Ti3C2 2D MXene: Recent Progress and Perspectives in Photocatalysis

Interface Engineering, Charge Carrier Dynamics, and Solar-Driven Applications of Halide Perovskite/2D Material Heterostructured Photocatalysts

Halide perovskites (HPs), renowned for their intriguing optoelectronic properties, such as robust light absorption coefficient, long charge transfer distance, and tunable band structure, have emerged as a focal point in the field of photocatalysis. However, the photocatalytic performance of HPs is still inhibited by rapid charge recombination, insufficient band potential energy, and limited number of surface active sites. To overcome these limitations, the integration of two-dimensional (2D) materials, characterized by shortened charge transfer pathways and expansive surface areas, into HP/2D heterostructures presents a promising avenue to achieve exceptional interfacial properties, including extensive light absorption, efficient charge separation and transfer, energetic redox capacity, and adjustable surface characteristics. Herein, a comprehensive review delving into fundamentals, interfacial engineering, and charge carrier dynamics of HP/2D material heterostructures is presented. Numerous HP/2D material photocatalysts fabricated through diverse strategies and interfacial architectures are systematically described and categorized. More importantly, the enhanced charge carrier dynamics and surface properties of the HP/2D material heterostructures are thoroughly investigated and discussed. Finally, an analysis of the challenges faced in the development of HP/2D photocatalysts, alongside insightful recommendations for potential strategies to overcome these barriers, is provided.

Ti3C2Tx MXene-Based Hybrid Photocatalysts in Organic Dye Degradation: A Review

This review provides an overview of the fabrication methods for Ti3C2Tx MXene-based hybrid photocatalysts and evaluates their role in degrading organic dye pollutants. Ti3C2Tx MXene has emerged as a promising material for hybrid photocatalysts due to its high metallic conductivity, excellent hydrophilicity, strong molecular adsorption, and efficient charge transfer. These properties facilitate faster charge separation and minimize electron-hole recombination, leading to exceptional photodegradation performance, long-term stability, and significant attention in dye degradation applications. Ti3C2Tx MXene-based hybrid photocatalysts significantly improve dye degradation efficiency, as evidenced by higher percentage degradation and reduced degradation time compared to conventional semiconducting materials. This review also highlights computational techniques employed to assess and enhance the performance of Ti3C2Tx MXene-based hybrid photocatalysts for dye degradation. It identifies the challenges associated with Ti3C2Tx MXene-based hybrid photocatalyst research and proposes potential solutions, outlining future research directions to address these obstacles effectively.

MXene/PEDOT: PSS composite-modified electrode for electrochemical sensing of bilirubin by molecularly imprinted ortho-phenylenediamine

For the first time, a Ti3C2Tx-MXene and poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT: PSS) composite-modified electrode has been developed for electrochemical detection of the bilirubin (BR) by molecularly imprinted ortho-phenylenediamine (o-PD). BR is a biomarker for liver-related diseases. High levels of BR imply liver dysfunction; hence, its exact and rapid measurement is indispensable to its immediate diagnosis and treatment. The synergistic effects of MXene and PEDOT: PSS not only enhanced the electrochemical conductivity and provided a large electroactive surface area for better MIP polymerization but also improved the sensitivity, stability, and electro-catalytic activity of the developed electrode. This is the first study to combine MXene/PEDOT: PSS and molecularly imprinted orthophenylenediamine for BR sensing, which individually have demonstrated potential, but whose combined effects have never been explored in the context of BR detection. The successful synthesis and deposition of composite is confirmed by field emission scanning electron microscopy (FESEM) along with energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The electrochemical properties and surface morphology of the prepared electrode at every modification step were characterized by electrochemical techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS), and FESEM respectively. The MXene/PEDOT: PSS composite as an electrode modifier exhibited sensing of BR in the clinical relevant range of BR in human serum 0.1-20 mg/dL with a detection limit of 0.002 mg/dL. Additionally, the prepared electrode has excellent reproducibility, stability, selectivity, and repeatability and also showed acceptable results for the sensing of BR in human serum sample.

Graphitic Carbon Nitride for Photocatalytic Hydrogen Production from Water Splitting: Nano-Morphological Control and Electronic Band Tailoring

Semiconductor polymeric graphitic carbon nitride (g-C3N4) photocatalysts have garnered significant and rapidly increasing interest in the realm of visible light-driven hydrogen evolution reactions. This interest stems from their straightforward synthesis, ease of functionalization, appealing electronic band structure, high physicochemical and thermal stability, and robust photocatalytic activity. This review starts with the basic principle of photocatalysis and the development history, synthetic strategy, and structural properties of g-C3N4 materials, followed by the rational design and engineering of g-C3N4 from the perspectives of nano-morphological control and electronic band tailoring. Some representative results, including experimental and theoretical calculations, are listed to show the advantages of optimizing the above two characteristics for performance improvement in photocatalytic hydrogen evolution from water splitting. The existing opportunities and challenges of g-C3N4 photocatalysts are outlined to illuminate the developmental trajectory of this field. This paper provides guidance for the preparation of g-C3N4 and to better understand the current state of the art for future research directions.

Application of Biochar-Based Materials for Effective Pollutant Removal in Wastewater Treatment

With the growth of the global population and the acceleration of industrialization, the problem of water pollution has become increasingly serious, posing a major threat to the ecosystem and human health. Traditional water treatment technologies make it difficult to cope with complex pollution, so the scientific community is actively exploring new and efficient treatment methods. Biochar (BC), as a low-cost, green carbon-based material, exhibits good adsorption and catalytic properties in water treatment due to its porous structure and abundant active functional groups. However, BC's pure adsorption or catalytic capacity is limited, and researchers have dramatically enhanced its performance through modification means, such as loading metals or heteroatoms. In this paper, we systematically review the recent applications of BC and its modified materials for water treatment in adsorption, Fenton-like, electrocatalytic, photocatalytic, and sonocatalytic systems, and discuss their adsorption/catalytic mechanisms. However, most of the research in this field is at the laboratory simulation stage and still needs much improvement before it can be applied in large-scale wastewater treatment. This review improves the understanding of the pollutant adsorption/catalytic properties and mechanisms of BC-based materials, analyzes the limitations of the current studies, and investigates future directions.

Titanium Carbide (Ti3C2Tx) MXene for Sequestration of Aquatic Pollutants

The rapid expansion of industrialization has resulted in the release of multiple ecological contaminants in gaseous, liquid, and solid forms, which pose significant environmental risks to many different ecosystems. The efficient and cost-effective removal of these environmental pollutants has attracted global attention. This growing concern has prompted the synthesis and optimization of nanomaterials and their application as potential pollutant removal. In this context, MXene is considered an outstanding photocatalytic candidate due to its unique physicochemical and mechanical properties, which include high specific surface area, physiological compatibility, and robust electrodynamics. This review highlights recent advances in shaping titanium carbide (Ti3C2Tx) MXenes, emphasizing the importance of termination groups to boost photoactivity and product selectivity, with a primary focus on engineering aspects. First, a broad overview of Ti3C2Tx MXene is provided, delving into its catalytic properties and the formation of surface termination groups to establish a comprehensive understanding of its fundamental catalytic structure. Subsequently, the effects of engineering the morphology of Ti3C2Tx MXene into different structures, such as two-dimensional (2D) accordion-like forms, monolayers, hierarchies, quantum dots, and nanotubes. Finally, a concise overview of the removal of different environmental pollutants is presented, and the forthcoming challenges, along with their prospective outlooks, are delineated.

