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2023 Volume 39 Issue 10
2023, 39(10): 230503
doi: 10.3866/PKU.WHXB202305030
Abstract:
Traces of acetylene impurities in the feed gas during the subsequent industrial production process of polyethylene will inactivate ethylene polymerization. The semi-hydrogenation of acetylene to ethylene has been proved to be one of the most effective technologies for the purification of ethylene. Pd catalysts have been playing a leading role in industrial applications due to their excellent performance. However, as Pd is a precious metal, Pd catalysts are expensive. Thus, it is very important to design low-cost, high-selectivity, and high-conversion acetylene semi-hydrogenation catalysts. Here, we summarize the influence of single-metal catalysts based on the acetylene semi-hydrogenation mechanism. The hydrogenation ability of the catalysts should be neither too high nor too low. When other metals are added to palladium catalysts, bimetallic catalysts are formed, which can be classified into typical substitutional solid-solution alloy catalysts, intermetallic compound catalysts, and single-atom alloy catalysts. Regarding the influence of bimetallic catalysts on the performance of acetylene hydrogenation, metals other than Pd have different effects on the acetylene hydrogenation process due to the different structure and environment. While, the structure of the catalyst and the chemical environment ultimately affect the electronic structure of the active center of the catalyst. Based on this, we conclude that the key to the semi-hydrogenation of acetylene is the charge density of the active center of the catalyst, such as dual-atom sites and nano-single atoms; the electrons control the active center of the catalyst. Finely turning the electronic structure of single metal active sites will improve their catalytic activity, selectivity, and stability of the catalyst for acetylene semi-hydrogenation. Additionally, we propose a possible future direction for the development of high-performance acetylene semi-hydrogenation catalysts. Future catalysts for acetylene semi-hydrogenation able to precisely control the active sites to improve their catalytic activity, selectivity, and stability are the focus of researchers, such as the precise control of single-atom-site, dual-atom-site, and nano-single-atom-site catalysts. ![]()
Traces of acetylene impurities in the feed gas during the subsequent industrial production process of polyethylene will inactivate ethylene polymerization. The semi-hydrogenation of acetylene to ethylene has been proved to be one of the most effective technologies for the purification of ethylene. Pd catalysts have been playing a leading role in industrial applications due to their excellent performance. However, as Pd is a precious metal, Pd catalysts are expensive. Thus, it is very important to design low-cost, high-selectivity, and high-conversion acetylene semi-hydrogenation catalysts. Here, we summarize the influence of single-metal catalysts based on the acetylene semi-hydrogenation mechanism. The hydrogenation ability of the catalysts should be neither too high nor too low. When other metals are added to palladium catalysts, bimetallic catalysts are formed, which can be classified into typical substitutional solid-solution alloy catalysts, intermetallic compound catalysts, and single-atom alloy catalysts. Regarding the influence of bimetallic catalysts on the performance of acetylene hydrogenation, metals other than Pd have different effects on the acetylene hydrogenation process due to the different structure and environment. While, the structure of the catalyst and the chemical environment ultimately affect the electronic structure of the active center of the catalyst. Based on this, we conclude that the key to the semi-hydrogenation of acetylene is the charge density of the active center of the catalyst, such as dual-atom sites and nano-single atoms; the electrons control the active center of the catalyst. Finely turning the electronic structure of single metal active sites will improve their catalytic activity, selectivity, and stability of the catalyst for acetylene semi-hydrogenation. Additionally, we propose a possible future direction for the development of high-performance acetylene semi-hydrogenation catalysts. Future catalysts for acetylene semi-hydrogenation able to precisely control the active sites to improve their catalytic activity, selectivity, and stability are the focus of researchers, such as the precise control of single-atom-site, dual-atom-site, and nano-single-atom-site catalysts.
2023, 39(10): 230604
doi: 10.3866/PKU.WHXB202306043
Abstract:
Two-dimensional (2D) semiconductors offer an atomic thickness that facilitates superior gate field penetration and enables transistors to maintain shrinking with suppressed short-channel effects, thereby being considered as channel materials for future transistors in the post-Moore era. As a member of high-mobility 2D semiconductors, the air-stable Bi2O2Se with a moderate bandgap has drawn significant attention. Distinguished from other 2D materials, Bi2O2Se can be oxidized layer-by-layer to form a high-k native-oxide dielectric, Bi2SeO5, with an atomically sharp interface, similar to Si/SiO2 in the semiconductor industry. These characteristics make Bi2O2Se an ideal material platform for fabricating various devices with excellent performance, such as transistors, thermoelectrics, optoelectronics, sensors, flexible devices and memory devices. To realize advanced applications of 2D Bi2O2Se, it is essential to develop scalable and high-quality preparation methods with relatively low cost. Chemical vapor deposition (CVD) has shown promise in meeting these requirements. Over the past years, CVD has been widely used to synthesize 2D Bi2O2Se despite some remaining challenges. In this review, we summarize the recent progress in the controlled growth of 2D Bi2O2Se via the CVD method. We begin by introducing the crystal structure and properties of Bi2O2Se. Next, we focus on the morphology control of 2D Bi2O2Se, including various nucleation modes and different dimensionalities by carefully manipulating the CVD process. In terms of nucleation modes, in-plane and vertical epitaxial growth of Bi2O2Se, achieved by controlling the interaction between epitaxial layer and substrate, are reviewed. Wafer-scale continuous Bi2O2Se film facilitates the device integration while vertical 2D fins pave the way for fabricating high-performance fin field-effect-transistors (FinFET). As for the dimensionality control, the transition from 2D nanoplates to 1D nanoribbons is investigated. Parameters such as precursor ratio, growth temperature and types of catalyst play a key role in such transition. We then discuss the construction of ordered arrays of Bi2O2Se with the above morphology by selective growth and post treatment for potential device integration. In addition, we highlight the electrical quality improvement of the grown material via defect control and strain release. For example, both the Se poor growth condition and the out-of-plane strain-free growth contribute to higher mobility of Bi2O2Se. Lastly, we propose potential strategies for precise control of Bi2O2Se structures and quality. In order to meet the demands of advanced electronic applications, more efforts are expected to made to achieve uniform, transferable and site-specific preparation of high-quality single-crystal Bi2O2Se on a large scale. ![]()
