Recent progress on the growth mechanism of carbon nanotubes: a review

Fabrication of Fe-Zr, Co-Zr, and Ni-Zr Catalysts to Boost CNTs Synthesis from Plastic Wastes and the Electrocatalytic Oxygen Evolution Reaction

The efficient conversion of plastic wastes to high-value carbon materials like carbon nanotubes (CNTs) is one important issue about the rational recycling, reduction, and reuse of solid wastes. Herein, Fe-, Co-, and Ni-Zr catalysts were prepared and used for CNTs synthesis from polyethylene (PE) waste via a two-stage reaction system. At the same time, the effects of the PE/catalyst ratio and reaction temperature on CNTs synthesis have been studied. Compared with Co-Zr and Ni-Zr, Fe-Zr exhibited the best activity in CNTs synthesis from PE, and it achieved the highest CNTs yield of 806.3 mg/g (per gram of Fe-Zr) at 800 °C with a PE/catalyst ratio of 4. Furthermore, the obtained Fe-Zr/CNTs composite exhibited a low overpotential of 267 mV for the electrocatalytic oxygen evolution reaction (OER) at 20 mA/cm2 in 1 M KOH electrolyte solution, which was 21 mV lower than commercial RuO2 (288 mV) and 50 mV lower than Fe-Zr (317 mV). It was deduced that the in situ growth of CNTs reduced the charge transfer resistance and improved the electron transport efficiency of the Fe-Zr/CNTs composite, leading to superior activity in the electrocatalytic OER. This work provided detailed information for the preparation of the metal/CNTs composite from plastic wastes, which contributed positively to alleviate the environment and energy crisis.

Global Vision of the Reaction and Deactivation Routes in the Ethanol Steam Reforming on a Catalyst Derived from a Ni-Al Spinel

Ethanol steam reforming (ESR) over a Ni/Al2O3 catalyst prepared by reduction of a NiAl2O4 spinel is a promising alternative route to produce H2 from biomass. This work deepens into the effect of reaction conditions (450-650 °C, a steam/ethanol (S/E) ratio of 3-9, and a weight space time up to 1.3 h) and evaluates the time on stream evolution of the yields of H2, gaseous byproducts (CO, CO2, CH4, C2H4, C2H4O), and formed carbon/coke. The results are explained taking into consideration the thermodynamics, the extent of each individual reaction, and the catalyst deactivation. Up to 600 °C, the predominant intermediate in the H2 formation is C2H4 (formed by ethanol dehydration) with the preferential formation of nanostructured carbon (nanotubes/filaments) by C2H4 decomposition. The deposition of this type of carbon partially deactivates the catalyst, mainly affecting the extent of the C2H4 decomposition causing a sharp decrease in the H2 and carbon yields. Nevertheless, the catalyst reaches a pseudosteady state with an apparent constant activity for other reactions in the kinetic scheme. At 650 °C, C2H4O (formed by the ethanol dehydrogenation) is the main intermediate in the H2 formation, which is the precursor of an amorphous/turbostratic carbon (coke) formation that initially causes a rapid deactivation of the catalyst, affecting the ethanol dehydration and, to a lower extent, the reforming and water gas shift reactions. The increase in the S/E ratio favors the H2 formation, attenuates the catalyst deactivation due to the suppression of the ethanol dehydration to C2H4, and promotes the reforming, water gas shift, and carbon/coke gasification reactions. A H2 yield of 85% stable for 48 h on stream is achieved at 600 °C, with a space time of 0.1 h and an S/E ratio of 9.

Room temperature 3D carbon microprinting

Manufacturing custom three-dimensional (3D) carbon functional materials is of utmost importance for applications ranging from electronics and energy devices to medicine, and beyond. In lieu of viable eco-friendly synthesis pathways, conventional methods of carbon growth involve energy-intensive processes with inherent limitations of substrate compatibility. The yearning to produce complex structures, with ultra-high aspect ratios, further impedes the quest for eco-friendly and scalable paths toward 3D carbon-based materials patterning. Here, we demonstrate a facile process for carbon 3D printing at room temperature, using low-power visible light and a metal-free catalyst. Within seconds to minutes, this one-step photocatalytic growth yields rod-shaped microstructures with aspect ratios up to ~500 and diameters below 10 μm. The approach enables the rapid patterning of centimeter-size arrays of rods with tunable height and pitch, and of custom complex 3D structures. The patterned structures exhibit appealing luminescence properties and ohmic behavior, with great potential for optoelectronics and sensing applications, including those interfacing with biological systems.

Recent advancements in the use of plastics as a carbon source for carbon nanotubes synthesis - A review

Plastics, which majorly consist of polypropylene (PP), polyethylene (linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE) and high-density polyethylene (HDPE)), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), etc., are the most abundant municipal solid wastes (MSW). They have been utilized as a cheap carbon feedstock in the synthesis of carbon nanotubes (CNTs) because of their high hydrocarbon content, mainly carbon and hydrogen, especially for the polyolefins. In this review, the detailed progress made so far in the use of plastics (both waste and virgin) as cheap carbon feedstock in the synthesis of CNTs (only) over the years is studied. The primary aim of this work is to provide an expansive landscape made so far, especially in the areas of catalysts, catalyst supports, and the methods employed in their preparations and other operational growth conditions, as well as already explored applications of plastic-derived CNTs. This is to enable researchers to easily access, understand, and summarise previous works done in this area, forging ahead towards improving the yield and quality of plastic-derived CNTs, which could extend their market and use in other purity-sensitive applications.

