Introduction Of Structural Defects Research Articles

Melaminin Yerinde Polimerizasyonu ile Grafit Katmanlarının Genişletilmesi Üzerine Bir Çalışma

Graphene, renowned for its honeycomb lattice structure formed by densely packed sp2 hybridized carbon atoms, possesses exceptional electronic, thermal, chemical, and mechanical properties. The van der Waals-coupled graphene layers give rise to the well-known AB stacking, forming graphite. Despite the existence of several methods for graphite production, the production of graphene on a large scale remains challenging due to the lack of efficient techniques and the introduction of structural defects during the production process. Exfoliated graphite (EG), a potential solution, is typically derived from the thermal treatment of graphite intercalation compounds (GICs). Melamine, notably displaying significant expansion properties at low temperatures, has been used as an intercalation compound in limited studies. This study investigates the potential of melamine to induce the expansion of graphene layers when incorporated into graphite and subjected to thermal treatment. Raman and X-ray diffraction analyses were employed to assess structural changes.

Ordering kinetics of a tapered copolymer based on isoprene and styrene.

High molar mass copolymers with a tapered interface are mechanically tough materials with an accessible order-to-disorder transition temperature and hence processability. We report the first ordering kinetics for a tapered tetrablock copolymer in comparison to a conventional diblock copolymer made sequentially. We show that tapered copolymers belong to the Brazovskii "universality class," where fluctuations play a dominant role. Consequently, the order-to-disorder transition has a very weak, fluctuation-induced first-order character. The ordering kinetics of the lamellar phase from the supercooled disordered melt revealed several distinct differences associated with the range of metastability (increased), the timescales (bimodal), and the exact mechanism of ordering. The results are discussed in terms of the reduced interaction parameter and the introduction of structural defects within the lamellar grains.

Defect-Induced π-Magnetism into Non-Benzenoid Nanographenes.

The synthesis of nanographenes (NGs) with open-shell ground states have recently attained increasing attention in view of their interesting physicochemical properties and great prospects in manifold applications as suitable materials within the rising field of carbon-based magnetism. A potential route to induce magnetism in NGs is the introduction of structural defects, for instance non-benzenoid rings, in their honeycomb lattice. Here, we report the on-surface synthesis of three open-shell non-benzenoid NGs (A1, A2 and A3) on the Au(111) surface. A1 and A2 contain two five- and one seven-membered rings within their benzenoid backbone, while A3 incorporates one five-membered ring. Their structures and electronic properties have been investigated by means of scanning tunneling microscopy, noncontact atomic force microscopy and scanning tunneling spectroscopy complemented with theoretical calculations. Our results provide access to open-shell NGs with a combination of non-benzenoid topologies previously precluded by conventional synthetic procedures.

Amorphous MoSxOy/h-BNxOy Nanohybrids: Synthesis and Dye Photodegradation.

Molybdenum sulfide is a very promising catalyst for the photodegradation of organic pollutants in water. Its photocatalytic activity arises from unsaturated sulfur bonds, and it increases with the introduction of structural defects and/or oxygen substitutions. Amorphous molybdenum sulfide (a-MoSxOy) with oxygen substitutions has many active sites, which create favorable conditions for enhanced catalytic activity. Here we present a new approach to the synthesis of a-MoSxOy and demonstrate its high activity in the photodegradation of the dye methylene blue (MB). The MoSxOy was deposited on hexagonal boron oxynitride (h-BNO) nanoflakes by reacting h-BNO, MoCl5, and H2S in dimethylformamide (DMF) at 250 °C. Both X-ray diffraction analysis and high-resolution TEM show the absence of crystalline order in a-MoSxOy. Based on the results of Raman and X-ray photoelectron spectroscopy, as well as analysis by the density functional theory (DFT) method, a chain structure of a-MoSxOy was proposed, consisting of MoS3 clusters with partial substitution of sulfur by oxygen. When a third of the sulfur atoms are replaced with oxygen, the band gap of a-MoSxOy is approximately 1.36 eV, and the valence and conduction bands are 0.74 eV and −0.62 eV, respectively (relative to a standard hydrogen electrode), which satisfies the conditions of photoinduced splitting of water. When illuminated with a mercury lamp, a-MoSxOy/h-BNxOy nanohybrids have a specific mass activity in MB photodegradation of approximately 5.51 mmol g−1 h−1, which is at least four times higher than so far reported values for nonmetal catalysts. The photocatalyst has been shown to be very stable and can be reused.

