Enhancing the electrochemical conversion of carbon dioxide to value-added products on zinc oxide-MXene nanocomposite

Developing efficient and sustainable catalysts for CO2 electroreduction is critical to addressing the rising atmospheric CO2 levels and mitigating climate change. This study presents a novel ZnO-MXene (Ti2C) nanocomposite as a high-performance electrocatalyst for CO2 conversion, offering a strategic approach for generating valuable carbon-based feedstocks. The ZnO-MXene nanocomposites were synthesized via the wet impregnation method and comprehensively characterized using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). Electrochemical performance was assessed through linear sweep voltammetry (LSV), cyclic voltammetry (CV), and controlled potential coulometry, with gas chromatography employed for product quantification. ZnO-MX10 and ZnO-MX2.5 exhibited high selectivity for CH4 (79.3 % Faradaic efficiency, FE) at -0.56 VRHE and CO (76.8 % FE) at -0.78 VRHE, while significantly suppressing competing H2 evolution. The synergistic interaction between ZnO and MXene enhances charge transfer, increases active sites, and improves surface area, leading to superior electrochemical performance. Overall, this work introduces a novel ZnO-MXene nanocomposite with dual selectivity for CO and CH4, enhanced electroactive surface, and long-term stability. Unlike conventional Zn-based catalysts, which exhibit either limited selectivity or rapid degradation, our composite achieves 79.3 % Faradaic efficiency for CH4 and 76.8 % for CO, while suppressing H2 evolution. This unique tunability and stability make ZnO-MXene an attractive alternative to noble metal-based electrocatalysts.

Experimental and Computational Study on U(VI) Sorption Mechanisms of Single-Layered Ti3C2TX Nanosheets

Environmental contamination by U(VI) from radioactive wastewater has become a challenging concern in the development of nuclear energy. A highly efficient recovery of U(VI) from wastewater is essential for environmental remediation and can mitigate the depletion of conventional uranium resources. This study describes the synthesis of single-layered Ti3C2TX nanosheets by chemical exfoliation using ultrasonography. The single-layered structure promoted a high sorption capacity of 3.20 mmol/g for U(VI) (distribution constant Kd > 104 mL/g) and excellent selectivity in mine wastewater that contained numerous coexisting ions. Fragmentation of the Ti3C2TX nanosheets from micron-scale to nanoscale upon uranyl sorption was detected by small-angle X-ray scattering and transmission electron microscopy. Extended X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations demonstrated that uranyl groups coordinated with the terminal -OH and -F on the surface of the Ti3C2TX nanosheets. These findings provide imperative insights into the design and application of nanomaterials to effectively treat uranium-contaminated wastewater.

The potential of Ti3C2Tx-KH2PO4 and Ti3C2Tx-chitosan in the efficient removal of cesium from nuclear wastewater

Ti3C2Tx is synthesized from Ti3AlC2 by two common methods, HF and HF in situ. The synthesis approach is very practical regarding the structure, morphology, space between layers, type and number of surface-active sites and its specific surface. XRD, SEM, EDS, FTIR and BET analyzes were used to investigate the structure, morphology, type and number of surface-active sites. Under the operating conditions of cesium initial concentration ~ 150 ppm, ambient temperature, pH ~ 7.00 and time of 60 min, the cesium adsorption intensity with Ti3C2Tx-HF and Ti3C2Tx-HF in situ was obtained as 194 and 219.5 mg.g- 1, respectively. The structural results of modification with KH2PO4 show that in this modification, in addition to the increase of hydroxyl functional groups, the distance between the layers has also increased and the cesium adsorption intensity has increased to 338.75 mg.g- 1 under the above operating conditions. Meanwhile, in modification with Chitosan by increasing the frequency of functional groups and specific surface up to 3 times the effective specific surface of Ti3C2Tx-HF in situ, no significant change in the cesium adsorption intensity has been observed (247.5 mg.g- 1). Experiments were conducted to evaluate the effect of parameters of initial concentration of Cs+ (250 - 50 ppm), time (30-60 min), ambient temperature (298.15-318.15 K), solution pH (3.0-11.0) with the help of RSM design. RSM results show that the pH parameter is one of the most important parameters affecting the cesium adsorption intensity with Ti3C2(OH)x and Ti3C2(OH)x-KH2PO4. Also, with the increase in temperature, the adsorption intensity should increase. It is shown in the isotherm modeling that R2 matches well with the Freundlich isotherm model, which is based on the layered structure of Ti3C2(OH)x and Ti3C2(OH)x-KH2PO4 and the presence of active sites with different energy levels, which leads to heterogeneous adsorption. The consistency will be of the adsorbent selectivity investigation shows that the Cs+ hydration radius plays a decisive role in its high adsorption potential. Reduction of MXene by 0.1 M HCl was carried out in 3 steps. The experimental results show that 15% absorption has been achieved in the third stage. The results of structural analysis show that its structure has not changed and the reduction of active sites as a result of washing with acid has led to a decrease in adsorption.

Experimental exploring of Ti3C2Tx MXene for efficient and deep removal of magnesium in water sample

In this work, the mechanism and behaviour of magnesium adsorption with Ti3C2Tx adsorbent is investigated. Ti3C2Tx was synthesized by selective exfoliation of Al layer from Ti3AlC2 using acidic solutions of HF 40% and 12 M LiF/ 9 M HCl. The effect of the synthesis method on the structure, the interlayer distance, the type and abundance of the functional groups, the bonds formed, the surface area and the volume of the formed cavities were evaluated by X-ray diffraction, scanning electron microscopy, Energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller and fourier transform infrared analyses. The preliminary discontinuous tests of magnesium adsorption with Ti3C2Fx and Ti3C2(OH)x in 100 ppm concentration, pH ~ 7.00, ambient temperature and time of 3 h show 182.5 and 99 mg.g-1 the adsorption intensity, respectively. The difference in adsorption intensity with Ti3C2Fx is the result of the extensive tendency of Mg2+ to conduct electrochemical reactions with F- twice as much as OH- functional groups. By designing the RSM experiment, analytical, qualitative, optimization and modelling of the magnesium adsorption process with Ti3C2Fx adsorbent was carried out with the input variables of magnesium concentration, pH, ambient temperature and time. Isothermal modelling shows the agreement of the experimental results with the Langmuir model and endothermic thermodynamic modelling shows the spontaneity of the adsorption reaction. MXene adsorption-desorption with 0.1 M HCl was done in up to 4 steps. The adsorption results show that Ti3C2Fx can show up to 15% initial adsorption intensity by maintaining stability in up to 4 adsorption-desorption steps.

Cesium adsorption from an aqueous medium for environmental remediation: A comprehensive analysis of adsorbents, sources, factors, models, challenges, and opportunities

Considering the widespread and indispensable nature of nuclear energy for future power generation, there is a concurrent increase in the discharge of radioactive Cs into water streams. Recent studies have demonstrated that adsorption is crucial in removing Cs from wastewater for environmental remediation. However, the existing literature lacks comprehensive studies on various adsorption methods, the capacities or efficiencies of adsorbents, influencing factors, isotherm and kinetic models of the Cs adsorption process. A bibliometric and comprehensive analysis was conducted using 1179 publications from the Web of Science Core Collection spanning from 2014 to 2023. It reviews and summarizes current publication trends, active countries, adsorption methods, adsorption capacities or efficiencies of adsorbents, tested water sources, influencing factors, isotherm, and kinetic models of Cs adsorption. The selection of suitable adsorbents and operating parameters is identified as a crucial factor. Over the past decade, due to their notable capacity for Cs adsorption, considerable research has focused on novel adsorbents, such as Prussian blue, graphene oxide, hydrogel, and nanoadsorbents (NA). However, there remains a need for further development of application-oriented laboratory-scale experiments. Future research directions should encompass exploring adsorption mechanisms, developing new adsorbents or their combinations, practical applications of lab-scale studies, and recycling radioactive Cs from wastewater. Drawing upon this literature review, we present the most recent research patterns concerning adsorbents to remove Cs, outline potential avenues for future research, and delineate the obstacles hindering effective adsorption. This comprehensive bibliometric review provides valuable insights into prevalent research focal points and emerging trends, serving as a helpful resource for researchers and policymakers seeking to understand the dynamics of adsorbents for Cs removal from water.