Preparing high-concentration individualized carbon nanotubes for industrial separation of multiple single-chirality species

Industrial production of single-chirality carbon nanotubes is critical for their applications in high-speed and low-power nanoelectronic devices, but both their growth and separation have been major challenges. Here, we report a method for industrial separation of single-chirality carbon nanotubes from a variety of raw materials with gel chromatography by increasing the concentration of carbon nanotube solution. The high-concentration individualized carbon nanotube solution is prepared by ultrasonic dispersion followed by centrifugation and ultrasonic redispersion. With this technique, the concentration of the as-prepared individualized carbon nanotubes is increased from about 0.19 mg/mL to approximately 1 mg/mL, and the separation yield of multiple single-chirality species is increased by approximately six times to the milligram scale in one separation run with gel chromatography. When the dispersion technique is applied to an inexpensive hybrid of graphene and carbon nanotubes with a wide diameter range of 0.8-2.0 nm, and the separation yield of single-chirality species is increased by more than an order of magnitude to the sub-milligram scale. Moreover, with present separation technique, the environmental impact and cost of producing single-chirality species are greatly reduced. We anticipate that this method promotes industrial production and practical applications of single-chirality carbon nanotubes in carbon-based integration circuits.

Modifying the Molecular Structure of Carbon Nanotubes through Gas-Phase Reactants

Current approaches to carbon nanotube (CNT) synthesis are limited in their ability to control the placement of atoms on the surface of nanotubes. Some of this limitation stems from a lack of understanding of the chemical bond-building mechanisms at play in CNT growth. Here, we provide experimental evidence that supports an alkyne polymerization pathway in which short-chained alkynes directly incorporate into the CNT lattice during growth, partially retaining their side groups and influencing CNT morphology. Using acetylene, methyl acetylene, and vinyl acetylene as feedstock gases, unique morphological differences were observed. Interwall spacing, a highly conserved value in natural graphitic materials, varied to accommodate side groups, increasing systematically from acetylene to methyl acetylene to vinyl acetylene. Furthermore, attenuated total reflectance Fourier-transfer infrared spectroscopy (ATR-FTIR) illustrated the existence of intact methyl groups in the multiwalled CNTs derived from methyl acetylene. Finally, the nanoscale alignment of the CNTs grown in vertically aligned forests differed systematically. Methyl acetylene induced the most tortuous growth while CNTs from acetylene and vinyl-acetylene were more aligned, presumably due to the presence of polymerizable unsaturated bonds in the structure. These results demonstrate that feedstock hydrocarbons can alter the atomic-scale structure of CNTs, which in turn can affect properties on larger scales. This information could be leveraged to create more chemically and structurally complex CNT structures, enable more sustainable chemical pathways by avoiding the need for solvents and postreaction modifications, and potentially unlock experimental routes to a host of higher-order carbonaceous nanomaterials.

Ru Catalysts Supported on Bamboo-like N-Doped Carbon Nanotubes: Activity and Stability in Oxidizing and Reducing Environment

The catalysts with platinum-group metals on nanostructured carbons have been a very active field of research, but the studies were mainly limited to Pt and Pd. Here, Ru catalysts based on nitrogen-doped carbon nanotubes (N-CNTs) have been prepared and thoroughly characterized; Ru loading was kept constant (3 wt.%), while the degree of N-doping was varied (from 0 to 4.8 at.%) to evaluate its influence on the state of supported metal. Using the N-CNTs afforded ultrafine Ru particles (<2 nm) and allowed a portion of Ru to be stabilized in an atomic state. The presence of Ru single atoms in Ru/N-CNTs expectedly increased catalytic activity and selectivity in the formic acid decomposition (FAD) but had no effect in catalytic wet air oxidation (CWAO) of phenol, thus arguing against a key role of single-atom catalysis in the latter case. A remarkable difference between these two reactions was also found in regard to catalyst stability. In the course of FAD, no changes in the support or supported species or reaction rate were observed even at a high temperature (150 °C). In CWAO, although 100% conversions were still achievable in repeated runs, the oxidizing environment caused partial destruction of N-CNTs and progressive deactivation of the Ru surface by carbonaceous deposits. These findings add important new knowledge about the properties and applicability of Ru@C nanosystems.

Skin Cancer Management: Current Scenario And Future Perspectives

Skin cancer is a life-threatening disease and has caused significant loss to human health across the globe. Its prevalence has been increasing every year and is one of the common malignancies in the case of organ transplant recipients, of which 95% constitute basal cell and squamous cell carcinomas. The prime factor causing skin cancer is UV radiation. Around the 20th century, sunlight was the primary cause of skin cancer. A novel hypothesis by US scientists stated that cutaneous melanoma was mainly due to recurrent exposure to the sun, whereas keratinocyte cancer occurred due to progressive accumulation of sun exposure. Management of skin cancer is done via various approaches, including cryotherapy, radiotherapy, and photodynamic therapy. Post-discovery of X-rays, radiotherapy has proven to treat skin cancers to some extent, but the indications are uncertain since it depends upon the type of tumour and surgical treatment required for the patient. Due to various limitations of skin cancer treatment and increased severity, there is a requirement for cost-effective, novel, and efficient treatment. Various nanocarriers such as SLNs, magnetic nanoparticles, gold nanoparticles, carbon nanotubes, etc., are the potential carriers in the management and prognosis of both non-melanoma and melanoma skin cancer. Various research and review databases and patent reports have been studied, and information compiled to extract the results. The review also discusses the role of various nanocarriers in treating and diagnosing skin cancer.

