High-yield synthesis of hydroxylated boron nitride nanosheets and their utilization in thermally conductive polymeric nanocomposites.

Hexagonal boron nitride nanosheets (BNNSs) possess remarkable potential for various applications due to their unprecedented properties. However, the scalable production of BNNSs with both expansive surface and high solubility continues to present a significant challenge. Herein, we propose an innovative and efficient two-step method for manufacturing hydroxyl-functionalized BNNSs (OH-BNNSs). Initially, hydroxyl groups are covalently attached to bulk hexagonal boron nitride (h-BN) surfaces through H2O2 treatment. Then, the hydroxyl-functionalized h-BN undergoes exfoliation on account of a sudden increase in interlayer gas pressure generated by the vigorous decomposition of H2O2 in alkali solutions, resulting in the creation of OH-BNNSs. This approach produces relatively large flakes with an average dimension of 1.65 µm and a high yield of 45.2%. The resultant OH-BNNSs exhibit remarkable stability and dispersibility in a range of solvents. Their integration into thermoplastic polyurethane (TPU) significantly enhances both thermal conductivity and stability, attributed to the excellent compatibility with the resin matrix. This study represents a significant advancement in the functionalization and exfoliation of h-BN, opening new avenues for its promising applications in polymer composites.

Subchondral bone-inspired hydrogel scaffold for cartilage regeneration.

Promoting the in situ regeneration of cartilage without additional cells or cytokines remains challenging. Here, inspired by the unique microstructures of subchondral bone, a cell and cytokine free hydrogel scaffold for cartilage regeneration was developed via a strategy of directional lyophilization and postcrosslinking. This strategy achieved intersecting microchannels in an orderly arrangement and an aligned ladder-like texture in a semi-interpenetrating hydrogel network. The resulting hydrogel had similar mechanical properties to the native cartilage extracellular matrix. Incorporating chitosan into the rigid network also endowed the hydrogel with excellent hemostatic properties. By delicately tuning the components and postcrosslinking conditions, the hydrogel was further endowed with suitable swelling and degradation properties for cartilage regeneration. In vitro tests showed that the highly biocompatible hydrogel scaffold could facilitate the migration and chondrogenic differentiation of bone marrow mesenchymal stem cells. In vivo results further verified that the hydrogel could promote the in situ regeneration of cartilage in a rat model of osteochondral defects. In summary, the subchondral bone-like hydrogel revealed promising prospects in cartilage regeneration and a variety of bioremediation applications.

Tough and Resilient Hydrogels Enabled by a Multifunctional Initiating and Cross-Linking Agent.

Many high-strength hydrogels have been developed in recent years; however, few of them are both tough and resilient, and their intrinsic paradoxical nature makes designing a gel with both high toughness and high resilience a great challenge. To address this problem, we introduced both N,N,N,N-pentamethyldiethylenetriamine (PA) and N,N-methylenebisacrylamide (MBA) into polyacrylamide hydrogel networks to construct an entangled network that contains chemically cross-linked chains and branched chains simultaneously. The entanglements of branched chains can act as a physical cross-linking point to uniformly disperse stress on molecular chains, and chemical cross-linking ensures the stability of the hydrogel network. The increase in the number and length of branched chains is able to achieve an enhancement in strength while the slip of the entangled polymer chains can effectively achieve energy dissipation and can improve the toughness of the gel. Moreover, the resultant hydrogels exhibit an excellent resilience (>98%). Therefore, high toughness and resilience are achieved simultaneously. In addition, we also investigated the initiation mechanism of PA. This strategy creates a new way for the preparation of next-generation high toughness and high resilience hydrogel-based materials, which have promising applications in wearable, flexible strain/pressure sensors.

Preparation of High-Performance Composite Hydrogel Reinforced by Hydrophilic Modified Waste Rubber Powder.

In order to reduce the environmental pollution caused by waste rubber and to realize the recycling of resources, we proposed a facile method for the hydrophilic modification of waste rubber powder (HRP) and used it to reinforce a composite hydrogel. In the presence of toluene, dibenzoyl peroxide (BPO) diffused into the waste rubber powder. After the solvent was removed, BPO was adsorbed in the rubber powder, which was used to initiate the grafting polymerization of the acrylamide monomer on the rubber-water interface. As a result, the polyacrylamide (PAM) molecular chains were grafted onto the surface of the rubber powder to realize hydrophilic modification. The success of the grafting modification was confirmed by FTIR, contact angle testing, and thermogravimetric analysis. The hydrophilic modified waste rubber powder was used to reinforce the PAM hydrogel. Mechanical tests showed that the tensile strength and elongation at the break of the composite hydrogel reached 0.46 MPa and 1809%, respectively, which was much higher than those of pure PAM hydrogel. Such a phenomenon indicates that the waste rubber particles had a strengthening effect.

