Photocatalytic degradation of paracetamol on Pd-BiVO4 under visible light irradiation.

In this study, Pd-BiVO4 bearing highly dispersed Pd nanoparticles was prepared from pure BiVO4 using an impregnation method. The pure BiVO4 and Pd-BiVO4 catalysts were characterized by X-ray diffraction, scanning electron microscopy, UV-visible diffuse reflection, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results showed that the prepared catalysts had a monoclinic scheelite structure and exhibited a flake-like morphology. Pd-BiVO4 showed a distinct response in the visible light region, with an extended absorption edge at 550 nm. According to the Scherrer formula, the nanocrystal particle sizes of the BiVO4 and Pd-BiVO4 catalysts were 35 and 28 nm, respectively. Highly dispersed Pd nanoparticles with sizes of 2.5 ±â€¯0.5 nm were observed on the BiVO4 surface. Two Pd valence states, Pd(II) and Pd(0), were identified in a 2:1 ratio. Pd-BiVO4 exhibited excellent activity for paracetamol (PCT) degradation, with 100% removal achieved in 1 h under visible light irradiation. During degradation, the mineralization ratio reached up to 40% total organic carbon removal. Two highly active species, namely, hydroxyl and superoxide radicals, were determined by electron spin resonance (ESR). Furthermore, the potential degradation of PCT in this system was proposed based on intermediate information obtained using HPLC-MS and Gauss analysis. The high dispersion and small size of Pd nanoparticles might favor the removal of emerging contaminants using the Pd-BiVO4 photocatalytic system.

Influence of DOM components, salinity, pH, nitrate, and bicarbonate on the indirect photodegradation of acetaminophen in simulated coastal waters.

The indirect photodegradation behaviors of acetaminophen (APAP) were investigated in the presence of four kinds of dissolved organic matter (DOM) and were also assessed in the presence of seawater components and conditions such as salinity, pH, nitrate and bicarbonate. The results showed three important findings: firstly, in the indirect photolysis of APAP, the contributions of 3DOM*, ·OH and 1O2 were >85.0%, 2.3-9.9% and 0.8-2.6% at pH 8.0. Secondly, DOM was divided into four terrestrial humic-like components by Excitation-emission matrix spectroscopy (EEMs) combined with parallel factor analysis (PARAFAC). This study showed a good linearity between DOM fluorescence components and the indirect photodegradation of APAP (R2 = 0.92) and the differences in photodegradation rates of APAP among various DOM solutions were due to the diverse compositions of DOM. Finally, salinity was an important factor influencing the removal of APAP, and the APAP photodegradation rate constants increased from (3.33 ±â€¯0.07) × 10-5 s-1 to (1.25 ±â€¯0.05) × 10-4 s-1 with increasing salinity. The increased pseudo-first-order rate constants for photolysis of APAP with increasing salinity, pH and nitrate were attributed to the enhanced generation of reactive intermediates (RI) and easier reactions between RI and APAP. The increased APAP removal rate constant with increasing bicarbonate was likely ascribed to the yield of ∙CO3-. This is the first report of the roles of DOM components and salinity on the indirect photolysis of APAP. These findings would be essential to predict the photochemical fate of APAP and would also allow for a better understanding of the environmental fate of other phenolic contaminants.

Decomposition of acetaminophen in water by a gas phase dielectric barrier discharge plasma combined with TiO2-rGO nanocomposite: Mechanism and degradation pathway.

