## 1 Introduction  
The photocatalytic degradation of organic pollutants on semiconductor materials is of particular significance for wastewater treatment, since the photocatalytic degradation is often realizable under mild conditions. In this sense, traditional semiconductor materials such as TiO\({}_{2}\), ZnO, and Ag\({}_{3}\)PO\({}_{4}\) are often utilized as the photocatalysts, due to their low cost, good stability, non-toxicity, and desired environmental acceptance [1; 2; 3; 4]. Among them, TiO\({}_{2}\) is a representative photocatalyst widely used for the photocatalytic degradation of organic compounds and water splitting to produce hydrogen [1].  
The large-scale application of TiO\({}_{2}\) photocatalyst, however, is limited by three drawbacks. Firstly, TiO\({}_{2}\) is only responsive to ultraviolet light (3%-5% of sunlight) and has a low utilization efficiency of sunlight. Secondly, TiO\({}_{2}\) powder is difficult to separate from the reaction system for reusing the degradation system, and the photocatalyst in combination with inorganic materials used for separation has good access to water medium to cause secondary pollution. Fortunately, some TiO\({}_{2}\) based thin layers/films can achieve good separation from water [5; 6]. Thirdly, TiO\({}_{2}\) photocatalyst has a high recombination rate of electron-hole pairs, which seriously affects its photocatalytic efficiency [7]. For getting rid of the above-mentioned drawbacks, some researchers conducted selective metal doping to improve the photocatalytic activity of TiO\({}_{2}\) and enhance its response in the visible-light region so as to acquire increased photocatalytic efficiency. Some of representative research in this aspect point to the preparation and photocatalytic activity evaluation of a series of titania-metal composites doped with transition metals [8; 9], noble metals [10; 11; 12], and nonmetals [13; 14; 15].  
Previous studies demonstrate that cupric ion is suitable for doping various visible light-responsive photocatalysts [16; 17], since Cu element is of relatively low cost and abundant origin as well as low potential. More important, the two kinds of copper cation, Cu\({}^{2+}\) and Cu\({}^{+}\), can comprise Cu\({}^{2+}\)/Cu\({}^{+}\) and Cu\({}^{2+}\)/Cu electrodes with a redox potential of 0.16 V and 0.52 V, respectively. This means that the electrons (e\({}^{-}\)) generated upon the photo-excitation of photocatalyst can be directly trapped by Cu\({}^{2+}\), thereby leaving the holes with positive charge (\(h^{+}\)). The as-generated holes can escape from the oxidative valence of the photocatalyst to degrade organic compounds. In this way, metal ion-doped semiconductor materials can provide semiconductor-based photocatalysts with charge trapping sites, thereby reducing the electron-hole pair recombination rate of the latter and extending their light response range [17]. Even so, unfortunately, the metal ion-doped semiconductor-based photocatalysts still face challenge of separation from the photocatalytic reaction system and are accessible to the water system, thereby causing secondary pollution.  
Bearing those considerations in mind, here we attempt to design a novel photocatalyst consisting of TiO\({}_{2}\)/Cu composite (abridged as TC) and porous polymer. We focus on porous polymers (PP) linked by covalent-organic frameworks, because they exhibit excellent adsorption performance toward gases and liquids as well as good photo activity and chemical stability, while they can be easily separated from photocatalytic reaction system. This article reports the preparation of PP/TiO\({}_{2}\) composites doped by Cu\({}^{2+}\) (denoted as PPTC). It also deals with the photocatalytic performance of the as-prepared TiO\({}_{2}\), TC, and PPTC toward the degradation of \(N\),\(N\)-dimethylformamide (DMF), methyl orange, phenol, and methylene blue under the irradiation of simulated sunlight (Xe lamp light) and natural sunlight.