Oxygen-modified graphitic carbon nitride with nitrogen-defect for metal-free visible light photocatalytic H2O2 evolution

Efficient photocatalytic hydrogen peroxide production over S-scheme In2S3/molten salt modified C3N5 heterojunction

Graphitic phase carbon nitride (g-C3N5), as a novel n-type metal-free material, is employed as a visible light-receptive catalyst because of its narrow band gap and abundant nitrogen. To overcome the low carrier mobility efficiency of g-C3N5, its modification by K ions was adopted. In addition, In2S3 was selected to couple with modified g-C3N5 to overcome the recombination of photogenerated e-/h+. As a novel photocatalytic material, it was proven to possess a high visible light absorption capacity and a strong H2O2 production ability (up to 3.89 mmol⋅L-1 in 2 h). Moreover, a S-scheme heterojunction structure was successfully constructed between the two materials, which was tested and confirmed to be successful in raising the photogenerated e-/h+ separation efficiency. Ultimately, the primary processes of photocatalytic H2O2 production were summarized by superoxide radical and rotating disc electron measurements. This research provides a fresh perspective for the synthesis of C3N5-based S-scheme heterojunction photocatalysts for producing H2O2.

New insight into the effects of p-benzoquinone on photocatalytic reduction of Cr(VI) over Fe-doped g-C3N4

It is of great significance to establish an effective method for removing Cr(VI) from wastewater. Herein, Fe-doped g-C3N4 (namely Fe-g-C3N4-2) was synthesized and then employed as photocatalyst to conduct the test of Cr(VI) reduction. Notably, the embedding of Fe ion in g-C3N4 can offer the Fe2+/Fe3+ redox couples, so reducing the interfacial resistance of charge transfer and suppressing the recombination of photogenerated electrons and holes. The impurity energy levels will form in g-C3N4 after the introduction of Fe ion, thereby boosting the light absorption capacity of catalyst. Thus, Fe-g-C3N4-2 showed good performance in photocatalytic Cr(VI) reduction, and the reduction efficiency of Cr(VI) can reach 39.9% within 40 min. Different with many previous studies, current work unexpectedly found that the addition of p-benzoquinone (BQ) can promote the Cr(VI) reduction, and the reduction efficiency of Cr(VI) over Fe-g-C3N4-2 was as high as 93.2% in the presence of BQ (1.5 mM). Further analyses showed that BQ can be reduced to hydroquinone (HQ) by photogenerated electrons, and UV light can also directly induce BQ to generate HQ by using H2O as the hydrogen donor. The HQ with reducing ability can accelerate the Cr(VI) reduction. In short, current work shared some novel insights into photocatalytic Cr(VI) reduction in the presence of BQ. Future research should consider possible reactions between photogenerated electrons and BQ. For the UV-induced photocatalysis, the suitability of BQ as the scavenger of O2•‒ must be given carefully consideration.

Photocatalytic H2O2 production from water and air using porous organic polymers

Producing hydrogen peroxide (H2O2) from H2O and O2 under visible light irradiation is a promising solar-to-chemical energy conversion technology. Hydrogen peroxide has versatile applications as a green oxidant and liquid energy carrier but has been produced through energy-intensive and complex anthraquinone processes. Herein, we report the rational design of efficient and stable porous organic polymer (POP) containing redox centers, anthraquinone photocatalyst (ANQ-POP) for solar H2O2 production. ANQ-POP is readily synthesized with stable dioxin-linkages via efficient one-pot, transition-metal-free nucleophilic aromatic substitution reactions between 1,2,3,4,5,6,7,8-octafluoro-9,10-anthraquinone (OFANQ) and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP). Exhibiting a fibrillar morphology, ANQ-POP boasts a high surface area of 380 m2∙g-1 and demonstrates thermal stability. With 10 % ethanol, ANQ-POP yields an H2O2 production rate of 320 μmol g-1 under visible light irradiation. Moreover, ANQ-POP alone can efficiently produce H2O2 without any photosensitizers and cocatalysts. Density functional theory calculations reveal that the quinone groups of the anthraquinone moieties can serve as redox centers for H2O2 production under light irradiation. Furthermore, unlike most conventional photocatalysts, it can produce H2O2 using only water and air by catalyzing both oxygen reduction and evolution reactions under light irradiation. Our findings provide an efficient, eco-friendly pathway for photocatalytic production of H2O2 under mild reaction conditions using a dioxin-derived POP-based photocatalyst.

Utilising the Nanozymatic Activity of Copper-Functionalised Mesoporous C3 N5 for Sensing Biomolecules

Designing unique nanomaterials for the selective sensing of biomolecules is of significant interest in the field of nanobiotechnology. In this work, we demonstrated the synthesis of ordered Cu nanoparticle-functionalised mesoporous C3 N5 that has unique peroxidase-like nanozymatic activity for the ultrasensitive and selective detection of glucose and glutathione. A nano hard-templating technique together with the in-situ polymerisation and self-assembly of Cu and high N-containing CN precursor was adopted to introduce mesoporosity as well as high N and Cu content in mesoporous C3 N5 . Due to the ordered structure and highly dispersed Cu in the mesoporous C3 N5 , a large enhancement of the peroxidase mimetic activity in the oxidation of a redox dye in the presence of hydrogen peroxide could be obtained. Additionally, the optimised Cu-functionalised mesoporous C3 N5 exhibited excellent sensitivity to glutathione with a low detection limit of 2.0 ppm. The strong peroxidase activity of the Cu-functionalised mesoporous C3 N5 was also effectively used for the sensing of glucose with a detection limit of 0.4 mM through glucose oxidation with glucose oxidase. This unique Cu-functionalised mesoporous C3 N5 has the potential for detecting various molecules in the environment as well as for next-generation glucose and glutathione diagnostic devices.