Two-dimensional (2D) semiconductors offer an atomic thickness that facilitates superior gate field penetration and enables transistors to maintain shrinking with suppressed short-channel effects, thereby being considered as channel materials for future transistors in the post-Moore era. As a member of high-mobility 2D semiconductors, the air-stable Bi2O2Se with a moderate bandgap has drawn significant attention. Distinguished from other 2D materials, Bi2O2Se can be oxidized layer-by-layer to form a high-k native-oxide dielectric, Bi2SeO5, with an atomically sharp interface, similar to Si/SiO2 in the semiconductor industry. These characteristics make Bi2O2Se an ideal material platform for fabricating various devices with excellent performance, such as transistors, thermoelectrics, optoelectronics, sensors, flexible devices and memory devices. To realize advanced applications of 2D Bi2O2Se, it is essential to develop scalable and high-quality preparation methods with relatively low cost. Chemical vapor deposition (CVD) has shown promise in meeting these requirements. Over the past years, CVD has been widely used to synthesize 2D Bi2O2Se despite some remaining challenges. In this review, we summarize the recent progress in the controlled growth of 2D Bi2O2Se via the CVD method. We begin by introducing the crystal structure and properties of Bi2O2Se. Next, we focus on the morphology control of 2D Bi2O2Se, including various nucleation modes and different dimensionalities by carefully manipulating the CVD process. In terms of nucleation modes, in-plane and vertical epitaxial growth of Bi2O2Se, achieved by controlling the interaction between epitaxial layer and substrate, are reviewed. Wafer-scale continuous Bi2O2Se film facilitates the device integration while vertical 2D fins pave the way for fabricating high-performance fin field-effect-transistors (FinFET). As for the dimensionality control, the transition from 2D nanoplates to 1D nanoribbons is investigated. Parameters such as precursor ratio, growth temperature and types of catalyst play a key role in such transition. We then discuss the construction of ordered arrays of Bi2O2Se with the above morphology by selective growth and post treatment for potential device integration. In addition, we highlight the electrical quality improvement of the grown material via defect control and strain release. For example, both the Se poor growth condition and the out-of-plane strain-free growth contribute to higher mobility of Bi2O2Se. Lastly, we propose potential strategies for precise control of Bi2O2Se structures and quality. In order to meet the demands of advanced electronic applications, more efforts are expected to made to achieve uniform, transferable and site-specific preparation of high-quality single-crystal Bi2O2Se on a large scale.
2023, 39(10): 230503
doi: 10.3866/PKU.WHXB202305033
Abstract:
Palladium, a key component of three-way catalysts used in automobile exhaust treatment, plays a pivotal role in complete oxidation of alkanes and low-temperature oxidation of CO. Under oxygen-rich conditions, a thin oxide layer spontaneously forms on the palladium surface. To understand the influence of the oxidized palladium surface on the active phase of low-temperature hydrocarbon oxidation, we have conducted a comprehensive study of the oxidation process on Pd(100) and its impact on propane oxidation. Our experimental results reveal that under varying oxidation conditions, the Pd(100) surface sequentially forms three different monolayered oxide phases, namely, (2 × 2)-O, (5 × 5)-PdO and (\begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} \begin{document}$ \sqrt{\text{5}} $\end{document} ![]()
Palladium, a key component of three-way catalysts used in automobile exhaust treatment, plays a pivotal role in complete oxidation of alkanes and low-temperature oxidation of CO. Under oxygen-rich conditions, a thin oxide layer spontaneously forms on the palladium surface. To understand the influence of the oxidized palladium surface on the active phase of low-temperature hydrocarbon oxidation, we have conducted a comprehensive study of the oxidation process on Pd(100) and its impact on propane oxidation. Our experimental results reveal that under varying oxidation conditions, the Pd(100) surface sequentially forms three different monolayered oxide phases, namely, (2 × 2)-O, (5 × 5)-PdO and (
2023, 39(10): 230503
doi: 10.3866/PKU.WHXB202305034
Abstract:
Direct methanol fuel cells (DMFCs) hold great promise as clean energy conversion devices in the future. Noble metal nanocatalysts, renowned for their exceptional catalytic activity and stability, play a crucial role in DMFCs. Among these catalysts, Pt- and Pd-based nanocatalysts are widely recognized as the most effective catalysts for the electrochemical methanol oxidation reaction (MOR), which is the key half-cell reaction in DMFCs. However, due to the high cost of Pt- and Pd-based materials, there is a strong desire to further enhance their catalytic performance. One of the most promising approaches for it is to develop noble metal-based alloy nanocatalysts, which have shown great potential in improving electrocatalytic activity. Notably, advancements in phase engineering of nanomaterials (PEN) have revealed that noble metal-based nanomaterials with unconventional phases exhibit superior catalytic properties in various catalytic reactions compared to their counterparts with conventional phases. To obtain noble metal-based nanocatalysts with unconventional crystal phases, wet-chemical epitaxial growth has been employed as a facile and effective method, utilizing unconventional-phase noble metal nanocrystals as templates. Nevertheless, epitaxially growing bimetallic alloy nanostructures with unconventional crystal phases remains a challenge, impeding further exploration of their catalytic performance in electrochemical reactions such as MOR. In this study, we utilize 4H hexagonal phase Au (4H-Au) nanoribbons as templates for the epitaxial growth of unconventional 4H hexagonal PdFe, PdIr, and PdRu, resulting in the formation of 4H-Au@PdM (M = Fe, Ir, and Ru) core-shell nanoribbons. As a proof-of-concept application, we investigate the electrocatalytic activity of the synthesized 4H-Au@PdFe nanoribbons towards MOR, which exhibit a mass activity of 3.69 A·mgPd−1, i.e., 10.5 and 2.4 times that of Pd black and Pt/C, respectively, placing it among the best Pd- and Pt-based MOR electrocatalysts. Our strategy opens up an avenue for the rational construction of unconventional-phase multimetallic nanostructures to explore their phase-dependent properties in various applications. ![]()