Acetaminophen (APAP) served as the model pollutant to evaluate the feasibility of pollutant removal by gas phase dielectric barrier discharge plasma combined with the titanium dioxide-reduced Graphene Oxide (TiO2-rGO) nanocomposite. TiO2-rGO nanocomposite was prepared using the modified hydrothermal method and characterized by TEM and XPS before and after plasma process. The results indicated that the APAP degradation efficiency was significantly improved to 92% after 18min of discharge plasma treatment coupling 0.25gL-1 TiO2-rGO 5%wt at 18kV, compared with the plasma alone and plasma combined with P25 TiO2. The degradation mechanism for APAP in this system was studied by investigating the effects of the operational variables (e.g. discharge voltage and pH value) and the amount of the generated active species; and the results showed that O3 and H2O2 yields were influenced notably by adding TiO2-rGO. Also, it was observed that, compared with unused TiO2-rGO, the photocatalytic performance of used TiO2-rGO declined after several recirculation times due to the further reduction of Graphene Oxide in plasma system. Finally, intermediate products were analyzed by UV-vis spectrometry and HPLC/MS, and possible transformation pathways were identified with the support of theoretically calculating the frontier electron density of APAP.

Enhanced photo-degradation of paracetamol on n-platinum-loaded TiO2: The effect of ultrasound and OH/hole scavengers.

Elimination/mineralization of paracetamol (PCT) was investigated by catalytic oxidation under ultrasound, UV and both. The catalyst was synthesized by immobilization of nPt on TiO2 to benefit from the ability of Pt to facilitate charge transfer processes and to separate e(-)/h(+) pairs. It was found that increasing the Pt-loading enhanced the rate of sonochemical reactions, but retarded that of photolytic reactions, due to reduced UV absorption on the surface. Simultaneous application of sonolysis and photolysis was synergistic due to disaggregation of the particles and homogenization of the active species over the catalyst surface. The decay of PCT was highly dependent on the availability of OH, as the reactions were nearly terminated in the presence of a strong OH scavenger-2-propanol. However, a remarkable rate enhancement was observed in the presence of a suitable dose of I(-), which scavenges both OH and hvb(+). The result was explained by the production of excess radicals upon sonolysis of iodide solutions, and the reactivity of PCT with them. Finally, carbon mineralization was significantly hindered in the presence of both scavengers due to increased competition for OH and inefficient formation of hydroquinone arising from reduced availability of hvb(+).

Mineralization of paracetamol in aqueous solution with advanced oxidation processes.

Paracetamol is a common analgesic drug widely used in all regions of the world more than hundred tonnes per year and it poses a great problem for the aquatic environment. Its phenolic intermediates are classified as persistent organic pollutants and toxic for the environment as well as human beings. In the present study, the irradiation of aqueous solutions of paracetamol with 60Co gamma-rays was examined on a laboratory scale and its degradation path was suggested with detected radiolysis products. The synergic effect of ozone on gamma-irradiation was investigated by preliminary ozonation before irradiation which reduced the irradiation dose from 5 to 3 kGy to completely remove paracetamol and its toxic intermediate hydroquinone from 6 to 4 kGy as well as increasing the radiation chemical yield (Gi values 1.36 and 1.66 in the absence and presence of ozone, respectively). The observed amount of formed hydroquinone was also decreased in the presence of ozone. There is a decrease in pH from 6.4 to 5.2 and dissolved oxygen consumed, which is up to 0.8 mg l(-1), to form some peroxyl radicals used for oxidation. Analytical measurements were carried out with gas chromatography/mass spectrometry and ion chromatography (IC) both qualitatively and quantitatively. Amounts of paracetamol and hydroquinone were measured with gas chromatography after trimethylsilane derivatization. Small aliphatic acids, such as acetic acid, formic acid and oxalic acid, were measured quantitatively with IC as well as inorganic ions (nitrite and nitrate) in which their yields increase with irradiation.

UV-induced photocatalytic degradation of aqueous acetaminophen: the role of adsorption and reaction kinetics.

