Photocatalytic Degradation of p-chlorophenol: Influence of Supports and Sol-gel Synthesised TiO2

George Fox N0427541@my.ntu.ac.ukSupervised By Dr Valeria Puddu

Introduction

Research Aims Reactor Configuration

Results and Discussion

References

Chlorophenols are toxic, water persistent pollutants found in the effluent of pharmaceutical and paper industries (1).TiO2 nanoparticles have shown promise for the photocatalytic degradation of p-chlorophenol (p-cp) in aqueous solution (2). The use of TiO2 slurry in AOP’s has lead to scaling up difficulties, with constant system filtration required. Degussa P-25 TiO2 is considered the benchmark photocatalyst for degradation of most organic pollutants. Pure anatase phase TiO2 has been synthesized using the simple sol-gel technique. Photocatalysis of p-cp has been performed with both P-25 (~70% anatase, 30% rutile) and anatase TiO2 in slurry and support systems. 1. To investigate the photocatalytic

degradation rate of TiO2/UV systems on p-cp in slurry and support reactor.

2. To analyse support durability and catalytic lifetime.

3. To synthesize pure anatase phase TiO2 using the sol-gel method and compare its activity to Degussa P-25 TiO2.

MethodologyDegradation was performed in a simple photocatalytic reactor. An initial p-cp concentration of 80mgL and TiO2 loading of 0.3gL were employed.

After system equilibration regular samples were withdrawn and analysed with a Perkin Elmer Lambda 25 UV-vis spectrometer at 279nm.

TiO2 supports were manufacture following a variation on the heat-attachment method (3).

Figure 2 – Diagram of photoreactor configuration.

Photoreactor conditions were constant throughout the study, with the only change being the replacement of TiO2 slurry for immobilized glass supports. Before degradation of p-cp the light source was equilibrated to achieve constant output.

1) A. Zhihui, Y. Peng, and L. Xiaohua, Chemosphere, 2005, 60, 824-827

2) A.T. Nguyen, R. Juang, Journal of Environmental Management, 2015, 147, 271-277

3) M. A. Behnajady, N. Modirsshahla, M. Mirzamohammady, B. Vahid, B. Behnajady, Journal of Hazardous Materials, 2008, 160, 508-513

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P-25 SlurryP-25 SupportsSol-gel SlurrySol-gel Supports

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Figure 1 – P-25 coated glass support

Amorphous TiO2 nanoparticles were synthesised using a sol-gel method utilizing stoichiometric amounts of solvent and Ti precursor. Particles were dried and calcinated at 400°c.

p-cp Degradation

Figure 3 – % p-cp degradation by slurry and support systems (P-25 & anatase)

p-cp was successfully degraded by 41% using P-25 slurry. Applying Langmuir-Hinshelwood Kinetics to the first order reaction showed the rate of degradation to be 1.8 x 10-3 min-1. The rate and % degradation were discovered to be comparable to that shown by P-25 supports (36% and 1.63 x 10-3 min-1).

XRD analysis of sol-gel TiO2

Figure 4 – XRD spectrum of sol-gel TiO2 showing anatase peak at 101

XRD showed sol-gel TiO2 was purely anatase, with an average crystallite size of 2nm. SEM imaging showed particle agglomeration between 0.5 to 3.0um. Agglomeration resulted in a poor anatase

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TiO2 slurry accounting for the lesser activity of 1.1 x 10-3min-1 and lower % degradation (32%) observed.

Support Durability

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Total Anatase Mass

Anatase lost after 1st degM

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Figure 5 – Comparison of mass lost from P-25 and anatase supports

P-25 and anatase supports show large differences in durability. After one degradation there was a five fold increase in mass lost from anatase supports.

Conclusions1. P-25 and anatase TiO2 show similar

rates of p-cp degradation in slurry and support systems respectively.

2. P-25 supports exhibited superior durability to respective anatase support, and show good catalytic lifetime over three degradations.

3. Pure anatase TiO2 nanoparticles can be synthesised following a simple sol-gel method. Particles showed agglomeration between 0.5-3.0um, providing explanation for the slightly decreased rate of anatase slurry.