Two-dimensional MXene Nanosheets Research Articles

Self-chargeable supercapacitor made with MXene-bacterial cellulose nanofiber composite for wearable devices

The development of wearable electronics is restricted by the developments of supporting energy storage devices, especially flexible supercapacitors. Nowadays, miniaturized supercapacitors based on MXenes due to their obvious advantages in the specific capacity have received extensive attention. The energy existing in the surrounding environment has been used to directly charge energy storage devices. However, the hybrid wearable electronics integrated supercapacitors are mechanically connected through metal wires leading to non-compact devices. Thus, it is urgent to develop a general and universal method to fabricate high-performance robust MXene-based flexible electrodes with high electrical conductivity and apply them to self-chargeable supercapacitors and compact wearable devices. Herein, the bacterial cellulose (BC) nanofibers are used as a crosslinking agent to connect two-dimensional MXene nanosheets through the hydrogen bond, which greatly improves the mechanical strength of MXene-bacterial cellulose (MXene-BC) composite films (Young's modulus reaching 6.8 GPa). The supercapacitors made with the electrodes of MXene-BC composite films (BC content is 10%) present high capacitance behavior (areal capacitance up to 346 mF cm−2) because the introduction of BC nanofibers increases the interlayer spacing of MXene nanosheets, providing more storage space for the ions in the electrolyte. Then, a self-chargeable supercapacitor is proposed based on the combination of a zinc-air (Zn-air) battery and a supercapacitor. The self-chargeable supercapacitor can realize self-charging after dropping a drop of electrolyte solution into the Zn-air battery. The charging voltage of a single self-chargeable supercapacitor can reach 0.6 V after adding artificial sweat as the electrolyte. Finally, a smart wristband with the function of self-charging is proposed, which can absorb the sweat generated by the human for self-chargeable supercapacitors to drive the pedometer integrated within the smart wristband to work. The proposed self-chargeable supercapacitors are simple and effective, not restricted by the use environment, providing a promising way for self-powered wearable electronics.

Flexible Piezoelectric Nanogenerator Based on Cellulose Nanofibril/MXene Composite Aerogels for Low-Frequency Energy Harvesting

Cellulose is emerging as a green and sustainable material in piezoelectric nanogenerators (PENGs) for ambient energy harvesting, although its relatively low piezoelectric coefficient still remains a challenge, hindering the potential applications. In this report, a flexible PENG with considerable energy conversion capacity was fabricated by using a polydimethylsilane (PDMS)-encapsulated cellulose nanofibril (CNF)/Ti3C2Tx (MXene) composite aerogel film, which is capable of collecting low-frequency energy such as energy from human activities. The use of two-dimensional MXene nanosheets not only optimizes the structural regularity of the CNF network but also induces a local polarization locking to align cellulosic dipoles. This strategy essentially improved the piezoelectric property of cellulose, avoiding the conventional energy consuming method (i.e., electrical poling) to strengthen piezoelectricity. Moreover, the thin layer of PDMS endows the PENG with good mechanical stability and flexibility; meanwhile, it prevents MXene from oxidizing so as to maintain its activity. The optimized CNF/MXene-PENG containing 10 wt % MXene generates a dramatically improved voltage of 30.8 V and a current of 0.49 μA. This work provides an easy and effective pathway to access cellulosic materials with enhanced piezoelectricity, aiming to approach flexible, green, and low-cost PENGs for new-generation electronics.

