Defective Anatase TiO_2−x Mesocrystal Growth In Situ on g‐C₃N₄ Nanosheets: Construction of 3D/2D Z‐Scheme Heterostructures for Highly Efficient Visible‐Light Photocatalysis

Abstract

Environmental remediation by employing visible-light-active semiconductor heterostructures provides effective solutions for handling emerging contaminants by a much greener and lower cost approach compared with other methods. This report demonstrates that the in situ growth of nanosized single-crystal-like defective anatase TiO mesocrystals (DTMCs) on g-C N nanosheets (NSs) can produce a 3D/2D DTMC/g-C N NS heterostructure with the two components held together by chemical bonds to form tight interfaces. This nanostructured heterostructure displayed remarkably improved photocatalytic activity toward the removal of the model pollutants Methyl Orange (MO) and Cr under visible-light irradiation in comparison with the pristine DTMC and g-C N NS components, which suggests that both the oxidation and reduction abilities of the DTMC/g-C N NSs were simultaneously enhanced after fabrication. On the basis of the results of a systematic characterization, a reasonable mechanism for the photocatalytic activity based on a direct Z-scheme heterojunction is proposed and further verified by the measurement of OH. This novel Z-scheme heterojunction endows the heterostructure with improved photogenerated electron/hole pair separation and a strong redox ability for the efficient degradation of wastewater pollutants. This work will be useful for the design and fabrication of direct Z-scheme heterostructured photocatalysts with novel architectures for applications in energy conversion and environmental remediation.

Titanium Dioxide (TiO2) Mesocrystals: Synthesis, Growth Mechanisms and Photocatalytic Properties

“…Upon microwave treatment of the obtained suspension, anatase TiO2 mesocages with a single-crystal-like structure were found to be evenly anchored on graphene nanosheets [59]. Most recently, our group demonstrated that through in situ growth of nanosized defective anatase TiO2-x mesocrystals (DTMCs) on g-C3N4 nanosheets (NSs), a novel 3D/2D DTMC/g-C3N4 NS heterostructure with tight interfaces could be formed ( Figure 14) [183].…”

“…Apart from the above-mentioned doping strategies, the coupling of TiO 2 mesocrystals with appropriate foreign elements to construct TiO 2 mesocrystal-based heterostructures is considered to be another effective way to enhance the light absorbance capability as well as inhibit the photoinduced charge carrier recombination [17,18,21]. Hitherto, various kinds of foreign elements have been successfully utilized to modify anatase TiO 2 mesocrystals [59,60,[169][170][171][172][173][174][175][176][177][178][179][180][181][182][183]. For example, Sun's group successfully fabricated spindle-like TiO 2 /CdS composites by uniformly distributing CdS nanoparticles onto nanoporous anatase mesocrystals via the simple hydrothermal and hot-injection methods [170].…”

“…In addition to the aforementioned doping strategy, the coupling of TiO 2 mesocrystals with appropriate foreign materials to construct TiO 2 -mesocrystal-based heterostructures is considered to be another useful methodology to broaden the light absorbance region of the material to visible light or even near-infrared (NIR) light, as well as to facilitate the mobility of photogenerated charge carriers within the particle [169][170][171][172][173][174][175][176][177][178][179][180][181][182][183]. For example, by utilizing CdS nanocrystals to modify spindle-shaped nanaporous anatase TiO 2 mesocrystals, Sun's group combined the advantages of the individual material, including (1) augmented specific surface area to provide more absorption and reactive sites; (2) TiO 2 mesocrystal substrate with high crystallinity and porosity to facilitate charge transport;…”

“…Apart from the adjustment of deposited guest particles, it was also demonstrated that efficient defect-state-induced hot electron transfer could be found in the as-prepared Au nanoparticles/reduced TiO 2 mesocrystal photocatalysts, which lead to the enhanced photoreactivity of the photocatalyst in removing methylene blue (MB) [182]. Most recently, our group evaluated the photoreactivity of the 3D/2D DTMC/g-C 3 N 4 NS heterostructure with chemically bonded tight interfaces and found that the as-fabricated composite photocatalyst displayed much higher visible-light-driven photoreactivity toward removing the pollutants of MO and Cr(VI) than the corresponding DTMCs and g-C 3 N 4 NSs counterparts ( Figure 18) [183]. Systematic characterization results indicated that such an enhancement in the photoredox ability of the composite photocatalyst was based on the direct Z-scheme charge separation, as verified by the •OH-trapping experiment.…”

“…(e) Schematic presentation of the in situ growth of TiO 2 mesocrystals on a g-C 3 N 4 nanosheet. Reprinted with permission from[183]. Copyright John Wiley & Sons Inc., 2018.…”