Ten years of laser-induced graphene: impact and future prospect on biomedical, healthcare, and wearable technology

Since its introduction in 2014, laser-induced graphene (LIG) from commercial polymers has been gaining interests in both academic and industrial sectors. This can be clearly seen from its mass adoption in various fields ranging from energy storage and sensing platforms to biomedical applications. LIG is a 3-dimensional, nanoporous graphene structure with highly tuneable electrical, physical, and chemical properties. LIG can be easily produced by single-step laser scribing at normal room temperature and pressure using easily accessible commercial level laser machines and materials. With the increasing demand for novel wearable devices for biomedical applications, LIG on flexible substrates can readily serve as a technological platform to be further developed for biomedical applications such as point-of-care (POC) testing and wearable devices for healthcare monitoring system. This review will provide a comprehensive grounding on LIG from its inception and fabrication mechanism to the characterization of its key functional properties. The exploration of biomedicals applications in the form of wearable and point-of-care devices will then be presented. Issue of health risk from accidental exposure to LIG will be covered. Then LIG-based wearable devices will be compared to devices of different materials. Finally, we discuss the implementation of Internet of Medical Things (IoMT) to wearable devices and explore and speculate on its potentials and challenges.

Bio-based anode material production for lithium-ion batteries through catalytic graphitization of biochar: the deployment of hybrid catalysts

Producing sustainable anode materials for lithium-ion batteries (LIBs) through catalytic graphitization of renewable biomass has gained significant attention. However, the technology is in its early stages due to the bio-graphite's comparatively low electrochemical performance in LIBs. This study aims to develop a process for producing LIB anode materials using a hybrid catalyst to enhance battery performance, along with readily available market biochar as the raw material. Results indicate that a trimetallic hybrid catalyst (Ni, Fe, and Mn in a 1:1:1 ratio) is superior to single or bimetallic catalysts in converting biochar to bio-graphite. The bio-graphite produced under this catalyst exhibits an 89.28% degree of graphitization and a 73.95% conversion rate. High-resolution transmission electron microscopy (HRTEM) reveals the dissolution-precipitation mechanism involved in catalytic graphitization. Electrochemical performance evaluation showed that the trimetallic hybrid catalyst yielded bio-graphite with better electrochemical performances than those obtained through single or bimetallic hybrid catalysts, including a good reversible capacity of about 293 mAh g-1 at a current density of 20 mA/g and a stable cycle performance with a capacity retention of over 98% after 100 cycles. This study proves the synergistic efficacy of different metals in catalytic graphitization, impacting both graphite crystalline structure and electrochemical performance.

Recent Advances in Synthesis of Graphite from Agricultural Bio-Waste Material: A Review

Graphitic carbon is a valuable material that can be utilized in many fields, such as electronics, energy storage and wastewater filtration. Due to the high demand for commercial graphite, an alternative raw material with lower costs that is environmentally friendly has been explored. Amongst these, an agricultural bio-waste material has become an option due to its highly bioactive properties, such as bioavailability, antioxidant, antimicrobial, in vitro and anti-inflammatory properties. In addition, biomass wastes usually have high organic carbon content, which has been discovered by many researchers as an alternative carbon material to produce graphite. However, there are several challenges associated with the graphite production process from biomass waste materials, such as impurities, the processing conditions and production costs. Agricultural bio-waste materials typically contain many volatiles and impurities, which can interfere with the synthesis process and reduce the quality of the graphitic carbon produced. Moreover, the processing conditions required for the synthesis of graphitic carbon from agricultural biomass waste materials are quite challenging to optimize. The temperature, pressure, catalyst used and other parameters must be carefully controlled to ensure that the desired product is obtained. Nevertheless, the use of agricultural biomass waste materials as a raw material for graphitic carbon synthesis can reduce the production costs. Improving the overall cost-effectiveness of this approach depends on many factors, including the availability and cost of the feedstock, the processing costs and the market demand for the final product. Therefore, in this review, the importance of biomass waste utilization is discussed. Various methods of synthesizing graphitic carbon are also reviewed. The discussion ranges from the conversion of biomass waste into carbon-rich feedstocks with different recent advances to the method of synthesis of graphitic carbon. The importance of utilizing agricultural biomass waste and the types of potential biomass waste carbon precursors and their pre-treatment methods are also reviewed. Finally, the gaps found in the previous research are proposed as a future research suggestion. Overall, the synthesis of graphite from agricultural bio-waste materials is a promising area of research, but more work is needed to address the challenges associated with this process and to demonstrate its viability at scale.

