MXenes, a relatively new class of two-dimensional (2D) transition-metal carbides, carbonitrides, and nitrides, exhibit unique properties such as high electronic conductivity, a wide range of optical characteristics, hydrophilicity, and mechanical stability. Because of the high electronic conductivity, MXenes have shown promise in many applications, such as energy storage, electromagnetic interference shielding, antennas, and transparent coatings. 2D titanium carbide (Ti 3 C 2 T x , where T x represents surface terminations), the first discovered and most studied MXene, has the highest electronic conductivity exceeding 10 000 S cm −1 . There have been several efforts to alter the conductivity of MXenes, such as manipulation of the transition-metal layer and control of surface terminations. However, the impact of the C and N site composition on electronic transport has not been explored. In this study, the effects of synthesis methods on optoelectronic properties of 2D titanium carbonitride, Ti 3 CNT x , were systematically investigated. We show that Ti 3 CNT x , which hosts a mix of carbon and nitrogen atoms in the X layer, has lower electronic conductivity and a blue shift of the main absorption feature within the UV−visible spectrum, compared to Ti 3 C 2 T x . Moreover, intercalants such as water and tetraalkylammonium hydroxides decrease the electronic conductivity of MXene due to increased interflake resistance, leading to an increase in resistivity with decreasing temperature as observed in ensemble transport measurements. When the intercalants are removed, Ti 3 CNT x exhibits its intrinsic metallic behavior in good agreement with Hall measurements and transport properties measured on single-flake field-effect transistor devices. The dependence of conductivity of Ti 3 CNT x on the presence of intercalants opens wide opportunities for creating MXene-based materials with tunable electronic properties.

MXenes, a large family of 2D transition metal carbides and nitrides, have shown potential in energy storage and optoelectronic applications. Here, the optoelectronic and pseudocapacitive properties of titanium carbide (Ti 3 C 2 T x ) are combined to create a MXene electrochromic device, with a visible absorption peak shift from 770 to 670 nm and a 12% reversible change in transmittance with a switching rate of <1 s when cycled in an acidic electrolyte under applied potentials of less than 1 V. By probing the electrochromic effect in different electrolytes, it is shown that acidic electrolytes (H 3 PO 4 and H 2 SO 4 ) lead to larger absorption peak shifts and a higher change of transmittance than the neutral electrolyte (MgSO 4 ) (Δλ is 100 nm vs 35 nm and ΔT 770 nm is ≈12% vs ≈3%, respectively), hinting at the surface redox mechanism involved. Further investigation of the mechanism by in situ X-ray diffraction and Raman spectroscopy reveals that the reversible shift of the absorption peak is attributed to protonation/deprotonation of oxide-like surface functionalities. As a proof of concept, it is shown that Ti 3 C 2 T x MXene, dip-coated on a glass substrate, functions as both transparent conductive coating and active material in an electrochromic device, opening avenues for further research into optoelectronic and photonic applications of MXenes.

A simple and generic strategy is proposed to pattern thin films deposited by a solution processable route. A soft approach based on an automated scalpel technique is developed to engrave thin films in a single step for sculpting functional planar devices. MXenes—the emerging family of 2D transition metal carbides and nitrides—combine metallic conductivity and hydrophilicity, enabling solution processing of transparent conducting electrodes (TCEs) under ambient conditions. Scalable dip coating is employed to process titanium carbide, Ti3C2, MXene thin films with excellent optoelectronic properties, achieving electrical Figure of merit up to 14. Automated scalpel engraving is adopted to fabricate transparent and semi‐transparent MXene microsupercapacitors in a single step, hitherto not reported. Combining TCE and pseudocapacitive characteristics, MXene devices show excellent capacitive storage capabilities at high rates, without the aid of external metal current collectors. This technique allows for maskless patterning of solution processed thin films without losing intrinsic physicochemical properties and can be extended to fabricate heterostructured hybrid devices out of solution processable materials.

The fabrication of small anatase titanium dioxide (TiO2) nanoparticles (NPs) attached to larger anisotropic gold (Au) morphologies by a very fast and simple two-step microwave-assisted synthesis is presented. The TiO2/Au NPs are synthesized using polyvinylpyrrolidone (PVP) as reducing, capping and stabilizing agent through a polyol approach. To optimize the contact between the titania and the gold and facilitate electron transfer, the PVP is removed by calcination at mild temperatures. The nanocatalysts activity is then evaluated in the photocatalytic production of hydrogen from water/ethanol mixtures in gas-phase at ambient temperature. A maximum value of 5.3 mmol·gcat-1·h−1 (7.4 mmol·gTiO2-1·h−1) of hydrogen is recorded for the system with larger gold particles at an optimum calcination temperature of 450°C. Herein we demonstrate that TiO2-based photocatalysts with high Au loading and large Au particle size (≈50 nm) NPs have photocatalytic activity.

The preparation and manipulation of crystalline yet bendable functional complex oxide membranes has been a long-standing issue for a myriad of applications, in particular, for flexible electronics. Here, we investigate the viability to prepare magnetic and crystalline CoFe 2 O 4 (CFO) membranes by means of the Sr 3 Al 2 O 6 (SAO) sacrificial layer approach using chemical deposition techniques. Meticulous chemical and structural study of the SAO surface and SAO/CFO interface properties have allowed us to identify the formation of an amorphous SAO capping layer and carbonates upon air exposure, which dictate the crystalline quality of the subsequent CFO film growth. Vacuum annealing at 800 °C of SAO films promotes the elimination of the surface carbonates and the reconstruction of the SAO surface crystallinity. Ex-situ atomic layer deposition of CFO films at 250 °C on air-exposed SAO offers the opportunity to avoid hightemperature growth while achieving polycrystalline CFO films that can be successfully transferred to a polymer support preserving the magnetic properties under bending. Float on and transfer provides an alternative route to prepare freestanding and wrinkle-free CFO membrane films. The advances and challenges presented in this work are expected to help increase the capabilities to grow different oxide compositions and heterostructures of freestanding films and their range of functional properties.