A comparative study on the structural features of humic acids extracted from lignites using comprehensive spectral analyses

Application of Alkaline Deep Eutectic Solvents as a Green Alternative to the Traditional Extractants for the Isolation of Humic Substances

The presented study focused on the possibility of using alkaline deep eutectic solvents (ADESs) as green extractants for the isolation of humic substances (HSs) from peat and lignite in a process intensified by ultrasound. For this purpose, the extraction procedure was statistically described on the basis of the Box-Behnken design, and the carboxyl group content in the obtained products was optimized due to the ADES composition, ultrasound intensity, and extraction time. For optimal extraction conditions, the experimental carboxyl content in the isolated products was equal to 3.71 and 2.96 mmol g-1 for the HSs extracted from peat and lignite, respectively. These values were similar to the results for the reference samples, which were HSs extracted using 0.1 M NaOH, as well as humic acids and sodium humates purchased from Sigma-Aldrich. The qualitative assessment of the products obtained was based on spectroscopic methods, including FTIR, 1H NMR, and UV-vis. The analyses carried out for the isolated samples revealed the characteristic structures of HSs, including components of aliphatic chains and aromatic core as well as carboxyl, ester, and amino groups. Simultaneously, the results of the spectral ratio of E 280/E 472 showed the significant differences between the relative amount of lignin for the samples tested.

Phosphorus Acquisition Efficiency and Transcriptomic Changes in Maize Plants Treated with Two Lignohumates

Lignohumates are increasing in popularity in agriculture, but their chemistry and effects on plants vary based on the source and processing. The present study evaluated the ability of two humates (H1 and H2) to boost maize plant performance under different phosphorus (P) availability (25 and 250 μM) conditions in hydroponics, while understanding the underlying mechanisms. Humates differed in chemical composition, as revealed via elemental analysis, phenol and phytohormone content, and thermal and spectroscopic analyses. H1 outperformed H2 in triggering plant responses to low phosphorus by enhancing phosphatase and phytase enzymes, P acquisition efficiency, and biomass production. It contained higher levels of endogenous auxins, cytokinins, and abscisic acid, likely acting together to stimulate plant growth. H1 also improved the plant antioxidant capacity, thus potentially increasing plant resilience to external stresses. Both humates increased the nitrogen (N) content and acted as biostimulants for P and N acquisition. Consistent with the physiological and biochemical data, H1 upregulated genes involved in growth, hormone signaling and defense in all plants, and in P recycling particularly under low-P conditions. In conclusion, H1 showed promising potential for effective plant growth and nutrient utilization, especially in low-P plants, involving hormonal modulation, antioxidant enhancement, the stimulation of P uptake and P-recycling mechanisms.

Co-Thermal Oxidation of Lignite and Rice Straw for Synthetization of Composite Humic Substances: Parametric Optimization via Response Surface Methodology

In this study, Baoqing lignite (BL) and rice straw (RS), which were the representatives of low-rank coal and biomass, were co-thermally oxidized to produce composite humic substances (HS), including humic acid (HA) and fulvic acid (FA). Taking HS content as the output response, the co-thermally oxidizing conditions were optimized through single factor experiment and response surface methodology (RSM). The structures of HA and FA prepared under optimized conditions were analyzed by SEM, UV, and FTIR. Results showed that HS content was clearly influenced by the material ratio, oxidation time, and oxidation temperature, as well as their interactions. The optimized co-thermal oxidization condition was as follows: BL and RS pretreated with a material ratio of 0.53, oxidation time of 59.50 min, and oxidation temperature of 75.63 °C. Through verification, the experimental value (62.37%) had a small relative error compared to the predicted value (62.27%), which indicated that the developed models were fit and accurate. The obtained HA had a tightly packed block structure; FA had a loosely spherical shape. The molecular weight of FA was 2487 Da and HA was 20,904 Da; both had a smaller molecular weight than that reported in other literature. FA showed strong bands at 1720 cm^-1, thus confirming the presence of more oxygen-containing functional groups. The appearance of double peaks at 2900~2980 cm^-1 indicated that HA contains more aliphatic chains. The co-thermal oxidation of BL and RS gives a new method for the synthesis of HS, and the optimization of co-thermal oxidation conditions will provide fundamental information for the industrialization of composite HS.

Extraction optimization and quality evaluation of humic acids from lignite using the cell-free filtrate of Penicillium ortum MJ51

Bio-solubilization of lignite is a promising technology to transform coal into humic acids (HAs) which are broadly used in agriculture. In this work, HAs were extracted from lignite using the cell-free filtrate (CFF) of Penicillium ortum MJ51. The extraction method was optimized using response surface methodology (RSM) based on the interactive effects of nitric acid concentrations, coal loading ratio, extraction temperature and time as input factors, and the absorbance of HAs at 450 nm wavelength as the output response. Under optimized conditions (lignite pretreated with 4.7 N HNO3, coal loading ratio of 4.9%, temperature of 77.3 °C and time of 8.6 hours), the absorbance at 450 nm peaked at 70.28, and the concentration and extraction yield of HAs were 31.3 g L-1 and 63.9%, respectively, which were dramatically higher than those observed for traditional biological methods (0.7 g L-1 and 14.1%, respectively). The qualities of HAs produced under optimized conditions were evaluated and compared with those extracted by the conventional chemical method. The optimized process resulted in better HA quality indices, including lower molecular mass; higher nitrogen; less aromatic carbon; more aliphatic and carboxylic carbon; and higher bioactivity for promoting plant growth. Moreover, the anti-flocculation ability was improved, thereby supporting its applicability in agriculture. Extraction of HAs from lignite using the CFF of P. ortum MJ51 provides a novel technological approach for the efficient conversion of lignite to bio-active HAs.