Molten salt electro-preparation of graphitic carbons

Graphite has been used in a wide range of applications since the discovery due to its great chemical stability, excellent electrical conductivity, availability, and ease of processing. However, the synthesis of graphite materials still remains energy-intensive as they are usually produced through a high-temperature treatment (>3000°C). Herein, we introduce a molten salt electrochemical approach utilizing carbon dioxide (CO₂) or amorphous carbons as raw precursors for graphite synthesis. With the assistance of molten salts, the processes can be conducted at moderate temperatures (700-850°C). The mechanisms of the electrochemical conversion of CO₂ and amorphous carbons into graphitic materials are presented. Furthermore, the factors that affect the graphitization degree of the prepared graphitic products, such as molten salt composition, working temperature, cell voltage, additives, and electrodes, are discussed. The energy storage applications of these graphitic carbons in batteries and supercapacitors are also summarized. Moreover, the energy consumption and cost estimation of the processes are reviewed, which provides perspectives on the large-scale synthesis of graphitic carbons using this molten salt electrochemical strategy.

Ab Initio Simulation of Amorphous Graphite

An amorphous graphite material has been predicted from molecular dynamics simulation using ab initio methods. Carbon materials reveal a strong proclivity to convert into a sp^{2} network and then layer at temperatures near 3000 K within a density range of ca. 2.2-2.8  g/cm^{3}. Each layer of amorphous graphite is a monolayer of amorphous graphene including pentagons and heptagons in addition to hexagons, and the planes are separated by about 3.1  Å. The layering transition has been studied using various structural and dynamical analyses. The transition is unique as one of partial ordering (long range order of planes and galleries, but topological disorder in the planes). The planes are quite flat, even though monolayer amorphous graphene puckers near pentagonal sites. Interplane cohesion is due partly to non-Van der Waals interactions. The structural disorder has been studied closely, especially the consequences of disorder to electronic transport. It is expected that the transition elucidated here may be salient to other layered materials.

Improved Method for Preparing Nanospheres from Pomelo Peel to Achieve High Graphitization at a Low Temperature

Biomass waste is a valuable resource that can be recovered, reused, and is renewable. However, converting biomass waste to a high degree of order is a bigger challenge, and graphitization at low temperatures is even more difficult. This paper proposes an improved method (Ni element catalysis) for highly graphitizing pomelo peel at low temperatures (750 –900 °C). In this paper, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), and high-resolution transmission electron microscopy (HRTEM) were used to study the method and the effect of temperature on structural changes during graphitization. Under the improved method, pomelo peel was transformed into nano-spherical graphitized material. The degree of graphitization reached 80.23% at 900 °C, which was 31.39% higher than that of the traditional method. Furthermore, through HRTEM, the lattice fringe spacing was observed to be 0.337 nm, which is between pure graphite (0.3354 nm) and amorphous graphite (0.3440 nm). In this paper, the improved method can obtain highly graphitized nanospheres at low temperatures, thus reducing energy consumption, reducing environmental pollution, and promoting sustainable development.

Improving Nonenzymatic Biosensing Performance of Electrospun Carbon Nanofibers decorated with Ni/Co Particles via Oxidation

Nonenzymatic biosensors do not require enzyme immobilization nor face degradation problem. Hence, nonenzymatic biosensors have recently attracted growing attention due to the stability and reproducibility. Here, a comparative study was conducted to quantitatively evaluate the glucose sensing of pure/oxidized Ni, Co, and their bimetal nanostructures grown on electrospun carbon nanofibers (ECNFs) to provide a low-cost free-standing electrode. The prepared nanostructures exhibited sensitivity (from 66.28 to 610.6 μA mM^-1 cm^-2), linear range of 2-10 mM, limit of detection in the range of 1 mM, and the response time (< 5 s), besides outstanding selectivity and applicability for glucose detection in the human serum. Moreover, the oxidizable interfering species, such as ascorbic acid (AA), uric acid (UA), and dopamine (DA), did not cause interference. Co-C and Ni-C phase diagrams, solid-state diffusion phenomena, and rearrangement of dissolved C atoms after migration from metal particles were discussed. This study undoubtedly provides new prospects on the nonenzymatic biosensing performance of mono-metal, bimetal, and oxide compounds of Ni and Co elements, which could be quite helpful for the fabrication of biomolecules detecting devices.

