Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod Immobilized Ag 3 PO 4 photocatalyst for micro-pollutants removal in a continuous flow annular photoreactor Athanasia Petala ⁎ , Dimitra Spyrou, Zacharias Frontistis ⁎ , Dionissios Mantzavinos, Dimitris I. Kondarides Department of Chemical Engineering, University of Patras, Caratheodory 1, University Campus, GR-26504 Patras, Greece ARTICLE INFO Keywords: Silver phosphate Continuous flow reactor Long-term experiment Sulfamethoxazole Photocatalysis ABSTRACT The present work evaluates the efficiency of immobilized silver phosphate (Ag 3 PO 4 ) catalyst for the removal of emerging micro-pollutants under continuous flow conditions. The Ag 3 PO 4 nanoparticles were grown on TiO 2 pellets, which served as supporting material, and incorporated into an annular lab-made photoreactor operating in continuous mode. The photocatalyst was characterized by means of X-Ray diffraction (XRD) and scanning electron microscopy (SEM) acquiring data about its crystallographic structure and chemical composition at different times of irradiation. The activity of the present system was investigated for long-term operation for the destruction of 0.5 mg/L sulfamethoxazole (SMX) at a flow rate of 2 mL/min, which corresponds to a residence time of 11 min. The photocatalyst shows high removal efficiency (ca 75%) even after 74 h of operation. Consecutive experiments using the same photocatalyst were also carried out varying initial SMX concentration, residence time, type of micro-pollutants and the water matrix. SMX removal was found to increase decreasing flow rate in the range 4-1 mL/min and SMX concentration in the range 2-0.5 mg/L. Treatment efficiency in the case of different micro-pollutants like propylparaben and bisphenol A reached 60%, proving the wide-range applicability of Ag 3 PO 4 catalyst. Moreover, when the water matrix was switched from ultrapure water (UPW) to bottled water or UPW spiked with bicarbonate or chloride only a slight deterioration on SMX removal was recorded. However, the presence of humic acid in the water matrix was found to decrease the photocatalytic activity. 1. Introduction Despite the controversial opinions considering the low recorded efficiencies that hampers its practical application, photocatalysis holds a prominent position among advanced oxidation processes (AOPs), with the number of relevant publications remaining unabated [1,2]. This is due to the possibility of using solar light, thus leading to decontami- nation of waters and wastewaters using green energy. However, the development of an industrially attractive photocatalytic system for re- moving pathogens and pharmaceuticals from wastewaters, requires further research towards two directions: photocatalyst development and process optimization. It is well-known that despite the numerous advantages of TiO 2 as a photocatalyst, its wide band-gap restrains the amount of solar energy that can be exploited. Doping TiO 2 with metallic [3] or non-metallic [4] elements is the most-studied approach for improving its optical prop- erties. However, the increased response of doped TiO 2 photocatalysts to solar irradiation is not necessarily accompanied by a simultaneous improvement of their photocatalytic activity. This led a significant number of researchers towards the development of photocatalysts, other than TiO 2 , with inherent visible light absorption properties [5]. Among the visible light-responsive photocatalysts investigated so far, promising results have been obtained for bismuth vanadate (BiVO 4 ) [6], graphitic carbon nitride (g-C 3 N 4 )[7], red phosphorus [8] and silver orthophosphate (Ag 3 PO 4 )[9]. More precisely, BiVO 4 ’s suitable band gap (2.4–2.5 V) allows the production of electron-hole pairs through the absorption of visible light photons, making it a promising photo- catalytic material [10]. However, without either coupling it with other semiconductors or depositing on its surface metal nanoparticles its photocatalytic activity is low, due to the rapid recombination of photo- generated species [11]. Another noble-metal-free photocatalyst that has been extensively investigated in recent years is g-C 3 N 4 [12]. g-C 3 N 4 is a polymeric semiconductor material made up of abundant elements with a medium band gap equal to ∼ 2.7 eV. Due to its suitable position of conduction band (-1.2 V vs NHE), g-C 3 N 4 has shown sufficient H 2 evolution activity [13]. On the other hand, photogenerated holes have https://doi.org/10.1016/j.cattod.2018.10.062 Received 18 July 2018; Received in revised form 17 September 2018; Accepted 24 October 2018 ⁎ Corresponding authors. E-mail addresses: natpetala@chemeng.upatras.gr (A. Petala), zfrontistis@chemeng.upatras.gr (Z. Frontistis). Catalysis Today xxx (xxxx) xxx–xxx 0920-5861/ © 2018 Published by Elsevier B.V. Please cite this article as: Petala, A., Catalysis Today, https://doi.org/10.1016/j.cattod.2018.10.062