Photocatalytic behaviour of WO3/TiO2-N for diclofenac degradation using simulated solar radiation as an activation source

Abstract

In this study, the photocatalytic removal of an emerging contaminant, diclofenac (DCF) sodium, was performed using the nitrogen-doped WO/TiO-coupled oxide catalyst (WO/TiO-N). The catalyst synthesis was accomplished by a sol-gel method using tetrabutyl orthotitanate (CHOTi), ammonium p-tungstate [(NH)HWO·4HO] and ammonium nitrate (NHNO) as the nitrogen source. For comparison, TiO and WO/TiO were also prepared under similar conditions. Analysis by X-ray diffraction (XRD), N adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance UV-Vis spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS) were conducted to characterize the synthesized materials. The photocatalytic efficiency of the semiconductors was determined in a batch reactor irradiated with simulated solar light. Residual and mineralized DCF were quantified by high-performance liquid chromatography, total organic carbon analysis and ion exchange chromatography. The results indicated that the tungsten atoms were dispersed on the surface of TiO as WO. The partial substitution of oxygen by nitrogen atoms into the lattice of TiO was an important factor to improve the photocatalytic efficiency of WO/TiO. Therefore, the best photocatalytic activity was obtained with the WO/TiO-N catalyst, reaching 100% DCF transformation at 250 kJ m and complete mineralization at 400 kJ m of solar-accumulated energy.

Recent Achievements in Development of TiO2-Based Composite Photocatalytic Materials for Solar Driven Water Purification and Water Splitting

“…Subsequently, W 6+ traps photogenerated e − to form its reduced state W 5+ , while the redox reaction occurs further by returning to its original oxidation state in reaction with adsorbed O 2 on the composite catalyst surface (similarly as discussed above in the case of "pure" TiO 2 /WO 3 ), thus leading to improved charge separation and the formation of ROS, which contributed in DCF degradation and mineralization of formed intermediates. The same authors studied the degradation of DCF with another enhanced WO 3 /TiO 2 composite (N-doped TiO 2 ), and again reported high degradation and mineralization rates; 100% according to both indicators under 250 kJ/m 2 and 400 kJ/m 2 of solar-accumulated energy, respectively [31]. They stressed that the same mechanism that was responsible for the enhancement of photocatalyst activity in C-doped WO 3 /TiO 2 composite [32] also improved the performance of N-doped WO 3 /TiO 2 [31].…”

“…The same authors studied the degradation of DCF with another enhanced WO 3 /TiO 2 composite (N-doped TiO 2 ), and again reported high degradation and mineralization rates; 100% according to both indicators under 250 kJ/m 2 and 400 kJ/m 2 of solar-accumulated energy, respectively [31]. They stressed that the same mechanism that was responsible for the enhancement of photocatalyst activity in C-doped WO 3 /TiO 2 composite [32] also improved the performance of N-doped WO 3 /TiO 2 [31].…”

“…TiO 2 /WO 3 Tungsten oxide (WO 3 ), which is a visible light active photocatalyst with band gap of 2.4-2.8 eV, is a promising candidate for photocatalytic applications, due to its oxidative properties, nontoxicity, low cost, and stability in acidic solutions. In addition, WO 3 directly matches the band positions of TiO 2 to form a heterojunction (Type II Heterojunction) [29][30][31][32]. Several authors studied the application of TiO 2 /WO 3 composites for the degradation of various CECs; either pesticides or pharmaceuticals (Table 1).…”

Photocatalytic Degradation of Diclofenac Using Al2O3-Nd2O3 Binary Oxides Prepared by the Sol-Gel Method

“…Diclofenac is an anti-inflammatory drug used frequently by human beings which is discharged into the wastewater causing further pollution in different sources of drinking water [12][13][14], since it is very stable against the conventional treatments of water [15,16]. The persistence in ecosystems occurs due to the low biodegradability and this is also a reason for the incomplete removal in water treatments based on microbiological activity [14][15][16][17].…”

In-situ synthesis of mixed phase electrospun TiO2 nanofibers: a novel visible light photocatalyst

“…Therefore, there is a need for the development of visible light responsive photocatalyst. Recently many efforts have been taken to improve the visible light active photocatalytic properties of TiO 2 such as by doping with metals [10][11][12][13][14] and nonmetals [15][16][17][18], deposition of noble metals [19][20][21], surface fluorination [22] and controlling crystal facets [23], by creating heterojunction by coupling with other semiconductor materials having suitable band gap [24][25][26][27][28]. Design of nano structures having different morphologies like nanoflower [29], nanofibers [30], nanorod [31], coupling with carbanious materials like grapheme [32], carbon nanotube [33], and development of porous nanostructures [19] have also been proposed to increase visible light absorbance and to reduce the electron-hole pair recombination rate of TiO 2 .…”