synergistic effect between tio2 sol–gel and degussa p25 in dye photodegradation

1 23

Journal of Sol-Gel Science andTechnology ISSN 0928-0707Volume 66Number 3 J Sol-Gel Sci Technol (2013) 66:472-480DOI 10.1007/s10971-013-3034-5

Synergistic effect between TiO2 sol–gel andDegussa P25 in dye photodegradation

Luminita Andronic, Dana Perniu &Anca Duta

1 23

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Synergistic effect between TiO2 sol–gel and Degussa P25in dye photodegradation

Luminita Andronic • Dana Perniu •

Anca Duta

Received: 17 December 2012 / Accepted: 8 April 2013 / Published online: 16 April 2013

� Springer Science+Business Media New York 2013

Abstract The TiO2 powders were synthesized by versa-

tile and low cost sol–gel process using HNO3 and titanium

tetra-isopropoxide (volumetric ratio of 4:1) following by

the hydrolysis reaction. The powders show the two poly-

morphs of TiO2: 96 % anatase and 4 % brookite, due to

acidic condition (pH = 3). Thin films of titanium oxide

were obtained by dip-coating, using the sol–gel of titanium

oxide mixed with commercial Degussa P25 into a weight

ratio 1:1 or 1:1.5, to enhance the synergistic effect of

anatase/rutile ratio aiming at increasing the efficiency of

the TiO2 photocatalyst in dyes degradation. The thin film

surface (charge and morphology) was controlled by poly-

mer (poly-ethylene glycol) and surfactant (Sodium dodecyl

sulphate, Triton X100) addition. The titanium oxide was

characterized by particle size analyzer, contact angle

measurements, X-ray diffraction, scanning electron

microscopy, and atomic force microscopy. The photocat-

alytic properties of powders and coatings were evaluated

based on the degradation efficiency of two reference dyes

(methyl orange and methylene blue). The results outline

that poly(ethylene glycol) and films morphologies are the

most influential factors that affecting the photocatalytic

activity.

Keywords Titanium oxide � Surfactant/polymer �Sol–gel �Dip-coating � Photocatalysis

1 Introduction

Titanium oxide is a semiconductor with photochemical and

optical properties used in photovoltaic cells [1–3], as

photocatalysts [4–6], and sensors [7]. Mesoporous titania

had gained attention because of the potential ordered

arrangements with uniform pore sizes, high pore volume,

and specific surface area.

Titania photocatalyst can be used as powders or as thin

films, coated on a substrate. Most experiments use powder

particles suspended in contaminated water, which provides

a large surface area but raises recovery issues after treat-

ment [8]. A reduction in performance is reported in aque-

ous systems for immobilized TiO2 compared to the

unsupported catalyst [9].

The methods used for the synthesis of titanium oxide

powder include alkali precipitation, thermal decomposition

[10], hydrothermal synthesis [11], sol–gel [12] and many

other routes. Among these, the sol–gel route remains one of

the most attractive, due to the material’s control during

preparation, low processing cost, the possibility of pre-

paring powders or thin films [13, 14]. Thin films are

obtained using organic and inorganic precursors and the

deposition on the substrate can be further done by dipping,

spin coating or doctor blade techniques [15, 16]. The layers

obtained produce samples with good homogeneity and

reproducibility.

Mesoporous materials can be synthesized by self-

assembly between organic surfactant and titanium oxide

[17, 18]; the surfactant forms micelle surrounded by tita-

nium oxide and serves as a sacrificial template for mes-

opores, directing the growth and the morphology of the

materials. So, titanium oxide can be fabricated via sol–gel

synthesis templated by a supramolecular assembly of

organic surfactants.

