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2024 Volume 40 Issue 5
2024, 40(5): 230502
doi: 10.3866/PKU.WHXB202305029
Abstract:
Metal nanoclusters are rising stars in material science, and one advantage is their atomically precise tunability. It is well known that metal doping can efficiently modify the properties of metal nanoclusters. In particular, without altering the parent nanocluster framework, doping a single heterometal atom can tailor the properties of metal nanoclusters and aid investigations of the structure–property relationship of metal nanoclusters. To our knowledge, the simultaneous synthesis of a single heterometal-doped nanocluster and its parent nanocluster is challenging and has not been previously reported; however, this is highly desirable because it can prevent the influence of trace impurities and allow comparison between doped and undoped nanoclusters. The single Cd-doped gold nanocluster Au22Cd1(S-Adm)16 (S-Adm = 1-adamantanethiolate) has been previously synthesized and structurally elucidated. However, the structure of the parent nanocluster, Au23(S-Adm)16, remains unknown, inspiring this investigation. In this study, we synthesized Au23(S-Adm)16 and its single-doped Au22Cd1(S-Adm)16 nanocluster in one pot for the first time, and we resolved their structures using single-crystal X-ray crystallography. The structure of Au22Cd1(S-Adm)16 is similar to that of Au23(S-Adm)16 except that a kernel Au atom in Au23(S-Adm)16 is replaced with a Cd atom. This Cd replacement causes the kernel Au―Au bond length to increase owing to the loosening of the original closely packed structure. In contrast to prior reports, Au23(S-Adm)16 is surprisingly more stable than Au22Cd1(S-Adm)16, as determined via ultraviolet visible-near infrared (UV-Vis-NIR) spectroscopy at 80 ℃. This stability was attributed to the decrease in the kernel Au―Au bond length. Although the maximum absorption of Au22Cd1(S-Adm)16 slightly red-shifted from 605 to 608 nm after Cd doping, the molar extinction coefficient of Au23(S-Adm)16 at 605 nm was approximately twice that of Au22Cd1(S-Adm)16 at 608 nm. Thus, the increase in kernel Au―Au bond length may decrease the photoexcitation electron transfer efficiency owing to lengthening of the photoexcitation electron transfer pathway. As further support for this opinion, although the two nanoclusters showed similar emission profiles and maxima (750 nm for Au23(S-Adm)16 and 760 nm for Au22Cd1(S-Adm)16), they exhibited obvious emission intensity differences. Specifically, the quantum yield of Au23(S-Adm)16 (approximately 3.160 × 10−5) was found to be 1.13 times that of Au22Cd1(S-Adm)16 (approximately 2.793 × 10−5). Thus, the stability and absorption and emission intensities correlate with the kernel Au―Au bond length.This study shows that two metal nanoclusters with slight structural differences can exhibit different properties in terms of optical and thermal stability, providing a good reference for studying their structure–property relationships. ![]()
Metal nanoclusters are rising stars in material science, and one advantage is their atomically precise tunability. It is well known that metal doping can efficiently modify the properties of metal nanoclusters. In particular, without altering the parent nanocluster framework, doping a single heterometal atom can tailor the properties of metal nanoclusters and aid investigations of the structure–property relationship of metal nanoclusters. To our knowledge, the simultaneous synthesis of a single heterometal-doped nanocluster and its parent nanocluster is challenging and has not been previously reported; however, this is highly desirable because it can prevent the influence of trace impurities and allow comparison between doped and undoped nanoclusters. The single Cd-doped gold nanocluster Au22Cd1(S-Adm)16 (S-Adm = 1-adamantanethiolate) has been previously synthesized and structurally elucidated. However, the structure of the parent nanocluster, Au23(S-Adm)16, remains unknown, inspiring this investigation. In this study, we synthesized Au23(S-Adm)16 and its single-doped Au22Cd1(S-Adm)16 nanocluster in one pot for the first time, and we resolved their structures using single-crystal X-ray crystallography. The structure of Au22Cd1(S-Adm)16 is similar to that of Au23(S-Adm)16 except that a kernel Au atom in Au23(S-Adm)16 is replaced with a Cd atom. This Cd replacement causes the kernel Au―Au bond length to increase owing to the loosening of the original closely packed structure. In contrast to prior reports, Au23(S-Adm)16 is surprisingly more stable than Au22Cd1(S-Adm)16, as determined via ultraviolet visible-near infrared (UV-Vis-NIR) spectroscopy at 80 ℃. This stability was attributed to the decrease in the kernel Au―Au bond length. Although the maximum absorption of Au22Cd1(S-Adm)16 slightly red-shifted from 605 to 608 nm after Cd doping, the molar extinction coefficient of Au23(S-Adm)16 at 605 nm was approximately twice that of Au22Cd1(S-Adm)16 at 608 nm. Thus, the increase in kernel Au―Au bond length may decrease the photoexcitation electron transfer efficiency owing to lengthening of the photoexcitation electron transfer pathway. As further support for this opinion, although the two nanoclusters showed similar emission profiles and maxima (750 nm for Au23(S-Adm)16 and 760 nm for Au22Cd1(S-Adm)16), they exhibited obvious emission intensity differences. Specifically, the quantum yield of Au23(S-Adm)16 (approximately 3.160 × 10−5) was found to be 1.13 times that of Au22Cd1(S-Adm)16 (approximately 2.793 × 10−5). Thus, the stability and absorption and emission intensities correlate with the kernel Au―Au bond length.This study shows that two metal nanoclusters with slight structural differences can exhibit different properties in terms of optical and thermal stability, providing a good reference for studying their structure–property relationships.
