Resin-gel synthesis has the ability to become a powerful technique for the synthesis of multi-phase nanoparticles. This study aimed to take further steps into investigating the mechanism of the resin-gel synthesis based on phase differentiation of titania, in the hope to describe optimal synthetic conditions for desired polymorph production with tailored particle size. Solvent, polymer chain length, heating rate and the 
use of citric acid has been varied previously. The results obtained suggested that the working theory of the 
resin-gel synthesis may be incorrect as there was significant phase differentiation based on the solvent 
used. This work explored the effects of the stoichiometric ratio of PEG to TiCl4 and the effect of heating 
rates to clarify the reaction mechanism.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3494

Franklyn, P.J.

Narrandes, A.

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 1 No 1, 01PCN40(4pp) (2012) 
 
 
2304-1862/2012/1(1)01PCN40(4) 01PCN40-1  2012 Sumy State University 
Unlocking the Secrets Behind the Resin-Gel Synthesis for the Controlled  
Formation of Anatase and Rutile 
 
P. J. Franklyn*, A. Narrandes† 
 
Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg, WITS, 2050, 
South Africa 
 
(Received 23 June 2012; published online 13 August 2012) 
 
Resin-gel synthesis has the ability to become a powerful technique for the synthesis of multi-phase na-
noparticles. This study aimed to take further steps into investigating the mechanism of the resin-gel syn-
thesis based on phase differentiation of titania, in the hope to describe optimal synthetic conditions for de-
sired polymorph production with tailored particle size. Solvent, polymer chain length, heating rate and the 
use of citric acid has been varied previously. The results obtained suggested that the working theory of the 
resin-gel synthesis may be incorrect as there was significant phase differentiation based on the solvent 
used. This work explored the effects of the stoichiometric ratio of PEG to TiCl4 and the effect of heating 
rates to clarify the reaction mechanism. 
 
Keywords: Titania, Resin-Gel, PEG, XRD, TEM, Flame Synthesis. 
 
  PACS numbers: 61.46.Hk, 61.05.C – 
 
 
                                                          
* Paul.Franklyn@wits.ac.za 
† Ashvir.Narrandes@students.wits.ac.za 
1. INTRODUCTION 
 
The resin-gel synthesis technique is a modification 
of the Pechini method for the fabrication of nano-
materials. It involves the addition of a long chain pol-
ymer to a stable solution of metal ions within a solvent 
matrix to form a polymeric resin [1]. It has been shown 
in previous research that the choice of solvent plays a 
role in determining the eventual products of the syn-
thesis, even though the solvent is not present during 
the final burning stage when the particles are formed. 
The choice of ethanol leads almost exclusively to the 
formation of anatase, while using water with nitric acid 
leads to a mix of anatase and rutile dependent on the 
molecular weight of the polymer that is used. In addi-
tion it has been determined that the addition of citric 
acid to the solvent matrix leads to the almost exclusive 
formation of anatase. 
The accepted working theory has been that the metal 
ions coordinate to the polymer initially and, following 
complete solvent evaporation, are then agglomerated into 
nanoparticles during flame synthesis of the reaction mix-
ture [1]. Previous work we have performed has shown 
that this may not be the correct mechanism and that the 
formation of local clusters of metal ions that are co-
ordinated by the solvent and any other species present in 
the liquid medium followed by coordination of these clus-
ters to the polymer is a more likely mechanism. 
Although relatively unexplored, resin-gel synthesis 
affords the opportunity to synthesize a multi-phase ma-
terial using a single reaction step. This is in contrast to 
most other synthesis methods that invariably produce 
the phase corresponding to a global energy minimum. 
Hence, it has the potential to become a much sought 
after, powerful technique for the fabrication of a wide 
range of multi-phase nanomaterials.  
Titanium dioxide is a well understood material. 
Phase transition temperatures, abundance, stability 
and many other properties have been extensively stud-
ied and reported [2]. In addition, its nanoparticulate 
form has found numerous applications in the field of 
photocatalysis, photovoltaics and sensors [3 -5]. The 
most common and stable phase of titania is rutile fol-
lowed by anatase and then brookite [2]. Numerous lit-
erature reports state that under the correct conditions 
of temperature and/or pressure, anatase and brookite 
will irreversibly convert to rutile – the thermodynami-
cally stable polymorph [6 – 9]. This conversion property 
of TiO2 makes it an ideal candidate on which to model 
the resin-gel synthesis technique to produce multi-
phase titania in a single sample. 
The primary aim of this study was to further ad-
vancements into understanding the mechanism of op-
eration of the resin-gel synthesis. This task was under-
taken by considering the effect of changing some of the 
parameters that influence the resin-gel synthesis 
method. Using a TiCl4 precursor, the heating rate and 
the stoichiometric amount of polymer relative to the 
amount of TiCl4 at several PEG chain lengths was ex-
plored. The data generated from these variations al-
lowed for the refinement of the new, proposed mecha-
nism of resin-gel synthesis. 
 
