Two-dimensional Nanoparticle Research Articles

Step-scheme heterojunction g-C3N4/TiO2 for efficient photocatalytic degradation of tetracycline hydrochloride under UV light

Construction of heterojunction between semiconductors is considered an effective strategy for enhancing photocatalytic capability. Herein, this work prepared an abundant porous g-C3N4/TiO2 photocatalyst, with the two-dimensional (2D) nanosheet g-C3N4 and nanoparticle TiO2. The heterojunction both enhanced the ultraviolet (UV) light absorption ability, and inhibited the recombination of photogenerated electron-hole (h+) pairs. As expected, the optimal 4 % g-C3N4/TiO2 (g-C3N4:TiO2 = 1:25) exhibited a prominent degradation efficiency of 96.53 % in the photocatalytic performance of tetracycline hydrochloride (TCH) under UV irradiation. The recycling of the heterojunction photocatalyst g-C3N4/TiO2 remained stability and reusability. The main active species were·O2-, h+ and·OH, and the formation of internal electric field on the step-scheme (S-scheme) heterojunction interface accelerated the migration of photogenerated carriers. Moreover, several environmental factors on degradation such as dose, pH, and the initial concentration of TCH were investigated. This work could be spread to the conceive of other S-scheme heterojunction photocatalysts in application to different environmental demands.

Simple Fabrication of Polyvinylidene Fluoride/Graphene Composite Membrane with Good Lipophilicity for Oil Treatment.

Graphene (GE) is an emerging type of two-dimensional functional nanoparticle with a tunable passageway for oil molecules. Herein, polyvinylidene fluoride (PVDF)/GE composite membranes with controllable pore structure were fabricated with a simple non-solvent-induced phase separation method. The change of crystallinity and crystal structure (α, β, γ, etc.) generated is due to the addition of GE, which benefits the design of a suitable pore structure for oil channels. Meanwhile, the hydrophobicity and thermal stability of the composite membrane were obviously enhanced. With 3 wt % GE, the contact angle was 124.6°, which was increased greatly compared to that of the GE-0 sample. Moreover, the rate of the phase transition process was affected by the concentration of casting solution, temperature, and composition of the coagulation bath. For example, the composite membrane showed better oil–water separation properties when the coagulation bath was dioctyl phthalate. In particular, the oil flux and separation efficiencies were up to 2484.08 L/m2·h and 99.24%, respectively. Consequently, PVDF/GE composite membranes with excellent lipophilicity may have good prospects for oily wastewater treatment.

Nanofluid Formulations Based on Two-Dimensional Nanoparticles, Their Performance, and Potential Application as Water-Based Drilling Fluids.

The development of sustainable, cost-efficient, and high-performance nanofluids is one of the current research topics within drilling applications. The inclusion of tailorable nanoparticles offers the possibility of formulating water-based fluids with enhanced properties, providing unprecedented opportunities in the energy, oil, gas, water, or infrastructure industries. In this work, the most recent and relevant findings related with the development of customizable nanofluids are discussed, focusing on those based on the incorporation of 2D (two-dimensional) nanoparticles and environmentally friendly precursors. The advantages and drawbacks of using 2D layered nanomaterials including but not limited to silicon nano-glass flakes, graphene, MoS2, disk-shaped Laponite nanoparticles, layered magnesium aluminum silicate nanoparticles, and nanolayered organo-montmorillonite are presented. The current formulation approaches are listed, as well as their physicochemical characterization: rheology, viscoelastic properties, and filtration properties (fluid losses). The most influential factors affecting the drilling fluid performance, such as the pH, temperature, ionic strength interaction, and pressure, are also debated. Finally, an overview about the simulation at the microscale of fluids flux in porous media is presented, aiming to illustrate the approaches that could be taken to supplement the experimental efforts to research the performance of drilling muds. The information discussed shows that the addition of 2D nanolayered structures to drilling fluids promotes a substantial improvement in the rheological, viscoelastic, and filtration properties, additionally contributing to cuttings removal, and wellbore stability and strengthening. This also offers a unique opportunity to modulate and improve the thermal and lubrication properties of the fluids, which is highly appealing during drilling operations.