Recent Advances in Piezoelectric Coupled with Photocatalytic Reaction System: Synergistic Mechanism, Enhancement Factors, and Application

The field of photocatalysis has demonstrated numerous advantages in the domains of environmental protection, energy, and materials science. However, conventional modification methods fail to simultaneously enhance carrier separation efficiency, redox capacity, and visible light absorption solely through light activation due to the intrinsic band structure limitations of photocatalysts. In addition to modification methods, the introduction of an external field, such as a piezoelectric field, can effectively address deficiencies in each step of the photocatalytic process and enhance the overall performance. The assistance of a piezoelectric field overcomes the limitations inherent in traditional photocatalytic systems. Hence, this review provides a comprehensive overview of recent advancements in piezoelectric-assisted photocatalysis and thoroughly investigates the interaction between the alternating piezoelectric field and photocatalytic processes. Various ideas for synergistic enhancement of the piezoelectric and photocatalytic properties are also explored. This multifield catalytic system shows remarkable performance in stability, pollutant degradation, and energy conversion, distinguishing it from single catalytic systems. Finally, an in-depth analysis is conducted to address the challenges and prospects associated with piezoelectric photocatalysis technology.

Ti3C2 quantum dots-modified oxygen-vacancy-rich BiOBr hollow microspheres toward optimized photocatalytic performance

The Ti3C2 quantum dots (QDs)/oxygen-vacancy-rich BiOBr hollow microspheres composite photocatalyst was prepared using solvothermal synthesis and electrostatic self-assembly techniques. Together, Ti3C2QDs and oxygen vacancies (OVs) enhanced photocatalytic activity by broadening light absorption and improving charge transfer and separation processes, resulting in a significant performance boost. Meanwhile, the photocatalytic efficiency of Ti3C2 QDs/BiOBr-OVs is assessed to investigate its capability for oxygen evolution and degradation of tetracycline (TC) and Rhodamine B (RhB) under visible-light conditions. The rate of oxygen production is observed to be 5.1 times higher than that of pure BiOBr-OVs, while the photocatalytic degradation rates for TC and RhB is up to 97.27% and 99.8%, respectively. The synergistic effect between Ti3C2QDs and OVs greatly enhances charge separation, leading to remarkable photocatalytic activity. Furthermore, the hollow microsphere contributes to the enhanced photocatalytic performance by facilitating multiple light scatterings and providing ample surface-active sites. The resultant Ti3C2QDs/BiOBr-OVs composite photocatalyst demonstrates significant potential for environmental applications.

Insights on the efficiency and contribution of single active species in photocatalytic degradation of tetracycline: Priority attack active sites, intermediate products and their toxicity evaluation

Photocatalysis has been proven to be an excellent technology for treating antibiotic wastewater, but the impact of each active species involved in the process on antibiotic degradation is still unclear. Therefore, the S-scheme heterojunction photocatalyst Ti3C2/g-C3N4/TiO2 was successfully synthesized using melamine and Ti3C2 as precursors by a one-step calcination method using mechanical stirring and ultrasound assistance. Its formation mechanism was studied in detail through multiple characterizations and work function calculations. The heterojunction photocatalyst not only enabled it to retain active species with strong oxidation and reduction abilities, but also significantly promoted the separation and transfer of photo-generated carriers, exhibiting an excellent degradation efficiency of 94.19 % for tetracycline (TC) within 120 min. Importantly, the priority attack sites, degradation pathways, degradation intermediates and their ecological toxicity of TC under the action of each single active species (·O2-, h+, ·OH) were first positively explored and evaluated through design experiments, Fukui function theory calculations, HPLC-MS, Escherichia coli toxicity experiments, and ECOSAR program. The results indicated that the preferred attack sites of ·O2- on TC were O20, C7, C11, O21, and N25 atoms with high f+ value. The toxicity of intermediates produced by ·O2- was also lower than those produced by h+ and ·OH.

Novel Optical Modulator Photonic Device Based on TiN/Ti3C2 Heterojunction

Due to the ability of optical modulators to achieve rapid modulation of optical signals, meeting the demands of high-speed data transmission, modulators based on different novel nanomaterials have become one of the research hotspots over the past dacade. Recently, TiN/Ti3C2 heterojunction exhibits highly efficient thermo-optic performance and extremely strong stability. Therefore, we have demonstrated an all-optical modulator based on the principle of Michelson interference and the thermo-optic effect in this paper. The modulator employs a TiN/Ti3C2 heterojunction-coated microfiber (THM) and further demonstrates its ability to generate phase shifts through an ASE light source. The modulator, with a phase shift slope of 0.025π/mW, can also convert the phase shifts of signal light into amplitude modulation through Michelson interference. The fixed signal light wavelength is 1552.09 nm, and the modulation depth is stable at about 26.4 dB within a wavelength detuning range of -10 to 6 nm; The waveforms of signal light at modulation rates of 500 Hz, 1000 Hz, 2000 Hz, and 3000 Hz were tested, and a 3 dB modulation bandwidth of 2 kHz was measured. The all-optical modulator based on THM has the advantages of high efficiency and stability and has broad application prospects in the fields of all-optical signal processing and high-speed optical communication.

Detection of acetaminophen and P-aminophenol simultaneously by an electrochemical sensor based on Fe-NC derivatives attached with Ti3C2 QDs

In this paper, Ti3C2 QDs and Fe-ZIF-8 were synthesized by a straightforward hydrothermal method. Fe-ZIF-8 was pyrolyzed at high temperatures to obtain Fe-nanoclusters (Fe-NC). Then Fe-NC is mixed with Ti3C2 QDs to form a new composite material (Ti3C2 QDs/Fe-NC), and its microstructure and composition were analyzed by technology. The proposed material can detect acetaminophen (PA) and P-aminophenol (4-AP) simultaneously with excellent detection performance. With the best conditions, the linear ranges and detection limits were 0.50-210.00 μM, 0.03 μM (S/N = 3) and 0.50-150.00 μM, 0.06 μM (S/N = 3) for PA and 4-AP, respectively. The sensor has lower detection limits and wider linear ranges, and can successfully detect 4-AP and PA in river water and acetaminophen tablets at the same time, showing potential practical application prospects. Especially, this study reports the modification of MOF derivatives with Ti3C2 QDs for the first time, which expands the application scope of Quantum Dots and MOF derivatives.

N-doped Ti3C2-reinforced porous g-C3N4 for photocatalytic contaminants degradation and nitrogen reduction

Herein, a series of N-doped Ti3C2/porous g-C3N4 composites are ultrasonically prepared from N-doped Ti3C2 and porous g-C3N4 under N2 atmosphere. The structure, morphology, and optical characteristics of the as-prepared composites are characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, etc. Moreover, photocatalytic measurements show that N-doped Ti3C2 is an excellent modifier for porous g-C3N4 to heighten its photocatalytic activity. Only 44.1% of rhodamine B can be degraded by the photocatalysis of pristine porous g-C3N4, while the photocatalytic degradation ratio of rhodamine B can reach up to 97.5% for the optimal N-doped Ti3C2 loading composites under visible light for 15 min. Moreover, the photocatalytic tests of N2 fixation confirm that the optimal composites show the highest production yield of NH4+ (11.8 μmol gcat-1 h-1), which is 2.11-folds more than that of porous g-C3N4 (5.6 μmol gcat-1 h-1). The reinforced photocatalytic properties are revealed to profit from the more photogenerated electrons and holes' separation, higher ability for light response, and more abundant active sites. This work develops the route for boosting the photocatalytic properties of porous g-C3N4 with N-doped Ti3C2.