Thermal transport in pristine and defective two-dimensional polyaniline ([formula omitted

Two-dimensional polyaniline (2D-PANI) with semiconductor properties, a single crystalline carbon nitride with a stoichiometry of C3N, has attracted a lot of interest after its successful synthesis. In this study, the thermal transport properties in pristine and defective 2D-PANI were explored by extensive molecular dynamics (MD) simulations. Results based on three different versions of the MD method consistently showed that the lattice thermal conductivity of the pristine 2D-PANI is up to around 2000Wm−1K−1. It decreases significantly after the introduction of structural defects and is essentially in a low-power law with the defects concentration. In addition, the difference in the weakening of thermal conductivity between vacancy and topological defects stems mainly from their respective differential effects on the low-frequency out-of-plane phonons. Remarkably, it also reveals the potential mutual constraints between anharmonic phonon-phonon scattering and phonon-defect scattering. These findings provide guidance for the thermal management of 2D-PANI-based electronic devices and are also expected to advance their application in the field of thermal design of nanomaterials.

Spatio-Chemical Heterogeneity of Defect-Engineered Metal-Organic Framework Crystals Revealed by Full-Field Tomographic X-ray Absorption Spectroscopy.

The introduction of structural defects in metal-organic frameworks (MOFs), often achieved through the fractional use of defective linkers, is emerging as a means to refine the properties of existing MOFs. These linkers, missing coordination fragments, create unsaturated framework nodes that may alter the properties of the MOF. A property-targeted utilization of this approach demands an understanding of the structure of the defect-engineered MOF. We demonstrate that full-field X-ray absorption near-edge structure computed tomography can help to improve our understanding. This was demonstrated by visualizing the chemical heterogeneity found in defect-engineered HKUST-1 MOF crystals. A non-uniform incorporation and zonation of the defective linker was discovered, leading to the presence of clusters of a second coordination polymer within HKUST-1. The former is suggested to be responsible, in part, for altered MOF properties; thereby, advocating for a spatio-chemically resolved characterization of MOFs.

Spatio‐Chemical Heterogeneity of Defect‐Engineered Metal–Organic Framework Crystals Revealed by Full‐Field Tomographic X‐ray Absorption Spectroscopy

AbstractThe introduction of structural defects in metal–organic frameworks (MOFs), often achieved through the fractional use of defective linkers, is emerging as a means to refine the properties of existing MOFs. These linkers, missing coordination fragments, create unsaturated framework nodes that may alter the properties of the MOF. A property‐targeted utilization of this approach demands an understanding of the structure of the defect‐engineered MOF. We demonstrate that full‐field X‐ray absorption near‐edge structure computed tomography can help to improve our understanding. This was demonstrated by visualizing the chemical heterogeneity found in defect‐engineered HKUST‐1 MOF crystals. A non‐uniform incorporation and zonation of the defective linker was discovered, leading to the presence of clusters of a second coordination polymer within HKUST‐1. The former is suggested to be responsible, in part, for altered MOF properties; thereby, advocating for a spatio‐chemically resolved characterization of MOFs.

SOLVOTHERMAL SYNTHESIS OF Sb2S3 NEEDLES AND STUDY OF THE EFFECT OF THEIR INTERGROWTH ON THEIR OPTICAL PROPERTIES

Antimony trisulfide (Sb2S3) was successfully synthesized by the solvothermal route using either inorganic SbCl3 or organic C8H10K2O15Sb2 antimony precursors, and carbon disulfide as sulfur precursor with ethylene glycol as the solvent. The use of SbCl3 resulted in single needles, while C8H10K2O15Sb2 conducted to needle-bundles. In both cases, the crystal structure is orthorhombic (Stibnite), as a single phase. The introduction of structural defects caused by the intergrowth is evidenced by Raman spectroscopy. The defects originate a variation of the optical bandgap of the material.

