Photocatalytic degradation of β-blockers in TiO2 with metoprolol as model compound. Intermediates and total reaction mechanism

Photocatalytic Degradation of Naproxen: Intermediates and Total Reaction Mechanism

Photochemical and photocatalytic oxidation of naproxen (NPX) with UV-A light and commercial TiO2 under constant flow of oxygen have been investigated. Adsorption experiments indicated that 90% of the solute remained in the solution. Combined chemical analysis of samples on the photochemical degradation indicated that NPX in an aqueous solution (20 ppm) is efficiently transformed into other species but only 18% of the reactant is mineralized into CO2 and water after three hours of reaction. Performing the photocatalytic oxidation in the presence of TiO2, more than 80% of the organic compounds are mineralized by reactive oxidation species (ROS) within four hours of reaction. Analysis of reaction mixtures by a combination of analytical techniques indicated that naproxen is transformed into several aromatic naphthalene derivatives. These latter compounds are eventually transformed into polyhydroxylated aromatic compounds that are strongly adsorbed onto the TiO2 surface and are quickly oxidized into low-molecular-weight acids by an electron transfer mechanism. Based on this and previous studies on NPX photocatalytic oxidation, a unified and complete degradation mechanism is presented.

The Visible-Light-Driven Activity of Biochar-Doped TiO2 Photocatalysts in β-Blockers Removal from Water

Water is the most important life-giving resource on earth. Nowadays, intensive growth of the world population has resulted in increased water consumption and the production of wastewater. Additionally, the presence of pharmaceuticals in treated conventional wastewater or even in the environment is strictly indicating that present techniques of wastewater treatment are not efficient enough and are not designed to remove such pollutants. Scarce water resources in the world are the main driving force for the innovation of novel techniques of water and wastewater treatment. Photocatalysis, as one of the advanced oxidation processes, enables the transformation of recalcitrant and toxic pollutants into CO₂, water, and inorganic salts. In the present paper, the photocatalytic oxidation of β-blockers-metoprolol and propranolol-are described. For photocatalytic oxidation, novel TiO₂ photocatalysts modified with biochar were used. Photocatalysts were prepared by sol-gel method and the effect of photocatalysts type, presence of inorganic ions, dissolved organic matter, and different water matrix was established. The results indicate that using only the decrease in the tested pollutant concentration is not effective enough in establishing the treatment method's safety. There is a need to use additional testing such as ecotoxicity tests; however, the key parameter is the properly chosen tested organism.

A novel Sm doped Cr2O3 sesquioxide-decorated MWCNTs heterostructured Fenton-like with sonophotocatalytic activities under visible light irradiation

Novel Sm doped Cr₂O₃ decorated MWCNTs nanocomposite photocatalyst was successfully prepared by a facile hydrothermal method for metoprolol (MET) degradation. A heterogeneous photo -Fenton like system was formed with the addition of H₂O₂ for ultrasonic irradiation (US), visible light irradiation (Vis) and dual irradiation (US/Vis) systems. The intrinsic characteristics of Sm doped Cr₂O₃ decorated MWCNTs nanocomposite was comprehensively performed using state-of-art characterization tools. Optical studies confirmed that Sm doping shifted the absorbance of Cr₂O₃ towards the visible-light region, further enhanced by MWCNTs incorporation. In this study, degradation of metoprolol (MET) was investigated in the presence of Cr₂O₃ nanoparticles, Sm doped Cr₂O₃ and Sm doped Cr₂O₃ decorated MWCNTs nanocomposites using sonocatalysis and photocatalysis and simultaneously. Several different experimental parameters, including irradiation time, H₂O₂ concentration, catalyst amount, initial concentration, and pH value, were optimized. The remarkably enhanced sonophotocatalytic activity of Sm doped Cr₂O₃ decorated MWCNTs could be attributed to the more formation of reactive radicals and the excellent electronical property of Sm doping and MWCNTs. The rate constant of degradation using sonophotocatalytic system was even higher than the sum of rates of individual systems due to its synergistic performance based on the kinetic data. A plausible mechanism for the degradation of MET over Sm-Cr₂O₃/MWCNTs is also demonstrated by using active species scavenger studies and EPR spectroscopy. Our findings imply that (^•OH), (h⁺) and (^•O₂^-) were the reactive species responsible for the degradation of MET based on the special three-way Fenton-like mechanism and the dissociation of H₂O₂. The durability and stability of the nanocomposite were also performed, and the obtained results revealed that the catalysts can endure the harsh sonophotocatalytic conditions even after fifth cycles. Mineralization experiments using the optimized parameters were evaluated as well. The kinetics and the reaction mechanism with the possible reasons for the synergistic effect were presented. Identification of degraded intermediates also investigated.

