2.3. Pretreatment of metallic powder
The Zn and Fe powder were treated with 0.4% H2SO4 and then
repeatedly rinsed with deionized water five times to remove oil
film and oxides on the surface of the metallic powder. The cleaned
metallic powder were dried in a vacuum oven at 60 C for 2 h and
then stored in a sealed desiccator.
2.4. Characterization of metallic powder
The specific surface area of micro-scale zinc powder was
34.89 m2
/g and that of micro-scale iron was 22.55 m2
/g, as
measured by the BrunauereEmmeteTeller gas adsorption isotherm
with N2 gas on a V-sorb 2800P surface area analyzer (Gold App
Instruments, China). The surface morphological analyses of zinc
powder were performed using a Hitachi Se3000N scanning electron
microscope (Hitachi, Japan) at a 10 kV beam potential.
2.5. Endosulfan removal experiments in water
A total of 0.2 g of pre-cleaned Zn(0) was added into 200 mL of
acetate buffer with endosulfan (40 mg/L, pH 4). The reaction bottles
were sealed with rubber plugs and placed in a magnetic stirring
apparatus (HJ-4, Guohua Company, China) at room temperature
(22 ± 0.1 C). Control experiments were also performed in the
buffer solution with endosulfan without Zn(0). The experiment was
performed in triplicate and the reaction time was 180 min. The
samples were withdrawn by syringe at the given times, extracted
by ethyl acetate using a separatory funnel and analyzed by GC. The
extraction method was less interference from impurities and with
high recovery (above 87.92%).
The phosphate buffer (pH 7) and carbonate buffer (pH 9) were
chosen to evaluate the effect of pH on the degradation according to
the above procedure.
To compare the influence of oxic and anoxic conditions on the
degradation of endosulfan, the comparison test under anoxic conditions
was performed in acetate buffer (pH 4). The vial was first
purged with nitrogen to assume the absence of dissolved oxygen,
and then a continuous nitrogen sparging flow (3 mL/min) was run
during the reaction.
Moreover, the experiment was conducted using Fe(0) instead of
Zn(0) in the acetate buffer containing 40 mg/L endosulfan and 0.2 g
pre-cleaned metal under oxic condition to compare the degradation
ability.