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The SrCO3/AgI photocatalysts were prepared via a co-precipitation method by using SrCO3 as a co-photocatalyst and AgI as a photo sensitizer. X-ray diffraction, field emission scanning electron microscope, X-ray photoelectron spectrometer, UV-vis diffuse reflectance spectroscopy and electrochemical impedance spectroscope were used to analyze the structure, micro-morphology, chemical compositions, optical properties and photo-generated carrier behaviors of the as-prepared samples, respectively. The photocatalytic degradation mechanism of the as-developed composites was also proposed. Analysis results show SrCO3, an insulator, can improve the photocatalytic performances and recyclability of AgI for degrading tetracycline under visible light. As the theoretical molar ratio of Sr(NO3)2 to AgNO3 increases, the degradation efficiency of the hybrids first increases and then descends. When the theoretical molar ratio of that is 1: 1, it acquires the maximum of 66.6% within 8 min. This is higher than 32.0% of pure AgI and 34.0% of SrCO3. Moreover, after three times degradations it is 63.0%, which is higher than 13.6% of AgI. The improvement of the photocatalytic performance of the sample is attributed to the construction of hybrids. The main activated species in catalysis process are superoxide radicals.

The SnO2 quantum dots (SnO2QDs)/ZnS nanosheets (ZnSNs) heterojunction was fabricated via an in-situ synthetic method at room temperature. Rhodamine B, potassium dichromate, and tetracycline were used to discuss the photocatalytic activities of the as-prepared samples under the visible light illumination. The photocatalytic mechanism of the as-prepared samples was also proposed. The experimental results indicate that the degradation efficiency of the as-prepared SnO2QDs/ZnSNs heterojunction first increases and then decreases with increasing the usage of ZnSNs. When the mass ratio of SnO2QDs to ZnSNs is 1: 2 in 180 min, the asprepared samples have the highest degradation efficiency of 89.1% for rhodamine B, 97.7% for potassium dichromate, and 83.8% for tetracycline, which are much higher than 51.7%, 26.8%, and 0.9% of pure SnO2QDs as well as 37.9%, 87.1%, and 19.1% of pure ZnSNs, respectively. After it is repeatedly degraded for 3 times, it possesses the degradation efficiency of 62.5% for rhodamine B, which increases by 200.5% in comparison with 20.8% of the pure SnO2QDs. Moreover, the enhanced photocatalytic performances of the as-prepared hybrids are attributed to the formation of heterojunction between the SnO2QDs and ZnSNs. In addition, hydroxyl radicals and superoxide anion radicals play major roles during the photocatalytic degradation process, while holes play a minor role.

The CdS/ spherical g-C3N4 n-n heterojunction photocatalyst was fabricated via a solvothermal method. The tetracycline was used to characterize the photocatalytic properties of the as-developed hybrids. The photocatalytic degradation mechanism of the as-developed heterojunction photocatalyst was also analyzed. Research results show that CdS nanoparticles are well dispersed in the surface layer of spherical g-C3N4. Moreover, the mass ratio of CdS to spherical g-C3N4 will influence the photocatalytic activity of the asdeveloped composites, which shows the trend of first increasing and then decreasing as it increased. When the mass ratio is 7:1, in 25 min, the as-developed heterojunction shows 93.2 % of the maximum photocatalytic efficiency and still exhibits 83.6 % after 5 times cycle testing. Moreover, the as-developed hybrids can accelerate the electron transport and improve the separation efficiency of photo-generated carriers compared with pure samples. In addition, the holes and superoxide radicals are dominating active species during the photocatalytic degradation process.

SnO2/AgIO4 hybrids were fabricated by an in-situ synthetic method at room temperature. The structure, morphology, light response range, separation efficiency of the electron-hole pairs and elements of the as-synthesized samples were characterized by adopting X-ray diffraction, scanning electron microscopy, UV-Vis diffuse reflectance spectroscopy, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy, respectively. The synergistically photocatalytic degradation mechanism of the as-synthesized composites was also proposed. The experimental results reveal that under the visible light irradiation the as-synthesized SnO2/AgIO4 hybrids can enhance the photocatalytic degradation efficiency of rhodamine B compared to pure samples. With increasing the molar ratios of AgIO4 to SnO2, it displays the trend of first increasing and then decreasing. When it is 1:2 in 150 min, the as-prepared hybrids have the highest degradation efficiency of 93.1%, which increases by 6550.0%, 30.5%, and 1505.0% compared to those of pure SnO2, AgIO4, and TiO2 (P25), respectively. Moreover, the Sn-O-Ag cross-linking bonds are formed at the interfaces of SnO2 and AgIO4. In addition, superoxide anion radicals and holes play a major role in the process of photodegradation.

Zn2SnO4/few-layer boron nitride nanosheets (FBNNS) hybrids were synthesized via a one-step hydrothermal method. The structures, morphology, optical properties, electron transformation and separation of the as-prepared products were characterized by X-ray diffraction, transmission electrical microscopy, UV-vis diffuse reflectance spectroscopy and electrochemical impedance spectroscopy, respectively. Rhodamine B was used to evaluate the photocatalytic activities of the as-prepared samples under visible light illumination. The photocatalytic mechanism was also explored. Experimental results showed that the degradation efficiency of rhodamine B was firstly increased and then decreased with increasing the usage amount of FBNNS. When it was 9 wt% based on the weight of Zn2SnO4, the degradation efficiency of the as-prepared Zn2SnO4/FBNNS-9 wt% composites reached to the maximum of 97.5% in 180 min, which was higher than 39.2 % of pure Zn2SnO4. Moreover, the holes played mainly active roles in photocatalytic reaction process. In addition, the as-prepared hybrids could enhance the separation efficiency of photoexcited carriers compared to pure Zn2SnO4.