Molecule Channels Directed by Cation-Decorated Graphene Oxide Nanosheets and Their Application as Membrane Reactors

As(III) removal from drinking water using FMCTO@Fe3O4 in the adsorption-magnetic separation-sand filtration equipment: Trade-off between As removal efficiency and adsorbent utilization rate

Due to the carcinogenicity and high environmental mobility of arsenic (As), its contamination in the groundwater environment is widespread, continuously threatening human health through the food chain. The adsorption technologies for As removal, which demonstrate simplicity and cost-effectiveness, have received much attention. Despite these merits, the difficult separation between adsorbent and As-contaminated water in traditional adsorption limited the development of large-scale applications. An adsorbent of Fe-Mn-Cu ternary oxide modified with magnetite (FMCTO@Fe3O4) was synthesized to develop a highly efficient As removal device based on an Adsorption-magnetic separation integrated safety device. Its safety and applicability were evaluated by optimizing the reactor design parameters using dynamic experiments. X-ray photoelectron spectroscopy, X-ray diffraction, and zeta potential results show that FMCTO@Fe3O4 has high adsorption and oxidation performance, in which 77 % of As(III) in the section was oxidized to As(V). As particle (As-p) electrostatically adsorbed to the surface of the material, with a removal efficiency of 84 % in the magnetic separation section and manganese sand filtration section. In this process, FMCTO@Fe3O4 isolated from magnetic separation section showed far stronger adsorption capacity. Specifically, FMCTO@Fe3O4, after being used 2 or 3 times, achieved an 80 % As(tot) removal efficiency. The section B functional area recycled Fe (99.24 %), Cu (98.2 %), and Mn (98.6 %), which demonstrated the equipment with higher stability and economic recovery. This device is promising in groundwater As removal, providing theoretical support and application innovation for drinking water safety and security.

Graphene oxide-based materials as proton-conducting membranes for electrochemical applications

The rapid advancements of graphene oxide (GO)-based membranes necessitate the understanding of their properties and application potential. Generally, proton (H+)-conducting membranes, including GO-based ones, are crucial components in various energy-relevant devices, significantly determining the transport process, selectivity, and overall efficiency of these devices. Particularly, GO-based membranes exhibit great potential in electrochemical applications owing to their remarkable conductivity and ease of undergoing further modifications. This review is aimed at highlighting recent functionalization strategies for GO with diverse substrates. It is also aimed at emphasizing how these modifications can enhance the electrochemical performances of GO-based membranes. Notably, key aspects, such as the enhanced H+-transfer kinetics, improved conductivity, functionalities, and optimization, of these membranes for specific applications are discussed. Additionally, the existing challenges and future directions for the field of functionalized GO are addressed to achieve precise control of the functionalities of these membranes as well as advance next-generation electrochemical devices.

Large-Area Layered Membranes with Precisely Controlled Nano-Confined Channels

Two-dimensional (2D) nanosheets-based membranes, which have controlled 2D nano-confined channels, are highly desirable for molecular/ionic sieving and confined reactions. However, it is still difficult to develop an efficient method to prepare large-area membranes with high stability, high orientation, and accurately adjustable interlayer spacing. Here, we present a strategy to produce metal ion cross-linked membranes with precisely controlled 2D nano-confined channels and high stability in different solutions using superspreading shear-flow-induced assembly strategy. For example, membranes based on graphene oxide (GO) exhibit interlayer spacing ranging from 8.0±0.1 Å to 10.3±0.2 Å, with a precision of down to 1 Å. At the same time, the value of the orientation order parameter (f) of GO membranes is up to 0.95 and GO membranes exhibit superb stability in different solutions. The strategy we present, which can be generalized to the preparation of 2D nano-confined channels based on a variety of 2D materials, will expand the application scope and provide better performances of membranes.

Functionalized 2D membranes for separations at the 1-nm scale

The ongoing evolution of two-dimensional (2D) material-based membranes has prompted the realization of mass separations at the 1-nm scale due to their well-defined selective nano- and subnanochannels. Strategic membrane functionalization is further found to be key to augmenting channel accuracy and efficiency in distinguishing ions, gases and molecules within this range and is thus trending as a research focus in energy-, resource-, environment- and pharmaceutical-related applications. In this review, we present the fundamentals underpinning functionalized 2D membranes in various separations, elucidating the critical "method-interaction-property" relationship. Starting with an introduction to various functionalization strategies, we focus our discussion on functionalization-induced channel-species interactions and reveal how they shape the transport- and operation-related features of the membrane in different scenarios. We also highlight the limitations and challenges of current functionalized 2D membranes and outline the necessary breakthroughs needed to apply them as reliable and high-performance separation units across industries in the future.

