Covalent Functionalization of Two-Dimensional Black Phosphorus Nanosheets with Porphyrins and Its Photophysical Characterizations

Black phosphorus nanosheets (BPNSs) are a rising star among 2D materials and hold applications in a wide range of research areas. However, the poor stability of BPNSs due to chemical degradation in the presence of air and water limits their practical applications. Chemical functionalization is a promising strategy to improve the stability and impart new properties to BPNSs. Herein, functional porphyrin units are attached onto BPNSs through a direct phosphorus–carbon linkage using diazonium chemistry. The porphyrin functionalized BPNSs are characterized using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR) and transmission electron microscopy (TEM) analyses. The formation of a P–C bond between BPNSs and porphyrin units is confirmed by the appearance of a new peak at 131.16 eV in the high resolution P 2p XPS spectrum. A control experiment under similar conditions with diazonium free porphyrins further supports the covalent attachment by precluding noncovalent interactions between porphyrins and BPNSs in the hybrid. Furthermore, the photophysical properties of the BPNS–TPP hybrid were investigated in detail using steady state and time-resolved spectroscopic techniques. Importantly, the porphyrin functionalized BPNSs exhibit an improved ambient stability compared to pristine BPNSs, confirmed by UV-Vis absorption and XPS measurements. This study proposes a potential useful route to obtain stable functional BPNSs, holding promising applications in optoelectronic devices such as nonlinear optics and solar energy harvesting devices

Noncovalent functionalization of Ti3C2TX using cationic porphyrins with enhanced stability against oxidation

Ti3C2TX, as the most explored MXenes, are a rising star among 2D materials due to their astonishing physicochemical properties. However, their practical applications remain extremely challenging because of chemical degradation into TiO2\ua0nanoparticles due to oxidation. Chemical functionalization is an effective way to improve their stability against oxidation and tune the physicochemical properties of 2D materials. In this paper, Ti3C2TX\ua0is noncovalently functionalized using two different cationic porphyrins and the two hybrids show good stabilities in water against oxidation. The electrostatic interactions between the cationic porphyrins and the Ti3C2TX\ua0nanosheets are confirmed by the changes in the zetapotential and the photophysical measurements. The hybrids show a red shifted Soret band of the porphyrins with a complete quenching of the fluorescence emission, which confirms the effective interactions and an energy/electron transfer between the porphyrins and the Ti3C2TX\ua0nanosheets. The exfoliated and functionalized Ti3C2TX\ua0are characterized using various microscopic and spectroscopic techniques. The two hybrids exhibit pH dependent release of cationic porphyrins particularly under acidic conditions. This study proposes a potentially useful strategy for the preparation of highly stable and functional MXenes towards promising applications in biomedicines, optoelectronics and sensors

Recent Advances in Chemical Functionalization of 2D Black Phosphorous Nanosheets

Owing to their tunable direct bandgap, high charge carrier mobility, and unique in-plane anisotropic structure, black phosphorus nanosheets (BPNSs) have emerged as one of the most important candidates among the 2D materials beyond graphene. However, the poor ambient stability of black phosphorus limits its practical application, due to the chemical degradation of phosphorus atoms to phosphorus oxides in the presence of oxygen and/or water. Chemical functionalization is demonstrated as an efficient approach to enhance the ambient stability of BPNSs. Herein, various covalent strategies including radical addition, nitrene addition, nucleophilic substitution, and metal coordination are summarized. In addition, efficient noncovalent functionalization methods such as van der Waals interactions, electrostatic interactions, and cation–π interactions are described in detail. Furthermore, the preparations, characterization, and diverse applications of functionalized BPNSs in various fields are recapped. The challenges faced and future directions for the chemical functionalization of BPNSs are also highlighted

Efficient Visible‐to‐UV Photon Upconversion Systems Based on CdS Nanocrystals Modified with Triplet Energy Mediators

