With the rapid development of industry and textile industry, problems, such as energy shortage and environmental pollution, are becoming increasingly serious. Semiconductor photocatalytic technology is regarded as one of the ideal means to solve the problems, due to its advantages of utilizing sunlight to degrade pollutants, decompose water to produce hydrogen and reduce CO₂. In bismuth oxyhalide materials, bismuth oxychloride (BiOCl) has attracted much attention, due to its unique layered structure, suitable band structure (~3.4 eV) and high chemical stability. The alternating stacking structure of [Bi₂O₂]²⁺ layer and Cl^- layer results in an internal electric field and effectively promote the separation of photo generated electron hole pairs, endowing it with excellent photo-oxidation ability. However, the absorption of visible light by BiOCl is limited by its wider bandgap (only 4%–5% of the solar spectrum), so that its practical applications are severely limited. Cadmium sulfide (CdS), a typical narrow-band semiconductor (~2.4 eV) complementary to BiOCl, is characterized by a wide visible light response range (absorption edge ~520 nm), a relatively negative reduction potential (−0.5 eV) and other advantages. CdS has high reactivity in hydrogen production and pollutant degradation. In response to the above issues, a hydrothermal thermal assisted liquid-phase self-assembly strategy was proposed to produce high interface coupling BiOCl/CdS heterojunction materials, where BiOCl was synthesized by using hydrothermal method and CdS was synthesized by using water bath method. Finally, BiOCl/CdS heterojunction was obtained by thermally assisted liquid-phase self-assembly method.

To synthesize BiOCl/CdS composite photocatalyst, 300 mg BiOCl catalyst was weighed and placed in a conical flask containing 60 mL H₂O. C₂H₅NS was added and the mixture was allowed to adsorb in the dark for 30 min. CdCl₂ was then added and the mixture was heated in water bath at 90℃ for 2 h. The precipitate was centrifuged alternately with deionized water and anhydrous ethanol four times. The treated precipitate was placed in a constant-temperature drying oven and dried at 60℃ to obtain target product.

The synthesized sample is indicated by XRD and SEM results to be a flower-shaped BiOCl powder with high crystallinity. The presence of Bi, O, Cl, S and Cd elements in the material was confirmed by using EDS and XPS. In TC degradation results, it was shown that, with increased content of CdS, the degradation performance of the BiOCl/CdS composite material exhibited a trend of initial increase and then decrease. Among these, the highest catalytic activity was exhibited by BiOCl/CdS-2 (66.69%), representing an approximately 15.17% improvement over the 51.52% observed for flower-shaped BiOCl. This enhancement is closely related to heterojunction construction and improved photogenerated carrier separation efficiency.

A BiOCl/CdS heterojunction photocatalyst was successfully constructed, whose degradation performance and mechanism of action on tetracycline hydrochloride were systematically studied. It is experimentally indicated that the visible light response ability is limited by the wide bandgap (~3.2 eV) of single flower-shaped BiOCl, whereas pure CdS despite possessing narrow bandgap advantages is characterized by weak photocatalytic degradation ability due to high photogenerated carrier recombination rates and photocorrosion issues. Optimized photocatalytic performance was achieved through regulation of CdS loading in the BiOCl/CdS heterojunction composite. Among them, BiOCl/CdS-2 showed the highest activity (degradation rate of 66.69%), which was 15.17% higher than that of pure BiOCl (51.52%). The performance enhancement is attributed to two collaborative mechanisms, i.e., band regulation and interface effects. With band regulation, the light response range is broadened and visible light capture capability is enhanced through the introduction of narrow bandgap CdS. IniInterface effect, photo-generated electrons are driven by the heterojunction to migrate from the CdS conduction band to the BiOCl conduction band, while holes are transferred to the CdS valence band, thus effectively suppressing carrier recombination and extending charge lifetime. It should be noted that a threshold exists for CdS loading. Excessive CdS (e.g., BiOCl/CdS-3) would cause particle aggregation on BiOCl surface, resulting in active sites being shielded, light absorption being hindered and degradation efficiency being decreased.

With the continuous development of industry, environmental problems are becoming increasingly serious. As a new means of green and clean strategy, photocatalysis has been widely explored. Bismuth oxychloride (BiOCl) has attracted much attention in many fields due to its unique layered structure, adjustable band gap (~3.4 eV) and excellent photochemical stability. However, the BiOCl materials synthesized by using the traditional methods have problems, such as limited specific surface area, high recombination rate of electrons and holes and insufficient surface active sites. In order to solve these problems, BiOCl powders with different morphologies were prepared by using ethanol and water, with their structure and photocatalytic performance to be analyzed to explore the influence of solvents on performance of the BiOCl photocatalysts.

Three BiOCl photocatalytic samples were prepared by using water, alcohol and alcohol-water as solvents. Specifically, 0.2 mmol Bi(NO₃)₃·5H₂O was weighed and dissolved into a mixed solution with a total volume of 60 mL (ethylene glycol∶water=x∶60-x; x=0, 30, 60), followed by ultrasonic dispersion for 30 min. 0.2 mmol KCl was added to the above solution, with vigorous stirring with magnetic stirring for 1 h to trigger full reaction. Finally, the solution was transferred to a stainless steel high-pressure reactor and reacted at 160 ℃ for 12 h. After the reaction was finished, the product was washed twice with anhydrous ethanol and deionized water, and then dried with a freeze dryer. Morphology and structural characteristics of BiOCl synthesized at different solvent conditions were analyzed by using SEM, XPS and XRD. Photocatalytic performance of BiOCl was studied through the degradation of acetic acid and CIP in two different systems, while the difference in photocatalytic performance and internal mechanism of the BiOCl were also discussed

The samples synthesized with three different solvents had very different morphologies. When water was used as the solvent, BiOCl tended to grow into a flake structure. When alcohol-water was used as solvent, its size decreased and became nanosheet. When glycol was used as a solvent, it self-assembled into flower spheres. XRD results suggested that BiOCl has a higher (001) and the same crystal face direction, when water is used as the solvent. According to XPS results, the oxygen vacancy (OVs) ratio was higher, when alcohol and water acted together. With the photocatalytic degradation performances, it was found that the BiOCl prepared in alcohol-water had the highest degradation rate for acetic acid, with degradation rate of 6.425 min^-1. In the ciprofloxacin (CIP) degradation system, the flower-like BiOCl prepared in ethylene glycol had the highest photodegradation efficiency, while the degradation efficiency was 87.2% and the degradation rate was about 0.02954 min^-1.

In this paper, morphology and structure of BiOCl photocatalytic materials were adjusted by using ethanol and water as a double solvent system. The prepared BiOCl samples were characterized by using SEM, XRD and XPS. The addition of ethylene glycol played a linking effect on the BiOCl photocatalyst and inhibited the growth of (001) and crystal faces in the same direction of BiOCl crystals. The addition of ethylene glycol can promote the formation of OVs, with proportion to be highest when ethylene glycol and water were used together. Through the degradation of acetic acid and ciprofloxacin (CIP) in two different systems, it was found that BiOCl containing oxygen vacancy had higher photodegradation activity in the acetic acid degradation system, while BiOCl with unique three-dimensional flower structure had higher degradation activity in the CIP degradation system.