L. Andronic (&) � D. Perniu � A. Duta (&)

Centre: Renewable Energy Systems and Recycling, Transilvania

University of Brasov, Eroilor, 29, 500036 Brasov, Romania

e-mail: [email protected]

A. Duta

e-mail: [email protected]

123

J Sol-Gel Sci Technol (2013) 66:472–480

DOI 10.1007/s10971-013-3034-5

Author's personal copy

The major influence of additives is in preventing and/or

enlarging the macro-pores formation, improving pore in-

terconnectivity, and contributes at the hydrophilicity of the

films surface. Sodium dodecyl sulphate (SDS), Triton

X100 (TX) and poly(ethylene glycol) (PEG) have been

employed to template the self-assembly of titania interfa-

cial films with organometallic compounds as precursors.

In this paper mesoporous TiO2 was investigated as

powder or thin film prepared by sol–gel respectively dip-

ping methods, having the surface and photocatalytic

properties controlled via surfactant (Triton X100, SDS) or

polymer (PEG). Methyl orange (MO) and methylene blue

(MB) solutions were used as reference dyes to evaluate the

activity of the TiO2 film as photocatalyst.

2 Experimental procedure

2.1 Materials

The materials used for sol–gel powders (based matrix)

were:

– titanium tetra-isopropoxide, TTIP, Aldrich,

Ti[OCH(CH3)2]4, purity, C97.0 %, M = 284.22,

– Nitric acid (HNO3 conc. 65 %, Scharlau, M = 63.01,

D = 1.41 g/cm3).

The materials used for titanium oxide thin films, used as

photocatalyst, were:

– TiO2 sol–gel powder (annealed at 500 �C for 3 h);

– TiO2 powder Degussa P25, Evonik, BET surface area

55 ± 15 m2/g; average primary particle size around

30 nm, purity above 97 % and a 80:20 anatase: rutile

ratio.

– ethanol, S.C. PAM Corporation, purity 99.2 %,

M = 46.01,

– acetylacetone, AcAc, Alfa Aesar, C5H8O2, purity

99.9 %, M = 100.13,

– poly(ethylene glycol) (PEG400), Scharlau Chemie,

purity 99 %, M = 380–420, D = 1.13 g/cm3,

– t-Octylphenoxypolyethoxyethanol, Triton X100 (TX),

Scharlau Chemie, laboratory grade, M = 646.37

g/mol, D = 1.07 g/cm3,

– dodecyl sulfate sodium salt (SDS), Sigma-Aldrich,

ACS reagent, purum C99 %, M = 288.38 g/mol,

The materials used in the photocatalytic tests were:

– Methyl orange—4-dimethylaminoazobenzene-40-sul-

fonic acid sodium salt (IUPAC), Scheme 1.

– Methylene blue—3,7-bis(dimethylamino)- phenothia-

zin-5-ium chloride (IUPAC), Scheme 1.

2.2 Photocatalysts preparation

2.2.1 Titanium oxide sol–gel powders

The TiO2 sol was synthesized in the acid catalyzed sol–gel

formation method, using 60 mL of 1 M HNO3 and 15 mL

of titanium tetra-isopropoxide, following the hydrolysis

reaction. Titanium tetra-isopropoxide was added gradually

to the HNO3 aqueous solution, under continuous stirring

for 3 h to produce a transparent sol. Subsequently, the pH

of the colloid solution was adjusted to 3 with the addition

of 1 M NaOH, resulting in a turbid colloid. The pH

adjustment was necessary to prevent the destruction of the

adsorbent structure during the reaction with the acid. The

mixed suspension was agitated by a magnetic stirrer for

another 2 h, at room temperature to permit aging, and was

followed by filtration (Millipore 0.45 lm). The method for

obtaining the titanium dioxide sol–gel powder has been

previously described [19].

The surface of the titania particles was modified by

using surfactants and polymer. The surfactants and poly-

mer molecules are eliminated at 500 �C, during heat

treatment, determining pore formation allowing adsorption

of dye molecules and favoring the photodegradation

process.

The concentration of additive (100 ppm) was obtained

by adding appropriate amounts of additives into 60 mL of

1 M HNO3 solution (using a surfactant stock solution of

4,000 ppm). The resulting TiO2 powder was dried in a

furnace for 1 h at 100 �C and finally the powder was

annealed at 500 �C for 3 h. The experiments were per-

formed at room temperature.

