Synthesis and characterization of carbon dots from coconut shell by optimizing the hydrothermal carbonization process

Coconut shell is one of the major agro-by products vis-a-vis agro-waste generated by coconut processing units. At present, Coconut shells are largely utilized as feed material for thermal power conversion by various allied industrial sectors, which is a highly energy inefficient and ecologically unfriendly process. The present study aimed to generate activated carbon dots/ carbon nanomaterials with a wide range of potential applications through a relatively less energy dependant hydrothermal carbonization process. Hydrothermal carbonization is a one-step, simple, low cost and environmental friendly approach to obtain carbon dots. The findings demonstrate that coconut shells when subjected to hydrothermal carbonization process at 250ᵒC for 6 h produced uniform-sized, stable, negatively charged and amorphous forms of carbon dots. Characterization of carbon dots using High-Resolution Transmission Electron Microscopy (HR-TEM), Scanning Electron Microscopy (SEM), Selected Area Electron Diffraction (SAED), X- ray Diffractometer (XRD), UV- Visible Spectroscopy, Particle Size Analyzer (PSA), Brunauer–Emmett-Teller (BET) Analyzer, Elemental Dispersive X-ray (EDX) analyzer and Fourier Transform Infrared Spectroscopy (FTIR) had conclusively confirmed the versatility of the carbon dots generation process and were able to achieve stable 2 nm-sized, spherical shaped carbon dots with numerous downstream applications. The study will help the conversion of agro-waste coconut shells into useful bio-based fluorescent carbon dots.

Evolution mechanism of cyclized structure of PAN-based pre-oxidized fiber during low temperature carbonization process

The low temperature carbonization process is an important stage to realize the structural transition from the organic cyclized structure of PAN based pre-oxidized fiber to the inorganic pseudo-graphite structure of the ultimate carbon fiber. In the present paper, the evolution mechanism of cyclized structure and aggregation structure of PAN stabilized fiber during low temperature carbonization was studied by means of TGA, 13C-NMR, XRD, XPS and Raman. The results indicated that when the heat-treated temperature was lower than 450 °C, the mainly chemical reactions were the dehydrogenation and pyrolysis reactions in acyclic linear molecular chain or partial cyclized structure. At this stage, the growth of cyclized structure was not obvious. While the original ordered structure was destroyed gradually and the internal stress increased significantly. It induced the cyclized structure to be further oriented. When the temperature was higher than 450 °C, the polycondensation and reconstruction in aromatic heterocyclic structure was more important. The early aromatic heterocycles had many different structural scales, poor homogeneity and many defects in the heterocycles. At this stage, a new pseudo-graphite crystalline structure gradually formed and the d-spacing of graphite layer decreased slightly and crystallites size increased slowly with the increase of heat-treated temperature. When the temperature was higher than 550 °C, the pseudo-graphite base structure gradually formed. The d-spacing were further reduced slightly, and the crystallites size increased slowly. A new ordered basis structure was gradually developed into carbon fiber.

Initial Stage Carbonization of γ-Fe(100) Surface in C2H2 under High Temperature: A Molecular Dynamic Simulation

In the present work, initial stage carbonization of γ-Fe(100) surface in C2H2 from 1000 K to 1600 K has been investigated by a molecular dynamic (MD) simulation, based on which the atomic mechanism of initial stage carbonization was provided. The absorption of C and H atoms during the carbonization process under different temperatures was analyzed. The related distributions of C and H atoms in carbonized layer were provided. The results manifested that higher temperature enhanced the inward diffusion of C and H, meanwhile caused the desorption of H atom. Furthermore, the effect of preset polycrystal γ-Fe on the carbonization process has been discussed, indicating a promoting role to the absorption and inner diffusion of C and H atom. The results of this study may support the optimal design of high-performance steel to some extent.