High-Performance Detection of Exosomes Based on Synergistic Amplification of Amino-Functionalized Fe3O4 Nanoparticles and Two-Dimensional MXene Nanosheets

Exosomes derived from cancer cells have been recognized as a promising biomarker for minimally invasive liquid biopsy. Herein, a novel sandwich-type biosensor was fabricated for highly sensitive detection of exosomes. Amino-functionalized Fe3O4 nanoparticles were synthesized as a sensing interface with a large surface area and rapid enrichment capacity, while two-dimensional MXene nanosheets were used as signal amplifiers with excellent electrical properties. Specifically, CD63 aptamer attached Fe3O4 nanoprobes capture the target exosomes. MXene nanosheets modified with epithelial cell adhesion molecule (EpCAM) aptamer were tethered on the electrode surface to enhance the quantification of exosomes captured with the detection of remaining protein sites. With such a design, the proposed biosensor showed a wide linear range from 102 particles μL-1 to 107 particles μL-1 for sensing 4T1 exosomes, with a low detection limit of 43 particles μL-1. In addition, this sensing platform can determine four different tumor cell types (4T1, Hela, HepG2, and A549) using surface proteins corresponding to aptamers 1 and 2 (CD63 and EpCAM) and showcases good specificity in serum samples. These preliminary results demonstrate the feasibility of establishing a sensitive, accurate, and inexpensive electrochemical sensor for detecting exosome concentrations and species. Moreover, they provide a significant reference for exosome applications in clinical settings, such as liquid biopsy and early cancer diagnosis.

Integrated dual-channel electrochemical immunosensor for early diagnosis and monitoring of periodontitis by detecting multiple biomarkers in saliva.

Periodontitis, as the sixth prevalence chronic inflammation worldwide, has inconspicuous and often-overlooked symptoms at early stage, eventually leading to permanent damage to the teeth and supporting tissues. The timely and accurate diagnosis of periodontitis and monitoring its progress appear to be particularly important for clinical treatment. Herein, a dual-channel electrochemical immunosensor was developed for the synchronized detection of two periodontitis-related biomarkers in saliva: interleukin-1β (IL-1β) and matrix metalloproteinase-8 (MMP-8). Owing to its miniaturization, detachability, and portability, this sensor has the potential to detect multiple biomarkers in a point-of-care manner for the early diagnosis and monitoring of periodontitis. The nanocomposites consisted of iridium oxide nanotubes and two-dimensional MXene nanosheets enhance the electrochemical performance of the sensor, achieving excellent sensitivity with wide detection ranges of 0.1-100 and 1-200ngmL-1, low limits of detection of 0.014 and 0.13ngmL-1, and relatively high correlation coefficients of 0.9911 and 0.9990 for IL-1β and MMP-8, respectively. Furthermore, this device possesses excellent selectivity in complex samples without cross-talk, as well as high recovery and accuracy in spiked artificial saliva. Importantly, the dual-channel device achieves higher diagnostic accuracy for different stages of periodontitis when MMP-8 and IL-1β were simultaneously monitored within clinicopathological saliva. This work proposes a considerable potential for early diagnosis and severity distinguishment of periodontitis in a point-of-care manner, which would be beneficial for progression prediction, treatment guidance, and prognosis assessment of periodontitis.

A Single Electronic Tattoo for Multisensory Integration.

Wearable electronics are garnering growing interest in various emerging fields including intelligent sensors, artificial limbs, and human-machine interfaces. A remaining challenge is to develop multisensory devices that can conformally adhere to the skin even during dynamic-moving environments. Here, a single electronic tattoo (E-tattoo) based on a mixed-dimensional matrix network, which integrates two-dimensional MXene nanosheets and one-dimensional cellulose nanofibers/Ag nanowires, is presented for multisensory integration. The multidimensional configurations endow the E-tattoo with excellent multifunctional sensing capabilities including temperature, humidity, in-plane strain, proximity, and material identification. In addition, benefiting from the satisfactory rheology of hybrid inks, the E-tattoos are able to be fabricated through multiple facile strategies including direct writing, stamping, screen printing, and three-dimensional printing on various hard/soft substrates. Especially, the E-tattoo with excellent triboelectric properties also can serve as a power source for activating small electronic devices. It is believed that these skin-conformal E-tattoo systems can provide a promising platform for next-generation wearable and epidermal electronics.