Comparative Retention Analysis of Intercalated Cations Inside the Interlayer Gallery of Lamellar and Nonlamellar Graphene Oxide Membranes in Reverse Osmosis Process: A Molecular Dynamics Study

Over the past decade, multilayered graphene oxide (GO) membranes have emerged as promising candidates for desalination applications. Despite their potential, a comprehensive understanding of separation mechanisms remains elusive due to the intricate morphology and structural arrangement of interlayer galleries. Moreover, a critical concern of multilayered GO membranes is their susceptibility to swelling within aqueous environments, which hinders their practical implementation. Therefore, this study introduces cation intercalation within GO laminates to elucidate the underlying factors governing swelling behavior and subsequently mitigate it. Moreover, this study performed nonequilibrium molecular dynamics simulations on the cation (Mg2+ or K+)-intercalated lamellar and nonlamellar GO membranes to understand the effect of the arrangement of GO sheets on the retention time of intercalated cations within GO layers, water permeance, and salt rejection mechanism in the reverse osmosis process using cation-intercalated GO membranes. Our results highlight that lamellar GO membranes exhibit higher water permeance, attributed to their well-defined interlayer gallery structure. On the other hand, nonlamellar GO membranes display superior salt rejection due to their complex interlayer gallery structure that impedes salt permeation. Moreover, the structural complexity of nonlamellar GO membranes contributes to greater stability by retention of the more intercalated cations for a longer time within the layers. Furthermore, it is observed that a higher percentage of Mg2+ cations remained inside the GO laminates as compared to K+ cations, hence resulting in the greater stability of the Mg2+-intercalated GO membrane in the aqueous environment.

Selective Ion Transport in Two-Dimensional Lamellar Nanochannel Membranes

Precise and ultrafast ion sieving is highly desirable for many applications in environment-, energy-, and resource-related fields. The development of a permselective lamellar membrane constructed from parallel stacked two-dimensional (2D) nanosheets opened a new avenue for the development of next-generation separation technology because of the unprecedented diversity of the designable interior nanochannels. In this Review, we first discuss the construction of homo- and heterolaminar nanoarchitectures from the starting materials to the emerging preparation strategies. We then explore the property-performance relationships, with a particular emphasis on the effects of physical structural features, chemical properties, and external environment stimuli on ion transport behavior under nanoconfinement. We also present existing and potential applications of 2D membranes in desalination, ion recovery, and energy conversion. Finally, we discuss the challenges and outline research directions in this promising field.

Al3+ Modification of Graphene Oxide Membranes: Effect of Al Source

Graphene oxide (GO) membranes are promising materials for water filtration applications due to abundant nanochannels in the membrane structure. Because GO membranes are unstable in water, metal cations such as Al3+ are often introduced to the membrane structure to promote cross-linking between individual GO sheets. Here, we describe a simple yet versatile method to incorporate Al3+ into GO membranes formed via a slow self-assembly process. Specifically, we directly added aluminum to acidic GO sheet solutions from a variety of sources: Al2O3, AlCl3 and Al foil. Each species reacts differently with water, which can affect the GO solution pH and thus the density of carboxylate groups on the sheet edges available for cross-linking to the Al3+ cations. We demonstrate through characterization of the GO sheet solutions as well as the as-formed membranes' morphologies, hydrophobicities, and structures that the extent to which the Al3+ cross-links to the GO sheet edges vs. the GO sheet basal planes is dependent on the Al source. Our results indicate that greatest enhancements in the membrane stability occur when electrostatic and coordination interactions between Al3+ and the carboxylate groups on the GO sheet edges are more extensive than Al3+-π interactions between basal planes.

