الرحيم الرحمن الله بسم

Islamic University – GazaFaculty of ScienceChemistry Department

Title of ResearchSynthesis and application of

Diethylentriamine polysiloxane Immobilized ligand

Prepared by :

Mohammad Hassan raidah & Ahmad marwan alashi

Supervised by :

Dr. Nizam M. El Ashgar

Submitted in Partial FulfilmentOf the Requirements for B.S Degree

July 2008

الرحيم الرحمن الله بسمال والذين يعلمون الذين يستوي هل قل )

(يعلمونالعظيم الله صدق

( 9 آية – الزمر سورة )

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We very pleased to thanks my God , who give us these

successful because he said in holy Qurane .

يعلمون ال والذين يعلمون الذين يستوي هل قل

Special thanks to us guides DR. Nizam M. El-Ashgar we very

greatful for his advices and information which helped us in this

research .

We thanks all who works in chemistry department to all help us

in doing this research , and teach us for four years

For my best guides … who have been with me in every step in my scientist way .For us dears fathers , mothers , brothers and sisters .

For all Palestinian Materies

ABSTRACT

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Porous solid polysiloxane ligand system have been prepared

using sol-gel process either before or after polymerization.

The ligand is triamine.

Polymer name is diethylenetriaminepolysiloxane

The polysiloxane-Immoblized ligand system show high potential for

extraction of some heavy metal ions including Copper, Nickel

and ,Cobalt. uptake of metal ions increases in the order:

Cu2+ Ni2+ Co2+

Several conditions such as :time , pH ,Concentration ,buffer type ,

particle size and , shaking were used to reach the optimum metal

uptake capacity

We introduction onto polysiloxane net work the new functionlized

ligand system exhibit high capacities for uptake of metal ions

The ligand system also show high selectivity to separate a mixture of

metal ion.

These immobilized ligand systems were also, used and tested for

removal of toxic heavy metal ions from wastewater.

The optimum pH appeared to be pH=5.2 using acetate buffer as an

eluent, th preconcentration chemisorbed metal ions were regenerated

from the solid extraction using 0.5M HCl

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This research is concerned with the preparation of some functionalized

insoluble inorganic polymers and using them as metal-extraction agents from aqueous

solution.

Fundamentally, two types of polymeric matrices can be considered, organic

and inorganic matrices. Recently, attention has been turned to inorganic polymeric

compounds because of their thermal stability at high temperature, rigidity and general

chemical inertness. Many organic polymers suffer from defects such as variable degrees

of swelling in solvents and limited thermal stability(1).

The polysiloxane-immobilized ligands are important class of inorganic supports,

particularly silica-based matrices, with chemical composition and properties give them

an intermediate position between typical inorganic matrices (silica, silicates, quarts,

etc.) and organic polymers, since they contain both a silica-oxygen, framework and

organic radicals (functional groups) attached to silicon atoms(2).

The aim of the present work is to exploit the potential of the functionalized

chelating polysiloxane for analytical applications such as extraction and separation of

some toxic heavy metals such as Cu2+, Ni2+, Co2+. Cadmium is considered as a highly

toxic element, and tends lo be accumulated with even very low exposures because

its excretion is extremely slow. It also causes on low chronic exposure, hypertension

and kidney damage. Zinc and copper have relative toxicity. The choice of chelating

functional groups over others as extractants is due to the high stability constants

associated with them, thus making them suitable as extractants even for heavier metal

ions in dilute solutions(3). These materials find many applications in catalysis, water,

and wastewater treatment, hydrometallurgy, industrial processes, and miscellaneous

applications in analytical chemistry(4).

1. Polymeric Supports.

Polymeric matrices are classified into two categories,

1.1 Organic Polymeric Supports.

Insoluble organic polymers usually have a three dimensional, cross-linked

matrix of hydrocarbon chains resulting from the polymerization of a suitable mixture of

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monomers, to form a cross-linked network in such away the functional ligand groups

can later be introduced. The degree of cross-linking determines the properties of

polymeric structure and its solubility.

Linear non-cross-linked polymers are soluble, while highly cross-linked

polymers limit the mobility of the functionalized organic side chains. Hence prop

adjustments of the degree of cross-linking must be carried out to obtain a suitable

support. The organic polymeric matrices are formed in two general ways.

a) Addition Polymers:

These polymers have cross-linked structures formed by free-radical

polymerization of mixtures of olefinic and diolefinic organic compounds(5). A

well-known example of this type is the polymerization of styrene with difunctional

divinylbenzene (DVB). By varying the amount of divinylbenzene in the reactants

mixture, the degree of cross-linking can be adjusted (Scheme 1.1)

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Scheme 1.1

b) Poly condensation Polymers:

These are cross-linked structures with high molecular weight, usually formed

by ionic organic reactions from small poly functional monomers through the removal

of small molecules such as water, alcohol or ammonia. New C-C, C-N, C-O or other

bonds are formed(5). For example; p-substituted phenol may condense with

formaldehyde to yield linear condensation polymers with no cross-linking. The Para -

position is occupied and the meta- position is inaccessible to the aldehyde (Scheme

1.2)

Scheme 1.2

On the other hand, if unsubstituted phenol is added, across-linked polymeric matrix is

formed and hence a rigid three-dimensional structure may be obtained (Scheme 1.3).

Scheme 1.3

By varying the content of phenol its the reaction mixture the degree of cross linking

can be adjusted. Such organic condensation polymers have poor chemical am

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mechanical stability as they can easily undergo hydrolytic and cleavage reactions.

