Carbon nanotubes for sustainable energy applications

Synergism in carbon nanotubes and carbon-dots: counter electrode of a high-performance dye-sensitized solar cell

Dye-sensitized solar cells (DSSCs) play a crucial role in the realm of renewable energy technology by converting solar energy into electrical energy in an efficient and cost-effective way. In the pursuit of improving the photoconversion efficiency (PCE) of DSSCs, this work aims at fabricating a new counter electrode (CE) using a binary composite of heteroatom-doped carbon dots (C-dots) and functionalized multi-walled carbon nanotubes (o-MWCNTs). We demonstrate that this binary composite exhibits superior performance to pristine o-MWCNTs, resulting in a remarkable enhancement in the PCE. The PCE of the o-MWCNT/C-dots composite was measured at an impressive 4.28%, significantly outperforming the pristine o-MWCNT electrode, which yielded an efficiency of 2.24%. The enhanced performance of the o-MWCNT/C-dots composite can be attributed to the synergistic effects of heteroatom-doped C-dots since their binding to the o-MWCNTs by activated oxygenic surface functional groups increases the surface area from 218 to 253 m2 g-1. This enhanced surface area results from the reduction of π-π stacking interactions of the individual tubes and production of a new hollow channel in the structure that provides an ideal scaffold for I2 adsorption and electron transfer. We demonstrate the role of C-dots on MWCNT's property modulation toward higher PCE by density functional theory (DFT) calculation and electrochemical analysis. Electron-excess N and S doped C-dots exhibit strong catalytic activity, allowing for rapid electron transfer processes in the CE-electrolyte surface via the donor acceptor mechanism, whereas electron-deficient B doped C-dots undermine the cell performance by forming a charge recombination trap at the CE surface. The synthesized composite has higher redox reversibility up to 100 CV cycles and chemical stability, studied by the post-performance material characterization. The findings offer a promising avenue for the development of high-performance DSSCs, which will help to promote sustainable and renewable energy technologies.

Nanocarbon for Energy Material Applications: N2 Reduction Reaction

Nanocarbons are an important class of energy materials and one relevant application is for the nitrogen reduction reaction, i.e., the direct synthesis of NH₃ from N₂ and H₂ O via photo- and electrocatalytic approaches. Ammonia is also a valuable energy or hydrogen vector. This perspective paper analyses developments in the field, limiting discussion to nanocarbon-based electrodes. These aspects are discussed: i) active sites related to charge density differences on C atoms associated to defects/strains, ii) doping with heteroatoms, iii) introduction of isolated metal ions, iv) creation and in situ dynamics of metal oxide(hydroxide)/nanocarbon boundaries, and v) nanocarbon characteristics to control the interface. Discussion is focused on the performances and mechanistic aspects. Aim is not a systematic state-of-the-art report but to highlight the need to use a different perspective in studying this challenging reaction by using selected papers. Notwithstanding the large differences in the proposed nature of the active sites, fall all within a restricted range of performances, far from the targets. A holistic approach is emphasized to make a breakthrough advance.

Electroanalytical overview: utilising micro- and nano-dimensional sized materials in electrochemical-based biosensing platforms

Research into electrochemical biosensors represents a significant portion of the large interdisciplinary field of biosensing. The drive to develop reliable, sensitive, and selective biosensing platforms for key environmental and medical biomarkers is ever expanding due to the current climate. This push for the detection of vital biomarkers at lower concentrations, with increased reliability, has necessitated the utilisation of micro- and nano-dimensional materials. There is a wide variety of nanomaterials available for exploration, all having unique sets of properties that help to enhance the performance of biosensors. In recent years, a large portion of research has focussed on combining these different materials to utilise the different properties in one sensor platform. This research has allowed biosensors to reach new levels of sensitivity, but we note that there is room for improvement in the reporting of this field. Numerous examples are published that report improvements in the biosensor performance through the mixing of multiple materials, but there is little discussion presented on why each nanomaterial is chosen and whether they synergise well together to warrant the inherent increase in production time and cost. Research into micro-nano materials is vital for the continued development of improved biosensing platforms, and further exploration into understanding their individual and synergistic properties will continue to push the area forward. It will continue to provide solutions for the global sensing requirements through the development of novel materials with beneficial properties, improved incorporation strategies for the materials, the combination of synergetic materials, and the reduction in cost of production of these nanomaterials.