A microwave irradiation-persulfate-formate system for achieving the detoxification and alkali-activated composite geopolymerization of the chromate-contaminated soil.

A microwave (MA) irradiation-persulfate-formate system was constructed to detoxify Cr contamination and solidify the geopolymerization of the alkali-activated composite material. Three series of experiments were correspondingly conducted to evaluate the treatment for the chromate-contaminated soil. The changes in the molar ratios of formate to persulfate and the mass rates of fortifier to soil led to a significantly greater reduction of CrVI in the detoxification experiments. The increase of blast furnace slag from 50% to 80% in the composite cementitious materials (CCM) intensified the immobilization efficiencies of chromate and the compressive strengths of geopolymer blocks. MA irradiation potentially enhanced the binding of Ca cations to the aluminosilicate compounds. The degree of reaction in the phenomenological kinetics model mathematically verified the geopolymerization process. Ettringite was formed within the structure of the geopolymer in the coupling system. Sulfate radicals released from persulfate not only contributed to the detoxification process but also strengthened the immobilization process.

Microwave irradiation coupled with zero-valent iron that enhances the composite geopolymerization of chromite ore processing residue and its mechanisms.

In this work, microwave (MW) irradiation was employed to enhance the zero-valent iron (ZVI)-dominated de-contamination of chromite ore processing residue (COPR). A coupling system and the traditional two-step procedure were both conducted to evaluate the effects of MW irradiation on the reduction and the incorporation of COPR into the composite materials-based geopolymers. The factors including the ratios of liquid to solid, the mass ratios of ZVI to COPR, and the acid dosage had some obvious influence on the reduction of COPR in the MW system. The compressive strengths of 31.54 and 41.56 MPa were determined from the two-step procedure and the coupling system at the COPR dosage of 10% (mass ratio), respectively. The employment of MW irradiation not only strengthened the formation of the geopolymer matrices but also improved the chemical stabilization of Cr species in the solidified blocks. The coupled process was more conducive to incorporating the treated COPR into the geopolymer-based crystalline microstructures compared with the subsequent usage of ZVI reduction and MW irradiation.

Hydroxyapatite nanoparticle functionalized activated carbon particle electrode that removes strontium from spiked soils in a unipolar three-dimensional electrokinetic system.

Biohazard performance of Sr radionuclide can be significantly magnified by its release from the contaminated sedimentation. In this study, hydroxyapatite nanoparticle-functionalized activated carbon electrode (AC-HAP) was synthesized and stacked to the cathode compartment of the electrokinetic (EK) system to develop a unipolar three-dimensional (3D) electrochemical process for Sr2+ removal from spiked soils. Sr2+ adsorption by AC-HAP can be fitted by the pseudo-first-order and pseudo-second-order kinetic models and the Langmuir, Freundlich, and Temkin isotherm models. The largest monolayer adsorption capacity of AC-HAP of 69.49 mg g-1 was evaluated in the pH range of 10-12 and at 40 °C. 3D EK further intensified the adsorption process of AC-HAP and the corresponding Sr2+ removal from aqueous environments. Voltage gradients and proposing time had a significant effect on the migration and transmission of Sr2+ in the electrolyzer. The influence of competitive ions on Sr2+ removal in the stock solutions followed Al3+ < Mg2+ < K+ < Na+ < Ca2+ while followed Al3+ < Na+ < K+ < Mg2+ < Ca2+ in 3D EK. The first three cycles for AC-HAP had taken roughly 50% of the reusability percentage. Sr2+ removal from spiked samples in 3D EK was achieved by acid dissolution, electromigration, and selective uptake on particle electrode.

A Degradable and Self-Healable Vitrimer Based on Non-isocyanate Polyurethane.

