Ultrathin Morphology Research Articles

Cl-doped carbon nitride nanostrips for remarkably improving visible-light photocatalytic hydrogen production

Visible-light-driven photocatalysts for hydrogen production have been made great progress in recent years, there yet remain grand spaces to be improved further for implementing practical feasibility. We herein report a chlorine doped carbon nitride (Cl-p-C3N4) with ultrathin nanostrips morphology, which displays excellent photocatalytic hydrogen generation performance (5976 μmol h−1 g−1, 16.5 times higher than that of bulk C3N4) under visible light irradiation, with an apparent quantum yield of 8.91% at 420 nm. Experimental results and DFT calculations show that the ultrathin Cl-p-C3N4 nanostrips with heteroatom doping are greatly conducive to reduce the band gap, increase the surface area, and promote the separation efficiency of the photogenerated charge carrier, leading to the improvement of the charge carrier migration to the material surface or co-catalyst during the photocatalytic reaction. This work sheds light on the effective strategy to construct excellent photocatalyst by reasonably regulating the band structure and morphology.

Crumple-textured polyamide membranes via MXene nanosheet-regulated interfacial polymerization for enhanced nanofiltration performance

Nanofiltration (NF) membranes based on polyamide (PA) chemistry have been broadly utilized in saline water desalination and advanced treatment of drinking water. The creation of a nanomaterial interlayer between the support and PA film is known as a promising strategy to improve the filtration performance of traditional PA NF membranes. However, an ultrahigh selective PA NF film featuring ultrathin and crumple-like morphology is still in great challenge. Herein, a highly efficient NF membrane with both enhanced water permeance and salt rejections was prepared via a brush-painting MXene-assisted interfacial polymerization (MA-IP) process. An ultrathin and crumple-textured PA film with ~15 nm thickness was constructed on the MXene-painted polyethersulfone support. The effects of MXene painting cycles on the performance of the support and subsequent PA layer were systematically characterized. The presence of the MXene layer increased the hydrophilicity and PIP adsorption of the pristine support, leading to an accelerated IP reaction rate. The resultant NF membranes exhibited rougher surface, greater hydrophilicity, higher electronegativity and denser skin layer. Excellent water permeability of 27.8 ± 2.1 L m−2 h−1 bar−1 together with satisfactory α(NaCl/Na2SO4) of ~480 was obtained for the MXene-interlayered NF membrane, overcoming the trade-off effects between water permeance and salt selectivity. The MA-IP strategy of this work is expected to provide a new approach for fabricating low-pressure NF membranes for brackish water desalination.

Fabrication of ultra-thin g-C3N4 nanoplates for efficient visible-light photocatalytic H2O2 production via two-electron oxygen reduction

Photocatalytic generation of hydrogen peroxide (H2O2) is a sustainable technique to realize the solar-energy conversion. Here, ultrathin graphitic carbon nitride (g-C3N4) nanoplates with thickness of 1–3 nm was introduced for the efficient H2O2 production. The as-obtained nanoplates demonstrated the H2O2 production rate of 43.07 μmol g−1 h−1 and about 4 times as high as the pristine g-C3N4. Experimental results reflected that the ultrathin morphology offered an increased surface area, more active sites, smaller charge transfer length and stronger redox ability than that of the bulk counterparts. Moreover, the introduction of ultrathin structure switched the H2O2 production pathway from a two-step single-electron reduction to a one-step two-electron reduction route. This study offered the deep elucidation of the influence of ultrathin structure on the photoactivity of semiconductor photocatalysts.

