Differential influences of forest floor-pyrolyzed biochar-derived and leached dissolved organic matter interaction with natural iron-bearing minerals in forest subsoil on the formation of mineral-associated soil organic matter.

The vertical sequestration of dissolved organic matter (DOM) by iron minerals along the soil profile is assumed to be central to the long-term storage of the soil organic matter (SOM) pool. However, there is limited information available about how the interaction between DOM and natural iron-bearing minerals shape mineral SOM associations quantitatively and qualitatively in forest subsoils. Here, we systematically investigated the influences of forest organic layer-pyrolyzed biochar-derived DOM (BDOM) and leached DOM (LDOM) on quantity, molecular composition, and diversity of deposition layer-derived iron minerals-associated OM by using Fourier transform ion cyclotron resonance mass spectrometry and other complementary spectroscopy. Results indicated natural iron minerals (FeOx1 and FeOx2) had a greater capacity for sorbing LDOM with higher aromaticity and molecular weight than those of BDOM, and the higher proportion of goethite and short-order-range phase in natural iron minerals was closely related to the increased OM adsorption capacity. We also observed the preferential sorption of oxygen/nitrogen-rich polycyclic aromatic compounds and carboxylic-containing compounds in LDOM and concurrent the potential release of lignin-like/aromatics compounds and carboxyl/nitrogen-less aliphatic compounds from native OM coprecipitates into the solution. However, unsaturated and oxidized phenolic compounds in BDOM had a stronger affinity for FeOx through hydrophobic partitioning and specific polar interactions, and concomitantly the partial release of nitrogen-free aliphatic and other carboxyl-rich compounds. More nitrogen structures in aromatic-containing compounds can improve the saturation level and polarity of BDOM. Compared with BDOM, LDOM exerted a stronger control over the exchange of native OM from subsoil natural iron-bearing minerals and substantially enhanced the molecular diversity of the reconstituted mineral-associated OM during the adsorptive fractionation. Overall, these findings suggest the compositional evolution of DOM profoundly shapes SOM formation and persistence in forest subsoils, which is the key to understanding DOM cycling and contaminant fate during its passage through the soil.

[Effect of Coconut Fiber Biochar and Its Nitrate Modification on Pb Passivation in Paddy Soils].

The effects of coconut fiber biochar (CFB) and nitrate-modified coconut fiber biochar (NCFB) on the passivation of exogenous lead (Pb) in paddy soils and their underlying mechanisms were investigated using soil incubation experiments combined with spectroscopic techniques such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), synchrotron radiation X-ray fluorescence (SRXRF), and Fourier transform infrared absorption spectroscopy (FTIR). The effects of NCFB and CFB on the passivation of exogenous lead (Pb) in paddy soils and its underlying mechanisms were investigated. Compared with that of CFB, the inner wall of NCFB honeycomb pores was rougher, and the amount of alcohol-phenol-ether functional groups containing the C-O structure and the amount of carboxyl groups containing the C[FY=,1]O/O[FY=,1]C-O structure on the surface of CFB was significantly decreased after nitric acid modification. Compared with that in the control (without biochar) paddy soil after 150 d of incubation, the EDTA-extracted Pb content in the paddy soil with CFB and NCFB was reduced by 39.7% and 105.4%, respectively. The carbonate-bound and Fe-Mn oxide-bound Pb contents were significantly lower, and the organic-bound and residue Pb contents were significantly higher in the NCFB-added soil. The SRXRF scans showed that the exogenous Pb was enriched in the microregions of CFB particles rich in Ca and Cu elements and relatively less so in the microregions of soil aggregates rich in the Fe, Mn, and Ti elements. In addition, the characteristic peaks of carboxylates (1384 cm-1) in A-CFBPb and A-NCFBPb were significantly enhanced in the incubation experiment in the presence of exogenous Pb compared to A-CFB and A-NCFB in the absence of exogenous Pb. The addition of CFB or NCFB was more effective in passivating exogenous Pb in paddy soils and promoted the gradual transformation of Pb from unstable to more stable forms in paddy soils to achieve the effect of passivating Pb. The greater amount of carboxyl functional groups in NCFB participated in the passivation of exogenous Pb, which made NCFB more effective than CFB in passivating Pb. NCFB was more effective than CFB in passivating exogenous Pb in paddy soils due to its rougher inner walls of honeycomb pores and abundant carboxyl functional groups. In tropical areas such as Hainan, coconut fiber biochar and its modification can be considered as an environmentally friendly candidate method for the remediation of soil Pb contamination.

