Organic Nanosheets Research Articles

Bottom-Up Synthesis of Crystalline Covalent Organic Framework Nanosheets, Nanotubes, and Kippah Vesicles: An Odd-Even Effect Induction.

Few-layer organic nanosheets are becoming increasingly attractive as two-dimensional (2D) materials due to their precise atomic connectivity and tailor-made pores. However, most strategies for synthesizing nanosheets rely on surface-assisted methods or top-down exfoliation of stacked materials. A bottom-up approach with well-designed building blocks would be the convenient pathway to achieve the bulk-scale synthesis of 2D nanosheets with uniform size and crystallinity. Herein, we have synthesized crystalline covalent organic framework nanosheets (CONs) by reacting tetratopic thianthrene tetraaldehyde (THT) and aliphatic diamines. The bent geometry of thianthrene in THT retards the out-of-plane stacking, while the flexible diamines introduce dynamic characteristics into the framework, facilitating nanosheet formation. Successful isoreticulation with five diamines with two to six carbon chain lengths generalizes the design strategy. Microscopic imaging reveals that the odd and even diamine-based CONs transmute to different nanostructures, such as nanotubes and hollow spheres. The single-crystal X-ray diffraction structure of repeating units indicates that the odd-even linker units of diamines introduce irregular-regular curvature in the backbone, aiding such dimensionality conversion. Theoretical calculations shed more light on nanosheet stacking and rolling behavior with respect to the odd-even effects.

Unlocking the potential of proton conductivity in guanidinium-based ionic covalent organic nanosheets (iCONs) through pore interior functionalization

Recently, scientists have been exploring the incorporation of proton carriers such as water and phosphoric acid (PA) into the pores and channels of porous materials to enhance proton conduction performance. Ionic covalent organic nanosheets (iCONs) have been identified as promising functional materials due to their inbuilt ionic interfaces, which can facilitate strong interaction with counter ions present inside the pore structure and thus shorten ion transport pathways. However, there is a lack of research related to proton conductivity in iCONs loaded with PA. To address this, we prepared three functionalized guanidinium-based iCONs using a solvothermal condensation reaction between guanidinium amine (TG) and functionalized terephthaldehyde (Da, Dha, and Dma). PA was also incorporated into the iCON structure via ex situ loading to observe its effects on proton conduction performance. The results showed that both the iCONs and PA–iCONs were highly stable in water, organic solvents, acidic and basic media. Amongst these PA–iCONs, one with hydroxyl‑functionalization (PA–DhaTG) displayed high proton conductivity at 90 °C and 95% relative humidity due to a Grotthuss mechanism for protons. These functionalized guanidinium-based iCONs could prove useful for applications in energy conversion devices.

Monodisperse covalent organic nanosheets by in-situ oxidation method for efficient ion/molecule separation

Two-dimensional (2D) covalent organic nanosheets (CONs) are layered crystalline porous polymers comprising periodically extended graphene-like structures, and have great application potential in membrane separation field due to the advantages of abundant optional monomers, tunable pore size and structure, facilely-tailored functionality and pre-designed properties. However, unlike graphene oxide (GO) membranes, it is hard to directly prepare 2D CON membranes by vacuum filtration because of the difficulties in preparation of ultra-thin, large-sized and well-dispersed 2D CONs. Herein, an improved buffering interlayer interface method was proposed to realize a facile one-step synthesis of GO-like CON oxides by using H2O2 as an in-situ oxidant in the buffer layer. The stereoscopic fulcrum-oxygen sites introduced into the structure of CONs lead to weaken interactions between CON layers and increased hydrophilicity, which contributes to subsequent preparation of monodisperse nanosheets. The membranes fabricated with the as-prepared monodisperse nanosheets can realize high-efficiency transport of metal ions with a precise charge-discriminated group separation ability and efficient ion rejection. The strategy of in-situ oxidation to prepare monodisperse CONs proposed in this study provides a valuable approach for the preparation of novel functionalized CONs and the achievement of fast membrane separation performance.

