Removal of metronidazole by TiO2 and ZnO photocatalysis: a comprehensive comparison of process optimization and transformation products

Synthesis and photodegradation performance of a heterostructure ferromagnetic photocatalyst based on MWCNTs functionalized with (3-glycidyloxypropyl)trimethoxysilane and decorated with tungsten trioxide for metronidazole and acetaminophen degradation in aqueous environments

The presence of metronidazole (MNZ) and acetaminophen (ACE) in aquatic environments has raised growing concerns regarding their potential impact on human health. Incorporating various patterns into a photocatalytic material is considered a critical approach to achieving enhanced photocatalytic efficiency in the photocatalysis process. In this study, WO3 nanoparticles, which were immobilized onto ferromagnetic multi-walled carbon nanotubes that were functionalized using (3-glycidyloxypropyl)trimethoxysilane (FMMWCNTs@GLYMO@WO3), exhibited remarkable efficiency in removing MNZ and ACE (93% and 97%) in only 15 min. In addition, the new visible-light FMMWCNTs@GLYMO@WO3 nanoparticles as a magnetically separable photocatalyst were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), EDS-mapping, vibrating sample magnetometry (VSM), thermogravimetric analysis (TGA), diffuse reflectance spectroscopy (DRS), high-performance liquid chromatography (HPLC), and total organic carbon (TOC) due to detailed studies (morphological, structural, magnetic and optical properties) of the photocatalyst. In-depth spectroscopic and microscopic characterization of the newly developed ferromagnetic FMMWCNTs@GLYMO@WO₃ (III) photocatalyst revealed a spherical morphology, with nanoparticle diameters averaging between 23 and 39 nm. Compared to conventional multiwall carbon nanotube and WO₃ photocatalysts, FMMWCNTs@GLYMO@WO₃ (III) demonstrated superior photocatalytic activity. Remarkably, it exhibited excellent reusability, maintaining its efficiency over a minimum of five cycles in the degradation of metronidazole (MNZ) and acetaminophen (ACE).

Photocatalytic degradation of metronidazole and oxytetracycline by novel l-Arginine (C, N codoped)-TiO2/g-C3N4: RSM optimization, photodegradation mechanism, biodegradability evaluation

Removal of Metronidazole (MNZ) and Oxytetracycline (OTC) from wastewater by the prepared (C, N codoped)-TiO₂/g-C₃N₄ (Graphitic carbon nitride) was examined. l-Arginine (C, N codoped)-TiO₂ and l-Arginine (C, N codoped)-TiO₂/g-C₃N₄ photocatalysts were successfully synthesized through the sol-gel method, and optimal ratio of l-arginine:TiO₂, as well as l-arginine/TiO₂:g-C₃N₄, was determined by a kinetic study of photodegradation process. The maximum photocatalytic removal rate (0.065 min^-1 for MNZ removal) was observed using 1% l-Arginine-TiO₂/g-C₃N₄ (1:1) under visible light illumination, 2.2 and 6.5 times greater than those of 1% l-Arginine-TiO₂ and pure TiO₂, respectively. l-Arginine (1%)-TiO₂/g-C₃N₄ (1:1) (co-doped-TCN) was investigated using X-ray diffraction analysis (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX), Photo-luminescence (PL), and Differential Reflectance Spectroscopy (DRS) as the best-performing photocatalyst. Response surface methodology (RSM) was used to study the effect of co-doped-TCN dosage (0.5-1.0 g/L), pH of simulated wastewater (4-10), initial concentration of MNZ and OTC (50-100 mg/L), and irradiation time (30-90 min for MNZ and 20-40 min for OTC) on removal efficiency of the antibiotics. Also, their optimum values were determined by RSM. The treated pharmaceutical wastewater showed high biodegradability features with 5-day biological oxygen demand/chemical oxygen demand (BOD₅/COD) of 0.51 and 0.46 after 40 and 100 min reaction for OTC and MNZ, respectively. The order of reactive species responsible for the photodegradation of pollutants was •O₂^─> •OH > h⁺>¹O₂. The effect of inorganic anions showed that all anions decreased the removal efficiency of both antibiotics in order of NO₃^─> Cl^─ >SO₄^2─>HPO₄^2─ >HCO₃^─ for MNZ and NO₃^─> SO₄^2─ > Cl^─ >HPO₄^2─ >HCO₃^─ for OTC. Also, introducing different oxidants improved the photocatalytic removal efficiency with the order of H₂O₂>K₂S₂O₈> KBrO₃.

