Nanostructured cerium-doped ZnO for photocatalytic degradation of pharmaceuticals in aqueous solution

Recent progress in defect-engineered metal oxides for photocatalytic environmental remediation

Rapid industrial advancement over the last few decades has led to an alarming increase in pollution levels in the ecosystem. Among the primary pollutants, harmful organic dyes and pharmaceutical drugs are directly released by industries into the water bodies which serves as a major cause of environmental deterioration. This warns of a severe need to find some sustainable strategies to overcome these increasing levels of water pollution and eliminate the pollutants before being exposed to the environment. Photocatalysis is a well-established strategy in the field of pollutant degradation and various metal oxides have been proven to exhibit excellent physicochemical properties which makes them a potential candidate for environmental remediation. Further, with the aim of rapid industrialization of photocatalytic pollutant degradation technology, constant efforts have been made to increase the photocatalytic activity of various metal oxides. One such strategy is the introduction of defects into the lattice of the parent catalyst through doping or vacancy which plays a major role in enhancing the catalytic activity and achieving excellent degradation rates. This review provides a comprehensive analysis of defects and their role in altering the photocatalytic activity of the material. Various defect-rich metal oxides like binary oxides, perovskite oxides, and spinel oxides have been summarized for their application in pollutant degradation. Finally, a summary of existing research, followed by the existing challenges along with the potential countermeasures has been provided to pave a path for the future studies and industrialization of this promising field.

Fungal Bioremediation of the β-Lactam Antibiotic Ampicillin under Laccase-Induced Conditions

Due to widespread overuse, pharmaceutical compounds, such as antibiotics, are becoming increasingly prevalent in greater concentrations in aquatic ecosystems. In this study, we investigated the capacity of the white-rot fungus, Coriolopsis gallica (a high-laccase-producing fungus), to biodegrade ampicillin under different cultivation conditions. The biodegradation of the antibiotic was confirmed using high-performance liquid chromatography, and its antibacterial activity was evaluated using the bacterial growth inhibition agar well diffusion method, with Escherichia coli as an ampicillin-sensitive test strain. C. gallica successfully eliminated ampicillin (50 mg L-1) after 6 days of incubation in a liquid medium. The best results were achieved with a 9-day-old fungal culture, which treated a high concentration (500 mg L-1) of ampicillin within 3 days. This higher antibiotic removal rate was concomitant with the maximum laccase production in the culture supernatant. Meanwhile, four consecutive doses of 500 mg L-1 of ampicillin were removed by the same fungal culture within 24 days. After that, the fungus failed to remove the antibiotic. The measurement of the ligninolytic enzyme activity showed that C. gallica laccase might participate in the bioremediation of ampicillin.

Mechanistic understanding of green synthesized cerium nanoparticles for the photocatalytic degradation of dyes and antibiotics from aqueous media and antimicrobial efficacy: A review

In recent years, extensive research endeavors are being undertaken for synthesis of an efficient, economic and eco-friendly cerium oxide nanoparticles (CeO2 NPs) using plant extract mediated greener approach. A number of medicinal plants and their specific parts (flowers, bark, seeds, fruits, seeds and leaves) have been found to be capable of synthesizing CeO2 NPs. The specific key phytochemical constituents of plants such as alkaloids, terpenoids, phenolic acids, flavones and tannins can play significant role as a reducing, stabilizing and capping agents in the synthesis of CeO2 NPs from their respective precursor solution of metal ions. The CeO2 NPs are frequently using in diverse fields of science and technology including photocatalytic degradation of dyes, antibiotics as well as antimicrobial applications. In this review, the mechanism behind the green synthesis CeO2 NPs using plant entities are summarized along with discussion of analytical results from characterization techniques. An overview of CeO2 NPs for water remediation application via photocatalytic degradation of dyes and antibiotics are discussed. In addition, the mechanisms of antimicrobial efficacy of CeO2 NPs and current challenges for their sustainable application at large scale in real environmental conditions are discussed.

