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C, Volume 8, Issue 2 (June 2022) – 13 articles

Cover Story (view full-size image): A new purification procedure of carbon nanoforms is proposed. While synthesis leads to a distribution of unwished products, many purification strategies exist. A successful one is combustion. However, the temperature has to be carefully chosen to maximize the reaction selectivity. Moreover, it depends on many factors, such as the material but also the reactor and parameters of gas. Temperature optimization typically relies on fastidious multiple isotherms and analysis of the product or unprecise constant heating rate measurement. We demonstrate here that a thermogravimetric method, the constant decomposition rate thermal analysis, is particularly well adapted to answer this question. It successfully allowed purifying the challenging case of multiwall carbon nanotubes and should be valuable for other carbonaceous forms. View this paper
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Article
Development of Disposable and Flexible Supercapacitor Based on Carbonaceous and Ecofriendly Materials
C 2022, 8(2), 32; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020032 - 07 Jun 2022
Viewed by 537
Abstract
A novel flexible supercapacitor device was developed from a polyethylene terephthalate substrate, reused from beverage bottles, and a conductive ink based on carbon black (CB) and cellulose acetate (CA). The weight composition of the conductive ink was evaluated to determine the best mass [...] Read more.
A novel flexible supercapacitor device was developed from a polyethylene terephthalate substrate, reused from beverage bottles, and a conductive ink based on carbon black (CB) and cellulose acetate (CA). The weight composition of the conductive ink was evaluated to determine the best mass percentage ratio between CB and CA in terms of capacitive behavior. The evaluation was performed by using different electrochemical techniques: cyclic voltammetry, obtaining the highest capacitance value for the device with the 66.7/33.3 wt% CB/CA in a basic H2SO4 solution, reaching 135.64 F g−1. The device was applied in potentiostatic charge/discharge measurements, achieving values of 2.45 Wh kg−1 for specific energy and around 1000 W kg−1 for specific power. Therefore, corroborated with electrochemical impedance spectroscopy assays, the relatively low-price proposed device presented a suitable performance for application as supercapacitors, being manufactured from reused materials, contributing to the energy storage field enhancement. Full article
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Communication
Burn Them Right! Determining the Optimal Temperature for the Purification of Carbon Materials by Combustion
C 2022, 8(2), 31; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020031 - 24 May 2022
Viewed by 499
Abstract
A new purification procedure for carbon nanoforms is proposed. It was tested on multiwall carbon nanotubes (MWCNTs) prepared by arc discharge, which is among the most challenging of cases due to the chemical and structural similarity between the MWCNTs and most of the [...] Read more.
A new purification procedure for carbon nanoforms is proposed. It was tested on multiwall carbon nanotubes (MWCNTs) prepared by arc discharge, which is among the most challenging of cases due to the chemical and structural similarity between the MWCNTs and most of the impurities to be removed. Indeed, the various methods for synthesizing carbon nanoforms lead to a distribution of carbonaceous products, such as carbon shells, carbon spheres, fullerenes, and a variety of other species. Thus, many strategies to purify the desired products have been developed. Among the most successful ones, thermal oxidation (combustion) seems particularly efficient. To be successful while preserving a reasonable amount of MWCNTs, the combustion temperature has to be carefully selected. Moreover, the ideal combustion temperature does not only depend on the material to be treated but also on the overall system used to perform the reaction, including the reactor type and the parameters of the gaseous reactant. Typically, the optimization of the purification relies on multiple experiments and analysis of the products. However, to the best of our knowledge, a strategy to determine a priori the most suitable temperature has not been reported yet. We demonstrate here that a thermogravimetric method, namely the constant decomposition rate thermal analysis (CRTA), is particularly well adapted to answer this question. An isothermal treatment based on the results obtained from a CRTA program allowed arc-MWCNTs to be successfully purified from graphenic shells while optimizing the yield of the MWCNTs. This strategy is believed to be valuable not only for purifying MWCNTs but also for the purification of other carbonaceous forms, including new carbon nanoforms. Full article
(This article belongs to the Collection Young Carbon Scientists)
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Article
Plasma-Enhanced Carbon Nanotube Fiber Cathode for Li-S Batteries
C 2022, 8(2), 30; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020030 - 22 May 2022
Viewed by 502
Abstract
Fiber-shaped batteries have attracted much interest in the last few years. However, a major challenge for this type of battery is their relatively low energy density. Here, we present a freestanding, flexible CNT fiber with high electrical conductivity and applied oxygen plasma-functionalization, which [...] Read more.
