Nanosheet Aerogels Research Articles

Multienzyme-like MnO2@Ag aerogel as SERS/colorimetric sensing platform for the fermentation process of tea and assess the total antioxidant capacity

The unique feature of tea fermentation is the oxidation of polyphenols, which contributes to the distinct total antioxidant capacity (TAC) of different teas. In this study, we designed and synthesized a MnO2@Ag nanosheet aerogel with diverse enzyme-like activity. It exhibits an intrinsic laccase-like activity, capable of effectively oxidizing catechins to mimic the tea fermentation process, thereby generating quinone-type oxidation products (oxCC). Additionally, the MnO2@Ag aerogel exhibits surface-enhanced Raman scattering (SERS) activity, which allows for the sensitive detection of epigallocatechin gallate (EGCG) down to 1 µM. By utilizing the EGCG-induced MnO2@Ag aerogel, we have established an EGCG-TAC sensing platform to evaluate the TAC of various teas. The results indicate that the TAC of green tea > oolong tea > black tea > Pu'er tea, with Xinyang Maojian exhibiting the strongest TAC in green tea, reaching 889 µM EGCG.

Ni3S2/Ni2O3 heterojunction anchored on N-doped carbon nanosheet aerogels for dual-ion hybrid supercapacitors

As a member of transition metal sulfides, Ni3S2 has been reported as one type of the effective pseudocapacitive electrode materials for supercapacitors, due to its good electrical conductivity and high electrochemical activity. To further improve the energy density of the Ni3S2-based supercapacitors, we propose a novel approach to the Ni3S2/Ni2O3 heterojunction anchored on N-doped carbon nanosheet aerogels (Ni3S2/Ni2O3@N-CNA), which is used as the cathode for Zn-ion hybrid supercapacitors with the dual-ion electrolytes. The Ni3S2/Ni2O3@N-CNA samples can be prepared through the bubble-templated polymerization of pyrrole and the carbonization of the polypyrrole nanosheet hydrogel/Ni2+. The Ni3S2/Ni2O3@N-CNA cathode is immersed into the Li-ion catholyte for Li+ storage, while the Zn foil anode is immersed into the Zn-ion anolyte for Zn2+ storage. Electrochemical kinetic analysis of the dual-ion hybrid supercapacitor indicates its evident capacitance characteristic. Additionally, theoretical calculations reveal that the Ni3S2/Ni2O3 heterojunction can facilitate the adsorption and dehydration of a hydrated Li+ ion to further play a great role in the enhancement of pseudocapacitance. Based on the novel strategy of the alkaline dual-ion electrolytes, this dual-ion hybrid supercapacitor with the high energy density (64.2 Wh kg−1) opens up a new avenue to develop high-performance Zn-ion hybrid supercapacitors.

Hierarchically porous N-doped carbon nanosheet aerogel cathodes for Zn-ion hybrid supercapacitors with superhigh energy density

Carbon nanomaterials with large specific surface area and high electronic conductivity, have been widely used as capacitive cathode materials for Zn-ion hybrid supercapacitors. Doping of heteroatoms and regulation of pore structure are crucial for boosting the energy storage performances of the carbon-based cathodes. We propose a N-doped carbon nanosheet aerogel (N-CNAG) with high active N content and hierarchically porous structure, which can be prepared by the bubble-templated polymerization of Py and the carbonization of the PPy nanosheet hydrogel (PPyNHG). The high active N content of N-CNAG can produce high pseudocapacitance through the N-dependent electrochemical redox reactions. The hierarchically porous structure of N-CNAG can facilitate fast electrolyte ion diffusion. Based on the Zn anode and the N-CNAG cathode, the Zn-ion hybrid supercapacitor can provide a remarkable specific capacitance of 706 F g−1 at 1 A g−1 and the rate capability of 50 % from 1 A g−1 to 5 A g−1, mainly attributed to the high active N content and the hierarchically porous structure of N-CNAG. Additionally, this Zn-ion hybrid supercapacitor provides the superhigh energy density of 392 Wh kg−1 at 1 kW kg−1 and the cycling stability of 87.4 % after 10,000 cycles, holding great potential for developing high-energy-density Zn-ion hybrid supercapacitors.

Revealing Disparities in Porous Networks Between Yttria Aerogel Assemblies with Nanosheets and Nanoparticles and Their Ultrathermal Insulation and Optical Properties.