In the case of the mesoporous titania films, the titanium

precursor (Titanium tetra-isopropoxide) is dispersed in a

HNO3/surfactant system to prepare a sol. The morphology

of the meso-structure is primarily determined by the con-

figuration of the self-assembled organic surfactants in these

systems, which may change during the sol reaction.

Scheme 1 Dyes chemical

structure

J Sol-Gel Sci Technol (2013) 66:472–480 473

123


Samples were recorded as follows: S was the TiO2

powder prepared without additive, S-TX, S-SDS and

S-PEG were TiO2 powders obtained using the sol–gel

method by adding TX, SDS and PEG respectively.

2.2.2 Dip-coating titanium oxide films

Thin films of titanium oxide were obtained by dip-coating,

using the sol–gel titanium oxide powder. The sol–gel

powder was mixed with Degussa P25 in a weight ratio 1:1

and 1:1.5, respectivelly. The colloid paste is formed by

mixing 2 g TiO2 powder (sol–gel and Degussa P25) with

2 mL acetylacetone, additive (PEG, Triton X100 or SDS)

(100 ppm) and ethanol, the total volume of paste was

25 mL. Finally, the glass substrate (1.5 9 2.5 cm2)

cleaned using ethanol, distilled water and acetone in suc-

cessive sonication processes was immersed for 1, 2 or 3

times. After drying in air at 60 �C for about 2 min, the

films were annealed in an oven at 500 �C, for 6 h. The

photocatalysis tests have shown that the films dipping for 3

times shows a high catalytic activity compared to the films

immersed for 1 or 2 times. So, further discussions will be

worn only for films immersed for 3 times.

2.3 Materials characterization

2.3.1 Powders characterization

X-Ray diffraction (XRD) measurements were carried out

with a Brucker D8 Discover X-ray diffractometer at 40 kV

and 20 mA (CuKa radiation, k = 0.15406 nm), in order to

determine the crystalline phases; the crystallite sizes in the

powders were calculated by substituting the half-width of a

chosen peak into the Debye–Scherrer equation. Morpho-

logical studies of the catalyst were carried out using a

Hitachi Model 3400 Scanning Electron Microscope at an

applied voltage of 18 kV. The particle sizes and zeta

potential of the powders were measured using a particle

size analyzer (Zetasizer Nano-ZS90-MALVERN Instru-

ment). To determine the point of zero charge of the TiO2

samples, the concentration in the suspension of TiO2 sol–

gel powders was kept constant.

2.3.2 Films characterization

The surface morphology was investigated by Atomic Force

Microscopy (AFM, NT-MDT model NTGRA PRIMA EC).

The images were taken in semi-contact mode with

‘‘GOLDEN’’ silicon cantilever (NCSG10, force constant

0.15 N/m, tip radius 10 nm). Scanning was conducted on

three different places (a certain area of 5 9 5 lm for each

section) randomly chosen, at a scanning rate of 1 Hz. The

surface wettability behavior (hydrophobic-hydrophilic) of

the films was examined by static contact angle measure-

ments, with the sessile drop method using an OCA-20

Contact Angle-meter (DataPhysics Instruments) at room

temperature. A drop of liquid (22 lL) was placed, with

1 lL/s velocity, on the thin films, and the contact angle was

measured during 30 s, with one second step. Measurements

were performed on three different points on each film and

the mean value was calculated. The liquid used for mea-

surements was glycerol, having the surface tension

r = 73.40 mN/m (rd = 36.40 mN/m; rp = 37.00 mN/m,

where rp is the polar component and rd the dispersive

component).

2.4 Dyes photodegradation

The photocatalytic activity of the powders and films were

evaluated by standard dyes (methyl orange and methylene

blue) photodegradation. The reactor for photodegradation

experiments consists of a static cylindrical flasks equipped

with three F18 W/T8 black light tubes (Philips) (UVA

light, typically 340–400 nm, with kmax (emission) =

365 nm).