2024, 40(5): 230501
doi: 10.3866/PKU.WHXB202305018
Abstract:
Cholesteric liquid crystal (CLC) microdroplets, as three-dimensional photonic crystals, exhibit high spatial symmetry. In these microdroplets, LC molecules are aligned parallel to the surface of the spherical geometry, while the helical axes are radially oriented. This symmetrical helical superstructure arrangement forms a Bragg-onion structure within the CLC microdroplets, resulting in selective reflection of a specific wavelength in all directions. Due to their unique angle-independent photonic bandgap (reflection wavelength), CLC microdroplets have emerged as promising optical materials for applications such as omnidirectional lasers, reflective displays, and microsensors. Recently, there has been growing interest in capillary microfluidic technologies, which allow the fabrication of monodisperse and complex CLC microdroplets with regular molecular alignment in a continuous, controllable, and high-throughput manner. This review primarily focuses on CLC microdroplets fabricated using capillary microfluidic technologies. Firstly, the characteristics of capillary microfluidic technology are outlined, along with three important parameters for fabricating CLC microdroplets: inertial, viscous, and interfacial forces. Capillary microfluidic devices typically consist of hydrophilic or hydrophobic tapered capillaries inserted into a square capillary. The principle of immiscible liquids is utilized to select suitable solution systems. By designing the device structures and choosing appropriate solution systems, single, double, triple, and even multiple CLC microdroplets can be fabricated. Secondly, the optical properties of CLCs confined in spherical geometries are discussed. CLC self-organizes into ordered helical superstructures while maintaining fluidity, leading to symmetrical pitch lengths in CLC microdroplets that respond to stimuli. The mechanisms and strategies for tuning the structural colors of CLC microdroplets under varying temperatures, solvents, and light conditions are demonstrated. Additionally, the unique photonic cross-communication between closely packed, monodisperse CLC microdroplets is explained in the context of single, double, or opposite-handedness helical superstructures in CLCs. Furthermore, the review reports on the current and prospective applications of CLC microdroplets in omnidirectional lasers, reflective displays, and microsensors. Various methods for inducing lasing in CLC microdroplets are presented, including distributed feedback resonators, Bragg reflection resonators, and whispering gallery modes. Flexible reflection labels and security labels are generated by incorporating different materials in each layer of the microdroplets or by leveraging the unclonable photonic cross-communication micropatterns observed in hexagonally close-packed CLC microdroplets. The responsive pitch lengths and molecular alignments of CLC microdroplets also make them suitable candidates for colorimetric reporters and optical biosensors. Finally, the review briefly discusses the existing challenges and opportunities in the field of CLC microdroplets, offering a forecast for future developments. ![]()
Cholesteric liquid crystal (CLC) microdroplets, as three-dimensional photonic crystals, exhibit high spatial symmetry. In these microdroplets, LC molecules are aligned parallel to the surface of the spherical geometry, while the helical axes are radially oriented. This symmetrical helical superstructure arrangement forms a Bragg-onion structure within the CLC microdroplets, resulting in selective reflection of a specific wavelength in all directions. Due to their unique angle-independent photonic bandgap (reflection wavelength), CLC microdroplets have emerged as promising optical materials for applications such as omnidirectional lasers, reflective displays, and microsensors. Recently, there has been growing interest in capillary microfluidic technologies, which allow the fabrication of monodisperse and complex CLC microdroplets with regular molecular alignment in a continuous, controllable, and high-throughput manner. This review primarily focuses on CLC microdroplets fabricated using capillary microfluidic technologies. Firstly, the characteristics of capillary microfluidic technology are outlined, along with three important parameters for fabricating CLC microdroplets: inertial, viscous, and interfacial forces. Capillary microfluidic devices typically consist of hydrophilic or hydrophobic tapered capillaries inserted into a square capillary. The principle of immiscible liquids is utilized to select suitable solution systems. By designing the device structures and choosing appropriate solution systems, single, double, triple, and even multiple CLC microdroplets can be fabricated. Secondly, the optical properties of CLCs confined in spherical geometries are discussed. CLC self-organizes into ordered helical superstructures while maintaining fluidity, leading to symmetrical pitch lengths in CLC microdroplets that respond to stimuli. The mechanisms and strategies for tuning the structural colors of CLC microdroplets under varying temperatures, solvents, and light conditions are demonstrated. Additionally, the unique photonic cross-communication between closely packed, monodisperse CLC microdroplets is explained in the context of single, double, or opposite-handedness helical superstructures in CLCs. Furthermore, the review reports on the current and prospective applications of CLC microdroplets in omnidirectional lasers, reflective displays, and microsensors. Various methods for inducing lasing in CLC microdroplets are presented, including distributed feedback resonators, Bragg reflection resonators, and whispering gallery modes. Flexible reflection labels and security labels are generated by incorporating different materials in each layer of the microdroplets or by leveraging the unclonable photonic cross-communication micropatterns observed in hexagonally close-packed CLC microdroplets. The responsive pitch lengths and molecular alignments of CLC microdroplets also make them suitable candidates for colorimetric reporters and optical biosensors. Finally, the review briefly discusses the existing challenges and opportunities in the field of CLC microdroplets, offering a forecast for future developments.
2024, 40(5): 230601
doi: 10.3866/PKU.WHXB202306011
Abstract:
Sodium-ion energy storage devices are considered as an ideal substitute for popular lithium-ion counterparts because of its resource richness and environmental friendliness. Among the various sodium-ion energy storage devices, sodium-ion capacitors (SICs) have the combined advantages in high energy and power densities as well as long-term cycling stability in theory. Antimony (Sb) is considered as an attractive anode material for SICs due to its high theoretical capacity of 660 mAh∙g−1, low operating potential (0.5–0.8 V vs. Na/Na+), and high density of 6.68 g∙cm−3. However, the large volume change of Sb during the Na+ insertion leads to fast decay in capacity and poor rate capability, which becomes a fundamental issue greatly hindering the practical application. Herein, a facile galvanic replacement approach is proposed for the synthesis of an ultrafine amorphous Sb nanoparticles anchoring on carbon coated two-dimensional (2D) reduced graphene oxides (RGO). Half-cell test (vs. metal Na) shows that as-prepared Sb-C@RGO anode delivers a high specific capacity of 521.5 mAh∙g−1 at 0.1 A∙g−1. As the current density increases to 10 A∙g−1, Sb-C@RGO anode still maintains a specific capacity of 83.5 mAh∙g−1, suggesting its high-rate properties. The excellent Na+ charge storage property of Sb-C@RGO anode is primarily due to its unique 2D hybrid architecture, which largely increases the atomic interface contact with Na+ and shortens ion diffusion path, thus facilitating ion/electron transfer. To demonstrate the feasibility of Sb-C@RGO as the high-performance electrode for emerging energy-storage devices, a hybrid cell configuration (e.g., SIC) was fabricated by employing the Sb-C@RGO as the negative electrode (battery type) and home-made activated carbon (PDPC) as the positive electrode (capacitive type) in a Na+ based organic electrolyte. This SIC is capable of operating at a high voltage of 4.0 V and exhibiting a high energy density of 140.75 Wh∙kg−1 at a power density of 250.84 W∙kg−1. Even the power density is magnified ~50 times to 12.43 kW∙kg−1, this SIC still delivers a high energy density of 55 Wh∙kg−1. Within a short charge/discharge of ~3.2 min, this SIC can store/release quite a high energy density of 108.5 Wh∙kg−1, which represents the remarkable performance among the reported Sb-based capacitors. In addition, this SIC shows the good cycling stability with an acceptable capacity retention value of 66.27% after 1000 cycles at a current density of 2 A∙g−1. Our results may provide insight into the rational design and construction of high-capacity Sb-based anode materials for advanced sodium-ion based energy storage devices. ![]()
