Environmental contextCarbon sequestration and dynamics are influenced by adsorptive fractionation of dissolved organic matter (DOM) on minerals. We found that the molecular fractionation of DOM on ferrihydrite was highly dependent on the presence of Na, Ca and Cu ions in water. These results advance our mechanistic understanding of the dynamic behaviour of DOM, and contribute to predicting carbon cycling and contaminant behaviour in the natural environment. AbstractThe adsorptive fractionation of dissolved organic matter (DOM) at the ferrihydrite and water interface is a key geochemical process controlling DOM compositions and reactivity, thus affecting carbon cycling and contaminant behaviour in the environment. However, the effects of cations on DOM fractionation and the underlying mechanisms are poorly understood. In this study, Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) combined with spectroscopic methods were employed to investigate molecular fractionation of DOM on ferrihydrite under different cations in the background electrolytes, including Na, Ca, and Cu ions. The results indicated that DOM fractionation was influenced by the combined effects of cation type, intrinsic molecular property, and extent of DOM adsorption. DOM adsorption on ferrihydrite exhibited the strongest and the weakest fractionation under Na and Ca background electrolytes, respectively. Both Ca and Cu background electrolytes reduced the adsorption of highly unsaturated and phenolic/polyphenolic molecules with high molecular weight and number of O atoms. In addition to the molecular acidity, the complexation of Ca and Cu ions to DOM binding sites and the coagulation effect of divalent cations may affect molecular fractionation. Additionally, DOM fractionation was enhanced with increasing DOM adsorption. Our results contribute to predicting carbon cycling and contaminant behaviour in the natural environment.

We elucidated the spatial distribution of DOM on allophane and the mechanisms controlling the adsorptive fractionation of DOM molecules.

Cold crystallization of PLA can improve its affinity to PCL in their blends, and crystallized PLA domains have better nucleation effect to PCL crystallization relative to amorphous PLA ones.

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Engaged learners are effective learners. Even though it is widely recognized that engagement plays a vital role in learning effectiveness, engagement remains to be an elusive psychological construct that is yet to find a consensus definition and reliable measurement. In this study, we attempted to discover the plausible operational definitions of engagement within an online learning context. We achieved this goal by first deriving a set of interpretable features on dynamics of eyes, head and mouth movement from facial landmarks extractions of video recording when students interacting with an online tutoring system. We then assessed their predicative value for engagement which was approximated by synchronized measurements from commercial EEG brainwave headset worn by students. Our preliminary results show that those features reduce root mean-squared error by 29% compared with default predictor and we found that the random forest model performs better than a linear regressor.

The reactivity and bioavailability of heavy metals in soils are controlled by their binding to reactive soil components, including soil organic matter (SOM), metal (hydr)oxides, and clay minerals. In this study, we specifically investigated how soil components and SOM binding sites controlled metal partition at various chemistry conditions. We used the Windermere Humic Aqueous Model (WHAM 7) to predict the solid-solution partition and speciation of Cd, Cu, Ni, Pb, and Zn based on compiled literature data including 98 soil samples from five continents. Based on the root-mean-square-error (RMSE) values of logarithm of dissolved metal concentrations between model predictions and experimental results, WHAM 7 reasonably predicted metal partition equilibrium over a wide range of reaction conditions, with RMSE less than 0.5 for Cd and Zn, and less than 1.0 for the other three metals. Soil organic matter dominated metal binding at most acidic to neutral pH, clay minerals were significant at low pH, and iron (hydr)oxides might effectively compete with SOM for metal binding when pH was high. For all five heavy metals, WHAM 7 predicted the bidentate bindings were the dominant form of metal complexes, in which both complexes formed by two carboxylic sites and that by one carboxylic and another phenolic sites were major complexes. The formation of monodentate complexes and electrostatic outer-sphere complexes was significant at low pH, while tridentate complexes were only significant at high pH values. The modeling results help to accurately predict the environmental behavior of heavy metals in pH 3 to 7 soil environments.