Aqueous solutions of humic acid (HA) derivatized by a catalyzed O-alkylation reaction with methyl, pentyl, and benzyl groups at 40, 60, and 80% of total HA acidity were used to wash off polycyclic aromatic hydrocarbons (PAHs) from two contaminated soils. The enhanced surfactant properties enabled the alkylated HA to remove phenanthrene, anthracene, fluoranthene, and pyrene from both soils more extensively than the original unmodified HA, the 60% benzylation generally showing the greatest soil washing efficiency. For both soils, all alkylated HA revealed greater PAH removals than Triton X-100 nonionic surfactant, while the benzylated and methylated HA nearly and fully matched pollutants release by the anionic SDS in the coarse- and fine-textured soils, respectively. A consecutive second washing with 60% benzylated HA removed additional PAHs, in respect to the first washing, from the coarser-textured soil, except for fluoranthene, while removal from the finer-textured soil incremented even more for all PAHs. These findings indicate that the enhanced hydrophobicity obtained by a simple and unexpensive chemical derivatization of a natural humic surfactant can be usefully exploited in the washing of polluted soils, without being toxic to the soil biota and by potentially promoting the subsequent bio-attenuation of organic pollutants.

Humic susbtances (HS) are increasingly applied as biostimulants in agriculture, though their mechanism of action is not yet completely understood due to their complex and heterogeneous composition. Here, we isolated thirteen different humic and fulvic acids from different sources, such as soils, composts, peat, leonardite and lignite, and characterized the distribution of their carbon components by 13 C-CPMAS–NMR spectroscopy. Callus of Pinus Laricio , as a model plant species, was treated with different humic extracts and its growth and content of carbohydrates, phenols, and enzyme related to the nitrogen metabolism (invertase, glutamine synthetase, glutamate synthase, phosphoenoly pyruvate carboxylase, malate dehydrogenase) and stress resistance (catalase) were monitored. While a multivariate statistical analysis of NMR results well-separated the HS characteristics based on their origin, humic materials generally increased callus growth, as expected, with largest effects being exerted by the mostly polar humic acids from composts. However, the rest of measured parameters were not linearly related to hydrophobicity and aromaticity of humic isolates as well as their origin, but their conformational dynamics had to be advocated to explain their effects on callus cellular components. This work confirms that HS of various origin can act as sustainable biostimulants of plant growth, though the comprehension of their effects on plants biochemical activities requires further research and additional understanding of their molecular composition and conformational behaviour. Graphical Abstract

Humic acids (HAs) provide an important bio-source for redox-active materials. Their functional chemical groups are responsible for several properties, such as metal ion chelating activity, adsorption ability towards small molecules and antibacterial activity, through reactive oxygen species (ROS) generation. However, the poor selectivity and instability of HAs in solution hinder their application. A promising strategy for overcoming these disadvantages is conjugation with an inorganic phase, which leads to more stable hybrid nanomaterials with tuneable functionalities. In this study, we demonstrate that hybrid humic acid/titanium dioxide nanostructured materials that are prepared via a versatile in situ hydrothermal strategy display promising antibacterial activity against various pathogens and behave as selective sequestering agents of amoxicillin and tetracycline antibiotics from wastewater. A physicochemical investigation in which a combination of techniques were utilized, which included TEM, BET, 13C-CPMAS-NMR, EPR, DLS and SANS, shed light on the structure-property-function relationships of the nanohybrids. The proposed approach traces a technological path for the exploitation of organic biowaste in the design at the molecular scale of multifunctional nanomaterials, which is useful for addressing environmental and health problems that are related to water contamination by antibiotics and pathogens.

Sustainable and precision agriculture requires that agroproducts be employed for plants' benefits with maximum efficiency and reduced environmental hazard. Since hydrogels may become efficient vehicles for agroproduct spreading, we prepared novel humo-pectic hydrogels by first blending low methyl-esterified pectin with either humic substances (HS) extracted from different composted biomasses or humic-like substances (HULIS) from depolymerized lignocellulose waste derived by biorefinery activities and, then, by cross-linking with calcium chloride through ionotropic gelation. Hydrogels were characterized by solid-state C-13 NMR spectroscopy, scanning electron microscopy (SEM), magnetic resonance imaging (MRI) and rheological analyses. Their ability to work as controlled-release systems was tested by kinetically monitoring the release of a previously incorporated phloroglucinol. Our results indicated that the hydrogels made with HULIS (HP-HULIS) showed a better controlled-release property than those containing HS (HP-HS). This highly depended on the larger content of oligosaccharides, lesser porosity, and greater cross-linking density of HP-HULIS as compared to HP-HS. Our study suggests that the development of a technology based on such novel humo-pectic hydrogels as carriers of bioactive compounds may represent a promising strategy for the controlled and environmentally safe delivery of agroproducts to crops.

