Analysis on D2D Heterogeneous Networks with State-Dependent PriorityTraffic

In this work, we consider the performance analysis of state dependent priority traffic and scheduling in device to device (D2D) heterogeneous networks. There are two priority transmission types of data in wireless communication, such as video or telephone, which always meet the requirements of high priority (HP) data transmission first. If there is a large amount of low priority (LP) data, there will be a large amount of LP data that cannot be sent. This situation will cause excessive delay of LP data and packet dropping probability. In order to solve this problem, the data transmission process of high priority queue and low priority queue is studied. Considering the priority jump strategy to the priority queuing model, the queuing process with two priority data is modeled as a two-dimensional Markov chain. A state dependent priority jump queuing strategy is proposed, which can improve the discarding performance of low priority data. The quasi birth and death process method (QBD) and fixed point iteration method are used to solve the causality, and the steady-state probability distribution is further obtained.Then, performance parameters such as average queue length, average throughput, average delay and packet dropping probability for both high and low priority data can be expressed. The simulation results verify the correctness of the theoretical derivation. Meanwhile, the proposed priority jump queuing strategy can significantly improve the drop performance of low-priority data.     

A Joint Algorithm for Resource Allocation in D2D 5G Wireless Networks

With the rapid development of Internet technology, users have an increasing demand for data. The continuous popularization of traffic-intensive applications such as high-definition video, 3D visualization, and cloud computing has promoted the rapid evolution of the communications industry. In order to cope with the huge traffic demand of today’s users, 5G networks must be fast, flexible, reliable and sustainable. Based on these research backgrounds, the academic community has proposed D2D communication. The main feature of D2D communication is that it enables direct communication between devices, thereby effectively improve resource utilization and reduce the dependence on base stations, so it can effectively improve the throughput of multimedia data. One of the most considerable factor which affects the performance of D2D communication is the co-channel interference which results due to the multiplexing of multiple D2D user using the same channel resource of the cellular user. To solve this problem, this paper proposes a joint algorithm time scheduling and power control. The main idea is to effectively maximize the number of allocated resources in each scheduling period with satisfied quality of service requirements. The constraint problem is decomposed into time scheduling and power control subproblems. The power control subproblem has the characteristics of mixed-integer linear programming of NP-hard. Therefore, we proposed a gradual power control method. The time scheduling subproblem belongs to the NP-hard problem having convex-cordinality, therefore, we proposed a heuristic scheme to optimize resource allocation. Simulation results show that the proposed algorithm effectively improved the resource allocation and overcome the co-channel interference as compared with existing algorithms.     

2D Metal Oxyhalide‐Derived Catalysts for Efficient CO2 Electroreduction

Electrochemical reduction of CO₂ is a compelling route to store renewable electricity in the form of carbon‐based fuels. Efficient electrochemical reduction of CO₂ requires catalysts that combine high activity, high selectivity, and low overpotential. Extensive surface reconstruction of metal catalysts under high productivity operating conditions (high current densities, reducing potentials, and variable pH) renders the realization of tailored catalysts that maximize the exposure of the most favorable facets, the number of active sites, and the oxidation state all the more challenging. Earth‐abundant transition metals such as tin, bismuth, and lead have been proven stable and product‐specific, but exhibit limited partial current densities. Here, a strategy that employs bismuth oxyhalides as a template from which 2D bismuth‐based catalysts are derived is reported. The BiOBr‐templated catalyst exhibits a preferential exposure of highly active Bi () facets. Thereby, the CO₂ reduction reaction selectivity is increased to over 90% Faradaic efficiency and simultaneously stable current densities of up to 200 mA cm^?2 are achieved—more than a twofold increase in the production of the energy‐storage liquid formic acid compared to previous best Bi catalysts.     

