Tetracycline (TC) is often detected from groundwater, surface water and sewage treatment systems as a new source of water pollution. It has caused "pseudo-persistence" pollution to water bodies, leading to an increase in drug-resistant pathogenic microorganisms, which has aroused widespread concern (Zhou et al. 2020; Islam et al. 2019; Du et al. 2019). In recent years, physical and chemical methods, biological treatment methods, and chemical treatment methods have been devoted into the removal of TC from wastewater (Qu et al. 2020; Zhao et al. 2019). Among them, photocatalysis technology, as an advanced oxidation technology, has the advantages of utilizing the potential advantages of sunlight and high processing efficiency, and is used for the treatment of refractory organic pollutants (Khodadadi et al. 2019; Zhang et al. 2020; Wang et al. 2017). However, there are not many reports on the degradation of antibiotics by photocatalytic technology, so it is necessary to intensify efforts to explore the use of photocatalytic technology to treat antibiotic wastewater(Yu et al. 2019; Wei et al. 2020).
Hydroxyapatite (HA), which is the main inorganic component in bone and enamel, has the advantages of good biocompatibility, safety and non-toxicity, and is therefore widely used in biomedical materials (Yadav et al. 2020; Farraris et al. 2020; He et al. 2019), drug carriers (Yi et al. 2016; Xiong et al. 2016) and catalysts (Schiavoni et al. 2018; Shariffuddin et al. 2013). At the same time, due to the simple preparation process and low cost of HA, it is also widely used in the fields of catalyst carrier and water body repair. However, the photocatalytic activity of HA is still much lower than expected because of its poor charge transport, slow redox reaction kinetics, and low carrier mobility. Therefore, the development of a modification strategy to improve the HA charge kinetics is essential for achieving high performance HA (Reeta Mary et al. 2018; Valizadeh et al. 2014; Ekka et al. 2018; Lv et al. 2019; Jiraborvornpongsa et al. 2019; Huang et al. 2017). At present, several modification strategies have been shown to improve the photocatalytic efficiency of HA, including material design and preparation(Reeta Mary et al. 2018), cocatalyst deposition (Lv et al. 2019) and elemental doping (jiraborvornpongsa et al. 2019; Ishisone et al. 2020). Several groups have reported that synthetic HA has better degradation properties of organic dyes by controlling the preparation conditions of hydroxyapatite. Nathanael et al. prepared a TiO2-HAP composite by high-speed centrifugal gravity mixing of hydroxyapatite and Ti(OH)4 colloids (Joseph Nathanael et al. 2010). Compared with hydroxyapatite or TiO2 alone, the composite catalyst was under ultraviolet light. It has better degradation ability to methyl orange. Reddy et al. used hydroxyapatite to degrade calcium and magnesium indicators under ultraviolet light, which can remove 92% of COD and improve the biodegradability of dye wastewater (Reddy et al. 2007). They believe that UV irradiation can change the electronic structure of PO43− on the surface of hydroxyapatite, generate oxygen vacancies and active •O2‒, and then degrade dye molecules. Although the research on the degradation of pollutants using hydroxyapatite composite photocatalyst has made some progress, there are some disadvantages. For example, hydroxyapatite can only be used as a support, and only plays an auxiliary role in the photocatalytic process. The preparation process of HA composite catalyst is complicated and their structure is unstable. Generally, the prepared composite catalyst can only be used under ultraviolet irradiation. Although the introduction of precious metals can increase the visible light activity of composite materials, it also increases manufacturing costs. Based on the characteristics of hydroxyapatite with different surface activity, the development of highly active hydroxyapatite photocatalyst has certain theoretical significance and practical value.
Here, HA particles were first prepared by using a novel bacterial induction method. The crystal structure, morphological characteristics, and specific surface area of HA particles were studied, and the photocatalysis of the prepared HA particles on the degradation of tetracycline (TC) under ultraviolet light was studied. This synthesis method is different from the conventional synthesis methods. Phosphatase can be released by Bacillus subtilis to control apatite mineralization. A large number of fine-pored, high specific surface area HA crystal materials are surprisingly obtained. HA itself has good photocatalytic activity, and it does not need to add other photosensitive materials to enhance its photocatalytic performance. In addition, the intrinsic relationship between crystal morphological characteristics and photocatalytic activity of HA was preliminarily discussed. This work provided a simple method for improving the photocatalytic activity of HA, and also deepened the understanding of the photocatalytic mechanism of phosphate photocatalysts.