Facile preparation of ionic porous networks (IPNs) with large and permanent porosity is highly desirable for CO₂ capture and transformation but remains a challenge. Here we report a one-pot base-mediated construction of nitrogen-rich IPNs through a combination of nucleophilic substitution and quaternisation chemistry from H-imidazole. This strategy, as proven by the model reactions of 1H-imidazole or 1-methyl-1H-imidazole with cyanuric chloride, allows for fine regulation of porosity and physicochemical properties, leading to nitrogen-rich IPNs featuring abundant ionic units and radicals. The as-prepared networks, termed IPN-CSUs, efficiently capture CO₂ (80.1 cc g⁻¹ at 273 K/1 bar) with an ideal CO₂/N₂ selectivity of 139.7. They can also effectively catalyse the cycloaddition reaction between CO₂ and epoxides with high yields of up to 99% under mild conditions (0.1 MPa, 298 K), suggesting their possible applications in the fields of both selective molecular separation and conversion. Unlike the previously known strategies generally involving single coupling chemistry, our strategy combining two coupling routes in one pot appears to be unique and potentially applicable to other building blocks.

2D materials such as graphene, graphene oxide (GO), reduced graphene oxide (rGO) and MXene, possess unique properties, e.g., high carrier mobilities, mechanical flexibility, good thermal conductivity, and high optical and UV adsorption. They are potentially applicable in the fields of electronics, optoelectronics, catalysts, energy storage facilities, sensors, solar cells, lithium batteries, and so on. Normally, weak interactions and irregular packing or stacking of 2D layers may adversely offset or weaken to some extent their 2D effects such as mechanical and electrical properties at a macroscale. In this regard, it is required to spatially organize 2D materials into macroscopic forms of a well-defined shape (e.g. fibers, films, or 3D structures) in a way that can simultaneously preserve favorable 2D properties and functions shown at the nanoscale, and facilitate their compatibility with the state-of-the-art industrial processes. In my thesis, different types of 2D materials, here GO, rGO and MXene together with polymers were rationally assembled into functional composite materials. The synergistic molecular crosslinking strategy was utilized and controlled in such composite materials for the sake of better performance. My thesis mainly involves four parts:

(1) Tough and strong GO composite films via a polycationitrile approach. The interface between GO nanosheets was reinforced via an intermolecular covalent crosslinking approach called “polycationitrile chemistry”. As a result, the mechanical performance of the as-prepared GO-based composite films was enhanced and maintained even at an extremely high relative humidity of 98%.

(2) rGO-poly(ionic liquid) (PIL) composite films with high mechanical performance. The rGO/PIL composite films were designed and fabricated, where the synergistic supramolecular interactions between PIL and rGO layer enable high electrical conductivity and favorable mechanical properties.

(3) Regenerated cellulose (RC)/MXene composite nanofibers for personal heating management. I harnessed a biodegradable RC-based fibrous matrix to bond with inorganic MXene nanoflakes via electrospinning method. Via hybridization, the as-formed RC/MXene nanofibers present a promotion of mechanical performance and photothermal conversion capability. As a personal heating cloth, it realizes energy-saving outdoor thermoregulatory.

(4) RC/MXene solar absorber for solar-driven interfacial water evaporation. The RC/MXene composite nanofibers integrate considerable merits of excellent mechanical performance, wettability, and fast steam generation rate. The RC/MXene solar absorber offers significant values for the practical application of solar-driven steam generation.

Sand, an abundant resource from the nature, is a promising candidate for oil/water separation. Herein, raw sand was designed with switchable surface wettability to enable recyclability and versatility in practical oil/water separation. The smart sand was fabricated by grafting pH-responsive poly(4-vinylpyridine) (P4VP) and oleophilic/hydrophobic octadecyltrimethoxysilane (OTS) onto its surface. The decorated sand can be used as the oil sorbent for controllable oil sorption and desorption in response to different pHs, as well as a filter to selectively separate either oil or water on demand. This novel design offers an intelligent, low-cost, large-scale, and highly efficient route to potentially settle the issues of industrial oily wastewater and oil spill.

