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It is found that all ethylacetate groups (-CO Et) were completely hydrolyzed to ‘the acid form (— CO2H). ag ne 1 The ‘°C NMR spectra for the immobilized iminodiacetic acid and for the immobilized diethyliminodiacetate ligand systems are used to examine the extent of hydrolysis of eth- oxy groups after treating the immobilized diethyliminodiac- etate with hydrochloric acid [47] as given below.

Figure 19 It is found that all ethylacetate groups (-CO Et) were completely hydrolyzed to ‘the acid form (— CO2H). ag ne 1 The ‘°C NMR spectra for the immobilized iminodiacetic acid and for the immobilized diethyliminodiacetate ligand systems are used to examine the extent of hydrolysis of eth- oxy groups after treating the immobilized diethyliminodiac- etate with hydrochloric acid [47] as given below.

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1.1.3.1. Chemical reaction of silica. The enhanced acidity of silica surface gives it a high degree of chemical reactivity, so it can react with many coupling agents to immobilize organo-functionalized silanes [32] (Scheme 3), in which Lis- ichkin and Zaitsev’s teams have made an important contri- bution [33,34].
1.1.3.1. Chemical reaction of silica. The enhanced acidity of silica surface gives it a high degree of chemical reactivity, so it can react with many coupling agents to immobilize organo-functionalized silanes [32] (Scheme 3), in which Lis- ichkin and Zaitsev’s teams have made an important contri- bution [33,34].
Many different intermediates are possible. This means that it is very hard to give an exact thermodynamic descrip- tion of what might be possible or not, in the sol-gel reac- tion paths. The effect of the different reaction parameters (Organic radical of the OR group, solvent, catalyst, tem- perature and concentration) has to be investigated experi- mentally, and the conclusions have to be drawn from these results [83].
Many different intermediates are possible. This means that it is very hard to give an exact thermodynamic descrip- tion of what might be possible or not, in the sol-gel reac- tion paths. The effect of the different reaction parameters (Organic radical of the OR group, solvent, catalyst, tem- perature and concentration) has to be investigated experi- mentally, and the conclusions have to be drawn from these results [83].
When the pore liquid is removed at or near ambient pressure by thermal evaporation, the dry gel is called a 1.2.2.4. Gelation. Gelation of the sol occurs when inter- connection between particles of the sol increases forcing the sol to become more viscous (gel-point) thereby losing its fluidity. At the initial stages of polymerization, the sila- nol functional groups at the surface of the growing parti- cles are partly deprotonated and their negative charge provides a repulsion barrier that stabilizes the sol. Later,
When the pore liquid is removed at or near ambient pressure by thermal evaporation, the dry gel is called a 1.2.2.4. Gelation. Gelation of the sol occurs when inter- connection between particles of the sol increases forcing the sol to become more viscous (gel-point) thereby losing its fluidity. At the initial stages of polymerization, the sila- nol functional groups at the surface of the growing parti- cles are partly deprotonated and their negative charge provides a repulsion barrier that stabilizes the sol. Later,
solvent evaporation and water consumption by alkoxy silane hydrolysis concentrated the solution and destabilized the suspension [84].
solvent evaporation and water consumption by alkoxy silane hydrolysis concentrated the solution and destabilized the suspension [84].
