Unraveling the Formation Mechanism of Dendritic Fibrous Nanosilica

Enhancing potassium ions adsorption on mesoporous carbon spheres with abundant internal surface via engineering sulfur doping sites towards superior rate capability

Mesoporous carbon spheres (MCSs) show great potential for using as high-performance anodes in potassium-ion batteries (PIBs). Design and synthesis of MCSs with suitable multiscale structures and heteroatom doping or co-doping in MCSs are successfully employed to optimize the ion and electron transportation, however, it is still a challenge to explore MCS-based anodes with satisfactory potassium storage performance. In this work, we report novel S-doped MCS samples with abundant internal surfaces for potassium storage. The S doping sites are controlled during the synthesis, and the effect of different doping sites on the potassium storage is systematically studied. It is found that S doping between the carbon layers enlarges interlayer spacing and facilitates potassium ion adsorption. Consequently, the optimized sample shows an excellent rate capability of 144 mAh/g at 5.0 A/g, and a high reversible specific capacity of 325 mAh/g after 100 cycles at 0.1 A/g with a capacity retention of 91.2%. The important role of element doping sites on ion adsorption and ion storage performance is confirmed by theoretical investigations. Controlling the doping sites in MCSs provides a new approach to designing high-performance electrodes for energy storage and conversion applications.

Exploiting the Synergism of a Carbon-Catalyst Interface to Achieve Magneto-Electrocatalytic Overall Water Splitting at 2.197 V

The desire to electrolyze water at low energy and high kinetics for achieving rapid H2 production forms the holy grail for the paradigm shift to a sustainable H2-driven economy. While alkaline electrolysis is preferred due to the use of earth-abundant catalysts, its sluggish kinetics and high overpotential are the persistent challenges. Addressing this, we demonstrate the coupling of an externally applied magnetic field (Hext) to a synergistically designed interface of nanostructured carbon floret with antiferromagnetic NiO nanoflakes that act in unison to achieve rapid hydrogen generation (6.3 N m3 h-1 W-1) that is comparable with existing technologies. Specifically, the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) overpotentials are simultaneously reduced by 10 and 7%, respectively, under the influence of a weak fridge magnet (Hext = 200 mT). Consequently, ∼11% improvement in the energy efficiency is observed with a 21% reduced cell voltage for overall water splitting. The stability of the system is demonstrated over a prolonged lifetime of ∼95 h. This performance enhancement with Hext for both HER and OER is explained in terms of improved kinetic facility for the reaction and lower resistance of charge transfer pathway. Moreover, the electrocatalyst is seen to retain the improved performance for prolonged usage (∼3 h) even after the removal of the Hext, and hence, it provides an energy-efficient hydrogen and oxygen generation pathway.

Phonon-Engineered Hard-Carbon Nanoflorets Achieving Rapid and Efficient Solar-Thermal Based Water Evaporation and Space-Heating

Generation and utilization of green heat produced from solar energy demand broadband absorbers with the elusive combination of strong phonon-driven photon thermalization and, contrastingly, weak phonon-lattice thermal conductivity. Here, we report a new class of porous, nanostructured hard-carbon florets (NCFs) consisting of isotropically assembled conical microcavities for greater light entrapment and efficient broad-band absorption (95% over 250-2500 nm). Resembling marigolds, the NCF exhibits short-range graphitic order that promotes instantaneous and efficient solar-thermal conversion (ηSTC = 87%) while exhibiting long-range intrinsic disorder providing low thermal conductivity (1.5 W m-1 K-1) to minimize thermal loss (13%). Solution processable NCF coatings on arbitrarily substrates (filter paper, terracotta, Cu and Al tubes) generate surface temperature of 400 ± 2 K and exhibit high thermal effusance (519 W s0.5 m-2 K-1) to achieve highest combination of (a) rate of solar-driven interfacial water evaporation (Rw = 5.4 kg m-2 h-1, 2 sun), (b) solar-vapor conversion efficiency (ηSVC = 186%), and (c) ηSTC (87%) among known materials. Such robust performance is retained for beyond 30 days of continuous operation and under different solar power (1 sun to 5 sun). Furthermore, active space heating (outlet air temperature = 346 ± 3 K) using NCF coatings is demonstrated.