Metal-Free Highly Stable and Crystalline Covalent Organic Nanosheet for Visible-Light-Driven Selective Solar Fuel Production in Aqueous Medium

Conversion of CO2 into solar fuels via artificial photosynthesis is one of the most promising and sustainable approaches to mitigate global warming and worldwide energy shortage. Covalent organic frameworks (COFs) exhibit well-defined arrangements of building blocks, tunable porosity, and high thermal and chemical stability in harsh conditions. The tunable band gaps of COFs by suitably introducing chromophoric light-harvesting units make them a unique class of metal-free heterogeneous photocatalysts for the successful conversion of CO2 to solar fuel. In this work, we report a simple, efficient, and low-cost 2D COF (TTA-Tz) composed of 1,3,5-tris-(4-aminophenyl)triazine (TTA) and 4,4′-(thiazolo[5,4-d]thiazole-2,5-diyl)dibenzaldehyde (Tz) for photocatalytic CO2 reduction. The 2D-layered COF is exfoliated into ultrathin covalent organic nanosheets (CONs), which shows visible-light-driven photoreduction of CO2 to CO (yield = 2.8 mmol g–1, rate = 82 μmol h–1 g–1, and selectivity >99%) in aqueous medium without an external sacrificial electron donor. Interestingly, for a mixed solvent system, the CO evolution rate (163 μmol g–1 h–1) is found double than the aqueous medium case with 99% selectivity. By introducing both BNAH and TEA as sacrificial electron donors, the significant amount of CH4 (499 μmol g–1) is produced and the rate of CO evolution (310 μmol g–1 h–1) is further enhanced. The mechanistic insight of CO2 reduction is studied by DFT-based theoretical calculation, which is further supported by in situ diffuse reflectance spectroscopy study.

In Vivo Fluorescence Molecular Imaging Using Covalent Organic Nanosheets Without Labeling.

Organic nanomaterials, as nanocarrier platforms, have tremendous potential for biomedical applications. The authors successfully prepared novel two-dimensional covalent organic nanosheets (CONs) that can be used as efficient in vivo bioimaging probes by condensing 1,3,5-triformylglucinol (Tp) and 2,7-diaminopyrene (Py) to produce TpPy covalent organic frameworks (COFs). TpPy COFs are then subjected to a liquid exfoliation process to obtain TpPy CONs (< 200nm in size and < 1.7nm in thickness). TpPy CONs disperse well in water to provide a stable, homogeneous colloidal suspension, which shows favorable photoluminescence properties. Cell viability tests using MDA-MB-231 and RAW 264.7 cells reveal that TpPy CONs are low in cytotoxicity. Confocal microscopy reveals clear fluorescent cell images after incubation with TpPy CONs for 24h, without reduction in cell activity or cytosolic aggregation. To investigate the biological behavior of the TpPy CONs, the authors perform an in vivo fluorescence imaging study using MDA-MB-231 tumor-bearing mice. After intravenous injection of TpPy CONs disperse in phosphate-buffered saline (PBS), persistent and strong fluorescence signals are observed in the tumor region, with low background signals from normal tissues at 1, 3, 12, and 24h after injection. Furthermore, these in vivo imaging results concurred with ex vivo biodistribution and histological results.

Hierarchical Nanoarchitectonics of Ultrathin 2D Organic Nanosheets for Aqueous Processed Electroluminescent Devices.

Ultrathin 2D organic nanosheets (2DONs) with high mobility have received tremendous attention due to thickness of few molecular layers. However, ultrathin 2DONs with high luminescence efficiency and flexibility simultaneously are rarely reported. Here, the ultrathin 2DONs (thickness: 19nm) through the modulation of tighter molecular packing (distance: ≈3.31Å) achievable from the incorporation of methoxyl and dipenylamine (DPA) groups into 3D spirofluorenexanthene (SFX) building blocks is successfully prepared. Even with closer molecular stacking, ultrathin 2DONs still enable the suppression of aggregation quenching to exhibit higher quantum yields of blue emission (ΦF = 48%) than that on amorphous film (ΦF = 20%), and show amplified spontaneous emission (ASE) with a mediate threshold (332mWcm-2 ). Further, through drop-casting method, the ultrathin 2DONs are self-organized into large-scale flexible 2DONs films (1.5 × 1.5cm) with the low hardness (H: 0.008Gpa) and low Young's modulus (Er : 0.63Gpa). Impressively, the large-scale 2DONs film can realize electroluminescence performances with a maximum luminance (445cdm-2 ) and low turn on voltage (3.7V). These ultrathin 2DONs provide a new avenue for the realization of flexible electrically pumping lasers and intelligent quantum tunneling systems.

