Photocatalytic degradation of trace carbamazepine in river water under solar irradiation

Carbamazepine Removal by Clay-Based Materials Using Adsorption and Photodegradation

Carbamazepine (CBZ) is one of the most common emerging contaminants released to the aquatic environment through domestic and pharmaceutical wastewater. Due to its high persistence through conventional degradation treatments, CBZ is considered a typical indicator for anthropogenic activities. This study tested the removal of CBZ through two different clay-based purification techniques: adsorption of relatively large concentrations (20–500 μmol L−1) and photocatalysis of lower concentrations (<20 μmol L−1). The sorption mechanism was examined by FTIR measurements, exchangeable cations released, and colloidal charge of the adsorbing clay materials. Photocatalysis was performed in batch experiments under various conditions. Despite the neutral charge of carbamazepine, the highest adsorption was observed on negatively charged montmorillonite-based clays. Desorption tests indicate that adsorbed CBZ is not released by washing. The adsorption/desorption processes were confirmed by ATR-FTIR analysis of the clay-CBZ particles. A combination of synthetic montmorillonite or hectorite with low H2O2 concentrations under UVC irradiation exhibits efficient homo-heterogeneous photodegradation at μM CBZ levels. The two techniques presented in this study suggest solutions for both industrial and municipal wastewater, possibly enabling water reuse.

Peroxyl radicals from diketones enhanced the indirect photochemical transformation of carbamazepine: Kinetics, mechanisms, and products

In surface waters, photogenerated transients (e.g., hydroxyl radicals, carbonate radicals, singlet oxygen and the triplet states of dissolved organic matter) are known to play a role in the transformation of biorecalcitrant carbamazepine (CBZ). Small diketones, such as acetylacetone (AcAc) and butanedione (BD), are naturally abundant and have been proven to be effective precursors of carbon and oxygen centered radicals. However, the photochemical kinetics and mechanisms of coexisting diketones and CBZ are barely known. Herein, the effects of AcAc and BD on the photochemical conversion of CBZ were investigated compared with H₂O₂ which was the main ·OH precursor in the environment. An enhancing effect was observed for the degradation of CBZ by the addition of diketones. The enhancing effect of diketones was pH-dependent and much more significant than H₂O₂ under simulated solar irradiation. On the basis of the identification of transient species and the competition kinetic model, organic peroxyl radicals were found to play a dominant role in CBZ photodegradation, and the second-order rate constants of the reaction between CBZ and peroxyl radicals were determined to be approximately 10⁷-10⁸ M^-1s^-1. Furthermore, mutagenic acridine was found to be the major cumulative intermediate with a yield of > 30% in the presence of diketones, which might be an environmental concern. This work indicates that the coexistence of diketones and persistent organic pollutants might lead to some detrimental effects on aquatic environments if the water is exposed to sunlight.

Postflood Monitoring in a Subtropical Estuary and Benchmarking with PFASs Allows Measurement of Chemical Persistence on the Scale of Months

Measurements of chemical persistence in natural environments can provide insight into behavior not easily replicated in laboratory studies. However, it is difficult to find environmental situations suitable for such measurements, particularly for substances with half-lives exceeding several weeks. The objective of this study was to demonstrate that a strategic postflood monitoring campaign can be used to quantify transformation half-lives on the scale of months in a real aquatic system. Water samples were collected in the upper Brisbane River estuary on 36 occasions over 37 weeks and analyzed for 127 pharmaceuticals and personal care products (PPCPs), pesticides, and perfluoroalkyl substances (PFASs). High quality time trend data were obtained for 41 substances. For many of these, data on the input of a wastewater treatment plant to the upper estuary were also obtained. A mass balance model of the estuary stretch was formulated and parametrized using PFASs as persistent benchmarking chemicals. Transformation half-life estimates were obtained for 10 PPCPs and 7 pesticides ranging from 18 to 260 days. Furthermore, insight was obtained into dominant transformation processes as well as the magnitude of chemical inputs to the estuary and their sources. The approach developed shows that under certain conditions, estuaries can be used to quantify the persistence of organic contaminants with half-lives of the order of several months.

Synergistic effect of sonication on photocatalytic oxidation of pharmaceutical drug carbamazepine

