Rapid water disinfection using vertically aligned MoS2 nanofilms and visible light

Journal name:
Nature Nanotechnology
Volume:
11,
Pages:
1098–1104
Year published:
DOI:
doi:10.1038/nnano.2016.138
Received
Accepted
Published online

Abstract

Solar energy is readily available in most climates and can be used for water purification. However, solar disinfection of drinking water mostly relies on ultraviolet light, which represents only 4% of the total solar energy, and this leads to a slow treatment speed. Therefore, the development of new materials that can harvest visible light for water disinfection, and so speed up solar water purification, is highly desirable. Here we show that few-layered vertically aligned MoS2 (FLV-MoS2) films can be used to harvest the whole spectrum of visible light (∼50% of solar energy) and achieve highly efficient water disinfection. The bandgap of MoS2 was increased from 1.3 to 1.55 eV by decreasing the domain size, which allowed the FLV-MoS2 to generate reactive oxygen species (ROS) for bacterial inactivation in the water. The FLV-MoS2 showed a ∼15 times better log inactivation efficiency of the indicator bacteria compared with that of bulk MoS2, and a much faster inactivation of bacteria under both visible light and sunlight illumination compared with the widely used TiO2. Moreover, by using a 5 nm copper film on top of the FLV-MoS2 as a catalyst to facilitate electron–hole pair separation and promote the generation of ROS, the disinfection rate was increased a further sixfold. With our approach, we achieved water disinfection of >99.999% inactivation of bacteria in 20 min with a small amount of material (1.6 mg l–1) under simulated visible light.

At a glance

Figures

  1. FLV-MoS2 disinfection schematic.
    Figure 1: FLV-MoS2 disinfection schematic.

    a, The ROS-formation potentials with respect to the vacuum level. b, Schematic that shows the FLV-MoS2 inactivating bacteria in water through visible-light photocatalytic ROS generation.

  2. FLV-MoS2 morphology and band-structure characterization.
    Figure 2: FLV-MoS2 morphology and band-structure characterization.

    a, TEM image (top view) of FLV-MoS2 shows the as-grown vertically standing layers. b, Absorption spectrum of 40 nm FLV-MoS2. c, Photograph of the FLV-MoS2 film patterned with the Au line for the scanning Kelvin probe measurement. d, Line-scan data show the Fermi level (EF) of FLV-MoS2 at each position on the white line in c. e, Mapping of the FLV-MoS2 film shows the Fermi level of each point on the film. f, The band position of FLV-MoS2 with respect to the ROS formation potential and the bulk MoS2 band position. CB, conduction band.

  3. FLV-MoS2 disinfection performance.
    Figure 3: FLV-MoS2 disinfection performance.

    a, Comparison of the disinfection performances of FLV-MoS2 with both light control without FLV-MoS2 and FLV-MoS2 in the dark to confirm the visible-light photocatalytic effect. b, Disinfection performances of FLV-MoS2 compared with those of horizontal nano-MoS2 and bulk MoS2. c, Spectra of illuminating light sources, solar simulator with a UVF and solar simulator with a red-pass filter. d, Disinfection performances using different light sources, the solar simulator with a UVF and the solar simulator with a red-pass filter. e, Raman spectra of FLV-MoS2 and TiO2 films. f, Comparison of disinfection performance between FLV-MoS2 and TiO2 films under both visible-light and real-sunlight illumination. In the disinfection performances, the error bars represent the s.d. of three replicate measurements and the data point with a grey circle means no live bacteria were detected. a.u., arbitrary units.

  4. Performance enhancement of FLV-MoS2 by 5 nm of catalysts of Cu or Au.
    Figure 4: Performance enhancement of FLV-MoS2 by 5 nm of catalysts of Cu or Au.

    a, TEM images (top view) show the morphology of Cu–MoS2 and Au–MoS2 after deposition. b, XPS characterization of Cu–MoS2 and Au–MoS2 shows the presence of Cu and Au. c, Schematic that shows the enhancement of electron–hole separation to facilitate the electrons to participate in ROS-generation reactions after Cu/Au deposition. d, Disinfection-performance comparison of Cu–MoS2 and Au-MoS2 with pristine FLV-MoS2 shows the rapid disinfection by Cu–MoS2 and Au–MoS2 after deposition of the catalysts. e, Disinfection-performance comparison of Cu–MoS2 with the literature values of other photocatalysts using E. coli. The plot shows the log inactivation of E. coli with respect to illumination time for all the photocatalysts in the comparison: (1) Cu–MoS2 (this work, 2 cm2 film equivalent to 1.6 mg l–1), (2) TiO2–CdS (ref. 25) (1 cm2 film), (3) ZnO/Cu (ref. 48) (100 mg l–1), (4) GO–CdS (ref. 34) (100 mg l–1), (5) BV (ref. 36) (100 mg l–1), (6) GO–C3N4 (ref. 37) (100 mg l–1) and (7) SGO–ZnO–Ag (ref. 35) (100 mg l–1). Details of the conditions for the photocatalytic-disinfection experiments (sample concentration, light source and intensity, and bacteria strain) are given in Supplementary Table 1. The final inactivation efficiencies are limited by the initial bacterial concentration. NA, not available.

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Author information

Affiliations

  1. Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA

    • Chong Liu,
    • Desheng Kong,
    • Po-Chun Hsu,
    • Hongtao Yuan,
    • Hyun-Wook Lee,
    • Yayuan Liu,
    • Kai Yan,
    • Dingchang Lin &
    • Yi Cui
  2. Department of Applied Physics, Stanford University, Stanford, California 94305, USA

    • Haotian Wang
  3. Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA

    • Shuang Wang
  4. Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305, USA

    • Peter A. Maraccini,
    • Kimberly M. Parker &
    • Alexandria B. Boehm
  5. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94305, USA

    • Yi Cui

Contributions

C.L. and Y.C. developed the concept. C.L. synthesized the samples and conducted the disinfection measurement and material characterizations. D.K. and H.W. helped with the material synthesis. P.-C.H. and S.W. helped with the optical measurement. H.Y. helped with the Kelvin probe measurement. H.-W.L. did the TEM characterization. D.K. helped with the Raman spectroscopy measurement. Y.L. helped with catalyst measurements. P.A.M. helped with estimation of the real-sunlight spectrum. K.M.P. helped with HPLC measurement. C.L., A.B.B. and Y.C. analysed the data and co-wrote the paper. K.Y. and D.L. provided important experimental insights. All the authors discussed the whole paper.

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The authors declare no competing financial interests.

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