Title:
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A visible-light assisted dual purpose photoelectrochemical cell for simultaneous removal of heavy metals and organic pollutants in wastewater
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Water pollution is a major global issue which poses a serious threat to human
health as well as the aquatic environment. In particular, dissolved heavy metal
species and persistent organic pollutants (POPs) have been regarded as major
problems due to their high toxicity and non-biodegradability. Adsorbents and
membrane filtration are the most widely used technologies for the treatment of
contaminated waste water, however the high cost and environmental implications
of these technologies have encouraged a paradigm shift to the use of
photocatalytic processes for wastewater treatment. In this work, an innovative
photoelectrochemical process for simultaneous removal of heavy metal ions and
POPs from wastewater was developed and demonstrated using a
photoelectrochemical cell (PEC) with a W03 photoanode under sunlight
irradiation. Synthetic wastewater samples containing 0.5 M of NaCI, 10 ppm of
methylene blue (MB, organic pollutant), 500 ppm of CuCh or 500 ppm NiCh
were tested as the first examples for demonstration of the principle, device and
process. The results showed that upon irradiation of simulated sunlight on the
photoanode, metal ions (Cu2+ and Ni2+) can be recovered as metals at the cathode.
MB was simultaneously decomposed at the photoanode without using any
additional chemicals. The cell voltage required for this dual purpose process was
as much as 71 % or 57 % lower than that required for conventional
electrodeposition of Cu or Ni respectively with an inert anode. Current efficiency
for electrodeposition in the PEC could be adjusted close to 100 % depending on
applied cell voltage, minimising charge loss for H2 evolution. Meanwhile, as a
potential photocatalyst, CNTs/W03 hybrids were successfully synthesised by a
surfactant aided sol-gel method and tested for their photocatalytic performance. It
was found that the addition of CNTs to W03 by either hybridisation or mechanical
mixing caused a significant drop of both photocurrent and photovoltage of W03,
presumably due to the interfacial electronic structure between W03 and CNTs.
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