Environmentally friendly loading of palladium nanoparticles on nanoporous PET track-etched membranes grafted by poly(1-vinyl-2-pyrrolidone) via RAFT polymerization for the photocatalytic degradation of metronidazole

Nanoporous track-etched membranes (TeMs) are highly versatile materials that have shown promise in various applications such as filtration, separation, adsorption, and catalysis due to their mechanical integrity and high surface area. The performance of TeMs as catalysts for removing toxic pollutants is greatly influenced by the pore diameter, density, and functionalization of the nanochannels. In this study, the synthesis of functionalized poly(ethylene terephthalate) (PET) TeMs with Pd nanoparticles (NPs) as catalysts for the photodegradation of the antibiotic metronidazole (MTZ) was methodically investigated and their catalytic activity under UV irradiation was compared. Before loading of the Pd NPs, the surface and nanopore walls of the PET TeMs were grafted by poly(1-vinyl-2-pyrrolidone) (PVP) via UV-initiated reversible addition fragmentation chain transfer (RAFT)-mediated graft copolymerization. The use of RAFT polymerization allowed for precise control over the degree of grafting and graft lengths within the nanochannels of PVP grafted PET TeMs (PVP-g-PET). Pd NPs were then loaded onto PVP-g-PET using several environmentally friendly reducing agents such as ascorbic acid, sodium borohydride and a plant extract. In addition, a conventional thermal reduction technique was also applied for the reduction of the Pd NPs. The grafting process created a surface with high-sorption capacity for MTZ and also high stabilizing effect for Pd NPs due to the functional PVP chains on the PET substrate. The structure and composition of the composite membranes were elucidated by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, thermogravimetry, contact angle measurements and energy dispersive X-ray (EDX), X-ray photoelectron (XPS) and Fourier transform infra-red (FTIR) spectroscopies. The effects of different types of reducing agents, pH, the amount of loaded catalyst and MTZ concentration on the MTZ catalytic degradation efficiency of the obtained composites were investigated. The efficiency of the catalyst prepared in the presence of ascorbic acid was superior to the others (89.86% removal at 30 mg L^-1 of MTZ). Maximum removal of MTZ was observed at the natural pH (6.5) of the MTZ solution at a concentration of 30 mg per L MTZ. The removal efficiency was decreased by increasing the catalyst dosage and the initial MTZ concentration. The reaction rate constant was reduced from 0.0144 to 0.0096 min^-1 by increasing the MTZ concentration from 20 to 50 mg L^-1. The photocatalyst revealed remarkable photocatalytic activity even after 10 consecutive cycles.

Simultaneous hydrodynamic cavitation and glow plasma discharge for the degradation of metronidazole in drinking water

