Investigation on the Physical and Chemical Properties of Hydrochar and Its Derived Pyrolysis Char for Their Potential Application: Influence of Hydrothermal Carbonization Conditions

Hydrothermal carbonization (HTC) is an aqueous-phase procedure to prepare charred material using biomass. To obtain a charred material with high porosity, ash content, and thermal recalcitrance, it is necessary to investigate the influence of HTC conditions (peak temperature, retention time, and feedstock type) on the properties of hydrochar and its derived pyrolysis char (HDPC). Additionally, the relative importance of these conditions for the selected properties was also investigated by heterogeneity index. The results indicated that the properties of both hydrochar and HDPC samples were greatly influenced by the HTC process. The ash content and major metal elements (Na, Mg, K, and Ca) of hydrochar and HDPC samples were strongly influenced by the feedstock type; other properties, such as surface area, carbon sequestration potential, total carbon, total nitrogen, and dissolved organic carbon were moderately influenced by the feedstock type. Overall, this study provided new insights into the relative importance of different HTC conditions in the properties of hydrochar and HDPC samples, which was an important process toward obtaining a “required” charred material for environmental remediation

Novel and High-Performance Magnetic Carbon Composite Prepared from Waste Hydrochar for Dye Removal

In recent years, more and more attention has been paid to the hydrothermal liquefaction (HTL) of waste biomass for the production of bio-oil and hydrochar (a solid residue from HTL process). However, hydrochar possesses limited porosity and surface area, hindering its environmental application. In the present work, to promote the development of a sustainable application of waste biomass, waste hydrochar was activated and modified to a novel magnetic carbon composite, which exhibited high performance for dye removal from aqueous solutions. The composite possessed a saturation magnetization of 38.5 emu g^–1 at room temperature and could be facilely attracted from an aqueous solution by an external magnet. The as-prepared composite exhibited a superior malachite green (MG) adsorption capacity (476 mg g^–1), which was much higher than the known magnetic adsorbents. Our results suggested that the waste hydrochar could be efficiently transformed to a high-performance sustainable material for dye removal

MOESM1 of Methane potentials of wastewater generated from hydrothermal liquefaction of rice straw: focusing on the wastewater characteristics and microbial community compositions

Additional file 1: Table S1. Characteristics of rice straw and the following line is standard error of each value; Table S2. Number of the high-quality sequences; Figure S1. COD, TOC and pH values of HTLWW samples under different HTL conditions; Figure S2. Comparison of methane production potentials of samples 200 °C–0.5 h, 260 °C–0.5 h and 200 °C–4 h

Facile Fabrication of Magnetic Carbon Composites from Hydrochar via Simultaneous Activation and Magnetization for Triclosan Adsorption

Advanced magnetic carbon composites with high specific surface area and high microporosity are required for both environmentally and agriculturally related applications. However, more research is needed for the development of a facile and highly efficient synthesis process. In the present work, a novel approach of simultaneous activation and magnetization is proposed for the fabrication of magnetic carbon composites via the thermal pyrolysis of hydrochar (i.e., a solid residue from a hydrothermal carbonization process) that has been pretreated with mixtures of ferric chloride (FeCl₃) and zinc chloride (ZnCl₂). The main objective of this study is the investigation of the variation of characteristics of magnetic carbon composites produced at various conditions, as well as triclosan (TCS) adsorption behavior on such composites. This presented simple one-step synthesis method has the following advantages: (a) the hydrochar is activated with high surface area and pore volume (up to 1351 m²/g and 0.549 cm³/g, respectively), (b) activation and magnetization are simultaneously achieved without further modification, (c) the magnetic particles (γ-Fe₂O₃) are stable under an acidic medium (pH of 3.0 and 4.0), and (d) the products have the potential to remove TCS from aqueous solutions with a maximum adsorption capacity of 892.9 mg/g. The results indicate the effectiveness of this facile synthesis strategy in converting low-value biowaste into a functional material with high performance for pollutant removal from aqueous solutions

