## 1 Introduction  
Due to increasing environmental problems currently, a lot of studies have been performed to develop new materials to control environmental pollution, especially the high performance purification of polluted water and air [1; 2; 3; 4; 5]. It is well known that the removal of pollutants from water and air systems could be achieved by several physical and chemical processes including physical adsorption, chemical oxidation, electrocatalysis, and photocatalysis [6; 7; 8], among these methods, the photocatalysis strategy shows high potential due to its advantages, such as pollution-free, clean, safe, economic, and high-efficient properties. Therefore, the environmental treatment through photocatalysis degradation of pollutants has attracted more and more interests in recent years. Titanium dioxide (TiO\({}_{2}\)) has been widely used as a photocatalyst due to its strong, light-based oxidizing abilities [9; 10], while the wide bandgap (>3.2 eV) of TiO\({}_{2}\) limits its applications in the visible region and in the fast electron-hole recombination related to the enhanced catalytic activity [11; 12; 13]. Several previous studies proved that the photocatalytic efficiency of TiO\({}_{2}\) can be greatly improved by introducing other light-sensitive nanomaterials (such as quantum dots) with TiO\({}_{2}\)[13; 14; 15; 16]. The advantage of dimensional quantization is that the visible light response range can be adjusted by controlling the particle size. Meanwhile, a single photon in a quantum dot (QD) can generate multiple charge carriers. Thus, the energy of the photon is much higher than the band gap, generating multiple excitation electrons and increased photocurrent signal [16]. Carbon quantum dots (CQDs) have exhibited wide applications in the field of photocatalysis due to their high fluorescent quantum effect, low toxicity, and facile preparation [13; 15; 16; 17]. CQDs can be used as a place to store electrons of TiO\({}_{2}\) under ultraviolet light and play an important role in electron-hole separation. When irradiated by visible light, CQDs, as a photosensitizer, can produce excited electrons to make TiO\({}_{2}\) sensitized. For instance, it has been found that the hydrogen evolution rate of TiO\({}_{2}\) doped by CQDs can be significantly increased under visible light (>450 nm) [18]. In another case, [PERSON] and co-workers conjugated N-doped CQDs with rutile TiO\({}_{2}\) to create a novel hybrid rod structure, which exhibited an enhanced photocatalytic ability towards the degradation of rhodamine dye [19]. For the facile fabrication of TiO\({}_{2}\)-based three-dimensional (3D) materials, other supporting materials like polymer foam or graphene are needed [20; 21; 22]. It has been found that graphene oxide (GO) reveals enhanced functions by combining with a lot of polymers [23; 24; 25; 26]. In particular, the combination between GO and polyurethane foam (PUF) made it possible to fabricated novel 3D structured materials for various applications [27; 28; 25]. For example, [PERSON] et al. have immersed melamine foams in the reduced GO solution to prepare super hydrophobic composites for oil adsorption [27]. In another case, [PERSON] and co-workers have applied the dipping method to load GO onto the melamine foam framework, and then used polydimethylsiloxane to form the superhydrophobic foam [28]. It has been found that the as-synthesized foam can absorb oil and organic solvent that are over 165 times its weight with good circulability. Inspired by these studies, we propose novel 3D PUF-supported GO foams that doped with CQDs-modified TiO\({}_{2}\) particles (the process is shown in Scheme 1), which enable the as-prepared GO or TiO\({}_{2}\) foams with improved photocatalytic efficiency. To achieve our aim, we first synthesized CQDs/TiO\({}_{2}\) particles via an in-situ hydrothermal method, which were then mixed with GO and loaded onto 3D PUF for final fabrication of 3D GO foam doped with CQDs/TiO\({}_{2}\) particles (CQDs/TiO\({}_{2}\)/GO).