INTERACTION OF CATIONS WITH SH-MODIFIED SILICA-GEL - THERMOCHEMICAL STUDY THROUGH CALORIMETRIC TITRATION AND DIRECT EXTENT OF REACTION DETERMINATION

The reaction of silica gel with 3-(trimethoxysilyl)propane-l-thiol, MP TS, produced a thiol-modified silica gel, Sil-SH. This material remove s silver, mercury, copper, zinc and nickel ions from aqueous solutions . Enthalpy changes that occur in the interactions between Sil-SH and t hese cations were obtained by a calorimetric titration technique, in w hich thermal effects and the quantities of cations that interact at ea ch titration point were determined simultaneously. From this procedure , values of the maximum capacity of interaction (N-3), enthalpies of i nteraction at different coverages of the surface [Delta(int(i))H-m] an d integral enthalpy of interaction for a monolayer (Delta(mon)H(m)) ha ve been established. It is shown that this method permits charting the basic sites created upon modification. From Delta(int(i))H-m values, the sequence of the interaction strength between the basic sites of th e silica-attached MPTS and the cations is Hg2+ > Ag+ > Cu2+ > Ni2+ > Z n2+, agreement with the concept of hard and soft acids and bases. The influence of some parameters concerning the thermodynamics of solvatio n of the indicated transition metals has been also taken into account in the investigation of these interaction processes.