Recent advancements have introduced anisotropic structures, particularly 2D nanosheets, into aerogels, resulting in unique morphologies and exceptional properties that differ from those assembled by isotropic nanoparticles. However, exploration of the distinct porous networks and the resulting properties is limited. We focus on rare earth yttria (Y2O3) aerogels as a case in point and demonstrate the synthesis of aerogels with nanosheet and nanoparticle assemblies using elaborative sol-gel chemistry. With the aid of X-ray computed tomography, three-dimensional visualizations of the aerogels provide relative compressive views of the porous network, revealing that the Y2O3 aerogel assembled by nanosheets possesses a hierarchical pore structure characterized by uneven pore distribution, particularly the presence of macropores throughout; in contrast, these consist of nanoparticles exhibiting a relative uniform pore distribution. High-temperature examinations indicate that the nanosheet aerogels are much more stable with a specific surface area of 64 m2·g-1 after being exposed at 1300 °C; meanwhile, the aerogels present durable and efficient thermal insulation performances. The exceptional thermal properties are attributed to the synergistic effects of the nanosheets' crystalline nature and the hierarchical porous network. The nanosheet Y2O3 aerogel also exhibited superior luminescent emission characteristics, further enhancing its potential for various applications. Our findings provide further insights into optimization of the microstructures in nanoporous aerogels, particularly through the utilization of anisotropic nanosheets.

Highly Selective Pd Nanosheet Aerogel Catalyst with Hybrid Strain Induced by Laser Irradiation and P Doping Postprocess (Small 4/2023)

Hybrid Strains The defect-rich crystalline/amorphous Pd nanosheet aerogel with hybrid microstrain and lattice strain is synthesized by combining laser irradiation in liquid and phosphorus doping methods. The measured mass activity, specific activity and C1-path selectivity of the Pd nanosheet aerogel are 4.48, 3.06 and 5.06 times higher than those of commercial Pd/C, respectively. More details can be found in article number 2205587 by Yan Zhao and co-workers.

Highly Selective Pd Nanosheet Aerogel Catalyst with Hybrid Strain Induced by Laser Irradiation and P Doping Postprocess.

Strain engineering of electrocatalysts provides an effective strategy to improve the intrinsic catalytic activity. Here, the defect-rich crystalline/amorphous Pd nanosheet aerogel with hybrid microstrain and lattice strain is synthesized by combining laser irradiation and phosphorus doping methods. The surface strain exhibited by the microstrain and lattice strain shifts the d-band center of the electrocatalyst, enhancing the adsorption of intermediates in the ethanol oxidation reaction and thus improving the catalytic performances. The measured mass activity, specific activity and C1-path selectivity of the Pd nanosheet aerogel are 4.48, 3.06, and 5.06 times higher than those of commercial Pd/C, respectively. These findings afford a new strategy for the preparation of highl activity and C1 pathway selective catalysts and provide insight into the catalytic mechanism of strain-rich heterojunction materials based on tunable surface strain values.

An invisible hand: Hydrogen bonding guided synthesis of ultrathin two-dimensional amorphous TiO2 nanosheets

Ultrathin two-dimensional (2D) porous nanosheets are one of the most promising nanomaterials in various applications, whereas their synthesis is still challenging. Herein, ultrathin 2D amorphous TiO2 (a-TiO2) porous nanosheet aerogel is synthesized via a surfactant-free assembly process followed by low-temperature calcination. The co-existing O—O and —OH groups on the surface of TiO2 precursor break the 3D spherical symmetry, and the hydrogen bonding among the TiO2 precursors is proposed as the main driving force guiding the 2D assembly. The surfactant-free assembly endows the ultrathin a-TiO2 porous nanosheet with improved ionic and electronic conductivity. The porous structure provides high surface area and easy electrolyte penetration, accelerating the Li ion diffusion rate of the a-TiO2 porous nanosheet. Attributing to the above advantages, the obtained a-TiO2 porous nanosheets are one of the best anode materials for lithium-ion batteries, which is proved by the enhanced electrochemical performance.