Fiber-shaped batteries have attracted much interest in the last few years. However, a major challenge for this type of battery is their relatively low energy density. Here, we present a freestanding, flexible CNT fiber with high electrical conductivity and applied oxygen plasma-functionalization, which was successfully employed to serve as an effective cathode for Li-S batteries. The electrochemical results obtained from the conducted battery tests showed a decent rate capability and cyclic stability. The cathode delivered a capacity of 1019 mAh g−1 at 0.1 C. It accommodated a high sulfur loading of 73% and maintained 47% of the initial capacity after 300 cycles. The demonstrated performance of the fiber cathode provides new insights for the designing and fabrication of high energy density fiber-shaped batteries. Full article
(This article belongs to the Special Issue Frontier Applications of Carbon Nanotube-Based Materials)
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Review
Recent Progress in Synthesis and Application of Activated Carbon for CO2 Capture
C 2022, 8(2), 29; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020029 - 14 May 2022
Viewed by 600
Abstract
Greenhouse gas emissions to the atmosphere have been a long-standing issue that has existed since the Industrial Revolution. To date, carbon dioxide capture through the carbon capture, utilization, and storage approach has been one of the feasible options to combat the strong release [...] Read more.
Greenhouse gas emissions to the atmosphere have been a long-standing issue that has existed since the Industrial Revolution. To date, carbon dioxide capture through the carbon capture, utilization, and storage approach has been one of the feasible options to combat the strong release of carbon dioxide into the atmosphere. This review focuses in general on the utilization of activated carbon as a tool when performing the carbon-capture process. Activated carbon possesses a lower isosteric heat of adsorption and a stronger tolerance to humidity as compared to zeolites and metal–organic frameworks, despite the overall gas-separation performance of activated carbon being comparatively lower. In addition, investigations of the activation methods of activated carbon are summarized in this review, together with an illustration of CO2 adsorption performance, in the context of process simulations and pilot-plant studies. This is followed by providing future research directions in terms of the applicability of activated carbon in real CO2 adsorption processes. Full article
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Article
The Evaluation of Quality of the Co-Firing Process of Glycerine Fraction with Coal in the High Power Boiler
C 2022, 8(2), 28; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020028 - 12 May 2022
Viewed by 565
Abstract
The article presents the test results of the co-firing process of a glycerine fraction derived from the production of liquid biofuels (fatty acid methyl esters) with coal. The test was performed in industrial conditions using a steam boiler with a capacity of approx. [...] Read more.