Superhydrophobic Ni-Reduced Graphene Oxide Hybrid Coatings with Quasi-Periodic Spike Structures

Recently, sophisticated technologies are applied to design a certain surface nature that can have superhydrophobic properties. Thus, a simple spray technique was introduced to prepare a superhydrophobic surface using rGO with Ni-S system (rGO-Ni) by using NiSO₄ catalyst under microwave irradiation at various reaction times of 5, 10, 20, and 30 min. The GO reduction was conducted at a fixed Ar/H₂ ratio, a flow rate of 0.4 L/min, microwave power of 720 W, and a mass of 0.5 g. GO powder with nickel sulfate catalyst was treated under Ar/H₂ (4:1) mixture for GO reduction, where Ar and H₂ were expected to prevent the rebinding of oxygen released from GO. The result of XRD and Raman measurement confirms that rGO-Ni prepared at reaction time 20 min exhibit the highest reduction of GO and the presence of various Ni-S crystal structures such as NiS, NiS₂, Ni₃S₂, and Ni₃S₄ due to decomposition of NiSO₄. The rGO-Ni coating performance shows superhydrophobic nature with a contact angle of 150.1°. The AFM images show that the addition of nickel to rGO produces a quasi-periodic spike structure, which increases the superhydrophobicity of the r-GO-Ni coated glass with a contact angle of 152.6°. It is emphasized that the proposed simple spray coating using rGO-Ni provides a more favorable option for industry application in obtaining superhydrophobic surfaces.

Structural Investigation of the Synthesized Few-Layer Graphene from Coal under Microwave

This study focused on the structural investigation of few-layer graphene (FLG) synthesis from bituminous coal through a catalytic process under microwave heat treatment (MW). The produced FLG has been examined by Raman spectroscopy, XRD, TEM, and AFM. Coal was activated using the potassium hydroxide activation process. The FLG synthesis processing duration was much faster requiring only 20 min under the microwave radiation. To analyse few-layer graphene samples, we considered the three bands, i.e., D, G, and 2D, of Raman spectra. At 1300 °C, the P10% Fe sample resulted in fewer defects than the other catalyst percentages sample. The catalyst percentages affected the structural change of the FLG composite materials. In addition, the Raman mapping showed that the catalyst loaded sample was homogeneously distributed and indicated a few-layer graphene sheet. In addition, the AFM technique measured the FLG thickness around 4.5 nm. Furthermore, the HRTEM images of the P10% Fe sample contained a unique morphology with 2–7 graphitic layers of graphene thin sheets. This research reported the structural revolution with latent feasibility of FLG synthesis from bituminous coal in a wide range.

Microwave-Assisted Coal-Derived Few-Layer Graphene as an Anode Material for Lithium-Ion Batteries

A few-layer graphene (FLG) composite material was synthesized using a rich reservoir and low-cost coal under the microwave-assisted catalytic graphitization process. X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were used to evaluate the properties of the FLG sample. A well-developed microstructure and higher graphitization degree were achieved under microwave heating at 1300 °C using the S5% dual (Fe-Ni) catalyst for 20 min. In addition, the synthesized FLG sample encompassed the Raman spectrum 2D band at 2700 cm-1, which showed the existence of a few-layer graphene structure. The high-resolution TEM (transmission electron microscopy) image investigation of the S5% Fe-Ni sample confirmed that the fabricated FLG material consisted of two to seven graphitic layers, promoting the fast lithium-ion diffusion into the inner surface. The S5% Fe-Ni composite material delivered a high reversible capacity of 287.91 mAhg-1 at 0.1 C with a higher Coulombic efficiency of 99.9%. In contrast, the single catalyst of S10% Fe contained a reversible capacity of 260.13 mAhg-1 at 0.1 C with 97.96% Coulombic efficiency. Furthermore, the dual catalyst-loaded FLG sample demonstrated a high capacity-up to 95% of the initial reversible capacity retention-after 100 cycles. This study revealed the potential feasibility of producing FLG materials from bituminous coal used in a broad range as anode materials for lithium-ion batteries (LIBs).