Exploration of the H2O2 Oxidation Process and Characteristic Evaluation of Humic Acids from Two Typical Lignites

To study the effect of H2O2 on the content and properties of humic acids (HAs) in lignites, the experimental conditions including oxidation time, H2O2 concentration, and the solid-liquid ratio were investigated. Under the optimum oxidation conditions, the contents of HAs of YL and HB lignite were 45.4 and 40.9%, respectively. The HAs extracted from oxidized and raw lignites were characterized and compared. The results showed that the HAs extracted from oxidized lignites contain more total acidic groups, carboxyl groups, and aliphatic carbon than that in HAs extracted from raw lignites, and their hydrophilic-hydrophobic index value is higher and thermooxidative stability is better than those in HAs extracted from raw lignites. In addition, the composition of polycyclic aromatic hydrocarbons and fluorophore types in HAs extracted from oxidized lignites are similar to the HAs extracted from raw lignites. The results indicated that the oxidation operation can increase the content of HAs in lignites, and simultaneously increase the content of oxygen-containing functional groups and biological activity of HAs, which provided a reference for the subsequent application of HAs.

Preparation and characterization of an eco-friendly dust suppression and sand-fixation liquid mulching film

An eco-friendly dust suppression and sand-fixation liquid mulching film was prepared via a facile secondary spraying process in this work. Water polyurethane (WPU) was blended with dissolved humic acid (HA) firstly, and then the blend solutions (HWPU) were sprayed on the surface of cationic starch (CS) / sodium lignosulfonate (LS) film to synthesize the liquid mulching film (CLS-HWPU). The effects of liquid mulching film composition on mechanical properties in dry and wet states were investigated. The results showed that the optimal composition of liquid mulching film was: 3% (CS), 0.9 % (LS), 1.5 % (glycerol), 2% (HA), and 30 % (WPU). The CLS-HWPU liquid mulching films were characterized in terms of light transmittance, degradation performance test, contact angle test, scanning electron microscopy (SEM), total reflectance-Fourier transform infrared spectrometer (ATR-FTIR), thermo gravimetric analysis (TGA), and erosion resistance test. The results indicated that the CLS-HWPU film had good UV resistance, thermal stability, anti-erosion, and biodegradation. The CLS-HWPU film meets the demand of dust suppression and sand-fixation in dusty areas and desertification environments, which opens a new application field for liquid mulching film with high safety and environmental protection.

Subcritical water extraction of organic acids from chicken manure

BACKGROUND

Chicken manure waste has a wide range of organic substances and mineral elements. This enriched source has stimulated great scientific interest in finding cleaner and more environmentally benign nutrient recovery options. This study aimed to determine an effective and eco-friendly method (i.e. subcritical water extraction) for processing fresh poultry manure.

RESULTS

The high content of total organic carbon, including humic acids carbon and fulvic acids carbon, in extract was found to release under subcritical conditions. The organic compounds obtained by extraction with subcritical water correspond to humic acid in composition because of the presence in the sample of all the functional groups: polymer bonded by molecular hydrogen bond (3400 cm^-1 ), the presence of CH₂ and CH₃ groups (2870 cm^-1 ), the presence of carboxyl groups (1720 cm^-1 ) and quinones (1640-1680 cm^-1 ). The solid phase left over was characterized by a high content of organic carbon, phosphorus, potassium, and microelements. The maximum extraction of humic acid and fulvic acid carbon was found between 210 and 250 °C at a pressure of 50-60 atm, and the content was a maximum of 3647.2 × 10^-6 g kg^-1 at an extraction temperature of 250 °C.

CONCLUSION

Given the high content of humic acid found in the extracted medium, the proposed subcritical extraction opens up new opportunities for nutrients recovery in the poultry industry. © 2020 Society of Chemical Industry.

Nanocolloids, but Not Humic Acids, Augment the Phytotoxicity of Single-Layer Molybdenum Disulfide Nanosheets

Engineered nanomaterials (ENMs), especially transition metal dichalcogenide (TMDC), have received great attention in recent years due to their advantageous properties and applications in various fields and are inevitably released into the environment during their life cycle. However, the effect of natural nanocolloids, widely distributed in the aquatic environment, on the environmental transformation and ecotoxicity of ENMs remains largely unknown. In this study, the effects of natural nanocolloids were compared to humic acid on the environmental transformation and ecotoxicity of single-layer molybdenum disulfide (SLMoS₂), a representative TMDC. SLMoS₂ with nanocolloids or humic acid (HA) enhanced their dispersion and Mo ion release in deionized water. Nanocolloids induced growth inhibition, reactive oxygen species (ROS) elevation, and cell permeability. Low-toxicity SLMoS₂ combined with nanocolloids will enhance the above adverse effects. SLMoS₂-nanocolloids induced serious damage (cell distortion and deformation), SLMoS₂ internalization, and metabolic perturbation on Chlorella vulgaris (C. vulgaris). In contrast, the addition of HA induced the growth promotion and lower ROS level, inhibited the internalization of SLMoS₂, and mitigated metabolic perturbation on C. vulgaris. This work provides insights into the effect of natural nanocolloids on the behaviors and biological risks of ENMs in aquatic environments, deserving substantial future attention.