Electrocatalytic ammonia synthesis on Fe@MXene catalyst as cathode of intermediate-temperature proton-conducting solid oxide cell

As the only carbon-free energy carrier without CO2 emission upon decomposition, ammonia is an ideal storage medium for H2. However, the current low efficiency of ammonia synthesis is a main challenge on intermediate-temperature proton-conducting electrochemical cells. Herein, we develop a novel non-precious cathode catalyst consisting of Fe nanoparticles loaded on two-dimensional MXene nanosheets (Fe@MXene) that can achieve a high Faradaic efficiency of 8.4% and an NH3 yield of 8.24 × 10−9 mol. s−1·cm−2 on an anode-supported Ba0·95Ce0·6Tb0·1Y0·2Zr0·1O3-δ-based electrolyte. The resultant catalyst with high specific surface area and catalytic active sites is beneficial to N2 reduction, resulting from the effective activation of N2 molecules imposed by the transported protons. The mechanism of catalytic NRR reveals that Fe@MXene catalyst can increase the electrocatalytic efficiency because of the improvement in the reaction rate constant. These show a promising catalyst of Fe@MXene for N2 reduction reaction using intermediate-temperature proton-conducting solid oxide cell.

Sandwich-like heterostructured nanomaterials immobilized laccase for the degradation of phenolic pollutants and boosted enzyme stability

A novel magnetic 2D/2D heterogeneous structure MXene@NiFe-LDH@Fe3O4 was prepared for immobilization of laccase. In this work, two-dimensional MXene nanosheets with abundant surface functional groups were heterogeneously assembled with layered double hydroxide (LDH) by in situ co-precipitation method, and magnetic nanoparticle Fe3O4 with excellent biocompatibility and rapid separation of materials and substrates was introduced subsequently, and then silane coupling agent was coated on the surface of MXene@NiFe-LDH@Fe3O4. The functionalized MXene@NiFe-LDH@Fe3O4 was employed as a carrier to immobilize laccase from Trametes-Versicolor. The enzyme loading of the nanocomposite material is as high as 167.9 mg/g. Compared with free enzymes, the immobilized laccase showed a notable improvement in stability in a wider range of pHs (2.0–8.0), temperatures (25–60 °C), and organic solvent concentration (1–5 M). The reusability study suggested that after 7 cycles of repeated catalysis, the degradation efficiency could reach 55.5% for 2,4-dichlorophenol, 92.1% for bisphenol A and70.9% for pyrocatechol. The results provide a new carrier preparation strategy for the efficient immobilization of laccase.

Toughening of vinyl ester resins by two-dimensional MXene nanosheets

Toughening of vinyl ester resins by two-dimensional MXene nanosheets

Low-Temperature Photothermal Therapy Based on Borneol-Containing Polymer-Modified MXene Nanosheets.

Noninvasive photothermal therapy (PTT) is an emerging strategy for eliminating multidrug-resistant (MDR) bacteria that achieve sterilization by generating temperatures above 50 °C; however, such a high temperature also causes collateral damage to healthy tissues. In this study, we developed a low-temperature PTT based on borneol-containing polymer-modified MXene nanosheets (BPM) with bacteria-targeting capabilities. BPM was fabricated through the electrostatic coassembly of negatively charged two-dimensional MXene nanosheets (2DM) and positively charged quaternized α-(+)-borneol-poly(N,N-dimethyl ethyl methacrylate) (BPQ) polymers. Integrating BPQ with 2DM improved the stability of 2DM in physiological environments and enabled the bacterial membrane to be targeted due to the presence of a borneol group and the partially positive charge of BPQ. With the aid of near-infrared irradiation, BPM was able to effectively eliminate methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli) through targeted photothermal hyperthermia. More importantly, BPM effectively eradicated more than 99.999% (>5 orders of magnitude) of MRSA by localized heating at a temperature that is safe for the human body (≤40 °C). Together, these findings suggest that BPM has good biocompatibility and that membrane-targeting low-temperature PTT could have great therapeutic potential against MDR infections.

