258
factors for metal ions were found to be between 20 and 300 with fast adsorption
kinetics [83]. CNTs have also been extensively studied for pre-concentrating a variety of organic compounds, many of which were done in real water samples [39].
Adsorption of charged species to CNTs results in changes of conductance, providing the basis for the correlation between analyte concentration and current fluctuation [214]. Other nanomaterials such as nano-Au and QDs have also been used.
Nano-Au was used to detect pesticides at ppb levels in a colorimetric assay; modified nano-Au was shown to detect Hg
2+
and CH 3 Hg
+
rapidly with high sensitivity
and selectivity [183, 188]. QD-modified TiO 2 nanotubes lowered the detection limits of PAHs to the level of pica-mole per liter based on fluorescence resonance
energy transfer [342]. A nanosensor based on CoTe QDs immobilized on a glassy
carbon electrode surface was reported to detect bisphenol A in water at concentrations as low as 10 nM within 5 s [347].
Multifunctional Devices
The advance in functional nanomaterials and their convergence with conventional
technologies bring opportunities in designing a new family of nanotechnologyenabled multifunctional water treatment devices which are capable of performing
multiple tasks in one device. Such multifunctional systems can enhance the overall
performance and avoid excessive redundancy, miniaturizing the footprint. Therefore,
the multifunctional concept is especially advantageous in decentralized and smallscale applications. Different functional nanomaterials can be integrated onto a common platform based on treatment requirement. Besides magnetic nanoparticles,
membranes are a good and extensively studied platform to construct multifunctional
devices. Notably, electrospun nanofibers have drawn much attention as an excellent
nanomaterial carrier. Owing to the high performance, small footprint, and modular
design of nanotechnology-enabled devices, it is envisaged that different functionalities can be assembled in layers of cartridges or as modules arranged in series,
allowing optimization/regeneration of each functionality separately [267]. The
capacity and functionality of such nanotechnology-enabled systems can be easily
manipulated by plugging in or pulling out modules.
Retention and Reuse of Nanomaterials
The retention and reuse of nanomaterials are key aspects of nanotechnology-enabled
device design due to both cost and public health concerns. It can be usually achieved
by applying a separation device or immobilizing nanomaterials in the treatment
system. A promising separation process is membrane filtration which allows continuous operation with small footprint and chemical use. Ceramic membranes are
more advantageous than polymeric membranes in photocatalytic or catalytic ozonation applications as they are more resistant to UV and chemical oxidants [48]. The
suspended particles in the receiving water are detrimental to reactor membrane
13 Wastewater
factors for metal ions were found to be between 20 and 300 with fast adsorption
kinetics [83]. CNTs have also been extensively studied for pre-concentrating a variety of organic compounds, many of which were done in real water samples [39].
Adsorption of charged species to CNTs results in changes of conductance, providing the basis for the correlation between analyte concentration and current fluctuation [214]. Other nanomaterials such as nano-Au and QDs have also been used.
Nano-Au was used to detect pesticides at ppb levels in a colorimetric assay; modified nano-Au was shown to detect Hg
2+
and CH 3 Hg
+
rapidly with high sensitivity
and selectivity [183, 188]. QD-modified TiO 2 nanotubes lowered the detection limits of PAHs to the level of pica-mole per liter based on fluorescence resonance
energy transfer [342]. A nanosensor based on CoTe QDs immobilized on a glassy
carbon electrode surface was reported to detect bisphenol A in water at concentrations as low as 10 nM within 5 s [347].
Multifunctional Devices
The advance in functional nanomaterials and their convergence with conventional
technologies bring opportunities in designing a new family of nanotechnologyenabled multifunctional water treatment devices which are capable of performing
multiple tasks in one device. Such multifunctional systems can enhance the overall
performance and avoid excessive redundancy, miniaturizing the footprint. Therefore,
the multifunctional concept is especially advantageous in decentralized and smallscale applications. Different functional nanomaterials can be integrated onto a common platform based on treatment requirement. Besides magnetic nanoparticles,
membranes are a good and extensively studied platform to construct multifunctional
devices. Notably, electrospun nanofibers have drawn much attention as an excellent
nanomaterial carrier. Owing to the high performance, small footprint, and modular
design of nanotechnology-enabled devices, it is envisaged that different functionalities can be assembled in layers of cartridges or as modules arranged in series,
allowing optimization/regeneration of each functionality separately [267]. The
capacity and functionality of such nanotechnology-enabled systems can be easily
manipulated by plugging in or pulling out modules.
Retention and Reuse of Nanomaterials
The retention and reuse of nanomaterials are key aspects of nanotechnology-enabled
device design due to both cost and public health concerns. It can be usually achieved
by applying a separation device or immobilizing nanomaterials in the treatment
system. A promising separation process is membrane filtration which allows continuous operation with small footprint and chemical use. Ceramic membranes are
more advantageous than polymeric membranes in photocatalytic or catalytic ozonation applications as they are more resistant to UV and chemical oxidants [48]. The
suspended particles in the receiving water are detrimental to reactor membrane
13 Wastewater