Structural Design and Fabrication of Multifunctional Nanocarbon Materials for Extreme Environmental Applications

Extreme environments represent numerous harsh environmental conditions, such as temperature, pressure, corrosion, and radiation. The tolerance of applications in extreme environments exemplifies significant challenges to both materials and their structures. Given the superior mechanical strength, electrical conductivity, thermal stability, and chemical stability of nanocarbon materials, such as carbon nanotubes (CNTs) and graphene, they are widely investigated as base materials for extreme environmental applications and have shown numerous breakthroughs in the fields of wide-temperature structural-material construction, low-temperature energy storage, underwater sensing, and electronics operated at high temperatures. Here, the critical aspects of structural design and fabrication of nanocarbon materials for extreme environments are reviewed, including a description of the underlying mechanism supporting the performance of nanocarbon materials against extreme environments, the principles of structural design of nanocarbon materials for the optimization of extreme environmental performances, and the fabrication processes developed for the realization of specific extreme environmental applications. Finally, perspectives on how CNTs and graphene can further contribute to the development of extreme environmental applications are presented.

Structure-oriented conversions of plastics to carbon nanomaterials

The accumulation of waste plastics has caused serious environmental issues due to their unbiodegradable nature and hazardous additives. Converting waste plastics to different carbon nanomaterials (CNMs) is a promising approach to minimize plastic pollution and realize advanced manufacturing of CNMs. The reported plastic-derived carbons include carbon filaments (i.e. carbon nanotubes and carbon nanofibers), graphene, carbon nanosheets, carbon sphere, and porous carbon. In this review, we present the influences of different intrinsic structures of plastics on the pyrolysis intermediates. We also reveal that non-charring plastics are prone to being pyrolyzed into light hydrocarbons while charring plastics are prone to being pyrolyzed into aromatics. Subsequently, light hydrocarbons favor to form graphite while aromatics are inclined to form amorphous carbon during the carbon formation process. In addition, the conversion tendency of different plastics into various morphologies of carbon is concluded. We also discuss other impact factors during the transformation process, including catalysts, temperature, processing duration and templates, and reveal how to obtain different morphological CNMs from plastics. Finally, current technology limitations and perspectives are presented to provide future research directions in effective plastic conversion and advanced CNM synthesis.

The impact factors in transforming plastics into carbon nanomaterials are reviewed.

The carbon morphology tendency from different plastics is revealed.

Directions for future research on plastic carbonization are presented.

Thermochemical Conversion of Plastic Waste into Fuels, Chemicals, and Value-Added Materials: A Critical Review and Outlooks

Plastic waste is an emerging environmental issue for our society. Critical action to tackle this problem is to upcycle plastic waste as valuable feedstock. Thermochemical conversion of plastic waste has received growing attention. Although thermochemical conversion is promising for handling mixed plastic waste, it typically occurs at high temperatures (300-800 °C). Catalysts can play a critical role in improving the energy efficiency of thermochemical conversion, promoting targeted reactions, and improving product selectivity. This Review aims to summarize the state-of-the-art of catalytic thermochemical conversions of various types of plastic waste. First, general trends and recent development of catalytic thermochemical conversions including pyrolysis, gasification, hydrothermal processes, and chemolysis of plastic waste into fuels, chemicals, and value-added materials were reviewed. Second, the status quo for the commercial implementation of thermochemical conversion of plastic waste was summarized. Finally, the current challenges and future perspectives of catalytic thermochemical conversion of plastic waste including the design of sustainable and robust catalysts were discussed.

Facile and green preparation of solid carbon nanoonions via catalytic co-pyrolysis of lignin and polyethylene and their adsorption capability towards Cu(ii)

Carbon nanomaterials, such as carbon nanoonions (CNOs), possess promising applications in various fields. There are urgent demands to synthesize carbon nanomaterials from a green and renewable carbon source. In this study, solid CNOs with relatively uniform size distribution (with diameters of about 30-50 nm), abundant structure defects and oxygen-containing surface functional groups (such as -OH and -COOH) are developed from co-pyrolysis of lignin (LG) and polyethylene (PE) in the presence of Ni-based catalysts. The type of catalyst, the concentration of catalyst and catalytic co-pyrolysis temperature play important roles in the morphologies and properties of CNOs as confirmed by TEM and SEM. Furthermore, the produced CNOs can act as a low-cost and highly-efficient adsorbent to remove Cu(ii) from aqueous solution according to a homogeneous monolayer, chemical action-dominated, endothermic and spontaneous process. The theoretical maximum adsorption capacity of CNOs calculated from the Langmuir model is 100.00 mg g-1. Surface deposition, complexation, π electron-cation interaction and electrostatic interaction are responsible for the adsorption of Cu(ii) using the prepared CNOs.

