## 3 Results and Discussion
### Adsorption and Photocatalytic Degradation of Dyes  
The as-prepared 3D CQDs/TiO\({}_{2}\)/GO foams with different loading amount of CQDs/TiO\({}_{2}\) particles (10, 20, and 30 mg) were used to adsorb and photocatalytic degrade dyes, MB and rhodamine by using a 350 W xenon lamp as the source of visible light. Under the irradiation condition, the electrons in the value band (VB) of TiO\({}_{2}\) were stimulated to transit to the conduction band (CB) and release photoelectrons. Hydroxyl radicals and oxygen radicals were produced by the interaction of water and oxygen with electrons and photons. These two radicals can degrade dyes into H\({}_{2}\)O and CO\({}_{2}\) (Figure S2) The CQDs with an up-conversion performance can convert visible light into ultraviolet light at 300-400 nm, which stimulates the generation of electrons and holes in TiO\({}_{2}\). The result of our experiment (Figure S3) exhibits an up-conversion at 300-400 nm, which is consistent with Reference [35]. Then the pairs of electron and hole can migrate to the surface of particles to initiate the generation of oxygen-free radicals, which can degrade the dyes. At the same time, the GO network can conduct the electrons, put off the recombination of electron holes, and provide more active sites for photocatalysis.  
Figure 6a,b presents the degradation effect of MB and rhodamine versus time with different catalytic agents. Due to the foams being porous, they have a high adsorption effects on dyes. To make it clearer for the adsorption and degradation effects of 3D CQDs/TiO\({}_{2}\)/GO foams, the bare PUF foam, GO foam, and CQD/GO foam were used as a control material for the photocatalytic experiments to exclude the effect of adsorption on this experiment. It is clear that the use of larger amounts of CQDs/TiO\({}_{2}\) particles for the GO foam could cause a quicker degradation of both dyes. For instance, when the foam was loaded with 30 mg CQDs/TiO\({}_{2}\), it is about 2 h faster than GO alone for the degradation of MB, and 1 h faster for the degradation of rhodamine, which indicated the superiority of CQDs/TiO\({}_{2}\)/GO foam for photocatalysis. In order to exclude the effect of adsorption, dark field experiments were carried out in order to study the photocatalytic mechanism, as shown in Figure S4. It could be summarized that the photocatalytic degradation has an important effect on removement of dyes. Foams cannot get rid of all the dyes for 6h at dark while the dyes could be completely removed with irradiation, which showed that the main mechanism of dye removal in this experiment is the photocatalytic degradation.  
Figure 5: SEM images of (**a,b**) polyurethane foam (PUF)-supported GO/CQDs/TiO\({}_{2}\) foam with 12 h reaction, and (**c,d**) PUF foam.  
To further illustrate the advance of the CQDs/TiO\({}_{2}\) nanoparticle for the photocatalysis of dyes, the light-based degradation efficiency between P25-TiO\({}_{2}\) and CQDs/TiO\({}_{2}\) nanoparticles was compared after one hour of light irradiation (Figure 6c). In this test, 30 mg P25-TiO\({}_{2}\) and 30 mg CQDs/TiO\({}_{2}\) were used to degrade MB under xenon lamp with stirring. The time of the photocatalytic degradation greatly reduced due to the fuller contact of nanoparticles with dyes. It is found that the degradation effect of dyes was remarkably improved by using CQDs/TiO\({}_{2}\) nanoparticles.  
The reusability test of the fabricated CQDs/TiO\({}_{2}\)/GO foam is shown in Figure 6d. The recycling experiment was tested five times, each experiment was illuminated for three hours and the foam was washed several times by deionized water and ethanol, and then dried for use. The used foam kept a high photocatalytic ability for dyes, indicating that the photocatalyst and the framework are relatively strong, and the catalytic performance would not reduce obviously after dye degradation.