Self-assembly Of Precursors Research Articles

Construction of 3D BN network with high-density thermal conductive paths

Efficient heat dissipation is essential to further improve the integration of high-power electronic packaging devices. Three-dimensional BN networks with high-density thermal conductive paths were designed as the heat transfer skeleton of thermal interface materials. 3D networks with high-density thermal conductive paths inlaid between oriented BN paths were constructed using precursor self-assembly and freeze-drying to improve the thermal conductivity of polymeric materials. The results show that high-density thermally conductive paths have stronger polymer-enhanced thermal conductivity than directional thermal paths and compared with pure TPU, the thermal conductivity of TPU/BN-2 under low BN filling content (10%wt) is increased by 250 % and 286.5 % in the through surface and flat surface respectively. This work provides new ideas for the preparation of polymer composites for thermal interface materials in electronic packaging and integrated circuits with excellent thermal management properties.

On-surface polymerization reactions of dibrominated hexaphenylbenzene influenced by densely packed self-assembly.

Controlled bottom-up fabrication of molecular nanostructures through on-surface reactions of tailor-made precursors is of scientific and technological interest. Recently, on-surface polymerization reactions influenced by precursor self-assembly have been reported. Thus, a fundamental understanding of the reaction process is a prerequisite for controlled formation. Herein, we report on the influence of molecular self-assembly of dibrominated hexaphenylbenzene (Br2-HPB) on the on-surface polymerization reactions on a Au(111) substrate. By using low-temperature scanning tunnelling microscopy (STM), we find that the polymerization of Br2-HPB proceeds while maintaining the long-range ordered self-assembly, despite a decrease in HPB-HPB distance due to debromination and successive covalent bonding of Br2-HPB. From the STM investigations of the polymerization process, we conclude that the polymerization of Br2-HPB is accompanied by molecular rotations to maintain the periodic array of the self-assembled structure, contrary to the conventional understanding of the polymerization of the self-assembled precursor layer.

Room-Temperature Salt Template Synthesis of Nitrogen-Doped 3D Porous Carbon for Fast Metal-Ion Storage.

The water-soluble salt-template technique holds great promise for fabricating 3D porous materials. However, an equipment-free and pore-size controllable synthetic approach employing salt-template precursors at room temperature has remained unexplored. Herein, we introduce a green room-temperature antisolvent precipitation strategy for creating salt-template self-assembly precursors to universally produce 3D porous materials with controllable pore size. Through a combination of theoretical simulations and advanced characterization techniques, we unveil the antisolvent precipitation mechanism and provide guidelines for selecting raw materials and controlling the size of precipitated salt. Following the calcination and washing steps, we achieve large-scale and universal production of 3D porous materials and the recycling of the salt templates and antisolvents. The optimized nitrogen-doped 3D porous carbon (N-3DPC) materials demonstrate distinctive structural benefits, facilitating a high capacity for potassium-ion storage along with exceptional reversibility. This is further supported by in situ electrochemical impedance spectra, in situ Raman spectroscopy, and theoretical calculations. The anode shows a high rate capacity of 181 mAh g-1 at 4 A g-1 in the full cell. This study addresses the knowledge gap concerning the room-temperature synthesis of salt-template self-assembly precursors for the large-scale production of porous materials, thereby expanding their potential applications for electrochemical energy conversion and storage.

Cu/CuOx@C Composite as a High-Efficiency Electrocatalyst for Oxygen Reduction Reactions

Among clean energy transformation devices, fuel cells have gained special attention over the past years; however, advancing appropriate non-valuable metal impetuses to halfway supplant the customary Pt/C impetus is still in progress. In this paper, we propose a specific electrocatalyst in the formula of highly-active Cu species, associated with coated carbon (Cu@C-800), for oxygen reduction reaction (ORR) through post-treatment of a self-assembled precursor. The optimized catalyst Cu@C-800 showed excellent ORR performance (i.e., the onset potential was 1.00 V vs. RHE, and half-wave potential of 0.81 V vs. RHE), high stability, resistance to methanol, and high four-electron selectivity. The enhancement is attributed to the synergy between the carbon matrix and a high explicit surface region and rich Cu nano-species.

