Enhanced nonsacrificial photocatalytic generation of hydrogen peroxide under visible light using modified graphitic carbon nitride with doped phosphorus and loaded carbon quantum dots: constructing electron transfer channel

Insights on the efficiency and contribution of single active species in photocatalytic degradation of tetracycline: Priority attack active sites, intermediate products and their toxicity evaluation

Photocatalysis has been proven to be an excellent technology for treating antibiotic wastewater, but the impact of each active species involved in the process on antibiotic degradation is still unclear. Therefore, the S-scheme heterojunction photocatalyst Ti3C2/g-C3N4/TiO2 was successfully synthesized using melamine and Ti3C2 as precursors by a one-step calcination method using mechanical stirring and ultrasound assistance. Its formation mechanism was studied in detail through multiple characterizations and work function calculations. The heterojunction photocatalyst not only enabled it to retain active species with strong oxidation and reduction abilities, but also significantly promoted the separation and transfer of photo-generated carriers, exhibiting an excellent degradation efficiency of 94.19 % for tetracycline (TC) within 120 min. Importantly, the priority attack sites, degradation pathways, degradation intermediates and their ecological toxicity of TC under the action of each single active species (·O2-, h+, ·OH) were first positively explored and evaluated through design experiments, Fukui function theory calculations, HPLC-MS, Escherichia coli toxicity experiments, and ECOSAR program. The results indicated that the preferred attack sites of ·O2- on TC were O20, C7, C11, O21, and N25 atoms with high f+ value. The toxicity of intermediates produced by ·O2- was also lower than those produced by h+ and ·OH.

Dual Channel H2O2 Photosynthesis in Pure Water over S-Scheme Heterojunction Cs3PMo12/CC Boosted by Proton and Electron Reservoirs

Dual channel photo-driven H2O2 production in pure water on small-scale on-site setups is a promising strategy to provide low-concentrated H2O2 whenever needed. This process suffers, however, strongly from the fast recombination of photo-generated charge carriers and the sluggish oxidation process. Here, insoluble Keggin-type cesium phosphomolybdate Cs3PMo12O40 (abbreviated to Cs3PMo12) is introduced to carbonized cellulose (CC) to construct S-scheme heterojunction Cs3PMo12/CC. Dual channel H2O2 photosynthesis from both H2O oxidation and O2 reduction in pure water has been thus achieved with the production rate of 20.1 mmol L-1 gcat. -1 h-1, apparent quantum yield (AQY) of 2.1% and solar-to-chemical conversion (SCC) efficiency of 0.050%. H2O2 accumulative concentration reaches 4.9 mmol L-1. This high photocatalytic activity is guaranteed by unique features of Cs3PMo12/CC, namely, S-scheme heterojunction, electron reservoir, and proton reservoir. The former two enhance the separation of photo-generated charge carriers, while the latter speeds up the torpid oxidation process. In situ experiments reveal that H2O2 is formed via successive single-electron transfer in both channels. In real practice, exposing the reaction system under natural sunlight outdoors successfully results in 0.24 mmol L-1 H2O2. This work provides a key practical strategy for designing photocatalysts in modulating redox half-reactions in photosynthesis.

Enhanced Visible-Light H2O2 Production over Pt/g-C3N4 Schottky Junction Photocatalyst

Photocatalytic for hydrogen peroxide (H2O2) production is thought as a promising technology owing to its clean and green properties with the cheap and easily available raw materials of H2O and O2. Herein, Pt/g-C3N4 Schottky junction photocatalysts with ultralow Pt contents (0.025-0.1 wt %) were successfully fabricated by an impregnation-reduction method. It can efficiently reduce O2 to generate H2O2 without a sacrificial agent under visible-light irradiation. The yield of H2O2 produced over Pt0.05/g-C3N4 with the optimal 0.05 wt % Pt reached 31.82 μM, which was 2.46 times that of g-C3N4 and higher than most of those in the literature. It also showed good stability in three repeated tests. The deposition of highly dispersed metal Pt nanoparticles with low and limited content can expose enough active Pt atoms, significantly enhance the separation efficiency of photogenerated carriers, and reduce its negative effect on H2O2 decomposition, resulting in improved and outstanding efficiency of H2O2 production. The ·O2- radicals were found to be the main active species. The mechanism of photocatalytic H2O2 production was confirmed to be a two-step single electron route (O2 + e-→ ·O2- → H2O2).