Demethanation Trend of Hydrochar Induced by Organic Solvent Washing and Its Influence on Hydrochar Activation

Hydrochar derived from hydrothermal carbonization (HTC) has been recognized as a promising carbonaceous material for environmental remediation. Organic solvents are widely used to extract bio-oil from hydrochar after HTC, but the effects of solvent extraction on hydrochar characteristics have not been investigated. This study comprehensively analyzed the effects of different washing times and solvent types on the hydrochar properties. The results indicate that the mass loss of hydrochar by tetrahydrofuran washing occurred mainly in the first 90 min, and the loss ratios of elements followed a descending order of H > C > O, resulting in a decrease in the H/C atomic ratio and an increase in the O/C atomic ratio. The use of various solvents for washing brought about hydrochar loss ratios in a descending order of petroleum ether < dichloromethane < acetone < tetrahydrofuran. The results from the Van Krevelen diagram and Fourier transform infrared, ¹³C nuclear magnetic resonance, and X-ray photoelectron spectroscopies further confirmed that demethanation controlled this washing process. Most importantly, the surface area of hydrochar increased after bio-oil removal via washing, which promoted the surface area development for hydrochar-derived magnetic carbon composites, but to some extent decreased the microporosity. Additionally, hydrochar washing by organic solvent has important implications for the global carbon cycle and its remediation application

Joule Heating Induced Reductive Iron–Magnesium Bimetallic Nanocomposite for Eminent Heavy Metal Removal

Fe0-based materials exhibit great power in removing heavy metals, but their passivation issues remain a challenge. Guided by the synergistic effects within bimetallic modifications, a novel reductive FeMg bimetallic nanocomposite (FeMg/NC) was constructed using flash Joule heating technology. The ultrafast heating and quenching process achieved a phase-fusional structure comprising Fe0 and Mg0 encapsulated in the resulting aromatic-carbon layer. Incorporation of highly reductive Mg0 into Fe0-based material led to an approximately 2–3 times enhancement in pollutant removal efficiency compared to monometallic nanocomposites. Experiments and theoretical calculations revealed that this augmented removal efficiency arose from the FeMg dual-site synergistic effect, facilitating the interaction between FeMg/NC and the targeted pollutants. That is, adsorption led to the directional inward diffusion of pollutants, and the outward release of electrons from this formed phase-fusion structure was accelerated via the electron delocalization effect. Therefore, FeMg/NC exhibited excellent removal capacities for typical heavy metals (including Cr(VI), Sb(V), Ni(II), and Cu(II)). This study demonstrates the flexibility of Joule heating technology for constructing bimetallic nanocomposite, which can effectively address heavy metal pollution and opens up endless possibilities for developing more impactful environmental remediation materials

Influences of Temperature and Metal on Subcritical Hydrothermal Liquefaction of Hyperaccumulator: Implications for the Recycling of Hazardous Hyperaccumulators

Waste <i>Sedum plumbizincicola</i>, a zinc (Zn) hyperaccumulator during phytoremediation, was recycled via a subcritical hydrothermal liquefaction (HTL) reaction into multiple streams of products, including hydrochar, bio-oil, and carboxylic acids. Results show approximately 90% of Zn was released from the <i>S. plumbizincicola</i> biomass during HTL at an optimized temperature of 220 °C, and the release risk was mitigated via HTL reaction for hydrochar production. The low-Zn hydrochar (∼200 mg/kg compared to original plant of 1558 mg/kg) was further upgraded into porous carbon (PC) with high porosity (930 m²/g) and excellent capability of carbon dioxide (CO₂) capture (3 mmol/g). The porosity, micropore structure, and graphitization degree of PCs were manipulated by the thermal recalcitrance of hydrochar. More importantly, results showed that the released Zn²⁺ could effectively promote the production of acetic acid via the oxidation of furfural (FF) and 5-(hydroxymethyl)-furfural (HMF). Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with negative electrospray ionization analysis confirmed the deoxygenation and depolymerization reactions and the production of long chain fatty acids during HTL reaction of <i>S. plumbizincicola</i>. This work provides a new path for the recycling of waste hyperaccumulator biomass into value-added products