Enhancing Cr(vi) removal performance of Ti3C2T x through structural modification by using a spray freezing method

Structural modification is expected to be a facile way to enhance the adsorption performance of MXene. In this work, the structural modification of Ti3C2T x was carried out by a spray freezing method, and two kinds of nano-structure (spherical and flaky) of Ti3C2T x were prepared by adjusting the solution concentration of Ti3C2T x . Then the Cr(vi) adsorption capacity and removal efficiency of the spherical and flaky Ti3C2T x was investigated, respectively. It is found that flaky Ti3C2T x was produced with a Ti3C2T x concentration of 3 mg mL-1, while spherical Ti3C2T x was obtained with a concentration of 6 mg mL-1. The long diameter of flaky Ti3C2T x is about 8-10 μm, and the specific surface area is 17.81 m2 g-1. While spherical Ti3C2T x had a diameter of about 1-4 μm and a specific surface area of 17.07 m2 g-1. The optimized structure of flaky and spherical Ti3C2T x improves the maximum adsorption capacity by 97% and 33%, respectively, compared with the few-layer Ti3C2T x . The maximum adsorption capacity of flaky Ti3C2T x was 928 mg g-1, while that of spherical Ti3C2T x was 626 mg g-1. The adsorption capacity of both Ti3C2T x structures decreased with the increase of pH, and reached the maximum value at pH = 2; meanwhile, the adsorption capacity of both Ti3C2T x structures increased with the increase of Cr(vi) concentration. The adsorption of Cr(vi) on flaky Ti3C2T x was very fast, reaching equilibrium in 3 min, while spherical Ti3C2T x took 5 min. The adsorption of Cr(vi) on both Ti3C2T x structures belonged to the monolayers, heat-absorbing chemical adsorption, and the diffusion process of Cr(vi) was regulated by the external diffusion and internal diffusion of particles. Its adsorption mechanism was the combination of reductive adsorption and electrostatic adsorption.

Effective radioactive strontium removal using lithium titanate decorated Ti3C2Tx MXene/polyacrylonitrile beads

A lithium titanate-decorated Ti3C2Tx MXene (LTO-MX) composite was synthesized through etching and alkali processes, and subsequently immobilized using polyacrylonitrile (PAN) polymer via a phase inversion method. In the batch study, the strontium adsorption behavior followed the Redlich-Peterson isotherm and the pseudo-second-order kinetic models. The maximum adsorption capacity for strontium reached 24.05 mg/g. Furthermore, a continuous fixed-bed column study was performed using the LTO-MX PAN beads to remove strontium from aqueous solutions. The dynamic behavior of column adsorption was examined under various operating parameters such as initial strontium concentration, flow rate, and bed height. Dynamic modeling was employed to describe adsorption breakthrough properties based on these experimental data. Both the Thomas and Yoon-Nelson models accurately simulated the breakthrough curves. The proposed mechanisms for strontium adsorption included encapsulation, electrostatic attraction, cation exchange, and surface complexation. These results demonstrate the effectiveness of LTO-MX PAN beads as adsorbents for the continuous removal of strontium from radioactive wastewater.

Modification of Ti3C2Tx nanostructure with KH2PO4 and chitosan for effective removal of strontium from nuclear waste

Nanostructure titanium carbide MXene (Ti3C2Tx) was modified with KH2PO4 and chitosan to effectively remove strontium from nuclear wastewater. Nuclear waste includes radionuclides of uranium, thorium, strontium, and cesium, which are classified depending on the concentration of radionuclides. Nuclear waste with a high strontium concentration is the production waste of radiopharmaceutical production centers. Ti3C2Tx was synthesized from Ti3AlC2 using HF40% and HF in situ (MILD-Ti3C2Tx) in 24 h at 313.15 and 333.15 K. Morphology, structure, and functional groups were investigated using the XRD, SEM, EDS, FTIR, and BET analyses. The Sr(II)'s adsorption capacity on Ti3C2Tx-HF and Ti3C2Tx-HF in situ was obtained as 61.9 and 253.5 mg g-1, respectively (temperature, 298.15 K; pH, 7.00; contact time, 180 min; and Sr(II) concentration, 150 mg l-1). Ti3C2Tx-HF in situ showed fourfold adsorption due to more hydroxyl functional groups and larger interlayer spacing. Ti3C2Tx was modified with KH2PO4 and chitosan to investigate the mechanism of change of Sr(II)'s adsorption capacity, which increased to 370 and 284 mg g-1, respectively. The structural results of modified Ti3C2Tx showed that the surface functional groups increased when modified with chitosan. In addition, modification with KH2PO4, through encapsulating large amounts of KH2PO4 between Ti3C2Tx layers, increased the possibility of Sr(II) diffusion between layers and electrochemical interactions with hydroxyl groups, and thus, increased its adsorption. Some experiments were designed to investigate the effect of parameters like initial concentration of Sr(II), contact time, temperature, and pH solution, as well as modified- and unmodified-Ti3C2Tx on adsorbent. The results revealed that the adsorption process of Sr(II) with pristine and modified-Ti3C2Tx follows pseudo-second-order kinetics and Freundlich heterogeneous isotherm model. Freundlich model isotherm indicates the presence of various functional groups on the surface and between the pristine and modified Ti3C2Tx layers. Electrostatic reactions and intra-sphere complexation were the two dominant mechanisms of the adsorption process.

Molten salt synthesis of MXene-derived hierarchical titanate for effective strontium removal

The removal and recovery of radioactive Sr(II) from wastewater and seawater has been of great concern due to the negative environmental impacts of nuclear energy development and the potential risk of nuclear accidents. Herein, a facile molten salt synthesis strategy was developed to systematically investigated the reaction of different types of MXenes with nitrates. Among the products, K+ intercalated hierarchical titanate nanostructures (K-HTNs) obtained from the direct chemical transformation of multilayered Ti3C2Tx exhibited unique layered structures, good physicochemical properties, and outstanding adsorption performance for Sr(II). The maximum adsorption capacity of Sr(II) by K-HTNs reached 204 mg·g-1 at ambient temperature, and the good regeneration and reusability of the titanate was also demonstrated. K-HTNs showed preferential selectivity for Sr(II) in different environmental media containing competing ions, and the removal efficiency of Sr(II) in real seawater was as high as 93.3 %. The removal mechanism was elaborated to be the exchange of Sr2+ with K+/H+ in the interlayers of K-HTNs, and the adsorbed Sr(II) had a strong interaction with Ti-O- termination on the titanate surface. Benefiting from the merits of rapid and scalable synthesis and excellent adsorption performance, MXene-derived K-HTNs have broad application prospects for the purification of 90Sr-contaminated wastewater and seawater.

