Lanqing Li

Continuous cropping obstacles are a significant challenge to sustainable agricultural development, with the accumulation of phenolic allelopathic substances being one of the main causes of these obstacles. In this study, different modified biochars (10P-BC, 30P-BC, and 50P-BC) were prepared by modifying distiller’s grains biochars with different proportions of H3PO4 (1:9, 3:7, and 1:1), and their ability to remove representative phenolic allelochemicals (p-hydroxybenzoic acid (p-HBA), vanillin (Van), and coumarin (Cou)) was investigated. The physicochemical properties were determined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The adsorption characteristics and mechanism of the modified biochar on phenols were discussed by experiments on pH, adsorption cycle times, and other factors combined with adsorption kinetics, adsorption isotherm, and thermodynamic model fitting. It was found that the modified biochars with different H3PO4 ratios optimized their porous structure and introduced phosphorus–oxygen functional groups (PO, C–O–P, CO). At lower pH, the modified biochar showed a better adsorption effect, and after five adsorption–desorption cycles, it could still maintain about 40% of the initial adsorption capacity. The adsorption experiment conforms to the pseudo-second-order kinetic model and shows a good fit with the Freundlich model. The adsorption process is an exothermic and entropy-reducing physicochemical adsorption process involving various synergistic effects such as pore filling, hydrogen bonding, weak electrostatic interaction, and π–π interaction. Pot experiments showed that the addition of the 1% biochar increased the dry weight, fresh weight, and soil organic matter of asparagus lettuce. This study provides an efficient and sustainable solution for recycling agricultural waste and overcoming the barriers to continuous cultivation and has broad application prospects.

Using traditional Chinese medicine residues as raw materials, different biochars (BC) were prepared through oxygen-limited pyrolysis at 300 °C, 500 °C, and 700 °C, and BC was ball-milled to produce ball-milled biochar (BMC). Using these adsorbents to adsorb the allelopathic autotoxic substance quercetin. The physical and chemical properties of various biochars derived from traditional Chinese medicine residues were characterized using the Brunauer-Emmett-Teller-N2 surface areas (BET), scanning electron microscopy (SEM), Fourier transform IR spectroscopy (FTIR), X-ray diffraction (XRD), and Raman spectroscopy (Raman). The study investigated the effects of the initial pH value, different humic acid concentrations, and multiple adsorption-desorption experiments on the removal of quercetin from the solution. The article discusses the adsorption mechanism of quercetin in solution by biochar from a traditional Chinese medicine residue, based on the results of adsorption kinetics and adsorption isotherm fitting. The findings indicate that increasing the pyrolysis temperature reduces the oxygen-containing functional groups of BC, enhances the aromaticity, and stabilizes the carbon structure. The pore structure of BMC becomes more complex after ball milling, which increases the number of oxygen-containing functional groups on the surface. Among the samples tested, BMC700 exhibits the best adsorption performance, with an adsorption capacity of 293.3 mg·g^-1 at 318 K. The adsorption process of quercetin by BMC700 follows the pseudo-second-order kinetic model and the Freundlich adsorption isotherm model. The process is primarily a form of multimolecular layer adsorption. Its mechanism involves the pore-filling effect, hydrogen-bonding interaction, electrostatic interaction, and π-π coexistence, as well as the yoke effect. Additionally, they are highly recyclable and show promise in addressing continuous cropping issues.

In order to establish a method for simultaneous determination and extraction of quercetin and berberine in soil, HPLC-PDA multi-wavelength method was used to detect the content of berberine and quercetin in soil solution. The detection wavelength was 210 nm and 347 nm. The column temperature was 30 °C, the mobile phase A was acetonitrile, the mobile phase B was 0.1% phosphoric acid aqueous solution, and the flow rate was 1.0 mL min⁻¹. Under the condition of isocratic elution, quercetin and berberine were completely separated within 20 min. The detection limit concentration of quercetin was 0.078 mg L⁻¹, and the detection limit of berberine was 0.019 mg L⁻¹. Both of them reached the trace level, and the recovery rate was between 97.2% and 107.4%. The response surface method was used to optimize the ultrasonic extraction method. The three main factors of extraction concentration, extraction temperature and solid–liquid ratio were optimized to obtain the highest extraction efficiency. The optimum extraction efficiency was as follows: 1 g soil sample was extracted with 80% ethanol aqueous solution, ultrasonic time was 10 min, ultrasonic temperature was 44 °C, and solid–liquid ratio was 1 : 17 g mL⁻¹. The extracted quercetin and berberine concentrations were close to the predicted values of response surface optimization. The method of extracting and determining berberine and quercetin from soil established in this experiment is simple, fast, low cost and high safety. The feedback of the results also further verifies the feasibility in practical production and application, and provides reference value for further research and analysis of different allelochemicals in soil.