Hydrated Orthorhombic/Hexagonal Mixed-Phase WO₃ Core–Shell Nanoribbons for Hole-Mediated Photocatalysis

Abstract

Herein, we report the hydrothermal fabrication of hydrated hexagonal (h)/orthorhombic (o) mixed-phase (h-WO3/o-WO3·H2O) core–shell nanoribbons for the photodegradation of methylene blue (MB) under UV, visible, and monochromatic light excitations. The mixed-phase core–shell shows 2–3 times higher photocatalytic activity than the monoclinic (m)-WO3 and h-WO3 crystalline phases. The intercalated water, trap states, and prolonged carrier lifetimes play significant roles in the photocatalytic enhancement of the hydrated mixed phase. These developed nanosystems are rich in oxygen vacancies and show photoabsorption extended up to the near-infrared (NIR) region. Electrochemical spectroscopy revealed a reduced charge-transfer resistance in the mixed-phase compared with other crystalline phases. The underlying mechanism shows that the superiority of the mixed-phase core–shell over other crystalline phases is because of three factors. First, efficient carrier separation at the core–shell and mixed-phase junction; second, intercalated water from the reaction medium and the o-WO3·H2O phase; and third, electron trapping sites. The oxygen defects trap the photogenerated electrons and leave free holes. The tunnel structure of the mixed phase provides intercalation and easy diffusion of water molecules. The intercalated water molecules readily interact with the mobile holes to form hydroxyl radicals for activated photocatalysis. All of these factors contribute to the improved photocatalytic performance of the mixed-phase WO3 nanoribbons.

Self-Assembled p–n Homojunction in SnS2 Nanosheets for Enhanced Visible Light-Driven Photocatalysis

“…From the trapped sites, the electrons are transferred to the adsorbed O 2 molecule and generate O 2 · – radicals. According to Figure b, O 2 · – is the dominant species because their O 2 · – /O 2 conversion potential of −0.33 V vs RHE is less negative than SnS 2 ’s CB electron potential . Therefore, the CB electrons easily produce O 2 · – .…”

“…Furthermore, the • OH/OH − conversion potential of 2.7 V vs RHE is more positive than SnS 2 's VB. 71 Therefore, photogenerated holes are not as active as electrons to generate • OH. The radical scavenging and trapping experiments further confirm the reactivity of the different radical species.…”

“…According to Figure 8b, O 2 •− is the dominant species because their O 2 •− /O 2 conversion potential of −0.33 V vs RHE is less negative than SnS 2 's CB electron potential. 71 Therefore, the CB electrons easily produce O 2…”

Piezo-Photocatalytic and Photocatalytic Bismuth Vanadate Nanorods with Antibacterial Property

“…This plot also aids to measure the conduction band (CB) edge and valence band (VB) edge positions of the desired material/sample under investigation. According to the Mott–Schottky theory, the capacitance and potential are related by the equation: ) where “ C ” is the capacitance of the space charge region, e is the electron charge, ε is the dielectric constant of BiVO 4 (ε ∼ 68 Fm –1 ), and ε 0 is the vacuum permittivity which is given by 8.854 × 10 –12 Fm –1 , E applied and E FB are the applied and flat band potentials, N D is the carrier concentration (donor density), k is the Boltzmann constant, and T is the absolute temperature (298 K).…”

“…Surprisingly, the presence of CCl 4 and AA causes MB degradation to increase to 66.44 and 72.84%, respectively. The conclusion drawn is that the lack of O 2 •– radicals and electrons in the reaction chamber aids in producing more • OH radicals by the photogenerated holes, which speeds up the process of MB degradation …”