We are pleased to introduce the collection, 2022 Retrospective: Carbon-Based Materials. This collection aims to showcase original research and review-based papers on the most exciting developments of the past couple of years. The work presented here highlights the broad diversity of research performed across the section, and aims to put a spotlight on the main areas of interest. All research presented here seeks to display strong advances in theory, experiment, and methodology with applications to compelling problems. Authors are encouraged to showcase their most recent discoveries and to kickstart scientific discourse around them.

University of Alicante

University of Education Lahore

Polytechnic University of Turin

Drexel University

Frontiers in Materials

Carbon-Based Materials

2022 Retrospective: Carbon-Based Materials

Carbon is a brand element in the field of materials science, well-known for its versatility and unusual characteristics (<a href="#B5">Inagaki et al., 2014</a>). It has reshaped the materials around us, with better performance for advanced technological applications (<a href="#B6">Lan et al., 2021</a>). During the last 2 decades, graphene and carbon nanotubes (CNTs) remained the two most extensively used materials in materials science. When carbon in the form of carbon nanostructures, graphene, or carbon nanotubes (CNTs), is combined with other materials, it can significantly enhance their properties particularly the structural, electrical, optical, mechanical, thermal, and magnetic, making them suitable for applications ranging from electronics to environmental, and aerospace (<a href="#B2">Chowdhury et al., 2018</a>; <a href="#B4">Gopinath et al., 2021</a>). Carbon materials are considered as essential in all modern research fields where these play a critical role in the development of auspicious technologies and potential solutions for the modern challenges (<a href="#B3">Chung, 2004</a>; <a href="#B7">Liang et al., 2008</a>; <a href="#B1">Balandin, 2011</a>; <a href="#B9">Zhai et al., 2011</a>; <a href="#B8">Titirici et al., 2015</a>; <a href="#B6">Lan et al., 2021</a>).<a href="#F1">Figure 1A</a> shows the increasing trends of carbon materials with passage of time. As per Scopus database, the first paper with word “carbon” in title was published in 1863. The number of publications increased significantly from 1970 to 1990. However, these increased exceptionally afterward, and a total number of 50,350 research items were published in 2023. Materials science remained the dominant field for these contributions, following by Chemistry, Engineering, and Physics and Astronomy, as depicted in <a href="#F1">Figure 1B</a>. It is very important and interesting to mention here that these are publications with only word “carbon” in title; if we search the word(s) “graphene” or ‘carbon nanotube” in Scopus database, we respectively get the numbers 182,934 and 118,146, which are in addition to papers on “carbon”.Owing to great significance of carbon materials, a section of Frontiers in Materials has been dedicated to the Carbon-Based Materials. A Research Topic, “2022 Retrospective: Carbon-Based Materials,” was proposed to attribute the contributions of carbon materials. In this Research Topic, five research documents were published. The first research article was published by <a href="https://doi.org/10.3389/fmats.2022.839421">Karami, et al.</a> on Conversion of Waste Corn Biomass to Activated Bio-Char for Applications in Wastewater Treatment. The report demonstrates the conversion of waste corn to biochar which was further investigated for its potential applications. Authors have shown that the adsorption response of activated biochar was comparable to that with typical commercial activated carbon. The resultant product is very important and may offer its auspicious potential particularly in energy applications. The report is very useful for study of biochar assembly through facile and cost-effective methodology.The second research article was published by <a href="https://doi.org/10.3389/fmats.2022.862796">Quqa et al.</a> on Pressure Mapping Using Nanocomposite-Enhanced Foam and Machine Learning. The report suggests efficient machine learning strategies (radial basis function networks and deep neural networks) to effectively address the inverse electrical impedance tomography issues. The research is very fruitful in enhancing the resolution of reconstructed pressure maps. It is interesting to mention that the researchers have used carbon nanotubes for device fabrication. The study very beautifully presents the applications of carbon materials in medical domains through machine learning. This report is a good answer to question which may arise in many minds while having a look on <a href="#F1">Figure 1</a>, that what could be the applications of carbon materials in computer science!The third article in this Research Topic is a review article published by <a href="https://doi.org/10.3389/fmats.2022.870184">Mukherjee et al.</a> on Synthesis of Biochar From Lignocellulosic Biomass for Diverse Industrial Applications and Energy Harvesting: Effects of Pyrolysis Conditions on the Physicochemical Properties of Biochar. The article is useful particularly for early-stage researchers that are going to learn the preparation of biochar from biomass for further use in energy applications. The article includes valuable citations for the demonstrated study, and may offer various useful ideas for energy production from biochar at industrial scale. Moreover, the review provides worthy contents for physicochemical features of biochar.The fourth article was a mini review by <a href="https://doi.org/10.3389/fmats.2023.1192724">Caballero-Briones et al.</a> on International research in graphene-oxide based materials for net-zero energy, military and aeronautic applications catalysed by Tamaulipas, Mexico: a mini review. The article is unique as per its contents ranging from zero energy to aeronautic applications, summarizing the extreme potential of graphene-oxide (carbon), especially for photovoltaic, photocatalytic, thermonuclear, and aeronautic applications. An important aspect of the review is that it highlights the overseas collaborations for leveraging the materials synthesis for desired outcomes.The final article by <a href="https://doi.org/10.3389/fmats.2023.1218028">Bumajdad et al.</a> is also a review article on Nitrogen-enriched activated carbon derived from plant biomasses: a review on reaction mechanism and applications in wastewater treatment. This article enlightens the process for assembly of carbon from plant biomass which could be very fruitful for researchers working in this area of research with insufficient research facilities and resources. The article has discussions about the methodologies and involved reaction mechanisms for nitrogen enrichment of activated carbon. The review provides valuable findings and deep understandings about basis of the demonstrated study.Although, the articles in this proposed Research Topic are very limited as per broadness and scope of carbon materials, however, it acknowledges the contributions of carbon materials towards diversity of research directions. The Research Topic could specifically be beneficial for early-stage researchers at academia and industries for their understandings, research trainings and directions for future research particularly on carbon materials for energy applications.ZU: Conceptualization, Data curation, Formal Analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Validation, Visualization, Writing&#x2013;original draft, Writing&#x2013;review and editing.The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.The author declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Editorial: 2022 retrospective, carbon-based materials