Carbon nanotubes derived from waste cooking oil for the removal of emerging contaminants

Multi-walled carbon nanotube (MWCNT) were synthesized using ethyl acetate and waste cooking oil as more green and sustainable carbon sources, and further successfully applied for the adsorption of norfloxacin and 17α-ethinylestradiol.

Fe2P encapsulated in carbon nanowalls decorated with well-dispersed Fe3C nanodots for efficient hydrogen evolution and oxygen reduction reactions

The development of cost-effective, high-efficiency bifunctional electrocatalysts as alternatives to the state-of-the-art Pt-based materials toward the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is of great significance but still challenging. Herein, an advanced bifunctional electrocatalyst is presented, composed of Fe₂P encapsulated in carbon nanowalls decorated with well-dispersed Fe₃C nanodots (denoted as Fe₂P@Fe₃C/CNTs), which is achieved by a novel "inside-out" gas-solid reaction protocol. When functioning as a cathodic catalyst for water splitting, the Fe₂P@Fe₃C/CNT catalyst needs an ultralow overpotential of 83 mV to deliver a current density of 10 mA cm^-2, shows a small Tafel slope of 53 mV dec^-1 and ensures long-term stability for over 200 h in an alkaline electrolyte. Notably, the Fe₂P@Fe₃C/CNT catalyst exhibits an extremely impressive ORR performance with an onset potential (E_onset) of 1.060 V and a half-wave potential (E_1/2) of 0.930 V, excellent stability (≈94% activity retention after 36 000 s), and a strong methanol resistance ability, even far outperforming commercial Pt/C (E_onset = 0.955 V, E_1/2 = 0.825 V, ≈75% activity retention after less than 3500 s). Such outstanding HER and ORR performances are mainly ascribed to the improved corrosion resistance of the unique Fe₂P@C core-shell structures, the abundant catalytically active sites of ultrasmall Fe₃C nanodots incorporated in carbon nanowalls, and the good electrical conductivity of 2D graphitic carbon nanotubes used as a support.

Strategic Approach Towards Plastic Waste Valorization: Challenges and Promising Chemical Upcycling Possibilities

Plastic waste, which is one of the major sources of pollution in the landfills and oceans, has raised global concern, primarily due to the huge production rate, high durability, and the lack of utilization of the available waste management techniques. Recycling methods are preferable to reduce the impact of plastic pollution to some extent. However, most of the recycling techniques are associated with different drawbacks, high cost and downgrading of product quality being among the notable ones. The sustainable option here is to upcycle the plastic waste to create high-value materials to compensate for the cost of production. Several upcycling techniques are constantly being investigated and explored, which is currently the only economical option to resolve the plastic waste issue. This Review provides a comprehensive insight on the promising chemical routes available for upcycling of the most widely used plastic and mixed plastic wastes. The challenges inherent to these processes, the recent advances, and the significant role of the science and research community in resolving these issues are further emphasized.

Molecular Dynamics and Machine Learning in Catalysts

Given the importance of catalysts in the chemical industry, they have been extensively investigated by experimental and numerical methods. With the development of computational algorithms and computer hardware, large-scale simulations have enabled influential studies with more atomic details reflecting microscopic mechanisms. This review provides a comprehensive summary of recent developments in molecular dynamics, including ab initio molecular dynamics and reaction force-field molecular dynamics. Recent research on both approaches to catalyst calculations is reviewed, including growth, dehydrogenation, hydrogenation, oxidation reactions, bias, and recombination of carbon materials that can guide catalyst calculations. Machine learning has attracted increasing interest in recent years, and its combination with the field of catalysts has inspired promising development approaches. Its applications in machine learning potential, catalyst design, performance prediction, structure optimization, and classification have been summarized in detail. This review hopes to shed light and perspective on ML approaches in catalysts.

Intralayered Ostwald Ripening-Induced Self-Catalyzed Growth of CNTs on MXene for Robust Lithium-Sulfur Batteries

The distinguishable physicochemical properties of MXenes render them attractive in electrochemical energy storage. However, the strong tendency to self-restack owing to the van der Waals interactions between the MXene layers incurs a massive decrease in surface area and blocking of ions transfer and electrolytes penetration. Here, in situ generated Ti₃ C₂ T_x MXene-carbon nanotubes (Ti₃ C₂ T_x -CNTs) hybrids are reported via low-temperature self-catalyzing growth of CNTs on Ti₃ C₂ T_x nanosheets without the addition of any catalyst precursors. With combined spectroscopic studies and theoretical calculation results, it is certified that the intralayered Ostwald ripening-induced Ti₃ C₂ T_x nanomesh structure contributes to the uniform precipitation of ultrafine metal Ti catalysts on Ti₃ C₂ T_x , thus giving rise to the in situ CNTs formation on the surface of Ti₃ C₂ T_x with high integrity. Taking advantages of intimate electrolyte penetration, unobstructed 3D Li⁺ /e transport, and rich electroactive sites, the Ti₃ C₂ T_x -CNTs hybrids are confirmed to be ideal 3D scaffolds for accommodating sulfur and regulating the polysulfides conversion for high-loaded lithium-sulfur batteries.