Nanostructured titania supported on activated carbon (AC), termed as integrated photocatalytic adsorbents (IPCAs), were prepared by ultrasonication and investigated for the photocatalytic degradation of acetaminophen (AMP), a common analgesic and antipyretic drug. The IPCAs showed high affinity towards AMP (in dark adsorption studies), with the amount adsorbed proportional to the TiO2 content; the highest adsorption was at 10 wt% TiO2. Equilibrium isotherm studies showed that the adsorption followed the Langmuir model, indicating the dependence of the reaction on an initial adsorption step, with maximum adsorption capacity of 28.4 mg/g for 10 % TiO2 IPCA. The effects of initial pH, catalyst amount and initial AMP concentration on the photocatalytic degradation rates were studied. Generally, the AMP photodegradation activity of the IPCAs was better than that of bare TiO2. Kinetic studies on the photocatalytic degradation of AMP under UV suggest that the degradation followed Langmuir-Hinshelwood (L-H) kinetics, with an adsorption rate constant (K) that was considerably higher than the photocatalytic rate constant (k r), indicating that the photocatalysis of AMP is the rate-determining step during the adsorption/photocatalysis process.

Photonic efficiency of the photodegradation of paracetamol in water by the photo-Fenton process.

An experimental study of the homogeneous Fenton and photo-Fenton degradation of 4-amidophenol (paracetamol, PCT) is presented. For all the operation conditions evaluated, PCT degradation is efficiently attained by both Fenton and photo-Fenton processes. Also, photonic efficiencies of PCT degradation and mineralization are determined under different experimental conditions, characterizing the influence of hydrogen peroxide (H2O2) and Fe(II) on both contaminant degradation and sample mineralization. The maximum photonic degradation efficiencies for 5 and 10 mg L(-1) Fe(II) were 3.9 (H2O2 = 189 mg L(-1)) and 5 (H2O2 = 378 mg L(-1)), respectively. For higher concentrations of oxidant, H2O2 acts as a "scavenger" radical, competing in pollutant degradation and reducing the reaction rate. Moreover, in order to quantify the consumption of the oxidizing agent, the specific consumption of the hydrogen peroxide was also evaluated. For all operating conditions of both hydrogen peroxide and Fe(II) concentration, the consumption values obtained for Fenton process were always higher than the corresponding values observed for photo-Fenton. This implies a less efficient use of the oxidizing agent for dark conditions.

Ultrasonic degradation of acetaminophen in water: effect of sonochemical parameters and water matrix.

This paper deals about the sonochemical water treatment of acetaminophen (ACP, N-acetyl-p-aminophenol or paracetamol), one of the most popular pharmaceutical compounds found in natural and drinking waters. Effect of ultrasonic power (20-60 W), initial ACP concentration (33-1323 µmol L(-1)) and pH (3-12) were evaluated. High ultrasonic powers and, low and natural acidic pH values favored the efficiency of the treatment. Effect of initial substrate concentration showed that the Langmuir-type kinetic model fit well the ACP sonochemical degradation. The influence of organic compounds in the water matrix, at concentrations 10-fold higher than ACP, was also evaluated. The results indicated that only organic compounds having a higher value of the Henry's law constant than the substrate decrease the efficiency of the treatment. On the other hand, ACP degradation in mineral natural water showed to be strongly dependent of the initial substrate concentration. A positive matrix effect was observed at low ACP concentrations (1.65 µmol L(-1)), which was attributed to the presence of bicarbonate ion in solution. However, at relative high ACP concentrations a detrimental effect of matrix components was noticed. Finally, the results indicated that ultrasonic action is able to transform ACP in aliphatic organic compounds that could be subsequently eliminated in a biological system.

Synthesis of metabolites of paracetamol and cocaine via photooxidation on TiO2 catalyzed by UV light.

Prediction and synthesis of drug metabolites generated by photodegradation using TiO(2)/UV system in aqueous solution was performed to monitor illicit drugs and to support legal actions against drug dealers. Metabolism of paracetamol and cocaine applied as exemplary compounds was monitored by liquid chromatography mass spectrometry (LC-MS/MS) and direct analysis by electrospray ionization mass spectrometry (ESI-MS/MS). The experiments proved that simulated metabolic pathways of the drug samples are efficient and lead to the formation of products that are observed using living organisms or hepatocyte microsomal preparations. Routinely, TiO(2) nanopowders are used for complete degradation of unwanted waste to protect environment. We applied such system for prediction of potential metabolites of harmful substances, such as cocaine. The results demonstrate that TiO(2)/UV oxidative system can be an efficient, complementary method to the in vivo approaches to obtain important metabolites for further studies. Investigations using such methodology may be helpful for toxicologists providing a vital knowledge on metabolites derived from e.g. newly introduced cognitive enhancers (designer drugs), and home-made substances prepared from the over-the-counter tablets (legal highs).