A morphological study of bicontinuous concentric lamellar silica synthesized at atmospheric pressure and its application as an internal micro-reflector in dye-sensitized solar cells

KCC-1, a nanostructured silica material with a bicontinuous concentric lamellar (bcl) morphology, provides plenty of functional characteristics, such as an open channel structure, excellent accessibility, and a large surface area. Although bcl silica exhibits various superior properties, studies on its morphology and its application in dye-sensitized solar cells (DSSCs) are still limited. Therefore, this work aims to study the influence of the synthesis time on the morphology of bcl silica. Moreover, we used the synthesized bcl silica as internal micro-reflectors in DSSCs. The bcl silica was synthesized using the reflux method by varying synthesis times. The morphology of bcl silica was observed using FESEM and HRTEM. FESEM images show that bcl silica has bicontinuous lamellar walls arranged concentrically to form spherical particles. As the synthesis time increases, the average particle size of bcl silica increases. The quantization of bcl silica binary images shows that the average lamellar cross-sectional area ratio decreases with increasing synthesis time. The simulation of the Cahn-Hilliard's spinodal decomposition model using MATLAB also describes the lamellar cross-sectional area ratio of bcl silica. In addition, to characterize the FESEM image's texture, a Shannon entropy calculation was performed. The line and circular gray value intensity profiles of the HRTEM image show that bcl silica has a denser core than the outer part. The denser core proves that the lamellae in bcl silica are concentrically arranged towards the particle core. Furthermore, we added bcl silica to a photoanode to see the effect of bcl characteristics on the DSSC performance. The results show that the bcl silica significantly improves the light-harvesting efficiency in DSSCs due to its low refractive index and open channel structure.

Synthesis of Dendritic ZSM-5 Zeolite through Micellar Templating Controlled by the Amphiphilic Organosilane Chain Length

The synthesis of ZSM-5 zeolites by hydrothermal crystallization of protozeolitic nanounits functionalized with amphiphilic organosilanes of different chain length (Cn-N(CH3)2-(CH2)3-Si-(OCH3)3, n = 10, 14, 18 and 22) has been investigated. Well-developed dendritic nanoarchitectures were achieved when using C14 and C18 organosilanes, exhibiting a radial and branched pattern of zeolitic nanounits aggregates. In contrast, although C10 and C22 organosilanes led to materials with hierarchical porosity, they lack of dendritic features. These differences have been linked to the formation of an amorphous mesophase at the gel preparation stage for the C14 and C18 samples, in which the surfactant micelles are covalently connected with the protozeolitic nanounits through siloxane bonds. The presence of the dendritic nanostructure positively impacts both the textural and catalytic properties of ZSM-5 zeolite. Thus, ZSM-5 (C14) and ZSM-5 (C18) samples exhibit the largest contribution of mesoporosity in terms of both surface area and pore volume. On the other hand, when tested as catalysts in the aldol condensation of furfural with cyclopentanone, which is an interesting reaction for the production of sustainable jet fuels, the highest catalytic activity is attained over the dendritic ZSM-5 materials due to their remarkable accessibility and balanced Brønsted/Lewis acidity.

Synthesis of Graphdiyne Hollow Spheres and Multiwalled Nanotubes and Applications in Water Purification and Raman Sensing

Controlling the structure of graphdiyne (GDY) is crucial for the discovery of new properties and the development of new applications. Herein, the microemulsion synthesis of GDY hollow spheres (HSs) and multiwalled nanotubes composed of ultrathin nanosheets is reported for the first time. The formation of an oil-in-water (O/W) microemulsion is found to be a key factor controlling the growth of GDY. These GDY HSs have fully exposed surfaces because of the avoidance of overlapping between nanosheets, thereby showing an ultrahigh specific surface area of 1246 m² g^-1 and potential applications in the fields of water purification and Raman sensing.