Multidentate ligand groups can be introduced in these cross-linked polymer (Schemes,

1.1, 1.2 and 1.3) by substitution before or after polymerization.

1.1.1 Advantages and disadvantages of Organic Polymeric Supports.

Organic polymers can be modified by functionalization of ligand groups of

practical applications. These polymers have a number of advantages including:

i- Their chemistry is well established and well known.

ii- Selecting the appropriate functional groups.

iii- Their pore size can be adjusted.

iv- Their structural rigidity can be controlled.

v- They can be obtained as porous spherical beads.

vi- High degree of functionalization can be achieved, particularly for polymer,

containing aryl groups.

On the other hand, organic polymeric matrices have some disadvantages:

i- They are unstable under high pressure and disintegrate into smaller fragments, so

clog up columns at high pressure chromatographic operations(5).

ii- They are sensitive to high temperature and radiation.

iii- They swell in most organic solvents.

iv- Lack of chemical and mechanical stability.

So it is very important to search for other polymeric matrices which have superior

properties.

1.2 Inorganic Polymeric Supports.

Inorganic polymers are normally utilized for supporting functional groups. Examples

are: silica, glass: beads, clays, zeolites and polysiloxanes(4). These inorganic supports,

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particularly the silica-based matrices, offer several advantages over organic polymeric

supports, including:

i- Physical rigidity and high mechanical resistivity.

ii- Negligible swelling in both aqueous and organic solutions.

iii- Chemical inertness (low interaction with analytes and lower poisoning by

irreversible side reactions).

iv- High biodegradational, photochemical and thermal stability.

v- Good mechanical and heat transfer properties.

vi- Have a good ability to withstand high pressure .

vii- Greater control for diffusion factors which is inaccessible with organic polymers

because of variation of swelling as a function of solvent and pressure .

The main disadvantages of these inorganic polymers is its susceptibility to

degradation by basic solutions pH (6).

1.2.1 Silicon Compounds.

Compounds of silica are widely used for obtaining inorganic polymeric matrices and

play an important role in technology(7).

Silicon resembles carbon in the ability of forming covalent compounds, such as silica

gel and polysiloxane materials The chemical bond between the silicon and oxygen

atoms, Si-O, is called the (siloxane bond). The most frequently used inorganic

supports are silica and polysiloxanes. The backbone of these silica-based supports are

Si-O-Si linkages. The Si-O bond is formed by the (σ) bonding of the hybridized s and

p electrons of the silicon atom with the p electrons of oxygen. There is an additional

(π) bonding interaction of the unshared p electrons of the oxygen with the 3d orbital of

the silicon called p(π)-d(π) conjunction. The nature of p(π)-d(π) bonding measures the

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differences in the structure and the properties of the corresponding silicon and carbon

atoms (4).

The Si-O bond is very stable, its average bond energy which calculated from heats of

combustion is in the range (422-494 KJ/mol): and its bond length is 1.64 ± 0.03 A0 ,

which is substantially smaller than the length of the Si-O bond (1.83 A0), calculated

from individual atomic radii . The strength of the Si-O bond can be explained by its

substantial ionic character (40-50%) in addition to partial double bond character, due

to p(π)-d(π) interactions. The larger Si-O bond dissociation, energy compared with

that of C-O (35S KJ/mol) and Si-C bond energy (318 KJ/mol) bear testimony to the

strength of Si-O bond due to the existence of p(π)-d(π) interaction .

From practical point of view, it is useful to study silane-coupling agents, which are

special types of organosilicon compounds as they considered to be the starting and

intermediate products in the siloxane materials

1.2.2 Silane Coupling Agents.

Silane coupling agents have been used widely to modify surfaces for chemical.

applications, and lo immobilize chelating functional groups on silica gel and on

prepare organofunctionalized polysiloxane polymers.

Silane coupling agents have the general form X3Si-R where X is hydrolyzable group

and R represents an organo functional group. The organofunctional groups are chosen

for reactivity with the polymer, while the hydrolyzable groups X (Cl or OR) are

merely intermediates in formation of silanol groups for bonding to mineral surface.

Ordinarily, trialkoxysilane is used because it is easier to handle than the

trichlorosilane and the corrosive HC1 formed as a by product of hydrolysis is

undesirable(4).

Silane coupling agents combine the organic chemistry of organofunctional groups

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with inorganic chemistry of silicates to bridge the hydrophilic interface between

mineral substrate and organic polymer.

To form a bond between a ligand and the surface of silica, a molecule containing an

organofunctional ligand group, is reacted with the surface silanols. In principle this

can be achieved in several ways, all of which have been used to bond

organofunctional groups to inorganic structures (Scheme 1.4).

Where: R = an organofunctional group,

X= a readily hydrolysable group such as Cl. OR, NH2. OCOR.

Scheme 1.4

Method (iii) is preferred for bonding groups to silica because:

a) It produces an Si-C unit at the surface which is much more hydrolytically and

thermally stable than either an Si-O-C or Si-N-C unit.

b) Many organofunctional compounds of the type RSiX3 are readily available

c) It is a one-step reaction that is simple to carry out under mild conditions.

Therefore in principle any ligand that forms part of an organic molecule of the type

RSiX3 and hence bind to silica surface. However practically it is sometimes easier to

modify or replace an organic group already attached to the surface.

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1.3 The Polysiloxane Supports.

Polysiloxane-immobilized ligands or polyorganosiloxanes are intermediates in

composition between the pure inorganic silica and organic polymers such as

polystyrene. They are chemically modified insoluble polyorganosiloxane materials.