Electronic properties of carbon nanotubes as detected by photoemission and inverse photoemission

The relation between morphology and energy level alignment in carbon nanotubes (CNT) is a crucial information for the optimization of applications in nanoelectronics, optics, mechanics and (bio)chemistry. Here we present a study of the relation between the electronic properties and the morphology of single wall CNT (SWCNT), aligned multi wall CNT (MWCNT) and unaligned MWCNT. The CNT were synthesized via catalytic chemical vapor deposition in ultra-high vacuum conditions. Combined ultraviolet photoemission and inverse photoemission (IPES) spectra reveal a high sensitivity to the nanotube morphology. In the case of unaligned SWCNT the distinctive unoccupied Van Hove singularities (vHs) features are observed in the high resolution IPES spectra. Those features are assigned to semiconducting and metallic SWCNT states, according to calculated vHs DOS. The two MWCNT samples are similar in the diameter of the tube (about 15 nm) and present similar filled and empty electronic states, although the measured features in the aligned MWCNT are more defined. Noteworthy, interlayer states are also revealed. Their intensities are directly related to the MWCNT alignment. Focussing and geometrical effects associated to the MWCNT alignment are discussed to account the spectral differences.

The first-principles-based microkinetic simulation of the dry reforming of methane over Ru(0001)

As the temperature was increased, the generation rate of H₂ and CO in the DRM reaction on Ru(0001) gradually increased along with the ratio of H₂/CO generation rate.

Towards 3D self-assembled rolled multiwall carbon nanotube structures by spontaneous peel off

Controlling the 3D assembly of individual nanomaterials can be a challenging task. However, it opens up opportunities for the production of increasingly complex nanostructures. Unusual rolled multiwall carbon nanotube structures are synthesized here by simply inducing a change of precursor composition during the growth of multiwall carbon nanotube forests. The multiwall carbon nanotube structures are comprised of nitrogen-doped and undoped sections, and are obtained via a detailed peel off and roll mechanism. These results open new doors for the development of increasingly complex nanostructures.

Synthesis, Structure and Electrical Resistivity of Carbon Nanotubes Synthesized over Group VIII Metallocenes

The paper reports the synthesis of carbon nanotubes from ethanol over group VIII (Fe, Co, Ni) catalysts derived from corresponding metallocenes. Several unexpected cooperative effects are reported, which are never observed in the case of individual metallocenes such as the commonly used ferrocene catalyst Fe(C₅H₅)₂. The formation of very long (up to several µm) straight monocrystal metal kernels inside the carbon nanotubes was the most interesting effect. The use of trimetal catalysts (Fe_1-x-yCo_xNi_y)(C₅H₅)₂ resulted in the sharp increase in the yield of carbon nanotubes. The electrical conductivity of the produced nanotubes is determined by the nature of the catalyst. The variation of individual metals in the Ni-Co-Fe leads to a drop of the electrical resistivity of nanotube samples by the order of magnitude, i.e., from 1.0 × 10^-3 to 1.1 × 10^-5 Ω∙m. A controlled change in the electrophysical properties of the nanotubes can make it possible to expand their use as fillers in composites, photothermal and tunable magnetic nanomaterials with pre-designed electrical conductivity and other electromagnetic properties.

Stimuli-responsive and cellular targeted nanoplatforms for multimodal therapy of skin cancer

Interdisciplinary applications of nanopharmaceutical sciences have tremendous potential for enhancing pharmacokinetics, efficacy and safety of cancer therapy. The limitations of conventional therapeutic platforms used for skin cancer therapy have been largely overcome by the use of nanoplatforms. This review discusses various nanotechnological approaches experimented for the treatment of skin cancer. The review describes various polymeric, lipidic and inorganic nanoplatforms for efficient therapy of skin cancer. The stimuli-responsive nanoplatforms such as pH-responsive as well as temperature-responsive platforms have also been reviewed. Different strategies for potentiating the nanoparticles application for cancer therapy such as surface engineering, conjugation with drugs, stimulus-responsive and multimodal effect have also been discussed and compared with the available conventional treatments. Although, nanopharmaceuticals face challenges such as toxicity, cost and scale-up, efforts put-in to improve these drawbacks with continuous research would deliver exciting and promising results in coming days.

Construction of carbon nanorods supported hydrothermal carbon and carbon fiber from waste biomass straw for high strength supercapacitor

The development of high-performance flexible supercapacitor using biomass wastes as raw materials to overcome the high manufacturing cost has attracted excellent interest. Herein, a hierarchical structure of carbon nanorods supported hydrothermal carbons and carbon fibers (CNR/HTC/CFs) with superior electrochemical performance as well as high strength is successfully designed for the first-time using waste straw as a sustainable and economic carbon resource. The straw pyrolysis gases after purification are introduced to support the formation of high specific surface area CNRs via a simple vapor phase growth process. The CNR/HTC/CFs exhibit high mass specific capacitance of 269.47 F g^-1 under the scan rate of 3 mV s^-1 in three-electrode system. A high energy density of 15.54 Wh kg^-1 with the power density of 0.49 kW kg^-1 was obtained in the as-assembled all solid-state supercapacitor device with gel electrolyte, whose value retains as high as 6.99 Wh kg^-1 with the power density of 10.01 kW kg^-1. The tensile strength of the finally fibers can reach up to 2743 ± 467 MPa, which is sufficient for many practical industrial applications. This work provides a feasible synthetic strategy using sustainable biomass waste as raw materials to prepare high strength and capacitance energy storage devices.

