Photocatalysis technology is a new technology developed in the 1970s that can be used to treat organic and inorganic pollutants. The basic principle is that after the photocatalyst is irradiated by light of a specific wavelength, electron-hole pairs are formed through electron transition, and the photogenerated electrons and holes interact with oxygen and water respectively to produce active oxygen radicals with strong oxidation, and the strong oxidation of free radicals can oxidize and decompose the target substance. Photocatalytic degradation technology is more and more applied to the treatment of various pollutants because of its advantages of high efficiency, economy, environmental protection and safety. At present, when researchers use photocatalytic methods to degrade target pollutants, they generally mix the photocatalyst with the substrate of the reaction. Because photocatalyzed powders are easy to aggregate, and the separation process after the photocatalyzed reaction requires a lot of energy, which limits their large-scale application.

In response to this problem, the ultra-precision optical manufacturing innovation team led by Academician Zhuang Songlin and Professor Zhang Dawei at the University of Shanghai for Science and Technology used electrospinning technology to prepare flexible fiber electrospinning films with intersecting diameters of tens to thousands of nanometers. As the carrier of photocatalyst, a series of thin films with photocatalytic activity were prepared. When using this type of film to degrade target pollutants, it can provide more reaction sites due to its unique nanostructure, and can be easily extracted from the substrate after the reaction, avoiding the energy-consuming and time-consuming separation step, which is conducive to the recycling of photocatalyst, reducing energy consumption and reducing secondary pollution to the substrate. Two papers published by the team in the international leading journals J. Mater. Sci.Technol and Biomolecules have attracted wide attention. According to the latest ESI retrieval data, two papers are among the top 1% highly cited papers in ESI worldwide.

The work of attaching photocatalyst to electrospun films has been reported frequently. The usual method is to mix photocatalyst with electrospun precursor and prepare electrospun films loaded with photocatalyst under high voltage field. Due to the long time required by the electrospinning process, the photocatalyst will inevitably precipitate and agglomerate in the spinning precursor solution. On the one hand, it is easy to block the spinning head and affect the preparation efficiency of the electrospinning film. On the other hand, the agglomerating photocatalyst will greatly increase the recombination probability of photogenerated charge, thus reducing the photocatalytic efficiency. On the other hand, in the photocatalytic film prepared by this method, a large part of the photocatalyst is covered by electrospinning fibers, which reduces the photocatalytic reaction site and hinds the absorption of light radiation, which is not conducive to the photocatalytic reaction.

Based on the above status quo, PAN spinning solution containing Bi(NO3)3·5H2O and TBT was dissolved and electrospun film was made by electrospinning, and then the electrospun film was pre-oxidized and carbonized. In this process, Bi(NO3)3·5H2O and part of TBT are converted to multiphase BixTiyOz, part of TBT is converted to TiO2, PAN is converted to carbon through cyclization, dehydrogenation and other processes, while maintaining a flexible fiber state, and part of Bi3+ is reduced to metal Bi by carbon. Finally, flexible Bi/BixTiyOz-TiO2/CNFs were prepared. Under simulated sunlight irradiation, the reduction efficiency of Bi/BixTiyOz-TiO2/CNFs (S3) on Rhodamine can reach more than 97% within 20min. In this work, the difference in band structure between BixTiyOz and TiO2 is conducive to photogenerated charge separation, and the metal Bi element can optimize the transport effect of photogenerated electrons and holes. All three are embedded in nanoscale carbon fibers, which further inhibits the recombination of photogenerated charges. The material was synthesized by integrating the advantages of traditional photocatalyst modification techniques such as heterojunction construction, morphology control and noble metal modification, and showed good photocatalytic performance. The results were published in the international first-class journal J. Mater. Sci.Technol, with doctoral student Yao Liangtao as the first author and Professor Zhang Dawei as the corresponding author.

FIG. 1 Photocatalytic principle of flexible photocatalytic carbon nanofiber composite (Bi/BixTiyOz-TiO2/CNFs)

In order to further improve the efficiency of photocatalytic film degradation of target pollutants, we will look to the existing successful practice, hoping to find replicable experience to help improve the efficiency of electrospun film degradation of pollutants. The adsorption method of physical treatment has many advantages such as simple process, high efficiency and economical feasibility. In recent years, more and more work has been done to continuously reduce organic pollutants and heavy metal ions in the environment by surface modification treatment to give the membrane structure material adsorption function. Therefore, it is a feasible scheme to introduce adsorption capacity to photocatalytic films and degrade pollutants through adsorption-photocatalytic synergism. The scheme has the following advantages: First, the adsorption function is introduced into the membrane structure, which overcomes the problem that the traditional adsorbent is difficult to separate from the substrate and there may be secondary pollution; Second, the adsorption function can gather the target pollutant molecules on the membrane surface near the photocatalytic reaction site, which helps to improve the photocatalytic efficiency. Third, the photocatalyst on the photocatalytic film can decompose the adsorbed pollutants into small molecules, avoiding the chemical elution or physical calcination process that the traditional adsorbent may release toxic substances again during the regeneration process; Fourth, the film can achieve continuous reduction of pollutants all day long.

Based on this idea, we first prepared the g-C3N4/CQDs composite photocatalyst, and then dispersed the prepared g-C3N4/CQDs composite photocatalyst in the electrostatic spinning polymer solution of PCL, and prepared the electrospun film supported by g-C3N4/CQDs composite photocatalyst by electrospinning process. Finally, by surface modification, the adsorption capacity is introduced to the electrospun film prepared, and finally the electrospun film with adsorption-photocatalytic synergistic ability to degrade pollutants is obtained. We applied this film to the degradation of Aflatoxins (AFB1). After 30 min of visible light radiation, the concentration of AFB1 solution decreased by 96.9% through the synergistic effect of adsorption-photocatalysis. The results are published in Biomolecules, a leading international journal, with doctoral student Liangtao Yao as the first author and Professor Dawei Zhang as the corresponding author.

FIG. 2 Schematic diagram of electrospun film with "adsorption-photocatalysis" synergic function applied to AFB1 degradation

Paper link:

Job 1:

https://www.sciencedirect.com/science/article/pii/S1005030222008179?utm_campaign=STMJ_AUTH_SERV_PUBLISHED&utm_medium=ema il&utm_acid=264257752&SIS_ID=&dgcid=STMJ_AUTH_SERV_PUBLISHED&CMX_ID=&utm_in=DM318487&utm_source=AC_

Job 2:

https://www.mdpi.com/2218-273X/13/3/550