Insights into the CO2 Capture Characteristics within the Hierarchical Pores of Carbon Nanospheres Using Small-Angle Neutron Scattering

Understanding adsorption processes at the molecular level has transformed the discovery of engineered materials for maximizing gas storage capacity and kinetics in adsorption-based carbon capture applications. In this work, we studied the molecular mechanism of gas (CO₂, H₂, methane, and ethane) adsorption inside an interconnected porous network of carbon. This was achieved by synthesizing novel macro-meso-microporous carbon (M³C) nanospheres with interconnected pore structures. The M³Cs showed a CO₂ capture capacity of 5.3 mmol/g at atmospheric CO₂ pressure, with excellent kinetics. This was due to fast CO₂ adsorption within the interconnected hierarchical macro-meso-microporous M³C. In situ small-angle neutron scattering (SANS) under various CO₂ pressures indicated that the macro- and mesopores of M³C enable fast diffusion of CO₂ molecules inside the micropores, where adsorbed CO₂ molecules densify into a liquid-like state. This strong densification of CO₂ molecules causes fast CO₂ diffusion in the macro- and mesopores of M³C, restarting the adsorption cycle for fresh CO₂ molecules until all pores are completely filled. Notably, M³C also showed good capture capacities for hydrogen and various hydrocarbons, with excellent selectivity toward ethane over methane.

Tetraalkoxysilane-Assisted Self-Emulsification Templating for Controlled Mesostructured Silica Nanoparticles

Although mesoporous silica nanoparticles (MSNs) have been intensively investigated, their mesostructure and formation mechanism are still a topic of debate. Here, we show that MSNS are generated at the interface of the biphasic water-surfactant-triethanolamine-tetraalkoxysilane (TAOS) quaternary system. The spontaneous microemulsification of the hydrophobic TAOS generates microdroplets and direct micelles that both determine the particle size and the pore size. We confirmed also that the dendritic morphology with conical pores is an intermediate species, which readily transforms into regular MSNs concomitantly with the collapse of the microemulsion due to the continuous consumption of TAOS. The prominent effect of the microemulsion on the mechanism growth as a primary template is thoroughly investigated and named here tetraalkoxysilane-assisted self-emulsification templating.

Tunable synthesis of dendritic fibrous nano silica using 1-pentanol-water microemulsion at low oil to water ratio

Dendritic fibrous nanosilica (DFNS) is a suitable nano-carrier for loading pesticides with radially oriented pores and a large surface area. The microemulsion method is standard method to prepare DFNS, and 1-pentanol is taken to replace cyclohexane as an oil solvent due to its high stability and nontoxic property. The results showed that the volume ratio of 1-pentanol (oil) to water (O/W) and the molar ratio of hexadecyltrimethylammonium bromide (CTAB) to tetraethylorthosilicate (TEOS) had effected on morphology and adsorption properties of DFNS in the water-CTAB-1-pentanol-ethanol-trimethylbenzene (TMB) microemulsion system. DFNS with bicontinuous concentric lamellar morphologies can be synthesized in this microemulsion at the meager O/W volume ratio (0.025-0.045). It features a tight mesoporous structure with a thin dendritic fibrous in 0.03 to 0.04 O/W volume ratio. The particle sizes, surface areas, and porosity of DFNS were positively correlated with the addition of the silica precursor TEOS. The size of DFNS increased from 123 to about 220 nm with the CTAB/TEOS molar ratio decreasing from 0.119 to 0.050. When the molar ratio of CTAB to TEOS  = 0.119, DFNS has a smaller particle size (123 nm) with a larger surface area and abundant honeycomb mesopores; the low O/W volume ratio strategy provides theoretical support for the industrialization development of DFNS and nano-pesticides, which plays a profound role in promoting the sustainable development of pesticide reduction, efficiency and green agriculture.

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.