In this study, a novel hydrodynamic cavitation unit combined with a glow plasma discharge system (HC-GPD) was proposed for the degradation of pharmaceutical compounds in drinking water. Metronidazole (MNZ), a commonly used broad-spectrum antibiotic, was selected to demonstrate the potential of the proposed system. Cavitation bubbles generated by hydrodynamic cavitation (HC) can provide a pathway for charge conduction during glow plasma discharge (GPD). The synergistic effect between HC and GPD promotes the production of hydroxyl radicals, emission of UV light, and shock waves for MNZ degradation. Sonochemical dosimetry provided information on the enhanced formation of hydroxyl radicals during glow plasma discharge compared to hydrodynamic cavitation alone. Experimental results showed a MNZ degradation of 14% in 15 min for the HC alone (solution initially containing 300 × 10-6 mol L-1 MNZ). In experiments with the HC-GPD system, MNZ degradation of 90% in 15 min was detected. No significant differences were observed in MNZ degradation in acidic and alkaline solutions. MNZ degradation was also studied in the presence of inorganic anions. Experimental results showed that the system is suitable for the treatment of solutions with conductivity up to 1500 × 10-6 S cm-1. The results of sonochemical dosimetry showed the formation of oxidant species of 0.15 × 10-3 mol H2O2 L-1 in the HC system after 15 min. For the HC-GPD system, the concentration of oxidant species after 15 min reached 13 × 10-3 molH2O2L-1. Based on these results, the potential of combining HC and GPD systems for water treatment was demonstrated. The present work provided useful information on the synergistic effect between hydrodynamic cavitation and glow plasma discharge and their application for the degradation of antibiotics in drinking water.

Study on the photocatalytic degradation of metronidazole antibiotic in aqueous media with TiO2 under lab and pilot scale

Nowadays, the increased consumption of antibiotics, such as metronidazole (MTZ), leads to their introduction in wastewater as well as in the receiving surface waters due to their incomplete removal by conventional wastewater treatment plants. Heterogeneous photocatalysis is a versatile technology that can efficiently degrade such organic contaminants. In the present research, the photocatalytic degradation of MTZ with TiO₂ P25 was studied under lab and pilot (CPC reactor) conditions. The antibiotic was efficiently removed at high rates in both cases (100 % and 91 %) following pseudo-first order kinetics with rate constants equal to 0.0452 min^-1 (±RSD% = 0.68 % - 2.57 %) and 0.0462 L KJ^-1 (±RSD% = 8.94 % - 21.64 %) respectively. Also, by scavenging lab scale experiments, the contribution of the generated reactive species was investigated and hydroxy radicals (HO^•) were proposed as the predominant species. By applying high resolution mass spectrometry techniques, the transformation products (TPs) were identified and possible transformation pathways were proposed. The ecotoxicity of the TPs was assessed in silico using the ECOSAR software with the results revealing that most of them were less toxic than the parent compound. Similarly, the mutagenicity, developmental toxicity and bioconcentration factors of the TPs were predicted by utilizing the T.E.S.T. software and in their majority, were found to be less mutagenic and developmentally toxic than MTZ. The ecotoxicity monitoring with the Vibrio fischeri bioassay in both laboratory and pilot scale experiments indicated that through heterogeneous photocatalysis it is possible to reduce the toxicity of wastewater containing MTZ. Finally, the stability and reusability of the photocatalyst was investigated through three consecutive catalytic cycles with the results showing that the performance of TiO₂ decreased after each use. For the heterogeneous photocatalysis with TiO₂ to be a "real life" applicable technique, further studies focusing on catalyst regeneration and optimization of the catalytic conditions must be conducted.

g-C3N4 as Photocatalyst for the Removal of Metronidazole Antibiotic from Aqueous Matrices under Lab and Pilot Scale Conditions

