Effect of Specific Adsorption of Ions on Electrokinetic Properties of Variable Charge Soils

Studies were carried out by using electrophoretic method on the effects of the specific adsorption of the anions,such as SO4^2-,PO4^3-,and F^- ions,the cations,such as Ca^2+,Mn^2+,Zn^2+,and Cu^2+,ions,and the anions and cations coexisting,such as Zn^2+ and SO4^2= ions,on electrokinetic properties of the red soils as typical variable charge soils in China concerning variation in the specific ion species and concentrations,with an emphasis on the interaction between soil colloid surfaces and the ions in soil solutions.The results showed that the adsorption of specific ions led to a very pronounced decrease in zeta potentials of the soil colloids and a shift of the IEPs to lower values for specific anions,and an obvious increase in zeta potentials of the soil colloids and a shift of the IEPs to higher values for specific cations.Under circumstances of the specific anions and cations coexisting,for instance,Zn^2+ and SO4^2- ions,the zeta potentials changed with values higher than the value for SO4^2- alone and lower than that for Zn^2+ alone,and the IEP was between that for Zn^2+ and that for SO4^2-.The adsorption of Zn^2+ and Cu^2+ ions resulted in a reversal of the zeta potentials,and appearance of two IEPs for Zn^2+ and no IEP for Cu^2+,exhibiting interesting special effects of these kinds of metal ions.The higher the concentrations of the ions,the greater the change of the electrokinetic properties.

Specific Adsorption of Trivalent La, Ce and Y by Soils and Ferro-manganese Oxides and Its Mechanism

In this paper, the adsorption-desorption variations of trivalent La, Ce, Y and mixed rare earths are discussed. The curves of pH-rare earth element adsorption were very well fitted to the equation: InD =a+b pH. The selectivity of RE (rare earth element) ions by the samples decreased in the following order: Ce> RE> La> Y, but the sequences were: La> Ce> Y on kaolinite and Y> La on amorphous iron oxide. Since the trivalent RE ions existed in the form of RE(OH)2+ in the solutions from pH < 5.45 to 7.0, the ratio of H+ displaced to RE3+ adsorbed in micromole was proposed to be about 2. The specific adsorption mechanism for RE was proposed to be that the RE ions complexed with oxide surface and the ion-surface complex of Ce3+ promoted oxidization on Mn hydroxide.

Modulation of Electrochemical Oscillations by Specific Adsorption of Cl- during the Electrooxidation of Methanol on Pt Electrode

Potential oscillation during the electrocatalytic oxidation of methanol can be modulated by the specific adsorption of Cl- on the platinum electrode, which suppresses the electrocatalytic oxidation of methanol, and makes the cross cycle in the cyclic voltammogram become smaller and finally disappear with the increase of Cl- concentration. The method is also applicable to the electrocatalytic oxidation of other small organic molecules.

Specific Adsorption and Its Mechanisms of Rare Earth Elements by Soils and Oxides

There have been many studies on the adsorption-desorption behavior of heavy metals such as Cu, Zn, Co, Ni, Cd and Pb by soils in China and abroad, and their adsorption mechanisms have also been sought. The above research has demonstrated that the synthetic or soil oxides like Fe, Mn and Al oxides adsorb heavy metals specifically and their specific adsorption is greatly affected by the ambient pH. The proposed mechanisms for explaining the above phenomena are as follows: ion hydrolysis-adsorption, outer or in-

Effect of Zn Adsorption on Charge of Variable Charge Soils

The variation in apparent charge of two typical variable charge soils resulting from Zn adsorption were studied by KC1 saturation and NH4NO3 replacement methods. Results showed that zinc were adsorbed specifically to those sites with negative charge. As in different pH ranges, the percentages of specific and electrostatic adsorptions of zinc and the mechanisms of specific adsorption were different, the effects of Zn adsorption on apparent charge were varied and could be characterized as: when 1 mmol Zn2+ was adsorbed, a change about 1 mmol in the apparent charge was observed in the low pH range (Ⅰ), 1.4 to 1.5 mmol in the moderate pH range (Ⅱ) and 0.55 to 0.6 mmol in the high pH range (Ⅲ). These experimental data, in terms of soil charge, proved once more author's conclusion in the preceding paper (Sun, 1993) that in accordance with the behaviors of Zn adsorption by the variable charge soils in relation to pH, three pH ranges with different adsorption mechanisms were delineated; that is, in Range Ⅰ, specific adsorption was the predominant mechanism, in Ranges Ⅱ and Ⅲ, specific and electrostatic adsorptions co-existed, but their specific adsorption mechanisms were not identical.

Zn Adsorption by Variable Charge Soils in Relation to pH

Zn adsorption by pure oxides or in the presence of a high concentration of inner electrolyte has been extensively studied. But, in studies on Zn adsorption in the complicated soil system, especially in variable charge soils, profound knowledge about the adsorption mechanism still lacks. In this paper, taking Zn ion adsorption by two typical variable charge soils as the object of the study, author discusses the relation between Zn adsorption and pH and possible adsorption mechanisms. The results showed that in the low pH range where the amount of Zn adsorbed did not exceed 50% of Zn added, the specific adsorption was the dominant mechanism. The species of Zn specifically adsorbed was free Zn2+ ion. In the middle and high pH ranges, the mechanisms of specific and electrostatic adsorptions, co-existed, accounting for about 70% and 30% , respectively. Noteworthily, in the high pH range, the hydroxyl Zn ion (ZnOH +) from Zn2+ hydrolysis probably was a preferable species for specific adsorption.