Given the abundant solar light available on our planet, it is promising to develop an advanced fabric capable of simultaneously providing personal thermal management and facilitating clean water production in an energy-efficient manner. In this study, we present the fabrication of a photothermally active, biodegradable composite cloth composed of titanium carbide MXene and cellulose, achieved through an electrospinning method. This composite cloth exhibits favorable attributes, including chemical stability, mechanical performance, structural flexibility, and wettability. Notably, our 0.1-mm-thick composite cloth (RC/MXene IV) raises the temperature of simulated skin by 5.6 degrees C when compared to a commercially available cotton cloth, which is five times thicker under identical ambient conditions. Remarkably, the composite cloth (RC/MXene V) demonstrates heightened solar light capture efficiency (87.7%) when in a wet state instead of a dry state. Consequently, this cloth functions exceptionally well as a high-performance steam generator, boasting a superior water evaporation rate of 1.34 kg m(-2) h(-1) under one-sun irradiation (equivalent to 1000 W m(-2)). Moreover, it maintains its performance excellence in solar desalination processes. The multifunctionality of these cloths opens doors to a diverse array of outdoor applications, including solar-driven water evaporation and personal heating, thereby enriching the scope of integrated functionalities for textiles.

Maintaining human thermal comfort in the cold outdoors is crucial for diverse outdoor activities, e.g., sports and recreation, healthcare, and special occupations. To date, advanced clothes are employed to collect solar energy as a heat source to stand cold climates, while their dull dark photothermal coating may hinder pragmatism in outdoor environments and visual sense considering fashion. Herein, tailor-made white webs with strong photothermal effect are proposed. With the embedding of cesium–tungsten bronze (Cs_xWO₃) nanoparticles (NPs) as additive inside nylon nanofibers, these webs are capable of drawing both near-infrared (NIR) and ultraviolet (UV) light in sunlight for heating. Their exceptional photothermal conversion capability enables 2.5–10.5 °C greater warmth than that of a commercial sweatshirt of six times greater thickness under different climates. Remarkably, this smart fabric can increase its photothermal conversion efficiency in a wet state. It is optimal for fast sweat or water evaporation at human comfort temperature (38.5 °C) under sunlight, and its role in thermoregulation is equally important to avoid excess heat loss in wilderness survival. Obviously, this smart web with considerable merits of shape retention, softness, safety, breathability, washability, and on-demand coloration provides a revolutionary solution to realize energy-saving outdoor thermoregulation and simultaneously satisfy the needs of fashion and aesthetics.

Graphene oxide (GO) is a classic two dimensional (2D) building block that can be used to develop high-performance materials for numerous applications, particularly in the energy and environmental fields. Currently, the precise assembly of GO nanosheets into macroscopic nanohybrids of superior strength and toughness is desirable, and faces challenges and trade-offs. Herein, we exploited the freshly established polycationitrile method as a powerful molecular crosslinking strategy to engineer ultratough and ultrastrong GO/polymer hybrid films, in which a covalent triazine-based network was constructed in a mild condition to reinforce the interface between GO nanosheets. The tensile strength and toughness reached 585 +/- 25 MPa and 14.93 +/- 1.09 MJ m(-3), respectively, which, to the best of our knowledge, are the current world records in all GO-based hybrid films. As an added merit of the tailor-made polymer crosslinker, the high mechanical performance can be maintained in large part at an extremely high relative humidity of 98%. This emerging interface-engineering approach paves a new avenue to produce integrated strong-and-tough 2D nanohybrid materials that are useful in aerospace, artificial muscle, energy harvesting, tissue engineering and more.