The Application of 2d Mxene Nanosheet -Based Thermosensitive Gel Delivery System Loaded with Cisplatin and Imiquimod for Lung Cancer

Introduction

Lung cancer's high incidence and dismal prognosis with traditional treatments like surgery and radiotherapy necessitate innovative approaches. Despite advancements in nanotherapy, the limitations of single-treatment modalities and significant side effects persist. To tackle lung cancer effectively, we devised a temperature-sensitive hydrogel-based local injection system with near-infrared triggered drug release. Utilizing 2D MXene nanosheets as carriers loaded with R837 and cisplatin (DDP), encapsulated within a temperature-sensitive hydrogel-forming PEG-MXene@DDP@R837@SHDS (MDR@SHDS), we administered in situ injections of MDR@SHDS into tumor tissues combined with photothermal therapy (PTT). The immune adjuvant R837 enhances dendritic cell (DC) maturation and tumor cell phagocytosis, while PTT induces tumor cell apoptosis and necrosis by converting light energy into heat energy.

Methods

Material characterization employed transmission electron microscopy, X-ray photoelectron spectroscopy, phase transition temperature, and near-infrared thermography. In vitro experiments assessed Lewis cell proliferation and apoptosis using CCK-8, Edu, and TUNEL assays. In vivo experiments on C57 mouse Lewis transplant tumors evaluated the photothermal effect via near-infrared thermography and assessed DC maturation and CD4+/CD8+ T cell ratios using flow cytometry. The in vivo anti-tumor efficacy of MDR@SHDS was confirmed by tumor growth curve recording and HE and TUNEL staining of tumor sections.

Results

The hydrogel exhibited excellent temperature sensitivity, controlled release properties, and high biocompatibility. In vitro experiments revealed that MDR@SHDS combined with PTT had a greater inhibitory effect on tumor cell proliferation compared to MDR@SHD alone. Combining local immunotherapy, chemotherapy, and PTT yielded superior anti-tumor effects than individual treatments.

Conclusion

MDR@SHDS, with its simplicity, biocompatibility, and enhanced anti-tumor effects in combination with PTT, presents a promising therapeutic approach for lung cancer treatment, offering potential clinical utility.

Accelerating carrier separation to boost the photocatalytic CO2 reduction performance of ternary heterojunction Ag-Ti3C2Tx/ZnO catalysts

Developing low-cost and efficient photocatalyst/co-catalyst systems that promote CO2 reduction remains a challenge. In this work, Ag-Ti3C2Tx composites were made using a self-reduction technique, and unique Ag-Ti3C2Tx/ZnO ternary heterojunction structure photocatalysts were created using an electrostatic self-assembly process. The photocatalyst's close-contact heterogeneous interface increases photogenerated carrier migration efficiency. The combination of Ti3C2Tx and Ag improves the adsorption active sites and reaction centers for ZnO, making it a key site for CO2 adsorption and activation. The best photocatalysts had CO and CH4 reduction efficiencies of 11.985 and 0.768 μmol g-1 h-1, respectively. The CO2 conversion was 3.35 times better than that of pure ZnO, which demonstrated remarkable stability even after four cycle trials with no sacrificial agent. Furthermore, in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) and valence band spectroscopy were utilized to propose the photocatalytic reaction mechanism and electron transfer channels of the Ag-Ti3C2Tx/ZnO system, confirming that CHO* and CO* are the important intermediates in the generation of CH4 and CO. This study introduces a novel method for the development of new and efficient photocatalysts and reveals that Ti3C2Tx MXene is a viable co-catalyst for applications.

Chemical conversion of imine- into quinoline-linked covalent organic frameworks for photocatalytic oxidation

Post-synthetic modification is an important strategy for improving and enhancing the properties and functions of covalent organic frameworks (COFs). Two imine-linked COFs are converted into the quinolone-linked COFs by converting the dynamic imine linkages in the COFs into more robust quinolone ring via aza-Diels-Alder cycloaddition reaction. The prepared quinolone-linked COFs not only maintain good crystallinity and porosity, but also possess expanded conjugate planes, enhanced light absorption and excellent stability. The quinolone-linked COFs present remarkable performance of photocatalytic oxidation reactions, including oxidation of phenylboric acids, coupling of benzylamine, and oxidation of thioethers. This work is helpful for preparing organic porous photocatalytic materials with high performance and long life.

Efficient electron transport by 1D CuZnInS modified 2D Ti3C2 MXene for enhanced photocatalytic hydrogen production

The efficiency of the photocatalytic reactionis mainly determined by the effective separation of photogenerated electron (e-) and hole (h+). As a high electrical conductivity, two-dimensional (2D) Ti3C2 MXene is widely used as an electronic transmission intermediary with a large surface area and active terminal. In this work, 1D CuZnInS are loaded on the surface of 2D Ti3C2 MXene nanosheets to compound 1D/2D CuZnInS/Ti3C2 nanocomposites with effective inhibition of charge-carrier recombination. The H2 production rate of optimized 1D/2D CuZnInS/Ti3C2 composite reached 15.24 mmol h-1 g-1, which is 4.5 times than that of pure CuZnInS (3.38 mmol h-1 g-1), and the apparent quantum efficiencies (AQEs) of composite photocatalysts can reach 0.39% and 0.24% under light irradiation at 365 nm and 420 nm wavelength, respectively. In addition, 1D/2D CuZnInS/Ti3C2 has high stability after 10 cycles. The enhanced photocatalytic performance is attributed to the large specific surface area of 2D Ti3C2 nanosheets, which facilitates the separation and transfer of photogenerated e- and h+ pairs.

Controllable preparation of Ti3C2Tx/Ag composite as SERS substrate for ultrasensitive detection of 4-nitrobenzenethiol

Currently, metal carbonitride (MXene) has been identified as a hot research topic in the research area of surface-enhanced Raman scattering (SERS). In this study, Ti3C2Tx/Ag composite was fabricated as SERS substrate with different Ag contents. The fabricated Ti3C2Tx/Ag composites show good SERS behavior by detecting 4-Nitrobenzenethiol (4-NBT) probe molecules. Through calculation, the SERS enhancement factor (EF) of the Ti3C2Tx/Ag substrate was as high as 4.15 × 106. It is worth noting that the detection limit of 4-NBT probe molecules can be achieved ultralow concentration of 10-11 M. In this system, electromagnetic enhancement mechanism and chemical enhancement mechanism have synergistic effects on SERS phenomenon. Meanwhile, the Ti3C2Tx/Ag composite substrate exhibited good SERS reproducibility. In addition, the SERS detection signal hardly changed after 6 months of natural standing, and the substrate showed good stability. This work suggests that the Ti3C2Tx/Ag substrate could be used as a sensitivity SERS sensor for practical application, and could be applied in the field of environmental monitoring.

