Electronic Tuning of Covalent Triazine Framework Nanoshells for Highly Efficient Photocatalytic H₂O₂ Production

Abstract

and sustainable production technologies is highly urgent. Among many potential options, semiconductor-based photocatalytic H 2 O 2 synthesis from two-electron oxygen reduction at ambient conditions offers a promising strategy, which only uses clean and sustainable solar energy as the energy input. [8][9] The challenge is to explore advanced semiconductor photocatalysts with efficient charge-separation efficiency and favorable surface properties in order to shift the reaction pathway toward the desired H 2 O 2 product. Inorganic semiconductors (such as TiO 2 ) have been investigated for photocatalytic H 2 O 2 production. [10][11][12][13] However, they usually suffer from low H 2 O 2 production rate owing to their narrow light absorption range and undesirable catalytic degradation of H 2 O 2 on transition metals. [14][15] To this end, polymeric photocatalysts, exemplified by graphitic carbon nitride (g-C 3 N 4 ), have attracted increasing attention in recent years because of their tunable chemical structures and metal-free composition. [16][17][18][19] Previous studies revealed that the tri-s-triazine units in g-C 3 N 4 could facilitate the two-electron oxygen reduction by forming a complex with the O 2•− intermediate. [20][21][22] Despite the potential, their demonstrated photocatalytic activities were still unsatisfactory for practical applications.Covalent triazine frameworks (CTFs), as a new class of nitrogen-rich organic photocatalysts, have recently emerged owing to their excellent photocatalytic activities and stability for photocatalytic water splitting, [23][24][25][26] CO 2 reduction, [27][28] N 2 fixation, [29] and organic transformation. [30][31][32] In principle, their chemical and electronic structures can be precisely tuned by varying the corresponding precursors and synthetic routes, making them a versatile platform for designing photocatalysts on demand. [33] Notably, CTFs have intrinsic structural similarity to the polymeric skeletons of g-C 3 N 4 , both of which are constructed from primary triazine units. [34][35][36] This may imply the great potential of CTFs for photocatalytic H 2 O 2 production via the two-electron oxygen reduction. However, their applications in this field have been rarely studied up to now. Recently, Xu and co-workers first reported that the acetylene and diacetylenefunctionalized CTFs could be used as effective photocatalysts for photocatalytic H 2 O 2 production under visible light irradiation. [37] Unfortunately, their photocatalytic efficiency was quite

Benzaldehyde-Promoted (Auto)Photocatalysis under Visible Light: Pitfalls and Opportunities in Photocatalytic H2O2 Production

“…17,18 The observed effects might be negligible in very dilute solutions of benzyl alcohol, but they might represent a dominant mechanism under solvent-free (only benzyl alcohol) or biphasic (e.g., equivolumetric benzyl alcohol/water mixtures) conditions. [38][39][40][41][42][43] Two further points are noteworthy with respect to the visible light activity. Firstly, the designation of a 420 nm cut-off filter implies, per definitionem, that the transmittance at 420 nm is 50%, i.e., there can be a small portion of higher energy light still transmitted when using these filters.…”

Enhanced Photocatalytic H₂O₂ Production over Inverse Opal ZnO@ Polydopamine S-scheme Heterojunctions

“…Photocatalysis is a green and sustainable method to produce H2O2 since it is powered by inexhaustible sunlight 18 . Moreover, it also reduces our energy reliance on unsustainable fossil fuels and alleviates environmental pollution 15,19,20 .…”

Reaction Pathways toward Sustainable Photosynthesis of Hydrogen Peroxide by Polymer Photocatalysts

“…In 2014, Shiraishi et al reported that the graphitic carbon nitride ( g -C 3 N 4 ), a metal-free polymer semiconductor, can produce H 2 O 2 under photoirradiation using alcohol and molecular O 2 as the proton and oxygen sources, respectively . Inspired by this seminal work, numerous organic polymer-based photocatalysts have emerged in recent years for photocatalytic production of H 2 O 2 , including g -C 3 N 4 derivatives, − conjugated microporous polymers (CMPs), , covalent triazine frameworks (CTFs), , covalent organic frameworks (COFs), − linear conjugated polymers (LCPs), , and resorcinol-formaldehyde (RFs) resins. − Compared to their inorganic counterparts, these polymeric or “soft” materials are comprised of naturally abundant elements such as C, H, and N. Moreover, recent observation of long-lived charges in organic heterojunctions without electron/hole scavengers suggests that organic polymers are promising for driving kinetically challenging and technologically desirable redox reactions . Thus, they are up-and-coming candidates as low cost and easily processable materials for solar-driven H 2 O 2 production. − …”