A two-dimensional nanoparticle characterization method combining differential mobility analyzer and single-particle inductively coupled plasma-mass spectrometry with an atomizer-enabled sample introduction (ATM-DMA-spICP-MS): Toward the analysis of heteroaggregated nanoparticles in wastewater

Characterizing engineered nanoparticles (ENPs) in complex environmental matrices remains a challenging task. This work presents a two-dimensional size analysis method by combining differential mobility analyzer (DMA) and single-particle inductively coupled plasma-mass spectrometry (spICP-MS) with a new atomizer (ATM)-enabled sample introduction that is relatively easy to operate. The tailing of electrical mobility size distributions was solved by heating the aerosol flow, where water-shelled gold nanoparticles (AuNPs) were dehydrated, effectively eliminating the tailing. The improved method has a good sizing performance and can resolve the size fractions of mixed 30 nm and 50 nm AuNPs. It can reliably analyze 7.8 × 105 to 1.9 × 107 # of 50 nm AuNPs (or 4.1 × 105 to 107 # NPs/mL, equivalent to 0.6 to 14.3 μg Au/L) with a linear response and a limit of detection of 7.8 × 105 # AuNPs (equivalent to 4.1 × 105 # AuNPs/mL) that is relevant to NP concentrations in surface water and wastewater samples. The potential of this method to analyze environmental samples was demonstrated by characterizing AuNPs and silver nanoparticles (AgNPs) spiked in wastewater, where both NPs were revealed to form heteroaggregates with colloids existing in wastewater. The method can even directly analyze nanosized Ag particles inherent in the wastewater before adding external AgNPs. The result indicates that ATM-DMA-spICP-MS is a relatively simple two-dimensional size analysis method that has a great potential to characterize heteroaggregated NPs in aqueous environmental samples.

Quantifying the shape effect of plasmonic gold nanoparticles on photoacoustic conversion efficiency.

Gold nanoparticles with strong localized plasmonic effects have found wide applications in photoacoustic imaging, which are ascribed to their unique microscopic mechanism of converting photons to ultrasound. In this report, we quantitatively model the time-resolved temperature field, thermal expansion, and pressure distribution based on the finite element analysis method, and two-dimensional gold nanoparticles spanning from the triangle, square, pentagon, and hexagon to the circle have been systematically studied. Results show that the shape of gold nanoparticles has a nontrivial effect on photoacoustic conversion efficiency, and the square-shaped gold structure exhibits the best performance. Our findings could shed light on the shape design of high-performance photoacoustic agents in the future.

Self-assembled artificial enzyme from hybridized porous organic cages and iron oxide nanocrystals

HypothesisAlthough it is well-accepted that iron oxide nanoparticles are considered as artificial enzymes when their surface is hydrophilic, the enzyme-like properties of iron oxide nanoparticles with hydrophobic surface coating is unexplored. This work demonstrates that hydrophobic iron oxide nanocrystals coated with a layer of oleic acid could serve as artificial enzymes when their surface is covered by a layer of ionic surfactant. Furthermore, the co-assembly of iron oxide nanocrystals and porous organic cages could modulate their enzyme-like activities. ExperimentsCo-assembly of iron oxide (Fe3O4) nanocrystals with different size and porous organic cages (POCs) was performed by an emulsion-confined strategy to achieve hybridized Fe3O4/POCs co-assemblies. The peroxidase-mimic activity of these co-assemblies were assessed in the presence of 3, 3′, 5, 5′-Tetramethylbenzidine (TMB) and hydrogen peroxide. Finally, these co-assemblies were applied as sensors to detect glucose and hydrogen peroxide. FindingsCo-assembly of Fe3O4 nanocrystals and POCs resulted in the self-assembly of Fe3O4 nanoparticles into two-dimensional nanoparticle superlattices on the eight (111) facets of the octahedral POCs colloidal crystals. The unique oil-in-water (O/W) emulsion confined assembly method switches the Fe3O4 nanoparticles and POC crystals from hydrophobic to hydrophilic because of the strong hydrophobic interactions. Importantly, these co-assemblies dispersed in water showed strong peroxidase-mimic activity in water despite that their surface is covered by a bilayer of aliphatic chains. Furthermore, the intrinsic enzymatic activity of the co-assemblies is highly dependent on the size of the nanocrystals, and a higher catalytic activity is achieved from a larger sized Fe3O4 nanocrystal.