Experimental conditions for methyl orange (MO) deg-

radation on powders were: pH = 5.65 without added acid

or hydroxide, MO initial concentration 0.0125 mM,

amount of TiO2 powder was 4 g/L and UV irradiation time

was kept constant for 30 min.

In the photocatalytic experiment, the titanium oxide film

with a 3 cm2 area was added into 25 mL of 1.25 9

10-5 mol/L aqueous dyes solution and then irradiated.

Samples were placed in the middle of the photocatalytic

system and the irradiation intensity on the solution was 3

Lx. At the set time, the dyes concentration was measured

on a UV–Vis spectrophotometer (Perkin Elmer Lambda

25) at 463 nm for methyl orange, respectively 665 nm for

methylene blue.

Dark reactions were performed under the same condi-

tions without light irradiation. In the absence of the pho-

tocatalyst, the dyes solution (with and without H2O2), was

found to be stable under irradiation with UV light.

3 Results and discussions

3.1 The TiO2 powders characterizations

The XRD patterns of sol–gel powders (Fig. 1) shows the

two polymorphs of TiO2: 96–97 % anatase (JCPDS:

21-1272) and 3–4 % brookite (JCPDS: 03-0380). The

integrated peak intensities of the anatase (101) and brookite

(121) phases were used to determined the phase content,

according to Eqs. 1 and 2 [21].

474 J Sol-Gel Sci Technol (2013) 66:472–480

123


% A ¼ 0:886 � IA

0:886 � IA þ 2:721 � IBð1Þ

% B ¼ 2:721 � IA

0:886 � IA þ 2:721 � IBð2Þ

These results are in good agreement with those

previously reported by Neppolian et al. [20], showing

anatase and brookite phases in the TiO2 obtained by sol–

gel using titanium tetra isopropoxide (TTIP) as precursor.

Anatase shows Bragg’s reflection at 2h = 25.34�, 37.88�,

48.05�, 55.07� and 62.75�, corresponding to (101), (004),

(200), (211), (204), reported for tetragonal crystal planes of

anatase phase of TiO2 [21]. Brookite shows a small

Bragg’s reflection at 2h = 30.885� corresponding to the

(121) plane. The brookite phase is influenced by the pH

value during synthesis and Hu et al. [22] observed that the

peak intensity at 30.885� becomes weaker with increasing

pH from 2 to 4, and is fully disappearing at pH higher than

5. In the working conditions, the brookite could be formed

but the results show that the effect of the surfactant

additions should also be considered (besides pH), as the

anionic surfactant (SDS) prevents the formation of this

polymorph.

Crystallite size was calculated for anatase by using the

Scherrer formula. The average particle size obtained for

anatase from XRD data was less than 10 nm in the case of

the as-prepared powders and about 20 nm for the powders

sintered at 500 �C; sintering at higher temperature only

resulted in higher crystallinity and increased particle

diameter.

In Fig. 2 the SEM images of the powder samples pre-

pared using sol–gel process are presented, allowing to

assess morphological changes in the titanium oxide sur-

faces following self-assembled modification. The images

indicate that aggregates are composed of close-packed

smaller particles (crystallite or grains), with pores and

voids in the powders, which can be attributed to the large

amount of gases escaping out of the reaction mixture

during the thermal treatment.

The particle sizes and zeta potential of powders were

measured using a particle size analyzer, the result are

presented in Table 1. The particle size measured by the

zetasizer was larger than that observed by the XRD

because the zetasizer measures the hydrodynamic size of

the nano-particle. Zhang and collaborators have observed

the same behavior [23]. The experiments for evaluating the

point of zero charge in the TiO2 samples, used the same

powder concentration in the sol–gel suspension.

The titania point of zero charge (pHzpc) has significantly

different values depending on the synthesis method [24].