We prepared humo-pectic hydrogels through ionotropic gelation by crosslinking natural pectins of different degree of methyl-esterification with either humic substances (HS) extracted from cow manure compost or humic-like substances (HULIS) from depolymerized lignocellulose biorefinery waste. The hydrogels were characterized by solid-state 13C-NMR spectroscopy, scanning electron microscopy, spectroscopic magnetic resonance imaging and rheological analyses. Their ability to work as controlled release systems was tested by following the release kinetics of a previously incorporated model phenolic compound, like phloroglucinol. Our results indicated that the release properties of hydrogels were influenced by the molecular composition of HS and HULIS and by the different degrees of methyl-esterification of pectins. The hydrogel made by the high methoxyl pectin and HS showed the fastest rate of phloroglucinol release, and this was attributed not only to its morphological structure and crosslinking density but also to the least formation of ionic interactions between phloroglucinol and the polysaccharidic chains. Our study suggests that the efficiency of novel humo-pectic hydrogels as sustainable carriers of agroproducts to crops is related to a careful choice of the characteristics of their components.

Humic acids (HA) exhibit fascinating multifunctional features, yet degradation phenomena as well as poor stability in aqueous environments strongly limit their use. Inorganic nanoparticles are emerging as a powerful interface for the development of robust HA bio-hybrid materials with enhanced chemical stability and tunable properties. Hybrid organic-inorganic SiO2/HA nanostructures were synthesized via an in-situ sol-gel route, exploiting both physical entrapment and chemical coupling. The latter was achieved through amide bond formation between carboxyl groups of HA and the amino group of 3-aminopropyltriethoxysilane (APTS), as confirmed by Fourier-Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopy. Monodisperse hybrid nanoparticles about 90 nm in diameter were obtained in both cases, yet Electron Paramagnetic Resonance (EPR) spectroscopy highlighted the different supramolecular organization of HA. The altered HA conformation was reflected in different antioxidant properties of the conjugated nanoparticles that, however, resulted in being higher than for pure HA. Our findings proved the key role of both components in defining the morphology of the final system, as well as the efficacy of the ceramic component in templating the HA supramolecular organization and consequently tuning their functional features, thus defining a green strategy for bio-waste valorization.

Background We applied Fourier-Transformed Infrared Spectroscopy (FTIR) techniques in combination with selective humus extractions to investigate in situ the chemical features of organic matter in three soil profiles recently developed from Dutch sand dunes, under well-documented vegetation sequence and containing a relatively simple mineral-organic matter system. Water-soluble and alkaline-soluble extracts were also studied to match the changes of humus in the soil residues. Results Diffuse Reflectance Infrared Fourier Transform (DRIFT) and transmission spectra differed in resolution and sensitivity. DRIFT was superior in revealing structural information on the organic matter present in the soil samples whereas transmission spectra showed higher resolution for the bands of inorganic material at lower spectral frequencies. Differences between H and B horizons were due to the amount of hydrophilic organic acids, partly unsaturated, that were extracted by alkali. Extractable carboxylic acids and other hydrophilic compounds such as peptides and carbohydrates were larger in the less developed soils under pine and crowberry than in the more advanced profiles under beech. Humin residues from both H and B horizons retained unextractable aliphatic components and carboxylic groups involved in strong complexes with minerals, thereby confirming other findings that showed the largely aliphatic character of the unextractable humic fraction. Accumulation of poorly-soluble organic materials in these soils occur by protection from biodegradation due both to complexation with soil minerals and to a process by which apolar humic constituents form a separate hydrophobic phase where no biological activity can take place. Transport of poorly soluble compounds from H to B horizons, noticed especially in the more developed profiles, may have occurred through humic aggregates containing hydrophobic phases. Conclusions This work shows that the DRIFT technique in combination with soil chemical treatments can be suitably employed to investigate the changes of organic matter in whole soil samples and represents a valid tool to investigate the role of organic matter in soil profile development.

Facing an exploding population growth with consequent increase of agriculture intensification, new chemical technologies are being sought to limit organic matter losses and reduce land degradation. Here, we report that an effective organic carbon sequestration in different cropped soils of Italy is obtained by an in situ photo-oxidative coupling among soil humic molecules, when catalyzed under solar irradiation by a water-soluble biomimetic iron-porphyrin catalyst amended to field soils. A 3-year long field study showed that the catalyst-assisted in situ photochemical polymerization of humic matter enabled a yearly sequestration of soil organic carbon that ranged from 2.2 to 3.9 t ha(-1) y(-1), despite the periodical soil disturbance due to a conventional tillage management. This significant stabilization of organic matter was observed not only in bulk soils but also in water-stable aggregates, whose loss of organic carbon during separation was limited in catalyst-treated soils. Although crop yields were the same in treated and control soils, measurements of phospholipids fatty acids and soil enzyme activities indicated that the catalyzed in situ photo-oxidative coupling of humic molecules did not alter the structure and activity of microbial communities and the biological functions of soils. This innovative and ecologically safe catalytic technology may be developed as a useful soil management practice to stabilize organic matter in situ in arable soils, while concomitantly ensuring soil functions and sustainability of crop production.

