Microstructural tailoring of porous few-layer graphene-like biochar from kitchen waste hydrolysis residue in molten carbonate medium: Structural evolution and conductive additive-free supercapacitor application

Efficient Extraction of Phenols from Coal Tar and Preparation of Phenolic Resin-Based Porous Carbon for Advanced Supercapacitor Application

Developing simple and efficient extraction methods for phenolic substances from coal tar, which facilitate their direct transformation into high-performance electrode materials, holds considerable practical significance. In this study, amide-zinc chloride deep eutectic solvents are employed for efficient phenol extraction. The optimal phenol extraction process is subsequently investigated, and it is found that the robust hydrogen bonding interactions between solvents and phenols significantly enhance extraction efficiency. Notably, without the need for back-extraction, formaldehyde and tetraethyl orthosilicate are added to obtain phenolic resin, which can subsequently be directly carbonized to fabricate hydrangea-like porous carbon. The carbonization mechanism of the phenolic resin is studied, and the templating and activating roles of tetraethyl orthosilicate and zinc chloride assist in the formation of this unique structure. Furthermore, the flexible supercapacitor assembled using the prepared porous carbon and gel electrolyte achieves a high energy density of 31.0 Wh kg-1 and demonstrates broad temperature applicability ranging from -25 to 100 °C. This work directly converts the extracted phenolic compounds into phenolic resin and shows potential for fabricating porous carbon materials with diverse structures and enhanced capacitive performance.

A clean method for controlling pore structure development in potassium activation systems to improve CO2 adsorption properties of biochar

The conventional activator KOH poses issues of pollution and equipment corrosion in activated carbon production. This study proposes a low-cost, one-step synthetic method for the cleaner production of biomass-derived carbon. CO2 adsorbents with high specific surface area (550-1725 m2/g) and superior adsorption performance were prepared using a KCl-assisted activation process with three activators (KOH, KHCO3, K2CO3). The results demonstrated that KCl promoted the formation of a molten salt system in all the different activation processes, which improved the activation efficiency through the formation of a liquid-phase environment. The results show that KCl possesses both pore-creating and pore-modulating properties. We investigated the performance of the two properties and analyzed the influencing factors. Specifically, KCl increases the specific surface area and porosity of the material and also selectively increases the ultramicroporous content. The development and regulation of pore structure can be achieved through the selection of activator, temperature, and dosage of KCl. With the addition of KCl, the performance of the adsorbents in all systems improved due to optimized pore structure. Among them, the sample PB700-4 from KCl-assisted KHCO3 activation exhibited the highest CO2 adsorption of 4.51 mmol/g at 25 °C and 1 bar. The best sample, PC700-3, from the KCl-assisted K2CO3 activation system had an adsorption capacity of 4.48 mmol/g, which was superior to the best sample, PH800-3 (4.28 mmol/g), obtained from KCl-assisted KOH activation. Given the low corrosiveness and toxicity of KHCO3, K2CO3, and KCl, this study introduces a novel approach for cleaner production of activated carbons and advancements in gas separation technology.

Sustainable valorisation of kitchen waste through greenhouse solar drying and microwave pyrolysis- technology readiness level for the production of biochar

This study proposes an integrated and sustainable approach for the effective conversion of kitchen waste into valuable products through a two-step process. The primary step involves the implementation of greenhouse solar drying to reduce the moisture content of kitchen waste. The secondary step implies microwave pyrolysis for effective degradation of kitchen waste to biooil, biogas and biochar. Biooil and biogas can be used as renewable fuel source. Biochar can be used as soil amendment. Selection of atmospheric conditions for biochar preparation is discussed, highlighting its crucial role in biochar characteristics. This article highlights, technology readiness level of biochar production from kitchen waste to assess the economic viability for the scalability of the process. In this entirety, the conversion of kitchen waste to valuable products through microwave pyrolysis has significant potential to address the challenges posed by high moisture content and heterogenous nature. With continued research and innovation, it is possible to develop a wide array of value-added products from kitchen waste, ultimately leading to a more eco-friendly and economic approach to waste management.