Production Temperature Effects on the Structure of Hydrochar-Derived Dissolved Organic Matter and Associated Toxicity

Hydrochar is a carbonaceous material derived from hydrothermal liquefaction, and it carries good potential as a new material for environmental applications. However, little is known about the dissolved organic matter (DOM) associated with hydrochar and the consequences of its release. The relationship between the production temperature and the characteristics of DOM released from hydrochar as well as the associated biotoxicity was investigated using a suite of advanced molecular and spectroscopic tools. With the increase in production temperature, the resulted hydrochar-based DOM contained a higher content of phenols and organic acids but less sugars and furans. Meanwhile, the molecular structure of DOM shifted to lower molecular weight with higher organic contents containing <6 O atoms per compound, aromatics, and N-containing substances. While low-temperature hydrochar-derived DOM showed minimal biotoxicity, increase in production temperature to 330 °C led to a great rise in toxicity. This might be attributed to the increased contents of phenols, organic acids, and organics containing <6 O atoms and 1 N atom per compound. These results suggest that hydrochar-derived DOM have more negative impacts on the environment than the organics associated with biochar production. Such understanding highlights the importance of controlling the hydrochar production process

Production Temperature Effects on the Structure of Hydrochar-Derived Dissolved Organic Matter and Associated Toxicity

Hydrochar is a carbonaceous material derived from hydrothermal liquefaction, and it carries good potential as a new material for environmental applications. However, little is known about the dissolved organic matter (DOM) associated with hydrochar and the consequences of its release. The relationship between the production temperature and the characteristics of DOM released from hydrochar as well as the associated biotoxicity was investigated using a suite of advanced molecular and spectroscopic tools. With the increase in production temperature, the resulted hydrochar-based DOM contained a higher content of phenols and organic acids but less sugars and furans. Meanwhile, the molecular structure of DOM shifted to lower molecular weight with higher organic contents containing <6 O atoms per compound, aromatics, and N-containing substances. While low-temperature hydrochar-derived DOM showed minimal biotoxicity, increase in production temperature to 330 °C led to a great rise in toxicity. This might be attributed to the increased contents of phenols, organic acids, and organics containing <6 O atoms and 1 N atom per compound. These results suggest that hydrochar-derived DOM have more negative impacts on the environment than the organics associated with biochar production. Such understanding highlights the importance of controlling the hydrochar production process

Production Temperature Effects on the Structure of Hydrochar-Derived Dissolved Organic Matter and Associated Toxicity

Hydrochar is a carbonaceous material derived from hydrothermal liquefaction, and it carries good potential as a new material for environmental applications. However, little is known about the dissolved organic matter (DOM) associated with hydrochar and the consequences of its release. The relationship between the production temperature and the characteristics of DOM released from hydrochar as well as the associated biotoxicity was investigated using a suite of advanced molecular and spectroscopic tools. With the increase in production temperature, the resulted hydrochar-based DOM contained a higher content of phenols and organic acids but less sugars and furans. Meanwhile, the molecular structure of DOM shifted to lower molecular weight with higher organic contents containing <6 O atoms per compound, aromatics, and N-containing substances. While low-temperature hydrochar-derived DOM showed minimal biotoxicity, increase in production temperature to 330 °C led to a great rise in toxicity. This might be attributed to the increased contents of phenols, organic acids, and organics containing <6 O atoms and 1 N atom per compound. These results suggest that hydrochar-derived DOM have more negative impacts on the environment than the organics associated with biochar production. Such understanding highlights the importance of controlling the hydrochar production process