Photocatalytic, sono-photocatalytic oxidation of pharmaceutical drug of carbamazepine was successfully carried out using Ag/AgCl supported BiVO4 catalyst. For this purpose, firstly, photocatalytic oxidation was optimized by central composite design methodology and then synergistic effect of sonication was investigated. Low frequency (20 kHz) probe type and high frequency (850 kHz) plate type sonication at pulse and continuous mode were studied to degrade the carbamazepine (CBZ) containing wastewater. Pulse duties of 1:5 and 5:1 (on : off) were tested using the high frequency sonication system in the sono-photocatalytic oxidation of CBZ. The effects of frequency, power density measured from calorimetry by changing amplitudes were discussed in the sono-photocatalytic oxidation of CBZ. Complete carbamazepine removal was achieved at the optimum conditions of 5 ppm CBZ initial concentration with 1.5 g/L of catalysts loading and at an alkaline pH of 10 at the end of 4 h of photocatalytic reaction under visible LED light irradiation. Both low frequency and high frequency sonication systems caused an increase in photocatalytic efficiency in a shorter treatment time of 60 min. CBZ removal increased from 44% to 65.42% in low frequency sonication of 20 kHz at the amplitude of 20% (0.15 W/mL power density). In the case of high frequency ultrasonic system (850 kHz), CBZ removal increased significantly from 44% to 89.5 % at 75% amplitude (0.12 W/mL power density) within 60 min of reaction. Continuous mode sonication was observed to be more effective than that of pulse mode sonication not only for degradation efficiency and also for electrical energy consumption needed to degrade CBZ. Sono-catalytic oxidation was also conducted with simulated wastewater that contains SO42-, CO32-, NO3-, Cl- anions and natural organic component of fulvic acid. The CBZ degradation was inhibited slightly in the presence of NO3- and Cl-, and fulvic acid, however, the existence of SO42- and CO32- increased the degradation degree of CBZ. Toxicity tests were performed to determine the toxicity of untreated CBZ, and treated CBZ by photocatalytic, and sono-photocatalytic oxidations.

ZnIn2 S4 -Based Photocatalysts for Energy and Environmental Applications

As a fascinating visible-light-responsive photocatalyst, zinc indium sulfide (ZnIn₂ S₄ ) has attracted extensive interdisciplinary interest and is expected to become a new research hotspot in the near future, due to its nontoxicity, suitable band gap, high physicochemical stability and durability, ease of synthesis, and appealing catalytic activity. This review provides an overview on the recent advances in ZnIn₂ S₄ -based photocatalysts. First, the crystal structures and band structures of ZnIn₂ S₄ are briefly introduced. Then, various modulation strategies of ZnIn₂ S₄ are outlined for better photocatalytic performance, which includes morphology and structure engineering, vacancy engineering, doping engineering, hydrogenation engineering, and the construction of ZnIn₂ S₄ -based composites. Thereafter, the potential applications in the energy and environmental area of ZnIn₂ S₄ -based photocatalysts are summarized. Finally, some personal perspectives about the promises and prospects of this emerging material are provided.

In situ construction of Z-scheme FeS2/Fe2O3 photocatalyst via structural transformation of pyrite for photocatalytic degradation of carbamazepine and the synergistic reduction of Cr(VI)

Pyrite is the most abundant sulfide semiconductor mineral with excellent optical properties. However, few reports have investigated its photocatalytic activity because of the low photogenerated carrier separation efficiency. In this work, a Z-scheme FeS₂/Fe₂O₃ composite photocatalyst was fabricated in situ via structural transformation of pyrite through heat treatment. A remarkably enhanced photocatalytic performance was observed over the FeS₂/Fe₂O₃ composite photocatalyst. Compared with the pristine pyrite, the degradation efficiency of carbamazepine (CBZ) reached 65% at the added hexavalent chromium (Cr(Ⅵ)) concentration of 20 mg/L and the Cr(Ⅵ) was nearly completely reduced in the mixed system using FeS₂/Fe₂O₃ within 30 min under simulated solar light irradiation. The enhanced photocatalytic activity can be attributed to the efficient separation and transfer of photogenerated carriers in the FeS₂/Fe₂O₃ composite photocatalyst. This facilitated the generation of •OH, hole (h⁺) and •O₂^- species, which participated in the photocatalytic reaction with CBZ. Based on the measurement of the active species and electric properties, a Z-scheme electron transfer pathway was proposed for the FeS₂/Fe₂O₃ composite photocatalyst. This work broadens the application potential of pyrite in environmental remediation.

TBAOH assisted synthesis of ultrathin BiOCl nanosheets with enhanced charge separation efficiency for superior photocatalytic activity in carbamazepine degradation

Ultrathin nanosheets show great promise in photocatalytic technology, due to short path for electron transfer and large surface for reactant adsorption. However, there is no report that ultrathin nanosheets photocatalyst has been used to degrade carbamazepine (CBZ) in aquatic environment. This paper aimed at fabricating ultrathin BiOCl nanosheets to improve the photocatalytic degradation efficiency of CBZ. Herein, tetrabutylammonium hydroxide (TBAOH) was firstly applied to synthesize ultrathin BiOCl nanosheets (BiOCl-T) by a simple hydrolysis route in water at ambient conditions. TBAOH could act as a structure-directing agent, determining the structure and property of BiOCl-T. Assisted by TBAOH, BiOCl-T exhibited ultrathin nanosheets structure with preferential exposed (1 1 0) face. PL, photocurrent density, and EIS Nyquist plots demonstrated the enhanced charge separation efficiency in BiOCl-T. Furthermore, BiOCl-T displayed large pore size and specific surface area. Thus, BiOCl-T showed high photocatalytic activity toward CBZ degradation under simulated sunlight. Upon 30 min irradiation, the degradation efficiency of CBZ was 91.1% with fast degradation kinetics, which is 2.46 times higher than ordinary BiOCl. Active species of h⁺, O₂^-, and OH contributed to CBZ degradation reaction. The obtained result provides a novel viewpoint to fabricate ultrathin nanosheets and broadening their application in the degradation of recalcitrant pharmaceuticals.