Effect of specifically-adsorbed polysulfides on the electron transfer kinetics of sodium metal anodes

Room-temperature sodium-sulfur(RT Na-S)batteries hold great promise for large-scale energy storage applications owing to the high energy density and earth-abundance of Na and S.However,the dissolution and migration of sodium polysulfides,uncontrollable Na dendrite growth,and the lack of studies on Na electrodeposition kinetics have hindered the development of these batteries.Herein,we reveal the mechanism of sodium polysulfides on the Na plating/stripping kinetics using a three-electrode system.First,the kinetic behavior deviates from the commonly supposed Butler-Volmer model,which is well described by the Marcus model.In addition,the specific adsorption of polysulfides on the sodium electrode surface is a key factor influencing the kinetics.Higher-order polysulfides(S_(8)^(2-)and S_(6)^(2-))exhibit distinct specific adsorption behaviors because of their high adsorption energies compared to lower-order polysulfides(S_(4)^(2-)and S_(2)^(2-)).The electrostatic effect caused by specific adsorption can accelerate the kinetics,whereas the blocking effect can slow the kinetics.Thus,this competitive relationship enables low concentrations of high-order polysulfides to stimulate kinetics.This implies that a weak shuttle effect is beneficial for obtaining a stable Na deposition in RT Na-S batteries.An in-depth understanding of the Na electrodeposition kinetics provides beneficial clues for future metal sodium/electrolyte interface designs.

Adsorption of Anthraquinone Dyes from Aqueous Solutions by Penicillium Terrestre

Penicillium terrestre was used for removing four anthraquinone dyes from aqueous solution. The experiments were performed in Erlenmeyer flasks and spore suspension was used for inoculation. The results show that the mechanism of dye removal by penicillium terrestre is biosorption and the growing pellets exhibit higher adsorptive capacity than the resting or dead ones. The maximum removals of disperse blue 2BLN, reactive brilliant blue KN-R, acid anthraquinone blue and bromamine acid at the concentration of 120 mg/L by biosorptionof growing pellets are 10096, 100%, 96% and 91%, respectively. The 100.0% and 91.4% KN-R removals are achieved respectively at the much higher concentration of 250 and 400 mg/L. 2.5 g/L glucose is sufficient for 100% KN-R removal by growing pellets. Salinity （NaCl） increase from 0 to 2% （W/ V） moderately accelerates both mycelium growth and KN-R removal.

Effect of Electrolytes on Surface Charge Characteristics of Red Soils

The zero point of charge (ZPC) and the remaining charge σp at ZPC are two important parameters characterizing surface charge of red soils.Fourteen red soil samples of different soil type and parent material were treated with dithionite-citrate-dicarbonate (DCB) and Na2CO3 respectively.ZPC and σp of the samples in three indifferent electrolytes (NaCl,Na2SO4,and NaH2PO4) were determined.Kaolinite was used as reference.The results showed that ZPC of red soils was affected by the composition of parent materials and clay minerals and in significantly positive correlation with the content of total iron oxide (Fet),free iron oxide (Fed),amorphous iron oxide (Feo),aluminum oxide (Alo) and clay,but it was negatively correlated with the content of total silica (Sit).The σp of red soils was also markedly influenced by mineral components.Organic components were also contributing factor to the value of σp.The surface charges of red soils were evidently affected by the constitution of the electrolytes.Specific adsorption of anions in the electrolytes tended to make the ZPC of red soils shift to a higher pH value and to increase positive surface charges of the soils,thus leading to change of the σp value and decrease of the remaining net negative charges,even to the soils becoming net positive charge carriers.The effect of phosphate anion was greater than that of sulfate ion.

Microfluidic synthesis of thiourea modified chitosan microsphere of high specific surface area for heavy metal wastewater treatment

An improved biosorbent of thiourea modified chitosan microsphere（TMCM） with high specific surface,favorable mechanical strength and excellent adsorption performance had been synthesized via microfluidic technology. Polyethylene glycol was used as a significant component added in aqueous solution of chitosan to produce such microspheres through droplets forming, chemical crosslinking and pores creating. For the improvement of adsorption capacity, thiourea was considered as an excellent choice in increasing amino functional group by graft modification. The SEM, FTIR and EDS were employed to detect distinct features of TMCM. Copper（Ⅱ） was used to test the adsorption performance of TMCM. The experimental results indicated that TMCM exhibited higher adsorption capacity（q_e= 60.6 mg g_（-1）） and faster adsorption rate than that non-modified chitosan microsphere（NMCM）.The adsorption kinetic was described well by the pseudo-second order kinetic model, which suggested that chemical adsorption along with electrons transferring was dominant in adsorption process.