Visualizing Light-Induced Microstrain and Phase Transition in Lead-Free Perovskites Using Time-Resolved X-Ray Diffraction.

Metal halide perovskites have emerged as promising materials for optoelectronic applications in the last decade. A large amount of effort has been made to investigate the interplay between the crystalline lattice and photoexcited charge carriers as it is vital to their optoelectronic performance. Among them, ultrafast laser spectroscopy has been intensively utilized to explore the charge carrier dynamics of perovskites, from which the local structural information can only be extracted indirectly. Here, we have applied a time-resolved X-ray diffraction technique to investigate the structural dynamics of prototypical two-dimensional lead-free halide perovskite Cs3Bi2Br9 nanoparticles across temporal scales from 80 ps to microseconds. We observed a quick recoverable (a few ns) photoinduced microstrain up to 0.15% and a long existing lattice expansion (∼a few hundred nanoseconds) at mild laser fluence. Once the laser flux exceeds 1.4 mJ/cm2, the microstrain saturates and the crystalline phase partially transfers into a disordered phase. This photoinduced transient structural change can recover within the nanosecond time scale. These results indicate that photoexcitation of charge carriers couples with lattice distortion, which fundamentally affects the dielectric environment and charge carrier transport.

Conformational control of two-dimensional gold nanoparticle arrays in a confined geometry within a vesicular wall

The two-dimensional (2D) assembly of gold nanoparticles (AuNPs) in a confined geometry is a rare phenomenon that has not been experimentally verified for complex systems. In this study, this process was investigated in detail using two types of block copolymers with hydrophobic and hydrophilic blocks and a series of AuNPs of three different sizes protected by hydrophobic ligands. In aqueous solutions, the selected block copolymers self-assembled into vesicular nanostructures with a hydrophobic domain in the wall, which functions as a confined geometrical space for hydrophobic AuNPs (i.e., it exerts a confinement effect and restricts the movement of AuNPs). Small-angle X-ray scattering studies revealed that AuNPs of different sizes assembled differently in the same confined geometry of the vesicular wall. In addition, optimal conditions for the formation of a regular NP array in the hydrophobic domain were determined. The AuNPs successfully self-assembled into a regular 2D lattice structure, forming a shell around the vesicle, when their size matched the thickness of the hydrophobic domain of the vesicular nanostructure. This study provides guidelines for the fabrication of nanoparticle arrays with controlled structures, which could enhance the functionality of materials and their physical properties.

Defect-induced nonlinearity in 2D nanoparticles.

Optical nonlinearity depends on symmetry and symmetries vanish in the presence of defects. Vacancy defects in centrosymmetric crystals and thin films are a well-known source of even-order optical nonlinearity, e.g. causing second harmonic generation. The emerging ability to manipulate defects in two-dimensional materials and nanoparticles provides an opportunity for engineering of optical nonlinearity. Here, we demonstrate the effect of defects on the nonlinear optical response of two-dimensional dielectric nanoparticles. Using a toy model, where bound optical electrons of linear atoms are coupled by nonlinear Coulomb interactions, we model defect-induced nonlinearity. We find that defects at particle edges contribute strongly to even-order optical nonlinearity and that unique nonlinear signatures of different defect states could provide the smallest conceivable QR-codes and extremely high density optical data storage, in principle approaching 1 bit per atom.