Thermodynamic Picture of Phase Segregation during the Formation of Bicontinuous Concentric Lamellar (bcl) Silica

The thermodynamic picture describing the formation mechanism of bicontinuous concentric lamellar (bcl) nanostructured silica particles, bcl silica, was investigated thoroughly. A series of classical kinetics of bcl silica by varying the synthesis time were employed to observe the morphological evolution of bcl silica. The formation mechanism of bcl silica is proposed as the hydrolysis and condensation reactions in the reverse micelle, followed by the phase segregation process. The images of the whole part and the cross-section of bcl silica reveal that bcl silica can be obtained just 30 min after the synthesis starts. The particle morphology evolves from bicontinuous lamellar (bl) morphology, with the absence of the dense part in the center of the particle, to bicontinuous concentric lamellar (bcl) morphology. The theoretical part of this study is focused on the phase segregation process of the mixture. This process is divided thermodynamically into several reversible processes based on the reduced Helmholtz free energy state function. The type of the lamellar orientation (i.e., parallel or perpendicular orientation) changed as the stacked lamellae changed in thickness and was followed by the decrease in the free energy. It was merely shown that the segregation of the thin slab of the lamellar polysiloxane stack favors the perpendicular orientation. In contrast, the thick slab of the lamellar polysiloxane stack yields a complex lamellar structure consisting of perpendicular and parallel orientations. A lamellar polymer confined between two planar substrates can experience a topological transformation into a sphere due to an unfavorable environment, i.e., high surface tension. After the topological transformation, lamellae with a perpendicular orientation form bicontinuous lamellae, whereas the complex lamellar structure transforms into a bicontinuous concentric lamellar morphology.

Joule Heating-Driven Transformation of Hard-Carbons to Onion-like Carbon Monoliths for Efficient Capture of Volatile Organic Compounds

Soft graphitizable carbon-based multifunctional nanomaterials have found versatile applications ranging from energy storage to quantum computing. In contrast, their hard-carbon analogues have been poorly investigated from both fundamental and application-oriented perspectives. The predominant challenges have been (a) the lack of approaches to fabricate porous hard-carbons and (b) their thermally nongraphitizable nature, leading to inaccessibility for several potential applications. In this direction, we present design principles for fabrication of porous hard-carbon-based nanostructured carbon florets (NCFs) with a highly accessible surface area (∼936 m²/g), rivalling their soft-carbon counterparts. Subjecting such thermally stable hard-carbons to a synergistic combination of an electric field and Joule heating drives their transformation to free-standing macroscopic monoliths composed of onion-like carbons (OLCMs). This represents the first such structural transformation observed in sp²-based hard-carbon NCFs to sp²-networked OLCMs. Micro-Raman spectroscopy establishes the simultaneous increase in the intensity of D-, 2D-, and D + G-bands at 1341, 2712, and 2936 cm^-1 and is correlated to the reorganization in the disordered graphitic domains of NCFs to curved concentric nested spheres in OLCMs. This therefore completely precludes the formation of a nanodiamond core that has been consistently observed in all previously reported OLCs. The Joule heating-driven formation of OLCMs is accompanied by ∼5700% enhancement in electrical conductivity that is brought about by the fusion of outermost graphitic shells of OLCs to result in monolithic OLC structures (OLCMs). The porous and inter-networked OLCMs exhibit an excellent adsorption-based capture of volatile organic compounds such as toluene at high efficiencies (∼99%) over a concentration range (0.22-1.86 ppm) that is relevant for direct applications such as smoke filters in cigarettes.

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.

Gold cluster-loaded dendritic nanosilica: single particle luminescence and catalytic properties in the bulk

We report a hybrid material in which surface anchoring-induced enhanced luminescence of AuQC@BSA clusters on high surface area dendritic fibrous nanosilica of 800 nm diameter enabled their luminescence imaging at a single particle level. The photophysical and structural properties of the hybrid material were characterized by various spectroscopic and microscopic techniques. Concomitant imaging using scattering and luminescence of such mesostructures and their response to analytes have been used to develop a chemical sensor. The hybrid material was found to be catalytically active in silane to silanol conversion, and 100% conversion was observed in 4 h when the reaction was carried out at 30 °C in the presence of light. Such materials at submicron dimensions with enhanced surface area, emission in the solid state along with a high quantum yield of 12% in water along with enhanced scattering, and surface functionalities present numerous benefits for the creation of multifunctional materials.