The term "siloxane" was adopted for these polymers initially in analogy to ketone

since the structural unit of the chain R2SiO appears to correspond the ketone R2CO

(Scheme 1.5) however siloxane is a more appropriate term identifying the (Si-O)

bond(4).

Scheme 1.5

Most work on polysiloxanes seems to be hidden in patents. They find use in many

applications ranging from electric insulation, biomaterials, catalyst supports,

stationary phase in liquid chromatography and separation of metal ions from solutions.

Siloxane polymers are made from organosilane intermediates (monomers) which are

compounds of the general type X4-nSiRn, where R is alkyl or aryl group and X is a

group which can be hydrolyzed to SiOH such as chlorine or alkoxy, where 3 ≥ n ≥

1. The repeating unit of polyorganosiloxane consists of alternating silicon and oxygen

atoms in which organic radicals are attached to each silicon atom (Scheme 1.5).

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These polysiloxane-immobilized ligands usually prepared by the sol-gel process which(8,9)

proceeds via hydrolytic polycondensation of metal alkoxides. This process, which takes place

at room temperature includes two steps that may occur simultaneously Acid or base catalysis

may be used to enhance or control the sol-gel process.

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1.4.1 Preparation of Polysiloxane Immobilized Ligand System.

Insoluble polysiloxane ligand systems can be prepared by two methods:

Method 1:

Hydrolytic polycondensation of a mixture of tetraethyl orthosilicate (TEOS) and the

appropriate silane coupling agent in a definite mole ratio() (Khatib, 1985) through the

sol-gel process(9) (Hench and West, 1990). Acid or base (10)catalysis can be used to

enhance the two-step process, which, takes place at room temperature (Aelion, et al.,

1950).

Method 2:

Modification of the preformed polysiloxane immobilized ligand system by the

appropriate ligand group(12).

1.4.2 Sol-gel Process.

The sol-gel process, a method for the production of inorganic materials at

ambient temperature, was first reported some 150 years ago (Ebelman, 1846 and

Graham, 1864). The process is gaining renewed interest because it provides a

convenient way for incorporation, immobilization, entrapment, and encapsulation for

large variety of materials include; organic, inorganic, biomolecules, microorganisms,

tissue and indicators(13) (Hench, and west, 1990; Brinker and Scherer, 1989; Klein

and dun, 1988; Zusman and Rottman, 1990; Samuel, et al., 1994)

1.4.3 Steps of the Sol-gel Process.

The synthetic method of polysiloxanes by sol-gel process as its name implies,

involves the formation of a colloidal suspension (sol) and gelation of the sol to

form a wet gel (a globally connected solid matrix), which after drying forms "dry

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gel" state (xerogel) (12) (Brinker, 1988 and 1994).

The following steps summarizes the preparation of polysiloxane by the sol-gel

process.

1.4.3.1 Hydrolysis.

Most sol-gel techniques use water and low molecular weight tri- or/and tetra-

alkoxysilanes as gel precursors. Because alkoxysilanes are not miscible with water, a

common solvent is used for homogenization, although in some cases the released

alcohol can provide sufficient homogenization. Generally the hydrolysis reaction is

promoted by the addition of a catalyst. Hydrolysis leads to the formation of silanol

groups. Soluble intermediates produced in the alcohol-water medium include, silanols,

ethoxy silanols and oligomers of low molecular weight which formed at the first

stages of the process(12) (Hench and west, 1990)

SiOR + H2O SiOH + ROH

Two models for the hydrolysis reaction have been proposed, one in which a

trivalent (Swain, et al., 1949) and another in which a pentavalent (Keefer, 1984),

transition state is formed. Raman spectroscopic studies on the hydrolysis of TMSO

indicate that the model involving a pentavalent transition is correct(12) (Hench and

West, 1990).

Hydrolysis can be readily occur under acidic or basic catalysts.

1.4.3.2 Acid Catalyzed Hydrolysis:

In general, acids accelerate the hydrolysis process of alkoxysilane, the most frequently

used acid is hydrochloric acid. Other acids such as, acetic acid, phosphoric acid or

sulfuric acid have been used (Zhitova, 1969 and Segal, et al., 1960). It has been

suggested that the resulting gels are much the same whichever acid is used(12)

(Yurchenko, et al., 1970).

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It is proposed that the mechanism of hydrolysis under acidic condition is proceeded as

follows (Scheme 1.6).

Where: R = CH3 or C2H5.

Scheme 1.6

The proton is attracted by the oxygen atom of the OR group. This causes a shift of the

electron cloud of the Si-O bond toward oxygen, and the result the positive charge of

the silicon atom increases. A water molecule can now attack the silicon atom, and a

transition state is formed(12). (Hench and West, 1990).

1.4.3.3 Base Catalyzed Hydrolysis:

In case of base catalysis ion, the reaction is caused by a hydroxyl ion (Scheme 1.7).

here: R = H3 or C2H5.

Scheme 1.7

The OH- ion has high nucleophilic power and is able to attack the silicon atom

directly. These attacks are aimed toward the silicon atom as the Si atom carries the

highest positive charge.

1.4.3.4 Polycondensation.

The polycondensation of alkoxysilanes can be summarized in terms of two

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reactions: silanol-silanol condensation and silanol-ester condensation(12) (Hench and

west, 1990), (Scheme 1.8).

SiOH + SiOH Si-O-Si + H2O

or

SiOR + SiOH Si-O-Si + ROH

Where: R = CH3 or C2H5.

Scheme 1.8

For example the formation of the solid product from TMOS, (Scheme 1.9), (Hench

and West 1990).