Two humic acids extracted from a volcanic soil (HA1) and a leonardite (HA2) were used to form insoluble complexes with iron metals. To simulate the rhizospheric processes that displace iron from complexes of humic molecules and solubilize the soil humeome, the insoluble iron–humates were treated with a solution of siderophore deferoxamine mesylate (DFOM) and a mixture of citric, oxalic, tartaric and ketoglutaric acids, at different concentrations and contact times.

Agricultural practices that enhance organic matter content in soil can play a central role in sequestering soil organic carbon (SOC) and reducing greenhouse gases emissions.

Lignin of lignocellulosic residues from biomass for energy can be exploited in sustainable agriculture as plant stimulants. Lignin monomers or their microbial bioproducts are mainly responsible for the plant growth promotion exerted by humic matter in soil. The aim of this work was to verify the humic-like bioactivity of water-soluble lignin isolated from biomass for energy towards plant growth and relate the biostimulation to the lignin molecular structure.

Bioremediation is a low-cost technology, whose efficacy is often enhanced with preliminary mild physical–chemical remediation methods. A further advantage of bioremediation resides in its eco-compatibility and, thus, sustainability. Two autochthonous microbial strains, Methylobacterium populi VP2 and Aspergillus sydowii VP4, were isolated from a soil of a highly contaminated industrial site and used to degrade the aqueous extract of contaminants (AEC) obtained from the same polluted soil.

Two oxidative catalytic systems, titanium dioxide (TiO2) nanoparticles and a biomimetic Mn-porphyrin linked to montmorillonite through a spacer (MnP-M), were used to photo-polymerize soil organic matter (SOM) directly in situ on soil, with the aim to sequester organic carbon (OC) and reduce CO2 emissions from soil. We first validated, by infrared spectroscopy, thermogravimetric analysis (TGA), and proton spin–lattice relaxation time (T1ρH) in 13C cross-polarization magic angle spinning (13C CPMAS) nuclear magnetic resonance (NMR) spectra, the capacity of the nano-TiO2 catalyst to photo-oxidatively couple humic molecules together by covalent bonds, as already proved under MnP-M. Both catalysts turn the loosely associated humic superstructures into more stable and larger molecular masses through a photo-oxidative free radical coupling mechanism. Then, the addition of either nano-TiO2 or MnP-M to soil induced an in situ photo-polymerization of SOM, since exposure of catalyst-treated soils to solar light determined a significant reduction of respired CO2 and an increase in thermal stability of humic components and, consequently, in SOC content. This suggests that both nano-TiO2 and immobilized metal-porphyrin photo-catalysts effectively promote OC sequestration in soil and reduction of CO2 emissions from soil to atmosphere. Soil treatments with heterogeneous photo-catalysts may become a promising technology for the development of future agricultural practices aimed to increase SOM stabilization and contribute to mitigate global climate change.

Lignin was isolated with subcritical water:ethanol:CO2 (Sub-CW) from biorefinery biomasses, such as giant reed (AD) and miscanthus (MG), with recovery yields about 30% on Klason lignin. Their structural composition assessed by IR and NMR techniques, as well as Derivatization Followed by Reductive Cleavage (DFRC/GC-MS). The 2D HSQC-NMR spectra elucidated that the Sub-CW extracts contained different lignin dimers and co-extracted carbohydrates. The DFRC/GC-MS revealed that syringyl molecules were more abundant in AD, while guaiacyl monomers were predominant in MG. Lignin residues were derivatized with phospholane to quantitatively estimate the amount of OH groups by 31P NMR, showing a marked predominance of aliphatic units for both lignins, due to the presence of either hydroxyls in lignin side-chain or residual carbohydrates. Lignin residues derivatized with phospholane allowed to record 31P-DOSY NMR spectra. AD-lignin showed a smaller diffusivity constant than for MG-substrate, possibly because of the larger content of disaccharides in MG lignin. We showed that the molecular composition of lignin isolated by the Sub-CW technique may differ depending on the type of biomass used for the extraction, suggesting a different industrial application of lignin from various biomass.

