Electrostatic Assembly Process Research Articles

Interface engineering SnS2/MXene Nb2C self-powered photodetectors with high responsivity and detectivity

Research on two-dimensional (2D) materials and their van der Waals heterostructures (vdWHs) has generated a lot of interest in the fields of electronics and optoelectronics. However, the construction of 2D heterostructures remains a challenge because the most widely used deterministic placement method to perform 2D layer stacking often suffers from erratic control of lattice orientation over lattice orientations. Herein, a new 2D/2D SnS2/MXene Nb2C heterostructure for high-performance photodetectors (PDs) was designed and prepared by using a simple electrostatic assembly process. It was demonstrated that the combination of Nb2C MXene nanosheets (NSs) and SnS2 NSs significantly improved the performance of PDs by enhancing the charge transfer, carrier density, light adsorption, as well as by decreasing band bending edge and charge recombination. The SnS2/Nb2C PDs exhibited remarkable responsivity (102.44 μA/W) and ultrahigh specific detectivity (7.48 × 1012 Jones) at zero external bias under a 365 nm laser at level Ⅳ. Additionally, comprehensive investigations of energy level diagram derived from both experimental measurements and density functional theory calculations provided further insights of such photodetector system. This simple and reliable fabrication strategy opens a new avenue for the large-scale production of low-cost and high-quality MXenes-based heterogeneous bond for next-generation electronic and optoelectronic applications.

An electrochemiluminescence resonance energy transfer biosensor based on Luminol-LDH and CuS@Pt for detection of alpha-fetoprotein

Alpha-fetoprotein (AFP) is the best diagnostic marker for hepatocellular carcinoma (HCC) and plays an important role in the general surveillance of the population. Therefore, the establishment of an ultra-sensitive AFP assay is essential for the early screening and clinical diagnosis of HCC. In this work, we designed a signal-off biosensor for ultra-sensitive detection of AFP based on an electrochemiluminescent resonance energy transfer (ECL-RET) strategy using luminol intercalated layered bimetallic hydroxide (Luminol-LDH) as an ECL donor and Pt nanoparticles-grown on copper sulfide nanospheres (CuS@Pt) as ECL acceptor. The (Au NPs/Luminol-LDH)n multilayer nanomembrane synthesized by our intercalation and layer-by-layer electrostatic assembly process not only effectively immobilizes luminol but also significantly enhances the ECL signal. The CuS@Pt composite has well visible light absorption ability and can burst the light emitted from luminol by ECL-RET. The biosensor showed good linearity in the range from 10−5 ng mL−1 to 100 ng mL−1 and a minimum detection limit of 2.6 fg mL−1. Therefore, the biosensor provides a novel and efficient strategy for the detection of AFP, which is important for the early screening and clinical diagnosis of HCC.

Growing CoNi nanoalloy@N-doped carbon nanotubes on MXene sheets for excellent microwave absorption

• 0D CoNi nanoalloy-encapsulated 1D NCNT were grown on 2D Ti 3 C 2 T x sheets. • High surface areas and excellent thermal oxidation stabilities were achieved for the composite. • The minimum RL reached −55.3 dB at 2.1 mm. • The EAB of 4.3 GHz at 1.5 mm could be attained. Recently, two-dimensional MXene materials have attracted numerous attention in electromagnetic wave shielding/absorption. Hybridizing magnetic materials and constructing multi-dimensional structures in MXene is highly beneficial to improve electromagnetic wave absorption properties. Herein, we demonstrate a strategy for in situ growing 0D CoNi nanoalloy-encapsulated 1D N-doped carbon nanotubes on a 2D Ti 3 C 2 T x MXene sheet through an electrostatic assembly process followed by a high-temperature pyrolysis process. The resultant 201-structured MXene-CoNi@N-doped carbon nanotube (MXene-CoNi@NCNT) composites displayed high surface areas (55.6–103.7 m 2 /g), moderate magnetism (19.8–24.6 emu/g), and excellent thermal oxidation stabilities (≥ 307 °C). In addition, the unique 2D/0D/1D architectures entrusted the composites with abundant interfaces, various defects, and numerous nitrogen dopants. Taking advantage of the special 201 structure and the existence of both magnetic and dielectric loss, the MXene-CoNi@NCNT composite showed great impedance matching and strong attenuation performance. A strong reflection loss of –55.3 dB was achieved when the coating thickness was 2.1 mm, and a wide effective absorption bandwidth of 4.3 GHz was achieved at a thickness of 1.5 mm, much superior to that of similar absorbers. This work demonstrates a novel strategy for designing electromagnetic wave absorbers with magnetic and dielectric losses accompanied by multiple dimensional structures.

