The containment of microbial pathogenesis has emerged as a pressing and imperative concern, congruent with the United Nations' Sustainable Development Goal of ‘Good Health and Well-being’ [1]. The propagation of pathogens, majorly facilitated by frequently touched surfaces in densely populated spaces and non-sterile packed food items, underscores the urgency to address this challenge [[2], [3], [4], [5], [6]]. Conventionally, non-biodegradable agents such as antibiotics and common disinfectants have been employed to uphold pathogen-free environments [7]. However, the escalating threat of antimicrobial resistance has underscored the necessity for judicious use of synthetic antimicrobial agents, prompting a quest for alternative strategies [[8], [9], [10], [11], [12], [13], [14]].

In this context, the utilization of thin film coatings endowed with disinfection properties presents a promising avenue to combat antimicrobial challenges [6,11,[15], [16], [17], [18]]. Notably, semiconductor-based visible-light-active photocatalysts have garnered attention as potential candidates for antibacterial applications, attributed to their capacity to generate bactericidal reactive oxygen species (ROS) [[19], [20], [21]]. However, most of the materials exhibiting antibacterial properties through advanced oxidation processes are in powder form, and hence, practical disinfection applications necessitate coatings that remain efficacious not only in illuminated conditions but also in darkness [[22], [23], [24], [25]] . It can be noted that the photocatalytic capability could bestow self-cleaning attributes against organic contaminants upon these thin film coatings [26]. Nonetheless, it is worth highlighting that nanostructured thin films hold a distinct advantage for such applications, as they offer a substantially high actual-to-apparent surface area ratio, which is beneficial in effectively enhancing the contact area for (photo)catalysis [27,28].

Among such photocatalysts, ZnO stands out as a prominent contender, closely trailing TiO2 in popularity [[29], [30], [31], [32], [33]]. ZnO boasts a range of appealing attributes, including high biocompatibility, optoelectronic prowess, piezoelectric properties, antimicrobial efficacy, and the ability to fine-tune its band diagram via doping, all contributing to its remarkable photocatalytic potential [17,[34], [35], [36], [37], [38]]. Despite the trap states provided by oxygen vacancies that render visible-light photocatalysis feasible, ZnO's intrinsic photoluminescence can impede overall efficiency [39,40] . To surmount this, enhancement strategies often involve heteroatom doping (e.g., nitrogen, sulfur, phosphorous, etc.) or the creation of heterojunctions with other semiconductor materials [41,42]. Of current interest are two-dimensional vertically-aligned ZnO nanorods (NRs), offering distinctive optical, electronic, high surface area, and mechanical characteristics that find applications in realms such as sensing and energy harvesting [[43], [44], [45]]. Significantly, the synthesis of ZnO NRs often leads to the formation of homojunction between hexagonal bipods, facilitating efficient charge separation [33,46,47]. On a different note, AgBr, with a visible-light bandgap (~2.4 eV), is a well-established photosensitizer with remarkable antimicrobial properties in dark conditions [9,[48], [49], [50], [51], [52]]. While fabrication of AgBr thin films typically necessitates complex techniques like vapor deposition or vacuum deposition, a facile solution-based approach yielding heterojunctions holds allure for creating various functional compositions [53,54]. Though the conventional double decomposition reaction between silver nitrate and alkali halides has been used for depositing silver halides over various photocatalysts for generating heterojunctions, the process is known to result in the non-uniform and poly-disperse size distribution of the silver halide [[55], [56], [57]]. On the other hand, surfactant-based precursor, yielding highly dispersed and narrow size distribution of metal halide nanoparticles, is an attractive approach to overcome the interfacial tension between the two semiconductor components [48].

In the present study, we employ a spin-coatable surfactant-based precursor, specifically tetraoctylammonium bromide complex with silver nitrate (Ag-TOAB), to deposit varying amounts of AgBr onto vertically-aligned ZnO NRs. This solution-phase method offers benefits like ambient processing, cost-effectiveness, and easy tunability of AgBr content by altering solution concentration. We further investigate the structural, morphological, elemental, and dark-light dual-mode disinfection properties of these heterojunction thin film assemblies. Such a strategy is envisioned to yield a homogeneous coating of AgBr over ZnO NRs in a facile manner.