2D visible-light-driven TiO2@Ti3C2/g-C3N4 ternary heterostructure for high photocatalytic activity

Positioning MXenes in the Photocatalysis Landscape: Competitiveness, Challenges, and Future Perspectives

“…Therefore, high electrical conductivity and favorable energy structure of MXenes enable them as promising reservoir to trap and shuttle the photoelectrons generated from semiconductors ( Figure 8) and thus promote the separation of charge carriers and the photoactivity enhancement of MXenes-based composites. Such role of MXenes has been reported in various composite photocatalysts, including [34,99] Ti 3 C 2 T x /CdS, [71,114] Ti 3 C 2 T x /Bi 2 WO 6 , [69] [80] Ti 3 C 2 T x /Ag 3 PO 4 , [77] Ti 3 C 2 T x /α-Fe 2 O 3 , [115] TiO 2 @Ti 3 C 2 T x /g-C 3 N 4 , [96] Ti 3 C 2 T x /MoS 2 /TiO 2 , [104] Ti 2 CT x /TiO 2 /M (M = Ag, Pd, or Au), [116] Ti 2 CT x /C 3 N 4 , [117] Ti 3 C 2 T x /Cu 2 O/Cu, [118] Ti 3 C 2 T x /Pt/g-C 3 N 4 , [119] Ti 3 C 2 T x /BiOBr, [120] and Ti 3 C 2 T x /B-doped C 3 N 4 . [121] As various MXenes have been prepared experimentally [122,123] and their intrinsic electronic properties have been studied, [111,[124][125][126] other MXenes besides Ti 3 C 2 T x have attracted increasing research attention in the field of photocatalysis and been utilized as electron reservoir to promote the separation of charge carriers in semiconductors and thus enhance their photo activities.…”

“…[58] Increasing the treatment temperature or using oxidants (e.g., O 2 and H 2 O 2 ) is able to kinetically facilitate the oxidation of MXenes and thus reduces the reaction time significantly. [94][95][96] Thus far, the commonly used method to oxidize the surface transition metal atoms of MXenes to corresponding metal oxide semiconductors is thermal treatment, including hydrothermal reaction and annealing. [97][98][99] It has been reported that Ti 3 C 2 T x is partially oxidized into anatase TiO 2 in the presence of H 2 O and O 2 at 60 °C.…”

“…The literature survey reveals the fact that in most of the reported MXenes-based composite photocatalysts, MXenes often present the multilayered structure with accordion-like morphology instead of 2D nanosheets. [95][96][97][99][100][101]103,105,[132][133][169][170][171] As compared to 2D nanosheets, the accordion-like architecture makes it hard to sufficiently take advantage of the 2D structure of MXenes, which has been reflected by the microscopic structure of some MXenes-based composites. [97,[100][101]103,105] For example, when using accordion-like MXenes as platform for in situ growth of semiconductors, some semiconductors are grown at the open edge of MXenes rather than locating at the basal plane of MXenes.…”

“…[86] It is learned from the above discussion that MXenes exhibit variable work function/Fermi level, which enables them to serve as acceptors for both electrons and holes. [96,[99][100][101][103][104][105][115][116][117][118][119][120][121]132] The flexile electronic properties of MXenes definitely provide more possibilities to deliver their diverse functions and applications. On the other hand, such properties come with the challenges to precisely identify the specific electronic feature of MXenes considering that the type and geometrical conformations of surface terminations on MXenes are sensitive to the preparation conditions.…”

Recent Advances in Functional 2D MXene‐Based Nanostructures for Next‐Generation Devices

“…Recent research studies have shown that MXenes have promising potential for photocatalytic applications, due to some distinct properties: i) the high carrier mobility in MXene-based system efficiently promoting the separation and migration of photogenerated electron-hole pairs; ii) the tunable band gap of MXenes by altering their surface chemistries, for example, the terminated -F, -O, or -OH groups, or the arrangements of surface groups; iii) the abundant surface groups with more active sites on the surface of MXene. [178][179][180] It is noted that Ti 3 C 2 T x has already been employed as an efficient co-catalyst in g-C 3 N 4 , [181][182][183][184] Bi 2 WO 6 , [185] BP, [178] AgInS 2 , [65,186] SrTiO 3 , [187] hematite, [154] , anatase, [179,188,189] and so on, to further enhance their photocatalytic performance. For example, in 2018, the 2D MXene Ti 3 C 2 T x /2D g-C 3 N 4 nanosheet heterostructures were rationally designed and successfully synthesized by calcination of bulk Ti 3 C 2 and urea, where urea not only acts as the gas template to process the exfoliation of Ti 3 C 2 into Ti 3 C 2 T x nanosheets, but also as the precursor of g-C 3 N 4 to obtain 2D MXene Ti 3 C 2 T x /2D g-C 3 N 4 nanosheet heterostructures.…”