Molecular Interpretation of Pharmaceuticals’ Adsorption on Carbon Nanomaterials: Theory Meets Experiments

The ability of carbon-based nanomaterials (CNM) to interact with a variety of pharmaceutical drugs can be exploited in many applications. In particular, they have been studied both as carriers for in vivo drug delivery and as sorbents for the treatment of water polluted by pharmaceuticals. In recent years, the large number of experimental studies was also assisted by computational work as a tool to provide understanding at molecular level of structural and thermodynamic aspects of adsorption processes. Quantum mechanical methods, especially based on density functional theory (DFT) and classical molecular dynamics (MD) simulations were mainly applied to study adsorption/release of various drugs. This review aims to compare results obtained by theory and experiments, focusing on the adsorption of three classes of compounds: (i) simple organic model molecules; (ii) antimicrobials; (iii) cytostatics. Generally, a good agreement between experimental data (e.g. energies of adsorption, spectroscopic properties, adsorption isotherms, type of interactions, emerged from this review) and theoretical results can be reached, provided that a selection of the correct level of theory is performed. Computational studies are shown to be a valuable tool for investigating such systems and ultimately provide useful insights to guide CNMs materials development and design.

Use of iron mining tailings from dams for carbon nanotubes synthesis in fluidized bed for 17α-ethinylestradiol removal

This work reports the use of an iron ore tailings from waste dam as a catalyst and support for carbon nanotubes synthesis and their application in the adsorption of the 17α-ethinylestradiol hormone. The synthesis was carried out by Chemical Vapor Deposition (CVD) in a Fluidized Bed system using: ethylene at temperatures of 500, 600 and 700 °C, and acetonitrile at 500, 600, 700, 800 and 900 °C. The transmission electron microscopy (TEM) results showed that the two higher temperatures in each case favored the formation of nanostructures like carbon nanotubes (CNTs), with good yields. The ethylene source generated classic tubular structures of multiple walls. On the other hand, acetonitrile provided the formation of tubes with less organization, known as bamboo like. This morphology was caused by the insertion of nitrogen into the graphite structure (doping), which originates from the carbon source. The adsorptive capacity of the materials for 17α-Ethinylestradiol removal ranging from 9.2 mg g^-1 to 22.3 mg g^-1. The kinetic and adsorption isotherm studies were also performed for the systems. As for kinetics, all of them presented pseudo-second order behavior. In relation to the type of isotherm, the systems showed Freundlich behavior, that is, the adsorption occurs in multiple layers. Finally, it was concluded that the use of an iron ore tail as a catalyst in the production of CNTs by CVD is feasible. The materials synthesized still had good adsorptive capacity for an emerging contaminant, thus this study allowed the investigation of two environmental problems.

Efficient chemical vapour deposition and arc discharge system for production of carbon nano-tubes on a gram scale

Three indigenous systems-the underwater arc discharge setup, the inert environment arc discharge system, and the chemical vapor deposition (CVD) system-for the gram-scale production of carbon nanotubes were designed and fabricated. In this study, a detailed description of the development and fabrication of these systems is given. Carbon nanotubes were synthesized by using all the three systems, and comparative analyses of the morphology, composition, and purity were done. The synthesized materials were characterized using scanning electron microscopy, X-ray diffraction (XRD), and Raman spectroscopy. The scanning electron microscopy images show agglomerated tubed fiberlike structures in samples from the arc discharge setup, whereas samples from the CVD system do not show any tubelike structures decorated around the carbon nanotubes. Structural investigations done using powder XRD revealed the presence of the hexagonal crystallographic phase. Furthermore, the presence of the G and 2D bands reveals sp² hybridization and confirms the presence of carbon nanotubes in samples. In conclusion, carbon nanotubes synthesized via the CVD system is of high quality and quantity. Moreover, the CVD is a cheap, easy to operate, and energy-saving synthesis method compared with the other two methods.

Carbon Nanotubes: Synthesis via Chemical Vapour Deposition without Hydrogen, Surface Modification, and Application

The present study describes the growth of carbon nanotubes (CNTs) from liquefied petroleum gas (LPG) on an Fe2O3/Al2O3 precatalyst via a chemical vapour deposition (CVD) process without hydrogen. The obtained multiwalled CNTs exhibit a less-defective structure with an identical external diameter of tubes of around 50 nm. The growth mechanism of CNTs suggests that the Fe2O3/Al2O3 precatalyst is reduced to Fe/Al2O3 during the synthesis process using the products of LPG decomposition, and the tip-growth mechanism is suggested. The resulting CNTs are surface-modified with potassium permanganate in the acid medium and used as an adsorbent for copper from aqueous solutions. The Langmuir and Freundlich isotherm models are employed to evaluate the adsorption data, and the maximum adsorption capacity of Cu(II) is 163.7 mg·g−1.

Topologically immobilized catalysis centre for long-term stable carbon dioxide reforming of methane

A rooted catalyst, Ni#Y₂O₃, successfully inhibits the growth of carbon nanotubes in DRM.