2D Superlattices for Efficient Energy Storage and Conversion

2D genuine unilamellar nanosheets, that are, the elementary building blocks of their layered parent crystals, have gained increasing attention, owing to their unique physical and chemical properties, and 2D features. In parallel with the great efforts to isolate these atomic-thin crystals, a unique strategy to integrate them into 2D vertically stacked heterostuctures has enabled many functional applications. In particular, such 2D heterostructures have recently exhibited numerous exciting electrochemical performances for energy storage and conversion, especially the molecular-scale heteroassembled superlattices using diverse 2D unilamellar nanosheets as building blocks. Herein, the research progress in scalable synthesis of 2D superlattices with an emphasis on a facile solution-phase flocculation method is summarized. A particular focus is brought to the advantages of these 2D superlattices in applications of supercapacitors, rechargeable batteries, and water-splitting catalysis. The challenges and perspectives on this promising field are also outlined.     

Emerging 2D nanomaterials for biomedical applications

Two-dimensional (2D) nanomaterials are an emerging class of biomaterials with remarkable potential for biomedical applications. The planar topography of these nanomaterials confers unique physical, chemical, electronic and optical properties, making them attractive candidates for therapeutic delivery, biosensing, bioimaging, regenerative medicine, and additive manufacturing strategies. The high surface-to-volume ratio of 2D nanomaterials promotes enhanced interactions with biomolecules and cells. A range of 2D nanomaterials, including transition metal dichalcogenides (TMDs), layered double hydroxides (LDHs), layered silicates (nanoclays), 2D metal carbides and nitrides (MXenes), metal–organic framework (MOFs), covalent organic frameworks (COFs) and polymer nanosheets have been investigated for their potential in biomedical applications. Here, we will critically evaluate recent advances of 2D nanomaterial strategies in biomedical engineering and discuss emerging approaches and current limitations associated with these nanomaterials. Due to their unique physical, chemical, and biological properties, this new class of nanomaterials has the potential to become a platform technology in regenerative medicine and other biomedical applications.     

Heterostructures Based on 2D Materials: A Versatile Platform for Efficient Catalysis

The unique structural and electronic properties of 2D materials, including the metal and metal‐free ones, have prompted intense exploration in the search for new catalysts. The construction of different heterostructures based on 2D materials offers great opportunities for boosting the catalytic activity in electo(photo)chemical reactions. Particularly, the merits resulting from the synergism of the constituent components and the fascinating properties at the interface are tremendously interesting. This scenario has now become the state‐of‐the‐art point in the development of active catalysts for assisting energy conversion reactions including water splitting and CO₂ reduction. Here, starting from the theoretical background of the fundamental concepts, the progressive developments in the design and applications of heterostructures based on 2D materials are traced. Furthermore, a personal perspective on the exploration of 2D heterostructures for further potential application in catalysis is offered.     

Graded 2D/3D Perovskite Heterostructure for Efficient and Operationally Stable MA-Free Perovskite Solar Cells

Almost all highly efficient perovskite solar cells (PVSCs) with power conversion efficiencies (PCEs) of greater than 22% currently contain the thermally unstable methylammonium (MA) molecule. MA-free perovskites are an intrinsically more stable optoelectronic material for use in solar cells but compromise the performance of PVSCs with relatively large energy loss. Here, the open-circuit voltage (V_oc) deficit is circumvented by the incorporation of β-guanidinopropionic acid (β-GUA) molecules into an MA-free bulk perovskite, which facilitates the formation of quasi-2D structure with face-on orientation. The 2D/3D hybrid perovskites embed at the grain boundaries of the 3D bulk perovskites and are distributed through half the thickness of the film, which effectively passivates defects and minimizes energy loss of the PVSCs through reduced charge recombination rates and enhanced charge extraction efficiencies. A PCE of 22.2% (certified efficiency of 21.5%) is achieved and the operational stability of the MA-free PVSCs is improved.     

