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To effectively remove lead (Pb(II)) and bisphenol A (BPA) from wastewater, polyvinyl chloride modified magnetic hydrochar (PVC-AMHC) was synthesized through co-hydrothermal carbonization of polyvinyl chloride and corn straw, and subsequently activated using NaOH. Characterization demonstrated that both PVC and NaOH activation increased the content of oxygen-containing functional groups, and Fe3O4 was successfully loaded onto the material surface. Furthermore, PVC-AMHC displayed remarkable uptake capacity with the maximum uptake amount of Pb(II) (217.53 mg/g) and BPA (185.53 mg/g) at 130 and 30 min, respectively, under a wide pH range. Additionally, PVC-AMHC possessed high tolerance to different interference cations and maintained excellent adsorption performance during four regeneration cycles. The thermodynamic analysis suggested that the absorption processes of Pb(II) and BPA by PVC-MHC were spontaneous (-ΔG0) with an endothermic characteristic (+ΔH0). Adsorption mechanisms of Pb(II) on PVC-AMHC included complexation, electrostatic attraction, and pore filling, and those of BPA were mainly associated with hydrogen bonding and pore filling. In conclusion, PVC-AMHC was an environmentally friendly adsorbent with effectively simultaneous removal of Pb(II) and BPA from wastewater. Highlights: • PVC-AMHC is prepared via co-hydrothermal carbonization of polyvinyl chloride and corn straw, and activated by NaOH. • PVC modification and NaOH activation promote the increase of oxygen-containing functional groups of PVC-AMHC. • PVC-AMHC has excellent regeneration property and anti-interference ability to various co-existing ions. [ABSTRACT FROM AUTHOR]

Spent coffee grounds (SCGs), a by-product of coffee brewing, have high application potential. However, their high moisture content complicates conventional conversion without energy-intensive drying. This study explores a new route to convert SCGs to high-carbon bioproducts, such as hydrochar and bio-oil, through hydrothermal processing. The effect of the processing variables, i.e., temperature, residence time, and the application of the binary solvent as a reaction medium, on the distribution of the resultant bioproducts was investigated. The quality of the fabricated bioproducts was analyzed by means of instrumental techniques such as EA, ATR-FTIR, GC-MS, and GC-TCD-FID. Two dominant fractions were liquid bio-oil and solid hydrochar. The highest char yield (39 wt.%) was observed under milder conditions (low T and short residence times), while more severe conditions led to an increase in bio-oil formation, which reached a maximum of 46 wt.%. The resulting bio-oils were of similar quality, presenting high carbon content (71–74 wt.%) and energetic values (approximately 35 MJ/kg). Also, hydrochars showed a noticeable energy densification compared to raw materials, where the C content and HHV reached up to 73.8 wt.% and 30 MJ/kg, respectively. The addition of co-solvent to water improves the bio-oil yield as a result of the enhanced stabilization of reactive intermediates. [ABSTRACT FROM AUTHOR]

The escalating demand for energy across various sectors has led to a significant increase in greenhouse gas emissions, primarily due to the extensive use of fossil fuels. This study addresses the critical need for effective carbon capture adsorbents to mitigate environmental impacts. Bio-based activated carbons, known for their high surface area and pore volume, were synthesized from poplar and spruce sawdust through hydrothermal carbonization (HTC) followed by simultaneous carbonization and activation. HTC, aimed at enriching precursors with oxygen-rich surface functional groups, was conducted at temperatures of 180, 200, and 220 °C for 90 min. This process produced hydrochars that were subsequently activated at 800 °C in the presence of KOH under a nitrogen atmosphere. Remarkably, the activated carbons derived from poplar sawdust hydrochar (at a HTC temperature of 200 °C) and spruce sawdust hydrochar (at a HTC temperature of 220 °C) demonstrate superior specific surface areas of 1680.59 and 1231.57 m2/g, along with total pore volumes of 0.87 and 0.62 cm3/g, respectively. Moreover, both poplar and spruce hydrochar-based activated carbons exhibit high CO2 adsorption capacities of 3.75 and 3.43 mmol/g, respectively, at 24.85 °C and 1 atm. Their CH4 adsorption capacities are 1.52 and 1.42 mmol/g, respectively, under the same conditions. This work highlights the potential of bio-based activated hydrochars in applications such as indoor air quality improvement and industrial flue gas treatment, emphasizing the importance of pretreatment and activation conditions in optimizing adsorbent performance. [ABSTRACT FROM AUTHOR]

Abstract This study optimizes CO2 adsorption using hydrochar from de-oiled flaxseed (FDOP), a waste byproduct of the oil extraction industry, through hydrothermal carbonization (HTC). The aim is to enhance CO2 capture sustainably and cost-effectively. Using Response Surface Methodology (RSM), in optimal conditions achieved 1153.26 mg/g CO2 adsorption capacity under 215.15 °C synthesis temperature, 3.05 h synthesis time, 0.99 M acid concentration, 8.997 bar pressure, and 25.07 °C adsorption temperature. Statistical analysis (F-value: 44.48, R²: 0.9705) confirmed strong model reliability. Kinetic analysis showed both physical and chemical adsorption, while thermodynamic analysis revealed exothermic behavior (ΔH° values: -46.697 kJ/mol for M-225, -40.230 kJ/mol for MA-203). After 10 regeneration cycles, the adsorption capacity was reduced by only 2.8% and 3.1%, indicating excellent recyclability. This study highlights FDOP-derived hydrochar as a highly efficient, low-cost adsorbent, offering industrial applications for carbon capture and waste management.

