopy of cross-linked organic polymers: rational guidelines towards optimal sample preparation

Cross-linked polystyrenes (PS) are an important class of polymers, whose properties are strongly dependent on incorporated functionalities, for which detailed understanding of their structure remains a challenge. Here, we develop a rational guideline for dynamic nuclear polarization (DNP) sample formulation for cross-linked PS to interrogate their structure. We show that the DNP enhancement on a series of cross-linked PS bearing alkylammonium groups as prototypical organic polymers correlates with the polymer swelling properties in both apolar and polar formulations (TEKPol/1,1,2,2-tetrachloroethane and AMUPol/dimethyl sulfoxide). This work provides guidelines to easily optimize DNP formulation using a simple swelling test and enables natural abundance 15N NMR to be recorded on a series of PS-supported quaternary alkylammonium salts, allowing a detailed structural analysis.

Novel ultra-small Pd NPs on SOS spheres: a new catalyst for domino intramolecular Heck and intermolecular Sonogashira couplings

We report a novel catalyst Pd/SOS that catalyzes the dual C-C bond forming coupling of an iodoarene moiety with an internal alkene and an external alkyne via an intramolecular Heck reaction, followed by an intermolecular Sonogashira reaction, respectively. The catalyst was characterized using XRD, IR, XPS, SEM and TEM analyses. Notably, for the first time, cheap and readily available new silica [nanosilica on microsilica (SOS)] material-supported ultra-small Pd nanoparticles (2.20 nm) are employed for the efficient synthesis of dihydrobenzofuran and oxindole derivatives in a domino one-pot reaction. Significantly, a sub-molar quantity of Pd (0.3 mol%) was found to be sufficient to furnish the products in very good to near quantitative yields. Gratifyingly, the catalyst could be recycled up to five cycles with a marginal loss (∼no loss) of the product.

Synthesis of dendritic fibrous nanosilica over a cubic core (cSiO2@DFNS) with catalytically efficient silver nanoparticles for reduction of nitroarenes and degradation of organic dyes

In this study, dendritic fibrous core–shell silica particles having cubic morphology with uniform and vertical nanochannels have been successfully synthesised. The synthesized dendritic fibrous nanosilica over a cubic core (cSiO₂@DFNS) have been characterized by using various techniques, such as powder X-ray diffraction, TEM, FE-SEM, TGA EDS, FT-IR and N₂ adsorption–desorption experiments. The prepared DFNS particles demonstrated a very high surface area and pore diameter. Amine groups were functionalized on the fibres of cSiO₂@DFNS and after that silver nanoparticles could be successfully immobilized on amine functionalized cubic silica particles. Due to the presence of a high surface area and a uniform pore diameter, the silver nanoparticle loaded cSiO₂@DFNS could be successfully employed as an efficient and recoverable catalyst for reduction of toxic aromatic nitro compounds and degradation of organic dyes. Higher catalytic activity of the prepared material could be attributed to its fibrous morphology which could facilitate proper interactions of the reactants molecules with the silver nanoparticles.

Graphical abstract showing the reduction of nitroarenes and degradation of organic dyes using cSiO₂@DFNS@Ag.

The Comparison between Single Atom Catalysis and Surface Organometallic Catalysis

Single atom catalysis (SAC) is a recent discipline of heterogeneous catalysis for which a single atom on a surface is able to carry out various catalytic reactions. A kind of revolution in heterogeneous catalysis by metals for which it was assumed that specific sites or defects of a nanoparticle were necessary to activate substrates in catalytic reactions. In another extreme of the spectrum, surface organometallic chemistry (SOMC), and, by extension, surface organometallic catalysis (SOMCat), have demonstrated that single atoms on a surface, but this time with specific ligands, could lead to a more predictive approach in heterogeneous catalysis. The predictive character of SOMCat was just the result of intuitive mechanisms derived from the elementary steps of molecular chemistry. This review article will compare the aspects of single atom catalysis and surface organometallic catalysis by considering several specific catalytic reactions, some of which exist for both fields, whereas others might see mutual overlap in the future. After a definition of both domains, a detailed approach of the methods, mostly modeling and spectroscopy, will be followed by a detailed analysis of catalytic reactions: hydrogenation, dehydrogenation, hydrogenolysis, oxidative dehydrogenation, alkane and cycloalkane metathesis, methane activation, metathetic oxidation, CO₂ activation to cyclic carbonates, imine metathesis, and selective catalytic reduction (SCR) reactions. A prospective resulting from present knowledge is showing the emergence of a new discipline from the overlap between the two areas.