MXene nanosheet-derived N, S-codoped graphene quantum dots for ultrasensitive and selective detection of 3-nitro-l-tyrosine in human serum

3-Nitro-l-tyrosine (3NT) is an oxidative stress metabolite associated with neurodegenerative diseases such as Parkinson's disease and rheumatoid arthritis. In this study, the N, S-co-doped graphene quantum dots (NSGQDs) derived from nitrogen-doped Ti3C2Tx MXene nanosheet via the hydrothermal method in the presence of mercaptosuccinic acid was synthesized as an optical sensing probe to detect 3NT in human serum. Tetramethyl ammonium hydroxide, the nitrogen source and delamination agent, was used to prepare nitrogen-doped MXene nanosheets via one step at room temperature. The as-prepared NSGQDs are uniform with an average size of 1.2 ± 0.6 nm, and can be stable in aqueous solution for at least 90 d to serve as the fluorescence probe. The N atoms in N-MXene reduce the restacking and aggregation of MXene nanosheets, while the sulfur dopant in NSGQDs increases the quantum yield from 6.2 to 12.1 % as well as enhances the selectivity of 3NT over the other 12 interferences via coordination interaction with nitro group in 3NT. A linear range of 0.02-150 μM in PBS and 0.05-200 μM in human serum with a recovery of 97-108 % for 3NT detection is observed. Moreover, the limit of detection can be lowered to 4.2 and 7 nM in PBS and 1 × diluted human serum, respectively. Results obtained clearly indicate the potential application of the N-Ti3C2Tx derived NSGQD for effective detection of 3NT, which can open a window for the synthesis of doped GQDs via 2D MXene materials for ultrasensitive and selective detection of other biometabolites and biomarkers of neurodegenerative diseases in biological fluids.

MXenes as emerging adsorbents for removal of environmental pollutants

MXenes are a recently emerging class of two-dimensional nanomaterials that have gained considerable interest in the field of environmental protection. Owing to their high surface area, abundant terminal groups, and unique two-dimensional layered structures, MXenes have demonstrated high efficacy as adsorbents for various pollutants. Here we focused on the latest developments in the field of MXene-based adsorbents, including the structure and properties of MXenes, their synthesis and modification methods, and their adsorption performance and mechanisms for various pollutants. Among the pollutants that have been reported to be adsorbed by MXenes are radionuclides (U(VI), Sr(II), Cs(I), Eu(III), Ba(II), Th(IV), and Tc(VII)/Re(VII)), heavy metals (Hg(II), Cu(II), Cr(VI), and Pb(II)), dyes, per- and polyfluoroalkyl substances (PFAS), antibiotics (tetracycline, ciprofloxacin, and sulfonamides), antibiotic resistance genes (ARGs), and other contaminates. Moreover, future directions in MXene research are also suggested in this review.

Recent strategies, progress, and prospects of two-dimensional metal carbides (MXenes) materials in wastewater purification: A review

With the rapid development of industrialization, water pollution directly leads to the serious shortage of fresh water. As reported by the World Water Council, nearly 3.8 billion people will face water scarcity by 2030. Therefore, developing advanced nanomaterials to realize wastewater purification is a major challenge. Two-dimensional (2D) transition metal carbides (MXenes), as the emerging 2D layered nanomaterials, have been investigated for the applications of water purification treatment since first reported in 2011. Over 40 different MXenes have been developed for environmental remediation, and dozens more structures and properties are theoretically predicted. Here, we review the advances from the aspects of synthesis strategies for MXenes, purification mechanism, and their applications in wastewater treatment processes. The major points are 1) the synthesis and modification approaches for MXenes such as multi-layered stacked MXenes and delaminated MXenes 2) a discussion of current water remediation over MXene-based materials, 3) a brief introduction for removal behaviors and deep interaction mechanisms, 4) optimization strategies and key points for boosting the remediation performance of MXenes.

β-Cyclodextrin-Stabilized CuO/MXene Nanocomposite as an Electrode Material for High-Performance Supercapacitors

Supercapacitors are the best energy storage systems due to their high power density, quick charge/discharge rate, and long-term reliability. In this study, β-cyclodextrin-stabilized CuO nanoparticles (CuO@βCD NPs) were synthesized through a simple reduction method and anchored on the surface of MXene nanosheets in three different proportions (1:1, 4:1, and 1:4) to obtain CuO@βCD/MXene nanocomposites through the wet-impregnation method. The formation of CuO@βCD NPs and their physicochemical characteristics were verified by XRD, XPS, FE-SEM, and HR-TEM analysis. The actual focus is on the evaluation of the electrochemical performances of CuO@βCD, MXene, and CuO@βCD/MXene nanocomposites for supercapacitor applications. The cyclic voltammetry and galvanostatic charge-discharge analysis revealed the pseudocapacitance and an improved specific capacitance of 1693.43 F g-1 at 0.90 A g-1 for the CuO@βCD/MXene (1:1) nanocomposite. The electrochemical impedance analysis displays superior electrical conductivity with a low charge transfer resistance value on incorporating CuO@βCD between the MXene layers. Furthermore, the CuO@βCD/MXene (1:1) nanocomposite exhibited improved long-term cycling stability by retaining 86% of its initial specific capacitance even after the 10,000th cycle at the current density of 4.54 A g-1. Based on the electrochemical performance, the CuO@βCD/MXene (1:1) nanocomposite proves its suitability as an electrode material for supercapacitor application with long-term cycling stability and rate capability.

A label-free electrochemical biosensor based on PBA-Au-MXene QD for miR-122 detection in serum samples

A poly(n-butyl acrylate)-gold-MXene quantum dots (PBA-Au-MXene QD) nanocomposite-based biosensor is presented that is modified by unique antisense single-stranded DNA (ssDNA) and uses the electrochemical detection methods of DPV, CV, and EIS to early detect miR-122 as a breast cancer biomarker in real clinical samples. This fabrication method is based on advanced nanotechnology, at which a poly(n-butyl acrylate) (PBA) as a non-conductive polymer transforms into a conductive composite by incorporating Au-MXene QD. This biosensor had a limit of detection (LOD) of 0.8 zM and a linear range from 0.001 aM to 1000 nM, making it capable of detecting the low concentrations of miR-122 in patient samples. Moreover, it allows approximately 100% sensitivity and 100% specificity for miR-122 without extraction. The synthesis and detection characteristics were evaluated by different complementary tests such as AFM, FTIR, TEM, and FESEM. This new biosensor can have a high potential in clinical applications to detect breast cancer early and hence improve patient outcomes.

Cation-Intercalated Lamellar MoS2 Adsorbent Enables Highly Selective Capture of Cesium

Highly selective capture of cesium (Cs+) from complex aqueous solutions has become increasingly important owing to its (133Cs) indispensable role in some cutting-edge technologies and the environmental mobility of radioactive nuclide (137Cs) from nuclear wastewater. Herein, we report the development of cation-intercalated lamellar MoS2 as an effective Cs+ adsorbent with the advantages of facile synthesis and highly tunable layer spacing. Two types of cations, including Na+ and NH4+, were employed for the intercalations between adjacent layers of MoS2. The results demonstrated that the adsorption capacity of the NH4+-intercalated material (M-NH4+, 134 mg/g) for Cs+ clearly outperformed the others due to higher loading percentages of cations and larger layer spacing. The cesium partition coefficients for M-NH4+ in the presence of 100-fold competing ions all exceed 1 × 103 mL/g. A simulated complex aqueous solution containing 15.37 mg/L Cs+ and highly excess of competing ions Li+, Na+, K+, Mg2+, and Ca2+ (20-306 times higher) was introduced to prove the practical application potential using our best-performing M-NH4+, showing a good to excellent partition ability of Cs+ among other cations, especially for Cs/K and Cs/Na with separation factors of 58 and 212, respectively. The adsorption and selectivity mechanisms were clearly elucidated using various advanced techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. These results revealed that the good selectivity for Cs+ can be ascribed to the differences in Lewis acidities, hydration energy, cation sizes, and in particular, the divergence of coordination modes which was successfully achieved after tuning the layer distance via the cation intercalation strategy. In addition, the material has fast kinetics (<30 min), wide range of pH tolerance (4-10), and good reusability. Overall, our studies point out that the tunable lamellar MoS2-based materials are promising adsorbents for Cs+ capture and separation.