Direct methanol fuel cells (DMFCs) hold great promise as clean energy conversion devices in the future. Noble metal nanocatalysts, renowned for their exceptional catalytic activity and stability, play a crucial role in DMFCs. Among these catalysts, Pt- and Pd-based nanocatalysts are widely recognized as the most effective catalysts for the electrochemical methanol oxidation reaction (MOR), which is the key half-cell reaction in DMFCs. However, due to the high cost of Pt- and Pd-based materials, there is a strong desire to further enhance their catalytic performance. One of the most promising approaches for it is to develop noble metal-based alloy nanocatalysts, which have shown great potential in improving electrocatalytic activity. Notably, advancements in phase engineering of nanomaterials (PEN) have revealed that noble metal-based nanomaterials with unconventional phases exhibit superior catalytic properties in various catalytic reactions compared to their counterparts with conventional phases. To obtain noble metal-based nanocatalysts with unconventional crystal phases, wet-chemical epitaxial growth has been employed as a facile and effective method, utilizing unconventional-phase noble metal nanocrystals as templates. Nevertheless, epitaxially growing bimetallic alloy nanostructures with unconventional crystal phases remains a challenge, impeding further exploration of their catalytic performance in electrochemical reactions such as MOR. In this study, we utilize 4H hexagonal phase Au (4H-Au) nanoribbons as templates for the epitaxial growth of unconventional 4H hexagonal PdFe, PdIr, and PdRu, resulting in the formation of 4H-Au@PdM (M = Fe, Ir, and Ru) core-shell nanoribbons. As a proof-of-concept application, we investigate the electrocatalytic activity of the synthesized 4H-Au@PdFe nanoribbons towards MOR, which exhibit a mass activity of 3.69 A·mgPd−1, i.e., 10.5 and 2.4 times that of Pd black and Pt/C, respectively, placing it among the best Pd- and Pt-based MOR electrocatalysts. Our strategy opens up an avenue for the rational construction of unconventional-phase multimetallic nanostructures to explore their phase-dependent properties in various applications.
2023, 39(10): 230704
doi: 10.3866/PKU.WHXB202307046
Abstract:
Aramid fiber is highly regarded for its outstanding properties and is widely used in various industrial applications. Among the different types of aramid fibers, meta-aramids, particularly poly(m-phenylene isophthalamide) (PMIA), are known for their exceptional flame retardance, high-temperature resistance, excellent electrical insulation, and remarkable chemical stability. As a result, PMIA-based materials find extensive use in industries focused on fire prevention, heat protection, and related applications. However, PMIA fibers have limitations due to the lack of conjugation between amide and benzene ring bonds in their molecular structure, resulting in flexible segments with low crystallinity, which in turn leads to inferior mechanical strength. Researchers have shown great interest in nanocomposites as a means to overcome these limitations. In this context, graphene nanocomposites have gained significant attention. Graphene, with its benzene ring arrangement within its layers, easily bonds with polymers possessing a similar structure. This property makes graphene a promising candidate for enhancing the mechanical strength of aromatic polymers like PMIA. Moreover, small-sized graphene particles exhibit superior dispersibility within fibrous polymer matrices, leading to more effective reinforcement compared to larger graphene sheets. Consequently, incorporating high-quality, small-sized graphene into polymer matrices can substantially improve the properties of these polymers. There is a growing demand for enhancing the mechanical characteristics of aramid fibers to expand their applications beyond traditional uses. This research demonstrates how sub-micron-sized graphene improves the structural integrity and mechanical strength of PMIA fibers. The results show a remarkable 46% enhancement in tensile strength compared to unmodified PMIA fibers. While the graphene/PMIA fiber exhibits exceptional mechanical properties, it also holds great potential for applications in wearables, flexible sensors, and various other domains, thanks to graphene's versatile characteristics. This research underscores the importance of utilizing small-sized, high-quality graphene to develop more robust carbonaceous nanocomposite fibers suitable for a wide range of commercial purposes. Beyond its immediate impact on PMIA fibers, this research represents a significant step forward in advancing the utilization and growth of graphene materials in various applications. ![]()
Aramid fiber is highly regarded for its outstanding properties and is widely used in various industrial applications. Among the different types of aramid fibers, meta-aramids, particularly poly(m-phenylene isophthalamide) (PMIA), are known for their exceptional flame retardance, high-temperature resistance, excellent electrical insulation, and remarkable chemical stability. As a result, PMIA-based materials find extensive use in industries focused on fire prevention, heat protection, and related applications. However, PMIA fibers have limitations due to the lack of conjugation between amide and benzene ring bonds in their molecular structure, resulting in flexible segments with low crystallinity, which in turn leads to inferior mechanical strength. Researchers have shown great interest in nanocomposites as a means to overcome these limitations. In this context, graphene nanocomposites have gained significant attention. Graphene, with its benzene ring arrangement within its layers, easily bonds with polymers possessing a similar structure. This property makes graphene a promising candidate for enhancing the mechanical strength of aromatic polymers like PMIA. Moreover, small-sized graphene particles exhibit superior dispersibility within fibrous polymer matrices, leading to more effective reinforcement compared to larger graphene sheets. Consequently, incorporating high-quality, small-sized graphene into polymer matrices can