The presence of pharmaceuticals in water is a problem of utmost importance due to the various adverse effects that these compounds may have on aquatic organisms and also humans. Since conventional wastewater treatment plants fail to efficiently remove many of these compounds, new techniques such as heterogeneous photocatalysis have been developed that are capable of degrading them. In this study, graphitic carbon nitride (g-C3N4) was used as photocatalyst to remove metronidazole (MTZ), which is a widely prescribed antibiotic that has been reported as a potential carcinogen. The experiments were performed under lab and pilot scale conditions. During the lab scale experiments, 90.6% of the initial pharmaceutical concentration was removed after 360 min of irradiation and its removal followed a pseudo first order kinetic model with a degradation rate constant of k = 0.00618 min−1. Moreover, scavenging studies indicated that the indirectly produced hydroxy radicals contribute very little to the degradation mechanism. Through high precision mass spectrometry techniques, eight transformation products (TPs) were identified, and possible transformation pathways were suggested. Similarly, in the case of pilot scale experiments, 100 and 200 mg L−1 of g-C3N4 were used and the antibiotic’s removal also followed pseudo first order kinetics with k = 0.00827 min−1 and k = 0.00942 min−1, respectively. However, starting from low level inherent concentrations, only two TPs were identified. By using in silico tools (ECOSAR and T.E.S.T.), various ecotoxicological values were predicted for the TPs, which were generally found to be less toxic than the parent compound and with lower mutagenic and bioaccumulative potential. Moreover, the monitoring of the ecotoxicity with the in vitro Microtox bioassay showed that at the end of all the photocatalytic processes, the toxicity was reduced. In conclusion, this technique could have the potential to remove MTZ and other similar pharmaceuticals in full-scale applications. However, for this to happen with the highest possible efficiency, further studies must be conducted, focusing on improving the catalyst’s performance and reusability, improving the separation of catalyst as well as finding the optimum conditions for this process.

Graphene-based porous nanohybrid architectures for adsorptive and photocatalytic abatement of volatile organic compounds

Volatile organic compounds (VOCs) represent a considerable threat to humans and ecosystems. Strategic remediation techniques for the abatement of VOCs are immensely important and immediately needed. Given a unique set of optical, mechanical, electrical, and thermal characteristics, inimitable surface functionalities, porous structure, and substantial specific surface area, graphene and derived nanohybrid composites have emerged as exciting candidates for abating environmental pollutants through photocatalytic degradation and adsorptive removal. Graphene oxide (GO) and reduced graphene oxide (rGO) containing oxygenated function entities, i.e., carbonyl, hydroxyl, and carboxylic groups, provide anchor and dispersibility of their surface photocatalytic nanoscale particles and adsorptive sites for VOCs. Therefore, it is meaningful to recapitulate current state-of-the-art research advancements in graphene-derived nanostructures as prospective platforms for VOCs degradation. Considering this necessity, this work provides a comprehensive and valuable insight into research progress on applying graphene-based nanohybrid composites for adsorptive and photocatalytic abatement of VOCs in the aqueous media. First, we present a portrayal of graphene-based nanohybrid based on their structural attributes (i.e., pore size, specific surface area, and other surface features to adsorb VOCs) and structure-assisted performance for VOCs abatement by graphene-based nanocomposites. The adsorptive and photocatalytic potentialities of graphene-based nanohybrids for VOCs are discussed with suitable examples. In addition to regeneration, reusability, and environmental toxicity aspects, the challenges and possible future directions of graphene-based nanostructures are also outlined towards the end of the review to promote large-scale applications of this fascinating technology.

Simultaneous electrochemical degradation of tetracycline and metronidazole through a high-efficiency and low-energy-consumption advanced oxidation process

With the increasing complexity of water environment pollution, it is becoming ever more practical to study the simultaneous removal of multiple pollutants in water. Electrochemical advanced oxidation technology is considered to be one of the most promising green approaches for the degradation of organic pollutants. Herein, Ti³⁺ and oxygen vacancies (V_O) self-doped TiO_2-x nanotube array electrodes are employed to investigate the simultaneous degradation and an energy consumption assessment for the effective removal of the antibiotics tetracycline (TC) and metronidazole (MNZ). The electrocatalytic performance of the nanotube arrays prepared at different reduction times is significantly different. The electrochemical reduction of TiO₂ nanotube arrays for 10 min presents the best degradation performance for TC and MNZ. When a mixed solution of TC and MNZ is simultaneously degraded, the removal rate of TC (50 mg L^-1) and MNZ (50 mg L^-1) within 3 h reaches 100%, while the chemical oxygen demand (COD) removal rate is 79.1%. The energy consumption is significantly reduced compared to the degradation of a single substance. Simultaneously, the current utilization rate of the electrochemical degradation system is also significantly improved, with a specific energy consumption of only 85.78 kWh kg^-1 and an average current efficiency that can reach 20.2%.