A bubble-templated approach to holey N/S-codoped carbon nanosheet aerogels with honeycomb-like structure for supercapacitors

Holey graphene with unique in-plane holes at the basal plane of graphene, has shown extraordinary promise for high-rate supercapacitors (SCs), due to its hole architecture that can shorten ion diffusion paths and facilitate electrolyte ion penetration. However, holey graphene is usually fabricated through a chemical etching procedure to create holes, which requires rigorous etching conditions and a cumbersome purification process. We propose a novel holey N/S-codoped carbon nanosheet aerogel (HNS-CNA) with honeycomb-like structure, which can be fabricated through an unprecedented bubble-templated polymerization of pyrrole and the subsequent carbonization of the holey polypyrrole nanosheet hydrogel (H-PPyNH) precursors. The bubble-templated route to H-PPyNH is considered to be promising for large-scale commercialization, due to the superiority of this cost-effective solution procedure. With the voltage window of 2 V, the symmetric HNS-CNA-1 SC delivers a high specific capacitance of 129 F g−1 at 1 A g−1, cycling stability of 90.7% (after 10,000 cycles) and energy density of 71.7 Wh kg−1 at 1 kW kg−1, attributed to abundant holes and N/S co-doping characteristics, which can facilitate electrolyte ion diffusion and introduce pseudocapacitance respectively. This holey N/S-codoped carbon nanosheet aerogel opens up a facile approach to promising electrode materials for highly-efficient capacitive energy storage.

Three-dimensional reduced graphene oxide/montmorillonite nanosheet aerogels as electrode material for supercapacitor application

Three-dimensional reduced graphene oxide/montmorillonite nanosheet aerogels (RGMTAs) have been successfully fabricated through hydrothermal method. X-ray diffraction and field-emission scanning electron microscope were used to characterize the structures of RGMTAs, and the electrochemical performance was investigated by electrochemical measurements. The restacking of reduced graphene oxide aerogel can be effectively inhibited without obvious structure change by using a small amount of montmorillonite nanosheets (Mts). The reduced graphene oxide/Mts aerogel shows enhanced electrochemical performance with a high specific capacitance of 275 F g−1 at a current density of 1 A g−1, and excellent rate capability. Moreover, though it is not conductive, excessive Mts only slightly increase the equivalent series resistance and charge transfer resistance. This work demonstrates that 2D Mts can reduce the restacking degree of graphene sheets, and the 3D reduced graphene oxide/Mt. nanosheet aerogel is a potential electrode material for supercapacitor applications.

Polydopamine nanoparticles@MoS2 nanosheet aerogel-based ECL sensing system for MiRNA-126 detection

In this paper, we developed a novel electrochemiluminescence (ECL) sensing system based on polydopamine nanoparticles (PDA NPs) and MoS2 nanosheet aerogel. PDA NPs with phenylboronic acid (PBA) were synthesized as a novel kind of organic nano-luminophores. The PDA-PBA NPs had high ECL efficiency and regulable emitting wavelength (552 ~ 610 nm). MoS2 nanosheet aerogel played the important role in the improvement of ECL sensing performance. On the one hand, MoS2 nanosheet aerogel can load a large number of PDA-PBA NPs. The accommodation of PDA-PBA NPs in the MoS2 nanosheet aerogel kept the dispersed state, which prevented NPs aggregation and ECL quenching effect. On the other hand, the excellent conductivity of MoS2 nanosheet aerogel significantly facilitated the electron transfer. Electron injection with MoS2 nanosheet aerogel can effectively reduce the damage of PDA-PBA NPs by excessive hot electrons. As a result, the ECL signal of PDA-PBA NPs@MoS2 nanosheet aerogel have been amplified over 60 times than PDA NPs. Furthermore, the bright ECL light of PDA-PBA NPs@MoS2 nanosheet aerogel can be clearly observed with the smartphone. Finally, a target-catalyzed hairpin assembly (CHA) sensing mode was designed to visually detect MiRNA-126 (detection limit as 0.56 aM). The MoS2 nanosheet aerogel-based sensing system provided a new pathway in the development of ECL analysis research.

Constructing g-C3N4 quantum dots modified g-C3N4/GO nanosheet aerogel for UV-Vis-NIR driven highly efficient photocatalytic H2 production

The development of ultraviolet to near-infrared (UV-Vis-NIR) responsive photocatalysts offers a unique opportunity for the full use of solar energy to solve the energy and the environmental problems. Here, successful preparation of a three-dimensional (3D) porous photocatalyst of graphitic carbon nitride quantum dot (CNQDs) modified g-C3N4/graphene oxide composite aerogel (CNGO/CNQDs) via hydrothermal and vacuum injection method was reported. In this unique ternary 3D photocatalyst, graphene oxide could improve the separation of photogenerated electrons and holes and promote the charge separation, while the aerogel's 3D network structure provided a rich active site. Simultaneously, due to the appropriate up-conversion performance of the nitrogen carbide quantum dots, CNGO/CNQDs achieved a light response from ultraviolet (UV) to near-infrared (NIR). These properties endow it with a good photocatalytic performance. The hydrogen production efficiency of CNGO/CNQDs reached 1231 μmol h−1, which was 16 times more than that of matrix material. In addition, the apparent quantum yields (AQY) of CNGO/CNQDs at wavelengths of 420 nm and 700 nm were 13% and 0.116%, respectively.

