Catalysis with single-atom catalysts (SACs) exhibits outstanding reactivity and selectivity. However, fabrication of supports for the single atoms with structural versatility remains a challenge to ...be overcome, for further steps toward catalytic activity augmentation. Here, we demonstrate an effective synthetic approach for a Pt SAC stabilized on a controllable one-dimensional (1D) metal oxide nano-heterostructure support, by trapping the single atoms at heterojunctions of a carbon nitride/SnO2 heterostructure. With the ultrahigh specific surface area (54.29 m2 g–1) of the nanostructure, we obtained maximized catalytic active sites, as well as further catalytic enhancement achieved with the heterojunction between carbon nitride and SnO2. X-ray absorption fine structure analysis and HAADF-STEM analysis reveal a homogeneous atomic dispersion of Pt species between carbon nitride and SnO2 nanograins. This Pt SAC system with the 1D nano-heterostructure support exhibits high sensitivity and selectivity toward detection of formaldehyde gas among state-of-the-art gas sensors. Further ex situ TEM analysis confirms excellent thermal stability and sinter resistance of the heterojunction-immobilized Pt single atoms.
Hydroelectric nanogenerators have been previously proposed to recycle various water resources and polluted water. However, as conventional hydroelectric nanogenerators only utilize water resources, ...they cannot provide a fundamental solution for water recycling. In this study, a water purification membrane is proposed that can simultaneously generate electricity during the purification process (electricity generation and purification membrane (EPM)) for water recycling. As polluted water passes through the EPM, the water is purified in the perpendicular direction, while electricity is simultaneously produced in the horizontal direction by the movement of ions. Notably, the EPM exhibits high energy generation performance (maximum power 16.44 µW and energy 15.16 mJ) by the streaming effect of water‐streaming carbon nanotubes (CNTs). Moreover, by using a poly(acrylic acid)/carboxymethyl cellulose (PAA/CMC) binder to EPM, the energy‐generation performance and long‐term stability are substantially improved and outstanding mechanical stability is provided, regardless of the acidity of the water source (pH 1–10). More importantly, the EPM exhibits the water purification characteristics of >90% rejection of sub‐10 nm pollutants and potentiality of ångstrom level cation rejection, with simultaneous and continuous energy generation. Overall, this study proposes an efficient EPM model, which can be potentially used as a next‐generation renewable energy generation approach, thus laying the foundation for effective utilization of polluted water resources.
Energy generation from environmental sources such as water is mainly focused on the power generation characteristics. However, the purification technology of environmental sources are also desired techniques for recent environmental and energy global issues. In this work, bifunctional (energy generation and water purification) membranes are successfully developed by controlling the water flow directions on the membranes (electricity generation and purification membrane).
Single‐atom catalysts (SACs) supported on inorganic materials have attracted much attention in numerous research fields for their high catalytic performance. However, such SACs have been limited by ...the low metal loading, especially on different types of inorganic supports. Herein, a general approach is presented for preparing SACs on metallic, metal oxide, and perovskite nanosheet (NS) supports to reach a high metal loading of up to 3.94 wt%, by utilizing N‐doped graphene as a sacrificial template that spatially confines the single atoms (SAs). Specifically, the target support material precursors are adsorbed onto the SAs‐stabilized sacrificial template, followed by subsequent heat treatment to transfer the SAs to the support material and to remove the graphene layer. Pt SAs on oxide support exhibits little to no aggregation throughout >10 000 min of annealing at 275 °C, demonstrating high thermal stability, as also supported by ex situ post‐anneal electron microscopy and X‐ray absorption fine structure studies. As a proof‐of‐concept, Pt SACs on SnO2 NSs exhibit high catalytic activity toward chemiresistive sensing of acetone gas (response = 95.4 at 10 ppm, 7.6‐fold enhancement compared with pristine SnO2 NSs) and unprecedented stability under highly humid conditions (27.4% response deterioration at 95% relative humidity).
A general strategy is developed to fabricate various types of inorganic nanosheets (NSs) with high‐loading single‐atom catalysts (SACs). N‐doped graphene sacrificial template loaded with high‐loading Pt SACs can successfully transfer the SACs onto NSs‐structured support materials composed of binary and ternary metal oxides and metal. The SACs possess high thermal stability, owing to strong covalent metal–support interactions.
