Benefits and yields of simultaneous free chlorine and hydrogen generation in side-emitting optical fiber photocatalytic reactors

Decentralized water treatment requires resilient, consumable-free technologies that operate independently of complex supply chains. This study presents a side-emitting polymer optical fiber photocatalytic reactor immobilized with modified SrTiO₃ for the simultaneous generation of gaseous hydrogen fuel and disinfecting oxidants (free chlorine) in water. A three-factor response surface methodology was employed to quantify the interactive effects of the factors (salinity, catalyst loading, and light intensity) on the system responses. Statistical analysis identified two distinct limiting regimes: the aqueous free chlorine response is chemically limited by the salinity factor, allowing for precise control of disinfection capacity, whereas the hydrogen response is optically limited by the catalyst loading factor due to a “shielding effect” where excess particles block the light from the fiber core. Leveraging the independent relationship between these factors and responses, we established a tunable strategy with three distinct modes: a “Rapid Response” mode for emergency use that achieves critical disinfection levels (0.5 mg L⁻¹) in 10–20 minutes; a “Maintenance” mode that uses a continuous flow rate of 13 mL min⁻¹ to maintain a steady-state chlorine level within WHO safety standards (0.5–4.0 mg L⁻¹) to prevent microbial regrowth; and a “Fuel-Priority” mode that maximizes the hydrogen response (∼80 µmol h⁻¹). This work demonstrates a robust, dual-purpose infrastructure that transforms passive treatment units into active utility nodes which can provide both clean water and energy for off-grid applications.