Graphene and its derivatives are a classical group of two-dimensional (2D) building blocks possessing excellent mechanical and/or electrical properties in favor of preparing flexible electronic devices. Natural materials, such as nacre, provide inspiration and an exciting guideline for assembling 2D nanosheets into functional nanocomposites. In this context, despite recent advance, methods to assemble graphene-derived nanosheets into nanocomposites with the integrated enhancement of mechanical properties and electrical conductivity are eagerly pursued. Here, a rational design has been proposed and demonstrated, which utilizes synergistic supramolecular interactions between a polymeric additive and reduced graphene-oxide nanosheets to fabricate exceptional, integrated, strong, and tough nanocomposite films with high electrical conductivity. Such materials can be applied in areas such as, aerospace, artificial muscle, tissue engineering, and flexible electronics.

Shortage of clean water continues to grow around the world, and the recent solar-powered interfacial system has emerged as a sustainable, efficient and CO₂-neutral approach to produce clean water. However, complex contaminants in surface water accompanied with environment pollution set huge obstacles for harvesting clean water via previous strategies. Here we develop a solar-powered graphene/alginate hydrogel (GAH)-based clean water extractor of super resistance to the transport of complex contaminants and ultra-antifouling capacity. This GAH features a high selectivity in water transport by rejecting >99.5% of volatile organic compounds, >99.3% of ions (Na⁺, Mg²⁺, K⁺ and Ca²⁺) and 100% of non-volatile organic compounds and bacteria; meanwhile, GAH is capable of rejecting oil adhesion by forming a large contact angle >140° under water, deactivating nearly 100% bacteria on surface and preventing salt crystallization. Given such promising adaptability to a wide environment, this GAH can directly convert surface water of complex components into safe drinkable water.

CO₂ sensors are very important; however, their performance is limited by stability and selectivity. This study unveils a capacitive CO₂ sensor with a dielectric layer comprised of amine-functionalized cellulose nanofibril (CNF) foam, significantly enhanced by the addition of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The core innovation of this research lies in the strategic use of CNF-based foam, which leads to a substantial increase in sensor capacitance, setting a new standard in CO₂ monitoring technologies. The sensor showcases exceptional performance under ambient conditions, with marked improvements in sensitivity towards CO₂. The advancements are attributed to the chemisorption properties of the aminated CNFs combined with the DBU enhancement, facilitating more effective CO₂ capture. By integrating these materials, we present a sensor that opens new avenues for environmental monitoring, healthcare diagnostics, and industrial safety, establishing a new benchmark for capacitive CO₂ sensors in efficiency and environmental sustainability.

Herein, we established a synthetic route towards MXene/poly(ionic liquid) (PIL) composite porous membranes as a new platform of solar-thermal conversion materials. These membranes were made by a base-triggered ionic crosslinking process between a cationic PIL and a weak polyacid in solution in the presence of dispersed MXene nanosheets. A three-dimensionally interconnected porous architecture was formed with MXene nanosheets uniformly distributed within it. The unique characteristics of the as-produced composite membranes displays significant light-to-heat conversion and excellent performance for solar-driven water vapor generation. This facile synthetic strategy opens a new avenue for developing composite porous membranes as solar absorbers for the solar-driven water production from natural resources. 

Herein, we established a synthetic route towards MXene/poly(ionic liquid) (PIL) composite porous membranes as a new platform of solar-thermal conversion materials. These membranes were made by a base-triggered ionic crosslinking process between a cationic PIL and a weak polyacid in solution in the presence of dispersed MXene nanosheets. A three-dimensionally interconnected porous architecture was formed with MXene nanosheets uniformly distributed within it. The unique characteristics of the as-produced composite membranes displays significant light-to-heat conversion and excellent performance for solar-driven water vapor generation. This facile synthetic strategy opens a new avenue for developing composite porous membranes as solar absorbers for the solar-driven water production from natural resources.