Evaluation of advanced oxidation processes for β-blockers degradation: a review

This study summarizes the results of scientific investigations on the removal of the three most often used β-blockers (atenolol, metoprolol and propranolol) by various advanced oxidation processes (AOP). The free radical chemistry, rate constants, degradation mechanism and elimination effectiveness of these compounds are discussed together with the technical details of experiments. In most AOP the degradation is predominantly initiated by hydroxyl radicals. In sulfate radical anion-based oxidation processes (SROP) both hydroxyl radicals and sulfate radical anions greatly contribute to the degradation. The rate constants of reactions with these two radicals are in the 10⁹-10¹⁰ M^-1 s^-1 range. The degradation products reflect ipso attack, hydroxylation on the aromatic ring and/or the amino moiety and cleavage of the side chain. Among AOP, photocatalysis and SROP are the most effective for degradation of the three β-blockers. The operating parameters have to be optimized to the most suitable effectiveness.

Effective photocatalytic removal of selected pharmaceuticals and personal care products by elsmoreite/tungsten oxide@ZnS photocatalyst

In this study, elsmoreite/tungsten oxide is used to form a heterojunction with ZnS-containing industrial waste. The effect of the elsmoreite/tungsten oxide content on photocatalytic activity of ZnS using the different ratios of ZnS:Na₂WO₄ in the synthesis solution is estimated. The initial ZnS:Na₂WO₄ ratio leads to the formation of hexagonal WO₃∙0.33H₂O on the surface of ZnS. A further increase in the ZnS:Na₂WO₄ ratio results in the domination of cubic WO₃∙0.5H₂O over hexagonal WO₃. The ultraviolet-visible (UV-Vis) diffuse reflectance spectra of elsmoreite/tungsten oxide@ZnS composite photocatalysts show that the absorption onset shifts monotonously towards lower wavelengths from 450 nm to 400 nm. The microrods of hexagonal WO₃ and {111}-truncated submicron-sized crystals of WO₃∙0.5H₂O are grown on the ZnS surface. The transmission electron microscopy (TEM) results confirm the formation of a heterojunction between elsmoreite/tungsten oxide and ZnS. The photocatalytic activities of elsmoreite/tungsten oxide@ZnS composite photocatalysts are evaluated for the degradation of selected pharmaceuticals and personal care products (PPCPs): metoprolol - Mt, triclosan - TCS, and caffeine - CAF both in single and in mixture solutions. The elsmoreite/tungsten oxide@ZnS photocatalysts degrade 50% of Mt, 70% TCS, and 60% CAF in single solution and 35% of Mt, 20% of CAF, and 20% of TCS in mixture solution. Hydrated Mt and TCS are preferably adsorbed on the surface of WO₃∙0.5H₂O (111), and CAF has better affinity to the surface of WO₃. The elsmoreite/tungsten oxide@ZnS photocatalysts show a good reusability. Hydroxyl radicals (^•OH) and photogenerated holes (h⁺) are involved in the photocatalytic removal of Mt, while only h⁺ is involved in the photocatalytic removal of TCS. Interestingly, none of the above-mentioned species is involved in the photocatalytic removal of CAF. Also, nontoxic CAF is mainly degraded into intermediates with higher toxicity. The toxicity of the photocatalytically treated model wastewater in the mixture solution, tested with Vibrio fischeri, is much lower than that in the single solution.

