Microscopic structures of Zn(Ⅱ) adsorbed onto anatase TiO2 under different particle concentrations(Cp) were studied using the extended X-ray absorption fine structure(EXAFS) spectroscopy.Results of macroscopic adsorption-desorption isotherms indicated that Cp effect was obvious in the adsorption system.Adsorption isotherms decreased substantially with increasing Cp

and reversibility also decreased.Quantitative analysis on the EXAFS spectra showed that Zn(Ⅱ) was adsorbed onto the solid surface in the form of octahedral hydrous Zn(Ⅱ) ions

which were linked to the TiO2 surface by sharing the oxygen atoms

with an average bond length of RZn-O =(1.98±0.01) .EXAFS analysis of the second sphere resulted in two Zn-Ti atomic distances of(3.26 ± 0.01)  and(3.70 ± 0.01) 

corresponding to edge-sharing linkage(stronger adsorption site) and corner-sharing linkage(weaker adsorption site) respectively.For three adsorption samples with the same adsorption density and different equilibrium concentration

the number of stronger adsorption sites(N1) remained relatively stable while the number of weaker adsorption sites(N2) decreased with increasing Cp

making the proportion of two adsorption modes(N1/N2) rise from 0.629 to 0.690.These EXAFS results revealed the microscopic mechanism behind the macroscopic adsorption-desorption isotherm experiments.At the same time the basic hypothesis of MEA theory that the adsorption density is not a state variable has been verified.