2-Methylimidazole-tuned “4-Self” strategy based on benzimidazole-5-carboxylate for boosting oxygen reduction electrocatalysis

Rational design highly active transition metal or transition metal oxides/nanocarbon hybrids is one of the feasible way to deliver a cooperative oxygen reduction (ORR) with a synergistic effect of the hybrid interface. Herein, based on benzimidazole-5-carboxylate (BIMC), CoO/Co-N-C nanocomposites are fabricated via 2-methylimidazole (2-MeIm)-tuned “4-Self” strategy, namely, self-templating, self-adapting, self-assembly and self-catalysis. As a base competitive ligand with N and C sources, 2-MeIm modulates the dispersion of BIMC in methanol to generate collodial-like BIMC tiny particles, the coordination ability of BIMC to Co(II), the composition and morphology of the self-assembled precursor (Co-BM), and as well as the conductivity of the resultant electrocatalyst. Impressing, carbonization of Co-BM at 800 °C under N2 atmosphere endows the pyrolysis product (Co-BM-800) with the well-dispersed Co/CoO riveted on nitrogen-doped carbon, as well as the enhanced ORR performance in terms of positive onset-potential (0.890 V vs. RHE), large diffusion limiting current density (5.21 mA cm−2), and high stability.

Preparation of Hollow-Porous Rosin-Based Polyurethane Microspheres with pH-Responsive Characteristics

Preparation of polymer microspheres from naturally occurring resource is a challenge. Here, a rosin-based polyol (RAG) was used to prepare polyurethane resin (RPU) firstly, and then act as both self-assembled precursor and emulsifier, rosin based polyurethane microspheres (RPUMs) were prepared. In the process of self-emulsification, the RPU formed vesicles by self-assembly. The outer shell of the vesicle consisted of hydrophilic segments, while the inner shell contained the hydrophobic phase. After cross-linking the RPU and removal of the solvent in the core, the porous-hollow microspheres with pH-sensitive were obtained. The microspheres were characterized by optical microscope (OM), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The effect of type and amount of the hydrophilic chain extender, and solvent on the morphology, particle size and distribution, and buffer volume of the microspheres were determined. The best conditions for synthetic RPUMs were as follows: nNCO/nOH = 1, nRAG:n1-(2-hydroxyethyl) piperazine = 4:6, with azodiisobutyronitrile level of 1.0 wt.%, based on reactive monomers, mixing speed of both emulsification and polymerization at 400 r·min−1, the RPUMs synthesized had porous-hollow structure with a buffer volume of 1.6 mL.

Constructing supramolecular self-assembled porous g-C3N4 nanosheets containing thiophene-groups for excellent photocatalytic performance under visible light

Enhancing catalytic visible light capture and light utilization efficiency represent an important objective in graphitic carbon nitride (g-C3N4) research. Herein, a novel sulfur-containing thiophene-grafted g-C3N4 porous nanosheets (CM-CN-Th A) prepared via co-thermal polycondensation of supramolecular self-assembled precursors (CM) and 3-thiophenecarboxylic acid (Th A) is reported. The introduction of thiophene groups improved the optical properties of the synthesized catalyst in the visible range, enhanced charge carrier separation, and suppressed e-/h+ pair complexation compared to pristine g-C3N4. Various analytical techniques were employed to characterize the structure, morphology, and electrical and optical features of the synthesized catalysts. In the removal of rhodamine B (Rh B) from aqueous media, CM-CN-Th A displayed favorable photocatalytic activity (rate constant k of 0.0360 min−1) under visible light illumination (λ > 420 nm), with photocatalytic removal effieciency of 89.22%, mineralization efficiency of 45.34%; this value was maintained after five cycles. The catalyst also delivers superior photocatalytic activity for methyl orange (MO), methylene blue (MB), and crystalline violet (CV) degradation, demonstrating wide applicability for dye wastewater treatment. In addition, a possible photocatalytic mechanism of CM-CN-Th A is proposed by analyzing the experimental results of active species capture. This work offers a novel approach for the photodegradation of dye wastewater.

On-surface synthesis of 2D COFs via molecular assembly directed photocycloadditions: a first-principles investigation

Over the past decades, the rational synthesis of two-dimensional covalent organic framework (2D COFs) monolayer via on-surface chemistry has been widely explored. Herein, we propose the [2 + 2] photocycloaddition as a novel strategy for large-scale fabrication of COFs from theoretical perspective. Thanks to the symmetry forbidden of thermal [2 + 2] cycloaddition, the molecular precursors carrying vinyl groups will not chemically interact with each other during thermal annealing, which is essential to achieve molecular assembly. The subsequent photocycloaddition of these precursors may produce large-scale 2D COFs at low temperatures, in which the symmetry of molecular assembly remains unchanged. Our results show that 2D COFs can be produced via [2 + 2] photocycloadditions directed from self-assembled precursors, in which alkylbenzene molecules with vinyl groups on side chains exhibit appropriate intermolecular distances. By performing high-throughput calculations, several promising molecular precursors are proposed to achieve large-scale 2D COFs. This work provides an applicable strategy for the large-scale synthesis of 2D carbon materials.