The article presents the test results of the co-firing process of a glycerine fraction derived from the production of liquid biofuels (fatty acid methyl esters) with coal. The test was performed in industrial conditions using a steam boiler with a capacity of approx. 2 MW in one of the building materials manufacturing facilities. The process of co-firing a mixture of a 3% glycerine fraction and eco-pea coal was evaluated. The reference fuel was eco-pea coal. The combustion process, composition and temperature of exhaust gases were analyzed. Incorrect combustion of glycerine fraction may result in the emission of toxic, mutagenic, and carcinogenic substances, including polycyclic aromatic hydrocarbons. During the test of the combustion process of a mixture of glycerine fraction and eco-pea coal, a decrease in the content of O2, CO, and NOx was observed as well as an increase in the content of H2, CO2, and SO2 in the fumes and growth of temperature of exhaust gases in relation to the results of combustion to eco-pea coal. Reduced content of carbon monoxide in exhaust gases produced in the combustion could be caused by the high temperature of the grate or by an excessive amount of oxygen in the grate. The higher content of oxygen in glycerine changes the value of excess air coefficient and the combustion process is more effective. The bigger content of sulfur dioxide in burnt fuels containing the glycerine fraction could be caused by the presence of reactive ingredients contained in the glycerine fraction. The reduced content of nitrogen oxides in exhaust gases originating from the combustion of a fuel mixture containing a fraction of glycerine could be caused by lower content of nitrogen in the glycerine fraction submitted to co-firing with coal and also higher combustion temperature and amount of air in the combustion chamber. The increased content of carbon dioxide in exhaust gases originating from the combustion of fuel mixture containing glycerine fraction could be caused by the influence of glycerine on the combustion process. The increase of hydrogen in the glycerine fraction causes the flame temperature to grow and makes the combustion process more efficient. Full article
(This article belongs to the Section Combustion Emissions)
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Article
Chemical Production of Graphene Oxide with High Surface Energy for Supercapacitor Applications
C 2022, 8(2), 27; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020027 - 07 May 2022
Viewed by 700
Abstract
The chemical exfoliation of graphite to produce graphene and its oxide is undoubtedly an economical method for scalable production. Carbon researchers have dedicated significant resources to developing new exfoliation methods leads to graphene oxides with high quality. However, only a few studies have [...] Read more.
The chemical exfoliation of graphite to produce graphene and its oxide is undoubtedly an economical method for scalable production. Carbon researchers have dedicated significant resources to developing new exfoliation methods leads to graphene oxides with high quality. However, only a few studies have been dedicated to the effect of the starting graphite material on the resulting GO. Herein, we have prepared two different GOs through chemical exfoliation of graphite materials having different textural and structural characteristics. All samples have been subjected to structural investigations and comprehensive characterizations using Raman, X-ray diffraction, scanning electron microscopy, TGA, N2 physisorption, and FTIR spectroscopy. Our results provide direct evidence of how the crystallite size of the raw graphite affects the oxidation degree, surface functionality, and sheet size of the resulting GO. Building on these significant understandings, the optimized GO achieves a highly specific capacitance of 191 F·g−1 at the specific current of 0.25 A·g−1 in an aqueous electrolyte. This superior electrochemical performance was attributed to several factors, among which the specific surface area was accessible to the electrolyte ions and oxygenated functional groups on the surface, which can significantly modify the electronic structure of graphene and further enhance the surface energy. Full article
(This article belongs to the Collection Young Carbon Scientists)
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Review
Recent Advances on Capacitive Proximity Sensors: From Design and Materials to Creative Applications
C 2022, 8(2), 26; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020026 - 05 May 2022
Viewed by 706
Abstract
Capacitive proximity sensors (CPSs) have recently been a focus of increased attention because of their widespread applications, simplicity of design, low cost, and low power consumption. This mini review article provides a comprehensive overview of various applications of CPSs, as well as current [...] Read more.
Capacitive proximity sensors (CPSs) have recently been a focus of increased attention because of their widespread applications, simplicity of design, low cost, and low power consumption. This mini review article provides a comprehensive overview of various applications of CPSs, as well as current advancements in CPS construction approaches. We begin by outlining the major technologies utilized in proximity sensing, highlighting their characteristics and applications, and discussing their advantages and disadvantages, with a heavy emphasis on capacitive sensors. Evaluating various nanocomposites for proximity sensing and corresponding detecting approaches ranging from physical to chemical detection are emphasized. The matrix and active ingredients used in such sensors, as well as the measured ranges, will also be discussed. A good understanding of CPSs is not only essential for resolving issues, but is also one of the primary forces propelling CPS technology ahead. We aim to examine the impediments and possible solutions to the development of CPSs. Furthermore, we illustrate how nanocomposite fusion may be used to improve the detection range and accuracy of a CPS while also broadening the application scenarios. Finally, the impact of conductance on sensor performance and other variables that impact the sensitivity distribution of CPSs are presented. Full article
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Article
Pore Structure and Gas Diffusion Features of Ionic Liquid-Derived Carbon Membranes
C 2022, 8(2), 25; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020025 - 29 Apr 2022
Viewed by 621
Abstract
In the present study, the concept of Ionic Liquid (IL)-mediated formation of carbon was applied to derive composite membranes bearing a nanoporous carbon phase within their separation layer. Thermolytic carbonization of the supported ionic liquid membranes, prepared by infiltration of the IL 1-methyl-3-butylimidazolium [...] Read more.