Sodium-ion energy storage devices are considered as an ideal substitute for popular lithium-ion counterparts because of its resource richness and environmental friendliness. Among the various sodium-ion energy storage devices, sodium-ion capacitors (SICs) have the combined advantages in high energy and power densities as well as long-term cycling stability in theory. Antimony (Sb) is considered as an attractive anode material for SICs due to its high theoretical capacity of 660 mAh∙g−1, low operating potential (0.5–0.8 V vs. Na/Na+), and high density of 6.68 g∙cm−3. However, the large volume change of Sb during the Na+ insertion leads to fast decay in capacity and poor rate capability, which becomes a fundamental issue greatly hindering the practical application. Herein, a facile galvanic replacement approach is proposed for the synthesis of an ultrafine amorphous Sb nanoparticles anchoring on carbon coated two-dimensional (2D) reduced graphene oxides (RGO). Half-cell test (vs. metal Na) shows that as-prepared Sb-C@RGO anode delivers a high specific capacity of 521.5 mAh∙g−1 at 0.1 A∙g−1. As the current density increases to 10 A∙g−1, Sb-C@RGO anode still maintains a specific capacity of 83.5 mAh∙g−1, suggesting its high-rate properties. The excellent Na+ charge storage property of Sb-C@RGO anode is primarily due to its unique 2D hybrid architecture, which largely increases the atomic interface contact with Na+ and shortens ion diffusion path, thus facilitating ion/electron transfer. To demonstrate the feasibility of Sb-C@RGO as the high-performance electrode for emerging energy-storage devices, a hybrid cell configuration (e.g., SIC) was fabricated by employing the Sb-C@RGO as the negative electrode (battery type) and home-made activated carbon (PDPC) as the positive electrode (capacitive type) in a Na+ based organic electrolyte. This SIC is capable of operating at a high voltage of 4.0 V and exhibiting a high energy density of 140.75 Wh∙kg−1 at a power density of 250.84 W∙kg−1. Even the power density is magnified ~50 times to 12.43 kW∙kg−1, this SIC still delivers a high energy density of 55 Wh∙kg−1. Within a short charge/discharge of ~3.2 min, this SIC can store/release quite a high energy density of 108.5 Wh∙kg−1, which represents the remarkable performance among the reported Sb-based capacitors. In addition, this SIC shows the good cycling stability with an acceptable capacity retention value of 66.27% after 1000 cycles at a current density of 2 A∙g−1. Our results may provide insight into the rational design and construction of high-capacity Sb-based anode materials for advanced sodium-ion based energy storage devices.
2024, 40(5): 230503
doi: 10.3866/PKU.WHXB202305038
Abstract:
Intercepting tiny droplets in nano-emulsions is crucial for the development of membrane materials with pore diameters smaller than the droplet size, as per the size screening mechanism. While this method achieves high separation efficiency, it results in a decrease in separation flux. On the one hand, the use of macro-porous materials can increase the flux, but it does not guarantee high efficiency on the other hand. Fabricating superwetting materials that exhibit both high efficiency and flux in separating nanosized emulsions provides opportunities for overcoming the bottleneck yet how to extend the applicable range with high efficiency remains a challenge. To address this issue, we propose a strategy to enhance the hydrophilicity of supramolecular framework nanosheets by modifying hydrophilic graphene oxide (GO). By incorporating GO into the supramolecular framework (SF) composite membrane through a sequential pumping process onto a commercial matrix, we create a GO-assisted SF composite membrane capable of separating oil-in-water (O/W) emulsions containing nanosized droplets. The framework intercepts the dispersed tiny droplets in the emulsions through uniform nanoscale pores while also facilitating the demulsification process through electrostatic interaction on its negatively charged surface. The hydrophilic GO modification on the composite membrane enhances its water affinity and promotes the formation of a hydrated layer on the membrane surface. The resulting composite membrane exhibits a nanoscale cut-off size, a negatively charged surface, and oleophobicity under water. Importantly, it achieves high water flux and resistance to oil contamination. By leveraging the size screening and demulsification effects, the composite membrane efficiently removes nanosized oil droplets dispersed in O/W emulsions stabilized by non-ionic, anionic, and cationic surfactants. Particularly for emulsions containing ionic surfactants, no residual droplets are detected through dynamic light scattering (DLS) after separation. The filtrate exhibits a total organic carbon (TOC) content of less than 10 ppm, corresponding to a separation efficiency greater than 99.9%, which surpasses the standards of many countries and organizations. Furthermore, compared to the original SF membrane, the composite membrane demonstrates approximately 3.5 times higher separation permeation during the separation process of various emulsions. Additionally, the composite membrane exhibits an anti-fouling effect and achieves a high flux recovery rate, ensuring stable separation performance for 5 cycles through simple water washing treatment. The composite membrane retains its components throughout repeated use, exhibits thermal stability up to 150 ℃, and can withstand corrosive chemical environments, including 1 mol·L−1 HCl, 0.01 mol·L−1 NaOH, and 1 mol·L−1 NaCl. In this study, we realize the combination of two components with distinct structural and surface characteristics to fabricate a composite membrane through a simple method and achieve high-performance separation of nanosized O/W emulsions through synergistic functionality. ![]()
Intercepting tiny droplets in nano-emulsions is crucial for the development of membrane materials with pore diameters smaller than the droplet size, as per the size screening mechanism. While this method achieves high separation efficiency, it results in a decrease in separation flux. On the one hand, the use of macro-porous materials can increase the flux, but it does not guarantee high efficiency on the other hand. Fabricating superwetting materials that exhibit both high efficiency and flux in separating nanosized emulsions provides opportunities for overcoming the bottleneck yet how to extend the applicable range with high efficiency remains a challenge. To address this issue, we propose a strategy to enhance the hydrophilicity of supramolecular framework nanosheets by modifying hydrophilic graphene oxide (GO). By incorporating GO into the supramolecular framework (SF) composite membrane through a sequential pumping process onto a commercial matrix, we create a GO-assisted SF composite membrane capable of separating oil-in-water (O/W) emulsions containing nanosized droplets. The framework intercepts the dispersed tiny droplets in the emulsions through uniform nanoscale pores while also facilitating the demulsification process through electrostatic interaction on its negatively charged surface. The hydrophilic GO modification on the composite membrane enhances its water affinity and promotes the formation of a hydrated layer on the membrane surface. The resulting composite membrane exhibits a nanoscale cut-off size, a negatively charged surface, and oleophobicity under water. Importantly, it achieves high water flux and resistance to oil contamination. By leveraging the size screening and demulsification effects, the composite membrane efficiently removes nanosized oil droplets dispersed in O/W emulsions stabilized by non-ionic, anionic, and cationic surfactants. Particularly for emulsions containing ionic surfactants, no residual droplets are detected through dynamic light scattering (DLS) after separation. The filtrate exhibits a total organic carbon (TOC) content of less than 10 ppm, corresponding to a separation efficiency greater than 99.9%, which surpasses the standards of many countries and organizations. Furthermore, compared to the original SF membrane, the composite membrane demonstrates approximately 3.5 times higher separation permeation during the separation process of various emulsions. Additionally, the composite membrane exhibits an anti-fouling effect and achieves a high flux recovery rate, ensuring stable separation performance for 5 cycles through simple water washing treatment. The composite membrane retains its components throughout repeated use, exhibits thermal stability up to 150 ℃, and can withstand corrosive chemical environments, including 1 mol·L−1 HCl, 0.01 mol·L−1 NaOH, and 1 mol·L−1 NaCl. In this study, we realize the combination of two components with distinct structural and surface characteristics to fabricate a composite membrane through a simple method and achieve high-performance separation of nanosized O/W emulsions through synergistic functionality.
