Phosphate alteration of chloride behavior at the boehmite–water interface: New insights from ion-probe flow adsorption microcalorimetry

Sorption Dynamics and Energetics of Cinnamic Acid and Its Derivatives at the Ferrihydrite–Water Interface Determined by Flow-Adsorption Microcalorimetry

“…By comparison, the complementary reverse reactions (i.e., NO 3 replacing Cl or CIN) were exothermic with an E total of −3.10 and – 0.51 J g –1 , respectively. The similarity in the energetics between Cl/NO 3 (+3.15 J g –1 ) and NO 3 /Cl (−3.10 J g –1 ) is congruent with flow adsorption microcalorimetry studies of simple ion exchange reactions, which are completely reversible and occur via outer-sphere electrostatic interactions of anions (or cations) with metal oxides , and other charged surfaces. , The endothermic response of Cl/NO 3 relative to the exothermic response of NO 3 /Cl is reflective of the smaller ionic radius of Cl. , The unimodal shape and comparable reaction duration (30–35 min) of the Cl/NO 3 and NO 3 /Cl thermograms are also consistent with the simple reaction dynamics of outer-sphere ion exchange.…”

“…The multimodal sorption, slower sorption kinetics, and irreversibility apparent in CIN interactions at the ferrihydrite–water interface have also been observed for sulfate , and phosphate ,, sorption on various Al­(III) and Fe­(III) oxides. Gale et al attributed multimodal thermograms for phosphate sorption on boehmite to sorption occurring on differentially coordinated surface hydroxyls.…”

“…The multimodal sorption, slower sorption kinetics, and irreversibility apparent in CIN interactions at the ferrihydrite–water interface have also been observed for sulfate , and phosphate ,, sorption on various Al­(III) and Fe­(III) oxides. Gale et al attributed multimodal thermograms for phosphate sorption on boehmite to sorption occurring on differentially coordinated surface hydroxyls. Slower sorption kinetics has been attributed to steric hindrances and intraparticle diffusion. ,, The irreversibility of sulfate and phosphate sorption by ion exchange with NO 3 or Cl has been attributed to the phosphate being sorbed onto the same sites as NO 3 or Cl but via ligand rather than ion exchange .…”

“…Specifically, ligand exchange is an inner-sphere interaction with a much higher heat of sorption than simple ion exchange, an outer-sphere interaction. Harvey and Rhue as well as Gale et al found that ligand exchange for phosphate had a Δ H sorp that was an order of magnitude higher than simple ion exchange (i.e., 20–30 kJ mol –1 for ligand exchange vs 2–3 kJ mol –1 for simple ion exchange). The Δ H sorp for CIN to NO 3 -saturated ferrihydrite was 1.6 kJ mol –1 , more in line with physisorption or more appropriately a mixture of physisorption and ion exchange …”

A Flow Adsorption Microcalorimetry-Logistic Modeling Approach for Assessing Heterogeneity of Brønsted-Type Surfaces: Application to Pyrogenic Organic Materials

“…The increasing intensity of thermograms (and the total energy evolved E total given by integral of the thermograms), with pH is consistent with an increasingly negatively charged surface arising from continued deprotonation of pH-dependent moieties on the py OM surface. The E total, i during the probing of a (de)­protonated surfaceat a given pH, i is well-known to be directly proportional to the quantity of the probe ion (in our case K + ) sorbed ( Q total, i ) and from a contaminant perspective is reflective of metal retention capacity on py OM increasing with pH. − That is, E total, i = k ( Q total,i ) with the proportionality constant k being equal to the molar heat of sorption for the probe to the surface. Values for f COO–, i in eq can therefore be expressed as E total ,i / E total,max or Q total, i / Q total,max where E total,max and Q total,max are the integrated energy and sorbed quantity associated with maximum surface deprotonation.…”