In the present study, the concept of Ionic Liquid (IL)-mediated formation of carbon was applied to derive composite membranes bearing a nanoporous carbon phase within their separation layer. Thermolytic carbonization of the supported ionic liquid membranes, prepared by infiltration of the IL 1-methyl-3-butylimidazolium tricyanomethanide into the porous network of Vycor® porous glass tubes, was applied to derive the precursor Carbon/Vycor® composites. All precursors underwent a second cycle of IL infiltration/pyrolysis with the target to finetune the pore structural characteristics of the carbonaceous matter nesting inside the separation layer. The pore structural assets and evolution of the gas permeation properties and separation efficiency of the as-derived composite membranes were investigated with reference to the duration of the second infiltration step. The transport mechanisms of the permeating gases were elucidated and correlated to the structural characteristics of the supported carbon phase and the analysis of LN2 adsorption isotherms. Regarding the gas separation efficiency of the fabricated Carbon/Vycor® composite membranes, He/CO2 ideal selectivity values as high as 4.31 at 1 bar and 25 °C and 4.64 at 0.3 bar and 90 °C were achieved. In addition, the CO2/N2 ideal selectivity becomes slightly improved for longer second-impregnation times. Full article
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Article
Laser-Assisted Growth of Carbon-Based Materials by Chemical Vapor Deposition
C 2022, 8(2), 24; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020024 - 26 Apr 2022
Viewed by 668
Abstract
Carbon-based materials (CBMs) such as graphene, carbon nanotubes (CNT), highly ordered pyrolytic graphite (HOPG), and pyrolytic carbon (PyC) have received a great deal of attention in recent years due to their unique electronic, optical, thermal, and mechanical properties. CBMs have been grown using [...] Read more.
Carbon-based materials (CBMs) such as graphene, carbon nanotubes (CNT), highly ordered pyrolytic graphite (HOPG), and pyrolytic carbon (PyC) have received a great deal of attention in recent years due to their unique electronic, optical, thermal, and mechanical properties. CBMs have been grown using a variety of processes, including mechanical exfoliation, pulsed laser deposition (PLD), and chemical vapor deposition (CVD). Mechanical exfoliation creates materials that are irregularly formed and tiny in size. On the other hand, the practicality of the PLD approach for large-area high-quality CMB deposition is quite difficult. Thus, CVD is considered as the most effective method for growing CBMs. In this paper, a novel pulsed laser-assisted chemical vapor deposition (LCVD) technique was explored to determine ways to reduce the energy requirements to produce high quality CBMs. Different growth parameters, such as gas flow rate, temperature, laser energy, and deposition time were considered and studied thoroughly to analyze the growth pattern. CBMs are grown on Si and Cu substrates, where we find better quality CBM films on Cu as it aids the surface solubility of carbon. Raman spectroscopy confirms the presence of high-quality PyC which is grown at a temperature of 750 °C, CH4 gas flow rate of 20 sccm, a laser frequency of 10 Hz, and an energy density of 0.116 J/cm2 per pulse. It is found that the local pulsed-laser bombardment helps in breaking the carbon-hydrogen bonds of CH4 at a much lower substrate temperature than its thermal decomposition temperature. There is no significant change in the 2D peak intensity in the Raman spectrum with the further increase in temperature which is the indicator of the number of the graphene layer. The intertwined graphene flakes of the PyC are observed due to the surface roughness, which is responsible for the quenching in the Raman 2D signal. These results will provide the platform to fabricate a large area single layer of graphene, including the other 2D materials, on different substrates using the LCVD technique. Full article
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Article
On the Problem of “Super” Storage of Hydrogen in Graphite Nanofibers
C 2022, 8(2), 23; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020023 - 29 Mar 2022
Viewed by 883
Abstract
This article is devoted to some fundamental aspects of “super” storage in graphite nanofibers (GNF) of “reversible” (~20–30 wt.%) and “irreversible” hydrogen (~7–10 wt.%). Extraordinary results for hydrogen “super” storage were previously published by the group of Rodriguez and Baker at the turn [...] Read more.
