Ligand-Directed Shape Reconfiguration in Inorganic Materials.

Polymer elastomers with reversible shape-changing capability have led to significant development of artificial muscles, functional devices, and soft robots. By contrast, reversible shape transformation of inorganic nanoparticles is notoriously challenging due to their relatively rigid lattice structure. Here, the authors demonstrate the synthesis of shape-changing nanoparticles via an asymmetrical surface functionalization process. Various ligands are investigated, revealing the essential role of steric hindrance from the functional groups. By controlling the unbalanced structural hindrance on the surface, the as-prepared clay nanoparticles can transform their shape in a fast, facile, and reversible manner. In addition, such flexible morphology-controlled mechanism provides a platform for developing self-propelled shape-shifting nanocollectors. Owing to the ion-exchanging capability of clay, these self-propelled nanoswimmers (NS) are able to autonomously adsorb rare earth elements with ultralow concentration, indicating the feasibility of using naturally occurring materials for self-powered nanomachine.

Engineered two-dimensional nanomaterials: an emerging paradigm for water purification and monitoring.

Water scarcity has become an increasingly complex challenge with the growth of the global population, economic expansion, and climate change, highlighting the demand for advanced water treatment technologies that can provide clean water in a scalable, reliable, affordable, and sustainable manner. Recent advancements on 2D nanomaterials (2DM) open a new pathway for addressing the grand challenge of water treatment owing to their unique structures and superior properties. Emerging 2D nanostructures such as graphene, MoS2, MXene, h-BN, g-C3N4, and black phosphorus have demonstrated an unprecedented surface-to-volume ratio, which promises ultralow material use, ultrafast processing time, and ultrahigh treatment efficiency for water cleaning/monitoring. In this review, we provide a state-of-the-art account on engineered 2D nanomaterials and their applications in emerging water technologies, involving separation, adsorption, photocatalysis, and pollutant detection. The fundamental design strategies of 2DM are discussed with emphasis on their physicochemical properties, underlying mechanism and targeted applications in different scenarios. This review concludes with a perspective on the pressing challenges and emerging opportunities in 2DM-enabled wastewater treatment and water-quality monitoring. This review can help to elaborate the structure-processing-property relationship of 2DM, and aims to guide the design of next-generation 2DM systems for the development of selective, multifunctional, programmable, and even intelligent water technologies. The global significance of clean water for future generations sheds new light and much inspiration in this rising field to enhance the efficiency and affordability of water treatment and secure a global water supply in a growing portion of the world.

Amphiphilicity-adaptable graphene quantum dots to stabilize pH-responsive pickering emulsions at a very low concentration.

HYPOTHESIS: Stimuli-responsive Pickering emulsions have attracted considerable interest due to their widespread potential applications. Especially pH-responsive behavior could be easily implemented. In this work, we reported a pH-responsive Pickering emulsion based on amphiphilic graphene quantum dots at a low concentration which shows a great potential from the environmental and economic perspective. The stimuli responsive properties would make the smart Pickering emulsifiers recyclable and reusable. EXPERIMENTS: The amphiphilic-adaptable graphene quantum dots functionalized by alkyl groups (C-GQDs) were synthesized by a facile one-step pyrolysis method. The pH-responsive emulsion performances were investigated, and the mechanism of pH-responsive of C-GQDs was studied by dynamic light scattering. FINDINGS: The amphiphilicity of C-GQDs could be acquired controllably and effectively by this facile one-step pyrolysis method, which are able to stabilize Pickering emulsion at a very low concentration (0.001%). The amphiphilicity of C-GQDs are capable of changing in response to environmental stimuli. When the pH value of aqueous solution adjusts to 2, these C-GQDs aggregate in contrast to their stability in neutral condition due to the alternation of surface charges. The pH-responsive aggregation/ dispersion behavior of C-GQDs allows us to tune the interactions between oil-in-water emulsion droplets without introduction of destabilization agents. This will provide huge economic benefits in industrial applications in the future.

Bioinspired Multiple Stimuli-Responsive Optical Microcapsules Enabled by Microfluidics.

