Order–Disorder Engineering of Carbon Nitride for Photocatalytic H₂O₂ Generation Coupled with Pollutant Removal

Abstract

Highly crystalline carbon nitride (CCN), benefiting from the reduced structural imperfections, enables improved electron−hole separation. Yet, the crystalline phase with insufficient inherent defects suffers from a poor performance toward the reaction intermediate adsorption with respect to the amorphous phase. Herein, a crystalline−amorphous carbon nitride (CACN) with an isotype structure was constructed via a two-step adjacent calcination strategy. Through specific oxygen etching and crystallization, the formation of a built-in electric field at the interface could drive charge transfer and separation, thus promoting photoredox reaction. As expected, the optimized CACN exhibited a H 2 O 2 generation efficiency as high as 2.15 mM g cat −1 h −1 , paired with a promoted pollutant degradation efficiency, which outperform its crystalline (CCN) and amorphous [amorphous carbon nitride (ACN)] counterparts. The detailed electron/hole transportation via a built-in electronic field and free radical formation based on the enhanced adsorption of oxygen were considered, and the synchronous reaction pathway was carried out. This work paves a novel pathway for the synthesis of carbon nitride with an isotype structure from the perspective of interfacial engineering.

Visible Light Absorption Is Not Always Related to N-Doped TiO2 and High Photocatalytic Activity in Materials Synthesized by the Sol–Gel Method Using Urea and Ammonia as Precursors

“…The HR-TEM micrographs (Figure ) of U-TiO 2 -450 showed the presence of a crystalline structure conformed by hexagons with an interplanar spacing of 0.33 nm compatible with (002) planes in crystalline g-C 3 N 4 , and another one in concordance with anatase TiO 2 (101) planes exhibiting an interplanar spacing of 0.35 nm . That confirms the presence of g-C 3 N 4 /TiO 2 heterojunctions and a narrow interaction between both semiconductors.…”

Improving Charge Carrier Separation through S-Scheme-Based 2D–2D WS2/Sulfur-Doped g-C3N4 Heterojunctions for a Superior Photocatalytic O2 Reduction Reaction

“…The electrochemical impedance spectroscopy (EIS) technique for WS 2 , SCN, and 2.5WSCN heterojunction specimens under photon illumination is portrayed in Figure c. Generally, the radius of the semicircular arc in the Nyquist plot replicates the charge-transmission resistance of the photocatalyst, and a lower resistance means better conductivity and faster charge transferability. ,, As portrayed in Figure c, 2.5WSCN has the smallest Nyquist arc, validating the lowermost interfacial charge-transfer resistivity and superior channelization of photoinduced charge carriers. The formation of the 2D–2D S-scheme heterojunction through W–S bonding might be a key parameter that is accountable for improved separation and migration of photocarriers and boosted conductivity.…”

“…Figure c exhibits the formation and decomposition behavior of H 2 O 2 under the same reaction parameters. A kinetic model describing the zeroth-order kinetics for the production and first-order kinetics for decomposition has been proposed, and the corresponding rate constants were obtained by fitting the experimental results into expressions and [ H 2 O 2 ] = K normalf / K normald × { 1 − exp false( prefix− K d × t false) } K d = prefix− ln nobreak0em0.25em⁡ ⁡ false( C normalt / C 0 false) / t where K f and K d were the formation and decomposition rates, respectively, which work in combination to determine the final concentrations of produced H 2 O 2 . C t and C 0 represent the H 2 O 2 concentration at time t and initial concentrations for decomposition reactions, respectively.…”

“…Further, to divulge the active species accountable for the photocatalytic H 2 O 2 production, AgNO 3 , p-BQ, and TBA were employed as e – , • O 2 – , and • OH quenchers under photon illumination for 1 h in an O 2 -saturated environment, respectively (Figure a). , As represented in Figure S13, the photocatalytic H 2 O 2 generation was remarkably inhibited in the absence of IPA due to the fact that isopropanol was the primary source of hydrogen species. The active specimen can only interact with H 2 O molecules to generate H + ions without IPA, thereby resulting in a high energy barrier . However, a drastic reduction in H 2 O 2 production was witnessed after the addition of AgNO 3 into the reaction system, signifying that the electron plays a crucial role in the photocatalytic oxygen reduction reaction.…”