Origin of the Hierarchical Structure of Dendritic Fibrous Nanosilica: A Small-Angle X-ray Scattering Perspective

The discovery of dendritic fibrous nanosilica (DFNS) has attracted great attention to the field of catalysis, CO₂ capture, drug delivery due to its distinct morphology, and pore size distribution. Despite extensive research, the understanding of the DFNS formation process and its internal structure remains incomplete as microscopy and gas sorption techniques were not able to provide necessary in-depth structural information due to their inherent limitations. In the current work, we present a structural model of DFNS derived using small-angle X-ray scattering (SAXS) supported by ¹²⁹Xe nuclear magnetic resonance (NMR), which provided intricate details of DFNS and its internal structure. Mechanistic understanding of the DFNS formation and growth process was achieved by performing time-resolved SAXS measurements during the synthesis of DFNS, which unveils the evolution of two levels of a bicontinuous microemulsion structure responsible for intricate DFNS morphology. The validity and the accuracy of the SAXS method and the model were successfully established through a direct correlation among the functionality of the DFNS scattering profile and its pore size distribution, as well as results obtained from the ¹²⁹Xe NMR studies. It has been established that the DFNS structure originates from direct modulation of the bicontinuous structure controlled by a surfactant, a co-surfactant, and the silicate species formed during hydrolysis and the condensation reaction of the silica precursor.

Biotemplated Hollow Mesoporous Silica Particles as Efficient Carriers for Drug Delivery

We designed three types of hollow-shaped porous silica materials via a three-step biotemplate-directed method: porous hollow silica nanorods, hollow dendritic fibrous nanostructured silica (DFNS), and ultraporous sponge-like DFNS. The first step was making a biotemplate, for which we used cellulose nanocrystals (CNCs), consisting of rod-shaped nanoparticles synthesized by conventional acid hydrolysis of cellulose fibers. In a second step, core-shell samples were prepared using CNC particles as hard template by two procedures. In the first one, core-shell CNC-silica nanoparticles were synthesized by a polycondensation reaction, which exclusively took place at the surface of the CNCs. In the second procedure, a typical synthesis of DFNS was conducted in a bicontinuous microemulsion with the assistance of additives. DFNS was assembled on the surface of the CNCs, giving rise to core-shell CNC-DFNS structures. Finally, all of the silica-coated CNC composites were calcined, during which the CNC was removed from the core and hollow structures were formed. These materials are very lightweight and highly porous. All three structures were tested as nanocarriers for drug delivery and absorbents for dye removal applications. Dye removal results showed that they can adsorb methylene blue efficiently, with ultraporous sponge-like DFNS showing the highest adsorption capacity, followed by hollow DFNS and hollow silica nanorods. Furthermore, breast cancer cells show a lower cell viability when exposed to doxorubicin-loaded hollow silica nanorods compared with control or doxorubicin cultures, suggesting that the loaded nanorod has a greater anticancer effect than free doxorubicin.

Designing ultrafine PdCo alloys in mesoporous silica nanospheres with peroxidase-like activity and catalase-like activity

Nanomaterial-based artificial enzyme mimetics have attracted increasing attention because of their robust stability, adjustable activity, and cost-effectiveness. In this study, we developed a simple and effective method for the synthesis of highly dispersed ultrafine PdCo alloys with peroxidase- and catalase-like activities. The aberration-corrected transmission electron microscopy analysis verified that the cyanogel precursor in the mesoporous silica nanospheres (MSNs) was converted to PdCo alloy in NH3 at a high temperature. The PdCo alloy was homogenously distributed in MSNs as ultrafine and monodispersed particles. By selectively removing the Co species from the binary alloy through an acid-leaching approach, the role of each component in the enzyme-like mimetics was systematically studied. Using glutathione (GSH) as the model analyte, the potential application of PdCo@MSNs in GSH detection from complex cell media was confirmed via colorimetric assay. The ultrafine alloy size, double mimetic activities, and abundant loading space of PdCo@MSNs make them promising not only in clinical diagnosis but also in overcoming hypoxia-induced photodynamic therapy resistance in tumor treatment.