The point of zero charge for few commercial titanium

oxides are: 6.25 for Degussa P25 (75–80 % anatase and

25–20 % rutile) [25], the Sigma anatase has pHzpc = 2.9

[26], anatase TiO2 derived from Aldrich has pHzpc 4.2 and

Janssen powder (99 % anatase) has pHzpc of 2. pH control

is important for reproducibility of results.

The experimental data obtained using surfactant additives

show only slight variations (below one pH unit) showing that,

in terms of surface charge, any additive could be suitable.

The values (close to pH = 6) also show that surface charge

can be very easily changed, by very small amounts of acidic

or alkaline compounds, and the substrate is amphoteric, as

shown by the acid–base equilibrium (Eqs. 3 and 4) [27]:

TiOH þ Hþ $pKa1TiOHþ2 ð3Þ

TiOH þ HO� $pKa2TiO� þ H2O ð4Þ

The isoelectric point (pHzpc) is given by Eq. 5, where

pKa1 and pKa2 are the negative logarithms of dissociation

constants in acid and alkaline medium respectively:

pHzpc ¼1

2ðpKa1 þ pKa2Þ ð5Þ

When the pH\ pHzpc the surface charge of the titanium

oxide is positive and is negative if pH [ pHzpc; the surface

charge of the prepared powders is presented in Scheme 2

along with the charges corresponding to the methyl orange

molecules (negatively charged at pH values above 4.4). The

data show that the pH should be well controlled for

supporting electrostatic attraction between the photocatalyst

and the dye (a pre-requisite for photocatalysis).

As shown in Scheme 2, at the working solution pH

(5.65) attraction forces can be expected between the neg-

atively charged MO and the positively charged substrates

(S-TX, S-SDS and S-PEG), while repulsions are to be

expected for the pristine sample (obtained without surfac-

tant additives). This explains the 41 % efficiency degra-

dation of MO for the S sample, comparatively lower than

Fig. 1 The XRD patterns of TiO2 powders


123


for the samples with additives. The additive added in the

sol–gel powders increase the photocatalytic activity of the

samples also due to pHzpc of powders.

The photoreactivity experiments have shown that

methyl orange photodegradation depends on the particle

size of the TiO2 powders: an increase in the particle size

can result in the particles agglomeration and decreases the

photocatalytic degradation efficiency of Methyl orange.

3.2 Dip-coating films and photocatalytic activity

characterizations

Thin films of titanium oxide were obtained by dip-coating;

the sol–gel powder was mixed with Degussa P25 in a

weight ratio 1:1 or 1:1.5 to ensure the formation of a col-

loidal paste to adhere to the glass substrate to form

homogeneous layers without cracks, insuring a mechanical

stability that allows there long term use.

The XRD spectra of the films presented in Fig. 3 clearly

show the characteristic peaks for anatase (identified with

JCPDS: 21-1272) and rutile (identified with JCPDS:

73-1765) in the TiO2 sol–gel and mixed samples, thus

annealing treatment does not alter the initial sol–gel and

Degussa polymorphs; the percentage of brookite was found

to be 1–2 % and was neglected in the films. The mean sizes

of the self-assembly TiO2 nanoparticles, calculated by

Scherrer’s formula, are in the range of 18–22 nm

(Table 2).

Scheme 2 The influence of pH

on the MO-photocatalyst

interaction

Fig. 2 The SEM images of

sample S (a), S-TX (b), S-SDS

(c) and S-PEG (d)

Table 1 The properties of the TiO2 sol–gel powders

Samples Additives Particle size

average (nm)

pHzpc MO

degradation

(%)

S – 342 5.26 41

S-TX TX 245 6.17 52

S-SDS SDS 226 5.79 56

S-PEG PEG 264 6.17 49


123


The integrated peak intensities of the anatase (101) (IA)

and rutile (110) (IR) phases were used to calculate the rutile

phase content (% R) (Eq 6) [22], where IA and IR are the

X-ray integrated intensity of anatase (101) reflection and

rutile (110) reflection respectively.