Characterization of Physical Properties for Activated Carbon from Garlic Skin

Abstrak. Karbon aktif yang berasal dari biomassa telah menjadi bahan material dasar yang sudah digunakan secara luas untuk berbagai aplikasi eperti penyerapan, absorben, elektroda, penyimpan energi, dan aplikasi lainnya. Oleh karena itu perlu untuk pengoptimalkan sumber mentah karbon aktif berbiaya rendah dan memiliki porositas yang tinggi. Biomassa kulit bawang putih sebagai bahan dasar pembuatan karbon aktif melalui proses pra-karbonisasi, aktivasi kimia dengan aktivator KOH dan ZnCl2 dengan masing-masing kosentrasi sebesar 0,25 M, 0,5 M, dan 0,75 M dan tanpa aktivator kimia. Proses karbonisasi dengan suhu 600°C dialiri gas nitrogen dan diaktivasi fisika dengan suhu 850°C. Penyusutan massa karbon sebesar 29,4%. Nilai densitas dari elektroda karbon untuk aktivator KOH dengan kosentrasi 0,5M yaitu 0,64 g.cm-3dan untuk aktivator ZnCl2 dengan kosentrasi 0,5M yaitu 0,71 g.cm-3. Gugus fungsi yang dimiliki elektroda kulit bawang putih diidentifikasi sebagai C-C, C C (alkuna), C-H (alkana), dan (O-H) yaitu pada bilangan gelombang 1600 cm-1, 1500 cm-1, 2950 cm-1 dan 2900-3600 cm-1. Hasil penelitian menunjukkan bahwa pada aktivator KOH dan ZnCl2 dengan kosentrasi 0,5 M kondisi terbaik untuk variasi guna menunjang pengoptimalkan sumber mentah karbon aktif dan bisa digunakan dalam berbagai apliasi yang lebih luas. Abstract. Activated carbon derived from biomass has become a basic material that has been used widely for various applications such as absorption, absorbent, electrodes, energy storage, and other applications. Therefore, it is necessary to optimize the raw source of activated carbon which is low cost and has high porosity. Garlic skin biomass as a basic material for making activated carbon through a pre-carbonization process, chemical activation with KOH and ZnCl2 activators with concentrations of 0,25 M, 0,5 M, and 0,75 M respectively and without chemical activators. The carbonization process with a temperature of 600°C is flowed with nitrogen gas and is physically activated at a temperature of 850°C. Shrinkage of carbon by 29.4%. The density value of the carbon electrode for the KOH activator with a concentration of 0.5M is 0.64 g.cm-3 and for the ZnCl2 activator with a concentration of 0,5M is 0,71 g.cm-3. The functional groups possessed by the garlic skin electrode were identified as C-C, C = C (alkynes), C-H (alkanes), and (O-H), namely at the wave numbers 1600 cm-1, 1500 cm-1, 2950 cm-1 and 2900-3600 cm-1. The results showed that the KOH and ZnCl2 activators with a concentration of 0.5 M were the best conditions for variation in order to optimize the raw source of activated carbon and could be used in a wider variety of applications.

The effect of carbonization on the wood anatomy of Sclerolobium paniculatum Vogel

Considering the extraordinary diversity of the Brazilian Cerrado and the difficulties related to the inspection of environmental crimes, knowing the wood and charcoal anatomy of widely exploited species is important. Thus, this study aimed to verify the anatomical characteristics of the wood and charcoal of Sclerolobium paniculatum. Therefore, anatomical characterizations of the wood and the charcoal produced were performed in order to compare the characteristics of both materials and observe any possible changes in the anatomical properties after carbonization. The results exposed that the qualitative anatomical characteristics of S. paniculatum wood can be maintained after the carbonization process. However, quantitatively, the carbonization increased the vessel frequency value and height and width of rays, despite reducing the frequency of rays. The diameter of the vessels was not altered by carbonization. This characterization of the species can then serve as a database for future identification of charcoal produced with this wood. In addition, it can encourage increasing the quality of inspection and consequently reducing the illegal exploitation of the species in natural environments.