This article is devoted to some fundamental aspects of “super” storage in graphite nanofibers (GNF) of “reversible” (~20–30 wt.%) and “irreversible” hydrogen (~7–10 wt.%). Extraordinary results for hydrogen “super” storage were previously published by the group of Rodriguez and Baker at the turn of the century, which been unable to be reproduced or explained in terms of physics by other researchers. For the first time, using an efficient method of processing and analysis of hydrogen thermal desorption spectra, the characteristics of the main desorption peak of “irreversible” hydrogen in GNF were determined: the temperature of the highest desorption rate (Tmax = 914–923 K), the activation energy of the desorption process (Q ≈ 40 kJ mol−1), the pre-exponential rate constant factor (K0 ≈ 2 × 10−1 s−1), and the amount of hydrogen released (~8 wt.%). The physics of hydrogen “super” sorption includes hydrogen diffusion, accompanied by the “reversible” capture of the diffusant by certain sorption “centers”; the hydrogen spillover effect, which provides local atomization of gaseous H2 during GNF hydrogenation; and the Kurdjumov phenomenon on thermoelastic phase equilibrium. It is shown that the above-mentioned extraordinary data on the hydrogen “super” storage in GNFs are neither a mistake nor a mystification, as most researchers believe. Full article
(This article belongs to the Special Issue Carbon Materials for Physical and Chemical Hydrogen Storage)
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Review
A Review of Embodied Carbon in Landscape Architecture. Practice and Policy
C 2022, 8(2), 22; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020022 - 26 Mar 2022
Viewed by 925
Abstract
This paper aims to discuss the importance of the climate crisis and embodied carbon in the landscape architecture sector. The study was carried out in a multiprofessional team with the collaboration of the Landscape Institute (LI) Chartered Body of Landscape Architecture, UK, and [...] Read more.
This paper aims to discuss the importance of the climate crisis and embodied carbon in the landscape architecture sector. The study was carried out in a multiprofessional team with the collaboration of the Landscape Institute (LI) Chartered Body of Landscape Architecture, UK, and experts in the field. Using the expertise and knowledge of professionals as well as existing landscape examples and pioneering tools on carbon, this review paper focuses on the importance of low/net-zero carbon landscapes for our cities and regions and the ways in which these can contribute to the broader health and wellbeing of our communities. Examining the current situation on carbon methodologies and the latest knowledge on carbon calculations through a landscape lens, the paper explores why embodied carbon is important for open spaces/landscapes and the necessary policies to support a more efficient implementation of these concepts. The intensity of recent environmental challenges demands action. This review highlights the need for holistic approaches that integrate embodied carbon calculations on large-scale landscape design. Using the innovative example of the Pathfinder App, a carbon calculation tool, as well as other similar software, this paper argues that more steps are needed towards the calculation and adaptation of CO2 emissions resulting from design, construction and materials in landscape schemes. The low availability of carbon calculation tools, specially developed for landscape schemes, is a major concern for the profession as it creates several issues with the sustainable development of the landscape projects as well as fragmented policies that exclude spatial and open spaces. Even though carbon calculation and embodied carbon are being calculated in buildings or materials, it is a relatively new area when it comes to land, the landscape and open and green space, and therefore, this study will present and discuss some of the pioneering carbon calculation tools focusing on landscape projects. Full article
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Article
Engineering of Nanostructured Carbon Catalyst Supports for the Continuous Reduction of Bromate in Drinking Water
C 2022, 8(2), 21; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020021 - 22 Mar 2022
Viewed by 892
Abstract
Recent works in the development of nanostructured catalysts for bromate reduction in drinking water under hydrogen have highlighted the importance of the properties of the metallic phase support in their overall performance. Since most works in catalyst development are carried out in powder [...] Read more.