Degradation of carbamazepine in surface water: performance of Pd-modified TiO2 and Ce-modified ZnO as photocatalysts

Carbamazepine is a widely used antiepileptic drug to control and treat a variety of disorders that is frequently detected in surface water, and in municipal and urban wastewater. This recalcitrant pollutant could be removed by alternative advanced oxidation technology such as heterogeneous photocatalysis. Ce-modified ZnO and Pd-modified TiO2 were synthesized by a microwave-assisted sol-gel method. According to the characterizations (Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy), a mixture of oxides was determined in both materials: CeO2/ZnO and PdO/TiO2. Photocatalytic degradation of carbamazepine in pure water under visible light (3 h) was assayed. The degradation percentage obtained with each catalyst was 80%, 53%, 20%, and 9% for ZnO, Ce-modified ZnO, TiO2, and Pd-modified TiO2, respectively. The leaching of Zn as a possible source of water contamination was tested, finding the lowest value for Ce-modified ZnO by adjusting the initial pH up to neutrality. Later, an environmentally relevant concentration of carbamazepine (228 µg L-1) was assayed, using local surface water (pH = 8.3). Despite the presence of other compounds in the real water matrix, after 5 h of photocatalysis, a 56% of degradation of the pharmaceutical and low leaching of Zn were achieved. The use of Ce-modified ZnO activated by visible light is a promising strategy for the abatement of pharmaceutical active compounds.

Emerging aspects of metal ions-doped zinc oxide photocatalysts in degradation of organic dyes and pharmaceutical pollutants - A review

In recent periods, a broad assortment of continual organic contaminants has been released into our natural water resources. Indeed, it is exceedingly poisonous and perilous to living things; thus, the elimination of these organic pollutants before release into the water bodies is vital. A variety of techniques have been utilized to remove these organic pollutants with advanced oxidation photocatalytic methods with zinc oxide (ZnO) nanoparticles being commonly used as a capable catalyst for contaminated water treatment. Nevertheless, its broad energy gap, which can be only stimulated under an ultraviolet (UV) light source, and high recombination pairs of electrons and holes limit their photocatalytic behaviors. However, numerous methods have been suggested to decrease its energy gap for visible regions. Including, the doping ZnO with metal ions (dopant) can be considered as an effectual route not only the reason for a movement of the absorption edges toward the higher (visible light) region but also to lower the electron-hole pair (e--h+) recombination. This review concentrated on the impact of dissimilar types of metal ions (dopants) on the advancement in the degradation performance of ZnO. So, this work demonstrates a vital review of contemporary attainments in the alteration of ZnO nanoparticles for organic pollutants eliminations. Besides, the effect of doping ions including transition metals, rare earth metals, and metal ions (substitutional and interstitial) concerning numerous types of altered ZnO are summarized. The photodegradation mechanisms for pristine and metal-modified ZnO nanoparticles are also conferred.

Solar-light-driven photocatalytic degradation of pharmaceutical pollutants utilizing 2D g-C3N4/BiOCl composite

Pharmaceuticals, which have been praised for protecting countless lives, have become a new category of environmental pollutants in recent decades as most of these pharmaceutical compounds are discovered in water bodies in concentrations ranging from ng/L to mg/L. Recently, metal-free g-C₃N₄ (GCN)-based composites have received considerable attention for the degradation of pharmaceutical compounds. In this study, GCN/BiOCl composite was prepared using a simple ultrasonication-assisted stirring method and characterized using various analytical and spectroscopic techniques including XRD, FTIR, PL, Elemental mapping, UV-DRS, FESEM, HRTEM, and TGA. The as-prepared composite was utilized to degrade levofloxacin (LVX) under solar light irradiation and showed excellent stability for the degradation of LVX. Furthermore, the universality of the GCN/BiOCl composite was investigated by degrading diverse pharmaceuticals such as ofloxacin (OFX), norfloxacin (NOX), ciprofloxacin (COX), and ketorolac tromethamine (KTC) in an aqueous phase. Therefore, this work provides an effective method to degrade pharmaceutical contaminants simultaneously in water using GCN/BiOCl composite.