Cooked rice and the vegetables like lettuce are common kitchen waste, which are carbonaceous materials and have the potential as feedstock for the production of activated carbon. Cooking is similar to hydrothermal treatment (HTC), which might impact the subsequent activation of kitchen waste. In this study, the HTC of lettuce, rice, or their mixture and the activation of the resulting hydrochars were conducted. The results indicated that cross-polymerization between the N-containing organics from lettuce and the sugar derivatives from rice took place in their co-HTC, which significantly increased the hydrochar yield. Activation of the hydrochar from the co-HTC generated the AC with a yield of 2 times that from direct activation of mixed lettuce/rice. However, the co-HTC facilitated aromatization, reducing reactivity with K2C2O4 in activation and producing the AC with main micropores and low specific surface area. Activation of the hydrochar from HTC of rice followed the above trend, while that from lettuce was the opposite. The organics in lettuce were thermally unstable and could not undergo sufficient aromatization. The activation of hydrochar from HTC of lettuce thus generated the AC with the lowest yield, but the highest specific surface area (1684.9 m2/g), abundant mesopores, and superior capability for adsorption of tetracycline. However, the environmental impacts and energy consumption for the production of AC from the hydrochar of lettuce were higher than that from hydrochar of co-HTC.

This study optimizes CO2 adsorption using hydrochar from de-oiled flaxseed (FDOP), a waste byproduct of the oil extraction industry, through hydrothermal carbonization (HTC). The aim is to enhance CO2 capture sustainably and cost-effectively. Using Response Surface Methodology (RSM), in optimal conditions achieved 1153.26 mg/g CO2 adsorption capacity under 215.15 °C synthesis temperature, 3.05 h synthesis time, 0.99 M acid concentration, 8.997 bar pressure, and 25.07 °C adsorption temperature. Statistical analysis (F-value: 44.48, R²: 0.9705) confirmed strong model reliability. Kinetic analysis showed both physical and chemical adsorption, while thermodynamic analysis revealed exothermic behavior (ΔH° values: -46.697 kJ/mol for M-225, -40.230 kJ/mol for MA-203). After 10 regeneration cycles, the adsorption capacity was reduced by only 2.8% and 3.1%, indicating excellent recyclability. This study highlights FDOP-derived hydrochar as a highly efficient, low-cost adsorbent, offering industrial applications for carbon capture and waste management. [ABSTRACT FROM AUTHOR]

Modeling hydrothermal carbonization (HTC) and pyrolysis carbonization (PLC) for the conversion of biomass into high-quality biochar for various applications shows promise. Unlike the extensive modeling studies on lignocellulosic biomass, research on aquatic biomass (AB) had not been reported until now. In this study, we compiled 586 data points from existing literature and trained five tree-based models to predict the yields of hydrochar and pyrochar and their properties, including nitrogen recovery degree, energy density, energy recovery degree, and residual sulfur degree, based on 10 feedstock and process parameters. The random forest regression (RFR) model demonstrated the highest predictive accuracy among these models. It achieved R2 values ranging from 0.89 to 0.98 for hydrochar yield, nitrogen recovery degree of hydrochar, energy recovery degree of hydrochar, and residual sulfur degree of hydrochar. The extreme gradient boosting (XGB) model also showed exemplary performance, with R2 values between 0.84 and 0.94 for energy density of hydrochar, pyrochar yield, and nitrogen recovery degree of pyrochar. Results on feature importance highlighted that, beyond the well-documented impact of process parameters, the properties of biochar were significantly influenced by the elemental compositions, such as nitrogen and sulfur contents of the feedstock. The relationship between these factors was further elucidated using partial dependence plots. Finally, we used RFR model for hydrochar yield and XGB model for pyrochar yield as examples, to test generalization ability of developed models with new data, further explaining their application methods. Overall, this study provided valuable insights into predicting and understanding the HTC and PLC processes of AB to produce high-quality biochar for various applications using low resources and time costs. Besides, we presented an iterative learning application method where the developed models demonstrated exceptionally high performance with new data. This method is highly versatile and can be adopted across various directions in the field of machine learning. Highlights: • A machine-learning framework for producing biochar from aquatic biomass was developed. • XGB and RFR models showed the excellent performance for biochar yield and properties. • The developed models had high generalization ability (R2 = 0.97–0.98) through appropriate iterative operation. [ABSTRACT FROM AUTHOR]