Photocatalytic degradation of paracetamol: intermediates and total reaction mechanism.

The advanced oxidation of paracetamol (PAM) promoted by TiO(2)/UV system in aqueous medium was investigated. Monitoring this reaction by HPLC and TOC, it was demonstrated that while oxidation of paracetamol is quite efficient under these conditions, its mineralization is not complete. HPLC indicated the formation of hydroquinone, benzoquinone, p-aminophenol and p-nitrophenol in the reaction mixtures. Further evidence of p-nitrophenol formation was obtained following the reaction by UV-vis spectroscopy. Continuous monitoring by IR spectroscopy demonstrated the breaking of the aromatic amide present in PAM and subsequent formation of several aromatic intermediate compounds such as p-aminophenol and p-nitrophenol. These aromatic compounds were eventually converted into trans-unsaturated carboxylic acids. Based on these experimental results, an alternative deacylation mechanism for the photocatalytic oxidation of paracetamol is proposed. Our studies also demonstrated IR spectroscopy to be a useful technique to investigate oxidative mechanisms of pharmaceutical compounds.

Automatic dosage of hydrogen peroxide in solar photo-Fenton plants: development of a control strategy for efficiency enhancement.

The solar photo-Fenton process is widely used for the elimination of pollutants in aqueous effluent and, as such, is amply cited in the literature. In this process, hydrogen peroxide represents the highest operational cost. Up until now, manual dosing of H(2)O(2) has led to low process performance. Consequently, there is a need to automate the hydrogen peroxide dosage for use in industrial applications. As it has been demonstrated that a relationship exists between dissolved oxygen (DO) concentration and hydrogen peroxide consumption, DO can be used as a variable in optimising the hydrogen peroxide dosage. For this purpose, a model was experimentally obtained linking the dynamic behaviour of DO to hydrogen peroxide consumption. Following this, a control system was developed based on this model. This control system - a proportional and integral controller (PI) with an anti-windup mechanism - has been tested experimentally. The assays were carried out in a pilot plant under sunlight conditions and with paracetamol used as the model pollutant. In comparison with non-assisted addition methods (a sole initial or continuous addition), a decrease of 50% in hydrogen peroxide consumption was achieved when the automatic controller was used, driving an economic saving and an improvement in process efficiency.

Aquatic photochemistry of paracetamol in the presence of dissolved organic chromophoric material and nitrate.

PURPOSE: This study contains some new findings connected to the photolysis of the drug paracetamol (hereinafter APAP) especially in light of estimating natural conditions, and it will offer information to better evaluate environmental problems connected with this widely used analgesic agent. Only a few studies, so far, have focussed on the photodegradation process of APAP in the natural environment, and the question about the role of the colored/chromophoric dissolved organic matter (CDOM) and nitrate (NO3-) as photoinductors is almost open. METHODS: APAP dissolved in freshwater and pure laboratory water in the presence and absence of CDOM and NO3- ions was irradiated using weak-energy photon energies simulating natural conditions. RESULTS: CDOM and NO3- as photoinductors produced only the slow phototransformation of APAP under weak energy radiation, and APAP seemed to be practically resistant to direct photolysis under weak radiant energies available in natural conditions. The estimated reaction efficiencies, in addition to half-lives, speak for that NO3- and CDOM do not act as quite independent photoinductors but their effect in conjunction (CDOM-NO3- -water) is stronger than the separate ones. The principal phototransformation intermediates of APAP were mono-hydroxy derivatives, depending on available photon energies formed via ortho- or meta-hydroxylation, possessing substantial power of resistance to further specific transformation reactions. CONCLUSIONS: The estimated half-life of the phototransformation of APAP in the natural aqueous environment and in the presence of suitable photoinductors will be about 30 days or more.

