The rapid evolution of nanotechnology in recent years has been particularly in the development of nanoparticles that exhibit superior chemical stability and enhanced surface functionality [1]. Nanostructured metal oxides such as TiO₂, Fe₂O₃, CeO₂, ZnO, MnO₂, Fe₃O₄, SnO₂, and Cu₂O have been used to drive chemical reactions in photocatalytic applications using solar energy instead of conventional power sources [2]. Among these, α-Fe₂O₃ stands out for its stability, abundance, eco-friendliness, and narrow band gap (2.0–2.2 eV), making it a promising semiconductor for photocatalytic pollutant degradation and hydrogen production via water splitting [3]. The limited separation efficiency of electron–hole pairs in α-Fe₂O₃ is primarily attributed to its short hole diffusion length and poor electrical conductivity. Several strategies have been developed to enhance the separation efficiency of photoexcited charge carriers in α-Fe₂O₃, including material doping, surface modification, and the fabrication of heterostructures [4]. The integration of α-Fe₂O₃ with secondary semiconductors or metallic nanoparticles shifts the Fermi level closer to the conduction band, reducing charge recombination [5]. Recent studies further emphasize the functional versatility of Fe₂O₃ nanostructures in catalytic and electrochemical applications. For example, Wu et al. [6] demonstrated that shuttle-shaped α-Fe₂O₃ nanoparticles decorated on multi-walled carbon nanotubes significantly enhanced electron-transfer kinetics and surface reactivity in voltammetric sensing applications. Their findings highlight the intrinsic redox activity, chemical stability, and favorable band structure of Fe₂O₃, which enable efficient charge transport and catalytic responsiveness. Such properties make Fe₂O₃ a promising candidate not only for electrochemical sensing but also for photocatalytic and ROS-mediated systems.

The incorporation of rare-earth oxides with α-Fe₂O₃ improves the efficiency of electron–hole separation [7]. Within these heterojunction structures, photoinduced electrons are transferred to the semiconductor with the lower conduction band edge, whereas holes accumulate in the semiconductor with the higher (less anodic) valence band, thereby promoting directional charge transport and reducing recombination losses [8]. Cerium oxide (CeO₂) exhibits enhanced photocatalytic efficiency, primarily attributed to its small band gap and the redox behavior associated with the Ce3+/Ce4+ couple [9]. The enhancement of photocatalytic efficiency is attributed to the Ce(III)/Ce(IV) redox cycling, which enables effective electron transfer and the migration of charge carriers between CeO₂ and semiconductor partners, including TiO₂ [10], Cu₂O [11], ZnO [12], and CdS [13]. The dimensions and controlled morphology of these materials significantly impact their optical characteristics and their stability under reaction conditions. Semiconductor composites with high surface area, porosity, and supported catalysts are expected to exhibit improved photocatalytic activity by maximizing active-site exposure to reactants in solar-driven systems [14]. However, enhancing stability within photocatalytic systems remains challenging with this catalyst configuration, primarily due to photo-corrosion and insufficient dispersion of active sites [[15], [16], [17]]. Therefore, strategic synthetic design aimed at improving the photocatalytic efficiency of semiconductor–metal/semiconductor composites remains a key research objective.

Embedding metal or metal oxide nanoparticles within organic or inorganic matrix structures has been shown to improve photoexcited electron–hole pair separation [18]. Core-shell composite materials have demonstrated strong potential in solar energy conversion and enhanced photocatalytic activity. Well-studied examples include CeO₂@TiO₂ [10], BiVO₄@CeO₂ [19], TiO₂@CeO₂ [20], CdS@CeO₂ [21], and Fe@CeO₂ [22]. The adoption of a core–shell structure in photocatalytic systems effectively minimizes sunlight-induced surface defects while maximizing interfacial contact between the semiconductor shell and the metal or semiconductor core, thereby improving charge dynamics [23].