1D and 2D Field Effect Transistors in Gas Sensing: A Comprehensive Review

Rapid progress in the synthesis and fundamental understanding of 1D and 2D materials have solicited the incorporation of these nanomaterials into sensor architectures, especially field effect transistors (FETs), for the monitoring of gas and vapor in environmental, food quality, and healthcare applications. Yet, several challenges have remained unaddressed toward the fabrication of 1D and 2D FET gas sensors for real-field applications, which are related to properties, synthesis, and integration of 1D and 2D materials into the transistor architecture. This review paper encompasses the whole assortment of 1D—i.e., metal oxide semiconductors (MOXs), silicon nanowires (SiNWs), carbon nanotubes (CNTs)—and 2D—i.e., graphene, transition metal dichalcogenides (TMD), phosphorene—materials used in FET gas sensors, critically dissecting how the material synthesis, surface functionalization, and transistor fabrication impact on electrical versus sensing properties of these devices. Eventually, pros and cons of 1D and 2D FETs for gas and vapor sensing applications are discussed, pointing out weakness and highlighting future directions.     

An Optimal Algorithm for Resource Allocation in D2D Communication

The number of mobile devices accessing wireless networks is skyrocketing due to the rapid advancement of sensors and wireless communication technology. In the upcoming years, it is anticipated that mobile data traffic would rise even more. The development of a new cellular network paradigm is being driven by the Internet of Things, smart homes, and more sophisticated applications with greater data rates and latency requirements. Resources are being used up quickly due to the steady growth of smartphone devices and multimedia apps. Computation offloading to either several distant clouds or close mobile devices has consistently improved the performance of mobile devices. The computation latency can also be decreased by offloading computing duties to edge servers with a specific level of computing power. Device-to-device (D2D) collaboration can assist in processing small-scale activities that are time-sensitive in order to further reduce task delays. The task offloading performance is drastically reduced due to the variation of different performance capabilities of edge nodes. Therefore, this paper addressed this problem and proposed a new method for D2D communication. In this method, the time delay is reduced by enabling the edge nodes to exchange data samples. Simulation results show that the proposed algorithm has better performance than traditional algorithm.     

Photocatalytic degradation of mixed pollutants in aqueous wastewater using mesoporous 2D/2D TiO2(B)-BiOBr heterojunction

There are multiple contaminants in practical wastewater;and the photodegradation of mixed pollutants is a challenge in the field of photocatalysis.Herein,we design a mesoporous 2D/2D TiO2(B)-BiOBr hetero-junction photocatalyst for the photodegradation of mixed pollutants.Such a coupling structure results in an enhancement in the disconnection of photoexcited carriers,and the increase of absorption and reaction sites.The 2D/2D TiO2(B)-BiOBr demonstrates outstanding photocatalytic activity for photode-grading rhodamine B(RhB),methyl orange(MO),tetracycline hydrochloride(TCH),and bisphenol A(BPA)simultaneously under visible light,which is 4.7.1.4,23 and 16.4 times as high as that of original BiOBr,respectively.Our work represents a possible solution to devise promising and efficient photocatalysts for the treatment of practical wastewater in the near future.     

Environmentally‐Friendly Exfoliate and Active Site Self‐Assembly: Thin 2D/2D Heterostructure Amorphous Nickel–Iron Alloy on 2D Materials for Efficient Oxygen Evolution Reaction

A class of 2D layered materials exhibits substantial potential for high‐performance electrocatalysts due to high specific surface area, tunable electronic properties, and open 2D channels for fast ion transport. However, liquid‐phase exfoliation always utilizes organic solvents that are harmful to the environment, and the active sites are limited to edge sites. Here, an environmentally friendly exfoliator in aqueous solution is presented without utilizing any toxic or hazardous substance and active site self‐assembly on the inert base of 2D materials. Benefiting from thin 2D/2D heterostructure and strong interfacial coupling, the resultant highly disordered amorphous NiFe/2D materials (Ti3C2 MXene, graphene and MoS₂) thin nanosheets exhibit extraordinary electrocatalytic performance toward oxygen evolution reaction (OER) in alkaline media. DFT results further verify the experimental results. The study emphasizes a viable idea to probe efficient electrocatalysts by means of the synergistic effect of environmentally friendly exfoliator in aqueous solution and active site self‐assembly on the inert base of 2D materials which forms the unique thin 2D/2D heterostructure in‐suit. This new type of heterostructure opens up a novel avenue for the rational design of highly efficient 2D materials for electrocatalysis.     