Recovery from mechanical degradation of graphene by defect enlargement

The extraordinary properties of graphene have made it an elite candidate for a broad range of emerging applications since its discovery. However, the introduction of structural defects during graphene production often compromises the theoretically predicted performance of graphene-based technologies to a great extent. In this study, a counterintuitive defect enlargement strategy to recover from defect-induced mechanical degradation is explored, of which the realization may lead to an enhanced operating efficiency and manufacturing feasibility. Our molecular-dynamics simulation results show that the enlargement of a preexisting defect to an elliptical shape can potentially recover from the mechanical degradation that the very defect has caused. For a defective graphene sheet having a failure strain of 48% of the pristine graphene sheet, enlarging the defect can enhance the failure strain up to 80% of the pristine graphene sheet. The mechanism of degradation recovery lies in a reduced change in curvature during deformation, which is further solidified by theoretical quantification and stress-field analysis. This theory can also predict and pinpoint the location of the initiation of the fracture—where the curvature changes most significantly during the deformation. In addition, the influence of an elliptical defect on the mechanical properties of a graphene sheet is systematically studied, which is not well understood today. Finally, the degradation recovery potential of defect of various sizes is examined, showing that the initial defect that can create the highest degree of geometric asymmetry has the best potential for degradation recovery. This study investigates the recovery from defect-induced mechanical degradation and the influence of elliptical defects on the mechanical properties of a graphene sheet, which widens our understanding of the possibility of fine-tuning mechanical properties via defect engineering and has the potential to improve materials for emerging technologies such as supercapacitor devices.

Effect of Surface Finish on High-Temperature Oxidation of Steels in CO2, Supercritical CO2, and Air

Current and future power systems require steels resistant to high-temperature oxidation in CO2-rich environments. The introduction of structural defects by various surface treatments can profoundly affect the oxidation/corrosion behavior of steels in many environments. This effect is largely unexplored for steels exposed to high-temperature CO2, which is the focus of this work. We prepared Grade 22, Grade 91, 347H, and 310S steels with three different surface finishes, ranging from little to substantial surface damage, and exposed the steels to 1 bar CO2, 200 bar supercritical CO2, and laboratory air at 550 °C for up to 1500 h. Surface finish had little impact on the oxidation behavior of low-Cr (2 wt%) Grade 22 and high-Cr (25 wt%) 310S steels. In contrast, intermediate-Cr steels Grade 91 (8 wt%) and 347H (17 wt%) generally showed improved oxidation and carburization resistance with increasing extent of surface damage, which was attributed to the delay or prevention of the onset of Fe-rich oxide nodule growth. Comparison between exposure environments suggests that this effect is more complex for CO2 compared to air and that it is additionally affected by CO2 pressure. The results suggest that surface treatments should be considered as one approach to achieve improved corrosion resistance in high-temperature CO2, particularly for steels containing Cr levels near the transition that is required to form and maintain a protective Cr-rich oxide scale.

Simulation and synthesis of [formula omitted]-MoCl3 nanosheets on substrates by short time chemical vapor transport

α-molybdenum(III) chloride (α-MoCl3) belongs to layered van-der-Waals materials, which are in focus to exhibit interesting properties due to their weak chemical and magnetic interactions. Especially the structure of α-MoCl3 has been discussed in terms of symmetry breaking dimerization of Mo atoms at room temperature, which might led to exotic ground states. By exploiting the 2D materials characteristics, an investigation of physical properties on the nanoscale is intended. We herein demonstrate the probably first approach to synthesize phase pure, as-grown α-MoCl3 few-layer nanosheets by means of a pure short time chemical vapor transport (CVT) process. Vapor growth benefits from a one-step deposition of high crystalline α-MoCl3 nanosheets without stacking faults on a substrate. Thus, mostly applied subsequent delamination, associated with the introduction of structural defects, becomes redundant. According to the CVT process thermodynamic simulations of gas phase equilibria have been performed and the synthesis conditions could be optimized based on the calculation results. By CVT the as-grown nanolayers are deposited on sapphire (Al2O3) substrates by applying a temperature gradient of 70 K from 743 K to 673 K. Single crystalline sheets with thicknesses ≤75 nm down to five layer (3 nm) could be obtained by using a pure CVT process. According to the deposited nanostructures we approve the desired composition, morphology, phase purity and high crystallinity by using several microscopy and spectroscopy techniques. Furthermore, we show micro-RAMAN measurements which hint at a slight increase in phonon energies for nanosheets in comparison to the corresponding bulk phase.