Origin of the electrocatalytic activity in carbon nanotube fiber counter-electrodes for solar-energy conversion

Carbon nanotubes are a versatile platform to develop sustainable and stable electrodes for energy-related applications. However, their electrocatalytic activity is still poorly understood. This work deciphers the origin of the catalytic activity of counter-electrodes (CEs)/current collectors made of self-standing carbon nanotube fibers (CNTfs) using Co2+/Co3+ redox couple electrolytes. This is based on comprehensive electrochemical and spectroscopic characterization of fresh and used electrodes applied to symmetric electrochemical cells using platinum-based CEs as a reference. As the most relevant findings, two straight relationships were established: (i) the limiting current and stability increase rapidly with the surface concentration of oxygen-containing functional groups, and (ii) the catalytic potential is inversely related to the amount of residual metallic Fe catalyst nanoparticles interspersed in the CNTf network. Finally, the fine tuning of the metal nanoparticle content and the degree of functionalization enabled fabrication of efficient and stable dye-sensitized solar cells with cobalt electrolytes and CNTf-CEs outperforming those with reference Pt-CEs.

Electrochemical Performance of Graphitic Multi-walled Carbon Nanotubes with Different Aspect Ratios as Cathode Materials for Aluminum-ion Batteries

Graphitic multi-walled carbon nanotubes (MWCNTs) can function as high-performance cathode materials for rechargeable Al-ion batteries with well-defined discharging plateaus and reasonable charge/discharge C-rates. However, the main intercalation/deintercalation or adsorption/desorption path of AlCl4- anions into or onto G-MWCNTs has not been elucidated. Herein, we used battery cells comprised of G-MWCNTs with different aspect ratios, Al metal, and AlCl3/1-ethyl-3-methylimidazolium chloride ionic liquid as the cathode, anode, and electrolyte, respectively. The electrochemical performance of the Al||G-MWCNT cell increased as the aspect ratio of the G-MWCNT cathode increased (i. e., longer and thinner). The degree of defects of the G-MWCNTs was similar (0.15-0.22); hence, the results confirm that the main and alternate paths for the AlCl4- intercalation/de-intercalation or adsorption/desorption into/from or onto/from the G-MWCNT are the basal and edge planes, respectively. The step-like structures of defects on the basal plane provide the main reaction site for AlCl4- anions.

Environmental Fate of Multistressors on Carpet Shell Clam Ruditapes decussatus: Carbon Nanoparticles and Temperature Variation

Ruditapes decussatus is a native clam from the Southern Europe and Mediterranean area, relevant to the development of sustainable aquaculture in these regions. As sessile organisms, bivalves are likely to be exposed to chemical contaminations and environmental changes in the aquatic compartment and are widely used as bioindicator species. Carbon-based nanomaterials (CNTs) use is increasing and, consequently, concentrations of these contaminants in aquatic systems will rise. Therefore, it is imperative to assess the potential toxic effects of such compounds and the interactions with environmental factors such as water temperature. For this, we exposed R. decussatus clams to four different water temperatures (10, 15, 20 and 25 °C) in the presence or absence of CNTs for 96 h. Different parameters related with oxidative stress status, aerobic metabolism, energy reserves and neurotoxicity were evaluated. The relationship and differences among water temperatures and contamination were highlighted by principal coordinates analysis (PCO). CNTs exposure increased oxidative damage as protein carbonylation (PC) in exposed clams at 10 °C. Higher temperatures (25 °C) were responsible for the highest redox status (ratio between reduced and oxidized glutathione, GSH/GSSG) observed as well as neurotoxic effects (acetylcholinesterase—AChE activity). Antioxidant defenses were also modulated by the combination of CNTs exposure with water temperatures, with decrease of glutathione peroxidase (GR) activity at 15 °C and of glutathione S-transferases (GSTs) activity at 20 °C, when compared with unexposed clams. Clams energy reserves were not altered, probably due to the short exposure period. Overall, the combined effects of CNTs exposure and increasing water temperatures can impair R. decussatus cellular homeostasis inducing oxidative stress and damage.

