Preparation and Characterization of Physically Activated Carbon and Its Energetic Application for All-Solid-State Supercapacitors: A Case Study

Biomass-derived activated carbons have gained significant attention as electrode materials for supercapacitors (SCs) due to their renewability, low-cost, and ready availability. In this work, we have derived physically activated carbon from date seed biomass as symmetric electrodes and PVA/KOH has been used as a gel polymer electrolyte for all-solid-state SCs. Initially, the date seed biomass was carbonized at 600 °C (C-600) and then it was used to obtain physically activated carbon through CO₂ activation at 850 °C (C-850). The SEM and TEM images of C-850 displayed its porous, flaky, and multilayer type morphologies. The fabricated electrodes from C-850 with PVA/KOH electrolytes showed the best electrochemical performances in SCs (Lu et al. Energy Environ. Sci., 2014, 7, 2160) application. Cyclic voltammetry was performed from 5 to 100 mV s^-1, illustrating an electric double layer behavior. The C-850 electrode delivered a specific capacitance of 138.12 F g^-1 at 5 mV s^-1, whereas it retained 16 F g^-1 capacitance at 100 mV s^-1. Our assembled all-solid-state SCs exhibit an energy density of 9.6 Wh kg^-1 with a power density of 87.86 W kg^-1. The internal and charge transfer resistances of the assembled SCs were 0.54 and 17.86 Ω, respectively. These innovative findings provide a universal and KOH-free activation process for the synthesis of physically activated carbon for all solid-state SCs applications.

Diamond-like Carbon Patterning by the Submerged Discharge Plasma Technique via Soft Solution Processing

Submerged plasma-assisted discharge direct patterning of diamond-like carbon (DLC) onto the silicon substrate in ambient conditions has succeeded as a new and novel soft solution process. In this environmentally benign technique, a copious amount of pure ethanol (ca. 4 mL) was locally activated with a maximum of ca. 0.23 mkWh by an as-electrochemically synthesized ultrasharp tungsten tip. With the assisted submerged plasma, the decomposed ethanol molecules are anodically patterned directly onto the silicon substrate in ambient conditions. The physical nature of DLC patterns was accessed by profilometry, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy analysis. Furthermore, Fourier-transform infrared, Raman, and X-ray photoelectron spectra were analyzed for chemical compositions and structures, such as surface functionalization, carbon-carbon bonding, and sp²-sp³ ratio, respectively. From a Berkovich-configured nanoindentation analysis, Young's modulus and hardness have shown increasing trend with increasing sp³-sp² ratio in DLC patterns of 68.5 and 2.8 GPa, respectively. From the electrochemical cyclovoltammetry analysis, a maximum areal specific capacitance of 205.5 μF/cm² has been achieved at a scan rate of 5 mV/s. The one-step, green, and environmentally sustainable approach of rapid formation of DLC patterns is thus a promising technique for various carbon-based electrode fabrication processes.

Migration: A Neglected Potential Contribution of HCl-Oxidized Au(0)

In this study, the typical oxidation process of Au/C catalysts exposed to HCl is presented. Although the process violates the standard electrode potentials, the "oxidized" tendency of Au(0) species is analyzed. This oxidation behavior can only be triggered over the Au/C sample within residual cationic Au species, and terminated over the completely metallic Au(0)/C sample. This study demonstrates that the presence of surface chlorination species cannot facilitate the oxidation of Au(0) and Au(I) when the sample is treated with HCl alone, which excludes the oxidation paths of: Au(0) → Au(III) and Au(I) → Au(III). The reported "HCl-oxidized Au(0)" behavior is partially caused by the migration of Au(III) species in the carbon bulk-phase, which occurs outside the XPS detection limit region and into the detection limit rather than the "HCl-oxidized Au(0)" itself. The mechanism of driving the bulk-phase Au(III) migrated from the steady destabilized state to the carbon surface is then studied. This study demonstrates that the migration of Au cannot be neglected behind the curious oxidation phenomenon by HCl, which provides a new perspective for the oxidation of other noble metals by HCl.