Recent developments in MAS DNP-NMR of materials

Solid-state NMR spectroscopy is a powerful technique for the characterization of the atomic-level structure and dynamics of materials. Nevertheless, the use of this technique is often limited by its lack of sensitivity, which can prevent the observation of surfaces, defects or insensitive isotopes. Dynamic Nuclear Polarization (DNP) has been shown to improve by one to three orders of magnitude the sensitivity of NMR experiments on materials under Magic-Angle Spinning (MAS), at static magnetic field B₀ ≥ 5 T, conditions allowing for the acquisition of high-resolution spectra. The field of DNP-NMR spectroscopy of materials has undergone a rapid development in the last ten years, spurred notably by the availability of commercial DNP-NMR systems. We provide here an in-depth overview of MAS DNP-NMR studies of materials at high B₀ field. After a historical perspective of DNP of materials, we describe the DNP transfers under MAS, the transport of polarization by spin diffusion and the various contributions to the overall sensitivity of DNP-NMR experiments. We discuss the design of tailored polarizing agents and the sample preparation in the case of materials. We present the DNP-NMR hardware and the influence of key experimental parameters, such as microwave power, magnetic field, temperature and MAS frequency. We give an overview of the isotopes that have been detected by this technique, and the NMR methods that have been combined with DNP. Finally, we show how MAS DNP-NMR has been applied to gain new insights into the structure of organic, hybrid and inorganic materials with applications in fields, such as health, energy, catalysis, optoelectronics etc.

Dynamic Nuclear Polarization / solid-state NMR of membranes. Thermal effects and sample geometry

Whereas specially designed dinitroxide biradicals, reconstitution protocols, oriented sample geometries and NMR probes have helped to much increase the DNP enhancement factors of membrane samples they still lag considerably behind those obtained from glasses made of protein solutions. Here we show that not only the MAS rotor material but also the distribution of the membrane samples within the NMR rotor have a pronounced effect on the DNP enhancement. These observations are rationalized with the cooling efficiency and the internal properties of the sample, monitored by their T₁ relaxation, microwave ON versus OFF signal intensities and DNP effect. The data are suggestive that for membranes the speed of cooling has a pronounced effect on the membrane properties and concomitantly the distribution of biradicals within the sample.

Brute-force solvent suppression for DNP studies of powders at natural isotopic abundance

A method based on highly concentrated radical solutions is investigated for the suppression of the NMR signals arising from solvents that are usually used for dynamic nuclear polarization experiments. The presented method is suitable in the case of powders, which are impregnated with a radical-containing solution. It is also demonstrated that the intensity and the resolution of the signals due to the sample of interest is not affected by the high concentration of radicals. The method proposed here is therefore valuable when sensitivity is of the utmost importance, namely samples at natural isotopic abundance.

Facile synthesis to tune size, textural properties and fiber density of dendritic fibrous nanosilica for applications in catalysis and CO2 capture

Morphology-controlled nanomaterials such as silica play a critical role in the development of technologies for use in the fields of energy, environment (water and air pollution) and health. Since the discovery of Stöber's silica, followed by the discovery of mesoporous silica materials (MSNs) such as MCM-41 and SBA-15, a surge in the design and synthesis of nanosilica with various sizes, shapes, morphologies and textural properties (surface area, pore size and pore volume) has occurred. Dendritic fibrous nanosilica (DFNS; also known as KCC-1) is one of the recent discoveries in morphology-controlled nanomaterials. DFNS shows exceptional performance in large numbers of fields, including catalysis, gas capture, solar energy harvest, energy storage, sensors and biomedical applications. This material possesses a unique fibrous morphology, unlike the tubular porous structure of various conventional silica materials. It has a high surface area to volume ratio, with improved accessibility to the internal surface, tunable pore size and pore volume, controllable particle size and, importantly, improved stability. However, synthesis of DFNS with controllable size, textural properties and fiber density is still tricky because of several of the steps involved. This protocol provides a comprehensive step-wise description of DFNS synthesis and advice regarding how to control size, surface area, pore size, pore volume and fiber density. We also provide details of how to apply DFNS in catalysis and CO₂ capture. Detailed characterization protocols for these materials using scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption and thermal gravimetric analysis (TGA) studies are also provided.

Reducing the computational cost of NMR crystallography of organic powders at natural isotopic abundance with the help of 13 C-13 C dipolar couplings

Structure determination of functional organic compounds remains a formidable challenge when the sample exists as a powder. Nuclear magnetic resonance crystallography approaches based on the comparison of experimental and Density Functional Theory (DFT)-computed ¹ H chemical shifts have already demonstrated great potential for structure determination of organic powders, but limitations still persist. In this study, we discuss the possibility of using ¹³ C-¹³ C dipolar couplings quantified on powdered theophylline at natural isotopic abundance with the help of dynamic nuclear polarization, to realize a DFT-free, rapid screening of a pool of structures predicted by ab initio random structure search. We show that although ¹³ C-¹³ C dipolar couplings can identify structures possessing long range structural motifs and unit cell parameters close to those of the true structure, it must be complemented with other data to recover information about the presence and the chemical nature of the supramolecular interactions.

