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Ultrathin g-C3N4 nanosheets have been fabricated via a two-step calcination regulated by melamine precursors at a high heating rate (30 °C min−1). The resulting g-C3N4 nanosheets were further employed as carriers for the growth of carbon quantum dots (CQDs) and (110) exposed α-Fe2O3 through the PVP-enabled adsorption effects by a solvothermal process. It was discovered that the so fabricated ternary photocatalyst α-Fe2O3/CQD@g-C3N4 presented a broad-spectrum absorption range (up to 800 nm) and particularly enhanced active sites of photogenerated electrons for highly efficient photocatalytic oxygen reduction toward H2O2 evolution in pure water. A H2O2 production rate of 1.16 μM min−1 could be expected for the developed photocatalyst under visible light irradiation, which is about 19 times faster than that of pure ultrathin g-C3N4. Herein, the loaded Fe2O3 could transform the H2O2 evolution from two-step single-electron reduction into one-step two-electron one, as verified by the various active species experiments and rotating ring-disk electrode tests. This work presents a new perspective in designing ultrathin g-C3N4 through a simple method of precursor-regulated calcination, which features more outstanding advantages than the conventional exfoliation of bulk g-C3N4 towards ultrathin g-C3N4. More importantly, it provides an optimized photocatalytic reaction route of two-electron oxygen reduction for efficient H2O2 production in pure water under visible light irradiation, without the need for noble metals or organic sacrificial agents. [ABSTRACT FROM AUTHOR]

Tubular In 2 O 3 was fabricated by the annealing of In-MIL-68 and further treated by Ar plasma to yield oxygen vacancies (O v ) followed by the growth of In 2 S 3 nanoflowers. Unexpectedly, the resulting porous In 2 S 3 @In 2 O 3 composites were discovered to display a broad visible-light response and especially enhanced capacities for efficient photocatalytic production of H 2 O 2 in pure water, with a rate of 4.59 μmol·g -1 ·min -1 . An apparent quantum yield of 28.9% at 420 nm can also be expected without the use of noble metals or organic scavengers. Herein, the high light utilization might be profited from their porous tubular heterostructure for powerful "light captivity". Moreover, the Ar plasma-derived O v sites on the composites might tune the H 2 O 2 generation route from the single-electron reduction to the two-electron one toward the significantly enhanced photocatalysis, as validated by the Koutecky-Levich plots. This work demonstrates a new perspective of designing porous heterostructures with the advantages of high light harvest and plasma-derived O v active sites. Importantly, it may provide a promising defect-induced strategy of two-electron reduction triggered by the plasma treatment for the efficient photocatalytic H 2 O 2 production under visible light.

A selective photoelectrochemical (PEC) sensor has been designed for the signal-on detection of H 2 S using g-C 3 N 4 nanosheets that were treated with N 2 plasma for depositing Cd probes. It was discovered that the yielded Cd/N@g-C 3 N 4 nanocomposites could present enhanced photocurrents of specific responses to H 2 S under visible light irradiation, in contrast to the ones without the pretreatment of N 2 plasma showing no H 2 S response. Herein, the Cd probes deposited on g-C 3 N 4 nanosheets might react with H 2 S to generate CdS on Cd/N@g-C 3 N 4 , forming the efficient heterojunctions. Especially, the plasma-derived N contents might act as the "bridge" to promote charge transfer between the generated CdS and g-C 3 N 4 , resulting in the "signal-on" PEC responses to H 2 S. A selective PEC sensor was thereby developed for sensing H 2 S of concentrations linearly ranging from 40.0 to 10,000 pM, with a detection limit of about 21 pM. Also, the feasibility of sensing H 2 S in industrial waste gas was demonstrated by recovery tests. More importantly, this N 2 plasma treatment route for g-C 3 N 4 nanosheets may open a new door toward the construction of a Cd probe-based heterojunction for the signal-on PEC sensing platform, which is promising for the wide application in the fields of environmental monitoring, food safety, and biomedical analysis.