Functionalization of a Metal-Organic Framework Semiconductor for Tuned Band Structure and Catalytic Activity

This study presents two strategies to modify the thermally stable crystalline UiO-66(Zr) metal-organic framework (MOF) structure, in which the organic struts have been functionalized to modulate the electronic band structure and the catalytic activity toward selective oxidation of benzyl alcohol to benzaldehyde. The two strategies include the functionalization of the organic struts with branched ligands and manually creating structural defects with unsaturated organic linkers. The computational and experimental results show that functional groups such as -NH2 and -NO2 attached to the main organic strut modify the electronic environment of the photoactive aromatic carbon and thereby reduce the optical bandgap by 1 eV, improving the photocatalytic activity. Whereas the introduction of structural defects by the organic linker desaturation provides a shift in the highest occupied molecular orbital (HOMO), resulting from a decrease in the strut coordination with the inorganic knots, modulating the catalytic activity without light illumination.

Cellulose Nanocrystal-ZnO Nanohybrids for Controlling Photocatalytic Activity and UV Protection in Cosmetic Formulation.

A high-performance semiconductor zinc oxide (ZnO) on melamine formaldehyde-coated cellulose nanocrystals (MFCNCs) was synthesized and evaluated for its application in smart cosmetics. These ZnO@MFCNC hybrid nanostructures were evaluated for their in vitro sun protection factor performance and photocatalytic activity under simulated UV and solar radiation. The photodegradation kinetics of a model pigment (methylene blue) was fitted to the Langmuir–Hinshelwood model. A 4-fold increase in the photocatalytic activity of ZnO@MFCNCs was observed when compared to pure ZnO. This is associated with (i) increased specific surface area provided by the MFCNC template, (ii) confined surface energy and controlled growth of ZnO nanoparticles, and (iii) entrapment of photoinduced charge carriers in the pores of the core–shell MFCNC rod, followed by fast promotion of interfacial e-charge transfer to the surface of the catalyst. The present study demonstrates how an increase in photocatalytic activity can be engineered without the introduction of structural defects or band gap tailoring of the semiconductor. The aqueous-based ZnO@MFCNC hybrid system displayed attractive UV-absorption and photocatalytic characteristics, offering the conversion of this renewable and sustainable technology into intelligent cosmetic formulations.

Reduced graphene oxide: An alternative for Magnetic Resonance Imaging contrast agent

Graphene oxide (GO) has never been considered as a Magnetic Resonance Imaging (MRI) contrast agent since it was conceived as a diamagnetic material. There is a possibility that introduction of structural defects or manipulation of oxygen functionalities in GO change its magnetic response and provided a chance for GO to be a contrast agent for MRI. For this purpose, reduced graphene oxide (RGO) was treated by irradiation and annealing procedures. The study on the magnetic properties of the samples confirmed that the competition between the structural defects and oxygen functionalities to magnetic moments determines the magnetism in RGO.

Structural defects in a nanomesh of bulk MoS2 using an anodic aluminum oxide template for photoluminescence efficiency enhancement

Two-dimensional (2D) materials beyond graphene have attracted considerable interest because of the zero bandgap drawbacks of graphene. Transition metal dichalcogenides (TMDs), such as MoS2 and WSe2, are the potential candidates for next 2D materials because atomically thin layers of TMDs exhibit unique and versatile electrical and optical properties. Although bulk TMDs materials have an indirect bandgap, an indirect-to-direct bandgap transition is observed in monolayers of TMDs (MoS2, WSe2, and MoSe2). Optical properties of TMD films can be improved by the introduction of structural defects. For example, large-area spatial tuning of the optical transition of bulk MoS2 films is achieved by using an anodic aluminum oxide (AAO) template to induce structural defects such as edge- and terrace-terminated defects in a nanomesh structure. Strong photoluminescence emission peaks with a band gap of 1.81 eV are observed, possibly because of radiative transition at the defect sites. This work shows that the AAO template lithography method has potential for the production of homogenous large-scale nanomesh structures for practical semiconductor processing applications in future MoS2-based electronic and optical devices.