Recent Advances in Black Phosphorous-Based Photocatalysts for Degradation of Emerging Contaminants

The recalcitrant nature of emerging contaminants (ECs) in aquatic environments necessitates the development of effective strategies for their remediation, given the considerable impacts they pose on both human health and the delicate balance of the ecosystem. Semiconductor-based photocatalytic technology is recognized for its dual benefits in effectively addressing both ECs and energy-related challenges simultaneously. Among the plethora of photocatalysts, black phosphorus (BP) stands as a promising nonmetallic candidate, offering a host of advantages including its tunable direct band gap, broad-spectrum light absorption capabilities, and exceptional charge mobility. Nevertheless, pristine BP frequently underperforms, primarily due to issues related to its limited ambient stability and the rapid recombination of photogenerated electron-hole pairs. To overcome these challenges, substantial research efforts have been devoted to the creation of BP-based photocatalysts in recent years. However, there is a noticeable absence of reviews regarding the advancement of BP-based materials for the degradation of ECs in aqueous solutions. Therefore, to fill this gap, a comprehensive review is undertaken. In this review, we first present an in-depth examination of the fabrication processes for bulk BP and BP nanosheets (BPNS). The review conducts a thorough analysis and comparison of the merits and limitations inherent in each method, thereby delineating the most auspicious avenues for future research. Then, in line with the pathways followed by photogenerated electron-hole pairs at the interface, BP-based photocatalysts are systematically categorized into heterojunctions (Type I, Type II, Z-scheme, and S-scheme) and hybrids, and their photocatalytic performances against various ECs and the corresponding degradation mechanisms are comprehensively summarized. Finally, this review presents personal insights into the prospective avenues for advancing the field of BP-based photocatalysts for ECs remediation.

In situ synthesis of g-C3N4/Ti3C2Tx nano-heterostructures for enhanced photocatalytic H2 generation via water splitting

Herein, we demonstrated the in situ synthesis of g-C3N4/Ti3C2Tx nano-heterostructures for hydrogen generation under UV visible light irradiation. The formation of the g-C3N4/Ti3C2Tx nano-heterostructures was confirmed via powder X-ray diffraction and supported by XPS. The FE-SEM images indicated the formation of layered structures of MXene and g-C3N4. HR-TEM images and SAED patterns confirmed the presence of g-C3N4 together with Ti3C2Tx nanosheets, i.e., the formation of nano-heterostructures of g-C3N4/Ti3C2Tx. The absorption spectra clearly showed the distinct band gaps of g-C3N4 and Ti3C2Tx in the nano-heterostructure. The increase in PL intensity and broadening of the peak with an increase in g-C3N4 indicated the suppression of electron-hole recombination. Furthermore, the nano-heterostructure was used as a photocatalyst for H2 generation from water and methylene blue dye degradation. The highest H2 evolution (1912.25 μmol/0.1 g) with good apparent quantum yield (3.1%) and an efficient degradation of MB were obtained for gCT-0.75, which was much higher compared to that of the pristine materials. The gCT-0.75 nano-heterostructure possessed a high surface area and abundant vacancy defects, facilitating the separation of charge carriers, which was ultimately responsible for this high photocatalytic activity. Additionally, TRPL clearly showed a higher decay time, which supports the enhancement in the photocatalytic activity of the gCT-0.75 nano-heterostructure. The nano-heterostructure with the optimum concentration of g-C3N4 formed a hetero-junction with the linked catalytic system, which facilitated efficient charge carrier separation also responsible for the enhanced photocatalytic activity.

Nano-sized aggregate Ti3C2-TiO2 supported on the surface of Ag2NCN as a Z-scheme catalyst with enhanced visible light photocatalytic performance

Exposing the photocatalyst's highly active facets and hybridizing the photocatalyst with suitable cocatalysts in the proper spot have been recognized as strong methods for high-performance photocatalysts. Herein, Ag2NCN/TiO2-Ti3C2 composites were synthesized by applying simple calcination and physically weak interaction deposition processes to obtain an excellent photocatalyst for Rhodamine B (Rh B) degradation when exposed to visible light. The findings from the experiments reveal that the Ag2NCN/TiO2-Ti3C2400 composite exhibited an outstanding photocatalytic rate in 80 min, with the highest Rh B degradation rate (k = 0.03889 min-1), which was 16 times higher than that of pure Ag2NCN (k = 0.00235 min-1) and 2.2 times higher than that of TiO2-Ti3C2400 (k = 0.01761 min-1). The results from the following factors: (i) the powerful interfacial contact created by the in situ formation of TiO2, and the superior electrical conductivity of Ti3C2 that makes carrier separation possible; (ii) TiO2 with electron-rich (101) facets are deposited on the surface of Ag2NCN, significantly reducing charge carrier recombination by trapping photoelectrons; (iii) a Z-type heterojunction is constructed between nanosize aggregate Ti3C2-TiO2 and Ag2NCN with non-metal Ti3C2 as the solid medium, improving the transfer and separation of photogenerated charges and inhibiting the recombination of electrons and holes. Additionally, the redox ability of the composite photocatalyst is enhanced. Furthermore, the analyses of active species showed that photogenerated superoxide radicals and holes were the principal active agents inside the photodegradation of Rh B. Moreover, the composite exhibited outstanding photo-stability.

A MXene-BiFeO3-ZnO nanocomposite photocatalyst served as a high-performance supercapacitor electrode

MXenes have attracted considerable attention in the field of energy storage and conversion due to their high surface area, excellent electrical conductivity, and ability to intercalate various ions. However, simultaneously achieving high capacitance, rate capability, cycling stability, and mechanical flexibility is a significant challenge for designing MXene-based supercapacitors. In this article, we explored MXene-BiFeO3-ZnO nanocomposites for both photocatalytic and electric double-layer supercapacitor applications. While the BiFeO3-ZnO nanohybrid heterostructure improves the charge separation properties in nanocomposite photocatalysts, it was applied as an interlayer spacer between the MXene layers to prevent the stacking effect of electrodes in the supercapacitor. Furthermore, the optimization of MXene content in the nanocomposite was established by photocatalytic studies on methylene blue dye, which revealed a maximum of 98.72% degradation under direct sunlight with superior stability. The electrochemical studies on the best composition material reveal a maximum areal capacitance (Ccv) of 142.8 mF cm-2, an energy density (E) of 1.65 μW h cm-2, and a capacitive retention of 99.98% after 8000 cycles at 7 μA cm-2. Additionally, the flexible solid-state supercapacitor fabricated with the same material demonstrates an areal capacitance of 47.6 mF cm-2 and a capacitive retention of 66% after 8000 cycles at 7 μA cm-2, with potential for high-performance flexible supercapacitors.