Enhanced and sustained pesticidal activity of a graphene-based pesticide delivery system against the diamondback moth Plutella xylostella

BACKGROUND

Traditional abamectin (Abm) formulations have several shortcomings, such as low water solubility, burst release behavior, poor photostability, and short persistence periods, which decrease their pesticidal activity and the risks they pose to the environment. Nanomaterial-based pesticide delivery systems (PDSs) provide new strategies for the efficient and safe application of pesticides. Here, we developed Abm-loaded graphene oxide (Abm/GO) as a PDS for the sustained release of Abm, which shows enhanced control efficacy against Plutella xylostella.

RESULTS

The hydrophobic Abm molecule was effectively loaded on GO nanocarrier by a physisorption method, which formed a uniform and stable Abm/GO nanoformulation. GO possesses high adsorption capacity and can effectively load Abm. The Abm/GO nanoformulation shows enhanced water dispersion stability and can remain stable during a 2-year storage period in contrast to the water-insoluble Abm. In addition, the Abm/GO nanoformulation exhibits sustained pesticide release behavior and possesses significantly improved anti-ultraviolet properties. Thus, the Abm/GO nanoformulation shows superior pesticidal activity compared with Abm. Abm/GO showed negligible toxicity to maize seedlings, and its GO nanocarrier can reduce the cytotoxicity of Abm to A549 cells.

CONCLUSION

GO-based PDSs can effectively overcome the disadvantages of traditional pesticides, such as their insolubility, burst release behavior, instability, and short persistence period. GO shows much future promise in agriculture in light of its industrialization potential. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Understanding water transport through graphene-based nanochannels via experimental control of slip length

The water transport along graphene-based nanochannels has gained significant interest. However, experimental access to the influence of defects and impurities on transport poses a critical knowledge gap. Here, we investigate the water transport of cation intercalated graphene oxide membranes. The cations act as water-attracting impurities on the channel walls. Via water transport experiments, we show that the slip length of the nanochannels decay exponentially with the hydrated diameter of the intercalated cations, confirming that water transport is governed by the interaction between water molecules and the impurities on the channel wall. The exponential decay of slip length approximates non-slip conditions. This offers experimental support for the use of the Hagen-Poiseuille equation in graphene-based nanochannels, which was previously only confirmed by simulations. Our study gives valuable feedback to theoretical predictions of the water transport along graphene-based channels with water-attracting impurities.

Using Al3+ to Tailor Graphene Oxide Nanochannels: Impact on Membrane Stability and Permeability

Graphene oxide (GO) membranes, which form from the lamination of GO sheets, attract much attention due to their unique nanochannels. There is much interest in controlling the nanochannel structures and improving the aqueous stability of GO membranes so they can be effectively used in separation and filtration applications. This study employed a simple yet effective method of introducing trivalent aluminum cations to a GO sheet solution through the oxidation of aluminum foil, which modifies the nanochannels in the self-assembled GO membrane by increasing the inter-sheet distance while decreasing intra-sheet spacing. The Al3+ modification resulted in an increase in membrane stability in water, methanol, ethanol, and propanol, yet decreased membrane permeability to water and propanol. These changes were attributed to strong interactions between Al3+ and the membrane oxygenated functional groups, which resulted in an increase in membrane hydrophobicity and a decrease in the intra-sheet spacing as supported by surface tension, contact angle, atomic force microscopy, and X-ray photoelectron spectroscopy measurements. Our approach for forming Al3+ modified GO membranes provides a method for improving the aqueous stability and tailoring the permeation selectivity of GO membranes, which have the potential to be implemented in vapor separation and fuel purification applications.

Recent progress on fabrication methods of graphene-based membranes for water purification, gas separation, and energy sustainability

Graphene-based layered materials have got significant interest in membrane technology for water desalination, gas separation, organic nanofiltration, pervaporation, proton exchange applications, etc. and show remarkable results. Up to date, various methods have been developed for fabrication of high performance membrane. Most of them are only suitable for research purposes, but not appropriate for mass transport barrier and membrane applications that require large-area synthesis. In this comprehensive review, we summarized the current synthesis and fabrication methods of graphene-based membranes. Emphasis will be given on fabrication of both graphene-based nanoporous and lamellar membranes. Finally, we discuss the current engineering hurdles and future research directions yet to be explored for fabrication of such membranes.