Green Nanotechnology: Advancement in Phytoformulation Research

The ultimate goal of any scientific development is to increase well-being and human health. Novel strategies are required for the achievement of safe and effective therapeutic treatments beyond the conventional ones, and society needs new requirements for new technologies, moving towards clean and green technology development. Green nanotechnology is a branch of green technology that utilizes the concepts of green chemistry and green engineering. It reduces the use of energy and fuel by using less material and renewable inputs wherever possible. Green nanotechnology, in phytoformulations, significantly contributes to environmental sustainability through the production of nanomaterials and nanoproducts, without causing harm to human health or the environment. The rationale behind the utilization of plants in nanoparticle formulations is that they are easily available and possess a broad variability of metabolites, such as vitamins, antioxidants, and nucleotides. For instance, gold (Au) nanoparticles have attracted substantial attention for their controllable size, shape, and surface properties. A variety of copper (Cu) and copper oxide (CuO) nanoparticles have also been synthesized from plant extracts. Titanium dioxide and zinc oxide nanoparticles are also important metal oxide nanomaterials that have been synthesized from a number of plant extracts. International and domestic laws, government and private-party programs, regulations and policies are being carefully reviewed and revised to increase their utility and nurture these nanoscale materials for commercialization. Inspiring debates and government initiatives are required to promote the sustainable use of nanoscale products. In this review, we will discuss the potential of the utilization of plant extracts in the advancement of nanotechnology.

Catalysis by hybrid sp2/sp3nanodiamonds and their role in the design of advanced nanocarbon materials

Hybrid sp²/sp³nanocarbons, in particular sp³-hybridized ultra-dispersed nanodiamonds and derivative materials, such as the sp³/sp²-hybridized bucky nanodiamonds and sp²-hybridized onion-like carbons, represent a rather interesting class of catalysts still under consideration.

Carbon-Based Microbial-Fuel-Cell Electrodes: From Conductive Supports to Active Catalysts

Microbial fuel cells (MFCs) have attracted considerable interest due to their potential in renewable electrical power generation using the broad diversity of biomass and organic substrates. However, the difficulties in achieving high power densities and commercially affordable electrode materials have limited their industrial applications to date. Carbon materials, which can exhibit a wide range of different morphologies and structures, usually possess physiological activity to interact with microorganisms and are therefore fast-emerging electrode materials. As the anode, carbon materials can significantly promote interfacial microbial colonization and accelerate the formation of extracellular biofilms, which eventually promotes the electrical power density by providing a conductive microenvironment for extracellular electron transfer. As the cathode, carbon-based materials can function as catalysts for the oxygen-reduction reaction, showing satisfying activities and efficiencies nowadays even reaching the performance of Pt catalysts. Here, first, recent advancements on the design of carbon materials for anodes in MFCs are summarized, and the influence of structure and surface functionalization of different types of carbon materials on microorganism immobilization and electrochemical performance is elucidated. Then, synthetic strategies and structures of typical carbon-based cathodes in MFCs are briefly presented. Furthermore, future applications of carbon-electrode-based MFC devices in the energy, environmental, and biological fields are discussed, and the emerging challenges in transferring them from laboratory to industrial scale are described.