Heterogeneous Advanced Oxidation Processes: Current Approaches for Wastewater Treatment

Nowadays, water pollution is one of the most dangerous environmental problems in the world. The presence of the so-called emerging pollutants in the different water bodies, impossible to eliminate through conventional biological and physical treatments used in wastewater treatment plants due to their persistent and recalcitrant nature, means that pollution continues growing throughout the world. The presence of these emerging pollutants involves serious risks to human and animal health for aquatic and terrestrial organisms. Therefore, in recent years, advanced oxidation processes (AOPs) have been postulated as a viable, innovative and efficient technology for the elimination of these types of compounds from water bodies. The oxidation/reduction reactions triggered in most of these processes require a suitable catalyst. The most recent research focuses on the use and development of different types of heterogeneous catalysts, which are capable of overcoming some of the operational limitations of homogeneous processes such as the generation of metallic sludge, difficult separation of treated water and narrow working pH. This review details the current advances in the field of heterogeneous AOPs, Fenton processes and photocatalysts for the removal of different types of emerging pollutants.

Nanophotocatalysis for the Removal of Pharmaceutical Residues from Water Bodies: State of Art and Recent Trends

Background:

The occurrence of pharmaceuticals in surface and drinking water is ubiquitous and is a major concern of researchers. These compounds cause a destructive impact on aquatic and terrestrial life forms, and the removal of these compounds from the environment is a challenging issue. Existent conventional wastewater treatment processes are generally inefficacious because of their low degradation efficiency and inadequate techniques associated with the disposal of adsorbed pollutants during comparatively effective methods like the adsorption process.

Remediation Method:

Semiconductor-mediated photocatalysis is an attractive technology for the efficient removal of pharmaceutical compounds. Among various semiconductors, TiO2 and ZnObased photocatalysts gained much interest during the last years because of their efficiency in decomposing and mineralizing the lethal organic pollutants with the utilization of UV-visible light. Incessant efforts are being undertaken for tuning the physicochemical, optical, and electronic properties of these photocatalysts to strengthen their overall photocatalytic performance with good recycling efficiency.

Results:

This review attempts to showcase the recent progress in the rational design and fabrication of nanosized TiO2 and ZnO photocatalysts for the removal of pollutants derived from the pharmaceutical industry and hospital wastes.

Conclusion:

Photocatalysis involving TiO2 and ZnO provides a positive impact on pollution management and could be successfully applied to remove pharmaceuticals from wastewater streams. Structure modifications, the introduction of heteroatoms, and the integration of polymers with these nano photocatalysts offer leapfrogging opportunities for broader applications in the field of photocatalysis.

Changes in levels of N-nitrosamine formed from amine-containing compounds during chloramination via photocatalytic pretreatment with immobilized TiO2: Effect of source water and pH

We investigated the effectiveness of photocatalytic pretreatment (PCP) of precursors in minimizing the formation potentials (FPs) of carcinogenic nitrosamines, including N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), and N-nitrosodiethanolamine (NDELA), during water chloramination. A steel mesh substrate with immobilized TiO₂ was highly efficient at mitigating nitrosamine formation and removing targeted precursors such as ranitidine, nizatidine, trimebutine, triethanolamine, and metoclopramide. Compared to UVC/H₂O₂, PCP under UVA irradiation (intensity of 0.67 mW cm^-2) was more effective for reducing nitrosamine-FPs during post-chloramination. However, the PCP efficacies varied with the water source, pretreatment pH, and irradiation time. For example, PCP of eutrophic water increased the NDMA-FPs, but produced notable reductions (up to 99%) for NDELA- and NDEA-FPs. Shorter irradiation times, up to 15 min, increased the NDELA-FP in triethanolamine, and the NDMA-FP in nizatidine and trimebutine. However, the nitrosamine-FP decreased by > 50% after PCP at a pH > 5.6, following irradiation for 120 min. Oxygen addition, N-de(m)ethylation, and N-dealkylation were responsible for decreasing nitrosamine-FPs via the destruction of key moieties; this has been elucidated by mass spectroscopy. This study suggests that PCP could be used as an alternative strategy for minimizing nitrosamine-FPs during water treatment.

