Nanodiamond–TiO₂ composites for photocatalytic degradation of microcystin-LA in aqueous solutions under simulated solar light

Abstract

Titanium dioxide (TiO2) has been under intensive investigation for photocatalytic degradation of cyanobacterial toxins. In order to develop more efficient photocatalysts, TiO2 and oxidized nanodiamonds (NDox) were combined as a composite catalyst (NDox-TiO2), which was tested in the oxidation of microcystin-LA (MC-LA), a cyanotoxin frequently found in freshwaters.NDox-TiO2 and neat TiO2 photocatalysts were prepared by a liquid phase deposition method. A wide variety of analytical techniques, including physical adsorption of nitrogen, X-ray diffraction (XRD), UV-Vis and IR diffuse reflectance spectroscopies (DRUV-Vis and DRIFT), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were used to characterize the materials. The performance of the photocatalysts was studied under both simulated solar and visible light.Kinetic results show remarkable efficiency for the NDox-TiO2 composite under simulated solar light irradiation with a synergistic factor of more than 15 relative to neat TiO2, while negligible photocatalytic activity was observed for the degradation of MC-LA when NDox-TiO2 was used under visible light illumination due to the wide band gap of the composite material. The photocatalytic efficiency of NDox-TiO2 was ascribed to the good dispersion of both phases in the composite material, facilitating the possible electronic interaction at the heterojunction interface between NDox and TiO2.

Metal-Free g-C3N4/Nanodiamond Heterostructures for Enhanced Photocatalytic Pollutant Removal and Bacteria Photoinactivation

“…According to previous reports [62,63], these recombination paths come from the sp 3 C-N σ band, sp 2 C-N π band, and the lone pair (LP) state of the bridge N atom transitions, respectively, as depicted in the inset of Figure 7b. Additionally, the pure DNC did not show PL signal under these conditions, and as the amount of DNC increased, the overall PL intensity of the heterojunction was lowered, indicating that photogenerated electrons in the excited g-C3N4 are transferred to the DNC immediately after the photo-production, reducing, therefore, the recombination rate of charge carriers, as also reported before [25,29,30,61].…”

“…Relatively few works have applied DNC for photocatalytic degradation of pollutants [16,28,29], and even fewer have explored g-C 3 N 4 /DNC heterojunctions for wastewater purification and H 2 production [16,25,30]. Due to the various loose ends in the discussion on the chemical, physical, and photocatalytic properties of this system, further studies are highly desired.…”

Emerging applications of nanodiamonds in photocatalysis

“…Oxidized nanodiamonds/titanium dioxide (ND ox -TiO 2 ) prepared by liquid phase deposition method showed enhanced photocatalytic activity in the oxidation of microcystin-LA (MC-LA), a cyanotoxin usually found in water [81]. The apparent first order constants (K app ) of ND ox -TiO 2 (K app = 4.4 × 10 −1 min −1 ) is 15 times larger than that of pristine TiO 2 (K app = 2.8 × 10 −2 min −1 ) under visible light irradiation, and the enhanced photocatalytic degradation activity is probably attributed to electronic interphase interaction between TiO 2 and ND ox phases.…”

“…the enhanced photocatalytic pharmaceuticals (DP and amX) degradation activity of treated nDs modified tio 2[81]. normalized concentration of (a) DP and (b) amX as a function of time for tio 2 and nD-tio 2 (1.0 g l −1 ) composites under near-uV/Vis irradiation.…”

Irradiation-catalysed degradation of methyl orange using BaF 2 –TiO 2 nanocomposite catalysts prepared by a sol–gel method

“…When TiO 2 (as a semiconductor material) is irradiated with UV, the active centre of TiO 2 is photoactivated and an electron/hole (e/h + ) couple is obtained [12][13][14][15][16]. The electron/hole pair further reacts with oxygen and water to produce superoxide radical ion ðO †À 2 Þ and hydroxyl radical (HO•), both of which are very reactive and strongly oxidizing to be capable of effectively catalysing the degradation of organic pollutants and saving reaction time.…”