Graphical Abstract

Deep learning prediction and experimental investigation of specific capacitance of nitrogen-doped porous biochar

N-doped porous biochar is a promising carbon material for supercapacitor electrodes due to its developed pore structure and high chemical activity which greatly affect the capacitive performance. Predicting the capacitance and exploring the most influential factors are of great significance because it can not only avoid the trial-and-error experiments but also provide guidance for the synthesis of biochar with the aim of capacitance enhancement. In this study, a CNN model with ReLU activation function was established using DenseNet architecture for specific capacitance prediction. The importance and impacts of the physiochemical properties of N-doped porous biochar to the capacitance were revealed. With the guidance of the model, N-doped porous biochar samples with high capacitance were synthesized, the data of which were further used for model validation. This study provides not only a deep learning model which can be used in practice for capacitance prediction but also directions for the synthesis of N-doped porous biochar with high capacitive performance.

Mechanisms of adsorption and functionalization of biochar for pesticides: A review

Agricultural production relies heavily on pesticides. However, factors like inefficient application, pesticide resistance, and environmental conditions reduce their effective utilization in agriculture. Subsequently, pesticides transfer into the soil, adversely affecting its physicochemical properties, microbial populations, and enzyme activities. Different pesticides interacting can lead to combined toxicity, posing risks to non-target organisms, biodiversity, and organism-environment interactions. Pesticide exposure may cause both acute and chronic effects on human health. Biochar, with its high specific surface area and porosity, offers numerous adsorption sites. Its stability, eco-friendliness, and superior adsorption capabilities render it an excellent choice. As a versatile material, biochar finds use in agriculture, environmental management, industry, energy, and medicine. Added to soil, biochar helps absorb or degrade pesticides in contaminated areas, enhancing soil microbial activity. Current research primarily focuses on biochar produced via direct pyrolysis for pesticide adsorption. Studies on functionalized biochar for this purpose are relatively scarce. This review examines biochar's pesticide absorption properties, its characteristics, formation mechanisms, environmental impact, and delves into adsorption mechanisms, functionalization methods, and their prospects and limitations.

Cottonseed meal derived porous carbon prepared via the protease pretreatment and reduced activator dosage carbonization for supercapacitor

The high catalytic activity and specificity of enzymes can be used to pretreat biomass. Herein, the resourceful, reproducible, cheap, and crude protein-rich cottonseed meal (CM) is selected as a precursor and the protease in the K2CO3-KHCO3 buffer solution is used as the enzyme degradation substance to pretreat CM. The crude protein content is significantly reduced by the protease degradation, and, meanwhile, it results in a looser and porous structure of CM. What is more, it significantly reduces the amount of activator. In the subsequent carbonization process, the K2CO3-KHCO3 in the buffer solution is also used as an activating agent (the mass ratio of CM to activator is 2:1), and after carbonization, the O, S, and N doped porous carbon is obtained. The optimized PCM-800-4 exhibits high heteroatom contents and a hierarchical porous structure. The specific capacitance of the prepared porous carbon reaches up to 233 F g-1 in 6M KOH even when 10 mg of active material is loaded. In addition, a K2CO3-KHCO3/EG based gel electrolyte is prepared and the fabricated flexible capacitor exhibits an energy density of 15.6 Wh kg-1 and a wide temperature range (-25 to 100 °C). This study presents a simple enzymatic degradation and reduced activator dosage strategy to prepare a cottonseed meal derived carbon material and looks forward to preparing porous carbon using other biomass.

Valorization of Biomass-Derived Polymers to Functional Biochar Materials for Supercapacitor Applications via Pyrolysis: Advances and Perspectives

Polymers from biomass waste including plant/forest waste, biological industrial process waste, municipal solid waste, algae, and livestock are potential sources for renewable and sustainable resources. Converting biomass-derived polymers to functional biochar materials via pyrolysis is a mature and promising approach as these products can be widely utilized in many areas such as carbon sequestration, power production, environmental remediation, and energy storage. With abundant sources, low cost, and special features, the biochar derived from biological polymeric substances exhibits great potential to be an alternative electrode material of high-performance supercapacitors. To extend this scope of application, synthesis of high-quality biochar will be a key issue. This work systematically reviews the char formation mechanisms and technologies from polymeric substances in biomass waste and introduces energy storage mechanisms of supercapacitors to provide overall insight into the biological polymer-based char material for electrochemical energy storage. Aiming to enhance the capacitance of biochar-derived supercapacitor, recent progress in biochar modification approaches including surface activation, doping, and recombination is also summarized. This review can provide guidance for valorizing biomass waste to functional biochar materials for supercapacitor to meet future needs.