Fabrication of two-dimensional MXene nanosheets loading Cu nanoparticles as lubricant additives for friction and wear reduction

Herein, the MXene@Cu nanocomposites were prepared via electrostatic adsorption of Cu2+ and then in-situ reduction. The Cu2+ is uploaded on the surface of MXene nanosheets via electrostatic adsorption, which was followed by in-situ reduction with NaBH4 to obtain Cu nanoparticle attached MXene (MXene@Cu) hybrids. The results revealed that the friction coefficient of MXene@Cu decrease from 0.434 to 0.110 and the wear volume loss decreased by 88.1% via changing the loading amount of Cu nanoparticles. The excellent tribological performance of MXene@Cu is attributed to the synergistic effect of MXene nanosheets and Cu nanoparticle, which can adsorb on the surface of friction pair and induce tribochemical reaction. A stable protective film is formed on the worn surface, thereby reducing fiction and wear.

Biocompatible, stretchable, and compressible cellulose/MXene hydrogel for strain sensor and electromagnetic interference shielding

ABSTRACT With the booming growth of flexible human-computer interactions and telecommunications, it is desirable to fabricate a high-sensitivity strain sensor to monitor human movement and develop an electromagnetic interference (EMI) shielding materials to protect modern microelectronics and humans from electromagnetic damage. Herein, the biocompatible, stretchable, and compressible cellulose/MXene hydrogel has been prepared to first realize the dual-functional applications in strain sensor and EMI shielding. Two-dimensional MXene nanosheets serve as conductive sensing materials and fillers to construct conductive networks. The hydrogen bond interaction between them enhances the mechanical property of hydrogel. Benefiting from the excellent electrical conductivity and good mechanical property of the cellulose/MXene hydrogel, the resultant strain sensor displays excellent tensile strain (~144.4%), high sensitivity (gauge factor ~ -6.97), adjustable detection range (0-68.7%), fast response time (~100 ms), and great stability (~1000 cycles). It can monitor human motion, including pulse beating, speech recognition, writing sensing and pressure distribution induction of 4 × 4 sensor array platform. Moreover, the cellulose/MXene hydrogel presents an absorption-predominant EMI shielding performance in the frequency of X-band. This work provides a new inspiration for the development of multifunctional hydrogel in artificial intelligence, human-computer interaction, and EMI shielding technique.

Smart MXene/agarose hydrogel with photothermal property for controlled drug release

Smart hydrogels responsive to minimally invasive near-infrared (NIR) light have great potential in localized drug delivery for cancer treatment, but they still show some limitations such as low photothermal conversion, poor photothermal stability, and improper temperature range in biomedical applications. In this paper, the two-dimensional MXene nanosheets with high photothermal conversion efficiency as well as photothermal stability was firstly prepared, then the MXene nanosheets and the therapeutic drug were embedded in the low-melting-point agarose hydrogel network to fabricate the drug-loaded MXene/agarose hydrogel (MXene@Hydrogel). With the addition of low concentration of MXene (20 ppm), the MXene@Hydrogel could quickly rise to 60 °C under NIR irradiation and melt to release the encapsulated drugs. Importantly, the drug on/off release and the kinetics could be easily controlled with varied agarose concentration, MXene concentration, light intensity, and exposure time. In addition, the drug doxorubicin retained the anticancer activity after released from the MXene@Hydrogel network under NIR irradiation. With the excellent biocompatibility, the newly fabricated NIR-responsive MXene@Hydrogel offers a novel way for the development of smart hydrogel-based drug delivery system for localized cancer treatment.