High adsorption performance for trace lead (II) cation from sewage by Fe/Cu metal organic nanosheets modified with terephthalic acid

A two-dimensional nanoflake (Fe/Cu-TPA) was prepared through a simple ultrasonic-centrifuge method. Fe/Cu-TPA has prominent performance on the removal of Pb2+ with low consistences. More than 99% lead (II) (Pb2+) was removed. The adsorption equipoise was established within 60 min for 50 mg L−1 Pb2+. Fe/Cu-TPA shows excellent regenerability with 19.04% decline of Pb2+ adsorption competence in 5 cycles. There are two models for Fe/Cu-TPA adsorption of Pb2+, pseudo-second-order dynamic model and Langmuir isotherm model, with a utmost adsorption competence of 213.56 mg g−1. This work offers a new candidate material for the industrial-grade Pb2+ adsorbents with promising application prospect.

Benzimidazole-based covalent organic polymer nanosheets incorporated in mesoporous organosilica nanoparticles with excitation-dependent fluorescence for sensing of Cu2+

A novel type of small-sized nanosheets (TD-Si) was prepared by chemical exfoliating stacked bulk materials of benzimidazole-based covalent organic polymer (TpDAB). Then TD-Si was used as organosiloxane precursor to incorporate into silica frameworks of mesoporous organosilica nanoparticles (TD-MONs) using CTAB as structural-directing agents. The obtained TD-MONs show a clearly hexagonal mesoporous structure with high surface area. Moreover, the optical properties of TD-MONs were measured with fluorescence and Ultraviolet–visible (UV–vis) spectroscopies. The results showed that TD-MONs possessed excitation wavelength dependent fluorescence and had better fluorescence properties due to the reduction of π-π stacking between nano-layers of TpDAB polymer. The emission peaks of TD-MONs were red-shifted as the excitation wavelength increases and TD-MONs exhibited the optimal fluorescence emission at 525 nm when excited at 400 nm. TD-MONs showed high selectivity, sensitivity and recyclability toward copper ions and could be used for the detection of Cu2+ with a low limit of detection (LOD) as low as 3.77 × 10−7 M. In addition, the coordination interaction between TD-MONs and copper ions was demonstrated by FT-IR spectra and high-resolution X-ray photoelectron spectra, and further proved that the binding sites were carbonyl oxygen atoms and imidazole nitrogen atoms in TD-MONs. Therefore, TD-MONs is expected to be a high-sensitive chemical sensor for detecting Cu2+.

Synthesis of 2D Metal-Organic Nanosheets (MONs) by Liquid Phase Exfoliation: Applications in Effective Delivery of Antiulcer Drugs and Selective Adsorption and Removal of Cationic Dyes.

Nowadays, the fabrication of 2D metal-organic nanosheets (2D MONs) has entered the research arena fascinating researchers worldwide. However, a lack of efficient and facile methods has remained a bottleneck for the manufacturing of these 2D MONs. Herein, a 2D metal-organic framework (MOF), i.e., 2D Cu-MOF, was synthesized using a facile and convenient stirring method by using 4,4'-trimethylenedipyridine (TMDP) as an organic linker. The as-prepared MOF was characterized in detail and based on single crystal X-ray diffraction analysis, it was established that tangled layers in the 2D Cu-MOF are interconnected to produce thick strands. These tangled layers could be easily separated via ultrasonication-induced liquid phase exfoliation (UILPE) to give the 2D Cu-MON as illustrated through Tyndall light scattering and exhaustive microscopic exploration such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The application of this 2D Cu-MON was assessed in the field of drug delivery revealing exceptional drug loading for the drug lansoprazole (LPZ) by 2D Cu-MONs as well as drug release in the acidic and neutral medium demonstrating that the 2D Cu-MON is an excellent carrier for antiulcer drug delivery. For environmental protection, the application of 2D Cu-MON was also examined toward the removal of various cationic and anionic dyes with excellent selectivity toward cationic dye removal. The plausible mechanism for dye removal indicated the involvement of cation-π and π-π interactions, for the effective adsorption of cationic dyes as well as a increase in the surface area of 2D Cu-MON by UILPE. Remarkably, the high drug loading and dye removal are imputed to the increase in surface area by UILPE. In a nutshell, the developed 2D Cu-MON will prove to be beneficial for application in the field of drug delivery as well as for wastewater treatment.

