Integrated flexible photocatalytic composite nanofiber membranes combined in-situ grown CQDs/g-C3N4 with thermally etched porous silica

[Display omitted] •CQDs/g-C3N4 successfully grown in-situ on flexible SiO2 NFMs.•The alkaline thermal etching effect causes SiO2 NFs to form porous structures.•The porous structure avoids aggregation of catalysts and provides more active sites.•CQDs/g-C3N4@SiO2 NFMs exhibit significantly enhanced photocatalytic activity.•The composites have excellent reusability and can be recovered directly from water. In recent years, various semiconductor photocatalysts have been developed for wastewater treatment. However, traditional bulk photocatalysts suffer from powder agglomeration, difficult recovery, and secondary pollution, which hinders their large-scale application. Herein, the in-situ growth of carbon quantum dots/graphitic carbon nitride (CQDs/g-C3N4) was successfully achieved on flexible silica nanofiber membranes (SiO2 NFMs), which were synthesized by combining electrospinning with thermal polycondensation. It was found that the conversion of smooth membranes into porous surfaces due to the thermal etching effect of alkaline atmosphere during the creation of CQDs/g-C3N4, which not only facilitated the adsorption of tetracycline (TC), but also provided more active sites for photodegradation. Under visible light irradiation, the obtained CQDs/g-C3N4@SiO2 NFMs showed exceptional photocatalytic activity toward TC, with first order kinetic constants of 3.88 and 48.86 times greater than g-C3N4@SiO2 NFMs and SiO2 NFMs, respectively. The radical trapping experiments revealed that •O2-, 1O2, h+, and •OH were the active species in photocatalytic degradation. The photocatalytic degradation was evaluated under initial pH, inorganic anions, and natural aqueous substrate, which shows good applicability. In addition, CQDs/g-C3N4@SiO2 NFMs exhibited high stability and reusability. And the integrated composite membranes can be directly recovered from water after the immobilization of photocatalysts. To sum up, with the advantages of high photocatalytic activity, flexibility, easy separation, and recovery, CQDs/g-C3N4@SiO2 NFMs are prospective catalysts for practical applications in water remediation.