Persulfate activation by nano zero-valent iron for the degradation of metoprolol in water: influencing factors, degradation pathways and toxicity analysis

In this study, nano zero-valent iron (nZVI) was utilized to activate persulfate (PS) for the degradation of metoprolol (MTP), a commonly used drug for curing cardiovascular diseases, in water. Quenching tests indicated that both the sulfate radical (SO₄˙⁻) and hydroxyl radical (˙OH) contributed to the degradation of MTP, while SO₄˙⁻ seemed to play a large role under natural pH conditions. Batch tests were conducted to investigate the effects of several influencing factors, such as PS concentration, initial MTP concentration, pH, temperature and common anions, on the degradation performance of MTP. Generally, lower MTP concentration and pH values, and higher PS concentration and temperature favoured MTP degradation. HCO₃⁻, NO₃⁻ and SO₄²⁻ were found to inhibit MTP degradation, while Cl⁻ enhanced MTP degradation. Several corrosion products of nZVI, including Fe₃O₄, Fe₂O₃ and FeSO₄, were formed during the reaction, which was reflected by the combined XRD and XPS analysis. Degradation pathways of MTP were proposed according to the identified transformation products, and the peak areas of the major products along with the time were also monitored. Finally, the toxicity of the reaction solution was assessed by experiments using Aliivibrio fischeri. Overall, it could be concluded that nZVI/PS might be a promising method for the rapid treatment of MTP-caused water pollution.

The influencing factors, mechanism and toxicity of MTP degradation by nZVI activated persulfate were investigated.

The single/co-adsorption characteristics and microscopic adsorption mechanism of biochar-montmorillonite composite adsorbent for pharmaceutical emerging organic contaminant atenolol and lead ions

An eco-friendly corncob biochar based montmorillonite composite (Cc-Mt) was synthesized for the single adsorption and co-adsorption of lead (Pb(II)) and a pharmaceutical emerging organic contaminant Atenolol (ATE). In single adsorption system, the maximum equilibrium capacity of Cc-Mt for Pb (II) and ATE were 139.78 mg g^-1 and 86.86 mg g^-1, respectively, but for montmorillonite just 98.69 mg g^-1 and 69.68 mg g^-1, for corncob biochar just 117.54 mg g^-1 and 47.29 mg g^-1. Meanwhile,co-adsorption properties of ATE and Pb(II) on Cc-Mt composite were performed and found that the influence of ATE on the adsorption of Pb(II) was greater than the effect of Pb(II) on that of ATE. Moreover, Multiwfn program based on quantum chemical calculation was used to quantitatively analyze electrostatic potential (ESP) distribution, average local ionization energy (ALIE) distribution and their minimum points on neutral ATE and protonated ATE (PATE) molecules to reveal the microscopic adsorption mechanism of Cc-Mt composite to ATE, the results showed that the amino N and amide oxygen atom were easier to provide lone pair of electrons, generating hydrogen bonds or strong electrostatic interactions with functional groups on the surface of Cc-Mt, meanwhile hydroxyl O atom was also a possible reaction site. For PATE molecules, only the oxygen atom of the amide group was the most likely reactive site.

Insights into the isotherm and kinetic models for the coadsorption of pharmaceuticals in the absence and presence of metal ions: A review

Pharmaceuticals are a wide class of emerging pollutants due to their continuous and the increasing consumption of users. These pollutants are usually found in the real environment as mixtures alone or with metal ions. Thus, the migration risk increases, which complicates the removal of pharmaceuticals because of the combined and synergistic effects. The focus of treatment of pharmaceutical mixtures and their coexistence with metals is of considerable importance. For this purpose, adsorption has been efficiently applied to several studies for the treatment of such complex systems. In this article, the coadsorption behavior of pharmaceuticals in the absence and existence of metals on several adsorbents has been reviewed. The adsorption isotherms and kinetics of these two systems have been analyzed using different models and discussed. Important challenges and promising routes are suggested for the future development of the coadsorption of the studied systems. This article provides an overview on the most utilized and effective adsorbents, widely studied adsorbates, best applied isotherm and kinetic models, and competitive effect in coadsorption of pharmaceuticals, both with and without metals.