2D Material Nanofiltration Membranes: From Fundamental Understandings to Rational Design

Since the discovery of 2D materials, 2D material nanofiltration (NF) membranes have attracted great attention and are being developed with a tremendously fast pace, due to their energy efficiency and cost effectiveness for water purification. The most attractive aspect for 2D material NF membranes is that, anomalous water and ion permeation phenomena have been constantly observed because of the presence of the severely confined nanocapillaries (<2 nm) in the membrane, leading to its great potential in achieving superior overall performance, e.g., high water flux, high rejection rates of ions, and high resistance to swelling. Hence, fundamental understandings of such water and ion transport behaviors are of great significance for the continuous development of 2D material NF membranes. In this work, the microscopic understandings developed up to date on 2D material NF membranes regarding the abnormal transport phenomena are reviewed, including ultrafast water and ion permeation rates with the magnitude several orders higher than that predicted by conventional diffusion behavior, ion dehydration, ionic Coulomb blockade, ion-ion correlations, etc. The state-of-the-art structural designs for 2D material NF membranes are also reviewed. Discussion and future perspectives are provided highlighting the rational design of 2D material membrane structures in the future.

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.

A Novel Strategy to Fabricate Cation-Cross-linked Graphene Oxide Membrane with High Aqueous Stability and High Separation Performance

Graphene oxide (GO) membranes have shown enormous promise in desalination and molecular/ionic sieving. However, the instability of GO membranes in aqueous solutions seriously hinders their practical applications. Herein, we report a novel and simple strategy to fabricate stable GO membranes in water-based environments through the insertion of various metal cations from metal foils (e.g., copper (Cu), iron (Fe), nickel (Ni), and zinc (Zn) foils) and natural deposition. Based on the cation-π, coordination, and electrostatic interaction between metal cations and GO nanosheets, the aqueous stability and mechanical strength of the membranes are significantly improved. The permeation rates for acetone, toluene, and p-xylene molecules across the GO membrane cross-linked by copper ions with a deposition time of 24 h are 0.966, 0.074, and 0.100 mol m^-2 h^-1, respectively. Moreover, this membrane displays excellent separation performance, and the separation factor of K⁺/Mg²⁺ is up to 68.8 in mono-/multivalent metal cation sieving, which indicate the effective molecular/ionic sieving performance. Meanwhile, the ionic sieving of the GO membrane cross-linked by copper ions has excellent repeatability and long-term stability. The versatility of this natural deposition strategy to fabricate GO membranes cross-linked by metal cations is investigated by using Fe foil, Zn foil, and Ni foil as well as other porous substrates such as polyvinylidene fluoride (PVDF), polyethersulfone (PES), and nylon membranes and filter paper. This fabrication strategy also enables low-cost preparation of large-area GO membranes. Therefore, GO membranes cross-linked by metal cations and prepared by this simple metal cation incorporation strategy have large potential application for molecular/ionic sieving in various solution systems.

Precisely Tunable Ion Sieving with an Al13-Ti3C2Tx Lamellar Membrane by Controlling Interlayer Spacing

Two-dimensional (2D) membranes exhibit exceptional properties in molecular separation and transport, which reveals their potential use in various applications. However, ion sieving with 2D membranes is severely restrained due to intercalation-induced swelling. Here, we describe how to efficiently stabilize the lamellar architecture using Keggin Al₁₃ polycations as pillars in a Ti₃C₂T_x membrane. More importantly, interlayer spacing can be easily adjusted with angstrom precision over a wide range (2.7-11.2 Å) to achieve selective and tunable ion sieving. A membrane with narrow d-spacing demonstrated enhanced selectivity for monovalent ions. When applied in a forward osmosis desalination process, this membrane exhibited high NaCl exclusion (99%) with a fast water flux (0.30 L m^-2 h^-1 bar^-1). A membrane with wide d-spacing showed notable selectivity, which was dependent on the cation valence. When it was applied to acid recovery from iron-based industrial wastewater, the membrane showed good H⁺/Fe²⁺ selectivity, which makes it a promising substitute for traditional polymeric membranes. Thus, we introduce a possible route to construct 2D membranes with appropriate structures to satisfy different ion-sieving requirements in diverse environment-, resource-, and energy-related applications.

