Civil Engineering Reference
In-Depth Information
40
50
Flow: 5.5 mL/min
Flow: 11 mL/min
PCP
Phenol
Chloride
40
30
PCP in feed
PCP in eluent
Phenol in eluent
chloride in eluent
30
20
20
Range of PCP:
6.5-7.5 mg L
-1
Range of PCP: 3.2-4.7
mg L
-1
10
10
0
0
500
2000
3500 5000
Elution volume, mL
6500
8000
9500
0
20
40
60
80
100
120
(
a
)
Time, min
(
b
)
Figure 17.11
Variation in concentration of PCP, phenol and chloride due to catalytic action of Pd-BC
composite in batch (a) and continuous l ow (b) experiment.
synthesized by sol-gel technique using BC pores as reaction chambers. In order to
control the synthesis reaction and hence the size of TiO
2
nanoparticles, water mol-
ecules in BC were displaced with ethanol i rst by immersing the BC hydrogel into an
ethanol-containing solution. h e ethanol concentration is increased gradually to 99%
so that only bound water is present and the free water is completely replaced with etha-
nol. h e ethanol-treated BC was ini ltrated with TiO
2
nanoparticles using Ti-butoxide
as the precursor. h e nanoparticles of TiO
2
are photocatalytic only in the presence of
UV radiation, which is only ~4% of the solar radiation received on earth. In order to
increase the catalytic activity to visible radiation as well, the TiO
2
nanoparticles are
doped with S, N or P. h e TiO
2
nanoparticles were found to be ~ 7.5 nm in size and
uniformly distributed along the BC i bers (Figure 17.12a). Photocatalytic degradation
rate of methyl orange (MO) was investigated and it was found that degradation rate
of MO by TiO
2
-BC composite is higher than that by P25 due to large specii c surface
area of TiO
2
nanoparticles on the surface of BC i bers. In addition, the degradation
rate of MO by N-TiO
2
-BC is higher than that by TiO
2
-BC. h is is due to the higher
photocatalytic activity of N-TiO
2
-BC composites because of their larger absorbance of
visible light (i gure 17.12b). Another material which exhibits photoactivated catalytic
activity is CdS. h ese nanoparticles have been synthesized using a procedure similar
to that used to synthesize TiO
2
[43] . h e CdCl
2
and thiourea solution mixture was used
as the precursor to ini ltrate BC with CdS. h e particles were found to be 10-20 nm in
size and became agglomerated for long reaction times, ~ 7 hours. h e decoloration of
methyl orange investigated using both pure CdS and CdS-BC composite shows that the
ef ective rate constant for the composite is two orders of magnitude higher. h e reus-
ability for 90 min cycle time was determined up to 5 dif erent cycles and it was found to
decrease from 82% to 77.3%, which indicates the life of the catalyst.
Apart from using BC as a simple carrier or support material for catalyst particles, it
has been shown to be a good template as well. Both ZnO with a nanoporous structure
and a i brous TiO
2
structure were successfully synthesized by pyrolyzing the BC at high
temperatures [44,45]. To synthesize ZnO nanoporous structure BC was ini ltrated with
Zn-acetate, which on heating to temperature > 500°C forms ZnO and also pyrolyzes
the BC. h is was found to be highly ef ective in decolorizing methyl orange due to
the extremely large specii c area present in the nanoporous structure. h e nanoi brous
structure of TiO
2
synthesized by pyrolyzing BC at 500°C from TiO
2
-BC hybrid having a
