Yonggang Xiang

Light-Switchable Oxygen Vacancies in Ultrafine Bi5O7Br Nanotubes for Boosting Solar-Driven Nitrogen Fixation in Pure Water

Solar-driven reduction of dinitrogen (N2 ) to ammonia (NH3 ) is severely hampered by the kinetically complex and energetically challenging multielectron reaction. Oxygen vacancies (OVs) with abundant localized electrons on the surface of bismuth oxybromide-based semiconductors are demonstrated to have the ability to capture and activate N2 , providing an alternative pathway to overcome such limitations. However, bismuth oxybromide materials are susceptible to photocorrosion, and the surface OVs are easily oxidized and therefore lose their activities. For realistic photocatalytic N2 fixation, fabricating and enhancing the stability of sustainable OVs on semiconductors is indispensable. This study shows the first synthesis of self-assembled 5 nm diameter Bi5 O7 Br nanotubes with strong nanotube structure, suitable absorption edge, and many exposed surface sites, which are favorable for furnishing sufficient visible light-induced OVs to realize excellent and stable photoreduction of atmospheric N2 into NH3 in pure water. The NH3 generation rate is as high as 1.38 mmol h-1 g-1 , accompanied by an apparent quantum efficiency over 2.3% at 420 nm. The results presented herein provide new insights into rational design and engineering for the creation of highly active catalysts with light-switchable OVs toward efficient, stable, and sustainable visible light N2 fixation in mild conditions.

Highly efficient visible light induced photocatalytic activity of a novel in situ synthesized conjugated microporous poly(benzothiadiazole)–C3N4 composite

In this study, a novel π-conjugated microporous poly(benzothiadiazole)–graphitic carbon nitride (BBT–C3N4) photocatalyst was synthesized through a facile in situ palladium-catalyzed Sonogashira–Hagihara cross-coupling polycondensation of 4,7-dibromobenzo[c][1,2,5]thiadiazole with 1,3,5-triethynylbenzene in the presence of evenly dispersed g-C3N4 using mixed DMF/TEA as solvent at 80 °C. Systematic characterization results revealed that BBT was equally dispersed on the surface of C3N4 with chemical bonds. The photocatalytic tests showed that this BBT–C3N4 composite exhibited enhanced photocatalytic removal of both sulfathiazole and Cr(VI) in comparison with the pure BBT and C3N4 as well as a mechanical mixture of BBT and C3N4, indicating that the oxidation and reduction abilities of BBT–C3N4 were simultaneously enhanced after composition under visible light irradiation. This was subsequently confirmed by radical detection, PL analysis and scavenger experiments as well. Holes and photoelectrons were demonstrated to be the main active species during the photocatalytic removal of sulfathiazole and Cr(VI), respectively. A possible photoelectron transfer mechanism for efficient photoinduced electron–hole separation of BBT–C3N4 composites is proposed based on all the results. This study provides new insight into the design of highly efficient visible light-driven photocatalysts with superior redox ability for wastewater treatment.

Enhanced visible light photocatalytic activity of TiO2 assisted by organic semiconductors: a structure optimization strategy of conjugated polymers

The search for high-efficient TiO2-based heterojunction photocatalyst for photocatalytic H2 evolution and pollutant removal remains a great challenge. In this study, linear conjugated polymer B-BT-1,4-E consisting of alternating electron donor and electron acceptor was incorporated on the surface of TiO2 to form a binary composite in the facile in situ strategy. B-BT-1,4-E/TiO2 exhibited superior photocatalytic activity under visible light irradiation (λ ≥ 420 nm). The hydrogen evolution rate (HER) of 16.7% B-BT-1,4-E/TiO2 reached 220.4 μmol h−1 without additional noble metal (Pt), and the optimized 13.3% B-BT-1,4-E/TiO2 also displayed outstanding CIP degradation efficiency with a kinetic constant of 0.232. Based on extensive characterization results from UV-Vis diffused reflectance spectra (DRS), electron spin resonance (ESR), photocurrent, electrochemical impedance spectroscopy (EIS) and photoluminescence (PL), the enhanced photocatalytic activity of B-BT-1,4-E/TiO2 heterojunction can be attributed to broader visible light absorption range, faster charge separation and transfer. Moreover, a reasonable photocatalytic mechanism is also proposed. In comparison to reported CMP(BBT)/TiO2, HER and kinetic constants of CIP degradation with B-BT-1,4-E/TiO2 as the photocatalyst were increased by 7.3 times and 3.1 times, respectively. This study demonstrated that intrinsic merits of conjugated polymers made them promising candidates for exploring more efficient organic semiconductor–inorganic semiconductor heterojunction photocatalysts.

Synergistic design for enhancing solar-to-hydrogen conversion over a TiO2-based ternary hybrid

Enhancing the visible light responsiveness and photoactivity of TiO2 is of strategic significance and is one of the hottest research frontiers. Traditional papers focus on extending the universality of each method with a series of different mechanisms, but only a few studies have discovered the huge importance of the synergistic enhancement effect when two or more conventional strategies are combined for one TiO2 nanoparticle. Herein, a ternary pizza-like BE–Au–TiO2 hybrid is deliberately designed based on a conjugated polymer (a modified poly(benzothiadiazole) flake, B-BT-1,4-E, denoted as BE) acting as a photosensitizer, Au nanoparticles serving as a surface plasmon resonance (SPR) source, and TiO2 for electron collection and as a H2 production medium. The mechanisms of sensitization and SPR-enhancement can be combined together to overcome the drawbacks of insufficient electron separation and transfer, and significantly improve the internal electron transfer efficiency over each mono-mechanism. Finally, the visible light-driven H2 production rate of the BE–Au–TiO2 hybrid is ∼1.9 and ∼68 times faster than that of BE–TiO2 and Au–TiO2, respectively, and a high AQY of 7.8% at 420 nm is obtained. This work opens a new window leading to the design of highly efficient photocatalytic H2 production performance.