Hierarchical optofluidic microreactor for water purification using an array of TiO2 nanostructures

Abstract

Clean water for human consumption is, in many places, a scarce resource, and efficient schemes to purify water are in great demand. Here, we describe a method to dramatically increase the efficiency of a photocatalytic water purification microreactor. Our hierarchical optofluidic microreactor combines the advantages of a nanostructured photocatalyst with light harvesting by base substrates, together with a herringbone micromixer for the enhanced transport of reactants. The herringbone micromixer further improves the reaction efficiency of the nanostructured photocatalyst by generating counter-rotating vortices along the flow direction. In addition, the use of metal-based substrates underneath the nanostructured catalyst increases the purification capacity by improving the light-harvesting efficiency. The photocatalyst is grown from TiO2 as a nanohelix film, which exhibits a large surface-to-volume ratio and a reactive microstructure. We show that the hierarchical structuring with micro- to nanoscale features results in a device with markedly increased photocatalytic activity as compared with a solid unstructured catalyst surface. This is evidenced by the successful degradation of persistent aqueous contaminants, sulfamethoxazole, and polystyrene microplastics. The design can potentially be implemented with solar photocatalysts in flow-through water purification systems.

Photocatalytic degradation of different types of microplastics by TiOx/ZnO tetrapod photocatalysts

“…Consequently, photodegradation processes including the effect of illumination and the effects of a number of different photocatalysts on degradation/chemical changes of different plastics have been investigated in recent years [ [17] , [18] , [19] , [20] , [21] , [22] , [23] , [24] , [25] , [26] , [27] , [28] , [29] , [30] , [31] , [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] , [41] , [42] , [43] , [44] ], and the results have been summarized in Table S1 . The degraded plastics include polyolefins, such as polyethylene (PE) and polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) polyethylene terephthalate (PET), polyamide fibers, and poly(methylmethacrylate) [ 1 , 8 , 9 , 12 ].…”

“…There are many possible candidates for photocatalyst materials. Metal oxides, such as ZnO [ 27 , 28 ] and TiO 2 [ [20] , [21] , [22] , [23] , [29] , [30] , [31] , [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] ], have been among commonly investigated photocatalysts for microplastics degradation [ 4 , 7 , 9 ]. While complete degradation of PE under UV-C light (254 nm) was reported for TiO 2 , negligible degradation of PE was obtained under UV-A (365 nm) and visible illumination [ 20 ].…”