Hydrolysis:

Condensation:

Scheme 1.9

Further polycondensation occurs to produce SiO2 network (Scheme 1.10).

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Scheme 1.10

Many different intermediates are possible. This means that it is very hard to

give an exact thermodynamic description of what might be possible or not, in the sol-

gel reaction paths. The effect of the different reaction parameters (Organic radical of

the OR group, solvent, catalyst, temperature and concentration) has to be investigated

experimentally, and the conclusions have to drawn from these results (Schmidt, 1984).

The H2O and alcohol expelled from the reaction remain in the pores of the network.

The hydrolytic ability of the Si-O-Si bond is responsible for the differences between

organic and inorganic polycondensation. Organic polymers evolve through the

formation of dimmers, trimmers, and linear chains, which cross-link to form the gel

state. Inorganic particles, however evolve either through aggregation of small colloids

or by addition of low molecular weight particles to larger ones (Lev, et al., 1995).

1.4.3.4 Gelation.

Gelation of the sol formed when interconnection between particles of the sol increases

forcing the sol to become more viscous (gel-point) so lose its fluidity. At the initial

stages of polymerization, the silanol functional groups at the surface of the growing

particles are partly deprotonated and their negative charge provides a repulsion barrier

that stabilizes the sol. Latter, solvent evaporation and water consumption by alkoxy

silane hydrolysis concentrated the solution and destabilize the suspension (12) (Lev, et

al., 1995).

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1.4.3.5 Drying .

During the last stages of gelation, water and the organic solvent evaporate from the

pores of the glassy material and the volume of the solid shrinks gradually (In some

cases, the final volume of the xerogel is 10% of the initial volume of the gel).

During the drying phase, some of the larger pores are emptied while smaller pores

remain wetted by the solvent, creating large internal pressure gradients. This process

causes cracking and fracture in large monoliths. Addition of surfactants, such as

Triton-X, were suggested to prevent these fractures (Lev, et al., 1995). Drying the wet

gel under monitored conditions also, give free cracks monolith (Hussien, 2001).

1.4.3.6 Aging.

In this stage, the polycondensation reactions, formation of new bonds, water

and alcohol are still occurs as a function of time (Dave, et al., 1994). Additional cross-

linking and spontaneous shrinking occurs. As a result composition, structure and

properties of the gel continue changing with time (Shibayama and saigo, 1995;

Campostrini, et al., 1996). The gel is aged to complete the reaction, which include

further hydrolysis and resterification. The strength of the gel increases with aging

(Scheme 1.11).

SiOR + H2O SiOH + ROH

SiOH + ROH SiOR + H2O

Scheme 1.11

1.4.4 General methods of Preparation.

The basic synthetic method of functionalized polysiloxane through the sol-gel process

is the hydrolytic polycondensation of a mixture of tri- and tetra- silane agents

(monomers); [R’Si(OR)3 and Si(OR)4](10) (Khatib and Parish, 1989). More than two

components of alkoxysilane may be used to form the functionalized polysiloxane.

Tetraalkoxysilane (eg. TEOS) is the base component which gives the polysiloxane its

rigidity due to the cross-linking polymerization (Khatib, 1985), (Scheme 1.12).

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R = Me or Et R’ = Organofunctionalized ligand

Scheme 1.12

The porous structure of the functionalized polysiloxane can be modified by

varying the conditions of gelation, such as pH of the reactants sol, temperature during

gel sedimentation and drying conditions of the gel, etc., (6) (Jaber, 1983).

The first preparation of functionalized polysiloxane was by Neimark and

coworkers (15) (Chuiko, et al., 1966). It was based on the hydrolytic polycondensation

of TEOS and 3-aminopropyltrimethoxysilane in the presence of methanol as solvent

in alkaline media.

Solid ligands was firstly prepared by Khatib(10) by hydrolysis and

condensation tetraethylorthosilicate with alkoxysilane agents carrying functional

groups in appropriate molar ratio of the mixture (Khatib, 1985).

Recently, during the last twenty years several fucntionalized polysiloxanes

have been prepared (16,24) (El-Nahhal and Parish, 1993; Parish et al., 1989, 1993,

1999; Ahmed and Parish, 1993; El-Nasser and Parish, 1999; El-Nahhal et al., 1999,

2000, 2001, 2002) and their structure have been characterized (25,26) (El-Nahhal, et al,

1996; Yang, el al. 1997; El-Nahhal et al 2001) and different applications based on the

prepared polysiloxanes have been studied(16,24) (El-Nahhal et al., 2000, 2001, 2002).

1.4.4.1 Sol-Gel Method.

Polysiloxanes bearing halide groups (I or Cl) were prepared by hydrolytic

condensation of a mixture of TEOS and 3-halopropyltrimethoxysilane to give

functionalized 3-halopropyl polysiloxane. The reaction was catalyzed by Bu2Sn(OAc)2

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or HCl(16,24).(Khatib, 1989; Ahmed, 1993). The optimum ratio of

TEOS/Halopropyltrimethoxysilane is 2:1(10,17). (Khatib, 1985; Ahmed, 1993)

(Scheme 1.13).

Scheme 1.13

1.4.4.2 The Modification Method.

Since few number of silane coupling agents is available, the modification

method was used to prepare the appropriate polysiloxane ligand systems.

Most of the insoluble functionalized polysiloxanes can be modified with new ligand

groups. This method was used for the synthesis of many modified polysiloxanes,

where the silane coupling agent is not available. The produced polysiloxane

immobilized ligand systems exhibit higher density of ligand groups or ligand sites

than silica functionalized with the same ligand groups(16,24) (Khatib and Parish,

1989).