The effectiveness and adsorption mechanism of iron-carbon nanotube composites for removing phosphate from aqueous environments

This study successfully employed iron-carbon nanotubes (Fe-CNT) to recover phosphate (P) from water. We examined the effects of various iron concentrations denoted by Fe-CNT-1 and Fe-CNT-2 on P removal and compared them with pristine carbon nanotubes (CNTs). The adsorption capacity of Fe-CNTs was much better than pristine CNTs. According to the high adsorption capacity, Fe-CNT-2 sample was very effective for P recovery and exhibits ∼7 times higher P removal efficiency than that of pristine CNTs. The characterization of the as-obtained adsorbent (Fe-CNT-2) and pristine CNTs were performed using X-ray diffraction, Brunauer-Emmett-Teller method, Field emission scanning electron microscope coupled with energy-dispersive spectroscopy detector (FESEM-EDS), X-ray photoelectron spectroscopy and Transmission electron microscopy. Results demonstrated that iron oxide nanoparticles were successfully deposited on the surface of CNT. The adsorption kinetics and isotherm studies for P removal showed pseudo-second-order rate constants (R² > 0.99) and the Langmuir isotherm (R² > 0.99) respectively, thus revealing that the nature of adsorption was chemisorption. The estimated Langmuir adsorption capacity of Fe-CNT-2 was 36.5 mgP/g or 112 mg PO₄/g at an equilibrium time of 3 h. The ionic strength provided by SO₄^2-, NO₃^-, and Cl^- demonstrated no considerable influence on phosphate adsorption. Moreover, the P adsorbed Fe-CNT-2 was efficiently recovered with different concentrations of desorbing reagents, such as NaOH and NaCO₃^2-. Moreover, the findings of X-ray photoelectron spectroscopy (XPS) analysis demonstrated that OH group played a major role in the P removal by Fe-CNT-2. The findings of this study demonstrate that Fe-CNT-2 had a great deal of application as an effective and stable adsorbent for the P recovery from aquatic environments.

Modulating the surface structure of nanodiamonds to enhance the electronic metal–support interaction of efficient ruthenium catalysts for levulinic acid hydrogenation

The annealed nanodiamond-supported Ru NPs with high electron density exhibit efficient activity and high stability for hydrogenation of levulinic acid.

The Effect of sp2 Content in Carbon on Its Catalytic Activity for Acetylene Hydrochlorination

We report the influence of sp² content in carbon catalyst on the catalytic activity for acetylene hydrochlorination. Nanodiamonds (NDs) were used as the precursor and calcinated under different temperatures. The resulting ND500, ND700, ND900, and ND1100 catalysts were characterized, and the sp² content increased with increasing calcination temperature. The specific activities of the catalysts first increased and then decreased with increasing sp² content. The highest catalytic activity could be obtained in the ND-900 catalyst with a sp² value of 43.9%. The density functional theory results showed that the adsorption sites for acetylene and hydrogen chloride were located at the interface between sp² and sp³ configuration.

The reaction mechanism of acetylene hydrochlorination on defective carbon supported ruthenium catalysts identified by DFT calculations and experimental approaches

The electron density of ruthenium ions in RuCl3/AC-D catalyst increases, which reduces the energy barrier of the main reaction and inhibits the side reactions.

Mixed sp2-sp3 Nanocarbon Materials: A Status Quo Review

Carbon nanomaterials with a different character of the chemical bond-graphene (sp2) and nanodiamond (sp3)-are the building bricks for a new class of all-carbon hybrid nanomaterials, where the two different carbon networks with sp3 and sp2 hybridization coexist, interacting and even transforming into one another. The extraordinary physiochemical properties defined by the unique electronic band structure of the two border nanoallotropes ensure the immense application potential and versatility of these all-carbon nanomaterials. The review summarizes the status quo of sp2 - sp3 nanomaterials, including graphene/graphene-oxide-nanodiamond composites and hybrids, graphene/graphene-oxide-diamond heterojunctions, and other sp2-sp3 nanocarbon hybrids for sensing, electronic, and other emergent applications. Novel sp2-sp3 transitional nanocarbon phases and architectures are also discussed. Furthermore, the two-way sp2 (graphene) to sp3 (diamond surface and nanodiamond) transformations at the nanoscale, essential for innovative fabrication, and stability and chemical reactivity assessment are discussed based on extensive theoretical, computational and experimental studies.

Constructing green mercury-free catalysts with single pyridinic N species for acetylene hydrochlorination and mechanism investigation

A green bifunctional polymer for acetylene hydrochlorination is directly used as a catalyst and then used as a precursor to prepare an N-doped carbon catalyst.