Highly Efficient Ionic Photocurrent Generation through WS2‐Based 2D Nanofluidic Channels

The unique feature of nacre‐like 2D layered materials provides a facile, yet highly efficient way to modulate the transmembrane ion transport from two orthogonal transport directions, either vertical or horizontal. Recently, light‐driven active transport of ionic species in synthetic nanofluidic systems attracts broad research interest. Herein, taking advantage of the photoelectric semiconducting properties of 2D transition metal dichalcogenides, the generation of a directional and greatly enhanced cationic flow through WS₂‐based 2D nanofluidic membranes upon asymmetric visible light illumination is reported. Compared with graphene‐based materials, the magnitude of the ionic photocurrent can be enhanced by tens of times, and its photo‐responsiveness can be 2–3.5 times faster. This enhancement is explained by the coexistence of semiconducting and metallic WS₂ nanosheets in the hybrid membrane that facilitates the asymmetric diffusion of photoexcited charge carriers on the channel wall, and the high ionic conductance due to the neat membrane structure. To further demonstrate its application, photonic ion switches, photonic ion diodes, and photonic ion transistors as the fundamental elements for light‐controlled nanofluidic circuits are further developed. Exploring new possibilities in the family of liquid processable colloidal 2D materials provides a way toward high‐performance light‐harvesting nanofluidic systems for artificial photosynthesis and sunlight‐driven desalination.     

Hybridized 2D Nanomaterials Toward Highly Efficient Photocatalysis for Degrading Pollutants: Current Status and Future Perspectives

Organic pollutants including industrial dyes and chemicals and agricultural waste have become a major environmental issue in recent years. As an alternative to simple adsorption, photocatalytic decontamination is an efficient and energy‐saving technology to eliminate these pollutants from water environment, utilizing the energy of external light, and unique function of photocatalysts. Having a large specific surface area, numerous active sites, and varied band structures, 2D nanosheets have exhibited promising applications as an efficient photocatalyst for degrading organic pollutants, particularly hybridization with other functional components. The novel hybridization of 2D nanomaterials with various functional species is summarized systematically with emphasis on their enhanced photocatalytic activities and outstanding performances in environmental remediation. First, the mechanism of photocatalytic degradation is given for discussing the advantages/shortcomings of regular 2D materials and identifying the importance of constructing hybrid 2D photocatalysts. An overview of several types of intensively investigated 2D nanomaterials (i.e., graphene, g‐C₃N₄, MoS₂, WO₃, Bi₂O₃, and BiOX) is then given to indicate their hybridized methodologies, synergistic effect, and improved applications in decontamination of organic dyes and other pollutants. Finally, future research directions are rationally suggested based on the current challenges.     

Efficient 2D Analysis of Interfacial Thermoelastic Stresses in Multiply Bonded Anisotropic Composites with Thin Adhesives

