(544gh) Degradation of Phenol By Heterogeneous Photocatalysis with TiO2-Modified BLACK MUD Catalysts

DEGRADATION OF PHENOL BY
HETEROGENEOUS PHOTOCATALYSIS WITH TiO₂-MODIFIED BLACK MUD CATALYSTS

LOURENÇO
VS¹ e ASENCIOS YJO²

¹ Faculdade de Tecnologia de Praia
Grande. Centro Estadual de Educação Tecnológica Paula Souza

² Instituto do Mar, Universidade
Federal de São Paulo, Campus Baixada Santista

E-mail
para contato: yvan.jesus@unifesp.br

Abstract. This work intends to
evaluate photocatalytic properties of Peruíbe 's Black Mud, in the phenol degradation
process by heterogeneous-photocatalysis. The Black Mud was tested as a catalyst
in this process, pure and also doped with commercial TiO₂. Three
conditions were tested: in the dark, in the presence of UV-C radiation (UV-C,
254 nm), and in the presence of H₂O₂ plus UV-C light (UV-C,
254 nm; Fotofenton). The catalysts were characterized by XRD, EDX and Fourier FTIR.
The reaction was monitored by UV-Vis Spectroscopy. The tests indicate that
Black Mud presents photocatalytic properties for degradation of phenol in
aqueous medium; this property is improved by the doping of TiO₂ in
low concentrations (10%w/w).

1. INTRODUCTION

Phenol is an organic molecule formed
by benzene compounds attached to one or more hydroxyls. Hydroxy-benzene or
commonly called phenol has a molecular formula C₆H₅OH, is
a compound considered extremely toxic to aquatic life, even at very low
concentrations (Rangel and Britto, 2008). The treatment processes used to treat
phenolic compounds in wastewater are usually conventional methods, which have
low efficiency. Heterogeneous photocatalysis, is a good and recent technique,
and is effective in the degradation of organic molecules in water (Teixeira and
Jardim, 2009).

The black mud, found in the river
channel of Rio Preto in the city of Peruíbe (Silva et al., 2016), presents a
porous material, with good adsorption and ion exchange capacity for the presence
of ions. It has never been studied for catalysis application, so this work aims
to evaluate the photocatalytic properties of the Black Mud.

2. METHODOLOGY

Preparation of the catalysts: The
Black Mud used was in natura. For the preparation of the catalysts, the sludge was
washed and calcinated in a muffle furnace at 550 °C for 1h. Five catalysts were
prepared: pure black mud (LN), pure titanium oxide (TiO₂), and three
mixtures of black mud with 5% (5TiLN), 10% (10TiLN) and 15% of TiO₂
(15TiLN), wt%. Doping was performed by TiO₂ impregnation (stirring,
slow evaporation and further calcination). The catalysts were characterized by
X-ray diffraction (XRD), X-ray dispersive energy spectroscopy (SEM-EDX) and
Fourier transform infrared spectroscopy (FTIR).

Photocatalytic tests were
performed using the ratio (1 g_catalyst.L_efluent^-1),
at 25ºC and pH 3 (previously established data). Three conditions were tested:
Adsorption (in the dark, for 1 hour), Heterogeneous -photocatalysis in UV
radiation (254 nm), Photo-fenton (UV radiation plus 2mL H₂O₂,
30% v/v). The phenol initial concentration was 26 mg.L^-1. UV
irradiation time was for 5 hours. The phenol concentration was monitored by
colorimetric test (method 9065) (EPA, 1986), using a UV-Vis Spectrophotometer.

3. RESULTS AND DISCUSSION

Characterization: XRD results are
present in Fig. 1. These results show that the catalysts based on Black Mud presented
the crystalline phase of SiO₂ in the form of alpha-quartz as predominant
phase, and the crystalline phase of muscovite of the formula KAl₂Si₃AlO₁₀(OH)₂
in a lesser extent. Peaks related to the crystallographic phase of TiO₂
Anatase were also found in catalysts containing TiO₂. FTIR analysis also
reveals the most characteristic band of SiO₂, and the increase in
the formation of three-dimensional amorphous Si-O-Si units occurred after
doping with TiO₂ (Frost, 1995). The spectrum also presented a
characteristic band of hydroxyl groups on surface, the presence of TiO₂
increased the presence of hydroxyl groups. (Silverstein, Werbster and Kiemle,
2006).

Figure 1. XRD results of the
catalysts (A = Anatase; Q = quartz, M = muscovite)

In the chemical analysis done by
EDX, the catalysts presented about 50% of oxygen, the amount of aluminum,
silicon and titanium varied according to the Ti doping. The oxygen present in
the catalysts is associated with Fe, Si, Al forming SiO₂, Al₂O₃,
Fe₂O₃ and other oxides such as TiO₂  (Guzzo,
2008).

Catalytic Test: For the analysis of
the degradation of phenol, the spectral scan by a UV-VIS spectrophotometer of
200-400nm of the solution was obtained before and after the photocatalytic
tests, the decharacterization of the profiles indicated the degradation or the
formation of the intermediate compounds. Phenol can form catechol, hydroquinone
or resorcinol, until it forms acids that degrade CO₂ and H₂O
(Carja et al., 2014).

In the dark test (Adsorption) the
catalysts did not significantly adsorb phenol (dosage studied up to 8 g_cat.L_efluent^-1).
In the heterogeneous- photocatalysis the LN sample did not significantly
de-characterize the phenol band, the doping with TiO₂ in the
concentrations of 5 and 10% improved the photocatalytic activity of the Black Mud;
the doping with 15% was not favorable. The 5TiLn and 10TiLn catalysts more
significantly decharacterized the phenol solution band in the region below 250
nm which are characteristic of hydroxyl groups, carboxylic acids and linear
aldehydes.

To optimize the photocatalytic
process, a test was performed reducing the distance between UV light and becker
by 50%, while increasing the radiation incidence surface by 3 times (using the
same conditions as in the previous tests); the final concentrations of phenol
were: 10 mg.L^-1 for LN sample (1g_catalyst.L^-1),
and 12 mg.L^-1 for 10TiLn sample (1g_catalyst.L^-1);
thus improving significantly the photocatalytic process.

In the case of Fotofenton (UV
light 254 nm + H₂O₂) the concentrations of phenol after
the photocatalytic process were: TiO₂ (1.72 mg.L^-1), LN
(3.74 mg.L^-1), 5TiLn (3.31 mg .L^-1), 10TiLn (1.87 mg.L^-1),
15TiLn (0.86 mg.L^-1). The 15% TiO₂ in the mixture of
Ti-Black Mud presented the best result overall, even better than the pure TiO₂,
meaning that the mixture Ti-Black Mud is a promising catalyst for degradation
of the molecules of phenol.

It is clearly evident the evidence
influence of the H₂O₂ when TiO₂ is present in
the catalysts. The Pure Black Mud also showed improvement with the solution of
hydrogen peroxide, being able to degrade more than 75% of phenol. 

4. CONCLUSIONS

The Black Mud presented photocatalytic
activity, being the first work in the area in Brazil. The materials resulted
from the doping of the Black Mud with low quantities of TiO₂ is
promissory because these presented photocatalytic properties similar to that of
TiO₂-Anatase. This is very benefits to the application in
photocatalysis. The best results for phenol removal were with the presence of H₂O₂.
The presence of alpha-quartz and the porous structure of the Black Mud can
bring benefits to future studies, representing a great contribution for future
studies in materials sciences.

5. ACKNOWLEDGMENTS

The authors thank the São Paulo Research Foundation (FAPESP) for the
financial support (process Nº: 2014/24940-5).

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