Optical microcapsules encapsulating optical materials inside a symmetric spherical confinement are significant elements for the construction of optical units and the integration of optical arrays. However, the multiple stimuli-responsive characteristic of optical microcapsules still remains a challenge due to the insuperable physical barrier between the optical material core and the outside shell and the lack of effective mechanisms to trigger the dynamic switch of the encapsulated optical materials. Inspired by the dual-mode optical modulation of chameleon skins, a novel biomimetic binary optical microcapsule that combines the visible light reflection of chiral nematic liquid crystals and photoluminescence emission of rare-earth complexes is assembled by microfluidic emulsification and interfacial polymerization. The reflected color, fluorescent intensity, and size of the optical microcapsules are facilely controlled in the microfluidic chip by adjusting the composition and flow rate of the injected fluids. Most importantly, the biomimetic binary optical microcapsules demonstrate three reversible responsive behaviors, thermotropic reflection evolution, temperature-dependent fluorescence emission, and Fredericks electro-optical response. The bioinspired multiple stimuli-responsive optical microcapsules enabled by microfluidics provide a templated strategy to manufacture the next generation of intelligent optical units and to achieve the dynamic response of hybrid photonic devices.

Colloidal Nanosurfactants for 3D Conformal Printing of 2D van der Waals Materials.

Printing techniques using nanomaterials have emerged as a versatile tool for fast prototyping and potentially large-scale manufacturing of functional devices. Surfactants play a significant role in many printing processes due to their ability to reduce interfacial tension between ink solvents and nanoparticles and thus improve ink colloidal stability. Here, a colloidal graphene quantum dot (GQD)-based nanosurfactant is reported to stabilize various types of 2D materials in aqueous inks. In particular, a graphene ink with superior colloidal stability is demonstrated by GQD nanosurfactants via the π-π stacking interaction, leading to the printing of multiple high-resolution patterns on various substrates using a single printing pass. It is found that nanosurfactants can significantly improve the mechanical stability of the printed graphene films compared with those of conventional molecular surfactant, as evidenced by 100 taping, 100 scratching, and 1000 bending cycles. Additionally, the printed composite film exhibits improved photoconductance using UV light with 400 nm wavelength, arising from excitation across the nanosurfactant bandgap. Taking advantage of the 3D conformal aerosol jet printing technique, a series of UV sensors of heterogeneous structures are directly printed on 2D flat and 3D spherical substrates, demonstrating the potential of manufacturing geometrically versatile devices based on nanosurfactant inks.

Computational ghost imaging via adaptive deep dictionary learning.

Ghost imaging has gone through from quantum to classical pseudothermal to computational field over the last two decades. As a kernel part in computational ghost imaging (CGI), the reconstruction algorithm plays a decisive role in imaging quality and system practicality. In order to introduce more prior knowledge into the reconstruction algorithm, existing research adds image patch prior into CGI and improves the imaging efficiency. In this paper, the total variation minimization algorithm via adaptive deep dictionary learning (TVADDL) is proposed to update an adaptive deep dictionary through the CGI reconstruction process. The proposed algorithm framework is able to capture more precise texture features with a multi-layer architecture dictionary and adapt the learned dictionary by gradient descent on CGI reconstruction loss value. The results of simulation and experiment show that TVADDL can achieve higher peak signal-to-noise ratio than the algorithms without patch prior and the algorithms using the shallow dictionary or non-adaptive deep dictionary.

AC Electrodeposition of PEDOT Films in Protic Ionic Liquids for Long-Term Stable Organic Electrochemical Transistors.

Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)-based organic electrochemical transistors (OECTs) are widely utilized to construct highly sensitive biosensors. However, the PSS phase exhibits insulation, weak acidity, and aqueous instability. In this work, we fabricated PEDOT OECT by alternating current electrodeposition in protic ionic liquids. The steady-state characteristics were demonstrated to be stable in long-term tests. In detail, the maximum transconductance, the on/off current ratio, and the hysteresis were stable at 2.79 mS, 504, and 0.12 V, respectively. Though the transient behavior was also stable, the time constant could reach 218.6 ms. Thus, the trade-off between switching speed and stability needs to be considered in applications that require a rapid response.

Accelerated Design of Catalytic Water-Cleaning Nanomotors via Machine Learning.