Cation-π Interactions in Graphene-Containing Systems for Water Treatment and Beyond

Cation-π interactions are common in nature, especially in organisms. Their profound influences in chemistry, physics, and biology have been continuously investigated since they were discovered in 1981. However, the importance of cation-π interactions in materials science, regarding carbonaceous nanomaterials, has just been realized. The interplay between cations and delocalized polarizable π electrons of graphene would bring about significant changes to the intrinsic characteristics of graphene and greatly affect the device performance based on graphene and its derivatives. Here, the cation-π interactions in graphene containing systems for water treatment applications (e.g., separation membranes, adsorbents) are highlighted. The cross-linking effects caused by cation-π interactions contribute to membrane stability and selectivity and enhanced adsorption. Their roles in dominating the performance of graphene-based structures for other specific applications are also discussed. Relevant theoretical modeling and calculations are summarized to offer an in-depth understanding of the underlying mechanisms which can help in designing more functional materials and structures. Perspectives on the potential directions that deserve effort are also presented.

Coordination-Driven Hierarchical Assembly of Hybrid Nanostructures Based on 2D Materials

2D materials have received tremendous scientific and engineering interests due to their remarkable properties and broad-ranging applications such as energy storage and conversion, catalysis, biomedicine, electronics, and so forth. To further enhance their performance and endow them with new functions, 2D materials are proposed to hybridize with other nanostructured building blocks, resulting in hybrid nanostructures with various morphologies and structures. The properties and functions of these hybrid nanostructures depend strongly on the interfacial interactions between 2D materials and other building blocks. Covalent and coordination bonds are two strong interactions that hold high potential in constructing these robust hybrid nanostructures based on 2D materials. However, most 2D materials are chemically inert, posing problems for the covalent assembly with other building blocks. There are usually coordination atoms in most of 2D materials and their derivatives, thus coordination interaction as a strong interfacial interaction has attracted much attention. In this review, recent progress on the coordination-driven hierarchical assembly based on 2D materials is summarized, focusing on the synthesis approaches, various architectures, and structure-property relationship. Furthermore, insights into the present challenges and future research directions are also presented.

Surface defect-rich g-C3N4/TiO2 Z-scheme heterojunction for efficient photocatalytic antibiotic removal: rational regulation of free radicals and photocatalytic mechanism

Surface defect engineering was employed to introduce two different surface defect structures (i.e., nitrogen vacancies on g-C₃N₄ and oxygen vacancies on TiO₂) on the surface of g-C₃N₄/TiO₂ for efficient photocatalytic antibiotic removal.

Regulating the Interlayer Spacing of Graphene Oxide Membranes and Enhancing their Stability by Use of PACl

Graphene oxide (GO) is an ideal membrane material for water treatment due to its outstanding physicochemical properties and unique lamellar structure. However, the separation performance and practical application of GO membranes are mainly affected by the interlayer spacing and stability in aqueous solutions. Here, we report a novel and facile approach to fabricating GO membranes with adjustable interlayer spacing and high stability in aqueous solutions through cross-linking with polyaluminum chloride (PACl). With this approach, the lamellar spacing can be adjusted by changing the OH/Al ratios (B values) of the PACl, and the GO nanosheets can be tightly bonded by the strong electrostatic effect that PACl provides between them. The average interlayer spacing of the GO layer could be varied approximately in the range of 0.80-1.09 nm. The PACl-GO membranes demonstrated excellent stability in water and inorganic/organic solutions when the concentration of PACl was 0.1, 1, and 10 mM, remaining unchanged for at least 2 weeks. Moreover, the PACl-GO membranes featured exceptional sieving capabilities for model and natural organic substrates, while it was also observed that increasing the interlayer spacing of the PACl-GO membranes increased both the membrane flux and the separation performance of organic matter.

Self-Crosslinked MXene (Ti3C2Tx) Membranes with Good Antiswelling Property for Monovalent Metal Ion Exclusion