Durable and super-hydrophilic/underwater super-oleophobic two-dimensional MXene composite lamellar membrane with photocatalytic self-cleaning property for efficient oil/water separation in harsh environments

Super-wetting membranes with outstanding permeation and anti-fouling performance are promising candidates for highly-efficient oily wastewater treatment. Herein, we designed a facile strategy to fabricate the super-hydrophilic/underwater super-oleophobic two-dimensional MXene-based composite membrane via vacuum-assisted self-assembly of two-dimensional MXene nanosheets on porous polyvinylidene fluoride (PVDF) substrate and in situ mineralization of photocatalyst β-FeOOH on the membrane surface. Benefiting from the inherent super-wettability and regulated lamellar structure (Short transport pathway and abundant nanochannels), the resultant MXene-based composite membrane displayed fast permeation flux (500.38–1022.7 L m−2 h−1) and favorable separation efficiency (99.32–99.72%) for a series of micro-scaled oil-in-water emulsions. Importantly, the excellent photo-induced self-cleaning capability and low oil-adhesion contributed to the high anti-fouling resistance, outstanding reusability, and durability of 2D MXene composite membrane. Moreover, the 2D MXene composite membrane exhibited superior chemical stability, which enabled it to maintain highly efficient oil/water separation performance in high-temperature, high salty, and strongly corrosive conditions. This work provides a feasible route to fabricate durable super-wetting 2D membranes with photo-Fenton self-cleaning capability for the oily wastewater treatment in harsh environments.

Tuning functional two-dimensional MXene nanosheets to enable efficient sulfur utilization in lithium-sulfur batteries

Practicality of lithium-sulfur batteries is severely hindered by the notorious polysulfide-shuttle phenomenon, leading to rapid capacity fade. This issue is aggravated with increase in sulfur loading, causing low-coulombic efficiency and cycle life. Herein, we present a facile strategy to combine hydrophobic sulfur and hydrophilic, conductive Ti 3 C 2 T z -MXene via one-step surface functionalization using di(hydrogenated tallow)benzylmethyl ammonium chloride (DHT). The latter renders the Ti 3 C 2 T z surface hydrophobic, making it readily dispersible in sulfur dissolved in a carbon disulfide (CS 2 ) solvent. By evaporating the solvent, we conformally coat the DHT-Ti 3 C 2 T z (DMX) with sulfur. The developed composite, with higher available active area, enables effective trapping of lithium polysulfides (LiPs) on the electroactive sites within the cathode, leading to improvement in electrochemical performance at higher sulfur loadings. The DMX/S cathodes function with high sulfur loading of ∼10.7 mg·cm −2 and deliver a stable areal capacity of ∼7 mAh·cm −2 for 150 cycles. Moreover, a DMX/S cathode in a pouch-cell configuration retains ∼770 mAh·g −1 after ∼200 cycles at 0.2C (85.5% retention). Ex situ studies elucidate the nature of the LiPs-MXene interaction and the effect of surface functionalization towards improved performance. DHT functionalized hydrophobic MXenes (DMX) form a stable colloidal solution in CS 2 Atomically thin, metallically conductive DMX improves sulfur utilization in composites DMX/S cathode delivers good cycling stability at a high sulfur loading of 10.7 mg·cm −2 Emphasis on cathode development, pouch-cell performance, and nature of the interactions Rechargeable lithium-sulfur (Li-S) batteries have the potential to replace lithium-ion batteries because of their higher specific energy. Pai et al. report a surface fictionalization strategy to enable maximum sheet-surface area use of 2D-MXenes in Li-S batteries, which enables high sulfur loading, capacity retention, and long cycle life.

Fluorescent nitrogen-doped Ti3C2 MXene quantum dots as a unique “on-off-on” nanoprobe for chrominum (VI) and ascorbic acid based on inner filter effect