Rational design of Fe-doped K0.8Ti1.73Li0.27O4@rGO as a high-rate and long-cycle-life anode for lithium-ion batteries

K0.8Ti1.73Li0.27O4 (KLTO) is an important titanium-based anode material for lithium-ion batteries (LIBs) and is expected to become an alternative to carbonaceous materials on account of its nontoxicity, low cost, and high safety performance. However, it suffers from poor specific capacity at high charge–discharge rates due to its low conductivity and obstructed Li-ion diffusion. In this work, an Fe-doped KLTO@rGO (Fe-KLTO@rGO) composite prepared by following a simple electrostatic assembly process and its high-rate and long-cycle-life-performance as an anode in LIBs is obtained. The Fe-KLTO@rGO composite sample has an excellent specific capacity of 330 and 105 mAh g−1 at a current density of 1 C (1 C = 175 mA g−1) and 50 C, respectively. In addition, the Fe-KLTO@rGO composite sample can carry out a long cycle of 3000 cycles at a rate of 50 C, and the specific capacity remains at 127 mAh g−1.

Synthesis of 2D/2D CoAl-LDHs/Ti3C2Tx Schottky-junction with enhanced interfacial charge transfer and visible-light photocatalytic performance

The layered double hydroxides (LDHs) are potential non-noble metal photocatalysts. Unfortunately, the intrinsic activity of bulk LDHs is relatively low, which limits their use. Herein, the ultrathin, porous and vacancy-rich CoAl-LDHs nanosheets were prepared by exfoliation strategy. Then, they were assembled with the early transition-metal carbides nanosheets (MXenes, Ti3C2Tx) to afford a hybrid 2D/2D CoAl-LDHs/Ti3C2Tx photocatalyst via electrostatic assembly process. The experiments indicated that the CoAl-LDHs/Ti3C2Tx hybrids performed an excellent visible-light photocatalytic activity for tetracycline hydrochloride (96.67 %) degradation. Diversified characterization techniques (SEM, TEM, AFM, N2 adsorption-desorption analysis, XRD, FTIR, UV–vis DRS, photoelectrochemical test) and density functional theory calculations (electronic and optical properties) have indicated that such excellent photocatalytic activity was ascribed to the synergy and the Schottky heterojunction formation between CoAl-LDHs nanosheets and Ti3C2Tx nanosheets, which possessed markedly visible-light absorption, high specific surface area, rapid electrons transfer and depressed electron-hole pairs recombination.

Morphology-controlled synthesis of red-emitting CdTe@SrSO4 composites phosphors for white LEDs

Red-emitting CdTe@SrSO4 composites phosphors have been successfully fabricated via a two-step precipitation and following electrostatic assembly process. By adjusting the molar ratio of [Sr2+]/[SO42−], the morphologies of SrSO4 products vary from rods to rhombs with the increasing thickness, and comparative luminescence properties and phase formation mechanism of as-prepared CdTe@SrSO4 composites have been investigated. The CdTe@SrSO4 composites with a rod-like shape show optimum luminescence properties, as well as relatively good thermal stability. White LED prototype based on the CdTe@SrSO4 composites has been fabricated, and a CIE coordinate of (0.400, 0.389), the correlated color temperature (CCT) of 3600 K, and color rendering index (CRI) of 94.3 can be achieved. The results indicate that CdTe@SrSO4 composites may have potential in phosphor-converted white LEDs.