A Strategy for Probing the Evolution of Crystallization Processes by Low-Temperature Solid-State NMR and Dynamic Nuclear Polarization

Crystallization plays an important role in many areas, and to derive a fundamental understanding of crystallization processes, it is essential to understand the sequence of solid phases produced as a function of time. Here, we introduce a new NMR strategy for studying the time evolution of crystallization processes, in which the crystallizing system is quenched rapidly to low temperature at specific time points during crystallization. The crystallized phase present within the resultant "frozen solution" may be investigated in detail using a range of sophisticated NMR techniques. The low temperatures involved allow dynamic nuclear polarization (DNP) to be exploited to enhance the signal intensity in the solid-state NMR measurements, which is advantageous for detection and structural characterization of transient forms that are present only in small quantities. This work opens up the prospect of studying the very early stages of crystallization, at which the amount of solid phase present is intrinsically low.

Ion exchange and binding in selenium remediation materials using DNP-enhanced solid-state NMR spectroscopy

Selenate-loaded selenium water remediation materials based on polymer fibres have been investigated by dynamic nuclear polarization (DNP) enhanced solid-state NMR. For carbon-13 a significant reduction in experiment time is obtained with DNP even when compared with conventional carbon-13 NMR spectra recorded using larger samples. For the selenium remediation materials studied here this reduction allows efficient acquisition of {¹H}-⁷⁷Se heteronuclear correlation spectra which give information about the nature of the binding of the remediated selenate ions with the grafted side chains which provide the required ion exchange functionality.

Solution-phase synthesis of two-dimensional silica nanosheets using soft templates and their applications in CO2 capture

The solution-phase synthesis of silica nanosheets with tunable thickness and textural properties is still a challenge. We have developed a robust protocol to synthesize silica nanosheets using lamellar micelles as soft templates in a water-cyclohexane solvent mixture. The synthesized silica nanosheets (∼3.7 nm) possess significantly improved textural properties, with as high as 1420 m2 g-1 surface area and 3.47 cm3 g-1 pore volume. When functionalized with tetraethylenepentamine (TEPA) molecules using a physisorption method, the silica nanosheets showed a CO2 working capture capacity of 3.8 mmol g-1 at 75 °C with fast capture kinetics and good sorbent stability.

Room temperature CO oxidation catalysed by supported Pt nanoparticles revealed by solid-state NMR and DNP spectroscopy

A series of 1 and 2 nm sized platinum nanoparticles deposited on different support materials are investigated by solid-state NMR combined with dynamic nuclear polarization (DNP).

Improving the size uniformity of dendritic fibrous nano-silica by a facile one-pot rotating hydrothermal approach

This article provides a facile, low-cost, and reproducible one-pot rotating hydrothermal approach to synthesize dendritic fibrous nano-silica with outstanding uniformity.

Exploring Applications of Covalent Organic Frameworks: Homogeneous Reticulation of Radicals for Dynamic Nuclear Polarization

Rapid progress has been witnessed in the past decade in the fields of covalent organic frameworks (COFs) and dynamic nuclear polarization (DNP). In this contribution, we bridge these two fields by constructing radical-embedded COFs as promising DNP agents. Via polarization transfer from unpaired electrons to nuclei, DNP realizes significant enhancement of NMR signal intensities. One of the crucial issues in DNP is to screen for suitable radicals to act as efficient polarizing agents, the basic criteria for which are homogeneous distribution and fixed orientation of unpaired electrons. We therefore envisioned that the crystalline and porous structures of COFs, if evenly embedded with radicals, may work as a new "crystalline sponge" for DNP experiments. As a proof of concept, we constructed a series of proxyl-radical-embedded COFs (denoted as PR( x)-COFs) and successfully applied them to achieve substantial DNP enhancement. Benefiting from the bottom-up and multivariate synthetic strategies, proxyl radicals have been covalently reticulated, homogeneously distributed, and rigidly embedded into the crystalline and mesoporous frameworks with adjustable concentration ( x%). Excellent performance of PR( x)-COFs has been observed for DNP 1H, 13C, and 15N solid-state NMR enhancements. This contribution not only realizes the direct construction of radical COFs from radical monomers, but also explores the new application of COFs as DNP polarizing agents. Given that many radical COFs can therefore be rationally designed and facilely constructed with well-defined composition, distribution, and pore size, we expect that our effort will pave the way for utilizing radical COFs as standard polarizing agents in DNP NMR experiments.