Robust photocatalytic hydrogen production on metal-organic layers of Al-TCPP with ultrahigh turnover numbers

The development of robust photocatalytic systems is key to harvest the solar power for hydrogen production. In the current study, a series of aluminum-based porphyrinic metal organic frameworks (Al-TCPP) with various morphologies of bulk, carambola-like and nanosheets are synthesized with modulated layer thickness. Morphology-dependent photocatalytic activities in hydrogen production are witnessed and inversely correlate to the thickness of the Al-TCPP micro-platelets or nanosheets. Particularly, the exfoliated metal organic layers (MOLs) of Al-TCPP demonstrated a high hydrogen yield rate of 1.32 × 104 µmol h−1 g−1 that is 21-fold of that from the bulk catalyst, as well as an exceptional TON of 6704 that seldom seen in literature. Through comprehensive photochemical characterizations, the remarkable photocatalytic performance of Al-TCPP-MOL is attributed to the great charge separation efficiency and transfer kinetics endowed by the ultrathin 2D morphology with extended active surface area.

Graphene-Based Two-Dimensional Mesoporous Materials: Synthesis and Electrochemical Energy Storage Applications.

Graphene (G)-based two dimensional (2D) mesoporous materials combine the advantages of G, ultrathin 2D morphology, and mesoporous structures, greatly contributing to the improvement of power and energy densities of energy storage devices. Despite considerable research progress made in the past decade, a complete overview of G-based 2D mesoporous materials has not yet been provided. In this review, we summarize the synthesis strategies for G-based 2D mesoporous materials and their applications in supercapacitors (SCs) and lithium-ion batteries (LIBs). The general aspect of synthesis procedures and underlying mechanisms are discussed in detail. The structural and compositional advantages of G-based 2D mesoporous materials as electrodes for SCs and LIBs are highlighted. We provide our perspective on the opportunities and challenges for development of G-based 2D mesoporous materials. Therefore, we believe that this review will offer fruitful guidance for fabricating G-based 2D mesoporous materials as well as the other types of 2D heterostructures for electrochemical energy storage applications.

Antisolvent Route to Ultrathin Hollow Spheres of Cerium Oxide for Enhanced CO Oxidation.

Cerium(IV) oxide (CeO2), or ceria, is one of the most abundant rare-earth materials that has been extensively investigated for its catalytic properties over the past two decades. However, due to the global scarcity and increasing cost of rare-earth materials, efficient utilization of this class of materials poses a challenging issue for the materials research community. Thus, this work is directed toward an exploration of making ultrathin hollow ceria or other rare-earth metal oxides and mixed rare-earth oxides in general. Such a hollow morphology appears to be attractive, especially when the thickness is trimmed to its limit, so that it can be viewed as a two-dimensional sheet of organized nanoscale crystallites, while remaining three-dimensional spatially. This ensures that both inner and outer shell surfaces can be better utilized in catalytic reactions if the polycrystalline sphere is further endowed with mesoporosity. Herein, we have devised our novel synthetic protocol for making ultrathin mesoporous hollow spheres of ceria or other desired rare-earth oxides with a tunable shell thickness in the region of 10 to 40 nm. Our ceria ultrathin hollow spheres are catalytically active and outperform other reported similar nanostructured ceria for the oxidation reaction of carbon monoxide in terms of fuller utilization of cerium. The versatility of this approach has also been extended to fabricating singular or multicomponent rare-earth metal oxides with the same ultrathin hollow morphology and structural uniformity. Therefore, this approach holds good promise for better utilization of rare-earth metal elements across their various technological applications, not ignoring nano-safety considerations.

Alloy-strain-output induced lattice dislocation in Ni3FeN/Ni3Fe ultrathin nanosheets for highly efficient overall water splitting

d-Ni3FeN/Ni3Fe with rich lattice defects, combining the ultrathin 2D morphology and the interface between Ni3FeN and Ni3Fe, endows the electrocatalyst with excellent performance for both the OER and HER in alkaline media.

New Insights into Co-pyrolysis among Graphitic Carbon Nitride and Organic Compounds: Carbonaceous Gas Fragments Induced Synthesis of Ultrathin Mesoporous Nitrogen-Doped Carbon Nanosheets for Heterogeneous Catalysis.