New polysiloxane ligand systems were prepared by the reaction between the

iodopropyl polysiloxane ligand system (P-I) and diethyliminodiacetate

HN(CH2COOEt)2 which then was hydrolyzed to give the functionalized

polysiloxane immobilized iminodiacetic acid (P-IDA) (12) (scheme 1.14).

Scheme 1.14

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The diethyliminodiacetate polysiloxane ligand system was then modified with

ethylenediamine and diethylenetriamine by direct reaction (12) (Scheme 1.15).

Scheme 1.15a

Another new polysiloxane immobilized ligand system was prepared by the reaction

between iodopropyl ligand system (P-I) with ethy-2-aminobenzoate (EAB) (12)

(Scheme1.15).

(scheme 1.15b)

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The ethyl-2-iminobenzoate polysiloxane ligand system was then modified with either

ethylenediamine or diethylenelriamine by direct reaction(12) (Scheme 1.16)

(Scheme 1.16)

1.16a

Scheme1.16a

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25

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Preparation of polysiloxane-Immobilized Triamine Ligand System (PTA)

Diethylenetriamine has been used as Chelating ligand for many decades interoduce

into the polysiloxane by direct reaction with halogenofunctionalized polysiloxane (19)

Prepared this ligand system by the reaction of 3-Iodopropylpolysiloxane with an

excess diethylenetriamine in the presence of triethylamine

This reaction carried out under nitrogen ,for 48 hours. The solid material was washed

and dried under vacuum ,

1.4.5 Characterization of Functionalized Polysiloxanes.

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Many attentions have been exerted in the past on the preparation of new

functionalized polysiloxanes but few studies have been reported to characterize these

new insoluble polymeric systems.

Elemental analysis was the essential technique used to characterize such

polymers by many workers (Khatib, 1985; Ahmed, 1991; Habibi, 1988; Parish, et al.,

1989; El-Nahhal, et al, 1993; El-Kurd, 1998; El-Ashgar, 1999; Nassar, 2001). As the

polysiloxanes are insoluble in solvents they are difficult to be characterized by

classical spectroscopic instruments such as UV, VIS, NMR. Only limited methods are

available (Ahmed, 1991). IR spectra have been used for the identification of the main

functional groups attached to these ligand systems(16,24), (Ahmed, 1991; El-Kurd,

1998; El-Ashgar, 1999, El-Hashash, 2000, Nassar; 2001).

Recently, in the last ten years great efforts have been exerted to characterize the

structures of functionalized polysiloxanes using high resolution solid state NMR

technique as well as other techniques (24,25) (Yang, et al., 1996; Yang et al., 1997; El-

Nahhal, et al., 1996; Yang et al., 1997; El-Nahhal et al., 2000).

Valuable information was obtained from solid state 29Si, 15N, 13C, and 1H NMR

spectra, which assist characterization of these polysiloxane-immobilized ligand

systems. Other techniques such as XPS, TGA and TDG were also help in

characterization. Characterization of functionalized polysiloxanes include: the matrix

(Si-O)n, net work , the polysiloxane surface and the functional groups. A brief

explanation of the different technical methods will be discussed in the following

sections.

1.4.5.1 CP-MAS NMR.

When magnetically active nuclei in the solid state placed into a magnetic field, no

given nucleus will resonate at a precise value, but will resonate over a fairly wide

frequency range. This line broadening is generally severe enough to prevent the

observation of NMR fine structure(12).

A new technique, based on Magic Angle Spinning, (MAS), is used for solids

and highly viscous samples(27) (Engelhard & Michel, 1987; Bleam, 1991). This

technique is based on the appropriate averaging of the various solid-state interactions,

28

by spinning the sample at a certain angle to the applied magnetic field. In other hand,

the relaxation times of nuclei from their ground state can be very long in solid matrix.

Therefore modern solid state NMR spectrometers have the possibility of cross-

polarization, (CP) (28), (Engelhard & Michel, 1987; Bleam, 1991). This cross

polarization was originally designed to enhance the sensitivity of nuclei with a low

magnetogyric ratio () or a low natural abundance. It is used in solid state for

permitting an improvement of the signal to noise ratio.

1.4.5.2 29Si NMR

29Si CP-MAS NMR spectra are expected to provide valuable information about the

nature of attachment of the various silicon atoms and on the stability of the attachment

of these ligands.

The 29Si NMR spectra of the immobilized polysiloxanes ligand systems show two

regions of major intensities occurred at about -105 and -60 ppm. These two positions

correspond to Si(-O-)4 and RSi(-O-)3 units, respectively, where R is an

organofunctional group. The -105 ppm pattern is composed of at least three

contributions, at about -91, -100 and -108 ppm, due to the following typesof species;

(≡Si)2Si(OR')2, (≡SiO)3SiOR' and siloxane bridges (≡Si)4Si respectively, where R'=Et,

Me or H. These types are often referred to as Q2, O3 and Q4 sites respectively (12)

(Yang et al., 1997).

In 29Si NMR spectroscopy, siloxane bridges and different surface silanols, which are

single (either isolated or vicinal) and double (geminal), (Scheme, 2.24) have been

distinguished (Vansant, 1995; Maciel and Sindrof, ). The single silanols are referred

as Q3 sites (-94 ppm) and the double Q2 sites (-100 ppm).

