1 3
Topics in Current Chemistry (2020) 378:7
photoelectrocatalysis are generally composed of photocatalyst and co-catalyst
deposited on conductive glass. Different photocatalytic materials have been used
in photoelectrocatalysis, among which TiO 2 is one of the most widely studied
semiconductors and is used as photoanode. Other materials active in the presence
of visible light have also been used for their good performance as photoanodes
[139].
However, if the photoanode consists of only one component, it is characterized
by the problem of recombination of the charges. For this reason, making changes
to the composition of the photoanode can be useful. In particular, an interesting
approach is the use of co-catalysts, and among these, graphitic materials are very
promising. Graphitic materials with two-dimensional structures are characterized by
excellent electrical conductivity and can be used as electron transporters in order to
improve the separation of photogenerated charge carriers and to enhance photoelectrocatalytic activity [137]. Various studies have investigated the ability of graphene
to attract and transport electrons, improve the adsorption of reagents, and confer the
ability to absorb light in the visible field to semiconductors [140–144].
4.2 Gray‑ and Stormwater Treatment
Gray water includes wastewater generated by households from sources such as sinks,
showers, baths, laundry washing machines, and dishwashers, but does not include
fecal-contaminated sources. Stormwater originates from precipitation events, including snow and ice melt. Stormwater can be absorbed in soil, stored in water bodies as
surface water (e.g., in ponds and lakes), evaporate, or be transported via streams
and rivers. HPC has seen some research applications in gray-water and harvested
stormwater treatment. Wang et al. [145] used TiO 2 -graphene oxide composites at
various percentages in artificial stormwater for the disinfection of spiked E. coli
under solar light. While the catalyst showed good reusability, even after ten cycles,
in the optimal case only up to 1 log removal was reported from an initial bacterial
load of 10
4
CFU/mL. The catalyst, due to its surface charge, was very efficient in
reducing TSS by co-sedimentation of any waterborne particles with the photocatalyst. The authors suggest that such a treatment could take place with photocatalysis
during daytime, coupled with a long period of sedimentation for catalyst recovery
and TSS reduction overnight. However, the application of HPC for gray-water or
stormwater is not ideal—HPC, as a process that is reactive to virtually all organic
compounds, would benefit from an initial biological process in order to remove biodegradable organic compounds. Such a setup was demonstrated by Garcia et al. following the removal of TOC in rainwater using a combined ozonation-photocatalytic
system, but only after treatment in a bioreactor for the removal of biodegradable
compounds [146]. Other examples of gray-water treatment by HPC have also been
reported [147, 148]. While research on HPC treatment of gray/stormwater has been
published, it is a very small part of water treatment. Both in terms of microbial contamination and potentially toxic compounds, gray/stormwater is of negligible importance relative to wastewater.
245
Reprinted from the journal
Topics in Current Chemistry (2020) 378:7
photoelectrocatalysis are generally composed of photocatalyst and co-catalyst
deposited on conductive glass. Different photocatalytic materials have been used
in photoelectrocatalysis, among which TiO 2 is one of the most widely studied
semiconductors and is used as photoanode. Other materials active in the presence
of visible light have also been used for their good performance as photoanodes
[139].
However, if the photoanode consists of only one component, it is characterized
by the problem of recombination of the charges. For this reason, making changes
to the composition of the photoanode can be useful. In particular, an interesting
approach is the use of co-catalysts, and among these, graphitic materials are very
promising. Graphitic materials with two-dimensional structures are characterized by
excellent electrical conductivity and can be used as electron transporters in order to
improve the separation of photogenerated charge carriers and to enhance photoelectrocatalytic activity [137]. Various studies have investigated the ability of graphene
to attract and transport electrons, improve the adsorption of reagents, and confer the
ability to absorb light in the visible field to semiconductors [140–144].
4.2 Gray‑ and Stormwater Treatment
Gray water includes wastewater generated by households from sources such as sinks,
showers, baths, laundry washing machines, and dishwashers, but does not include
fecal-contaminated sources. Stormwater originates from precipitation events, including snow and ice melt. Stormwater can be absorbed in soil, stored in water bodies as
surface water (e.g., in ponds and lakes), evaporate, or be transported via streams
and rivers. HPC has seen some research applications in gray-water and harvested
stormwater treatment. Wang et al. [145] used TiO 2 -graphene oxide composites at
various percentages in artificial stormwater for the disinfection of spiked E. coli
under solar light. While the catalyst showed good reusability, even after ten cycles,
in the optimal case only up to 1 log removal was reported from an initial bacterial
load of 10
4
CFU/mL. The catalyst, due to its surface charge, was very efficient in
reducing TSS by co-sedimentation of any waterborne particles with the photocatalyst. The authors suggest that such a treatment could take place with photocatalysis
during daytime, coupled with a long period of sedimentation for catalyst recovery
and TSS reduction overnight. However, the application of HPC for gray-water or
stormwater is not ideal—HPC, as a process that is reactive to virtually all organic
compounds, would benefit from an initial biological process in order to remove biodegradable organic compounds. Such a setup was demonstrated by Garcia et al. following the removal of TOC in rainwater using a combined ozonation-photocatalytic
system, but only after treatment in a bioreactor for the removal of biodegradable
compounds [146]. Other examples of gray-water treatment by HPC have also been
reported [147, 148]. While research on HPC treatment of gray/stormwater has been
published, it is a very small part of water treatment. Both in terms of microbial contamination and potentially toxic compounds, gray/stormwater is of negligible importance relative to wastewater.
245
Reprinted from the journal