Turning Perspective in Photoelectrocatalytic Cells for Solar Fuels

The development of new devices for the use and storage of solar energy is a key step to enable a new sustainable energy scenario. The route for direct solar-to-chemical energy transformation, especially to produce liquid fuels, represents a necessary element to realize transition from the actual energy infrastructure. Photoelectrocatalytic (PECa) devices for the production of solar fuels are a key element to enable this sustainable scenario. The development of PECa devices and related materials is of increasing scientific and applied interest. This concept paper introduces the need to turn the viewpoint of research in terms of PECa cell design and related materials with respect to mainstream activities in the field of artificial photosynthesis and leaves. As an example of a new possible direction, the concept of electrolyte-less cell design for PECa cells to produce solar fuels by reduction of CO2 is presented. The fundamental and applied development of new materials and electrodes for these cells should proceed fully integrated with PECa cell design and systematic analysis. A new possible approach to develop semiconductors with improved performances by using visible light is also shortly presented.

Reaction mechanisms of carbon dioxide, ethylene oxide and amines catalyzed by ionic liquids BmimBr and BmimOAc: a DFT study

The binary ionic liquids BmimBr and BmimOAc have the important electrostatic and hydrogen bond effects on the catalytic conversion of carbon dioxide, ethylene oxide and aniline to 3-phenyl-2-oxazolidionone.

Interactions between metal species and nitrogen-functionalized carbon nanotubes

Surface functionalities and defects strongly influence the interactions between metal species and nitrogen-functionalized carbon nanotubes.

Carbonaceous materials and their advances as a counter electrode in dye-sensitized solar cells: challenges and prospects

Dye-sensitized solar cells (DSSCs) serve as low-costing alternatives to silicon solar cells because of their low material and fabrication costs. Usually, they utilize Pt as the counter electrode (CE) to catalyze the iodine redox couple and to complete the electric circuit. Given that Pt is a rare and expensive metal, various carbon materials have been intensively investigated because of their low costs, high surface areas, excellent electrochemical stabilities, reasonable electrochemical activities, and high corrosion resistances. In this feature article, we provide an overview of recent studies on the electrochemical properties and photovoltaic performances of carbon-based CEs (e.g., activated carbon, nanosized carbon, carbon black, graphene, graphite, carbon nanotubes, and composite carbon). We focus on scientific challenges associated with each material and highlight recent advances achieved in overcoming these obstacles. Finally, we discuss possible future directions for this field of research aimed at obtaining highly efficient DSSCs.

Carbon nanotube catalysts: recent advances in synthesis, characterization and applications

Carbon nanotubes are promising materials for various applications.

Opportunities and challenges of nanotechnology in the green economy

In a world of finite resources and ecosystem capacity, the prevailing model of economic growth, founded on ever-increasing consumption of resources and emission pollutants, cannot be sustained any longer. In this context, the "green economy" concept has offered the opportunity to change the way that society manages the interaction of the environmental and economic domains. To enable society to build and sustain a green economy, the associated concept of "green nanotechnology" aims to exploit nano-innovations in materials science and engineering to generate products and processes that are energy efficient as well as economically and environmentally sustainable. These applications are expected to impact a large range of economic sectors, such as energy production and storage, clean up-technologies, as well as construction and related infrastructure industries. These solutions may offer the opportunities to reduce pressure on raw materials trading on renewable energy, to improve power delivery systems to be more reliable, efficient and safe as well as to use unconventional water sources or nano-enabled construction products therefore providing better ecosystem and livelihood conditions.However, the benefits of incorporating nanomaterials in green products and processes may bring challenges with them for environmental, health and safety risks, ethical and social issues, as well as uncertainty concerning market and consumer acceptance. Therefore, our aim is to examine the relationships among guiding principles for a green economy and opportunities for introducing nano-applications in this field as well as to critically analyze their practical challenges, especially related to the impact that they may have on the health and safety of workers involved in this innovative sector. These are principally due to the not fully known nanomaterial hazardous properties, as well as to the difficulties in characterizing exposure and defining emerging risks for the workforce. Interestingly, this review proposes action strategies for the assessment, management and communication of risks aimed to precautionary adopt preventive measures including formation and training of employees, collective and personal protective equipment, health surveillance programs to protect the health and safety of nano-workers. It finally underlines the importance that occupational health considerations will have on achieving an effectively sustainable development of nanotechnology.