Structure of Coal-Derived Metal-Supported Few-Layer Graphene Composite Materials Synthesized Using a Microwave-Assisted Catalytic Graphitization Process

Metal-supported few-layer graphene (FLG) was synthesized via microwave-assisted catalytic graphitization owing to the increasing demand for it and its wide applications. In this study, we quickly converted earth-abundant and low-cost bituminous coal to FLG over Fe catalysts at a temperature of 1300 °C. X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and N2 adsorption-desorption experiments were performed to analyze the fabricated metal-supported FLG. The results indicated that the microwave-irradiation temperature at a set holding-time played a critical role in the synthesis of metal-supported FLG. The highest degree of graphitization and a well-developed pore structure were fabricated at 1300 °C using a S10% Fe catalyst for 20 min. High-resolution transmission electron microscopy analysis confirmed that the metal-supported FLG fabricated via microwave-assisted catalytic graphitization consisted of 3-6 layers of graphene nanosheets. In addition, the 2D band at 2700 cm-1 in the Raman spectrum of the fabricated metal-supported FLG samples were observed, which indicated the presence of few-layer graphene structure. Furthermore, a mechanism was proposed for the microwave-assisted catalytic graphitization of bituminous coal. Here, we developed a cost-effective and environmental friendly metal-supported FLG method using a coal-based carbonaceous material.

A Modification of Palm Waste Lignocellulosic Materials into Biographite Using Iron and Nickel Catalyst

This paper presents an alternative way to maximize the utilization of palm waste by implementing a green approach to modify lignocellulosic materials into a highly crystalline biographite. A bio-graphite structure was successfully synthesized by converting lignocellulosic materials via a simple method using palm kernel shell (PKS) as a carbon precursor. This involved the direct impregnation of a catalyst into raw material followed by a thermal treatment. The structural transformation of the carbon was observed to be significantly altered by employing different types of catalysts and varying thermal treatment temperatures. Both XRD and Raman spectroscopy confirmed that the microstructural alteration occurred in the carbon structure of the sample prepared at 800 and 1000 °C using iron, nickel or the hybrid of iron-nickel catalysts. The XRD pattern revealed a high degree of graphitization for the sample prepared at 1000 °C, and it was evident that iron was the most active graphitization catalyst. The presence of an intensified peak was observed at 2θ = 26.5°, reflecting the formation of a highly ordered graphitic structure as a result of the interaction between the iron catalyst and the thermal treatment process at 1000 °C. The XRD observation was further supported by the Raman spectrum in which PKS-Fe1000 showed a lower defect structure associated with the presence of a significant amount of graphitic structure, as a low value of (Id/Ig) ratio was reported. An HRTEM image showed a well-defined lattice fringe seen on the structure for PKS-Fe1000; meanwhile, a disordered microstructure was observed for the control sample, indicating that successful structural modification was achieved with the aid of the catalyst. Further analysis from BET found that the PKS-Fe1000 developed a surface area of 202.932 m2/g with a pore volume of 0.208 cm3/g. An overall successful modification from palm waste into graphitic material was achieved. Thus, this study will help those involved in waste management to evaluate the possibility of a sustainable process for the generation of graphite material from palm waste. It can be concluded that palm waste is a potential source of production for graphite material through the adoption of the proposed waste management process.

Microwave-Assisted Preparation of Activated Carbon Modified by Zinc Chloride as a Packing Material for Column Separation of Saccharides

Activated carbon, an amorphous carbon material with a high specific surface area and void fraction, is widely used as an economical adsorbent in many fields. In this work, a kind of new activated carbon composite for saccharide column separation was prepared by zinc chloride impregnating and microwave heating. The structural characterizations validate the increase in porosity and the specific surface area of the activated carbon as well as the change of the activated carbon crystallite lattice. The chemical characterizations validate the increase in the number of oxygen-containing functional groups and structural bonding of zinc with the activated carbon surface. Compared with the blank control, the surface Zn element improves the adsorption selectivity of the activated carbon to the target saccharides. Under the special mechanism of microwaves, the pores created by expansion from the inside to the outside facilitate the free flow of the mobile phase. The eight saccharides can be separated by the columns packed with the activated carbon impregnated with 40% and 70% zinc chloride.