Ultrathin nickel phosphide nanosheet aerogel electrocatalysts derived from Ni-alginate for hydrogen evolution reaction

Transition metal phosphides (TMPs) have been regarded as an alternative to Pt-based catalysts for hydrogen evolution reaction (HER) on account of their high performance and low cost. The ultrathin two-dimensional (2D) nanosheets of TMPs can expose abundant active sites and facilitate the transfer of mass/charge to enhance HER performance. However, the synthesis of ultrathin 2D nanosheets of TMPs is still a great challenge. Herein, we reported a novel and scalable strategy to prepare 2D ultrathin nickel phosphide nanosheets (∼2.5 nm) by using alginate as precursor through ice-templating process. The role of ice-templating is that the growth of the ice crystals would squeeze Ni-alginate into 2D nanosheets, and then forming Ni-alginate aerogels. The three-dimensional (3D) interconnected porous network of aerogels was advantageous to reduce the lattice strains of subsequent oxidation and phosphorization process. It is the key step to prepare 2D ultrathin nickel phosphides (Ni2P and Ni5P4) nanosheets. As expected, all the prepared Ni5P4 nanosheet aerogels displayed remarkable HER performance in 1 M KOH electrolyte. Especially, due to their ultrathin 2D nanosheets and high P percentage, the Ni5P4-500-350 sample with excellent long-term stability exhibits a low overpotential of 147 mV at current density of 10 mA cm−2 and a low Tafel slope of 57 mV dec−1.

Mechanistic insight into high-efficiency sodium storage based on N/O/P-functionalized ultrathin carbon nanosheet

Heteroatom functionalized carbon materials are considered as the most promising candidate for SIBs, which display excellent Na+ storage performance. However, the relationship between the structure and electronic properties and sodium storage isn't completely revealed for heteroatom-functionalized carbon, including the effect of heteroatom on conductivity and charge distribution of carbon, the possible stable adsorption model for Na+ ion, and the diffusion characteristic of Na+ ion between heteroatom-functionalized carbon layers. Herein, we synthesize N/O/P-functionalized ultrathin carbon nanosheet aerogels (NOP–CNSAs) via a simple thermal treatment method. The prepared NOP–CNSAs possess ultrahigh specific surface area (SSA) and ultrathin thickness of ~1 nm. The density functional theory (DFT) calculations find that the N/O/P-functionalization in the carbon nanosheets can boost the electronic conductivity of carbon and increase the charge accumulation region around the heteroatoms functionalized bilayer carbon. This results in an increase adsorption energy (−2.64 eV) of Na+, and a decrease in barrier energy values of Na+ diffusion (0.13 eV) in N/O/P-functionalized carbon. When evaluating NOP–CNSAs as anode materials for SIBs, the specific capacity of the sample is 317 mA h g−1 at 100 mA g−1, and the cycling stability is outstanding (182 mA h g−1 at 1000 mA g−1 over 3000 cycles).

3D graphene aerogel wrapped 3D flower-like Fe3O4 as a long stable and high rate anode material for lithium ion batteries

Flower-like Fe3O4/graphene aerogel (Fe3O4/GA) composite was prepared by water-bath vitamin C reduction self-assembly process followed by a heat treatment under N2 atmosphere. The morphological and structural results demonstrate that 3D flower-like Fe3O4 particles are homogenously embedded into the 3D conductive network of graphene nanosheet aerogels. Based on this unique structure, flower-like Fe3O4/GA composite exhibits a high reversible capacity of 797 mAh g−1 at 0.2 A g−1, and good rate capacity of 551 mAh g−1 at 3.2 A g−1 as well as excellent cycling performance with a stable capacity of ~1138 mAh g−1 after 100 cycles at 0.2 A g−1 compared with bare flower-like Fe3O4 electrode. Our work demonstrates this self-assembly approach can be used to prepare other electroactive metal oxides/graphene composite for the application of lithium ion batteries.

Sub-1.5 nm Ultrathin CoP Nanosheet Aerogel: Efficient Electrocatalyst for Hydrogen Evolution Reaction at All pH Values.