Investigation of the dielectric and thermal conductive properties of core–shell structured HGM@hBN/PTFE composites

Porous polymer materials have been widely used for the preparation of low dielectric constant materials, but they also suffer from high moisture absorption and decreased thermal conductivity. In this study, core–shell structured hexagonal boron nitride coated hollow glass microsphere (HGM@hBN) particles were prepared using an electrostatic-assembly process and incorporated into poly(tetrafluoroethylene) (PTFE). The composites exhibited decreased dielectric constants due to the implantation of air, which is mainly encapsulated in HGM. The hBN layer on the surface of HGM effectively enhanced composite thermal conductivity due to its special core-shell form. The 30 vol% HGM@hBN/PTFE composites had a low dielectric constant of 1.68, low moisture absorption of 0.11%, and thermal conductivity (0.276 W/mK) was improved by 43% compared with that of 30 vol% HGM/PTFE composites. This study provides a facile and cost-effective strategy for fabricating polymer composites with low dielectric constant, low moisture absorption and no deteriorated thermal conductivity simultaneously.

Laminated chitosan-based composite sponges for transmucosal delivery of novel protamine-decorated tripterine phytosomes: Ex-vivo mucopenetration and in-vivo pharmacokinetic assessments

In the current study, laminated chitosan (CS):hydroxypropyl methylcellulose (HPMC) composite sponges were exploited as solid matrices for buccal delivery of tripterine phytosomes functionalized with novel mucopenetrating protamine layer (PRT-TRI-PHY). Tripterine (TRI) is a herbal drug widely investigated as a potential anticancer candidate against various types of cancers. However, clinical use of TRI is handicapped by its low oral bioavailability. To surmount TRI pharmaceutical obstacles, TRI phytosomes (TRI-PHY) were prepared using solvent evaporation technique then coated with a protamine layer via electrostatic assembly process. The developed PRT-TRI-PHY showed a nano-metric size of 250 nm and positive zeta potential (+21.6 mV). Sponges loaded with PRT-TRI-PHY demonstrated a sustained release profile with superior mucoadhesion characteristics compared with the counterparts loaded with uncoated TRI-PHY. The ex-vivo permeation study via chicken pouch mucosa revealed that sponges loaded with PRT-TRI-PHY demonstrated 2.3-folds higher flux value compared with sponges loaded with uncoated TRI-PHY. Additionally, in-vivo pharmacokinetic study in healthy rabbits revealed the significantly higher bioavailability of PRT-TRI-PHY compared with TRI-PHY with relative bioavailability of 244%. Conclusively, mucoadhesive CS-HPMC sponges loaded with a novel mucopenetrating nanocarrier, PRT-TRI-PHY, could significantly improve the absorption of tripterine via buccal mucosa which would be of prime importance for its clinical utility.

A novel NiCo2O4@GO hybrid composite with core-shell structure as high-performance anodes for lithium-ion batteries

In this study, a unique core-shell structural composite with graphene oxide nanosheets wrapping the hierarchical porous NiCo2O4 microspheres (NiCo2O4@GO) has been successfully prepared by a facile electrostatic assembly process between positively charged hierarchical porous NiCo2O4 microspheres and negatively charged graphene oxide (GO). When used as an anode for lithium-ion batteries (LIBs), the core-shell structured NiCo2O4@GO can not only suppress the aggregation and large volume change of NiCo2O4 microspheres, but also provide faster kinetics for both electrons and lithium ions during charge-discharge process. Moreover, NiCo2O4 microspheres wrapped with GO can restrict the decomposition of the electrolyte and yielding a stable solid electrolyte interphase (SEI) layer during cycling. Due to these merits, the core shell structured NiCo2O4@GO hybrid composite demonstrated a high initial reversible capacity of 1046.6 mAh g−1 at a current density of 50 mA g−1 with capacity retention of 77.6% after 100 cycles, the hybrid composite material can still deliver 387.4 mAh g−1 even at a high current density of 4 A g−1, significantly higher than 187.6 mAh g−1 for the pure NiCo2O4 microspheres. The outstanding electrochemical performance of the core-shell NiCo2O4@GO hybrid composite demonstrated that it has great potential as high-performance anode material for lithium-ion batteries.