2024, 40(5): 230305
doi: 10.3866/PKU.WHXB202303050
Abstract:
Owing to its high energy density, sustainability, and pollution-free combustion, hydrogen is considered one of the most promising emerging energy carriers to replace conventional fossil fuels. Among the various hydrogen production technologies, electrolytic water splitting has gained significant attention thanks to its high efficiency and environmentally friendly characteristics. However, the large-scale application of electrolytic water splitting is often hindered by the limitations imposed by the anodic oxygen evolution reaction (OER). To overcome this challenge, a promising alternative approach is to replace the OER with the electrocatalytic glycerol oxidation reaction (GOR) at the anode. This substitution can lead to energy savings and enhanced efficiency of electrolytic water splitting for hydrogen production, thereby further promoting the development of hydrogen as a clean energy source. However, the application of the GOR at anode requires efficient, cost-effective, and highly selective electrocatalysts. To this end, we report the development of a novel acid-alkaline dual-electrolyte flow electrolyzer (AADEF-electrolyzer) by coupling the GOR at the alkaline anode with the hydrogen evolution reaction (HER) at the acidic cathode. A self-supported NiCo2O4 nanoneedle electrode material (NiCo2O4/NF) has been in situ grown on nickel foam (NF) using a simple hydrothermal-calcination method. The electrode demonstrates excellent electrocatalytic performance for the GOR, achieving high electrolysis current density at low potentials and exhibiting high selectivity for formate production, with the Faraday efficiency exceeding 85%. Density functional theory (DFT) calculations imply that NiCo2O4 has a lower energy barrier for the reaction and that the presence of Ni facilitates the reduction of the Co state density, thereby promoting the GOR. An innovative AADEF-electrolyzer was constructed by utilizing NiCo2O4/NF as the anode for the GOR and an acidic cathode for the HER. Experimental results indicate that the AADEF-electrolyzer exhibits excellent GOR performance with a low overpotential and high selectivity toward formate production. It requires a voltage of only 0.36 V to achieve a current density of 10 mA·cm−2 and long-term stability with a Faraday efficiency close to 100% for hydrogen production. The low-cost and easily fabricated self-supported electrode material, together with the acid-alkaline dual-electrolyte flow electrolyzer, provide an innovative strategy for developing hybrid electrolysis systems. ![]()
Owing to its high energy density, sustainability, and pollution-free combustion, hydrogen is considered one of the most promising emerging energy carriers to replace conventional fossil fuels. Among the various hydrogen production technologies, electrolytic water splitting has gained significant attention thanks to its high efficiency and environmentally friendly characteristics. However, the large-scale application of electrolytic water splitting is often hindered by the limitations imposed by the anodic oxygen evolution reaction (OER). To overcome this challenge, a promising alternative approach is to replace the OER with the electrocatalytic glycerol oxidation reaction (GOR) at the anode. This substitution can lead to energy savings and enhanced efficiency of electrolytic water splitting for hydrogen production, thereby further promoting the development of hydrogen as a clean energy source. However, the application of the GOR at anode requires efficient, cost-effective, and highly selective electrocatalysts. To this end, we report the development of a novel acid-alkaline dual-electrolyte flow electrolyzer (AADEF-electrolyzer) by coupling the GOR at the alkaline anode with the hydrogen evolution reaction (HER) at the acidic cathode. A self-supported NiCo2O4 nanoneedle electrode material (NiCo2O4/NF) has been in situ grown on nickel foam (NF) using a simple hydrothermal-calcination method. The electrode demonstrates excellent electrocatalytic performance for the GOR, achieving high electrolysis current density at low potentials and exhibiting high selectivity for formate production, with the Faraday efficiency exceeding 85%. Density functional theory (DFT) calculations imply that NiCo2O4 has a lower energy barrier for the reaction and that the presence of Ni facilitates the reduction of the Co state density, thereby promoting the GOR. An innovative AADEF-electrolyzer was constructed by utilizing NiCo2O4/NF as the anode for the GOR and an acidic cathode for the HER. Experimental results indicate that the AADEF-electrolyzer exhibits excellent GOR performance with a low overpotential and high selectivity toward formate production. It requires a voltage of only 0.36 V to achieve a current density of 10 mA·cm−2 and long-term stability with a Faraday efficiency close to 100% for hydrogen production. The low-cost and easily fabricated self-supported electrode material, together with the acid-alkaline dual-electrolyte flow electrolyzer, provide an innovative strategy for developing hybrid electrolysis systems.
