Kinetic ATR-FTIR Studies on Phosphate Adsorption on Iron (Oxyhydr)oxides in the Absence and Presence of Surface Arsenic: Molecular-Level Insights into the Ligand Exchange Mechanism
Bibliographic record
Abstract
The surface chemistry of phosphorus and arsenic compounds in their organic and inorganic forms is of great interest to the scientific and industrial communities due to its role in controlling their transport, bioaccessibility and speciation. We report herein in situ and surface-sensitive rapid kinetic studies on the adsorption of phosphate to Fe (oxyhydr)oxides in the presence and absence of dimethylarsinic acid (DMA) and arsenate. These studies were conducted at pH 7 using ATR-FTIR in the flow mode, which were complemented with detailed kinetic analysis of the desorption behavior of DMA and arsenate over the same range of aqueous [phosphate]. Values for apparent rates of adsorption and desorption were extracted from the time dependence of given spectral components characteristic of surface phosphate, DMA, or arsenate. Results show that pseudo adsorption rate constants of phosphate on Fe (oxyhydr)oxide films increase in this order: arsenate-covered < DMA-covered ≤ freshly prepared. Also, pseudo desorption rate constants of DMA complexes are 7-12 times higher than arsenate using phosphate as a desorbing agent. When these results are combined with earlier work on the thermodynamics, kinetics, and structure of surface complexes, they suggest that, during initial times of surface interactions, increasing organic substitution on arsenate increases the proportion of relatively weakly bonded complexes (monodentate and outer-sphere).
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".