As a key kind of evolving carbonaceous adsorbent, nitrogen-enriched activated carbon has drawn a lot of focus due to its better physiochemical ability to eliminate an extensive range of wastewaters contaminants under severe conditions. Its environment-friendly character is one more reason behind this focus. Nitrogen also has immense effect on activated carbon structures’ pollutants adsorption capability; therefore, it is an area of interest. Reports concerning the reaction pathway of C-N (carbon-nitrogen) bond creation on AC surface are limited. Determining such mechanisms is challenging but critical to understand bond characteristics after carbonization. Moreover, it is vital to ascertain real-time kinetics concerning adsorption phenomena in liquid phase. Such a latest trend indicates that regulated nitrogen uses for carbonaceous substances having a biomass-based origin can provide the desired morphological characteristics produced through interconnections, production of enclosed holes, enhanced surface area, better adsorption ability, and many other benefits in contrast to conventional carbon-based substances. This review points out the developments in the main processes to introduce nitrogen atoms into the carbon matrix by utilizing different N-comprising chemical compounds. The nitrogen enrichment processes, reaction mechanisms and effects of nitrogen incorporation on the plant biomass-derived activated carbons (NEACs) are presented in brief. On the basis of their established physicochemical attributes, the adsorption performances of different biomass-derived NEACs have also been dealt with. More significantly, the review covers the technical issues in the present phase, topical trends, research gaps, economic viability along with a technical alignment recommendation to address the prevailing disadvantages.

