Photocatalytic water remediation is an effective approach for wastewater treatment; however, conventional powdered photocatalysts face challenges, including agglomeration, difficult separation, and inefficient light utilization due to their tendency to sink in water. Inspired by the buoyancy and water purification ability of water hyacinth, a self-floating photocatalytic system, Water Hyacinth-Inspired Purifier (WHIP), was developed by integrating TiO2 photocatalysts onto a porous polydimethylsiloxane substrate, with a central closed-pore structure mimicking the sponge tissue of water hyacinth. This biomimetic design ensures stable flotation under static and dynamic flow conditions, maximizing light exposure for efficient photocatalysis. WHIP effectively degraded various contaminants, including methylene blue (99.5 ± 0.4%), rhodamine 6G (98.6 ± 1.5%), methyl orange (72.6 ± 6.4%), and nanoplastics. To assess its scalability and versatility, a large-scale WHIP incorporating a TiO2/graphdiyne photocatalyst was fabricated, achieving 94.9% methylene blue removal under real ambient conditions. These findings highlight WHIP’s potential as a sustainable environmental remediation technology.