Hydrophilic magnetic Ti3C2Tx-based nanocomposite as an efficient boron adsorbent: Synthesis, characterization, and application

It is widely recognized that wastewater containing boron is an environmental issue. Therefore, the development of adsorbents with excellent adsorption capacity, stability, and recyclability is essential in water treatment applications. A Fe3O4/PDA/Ti3C2Tx/PEI/DHHA nanocomposite has been prepared that can be used to separate and recover boric acid by adjusting the pH of the solution, based on the affinity theory of boric acid and cis-diol. Through series characterization, it was determined that the adsorbent possessed good magnetic properties, high hydrophilicity and high loading capacities. In this study, 4-formylphenylboronic acid (FPBA) was selected as the model compound. The nanocomposite exhibited an adsorption equilibrium time of 10 h and an adsorption capacity of 98.99 mg/g at pH = 8.5 and 25 °C. The Langmuir isothermal model and the quasi-secondary kinetic model are both appropriate for describing the adsorption process. Thermodynamic results suggest that adsorption is a spontaneous chemisorption process. Furthermore, the nanocomposite retains good regeneration performance after five adsorption-desorption cycles.

Can MXene be the Effective Nanomaterial Family for the Membrane and Adsorption Technologies to Reach a Sustainable Green World?

Environmental pollution has intensified and accelerated due to a steady increase in the number of industries, and exploring methods to remove hazardous contaminants, which can be typically divided into inorganic and organic compounds, have become inevitable. Therefore, the development of efficacious technology for the separation processes is of paramount importance to ensure the environmental remediation. Membrane and adsorption technologies garnered attention, especially with the use of novel and high performing nanomaterials, which provide a target-specific solution. Specifically, widespread use of MXene nanomaterials in membrane and adsorption technologies has emerged due to their intriguing characteristics, combined with outstanding separation performance. In this review, we demonstrated the intrinsic properties of the MXene family for several separation applications, namely, gas separation, solvent dehydration, dye removal, separation of oil-in-water emulsions, heavy metal ion removal, removal of radionuclides, desalination, and other prominent separation applications. We highlighted the recent advancements used to tune separation potential of the MXene family such as the manipulation of surface chemistry, delamination or intercalation methods, and fabrication of composite or nanocomposite materials. Moreover, we focused on the aspects of stability, fouling, regenerability, and swelling, which deserve special attention when the MXene family is implemented in membrane and adsorption-based separation applications.

MXenes - Versatile 2D materials for identification of biomarkers and contaminants in large scale environments - A review

Recent years have seen a lot of interest in transition metal carbides/carbonitrides (MXenes), Which is one of newly proliferating two-dimensional (2D) materials.The advantages and applications of synthesizing MXenes-based biosensing systems are interesting. There is an urgent requirement for synthesis of MXenes. Through foliation, physical adsorption, and interface modification,it has been proposed that many biological disorders are related to genetic mutation. Majority of mutations were discovered to be nucleotide mismatches. Consequently, accurate -nucleotide mismatched discrimination is crucial for both diagnosing and treating diseases. To differentiate between such a sensitivealterations in the DNA duplex, several detection methods, particularly Electrochemical-luminescence (ECL) ones, have really been investigated.M_n+1X_nT_x is common name for MXenes, a novel family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, where T stands for interface termination units (i.e. = O, OH, and/or F). These electronic characteristics of MXenes may be changed between conductive to semiconducting due to abundant organometallic chemistry.Solid-state ECL sensors predicated on MXene would provide the facile nucleotide detection and convenience for usage with minimal training, mobility and possibly minimal cost.This study emphasizes upcoming requirements and possibilities in this area while describing the accomplishments achieved in the usage and employing of MXenes in the research and development of facile biomarkerdetection and their significance in designing electrochemical sensors. Opportunities are addressed for creating 2D MXene materials sensors and devices with incorporated biomolecule sensing. MXenes Carry out this process sensors, address the advantages of using MXenes and their variants as detecting materials for gathering different types of data, and attempt to clarify the design principles and operation of related MXene-based sensors, such as nucleotide detection, Single nucleotide detectors, Cancer theranostics, Biosensing capabilities, Gliotoxin detection, SARS-COV-2 nucleocapsid detection, electrochemical sensors, visual sensors, and humidity sensors. Finally, we examine the major issues and prospects for MXene-based materials used in various sensing applications.

Development of high-capacity surface-engineered MXene composite for heavy metal Cr (VI) removal from industrial wastewater

The substantial quantity of Cr(VI) contaminants in the aqueous atmosphere is a major environmental fear that cannot be overlooked. For the first time, MXene and chitosan-coated polyurethane foam have been employed for wastewater treatment, including heavy metal ions (Cr (VI)) through a fixed-bed column study. It is also the most inexpensive, lightweight, and globally friendly material tested. The Mxene and chitosan-coated polyurethane foam hybrid materials were thoroughly investigated using FTIR (Fourier transform infrared), SEM (scanning electron microscope), XPS (X-ray photoelectron spectroscopy) and XRD (X-ray diffraction). The presence of the rough surface and the pore creation in the Mxene- MX₃@CS₃@PUF should rise its surface area, which is useful to interact the surface-active assembly of MX₃@CS₃@PUF and the Cr(VI) contaminations in the aqueous solution. With the help of the ion exchange mechanism and electrostatic contact, negatively charged MXene hexavalent ions were being adsorbed on the surface. MXene and chitosan have been coated on PUF foam in the form of three different layers, which shows the highest adsorption capacity, where up to ∼70% Cr (VI) was removed in the first 10 min and more than 60% elimination after 3 h when the metal ion concentration was 20 ppm. The electrostatic interaction between the negative charge MXene and the positive charge chitosan on the surface of PUF, which was absent in MX@PUF, is accountable for the high removal efficiency. This was done through a sequence of fixed-bed column studies, which took place in the continuous flowing of wastewater.

A novel electrochemical biosensor based on signal amplification of Au HFGNs/PnBA-MXene nanocomposite for the detection of miRNA-122 as a biomarker of breast cancer

Cancer is one of the leading causes of death worldwide and a crisis for global health. Breast cancer is the second most common cancer globally. In the perusal, a novel electrochemical biosensor amplified with hierarchical flower-like gold, poly (n-butyl acrylate), and MXene (AuHFGNs/PnBA-MXene) nanocomposite and activated by highly special antisense ssDNA (single-stranded DNA) provide a promising alternative for miRNA-122 detection as a biomarker of breast cancer. The biosensor presented a detection limit of 0.0035 aM (S/N = 3) with a linear range from 0.01 aM to 10 nM. The platform was tried on 20 breast cancer miRNAs extracted from actual serum specimens (10 positives and 10 negatives). Founded on the quantitatively obtained outcomes and statistic analysis (t-test, box-graph, receiver performance characteristic curve, and cut-off amount), the biosensor showed a meaningful discrepancy between the native and positive groups with 100% specificity and 100% sensitivity. While, RT-qPCR showed less specificity and sensitivity (70% specificity, 100% sensitivity) than the proposed biosensor. To assess the quantitative capacity and biosensor detection limit for clinical tests, the biosensor diagnosis performance for continually diluted miRNA extracted from patients was compared to that gained by RT-qPCR results, indicating that the biosensor detection limit was lower than RT-qPCR. ssDNA/AuHFGN/PnBA-MXene/GCE displayed little cross-reaction with other sequences and also showed desirable stability, reproducibility, and specificity and stayed stable until 32 days. As a result, the designed biosensor can perform as a hopeful method for diagnosis applications.