In engineering practice, analysis of interfacial thermal stresses in composites is a crucial task for assuring structural integrity when sever environmental temperature changes under operations. In this article, the directly transformed boundary integrals presented previously for treating generally anisotropic thermoelasticity in two-dimension are fully regularized by a semi-analytical approach for modeling thin multi-layers of anisotropic/isotropic composites, subjected to general thermal loads with boundary conditions prescribed. In this process, an additional difficulty, not reported in the literature, arises due to rapid fluctuation of an integrand in the directly transformed boundary integral equation. In conventional analysis, thin adhesives are usually neglecteddue to modeling difficulties. A major concern arises regarding the modeling error caused by such negligence of the thin adhesives. For investigating the effect of the thin adhesives considered, the regularized integral equation is applied for analyzing interfacial stresses in multiply bonded composites when thin adhesives are considered. Since all integrals are completely regularized, very accurate integration values can be still obtained no matter how the source point is close to the integration element. Comparisons are made for some examples when the thin adhesives are considered or neglected. Truly, this regularization task has laid sound fundamentals for the boundary element method to efficiently analyze the interfacial thermal stresses in 2D thin multiply bonded anisotropic composites.     

Economizing Production of Diverse 2D Layered Metal Hydroxides for Efficient Overall Water Splitting

2D layered metal hydroxides (LMH) are promising materials for electrochemical energy conversion and storage. Compared with exfoliation of bulk layered materials, wet chemistry synthesis of 2D LMH materials under mild conditions still remains a big challenge. Here, an “MgO‐mediated strategy” for mass production of various 2D LMH nanosheets is presented by hydrolyzing MgO in metal salt aqueous solutions at room temperature. Benefiting from this economical and scalable strategy, ultrathin LMH nanosheets (M = Ni, Fe, Co, NiFe, and NiCo) and their derivatives (e.g., metal oxides and sulfides) can be synthesized in high yields. More importantly, this strategy opens up opportunities to fabricate hierarchically structured LMH nanosheets, resulting in high‐performance electrocatalysts for the oxygen‐ and hydrogen‐evolution reactions to realize stable overall water splitting with a low cell voltage of 1.55 V at 10 mA cm⁻². This work provides a powerful platform for the synthesis and applications of 2D materials.     

Interface Engineering in 2D/2D Heterogeneous Photocatalysts

Assembling different 2D nanomaterials into heterostructures with strong interfacial interactions presents a promising approach for novel artificial photocatalytic materials. Chemically implementing the 2D nanomaterials’ construction/stacking modes to regulate different interfaces can extend their functionalities and achieve good performance. Herein, based on different fundamental principles and photochemical processes, multiple construction modes (e.g., face-to-face, edge-to-face, interface-to-face, edge-to-edge) are overviewed systematically with emphasis on the relationships between their interfacial characteristics (e.g., point, linear, planar), synthetic strategies (e.g., in situ growth, ex situ assembly), and enhanced applications to achieve precise regulation. Meanwhile, recent efforts for enhancing photocatalytic performances of 2D/2D heterostructures are summarized from the critical factors of enhancing visible light absorption, accelerating charge transfer/separation, and introducing novel active sites. Notably, the crucial roles of surface defects, cocatalysts, and surface modification for photocatalytic performance optimization of 2D/2D heterostructures are also discussed based on the synergistic effect of optimization engineering and heterogeneous interfaces. Finally, perspectives and challenges are proposed to emphasize future opportunities for expanding 2D/2D heterostructures for photocatalysis.     

CNTs Bridged Basal-Plane-Active 2H-MoS2 Nanosheets for Efficient Robust Electrocatalysis

2D 2H-phase MoS₂ is promising for electrocatalytic applications because of its stable phase, rich edge sites, and large surface area. However, the pristine low-conductive 2H-MoS₂ suffers from limited electron transfer and surface activity, which become worse after their highly likely aggregation/stacking and self-curling during applications. In this work, these issues are overcome by conformally attaching the intercalation-detonation-exfoliated, surface S-vacancy-rich 2H-MoS₂ onto robust conductive carbon nanotubes (CNTs), which electrically bridge bulk electrode and local MoS₂ catalysts. The optimized MoS₂/CNTs nanojunctions exhibit outstanding stable electroactivity (close to commercial Pt/C): a polarization overpotential of 79 mV at the current density of 10 mA cm⁻² and the Tafel slope of 33.5 mV dec⁻¹. Theoretical calculations unveil the metalized interfacial electronic structure of MoS₂/CNTs nanojunctions, enhancing defective-MoS₂ surface activity and local conductivity. This work provides guidance on rational design for advanced multifaceted 2D catalysts combined with robust bridging conductors to accelerate energy technology development.     

