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Review
. 2015 Jan 14;20(1):1319-56.
doi: 10.3390/molecules20011319.

The viability of photocatalysis for air purification

Stephen O Hay  1 , Timothy Obee  2 , Zhu Luo  3 , Ting Jiang  4 , Yongtao Meng  5 , Junkai He  6 , Steven C Murphy  7 , Steven Suib  8
Affiliations
Review

The viability of photocatalysis for air purification

Stephen O Hay et al. Molecules. .

Abstract

Photocatalytic oxidation (PCO) air purification technology is reviewed based on the decades of research conducted by the United Technologies Research Center (UTRC) and their external colleagues. UTRC conducted basic research on the reaction rates of various volatile organic compounds (VOCs). The knowledge gained allowed validation of 1D and 3D prototype reactor models that guided further purifier development. Colleagues worldwide validated purifier prototypes in simulated realistic indoor environments. Prototype products were deployed in office environments both in the United States and France. As a result of these validation studies, it was discovered that both catalyst lifetime and byproduct formation are barriers to implementing this technology. Research is ongoing at the University of Connecticut that is applicable to extending catalyst lifetime, increasing catalyst efficiency and extending activation wavelength from the ultraviolet to the visible wavelengths. It is critical that catalyst lifetime is extended to realize cost effective implementation of PCO air purification.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Generic Multi-stage, Honeycomb-Monolith Photocatalytic Reactor.
Figure 2
Figure 2
The effect of flow velocity on the effective CADR is opposite to the effect on SPE and gives a more accurate picture of the effect of air purification to HVAC professionals. A generic HVAC design is assumed.
Figure 3
Figure 3
Measured PCO reaction rates for VOCs of interest in indoor air; UV 1-mW/cm2, 6000 ppm water level.
Figure 4
Figure 4
Measured PCO products vary with increasing concentration. Complete mineralization occurs at low concentrations. A different version of this diagram is shown in ref. [7].
Figure 5
Figure 5
A partial surface layer of WO3 modifies the catalyst surface, this changes the binding energies in such a manner that VOC adsorption can compete with water adsorption on the catalyst surface. The relative rate is the PCO removal rate observed for (WO3-TiO2) minus the PCO removal rate for (TiO2) divided by the removal rate for (TiO2).
Figure 6
Figure 6
Photo-oxidation Reactor.
Figure 7
Figure 7
Photocatalytic reactor design flow diagram.
Figure 8
Figure 8
Comparison of model and experiment for formaldehyde in a 2-UV banks, 3-honeycomb monolith photoreactor. A similar version of this figure is published in Ref. [13].
Figure 9
Figure 9
HVAC Schematics of air purifier installation; 35 ton rooftop with VAV, economizer and desiccant wheel.
Figure 10
Figure 10
(a) Surface area change and (b) pore volume change in doped titania systems as a function of calcination temperature (T = 50 °C, 200 °C, 300 °C, 400 °C and 500 °C).
Figure 11
Figure 11
X-ray diffraction pattern for UCT-TiO2 materials. Inset image: adsorption ability and photocatalytic ability of UCT-TiO2 compared to P25 tested in dark and visible light conditions, respectively. The efficiency was calculated by C/C0 (dye concentration in different time/initial dye concentration).
Figure 12
Figure 12
(a) Adsorption of siloxane on the adsorbents over time, UCT material compared to activated carbon; (b) Pore size distribution of mesoporous aluminosilicate.
Figure 13
Figure 13
(a) SEM images; (b) HRTEM, (in set, selected area diffraction (SAD)); (c) O2-temperature programmed desorption (inset, XRD pattern) of AMO.
Figure 14
Figure 14
MnO2 nanowire membrane for dye degradation: (a) overall view of MnO2 nanowire membrane; (b) SEM image of the MnO2 nanowire membrane; (c) in-situ membrane reaction system; (d) the UV-Vis spectra of the catalytic degradation of methyl orange by MnO2 nanowire membrane.
See this image and copyright information in PMC

References

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