2. EXPERIMENTAL PROCEDURE 
 
2.1 The effect of PEG stoichiometry 
 
To accommodate for the large quantities of PEG to 
be included in the reaction mixture, two batch solutions 
of TiCl4 in water were prepared. The first involved the 
addition of 6.0 ml of TiCl4 (0.055 mol) to excess distilled 
water (144 ml). Concentrated nitric acid (12 ml) was 
then added to aid solubility of TiCl4 in water. The re-
sulting solution was split into six equal parts and half 
the stoichiometric quantity of PEG of different chain 
lengths was added to each such that the mole ratio of 
TiCl4:PEG equalled 1:0.5. The actual quantities of PEG 
added to each solution are given in Table 1.  
 P.J. FRANKLYN, A. NARRANDES PROC. NAP 1, 01PCN40 (2012) 
 
 
01PCN40-2 
For the second batch solution*, 1.5 ml of TiCl4 
(0.014 mol) was added to 36 ml excess distilled water 
followed by 3 ml of concentrated nitric acid. After the 
solution had been split into 3 equal parts, half the stoi-
chiometric amount of PEG was added to each solution 
as given in table 1. 
 
Table 1 – Amounts of PEG of varying molecular weight used 
for synthesis in a 1:0.5 stoichiometric ratio with TiCl4. PEG 
marked with a * came from a second batch. 
 
Average poly-
mer molecular 
weight /g.mol-1 
Theoretical 
amount required for 
stoichiometry /g 
Actual 
amount used 
/g 
200 0.92 0.918 
400 1.84 1.91 
1500 6.885 6.92 
3000 13.77 13.50 
4000 18.20 18.20 
6000 22.22 22.28 
8000 36.72 36.72 
10000* 22.75 22.86 
12000* 27.30 27.30 
20000* 45.50 45.77 
   
For the synthesis of the stoichiometric equivalent 
ratio (TiCl4:PEG in a 1:1 ratio), two batch solutions 
were prepared for the same reason described above. 
For the first batch, TiCl4 (2.5 ml, 0.023 mol) was added 
to 60 ml distilled water and 5 ml of concentrated nitric 
acid was then introduced. The actual amount of poly-
mer added to each solution is given in Table 2.  
The second batch‡ involved the addition of 0.75ml of 
TiCl4 (6.8 mmol) to 18 ml of distilled water followed by 
1.5 ml of concentrated nitric acid. Appropriate amounts 
of different molecular weight PEG were then added to 
the three equally divided solutions (table 2).  
Each mixture mentioned above was stirred and 
heated sufficiently to ensure complete homogeneity; 
and prepared in duplicate to allow for two different 
heating rates prior to fame synthesis. 
 
Table 2 – Amounts of PEG of varying molecular weight used 
for synthesis in a 1:1 stoichiometric ratio with TiCl4. PEG 
marked with ‡ came from a second batch 
 
Average poly-
mer molecular 
weight /g.mol-1 
Theoretical 
amount required for 
stoichiometry /g 
Actual 
amount used 
/g 
200 0.92 0.92 
400 1.84 1.89 
1500 6.885 6.87 
3000 13.77 13.50 
4000 18.20 18.20 
6000 22.22 22.29 
8000 36.72 36.72 
10000‡ 22.75 22.76 
12000‡ 27.29 27.490 
20000‡ 45.48 45.21 
 
2.2 Variation in the heating rate 
 
Following the complete evaporation of excess sol-
vent from each polymer mixture, two different heating 
methods were used to engage flame synthesis of the 
polymer. 
The first method involved the conventional heating 
of the polymer mixture. Each mixture was added into a 
crucible. The crucible was placed in a sand bath (so as 
to ensure uniform heating) and heated until each mix-
ture had reached its auto-ignition point. A flame source 
was then used to ignite each sample. The black ap-
pearance of the samples suggested that a carbon coat-
ing had been deposited onto the nanoparticles, hence 
each sample was allowed to cool before being calcined 
in a muffle furnace at 773 K for one hour. 
The second heating method involved heating a cast 
iron vessel to 1173 K in a muffle furnace. Following 
complete evaporation of excess solvent from each mix-
ture, the molten polymer gel was added to the vessel. 
As was expected, due to the high temperatures, the 
polymer samples spontaneously ignited on account of 
them passing their flash points. The excessive temper-
atures also promoted the calcination of each sample 
immediately following polymer pyrolysis.  
 