The ability of self-propelled nanoparticles to convert environmental energy into locomotion has led to several nanomotor prototypes that are promising in numerous real-world applications. However, the vast variety of nanoparticle designs prevents rapid identification of the optimal composition for a given application. In this study, we applied machine learning methods to predict the self-propulsion speed and water-cleaning efficiency of micro/nanomotors (MNMs), where the quality of machine learning predictions was evaluated based on the statistical values. The average absolute error of predicted velocity and predicted efficiency are determined to be as low as 0.10 and 0.12, respectively. In addition, by comparing the prediction results based on 13 features using four different machine learning algorithms, we are able to identify several key features that are important to effectively environmental decontamination, such as particle size, catalyst type, and aspect ratio. Following the guidelines deduced from these models, a high-efficiency Pt-coated nanomotor was designed and synthesized, of which the experimental results were compared with the machine learning predictions, showing an accurate prediction with a less than 15% of prediction error. In the range of our theoretical/experimental conditions, we showed that a gradient boosting algorithm is the most promising method for predicting the environmental decontamination behavior of MNMs, a machine-learning algorithm rarely used in the nanomaterial field in current practice.

Growth of Colloidal Nanoplate Liquid Crystals Using Temperature Gradients.

Controlling colloidal self-assemblies using external forces is essential to develop modern electro-optical and biomedical devices. Importantly, shape anisotropic colloids can provide optical properties such as birefringence. Here we demonstrate that external temperature gradients can be effective in controlling nematic liquid crystalline (LC) order in suspensions of plate-like colloids also known as nanoplates. Nanoplates, in an isotropic suspension, wherein their orientations are random, could be effectively moved using a temperature gradient environment causing a phase transition to LC nematic phase. Such controllably formed nematic phase featured large nematic monodomains and enabled topologically more stable structures that were evident from the absence of hedgehog-type defects which are typically found in nematics formed spontaneously via nucleation and growth mechanism in a sufficiently high concentration suspension of nanoplates. Due to their high surface area-to-volume ratio and excellent thermophoretic properties, nanoplates can prove to be ideal candidates for transport of biomolecules through temperature varying environments.

Iridescence in nematics: Photonic liquid crystals of nanoplates in absence of long-range periodicity.

Photonic materials with positionally ordered structure can interact strongly with light to produce brilliant structural colors. Here, we found that the nonperiodic nematic liquid crystals of nanoplates can also display structural color with only significant orientational order. Owing to the loose stacking of the nematic nanodiscs, such colloidal dispersion is able to reflect a broad-spectrum wavelength, of which the reflection color can be further enhanced by adding carbon nanoparticles to reduce background scattering. Upon the addition of electrolytes, such vivid colors of nematic dispersion can be fine-tuned via electrostatic forces. Furthermore, we took advantage of the fluidity of the nematic structure to create a variety of colorful arts. It was expected that the concept of implanting nematic features in photonic structure of lyotropic nanoparticles may open opportunities for developing advanced photonic materials for display, sensing, and art applications.

Capillary-Based Microfluidic Fabrication of Liquid Metal Microspheres toward Functional Microelectrodes and Photothermal Medium.

Liquid metals (LMs) possess tremendous potential applications in flexible electronic devices, heat flow management, and smart actuators. Splitting the bulk LMs into microspheres is of great significance to fabricate free-standing and microscale LM-based functional materials and devices. However, it is difficult to disperse the bulk LMs into microspheres because of their large surface tension and high density. In this work, the capillary-based microfluidic chip is employed to continuously and automatically generate LM microspheres in a large scale. The capillary-based microfluidic fabrication is universally applicable in ionic aqueous solution, hydrophobic solution, and the polymeric aqueous solution. The precise size control of LM microspheres can be easily realized by the co-flowing configuration in the microchannels. The coefficient of size variation of monodispersed LM microspheres can be controlled to as low as 0.47%. The free-standing LM microspheres can be used as functional microelectrodes within a wide temperature range from -19.8 to 20 °C and to fabricate tunable integrated circuits with different output powers. Most importantly, the LM microspheres exhibit photothermal property, which is used to make the optical sensor with linear response and to conduct the solar energy harvesting. The capillary-based microfluidic fabrication of LM microspheres provides a facile and templated methodology for processing bulk LMs into microscale units. The LM microspheres with excellent electrical conductivity and photothermal property hold great promise for the development of miniature soft electronics, light-driven actuators, and energy conversion medium.