Composite Li-ion battery cathodes formed via integration of carbon nanotubes or graphene nanoplatelets into chemical preintercalation synthesis of bilayered vanadium oxides

Bilayered vanadium oxides are attractive cathode materials for rechargeable batteries. The expanded interlayer space and versatile chemistries of these oxides yield high specific capacities. However, capacity retention and rate performance are limited due to structural instability and low electronic conductivity of these materials. Assembling the oxides with one- and two-dimensional carbon nanoparticles may produce highly efficient heterointerfaces that would enhance electrochemical charge storage properties. Here, we synthesize for the first time bilayered vanadium oxide composites with carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs). The nanostructured carbons were initially functionalized by flash oxidation in air to create polar groups on the carbon surface, producing fCNTs and fGNPs, and improve compatibility with an aqueous chemical preintercalation synthesis route. Lithium preintercalated bilayered vanadium oxide, LVO (LVO = δ-LixV2O5·nH2O), was selected as a redox active oxide component to facilitate Li+ ion diffusion through the interlayer region of δ-V2O5. A one-step process was developed to synthesize LVO/fCNT and LVO/fGNP composites by an in situ low temperature sol-gel method. We observed marked improvements in capacity retention and rate performance in the nanocomposites as compared to the pristine oxide, which were attributed to both improved electron transport and heterointerface stabilization effect enabled by integration with fCNTs and fGNPs. This work illustrates the ability to enhance material functionality through the in situ synthesis of nanocomposites with controllable heterointerface.

Dynamic nano-assemblies based on two-dimensional inorganic nanoparticles: Construction and preclinical demonstration.

Dynamic drug delivery systems (DDSs) have the ability of transforming their morphology and functionality in response to the biological microenvironments at the disease site and/or external stimuli, show spatio-temporally controllable drug delivery, and enhance the treatment efficacy. Due to the large surface area and modification flexibility, two-dimensional (2D) inorganic nanomaterials are being increasingly exploited for developing intelligent DDSs for biomedical applications. In this review, we summarize the engineering methodologies used to construct transformable 2D DDSs, including changing compositions, creating defects, and surface dot-coating with polymers, biomolecules, or nanodots. Then we present and discuss dynamic inorganic 2D DDSs whose transformation is driven by the diseased characteristics, such as pH gradient, redox, hypoxia, and enzyme in the tumor microenvironment as well as the external stimuli including light, magnetism, and ultrasound. Finally, the limitations and challenges of current transformable inorganic DDSs for clinical translation and their in vivo safety assessment are discussed.

Two-Time Intensity Correlation in a Driven V-Type Quantum Emitter Near a Plasmonic Nanostructure

We analyze the two-time intensity correlation function of the fluorescent field emitted by a three-level V-type quantum emitter located in the vicinity of a two-dimensional periodic plasmonic nanostructure. Due to the interaction of the quantum emitter with an electromagnetic field, the ground state population is excited to the upper levels, presenting decay due to spontaneous emission. The distinctive characteristic of this system is that the decay rates for a quantum emitter with dipole orientation perpendicular and normal to the surface of the nanostructure array exhibit large differences which vary with the distance between the quantum emitter and the two-dimensional nanoparticle array. This leads to simulation of quantum interference effects in spontaneous emission. By studying the dependence of the two-time intensity correlation function on specific physical parameters of the hybrid structure, including the intensity of the applied field, the detuning from resonance, the distance between the quantum emitter and the plasmonic nanostructure, as well as the spacing between the upper levels, we demonstrate a strong modification of the two-time intensity correlation functions. We also identify the conditions under which the two-time intensity correlation function is maximized, an effect which is associated to the bunching to antibunching transition of the emitted photons.

