# Graphene Quantum Dots Doped PVDF(TBT)/PVP(TBT) Fiber Film with Enhanced Photocatalytic Performance
## 1 Introduction  
In 1972, [PERSON] and [PERSON] first discovered that titanium dioxide (TiO\({}_{2}\)) had photocatalytic properties [1]. TiO\({}_{2}\) photocatalysts have been extensively investigated in the fields of water splitting to produce hydrogen [2; 3; 4; 5; 6], organic dye decomposition [7; 8; 9], sewage purification [10], and air filtration [11] due to its non-toxicity, low cost, high activity, and high efficiency [2; 3; 4; 5; 12]. Furthermore, TiO\({}_{2}\) has a relatively broad bandgap, which is about 3.2 eV. This causes the pure TiO\({}_{2}\) photocatalyst to only absorb light within the ultraviolet region. However, ultraviolet light only accounts for 5% of the sunlight. The low-usage of sunlight and the low separation rate of photoexcited electron-hole pairs significantly lower its photocatalytic efficiency and hinder the application of TiO\({}_{2}\) photocatalysts in practice [13; 14; 15; 16]. In addition to TiO\({}_{2}\), there are many other types of common photocatalysts includingZnO, WO\({}_{3}\), Bi\({}_{2}\)O\({}_{3}\), Fe\({}_{2}\)O\({}_{3}\), CdS, CuS, PbS, ZnS, SnO\({}_{2}\), and SrTiO\({}_{3}\)[12]. However, some of these materials are expensive, and most of these materials are susceptible to chemical or photochemical corrosion, which dramatically limits their use for practical photocatalysis. To overcome these shortcomings of TiO\({}_{2}\) photocatalysts, scientists have made a variety of achievements on TiO\({}_{2}\) photocatalysts to improve their catalytic performance. These methods include increasing its specific surface area [17], semiconductor composite, noble metal deposition [18], and metal/nonmetal ion doping [19; 20; 21; 22]. However, some precursors of heterojunction semiconductors such as transition metal ions may cause environmental pollution. Recently, carbon quantum dots (CQDs) as green photocatalysts or photocatalyst promoters have been widely investigated [23; 24; 25]. CQDs have strong absorption in a broad spectral range and have excellent photobleaching stability, low cytotoxicity, and up-conversion luminescence properties [26; 27; 28; 29]. Graphene quantum dots (GQDs) have higher crystallinity than conventional CQDs. The high degree of crystallinity allows GQDs to show excellent electron transport ability, thereby extending the carrier lifetime [30; 31; 32; 33]. However, compared to solar cells [34; 35; 36], biosensing [37; 38], and bioimaging [39; 40; 41], there are fewer studies on GQDs as photocatalysts, which is getting more and more attention from researchers. Electrospinning is an excellent technique for preparing polymeric materials, which can be used to produce fiber films of tens to hundreds of nanometers in diameter. The fiber film fabricated with electrospinning generally has a large specific surface area and can be used to immobilize a large amount of the photocatalyst to improve photocatalytic performance [42]. Among various polymers, polyvinylidene fluoride (PVDF) [43; 44; 45] is one of the most commonly used photocatalyst supports due to its good mechanical strength, chemical, and thermal stabilities [46; 47]. In addition, PVDF is also readily available and relatively inexpensive, which facilitates its wide use in various applications [45; 48]. As a synthetic water-soluble polymer compound, polyvinyl pyrrolone (PVP) [49; 50] shows the general properties of water-soluble polymer compounds and excellent biocompatibility, and does not irritate skin, mucous membranes, eyes, etc. In this study, we mixed PVDF and water-soluble PVP with tetrabutyl titanate (TBT) and then electrospun it into a nanofiber film, polyvinylidene fluoride (tetrabutyl titanate)/polyvinyl pyrrolone ((tetrabutyl titanate)) [PVDF(TBT)/PVP(TBT)]. PVP in the hybrid nanofiber film can be dissolved by deionized water to form pores [51; 52]. Then, GQDs are deposited onto the PVDF(TBT)/PVP(TBT) film through a hydrothermal reaction of the film with anhydrous glucose.