Environmental Engineering Reference
In-Depth Information
nanocomposites, for example, nanocarbon-polymer nanocomposites prepared via electrolytically generated NCC and
polyethylenimine [1, 23]. A similar method can be used to prepare nanocarbon-metal nanocomposites (NCMC) as the NPC to
control cyanobacteria [24].
11.3
materials anD equipment
NCC was prepared by the electrochemical method described in our previous works [1, 21, 23]. The process was based on the
use of an inexpensive two-electrode device in which an anode and a cathode made from high-density isotropic graphites OEG4
(Russia) (65 mm × 30 mm × 15 mm) were transformed into carbon colloidal particles. The anode and the cathode were immersed
in a plastic electrolytic cell (120 mm × 140 mm × 105 mm) filled with distilled or deionized water as the electrolyte. The distance
between the electrodes was varied from 10 to 120 mm in the current density range 0.1-3 mA/cm
2
at a constant voltage of 60V.
The electrolytic cell was installed on the magnetic stirrer in order to provide water flowing between the electrodes. That allows
saturating the electrolyte with carbon colloids and discharging the gas generated on the surface of electrodes due to the electrol-
ysis of water. The process of device operation involved two repeatable consecutive steps: (1) electrolysis for 10 min (2) and
electrolyte stirring for 60 s. The process was executed automatically using ST-T2 twin timer controller (RIKO Opto-electronics
Technology Co., Ltd., Taiwan).
The NCC preparation process was executed in two stages: anode activation and carbon nanoparticles generation. At the first
stage, the electrolyte has low conductivity, electric current density is small, about 0.1-0.2 mA/cm
2
, and the oxidation reaction
is slow. The duration of this stage is about 50 h and depends on the quality (density) of graphite. At this stage, the voltage bet-
ween the electrodes is high, about 60-100V. As the reaction proceeds, the conductivity of the electrolyte is abruptly increased,
the current density goes beyond 10 mA/cm
2
, and the oxidization reaction sets in. As a result, the carbon electrode is finely split
with follow-up covering by the carboxyl group.
At the second stage, the electric current density between the electrodes is about 3-4 mA/cm
2
. The NCC is stable for at least
150 days. If the current density values are greater than 8-10 mA/cm
2
, the rate of oxygen diffusion through the electrode is so
high that the pressure inside the electrode causes its disintegration. In this case, the synthesized NCC is not stable, and its
precipitation is observed in 2-3 weeks.
The size and shape of nanoparticles were determined with transmission electron microscopy (TEM) (LEO-912-OMEGA,
Carl Zeiss, Germany). The concentration of Ti in the solutions was determined by neutron activation analysis by irradiating
water samples in the nuclear reactor of the Institute of Nuclear Physics (Tashkent, Uzbekistan).
The Ge(Li) detector with a resolution of about 1.9 keV at 1.33 MeV and a 4096-channel analyzer was used for the detection
of γ-ray quanta. The area under the γ-peak of radionuclide
51
Ti (half-life
T
1/2
= 5.8 min, energy of the γ-peak
E
γ = 0.319 MeV)
was measured to determine the concentration of Ti.
PCBs from the transformer (“transformer oil”) were used. The analysis of PCBs was performed by gas chromatography-mass
spectrometry (GC/MS) (Agilent Technologies 6890N network gas chromatography system with 5973 inert mass selective detection
(MSD)) operating in the SIM mode. The PCBs were separated using a DB-5 (60 m, 0.25 mm, 0.25 lm) chromatographic column.
The concentrations of DDT, C
12
h
8
Cl
6
, and C
6
h
6
Cl
6
were determined in accordance with the Standard Methods
(Russia) for Testing Chemical Procedures (method for determining residual quantities of pesticides) for the evaluation
of disinfection [25].
The photocatalytic destruction of DDT, C
12
h
8
Cl
6
, and C
6
h
6
Cl
6
in the NCMC (Ti) suspension under UV illumination was
investigated in order to evaluate the photocatalytic activity of the nanoparticles. Aldrin and lindane water solutions, aldrin,
linden and DDT powders, and transformer oils containing PCBs were filled or put into Petri dishes. A 60-w UV lamp (DB-60,
Russia) fixed at a distance of 25 cm above the solution surface was used as the UV light source and provided radiation power
of 1 w/m
2
within the 220- to 320-nm region.
11.4
results anD Discussions
11.4.1
synthesis of npc
Experiments have shown that the yield of NCMC (Ti) in the electrolysis process depends on the voltage V between the elec-
trodes and the ph of the solution. figure 11.1 shows the yield
dC
Ti
/
dt
of Ti 6 min after the start of the electrolysis process, where
C
Ti
is the concentration of Ti in the electrolyte. The yield
dC
Ti
/
dt
increases with increasing voltage between the electrodes up to
12-13V but then it decreases slowly. This behavior is explained by the formation of trivalent titanium on the surface of the Ti
