Hierarchical Lignin-Based Carbon Matrix and Carbon Dot Composite Electrodes for High-Performance Supercapacitors

Carbon Dioxide Capture on Oxygen- and Nitrogen-Containing Carbon Quantum Dots

To address global climate change challenges, an effective strategy involves capturing CO2 directly at its source using a sustainable, low-cost adsorbent. Carbon quantum dots (CQDs), derived from lignin, are employed to modify the internal surface of an activated carbon adsorbent, enabling selective adsorption based on electrostatic interactions. By manipulating charge distribution on CQDs through either doping (nitrogen) or functionalization (amine, carboxyl, or hydroxyl groups), the study confirms, through classical molecular dynamics simulations, the potential to adjust binding strength, adsorption capacity, and selectivity for CO2 over N2 and O2. For simulations with a single component gas, maximum selectivities of 3.6 and 6.7 are shown for CO2/N2 and CO2/O2, respectively, at 300 K. Simulations containing a wet flue gas indicate that the presence of water increases the CO2/N2 and CO2/O2 selectivities. The highest CO2/H2O selectivity obtained from a CQD/graphite system is 4.3. A comparison of graphite and lignin-based carbon composite (LBCC) substrates demonstrated that LBCC has enhanced adsorptive capacity. The roughness of the LBCC substrate prevents the diffusion of the CQD on the surface. This computational study takes another step toward identifying optimal CQD atomic architecture, dimensions, doping, and functionalization for a large-scale CQD/AC adsorbent solution for CO2 capture.

Applications of carbon quantum dots in electrochemical energy storage devices

Supercapacitors (SCs), including electric double-layer capacitors (EDLCs), pseudocapacitors, and hybrid capacitors, are esteemed for their high power density and attractive features such as robust safety, fast charging, low maintenance, and prolonged cycling lifespan, sparking significant interest. Carbon quantum dots (CQDs) are fluorescent nanomaterials with small size, broad excitation spectrum, stable fluorescence, and adjustable emission wavelengths. They are widely used in optoelectronics, medical diagnostics, and energy storage due to their biocompatibility, low toxicity, rich surface functional groups, abundant electron-hole pairs, large specific surface area, and tunable heteroatom doping. In this short review, we briefly discussed the advantages and disadvantages of bottom-up and top-down of CQD synthesis methods. The arc-discharge technique, laser ablation technique, plasma treatment, ultrasound synthesis technique, electrochemical technique, chemical exfoliation, and combustion are among the initial top-down approaches. The subsequent section delineates waste-derived and bottom-up methods, encompassing microwave synthesis, hydrothermal synthesis, thermal pyrolysis, and the metal-organic framework template-assisted technique. In addition, this short review focuses on the operational mechanism of supercapacitors, their properties, and the utilization of CQDs in supercapacitors.

Novel Kraft Softwood Lignin-Derived Carbon Quantum Dots: Synthesis, Characterization, and In Vitro Cytocompatibility

Carbon quantum dots (CQDs) have been investigated for biomedical applications in medical imaging due to their fluorescent properties, overall long-term stability, and excellent cytocompatibility and biocompatibility. Lignin is an organic polymer in the tissues of woody plants. It is also considered a byproduct of the wood and pulp industries. Hence, it presents as a renewable source of carbon nanoparticles. In this study, we report the synthesis and material and biological characterization of two colloidal suspensions of CQDs in water derived from lignin-based carbon. One was the native form of CQDs derived from lignin carbon, and the second was doped with nitrogen to evaluate material differences. Material characterization was carried out using various commonly used techniques, including Fourier transform infrared spectroscopy (FTIR), emission and absorbance spectra, zeta potential, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Thin films of CQDs were formed on glass and silicon substrates to assess the in vitro cytocompatibility with human mesenchymal stem cells (hMSCs). Observations suggest that the two forms of CQDs promote cell attachment within 24 h and sustain it for at least 7 days. The overall structure and shape of cells suggest a lack of any adverse or toxic effects of CQDs. The data lay down the novel foundation to support the use of lignin-derived CQDs in tissue engineering applications.

Lignocellulosic Biomass-Based Carbon Dots: Synthesis Processes, Properties, and Applications

Carbon dots (CDs), a new type of carbon-based fluorescent nanomaterial, have attracted widespread attention because of their numerous excellent properties. Lignocellulosic biomass is the most abundant renewable natural resource and possesses broad potential to manufacture different composite and smart materials. Numerous studies have explored the potential of using the components (such as cellulose, hemicellulose, and lignin) in lignocellulosic biomass to produce CDs. There are few papers systemically aiming in the review of the state-of-the-art works related to lignocellulosic biomass-derived CDs. In this review, the significant advances in synthesis processes, formation mechanisms, structural characteristics, optical properties, and applications of lignocellulosic biomass-based CDs such as cellulose-based CDs, hemicellulose-based CDs and lignin-based CDs in latest research are reviewed. In addition, future research directions on the improvement of the synthesis technology of CDs using lignocellulosic biomass as raw materials to enhance the properties of CDs are proposed. This review will serve as a road map for scientists engaged in research and exploring more applications of CDs in different science fields to achieve the highest material performance goals of CDs.