Aquatic humic substances (AHSs) differ from one environment to another depending on land use and occupation. In addition, the effects of planting sugarcane on AHSs are not well known. Thus, the aim of this study was to characterize AHSs extracted from a river in a typical region of sugarcane cultivation during dry and rainy seasons. The main characteristics of the AHSs were obtained using Fourier transformation infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and off-line pyrolysis coupled with gas chromatography and mass spectrometry (off-line tetramethylammonium hydroxide (TMAH)-GC-MS-thermochemolysis). The FTIR and NMR results were used to infer that no distinctions occurred between the sampling periods. The samples were composed of aromatic groups that were potentially associated with the presence of residual vegetable materials (lignin). The results of the off-line TMAH-GC-MS-thermochemolysis indicated that the structures of the AHSs had uniform compositions that were rich in fatty acid methyl esters (FAMEs), polysaccharide derivatives, aliphatic biopolymers derived from plants, long hydrocarbon chains, branched alkyl groups and methylene carbons. Thus, the results showed that the AHSs obtained from the sugarcane cultivation area during the crop period mainly consisted of resistant aliphatic hydrocarbons, which are derivatives of lignin and FAMEs in compounds rich in humic acid. Therefore, we concluded that sugarcane cultivation produces changes in AHSs because greater amounts of lignin derivatives were observed during the dry season, corresponding to sugarcane cultivation.

The influence of pH on the formation of host-guest complexes between the cucurbit[7]uril (CB[7]) macrocyclic host and three auxin plant hormones, namely indole-3-acetic acid (IAA), 2-naphthalene acetic acid (2-NAA), and 2,4-dichlorophenoxyacetic acid (2,4-D), was studied by 1H NMR and relaxation experiments.

Two novel heterogeneous biomimetic catalysts were synthesized by immobilizing a mesotetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of manganese (III) chloride on both kaolinite and montmorillonite clay minerals, previously functionalized with a molecular spacer whose terminal nitrogen atom coordinates the metal in the porphyrin ring. The clay functionalization by a 3-(1-imidazolyl)propylcarbamoyl-3′-aminopropyl-triethoxysilane spacer was proved by X-ray diffraction, elemental analysis, DRIFT-IR, 13Cand 29Si-CPMAS-NMR spectroscopies, and the percent of manganese–porphyrin immobilized by the spacer coordination calculated by spectrophotometry. The activity of the novel catalysts was evaluated in the oxidative coupling reaction of catechol, a humic phenol, using H2O2 as oxygen donor. The rate of catechol oxidation catalyzed by both heterogeneous catalysts was about four times as fast as that catalyzed by the free manganese–porphyrin, and depended on the

The meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of manganese(III) chloride [Mn-(TDCPPS)Cl] biomimetic catalyst immobilized on spacer-functionalized kaolinite clay mineral was employed in the oxidative coupling reaction of a dissolved humic acid (HA) suprastructure with either chemical (H2O2) or UV-light oxidation. The changes in molecular size of humic matter subjected to catalyzed oxidative reaction were followed by high-performance size exclusion chromatography (HPSEC) with UV-vis and refractive index (RI) detectors in series, and by thermogravimetric (TGA) analysis. Both the enhanced molecular size shown by differences between HPSEC chromatograms of humic reaction mixtures at either pH 6 or 3.5 and the increase of thermogravimetric stability suggest that the heterogeneous biomimetic catalysis promoted the stabilization of humic conformations by new intermolecular covalent bonds during oxidative coupling. The similarity between chemical and light-induced oxidation results suggests potential multiple applications of the kaolinite-supported heterogeneous catalyst in controlling the reactivity of natural organic matter within biogeochemical cycles and environmental reactions.

Two novel heterogeneous biomimetic catalysts were synthesized by immobilizing a meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of manganese (III) chloride on both kaolinite and montmorillonite clay minerals, previously functionalized with a molecular spacer whose terminal nitrogen atom coordinates the metal in the porphyrin ring. The clay functionalization by a 3-(1-imidazolyl)propylcarbamoyl-3′-aminopropyl-triethoxysilane spacer was proved by X-ray diffraction, elemental analysis, DRIFT-IR, 13C- and 29Si-CPMAS-NMR spectroscopies, and the percent of manganese–porphyrin immobilized by the spacer coordination calculated by spectrophotometry. The activity of the novel catalysts was evaluated in the oxidative coupling reaction of catechol, a humic phenol, using H2O2 as oxygen donor. The rate of catechol oxidation catalyzed by both heterogeneous catalysts was about four times as fast as that catalyzed by the free manganese–porphyrin, and depended on the amount of catalyst immobilized on clay minerals. Moreover, the activity of the heterogeneous catalysts remained effective for at least two sequential reaction cycles, although at a decreasing rate. We showed that the immobilization of a biomimetic catalyst on clay minerals increased the catalytic efficiency and allowed the catalyst recycling and reuse for additional reactions. Metal–porphyrins immobilized on clay minerals through a flexible spacer may act as environment-friendly heterogeneous catalysts to control phenolic molecules in environmental humus.