Fabrication of rGO/g-C3N4 composites via electrostatic assembly towards charge separation control

rGO/g-C3N4 nanoheterostructures created by an electrostatic assembly process from carboxyl and amino groups via π–π stacking interaction revealed good conduction and enhanced photocatalysis properties.

A facile approach for preparation of polystyrene/graphene nanocomposites with ultra-low percolation threshold through an electrostatic assembly process

Improving the dispersion of graphene nanosheets (GN) in a polymer matrix is a critical step in lowering the percolation threshold of nanocomposites. In this paper, an effective method based on an electrostatic assembly process is reported. Polystyrene (PS) latex was first prepared by using hexadecyl trimethyl ammonium bromide (CTAB) as a cationic surfactant, which created positive charges on the surface of the PS micelles. An in situ demulsification process was then conducted by adding negatively charged graphene oxide (GO) particles into the positively charged PS latex. Thus, GO sheets were attached spontaneously to the surfaces of PS particles through electrostatic adsorption. Followed by in situ reduction and hot pressing, the agglomeration of GN was largely prohibited by the PS microspheres and facilitated the formation of GN networks in the PS matrix. The obtained PS/GN nanocomposites exhibited excellent electrical properties with a percolation threshold as low as 0.054 vol.% GN. When the GN content reached 1.53 vol.%, the electrical conductivity was 46.32 S/m and the thermal conductivity 0.47 W/mk. This strategy represents a new environment-friendly pathway, which is also applicable for other polymer matrices, for large-scale production of polymer composites with fully interconnected graphene networks at ultra-low GN content.

From Solution to Biointerface: Graphene Self-Assemblies of Varying Lateral Sizes and Surface Properties for Biofilm Control and Osteodifferentiation.

Bringing multifunctional graphene out of solution through facile self-assembly to form 2D surface nanostructures, with control over the lateral size and surface properties, would be an intriguing accomplishment, especially in biomedical fields where biointerfaces with functional diversity are in high demand. Guided by this goal, in this work, we built such graphene-based self-assemblies on orthopedic titanium, attempting to selectively regulate bacterial activities and osteoblastic functions, which are both crucial in bone regeneration. Briefly, large-area graphene oxide (GO) sheets and functionalized reduced GO (rGO) micro-/nanosheets were self-assembled spontaneously and controllably onto solid Ti, through an evaporation-assisted electrostatic assembly process and a mussel-inspired one-pot assembly process, respectively. The resultant layers were characterized in terms of topological structure, chemical composition, hydrophilicity, and protein adsorption properties. The antibacterial efficacies of the assemblies were examined by challenging them with pathogenic Staphylococcus aureus (S. aureus) bacteria that produce biofilms, whereby around 50% antiadhesion effects and considerable antibiofilm activities were observed for both layer types but through dissimilar modes of action. Their cytocompatibility and osteogenic potential were also investigated. Interfaced with MC3T3-E1 cells, the functionalized rGO sheets evoked better cell adhesion and growth than GO sheets, whereas the latter elicited higher osteodifferentiation activity throughout a 28-day in vitro culture. In this work, we showed that it is technically possible to construct graphene interface layers of varying lateral dimensions and surface properties and confirmed the concept of using the obtained assemblies to address the two major challenges facing orthopedic clinics. In addition, we determined fundamental implications for understanding the surface-biology relationship of graphene biomaterials, in efforts to better design and more safely use them for future biomedicine.