Design and Microwave-Assisted Synthesis of TiO2-Lanthanides Systems and Evaluation of Photocatalytic Activity under UV-LED Light Irradiation

The TiO2-Eu and TiO2-La systems were successfully synthesized using the microwave method. Based on the results of X-ray diffraction analysis, it was found that regardless of the analyzed systems, two crystal structures were noted for the obtained samples: anatase and rutile. The analysis, such as XPS and EDS, proved that the doped lanthanum and europium nano-particles are present only on the TiO2 surface without disturbing the crystal lattice. In the synthesized systems, there were no significant changes in the bandgap energy. Moreover, all the obtained systems were characterized by high thermal stability. One of the key objectives of the work, and a scientific novelty, was the introduction of UV-LED lamps into the metronidazole photo-oxidation pathway. The results of the photo-oxidation study showed that the obtained TiO2 systems doped with selected lanthanides (Eu or La) show high efficiency in the removal of metronidazole, and at the same consuming nearly 10 times less electricity compared to conventional UV lamps (high-pressure mercury lamp). Liquid-chromatography mass-spectrometry (LC-MS) analysis of an intermediate solution showed the presence of fragments of the degraded molecule by m/z 114, 83, and 60, prompting the formulation of a plausible photodegradation pathway for metronidazole.

Enhanced effect of pyrite on the removal of metronidazole by zero valent iron

The abuse and improper disposal of antibiotics including metronidazole (MNZ) result in serious contamination in aquatic environments. In this study, pyrite, which was not reactive for MNZ removal, was simply mixed with zero valent iron (ZVI) to efficiently remove MNZ in anaerobic aqueous solutions. A dual ZVI/pyrite system consisting of ZVI (1.0 g/L) and pyrite (4.0 g/L) removed MNZ completely in 360 min within a broad pH₀ range (5.0-9.0), and it still maintained a high removal efficiency (~80%) even at a high pH₀ of 10.0. By contrast, single ZVI (1.0 g/L) showed much lower efficiency (4.8%-22.0%) within the same pH₀ range (5.0-10.0). On investigating the mechanism of MNZ removal, the cooperation between ZVI and pyrite enhanced the surface corrosion of ZVI and facilitated the redox cycle of Fe(III)/Fe(II) to generate more sorbed Fe(II), which was a dominant reactive species for MNZ removal. Pyrite also activated the ZVI surface to form FeS@Fe in situ, accelerating the electron transfer from Fe⁰ core to the surface-enriched MNZ, and stimulated the formation of green rust sulfate on the ZVI surface to further promote MNZ removal. LC-MS analysis confirmed ZVI/pyrite reductively transformed MNZ into readily biodegradable products by denitration and cleavage of hydroxyethyl.

New insights into the mechanisms of tartaric acid enhancing homogeneous and heterogeneous copper-catalyzed Fenton-like systems

The specific roles of tartaric acid (TA), as an eco-friendly ligand, in homogeneous and heterogeneous copper-catalyzed systems were systematically revealed and new mechanisms of TA enhancing the three Fenton-like processes were proposed to provide a theoretical significance in overcoming the deficiency of conventional Fenton processes. The results identified hydroxyl radical (•OH) as the main species responsible for the simultaneous decomposition of TA and metronidazole (MNZ) according to TOC removal. The ESR technique was used to detect superoxide radicals (•O₂^-), carbon-centered radical (•R) and hydrogen radical (•H) in the Cu²⁺/TA/H₂O₂ system, which contributed to the acceleration of the Cu²⁺/Cu⁺ redox cycle. The enhancing effect of TA on the homogeneous process was ascribed to the formation of a soluble complex with Cu²⁺, which favored the pH range extension, Cu⁺ oxidation, and radical generation. Moreover, the adsorption of TA on the catalysts surface promoted the consumption of H₂O₂, inducing •OH generation. The formed surface complex (≡Cu²⁺-TA) also accelerated the regeneration of ≡Cu⁺, which was confirmed by density functional theory (DFT) calculation and surface characterization analysis (SEM, XRD, and XPS). The possible degradation pathways of MNZ in TA-modified Fenton-like system were also clarified.

