Photocatalytic degradation of four non-steroidal anti-inflammatory drugs in water under visible light by P25-TiO2/tetraethyl orthosilicate film and determination via ultra performance liquid chromatography electrospray tandem mass spectrometry
Introduction
Pharmaceuticals and personal care products (PPCPs) concept was first proposed by Daughton [1] in 1999 and subsequently received wide attention as an emerging class of potentially harmful environmental pollutants. Non-steroidal anti-inflammatory drugs (NSAIDs) belong to PPCPs, which have been widely used for human and veterinary as antibacterial drugs [2]. These pharmaceuticals are excreted by animals and human beings, then released into the aquatic environment, and cause pollution of surface, ground and drinking water. A huge number of pharmaceutical contaminations in lakes, rivers and drinking water have been already detected [3], [4], [5]. Different treatment methods have been reported, such as coagulation–flocculation, biodegradation, biofiltration, ozonation, chemical precipitation and adsorption [6]. However, it is reported that these conventional treatment could only remove a part of PPCPs [7]. Failure to reduce pharmaceuticals in water treatment plants could enable these substances to contaminate aquatic environments. This fact has lead to the recent emergence of concern about the safety issue to drinking water, reclaimed and reused waste water, and aquatic ecosystems. Therefore PPCPs must be removed or degraded if we assure that they will not contaminate aquatic environment.
Fortunately, many innovative water treatment technologies have been raised recently, and “advanced oxidation processes (AOPs)” is one of them, for mineralization of refractory organic compounds [8], [9]. Among these AOPs, heterogeneous photocatalysis applying semiconductor catalysts (TiO2, ZnO, Fe2O3, and ZnS) has demonstrated its high efficiency in degrading a wide range of refractory organics into readily biodegradable compounds. Also, TiO2 as one of the most promising photocatalysts has attracted special attention because of its wide band gap, chemical and light stability and environment friendly, it is able to degrade organic pollutants into H2O and CO2 under UV light finally [10], [11].
However, the application of such TiO2 catalysts for water treatment experiences a series of technical challenges. The fine particle size of the TiO2, large surface area-to-volume ratio and surface energy creates a strong tendency for catalyst agglomeration and decrease the activities of TiO2 in the reaction system. Therefore, immobilization of TiO2 on various substrates, such as glass, quartz beads and glass fibers, has been a hot issue in recent years to assist the separation and recycling of the catalyst [12].
Moreover, low photocatalytic activity under visible light is still a major factor that obstructs TiO2 from large-scale applications [13], [14], many efforts have been devoted to overcome the obstructions. The development of visible light-induced photocatalytic materials has been achieved through the doping of transition metals, such as Cr, V, and Fe, or non-metals, such as C, N, and S, into TiO2 [15], [16]. Among them, non-metal doping of TiO2 has shown great promise in achieving visible light responsive photocatalysts. In recent years, it is found that the surface treatment of TiO2 with silica sources would achieve the enhancement of the photocatalytic activity [17], [18], [19]. Silica source is believed to benefit the dispersion of TiO2 nanoparticles and promote adsorbing organics and transfer them to active sites on TiO2 [20].
The main objective of this study is apply the technique of P25-TiO2/tetraethyl orthosilicate (TEOS) film on glazed ceramic surface to obtain an efficient and nontoxic degradation method of four NSAIDs. Salicylic acid, ibuprofen, naproxen and diclofenac were selected to represent NSAIDs because of their extensive usage. The structures of these four drugs are shown in Table 1. The influencing parameters and kinetics of degradation of four NSAIDs were investigated. Also, the degradation products and probable photocatalytic degradation pathway of naproxen were discussed. An UPLC–MS/MS analysis method was developed to support this study. The excellent photocatalytic activity of P25-TiO2/TEOS films shows application potential in degrading NSAIDs organic pollutants in water.
Section snippets
Materials and reagents
Degussa P25-TiO2 nanoparticles with an average particle size of 21 nm were purchased from Degussa Corporation Germany. Tetraethyl orthosilicate (TEOS, 98% Aldrich) was purchased from Sigma–Aldrich (United States). Ethanols, 4-hydroxy-4-methyl-2-pentanone (DAA) were analytical grade and purchased from Beijing Chemical Works. Salicylic acid and diclofenac sodium were purchased from The China drugs and Biological Products Inspection Institute. Naproxen was purchased from The Dr. Ehrenstorfer
Determination of four drugs in water samples
The specificity of the method was evaluated with analyzing spiked sample and blank sample. Fig. 2 is the chromatogram of spiked samples of salicylic acid (SAC), ibuprofen (IBU), naproxen (NAP) and diclofenac (DIC). The UPLC–MS/MS method using the MRM mode for determination of four drugs in water samples is rapid, sensitive, confirmed and specified.
A number of performance parameters such as linearity, limit of detection (LOD), limit of quantification (LOQ), were evaluated and results are shown
Conclusions
Photocatalytic degradation of four NSAIDs in water is investigated using a novel P25-TiO2/TEOS film under visible light irradiation. Influences of several parameters, such as adsorption, stir, initial pH, amount of P25-TiO2/TEOS and irradiation time of the photocatalytic process are performed. The degradation reached maximum and kept constant within 10 h of irradiation. The degradations of salicylic acid, ibuprofen, naproxen and diclofenac under optimum conditions are 76%, 85%, 94% and 65%,
Acknowledgement
This work was supported by the public welfare project of General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China (201110020).
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