Abstract
Acetaminophen (APAP), a non-steroidal anti-inflammatory drug, is the most commonly detected wastewater contaminant together with caffeine (CAF), that is used both in beverages and food but also in medicine. The presence of pharmaceuticals in the wastewater effluent have confirmed that nowadays existing wastewater treatment methods are not effective enough in pharmaceuticals removal. The aim of presented studies was the determination of the photocatalytic efficiency of TiO2 based nanocomposites in the removal of APAP and CAF from water under visible light irradiation. The process of photocatalytic removal of APAP from water in the presence of CAF was performed using TiO2-SiO2 photocatalysts containing multiwalled carbon nanotubes (MWCNT) characterized by high surface area (up to 420.8 ± 12.6 m2 g−1), narrow pore diameter (3–4 nm) and uniform anatase TiO2 crystallites (5–6 nm) with reduced band gap energy (up to 2.82 eV). The high resistance of CAF to photocatalytic decomposition under visible light irradiation was noted. Slight removal of CAF (29.4 ± 2.7%) was observed after 60 min of irradiation using nanocomposite with lowest MWCNT addition (0.15 wt%). The presence of CAF hindered APAP photocatalytic oxidation. CNT10, nanocomposite that was the most effective in APAP removal (81.6 ± 0.6%) enabled to remove APAP in the presence of CAF only by 48.0 ± 4.3% during visible light irradiation. The best results of APAP removal in the presence of CAF were obtained over CNT1 (47.6 ± 2.4%), that contained 0.15 wt% of MWCNT. The kinetics of APAP, CAF and APAP with CAF photocatalytic degradation and mineralization proceeded according to a pseudo-first-order reaction model and APAP kDOC was significantly reduced in the CAF presence (up to almost 4 times). The photocatalytic APAP removal in the presence of CAF over MWCNT-TiO2-SiO2 proceeded via photo generated holes and, in lower extend, OH radicals. Photocatalytically treated model water containing APAP and CAF revealed no toxicity to Vibrio fischeri.
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