Controlled synthesis of polymer-based porous membranes via innovative methods is of considerable interest, yet it remains a challenge. Herein, we established a general approach to fabricate porous polyelectrolyte composite membranes (PPCMs) from poly-(ionic liquid) (PIL) and MXene via an ice-assisted method. This process enabled the formation of a uniformly distributed macroporous structure within the membrane. The unique characteristics of the as-produced composite membranes display significant light-to-heat conversion and excellent performance for solar-driven water vapor generation. This facile synthetic strategy breaks new ground for developing composite porous membranes as high-performance solar steam generators for clean water production.

Controlled regulation of polymer-based porous membranes via innovative methods is of considerable interest yet it remains a challenge. Herein, we established a general approach to fabricate porous polyelectrolyte composite membranes (PPCM)s from poly(ionic liquid) (PIL) and MXene via an ice-templating method. This process enabled the formation of a uniformly distributed macroporous structure within the membrane. The unique characteristics of the as-produced composite membranes displays significant light-to-heat conversion and excellent performance for solar-driven water vapor generation. This facile synthetic strategy breaks new grounds for developing composite porous membranes as high-performance solar steam generator for clean water production.

Assembling two-dimensional (2D) materials by polyelectrolyte often suffers from inhomogeneous microstructures due to the conventional mixing-and-simultaneous-complexation procedure (mix-and-complex) in aqueous solution. Herein a mix-then-on-demand-complex concept via on-demand in situ cascade anionization and ionic complexation of 2D materials is raised that drastically improves structural order in 2D assemblies, as exemplified by classical graphene oxide (GO)-based ultrathin membranes. Specifically, in dimethyl sulfoxide, the carboxylic acid-functionalized GO sheets (COOH-GOs) were mixed evenly with a cationic poly(ionic liquid) (PIL) and upon filtration formed a well-ordered layered composite membrane with homogeneous distribution of PIL chains in it; next, whenever needed, it was alkali-treated to convert COOH-GO in situ into its anionized state COO--GO that immediately complexed ionically with the surrounding cationic PIL chains. This mix-then-on-demand-complex concept separates the ionic complexation of GO and polyelectrolytes from their mixing step. By synergistically combining the PIL-induced hydrophobic confinement effect and supramolecular interactions, the as-fabricated nanofiltration membranes carry interface transport nanochannels between GO and PIL, reaching a high water permeability of 96.38 L m(-2) h(-1) bar(-1) at a maintained excellent dye rejection 99.79% for 150 h, exceeding the state-of-the-art GO-based hybrid membranes. The molecular dynamics simulations support the experimental data, confirming the interface spacing between GO and PIL as the water transport channels.

Sustainable materials are needed to mitigate against the increase in energy consumption resulting from population growth and urbanization. Here, we report fully biobased nanocomposite films and coatings that display efficient photothermal activity and selective absorption of ultraviolet (UV) radiation. The nanocomposites with 20 wt % of lignin nanoparticles (LNPs) embedded in a chitosan matrix displayed an efficient UV blocking of 97% at 400 nm along with solar energy-harvesting properties. The reflectance spectra of the nanocomposite films revealed the importance of well-dispersed nanoparticles in the matrix to achieve efficient UV-blocking properties. Finally, yet importantly, we demonstrate the nanocomposites with 20 wt % LNPs as photothermal glass coatings for passive cooling of indoor temperature by simply tailoring the coating thickness. Under simulated solar irradiation of 100 mW/cm², the 20 μm coating achieved a 58% decrease in the temperature increment in comparison to the system with uncoated glass. These renewable nanocomposite films and coatings are highly promising sustainable solutions to facilitate indoor thermal management and improve human health and well-being.