Recent advances in new generation nanocomposite materials for adsorption of pharmaceuticals from aqueous environment

With rapid increase in the human population, a large amount of wastewater is generated every year. The availability of fresh water is decreasing at an alarming rate due to rapid industrialization and agricultural development. Pharmaceutical drugs which are credited for improving standards of life worldwide have emerged as major water contaminants, raising global concern about their potential risk to human health and environment. The presence of pharmaceutical compounds is detected in surface water (sea, river, lakes, etc.), groundwater, effluents from municipal, hospitals, and wastewater treatment plants, and even in drinking water. Efficient removal of pharmaceutical pollutants still remains a challenging task. Many techniques, including photodegradation, photocatalysis, oxidation, reverse osmosis, biodegradation, nanofiltration, adsorption, etc., have been used for the remediation of wastewater. Adsorption of pharmaceutical compounds on nanoadsorbents, as a low-cost and feasible technology, has gained immense popularity for wastewater treatment over the last decade. Adsorption techniques can be integrated with wastewater treatment plants to achieve efficient removal on an industrial level. Herein, we review the literature on the remediation techniques used for the pharmaceutical waste treatment using carbon nanotubes, metal oxides, nanoclay, and new-generation MXenes via adsorption. These materials show excellent adsorptive properties owing to their high surface area, low cost, high porosity, easy functionalization, and high surface reactivity. The adsorption mechanism of the nanoadsorbents and their reusability as a factor of sustainability have also been included in the review. The factors affecting the adsorption, including pH, the concentration of adsorbate, ionic strength, and adsorbate dose, have also been discussed.

New insights into MXene applications for sustainable environmental remediation

Multiple ecological contaminants in gaseous, liquid, and solid forms are vented into ecosystems due to the huge growth of industrialization, which is today at the forefront of worldwide attention. High-efficiency removal of these environmental pollutants is a must because of the potential harm to public health and biodiversity. The alarming concern has led to the synthesis of improved nanomaterials for removing pollutants. A path to innovative methods for identifying and preventing several obnoxious, hazardous contaminants from entering the environment is grabbing attention. Various applications in diverse industries are seen as a potential directions for researchers. MXene is a new, excellent, and advanced material that has received greater importance related to the environmental application. Due to its unique physicochemical and mechanical properties, high specific surface area, physiological compatibility, strong electrodynamics, and raised specific surface area wettability, its applications are growing. This review paper examines the most recent methods and trends for environmental pollutant removal using advanced 2D Mxene materials. In addition, the history and the development of MXene synthesis were elaborated. Furthermore, an extreme summary of various environmental pollutants removal has been discussed, and the future challenges along with their future perspectives have been illustrated.

Rapid growth of MXene-based membranes for sustainable environmental pollution remediation

Water consumption has grown in recent years due to rising urbanization and industry. As a result, global water stocks are steadily depleting. As a result, it is critical to seek strategies for removing harmful elements from wastewater once it has been cleaned. In recent years, many studies have been conducted to develop new materials and innovative pathways for water purification and environmental remediation. Due to low energy consumption, low operating cost, and integrated facilities, membrane separation has gained significant attention as a potential technique for water treatment. In these directions, MXene which is the advanced 2D material has been explored and many applications were reported. However, research on MXene-based membranes is still in its early stages and reported applications are scatter. This review provides a broad overview of MXenes and their perspectives, including their synthesis, surface chemistry, interlayer tuning, membrane construction, and uses for water purification. Application of MXene based membrane for extracting pollutants such as heavy metals, organic contaminants, and radionuclides from the aqueous water bodies were briefly discussed. Furthermore, the performance of MXene-based separation membranes is compared to that of other nano-based membranes, and outcomes are very promising. In order to shed more light on the advancement of MXene-based membranes and their operational separation applications, significant advances in the fabrication of MXene-based membranes is also encapsulated. Finally, future prospects of MXene-based materials for diverse applications were discussed.

Chemically Exfoliated Titanium Carbide MXene for Highly Sensitive Electrochemical Sensors for Detection of 4-Nitrophenols in Drinking Water

Soil and water contamination by numerous pollutants has been increasingly posing threats to food, water, agriculture, and human health. Using novel nanoscale materials to develop rapid electrochemical sensors is very promising due to the discovery of a number of new two-dimensional (2D) electronic materials. Of particular importance is 2D transition-metal carbide MXene that has been shown to possess transformative properties pertaining to its physical, chemical, and environmental characteristics, leading to their potential sensor applications. Designing electrochemical sensors using MXene has the potential to pave the way for monitoring environmental pollutants. Here, a stacked layer of chemically exfoliated MXene (Ti₃C₂T _x ) was demonstrated as an electrochemical sensor for detection of 4-nitrophenol (4-NP) with high sensitivity and a low limit of detection. Successful selective exfoliation of the MAX (Ti₃AlC₂) phase of the material by chemical etching without oxidation is shown to be the key to achieving higher sensitivity and a lower detection limit. In the optimal conditions, the proposed MXene sensor electrodes were capable of detecting 4-NP in a broad concentration range from 500 nM to 100 μM with a good linear sensing range (regression fit, R = 0.995). The higher sensitivity and notable limit of detection reached about 16.35 μA μM^-1 cm^-2 and 42 nM/L, respectively, with good reproducibility and repeatability. The real-time application of the proposed MXene sensor electrodes was confirmed by testing in tap water samples with excellent recoveries of 95-99%.

Microwave-assisted synthesis of MnO2 nanosorbent for adsorptive removal of Cs(I) and Sr(II) from water solutions

In this study, a flower-like porous δ-MnO₂ nanostructure was synthesized by a microwave-assisted hydrothermal process for adsorptive removal of strontium (Sr(II)) and cesium (Cs(I)) from wastewater. The prepared δ-MnO₂ nanosorbent exhibited superior affinity for Sr(II) over Cs(I) in the single-solute system, with partition coefficient (PC) values of 10.2 and 2.3 L/g, respectively, at pH 6.0. In the two-solute system, the flower-like δ-MnO₂ also adsorbed Sr(II) (PC = 3.81 L/g) more selectively than Cs(I) (PC 1.15 L/g). Further, their adsorption capacities decreased by 12 and 16%, respectively, relative to the single-solute system. In contrast, adsorption of the ions onto δ-MnO₂ was affected less sensitively in dual than in single system when changes occurred in environmental variables such as pH (2-8) and ionic strength (1-100 mM). Adsorption kinetics, thermodynamics, and isotherm studies demonstrated the pivotal role of the monolayer surface active sites of endothermic δ-MnO₂ (e.g., a complexation interaction with Mn-OH). Furthermore, the δ-MnO₂ nanosorbent exhibited good regenerability, retaining more than 80% of its adsorption capacity when tested over four reuse cycles. The overall results of this study are expected to help establish strategies to effectively remove metal contaminants from wastewater using a green and low-cost hierarchical nanosorbent.

Application of MXene in the diagnosis and treatment of breast cancer: A critical overview

Breast cancer is the second most common cancer worldwide. Prognosis and timely treatment can reduce the illness or improve it. The use of nanomaterials leads to timely diagnosis and effective treatment. MXenes are a 2D material with a unique composition of attributes, containing significant electrical conductance, high optical characteristics, mechanical consistency, and excellent optical properties. Current advances and insights show that MXene is far more promising in biotechnology applications than current nanobiotechnology systems. MXenes have various applications in biotechnology and biomedicine, such as drug delivery/loading, biosensor, cancer treatment, and bioimaging programs due to their high surface area, excellent biocompatibility, and physicochemical properties. Surface modifications MXenes are not only biocompatible but also have multifunctional properties, such as aiming ligands for preferential agglomeration at the tumor sites for photothermal treatment. Studies have shown that these nanostructures, detection, and breast cancer therapy are more acceptable than present nanosystems in in vivo and in vitro. This review article aims to investigate the structure of MXene, its various synthesis methods, its application to cancer diagnosis, cytotoxicity, biodegradability, and cancer treatment by the photothermal process (in-vivo and in-vitro).