As a key kind of evolving carbonaceous adsorbent, nitrogen-enriched activated carbon has drawn a lot of focus due to its better physiochemical ability to eliminate an extensive range of wastewaters contaminants under severe conditions. Its environment-friendly character is one more reason behind this focus. Nitrogen also has immense effect on activated carbon structures&#x2019; pollutants adsorption capability; therefore, it is an area of interest. Reports concerning the reaction pathway of C-N (carbon-nitrogen) bond creation on AC surface are limited. Determining such mechanisms is challenging but critical to understand bond characteristics after carbonization. Moreover, it is vital to ascertain real-time kinetics concerning adsorption phenomena in liquid phase. Such a latest trend indicates that regulated nitrogen uses for carbonaceous substances having a biomass-based origin can provide the desired morphological characteristics produced through interconnections, production of enclosed holes, enhanced surface area, better adsorption ability, and many other benefits in contrast to conventional carbon-based substances. This review points out the developments in the main processes to introduce nitrogen atoms into the carbon matrix by utilizing different N-comprising chemical compounds. The nitrogen enrichment processes, reaction mechanisms and effects of nitrogen incorporation on the plant biomass-derived activated carbons (NEACs) are presented in brief. On the basis of their established physicochemical attributes, the adsorption performances of different biomass-derived NEACs have also been dealt with. More significantly, the review covers the technical issues in the present phase, topical trends, research gaps, economic viability along with a technical alignment recommendation to address the prevailing disadvantages.

Nitrogen-enriched activated carbon derived from plant biomasses: a review on reaction mechanism and applications in wastewater treatment

Graphene oxide, as a nanoscopic platform for functional materials, has been extensively studied for several applications. The present Mini Review stresses the collaborative research in graphene-oxide materials pivoted from the Group of Materials and Technologies for Energy, Health, and Environment at an Instituto Politecnico Nacional unit in Tamaulipas, in Northeastern Mexico, with Mexican, Turkish, and British collaborators. This review covers the recent works on photovoltaic and photocatalytic materials, coatings for thermonuclear reactors, and composites and metamaterials for military and aeronautic applications.

Graphene oxide, as a nanoscopic platform for functional materials, has been extensively studied for several applications. The present Mini Review stresses the collaborative research in graphene-oxide materials pivoted from the Group of Materials and Technologies for Energy, Health, and Environment at an Instituto Politecnico Nacional unit in Tamaulipas, in Northeastern Mexico, with Mexican, Turkish, and British collaborators. This review covers the recent works on photovoltaic and photocatalytic materials, coatings for thermonuclear reactors, and composites and metamaterials for military and aeronautic applications.

International research in graphene-oxide based materials for net-zero energy, military and aeronautic applications catalysed by Tamaulipas, Mexico: a mini review

The excessive dependency on fossil fuel resources could be curtailed by the efficient conversion of lignocellulosic biomass. Biochar, a porous carbonaceous product synthesized exploiting thermochemical conversion pathway, could be an environment-friendly replacement of fossil fuel resources. Slow pyrolysis, a sub-class among various thermochemical conversion techniques, has gained immense popularity owing to its potential to convert biomass to biochar. Furthermore, biochar obtained as the by-product of slow pyrolysis has attracted enormous popularity due to its proven role and application in the multidisciplinary areas of engineering and environmental remediation applications. The physicochemical quality of biochar and its performance is significantly dependent on the feedstock type and pyrolysis process parameters. Therefore, further experimental research and investigations in terms of lignocellulose biomass type and pyrolytic process parameters (temperature, heating rate and reaction time) are essential to produce biochar with desired physicochemical features for effective utilization. This review presents an updated report on slow pyrolysis of lignocellulosic biomass, impact of different pyrolysis parameters and degradation pathway involved in the evolution properties of biomass. The influence of the feedstock type and lignocellulosic composition on the biochar properties are also discussed meticulously. The co-relationship between biochar yield at different pyrolysis temperatures and the development of textural properties provides valuable information for their effective utilization as a functional carbon material. Additionally, an extensive study was undertaken to collate and discuss the excellent physicochemical characteristics of biochar and summarizes the benefits of biochar application for diverse industrial purposes. Biochar is acknowledged for its excellent physicochemical properties owing to the thermal treatment and as a result its prospective diverse industrial applications such as for soil treatment, carbon sequestration, adsorbent (wastewater treatment or CO2 capture), producing activated carbon for gold recovery, energy storage and supercapacitor are summarized systematically in this review paper. For instance, biochar when applied in soil have shown improvement in soil respiration by 1.9 times. Furthermore, biochar when used to capture CO2 from flue gas stream under post-combustion scenario has demonstrated superior capture performance (2.8 mmol/g) compared to commercial activated carbon. This paper identified the knowledge gaps and outlooks in the field of the advancements of biochar from slow pyrolysis for targeted engineering applications mainly in the field of environmental remediation and energy harvesting.