Inducing defects in ordered mesoporous carbons via the block copolymer-templated high-temperature carbonization of nitrogen-containing polymeric precursors

Structural defects in graphene directly influence its electronic structure and can lead to the development of unique properties. However, the introduction of defects into ordered mesoporous graphitic carbons has yet to be demonstrated. Herein, defects were successfully introduced into the graphitic carbon lattice of well-ordered hexagonal mesoporous carbons via a block copolymer soft-template method and high-temperature carbonization. Small-angle X-ray scattering, scanning electron microscopy, and nitrogen adsorption measurements revealed that well-ordered ~4 nm cylindrical mesoporous structures with high surface areas (532 m2g−1) and good mesoporosity were maintained after high-temperature carbonization up to 1500 °C and mechanical milling. Raman and CHN elemental analyses suggested that defects were introduced into the graphitic carbon lattice through surface reconstruction induced by N-atom removal during heat treatment. The obtained robust and well-ordered N-containing mesoporous carbons with deliberately introduced defects are considered promising materials for electrochemical reactions and as catalyst supports. The introduction of structural defects into ordered mesoporous carbons is demonstrated based on block copolymer-templating and high-temperature carbonization of N-containing polymers. N-atom removal during high-temperature heat treatment induces structural defect formation, and the use of soft-templating yields dense mesostructures tough enough to maintain ordering upon defect introduction.Please change the graphical abstract to the revised one sent by email separately.

Metal-Free Carbocatalysis in Advanced Oxidation Reactions.

Catalytic processes have remarkably boosted the rapid industrializations in chemical production, energy conversion, and environmental remediation. As one of the emerging applications of carbocatalysis, metal-free nanocarbons have demonstrated promise as catalysts for green remediation technologies to overcome the poor stability and undesirable metal leaching in metal-based advanced oxidation processes (AOPs). Since our reports of heterogeneous activation of persulfates with low-dimensional nanocarbons, the novel oxidative system has raised tremendous interest for degradation of organic contaminants in wastewater without secondary contamination. In this Account, we showcase our recent contributions to metal-free catalysis in advanced oxidation, including design of nanocarbon catalysts, exploration of intrinsic active sites, and identification of reactive species and reaction pathways, and we offer perspectives on carbocatalysis for future environmental applications. The journey starts with the discovery of peroxymonosulfate (PMS) and peroxydisulfate (PDS) activation by graphene-based materials. With the systematic investigations on most carbon allotropes, for the first time the carbocatalysis for PMS or PDS activation was correlated with the pristine carbon configuration, oxygen functionality (ketonic groups), defect degree (exposed edge sites and vacancies), and dimensional structure. Moreover, an intrinsic difference in catalytic oxidation does exist between PMS and PDS activation. For example, the PMS/carbon reaction is dominated by free radicals, while PDS/carbon catalysis was unveiled as a singlet oxygen- or nonradical-based process in which the surface-activated PDS complex directly degrades the organic pollutants without relying on the generation of free radicals. Nitrogen doping significantly enhances the carbocatalysis because of the positively charged carbon domains, which strongly bind with persulfates to form reactive intermediates toward organic reactions. More importantly, N doping substantially alters the catalytic oxidation from a radical process to a nonradical pathway in PMS activation. Codoping of sulfur or boron with nitrogen at a rational level will synergistically promote the catalysis as a result of the formation of more catalytic centers by improved charge/spin redistribution of the carbon framework. Furthermore, a structure-performance relationship was established for annealed nanodiamonds with a characteristic sp3/sp2 (core/shell) hybridization, where the catalytic pathways were intimately dependent on the thickness of the graphitic shells. Interestingly, the introduction of structural defects and N dopants into the well-defined graphitic carbon framework and alteration of graphene/diamond hybrids can transform the persulfate/carbon system from a radical oxidation pathway to a nonradical pathway. Encapsulation of metal nanoparticles within carbon layers further modulates the electronic states of the interacting carbon via charge transport to increase the electron density. Overall, this Account contributes to unveiling the mist of carbocatalysis in AOPs and to summarizing the achievements of metal-free remediation. We also present future research directions on underpinning the knowledge base to facilitate the applications of nanocarbons in sustainable catalysis and environmental chemistry.