2.3 Characterization and Analysis  
 
PXRD and TEM were used as the main forms of 
characterization techniques to deduce the presence of 
the different phases and particle sizes of titania. 
A Bruker D2 Phaser diffractometer using Co Kα ra-
diation in conjunction with a 0.6 mm slit and primary 
and secondary soller slits at 2.5°. A LYNXEYE® detec-
tor was used with this diffractometer. Each sample was 
placed on a zero background sample holder and ana-
lysed between 20° and 60° 2θ angles in increments of 
0.026°. TEM analysis was used to confirm the data ob-
tained using XRD. A Tecnai F20 at 200 kV was em-
ployed for this task. 
The Spurr and Myers equation was used to determine 
the mass per cent of anatase and rutile produced in each 
sample synthesised. The equation considers the intensi-
ties of the anatase (101) and rutile (110) peaks and has 
an inherent 5 % error by mass. Particle size analysis was 
performed using the instrumentally corrected Scherrer 
equation with K = 0.91. 
 
3. RESULTS AND DISCUSSION 
 
It should be noted here that crystallite size data was 
only obtained from samples that showed significant 
amounts of either polymorph. Using the current data 
extraction method for crystallite size analysis, a signifi-
cantly non-intense peak was difficult to analyse for crys-
tallite size and phase composition data. 
 
3.1 Conventional heating 
 
Figures 1 and 2 compare the mass per cent of ana-
tase and rutile formed across a range of PEG molecular 
weights at different mole ratios using the conventional 
heating rate. Comparing these figures, it is apparent 
that the ratio of metal ions to PEG had a significant 
bearing on the phase that was produced. When half as 
much PEG was employed, the amount of rutile appeared 
to increase across the range of PEG chain lengths. How-
ever, when the mole ratio of PEG to Ti ions was the 
same, the amount of rutile decreased as a function of 
increasing polymer chain length. This effect may be ex-
plained in terms of a protecting effect inferred by the 
polymer on the forming nanoparticle. If this is thought 
 UNLOCKING THE SECRETS BEHIND THE… PROC. NAP 1, 01PCN40 (2012) 
 
 
01PCN40-3 
to be true then the greater the amount of polymer within 
any sample, the greater the protecting effect will be and 
the less likely anatase will convert to rutile. 
 
 
 
Fig. 1 – Variation of anatase and rutile mass per cent and 
particle size formed as function of increasing PEG molecular 
weight in a Ti:PEG 1:0.5 conventional heat synthesis  
 
The amount of anatase formed does not exhibit a 
similar trend. In figure 2, it is clear that the amount of 
anatase formed across the range of PEG molecular 
weights first increases then decreases. Longer chain 
lengths promote the formation of anatase.  
 
 
 
Fig. 2 – Variation of anatase and rutile mass per cent and 
particle size formed as function of increasing PEG molecular 
weight in a Ti:PEG 1:1 conventional heat synthesis 
 
The relationship between particle size and the 
amount of each phase formed was interesting. For both 
anatase and rutile, larger particles were formed when 
the amount of that particular phase was lower for a 
given sample. This inverse relationship may serve as a 
means to refine a component of the mechanism of the 
resin-gel synthesis in the following manner: it is as-
sumed that during the burn process, reaction chambers 
are formed that contain the developing nanoparticle. 
These chambers are governed by the size of the poly-
mer chain post flame induced scission. The size of the 
chamber will govern the size of the nanoparticles. If 
there is very little space, only anatase will form. Given 
the small, cubic nature of the particles (as witnessed in 
HRTEM – figure 3) it is possible that these anatase 
particles will form in great numbers. 
This will result in large amounts of small anatase par-
ticles being formed. If however, the reaction chamber is 
larger, anatase will convert to rutile nanorods (figure 
4A). If the chamber is bigger still, the formed nanorods 
will cluster together around a single crystal axis into a 
ball (figure 4B). Therefore, large rutile particles are 
formed in small numbers. 
 