2D heterogeneous oxide nanosheets (NSs) have attracted much attention in various scientific fields owing to their exceptional physicochemical properties. However, the fabrication of 2D oxide NSs with ...abundant p–n interfaces and large amounts of mesopores is extremely challenging. Here, a facile synthesis of highly porous 2D heterogeneous oxide NSs (e.g., SnO2/CoOx) is suggested through a 2D oxide exfoliation approach combined with a fast galvanic replacement reaction (GRR). The ultrathin (<5 nm) layered CoOx NSs are simply prepared by ion‐exchange exfoliation and a subsequent GRR process that induces a rapid phase transition from p‐type CoOx to n‐type SnO2 metal oxides (<10 min). The controlled GRR process enables the creation of heterogeneous SnO2/CoOx NSs consisting of small SnO2 grain sizes (<10 nm), high porosity, numerous heterojunctions, and sub‐10 nm thickness, which are highly advantageous characteristics for chemiresistive sensors. Due to the advantage of these features, the porous SnO2/CoOx NSs exhibit an unparalleled HCHO‐sensing performance (Rair/Rgas > 35 @ 5 ppm with a response speed of 9.34 s) with exceptional selectivity compared to that of the state‐of‐the‐art metal oxide‐based HCHO gas sensors.
Highly porous heterogeneous SnO2/CoOx 2D nanosheets are successfully achieved by exfoliation combined with a galvanic replacement reaction. The thin‐walled (<5 nm) exfoliated p‐type CoOx nanosheets are transformed into porous, thin‐walled (<10 nm) n‐type SnO2 nanosheets via galvanic replacement. The porous SnO2/CoOx 2D nanosheets show superior HCHO‐sensing performance with stable mechanical flexibility compared to reported state‐of‐the‐art HCHO sensors.
Conductive metal–organic frameworks (cMOFs) are emerging materials for various applications due to their high surface area, high porosity, and electrical conductivity. However, it is still ...challenging to develop cMOFs having high surface reactivity and durability. Here, highly active and stable cMOF are presented via the confinement of bimetallic nanoparticles (BNPs) in the pores of a 2D cMOF, where the confinement is guided by dipolar‐interaction‐induced site‐specific nucleation. Heterogeneous metal precursors are bound to the pores of 2D cMOFs by dipolar interactions, and the subsequent reduction produces ultrasmall (≈1.54 nm) and well‐dispersed PtRu NPs confined in the pores of the cMOF. PtRu‐NP‐decorated cMOFs exhibit significantly enhanced chemiresistive NO2 sensing performances, owing to the bimetallic synergies of PtRu NPs and the high surface area and porosity of cMOF. The approach paves the way for the synthesis of highly active and conductive porous materials via bimetallic and/or multimetallic NP loading.
Ultrasmall bimetallic nanoparticles (BNPs) are confined in pores of 2D conductive metal–organic frameworks (cMOFs). BNPs in cMOFs significantly improve the NO2‐sensing performance, owing to the bimetallic synergies of PtRu NPs and the high surface area and porosity of the cMOF.
Research on high‐efficiency and cost‐efficient catalysts for oxygen reduction reaction (ORR) is still a vital but challenging issue for commercializing metal–air batteries. Herein, a ...single‐molecule/atom hybrid catalyst is developed to boost the ORR, in which iron phthalocyanine molecules containing molecular Fe─N4 moieties couple with atomic Co─N4 sites on the surface of polyhedral carbon. Density functional theory calculations reveal that face‐to‐face laminated construction of Fe─N4 and Co─N4 in the hybrid catalyst can effectively modulate the electronic structure of active iron atoms and reduce the energy barrier of the rate‐determining step for ORR. As a result, this hybrid catalyst demonstrates excellent ORR performance, featuring a half‐wave potential of 0.904 V, a peak power density of 238.3 mW cm−2 for zinc–air battery, and outstanding electrocatalytic stability. This work offers a distinctive and robust molecular/atomic engineering approach to creating efficient electrocatalysts, advancing the fields of metal–air batteries.