Where, X = NH,, H,N(CH,),NH,,H,N(CH,),NH(CH,),NH,, -N*(CH,)CI, -N(Et), The hydrolysis of amino-—ligand system alone (under these conditions) results in the formation of o igomers which are completely soluble in water [35]. Condensation, using TEOS in the optimum ratio of TEOS/aminopropyl- trimethoxysilane (2:1), minimizes the formation o oligomers to a very small extent. The immobilized mono- amine ligand exhibits high po ential for metal u f soluble ptake of divalent metal ions (Co", Ni‘, Cu? and Zn°*). Maxi- mum metal uptake capacities Lower metal uptake occurs at are obtained at pH 5-7. ow pH < 4 due to proton- ation of the amino groups [39,46]. The immobilized mono- amine ligand exhibits high potential for separation of copper(II) from aqueous solu ion containing Co 2+ yet , Ni and Cu". The ligand system has been shown to be an effec-
Where, X = NH,, H,N(CH,),NH,,H,N(CH,),NH(CH,),NH,, -N*(CH,)CI, -N(Et), The hydrolysis of amino-—ligand system alone (under these conditions) results in the formation of o igomers which are completely soluble in water [35]. Condensation, using TEOS in the optimum ratio of TEOS/aminopropyl- trimethoxysilane (2:1), minimizes the formation o oligomers to a very small extent. The immobilized mono- amine ligand exhibits high po ential for metal u f soluble ptake of divalent metal ions (Co", Ni‘, Cu? and Zn°*). Maxi- mum metal uptake capacities Lower metal uptake occurs at are obtained at pH 5-7. ow pH < 4 due to proton- ation of the amino groups [39,46]. The immobilized mono- amine ligand exhibits high potential for separation of copper(II) from aqueous solu ion containing Co 2+ yet , Ni and Cu". The ligand system has been shown to be an effec-
: The immobilized thiol-monoamine and thiol-diamine ligand systems form metal(II) complexes when treated with
: The immobilized thiol-monoamine and thiol-diamine ligand systems form metal(II) complexes when treated with
aqueous metal(II) ion solutions (M = Ni**, Cu**, Cd? ‘and Hg**) [104]. Polysiloxane immobilized by hybrid mixture of triamine-thiol ligand as chelating functional groups exhibits high potential for extraction and preconcentration of divalent metal ions such as Co?*, Ni** and Cu?* at an optimum condition [42]. The optimum uptake results indi- cate that the triamine-thiol ligand seems to form 1:1 metal to ligand complexes [42]. 1.4. Modification method of functionalized polysiloxane xerogels
aqueous metal(II) ion solutions (M = Ni**, Cu**, Cd? ‘and Hg**) [104]. Polysiloxane immobilized by hybrid mixture of triamine-thiol ligand as chelating functional groups exhibits high potential for extraction and preconcentration of divalent metal ions such as Co?*, Ni** and Cu?* at an optimum condition [42]. The optimum uptake results indi- cate that the triamine-thiol ligand seems to form 1:1 metal to ligand complexes [42]. 1.4. Modification method of functionalized polysiloxane xerogels
Polysiloxane immobilized diamine and systems were prepared by the reaction o chloropropyl-functionalized polysiloxane with ethy diamine and diethylene triamine, respec ively [45,46, triamine ligand f iodopropyl- or ene 00] (Scheme 21). It is found that the immobilized triamine ligand system prepared by the sol-gel route results in a high amount of complexing ligand (7.3 mmo g 'ligand) t nan the treatment of iodopolysiloxane with diethylene triamine (4.0 mmol g~'). The immobilized and triamine ligand sys- tem exhibit high potential for the extraction of diva metal ions (Co**, Ni* and Cu’*) [45]. The immobilized diamine ligand system forms metal(II) chelate complexes when treated with divalent metal ions (Cu*?, Zn‘? and ent El-Nahhal and co-workers [47,103] used an alternative method to prepare polysiloxane-immobilized system bear- ing the iminodiacetate groups. The iodopropyl polysilox- ane reacted with diethyliminodiacetate, followed by hydrolysis using HCI (Scheme 23). This immobilized ligand system exhibits high potential for the extraction of various divalent and trivalent metal ions (Fe*", Co7*, Ni2*, Cu?* and Zn?*). The analysis reveals that 1:1 metal-to-ligand complexes are accomplished [47].
Polysiloxane immobilized diamine and systems were prepared by the reaction o chloropropyl-functionalized polysiloxane with ethy diamine and diethylene triamine, respec ively [45,46, triamine ligand f iodopropyl- or ene 00] (Scheme 21). It is found that the immobilized triamine ligand system prepared by the sol-gel route results in a high amount of complexing ligand (7.3 mmo g 'ligand) t nan the treatment of iodopolysiloxane with diethylene triamine (4.0 mmol g~'). The immobilized and triamine ligand sys- tem exhibit high potential for the extraction of diva metal ions (Co**, Ni* and Cu’*) [45]. The immobilized diamine ligand system forms metal(II) chelate complexes when treated with divalent metal ions (Cu*?, Zn‘? and ent El-Nahhal and co-workers [47,103] used an alternative method to prepare polysiloxane-immobilized system bear- ing the iminodiacetate groups. The iodopropyl polysilox- ane reacted with diethyliminodiacetate, followed by hydrolysis using HCI (Scheme 23). This immobilized ligand system exhibits high potential for the extraction of various divalent and trivalent metal ions (Fe*", Co7*, Ni2*, Cu?* and Zn?*). The analysis reveals that 1:1 metal-to-ligand complexes are accomplished [47].