substantially improve the properties of these polymers. There is a growing demand for enhancing the mechanical characteristics of aramid fibers to expand their applications beyond traditional uses. This research demonstrates how sub-micron-sized graphene improves the structural integrity and mechanical strength of PMIA fibers. The results show a remarkable 46% enhancement in tensile strength compared to unmodified PMIA fibers. While the graphene/PMIA fiber exhibits exceptional mechanical properties, it also holds great potential for applications in wearables, flexible sensors, and various other domains, thanks to graphene's versatile characteristics. This research underscores the importance of utilizing small-sized, high-quality graphene to develop more robust carbonaceous nanocomposite fibers suitable for a wide range of commercial purposes. Beyond its immediate impact on PMIA fibers, this research represents a significant step forward in advancing the utilization and growth of graphene materials in various applications.
2023, 39(10): 230600
doi: 10.3866/PKU.WHXB202306004
Abstract:
Water, as one of the most abundant natural resources on Earth, possesses immense energy potential. Therefore, harnessing useful energy from water has always been a pursuit. With the rapid advancement of nanoscience and nanotechnology, emerging hydrovoltaic technologies have made it possible to extract electricity from various forms of water through nanomaterial-water interactions. Among these technologies, power generation through the gas-liquid phase transformation of water has garnered significant interest, particularly in the context of electricity generation induced by moisture adsorption and water evaporation. Several factors contribute to the importance of this approach. Firstly, water primarily exists on Earth in liquid and gaseous states. As integral components of the Earth's water cycle, the reversible processes of water vaporization and condensation, which involve the gas-liquid phase transformation, are less restricted by factors such as time, space, geographic location, and environment. Therefore, power generation enabled by moisture/evaporation holds promise as a solution to global energy challenges. Secondly, this method of electricity generation occurs spontaneously and requires minimal artificial assistance or intervention. Thirdly, significant advancements have been made in performance output, delivering sustained volt-level voltage and direct current, surpassing previously reported hydrovoltaic phenomena. Lastly, the electricity production process based on renewable water resources emits no greenhouse gases or pollutants. Given its abundant source, high spontaneity, excellent performance, and environmentally friendly nature, moisture/evaporation-induced electricity generation is expected to emerge as a disruptive future energy technology. In light of this, this review provides a comprehensive overview of the evolution and recent progress in electricity generation induced by moisture adsorption and water evaporation. It explores the underlying interaction mechanisms at the water-material interface and discusses various proposed power generation mechanisms, including ion concentration difference-induced diffusion, streaming potential, ionovoltaic effect, and pseudostreaming. Additionally, it introduces various nanomaterial systems, such as carbon-based materials, polymers, solid oxides, metal derivatives, non-metallic semiconductors, and biological membranes. The review also examines device structures and optimization strategies for further enhancement. Furthermore, it outlines the applications of power generators in direct energy supply, self-powered sensing, electronic components, and other fields. Finally, the review addresses the main challenges and future directions of this emerging technology, aiming to provide valuable research ideas for high-performance power generation devices. ![]()
Water, as one of the most abundant natural resources on Earth, possesses immense energy potential. Therefore, harnessing useful energy from water has always been a pursuit. With the rapid advancement of nanoscience and nanotechnology, emerging hydrovoltaic technologies have made it possible to extract electricity from various forms of water through nanomaterial-water interactions. Among these technologies, power generation through the gas-liquid phase transformation of water has garnered significant interest, particularly in the context of electricity generation induced by moisture adsorption and water evaporation. Several factors contribute to the importance of this approach. Firstly, water primarily exists on Earth in liquid and gaseous states. As integral components of the Earth's water cycle, the reversible processes of water vaporization and condensation, which involve the gas-liquid phase transformation, are less restricted by factors such as time, space, geographic location, and environment. Therefore, power generation enabled by moisture/evaporation holds promise as a solution to global energy challenges. Secondly, this method of electricity generation occurs spontaneously and requires minimal artificial assistance or intervention. Thirdly, significant advancements have been made in performance output, delivering sustained volt-level voltage and direct current, surpassing previously reported hydrovoltaic phenomena. Lastly, the electricity production process based on renewable water resources emits no greenhouse gases or pollutants. Given its abundant source, high spontaneity, excellent performance, and environmentally friendly nature, moisture/evaporation-induced electricity generation is expected to emerge as a disruptive future energy technology. In light of this, this review provides a comprehensive overview of the evolution and recent progress in electricity generation induced by moisture adsorption and water evaporation. It explores the underlying interaction mechanisms at the water-material interface and discusses various proposed power generation mechanisms, including ion concentration difference-induced diffusion, streaming potential, ionovoltaic effect, and pseudostreaming. Additionally, it introduces various nanomaterial systems, such as carbon-based materials, polymers, solid oxides, metal derivatives, non-metallic semiconductors, and biological membranes. The review also examines device structures and optimization strategies for further enhancement. Furthermore, it outlines the applications of power generators in direct energy supply, self-powered sensing, electronic components, and other fields. Finally, the review addresses the main challenges and future directions of this emerging technology, aiming to provide valuable research ideas for high-performance power generation devices.