Fabrication of magnetic irregular hexagonal-Fe3O4 sheets/reduced graphene oxide composite for supercapacitors

The magnetic irregular hexagonal-Fe3O4 sheets/reduced graphene oxide composite (HFGC) was fabricated via colloidal electrostatic assembly process, followed a heat treatment process. The TEM images showed that irregular hexagonal-Fe3O4 sheets generated from Fe(OH)3 colloid particles were loaded onto reduced graphene oxide (rGO) sheets. The ideal rectangular cyclic voltammetry (CV) curves of HFGC in different scan rates indicated the character of double layer capacitance with the excellent capacitive behavior. Tested by the galvanostatic charge–discharge (GCD) experiments in 6M KOH aqueous electrolyte, HFGC exhibited a specific capacitance of 193Fg−1 at 0.3Ag−1. Furthermore, the cycling stability of HFGC was tested under a density of 0.5Ag−1. The capacitance maintain as 90.4% after 1000 cycles, indicating the desirable cyclic stability.

Electronic states of organic semiconductors vis-à-vis interactions between molecules in a submonolayer through time-restricted electrostatic assembly

We have made in-depth studies to revisit time-restricted layer-by-layer (LbL) electrostatic assembly process of a couple of organic molecules. The studies have been made in relation to electronic states of metal phthalocyanines. We show that by shortening dipping time for adsorption of the active molecules, mass adsorbed in each monolayer can be decreased and hence intermolecular spacing between the molecules can be increased. We have characterized the (sub)monolayers deposited on an electrode with scanning tunneling microscope tip to record tunneling current through the molecules. Results show that the highest occupied molecular orbitals and lowest unoccupied molecular orbitals, and also the difference between the orbitals, that is, the transport gap of the molecules in a (sub)monolayer depends on the dipping time of LbL assembly or molecule-to-molecule separation. We show that interactions between molecules in a monolayer decrease the transport gap of the metal phthalocyanines.

Controlled electrostatic assembly of quantum dots vis-à-vis their electronic coupling and transport gap

We correlate the electronic coupling between quantum dots and the transport gap of nanoparticle-passivated Si substrates. We vary the length of the stabilizers of CdS nanoparticles, which in turn alters the particle-to-particle separation and hence the electronic coupling between them. We also control the electronic coupling using time-restricted electrostatic-assembly of quantum dots, using short periods of time so that an incomplete monolayer or a sub-monolayer of CdS forms. In such a sub-monolayer, the nanoparticles remain isolated from each other with a controllable particle-to-particle separation. From electronic absorption spectroscopy of multilayer films and atomic force microscopy of a monolayer, we evidenced sub-monolayer formation in the controlled electrostatic assembly process. We measure the current-voltage characteristics of nanoparticle-passivated substrates with a scanning tunnelling microscope; we show that the transport gap of nanoparticle-passivated substrates depends on the electronic coupling between CdS particles in the monolayer.

Layer-by-Layer Electrostatic-Assembly: Magnetic-Field Assisted Ordering of Organic Molecules

During the layer-by-layer (LbL) electrostatic assembly process, we orient organic molecules (nickel phthalocyanine) by an external magnetic field. Orientation of the magnetic moment of the molecules in a monolayer is immobilized by depositing a monolayer of a suitable polycation. Due to the orientation of magnetic moments, the electrostatic adsorption process becomes enhanced in subsequent layers. By cycling the deposition sequence layer after layer, we have achieved highly ordered and closely packed LbL films of the molecules with their magnetic moments oriented perpendicular to the substrate. Nonmagnetic copper phthalocyanine expectedly showed neither a magnetic-field assisted alignment nor an enhanced adsorption in LbL film deposition process.

Nanoplated bismuth titanate sub-microspheres for protein immobilization and their corresponding direct electrochemistry and electrocatalysis

