## 1 Introduction
### Advanced Treatment Strategies for Emerging Contaminant Mitigation
#### Advanced Oxidation Processes (AOPs)
Advanced oxidation processes (AOPs) have emerged as effective strategies for degrading a broad spectrum of organic and inorganic pollutants through the generation of highly reactive oxidative species. Among them, heterogeneous photocatalysis has garnered considerable attention due to its potential to achieve complete mineralization of contaminants under mild conditions, using light as the driving force and a solid photocatalyst to initiate redox reactions [45; 46; 47]. Although numerous advanced treatment techniques have been developed for removing emerging contaminants, a comparative analysis reveals significant trade-offs in performance, cost, and environmental impact. For instance, ozonation, and UV/H\({}_{2}\)O\({}_{2}\)-based AOPs are widely accepted for their strong oxidation potential; however, several studies have highlighted concerns about toxic byproduct formation and energy-intensive operation, particularly at large scales [7]. Conversely, adsorption-based methods using activated carbon or biochar are praised for their simplicity and low cost, but still suffer from non-specificity and challenges in adsorbent regeneration, raising questions about long-term sustainability [7]. Photocatalysis, particularly using semiconductors like TiO\({}_{2}\) or ZnO, presents a promising alternative due to its potential for complete mineralization of organic pollutants. However, its scalability remains contested. While some authors emphasize its versatility and environmental compatibility [11], others caution that rapid charge recombination, low visible-light response, and reduced activity under real water matrices severely limit its practical applicability [11]. Notably, studies diverge on the actual impact of heterojunction formation. While TiO\({}_{2}\)/g-C\({}_{3}\)N\({}_{4}\) and BiVO\({}_{4}\)/graphene composites show promising synergy, some reports fail to replicate enhanced activity due to interface instability or inconsistent synthesis quality [11]. Furthermore, a persistent controversy surrounds the use of noble metal dopants (e.g., Ag, Pt, Au). Although these elements boost efficiency via plasmonic enhancement, critics argue that cost, toxicity, and environmental persistence undermine their real-world viability [14]. A recent trend toward earth-abundant, metal-free photocatalysts attempts to address these issues, though their performance and stability under dynamic conditions remain under investigation [3]. In terms of system-level integration, the literature increasingly supports hybrid configurations (e.g., photocatalysis + membranes or Fenton processes), yet consensus is lacking regarding optimal reactor design. Some researchers advocate for modular, immobilized reactors for field use [1], while others find that slurry reactors, despite recovery challenges, offer superior degradation rates [1]. These discrepancies underscore the need for standardized testing protocols and more pilot-scale demonstrations to reconcile laboratory results with real-world expectations. Therefore, heterogeneous photocatalysis is particularly attractive for water treatment applications because it does not require the addition of chemical reagents and can utilize renewable solar energy. Over the past two decades, extensive research has been devoted to developing more efficient photocatalytic materials and their reuse over numerous cleaning cycles, optimizing reactor designs, and evaluating photocatalytic performance under real-world conditions. Nonetheless, challenges remain in scaling up laboratory successes, improving the selectivity and durability of photocatalysts, and ensuring their environmental safety. This review focuses specifically on the use of heterogeneous photocatalysis for the removal of emerging organic contaminants in water and wastewater, including pharmaceuticals, endocrine disruptors, personal care products, and industrial chemicals. The scope includes laboratory-scale research, pilot-scale studies, and practical considerations for integration into existing treatment systems.