2023, 39(10): 230602
doi: 10.3866/PKU.WHXB202306026
Abstract:
Communication technology has been rapidly advancing and widely applied in various fields, and optical fiber communication has become the fundamental basis of modern information communication, thanks to its high capacity and low loss. Optical modulators, which are essential devices in optical fiber communication systems, are typically based on bulk crystal electrical and optoelectronic devices. However, these devices have a drawback that they affect the quality of light in high-density transmission processes, thereby limiting the potential of optical fiber communication to achieve high-speed and high-capacity performance. To overcome this dilemma, researchers have been devoted to developing all-fiber devices capable of modulating, amplifying and detecting optical signals without interrupting the optical fiber transmission process. In recent years, many new types of optical fibers with different structures have been designed and fabricated. Among them, two-dimensional materials are exciting considerable attention in the field of optical modulation due to their unique properties that enhance the interaction between light and matter. Optical fiber-type modulators based on two-dimensional material hybrid fibers are expected to bring new opportunities for optical fiber communication. In this article, we will introduce various methods of combining two-dimensional materials with different structures of optical fibers, such as fiber end-face composites, hole inner-wall composites, tapered composites and side-polished composites structures. These methods can effectively integrate the advantages of both two-dimensional materials and optical fibers, and create novel optical modulators with high performance and functionality. We will also present some examples of optical modulators based on two-dimensional material hybrid fibers, including MoS2-based all-optical wavelength modulators, graphene-based electro-optical absorption modulators, and MXene-based thermo-optical phase modulators. These devices can modulate the wavelength, intensity or phase of optical signals by exploiting the optical, electrical or thermal properties of two-dimensional materials. The modulation of optical signals is achieved by changing the real and imaginary parts of the refractive index of two-dimensional materials through external optical, electric or thermal fields. In addition, we will summarize the modulation principles, processes and applications of two-dimensional material hybrid fiber modulators in different domains, such as all-optical, electro-optical, and thermo-optical. We will compare their advantages and disadvantages with conventional optical modulators based on bulk crystal devices, and explore their potential for improving the performance and efficiency of optical fiber communication systems. Finally, we will discuss the opportunities and challenges faced by the field of two-dimensional material hybrid fibers, and take a look at the perspectives for future research directions and developments. ![]()
Communication technology has been rapidly advancing and widely applied in various fields, and optical fiber communication has become the fundamental basis of modern information communication, thanks to its high capacity and low loss. Optical modulators, which are essential devices in optical fiber communication systems, are typically based on bulk crystal electrical and optoelectronic devices. However, these devices have a drawback that they affect the quality of light in high-density transmission processes, thereby limiting the potential of optical fiber communication to achieve high-speed and high-capacity performance. To overcome this dilemma, researchers have been devoted to developing all-fiber devices capable of modulating, amplifying and detecting optical signals without interrupting the optical fiber transmission process. In recent years, many new types of optical fibers with different structures have been designed and fabricated. Among them, two-dimensional materials are exciting considerable attention in the field of optical modulation due to their unique properties that enhance the interaction between light and matter. Optical fiber-type modulators based on two-dimensional material hybrid fibers are expected to bring new opportunities for optical fiber communication. In this article, we will introduce various methods of combining two-dimensional materials with different structures of optical fibers, such as fiber end-face composites, hole inner-wall composites, tapered composites and side-polished composites structures. These methods can effectively integrate the advantages of both two-dimensional materials and optical fibers, and create novel optical modulators with high performance and functionality. We will also present some examples of optical modulators based on two-dimensional material hybrid fibers, including MoS2-based all-optical wavelength modulators, graphene-based electro-optical absorption modulators, and MXene-based thermo-optical phase modulators. These devices can modulate the wavelength, intensity or phase of optical signals by exploiting the optical, electrical or thermal properties of two-dimensional materials. The modulation of optical signals is achieved by changing the real and imaginary parts of the refractive index of two-dimensional materials through external optical, electric or thermal fields. In addition, we will summarize the modulation principles, processes and applications of two-dimensional material hybrid fiber modulators in different domains, such as all-optical, electro-optical, and thermo-optical. We will compare their advantages and disadvantages with conventional optical modulators based on bulk crystal devices, and explore their potential for improving the performance and efficiency of optical fiber communication systems. Finally, we will discuss the opportunities and challenges faced by the field of two-dimensional material hybrid fibers, and take a look at the perspectives for future research directions and developments.