 
Fig. 3 – Anatase nanoparticles with approximate cubic mor-
phology from short-chain PEG synthesis  
 
 
 
Fig. 4 – A) Rutile particles forming nanorods. B) Rutile nano-
rods clustering into a nanoball 
 
As was expected, particle size increased dramatical-
ly post-calcination (figures 5 and 6). This is due to par-
ticles sintering together into larger clusters. Calcina-
tion also had the effect of converting some of the 
formed anatase particles into rutile. This result was 
also expected. 
 
 
 
Fig. 5 – Variation of anatase and rutile mass per cent and parti-
cle size formed as a function of increasing PEG molecular weight 
in a Ti:PEG 1:0.5 conventional synthesis (post-calcination) 
 
3.2 Rapid heating 
 
Figures 7 and 8 depict the changes in mass per-
centage and particle sizes formed during the rapid heat 
synthesis at two different metal ion:PEG ratios.  
Figure 7 shows an interesting trend with regard to 
the amount of rutile formed as a function of increasing 
molecular weight. There appears to be an oscillating 
trend whereby some chain lengths produce more rutile 
A B 
 P.J. FRANKLYN, A. NARRANDES PROC. NAP 1, 01PCN40 (2012) 
 
 
01PCN40-4 
and others less. It is thought that scission of the chain 
occurs at specific points for different polymers depending 
on the length of the chain used in the synthesis.  
 
 
 
Fig. 6 – Variation of anatase and rutile mass per cent and 
particle size formed as function of increasing PEG molecular 
weight in a Ti:PEG 1:1 synthesis (post-calcination) 
 
The inverse trend of particle size and the mass per-
centage of each phase formed was again observed and 
pronounced for rutile. Figure 7 also shows a clear trend 
of the size of each polymorph as a function of polymer 
chain length. Figures 7 and 8 show that rutile particles 
were larger than anatase particles. This, together with 
the oscillating trend observed for rutile may be ration-
alised in terms of the reaction chambers mentioned 
above. The clear trends observed from figure 7 are not 
witnessed in figure 8. While the inverse relationship 
between the amount of rutile and particle size formed 
was maintained, the oscillating nature described above 
was non-existant. From figure 8, the 8000 g/mol PEG 
produced a small amount of rutile in comparison to the 
other chain lengths. 
 
 
 
Fig. 7 – Variation of anatase and rutile mass per cent and 
particle size formed as a function of increasing PEG molecular 
weight in a Ti:PEG 1:0.5 rapid heat synthesis 
The differences observed across the stoichiometric 
ratios may be attributed to the polymer affording pro-
tection to the forming nanoparticle, as mentioned.  
Comparing figures 1 and 7, across the series of dif-
ferent polymer chain lengths, for the Ti:PEG in a 1:0.5 
ratio, rutile formation is enhanced when the samples are 
burned according to the conventional method. A plausi-
ble explanation for this observation is that if the samples 
were heated rapidly, the formed anatase particles would 
not have sufficient time to cluster together and form 
rutile. If, however, they were heated slowly, the forming 
anatase would have sufficient time to react with other 
anatase particles, thereby forming larger amounts of 
rutile. A similar trend could not be obtained at the high-
er stoichiometric ratio (comparing figures 2 and 8). 
 
 
 
Fig. 8 – Variation of anatase and rutile mass per cent and 
particle size formed as a function of increasing PEG molecular 
weight in a Ti:PEG 1:1 rapid heat synthesis 
 
4. CONCLUSION 
 
The molecular weight and relative molar amount of 
PEG in the reaction mixture affect phase and particle 
size formation. The results indicate that the presence 
of large amounts of polymer protect the forming ana-
tase particle, inhibiting its conversion to rutile. The 
reproducible trend of the inverse relationship between 
particle size and the mass percent of a respective phase 
lends support to the formation of reaction chambers, 
within which anatase forms and is allowed to convert 
to rutile in different ways, depending on the size of the 
chamber. A rapid ignition of the mixtures does not pro-
vide sufficient time for the conversion of anatase to 
rutile and so lends itself to the formation of anatase. 
No explanation is yet available for the large amount of 
rutile formed when a high mole ratio of PEG was em-
ployed and the ignition performed at a rapid rate. The 
sometimes random variation in rutile ratios is a factor 
that is still under investigation. Further work is also 
continuing to determine the crystallite size:rutile ratio 
relationship with respect to synthesis conditions. 
 