A Two-Dimensional Nanoparticle Characterization Method Combining Differential Mobility Analyzer and Single-Particle Inductively Coupled Plasma-Mass Spectrometry with an Atomizer-Enabled Sample Introduction (Atm-Dma-Spicp-Ms): Towards the Analysis of Heteroaggregated Nanoparticles in Wastewater

A Two-Dimensional Nanoparticle Characterization Method Combining Differential Mobility Analyzer and Single-Particle Inductively Coupled Plasma-Mass Spectrometry with an Atomizer-Enabled Sample Introduction (Atm-Dma-Spicp-Ms): Towards the Analysis of Heteroaggregated Nanoparticles in Wastewater

Folding of two-dimensional nanoparticle superlattices enabled by emulsion-confined supramolecular co-assembly.

Folding of two-dimensional nanoparticle superlattices is achieved through templated assembly on as-formed supramolecular nanosheets, which undergo a folding process within the emulsion droplets during the evaporation of the inner phase liquid. Building the folded nanoparticle superlattices opens a new gateway to reshape the properties of inorganic solids.

Algorithmically Guided Optical Nanosensor Selector (AGONS): Guiding Data Acquisition, Processing, and Discrimination for Biological Sampling.

Here, we report a biomarker-free detection of various biological targets through a programmed machine learning algorithm and an automated computational selection process termed algorithmically guided optical nanosensor selector (AGONS). The optical data processed/used by algorithms are obtained through a nanosensor array selected from a library of nanosensors through AGONS. The nanosensors are assembled using two-dimensional nanoparticles (2D-nps) and fluorescently labeled single-stranded DNAs (F-ssDNAs) with random sequences. Both 2D-np and F-ssDNA components are cost-efficient and easy to synthesize, allowing for scaled-up data collection essential for machine learning modeling. The nanosensor library was subjected to various target groups, including proteins, breast cancer cells, and lethal-7 (let-7) miRNA mimics. We have demonstrated that AGONS could select the most essential nanosensors while achieving 100% predictive accuracy in all cases. With this approach, we demonstrate that machine learning can guide the design of nanosensor arrays with greater predictive accuracy while minimizing manpower, material cost, computational resources, instrumentation usage, and time. The biomarker-free detection attribute makes this approach readily available for biological targets without any detectable biomarker. We believe that AGONS can guide optical nanosensor array setups, opening broader opportunities through a biomarker-free detection approach for most challenging biological targets.

Toy model of harmonic and sum frequency generation in 2D dielectric nanostructures

Optical nonlinearities of matter are often associated with the response of individual atoms. Here, using a toy oscillator model, we show that in the confined geometry of a two-dimensional dielectric nanoparticle a collective nonlinear response of the atomic array can arise from the Coulomb interactions of the bound optical electrons, even if the individual atoms exhibit no nonlinearity. We determine the multipole contributions to the nonlinear response of nanoparticles and demonstrate that the odd order and even order nonlinear electric dipole moments scale with the area and perimeter of the nanoparticle, respectively.

Quality factor of plasmonic monopartite and bipartite surface lattice resonances

Surface lattice resonance (SLR) is the collective excitation of nanoparticle resonances arising from the hybridization between localized surface plasmons (LSPs) and propagating Rayleigh anomalies (RAs). When comparing with the corresponding LSPs, SLRs exhibit a much higher quality factor. In fact, as the quality factor depends on the constituting resonances and their hybridization, how one can parametrize it in an analytic form is an important issue. We have studied the SLRs arising from two-dimensional Au monopartite nanoparticle arrays by angle- and polarization-resolved reflectivity spectroscopy, temporal coupled mode theory (CMT), and finite-difference time-domain simulation. The scattering matrix of the SLRs is formulated, revealing the importance of the spectral detuning and the interaction strengths between the LSP and the RAs in governing the quality factor. We then extend the CMT approach to study bipartite arrays where a nanoparticle dimer is employed and find the coupling between two LSPs plays a major role in further boosting the quality factor. Specifically, the coupling takes part in controlling the detuning factor as well as determining whether the coupled bright or dark mode is hybridized with the RAs. The dark mode hybridization can strongly enhance the quality factor, which is otherwise not possible in the monopartite counterparts.