Numerous studies have reported that metal doping within the Fe₂O₃ nanoparticle lattice improves bioactivity [24]. Al-Zahrani et al. [25] demonstrated that Ag-doped Fe₂O₃ (Ag/Fe₂O₃) exhibits markedly improved antibacterial performance against pathogenic bacteria such as B. subtilis, S. aureus, E. coli, and P. aeruginosa. Furthermore, Atul et al. [26] reported that Fe₂O₃ nanoparticles doped with cobalt, nickel, or zinc demonstrated enhanced and broader antimicrobial activity against Candida albicans, Candida tropicalis, Candida parapsilosis, and Candida neoformans. These results highlight metal-ion doping as an effective strategy to improve the antimicrobial performance of Fe₂O₃ nanoparticles. Rahdar et al. [27] reported that Co-doped Fe₂O₃ effectively inhibited several pathogenic bacteria and fungi, including S. dysenteriae, K. pneumoniae, A. baumannii, S. pyogenes, F. oxysporum, A. fumigatus, and C. albicans. Collectively, the results suggest that plant-mediated doped Fe₂O₃ nanoparticles have strong potential for antibacterial, antifungal, and anticancer applications [[28], [29]].

Cerium exhibits redox flexibility, enabling it to act as an antioxidant when present as Ce3+ [30], and as a pro-oxidant in the Ce4+ state [31]. The pro-oxidant behavior promotes the formation of reactive oxygen species, which contribute to its antibacterial effectiveness by disrupting cellular processes [31]. Thus, the combination of cerium's biocompatibility, catalytic capability, and redox versatility has the potential to generate materials with significantly enhanced biomedical activity [[24], [32], [33], [34], [35]]. The increasing prevalence of recalcitrant organic pollutants and pathogenic microorganisms in aquatic environments has intensified the demand for advanced photochemical materials capable of simultaneous environmental remediation and biological control [[36], [37], [38]]. Semiconductor metal oxides such as CeO₂ and Fe₂O₃ have attracted considerable attention due to their chemical stability, tunable redox properties, and ability to generate reactive oxygen species (ROS) under light irradiation. Recent investigations have demonstrated that heterojunction engineering, oxygen-vacancy modulation, and interfacial electronic coupling significantly enhance charge separation efficiency and photocatalytic performance in metal oxide systems [[39], [40], [41]]. In particular, Ce-based composites have shown promising redox cycling through the Ce3+/Ce4+ couple, while Fe₂O₃ offers visible-light responsiveness and favorable band alignment. Despite these advances, most reported systems primarily focus on either photocatalytic dye degradation or antimicrobial activity independently, with limited efforts to correlate heterojunction-induced charge dynamics with ROS-mediated multifunctional performance. Photocatalytic systems can be further enhanced by introducing chemical activators, such as sodium borohydride (NaBH₄) and peroxymonosulfate (PMS).

NaBH₄ facilitates rapid electron transfer, while PMS activation generates highly reactive sulfate radicals (SO₄•−), thereby significantly accelerating pollutant degradation. Such synergistic activation strategies improve charge-carrier utilization and broaden the scope of advanced oxidation processes in wastewater treatment [[42], [43]]. In addition to photocatalysis, several advanced oxidation processes have been widely employed for pollutant removal, among which the Fenton and Fenton-like reactions are particularly effective. The Fenton process utilizes Fe2+-mediated activation of H₂O₂ to generate highly reactive hydroxyl radicals (•OH), which rapidly degrade organic contaminants. However, limitations such as narrow pH range, sludge formation, and secondary waste generation motivate the development of more sustainable photochemical alternatives [[44], [45]].

Contemporary literature highlights that dual-metal and interface-engineered systems significantly enhance photochemical performance by modulating charge-transfer pathways and redox synergy. For instance, Gunawan et al. [46] demonstrated that distinguishing the catalytic roles of Ni and Fe in NiFeOx systems improves water-oxidation kinetics by enabling interfacial electronic differentiation. Similarly, microwave-assisted and interface-controlled nanocomposites have shown enhanced catalytic degradation efficiency through improved crystallinity and defect modulation [47]. More recently, biohybrid and immobilized photoredox systems have integrated catalytic and microbial platforms to enable sustainable pollutant reduction [48], while S-scheme heterojunctions with chemically bonded interfaces have been reported to significantly enhance charge separation and redox preservation during photocatalytic CO₂ reduction [49]. These studies collectively underscore that interfacial chemical bonding, defect engineering, and directional charge migration are decisive factors governing advanced photocatalytic systems.

In this work, we report a combustion-synthesized CeO₂/Fe₂O₃ heterojunction engineered to enhance interfacial electronic coupling and reactive oxygen species generation. Unlike previously reported systems, the present study establishes a direct structure–property–function relationship through integrated structural characterization, kinetic analysis, scavenger validation, LC–MS mineralization studies, and ROS-mediated antibacterial and DNA fragmentation assessment. This combined photochemical and biological investigation provides deeper insight into the multifunctional potential of Ce-based heterostructures.