An overview of MXene-Based nanomaterials and their potential applications towards hazardous pollutant adsorption

With the massive development of industrialization, multiple ecological contaminants in gaseous, liquid, and solid forms are vented into habitats, which is currently at the forefront of worldwide attention. Because of the possible damage to public health and eco-diversity, high-efficiency clearance of these environmental contaminants is a serious concern. Improved nanomaterials (NMs) could perform a significant part in the exclusion of contaminants from the atmosphere. MXenes, a class of two-dimensional (2D) compounds that have got tremendous consideration from researchers for a broad array of applications in a variety of industries and are viewed as a potential route for innovative solutions to identify and prevent a variety of obstreperous hazardous pollutants from environmental compartments due to their exceptional innate physicochemical and mechanical features, including high specific surface area, physiological interoperability, sturdy electrodynamics, and elevated wettability. This paper discusses the recent progress in MXene-based nanomaterials' applications such as environmental remediation, with a focus on their adsorption-reduction characteristics. The removal of heavy metals, dyes, and radionuclides by MXenes and MXene-based nanomaterials is depicted in detail, with the adsorption mechanism and regeneration potential highlighted. Finally, suggestions for future research are provided to ensure that MXenes and MXene-based nanomaterials are synthesized and applied more effectively.

Removal of Malachite Green Dye from Water Using MXene (Ti3C2) Nanosheets

In the present study, new emerging 2D Mxene nanosheets (MXNSs) were synthesized from MAX phase powders of Ti3AlC2 and then characterized using a scanning electron microscope (SEM) and X-ray diffraction (XRD) to explore the chemical and physical properties of the prepared MXNS. The characterization of the synthesized MXNS indicated the formation of exfoliated 2D MXene nanosheets (Ti3C2) as a result of the HF treatment of the MAX phase, which was confirmed by XRD measurements, as the characteristic peaks of 2D MXene nanosheets were only observed. The synthesized MXNS was then used as a solid adsorbent for removing malachite green dye (MG) from water. The effects of different operational factors such as MXNS dose, solution temperature, time, MG concentration, solution pH, and ionic strength have also been evaluated. The adsorption results showed that the temperature of the solution, as well as its pH, significantly influenced MG removal when using MXNS. The optimum removal was obtained within 150 min, with 20 mg of MXNS at ambient temperature and a pH value of 6.0. The maximum removal capacity obtained was 4.6 mg MG per g of MXNS using 5 mg of MXNS with a removal efficacy of 46.0%, and the minimum removal capacity obtained was 2.5 mg MG per g of MXNS using 20 mg of MXNS with a removal efficacy of 99.1%. Finally, the results displayed that the MXNS solid adsorbent was able to absorb a high percentage of MG and maintained reasonable efficiency for four consecutive cycles, indicating that MXNS could be a promising adsorbent in wastewater remediation and environmental sustainability.

Insight into UV-induced simultaneous photocatalytic degradation of Ti3C2Tx MXene and reduction of U(VI)

With the development of MXene as the efficient adsorbent for U(VI), the tendency of MXene coming into contact with U(VI) in wastewaters increases. Motivated by UV light irradiation applied in wastewater treatments, the UV light induced photochemical co-transformation of Ti₃C₂T_x MXene and U(VI) is studied. To clarify the role of U(VI) induced Ti₃C₂T_x aggregation in phototransformation of Ti₃C₂T_x, the aggregation kinetics of Ti₃C₂T_x in the presence of various valent radioactive ions are investigated, obtaining the critical coagulation concentrations (CCC) of Ti₃C₂T_x for Cs⁺, Sr²⁺, UO₂²⁺, Eu³⁺, and Th⁴⁺. Besides, the colloidal stability of UV-induced Ti₃C₂T_x as a function of standing time is discussed. The results show that the aggregation behavior of Ti₃C₂T_x induced by radioactive ions follows the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and the Schulze-Hardy rule. The UV irradiation will change the physicochemical properties and colloidal stabilities of Ti₃C₂T_x. Furthermore, the degradation of Ti₃C₂T_x can be accelerated by UV irradiation and further promoted by the presence of U(VI). The removal of U(VI) is highest in the case of Ti₃C₂T_x combined with UV irradiation via adsorption and reduction. This study provides an example demonstrating that the simultaneous transformation of Ti₃C₂T_x (adsorbent) and U(VI) (adsorbate) to mild toxic components.

Prospects of titanium carbide-based MXene in heavy metal ion and radionuclide adsorption for wastewater remediation: A review

Contamination of water sources with various organic and inorganic non-biodegradable pollutants is becoming a growing concern due to industrialization, urbanization, and the inefficiency of traditional wastewater treatment processes. Transition Metal Carbides/Nitrides (MXenes) are emerging as advanced nanomaterials of choice for treating contaminated water owing to their excellent conductivity, mechanical flexibility, high specific surface area, scalable production, rich surface functionalities, and layered morphology. MXenes have demonstrated enhanced ability to adsorb various organic and inorganic contaminants depending upon their surface terminal groups (-OH, -F, and -O) and interlayer spacing. Titanium carbide (Ti₃C₂T_x) is most researched to date due to its ease of processing and stability. Ti₃C₂T_x has shown excellent performance in absorbing heavy metal ions and radioactive heavy metals. This review summarizes state-of-the-art Ti₃C₂T_x synthesis, including selective etching techniques, optimization of the desired adsorption features (controlling surface functional groups, intercalation, sonication, and functionalization), and regeneration and adsorption mechanism to remove contaminants. Furthermore, the review also compares the adsorption performance of Ti₃C₂T_x with other commercial adsorbents (including chitosan, cellulose, biomass, and zeolites). Ti₃C₂T_x has been found to have an adsorption efficiency of more than 90% in most studies due to its layered structure, which makes the functional groups easily accessible, unique and novel compared to other conventional nanomaterials and adsorbents. The challenges, potential solutions, and prospects associated with the commercial development of Ti₃C₂T_x as adsorbents are also discussed. The review establishes a framework for future wastewater treatment research using MXenes to address the global problem of water scarcity.

MXenes as emerging nanomaterials in water purification and environmental remediation

Environmental pollution has accelerated and intensified because of the acceleration of industrialization, therefore fabricating excellent materials to remove hazardous pollutants has become inevitable. MXenes as emerging transition metal nitrides, carbides or carbonitrides with high conductivity, hydrophilicity, excellent structural stability, and versatile surface chemistry, become ideal candidates for water purification and environmental remediation. Particularly, MXenes reveal excellent sorption capability and efficient reduction performance for various contaminants of wastewater. In this regard, a comprehensive understanding of the removal behaviors of MXene-based nanomaterials is necessary to explain how they remove various pollutants in water. The eliminate process of MXene-based nanomaterials is collectively influenced by the physicochemical properties of the materials themselves and the chemical properties of different contaminants. Therefore, in this review paper, the synthesis strategies and properties of MXene-based nanomaterials are briefly introduced. Then, the chemical properties, removal behaviors and interaction mechanisms of heavy metal ions, radionuclides, and organic pollutants by MXene-based nanomaterials are highlighted. The overview also emphasizes associated toxicity, secondary contamination, the challenges, and prospects of the MXene-based nanomaterials in the applications of water treatment. This review can supply valuable ideas for fabricating versatile MXene nanomaterials in eliminating water pollution.

Iron oxide (Fe3O4)-laden titanium carbide (Ti3C2Tx) MXene stacks for the efficient sequestration of cationic dyes from aqueous solution

We prepared two-dimensional (2D) stack-structured magnetic iron oxide (Fe₃O₄) nanoparticle anchored titanium carbide (Ti₃C₂T_x) MXene material (Ti₃C₂T_x/Fe₃O₄). It was used as a potential adsorbent to remove carcinogenic cationic dyes, such as methylene blue (MB) and rhodamine B (Rh B), from aqueous solutions. Ti₃C₂T_x/Fe₃O₄ exhibited maximum adsorption capacities of 153 and 86 mg g^-1 for MB and Rh B dyes, respectively. Batch adsorption experimental data fits the Langmuir model well, revealing monolayer adsorption of MB and Rh B onto the adsorption sites of Ti₃C₂T_x/Fe₃O₄. Additionally, Ti₃C₂T_x/Fe₃O₄ showed rapid MB/Rh B adsorption kinetics and attained equilibrium within 45 min. Moreover, Ti₃C₂T_x/Fe₃O₄ demonstrated recyclability over four cycles with high stability due to the presence of magnetic Fe₃O₄ nanoparticles. Furthermore, it exhibited remarkable selectivities of 91% and 88% in the presence of co-existing cationic and anionic dyes, respectively. Given the extraordinary adsorption capacities, Ti₃C₂T_x/Fe₃O₄ may be a promising material for the effective removal of cationic dyes from aqueous media.