Facile one-step microwave-assisted modification of kaolinite and performance evaluation of pickering emulsion stabilization for oil recovery application.

A facile one-step microwave-assisted method was proposed for kaolinite intercalation and grafting. The structure, morphology, composition, and size distribution of kaolinite sheets were investigated using various methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric (TG) analysis. The potential application of the modified kaolinite as an oil/water emulsion stabilizer was studied. The results verified that intact kaolinite sheets were obtained. The dodecane/water emulsion stabilized by the modified kaolinite remained stable for more than 60 days. The effective performance suggests that the effectiveness of the proposed kaolinite modification method may be useful for Pickering emulsion stabilization in oil recovery applications.

Natural Halloysites-Based Janus Platelet Surfactants for the Formation of Pickering Emulsion and Enhanced Oil Recovery.

Janus colloidal surfactants with opposing wettabilities are receiving attention for their practical application in industry. Combining the advantages of molecular surfactants and particle-stabilized Pickering emulsions, Janus colloidal surfactants generate remarkably stable emulsions. Here we report a straightforward and cost-efficient strategy to develop Janus nanoplate surfactants (JNPS) from an aluminosilicate nanoclay, halloysite, by stepwise surface modification, including an innovative selective surface modification step. Such colloidal surfactants are found to be able to stabilize Pickering emulsions of different oil/water systems. The microstructural characterization of solidified polystyrene emulsions indicates that the emulsion interface is evenly covered by JNPS. The phase behaviors of water/oil emulsion generated by these novel platelet surfactants were also investigated. Furthermore, we demonstrate the application of JNPS for enhanced oil recovery with a microfluidic flooding test, showing a dramatic increase of oil recovery ratio. This research provides important insights for the design and synthesis of two-dimensional Janus colloidal surfactants, which could be utilized in biomedical, food and mining industries, especially for circumstances where high salinity and high temperature are involved.

Self-assembly of anisotropic red blood cell (RBC)-like colloidal particles.

Non-spherical colloidal particles, as basic building blocks, exhibit special capability in constructing novel materials. In this work, red blood cell (RBC)-like, anisotropic particles were synthesized and the self-assembly of the RBC-like particles was then carried out at the air-water interface. Subsequently, multilayer 3D structured colloidal crystals were also fabricated. The as-prepared colloidal crystal film displays beautiful Bragg diffraction, which can be used to construct a photonic crystal. After that, the self-assembly of binary colloidal particles was explored to design well-patterned binary colloidal crystals. This facile self-assembly approach to prepare colloidal crystals may extend to other anisotropic building blocks, providing guidance for the fabrication of more complex and flexible materials.

All-inorganic perovskite quantum dots stabilized blue phase liquid crystals.

All-inorganic perovskite quantum dots (PQDs) have been effectively incorporated in the three-dimensional ordered structure of blue phase liquid crystals (BPLCs) to stabilize the BPLCs. Uniform dispersion, reduced phase transition temperature, widened BP temperature range, dynamic and fast electro-optical response and static optical display of selective reflection mode and photoluminescence mode have been confirmed with a given concentration of PQDs. Such a novel strategy of assembling all-inorganic PQDs in BPLCs shows favorable prospects for wide-range and near room temperature BPLCs, responsive BPLCs, multifunctional display materials and tunable bandgap lasers.

Assembly and Chiral Memory Effects of Dynamic Macroscopic Supramolecular Helices.

Macroscopic enantiomerically pure helical supramolecular fibers are bottom-up assembled in aqueous media from a chiral π-electron donor template and an achiral π-electron acceptor. The helices can be assembled to the sub-millimeter scale with controlled handedness. These dynamic supramolecular architectures allow for a quantitative exchange of the chiral donor template with achiral analogues. During this process, a chiral memory effect was observed, affording enantiomerically pure helices composed entirely of achiral components.

Electrostatic-Driven Dynamic Jamming of 2D Nanoparticles at Interfaces for Controlled Molecular Diffusion.