The excessive dependency on fossil fuel resources could be curtailed by the efficient conversion of lignocellulosic biomass. Biochar, a porous carbonaceous product synthesized exploiting thermochemical conversion pathway, could be an environment-friendly replacement of fossil fuel resources. Slow pyrolysis, a sub-class among various thermochemical conversion techniques, has gained immense popularity owing to its potential to convert biomass to biochar. Furthermore, biochar obtained as the by-product of slow pyrolysis has attracted enormous popularity due to its proven role and application in the multidisciplinary areas of engineering and environmental remediation applications. The physicochemical quality of biochar and its performance is significantly dependent on the feedstock type and pyrolysis process parameters. Therefore, further experimental research and investigations in terms of lignocellulose biomass type and pyrolytic process parameters (temperature, heating rate and reaction time) are essential to produce biochar with desired physicochemical features for effective utilization. This review presents an updated report on slow pyrolysis of lignocellulosic biomass, impact of different pyrolysis parameters and degradation pathway involved in the evolution properties of biomass. The influence of the feedstock type and lignocellulosic composition on the biochar properties are also discussed meticulously. The co-relationship between biochar yield at different pyrolysis temperatures and the development of textural properties provides valuable information for their effective utilization as a functional carbon material. Additionally, an extensive study was undertaken to collate and discuss the excellent physicochemical characteristics of biochar and summarizes the benefits of biochar application for diverse industrial purposes. Biochar is acknowledged for its excellent physicochemical properties owing to the thermal treatment and as a result its prospective diverse industrial applications such as for soil treatment, carbon sequestration, adsorbent (wastewater treatment or CO2 capture), producing activated carbon for gold recovery, energy storage and supercapacitor are summarized systematically in this review paper. For instance, biochar when applied in soil have shown improvement in soil respiration by 1.9 times. Furthermore, biochar when used to capture CO2 from flue gas stream under post-combustion scenario has demonstrated superior capture performance (2.8&nbsp;mmol/g) compared to commercial activated carbon. This paper identified the knowledge gaps and outlooks in the field of the advancements of biochar from slow pyrolysis for targeted engineering applications mainly in the field of environmental remediation and energy harvesting.

Synthesis of Biochar From Lignocellulosic Biomass for Diverse Industrial Applications and Energy Harvesting: Effects of Pyrolysis Conditions on the Physicochemical Properties of Biochar

Pressure mapping has garnered considerable interest in the healthcare and robotic industries. Low-cost and large-area compliant devices, as well as fast and effective computational algorithms, have been proposed in the last few years to facilitate distributed pressure sensing. One approach is to use electrical impedance tomography (EIT) to reconstruct the contact pressure distribution of piezoresistive materials. While tremendous success has been demonstrated, conventional algorithms may be unsuitable for real-time monitoring due to its computational demand and runtime. Moreover, the low resolution of reconstructed images is a well-known issue related to the regularization strategies typically employed for traditional EIT methods. Therefore, in this study, two different supervised machine learning (ML) approaches, namely, radial basis function networks and deep neural networks, were employed to efficiently solve the inverse EIT problem and improve the resolution of reconstructed pressure maps. The demonstration of high-resolution pressure mapping, specifically, for identifying pressure hotspots, was achieved using a carbon nanotube-based thin film integrated with foam.