Two dimensional MXenes as emerging paradigm for adsorptive removal of toxic metallic pollutants from wastewater

Effective methods for removing harmful metals from wastewater have had a huge impact on reducing freshwater scarcity. Because of its excellent removal effectiveness, simplicity and low cost at ambient conditions, adsorption is one of the most promising purifying approaches. MXene-based nanoarchitectures have proven to be effective adsorbents in a variety of harmful metal removal applications. This owes from the distinctive features such as, hydrophilicity, high surface area, electron-richness, great adsorption capacity, and activated metallic hydroxide sites of MXenes. Given the rapid advancement in the design and synthesis of MXene nanoarchitectures for water treatment, prompt updates on this research area are needed that focus on removal of toxic metal, such as production routes and characterization techniques for the advantages, merits and limitations of MXenes for toxic metal adsorption. This is in addition to the fundamentals and the adsorption mechanism tailored by the shape and composition of MXene based on some representative paradigms. Finally, the limits of MXenes are highlighted, as well as their potential future research directions for wastewater treatment. This manuscript may initiate researchers to improve unique MXene-based nanostructures with distinct compositions, shapes, and physiochemical merits for effective removal of toxic metals from wastewater.

Methods of synthesis, characteristics, and environmental applications of MXene: A comprehensive review

MXene, comprised of two-dimensional transition metal carbides/nitride, has emerged as a novel material suitable for environmental remediation of toxic compounds. Due to their inherent and superior physical and chemical properties, MXene is employed in separation techniques like photocatalysis, adsorption, and membrane separation. MXene is equipped with a highly hydrophilic surface, ion exchange property, and robust surface functional groups. In this review paper, a comprehensive discussion on the structural patterns, preparation, properties of MXene and its application for the removal of toxic pollutants like Radionuclide, Uranium, Thorium, and dyes is presented. The mechanism of removal of the pollutants by MXene is extensively reviewed. Synthesis of MXene based membranes, their properties, and application for water purification and properties were also discussed. This review will be highly helpful to understand critically the methods of synthesis and use of MXene material for priority environmental pollutants removal. In addition, the challenges behind the synthesis and use of MXene for decontamination of pollutants were reviewed and reported.

Two-Dimensional Nanomaterials for the Removal of Pharmaceuticals from Wastewater: A Critical Review

The removal of pharmaceuticals from wastewater is critical due to their considerable risk on ecosystems and human health. Additionally, they are resistant to conventional chemical and biological remediation methods. Two-dimensional nanomaterials are a promising approach to face this challenge due to their combination of high surface areas, high electrical conductivities, and partially optical transparency. This review discusses the state-of-the-art concerning their use as adsorbents, oxidation catalysts or photocatalysts, and electrochemical catalysts for water treatment purposes. The bibliographic search bases upon academic databases including articles published until August 2021. Regarding adsorption, high removal capacities (>200 mg g−1) and short equilibrium times (<30 min) are reported for molybdenum disulfide, metal-organic frameworks, MXenes, and graphene oxide/magnetite nanocomposites, attributed to a strong adsorbate-adsorbent chemical interaction. Concerning photocatalysis, MXenes and carbon nitride heterostructures show enhanced charge carriers separation, favoring the generation of reactive oxygen species to degrade most pharmaceuticals. Peroxymonosulfate activation via pure or photo-assisted catalytic oxidation is promising to completely degrade many compounds in less than 30 min. Future work should be focused on the exploration of greener synthesis methods, regeneration, and recycling at the end-of-life of two-dimensional materials towards their successful large-scale production and application.

Thorium(IV) adsorption onto multilayered Ti3C2Tx MXene: a batch, X-ray diffraction and EXAFS combined study

The interlayer regulation of layered environmental adsorption materials such as two-dimensional early transition metal carbides and carbonitrides (MXenes) plays an important role in their purification performance for specific pollutants. Here the enhanced uptake of Th^IV by multilayered titanium carbides (Ti₃C₂T_x) through a hydrated intercalation strategy is reported. Th^IV adsorption behaviors of three Ti₃C₂T_x samples with different c lattice parameters were studied as a function of contact time, pH, initial concentration, temperature and ion strength in batch experiments. The results indicated that the Th^IV uptake was pH and ionic strength dependent, and the adsorption process followed the pseudo-second-order kinetics and the heterogeneous isotherm (Freundlich) model. Thermodynamic data suggested that the adsorption process of all MXene samples was a spontaneous endothermic reaction. The dimethyl sulfoxide intercalated hydrated Ti₃C₂T_x featured the largest interlayer space and exhibited the highest Th^IV adsorption capacity (162 mg g^-1 at pH 3.4 or 112 mg g^-1 at pH 3.0), reflecting the significant increase in available adsorption sites from Ti₃C₂T_x interlayers. The adsorption mechanism has been clarified based on adsorption experiments and spectroscopic characterizations. An ion exchange process was proposed for the interaction between hydrated MXenes and Th^IV, where H⁺ from surface [Ti-O]^-H⁺ groups were the primary active sites on Ti₃C₂T_x. Extended X-ray absorption fine structure (EXAFS) fitting results, in combination with X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses, clearly indicated that Th^IV mainly formed the outer-sphere complexes on Ti₃C₂T_x surface through electrostatic interaction under strong acid conditions, while at pH > 3.0 the adsorption mechanism was determined by inner-sphere coordination and electrostatic interaction together.

MXene (Ti3C2) Based Pesticide Delivery System for Sustained Release and Enhanced Pest Control

A multifunctional nanomaterials based pesticide delivery system provides a powerful strategy for the efficient utilization of pesticides. We present here the application of a 2D MXene (Ti₃C₂) nanomaterial for pesticide delivery and plant protection. Avermectin (AV), a hydrophobic and unstable insecticide, was chosen as the model pesticide. In our study, AV@Ti₃C₂ was formed by fast adsorption of AV on Ti₃C₂, with a maximum loading capacity of 81.44%. Compared with hydrophobic AV, AV@Ti₃C₂ exhibited significantly improved water solubility, which is beneficial for ensuring the bioactivity of pesticide. The AV@Ti₃C₂ nanoformulation showed pH responsive slow-release behavior, overcoming the burst-release of conventional AV formulations. Besides, AV@Ti₃C₂ possessed excellent photostability under UV irradiation, which prolonged the persistent period of AV. Therefore, AV@Ti₃C₂ performed sustaining and enhanced antipest activity, according to the bioactivity assay. Furthermore, AV@Ti₃C₂ showed satisfactory biosafety, with no negative effect to the germination and growth of maize. Our current research provides a potential candidate, AV@Ti₃C₂, for pest control, and also broadens the application of 2D MXene materials in plant protection and sustainable agriculture.