Transition metal phosphides (TMPs) are certified high performance electrocatalysts for the hydrogen evolution reaction (HER). The ultrathin 2D structure of TMPs can offer abundant adsorption sites to boost HER performance. Herein, an ice-templating strategy is developed to prepare CoP aerogels composed of 2D ultrathin CoP nanosheets (<1.5 nm) using sustainable alginate biomass (seaweed extract) as the precursor. The highly porous aerogel structure can not only deliver facile mass transfer, but also prevent aggregation of the nanosheets into layered structures. As expected, the obtained CoP nanosheet aerogels exhibit remarkable stability and excellent electrocatalytic HER performance at all pH values. For instance, the sample CoP-400 presents a low overpotential of 113, 154, and 161 mV versus RHE at a current density of 10 mA cm-2 in 0.5 m H2SO4, 1 m KOH, and 1 m phosphate buffer solution, respectively. In addition, CoP-400 displays low Tafel slopes at all pH values due to the interconnected highly porous structure of the aerogel, indicating that the sample can provide low-resistance channels for mass transport. Density functional theory calculations reveal that P-top and Co bridge on (011) facet of CoP are more favorable sites during the process of HER in acid and alkaline solutions, respectively.

1D ultrafine SnO2 nanorods anchored on 3D graphene aerogels with hierarchical porous structures for high-performance lithium/sodium storage

SnO2 is considered as one of the most promising alternative anode materials for lithium ion batteries (LIBs) and sodium ion batteries (SIBs) due to high specific capacity, low discharge voltage plateau and environmental friendliness. In this work, 1D ultrafine SnO2 nanorods anchored on 3D graphene aerogel (SnO2 NRs/GA) composite is prepared through a simple reduction-induced self-assembly method in the solution of graphene oxide (GO), Vitamin C and SnO2 nanoparticles. Vitamin C plays an important role in the reduction of GO. The structural and morphological characterizations demonstrate that 1D ultrafine SnO2 nanorods are uniformly and tightly anchored on the surface of 3D graphene nanosheet aerogels. The unique 3D network structure as well as the synergistic effect between 3D graphene nanoshhet and 1D SnO2 nanorods endows the as-prepared SnO2 NRs/GA composite with the good electrochemical lithium/sodium storage performance. It delivers the high initial discharge capacity (1713 mA h g−1 at 0.1 A g−1 for LIBs and 539 mA h g−1 at 0.05 A g−1 for SIBs) and good cycle stability (869 mA h g−1 at 0.1 A g−1 after 50 cycles for LIBs and 232 mA h g−1 at 0.05 A g−1 after 100 cycles for SIBs). Moreover, the SnO2 NRs/GA composite exhibits excellent cycle stability for SIBs with a high reversible capacity of 96 mA h g−1 at as high as 1 A g−1 for 500 cycles. This work provides a simple method to fabricate the electro-active materials-graphene aerogel composites for high-performance LIBs and SIBs.

Constructing three-dimensional porous graphene-carbon quantum dots/g-C3N4 nanosheet aerogel metal-free photocatalyst with enhanced photocatalytic activity

Photocatalysis has been widely considered to be an effective way for solving the worldwide environmental pollution issues. Herein, a new type of three-dimensional (3D) ternary graphene-carbon quantum dots/g-C3N4 nanosheet (GA-CQDs/CNN) aerogel visible-light-driven photocatalyst was synthesized via a two-step hydrothermal method. In this unique ternary photocatalyst, both carbon quantum dots (CQDs) and reduced graphene oxide (rGO) could improve the visible light absorption and promote the charge separation. Furthermore, reduced graphene oxide (rGO) could act as a supportor for the 3D framework. Such a ternary system overcame the drawbacks of bulk g-C3N4 (BCN) and achieved the enhanced photocatalytic activity and long-term stability. As a result, the methyl orange (MO) removal ratio of GA-CQDs/CNN-24% was up to 91.1%, which was about 7.6 times higher than that of bulk g-C3N4 (BCN) under the identical conditions. Moreover that GA-CQDs/CNN-24% exhibited inappreciable loss of photocatalytic activity after four-cycle degradation processes. Finally, the photocatalytic mechanism of GA-CQDs/CNN-24% was interpreted both theoretically and experimentally.

A 3D hybrid of layered MoS2/nitrogen-doped graphene nanosheet aerogels: an effective catalyst for hydrogen evolution in microbial electrolysis cells

A novel 3D hybrid of layered MoS2/nitrogen-doped graphene nanosheet aerogels exhibits significantly enhanced catalytic activity for bio-electrochemical hydrogen evolution.