Waste Tire Heat Treatment to Prepare Sulfur Self-Doped Char: Operando Insight into Activation Mechanisms Based on the Char Structures Evolution

Waste tire (WT) can be heat-treated to be high-quality sulfur self-doped char via pyrolysis and K2FeO4-assisted activation processes. This work aimed at further studying the activation mechanisms based on the char structures evolution by operando experimental method. Activation treatment process (from 50 °C to 800 °C and then held for 3 h) was divided into six typical stages (S1–S6) and consisted of carbonization process (S1–S4) and effective activation process (S4–S6). During the carbonization process, the specific capacitance only increased from 0.2 F/g to 12.4 F/g, aromatic ring systems and alkyl-aryl C-C bonds generated, S 2p3/2 (sulphide bridge) was mainly gradually consumed. During the effective activation process, the specific capacitance hugely increased from 12.4 F/g to 112.5 F/g, aromatic ring systems and alkyl-aryl C-C bonds turned to ordered graphitic char. The pores massively generated from S4 to S5, while micropores partly formed to larger and mesopores+macropores fractionally converting to smaller from S5 to S6. Besides, both S 2p3/2 and S 2p5/2 (sulphone bridge) were enriched after S5. Furthermore, the key structural parameters for huge improvement of specific capacitance were found and it further revealed that mesopores+macropores possessed stronger promotion effect than micropores and S 2p3/2 was more beneficial than S 2p5/2.

Synthesis of activated carbon electrodes from date seeds with a variety of separators for supercapacitor cell applications

Abstrak. Karbon aktif yang berasal dari biomassa telah menjadi bahan elektroda paling kompetitif untuk superkapasitor karena sifatnya yang terbarukan dan berkelanjutan. Upaya optimalisasi dilakukan untuk proses pembuatan sel superkapasitor dengan memvariasikan separator agar dapat memperoleh kapasitansi spesifik yang tinggi. Biomassa biji kurma sebagai bahan dasar pembuatan elektroda karbon melalui proses prakarbonisasi, aktivasi kimia dengan aktivator KOH 0,3M, proses karbonisasi dengan suhu 650oC dialiri gas nitrogen. Penyusutan massa karbon sebesar 24,59%. Nilai densitas dari elektroda karbon setelah dilakukan proses karbonisasi adalah 0,852 g cm-3. Analisis struktur mikro menunjukkan bahwa elektroda karbon bersifat amorf ditunjukkan dengan adanya puncak pada sudut 2θ sekitar 24o dan 44o. Kapasitansi spesifik ditentukan dengan metode Cyclic Voltametry dan didapati sebesar 217,22; 176,18; dan 82,8 F/g masing-masing untuk variasi separator kertas whatman, kertas saring, dan membran telur ayam. Hasil penelitian menunjukkan bahwa pada kertas whatman merupakan separator terbaik untuk elektroda karbon dari biji kurma. Oleh karena itu karbon aktif yang dibuat dari biji kurma dengan biaya rendah, ketersedian mudah, dan berkelanjutan dapat diaplikasikan sebagai bahan elektroda untuk superkapasitor.Abstract. Activated carbon derived from biomass has become the most competitive electrode material for supercapacitors due to its renewable and sustainable nature. Optimization efforts are made for the process of making supercapacitor cells by varying the separator in order to obtain a high specific capacitance. Date seed biomass as the basic material for making carbon electrodes through a pre-carbonization process, chemical activation with a KOH activator of 0.3M, the carbonization process at a temperature of 650oC flowed with nitrogen gas. Shrinkage of carbon by 24.59%. The density value of the carbon electrode that was carried out by the carbonization process was 0.852 g.cm-3. The microstructure analysis showed that the carbon electrode was amorphous indicated by the presence of a peak at an angle of 2θ around 24o and 44o. Specific capacitance was determined by the Cyclic Voltametry method and was found to be 217.22, 176.18, and 82.8 F/g respectively for the Whatman paper, filter paper, and chicken egg membrane separator variations. The results showed that whatman paper was the best separator for carbon electrodes from date palm seeds. Therefore, activated carbon made from date seeds with low cost, easy availability, and sustainability can be applied as an electrode material for supercapacitors.Keywords: Date seed, Activated Carbon, Supercapacitor, Carbon Electrode, Separator