Molecular Determination of Organic Adsorption Sites on Smectite during Fe Redox Processes Using ToF-SIMS Analysis

Abstract

Turnover of soil organic carbon (SOC) is strongly affected by a balance between mineral protection and microbial degradation. However, the mechanisms controlling the heterogeneous and preferential adsorption of different types of SOC remain elusive. In this work, the heterogeneous adsorption of humic substances (HSs) and microbial carbon (MC) on a clay mineral (nontronite NAu-2) during microbial-mediated Fe redox cycling was determined using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results revealed that HSs pre-adsorbed on NAu-2 would partially inhibit structural modification of NAu-2 by microbial Fe(III) reduction, thus retarding the subsequent adsorption of MC. In contrast, NAu-2 without precoated HSs adsorbed a significant amount of MC from microbial polysaccharides as a result of Fe(III) reduction. This was attributed to the deposition of a thin Al-rich layer on the clay surface, which provided active sites for MC adsorption. This study provides direct and detailed molecular evidence for the first time to explain the preferential adsorption of MC over HSs on the surface of clay minerals in iron redox processes, which could be critical for the preservation of MC in soil. The results also indicate that ToF-SIMS is a unique tool for understanding complex organic−mineral−microbe interactions.

Molecular Imaging Reveals Two Distinct Mixing States of PM2.5 Particles Sampled in a Typical Beijing Winter Pollution Case

“…Due to the complexity of ToF-SIMS spectral data, principal component analysis (PCA) 44,45 was used to extract effective chemical information following procedures described in our previous work. 37,46 SEM Analysis, Cation and Anions Analysis, Environmental, and Meteorological Data Collection. Details are shown in SI.…”

“…The scanning size of the Ar cluster ion beam was 500 μm × 500 μm, and the sputtering rate for typical organic materials (such as Trehalose and Irganox 1010) was about 2.0 nm/s. , During data collection, a low-energy electron flood gun was used to compensate for surface charging. Due to the complexity of ToF-SIMS spectral data, principal component analysis (PCA) , was used to extract effective chemical information following procedures described in our previous work. , …”

Adsorption Mechanism of Methylene Blue on Purified Red Phosphorus and Effects of Different Temperatures on Methylene Blue Desorption

“…Adsorbents include activated carbon [29,30], sewage sludge [31,32], clay [33,34], agriculture waste [35] and so on. Red phosphorus (RP) is earth-abundant and has a high specific surface area and a porous structure [36].…”