N-doped carbon materials are well known as promising metal-free catalysts and applied in innumerable industrial synthetics. However, most of the N-doped carbon materials obtained by conventional synthetic means exhibit generally low mesoporosity, and their reported pore volumes reached only 1-3 cm3 g-1, which greatly limits their further industrial application in heterogeneous catalysis. Especially for oxidation reaction of alkylbenzenes, this type of reaction is almost always accompanied by many different byproducts, while the reaction activity and selectivity are mainly affected by mesoporosity of catalysts. Traditionally, graphitic carbon nitride (GCN) is commonly considered as a self-sacrificed nitrogen source together with multifarious organic compounds to obtain N-doped carbon materials by a co-pyrolysis process. However, the mechanisms of formation process are still complex and uncontrollable to date. In this work, we present a novel co-pyrolysis synthetic strategy by a facile chemical vapor deposition method for preparing a series of ultrathin N-doped carbon nanosheets with high mesoporosity. More importantly, it is found that GCN containing abundant hydrogen bonds can be irreversibly anchored by carbonaceous gas fragments (CxHy+) released from various organic substances via thermogravimetry-differential thermal analysis coupled with mass spectrometry and X-ray photoelectron spectroscopy analysis, and the CxHy+ fragments exhibit a non-negligible role during the transformation. Our results further demonstrated that the residue of incompletely decomposed GCN is a key point to enlarge porosity in final products which are obtained via mixing pyrolysis between an organic precursor and GCN (or GCN precursors). Benefitting from the outstanding mesoporosity and ultrathin morphology, the representative ABCNS-900 exhibits excellent catalytic performance for oxidizing ethylbenzene to acetophenone with extremely low dosage and high selectivity. Our findings show a universal synthetic strategy for ultrathin N-rich carbon nanosheets with a high mesopore volume, further promoting the application of N-doped carbon materials in heterogeneous catalytic industry.

Ultrathin Transition Metal Chalcogenide Nanosheets Synthesized via Topotactic Transformation for Effective Cancer Theranostics.

Ultrathin transition metal chalcogenide (TMC) nanosheets with ultrahigh photothermal conversion efficiency (η) and excellent stability are strongly desired in the application of photothermal therapy (PTT). However, the current synthetic methods of ultrathin TMC nanosheets have issues in obtaining uniform morphology, good dispersion, and satisfactory PTT behavior. Herein, ultrathin nanosheets of CoFe-selenide (CFS) with a finely controlled structure were prepared via a topological structural transformation process from an ultrathin CoFe-layered double hydroxide (LDH) precursor, followed by surface modification with poly(ethylene glycol) (PEG). The as-prepared CFS-PEG nanosheets inherit the ultrathin morphology of CoFe-LDH and exhibit an outstanding photothermal performance with a η of 74.5%, which is the first rank level of reported two-dimensional (2D) TMC nanosheet materials. The CFS-PEG nanosheets possess a satisfactory photoacoustic (PA) imaging capability with an ultralow detection limit (5 ppm) and simultaneously superior T2 magnetic resonance imaging (MRI) performance with a large transverse MR relaxivity value (r2) of 347.7 mM-1 s-1. Moreover, in vitro and in vivo assays verify superior anticancer activity with a dramatic photoinduced cancer cell apoptosis and tumor ablation. Therefore, a successful paradigm is provided for rational design and preparation of ultrathin TMC nanosheets in this work, holding enormous potential in cancer theranostics.

Multicomponent Transition Metal Dichalcogenide Nanosheets for Imaging-Guided Photothermal and Chemodynamic Therapy.

Transition metal dichalcogenides (TMDs) have received considerable attention due to their strong absorption in the near‐infrared (NIR) region, strong spin‐orbit coupling, and excellent photothermal conversion efficiency (PCE). Herein, CoFeMn dichalcogenide nanosheets (CFMS NSs) are prepared via facile vulcanization of a lamellar CoFeMn‐layered double hydroxide (LDH) precursor followed by polyvinyl pyrrolidone modification (to give CFMS‐PVP NSs), and found to show excellent photoacoustic (PA) imaging and synergistic photothermal/chemodynamic therapy (PTT/CDT) performance. The as‐prepared CFMS‐PVP NSs inherit the ultrathin morphology of the CoFeMn‐LDH precursor and exhibit an outstanding photothermal performance with a η of 89.0%, the highest PCE reported to date for 2D TMD materials. Moreover, 50% of maximum catalytic activity (Michaelis–Menten constant, K m) is attained by CFMS‐PVP NSs with 0.26 × 10−3 m H2O2 at 318 K, markedly lower than the endogenous concentration of H2O2 inside tumor cells. In addition, complete apoptosis of HepG2 cancer cells and complete tumor elimination in vivo are observed after treatment with CFMS‐PVP NSs at a low dose, substantiating the NSs’ remarkable PTT/CDT efficacy. This work provides a new and facile approach for the synthesis of high‐quality multicomponent TMD nanosheets with precise process control, the potential for mass production, and outstanding performance, providing great promise in cancer theranostics.

