pH effect on acetate adsorption at Pt(111) electrode

pKa as a Predictive Descriptor for Electrochemical Anion Adsorption

The adsorption of anions onto metal surfaces is important in many applications including effective (electro)catalyst design, metal surface modification, and contaminant removal in wastewater treatment. In electrocatalysis, anions can be both reactive intermediates or site-blocking spectators, where their adsorption strength therefore dictates the rate of reaction. In this work, we have measured the adsorption energy of a series of carboxylic acids on a Pt (111) single-crystal electrode surface from aqueous solution. We find that the adsorption strength of the carboxylate anion is linearly correlated with its acid-dissociation constant (pKa) and therefore the heterolytic O-H bond dissociation strength in solution. Using density functional theory modeling, we split the anion adsorption energy into a sum of the adsorption energy and electron affinity of a neutral (carboxyl) radical. Surprisingly, the adsorption energy of the carboxyl radicals are similar and therefore the large difference in electron affinity is what dictates anion adsorption strength; the greater the cost in energy to remove the electron from the anion upon adsorption, the weaker its binding. Therefore, at least within a class of anions with similar structure and surface binding atoms, both electron affinity and acidity are predictive descriptors of adsorption strength.

Study on the Adsorption Performance and Adsorption Mechanism of Graphene Oxide by Red Sandstone in Aqueous Solution

In order to deal with the increasingly serious pollution of graphene oxide (GO) to the environment. In this paper, the use of red sandstone to treat GO-contaminated aqueous solution is proposed for the first time, and the adsorption capacity and adsorption mechanism of red sandstone to GO are discussed. The controlled variable method was used to explore the optimal pH, concentration, and quality of red sandstone for GO aqueous solution. The adsorption isotherm, thermodynamics, and adsorption kinetics were fitted. Adsorption characterization tests were performed using XRD, AFM, XPS, FT-IR, SAP, TEM, SAP, laser particle size analyzer, and SEM. The results show that when $T=303\text{K}$ , the optimum adsorption condition of red sandstone for GO is $\text{pH}=4$ , the mass of the adsorbent is 40 mg, and when the concentration of GO is 80 mg/L, the adsorption capacity is 90 mg/g. The adsorption isotherm model fits the Langmuir model. The adsorption thermodynamic experiments and fitting results show that the reaction is endothermic. XRD and FT-IR tests showed that CaCO3 in red sandstone was involved in the adsorption of GO. SEM, TEM, and AFM microscopic results showed that GO was adsorbed on the surface of red sandstone particles. The XPS test showed that Ca2+ in red sandstone and C=O bond in GO undergo ionic or coordination reaction. The adsorption kinetics fit a pseudo-second-order kinetic model. This study will provide some references for the removal of GO in the environment and the interaction mechanism with natural minerals.

Facile Synthesis of Thiol-Functionalized Magnetic Activated Carbon and Application for the Removal of Mercury(II) from Aqueous Solution

To improve the adsorption capacity, reduce the disposal cost, and enhance the separation efficiency of common activated carbon as an adsorbent in wastewater treatment, a novel thiol-modified magnetic activated carbon adsorbent of NiFe₂O₄-PAC-SH was successfully synthesized with a facile and safe hydrothermal method without any toxic and harmful reaction media. The as-prepared NiFe₂O₄-PAC-SH can effectively remove mercury(II) ions from aqueous solution. The maximal adsorption capacities from the experiment and Langmuir fitting achieve 298.8 and 366.3 mg/g at pH 7, respectively, exceeding most of adsorptive materials. The as-prepared NiFe₂O₄-PAC-SH has an outstanding regeneration performance, remarkable hydrothermal stability, and efficient separation efficiency. The data of kinetics, isotherms, and thermodynamics show that the adsorption of mercury(II) ions is spontaneous and exothermic. Ion exchange and electrostatic attraction are the main adsorption factors. The experimental results exhibit that the NiFe₂O₄-PAC-SH can be a prominent substitute for conventional activated carbon as an adsorbent.