Visible light photodegradation of dyes and paracetamol by direct sensitization mechanism onto metallic MoO2 nanocrystals

Abstract

MoO 2 nanocrystals were prepared by solvothermal treatment of a Mo chloromethoxide at 250 • C in oleic acid. The monoclinic MoO 2 phase, with a mean crystallite size of 29 nm, formed through reduction of molybdenum bronzes. The as-prepared MoO 2 nanocrystals were free from organics, allowing their use in photodegradation tests of organic pollutants (methylene blue, rhodamine B, paracetamol), without any preliminary purification treatment of the nanocrystals. It was found that MoO 2 was an efficient adsorbent of methylene blue (43 mg g − 1 for 1.5 × 10 − 4 M concentration) in the dark and an efficient photodegradation catalyst under visible light (all methylene blue removed from the solution after 240 min). From the analysis of the combined photodegradation tests of rhodamine B and paracetamol, it was clarified that direct sensitization was responsible for photodegradation. This finding was related to the work function value of metallic MoO 2 , placed at more negative values if compared with other metallic materials.

One-Step Calcination to Gain Exfoliated g-C3N4/MoO2 Composites for High-Performance Photocatalytic Hydrogen Evolution

“…On the basis of the chemical states of C and N elements discussed above, it can be concluded that the composite does contain g-C 3 N 4 . As for the Mo 3d spectrum of the optimal sample CNM-4 ( Figure 3 c), there are three groups of peaks with binding energy at 230.30 and 233.31 eV, 231.36 and 235.30 eV, as well as 232.27 and 236.37 eV, representing the electron spin splitting of 3d 5/2 and 3d 3/2 of Mo 4+ , Mo 5+ , and Mo 6+ in the composites, respectively [ 20 , 27 ]. The XPS spectrum of the Mo element revealed that the oxidation state of Mo atoms in the composites involved Mo 4+ , Mo 5+ , and Mo 6+ , with the Mo 5+ and Mo 6+ states attributed to the Jahn–Teller effect caused by lattice distortion [ 28 ].…”

“…Among semiconductor materials, MoO 2 has excellent electrical conductivity and photoelectrochemical activity due to its unique metallic properties which are attributed to the fermi level of MoO 2 provided by its 4d orbital [ 18 , 19 ]. Therefore, MoO 2 has been widely investigated and applied in photocatalysis, electrocatalysis, batteries, and other fields [ 20 , 21 , 22 ]. Recently, researchers have reported some work on g-C 3 N 4 /MoO 2 composites for photocatalysis.…”