Single‐Atom In‐Doped Subnanometer Pt Nanowires for Simultaneous Hydrogen Generation and Biomass Upgrading

AbstractReplacing the anodic oxygen evolution reaction (OER) with a thermodynamically favorable ethanol oxidation reaction (EOR) is regarded as a promising approach to simultaneously realize energy‐saving H2 evolution and high‐value chemical production. Herein, the single‐atom In‐doped subnanometer Pt nanowires (SA In‐Pt NWs) as high‐performance electrocatalysts for both the hydrogen evolution reaction (HER) and EOR under universal pH conditions is designed. The SA In‐Pt NWs/C can be employed to integrate HER with EOR to avoid the large overpotential caused by sluggish OER, which requires a smaller voltage of 0.62 V to reach 10 mA cm–2 compared with that of water splitting (2.07 V). The reaction also exhibits a high faradaic efficiency of over 93% in upgrading ethanol to valuable acetate in the anodic cell. Mechanistic investigations indicate that the combination of the ultrathin 1D morphology and single‐atom In decoration provides the maximum number of active sites and effectively activates Pt atoms for catalysis. Density functional theory calculations further demonstrate that doped In can effectively promote the HER, while also promoting the conversion of ethanol to acetate. Moreover, through the use of SA In‐Pt NWs/C as electrocatalysts, many other alcohols can also be employed as anodic feedstock to achieve coupled electrolysis.

Precisely Controlled Two-Dimensional Rhombic Copolymer Micelles for Sensitive Flexible Tunneling Devices

Nanoscale two-dimensional (2D) organic materials have attracted significant interest on account of their unique properties, which result from their ultrathin and flat morphology. Supramolecular 2D ...

2D titanium carbide(MXene) nanosheets and 1D hydroxyapatite nanowires into free standing nanocomposite membrane: in vitro and in vivo evaluations for bone regeneration.

Bone loss or insufficiency remains a great challenge for implant integrated and subsequently functional loading, where developing biomaterials to augment bone quantity and regenerate alveolar bone defects at implant site is vitally necessary. Recently, MXene, as a large new family of 2D materials, exhibits a great prospect in biomedical applications owing to its ultrathin structure and morphology with a range of extraordinary properties such as chemical, electronic, optical and biological properties etc. Besides, hydroxyapatite is a favorable biomaterial with outstanding bioactivity and osteogenic capacity. In this study, we prepared free standing UHAPNWs/MXene nanocomposite membranes via introducing ultralong hydroxyapatite nanowires (UHAPNWs) with different weight ratios into MXene to explore their potential in bone regeneration. SEM, XPS, FTIR, XRD, tensile strength, Young's modulus and water contact angles were used to characterize the morphology, chemical composition, surface properties, mechanical properties and hydrophilicity of the materials. Subsequently, in vitro studies like cell adhesion, proliferation and osteogenic differentiation of MC3T3-E1 were evaluated. The incorporation of UHAPNWs improved mechanical properties and hydrophilicity with an enhancement in cell adhesion, proliferation, and osteogenic differentiation. More importantly, 10wt% UHAPNWs/MXene exhibited the optimal mechanical properties while biological improvement was more pronounced along with the addition of UHAPNWs when the weight fraction of UHAPNWs was from 0 to 30wt%. Furthermore, in vivo experiments the UHAPNWs/MXene nanocomposite membranes effectively enhanced bone tissue formation quantitatively and qualitatively in a rat calvarial bone defect. Therefore, an appropriate amount of UHAPNWs into MXene plays a positive and evident role in enhancing mechanical properties, biocompatibility and osteoinductivity, leading a novel inorganic composite material for regeneration of bone tissue.