Progress and Challenges of Mercury-Free Catalysis for Acetylene Hydrochlorination

Activated carbon-supported HgCl2 catalyst has been used widely in acetylene hydrochlorination in the chlor-alkali chemical industry. However, HgCl2 is an extremely toxic pollutant. It is not only harmful to human health but also pollutes the environment. Therefore, the design and synthesis of mercury-free and environmentally benign catalysts with high activity has become an urgent need for vinyl chloride monomer (VCM) production. This review summarizes research progress on the design and development of mercury-free catalysts for acetylene hydrochlorination. Three types of catalysts for acetylene hydrochlorination in the chlor-alkali chemical industry are discussed. These catalysts are a noble metal catalyst, non-noble metal catalyst, and non-metallic catalyst. This review serves as a guide in terms of the catalyst design, properties, and catalytic mechanism of mercury-free catalyst for the acetylene hydrochlorination of VCM. The key problems and issues are discussed, and future trends are envisioned.

Synergistic effect of two action sites on a nitrogen-doped carbon catalyst towards acetylene hydrochlorination

Whether the reaction pathway is steady or dynamic over the whole life cycle of a catalyst process can facilitate our understanding of its catalytic behavior. Herein, the dynamic reaction pathways of nitrogen-doped carbon catalysts are investigated in acetylene hydrochlorination. When triggered, the reaction follows the Langmuir-Hinshelwood mechanism with pyrrolic N and pyridinic N as dual active sites. However, pyridinic N is deactivated first, due to the strong adsorption of hydrogen chloride, causing the reaction to further run with pyrrolic N as the single active site and follow the Eley-Rideal mechanism. This work provides a new promising way to study the catalytic behavior of nitrogen-doped carbon catalysts.

Active centre and reactivity descriptor of a green single component imidazole catalyst for acetylene hydrochlorination

A green catalyst for acetylene hydrochlorination yielding a VCM is presented using imidazole as a single component metal-free catalyst. The mechanisms and reactivities of imidazole-catalyzed acetylene hydrochlorination have been investigated by combined computational and experimental studies. The electronic effects of ortho-substituents on the reactivities have also been investigated. Through theoretical calculations and experimental studies, the nitrogen-atom including a lone pair active site of single component imidazole for metal-free acetylene hydrochlorination is proposed. It is suggested that the nitrogen-atom including a lone pair of imidazole adsorbs an HCl molecule to form an imidazole-HCl complex, which serves as the active catalyst to participate in the reaction process of acetylene hydrochlorination. Besides, the results show that C₂H₂ assists in the electrophilic addition of HCl, undergoing an almost planar six-membered ring transition state. Computational studies on the ortho-substitution of the active sites will have an important impact on the catalytic efficiency.

Nitrogen-doped porous carbon from biomass with superior catalytic performance for acetylene hydrochlorination

Acetylene hydrochlorination is an important aspect of the industrial synthesis of polyvinyl chloride, but it requires a toxic mercury chloride catalyst. Here we report a green, highly efficient and low cost nitrogen-doped soybean meal carbon (SBMC) catalyst obtained from the simple carbonization of biomass soybean meal (SBM) in the presence of zinc chloride. This material exhibits excellent catalytic performance during acetylene hydrochlorination, with an initial acetylene conversion greater than 99% and 98% selectivity for vinyl chloride at 200 °C over 110 h. Analyses by X-ray photoelectron spectroscopy and temperature programmed desorption as well as catalytic activity evaluations show that pyridinic species are the active sites for hydrogen chloride, while pyrrolic N species are the main active sites for acetylene. An analysis of charge calculations based on model catalysts further indicates that the activity of pyrrolic N species essentially determines the performance of the SBMC catalyst. This investigation of the mechanism of acetylene hydrochlorination over SBMC confirms that such nitrogen-doped catalysts have two different active sites for the adsorption and activation of hydrogen chloride and acetylene molecules. This mechanism is different from that associated with metal chloride catalysts such as HgCl₂. This SBMC catalyst is a potential alternative to HgCl₂@AC catalysts for vinyl chloride synthesis and suggests a new means of designing carbon catalysts with basic surfaces for acetylene hydrochlorination.

A green, highly efficient and low-cost nitrogen-doped soybean metal carbon (SBMC) catalyst obtained from the simple carbonization of biomass soybean meal (SBM) in the presence of zinc chloride.

Boron-doped carbon nanodots dispersed on graphitic carbon as high-performance catalysts for acetylene hydrochlorination

Boron-doped carbon nanodot materials, comprising evenly distributed BC₃-nanodots in a layered carbon matrix, are prepared through a pre-assembly assisted carbonization synthetic strategy.

Generalized reactivity descriptor of defective carbon catalysts for acetylene hydrochlorination: the ratio of sp2 : sp3 hybridization

Surface engineering of sp² and sp³ oriented carbons with optimized hybridization configuration makes excellent metal free catalysts for acetylene hydrochlorination