Current advancements on the fabrication, modification, and industrial application of zinc oxide as photocatalyst in the removal of organic and inorganic contaminants in aquatic systems

Industrial wastewaters contain hazardous contaminants that pollute the environment and cause socioeconomic problems, thus demanding the employment of effective remediation procedures such as photocatalysis. Zinc oxide (ZnO) nanomaterials have emerged to be a promising photocatalyst for the removal of pollutants in wastewater owing to their excellent and attractive characteristics. The dynamic tunable features of ZnO allow a wide range of functionalization for enhanced photocatalytic efficiency. The current review summarizes the recent advances in the fabrication, modification, and industrial application of ZnO photocatalyst based on the analysis of the latest studies, including the following aspects: (1) overview on the properties, structures, and features of ZnO, (2) employment of dopants, heterojunction, and immobilization techniques for improved photodegradation performance, (3) applicability of suspended and immobilized photocatalytic systems, (4) application of ZnO hybrids for the removal of various types of hazardous pollutants from different wastewater sources in industries, and (5) potential of bio-inspired ZnO hybrid nanomaterials for photocatalytic applications using renewable and biodegradable resources for greener photocatalytic technologies. In addition, the knowledge gap in this field of work is also highlighted.

Cerium-, Europium- and Erbium-Modified ZnO and ZrO2 for Photocatalytic Water Treatment Applications: A Review

In the last decades photocatalysis has become one of the most employed technologies for the implementation of the so-called Advanced Oxidation Processes (AOPs) for the removal of harmful pollutants from wastewaters. The materials identified as the best photocatalysts are transition metal oxides, in which the band structure allows charge carrier separation upon solar irradiation. The photoinduced charge carrier can thus cause oxidative and reductive redox reactions at the surface, inducing the formation of the radical species able to initiate the AOPs. Despite the great advantages of this process (non-toxic, cheap and environmentally clean), the main drawback lies in the fact that the most efficient semiconductors are only able to absorb UV irradiation, which accounts for only 5% of the total solar irradiation at the Earth’s surface and not enough to generate the required amount of electron-hole pairs. On the other hand, many efforts have been devoted to the sensitization of wide band gap transition metal oxides to visible light, which represents a higher percentage (almost 45%) in the solar electromagnetic spectrum. Among all the strategies to sensitize transition metal oxides to visible irradiation, doping with lanthanides has been less explored. In this regard, lanthanides offer a unique electronic configuration, consisting in 4f orbitals shielded by a 5s5p external shell. This occurrence, coupled with the different occupation of the localized 4f orbitals would provide an astounding opportunity to tune these materials’ properties. In this review we will focus in depth on the modification of two promising photocatalytic transition metal oxides, namely ZnO and ZrO2, with cerium, europium and erbium atoms. The aim of the work is to provide a comprehensive overview of the influence of lanthanides on the structural, optical and electronic properties of the modified materials, emphasizing the effect of the different 4f orbital occupation in the three considered doping atoms. Moreover, a large portion of the discussion will be devoted to the structural-properties relationships evidencing the improved light absorption working mechanism of each system and the resulting enhanced photocatalytic performance in the abatement of contaminants in aqueous environments.