reaction of polysiloxane-immobilized amine ligand system with methylchloroacetate or ethylchloroacetate (Scheme 24) [102,105]. Treatment of aqueous solutions of divalent metal ions with polysiloxane glycinate ligand system dem- onstrates that this material exhibits high potential for pre- concentration of divalent metal ions (Cu?*, Zn** and Cd?) at optimum conditions [102,105].
reaction of polysiloxane-immobilized amine ligand system with methylchloroacetate or ethylchloroacetate (Scheme 24) [102,105]. Treatment of aqueous solutions of divalent metal ions with polysiloxane glycinate ligand system dem- onstrates that this material exhibits high potential for pre- concentration of divalent metal ions (Cu?*, Zn** and Cd?) at optimum conditions [102,105].
It might be expected that the maximum metal loading would correspond to one metal per two glycinate groups. This stoichiometry was not achieved and low metal uptake was found [101]. The low metal uptake may be due to irreg- ularity of the distribution of glycinate groups on the poly- mer matrix. When used as chromatographic stationary
It might be expected that the maximum metal loading would correspond to one metal per two glycinate groups. This stoichiometry was not achieved and low metal uptake was found [101]. The low metal uptake may be due to irreg- ularity of the distribution of glycinate groups on the poly- mer matrix. When used as chromatographic stationary
polysiloxane ligand and 2:1 metal-to-ligand complexes for the iminobis(N-diethylenetriamineacetamide) ligand sys- tems. The immobilized iminobis(N-diethylenetriamineace- tamide) ligand system showed a high efficiency of 92-95% after recovery from its primary metal complexes. These immobilized ligand systems were found to be very stable at pH 6-8, but they undergo substantial leaching upo treatment with acidic and basic solutions [106,107]. This immobilized iminobis(N-2-aminoethylacetamide) ligand system exhibits high potential for separation of Cu(II), Ni) and Co(II) from aqueous solution containing the three metal ions by pH control [109]. The ligand system
polysiloxane ligand and 2:1 metal-to-ligand complexes for the iminobis(N-diethylenetriamineacetamide) ligand sys- tems. The immobilized iminobis(N-diethylenetriamineace- tamide) ligand system showed a high efficiency of 92-95% after recovery from its primary metal complexes. These immobilized ligand systems were found to be very stable at pH 6-8, but they undergo substantial leaching upo treatment with acidic and basic solutions [106,107]. This immobilized iminobis(N-2-aminoethylacetamide) ligand system exhibits high potential for separation of Cu(II), Ni) and Co(II) from aqueous solution containing the three metal ions by pH control [109]. The ligand system
Two immobilized macrocyclic ligand systems P-M1 and P-M2 were prepared by treatment of the iminobis(/V-ethy- lenediamineacetamide) and iminobis(N-diethylenetriami- neacetamide) ligand systems with 1,3-dibromopropane, respectively (Schemes 30 and 31, respectively). The poly- siloxane-immobilized macrocyclic 1,4,7,11,14-pentaaza- pentadecane-3,15-dione ligand system (P-M1) was The polysiloxane-immobilized macrocyclic 1,4,7,10, 14, ,3-dibromopropane [114]. T 7,20-heptaazadocosane-3,21-dione ligand system was pre- pared by the reaction of the immobilized diethyliminodiac- etate ligand system with diethylene triamine followed by he new macrocyclic ligand system P-M2 shows high potential towards metal ions, including Fe*, Co”, Ni? and Zn”, and it was very selective oward copper ions. Comp exation with copper ions
Two immobilized macrocyclic ligand systems P-M1 and P-M2 were prepared by treatment of the iminobis(/V-ethy- lenediamineacetamide) and iminobis(N-diethylenetriami- neacetamide) ligand systems with 1,3-dibromopropane, respectively (Schemes 30 and 31, respectively). The poly- siloxane-immobilized macrocyclic 1,4,7,11,14-pentaaza- pentadecane-3,15-dione ligand system (P-M1) was The polysiloxane-immobilized macrocyclic 1,4,7,10, 14, ,3-dibromopropane [114]. T 7,20-heptaazadocosane-3,21-dione ligand system was pre- pared by the reaction of the immobilized diethyliminodiac- etate ligand system with diethylene triamine followed by he new macrocyclic ligand system P-M2 shows high potential towards metal ions, including Fe*, Co”, Ni? and Zn”, and it was very selective oward copper ions. Comp exation with copper ions
