Iron and organic carbon (OC) biogeochemical cycling is highly correlated, and dissolved organic matter (DOM), a highly reactive component of soil and water environments, is the main OC source. However, the micro-mechanism of the molecular fractionation of DOM, the spatial OC distribution on iron (oxyhydr)oxides, and how these factors further affect their redox properties remain to be fully understood. Therefore, this study investigated the DOM adsorption properties of iron (oxyhydr)oxides with different crystallinities at the molecular level through the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and transmission electron microscopy/electron energy loss spectroscopy (TEM–EELS) analyses of the liquid-solid phases. Owing to the limited number of adsorption sites, OC sequestration on goethite and hematite surfaces generally followed an “onion” model, in the order of preference of aromatic, aliphatic, and carboxylic acid-rich compounds. Combined with dielectric electrochemical tests and charge differential density calculations, the results revealed that the complexation effect produced by iron ions increased the electron-accepting capacity (EAC) of the DOM remaining in the aqueous solution. In contrast, molecular selective adsorption and oxidative polymerization significantly enhanced the EAC of DOM adsorbed on the surface fraction of iron (oxyhydr)oxides. These findings help elucidate the mechanism of OC sequestration by iron (oxyhydr)oxides. The increased EAC may affect various biogeochemical processes, such as methane production and microbial Fe(III) reduction, facilitating the prediction of OC cycling in natural environments.
Lingyu Han,Cunzhi Zhang,Nuo Dong,Jixin Yang,Qiuyue Zheng,Xiaobo Zhang,Ronggang Liu,Jijuan Cao,Bing Hu
Segregative phase separation technology demonstrates substantial potential for precise molecular fractionation in food and biomaterial applications. The investigation elucidates the causal relationship between viscosity variations and phase separation dynamics, which govern molecular fractionation in GA/HPMC composite systems. By conducting a comparative analysis of two GA subtypes (CGA and SGA) and three HPMC grades with controlled viscosity gradients, we utilized gel permeation chromatography-multi-angle laser light scattering (GPC-MALLS) coupled with rheological characterization to elucidate the critical relationship between continuous phase viscosity and fractionation efficiency. Notably, increasing HPMC viscosity significantly intensified phase separation, resulting in selective enrichment of arabinogalactan-protein complexes: from 6.3% to 8.5% in CGA/HPMC systems and from 27.3% to 36.5% in SGA/HPMC systems. Further mechanistic investigation revealed that elevated HPMC viscosity enhances thermodynamic incompatibility while slowing interfacial mass transfer, synergistically driving component redistribution. These findings establish a quantitative viscosity–fractionation relationship, offering theoretical insights for optimizing GA/HPMC systems in emulsion stabilization, microencapsulation, and functional biopolymer purification via viscosity-mediated phase engineering.
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