2024, 40(5): 230502
doi: 10.3866/PKU.WHXB202305028
Abstract:
Due to rapid industrial development and human activities, CO2 emissions have led to serious environmental/ecological problems and climate changes such as global warming. Due to this situation, achieving carbon neutrality has become an urgent mission to improve the future of mankind. The use of the electrocatalytic CO2 reduction reaction (CO2RR) to produce higher-value fuels and chemicals is an effective strategy for reducing CO2 emissions and easing the energy crisis. The water oxidation half-reaction (WOR), which occurs at the anode in a traditional CO2RR system, typically suffers from slow kinetics, a large overpotential, and high energy consumption. The organic pollutant formaldehyde (HCHO) is oxidized into industrial materials (such as formic acid) under neutral conditions, which is of great significance for the sustainable production of energy and lessening environmental pollution. In addition, the number of electron transfers involved and the required potential for the HCHO oxidation half-reaction (FOR) are smaller than those of WOR, suggesting that FOR could potentially replace WOR as a coupling reaction with CO2 reduction. In this study, FOR at a MnO2/CP anode is introduced to produce a novel paired CO2RR/FOR system. The current density and generation rate of CO2RR products in this paired CO2RR/FOR system are generally larger than those of conventional CO2RR/WOR systems at the same applied potential. Moreover, in paired CO2RR/FOR systems, HCHO can be selectively converted into HCOOH at certain applied potentials. Nearly 90% of the HCHO can be selectively converted to HCOOH with a conversion efficiency of about 48% at a cell voltage of 3.5 V in a two-electrode paired CO2RR/FOR system. More significantly, under a different working current, the potentials required for FOR are systemically smaller than those for WOR. At −10 mA∙cm−2, the cell voltage of the paired CO2RR/FOR system can be reduced by 210 mV, and the required electric energy for the paired CO2RR/FOR system can be reduced by 45.13% compared with the sum of single CO2RR and FOR systems. Notably, when a commercial polysilicon solar cell is used as the power supply, improvements in the current density, the generation rate of CO2RR products, and the HCHO to HCOOH selectivity can be still achieved in the paired CO2RR/FOR system. The present work will inspire further studies for developing novel paired CO2RR systems for the cost-effective, simultaneous conversion of CO2 and organic pollutants into valuable chemicals. ![]()
Due to rapid industrial development and human activities, CO2 emissions have led to serious environmental/ecological problems and climate changes such as global warming. Due to this situation, achieving carbon neutrality has become an urgent mission to improve the future of mankind. The use of the electrocatalytic CO2 reduction reaction (CO2RR) to produce higher-value fuels and chemicals is an effective strategy for reducing CO2 emissions and easing the energy crisis. The water oxidation half-reaction (WOR), which occurs at the anode in a traditional CO2RR system, typically suffers from slow kinetics, a large overpotential, and high energy consumption. The organic pollutant formaldehyde (HCHO) is oxidized into industrial materials (such as formic acid) under neutral conditions, which is of great significance for the sustainable production of energy and lessening environmental pollution. In addition, the number of electron transfers involved and the required potential for the HCHO oxidation half-reaction (FOR) are smaller than those of WOR, suggesting that FOR could potentially replace WOR as a coupling reaction with CO2 reduction. In this study, FOR at a MnO2/CP anode is introduced to produce a novel paired CO2RR/FOR system. The current density and generation rate of CO2RR products in this paired CO2RR/FOR system are generally larger than those of conventional CO2RR/WOR systems at the same applied potential. Moreover, in paired CO2RR/FOR systems, HCHO can be selectively converted into HCOOH at certain applied potentials. Nearly 90% of the HCHO can be selectively converted to HCOOH with a conversion efficiency of about 48% at a cell voltage of 3.5 V in a two-electrode paired CO2RR/FOR system. More significantly, under a different working current, the potentials required for FOR are systemically smaller than those for WOR. At −10 mA∙cm−2, the cell voltage of the paired CO2RR/FOR system can be reduced by 210 mV, and the required electric energy for the paired CO2RR/FOR system can be reduced by 45.13% compared with the sum of single CO2RR and FOR systems. Notably, when a commercial polysilicon solar cell is used as the power supply, improvements in the current density, the generation rate of CO2RR products, and the HCHO to HCOOH selectivity can be still achieved in the paired CO2RR/FOR system. The present work will inspire further studies for developing novel paired CO2RR systems for the cost-effective, simultaneous conversion of CO2 and organic pollutants into valuable chemicals.
2024, 40(5): 230504
doi: 10.3866/PKU.WHXB202305047
Abstract:
The use of solar energy as an inexhaustible resource to conduct photocatalytic water splitting in hydrogen (H2) production can alleviate the worldwide energy crisis and achieve carbon neutrality. However, research in photocatalytic H2 evolution reaction (HER) is extremely challenging in terms of exploring the current development of an active and durable graphitic carbon nitride (g-C3N4)-based photocatalyst. Several parameters of pristine g-C3N4 require structural, physical, and chemical improvements, such as optimization of the surface area, electron transfer, and photo-generated carrier recombination, to render the g-C3N4 suitable for photocatalysis. In this study, the development of an efficient and robust S-doped g-C3N4 (S-g-CN) catalyst was pursued that involves doping nitrogen (N) active sites of g-C3N4 with sulfur (S) dopants via one-step calcination of the sulphate and melamine precursors. A combination of structural and spectroscopic fingerprints was established to distinctly determine the realization of S-doping onto the g-C3N4 structure. We obtained the optimum Gibbs free energy of adsorbed hydrogen (ΔGH*) for S-g-CN at the S active sites, which is nearly zero (~0.26 eV), suggesting that the filled S dopants play an essential role in optimizing the adsorption and desorption processes of H-active intermediates. The results of atomic force and transmission electron microscopies (AFM and TEM) demonstrated that the produced S-g-CN catalyst has an ultrathin nanosheet structure with a lamellar thickness of approximately 2.5 nm. A subsequent N2 sorption isotherms test revealed a substantial increase in the specific surface area after the integration of S dopants into the g-C3N4 nanoskeleton. Moreover, the incorporation of S atoms into the g-C3N4 significantly increased the carrier concentrations, improving the transfer, separation, as well as the oxidation and reduction abilities of the photo-generated electron-hole pairs. Leveraging the favorable material characteristics of the S-doped two-dimensional nanostructures, the resulting S-g-CN achieved a high H2 evolution rate of 4923 μmol·g−1·h−1, which is 28 times higher than that of the pristine g-C3N4. Additionally, the developed S-g-CN possessed a high apparent quantum efficiency (3.64%) at visible-light irradiation. When compared to the recently reported S-doped g-C3N4-based photocatalysts, our optimal S-g-CN catalyst (S-CN1.0) showed one of the best HER catalytic activities. Our rational design is based on an effective strategy that not only explored a promising HER photocatalyst but also aimed to pave the way for the development of other high-performance g-C3N4 based catalysts. ![]()
The use of solar energy as an inexhaustible resource to conduct photocatalytic water splitting in hydrogen (H2) production can alleviate the worldwide energy crisis and achieve carbon neutrality. However, research in photocatalytic H2 evolution reaction (HER) is extremely challenging in terms of exploring the current development of an active and durable graphitic carbon nitride (g-C3N4)-based photocatalyst. Several parameters of pristine g-C3N4 require structural, physical, and chemical improvements, such as optimization of the surface area, electron transfer, and photo-generated carrier recombination, to render the g-C3N4 suitable for photocatalysis. In this study, the development of an efficient and robust S-doped g-C3N4 (S-g-CN) catalyst was pursued that involves doping nitrogen (N) active sites of g-C3N4 with sulfur (S) dopants via one-step calcination of the sulphate and melamine precursors. A combination of structural and spectroscopic fingerprints was established to distinctly determine the realization of S-doping onto the g-C3N4 structure. We obtained the optimum Gibbs free energy of adsorbed hydrogen (ΔGH*) for S-g-CN at the S active sites, which is nearly zero (~0.26 eV), suggesting that the filled S dopants play an essential role in optimizing the adsorption and desorption processes of H-active intermediates. The results of atomic force and transmission electron microscopies (AFM and TEM) demonstrated that the produced S-g-CN catalyst has an ultrathin nanosheet structure with a lamellar thickness of approximately 2.5 nm. A subsequent N2 sorption isotherms test revealed a substantial increase in the specific surface area after the integration of S dopants into the g-C3N4 nanoskeleton. Moreover, the incorporation of S atoms into the g-C3N4 significantly increased the carrier concentrations, improving the transfer, separation, as well as the oxidation and reduction abilities of the photo-generated electron-hole pairs. Leveraging the favorable material characteristics of the S-doped two-dimensional nanostructures, the resulting S-g-CN achieved a high H2 evolution rate of 4923 μmol·g−1·h−1, which is 28 times higher than that of the pristine g-C3N4. Additionally, the developed S-g-CN possessed a high apparent quantum efficiency (3.64%) at visible-light irradiation. When compared to the recently reported S-doped g-C3N4-based photocatalysts, our optimal S-g-CN catalyst (S-CN1.0) showed one of the best HER catalytic activities. Our rational design is based on an effective strategy that not only explored a promising HER photocatalyst but also aimed to pave the way for the development of other high-performance g-C3N4 based catalysts.
