Simultaneous catalytic ozonation degradation of metronidazole and removal of heavy metal from aqueous solution using nano-magnesium hydroxide

Facile fabrication of Fe3O4@Mg(OH)2 magnetic composites and their application in Cu(ii) ion removal

In this study, we fabricated magnetic Fe3O4@Mg(OH)2 composites through the seed deposition technique to achieve Cu(ii) ion removal from aqueous solutions. As indicated by the characterization results, three-dimensional flower-like spheres composed of external Mg(OH)2 were formed, with nano-Fe3O4 particles uniformly embedded in the "flower petals" of the spheres. The efficacy of Fe3O4@Mg(OH)2-3 in Cu(ii) ion removal was examined through batch experiments. The impact of solution pH on removal efficiency was examined, and the pseudo-second-order model and the Langmuir model provided good fits to the adsorption kinetics and isotherm data, respectively. Remarkably, Fe3O4@Mg(OH)2-3 exhibited a significant removal capacity of 1051.65 mg g-1 for Cu(ii) ions. Additionally, the composite displayed a notable saturation magnetization value of 17.3 emu g-1, facilitating isolation from sample solutions through external magnetic fields after Cu(ii) ion absorption. At the solid-liquid interface, a mechanism involving ion exchange between Mg(ii) and Cu(ii) cations was realized as the mode of Cu(ii) ion removal. The composites' effective adsorption properties and rapid magnetic separation highlighted their suitability for use in treating copper-contaminated water.

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.

Degradation of bisphenol A: a contaminant of emerging concern, using catalytic ozonation by activated carbon impregnated nanocomposite-bimetallic catalyst

Rampant water pollution events and rising water demand caused by exponential population growth and depleting freshwater resources speak of an impending water crisis. The inability of conventional wastewater treatment systems to remove contaminants of emerging concern (CECs) such as bisphenol A (BPA) beckons for new and efficient technologies to remove them from wastewater and water sources. Advanced oxidation processes such as ozonation are primarily known for their capability to oxidize and degrade organic entities in water, but optimum mineralization levels were hard to achieve. In this study, we synthesized an activated carbon impregnated nanocomposite-bimetallic catalyst (AC/CeO₂/ZnO) and used it along with ozonation to remove BPA from water. The catalyst was characterized using BET, XRD, FESEM, Raman spectra, and DLS studies. Catalytic ozonation achieved TOC removal 25% higher than non-catalytic ozonation process. The degradation pathway of BPA was proposed using LC-MS/LC-Q-TOF studies that found six main aromatic degradation byproducts. Catalytic ozonation and non-catalytic ozonation followed similar degradation pathways. The formation of persistent aliphatic acidic byproducts in the treated sample made total organic carbon (TOC) removal above 61% difficult.

Recent advances in photocatalytic remediation of emerging organic pollutants using semiconducting metal oxides: an overview

Many untreated and partly treated wastewater from the home and commercial resources is being discharged into the aquatic environment these days, which contains numerous unknown and complex natural and inorganic compounds. These compounds tend to persist, initiating severe environmental problems, which affect human health. Conventionally, physicochemical treatment methods were adopted to remove such complex organic chemicals, but they suffer from critical limitations. Over time, photocatalysis, an advanced oxidation process, has gained its position for its efficient and fair performance against emerging organic pollutant decontamination. Typically, photocatalysis is a green technology to decompose organics under UV/visible light at ambient conditions. Semiconducting nanometal oxides have emerged as pioneering photocatalysts because of large active surface sites, flexible oxidation states, various morphologies, and easy preparation. The current review presents an overview of emerging organic pollutants and their effects, advanced oxidation processes, photocatalytic mechanism, types of photocatalysts, photocatalyst support materials, and methods for improving photodegradation efficiency on the degradation of complex emerging organic pollutants. In addition, the recent reports of metal-oxide-driven photocatalytic remediation of emerging organic pollutants are presented in brief. This review is anticipated to reach a broader scientific community to understand the first principles of photocatalysis and review the recent advancements in this field.

Combined Iron-Loaded Zeolites and Ozone-Based Process for the Purification of Drinking Water in a Novel Hybrid Reactor: Removal of Faecal Coliforms and Arsenic

This study was carried out to provide a novel solution to treat drinking water at household levels, specifically removing arsenic (As) and faecal coliforms (microbes). In the current investigation, a synergistic iron-loaded zeolites and ozonation process (O3/Fe-ZA) was used for the first time in a modified batch reactor to remove coliform bacteria and arsenic in tap water. Moreover, the study utilizes the human health risk assessment model to confirm the health risk due to As intake in drinking water. The risk assessment study revealed a health risk threat among the residents suffering from the adverse effects of As through its intake in drinking water. Furthermore, the results also suggested that the O3/Fe-ZA process significantly removes faecal coliforms and As, when compared with single ozonation processes. Additionally, the ozone dose 0.2 mg/min and Fe-ZA dose of 10 g (in the O3/Fe-ZA process) gives the maximum removal efficiency of 100% within 15 min for faecal coliform removal. In 30 min, the removal efficiency of 88.4% was achieved at the ozone dose of 0.5 mg/min and 93% removal efficiency was achieved using 10 g Fe-ZA for the removal of As in the O3/Fe-ZA process. Hence, it was concluded that the O3/Fe-ZA process may be regarded as an effective method for removing faecal coliforms and As from drinking water compared to the single ozonation processes.

Comparison of Ag and AgI-Modified ZnO as Heterogeneous Photocatalysts for Simulated Sunlight Driven Photodegradation of Metronidazole

Ag and AgI-modified ZnO composites (Ag/ZnO and AgI/ZnO) were synthesized in facile ways. The photocatalysts were used for the photodegradation of metronidazole (MNZ) under the irradiation of simulated sunlight. The results of experiments showed that both Ag/ZnO and AgI/ZnO had a specific molar ratio to reach the best performance. Ag/ZnO performed better in the photodegradation of MNZ than AgI/ZnO under the same conditions. The reaction rate constant of AgI/ZnO was less affected by the variation of initial concentration of MNZ or pH values. The main reactive oxygen species of the photocatalytic process are OH, O2− and h+, but the free radicals which play the most critical part differ in Ag/ZnO and AgI/ZnO. Several intermediates were revealed by LC–MS/MS analysis. The stability of the photocatalysts was evaluated by a series of repeated MNZ photodegradation experiments. The results showed that AgI/ZnO had better stability than Ag/ZnO.