Synthesis of MXene/COF/Cu2O heterojunction for photocatalytic bactericidal activity and mechanism evaluation

Reasonably combining the advantages of heterojunction constructed by a variety of two-dimensional materials and metal oxide nanoparticles (NPs) is an effective strategy to improve the efficiency of photocatalytic sterilization. In this work, TpPa-1-COF, as a stable semiconductor, was in situ grown on Ti3C2-MXene through the Schiff base reaction and anchored with Cu2O NPs to obtain an efficient photocatalytic bactericide. Electrochemical impedance spectroscopy and photoluminescence spectra of nanocomposites showed that the photogenerated carrier migration rate as well as the production of reactive oxygen species was improved and the carrier life was prolonged. The work function at the interface was analyzed by using the first principle calculation based on density functional theory. Both TpPa-1/Ti3C2 interface and Ti3C2/Cu2O interface had large built-in electric field to promote the migration of carriers between layers, so as to realize efficient photocatalysis and reduce photo-corrosion. The obtained Ti3C2/TpPa-1/ Cu2O nanocomposites showed excellent antibacterial rates against S. aureus and P. aeruginosa, which were antibacterial rates of 98.90% and 99.62% and were increased by 50% and 33% compared with pure TpPa-1-COF. It provides a new idea for the development of photocatalytic bactericides in the field of marine antifouling.

Application of pair distribution function analysis to structural investigation of alumina supported MoS2 catalysts

Total X-ray scattering and atomic pair distribution analysis (PDF) were used to study structure of anisotropic two-dimensional (2D) MoS2 nanoparticles in MoS2/Al2O3 catalysts. We demonstrated that PDF analysis can be used not only to determine the atomic ordering but also to assess the geometry and size of 2D MoS2 nanoparticles in the catalysts. In refinement of PDFs, discrete atomistic modeling was used to account for finite size and shape effects. The values of MoS2 slab length elucidated from the PDF data were smaller than values obtained from high-resolution transmission electron microscopy (HRTEM) data due to defectiveness and multi-domain structure of the MoS2 nanoparticles. It was suggested that increase in the temperature of heat treatment of oxide precursors leads to decrease in deformation of the MoS2 nanoparticles in sulfided catalysts.

Aligned Ti3C2Tx MXene for 3D Micropatterning via Additive Manufacturing.

Selective deposition and preferential alignment of two-dimensional (2D) nanoparticles on complex and flexible three-dimensional (3D) substrates can tune material properties and enrich structural versatility for broad applications in wearable health monitoring, soft robotics, and human-machine interfaces. However, achieving precise and scalable control of the morphology of layer-structured nanomaterials is challenging, especially constructing hierarchical architectures consistent from nanoscale alignment to microscale patterning to complex macroscale landscapes. This work demonstrated a scalable and straightforward hybrid 3D printing method for orientational alignment and positional patterning of 2D MXene nanoparticles. This process involved (i) surface topology design via microcontinuous liquid interface production (μCLIP) and (ii) directed assembly of MXene flakes via capillarity-driven direct ink writing (DIW). With well-managed surface patterning geometry and printing ink quality control, the surface microchannels constrained MXene suspensions and leveraged microforces to facilitate preferential alignment of MXene sheets via layer-by-layer additive depositions. The printed devices displayed multifunctional properties, i.e., anisotropic conductivity and piezoresistive sensing with a wide sensing range, high sensitivity, fast response time, and mechanical durability. Our fabrication technique shows enormous potential for rapid, digital, scalable, and low-cost manufacturing of hierarchical structures, especially for micropatterning and aligning 2D nanoparticles not easily accessible through conventional processing methods.