2023, 39(10): 230603
doi: 10.3866/PKU.WHXB202306037
Abstract:
The selective conversion of methane to C2 hydrocarbons offers a sustainable approach to utilize natural gas efficiently and reduce reliance on conventional fossil fuels. Unlike the conventional thermal catalytic conversion that requires high temperatures and pressures, the photocatalytic pathway enables methane activation and selective conversion under mild conditions, holding great promise as a sustainable method. However, achieving the efficient generation of C2 compounds under flowing conditions using cost-effective photocatalysts remains great challenge. In this work, we synthesized an ultralow loading AuPd alloy nanoparticle-supported on TiO2 (Au0.05-Pd0.05/TiO2) photocatalyst via simple chemical reduction. Characterization using X-ray diffraction (XRD), aberration corrected high-angle annular dark field scanning transmission electron microscopy (AC-HAADF-STEM) and in situ CO-diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirmed its composition and structure. The performance of the Au0.05-Pd0.05/TiO2 photocatalyst in methane conversion was evaluated under flow-reaction conditions. Remarkably, the photocatalyst efficiently converted methane containing water vapor into C2 compounds, including ethane and ethylene, with a remarkable C2 production rate of up to 10092 μmol∙g−1∙h−1 and a selectivity of 77%. While water vapor was not essential for methane conversion, its presence enhanced the production of ethane and ethylene while suppressing overoxidation to CO2. The photocatalyst demonstrated excellent stability, maintaining its catalytic activity even after continuous reaction for 32 h, surpassing previously reported results. With the assistant of transient photocurrent response test, in situ X-ray photoelectron spectroscopy spectra and in situ DRIFTS, we uncovered that the exceptional catalytic activity of Au0.05-Pd0.05/TiO2 originates from the synergistic effect of Au and Pd, which promotes the separation of photogenerated carriers and facilitates the C-C bond coupling of ·CH3 to produce C2 compounds. Furthermore, XPS characterization revealed that the introduction of water vapor replenished consumed lattice oxygen during the methane activation process, thus contributing to the catalyst's stability. This study not only offers a cost-effective and efficient photocatalyst for methane conversion but also provides insights into the fundamental mechanism of photocatalytic methane conversion. We believe that our work will inspire the exploration of inexpensive catalysts with simple preparation methods, driving advancements in efficient methane to C2 compound conversion and contributing to sustainable photocatalytic pathways for the future.![]()
The selective conversion of methane to C2 hydrocarbons offers a sustainable approach to utilize natural gas efficiently and reduce reliance on conventional fossil fuels. Unlike the conventional thermal catalytic conversion that requires high temperatures and pressures, the photocatalytic pathway enables methane activation and selective conversion under mild conditions, holding great promise as a sustainable method. However, achieving the efficient generation of C2 compounds under flowing conditions using cost-effective photocatalysts remains great challenge. In this work, we synthesized an ultralow loading AuPd alloy nanoparticle-supported on TiO2 (Au0.05-Pd0.05/TiO2) photocatalyst via simple chemical reduction. Characterization using X-ray diffraction (XRD), aberration corrected high-angle annular dark field scanning transmission electron microscopy (AC-HAADF-STEM) and in situ CO-diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirmed its composition and structure. The performance of the Au0.05-Pd0.05/TiO2 photocatalyst in methane conversion was evaluated under flow-reaction conditions. Remarkably, the photocatalyst efficiently converted methane containing water vapor into C2 compounds, including ethane and ethylene, with a remarkable C2 production rate of up to 10092 μmol∙g−1∙h−1 and a selectivity of 77%. While water vapor was not essential for methane conversion, its presence enhanced the production of ethane and ethylene while suppressing overoxidation to CO2. The photocatalyst demonstrated excellent stability, maintaining its catalytic activity even after continuous reaction for 32 h, surpassing previously reported results. With the assistant of transient photocurrent response test, in situ X-ray photoelectron spectroscopy spectra and in situ DRIFTS, we uncovered that the exceptional catalytic activity of Au0.05-Pd0.05/TiO2 originates from the synergistic effect of Au and Pd, which promotes the separation of photogenerated carriers and facilitates the C-C bond coupling of ·CH3 to produce C2 compounds. Furthermore, XPS characterization revealed that the introduction of water vapor replenished consumed lattice oxygen during the methane activation process, thus contributing to the catalyst's stability. This study not only offers a cost-effective and efficient photocatalyst for methane conversion but also provides insights into the fundamental mechanism of photocatalytic methane conversion. We believe that our work will inspire the exploration of inexpensive catalysts with simple preparation methods, driving advancements in efficient methane to C2 compound conversion and contributing to sustainable photocatalytic pathways for the future.
