Publications

Electronic waste (e‐waste) contains substantial quantities of valuable precious metals, particularly gold (Au). However, inefficient metal recovery leads to these precious metals being discarded in landfills, causing significant water and environmental contamination. This study introduces a two‐dimensional (2D) electrode with a layered graphene oxide membrane functionalized by chitosan (GO/CS). The GO/CS membrane acts as an ion‐selective layer and demonstrates capabilities in the electrochemical extraction and reduction of Au ions. The multiple functional groups of GO and CS offer high cooperativity in ion extraction and reduction, achieving 95 wt.% extraction efficiency within 10 min. The simultaneous extraction and electrocatalytic reduction of Au ions within the membrane leads to the formation of ready‐to‐use metallic Au forms such as chips and sensors. Such an approach eliminates the processing steps required to convert extracted gold into functional products, reducing time, cost, and energy. This direct formation of usable Au components enhances the efficiency of the recovery process, making it economically viable and environmentally sustainable. The gold mining market is projected to be valued at $270 billion by 2032, with the recycling segment reaching $10.8 billion, highlighting the substantial benefits and economic potential of efficient e‐waste recycling technologies.

Plasmon spectroscopy of the thinnest possible membrane, a single layer of carbon atoms, graphene, has been carried out in conjunction with ab initio calculations of the low loss function. We observe π‐ and π + σ‐surface plasmon modes in free‐standing single sheets at 4.7 eV and 14.8 eV which are substantially red‐shifted from their values in graphite. These modes are in very good agreement with the theoretical spectra which find the π‐ and π + π in‐plane modes of graphene at 4.5 eV and 14.5 eV. We also find that there is little loss caused by out‐of‐plane modes for energies less than about 10 eV. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

No abstract is provided for this article.

Compared with single-layer two-dimensional (2D) materials, bilayer, trilayer, and few-layer 2D materials exhibit enhanced band structure tunability, improved electrical and thermal properties, and superior mechanical strength and barrier performance. However, the layer-controlled synthesis of 2D films with high layer number uniformity remains challenging, due to the difficulty in the additional layer nucleation and the effective realization of layer-by-layer growth. Herein, we report an edge-feeding synchronous epitaxial growth mode breaking the limit of traditional epitaxy theories. An efficient heterogeneous Cu-Cu₂O catalyst is demonstrated, where graphene edge-surrounding Cu₂O is crucial in precursor dissociation, atomic carbon diffusion, and edge energy reduction. The synchronous growth method can be generalized to the layer-controlled synthesis of 2-7-layer graphene films. Relying on this growth strategy, we successfully achieved the industrial-scale production of homogeneous A3-sized ABA-trilayer graphene films (42 × 30 square centimeters) with good mechanical properties and peeling-transferring intactness. Our method offers a robust strategy for the layer-controlled synthesis of 2D material films.

No abstract is provided for this article.

We demonstrate a simple method to tune the electrical properties of graphene synthesized by chemical vapor deposition (CVD) with dual-side chemical doping – the bottom-side doping<italic>via</italic>substrate modification with NH₂-SAMs and the top-side doping with diethylenetriamine (DETA) molecules.

Graphene oxide (GO) based multi-layered membranes have shown outstanding molecular-sieving properties for gas separation, surpassing the upper bound for polymeric membranes especially for hydrogen decarbonization. At the same time, the mechanism of gas permeation through such 2D GO membranes is very different in comparison to the traditional polymeric membranes due to multilayer, laminated nature of the former. For strategical design of novel membranes based on two-dimensional materials, it is important to understand the mechanism and to be able to measure two key parameters for gas transport: diffusivity and solubility. Such measurements are well established for the characterization of transport properties of bulk polymeric membranes. However, it is still a challenge to measure gas diffusion coefficients directly and accurately in ultra-thin multi-layered membranes. The lack of characterization limits our understanding of the mechanisms of gas transport though such membranes. In this work, we applied a time-lag method to determine the diffusivities for He, H2, O2, N2, CH4, CO2 and H2/CO2 equimolar mixture by on-line mass spectrometry. In contrast to polymeric membranes, the diffusivity and diffusion activation energy for all gases in 2D membranes are exponentially dependent on pathway length. Thus, in 2D membrane we can use an easy strategy to precisely regulate permeability and selectivity by the adjustment of the number of nanolayers and the size of 2D flakes, which is not possible using traditional polymeric membranes. This study is important for both the characterization and the standardization of gas transport properties of multi-layered membranes, and the design of novel membranes based on 2D materials.

No abstract is provided for this article.

Investigated resonant tunneling through defect levels in h-BN barrier van der Waals heterostructures. The effect of multiplication of tunnel resonances through these levels was found, due to the influence of a high degree of defectiveness of the structure of the neighboring layer of graphene, created by intentionally processing in plasma. Various mechanisms of such influence are discussed.

Atomically thin layers of materials, which are just a few atoms in thickness, present an attractive option for future electronic devices. Herein we characterize, optically and electronically, atomically thin tungsten disulphide (WS2), a layered semiconductor. We provide the distinctive Raman and photoluminescence signatures for single layers, and prepare field-effect transistors where atomically thin WS2 serves as the conductive channel. The transistors present mobilities μ = 10 cm(2) V(-1) s(-1) and exhibit ON/OFF ratios exceeding 100,000. Our results show that WS2 is an attractive option for applications in electronic and optoelectronic devices and pave the way for further studies in this two-dimensional material.

The quantum capacitance of graphene can be negative when the graphene is placed in a strong magnetic field, which is a clear experimental signature of positional correlations between electrons. Here we show that the quantum capacitance of graphene is also strongly affected by its dielectric polarizability, which in a magnetic field is wave-vector dependent. We study this effect both theoretically and experimentally. We develop a theory and numerical procedure for accounting for the graphene dielectric response, and we present measurements of the quantum capacitance of high-quality graphene capacitors on boron nitride. Theory and experiment are found to be in good agreement.

We uncover the constitutive relation of graphene and probe the physics of its optical phonons by studying its Raman spectrum as a function of uniaxial strain. We find that the doubly degenerate E(2g) optical mode splits in two components: one polarized along the strain and the other perpendicular. This splits the G peak into two bands, which we call G(+) and G(-), by analogy with the effect of curvature on the nanotube G peak. Both peaks redshift with increasing strain and their splitting increases, in excellent agreement with first-principles calculations. Their relative intensities are found to depend on light polarization, which provides a useful tool to probe the graphene crystallographic orientation with respect to the strain. The 2D and 2D(') bands also redshift but do not split for small strains. We study the Gruneisen parameters for the phonons responsible for the G, D, and D(') peaks. These can be used to measure the amount of uniaxial or biaxial strain, providing a fundamental tool for nanoelectronics, where strain monitoring is of paramount importance.