Step-by-Step Guide for Synthesis and Delamination of Ti3 C2 Tx MXene

To advance the MXene field, it is crucial to optimize each step of the synthesis process and create a detailed, systematic guide for synthesizing high-quality MXene that can be consistently reproduced. In this study, a detailed guide is provided for an optimized synthesis of titanium carbide (Ti3 C2 Tx ) MXene using a mixture of hydrofluoric and hydrochloric acids for the selective etching of the stoichimetric-Ti3 AlC2 MAX phase and delamination of the etched multilayered Ti3 C2 Tx MXene using lithium chloride at 65 °C for 1 h with argon bubbling. The effect of different synthesis variables is investigated, including the stoichiometry of the mixed powders to synthesize Ti3 AlC2 , pre-etch impurity removal conditions, selective etching, storage, and drying of MXene multilayer powder, and the subsequent delamination conditions. The synthesis yield and the MXene film electrical conductivity are used as the two parameters to evaluate the MXene quality. Also the MXenes are characterized with scanning electron microscopy, x-ray diffraction, atomic force microscopy, and ellipsometry. The Ti3 C2 Tx film made via the optimized method shows electrical conductivity as high as ≈21,000 S/cm with a synthesis yield of up to 38 %. A detailed protocol is also provided for the Ti3 C2 Tx MXene synthesis as the supporting information for this study.

Photocatalytic Activity of the Oxidation Stabilized Ti3 C2 Tx MXene in Decomposing Methylene Blue, Bromocresol Green and Commercial Textile Dye

Two-dimensional MXenes are excellent photocatalysts. However, their low oxidation stability makes controlling photocatalytic processes challenging. For the first time, this work elucidates the influence of the oxidation stabilization of model 2D Ti3 C2 Tx MXene on its optical and photocatalytic properties. The delaminated MXene is synthesized via two well-established approaches: hydrofluoric acid/tetramethylammonium hydroxide (TMAOH-MXene) and minimum intensive layer delamination with hydrochloric acid/lithium fluoride (MILD-MXene) and then stabilized by L-ascorbic acid. Both MXenes at a minimal concentration of 32 mg L-1 show almost 100% effectiveness in the 180-min photocatalytic decomposition of 25 mg L-1 model methylene blue and bromocresol green dyes. Industrial viability is achieved by decomposing a commercial textile dye having 100 times higher concentration than that of model dyes. In such conditions, MILD-MXene is the most efficient due to less wide optical band gap than TMAOH-MXene. The MILD-MXene required only few seconds of UV light, simulated white light, or 500 nm (cyan) light irradiation to fully decompose the dye. The photocatalytic mechanism of action is associated with the interplay between surface dye adsorption and the reactive oxygen species generated by MXene under light irradiation. Importantly, both MXenes are successfully reused and retained approximately 70% of their activity.

Ti3 C2 TX MXene Ink Direct Writing Flexible Sensors for Disposable Paper Toys

Flexible electronics have gained great attention in recent years owing to their promising applications in biomedicine, sustainable energy, human-machine interaction, and toys for children. Paper mainly produced from cellulose fibers is attractive substrate for flexible electronics because it is biodegradable, foldable, tailorable, and light-weight. Inspired by daily handwriting, the rapid prototyping of sensing devices with arbitrary patterns can be achieved by directly drawing conductive inks on flat or curved paper surfaces; this provides huge freedom for children to design and integrate "do-it-yourself (DIY)" electronic toys. Herein, viscous and additive-free ink made from Ti3 C2 TX MXene sediment is employed to prepare disposable paper electronics through a simple ball pen drawing. The as-drawn paper sensors possess hierarchical microstructures with interweaving nanosheets, nanoflakes, and nanoparticles, therefore exhibiting superior mechanosensing performances to those based on single/fewer-layer MXene nanosheets. As proof-of-concept applications, several popular children's games are implemented by the MXene-based paper sensors, including "You say, I guess," "Emotional expression," "Rock-Paper-Scissors," "Arm wrestling," "Throwing game," "Carrot squat," and "Grab the cup," as well as a DIY smart whisker for a cartoon mouse. Moreover, MXene-based paper sensors are safe and disposable, free from producing any e-waste and hazard to the environment.

Green, HF-Free Synthesis of MXene Quantum Dots and their Photocatalytic Activity for Hydrogen Evolution

A general methodology to prepare MXene quantum dots (MxQDs) with yields over 20% by liquid-phase laser ablation of the MAX phase is reported. Mechanical and thermal shock by 532 nm laser pulses (7 ns fwhp, 50 mJ × pulse^-1 , 1 Hz pulse frequency) produces MAX etching and exfoliation to form MXene QDs, avoiding the use of HF. The process can be followed by absorption and emission spectroscopy and by dynamic laser scattering and it appears to be general, being applied to Ti₃ AlC₂ , Ti₂ AlC, Nb₂ AlC, and V₂ AlC MAX phases. Density functional theory calculations indicate that, depending on the surface terminal groups, the diminution of the MXene size to the nanometric scale makes it possible to control the band gap of the MXene. The photocatalytic activity of these MXene QDs for hydrogen evolution has been observed, reaching an H₂ production for the most efficient Ti₃ C₂ QDs as high as 2.02 mmol × g^-1 × h^-1 .

Tuning the Hydroxyl Density of MXene to Regulate the Electrochemical Performance of Anchored Cobalt Phthalocyanine for CO2 Reduction

Precise electronic state regulation through coordination environment optimization by metal-support interaction is a promising strategy to facilitate catalysis reaction, while the limited density of functional groups in the bulk substrate restricts the regulation degree. Herein, different sizes of Ti₃C₂T_x MXene with hydroxyl (-OH) terminal including the MXene layer (ML-OH, 3 μm), the MXene nanosheet (MNS-OH, 600 nm), and the MXene quantum dot (MQD-OH, 8 nm) were prepared to anchor CoPc, and the effect of -OH density on the performance of electrochemical CO₂ reduction was systematically investigated. Notably, a linear relationship was established by plotting reactivity vs hydroxyl density. With the highest -OH density, CoPc/MQD-OH exhibits a superior Faradaic efficiency for CO formation (FE_CO) of ∼100% at -0.9 to -1.0 V vs RHE and a high FE_CO of >90% over a wide potential window from -0.8 to -1.4 V. The mechanism exploration shows that the axial coordination interaction of the -OH terminal with Co increases the electron density of the Co site, thus promoting the adsorption and activation of CO₂. This work provides a new insight into designing of molecular catalysts with high efficiency and tunable structure for other electrochemical conversions.

S-Scheme and Schottky Junction Synchronous Regulation Boost Hierarchical CdS@Nb2O5/Nb2CTx (MXene) Heterojunction for Photocatalytic H2 Production

Photocatalytic water cracking hydrogen (H₂) production is a promising clean energy production technology. Therefore, a ternary CdS@Nb₂O₅/Nb₂CT_x (MXene) heterojunction with hierarchical structure was designed to promote photocatalytic H₂ evolution. When Na₂S/Na₂SO₃ and lactic acid were used as sacrificial agents, the hydrogen evolution reaction (HER) rates of the optimized photocatalyst were 1501.7 and 2715.8 μmol g^-1 h^-1, with 12.4% and 26.1% apparent quantum efficiencies (AQE) at 420 nm, respectively. Its HER performance was 10.9-fold higher than that of pure CdS and remained 87% activity after five rounds of cycle tests. Such an enhancement stems from the excellent light absorption properties, tight interfacial contact, fast charge transfer channel, and sufficient active sites. Mechanism analysis demonstrates that S-scheme and Schottky junction synchronous regulation boost hierarchical CdS@Nb₂O₅/Nb₂CT_x for photocatalytic H₂ production. This work creates possibilities for manufacturing Nb-based MXene photocatalysts for converting solar energy and other applications.