2023, 39(10): 230603
doi: 10.3866/PKU.WHXB202306038
Abstract:
Graphene offers exceptional properties, such as ultra-high carrier mobility, near-ballistic transport characteristics, and ultra-high-frequency operational response, making it an ideal material for radio-frequency devices and high-speed optical communications. To realize its potential applications, high-quality graphene films must be integrated onto target substrates with reliability, uniformity, and scalability. Despite significant progress in the chemical vapor deposition of high-quality graphene on catalytic metal substrates, the transfer of such films onto application-targeted substrates remains necessary for large-scale technological use, but it faces challenges like contaminations and cracks. Graphene's flexibility and single-atom thickness make it vulnerable to damage and folding during the transfer process due to force disturbances and uneven force distribution. Traditional graphene transfer methods employ organic polymers as a medium and remove them using organic solvents after transferring graphene onto the desired substrates. However, this repetitive process generates organic waste and leaves unavoidable contamination due to the limited solubility of the polymer. Furthermore, selective interlacing of organic solvents during polymer removal can detach graphene from the substrate and cause cracks. In this study, we demonstrate a novel approach to address these issues. Instead of using organic polymers, we directly use the photoresist as the transfer medium to mechanically delaminate graphene from the metal growth substrate onto the targeted substrate. By doing so, we eliminate the need for repeated polymer coating on the graphene surface, enabling successful transfer without crack formation, wrinkles, or unintentional doping. The strong interaction between graphene and the photoresist, coupled with the weakened interaction between graphene and the growth substrate due to oxidation, ensures crack-free delamination. Moreover, the photoresist serves as a patterned mask plate for exposure, etching, and other subsequent device fabrication processes. As a result, the electrical properties of graphene are improved, achieving an average carrier mobility of 6200 cm2·V−1·s−1. This integrated approach not only enhances the device performance of two-dimensional materials but also paves the way for future applications of such materials in electronics and photonics. In conclusion, our method offers a promising solution for the successful transfer and device fabrication of graphene, enhancing its potential in the field of electronics and photonics. ![]()
Graphene offers exceptional properties, such as ultra-high carrier mobility, near-ballistic transport characteristics, and ultra-high-frequency operational response, making it an ideal material for radio-frequency devices and high-speed optical communications. To realize its potential applications, high-quality graphene films must be integrated onto target substrates with reliability, uniformity, and scalability. Despite significant progress in the chemical vapor deposition of high-quality graphene on catalytic metal substrates, the transfer of such films onto application-targeted substrates remains necessary for large-scale technological use, but it faces challenges like contaminations and cracks. Graphene's flexibility and single-atom thickness make it vulnerable to damage and folding during the transfer process due to force disturbances and uneven force distribution. Traditional graphene transfer methods employ organic polymers as a medium and remove them using organic solvents after transferring graphene onto the desired substrates. However, this repetitive process generates organic waste and leaves unavoidable contamination due to the limited solubility of the polymer. Furthermore, selective interlacing of organic solvents during polymer removal can detach graphene from the substrate and cause cracks. In this study, we demonstrate a novel approach to address these issues. Instead of using organic polymers, we directly use the photoresist as the transfer medium to mechanically delaminate graphene from the metal growth substrate onto the targeted substrate. By doing so, we eliminate the need for repeated polymer coating on the graphene surface, enabling successful transfer without crack formation, wrinkles, or unintentional doping. The strong interaction between graphene and the photoresist, coupled with the weakened interaction between graphene and the growth substrate due to oxidation, ensures crack-free delamination. Moreover, the photoresist serves as a patterned mask plate for exposure, etching, and other subsequent device fabrication processes. As a result, the electrical properties of graphene are improved, achieving an average carrier mobility of 6200 cm2·V−1·s−1. This integrated approach not only enhances the device performance of two-dimensional materials but also paves the way for future applications of such materials in electronics and photonics. In conclusion, our method offers a promising solution for the successful transfer and device fabrication of graphene, enhancing its potential in the field of electronics and photonics.
2023, 39(10): 230701
doi: 10.3866/PKU.WHXB202307012
Abstract:
In electromagnetic spectrum, terahertz (THz) wave is between light and microwave. Its photon energy is much lower than normal infrared light and its frequency is higher than microwave. Therefore, it is hard to implement techniques of these two spectral ranges into THz spectrum, especially techniques in generation, modulation and detection. This has hindered the exploitation of THz spectrum although recent studies have showed its promising potentials in industries such as semiconductors, biotechnology, communications, imaging and so on. In THz detection, it is critical to have detectors with high response speed, high sensitivity and capability of operating at room temperature. In this study, we have designed a bow-tie antenna and integrated it into a graphene photodetector. By simulating with finite element analysis, we optimize the total length of the bow-tie antenna as about 50 μm and a gap of about 800 nm in the middle in order to target at 2.7 THz wave. By design, the antenna localizes the THz radiation to the narrow gap and enhances the local electric field by more than 20 times. Inside the same narrow gap, we build a graphene pn junction by applying different voltages on the two halves of the antenna, which also function as two independent gate electrodes in the device. In this device geometry, the absorption enhancement region overlaps with photocarrier separation regions in graphene, which therefore greatly increases photocurrent generation as firstly reported in Ref.25 . In addition to the antenna, we also design the channel. Firstly, we use BN-encapsulated graphene which has shown low residual doping (residual doping concentration of 1.3 × 1011 cm−2) and high mobility (μ up to 20000 cm2∙V−1∙s−1 at room temperature) in the device. The high‑quality graphene as channel guarantees a large seeback-coefficient difference at the pn junction and fast photoresponse. Secondly, the channel width at the antenna gap is reduced for further increasing the electron temperature and photocarrier-separating efficiency. Whereas the channel width at the contact is maintained for decreasing the contact resistance. With the antenna and channel design in an as-fabricated device, the photocurrent is enhanced by up to 2 orders of magnitude when the polarization of incident wave coincides with the optimized polarization of the antenna. The corresponding noise equivalent power (NEP) is calculated as about 1 nW∙Hz−1/2 if Johnson-Nyquist noise is assumed as the dominating noise. Moreover, the operating frequency is measured as larger than 5 kHz, which, together with the enhanced photoresponse, indicates that our design is a promising candidate for THz detection. ![]()
In electromagnetic spectrum, terahertz (THz) wave is between light and microwave. Its photon energy is much lower than normal infrared light and its frequency is higher than microwave. Therefore, it is hard to implement techniques of these two spectral ranges into THz spectrum, especially techniques in generation, modulation and detection. This has hindered the exploitation of THz spectrum although recent studies have showed its promising potentials in industries such as semiconductors, biotechnology, communications, imaging and so on. In THz detection, it is critical to have detectors with high response speed, high sensitivity and capability of operating at room temperature. In this study, we have designed a bow-tie antenna and integrated it into a graphene photodetector. By simulating with finite element analysis, we optimize the total length of the bow-tie antenna as about 50 μm and a gap of about 800 nm in the middle in order to target at 2.7 THz wave. By design, the antenna localizes the THz radiation to the narrow gap and enhances the local electric field by more than 20 times. Inside the same narrow gap, we build a graphene pn junction by applying different voltages on the two halves of the antenna, which also function as two independent gate electrodes in the device. In this device geometry, the absorption enhancement region overlaps with photocarrier separation regions in graphene, which therefore greatly increases photocurrent generation as firstly reported in Ref.