Remarkable Pyro-Catalysis of g-C3N4 Nanosheets for Dye Decoloration under Room-Temperature Cold-Hot Cycle Excitation.

Pyroelectric materials have the ability to convert the environmental cold-hot thermal energy such as day-night temperature alternation into electrical energy. The novel pyro-catalysis technology can be designed and realized on the basis of the product coupling between pyroelectric and electrochemical redox effects, which is helpful for the actual dye decomposition. The organic two-dimensional (2D) graphic carbon nitride (g-C3N4), as an analogue of graphite, has attracted considerable interest in the field of material science; however, its pyroelectric effect has rarely been reported. In this work, the remarkable pyro-catalytic performance was achieved in the 2D organic g-C3N4 nanosheet catalyst materials under the continuous room-temperature cold-hot thermal cycling excitation from 25 °C to 60 °C. The pyro-catalytic RhB dye decoloration efficiency of the 2D organic g-C3N4 can reach ~92.6%. Active species such as the superoxide radicals and hydroxyl radicals are observed as the intermediate products in the pyro-catalysis process of the 2D organic g-C3N4 nanosheets. The pyro-catalysis of the 2D organic g-C3N4 nanosheets provides efficient technology for wastewater treatment applications, utilizing the ambient cold-hot alternation temperature variations in future.

Reducing dielectric confinement effect in ionic covalent organic nanosheets to promote the visible-light-driven hydrogen evolution

Ultra-thin two-dimensional (2D) organic semiconductors are promising candidates for photocatalysts because of the short charge diffusion pathway and favorable exposure of active sites plus the versatile architecture. Nonetheless, the inherent dielectric confinement of 2D materials will induce a strong exciton effect hampering the charge separation. Herein, we demonstrated an effective way to reduce the dielectric confinement effect of 2D ionic covalent organic nanosheets (iCONs) by tailoring the functional group via molecular engineering. Three ultra-thin CONs with different functional groups and the same ionic moieties were synthesized through Schiff base condensation between ionic amino monomer triaminoguanidinium chloride (TG) and aldehyde linkers. The integration of the hydroxyl group was found to significantly increase the dielectric constant by enhancing the polarizability of ionic moieties, and thus reduced the dielectric confinement and the corresponding exciton binding energy (Eb). The champion hydroxyl-functional iCON exhibited promoted exciton dissociation and in turn a high photocatalytic hydrogen production rate under visible-light irradiation. This work provided insights into the rationalization of the dielectric confinement effect of low-dimensional photocatalysts.

Nanoscale Control of the Surface Functionality of Polymeric 2D Materials.

Typically, 2D nanosheets have a homogeneous surface, making them a major challenge to structure. This studyproposes a novel concept of 2D organic nanosheets with a heterogeneously functionalized surface. This workachieves this by consecutively crystallizing two precisely synthesized polymers with different functional groups in the polymer backbone in a two-step process. First, the core platelet is formed and then the second polymer is crystallized around it. As a result, the central area of the platelets has a different surface functionality than the periphery. This concept offers two advantages: the resulting polymeric 2D platelets are stable in dispersion, which simplifies further processing and makes both crystal surfaces accessible for subsequent functionalization. Additionally, a wide variety of polymers can be used, making the process and the choice of surface functionalization very flexible.