Geminal (Q2) Isolated (Q3) Vicinal (Q3)

-94 ppm -100 ppm -100 ppm

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Scheme 1.17

Further observations of polysiloxanes surface obtained by hydrolytic

polycondensation are confirmed using 29Si CP MAS. Based assignments of spectra

have been elaborated by De hann and co-workers by studying aminopropyltrimethoxy

silane modified polysiloxane(29) (De Hann, et al., 1986). Comparing the shielding

effects of ethoxy and hydroxy substituents, they proposed that and hydrolyzed and

non-hydrolyzed monodentate species have a different peak positions (Scheme 2.25).

-67 ppm -59 ppm -52.9 ppm -49 ppm

Scheme 1.18

1.4.5.3 1H NMR.

The proton NMR should in principle be an extremely useful tool in the

characterization of surface hydroxyls. This technique is complementary to silicon

NMR, for the identification of silanol groups, since it discerns free and bridged

hydroxyls as not as silicon NMR single and geminal hydroxyls.

However, proton NMR on solid samples is encumbered by the severe broadening

effects of strong 1H-1H magnetic dipolar interactions. If these effects are not too large,

because of the large 1H-1H internuclear distances and/or fast motional averaging, then

sharp 1H NMR resonances can often be achieved by magic-angle-spinning (MAS) (12)

(Vansant, et al., 1995).

A well resolved 1H NMR of silica surface was not produced before 1988 by

Bronnimann's technique (Bronnimann, et al., 1988), which was further developed by

Haukka and co-workers(30,31) (Haukka, 1993; Haukka, 1994).

30

The 1H MAS NMR spectra of surface silanol resemble infrared spectra: one broad

peak is attributed to hydrogen bonded silanols and one sharper peak to the isolated

silanols.

1.4.5.4 13C NMR.

Solid state 13C CP-MAS NMR spectroscopy is very useful for characterizing the

pendent groups of the polysiloxane-immobilized ligand systems. Chemical shifts

reveal details of chemical form or structure and both chemical shifts and line widths

provide some information on the nature of interactions (e.g., hydrogen bonding) of the

ligand groups with the polysiloxane framework or with other ligand groups.

In addition to characterize functionalized ligand groups of polysiloxanes, this

technique is used to detect the extent of hydrolysis the alkoxy groups during sol-gel

process.

The 13C NMR indicates a loss of ethoxy groups as no peaks are observed at

57.6 ppm (-OCH2-) and 15.9 ppm (-OCH2CH3) (25,26) (Yang et al., 1996; Chiang et

al., Yang et al., 1997).

Other valuable information could be obtained from 13C NMR included:

detection of leaching soluble oligomers from the polysiloxane matrix upon treatment

with acidic and basic solutions due to the hydrolysis of the polysiloxane networks

under these conditions (25,26) (Yang, et al., 1997).

It is also used to indicate how the organic functionalities distributed in the

polysiloxane matrices (Yang 1997).

1.4.5.5 15N NMR.

15N CP-MAS NMR spectra of amine ligand systems can be expected to provide useful

information about the environments of the amine groups and their interactions with

each other or with proton donors or acceptors, e.g., silanols of silica-like regions of the

polysiloxane framework. (Yang, et al., 1997). It is also used to confirm the

31

coordination behavior between the amine binding ligands and metal ions(25,26) (Yang

et al., 1997).

1.4.5.6 FTIR Studies.

Infrared spectroscopy has been widely applied when studying the silica and

polysiloxane surfaces (Vansant, 1995). The FTIR spectroscopic studies for

polysiloxanes-immobilized ligand systems show three main regions as given in the

following Table.

Frequency cm-1 Species

3746 Free OH

3742 Geminal OH

3730-3720 Hydrogen perturbed OH

3650 Intraglobular OH

3520 Oxygen perturbed OH

3400-3500 Molecular adsorbed H2O

2000-1870 Skeleton overtone vibrations

1625 Bending O-H (molecular water)

1285-985 Asymmetrical Si-O-Si stretching

970 Si-O-(H….H2O) bending

870 Bending O-H (silanol)

FTIR spectra also used to detect many functional groups at their ordinary

assignments, such as amines (El-Nahhal, et al., 2000;El-Nahhal, et al., 2001, Zaggout,

32

et al., 2001)) amides, (El-Nahhal, et al, 1999) carboxylic and .esters(12) (Parish, et al.,

1999; El-Nahhal, et al., 1999; El-Nahhal, et al., 2000, Leyden, 1980).

1.4.6 APPLICATIONS.

These materials have several applications. These applications include:

preconcentration and extraction of divalent metal ions from aqueous solutions ions. It

also used as solid phase for separation of a mixture of metal ions. These immobilized

ligand systems were also, used and tested for removal of toxic heavy metal ions from

wastewater(12).

33

34

2. Experimental

2.1. Reagents and Materials.

Tetraethylorthosilicate, diethylenetriaminopropytrimethoxysilane, were purchased

from MERCK and used as received. Diethyl ether and methanol (spectroscopic grade) were

used as received. Solutions of metal ions of the appropriate concentrations were prepared by

dissolving the metal chloride (analar grade) in deionized water. pH range of 3-6 was

controlled by using acetic acid (0.1 M)/sodium acetate (0.1 M) buffer solutions.

2.2. General Techniques.

Analysis for carbon, hydrogen and nitrogen was carried out, using an Elemental

Analyzer EA 1110-CHNS CE Instrument. The concentrations of metal ions in their aqueous

buffer solutions were measured using a Perkin-Elmer A Analyst-100 spectrometer. The

infrared spectra for the materials were recorded on a Perkin-Elmer FTIR spectrometer using

KBr disk in the range 4000 to 400 cm1. All pH measurements were carried out using HM-40

V pH Meter.