Two-dimensional (2D) MXene-based lamellar membranes play transformative roles in membrane filtration technology. Their practical use in water treatment is however hindered by several hurdles, e.g., unfavorable swelling due to weak interactions between adjacent MXene nanosheets, tortuous diffusion pathways of layered stacking, and the intrinsic aquatic oxidation-prone nature of MXene. Herein, nanoporous 2D/2D heterostructure membranes are elaborately constructed via solution-phase assembly of oppositely charged MXene and modified layered double hydroxide (MLDH) nanosheets. As a multifunctional component, positively charged holey MLDH nanosheets were first tailor-made to serve simultaneously as a binder, spacer and surface-modifier; next they were intercalated into negatively charged MXene lamella to enhance structural stability and mass transfer of membranes. As a result, the as-prepared MLDH@MXene heterostructure membranes successfully break the persistent trade-off between high permeability and selectivity while mitigating the common drawbacks in 2D MXene-based lamellar membranes, e.g., swelling issues, restacking problems, and vulnerable chemical stability. Noticeably, at an operating pressure of 4 bar and a feed solution of 100 ppm of Congo red, the heterostructure membranes enable a threefold jump in permeability (332.7 +/- 20 L m(-2) h(-1 )bar(-1)) when compared to the pristine MXene membrane (119.3 +/- 18 L m(-2 )h(-1) bar(-1)), and better operational stability without compromising the rejection.

Understanding the reconstruction of surface sites is crucial for gaining insights into the true active sites and catalytic mechanisms. While extensive research has been conducted on reconstruction behaviors of atomically dispersed metallic catalytic sites, limited attention has been paid to non-metallic ones despite their potential catalytic activity comparable or even superior to their noble-metal counterpart. Herein, we report a carbonaceous, atomically dispersed non-metallic selenium catalyst that displayed exceptional catalytic activity in the hydrazine oxidation reaction (HzOR) in alkaline media, outperforming the noble-metal Pt catalysts. In situ X-ray absorption spectroscopy (XAS) and Fourier transform infrared spectroscopy revealed that the pristine SeC₄ site pre-adsorbs an ∗OH ligand, followed by HzOR occurring on the other side of the OH–SeC₄. Theoretical calculations proposed that the pre-adsorbed ∗OH group pulls electrons from the Se site, resulting in a more positively charged Se and a higher polarity of Se–C bonds, thereby enhancing surface reactivity toward HzO/R.

Herein, we report a simple and versatile synthetic approach towards siloxane-based poly(ionic liquid)s (PILs) with unusually low glass transition temperatures (T_g) down to −73°C, and thus “liquid-like” behavior at room temperature. We designed a polydimethylsiloxane-derived copolymer carrying dialkylimidazolium moieties, and by careful selection of the side-chain length and the type of anions we were able to manipulate its T_g over a wide range and reach high ionic conductivities (σ_DC) up to 4.8 × 10⁻⁵ S/cm at 300 K. The ionized species make up only a minor fraction (<25 mol%) of the overall repeating units and are supposedly randomly distributed: Yet our results indicate dramatic effects on the thermal properties due to repulsive interactions between ionic and non-ionic segments.

A series of organic phosphonic acids (OPAs) were applied as multifunctional spacers to enlarge the inner space of carbide MXene (Ti3C2Tx) laminates. A synergistic improvement in permeance, rejection and stability is achieved via introducing OPA to create pillared laminates. This strategy provides a universal way to regulate transport channels of MXene-based membranes.

Two-dimensional (2D) MXene-based lamellar membranes bearing interlayers of tunable hydrophilicity are promising for high-performance water purification. The current challenge lies in how to engineer the pore wall's surface properties in the subnano-confinement environment while ensuring its high selectivity. Herein, poly(ionic liquid)s, equipped with readily exchangeable counter anions, succeeded as a hydrophilicity modifier in addressing this issue. Lamellar membranes bearing nanochannels of tailorable hydrophilicity are constructed via assembly of poly(ionic liquid)-armored MXene nanosheets. By shifting the interlayer galleries from being hydrophilic to more hydrophobic via simple anion exchange, the MXene membrane performs drastically better for both the permeance (by two-fold improvement) and rejection (≈99 %). This facile method opens up a new avenue for building 2D material-based membranes of enhancing molecular transport and sieving effect.