Methane reforming at low temperatures is of growing importance to mitigate the environmental impact of the production of synthesis gas, but it suffers from short catalyst lifetimes due to the severe deposition of carbon byproducts. Herein, we introduce a new class of topology-tailored catalyst in which tens-of-nanometer-thick fibrous networks of Ni metal and oxygen-deficient Y₂O₃ are entangled with each other to form a rooted structure, i.e., Ni#Y₂O₃. We demonstrate that the rooted Ni#Y₂O₃ catalyst stably promotes the carbon-dioxide reforming of methane at 723 K for over 1000 h, where the performance of traditional supported catalysts such as Ni/Y₂O₃ diminishes within 100 h due to the precluded mass transport by accumulated carbon byproducts. In situ TEM demonstrates that the supported Ni nanoparticles are readily detached from the support surface in the reaction atmosphere, and migrate around to result in widespread accumulation of the carbon byproducts. The long-term stable methane reforming over the rooted catalyst is ultimately attributed to the topologically immobilized Ni catalysis centre and the synergistic function of the oxygen-deficient Y₂O₃ matrix, which successfully inhibits the accumulation of byproducts.

Can single-walled carbon nanotube diameter be defined by catalyst particle diameter?

The need of designing and controlling single-walled carbon nanotube (SWCNT) properties is a challenge in a growing nanomaterials-related industry. Recently, great progress has been made experimentally to selectively control SWCNT diameter and chirality. However, there is not yet a complete understanding of the synthesis process and there is a lack of mathematical models that explain nucleation and diameter selectivity of stable carbon allotropes. Here, in-situ analysis of chemical vapor deposition SWCNT synthesis confirms that the nanoparticle to nanotube diameter ratio varies with the catalyst particle size. It is found that the tube diameter is larger than that of the particle below a specific size (d_c ≈ 2nm) and above this value is smaller than particle diameters. To explain these observations, we develop a statistical mechanics based model that correlates possible energy states of a nascent tube with the catalyst particle size. This model incorporates the equilibrium distance between the nucleating SWCNT layer and the metal catalyst (e.g. Fe, Co, Ni) evaluated with density functional theory (DFT) calculations. The theoretical analysis explains and predicts the observed correlation between tube and solid particle diameters during growth of supported SWCNTs. This work also brings together previous observations related to the stability condition for SWCNT nucleation. Tests of the model against various published data sets and our own experimental results show good agreement, making it a promising tool for evaluating SWCNT synthesis processes.

Co9 S8 -Catalyzed Growth of Thin-Walled Graphite Microtubes for Robust, Efficient Overall Water Splitting

Co₉ S₈ crystals can catalyze the growth of thin-walled graphite microtubes (GMTs) through a catalytic chemical vapor deposition (CCVD) process using thiourea as the precursor. The growth of GMTs follows a tip-growth mechanism with tube diameters up to a few micrometer. The hollow interiors of the GMTs are filled with carbon nanotubes and wrinkled graphene layers, which form a unique nanotube/graphene-in-microtube structure. As-formed GMTs are N,S-codoped with lots of Co₉ S₈ nanoparticles encapsulated in their inner walls. These GMTs are room-temperature ferromagnets and can be loaded on Ni foams to work as binder-free electrocatalysts with low overpotential (310 mV at 50 mA cm^-2 for the oxygen evolution reaction (OER) and 284 mV at 50 mA cm^-2 for the hydrogen evolution reaction (HER)) and long-term durability (continuous work for 120 h without loss in performance). Our research proves that metal sulfides can catalyze the growth of graphite microtubes and as-formed GMTs may potentially be used as functional building blocks to construct new kinds of electrochemical devices for various energy-related applications.

Probing the enhanced catalytic activity of carbon nanotube supported Ni-LaOx hybrids for the CO2 reduction reaction

Oxygenated functionalized carbon nanotube (oCNT) supported LaO_x-promoted Ni nanoparticles (10Ni-xLa/oCNT) were prepared by the co-impregnation method and tested for synthetic natural gas from the CO₂ reduction reaction. Several advanced characterization methods, including atomic resolution scanning transmission electron microscopy (STEM), temperature programmed experiments (TPSR, CO₂-TPD, and H₂-TPR) and X-ray photoelectron spectroscopy (XPS), were applied to explore, for the first time, the origin of structure modulation of LaO_x species on oCNT supported Ni-LaO_x hybrids and the structure-activity relationship over the CO₂ reduction reaction. The Z-contrast STEM-HAADF results revealed that the LaO_x species are mostly in the size of the sub-nano scale and highly dispersed on the surface of Ni nanoparticles and oCNT, and consequently no diffraction peak of LaO_x was observed from XRD results. TEM analysis showed that the Ni nanoparticle sizes were similar among all samples either after reduction or after reaction due to the relatively strong interaction between Ni and oxygenated groups on CNT supports, regardless of the influence of the La mass loading. It was suggested that the catalytic performance trend was due to the structural variation rather than the size effect. The LaO_x modulation catalyst with 2 wt% of La metal loading not only presented low CO₂ activation temperature at only 163 °C, but also resulted in extremely high CH₄ selectivity (100%) compared with the initial supported Ni catalyst (52.7% of CH₄ selectivity at 300 °C).