Salt-Assisted Low-Temperature Growth of 2D Bi2O2Se with Controlled Thickness for Electronics

Bi₂O₂Se is the most promising 2D material due to its semiconducting feature and high mobility, making it propitious channel material for high-performance electronics that demands highly crystalline Bi₂O₂Se at low-growth temperature. Here, a low-temperature salt-assisted chemical vapor deposition approach for growing single-domain Bi₂O₂Se on a millimeter scale with thicknesses of multilayer to monolayer is presented. Because of the advantage of thickness-dependent growth, systematical scrutiny of layer-dependent Raman spectroscopy of Bi₂O₂Se from monolayer to bulk is investigated, revealing a redshift of the A_1g mode at 162.4 cm⁻¹. Moreover, the long-term environmental stability of ≈2.4 nm thick Bi₂O₂Se is confirmed after exposing the sample for 1.5 years to air. The backgated field effect transistor (FET) based on a few-layered Bi₂O₂Se flake represents decent carrier mobility (≈287 cm² V⁻¹s⁻¹) and an ON/OFF ratio of up to 10⁷. This report indicates a technique to grow large-domain thickness controlled Bi₂O₂Se single crystals for electronics.     

Ultra-low-temperature process effects on microscale abrasion of tool steel AISI D2

Ultra-low-temperature process treatments could raise tool steel wear resistance through microstructural change that occurs on the material, enhancing, that way, tools and dies lifetime. To investigate the tool steel wear resistance impact, micro-abrasive wear tests were carried out and an analysis based on the Archard’s law was considered, evaluating specimen mass loss by laser interferometry. Micro-hardness, X-ray diffractometry, scanning and optical microscopy and carbides quantitative evaluation were carried out aiming to material characterisation. Results demonstrated a micro-hardness improvement, ranging from 0.9–4.7% for the cryogenically treated specimens, when compared to the bulk material. This effect is related, mainly, to the retained austenite transformation and to the increase of fine secondary carbides dispersed amount in the martensitic matrixes cryogenically treated.     

Scalable Synthesis of Holey Deficient 2D Co/NiO Single-Crystal Nanomeshes via Topological Transformation for Efficient Photocatalytic CO2 Reduction

Preparation of holey, single-crystal, 2D nanomaterials containing in-plane nanosized pores is very appealing for the environment and energy-related applications. Herein, an in situ topological transformation is showcased of 2D layered double hydroxides (LDHs) allows scalable synthesis of holey, single-crystal 2D transition metal oxides (TMOs) nanomesh of ultrathin thickness. As-synthesized 2D Co/NiO-2 nanomesh delivers superior photocatalytic CO₂-syngas conversion efficiency (i.e., V_CO of 32460 µmol h⁻¹ g⁻¹ CO and $V_{{\mathrm{H}}_2}$ of 17840 µmol h⁻¹ g⁻¹ H₂), with V_CO about 7.08 and 2.53 times that of NiO and 2D Co/NiO-1 nanomesh containing larger pore size, respectively. As revealed in high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), the high performance of Co/NiO-2 nanomesh primarily originates from the edge sites of nanopores, which carry more defect structures (e.g., atomic steps or vacancies) than basal plane for CO₂ adsorption, and from its single-crystal structure adept at charge transport. Theoretical calculation shows the topological transformation from 2D hydroxide to holey 2D oxide can be achieved, probably since the trace Co dopant induces a lattice distortion and thus a sharp decrease of the dehydration energy of hydroxide precursor. The findings can advance the design of intriguing holey 2D materials with well-defined geometric and electronic properties.