3D printing of inorganic nanomaterials by photochemically bonding colloidal nanocrystals.

3D printing of inorganic materials with nanoscale resolution offers a different materials processing pathway to explore devices with emergent functionalities. However, existing technologies typically involve photocurable resins that reduce material purity and degrade properties. We develop a general strategy for laser direct printing of inorganic nanomaterials, as exemplified by more than 10 semiconductors, metal oxides, metals, and their mixtures. Colloidal nanocrystals are used as building blocks and photochemically bonded through their native ligands. Without resins, this bonding process produces arbitrary three-dimensional (3D) structures with a large inorganic mass fraction (~90%) and high mechanical strength. The printed materials preserve the intrinsic properties of constituent nanocrystals and create structure-dictated functionalities, such as the broadband chiroptical responses with an anisotropic factor of ~0.24 for semiconducting cadmium chalcogenide nanohelical arrays.

Molecular size-dependent compositions and lead (II) binding behaviors of two origins of organic fertilizers-derived dissolved organic matter.

The application of organic fertilizers caused large amounts of dissolved organic matter (DOM) entering the soil environment and influencing the behaviors and fates of heavy metals. Here, we investigated the molecular weight-dependent (high molecular weight [HMW], 1 kDa-0.7 µm; low molecular weight [LMW], <1 kDa) compositions and lead (Pb) binding behaviors of DOM derived from sheep manure-based (SMOF) and shrimp peptide-based organic fertilizers (SPOF) using chromophoric and fluorescent spectroscopy, Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and two-dimensional correlation spectroscopy (2D-COS). Results showed that SMOF released more DOM with higher aromaticity and hydrophobicity, containing more fluvic-like components, carboxylic-rich alicyclic molecules (CRAMs) and lignin phenolic compounds compared to SPOF-DOM with more microbially-transformed heteroatom-containing compounds (CHON, CHONS and CHOS). Furthermore, there was more aromatic compounds with ample carboxyl and hydroxyl groups in HMW-DOM but abundant protein-like components and heteroatom-containing compounds (CHONS and CHOS) in LMW-DOM. SMOF-DOM exhibited more obvious MW-dependent heterogeneity in molecular components compared to SPOF-DOM with higher molecular diversity. Moreover, 2D-COS indicated phenol and carboxyl groups in SMOF-DOM and polysaccharides in SPOF-DOM exhibited superior binding affinities for Pb. Pb binding to HMW-DOM derived from SMOF first occurred in the phenolic groups in fulvic-like substances, while polysaccharides in LMW-DOM first participated in the binding of Pb. In contrast, irrespective of MWs, polysaccharides and humic-like substances with aromatic (CC) groups in SPOF-DOM displayed a faster response to Pb. Furthermore, the polysaccharides which preferentially participated in the binding of Pb to SPOF-DOM and SMOF-derived LMW-DOM may pose a higher risk of Pb in the environment. These results were helpful to understand the effects of sources and size-dependent compositions of DOM on the associated risks of heavy metals in the environments.

3D nanoprinting of semiconductor quantum dots by photoexcitation-induced chemical bonding.

Three-dimensional (3D) laser nanoprinting allows maskless manufacturing of diverse nanostructures with nanoscale resolution. However, 3D manufacturing of inorganic nanostructures typically requires nanomaterial-polymer composites and is limited by a photopolymerization mechanism, resulting in a reduction of material purity and degradation of intrinsic properties. We developed a polymerization-independent, laser direct writing technique called photoexcitation-induced chemical bonding. Without any additives, the holes excited inside semiconductor quantum dots are transferred to the nanocrystal surface and improve their chemical reactivity, leading to interparticle chemical bonding. As a proof of concept, we printed arbitrary 3D quantum dot architectures at a resolution beyond the diffraction limit. Our strategy will enable the manufacturing of free-form quantum dot optoelectronic devices such as light-emitting devices or photodetectors.