## 6 Recent Developments and Innovative Approaches
### Hybrid and Synergistic Systems  
To improve treatment performance and tackle a broader range of contaminants, photocatalysis is increasingly combined with other processes:  
* Photocatalysis-membrane filtration: Integrated systems use membranes for catalyst recovery and additional separation, improving water quality and reusability.
* Photocatalysis-adsorption: Combining photocatalysts with porous adsorbents (e.g., activated carbon, zeolites, MOFs) enhances pollutant uptake and facilitates degradation.
* Photocatalysis-Fenton or photo-Fenton processes: These synergistic systems increase radical generation, especially under acidic conditions, accelerating degradation rates.
* Photocatalysis-biological treatment: Pre- or post-biological treatments are used to complement photocatalytic oxidation, especially for biodegradable intermediates.  
Figure 13: Conceptual advances and strategic innovations in photocatalytic water treatment: (**a**) strategies for enhancing visible-light-responsive photocatalysts in water treatment; (**b**) hybrid and synergistic systems enhancing photocatalytic water treatment; (**c**) harnessing solar energy in photocatalytic reactor designs for water purification; (**d**) smart and stimuli-responsive photocatalysts for adaptive water treatment; (**e**) AI-driven strategies for photocatalyst design and optimization.  
A study performed by [PERSON] et al. [166] investigated the removal of perfluorooctanoic acid (PFOA) from groundwater using a combination of nanofiltration and photocatalysis. The nanofiltration process achieved a 99.62% removal efficiency, and the subsequent photocatalytic treatment degraded 59.64% of the rejected PFOA. This hybrid approach significantly reduced the environmental release of PFOA compared to nanofiltration alone. [PERSON] et al. [94] studied the synergistic integration of adsorption and photocatalysis for enhanced degradation of organic pollutants. This research focuses on the development of a composite material derived from ZIF-67, resulting in cobalt-embedded nitrogen-doped nanoporous carbon (Co-N/C). The material exhibited a well-distributed structure with a suitable specific surface area and abundant active sites. These characteristics contribute to its dual functionality: (i) Adsorption: The nanoporous structure facilitates the initial uptake of organic pollutants, such as rhodamine B (RhB), from aqueous solutions; (ii) Photocatalysis: Upon light irradiation, the material effectively degrades the adsorbed pollutants, leading to their mineralization.  
Figure 13b illustrates the integration of photocatalysis with complementary treatment processes to improve the efficiency and broaden contaminant removal. It highlights four key hybrid approaches: membrane filtration for catalyst recovery and enhanced separation, adsorption using porous materials for increased pollutant uptake, Fenton and photo-Fenton processes for accelerated radical generation, and biological treatments that support the degradation of intermediate byproducts. These synergistic combinations enhance the overall water treatment performance and adaptability to complex water matrices.