Photocatalytic Degradation of 1,4-Dioxane and Malachite Green over Zinc Oxide/Cellulose Nanofiber Using UVA/B from Direct Sunlight and a Continuous Flow Reactor

Concerns over water contamination by biorecalcitrant, persistent organic pollutants have emphasized the need for effective, cheap, and scalable treatment methods. Photocatalysis offers the potential advantages of using air as the oxidant, ambient conditions for reaction, and sunlight as the source of energy; however, identifying a sustainable catalyst support and sunlight-active, earth-abundant photocatalysts is challenging. This study demonstrates for the first time the development of a ZnO/cellulose nanofiber (CNF) continuous flow photoreactor for fast and effective degradation of industrial pollutants 1,4-dioxane and malachite green and model pollutant methylene blue in water. The novel sun-flow reactor consists of open, interconnected parallel channels with a continuous flow of water containing the chosen pollutant circulated over the catalyst under ultraviolet (UV)A/B irradiation from direct sunlight. Mass spectrometry (MS), gas chromatography (GC)-MS, liquid chromatography (LC)-MS, and inductively coupled plasma (ICP)-MS analyses were used to investigate and quantify the extent of degradation and the byproducts formed in the process. Aqueous solutions of 10 ppm methylene blue and malachite green, as well as their reaction byproducts, were reduced below 0.1 ppm (the detection limit) with an energy per order (EE/O) figure of merit of 2.2 kWh/m3 per order. A 3.5 ppm aqueous solution of 1,4-dioxane was reduced to 0.034 ppm with an EE/O figure of merit of 1.6 kWh/m3 per order.