A Brief Photocatalytic Study of ZnO Containing Cerium towards Ibuprofen Degradation

Ibuprofen (IBU) is one of the most-sold anti-inflammatory drugs in the world, and its residues can reach aquatic systems, causing serious health and environmental problems. Strategies are used to improve the photocatalytic activity of zinc oxide (ZnO), and thosethat involvethe inclusion of metalhave received special attention. The aim of this work was to investigate the influence of the parameters and toxicity of a photoproduct using zinc oxide that contains cerium (ZnO-Ce) for the photodegradation of ibuprofen. The parameters include the influence of the photocatalyst concentration (0.5, 0.5, and 1.5 g L⁻¹) as well as the effects of pH (3, 7, and 10), the effect of H₂O₂, and radical scavengers. The photocatalyst was characterized by Scanning Electron Microscopy-Energy Dispersive Spectroscopy, Transmission electron microscopy, Raman, X-Ray Diffraction, surface area, and diffuse reflectance. The photocatalytic activity of ibuprofen was evaluated in an aqueous solution under UV light for 120 min. The structural characterization by XRD and SEM elucidated the fact that the nanoparticle ZnO contained cerium. The band gap value was 3.31 eV. The best experimental conditions for the photodegradation of IBU were 60% obtained in an acidic condition using 0.50 g L⁻¹ of ZnO-Ce in a solution of 20 ppm of IBU. The presence of hydrogen peroxide favored the photocatalysis process. ZnO-Ce exhibited good IBU degradation activity even after three photocatalytic cycles under UV light. The hole plays akey role in the degradation process of ibuprofen. The toxicity of photolyzed products was monitored against Artemia salina (bioindicator) and did not generate toxic metabolites. Therefore, this work provides a strategic design to improve ZnO-Ce photocatalysts for environmental remediation.

High efficiency of osmotically stable laccase for biotransformation and micro-detoxification of levofloxacin in the urea-containing solution: Catalytic performance and mechanism

Laccase-catalyzed oxidation was applied in the biotransformation of levofloxacin (a potentially environmental antibiotic contamination); however, the enzyme may denature in urea-containing wastewater and lead to the formation of an inactive form followed by decreasing the yield of the bio-removal. In this study, the osmolytes-stabilized laccase was used to eliminate levofloxacin in the urea-containing solution. Sorbitol and proline 100 mM appeared to be the two most efficient laccase protectants against the urea-induced denaturation. In a 1-M urea solution, the maximum velocity (V_max) of laccase was estimated to be 39.1 μmol min^-1 mg^-1. This value was improved to 101.7 and 51.8 μmol min^-1 mg^-1 in the presence of sorbitol and proline, respectively. In optimal conditions for the elimination of levofloxacin, sorbitol- and proline-treated laccase led to 82.9 % and 76.2 % bio-removal of the applied fluoroquinolone in 1 M urea solution, respectively. Biotransformation products of the parent antibiotic were spectroscopically analyzed that assigned to different reaction pathways including demethylation, defluorination, decarboxylation, deamination, and hydroxylation. A micro-toxicity study concerning the growth of some Gram⁺ and Gram^- bacteria exhibited decreasing in inhibition of laccase-treated levofloxacin after a 10-h incubation at 37 °C.

Incorporating W cations into ZnO nanosheets: an efficient method towards ZnO/ZnWO4 photocatalysts for highly effective degradation of organic compounds under UV and visible-light irradiation

Novel ZnO/ZnWO₄ photocatalysts were synthesized for the removal of RhB dye with an excellent photocatalytic performance.