Communication—Bimetallic-MOFs-Derived ZnO/Bi2O3 Composites as Anode Materials for Advanced Zinc-Based Batteries

In this study, the nano-sized ZnO/Bi2O3 composites were synthesized with the zinc-bismuth bimetallic-MOFs as the precursor for the first time. The metal ions were homogeneously anchored on the self-assembled precursor with a structure of hollow sphere. The results showed that the obtained ZnO presented a typical structure of hexagonal prismatic and an even distribution of element Zn and Bi was realized. Utilized as anode materials of Zn/Ni battery, the composites displays an ultra-high average discharge capacity of 630 mAh g−1 at 1 C and longer cycle life than the unmodified pure ZnO.

Synthesis of highly porous g-C3N4 nanotubes for efficient photocatalytic degradation of sulfamethoxazole

Pyrolysis of supramolecular assembly precursor is a promising method to prepare graphite carbon nitride (g-C3N4), and the topological structure of the precursor assemblies largely determine the morphology and photoelectric properties of g-C3N4. In this paper, uniformly and highly porous g-C3N4 nanotubes were synthesized under the assistance of 1,5-naphthalene disulfonic acid (NA) through the melamine (MA)-cyanuric acid (CA) precursor self-assembly strategy. The as-synthesized g-C3N4 nanotubes in the presence of 75 mg/L NA (MNCA-75) exhibited the highest BET surface area (SBET) of 100.40 m2/g, and the smallest band gap (Eg) of 2.31 eV. 10 mg/L of sulfamethoxazole (SMX) was completely degraded within 120 min with the MNCA-75, and the degradation reaction conformed to pseudo-first-order kinetics. This paper reported a facile but effective method to prepare highly porous g-C3N4 nanotubes with large surface area and excellent photocatalytic performance.

On-surface formation of metal–organic coordination networks with C⋯Ag⋯C and C=O⋯Ag interactions assisted by precursor self-assembly

Surface-bound reactions are commonly employed to develop nanoarchitectures through bottom-up assembly. Precursor molecules are carefully designed, and surfaces are chosen with the intention to fabricate low-dimensional extended networks, which can include one-dimensional and two-dimensional structures. The inclusion of functional groups can offer the opportunity to utilize unique chemistry to further tune the bottom-up method or form novel nanostructures. Specifically, carbonyl groups open up new avenues for on-surface coordination chemistry. Here, the self-assembly and formation of an organometallic species via the thermally induced reaction of 3,6-dibromo-9,10-phenanthrenequinone (DBPQ) molecules were studied on Ag(100) and Ag(110). Low-temperature ultrahigh vacuum scanning tunneling microscopy revealed the room temperature formation of self-assemblies defined by hydrogen and halogen bonds on Ag(100). Following a thermal anneal to 300 °C, DBPQ on Ag(100) was found to form metal-organic coordination networks composed of a combination of organometallic species characteristics of Ullmann-like coupling reactions and carbonyl complexes. On Ag(110), the C-Br bonds were found to readily dissociate at room temperature, resulting in the formation of disordered organometallic species.

Designing 2D covalent networks with lattice Monte Carlo simulations: precursor self-assembly.

Organic synthesis reactions in the adsorbed phase have been recently an intensively studied topic in heterogeneous catalysis and material engineering. One of such processes is the Ullmann coupling in which halogenated organic monomers are transformed into covalently bonded polymeric structures. In this work, we use the lattice Monte Carlo simulation method to study the on-surface self-assembly of organometallic precursor architectures comprising tetrasubstituted naphthalene building blocks with differently distributed halogen atoms. In the coarse grained approach adopted herein the molecules and metal atoms were modeled by discrete segments, two connected and one, respectively, placed on a triangular lattice representing a (111) metallic surface. Our simulations focused on the influence of the intramolecular distribution of the substituents on the morphology of the resulting superstructures. Special attention was paid to the molecules that create porous networks characterized by long-range order. Moreover, the structural analysis of the assemblies comprising prochiral building blocks was made by running simulations for the corresponding enantiopure and racemic adsorbed systems. The obtained results demonstrated the possibility of directing the on-surface self-assembly towards networks with controllable pore shape and size. These findings can be helpful in designing covalently bonded 2D superstructures with predefined architecture and functions.