2024, 40(5): 230504
doi: 10.3866/PKU.WHXB202305043
Abstract:
This study focuses on exploring efficient photocatalysts for water splitting, which holds great potential for harnessing hydrogen (H2) as a renewable energy source. Modulating the heterojunction interface is known to enhance charge carrier separation and solar energy utilization, thereby boosting photocatalytic activity. In this work, a mechanical mixing-assisted self-assembly approach was developed to construct a heterojunction between NiPS3 (NPS) nanosheets (NSs) and C3N5 (CN) NSs. Specifically, two-dimensional (2D) NPS NSs were tightly deposited on 2D CN NSs surface to gain a 2D/2D heterostructure. The photocatalytic performance of the synthesized photocatalysts was determined by their ability to generate H2 through water splitting, both in deionized (DI) water and seawater, under visible light. The resulting NPS NSs/CN NSs (NPS/CN) composites possessed boosted photocatalytic hydrogen evolution (PHE) activity related to CN NSs and NPS NSs. This improvement was assigned to the synergistic effect of increased light-harvesting capacity and heterojunction formation. Nevertheless, an excessive amount of deposited NPS NSs on the surface of CN NSs was found to reduce the light absorption of the CN NSs component in the NPS/CN composites, resulting in decreased PHE activity. Therefore, it was determined that an appropriate mass ratio between the two components is necessary to achieve excellent photocatalytic activity for the NPS/CN composites. The optimized photocatalyst, referred to as 3-NPS/CN, demonstrated the highest visible-light-driven PHE efficiency of 47.71 μmol∙h−1, which was 2385.50 times higher than that of CN NSs. Moreover, 3-NPS/CN also exhibited excellent PHE activity in seawater, with a rate of 8.99 μmol∙h−1. The photoelectrochemical, steady-state photoluminescence (PL), time-resolved PL (TR-PL), steady-state surface photovoltage (SPV) and time-resolved surface photovoltage (TPV) techniques were performed to investigate the charge separation and migration behaviors of various photocatalysts. Based on the characterization results, our group proposed a reasonable PHE mechanism. In the NPS/CN photocatalysts, photo-induced electrons rapidly migrated from the conduction band (CB) of CN NSs to the CB of NPS NSs due to the potential difference and strong interfacial electronic coupling between the two materials. The photogenerated electrons accumulated on the CB of the NPS NSs component efficiently reduced protons to generate H2 molecules. Concurrently, photogenerated holes on the valence band (VB) of CN NSs and NPS NSs were consumed with the assistance of triethanolamine (TEOA) molecules. This study presents a facile method for fabricating 2D/2D heterostructured photocatalysts, which hold promise for efficient and robust implementation in energy applications. ![]()
This study focuses on exploring efficient photocatalysts for water splitting, which holds great potential for harnessing hydrogen (H2) as a renewable energy source. Modulating the heterojunction interface is known to enhance charge carrier separation and solar energy utilization, thereby boosting photocatalytic activity. In this work, a mechanical mixing-assisted self-assembly approach was developed to construct a heterojunction between NiPS3 (NPS) nanosheets (NSs) and C3N5 (CN) NSs. Specifically, two-dimensional (2D) NPS NSs were tightly deposited on 2D CN NSs surface to gain a 2D/2D heterostructure. The photocatalytic performance of the synthesized photocatalysts was determined by their ability to generate H2 through water splitting, both in deionized (DI) water and seawater, under visible light. The resulting NPS NSs/CN NSs (NPS/CN) composites possessed boosted photocatalytic hydrogen evolution (PHE) activity related to CN NSs and NPS NSs. This improvement was assigned to the synergistic effect of increased light-harvesting capacity and heterojunction formation. Nevertheless, an excessive amount of deposited NPS NSs on the surface of CN NSs was found to reduce the light absorption of the CN NSs component in the NPS/CN composites, resulting in decreased PHE activity. Therefore, it was determined that an appropriate mass ratio between the two components is necessary to achieve excellent photocatalytic activity for the NPS/CN composites. The optimized photocatalyst, referred to as 3-NPS/CN, demonstrated the highest visible-light-driven PHE efficiency of 47.71 μmol∙h−1, which was 2385.50 times higher than that of CN NSs. Moreover, 3-NPS/CN also exhibited excellent PHE activity in seawater, with a rate of 8.99 μmol∙h−1. The photoelectrochemical, steady-state photoluminescence (PL), time-resolved PL (TR-PL), steady-state surface photovoltage (SPV) and time-resolved surface photovoltage (TPV) techniques were performed to investigate the charge separation and migration behaviors of various photocatalysts. Based on the characterization results, our group proposed a reasonable PHE mechanism. In the NPS/CN photocatalysts, photo-induced electrons rapidly migrated from the conduction band (CB) of CN NSs to the CB of NPS NSs due to the potential difference and strong interfacial electronic coupling between the two materials. The photogenerated electrons accumulated on the CB of the NPS NSs component efficiently reduced protons to generate H2 molecules. Concurrently, photogenerated holes on the valence band (VB) of CN NSs and NPS NSs were consumed with the assistance of triethanolamine (TEOA) molecules. This study presents a facile method for fabricating 2D/2D heterostructured photocatalysts, which hold promise for efficient and robust implementation in energy applications.
