Heteroatom-Doped Hierarchically Porous Biochar for Supercapacitor Application and Phenol Pollutant Remediation

Statistics design for the synthesis optimization of lignin-sulfonate sulfur-doped mesoporous carbon materials: promising candidates as adsorbents and supercapacitors materials

This study employed lignin-sulfonated (LS) to develop biobased carbon materials (LS-Cs) through a sulfur-doping approach to enhance their physicochemical properties, adsorption capabilities, and energy storage potentials. Various characterization techniques, including BET surface area analysis, SEM imaging, XPS, Raman spectroscopy, and elemental composition (CHNS), were employed to assess the quality of the LS-Cs adsorbent and electrode samples. Response Surface Methodology (RSM) was utilized for optimizing the two main properties (specific surface area, ABET, and mesopore area, AMESO) by evaluating three independent factors (i.e., activation temperature, ZnCl2:LS ratio, and sulfur content). According to the statistical analysis, ABET and AMESO were affected by ZnCl2 and sulfur content, while the pyrolysis temperature did not affect the responses in the studied conditions. It was found that increasing the ZnCl2 and sulfur contents led to an increment of the ABET and AMESO values. The LS-C materials exhibited very high ABETvalues up to 1993 m2 g-1 and with predominantly mesoporous features. The S-doping resulted in LS-Cs with high sulfur contents in their microstructures up to 15% (wt%). The LS-C materials were tested as adsorbents for sodium diclofenac (DCF) adsorption and reactive orange 16 dye (RO-16) and as electrodes for supercapacitors. The LS-Cs exhibited excellent adsorption capacity values for both molecules (197-372 mg g-1) for DCF, and (223-466 mg g-1) for RO-16. When tested as electrodes for supercapacitors, notably, LS-C3, which is a doped sample with sulfur, exhibited the best electrochemical performance, e.g. high specific capacitance (156 F/g at 50 mV/s), and delivered an excellent capacitance after 1000 cycles (63 F/g at 1 A/g), which denotes the noteworthy capacitive behavior of the S-doped electrode. Thus, the present work suggests an eco-friendly resource for developing effective, productive carbon materials for adsorbent and electrodes for SC application. However, further studies on the complete application of these materials as adsorbents and electrodes are needed for a deeper understanding of their behavior in environmental and energy storage applications.

Nano-Biochar Prepared from High-Pressure Homogenization Improves Thermal Conductivity of Ethylene Glycol-Based Coolant

As an environmentally friendly material, biochar is increasingly being utilized in the field of heat transfer and thermal conduction. In this study, nano-biochar was prepared from high-pressure homogenization (HPH) using sesame stalks as the raw material. It was incorporated into ethylene glycol (EG) and its dispersion stability, viscosity, and thermal conductivity were investigated. The nano-biochar was stably dispersed in EG for 28 days. When the concentration of the nano-biochar added to EG was less than 1%, the impact on viscosity was negligible. The addition of 5 wt.% nano-biochar to EG improved the thermal conductivity by 6.72%, which could be attributed to the graphitized structure and Brownian motion of the nano-biochar. Overall, nano-biochar has the potential to be applied in automotive thermal management.

Water hyacinth derived hierarchical porous biochar absorbent: Ideal peroxydisulfate activator for efficient phenol degradation via an electron-transfer pathway