Efficient photocatalytic overall water splitting on metal-free 1D SWCNT/2D ultrathin C3N4 heterojunctions via novel non-resonant plasmonic effect

Localized surface plasmon resonance (LSPR) photocatalysts for water splitting have attracted extensive interests. Noble metal LSPR materials suffer from high costs and negative impacts to environment, while metal-free materials usually have low efficiencies. In this work, we demonstrate that one-dimensional carbon nanotubes/two-dimensional ultrathin carbon nitride (1D SWCNT/2D C3N4) can serve as non-resonant plasmonic photocatalysts. The catalyst shows a stoichiometric production of H2 (49.8 μmol g−1 h−1) and O2 (22.8 μmol g−1 h−1) in overall water splitting, with a prominent H2 production rate of 1346 μmol g−1 h−1. The significantly enhanced photocatalysis is attributed to the non-resonant plasmonic effect, as confirmed by the increased spectral response within both ultraviolet and visible light regions, and the results of finite element method simulation. Moreover, the contributions from ultrathin morphology, long average carrier lifetime (2.54 ns), and the electronic coupling effect of the nanohybrids collectively intensify the photocatalytic water splitting.

POM‐Incorporated CoO Nanowires for Enhanced Photocatalytic Syngas Production from CO2

AbstractUtilizing sustainable energy for chemical activation of small molecules, such as CO2, to produce important chemical feedstocks is highly desirable. The simultaneous production of CO/H2 mixture (syngas) from photoreduction of CO2 and H2O is highly promising. However, the relationships between structure, composition, crystallinity, and photocatalytic performance are still indistinct. Here, amorphous ultrathin CoO nanowires and polyoxometalate incorporated nanowires with even lower crystallinity were synthesized. The POM‐incorporated ultrathin nanowires exhibit high photocatalytic syngas production activity, reaching H2 and CO evolution rates of 11555 and 4165 μmol g−1 h−1 respectively. Further experiments indicate that the ultrathin morphology and incorporation of POM both contribute to the superior performance. Multiple characterizations reveal the enhanced charge–hole separation efficiency of the catalyst would facilitate the photocatalysis.

POM-Incorporated CoO Nanowires for Enhanced Photocatalytic Syngas Production from CO2.

Utilizing sustainable energy for chemical activation of small molecules, such as CO2 , to produce important chemical feedstocks is highly desirable. The simultaneous production of CO/H2 mixture (syngas) from photoreduction of CO2 and H2 O is highly promising. However, the relationships between structure, composition, crystallinity, and photocatalytic performance are still indistinct. Here, amorphous ultrathin CoO nanowires and polyoxometalate incorporated nanowires with even lower crystallinity were synthesized. The POM-incorporated ultrathin nanowires exhibit high photocatalytic syngas production activity, reaching H2 and CO evolution rates of 11555 and 4165 μmol g-1 h-1 respectively. Further experiments indicate that the ultrathin morphology and incorporation of POM both contribute to the superior performance. Multiple characterizations reveal the enhanced charge-hole separation efficiency of the catalyst would facilitate the photocatalysis.

3D freestanding flower-like nickel-cobalt layered double hydroxides enriched with oxygen vacancies as efficient electrocatalysts for water oxidation

