Qinmin
Zheng
a,
David T.
Tan
b and
Danmeng
Shuai
*a
aDepartment of Civil and Environmental Engineering, The George Washington University, 800 22nd St NW Suite 3530, Science and Engineering Hall, Washington, DC 20052, USA. E-mail: danmengshuai@gwu.edu
bDepartment of Civil, Environmental, and Geo-Engineering, University of Minnesota, 500 Pillsbury Drive SE, Minneapolis, Minnesota 55455, USA
First published on 28th October 2015
Photocatalysis holds great promise for sustainable water treatment due to the generation of reactive radicals for efficient contaminant removal, minimized chemicals consumption, and the utilization of renewable, inexhaustible solar energy (DOI: 10.1021/cr00033a004, DOI: 10.1021/cr00018a003). The most widely used photocatalyst for water treatment, titanium dioxide (TiO2), requires UV excitation. However, UV only accounts for 4% of solar energy, and the dependence of current photocatalysts on UV compromises the efficiency and feasibility of solar powered water treatment. Disinfection, an important water treatment process for the inactivation of pathogenic microorganisms, also requires UV radiation with a wavelength of 250–260 nm. Therefore, the development of novel photocatalysts, and photophysical and photochemical processes for the use of optical radiation with a longer wavelength, such as visible light that accounts for 40% of solar energy, would present a major breakthrough for solar powered water treatment. A unique photoluminescence process, upconversion, has recently drawn attention for its ability to convert low energy photons (e.g., visible light) into high energy photons (e.g., UV light) for antimicrobial purposes (DOI: 10.1021/es200196c, DOI: 10.1021/es405229p). In this research highlight, we discuss three innovative materials used in photocatalysis and photoluminescence for water treatment applications, including graphitic carbon nitride (g-C3N4), red phosphorus, and upconversion phosphors (Y2SiO5 doped with Pr and Li).Fig. 1 (a) Atomic force microscopic image of SL g-C3N4; (b) the reaction rate constants of rhodamine B photocatalytic degradation on different photocatalysts; and (c) comparison of the photocatalytic performance of total ammonia nitrogen (TAN) removal on different photocatalysts. SL and NS represent atomic single layer and nanosheet, respectively. Adapted from DOI: 10.1039/C3RA45776A with permission of The Royal Society of Chemistry, and reprinted with permission from DOI: 10.1021/es503073z. Copyright 2014 American Chemical Society. |
Fig. 2 (A) Photocatalytic inactivation kinetics under xenon lamp and sunlight irradiation in the presence of red phosphorus; (B) photocatalytic inactivation efficiencies under different monochromatic LED irradiation (red 610–650 nm, yellow 570–620 nm, green 470–570 nm, and blue 440–490 nm). Reprinted with permission from DOI: 10.1021/acs.est.5b00531. Copyright 2015 American Chemical Society. |
Fig. 3 Proposed bactericidal mechanism of red phosphorus under visible light irradiation. Red phosphorus generates ROS under irradiation, and ROS subsequently inhibit bacterial metabolism on cell membranes and oxidize intracellular components. Reprinted with permission from DOI: 10.1021/acs.est.5b00531. Copyright 2015 American Chemical Society. |
Fig. 4 Utilization of visible-to-ultraviolet upconversion phosphor coating for light-activated antimicrobial materials. Energy diagram depicts excited-state absorption of visible light from the ground-state configuration, G, to the excited states, E1 and E2, to emit a UVC photon upon relaxation. Reprinted with permission from DOI: 10.1021/es200196c. Copyright 2011 American Chemical Society. |
Fig. 5 (a) Inactivation of Bacillus subtilis spores on ceramic and dip-coated film surfaces with exposure to visible fluorescent light. (b) UVC dose–response curve showing Bacillus subtilis spore inactivation under low intensity UVC irradiation (0.04 mW cm−2). Reprinted with permission from DOI: 10.1021/es405229p. Copyright 2014 American Chemical Society. |
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