Continuous-flow photocatalytic treatment of pharmaceutical micropollutants: activity, inhibition, and deactivation of TiO2 photocatalysts in natural water matrices

photocatalyst;deactivation;inhibition;pharmaceuticals

Carbonaro, Sean ; Strathmann ; Timothy J.

关键词: photocatalyst;    deactivation;    inhibition;    pharmaceuticals;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/34476/Carbonaro_Sean.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Titanium dioxide (TiO2) photocatalysts have been shown to be effective at degrading a wide range of organic micropollutants under ideal laboratory solution conditions (e.g., deionized water). However, little research has been performed regarding photocatalyst performance in more complex matrices representative of contaminated water sources (e.g., wastewater effluent, groundwater). Here, a benchtop continuous-flow reactor was developed for the purpose of studying the activity, inhibition, and deactivation of immobilized TiO2 photocatalysts during water treatment applications. As a demonstration, degradation of four model pharmaceutical micropollutants (iopromide, acetaminophen, sulfamethoxazole, and carbamazepine) was monitored in both deionized water (DI), biologically treated wastewater effluent (WWE), and groundwater (GW) to study the effects of non-target constituents present in the latter matrix. Reactor performance was shown to be sufficiently stable over 7 days when treating micropollutants in DI. When reactor influent was switched WWE, photocatalytic degradation of individual micropollutants was inhibited to varying degrees, ranging from 42 to 86%. However, most of the catalyst activity was recovered upon switching back to the DI matrix after 4 d, suggesting mostly competitive inhibition of the photocatalysts by WWE matrix components (e.g., effluent organic matter scavenging of OH) rather than irreversible catalyst deactivation. Experiments conducted using pretreated WWE and synthetic WWE mimic solutions indicated that both organic and inorganic constituents in WWE contributed to the observed catalyst inhibition. Analysis of immobilized TiO2 thin films after 4 d of continuous treatment of the WWE matrix indicated minor deterioration of the porous thin film. Photocatalytic degradation rates of micropollutants displayed different trends on a GW-exposed photocatalyst. Easily oxidizable compounds (acetaminophen and sulfamethoxazole) were little affected by catalyst exposure to GW, while more recalcitrant compounds (iopromide and carbamazepine) were significantly inhibited. Significant calcium precipitation was found on the catalyst using SEM-EDS. Oxalic acid was found to be an effective rinsing solution of the catalyst. It is suspected that calcium, manganese, and iron are the primary groundwater constituents responsible for catalyst deactivation, but further tests are needed to confirm. Results demonstrate the marked influence of non-target constituents present in complex matrices on long-term catalyst activity and highlight the need for increased study of this important issue to further the development of practical photocatalytic water treatment technologies.