The MXene quantum dots (MQDs) derived from two-dimensional MXene nanosheets is a kind of rising-star nanomaterial recently, exhibiting important applications in many fields, while the investigation of element-doping MQDs with better performances for chem/biosensing is jut beginning. In this work, by cutting Ti3C2 MXene nanosheets with a simple method, we synthesized firstly nitrogen-doping Ti3C2 MQDs (N-Ti3C2 MQDs) which displays remarkable excitation-dependent photoluminescence and photobleaching resistance. Interestingly, the fluorescence of N-Ti3C2 MQDs can be quenched by chromium (VI) (Cr(VI)) owing to the existence of Inner filter effect and static quenching, triggering a fluorescent “on-off” signal; on account of the oxidation-reduction reaction between ascorbic acid (AA) and Cr(VI), the related fluorescence of N-Ti3C2 MQDs can be further recovered in the presence of AA, inducing an “off-on” fluorescence response. Thus, N-Ti3C2 MQDs was then used as nanoprobe for the fluorescent detection of Cr(VI) and AA, and the developed sensing method was verified to possess great sensitivity with the wide linear ranges from 0.1–500.0 μM toward both Cr(VI) and AA as well as low detection limits of 0.012 μM for Cr(VI) and 0.02 μM for AA. Furthermore, the investigation about the selectivity and practical application demonstrated N-Ti3C2 MQDs has important actual values for Cr(VI) and AA sensing.

The MXene/water nanofluids with high stability and photo-thermal conversion for direct absorption solar collectors: A comparative study

The efficient utilization of solar energy is a prominent problem in the field of energy in today’s society. The judicious combination of nanofluid and direct absorption solar collector (DASC) is one of the effective ways to solve this problem. Two-dimensional nanomaterials have attracted significant research attentions because of their unique optical and thermophysical properties. In this paper, two-dimensional MXene nanosheets were prepared by in-situ etching. Then different concentrations (5, 10, 20, 40, 60 ppm, respectively) of MXene and graphene nanofluids were obtained by two-step method. The optical and thermal conductivity of the two nanofluids were further tested. The MXene nanofluids exhibited advanced optical properties due to the LSPR effect of MXene nanosheets, but the graphene nanofluids had higher thermal conductivity. When the concentration was 20 ppm, the photothermal conversion efficiency of MXene nanofluids reached a maximum of 63.35%, which was 4.34% higher than that of graphene nanofluids. Finally, through the analysis of local conversion efficiency, the working conditions of DASC were further optimized.

High-performing composite membrane based on dopamine-functionalized graphene oxide incorporated two-dimensional MXene nanosheets for water purification

With unique structural and physicochemical properties, the upcoming two-dimensional (2D) materials have become promising candidates for the design and fabrication of high-performance membranes. In this work, for the first time, the dopamine-functionalized graphene oxide (DGO) nanosheets were intercalated into the MXene (Ti3C2Tx) nanosheets, and subsequently, a series of novel DGO/MXene composite membranes were prepared via vacuum filtration on hydrophilic polyvinylidene fluoride (PVDF) membranes as the support layer. The effect of mass ratios between DGO and MXene on the resulting membrane structure and overall performances were systematically investigated in detail. Incorporation of DGO increased the mechanical stability of composite membrane, but reduced its interlayer spacing. The most suitable composite membrane, M4 (MXene: DGO = 1:2) with nearly 2 µm thickness of functional layer, exhibited an excellent dye rejection ratio 98.1% (for Direct Red 28) and 96.1%( for Direct Black 38) as along with a high value of water flux (63.5 Lm−2 h−1) at a pressure of 0.1 MPa, compared with the pure MXene and DGO membranes. Furthermore, molecular dynamics (MD) simulation indicated that the permeation rate of water molecules across the active layer was directly determined by the interlayer spacing of nanosheets. Additionally, composite membrane M4 displayed a relatively low rejection ratio of differently charged salts (9.7% for Na+) and (4.3% Mg2+).

