Gaseous
arsenic emitted from coal combustion flue gas (CCFG) causes
not only severe contamination of the environment but also the failure
of selective catalytic reduction (SCR) catalysts in power plants.
Development of inexpensive and effective adsorbents or techniques
for the removal of arsenic from high-temperature CCFG is crucial.
In this study, halloysite nanotubes (HNTs) at low price were modified
with CuCl2 (CuCl2–HNTs) through ultrasound
assistance and applied for capturing As2O3(g)
in simulated flue gas (SFG). Experiments on arsenic adsorption performance,
adsorption mechanism, and adsorption energy based on density functional
theory were performed. Modification with CuCl2 clearly
enhanced the arsenic uptake capacity (approximately 12.3 mg/g) at
600 °C for SFG. The adsorbent exhibited favorable tolerance to
high concentrations of NO
x
and SO
x
. The As2O3(III) was
oxidized and transformed into As2O5(V) on the
CuCl2–HNTs. The Al–O bridge had the highest
adsorption energy for the O end of the As–O group (−2.986
eV), and the combination formed between arsenic-containing groups
and aluminum was stable. In addition, the captured arsenic could be
stabilized in the sorbent at high temperature, making it possible
to use the sorbent before the SCR system. This demonstrates that CuCl2–HNTs is a promising sorbent for arsenic oxidation
and removal from CCFG.
One novel/multifunctional selenium-doped SrFeO3‑δ/HNTs composite was fabricated and used for immobilization of gaseous
mercury. The composite showed excellent performances for Hg0 removal via adsorption coupled with photocatalytic oxidation in
visible-light conditions. The adsorption capacity of 4271.15 μg·g–1, rate of 5.0 μg·g–1·min–1, and removal efficiency of ∼100% were obtained
under N2+O2, which was further confirmed by
reaction kinetics. SrFeO3‑δ was selenized
into iron diselenide and a Se–Fe bond with high affinity toward
Hg0. In addition, the yielding of •O2
– and the separation of photoexcited electrons
and holes (h+) promoted the photocatalytic oxidation of
mercury. The composite with intrinsic magnetism could be easily recycled
for reuse by magnetic separation. Moreover, the composite possessed
favorable tolerance to the complicated flue gas. An online lab-built
thermal decomposition system demonstrated that the immobilized Hg
was primarily HgSe, which exhibited very high stability and low toxicity.
Density functional theory (DFT) calculations proved that the composite
was half metal with magnetism, indicating that Hg on Se-SrFeO3‑δ/HNTs formed the stable structure releasing
1.055 eV. The doping of selenium promoted the charge transfer between
O (2p) and Hg (6s), which also favored Hg0 removal. Se-SrFeO3‑δ/HNTs with recyclability possess great potentials
for Hg0 efficient removal and immobilization/detoxification
from flue gas.
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