2024, 40(5): 230701
doi: 10.3866/PKU.WHXB202307016
Abstract:
Developing novel nanostructures to enhance the efficiency of solar-to-chemical conversion through integrated photocatalytic hydrogen (H2) evolution and organic transformation holds great promise in addressing pressing energy and environmental crises. Ternary metal sulfides have garnered considerable attention in photocatalytic H2 production due to their tunable bandgap and excellent visible light response. Among them, Zn0.5Cd0.5S stands out as a reduction photocatalyst with a narrow bandgap, a high conduction band level, and excellent resistance to photocorrosion. However, unitary Zn0.5Cd0.5S suffers from a high recombination rate of photogenerated electron/hole pairs, resulting in only a small fraction of charge carriers being involved in the photoreactions, leading to a low quantum efficiency that falls short of practical demand. WO3, a typical oxidation photocatalyst with a lower valence band position and strong oxidization ability, is an ideal candidate for constructing an S-scheme heterojunction with Zn0.5Cd0.5S. Herein, a core-shell structured WO3/Zn0.5Cd0.5S heterojunction with Zn0.5Cd0.5S nanosheets vertically growing out of WO3 nanofibers is fabricated through electrospinning and hydrothermal methods. The distinct disparity in work functions leads to the transfer of electrons from Zn0.5Cd0.5S to WO3 upon contact, creating an interfacial electric field (IEF) and simultaneously bending the energy bands at the interface. As a consequence of IEF, bent energy bands, and coulomb attraction, the photogenerated electrons in the conduction band of WO3 migrate to the valence band of Zn0.5Cd0.5S and recombine with its photoinduced holes, signifying the formation of an S-scheme heterojunction between WO3 and Zn0.5Cd0.5S and enabling efficient separation of powerful charge carriers, as evidenced by in situ irradiated X-ray photoelectron spectroscopy, electron paramagnetic resonance, and time-resolved fluorescence spectroscopy analyses. Benefiting from the unique S-scheme photocatalytic mechanism, along with the effective chemisorption and activation of reactants on the catalyst, the optimized WO3/Zn0.5Cd0.5S heterostructures exhibit exceptional photocatalytic performance in H2 production (715 μmol∙g−1∙h−1) and the transformation from lactic acid to pyruvic acid without the need for any noble metal cocatalyst, achieving the full utilization of photoinduced electrons and holes. In situ diffuse reflectance infrared Fourier transform spectroscopy, as well as density functional theory simulations, reveal the photoreaction mechanism of H2 production and organic transformation. This work offers valuable insights into the design and investigation of the mechanism behind novel S-scheme heterojunction photocatalysts, enabling high-performance H2 production and simultaneous organic transformation. ![]()
Developing novel nanostructures to enhance the efficiency of solar-to-chemical conversion through integrated photocatalytic hydrogen (H2) evolution and organic transformation holds great promise in addressing pressing energy and environmental crises. Ternary metal sulfides have garnered considerable attention in photocatalytic H2 production due to their tunable bandgap and excellent visible light response. Among them, Zn0.5Cd0.5S stands out as a reduction photocatalyst with a narrow bandgap, a high conduction band level, and excellent resistance to photocorrosion. However, unitary Zn0.5Cd0.5S suffers from a high recombination rate of photogenerated electron/hole pairs, resulting in only a small fraction of charge carriers being involved in the photoreactions, leading to a low quantum efficiency that falls short of practical demand. WO3, a typical oxidation photocatalyst with a lower valence band position and strong oxidization ability, is an ideal candidate for constructing an S-scheme heterojunction with Zn0.5Cd0.5S. Herein, a core-shell structured WO3/Zn0.5Cd0.5S heterojunction with Zn0.5Cd0.5S nanosheets vertically growing out of WO3 nanofibers is fabricated through electrospinning and hydrothermal methods. The distinct disparity in work functions leads to the transfer of electrons from Zn0.5Cd0.5S to WO3 upon contact, creating an interfacial electric field (IEF) and simultaneously bending the energy bands at the interface. As a consequence of IEF, bent energy bands, and coulomb attraction, the photogenerated electrons in the conduction band of WO3 migrate to the valence band of Zn0.5Cd0.5S and recombine with its photoinduced holes, signifying the formation of an S-scheme heterojunction between WO3 and Zn0.5Cd0.5S and enabling efficient separation of powerful charge carriers, as evidenced by in situ irradiated X-ray photoelectron spectroscopy, electron paramagnetic resonance, and time-resolved fluorescence spectroscopy analyses. Benefiting from the unique S-scheme photocatalytic mechanism, along with the effective chemisorption and activation of reactants on the catalyst, the optimized WO3/Zn0.5Cd0.5S heterostructures exhibit exceptional photocatalytic performance in H2 production (715 μmol∙g−1∙h−1) and the transformation from lactic acid to pyruvic acid without the need for any noble metal cocatalyst, achieving the full utilization of photoinduced electrons and holes. In situ diffuse reflectance infrared Fourier transform spectroscopy, as well as density functional theory simulations, reveal the photoreaction mechanism of H2 production and organic transformation. This work offers valuable insights into the design and investigation of the mechanism behind novel S-scheme heterojunction photocatalysts, enabling high-performance H2 production and simultaneous organic transformation.