Catalytic nanosponges of acidic aluminosilicates for plastic degradation and CO2 to fuel conversion

The synthesis of solid acids with strong zeolite-like acidity and textural properties like amorphous aluminosilicates (ASAs) is still a challenge. In this work, we report the synthesis of amorphous "acidic aluminosilicates (AAS)", which possesses Brønsted acidic sites like in zeolites and textural properties like ASAs. AAS catalyzes different reactions (styrene oxide ring-opening, vesidryl synthesis, Friedel-Crafts alkylation, jasminaldehyde synthesis, m-xylene isomerization, and cumene cracking) with better performance than state-of-the-art zeolites and amorphous aluminosilicates. Notably, AAS efficiently converts a range of waste plastics to hydrocarbons at significantly lower temperatures. A Cu-Zn-Al/AAS hybrid shows excellent performance for CO₂ to fuel conversion with 79% selectivity for dimethyl ether. Conventional and DNP-enhanced solid-state NMR provides a molecular-level understanding of the distinctive Brønsted acidic sites of these materials. Due to their unique combination of strong acidity and accessibility, AAS will be a potential alternative to zeolites.

Comprehensive understanding of the synthesis and formation mechanism of dendritic mesoporous silica nanospheres

The interest in the design and controlled fabrication of dendritic mesoporous silica nanospheres (DMSNs) emanates from their widespread application in drug-delivery carriers, catalysis and nanodevices owing to their unique open three-dimensional dendritic superstructures with large pore channels and highly accessible internal surface areas. A variety of synthesis strategies have been reported, but there is no basic consensus on the elucidation of the pore structure and the underlying formation mechanism of DMSNs. Although all the DMSNs show a certain degree of similarity in structure, do they follow the same synthesis mechanism? What are the exact pore structures of DMSNs? How did the bimodal pore size distributions kinetically evolve in the self-assembly? Can the relative fractions of small mesopores and dendritic large pores be precisely adjusted? In this review, by carefully analysing the structures and deeply understanding the formation mechanism of each reported DMSN and coupling this with our research results on this topic, we conclude that all the DMSNs indeed have the same mesostructures and follow the same dynamic self-assembly mechanism using microemulsion droplets as super templates in the early reaction stage, even without the oil phase.

Compositional Control as the Key for Achieving Highly Efficient OER Electrocatalysis with Cobalt Phosphates Decorated Nanocarbon Florets

Compositional interplay of two different cobalt phosphates (Co(H₂ PO₄ )₂ ; Co-DP and Co(PO₃ )₂ ; Co-MP) loaded on morphologically engineered high surface area nanocarbon leads to an increased electrocatalytic efficiency for oxygen evolution reaction (OER) in near neutral conditions. This is reflected as significant reduction in the onset overpotential (301 mV) and enhanced current density (30 mA cm^-2 @ 577 mV). In order to achieve uniform surface loading, organic-soluble thermolabile cobalt-bis(di-tert-butylphosphate) is synthesized in situ inside the nanocarbon matrix and subsequently pyrolyzed at 150 °C to produce Co(H₂ PO₄ )₂ /Co(PO₃ )₂ (80:20 wt%). Annealing this sample at 200 or 250 °C results in the redistribution of the two phosphate systems to 55:45 or 20:80 (wt%), respectively. Detailed electrochemical measurements clearly establish that the 55:45 (wt%) sample prepared at 200 °C performs the best as a catalyst, owing to a relay mechanism that enhances the kinetics of the 4e^- transfer OER process, which is substantiated by micro-Raman spectroscopic studies. It is also unraveled that the engineered nanocarbon support simultaneously enhances the interfacial charge-transfer pathway, resulting in the reduction of onset overpotential, compared to earlier investigated cobalt phosphate systems.