Amino-functionalized POSS nanocage-intercalated titanium carbide (Ti3C2Tx) MXene stacks for efficient cesium and strontium radionuclide sequestration

In this work, we prepared two-dimensional (2D) stack-structured aminopropylIsobutyl polyhedral oligomeric silsesquioxane (POSS-NH₂) intercalated titanium carbide (Ti₃C₂T_x) MXene material (Ti₃C₂T_x/POSS-NH₂) using a post-intercalation strategy as a potential adsorbent for the removal of cesium (Cs⁺) and strontium (Sr²⁺) ions from aqueous solutions. Ti₃C₂T_x/POSS-NH₂ exhibited unprecedented adsorption capacities of 148 and 172 mg g^-1 for Cs⁺ and Sr²⁺ ions, respectively. Batch adsorption experimental data well fitted the Freundlich isotherm model, which revealed multilayer adsorption of Cs⁺ and Sr²⁺ ions onto heterogeneous -OH, -F, -O, and -NH₂ adsorption sites of Ti₃C₂T_x/POSS-NH₂ with different energies. Ti₃C₂T_x/POSS-NH₂ exhibited rapid Cs⁺/Sr²⁺ ions adsorption kinetics and attained equilibrium within 30 min. Also, Ti₃C₂T_x/POSS-NH₂ exhibited recyclable capability over three cycles and remarkable selectivities of 89% and 93% for Cs⁺ and Sr²⁺ ions, respectively, in the presence of co-existing mono- and divalent cations. We suggest the high adsorption capacity of Ti₃C₂T_x/POSS-NH₂ might be due to the synergistic effects of (i) increased inter-lamellar distance between Ti₃C₂T_x galleries due to POSS-NH₂ intercalation, enabling diffusion and encapsulation of large numbers of Cs⁺/Sr²⁺ ions, (ii) strong complexation of amine (-NH₂) groups of POSS-NH₂ with Cs⁺/Sr²⁺ ions, and (iii) the presence of large numbers of heterogeneous surface functional groups (e.g., -OH, -F, and -O), which resulted in the adsorptions of Cs⁺/Sr²⁺ ions through electrostatic, ion exchange, and surface complexation mechanisms. Given the extraordinary adsorption capacities observed, intercalation appears to be a promising strategy for the effective removal of radioactive Cs⁺ and Sr²⁺ ions from aqueous media.

A decade of exploring MXenes as aquatic cleaners: Covering a broad range of contaminants, current challenges and future trends

Clean water, the elixir of life, is of tremendous importance in achieving environmental sustainability and the balanced functioning of our ecosystem. Coupled with population growth, several anthropogenic activities and environmental catastrophes have together contributed to an alarming increase in the concentration of toxic pollutants in water bodies. Diversified physiochemical conditions of water matrices, ranging from mining drainage to seawater, is the critical challenge in designing adsorbents. MXenes, a new class of 2D layered materials, are transition metal nitrides, carbides, carbonitrides or borides formed through selective etching process. MXenes are known to have high surface area and activity with biological compatibility and chemical stability and therefore are promising adsorbents and have been explored for a broad range of contaminants. This review starts with a brief about environmental contaminants followed by synthesis and modifications of MXenes. It then revolves around their so far explored adsorbing and degradation properties for different contaminants ranging from toxic metals, inorganic ions, and radionuclides to various organic pollutants, including dyes, pharmaceuticals, aromatic hydrocarbons, and pesticides, etc. Finally, we have discussed associated toxicity, secondary contamination, future trends, and challenges in ascertaining scalability and wide-range applicability of MXenes in natural environmental conditions to make them a warrior of water sustainability.

Photocatalytic degradation of methyl orange dye by Ti3C2-TiO2 heterojunction under solar light

Photocatalytic activity is a feasible solution to tackle environmental pollution caused by industrial pollutants. In this research, Ti₃C₂-TiO₂ composite with a unique structure was fabricated successfully via a hydrothermal method. Especially, the in-situ transformation of TiO₂ from Ti₃C₂ MXene creates an intimate heterostructure, which leads to prolonging separation and migration of charged carriers. Thus, this Ti₃C₂-TiO₂ composite enhances effectively methyl orange (MO) degradation efficiency (around 99%) after 40 light-exposed minutes. Besides, the optimal concentration of MO solution was estimated at 40 mg/L and Ti₃C₂-TiO₂ photocatalyst also exhibited good stability after five runs. Moreover, the radical trapping test and the MO photodegradation mechanism over Ti₃C₂-TiO₂ system were also demonstrated. This research illustrates the potential of MXenes as effective co-catalysts for photocatalysis and extends the applications of two-dimensional materials.

DOPO-Decorated Two-Dimensional MXene Nanosheets for Flame-Retardant, Ultraviolet-Protective, and Reinforced Polylactide Composites

This study presents a novel and facile strategy for fabricating fire-resistant, ultraviolet (UV)-shielding, and tensile-enhanced polylactide (PLA) composites using two-dimensional (2D) MXene (Ti₃C₂) flakes chemically modified with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The thermal and burning performances of PLA composites were demonstrated by the limiting oxygen index, UL-94 test, and cone calorimetry. The UV-shielding and tensile performances were also examined. The results revealed that PLA/Ti₃C₂-DOPO (3 wt %) displayed a V-0 rating in the UL-94 test. The enhancement against fire hazard was reflected by the significant reduction in the peak heat release rate (33.7%), total heat release (47%), peak CO production (58.8%), and total smoke production (41.7%). The improved fire-safety performance of the composites is attributed to the interplay of catalytic, barrier, and condensed effects of the Ti₃C₂-DOPO nanosheets in the PLA matrix. PLA/Ti₃C₂-DOPO also showed an increase (∼9%) in tensile strength and an "Excellent" level (UPF 50+) in the UV-protection assessment. In all, this study introduces a novel chemical modification strategy for 2D MXene flakes to fabricate multifunctional PLA composites, which are promising candidates for next-generation sustainable and protective plastic products.

Potential environmental applications of MXenes: A critical review

Various environmental pollutants (e.g., air, water and solid pollutants) are discharged into environments with the rapid development of industrializations, which is presently at the forefront of global attention. The high efficient removal of these environmental pollutants is of important concern due to their potential threat to human health and eco-diversity. Advanced nanomaterials may play an important role in the elimination of pollutants from environmental media. MXenes as the new intriguing class of graphene-like 2D transition metal carbides and/or carbonitrides have been widely used in energy storage, environmental remediation benefitting from exceptional structural properties such as highly active sites, high chemical stability, hydrophilicity, large interlayer spacing, huge specific surface area, superior sorption-reduction capacity. However, the comprehensive investigation concerning the removal of various environmental pollutants on MXenes is yet not available up to date. In this review, we summarized the synthesis and properties of MXenes to demonstrate the key roles in ameliorating their adsorption performance; then the recent advances and achievements in environmental application of MXenes on the removal of gases, organics, heavy metals and radionuclides were comprehensively reviewed in details; Finally, the formidable challenges and further perspectives regarding utilizing MXene in environmental remediation were proposed. Hopefully, this review can provide the useful information for environmental scientists and material engineers on designing versatile MXenes in actual environmental applications.

Recent advances in the adsorptive remediation of wastewater using two-dimensional transition metal carbides (MXenes): a review

MXenes, since their discovery in 2011, have garnered significant research attention for a variety of applications due to their exciting physico-chemical properties.

A review on MXene-based nanomaterials as adsorbents in aqueous solution

Environmental pollution has intensified and accelerated due to a steady increase in the number of industries, and finding methods to remove hazardous contaminants, which can be typically divided into inorganic and organic compounds, have become inevitable. One of the widely used water treatment technologies is adsorption and various kinds of adsorbents for the removal of inorganic and organic contaminants from water have been discovered. Recently, MXene, as an emerging nanomaterial, has gained rapid attention owing to its unique characteristics and various applicability. Particularly, in the area of adsorptive application, MXene and MXene-based adsorbents have shown great potential in a large number of studies. In this regard, a comprehensive understanding of the adsorptive behavior of MXene-based nanomaterials is necessary in order to explain how they remove inorganic and organic contaminants in water. Adsorption by MXene-based adsorbents tends to be highly influenced by not only the physicochemical properties of these adsorbents but also water quality, such as pH value, temperature, background ion, and natural organic matter. Therefore, in this review paper, the effect of various water quality on the adsorption of inorganic and organic contaminants by various types of MXene and MXene-based adsorbents is explored. Furthermore, this review also covers general trends in the synthesis of MXene and regeneration of MXene-based adsorbents in order to assess their stability.