Organic Semiconductor Nanosheets for Sulfite Detecting Based on Activation of Sulfite and a Synergetic Chemiluminescence Resonance Energy Transfer Process in a Mild System of Fe2+-SO32.

Sulfur dioxide (SO2) as one kind of air pollution not only causes extreme environmental pollution but also negatively affects human health. Chemiluminescence (CL) methods applied for sulfite analysis with high selectivity based on activating sulfite with oxidants are always implemented in acid media with a high background rise. In this work, we proposed to develop a mild CL system of Fe2+-SO32- to detect sulfite under neutral conditions and provide in situ CL spectral data for deeply studying the CL mechanism of Fe2+-SO32-. Herein, we first synthesized one type of water-soluble supramolecular nanosheets, APDI NSs, which had a strong oxidation potential (+2.9 V) due to a π-conjugated system for activation of sulfite to enhance the generation of SO3̇- and other active radicals, and strong a CL signal from the APDI NSs-Fe2+-SO32- system was generated. By studying the CL mechanism under acidic and neutral conditions, a new CL reaction pathway (path-1) and a key intermediate, S2O42-, from the reaction of Fe2+ and SO32- were found. The CL signal was emitted by SO2* after oxidation of S2O42- by strong oxidants like SO4•- and further amplified by APDI NSs through the CL resonance energy transfer (CRET) process. Based on the APDI NSs-Fe2+-SO32- system under neutral conditions, a CL method for detecting SO32- was established. The detection limit was 2.7 × 10-8 M (S/N = 3), and the recovery rates in spiked water samples were in the range of 87%-101%. This study strengthens the understanding of the CL reaction process of the Fe2+-SO32- system and provides a mild sulfite sensing platform for environmental samples.

Hybridization of Layered Titanium Oxides and Covalent Organic Nanosheets into Hollow Spheres for High-Performance Sodium-Ion Batteries with Boosted Electrical/Ionic Conductivity and Ultralong Cycle Life.

While development of a sodium-ion battery (SIB) cathode has been approached by various routes, research on compatible anodes for advanced SIB systems has not been sufficiently addressed. The anode materials based on titanium oxide typically show low electrical performances in SIB systems primarily due to their low electrical/ionic conductivity. Thus, in this work, layered titanium oxides were hybridized with covalent organic nanosheets (CONs), which exhibited excellent electrical conductivity, to be used as anodes in SIBs. Moreover, to enlarge the accessible areas for sodium ions, the morphology of the hybrid was formulated in the form of a hollow sphere (HS), leading to the highly enhanced ionic conductivity. This synthesis method was based on the expectation of synergetic effects since titanium oxide provides direct electrostatic sodiation sites that shield organic components and CON supports high electrical and ionic conductivity with polarizable sodiation sites. Therefore, the hybrid shows enhanced and stable electrochemical performances as an anode for up to 2600 charge/discharge cycles compared to the HS without CONs. Furthermore, the best reversible capacities obtained from the hybrid were 426.2 and 108.5 mAh/g at current densities of 100 and 6000 mA/g, which are noteworthy results for the TiO2-based material.

S-scheme enhanced photocatalysis on graphitic carbon nitride functionalized with perylene tetracarboxylic diimide

It is a challenge to realize the catalytic conversion of ammonia by photocatalysis under mild conditions, because it is limited by the high photoinduced carrier recombination rate and low photo-absorption efficiency. Herein, we perform the condensation reaction of 3,4,9,10-perylenetetracarboxylic diimide (PTCDA) with graphitic carbon nitride (g-C3N4) nanosheets to obtain a novel organic semiconductor perylene tetracarboxylic diimide (PTCDI) modified g-C3N4 S-scheme heterostructure (named PTCDI@g-C3N4) via thermal-etching and bath process. The obtained PTCDI@g-C3N4 composite shows an obvious improvement in photocatalytic nitrogen reduction rate of 7308.9 μmol L−1 g−1h−1 with methanol under the Xe lamp irradiation, higher than g-C3N4 nanosheets (1215.3 μmol L−1 g−1 h−1). The excellent photocatalytic performance of PTCDI@g-C3N4 heterostructure is ascribed to two advantages: (1) The S-scheme heterojunction between organic semiconductor PTCDI and g-C3N4 nanosheets is profit to suppress carrier recombination and enhance electron utilization efficiency; (2) The utilization rate of g-C3N4 nanosheets to light was promoted due to the existence of PTCDI with broad visible light absorption. This work may help to provide a possibility to realize efficient photocatalytic nitrogen fixation by preparing organic-nonmetallic heterostructure through facile methods.