REFERENCES 
 
1. J.  Lin, M. Yu, C. Lin, X. Liu, J. Phys. Chem. C. 111, 5835- 
(2007). 
2. X. Chen, S.S  Mao, Chem. Rev. 107, 2891 (2007). 
3. M.R  Hoffman, S.T. Martin, W. Choi, D.W. Wahneman. 
Chem. Rev. 95, 69 (1995). 
4. Optoeletronics Properties of Inorganic Compounds 
(Ed. D.M. Roundhill, J.P. Facker) (New York: Plenum: 
1999). 
5. G. Sheveglieri, Gas Sensors (Dordrecht: Kluwer: 1992). 
6.  Y. Hwu, Y.D. Yao, N.F. Cheng, C.Y. Tung, M.H. Lin, 
Nanostruct. Mater. 9, 355 (1997). 
7. X.Y. Ding, X.H Liu, J. Mater. Res. 13, 2556 (1998). 
8. H. Zhang, J.F Banfield, J. Mater. Chem. 8, 2073 (1998). 
9. X, Ye, J. Sha, Z. Jiao, L. Zhang, Nanostruct. Mater. 8, 919 
(1998). 


English

Unlocking the Secrets Behind the Resin-Gel Synthesis for the Controlled  Formation of Anatase and Rutile