An Ultrahighly Pressure Sensitive Electronic Fish Skin for Underwater Wave Sensing

Underwater flexible sensors have a future for wide application, which is promising for attaching them to underwater creatures to monitor vital signals and biomechanical analysis of their motion and perceive tiny environmental disturbances. However, the pressure waves induced by biological swimming are extremely weak and susceptible to undercurrents, making them difficult to sense. Here, we report an ultrahighly sensitive biomimetic electronic fish skin designed by embedding an artificial pseudocapacitive-based hair cell into a simulated canal neuromast encapsulation structure, in which the artificial hair cell, as the key sensitive unit, is assembled from hybrid film electrodes and polyurethane-acidic electrolyte foam. Such a film is prepared by inter-cross-linking MXene and holey reduced graphene oxide with the assistance of l-cysteine, effectively increasing the interfacial capacitance and alleviating the oxidation issues of MXene. Meanwhile, the acidic foam with high porosity shows great compressibility to adapt to a high-pressure underwater environment. Consequently, the device exhibits ultrahighly sensitivity (maximum sensitivity ∼173688 kPa^-1) over a wide range of depths (0-100 m) and remains stable after 10000 repeated tests. As an example case, the device is integrated as a motion monitoring system to identify the minor disturbances triggered by instantaneous postural changes of fish. The electronic fish skin is expected to demonstrate enormous potentials in flow field monitoring, ocean current detecting, and even seismic waves warning.

Retrospective insights into recent MXene-based catalysts for CO2 electro/photoreduction: how far have we gone?

The electro/photocatalytic CO₂ reduction reaction (CO₂RR) is a long-term avenue toward synthesizing renewable fuels and value-added chemicals, as well as addressing the global energy crisis and environmental challenges. As a result, current research studies have focused on investigating new materials and implementing numerous fabrication approaches to increase the catalytic performances of electro/photocatalysts toward the CO₂RR. MXenes, also known as 2D transition metal carbides, nitrides, and carbonitrides, are intriguing materials with outstanding traits. Since their discovery in 2011, there has been a flurry of interest in MXenes in electrocatalysis and photocatalysis, owing to their several benefits, including high mechanical strength, tunable structure, surface functionality, high specific surface area, and remarkable electrical conductivity. Herein, this review serves as a milestone for the most recent development of MXene-based catalysts for the electrocatalytic and photocatalytic CO₂RR. The overall structure of MXenes is described, followed by a summary of several synthesis pathways classified as top-down and bottom-up approaches, including HF-etching, in situ HF-formation, electrochemical etching, and halogen etching. Additionally, the state-of-the-art development in the field of both the electrocatalytic and photocatalytic CO₂RR is systematically reviewed. Surface termination modulation and heterostructure engineering of MXene-based electro/photocatalysts, and insights into the reaction mechanism for the comprehension of the structure-performance relationship from the CO₂RR via density functional theory (DFT) have been underlined toward activity enhancement. Finally, imperative issues together with future perspectives associated with MXene-based electro/photocatalysts are proposed.

Improving the Photocatalytic Activity of Ti3C2 MXene by Surface Modification of N Doped

Methyl orange dye (MO) is one of the azo dyes, which is not only difficult to degrade but also hazardous to human health, therefore, it is necessary to develop an efficient photocatalyst to degrade MO. In this paper, a facile and low-cost elemental doping method was used for the surface modification of Ti₃C₂ MXene, i.e., nitrogen-doped titanium carbide was used as the nitrogen source, and the strategy of combining solvent heat treatment with non-in situ nitrogen doping was used to prepare N-Ti₃C₂ MXene two-dimensional nanomaterials with high catalytic activity. It was found that the catalytic efficiency of N-Ti₃C₂ MXene materials was enhanced and improved compared to the non-doped Ti₃C₂ MXene. In particular, N-Ti₃C₂ 1:8 MXene showed the best photo-catalytic ability, as demonstrated by the fact that the N-Ti₃C₂ 1:8 MXene material successfully degraded 98.73% of MO (20 mg/L) under UV lamp irradiation for 20 min, and its catalytic efficiency was about ten times that of Ti₃C₂ MXene, and the N-Ti₃C₂ photo-catalyst still showed good stability after four cycles. This work shows a simplified method for solvent heat-treating non-in situ nitrogen-doped Ti₃C₂ MXene, and also elaborates on the photo-catalytic mechanism of N-Ti₃C₂ MXene, showing that the high photo-catalytic effect of N-Ti₃C₂ MXene is due to the synergistic effect of its efficient charge transfer and surface-rich moieties. Therefore, N-Ti₃C₂ MXene has a good prospect as a photo-catalyst in the photocatalytic degradation of organic pollutants.

Potassium Poly(heptazine imide) Coupled with Ti3C2 MXene-Derived TiO2 as a Composite Photocatalyst for Efficient Pollutant Degradation

The photocatalytic degradation of pollutants is an effective and sustainable way to solve environmental problems, and the key is to develop an efficient, low-cost, and stable photocatalyst. Polymeric potassium poly(heptazine imide) (K-PHI), as a new member of the carbon nitride family, is a promising candidate but is characterized by a high charge recombination rate. To solve this problem, K-PHI was in-situ composited with MXene Ti₃C₂-derived TiO₂ to construct a type-II heterojunction. The morphology and structure of composite K-PHI/TiO₂ photocatalysts were characterized via different technologies, including TEM, XRD, FT-IR, XPS, and UV-vis reflectance spectra. Robust heterostructures and tight interactions between the two components of the composite were verified. Furthermore, the K-PHI/TiO₂ photocatalyst showed excellent activity for Rhodamine 6G removal under visible light illumination. When the weight percent of K-PHI in the original mixture of K-PHI and Ti₃C₂ was set to 10%, the prepared K-PHI/TiO₂ composite photocatalyst shows the highest photocatalytic degradation efficiency as high as 96.3%. The electron paramagnetic resonance characterization indicated that the^·OH radical is the active species accounting for the degradation of Rhodamine 6G.

Ultrasound-pretreatment combined with Ti3C2-TiO2-AuNPs enhancing the electrogenerated chemiluminescence of the air-saturated luminol for exosomes detection

It is still a great challenge to develop effective strategies to improve the low electrogenerated chemiluminescence (ECL) of air-saturated luminol. Herein, the synergistic effects of Ti₃C₂-TiO₂-AuNPs nano hybrid and high-intensity focused ultrasound pretreatment (ultrasound-pretreatment) were used to significantly improve the ECL emission of the air-saturated luminol, and the mechanism was proposed. The ultrasound-pretreatment as a green method with the cavitation effect could form O₂^-• and H₂O₂ in situ as an initiator. TiO₂ and Au nanoparticles (AuNPs) were in situ decorated on the Ti₃C₂ surface to form Ti₃C₂-TiO₂-AuNPs, and it was proved as a highly efficient booster which could catalyze and aggregate H₂O₂ to the O₂^-•. The utilization rate of intermediates has been greatly improved. Exosomes as model targets can be sensitively detected by the ECL sensor. The detection limit was 195 particles μL^-1. The detection results of exosomes in actual samples are satisfactory. We believe that the ultrasound-pretreatment strategy could be extended to the sensitive detection in the biological sample.