Development of pseudo 3D covalent organic framework nanosheets for sensitive and selective biomolecule detection of infectious disease

Immediately after sample collection, pseudo-3D covalent organic structure nanosheets can instantly detect Covid-19 with high selectivity and without any further cost-effective and time-consuming RT-PCR step or amplifications.

Correction: Generation of covalent organic framework-derived porous N-doped carbon nanosheets for highly efficient electrocatalytic hydrogen evolution

Correction for ‘Generation of covalent organic framework-derived porous N-doped carbon nanosheets for highly efficient electrocatalytic hydrogen evolution’ by Sayan Halder et al., Energy Adv., 2023, https://doi.org/10.1039/d3ya00325f.

Generation of covalent organic framework-derived porous N-doped carbon nanosheets for highly efficient electrocatalytic hydrogen evolution

N-doped carbon nanosheets derived from triazine-containing polyimide-based covalent organic framework (TP-COF) exhibit outstanding electrocatalytic hydrogen evolution.

Long-term cycling stability of a SnS2-based covalent organic nanosheet anode for lithium-ion batteries

A CON are hybridized with layered SnS2 to improve electrical conductivity and structural stability of SnS2 for lithium ion battery systems. Therefore, the hybrid shows outstanding performances over 5600 charge/discharge cycles.

Facile synthesis of a new covalent organic nanosheet (CON-KEY1) based on polyamide links as an effective heterogeneous catalyst in C-C cross coupling reactions.

C-C coupling reactions represent a fundamental synthetic methodology widely employed in academic and industrial settings. Herein, we present a report on developing and synthesizing a heterogeneous catalyst that is environmentally compatible and has recycling capabilities. Furthermore, the utilization of this catalyst for C-C coupling reactions was explored. A novel amide-based CON was prepared via the reaction of a novel [2,2'-bipyridine]-5,5'-diamine (BDA) and 1,3,5-tris(4-carboxyphenyl) (TCB). TCB was activated with carbonyl diimidazole (CDI) and then reacted with BDA to synthesize favorable CON (i.e., CON-KEY1). Finally, the CON synthesized was reacted with palladium chloride ions, and the palladium-containing organocatalytic complex was decorated with the abbreviated Pd/CON-KEY1. This new heterogeneous complex was fully characterized through the required techniques, including FT-IR, EDX, XRD, TEM, SEM, ICP, TGA-DTA, N2 isotherms, and elemental mapping analysis. Computer simulation results include a multi-sheet 2D framework proposed by CON-KEY1. As a result, palladium ions were found to be arranged between the layers and on the CON surface. This heterogeneous complex functioned as a catalyst precursor in both the Suzuki-Miyaura coupling reaction of aryl boronic acids with aryl halides and the Heck reaction of aryl halides with acrylate derivatives or styrene. The desired coupling products with various functional groups were successfully attained with excellent yields of up to 98%. Simple set-up, improved yields, short reaction times, non-toxic solvents, catalyst durability, and high turnover frequency are among the distinct advantages of this synthetic method. Some other outstanding features of this catalytic system include convenient separation of catalysts and products, high yields, almost complete conversion, high selectivity, and good turnover frequency (TOF). The results show that the highest product efficiency in the reaction was achieved in the shortest possible time using Pd/CON-KEY1. Theoretical studies demonstrated the precedence of the palladium complexation with nitrogen atoms of CON-KEY1 rather than oxygen ones. Natural Bond Orbital (NBO) analysis affirmed that the system with Pd-N bonds (Eg = 0.089 eV) is more reactive with high electron conductivity compared to the Pd-O system (Eg = 0.120 eV).