High-efficiency transformation of amorphous carbon into graphite nanoflakes for stable aluminum-ion battery cathodes

Highly efficient strategies for the transformation of amorphous carbon into graphite with high graphitization and crystallinity features have been significantly pursued in recent years; however, critical issues, including high processing temperature, insufficient graphitization, introduction of catalyst impurities, complicated post-purification procedures, and generation of greenhouse gas, still remain in traditional approaches. For significantly addressing these challenges, herein, a highly efficient catalyst-free, eco-friendly and low-temperature electrochemical transformation strategy was proposed for the preparation of highly graphitized porous graphite nanoflakes. Using inert SnO₂ as an anode in CaCl₂-LiCl molten salts, the graphitization transformation of amorphous carbon materials could be realized at 700 °C, approaching the record in high-efficiency converting amorphous carbon to graphite; moreover, systematical analysis was performed to understand the electrochemical transformation of amorphous carbon into highly graphitized graphite nanoflakes. For extending their valuable applications, the as-prepared graphite nanoflakes were further utilized as cathodes in aluminum-ion batteries, which exhibited significantly promising energy storage performance; moreover, an initial discharge capacity of 63.6 mA h g^-1 at a current density of 200 mA g^-1 was achieved, which eventually became 55.5 mA h g^-1 with a coulombic efficiency of 95.4% after 1000 cycles; thus, these cathodes exhibited stable long-term cycling performance. The combination of low-temperature electrochemical transformation and the subsequent high-performance applications of these nanoflakes in energy storage indicates that the proposed strategy is highly efficient for the transformation and utilization of abundant amorphous carbon resources for the realization of high value-added applications.

En masse pyrolysis of flexible printed circuit board wastes quantitatively yielding environmental resources

This paper reports the recycling of flexible printed circuit board (FPCB) waste through carbonization of polyimide by dual pyrolysis processes. The organic matter was recovered as pyrolyzed oil at low temperatures, while valuable metals and polyimide-derived carbon were effectively recovered through secondary high temperature pyrolysis. The major component of organics extracted from FPCB waste comprised of epoxy resins were identified as pyrolysis oils containing bisphenol-A. The valuable metals (Cu, Ni, Ag, Sn, Au, Pd) in waste FPCB were recovered as granular shape and quantitatively analyzed via ICP-OES. In attempt to produce carbonaceous material with increased degree of graphitization at low heat-treatment conditions, the catalytic effect of transition metals within FPCB waste was investigated for the efficient carbonization of polyimide films. The morphology of the carbon powder was observed by scanning electron microscopy and graphitic carbonization was investigated with X-ray analysis. The protocols outlined in this study may allow for propitious opportunities to salvage both organic and inorganic materials from FPCB waste products for a sustainable future.

Carbon dioxide electrolysis and carbon deposition in alkaline-earth-carbonate-included molten salts electrolyzer

Alkaline-earth-carbonate-included molten salts sustain continuous CO₂ capture and electrochemical conversion.

Effect of BaCO3 addition on the CO2-derived carbon deposition in molten carbonates electrolyzer

Atmospheric carbon dioxide is facilely transformed into carbon materials in Ba-containing or Ba-free carbonates eutectic.

Microwaves effectively examine the extent and type of coking over acid zeolite catalysts

Coking leads to the deactivation of solid acid catalyst. This phenomenon is a ubiquitous problem in the modern petrochemical and energy transformation industries. Here, we show a method based on microwave cavity perturbation analysis for an effective examination of both the amount and the chemical composition of cokes formed over acid zeolite catalysts. The employed microwave cavity can rapidly and non-intrusively measure the catalytically coked zeolites with sample full body penetration. The overall coke amount is reflected by the obtained dielectric loss (ε″) value, where different coke compositions lead to dramatically different absorption efficiencies (ε″/cokes’ wt%). The deeper-dehydrogenated coke compounds (e.g., polyaromatics) lead to an apparently higher ε″/wt% value thus can be effectively separated from lightly coked compounds. The measurement is based on the nature of coke formation during catalytic reactions, from saturated status (e.g., aliphatic) to graphitized status (e.g., polyaromatics), with more delocalized electrons obtained for enhanced Maxwell–Wagner polarization.

Catalyst deactivation by coke deposition is a major drawback in industrial processes. Here, the authors show a non-intrusive microwave cavity perturbation technique as a powerful tool to determine the nature and extent of coke accumulation in industrially-relevant zeolite catalysts.