Dynamically engineering the interfacial interaction of nanoparticles has emerged as a new approach for bottom-up fabrication of smart systems to tailor molecular diffusion and controlled release. Janus zwitterionic nanoplates are reported that can be switched between a locked and unlocked state at interfaces upon changing surface charge, allowing manipulation of interfacial properties in a fast, flexible, and switchable manner. Combining experimental and modeling studies, an unambiguous correlation is established among the electrostatic energy, the interface geometry, and the interfacial jamming states. As a proof-of-concept, the well-controlled interfacial jamming of nanoplates enabled the switchable molecular diffusion through liquid-liquid interfaces, confirming the feasibility of using nanoparticle-based surfactants for advanced controlled release.

Defect-induced betavoltaic enhancement in black titania nanotube arrays.

Utilizing high-energy beta particles emitted from radioisotopes for long-lifetime betavoltaic cells is a great challenge due to their low energy conversion efficiency (ECE). Here we report a betavoltaic cell fabricated using black titania nanotube arrays (TiO2 NTAs) by electrochemical anodization and Ar-annealing techniques. The obtained samples show enhanced electrical conductivity as well as Vis-NIR light absorption by the introduction of oxygen vacancy (OV) and Ti3+ defects in reduced TiO2-x NTAs. A 20 mCi63 Ni source was assembled into TiO2 NTAs to form a sandwich-type betavoltaic cell. By I-V measurements, the Ar-annealed TiO2 NTAs at 650 °C exhibited a maximum ECE of 3.65% with Voc = 1.13 V, Jsc = 103.3 nA cm-2, and Pmax = 37 nW cm-2. In comparison with air-annealed TiO2 NTAs, the enhancement of the betavoltaic effect in reduced TiO2-x NTAs can be attributed to the suppression of e-h recombination induced by the generation of OV and Ti3+ defects, serving as electron donors as well as electron traps that not only contribute to the increase of electrical conductance, but also facilitate the charge carrier separation.

Hierarchical, Self-Healing and Superhydrophobic Zirconium Phosphate Hybrid Membrane Based on the Interfacial Crystal Growth of Lyotropic Two-Dimensional Nanoplatelets.

We demonstrate a facile route to in situ growth of lyotropic zirconium phosphate (ZrP) nanoplates on textiles via an interfacial crystal growing process. The as-prepared hybrid membrane shows a hierarchical architecture of textile fibers (porous platform for fluid transport), ZrP nanoplatelets (layered scaffolds for chemical barriers), and octadecylamine (organic species for superhydrophobic functionalization). Interestingly, such a hybrid membrane is able to separate the oily wastewater with a high separation efficiency of 99.9%, even at in harsh environments. After being chemically etched, the hybrid membrane is able to restore its hydrophobicity autonomously and repeatedly, owing to the hierarchical structure that enables facile loading of healing agent. We anticipate that the concept of implanting superhydrophobic self-healing features in anisotropic structure of lyotropic nanoparticles will open up new opportunities for developing advanced multifunctional materials for wastewater treatment, fuel purification, and oil spill mitigation.

Betavoltaic Enhancement Using Defect-Engineered TiO2 Nanotube Arrays through Electrochemical Reduction in Organic Electrolytes.

Utilizing high-energy beta particles emitted from radioisotopes for long-lifetime betavoltaic cells is a great challenge due to low energy conversion efficiency. Here, we report a betavoltaic cell fabricated using TiO2 nanotube arrays (TNTAs) electrochemically reduced in ethylene glycol electrolyte (EGECR-TNTAs) for the enhancement of the betavoltaic effect. The electrochemical reduction of TNTAs using high cathodic bias in organic electrolytes is indeed a facile and effective strategy to induce in situ self-doping of oxygen vacancy (OV) and Ti3+ defects. The black EGECR-TNTAs are highly stable with a significantly narrower band gap and higher electrical conductivity as well as UV-vis-NIR light absorption. A 20 mCi of 63Ni betavoltaic cell based on the reduced TNTAs exhibits a maximum ECE of 3.79% with open-circuit voltage of 1.04 V, short-circuit current density of 117.5 nA cm-2, and a maximum power density of 39.2 nW cm-2. The betavoltaic enhancement can be attributed to the enhanced charge carrier transport and separation as well as multiple exciton generation of electron-hole pairs due the generation of OV and Ti3+ interstitial bands below the conductive band of TiO2.