A 2D membrane-based separation technique has been increasingly applied to solve the problem of fresh water shortage via ion rejection. However, these 2D membranes often suffer from a notorious swelling problem when immersed in solution, resulting in poor rejection for the monovalent metal ion. The design of the antiswelling 2D lamellar membranes has been proved to be a big challenge for highly efficient desalination. Here a kind of self-crosslinked MXene membrane is proposed for ion rejection with an obviously suppressed swelling property, which takes advantage of the hydroxyl terminal groups on the MXene nanosheets by forming Ti-O-Ti bonds between the neighboring nanosheets via the self-crosslinking reaction (-OH + -OH = -O- + H₂O) through a facile thermal treatment. The permeation rates of the monovalent metal ions through the self-crosslinked MXene membrane are about two orders of magnitude lower than those through the pristine MXene membrane, which indicates the obviously improved performance of the ion exclusion by self-crosslinking between the MXene lamellae. Moreover, the excellent stability of the self-crosslinked MXene membrane during the 70 h long-term ion separation also demonstrates its promising antiswelling property. Such a facile and efficient self-crosslinking strategy gives the MXene membrane a good antiswelling property for metal ion rejection, which is also suitable for many other 2D materials with tunable surface functional groups during membrane assembly.

Carboxymethyl Chitosan Modified Carbon Nanoparticle for Controlled Emamectin Benzoate Delivery: Improved Solubility, pH-Responsive Release, and Sustainable Pest Control

Environmentally friendly pesticide delivery systems have drawn extensive attention in recent years, and they show great promise in sustainable development of agriculture. We herein report a multifunctional nanoplatform, carboxymethyl chitosan modified carbon nanoparticles (CMC@CNP), as the carrier for emamectin benzoate (EB, a widely used insecticide), and investigate its sustainable antipest activity. EB was loaded on CMC@CNP nanocarrier via simple physisorption process, with a high loading ratio of 55.56%. The EB@CMC@CNP nanoformulation showed improved solubility and dispersion stability in aqueous solution, which is of vital importance to its practical application. Different from free EB, EB@CMC@CNP exhibited pH-responsive controlled release performance, leading to sustained and steady EB release and prolonged persistence time. In addition, the significantly enhanced anti-UV property of EB@CMC@CNP further ensured its antipest activity. Therefore, EB@CMC@CNP exhibited superior pest control performance than free EB. In consideration of its low cost, easy preparation, free of organic solution, and enhanced bioactivity, we expect, CMC@CNP will have a brilliant future in pest control and green agriculture.

A label-free quantification method for measuring graphene oxide in biological samples

Characterization of carbonaceous nanomaterials (CNMs) exposure is a key step and of great importance towards a better understanding of their toxicity and underlying mechanisms. However, it has been bottlenecked for lack of valid methods capable of quantifying cell-associated CNMs. Here, we developed a new economical and convenient method based on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) that could accumulate graphene oxide (GO) at the interface between the loading well and the gel. The sharp black band formed there can be digitalized and the intensity quantified, which was proportional to the amount of GO loaded onto the gel. The method has a detection limit of 84.1 ng. We showed that the amount of GO in three different cell models, mouse macrophage cells (Raw264.7), human epithelial cells (A549) and mouse mesenchymal stem cells (MSC), could be accurately quantified by this assay, with the uptake rates decreasing in the order of MSC > Raw264.7 > A549. The results were consistent with the fluorescent imaging on cells exposed to fluorescence-labeled GO and TEM examination on ultrathin cell sections. The surprisingly highest uptake rate of MSC might be due to their abundant intracellular vesicles, which deserves further investigation. The novel method provides a complementary quantitative tool to the use of radioactive markers and fluorescent labeling of carbon nanomaterials and may facilitate the toxicological studies on carbon nanomaterials.

Attapulgite nanofibers and graphene oxide composite membrane for high-performance molecular separation

Graphene oxide (GO) based membranes are widely adopted in molecular separation based on size exclusion effect by stacked GO sheets. Both high flux and efficient rejection of GO-based membranes for long-term operation are highly expected for practical applications. Here, an attapulgite (ATP) nanofibers/ GO composite (ATP/GO) membrane is assembled by filtration of mixed aqueous colloidal suspensions of ATP and GO. Due to the modification of interlayer distance and surface property of GO membrane by ATP, the ATP/GO membrane demonstrates excellent separation performance, with a high water flux of 221.16 Lm^-2 h^-1bar^-1, 7.7 times higher than that of pure GO membrane. Meanwhile, the rejection of ATP/GO is also slightly improved comparing with that of GO membrane. It is also found that increasing the thickness of the membrane is effective to enhance rejection percentage. The ATP/GO membranes reported here show high efficiency for molecular separation, which demonstrates potential applications in water purification and environmental protection.