Multi-function adsorbent-photocatalyst MXene-TiO2 composites for removal of enrofloxacin antibiotic from water

MXenes, a new family of two-dimensional transition metal carbides or nitrides, have attracted tremendous attention for various applications due to their unique properties such as good electrical conductivity, hydrophilicity, and ion intercalability. In this work, Ti₃C₂ MXene, or MX, is converted to MX-TiO₂ composites using a simple and rapid microwave hydrothermal treatment in HCl/NaCl mixture solution that induces formation of fine TiO₂ particles on the MX parent structure and imparts photocatalytic activity to the resulting MX-TiO₂ composites. The composites were used for enrofloxacin (ENR), a frequently found contaminating antibiotic, removal from water. The relative amount of the MX and TiO₂ can be controlled by controlling the hydrothermal temperature resulting in composites with tunable adsorption/photocatalytic properties. NaCl addition was found to play important role as composites synthesized without NaCl could not adsorb enrofloxacin well. Adding NaCl into the hydrothermal treatment causes sodium ions to be simultaneously intercalated into the composite structure, improving ENR adsorption greatly from 1 to 6 mg ENR/g composite. It also slows down the MX to TiO₂ conversion leading to a smaller and more uniform distribution of TiO₂ particles on the structure. MX-TiO₂/NaCl composites, which have sodium intercalated in their structures, showed both higher ENR adsorption and photocatalytic activity than composites without NaCl despite the latter having higher TiO₂ content. Adsorbed ENR on the composites can be efficiently degraded by free radicals generated from the photoexcited TiO₂ particles, leading to high photocatalytic degradation efficiency. This demonstrates the synergetic effect between adsorption and photocatalytic degradation of the synthesized compounds.

High-Intensity Focused Ultrasound Combined with Ti3C2-TiO2 to Enhance Electrochemiluminescence of Luminol for the Sensitive Detection of Polynucleotide Kinase

Luminol is a classic electrochemiluminescence (ECL) luminophore. The luminol-O₂ ECL system suffers from a problem, that is, the conversion rate of dissolved O₂ into reactive oxygen species (ROS) is low. In this work, we used high-intensity focused ultrasound (HIFU) pretreatment combined with Ti₃C₂-TiO₂ to construct a highly sensitive luminol-O₂ ECL system for the specific detection of polynucleotide kinase (PNK) first. On the one hand, HIFU generated ROS in situ as a coreactant via the cavitation effect to boost the luminol emission. On the other hand, Ti₃C₂-TiO₂ was prepared in situ via Ti₃C₂ as a reducing agent, and it can aggregate and catalyze ROS generated in situ by HIFU. Moreover, the Ti on the Ti₃C₂-TiO₂ surface could bind to phosphate groups through chelation, thereby realizing highly specific detection of PNK. The sensor has a linear relationship range of 1.0 × 10^-5 to 10.0 U mL^-1, and the limit of detection is 1.48 × 10^-7 U mL^-1, which is superior to most existing methods. The sensor performance in HeLa cell lysate was measured with a satisfactory result. The designed ECL biosensor has potential applications in biological analysis and clinical diagnosis.

Recent advances and perspectives of emerging two-dimensional transition metal carbide/nitride-based materials for organic pollutant photocatalysis

This review outlines the fabrication strategies, morphological structures, electronic properties and applications of MXene based materials for photocatalysis in the treatment of recalcitrant organic pollutants (dyes, phenols, antibiotics and pharmaceuticals).

High-Throughput Microfluidic Production of Bimetallic Nanoparticles on MXene Nanosheets and Application in Hydrogen Peroxide Detection

Nanoparticle-functionalized transition-metal carbides and nitrides (MXenes) have attracted extensive attention in electrochemical detection owing to their excellent catalytic performance. However, the mainstream synthetic routes rely on the batch method requiring strict experimental conditions, generally leading to low yield and poor size tunability of particles. Herein, we report a high-throughput and continuous microfluidic platform for preparing a functional MXene (Ti₃C₂T_x) with bimetallic nanoparticles (Pt-Pd NPs) at room temperature. Two 3D micromixers with helical elements were integrated into the microfluidic platform to enhance the secondary flow for promoting transport and reaction in the synthesis process. The rapid mixing and strong vortices in these 3D micromixers prevent aggregation of NPs in the synthesis process, enabling a homogeneous distribution of Pt-Pd NPs. In this study, Pt-Pd NPs loaded on the MXene nanosheets were synthesized under various hydrodynamic conditions of 1-15 mL min^-1 with controlled sizes, densities, and compositions. The mean size of Pt-Pd NPs could be readily controlled within the range 2.4-9.3 nm with high production rates up to 13 mg min^-1. In addition, synthetic and electrochemical parameters were separately optimized to improve the electrochemical performance of Ti₃C₂T_x/Pt-Pd. Finally, the optimized Ti₃C₂T_x/Pt-Pd was used for hydrogen peroxide (H₂O₂) detection and shows excellent electrocatalytic activity. The electrode modified with Ti₃C₂T_x/Pt-Pd here presents a wide detection range for H₂O₂ from 1 to 12 000 μM with a limit of detection down to 0.3 μM and a sensitivity up to 300 μA mM^-1 cm^-2, superior to those prepared in the traditional batch method. The proposed microfluidic approach could greatly enhance the electrochemical performance of Ti₃C₂T_x/Pt-Pd, and sheds new light on the large-scale production and catalytic application of the functional nanocomposites.

Advances in Titanium Carbide (Ti3C2T x ) MXenes and Their Metal-Organic Framework (MOF)-Based Nanotextures for Solar Energy Applications: A Review

Introducing new materials with low cost and superior solar harvesting efficiency requires urgent attention to solve energy and environmental challenges. Titanium carbide (Ti3C2T x ) MXene, a 2D layered material, is a promising solution to solve the issues of existing materials due to their promising conductivity with low cost to function as a cocatalyst/support. On the other hand, metal-organic frameworks (MOFs) are emerging materials due to their high surface area and semiconducting characteristics. Therefore, coupling them would be promising to form composites with higher solar harvesting efficiency. Thus, the main objective of this work to disclose recent development in Ti3C2T x -based MOF nanocomposites for energy conversion applications to produce renewable fuels. MOFs can generate photoinduced electron/hole pairs, followed by transfer of electrons to MXenes through Schottky junctions for photoredox reactions. Currently, the principles, fundamentals, and mechanism of photocatalytic systems with construction of Schottky junctions are critically discussed. Then the basics of MOFs are discussed thoroughly in terms of their physical properties, morphologies, optical properties, and derivatives. The synthesis of Ti3C2T x MXenes and their composites with the formation of surface functionals is systematically illustrated. Next, critical discussions are conducted on design considerations and strategies to engineer the morphology of Ti3C2T x MXenes and MOFs. The interfacial/heterojunction modification strategies of Ti3C2T x MXenes and MOFs are then deeply discussed to understand the roles of both materials. Following that, the applications of MXene-mediated MOF nanotextures in view of CO2 reduction and water splitting for solar fuel production are critically analyzed. Finally, the challenges and a perspective toward the future research of MXene-based MOF composites are disclosed.

