Gongduan Fan,Banghao Du,Jinjin Zhou,Zhongsen Yan,Yifan You,Jing Luo
The practical application of photocatalytic technology in the natural water body is limited by the low reuse capability and potential secondary pollution risk of powder catalysts. Consequently, it is highly desirable to develop the stable floating photocatalytic composites for efficient alleviating harmful algal blooms. In this study, the self-floating Ag 2 O/g-C 3 N 4 /hydrogel composites with a porous three-dimension (3D) network nanostructure via the cross-linking of chitosan and polyvinyl alcohol have been synthesized. The effects of doping load, initial algal density and dissolved organic matter on Microcystis aeruginosa ( M . aeruginosa ) removal were investigated by Ag 2 O/g-C 3 N 4 /hydrogel under visible light irradiation. Among the synthesized photocatalysts, the 20-Ag 2 O/g-C 3 N 4 /hydrogel showed the highest adsorption, good reusability performance and excellent photocatalytic activity within 4 h for the removal of M . aeruginosa . Algal cell membrane and phycobiliprotein were severely damaged during the photocatalytic process. The inactivation mechanisms are attributed to the water-adsorbing swelling of the hydrogel and the generated reactive oxygen species (mainly ·O 2 − and ·OH) by Ag 2 O/g-C 3 N 4 . Moreover, the antioxidant system of the algae cells was also collapsed under the effects of reactive oxygen species. The superoxide dismutase (SOD) and catalase (CAT) content of algal cells decreased rapidly after photocatalytic reaction by Ag 2 O/g-C 3 N 4 /hydrogel, while the malondialdehyde (MDA) activity was higher than that of the control group. The self-floating Ag 2 O/g-C 3 N 4 /hydrogel photocatalyst would have real practical applications for harmful algae in the fields of natural water body.
Gongduan Fan,Jiuhong Lin,Mingqian Xia,Jing Luo,Banghao Du,Heliang Pang,Zhongsen Yan
Photocatalysis has attracted much attention as an emerging algae removal technology, but the inactivation performance is inevitably affected by the extracellular polymeric substance (EPS) produced by algae. In this study, a photocatalyst (Ag 2 O/g-C 3 N 4 ) with efficient algae inactivation is adopted to investigate the interactions with EPS, and the impact of EPS on photocatalytic algae removal is studied. The results show that EPS can adhere to the surface of Ag 2 O/g-C 3 N 4 by electrostatic force. The interaction with EPS decreases the surface zeta potential of the Ag 2 O/g-C 3 N 4 from 7.71 to −22.3 mV with the increase in EPS concentration, and the maximum ratio of particle size increases from 825 to 1281 nm. In addition, the interaction with EPS inhibits the release of Ag + in Ag 2 O/g-C 3 N 4 by half, thus, the toxicity of metal ions will be alleviated. Meanwhile, EPS can also be degraded by Ag 2 O/g-C 3 N 4 , indicating that EPS can work as a radical scavenger to protect the algae cells. Without the protection of EPS, 97.8% of algae cells are inactivated after 5 h photocatalysis. Therefore, more attention should be given to the interaction between EPS and photocatalyst to promote the design and application of the photocatalytic.
Ag2O/g-C3N4 p–n heterojunctions were successfully fabricated by a facile photochemical method and applied as a photocatalyst in the degradation of antibiotic tetracycline hydrochloride (TC-HCl) under visible light irradiation. The samples were well characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS). The results demonstrated that Ag2O nanoparticles with sizes of 5–15 nm were distributed on the surface of g-C3N4 to form the Ag2O/g-C3N4 p–n heterojunctions. The heterojunctions were conducive to the high dispersibility of small Ag2O nanoparticles and the efficient separation of photogenerated electron–hole pairs, resulting in the enhancement of photocatalytic activity by using Ag2O/g-C3N4 heterojunctions as the photocatalyst compared to pure Ag2O and g-C3N4 in TC-HCl degradation. In particular, the degradation rate of TC-HCl was 1.21 and 3.52 times higher than that of pure Ag2O and g-C3N4, respectively. Furthermore, the stability of the Ag2O/g-C3N4 photocatalyst toward the degradation process under visible light irradiation was investigated.
Novel visible-light-driven Ag/Ag2O@g-C3N4 (AAC) hybrid materials were synthesized successfully via a green, facile hydrothermal treatment approach by reducing AgNO3 using carbon nanodots as reducing agent for the first time. Natural leaves were used as precursors to prepare carbon nanodots. By adjusting the feed mass ratio of AgNO3 to carbon nanodots, the average diameter of Ag/Ag2O can be modulated from 8 to 33 nm. The effects of Ag/Ag2O deposition on the optical and photocatalytic performance of AAC in the degradation of rhodamine B (RhB) under visible light irradiation were systematically investigated. It was found that the Ag/Ag2O content greatly influences the photocatalytic activity of AAC nanocomposites. A suitable amount of Ag/Ag2O in the AAC system could obtain the best photocatalytic activity. The experimental results indicated that all the AAC nanocomposites showed higher photocatalytic activities compared with that of pure g-C3N4. The remarkable visible-light photocatalytic activity of AAC heterostructures could be attributed to their absorption in the visible region and low recombination rate of the electron–hole pairs because of the heterojunction formed between Ag2O and g-C3N4. In addition, Ag nanoparticles are believed to play an essential role in affecting the photoreactivity because they are able to trap electrons, further separate the electron–hole pairs, and prolong the life of electron–hole pairs. In other words, it can be concluded that the increased photocatalytic activity of AAC was attributed to the synergic effect between g-C3N4, Ag2O and Ag. It is believed that the present work could render useful information for steering the design and application of noble nanoparticle loaded g-C3N4-based heterojunction composites with high photocatalytic activity.
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