Biomimetic Dual Absorption-Adsorption Networked MXene Aerogel-Pump for Integrated Water Harvesting and Power Generation System.

Harvesting atmospheric water and converting it into electricity play vital roles in advancing next-generation energy conversion systems. However, the current water harvester systems suffer from a weak water capture ability and poor recyclability due to high diffusion barriers and low sorption kinetics, which significantly limit their practical application. Herein, we drew inspiration from the natural "Pump effect" observed in wood and successfully developed a dual "absorption-adsorption" networked MXene aerogel atmospheric water harvester (MAWH) through ice templating and confining LiCl processes, thereby serving multiple purposes of clean water production, passive dehumidification, and power generation. The MAWH benefits from the dual H-bond network of MXene and cellulose nanocrystals (absorption network) and the hygroscopic properties of lithium chloride (adsorption network). Furthermore, its aligned wood-like channel structure efficiently eliminates water nucleation near the 3D network, resulting in fast moisture absorption. The developed MAWH demonstrates a high moisture absorption ability of 3.12 g g-1 at 90% relative humidity (RH), featuring rapid vapor transport rates and durable cyclic performance. When compared with commercial desiccants such as the 4A molecular sieve and silica gel, the MAWH can reduce the RH from 80% to 20% within just 6 h. Most notably, our integrated MAWH-based water harvesting-power generation system achieves a high voltage of ∼0.12 V at 77% RH, showcasing its potential for practical application. These developed MAWHs are considered as high-performance atmospheric water harvesters in the water collection and power generation field.

Eliminating trade-offs between optical scattering and mechanical durability in aerogels as outdoor passive cooling metamaterials.

Passive cooling is a promising approach for reducing the large energy consumption to achieve carbon neutrality. Foams/aerogels can be considered effective daytime cooling materials due to their good solar scattering and thermal insulation capacity. However, the contradiction between the desired high solar reflectivity and mechanical performance still limits their scalable production and real application. Herein, inspired by the "Floor-Pillar" concept in the building industry, a multi-structure assembly-induced ice templating technology was used to construct all-cellulosic aerogels with well-defined biomimetic structures. By using cellulose nanofibers (CNFs) as pillars and cellulose nanocrystals (CNCs) as floors and methyltrimethoxysilane (MTMS) as a crosslinking material, an all-cellulosic aerogel (NCA) exhibiting high mechanical strength (mechanical strength = 0.3 MPa at 80% compression ratio, Young's modulus = 1 MPa), ultralow thermal conductivity (28 mW m-1 K-1), ultrahigh solar reflectance (97.5%), high infrared emissivity (0.93), as well as excellent anti-weather function can be achieved, exceeding the performance of most reported cellulosic aerogels. Furthermore, the mechanisms of the improved mechanical strength and stimulated superior solar reflectance of NCA were studied in detail using finite element simulations and COMSOL Multiphysics. As a result, the NCA can achieve a cooling efficiency of 7.5 °C during the daytime. The building energy stimulus demonstrated that 44% of cooling energy can be saved in China annually if the NCA is applied. This work lays the foundation for the preparation of biomass aerogels for energy-saving applications.

Tree transpiration-inspired cellulose aerogel with engineered cold-evaporated surface for promoting structural stability and minimizing energy loss.

Solar-driven evaporation technology could significantly relieve the fresh-water crisis in the world. However, several problems, such as poor structural stability, low photothermal conversion capacity, and single heat source of traditional evaporators limited the promotion of fresh-water production efficiency. Herein, inspired by tree transpiration, we report a hydrophilic three-dimensional (3D) cellulose-based evaporator similar to the root of a tree, which can pump the bottom water to the evaporation surface for vapor generation. The aldehyde-based cellulose nanocrystals/ethylene imine polymer (ACP) aerogel was developed through Schiff base reaction to enhance the chain entangle capacity of the cellulose nanocrystals (CNCs) aerogel in water. Coating the ACP aerogel with lignin-derived photothermal material created the double-layered solar-driven evaporator (ACP-7LM), achieving a remarkable surface temperature of 35.9 °C in water under 1 sun irradiation for 1 h. The ACP-7LM exhibited an impressive evaporation rate of 1.60 kg m-2 h-1, leveraging its structural stability and excellent photothermal conversion. Increasing the cold evaporation surface (adjusting exposure height from 0 cm to 4 cm) of ACP-7LM aerogel maintained a lower temperature compared to ambient temperature on the side surface during evaporation, which harvest heat energy from environment and minimize energy loss. This enhanced environmental heat absorption boosted the ACP-7LM's evaporation rate to 3.76 kg m-2 h-1, a 2.35-fold increase over the ACP-7LM (0 cm). This solar-driven evaporator offers an efficient, innovative approach to elevate evaporation rates and address the global water crisis by simultaneously enhancing heat absorption capacity and photothermal conversion efficiency.