Multi-dimensional hierarchical CoS2@MXene as trifunctional electrocatalysts for zinc-air batteries and overall water splitting

The demanding all-in-one electrocatalyst system for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in zinc-air batteries or water splitting requires elaborate material manufacturing, which is usually complicated and time-consuming. Efficient interface engineering between MXene and highly active electrocatalytic species (CoS2) is, herein, achieved by an in situ hydrothermal growth and facile sulfurization process. The CoS2@MXene electrocatalyst is composed by one-dimensional CoS2 nanowires and two-dimensional MXene nanosheets, which lead to a hierarchical structure (large specific surface area and abundant active sites), a spatial electron redistribution (high intrinsic activity), and high anchoring strength (superior performance stability). Therefore, the electrocatalyst achieves enhanced catalytic activity and long-time stability for ORR (a half-wave potential of 0.80 V), OER (an overpotential of 270 mV at 10 mA cm−2, i.e., η10 = 270 mV) and HER (η10 = 175 mV). Furthermore, the asymmetry water splitting system based on the CoS2@MXene composites delivers a low overall voltage of 1.63 V at 10 mA cm−2. The solid-state zinc-air batteries using CoS2@MXene as the air cathode display a small charge-discharge voltage gap (0.53 V at 1 mA cm−2) and superior stability (60 circles and 20-h continuous test). The energy interconversion between the chemical energy and electricity can be achieved by a self-powered system via integrating the water splitting system and quasi-solid-state zinc-air batteries. Supported by in situ Raman analyses, the formation of cobalt oxyhydroxide species provides the active sites for water oxidation. This study paves a promising avenue for the design and application of multifunctional nanocatalysts.

Catalytic oxidation of naproxen in cobalt spinel ferrite decorated Ti3C2Tx MXene activated persulfate system: Mechanisms and pathways

Naproxen (NPX) is a nonsteroidal anti-inflammatory drug that, at concentrations of 20 ng/L to several µg/L in aqueous environments, can cause detrimental effects to human and ecosystem health. A heterogeneous nanocatalyst composed of two-dimensional MXene nanosheets functionalized with CoFe2O4 nanoparticles was fabricated by liquid self-assembly for the activation of persulfate (PS) to degrade NPX. Approximately 99.1% of NPX was degraded within 90 min with the addition of 0.5 mM PS at 1 g/L of CoFe2O4@MXene dosage. To better understand the removal process, different influencing parameters, including the solution pH, catalyst dosage, and PS concentration, during NPX removal were studied. Radical scavenging and electron spin resonance experiments revealed that both radical (i.e., O2−, OH, SO4−, and S2O8−) and nonradical (i.e., 1O2) pathways were involved in the catalytic degradation of NPX. The results suggest that CoFe2O4@MXene/PS is a promising catalytic system for the treatment of water polluted with NPX.

Oxygen vacancies-enriched sub-7 nm cross-linked Bi2.88Fe5O12- nanoparticles anchored MXene for electrochemical energy storage with high volumetric performances

Abstract To improve the structure stability and accelerate electrochemical reaction kinetics, oxygen vacancies-enriched sub-7 nm Bi2.88Fe5O12-x nanoparticles with high electrochemical activity have been elaborately anchored on two-dimensional MXene nanosheets through a facile electrostatic assembly approach for electrochemical energy storage. MXene nanosheets could not only effectively buffer the serious volume change of Bi2.88Fe5O12-x nanoparticles but also facilitate fast electron transfer as a flexible, well-conductive but robust substrate in the fast charge/discharge processes. Owing to the three-dimensional distinct structure and the strong synergistic effects between MXene and Bi2.88Fe5O12-x nanoparticles, the obtained composite exhibits impressive electrochemical performances. The composite electrode possesses high gravimetric specific capacity of 176 mAh g−1 with ultrahigh volumetric specific capacity of 476 mAh cm−3 at 0.5 A g−1 in an aqueous electrolyte, superior to those of the so-far reported Bi2O3-based electrode materials. In addition, our fabricated asymmetric device displays a high volumetric energy density of 177 Wh L−1 and remarkable cycling performance with 93.3% retention ratio after 10,000 cycles. Moreover, the resultant MXene/Bi2.88Fe5O12-x composite presents high reversible specific capacity of 805 mAh g−1 for Li-ion storage, corresponding to the volumetric specific capacity of 2176 mAh cm−‍3.