Development of a new SLE-SPE-HPLC-MS/MS method for the determination of selected antibiotics and their transformation products in anthropogenically altered solid environmental matrices

The presence of antibiotic residues, their bioactive metabolites and other transformation products in the environment may adversely affect the organisms that live in the environment and may also contribute to increasing the antibiotic resistance of bacteria. It is particularly difficult to determine the types of contaminants in solid samples, in particular, those that are anthropogenically changed, e.g., as a result of controlled biochemical processes. Therefore, the aim of this research was to develop of a new method for the determination of twelve antibiotics belonging to different groups, such as penicillins, sulfonamides, tetracyclines, quinolones, imidazoles and cefalosporins, in digested manure and activated sludge samples, which were used as examples of anthropogenically altered environmental solid samples. The analyses were performed using high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). The solid-liquid extraction (SLE) method to isolate analytes from digested manure and activated sludge was developed and optimized, the same as clean-up procedure followed by solid phase extraction (SPE). The recovery ranged from 45 to 85%. Finally, the validated method was applied to the determination of the selected antibiotics in manure and activated sludge samples after an anaerobic digestion process.. An additional aim of the study was to verify whether the developed method allows simultaneous detection of transformation products of the studied antibiotics in solid samples. The study showed that by optimizing the analysis conditions, it is possible to simultaneously determine the selected antibiotics and their transformation products (including their epimeric forms), which can significantly improve the ability to control the efficiency of the biological processes used in this area. In practice, this means that the developed methodology may be particularly useful in the context of research and other works related to the anaerobic digestion of activated sludge, manure or other solid substrates of environmental origin.

Application of ZnO nanorods doped with Cu for enhanced sonocatalytic removal of Cr(VI) from aqueous solutions

The aim of this research was to develop a simple and inexpensive process for reduction of Cr(VI) to Cr(III). Zinc oxide nanoparticles were synthesized with an easy co-precipitation procedure, and the addition of Cu²⁺ doping agent effectively enhanced the Cr(VI) reduction in the presence of ultrasound (US). XRD, FT-IR, FE-SEM, EDX, VSM, and XPS were used to determine the structural specifications of the zinc oxide nanoparticles. Under optimal conditions such as pH 3, initial Cr(VI) content of 20 mg/L, and catalyst dosage of 0.8 g/L, the ultrasonic/Cu-ZnO process showed a higher sonocatalytic activity (96.83%) than ultrasonic/ZnO (67.36%) after 60 min. By increasing pH and Cr(VI) concentration, the removal efficacy of Cr(VI) declined. The experimental data was well described with the first-order kinetic model. When initial Cr(VI) concentration increased from 10 to 50 mg/L, the first-order rate constant declined from 0.2326 to 0.0019 min^-1 and electrical energy per order (E_EO) enhanced from 19.81 to 2425.26 kWh/m³. Also, the ultrasonic/Cu-ZnO system exhibited considerable sonocatalytic performance in Cr(VI) reduction in the presence of hydrogen peroxide and citric acid, and complete removal was achieved within 60 min. The presence of anions negatively affected Cr(VI) reduction. Complete reduction was attained when ultrasound was applied at a power of 100 W. The catalyst activity was well maintained up to six consecutive cycles. In addition, the removal efficiency was approximately 62 and 65% for field water and real electroplating wastewater samples, respectively.