Wood Lamella-Inspired Photothermal Stearic Acid-Eutectic Gallium-Indium-Based Phase Change Aerogel for Thermal Management and Infrared Stealth.

Eutectic Gallium-Indium (EGaIn) liquid metal is an emerging phase change metal material, but its low phase transition enthalpy and low light absorption limit its application in photothermal phase change energy storage materials (PCMs) field. Here, based on the dipole layer mechanism, stearic acid (STA)-EGaIn-based PCMs which exhibit extraordinary solar-thermal performance and phase change enthalpy are fabricated by ball milling method. The wood lamella-inspired cellulose-derived aerogel and molybdenum disulfide (MoS2 ) are used to support the PCMs by the capillary force and decrease the interfacial thermal resistance. The resulted PCMs achieved excellent photothermal conversion performance and leakage proof. They  have excellent thermal conductivity of 0.31 W m-1 K-1 (this is increased by 138% as compared with pure STA), and high phase change enthalpy of187.50 J g-1 , which is higher than the most of the reported PCMs. Additionally, the thermal management system and infrared stealth materials based on the PCMs are developed. This work provides a new way to fabricate smart EGaIn-based PCMs for energy storage device thermal management and infrared stealth.

Cellulose-based evaporator with dual boost of water transportation and photothermal conversion for highly solar-driven evaporation.

Two-dimensional (2D) evaporation systems could significantly reduce the heat conduction loss compared with the photothermal conversion materials particles during the evaporation process. But the normal layer-by-layer self-assembly method of 2D evaporator would reduce the water transportation performance due to the highly compact channel structures. Herein, in our work, the 2D evaporator with cellulose nanofiber (CNF), Ti3C2Tx (MXene) and polydopamine modified lignin (PL) by layer-by-layer self-assembly and freeze-drying methods. The addition of PL also enhanced the light absorption and photothermal conversion performance of the evaporator due to the strong conjugation and π-π molecular interactions. After the combination process of layer-by-layer self-assembly and freeze-drying process, the as-prepared freeze-dried CNF/MXene/PL (f-CMPL) aerogel film exhibited highly interconnected porous structure with promoted hydrophilicity (enhanced water transportation performance). Benefiting these favorable properties, the f-CMPL aerogel film showed enhanced light absorption performance (surface temperature could be reached to 39 °C under 1 sun irradiation) and higher evaporation rate (1.60 kg m-2 h-1). This work opens new way to fabricate cellulose-based evaporator with highly evaporation performance for the solar steam generation and provides a new idea for improving the evaporation performance of 2D cellulose-based evaporator.

Dynamically Tunable All-Weather Daytime Cellulose Aerogel Radiative Supercooler for Energy-Saving Building.

A passive cooling strategy without any electricity input has shown a significant impact on overall energy consumption globally. However, designing tunable daytime radiative cooler to meet requirement of different weather conditions is still a big challenge, especially in hot, humid regions. Here, a novel type of tunable, thermally insulating and compressible cellulose nanocrystal (CNC) aerogel coolers is prepared via chemical cross-linking and unidirectional freeze casting process. Such aerogel coolers can achieve a subambient temperature drop of 9.2 °C under direct sunlight and promisingly reached the reduction of ∼7.4 °C even in hot, moist, and fickle extreme surroundings. The tunable cooling performance can be realized via controlling the compression ratio of shape-malleable aerogel coolers. Furthermore, energy consumption modeling of using such aerogel coolers in buildings in China shows 35.4% reduction of cooling energy. This work can pave the way toward designing high-performance, thermal-regulating materials for energy consumption savings.

Temperature-Invariant Superelastic Multifunctional MXene Aerogels for High-Performance Photoresponsive Supercapacitors and Wearable Strain Sensors.

Assembling MXene two-dimensional (2D) nanosheets solely into structurally robust three-dimensional (3D) multifunctional macroarchitectures with temperature-invariant elasticity is significant for widening their potential applications but has remained exceedingly challenging. To this end, a facile freeze-induced co-assembly was developed to allow the disparate integration of MXene 2D nanosheets into the directive heterogeneities to easily customize the controllable 3D architectures for geometry accessibility, structure integrity, and function adaptability. With functionalized cellulose nanocrystal serving as a structural modifier and cross-linking by polyurethane as well as manipulating the directionally ice templating process, multilevel nanostructured configurations with interconnected porous channels could be obtained for biomimetic aerogel electrodes across multiple length scales. Benefiting from the high ion pathway from the low-tortuosity topology, MXene aerogels showed outstanding electrochemical property (225 F/g), high-rate capacity, and temperature-invariant superelasticity (from 0 to 150 °C), which surpassed some of the best reported values. MXene quasi-solid-state supercapacitors presented superior electrochemistry (energy density: 38.5 µWh/cm2) and outstanding cycle ability (86.7% after 4000 cycles). Exhibiting excellent photoresponse capacity, they could be used as an integrated photodetector. More importantly, specially designed bio-mimicking structures with mechanically self-adaptive resilience could promote MXene 3D aerogels to apply in wearable electronic devices, monitoring various human motions. This work will shed light on MXene aerogels for smart and self-powered lightweight electronics.