2024, 40(5): 230402
doi: 10.3866/PKU.WHXB202304027
Abstract:
Two-dimensional (2D) layered materials have attracted widespread research interest and have significantly promoted the development of chemistry, material science, and condensed matter physics. Since the emergence of graphene, 2D materials with unique mechanical, thermal, optical, and electrical properties have been developed. In the case of graphene, its extraordinary mechanical strength, carrier mobility, thermal conductivity, and light-absorption over the whole spectral range in UV-Vis and near infrared guarantee a wide range of prospective applications. The electronic structure and properties of graphene flakes are dominated by their thickness, twist angle, and dielectric environment. Tailoring the interlayer interactions of graphene layers can provide additional opportunities for developing optical and electrical nanodevices, resulting in pioneering outcomes, such as the magic-angle graphene. Over the past decade, one of the most active research directions in the field of 2D materials has been the development of novel techniques that can probe the thickness-dependent physical properties of layered materials. In contrast with the intensively studied mechanical, electrical, and optical properties, microscopic investigations of the thermal characteristics of graphene flakes remain to be explored. Photothermal (PT) microscopy is a new all-optical microscopic imaging technique that has gained substantial attention and undergone long-term development in recent years, especially in the fields of nanomaterials and life sciences. The fundamental principle of PT microscopy is to heat the target sample based on the absorption of a heating beam and use a probe beam to indirectly capture information on microscale heat generation and transport. Inspired by several pioneering studies, we conducted a comparative study of the thickness-dependent PT properties of mechanically exfoliated graphene flakes in two different PT media, i.e., air and glycerol. Whereas a nonlinear relationship between the PT intensity and sample thickness was observed in both media, the PT intensities from the two media were distinct. A high-contrast and non-monotonic PT response was observed in glycerol. The PT intensity of monolayer graphene was higher than that of bilayer graphene, and the PT intensities of graphene flakes with 2–4 layers exhibited a good linear relationship with the thickness. We also analyzed the relationship between the PT intensity and heating or probe power, demonstrating that the PT intensity as well as the absorption cross-section of graphene derived from the PT signal vary linearly with the power of both laser beams. Our study provides insights into light absorption and thermal relaxation features of graphene flakes of different thicknesses, which can guide future studies on the thermal properties of layered materials and their heterostructures. ![]()
Two-dimensional (2D) layered materials have attracted widespread research interest and have significantly promoted the development of chemistry, material science, and condensed matter physics. Since the emergence of graphene, 2D materials with unique mechanical, thermal, optical, and electrical properties have been developed. In the case of graphene, its extraordinary mechanical strength, carrier mobility, thermal conductivity, and light-absorption over the whole spectral range in UV-Vis and near infrared guarantee a wide range of prospective applications. The electronic structure and properties of graphene flakes are dominated by their thickness, twist angle, and dielectric environment. Tailoring the interlayer interactions of graphene layers can provide additional opportunities for developing optical and electrical nanodevices, resulting in pioneering outcomes, such as the magic-angle graphene. Over the past decade, one of the most active research directions in the field of 2D materials has been the development of novel techniques that can probe the thickness-dependent physical properties of layered materials. In contrast with the intensively studied mechanical, electrical, and optical properties, microscopic investigations of the thermal characteristics of graphene flakes remain to be explored. Photothermal (PT) microscopy is a new all-optical microscopic imaging technique that has gained substantial attention and undergone long-term development in recent years, especially in the fields of nanomaterials and life sciences. The fundamental principle of PT microscopy is to heat the target sample based on the absorption of a heating beam and use a probe beam to indirectly capture information on microscale heat generation and transport. Inspired by several pioneering studies, we conducted a comparative study of the thickness-dependent PT properties of mechanically exfoliated graphene flakes in two different PT media, i.e., air and glycerol. Whereas a nonlinear relationship between the PT intensity and sample thickness was observed in both media, the PT intensities from the two media were distinct. A high-contrast and non-monotonic PT response was observed in glycerol. The PT intensity of monolayer graphene was higher than that of bilayer graphene, and the PT intensities of graphene flakes with 2–4 layers exhibited a good linear relationship with the thickness. We also analyzed the relationship between the PT intensity and heating or probe power, demonstrating that the PT intensity as well as the absorption cross-section of graphene derived from the PT signal vary linearly with the power of both laser beams. Our study provides insights into light absorption and thermal relaxation features of graphene flakes of different thicknesses, which can guide future studies on the thermal properties of layered materials and their heterostructures.
2024, 40(5): 230404
doi: 10.3866/PKU.WHXB202304043
Abstract:
Gold nanorods (Au NRs) have been widely used in the optics, electricity, informatics, and biomedical fields in recent years. However, Au NRs with specialized requirements cannot be prepared by conventional methods. For instance, in photothermal therapy, Au NRs with high aspect ratios (ARs) are desirable for increasing tissue penetration and reducing the burning of human skin during treatment. However, when their ARs were adjusted to match the laser used in second near-infrared windows (NIR-II), the length and width of the Au NRs simultaneously increased. This increase in width reduces its photothermal conversion efficiency. Unfortunately, tuning the ARs of Au NRs at a fixed width requires complex procedures. In this study, we developed a new seeded-growth method to synthesize different ARs of fixed width Au NRs (FW-Au NRs). To the best of our knowledge, this is the first study to adjust the length of FW-Au NRs by introducing lauryl alcohol (LA) molecules into the traditional seeded growth method. Moreover, the length span of FW23-Au, FW14-Au, and FW6.5-Au NRs (the superscript numbers denote the width of Au NRs in nm) was adjusted between 130 and 38.4 nm, 109 and 26.4 nm, and 16 and 46 nm, respectively, by judiciously selecting the corresponding reaction conditions. Notably, the lengths of the Au NRs can be readily achieved at a fixed width over a wide range. In addition, their ARs were tuned at a fixed width by adjusting only their length, instead of simultaneously varying their length and width. In addition, their widths were maintained between 6.5 and 23 nm by adjusting [AgNO3] between 0.24 and 0.30 mmol∙L−1 in the presence of LA. Furthermore, the synergetic effect of Ag+ and LA on the density of the cetyltrimethylammonium (CTA)-Br-Ag+ complexes distributed on the facets of added Au-NP seeds, which can impact their symmetry-breaking efficiency (SBE) and the particle number of Au-NP seeds that grow into final Au NRs, is key to the synthesis of FW-Au NRs. The results of this study offer a flexible and reliable method to tune the length of Au NRs with a fixed width and pave the way for achieving an on-demand synthesis of Au NRs, especially for cancer photothermal therapy. ![]()
Gold nanorods (Au NRs) have been widely used in the optics, electricity, informatics, and biomedical fields in recent years. However, Au NRs with specialized requirements cannot be prepared by conventional methods. For instance, in photothermal therapy, Au NRs with high aspect ratios (ARs) are desirable for increasing tissue penetration and reducing the burning of human skin during treatment. However, when their ARs were adjusted to match the laser used in second near-infrared windows (NIR-II), the length and width of the Au NRs simultaneously increased. This increase in width reduces its photothermal conversion efficiency. Unfortunately, tuning the ARs of Au NRs at a fixed width requires complex procedures. In this study, we developed a new seeded-growth method to synthesize different ARs of fixed width Au NRs (FW-Au NRs). To the best of our knowledge, this is the first study to adjust the length of FW-Au NRs by introducing lauryl alcohol (LA) molecules into the traditional seeded growth method. Moreover, the length span of FW23-Au, FW14-Au, and FW6.5-Au NRs (the superscript numbers denote the width of Au NRs in nm) was adjusted between 130 and 38.4 nm, 109 and 26.4 nm, and 16 and 46 nm, respectively, by judiciously selecting the corresponding reaction conditions. Notably, the lengths of the Au NRs can be readily achieved at a fixed width over a wide range. In addition, their ARs were tuned at a fixed width by adjusting only their length, instead of simultaneously varying their length and width. In addition, their widths were maintained between 6.5 and 23 nm by adjusting [AgNO3] between 0.24 and 0.30 mmol∙L−1 in the presence of LA. Furthermore, the synergetic effect of Ag+ and LA on the density of the cetyltrimethylammonium (CTA)-Br-Ag+ complexes distributed on the facets of added Au-NP seeds, which can impact their symmetry-breaking efficiency (SBE) and the particle number of Au-NP seeds that grow into final Au NRs, is key to the synthesis of FW-Au NRs. The results of this study offer a flexible and reliable method to tune the length of Au NRs with a fixed width and pave the way for achieving an on-demand synthesis of Au NRs, especially for cancer photothermal therapy.