A facile approach for sulphur and nitrogen co-doped carbon nanodots to improve photothermal eradication of drug-resistant bacteria

In this study, we produced S, N co-doped CNDs (SN@CNDs) by using dimethyl sulfoxide (DMSO) and formamide (FA) as single sources of S and N, respectively. We varied the S/N ratios by adjusting the volume ratios of DMSO and FA and investigated their effect on the red-shift of the CNDs' absorption peak. Our findings demonstrate that SN@CNDs synthesized using a volume ratio of 5:6 between DMSO and FA exhibit the most significant absorption peak redshift and enhanced near-infrared absorption performance. Based on comparative analysis of the particle size, surface charge, and fluorescence spectrum of the S@CNDs, N@CNDs, and SN@CNDs, we propose a possible mechanism to explain the change of optical properties of CNDs due to S, N doping. Co-doping creates a more uniform and smaller band gap, resulting in a shift of the Fermi level and a change in energy dissipation from radioactive to non-radiative decay. Importantly, the as-prepared SN@CNDs exhibited a photothermal conversion efficiency of 51.36% at 808 nm and demonstrated exceptional photokilling effects against drug-resistant bacteria in both in vitro and in vivo experiments. Our facile method for synthesizing S and N co-doped CNDs can be extended to the preparation of other S and N co-doped nanomaterials, potentially improving their performance.

Alkali-assisted engineering of ultrathin graphite phase carbon nitride nanosheets with carbon vacancy and cyano group for significantly promoting photocatalytic hydrogen peroxide generation under visible light: fast electron transfer channel

Exfoliating bulk graphite phase carbon nitride (g-C₃N₄) into 2D nanosheets is considered to be an effective method to enhance its photocatalytic activity. However, optical absorption capacity of the exfoliated g-C₃N₄ nanosheets are lower than that of the original bulk g-C₃N₄ due to the quantum size effect. Here, the ultrathin graphite phase carbon nitride nanosheets containing both carbon vacancy and cyano group (UCNS₅₈₀) were prepared by two-step calcination in air with the assistance of KOH. The formation and position of carbon vacancy and cyano group were first investigated and determined. The simultaneous introduction of carbon vacancy and cyano group not only improved light absorption range and intensity of g-C₃N₄ nanosheets, but also more importantly constructed a fast transfer channel for photogenerated electrons, further enhancing the separation efficiency and migration ability of photogenerated carriers. The cyano group as the accumulation center of photogenerated electrons and the oxygen adsorption center increased the proportion of one-step two-electrons reaction path to efficiently generate H₂O₂. As a result, UCNS₅₈₀ exhibited highly boosted H₂O₂ generation activity, its H₂O₂ production yield for 6 h reached 939 µmol/L and the formation rate was up to 4167 µM h^-1 g^-1, which was in priority in the reported literature under the same conditions.

Enhancing oxidation ability of graphitic carbon nitride photocatalysts to promote lignin Cα-Cβ bond cleavage in micellar aqueous media

As the most abundant aromatic resource, lignin is an appreciated biomass material to obtain aromatic high-value chemicals. However, the selective cleavage of lignin C_α-C_β bonds under mild conditions constitutes a challenge. Herein, a photocatalyst having high oxidation capacity was successfully synthesized by codoping S and Cl atoms into graphite carbon nitride (g-C₃N₄). The resulting S,Cl/CN-1.5 photocatalyst exhibits enhanced photogenerated electron-hole separation ability and higher valence band potential than g-C₃N₄. S,Cl/CN-1.5 can efficiently break lignin C_α-C_β bonds in micellar aqueous medium to produce benzaldehyde and benzyl alcohol as the main products. Mechanism studies show that the photocatalytic cleavage of lignin C_α-C_β bonds proceeds via single-electron transfer and C_β radical mechanisms in which hydroxyl radicals and photogenerated holes play an important role. Isotopic experiments show that the O atoms required for the photocatalytic cleavage of lignin C_α-C_β bonds come from water in the micellar aqueous medium based on the full contact between water and substrate. Although O₂ atmosphere is beneficial for the photocatalytic efficiency, O₂ is not necessary for the photocatalytic cleavage of lignin C_α-C_β bonds. This research provides a useful guide for designing efficient photocatalysts to depolymerize lignin into high-value chemicals.