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 1 No 1, 01PCN40(4pp) (2012)   2304-1862/2012/1(1)01PCN40(4) 01PCN40-1  2012 Sumy State University Unlocking the Secrets Behind the Resin-Gel Synthesis for the Controlled  Formation of Anatase and Rutile  P. J. Franklyn*, A. Narrandes†  Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg, WITS, 2050, South Africa  (Received 23 June 2012; published online 13 August 2012)  Resin-gel synthesis has the ability to become a powerful technique for the synthesis of multi-phase na-noparticles. This study aimed to take further steps into investigating the mechanism of the resin-gel syn-thesis based on phase differentiation of titania, in the hope to describe optimal synthetic conditions for de-sired polymorph production with tailored particle size. Solvent, polymer chain length, heating rate and the use of citric acid has been varied previously. The results obtained suggested that the working theory of the resin-gel synthesis may be incorrect as there was significant phase differentiation based on the solvent used. This work explored the effects of the stoichiometric ratio of PEG to TiCl4 and the effect of heating rates to clarify the reaction mechanism.  Keywords: Titania, Resin-Gel, PEG, XRD, TEM, Flame Synthesis.    PACS numbers: 61.46.Hk, 61.05.C –                                                             * Paul.Franklyn@wits.ac.za † Ashvir.Narrandes@students.wits.ac.za 1. INTRODUCTION  The resin-gel synthesis technique is a modification of the Pechini method for the fabrication of nano-materials. It involves the addition of a long chain pol-ymer to a stable solution of metal ions within a solvent matrix to form a polymeric resin [1]. It has been shown in previous research that the choice of solvent plays a role in determining the eventual products of the syn-thesis, even though the solvent is not present during the final burning stage when the particles are formed. The choice of ethanol leads almost exclusively to the formation of anatase, while using water with nitric acid leads to a mix of anatase and rutile dependent on the molecular weight of the polymer that is used. In addi-tion it has been determined that the addition of citric acid to the solvent matrix leads to the almost exclusive formation of anatase. The accepted working theory has been that the metal ions coordinate to the polymer initially and, following complete solvent evaporation, are then agglomerated into nanoparticles during flame synthesis of the reaction mix-ture [1]. Previous work we have performed has shown that this may not be the correct mechanism and that the formation of local clusters of metal ions that are co-ordinated by the solvent and any other species present in the liquid medium followed by coordination of these clus-ters to the polymer is a more likely mechanism. Although relatively unexplored, resin-gel synthesis affords the opportunity to synthesize a multi-phase ma-terial using a single reaction step. This is in contrast to most other synthesis methods that invariably produce the phase corresponding to a global energy minimum. Hence, it has the potential to become a much sought after, powerful technique for the fabrication of a wide range of multi-phase nanomaterials.  Titanium dioxide is a well understood material. Phase transition temperatures, abundance, stability and many other properties have been extensively stud-ied and reported [2]. In addition, its nanoparticulate form has found numerous applications in the field of photocatalysis, photovoltaics and sensors [3 -5]. The most common and stable phase of titania is rutile fol-lowed by anatase and then brookite [2]. Numerous lit-erature reports state that under the correct conditions of temperature and/or pressure, anatase and brookite will irreversibly convert to rutile – the thermodynami-cally stable polymorph [6 – 9]. This conversion property of TiO2 makes it an ideal candidate on which to model the resin-gel synthesis technique to produce multi-phase titania in a single sample. The primary aim of this study was to further ad-vancements into understanding the mechanism of op-eration of the resin-gel synthesis. This task was under-taken by considering the effect of changing some of the parameters that influence the resin-gel synthesis method. Using a TiCl4 precursor, the heating rate and the stoichiometric amount of polymer relative to the amount of TiCl4 at several PEG chain lengths was ex-plored. The data generated from these variations al-lowed for the refinement of the new, proposed mecha-nism of resin-gel synthesis.  2. EXPERIMENTAL PROCEDURE  2.1 The effect of PEG stoichiometry  To accommodate for the large quantities of PEG to be included in the reaction mixture, two batch solutions of TiCl4 in water were prepared. The first involved the addition of 6.0 ml of TiCl4 (0.055 mol) to excess distilled water (144 ml). Concentrated nitric acid (12 ml) was then added to aid solubility of TiCl4 in water. The re-sulting solution was split into six equal parts and half the stoichiometric quantity of PEG of different chain lengths was added to each such that the mole ratio of TiCl4:PEG equalled 1:0.5. The actual quantities of PEG added to each solution are given in Table 1.   P.J. FRANKLYN, A. NARRANDES PROC. NAP 1, 01PCN40 (2012)   01PCN40-2 For the second batch solution*, 1.5 ml of TiCl4 (0.014 mol) was added to 36 ml excess distilled water followed by 3 ml of concentrated nitric acid. After the solution had been split into 3 equal parts, half the stoi-chiometric amount of PEG was added to each solution as given in table 1.  Table 1 – Amounts of PEG of varying molecular weight used for synthesis in a 1:0.5 stoichiometric ratio with TiCl4. PEG marked with a * came from a second batch.  