An oxygen reduction electrocatalyst is designed by introducing Co atom to regulate FePc. FePc containing Fe─N4 moieties is coupled with a single‐atom Co catalyst featuring Co─N4 sites, resulting in a face‐to‐face laminated arrangement of Fe─N4 and Co─N4 within the hybrid catalyst. Such an oxygen reduction electrocatalyst revealed exceptional ORR performance and assembled both liquid‐state and solid‐state zinc–air batteries, which exhibit an enormous power density.
In article number 1903012, Hee Jung Park, Il‐Doo Kim, and co‐workers develop porous and heterogeneous SnO2/CoOx nanosheets by combining exfoliation with galvanic replacement reaction. Due to the high ...porosity, thin‐thickness (<10 nm), and numerous heterogeneous junctions, the heterogeneous SnO2/CoOx nanosheets show super‐sensitive HCHO sensing characteristics with a rapid response (<10 sec).
Hydrogen (H2) is one of the next-generation energy sources because it is abundant in nature and has a high combustion efficiency that produces environmentally benign products (H2O). However, H2/air ...mixtures are explosive at H2 concentrations above 4%, thus any leakage of H2 must be rapidly and reliably detected at much lower concentrations to ensure safety. Among the various types of H2 sensors, chemiresistive sensors are one of the most promising sensing systems due to their simplicity and low cost. This review highlights the advances in H2 chemiresistors, including metal-, semiconducting metal oxide-, carbon-based materials, and other materials. The underlying sensing mechanisms for different types of materials are discussed, and the correlation of sensing performances with nanostructures, surface chemistry, and electronic properties is presented. In addition, the discussion of each material emphasizes key advances and strategies to develop superior H2 sensors. Furthermore, recent key advances in other types of H2 sensors are briefly discussed. Finally, the review concludes with a brief outlook, perspective, and future directions.
Continuous monitoring of hydrogen sulfide (H2S) in human breath for early stage diagnosis of halitosis is of great significance for prevention of dental diseases. However, fabrication of a highly ...selective and sensitive H2S gas sensor material still remains a challenge, and direct analysis of real breath samples has not been properly attempted, to the best of our knowledge. To address the issue, herein, we introduce facile cofunctionalization of WO3 nanofibers with alkaline metal (Na) and noble metal (Pt) catalysts via the simple addition of sodium chloride (NaCl) and Pt nanoparticles (NPs), followed by electrospinning process. The Na-doping and Pt NPs decoration in WO3 grains induces the partial evolution of the Na2W4O13 phase, causing the buildup of Pt/Na2W4O13/WO3 multi-interface heterojunctions that selectively interacts with sulfur-containing species. As a result, we achieved the highest-ranked sensing performances, that is, response (R air/R gas) = 780 @ 1 ppm and selectivity (R H2S/R EtOH) = 277 against 1 ppm ethanol, among the chemiresistor-based H2S sensors, owing to the synergistic chemical and electronic sensitization effects of the Pt NP/Na compound cocatalysts. The as-prepared sensing layer was proven to be practically effective for direct, and quantitative halitosis analysis based on the correlation (accuracy = 86.3%) between the H2S concentration measured using the direct breath signals obtained by our test device (80 cases) and gas chromatography. This study offers possibilities for direct, highly reliable and rapid detection of H2S in real human breath without the need of any collection or filtering equipment.
The concept of integrating diverse functional 2D materials into a heterostructure provides platforms for exploring physics that cannot be accessed in a single 2D material. Here, physically mixing two ...2D materials, MXene and MoS2, followed by freeze-drying is utilized to successfully fabricate a 3D MoS2/MXene van der Waals heterostructure aerogel. The low-temperature synthetic approach effectively suppresses significant oxidation of the Ti3C2T x MXene and results in a hierarchical and freestanding 3D heterostructure composed of high-quality MoS2 and MXene nanosheets. Functionalization of MXene with a MoS2 catalytic layer substantially improves sensitivity and long-term stability toward detection of NO2 gas, and computational studies are coupled with experimental results to elucidate that the mechanism behind enhancements in the gas-sensing properties is effective inhibition of HNO2 formation on the MXene surface, due to the presence of MoS2. Overall, this study has a great potential for expansion of applicability to other classes of two-dimensional materials as a general synthesis method, to be applied in future fields of catalysis and electronics.
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