Pressure mapping has garnered considerable interest in the healthcare and robotic industries. Low-cost and large-area compliant devices, as well as fast and effective computational algorithms, have been proposed in the last few years to facilitate distributed pressure sensing. One approach is to use electrical impedance tomography (EIT) to reconstruct the contact pressure distribution of piezoresistive materials. While tremendous success has been demonstrated, conventional algorithms may be unsuitable for real-time monitoring due to its computational demand and runtime. Moreover, the low resolution of reconstructed images is a well-known issue related to the regularization strategies typically employed for traditional EIT methods. Therefore, in this study, two different supervised machine learning (ML) approaches, namely, radial basis function networks and deep neural networks, were employed to efficiently solve the inverse EIT problem and improve the resolution of reconstructed pressure maps. The demonstration of high-resolution pressure mapping, specifically, for identifying pressure hotspots, was achieved using a carbon nanotube-based thin film integrated with foam.

Pressure Mapping Using Nanocomposite-Enhanced Foam and Machine Learning

This study proposes the conversion of waste corn grains contaminated by deoxynivalenol (also known as vomitoxin), a mycotoxin produced by plant pathogens, into a value-added product. Batches of 500 g of contaminated corn grains were pyrolyzed in a batch reactor by thermal treatment at temperatures up to 500°C with a 15°C/min heating rate and generating condensable vapors, gases and solid bio-char. The bio-char produced was subsequently activated in a furnace at 900°C, using CO2 as an activation agent, at different residence times. The effect of activation residence time on the characteristics of the activated bio-char, varying it from 0.5 to 3 h, was investigated. Characterization tests included BET surface area, SEM, TG-FTIR, pH, and XRD on both bio-char and activated bio-char. BET results illustrated a significant increase of the surface area from 63 to 419 m2g−1 and pore volume from 0.04 to 0.23 cm3g−1 by increasing the activation time from 0.5 to 3 h. SEM images visually confirmed a considerable increase in pore development. The pH significantly increased from 6 to 10 after activation, due to the elimination of acidic functional groups. The proximate analysis showed the stable carbon of the activated char reaching approximately 90 wt%, making it promising for catalyst/adsorbent applications. The adsorption performance of activated bio-char was tested by utilizing three different model molecules with different characteristics: methylene blue, methyl orange, and ibuprofen. Among all activated bio-char samples, activated bio-char with 3 h activation time showed the highest adsorption capacity, with a total adsorption (25 mg/g of activated bio-char) of methylene blue after 5 min. The results showed that the adsorption capacity of the activated bio-char was similar to that of valuable commercial activated carbon.

This study proposes the conversion of waste corn grains contaminated by deoxynivalenol (also known as vomitoxin), a mycotoxin produced by plant pathogens, into a value-added product. Batches of 500&nbsp;g of contaminated corn grains were pyrolyzed in a batch reactor by thermal treatment at temperatures up to 500°C with a 15°C/min heating rate and generating condensable vapors, gases and solid bio-char. The bio-char produced was subsequently activated in a furnace at 900°C, using CO2 as an activation agent, at different residence times. The effect of activation residence time on the characteristics of the activated bio-char, varying it from 0.5 to 3&nbsp;h, was investigated. Characterization tests included BET surface area, SEM, TG-FTIR, pH, and XRD on both bio-char and activated bio-char. BET results illustrated a significant increase of the surface area from 63 to 419&nbsp;m2g−1 and pore volume from 0.04 to 0.23&nbsp;cm3g−1 by increasing the activation time from 0.5 to 3&nbsp;h. SEM images visually confirmed a considerable increase in pore development. The pH significantly increased from 6 to 10 after activation, due to the elimination of acidic functional groups. The proximate analysis showed the stable carbon of the activated char reaching approximately 90&nbsp;wt%, making it promising for catalyst/adsorbent applications. The adsorption performance of activated bio-char was tested by utilizing three different model molecules with different characteristics: methylene blue, methyl orange, and ibuprofen. Among all activated bio-char samples, activated bio-char with 3&nbsp;h activation time showed the highest adsorption capacity, with a total adsorption (25&nbsp;mg/g of activated bio-char) of methylene blue after 5&nbsp;min. The results showed that the adsorption capacity of the activated bio-char was similar to that of valuable commercial activated carbon.