Binary control of enzymatic cleavage of DNA origami by structural antideterminants.

Controlling DNA nanostructure interaction with protein is essential in developing nanodevices with programmable function, reactivity, and stability for biological and medical applications. Here, we show that the sequence-specific action of restriction endonucleases towards sharp triangular or rectangular DNA origami exhibits a novel, binary ‘on/off’ behaviour, as canonical recognition sites are either essentially fully reactive, or strongly resistant to enzymatic cutting. Moreover, introduction of structural defects in the sharp triangle can activate an otherwise unreactive site, with a site-to-defect distance of ∼50 nm. We argue that site reactivity is dependent upon programmable, mechanical coupling in the two-dimensional DNA origami, with specific structural elements, including DNA nicks and branches proximal to the sites that can function as negative(anti) determinants of reactivity. Empirically modelling the constraints to DNA degrees of freedom associated with each recognition site in the sharp triangle can rationalize the pattern of suppressed reactivity towards nine restriction endonucleases, in substantial agreement with the experimental results. These results provide a basis for a predictive understanding of structure-reactivity correlates of specific DNA nanostructures, which will allow a better understanding of the behaviour of nucleic acids under nanoscale confinement, as well as in the rational design of functional nanodevices based on self-assembling nucleic acids.

Hydrogen storage in Titanium-doped single-walled carbon nanotubes with Stone-Wales defects

The hydrogen storage capacity of Titanium-doped single-walled carbon nanotubes (SWCNT) containing the Stone-Wales 5,8 defects was studied using molecular dynamics simulations. The equilibrium doping sites and their stability were estimated using density functional theory. Although introduction of structural defects and dopant atom decreases the formation and cohesive energies, the drop in these energies is not large enough to hinder the thermodynamic feasibility of formation of these structures. Moreover, we observed that the stability of SWCNTs, where Ti is doped by replacing two carbon atoms is similar to that of the defect-free nanotube. This particular novel configuration (D5) was also obtained by rearranging the bonds in the 5 and 8-member rings of the Stone-Wales defect. Doping Ti on the defective rings has a more significant effect on the adsorption of hydrogen than doping on the regular 6-member rings. The D5 SWCNT showed the highest gravimetric and volumetric storage capacities at a temperature of 298K and a moderate pressure of 140atm. We also compared the performance of the D5 SWCNT with a recently reported Ti-doped porphyrin SWCNT and observed that the storage capacity of the D5 SWCNT was significantly higher at similar conditions. Our results suggest that Ti-doped SWCNTs with the Stone-Wales (5,8) defects show a promising potential to meet the ultimate goal set by the US Department of Energy for hydrogen storage.

Controllable Nanotribological Properties of Graphene Nanosheets

Graphene as one type of well-known solid lubricants possesses different nanotribological properties, due to the varied surface and structural characteristics caused by different preparation methods or post-processes. Graphene nanosheets with controllable surface wettability and structural defects were achieved by plasma treatment and thermal reduction. The nanotribological properties of graphene nanosheets were investigated using the calibrated atomic force microscopy. The friction force increases faster and faster with plasma treatment time, which results from the increase of surface wettability and the introduction of structural defects. Short-time plasma treatment increasing friction force is due to the enhancement of surface hydrophilicity. Longer-time plasma treatment increasing friction force can attribute to the combined effects of the enhanced surface hydrophilicity and the generated structural defects. The structural defects as a single factor also increase the friction force when the surface properties are unified by thermal reduction. The surface wettability and the nanotribological properties of plasma-treated graphene nanosheets can recover to its initial level over time. An improved spring model was proposed to elaborate the effects of surface wettability and structural defects on nanotribological properties at the atomic-scale.