% R ¼ 1

1þ 0:8 � IA

IB

� 100 ð6Þ

Two-dimensional AFM images (Fig. 4) reveal the

formation of crystalline aggregates with diameters

between 300 and 800 nm and micro crystalline

agglomerates with high porosity. The AFM studies

demonstrate a highly and uniform granular surface, with

shape and density strongly depending on TiO2 sol–gel/

TiO2 Degussa P25 ratio. Increasing the amount of Degussa

leads to crystalline aggregates, and surface roughness

increases (Table 2). As the roughness data show,

morphology change is not only due to mixing different

powders (sol–gel and Degussa) but also the result of their

controllable assembly by using different additives, as the

major differences between TX and SDS outline.

The contact angle measurements on solid surfaces are

influenced by morphology and surface roughness [28]. The

contact angle measurements (Fig. 5) were performed con-

sidering the possible influence of the morphology and the

crystallinity on the surface properties. The analysis is

strongly dependent on the liquid and surface nature and

solid/liquid contact time [29].

Firstly, water contact angles were measured and were

found to be very small between 6� and 8�, indicating a

highly hydrophilic surface. However, as the water mole-

cules in contact with the surface get absorbed into the pores

also due to capillarity effects, the contact angle diminishes

very quickly eventually rendering the film super-hydro-

philic. Therefore, experiments were extended by using

glycerol. As listed in Table 2, the static contact angle

between glycerol and the surface was between 40� and

64�. The results show that PEG additive is a pore former

Fig. 3 The XRD patterns of the

films

Table 2 The correlation between films properties

Samples Additives SG/DEG ratio Crystallites size (d) and

crystalline phase (%)

Average

roughness (nm)

Contact angle

(degree)

Dyes degradation (%)

Anatase Rutile MO MB

d (nm) % d (nm) % O2 H2O2 O2 H2O2

D (Degussa P25) – – 25 80.7 39 19.3 70 39 26 44 40 67

S1D1 – 1:1 27 88 30 12 125 40 22 24 28 56

S1D1.5 – 1:1.5 33 87.2 31 12.8 126 40 29 21 20 55

S1D1-TX TX 1:1 22 90 27 10 121 55.5 22 18 45 53

S1D1.5-TX TX 1:1.5 18 88.2 22 11.8 138 49 28 19 48 55

S1D1-SDS SDS 1:1 18 92.15 27 7.85 45 43.5 27 19 51 59

S1D1.5-SDS SDS 1:1.5 18 91.25 18 8.75 80 50 36 30 52 55

S1D1-PEG PEG 1:1 19 91.85 21 8.15 86 57.4 32 25 59 66

S1D1.5-PEG PEG 1:1.5 18 91.27 20 8.72 92 64 32 30 26 53


123


and its addition leads to lowering the wetting behavior. We

studied the spreading kinetics of glycerol droplets on films

(Fig. 5) for the first 30 s after drop contact with the coat-

ing. The effect of the surfactant/polymer addition is prac-

tically lost in the films with Degussa P25 excess and the

reasons should be found in the surface chemistry and less

in morphology since this trend is not reproduced by

roughness.

The photocatalytic activity of catalysts was evaluated in

terms of the degradation of the methyl orange and meth-

ylene blue solutions under UV irradiation. The efficiency

of the dyes degradation was calculated based on the con-

centration changes (Eq. 7), and the comparison of the

photocatalytic activity of the films was carried out. The

results are shown in Fig. 6.

g ¼ C0 � C

C0

� 100 ð7Þ

where g is the dyes degradation efficiency, c0 and c are

concentrations of the dye at initial and a given reaction

time (min), respectively.