On-surface Synthesis of a Chiral Graphene Nanoribbon with Mixed Edge Structure.

Chiral graphene nanoribbons represent an important class of graphene nanomaterials with varying combinations of armchair and zigzag edges conferring them unique structure‐dependent electronic properties. Here, we describe the on‐surface synthesis of an unprecedented cove‐edge chiral GNR with a benzo‐fused backbone on a Au(111) surface using 2,6‐dibromo‐1,5‐diphenylnaphthalene as precursor. The initial precursor self‐assembly and the formation of the chiral GNRs upon annealing are revealed, along with a relatively small electronic bandgap of approximately 1.6 eV, by scanning tunnelling microscopy and spectroscopy.

The Instability of Monolayer-Thick PbSe on VSe2

Two-dimensional monolayers derived from 3D bulk structures remain a relatively unexplored class of materials because of the challenge of stabilizing nonepitaxial interfaces. Here, we report an unusual reconstruction during the deposition of precursors when targeting the synthesis of heterostructures with an odd number of PbSe monolayers. Multilayer elemental precursors of Pb|Se + V|Se were deposited to have the correct number of atoms to form [(PbSe)1+δ]q(VSe2)1 where q is the number of PbSe monolayers in the heterostructure. Structural analysis of the self-assembled precursor via X-ray reflectivity, X-ray diffraction, and HAADF-STEM suggests three different behaviors upon deposition. Precursors with q ≥ 7 and even values of q have the targeted nanoarchitectures after deposition, which are maintained as the products are self-assembled through a near diffusionless process. Significant lateral surface diffusion occurred during the deposition of precursors with q = 1, 3, and 5, resulting in the precursor to have a different nanoarchitecture than targeted. Additional perpendicular long-range diffusion occurs during self-assembly of these precursors, resulting in different final products than targeted. Density functional theory (DFT) calculations of PbSe blocks show that the odd-numbered layers are less stable than the even-numbered layers, which suggests an energetic driving force for the observed rearrangement. This work highlights the importance of understanding the reaction mechanism when attempting to prepare 2D layers of constituents with bulk 3D structures.

Synthesis of tubular g-C3N4 via a H2SO4-assisted precursor self-assembly strategy for enhanced photocatalytic degradation of organic pollutant

Nanostructured graphitic carbon nitride (g-C3N4) has attracted enormous attention as a promising visible-light photocatalyst because of its unique physicochemical properties. However, controlling the nanostructure of g-C3N4 is challenging because the most common template methods are high-cost and high-risk intensive as well as tedious. In this work, tubular g-C3N4 is prepared in situ by annealing a melamine-cyanurate supramolecular array, which is conducted through a H2SO4-assisted precursor self-assembly strategy. The as-prepared samples are characterized by X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller analysis, and other photoelectrochemical measurements. Moreover, the band structure of the g-C3N4 nanotubes is investigated to elucidate the carrier separation mechanism. The result shows that the g-C3N4 nanotubes have a hollow structure (average diameter: 0.2–1.2 μm, length: 10–50 μm, and thickness: 15–20 nm) and an enhanced electronic structure. Owing to the high specific surface area of their hierarchical pores and the efficient charge separation of their 1D feature, the g-C3N4 nanotubes exhibit high photocatalytic methylene blue (MB)/tetracycline (TC) degradation rates of 0.0265 min−1 and 0.0110 min−1, which are three and seven times higher than those of Bulk g-C3N4, respectively. Therefore, this study provides a facile and effective strategy for the construction of carbon nitride nanostructures.

Low-temperature preparation of novel stabilized aluminum titanate ceramic fibers via nonhydrolytic sol-gel method through linear self-assembly of precursors

Stabilized aluminum titanate fibers were prepared via nonhydrolytic sol-gel (NHSG) method through linear self-assembly of precursors. The results show that NHSG method generates the heterogeneous condensation with the formation of Al–O–Ti, Mg–O–Ti, Fe–O–Ti, Mg–O–Al, Fe–O–Ti bonds, which ensures that magnesium ions and iron ions can enter aluminium titanate lattice and stabilize it at 750 °C. Bimolecular associated structure of chlorotitanium ethoxide titanium precursor promotes the self-linear-assemble of all precursors, which enables the excellent spinnability of sol. Stabilized aluminum titanate fibers have excellent corrosion resistance. The thermal expansion coefficient of stabilized aluminum titanate ceramic is −0.142 × 10−6°C−1.