Recent works in the development of nanostructured catalysts for bromate reduction in drinking water under hydrogen have highlighted the importance of the properties of the metallic phase support in their overall performance. Since most works in catalyst development are carried out in powder form, there is an overlooked gap in the correlation between catalyst support properties and performance in typical continuous applications such as fixed bed reactors. In this work, it is shown that the mechanical modification of commercially available carbon nanotubes, one of the most promising supports, can significantly enhance the activity of the catalytic system when tested in a stirred tank reactor, but upon transition to a fixed bed reactor, the formation of preferential pathways for the liquid flow and high pressure drops were observed. This effect could be minimized by the addition of an inert filler to increase the bed porosity; however, the improvement in catalytic performance when compared with the as-received support material was not retained. The operation of the continuous catalytic system was then optimized using a 1 wt.% Pd catalyst supported on the as-received carbon nanotubes. Effluent and hydrogen flow rates as well as catalyst loadings were systematically optimized to find an efficient set of parameters for the operation of the system, regarding its catalytic performance, capacity to treat large effluent flows, and minimization of catalyst and hydrogen requirements. Experiments carried out in the presence of distilled water as a reaction medium demonstrate that bromate can be efficiently removed from the liquid phase, whereas when using a real water matrix, a tendency for the deactivation of the catalyst over time was more apparent throughout 200 flow passages over the catalytic bed, which was mostly attributed to the competitive adsorption of inorganic matter on the catalyst active centers, or the formation of mineral deposits blocking access to the catalyst. Full article
(This article belongs to the Special Issue Frontier Applications of Carbon Nanotube-Based Materials)
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Article
Chemical Reduction of GO: Comparing Hydroiodic Acid and Sodium Borohydride Chemical Approaches by X-ray Photoelectron Spectroscopy
C 2022, 8(2), 20; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020020 - 22 Mar 2022
Viewed by 803
Abstract
The efficiency of two wet chemical processes based on hydroiodic acid (HI) and sodium borohydride (NaBH4) used to reduce graphene oxide (GO) have been studied. At this aim, the oxygen abundance of reduced graphene oxide (rGO) was studied as a function [...] Read more.
The efficiency of two wet chemical processes based on hydroiodic acid (HI) and sodium borohydride (NaBH4) used to reduce graphene oxide (GO) have been studied. At this aim, the oxygen abundance of reduced graphene oxide (rGO) was studied as a function of the reductant concentration. A number of rGO samples were produced and their chemical compositions were studied using X-ray photoelectron spectroscopy. The analyses show that the reduction of the oxygen concentration proceeds non-linearly. At the beginning, when pristine GO is utilized a higher extent of reduction is obtained. The oxygen concentration decreases from ~32% to 10.5% by increasing the HI concentration to 0.24 M. A steeper reduction was observed for NaBH4, where the oxygen concentration lowers to ~13.6% using just 50 mg of NaBH4. Next, reduction reactions performed with increasing amounts of reductants in aqueous suspensions show a progressive saturation effect, indicating a limit in the final oxygen concentration. We obtained a residual oxygen concentration of 5.3% using 7.58 M of HI and 8.6% with 1200 mg of NaBH4. The chemical analysis highlights that the reduction of the oxygen concentration in rGO samples is mainly derived from the cleavage of C-OH bonds and the next reconstruction of C-C bonds. Full article
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