Enhanced Adsorption of Toxic and Biologically Active Levofloxacin Residuals from Wastewater Using Clay Nanotubes as a Novel Fixed Bed: Column Performance and Optimization

Kaolinite nanotube particles (KNTs) were synthesized by a chemical exfoliation and scrolling process in the existence of sonication waves. The KNT product was identified as a mesoporous material (12 nm in pore diameter) with high surface area (105 m²/g) and promising adsorption affinity for the levofloxacin antibiotic (LVOX) residuals in wastewater. The KNT particles were used as a fixed bed in the continuous adsorption column system for LVOX considering the essential variables. The investigation of the KNT fixed bed in a continuous column for 1800 min verified its suitability to reduce the LVOX content in 9 L of polluted solutions by 80.4%. This was recognized after using the KNT bed of 4 cm in height, a flow rate of 5 mL/min, a pH value of 8, a total flow interval of 1800 min, and an LVOX concentration of 10 mg/L. The regeneration study of the bed declared effective recyclability properties for the KNT particles in the LVOX adsorption column system. The dynamic properties of the KNT bed-based column system were explained based on Thomas, Adams-Bohart, and the Yoon-Nelson kinetic models. The LVOX adsorption reaction by KNTs follows Langmuir behavior with homogeneous and monolayer uptake form. The Gaussian energy (2.05 kJ/mol) and the thermodynamic parameters emphasized physical, spontaneous, and exothermic adsorption reactions for LVOX by KNTs.

Instantaneous oxidation of levofloxacin as toxic pharmaceutical residuals in water using clay nanotubes decorated by ZnO (ZnO/KNTs) as a novel photocatalyst under visible light source

Kaolinite nanotubes were synthesized by a simple scrolling process and decorated by ZnO nanoparticles as a novel nanocomposite (ZnO/KNTs). The synthetic ZnO/KNTs composite was characterized as an effective photocatalyst in the oxidation of levofloxacin pharmaceutical residuals in the water resources. The composite displays a surface area of 95.4 m²/g, average pore diameter of 5.8 nm, and bandgap energy of 2.12 eV. It is of high catalytic activity in the oxidation of levofloxacin in the presence of visible light source. The complete oxidation for 10 mg/L of levofloxacin was recognized after 55 min, 45 min, and 30 min with applying 30 mg, 40 mg, and 50 mg of ZnO/KNTs as catalyst dosage, respectively. Additionally, it achieved complete oxidation for 20 mg/L and 30 mg/L of levofloxacin after 45 min and 75 min, respectively using 50 mg as catalyst dosage. The degradation efficiency was confirmed by detecting the residual TOC after the treatment tests and the formed intermediate compounds were identified to suggest the degradation pathways. In addition to the oxidation pathway, the mechanism was evaluated based on the active trapping tests that proved the dominance of hydroxyl radicals as the essential active species. Finally, the ZnO/KNTs composite is of promising recyclability properties and achieved better results than several studied photocatalysts in literature.

Enhanced decontamination of levofloxacin as toxic pharmaceutical residuals from water using CaO/MgO nanorods as a promising adsorbent

Novel MgO/CaO nanocomposite (MgO/CaO NRs) was synthesized by the hydrothermal method using diatomite porous frustules as a substrate under the microwave irradiation. The composite appeared as well crystalline rod-like nanoparticles with 52.3 nm as average particle size and 112.8 m²/g as BET surface area. The synthetic MgO/CaO NRs were addressed as a novel adsorbent for promising removal of levofloxacin (LVX) as pharmaceutical residuals. The adsorption studies revealed effective uptake of levofloxacin by MgO/CaO NRs with theoretical q_max of 106.7 mg/g and the equilibrium time of 720 min considering the best pH value (pH 7). The equilibrium studies highly fitted with the Langmuir model of monolayer adsorption considering the values of Chi-squared (χ²) and determination coefficient. The estimated adsorption energy from Dubinin–Radushkevich (0.2 kJ/mol) signifies physisorption mechanisms that might be coulombic attractive forces considering the kinetic studies. The thermodynamic addressing for the reactions verified their spontaneous and exothermic nature within a temperature range from 303 to 333 K. Additionally, the prepared MgO/CaO NRs show significant recyclability properties to be used in realistic remediation process and its uptake capacity is higher than several studied adsorbents in literature.