Converting Agroforestry Biowaste into Stable Near-Natural Chars via Hydrothermal Humification and Pyrolysis for Immobilizing Plasticizer

Tao Xue, Yi Li, Zimo Chen, Chao Kong, Biyun Feng, Changyin Zhu, Yinlong Zhang, Jianming Xue and Hu Cheng ()
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Tao Xue: Co-Innovation Center for the Sustainable Forestry in Southern China, College of Ecology and the Environment, Nanjing Forestry University, Nanjing 210037, China
Yi Li: Co-Innovation Center for the Sustainable Forestry in Southern China, College of Ecology and the Environment, Nanjing Forestry University, Nanjing 210037, China
Zimo Chen: Co-Innovation Center for the Sustainable Forestry in Southern China, College of Ecology and the Environment, Nanjing Forestry University, Nanjing 210037, China
Chao Kong: Changzhou Agricultural Comprehensive Technology Extension Center, Changzhou 213002, China
Biyun Feng: Changzhou Agricultural Comprehensive Technology Extension Center, Changzhou 213002, China
Changyin Zhu: Co-Innovation Center for the Sustainable Forestry in Southern China, College of Ecology and the Environment, Nanjing Forestry University, Nanjing 210037, China
Yinlong Zhang: Co-Innovation Center for the Sustainable Forestry in Southern China, College of Ecology and the Environment, Nanjing Forestry University, Nanjing 210037, China
Jianming Xue: New Zealand Forest Research Institute (Scion), Christchurch 8440, New Zealand
Hu Cheng: Co-Innovation Center for the Sustainable Forestry in Southern China, College of Ecology and the Environment, Nanjing Forestry University, Nanjing 210037, China

Agriculture, 2025, vol. 15, issue 11, 1-15

Abstract: To ensure agricultural safety and ecological security, it is crucial to effectively immobilize emerging organic pollutants, such as plasticizers, to prevent their migration in various environmental matrices. However, the ideal immobilization agent with the advantages of being environmentally friendly is very rare. In this study, low-cost and stable near-natural immobilization agents, char-derived artificial humic acids, CHAs, were proposed and prepared via hydrothermal humification (180 °C) and pyrolysis (300, 500, or 700 °C) of agroforestry biowaste. The resulting CHAs exhibit high purity (composed primarily of C (67.28–81.35%), O (6.65–21.64%), H (1.40–5.28%), and N (0.36–0.58%)) with remarkably low ash content (5.43–10.02%). Characterization revealed a compact structure with a limited porosity with small surface area (0.27–0.32 m 2 g −1 ) and pore volume (2.99–3.43 × 10 −4 cm 3 g −1 ). Notably, high-temperature pyrolysis induced consumption of oxygen-containing functional groups while promoting aromatic structure formation. The sorption behavior of diethyl phthalate, a representative plasticizer, on CHAs was well described by both Langmuir isotherm and pseudo-second-order kinetic models. The CHAs exhibited remarkable sorption performance for diethyl phthalate, with a maximum sorption capacity reaching 3345 mg kg −1 as determined by the Langmuir model. The sorption of diethyl phthalate onto CHAs is mainly multi-layer sorption dominated by physical processes, mainly including pore filling, partitioning, hydrogen bonding, and π–π stacking. Mean sorption energies ranging from 2.56 to 4.99 × 10 −3 kJ mol −1 indicate the predominance of physical sorption mechanisms. This study developed a method to convert the liquid by-product produced during hydrothermal humification of biowaste into stable near-natural and carbon-rich char materials, and the proposed materials show great promise in immobilizing pollutants from various environmental matrices.

Keywords: diethyl phthalate; humic acid; hydrothermal humification; pyrolysis; biochar (search for similar items in EconPapers)
JEL-codes: Q1 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 (search for similar items in EconPapers)
Date: 2025
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