Interfacial Strain-Modulated Nanospherical Ni2 P by Heteronuclei-Mediated Growth on Ti3 C2 Tx MXene for Efficient Hydrogen Evolution

Interface modulation of nickel phosphide (Ni₂ P) to produce an optimal catalytic activation barrier has been considered a promising approach to enhance the hydrogen production activity via water splitting. Herein, heteronuclei-mediated in situ growth of hollow Ni₂ P nanospheres on a surface defect-engineered titanium carbide (Ti₃ C₂ T_x ) MXene showing high electrochemical activity for the hydrogen evolution reaction (HER) is demonstrated. The heteronucleation drives intrinsic strain in hexagonal Ni₂ P with an observable distortion at the Ni₂ P@Ti₃ C₂ T_x MXene heterointerface, which leads to charge redistribution and improved charge transfer at the interface between the two components. The strain at the Ni₂ P@Ti₃ C₂ T_x MXene heterointerface significantly boosts the electrochemical catalytic activities and stability toward HER in an acidic medium via a combination between experimental results and theoretical calculations. In a 0.5 m H₂ SO₄ electrolyte, the Ni₂ P@Ti₃ C₂ T_x MXene hybrid shows excellent HER catalytic performance, requiring an overpotential of 123.6 mV to achieve 10 mA cm^-2 with a Tafel slope of 39 mV dec^-1 and impressive durability over 24 h operation. This approach presents a significant potential to rationally design advanced catalysts coupled with 2D materials and transition metal-based compounds for state-of-the-art high efficiency energy conversions.

A Review on MXene Synthesis, Stability, and Photocatalytic Applications

Photocatalytic water splitting, CO₂ reduction, and pollutant degradation have emerged as promising strategies to remedy the existing environmental and energy crises. However, grafting of expensive and less abundant noble-metal cocatalysts on photocatalyst materials is a mandatory practice to achieve enhanced photocatalytic performance owing to the ability of the cocatalysts to extract electrons efficiently from the photocatalyst and enable rapid/enhanced catalytic reaction. Hence, developing highly efficient, inexpensive, and noble-metal-free cocatalysts composed of earth-abundant elements is considered as a noteworthy step toward considering photocatalysis as a more economical strategy. Recently, MXenes (two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides) have shown huge potential as alternatives for noble-metal cocatalysts. MXenes have several excellent properties, including atomically thin 2D morphology, metallic electrical conductivity, hydrophilic surface, and high specific surface area. In addition, they exhibit Gibbs free energy of intermediate H atom adsorption as close to zero and less than that of a commercial Pt-based cocatalyst, a Fermi level position above the H₂ generation potential, and an excellent ability to capture and activate CO₂ molecules. Therefore, there is a growing interest in MXene-based photocatalyst materials for various photocatalytic events. In this review, we focus on the recent advances in the synthesis of MXenes with 2D and 0D morphologies, the stability of MXenes, and MXene-based photocatalysts for H₂ evolution, CO₂ reduction, and pollutant degradation. The existing challenges and the possible future directions to enhance the photocatalytic performance of MXene-based photocatalysts are also discussed.

Fabrication of 2D/2D BiOBr/g-C3N4 with efficient photocatalytic activity and clarification of its mechanism

Precise regulation of photoexcited charge carriers for separation and transportation is a core requirement for practical application in the photocatalysis field. Herein, a 2D/2D BiOBr/g-C₃N₄ heterojunction is prepared by a self-assembly method and exhibits enhanced and stable activity for photocatalytic degradation of bisphenol A (BPA) and norfloxacin (NFA) under visible light. Compared to pure g-C₃N₄, the kinetic constants of BPA and NFA degradation over BiOBr/g-C₃N₄ are enhanced by about 14.74 and 4.01 times, respectively. The separation and transportation mechanism for the photoexcited charge carriers is clarified by electron paramagnetic resonance (EPR), in situ X-ray photoelectron spectroscopy (in situ XPS), and theoretical calculations. The results show that BiOBr/g-C₃N₄ exhibits the feature of a relative p-n junction, in which the charges photoexcited on BiOBr/g-C₃N₄ with high redox potentials can be kept and spatially separated. Moreover, the built-in electric field with the direction of g-C₃N₄ → BiOBr and the opportune band curvature provide the driving force for charge separation and transportation. Additionally, BPA and NFA degradation intermediates are also detected by liquid chromatography-mass spectrometry. It is of great significance to fabricate efficient photocatalysts for environmental purification and other targeted reactions.

Investigation of the effect of antibiotics on 5-formylcytosine content in mazie seedling tissues based on photoelectrochemical biosensor

Given the improved photoactivity of Bi₂S₃ by MXene, an article photoelectrochemical biosensor was designed for 5-formyl-2'-deoxycytidine (5fdCTP) detection, where Bi₂S₃: MXene was selected as photoactive material, polydopamine was used as solid electron donor and 5fdCTP capture reagent, calcined ZIF-8(C-ZIF-8) was chosen as the artificial enzyme. With the catalyzed by C-ZIF-8, 4-chloro-1-naphthol was allegro oxidized by H₂O₂ to form the insoluble benzo-4-chlorohexadienone, and then deposited on the surface of the electrode, Resulting in a decrease of the PEC response. Under the optimum conditions, the sensor has a linear range of 0.001-200 nM and a detection limit of 0.51 pM (3σ). The suitability of the developed method was appraised by investigating the effect of antibiotics on 5fdCTP content in the genomic DNA of the roots of maize seedlings. As a new detection platform, the application of this approach can be expanded to investigative the impact of other pollutants on the content of 5fdCTP in plant or animal tissues, explore the feasibility of 5fdCTP as a new indicator for the ecotoxicological effect of pollutants, and the photoelectrochemical method as a new assessment technique for the ecotoxicological effects of pollutants.

Electrically conductive porous MXene-polymer composites with ultralow percolation threshold via Pickering high internal phase emulsion templating strategy

HYPOTHESIS

Constructing a segregated network in electrically conductive polymer composites (ECPCs) is an effective method to lower the electrical percolation threshold. The segregated network structure can be formed naturally via polymerizing Pickering high internal phase emulsions (HIPEs) because solid particles are assembled at water-oil interfaces. However, most Pickering stabilizers show poor electrical conductivity. In this work, we propose a facile method to prepare lightweight ECPCs with well-controlled segregated structure via Ti₃C₂T_x-stabilized HIPE templating.

EXPERIMENTS

Hydrophilic Ti₃C₂T_x flakes are delicately hydrophobized with a double-chain cation surfactant. The morphology of Ti₃C₂T_x flakes is investigated by transmission electron microscopy (TEM) and atom force microscopy (AFM). The surface properties of modified Ti₃C₂T_x are characterized by zeta potential and water contact angle tests. The stability of Ti₃C₂T_x-stabilized emulsions, and the structure of prepared ECPCs are systematically investigated.

FINDINGS

Surface modified Ti₃C₂T_x flakes are used to stabilize water-in-oil (w/o) HIPEs for the first time. After the polymerization of continuous oil phase, ECPCs are successfully prepared with closed-cell porous structure. The pore size and size distribution of porous composites can be tailored by varying the content of Ti₃C₂T_x flakes. The Ti₃C₂T_x flakes are mainly immobilized at the water-oil interface and eventually form the segregated network in composites. Combining the unique segregated network and the outstanding metallic conductivity of Ti₃C₂T_x, the prepared porous polymer composites exhibit good conductivity even with ultralow Ti₃C₂T_x content of 0.016 vol%.