Average poly-mer molecular weight /g.mol-1 Theoretical amount required for stoichiometry /g Actual amount used /g 200 0.92 0.918 400 1.84 1.91 1500 6.885 6.92 3000 13.77 13.50 4000 18.20 18.20 6000 22.22 22.28 8000 36.72 36.72 10000* 22.75 22.86 12000* 27.30 27.30 20000* 45.50 45.77    For the synthesis of the stoichiometric equivalent ratio (TiCl4:PEG in a 1:1 ratio), two batch solutions were prepared for the same reason described above. For the first batch, TiCl4 (2.5 ml, 0.023 mol) was added to 60 ml distilled water and 5 ml of concentrated nitric acid was then introduced. The actual amount of poly-mer added to each solution is given in Table 2.  The second batch‡ involved the addition of 0.75ml of TiCl4 (6.8 mmol) to 18 ml of distilled water followed by 1.5 ml of concentrated nitric acid. Appropriate amounts of different molecular weight PEG were then added to the three equally divided solutions (table 2).  Each mixture mentioned above was stirred and heated sufficiently to ensure complete homogeneity; and prepared in duplicate to allow for two different heating rates prior to fame synthesis.  Table 2 – Amounts of PEG of varying molecular weight used for synthesis in a 1:1 stoichiometric ratio with TiCl4. PEG marked with ‡ came from a second batch  Average poly-mer molecular weight /g.mol-1 Theoretical amount required for stoichiometry /g Actual amount used /g 200 0.92 0.92 400 1.84 1.89 1500 6.885 6.87 3000 13.77 13.50 4000 18.20 18.20 6000 22.22 22.29 8000 36.72 36.72 10000‡ 22.75 22.76 12000‡ 27.29 27.490 20000‡ 45.48 45.21  2.2 Variation in the heating rate  Following the complete evaporation of excess sol-vent from each polymer mixture, two different heating methods were used to engage flame synthesis of the polymer. The first method involved the conventional heating of the polymer mixture. Each mixture was added into a crucible. The crucible was placed in a sand bath (so as to ensure uniform heating) and heated until each mix-ture had reached its auto-ignition point. A flame source was then used to ignite each sample. The black ap-pearance of the samples suggested that a carbon coat-ing had been deposited onto the nanoparticles, hence each sample was allowed to cool before being calcined in a muffle furnace at 773 K for one hour. The second heating method involved heating a cast iron vessel to 1173 K in a muffle furnace. Following complete evaporation of excess solvent from each mix-ture, the molten polymer gel was added to the vessel. As was expected, due to the high temperatures, the polymer samples spontaneously ignited on account of them passing their flash points. The excessive temper-atures also promoted the calcination of each sample immediately following polymer pyrolysis.   2.3 Characterization and Analysis   PXRD and TEM were used as the main forms of characterization techniques to deduce the presence of the different phases and particle sizes of titania. A Bruker D2 Phaser diffractometer using Co Kα ra-diation in conjunction with a 0.6 mm slit and primary and secondary soller slits at 2.5°. A LYNXEYE® detec-tor was used with this diffractometer. Each sample was placed on a zero background sample holder and ana-lysed between 20° and 60° 2θ angles in increments of 0.026°. TEM analysis was used to confirm the data ob-tained using XRD. A Tecnai F20 at 200 kV was em-ployed for this task. The Spurr and Myers equation was used to determine the mass per cent of anatase and rutile produced in each sample synthesised. The equation considers the intensi-ties of the anatase (101) and rutile (110) peaks and has an inherent 5 % error by mass. Particle size analysis was performed using the instrumentally corrected Scherrer equation with K = 0.91.  3. RESULTS AND DISCUSSION  It should be noted here that crystallite size data was only obtained from samples that showed significant amounts of either polymorph. Using the current data extraction method for crystallite size analysis, a signifi-cantly non-intense peak was difficult to analyse for crys-tallite size and phase composition data.  3.1 Conventional heating  Figures 1 and 2 compare the mass per cent of ana-tase and rutile formed across a range of PEG molecular weights at different mole ratios using the conventional heating rate. Comparing these figures, it is apparent that the ratio of metal ions to PEG had a significant bearing on the phase that was produced. When half as much PEG was employed, the amount of rutile appeared to increase across the range of PEG chain lengths. How-ever, when the mole ratio of PEG to Ti ions was the same, the amount of rutile decreased as a function of increasing polymer chain length. This effect may be ex-plained in terms of a protecting effect inferred by the polymer on the forming nanoparticle. If this is thought  UNLOCKING THE SECRETS BEHIND THE… PROC. NAP 1, 01PCN40 (2012)   01PCN40-3 to be true then the greater the amount of polymer within any sample, the greater the protecting effect will be and the less likely anatase will convert to rutile.    Fig. 1 – Variation of anatase and rutile mass per cent and particle size formed as function of increasing PEG molecular weight in a Ti:PEG 1:0.5 conventional heat synthesis   The amount of anatase formed does not exhibit a similar trend. In figure 2, it is clear that the amount of anatase formed across the range of PEG molecular weights first increases then decreases. Longer chain lengths promote the formation of anatase.     Fig. 2 – Variation of anatase and rutile mass per cent and particle size formed as function of increasing PEG molecular weight in a Ti:PEG 1:1 conventional heat synthesis  The relationship between particle size and the amount of each phase formed was interesting. For both anatase and rutile, larger particles were formed when the amount of that particular phase was lower for a given sample. This inverse relationship may serve as a means to refine a component of the mechanism of the resin-gel synthesis in the following manner: it is as-sumed that during the burn process, reaction chambers are formed that contain the developing nanoparticle. These chambers are governed by the size of the poly-mer chain post flame induced scission. The size of the chamber will govern the size of the nanoparticles. If there is very little space, only anatase will form. Given the small, cubic nature of the particles (as witnessed in HRTEM – figure 3) it is possible that these anatase particles will form in great numbers. This will result in large amounts of small anatase par-ticles being formed. If however, the reaction chamber is larger, anatase will convert to rutile nanorods (figure 4A). If the chamber is bigger still, the formed nanorods will cluster together around a single crystal axis into a ball (figure 4B). Therefore, large rutile particles are formed in small numbers.   