Transition metal-assisted carbonization of small organic molecules toward functional carbon materials

Nanostructured carbon materials with large surface area and desired chemical functionalities have been attracting considerable attention because of their extraordinary physicochemical properties and great application potentials in catalysis, environment, and energy storage. However, the traditional approaches to fabricating these materials rely greatly on complex procedures and specific precursors. We present a simple, effective, and scalable strategy for the synthesis of functional carbon materials by transition metal-assisted carbonization of conventional small organic molecules. We demonstrate that transition metals can promote the thermal stability of molecular precursors and assist the formation of thermally stable polymeric intermediates during the carbonization process, which guarantees the successful preparation of carbons with high yield. The versatility of this synthetic strategy allows easy control of the surface chemical functionality, porosity, and morphology of carbons at the molecular level. Furthermore, the prepared carbons exhibit promising performance in heterogeneous catalysis and electrocatalysis.

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.

Carbon-Based Nanomaterials from Biopolymer Lignin via Catalytic Thermal Treatment at 700 to 1000 °C

We report the preparation of carbon-based nanomaterials from biopolymer kraft lignin via an iron catalytic thermal treatment process. Both the carbonaceous gases and amorphous carbon (AC) from lignin thermal decomposition were found to have participated in the formation of graphitic-carbon-encapsulated iron nanoparticles (GCEINs). GCEINs originating from carbonaceous gases have thick-walled graphitic-carbon layers (10 to 50) and form at a temperature of 700 °C. By contrast, GCEINs from AC usually have thin-walled graphitic-carbon layers (1 to 3) and form at a temperature of at least 800 °C. Iron catalyst nanoparticles started their phase transition from α-Fe to γ-Fe at 700 °C, and then from γ-Fe to Fe₃C at 1000 °C. Furthermore, we derived a formula to calculate the maximum number of graphitic-carbon layers formed on iron nanoparticles via the AC dissolution-precipitation mechanism.

Catalytic CVD synthesis of boron nitride and carbon nanomaterials - synergies between experiment and theory

Low-dimensional carbon and boron nitride nanomaterials - hexagonal boron nitride, graphene, boron nitride nanotubes and carbon nanotubes - remain at the forefront of advanced materials research. Catalytic chemical vapour deposition has become an invaluable technique for reliably and cost-effectively synthesising these materials. In this review, we will emphasise how a synergy between experimental and theoretical methods has enhanced the understanding and optimisation of this synthetic technique. This review examines recent advances in the application of CVD to synthesising boron nitride and carbon nanomaterials and highlights where, in many cases, molecular simulations and quantum chemistry have provided key insights complementary to experimental investigation. This synergy is particularly prominent in the field of carbon nanotube and graphene CVD synthesis, and we propose here it will be the key to future advances in optimisation of CVD synthesis of boron nitride nanomaterials, boron nitride - carbon composite materials, and other nanomaterials generally.

Confirming the key role of Ar+ ion bombardment in the growth feature of nanostructured carbon materials by PECVD

In order to confirm the key role of Ar⁺ ion bombardment in the growth feature of nanostructured carbon materials (NCMs), here we report a novel strategy to create different Ar⁺ ion states in situ in plasma enhanced chemical vapor deposition (PECVD) by separating catalyst film from the substrate. Different bombardment environments on either side of the catalyst film were created simultaneously to achieve multi-layered structural NCMs. Results showed that Ar⁺ ion bombardment is crucial and complex for the growth of NCMs. Firstly, Ar⁺ ion bombardment has both positive and negative effects on carbon nanotubes (CNTs). On one hand, Ar⁺ ions can break up the graphic structure of CNTs and suppress thin CNT nucleation and growth. On the other hand, Ar⁺ ion bombardment can remove redundant carbon layers on the surface of large catalyst particles which is essential for thick CNTs. As a result, the diameter of the CNTs depends on the Ar⁺ ion state. As for vertically oriented few-layer graphene (VFG), Ar⁺ ions are essential and can even convert the CNTs into VFG. Therefore, by combining with the catalyst separation method, specific or multi-layered structural NCMs can be obtained by PECVD only by changing the intensity of Ar⁺ ion bombardment, and these special NCMs are promising in many fields.

Hierarchical self-entangled carbon nanotube tube networks

Three-dimensional (3D) assemblies based on carbon nanomaterials still lag behind their individual one-dimensional building blocks in terms of mechanical and electrical properties. Here we demonstrate a simple strategy for the fabrication of an open porous 3D self-organized double-hierarchical carbon nanotube tube structure with properties advantageous to those existing so far. Even though no additional crosslinking exists between the individual nanotubes, a high reinforcement effect in compression and tensile characteristics is achieved by the formation of self-entangled carbon nanotube (CNT) networks in all three dimensions, employing the CNTs in their high tensile properties. Additionally, the tubular structure causes a self-enhancing effect in conductivity when employed in a 3D stretchable conductor, together with a high conductivity at low CNT concentrations. This strategy allows for an easy combination of different kinds of low-dimensional nanomaterials in a tube-shaped 3D structure, enabling the fabrication of multifunctional inorganic-carbon-polymer hybrid 3D materials.

Low-dimensional nanomaterials are crucial conducting components of stretchable electronics, but their mechanical reinforcement remains challenging. Here, the authors infiltrate carbon nanotubes into a porous ceramic network to produce a 3D nanofelted self-entangled assembly with high conductivity and mechanical stability.