Our previously studies [19, 30] showed MO degradation

efficiency of 26 and 40 % of MB degradation in dye/O2/

TiO2 Degussa system. Titanium oxide Degussa P25 is often

reported as most efficient photocatalyst [31, 32] due to its

phase composition 80 % anatase and 20 % rutile. The

results presented in Table 2 show a significant increase of

the photodegradation activity of the films obtained by

mixing the Degussa powder with the sol–gel powder

reported in this paper; this increase is not the result of a

Fig. 4 The AFM 2D images of the films

Fig. 5 Spreading kinetics of

glycerol droplets for TiO2 sol–

gel: Degussa ratio 1:1 (a),

respectively 1:1.5 (b)


123


higher efficiency of the sol–gel powder because films

obtained by mixing sol–gel and Degussa powders are less

effective than Degussa P25, both in MO and in MB oxi-

dation. Significantly higher efficiencies are obtained when

using additives (surfactants and especially PEG) therefore

one may suppose a reciprocal activation due to morphology

changes (as outlined by AFM) and a anatase % increase in

a synergistic effect. This effect has a similar trend with the

contact angles variations, being registered simultaneous

with the increase of the contact angle, therefore it can be

the result of limiting water adsorption, allowing direct dye

adsorption on the photocatalyst. This assumption is con-

firmed by the fact that in systems containing hydrogen

peroxide (electron trapper and source of active HO. radi-

cals) this effect is no longer registered. Following the

results, one may conclude that, for getting this effect,

additives controlling/limiting too high hydrophilic behav-

ior (as PEG) are recommended.

The difference between the efficiencies in MO and MB

degradation is related to their stability but mainly to their

different molecular volumes: 0.576 nm3 for MO (1.68 nm 9

0.49 nm 9 0.7 nm) and 0.348 nm3 for MB (1.43 nm 9 0.61

nm 9 0.4 nm), therefore we can conclude that the substrates

accessibility (density/porosity) also plays an important role.

4 Conclusions

A low cost and versatile method of TiO2 immobilization on

surfaces was conducted with surfactant and polymer

assembly to prepare mesoporous films that perform in the

photodegradation of organic contaminants.

X-ray diffraction of the TiO2 powder obtained by sol–

gel and treated at 500 �C revealed a higher crystallized

material, and two polymorphs corresponding to 96 % of

anatase and 4 % of brookite, with the average particle size

was about 20 nm for anatase. The brookite phase is

influenced by the pH value during synthesis. In the working

conditions, the brookite could be formed but the results

show that the effect of the surfactant additions should also

be considered (besides pH), as the anionic surfactant (SDS)

prevents the formation of this polymorph.

Anatase TiO2 is always regarded as the most effective

reagent for photocatalytic degradation of organic pollutants in

water. The powder presents pores and voids, which can be

attributed to the interaction between surfactant/polymer and to

the large amount of gases escaping out of the reaction mixture

during the thermal treatment. The additive included in the sol–

gel powders increase the photocatalytic activity of the samples

due to modification of the pHzpc of powders. This explains

41 % efficiency degradation of MO for S sampling compar-

atively lower than for the samples with additives.

Porous dip-coating films would be improved by con-

trolling the sol–gel condition and surfactant/polymer

composition; this work provides a significant contribution

to the formation of porous TiO2 thin film templated by a

surfactant/polymer, as well as dyes degradation.

By mixing sol gel powders with commercial Degussa

P25 a synergistic effect was registered with significantly

higher photodegradation efficiencies of methyl orange and

methylene blues. The mixed films obtained using PEG

(S1D1-PEG) show an increase in the photodegradation

efficiency of 23 % for MO and 47 % for MB, corre-

sponding to a 14 % increase in the anatase content of the

film, a 23 % increase in roughness and almost 50 %

increase in the contact angle. These data show that there is

a combined action of the key factors (polymorphism,

roughness and wetting behavior) that supports the effi-

ciency increase in the rutile/anatase mixtures.

Acknowledgments This paper is supported by the Sectoral Opera-

tional Programme Human Resources Development (SOP HRD),

financed from the European Social Fund and by the Romanian

Government under the Contract Number POSDRU ID59323.

Fig. 6 The photodegradation

efficiency of dyes: Methyl

orange (a) and Methylene blue

(b)


123


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synergistic effect between tio2 sol–gel and degussa p25 in dye photodegradation

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