A layered inorganic perovskite sub-micrometer-scale material, nanoplated bismuth titanate (Bi 4Ti 3O 12) sub-microspheres (NBTSMs) constructed with tens of Bi 4Ti 3O 12 nanoplates, was for the first time synthesized by a facile hydrothermal synthesis strategy. The NBTSMs were employed as a supporting matrix to explore a novel immobilization and biosensing platform of redox proteins through a combined hydrogen bond and electrostatic assembly process. Biocompatibility, stability, reproducibility, and electrochemical and electrocatalytic properties of the resulting NBTSMs-based composite were studied by UV–vis absorption, FTIR, and electrochemical methods. The research results revealed that the NBTSMs-based composite was a satisfying matrix for proteins to effectively retain their native structure and bioactivity. With advantages of the Bi 4Ti 3O 12 layered material, facilitated direct electron transfer of the metalloenzymes with an apparent heterogeneous electron transfer rate constant ( k s) of 20.0 ± 3.8 s −1 was acquired on the NBTSMs-based enzyme electrode. The NBTSMs-based biosensor demonstrated significant electrocatalytic activity for the reduction of hydrogen peroxide with an apparent Michaelis–Menten constant (204 μM), wide linear range (2–430 μM), and low detection limit (0.46 μM, S/N = 3). These indicated that the nanoplate-constructed Bi 4Ti 3O 12 sub-microspheres were one of ideal candidate materials for direct electrochemistry of redox proteins and the construction of the related enzyme biosensors, and may find potential applications in biomedical, food, and environmental analysis and detection.

Facile control of thermo-responsive wettability through an all-electrostatic self-assembling process

We describe the facile fabrication of a thermo-responsive wetting surface through an electrostatic assembly process and the use of thermo-responsive polyelectrolyte copolymers. The organic–inorganic nanostructured films were prepared through the layer-by-layer assembly of negatively charged silica nanoparticles (11 nm) and positively charged poly(allylamine hydrochloride) (PAH). The thermo-responsive polyelectrolyte copolymer, poly(allylamine hydrochloride)- g-poly( N-isopropylacrylamide) (PAH- g-PNIPAAm), was synthesized by grafting a carboxylic end group of PNIPAAm on to the PAH. The nanostructured surfaces modified with PAH- g-PNIPAAm exhibit enhanced thermal switching of surface wettability. Our approach provides a versatile strategy for control over the thermo-responsive wettability of substrates with complex structures for various applications such as sensors, microfluidics, etc.

Core−Shell Hybrid Nanoparticles with Functionalized Quantum Dots and Ionic Dyes: Growth, Monolayer Formation, and Electrical Bistability

We report growth, monolayer formation, and (electrical bistability and memory phenomenon) properties of hybrid core-shell nanoparticles. While inorganic quantum dots, such as CdS or CdSe, act as the core, a monolayer of ionic organic dye molecules, electrostatically bound to the surface of functionalized quantum dots, forms the shell. We form a monolayer of the core-shell hybrid nanoparticles via a layer-by-layer electrostatic assembly process. Growth and monolayer formation of the organic-inorganic hybrid nanoparticles have been substantiated by usual characterization methods, including electronic absorption spectroscopy of dispersed solution and atomic force microscope images of scratched films. Devices based on the hybrid nanoparticles have exhibited electrical bistability and memory phenomena. From the comparison of these properties in core-shell nanoparticles and in its components, we infer that the degree of conductance switching or on/off ratio is substantially higher in the hybrid nanoparticles. Also, they (core-shell particles) provide routes to tune the bistability and memory phenomena by choosing either of the components. A monolayer of hybrid nanoparticles has been characterized by a scanning tunneling microscope tip as the other electrode. We show that a single core-shell hybrid nanoparticle can exhibit bistability with an associated memory phenomenon. Charge confinement, as evidenced by an increase in the density of states, has been found to be the mechanism of electrical bistability.

Incorporating Azo-group-functionalized Molecular-Junctions between Metal Nanoelectrodes to produce High-Rectification-Memory Nanodevices

AbstractThis report presents the functioning of a molecular memory device with azo-group-functionalized molecular-junctions between metal nanoelectrodes. These junctions are fabricated by a novel electrostatic-assembly process to incorporate azo-group containing polyelectrolyte (AP) between oppositely charged gold nanoparticles (GNP), functioning as nanoelectrodes. The device exhibits a bistable electronic memory effect induced by charge-transfer between AP and GNP, which can be controlled by photo-excitation of the AP. The ON and OFF memory states were found to have a rectification in the range of ∼5000 – 10000. This study will open avenues for development of next-generation molecular systems and devices to produce novel optoelectronic properties.