Grain-Boundary-Induced Drastic Sensing Performance Enhancement of Polycrystalline-Microwire Printed Gas Sensors

The development of materials with high efficiency and stable signal output in a bent state is important for flexible electronics. Grain boundaries provide lasting inspiration and a promising avenue for designing advanced functionalities using nanomaterials. Combining bulk defects in polycrystalline materials is shown to result in rich new electronic structures, catalytic activities, and mechanical properties for many applications. However, direct evidence that grain boundaries can create new physicochemical properties in flexible electronics is lacking. Here, a combination of bulk electrosensitive measurements, density functional theory calculations, and atomic force microscopy technology with quantitative nanomechanical mapping is used to show that grain boundaries in polycrystalline wires are more active and mechanically stable than single-crystalline wires for real-time detection of chemical analytes. The existence of a grain boundary improves the electronic and mechanical properties, which activate and stabilize materials, and allow new opportunities to design highly sensitive, flexible chemical sensors.

Metal-Organic-Framework-Based Catalysts for Photoreduction of CO2

Photoreduction of CO₂ into reusable carbon forms is considered as a promising approach to address the crisis of energy from fossil fuels and reduce excessive CO₂ emission. Recently, metal-organic frameworks (MOFs) have attracted much attention as CO₂ photoreduction-related catalysts, owing to their unique electronic band structures, excellent CO₂ adsorption capacities, and tailorable light-absorption abilities. Recent advances on the design, synthesis, and CO₂ reduction applications of MOF-based photocatalysts are discussed here, beginning with the introduction of the characteristics of high-efficiency photocatalysts and structural advantages of MOFs. The roles of MOFs in CO₂ photoreduction systems as photocatalysts, photocatalytic hosts, and cocatalysts are analyzed. Detailed discussions focus on two constituents of pure MOFs (metal clusters such as Ti-O, Zr-O, and Fe-O clusters and functional organic linkers such as amino-modified, photosensitizer-functionalized, and electron-rich conjugated linkers) and three types of MOF-based composites (metal-MOF, semiconductor-MOF, and photosensitizer-MOF composites). The constituents, CO₂ adsorption capacities, absorption edges, and photocatalytic activities of these photocatalysts are highlighted to provide fundamental guidance to rational design of efficient MOF-based photocatalyst materials for CO₂ reduction. A perspective of future research directions, critical challenges to be met, and potential solutions in this research field concludes the discussion.

Precisely Controlling Nanochannels of Graphene Oxide Membranes through Lignin-Based Cation Decoration for Dehydration of Biofuels

Lignin-based cations introduced into graphene oxide (GO) have been found to bring about stabilization of the nanostructure and the active sites and to give rise to various interactions for subsequent modification with polyelectrolyte and nanospacers, with a view to precisely controlling the nanochannels of the GO-based membranes. The resulting membranes exhibited excellent performance in biofuel dehydration with water flux of 4000-6000 g m^-2  h^-1 , which exceeds that of the state-of-the-art polymeric and GO-based membranes.

Bioinspired graphene membrane with temperature tunable channels for water gating and molecular separation

Smart regulation of substance permeability through porous membranes is highly desirable for membrane applications. Inspired by the stomatal closure feature of plant leaves at relatively high temperature, here we report a nano-gating membrane with a negative temperature-response coefficient that is capable of tunable water gating and precise small molecule separation. The membrane is composed of poly(N-isopropylacrylamide) covalently bound to graphene oxide via free-radical polymerization. By virtue of the temperature tunable lamellar spaces of the graphene oxide nanosheets, the water permeance of the membrane could be reversibly regulated with a high gating ratio. Moreover, the space tunability endows the membrane with the capability of gradually separating multiple molecules of different sizes. This nano-gating membrane expands the scope of temperature-responsive membranes and has great potential applications in smart gating systems and molecular separation.

The smart regulation of substance permeability is highly desirable for membrane separation technologies. Here, the authors design a poly(N-isopropylacrylamide)-grafted graphene oxide membrane with temperature tunable lamellar spaces, allowing for water gating and size-variable molecular separations.

Improved performance of hole-transporting layer-free perovskite solar cells by using graphene oxide sheets as the nucleation centers

Graphene oxide sheets (GOSs) are introduced between indium tin oxide (ITO) and CH₃NH₃PbI₃ in inverted hole-transport layer-free planar heterojunction perovskite solar cells.