2023, 39(10): 230702
doi: 10.3866/PKU.WHXB202307028
Abstract:
As a new member of graphene materials family, super graphene-skinned material is a type of graphene composite materials made by directly depositing continuous graphene layers on traditional materials via chemical vapor deposition (CVD) process. By growing high-performance graphene "skin", the traditional materials are given new functionalities. The atomically thin graphene hitches a ride on the traditional material carriers to market. Beyond coating graphene powder on traditional materials, the directly-grown continuous graphene "skin" keeps its intrinsic excellent properties to a great extent, and holds the promise on future applications. Super graphene-skinned material is an innovative pathway for applications of continuous graphene films, which avoids the challenging peeling-transfer process and solves the non-self-supporting issue of ultrathin graphene film. The graphene skin almost has no influence on macroscale morphology of the supporting substrate, which leads to the high process compatibility of super graphene-skinned material in practical application scenarios. Therefore, graphene-skinned materials would exhibit their excellent performance without changing the processing of current engineering materials, and will be pushed to real industrial applications relying on the broad market of current engineering materials.Super graphene-skinned materials can be categorized into graphene-skinned metallic materials and graphene-skinned nonmetallic materials. Depending on the different morphologies of supporting substrate materials including foil, fiber, powder, foam, etc., one can obtain graphene-skinned foil, graphene-skinned fiber, graphene-skinned powder, graphene-skinned foam, etc. Additionally, together with post-processing treatments and compositing with other materials, great versatilities can be expected for super graphene-skinned materials. As a typical example, graphene-skinned glass fiber, combining the excellent properties of graphene and glass fiber, such as the high electrical conductivity and thermal conductivity of graphene, along with the remarkable mechanical strength and flexibility of glass fiber. Graphene-skinned glass fiber presented wonderful electrothermal performances with fast heating rate and high heating uniformity, which has been successfully applied for the anti/deicing of aircraft and wind blade. The new concept of super graphene-skinned material opens up a new avenue for practical applications of continuous graphene films, strongly promotes the fusion of graphene and traditional materials, and provides new power for accelerating the graphene industry.![]()
As a new member of graphene materials family, super graphene-skinned material is a type of graphene composite materials made by directly depositing continuous graphene layers on traditional materials via chemical vapor deposition (CVD) process. By growing high-performance graphene "skin", the traditional materials are given new functionalities. The atomically thin graphene hitches a ride on the traditional material carriers to market. Beyond coating graphene powder on traditional materials, the directly-grown continuous graphene "skin" keeps its intrinsic excellent properties to a great extent, and holds the promise on future applications. Super graphene-skinned material is an innovative pathway for applications of continuous graphene films, which avoids the challenging peeling-transfer process and solves the non-self-supporting issue of ultrathin graphene film. The graphene skin almost has no influence on macroscale morphology of the supporting substrate, which leads to the high process compatibility of super graphene-skinned material in practical application scenarios. Therefore, graphene-skinned materials would exhibit their excellent performance without changing the processing of current engineering materials, and will be pushed to real industrial applications relying on the broad market of current engineering materials.Super graphene-skinned materials can be categorized into graphene-skinned metallic materials and graphene-skinned nonmetallic materials. Depending on the different morphologies of supporting substrate materials including foil, fiber, powder, foam, etc., one can obtain graphene-skinned foil, graphene-skinned fiber, graphene-skinned powder, graphene-skinned foam, etc. Additionally, together with post-processing treatments and compositing with other materials, great versatilities can be expected for super graphene-skinned materials. As a typical example, graphene-skinned glass fiber, combining the excellent properties of graphene and glass fiber, such as the high electrical conductivity and thermal conductivity of graphene, along with the remarkable mechanical strength and flexibility of glass fiber. Graphene-skinned glass fiber presented wonderful electrothermal performances with fast heating rate and high heating uniformity, which has been successfully applied for the anti/deicing of aircraft and wind blade. The new concept of super graphene-skinned material opens up a new avenue for practical applications of continuous graphene films, strongly promotes the fusion of graphene and traditional materials, and provides new power for accelerating the graphene industry.