In this paper, a facile hydrothermal pretreatment and molten salt activation route was presented for preparing a self-doped porous biochar (HMBC) from a nitrogenous biomass precursor of water hyacinth. With an ultrahigh specific surface area (2240 m2 g-1), well-developed hierarchical porous structure, created internal structural defects and doped surface functionalities, HMBC exhibited an excellent adsorption performance and catalytic activity for phenol removal via peroxydisulfate (PDS) activation. Specifically, the porous structure promoted the adsorption of PDS on HMBC, forming a highly active HMBC/PDS* complex and thereby increasing the oxidation potential of the system. Meanwhile, the carbon defective structure, graphitic N and CO groups enhanced the electron transfer process, favoring the HMBC/PDS system to catalyze phenol oxidation via an electron transfer dominated pathway. Thus, the system degraded phenol effectively with an ultralow activation energy of 4.9 kJ mol-1 and a remarkable oxidant utilization efficiency of 8.2 mol mol-oxidant-1 h-1 g-1. More importantly, the system exhibited excellent resistance to water quality and good adaptability for decontaminating different organic pollutants with satisfactory mineralization efficiency. This study offers valuable insights into the rational designing of a low-cost biochar catalyst for efficient PDS activation towards organic wastewater remediation.

Effect of Surface Modification by Oxygen-Enriched Chemicals on the Surface Properties of Pine Bark Biochars

Sustainable waste utilization techniques are needed to combat the environmental and economic challenges faced worldwide due to the rising population. Biochars, due to their unique surface properties, offer opportunities to modify their surface to prepare application-specific materials. The aim of this research is to study the effects of biochar surface modification by oxidizing chemicals on biochar properties. Pine bark biochar was modified with sulfuric acid, nitric acid, hydrogen peroxide, ozone, and ammonium persulfate. The resulting biochars’ pH, pH at the point of zero charges, and concentration of acidic and basic sites were determined using laboratory experimentation. Instrumental techniques, such as infrared and X-ray photoelectron spectroscopy, were also obtained for all biochar samples. X-ray photoelectron spectra showed that oxygen content increased to 44.5%, 42.2%, 33.8%, 30.5%, and 14.6% from 13.4% for sulfuric acid, ozone, nitric acid, hydrogen peroxide, and ammonium persulfate, respectively. The pH at the point of zero charges was negatively correlated with the difference in concentration of acidic and basic sites in biochar samples, as well as the summation of peak components representing C=O double bonds and carboxylic groups. The results suggest that designer biochars can be prepared by understanding the interaction of oxygenated chemicals with biochar surfaces.

Electrochemical Performance of Chemically Activated Carbons from Sawdust as Supercapacitor Electrodes

Activated carbons (ACs) have been the most widespread carbon materials used in supercapacitors (SCs) due to their easy processing methods, good electrical conductivity, and abundant porosity. For the manufacture of electrodes, the obtained activated carbon based on sawdust (karagash and pine) was mixed with conductive carbon and polyvinylidene fluoride as a binder, in ratios of 75% activated carbon, 10% conductive carbon black, and 15% polyvinylidene fluoride (PVDF) in an N-methyl pyrrolidinone solution, to form a slurry and applied to a titanium foil. The total mass of each electrode was limited to vary from 2.0 to 4.0 mg. After that, the electrodes fitted with the separator and electrolyte solution were symmetrically assembled into sandwich-type cell construction. The carbon's electrochemical properties were evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge (CGD) studies in a two-electrode cell in 6M KOH. The CV and CGD measurements were realized at different scan rates (5-160 mV s^-1) and current densities (0.1-2.0 A g^-1) in the potential window of 1 V. ACs from KOH activation showed a high specific capacitance of 202 F g^-1 for karagash sawdust and 161 F g^-1 for pine sawdust at low mass loading of 1.15 mg cm^-2 and scan rate of 5 mV s^-1 in cyclic voltammetry test and 193 and 159 F g^-1 at a gravimetric current density of 0.1 A g^-1 in the galvanostatic charge-discharge test. The specific discharge capacitance is 177 and 131 F g^-1 at a current density of 2 A g^-1. Even at a relatively high scan rate of 160 mV s^-1, a decent specific capacitance of 147 F g^-1 and 114 F g^-1 was obtained, leading to high energy densities of 26.0 and 22.1 W h kg^-1 based on averaged electrode mass. Surface properties and the porous structure of the ACs were studied by scanning electron microscopy, energy-dispersive X-ray analysis, Raman spectroscopy, and the Brunauer-Emmett-Teller method.