°Si NMR and elemental analysis data for the immobi- lized monoamine ligand system showed that these materials undergo some leaching when treated with acid or metal ion solutions [100]. The leaching ligand containing species were also identified and characterized [99]. °°Si CP-MAS and *’Si DP-MAS NMR spectra were used to elucidate the structure of the immobilized monoamine and 3-chloropropyl polysiloxane systems (e.g. determination of the relative amounts of R-Si(—O-)3 and Si(—O—)4 moieties of various types). The hypothetical repre- sentation structures, i.e. The immobilized amine and the chloropropyl ligand system, are determined [100].
°Si NMR and elemental analysis data for the immobi- lized monoamine ligand system showed that these materials undergo some leaching when treated with acid or metal ion solutions [100]. The leaching ligand containing species were also identified and characterized [99]. °°Si CP-MAS and *’Si DP-MAS NMR spectra were used to elucidate the structure of the immobilized monoamine and 3-chloropropyl polysiloxane systems (e.g. determination of the relative amounts of R-Si(—O-)3 and Si(—O—)4 moieties of various types). The hypothetical repre- sentation structures, i.e. The immobilized amine and the chloropropyl ligand system, are determined [100].
t has been reported that the relatively broad signals of '5C NMR spectra of the immobilized monoamine compared wit h that of 3-chloro- and 3-(trimethylammonium)propyl polysiloxane in the immobilized monoamine ligand system may involve hydrogen bonding between the amine groups and surface silanols or other ligand groups (structures I, II and III) [41,100] as given below: For these systems, the presence of a lot of water mole- cules on the silica surface may have involved in the hydro- gen bonding with the amine and silanol groups. The °C NMR spectra of immobilized monoamine ligand system after silylation with hexamethyldisilazane (Me3Si).NH were used to examine the structural changes in the (-CH,CH,—-NH>) group, after the surface silanols are capped by Me;3Si groups causing an effect in the hydrogen bonding between surface silanols and amine groups. A comparison is made between the °C NMR spectra of immobilized monoamine ligand system and that of the polysiloxane-immobilized diethylpropyl amine and the polysiloxane-immobilized trimethylpropyl ammonium hydrochloride, where the amine—amine (structure I) and amine-silanols (structures II and III) hydrogen bonding are not possible, respectively [41]. acme i ee
t has been reported that the relatively broad signals of '5C NMR spectra of the immobilized monoamine compared wit h that of 3-chloro- and 3-(trimethylammonium)propyl polysiloxane in the immobilized monoamine ligand system may involve hydrogen bonding between the amine groups and surface silanols or other ligand groups (structures I, II and III) [41,100] as given below: For these systems, the presence of a lot of water mole- cules on the silica surface may have involved in the hydro- gen bonding with the amine and silanol groups. The °C NMR spectra of immobilized monoamine ligand system after silylation with hexamethyldisilazane (Me3Si).NH were used to examine the structural changes in the (-CH,CH,—-NH>) group, after the surface silanols are capped by Me;3Si groups causing an effect in the hydrogen bonding between surface silanols and amine groups. A comparison is made between the °C NMR spectra of immobilized monoamine ligand system and that of the polysiloxane-immobilized diethylpropyl amine and the polysiloxane-immobilized trimethylpropyl ammonium hydrochloride, where the amine—amine (structure I) and amine-silanols (structures II and III) hydrogen bonding are not possible, respectively [41]. acme i ee
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