2.3. Preparation.

2.3.1. Preparation of Polysiloxane-Immobilized Diethylenetriamine Ligand

System (P-DTA).

Polysiloxane-Immobilized diethylenetriamine (P-DTA) was prepared by adding

diethylenetriaminopropytrimethoxysilane (13.27, 50 mmol) to a stirred solution of

tetraethylorthosilicate (20.83 g, 100 mmol) in 15 mL methanol and HCl (4.95 mL, 0.42 M).

Gelation occurred within few seconds. The product was left to stand for 12 hours then dried

in vacuum oven at 90 oC. The material was crushed, sieved, washed successively with 50 mL

portions of 0.025 M NaOH, water, methanol and diethyl ether and then dried in vacuum oven

at 90 oC at 0.1 torr for 10 hours.

2.4. Batch Experiments.

A 100 mg of the functionalized polysiloxane-immobilized ligand system, P-DTA was

shaken with 25 cm3 of 0.02 M aqueous solution of the appropriate metal ions (Co2+, Ni2+ and

Cu2+) using 100-cm3 polyethylene bottles. Determination of the metal ion concentration was

35

carried out by allowing the insoluble complex to settle down, withdrawing an appropriate

volume of the supernatant using a micropipette and then diluting to the linear range of the

calibration curve for each metal using AAS. The maximum metal ion uptake capacity was

calculated as mg of M2+/g ligand. Each study was performed at least in a triplicate.

2.5. Column experiments.

2.5.1. Preconcentration Experiment.

A glass column (250 mm long, 10 mm diameter) was washed sequentially with 0.1 M

nitric acid, water and acetone. It was then oven-dried and packed with a bed (5.0 g, 60-80

mesh) of the diethylenetriamine immobilized ligand system, P-DTA. The packed material

was activated for each run by washing with 15 cm3 of aqueous solution of 0.5 M

hydrochloric acid, followed by deionized water and finally with acetate buffer solution at pH

5.5. Solutions (50 cm3, 100 ppm) of each metal ion at different pH values were eluted with a

flow rate at 1.0-1.5 cm3 min-1 by gravity. When needed, vacuum pump was used to reach the

desired flow rate. In another experiment, the column containing the bed (5.0 g, 60-80 mesh)

of P-DTA, was activated as mentioned previously and solutions of different concentrations

(0.0005 – 1.0 M) buffered at pH 5.5 were passed through the column with a flow rate at 1.0-

1.5 cm3 min-1. The chemisorbed metal ion was eluted by passing 50 cm3 of an aqueous 0.5 M

hydrochloric acid. The metal ions were quantified by atomic absorption spectroscopy.

2.5.2. Column Separation Experiment.

The column was packed with the functionalized diethylenetriaminopolysiloxane, P-

DTA (5.0 g, 60-80 mesh). After each use the column was flushed with 0.50 M hydrochloric

acid, followed by deionized water, to remove any uneluted metal contaminant. Before any

sample injection, the column was preconditioned by passage of 25 cm3 of the appropriate

buffered aqueous solution to equilibrate the column as that of the working solution. Solution

of a mixture of metal ions (Co2+, Ni2+ and Cu2+, each of 100 ppm) was injected in the column.,

then buffered solutions of controlled pH were passed through the column at a flow rate of 1.0

-1.5 cm3 min-1 by gravity. The eluates were collected in fractions with a volume range 5-10

cm3. Each fraction was diluted to 50 cm3 and the amount of metal ion (mg) in each fraction

was determined using atomic absorption spectroscopy. The retained metals on the ligand

system were eluted with 10 cm3 of 0.50 M hydrochloric acid. The solution was then diluted

to 50 cm3 and the metal concentrations in the solution were determined by using atomic

absorption spectroscopy.

36

37

1.1.1 3. Results and Discussion

3.1 Synthesis of Polysiloxane-immobilized Triamine Ligand System (P-DTA).

The diethylenetriamine polysiloxane ligand system (P-DTA) was made by hydrolytic

polyucondnsation between TEOS and diethylenetriaminopropyltrimethoxysilane (Scheme 1).

The elemental analysis results of the prepared polysiloxane are given in Table 1. The

functional group content of the ligand system is higher than previously reported results [15].

It is found that percentages of C and N are slightly lower than expected due to formation of

small oligomers which leached during the washing process [10, 30-32]. Formation of these

small oligomers is enhanced by the presence of self base catalyzed amino groups which lead

to rapid gelation, so small amounts of non-cross linked oligomers are formed [10, 30-32].

The equal ratios of both expected and found results confirm that complete functionalized

ligand leached.

Scheme 1

Table 1: Elemental analysis for polysiloxane-immobilized triamine ligand system (P-

DTA).

mmol N/gC/NN%H%C%Element

9.52.3313.285.7326.56Expected

8.52.3811.895.924.34Found

3.2. FTIR Spectrum.

38

4000.0 3000 2000 1500 1000 400.0

20.5

25

30

35

40

45

50

55

60

65

70

75

80

85

88.1

cm-1 cm-1

%T %T

3453.84

1641.17

1520.75

1067.68

789.93

582.04

461.28

2952.02

The FTIR spectrum of the immobilized diethylenetriaminepolysiloxane, P-DTA

ligand system is given in Fig. 1. The figure shows three characteristic absorption regions at

3500-3200 cm-1 due to (OH), (NH) or (NH2), 1650-1560 cm-1 due to (OH), (NH2) or

(NH) and 1200-900 cm-1 due to (Si-O) respectively. The s strong bands at 3453 cm-1 and

1641 cm -1 are due to (NH2/NH/OH) and ( NH2/NH/OH) vibrations respectively. This

confirms that the diethylenetriamine functional group is chemically bonded to the

polysiloxane surface.