Synchronization iodine surface modification and lattice doping porous carbon nitride for photocatalytic hydrogen production

Reaction active surface area and energy band structure determine the visible-light photocatalytic property of semiconductor catalyst such as graphitic carbon nitride (CN). Herein, synchronization iodine surface modified and doped porous carbon nitride (CNI) was prepared. The self-assembly precursors from urea and ammonium iodide were firstly obtained by liquid nitrogen-assisted rapid re-crystallization and lyophilization technology. After the heat treatment of above precursors, CNI was easily synthesized. Compared with bulk CN, CNI shows large specific surface area (57.59 m2 g−1), due to freeze-drying treatment and thermal decomposition of ammonium iodide. As electron donors, iodine species can enrich the electron density in the carbon nitride network and tune the electronic band structure. It is important the surface iodine modification can bound the positive charge holes to inhibit the recombination of photogenerated carriers. As a result, CNI exhibits prompted photocatalytic hydrogen evolution rate of 114.0 μmol h−1 under visible-light irradiation (λ > 420 nm), better than that of bulk CN. This work may provide a promising rapid method for designing another porous and effective semiconductor photocatalysts.

A facile method to synthesize hierarchical nano-sized zeolite beta

Abstract A one-pot two-stage synthesis method was developed to synthesize hierarchical nano-sized zeolite beta. The two-stage included the generation of nano-sized zeolite beta precursor and the self-assembly of the zeolite beta precursor around structure directing agent, hexadecyl trimethyl ammonium bromide. The influence of the hydrothermal synthesis time and pH value of the zeolite beta precursors, hydrothermal treatment duration, SDA concentration, and water content during nano-sized zeolite beta precursor self-assembly on the properties of final solid products were studied. The samples were characterized by nitrogen adsorption (BET), NH3-TPD, X-ray powder diffraction, solid state-NMR, and TEM. With the present synthesis method and conditions, compared with the conventional nano-sized zeolite beta synthesis, a longer zeolite precursor crystallization time was required for the successful transformation of the amorphous aluminosilicates precursors into crystalline beta assemblies with hierarchical structure. The further crystallization of zeolite beta precursors during the precursor assembly did not occur under studied pH range, hydrothermal treatment duration, SDA concentration, and water content.

Self-Assembly Precursor-Derived MoP Supported on N,P-Codoped Reduced Graphene Oxides as Efficient Catalysts for Hydrogen Evolution Reaction.

The design and synthesis of high-activity earth-abundant material-based electrocatalysts for hydrogen evolution reaction (HER) are of great significance. Here we develop a novel method to prepare a MoP nanoparticle supported on N,P-codoped reduced graphene oxides (MoP/N,P-rGO) by pyrolysis of the self-assembled precursor. Benefiting from the selected components of the assembly, P and N atoms are mixed at the molecular level, which leads to MoP nanoparticles uniformly attaching to the graphene substrate and a certain amount of N and P atoms codoping to graphene. The obtained MoP/N,P-rGO exhibits a good HER performance that only needs an overpotential of 115 mV to achieve a HER current density of 10 mA cm-2. The enhanced HER performance is due to the well-dispersed MoP nanoparticles and the synergistic effect from the doped graphene substrate. It shows that the selected functional components integrated by the self-assembly process are appropriate precursors for the synthesis of high-quality HER electrocatalysts.

Photoinduced Self-Assembled Nanostructures and Permanent Polaron Formation in Regioregular Poly(3-hexylthiophene).

Solution processing of conjugated polymers into ordered self-assembled precursors has attracted great interest in the past years owing to the ability to manipulate their structural and physical properties. Regioregular poly(3-hexylthiophene) (P3HT) has become the benchmark polymer in this scenario, where ordered lamellar structures significantly improve carrier mobility of the thin films due to increased crystallinity, extended intrachain conjugation, and ordered interchain π-stacking. Here, a new photoinduced approach is presented for the generation of highly ordered P3HT aggregate structures that is amenable to the use of visible light to control the aggregate formation. Strong intra- and interchain interactions in the solution precursors allow for permanent formation of localized and delocalized polarons that are stable for months. Spin-coated thin films are found to preserve, in part, the morphological and physical properties of the aggregated P3HT solution precursors with high degree of crystallinity and short π-stack interchain distances.