Luminescence of carbon quantum dots and their application in biochemistry

Similar to fullerenes, carbon nanotubes and graphene, carbon dots (CDs) are causing a lot of research work in their own right. CDs are a type of surface-passivated quantum dot that contain carbon atoms. Their distinctive characteristics, such as luminescent emission that varies with size and wavelength, resistance to photobleaching, easy biological binding, lack of toxicity, and economical production without the need for intricate synthetic processes, have led to a noteworthy surge in attention within the research community. Different techniques can be utilized to create these CDs, spanning from basic candle burning to laser ablation. This review article delves into the principles of fluorescence technology, providing insights into how different synthesis methods of quantum dots impact their luminescent properties. Additionally, it highlights the latest applications of quantum dots in catalysis and biomedical fields, with special emphasis on the current status of luminescent properties in biology and chemistry. Towards the end, the article discusses the limitations of quantum dots in current practical applications, pointing out that CDs hold promising potential for future applications.

Multilayered LDH/Microcapsule Smart Epoxy Coating for Corrosion Protection

A multilayered smart epoxy coating for corrosion prevention of carbon steel was developed and characterized. Toward this direction, as a first step, zinc-aluminum nitrate-layered double hydroxide (Zn/Al LDH) was synthesized using the hydrothermal crystallization technique and then loaded with dodecylamine (DOD), which was used as an inhibitor (pH-sensitive). Similarly, the synthesis of the urea-formaldehyde microcapsules (UFMCs) has been carried out using the in-situ polymerization method, and then the microcapsules (LAUFCs) were encapsulated with linalyl acetate (LA) as a self-healing agent. Finally, the loaded Zn/Al LDH (3 wt %) and modified LAUFCs (5 wt %) were reinforced into an epoxy matrix to develop a double-layer coating (DL-EP). For an exact comparison, pre-layer epoxy coatings comprising 3 wt % of the loaded Zn/Al LDH (referred to as LDH-EP), top-layer epoxy coatings comprising 5 wt % linalyl acetate urea-formaldehyde microcapsules (referred to as UFMLA COAT), and a blank epoxy coating (reference coating) were also developed. The developed epoxy coatings were characterized using various techniques such as XRD, XPS, BET, TGA, FTIR, EIS, etc. Electrochemical tests performed on the synthesized coatings indicate that the DL-EP demonstrates improved self-healing properties compared to LDH-EP and UFMLA COAT.

Local Structure Analysis and Modelling of Lignin-Based Carbon Composites through the Hierarchical Decomposition of the Radial Distribution Function

Carbonized lignin has been proposed as a sustainable and domestic source of activated, amorphous, graphitic, and nanostructured carbon for many industrial applications as the structure can be tuned through processing conditions. However, the inherent variability of lignin and its complex physicochemical structure resulting from feedstock and pulping selection make the Process-Structure-Property-Performance (PSPP) relationships hard to define. In this work, radial distribution functions (RDFs) from synchrotron X-ray and neutron scattering of lignin-based carbon composites (LBCCs) are investigated using the Hierarchical Decomposition of the Radial Distribution Function (HDRDF) modelling method to characterize the local atomic environment and develop quantitative PSPP relationships. PSPP relationships for LBCCs defined by this work include crystallite size dependence on lignin feedstock as well as increasing crystalline volume fraction, nanoscale composite density, and crystallite size with increasing reduction temperature.

Lithium and Sodium Ion Binding Mechanisms and Diffusion Rates in Lignin-Based Hard Carbon Models

Hard carbons are the primary candidate for the anode of next-generation sodium-ion batteries for large-scale energy storage, as they are sustainable and can possess high charge capacity and long cycle life. These properties along with diffusion rates and ion storage mechanisms are highly dependent on nanostructures. This work uses reactive molecular dynamics simulations to examine lithium and sodium ion storage mechanisms and diffusion in lignin-based hard carbon model systems with varying nanostructures. It was found that sodium will preferentially localize on the surface of curved graphene fragments, while lithium will preferentially bind to the hydrogen dense interfaces of crystalline and amorphous carbon domains. The ion storage mechanisms are explained through ion charge and energy distributions in coordination with snapshots of the simulated systems. It was also revealed that hard carbons with small crystalline volume fractions and moderately sized sheets of curved graphene will yield the highest sodium-ion diffusion rates at ∼10-7 cm2/s. Self-diffusion coefficients were determined by mean square displacement of ions in the models with extension through a confined random walk theory.