Fig. 3 – Anatase nanoparticles with approximate cubic mor-phology from short-chain PEG synthesis     Fig. 4 – A) Rutile particles forming nanorods. B) Rutile nano-rods clustering into a nanoball  As was expected, particle size increased dramatical-ly post-calcination (figures 5 and 6). This is due to par-ticles sintering together into larger clusters. Calcina-tion also had the effect of converting some of the formed anatase particles into rutile. This result was also expected.    Fig. 5 – Variation of anatase and rutile mass per cent and parti-cle size formed as a function of increasing PEG molecular weight in a Ti:PEG 1:0.5 conventional synthesis (post-calcination)  3.2 Rapid heating  Figures 7 and 8 depict the changes in mass per-centage and particle sizes formed during the rapid heat synthesis at two different metal ion:PEG ratios.  Figure 7 shows an interesting trend with regard to the amount of rutile formed as a function of increasing molecular weight. There appears to be an oscillating trend whereby some chain lengths produce more rutile A B  P.J. FRANKLYN, A. NARRANDES PROC. NAP 1, 01PCN40 (2012)   01PCN40-4 and others less. It is thought that scission of the chain occurs at specific points for different polymers depending on the length of the chain used in the synthesis.     Fig. 6 – Variation of anatase and rutile mass per cent and particle size formed as function of increasing PEG molecular weight in a Ti:PEG 1:1 synthesis (post-calcination)  The inverse trend of particle size and the mass per-centage of each phase formed was again observed and pronounced for rutile. Figure 7 also shows a clear trend of the size of each polymorph as a function of polymer chain length. Figures 7 and 8 show that rutile particles were larger than anatase particles. This, together with the oscillating trend observed for rutile may be ration-alised in terms of the reaction chambers mentioned above. The clear trends observed from figure 7 are not witnessed in figure 8. While the inverse relationship between the amount of rutile and particle size formed was maintained, the oscillating nature described above was non-existant. From figure 8, the 8000 g/mol PEG produced a small amount of rutile in comparison to the other chain lengths.    Fig. 7 – Variation of anatase and rutile mass per cent and particle size formed as a function of increasing PEG molecular weight in a Ti:PEG 1:0.5 rapid heat synthesis The differences observed across the stoichiometric ratios may be attributed to the polymer affording pro-tection to the forming nanoparticle, as mentioned.  Comparing figures 1 and 7, across the series of dif-ferent polymer chain lengths, for the Ti:PEG in a 1:0.5 ratio, rutile formation is enhanced when the samples are burned according to the conventional method. A plausi-ble explanation for this observation is that if the samples were heated rapidly, the formed anatase particles would not have sufficient time to cluster together and form rutile. If, however, they were heated slowly, the forming anatase would have sufficient time to react with other anatase particles, thereby forming larger amounts of rutile. A similar trend could not be obtained at the high-er stoichiometric ratio (comparing figures 2 and 8).    Fig. 8 – Variation of anatase and rutile mass per cent and particle size formed as a function of increasing PEG molecular weight in a Ti:PEG 1:1 rapid heat synthesis  4. CONCLUSION  The molecular weight and relative molar amount of PEG in the reaction mixture affect phase and particle size formation. The results indicate that the presence of large amounts of polymer protect the forming ana-tase particle, inhibiting its conversion to rutile. The reproducible trend of the inverse relationship between particle size and the mass percent of a respective phase lends support to the formation of reaction chambers, within which anatase forms and is allowed to convert to rutile in different ways, depending on the size of the chamber. A rapid ignition of the mixtures does not pro-vide sufficient time for the conversion of anatase to rutile and so lends itself to the formation of anatase. No explanation is yet available for the large amount of rutile formed when a high mole ratio of PEG was em-ployed and the ignition performed at a rapid rate. The sometimes random variation in rutile ratios is a factor that is still under investigation. Further work is also continuing to determine the crystallite size:rutile ratio relationship with respect to synthesis conditions.  REFERENCES  1. J.  Lin, M. Yu, C. Lin, X. Liu, J. Phys. Chem. C. 111, 5835- (2007). 2. X. Chen, S.S  Mao, Chem. Rev. 107, 2891 (2007). 3. M.R  Hoffman, S.T. Martin, W. Choi, D.W. Wahneman. Chem. Rev. 95, 69 (1995). 4. Optoeletronics Properties of Inorganic Compounds (Ed. D.M. Roundhill, J.P. Facker) (New York: Plenum: 1999). 5. G. Sheveglieri, Gas Sensors (Dordrecht: Kluwer: 1992). 6.  Y. Hwu, Y.D. Yao, N.F. Cheng, C.Y. Tung, M.H. Lin, Nanostruct. Mater. 9, 355 (1997). 7. X.Y. Ding, X.H Liu, J. Mater. Res. 13, 2556 (1998). 8. H. Zhang, J.F Banfield, J. Mater. Chem. 8, 2073 (1998). 9. X, Ye, J. Sha, Z. 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Unlocking the Secrets Behind the Resin-Gel Synthesis for the Controlled Formation of Anatase and Rutile

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