Economic, efficient, and stable layered double hydroxides (LDHs) based oxygen evolution reaction (OER) electrocatalysts are recognized as promising substitutions of precious catalysts. While LDHs composites suffer from low intrinsic activity, which slightly impedes their wide utilization in energy conversion. Here, we demonstrate a kind of three-dimensional (3D) freestanding flower-like NiCo-LDHs materials with abundant oxygen vacancies are synthesized for electrocatalytic OER application. Simple solvent-thermal method is conducted in ethanol-N, N-dimethylformamide (DMF) mixed solution, which owns slight etching effect to obtain 3D open structures. The as-synthesized Ni1Co1-LDHs-E1D1 composite (in which molar ratio of nickel‑cobalt and volume ratio of ethanol-DMF are both 1:1) is characterized with abundant oxygen vacancies on surface and ultrathin nanosheets morphology with large surface area. It exhibits a relatively low overpotential (260 mV) to drive the current density of 10 mA cm−2 with a low Tafel slope of 72 mV dec−1, as well as high durability in alkaline solution. This work confirms an ingenious strategy for designing 3D vacancy-rich LDHs functional electrocatalytic materials.

GLAD Magnetron Sputtered Ultra-Thin Copper Oxide Films for Gas-Sensing Application

Copper oxide (CuO) ultra-thin films were obtained using magnetron sputtering technology with glancing angle deposition technique (GLAD) in a reactive mode by sputtering copper target in pure argon. The substrate tilt angle varied from 45 to 85° and 0°, and the sample rotation at a speed of 20 rpm was stabilized by the GLAD manipulator. After deposition, the films were annealed at 400 °C/4 h in air. The CuO ultra-thin film structure, morphology, and optical properties were assessed by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), X-ray reflectivity (XRR), and optical spectroscopy. The thickness of the films was measured post-process using a profilometer. The obtained copper oxide structures were also investigated as gas-sensitive materials after exposure to acetone in the sub-ppm range. After deposition, gas-sensing measurements were performed at 300, 350, and 400 °C and 50% relative humidity (RH) level. We found that the sensitivity of the device is related to the thickness of CuO thin films, whereas the best results are obtained with an 8 nm thick sample.

Low-temperature chemical vapor deposition growth of graphene films enabled by ultrathin alloy catalysts

This report introduces a method for fabricating graphene at low temperatures via chemical vapor deposition enabled by ultrathin (∼1 nm) nickel-gold (Ni-Au) catalysts. The unique combination of high carbon (C) solubility Ni, low C solubility Au, and an ultrathin layer of a catalyst demonstrates the effectiveness to produce graphene at 450 °C with the layer number independent of growth duration. In contrast to grain-boundary defined catalyst morphology found in thicker (>20 nm) metal catalysts, the ultrathin catalyst morphology leads to the formation of nanoscale metal “islands” during the growth process, which results in curved graphene covering the catalyst. To test the effect of preactivation of the ultrathin catalyst for the formation of graphene, a preanneal process of the catalyst followed by the introduction of a carbon precursor was also investigated. The preanneal process resulted in the formation of carbon nanotubes (CNTs) in lieu of graphene, displaying the impact of the catalytic surface treatment in relation to the produced materials. The results and discussion presented here detail a low-temperature nanoscale manufacturing process that allows for the production of either graphene or CNTs on an ultrathin catalyst.

Synthesis of Pd-Pt Ultrathin Assembled Nanosheets as Highly Efficient Electrocatalysts for Ethanol Oxidation.

Control over composition and morphology of nanocrystals (NCs) is significant to develop advanced catalysts applicable to polymer electrolyte membrane fuel cells and further overcome the performance limitations. Here, we present a facile synthesis of Pd-Pt alloy ultrathin assembled nanosheets (UANs) by regulating the growth behavior of Pd-Pt nanostructures. Iodide ions supplied from KI play as capping agents for the {111} plane to promote 2-dimensional (2D) growth of Pd and Pt, and the optimal concentrations of cetyltrimethylammonium chloride and ascorbic acid result in the generation of Pd-Pt alloy UANs in high yield. The prepared Pd-Pt alloy UANs exhibited the remarkable enhancement of the catalytic activity and stability toward ethanol oxidation reaction compared to irregular-shaped Pd-Pt alloy NCs, commercial Pd/C, and commercial Pt/C. Our results confirm that the Pd-Pt alloy composition and ultrathin 2D morphology offer high accessible active sites and favorable electronic structure for enhancing electrocatalytic activity.