The mechanistic role of a support-catalyst interface in electrocatalytic water reduction by Co3O4 supported nanocarbon florets

Comprehending the mechanistic involvement of a support-catalyst interface is critical for effective design of industrially relevant electrocatalytic processes such as the alkaline hydrogen evolution reaction (alHER). The understanding of the kinetically sluggish alHER exhibited by both Pt and Pt-group-metal-free catalysts is primarily derived from indirect electrochemical parameters such as the Tafel slope. To address these issues, we establish the critical role of a nanocarbon floret (NCF) based electrochemical support in generating a key cobalt-oxohydroxo (OH-Co[double bond, length as m-dash]O) intermediate during the alHER through operando Raman spectro-electrochemistry. Specifically, interfacial nano-engineering of a newly designed carbon support (NCF) with a spinel Co₃O₄ nanocube catalyst is demonstrated to achieve a facile alHER (-0.46 V@10 mA cm^-2). Such an efficient alHER is mainly attributed to the unique lamellar morphology with a high mesoporous surface area (936 m² g^-1) of the NCF which catalyses the rate-determining water dissociation step and facilitates rapid ion diffusion. The dissociated water drives the formation of the OH-Co[double bond, length as m-dash]O intermediate, spectroscopically captured for the first time through the emergence of a νOH-Co[double bond, length as m-dash]O Raman peak (1074 cm^-1). The subsequent alHER proceeds through the Volmer-Heyrovsky route (119 mV dec^-1) via the T_d Co²⁺↔ Co³⁺↔ Co⁴⁺ oxidative pathway. Concomitant graphitization of the NCF through the disappearance of νsp³C-H (2946 cm^-1) supports the co-operative dynamics at the Co₃O₄-NCF interface. Thus, the NCF positively contributes towards the lowering of the overpotential with a low charge-transfer resistance (R_ct = 35.8 Ω) and high double layer capacitance (C_dl = 410 mF cm^-2).

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.

Tunable porous silica nanoparticles as a universal dye adsorbent

Here, we report selective adsorption of cationic dyes methylene blue (MB) and rhodamine B (RB) and anionic dyes methyl orange (MO) and bromo cresol green (BCG) by modifying the surface of cetyl trimethyl ammonium bromide (CTAB) coated porous silica nanoparticles (PSN). We used a top down approach to synthesize PSN (porous silica nanoparticles) without high temperature calcination. X-ray diffraction study confirms the formation of pure phase silica nanoparticles. SEM analysis reveals that the particle morphology is spherical and the size range lies in-between 150-200 nm. We have studied the dye adsorption properties for three cases of PSN at varying calcination temperatures of 100 °C, 250 °C and 500 °C, respectively. Thermal study has been performed in the temperature range of 50-800 °C to check the calcination temperature. In this report, we have tuned the surface properties for selective adsorption of cationic and anionic dyes in water. In the first case, 100 °C calcined PSN selectively adsorb only anionic dyes, whereas in the second case, 500 °C calcined PSN adsorb only cationic dyes and finally, an optimized calcination temperature ≈250 °C could be used for all types of dye to be adsorbed irrespective of charges on the dyes. The mode of interaction of dyes with PSN has been explained with a proper mechanism in all three cases. The adsorptions of dyes are confirmed by UV-Vis spectroscopy. Adsorption capacity and regenerable performance of adsorbents have also been studied.

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.

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.

Self-Assembled Photonic Crystals of Monodisperse Dendritic Fibrous Nanosilica for Lasing: Role of Fiber Density

Photonic crystals are essentially a periodic ("crystalline") arrangement of dielectric nanoparticles that respond in unison to incident light. They can be used to harvest light in various applications such as photocatalysis, solar cells, and lasing. In this work, we prepared the photonic crystals of dendritic fibrous nanosilica (DFNS) by their self-assembly. Because of the narrow particle size distribution of the as-synthesized DFNS, they readily formed colored photonic crystals. The photonic band gap was found to be tunable by using DFNS of various sizes and fiber densities. Notably, even after having similar particle sizes (but with different fiber densities), they showed different photonic band gaps, indicating that the fiber density plays a role in the band gap of photonic crystals. Such observations have not been reported before. This could have arisen from the difference in their refractive indices because of the difference in their fiber densities and hence the variation in the silica content, leading to a different optical signature.