Fig

. 1. F

TIR

sp

ectr

um

of

P-D

TA

.

39

3.3 Metal Uptake Capacity of P-DTA

The metal ion uptake capacity of Co2+, Ni2+ and Cu2 +, was determined by shaking the

functionalized ligand system, P-DTA with buffered metal ions solutions for 48 hours. The

results in mg M2+/ g ligand are given in Table 2. The elemental analysis of nitrogen of the

immobilized ligand (P-DTA) as given in Table 1 was 11.89% i.e. 2.8 mmol N/g ligand.

Comparing this value with the maximum metal ion uptake, it is possible to suggest that not

all functional groups are accessible to binding with the metal ions assuming the ligand to

metal complexation ratio is 1:1. It is clear that uptake of metal ions increases in the order:

Cu2+ Ni2+ Co2+

Table 2: Maximum metal uptake by P-DTA

Maximum Uptake Co2+ Ni2+ Cu2+

mg M2+/g Ligand 97 104.2 129

mmol M2+/g Ligand 1.64 1.77 2.03

3.4. Effect of pH on the metal ions chemisorption.

The influence of pH of the aqueous solution on the retention of cobalt, nickel and

cupper was investigated in the pH range 3-6 by using acetate buffer solution. The results are

depicted in Fig. 2. The recovery values of the analyte ions were generally found to be very

small at low pH values and increases by increasing pH. Maximum retention occurs at pH 5.5.

In case of cupper about 100% was retained while 93% and 88 % were retained in case of

nickel and cobalt respectively.

40

0

20

40

60

80

100

120

2.5 3 3.5 4 4.5 5 5.5 6 6.5

pH

% o

f m

eta

l io

n r

eta

ined

Cu(II) retained Ni(II) retained Co(II) retained

Fig. 2. Chemisorption of metal ions by P- DTA versus pH values.

3.4. Preconcentration of metal ions.

The ability of P-ABT to preconcentarte metal ions from aqueous solution was

evaluated using aqueous solutions of metal ions at different concentartions. The results are

given in Fig. 3. The amount of metal ion recovered by the ligand system increases with

increasing concentration up to the maximum value. Based on elemental analysis of N (11.89

%) of the ligand system (each ligand contains 3 N atoms), there was 2.8 mmol ligand per

gram of immobilized system. Assuming 1:1 complex formation of M:L mole ratio the

maximum loading (theoretically) of metal ion would be 179 mg Cu, 164 mg Ni and 165 mg

Co per gram ligand system. The maximum chemisorption values were obtained at

concentration of 0.5 M of the eluted metal ions and found to be 128 mg Cu, 104 mg Ni and

97 mg Co per gram ligand system. These values represent preconcentration efficiency of the

column in percentages of 73.5 %, 63.4 % and 58.8 % for copper, nickel and cobalt

respectively. At low metal ios concentration, 100 % extractions were achieved. This

promises the column to be an excellent preconcentration system for these metal ions.

41

0

20

40

60

80

100

120

140

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

Con. of metal ion (M)

mg

of

met

al i

on

ret

ain

ed

Co(II) Ni(II Cu(II

Fig. 3. Preconcentration of Co(II), Ni(II) and Cu(II) as a function of concentration (5.0 g

of ligand system, flow rate 1.0 -1.5 cm3 min-1 , pH = 5.5).

3.5 .Separation of metal ions.

Separation of a mixture of metal ions Cu(II), Ni(II) and Co(II) was performed by

elution with buffer solutions at different pH values. Three bands were observed by pH

control. A blue color band of Cu(II) was observed upstream followed by a green and a pink

bands of Ni(II) and Co(II) respectively. These metal ions were eluted cleanly from the

mixture by pH control. Fig. 4 shows the separation of Cu(II), Ni(II) and Co(II) metal ions as a

function of elution volume at variable pH values. Complete separation of Co(II), Ni(II) and

Cu(II) from solution mixture was performed and improved by stepwise pH control of the

eluent . The desorbed amount of metal was calculated from the total fractions of 500 cm3.

Three well resolved peaks of cobalt, nickel and copper ions were obtained, at pH 4.5, 4 and

0.1 N HNO3 respectively. This promises the ligand system to be efficient in a clean

separation of these metal ions.

42

0

5

10

15

20

25

30

35

40

0 50 100 150 200 250 300 350 400 450 500 550

Volume of eluent (mL)

mg

M(I

I) d

eso

rbed

Ni(II) Co(II) Cu(II)

pH 4.5

pH 4 0.1 M HNO3

Fig. 4. Separation of a mixture of Co(II), Ni(II) and Cu(II), (5.0 g of ligand system, flow

rate 1.0 -1.5 cm3 min-1 , pH = 5.5, total eluent volume = 500 cm3).

Conclusion

The immobilized diethylenetriamine ligand system was prepared by direct sol-gel

hydrolytic polycondensation reaction of diethylenetriaminopropyltrimethoxysilane and

tetraethylorthosilicate monomers at ambient temperature. This ligand system has been shown

to be an effective solid-phase preconcentration agent for cobalt, nickel and copper at pH 5.5.

The ligand system exhibits high potential for separation of a mixture of Co2+, Ni2+ and Cu2+

metal ions from aqueous solution by pH control.

43

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