Developing degradable and self-healable elastomers composed of reusable resources is of great value but is rarely reported because of the undegradable molecular chains. Herein, we report a class of degradable and self-healable vitrimers based on non-isocyanate polyurethane elastomer. Such vitrimers are fabricated by copolymerizing bis(6-membered cyclic carbonate) and amino-terminated liquid nitrile rubber. The networks topologies can rearrange by transcarbonation exchange reactions between hydroxyl and carbonate groups at elevated temperatures; as such, vitrimers after reprocessing can recover 82.9-95.6% of initial tensile strength and 59-131% of initial storage modulus. Interestingly, the networks can be hydrolyzed and decarbonated in the strong acid solution to recover 75% of the pure di(trimethylolpropane) monomer. Additionally, the elastomer exhibits excellent self-healing efficiency (~88%) and fracture strain (~1,200%) by tuning the monomer feeding ratio. Therefore, this work provides a novel strategy to fabricate the sustainable elastomers with minimum environmental impact.

Room-temperature autonomous self-healing glassy polymers with hyperbranched structure.

Glassy polymers are extremely difficult to self-heal below their glass transition temperature (T g) due to the frozen molecules. Here, we fabricate a series of randomly hyperbranched polymers (RHP) with high density of multiple hydrogen bonds, which show T g up to 49 °C and storage modulus up to 2.7 GPa. We reveal that the hyperbranched structure not only allows the external branch units and terminals of the molecules to have a high degree of mobility in the glassy state, but also leads to the coexistence of "free" and associated complementary moieties of hydrogen bonds. The free complementary moieties can exchange with the associated hydrogen bonds, enabling network reconfiguration in the glassy polymer. As a result, the RHP shows amazing instantaneous self-healing with recovered tensile strength up to 5.5 MPa within 1 min, and the self-healing efficiency increases with contacting time at room temperature without the intervention of external stimuli.

Hydrogen bonding sewing interface.

The strong force that originates from breaking covalent bonds can be easily quantified through various testing platforms, while weak interfacial sliding resistance (ISR), originating from hydrogen bonding or van der Waals (vdW) forces, is very challenging to measure. Facilitated by an in-house nanomechanical testing system, we are able to precisely quantify and clearly distinguish the interfacial interactions between individual carbon fibers and several substrates governed by either hydrogen bonding or vdW forces. The specific ISR of the interface dominated by vdW forces is 3.55 ± 0.50 µN mm-1 and it surprisingly increases to 157.86 ± 44.18 µN mm-1 if the interface is bridged by hydrogen bonding. The ad hoc studies demonstrate that hydrogen bonding rather than vdW forces has great potential in sewing the interface if both surfaces are supportive of the formation of hydrogen bonds. The findings will enlighten the engineering of interfacial interactions and further mediate the entire mechanical performance of structures.

Self-recovery magnetic hydrogel with high strength and toughness using nanofibrillated cellulose as a dispersing agent and filler.

Fe3O4 nanocomposite hydrogels, with intrinsic magnetism, can be potentially applied in extensive fields. However, the poor mechanical properties and complex fabrication processes of conventional magnetic hydrogels seriously limit their advanced applications. Herein, this work demonstrates an efficient and easily industrialized method to prepare self-recovery magnetic hydrogels with excellent mechanical performances. In this method, Fe3O4 nanoparticles were facilely dispersed in polyacrylamide (PAM) hydrogels with the assistance of nanofibrillated cellulose (NFC), resulting in good magnetism. The tensile strength and elongation at break of hydrogels increase from 150 to 780 KPa, 1400% to 2960%, respectively, due to the unique network structure and the strong hydrogen bonding interaction between NFC and PAM. Moreover, the obtained hydrogels possess the satisfactory self-recovery ability, thermal stability, and shear resistance. We believe this efficient and simple method can expand the application of high-performance composite hydrogels in biological, medical and environmental fields.

Calibrating conservative and dissipative response of electrically-driven quartz tuning forks.

Determining sensor parameters is a prerequisite for quantitative force measurement. Here we report a direct, high-precision calibration method for quartz tuning fork (TF) sensors that are popular in the field of nanomechanical measurement. In the method, conservative and dissipative forces with controlled amplitudes are applied to one prong of TF directly to mimic the tip-sample interaction, and the responses of the sensor are measured at the same time to extract sensor parameters. The method, for the first time, allows force gradient and damping coefficient which correspond to the conservative and dissipative interactions to be measured simultaneously. The calibration result shows surprisingly that, unlike cantilevers, the frequency shift for TFs depends on both the conservative and dissipative forces, which may be ascribed to the complex dynamics. The effectiveness of the method is testified by force spectrum measurement with a calibrated TF. The method is generic for all kinds of sensors used for non-contact atomic force microscopy (NC-AFM) and is an important improvement for quantitative nanomechanical measurement.