Fischer-Tropsch reaction on a thermally conductive and reusable silicon carbide support

The Fischer-Tropsch (FT) process, in which synthesis gas (syngas) derived from coal, natural gas, and biomass is converted into synthetic liquid fuels and chemicals, is a strongly exothermic reaction, and thus, a large amount of heat is generated during the reaction that could severely modify the overall selectivity of the process. In this Review, we report the advantages that can be offered by different thermally conductive supports, that is, carbon nanomaterials and silicon carbide, pure or doped with different promoters, for the development of more active and selective FT catalysts. This Review follows a discussion regarding the clear trend in the advantages and drawbacks of these systems in terms of energy efficiency and catalytic performance for this most-demanded catalytic process. It is demonstrated that the use of a support with an appropriate pore size and thermal conductivity is an effective strategy to tune and improve the activity of the catalyst and to improve product selectivity in the FT process. The active phase and the recovery of the support, which also represents a main concern in terms of the large amount of FT catalyst used and the cost of the active cobalt phase, is also discussed within the framework of this Review. It is expected that a thermally conductive support such as β-SiC will not only improve the development of the FT process, but that it will also be part of a new support for different catalytic processes for which high catalytic performance and selectivity are strongly needed.

Polyvinylidene fluoride/siloxane nanofibrous membranes for long-term continuous CO2 -capture with large absorption-flux enhancement

In a CO2 membrane contactor system, CO2 passes through a hydrophobic porous membrane in the gas phase to contact the amine absorbent in the liquid phase. Consequently, additional CO2 gas is absorbed by amine absorbents. This study examines highly porous polyvinylidene fluoride (PVDF)/siloxane nanofibrous layers that are modified with hydrophobic fluoroalkylsilane (FAS) functional groups and successfully coated onto a macroporous Al2 O3 membrane. The performance of these materials in a membrane contactor system for CO2 absorption is also investigated. Compared with pristine PVDF nanofibrous membranes, the PVDF/siloxane nanofibrous membranes exhibit greater solvent resistance and mechanical strength, making them more suitable for use in CO2 capture by the membrane contactor. The PVDF/siloxane nanofibrous layer in highly porous FAS-modified membranes can prevent the wetting of the membrane by the amine absorbent; this extends the periods of continuous CO2 absorption and results in a high CO2 absorption flux with a minimum of 500 % enhancement over that of the uncoated membranes. This study suggests the potential use of an FAS-modified PVDF/siloxane nanofibrous membrane in a membrane contactor system for CO2 absorption. The resulting hydrophobic membrane contactor also demonstrates the potential for large-scale CO2 absorption during post-combustion processes in power plants.

Methane adsorption on aggregates of fullerenes: site-selective storage capacities and adsorption energies

Methane adsorption on positively charged aggregates of C60 is investigated by both mass spectrometry and computer simulations. Calculated adsorption energies of 118-281 meV are in the optimal range for high-density storage of natural gas. Groove sites, dimple sites, and the first complete adsorption shells are identified experimentally and confirmed by molecular dynamics simulations, using a newly developed force field for methane-methane and fullerene-methane interaction. The effects of corrugation and curvature are discussed and compared with data for adsorption on graphite, graphene, and carbon nanotubes.