[Physico-chemical stability and sterility of non-opioid analgesics in solution]. / Stabilité physicochimique et bactériologique d'associations d'antalgiques de classe I en solution.

OBJECTIVES: The combination of non-opioid analgesic drugs (P: paracetamol, K: ketoprofen and N: nefopam) is currently recommended for postoperative pain control. In practice, these analgesics are often administered in the same solution. We investigated the chemical stability and sterility of three mixtures of analgesics (P+K, P+N and K+N). METHODS: For each mixture, concentrations of active principles were measured using high-performance liquid chromatography over 24 hours. These mixtures were cultured for microbiological colonization. RESULTS: Our study demonstrated chemical and bacteriologic stability of these three mixtures over a 24-hour period. The results allow the use of P+K, P+N and K+N in the same ready to use solution.

[Photodegradation of paracetamol in nitrate solution].

The photodegradation of paracetamol in nitrate solutions in the range of environmental concentration was studied using mercury lamp with middle pressure as simulated solar source. Experiments were carried out to study the influences of pH value, nitrate concentration and the substances such as humic substance, bicarbonate, which are popular in natural water, on the photodegradation of paracetamol in nitrate solutions. The results demonstrate that the photodegradation of paracetamol follows a pseudo-first-order kinetics and the photodegradation rate increases rapidly with increasing initial concentration of nitrate. The first order constant increases with the increase of pH and the concentration of bicarbonate. When SRFA concentration is more than 10 mg/L, the presence of SRFA stimulates the photodegradation of paracetamol. The addition of NOHA decreases the photodegradation rate of paracetamol. Hydroxyl radical is found in the reaction solutions using methanol and isopropanol as its molecular probes. We identified the photodegradation products of paracetamol in the presence of nitrate with GC/MS methods. The photodegradation pathways of paracetamol are also discussed.

Advanced oxidation chemistry of paracetamol. UV/H(2)O(2)-induced hydroxylation/degradation pathways and (15)N-aided inventory of nitrogenous breakdown products.

The advanced oxidation chemistry of the antipyretic drug paracetamol (1) with the UV/H(2)O(2) system was investigated by an integrated methodology based on (15)N-labeling and GC-MS, HPLC, and 2D (1)H, (13)C, and (15)N NMR analysis. Main degradation pathways derived from three hydroxylation steps, leading to 1,4-hydroquinone/1,4-benzoquinone, 4-acetylaminocatechol and, to a much lesser extent, 4-acetylaminoresorcine. Oxidation of the primary aromatic intermediates, viz. 4-acetylaminocatechol, 1,4-hydroquinone, 1,4-benzoquinone, and 1,2,4-benzenetriol, resulted in a series of nitrogenous and non-nitrogenous degradation products. The former included N-acetylglyoxylamide, acetylaminomalonic acid, acetylaminohydroxymalonic acid, acetylaminomaleic acid, diastereoisomeric 2-acetylamino-3-hydroxybutanedioic acids, 2-acetylaminobutenedioic acid, 3-acetylamino-4-hydroxy-2-pentenedioic acid, and 2,4-dihydroxy-3-acetylamino-2-pentenedioic acid, as well as two muconic and hydroxymuconic acid derivatives. (15)N NMR spectra revealed the accumulation since the early stages of substantial amounts of acetamide and oxalic acid monoamide. These results provide the first insight into the advanced oxidation chemistry of a 4-aminophenol derivative by the UV/H(2)O(2) system, and highlight the investigative potential of integrated GC-MS/NMR methodologies based on (15)N-labeling to track degradation pathways of nitrogenous species.