Unravelling Hydrogen Adsorption Kinetics on Ir(111)Electrode in Acid Solutions by Impedance Spectroscopy

The kinetics for hydrogen(H)adsorption on Ir(111)electrode has been studied in both HClO_(4) and H_(2)SO_(4) solutions by impedance spectroscopy.In HClO_(4),the adsorption rate for H adsorption on Ir(111)increases from 1.74×10^(-8)mol·cm^(-2)·s^(-1) to 3.47×10^(-7)mol·cm^(-2)·s^(-1) with the decrease of the applied potential from 0.2 V to 0.1 V(vs.RHE),which is ca.one to two orders of magnitude slower than that on Pt(111)under otherwise identical condition.This is explained by the stronger binding of water to Ir(111),which needs a higher barrier to reorient during the under potential deposition of H from hydronium within the hydrogen bonded water network.In H_(2)SO_(4),the adsorption potential is ca.200 mV negatively shifted,accompanied by a decrease of adsorption rate by up to one order of magnitude,which is explained by the hindrance of the strongly adsorbed sulfate/bisulfate on Ir(111).Our results demonstrate that under electrochemical environment,H adsorption is strongly affected by the accompanying displacement and reorientation of water molecules that initially stay close to the electrode surface.

Significance of Ligand Exchange Relating to Sulfate in Retarding Acidification of Variable Charge Soils Caused by Acid Rain

For the purpose of evaluating the role of ligand exchange of sulfate ions in retarding the rate of acidification of variable charge soils, the changes in pH after the addition of different amounts of HNO_3 or H_2SO_4 to representative soils of China were measured. A difrerence between pH changes caused by the two kinds of acids was observed only for variable charge soils and kaolinite, but not for consted charge soils and bentonite. The larger the proportion of H_2SO_4 in the HNO_3-H_2SO_4 mixture, the lower the calculated H￣+ ion activities remained in the suspension. The difference in H￣+ ion activities between H_2SO_4 systems and HNO_3 systems was larger for soils with a low base-saturation (BS) percentage than those with a high BS percentage. The removal of free iron oxides from the soil led to a decrease in the difference, while the coating of Fe_2O_3 ona bentonite resulted in a remarkable appearance of the difference. The effect of ligand exchange on the acidity status of the soil varied with the soil type. SurfaCe soils with a hash organic matter content showed a less pronounced effect of ligand exchange than subsoils did. It was estimated that when acid rain chiefly containing H_2SO_4 was deposited on variable charge soils the acidilication rate might be slower by 20%-40% than that when the acid rain chiefly contained HNO_3 for soils with a high organic matter content, and that the rate might be half of that caused by HNO_3 for soils with a low organic matter content, especially for latosols.

Effect of Sulfate Adlayer on Formic Acid Oxidation on Pd(111) Electrode

The kinetics of formic acid oxidation (FAO) on Pd(111) in 0.1 mol/L H2SO4+0.1 mol/L HCOOH with and without addition of Na2SO4 is studied using cyclic voltammetry and potential step method, which is compared with that in 0.1 mol/L HClO4. It is found that adsorbed sulfate has significant inhibition effect on FAO kinetics. After addition of 0.05 mol/L or 0.1 mol/L Na2SO4, FAO current in the negative-going scan is found to be significantly smaller than that at the same potential in the positive-going scan. We speculate that at potentials positive of the phase transition potential for the (SO4*ad)m+[(H2O)n-H3O+] or(SO4*ad)m+[Na+(H2O)n-H3O+] adlayer, the adlayer structure probably becomes denser and more stable with the increase of potential or with the addition of Na2SO4. The formation of connected adlayer network greatly enhance the stability of the adlayer, and the insertion of positive-charged H+ or Na+ into the adlayer network further reduces the electrostatic repulsion between partially charged sulfates. As a result, the destruction/desorption of compact sulfate adlayer becomes more difficult, which leaves much less free sites on the surface for FAO, and thus FAO kinetics at higher potentials and in the subsequent negative-going potential scan is significantly inhibited.

INDIRECT VOLTAMMETRIC DETERMINATION OF TRACE SULFATE IN NATURAL WATERS WITH THE ADSORPTIVE COMPLEX WAVE OF LEAD(Ⅱ)-TETRAKIS (4-TRIMETHYLAMMONIUM PHENYL) PORPHYRIN

The indirect voltammetric determination of trace sulfate (2.0×10^(-6)～4.0×10^(-5) mol/L ) with the adsorptive complex wave of lead(Ⅱ)-tetrakis (4-trimethylammonium phenyl) porphyrin (PbTTMAPP) is reported.This method has been used for the analysis of natural waters with satisfactory results.

Chitosan—The Application of a Natural Polymer against Iron Hydroxide Deposition

As a consequence of mining, heavy metal ions can be exposed to the environment hence contaminate ground water and surface water amongst others. The natural polymer chitosan was proved to be an excellent adsorber material for the effective removal of iron and sulfate ions in batch as well as in column experiments. The adsorption behavior of iron ions, as well as sulfate ions was investigated by utilizing chitosan flakes as a natural adsorbent. The removal was studied using adsorbance measurements, SEM and SEM-EDX. The adsorption capacity of chitosan was determined at different times. The received adsorption capacities for iron ions were very promising with a maximum adsorption capacity of 85 mg/g and a rate of separation of 100%. The maximum adsorption capacity obtained for sulfate ions was 188.8 mg/g and a rate of 80%.