Developing high-performance visible-to-UV photon upconversion systems based on triplet–triplet annihilation photon upconversion (TTA-UC) is highly desired, as it provides a potential approach for UV light-induced photosynthesis and photocatalysis. However, the quantum yield and spectral range of visible-to-UV TTA-UC based on nanocrystals (NCs) are still far from satisfactory. Here, three different sized CdS NCs are systematically investigated with triplet energy transfer to four mediators and four annihilators, thus substantially expanding the available materials for visible-to-UV TTA-UC. By improving the quality of CdS NCs, introducing the mediator via a direct mixing fashion, and matching the energy levels, a high TTA-UC quantum yield of 10.4% (out of a 50% maximum) is achieved in one case, which represents a record performance in TTA-UC based on NCs without doping. In another case, TTA-UC photons approaching 4\ua0eV are observed, which is on par with the highest energies observed in optimized organic systems. Importantly, the in-depth investigation reveals that the direct mixing approach to introduce the mediator is a key factor that leads to close to unity efficiencies of triplet energy transfer, which ultimately governs the performance of NC-based TTA-UC systems. These findings provide guidelines for the design of high-performance TTA-UC systems toward solar energy harvesting

The Art of Constructing Black Phosphorus Nanosheet Based Heterostructures: From 2D to 3D

Assembling different kinds of 2D nanosheets into heterostructures presents a promising way of designing novel artificial materials with new and improved functionalities by combining the unique properties of each component. In the past few years, black phosphorus nanosheets (BPNSs) have been recognized as a highly feasible 2D material with outstanding electronic properties, a tunable bandgap, and strong in-plane anisotropy, highlighting their suitability as a material for constructing heterostructures. In this study, recent progress in the construction of BPNS-based heterostructures ranging from 2D hybrid structures to 3D networks is discussed, emphasizing the different types of interactions (covalent or noncovalent) between individual layers. The preparation methods, optical and electronic properties, and various applications of these heterostructures—including electronic and optoelectronic devices, energy storage devices, photocatalysis and electrocatalysis, and biological applications—are discussed. Finally, critical challenges and prospective research aspects in BPNS-based heterostructures are also highlighted

Spin-Coated Heterogenous Stacked Electrodes for Performance Enhancement in CMOS-Compatible On-Chip Microsupercapacitors

Integration of microsupercapacitors (MSCs) with on-chip sensors and actuators with nanoenergy harvesters can improve the lifetime of wireless sensor nodes in an Internet-of-Things (IoT) architecture. However, to be easy to integrate with such harvester technology, MSCs should be fabricated through a complementary-metal-oxide-semiconductor (CMOS) compatible technology, ubiquitous in electrode choice with the capability of heterogeneous stacking of electrodes for modulation in properties driven by application requirements. In this article, we address both these issues through fabrication of multielectrode modular, high energy density microsupercapacitors (MSC) containing reduced graphene oxide (GO), GO-heptadecane-9-amine (GO-HD9A), rGO-octadecylamine (rGO-ODA), and rGO-heptadecane-9-amine (rGO-HD9A) that stack through a scalable, CMOS compatible, high-wafer-yield spin-coating process. Furthermore, we compare the performance of the stack with individual electrode MSCs fabricated through the same process. The individual electrodes, in the presence of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide (EMIM-TFSI), demonstrate a capacitance of 38, 30, 36, and 105 μF/cm^2\ua0at 20 mV/s^1\ua0whereas the fabricated stack of electrodes demonstrates a high capacitance of 280 μF/cm^2 at 20 mV/s^1 while retaining and enhancing the material-dependent capacitance, charge retention, and power density

Carbon-Based Electrode Materials for Microsupercapacitors in Self-Powering Sensor Networks: Present and Future Development

There is an urgent need to fulfill future energy demands for micro and nanoelectronics. This work outlines a number of important design features for carbon-based microsupercapacitors, which enhance both their performance and integration potential and are critical for complimentary metal oxide semiconductor (CMOS) compatibility. Based on these design features, we present CMOS-compatible, graphene-based microsupercapacitors that can be integrated at the back end of the line of the integrated circuit fabrication. Electrode materials and their interfaces play a crucial role for the device characteristics. As such, different carbon-based materials are discussed and the importance of careful design of current collector/electrode interfaces is emphasized. Electrode adhesion is an important factor to improve device performance and uniformity. Additionally, doping of the electrodes can greatly improve the energy density of the devices. As microsupercapacitors are engineered for targeted applications, device scaling is critically important, and we present the first steps toward general scaling trends. Last, we outline a potential future integration scheme for a complete microsystem on a chip, containing sensors, logic, power generation, power management, and power storage. Such a system would be self-powering