On the configuration of supercapacitors for maximizing electrochemical performance

Supercapacitors, which are attracting rapidly growing interest from both academia and industry, are important energy-storage devices for acquiring sustainable energy. Recent years have seen a number of significant breakthroughs in the research and development of supercapacitors. The emergence of innovative electrode materials (e.g., graphene) has clearly provided great opportunities for advancing the science in the field of electrochemical energy storage. Conversely, smart configurations of electrode materials and new designs of supercapacitor devices have, in many cases, boosted the electrochemical performance of the materials. We attempt to summarize recent research progress towards the design and configuration of electrode materials to maximize supercapacitor performance in terms of energy density, power density, and cycle stability. With a brief description of the structure, energy-storage mechanism, and electrode configuration of supercapacitor devices, the design and configuration of symmetric supercapacitors are discussed, followed by that of asymmetric and hybrid supercapacitors. Emphasis is placed on the rational design and configuration of supercapacitor electrodes to maximize the electrochemical performance of the device.

Cell cycle regulation by carboxylated multiwalled carbon nanotubes through p53-independent induction of p21 under the control of the BMP signaling pathway

This report describes how carboxylated multiwalled carbon nanotubes (MWCNTs) induce p53-independent p21 expression and cell cycle arrest. MWCNTs suppress BMP signaling and lead to the downregulation of Id protein production and the upregulation of p21 because p21 expression is directly controlled by Id proteins through their regulation of the E-box motifs in the p21 promoter. The overexpressed p21 protein then binds to the cyclin D/cdk4,6 complexes and inhibits the phosphorylation of Rb protein. Hypophosphorylation of Rb prevents the release of E2F factors and causes cell cycle arrest. These findings provide valuable insight into a mechanistic understanding of carbon nanotubes' effects on cellular functions.

New insights from microcalorimetry on the FeOx/CNT-based electrocatalysts active in the conversion of CO2 to fuels

Fe oxide nanoparticles show enhanced electrocatalytic performance in the reduction of CO(2) to isopropanol when deposited on an N-functionalized carbon nanotube (CNT) support rather than on a pristine or oxidized CNT support. XRD and high-resolution TEM were used to investigate the nanostructure of the electrocatalysts, and CO(2) adsorptive microcalorimetry was used to study the chemical nature of the interaction of CO(2) with the surface sites. Although the particles always present the same Fe(3)O(4) phase, their structural anisotropy and size inhomogeneity are consequences of the preparation method of the carbon surface. Two types of chemisorption sites have been determined by using microcalorimetry: irreversible sites (280 kJ mol(-1)) at the uncoordinated sites of the facets and reversible sites (120 kJ mol(-1)) at the hydrated oxide surface of the small nanoparticles. N-Functionalization of the carbon support is advantageous, as it causes the formation of small nanoparticles, which are highly populated by reversible chemisorbing sites. These characteristic features correlate with a higher electrocatalytic performance.

Towards artificial leaves for solar hydrogen and fuels from carbon dioxide

The development of an "artificial leaf" that collects energy in the same way as a natural one is one of the great challenges for the use of renewable energy and a sustainable development. To avoid the problem of intermittency in solar energy, it is necessary to design systems that directly capture CO(2) and convert it into liquid solar fuels that can be easily stored. However, to be advantageous over natural leaves, it is necessary that artificial leaves have a higher solar energy-to-chemical fuel conversion efficiency, directly provide fuels that can be used in power-generating devices, and finally be robust and of easy construction, for example, smart, cheap and robust. This review discusses the recent progress in this field, with particular attention to the design and development of 'artificial leaf' devices and some of their critical components. This is a very active research area with different concepts and ideas under investigation, although often the validity of the considered solutions it is still not proven or the many constrains are not fully taken into account, particularly from the perspective of system engineering, which considerably limits some of the investigated solutions. It is also shown how system design should be included, at least at a conceptual level, in the definition of the artificial leaf elements to be investigated (catalysts, electrodes, membranes, sensitizers) and that the main relevant aspects of the cell engineering (mass/charge transport, fluid dynamics, sealing, etc.) should be also considered already at the initial stage because they determine the design and the choice between different options. For this reason, attention has been given to the system-design ideas under development instead of the molecular aspects of the O(2) - or H(2) -evolution catalysts. However, some of the recent advances in these catalysts, and their use in advanced electrodes, are also reported to provide a more complete picture of the field.