Synthesis of spiroindenopyridazine-4H-pyran derivatives using Cr-based catalyst complexes supported on KCC-1 in aqueous solution

An efficient bis(2-dodecylsulfanyl-ethyl)-amine·CrCl3 complex supported on KCC-1 (KCC-1/SNS/Cr) has been developed for the synthesis of spiroindenopyridazine-4H-pyran, providing excellent yields of the corresponding products with remarkable chemoselectivity. This morphology ultimately leads to higher catalytic activity for the KCC-1-supported nanoparticles. The KCC-1/SNS/Cr NPs were thoroughly characterized by using TEM, SEM, TGA, FT-IR, ICP-MS, and BET. The recycled catalyst has been analyzed by ICP-MS showing only minor changes in morphology after the reaction, thus confirming the robustness of the catalyst.

Synthesis of N-[(2-hydroxyethoxy)carbonyl]glycine from carbon dioxide, ethylene oxide, and α-amino acid by ionic gelation of sodium tripolyphosphate (TPP) and spirulina supported on magnetic KCC-1 in aqueous solution

Ionic gelation supported on Fe₃O₄/KCC-1 has been developed for the synthesis of N-[(2-hydroxyethoxy)carbonyl]glycine from carbon dioxide, ethylene oxide, and α-amino acid.

Dendritic fibrous nano-silica supported gold nanoparticles as an artificial enzyme

We report a dendritic fibrous nano-silica supported gold nanoparticles (DFNS/Au) as peroxidase like artificial enzyme. This study indicates the unique role of fibrous morphology of DFNS for enhancement in enzymatic activity. A solvent dependent selectivity towards a two-electron oxidation product, TMB-diamine, has also been observed.

Unraveling the Formation Mechanism of Dendritic Fibrous Nanosilica

We studied the formation mechanism of dendritic fibrous nanosilica (DFNS) that involves several intriguing dynamical steps. Through electron microscopy and real-time small-angle X-ray scattering studies, it has been demonstrated that the structural evolution of bicontinuous microemulsion droplets (BMDs) and their subsequent coalescence, yielding nanoreactor template, is responsible for to the formation of complex DFNS morphology. The role of cosurfactant has been found to be quite crucial, which allowed the understanding of this intricate mechanism involving the complex interplay of self-assembly, dynamics of BMDs formation, and coalescence. The role of BMDs in formation of DFNS has not been reported so far and the present work allows a deeper molecular-level understanding of DFNS formation.

Dynamic nuclear polarization for sensitivity enhancement in modern solid-state NMR

The field of dynamic nuclear polarization has undergone tremendous developments and diversification since its inception more than 6 decades ago. In this review we provide an in-depth overview of the relevant topics involved in DNP-enhanced MAS NMR spectroscopy. This includes the theoretical description of DNP mechanisms as well as of the polarization transfer pathways that can lead to a uniform or selective spreading of polarization between nuclear spins. Furthermore, we cover historical and state-of-the art aspects of dedicated instrumentation, polarizing agents, and optimization techniques for efficient MAS DNP. Finally, we present an extensive overview on applications in the fields of structural biology and materials science, which underlines that MAS DNP has moved far beyond the proof-of-concept stage and has become an important tool for research in these fields.

Dendritic Fibrous Nanosilica for Catalysis, Energy Harvesting, Carbon Dioxide Mitigation, Drug Delivery, and Sensing

Morphology-controlled nanomaterials such as silica play a crucial role in the development of technologies for addressing challenges in the fields of energy, environment, and health. After the discovery of Stöber silica, followed by that of mesoporous silica materials, such as MCM-41 and SBA-15, a significant surge in the design and synthesis of nanosilica with various sizes, shapes, morphologies, and textural properties has been observed in recent years. One notable invention is dendritic fibrous nanosilica, also known as KCC-1. This material possesses a unique fibrous morphology, unlike the tubular porous structure of various conventional silica materials. It has a high surface area with improved accessibility to the internal surface, tunable pore size and pore volume, controllable particle size, and, importantly, improved stability. Since its discovery, a large number of studies have been reported concerning its use in applications such as catalysis, solar-energy harvesting, energy storage, self-cleaning antireflective coatings, surface plasmon resonance-based ultrasensitive sensors, CO2 capture, and biomedical applications. These reports indicate that dendritic fibrous nanosilica has excellent potential as an alternative to popular silica materials such as MCM-41, SBA-15, Stöber silica, and mesoporous silica nanoparticles. This Review provides a critical survey of the dendritic fibrous nanosilica family of materials, and the discussion includes the synthesis and formation mechanism, applications in catalysis and photocatalysis, applications in energy harvesting and storage, applications in magnetic and composite materials, applications in CO2 mitigation, biomedical applications, and analytical applications.