3D-cellulose acetate-derived hierarchical network with controllable nanopores for superior Li+ transference number, mechanical strength and dendrites hindrance.

The dendrites is deemed to be one of the most crucial problems for lithium-ion batteries because it hampers their safety and cycling performance severely. Herein, a cellulose acetate-based separator with uniformly distributed nanopores was engineered and successfully prepared through a simple one-step process. The controlled nanopores promoted uniform transmission of ions and the cellulose acetate backbone inhibited the transference of anions, and prevented large-scale accumulation of lithium ions, thereby restricting the nucleation and growth of dendrites. The 3D-networked separator exhibited capacity retention of 78.6% after 900 cycles at 1C, with the breaking elongation and the strength increased by 620% and 28.4%, respectively, which originated from the porosity controlling of the nanofiber inter-bridging. The nanopore-assembled structure of 3D-hierarchy with MOFs provided the channels for the lithium ions transference through the separator and hence tackled the major challenge of mechanical vulnerability and electrochemical instability, which have never been reported before. Therefore, the developed strategy may offer a powerful and effective alternative for conventional approach of occurring dendrites post-treatments for higher ionic conductivity.

Strong biodegradable cellulose materials with improved crystallinity via hydrogen bonding tailoring strategy for UV blocking and antioxidant activity.

It has been a huge challenge to obtain simultaneously excellent mechanical strength and desirable multifunctionality from the cellulose nanocrystals (CNC) based food packing materials. In this work, we demonstrated a hydrogen bonding tailoring strategy that can produce CNC/lignin films with UV blocking and antioxidant activity, while bypassing the loss of mechanical strength. Using a hyperbranched polyester, lignin was first functionalized to increase the amount of hydroxyl groups, thereby increasing the intermolecular interactions. By assembling the polyester modified lignin (H-lignin) into CNC matrix, the hydrogen bonding crosslinks between the H-lignin and CNC chains were successfully promoted, resulting in the CNC composites with the significantly improved mechanical strength, UV blocking and antioxidant activity. The phenolic structure and the hydrogen donation of H-lignin also endowed the resulting CNC composites with excellent UV blocking and antioxidant activity. The experimental results indicated that the H-lignin could bring about 34% and 63% increase in tensile strength and Young's modulus, respectively, higher than the reported ones. The CNC-based composites showed better thermal stability and improved crystallinity property. The H-lignin provides a new insight into the multifunctional exploration of CNC-based composite. This work opens a new avenue for the next generation's biodegradable food packing materials from cellulose-sourced composites.

Ultralight Programmable Bioinspired Aerogels with an Integrated Multifunctional Surface for Self-Cleaning, Oil Absorption, and Thermal Insulation via Coassembly.

Creating a configurable and controllable surface for structure-integrated multifunctionality of ultralight aerogels is of significance but remains a huge challenge because of the critical limitations of mechanical vulnerability and structural processability. Herein, inspired by Salvinia minima, the facile and one-step coassembly approach is developed to allow the structured aerogels to spontaneously replicate Salvinia-like textures for function-adaptable surfaces morphologically. The in situ superimposed construction of bioinspired topography and intrinsic topology is for the first time performed for programmable binary architectures with multifunctionality without engendering structural vulnerability and functional disruption. By introducing the binding groups for hydrophobicity tailoring, functionalized nanocellulose (f-NC) is prepared via mechanochemistry as a structural, functional, and topographical modifier for a multitasking role. The self-generated bioinspired surface with f-NC greatly maintains the structural unity and mechanical robustness, which enable self-adaptability and self-supporting of surface configurations. With fine-tuning of nucleation-driving, the binary microstructures can be controllably diversified for structure-adaptable multifunctionalities. The resulting ultralight S. minima-inspired aerogels (e.g., 0.054 g cm-3) presented outstanding temperature-endured elasticity (e.g., 90.7% high-temperature compress-recovery after multiple cycles), durable superhydrophobicity, anti-icing properties, oil absorbency efficiency (e.g., 60.2 g g-1), and thermal insulating (e.g., 0.075 W mK-1), which are superior to these reported on the overall performance. This coassembly strategy offers the opportunities for the design of ultralight materials with topography- and function-tailorable features to meet the increasing demands in many fields such as smart surfaces and self-cleaning coatings.