Hybridizing Ag-Doped ZnO nanoparticles with graphite as potential photocatalysts for enhanced removal of metronidazole antibiotic from water

In this study, the ZnO nanoparticles were doped with Ag and then hybridized on graphite (GP) layer (Ag-ZnO/GP) by a hydrothermal method, which was used as photocatalysts to remove metronidazole (MNZ) antibiotic from aqueous solutions. The fine structure, morphologies, and optical properties of the synthesized composites were first examined. The incorporation of Ag would readily reduce the rate of the recombination of electron-hole pairs and enhance the photocatalytic activity in a wide range of light wavelength. The graphite surface also acted as an electron sink to efficiently inhibit the photocorrosion of ZnO, thereby improving the photostability of the composites. The composition of the composite was optimized to be 0.5 wt% GP/ZnO and 1.0 wt% Ag/ZnO according to the extent of the enhancement of photocatalytic activity. In a solution containing 30 mg L^-1 of MNZ and 0.5 g L^-1 of Ag-ZnO/GP composite, it was shown that 88.5% and 97.3% of MNZ was removed after 60 min of 100-W UV and 180-min solar irradiation, respectively. Moreover, six over a total of eleven transformation products formed during UV photocatalysis were ascribed to the roles of reactive holes (h⁺), all which were detected and identified by high-resolution liquid chromatography-mass spectrometry (LC-MS). Finally, the pathways of MNZ degradation over Ag-ZnO/GP composite were proposed.

Graphene and graphene-based nanocomposites used for antibiotics removal in water treatment: A review

Due to their extensive application in human and veterinary medicine, antibiotics have been found worldwide and studied as new pollutants in the aquatic environment. In order to remove such pollutants, adsorption and photocatalysis have attracted tremendous attention because of their great potential in antibiotics removal from aqueous solutions. Graphene, as a novel two-dimensional nanomaterial, possesses unique structure and physicochemical properties, which can be used to efficiently adsorb and photodegrade antibiotics. This review provides an overview of the adsorptive and catalytic properties of graphene, and recent advances in adsorption and photodegradation of antibiotics by graphene and its derivatives. The factors that affect the adsorption and photodegradation of antibiotics are reviewed and discussed. Furthermore, the underlying mechanisms of adsorption and photodegradation are summarized and analyzed. Meanwhile, statistical analysis is conducted based on the number of papers and the maximum adsorption and photodegradation ability on various antibiotics removal. Finally, some unsolved problems together with major challenges that exist in the fabrication and application of graphene-based nanocomposites and the development for antibiotics removal is also proposed. This work provides theoretical guidance for subsequent research in the field of adsorption and photocatalytic removal of antibiotics from aqueous solution, especially on influence factors and mechanisms aspects.

Removal of metronidazole and amoxicillin mixtures by UV/TiO2 photocatalysis: an insight into degradation pathways and performance improvement

The degradation efficiencies and pathways of metronidazole (MNZ) and amoxicillin (AMX) in binary mixtures by UV/TiO₂ photocatalysis were studied. The presence of AMX significantly decreased the degradation of MNZ, whereas the existence of MNZ slightly reduced the degradation of AMX. This is basically due to the difference in attack ability of oxidizing agents present during TiO₂ photocatalysis. All oxidizing agents (hydroxyl radicals, superoxide radicals, and holes) could attack AMX molecules, but hydroxyl radicals showed insignificant attack ability in MNZ degradation. In TiO₂ photocatalysis of binary mixture, six transformation products were recognized by a high-resolution LC-QTof/MS. Because of competitive effect, only one product was sourced from MNZ degradation and four others were formed due to AMX degradation. The remaining one was a new product of the side reaction. This work indicated that the molecular structure of AMX determined its preferred degradation in a mixture. It not only affected the removal of antibiotics but also figured out the appearance of transformation products. In contrast to single systems, the extent of degradation reduced for each antibiotic in the presence of the second antibiotic was related to the availability of degradation pathways of each antibiotic. Moreover, suitable pH programming was applied to enhance the mineralization of the mixtures.